A flexible solid desiccant body is disclosed comprising finely
divided particles of desiccant material, such as molecular sieve,
homogeneously distributed and bound in a moisture transmissive aliphatic
epoxy polymer matrix. The desiccant bodies are especially adapted
for use as drier materials in refrigerant fluid systems. The flexible
bodies are shaped in various sheet, tubular, rod and other forms
and can be placed at various locations in refrigerant fluid systems.
What is claimed is:
1. A flexible solid desiccant body comprising finely divided particles
of desiccant material homogeneously distributed and encapsulated
in a moisture transmissive polymer solid matrix of a cured thermoset
aliphatic epoxy resin.
2. The desiccant body of claim 1 wherein said matrix is moisture
3. The desiccant body of claim 1 wherein said resin is a copolymeric
resin of a lower alkylene oxide.
4. The desiccant body of claim 1 wherein said polymer matrix includes
a flexibilizing modifier.
5. The desiccant body of claim 3 wherein said resin is a copolymer
of epichlorohydrin and ethylene oxide.
6. The desiccant body of claim 5 wherein said polymer contains
about 70% epichlorohydrin and about 30% by weight ethylene oxide.
7. The desiccant body of claim 1 wherein said desiccant is a molecular
8. The desiccant body of claim 7 wherein said sieve material is
a synthetic zeolite.
9. The desiccant body of claim 1 wherein the desiccant is contained
in an amount of about 10 to about 90% by weight based upon total
desiccant-polymer matrix weight with the proviso that as the desiccant
increases toward about 90% by weight then a flexibilizing modifier
in an effective flexibilizing amount is included in said cured matrix.
10. A flexible solid desiccant body for drying refrigerant fluids
comprising finely divided particles of molecular sieve material
homogeneously distributed and encapsulated in a moisture transmissive
and sorptive polymer solid matrix of a cured thermoset aliphatic
11. The desiccant body of claim 10 wherein said resin is a copolymeric
resin of lower alkylene oxide.
12. The desiccant body of claim 10 wherein said resin is a copolymer
of epichlorohydrin and ethylene oxide.
13. The desiccant body of claim 12 further containing an external
14. The desiccant body of claim 13 wherein said modifier is dioctylphthalate.
15. The desiccant body of claim 11 wherein the molecular sieve
material is contained in an amount of from about 40% by weight to
about 80% by weight of total molecular sieve material-polymer matrix
16. The desiccant body of claim 15 wherein said molecular sieve
comprises a synthetic zeolite.
17. The desiccant body of claim 10 shaped in tubular form.
18. The desiccant body of claim 10 shaped in sheet form.
19. The desiccant body of claim 10 shaped in tubular form having
20. The desiccant body of claim 19 having internal radially extending
vanes and a core interconnecting said vanes.
21. The desiccant body of claim 10 having an opencelled structure.
BACKGROUND OF THE INVENTION
Desiccants have been used in refrigeration systems for drying,
and maintaining dry, refrigerant liquids, such as fluorochlorohydrocarbons.
Dry fluid in refrigerant systems is essential because humidity causes
serious difficulties such as ice formation or hydrolysis or refrigerant
fluids to corrosive acids. The conditions of use vary somewhat from
one type of refrigerant system to another. For example, in automotive
refrigeration systems, the desiccant is subject to a much higher
vibration and attrition than that normally found in non-automotive
refrigeration systems. To combat attrition problems in automotive
refrigeration, it has been proposed to protect the desiccant in
several ways. One known method is to encase desiccant beads or granules
in wool or polypropylene felt bags. These bags must be heat sealed
or end-sewn to reduce desiccant loss, abrasion and/or dust in the
cooling liquid. Further attrition problems are encountered by loosened
bag fibers due to cooling liquid flow and vibration. In the case
of polypropylene, there is a potential attrition problem and loss
of drying efficiency due to melting or thermoplasticity of the polypropylene
bags in use. Other attempts have been made to sandwich the desiccant
material between fiberglass pads and metal screens. Such assemblies
are cumbersome and costly, and difficulties are still encountered
by attrition and escape of desiccant.
It has also been proposed to employ drying agents together with
binding agents. Bonded blocks of desiccant with aluminum phosphate
are suggested in U.S. Pat. No. 2583812; organic binders such as
phenol-formaldehyde, melamine-formaldehyde, polyvinyl acetate, polyethylene,
polyvinyl chloride, polystyrene, methyl cellulose, polyvinylbutyral,
epoxide resin formed from epichlorohydrin and Bisphenol-A, i.e.,
22 bis (4 hydroxyphenyl) propane, and polyurethanes are suggested
in U.S. Pat. Nos. 3025233; 3091550; 3375933; 3687297; Re.
25400; 3545622 and 3538020. These desiccant bodies suffer from
one or more disadvantages, for example, rigidity which causes cracking
and attrition, insufficient water sorption capacity, swelling or
solution in the refrigerant, lack of sufficient permeability for
the liquid refrigerant and water molecules, chemical instability,
lack of heat resistivity, sensitivity to vibration and shock, and
heterogeneity of desiccant particles in the binder matrix, among
SUMMARY OF THE INVENTION
This invention is directed to flexible desiccant bodies and, in
particular, shaped bodies adapted for use in refrigerant systems.
The flexible desiccant body of this invention overcomes the multi-faceted
problems and disadvantages associated with known desiccant bodies
developed in the background of this invention. In accordance with
this invention, a flexible solid desiccant body comprises finely
divided particles of desiccant homogeneously distributed and bound
in a moisture transmissive polymer matrix of a cured thermoset aliphatic
epoxy resin. Moisture sorbtive resin matrices are also provided
by this invention. In a presently most preferred form, the resin
is a copolymeric resin of a lower alkylene oxide, for example, a
copolymer of epichlorohydrin and ethylene-oxide. The desiccant is
preferably a molecular sieve material such as synthetic zeolite
characterized by pores of molecular dimensions and uniform size
and having an ability to adsorb small moisture molecules.
It has been found that desiccant particles can be homogeneously
distributed and bound in a particular moisture sorptive polymer
matrix and a number of advantages are secured thereby. The homogeneous
body of desiccant material is flexible, that is to say, it has properties
of elasticity or compressibility or flexibility which help to dissipate
the energy and forces produced during the states of vibration and
mechanical shock. This flexible homogeneous body removes the hazard
of the desiccant and desiccant binder from breaking and releasing
small particles from the body. Flexibility is achieved by an elastomeric
polymer matrix of a cured aliphatic epoxy resin. In one preferred
form, the matrix further includes a flexibilizing modifier. The
matrix of the desiccant body is a cured thermoset polymer which
provides chemical stability in order to avoid attack by fluids to
which it is exposed in the refrigerant system, such as halogenated
hydrocarbons and refrigeration oil at both high and low temperatures.
Another important aspect of the particular polymer matrix is its
moisture transmissive nature, that is to say, its ability to transmit
moisture or moisture vapor such that the desiccant material which
is homogeneously bound in the matrix may receive and trap moisture
in the internal matrices of the solid body. In another of its aspects,
the preferred polymer matrix has the capability of sorbing moisture.
Thus, both the matrix and desiccant function in this preferred form
of the invention to sorb moisture. The desiccant body of this invention
maintains its properties of flexibility, resistance to swelling
and attack by refrigerant fluids and oils even upon exposure to
extremely low temperatures and high temperatures.
This invention provides a method for mixing a powdered molecular
sieve material in a moldable polymeric mass such that a homogeneous
mixture can be prepared and extruded or molded continuously into
various shapes or forms and to permit such molded forms to be used
as solid desiccant bodies having rates of adsorption or absorption
comparable to such desiccant materials alone. The molded forms of
this invention have been found suitable for use as desiccant bodies
to dry refrigerant fluids employed in refrigeration systems, particularly
automotive systems. Furthermore, by reason of the flexibility of
the polymer-molecular sieve product in accordance with the principles
of this invention, it is capable of dissipating and withstanding
energy imparted thereto and avoiding attrition otherwise associated
with known automotive desiccant products used for similar purposes.
In another of its advantageous aspects, the desiccant bodies of
this invention are shaped in tubular, rod-like, sheetlike flexible
or unique forms which enable them to be used in the lines of refrigerant
fluids as conduits therefor and, by reason of such various shapes,
the bodies may be universally adapted as driers in a multitude of
end-uses. For example, physical location of the desiccant employing
the body of this invention is not a limitation, in accordance with
the principles of this invention, as it is with presently used desiccants
and methods in the automotive refrigerator systems or commercial
household refrigerators. The desiccant body can form a tubular conduit
for conveying refrigerant fluids, for example. Also, it can be used
as a liner for a refrigerant hose. A filter for desiccant particles
is no longer necessary in automotive refrigerant systems including
my desiccant bodies because desiccant particles do not come loose
during use. Also, in another embodiment of this invention, an open
cell structure is provided to serve as a filter damping agent and
A particularly unique desiccant body is provided by this invention
which is shaped in tubular or conduit form having exposed vanes
or protrusions, external or internal. One such body has radially
extending internal vanes and a core interconnecting the vanes. In
cross-section, this body looks like a "wagon-wheel". This
unique body has been found advantageous for use in refrigerant systems
and provides fluid damping, high surface area to weight ratio and
refrigerant fluid-desiccant body contact without impeding fluid
flow, among its other attributes.
In the polymer-desiccant body, a sufficient amount of the particulate
desiccant material is needed in the polymer matrix in order for
it to perform its drying function. Generally, desiccant particles
are contained in an amount of about 10-90% by weight of total desiccant-polymer
weight. At increased desiccant levels within this range it has been
found that a flexibilizing modifier may be needed to maintain flexibility
of the polymer matrix. Such flexibilizing modifier may be internal,
i.e., a part of polymer chains or external, i.e., by the addition
of external plasticizers. In one form, it has been unexpectedly
found that an external plasticizer can be used in the polymer matrix
without loss in matrix strength or flexibility during usage. In
the preferred copolymeric resins of ethylene oxide of this invention,
molecular sieve material is contained in the matrix in an amount
from about 40% by weight to about 80% by weight and an external
flexibilizing modifier, e.g., dioctylphthalate, is contained in
a flexibilizing amount.
As mentioned, the moisture sorptive polymer matrix is a cured thermoset
aliphatic epoxy resin. Such thermoset resins provide flexible or
elastomeric properties to the matrix. In particular, copolymeric
resins of lower alkylene oxides have been found sufficiently moisture
sorptive, moisture transmissive and to provide excellent physical
and chemical properties as a drier matrix, particularly for refrigerant
fluids. The alkylene oxide precurser in the polymer provides moisture
sorptivity while the other comonomer or comonomer precurser has
relatively less sorptivity for moisture such that the cured polymer
matrix provides controlled moisture sorptivity with desired chemical
and physical properties. A copolymer of epichlorohydrin and ethylene
oxide in a 70:30 weight ratio has been found satisfactory. However,
it is to be understood that other aliphatic copolymers where the
lower alkylene oxide is propylene oxide for example, and the other
aliphatic comonomer is other than epichlorohydrin, can be used in
varying ratios to achieve the results of this invention. Exemplary
of monomers which may be polymerized to form an aliphatic epoxy
polymer matrix include epoxides, the alkylene oxides such as ethylene
oxide, propylene oxide, butene oxides, isobutylene epoxide, substituted
alkylene oxides such as epichlorohydrin, epibromohydrin, methallyl
chloride epoxide, trifluoromethyl ethylene oxide, perfluoropropylene
oxide, perfluoroethylene oxide, vinyl chloride epoxide, dichloroisobutylene
epoxides, 12-dichloro-34-epoxybutane, 1-chloro-34-epoxybutane,
1-chloro-45-epoxypentane, 11-dichloro-23-epoxypropane, 111-trichloro-23-epoxypropane,
111 -trichloro-34-epoxybutane, etc., cycloaliphatic epoxides
such as cyclohexene oxides, vinyl cyclohexene oxides (mono- and
dioxides), .alpha.-pinene epoxide, dipentene epoxide, etc., epoxy
ethers such as alkyl glycidyl ethers as, for example, methyl glycidyl
ether, ethyl glycidyl ether, isopropyl glycidyl ether, isobutyl
glycidyl ether, tertbutyl glycidyl ether, n-hexyl glycidyl ether,
n-octyl glycidyl ether, etc., unsaturated glycidyl ethers such as
vinyl glycidyl ether, allyl glycidyl ether, etc., glycidyl esters
such as glycidyl acetate, glycidyl propionate, glycidyl pivalate,
glycidyl methacrylate, glycidyl acrylate, etc., alkyl glycidates
such as methyl glycidate, ethyl glycidate, etc. Alkylene oxides
and the monosubstituted derivatives thereof such as ethylene oxide,
propylene oxide, epichlorohydrin, are most preferred to provide
the physical and chemical characteristics required by the product
of this invention as developed above. Such aliphatic copolymers
of alkylene oxides and other aliphatic comonomers are described
in U.S. Pat. Nos. 3135705; 3218269; 3158591; 3186958 and
3239486. The disclosures of these patents relating to copolymeric
epoxy resins of alkylene oxides and other comonomeric aliphatic
moieties, and their methods of preparation are incorporated herein
by reference, it being understood that other aliphatic copolymers
can be used in accordance with this invention. The aliphatic copolymers
such as epichlorohydrin and ethylene oxide copolymers as described
above may be cured with known curing agents, additives, accelerators,
flexibilizers and antioxidants to provide flexible or elastomeric
matrices as disclosed in the above patents, and such variations
are not limitations upon the scope of this invention. Aromatic copolymers
of epichlorohydrin-bis phenol A have not been found suited for purposes
of this invention due to their extremely slow vapor transmission
rates, lack of desired sorbtivity and rigid or brittle nature, among
Desiccant materials suitable for use include particulate molecular
sieves, activated alumina, silica gel, etc., as disclosed in the
above prior art patents. Molecular sieve materials including zeolites,
natural or synthetic, have been found to be presently preferred.
Suitable molecular sieve materials are disclosed in U.S. Pat. Nos.
2882244 2844243 and 3130007. These zeolite molecular sieves
are described in several publications; for example, Breck et al.,
J. Am. Chem. Soc., 78 2338 (1956), Breck et al., J. Am. Chem. Soc.,
78 5963 (1956), and Reed et al., J. Am. Chem. Soc., 78 5972 (1956).
This invention and its operating parameters will be further understood
with reference to the drawing and following specific examples which
are presently preferred modes of practicing this invention.
FIG. 1 is a perspective view of a tubular flexible body of this
FIG. 2 is a cross-sectional view of FIG. 1.
Referring to the drawing, an extruded tubular flexible desiccant
body 3 is illustrated having internal vanes 4 and core 5. The vanes
4 extend radially in cross-section of the body and are reinforced
by the integral core 5 which is formed along the axis of the body.
The finely divided desiccant particles 7 e.g., 1-10 microns, are
homogeneously dispersed and bound in the polymer matrix and are
exaggerated in the drawing. The desiccant body can be shaped to
fit into a dehydrator cannister, for example, of a refrigeration
apparatus where refrigerant fluid enters the tubular body at one
end, passes through the channels 6 formed by the internal vanes,
and leaves the body at its opposite end in a dry state.
Zeolite (Linde Air Products Type 4A) in the amount of 195 grams
(1-10 microns particle size) is mixed with 100 grams of epichlorohydrin-ethylene
oxide copolymer (70:30 weight ratio). After the ingredients are
mixed for about 3 minutes on a standard laboratory Banbury type
mixer, 20 parts dioctylphthalate plasticizer are added along with
other additives. Other additives include 5 grams dibasic lead phosphite
as an antioxidant or stabilizer, 1 gram zinc stearate (lubricant),
1 gram of wax (extrusion aid), 2 grams of 2-mercapto imidazoline
curing catalyst containing 25% inert carrier and 5 grams carbon
black filler. After mixing for another 5 minutes, the compound is
then put on a two roll mill where 1.5 grams of ethylene thiourea
(curing agent) is added. Temperature during the Banbury mixing is
held at about 300.degree. F. The mixture is then extruded into an
elongated "wagon-wheel" shape, as shown in the drawing,
and cured in a hot air oven at 320.degree. F for 30 minutes. The
specific gravity of the resulting homogeneous body is about 1.4
g./cc. The wagon-wheel shaped body provides a surface to weight
ratio which has been found advantageous for moisture sorptivity
without restricting fluid flow in refrigerating systems.
The mixing temperature in the Banbury of Example I was held to
200.degree. F while everything else remained the same as in Example
I. The resulting product specific gravity is about 1.0 g./cc. This
phenomenon is due to the zeolite which acts as a blowing agent and
the blowing efficiency is reduced as the mixing temperature is raised.
Zeolite 4-A in the amount of 300 grams (1-5 microns particle size)
is mixed with 100 grams of copolymer as in Example I. After mixing
for 3 minutes, on a standard laboratory Banbury type mixer, the
plasticizer is added along with the other additives as in Example
I. The plasticizer used is dioctylphthalate in the amount of 30
grams. The remainder of the process is the same as in Example I.
Example I is followed except that the homogeneous mixture is not
extruded, but is molded in a 3 ton press at 320.degree. F for 30
minutes. The resulting compound had a specific gravity of 1.6 g./cc.
In an alternate embodiment of the invention, the copolymer with
zeolite is employed to make an open-cell foam structure. This homogeneous
mixture in the open-cell foam form can be used as a combined filter,
a desiccant, and a damping agent in refrigeration systems. The dominant
property of the foam structure is its permeability to fluids. An
example of a method of manufacture is shown below in Example V.
Zeolite (Type 4A) in the amount of 195 grams (1-5 microns particle
size) is mixed with 100 grams of copolymer as in Example 1. Blowing
agents such as halogenated hydrocarbon liquids are added in an amount
of about 18 grams. These ingredients are mixed in a Banbury along
with 40 grams dioctylphthalate for about 7 minutes and then placed
on a two roll mill where the cure system is added. The cure system
includes 5 grams of dibasic lead phosphite, 7 grams of dibasic lead
phthalate, 1 gram of carbon black and 2 grams of hexamethylenediamine
carbamate. Samples should be compression molded for about 9 minutes
at 347.degree. F. While under pressure the mold should be allowed
to cool at 220.degree. F and then opened. The products are then
post cured for 30 minutes at 325.degree. F to produce the finished
product. Other polymer-desiccant combinations can be used as above
and the examples should not be limiting factors on this invention.
Also, other blowing agents and cure methods may be used.
The flexible molded desiccant polymer-molecular sieve compositions
of the foregoing examples have been found to be very suitable as
drier materials for air conditioning systems. For example, a molded
body of the type produced in Example I, when compared with granular
molecular sieve materials and activated alumina, alone, possesses
a very favorable moisture sorptive capacity. The moisture sorbing
capacity for an Example I type body is about 11% by weight as compared
to about 16% by weight for molecular sieve material alone and about
11% by weight for activated alumina alone. However, the problems
associated with the use of such granular desiccant materials, as
detailed in the background of this invention, are eliminated by
the molded molecular sieve-polymer desiccants of this invention.
Also, loss of desiccant materials during production is negligible
compared to assembly of prior art bags and beads, etc. In addition,
a refrigerant filter for desiccant particles is no longer necessary
for use with the desiccant body of this invention because particles
do not come loose as with prior assemblies of molecular sieve and
activated alumina beads or powders. The molded bodies of this invention
are easy to handle and to assemble in a refrigerant system. Furthermore,
because of the homogeneous nature of the molded composition, it
can be molded or extruded into almost any shape and the physical
location of the desiccant in the refrigerant system according to
this invention is not limited as it is with presently used molecular
sieve beads or powders in automotive refrigeration systems. Furthermore,
unlike activated alumina or molecular sieve powder and beads heretofore
employed as desiccant materials in refrigeration systems, extra
parts such as baffles, pads, bags, screens or the like can be eliminated.
It has been surprisingly found that 15 cubic inches of activated
alumina or 4 cubic inches of molecular sieve material are equivalent
in water sorbing capacity to 3 cubic inches of polymer-molecular
sieve material of this invention having a bulk density of 1.28 g./cc.
Therefore, even though the molecular sieve material is embodied
in the polymer matrix, the sorbing capacity of the thus formed body
is greater than a greater volume of molecular sieve or activated
alumina alone. This exhibits the unexpected dual sorptive capacity
of the desiccant bodies of this invention. Furthermore, when the
molecular sieve-polymer body of this invention is aged at 180.degree.
F for 72 hours with Freon 12 and refrigeration oil, there is no
noticeable volume change, and the hardness, elongation and tensile
strengths of the body remain virtually the same as the original
material before test. Also, when the molecular sieve-polymer body
is aged at -40.degree. F for 72 hours in Freon 12 and refrigeration
oil, tensile strength, elongation, hardness and volume change are
virtually negligible as compared with the originally molded material.
The molded body at -40.degree. F is still flexible and a visual
inspection after test indicates that the polymer-molecular sieve
body does not show any deterioration of the material. All of these
results indicate that the desiccant material of this invention is
exceedingly useful as drier material for air conditioning systems
and that, unlike activated alumina or molecular sieve beads and
powder which required protection in order to avoid deterioration
due to vibration shock in such refrigeration systems, the desiccant
material of this invention does not deteriorate because of its flexibility
thus provides excellent handling and installation properties in
comparison to previously used beads and powder. Also, the molded
molecular sieve-polymer bodies of this invention may be regenerated
for continued use.
All of the above data demonstrates that the desiccant bodies of
this invention provide advantages in commercial and automotive air
conditioning refrigerant systems. The desiccant bodies also have
several advantages over present methods of desiccation, including
no attrition problems which could otherwise cause the failure of
many refrigeration systems. Further, high cost internals such as
wool or polypropylene filled bags, fiberglass pads or the like which
have been used to protect the desiccant powder or beads in the past
are not required; and due to variability of shape, the desiccant
material is virtually unlimited in where it can be placed in the
refrigerant system. Inventive desiccant bodies of the type exemplified
exhibit little or no swell under test, for example, -1.28 linear
swell in 4 days at 70.degree. F in Freon 12 at -0.60% linear swell
in 4 days at 250.degree. F and a volume change at 257.degree. F
in compressor oil (ASTM Oil No. 1) at the end of 3 days is 0.2%
and at the end of 28 days is 0.2%. Therefore, the desiccant body
is compatible with refrigerant fluids and has oil resistance which
makes it extremely adaptable for its intended use in refrigerant
systems. The sorption rate of desiccant bodies can also be designed
to fit the particular needs of end-use by varying their surface
areas upon extrusion or molding.
Other embodiments of this invention will become apparent in view
of the above description without departing from the spirit and scope