MXPA96003555A - Process for the preparation of polymers of absmultimoda - Google Patents

Abstract

The present invention relates to rubber modified monovinylidene aromatic copolymers having an improved combination of gloss, hardness, and melt flow characteristics, by a process wherein a rubber latex having a specified particle size is partially agglomerated , it is copolymerized by emulsion grafting to a specified ratio of the graft copolymer to the rubber (G: R), and a molecular weight of the specified graft copolymer, and further agglomerated during the subsequent operations of dehydration and / or melt mixing.

Description

PROCESS FOR THE PREPARATION OF POLYMERS OF ABS MU TIMODALEB Background of the Invention This invention pertains to the methodology for preparing monovinylidene-modified aromatic copolymers with rubber of the kind that is commonly referred to in the art as ABS resins. In particular, it belongs to a subcategory of these resins, where the grafted rubber particles dispersed therein exhibit a particle size distribution that is of a multimodal character (i.e. having two or more distinct peaks in the distribution of particles). particle sizes), and wherein at least two of the various peaks of particle sizes can be attributed to (i.e., component of) polymerized rubber emulsion graft particles. Styrenic polymers modified with rubber, * -. such as acrylonitrile / butadiene / styrene resins (ABS), and high impact polystyrene resins (HIPS), are well known in the art and in the industry, and find use in a wide variety of practical applications, including use in computers and commercial equipment housings, component parts of different home appliances, ornaments and other parts in the automotive industry. It is also known in the art, at least as a general proposition, that a range of combinations of different physical and steric properties can be imparted to these rubber-modified styrenic polymer compositions, by adjusting or controlling the size of the polymer. the particles and the particle size distribution, of the grafted rubber or elastomeric particles that are dispersed within, and which impart hardness and impact resistance to such polymeric compositions. Accordingly, for example, in U.S. Patent No. 3,509,235 to Aubrey, compositions are described which have bi-orderal particle size distributions, wherein a first group of relatively large size (from 0.8 to 2 microns in diameter) number average) of grafted rubber particles, constitute a minor portion (from 3 to 30 weight percent) of the total grafted particles, and are prepared by suspension graft polymerization techniques, and wherein the highest proportion by weight of the grafted rubber particles are prepared by emulsion graft polymerization, and have a number average particle size of 0.01 to 0.25 microns. BS resin compositions having size distributions of bimodal grafted rubber particles have also been described, wherein the relatively small grafted rubber particles and the relatively larger sized particles contained therein are both prepared by polymerization techniques of emulsion graft. In these cases, the grafted rubber particles of relatively large size (for example, having an average diameter of 0.25 microns or more) can be obtained by growing separately from the underlying rubber latex to the desired large particle size, using carefully controlled emulsion polymerization conditions (and, typically, during very extended reaction times), and then the large rubber latex is mixed with the small rubber latex, either before or subsequent to the polymerization of desired emulsion graft thereof. See, for example, U.S. Patent No. 4,009,227 to Ott and collaborators, and U.S. Patent No. 5,008,331 to Kawashima et al. Alternatively, a rubber latex of relatively smaller size (eg, having an average diameter of 0.05 to 0.15 microns) can be agglomerated to form the particles of large size (or can be partially agglomerated to simultaneously provide both large and small particles) before the emulsion graft polymerization process. (See, for example, U.S. Patent Number 4,419,496 of Henton et al.).

Typically, when the polymerized emulsion graft particles of relatively large size are separately "grown" to the desired size in their own step or independent emulsion polymerization operation, they are generally characterized by having a peak size distribution of simple or monomodal particles very narrow by themselves, which falls near the average particle size in volume of the large particle size group taken as a whole. In contrast, when the large-sized particles are generated instead by agglomeration or partial agglomeration of the smaller rubber latex particles, they typically exhibit a very broad particle size distribution or "polydispersity", which extends further or less uniformly over the entire size range of the individual agglomerated particles. ABS compositions called trimodal are also known in the art. Exemplary compositions of this type are described in U.S. Patent No. 4,430,478 to Schmitt et al., And in U.S. Patent No. 4,713,420 to Henton, wherein trimodal ABS compositions containing two different groups of rubber particles polymerized with emulsion graft (one group having a relatively small size, for example, which averages 0.25 microns or less, and the other having an average size greater than 0.25 microns) in combination with grafted rubber particles of relatively large size (for example, greater than 0.5 microns of average volume) 5 obtained by means of a graft polymerization process in bulk, in solution, or in suspension. Although improvements in the overall balance of physical properties can be obtained (for example, resistance to ^ impact, tensile strength, and melt flow characteristics) and aesthetics (eg, gloss and surface appearance) with the aforementioned multimodal ABS compositions (ie, in relation to those of otherwise similar monomodal compositions). ), the general trend of other improvements in a property or characteristic, such as impact resistance that comes only at the expense of some other property, such as gloss and / or melt flow in the context of these multimodal ABS resin compositions. Therefore, it would be desirable to provide a The element by which an improvement in one or more properties within these compositions could be obtained (e.g., melt flowability and / or impact strength and / or gloss) without significant sacrifices coupled in the remaining properties of interest.

Summary of the Invention A means has now been found for preparing ABS resin compositions of multimodal grafted rubber particle sizes, which exhibit better impact strength and / or melt flow, while undergoing little or no sacrifice in their gloss characteristics. desirable Accordingly, the present invention, in one of its main aspects, is a process for the preparation of a rubber modified monovinylidene aromatic copolymer composition, this process comprising the steps of: A. preparing or obtaining an aqueous elastomeric polymer emulsion initial containing, on a total weight basis of the polymer emulsion, from 25 to 50 weight percent of colloidally dispersed small particles of an elastomeric conjugated diene polymer having a volume average particle size of 0.15 to 0.22 microns; B. Partially agglomerate the initial polymer emulsion to cause at least 5 but less than 50 weight percent of the dispersed small particles to agglomerate, cohere, or otherwise physically associate with each other, to form colloidal polymer particles enlarged dispersions having an average particle size by volume, determined by the exclusion of all particles having diameters less than 0.25 microns, of approximately 0.4 microns or more; C. polymerizing with graft, under emulsion polymerization conditions, the partially agglomerated polyeric emulsion, with a monomer mixture comprising, on a peeled basis of the monomer mixture, 40 to 90 weight percent of an aromatic monomer of monovinylidene, 10 to 40 weight percent of an ethylenically unsaturated nitrile monomer, and 0 to 30 weight percent of one or more monomers of acrylate ester, methacrylate ester, or N-substituted maleimide, to form a graft copolymer latex (also referred to herein as a "grafted rubber concentrate" or "GRC"), wherein: (a) the elastomeric polymer component from the initial polymer emulsion constitutes 40 to 70 percent on pono of the polymeric solids contained therein, (b) the weight ratio of the amount of monovinylidene aromatic copolymer (G) chemically grafted to the elastomeric polymer particles dispersed, to the amount of the same dispersed elastomeric polymer (R), is from 0.2 to 0.4, and (c) the weight average molecular weight of the grafted and ungrafted monovinylidene aromatic copolymer formed in the graft polymerization process is in the scale of 50,000 n 130,000; D. repairing the resulting emulsion polymerized graft copolymer, from its aqueous medium; and E. Melt-blending the graft copolymer emulsion polymerization copolymer with an ethylenically unsaturated / aromatic monovinylidene nitrile copolymer, or with an ethylenically unsaturated / aromatic monovinylidene-modified nitrile graft copolymer with bulk polymerized rubber, in solution, or in suspension; further characterizing this process (and the rubber-modified copolymer product prepared therefrom) because the total population of elastomeric polymer particles copolymerized in emulsion graft having < .J a diameter of 0.25 microns or greater, is increased by at least 10 weight percent based on total particles of elastomeric polymer copolymerized with emulsion graft between the termination of step (C) of graft polymerization, and the termination of step (E) of the operation of fusion mixture. The fact that a significant portion of the relatively small grafted rubber particles (ie, those having a particle size of less than 0.25 microns) melt agglomerates (i.e., coalesce or otherwise physically associate with one another). with others and / or with the relatively larger particles) after the graft polymerization operation of step (C), it is considered to be particularly surprising, in light of the teachings contained in column 1, lines 49 to 56 of the above-mentioned US Pat. No. 4,009,227 to Ott et al., Which is for the purpose of not occurring this phenomenon of agglomeration in proportions by weight of the rubber graft (G: R) greater than 0.2. As used in the present, the terms "elastomer" and "rubber", and the terms "elastomeric" and "rubberized" are used interchangeably to connote a polymeric material having a second glass transition temperature (Tg) of 0 ° C or less (from ^ preference -20 ° C or lower). The terms "emulsion" and "latex", as used herein, are also used interchangeably to connote a composition wherein the separated polymer particles are colloidally dispersed within a continuous aqueous medium. The phrases "average in volume" and "averaged volume" as used herein, connote the average volume diameter of the particular group of elastomeric polymer or particles of grafted elastomeric polymer that are being referenced or characterized. East The parameter is also referred to in the art as the diameter "D50" and specifically represents the point in the distribution of particle sizes for the group in question where 50 percent by volume of the group falls at or above that value of size, and where the other 50 percent by volume falls at or below that value.

In cases where the grafted or non-grafted elastomeric polymer of interest is in the form of a colloidally dispersed aqueous polymer emulsion, the average particle size and the particle size distribution can be conveniently determined according to the hydrodynamic chromatography techniques. (HOC) known. On the other hand, when the polymer composition whose average particle size and size distribution of the dispersed elastomeric polymer are to be determined, is in the form of a solid material at room temperature, thermoplastic, melt blended, this can be conveniently carried out by way of well-known techniques of Electron Transmission Micrography (TEM). The weight average molecular weights (1 ^,) referred to herein with respect to both the grafted monovinylidene and non-grafted aromatic copolymer constituents, should be understood as determined by gel permeation chromatography (GPC) techniques calibrated with standards. of polyethylene.

Detailed Description of the Invention As noted above, the initial step in the process of the present invention is to obtain (e.g., acquire) or prepare an initial aqueous emulsion of an elastomeric (i.e., rubberized) polymer wherein the particles of The colloidally polymerized polymer dispersed therein is composed of an elastomeric conjugated diene polymer, and has a volume average particle size of 0.15 to 0.22 microns. Typically, this initial aqueous polymer emulsion will contain, on a total weight basis of the emulsion, from 25 to 50 (preferably from 30 to 50, and most preferably from 30 to 45) percent by weight of the colloidal polymerized polymer particles. scattered. ? . This initial emulsion will also typically be characterized by a relatively narrow monomodal particle size distribution with the individual rubber polymer particles contained therein in a size from a minimum of 0.1 microns to a maximum of 0.25 microns. The rubberized polymers which may suitably constitute the particles dispersed within the initial aqueous emulsion include any homopolymer or copolymer of elastomeric conjugated diene (specifically 1,3-conjugated diene) having a glass transition temperature second order of 0 ° C or less (preferably -20 ° C or less). Preferred among these polymers rubberized for use herein, are homopolymers and copolymers of 1,3-conjugated diene (especially 1,3-butadiene and isoprene), from 70 to 99 (especially from 90 to 97) percent by weight of these 1,3-conjugated diene monomers, with 1 to 30 (especially 3 to 10) percent by weight of one or more monoethylenically unsaturated monomers (especially monovinylidene aromatic monomers such as styrene, ethylenically unsaturated nitrile monomers such as acrylonitrile, esters of unsaturated carboxylic acids such as methyl methacrylate, ethyl acrylate, and butyl acrylate). The preferred initial aqueous elastomeric polymer emulsions for use herein are those having a relatively narrow monomodal particle size distribution and having an average particle size in rubber on the scale of 0.15 to 0.2 (especially from 0.15 to 0.18 or 0.19) microns. Aqueous polymer emulsions of relatively small size of the aforementioned kind, and processes for their preparation, are well known in the art. See in this regard, for example, U.S. Patent Number 3,509,237; 3,928,494; 4,243,769 and 4,250,271. Typically, the aqueous polymeric emulsion emulsions employed herein are of the kind in which the dispersed rubberized polymer particles thereof exhibit a swelling index of 9 to 25 (preferably 10 to 20 and especially 12 to 16). determined from the viscosity of a dilute dispersion of swollen latex particles in tetrahydrofuran.

The second step in the process of the present invention involves partially agglomerating the relatively small sized aqueous elastomeric polymer emulsion described above, to cause 5 to 50 weight percent of the small sized dispersed polymer particles to agglomerate, coalesce , or otherwise become physically associated with each other to form enlarged elastomeric particles, which are still colloidally dispersed within the surrounding continuous aqueous medium, and which taken as a group of enlarged particles (i.e., excluding all elastomeric particles colloidally individual dispersed ones having diameters less than 0.25 microns), have a particle size in averaged volume of at least 0.4 microns (especially 0.4 to 0.8 or 1 micron). Typically, the resulting group or population of enlarged particles will be characterized as having a relatively wide size distribution (eg, polydispersed), the individual particles contained therein being from a minimum size of 0.25 (preferably 0.3). microns to a maximum of 2.5 (preferably 2) microns, determined by known hydrodynamic chromatography techniques (HDC). In certain cases, it is convenient and preferred to conduct the second step of the indicated process, in such a way that from 10 or 15 to 45 or 50 (especially from 20 to 40) percent by weight of the dispersed elastomeric polymer particles of Small size initials, become the elastomeric polymer constituent of the indicated enlarged particle size. 5 Suitable techniques to be employed in performing the step of the desired partial agglomeration process are well known in the art, and as a general proposition, include those illustrated in the Patents of the United States of America Numbers? 3,551,370; 3,666,704; 3,956,218 and 3,825,621. A particularly preferred partial agglomeration technique to be employed herein is one which is described and claimed in U.S. Patent No. 4,419,496 to Henton et al., And which involves the use of an agent Binder (AgAg) which itself is an aqueous polymer emulsion containing colloidally dispersed "core / shell" polymer particles, wherein the "core" portion thereof is of an elastomeric character, and the shell portion thereof they are comprises a copolymer of a higher proportion (eg, 80 to 99.5 weight percent) of a lower alkyl ester of an ethylenically unsaturated carboxylic acid (eg, an acrylate or alkyl methacrylate ester of 1 to 4 atoms) carbon), and a smaller proportion (for example, from 0.5 to 20 weight percent) of an ethylenically unsaturated mono- or di-functional carboxylic acid (e.g., acrylic acid, methacrylic acid, maleic acid, and fumaric acid). The graft polymerization of the resulting partially agglomerated aqueous elastomeric polymer emulsion is conducted in accordance with well-known emulsion graft polymerization techniques. Typically, this involves adding the desired monomer mixture with which the rubberized emulsion is to be grafted into this emulsion (eg, batchwise or on a gradual continuous addition basis) together with the desired initiators and chain transfer agents. which are conventionally employed within these emulsion graft polymerization processes. As mentioned above, the indicated monomeric graft mixture employed herein, typically comprises 40 to 80 or 90 percent by weight of a monovinylidene aromatic monomer in combination with 10 or 20 to 40 percent by weight of an ethylenically unsaturated nitrile monomer, and 0 to 30 weight percent of one or more monomers of acrylate ester, methacrylate ester, or N-substituted maleimide. Preferably, the indicated monomer mixture (and the copolymer prepared therefrom) is composed of 50 to 80 or 85 (especially 55 or 60 to 75 or 80) percent by weight of a monovinylidene aromatic monomer; 15 or 20 to 40 (especially 15 or 20 to 30 or 35) percent by weight of an ethylenically unsaturated nitrile monomer; and from 0 to 20 or to 25 (especially from 0 to 10 or 15) percent by weight of an acrylate or methacrylate ester monomer, or of an N-substituted maleimide monomer. Examples of the monovinylidene aromatic monomers that are suitable for use herein are styrene; alpha-alkyl monovinylidene monoaromatic compounds (for example, alpha-methylstyrene, alpha-ethylstyrene, alpha-methylvinyltoluene, and alpha-methyldialkylstyrene); ring-substituted alkyl styrenes (eg, ortho-, meta-, and para-vinyltoluene; o-ethylstyrene; p-ethylstyrene 2,4-dimethylstyrene; and p-butyl tertiary styrene); ring-substituted haloestyrenes (eg, o-chlorostyrene, p-chlorostyrene, o-bromostyrene, and 2,4-dichlorostyrene); styrenes halosubstituted by ring alkyl ring (for example, 2-chloro-4-methylstyrene and 2,6-dichloromethylstyrene); vinylnaphthalene; vinylanthracene Alkyl substituents generally have from 1 to 4 carbon atoms, and may include isopropyl and isobutyl groups. If desired, mixtures of these monovinylidene aromatic monomers can be used.

Examples of the ethylenically unsaturated nitrile monomers for use herein include acrylonitrile, methacrylonitrile, ethacrylonitrile, fumaronitrile, and maleonitrile, with acrylonitrile being especially preferred. Acrylate and methacrylate esters suitable for use as monomers optionally present herein include methyl methacrylate, methyl acrylate, ethyl acrylate, normal butyl acrylate, and 2-ethylhexyl acrylate. The N-substituted maleimide monomers suitable for use herein include N-alkyl alkyl maleimides such as N-methyl maleimide, N-ethyl maleimide, N-propyl maleimide, maleimide. N-isopropyl, and tertiary N-butylmaleimide; N-cycloalkyl maleimides such as N-cyclohexyl maleimide; N-aryl maleimides such as N-phenyl maleimide and N-naphthyl maleimide, with N-phenyl maleimide particularly preferred. In conducting the indicated emulsion graft polymerization step, the amount of the aforementioned monomer mixture employed therein is typically from 40 to 150 (preferably from 40 to 125, more preferably from 40 to 110, and especially from 40 or 50 to 100) parts by weight per 100 parts by weight of the dispersed elastomeric polymer solids contained within the partially agglomerated polymer emulsion to be polymerized with graft therein. Accordingly, the elastomeric polymer component initially present of the resultant graft polymerized elastomeric polymer latex typically constitutes 40 to 70 (preferably 45 to 70, and more preferably 50 to 65 or 70) by weight percent of the total polymer solids contained therein. As is well known in the art, typically complete or perfect grafting efficiency is not achieved in conventional emulsion graft polymerization processes. As a result, it is inherently formed when at least some portion of ethylenically unsaturated / aromatic monovinylidene nitrile copolymer does not grafted during the step of the indicated graft polymerization process, the actual quantitative amount thereof being dependent on a variety of factors such as, for example, the elastomeric polymer solids content of the initial latex, the weight ratio of the monomeric graft mixture to the elastomeric polymer solids, the type of initiator and the amount employed within the graft polymerization process, and the actual polymerization conditions employed. On the other hand, a substantial proportion of the The ethylenically unsaturated / aromatic monovinylidene nitrile copolymer formed during graft polymerization does combine chemically with, or bind (ie, graft) to the dispersed elastomeric polymer particles. In the specific case by hand, this graft polymerization process is carefully conducted to ensure that the weight ratio of the polymer grafted to the rubberized or elastomeric polymer substrate, i.e. the ratio of the graft to the rubber or G: R, is in the scale from 0.2 to 0.4 (especially from 0.25 to 0.35). The molecular weight of the grafted and ungrafted monovinylidene ethylenically unsaturated / aromatic nitrile copolymer formed within this emulsion graft polymerization process is also considered as an important feature within the context of the present invention. As noted above, this grafted and ungrafted polymer generally should have a weight average molecular weight in the range of 50,000 to 130,000, for the purposes of the present invention, with an especially preferred scale being 80,000 to 120,000 for that purpose. Following the step of the emulsion graft polymerization process described above, the resultant bimodally grafted elastomeric polymer particles, they are separated from the continuous aqueous medium where they are dispersed colloidally. Specifically, this is done as a preparation step before blending with the ethylene-unsaturated / aromatic monovinylidene-modified, rubber-modified, nitrile copolymer, graft-polymerized, bulk, solution, or suspension, or with the copolymer of 5 ethylenically unsaturated / aromatic monovinylidene nitrile not modified with rubber, which is used within step (E) of the present process. There are a variety of known techniques available, and generally adequate, to perform the step or the required separation operation (also commonly referred to as "dehydration"). These all involve essentially destabilizing and coagulating the grafted elastomeric polymer emulsion, and subsequently separating the aqueous medium from the coagulated grafted polymer particles which is no longer disperse in a colloidal and stable manner therein. As is well known to those skilled in the art, this coagulation operation is different from, and should not be confused with, the step of the partial "agglomeration" process discussed above. In In particular, the key points of distinction reside in the facts that: (a) the colloidal stability of the dispersed polymer particles is not destroyed in the partial agglomeration process, and (b) the agglomeration step involves the treatment of the particles of rubber dispersed in a stage where they do not have a non-rubberized outer protective layer (i.e., a rigid polymer or relatively high melting point) to prevent massive or complete coalescence of the rubber particles, which would otherwise occur over a complete destabilization of non-grafted rubber latex. In contrast, the coagulation step involves an essentially complete destabilization of the grafted rubber latex, and therefore, completely destroys its colloidal stability. However, since this occurs after the individual dispersed rubber particles have been provided with a "protective" layer grafted with a relatively high glass transition temperature, mass or complete coalescence of the particles is prevented in this manner. individual rubber particles in a large and simple rubber mass, as would otherwise be the case with the destabilization of latex. In summary, the ethylenically unsaturated ethylenically unsaturated monovinylidene nitrile copolymer layer which is in place at that stage on the individual dispersed polymerized particle particles, prevents or at least reduces the irreversible coalescence of the individual grafted polymer particles. on the destabilization of the latex, and for that reason, it preserves the individual separate character of the rubber particle, and the basic bimodal particle size distribution, as originally established in the step of the partial agglomeration process described above. Included within the various known elements for coagulating and dehydrating properly the grafted elastomeric polymer emulsions present, are so-called "chemical coagulation" methods, which typically involve the treatment of the emulsion with multivalent inorganic salts, such as magnesium chloride, magnesium sulfate, aluminum sulfate, calcium chloride, calcium sulfate, or acid reagents such as sulfuric acid, acetic acid, and phosphoric acid; the so-called "mechanical finish" that typically involves the application of heat and tear to destabilize the latex; and the so-called "freezing coagulation" that involves the destabilization of the latex by means of freezing the continuous aqueous medium, as the medium to destroy the colloidal stability of the latex in question. Among the methods indicated, mechanical finishing and freezing coagulation (especially mechanical finishing) are preferred for use herein, because they do not involve the addition of substantial amounts of products. chemicals or reagents, and therefore, result in a cleaner reclaimed grafted rubber product having substantially better color and color stability characteristics. The dehydration operation previously described typically is conducted exclusively on the polymerized elastomeric polymer latex with emulsion graft resulting directly from step (C) thereof. However, in some cases, the monovinylidene ethylenically unsaturated / aromatic nitrile copolymer to be employed in the subsequent melt blending operation (i.e., step (E) of the present) will be of a variety not modified with rubber, and it will be initially prepared and / or will be acquired in the form of an aqueous emulsion thereof. In such cases, it will often be convenient and preferred to combine the grafted rubber material and the unmodified copolymer with rubber in latex form (ie, be a simple aqueous liquid pre-mixing operation) prior to the dehydration operation of the step (D), and then simultaneously coagulate and dehydrate both the grafted rubber latex and the unmodified copolymer with rubber in the same dehydration operation. The last step of the process of the present invention involves the melt-blending of the polymerized elastomeric material with emulsion grafting with a relatively high rubber content (sometimes referred to in the art as a "grafted rubber concentrate" or "GRC") , with an ethylenically unsaturated / aromatic monovinylidene nitrile copolymer not modified with rubber, and / or with an ethylenically unsaturated / aromatic monovinylidene-modified rubbery nitrile copolymer, graft polymerized, bulk, in solution, or in suspension. The unmodified monovinylidene aromatic copolymers with rubber suitable for this melt blending use include those in which monovinylidene aromatic monomers of the above-described kind (preferably in a greater proportion by weight), and ethylenically nitrile monomers. unsaturated, as also described hereinabove (preferably in minor proportions by weight), are copolymerized together, either ls- with or without minor amounts (eg, from 1 to 10, or from 15 to 20 percent in weight) of different optional monomers, such as, for example, acrylate or methacrylate esters and N-substituted maleimide monomers. Typically, monovinylidene aromatic monomer (especially styrene) will constitute 50 to 90 (preferably 60 or 65 to 80 or 85) percent by weight of the polymer not modified with rubber; the unsaturated nitrile monomer (especially acrylonitrile) will constitute 10 to 50 (preferably 15 0 to 20 to 35 or 40) percent in weight thereof; and the optional monomer constituents indicated (especially N-substituted maleimides such as N-phenyl maleimide), if used, will be used in an amount of 20 weight percent or less, and preferably in an amount of 15 percent or less. less. These unmodified monovinylidene aromatic copolymers with rubber can be suitably prepared for use herein by any of the well-known polymerization techniques, including emulsion polymerization, bulk (or "bulk"), suspension, or in solution. Especially preferred unmodified monovinylidene aromatic copolymers for use herein are those having a weight average molecular weight of 70,000 to 130,000 (more preferably 75,000 to 115,000) based on gel permeation chromatography using polystyrene standards. . Rubber-modified monovinylidene aromatic copolymers, graft polymerized, bulk, in solution, or in suspension, for use in melt blending with the emulsion grafted rubber concentrate (GRC) materials described hereinabove, include those wherein the ungrafted matrix portion and the grafted and occluded rigid polymer portions thereof generally correspond in their chemical composition to the rubber unmodified copolymers described above, and which are prepared by first dissolving a previously made rubberized polymer (typically in an amount constituting 5 to 25 weight percent of the total polymerizable mixture) within the monomer mixture to be employed in the preparation of the desired monovinylidene aromatic copolymer. Preferably, these rubber modified monovinylidene aromatic copolymers have a weight average molecular weight in the range of 100,000 to 200,000 (more preferably 120,000 to 200,000). Suitable elastomeric polymer materials to be used as the rubber modifier in these graft copolymers mass polymerized, in solution, or in suspension, include diene rubbers, ethylene / propylene rubbers, ethylene / propylene / non-conjugated diene rubbers ( EPDM), acrylate rubbers, polyisoprene rubbers, halogen-containing rubbers, and mixtures thereof, as well as interpolymers of rubber-forming monomers with other copolymerizable monomers. Preferably, the rubberized polymer modifier for this particular polymer ingredient is an elastomeric conjugated diene homopolymer or copolymer of the kind described hereinabove with respect to the dispersed, hydrated polymeric particles of the initial aqueous polymeric emulsion that is employed. as the initial starting material in the present. Elastomeric block copolymers, 60 to 80 weight percent conjugated dienes, such as 1,3-butadiene and isoprene, with 20 to 40 weight percent styrene are also beneficially employed for this purpose. In a particularly preferred embodiment herein, portions of the ethylenically unsaturated / aromatic monovinylidene nitrile copolymer of both the graft rubber concentrate graft polymerized by emulsion and the non-rubber modified or rubber modified copolymer of step (E) which are melt-blended therewith are binary styrene / acrylonitrile (SAN) copolymers each having an acrylonitrile content in the range of 20 to 40 weight percent (taken on a weight basis of the copolymer of styrene / acrylonitrile only, that is, excluding any portion of the leuulated polymer thereof for calculation purposes), and which differ from each other in terms of their respective acrylonitrile contents by not more than 5 or 6 (preferably no more from 2. 5, and more preferably less than 1.5) percentage points. It has been observed that these compositions Particularly preferred exhibits a remarkably reduced sensitivity to brightness (i.e., variability in brightness values measured as a function of varied molding temperatures) than otherwise comparable compositions, wherein the contents of acrylonitrile indicated differ from each other by more than 5 or 6 percentage points. In another especially preferred embodiment, the copolymer of ethylenically unsaturated / aromatic monovinylidene modified with rubber or not modified with rubber which is mixed with the bimodal grafted rubber concentrate component in step (C) of the present, is one having a smaller amount (eg, from 2 to 30, preferably from 4 to 15 weight percent) of an N-substituted maleimide monomer (especially N-phenyl maleimide) polymerized therein. The presence of this additional monomer is beneficial, since it serves to increase the heat resistance and / or the heat distortion temperature of the resulting polymer composition, and to thereby improve its property for use in applications and / or / U end-use environments that involve exposure to a high temperature. As a result of the process described herein, a rubbery monovinylidene aromatic copolymer composition of a size is provided of multimodal grafted rubber particles, which comprises, as a minimum, at least two different groups of rubber particles polymerized with emulsion graft. One of the particle groups consists of relatively small particles that: (a) have an individual size of 0.1 to less than 0.25 microns; (b) as a group exhibit a very narrow, sharp, and well-defined particle size distribution spread, at or near the value of the average volume size for the group; and (c) as a group they have an average particle size by volume (ie, particle diameter) on the scale of 0.15 to 0.22 (preferably 0.15 to 0.2) microns. The other of the groups of rubber particles polymerized with emulsion grafting is composed of relatively large emulsion grafted rubber particles which: (a) are of an individual size of 0.25 microns to about 2 microns or more; (b) as a group they exhibit a very broad polydispersity particle size distribution over the indicated size scale of 0.25 to 2 microns; and (c) as a group they have an average particle size by volume of 0.4 to 1 (especially 0.4 to 0.8) microns. As briefly mentioned in the foregoing, the partial latex agglomeration operation of step (B) is conducted in such a manner as to agglomerate from 5 to 50 (especially from 20 to 40) percent by weight of the rubber particles. small ones initially present (ie, less than 0.25 microns) to form enlarged particles that have sizes of 0.25 microns or more. Accordingly, upon completion of the partial agglomeration process of step (B), from 50 to 95 (more preferably from 50 to 80 or to S5) percent "p weight of the colloidally dispersed rubber particles will fall on the size scale of less than 0.25 microns, and from 5 to 50 (more preferably 15 or 20 to 50) percent of the remaining weight of these dispersed rubber particles will fall within the size range of 0.25 microns or more. As also briefly mentioned above, a phenomenon of particle size growth of a subsequent step (B) (ie, subsequent partial agglomeration) has been observed in relation to the practice of the present invention. In particular, it has been found that from 10 to 35 or 40 (more typically 15 to 25 or 30) additional weight percent of the relatively small rubber particles initially present (i.e., one i'c "diameter) less than 0.25 microns) are converted into particles of relatively large size (ie, greater than 0.25 microns) following the graft polymerization of step (C) thereof, therefore, for example, in cases where The partial agglomeration step of step (B) is conducted to agglomerate about 25 weight percent of the , .-. small particles initially present in particles of larger size (ie 0.25 microns and more), the phenomenon of additional agglomeration or "downstream" The indicated or growth-in-size, effectively results in a distribution of rubber particles polymerized by final emulsion grafting such that at least 35 percent by weight (preferably 35 or 40 to 60 or 65 percent by weight). weight) of the rubber particles 5 polymerized by emulsion grafting, are 0.25 microns or more in size in the polymer composition mixed by final melting. In some especially preferred embodiments herein, from 35 to 45 weight percent of the rubber particles initially present, agglomerate to a size of 0.25 microns or more in the partial agglomeration process of step (B), and the further agglomeration or "downstream" further results in more than 50 weight percent (especially 55 to 65 weight percent) of the The rubber particles polymerized by emulsion grafting fall within the scale of sizes described above greater than 0.25 (for example, 0.25 to 2) microns. Seen from a slightly different perspective, the phenomenon of additional particle size growth of the Step 15 (D) and / or (E) can be seen as one where 10 or 15 to 65 or 70 (more typically 15 or 20 to 60, and especially 20 or 25 to 50) cent of the small particles (ie, less than 0.25 microns) that were immediately following the operation of partial agglomeration of step (B), they become particles of a size of 0.25 microns or greater during the subsequent operations of dehydration and / or fusion mixing. In some inetancias where the grafted rubber concentrate material polymerized by grafting in The above-described bimodal emulsion is melt-blended with an ethylenically unsaturated / aromatic monovinylidene nitrile copolymer not modified with rubber, the resulting or final polymer composition will itself have a bimodal grafted rubber particle size distribution where all the particles of grafted rubber dispersed therein are of the variety polymerized by emulsion grafting, and have a particle size distribution of the subsequent blend by melting of the kind described hereinabove. On the other hand, when the grafted rubber concentrate material polymerized by bimodal emulsion grafting described above is melt-blended with a graft polymerized copolymer in bulk, in solution, or in suspension that is itself modified with rubber, the polymer composition The resulting final will contain two morphologically different groups of grafted rubber particles. One of these groups, of course, is composed of the grafted rubber concentrate material of the bimodal particle size distribution described above, as is well known in the art, and is characterized by a generally solid rubber particle morphology (ie. say, not significantly occluded with the rigid matrix copolymer) when examined by conventional Electron Transmission Microscope (TEM) techniques. Within this group polymerized by emulsion grafting, generally solid of grafted rubber particles, the small non-agglomerated portion thereof will typically be of a generally spherical shape, and the relatively large sized portion thereof agglomerated will be of large spherical particles. completely coalesced, to partially coalesced or partially fused groups of the initial small particles. The other type or group of dispersed grafted rubber particles is that which is provided by the monovinylidene aromatic copolymer component copolymerized by grafting in bulk, in solution, or in suspension, modified with rubber. As is well known, this last type of grafted rubber particles are typified by a morphology of rubber particles where significant amounts of rigid (ie, non-rubberized) copolymer are trapped (ie, "occluded") with the particle. of rubber itself, and are visible as,. such by means of Transmission Microscope analysis of Electrons This group of occluded rubber particles will typically have a size of 0.3 microns to 10 microns on a basis of individual particles, and taken as a group, they will typically have an average particle size by volume on the scale of 0.5 to 5 (preferably 0.5 to 3 or 4) microns. Unsubstituted nitrile / aromatic monovinylidene copolymer resins rubberized, bulk graft polymerized, in solution, or in suspension, suitable for use herein, will typically have a rubber content on the scale of 5 to 25 ( 5 to 15 or 20 percent by weight), and typically will contain amounts of grafted and occluded rigid copolymer corresponding to 0.5 to 3 or 4 parts by weight thereof per part by weight of the impact modifier rubber contained therein. same. In accordance with the foregoing, and as is customary for these mass-modified, suspension or rubber-modified graft copolymer materials, a significant amount (for example, 20 or 25 up to 85 or 90% by weight) is used. weight percent) of these compositions may be composed of ethylenically unsaturated / aromatic nitrile copolymer of monovinylidene no. grafted (also referred to in the art as "free matrix"). Typically, the finished melt blending compositions herein will have a total polymer content of 5 to 30 (especially 10 to 25) percent by weight, based on a weight basis of the total polymer composition. In instances where the bimodal grafted rubber concentrate is melt blended with a graft copolymer in bulk, in solution, or in rubber-modified suspension, the rubberized polymer portion provided by the emulsion polymerized grafted rubber concentrate, typically it will constitute from 5 to 95 (preferably from 10 to 90, and more preferably from 50 or from 55 to 75 or to 85) percent by weight of the total rubber content, the rest being provided by the polymerized component by bulk grafting, in solution, or in suspension. In conducting the aforementioned melt blending operation, they will typically be combined together to form 100 parts by weight of the polymeric composition modified with multimodal rubber. finished: (a) from 10 to 75 (preferably from 15 to 60) parts by weight of the dehydrated bimodal grafted rubber concentrate component (ie, from step (D) of the present process), and (b) from 25 to 90 (especially from 40 to 85) parts by weight of the monovinylidene ethylenically unsaturated / aromatic nitrile copolymer not modified with rubber - mentioned, and / or the ethylenically unsaturated / aromatic monovinylidene nitrile copolymer component polymerized by grafting in bulk, in solution, or in suspension, modified with rubber. # Naturally, any and all of the desired types of conventional additive materials, such as ultraviolet stabilizers, lubricants, fillers, colorants, pigments, and antioxidants, can also be conveniently incorporated into polymer compositions of rubber particle size. multimodal elements present in their quantitative proportions normally used, in conjunction with the aforementioned fusion mixing operations. The present invention is further understood and illustrated by reference to the following exemplary embodiments, wherein all parts and percentages are presented on a weight basis, unless specifically indicated otherwise.

Examples 1? In these examples, three different emulsion graft polymerized grafted rubber concentrates (ie, Examples 1 and 2, and Comparative Example A) are prepared using 3 rubber latexes of 1,3-butadiene / styrene / acrylonitrile copolymer ( weight ratio 92 to 93/5 to 6/1 to 3) different initials (having different particle sizes of volume averaged for the colloidally dispersed rubber particles contained therein), as the initial starting materials. Each of these latexes was initially characterized (ie, in its original form) by having relatively narrow monomodal rubber particle size distributions, where the peak in the size distribution falls at or near the average particle size. '"" * per volume indicated in Table I below for the individual rubber latex in question. Each of these latexes was partially agglomerated using a binder latex (in accordance with US Pat. No. 4,419,496 Henton) core / shell (elastomeric 1,3-butadiene / styrene copolymer copolymer core). ethyl acrylate / methacrylic acid copolymer shell), to make 20 to 40 weight percent of the rubber particles It dispersed relatively small (ie, less than 0.25 microns in diameter) initially present, will agglomerate with each other to form enlarged rubber particles with individual particle sizes greater than 0.25 microns (ie, between 0.25 microns and 2 microns), determined by analysis of hydrodynamic chromatography. The resulting partially agglomerated rubber latexes are then polymerized by grafting with a weight ratio of 77:23 of a monomeric mixture of styrenes: acrylonitrile (SAN), to form latexes of grafted rubber concentrate of bimodal rubber particle size, with a rubber content in the range of 54 to 65 percent (base by weight of solids); proportions of styrene copolymer: grafted acrylonitrile: rubber (G: R) on the scale from 0.26 to 0.33; and weight average molecular weights of the styrene-acrylonitrile copolymer (M ^ on the scale of 88,000 to 99,000, as measured by gel permeation chromatography, using polystyrene standards.) These latexes of bimodal grafted rubber concentrate are dehydrated and recovered then in a way solid by coagulation by freezing and centrifugation, or by mechanical isolation according to U.S. Patent No. 4,299,952 of Pingle, and melt-blended in a Welding Engineers double-screw counter-rotating extruder, at a weight ^ '. 79:21 of styrene copolymer resin: acrylonitrile (weight average molecular weight = 99,000), to form three ABS resins of a different finished bimodal particle size, with rubber content of 19 weight percent (on a weight basis of the finished ABS resin). During these operations of dehydration and fusion mixing, there is another agglomeration of the small grafted rubber particles (ie, less than 0.25 microns) with the result that, after melting, more than 50 percent in weight of grafted rubber particles 0 have sizes (determined by means of electron microecopes) greater than 0.25 microns. The characteristics and properties of the ABS resins of a resulting bimodal rubber particle size are stipulated in Table I.

TABLE I 1. ASTM D1238, Condition I 2. ASTM D256 * Estimated Values N.D. = Not Determined As can be seen from the results of Table I, the ABS resins prepared in accordance with the present invention have significantly better melt flow index values than the Comparative Resin, without a significant combined sacrifice in the properties of brightness and impact of the same.

Example 3 In this example, essentially the procedures of Examples 1 and 2 were repeated to prepare two resins Additional ABS The first, Example 3, was in accordance with the present invention, and had a particle size of the rubber latex from the starting point greater than 0.15 microns (specifically, 0.177 microns), and then the partial agglomeration was grafted with a weight ratio of 78:22 of SAN copolymer M ^ = 89,000) to a G: R value of less than 0.4 (specifically, 0.24). The second was a comparative experiment, Comparative Example B, in which the particle size of the rubber latex from the initial point was 0.124 microns, and where it was grafted (following the partial agglomeration) with a weight ratio of 69.3 : 30.7 SAN copolymer (Mw = 123,000) up to a G: R ratio of approximately 0.6. The specific characteristics and properties of the resulting ABS resins are stipulated in Table II.

Example 4 In another series of experiments, an ABS resin (ie, Example 4) was prepared which was very similar to that of Example 3, with the exception of: (a) that its initial rubber latex particle size was 0.159 microns; (b) his l j of grafted SAN was 103,000; (c) its rubber-to-rubber ratio was 0.3; (d) its grafted SAN contained 30.5 percent NA, and (e) its overall rubber content was 22 percent by weight. The other ABS resin (Comparative Example C) is essentially the same as Comparative Example B, except for having an acrylonitrile content of grafted SAN of 28 percent; an M ^ of grafted SAN of 124,000; and a total rubber content of 22 weight percent. The specific characteristics and properties of the latter two resins are also stipulated in Table II.

TABLE II 1. ASTM D1238, Condition I 2. ASTM D256 * Estimated Values N.D. = Not Determined Examples 5 and 6 In these examples, essentially the procedures of Examples 1 and 2 were repeated to prepare two ABS resin of a different bimodal particle size, both of which were in accordance with the present invention, but which were grafted up to two different proportions of G: R (ie, 0.28 and 0.4, respectively). The properties and characteristics of the resulting ABS resins are stipulated in Table III. As can be seen from the data in Table III. Both materials have large particle populations (0.25 to 2 microns) less than 50 weight percent following the partial agglomeration of step (B), but then exhibited large particle populations greater than 50 weight percent after mixing by fusion in the finished ABS resin.

TABLE III . ASTM D1238, Condition I. ASTM D256 Examples 7-9 In this series of examples, again substantially the procedure of Examples 1 and 2 was repeated to prepare three ABS resins of a different bimodal rubber particle size, all of which were in accordance with the present invention, but they had different degrees of "bad coupling", such as between the AN content of their respective constituents of grafted SAN and fusion-mixed SAN. The properties and characteristics of the resulting ABS resins are summarized in Table IV. As can be seen from the data of Table IV, the resins (ie, Examples 8 and 9), wherein the acrylonitrile contents of SAN grafted and SAN mixed by melting were within about 5 percentage points one on the other, they exhibited substantially less sensitivity to brightness as a function of the molding temperature of the test sample.

TABLE IV 1. ASTM D1238, Condition I 2. ASTM D256 * Estimated Values N.D. = Not Determined Although the present invention has been described and illustrated with reference to certain specific embodiments and examples thereof, this should not be understood or construed in any way to limit the scope of the invention currently claimed.

Claims (12)

1. A process for the preparation of a rubber modified monovinylidene aromatic copolymer composition, this process comprising the steps of: A. preparing or obtaining an initial aqueous elastomeric polymer emulsion containing, on a base in - to the total weight of the polymer emulsion, from 25 to 50 weight percent of colloidally dispersed small particles of an elastomeric conjugated diene polymer having an average volume particle size of 0.15 to 0.22 microns; B. Partially agglomerate the initial polymeric emulsion 15 to cause at least 5 but less than 50 weight percent of the small, dispersed particles to agglomerate, cohere, or otherwise physically associate with each other to form particles enlarged colloidally dispersed polymers having a volume average particle size, determined by exclusion of all particles having diameters less than 0.25 microns, of about 0.4 microns or more; C. polymerizing with graft, under polymerization emulsion conditions, the polymer emulsion Partially agglomerated, with a monomer mixture comprising, on a weight basis of the monomer mixture, from 40 to 90 weight percent of a monovinylidene aromatic monomer, from 10 to 40 weight percent of an ethylenically nitrile monomer unsaturated, and from 0 to 30 weight percent of one or more monomers of acrylate ester, methacrylate ester, or N-substituted maleimide, to form a graft copolymer latex wherein: (a) the elastomeric polymer component from the initial polymer emulsion it constitutes from 40 to 70 weight percent of the polymer solids contained therein, (b) the weight ratio of the amount of the chemically grafted aromatic copolymer (G) to the dispersed elastomeric polymer particles. , to the amount of the same dispersed elastomeric polymer (R), is from 0.2 to 0.4, and (c) the weight average molecular weight of the monovinylidene aromatic copolymer graft and non-grafted Grade formed in the graft polymerization process is in the range of 50,000 to 130,000; D. repairing the resulting emulsion polymerized graft copolymer, from its aqueous medium; and E. Melt-blending the graft copolymer emulsion polymerization copolymer with an ethylenically unsaturated / aromatic monovinylidene nitrile copolymer, or with an ethylenically unsaturated / aromatic monovinylidene-modified nitrile graft copolymer with bulk polymerized rubber, in solution , or in suspension; This process is further characterized in that the total population of elastomeric polymer particles copolymerized in emulsion graft having a diameter of 0.25 microns or greater is increased by at least 10 weight percent based on total particles of elastomeric polymer copolymerized with emulsion graft between the termination of step (C) of graft polymerization, and the termination of step (E) of the melt blending operation.

2. The process of claim 1, wherein the -L-- < "ethylenically unsaturated / aromatic monovinylidene nitrile copolymer, or the non-grafted matrix portion of the ethylene-unsaturated / aromatic monovinylidene-nitrile graft copolymer modified with rubber, bulk polymerization, in solution, or in suspension, used 15 in step (E), it has a weight average molecular weight of 70,000 to 200,000.

3. The process of claim 2, wherein the monovinylidene aromatic monomer component of the emulsion graft copolymer copolymer latex 20 (C), and of the ethylenically unsaturated / aromatic monovinylidene copolymer, or of the bulk polymerized graft copolymer, in solution, or in suspension of step (E), comprises styrene, and wherein the ethylenically unsaturated nitrile monomer component of both copolymers comprises 5-acrylonitrile.

4. The process of claim 1, wherein the ethylenically unsaturated / aromatic monovinylidene nitrile copolymer portion of the graft copolymer latex of step C is a binary copolymer of 5 styrene / acrylonitrile (SAN), having an acrylonitrile content (X) in the range of 20 to about 40 weight percent; the ethylenically unsaturated / aromatic monovinylidene nitrile copolymer, or the portion of the ethylenically unsaturated / aromatic nitrile copolymer of jrtz) monovinylidene of the graft copolymer modified with bulk polymerized rubber, in solution, or in suspension employed in step E, is a styrene / acrylonitrile binary copolymer (SAN) having an acrylonitrile (Y) content in the range of about 20 to about 40 percent in 15 weight; and the numerical difference between X and Y is about 6 percent or less. The process of claim 3, wherein the ethylenically unsaturated / aromatic monovinylidene nitrile copolymer employed in step (E), is a non-copolymer 20 modified with styrene and acrylonitrile rubber, and has a weight average molecular weight of 70,000 to 130,000. The process of claim 3, wherein the ethylenically unsaturated / aromatic monovinylidene nitrile copolymer employed in step (E), comprises a Rubber modified styrene / acrylonitrile graft copolymer, bulk polymerized, in solution, or in suspension, wherein the non-grafted styrene / acrylonitrile copolymer portion thereof, has a weight average molecular weight of 100,000 to 200,000. The process of claim 3, wherein the ethylenically unsaturated / aromatic monovinylidene nitrile copolymer employed in step (E), comprises a graft polymer prepared by graft polymerization of a monomer mixture comprising styrene and > t) acrylonitrile, under bulk polymerization conditions, in solution, or in suspension, on a 1,3-conjugated diene homopolymer or copolymer rubber. The process of claim 7, wherein the monomer mixture comprising styrene and acrylonitrile, further comprises, on a weight basis of the monomer mixture, from 2 to 30 weight percent of an N-substituted maleimide monomer . The process of claim 8, wherein the N-substituted maleimide monomer is N-phenyl maleimide. 10. The process of claim 3, wherein the ethylenically unsaturated / aromatic monovinylidene nitrile copolymer employed in step (E) is a terpolymer not modified with styrene rubber, acrylonitrile, and N-phenyl maleimide. 11. The process of claim 1, wherein the emulsion graft copolymer copolymer latex ("C") has a content of the elastomeric polymer component from 45 to 70 weight percent, and has a by weight of the graft copolymer to the elastomeric polymer (G: R ratio) of 0.25 to 0.3

5. The process of claim 1, wherein the total population of elastomeric copolymer copolymer particles by emulsion graft having an average volume diameter of 0.25 microns or more is increased by at least 25 weight percent on a base of elastomeric particles copolymerized by total emulsion grafting during the operations of separation and fusion mixing of steps (D) and (E).