Process for producing a foamed polymer endowed with high resistance to solvents and high temperature resistance

Abstract: A process for producing a foamed polymer comprises the steps of: mixing, in a dissolver, a mixture constituted by at least one isocyanate and a first unsaturated anhydride, adding to the mixture, a second aromatic anhydride, at least one foaming agent, a vinylidene compound, poly(vinyl chloride) and a heat stabilizer; until a paste is obtained curing said paste at atmospheric pressure, and at a temperature not higher than 80°C; completing the curing of the paste-like mixture under pressure, by increasing temperature up to 180°C and subsequent cooling, until partially foamed germs are obtained; and completing the germ foaming process, by heating.

Description: The preferred, well-known manufacturing process to produce a cellular foamed body based on a vinyl chloride polymer or copolymer, uses a mixture of one or more isocyanates, such as toluenediisocyanate, polymethylenepolyphenylisocyanate, poly(vinyl chloride), maleic anhydride, phtalic anhydride, one or more vinylidene compounds, such as styrene and acrylonitrile, a foaming agent, such as azodiisobutyronitrile, one or more stabilizer compounds, such as tribasic lead sulfate, dibasic Lead phosphite, dibasic lead phthalate, or barium-cadmium-zinc, lead-barium complexes. Said mixture, which, after compounding, shows a paste-like consistency, is poured into a mould, and then the temperature of the mould is increased, under pressure, until a value of 180°C is reached, to cause poly(vinyl chloride) to gel. The semifoamed article obtained in that way -- also designated "germ" -- will be caused to complete its foaming by heating it in the presence of water or steam. NL-A-135 779 describes a process of this type - others methods to produce a cellular foamed body based on a vinyl chloride polymer are for instance described in FR-A-1 266 487 and EP-A-74 907. EP-A-74907 relates to a process for producing a cellular foamed product by extrusion of a mixture comprising: a poly(vinyl chloride), a foaming agent and an organic anhydride. The obtained product is cut in pieces which are foamed in water at a temperature over 70°C. These types of production methods are not very suitable for a large-scale commercial production, in that compound lots exceeding a certain weight -- about 300-400 kg -- cannot be prepared, with the number of produced germs being consequently reduced; the solution containing maleic anhydride, vinylidene compound, isocyanate is laborious and not very reliable, and, inasmuch as it is prepared at a temperature comprised within the range of from 30°C to 35°C, when it comes into contact with the other components, the above described mixture causes the compound which is being prepared to densify, and eventually causes it to become unusable. The general purpose of the present invention is of solving the above technical problems, by providing a production process which can be used at the commercial level, in a reliable and certain way. The present invention relates to a process for producing a foamed polymer, comprises the following steps: inside a dissolver, mixing a mixture constituted by at least one isocyanate and a first unsaturated anhydride, which is charged to the dissolver in the liquid state and at a temperature of around 70°C ; progressively cooling said mixture, with continuous stirring, until a temperature not higher than 22°C is reached; adding to the mixture, with continuous stirring, a second aromatic anhydride, at least one foaming agent, poly(vinyl chloride), and a heat stabilizer; keeping said mixture with continuous stirring, at said temperature, until a mixture with a paste-like consistency (a "paste") is obtained, which is poured, after a preliminary filtration, into a mould, or container; curing the paste by charging the container to an oven under atmospheric pressure and at a temperature not higher than 80°C; causing the paste to undergo complete curing under pressure, by increasing the temperature up to 180°C, and subsequent cooling until partially foamed germs are obtained; and completing the germ foaming process by heating in water, or inside ovens in the presence of steam. Particular embodiments of the process according to the present invention are disclosed in the following disclosure, and are defined in the dependent claims. One or more isocyanates, such as 2,4-2,6-toluene-diisocyanate, 4,4'-diphenylmethane diisocyanate, and a first unsaturated anhydride, such as maleic anhydride, are charged to a dissolver. Maleic anhydride, charged in the liquid state, at the temperature of 70°C, with the reaction mixture being kept constantly stirred, with the impeller of the dissolver revolving at a peripheral speed comprised within the range of from 6 meter/second to 9 meter/second, preferably of 8 meter/second (20 feet/second to 30 feet/second, preferably of 26.8 feet/second), said mixture is progressively cooled, until a temperature is reached, which is comprised within the range of from 14°C to 18°C. After reaching this temperature, which is then kept constant, a second anhydride, such as phthalic anhydride, one or more foaming agents, such as azodiisobutyronitrile and azodicarbonamide, a vinylidene compound, such as styrene, poly(vinyl chloride) and a heat stabilizer, are added to the dissolver. The compounding is continued, still with cooling, with the peripheral speed of the impeller set at a value comprised within the range of from 16 meter/second to 23 meter/second, and preferably of 20 meter/second (53 feet/second to 76 feet/second, and preferably of 67 feet/second). In that way, a perfectly homogeneous paste-like compound ("paste") is obtained, which, after filtration, is poured into suitable containers for the subsequent "curing" process, or directly into the mould(s). During this operation, the temperature of the compound is kept comprised within the range of from 18°C to 22°C. The filtration of the paste is essential, in order to eliminate the presence of impurities deriving from the raw materials which are used to prepare the compound, to prevent that, during the foaming step, in the cellular structure of the foamed plastic article cavities or cracks may develop, which would then render unusable the finished article. The "grafting" reaction of maleic anhydride-styrene-poly(vinyl chloride) is initiated by charging the paste, inside suitable containers, to ovens inside which air is kept circulating at a speed of 0.5-2 m/second, relative environmental humidity is of 15-20%, and temperature is comprised within the range of from a value of 35°C up to a value of 80°C, for a reaction time of from 1 to 6 hours. In that way, bodies are obtained, the hardness of which is such that they can be mechanically handled to be charged to the hollows of the moulds. The reaction is then brought to completeness under pressure, and progressively increasing temperature, with the foaming agents undergoing decomposition -- with azodiisobutyronitrile also acting as a "polymerization initiator -- and when the temperature of 170°C-180°C is reached, the gelation of poly(vinyl chloride) takes place. During the cooling step, partially foamed germs are obtained, which will end their foaming process by being heated inside ovens, in the presence of steam. The process of paste "curing" makes it possible the time of "pressure heating/cooling" cycle, to be reduced to an extent of from a 30% up to a 40%, with the depth of the hollow of the mould being the same, as compared to the production processes known from the prior art. Inside ovens at atmospheric pressure, under such a dynamic atmosphere of saturated steam that in each point inside the oven, the difference between the local temperature and the setpoint temperature of oven is of ±2°C, with isocyanates and anhydrides reacting with water, the semifoamed germs will end their foaming process, reaching the desired density, within a time ranging from 4 to 35 hours. In order to obtain a cellular foamed article anyway endowed with high temperature resistance and good resistance to chemical attack, by following the same operating modalities, a paste can be used, which consists of a mixture of one or more isocyanates, such as 2,4-2,6-toluenediisocyanate and/or 4,4'-diphenyl methane diisocyanate, two anhydrides, such as maleic anhydride and phthalic anhydride, poly(vinyl chloride), one or more foaming agents, such as azodiisobutyronitrile and azodicarbonamide, one or more heat stabilizers, and, if desired, high-colouring power pigments. Examples for the production on the industrial scale, according to the present process, of cellular foamed articles based on poly(vinyl chloride). Example 1 In a paste constituted by a mixture of: from 1 % to 20 % of 4,4'-diphenylmethane diisocyanate ; from 10 % to 30 % of 2,4-2,6-toluene diisocyanate ; from 5 % to 10 % of maleic anhydride; from 40 % to 60 % of poly(vinyl chloride); from 3 % to 10 % of phthalic anhydride; from 0.5 % to 7 % of azodiisobutyronitrile ; from 0.1 % to 5 % of azodicarbonamide from 1 % to 5 % of styrene ; and from 0.5 % to 2 % of dibasic lead phthalate, wherein the percentage of the individual components by weight is referred to the total weight of the compound, and said compound is mixed in the dissolver, is filtered, is poured directly into the mould, after the "curing" process and the subsequent transfer of the cured bodies into the mould, after performing the "pressure heating/cooling" cycle, the semifoamed germs will end their expansion inside ovens under a dynamic atmosphere of saturated steam. The cellular foamed article will be submitted to a thermal treatment inside air ovens, at a temperature comprised within the range of from a value of 80°C to a value of 125°C, for a time comprised within the range of from 24 hours to 120 hours, and as the result, a cellular foamed article will be obtained, which has a density of 55 kg/m 3 , a flexural heat distorsion temperature comprised within the range of from 130°C to 140°C, a compression strength at the temperature of 80°C of 4.1 kg/cm 2 , a very high chemical resistance such that, e.g., the absorption of styrene after a 2-hour soaking of a sample of foamed article is of 2% by weight, relatively to the weight of the tested product, suitable for withstanding industrial processing cycles involving temperatures of 120°C, pressures of 1 kg/cm 2 for a time of 90 minutes. Example 2 By performing the production cycle set forth in Example 1, and using a mixture consisting of: from 1 % to 10 % of 4,4'-diphenylmethane diisocyanate; from 1 % to 27 % of 2,4-2,6-toluene diisocyanate ; from 6 % to 9 % of maleic anhydride; from 50 % to 55 % of poly(vinyl chloride); from 0.1 % to 1 % of azodiisobutyronitrile; from 0.1 % to 1 % of azodicarbonamide; from 1 % to 2.8% of styrene; from 5 % to 10 % of talc of "Micronic 00S" type; and from 0.5 % to 2.5% of tribasic lead sulfate; With the percentage of the individual components by weight being referred to the total weight of the compound, the semi foamed germs having reached the desired foaming rate, after a thermal treatment inside air ovens inside which temperature is comprised within the range of from a minimum value of 90°C to a maximum value of 140°C, for a time comprised within the range of from a minimum time of 48 hours to a maximum time of 360 hours, a cellular foamed article is obtained, which has a density of 300 kg/m 3 , and is endowed with characteristics of flexural heat distorsion temperature comprised within the range of from 150°C to 160°C, compression strength at room temperature of 100 kg/cm 2 , a nearly perfect chemical resistance in that, its styrene absorption after a 2-hour soaking of a sample of foamed article is of 0.1-0.2% by weight, relatively to the weight of the tested product, suitable for being used in industrial production cycles involving temperatures of 130°C, pressures of from 2 to 4 kg/cm 2 for a time of up to 5 hours. Example 3 A paste composed by a mixture of: from 2 % to 20 % of 4,4'-diphenylmethane diisocyanate; from 10 % to 29 % of 2,4-2,6-toluene diisocyanate; from 5 % to 12 % of maleic anhydride; from 49 % to 60 % of poly(vinyl chloride); from 4 % to 13 % of phthalic anhydride; from 0.5 % to 7 % of azodiisobutyronitrile; from 0.1 % to 2 % of azodicarbonamide ; and from 0.5 % to 1.5% of dibasic lead phosphite, with the percentages of individual components by weight being referred to the total weight of the compound, still according to the present manufacturing process, will yield a cellular foamed article having a density of 80 kg/m 3 , a flexural heat distorsion temperature of 100°C, a styrene absorption after a 2-hour soaking of the whole sample, of 1.7% by weight, relatively to the weight of the tested sample, good elasticity characteristics, constant use temperature of 80°C. Example 4 A paste composed by a mixture of: from 5 % to 15 % of 4,4'-diphenylmethane diisocyanate; from 15 % to 25 % of 2,4-2,6-toluene diisocyanate ; from 3 % to 10 % of maleic anhydride; from 45 % to 55 % of poly(vinyl chloride); from 8 % to 14 % of phthalic anhydride; from 2 % to 10 % of azodiisobutyronitrile; from 0.02% to 2 % of azodicarbonamide; and from 0.2 % to 2 % of polybasic lead phosphite-sulfate, with the percentages of individual components by weight being referred to the total weight of the compound, still according to the present manufacturing process, will yield a cellular foamed article having a density of 30 kg/ m 3 , a flexural heat distorsion temperature of 100°C, a compression strength of 2.7 kg/cm 2 at room temperature, a styrene absorption, according to the modalities of the preceding examples, of 6%, the structure of the cells is fine and regular. The purpose mentioned in the preamble of the disclosure is thus achieved.

Claims: A process for producing a foamed polymer, comprises the following steps: inside a dissolver, mixing a mixture constituted by at Least one isocyanate and a first unsaturated anhydride, which is charged to the dissolver in the liquid state and at a temperature of around 70°C; progressively cooling said mixture, with continuous stirring, until a temperature not higher than 22°C is reached; adding to the mixture, with continuous stirring, a second aromatic anhydride, at least one foaming agent, poly(vinyl chloride), and a heat stabilizer; keeping said mixture with continuous stirring, at said temperature, until a mixture with a paste-like consistency (a "paste") is obtained, which is poured, after a preliminary filtration, into a mould, or container; curing the paste by charging the container to an oven under atmospheric pressure and at a temperature not higher than 80°C; causing the paste to undergo complete curing under pressure, by increasing the temperature up to 180°C, and subsequent cooling until partially foamed germs are obtained; and completing the germ foaming process by heating in water, or inside ovens in the presence of steam. A process according to claim 1, characterized in that a vinylidene compound is also added to said mixture. A process according to claim 1, characterized in that: said mixture is constituted by 2,4-2,6-toluene diisocyanate and/or 4,4'-diphenylmethane diisocyanate and maleic anhydride; said second aromatic anhydride is constituted by phthalic anhydride; said foaming agents are azodiisobutyronitrile and/or azodicarbonamide; said vinylidene compound is styrene. A process according to claims 1 and 3, characterized in that: said first liquid, unsaturated anhydride is at a temperature of round 70°C; the mixture is kept with constant stirring, with the impeller of the dissolver having a peripheral speed comprised within the range of from 6 meter/second to 9 meter/second (20 feet/second to 30 feet/second); said mixture is progressively cooled until a temperature comprised within the range of from 14°C to 18°C is reached; after reaching and maintaining said temperature, to the mixture inside the dissolver said second aromatic anhydride, said at least one foaming agent, a vinylidene compound, poly(vinyl chloride) and a heat stabilizer are added; still with cooling, compounding is continued and the peripheral speed of the impeller is set at a value comprised within the range of from 16 meter/second to 23 meter/second (53 feet/second up to 76 feet/second) the resulting, perfectly homogeneous, paste is poured, after being filtered, into suitable containers, for the subsequent "curing" process, or directly into a mould, at a temperature which is kept comprised within the range of from 18°C up to 22°C; the paste contained inside the suitable containers is charged to ovens inside which, with air circulation, wherein air circulates at a speed of 0.5-2 m/second, the relative humidity inside the chamber is of 15-20%, the temperature is comprised within the range of from a value of 35°C up to a value of 80°C, for a time period ranging between 1 and 6 hours, the "grafting" reaction of maleic anhydride-styrene-poly(vinyl chloride) is initiated; under pressure, and progressively increasing the operating temperature, the reaction is completed, with decomposition of the foaming agents, with azodilsobutyronitrile also acting as the "polymerization initiator", and when the temperature of 170°C-180°C is reached, the gelation of poly(vinyl chloride) takes place. by cooling, partially foamed germs are obtained, which will complete their foaming process by being submitted to heating in water, or inside ovens, in the presence of steam. A process according to claim 1, characterized in that: said mixture is constituted by 2,4-2,6-toluene diisocyanate and/or 4,4'-diphenylmethane diisocyanate and maleic anhydride; said second aromatic anhydride is constituted by phthalic anhydride; said foaming agents are azodiisobutyronitrile and/or azodicarbonamide. A process according to claims 1 and 5, characterized in that: said first liquid, unsaturated anhydride is at a temperature of round 70°C; the mixture is kept with constant stirring, with the impeller of the dissolver having a peripheral speed comprised within the range of from 6 meter/second to 9 meter/second (20 feet/second to 30 feet/second) said mixture is progressively cooled until a temperature comprised within the range of from 14°C to 18°C is reached; after reaching and maintaining such a temperature value, to the mixture inside the dissolver said second aromatic anhydride, said at least one foaming agent, poly(vinyl cloride), and a heat stabilizer are added; still with cooling, the compounding is continued and the peripheral speed of the impeller is set at a value comprised within the range of from 15 meter/second to 23 meter/second (50 feet/second up to 76 feet/second) the resulting, perfectly homogeneous, paste is poured, after being filtered, into suitable containers, for the subsequent "curing" process, or directly into a mould, at a temperature which is kept comprised within the range of from 18°C up to 22°C; the paste contained inside the suitable containers is charged to ovens inside which, with air circulation, wherein air circulates at a speed of 0.5-2 m/second, the relative humidity inside the chamber is of 15-20%, the temperature is comprised within the range of from a minimum value of 35°C up to a maximum value of 80°C, for a time period ranging between 1 and 6 hours, said paste undergo curing; under pressure, and progressively increasing the operating temperature, the reaction is completed, with the decomposition taking place of the foaming agents, with azodiisobutyronitrile also acting as the "polymerization initiator", and when the temperature of 170°C-180°C is reached, the gelation of poly(vinyl chloride) taking place. by cooling, partially foamed germs are obtained, which will complete their foaming process by being submitted to heating in water, or inside ovens, in the presence of steam. A process according to claim 1, in which said paste is constituted by a mixture of : from 1 % to 20 % of 4,4'-diphenylmethane diisocyanate; from 10 % to 30 % of 2,4-2,6-toluene diisocyanate ; from 5 % to 10 % of maleic anhydrides; from 40 % to 60 % of poly(vinyl chloride); from 3 % to 10 % of phthalic anhydride; from 0.5 % to 7 % of azodiisobutyronitrile; from 0.1 % to 3 % of azodicarbonamide; from 1 % to 5 % of styrene ; and from 0.5 % to 2 % of dibasic lead phthalate. A process according to claim 1, in which said paste is constituted by a mixture of : from 1 % to 10 % of 4,4'-diphenylmethane diisocyanate; from 1 % to 27 % of 2,4-2,6-toluene diisocyanate ; from 6 % to 9 % of maleic anhydride; from 50 % to 55 % of poly(vinyl chloride); from 0.1 % to 1 % of azodiisobutyronitrile; from 0.1 % to 1 % of azodicarbonamide; from 1.5 % to 2.8% of styrene; from 5 % to 10 % of talc of "Micronic 00S" type having a granulometry D95=28.5 µm, D75=17.0 µm, D50=10.2 µm, D25=5.4µm; and from 0.5 % to 2.5% of tribasic lead sulfate. A process according to claim 1, in which said paste is constituted by a mixture of: from 2 % to 20 % of 4,4'-diphenylmethane diisocyanate; from 10 % to 29 % of 2,4-2,6-toluene diisocyanate; from 5 % to 12 % of maleic anhydride; from 49 % to 60 % of poly(vinyl chloride); from 4 % to 13 % of phthalic anhydride ; from 0.5 % to 7 of azodlisobutyronitrile; from 0.1 % to 2 % of azodicarbonamide; and from 0.5 % to 1.5% of dibasic lead phosphite. A process according to claim 1, in which said paste is constituted by a mixture of from 3 % to 15 % of 4,4'-diphenylmethane diisocyanate; from 15 % to 25 % of 2,4-2,6-toluene diisocyanate from 3 % to 10 % of maleic anhydride; from 45 % to 55 % of poly(vinyl chloride); from 8 % to 14 % of phthalic anhydride ; from 2 % to 10 % of azodiisobutyronitrile; from 0.02% to 2 % of azodicarbonamide; and from 0.2% to 2 % of polybasic lead phosphite-sulfate. A process according to claim 1, characterized in that in order to increase its characteristics of high temperature resistance, the foamed, cellular article is submitted to a thermal treatment in air ovens, inside which the temperature is comprised within the range of from a value of 80°C, up to a value of 140°C, and for a time period ranging from a value of 24 hours, up to a value of 360 hours.

Inventors: LAURI LEONE, LAURI, LEONE
Applicants: POLIMEX S P A, POLIMEX S.P.A.
Application year: 1992
Main classification: C08J9
IPC codes: B29C39, C08L75, C08J9, C08G101, C08G18, B29K105