MXPA98010702A - Polymeric compositions of high brightness, high resistance to fissures by environment tension and high resistance to impact - Google Patents

Abstract

Se suministra una composición polimérica, la cual exhibe una combinación de alto brillo y alta resistencia a fisuras de tensiones ambientales, esta composición comprende:(a) un poliestireno de alto impacto, que tiene un brillo a 60 grados mayor del 85%y una resistencia al impacto mayor de 3.81 m-kg/cm;(b) un polietileno de alta densidad, el cual tiene una densidad mayor o igual a aproximadamente 0.94 g/cm2, y el cual tiene un exponente de tensión menor o igual a aproximadamente 1.70;y (c) un polímero compatibilizador para los componentes (a) y (b), seleccionado del grupo que consta de copolímeros de dos bloques de estireno y butadieno, copolímeros de tres bloques de estireno y butadieno, copolímeros de dos bloques de estireno e isopreno, copolímeros de tres bloques de estireno e isopreno;en que el brillo a 60 grados de la composición es mayor o igual a aproximadamente el 85%y la resistencia a la fisura de tensión ambiental, medida en minutos hasta la ruptura a 70 kg/cm2, es mayor de aproximadamente 60.

Description

POLYMERIC COMPOSITIONS PE HIGH GLOSS, HIGH RESISTANCE TO GREEN ENVIRONMENTAL STRESS YALTA IMPACT RESISTENCE The present invention relates to polymeric compositions that exhibit a combination of high gloss and high crack resistance due to environmental stress, especially to high impact polystyrene compositions. More particularly, the invention relates to high impact polystyrene compositions, containing vinyl aromatic polymers, modified with rubber, and certain particular polyolefins, to molded and thermally formed articles, obtained from such compositions, and methods for their production. Also, the invention relates to compounds with a gloss finish layer, obtained from the polymeric compositions, and to methods for their manufacture.

BACKGROUND It is well known to obtain high gloss compositions from vinyl aromatic polymers, modified with rubber, such as, for example, high impact polystyrene. A disadvantage of such compositions, however, is that they are very susceptible to stress cracking, as they are exposed to oils, fats, detergents or environmental cleaners. Thus, the known compositions are deficient in the property of resistance to the formation of fissures by environmental stresses, although they have good gloss properties. The crack resistance by environmental stresses of such compositions has been addressed in the prior art. For example, in patent US 5543461, the resistance to environmental stress cracking of impact modified styrenic polymers has increased, increasing the particle size of the impact modifier, and in US Patent 4144204, high impact polystyrene compositions. , with increased resistance to environmental stress cracks occurred, in which the rubber particles have a diameter of at least 4 microns. In US patent 4939207, mixtures of a vinyl aromatic polymer, a polyolefin, a star block copolymer of a vinyl aromatic monomer and a conjugated diene, are provided with good chemical resistance. However, in all the examples of the prior art, the high gloss properties of the resulting compositions are lost. As a result, the known compositions do not provide high impact polystyrene compositions, which exhibit a combination of both high gloss and a desired resistance to the formation of environmental stress cracks. Such compositions will be particularly advantageous for the thermal formation or sheet extrusion as a gloss finish layer on a co-extruded sheet for good packing applications or a refrigerator liner or, for example, as molded articles, such as the microtelephonic devices subject to attack by natural oils on the skin.

SUMMARY OF THE INVENTION According to the invention, a polymer composition is provided which exhibits a combination of high gloss and high resistance to the formation of environmental stress cracks, which comprises: (a) an aromatic vinyl polymer, modified with rubber high gloss; and (b) a polyolefin, which has a stress exponent less than 1.70, in which the 60 degree gloss of the composition is greater than about 85%, and the environmental stress crack resistance, measured in minutes to rupture , at 70 kg / cm2 is greater than about 60. Surprisingly, it has been found that when a particular polyolefin (b), which has a tensile component of less than 1.7 is used, the resulting composition has an advantageous combination of high gloss and a desired level of resistance to stress cracks.

Advantageously, the polymer composition further comprises a compatibilizing polymer (c). In another embodiment, the polymer composition further comprises a low gloss polymer (d). The invention also supplies molded thermoplastic articles, obtained from the previous polymer composition. In addition, an extruded thermoplastic sheet of the above composition is supplied, as well as the thermally formed articles of this sheet. Also, a multilayer thermoplastic composite is provided, comprising a substrate layer and a gloss finish layer, obtained from the above polymer composition. In addition, methods are provided to obtain the aforementioned articles, sheets and composites.

DESCRIPTION OF THE DRAWINGS Figure 1 is a diagram of the melt index-type environmental stress cracking resistance (ESCR) measuring device used to measure this resistance to environmental stress cracks.

DETAILED DESCRIPTION OF THE INVENTION The composition of the invention includes an aromatic vinyl polymer (a), modified with high gloss rubber, a polyolefin (b) having a tension component of less than 1.70, and a compatibilizing polymer (c). The particular aspects of each will now be discussed in detail. (a) Vinyl aromatic polymer, modified with high gloss rubber The vinyl aromatic polymers modified with rubber, of the invention, comprise a polymer matrix, in which the elastomeric polymer particles are dispersed. They are characterized by having a surface brightness at 60 degrees, greater than 85%, preferably greater than 90%. The impact strength of the rubber modified vinyl aromatic polymers of the invention will generally be greater than 3.81 m-kg / cm, as measured by the Izod slotted impact test. Preferably, the impact strength will be greater than 6.53 m-kg / cm and more preferably greater than 10.89 m-kg / sm. A preferred polymer matrix comprises styrene. Such compositions are typically described as high impact polystyrene or HIPS. More generally, suitable rubber-modified vinyl aromatic polymers include modified rubber homo-polymers of C6-C20 vinyl aromatic monomers, rubber-modified copolymers of two or more such rubber modified monomers and copolymers. or more of these monomers with up to 25 weight percent of a copolymerizable comonomer, in addition to a vinyl aromatic monomer. Examples of suitable vinyl aromatic monomers are styrene, vinyl toluene, alpha-methyl styrene, t-butyl styrene and chlorostyrene. Examples of suitable copolymerizable comonomers, in addition to the vinyl aromatic monomer, are N-phenyl-maleimide, acrylamide, maleic anhydride, acrylic acid, n-butyl acrylate and methyl methacrylate. Suitable elastomeric polymers, used to modify the impact properties of the above vinyl aromatic polymers, are those having a glass transition temperature less than 0 ° C, preferably less than -20 ° -c. Examples of suitable elastomeric polymers are the homopolymers of C4-C6 1,3-dienes, especially butadiene or isoprene, copolymers of one or more vinyl aromatic monomers and one or more C4-C6 1,3-diene, especially butadiene or isoprene; copolymers of ethylene and propylene or of ethylene, propylene and a non-conjugated diene, especially 1,6-hexadiene or ethylidene-nor-bornene; C4-C6 alkyl acrylate homopolymers; copolymers of C4-C6 alkyl acrylates and copolymerizable comonomers, especially an aromatic vinyl monomer or a C1-C4 alkyl methacrylate. Also included are the graft polymers of the above elastomeric polymers, in which the graft polymer is an aromatic vinyl polymer. A preferred vinyl aromatic monomer for use in all the above elastomeric polymers is styrene. Preferred elastomeric polymers are based on 1,3-dienes, in that they are homopolymers or copolymers of one or more monomers having a 1,3-conjugated diene structure. A more preferred eleastomeric polymer is polybutadiene or a copolymer of styrene and butadiene, or a combination of such polymers. The above elastomeric polymers can be prepared by anionic polymerization techniques in solution or by processes of solution, mass, emulsion or suspension initiated from free radial. The elastomeric polymers prepared by the emulsion polymerization can be agglomerated to produce larger particles, having a bimodal or trimodal particle size distribution, etc., if desired. Aromatic vinyl polymers modified with rubber are well known in the art and are commercially available. A highly preferred vinyl aromatic polymer is polystyrene and the modified impact polymer is polystyrene at a high temperature. A high-impact, high-impact polystyrene is prepared by the bulk solution or polymerization technique and contains from 5 to 15 (more preferably from 6 to 9) percent by weight of polybutadiene rubber. Highly-preferred high-impact polystyrenes are those in which the polystyrene matrix has a weight-average molecular weight, MW, of 100,000 to 300,000 (preferably from 120,000 to 240,000 and more preferably from 150,000 to 325,000), the molecular weights were determined by gel permeation chromatography, which employs a polystyrene standard. Suitable modified rubber polymers are prepared by mixing the elastomeric polymer are the matrix polymer, prepared previously, having the desired chemical composition, by the graft polymerization of the matrix, in the presence of a previously dissolved elastomeric polymer, or by a combination of such techniques Preferably, the rubber-modified vinyl aromatic polymers are prepared by dissolving the elastomeric polymer in one or more monomers, optionally in the presence of a solvent or diluent and polymerizing the resulting solution, conveniently while stirring the solution , so as to prepare an impact modified, grafted, dispersed polymer having particles containing occlusions of the dispersed matrix polymer completely through the resulting polymer matrix. Such rubber-modified polymers, known as high impact polymers, polymerized in bulk or solution, are well known in the art and are commercially available. Additional amounts of the elastomeric polymer, especially the elastomeric emulsion polymers, may be mixed in the vinyl aromatic polymer, modified with rubber, if desired. The dispersed particles of the aforementioned elastomeric polymers can be characterized as having an average diameter. As used herein, the average diameter refers to the average volume diameter, determined by a Horiba CAPA700 particle size analyzer. In general, as the average diameter of the dispersed particles decreases, the brightness of the resulting composition increases. In a particularly preferred embodiment of the invention, the vinyl aromatic polymer, modified with rubber, comprises a polystyrene matrix, in which the dispersed elastomeric polymer particles, having an average diameter of less than about 1.0 miera. Preferably, the average diameter is less than 0.8 miera, and more preferably less than about 0.6 miera. The diameter of the particles is preferably greater than about 0.1 miter and more preferably greater than about 0.2 miera. An example, commercially available, is the Polystyren 525K, sold by BASF Corporation.

The dispersed elastomeric polymer particles are characterized by a particle size distribution. This particle size distribution is often represented by a plot of the weight of the particles present, as a function of the average diameter of the particles. The weight of the particles present can be expressed in any absolute unit or in relative terms, and can represent any total weight or fraction of weight. The terms monomodal, bimodal and trimodal, are used to describe graphs of the particle size distribution, which have one, two and three, etc. , separated crests, respectively. The term multimodal is used as a general term for the bimodal, trimodal and major terms. The peaks or maxims of the graphs correspond to the average diameters of the particles present in the composition. The rubber modified vinyl aromatic polymers, (a), of the present invention, may have monomodal or multimodular particle size distributions. In a preferred multimodal distribution, a first maximum in the particle size distribution graph corresponds to particles with an average diameter smaller than one miera, while a second maximum corresponds to particles with an average diameter greater than one miera. More preferably, the second maximum corresponds to particles with an average diameter greater than 2 microns. In a preferred embodiment, the particle size represented by the second maximum is less than 10 microns and, more preferably, less than 8 microns. Larger particles are present in smaller amounts than small particles. Preferably, the larger particles are present in less than 20%, based on the total weight of the particles. More preferably, they are present in less than 10% and more preferably in less than 6%. If the larger particles are present, they are preferably 1% or more of the total weight of the particles, preferably more than about 3%. The rubber modified vinyl aromatic polymers, (a), which have multimodal particle size distributions, can be prepared by polymerizing the aromatic vinyl monomers in the presence of elastomeric polymer particles, which have the desired distribution, also they can be prepared by mixing or stirring vinyl aromatic polymers, individually modified with rubber, each with monomodal distributions. An example of a bimodal distribution is an aromatic vinyl polymer, modified with rubber, according to the invention, is disclosed in patent US 4493922, incorporated herein by reference. (b) Polyolefin The polyolefin of the invention is preferably an ethylene homopolymer or copolymer. If it is an ethylene copolymer, it will preferably be a copolymer of ethylene with one or more other olefinic monomers having from 3 to 10 carbon atoms, named C3-C10 monomers. Examples of C3-C10 monomers are olefins, such as propylene, butene, hexene, octene and decene. The C3-C10 monomers are generally present at up to 20 weight percent, based on the total weight of the olefin. Preferably, the C3-C10 monomers are present at a maximum of 10% by weight and more preferably the maximum is 6% by weight. The C3-C10 monomers are present at a minimum of 1% by weight and preferably at least 3% by weight. In general, polyolefins suitable for use in the invention have a voltage exponent less than about 1.70. The stress exponent was determined by measuring the output of a melting indicator at two voltages (load of 2160 g and 6480 g) with the use of ASTM melt index test method procedures, and calculating the stress exponent, according to with the following formula: Tension exponent = (1 / 0.477) x log (extruded weight with 6480 g weight / weight extruded with 2160 g weight.) It is generally believed that the voltage exponent values of less than about 1.5 indicate a molecular distribution of that relatively narrow, while values above about 1.7 indicate a relatively broad molecular weight distribution. The formula of the stress exponent can be manipulated algebraically to a form that can be interpreted more easily: Tension exponent = 1.00 + (1 / 0.477) log (extruded weight with 6480 g of weight / 3 x extruded weight with 2160 g of weight) From this formula, it is seen that when the weight extruded at a higher pressure is three times that extruded at a lower pressure, then the log term is equal to zero, and the voltage exponent is 1.00. This corresponds to the Neonian flow - at 3 times the pressure, the flow is three times greater. Deviations from the Newtonian flow will cause the amount extruded at the higher pressure to exceed the amount extruded at the lower pressure by a factor greater than the ratio of the higher pressure to the lower pressure. In that case, the voltage exponent will be greater than 1.0 and will increase as the flow of the higher pressure increases. It has been found that polyolefins having a low stress exponent, an empirically determined cut-off point can be caused in the present invention, to deliver compositions having a combination of high gloss and a suitable stress cracking resistance . Thus, in general, poly-olefins suitable for use in the invention will have a voltage exponent less than about 1.70. The most preferred polyolefins have a stress exponent less than about 1.30. Polyolefins with intermediate values of the stress exponent, such as 1.60, 1.50 and 1.40, will generally be preferred to polyolefins of strain exponent of 1.70. The density of the polyolefin can be selected over a wide range. In general, densities between approximately 0.88 g / cm3 and 0.96 g / cm3 or greater can be selected, depending on the polymerization conditions and the catalysts used. It is preferred that the density of the polyolefin be greater than 0.915 g / cm3. More preferably, the density of the polyolefin is greater than 0.94 g / cm 3. Especially preferred, the density is greater than 0.95 g / cm3. It is believed that the higher the density of the polyolefin, the greater will be its effect in increasing the crack resistance of the environmental stress of the resulting composition. Therefore, it is expected that if a relatively lower density, in the preferred range, is selected, then relatively more polyolefin may be necessary in the resulting composition to achieve the desired strength of environmental stress cracks. A particularly preferred polyolefin is high density polyethylene with a density greater than 0.94 g / cm 3, preferably greater than 0.95 g / cm 3. These polyolefins are commercially available. Examples include Fortiflex® T-50-200 and Fortiflex® F-621S, sold by Solvay Polymers, and Petrothene LT 6194-69, sold by Millennium Petrochemicals, Inc. (c) Compatibilizing Polymer The compatibilizing polymer (c) is an interfacial agent, which is believed to have the ability to improve the adhesion between the vinyl aromatic polymer modified with rubber, and the polyolefin. Suitable compatibilizing polymers are readily determined by preparing a mixture of components (a) and (b) and comparing the physical properties, especially impact strength and ductility, with a similar mixture containing the compatibilizing polymer. Suitable compatibilizing polymers will generally produce an increase in both impact resistance and ductility. Preferably, such an increase in both properties is at least 10 percent, more preferably 20 percent. Conveniently, these polymers are elastomers, ie, polymers having a glass transition temperature (Tg) less than 0 ° C, preferably lower than -20 ° C, with a weight average molecular weight MW of 10,000 to 150,000, more preferably 20,000 to 100,000 and especially preferred from 50,000 to 100,000, as determined by gel permeation chromatography, with the use of a polystyrene standard. Preferred compatibilizing polymers are elastomeric polymers containing an aromatic vinyl monomer and a monomer other than an aromatic vinyl monomer, especially a C2-C18 alpha-olefin, or a conjugated or non-conjugated diene. Especially preferred are elastomeric, thermoplastic block copolymers of one or more vinyl aromatic monomers and one or more dienes "C4-C6 conjugates, in which the preferred vinyl aromatic monomer is styrene, and preferred diene monomers include butadiene, isoprene and mixtures thereof. It has been found that elastomeric block copolymers having a styrene content of % p plus, are particularly suitable as the compatibilizing polymer (c) Preferably, the styrene content will be 35% or more, and more preferably 40% or greater.All percentages are based on the weight of the total monomer present in the elastomeric block copolymer Such block copolymers include AB block copolymers, ABA three block copolymers, block and block copolymers, when tapered, partially tapered (ie the taper between them is less than all the blocks) or hydrogenated, and their mixtures An example of a preferred block copolymer is Vector 6241D, sold by Dexco Polymers It is a three-block copolymer, A-B-A, of styrene-butadiene-styrene, with 43% by weight of styrene, and a MW molecular weight of 63,000. (d) Low-gloss polymer In addition to the high-gloss, rubber-modified vinyl aromatic polymers, (a), the polymer compositions of the invention may advantageously contain relatively minor amounts of vinyl aromatic polymers, modified with rubber, which have a reduced surface gloss, relative to high gloss polymers (a). A low gloss polymer, especially preferred, is high impact, low gloss polystyrene, or low gloss HIPS. Typically, the preferred low gloss HIPS will have a surface brightness at 60 degrees less than 85%. A low gloss HIPS is characterized by larger diameter elastomeric polymer particles, which are dispersed in the polystyrene matrix, which is the case with high gloss HIPS. Larger particle sizes, in turn, lead to compositions that have a higher impact resistance. Preferably, the average particle diameter of the low gloss HIPS will be greater than one miera. More preferably, the diameter will be greater than two microns. A preferred low gloss HIPS will have particles with an average diameter between 2 and 8 microns. It is thus seen that the particle diameter is preferably less than 8 microns. Thus, it has been found that up to 20%, based on the total weight of the polymer composition, of the low-gloss rubber modified polymer can be added, in order to raise the impact resistance of the compositions. resulting Preferably, the amount will be less than 10% and more preferably less than 6%. The polymer compositions with a combination of high gloss and high resistance to environmental stress cracks are formulated from components (a), (b), (c) and optionally (d), above. The compatibilizing polymer (c) will be present in an amount effective to compatibilize the components (a) and (b). In general, this will be approximately 1 to 30% by total weight of components (a), (b) and (c). Preferably, the compatibilizer polymer (c) will be present at 2 to 25 weight percent and more preferably 3 to 20 weight percent, based on the total weight of components (a), (b) and (c) ). The polyolefin (b) is present in an amount sufficient to raise the strength of environmental stress cracks to an acceptable level. In general, this amount will be greater than 10%. Preferably, the content of component (b) is about 15% or more and more preferably greater than or equal to 20%. On the other hand, high levels of the polyolefin (b) tend to decrease the stiffness of the final composition of its optimum level. For this reason, the level should generally be less than 50% by weight. It is preferred that the level be less than 40%. More preferably, the level of the polyolefin (b) will be less than 35%. All percentages are percentages by weight, based on the total weight of components (a), (b) and (c). The rest of the composition will be composed of the vinyl aromatic polymer, modified with rubber, (a). Thus, the content of (a) will vary from a minimum of 30% to a maximum of approximately 94% by weight. A preferred range is 50% to 88%, while the most preferred range will be 60 to 81% by weight. Again, all percentages are by weight, based on the total weight of components (a), (b) and (c). As mentioned above, component (d) may optionally be present at a level up to about 20%, based on the total weight of the composition of components (a), (b), (c) and (d). Component (d) is preferably present at 10% or less, and more preferably at 6% or less, the percentages are again based on the total weight of the composition of components (a), (b), ( c) and (d). Alternatively, other additives may be added to the polymer compositions of the invention. Examples include dyes, antioxidants, mold release agents, antistatic agents, and the like. Components (a), (b), (c) and other optional additives can be composed of any conventional resource. These compositional resources are well known in the art and are described, for example, in the handbook of Meadows Ed. Plastics Engineering Handbook, 4th Edition, Chapter 29, pages 848-858. For example, they can be compounded and extruded in a single screw Brabender apparatus, at a temperature between 180 and 240 ° C. Articles, which include the test specimens, can be molded from the compositions with the use of conventional injection molding or compression molding techniques, as described in the Frados manual, Ed. Plastics Enaineerin Handbook, 4th Edition, Chapter 4, pages 83-104. For example, the articles can be molded in a screw type injection molding machine, at a material temperature between 180 and 250 ° C, and a mold temperature between 20 and 70 ° C. The articles can also be obtained by conventional thermal forming techniques. For example, a composition comprising components (a), (b) and (c) is extruded into a thermoplastic sheet. Next, the sheet is thermally formed in the desired configuration, according to known techniques, such as those described in the Ed. Plastics Handbook Encrineerinq Handbook, 4th Edition, Chapter 12, pages 273-325. Advantageously, a multilayer thermoplastic composite can be provided, wherein an outer layer of the compound comprises a composition of the invention, described above. In one mode, a composition of the components (a), (b) and (c) can be co-extruded with a thermoplastic layer of the substrate, to form a co-extruded sheet. Alternatively, components (a), (b) and (c) can be extruded into a thermoplastic sheet, which is then laminated onto a thermoplastic layer of the substrate. This thermoplastic layer of the substrate preferably has the high stiffness and impact resistance desired, so that the resultant multilayer thermoplastic composite will be rigid and impact resistant. The thermoplastic layer itself of the substrate may comprise more than one layer and the multilayer thermoplastic composite may comprise additional layers, without departing from the scope of the invention. A preferred substrate thermoplastic layer is a low gloss HIPS. In such a case, the high gloss compositions, described above, will form a brightness over the low gloss HIPS of the substrate. This is advantageous, because the low gloss HIPS of the substrate is less expensive than the high gloss compositions and can therefore be economically used as a core layer to provide superior stiffness and impact resistance, while the The gloss finish obtained from components (a), (b) and (c), provide superior surface gloss properties and a suitable resistance to environmental stress cracks. One more advantage of the fact that the shine finish made of the components (a), (b) and (c), is itself based on the fact that HIPS or HIPS-like compounds have an increased adhesion to the HIPS substrate in relation to that of the other gloss finishes obtained, for example, from polyolefins or of another high-gloss thermoplastic material, such as ABS. The multilayer, sheet-shaped thermoplastic composite can be transformed by conventional means, as described above. The resulting thermally formed articles are advantageous for use in refrigerator liners or as food packages, where a combination of high gloss and convenient resistance to environmental stress cracks is required. The polymer compositions of the invention have a brightness at 60 degrees greater than 85% and preferably greater than 90%. The brightness at 60 degrees was measured in accordance with ASTM D523. The invention is also characterized by a resistance to environmental stress cracks, measured in minutes, up to rupture, at 70 kg / cm2, of greater than about 60. This resistance of environmental stress cracks was measured with the ESCR apparatus of melt index cord, shown in Figure 1. A cord 12 of the melt index of the material to be tested is held between the retaining clips 14 and 15 of the cord. A weight 18 is attached to the retaining clip 15 of the bottom. The diameter of the bead of the melt index and the mass of the weight are selected such that the pressure in the bead of melt index is 70 kg / cm 2. In a cup 16 fixed to the melt index cord, a mixture of 50% by weight of cottonseed oil and 50% by weight of oleic acid was placed, and the timer 22 was started. The test proceeded until the cord 12 was broken and the weight 18 fell on the micro-switch 20. This event stopped the timer 22. The elapsed time, in minutes, between the start and the end of the test was read from the stopwatch and was presented as minutes for the rupture with a pressure of 70 kg / cm2.

EXAMPLES The following materials were used in the examples: Fortiflex T-50-200, is a high density polyethylene, sold by Solvay Polymers. It has a density of 0.953 g / cm2 and a melt index of 2.4. The voltage exponent is 1.26. Fortiflex F-621S is a high density polyethylene, sold by Solvay Polymers. It has a density of 0.953 g / cm2 and a melt index of 1.1. The voltage exponent is 1.22. Dow 12065 is a high density polyethylene sold by Dow Chemical. It has a density of 0.965 g / cm2 and a melt index of 0.9. The voltage exponent is 1.72. Quantum LT 6194 is a high density polyethylene, sold by Millennium Petrochemicals, Inc. It is currently sold under the name of Prtothee LT 6194-69. It has a density of 0.96 g / cm2 and a melt index of 1.1. The voltage exponent is 1.68. HIPS-A is a high-gloss, high-impact HIPS with a bimodal particle size distribution. It has a surface brightness at 60 degrees of 93% and an Izod impact of 10.89 m-kg / cm. It is a blend of 96% high gloss HIPS with a rubber particle size of 0.2-0.8 microns, and 4% low gloss HIPS, with a rubber particle size of 2-6 microns. HIPS-B is a HIPS of medium brightness. It has a surface brightness at 60 degrees of 71% and an Izod impact of 17.42 m-kg / cm. HIPS-C is a HIPS of high brightness, medium impact. The rubber particles have a diameter of 0.2-0.8 microns. It has a surface brightness at 60 degrees of 96% and an Izod impact of 5.44 m-kg / cm. HIPS-D is a low gloss HIPS. The rubber particles have a diameter of 3-4 microns. The brightness at 60 degrees is 25% and the Izod impact at 10.88 m-kg / cm. Vector 624ID is sold by Dexco Polymers. It is a three-block copolymer, styrene-butadiene-styrene, with 43% by weight of styrene, and a MW molecular weight of 63,000. The physical properties in the examples were measured using injection molded test specimens, as follows: RFF 200 ac / 5 kg is the melt flow value, measured in accordance with ASTM D1238. The Izod is Izod slot-do impact resistance, measured in accordance with ASTM D256. Gardner is Gardner impact strength, as measured by ASTM D3029.

Vicat is the Vicat softening temperature, measured by ASTM D1525. The tensile elasticity, tensile rupture, modulus to tension and elongation to tension, were measured in accordance with ASTM D638. The brightness, 60 degrees, was measured on 3,175 mm thick injection molded discs, in accordance with ASTM D523. It is expressed as a percentage of reflectance. MIS-ESCR, min. 50/50 CO / OA, 70 kg / cm2, are the minutes until the rupture at 70 kg / cm2, measured according to the test procedure indicated schematically in Figure 1, when a 50/50 mixture of seed oil of cotton and oleic acid was applied to the melt index cord. The stress exponent was determined by measuring the production of the melting indicator at two voltages (2160 g and 6480 g load) using the procedures of the melt index test method and with the following formula: Tension exponent = (1 / 0.477) x log (extruded weight with 6480 g of weight / weight extruded with 2160 g of weight) In the following examples, the components were composed in a 1.905 cm single screw Brebander apparatus, at a temperature of 2002C. The test specimens were molded from the compositions in an Arburg laboratory machine of 794 grams, at a material temperature of 238 se and a mold temperature of 66 ° C.

Examples 1-4 These examples demonstrate the calculation of the polyolefin stress exponent (b) of the melt flow rate measurements at two different loads, expressed in g / 10 minutes, according to ASTM D1238. Example 3 shows that Dow 12065, a high density polyethylene, from Dow Chemical, has a voltage exponent, which is outside the scope of the invention.

RFF = Fusion Flow Regime Examples 5-9 These examples show the effect of the different polyolefins within and outside the scope of the invention on the gloss, ESCR and impact strength properties of the resulting compositions. Example 5 shows that HIPS-A has a brightness at 60 degrees of 93%, within the scope of the invention. His ESCR is very low, only 12 minutes until rupture at 70 kg / cm. Example 6 shows that adding component (c) alone has little effect on the ESCR or brightness. Example 7 shows a polyolefin (b), within the scope of the invention (Fortiflex T-50,200). The resulting composition has a brightness of 90% and the ESCR has been raised to 390 minutes. It is thus within the scope of the invention. Example 8 shows that a polyolefin (B), outside the scope of the invention, produces a polymer composition of insufficient gloss to achieve the object of the invention. Example 9 is another example of a polyolefin (b) within the scope of the invention. Note that the resulting brightness and ESCR values are within the invention.

EXAMPLES? -15 Examples 10 and 11 illustrate that if the polymer (a) modified with rubber, has a brightness lower than 85% (Example 10), then the resulting polymer composition will not have a high enough brightness to be within the scope of the invention (Example 11). Examples 12 and 13, on the other hand, show the results when an aromatic vinyl polymer (a), modified with rubber, within the scope of the invention, is used - brightness above 85% and ESCR above 60 minutes. Example 15 shows the result of using a rubber modified polymer (a) with a bimodal particle size distribution - excellent brightness results and ESCR are achieved with the use of a polyolefin (b) within the scope of the invention.

Examples 16-23 These examples show that up to 20% of a HIPS with a particle size of 2 to 8 microns (exemplified by HIPS-D) can be added to the composition. Examples 18 to 21 show the effect of the amount of the polyolefin (b). A level of 15% is preferred to raise the strength of environmental stress cracks to a desired level, while a level of 20% is more preferred (Example 21).

Claims (33)

1. CLAIMS 1. A polymeric composition, exhibiting a combination of high gloss and high resistance to environmental stress cracking, this composition comprises: (a) a high-gloss, rubber-modified vinyl aromatic polymer, and (b) a polyolefin, having a stress exponent less than about 1.70, where the 60 degree gloss of the composition is greater than about 85%, and the environmental stress crack resistance, measured in minutes to rupture, at 70 kg / cm2, is greater than approximately 60.
2. 2. The composition of claim 1, wherein the polymer (a), modified with rubber, has a brightness at 60 degrees greater than 85%.
3. 3. The composition of claim 2, wherein the polymer (a), modified with rubber, has an impact strength greater than 3,810 m-kg / cm.
4. 4. The composition of claim 2, wherein the component (a) is a high impact polystyrene, comprising a polystyrene matrix having dispersed elastomeric polymer particles.
5. 5. The composition of claim 4, wherein the elastomeric polymers are based on 1,3-dienes.
6. 6. The composition of claim 5, wherein the elastomeric polymers are selected from the group consisting of polybutadiene, copolymers of styrene and butadiene, and mixtures thereof.
7. 7. The composition of claim 4, wherein the particles have an average diameter of less than about one.
8. 8. The composition of claim 7, wherein the particles have an average diameter of less than about 0.6 miera and greater than about 0.2 miera.
9. 9. The composition of claim 4, which comprises high impact polystyrene (a), which has a monomodal particle size distribution.
10. 10. The composition of claim 4, wherein the particles have a bimodal particle size distribution, with a first maximum corresponding to the particles of average diameter smaller than one miera, and with a second maximum corresponding to particles with larger average diameter of a miera.
11. 11. The composition of claim 10, wherein the second maximum corresponds to particles with an average diameter greater than 2 microns and less than 8 microns.
12. 12. The composition of claim 11, wherein the first maximum corresponds to particles with an average diameter greater than 0.2 miera and less than 0.8 miera.
13. 13. The composition of claim 4, wherein the polyolefin (b) comprises a copolymer of ethylene and one or more olefinic C3-C19 monomers.
14. 14. The composition of claim 4, wherein the polyolefin (b) comprises a high density polyethylene, with a density equal to or greater than about 0.94 g / cm.
15. 15. The composition of claim 1, wherein the component (b) has a tension component, which is less than or equal to about 1.40.
16. 16. The composition of claim 15, wherein the component (b) has a tension component, which is less than or equal to about 1.30.
17. 17. The composition of claim 1, further comprising a compatibilizing polymer.
18. The composition of claim 17, wherein the compatibilizer polymer is a block copolymer of aromatic vinyl monomers and diene monomers.
19. 19. The composition of claim 18, wherein the aromatic vinyl monomer is styrene, and the diene monomer is selected from the group consisting of isoprene, butadiene and mixtures thereof.
20. 20. The composition of claim 19, wherein the styrene content of the compatibilizing polymer is greater than or equal to 35 weight percent, based on the total weight of the monomers in the compatibilizing polymer.
21. 21. The composition of claim 20, wherein the styrene content of the compatibilizer polymer is less than or equal to 85 percent by weight, based on the total weight of the monomers in the compatibilizer polymer.
22. 22. The composition of claim 18, wherein the compatibilizing polymer is a two-block copolymer A-B
23. 23. The composition of claim 18, wherein the compatibilizing polymer is a three-block copolymer A-B-A.
24. 24. The composition of claim 18, wherein the compatibilizer polymer is a star block copolymer.
25. 25. A polymeric composition, exhibiting a combination of high gloss and high resistance to environmental stress cracking, this composition comprises: (a) a high impact polystyrene, having a brightness at 60 degrees greater than 85% and a resistance to impact greater than 3.81 m-kg / cm, which includes a modified polystyrene with rubber, which has rubber particles with an average diameter of less than about one miera; (b) a high density polyethylene, which has a density greater than or equal to about 0.94 g / cm2, and which has an exponent of less than or equal to about 1.70; and (c) a compatibilizing polymer for components (a) and (b), selected from the group consisting of copolymers of two blocks of styrene and butadiene, copolymers of three blocks of styrene and butadiene, copolymers of two blocks of styrene and isoprene , copolymers of three blocks of styrene and isoprene, and their mixtures; in which the 60 degree gloss of the composition is greater than or equal to about 85% and the resistance to environmental stress crack, measured in minutes until rupture at 70 kg / cm2, is greater than about 60.
26. 26. The The composition of claim 25, wherein the strain exponent of the high density polyethylene (b) is less than or equal to about 1.40.
27. 27. The composition of claim 26, wherein the tension component of the high density polyethylene (b) is less than or equal to about 1.30.
28. 28. The composition of claim 25, further comprising a low gloss HIPS, having rubber particles with a diameter greater than one miera.
29. 29. The composition of claim 28, wherein the low gloss HIPS has rubber particles with a diameter greater than 2 microns.
30. 30. The composition of claim 29, wherein the low gloss HIPS is present in an amount up to 20%, based on the total weight of the composition.
31. 31. The composition of claim 30, wherein the low gloss HIPS is present in an amount up to 10% by weight, based on the total weight of the composition.
32. 32. The composition of claim 31, wherein the low gloss HIPS is present in an amount up to 6% by weight, based on the total weight of the composition.
33. 33. The composition of claim 25, wherein the weight percent of component (a) is from about 30 to 94%, the weight percent of component (b) is from about 10 to 40% and percent in weight of the component (c) is around 1 to 30%, all percentages are based on the total weight of the composition.