Semisolid polymerizable compositions, method of preparing the same and thermoset products thereof

Semisolid polymerizable compositions are obtained by combining unsaturated polyester resin syrup, aqueous sodium silicate and finely divided particulate calcium sulfate hemihydrate. The composition rapidly thickens to a semisolid state when the ingredients are mixed and retains its semisolid condition for extended periods of time. The unsaturated polyester resin syrup component of the mixture remains polymerizable until its polymerization is initiated, normally by means of heating in the presence of a high temperature polymerization initiator. Sufficient calcium sulfate hemihydrate is included to react with substantially all of the uncombined water in the other ingredients so that the resulting polymerizable composition is substantially free of uncombined water. The compositions may also contain inert fillers and/or reinforcing fibers. The compositions can be employed to produce coatings, laminates, cast articles, molded articles and other shaped articles. The compositions may be employed in either of two alternative procedures. In the direct processing of the compositions, they are mixed, immediately formed and immediately polymerized to produce useful products. In the two stage processing of the compositions, they are mixed, allowed to thicken without polymerization and are retained as a semisolid polymerizable composition which is useful as a molding compound in the form of dough molding compounds, sheet molding compounds or molding powders. In all of these procedures, the preferred compositions include reinforcing glass fibers as an essential ingredient.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to semisolid polymerizable unsaturated polyester 
resin syrup compositions, to methods of making such compositions, to 
methods of curing such compositions and to the thermoset products obtained 
by polymerizing such compositions. 
2. Description of the Prior Art 
Unsaturated polyester resin syrups have been employed in the production of 
a wide variety of products. See Polyester Resins and Their Applications, 
Bjorksten et al, Reinhold Publishing Company, New York, 1960 (Fourth 
Printing). The unsaturated polyester resin syrups customarily are 
reinforced with fibrous fillers such as glass fibers and also are extended 
with inert particulate fillers such as wood flour, silica, ground glass, 
clay, calcium carbonate, and the like. Typical end products include flat 
and profiled building sheets, automobile components, furniture, plumbing 
fixtures, ductwork, boats, electrical housing components, electrical 
circuit boards and the like. 
Copending application Ser. No. 544,966, supra, describes compositions 
containing unsaturated polyester resin syrups and aqueous sodium silicate 
which thicken and remain polymerizable until exposed to polymerizing 
conditions. In a preferred embodiment of my prior process, the unsaturated 
polyester resin syrup and the aqueous sodium silicate are combined and 
polymerized concurrently. In a further embodiment of the earlier 
invention, the aqueous sodium silicate and unsaturated polyester resin 
syrup are combined, with or without fillers, and allowed to thicken for 
subsequent reuse. One typical reuse is in the form of molding powders 
where the thickened mixtures are ground, chopped or pulverized for 
subsequent molding. 
One of the shortcomings of the polymerizable mixtures is that the 
requirement for thickening establishes some restraints on the ratio of 
aqueous sodium silicate and unsaturated polyester resin syrup which may be 
combined for developing specific thickening characteristics. The act of 
mixing the unsaturated polyester resin syrup with the aqueous sodium 
silicate brings about changes in the composition of both the aqueous 
sodium silicate and the unsaturated polyester resin syrup. Specifically 
the aqueous sodium silicate forms, at least in part, a hybrid silica gel. 
The unsaturated polyester resin syrup has its carboxylic end groups 
converted to carboxylate salts of sodium. Some quantities of free water 
are released in the resulting system. The resulting material is not an 
emulsion but instead appears to be a mixture of the ingredients. 
The mixture may harden rapidly or slowly to a final consistency depending 
upon the ratios of aqueous sodium silicate and unsaturated polyester resin 
syrup. There is a need for regulating the thickening rate and final 
consistency of such mixtures. Rapid thickening is particularly desirable 
when manufacturing sheet molding compounds, bulk molding compounds or 
molding powders. 
SUMMARY OF THE INVENTION 
According to the present invention, a quantity of calcium sulfate 
hemihydrate is added to the mixture of unsaturated polyester resin syrup 
and aqueous sodium silicate to absorb free water and provide a means for 
regulating the thickening rate and final consistency of the mixtures. 
The overall resulting mixtures are semisolid polymerizable compositions 
containing one part by weight of unsaturated polyester resin syrup, 
0.1-2.0 parts by weight of aqueous sodium silicate and 0.1-2.0 parts by 
weight of calcium sulfate hemihydrate. The amount of the calcium sulfate 
hemihydrate should be sufficient to combine with at least 85 percent by 
weight of the uncombined water which is contained in the other ingredients 
of the composition. In addition the mixtures can contain inert fillers 
which may be finely divided particulate substances or fibrous fillers in 
the amount of 0.1 to 5.0 parts by weight. Typical inert fillers include 
chalk, silica, ground glass, glass spheres, powdered stone, wood flour, 
glass fibers, perlite, vermiculite, asbestos fibers, animal fibers, 
vegetable fibers, plastic fibers and the like. 
In a preferred embodiment of the invention the calcium sulfate hemihydrate 
is mixed with the unsaturated polyester resin syrup and that mixture is 
combined with aqueous sodium silicate. After these ingredients have been 
combined the inert solids are thereafter introduced into the mixtures. 
The unsaturated polyester resin syrup also preferably contains an initiator 
for its polymerization, preferably a high temperature initiator such as 
dicumylperoxide, which will not initiate polymerization at the exothermic 
temperatures resulting from the act of mixing. Polymerization promoters 
also may be included in the syrup. 
UNSATURATED POLYESTER RESIN SYRUP 
This is a term applied to solutions of unsaturated polyester resins in 
copolymerizable monomers such as styrene, alpha methyl styrene, o-chloro 
styrene, vinyltoluene, acrylates and methacrylates, acrylic and 
methacrylic acid, divinylbenzene and the like. The unsaturated polyester 
resin is the polyesterification reaction product of dicarboxylic acids and 
polyhydric alcohols wherein at least a portion of the dicarboxylic acid 
has alpha-beta ethylenic unsaturation. The dicarboxylic acids may include 
dicarboxylic acid anhydrides such as maleic anhydride, phthalic anhydride, 
tetrahydrophthalic anhydride. Other dicarboxylic acids include phthalic 
acid, adipic acid, succinic acid, tetrahydrophthalic acid, 
tetrabromophthalic acid, maleic acid, fumaric acid and the like. Typical 
polyhydric alcohols include glycols such as ethylene glycol, propylene 
glycol, butylene glycol, neopentyl glycol, diethylene glycol, dipropylene 
glycol, polyethylene glycol, polypropylene glycol. Occasionally trihydric 
or higher polyols are employed in a polyester such as trimethylolethane, 
trimethylolpropane, pentaerythritol. Customarily a slight stoichiometric 
excess of the polyhydric alcohol is employed in the preparation of the 
unsaturated polyester resins. Customarily the copolymerizable monomer 
comprises from 10 to 40 weight percent of the resulting syrup, that is, 
the unsaturated polyester resin comprises 90 to 60 weight percent of the 
resin syrup. 
RESIN INITIATORS 
Typical initiators for unsaturated polyester resin syrups include peroxy 
materials such as benzoyl peroxide, cumene hydroperoxide, tertiary butyl 
peroxide and the like. A particularly useful peroxy initiator for room 
temperature curing is 2,5-dimethyl hexane-2,5-dimethyl-diper-2-ethyl 
hexoate. Customarily peroxy initiators are provided in the form of a paste 
wherein the peroxy ingredient is dispersed in a glycol. The initiators 
normally are provided in amounts up to about 5 percent of the weight of 
the unsaturated polyester resin. 
It is also customarily to include accelerators for the peroxy initiators in 
the form of organic metal salts such as cobalt nephthenate, cobalt 
octoate, molybdenum and copper and vanadium salts. 
For the two stage processing of the present compositions in the form of 
molding powders or molding compounds, a high temperature initiator is 
preferred such as cumyl peroxide. Preferably the high temperature 
initiator will be effective at temperatures below about 250.degree. F in 
order to minimize the vaporization of any free water which may be included 
in the system. 
AQUEOUS SODIUM SILICATE 
The aqueous sodium silicate is a liquid containing from 45 to 85 percent by 
weight water with the balance being sodium silicate. The weight ratio of 
SiO.sub.2 /Na.sub.2 O is from about 1.5 to about 3.75. Commercially 
available aqueous sodium silicate may be diluted with additional water if 
desired to facilitate handling. 
CALCIUM SULFATE HEMIHYDRATE 
Calcium sulfate hemihydrate is commercially available as a dry powder and 
is known as plaster of paris. It is available commercially in a variety of 
formulations with inert additives. When one part by weight of the calcium 
sulfate hemihydrate is combined with about 0.18 parts by weight water, the 
material hardens to form calcium sulfate dihydrate -- also known as 
gypsum. The calcium sulfate hemihydrate is the principal ingredient in 
most plasters. 
The calcium sulfate hemihydrate preferably is added to the unsaturated 
polyester resin syrup and well dispersed therein prior to addition of the 
aqueous sodium silicate. After the addition of aqueous sodium silicate, 
the mixture is stirred vigorously and experiences a viscosity-increase 
which results from the reaction of the sodium silicate with the 
unsaturated polyester. The viscosity continues to increase as the water 
from the aqueous sodium silicate combines with the calcium sulfate 
hemihydrate to form gypsum. The gypsum in the resulting material 
introduces beneficial fire retardant properties. When exposed to fires, 
the gypsum slowly releases its contained water and absorbs heat thereby. 
The amount of uncombined water in the other ingredients of the composition 
can be established by the selected ratio of aqueous sodium silicate to 
unsaturated polyester resin syrup. Sufficient calcium sulfate hemihydrate 
is included in the composition to react with at least 85 weight percent of 
the uncombined water from the other ingredients of the composition. In my 
aforementioned patent application Ser. No. 544,966, polymerizable mixtures 
of aqueous sodium silicate and unsaturated polyester resin syrup are 
described as being useful for molding compositions -- that is, 
compositions which are essentially tack-free yet still polymerizable. Such 
compositions, while being tack-free solid materials, nevertheless may 
contain appreciable quantities of uncombined water which is deleterious in 
the subsequent molding operations. Such uncombined water will vaporize 
under molding conditions and create unwanted void spaces in the resulting 
molded article. This undesirable blowing of molded parts can be avoided if 
the uncombined water is reacted with calcium sulfate hemihydrate according 
to this invention. At least 85 percent by weight of the uncombined water 
and preferably 100 percent by weight of the uncombined water is reacted 
with the calcium sulfate hemihydrate according to the present invention, 
thereby avoiding the undesirable blowing tendency of the compositions. 
INERT SOLIDS 
Inert solids may be added to the mixture for a variety of purposes such as 
reducing the cost of the materials, increasing the strength of the 
resulting products, increasing the hardness of the resulting products, 
increasing the fire retardance of the resulting products. Particulate 
fillers include powdered glass, silica, chalk, clays, wood flour, hydrated 
alumina, crushed stones, perlite, expanded vermiculite, and the like. 
Fibrous inert additives include glass fibers, asbestos, rock wool, 
vegetable fibers, animal fibers, plastic fibers. The inert solids comprise 
about 0.1 to 5.0 parts by weight for each one part by weight of 
unsaturated polyester resin syrup. 
The preferred compositions include reinforcing glass fibers of average 
length from one-quarter inch to about four inches. The glass fibers are 
normally provided from about 5 to about 30 percent by weight based upon 
the weight of the unsaturated polyester resin syrup in the composition. 
Another preferred active filler is aluminum oxide trihydrate sometimes 
called hydrated alumina. The hydrated alumina increases the physical 
strength of the resulting products, i.e., hardness and abrasion 
resistance. The alumina hydrate also increases fire resistance of the 
products because of its included water of hydration. Where hydrated 
alumina is employed, up to one part by weight (based on the weight of 
unsaturated polyester resin syrup) and up to about three parts by weight 
(based on the weight of the aqueous alkali metal silicate) may be added. 
Thus the amount of hydrated alumina should be less than the sum of (a) the 
weight of unsaturated polyester resin syrup and (b) three times the weight 
of aqueous sodium silicate. The hydrated alumina preferably is provided as 
a powder passing through a 325 mesh U.S. standard screen. 
DIRECT PROCESSING 
According to one embodiment of the invention the ingredients are mixed and 
promptly polymerized after shaping of the material into the desired 
configuration by means of molding, pressing, casting, spray-up, or lay-up 
techniques. In this embodiment the polymerization initiator for the 
unsaturated polyester resin syrup may be provided in the resin syrup 
itself or may be provided in the aqueous sodium silicate. The mixing can 
occur in a mixing tank, a turbulent flow pipe or by means of impingement 
of sprays of the ingredients. Inert fillers may be incorporated in either 
or both of the liquid ingredients, that is, the unsaturated polyester 
resin syrup and the aqueous sodium silicate. 
TWO STAGE PROCESSING 
In the alternative embodiment of this invention where the ingredients are 
combined to prepare a molding composition, the mixture is allowed to 
harden in strips or sheets or may be extruded in the form of "spaghetti" 
prior to final hardening. After the composition has hardened in a desired 
shape, the composition is cut to a convenient size and packaged for use 
when and as desired in the form of a molding powder. The expression 
molding "powder" is perhaps inexact since the materials frequently are 
provided in the forms of flakes, pellets, lumps or chopped spgahetti. In 
the molding powder application, chopped reinforcing fibers, particularly 
glass fibers, will normally be included. 
The molding powder, when used, is molded or pressed to a final desired 
shape and cured by heating or other initiation (e.g., radiation, electron 
bombardment, etc.). The molding powder may be stored for extended periods 
without losing its ability to polymerize when exposed to appropriate 
conditions. 
The cured product according to this invention, after polymerization of the 
unsaturated polyester resin syrup, will be homogeneous and will have the 
following characteristics: 
a. It will be substantially free of uncombined water; 
b. It will contain at least 5 percent by weight hybrid silica gel uniformly 
dispersed throughout its mass; 
c. It will contain calcium sulfate dihydrate uniformly dispersed throughout 
its mass; 
d. At least a portion of the unsaturated polyester resin will contain 
carboxylate salt groups rather than carboxylic acid end groups. 
Thermal curing of the molding powder is carried out at temperatures 
preferably below about 250.degree. F in order to minimize any tendency of 
hydrated water to vaporize and also to minimize rupturing and spalling of 
the resulting product.

EXAMPLE 1 
An unsaturated polyester resin syrup I contains 25 parts by weight styrene 
and 75 parts by weight of an unsaturated polyester resin which is obtained 
by polyesterification of 
16 mols phthalic anhydride 
40 mols maleic anhydride 
106 mols propylene glycol cooked to a final acid number of about 20. 
50 grams of the unsaturated polyester resin syrup I is combined with 50 
grams calcium sulfate hemihydrate and mixed well. 15 grams of aqueous 
sodium silicate containing 63 percent by weight water and having an 
SiO.sub.2 /Na.sub.2 O ratio of 3.2 is added to the mixture. The aqueous 
sodium silicate is commercially available from Philadelphia Quartz Company 
and is identified by the designation silicate N. 
Following the mixing of the two liquids, the mixture thickens rapidly and 
has the appearance of a modeling clay. After about 15 minutes the mixture 
is soft and pliable. After sitting overnight the mixture is hard and 
rocky. The material shows no measurable weight loss. 
EXAMPLE 2 
Example 1 was repeated with the exception that 1/2 gram of benzoyl peroxide 
was added to the unsaturated polyester resin syrup I. After the described 
mixing the resulting material was allowed to set overnight and then 
pulverized into a powder passing through a 50 mesh U.S. standard screen. 
The powder was placed in a heated mold at 100.degree. C and pressed in a 
press at 2,000 psi. When the mold was removed from the press and the 
sample removed from the mold, the powder had formed a hard continuous 
molded product. 
Another sample of the powdered material was placed in the bottom of the 
mold as just described. A sheet of glass fiber veil was applied to the top 
of the molding powder and the remainder of the mold was filled with a 
molding powder above the glass fiber veil. The mold was closed, placed in 
a press at 1,000 psi pressure at 100.degree. C. When the mold was removed, 
a hard continuous strong product was removed from the mold. 
EXAMPLE 3 
50 grams of the unsaturated polyester resin syrup I was combined with 60 
grams calcium sulfate hemihydrate. 10 grams of aqueous sodium silicate 
(silicate N) and 2 grams water was combined and added to the mixture. 
After vigorous mixing there was an immediate increase in viscosity of the 
mixture. The mixture was flattened between two pieces of cellophane and 
allowed to stand overnight. After one day the cellophane was removed, the 
sheet was cut into small strips approximately one-quarter inch wide and 
one-half inch long. The strips were sealed in a paint can and inspected 
periodically. After about 30 days, the strips showed no tendency to 
agglomerate but remained dispersed, soft and pliable. 
EXAMPLE 4 
50 grams of unsaturated polyester resin I was mixed with 60 grams calcium 
sulfate hemihydrate, 1 gram of dicumyl peroxide as a catalyst and mixed. A 
mixture of 10 grams aqueous sodium silicate (silicate N) was mixed with 2 
grams of water and this mixture was added to the resin mixture. An 
immediate viscosity increase was observed. The mixture was flattened 
between two pieces of cellophane. The following day the sheet was cut in 
half. The material was pliable. One-half of the sheet was placed in an 
oven and heated to 250.degree. F for ten minutes. When removed from the 
oven the piece had hardened to a cured polyester resin product. 
EXAMPLE 5 
50 grams of unsaturated polyester resin syrup I was combined with 60 grams 
calcium sulfate hemihydrate (C-base, United States Gypsum Company) and 2 
grams of powdered hydrated alumina. 1 gram of dicumyl peroxide was added 
to the blend as an initiator. A second mixture was produced from 15 grams 
aqueous sodium silicate (silicate N), 2 grams water and 20 grams hydrated 
alumina. The two mixtures were then combined and exhibited an immediate 
viscosity increase. The mixture was flattened between cellophane sheets. 
The following day the sheet was placed in an oven for 5 minutes at 
250.degree. F. When the sheet was removed from the oven it was a hard, 
cured polyester product. The sheet was placed in the flame of a Bunsen 
burner for two minutes. There are some smoke generation in the test but no 
independent flame developed. When the Bunsen burner was removed, the 
sample retained its shape.