Uniformly pigmented, low shrinking polyester molding compositions

There is disclosed thickened, low shrinkage polyester molding compositions having improved pigmentation. The improved pigmentation in thickenable polyester molding compositions containing a carboxylated vinyl ester polymer low profile additive is achieved either by incorporating a surfactant in the composition, by using as the low profile additive a vinyl acetate/maleic acid copolymer, or by a combination of the two methods.

The invention relates to a means for improving the uniformity of 
pigmentation in thickenable, low shrink polyester molding compositions. 
BACKGROUND OF THE INVENTION 
A major advance in commercial polyester molding technology was the 
introduction several years ago of chemically thickened systems. Chemical 
thickening is always employed in sheet molding compounds ("SMC"), and is 
increasingly being used in bulk molding compounds ("BMC"). In such 
systems, an alkaline material such as magnesium oxide or magnesium 
hydroxide is added to the uncured polyester along with fillers, glass 
fiber, and other standard materials. The alkaline material interacts with 
residual acidity in the polyester to build viscosity. The thickened system 
is relatively tackfree and easy to handle, and the high viscosity carries 
the glass fiber reinforcement to the extremities of the mold during 
crosslinking of the system. Thus, the use of thickened systems has made a 
major contribution to the commercial expansion of polyester molding. 
Another technical improvement that has made a significant contribution to 
commercial polyester molding technology is the use of low profile 
additives to reduce shrinkage during the curing reaction, and to thereby 
improve dimensional stability and surface smoothness. Low profile 
additives are thermoplastic polymers such as vinyl acetate polymers, 
polystyrene, acrylic polymers, and polycaprolactones. There are a number 
of theories that seek to explain the low profile or anti-shrinkage action 
of these polymers, but the one that seems to best explain the phenomenon 
is the following: 
The low profile additive is at least partly soluble in the uncured 
polyester/styrene solution. As the polyester/styrene mixture crosslinks, 
the thermoplastic polymer becomes incompatible or less soluble and at 
least partly comes out of solution. This action causes a volume expansion 
that compensates for the shrinkage that occurs when the polyester/styrene 
mixture crosslinks. 
When a low profile additive is employed in a thickened composition, the 
increase of viscosity that occurs can cause the low profile additive to 
separate, and thereby cause a tacky surface. This problem is usually most 
severe with the more reactive polyesters, i.e., those having lower 
molecular weight to double bond ratios. To combat this, carboxylic acid 
functionality is incorporated in the low profile additive. The 
thermoplastic polymer itself can then enter the thickening reaction, 
thereby ensuring that a tack-free surface will result. 
However, while alleviating the tackiness problem the introduction of these 
carboxyls into the thermoplastic can present other difficulties if not 
properly understood. For the thermoplastics to function optimally as 
shrinkage control agents they must become incompatible with the 
crosslinked polyester structure. Therefore, if the polyester resin, 
carboxylated thermoplastic, and thickening agent structure are not 
carefully controlled and balanced, the chemical thickening agent can bond 
the thermoplastic into the thermoset system through the carboxyl groups. 
This will reduce the amount of thermoplastic-thermoset incompatibility, 
thus reducing, and in extreme cases, actually eliminating the shrinkage 
control. 
Another property of these composites which can be notably effected by this 
thickening process is internal pigmentability. Because of the 
thermoplastic-thermoset incompatibility, low shrink, low profile SMC and 
BMC is more difficult to uniformly pigment than conventional SMC and BMC. 
By careful formulation, and with the use of certain pigments, it is 
possible to balance adequate shrinkage control and dimensional stability 
with internal pigmentation in thickened polyester composites using 
commercially available carboxylated polycaprolactone low profile additive. 
However, truly zero shrink thickened polyester composites have not yet 
been uniformly and reproducibly pigmented in commercial molds except when 
certain black pigments were used with carboxylated polycaprolactone low 
profile additive. 
DESCRIPTION OF THE INVENTION 
The invention provides a means for improving the uniformity of pigmentation 
in internally pigmented, thickened polyester molding compositions. In one 
aspect, the invention provides a curable composition comprising: 
(a) a polyester resin comprising the reaction product of an olefinically 
unsaturated dicarboxylic acid or anhydride and a polyol; 
(b) an olefinically unsaturated monomer that is copolymerizable with said 
polyester resin; 
(c) a thickening agent comprising an oxide or hydroxide of a metal of Group 
I, II, or III of the Periodic Table; 
(d) a pigment; 
(e) a carboxylated vinyl acetate polymer low profile additive; and 
(f) a surface active compound. 
In another aspect, the invention provides a curable composition comprising 
(a), (b), (c), and (d), as defined above, and (g) a low profile additive 
comprising a vinyl acetate/maleic acid copolymer. 
The invention also provides the cured composites produced by curing the 
above-described curable compositions. 
The polyesters that are employed in the invention are reaction products of 
a dicarboxylic acid or anhydride, with a polyhydric alcohol. The 
dicarboxylic acids or anhydrides that are employed to produce the 
polyester, either singly or in combination, must include those that 
contain olefin unsaturation, preferably wherein the olefin unsaturation is 
alpha, beta- to at least one of the carboxylic acid groups. Such acids 
include maleic acid or anhydride, fumeric acid, tetrahydrophthalic acid or 
anhydride, hexachloroendomethylene tetrahydrophthalic anhydride 
("chlorendic anhydride"), Diels-Alder adducts of maleic acid or anhydride 
with compounds having conjugated olefinic unsaturation, such adducts being 
exemplified by bicyclo[2.2.1]hept-5-en3-2,3-dicarboxylic anhydride, methyl 
maleic acid, and itaconic acid. Maleic acid or anhydride and fumaric acid 
are the most widely used commercially. 
In addition to the olefinically unsaturated acid or anhydride, saturated 
and/or aromatic dicarboxylic acids or anhydrides can also be employed in 
producing the polyester. Such acids include phthalic acid or anhydride, 
terephthalic acid, hexahydrophthalic acid or anhydride, adipic acid, 
isophthalic acid, and "dimer" acid (i.e., dimerized fatty acids). 
A polyol is also employed to produce the polyester. Such polyols include 
ethylene glycol, diethylene glycol, dipropylene glycol, butylene glycols, 
neopentyl glycol, glycerol and 1,1,1-trimethylolpropane. As a rule, not 
more than about 20 mole percent of the polyol will be a triol, with the 
remainder being one or more diols. 
As is known in the art, polyesters that are employed in thickened molding 
compositions must contain residual acidity in order to enter into the 
thickening reaction. The nature and production of the polyesters used in 
such applications are known in the art. 
The polyester composition of the invention also contains a monomer that 
contains ethylenic unsaturation, and which is copolymerizable with the 
polyester. Styrene is the preferred monomer in commercial practice today, 
although others can be used. Such others include vinyl toluene, methyl 
methacrylate, chlorostyrene, and diallyl phthalate. 
The said monomer is employed in the polyester composition for the purpose 
of dissolving the polyester (which is a solid at ambient temperatures, 
i.e., about 20.degree.-25.degree. C.) to ensure that the polyester 
composition is a fluid. Enough monomer is employed so that the thickness 
or viscosity of the fluid is such that the fluid can be processed 
conveniently. Excessive amounts of the monomer are normally to be avoided, 
because such excess can have an adverse effect on properties. For 
instance, too much of the monomer may tend to cause embrittlement of the 
cured polyester. Within these guidelines, effective proportions of the 
monomer are normally found within the range of from about 35 to about 70, 
and preferably 40 to 55, weight percent, based on weight of polyester plus 
monomer, plus low profile additive. 
A thickening agent is also employed in the invention. Such materials are 
known in the art, and include the oxides and hydroxides of the metals of 
Groups I, II and III of the Periodic Table. Specific illustrative examples 
of thickening agents include magnesium oxide, calcium oxide, zinc oxide, 
barium oxide, potassium oxide, magnesium hydroxide, and others known to 
the art. Thickening agents are normally employed in proportions of from 
about 0.1 to about 6 weight percent, based upon weight of polyester resin, 
plus monomer, plug low profile additive. 
Pigments are also employed in the invention. Illustrative examples include 
black iron oxide, titanium dioxide, carbon black, chrome yellow, 
phthalocyanine blue and green, ceramic black, chrome green, ultramarine 
blue, chrome-cobalt-alumina turquoise, cobalt aluminate (blue), brown iron 
oxide, ceramic yellow (antimony, titanium-chrome oxide), titanium pigments 
(yellow, buff), molydate (orange), chrome orange, manganese (violet), 
chrome-tin (pink), cadmium mercury (maroon, red, orange), and the like. 
Pigments are employed in the invention in conventional proportions, e.g., 
from about 0.5 to about 10 weight percent, based upon weight of polyester 
resin plus monomer plus low profile additive. 
The invention has shown improvement in pigmentability with all pigments 
thus far tested. 
In one aspect, the invention employs a carboxylated vinyl acetate polymer 
low profile additive. Such polymers include copolymers of vinyl acetate 
and ethylenically unsaturated carboxylic acids such as acrylic acid, 
methacrylic acid, maleic acid, fumaric acid, itaconic acid, and the like; 
vinyl acetate/vinyl chloride/maleic acid terpolymer, and the like. 
Reference is made to Comstock et al., U.S. Pat. No. 3,718,714 and Comstock 
et al. British Pat. No. 1,361,841, for descriptions of carboxylated vinyl 
acetate polymer low profile additives. 
The useful carboxylated vinyl acetate polymer low profile additives 
ordinarily have molecular weights within the range of from about 10,000 to 
about 250,000, and preferably from about 25,000 to about 175,000. They are 
usually employed in proportions of from about 6 to 20, and preferably from 
about 9 to 16, weight percent, based on weight of polyester plus low 
profile additive, plus monomer. 
As a general rule, the solution polymerized carboxylated vinyl acetate 
polymers are preferred in commercial practice because of their better 
batch-to-batch uniformity. 
The polyester molding composition may also contain one or more of the known 
types of conventional additives, which are employed for their known 
purposes in the usual amounts. The following are illustrative of such 
additives: 
1. Polymerization initiators such as t-butyl hydroperoxide, t-butyl 
perbenzoate, benzoyl peroxide, cumene hydroperoxide, methyl ethyl ketone 
peroxide, and others known to the art. The polymerization initiator is 
employed in a catalytically effective amount, such as from about 0.3 to 
about 2 to 3 weight percent, based on the weight of polyester plus monomer 
plus low profile additive; 
2. Fillers such as clay, hydrated alumina, silica, calcium carbonate and 
others known to the art; 
3. Reinforcing fillers such as glass fibers or fabrics, asbestos fibers or 
fabrics, various organic fibers or fabrics such as those made of 
polypropylene, acrylonitrile/vinyl chloride copolymer, and others known to 
the art; and 
4. Mold release agents or lubricants, such as zinc stearate, calcium 
stearate, and others known to the art. 
The polyester molding compositions of the invention can be cured under 
conditions similar to those used for known polyester compositions. Typical 
curing conditions are a temperature of from about 200.degree. to 
350.degree. F. for 1 to 4 minutes at a pressure of 300 to 2000 psi. 
In combination with the carboxylated vinyl acetate polymer low profile 
additives, the invention employs a surface active compound. A wide variety 
of surface active compounds can be employed. As a general rule, the ionic 
surface active compounds have given the best results. Classes of 
surfactants that deserve particular mention include: 
Alkali metal, alkaline earth metal, and ammonium sulfonates; 
certain ethylene oxide adducts of long chain (e.g., C.sub.9 -C.sub.18) 
aliphatic alcohols; 
certain polyoxyethylene-polyoxypropylene block copolymers; 
polyglycerol oleate; 
ethoxylated sorbitan monooleate; 
sodium 2-caprylic-1(ethyl beta oxipropanoic acid)imidazoline; 
ethoxylated alkylguanidine amine complex; 
sodium and methyl-N-long chain aliphatic taurate; 
sodium isethionate coconut ester; 
certain ethoxylated long chain alkylphenols; 
N-long chain aliphatic quaternary ammonium halide; 
Ethoxylated N-long chain aliphatic alcohol quaternary ammonium halide; and 
Polydimethylsiloxane oil and certain other silicones. 
The surfactant is employed in the invention in effective amounts, usually 
in the range of from about 0.1 to about 8 weight percent, based on weight 
and polyester plus low profile additive plus monomer. 
The Examples below discuss in more detail the nature and proportion of the 
surfactants that are used in the invention. 
In an alternative aspect of the invention, the low profile additive 
employed is a vinyl acetate/maleic acid copolymer. (The maleic acid can be 
replaced by the equivalent fumaric acid or maleic anhydride.) The maleic 
acid is used in the copolymer in conventional amounts, e.g., in amounts 
sufficient to provide about 0.1 to about 3 weight percent carboxyl groups, 
based on weight of copolymer. The molecular weight of the copolymer, and 
the amounts in which it is used, are conventional for carboxylated vinyl 
acetate low profile additives. The copolymer is used either with or 
without surfactant; although its use with a surfactant is preferred in 
most cases. 
Experimental 
In the Examples below, the following materials were used; 
Polyesters 
Polyester A--made from isophthalic acid, maleic anhydride, propylene 
glycol, and dipropylene glycol in approximate molar proportions of 
0.3:0.7:0.8:0.2, respectively; 
Polyester B--made from isophthalic acid, maleic anhydride, and propylene 
glycol in approximate molar proportions of 0.3:0.7:1.0, respectively; 
Polyester C--made from maleic anhydride and propylene glycol in molar 
proportions of 1:1.1; and 
Polyester D--made from isophthalic acid, maleic anhydride, and propylene 
glycol, in approximate molar proportions of 1.0:3,0:4.4, respectively. 
The above polyesters are further characterized as follows: 
TABLE I 
______________________________________ 
Weight % Molecular 
Acid Solids in Weight to 
Polyester 
Number Styrene Double Bond Ratio 
______________________________________ 
A 16.4 72.4 286.7 
B -- -- 244.4 
C 28.5 65.5 156.1 
D 19.9 65.4 224.7 
______________________________________ 
Miscellaneous Additives 
"Camel Wite"--Finely divided calcium carbonate used commercially as a 
filler in polyesters; 
Zinc Stearate--used as a mold release agent; 
t-Butyl perbenzoate--a peroxide initiator; 
p-Benzoquinone--a polymerization inhibitor; 
"RS-5988"--a 33 weight percent dispersion of magnesium oxide in a 
polypropylene maleate polyester; 
"Marino H"--Magnesium hydroxide; 
"Modifier M"--a 33 weight percent dispersion of magnesium oxide in a 
polypropylene maleate polyester; 
"JM-308A" glass fibers--1/4-inch chopped glass fibers, of medium hardness; 
"PPG-303" glass fibers--1/4-inch chopped glass fibers of medium harness, 
but a bit softer than JM-308A; and 
Alumina trihydrate--a flame retardant filler. 
Low Profile Additives 
LP-A--40 weight percent solids solution of a 99.2/0.8 (by weight) vinyl 
acetate/acrylic acid copolymer in styrene, having the following 
properties: 
Solution Viscosity 4000-6000 centipoises at 25.degree. C. 
Copolymer Inherent viscosity 0.48; 16-17 Ford cup 
M.sub.N 42,000 
M.sub.W 92,000 
LP-B--40 weight percent solids solution of vinyl acetate/maleic acid 
copolymer in styrene. Different versions contained from 0.7 to 2.1 weight 
percent maleic acid in the copolymer, the remainder being vinyl acetate. 
The styrene solution viscosities varied from about 3400 to about 16,000 
centiposes at 25.degree. C. The Ford Cup viscosities of the copolymer 
varied from 12.4 to 17.8; 
LP-C--35 weight percent solution of polystyrene in styrene, having a 
solution viscosity of 5000 cps at 25.degree. C.; and 
LP-D--33 weight percent solution of a copolymer of methyl methacrylate, 
ethyl acrylate, and acrylic acid (weight ratio 85:12.5:2.5) in styrene. 
Pigments 
PDI-1416--A green pigment; 
PDI-1600--An orange pigment; 
CM-3308--A gray pigment; 
CM-2015--a black pigment; and 
CM-3131--A blue pigment. 
(The pigments employed were all commercial materials marketed as 
dispersions in a low molecular weight polyester. The pigment weights 
indicated in the formulations below are all dispersion weights, and thus 
include the dispersing medium.) 
Surfactants 
The surfactants employed are described in the Examples below. 
Evaluation 
The evaluation of the pigmentation was done visually. Non-uniformity of 
pigmentation can be manifested in any of several ways, such as the 
presence of small spots on the sample, cloudiness, flow marks, waviness, 
lack of color depth, streaks, mottling, and other similar defects. In most 
cases, the various samples were compared with a control. (The control 
employed was usually a polyester molding composition containing thickener, 
pigment, LP-A low profile additive, and no surfactant.) 
The invention provides a means for improvement over polyester compositions 
containing LP-A low profile additive. Even though perfectly uniform 
pigmentation is not always provided, in its preferred aspects, the 
invention provides the best combination of uniform pigmentation and 
shrinkage control that is presently available in thickened polyester 
molding compositions.