Abstrict Formed is a new desiccant film made of an uncoated microporous
film secured to an uncoated laminate film wherein the inner surface
of both the microporous film and the laminate material are compatible.
This film is less expensive to form and produces a stronger bond
than conventional coated materials used for desiccant packaging.
Claims We claim:
1. A desiccant container comprising
a desiccant material surrounded by a laminated, water vapor permeable
desiccant packaging material, wherein said packaging material comprises
an uncoated microporous film having an inner and outer surface heat
sealed to an uncoated laminate film having an inner and outer surface,
wherein the uncoated microporous film comprises a different composition
from the uncoated laminate film, wherein edges of the inner surface
of the uncoated microporous film are sealed to edges of the inner
surface of the uncoated laminate film, and wherein the inner surface
of the uncoated microporous film and the inner surface of the uncoated
laminate film are comprised of compatible polymeric materials.
2. The desiccant container of claim 1 wherein the uncoated laminate
film has a lower moisture vapor transmission rate than the microporous
film.
3. The desiccant container of claim 1 wherein the microporous film
has an air permeability of less than about 400 Gurley seconds/100
ml.
4. The desiccant container of claim 1 wherein the uncoated microporous
film is produced from a polyethylene or polypropylene polyolefin
material.
5. The desiccant container of claim 1 wherein the inner surface
of the uncoated microporous film of the desiccant packaging material
comprises a water vapor permeable, uncoated polyolefinic polyethylene
material.
6. The desiccant container of claim 1 wherein the inner surface
of the uncoated microporous film of the desiccant packaging material
comprises a water vapor permeable, uncoated polyolefinic polypropylene
material.
7. The desiccant container of claim 1 wherein the inner surface
of the uncoated laminate film comprises a water vapor permeable
uncoated polyolefinic polyethylene compatible material.
8. The desiccant container of claim 1 wherein the inner surface
of the uncoated laminate film comprises a water vapor permeable
uncoated polyolefinic polypropylene compatible material.
9. The desiccant container of claim 1 wherein the inner surface
of the uncoated microporous film and the inner surface of the uncoated
laminate film comprise water permeable uncoated polyolefinic polyethylene
compatible material.
10. The desiccant container of claim 1 wherein the inner surface
of the uncoated microporous or nonwoven film and the inner surface
of the uncoated laminate film comprise water permeable uncoated
polyolefinic polypropylene compatible material.
11. The desiccant container of claim 1 wherein the softening temperature
of the inner surface of the uncoated laminate film is lower than
or equal to the softening temperature of the inner surface of the
uncoated microporous film.
12. The desiccant container of claim 1 wherein the outer layer
of the uncoated laminate film comprises a polyester or nylon or
polymer with a softening range higher than the inner surface of
the laminate film material.
Description BACKGROUND OF INVENTION
1. Field of Invention.
This invention relates to desiccant containers. More specifically,
this invention relates to a desiccant container containing a desiccant
material secured within a packaging material wherein the packaging
material is multilayered, wherein the layers are uncoated and wherein
the inner surfaces of the layers are formed from compatible materials.
2. Prior Art.
Desiccant containers which absorb water vapor, water, liquids and
the like are well known in the art. Generally, these containers
are comprised of a water or water vapor permeable packaging material
formed from fibrous or film products securely sealed together at
the edges of the packaging. The packaging material encapsulates
a desiccant material, such as silica gel. The volume of water or
water vapor absorbed by the desiccant container is generally determined
by the absorbent capacity of the desiccant material contained within
the container.
One type of desiccant container absorbs both water vapor and liquid
water by permitting both to pass through the packaging material
to be absorbed by the desiccant material. In some circumstances,
the packaging material for this type of product dissolves to permit
the desiccant material contained within the desiccant container
to have direct contact with the liquid. This type of product is
disclosed, for example, in U.S. Pat. Nos. 4749600 4725464
4224366 4853266 4748069 and EPO 562846 One disadvantage
of this type of liquid absorbing desiccant container is that once
the packaging material dissolves, liquid water which is initially
absorbed by the desiccant material may escape from the desiccant
container to contact the environment surrounding the desiccant container.
Another type of desiccant container absorbs water vapor but not
liquid water. The packaging material for this type of desiccant
container is designed to prevent water absorbed within the desiccant
container as water vapor from being released from the desiccant
container in the form of liquid water. This type of desiccant container
is especially useful during transportation of products over long
distances. This type of desiccant container is frequently used among
metal storage containers which hold products being shipped. In this
use, the desiccant container must absorb water vapor without releasing
liquid water from the container. Any release of water might result
in rusting of the associated metal storage containers. Even though
many current desiccant containers are "designed" not to
leak, because of the composition of the packaging material, leaks
often occur resulting in rusting of the storage containers.
In addition to the problems associated with producing a desiccant
container which does not release liquid water after absorption of
water vapor, it is also important that the packaging materials used
to encapsulate the desiccant product be inexpensive. Further, the
packaging material for such desiccant containers should also be
simple to produce and capable of manufacture using high speed production
facilities.
Current desiccant containers are usually formed of film laminates
which are sealed using heater seal bars. These conventional multipurpose
film materials are generally coated, with an adhesive normally on
the seal side. As a result, the strength of the packaging material
for the desiccant container is dependent on the strength of the
adhesive seal between the layers of the film laminate.
The packaging material for desiccant containers must also be microporous
so that water vapor can pass through the packaging material to be
absorbed by the desiccant material. Conventional desiccant packaging
utilizes a microporous layer or layers laminated to a vapor-permeable
polyolefinic material where the vapor permeable layer is different
in structure than the microporous layer. This second layer provides
additional strength and stability for the desiccant packaging material.
Strength and stability for the desiccant packaging is good if two
similar microporous layers are sealed together but this usually
requires special equipment such as impulse sealers which are slow
in operation. Because of this difference in structure, it is often
difficult to heat seal the microporous film to the second layer
by conventional melt sealing equipment because of the differences
in the softening points of the two layers. When two layers of a
conventional packaging material are sealed by softening the inside
portions of each layer, the softened film tends to adhere to the
heat seal bars or heat rolls of the sealing machine. Under these
circumstances a special heat-sealer is often necessary, such as
an impulse heat-sealer, in order to heat seal these differing layers.
When such a heat-sealer is used in an automatic packaging machine,
the automatic packaging machine operates slower than conventional
heat sealing equipment. Further, the laminated film that is formed
frequently is not strongly sealed. In addition, the cost of coated
types of films which are often used to form these desiccant containers
is higher than uncoated films.
Laminated films have been utilized for various types of containers
wherein the composition of the layers of the laminated film are
different. For example, U.S. Pat. No. 4332845 discloses a bag
used to encapsulate an oxygen absorbent, wherein the bag is composed
of a laminated sheet comprising a microporous film and one or more
gas permeable sheets laminated to one or both sides of the microporous
film. The film is selected from a number of conventional films including,
for example, Celgard.RTM. (manufactured by Celanese Corporation)
and Tyvek.RTM. (manufactured by E. I. DuPont). The lamination process
utilizes a low melting temperature adhesive secured to the inside
surface of a microporous material to laminate the microporous film
to the gas permeable layer. Alternatively, a portion of the gas
permeable sheet can be melted to secure it to the microporous layer.
U.S. Pat. No. 4856649 discloses a deodorizer parcel formed from
a composite sheet packaging material composed of a gas permeable
sheet, such as a sheet of paper or nonwoven cloth, laminated onto
several layers of a plastic film. The plastic films that are laminated
to the paper may comprise a laminate themselves comprised of a plastic
film with a high softening point secured to a plastic film with
a low softening point. The surface of the plastic film laminated
to the gas permeable sheet is composed of a different material than
the gas permeable sheet.
U.S. Pat. No. 4322465 discloses a sealed, parenteral container
for containing a parenteral solution. The packaging material for
the parenteral container is a water vapor barrier material which
includes a first plastic sheet, a second plastic sheet and a metal
sheet wherein the first and second plastic sheets are preferably
comprised of a polypropylene.
U.S. Pat. No. 4210686 discloses a multilayered plastic sheeting
material which is resistant to water vapor transmission. The first
layer is comprised of a block copolymer and a polystyrene secured
to a polyolefinic second layer.
U.S. Pat. No. 4769175 discloses an oxygen scavenger for preserving
foods or other articles in an oxygen-free environment, wherein the
packaging may consist of a nonwoven fabric or microporous film laminated
to various plastic films. The composition of each side of the laminate
may consist of a number of different polymers including polypropylene,
polyethylene and polyethylene terephthalate.
Finally, U.S. Pat. No. 5035731 discloses a moisture absorbent
insert for use in a cigarette container. The membrane surrounding
the absorbent material consists of a microporous membrane such as
Celgard.RTM. or a cellulose triacetate.
While these references disclose multilayered packaging materials,
some of which are used with desiccant materials, there are still
significant problems in the production of a packaging material for
desiccant containers and their use with specific types of desiccant
materials. During the production of conventional laminated packaging
materials, at least one side of the packaging material is generally
coated with an adhesive. This adhesive is heated to bind the two
layers together. Because of this adhesive, it is difficult for the
equipment utilized to form the desiccant packaging to work at peak
capacity. Weak seals which are frequently formed using this equipment
often result in significant down time for the equipment. In addition,
films laminated with adhesives do not form a strong bond between
the layers, which is desirable for desiccant packaging. In addition,
because coated films are more expensive than uncoated films, packaging
material formed using coated films tends to be more expensive than
laminated films formed from uncoated films.
Therefore it is an object of the invention to disclose a desiccant
container containing a desiccant material encapsulated by a laminated,
water vapor permeable desiccant packaging material formed using
conventional form-fill sealing equipment.
It is a further object of the invention to disclose a desiccant
container formed from a laminated, water vapor permeable desiccant
packaging material which exhibits great strength and is less costly
to produce than conventional desiccant packaging material.
It is a further object of the invention to disclose a desiccant
container formed from a laminated, water vapor permeable desiccant
packaging material, wherein the inside surfaces of facing layers
of the laminate are formed from compatible materials.
It is a still further object of the invention to disclose a desiccant
container formed from a laminated, water vapor permeable desiccant
packaging material comprising an uncoated microporous or nonwoven
film layer secured to an uncoated laminated film, wherein the inner
layers of the microporous film and the laminate film are composed
of compatible material.
It is a still further object of the invention to disclose a desiccant
container formed from a laminated, water vapor permeable desiccant
packaging material wherein the desiccant material contained within
the packaging material is a combination of calcium chloride and
starch, preferably a modified starch.
These and other objects and features of the present invention will
become apparent to those skilled in the art from a consideration
of the following detailed description, drawings and claims. The
description, along with the accompanying drawings, provides a selected
example of the construction of the product and process to illustrate
the invention.
SUMMARY OF INVENTION
In accordance with the present invention there is provided a desiccant
container for absorbing water vapor without releasing water from
the container comprising a desiccant material encapsulated by a
laminated, water vapor permeable desiccant packaging material, wherein
said packaging material comprises an uncoated microporous or nonwoven
film, heat sealed to an uncoated laminate film, wherein the uncoated
microporous or nonwoven film is produced from a different composition
than the uncoated laminate film, wherein the inner surface of the
uncoated microporous or nonwoven film is sealed to the inner surface
of the uncoated laminate film, and wherein the inner surface of
the uncoated microporous or nonwoven film and the inner surface
of the uncoated laminate film are comprised of compatible polymeric
materials. The desiccating material utilized with this desiccant
container may be a conventional desiccant material but, preferably,
it is comprised of a combination of calcium chloride and starch,
preferably modified corn starch.
In addition, there is disclosed a process for forming a desiccant
container for absorbing and immobilizing water vapor without releasing
water from the desiccant container comprising
(a) forming an uncoated microporous or nonwoven film having an
inner and outer surface,
(b) forming an uncoated, water vapor permeable laminated film having
an inner and outer surface, wherein the uncoated microporous or
nonwoven film comprises a different composition than the uncoated
laminated film and wherein the inner surface of the uncoated microporous
or nonwoven film is compatible with the inner surface of the uncoated
laminated film,
(c) sealing most of the edges of the inner surface of the microporous
film to the edges of the inner surface of the uncoated laminated
film to form a desiccant packaging sheet,
(d) filling the desiccant package with a desiccating material,
preferably a mixture of calcium chloride and starch, and
(e) sealing the remaining unsealed edges of the package to form
the desiccant container.
BRIEF DESCRIPTION OF THE DRAWINGS
This invention will now be described with reference to the accompanying
drawings in which:
FIG. 1 is a perspective view of the desiccant container.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Although the invention is adaptable to a wide variety of uses,
it is shown in the drawings for the purpose of illustration as embodied
in a desiccant container (10) for absorbing and immobilizing a liquid
comprised of a desiccant packaging material (12) encapsulating a
liquid absorbing and immobilizing desiccant material (14). See FIG.
1.
The desiccant packaging material (12) comprises a laminated film
layer (16) with an inner (18) and outer (20) surface preferably
formed from an uncoated microporous or nonwoven film layer sealed
to an uncoated, water vapor permeable laminate film (22) with an
inner (24) and outer (26) surface. The inner surface of the layers
are sealed at the edges as shown in FIG. 1.
Conventional microporous or nonwoven films used for the manufacture
of a laminated packaging material have been formed into a composite
film bonded to another layer of material. Conventionally, the bonding
of the two layers is accomplished by the use of an adhesive which
coats one or both of the inside surfaces of the layers. It has been
surprisingly discovered that strong, laminated desiccant packaging
materials can be produced from uncoated microporous or nonwoven
films.
The uncoated microporous or nonwoven film (16) comprises a film
having a plurality of fine openings, which film is gas permeable,
but water impermeable when there is no difference between the air
pressure outside of the film and inside of the film. The size of
the openings is preferably in the range of about 0.01 to 50 microns.
The uncoated microporous or nonwoven film may constitute a single
film layer or may comprise a laminate of separate microporous film
layers. Preferably the film is a single layer microporous film formed
from a polyolefinic material, such as polyethylene, polypropylene,
poly(fluorinated ethylene), ethylene vinyl acetate, ethylene acrylic
ester and the like. The uncoated microporous or nonwoven film may
be prepared by any conventional film forming process including cold
orientation of the film, orientation of different substance-containing
films, extraction of different substances from different substance-containing
films, extraction of different substance-containing film followed
by orientation of the treated film, cross-dispersing of a bundle
of fibers followed by heat-pressing the resulting film and any other
conventional procedures utilized for the formation of a microporous
film. Many such microporous films are commercially available and
are sold, for example, under the name Celgard.RTM. (Hoechst Celanese
Corporation), GORE-TEX.RTM. (Gore & Co. Gmbh) and Tyvek.RTM.
(E. I. DuPont). The preferred microporous film has a Gurley-type
air permeability of about 0.01 to 10000 sec./100 millimeters, preferably
1 to 1000 second/100 millimeters and most preferably less than
about 400 seconds/100 millimeters. Preferably, the microporous film
is a polyethylene or polypropylene-based microporous film and most
preferably a polyethylene spun-bonded paper such as Tyvek.RTM. 1059B
or 1037B manufactured by E. I. DuPont, or a polypropylene based
film, such as GDT II manufactured by San Ai, Ltd. of Osaka, Japan.
The second layer of the desiccant packaging material is preferably
formed from the uncoated laminate film (22). The laminate film can
be formed of conventional polymeric materials. The critical aspect
of the composition of the laminate film is that its inner surface
(24), which is bonded to the inner surface (18) of the uncoated
microporous or nonwoven film layer at the edges of the packaging
material, must be comprised of materials which are compatible with
the composition of the inner surface of the microporous or nonwoven
film layer. Materials that can be used to form this laminate film
include conventional polyolefinic materials such as polyolefinic
polypropylene, polyolefinic polyethylene, polyesters and the like.
Preferably, the uncoated laminate film has a lower moisture vapor
transmission rate than the microporous or nonwoven film. Also preferably
the softening temperature of the uncoated laminate film is lower
than or equal to the softening temperature of the inner surface
of the uncoated microporous film. Preferably the laminate film is
comprised of a laminated film comprising a high melting or softening
point material, such as polyester, located on one side laminated
to a lower melting point material, such as polypropylene on the
opposite side. Examples of acceptable laminate film include, for
example, RPP91-1964 or RPP1007a manufactured by RollPrint.
The outer surface (26) of the laminate film are preferably formed
from materials which are incompatible with the microporous layer,
such as materials having a higher melting or softening point than
that of the inner surface of the microporous film, such as polyester
material. In contrast, the inner surface of the laminate film (24)
must be formed from a material which is compatible with the inner
surface (18) of the microporous film. By having the two inner surfaces
formed from compatible materials, a strong bond is formed between
those layers when they are heat sealed together. "Compatible"
means that the materials mix on a molecular scale and will crystallize
homogeneously. Thus, while such layers may not have precisely the
same softening point, they should have softening points which are
consistent, so that the materials will mix on a molecular level.
Compatible bonds generally have a bond strength of at least about
5 lb./in. or more. For example, the compatible materials may include
high density, low density, or linear density polyethylenes as well
as nonoriented, bi-axially oriented or laminated polypropylenes.
In contrast, the outer surface of at least the laminate film should
be manufactured from incompatible materials such as polyester or
nylon or a polyethylene or polypropylene material with a higher
softening point than the inner surface of the laminate film material.
In addition, it is also critical that the inner surface of both
the laminate film and the microporous or nonwoven film be uncoated
with an adhesive. Coated film, when sealed to other coated or uncoated
films, frequently form poor quality, weak seals. In addition, the
sealing machines used for sealing coated films are also more expensive
and more difficult to operate, resulting in greater expense for
the manufacture of sealing coated films. Further, uncoated films
are generally less expensive than coated films, sometimes by as
much as 50 percent.
Suitable materials for use as the desiccant material to be incorporated
into the desiccant packages include conventional desiccating material
such as silica gel, clays, calcium chloride, alkali metal carboxylate
salts of starch--polyacrylonitrile and other products that absorb,
gel or thicken upon contact with water or water vapor, such as sodium
polyacrylate. However, it has been surprisingly discovered that
the preferred desiccant material is a mixture of calcium chloride
and starch, preferably a modified starch, such as MIRA-SPERSE.RTM.
623 626 and 629 produced by Staley Food Products. The composition
of this desiccant material is preferably about 20 to about 90 percent
calcium chloride mixed with about 80 to about 10 percent starch.
More preferably, the calcium chloride comprises about 50 to about
80 percent while the starch comprises about 50 to about 20 percent
of the composition.
The process for the formation of the desiccating container comprises
a number of steps. The desiccant packaging material is first formed.
To form the desiccant packaging material of the instant invention,
the uncoated microporous and nonwoven film (16) is first formed
or acquired from conventional sources. In a preferred embodiment
the microporous film is an uncoated microporous or non-woven film
such as Celgard.RTM. produced Hoechst Celanese Corporation, Tyvek.RTM.
Nos. 1059B and 1073B produced by E. I. DuPont or certain other polypropylene-based
non-woven films such as GDTI, II produced by San Ai of Osaka, Japan.
As stated above, the permeability of this microporous film should
be in the range of about 1 to about 1000 Gurley seconds per 100
millimeters and preferably less than about 400 seconds per 100 millimeters.
Following the formation of the uncoated microporous or nonwoven
film, the uncoated laminate film (22) is formed. As stated above,
this uncoated laminate film can be comprised of different layers
of the same or different materials laminated together. However,
the critical element of the composition of this material is that
the film must be uncoated and the inner surface (24) of the laminate
film, which is sealed to an inner surface (18) of the microporous
material, must be formed of a material which is "compatible"
with the inner surface of the uncoated microporous or nonwoven film.
In one preferred embodiment, the laminate film is a laminated film
containing a polyester material on the outer surface with a polypropylene
material on the inner surface, such as RPP 91-1964 made by RollPrint.
Another preferred embodiment is RPP 31-1007A, a polyethylene-based
material also manufactured by RollPrint.
Following the formation of the two layers, the edges of the layers
are sealed together by a conventional heat sealing procedure. One
of the advantages of the product formed from the instant invention
is that the bond formed between the two compatible, uncoated materials
has a significantly greater strength than conventional bonds utilizing
an adhesive coating. By utilizing the capability of compatible materials
to form a strong seal without using an adhesive, the strength of
the desiccant packaging material is significantly increased over
conventional packaging materials. In addition, these uncoated materials
have a lower cost of production and run better through the sealing
equipment.
The preferred desiccant material is then placed within the desiccant
packaging. By using the preferred desiccant material (14) formed
from calcium chloride and starch, preferably a modified starch,
lesser quantities of the desiccating material need be utilized than
for conventional desiccating containers and still achieve the same
amount of moisture absorbency.
Following the addition of the desiccant material to the desiccant
packaging material, the remaining unsealed edges of the desiccant
container are sealed to complete the formation of the desiccant
container.
EXAMPLES
Example 1
A microporous film manufactured by San Ai, of Osaka, Japan, known
as GDTII, was sealed to a laminate film, RPP 32-2011 manufactured
by RollPrint. Neither film was coated with an adhesive. The inner
surface of both layers was compatible as they are both polyethylene
materials. The edges of the inner surfaces of the materials were
sealed together by heated seal bars, where both front and back bars
are heated to 350.degree. F. Following the formation of this seal,
the strength of the seal was tested, using an Instron tensile strength
tester on an inch wide strip of the material. The average seal strength
in pounds force per square inch was 9.38 lb/in.sup.2.
Example 2
An uncoated polyethylene-based spun bonded microporous material,
Tyvek.RTM. 1059B manufactured by DuPont, was sealed to RPP 31-1071
manufactured by RollPrint. The inner surfaces of these two layers
were compatible because they were both polyethylene materials. Neither
of these films were coated with an adhesive. The edges of the inner
surfaces of the two films were sealed together by use of heated
seal bars with both front and back heated at a temperature of 350.degree.
F. Following the formation of this sealed laminated film, the strength
of the seal was tested using the procedure described in Example
1. The average seal strength was 10.21 lb./in.sup.2.
Example 3--Comparative Example
To compare the strength of the seals made with coated materials,
the following composite film was produced: the edge of a Desiview.RTM.
MP-20 film, manufactured by Wraps, Inc. of East Orange NJ, was sealed
to the edges of a Tyvek.RTM. 1059 material manufactured by DuPont
and coated by Oliver Products of Grand Rapids, Mich. with a 10 DP
adhesive coating. The two layers were sealed by use of heat seal
bars. The surfaces which were sealed together were incompatible
as the inner surface of the Desiview.RTM. film was comprised of
polyester polyolefin while the Tyvek.RTM. 1059 was a spun-bound,
polyethylene material. The strength of the seal was computed based
on the test described in Example 1. The average strength of the
seal was 2.77 lb/in.sup.2.
As is clear from these examples, desiccant packaging materials
formed from an uncoated microporous film sealed to an uncoated film
laminate where the inner surfaces of the films comprise compatible
materials are superior in performance over conventionally formed
desiccant packages sealed using an adhesive coating. Not only is
the strength of the seal between the two layers at least as strong
and generally stronger than that produced from coated materials,
but the price of the uncoated materials is significantly less. In
addition, because none of the layers of the packaging material are
coated, the packaging material can be formed using conventional
sealing equipment, such as resistance heated seal bars running at
peak efficiency. When the preferred desiccant material is utilized,
these desiccant packages also have water vapor absorption capabilities
at least as good as conventional desiccant packages formed from
coated microporous and laminated films. |