Phase stabilized polyester molding material

Abstract: The present invention relates to the discovery and de­ velopment of a novel class of phase stabilization additives for thermoset polyester resins. The use of these materials imparts improved glass read out and superior homogeneity when compared to art-disclosed systems thus producing an overall improved Class A quality thermoset polyester resin surface finish for a variety of products. The phase-stabilizing agents or additives of the present invention comprise a select group of compounds from three classes: fatty acids, dimer acids, and polyester polyols. More specifically, the phase-stabilizing agents of the present invention comprises a compound selected from the group consisting of: (i) a saturated or unsaturated C₅ to C₂₈ fatty acid; (ii) a C₂₀ to C₅₄ dimer acid or trimer acid; or (iii) a polyester polyol having an average molecular weight of about 200 to about 6,500.

Description: The present invention relates to a phase-stabilized sheet molding composition comprising: a) an unsaturated polyester resin having an average molecular weight between about 800 and 5000; b) a phase-stabilizing agent selected from the group consisting of fatty acids having from 5 to 28 carbon atoms, and mixtures thereof; c) an ethylenically unsaturated monomer and a free radical polymerization catalyst; d) an inert filler; e) a fiberous reinforcing material; f) a mold release agent; g) an isocyanate terminated urethane prepolymer dual functional additive having an equivalent ratio of NCO to OH from about 1.2/1 to about 5/1, comprising a polyol and a polyisocyanate, and being prepared by reacting: (i) one equivalent weight of a polyol having an average molecular weight of about 600 to 4000 and an average functionality of approximately 2 to approximately 6; and (ii) 1.2 to 5 equivalent weights of a polyisocyanate selected from the group consisting of 80:20 or 65:35 isomer mixture of the 2,4- and 2,6-isomeric forms of toluene di-isocyanate, ethylene di-isocyanate, propylene di-isocyanate, meta- and para-phenyl di-isocyanate, 4,4'-diphenyl methane di-isocyanate (MDI) or a mixture of MDI and its trifunctional cyclic adduct products containing carbodiimide linkages, 1,5-naphthalene di-isocyanate, para- and meta-xylene di-isocyanates, alkylene di-isocyanates, or polymeric MDI containing an average of two isocyanate groups per molecule, toluene di-isocyanate, polyisocyanate prepolymers of aromatic type, toluene di-isocyanate based adducts, aromatic/ aliphatic polyisocyanates and polyfunctional aliphatic isocyanates; wherein said reactants combine in a one-step addition process to yield an isocyanate terminated urethane prepolymer of controlled molecular weight to impart improved low shrink, dynamic impact strength and molding characteristics as measured by viscosity index properties in thermoset polyester resin products and particularly sheet molding compositions (SMC) by covalently binding to the polyester resin matrix; h) a Group IIA metallic oxide or hydroxide; and i) a linear polymer of approximately 400 to 200000 molecular weight, or mixtures of such polymers; wherein (i) said oxides and hydroxides are present in an amount sufficient to react with at least 30 percent, but not more than 75 percent of the carboxyl groups present; and (ii) said prepolymer is present in an amount sufficient to react with at least 10 percent, but not more than 105 percent of the hydroxyl groups present thereby forming an SMC of improved Class A quality finish. US 4 210 571 discloses compounds which are useful as "surfactant coupling agents" in the preparation of thermosetting resin compositions. The materials include carboxylic acid ester derivatives of mono-, di-, and tri-hydroxy fatty acid esters of C 1 to C 4 mono- and polyhydric alcohols. It is suggested that these agents are particularly useful in reducing the viscosity of highly-bonded filler prepolymer pastes to improve the dispersion of the filler and to promote the interaction of the filler and prepolymer so as to maintain and improve the properties of the final cured resin. US 4 210 572 discloses a thermosetting resin composite having an inorganic filler material and coupling agent. The coupling agents disclosed include mono-, di- and tri-long chain fatty acid esters of C 1 to C 4 mono- and polyhydric alcohols and polyoxyethylene derivatives of mono-, di-, and tri-hydroxy fatty acid esters of C 1 to C 4 mono- and polyhydric alcohols. It is suggested that the coupling agent is useful in reducing the viscosity of highly loaded filler prepolymer pastes to improve the dispersion of the filler and promote an interaction between the filler and the prepolymer. US 4 535 110 discloses a maturated moldable sheet molding compound suitable for molding under pressure, said molding compound having fillers and reinforcing materials dispersed in a thermosetting resin composition said resin being comprised primarily of an unsaturated polyester resin said resin including an aliphatically unsaturated monomer, a free radical polymerization catalyst and an internal mold release agent, said resin composition further containing a dual thickening system for modifying the viscosity of the resin composition, said dual thickening system comprising an oxide or hydroxide of magnesium or calcium and a polyisocyanate, wherein the polyisocyanate is an isocyanate terminated prepolymer having an NCO to OH ratio of from about 1.2/1 to 5/1 said isocyanate terminated prepolymer being the reaction product of one equivalent of a polyol having an average molecular weight of about 600 to 4000 and an average functionality between 2 and 6 with from 1.1 to 5 equivalent weights of a polyisocyanate selected from the group consisting of toluene diisocyanate, ethylene diisocyanate, phenyl diisocyanate, 4,4'-diphenyl methane diisocyanate (MDI), a mixture of 4,4'-diphenyl isocyanate and its trifunctional cyclic adduct containing carbodiimide linkages, 1,5-naphtalene diisocyanate, xylene diisocyanate, tetramethylene diisocyanate, and hexamethylene diisocyanate. In general, thermosetting polyester resin systems, particularly for sheet molding applications, have at least two distinct phases as a result of the diverse nature and character of the polyester resin component and the other components, as well as necessary monomers or carriers. In the maturation and molding process the various components have a tendency to separate. As a result, most advanced SMC matrices employ a low profile additive to retard or prevent shrinkage of the molded part during maturation. The polyester resin and the low profile additive are generally present - prior to the molding process - in two finely dispersed phases. During the maturation or molding process, the low profile agent prevents shrinkage by micro-phase separation; thus, micro-phase separation is acceptable. It is this micro-phase separation that provides the low-shrink action. However, if gross phase separation is allowed during the maturation process, such separation would result in surface flaws and imperfections which are unacceptable. This problem is especially critical in producing a Class A quality surface finish. Reducing or preventing gross phase separation is therefore highly desirable in such operations. US 3 219 604 discloses a method of making a modified polyester resin composition comprising providing (A) a polyester of a glycol with an alpha, beta-ethylenically unsaturated dicarboxylic acid having an acid value of 10 to 100, mixing the said polyester with (B) a copolymerizable ethylenically unsaturated monomer, (C) a metal compound selected from the group consisting of oxides, hydroxides and alkoxides in which the alkyl group contains 1 to 6 carbon atoms, of magnesium, aluminum and calcium, and (D) an aliphatic monocarboxylic acid having from 6 to 24 carbon atoms, and heating the resulting mixture in the presence of a polymerization inhibitor at a temperature of from 140 to 250°F for a period of from 5 minutes to 40 hours, whereby the said monocarboxylic acid becomes linked to the said polyester through a metal linkage, to produce a placticized resin composition characterized by increased viscosity, the amount of said monomer (B) being from 5 to 80 % by weight based on the entire weight of the composition, the amount of said metal compound (C) being from 0.1 to 3 parts by weight per 100 parts by weight of unmodified polyester (A), and the amount of said monocarboxylic acid (D) being from 1 to 15 parts by weight per 100 parts by weight of unmodified polyester (A). US 4 172 059 discloses a curable molding composition of a mixture of a thermosetting resin which is an unsaturated polyester resin, a terminally unsaturated vinyl ester resin or mixtures thereof, an olefinically unsaturated copolymerizable monomer, a chemical thickening agent and a filler, said curable composition comprising a thermoplastic polymeric low profile additive selected from the group consisting of vinyl acetate polymers, saturated polyesters, and mixtures of the same, and at least about 0.4 percent by weight of a viscosity reducing agent based on the combined weight of thermosetting resin, plus copolymerizable monomer, plus low profile additive, said viscosity reducing agent comprising an aliphatic monocarboxylic acid having at least 6 carbon atoms in the chain. As thickening agent may be used oxides and hydroxides of the metals of Group I, II and III of the Periodic Table. Alternatively a dual thickening system may be employed wherein, for example, a metallic oxide or hydroxide and polyisocyanate in amounts of polyisocyanate sufficient to react with at least thirty percent of the hydroxyl groups but not more than one hundred and five percent of the hydroxyl groups present and an amount of metallic oxide or hydroxide sufficient to react with at least thirty percent of the carboxyl groups but not more than seventy-five percent of the carboxyl groups present. Reference is made to Belgium Patent No. 849,135 to Epel et al. for a description of such dual thickening systems. According to BE-P-849 135 as polyisocyanate may be used: 4,4'-diphenylmethane di-isocyanate (MDI), a mixture of MDI and its cyclic addition product containing carbodiimide bonds, toluene-2,4-di-isocyanate, toluene-2,6-di-isocyanate, mixtures of 2,4- and 2,6-toluene-di-isocyanate, meta- and para-phenylene di-isocyanate, 1,5-naphthalene di-isocyanate, para- and meta-xylene di-isocyanates, alkylene di-isocyanates, such as tetramethylene di-isocyanate and hexamethylene di-isocyanate, 2,4- and 2,6-di-isocyanato methylcyclohexane, dicyclohexylmethane di-isocyanate, polymeric MDI containing an average of two to three isocyanate groups per molecule, poly-isocyanurate of toluene-di-isocyanate, polymethylene polyphenyl isocyanate, polyisocyanate prepolymers of aromatic type, toluene-di-isocyanate based adducts, aromatic/aliphatic polyisocyanates and polyfunctional aliphatic isocyanates. It is suggested that when used in an SMC (sheet molding composition) application where the thermoplastic is a polyalkyl acrylate or methacrylate, a viscosity-reducing agent which is an unsaturated aliphatic monocarboxylic acid of at least 6 carbon atoms is employed. Such aliphatic monocarboxylic acids are freqently an unsaturated fatty acid having from 6 to 24 or more carbon atoms in the chain and includes 9-dodecenoic, 9-tetradecenoic, palmitoleic, oleic, linoleic, linolenic, and the like acids, and the acid may be either straight chained or branched. The object of the invention is to provide a sheet molding composition with better low shrinkage, better surface and higher impact strength characteristics when compared to art-disclosed systems. The object of the invention is accomplished with the phase-stabilized sheet molding composition comprising: a) an unsaturated polyester resin having an average molecular weight between about 800 and 5000; b) a phase-stabilizing agent selected from the group consisting of fatty acids having from 5 to 28 carbon atoms, and mixtures thereof; c) an ethylenically unsaturated monomer and a free radical polymerization catalyst; d) an inert filler; e) a fiberous reinforcing material; f) a mold release agent; g) an isocyanate terminated urethane prepolymer dual functional additive having an equivalent ratio of NCO to OH from about 1.2/1 to about 5/1, comprising a polyol and a polyisocyanate, and being prepared by reacting: (i) one equivalent weight of a polyol having an average molecular weight of about 600 to 4000 and an average functionality of approximately 2 to approximately 6; and (ii) 1.2 to 5 equivalent weights of a polyisocyanate selected from the group consisting of 80:20 or 65:35 isomer mixture of the 2,4- and 2,6-isomeric forms of toluene di-isocyanate, ethylene di-isocyanate, propylene di-isocyanate, meta- and para-phenyl di-isocyanate, 4,4'-diphenyl methane di-isocyanate (MDI) or a mixture of MDI and its trifunctional cyclic adduct products containing carbodiimide linkages, 1,5-naphthalene di-isocyanate, para- and meta-xylene di-isocyanates, alkylene di-isocyanates, or polymeric MDI containing an average of two isocyanate groups per molecule, toluene di-isocyanate, polyisocyanate prepolymers of aromatic type, toluene di-isocyanate based adducts, aromatic/aliphatic polyisocyanates and polyfunctional aliphatic isocyanates; wherein said reactants combine in a one-step addition process to yield an isocyanate terminated urethane prepolymer of controlled molecular weight to impart improved low shrink, dynamic impact strength and molding characteristics as measured by viscosity index properties in thermoset polyester resin products, and particularly sheet molding compositions (SMC) by covalently binding to the polyester resin matrix; h) a Group IIA metallic oxide or hydroxide; and i) a linear polymer of approximately 400 to 200000 molecular weight, or mixtures of such polymers; wherein (i) said oxides and hydroxides are present in an amount sufficient to react with at least 30 percent, but not more than 75 percent of the carboxyl groups present; and (ii) said prepolymer is present in an amount sufficient to react with at least 10 percent, but not more than 105 percent of the hydroxyl groups present thereby forming an SMC of improved Class A quality finish. It is preferred that the phase-stabilizing agent is a fatty acid selected from the group consisting of lauric, palmitic, stearic, oleic, linoleic, linolenic, caproic, caprylic, capric, myristic, palmitoleic, cerotic, cetoleic, and mixtures thereof. It is particularly preferred that the phase-stabilizing agent is a fatty acid selected from the group consisting of myristic, lauric, palmitic, stearic, oleic, linoleic, linolenic, and mixtures thereof. It is most preferred that the phase-stabilizing agent is a mixture of stearic, palmitic, and myristic acids. It is preferred that the phase-stabilizing agent is present at a level of 0.25 to 20 percent by weight of the unsaturated polyester resin. It is particularly preferred that the phase-stabilizing agent is present at a level of 1.0 to 8 percent by weight of the unsaturated polyester resin. It is further particularly preferred that the phase-stabilizing agent is present at a level of 2 to 7 percent by weight of the unsaturated polyester resin. It is most preferred that the phase-stabilizing agent is present at a level of 3 to 6 percent by weight of the unsaturated polyester resin. It is further preferred that the sheet molding composition is further comprising a low shrink additive consisting essentially of a thermoplastic soluble in an ethylenically unsaturated monomer, said low shrink additive system present in an amount of 10 to 55 parts by weight per 100 parts of resin. In a further preferred embodiment the reinforcing fiber is present in an amount of 10 to 80 percent by weight. In a further preferred embodiment the inert filler is present in an amount of 20 parts to 1000 parts by weight per 100 parts of the pure polyester resin. In a particularly preferred embodiment the reinforcing fiber is fiberglass. It is further preferred that the Group IIA metal is selected from the group consisting of calcium, magnesium, and mixtures thereof. In a most preferred embodiment the metallic hydroxide is magnesium hydroxide. In another most preferred embodiment the metallic oxide is magnesium oxide. In a preferred embodiment the ethylenically unsaturated monomer is comprised of the group styrene, vinyl acetate or vinyl toluene. In a further preferred embodiment the ethylenically unsaturated monomer is present in an amount to give .5 to 3.5 moles of monomer unsaturation per mole of unsaturation in the polyester resin. In a particularly preferred embodiment the ethylenically unsaturated monomer is styrene. It is further particularly preferred that the low shrink additive is dissolved in said ethylenically unsaturated monomer. It is further particularly preferred that the low shrink additive is comprised of the group consisting of polymethyl methacrylate, polyvinyl acetate, polyurethane or polyvinyl chloride. In a most preferred embodiment the low shrink additive is polyurethane. It is preferred that the isocyanate terminated urethane prepolymer is present in an amount sufficient to react with between 10 and 105 percent of hydroxyl groups present. It is also preferred that the metallic oxide is present in an amount sufficient to react with between 30 and 75 percent of the carboxyl groups present. It is preferred that the phase-stabilized sheet molding composition is comprising as a) an unsaturated polyester resin one with a ratio of hydroxyl groups to carboxyl groups of approximately 5.7 to 0.8, an acid number of at least 14. It is particularly preferred that a second low shrink additive is present. Another subject-matter of the invention is a method for producing an improved sheet molding composition which has an improved Class A surface finish comprising the steps of admixing the components defined in Claim 1. Another subject-matter of the invention is a molded article formed by the application of heat and pressure to the composition defined by Claim 1. It has been surprisingly discovered that the use of certain additives, which comprise fatty acids some of which are suggested in the art as viscosity-reducing agents, in a specific SMC application as phase-stabilizing agent in spite of the resulting increase in the viscosity of the overall system (or in some cases the negligible effect on viscosity), results in a system which retains its phase stability even under the high temperatures and conditions encountered in molding processes and, more importantly, during the maturation process. These phase-stabilizing agents prevent phase separation of the constituents of the final system. As a result of the phase uniformity which results from the presence of the phase stabilizing agents, the different resins do not undergo gross separation during the maturation period at 90 - 104°F (32,2° - 40°C); the final cured product exhibits an imporoved Class A quality surface finish. The product also demonstrates a significant overall improvement in aesthetic, surface and (retains) good impact properties when compared with identical systems without these agents. The fatty acids useful in the present invention are the C 5 to C 28 saturated and unsaturated, branched or straight chain, fatty acids. Preferred materials include lauric, palmitic, stearic, oleic, linoleic, linolenic, caproic, caprylic, capric, myristic, palmitoleic acid, cerotic, cetoleic, and mixtures thereof. Highly preferred materials include lauric, palmitic, stearic, oleic, linoleic, linolenic acids, and mixtures thereof. In a highly preferred embodiment, a mixture of stearic, palmitic, and myristic acids is employed. These materials are items of commerce and are generally obtained by extraction from beef tallow, coconut oil, corn oil, cottonseed oil, olive oil, palm oil, palm kernel oil, and the like. When employed in the sheet molding compounds described herein, the phase-stabilizing agent or additive is blended in any conventional manner into the portion which contains the polyester resin. If this material is liquid, it may be premixed with an organic monomeric solvent such as an ethylenically unsaturated monomer selected from the group consisting of styrene, vinyl toluene, or vinyl acetate. It is ordinarily employed at a level of about 0.25 to about 20 percent by weight of the unsaturated polyester resin. More preferably, the phase-stabilizing agent or additive is employed at a level of 1.0 to 8, and still more preferably 2 to 7 percent by weight of unsaturated polyester resin. In a highly preferred embodiment, the phase-stabilizing agent or additive is employed at a level of 3 to 6 percent by weight of unsaturated polyester resin. In general, the SMCs of the present invention are prepared by mixing, blending, or otherwise contacting three submixtures or parts together. The first submixture or part generally contains the polyester resin, the low profile additive, the free radical catalyst, a polyol, the mold release agent, as well as other additives discussed in US 4 535 110. It is to this first submixture that the phase-stabilizing additives or agents are added. The second submixture or part generally contains the Group IIA metall oxide (or hydroxide), the pigment, and the carrier resin, such as an acrylic (which does not react with the Group IIA metal oxide or hydroxide). The third submixture or part is the dual functional additive or prepolymer described in US 4 535 110 entitled "Dual Functional Additive". The useful isocyanate terminated urethane prepolymers are based upon a polyether or polyester polyol, or a mixture thereof, and preferably a polyether polyol, and a di-isocyanate or polyisocyanate. The polyol used in the prepolymer is preferably a diol or triol having a molecular weight of approximately 600 to approximately 4000, an preferably about 2000, as exemplified by BASF's Pluracol P-2010, and a functionality of approximately 2 to approximately 6, preferably 2 to 3 and more preferably 2. The dual functional additive is formed in a one-step addition reaction between one equivalent weight of the polyol as described above and two equivalent weights of the polyisocyanate in the presence of approximately 0 - 1% of a conventional urethane catalyst such as stannous octoate, dibutyltin dilaurate, and the like, and the amount of such catalyst is determined according to the total weight of the urethane. The isocyanate terminated urethane additive thus formed should have an isocyanate to hydroxyl ratio NCO/OH of approximately 1.2/1 to approximately 5/1 and preferably NCO/OH between 1.8 to 3, and most preferably about 2. The isocyanate terminated urethane prepolymer is prepared by first reacting an organic polyisocyanate, and preferably a di-isocyanate with a polyol, using standard procedures to yield an isocyanate terminated prepolymer of controlled molecular weight and having an NCO/OH ratio of approximately 1.2/1 to approximately 5/1, and preferably NCO/OH beween 1.8 to 3, and most preferably about 2. The polyisocyanates used in the formation of the present invention include toluene di-isocyanate, such as the 80:20 or 65:35 isomer mixture of the 2,4- and 2,6 isomeric forms, ethylene di-isocyanate, propylene di-isocyanate, meta- and para-phenyl di-isocyanates, 4,4'-diphenyl methane di-isocyanate (MDI) or a mixture of MDI and its trifunctional cyclic adduct products containing carbodiimide linkages, 1,5 naphthalene di-isocyanate, para- and meta-xylene di-isocyanates, alkylene di-isocyanates such as tetra-methylene di-isocyanate and hexamethylene di-isocyanate, 2,4- and 2,6 di-isocyanate methylcyclohexane, dicyclohexylmethane di-isocyanate, and polymeric MDI containing an average of from two isocyanate groups per molecule. Other polyisocyanates which may be employed include polyisocyanate of toluene di-isocyanate, polyisocyanate prepolymers of aromatic type, toluene di-isocyanate based adducts, aromatic/aliphatic polyisocyanates and polyfunctional aliphatic isocyanate. The exact polyisocyanate employed is not critical, but di-isocyanates are preferred, and of these, 4,4' diphenyl methane di-isocyanate (MDI) or a mixture of MDI and its trifunctional cyclic adduct products containing carbodiimide linkages are preferred. It should be noted that differing results in respect to low shrinkage additives will be obtained by the use of different polyisocyanates and it is emphasized that di-isocyanates are preferred. The polyol reactant used in the dual functional additive is selected from either a polyester polyol or polyether polyol, preferably polyether polyols and mixtures of two or more such polyether polyol compounds. The polyol reactant, or mixture thereof, used has an average equivalent weight of between 600 to 4000 and a functionality of between 2 and 6, and preferably 2 to 3 and more preferably 2. Among suitable polyether polyols, it is contemplated that polyoxyalkylene polyols and mixtures thereof may be used. These can be prepared according to well known methods, such as by condensing an alkylene oxide, or mixture of alkylene oxides using random or stepwise addition, with a polyhydric initiator or a mixture of polyhydric initiators. The alkylene oxides contemplated for use in the prepolymer include ethylene oxides, propylene oxide, butylene oxides, amylene oxide, aralkylene oxides, such as trichlorobutylene oxide and such, and the most preferred alkylene oxide is propylene oxide or a mixture thereof with ethylene oxide using random or stepwise oxyalkylation. Polyhydric initiators used in preparing the prepolymer polyether polyol reactant include (a) aliphatic diols such as ethylene glycol, 1,3-propylene glycol, 1,2-propylene glycol, butylene glycols, butane diols, pentane diols and the like, (b) the aliphatic triols such as glycerol, trimethylolpropane, triethylolpropane, trimethylolhexane and the like, (c) the polyamines such as tetraethylene diamine and (d) the alkanolamines such as diethanolamine, triethanolamine, and the like. Preferably, the polyhydric initiators of choice for use in preparing the polyether polyol reactant is an aliphatic diol or triol such as ethylene glycol, propylene glycol, glycerol, trimethylolpropane, and the like. If a polyester polyol is selected for use as the polyol reactant of the dual functional additive, such a polyol is usually formed by reacting a polycarboxylic acid with a polyhydric initiator, such as a diol or triol. The polycarboxylic acids include oxalic, malonic, succinic, glutaric, adipic, pimelic, suberic, azelaic acid, and the like. Illustrative polyhydric alcohols include various diols and triols and higher functionality alcohols such as ethylene glycol, 1,3-propylene glycol, 1,2-propylene glycol, butylene glycols, butane diols, pentane diols, glycerol, trimethylolpropane, trimethylolhexane, hexane 1,2,6-triol and the like. When a polyether polyol reactant is to be created by the alkylene oxide polyhydric initiator reaction, usually a catalyst, such as the art-disclosed catalyst KOH, is added to speed up the reaction. The resulting polyether polyol should have an average molecular weight of approximately 600 to 4000. After reaction, the catalyst is preferably removed, leaving a polyether polyol suitable for reaction with the polyisocyanate reactants as discussed above to form the isocyanate terminated urethane prepolymer. In forming the isocyanate terminated urethane prepolymer, one equivalent weight of the polyol reactant as defined above is reacted with 1.2 to 5, and preferably two equivalent weights of a polyisocyanate as defined previously in the presence of any conventional urethane catalysts such as stannous octoate, dibutyltin dilaurate and the like, whereby the isocyanate groups are placed on the terminal ends of the prepolymer, thereby yielding the isocyanate terminated urethane prepolymer. It should be noted that the prepolymer may be made in the presence of a monomer after it has been made, without adversely affecting its function as a low profile additive and as a viscosity index modifier to impart the desired advantages. The isocyanate terminated urethane prepolymer additive may optionally be used with any of the conventional low shrink additives of the prior art, such as polyvinyl acetate and polymethyl methacrylate or a mixture thereof, or any other linear polymer having a molecular weight within the range of approximately 400 to about 200000, and preferably about 10000 to approximately 90000. Moreover, regardless of whether or not the prepolymer is used with a conventional low shrink additive, the ratio of the total amount of prepolymer to polyester resin should optimally be within the range of approximately 10 parts by weight of prepolymer to 90 parts by weight of polyester resin, to approximately 60 parts by weight of prepolymer to 40 parts by weight of polyester resin. When used in an SMC as defined above, the isocyanate terminated urethane prepolymer may be dissolved in styrene and then used like any other low shrink additive, and is employed in an amount sufficient to react with at least 10 percent but not more than 105 percent of the hydroxyl groups present in the reaction. The metallic oxide or hydroxide used in the dual thickening system is essentially a metal oxide or hydroxide from the Group IIA on the periodic table and comprises calcium or magnesium. Although calcium may be used in its various oxides and hydroxides, the magnesium is preferred inasmuch as superior results are achieved by the use of magnesium. Although the prepolymer may be used alone, it may also be used with a monomer from the group styrene, vinyl toluene and vinyl acetate and any other ethylenically unsaturated monomer and when so used, is ordinarily present in an amount to give .5 to 3.5 moles of monomer unsaturation per mole of unsaturation in the unsatured polyester resin. Styrene and vinyl toluene are preferred monomers, although others may be used. A free radical polymerization catalyst is also employed in the present invention. The catalyst is preferably present in an amount of 1.0 part per 100 parts of total resin and monomer, the parts being measured by weight. The free radical polymerization catalyst is added to the uncured composition so that upon heating to the activation temperature, the additive type cross-linking polymerization reaction will commence between the polymerizable monomer and the unsaturated polyester resin to form the matrix previously described. The catalyst is usually employed in an amount in the range of about .1 to 3.0 parts per 100 parts of the total monomer and resin and is usually a peroxide. The mold release agent useful in the present invention may be any of those used in the prior art, such as zinc stearate, calcium stearate, magnesium stearate, organic phosphate esters and other organic liquid internal mold release agents. They may be employed at their art-disclosed level. The reinforcing fibers are usually present in an amount of about 10 to 80 weight percent for sheet molding compositions and is preferably fiberglass. The preferred range for this reinforcing fiber is approximately 15 to 80 weight percent for use in thermoset polyester resin applications, such as an SMC. Any number of nonreinforcing fillers may be added to the composition to reduce overall material costs without sacrificing a significant degree of the desirable physical properties in the final product, or may be added to impart specific properties to the uncured compound. Any number of fillers may be used in an amount ranging from about 20 parts to 1000 parts by weight per 100 parts of the pure polyester resin in thermoset polyester resin applications, such as an SMC. In addition, the invention may, as previously stated, include a low shrink additive polymer or mixture, which is ordinarily dissolved in the same type of ethylenically unsaturated monomer in which the polyester resin is dissolved. Such low shrink additives include without limitation, those disclosed in US 4 535 110. In employing the dual functional additive described herein with thermoset polyester resin products as defined in Epel et al, and especially sheet molding compositions (SMC), the unsaturated polyester resin as described in Epel et al is dissolved in a monomer such as styrene, vinyl acetate or vinyl toluene. The dual thickening system of Epel et al is modified by the replacement of the organic polyisocyanate defined therein with the dual functional additive described above. A heat-activated free radical catalyst, such as an organoperoxide, hydroperoxide or azo compound, preferably a peroxide, is added to the polyester resin material. Inert fillers are added to reduce the overall cost of the SMC while not appreciably sacrificing the essential properties of the SMC. The modified dual thickening system is then added to the polyester resin in an amount such that the total amount of prepolymer to polyester resin is within the range of approximately 10 parts by weight of prepolymer to 90 parts by weight of polyester resin material to approximately 60 parts by weight of prepolymer to 40 parts by weight of polyester resin. Reinforcing fibers, such as fiberglass, are added to the SMC in a conventional manner. Once the fibers have been thoroughly admixed with the composition, the SMC is B-staged to a moldable consistency by aging at 90 to 104°F (32,2 to 40°C) for 3 to 5 days. After B-staging has occurred, the SMC may be stored for long periods of time without jeopardizing either its handleability or processability. After the material has been B-staged, it can be molded at 280 to 315°F (138 to 157°C) in 1 to 2 minutes, depending on the specific configuration, i.e. thickness, of the part being molded. EXAMPLE A B C D Polyester Resin 70 70 70 70 Polymethyl Methacrylate - - 22,5 22,5 t-Butyl Perbenzoate 1 1 1 1 Zinc Stearate 2 2 2 2 Fatty Acid phase stabilizing agent (50:45 palmitic:stearic) 2 - 2 - Calcium Carbonate 115 115 115 115 Magnesium Hydroxide 2,5 2,5 2,8 2,8 Prepolymer in solvent (75 percent solids) 30 30 7,5 7,5 Phase Stability acceptable unacceptable acceptable unacceptable

Claims: A phase-stabilized sheet molding composition comprising: a) an unsaturated polyester resin having an average molecular weight of approximately 800 to 5000; b) a phase-stabilizing agent selected from the group consisting of fatty acids having from 5 to 28 carbon atoms, and mixtures thereof; c) an ethylenically unsaturated monomer and a free radical polymerization catalyst; d) an inert filler; e) a fiberous reinforcing material; f) a mold release agent; g) an isocyanate terminated urethane prepolymer dual functional additive having an equivalent ratio of NCO to OH from about 1.2/1 to about 5/1, comprising a polyol and a polyisocyanate, and being prepared by reacting: (i) one equivalent weight of a polyol having an average molecular weight of about 600 to 4000 and an average functionality of approximately 2 to approximately 6; and (ii) 1.2 to 5 equivalent weights of a polyisocyanate selected from the group consisting of 80:20 or 65:35 isomer mixture of the 2,4- and 2,6-isomeric forms of toluene di-isocyanate, ethylene di-isocyanate, propylene di-isocyanate, meta- and para-phenyl di-isocyanate, 4,4'-diphenyl methane di-isocyanate (MDI) or a mixture of MDI and its trifunctional cyclic adduct products containing carbodiimide linkages, 1,5-naphthalene di-isocyanate, para- and meta-xylene di-isocyanates, alkylene di-isocyanates, or polymeric MDI containing an average of two isocyanate groups per molecule, toluene di-isocyanate, polyisocyanate prepolymers of aromatic type, toluene di-isocyanate based adducts, aromatic/aliphatic polyisocyanates and polyfunctional aliphatic isocyanates; wherein said reactants combine in a one-step addition process to yield an isocyanate terminated urethane prepolymer of controlled molecular weight to impart improved low shrink, dynamic impact strength and molding characteristics as measured by viscosity index properties in thermoset polyester resin products, and particularly sheet molding compositions (SMC) by covalently binding to the polyester resin matrix; h) a Group IIA metallic oxide or hydroxide; and i) a linear polymer of approximately 400 to 200000 molecular weight or mixtures of such polymers; wherein (i) said oxides and hydroxides are present in an amount sufficient to react with at least 30 percent, but not more than 75 percent of the carboxyl groups present; and (ii) said prepolymer is present in an amount sufficient to react with at least 10 percent, but not more than 105 percent of the hydroxyl groups present thereby forming an SMC of improved Class A quality finish. A composition according to Claim 1 wherein said phase-stabilizing agent is a fatty acid selected from the group consisting of lauric, palmitic, stearic, oleic, linoleic, linolenic, caproic, caprylic, capric, myristic, palmitoleic, cerotic, cetoleic, and mixtures thereof. A composition according to Claim 2 wherein said phase-stabilizing agent is a fatty acid selected from the group consisting of myristic, lauric, palmitic, stearic, oleic, linoleic, linolenic, and mixtures thereof. A composition according to Claim 3 wherein said phase-stabilizing agent is a mixture of stearic, palmitic, and myristic acids. A composition according to one of the Claims 1 to 4 wherein the phase-stabilizing agent is present at a level of 0.25 to 20 percent by weight of the unsaturated polyester resin. A composition according to Claim 5 wherein the phase-stabilizing agent is present at a level of 1.0 to 8 percent by weight of the unsaturated polyester resin. A composition according to Claim 6 wherein the phase-stabilizing agent is present at a level of 2 to 7 percent by weight of the unsaturated polyester resin. A composition according to Claim 7 wherein the phase-stabilizing agent is present at a level of 3 to 6 percent by weight of the unsaturated polyester resin. The sheet molding composition according to one of the Claims 1 to 8 and further comprising: a low shrink additive consisting essentially of a thermoplastic soluble in an ethylenically unsaturated monomer, said low shrink additive system present in an amount of 10 to 55 parts by weight per 100 parts of resin. The sheet molding composition of one of the Claims 1 to 9 wherein said reinforcing fiber is present in an amount of 10 to 80 percent by weight. The sheet molding composition of one of the Claims 1 to 10 wherein said inert filler is present in an amount of 20 parts to 1000 parts by weight per 100 parts of the pure polyester resin. The sheet molding composition of Claim 10 wherein said reinforcing fiber is fiberglass. The sheet molding composition of one of the Claims 1 to 12 wherein said Group IIA metal is selected from the group consisting of calcium, magnesium, and mixtures thereof. The sheet molding composition of Claim 13 wherein said metallic hydroxide is magnesium hydroxide. The sheet molding composition of Claim 13 wherein said metallic oxide is magnesium oxide. The sheet molding composition of one of the Claims 1 to 15 wherein the ethylenically unsaturated monomer is comprised of the group styrene, vinyl acetate or vinyl toluene. The sheet molding composition of one of the Claims 1 to 16 wherein the ethylenically unsaturated monomer is present in an amount to give .5 to 3.5 moles of monomer unsaturation per mole of unsaturation in the polyester resin. The sheet molding composition of Claim 16 wherein said ethylenically unsaturated monomer is styrene. The sheet molding composition of Claim 9 wherein said low shrink additive is dissolved in said ethylenically unsaturated monomer. The sheet molding composition of Claim 9 wherein said low shrink additive is comprised of the group consisting of polymethyl methacrylate, polyvinyl acetate, polyurethane or polyvinyl chloride. The sheet molding composition of Claim 19 wherein said low shrink additive is polyurethane. The sheet molding composition of one of the Claims 1 to 21 wherein said isocyanate terminated urethane prepolymer is present in an amount sufficient to react with between 10 and 105 percent of hydroxyl groups present. The sheet molding composition of one of the Claims 1 to 22 wherein said metallic oxide is present in an amount sufficient to react with between 30 and 75 percent of the carboxyl groups present. A phase-stabilized sheet molding composition according to one of the preceding Claims comprising as a) an unsaturated polyester resin one with a ratio of hydroxyl groups to carboxyl groups of approximately 5.7 to 0.8, an acid number of at least 14. A method for producing an improved sheet molding composition which has an improved Class A surface finish comprising the steps of admixing the components defined in Claim 1. A method according to Claim 25 wherein the phase-stabilizing agent is a mixture of stearic, palmitic, and myristic acids. A molded article formed by the application of heat and pressure to the composition defined by Claim 1. A molded article formed by the application of heat and pressure to the composition defined by Claim 4. A molded article formed by the application of heat and pressure to the composition defined by Claim 24. A composition according to Claim 24 wherein a second low shrink additive is present.

Inventors: GUHA PROBIR KUMAR, ISELER KENNETH ALFRED, YEN ROBERT CHENG-HSIAO, GUHA, PROBIR KUMAR, ISELER, KENNETH ALFRED, YEN, ROBERT CHENG-HSIAO
Applicants: BUDD CO, THE BUDD COMPANY
Application year: 1986
Main classification: C08L67
IPC codes: C08K5, C08G18, C08L27, C08L33, C08L67, B29B11, C08L1, C08J5