MXPA96006152A

MXPA96006152A - Mixes of metacril resins

Info

Publication number: MXPA96006152A
Application number: MXPA/A/1996/006152A
Authority: MX
Inventors: Lin Manhua; Shah Nilesh
Original assignee: Atohaas Holding Cv
Priority date: 1995-12-28
Filing date: 1996-12-05
Publication date: 1997-08-01

Abstract

The present invention relates to a novel composition of mixtures of methacrylate resins and to a method for obtaining the mixture composition, which has an improved resistance to the formation of cracks by solvents. The novel blend composition contains particles of the methacrylate matrix resin of a single-layer polymer and, optionally, a multilayer acrylic polymer. The particles of the single-layer polymer are derived from 50% or more of the methyl methacrylate, and have a weight-average molecular weight (Mw) of at least 120% of the Mw of the methacrylate matrix resin component of the mixing, the particles having a diameter of 50 to 500 nanometers, have been found to confer a value of the resistance to the formation of cracks by solvent to the methacrylate resin mixture, which is at least twice the value of the resistance to the absent formation of the polymer particles of a single layer. The resistance to the formation of cracks by solvents of the mixture can be improved, as much as by 10 times or more, on the resistance to the formation of cracks by solvents, of the resin only of the methacrylate matrix

Description

MIXES OF RESINS OF METACR1LAT0 This invention relates to a composition of methacrylate resin blends, which have improved resistance to solvent cracking. More specifically, the composition of the methacrylate resin blend has improved resistance to solvent cracking, which is achieved in a new, simple and inexpensive manner, while retaining the convenient acrylic properties of the blend composition, such as weathering durability, molding and calendering ability of fusion, appearance, and impact and mechanical resistance properties. Methacrylate resins are widely used in producing molded parts and articles of sheets, which have the known, convenient, "acrylic properties" mentioned above. However, acrylic polymers generally, and methacrylate resins in particular, can deteriorate in appearance and physical properties, when brought into contact with organic solvents, such as alcohols, gasoline, paint thinners and surface cleaning liquids. The improvement in the resistance of surface degradation by solvents, named "solvent crack resistance" or "crack resistance", has been the subject of considerable study in the art.

Methacrylate resins, ie, polymers and copolymers derived from at least 50% by weight of methyl methacrylate, are widely used commercially; those resins that have been obtained by cellular or continuous molding processes generally have an excellent resistance to solvent cracks, due to their very high molecular weights (typically exceeding one million daltons). But beyond the disadvantages of the high cost of producing cellular methacrylate resins or molding, these materials are also difficult to form into molded articles. A technical challenge in the art has been to produce methacrylate resins having good molding properties and obtaining leaves, with retention of good physical properties, while also achieving an excellent resistance to fissures of the molded or cellular sheet. U.A. Patent No. 5,324,781 ('781) discloses methacrylate-based resins containing certain types of multilayer polymer particles whose blends have improved solvent resistance. "Unfortunately, the polymer particles of the '781 patent require at least two layers (i.e., they are of the" core / shell "type) to confer crack resistance to the mixture, Specifically, the particles require an inner layer. of methacrylate of average molecular weight of very high viscosity and an outer layer of methacrylate having a lower molecular weight.The particles with these requirements, therefore, have relatively complex and expensive process steps in their production. The object of the present invention is to provide an improved resistance to cracking in methacrylate resins by a simple, lower cost method compared to known methods.We have discovered that the particles obtained from only one layer of a polymer composition, molecular weight and particle size specified, surprisingly confers improved resistance to cracks at a ezcla containing single-layer polymer particles ("SLP") thus defined, and a methacrylate matrix resin. The particle sizes of the SLPs of 50 to 500 nanometers (nm) are effective in the blend compositions of the invention and are preferably achieved by the emulsion polymerization. The blends of the invention have a crack resistance, equivalent or better, than known blends, which incorporate other polymers (for example, these "other polymers" require at least two layers), and at least twice, preferably five times , improved on the crack resistance of the methacrylate matrix resin alone. A) Yes, a composition of methacrylate resin mixtures is provided, which comprises: a) from 50 to 99 weight percent of a methacrylate matrix resin, derived from monomer units comprising at least 50 weight percent of methyl methacrylate and, optionally, up to 50 weight percent of at least one monoethylenically unsaturated monomer unit, selected from the group consisting of the alkyl acrylate alkyl, C2-C4 alkyl methacrylate, styrene and acryl -nitrile. the methacrylate matrix resin has a weight average molecular weight of at least 85,000 daltons; and b) from 1 to 50 weight percent of particles of a single layer polymer, derived from monomer units comprising at least 50 weight percent of methyl methacrylate and, optionally, up to 50 weight percent of at least one monoethylenically unsaturated monomer unit, selected from the group consisting of the alkyl acrylate I ~ Q, C2-C4 alkyl methacrylate, styrene and acrylonitrile; the one-layer polymer has a weight-average molecular weight of at least 120% of the weight average molecular weight of the methacrylate matrix resin and the one-layer polymer particles have a diameter of 50 to 500 nanometers. The composition of the methacrylate resin mixture of the invention, as demonstrated, for example, by the articles and sheets obtained from the mixture, has an improved value of solvent crack resistance by at least 2 times, preferably 5 times and more preferably 10 times, on the value of the solvent crack resistance demonstrated by the articles or sheets made with the methacrylate matrix resin of the mixture, in the absence of the SLP. The improved crack resistance thus provides valuable increased resistance to solvents, for example organic solvents, washing detergents and cleaners, and related liquids, in contact with the articles and sheets obtained from the blends of the invention. Detailed Description of the Invention "Single layer polymer" ("SLP") is understood to mean a polymer consisting of only a "layer" or "stage" (as will be described). The SLP is preferably prepared by the emulsion polymerization and has the composition defined herein. The suspension polymerization and continuous polymerization methods can also be used to prepare the SLP. However, it is characteristic of the SLP of the invention that this SLP does not require processes to "coat" the layer, or to add to the single layer one or more additional layers, or "stages" (a term commonly used in the production of an multilayer polymer, the "stage" refers to a separate layer or a coating of an additional polymer, in an underlying layer "), nor does it require any additional reaction or polymerization of another monomer or combination of monomers, in the presence of the SLP , so as to provide any additional "layer" on the SLP As used herein, the term "molecular weight" means the weight average molecular weight ("Mw"), unless otherwise indicated. Both the Mw and the number average molecular weight, Mn, are estimated by conventional chromatographic gel permeation methods (GPC) using poly (MMA) calibration standards. and resins (or polymers) of the mixture: "derived from monomer units comprising at least 50% of the MMA", means that a monomer mixture, comprising at least 50% of the MMA, is polyered by the polymerization conventional free radical in the carbon-to-carbon double bond of MMA, and other unsaturated monomers present, to form the resin (or polymer) as defined. The term "dalton" is the unit of atomic mass. The particles of the single layer polymer or copolymer used in obtaining the blends of the invention have relatively high molecular weights, ie, a weight average molecular weight which is at least 20% greater than the Mw of the resin of the invention. methacrylate matrix. Preferably the Mw of the SLP is greater than 50% and more preferably 100% or more of the Mw of the methacrylate matrix resin. In absolute terms, the typical Mw varies for effective SLPs from 105,000 to 2,000,000 daltons, preferably from 120,000 to 1,000,000 daltons and more preferably from 170,000 to 800,000 daltons. The preparation of the SLP particles is preferably carried out by emulsion polymerization, using known techniques and, of course, requiring only one stage, as described here. By this method, the product of the one-stage polymerization comprises a latex, that is, an aqueous composition containing dispersed single-layer polymer particles, of which the SLP particles of specific size (as measured by their diameter), can be isolated by conventional means of use in the mixture. Alternatively, the SLP latex can be mixed directly into other latexes containing other components of the mixture of the invention, and the latex mixture is then isolated by conventional means, such as spray drying or coagulation. The composition of the SLP and also of the resin of the methacrylate matrix comprises a polymer or copolymer derived from 50 to 100% of the MMA. MMA levels of 50 to 75%, particularly with styrene as the comonomer, may be found useful in injection molding applications, but other mixtures having more than 75% of the MMA and preferred mixtures have the resin of the methacrylate matrix and the SLP compositions derived from at least 85% by weight of the MMA. The glass transition temperature (Tg) of the mix compositions typically ranges from 50 to 120 ° C.; Preferred compositions, those having more than 85% MMA, traditionally have a Tg of at least 852C. The acrylic and methacrylic alkyl ("(meth) acrylic alkyl") monomers having alkyl groups containing up to 18 carbon atoms can be incorporated into the SLPs of the invention, but preferred, because of their cost, performance and availability, are those alkyl (meth) acrylic esters having alkyl groups with up to 8 carbon atoms. A more preferred composition of both the SLP and, independently, the methacrylate matrix resin, is derived from at least 90% of the MMA and at least one alkyl acrylate or alkyl methacrylate, selected from the methyl acrylate, ethyl acrylate. and butyl acrylate, and butyl methacrylate. Also, the blends can comprise the ethacrylic matrix resin, single layer particles and particles of one or more multi-layer acrylic polymers, the latter particles included in the mixture to improve, for example, impact strength or other properties of the mix, described more completely below. The blends of the invention are typically prepared by mixing pellets of the matrix resin with the SLP in powder form (typically obtained by spray drying an emulsion polymer from the SLP); mixing the pellets of the matrix resin with the SLP pellets; mixing the pellets of the matrix resin with the powder of the SLP and a multilayer acrylic polymer, in powder form; or by mixing pellets of a modified matrix resin on impact with the powder or pellets of the SLP. ("Pellets" are a form of the polymer, conventionally obtained by the extrusion of the melt, cutting the extruded cords into pieces and cooling, the resulting pellets are traditionally several millimeters in diameter and up to several centimeters in length.) the mixtures, just described, such as the melt mixture, typically can be carried out in a single or two screw extruder, at temperatures ranging from 150 to 300 ° C. The desired blend composition can also be formed by dispersing the SLP particles as a powder in a mixture of monomers that make up the matrix resin composition and polymerizing the SLP monomer / particle mixture by bulk or suspension polymerization. In the case of the modified multilayer polymer (ie impact modified), the compositions, emulsion polymer latex and, for example, a multilayer impact modifying acrylic polymer, can be mixed and the mixture isolated by drying of spraying or coagulation and then mixed with the matrix polymer. Alternatively, the latexes of the emulsion polymer of all three components (matrix resin, SLP and multilayer acrylic polymer, such as an impact modifying polymer) can be mixed in emulsion form and the mixed emulsion polymers are isolated by conventional methods. The resulting powder is then typically processed by conventional melt blending and extrusion into pellets for further handling, such as sheet melting or calendering or by injection molding into molded articles. Thus, a method is also provided for improving the solvent crack resistance of a methacrylate matrix resin, which is derived from monomer units of at least 50 weight percent methyl methacrylate, optionally, up to 50% by weight. weight percent of at least one monoethylenically unsaturated monomer unit, selected from the group consisting of Ci-Cg alkyl acrylate, C2-C4 alkyl methacrylate, styrene and acrylonitrile, the resin of the methacrylate matrix has a weight average molecular weight of at least 85,000 daltons. The method includes the following steps: a) adding to this methacrylate matrix resin the particles of a one-layer polymer, derived from monomer units comprising at least 50 weight percent methyl methacrylate and, optionally, up to 50 weight percent of at least one ethylenically unsaturated monomer unit, selected from the group consisting of the alkyl acrylate C ^ -Cg, C2-C4 alkyl methacrylate, styrene and acrylonitrile; the SLP particles added in an amount of 1 to 50 weight percent, based on the combined weight of the methacrylate matrix resin and the SLP particles, this SLP with a weight average molecular weight of at least 120% of the weight average molecular weight of the methacrylate matrix resin, and the SLP particles have a diameter of 50 to 500 nanometers; and b) melt-blending the methacrylate matrix resin containing the aggregated particles of the SLP, to form these SLP particles and the matrix resin, in which the mixture has a solvent crack resistance value, at least twice as much of the value of this resistance to solvent cracks of the methacrylate matrix resin. (The resistance to solvent cracks will be "identically measured", that is, a test for solvent cracking resistance is carried out and measured in both the mixture and the resin of the methacrylate matrix, under identical conditions.) As described above, the resin of the methacrylate matrix of the present invention comprises a copolymer prepared by polishing 50% or more of methyl methacrylate (MMA) and 0 to 50% of, for example, one or more of lower alkyl acrylates (ie C1-C3 alkyls). These C1-C3 alkyls include, for example, methyl, ethyl, propyl, butyl, hexyl, octyl and their isomers. While the (meth) acrylic esters of higher alkyls, ie those esters having alkyls with up to 18 carbon atoms, can be used as comonomers with MMA, preferred alkyl (meth) acrylates include methyl acrylate (MA), ethyl acrylate (EA) and butyl acrylate (BA) or butyl methacrylate. More preferred is a copolymer matrix resin comprising at least 90% by weight of the MMA with the EA and / or BA co-onomer. Of the acrylate comonomers, EA is most preferred. Thus, a highly preferred methacrylate resin comprises, for example, a copolymer derived from 90 to 96% MMA and from 4 to 10% EA. The one-layer polymers can have the same preferred compositions and ranges as those of the methacrylate matrix resins just described. Accurate correspondence of the compositions is not required to achieve improved crack resistance in the blends of the invention. However, clear mixtures, ie those that have transparency to visible light, will be made of components with equal refractive indexes, by known methods; Mixtures that do not require transparency also do not require components with corresponding refractive indices. A surprising finding of the invention that just the simple incorporation of the SLP, as defined, in the above methacrylate matrix resins, provides the improvement in the crack resistance, described above. The particle size in the range of 50 to 500 nm ensures that a portion of the SLP inter-acts sufficiently, during the fusion process, with the methacrylate matrix resin. Mixtures of particle sizes of the SLP can also be used to obtain the combination. While larger particle sizes in certain combinations of compositions may provide some degree of improvement in crack resistance, the critical particle size range of 50 to 500 nm substantially ensures crack resistance at least twice as much in the mixtures of the invention. While the Mw of the matrix polymer is at least 85,000 daltons, it varies from 85,000 to 220,000 daltons and more preferably from 85,000 to 160,000 daltons. Increasing the molecular weight of the polymer of the methacrylate matrix resin, otherwise being the same, increases the melt viscosity of the matrix polymer (thereby lowering the melt flow index) and the blend composition of which the polymer of matrix is a part. Increasing molecular weight also tends to improve the crack resistance of the mixture. The matrix polymers within the preferred internal MW values achieve an excellent combination of mechanical properties and flow behavior for molding and forming articles of the mixtures of the invention, particularly in the injection molding process. A highly preferred methacrylate matrix resin is within the range of 85,000 to 120,000 daltons; one Mw of the preferred effective SLP for the matrix resins within this range has an Mw ranging from 105,000 to 1,000,000 daltons. In general, the resin of the methacrylate matrix is a polymer or random copolymer, which is advantageously prepared by mass polymerization, catalyzed free radical of a mixture of monomers, for example, in a continuous flow, a stirred tank reactor, with an organic peroxide up to about 50% conversion. The monomer mixture of the polymer is pumped to a double screw extruder, devolatilizer, where the residual monomer is removed and other additives can be added. The technique for conducting this polymerization is described in the literature and is known to those skilled in the art. The polymer of the matrix resin can also be prepared by the volumetric, emulsion, or suspension molding polymerization. The resulting polymer or random copolymer can be isolated by spray drying or by coagulation or washing and other known drying methods. With respect to the above-mentioned multi-layer acrylic resin, impact modifier, it functions primarily to increase the physical properties of the mixture of the invention, for example, in its firmness and / or impact resistance. The preparation, mixing and use of the modifying resins of the type useful in the composition of this invention are also known. The preferred type of the modifying resin for use in the practice of the present invention is described, for example, in the patent of E. U. A., No. 3,793,402 ('402). As described in the patent • 402, the modifying resin comprises multilayer polymer particles. Generally speaking, such resins are prepared by the emulsion polymerization of a monomer mixture, in the presence of one or more polymer layers or layers, previously formed. More specifically, these resins are prepared from monomers in aqueous dispersion or emulsion and in which the successive monomeric charges are polymerized on or in the presence of a previously formed latex, prepared by the polymerization of a previous monomer charge (forming a new stage or layer). The polymer product of each stage or layer may comprise a homopolymer or copolymer. In this type of polymerization, the polymer of the subsequent layer binds to and intimately associates with the polymer of the preceding layer, thus providing a polymer of "multiple layers" (or "multiple stages"). The multilayer particles can be recovered from the latex in which they are formed by spray drying or by coagulation and drying. Spray drying can be advantageously carried out in the presence of a "drying aid", for example an acrylate-based resin, which can be the same as or different from the resin of the methacrylate matrix, described herein. The auxiliary drying resin should not adversely affect the chemical, physical or aesthetic properties of the composition or the articles obtained therefrom. A preferred drying auxiliary resin comprises, for example, a random copolymer of MMA and a (C 1 -C 4) alkyl acrylate and typically contains from 90 to about 99.9 wt% of MMA. In sharp contrast to the impact modifying polymers of the '402 patent and the two-layered polymers of the' 781 patent, the single layer polymers of the present invention are prepared in a simple and inexpensive manner and still, in a surprising manner and significant, increase the resistance to solvent and chemical cracks of the mixtures in which they are present. Without being bound to any particular theory, it is believed that the particles of the SLP are evenly distributed during the fusion mixture within the uniform and continuous methacrylate matrix resin. The particles contribute some of their high molecular weight chains to the matrix polymer in the intermediate neighborhood of the particles, while retaining their particle nature within the mixture. The contributed chains, in turn, decrease the propensity of the matrix polymer to suffer the known phenomenon of "entrainment" in the presence of a solvent. Regimes of both initiation and propagation of cracks are thus delayed, under these circumstances. The single-layer polymer particles are surprisingly effective in that they do not contain or require an outer layer of low molecular weight, to help disperse them in the matrix. This concept can be applied to matrix polymers of all kinds in which the behavior of the low deformation regime can be affected by the addition of relatively small amounts (ie, less than 50% of the resulting mixture) of particles of a single layer polymer, which has a higher molecular weight (by at least 20%) than the molecular weight of the matrix polymer. According to the proportions of the matrix resin, a multilayer acrylic resin, impact modifier (if present) and the particles of the SLP of the present invention, it is generally noted that it increases the impact resistance, but decreases the resistance to the tension and hardness, with the increase of the content of the resin modifier of the impact and increases the resistance to fissures with the increase of the content of particles of a layer. The matrix resin will comprise 50% to 99% by weight, the impact modifier resin from 0 to 50% by weight and the polymer particles from one layer to 1 to 50% of the composition of the mixture. If the mixture does not have a multilayer modifier resin present, a preferred range of the matrix resin to the SLP particles is 60 to 98% by weight and 2 to 40% by weight, respectively; a more preferred range is from 80 to 95% by weight and from 5 to 20% by weight, respectively. With these latter preferred ratios of matrix resin and SLP, if a multilayer, modifying acrylic resin is employed, a preferred level of use in the 60-98 / 40-2 mixture is 5 to 45 parts per hundred. (ppc), based on the weight of the matrix / SLP mixture; when used in the most preferred 80-95 ratio of the matrix polymer / 20-5 of the SLP, a preferred level of use of the modifier is from 10 to 40 ppc, based on the weight of the matrix / SLP blend. Optional ingredients that can be used in the composition of the present invention include, for example, color concentrates, for example, dyes and pigments, lubricants, UV stabilizers, thermal stabilizers, antioxidants, agents that improve the temperature of distortion of the heat, antistatic agents, blowing agents, physical or chemical, agents that form cores, agents to give a matt tone, flame retardants and process aids. In general, the amount of these optional ingredients will generally not exceed 5% by weight of the weight of the composition. Additionally, fillers, such as wood fibers, paperboard fibers, glass fibers, glass beads and minerals, such as calcium carbonate, talcum, titanium dioxide, barium sulfate and the like, can optionally be included in the composition of the present invention. The total amount of such optional fillers will generally not exceed 20% by weight of the weight of the composition. Mixtures of the invention can be molded, such as extruded, calendered from the melt, injection molded or otherwise formed into sheets or films or shaped articles, using conventional equipment. Useful articles that can be molded in this way from the mixing compositions have many uses and include, for example, sheets and molded products, such as exterior signs; clear, stained or opaque sheets for window panes; applications in automobiles, such as in glass and taillights; applications such as in windows and divisions for boats and mobile homes; bathroom accessories, such as bath tubs, spas, faucet handles and similar accessories; kitchen appliances, such as microwave oven doors and refrigerator shelves; medical devices for humans and animals, such as incubators and cages. These molded articles show improved resistance to solvent crack formation on similar molded articles, made of matrix resin or single acrylic / acrylic multi-layer additives. Examples General Data - Measurement of Properties Resistance to Solvents. The resistance to the formation of cracks by solvents was measured by holding an Izod bar to an accessory with a known curvature. The curvature selected for the following examples caused the external surface of the Izod bar to suffer a constant, known deformation, as indicated. A piece of filter paper was placed centrally on the bar and kept moist with the test solvent. The time elapsed before the appearance of the first fissures on the surface of the Izod bar was recorded. The measurement was repeated several times (up to 5) and the time periods were averaged. Gel Permeation Chromatography (GPC). The weight average molecular weight ("Mw") was estimated by the GPC, using calibrated curves based on the known molecular weight PMMA. Correlation to Mv was not required, but was able to be established from the GPC measurement and the Mark-Houwink equation. Particle Size The particle size of the SLP was measured by the dynamic dispersion of the light and the supplied estimates of the average particle diameter within 2%, based on the calibrated standards. Within the mixture, the particle size of the SLP was determined either by electron scanning microscopy (SEM) or by SEM field emission on the surface, or in cross section, of a piece made of the mixture. Tg. The glass transition temperature (Tg) was measured by differential scanning calorimetry and was considered accurate within 3 se. The Tg can also be estimated, within 52c, using the Flory-Fox equation, based on a known composition of copolymer. Undefined abbreviations still include the following: butyl methacrylate (BMA), comparative (Comp.), Example (Ex.), Weight (wt), gram (g), percent (%), second (sec); nanometers (nm), greater than / less than (> / <). The terms "SLP" and "SLP Additive" are synonymous, and both refer to the polymer of one layer. All percentages are in% by weight, unless indicated otherwise.

EXAMPLE 1 Preparation of a Mixture of Methacrylate Resins, Which Have an Improved Resistance to Crack Formation by Solvents A. Preparation of a Methacrylate Resin: A methacrylate resin was prepared from a monomer mixture, consisting of 96.0% by weight of MMA and 4.0% by weight of EA, by the continuous mass polymerization process, followed by pellet extrusion. The weight average molecular weight of the resin was 111,000. B. Preparation of a single layer polymer: SLP particles were prepared using standard emulsion procedures in which a "bead" polymer was prepared first, followed by the gradual addition of the same monomer composition to this bead. Thus, to a 5 liter reactor, equipped with a condenser, 1298.7 g of deionized water were charged together with 0.53 g of sodium carbonate; the mixture was heated to 82sc, while being sprayed with nitrogen and stirred at 180 rpm. After one hour, the heel load of the emulsified mixture of 166.1 g of MMA, 6.9 g of EA, 0.025 g of tertiary di-dodecyl disulfide, 0.52 g of sodium dodecylbenzenesulfonate and 57.15 g of deionized water were added to the reactor, along with 0.21 g of sodium persulfate. After completion of the exothermic reaction, the reactor temperature was adjusted to 87 se and 0.16 g of sodium persulfate was charged to the reactor, along with 45.0 g of deionized water. For 3.0 hours, an emulsified mixture of the same monomer composition as the bead was added gradually to the reactor, the charge containing 1494.72 g of MMA, 62.3 g of EA, 0.225 g of disodium tertiary di-dodecyl, 4.68. g of sodium dodecyl-benzenesulfonate and 367.72 g of deionized water. In the same period of time, 0.66 g of sodium persulfate was fed to the reactor together with 180.0 g of deionized water. The reactor was cooled 30 minutes after completing the charges. Particle polymer particles were isolated by spray drying and further characterized; the average particle size was 278 nm and the Mw was > 600,000. C. Preparation of a mixture of A and B. A mixture composition of ethacrylic resins was first obtained by dry mixing 15% by weight, based on the weight of the mixture, of SLP particles of Ex. IB, with 85% by weight of the methacrylate resin, 1A. The dry mix was then compounded in a molten form in a screw ventilated extruder, at 230-260SC, to produce pellets of the mixture by injection molding. The Izod bars were molded from the pellets of the mixture at 260SC. The resistance to solvent cracks was measured as described above in the Izod bars of this mixture of 85/15 // ethacrylic resin / methacrylic polymer of one layer, at a deformation of 0.5% The crack resistance was measured separately with two solvents , isopropanol / water (70/30 by weight) and gasoline, and provided the following times for crack formation: isopropanol / water, 692 seconds; gasoline, 211 seconds. The ethacrylic resin of 1A, which does not have the one-layer polymer present, gave times of resistance to cracks of only 56 and 21 seconds, respectively.

Example 2 Preparation of Additional Fissure-Resistant Mixtures Additional mixtures of solvent fissure-resistant formulations were prepared by dry blending the materials of Example 1A and IB, in the ratios shown in Table 1, to provide Examples 2A (95/5 ) and 2B (90/10), respectively. The mixtures were melt compounded and Izod bars were prepared for evaluation in an identical manner to that described in Example 1C. (Example 1C and the methacrylic resin of 1A not having the one layer polymer present (Comparative Example), are included in Table 1.) The data in Table 1 show an improved resistance to measured cracks (at least two times) in the mixture having 5 and 10% of the SLP present (Examples 2A and 2B) and an excellent improvement of the crack resistance (here, 10 times) in Example 1C, which has 15% by weight of the SLP .

Table l Resistance to isopropyl alcohol (70/30 by weight) and gasoline (0.5% distension =) EXAMPLE 3 Preparation of Effective Additives of the one-layer polymer for methacrylate resin mixtures having improved resistance to crack formation. hj_ Preparation of a one-layer MMA polymer; Mw = 875,000 To the equipment described in Example IB, an identical pre-charge of water and sodium carbonate was fed. The solution was heated, sprayed, stirred and the reaction was carried out in an identical manner to that described in Ex. IB, using the following fillers: heel filler, an emulsified mixture of 173.0 g of MMA, 0.025 g of tertiary di-dodecyl disulfide, 0.52 g of sodium dodecylbenzenesulfonate and 57.15 g of deionized water, with 0.21 g of sodium persulfate; after the exothermic reaction, for 3.0 hours, an emulsified mixture of the same monomer composition as that of the bead was fed: 1557 g of MMA, 0.225 g of tertiary di-dodecyl disulfide, 4.68 g of dodecylbenzene sulfonate of sodium and 367.72 g of deionized water. In the same period of time, 0.66 g of sodium persulfate was fed to the reactor in 180.0 g of deionized water. The reactor was cooled 30 minutes after completing the charges. The additive was isolated by spray drying and had an average particle size of 291 nm and an Mw of 875,000 daltons. B. Preparation of a polymer additive of an MMA layer; Mw = 312,000 An SLP was prepared in a manner similar to that of Example 3A, except that the initial charge of deionized water was 1297 g, the initial monomer emulsion contained 0.173 g of n-dodecyl mercaptan and the monomer emulsion. The crystals, added gradually, contained 1,557 g of n-dodecyl mercaptan. The additive was isolated by spray drying and had an average particle size of 293 nm and an Mw of 312,000.

C. Preparation of a polymer of an MMA layer; Mw = 88,400 An SLP was prepared in a manner similar to that of Example 3A, except that the initial charge of deionized water was 1284.85 g, the initial monomer emulsion contained 1384 g of n-dodecyl mercaptan and the emulsion of monomers, added gradually, contained 12.46 g of n-dodecyl mercaptan. The additive was isolated by spray drying and had an average particle size of 296 nm and an Mw of 88,400. D. Polymer Preparation of an MMA layer; Mw = 35,400 An SLP was prepared in a manner similar to that of Example 3A, except that the initial charge of deionized water was 1260.63 g, the initial monomer emulsion contained 3.81 g of n-dodecyl mercaptan and the emulsion of monomers, added gradually, contained 34.25 g of n-dodecyl mercaptan. The additive was isolated by spray drying and had an average particle size of 283 nm and an Mw of 35,400. Example 4 Preparations of the Components for Methacrylate Resin Mixtures. Fissure Resistant A. Matrix polymer emulsion: An MMA / EA copolymer // 96.0 / 4.0 of Mw = 110,000, was prepared by emulsion polymerization with a sodium persulfate initiator, chain transfer agent of n-dodecyl mercaptan, t-dodecyl disulfide as a stabilizer and sodium dodecylbenzenesulfonate as an emulsifier. The resulting emulsion in a methacrylate matrix resin was used directly in preparing the mixture of Example 4C, below. B. Impact Modifier Emulsion: A three-stage polymer having the following ratios by weight was prepared by the Owens method (US Patent No. 3,793,402): Stage: MMA / EA / allyl ethacrylate ( ALMA) 33.5 / 1.4 / 0.07; 2nd stage: butyl acrylate / styrene / ALMA = 36.3 / 7.9 / 0.9; 3rd stage: MMA / EA = 19.2 / 0.8. The emulsion polymerization was initiated with potassium persulfate and stabilized with potassium dodecylbenzene sulfonate. This emulsion of the impact modifier was prepared by mixing directly in Ex. 4C next. C_? Impact modifier mixture The 4B impact modifier emulsion (84 parts based on solids) was mixed with 10 parts of the 4A matrix polymer emulsion and 6 parts of a high molecular weight copolymer (Mw = 1, 000,000) of methyl methacrylate / ethyl acrylate, prepared by conventional emulsion polymerization with the emulsifier of sodium lauryl sulfate and the initiator of sodium persulfate. The emulsion mixture resulting from these three emulsion components was spray dried to produce a free flowing powder for use as an impact modifier mixture in the blends of Example 4D. D. Solvent Crack Resistant Mixtures Preparations: Solvent crack cracking formulations were prepared by dry blending the materials of Examples 1A, 3 and 4, in the ratios shown in Table 2. Mixtures were melt compounded and pellets were formed, and molded into Izod bars, as described in Example 1C. These steps provide the sample examples 4D-1 through 4D-4, which have an SLP of 15% by weight. The Mw of the SLP increased from 35K to 875K through the D-l to D-4 series. The crack resistance by the isopropanol solvent was measured at a 1.5% distention in Izod bars. A comparative example (4D) was included based on the matrix resin of Ex. 1A and the impact modifier mix 4C alone, and that does not contain the SLP. The mixtures and the test results are summarized in Table 2 and demonstrate that the one-layer polymeric additive increased the solvent resistance, even to a measurable degree, with the SLP having molecular weights less than 100.00 (Examples Comparative 4D-1 and 4D-2). However, crack resistance was improved at least twice when the Mw of the SLP exceeded the Mw of the matrix polymer by more than 20%. As it was shown, the higher the Mw of the SLP, there will be an improved resistance to fissures of the mixture, for example, achieving an improvement of more than 30 times in Example 4D-4. Comparative Example 4D, which does not have the SLP, exhibited poor crack resistance (29 seconds), compared to the crack resistance achieved in the presence of an effective SLP. Table 2 Resistance to Crack Formation by Isopropyl Alcohol / Aqua Solvents (70/30), (distension = 1.5%) EXAMPLE 5 Preparations of Additional Components for Fractal Resistant Methacrylate Resin Mixtures A. Preparation of the methacrylate resin: Additional methacrylate resins were prepared from a monomer mixture consisting of 96.0% by weight of MMA and 4.0 % by weight of EA, by a continuous mass polymerization process, followed by pellet extrusion. The weight average molecular weight of the resin was 111,000. í. Preparation of the Single Layer Polymer Additive: A duplicate preparation of Example IB was made, as described in Ex. IB. The particles were similarly isolated and had an Mw of 655,000 and a particle size of 269 nm. C_¡_ Preparation of the Polymeric Additive of a Layer: An SLP was prepared in a manner similar to that of Example IB, except that the initial water loading was 1297 g, the initial monomer emulsion contained 0.173 g of n-dodecyl mercaptan (DDM) and the monomer emulsion , added gradually, contained 1,557 g of DDM. The particles were similarly isolated and had an Mw of 259.00 and a particle size of 284 nm. D. Preparation of the Layer Polymer Additive: An SLP additive was prepared in a manner similar to that of Example IB, except that the initial charge of deionized water was 918.6 g, the initial monomer emulsion contained 4.33 g of dodecyl Sodium benzenesulfonate and 91.4 g of deionized water and the monomer emulsion, added gradually, contained 38.93 g of sodium dodecylbenzenesulfonate and 642.57 g of deionized water. The particles were similarly isolated and had an Mw of 581.00 and a particle size of 135 nm. E. Preparation of the Single-Layer Polymer Additive: A polymeric additive was prepared in a manner similar to that of Example IB, except that the initial charge of deionized water was 916.43 g, the initial monomer emulsion contained 0.173 g of the n-dodecyl -mercaptan, 4.33 g of sodium dodecyl-benzenesulfonate and 91.4 g of deionized water and the monomer emulsion, added gradually, contained 1,557 g of n-dodecyl mercaptan, 38.93 g of sodium dodecylbenzenesulfonate and 642.57 g of deionized water. The particles were similarly isolated and had an Mw of 243,000 and a particle size of 154 nm. Example 6 Preparation of Additional Methacrylate Mixtures, Resistant to Cracks. A series of fissure resistant formulations were prepared by dry blending the materials of Example 5 in the ratios shown in Table 3. These blends were melt compounded in a 2.5 cm ventilated extruder. , of a single screw, at a temperature of 230-260 SC, to produce pellets by injection molding. The Izod bars of these Examples were molded from the pellets at 260 ° C, providing Examples (6A-6E). The strain tests in these Examples were conducted as previously described, here at a distention of 1.0% with a ratio of 70/30 isopropanol / water (by weight). Table 3 Fracture Resistance in Isopropyl Alcohol / Aaua (70/30), (distension = 1.0%) The data summarized in Table 3 demonstrates that all four additives (5B-5E) impart crack resistance in solvents to the methacrylate matrix polymer defined by Example 5A. In this series, the higher molecular weight additives proved to be more effective than the lower molecular weight additives, and the additives with smaller particle sizes were more effective among the high molecular weight set (6B to 6D), providing excellent times of crack resistance of more than 10 times over the comparative example that does not have SLP: Example 7 Preparation of Additional Resins for Blends of Resistant Methacrylate Resins A_j_ Preparation of methacrylate resin of 60 MMA / 40 BMA: prepared an additional methacrylate resin from a monomer mixture consisting of 60.0% MMA and 40.0% BMA, by the continuous mass polymerization process, followed by pellet extrusion. The Mw of the resin was 162,000. B. Preparation of the 80 MMA / 20 BMA methacrylate resin: An additional methacrylate resin was prepared from a monomer mixture consisting of 80.0% MMA and 20.0% BMA, by the continuous mass polymerization process, followed by extrusion to pellets. The weight average molecular weight of the resin was 163,000. EXAMPLE 8 Preparation of Additional Fracture Resistant Methacrylate Mixtures A number of formulations for the fissure strength test were prepared by dry blending the resins of Example 7 with the SLP of Example 5D, in the ratios shown in Table 4 These mixtures were composed by melting in a 2.5 cm ventilated extruder. , of a single screw, at a temperature of 230 - 2602C, to produce pellets by injection molding. The Izod bars were molded from the pellets at 260SC, supplying Examples 8A-8D. The distension tests in these examples were conducted as previously described, here a distention of 1.0% with 70/30 isopropanol / water. Table 4 Crack resistance in isopropanol / acrua (70/30) (distension = 1.0%) These data demonstrate that the aggregate SLP showed some effect in improving the crack resistance of methacrylate resins containing high levels of the comonomer, here 40% and 20% BMA, respectively. Thus, the resin 7A was improved more (about 3 times) than the resin 7B (less than 2 times) by this particular mixture combination with the particles of the SLP of Example 5D. EXAMPLE 9 Preparation of Additional Resins for Testing Mixtures of Resistant Methacrylate Resins A. Preparation of the methacrylate resin: An additional methacrylate resin was prepared from a monomer mixture consisting of 96.0% MMA and 4.0% EA, by a continuous process of mass polymerization, followed by pellet extrusion. The Mw of the resin was 110,000. B. Preparation of the methacrylate resin: An additional methacrylate resin was prepared from a monomer mixture consisting of 97.0% MMA and 3.0% EA, by a continuous mass polymerization process, followed by pellet extrusion. The Mw of the resin was 198,000. The size of "particles" (pellets) of this material was approximately 2.0 mm. Comparative Example 9 Preparation of Additional Methacrylate Mixtures to Test Fissure Resistance A set of formulations was prepared to test the crack resistance of resin mixtures having the SLP-type component, with particle size greater than 500 nm, by dry mixing 15.0% of the resin of Example 9B with 85.0% of the matrix resin of Example 9A. The mixture was melt-compounded in a 2.5 c ventilated extruder. , of a screw, at a temperature of 230 - 260SC, to produce pellets by injection molding. The Izod bars of Ex. 9A and this mixture were molded at 260SC, providing Comparative Examples 9A and 9B. The deformation tests in these examples were conducted as previously described, here of 1.0%, with a ratio of 70/30 isopropanol / water (by weight). The results are shown in Table 5. Table 5 Crack resistance in Isopropanol / aqua // 70/30 (distension = 1.0%) These results showed that some degree of improvement in crack resistance occurred when the particle size of the higher molecular weight additive was significantly greater than 500 nm, but the crack resistance was much lower than that achieved with SLP particles having a composition similar to that of Resin 9B, but with a diameter particle size < 500 (such as, Examples 1C and 4D-3). EXAMPLE 10 Preparation of Additional Components for Fracture Resistant Methacrylate Resin Mixtures A. Single Layer Polymer Preparation: An SLP of 60 MMA / 40 BMA was prepared in a manner similar to that of Example IB, except that the loading of The bead contained 103.8 g of MMA and 69.2 g of BMA and the emulsified monomer mixture, gradually added, contained 934.2 g of MMA and 622.8 g of BMA. The particles were similarly isolated as in Ex. IB and had an Mw of 694,000 and a particle size of 269 nm. B. Preparation of a Single Layer Polymer: An SLP of 80 MMA / 20 BMA was prepared in a manner similar to that of Example 10A, except that the bead filler contained 138.4 g of MMA and 34.6 g of BMA and the gradually added emulsified monomer mixture contained 1245.6 g of MMA and 311.4 g of BMA. The particles were similarly isolated and had an Mw of 649,000 and a particle size of 274 nm. EXAMPLE 11 Preparation of Additional Fracture Resistant Methacrylate Mixtures A series of fissure resistant formulations was prepared by dry blending the materials of Example 10 and the MMA / BMA copolymers of Examples 7A and 7B, in the relationships shown in Table 6. These mixtures were melt compounded in a 2.5 cm ventilated extruder. of a screw, at a temperature of 230-2602C, to produce pellets by injection molding. The Izod bars of these examples were molded from the pellets at 260SC, supplying Examples 11A-11D. The strain tests in these examples were performed as previously described, here at a 1.0% distension with the 70/30 mixture of isopropanol / water (by weight). Table 6 Crack Resistance in Isopropanol / Water (70/30) (distension = 1.0%) These data show that the matrix (7A) with 60/40 // MMA / BMA was more responsive to the improvement of the crack resistance than the resin (7B) of the matrix of 80/20 // MMA / BMA. The effect of adding the SLP (here, of the same composition of the copolymer as the matrix resin) is clear from the above results, even in mixtures with etasrilato resins of compositions generally poor in the resistance to solvent cracks (due to its high content of the BMA). Thus, the presence of SLP particles with the methacrylate matrix resin showed an almost twofold improvement in crack resistance in the 11D mixture and a 10 fold improvement in the mixture of Example 11B over the resistance value fissures of the single resins of the respective methacrylate matrix.

Claims

CLAIMS 1. A composition of methacrylate resin blends, which comprises: a) from 50 to 99 weight percent of a methacrylate matrix resin, derived from monomer units comprising at least 50 weight percent of methyl methacrylate and, optionally, up to 50 weight percent of at least one monoethylenically unsaturated monomer unit, selected from the group consisting of the alkyl acrylate C ^ -Cg, C2-C4 alkyl methacrylate, styrene and Acrylonitrile the methacrylate matrix resin has a weight average molecular weight of at least 85,000 daltons; and b) from 1 to 50 weight percent of particles of a single layer polymer, derived from monomer units comprising at least 50 weight percent of methyl methacrylate and, optionally, up to 50 weight percent of at least one monoethylenically unsaturated monomer unit, selected from the group consisting of C 1 -Cg alkyl acrylate, C 2 -C 6 alkyl methacrylate, styrene and acrylonitrile; the one-layer polymer has a weight-average molecular weight of at least 120% of the weight average molecular weight of the methacrylate matrix resin and the one-layer polymer particles have a diameter of 50 to 500 nanometers.
2. The composition of the methacrylate resin mixtures according to claim 1, wherein the resin of the methacrylate matrix has a weight-average molecular weight of 85,000 to 120,000 daltons, and the one-layer polymer has a weight-average molecular weight of 105,000. to 1,000,000 daltons.
3. The composition of the methacrylate resin mixtures according to claim 1, wherein the one-layer polymer and the methacrylate matrix resin are independently derived from at least 85 percent by weight of the methyl methacrylate.
The composition of the methacrylate resin mixtures according to claim 1, wherein the one-layer polymer and the resin of the methacrylate matrix are independently derived from at least 90 weight percent methyl methacrylate and the C ^ -Cg alkyl acrylate is selected from methyl acrylate, ethyl acrylate and butyl acrylate, and the C2-C4 alkyl methacrylate is butyl methacrylate.
5. The composition of the methacrylate resin mixtures according to claim 1, wherein the improved solvent crack resistance of the mixture is at least 2 times greater than the value of the crack resistance of the matrix resin. of methacrylate.
6. A molded article comprising the composition of methacrylate resin mixtures according to claim 1.
7. The composition of the methacrylate resin mixtures according to claim 1, further comprising particles of a multilayer acrylic polymer.
The composition of the methacrylate resin mixtures according to claim 7, wherein the particles of the multilayer acrylic polymer comprise from 10 to 40 parts per hundred, based on the mixture of methacrylate resins, in which this mixture of methacrylate resins comprises from 80 to 95 percent of the methacrylate matrix and from 5 to 20 percent of the one-layer polymer.
9. A molded article, comprising the composition of methacrylate resin mixtures, according to claim 7.
10. A method for improving the resistance to solvent cracks of a methacrylate matrix resin, this method comprises the steps of : a) adding to a methacrylate matrix resin, derived from monomer units of at least 50 weight percent methyl methacrylate and, optionally, up to 50 weight percent of at least one monomer unit, unsaturated monoethylenically, selected from the group consisting of the C 1 -C alkyl acrylate, C 2 -C 4 alkyl methacrylate, styrene and acrylonitrile. the methacrylate matrix resin has a weight average molecular weight of at least 85,000 daltons; and particles of a one-layer polymer, derived from monomer units comprising at least 50 percent by weight of methyl methacrylate and, optionally, up to 50 percent by weight of at least one unit of monoethylenically unsaturated monomer , selected from the group consisting of the alkyl acrylate C ^ Cg, C2-C4 alkyl methacrylate, styrene and acrylonitrile; the particles of the one-layer polymer are added in an amount of 1 to 50 percent by weight, based on the combined weight of the resin of the methacrylate matrix and the single-layer polymer particles, this one-layer polymer has a weight average molecular weight of at least 120% of the weight average molecular weight of the methacrylate matrix resin and the single layer polymer particles have a diameter of 50 to 500 nanometers. and b) the melt mixture of the methacrylate matrix resin contains the particles of the SLP to form a mixture of these particles of the SLP and the matrix resin, in which this mixture has a value of resistance to cracks by solvents, of at least twice the value of the solvent crack resistance of the methacrylate matrix resin.