Nonwoven fabric and tea bag
Tea bag abstract
A nonwoven fabric characterized in that the nonwoven fabric is
a thermoplastic synthetic fiber nonwoven fabric having a fabric
weight of 7 to 50 g/m.sup.2, an average yarn diameter of 7 to 40
.mu.m, a partial heat contact bonding ratio of 5 to 30% and a content
of a delustering agent of 0.5% by weight or less, or a nonwoven
fabric laminate the major component of which is the thermoplastic
synthetic fiber nonwoven fabric, and that the nonwoven fabric has
a maximum opening diameter of 200 to 2,000 .mu.m, and shows a transparency
of 50% or more, a powder leakage ratio of 10% by weight or less
and a hydrophilicity of less than 10 sec, and a tea bag in which
the nonwoven fabric is used.
Tea bag claims
1. Process for the production of a composition for screening solar
radiation which comprises a transparent polymer incorporating an
interference pigment comprising a platelet shaped material, which
process comprises the steps of incorporating the interference pigment
into the polymer, and then stretching the resultant polymer in at
least one direction to at least twice its original length in that
direction.
2. Process according to claim 1, wherein following stretching the
polymer is converted into a woven net of tapes or monofilaments.
3. Composition for screening solar radiation, which comprises a
transparent polymer having incorporated therein an interference
pigment comprising a platelet shaped material, wherein the polymer
has been stretched in at least one direction to at least twice its
original length in that direction after incorporation of the pigment
coating.
4. Process according to claim 1, wherein the degree of stretching
of the polymer is at least 4 times its original length.
5. Composition for screening solar radiation, which comprises a
transparent polymer having incorporated therein an interference
pigment comprising a platelet shaped material, wherein the polymer
has a thickness of less than 50 .mu.m.
6. Composition according to claim 5, wherein the polymer is in
the form of a woven net of tapes or monofilaments.
7. Process according to claim 1, wherein the interference pigment
comprises a layered silicate, synthetic mica, glass platelets, ceramic
platelets or silica platelets.
8. Process according to claim 7, wherein the layered silicate is
mica, pyrophillite, sericite, talc or kaolin.
9. Process according to claim 1, wherein after stretching the polymer
has a thickness of less than 30 .mu.m.
10. Process according to claim 4, wherein the degree of stretching
is from 6 to 10 times.
11. Composition according to claim 3, wherein the degree of stretching
of the polymer is at least 4 times its original length.
12. Composition according to claim 11, wherein the degree of stretching
is from 6 to 10 times.
13. Composition according to claim 3, wherein the polymer is in
the form of a woven net of tapes or monofilaments.
14. Composition according to claim 3, wherein the interference
pigment comprises a layered silicate, synthetic mica, glass platelets,
ceramic platelets or silica platelets.
15. Composition according to claim 14 wherein the layered silicate
is mica, pyrophillite, sericite, talc or kaolin.
16. Composition according to claim 3, wherein after stretching
the polymer has a thickness of less than 30 .mu.m.
17. Composition according to claim 5, wherein the interference
pigment comprises a layered silicate, synthetic mica, glass platelets,
ceramic platelets or silica platelets.
18. Composition according to claim 17, wherein the layered silicate
is mica, pyrophillite, sericite, talc or kaolin.
19. Composition according to claim 5, wherein after stretching
the polymer has a thickness of less than 30 .mu.m.
Tea bag description
FIELD OF THE INVENTION
[0001] The present invention relates to a nonwoven fabric and a
tea bag in which the nonwoven fabric is used.
BACKGROUND ART
[0002] When components of tea, such as black tea, green tea and
oolong tea, are to be extracted, the tea bag system has often been
used in a simple method. Generally, paper is often used as a tea
bag material for a tea bag. However, because the paper has a dense
structure, the paper used as a tea bag material includes the following
problems: although the powder leakage is decreased, the paper shows
poor transparency and tea leaves in a tea bag are hardly seen; and
the paper cannot be heat sealed.
[0003] Furthermore, a nonwoven fabric of thermoplastic synthetic
fiber has recently been used as a tea bag material. The nonwoven
fabric is prepared by compositing a filaments yarn nonwoven fabric
and an extremely thin yarn nonwoven fabric, and the powder leakage
is decreased by utilizing a filtering effect of the extremely thin
yarn. Such a conventional nonwoven fabric of thermoplastic synthetic
fiber is excellent in that it can be heat sealed, and that the powder
leakage is decreased. However, the nonwoven fabric has the problem
that tea leaves in a tea bag cannot be seen due to insufficient
transparency, and the like problem. In particular, when tea leaves
of a high grade are used, that the state of tea leaves in a tea
bag cannot be seen is a great disadvantage.
[0004] In order to improve the transparency of a tea bag and the
high-grade feeling it gives, a coarse plain gauze fabric is processed
to form a bag shape. However, the resultant tea bag allows much
powder leakage. Moreover, the tea bag has a problem regarding in
waste treatment.
[0005] Japanese Unexamined Patent Publication (Kokai) No. 2001-131826
describes biodegradable monofilaments for tea bags composed of a
poly(L-lactic acid), having a size of 15 to 35 dtex, and showing
a boil-off shrinkage of 20% or less. However, the invention relates
to a tea bag prepared from a plain gauze fabric in which monofilaments
are used. The tea bag therefore has the problem that it allows much
powder leakage when the transparency of the fabric is increased.
[0006] Japanese Unexamined Patent Publication (Kokai) No. 2002-105829
describes a method of making a nonwoven fabric, of a thermoplastic
aliphatic polyester filament yarn, flexible by subjecting the fabric
to bending treatment. The patent publication discloses a filament
yarn nonwoven fabric having a fabric weight of 15 to 200 g/m.sup.2,
a size of 1.0 to 12 dtex and 4 to 50% of a partial heat contact
bonded portion. Moreover, the fabric has no problem about refuse
in waste treatment because the fabric is biodegradable. However,
there is no description in the patent publication of a nonwoven
fabric or a tea bag excellent in transparency, powder leakage, and
the like.
[0007] Japanese Unexamined Patent Publication (Kokai) No. 9-142485
describes a short fiber nonwoven fabric in which cellulose fiber
and biodegradable aliphatic polyester fiber are mixed. The nonwoven
fabric contains short fiber that has a size of 1 to 10 denier, is
partially heat bonded with a ratio of 5 to 50% or entirely heat
bonded, has excellent strength and processability, and is easily
degraded by microorganisms. The nonwoven fabric is utilized for
a bag for raw refuse, etc. However, there is no description in the
patent publication of a nonwoven fabric or a tea bag excellent in
transparency, powder leakage, and the like.
[0008] Japanese Unexamined Patent Publication (Kokai) No. 7-189136
discloses a light-shielding nonwoven fabric for which a sheath-core
yarn is used. A sheath-core conjugate yarn formed out of a polymer
as a sheath component that contains a decreased amount of inorganic
particles, and a polymer as a core component that contains an increased
amount of inorganic particles is used for the nonwoven fabric. Because
the nonwoven fabric contains a relatively large amount of inorganic
particles in the core component, the nonwoven fabric has excellent
shielding properties, and is useful for a printing substrate. However,
there is no description in the patent publication of a nonwoven
fabric or a tea bag excellent in transparency, powder leakage, and
the like.
[0009] Although Patent Publication WO 02/48443 discloses a nonwoven
fabric material for tea bags that is improved in transparency, there
is no description about powder leakage.
DISCLOSURE OF THE INVENTION
[0010] An object of the present invention is to solve the above
problems, and to provide a nonwoven fabric excellent in transparency,
showing decreased powder leakage and excellent bag formability,
and causing no refuse problem in waste treatment, and to provide
tea bags composed of the nonwoven fabric.
[0011] The present inventors have discovered that a nonwoven fabric
excellent in transparency and showing decreased powder leakage can
be obtained by combining a thermoplastic synthetic fiber material,
a content of a delustering agent, a yarn diameter of a yarn forming
the nonwoven fabric, a fabric weight, heat contact bonding conditions,
and the like, and by further investigating the transparency and
the maximum opening diameter of the fiber material. The present
invention has thus been achieved.
[0012] That is, the present invention is as explained below.
[0013] 1. A nonwoven fabric characterized in that the nonwoven
fabric is a thermoplastic synthetic fiber nonwoven fabric having
a fabric weight of 7 to 50 g/m.sup.2, an average yarn diameter of
7 to 40 .mu.m, a partial heat contact bonding ratio of 5 to 30%
and a content of a delustering agent of 0.5% by weight or less,
or a nonwoven fabric laminate the major component of which is the
thermoplastic synthetic fiber nonwoven fabric, and that the nonwoven
fabric has a maximum opening diameter of 200 to 2,000 .mu.m, and
shows a transparency of 50% or more, a powder leakage ratio of 10%
by weight or less and a hydrophilicity of less than 10 sec.
[0014] 2. The nonwoven fabric according to 1 mentioned above, wherein
the nonwoven fabric is characterized in that the nonwoven fabric
is a thermoplastic synthetic fiber nonwoven fabric having a fabric
weight of 12 to 30 g/m.sup.2, an average yarn diameter of 12 to
30 .mu.m, a partial heat contact bonding ratio of 5 to 30% and a
content of a delustering agent of 0.2% by weight or less, or a nonwoven
fabric laminate the major component of which is the thermoplastic
synthetic fiber nonwoven fabric, and that the nonwoven fabric has
a maximum opening diameter of 400 to 1,650 .mu.m, and shows a transparency
of 60% or more, a powder leakage ratio of 5% by weight or less and
a hydrophilicity of less than 10 sec.
[0015] 3. The nonwoven fabric according to 1 mentioned above, wherein
the nonwoven fabric is a laminate of a thermoplastic synthetic fiber
nonwoven fabric having an average yarn diameter of 7 to 15 .mu.m
and a thermoplastic synthetic fiber nonwoven fabric having an average
yarn diameter of 15 to 40 .mu.m.
[0016] 4. The nonwoven fabric according to any one of 1 to 3 mentioned
above, wherein the thermoplastic synthetic fiber nonwoven fabric
is a spun-bonded nonwoven fabric composed of a polyolefin filament
yarn.
[0017] 5. The nonwoven fabric according to any one of 1 to 3 mentioned
above, wherein the thermoplastic synthetic fiber nonwoven fabric
is a spun-bonded nonwoven fabric composed of a polyester filament
yarn.
[0018] 6. The nonwoven fabric according to 5 mentioned above, wherein
the thermoplastic synthetic fiber nonwoven fabric is a spun-bonded
nonwoven fabric composed of an aliphatic polyester filament yarn.
[0019] 7. The nonwoven fabric according to 6 mentioned above, wherein
the aliphatic polyester filament yarn is a filament yarn of a polyester
selected from a poly(D-lactic acid), a poly(L-lactic acid), a copolymer
of D-lactic acid and L-lactic acid, a copolymer of D-lactic acid
and a hydroxycarboxylic acid, a copolymer of L-lactic acid and a
hydroxycarboxylic acid, a copolymer of D-lactic acid, L-lactic acid
and a hydroxycarboxylic acid, or a blend of these polymers.
[0020] 8. The nonwoven fabric according to any one of 1 to 7 mentioned
above, wherein a synthetic resin or a fibrous material of 2 to 15
g/m.sup.2 having a melting point lower than that of the thermoplastic
synthetic fiber by 30 to 200.degree. C. is laminated to the thermoplastic
synthetic fiber nonwoven fabric.
[0021] 9. A tea bag prepared by filling a tea material to be extracted,
into a bag composed of the nonwoven fabric according to any one
of 1 to 8 mentioned above, and sealing the tea material.
[0022] 10. The tea bag according to 9 mentioned above, wherein
the bag is tetrahedral-shaped.
[0023] 11. The tea bag according to 9 or 10 mentioned above, wherein
the tea material to be extracted is black tea, green tea or oolong
tea.
[0024] The present invention is explained below in detail.
[0025] Examples of the thermoplastic synthetic fiber forming the
nonwoven fabric in the present invention include polyolefin fiber
such as polyethylene fiber, polypropylene fiber and copolymerized
polypropylene fiber, polyester fiber such as poly(ethylene terephthalate)
fiber, copolymerized polyester fiber and aliphatic polyester fiber,
composite yarn of core-sheath structure composed of a sheath that
is formed out of polyethylene, polypropylene, copolymerized polyester,
aliphatic polyester, or the like, and a core that is formed out
of polypropylene, poly(ethylene terephthalate), or the like, and
biodegradable fiber of poly(lactic acid), poly(butylene succinate),
poly(ethylene succinate), or the like. Short fiber or filament yarn
is used for the above fibers.
[0026] These fibers may be used singly, or at least two of them
may be used as a laminate. For example, a laminated nonwoven fabric
obtained by stacking a filament yarn nonwoven fabric and short fiber,
and heat embossing the stacked materials may be used.
[0027] In the present invention, the nonwoven fabric of thermoplastic
synthetic fiber has a fabric weight of 7 to 50 g/m.sup.2, preferably
10 to 40 g/m.sup.2, and more preferably 12 to 30 g/m.sup.2. When
the fabric weight is in the above range, the nonwoven fabric shows
good transparency, has suitable gaps among yarns, and exhibits decreased
powder leakage.
[0028] In the present invention, the nonwoven fabric of thermoplastic
synthetic fiber has an average yarn diameter of 7 to 40 .mu.m, preferably
10 to 35 .mu.m, and more preferably 12 to 30 .mu.m. When the average
yarn diameter is in the above range, the nonwoven fabric shows good
transparency and decreased powder leakage.
[0029] In the present invention, the partial heat contact bonding
ratio of the nonwoven fabric of thermoplastic synthetic fiber is
from 5 to 30%, and preferably from 7 to 27%. Partial heat contact
bonding of the nonwoven fabric decreases gaps among yarns forming
the nonwoven fabric, and can adjust the transparency, powder leakage,
strength, stiffness, and the like of the nonwoven fabric. When the
partial heat contact bonding ratio is less than 5%, bonded portions
formed by contact bonding are decreased, and powder leakage increases.
On the other hand, when the partial heat contact bonding ratio exceeds
30%, the powder leakage is decreased, and the transparency is improved
because bonded portions are increased; however, the feel of the
fabric is likely to become stiff, and the liquid permeability tends
to lower. In addition, the partial heat contact bonding ratio represents
a ratio of an area of heat contact bonded portions to the entire
area of the nonwoven fabric.
[0030] Examples of the method of partial heat contact bonding include
a method comprising passing a nonwoven fabric through a pair of
heating rolls consisting of an emboss roll having an uneven surface
structure and a flat roll having a smooth surface, thereby forming
heat contact bonded portions uniformly dispersed over the entire
nonwoven fabric.
[0031] Because a higher transparency (poor shielding properties)
of the nonwoven fabric of the invention is preferred, a decreased
amount of an inorganic additive, that is a delustering agent in
the yarn forming the nonwoven fabric of thermoplastic synthetic
fiber, is preferred. Accordingly, a nonwoven fabric of a bright
yarn or an ultra-bright yarn is preferred. The content of the delustering
agent is preferably 0.5% by weight or less, and more preferably
0.2% by weight or less. Although examples of the delustering agent
include conventionally used metal oxides such as titanium oxide,
magnesium stearate and calcium stearate, titanium oxide is preferred
in view of the particle stability and spinning stability.
[0032] For the nonwoven fabric of the invention, a combination
of a thin yarn layer and a thick yarn layer further improves the
powder leakage and transparency. For example, a laminate of a nonwoven
fabric of thermoplastic synthetic fiber having an average yarn diameter
as thin as 7 to 15 .mu.m and a fabric weight of 3 to 20 g/m.sup.2
and a nonwoven fabric of thermoplastic synthetic fiber having an
average yarn diameter as thick as 15 to 40 .mu.m and a fabric weight
of 4 to 30 g/m.sup.2 is preferred.
[0033] Because the nonwoven fabric of the present invention is
used in a bag-shaped article such as a tea bag, it is preferred
that the nonwoven fabric show a high bonding strength when heat
sealed by a bag-making machine. In order for the nonwoven fabric
of thermoplastic synthetic fiber to show good bonding strength and
good heat sealability, a synthetic resin or a fibrous material of
the resin having a melting point lower than that of the nonwoven
fabric by preferably 30 to 200.degree. C., more preferably 50 to
160.degree. C. is preferably laminated to the nonwoven fabric of
thermoplastic synthetic fiber on at least one side in an amount
of 2 to 15 g/m.sup.2, and more preferably 4 to 12 g/m.sup.2.
[0034] As a result of laminating a synthetic resin or a fibrous
material thereof having a melting point lower than that of a nonwoven
fabric of thermoplastic synthetic fiber to the nonwoven fabric,
whereby the laminate is made to have a difference in melting point
between the two materials, the synthetic resin or fibrous material
alone having a low melting point is softened or melted during heat
sealing, and acts as an adhesive to effectively give a high heat
sealing strength.
[0035] When the lamination amount of the synthetic resin or fibrous
material having a low melting point is in the above range, an amount
of a material that contributes as an adhesive is suitable, and an
adequate heat seal strength is obtained. Moreover, the transparency
of the nonwoven fabric is high, and the production cost is low.
In addition, the heat seal strength is preferably 1 N/5 cm or more,
and more preferably 3 N/5 cm or more.
[0036] Examples of the synthetic resin or fibrous material thereof
having a low melting point include a polyolefin resin such as a
linear low density polyethylene, a low density polyethylene, a polypropylene
and a copolymerized polypropylene, a polyester resin such as a linear
polyester and a copolymerized polyester, a synthetic resin such
as an ethylene-vinyl acetate copolymer resin, a polyamide resin
and a synthetic rubber resin or a fibrous material of the synthetic
resin, a composite fiber having a core-sheath structure that is
composed of a combination of a low melting point sheath component
such as a polyethylene, a polypropylene or a copolymerized polyester,
and a high melting point core component such as a polypropylene,
a copolymerized polyester, nylon-6 or a poly(ethylene terephthalate),
and a low-melting point fiber such as aliphatic acid ester fiber,
for example, poly(lactic acid) fiber and poly(butyl succinate) fiber.
[0037] Examples of the method of laminating the synthetic resin
or a fibrous material thereof having a low melting point to the
nonwoven fabric of thermoplastic synthetic fiber include a curtain
spraying method comprising melting the resin, and coating the nonwoven
fabric with the resultant semi-molten resin or fibrous material
thereof, a coating method comprising injecting the resin in a molten
state through a nozzle so that the nonwoven fabric is coated with
the resin, and a method comprising forming a fiber web out of mixed
fiber of a high melting point fiber and a low melting point fiber,
or a short fiber of composite fiber by carding procedure or an air-lay
procedure, stacking the fiber web and the nonwoven fabric of thermoplastic
synthetic fiber, and bonding the stacked materials with a heat roll,
or the like, to give a laminate of a nonwoven fabric.
[0038] Furthermore, in the present invention, it is preferred that
the nonwoven fabric of thermoplastic synthetic fiber causes no problem
in waste treatment, and that the nonwoven fabric be the one of aliphatic
polyester filament yarn composed of a biodegradable resin.
[0039] For example, a poly(lactic acid) polymer is preferably used
as the biodegradable resin. Preferred examples of the poly(lactic
acid) polymer include a poly(D-lactic acid), a poly(L-lactic acid),
a copolymer of D-lactic acid and L-lactic acid, a copolymer of D-lactic
acid and a hydroxycarboxylic acid, a copolymer of L-lactic acid
and a hydroxycarboxylic acid, a copolymer of D-lactic acid and L-lactic
acid and a hydroxycarboxylic acid, or a blend of these polymers.
The melting points of the above polymers are preferably 100.degree.
C. or more.
[0040] Examples of the hydroxycarboxylic acid used for the above
poly(lactic acid) polymer include glycolic acid, hydroxybutyric
acid, hydroxyvaleric acid, hydroxypentanoic acid, hydroxycaproic
acid, hydroxyheptanoic acid and hydroxyoctanoic acid. Of these acids,
glycolic acid and hydroxycaproic acid are preferred.
[0041] Although there is no specific limitation on the molecular
weight of the poly(lactic acid) polymer, the weight average molecular
weight is from 10,000 to 1,000,000, and preferably from 30,000 to
500,000 in view of the spinnability and the filament strength.
[0042] In order to increase the heat resistance, mechanical strength,
polymerization degree, flexibility, and the like, additives such
as a nucleating agent are added to the above polymer. Examples of
the nucleating agent include talc, titanium oxide, calcium carbonate,
magnesium carbonate and carbon. In order to make the crystallinity
of poly(lactic acid) fiber fall in a range of 10 to 40%, an addition
amount of the nucleating agent is preferably 0.5% by weight or less,
and more preferably 0.2% by weight or less. When the crystallinity
of the polymer is in the above range, the heat resistance and mechanical
strength of the polymer is sufficient, and the heat contact bondability
and biodegradability of the polymer are good.
[0043] There is no specific restriction on the method of producing
the nonwoven fabric. Known methods such as spin bonding, needle
punching, air laying and water needling can be applied thereto.
For example, when the spin bonding method is used, the method comprises
melting a synthetic resin with a melt spinning apparatus, injection
spinning the molten resin through a spinneret, drawing the spun
yarn with an air sucker, or the like, opening and collecting the
spun yarn on a conveyor net, passing the yarn between an emboss
roll and a smoothing roll, and partial heat contact bonding the
resultant web with a heat emboss roll to give a nonwoven fabric.
[0044] In the present invention, a spin-bonded nonwoven fabric
composed of a polyolefin filaments yarn or a polyester filaments
yarn is a preferred nonwoven fabric because the formation is uniform,
and in particular a uniform nonwoven fabric can be obtained with
low fabric weight. The uniform nonwoven fabric with low fabric weight
has the following advantages: no uneven fabric weight appears; gaps
among yarns become uniform; distribution of the pore diameter becomes
uniform; and the disadvantage that powder leakage caused by large
pores disappears. The spun-bonded nonwoven fabric is preferred because
it has a large strength with low fabric weight. For example, the
variation ratio of a fabric weight, 10 cm.times.10 cm, is 10% or
less, more preferably 7% or less, and still more preferably 5% or
less. In addition, variation ratio of a fabric weight (%)=[(standard
deviation)/(average fabric weight)].times.100
[0045] The nonwoven fabric of the present invention has a maximum
opening diameter of 200 to 2,000 .mu.m, preferably 300 to 1,800
.mu.m, and more preferably 400 to 1,650 .mu.m. When the maximum
opening diameter is less than 200 .mu.m, gaps among yarns forming
the nonwoven fabric are decreased, and the powder leakage is reduced;
however, the transparency becomes insufficient. On the other hand,
when the maximum opening diameter exceeds 2,000 .mu.m, gaps among
the yarns are increased, and the transparency is improved; however,
the powder leakage is increased.
[0046] FIG. 1 shows the relationship (line 1, left hand side scale)
between a maximum opening diameter and a transparency in examples
of the invention, and the relationship (line 2, right hand side
scale) between a maximum opening diameter and a powder leakage ratio.
The following are evident from FIG. 1: when the maximum opening
diameter is 200 .mu.m or more, the transparency of the nonwoven
fabric is markedly improved, and the powder leakage is low; however,
when the maximum opening diameter exceeds 2,000 .mu.m, the powder
leakage ratio tends to rapidly increase. That is, for a nonwoven
fabric, improvement of the transparency and suppression of the powder
leakage conflict each other. However, the present inventors have
made improvement of the transparency and suppression of the powder
leakage compatible by making the maximum opening diameter fall in
a range of 200 to 2,000 .mu.m.
[0047] The transparency of the nonwoven fabric of the invention
is 50% or more, preferably 55% or more, and more preferably from
60 to 100%. When the transparency is less than 50%, the contents
are hardly seen through the tea bag material, and the state thereof
is unclear. The transparency is obtained, as described later, by
measuring an Lw value of a white board and an Lb value of a black
board with a Macbeth spectrometer, and determining the difference
between the Lw value and the Lb value.
[0048] The powder leakage ratio of the nonwoven fabric of the invention
is 10% by weight or less, preferably 7% by weight or less, and more
preferably 5% by weight or less. When the powder leakage ratio exceeds
10% by weight, the powder leakage increases. As a result, use of
the nonwoven fabric as a tea filter results in leakage of much powder
in an extracted solution, and making the tea agreeable becomes difficult
due to the high content of a solid powder component. In addition,
the method of measuring powder leakage ratio is as described later.
[0049] The nonwoven fabric of the present invention is preferably
excellent in hydrophilicity so that it is rapidly submerged under
water without floating on the surface when it is placed in hot water.
The hydrophilicity of the nonwoven fabric of the invention is less
than 10 sec, preferably less than 7 sec, and more preferably less
than 5 sec. In order to make the hydrophilicity fall in a range
of less than 10 sec, the nonwoven fabric should be coated with,
for example, a hydrophilic agent in an amount of 0.05 to 5.0% by
weight, and preferably 0.1 to 3% by weight. In addition, when a
coating amount of the hydrophilic agent is excessive, the hydrophilic
agent is dissolved. As result, use of the nonwoven fabric for food
applications such as a tea bag causes a problem.
[0050] Examples of the hydrophilic agent include an aqueous solution,
an ethyl alcohol solution or an ethyl alcohol-water mixture solution
of such a surfactant used for food as a sorbitan aliphatic acid
ester, a polyglycerin aliphatic acid ester or a sucrose aliphatic
acid ester. Known methods such as a gravure roll system, a kiss
roll system, an immersion system or a spray system can be used as
the coating method.
[0051] The average apparent density of the nonwoven fabric of the
present invention is preferably from 0.05 to 0.25 g/cm.sup.3, and
more preferably from 0.08 to 0.22 g/cm.sup.3. The average apparent
density is related to a feel, stiffness, transparency and powder
leakage of the nonwoven fabric. When the average apparent density
falls in the above range, the nonwoven fabric is excellent in strength,
flexibility and transparency, and shows reduced powder leakage because
gaps among the yarns are suitable. Moreover, the nonwoven fabric
shows excellent bag formability during bag forming.
[0052] The nonwoven fabric of the present invention is useful as
a nonwoven fabric for a tea filter, and is preferably used as tea
bags prepared by subjecting the fabric to bag-making processing
to form flat or tetrahedral-shaped bags, and filling a material
to be extracted into the bags. There is no specific restriction
on the method of bag-making processing. For example, heat sealing,
melt sticking sealing, melt cutting sealing, ultrasonic sealing,
high frequency sealing, or the like sealing can be employed. Furthermore,
known bag-making machines can be used.
[0053] As a material to be extracted, for example, as tea leaves,
black tea, green tea or oolong tea is common. However, the material
to be extracted is not restricted to the above teas, and roasted
tea, green tea of a middle grade, barley tea, a herb, or the like,
may also be utilized.
[0054] The tea bag of the present invention may be a flat bag.
However, a tea bag having a three-dimensional shape is preferred
for the following reasons: the tea bag has a space, and tea leaves
can be well observed before immersion in hot water; moreover, when
the tea bag is placed in water, the state of the tea can be observed
much better; because the volume within the tea bag is large, swelling
and spreading of the tea leaves are good, and the tea is quickly
extracted. Preferred examples of the three-dimensional shape include
a tetragonal shape such as a triangular cone shape or a TetraPak
shape.
[0055] In general, tea bags having a three-dimensional shape are
filled with material to be extracted, packed in boxes, and marketed.
The tea bags each have a folded shape when packed in boxes. However,
when consumers take out the tea bags from the boxes and use them,
each tea bag preferably recovers the initial three-dimensional shape
rapidly. Because the nonwoven fabric of the present invention has
an average yarn diameter as thick as 7 to 40 .mu.m, it has good
resilient properties and a suitable stiffness. As a result the nonwoven
fabric is excellent in a three-dimensional shape recovery.
BRIEF DESCRIPTION OF THE DRAWING
[0056] FIG. 1 is a graph showing the relationship (line 1: left
hand side scale) between a maximum opening diameter and a transparency
of a nonwoven fabric in examples of the present invention, and the
relationship (line 2: right hand side scale) between a maximum opening
diameter and a powder leakage ratio thereof.
BEST MODE FOR CARRYING OUT THE INVENTION
[0057] The present invention is further explained below by making
reference to examples. However, the present invention is in no way
restricted thereto.
[0058] In addition, measurement methods, evaluation methods, and
the like, are as explained below.
[0059] (1) Fabric Weight (g/m.sup.2)
[0060] Measurements are made in accordance with JIS L 1906. Samples,
each 20 cm (longitudinal).times.25 cm (lateral), are cut out at
three sites, respectively. The weight of each sample is determined,
and the fabric weight in terms of weight per unit area is obtained
from the average.
[0061] (2) Average Yarn Diameter (.mu.m)
[0062] Microscopic photographs of yarns are taken at magnifications
of .times.500. The average yarn diameter is obtained from an average
of 10 yarns.
[0063] (3) Transparency (%)
[0064] The reflectivity of a sample is measured with a Macbeth
spectrometer of CE-3000 type (manufactured by Sakata Ink Co., Ltd.).
A difference between a white board Lw0 value and a black board Lb0
value, and used as a standard. From an Lw value and an Lb value
of a sample, the transparency of the sample is determined from the
following formula:
transparency (%)=[.DELTA.L/.DELTA.L0].times.100
[0065] wherein .DELTA.L0=Lw0-Lb0, and .DELTA.L=Lw-Lb.
[0066] (4) Powder Leakage Ratio (wt. %)
[0067] About 2 g of a filtering material for spinning (metal powder
CR 53, particle size classification of 25/50 mesh, 650/300 .mu.m,
manufactured by Taiheiyo Metal) is weighed out, and the weight W1
(g) is measured. The filtering material is placed on a nonwoven
fabric, 25 cm.times.25 cm, and shaken at 60 rpm for about 5 minutes
with a shaking machine. The weight W2 (g) of a filtering material
that has passed through the nonwoven fabric is then measured, and
the powder leakage ratio is obtained from the following formula:
powder leakage ratio (wt. %)=[W2/W1].times.100
[0068] (5) Air Permeability
[0069] The air permeability is obtained in accordance with JIS
L-1906 (Frajure method).
[0070] (6) Hydrophilicity
[0071] The hydrophilicity is measured in accordance with JIS L-1906
(dropping method). Water is dropped on a sample, and a time necessary
for the sample to permeate is measured. The results are evaluated
according to the following criteria:
[0072] {circle over (.circle-w/dot.)}: Water permeates the sample
within 5 sec.
[0073] O: Water permeates the sample within 10 sec.
[0074] X: Water does not permeate the sample for 10 sec or more.
[0075] (7) Average Apparent Density
[0076] The apparent density of a sample in terms of a weight per
unit volume is obtained from a fabric weight and a thickness of
the sample under a load of 10 kPa. The average apparent density
of the sample is obtained from an average of the measured values
at three sites.
[0077] (8) Maximum Opening Diameter
[0078] The maximum opening diameter is obtained in accordance with
JIS K-3832 (bubble point method).
[0079] A circular sample 40 mm in diameter is immersed in a liquid
so that all the pores of the sample are filled with the liquid by
capillary action. Air pressure is gradually applied to the sample
from the back side thereof. When the air pressure overcomes a liquid
surface tension within a capillary tube, an air bubble comes out;
the air pressure is measured. The initial bubble comes out of an
opening having the maximum opening diameter. The maximum opening
diameter can be calculated by determining the air pressure when
the initial bubble comes out.
[0080] (9) Seal Strength
[0081] Six samples, each being 5 cm wide and 30 cm long, are cut
out from a nonwoven fabric in the longitudinal direction. Six samples
are prepared in the same manner except that they are cut out in
the lateral direction. Each sample is sealed by ultrasonic waves
at three sites with a 1-mm thick round blade-shaped head horn of
an ultrasonic wave sealing machine having an output at 40 kHz (manufactured
by Brother Industries, Ltd.). Each sealed sample is attached to
a tensile testing machine in the vertical direction of the machine.
The sample is pulled at a tensile rate of 10 cm/min with a chuck-to-chuck
distance of 10 cm, and a maximum strength is measured. The average
of the six samples is determined, and defined as a seal strength.
[0082] (10) Melt Flow Rate (MFR)
[0083] Measurements on a sample are made in accordance with JIS
K-7210 "Flow test method of thermoplastic resin" (condition
14 in Table 1: a test temperature of 230.degree. C. and a test load
of 21.18 N), and the MFR is determined.
[0084] (11) Intrinsic Viscosity ([.eta.])
[0085] The intrinsic viscosity ([.eta.]) is a value obtained from
the following definition formula:
[.eta.]=lim (.eta..sub.r-1)/C
C.fwdarw.0
[0086] wherein .eta..sub.r (that is defined as a relative viscosity)
is a value obtained by dividing a viscosity of a diluted solution
at 35.degree. C. of a polymer dissolved in an o-chlorophenol solvent
having a purity of 98% or more by the viscosity of the above solvent
determined at the same temperature, and C is a polymer concentration
in terms of g/100 ml of the above solution.
EXAMPLES 1 TO 5, COMPARATIVE EXAMPLES 1 TO 2
[0087] A known spun bond method was used. A polypropylene resin
showing a MFR of 39, and having a titanium oxide content of 0.1%
by weight was spun through a spinneret by a melt spinning system.
The spun yarn was drawn with a high speed drawing apparatus, opened,
and collected to give a fiber web. The procedure was repeated while
a fabric weight and a yarn diameter were varied to give various
webs. Each web was then heat contact bonded by heat pressing between
an emboss roll and a smooth roll to give a spun-bonded, partial
heat contact bonded nonwoven fabric of polypropylene filaments yarn.
[0088] In any of Examples 1 to 5, each nonwoven fabric was then
coated with a sorbitan aliphatic acid ester as a hydrophilic agent
by a gravure roll system in an amount of 0.2 to 2.0% by weight,
and dried at 130.degree. C. to give a coated nonwoven fabric. In
addition, the nonwoven fabrics were not coated with the hydrophilic
agent in Comparative Examples 1 to 3.
[0089] Furthermore, in each of Examples 4 and 5, two types of thermoplastic
synthetic fiber webs differing from each other in a yarn diameter
and a fabric weight were used as an upper layer and a lower layer,
respectively, to give laminate of nonwoven fabrics.
[0090] Table 1 shows properties of the nonwoven fabrics thus obtained.
In addition, the numerical values in parentheses in the column of
"air permeability" are values each obtained from a sample
prepared by stacking two initial samples.
1 TABLE 1 Example Comp. Example 1 2 3 4 5 1 2 3 Upper Fabric weight
(g/m.sup.2) 12 25 40 15 10 10 65 40 layer Average yarn diameter
(.mu.m) 20 25 27 30 18 44 15 27 Lower Fabric weight (g/m.sup.2)
-- -- -- 10 15 -- -- -- layer Average yarn diameter (.mu.m) -- --
-- 25 25 -- -- -- Fabric weight (g/m.sup.2) 12 25 40 25 25 10 60
40 Partial heat contact bonding 25 15 10 15 15 5 35 10 ratio (%)
Coating amount of hydrophilic 0.2 0.4 2.0 0.2 0.3 0 0 0 agent(wt.
%) Average apparent density (g/cm.sup.3) 0.11 0.15 0.22 0.14 0.15
0.04 0.35 0.22 Air permeability (ml/cm.sup.2/sec) (180) 250 210
295 280 (235) 75 210 Transparency(%) 75 71 60 77 70 80 30 34 Powder
leakage ratio (wt. %) 4.5 1.5 0.7 2.5 1.0 19.5 0.2 0.7 Hydrophilicity(sec)
.circleincircle. .circleincircle. .circleincircle. .circleincircle.
.circleincircle. X X X Maximum opening diameter (.mu.m) 1650 650
350 750 650 2800 125 345 Seal Longitudinal 6.0 13.5 18.5 12.0 13.0
0.6 26.0 18.0 strength Lateral 4.0 7.5 12.5 8.5 7.2 0.3 17.5 12.0
(N/5 cm) Content of delustering agent (wt %) 0.1 0.1 0.1 0.1 0.1
0.1 0.1 0.7
[0091] It can be understood from Table 1 that the nonwoven fabrics
of the present invention (Examples 1 to 5) were excellent in transparency
and hydrophilicity and showed decreased powder leakage. Moreover,
as a result of measuring a variation ratio of a fabric weight, the
ratio was 6.5% in Example 2, and 4.7% in Example 5.
[0092] In contrast to the above results, the nonwoven fabric in
Comparative Example 1 showed much powder leakage and poor hydrophilicity
because the fabric had no hydrophilic agent coating, although the
fabric showed good transparency. Moreover, the nonwoven fabric in
Comparative Example 2 had large fabric weight, and a high density
of the yarn forming the fabric, and as a result, the fabric showed
decreased powder leakage; however, the fabric showed considerably
lowered transparency, and poor hydrophilicity because the fabric
had no hydrophilic agent coating. The nonwoven fabric in Comparative
Example 3 had a large content of a delustering agent, and as result
the fabric showed lowered transparency.
EXAMPLES 6 TO 10, COMPARATIVE EXAMPLES 4 TO 5
[0093] A partially heat contact bonded, spin-bonded nonwoven fabric
of a polyester filaments yarn was obtained in the same manner as
in Example 1 except that a bright resin of a poly(ethylene terephthalate)
(intrinsic viscosity of 0.76, titanium oxide content of 0.05% by
weight) was used in place of the polypropylene resin.
[0094] The nonwoven fabrics were then coated with a sorbitan aliphatic
acid ester as a hydrophilic agent in an amount of 0.1 to 0.5% by
weight with a gravure roll, and dried at 130.degree. C. In addition,
the nonwoven fabrics in Comparative Examples 4 and 5 were not coated
with a hydrophilic agent.
[0095] Furthermore, in each of Examples 9 and 10, two types of
thermoplastic synthetic fiber webs differing from each other in
a yarn diameter and a fabric weight were used as an upper layer
and a lower layer, respectively, to give a laminate of nonwoven
fabrics.
[0096] Table 2 shows properties of the nonwoven fabrics thus obtained.
In addition, the numerical values in parentheses in the column of
"air permeability" are values each obtained from a sample
prepared by stacking two initial samples.
2 TABLE 2 Example Comp. Example 6 7 8 9 10 4 5 Upper Fabric weight
(g/m.sup.2) 12 20 40 8 10 10 65 layer Average yarn diameter (.mu.m)
19 22 24 14 14 45 13 Lower Fabric weight (g/m.sup.2) -- -- -- 8
15 -- -- layer Average yarn diameter (.mu.m) -- -- -- 18 25 -- --
Fabric weight (g/m.sup.2) 12 20 40 16 25 10 65 Partial heat contact
bonding ratio (%) 25 15 10 25 15 3 40 Coating amount of hydrophilic
0.1 0.2 0.5 0.3 0.3 0 0 Agent (wt. %) Average apparent density (g/cm.sup.3)
0.11 0.15 0.20 0.14 0.18 0.03 0.37 Air permeability (ml/cm.sup.2/sec)
(170) 230 185 (145) 220 (265) 60 Transparency (%) 72 67 57 71 65
81 33 Powder leakage ratio (wt. %) 4.8 1.3 0.5 1.8 0.7 19.6 0.2
Hydrophilicity (sec) .circleincircle. .circleincircle. .circleincircle.
.circleincircle. .circleincircle. X X Maximum opening diameter (.mu.m)
1620 630 430 1150 570 2700 110 Seal Longitudinal 4.0 10.5 15.5 6.5
12.5 0.3 21.0 strength Lateral 3.0 6.5 11.0 3.7 7.8 0.1 13.5 (N/5
cm) Content of delustering agent (wt %) 0.05 0.05 0.05 0.05 0.05
0.05 0.05
[0097] It can be understood from Table 2 that the nonwoven fabrics
of the present invention (Examples 6 to 10) were excellent in transparency
and hydrophilicity and showed decreased powder leakage.
[0098] In contrast to the above results, the nonwoven fabric in
Comparative Example 4 showed much powder leakage and poor hydrophilicity,
although the fabric showed good transparency. Moreover, because
the yarn forming the nonwoven fabric in Comparative Example 5 had
a large yarn density, the fabric showed decreased powder leakage;
however, the fabric showed poor transparency and hydrophilicity.
EXAMPLES 11 TO 15, COMPARATIVE EXAMPLES 6 TO 7
[0099] A partially heat contact bonded nonwoven fabric of an aliphatic
polyester filaments yarn was obtained in the same manner as in Example
1 except that a biodegradable resin (titanium oxide content of 0.03%
by weight) of a poly(lactic acid)(copolymerization ratio (molecular
ratio) of D form/L form of 1.5/98.5; melting point of 173.degree.
C.; MFR of 13 g/10 min) was used in place of the polypropylene resin.
[0100] The nonwoven fabrics were then coated with a sorbitan aliphatic
acid ester as a hydrophilic agent in an amount of 0.2% by weight
with a gravure roll, and dried at 130.degree. C. In addition, the
fabrics in Comparative Examples 6 and 7 were not coated with a hydrophilic
agent.
[0101] Furthermore, in each of Examples 14 and 15, two types of
thermoplastic synthetic fiber webs differing from each other in
a yarn diameter and a fabric weight were used as an upper layer
and a lower layer, respectively, to give a laminate of nonwoven
fabrics.
[0102] Table 3 shows properties of the nonwoven fabrics thus obtained.
In addition, the numerical values in parentheses in the column of
"air permeability" are values each obtained from a sample
prepared by stacking two initial samples.
3 TABLE 3 Example Comp. Example 11 12 13 14 15 6 7 Upper Fabric
weight (g/m.sup.2) 12 20 30 8 10 11 64 layer Average yarn diameter
(.mu.m) 14 18 20 12 14 44 13 Lower Fabric weight (g/m.sup.2) --
-- -- 8 15 -- -- layer Average yarn diameter (.mu.m) -- -- -- 15
20 -- -- Fabric weight (g/m.sup.2) 12 20 30 16 25 11 64 Partially
heat contact bonding ratio (%) 25 15 5 25 15 4 38 Coating amount
of hydrophilic 0.1 0.2 0.5 0.1 0.2 0 0 agent (wt. %) Average apparent
density (g/cm.sup.3) 0.13 0.17 0.20 0.15 0.21 0.03 0.36 Air permeability
(ml/cm.sup.2/sec) (170) 215 190 (140) 205 (260) 58 Transparency
(%) 76 70 64 73 68 80 29 Powder leakage ratio (wt. %) 3.3 1.1 0.7
1.9 0.8 19.4 0.3 Hydrophilicity (sec) .circleincircle. .circleincircle.
.circleincircle. .circleincircle. .circleincircle. X X Maximum opening
diameter (.mu.m) 1650 830 670 960 740 2560 120 Seal Longitudinal
3.7 9.5 13.5 5.8 10.7 0.3 20.5 strength Lateral 2.8 6.3 10.2 4.1
7.4 0.1 13.0 (N/5 cm) Content of delustering agent (wt %) 0.03 0.03
0.03 0.03 0.03 0.03 0.03
[0103] It can be understood from Table 3 that the nonwoven fabrics
of the present invention (Examples 11 to 15) were excellent in transparency
and hydrophilicity, showed decreased powder leakage, and were also
excellent in biodegradability.
[0104] In contrast to the above results, the nonwoven fabric in
Comparative Example 6 showed much powder leakage and poor hydrophilicity,
although the fabric showed good transparency. Moreover, because
the yarn forming the nonwoven fabric in Comparative Example 7 had
a large yarn density, the fabric showed decreased powder leakage;
however, the fabric showed poor transparency and hydrophilicity.
EXAMPLE 16
[0105] The spun-bonded nonwoven fabric of a polypropylene filaments
yarn obtained in Example 2 was coated on one side with a fibrous
material in an amount of 10 g/m.sup.2 by curtain spraying a hot
melt resin to give a laminated nonwoven fabric. In addition, a polypropylene
resin (trade name of YH 151-1P, manufactured by Hitachi Chemical
Polymer Co., Ltd., melting point of 145.degree. C.) was used as
the hot melt resin. The melting point difference between the filaments
yarn and the hot melt resin was 60.degree. C. The laminated nonwoven
fabric thus obtained was then coated with a hydrophilic agent in
the same manner as in Example 2 to give a nonwoven fabric.
[0106] The nonwoven fabric thus obtained had the following properties:
a fabric weight of 35 g/m.sup.2; a variation ratio in the fabric
weight of 3.8%; a partial heat contact bonding ratio of 15%; a coating
amount of a hydrophilic agent of 0.4% by weight; an average apparent
density of 0.22 g/cm.sup.3; a transparency of 69%; a powder leakage
ratio of 1.2% by weight; a maximum opening diameter of 630 .mu.m;
and good hydrophilicity ({circle over (.circle-w/dot.)}). Moreover,
the strength of a seal formed by a heat sealing machine at 130.degree.
C. was 8.5 N/5 cm (longitudinal) and 4.3 N/5 cm (lateral). The nonwoven
fabric was excellent in heat sealability and transparency, showed
decreased powder leakage, and was suited to a filter for tea.
EXAMPLE 17
[0107] A fiber web was obtained by the air lay system from a composite
yarn (average yarn diameter of 18 .mu.m, a yarn length of 51 mm)
having a sheath-core structure that is formed out of a poly(ethylene
terephthalate) (melting point of 265.degree. C.) as a core and a
copolymerized polyester (melting point of 145.degree. C.) as a sheath.
The fiber web in an amount of 10 g/m.sup.2 and the spun-bonded nonwoven
fabric of a polyester filaments yarn obtained in Example 6 were
stacked. The stacked materials were passed through smoothing rolls
at 160.degree. C. to give a laminate of nonwoven fabrics. The laminate
of nonwoven fabrics thus obtained was then coated with a hydrophilic
agent in the same manner as in Example 6 to give a nonwoven fabric.
The nonwoven fabric thus obtained had the following properties:
a fabric weight of 22 g/m.sup.2; a variation ratio in the fabric
weight of 4.3%; a partial heat contact bonding ratio of 25%; a coating
amount of a hydrophilic agent of 0.1% by weight; an average apparent
density of 0.20 g/cm.sup.3; a transparency of 67%; a powder leakage
ratio of 3.2% by weight; a maximum opening diameter of 1,150 .mu.m;
and good hydrophilicity ({circle over (.circle-w/dot.)}). Moreover,
the strength of a seal formed by a heat sealing machine at 160.degree.
C. was 6.5 N/5 cm (longitudinal) and 4.8 N/5 cm (lateral). The nonwoven
fabric was excellent in heat sealability and transparency, showed
a decreased powder leakage, and was suited to a filter for tea.
EXAMPLE 18
Example of Tea Bags
[0108] A heat seal bag-making machine of three-dimensional forming
type (for forming a tetrahedral shape) was used. The nonwoven fabric
obtained in Examples 16 or 17 was slit to give a tape-like fabric
125 mm wide. Strings and tags were bonded to the fabric. The fabric
was then folded in the direction of width (125 mm), and the edges
were heat sealed with a width of 5 mm to form a cylindrical shape.
The cylindrically shaped fabric was heat sealed at portions corresponding
to the bottom portions at a pitch of 50 mm to give bags.
[0109] Two grams of black tea leaves were placed in each bag, and
the opening portion of the bag was heat sealed to give a tea bag.
[0110] When the tea bag was observed, it was excellent in transparency,
and the shape of the tea could be confirmed. When the tea bag was
placed in 200 ml of hot water in a cup, the bag was submerged under
water in 1 second. One could see the black tea leaves in the tea
bag spread and swell. The extracted solution of the black tea was
a delicious tea with a powerful scent.
INDUSTRIAL APPLICABILITY
[0111] The nonwoven fabric of the present invention is excellent
in transparency, shows decreased powder leakage, has heat sealability,
was excellent in bag-making processability, and exhibits good biodegradability.
The nonwoven fabric is therefore useful as a filter for materials
to be extracted such as black tea, green tea and oolong tea.
[0112] The tea bag of the present invention prepared by wrapping
a particle-shaped material to be extracted, that is, crushed leaves
of black tea, green tea, oolong tea, or the like, shows decreased
powder leakage, is submerged under hot water without floating when
placed therein, and exhibits quick extraction of the tea components.
In addition to the above advantages, because the material to be
extracted can be seen from the outside of the tea bag material,
the tea bag is particularly suited when tea leaves such as leaves
of high grade black tea are to be seen through the tea bag material. |