Abstrict A desiccant composition containing a deliquescent salt and a modified
starch containing from about 5 to about 95 percent of the deliquescent
salt and from about 5 to about 95 percent of the modified starch.
Claims What is claimed is:
1. A desiccant composition comprising a deliquescent salt and a
modified starch, wherein the deliquescent salt comprises at least
about 5 to about 95 percent of the composition by weight and the
modified starch from about 5 to about 95 percent of the composition,
by weight.
2. The desiccant composition of claim 1 wherein the deliquescent
salt comprises from about 20 to about 95 percent of the composition
by weight and the modified starch from about 5 to about 80 percent
of the composition by weight.
3. The desiccant composition of claim 1 wherein the deliquescent
salt comprises from about 50 to about 80 percent of the composition
by weight and the modified starch from about 20 to about 50 percent
of the composition by weight.
4. The desiccant composition of claim 1 wherein the modified starch
comprises a modified corn starch.
5. The desiccant composition of claim 1 wherein the deliquescent
salt is selected from the group consisting of alkali, ammonium,
alkali earth, earth and transition metal halides, sulfates, sulfites,
thiosulfates, nitrates, nitrites, phosphates, carbonates and carboxylates.
6. The desiccant composition of claim 1 wherein the deliquescent
salt is selected from the group consisting of LiCi, LiBr, LiI, ZnCl.sub.2
ZnBr.sub.2 LiI, Ca(NO.sub.3).sub.2 *2H.sub.2 O, NaHSO.sub.4 Mg(NO.sub.3)*6H.sub.2
O, KI, NaI, NaNO.sub.2 KBr, (NH.sub.4).sub.2 SO.sub.4 Na(C.sub.3
H.sub.3 O.sub.2)*3H.sub.2 O, Na.sub.2 S.sub.2 O.sub.3 NH.sub.4
Cl, KHSO.sub.4 Na.sub.2 CO.sub.3 *10H.sub.2 O, ZnSO.sub.4 *7H.sub.2
O, K.sub.2 HPO.sub.4 Na.sub.2 SO.sub.3 *7H.sub.2 O, NaF, K.sub.2
(CO.sub.3).sub.2 *2H.sub.2 O, Zn(NO.sub.3).sub.2 NH.sub.4 H.sub.2
PO.sub.4 and MgCl.sub.2.
7. The desiccant composition of claim 1 wherein the deliquescent
salt comprises magnesium chloride.
8. The desiccant composition of claim 1 wherein the deliquescent
salt is selected from the group consisting of zinc chloride and
lithium chloride.
9. The desiccant composition of claim 1 wherein the deliquescent
salt is selected from the group consisting of ammonium chloride,
ammonium sulfate and ammonium carbonate.
10. A desiccant composition for application under conditions where
the relative humidity is less than about 20 percent comprising a
deliquescent salt selected from the group consisting of ZnCl.sub.2
LiCl, ZnBr.sub.2 LiBr, ZnI.sub.2 LiI and a modified starch, wherein
the deliquescent salt comprises at least about 5 to about 95 percent
of the composition, by weight, and the modified starch comprises
from about 5 to about 95 percent of the composition, by weight.
11. The desiccant composition of claim 10 wherein the deliquescent
salt is selected from the group consisting of zinc chloride and
lithium chloride.
12. A desiccant composition for application under conditions where
the relative humidity is greater than about 20 percent, comprising
a deliquescent salt selected from the group consisting of Ca(NO.sub.3).sub.2
*2H.sub.2 O, NaHSO.sub.4 Mg(NO.sub.3)*6H.sub.2 O, KI, NaI, NaNO.sub.2
KBr, (NH.sub.4).sub.2 SO.sub.4 Na(C.sub.3 H.sub.3 O.sub.2)*3H.sub.2
O, Na.sub.2 S.sub.2 O.sub.3 NH.sub.4 Cl, KHSO.sub.4 Na.sub.2 CO.sub.3
*10H.sub.2 O, ZnSO.sub.4 *7H.sub.2 O, K.sub.2 HPO.sub.4 Na.sub.2
SO.sub.3 *7H.sub.2 O, NaF, K.sub.2 (CO.sub.3).sub.2 *2H.sub.2 O,
ZN(NO.sub.3).sub.2 NH.sub.4 H.sub.2 PO.sub.4 and MgCl.sub.2 and
a modified starch, wherein the deliquescent salt comprises at least
about 5 to about 95 percent of the composition, by weight, and the
modified starch comprises from about 5 to about 95 percent of the
composition, by weight.
13. The desiccant composition of claim 12 wherein the deliquescent
salt comprises magnesium chloride.
14. The desiccant composition of claim 12 wherein the deliquescent
salt is selected from the group consisting of NH.sub.4 Cl, (NH.sub.4).sub.2
SO.sub.4 and (NH.sub.4).sub.2 CO.sub.3.
15. A desiccant composition for application under conditions where
the relative humidity is greater than about 50 percent, comprising
a deliquescent salt selected from the group consisting of NH.sub.4
Cl, Na.sub.2 CO.sub.3 *10H.sub.2 O, (NH.sub.4).sub.2 SO.sub.4 Ca(NO.sub.3).sub.2
*2H.sub.2 O, Mg(NO.sub.3)*6H.sub.2 O, K.sub.2 HPO.sub.4 NH.sub.4
H.sub.2 PO.sub.4 ZnSO.sub.4 *7H.sub.2 O, Na(C.sub.3 H.sub.3 O.sub.2)*3H.sub.2
O, Na.sub.2 S.sub.2 O.sub.3 KBr, Na.sub.2 SO.sub.3 *7H.sub.2 O,
KI, NaI, NaNO.sub.2 NaF, KHSO.sub.4 and NaHSO.sub.4 and a modified
starch, wherein the deliquescent salt comprises at least about 5
to about 95 percent of the composition, by weight, and the modified
starch comprises from about 5 to about 95 percent of the composition,
by weight.
16. A desiccant container comprising a desiccant composition secured
within a water vapor permeable film product, wherein the desiccant
composition comprises a deliquescent salt and a modified starch,
wherein the deliquescent salt comprises at least about 5 to 95 percent
of the composition by weight and the modified starch from about
5 to 95 percent of the composition by weight.
17. The desiccant container of claim 16 wherein the deliquescent
salt comprises from about 20 to about 95 percent of the desiccant
composition by weight and the modified starch from about 5 to about
80 percent of the composition by weight.
18. The desiccant container of claim 16 wherein the deliquescent
salt comprises from about 50 to about 80 percent of the desiccant
composition by weight and the modified starch from about 20 to about
50 percent of the composition by weight.
19. The desiccant composition of claim 16 wherein the deliquescent
salt comprises magnesium chloride.
20. The desiccant composition of claim 16 wherein the deliquescent
salt is selected from the group consisting of zinc chloride and
lithium chloride.
21. The desiccant composition of claim 16 wherein the deliquescent
salt is selected from the group consisting of ammonium chloride,
ammonium sulfate and ammonium carbonate.
22. 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
a deliquescent salt and a modified starch wherein the deliquescent
salt comprises at least about 5 to 95 percent of the composition
by weight and the starch 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.
23. The process of claim 22 wherein the deliquescent salt comprises
magnesium chloride.
24. The process of claim 22 wherein the deliquescent salt is selected
from the group consisting of zinc chloride and lithium chloride.
25. The process of claim 22 wherein the deliquescent salt is selected
from the group consisting of ammonium chloride, ammonium sulfate
and ammonium carbonate.
Description 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 a deliquescent salt
and a modified starch.
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 and the temperature and relative humidity level of
the surrounding air.
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 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 blended
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 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 from the packaging which can cause problems,
for example, if the desiccant product is used in storage containers.
There are situations where absorption of moisture by a desiccant
product even at low humidity and low water vapor pressure is necessary,
such as when the product protected by the desiccant product can
be damaged by moisture. Usually traditional desiccants, such as
desiccant clays, silica gel, molecular sieve and calcium sulfate
are used in this situation. However, for some applications the capacity
for absorption of moisture of these desiccant products is too low.
An example where this problem can occur is the shipment of steel
products overseas. In order to avoid the rusting of these steel
products, it is important that the relative humidity level in the
container holding those steel products be maintained below about
40 percent at 25.degree. C. for as long as several weeks. While
conventional desiccant products, such as silica gel, can be effective
in absorbing moisture in some situations, they do not have the high
capacity for absorption that is necessary for extended periods of
time. Desiccant products with a higher capacity for absorption at
humidity levels below 40 percent relative humidity are needed in
this situation.
In other situations conventional desiccant products begin to absorb
moisture at relative humidity levels which are unnecessarily low.
In these situations a considerable portion of the absorption capacity
of the desiccant product is wasted because moisture is absorbed
at humidity levels where no damage can occur to the products being
shipped with the desiccant product. In addition, if the humidity
level then rises, there is a risk that these conventional desiccant
products will not have sufficient remaining absorption capacity
to absorb water vapor and protect the products being shipped.
In addition, it is sometimes difficult to utilize conventional
desiccant products with products which inherently have a high moisture
content, such as cocoa, coffee, tobacco and dog food. If the desiccant
product absorbs too much moisture at relatively low humidity levels,
these products may be damaged. Further, the high capacity of some
desiccant products to absorb moisture is wasted in these situations.
In addition, there is a risk that not enough absorption capacity
will be available during the entire shipping process, especially
when the humidity level rises.
While certain references disclose the use of calcium chloride and
other deliquescent salts as a desiccant either alone or in combination
with a number of different compositions, there is still a need for
improved desiccant products utilizing calcium chloride and other
deliquescent salts.
In addition, there is a need for a desiccant composition which
can be useful in both low humidity and high humidity applications.
Therefore it is an object of this invention to disclose a desiccant
composition containing calcium chloride and/or other deliquescent
salts as its major component.
It is a still further object of this invention to disclose a desiccant
composition containing calcium chloride or other deliquescent salts
mixed with a significant amount of a modified 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 or other deliquescent
salts and a modified starch.
It is a still further object of this invention to disclose a desiccant
composition containing calcium chloride or other deliquescent salts
where water absorbed 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 modified starch.
It is a still further object of the invention to disclose a desiccant
composition contained within a packaging material which is designed
for absorption of moisture in order to maintain a relatively low
humidity level.
It is a still further object of the invention to disclose a desiccant
composition contained within a packaging material which is designed
for absorption of moisture in order to maintain a relatively high
humidity level.
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
composition comprising calcium chloride and/or other deliquescent
salts and a modified starch, wherein the calcium chloride and/or
other deliquescent salts comprises at least about 5 to about 95
percent of the composition by weight and the modified starch from
about 5 to about 95 percent of composition. In the preferred embodiment
calcium chloride and/or other deliquescent salts comprises from
about 20 to about 95 percent of the composition by weight while
the modified starch comprises from about 5 to about 80 percent of
the composition by weight.
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) 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
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 milliliters, preferably
1 to 1000 second/100 milliliters and most preferably less than
about 400 seconds/100 milliliters. Preferably, the microporous film
is a polyethylene or polypropylene-based microporous film and most
preferably a polyethylene spun-bonded paper such as Tyvek.RTM. 1025
BL, 1059B or 107337B manufactured by E. I. DuPont, or a polypropylene
based film, such as GDT II and GDT IV 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
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 package include conventional desiccating material
such as silica gel, clays, natural or synthetic zeolites, calcium
chloride, alkali metal carboxylate salts of starch--polyacrylonitrile,
sodium polyacrylate, various deliquescent salts, wherein the anions
include nitrate, nitrite, chloride, bromide, fluoride, sulfate,
sulfite, thiosulfate, carbonate, carboxylate, phosphate and iodide
and wherein the cations include ammonium, alkali, alkaline earth,
earth and transition metals such as lithium, sodium, potassium,
rubidium, cesium, magnesium, calcium, strontium, barium, aluminum,
zinc, and iron and other desiccating products that absorb, gel or
thicken upon contact with water or water vapor. If low humidity
applications are desired (relative humidity less than about 20 percent),
the deliquescent salts include zinc chloride, lithium chloride,
zinc bromide, lithium bromide, zinc iodide and lithium iodide. When
medium to high humidity applications are desired (greater than 20
percent relative humidity), the deliquescent salts may include CaCl.sub.2
MgCl.sub.2 Zn(NO.sub.3).sub.2 and K.sub.2 (CO.sub.3)*2H.sub.2
O. When high humidity applications are desired (higher than 50 percent
relative humidity), the deliquescent salts may include (NH.sub.4).sub.2
SO.sub.4 NH.sub.4 Cl, Ca(NO.sub.3).sub.2 *2H.sub.2 O, Mg(NO.sub.3)*6H.sub.2
O, K.sub.2 HPO.sub.4 NH.sub.4 H.sub.2 PO.sub.4 KHSO.sub.4 Na.sub.2
CO.sub.3 *10H.sub.2 O, ZnSO.sub.4 *7H.sub.2 O, Na(C.sub.3 H.sub.3
O.sub.2)*3H.sub.2 O, Na.sub.2 S.sub.2 O.sub.3 KBr, Na.sub.2 SO.sub.3
*7H.sub.2 O, KI, NaI, NaNO.sub.2 NaF and NaHSO.sub.4.
It has been surprisingly discovered that a preferred desiccant
material can be produced from a mixture of a deliquescent salt,
such as those previously discussed, and a modified starch, 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 the deliquescent salt mixed with about 95 to about
5 percent of the modified starch. Preferably, the deliquescent salt
comprises about 20 to about 95 percent while the modified starch
comprises about 80 to about 5 percent of the composition. Most preferably
the deliquescent salt comprises about 50 to about 80 percent while
the modified starch comprises about 50 to about 20 percent of the
composition.
In low humidity applications (less than 20 percent relative humidity)
the preferred deliquescent salts in order of preference are: LiCl>ZnCl.sub.2
>ZnBr.sub.2 >LiBr>ZnI.sub.2 >LiI. In medium to high
humidity applications (greater than 20 percent relative humidity)
the deliquescent salts in order of preference are: CaCl.sub.2 =MgCl.sub.2
>K.sub.2 (CO.sub.3)*2H.sub.2 O>(Zn(NO.sub.3).sub.2. In high
humidity applications (greater than 50 percent relative humidity)
the deliquescent salts in order of preference are: NH.sub.4 Cl,
Na.sub.2 CO.sub.3 *10H.sub.2 O, (NH.sub.4).sub.2 SO.sub.4 Ca(NO.sub.3).sub.2
*2H.sub.2 O, Mg(NO.sub.3)*6H.sub.2 O, K.sub.2 HPO.sub.4 NH.sub.4
H.sub.2 PO.sub.4 ZnSO.sub.4 *7H.sub.2 O, Na(C.sub.3 H.sub.3 O.sub.2)*3H.sub.2
O, Na.sub.2 S.sub.2 O.sub.3 KBr, Na.sub.2 SO.sub.3 *7H.sub.2 O,
KI, NaI, NaNO.sub.2 NaF, KHSO.sub.4 and NaHSO.sub.4.
The modified starches that are utilized in this invention can include
conventionally modified starches, oxidized starch, enzyme-converted
starches and modified starches containing functional groups such
as hydroxyl, carbonyl, amino 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 granulation.
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 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, phosphated
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 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 modified 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 deliquescent
salt/water composition formed during the absorption of water by
the deliquescent salt.
The deliquescent salt/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. 1025 BL, 1059B and 1073B produced by E. I. DuPont or certain
other polypropylene-based non-woven films such as GDTI, II, IV 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 milliliters and preferably less than
about 400 seconds per 100 milliliters.
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 a deliquescent salt and 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 deliquescent salt and modified 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 deliquescent salt/modified starch composition. This simple
mixing of the two materials produces a desiccant composition with
great utility.
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
The water absorbing capability of a desiccant combination comprising
corn starch with calcium chloride was tested. 133 grams of a 3 to
1 mixture of calcium chloride to Mirasperse 629 modified waxy corn
starch sold by Staley Food Ingredients, Decatur, Ill. was placed
in a conventional desiccant bag for a desiccant product, which product
is sold by United Desiccants and known as "CONTAINER DRI.RTM.".
The desiccant bag was placed in environmental chamber of 80 percent
relative humidity at 25.degree. C. for about two months. The results
of this test are shown in attached Table 1.
Example 2
The same tests were run on a composition of 1 to 4 corn starch
to calcium chloride utilizing the same type of Mirasperse 624 modified
corn starch as was discussed in Example 1. The water absorption
over time is shown in the attached Table 1.
Example 3
The water absorbance of a conventional 500 gram CONTAINER DRI.RTM.
desiccant product produced by United Desiccants was compared with
the products of Examples 1 and 2 using the same procedures as were
used in Example 1. The water absorption capability of this product
over time is also shown in Table 1.
In addition, the capacity of a 1/4 ratio modified starch/calcium
chloride product of Example 2 was compared with the conventional
500 gram CONTAINER DRI.RTM. product. The capacity at 40 percent
relative humidity, moisture uptake at 40 percent relative humidity,
capacity at 80 percent relative humidity and moisture uptake at
80 percent relative humidity after two months are shown in Table
2.
TABLE 1 1:4 Corn Starch 1:3 Corn Starch to to Calcium Typical Calcium
Chloride Chloride ratio, Container Dri, Time, hr ratio, % CAPACITY
% CAPACITY % CAPACITY 5.5 8.252063 10.16 1.8 22.5 31.28282 36.4
2.5 24 36.53413 43.2 2.88 28.5 38.4096 45.04 10.59 94.5 54.83871
58.64 33 120 60.54014 64.4 38.06 150 92.04801 96.08 41.58 169 100.9002
104.08 46.11 174 108.8522 114.32 47.43 198 121.9805 116.3158 48.61
265 150.2626 147.0677 55
TABLE 2 MOISTURE MOISTURE CAPACITY UPTAKE (g) CAPACITY UPTAKE (g)
at 40% RH at 40% RH at 80% RH at 80% RH 1:4 RATIO 111.4 151.7 339.4
462.1 MODIFIED STARCH/ CaCl2 IN 5 3/4 .times. 7" BAG NORMAL
29.9 149.6 66.1 330.7 500 g CONTAINER DRI Bag
As is clear from these examples, greater water absorption is shown
for a composition of corn starch and calcium chloride in comparison
with the conventional desiccant material. This water absorption
capability is at least as good as conventional desiccant packages
conventionally sold. In addition, the desiccating composition of
Example 2 was compared with the CONTAINER DRI.RTM. product after
265 hours. Because of the capability of the starch to absorb the
water and the liquid calcium chloride on the surface of the calcium
chloride product, water did not leak from the container even after
three months.
Example 4
100 g of calcium chloride was mixed with 25 g of modified starch
(Mirasperse 629 manufactured by Staley Food Ingredients) and placed
in a bag manufactured according to U.S. Pat. No. 5743942. The
absorption capacity measured at 25.degree. C., 80 percent relative
humidity (r.h.) after 14 days was 230 percent by weight. The bag
did not show any signs of leakage through the microporous films
or seals, and the bag contained a firm gel (viscosity 33 Pas at
5 rpm, 15 Pas at 50 rpm).
Example 5
100 g of magnesium chloride was mixed with 25 g of modified starch
(Mirasperse 629 manufactured by Staley Food Ingredients) and placed
in a bag manufactured according to U.S. Pat. No. 5743942. The
absorption capacity measured at 25.degree. C., 80 percent r.h. after
14 days was 305 percent by weight. The bag did not show any signs
of leakage through the microporous films or seals, and the bag contained
a firm gel (viscosity 60 Pas at 5 rpm, 23 Pas at 50 rpm).
Example 6
100 g of magnesium chloride was mixed with 20 g of modified starch
(Mirasperse 629 manufactured by Staley Food Ingredients) and placed
in a bag manufactured according to U.S. Pat. No. 5743942. The
absorption capacity measured at 25.degree. C., 80 percent r.h. after
14 days was 307 percent by weight. The bag did not show any signs
of leakage through the microporous films or seals, and the bag contained
a firm gel (viscosity 32 Pas at 5 rpm, 21 Pas at 50 rpm).
As is clear from Examples 4 through 6 greater water absorption
occurs with a composition of a modified starch blended with magnesium
chloride than the same modified starch blended with calcium chloride.
This increased absorption capacity per weight can find great utility
when high moisture absorption capacities are required.
Example 7
100 g of CaCl.sub.2 ZnCl.sub.2 LiCl, (NH.sub.4).sub.2 CO.sub.3
NH.sub.4 Cl and NaHSO.sub.4 were individually mixed with 25 g of
modified starch (Mirasperse 629 manufactured by Staley Food Ingredients)
and placed in a bag manufactured according to U.S. Pat. No. 5743942.
The absorption capacity was measured at 25.degree. C., 80% r.h.,
25.degree. C., 20% r.h. and 25.degree. C. and 90% r.h. after 48
hours.
The following table summarizes the experimental results:
TABLE 3 Absorption at Absorption at Absorption at Salt 20% r.h.
80% r.h. 90% r.h. CaCl.sub.2 19% 127% 270% ZnCl.sub.2 25% 84% N.d.
LiCl 30% 146% N.d. (NH.sub.4).sub.2 CO.sub.3 0% 11% 70% NH.sub.4
Cl 0% 12% 140% NaHSO.sub.4 0% 56% N.d. N.d. = Not determined
All except one bag did not show any signs of leakage through the
microporous films or seals, and the bags contained firm gels (viscosity>25
Pas at 5 rpm, >15 Pas at 50 rpm). The mixture with NaHSO.sub.4
did not form a gel, due to the chemical breakdown of the starch
used.
The table clearly shows that a combination of ZnCl.sub.2 or LiCl
with starch is preferable if high capacity is needed at low relative
humidity levels.
If low absorption under humidity conditions less than about 80%
r.h. is required, mixtures of starch with NH.sub.4 Cl and (NH.sub.4).sub.2
CO.sub.3 are preferred, as they do not start to absorb significant
amounts of moisture at less than 80% r.h. but show considerable
absorption at higher humidity levels near the dew point. |