Abstrict
A filter cloth for air bags comprises a synthetic fiber woven fabric
having (1) a ground weave structure segment having a single plain
weave structure or a single twill weave structure and (2) a plurality
of high gas-permeability weave structure segments substantially
evenly distributed in the ground structure segment, exhibiting an
air permeability higher than that of the ground structure segment
and having (A) a mock leno weave structure having pinholes, (B)
a double plain weave structure or (C) a double twill weave structure,
and allows, when an air bag is formed from the cloth, a layout for
cutting and a cutting of the cloth to be made freely and when the
resultant air bag is inflated, the bag allows an inflation gas to
instantly flow out from the bag so as to ensure the safety of the
occupant.
Claims
We claim:
1. A filter cloth for air bags, comprising a woven fabric formed
from synthetic fiber yarns, and characterized in that the woven
fabric comprises
(1) a ground weave structure segment having a single plain weave
structure or a single twill weave structure; and
(2) a plurality of high gas permeability weave structure segments
formed in the ground weave structure segment at a substantially
constant distribution density, exhibiting a higher air permeability
than that of the ground weave structure segment, and having
(A) a mock leno weave structure having pinhole-like openings,
(B) a double plain weave structure; or
(C) a double twill weave structure.
2. The filter cloth for air bags as claimed in claim 1, wherein
the ground weave structure segment has a single plain weave structure
and the high gas-permeability structure segments have a mock leno
weave structure having pinhole-like openings.
3. The filter cloth for air bags as claimed in claim 1, wherein
the plurality of high gas-permeability weave structure segments
are distributed at substantially regular intervals in each of warp
and weft directions thereof in the ground weave structure segment.
4. The filter cloth for air bags as claimed in claim 1, wherein
each of the high gas-permeability weave segments having a mock leno
weave structure is composed of at least one mock leno weave structure
unit composed of 6 warp yarns and 6 weft yarns, and one pinhole-like
opening is formed in each mock leno weave structure unit.
5. The filter cloth for air bags as claimed in claim 4, wherein
the woven fabric is composed of repeating units each consisting
of one mock leno weave structure segment and a portion of the ground
weave structure segment located between the above-mentioned one
mock leno weave structure segment and another mock leno weave structure
segments adjacent thereto in both the warp and weft directions of
the woven fabric, each of the repeating units being composed of
7 to 100 warp yarns and 7 to 100 weft yarns.
6. The filter cloth for air bags as claimed in claim 1, wherein
each of the high gas-permeability mock leno weave structure segments
is composed of 9 warp yarns and 9 weft yarns, and has four pinhole-like
openings formed in each mock leno weave structure segment.
7. The filter cloth for air bags, as claimed in claim 6, wherein
the woven fabric is composed of repeating units each consisting
of one mock leno weave structure segment and a portion of the ground
weave structure segment located between the above-mentioned one
mock leno weave structure segment and another mock leno weave structure
segments located adjacent thereto in both the warp and weft directions
of the woven fabric, each of the repeating units being composed
of 9 to 100 warp yarns and 9 to 100 weft yarns.
8. The filter cloth for air bags as claimed in claim 1, wherein
the pinhole-like openings have a hole size of 50 to 500 .mu.m.
9. The filter cloth for air bag as claimed in claim 1, wherein
the pinhole-like openings are distributed at a distribution density
of 1 to 150 openings/6.45 cm.sup.2.
10. The filter cloth for air bags as claimed in claim 1, wherein
each of the high gas-permeability double plain weave structure segments
is composed of at least one double plain weave structure unit consisting
of 8 warp yarns in the total yarn number of both the front and back
side structures and 8 weft yarns in the total yarn number of both
the front and back side structures.
11. The filter cloth for air bags as claimed in claim 10, wherein
the woven fabric is composed of repeating units each consisting
of one double plain weave structure segment and a portion of the
ground weave structure segment located between the above-mentioned
one double plain weave structure segment and another double plain
weave structure segments adjacent thereto in both the warp and weft
directions of the woven fabric, each of the repeating units being
composed of 9 to 100 warp yarns and 9 to 100 weft yarns.
12. The filter cloth for air bags as claimed in claim 1, wherein
each of the double plain weave structure segments has an area of
3 to 200 mm.
13. The filter cloth for air bags as claimed in claim 1, wherein
the double plain weave structure segments are distributed in a density
of 1 to 150 segments/6.45 cm.sup.2.
14. The filter cloth for air bags as claimed in claim 1, wherein
each of the high gas-permeability double twill weave structure segments
is composed of at least one double twill weave structure unit consisting
of 12 warp yarns in the total yarn number of both the front and
back side structures and 12 weft yarns in the total yarn number
of both the front and back side structures.
15. The filter cloth for air bags as claimed in claim 14, wherein
the woven fabric is composed of repeating units each consisting
of one double twill weave structure segment and a portion of the
ground weave structure segment located between the above-mentioned
one double twill weave structure segment and another double twill
weave structure segments adjacent thereto in both the warp and weft
directions of the woven fabric, each of the repeating units being
composed of 13 to 100 yarns and 13 to 100 weft yarns.
16. The filter cloth for air bags as claimed in claim 1, wherein
each of the double twill weave structure segments has an area of
3 to 200 mm.sup.2.
17. The filter cloth for air bags as claimed in claim 1, wherein
the double twill weave structure segments are distributed at a density
of 1 to 150 segments/6.45 cm.sup.2.
18. The filter cloth for air bags as claimed in claim 1, wherein
the synthetic fiber yarns have a twist multiplier of 2500 or less.
19. The filter cloth for air bags as claimed in claim 1, wherein
the synthetic fiber yarns are nontwisted synthetic filament yarns.
20. The filter cloth for air bags as claimed in claim 1, wherein
the ground weave structure segment and the high gas-permeability
structure segments are formed from the same synthetic fiber yarns
as each other.
21. The filter cloth for air bags as claimed in claim 1, wherein
the synthetic fiber yarns are polyester filament yarns each having
an individual filament thickness of 0.5 to 3.0 denier and composed
of 140 to filaments.
22. The filter cloth for air bags as claimed in claim 1, wherein
the high gas-permeability structure segments have an air permeability
of three times or less that of the ground weave structure segment.
23. The filter cloth for air bags as claimed in claim 1, wherein
the high gas-permeability structure segments have a gas-permeability
of 0.6 ml/cm.sup.2 /sec/125 Pa or more.
24. The filter cloth for air bags as claimed in claim 1, wherein
the woven fabric has an average seam slippage value of 7 mm or less.
Description TECHNICAL FIELD
The present invention relates to a filter cloth for air bags for
automobiles and aircrafts. More particularly, the present invention
relates to a filter cloth for air bags having a plurality of high
gas-permeability structure segments substantially evenly distributed
and formed in a high density ground structure segment. The air bag
produced from the filter cloth allows, when a large amount of inflation
is blown into the air bag, a portion of the inflation gas to instantly
flow to the outside of the bag through the high gas-permeability
structure segments, to thereby enhance the safety of an occupant
of the vehicle, and enhances the resistance of the air bag to seam
slippage.
BACKGROUND ART
The performance requirements for a filter cloth for air bags are
as follows.
1 The woven fabric, from which an air bag is formed, should have
a relatively high gas permeability and, when an automobile or aircraft
collides and an inflation gas is introduced into the air bag, the
air bag can allow a portion of the inflation gas to substantially
evenly flow out so as to lower the gas temperature, to thereby prevent
burning of an occupant by the inflation gas introduced into the
air bag.
2 The filter cloth should appropriately filter a large mount of
the fine particles contained in the inflation gas and maintain the
air in the inside of the automobile or aircraft clean even after
the inflation of the air bag.
3 After inflation, the air bag should be quickly deflated by discharging
the inflation gas so as to not constrain the occupant.
As filter cloth for air bags meeting the above requirements, the
following prior arts are been known. U.S. Pat. No. 4,840,397 for
Katz et al. discloses an air bag device for a motorcar provided
with a filter for cleaning an inflation gas. The filter is formed
from a filter cloth which consists of a 2/1 twill weave made from
aramid fiber spun yarns. This woven fabric has a single weaving
structure and exhibits a high gas-permeability.
However, this filter cloth exhibits a poor resistance to seam slippage
due to the single weaving structure having a high gas-permeability.
Thus, when an inflation gas is blown into an air bag made from the
filter cloth, the inflation gas can be discharged only through very
small gaps formed between weaving yarns and distributed throughout
the filter cloth. Accordingly, the filter cloth exhibits an unsatisfactory
gas-discharging property and thus the air bag exhibits an unsatisfactory
deflating property.
Japanese Unexamined Patent Publication No. 3-16,853 discloses a
hollow weave fabric for air bags which is provided with specific
gas-discharging segments having a mock leno weave structure.
However, in the air bag, since the mock leno weave structure is
formed in vent hole portions (completely opening portions) specified
in the hollow weave segment structure, the resultant air bag exhibits
a poor deflating property after the introduction of the inflation
gas. Also, since the mock leno weave structure is formed in specific
portions of the woven fabric the air bag which can be produced from
the woven fabric is limited to a specific type of air bags having
a specific form.
European Unexamined Patent Publication (EP-A-) No. 442,373 (which
corresponds to Japanese Unexamined Patent Publication No. 4-214,437)
discloses a filter cloth consisting of a gas-discharging fabric.
This filter cloth per se is a woven fabric having a single weave
structure. Accordingly, this filter cloth has a poor resistance
to seam slippage, similar to that of the filter cloth disclosed
in the above-mentioned U.S. Patent. Also, when an inflation gas
is blown into the air bag made from the filter cloth, the inflation
gas can be discharged only through very small gaps formed between
the weaving yarns and distributed throughout the air bag, and thus
the air bag exhibits an unsatisfactory gas-discharging property
and thus a poor deflating property.
Japanese Unexamined Patent Publication No. 4-262,938 discloses
a filter cloth made from stretch-broken, fascinated yarns. However,
this cloth consists of a woven fabric having a single weave structure
similar to those disclosed in the above-mentioned prior arts and
thus has the similar disadvantages to those mentioned above.
Finally, German Unexamined Patent Publication (DE-A-) No. 4126709
corresponding to U.S. Pat. No. 5,131,434 and to Japanese Unexamined
Patent Publication No. 4-281,038 discloses a filter cloth having
a plurality of segments different in weave structure and thus in
gas permeability from each other. This cloth has weave structure
segments having a high gas-permeability and thus a moderate filtering
property, and other weave structure segments having a moderate or
low gas-permeability and suitable for sewing. Namely, in this filter
cloth, two or more segments different in function and in weave structure
from each other are arranged in an appropriate layout for cutting
of the cloth for the air bag.
According to the above-mentioned German patent publication specification,
the segments having a high cutting property and a high sewing property
for air bags are formed by a high density weave structure having
a low gas-permeability and a high seam slippage resistance; other
segments are formed by a moderate density weave structure having
a moderate gas-permeability and still other segments having a high
filtering property are formed by a low density weave structure having
a high gas-permeability.
However, this type of filter cloth is disadvantageous in that the
high cutting property, high sewing property segments are necessarily
formed over both the high density weave structure portions and the
moderate density weave structure portions and the moderate density
weave structure portions exhibit a poor seam slippage resistance.
Also this filter cloth has the commercial problem that since it
is designed and woven in specific weaving structures suitable for
an air bag of specific form and dimensions, the resultant filter
cloth can be employed only for a specific type of air bag having
a specific form and dimensions. The abovementioned German patent
publication specification includes no description relating to the
deflating property of the air bag after inflating.
Further, the high gas-permeability portions, which are so-called
windows, formed in the filter cloth for an air bag, are woven in
a 2/2 Panama weave structure to dimensions of a width of 40 cm and
a length of 30 cm. Therefore, the window portions have a weave structure
which exhibits a relatively high gas permeability compared to the
ground plain weave structure. Namely, the window portions are not
openings and thus must be formed over a relatively large area. The
presence of the large area of the window portions (high gas-permeability
portions) cause the freedom in trimming of the resultant filter
cloth for cutting for the production of the air bag to be small.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide a filter cloth
for air bags comprising a low gas-permeability ground weave structure
segment and a plurality of high gas-permeability weave structure
segments, and capable of being freely trimmed and cut into cloth
pieces for forming the air bag without restrictions on the trimming
and cutting due to the location of the high gas-permeability weave
structure segments.
Another object of the present invention is to provide a filter
cloth for air bags, which cloth exhibits an excellent seam slippage
resistance in every portion thereof, although the filter cloth has
a moderate gas-permeability.
Still another object of the present invention is to provide a filter
cloth capable of forming an air bag having an excellent seam slippage
resistance in every portion thereof in spite of its moderate gas-permeability,
an excellent deflating property after the inflation is completed,
and thus a high safety.
The filter cloth of the present invention for air bags comprises
a woven fabric formed from synthetic fiber yarns and is characterized
in that the woven fabric comprises (1) a ground weave structure
segment having a single plain weave structure or a single twill
weave structure; and (2) a plurality of high gas-permeability weave
structure segments formed in the ground weave structure segment
at a substantially constant distribution density, exhibiting a higher
air permeability than that of the ground weave structure segment,
and having:
(A) a mock leno weave structure having pinhole-like openings;
(B) a double plain weave structure; or
(C) a double twill weave structure.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an explanatory plane view of a weave structure of an
embodiment of the filter cloth of the present invention for air
bags;
FIG. 2 is an enlarged explanatory plan view of a high gas-permeability
mock leno weave structure segment involved in the weave structure
of FIG. 1;
FIG. 3 an explanatory cross-sectional profile of the mock leno
weave structure segment indicated in FIG. 1, along a line X--X';
FIG. 4 is an explanatory plane view of a weave structure of another
embodiment of the filter cloth of the present invention for air
bags;
FIG. 5 is an explanatory cross-sectional profile of the weave structure
indicated in FIG. 4, along a line X--X';
FIG. 6 is an explanatory plane view of a weave structure of still
another embodiment of the filter cloth of the present invention
for air bags;
FIG. 7 is an explanatory cross-sectional profile of the weave structure
indicated in FIG. 6, along a line X--X';
FIG. 8 is an explanatory plane view of a weave structure of further
another embodiment of the filter cloth of the present invention
for air bags; and
FIG. 9 is an explanatory cross-sectional profile of the weave structure
indicated in FIG. 8, along a line X--X'.
BEST MODE OF CARRYING OUT THE INVENTION
The present invention will be explained in detail, with reference
to the attached drawings.
(1) Constitution of the filter cloth for air bags.
1 A filter cloth having a plurality of high gas-permeability mock
leno weave structure segments distributed throughout the cloth and
having pinhole-like openings:
The constitution and functions of the mock leno weave structure
segments having pinhole-like openings formed in a weave structure
will be explained by referring to FIG. 1.
FIG. 1 shows a weave structure of a filter cloth composed of a
ground weave structure segment having a single plain weave structure
and high gas-permeability mock leno weave structure segments evenly
distributed in the ground weave structure segment. This weave structure
corresponds to that described in Example 5, which will be mentioned
hereinafter. FIG. 2 is a partially enlarged view of the high gas-permeability
mock leno weave structure segment of the filter cloth of FIG. 1,
and FIG. 3 shows a cross-sectional profile of the filter cloth of
FIG. 1, along the line X--X'. Referring to FIGS. 1, 2 and 3, a filter
cloth 1 is composed on a ground plain weave structure segment 2
and a plurality of high gas-permeability weave structure segments
3 evenly distributed in the ground weave structure segment and having
a mock leno weave structure.
The high gas-permeability mock leno weave structure segments 3
are composed of at least one mock leno weave structure unit. This
mock leno weave structure unit is composed of six warp yarns A to
F and six weft yarns a to f. The warp yarns A, C, D and F alternately
appear on the front surface and on the back surface of the weave
for every one weft yarn, in the same manner as in a plain weave
structure. However, the warp yarns B and E alternately appear on
the front surface and on the back surface of the weave for every
three weft yarns, in each mock leno weave structure. These warp
yarns B and E have a lower frequency in crossing with the weft yarns
than that of the warp yarns A, C, D and F. Therefore, the warp yarns
B and E are slightly raised outward from the front and back surfaces
of the woven fabric, and all the warp yarns are pushed against each
other due to the high warp density of the woven fabric. As shown
in FIGS. 1 and 2, the warp yarn C pushes the warp yarn B in the
left-direction and the warp yarn D pushes the warp yarn E in the
right direction. As a result, the warp yarn C moves in the left
direction while causing the warp yarns B and E to further raise
from the front and back surfaces of the woven fabric, and then get
under the warp yarns B, and the warp yarn D moves in the right direction
and gets under the warp yarn E. Accordingly, a small gap is formed
between the warp yarns C and D.
The same phenomenon as mentioned for the warp yarns happens for
the weft yarns. In the mock leno weave structure segments in FIGS.
1 to 3, the weft yarns a, c, d and f alternately appear on the front
and back surfaces of the woven fabric for every one warp yarns,
in the same manner as in the plain weave structure. The weft yarns
b and e alternately appear on the front and back surface of the
woven fabric for every three warp yarns. These weft yarns b and
e have a lower frequency in crossing with the warp yarns than that
of the weft yarns a, c, d and f, and thus, are slightly raised from
the woven fabric surfaces. Also, each weft yarn pushes the adjacent
weft yarns due to the high weft density of the woven fabric. Referring
to FIGS. 1 and 2, the weft yarn C pushes upward the weft yarn b
and the weft yarn d pushes downward the weft yarn e. As a result,
the weft yarn C moves downward so as to cause the weft yarns b and
c to further raise from the front and back surfaces of the woven
fabric, and then gets under the weft yarn b. The weft yarn d moves
upward and gets under the weft yarn e. Therefore, a small gap is
formed between the weft yarns c and d.
Referring to FIGS. 1 and 2, a small opening 4 defined by the warp
yarns C and D and the weft yarns c and d is in the form of a pinhole.
This pinhole-like opening 4 allows a large amount of an inflation
gas to pass in a short time through an air bag formed from the filter
cloth, and simultaneously improves the deflating property of the
air bag after the inflation is completed without reducing the seam
slippage resistance of the air bag. Referring to FIGS. 1 to 3, in
the ground plain weave structure segment 2, the warp yarns G, H,
I, J . . . alternately appear on the front and back surfaces of
the woven fabric with respect to every one weft yarn. Also, the
weft yarns g, h, i, j . . . alternately appear on the front and
back surfaces of the woven fabric with respect to every one warp
yarn. Namely, in this ground plain weave structure, each yarn has
the same flexural structure as the others, and a strong and dense
weave structure is formed. Therefore, the warp and weft yarns are
not allowed to move in relation to each other, and no pinhole-like
opening is formed in the ground weave structure segment. Accordingly,
the ground plain weave structure causes the seam slippage resistance
of the resultant woven fabric to be enhanced.
Generally, a woven fabric having a weave structure by which a high
gas-permeability is caused, tends to exhibit a poor resistance to
seam slippage. In the filter cloth of the present invention, however,
since the high gas-permeability weave structure segments having
the pinhole-like openings 4 are evenly distributed in a ground weave
structure segment having a high yarn density, the air bag made from
the filter cloth enables a large amount of an inflation gas to be
discharged instantly and simultaneously exhibits an excellent seam
slippage resistance.
In the filter cloth shown in FIGS. 1 to 3, the excellent seam slippage
resistance thereof is derived from the ground plain weave structure.
In this filter cloth, the pinhole-like openings formed in the mock
leno weave structure segments are very small, and thus do not affect
the seam slippage resistance of the filter cloth as a whole.
Also, in a conventional filter cloth which has a plain weave structure
or twill weave structure (each in a single weave structure) and
thus allows an inflation gas to be discharged through the whole
surface of the cloth, the gaps between the yarns are significantly
smaller than the pinhole-like openings of the filter cloth of the
present invention and therefore the air bag made from a conventional
filter cloth exhibits a poor deflating property after the inflation.
In the filter cloth of the present invention shown in FIGS. 1 to
3, however, the pinhole-like openings are larger than the gaps between
the yarns in the ground weave structure segment, and therefore,
the air bag made from this filter cloth exhibits a good deflating
property after the inflation. Accordingly, even in the unlikely
event that the air bag made from the filter cloth of the present
invention having the weave structure shown in FIGS. 1 to 3 were
erroneously inflated while a motorcar or aircraft is in operation,
the air bag can be immediately deflated and thus the vision of the
occupant is not obstructed for a long time. Also, this air bag can
reduce an acceleration (chest G or head G) force applied to the
body of an occupant upon clashing to the same extent as a conventional
air bag with vent holes. Conventional air bags made from a conventional
filter cloth and having a poor deflating property are disadvantageous
in that the chest G and head G are significantly high.
In the filter cloth of the present invention as shown in FIGS.
1 to 3, the pinhole-like openings are not distributed close to each
other, but straggle in the ground weave structure segments, namely
the tough and dense plain weave structure segment, and therefore
substantially do not obstruct the seam slippage resistance of the
filter cloth. Also, since the pinhole-like openings 4 are substantially
evenly distributed in the ground weave structure segment, the filter
cloth is advantageous in that the trimming of the cloth for cutting
for producing the air bag can be made freely, and thus the whole
filter cloth can be freely employed.
The gas-permeability of the whole filter cloth having mock leno
weave structure segments can be adjusted by controlling the opening
area of the pinhole-like openings and the number of the openings
per unit area of the cloth. Particularly, in the filter cloth composed
of high gas-permeability mock leno weave structure segments and
a ground plain weave structure segment, the gas-permeability of
the cloth can be increased by increasing the proportion of the mock
leno weave structure segments to the whole weave structure. Also,
to reduce the gas-permeability of the filter cloth, the proportion
of the ground plain weave structure segment to the whole weave structure
should be increased.
In the filter cloth of the present invention as mentioned above,
other weave structure segments than those mentioned above may be
included in the weave structure. For example, twill weave structure,
twill derivative weave structure, ripstop weave structure, mat weave
structure and/or crape weave structure segments may be mixed in
the ground weave structure segment, to closely control the gas-permeability
of the filter cloth to more than that of the ground plain weave
structure segment alone. However, the weave structure with highest
seam slippage resistance is a plain weave structure, and the addition
of other weave structures as mentioned above causes a reduction
in the seam slippage resistance.
Portions of the mock leno weave structure segments may be replaced
by other weave structures. However, the mock leno weave structure
can provide relatively large and appropriate pinhole-like openings
per smallest unit area of the cloth, so as to attain an effective
discharge of the inflation gas and a good deflation of the inflated
air bag, and can impart the highest seam slippage resistance to
the air bag.
The mock leno weave structure is a weave structure formed by partially
changing the plain weave structure and thus includes as portions
thereof the plain weave structure. Therefore, when the mock leno
weave structure is mixed in the plain weave structure, they are
fully compatible with each other. Also, the tensile strengths and
the ultimate elongations of these two structures are respectively
close to each other, and thus the mixed weave structure is most
appropriate for the filter cloth.
In the filter cloth of the present invention, preferably the ground
segment has a single plain weave structure and the high gas-permeability
segments have a mock leno weave structure in which pinhole-like
openings are formed. Also, in the filter cloth of the present invention,
the high gas-permeability weave structure segments are preferably
distributed at substantially regular intervals both in the warp
and weft directions in the ground weave structure segment.
The mock leno weave structure formed in the filter cloth of the
present invention is preferably a smallest mock leno weave structure
composed of 6 warp yarns (warp yarns A to F in FIGS. 1 and 2) and
6 weft yarns (weft yarns a to f in FIGS. 1 and 2), namely 12 yarns
in total. One smallest mock leno weave structure unit can include
one pinhole-like opening. The larger the area of the mock leno weave
structure segment necessary for forming one pinhole-like opening,
the smaller the area of the high density ground weave structure
segment in the resultant filter cloth and thus the lower the seam
slippage resistance of the resultant filter cloth.
The mock leno weave structure for the filter cloth of the present
invention may be the weave structure as shown in FIG. 4 (a plane
view) and FIG. 5 (a cross-sectional profile along the line X--X'
in FIG. 4). This weave structure corresponds to that described in
Example 7 hereinafter. In FIGS. 4 and 5, a filter cloth 1 is composed
of a ground plain weave structure segment 2 and mock leno weave
structure segments 3 distributed in the ground segment at a substantially
constant distribution density, and in each mock leno weave structure
segment, pinhole-like openings 4 are formed.
In this cloth, four pinhole-like openings 4 are formed per mock
leno weave structure unit. The mock leno weave structure indicated
in FIGS. 4 and 5 is composed of 9 warp yarns and 9 weft yarns, namely
18 yarns in total per weave structure unit thereof. Therefore, this
mock leno weave structure unit has a larger area than that of the
mock leno weave structure unit shown in FIGS. 1 to 3. However, since
the number of the pinhole-like openings per weave structure unit
of FIGS. 4 and 5 is four times that of FIGS. 1 to 3, the distribution
number of the pinhole-like openings in the whole filter cloth increases
and the gas-permeability of the cloth is increased. Where a filter
cloth having the same gas-permeability as that of the filter cloth
comprising the mock leno weave structure segments shown in FIGS.
1 to 3 is produced by utilizing the mock leno weave structure shown
in FIGS. 4 and 5, the occupation area proportion of the mock leno
weave structure segments to the ground weave structure segment can
be reduced to a relatively small value and thus a reduction of the
seam slippage resistance of the resultant filter cloth can be prevented.
To enhance the inflation gas-discharging effect and the deflating
property of the air bag, it is preferable to increase the occupation
area proportion of the mock leno weave structure segments to the
ground plain weave structure segment.
The filter cloth of FIGS. 1 to 3 is composed of repeating units
each consisting of one mock leno weave structure segment and a portion
of the ground weave structure segment located between the mock leno
weave structure segment, and another mock leno weave structure segments
adjacent thereto in both the warp and weft directions of the cloth.
Each repeating unit is preferably composed of 7 to 100 warp yarns
and 7 to 100 weft yarns. If the numbers of the warp and weft yarns
are less than 7, no ground weave structure can be formed, and thus
the resultant filter cloth exhibits a reduced seam slippage resistance.
Also, if the numbers of the warp and weft yarns are more than 100,
the occupation area proportion of the ground weave structure segment
becomes to high, the resultant filter cloth exhibits an excessively
reduced gas permeability, and thus the resultant filter cloth is
not suitable for air bags. More preferably, each repeating unit
is composed of 8 to 80 warp yarns and 8 to 80 weft yarns.
In the filter cloth of the present invention indicated in FIGS.
4 and 5, each repeating unit consisting of one mock leno weave structure
segment and a portion of a ground weave structure segment located
between two adjacent mock leno weave structure segments, in both
the warp and weft directions, is preferably composed of 9 to 100
warp yarns and 9 to 100 weft yarns. The repeat unit is more preferably
composed of 10 to 80 warp yarns and 10 to 80 weft yarns.
In the filter cloth of the present invention shown in FIGS. 1 to
5, the pinhole-like openings formed in the mock leno weave structure
segments preferably have a size of 50 to 500 .mu.m. The term "size"
of the pinhole openings refers to a diameter of a circumcircle of
the openings which are substantially circular or polygonal, or a
major axis length of the openings which are substantially oval.
If the size of the pinhole-like opening is less than 50 .mu.m,
it becomes difficult to discharge the inflation gas from the resultant
air bag, in an instant, and exhibits a decreased deflating property.
Also, if the pinhole-like opening size is more than 500 .mu.m, the
resultant mock leno weave structure segments exhibit a decreased
seam slippage resistance. More preferably, the size of the pinhole-like
openings is 80 to 400 .mu.m.
The pinhole-like openings mentioned above are preferably distributed
in the number of 1 to 150 per units per area of 6.45 cm.sup.2 (1
in.sup.2) of the filter cloth. If the number of the pinhole-like
openings is more than 150 holes/in.sup.2, the resultant filter cloth
exhibits a decreased seam slippage resistance. Also, if the pinhole-like
opening number is less than 1/6.45 cm.sup.2, it becomes difficult
for the resultant air bag to discharge the inflation gas in an instant,
and exhibits a decreased deflating property. More preferably, the
number of the pinhole-like openings is in the range of from 3 to
120 holes/in.sup.2.
The filter cloth of the present invention preferably has an average
gas-permeability of 0.6 ml/cm.sup.2 /sec/125 Pa or more. If the
gas-permeability is less than 0.6 ml/cm.sup.2 /sec/125 Pa, the resultant
air bag cannot instantly fully discharge a large amount of inflation
gas and thus the inner pressure of the air bag increases excessively,
endangering the occupant. Also, the deflating property of the air
bag is decreased. The gas-permeability is more preferably 0.7 ml/cm.sup.2
/sec/125 Pa or more, still more preferably 0.8 to 20 ml/cm.sup.2
/sec/125 Pa.
In the filter cloth of the present invention, it is preferable
that the gas-permeability of a portion of the cloth which exhibits
the highest gas-permeability is three times or less the gas-permeability
of another portion of the cloth which exhibits the lowest gas-permeability.
If the highest gas-permeability is more than three times the lowest
gas-permeability, the resultant filter cloth exhibits a reduced
evenness in gas-permeability, and thus the freedom in trimming and
cutting the filter cloth is reduced and the utilization efficiency
of the filter cloth decreases significantly.
A more preferable ratio of the highest gas-permeability to the
lowest gas-permeability is 2 or less, still more preferably 1.2:1
to 1.8:1. The filter cloth of the present invention, in which a
plurality of pinhole-like openings are substantially evenly distributed
in the dense ground weave structure segment, allows a smaller difference
between the highest gas-permeability and the lowest gas-permeability
portions than that of a conventional cloth having no pinhole-like
openings.
The filter cloth of the present invention having the above-mentioned
weave structure is characterized by a significantly low average
seam slippage value. Namely, by utilizing the present invention,
the average seam slippage value can be reduced to a level of 7 mm
or less. If the average seam slippage value is more than 7 mm, the
inflation gas can pass selectively through the opened seams and
thus the occupant gets burnt and the air bag is broken due to a
growth of the seam openings. More preferably, the average seam slippage
value is 5 mm or less.
2 A filter cloth having high gas-permeability weave structure segments
with a double plain weave structure:
FIGS. 6 and 7 show a weave structure of an embodiment of the filter
cloth of the present invention having the above-mentioned high gas-permeability
double plain weave structure segments, and correspond to Example
8 which will be shown hereinafter. FIG. 6 is an explanatory plane
view of the above-mentioned weave structure and FIG. 7 is an explanatory
cross-sectional profile of the weave structure of FIG. 6 along the
line X--X'. These drawings show a filter cloth in which a plurality
of double plain weave structure segments are evenly straggled in
a ground weave structure segment having a single plain weave structure.
The filter cloth shown in FIGS. 6 and 7 is composed of a ground
single plain weave structure segment 2 and double plain weave structure
segments 5 distributed in the ground segment. Each of the double
plain weave structure segments 5 is composed of at least one double
plain weave structure unit. In FIGS. 6 and 7, the double plain weave
structure segments 5 have a front side ply composed of 4 warp yarns
and 4 weft yarns and a back side ply composed of another 4 warp
yarns and another 4 weft yarns. These warp and weft yarns corresponds
to 8 warp yarns and 8 weft yarns from which the plain weave structure
of the single plain weave structure segment 2 is formed. In the
double plain weave structure, the warp and weft yarns commonly form
the front and back side plies which are separate structures from
each other. Therefore, the density of yarns appearing on the front
or back side ply is 1/3 of that of yarns in the ground single plain
weave structure segment 2. Namely, the width of the warp yarns A,
B and C and the width of the weft yarns a, b and c in the double
plain weave structure segment 5 are larger than that of the warp
yarns G and the width of the weft yarns g in the single plain weave
structure segment 5, and thus are in a significantly widened form.
Therefore, the double plain weave structure segment 5 exhibits an
increased gas-permeability. Nevertheless, since the fibers contained
in the yarns located in this segment 5 are evenly distributed, the
segment 5 exhibits an enhanced filtering effect for fine particles.
In the filter cloth of the present invention having the above-mentioned
high gas-permeability double plain weave structure segments, a repeating
unit consisting of one double plain weave structure segment, and
a portion of the ground weave structure segments located between
the one double plain weave structure segment and another double
plain weave structure segments located adjacent thereto in the warp
and weft directions, is preferably composed of 9 to 100 warp yarns
and 9 to 100 weft yarns.
Also, preferably, the double plain weave structure segments each
have an area of 3 to 200 mm. Further, preferably, the double plain
weave structure segments are distributed at a density of 1 to 150/6.45
cm.sup.2.
The filter cloth of the present invention in which the ground single
weave structure segment and the high gas-permeability double weave
structure segments each have a plain weave structure, has a highest
flexure frequency of the yarns and thus the densest structure having
a high tensile strength. Therefore, this filter cloth exhibits enhanced
seam slippage resistance and burst strength. The filter cloth having
the abovementioned weave structure is particularly suitable as a
filter cloth for forming air bags for driver's seat.
3 A filter cloth in which the high gas-permeability weave structure
is a double twill weave structure:
FIGS. 8 and 9 show another embodiment of the filter cloth of the
present invention and correspond to Example 9 which will be indicated
hereinafter. FIG. 8 shows an explanatory plane view of a filter
cloth having high gas-permeability double twill weave structure
segments, and FIG. 9 shows an explanatory cross-sectional profile
of the filter cloth of FIG. 8, along the line X--X'. These drawings
show a filter cloth in Which a plurality of double twill weave structure
segments are evenly straggled in a ground single twill weave structure
segment. In the filter cloth of FIGS. 8 and 9, a plurality of high
gas permeability double twill weave structure segments 7 are evenly
distributed in a ground single twill weave structure segment 6.
Each high gas-permeability double twill weave structure segment
consists of at least one double twill weave structure unit. For
example, the double twill weave structure unit shown in FIGS. 8
and 9 is composed of 12 warp yarns and 12 weft yarns, and in the
front side ply of the cloth, 6 warp yarns and 6 weft yarns appear,
and in the back side ply of the cloth, 6 warp yarns and 6 weft yarns
appear. Also, in the ground double weave structure segment, the
front side ply of the cloth has a 2/1 twill structure and the back
side ply of the cloth has a 1/2 twill weave structure. Compared
with this, in the high gas-permeability double twill weave structure
segment 7, both the front and back side plies of the cloth have
a 2/1 twill weave structure. As mentioned above, since the warp
yarns and the weft yarns in the high gas permeability double twill
weave structure segment 7 appear on both the front side ply surface
and the back side ply surface, the density of the yarns appearing
on each of the front and back surfaces is 1/2 of that of the single
twill weave structure. Also, the warp yarns A in the double twill
weave structure have a larger width than the width of the warp yarn
F in the single twill weave structure and becomes flat. Therefore,
the double twill weave structure exhibits the same enhancing effects
in the gas permeability and in the filtering efficiency, as those
of the double plain weave structure.
As mentioned above, the high gas-permeability double twill weave
structure segments are straggled preferably at a substantially constant
distribution density in a ground single twill weave structure segment.
Also, in the filter cloth of the present invention having the high
gas permeability double twill weave structure segments, a repeating
unit consisting of one double twill weave structure segment and
a portion of the ground segment located between the one double twill
weave structure segment and another double twill weave structure
segments located adjacent thereto in the warp and weft directions,
is preferably composed of 13 to 100 warp yarns and 13 to 100 weft
yarns.
Preferably, each double twill weave structure segment has an area
of 3 to 200 mm.sup.2. Also, the double twill weave structure segments
are preferably distributed at a density of 1 to 150/6.45 cm.sup.2.
In this filter cloth, since the ground single twill weave structure
segment and the high gas permeability double twill weave structure
segments have the twill weave structure, the twill weave-forming
yarns have a lower flexure frequency than that of the plain weave-forming
yarns, and thus the resistant filter cloth exhibits an increased
average gas-permeability. Therefore, this type of filter cloth is
suitable for forming air bags for a passenger's seat.
In the above-mentioned embodiments 2 and 3 of the filter cloth,
the ground plain or twill weave structure segment imparts a high
seam slippage resistance to the resultant filter cloth and the high
gas-permeability double plain or twill weave structure segments
impart a moderate gas-permeability to the resultant filter cloth.
Generally, the filter cloth for air bags is required to have a specific
gas-permeability which is variable depending on design of the driver's
or passenger's seat. The gas-permeability can be easily changed
by adjusting the occupation area ratio of the ground single weave
structure segment to the high gas-permeability double weave structure
segments. When the proportion of the occupation area of the double
weave structure segments becomes too high, although the resultant
filter cloth exhibits an enhanced gas-permeability, the seam slippage
resistance of the cloth becomes slightly poor. To maintain the seam
slippage resistance at as high a level as possible, it is preferable
that a plurality of double weave structure segments having an unit
area as small as possible be evenly distributed in as large a number
as possible in the ground single weave structure segment.
The term "to evenly distribute" means "to substantially
evenly distribute a plurality of double weave structure segments
in a continuous ground (matrix) weave structure segment without
local concentrations of the double weave structure segments, so
that the resultant filter cloth exhibits as a whole a uniform filtering
property, and thus can be subjected to a free trimming for cutting
without considering the positions of the double weave structure
segments." It is important that the double weave structure
segments are straggled in the ground single weave structure segment
to such an extent that a highest gas-permeability is 3 times or
less than lowest gas-permeability measured at random over a measurement
area of 100 cm.sup.2. If the double weave structure segments are
locally distributed, the gas-permeability of the resultant filter
cloth varies locally. Therefore, the filter cloth cannot be subjected
to free trimming for cutting into pieces for forming the air bag.
Also, the filter cloth with locally distributed double weave structure
segments exhibits a locally reduced seam slippage resistance. In
this case, when the resultant air bag is inflated, the seam having
the reduced seam slippage resistance is broken and enlarged so that
the air bag is broken.
In the embodiments 2 and 3 of the filter cloth, the yarn density
of the yarns appearing on the front or back side surface of each
high gas-permeability double weave structure segment is half of
that in the ground weave structure segment, and thus the yarns located
in the double weave structure segment have a larger width than those
in the ground segment and become significantly flattened. Preferably,
the largest width of the yarns appearing on each surface of the
double weave structure segment is at least 1.3 times the largest
width of the yarns located in the ground segment. When the ratio
is less than 1.3, the yarns in the double weave structure segment
are densely bundled and thus have a relatively small width. Therefore,
in the resultant segment, the gaps between the yarns become larger,
and the inflation gas can easily pass through the gaps between the
yarns. Accordingly, this filter cloth exhibits a decreased filtering
effect. Since the yarns in the double weave structure segment are
flattened and have an enlarged width, the resultant filter cloth
exhibits an enhanced filtering effect. Also, since the filter cloth
does not allow the inflation gas to pass through specific local
portions of the cloth, breakage or perforation of the air bag can
be prevented. The largest width of the yarns located in the double
weave structure is preferably 1.5 times or more but not more than
5.0 times the largest width of the yarns located in the ground weave
structure.
As yarns which can be easily flattened as mentioned above, filament
yarns can be used.
Also, in the filter cloth as mentioned above, preferably, each
double weave structure segment has a unit area as small as possible,
and a large number of the double weave structure segments are evenly
straggled in the ground weave structure segment. The unit area of
the double weave structure segments is preferably 3 to 200 mm.sup.2.
Also, the double weave structure segments are preferably straggled
at a distribution density of 1 to 150/6.45 cm.sup.2 (1 in.sup.2)
in the filter cloth.
As mentioned above, in the filter cloth of the present invention,
the repeating unit consisting of one high gas-permeability double
twill weave structure segment and a portion of the ground single
twill weave structure segment continued thereto is preferably composed
of 9 to 100 warp yarns and 9 to 100 weft yarns. If the warp and
weft yarn numbers are less than 9, the occupation area of the resultant
ground single twill weave structure portion in each repeating unit
becomes too small, and thus the seam slippage resistance is reduced.
Also, if the warp and weft yarn numbers are more than 100, the occupation
area of the single twill weave structure portion in the repeating
unit becomes too large and thus the resultant filter cloth exhibits
too low an average gas-permeability. More preferably, the repeating
unit is composed of 10 to 80 warp yarns and 10 to 80 weft yarns.
The filter cloth of the present invention having the high gas-permeability
double twill weave structure segments optionally comprise another
weave structure segments straggled in the ground weave structure
segment, in addition to the above-mentioned segments. Particularly,
in the filter cloth in which the ground segment thereof has a plain
weave structure, twill, twill derivative, ripstop, mat and/or crape
weave structure segments may be straggled, in the ground segment.
The inclusion of the other weave structures in the ground segment
can cause the resultant ground segment to exhibit a slightly increased
gas-permeability compared with that of the ground segment having
a plain weave structure alone.
The above-mentioned type of filter cloth preferably has an average
gas-permeability of 0.6 ml/cm.sup.2 /sec/125 Pa or more. If the
average gas-permeability is less than 0.6 ml/cm.sup.2 /sec/125 Pa,
the resultant air bag does not allow instant discharge of a large
amount of inflation gas, and thus the inner pressure of the air
bag increases; endangering the occupant. Also, in this case, the
resultant air bag exhibits a decreased deflating property. The average
gas-permeability of the filter cloth is more preferably 0.7 ml/cm.sup.2
/sec/125 Pa or more, still more preferably 0.8 to 20 ml/cm.sup.2
/sec/125 Pa.
In the above-mentioned type of filter cloth of the present invention,
the gas-permeability of the portion of the cloth which exhibits
the highest gas-permeability is preferably 3 times or less the gas-permeability
of another portion of the cloth which exhibits the lowest gas-permeability.
If the highest gas-permeability is more than 3 times the lowest
gas-permeability, the resultant filter cloth exhibits a reduced
evenness in gas-permeability and thus decreased freedom in trimming
for cutting the cloth into pieces for forming the air bag. Also,
sometimes, the sewing work of the filter cloth becomes difficult.
The ratio of the highest gas-permeability to the lowest gas-permeability
is more preferably 2.0:1 or less, still more preferably 1.2:1 to
1.8:1.
The above mentioned embodiments 2 and 3 of the filter cloth are
advantageous in their low average seam slippage value. Namely, the
filter cloths of types 2 and 3 preferably have an average seam slippage
value of 7 mm or less. Generally, when the average seam slippage
value is more than 7 mm, the inflation gas can easily pass selectively
through the opened seams so as to burn the occupant. Also, the inflated
air bag may be broken due to an enlargement of the opened seams.
The average seam slippage value is more preferably 6 mm or less.
(2) Production of types 1, 2 and 3 of filter clothes:
The filter cloth of the present invention can be produced from
warp and weft yarns consisting of synthetic fibers by using a popular
weaving machine (loom), for example a shuttle loom, water jet loom,
rapier loom or air jet loom usable for, for example, single plain
weave or single twill weave.
In this weaving procedure, the mock leno weave structure, double
plain weave structure and double twill weave structure for forming
the high gas-permeability weave structure segments can be included
in the ground weave structure by attaching a bobby device, jacquard
machine or tappet device to the weaving machine. Among the weaving
means for the filter cloth, a most preferable means is a water jet
loom equipped with a dobby device, because this means has a high
workability and a low operating cost.
The gray fabric produced by the weaving process is preferably scoured
and then heat-set to shrink and dimensionally fix the fabric in
the warp and weft directions thereof. The resultant fabric is used
as a filter cloth.
The production process will be further explained below.
As the synthetic fiber yarns, synthetic filament yarns, for example,
polyester and nylon filaments are preferably used. The synthetic
filament yarns have a higher tensile strength than that of spun
yarns or stretch-broken, fascinated yarns and thus are useful for
producing air bags having an enhanced burst strength.
Among the synthetic filament yarns usable for the present invention,
polyester filament yarns, especially ones having a yarn thickness
of 200 to 600 denier are preferred. If the yarn thickness is less
than 200 denier, the resultant air bag sometimes exhibits an unsatisfactory
burst strength. Also, if the yarn thickness is more than 600 denier,
the resultant filter cloth sometimes has too high a basis weight.
A more preferable yarn thickness is 250 to 550 denier, still more
preferably 300 to 500 denier.
In the filament yarns usable for the present invention, the individual
filaments, from which the yarns are formed, preferably have a thickness
of 0.5 to 3.0 denier. If the individual filament thickness is less
than 0.5 denier, the resultant filament yarns sometimes exhibit
an unsatisfactory weaving property. Also, if the thickness is more
than 3.0 denier, the resultant fabric exhibits too high a stiffness.
The individual filament thickness is more preferably 0.8 to 2.5
denier, still more preferably 1.0 to 2.3 denier.
The filament yarns usable for the present invention are preferably
each composed of 140 to 840 filaments. If the filament number is
less than 140, the resultant ground weave structure segment has
too high a gas-permeability and the gas-permeability of the specific
weave structure for the high gas-permeability segments becomes difficult
to control to a moderate level. Also, if the filament number is
more than 840, the resultant yarns become difficult to weave. A
more preferable filament number is 180 to 600, still more preferably
200 to 400.
The filament yarns, particularly the polyester filament yarns usable
for the present invention preferably have a tensile strength of
9 g/denier or more. If the tensile strength is less than 9 g/denier,
the resultant air bag sometimes exhibits an unsatisfactory burst
strength. A more preferable tensile strength of the filament yarns
is 9.2 to 12 g/denier.
The filament yarns usable for the present invention preferably
have a dry thermal shrinkage of 3 to 13% at a temperature of 150.degree.
C. If the thermal shrinkage is less than 3%, sometimes, the shrinkage
of the resultant woven fabric by the scouring and heat-setting procedures
is too low, and thus the gas-permeability of the ground weave structure
segment cannot be reduced to a desired level and the resultant woven
fabric does not exhibit a tensile strength high enough to impart
a satisfactory burst strength to the air bag. If the thermal shrinkage
is more than 13%, sometimes, it becomes difficult to evenly shrink
the woven fabric by the heatsetting procedure, and the mock leno,
double plain or double twill weave structure segments exhibit uneven
gas-permeability. The dry thermal shrinkage is more preferably 3.5
to 12%.
In the production of the filter cloth of the present invention,
the synthetic filament yarns, particularly the polyester filament
yarns are twisted at a twist multiplier of 2500 or less or untwisted,
and subjected to a weaving procedure. The twist multiplier refers
to a product of the square root of the thickness value in denier
of a filament yarn and a twist number in turns/m of the yarn. If
the twist multiplier is more than 2500, the gas-permeability of
the ground weave structure segment cannot be satisfactorily reduced,
and thus it becomes difficult to control the gas-permeability of
the resultant filter cloth to a desired value by a combination of
at least the ground segment and high gas-permeability segments.
The twist multiplier is more preferably 0 to 2300. Non-twisted filament
yarns are most preferable.
In the weaving of the filter cloth of the present invention, the
cover factors (which will be indicated by CF hereinafter) of the
warp yarns and the weft yarns in the gray fabric are preferably
controlled to 600 to 1300, respectively. The CF of the warp yarns
refers to a product of the square root value of the thickness (denier)
of the warp yarns and the warp density value (yarns/inch). The Cf
of the weft yarns refers to a product of the square root value of
the thickness (denier) of the weft yarns and the weft density value
(yarns/inch).
If the CF is less than 600, sometimes, it becomes impossible to
make the gaps between the filament yarns adjacent to each other
satisfactory small even when the filter cloth is heat-shrunk by
a dry-heat-setting procedure, thus the ground segment exhibits a
high gas-permeability and the resultant filter cloth exhibits a
poor seam slippage resistance. Also, if the CF is more than 1300,
the resultant filter cloth exhibits too high a filament packing,
and thus too high a friction between the filaments and too high
a restriction in movement of the filaments relative to each other.
Therefore, the filter cloth cannot be fully shrunk by the dry-heat
setting procedure, and the gas-permeability of the ground segment
is increased for the same reasons as mentioned above. The gray fabric
more preferably exhibits a cover factor of 750 to 1200.
In the production of the gray fabric for the filter cloth of the
present invention, it is preferred to control a difference in cover
factor between the warp yarns and the weft yarns to a level of 200
or less. If the differential cover factor is more than 200, where
an external force is applied to the filter cloth, the stress generated
in the cloth is concentrated in the direction in which the cover
factor is smaller, and thus the resultant air bag exhibits a reduced
burst strength. The differential cover factors between the warp
and weft yarns are more preferably 150 or less.
The gray fabric for the filter cloth of the present invention is
scoured and then a heat setting is applied to the scoured fabric
by a metal surface contact and tension type roll setting system
so as to fully shrink the fabric to an extent corresponding to the
dry thermal shrinkage of the filament yarns. In this procedure,
the filament yarns are fully shrunk and a crimped structure is generated
on the filament yarns per se.
In this shrinking procedure, to fully enhance the seam slippage
resistance of the filter cloth, it is important to fully increase
the cover factor of the ground structure segment. In the ground
structure segment, the shrinkage and the crimped structure are generated
by the heat-setting. To fully enhance the seam slippage resistance
of the ground structure segment, it is important to selectively
promote the shrinkage above and to present the generation of the
crimped structure as much as possible.
The metal surface contact, tension type rollsetting system is advantageous
in that the shrinkage of the filament yarns can be significantly
realized and the formation of the crimped structure can be prevented
to a moderate extent. In this case, the filament yarns must have
a moderate dry thermal shrinkage.
For example, when a tenter-processing system under substantially
non-tensing conditions, as disclosed in Canadian Patent No. 974,745
is utilized, crimps are easily generated. In this system, since
the edge ends of the fabric are held and the center portion of the
fabric is mainted under a loosened condition during the heatsetting
procedure, the fabric cannot be evenly tensed. Therefore the gas-permeability
and the seam slippage resistance of the resultant heat-set fabric
are sometimes uneven.
In consideration of the above-mentioned disadvantages, the metal
surface contact, tension type roll setting system is preferably
utilized for the present invention. In this case, when the woven
fabric is completely tensed, a tensile tension slightly lower than
the heat shrinkage stress generated in the fabric in the warp direction
thereof at the roll surface temperature, is preferably applied to
the fabric in the warp direction thereof to effect the heat-setting
under tension.
In this heat-setting, the woven fabric is shrunk to an extent corresponding
to the dry heat shrinkage of the filament yarns under the application
of a tension in all directions due to the tension applied in the
warp direction, and contact friction between the warp yarns and
the contact friction between the weft yarns. In this case, the generation
of an excessively crimped structure can be prevented. Due to these
phenomena, a moderate and even seam slippage resistance is created
in the ground structure segment.
By carrying out the roll setting in at least two steps at a low
temperature and at a high temperature, the filter cloth can be fully
and evenly shrunk. In this two step roll setting, preferably the
low temperature roll has a temperature of 130.degree. to 170.degree.
C. and the high temperature roll has a temperature of 160.degree.
to 220.degree. C. More preferably, the roll setting procedure is
carried out by using a roll setting system in which the roll temperatures
are raised in three steps from a first low temperature to a final
high temperature.
In the production of the finally finished product (filter cloth),
it is preferable that the scouring procedure cause the basis weight
of the fabric to increase by 2 to 15%, more preferably 3 to 13%
based on the basis weight of the gray fabric, and the heat setting
procedure cause the basis weight of the fabric to increase by 8
to 40%, more preferably 10 to 35% based on that of the gray fabric.
Also, in this filter cloth, the heat setting preferably causes
the ultimate elongation of the fabric to increase to a level of
20%/3 cm or more in both the warp and weft directions. If the ultimate
elongation of the heat-set fabric is less than 20%/3 cm, the resultant
air bag sometimes exhibits an unsatisfactory burst strength, and
the ultimate elongation is more preferably 25%/3 cm or more, still
more preferably 30%/3 cm or more.
The filter cloth is optionally subjected to a calendaring treatment.
By the calendaring, the gas-permeability can be slightly reduced,
and the fabric surface can be smoothed. This surface-smoothed fabric
effectively protects an occupant from injury by facial abrasion.
The calendaring can reduce the thickness of the fabric so as to
enhance the compactness of the resultant air bag. The filter cloth
of the present invention may be coated with a resin material. The
resin material may be selected from silicone rubbers and chloroprene
rubbers.
Where the synthetic filament yarns are polyester filament yarns,
the polyester polymer for forming the filament yarns may be selected
from, for example, polyethylene terephthalate, polybutylene terephthalate,
polyhexylene terephthalate, polyethylene naphthalate, polybutylene
naphthalate, and polyethylene-1,2-bis (phenoxy) ethane-4,4'-dicarboxylate.
Also, copolymers of the above-mentioned compounds with polyethylene
isophthalate, polybutylene terephthalate/naphthalate, and/or polybutylene
terephthalate/decanedicarboxylate can be utilized. Among these polymers,
polyethylene terephthalate is more preferable due to the fact that
the mechanical characteristics and the fiber-forming property thereof
are fully balanced with each other.
EXAMPLES
The filter cloth of the present invention will be further explained
by the following specific examples.
In the examples, the measurements of the physical properties of
the filaments and woven fabrics and the evaluation of the resultant
air bags were carried out as follows.
(1) Ratio of largest width of filament yarns in double weave structure
to that in single weave structure
Photographs of a front surface and a cross-section of a woven fabric
specimen were taken by an electron microscope. The photographing
was repeated ten times on random front surface portions and random
cross sections so that each photograph includes both the high gas-permeability
weave structure segment and the ground weave structure segment.
In each photograph, the largest widths of the filament yarns located
in the above mentioned segments, and a ratio of the largest width
of the filament yarns in the high gas permeability means structure
segment to that in the ground means structure segment were calculated.
(2) Gas-permeability
The gas-permeability of a filter cloth specimen was measured by
using a gas-permeability tester (trademark: FX3300, made by Textest
Co.) having a 100 cm.sup.2 orifice under a pressure of 0.5 inch
of mercury (125 Pa). With respect to the woven fabric specimen having
a width of 1.5 m and a length of 5 m, the gas-permeability thereof
was measured in 50 random portions thereof, and an average of the
measurement results were calculated. Also, the ratio of a highest
value to a lowest value thereof was calculated.
(3) Seam slippage value
The seam slippage value of a filter cloth specimen was measured
in accordance with Japanese Industrial Standard (JIS), L 1096, 6.21
Slippage Resistance, 6.21.1 beam Slipping Method. The sewing yarns
used were nylon 66 filament yarns with a thickness of 1260 denier
and the stretching load was 120 kgf. In the woven fabric having
mock leno weave structure segments, both the seam slippage value
on a line drawn between two adjacent mock leno weave structure segments,
which value is substantially the largest seam slippage value), and
the seam slippage value of the ground weave structure segment which
is substantially the smallest seam slippage value, were measured.
In the woven fabric having double weave structure segments, both
the seam slippage value on a line drawn between two double weave
structure segments, which is substantially the largest seam slippage
value) and the seam slippage value of the ground segment (which
is substantially the smallest seam slippage value) were measured.
Each of the above-mentioned seam slippage measurements was carried
out in both the warp and weft directions, and an average of all
the results in the warp and weft directions of the different weave
structure segments was calculated.
(4) Damage of seam of air bag by inflation thereof and fine particle-filtering
property of air bag
A 60 liter non-coated air bag for a motorcar driver's seat was
prepared from a top cloth consisting of a high density woven fabric
with a plain weave structure alone and a bottom cloth consisting
of one of the filter cloth specimens. An air bag module was prepared
by attaching an inflator (type 4, made by Morton International Co.)
to the air bag. An inflation test was applied to the air bag module.
After the inflation, the damage to the seam portions of the air
bag was observed. Also, the filtering property of the air bag for
fine particles contained in the inflation gas was visually evaluated
from the degree of staining of the inside surface of the air bag
filter cloth.
(5) Deflating property of air bag after inflation of air bag
The deflating behavior of the air bag after inflation thereof was
observed and evaluated by using a high speed videoscope.
Example 1
The polyester filament yarns having the yarn count indicated in
Table 1 were employed as warp and weft yarns for a woven fabric.
These warp and weft yarns were nontwisted yarns and subjected to
a weaving process using a water jet loom equipped with a dobby device
to produce a filter cloth consisting of a ground plain weave structure
segment and mock leno weave structure segments. The number of dents
of a reed was 15 dents/in, and three warp yarns were fed into each
dent of the reed. The resultant gray woven fabric had cover factors
of 961 in the warp direction and 976 in the weft direction.
The gray fabric was scoured and then dried at a temperature of
110.degree. C. for one minute in a metal surface contact, tension
type roll system while applying a tension to the fabric in the warp
direction thereof. Further in the above-mentioned system, the fabric
was heat set in two steps, namely, at a metal roll surface temperature
of 155.degree. C. for one minute, and then at a metal roll surface
temperature of 180.degree. C. for 1.5 minutes. The heat-set woven
fabric had a basis weight of 222 g/m.sup.2.
The gas-permeability and seam slippage value of the woven fabric
were measured. Then, a 60 liter air bag for a driver's seat was
produced from the woven fabric.
In the preparation of the air bag, a top cloth consisting of a
high density woven fabric with a plain weave structure alone was
combined with a bottom cloth consisting of the above-mentioned woven
fabric (filter cloth) by a double chain stitch seaming method.
The seam damage of the air bag upon being inflated and the deflating
property of the air bag after the inflation were measured and evaluated.
The results are all indicated in Table 1.
Examples 2 to 6 and Comparative Examples 1 to 3
In each of Examples 2 to 6 and Comparative Examples 1 to 3, a filter
cloth having the weave structures as indicated in Tables 1 to 4
were prepared from the polyester filament yarns or nylon 66 filament
yarns as indicated in Tables 1 to 4 by using a water jet loom equipped
with a dobby device.
The resultant gray fabric was scoured and heat-set by the same
procedures as in Example 1, to produce a filter cloth.
The physical properties of the filter cloth were measured. Then,
the filter cloth was converted to a 60 liter air bag for driver's
seat in the same manner as in Example 1. The performance of the
air bag was measured.
All the test results are shown in Tables 1 to 4.
TABLE 1 __________________________________________________________________________
Example No. Example Item 1 2 3 __________________________________________________________________________
Yarns Type Polyester Polyester Polyester Yarn thickness (denier)
420 420 420 Individual filament thickness (denier) 1.7 1.7 1.7 Filament
number 250 250 250 Gray Weave structure Mock leno Plain Mock leno
Plain Mock leno Plain woven Pinhole-like openings Formed Formed
Formed fabric Twist multiplier Warp 0 0 0 Weft 0 0 0 Cover factor
Warp 961 955 961 Weft 971 971 976 Finished Pinhole-like openings
Formed Formed Formed woven Basis weight (g/m.sup.2) 224 223 222
fabric Proportion of each weave structure 6.3 93.7 8.3 91.7 12.5
72.5 Yarn number of repeating unit 24/24 24/18 24/24 warp/weft Average
gas permeability/ 0.87 0.92 1.30 (ml/cm.sup.2 /sec/125 Pa) Highest
gas-permeability/ 1.15 1.19 1.14 lowest gas-permeability ratio Seam
slippage value (mm) Warp 1.6 1.2 2.2 1.6 2.2 1.9 Weft 1.7 1.0 2.4
1.6 2.8 2.0 Air bag Seam damage by gas inflation None None None
Deflating property after inflation Good Good Good General evaluation
Good Good Good __________________________________________________________________________
TABLE 2 __________________________________________________________________________
Example No. Example Item 4 5 5 __________________________________________________________________________
Yarns Type Polyester Polyester Nylon 66 Yarn thickness (denier)
420 420 420 Individual filament thickness (denier) 1.7 1.7 5.8 Filament
number 250 250 72 Gray Weave structure Mock leno Plain Mock leno
Plain Mock leno Plain woven Pinhole-like openings Formed Formed
Formed fabric Twist multiplier Warp 0 0 0 Weft 0 0 0 Cover factor
Warp 955 961 961 Weft 965 976 976 Finished Pinhole-like openings
Formed Formed Formed woven Basis weight (g/m.sup.2) 223 222 218
fabric Proportion of each weave structure 16.6 83.4 25.0 75.0 25.0
75.0 Yarn number of repeating unit 12/18 12/12 12/12 warp/weft Average
gas permeability/ 1.51 2.06 2.29 (ml/cm.sup.2 /sec/125 Pa) Highest
gas-permeability/ 1.25 1.34 1.42 lowest gas-permeability ratio Seam
slippage value (mm) Warp 2.7 2.5 3.0 2.5 3.1 2.4 Weft 2.7 2.3 2.8
2.6 2.8 2.6 Air bag Seam damage by gas inflation None None None
Deflating property after inflation Good Good Good General evaluation
Good Good Good __________________________________________________________________________
TABLE 3 ______________________________________ Example No. Item
Example 7 ______________________________________ Yarns Type Polyester
Yarn thickness (denier) 420 Individual filament thickness (denier)
1.7 Filament number 250 Gray Weave structure Mock Plain woven leno
fabric Pinhole-like openeings Formed Twist multiplier Warp 0 Weft
0 Cover factor Warp 984 Weft 984 Finished Pinhole-like openeings
Formed woven Basis weight (g/m.sup.2) 225 fabric Proportion of each
weave structure 12.5 87.5 Yarn number of repeating unit 36/36 warp/weft
Average gas permeability 1.62 (ml/cm.sup.2 /sec/125 Pa) Highest
gas-permeability/ 1.16 lowest gas-permeability ratio Seam slippage
value (mm) Warp 2.6 2.2 Weft 2.6 2.4 Air bag Seam damage by gas
inflation None Deflating property after inflation Good General evaluation
Good ______________________________________
TABLE 4 __________________________________________________________________________
Example No. Comparative Example Item 1 2 3 __________________________________________________________________________
Yarns Type Polyester Polyester Polyester Yarn thickness (denier)
500 420 420 Individual filament thickness (denier) 2.0 1.7 1.7 Filament
number 250 250 250 Gray Weave structure Plain Plain Twill woven
Pinhole-like openings None None None fabric Twist multiplier Warp
0 0 0 Weft 0 0 0 Cover factor Warp 1040 914 1107 Weft 1007 963 1188
Finished Pinhole-like openings None None None woven Basis weight
(g/m.sup.2) 210 181 234 fabric Proportion of each weave structure
100 100 100 Yarn number of repeating unit 2/2 2/2 4/4 warp/weft
Average gas permeability 0.98 1.87 3.94 (ml/cm.sup.2 /sec/125 Pa)
Highest gas-permeability/ 1.69 2.03 1.74 lowest gas-permeability
ratio Seam slippage value (mm) Warp 7.7 10.0 8.9 Weft 9.5 7.6 8.1
Air bag Seaqm damage by gas inflation Damaged Damaged Damaged Deflating
property after inflation Bad Bad Bad General evaluation Bad Bad
Bad __________________________________________________________________________
Example 8
The polyester filament yarns (made by Teijin Ltd.) as indicated
in Table 5 were provided as warp and weft yarns. These filament
yarns were non-twisted.
A gray woven fabric for a filter cloth having a ground single plain
weave structure segment and double plain weave structure segments
was produced from the polyester filament yarns by using a water
jet loom equipped with a dobby device. The reed of the loom had
a dent number of 15 dents/in and three warp yarns were fed to each
dent.
The gray fabric was scoured and then dried at a temperature of
110.degree. C. for one minute by using a metal surface-contact,
tension type roll system, while applying a tension to the fabric
in the warp direction thereof. Further, in this system, the woven
fabric was heat-set in two steps, namely at a metal roll surface
temperature of 155.degree. C. for about one minute and then at a
metal roll surface temperature of 190.degree. C. for 1.5 minutes.
The heat-set woven fabric had a basis weight of 240 g/m.sup.2. The
woven fabric was subjected to the gas-permeability test and the
seam slippage value test. From this woven fabric, a 60 liter air
bag for a driver's seat was produced. The performance of the air
bag was measured.
The test results are all shown in Table 5.
Examples 9 and 10
In each of Examples 9 and 10, a woven fabric for filter cloth consisting
of a ground single plain weave structure segment and double twill
(twill derivative) weave structure segments was produced from the
polyester filament yarns (made by Teijin Ltd.) or nylon 66 filament
yarns (made by Akzo) as shown in Table 5.
The woven fabric was scoured and heat-set in the same manner as
in Example 8 to provide a filter cloth. The physical properties
of the filter cloth were measured. Then the filter cloth was converted
to a 60 liter air bag for a driver's seat. The performance of the
air bahias measured.
The test results are shown in Table 5.
Comparative Example 4
A gray woven fabric for a filter cloth having a twill weave structure
alone was produced from polyester filament yarns (made by Teijin
Ltd.) as shown in Table 5 in the same manner as in Example 8. The
gray fabric was scoured and heat-set in the same manner as in Example
8.
The physical properties of the resultant filter cloth were measured.
The filter cloth was converted to a 60 liter air bag for a driver's
seat. The performance of the air bag was measured.
The test results are shown in Table 5.
TABLE 5 __________________________________________________________________________
Example No. Example Comparative 8 9 10 Example __________________________________________________________________________
4 Yarns Type Polyester Polyester Nylon 66 Polyester Yarn thickness
(denier) 420 420 420 420 Individual filament thickness (denier)
1.7 1.7 5.8 1.7 Filament number 250 250 72 250 Finished Weave structure
Double Single Double Single Double Single Twill woven plain plain
twill twill twill twill fabric (Ground) (Ground) (Ground) (Filter
Twist multiplier Cloth) Warp 0 0 0 0 Weft 0 0 0 0 Cover factor Warp
1188 1201 1165 1213 Weft 1157 1198 1151 1210 Basis weight (g/m.sup.2)
240 250 251 253 Proportion (*).sub.1 2.1 1.9 1.4 -- Average gas
permeability 1.52 2.69 3.07 2.98 (ml/cm.sup.2 /sec/125 Pa) Highest
gas-permeability/ 1.20 1.24 1.22 2.10 lowest gas-permeability ratio
Seam slippage value (mm) Warp 0.7 0.6 1.0 0.7 1.1 1.0 7.8 Weft 0.8
0.7 1.1 0.9 1.0 0.9 9.8 Air bag Seam damage by gas inflation None
None None Damaged Deflating property after inflation Good Good Good
Bad General evaluation Good Good Good Bad __________________________________________________________________________
Note: (*).sub.1 Proportion in largest width of filament yarns in
double weave structure to those in single weave structure
Industrial Applicability
The filter cloth of the present invention is useful for forming
at least a portion of various types of air bags, for example, air
bags for driver's seats, air bags for passenger's seats, air bags
for rear seats and air bags for door side seats.
The filter cloth of the present invention is useful for producing
various types of air bags. The air bags produced by using the filter
cloth of the present invention do not require the formation of vent
holes therein. For example, with respect to the air bags for driver's
seats, the filter cloth of the present invention is useful for forming
a top cloth located in a steering wheel, and with respect to the
air bags for passenger's seats, the filter cloth of the present
invention is useful for forming both side cloths. The filter cloth
of the present invention can be used to form the entire face of
the steering wheel side top cloth or a portion thereof. Also, where
the filter cloth of the present invention is used for the two side
cloths of the air bag, the entire two cloths of the air bag may
be formed by the filter cloth or portions of the two cloths may
be formed by the filter cloth. In these cases, the filter cloth
used for the occupant side top cloth may be a coated cloth or non-coated
cloth.
When the filter cloth is utilized to form the entire steering wheel
side top cloth of the air bag for the driver's seat, preferably
the gas-permeability of the filter cloth is adjusted to 0.6 to 2.0
ml/cm.sup.2 /sec/125 Pa. Also, where the filter cloth is utilized
to form the entire two side cloths Of the air bag for passenger's
seat, the gas-permeability of the filter cloth of the present invention
is preferably adjusted to 2.0 to 7.0 ml/cm.sup.2 /sec/125 Pa.
The filter cloth of the present invention has a plurality of high
gas-permeability structure segments evenly distributed in a dense
ground structure segments and thus exhibits a substantially uniform
gas-permeability throughout the cloth. Therefore, when air bag-forming
pieces are cut from the filter cloth for preparing the air bag,
the trimming of the cloth for cutting can be freely conducted and
thus the entire filter cloth can be freely utilized in all directions
thereof.
In the filter cloth of the present invention, though the high gas-permeability
structure segments exhibit a high gas-permeability, the filter cloth
exhibits a substantially uniform and excellent seam slippage resistance
throughout the cloth, because the occupation area of the high gas-permeability
segments is very small and the occupation area of the high density
ground segment is large.
Particularly, where pinhole-like openings are formed in the high
gas-permeability segments due to the specific weave structure thereof,
the area of the openings is large compared with area of gaps formed
between-yarns in the conventional twill weave structure or plain
weave structure, and thus the resultant air bag can effectively
discharge a large amount of inflation gas at an instant upon being
inflated. When the embodiment 1 of the filter cloth of the present
invention is used, the resultant air bag exhibits an excellent deflating
property after inflation. Therefore, the filter cloth can reduce
the chest G and the head G (gravity acceleration) generated upon
clashing, and cause the resultant air bag to exhibit a high safety
for occupant.
The filter cloth of the present invention has the cutting freedom
and the seam slippage resistance as mentioned below.
Since in the filter cloth of the present invention, the high gas-permeability
structure segments, which can effectively filter fine particles
in the inflation gas, are evenly straggled in a low gas-permeability,
a high density ground segment having a single weave structure, this
filter cloth is advantageous in that when cloth pieces for forming
an air bag are cut from the filter cloth, the trimming for cutting
can be carried out in random directions. Also, since the air bag
produced from the filter cloth exhibits an excellent seam slippage
resistance upon being inflated, no slippage and breakage of seams
of the air bag due to inflation occurs and thus no scattering of
fine particles in the inflation gas toward the outside happens.
Also, no damaging of the air bag by a pressure of a high temperature
gas locally concentrated to a slipped seam portion occurs. Therefore,
the filter bag of the present invention can form air bags having
a high safety.
When the filter cloth of the present invention is used, there is
no limitation to trimming (layout) and cutting and thus the cloth
can be entirely utilized. Also, the resultant air bag produced from
the filter cloth has an excellent seam slippage resistance and is
not damaged in the seams upon being inflated. Further, the filter
cloth of the present invention can fully filter the fine particles
in the inflation gas and prevent the escape of the fine particles.
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