Pigmentable Low Shrink Thermosetting Polyesters

The following examples illustrate the preferred embodiments of this invention but are not intended to limit the scope of this invention. Examples 1 to 9 inclusive pertain to addition polymers for the cross-linked polymer particles. Examples 11-13 illustrate condensation polymers, and Example 14-15 illustrate polymer particles having amino or oxirane groups.

Into a 3-liter-fluted resin kettle fitted with N.sub.2 inlet, thermometer, paddle stirrer, and condenser was placed 1000 grams of a 0.8% aqueous solution of hydroxyethyl cellulose. After bubbling N.sub.2 through the solution for 15 minutes, a solution comprising 198 grams of methyl methacrylate, 2 grams neopentylglycol diacrylate and 1.5 grams 2,2' azobisisobutyronitrile was added to the aqueous phase, vigorously agitated, and heated to 80.degree. C. An exotherm occured after about 20 to 30 minutes and was controlled by adding cold water through the condenser. The rate of agitation was thereafter decreased and after about one hour at 80.degree. C, the suspension was cooled. An excess of methanol was added to the suspension and this mixture was filtered, rinsed with methanol, and dried in a vacuum oven at 80.degree. C. Yield was nearly quanitative. The average particle size was 70-100 microns and polymer particles had a cross-linking density of 0.0543 equivalent cross-linking sites per kilogram of polymer.

a. Several styrene and methyl methacrylate copolymers as indicated in Table 1 hereinafter were produced in accordance with the method in Example 1. The average particle size ranged from 20-100 microns. The cross-link density ranged from about 0.0054 to 1.15 equivalent cross-linking sites per kilogram of polymer. Preferred results were achieved with cross-linking density from 0.016 to 0.38 equivalent cross-linking sites per kilogram of polymer when compounded into a pigmented low-shrink polyester resin system.

b. A vinyl acetate polymer particle was produced in 3-liter fluted resin flask containing 100 grams of an 0.8% aqueous solution of hydroxyethyl cellulose. The solution was agitated vigorously upon adding a solution comprising 98 grams of vinyl acetate, 2 grams of triallylisocyanurate and 1 gram isopropyl peroxycarbonate. The temperature was increased to 50.degree. C and held. After 30 minutes the reaction exothermed to about 65.degree. C and was held at this temperature for 4 hours. The mixture was cooled and the suspension particles were allowed to settle. The water was decanted and the product was vacuum filtered and dried to give particle sizes from about 15 to 60 microns in size with an average particle size of between about 30-40 microns. Several vinyl acetate polymers indicated in Table 1 were produced in accordance with this procedure having an average particle size of about 20 to 50 microns. The cross-link density ranged from about 0.01 to 2.0 equivalent cross-linking sites per kiolgram of polymer. Preferred results were achieved with cross-linking density from 0.05 to 1.0 equivalent cross-linking sites per kilogram of polymer when compounded into a pigmented low-shrink polyester resin system.

A dicyclopentadiene-modified polyester polymer was synthesized from the following raw materials:

9.9 gram moles of propylene glycol (752 grams)

2.0 gram moles of dicyclopentadiene (264 grams) 10.0 gram moles of maleic anhydride (980 grams).

Polymer synthesis was carried out in an ordinary reaction vessel suitable for batch processing of polyesters and including an agitator, heating means, condenser, and inert gas flow.

FIRST STEP: Formation of an acid terminated partial copolymer of propylene glycol-maleic ester was made by charging anhydride together with 3% xylene (based on the charge) into the reaction vessel and by heating under inert gas to 300.degree. F for holding at 300.degree. F for about 30 minutes until the acid number of the batch became constant. The acid number became constant at about 412 whereupon the second step commenced.

SECOND STEP: A prepolymer was prepared by adding the 2.0 moles of the dicyclopentadiene to the propylene-maleic partial copolymer at a reaction temperature of 308.degree. F. The 2.0 moles of dicyclopentadiene were mixed with 3% xylene and added to the reaction vessel at a steady and continuous rate for a time period of 30 minutes and the reaction then continued until the acid number of the batch leveled off at about 276.

THIRD STEP: A dicyclopentadiene-terminated polyester was prepared by charging the remaining 4.9 moles of propylene glycol to the foregoing prepolymer in the reaction vessel, together with0.3 grams of hydroquinone.The batch temperature was gradually increased to about 390.degree. F and further processed until an acid number 30 was reached. A test sample of 7 parts resin mixed with 3 parts styrene yielded a viscosity of 3,600 cps. at 77.degree. F, 0.5 grams of hydroquinone was added to the polymer which was then diluted with styrene to yield a dicyclopentadiene polyester resin containing a ratio of 70 weight parts of dicyclopentadiene polyester polymer and 30 weight parts of styrene monomer. Thereafter, about 1 gram ionol was added and the resin was discharged to a holding tank.

The resin composition of Example 3 was mixed at room temperature with the polymer particles of Example 1 by charging to a mixing vessel to give the following final composition:

15 weight parts polymer particles of Example 1

40 weight parts of polyester polymer (solids) of Example 3

45 weight parts by styrene.

The mixture was mildly agitated to form a uniform stabilized resin dispersion. The resulting resin had a viscosity of 1600 centipoises, a weight per gallon of 9.9 and SPI gel time of 9 minutes, an SPI reaction line of 12 minutes, and an SPI peak exothermic of 395.degree. F with 1% BPO at 180.degree. F.

A bulk molding compound was prepared by mixing together in a Baker-Perkins dough mixer the following materials (parts by weight):

Three-fourths of the indicated calcium carbonate and zinc stearate were first dry blended in the mixer. The t-butyl perbenzoate catalyst, the pigment, and remaining calcium carbonate were stirred into the liquid molding resin composition and that mixture slowly added to the material in the dough mixer while mixing continued. After thorough wetting of the calcium carbonate had been achieved, the magnesium hydroxide was added and mixing was continued for about two minutes. The chopped glassfiber reinforcement was added and mixing was continued for about 2 minutes until the glass had been thoroughly wetted. The mixing period after addition of the glass was kept as short as possible, consistent with achieving wetting of the glass and uniform dispersion of the glass and thickener, so as not to cause excessive breaking of the glass into shorter strands which would contribute less reinforcement to the molded articles to be produced from the bulk molding compound. The bulk molding compound was finally discharged from the mixer and held overnight (before molding) to insure that the thickening process was substantially complete.

A piece was molded in the following shape; about nine inches square and 1/8 inch thick having on one of its surfaces: (1) a straight rib about 1/2 inch deep tapering from about 7-5/16 inches long and 9/16 inch wide at the base to about 7-3/16 inches long and 3/8 inch wide at its flat outer extremity, having rounded ends and with its longitudinal centerline about one inch from the edge of the nine-inch square; (2) and L-shaped rib about 1/2 inch deep with branches about 7-1/2 inches long and 1-3/4 inches wide having centerlines about one inch from the edges of the nine-inch square, the long branch being parallel to the straight rib (1) above and near the opposite edge of the square, the width tapering from about 5/16 inch at the base to about 1/4 inch at its flat outer extremity and having rounded ends tapered at about the same angle as the straight rib (1) above; and three circular bosses centered at about 2 inch intervals along a line about 2-1/2 inches from the edge of the square adjacent to the long branch of the L-shaped rib (2) above and being, respectively, (a) about 1/2 inch deep and tapering from about one inch in diameter at the base to about 15/16 inch at its flat extremity, (b) about 1/4 inch deep and tapering from about one inch in diameter at the base to about 31/32 inch at its flat extremity, and (c) about 1/4 inch deep and tapering from about 5/8 inch diameter at the base to about 9/16 inch at its flat extremity, wherein all tapers were approximately flat except for 3 (c) in which the taper was more pronounced near the base and less pronounced near the extremity.

About 350 grams of the bulk molding compound from Example 5 was placed as a compact mass in he steel die which had been preheated to 295.degree. F on the cavity side and 285.degree. F on the plunger side, the die was quickly closed in a press, and held closed for two minutes. The press was then opened and the molded piece removed from the die. An excellent uniformly pigmented part was obtained.

Sheet molding compound was prepared by first mixing together, by successive additions in the order stated, the following materials (parts by weight):

The molding resin composition was introduced to a Cowles hgih speed mixer at about 1000 rpm. The speed was gradually increased with successive additions of CaCO.sub.3, zinc stearate, pigment, and t-butyl perbenzoate, so as to maintain a vortex but without excessive air entrainment, and the magnesium hydroxide thickener was not added until the previously added dry materials were thoroughly wetted and uniformity dispersed at which point the temperature was about 100.degree. F. After addition of the magnesium hydroxide, stirring was continued for about two minutes. This mixture was then discharged and promptly (before excessive thickening, i.e., viscosity increase, had occurred) introduced into a Brenner SMC machine wherein it was spread onto two sheets of polyethylene film to a thickness of about 1/16 inch of each sheet, the one inch glass strands distributed over the exposed surface of one of these sheets and the exposed surfaces of the two sheets then brought together by passing between a pair of rollers. Thorough wetting of the glass was accomplished by then passing the laminated sheet between successive sets of ridged rollers to provide a kneading action. The sheet molding compound so produced was about 1/8 inch thick and was held about 5 days before molding so as to insure substantial completion of the thickening process. An excellent uniformly pigmented sheet was produced.

Unsaturated thermosetting polyester resins were produced in a conventional manner by esterifying at temperatures up to about 300.degree. F (149.degree. C) glycol components with dicarboxylic components to produce a thermosetting, ethylenicaly unsaturated polyester polymer by condensation reaction and simultaneously removing water. The raw materials of each respective thermosetting, unsaturated polyester polymer are indicated in the following Table 2.

Thermosetting polyesters from Example 8 and lightly cross-linked polymer particles of Table 1 provided a two-component low-shrink molding resin that was combined just prior to making BMC or SMC molding compositions. Excellent pigmentation resulted in the finished molded part.

Lightly cross-linked polymer particles were produced by conventional latex processing techniques to produce inferior polymer particles which produced poor pigmented, low-shrink molding compositions. Table 3 indicates polymer particles having undesirable particle sizes and/or undesirable cross-linking density. Parts indicated are weight parts, cross-linking density is equivalent cross-linking sites per kilogram of polymer, and average particle size is in microns. Larger particle size polymer particles were made by suspension techniques.

The foregoing polymer particles produced poor pigmented low-profile parts when compounded, molded, and tested in accordance with the foregoing examples indicating that the preformed polymer particles must be controlled in size as well as cross-link density. Small particle size produced fair low-profile but poor pigmentation such as mottling, streaking and non-uniform color. Non-cross-linked particles similarly produced fair low-profile parts but poor pigmentation. Large polymer particles produced acceptable pigmentation but caused considerable porosity and discontinuity in the molded surfaces.

The following examples illustrate preformed condensation polymer particles in accordance with this invention but are not intended to limit the scope of this invention

A lightly unsaturated polyester polymer having minor amounts of unsaturation was produced by a conventional polyester fusion cook from the following components:

STEP 1. The foregoing raw materials were charged to a reactor and slowly heated up to about 300.degree. F to esterify dicaboxylic acid components with the polyol components, removing water of reaction, and holding until an acid number of 20 was obtained. The lightly unsaturated polyester polymer was dissolved in monomeric styrene to give a 67% by weight solution of the unsaturated polyester in styrene.

STEP 2. A 3-liter fluted resin kettle fitted with nitrogen inlet, thermometer, paddle stirrer, a condenser, and containing 1000 grams of 0.8% aqueous solution of hydroxyethylcellulose was utilized for suspension polymerization of the polyester-monomer mixture. After bubbling nitrogen through the aqueous solution for 15 minutes, a 200 gram mixture of polyesterstyrene from Step 1 together with 2 grams of lauroyl peroxide and 0.15% of sodium lauroyl sulfate were added to the aqueous solution preheated to about 80.degree. C (176.degree. F) over about 10 minutes with vigorous agitation. After about 30 minutes, the rate of agitation was decreased and after one hour the suspensions was cooled. Thereafter, the suspended lightly cross-linked polyester polymer was dried by centrifuging to remove a major portion of the water. The average particle size of the lightly cross-linked polyester particles was about 80-100 microns and having a cross-linked density of 0.359 equivalent cross-linking sites per kilogram of polymer.

Several lightly cross-linked polyester polymer particles were prepared in accordance with Example 11 by adding 55 grams of a monomer solution of a polyester polymer containing 40% monomer by weight as indicated in following Table 4. About 5% lauroyl peroxide based on the polymer-monomer solution was added to the polymer-monomer then charged to the resin kettle containing about 650 milliliters of an aqueous solution of 0.8% of hydroxyethylcellulose containing 0.15% of sodium lauroyl sulfate.The addition of the polyester-styrene mixture was completed in about 10 minutes while continuously heating the solution at 190.degree. F (88.degree. C) under vigorous agitation. The resulting lightly cross-linked polyester polymer particles were filtered and dried having an average particle size of about 70-100 microns and cross-linked density as indicated in the following Table 4. Cross-link density is in cross-linking sites per kilogram of polymer and particle size is in microns.

Several lightly cross-linked polyester polymer particles were produced in the manner indicated in Example 11 but with smaller particle sizes, or lacking cross-linking, or containing excessive cross-linking. The preformed polymer particles produced poorly pigmented and/or poor low-profile molded parts when compounded, molded, and tested in accordance with foregoing examples. Small particle size polymer particles below about 10 microns (average) produced fair low-profile but poor pigmentation such as mottling, streaking, and non-uniform color. Non-cross-linked polymer particles similarly produced poor pigmentation. Large particle size polymer particles above about 150 microns (average) produced discontinuities in the molded surface.

The following examples illustrate a preferred embodiment of this invention wherein the preformed polymer particles further include reactive amino or oxirane groups.

Into a 3-liter fluted resin kettle fitted with N.sub.2 inlet, thermometer, paddle stirrer and condenser was placed 1000 grams of a 0.8% aqueous solution of hydroxyethyl cellulose. After bubblng N.sub.2 through the solution for 15 minutes, a solution comprising 10 grams N-t-butyl-aminoethylmethacrylate, 2 grams neopentlyglycol diacrylate, and 188 grams methyl methacrylate plus 2 grams BPO (penzoyl peroxide) was added to the aqueous phase at a bath temperature of about 153.degree. F (67.degree. C) and vigorously agitated. The bath was thereafter heated to about 176.degree. F (80.degree. C). An exotherm occurred after about 20 minutes and was controlled by adding cold water through the condenser. The rate of agitation was thereafter decreased and after about one hour at 80.degree. C the suspension was cooled. The resulting suspended polymer particles were dried by centrifuging to remove a major portion of the water. Methanol was added to the particles which were then filtered and dried in a vacuum over at 60.degree. C. Yield was nearly quantitive. The average particle size was 45-50 microns and the polymer particles has a cross-linking density of 0.0543. The polymer had an amine content of 0.16% by weight of (N).

Several polymer particles listed in the following Table 5 were produced in accordance with the procedure of Example 14 having an average particle size of about 20 to 100 microns and a cross-link density ranging from 0.05 to 2 equivalent cross-linking sites per kilogram of polymer. The polymer particles were synthesized from monomers indicated on a weight basis and contain reactive amino groups or oxirane groups. Amino groups are in weight percent of (N) and oxirane groups are in weight percent of ##STR3##