Method for producing a laminated material

Abstract: A method for producing a laminated material comprising a lower layer of highly-expanded plasticized polyvinyl chloride with cross-linking and a surface layer of thermoplastic resin sheet laminated on an upper surface of said lower layer, said method comprising; sufficiently heating and kneading raw materials for the lower layer except a cross-linking agent and a blowing agent mixing with the reacting groups in an extruder; adding the cross-linking agent and the blowing agent; heating and kneading the obtained material at or less a reacting temperature of the cross-linking agent and a decomposition temperature of the blowing agent to obtain a sheet; heating the sheet to cross-link and expand the sheet to form the lower layer of cross-linked highly-expanded plasticized polyvinyl chloride; and laminating the surface layer of the thermoplastic resin on the upper surface of the lower layer. The polyvinyl chloride resin is (A) a polyvinyl chloride resin having reacting groups in its molecules, or (B) a mixture of a polyvinyl chloride resin having no reacting groups in its molecules and a thermoplastic resin having reacting groups in its molecules.

Description: The present invention relates to a method for producing a highly-expanded non-rigid foamed sheet with cross-linking having a highly homogeneous cell structure for an interior trim material especially for vehicles, and to a method for producing a light-weight laminated material having soft touch and good cushioning as well as excellent mouldability and high-frequency welding workabilty when using the foamed sheet. Conventionally, laminated materials are known as interior trim materials for vehicles having cushioning which are composed of (1) a surface layer of plasticized polyvinyl chloride sheet and a lower foamed layer of expanded polyalkene resin such as polyethene, and polypropene, bonded to the surface layer; (2) a surface layer of plasticized polyvinyl chloride sheet and a lower foamed layer of expanded plasticized polyvinyl chloride without cross-linking, bonded to the surface layer, (3) a surface layer of plasticized polyvinyl chloride sheet and a lower foamed layer of highly-expanded plasticized polyvinyl chloride with cross-linking laminated to the surface layer. In the case of the above-described laminated material (1), it is necessary to cross-link foamed resin layers with electron rays, and then to expand them by heating, which results in a large amount of capital investment. Since this method requires complicated treating processes, it is inferior in productivity. In addition, the laminated material is also inferior in high-frequency welding properties because the lower foamed layer is composed of an expanded polyolefin sheet. In the case of the above-described laminated material (2), the expanded sheet can be produced economically with the general production facilities. However, only an extremely low-expanded sheet is obtained, because of its upper expansion coefficient limit of 3-4. This laminated material lacks, therefore, in softness, light-weight, and cushioning. In addition, since the foamed layer of the laminated material is non-cross-linking, it is crushed when thermoformed so that moulded interior trim material for vehicle can not be obtained. In the case of the above-described laminated material (3), a soft, light and cushioning product can be obtained because of its highly-foamed layer. But the kneading and dispersal of the above-described resin component with a cross-linking agent and a blowing agent is imperfect. As a result of insufficiently controlled temperature and treating time during roll-mill kneading and sheeting by a calender, the cross-linking reaction proceeds partially so that it is difficult to homogeneously cross-link and expand it. As a result thereof, an expanded product with a homogeneous cross-linking structure and a homogeneous cell structure is not obtained, deep drawing mouldability in thermoforming is low, and interior trim material with highly accurate and sharp contours can not be obtained. In addition, because roll-mills are used for kneading and pelletizing, and because sheeting is carried out by means of a calender or an extruder, this process is inferior also in productivity. EP-A-0 019 910 describes such a method of manufacturing a low density synthetic resin foamed body which has some or all of the disadvantages mentioned above. In particular, Example 7 in this citation refers to a composite foamed body which includes 70 parts by weight of EVA (VA content 14%) and 15 parts by weight of vinyl chloride resin, wherein the raw materials excluding the blowing agent are mixed and kneaded by a roll. After adding the blowing agent the mixture is further kneaded, formed into a sheet and expanded. In the said Example 7, dicumylperoxide is used as a cross-linking agent. This means that the cross-linking reaction is a radical reaction. In the polymer, a radical is generated by the degradation of the peroxide so as to cross-link the polymer. Further, the process in Example 7 is a batch process. The aim of the present invention, therefore, is to provide a method for producing a highly-expanded plasticized polyvinyl chloride sheet having a homogeneous cross-linking structure and a homogeneous cell structure, which can be used to produce a laminated material. According to the invention, this is achieved by the method set out in claim 1. Further advantageous features are set out in sub-claims 2 to 16. In the present invention, highly-expanded plasticized polyvinyl chloride with cross-linking for a lower layer (hereinafter referred to as "lower foamed sheet") is formed first, and then thermoplastic resin (hereinafter referred to as "surface layer") is laminated onto the upper surface thereof. The lower foamed sheet is formed first. The raw materials for the lower layer and other materials except a cross-linking agent and a blowing agent (in other words, plasticizer, stabilizer, and pigment) are mixed, and the mixture thus obtained is put in an extruder directly or after pelletized. The mixture is sufficiently heated and kneaded, dispersing each mixing component homogeneously. Then the cross-linking agent and the blowing agent are added concurrently into the same extruder or a separate extruder or an another extruder, heated and kneaded, and dispersed homogeneously and sufficiently in the mixture. The mixture thus obtained is then sheeted with a T-die. The reason why the cross-linking agent and the blowing agent are added later, is as follows. The raw material mixed earlier is dispersed sufficiently and homogeneously with other components such as plasticizer. Thereafter, the cross-linking agent and the blowing agent are added sequentially through another feed port of the same extruder or a separate extruder, or added simultaneously into an another extruder with pre-pelletized mixture, and kneaded. Owing to closed and continuous kneading system, accurate kneading temperature, accurately controlled treatment, controlled time, and kneading effects which are characteristic of an extruder, the reacting groups of the resin and the cross-linking agent undergo a homogeneous cross-linking reaction at a reacting point. Therefore, a very strictly controlled reaction can take place, thereby forming a highly-expanded product with excellent and homogeneous cell structure. The blowing agent is also dispersed sufficiently to obtain an expanded product with homogeneous cell structure. In the conventional method wherein a cross-linking agent and a blowing agent are kneaded and treated concurrently with other components, such accurate dispersing and kneading, cross-linking structure, controlled reaction, and accurately controlled kneading temperature and time are impossible, and therefore, said expanded product with good cell structure, cross-linking structure, and compressive hardness pursued according to the present invention can never be obtained. The resin used for the lower layer foamed sheet according to the present invention may be either of (A) a polyvinyl chloride resin having reacting groups in its molecules, or (B) a mixture of a polyvinyl chloride resin having no reacting groups in its molecules and a thermoplastic resin having reacting groups in its molecules. The polyvinyl chloride resin having reacting groups in its molecules used in case (A) is a copolymer of a vinyl chloride monomer and a monomer containing a hydroxyl or a carboxyl group. Copolymers of a vinyl chloride monomer and a monomer selected from the group consisting of 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, acrylic acid, and methacrylic acid are preferable. The cross-linking agent used in the present invention is an isocyanate compound or an amine compound. 1-10 parts by weight of said cross-linking agent and 5-30 parts by weight of a blowing agent such as azodicarbonamide etc. which is generally used for polyvinyl chloride resin are added to 100 parts by weight of the polyvinyl chloride having reacting groups in its molecules. In case of less than 1 part by weight of the cross-linking agent, too little cross-linking occurs, resulting in too low melting viscosity of heated resin compositions in an expansion process. Thus, too much decomposition gas of the blowing agent escapes into the atmosphere, so only a low expansion coefficient is accomplished, and the desired highly-expanded product can not be obtained. In case of more than 10 parts by weight of the cross-linking agent, too much cross-linking occurs, resulting in a too high melting viscosity. Thus, the growth of cells is prohibited, and the desired highly-expanded product can also not be obtained. In case of less than 5 parts by weight of the blowing agent, its quantity is too small to obtain an expanded product with a desirable expansion coefficient. In case of more than 30 parts by weight of the blowing agent, its quantity is too large to obtain an expanded product with a desirable homogeneous cell structure. If the cross-linking agent and the blowing agent are added in a quantity out of the range specified above, the lower layer foamed sheet with desirable compressive hardness in the present invention can not be obtained, and the obtained lower layer foamed sheet has disadvantages in softness, light-weight and cushioning, and is also inferior in mouldability as an interior trim material. The polyvinyl chloride resin having no reacting group in (B) mixture is a polyvinyl chloride homopolymer, a copolymer of vinyl chloride and vinyl acetate, a copolymer of vinyl chloride and an alkene such as ethene, and propene, a copolymer of vinyl chloride and styrene, or a copolymer of vinyl chloride and vinyl ether. The thermoplastic resin having reacting groups in its molecules mixed with the polyvinyl chloride resin, contains a hydroxyl group, a carboxyl group, or an amino group. The thermoplastic resin is preferably a polyvinyl chloride resin, or an acrylic rubber containing, for example, a hydroxyl group or a carboxyl group, and is most preferably an alkyl acrylate ester. The polyvinyl chloride resin having no reacting groups in its molecules and the thermoplastic resin having reacting groups in its molecules are preferably mixed in the proportion of 20-80 parts by weight to 80-20 parts by weight. If the mixing thereof is performed out of the specified proportion, good cross-linked highly-expanded product in the present invention can not be obtained. 1-10 parts by weight of the cross-linking agent is mixed to 100 parts by weight of the thermoplastic resin having reacting groups in its molecules in said (B) mixture. 5-30 parts by weight of the blowing agent is mixed to 100 parts by weight of the (B) mixture of the polyvinyl chloride having no reacting groups in its molecules and the thermoplastic resin having reacting groups in its molecules. When the lower foamed sheet is formed, stabilizer for expanding of polyvinyl chloride, a plasticizer and pigment are mixed in addition to the above cross-linking agent and blowing agent. The plasticizer used in the present invention is, for example, trimellitic acid ester. 30-60 parts by weight of plasticizer is mixed to 100 parts by weight of total polyvinyl chloride resin having reacting groups and no reacting groups in its molecules. The quantity of the plasticizer affects the compressive hardness of the lower foamed sheet. The above described components for the lower layer foamed sheet are mixed, as described above, in an extruder, and the components are kneaded sufficiently homogeneously below a reacting temperature of the cross-linking agent and below a decomposition temperature of the blowing agent to form extruded unfoamed sheet by means of a T-die. The sheet is then heated on or above the reacting temperature of the cross-linking agent and on or above the decomposition temperature of the blowing agent, using any of a vertical type foam oven, a floating chamber type foam oven (a lateral wire netting type foam oven) or a salt bath, and- the sheet is thereby cross-linked and expanded so that a lower layer foamed sheet with a high expansion coefficient is obtained. It is preferable to form lower layer foamed sheet with an expansion coefficient of 5-30 and a thickness of 0.5-8 mm. As described above, lower layer foamed sheet in the expansion coefficient range and the thickness range is accomplished by choosing a cross-linking agent, a blowing agent and the plasticizer as well as their quantities. When lower layer foamed sheet is formed out of said both ranges, it has following disadvantages: 1) it is inferior in good cushioning due to light-weight and softness; 2) it is inferior in deep drawing mouldability at vacuum forming or air-pressure forming; and 3) its appearance quality as an interior trim material is low because its surface has defects such as craters. It is preferable that the lower layer foamed sheet has a compressive hardness of 0.05-1.0 kg/cm². As described above, lower layer foamed sheet in the compressive hardness range is accomplished by choosing a cross-linking agent, a blowing agent and a plasticizer as well as their quantities. If the compressive hardness is less than 0.05 kg/cm², the obtained lower foamed sheet is too soft, lacks in restoring force after to remove the compressive loading, and is inferior in cushioning as an interior trim material as well as in mouldability at thermoforming. If said compressive hardness is above 1.0 kg/cm², the above-described problems are resolved, but the obtained lower layer foamed sheet is too hard to accomplish softness. A surface layer comprising a thermoplastic resin is formed on the lower layer foamed sheet. The thermoplastic resin sheet used for said surface layer is a resin selected from the group consisting of polyvinyl chloride, copolymer of vinyl chloride and vinylacetate, polyurethane, copolymer of vinyl chloride and polyurethane, copolymer of vinyl chloride and an alkene such as ethene, propene and a mixture of polyvinyl chloride and AS resin, AAS resin, ABS resin nitrile rubber, acrylic rubber and/or EVA resin. These are used as a coloured sheet. AS resin, AAS resin, ABS resin, nitrile rubber, acrylic rubber and/or EVA resin act as a modifying agent for polyvinyl chloride. A plasticizer etc. are further added and mixed to the raw material for the surface layer and then from the mixture the sheet of the surface layer is formed by a calender or an extruder. The plasticizer used in the present invention is, for example, trimellitic acid ester. The modifying agent used in the present invention is, for example, ABS resin, AS resin, and AAS resin. It is preferable that the surface layer has a thickness of 0.2-1.5 mm and a Shore-A-hardness of 40-80. When the thickness of the surface layer is less than 0.2 mm and the surface hardness thereof is less than 40, the obtained laminated material is inferior in scratch resistance, abrasion resistance and mouldability. When the thickness of the surface layer is above 1.5 mm and the surface hardness thereof is above 80, the obtained laminated material is too heavy and too hard to realize light-weight and softness, and sharp contours can not be obtained at thermoforming. The hardness of the surface layer is controlled by choosing the material for the surface layer and the plasticizer as well as their quantities. 30-150 parts by weight of the plasticizer and 10-100 parts by weight of the modifying agent are added and mixed to 100 parts by weight of the polyvinyl chloride so as to obtain the surface layer, preferably having a Shore-A-hardness of 40-80. As described above, from the thermoplastic resin sheet is formed by a calender or an extruder, on which sheet are applied drawn patterns or printed patterns to form a surface layer. Then, the surface layer is laminated on the upper surface of the lower layer foamed sheet using a heat laminating method or an adhesive bonding method. Alternatively, a drawn pattern-detachable paper may be coated to obtain a patterned sheet, and a laminated material may be formed by either of the bonding methods. The drawn patterns or printed patterns may be applied after said laminated material has been formed. The laminated material according to the present invention is cut to a certain size to obtain products. These products are formed to various shapes corresponding to different interior trim locations in each vehicles using various molding methods such as vacuum forming, air-pressure forming, or press molding method. EXAMPLES With reference to the following examples, the present invention is described more detail. Example 1 Raw materials for lower layer foamed sheet as indicated in the following Table 1 were used. The raw materials were mixed in an extruder having a T-die except the azodicarbonamide of the blowing agent and the blocked isocyanate of the cross-linking agent. Kneading was performed at a temperature of 160 °C for about 2 minutes to disperse each of the components sufficiently homogeneously. Then the blowing agent and the cross-linking agent were added sequentially through another feed port of the same extruder, and mixed and kneaded with the homogeneously dispersed components at a temperature of 150 °C for about 3 minutes to disperse all the components completely homogeneously. Thereafter a coloured sheet having a thickness of about 1.2 mm was formed at a processing speed of about 4 m/min. Using a vertical type foam oven, the sheet was heated at a temperature of 240 °C for about 1 minute to cross-link and expand the sheet, thereby obtaining a lower layer foamed sheet having an expansion coefficient of about 15, a sheet thickness of about 3 mm and a compressive hardness of about 0.2 kg/cm². The obtained sheet had a very homogeneous cell structure because the blowing agent and cross-linking agent were dispersed sufficiently homogeneously in the components. From the raw materials for the surface layer components described in Table 1, a coloured sheet having a thickness of 0.45 mm and a surface hardness of 70 was formed by a calender. On the coloured sheet deep drawn leather patterns were applied with a conventional embossing machine. Using a reactive two-package polyurethane adhesive, the coloured sheet was bonded to the lower layer foamed sheet, thereby forming a laminated material. The laminated material was cut to a certain size with a cutter to obtain a product. By moulding the obtained product with a vacuum forming machine, obtained was an excellent laminated material for vehicle interior trim which was superior in light-weight, softness and cushioning, was sound- and heat-insulating, was superior in mouldability and in form retention after moulding, and also had both sharp formability and excellent high-frequency welding properties corresponding to deep drawing and complicated contours. Example 2 Raw materials for lower layer foamed sheet in the following Table 2 were used. The raw materials except a cross-linking agent and a blowing agent were mixed in an extruder having a strand-type die. Kneading and pelletizing was performed at a temperature of 170 °C for 90 seconds to disperse each of the components sufficiently homogeneously. Then, the blowing agent and the cross-linking agent were added into an another extruder having a T-die, and mixed and kneaded with the homogeneously dispersed components (pre-pelletized mixture) completely homogeneously at a temperature of 150 ° C for about 120 seconds. Thereafter a coloured sheet having a thickness of about 0.8 mm was formed at a processing speed of about 6 m/min. from the mixed and kneaded components. Using a vertical type foam oven, the sheet was then heated at a temperature of 220 ° C for about 1 minute to cross-link and expand the sheet, thereby obtaining a lower layer foamed sheet having an expansion coefficient of about 8, a sheet thickness of about 1.5 mm and a compressive hardness of about 0.5 kg/cm². From the raw materials for the surface layer described in Table 2, a coloured sheet having a thickness of 0.3 mm and a surface hardness of 55 was formed with an another extruder. Using an emboss roll in which leather patterns are applied on one of the laminating rolls, the lower layer foamed sheet was extruded and laminated, and deep drawn leather patterns were applied to the upper surface of the coloured sheet concurrently to obtain a laminated material. The laminated material was cut to a certain size with a cutter to obtain products. By moulding the obtained products with a vacuum forming machine, obtained was an excellent laminated material for vehicle interior trim material which was superior in light-weight, softness and cushioning, was sound- and heat-insulating, was superior in mouldability and in form retention after moulding, and also had both sharp formability and excellent high-frequency welding properties corresponding to deep drawing and complicated contours. The present invention relates to a method for producing a laminated material comprising a lower layer of cross-linked highly-expanded plasticized polyvinyl chloride and a surface layer of thermoplastic resin sheet laminated on the upper surface of said lower layer. A raw material used for the lower layer foamed sheet is either of (A) a polyvinyl chloride resin having reacting groups in its molecules, or (B) a mixture of a polyvinyl chloride resin having no reacting groups in its molecules and a thermoplastic resin having reacting groups in its molecules. The raw materials are previously heated and kneaded in an extruder. Then a cross-linking agent which reacts with the reacting groups of the raw materials and a blowing agent are added and kneaded in the same extruder or in an another extruder, thereby controlling the kneading temperature and treating temperature accurately. Therefore, not only a homogeneous cross-linking reaction is accomplished, but also a cross-linked highly-expanded product with good and homogeneous cell structure can be obtained. As a result thereof, an excellent product as interior trim material for vehicles which product is superior in light-weight, softness and cushioning, has a very high surface hardness, is superior in mouldability and in form retention after moulding, and also has excellent high-frequency welding properties can be obtained. The present invention wherein lower layer foamed sheet can be formed using only the same extruder or an another extruder, has also an advantage that the productivity can be improved due to easy and continuous production.

Claims: A method for producing a highly-expanded plasticized thermoplastic resin sheet including polyvinyl chloride resin comprising the steps of heating and kneading raw materials, a cross-linking agent and a blowing agent to obtain a sheet and heating the sheet to cross-link and expand the sheet to form a sheet of cross-linked highly-expanded plasticized polyvinyl chloride, characterised in that : (a) the polyvinyl chloride resin is (A) a copolymer of a vinyl chloride monomer and a monomer containing hydroxyl or carboxyl groups as a reacting group, or (B) a mixture of a polyvinyl chloride resin having no reacting group in its molecules and a thermoplastic resin having a hydroxyl group, a carboxyl group or an amino group in its molecules as a reacting group, (b) the cross-linking agent is an isocyanate compound or an amine compound, (c) first, raw materials except the cross-linking agent and the blowing agent are sufficiently mixed, heated and kneaded in an extruder to disperse them homogeneously, (d) after (c), the cross-linking agent and the blowing agent are added, and (e) the raw material, the cross-linking agent and the blowing agent are heated and kneaded below a reacting temperature of the cross-linking agent and a decomposition temperature of the blowing agent to obtain the sheet. A method according to claim 1, characterised in that the monomer containing hydroxyl or carboxyl groups in the (A) copolymer is a monomer selected from the group consisting of 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, acrylic acid and methacrylic acid. A method according to claim 1, characterised in that the monomer containing hydroxyl or carboxyl groups in the (A) copolymer is a hydroxyl group containing acrylate. A method according to claim 1, characterised in that the polyvinyl chloride resin having no reacting groups in the (B) mixture is a vinyl chloride homopolymer, a copolymer of vinyl chloride and vinyl acetate, a copolymer of vinyl chloride and an alkene, a copolymer of vinyl chloride and styrene, or a copolymer of vinyl chloride and vinyl ether. A method according to claim 4, characterised in that the thermoplastic resin having a hydroxyl group, a carboxyl group or an amino group in its molecules contained in the (B) mixture is a polyvinyl chloride having a hydroxyl group or a carboxyl group, or an acrylic rubber. A method according to claim 4, characterised in that the thermoplastic resin having a hydroxyl group, a carboxyl group or an amino group in its molecules contained in the (B) mixture is in alkyl acrylate ester resin having a hydroxyl group, a carboxyl group or an amino group. A method according to claim 4, characterised in that the thermoplastic resin having a hydroxyl group, a carboxyl group or an amino group in its molecules contained in the (B) mixture is a copolymer of vinyl chloride and hydroxypropyl acrylate. A method according to claim 1, characterised in that the blowing agent is an azodicarbonamide. A method according to claim 8, characterised in that 1-10 parts by weight of the cross-linking agent and 5-30 parts by weight of the blowing agent are mixed to 100 parts by weight of the (A) copolymer of the vinyl chloride monomer and the monomer containing a hydroxyl or a carboxyl group. A method according to claim 1, characterised in that 1-10 parts by weight of the cross-linking agent is mixed to 100 parts by weight of the thermoplastic resin having a hydroxyl group, a carboxyl group or an amino group in its molecules in the (B) mixture, and 5-30 parts by weight of said blowing agent is mixed to 100 parts by weight of the (B) mixture of the polyvinyl chloride having no reacting groups in its molecules and the thermoplastic resin having a hydroxyl group, a carboxyl group or an amino group in its molecules. A method according to claim 8, characterised in that the highly-expanded plasticized thermoplastic resin sheet has an expansion coefficient of 5-30, a thickness of 0.5-8 mm and a compressive hardness of 0.05-1.0 kg/cm². The method according to claim 4, characterised in that the polyvinyl chloride resin having no reacting groups in its molecules and the thermoplastic resin having a hydroxyl group, a carboxyl group or an amino group in its molecules are mixed in the proportion of 20-80 parts by weight to 80-20 parts by weight. A method according to claim 1, characterised in that a stabilizer for expanding of polyvinyl chloride, a plasticizer and a pigment are mixed. A method according to claim 13, characterised in that the plasticizer is trimellitic acid ester. A method according to claim 14, characterised in that the 30-60 parts by weight of the plasticizer is mixed to 100 parts by weight of (A) a copolymer of a vinyl chloride monomer and a monomer containing hydroxyl or carboxyl groups. A method for producing a laminated material comprising a lower layer produced by the method of claim 1 and a surface layer of thermoplastic resin sheet, characterised in further laminating the surface layer of the thermoplastic resin on the upper surface of the lower layer.

Inventors: AKIMOTO HIROFUMI, HIKI TOSHIMICHI, KONDO MASAYUKI, TAKEYAMA SADAYUKI, AKIMOTO, HIROFUMI, HIKI, TOSHIMICHI, KONDO, MASAYUKI, TAKEYAMA, SADAYUKI
Applicants: KYOWA LEATHER CLOTH, KYOWA LEATHER CLOTH CO., LTD.
Application year: 1988
Main classification: C08J9
IPC codes: C08J9, C08J5, B29C69, B32B27, B29C44, B32B5, B32B37