Disclosed is a new desiccant composition containing calcium chloride
and a modified starch, preferably a modified corn starch. The composition
contains from about 5 to about 95 percent calcium chloride and from
about 5 to about 95 percent starch.
What is claimed is:
1. A process for manufacturing a desiccant container comprising
(a) preparing a water vapor permeable film product,
(b) preparing a desiccant composition wherein the desiccant composition
comprises calcium chloride and a modified starch wherein the calcium
chloride comprises at least about 5 to 95 percent of the composition
by weight and the modified starch comprises from about 5 to about
95 percent of the composition by weight,
(c) placing the desiccant composition between layers of the water
vapor permeable film product, and
(d) sealing edges of the water vapor permeable film product around
the desiccant composition to produce the desiccant container.
2. The process of claim 1 wherein the calcium chloride comprises
from about 20 to about 95 percent of the desiccant composition by
weight and the modified starch comprises from about 5 to about 80
percent of the composition by weight.
3. The process of claim 1 wherein the calcium chloride comprises
from about 50 to about 80 percent of the desiccant composition by
weight and the modified starch comprises from about 20 to about
50 percent of the composition by weight.
4. The process of claim 1 wherein the modified starch comprises
a modified corn starch.
5. The process of claim 1 wherein the modified starch exhibits
a Brookfield viscosity of at least about 1 cps.
6. The process of claim 1 wherein the modified starch comprises
an oxidized starch.
7. The process of claim 1 wherein the modified starch comprises
an enzyme-converted starch.
8. The process of claim 1 wherein the modified starch comprises
at least one functional group selected from the group consisting
of hydroxyl, carbonyl, amido, and amino groups.
9. The process of claim 1 wherein the modified starch is modified
by a process selected from the group consisting of cross linking,
substitution and granulation.
10. The process of claim 1 wherein the modified starch is selected
from the group consisting of oxidized starches, enzyme-converted
starches and hydroxyethylated starches.
BACKGROUND OF INVENTION
1. Field of Invention
This invention relates to desiccant containers. More specifically,
this invention relates to a composition of material for use in a
desiccant container comprising a combination of calcium chloride
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
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.
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.
There are many common products that are utilized as desiccating
agents. Among the most common used include silica gel, calcium sulfate,
calcium fluoride, activated charcoal, molecular sieves, lithium
chloride, calcium chloride and other such products. A common list
of these drying agents is contained, for example, in Kirk-Othmer,
Encyclopedia of Chemical Technology, Volume 7 pages 378-398. Common
desiccating agents for use in conventional desiccant containers
are also disclosed in U.S. Pat. No. 5114003 which discloses the
use of a montmorillonite clay, silica gel, molecular sieve, calcium
oxide, calcium sulfate and calcium chloride. The use of silica gel,
alumino silicate, alumina, activated charcoal and molecular sieves
as desiccating agents are disclosed in U.S. Pat. No. 4464261.
Commercial grade calcium chloride is a widely used desiccant due
to its low cost and high degree of hygroscopicity. Calcium chloride
compacted in the form of particles or beads is used as a drying
agent, for example, in U.S. Pat. No. 3923944.
Mixtures and combinations of other materials have been combined
with calcium chloride to form desiccating products. For example,
polyethylene glycol was mixed with calcium chloride to form a desiccant
product in U.S. Pat. No. 3779936. In addition, U.S. Pat. No. 3334468
discloses the use of sodium chloride or sodium carbonate with calcium
chloride. Further, the combination of calcium chloride with magnesium,
lithium or ammonium salts is disclosed, for example, in U.S. Pat.
No. 3885926. The use of calcium chloride with a metal, for example,
iron fillings, is disclosed in U.S. Pat. No. 1798862. Further,
the use of activated carbon with calcium chloride as a desiccant
product is disclosed in U.S. Pat. No. 2027093.
U.S. Pat. No. 3390511 discloses the use of calcium chloride placed
on a carrier material for use as a gas dryer desiccant. The preferred
material that is utilized as the carrier for the calcium chloride
is sodium chloride. See also, U.S. Pat. No. 3334468. The desiccant
product in U.S. Pat. No. 3390511 preferably comprised about 90
to 97 percent sodium chloride as the carrier and about 10 to about
3 percent calcium chloride. In addition, sodium dichromate and trisodium
phosphate in minor amounts may be included in the product. While
the preferred carrier for the calcium chloride was sodium chloride,
other disclosed carriers included sugar, potassium chloride, potassium
nitrate, sodium nitrate and starch. See column 3 line 33. The percentage
of calcium chloride used in this product was 10 percent or less,
because the major component of the product was the carrier.
One of the problems in the utilization of calcium chloride as a
desiccating agent is that when the water is absorbed, it forms a
liquid mixture on the surface of the calcium chloride. This is discussed
in U.S. Pat. No. 3334468. With conventional desiccant products
this liquid may leak which can cause problems, for example, if the
desiccant product is used in storage containers.
While these references disclose the use of calcium chloride as
a desiccant either alone or combined with a number of different
compositions, there is still the need for improved desiccant products
utilizing calcium chloride.
Therefore it is an object of this invention to disclose a desiccant
composition containing calcium chloride as its major component.
It is a still further object of this invention to disclose a desiccant
composition containing calcium chloride mixed with a significant
amount of starch to form the desiccant composition.
It is a still further object of the invention to disclose a desiccant
composition contained within a packaging material, wherein the desiccant
composition is a combination of calcium chloride and starch, preferably
a modified starch.
It is a still further object of this invention to disclose a desiccant
composition containing calcium chloride where water absorbed by
the calcium chloride does not leak from the desiccant container.
It is a still further object of this invention to disclose a desiccant
composition contained within a packaging material wherein the desiccant
composition prevents leakage of water from within the package by
use of a 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
SUMMARY OF INVENTION
In accordance with the present invention there is provided a desiccant
composition comprising calcium chloride and starch, wherein the
calcium chloride comprises at least about 5 to about 95 percent
of the composition by weight and the starch from about 5 to about
95 percent of composition. In the preferred embodiment calcium chloride
comprises from about 20 to about 95 percent of the composition by
weight while the starch comprises from about 5 to about 80 percent
of the composition by weight. While the starch used may be unmodified,
in a preferred embodiment, it is a modified starch, preferably a
modified corn starch.
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.
The desiccant packaging material (12) may comprise any conventional
packaging material. Preferably, it 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
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 RPP-31-1007a 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 low-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
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 package include conventional desiccating material
such as silica gel, clays, calcium chloride, alkali metal carboxylate
salts of starch--polyacrylonitrile, sodium polyacrylate and other
desiccating products that absorb, gel or thicken upon contact with
water or water vapor. However, it has been surprisingly discovered
that a preferred desiccant material can be produced from a mixture
of calcium chloride and starch, preferably a modified starch, and
most preferably a modified corn starch, such as MIRA-SPERSE.RTM.
623 626 and 629 produced by A.E. Staley Manufacturing Company.
The composition of this desiccant material is preferably about 5
to about 95 percent calcium chloride mixed with about 95 to about
5 percent starch. Preferably, the calcium chloride comprises about
20 to about 95 percent while the starch comprises about 80 to about
5 percent of the composition. Most 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 starches that are utilized in this invention can include unmodified
starches, oxidized starch, enzyme-converted starches a and modified
starches containing functional groups such as hydroxyl, carbonyl,
amido and amino groups. The term "starch" therefore as
used throughout this specification and claims is intended to include
any member of the family of starches, or mixture of two or more
starches The preferred starch is a modified starch, such as an oxidized,
enzyme-converted starch. The modification to the starch may be chemical,
such as by crosslinking or substitution, or physical, such as by
Ordinary starch, such as pearl starch, is not commonly utilized
in its raw state because of its high viscosity and retrogradation,
which is a particular problem with unmodified starches. These p
problems are reduced substantially with modified starches, such
as hydroxyethylated starches. As such, most industries convert their
unmodified starches to modified starches, such as oxidized, enzyme
converted or hydroxyethylated starch. Alternatively, a further modified
starch, in the form of a cationic starch, can be used. However,
the cost of such cationic starch is significant in comparison to
either unmodified or hydroxyethylated starch. Critical to the choice
of starch is its ability to absorb water, preferably cool water,
i.e., less than about 40-50.degree. C.
In a preferred embodiment the starch when combined with water must
have a viscosity greater than water alone. When measured as Brookfield
viscosity, the viscosity should be at least about 1.0 cps. The critical
function supplied by the modified starch is the ability to mix with
water and thicken or gel water or the calcium chloride/water composition
formed during the absorption of water by calcium chloride.
The calcium chloride/corn starch desiccant composition can be used
not only with the desiccant container outlined above, but also with
any conventional desiccant container utilized for the absorption
of water or water vapor.
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 by 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 this product 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 may be necessary than
is used in conventional desiccating containers and still achieve
the same level of moisture absorbency.
The mixture of the calcium chloride and starch is prepared by placing
the two components in a conventional mixing apparatus, such as tumble
mixer or the two components can be fed directly into the desiccant
packaging from two separate feeds. Other than the physical mixing
of the materials, no additional processing is necessary for the
calcium chloride/starch composition. This simple mixing of the two
materials produces a desiccant composition with great utility.