MX2008007690A

MX2008007690A - Thermoplastic sheet containing a styrenic copolymer

Info

Publication number: MX2008007690A
Application number: MXMX/A/2008/007690A
Authority: MX
Inventors: M Krupinski Steven; J Styranec Thomas
Original assignee: Nova Chemicals Inc
Priority date: 2005-12-20
Filing date: 2008-06-13
Publication date: 2008-09-02

Abstract

A thermoplastic sheet containing a polymer composition including a polymer formed by polymerizing a mixture including 40%to 90%of styrenic monomers;5%to 45%of maleate-type monomers;0.1%to 25%by weight of elastomeric polymers with Mn greater than 12,000;and 0.1%to 10%by weight of low molecular weight polymers that include one or more monomers according to the formula CH2=CR3R2, where R3 is H or a Ci-C3 alkyl group and R2 is a C1-C22 linear, branched or cyclic alkyl or alkenyl groups. The low molecular weight polymer has Mn of from 400 to 12,000 and can optionally include functional groups. The thermoplastic sheet is made by extruding the polymer melt composition to provide a thermoplastic sheet. The thermoplastic sheets can be:. U. thermoformed into containers suitable for use in microwave heating of food.

Description

THERMOPLASTIC LAMINA CONTAINING A STIRENIC COPOLYMER FIELD OF THE INVENTION The present invention is directed to thermoplastic sheets containing rubber modified styrenic copolymers and articles formed from such thermoplastic sheets. BACKGROUND OF THE INVENTION It is known to copolymerize styrene and maleic anhydride as described, for example in U.S. Patent Nos. 2,971,939,2,769,804, and 3,336,267. In addition, it is known how to modify the styrene-maleic anhydride (SMA) copolymers with rubber. Generally, these copolymers are referred to as "rubber modified styrene-maleic anhydride copolymers". It is known that the rubber component provides increased resistance to impact and that the maleic anhydride component provides a high heat distortion temperature. Such materials are described, for example, in Patent No. 3,191,354. U.S. Patent No. 5,219,628 discloses a multi-layered container for use in cooking microwaved foods. The container includes a layer of thermoplastic polymer substrate that is not suitable for contact with food, and an inner layer that includes a mixture of styrene / maleic anhydride copolymer and a polymer selected from polystyrene, polystyrene No. Ref.: 193578 modified with rubber, polymethyl methacrylate, polymethyl methacrylate modified with rubber, polypropylene, and mixtures thereof. This patent also teaches that rubber-modified styrene / maleic anhydride copolymers can also be used, but are not preferred. It is also known how to produce various articles formed from foamed and foam-free thermoplastics such as polystyrene sheet or impact modified polystyrene sheet (in this case, high impact polystyrene sheet) by thermoforming methods. Many items are containers used for packaged foods. US Patent No. 5,106,696 describes a thermoformable, multi-layer structure for packaging materials and food. A first layer includes a polymer composition containing 49% to 90% by weight of a polyolefin, 10% to 30% by weight of a copolymer of styrene and maleic anhydride, 2% to 20% by weight of a compatibilizing agent, up to 5% by weight of a triblock copolymer of styrene and butadiene, and 20% by weight of talc. The second layer of the structure is made of polypropylene. In addition it is known how to improve the resistance to environmental stress cracking (ESCR) of high impact polystyrene (HIPS, for its acronym in English) and other impact modified styrenic polymers, such as acrylonitrile butadiene styrene plastic (ABS) and methyl methacrylate butadiene styrene (MBS) plastics, with the addition of polybutene. U.S. Patent No. 5,543,461 discloses a rubber modified graft thermoplastic composition containing 99 to 96% by weight of a rubber modified thermoplastic including 4 to 15% by weight of a gummy substrate that is distributed through a rubber matrix. super-particulate polymer in particles having an average particle size number from 6 to 12 microns and 96 to 85% by weight of a superstrate polymer; and 1 to 4% by weight of polybutene having an average molecular weight number from 900 to 2000. The super-stratum polymer can include 85% to 95% by weight of styrene and from 5% to 15% by weight of maleic anhydride. The ESCR of the styrenic polymers modified to impact is attributed to the large particle size of the impact modifier, in this case, 6 to 12 microns and to the use of the low molecular weight polybutene. Such thermoplastics find a quite significant market in household items, which are subject to chemicals that tend to cause cracks due to environmental stress (ESC), such as cleaners and in some cases, oily or fatty foods.

US Patent No. 5,543,461 also discloses, in the background section, that the thermoplastic having the best ESCR is Chevron 's HIPS grade 6755. This Chevron product contains 2 to 3% by weight of polybutene and has a rubbery phase dispersed with a average particle diameter volume between 4 and 4.5 microns. This Chevron product is associated with high impact polystyrene (HIPS) with ESCR properties and not with a styrene / rubber-modified maleic anhydride polymer. A number of process designs are described in the patent literature involving polymerization techniques, reactor configurations and mixing schemes that are used to incorporate the maleic anhydride into a styrene / maleic anhydride copolymer. Examples include Patents Nos. 4,328,327, 4,921, 906, and 3,919,354.

US Patent 3,919,354 discloses a styrene / maleic anhydride / diene rubber composition suitable for extrusion and molding and has a high heat distortion temperature and a desired impact resistance. The process for the preparation of the polymer involves modifying a styrene-maleic anhydride copolymer with diene rubber by polymerizing the styrene monomer and the anhydride in the presence of the rubber. More particularly, the process involves providing a styrene having rubber dissolved therein; stir the styrene / rubber mixture and initiate the polymerization of the free radical thereof; adding the maleic anhydride to the agitated mixture in a proportion substantially less than the polymerization index of the styrene monomer; and polymerize the styrene monomer and the maleic anhydride. The polymer contains rubber particles ranging from 0.02 to 30 microns dispersed through a polymer matrix of the styrene monomer and the anhydride with at least a significant portion of the rubber particles containing styrene monomer isolations. polymerized and maleic anhydride. This patent teaches that the polymers are suitable for extrusion within the sheet or film, which are then used for thermoforming inside the containers, packages and the like. Alternatively, the polymers can be injection molded into a wide variety of components such as tableware and heatable frozen food containers. However, polymers, such as those described in US Patent No. 3,919,354, are generally brittle, and therefore, capable of breaking, even though these polymers have the thermal properties to withstand temperatures above 210 ° F (98.8). ° C), temperature that is generally used in foods that are heated in a microwave oven. There is a need in the prior art for articles, such as containers that are suitable for packaged foods that can withstand temperatures needed to heat food in a microwave oven without the container curling, deforming, or breaking, especially during removal of the container from a microwave oven. SUMMARY OF THE INVENTION The present invention provides a thermoplastic sheet containing a polymer composition that includes a copolymer formed by the polymerization of a mixture comprising: about 40% to 90% by weight of one or more styrenic monomers; and about 5% to about 45% by weight of one or more maleate monomers; and combining the copolymer with about 0.1% to about 25% by weight of one or more elastomeric polymers having an average molecular weight number greater than 12,000; and about 0.1% to about 10% by weight of one or more low molecular weight polymers comprising repeating units of one or more monomers according to the formula CH2 = CR3R2, wherein R3 is H or a C? -C3 alkyl group and R2 is a linear, branched or cyclic C? ~ 22 alkyl or alkenyl group, wherein the low molecular weight polymer it has an average molecular weight number from 400 to 12,000 and may optionally include one or more functional groups selected from the group consisting of hydroxyl, amine, epoxy, carboxylic acid, carboxylic acid esters, and carboxylic acid anhydrides. The present invention is also directed to a method of making a thermoplastic sheet that includes providing the polymer composition described above in the form of a polymer melt and extruding the polymer composition to provide a thermoplastic sheet. The present invention further provides articles produced from the above-described thermoplastic sheets as well as containers suitable for use in the heating of microwaved foods formed from the thermoplastic sheets described above. The present invention further provides a container suitable for use in microwave food heating formed by the thermoforming of the thermoplastic sheet described above. DETAILED DESCRIPTION OF THE INVENTION Apart from the operation examples or where indicated otherwise, all the numbers or expressions that refer to quantities of ingredients, reaction conditions, etc., used in the specification and claims must be understood in accordance as modified in all cases by the term "approximately". Therefore, unless otherwise indicated, the numerical parameters set forth in the following specification and appended claims are approximations that may vary depending on the desired properties, which the present invention wishes to obtain. At least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter must at least be interpreted in light of the number of significant digits described and applying ordinary rounding techniques. Although the numerical ranges and parameters that establish the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as accurately as possible. Any numerical value, however, inherently contains certain errors that necessarily result from the standard deviation found in their respective test measurements. Also, it must be understood that any numerical range listed here is intended to include all subintervals included therein. For example, a range of "1 to 10" is intended to include all subintervals between and include the minimum enumerated value of 1 and the maximum enumerated value of 10; that is, it has a minimum value equal to or greater than 1 and a maximum value of equal to or less than 10. Because the numerical ranges described are continuous, they include each value between the minimum and maximum values. Unless expressly stated otherwise, the various numerical ranges specified in this application are approximations. As used herein, the terms "(meth) acrylic" and "(meth) acrylate" include both derivatives of acrylic and methacrylic acids, such as alkyl esters frequently referred to as acrylates and (meth) acrylates, the term " (meth) acrylate "means to understand. According to how it is used herein, the term "polymer" means to comprise, without limitation, grafted homopolymers, copolymers and copolymers. According to as used herein, the term "high impact polystyrene" refers to rubber modified polystyrene as known in the prior art. Also, "crystalline polystyrene" refers to polystyrene that does not contain other polymers, a non-limiting example is rubber. As used herein, "copolymers modified with styrene rubber and maleic anhydride and / or (me) linear, branched or cyclic alkyl acrylates of C? -C? 2"refers to polymeric compositions that include copolymers of styrene and maleic anhydride and / or (meth) acrylates linear, branched or cyclic alkyl of C? -C? 2 and a rubber and which are not understood by the description of the present polymeric composition and in particular that does not include the low molecular weight polymer according to what is described herein. Unless otherwise indicated, all molecular weight values are determined using gel impregnation chromatography (GPC) using appropriate polystyrene standards. Unless otherwise indicated, the molecular weight values indicated therein are the weight average molecular weights (Mw). As used herein, the terms "thermoplastic material" and "thermoplastic sheet" refer to materials that are capable of softening, fusing, and / or modifying their shape when heated and harden again when cooled. The present invention is directed to a thermoplastic sheet. According to as used herein, the term "thermoplastic sheet" refers to a sheet having a length corresponding to the extrusion direction (machine direction) of an extruder, a width corresponding to the perpendicular direction (cross direction) ) to the direction of extrusion and thickness. The thermoplastic sheet is characterized as containing a thermoplastic material that includes a polymeric composition.

The thermoplastic material in the present invention contains a polymer composition that includes a copolymer formed by polymerizing a polymerization mixture containing one or more styrenic monomers, one or more maleate monomers, and combining the copolymers with one or more elastomeric polymers, and one or more low molecular weight polymers. The styrenic monomers are present in the polymerization mixture and / or the copolymer formed at a level of at least 40%, in some cases at least 45% and in other cases at least 50% and may be present in up to 90%. %, in some cases up to 85%, in other cases up to 80%, and in some situations up to 75% by weight based on the polymerization mixture and / or the copolymer formed. The styrenic monomers may be present in the polymerization mixture and / or the copolymer formed at any level or may be in the range between any of the values listed above. Any suitable styrenic monomer can be used in the invention. Suitable styrenic monomers are those that provide the desirable properties in the present thermoplastic sheet according to what is described below. Non-limiting examples of suitable styrenic monomers include styrene, p-methyl styrene, α-methyl styrene, tertiary butyl styrene, dimethyl styrene, brominated or chlorinated nuclear derivatives thereof and combinations thereof. The maleate monomers are present in the polymerization mixture and / or the copolymer formed at a level of at least 5%, in some cases at least 10% and in other cases at least 15% and may be present in up to 45%, in some cases up to 40%, in other cases up to 35%, and in some situations up to 30% by weight based on the polymerization mixture and / or the copolymer formed. The maleate-type monomers may be present in the polymerization mixture and / or the copolymer formed at any level or may be in the range between any of the values listed above. Any suitable maleate-type monomer can be used in the invention. Suitable maleate monomers are those which provide the desirable properties in the present thermoplastic sheet as described below and include anhydrides, carboxylic acids and alkyl esters of maleate-type monomers, including, but not limited to maleic acid, fumaric acid and itaconic acid. Specific non-limiting examples of suitable maleate monomers include maleic anhydride, maleic acid, fumaric acid, linear, branched or cyclic alkyl esters of C? -C12 of maleic acid, linear, branched or cyclic C? ~ C alkyl esters? 2 of fumaric acid, itaconic acid, linear, branched or cyclic alkyl esters of C? -C? 2 of itaconic acid, and itaconic anhydride. The elastomeric polymers are combined with the copolymer and, in a particular embodiment of the invention, are present in the polymerization mixture at a level of at least 0.1%, in some cases at least 0.5%, in other cases at least 1%, and in some cases at least 2% and can be present in up to 25%, in some cases up to 20%, in other cases up to 15%, and in some situations up to 10% in weight based on the weight of the polymer composition. The elastomeric polymers may be present at any level or may be in the range between any of the values listed above. Any suitable elastomeric polymer can be used in the invention. In some embodiments of the invention, the elastomeric polymer blends are used to achieve the desired properties. Suitable elastomeric polymers are those which provide the desirable properties in the present thermoplastic sheet according to what is described below and are desirably able to resume their shape after being deformed. In one embodiment of the invention, the elastomeric polymers include, but are not limited to homopolymers of butadiene or isoprene or other conjugated diene, and randomly, block copolymers, AB diblock, or triblock ABA of a conjugated diene (non-limiting examples are butadiene and / or isoprene) with a styrenic monomer as defined above and / or acrylonitrile. In a particular embodiment of the invention, the elastomeric polymers include one or more block copolymers selected from the diblock and triblock copolymers of styrene-butadiene, styrene-butadiene-styrene, styrene-isoprene, styrene-isoprene-styrene, styrene-isoprene. - partially hydrogenated styrene and combinations thereof. As used herein, butadiene refers to 1,3-butadiene and when polymerized, repeats units that assume the 1,4-cis, 1,4-trans and 1,2-vinyl forms of the repeating units resulting along a polymer chain. In one embodiment of the invention, the elastomeric polymer has a number average molecular weight (Mn) greater than 12,000, in some cases greater than 15,000, and in other cases greater than 20,000 and a weight average molecular weight (Mw) of at least 25,000 in some cases no less than about 50,000, and in other cases no less than about 75,000 and the Mw can be up to 500,000, in some cases up to 400,000 and in other cases up to 300,000. The weight average molecular weight of the elastomeric polymer it can be any value or it can be in the interval between any of the values listed above. Non-limiting examples of the appropriate block copolymers that can be used in the invention include the STEREON® block copolymers available from Firestone Tire and Rubber Company, Akron, OH; the ASAPRENE ™ block copolymers available from Asahi Kasei Chemicals Corporation, Tokyo, Japan; the KRATON® block copolymers available from Kraton Polymers, Houston, TX; and the VECTOR® block copolymers available from Dexco Polymers LP, Houston, TX. The low molecular weight polymers are optionally combined with the copolymer and, in a particular embodiment of the invention, are present in the polymerization mixture at a level of at least 0.1%, in some cases at least 0.25%, in others cases at least 0.5%, and sometimes at least 1% and may optionally be present in up to 10%, in some cases up to 7.5%, and in other cases up to 5% by weight based on the polymer composition. The low molecular weight polymers may be present at any level or may be in the range between any of the values listed above. Any suitable low molecular weight polymer can be used in the invention. In some embodiments of the invention, combinations of low molecular weight polymers are used to achieve the desired properties.

Suitable low molecular weight polymers desirably include repeating units resulting from the polymerization of one or more monomers according to the formula CH2 = CR3R2, wherein R3 is H, methyl, ethyl, n-propyl or isopropyl group, and R2 is a branched or cyclic linear or branched alkyl or alkenyl group of C? ~ C22, in some cases Ci-Ciß, in other cases C? ~ C? 2, in some circumstances C2-C22í in other circumstances C2-Ci8, in some situations C2 -C? 2, in other situations C2-C6 in some cases Ci-Cβ, including conjugated dienes, and in other cases methyl, ethyl, n-propyl, isopropyl, ethenyl, propenyl, isopropenyl, butyl, isobutyl, butenyl or isobutenyl. In a particular embodiment of the invention, when R2 is methyl, R3 is not methyl and when R3 is methyl R2 is not methyl. In one embodiment of the invention, the low molecular weight polymers include repeating units resulting from the polymerization of one or more monomers selected from 1-butene, isobutylene, 2-butene, isoprene, butadiene, diisobutylene, 1-pentene, -pentene, 1-hexene, 2-hexene, 3-hexene, 1, 3-hexadiene 2, -hexadiene, isoprenol, ethylene, propylene and combinations thereof. In one embodiment of the invention, the low molecular weight polymers include one or more functional groups selected from hydroxyl, amine, epoxy, carboxylic acid, linear branched alkyl carboxylic acid esters or cyclic C? -C? 2 in some cases C? -C6, and carboxylic acid anhydride. The low molecular weight polymers of the present invention may have a weight average molecular weight number of at least 400, in some cases at least 500, and in other cases at least 750 and up to 12,000, in some circumstances up to 10,000, in other circumstances up to 8,000, in some cases up to 6,000, in other cases up to 4,000 and in some cases up to 2,000. The molecular weight can be determined using gel impregnation chromatography (GPC) using polystyrene standards. The molecular weight of the low molecular weight polymers can be any value or can be in the range between any of the values listed above. In a particular embodiment of the invention, low molecular weight polymers include polybutenes. Suitable polybutenes that can be used in the invention include, but are not limited to, INDOPOL® and PANALANE® products available from AMOCO Chemical Company, Chicago, IL. In another particular embodiment of the invention, low molecular weight polymers include polybutadienes. Suitable polybutadienes that can be used as the low molecular weight polymer of the invention include, but are not limited to, the KRASOL® product available from Kaucuk, a.s., Czech Republic.

In a particular embodiment of the invention, the low molecular weight polybutadienes may contain particular proportions of repeat units of 1,4-cis, 1,4-trans and 1,2-vinyl. In this modality, the 1,4-cis portion can be at least 5%, in some cases at least 10% and in other cases at least 15% and can be up to 30%, in some cases up to 25% and in other cases up to 20% by weight of the low molecular weight polybutadienes. In addition, the 1,4-trans portion can be at least 5%, in some cases at least 10% and in other cases at least 15% and can be up to 30%, in some cases up to 25% and in other cases up to 20% by weight of the low molecular weight polybutadienes. Additionally, the 1,2-vinyl portion can be at least 50%, in some cases at least 55% and in other cases at least 60% and can be up to 80%, in some cases up to 75% and in others cases up to 70% by weight of the low molecular weight polybutadienes. The total of the 1,4-cis, 1,4-trans and 1,2-vinyl portions of the low molecular weight polybutadiene repeat units does not exceed 100% by weight of the low molecular weight polybutadienes, but can be less than 100% The amount of 1,4-cis, 1,4-trans and 1,2-vinyl portions of the low molecular weight polybutadiene repeat units can be any of the values or range between any of the values listed above.

The polymer composition can be prepared by polymerizing the polymerization mixture in an appropriate reactor under polymerization conditions of the free radical. The low molecular weight polymer can be added to a styrene monomer / maleate monomer / elastomeric polymer feed, or it can be added to or in the polymerization reactor vessel, or it can be added to the partially polymerized syrup after it leaves the polymer. reactor and enter the devolatilizer. It is also envisaged that the low molecular weight polymer may be composed, in this case, mixed within the copolymer after the copolymer has left a devolatilizer, by means of an extruder, for example, a double screw extruder, in line or off-line as a separate operation after the rubber modified SMA copolymer has been pelletized. The term "devolatilizer" and the term "devolatilization system" as used herein means including all shapes and forms of devolatilizers including an extruder and / or a free-falling flash devolatilizer. The term "devolatilization" and the term "devolatilization step" as used herein means that it refers to a process, which may include an extruder and / or a free-falling flash devolatilizer. In one embodiment of the invention, the low polymer molecular weight is added to the reaction mixture of the elastomeric polymer, styrenic monomer and maleate monomer before the devolatilization step to improve the hardness, elongation, and heat distortion resistance properties of the polymeric composition, of the thermoplastic sheets and articles made in accordance with the invention. This polymeric composition can be used in applications where the resins of the prior art have been shown to be too fragile and / or the heat distortion resistance is inadequate. For example, and as discussed herein above, if packaged food containers made of maleic anhydride resins / styrenics modified with prior art rubber are heated in microwave ovens at temperatures higher than 210 ° F (98.8 ° C) ), the containers usually break when they are taken out of the oven. The thermoplastic sheet of the present invention can now be used in the manufacture of these types of containers without containers that break under normal use. The reason for the improvement in the polymer composition of the invention is not clear, and the inventors do not wish to be limited by any particular theory. However, it is believed that the addition of the low molecular weight polymer to the styrenic monomer / maleate monomer / elastomeric polymer combination prior to devolatilization it distributes the low molecular weight polymer in a way that improves the characteristics of the elastomeric polymer component. That is, it is believed that the low molecular weight polymer gravitates towards, surrounds and migrates within the elastomeric polymer and not the formation of the maleate / styrenic monomer component in view of the high polarity of the maleate / styrenic monomer matrix. Instead, it is theorized that the low molecular weight polymer used, particularly in accordance with the teachings of U.S. Patent No. 5,543,461, is distributed in the matrix together with the polystyrene and the rubber component. U.S. Patent No. 5,543,461 teaches that the rubber modified thermoplastic composition can be styrene / maleic anhydride modified with rubber and polybutene copolymer. However, the examples in the 61 patent only illustrate high impact polystyrene (HIPS) and improvements in ESCR, and both the examples and teachings of this M61 patent are silent with respect to the improvement in hardness or production of thermoplastic sheets of according to what is described here. Thus, U.S. Patent No. 5,543,461 teaches that the polybutene is in the range in amounts of 1 to 4% by weight and the rubber particle size is in the range of 6 to 12 microns. The inventors have found that the particle size of rubber used in the polymer composition of the invention is desirably less than 6 microns in order to provide the desired characteristics. The polymer composition of the invention can be prepared by polymerization techniques or compounding techniques, which are known to those skilled in the art. It has been found that the addition of low molecular weight polymer to the reactor or syrup leaving the reactor and before it enters the devolatilizer can provide even a higher degree of improvement in hardness, elongation, and distortion resistance properties by heat compared to the addition of the low molecular weight polymer in a compounding technique that requires that the low molecular weight polymer be added to the polymer composition in an extruder after devolatilizing and pelletizing or after devolatilizing but before pelletizing, more on which will be discussed in more detail below. The polymerization techniques used in the polymerization of the components of the polymer composition of the invention can be solution, bulk, bulk, suspension, or polymerization of the emulsion. In one embodiment of the invention, bulk polymerization methods are used. The polymer composition can be prepared at reacting the styrenic monomers, maleate-type monomers, and elastomeric polymers in an appropriate reactor under polymerization conditions of the free radical and addition of the low molecular weight polymer to the reactive mixture. Desirably, the maleate monomers are added to the styrenic monomers and the elastomeric polymer continuously at about the reaction rate to a stirred reactor to form a polymer composition having a uniform maleate monomer level. Polymerization of the polymerization mixture can be achieved by thermal polymerization generally between 50 ° C and 200 ° C; in some cases between 70 ° C and 150 ° C; and in other cases between 80 ° C and 140 ° C. Alternatively, initiators that generate free radicals can be used. Non-limiting examples of the free radical initiators that can be used include benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, di-tert-butyl peroxide, tert-butyl peroxybenzoate, dicumyl peroxide, eumenohydroperoxide, diisopropylbenzene hydroperoxide, diisopropyl peroxydicarbonate, tert-butyl perisobutyrate, tert-butyl peroxyisopropylcarbonate, tert-butyl peroxypivalate, methyl ethyl ketone peroxide, stearoyl peroxide, tert-butyl hydroperoxide, lauroyl peroxide, azobisisobutyronitrile and mixtures thereof. Generally, the initiator is included in the range of 0. 001 to 1.0% by weight, and in some cases in the order of 0.005 to 0.5% by weight of the polymerization mixture, depending on the monomers and the desired polymerization cycle. In one embodiment of the invention, the polymer composition is prepared by bulk solution or polymerization in the presence from 0.01 to 0.1% by weight based on the mixture of a tetrafunctional peroxide initiator of the formula: wherein R1 is selected from the t-C4-6 alkyl radicals and R is a neopentyl group, in the absence of a crosslinking agent. In a particular embodiment of the invention, the tetrafunctional initiator is selected from the group consisting of tetrakis- (t-amyl-peroxycarbonyloxymethyl) methane, and tetrakis- (t-butylperoxycarbonyloxy-methyl) methane. In some cases, the total amount of initiator required is added simultaneously with the raw material when the raw material is introduced into the reactor. Customary additives known in the prior art, such as stabilizers, antioxidants, lubricants, fillers, pigments, plasticizers, etc., can be added to the polymerization mixture. If desired, small amounts of antioxidants, such as alkylated phenols, for example, 2, 6-di-tert-butyl-p-cresol, phosphates such as trinonyl phenyl phosphite and mixtures containing tri (mono and dinonyl phenyl) phosphates, can be included in the feed stream. Such materials, in general, can be added at any stage during the polymerization process. A polymerization reactor that can be used in the production of the polymer composition of the invention is similar to that described in the aforementioned US Patents Nos. 2,769,804 and 2,989,517, the teachings of which the patents are incorporated herein by reference in their entirety. These configurations are adapted for the production, in a continuous manner, of solids, moldable polymers and copolymers of vinylidene compounds, particularly that of the aromatic monovinyl compounds, in this case, styrene. Of these two arrangements, that of U.S. Patent No. 2,769,804 is particularly desirable. In addition, the polymer composition of the present invention can be prepared according to that described in the North American Application Publication 2005/0020756. Generally, the arrangement of U.S. Patent No. 2,769,804 provides an entry or entries for the monomers or the raw material connected to the container of polymerization reactor. The reactor vessel is surrounded by a jacket, which has an inlet and outlet for the passage of a temperature control fluid through the jacket, and a mechanical agitator. A valve line leads from a lower section of the container and is connected to a devolatilizer, which can be any of the devices known in the prior art for the continuous vaporization and removal of volatile components from the formed resin leaving the container. For example, the devolatilizer may be a vacuum chamber through which the fine streams of the heated resin material passage, or a set of rollers for grinding the heated polymer inside a vacuum chamber, etc. The reactor is provided with usual means such as a gear pump to discharge the plasticized polymer with heat from the reactor to the devolatilizer. A steam line leads from the devolatilizer to a condenser, which condenses the vapors and effects the return of the recovered volatiles, for example, monomeric material, typically in liquid conditions as a recycle stream. In general, the arrangement for producing the polymer composition will generally include at least three apparatuses. These are a polymerization reactor vessel assembly which may include one or more reactor vessels, a devolatilization system, and a pelletizer. From according to what has been discussed above, some embodiments according to the invention use processes in which the low molecular weight polymer is added to the polymer in one of three locations, in this case, to the reactor vessel; after the reactor vessel and before the devolatilization system; or in a pelletising extruder where the combination or mixture of the polybutene within the polymer occurs. More particularly, a first method for preparing the polymer composition of the invention is to prepare a solution of the components, in this case, the low molecular weight polymer, maleate monomers, elastomeric polymer, and optionally an antioxidant and to dissolve this solution in the styrenic monomers which is then continuously fed to a polymerization reactor vessel which is equipped with a turbine agitator similar to that described in the previous paragraph. The initiator can be added to the reactor vessel in a second stream. The reactor is stirred so that the content mixes well and the temperature is maintained by the cooling fluid flowing in the jacket of the reactor. The output stream is fed continuously into the devolatilizer (first extruder), and the final product is pelletized. A second method involves adding the low molecular weight polymer and the styrenic monomer, the maleate type monomer, and the elastomeric polymer feed separately to the polymerization reactor vessel and then polymerize the feed in the presence of the low molecular weight polymer and the elastomeric polymer followed by devolatilization of the stream leaving the reactor vessel. The finished product can be pelletized after the devolatilization system. A third method involves forming a maleate monomer solution and the elastomeric polymer in the styrenic monomer continuously feeding this solution with the styrenic monomer into the polymerization reactor vessel to produce a partially polymerized styrenic syrup, and adding the low molecular weight polymer. to the partially polymerized syrup when it leaves the reactor vessel and before this syrup enters the devolatilization system. The finished product can be pelletized after the devolatilization system. A fourth method involves forming a solution of maleate monomer and elastomeric polymer in styrenic monomer, continuously feeding the solution with the styrenic monomer into a polymerization reactor vessel to produce a partially polymerized styrenic syrup, devolatilizing the stream leaving the vessel. polymerization reactor, and composing or mixing the low molecular weight polymer within the polymer that it flows either in an in-line extruder followed by pelletizing or in a separate extrusion step after the rubber-modified styrenic monomer-monomer-type copolymer has been pelletized. A fifth method involves forming a copolymer of maleate monomer and styrenic monomer and then composing the elastomeric polymer and optionally the low molecular weight polymer within the copolymer. Polymerization generally occurs in a conversion from 20 to 95%. Typically, the polymerization process results in the copolymerization of the styrenic and maleate monomers to form a continuous phase with the elastomeric polymer present in a dispersed phase. In one embodiment of the invention, at least some of the polymers in the continuous phase are grafted onto the elastomeric polymers in the dispersed phase. In one embodiment of the invention, the dispersed phase is present as discrete particles dispersed within the continuous phase. In addition to this embodiment, the volume of average particle size of the particulate phase dispersed in the continuous phase is at least about 0.1 μm, in some cases at least 0.5 μm and in other cases at least 1 μm. Also, the volume of the average particle size of the phase dispersed in the continuous phase can be up to approximately 11 μm, in some cases up to 6 μm, in other cases up to 5.5 μm, in some cases up to 5 μm and in other cases up to 4 μm. The particle size of the phase dispersed in the continuous phase can be any value listed above and can be in the range between any of the values listed above. In another embodiment of the invention, the aspect ratio of the discrete particles is from at least about 1, in some cases at least about 1.5 and in other cases at least about 2 and may be up to about 5, in some cases up to about 4 and in other cases at least up to about 3. The aspect ratio of the dispersed discrete particles can be any value or range between any of the values listed above. As a non-limiting example, the aspect ratio can be measured by scanning electron microscopy or light scattering. The average particle size and the aspect ratio of the dispersed phase can be determined using light scattering at low angle. As a non-limiting example, a Laser Diffraction Particle Size Analyzer Model LA-910 available from Horiba Ltd., Kyoto, Japan can be used. As a non-limiting example, a sample of rubber-modified polystyrene can be dispersed in methyl ethyl ketone. The suspended rubber particles can then be placed in a glass cell and subjected to light scattering. The scattered light of the particles in the cell can be passed through a condenser lens and converted into electrical signals by detectors located around the cell of the sample. As a non-limiting example, a He-Ne laser and / or a tungsten lamp can be used to provide light with a shorter wavelength. The particle size distribution can be calculated based on the Mié scattering theory of the angular measurement of the scattered light.

The copolymer resulting from the processes described above may have a weight average molecular weight (Mw, measured using GPC with polystyrene standards) of at least 20,000, in some cases at least 35,000 and in other cases at least 50,000. Also, the Mw of the resulting polymer can be up to 1,000,000, in some cases up to 750,000, and in other cases up to 500,000. The Mw of the resulting polymer can be any value or range between any of the values listed above. The polymer composition according to the invention can be characterized as having a VICAT softening temperature of greater than 100 ° C, in some circumstances greater than 110 ° C, in other circumstances greater than 115 ° C, in some cases greater than 116 ° C, in other cases greater than 117 ° C, and in some times greater than 118 ° C and can be up to 135 ° C in some cases up to 130 ° C. The VICAT softening temperature is determined in accordance with ASTM-D1525. The VICAT softening temperature can be any value or range between any of the values listed above. In order to form a thermoplastic sheet, the polymer composition described above is provided in the form of a polymer melt, typically by heating the polymer composition above its melting temperature and the polymer composition is then extruded to form a thermoplastic sheet. In one embodiment of the invention, a composite mixture including the present polymer composition and one or more other polymers may be used. Other suitable polymers which may be a composite mixture with the present polymeric composition include, but are not limited to, crystalline polystyrene, high impact polystyrenes, polyphenylene oxide, styrene and maleic anhydride copolymers and / or linear alkyl (meth) acrylates, branched or cyclic C? ~ C? 2, copolymers modified with styrene rubber and maleic anhydride and / or linear, branched or cyclic C? ~ C? 2 alkyl (meth) acrylates, polycarbonates, polyamides (such as nylons), polyesters (such as polyethylene terephthalate, PET), polyolefins (such as polyethylene, polypropylene, and ethylene-propylene copolymers), maleated polyolefins such as those available under the trade name BYNEL® from E.I. Du Pont de Nemours and Company, Wilmington, DE, polyvinylidene chloride, acrylonitrile / (meth) acrylate copolymers such as those available under the tradename BAREX® from BP Chemicals Inc., Cleveland, Ohio, ethylene / vinyl acetate copolymers, copolymers of ethylene vinyl alcohol, and combinations thereof. When a composite mixture is used, the mixture will typically include at least 10%, in some cases at least 25%, and in other cases at least 35% and up to 90%, in some cases up to 75%, and in others cases up to 65% by weight based on the mixture of the present polymer composition. Also, the mixture will typically include at least 10%, in some cases at least 25%, and in other cases at least 35% and up to 90%, in some cases up to 75%, and in other cases up to 65% in weight based on the mixture of the other polymers. The amount of the present polymer composition and other polymers in the mixture is determined based on the desired properties in the resulting thermoplastic sheet and / or article formed. The amount of the present polymer composition and other polymers in the mixture can be any value or range between any of the values listed above. The composition or polymer mixture can be extruded using the conventional extrusion equipment. The extruder may be a side-by-side type or may be a multizone extruder having at least a first primary zone or zone for fusing the polymer and a second extruder or zone. As a non-limiting example, in the extruder or primary zone, the polymer melt can be maintained at temperatures from about 425 ° F to 450 ° F (about 218 to 232 ° C). The polymer melt can then be fed from the primary extruder to the secondary extruder or passed from a primary zone to a secondary zone within the extruder maintained, as a non-limiting example, at a melting temperature of 269 ° F to 290 ° F. (approximately 132 ° C to 143 ° C). In the extruder or secondary zone, the polymer melt passes through the extruder cylinder by the action of a driving screw having deep trajectories and exerting low shear stress on the polymer melt. The polymer melt is cooled by means of the cooling fluid, typically, oil circulating around the extruder barrel. Generally, the melt is cooled to a temperature from about 250 ° F to about 290 ° F (about 121 ° C to 143 ° C). The melt or polymer mixture may also contain conventional additives known in the prior art such as light and heat stabilizers (for example hindered phenols and phosphite or phosphonite stabilizers) typically in amounts of less than about 2% by weight based on the mixture or polymer solution. Other additives may be added to and / or compounds within the polymeric composition for thermoplastic sheets according to the invention. Additional examples of suitable additives are softening agents; plasticizers, such as coumaron-indene resin, a terpene resin, and oils in an amount of about 2 parts by weight or less based on 100 parts by weight of polymer; dyes, pigments; anti-blocking agents; slip agents; lubricants; coloring agents; antioxidants; ultraviolet light absorbers; fillers; antistatic agents; Impact modifiers The pigment can be white or any other color. The white pigment can be produced by the presence of titanium oxide, zinc oxide, magnesium oxide, cadmium oxide, zinc chloride, calcium carbonate, magnesium carbonate, etc., or any combination thereof in the amount from 0.1 to 20% by weight, depending on the white pigment to be used. The colored pigment can be produced by carbon black, phthalocyanine blue, Congo red, titanium yellow or any other coloring agent known in the printing industry.

Examples of anti-blocking agents, glidants or lubricants are silicone oils, liquid paraffin, synthetic paraffin, mineral oils, petrolatum, petroleum wax, polyethylene wax, hydrogenated polybutene, higher fatty acids and metal salts thereof, linear fatty alcohols, glycerin, sorbitol, propylene glycol, fatty acid esters of monohydroxy or polyhydroxy alcohols, phthalates, hydrogenated castor oil, beeswax, acetylated monoglyceride, hydrogenated sperm oil, fatty acid esters of ethylenebis, and fatty amides superiors The organic antiblocking agents can be added in amounts ranging from 0.1 to 2% by weight. Examples of antistatic agents are glycerin fatty acid, esters, sorbitan fatty acid esters, propylene glycol fatty acid esters, stearyl citrate, pentaerythritol fatty acid esters, polyglycerin fatty acid esters, and fatty acid esters of glycerin and polyoxetilene. An antistatic agent can be in the range from 0.01 to 2% by weight. The lubricants can be in the range from 0.1 to 2% by weight. A retardant flame will be in the range from 0.01 to 2% by weight; the ultraviolet light absorbers will be in the range from 0.1 to 1%; and the antioxidants will be in the range from 0. 1 to 1% by weight. The above compositions are expressed as a percentage of the total weight of the polymer mixture. Fillers, such as talc, silica, alumina, calcium carbonate, barium sulfate, metallic powder, glass spheres, barium stearate, calcium stearate, aluminum oxide, aluminum hydroxide, clay, titanium dioxide, earth Diatoms and fiberglass can be incorporated into the polymer composition in order to reduce costs or add desired properties to the film or sheet. The amount of filler is desirably less than 10% of the total weight of the polymer composition as long as this amount does not alter the foaming properties of the film or sheet when temperature is applied thereto. The polymeric composition for the thermoplastic sheets of the invention may include impact modifiers. Examples of impact modifiers include high impact polystyrene (HIPS), styrene / butadiene block copolymers, styrene / ethylene / -butene / styrene block copolymers, styrene / ethylene copolymers. The amount of impact modifier used is typically in the range of 0.5 to 25% of the total polymer weight. The thermoplastic material is usually extruded to atmospheric pressure. The thermoplastic material is cooled to room temperature typically below about 25 ° C, which is below the glass transition temperature of the polymer composition and the sheet is stabilized. In one embodiment of the invention, the thermoplastic sheets, typically from about 15 to about 300 thousandths of an inch thick, can be extruded as plates or thin-walled tubes, which are expanded and oriented on an expandable tubular mandrel to produce a tube, which is cut to produce the sheet. These relatively thin sheets can be worn, typically 3 or 4 days and then can be thermoformed into articles, such as cups, trays, grills, covers, lids or other containers or pieces of containers suitable for use in heating food or liquids in a microwave oven. In addition to this mode, the thermoplastic sheets can be at least 5, in some situations at least 10, in other situations at least 15, in some cases at least 20, in some cases at least 30 thousandths of an inch , and in some cases at least 50 thousandths of an inch thick and can be up to 300, in some cases up to 250, in other cases up to 200, in some cases up to 150 and in other cases up to 125 thousandths of a second. inches thick. The thickness of the thermoplastic sheet is determined by the intended end use and the desired properties. The thickness of the thermoplastic sheet can be any value or range between any of the values listed above. More specifically, once the desired temperature is reached, the thermoplastic sheet is formed into the desired shape by known processes such as piston-assisted thermoforming wherein a piston pushes the thermoplastic sheet into a mold of the desired shape. The pressure and / or air gap can also be used to mold the desired shape. In one embodiment of the invention, the thermoformed article is used to package the food and one or more of the processes described above are performed in a protected and / or sterile environment and / or atmosphere. When used to package food or consumable liquids, the thermoformed article may be closed by itself or may include a container and a separate closure. Thus, in one embodiment of the invention, the food or consumable liquids are placed in the container and the container is closed. Optionally, the container can then be shrink-wrapped by an appropriate material according to what is known in the prior art. Desirably, the shrink wrapping may include printing on its surface. Alternatively, a label, which covers at least a portion of the container can be placed on it. In a particular embodiment of the invention, the label is placed in the thermoforming machine before forming the container and adhering to the container formed. In one embodiment of the invention, the thermoplastic sheet described above has a flexural modulus of thermoplastic sheet of at least 5,000 psi (351.53 kg / cm2), in some cases at least 6,000 psi (421.84 kg / cm2), in others cases at least 7,000 psi (492.14kg / cm2), in some cases at least 8,000 psi (703.06kg / cm2) and in other cases at least 10,000 psi. The flexural modulus of thermoplastic sheet is determined using a standardized test bar, which is attached to three points that are bent under controlled conditions similar to those described in ASTM D-790 using an Instron load frame (4204 or 4400) with accessories , available from Instron Corporation, Canton, MA. The load and deflection data are collected and evaluated. The inclination of the load-deflection curve, in the linear region, is a measurement of stiffness or rigidity of the material. The foam sheet materials, characteristically anisotropic, are evaluated in both the longitudinal or "dragging" direction and the transverse direction or "through the sheet". Flexural stiffness is the initial linear behavior of the material when subjected to bending deformation. The flexural stiffness is quantified by the respective value of the inclination of the initial linear portion of the curve. The module is the slope of the load-deflection curve normalized to the thickness. The test conditions used are: (a) 1.5 inches (3.81cm) in length, (b) crossing speed of 1 inch per minute, and (c) specimen of 4 inches (10.16cm) (length). In another embodiment of the invention, any of the thermoplastic sheets described above can be co-extruded or laminated with one or more materials to form a two-layer structure wherein the materials make up one layer (a top layer) and the thermoplastic sheet composes the second layer. layer or a thermoplastic sheet of the sandwich structure, wherein the thermoplastic sheet is included in the middle layer and the materials are included in the two outer layers. Materials that can be co-extruded or laminated can be selected from crystalline polystyrene, high impact polystyrenes, polyphenylene oxide, styrene and maleic anhydride copolymers and / or linear, branched or cyclic (meth) acrylates C? ~ C? , copolymers modified with styrene rubber and maleic anhydride and / or linear, branched or cyclic alkyl (meth) acrylates C? ~ C12, polycarbonates, polyamides (such as nylons), polyesters (such as terephthalate, polyethylene, PET), polyolefins (such as polyethylene, polypropylene, maleated polyolefins such as those available under the tradename BYNEL® from EI Du Pont de Nemours and Company, Wilmington, DE, and ethylene-propylene copolymers), polyvinylidene chloride, acrylonitrile copolymers / ( met) acrylate such as those available under the tradename BAREX® from BP Chemicals Inc., Cleveland, Ohio, ethylene / vinyl acetate copolymers, copolymers of vinyl alcohol and ethylene, and combinations thereof. More particularly, the method described above may include the step of extruding or laminating a top layer of solid sheet at least a portion of an upper surface of the thermoplastic sheet. Alternatively, the method described above may include the steps of: extruding or laminating a top layer on at least a portion of an upper surface of the thermoplastic sheet and extruding or laminating a bottom layer on at least a lower portion of the thermoplastic sheet to form a thermoplastic sheet of sandwich structure. As described above, the present invention provides articles that are formed by thermoforming any of the thermoplastic sheets described above to form articles. Due to the properties of the thermoplastic sheets, the articles they can include the appropriate containers to be used in heating food with microwaves. In one embodiment of the invention, the thermoplastic sheet or the co-extruded sheets according to the invention have a notched IZOD impact value, determined in accordance with ASTM D256, of at least 2, in some cases at least 2.5 (0.136). m-kg / cm) and in other cases at least 2.75 foot-pounds / inch (0.149m-kg / cm). Also, the IZOD impact with notch can be up to 6 and in some cases up to 5 ft-lb / inch (0.272m-kg / cm). The IZOD impact with notch can be any value listed above or range between any of the values listed above. In another embodiment of the invention, the thermoplastic sheet or the co-extruded sheets according to the invention have a swelling index value of at least about 10, in some cases at least about 12 and in other cases at least about 14. and can be up to about 20, in some cases up to about 18 and in other cases up to about 16. The swelling index is determined by dissolving a thermoplastic sample (0.4 grams) in toluene (20 ml, 30 ml if the percentage of insoluble material is expect it to be at least then 15%). The insoluble portion of the thermoplastic sample is separated from the soluble portion by centrifugation and dried to constant weight. The index of swelling is calculated as the ratio of the weight of the wet gel to the dry gel. The swelling index of the thermoplastic sheet or the coextruded sheets can be any value or range between any of the values listed above. In a further embodiment of the invention, the thermoplastic sheet or the co-extruded sheets according to the invention have an elongation at the rupture value of at least about 10%, in some cases at least about 12%, and in some cases at least about 14% and can be up to about 25%, in some cases up to about 24%, and in other cases up to about 22%, determined in accordance with ASTM D638. The breaking stress of the thermoplastic sheet or the co-extruded sheets can be any value or range between any of the values listed above. The containers resulting from the present invention are suitable for packaged foods and can withstand the temperatures needed to heat the food in a microwave oven without the container breaking, deforming or dripping. In addition, the containers maintain their shape, especially during the removal of the container out of the microwave oven. When the thermoplastic sheet is coextruded according to what was discussed above, the multilayer container The resultant is also suitable for use in microwave heating of foods with the same type of desirable characteristics. The present invention will be further described by reference to the following examples. The following examples are merely illustrative of the invention and are not intended to be limiting. Unless otherwise indicated, all percentages are by weight. EXAMPLES In the examples, the resins formed were injection molded into the test specimens, which were tested by the following methods. The elongation at break was measured by ASTM-D638; the IZOD impact on notch was measured by ASTM-D256; VICAT heat distortion temperature was measured by ASTM-D1525; the deflection temperature under load (DTUL) was measured by ASTM-D648 in specimens annealed at 70 ° C with a flexural stress of 264 psi (18.56 kg / cm2); and the instrumented impact was measured by ASTM D-3763 with a hole press of 38 millimeters in diameter. The results are tabulated in the tables below. EXAMPLE 1 This example compares the thermoplastic sheets prepared according to the present invention prepared on a laboratory scale. The formulations for the thermoplastic sheets were Prepared in accordance with the table below: 1 KRASOL® (hydroxy-terminated) available from AMOCO Chemical Company, Chicago, IL. 2 Mn approximately 2,000 3 Mn approximately 5,000 4 Antioxidant available from Great Lakes Chemical Co. , Indianapolis, IN. A solution containing maleic anhydride, polybutadiene, polybutadiene rubber, styrene-butadiene-styrene triblock copolymer rubber (SBS), and ANOX ™ PP18 (octadecyclic-3- (3 ', 5'-di-tert-butyl-hydroxyphenyl) ) propionate) was dissolved in a styrene monomer, and then continuously fed to a fully filled polymerization reactor equipped with a turbine agitator similar to that of the U.S. Patent No. 2,769,804. In particular, the system was a laboratory-scale line that included a cooled solvent tank, a feed tank, 2 reactors, a devolatilizing drum, and an extruder with a die with a single hole. The system was run as a single reactor system with approximately 50% solids. The only reactor used had a propeller anchor for mixing. The Benzoyl peroxide initiator, 0.01% of the main stream, was added into the reactor in a separate stream. The reactor was stirred so that it was well mixed. The reaction mass was maintained at 126 ° C by cooling through the reactor jacket. The average residence time in the reactor was 2.7 hours. The output stream contained 52% polymer and was then fed continuously into a devolatilizer in which the unreacted monomer was removed. The final product was pelleted and molded into test specimens and the test was performed using the methods outlined above. The following results were obtained for the samples: The improved IZOD and the swelling index values demonstrate the hardness properties of the present thermoplastic sheet, which maintains good VICAT and elongation in the breaking properties. Example 2 This example compares the thermoplastic sheets prepared according to the present invention prepared at the pilot plant scale. The formulations for the thermoplastic sheets were prepared according to the table below: 1 KRASOL® (hydroxy-terminated) available from AMOCO Chemical Company, Chicago, IL. 2 Mn approximately 2,000 3 Mn approximately 5,000 5 Antioxidant available from Ciba Specialty Chemical Corp., Tarrytown, NY. A solution containing maleic anhydride, polybutadiene, polybutadiene rubber, styrene-butadiene-styrene triblock copolymer rubber (SBS), and IRGANOX 1076 was dissolved in a styrene monomer, and then continuously fed to a fully filled polymerization reactor. with a turbine agitator similar to that of U.S. Patent No. 2,769,804. In particular, the system was a laboratory-scale line that included a feed tank, a jacket cooled reactor, a devolatilizing drum, and an extruder with a rotating drive screw with a 20 mm counter (NFM Welding Engineers Inc., Massillon , OH The system operated at 100 lb / hr (45.35kg / hr) with 20 Ib / hr (9.07kg / hr) when going to the extruder for devolatilization and 80 lb / hr when going to the devolatilization drum. of Benzoyl, 0.01% of the main stream, was added into the reactor in a separate stream The reactor was stirred so that it was well mixed The reaction mass was maintained at 126 ° C by cooling through the reactor jacket The average residence time in the reactor was 2.7 hours.The output stream contained 52% polymer and was then continuously fed into a devolatilizer in which the unreacted monomer was removed. The final product was pelleted and molded into test specimens and the test was performed using the methods outlined above. The following results were obtained for the samples: Property A D Impact IZOD with notch 3.70 2.75 3.15 4.10 (pielb / in) (0.201) (0.149! (0.171 '(0.223! The improved IZOD values demonstrate the hardness properties of the present thermoplastic sheet, which maintains good VICAT properties. The product of the laminated sample G was thermoformed into trays using a Hydrotpm single-tray thermoforming machine. The sheet was fixed leaving an area large enough to form on a female mold of a single cavity of a food tray. The thermoforming conditions are shown in the following table.

The dimensions of the tray were approximately 7 ' by 9"and 1" deep. A commercially available spaghetti meat sauce (RAGÚ®, Unilever Supply Chain Inc., Clinton, CT) was placed on the trays and cooked in a microwave oven at 600 W for 6 minutes at the maximum setting. The shape of the trays was unchanged, in this case, there were no noticeable deformations and no leakage. The present invention has been described with reference to the specific details of particular embodiments thereof. It is not intended that such details be considered as limitations on the scope of the invention except insofar as and to the extent that they are included in the appended claims. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims

CLAIMS Having described the invention as above, it is claimed as property contained in the following claims: 1. A thermoplastic sheet characterized in that it comprises a polymer composition containing a copolymer formed by polymerization of a mixture comprising: about 40% to 90% in weight of one or more styrenic monomers; and about 5% to about 45% by weight of one or more maleate monomers; and combining the copolymer with about 0.1% to about 25% by weight of one or more elastomeric polymers having an average molecular weight number greater than 12,000; and about 0.1% to about 10% by weight of one or more low molecular weight polymers comprising repeating units of one or more monomers according to the formula CH2 = CR3R2, wherein R3 is H or a C? -C3 alkyl group and R2 is a linear, branched or cyclic C1-C22 alkyl or alkenyl group. wherein the low molecular weight polymer has an average molecular weight number from 400 to 12,000 and may optionally include one or more functional groups selected from the group consisting of hydroxyl, amine, epoxy, carboxylic acid, carboxylic acid esters, and carboxylic acid anhydrides.
2. The thermoplastic sheet according to claim 1, characterized in that the styrenic monomers are selected from the group consisting of styrene, p-methyl styrene, α-methyl styrene, tertiary butyl styrene, dimethyl styrene, brominated or chlorinated nuclear derivatives of the same and combinations thereof.
3. The thermoplastic sheet according to claim 1, characterized in that the maleate-type monomers are selected from the group consisting of maleic anhydride, maleic acid, fumaric acid, linear, branched or cyclic alkyl esters of C? -C? 2 of maleic acid, linear, branched or cyclic alkyl esters of C? -C? 2 of fumaric acid, itaconic acid, linear, branched or cyclic alkyl esters of itaconic acid C? -C? 2, and itaconic anhydride.
4. The thermoplastic sheet according to claim 1, characterized in that the elastomeric polymers are selected from the group consisting of homopolymers of butadiene or isoprene, and randomly, block copolymers, diblock AB, or ABA triblock of a conjugated diene with a styrenic monomer and / or acrylonitrile.
5. The thermoplastic sheet according to claim 1, characterized in that the polymers Elastomers are one or more block copolymers selected from the group consisting of diblock and triblock copolymers of styrene-butadiene, styrene-butadiene-styrene, styrene-isoprene, styrene-isoprene-styrene, partially hydrogenated styrene-isoprene-styrene and combinations of the same.
The thermoplastic sheet according to claim 1, characterized in that the low molecular weight polymers include repeating units resulting from the polymerization of one or more monomers selected from 1-butene, isobutylene, 2-butene, isoprene, butadiene, diisobutylene, 1-pentene, 2-pentene, 1-hexene, 2-hexene, 3-hexene, 1,3-hexadiene, 2,4-hexadiene, isoprenol, ethylene, propylene and combinations thereof.
7. The thermoplastic sheet according to claim 1, characterized in that R is methyl, R is non-methyl and when R3 is methyl, R2 is not methyl.
8. The thermoplastic sheet according to claim 1, characterized in that the low molecular weight polymers comprise polybutadiene.
9. The thermoplastic sheet according to claim 8, characterized in that the polybutadiene has a content of 1,2-vinyl of at least 30% by weight based on the weight of the polybutadiene.
10. The thermoplastic sheet in accordance with claim 1, characterized in that the low molecular weight polymers contain one or more functional groups selected from the group consisting of hydroxyl, amine, epoxy, carboxylic acid, carboxylic acid esters, and carboxylic acid anhydrides.
The thermoplastic sheet according to claim 1, characterized in that the styrenic and maleate type monomers and the copolymers formed thereof comprise a continuous phase and the elastomeric polymers comprise a dispersed particulate phase having particles with an average particle size from about 0.1 microns to about 11 microns.
12. The thermoplastic sheet according to claim 11, characterized in that the aspect ratio of the dispersed particles is from about 1 to about 5.
The thermoplastic sheet according to claim 1, characterized in that the weight average molecular weight of the copolymer formed is from about 20,000 to about 1,000,000.
The thermoplastic sheet according to claim 1, characterized in that the thermoplastic sheet has a notched IZOD impact value, determined in accordance with ASTM D256, of at least 2.5 foot-pounds / inch (0.136m-kg / cm) ).
15. The thermoplastic sheet according to claim 1, characterized in that the thermoplastic sheet has a value of swelling index from about 10 to about 20.
The thermoplastic sheet according to claim 1, characterized in that the thermoplastic sheet has a value of breaking stress from about 10 to about 25%, determined in accordance with ATSM D638.
17. The thermoplastic sheet according to claim 1, characterized in that it further comprises one or more other polymers blended with the polymer composition.
The thermoplastic sheet according to claim 17, characterized in that the other polymers are selected from the group consisting of crystalline polystyrene, high impact polystyrenes, polyphenylene oxide, copolymers of styrene and maleic anhydride and / or (meth) acrylates of linear, branched or cyclic alkyl C? ~ C12, copolymers modified with styrene rubber and maleic anhydride and / or linear, branched or cyclic C? -C? 2 alkyl (meth) acrylates, polycarbonates, polyamides, polyesters, polyolefins, polyolefins maleated, polyvinylidene chloride, acrylonitrile / (meth) acrylate copolymers, ethylene / vinyl acetate copolymers, ethylene vinyl alcohol copolymers, and combinations thereof.
19. The thermoplastic sheet according to claim 17, characterized in that the polymer composition is present in from 10% to 9C% and the other polymers are present from 10% to 90% of the mixture based on the weight of the mixture.
20. The thermoplastic sheet according to claim 1, characterized in that it further comprises one or more additives selected from the group consisting of heat stabilizers, light stabilizers, softening agents; plasticizers, colorants, pigments; antiblock agents; sliding agents, lubricants; coloring agents; antioxidants; ultraviolet light absorbers; fillers; antistatic agents; impact modifiers, and combinations thereof.
21. An article characterized in that it is produced from the thermoplastic sheet according to claim 1.
22. The article according to claim 21, characterized in that the article is produced by thermoforming the thermoplastic sheet.
23. A container suitable for use in heating food with microwaves characterized in that it is formed of the thermoplastic sheet composition according to claim 1.
24. A method for producing a thermoplastic sheet characterized in that it comprises: to provide a polymer composition in polymer melt form prepared by the polymerization of a mixture comprises: about 40% up to 90% by weight of one or more styrenic monomers; and about 5% to about 45% by weight of one or more maleate monomers; and combining the copolymer with about 0.1% to about 25% by weight of one or more elastomeric polymers having an average molecular weight number greater than 12,000; and about 0.1% to about 10% by weight of one or more low molecular weight polymers comprising repeating units of one or more monomers according to the formula CH2 = CR3R2, wherein R3 is H or a C? -C3 alkyl group and R2 is a linear, branched or cyclic C1-C22 alkyl or alkenyl group. wherein the low molecular weight polymer has an average molecular weight number from 400 to 12,000 and may optionally include one or more functional groups selected from the group consisting of hydroxyl, amine, epoxy, carboxylic acid, carboxylic acid esters, and anhydrides of carboxylic acid; and extruding the polymer composition to provide a thermoplastic sheet
25. The method for producing a thermoplastic sheet of according to claim 24, characterized in that it comprises: adding the low molecular weight polymer to a partially polymerized syrup comprised of elastomeric polymer, styrenic monomers, and maleate monomers, after which syrup leaves a reactor and enters a devolatilizer.
26. The method for producing a thermoplastic sheet according to claim 24, characterized in that it comprises: forming a low molecular weight polymer solution, maleate type monomer, and elatomeric polymer in the styrenic monomer, continuously feeding the solution with the styrenic monomer within from a vessel of the polymerization reactor, and devolatilize the stream leaving the polymerization reactor vessel.
27. The method for producing a thermoplastic sheet according to claim 24, characterized in that it comprises: adding a mixture comprising a polymer of low molecular weight and elastomeric polymer inside the polymerization reactor vessel, polymerizing a feed of styrenic monomer and monomer Maleate type in the presence of the low molecular weight polymer and elastomeric polymer in a polymerization reactor vessel, and devolatilize the stream leaving the polymerization reactor vessel thereby producing the polymer composition.
28. The method for producing a thermoplastic sheet according to claim 24, characterized in that it comprises: forming a solution of maleate monomer and elastomeric polymer inside a polymerization reactor vessel to produce a partially polymerized styrenic syrup, adding the low weight polymer Molecularly to partially polymerized styrenic syrup after it leaves the reactor vessel and devolatilizes the stream after the low molecular weight polymer has been added to the partially polymerized styrenic syrup thereby producing the polymer composition.
29. The method for producing a thermoplastic sheet according to claim 24, characterized in that it comprises: forming a solution of maleate monomer and elastomeric polymer, continuously feeding the solution with the styrenic monomer into a polymerization reactor vessel to produce a partially polymerized styrenic syrup, devolatilizing the stream leaving the polymerization reactor vessel, and composing the low molecular weight polymer within the stream in an extrusion process thereby producing the polymer composition.
30. The method for producing a thermoplastic sheet according to claim 24, characterized in that the polymer composition is prepared by a solution or Bulk polymerization in the presence from 0.01 to 0.1% by weight based on the mixture of a tetrafunctional peroxide initiator of the formula: wherein R1 is selected from the t-C4_6 alkyl radicals and R is a neopentyl group, in the absence of a crosslinking agent.
31. The method for producing a thermoplastic sheet according to claim 30, characterized in that the tetrafunctional initiator is selected from the group consisting of tetrakis- (t-amyl-peroxycarbonyloxymethyl) methane, and tetrakis- (t-butylperoxycarbonyloxy-methyl) methane. .
32. The method for producing a thermoplastic sheet according to claim 24, characterized in that a crystallizing agent selected from the group consisting of calcium carbonate, barium stearate, aluminum oxide, aluminum hydroxide, talc, clay, titanium dioxide. , silica, diatomaceous earth, mixtures of citric acid and sodium bicarbonate is added to the polymer composition before extrusion.
33. The method for producing a thermoplastic sheet according to claim 24, characterized in that the styrenic monomers are selected from the group consisting of of styrene, p-methyl styrene, α-methyl styrene, tertiary butyl styrene, dimethyl styrene, brominated or chlorinated nuclear derivatives thereof and combinations thereof. 3 .
The method for producing a thermoplastic sheet according to claim 24, characterized in that the maleate-type monomers are selected from the group consisting of maleic anhydride, maleic acid, fumaric acid, linear, branched or cyclic alkyl esters of C? -C? 2 of maleic acid, linear, branched or cyclic alkyl esters of C? -C? 2 of fumaric acid, itaconic acid, linear, branched or cyclic alkyl esters of itaconic acid C? -C? 2, and itaconic anhydride.
35. The method for producing a thermoplastic sheet according to claim 24, characterized in that the elastomeric polymers are selected from the group consisting of homopolymers of butadiene or isoprene, and randomly, block copolymers, diblock AB, or triblock ABA of a conjugated diene with a styrenic monomer and / or acrylonitrile.
36. The method for producing a thermoplastic sheet according to claim 24, characterized in that the elastomeric polymers are one or more block copolymers selected from the group consisting of diblock and triblock copolymers of styrene-butadiene, styrene- butadiene-styrene, styrene-isoprene, styrene-isoprene-styrene, partially hydrogenated styrene-isoprene-styrene and combinations thereof.
37. The method for producing a thermoplastic sheet according to claim 24, characterized in that the low molecular weight polymers include repeat units resulting from the polymerization of one or more monomers selected from 1-butene, isobutylene, 2-butene, isoprene, butadiene, diisobutylene, 1-pentene, 2-pentene, 1-hexene, 2-hexene, 3-hexene, 1,3-hexadiene, 2,4-hexadiene, isoprenol, ethylene, propylene and combinations thereof.
38. The method for producing a thermoplastic sheet according to claim 24, characterized in that R2 is methyl, R3 is non-methyl and when R3 is methyl, R2 is not methyl.
39. The method for producing a thermoplastic sheet according to claim 24, characterized in that the low molecular weight polymers comprise polybutadiene.
40. The method for producing a thermoplastic sheet according to claim 24, characterized in that the polybutadiene has a content of 1,2-vinyl of at least 30% by weight based on the weight of the polybutadiene.
41. The method for producing a thermoplastic sheet according to claim 24, characterized in that the low molecular weight polymers contain one or more groups functional groups selected from the group consisting of hydroxyl, amine, epoxy, carboxylic acid, carboxylic acid esters, and carboxylic acid anhydride.
42. The method for producing a thermoplastic sheet according to claim 24, characterized in that the styrenic and maleate type monomers and the copolymers formed thereof comprise a continuous phase and the elastomeric polymers comprise a dispersed particulate phase having particles with a size of average particle from about 0.1 microns to about 11 microns.
43. The method for producing a thermoplastic sheet according to claim 42, characterized in that the aspect ratio of the dispersed particles is from about 1 to about 5.
The method for producing a thermoplastic sheet according to claim 24, characterized in that the weight average molecular weight of the copolymer formed is from about 20,000 to about 1,000,000.
45. The method for producing a thermoplastic sheet according to claim 24, characterized in that the thermoplastic sheet has a notched IZOD impact value, determined in accordance with ASTM D256, of at least 2.5 foot-pounds / inch (0.136m-kg) / cm).
46. The method for producing a thermoplastic sheet according to claim 24, characterized in that the The thermoplastic sheet has a melt index value from about 10 to about 20.
47. The method for producing a thermoplastic sheet according to claim 24, characterized in that the thermoplastic sheet has a tensile stress value from about 10 to about 25. %, determined in accordance with ATSM D638.
48. The method for producing a thermoplastic sheet according to claim 24, characterized in that prior to the step of extruding the polymer composition, a step is performed which includes mixing one or more of the other polymers with the polymer composition.
49. The method for producing a thermoplastic sheet according to claim 48, characterized in that the other polymers are selected from the group consisting of crystalline polystyrene, high impact polystyrenes, polypheemlene oxide, styrene and maleic anhydride copolymers and / or ( met) linear, branched or cyclic C1-C12 alkyl acrylates, copolymers modified with styrene rubber and maleic anhydride and / or linear, branched or cyclic C? -C? 2 alkyl (meth) acrylates, polycarbonates, polyamides, polyesters, polyolefms, maleated polyolefms, polyvinylidene chloride, acrylpropyl / (meth) acrylate copolymers, ethylene / vinyl acetate copolymers, ethylene vinyl alcohol copolymers, and combinations thereof.
50. The method for producing a thermoplastic sheet according to claim 48, characterized in that the polymer composition and the other polymers are mixed to form a mixture so that the polymer composition is present in from 10% to 90% and the other polymers are present from 10% to 90% of the mixture based on the weight of the mixture.
51. The method for producing a thermoplastic sheet according to claim 24, characterized in that the polymer composition further comprises one or more additives selected from the group consisting of heat stabilizers, light stabilizers, softening agents; plasticizers, colorants, pigments; antiblock agents; sliding agents, lubricants; coloring agents; antioxidants; ultraviolet light absorbers; fillers; antistatic agents; impact modifiers, and combinations thereof.
52. A thermoplastic sheet characterized in that it is made in accordance with claim 24.
53. An article characterized in that it is produced from the thermoplastic sheet according to claim 52.
54. A container suitable for use in heating food with microwaves characterized in that it is formed of the thermoplastic sheet according to claim 52.
55. The method for producing a thermoplastic sheet according to claim 24, characterized in that it comprises the step of extruding or laminating a top layer of solid sheet on at least a portion of an upper surface of the thermoplastic sheet.
56. The method for producing a thermoplastic sheet according to claim 55, characterized in that the upper layer of solid sheet comprises a resin selected from the group consisting of crystalline polystyrene, high impact polystyrenes, polyphenylene oxide, copolymers of styrene and maleic anhydride and or linear, branched or cyclic alkyl (meth) acrylates C? ~ C? 2, copolymers modified with styrene rubber and maleic anhydride and / or linear, branched or cyclic Ci-C12 (meth) alkyl acrylates, polycarbonates, polyamides, polyesters, polyolefins, maleated polyolefins, polyvinylidene chloride, acrylonitrile / (meth) acrylate copolymers, ethylene / vinyl acetate copolymers, ethylene alcohol copolymers vinyl, and combinations thereof.
57. A thermoplastic sheet characterized in that it is made according to the method according to claim 55.
58. An article characterized in that it is produced from the thermoplastic sheet according to claim 57.
59. A container suitable for use in the heating food with microwaves characterized in that it is formed of the thermoplastic sheet according to claim 57.
60. The method for producing a thermoplastic sheet according to claim 24, characterized in that it comprises the steps of: extruding or laminating a top layer on at least a portion of a top surface of the thermoplastic sheet: and extruding or laminating a bottom layer on at least a portion of a bottom surface of the thermoplastic sheet to form a sandwich structure thermoplastic sheet.
61. The method for producing a thermoplastic sheet according to claim 60, characterized in that the upper layer and the lower layer independently comprise a resin selected from the group consisting of crystalline polystyrene high impact polystyrenes, polyphenylene oxide, styrene copolymers and maleic anhydride and / or linear, branched or cyclic alkyl (meth) acrylates Ci-C 2, copolymers modified with styrene rubber and maleic anhydride and / or linear, branched or cyclic alkyl (meth) acrylates C? -C? 2, polycarbonates, polyamides, polyesters, polyolefins, maleated polyolefins, polyvinylidene chloride, acrylonitrile / (meth) acrylate copolymers, ethylene / vinyl acetate copolymers, ethylene vinyl alcohol copolymers, and combinations thereof.
62. A thermoplastic sheet of a sandwich structure characterized in that it is made according to the method of claim 61.
63. An article characterized in that it is made from the thermoplastic sheet of a sandwich structure according to claim 62.
64. A container suitable for use in heating food with microwaves characterized in that it is formed of the thermoplastic sheet according to claim 62.
65. A thermoplastic sheet characterized in that it is made according to the method of claim 48.
66. An article characterized in that it is produced from the thermoplastic sheet according to claim 65.
67. A container suitable for use in heating food with microwaves characterized in that it is formed of the thermoplastic sheet according to claim 65.
The method for producing a thermoplastic sheet according to claim 48, characterized in that it comprises the step of extruding or laminating a top layer of solid sheet over at least a portion of a surface top of the thermoplastic sheet.
69. The method for producing a thermoplastic sheet according to claim 68, characterized in that the upper layer of the solid sheet comprises a resin selected from the group consisting of crystalline polystyrene high impact polystyrenes, polyphenylene oxide, copolymers of styrene and anhydride maleic and / or linear, branched or cyclic alkyl (meth) acrylates C? -C? 2, copolymers modified with styrene rubber and maleic anhydride and / or linear, branched or cyclic C1-C12 alkyl (meth) acrylates, polycarbonates , polyamides, polyesters, polyolefins, maleated polyolefins, polyvinylidene chloride, acrylonitrile / (meth) acrylate copolymers, ethylene / vinyl acetate copolymers, ethylene vinyl alcohol copolymers, and combinations thereof.
70. A thermoplastic sheet characterized in that it is made according to the method of claim 68.
71. An article characterized in that it is produced from the thermoplastic sheet according to claim 70.
72. A container suitable for use in heating food with microwaves characterized in that it is formed of the thermoplastic sheet according to claim 70.
The method for producing a thermoplastic sheet of according to claim 48, characterized in that it comprises the steps of: extruding or laminating a top layer on at least a portion of an upper surface of the thermoplastic sheet: and extruding or laminating a bottom layer on at least a portion of a surface bottom of the thermoplastic sheet to form a thermoplastic sheet of sandwich structure.
74. The method for producing a thermoplastic sheet according to claim 73, characterized in that the upper layer and the lower layer independently comprise a resin selected from the group consisting of crystalline polystyrene, high impact polystyrenes, polyphenylene oxide, styrene copolymers and maleic anhydride and / or linear alkyl, branched cyclic C? ~ C12, copolymers modified with styrene rubber and maleic anhydride and / or (meth) linear, branched or cyclic C-C? 2, polycarbonates, polyamides, polyesters, polyolefms, maleated polyolefms, polyvinylidene chloride, acrylomethyl / (meth) acrylate copolymers, ethylene / vill acetate copolymers, ethylene vinyl alcohol copolymers, and combinations thereof.
75. A thermoplastic sheet of a sandwich structure characterized by being made in accordance with with the method of claim 73.
76. An article characterized in that it is produced from the thermoplastic sheet of a sandwich structure according to claim 75.
77. A container suitable for use in heating food with microwaves characterized in that it is formed of the thermoplastic sheet according to claim 75.
78. A two layer thermoplastic sheet characterized in that it comprises a first layer including the thermoplastic sheet according to claim 1 and a second layer comprising one or more reams selected from the group that consists of crystalline polystyrene, high impact polystyrenes, polyphenylene oxide, styrene and maleic anhydride copolymers and / or linear, branched or cyclic (meth) acrylates C? -C? 2, copolymers modified with styrene rubber and maleic anhydride and / or (meth) alkyl linear, branched or C-C? 2, poly-alkyl acyllates, poly carbonates, polyamides, polyesters, polyolefins, maleated polyolefms, polyvinylidene chloride, acrylonitrile / (meth) acrylate copolymers, ethylene / viml acetate copolymers, ethylene vinyl alcohol copolymers, and combinations thereof.
79. An article characterized in that it is produced from the two layers of thermoplastic sheet in accordance with the claim 78.
80. A container suitable for use in heating food with microwaves characterized in that it is formed of the thermoplastic sheet according to claim 78.
81. A thermoplastic sheet of a sandwich structure characterized in that it comprises middle layer including the thermoplastic sheet according to claim 1, and an upper layer and a lower layer independently comprising one or more resins selected from the group consisting of crystalline polystyrene, high impact polystyrenes, polyphenylene oxide, copolymers of styrene and maleic anhydride and / or linear, branched or cyclic alkyl (meth) acrylates C? -Ci2, copolymers modified with styrene rubber and maleic anhydride and / or linear, branched or cyclic C1-C? 2 alkyl (meth) acrylates, polycarbonates, polyamides, polyesters, polyolefins, polyolefins maleadas, polyvinylidene chloride, copolymers of a crilonitrile / (meth) acrylate, ethylene / vinyl acetate copolymers, ethylene vinyl alcohol copolymers, and combinations thereof.
82. An article characterized in that it is produced from the thermoplastic sheet of a sandwich structure according to claim 81.
83. A container suitable for use in the food heating with microwaves characterized in that it is formed of the thermoplastic sheet according to claim 81.
84. A container suitable for use in heating food with microwaves formed by thermoforming a thermoplastic sheet characterized in that it comprises a polymeric composition containing a copolymer formed by polymerization of a mixture comprising: about 40% to 90% by weight of one or more styrenic monomers; and about 5% to about 45% by weight of one or more maleate monomers; and combining the copolymer with about 0.1% to about 25% by weight of one or more elastomeric polymers having an average molecular weight number greater than 6,000; and optionally up to about 10% by weight of one or more low molecular weight polymers comprising one or more monomers according to the formula CH 2 = CR 3 R 2, wherein R 3 is H or a C 1 -C 3 alkyl group and R 2 is a group linear, branched or cyclic C alquilo-C22 alkyl or alkenyl, wherein the low molecular weight polymer has a number of molecular weight average from 400 to 6,000 and may optionally include one or more functional groups selected from the group consisting of hydroxyl, amine, epoxy, carboxylic acid, carboxylic acid esters, and carboxylic acid anhydrides.