Process for producing multilayer molded article

Abstract: A multilayer molded article with good appearance is produced by supplying a skin material (9) and a melt (8) of a thermoplastic resin between unclosed upper (1) and lower (2) molds and simultaneously molding the thermoplastic resin (8) to form a molded article and laminating the skin material (9) on a part of a surface of the molded article by pressing and cooling the thermoplastic resin in the molds, in which the lower mold (2) has a protruded part (3) at a position where an edge of the skin material (9) is located, the upper mold (1) has a depressed part at a position corresponding to the protruded part (3) of the lower mold, and, during molding, the edge of the skin material is fixed to the lower mold by sucking it through a gap (4) which opens at the protruded part or its root part.

Description: The present invention relates to a process for producing a multilayer molded article which comprises a thermoplastic resin body and a skin material which is laminated on a part of the thermoplastic resin body. A large number of plastic molded articles are used in many fields including the automobile and domestic electric appliance fields because of their low costs, free moldability and light weight. However, they have some drawbacks that they have poor appearance and cool feeling and they tend to be easily flawed. Then, it is highly desired to impart decoration and soft feeling to the plastic molded articles. Hitherto, to impart decoration to the plastic molded article, there have been many methods for producing a partly laminated multilayer molded article comprising a thermoplastic resin body and a skin material which is laminated on a part of the thermoplastic resin. When the partly laminated multilayer molded article is produced by supplying a resin melt between the skin material and a mold and closing the mold to press mold the article, it is important to precisely place the skin material on a desired part of the thermoplastic resin body and finish edges of the skin material with good appearance. To these ends, various molding methods have been proposed in which a measure for fixing the skin material is devised. For example, Japanese Patent Kokai Publication No. 150741/1984 discloses a method for producing a partly laminated multilayer molded article wherein edges of the skin material are clamped with a skin material-fixing plate and a lower mold. However, by this method, it is impossible to laminate the skin material on a center part of the molded article. Japanese Patent Kokai Publication No. 175111/1990 discloses a molding method wherein a skin material is clamped with a special jig and placed in the mold. However, this method cannot be used when the skin material has a complicated shape. A further method is disclosed in Japanese Patent Kokai Publication No. 26414/1989, wherein a partition wall is provided on the mold surface and the skin material is place on the mold surface with matching a parting part of the skin material with this partition wall to prevent dislocation of the skin material. It may be possible to design a part of the mold in a telescopic form and fix the position of the skin material by sucking the skin material through a gap between the upper and lower molds. But, the edges of the skin material are simple and the molded article loses high quality appearance. WO 90/03256 discloses a method and a device for producing rigid plastic products comprising a thermoformed, fiber-reinforced backing material provided with an outer layer at one side thereof. The two materials are preheated and thereafter brought together in a compression and molding tool wherein the layer is sucked against the walls of the lower mold via conduits opening into the mold cavity and fixed around the cavity by a clamping frame. One object of the present invention is to provide a method for producing a partly laminated multilayer molded article with no dislocation of a skin material by a simple method. Another object of the present invention is to provide a method for producing a partly laminated beautiful multilayer molded article having high quality appearance at edges of the skin material. These objects are solved by the features of the Claims. The invention is further described with reference to the enclosed drawings: Figs. 1A and 1B are cross sections of an example of the mold used in the method of the present invention in different steps, Fig. 2A is a plane view of a multilayer molded article to be produced by the method of the present invention using the mold of Fig. 1, Fig. 2B is a cross section along the line A-A of Fig. 2A, Figs. 3A and 3B are cross sections of another example of the mold used in the method of the present invention in different steps, Fig. 4 is a plane view of a multilayer molded article to be produced by the method of the present invention using the mold of Fig. 3. As the thermoplastic resin used for forming the body of the molded article, any one of conventional thermoplastic resins which are used in compression molding, injection molding and extrusion molding can be used. Specific examples are thermoplastic resins (e.g. polypropylene, polyethylene, polystyrene, acrylonitrile-styrene-butadiene copolymer, polyamide, etc.) and thermoplastic elastomers (e.g. ethylene-propylene block copolymer, styrene-butadiene block copolymer, etc.). The thermoplastic resin may contain at least one conventional additive, for example, a filler such as an inorganic filler and glass fiber; a pigment; a lubricant; and an antistatic agent. Examples of the skin material to be used in the process of the present invention are woven or nonwoven fabric, a net of metal, fiber or a thermoplastic resin, a paper or a metal foil which is lined with a sheet to be sucked; and a sheet or film of a thermoplastic resin (e.g. polyolefin, polyvinyl chloride, polyamide, etc.) and a thermoplastic elastomer (e.g. polyolefin type, polyester type, polyurethane type and polyvinyl chloride type thermoplastic elastomers) and the like. These skin materials may be ornamented by uneven design such as emboss, printing or dyeing. The skin material may be made of a foam. Further, the skin material may be a laminate of two or more of them which are bonded with, for example, an adhesive. In the molds to be used in the molding method of the present invention, the lower mold has a protruded part at the position where the edge of the skin material is located, the upper mold has a depressed part at the positions corresponding to the protruded part of the lower mold. At the protruded part or its root part, a gap opens for sucking the edge of the skin material to fix the skin material on the lower mold. In particular, when the gap opens in the protruded parts, suction marks on the skin material are hidden in grooves of the molded article. Therefore, an area of the opening of each gap can be made large and the skin material can be sucked with a large suction force, so that a stiff skin material can be fixed to the lower mold easily, and the article is produced with good efficiency. A shape of the protruded part and the depressed part is determined according to a shape of the molded article, a thickness and a design of the skin material. To finish the edges of the skin material beautifully, the protruded part has a width at its root part (a) of from 1 to 10 mm and a height (b) of 2 to 5 mm (cf. Fig. 2B). The gap for suction which is provided at the protruded part or its root has a width of from 0.05 to 1 mm. The gaps may be provided around the protruded part continuously or partly with suitable intervals. An upstand edge of the protruded part has a slope of at least 3 degrees from the plane of the lower mold to improve mold releasing of the molded article. The molding method of the present invention will be explained by making reference to the drawings. As shown in Fig. 1A, a skin material 9 is placed between unclosed upper and lower molds 1 and 2 with matching edges of the skin material 9 with protruded parts 3 formed on the lower mold 2. The skin material 9 is fixed to the lower mold 2 by sucking the edges of the skin material 9 with a reduced pressure through a gap 4. Then, a resin melt 8 is supplied between the skin material 9 and the upper mold 1, the molds are closed and pressed while cooling to mold the article of the thermoplastic resin. To avoid damage of the skin material 9, timings of the supply of the resin melt 8 and mold closing are important. The resin melt 8 is supplied through a conduit 7 provided in the upper mold 1 when a clearance between the upper and lower molds is from (C + 5) mm to (C + 100) mm wherein "C" is a mold clearance when the molding is finished at a mold closing rate of 30 mm/sec. or less. The molds are further closed to the clearance of C mm, pressed for a specific time and cooled to obtain the desired partly laminated multilayer molded article. The molding method of the present invention produces, with good efficiency, the partly laminated multilayer molded article having the skin material the edges of which are neatly embedded in the grooves of the molded article so that they are beautifully finished. Since an area having the skin material and an area having no skin material are separated by the groove, the molded article has high quality appearance. The molded article produced by the present invention is particularly suitable as an interior part of an automobile. The present invention will be illustrated by the following Examples which will not limit the scope of the present invention. Example 1 This Example explains the molding process using the upper and lower molds of Fig. 1 with which a molded article having a plane view of Fig. 2A is formed and which are set in a pressing machine having a clamping force of 300 tons. As a skin material, was used an embossed polyvinyl chloride sheet lined with a fabric having a total thickness of 0.7 mm (manufactured by Kyowa Leather Co., Ltd.), which was cut to a size of 650 mm x 700 mm. As a thermoplastic resin, was used polypropylene containing 15 % of talc (Sumitomo Noblen BPZ 5077 manufactured by Sumitomo Chemical Co., Ltd.; Melt flow index of 40 g/10 min.). This resin was molten and supplied in the molds as a resin melt 8 and molded. The upper and lower molds were maintained at 80°C and 60°C, respectively. The skin material was set on the lower mold with matching its edges to the protruded parts 3, and the edges of the skin material 8 were sucked via gaps having a width of 0.05 to 0.1 mm which opened at the protruded part through a suction hole 6, whereby the skin material was absorbed on the lower mold 2. The lower mold 2 was lifted at a rate of 200 mm/sec. When the cavity clearance reached 15 mm, the lower mold was stopped, and the above thermoplastic resin which had been heated and molten at 230°C was supplied between the skin material and the upper mold through a resin conduit 7 provided in the upper mold (Fig. 1A). When the lower mold 2 was further lifted up, the molten resin was flowed to fill the mold cavity (Fig. 1B). Then, the resin melt was compressed and formed. The final clearance between the upper and lower molds was 2.0 mm. After compressing and cooling the resin for 50 seconds, the molds were opened and the molded multilayer article was removed from the molds. The skin material had no wrinkle or breakage, and the edges of the skin material were embedded in the grooves of the molded article so that the article had good appearance. Example 2 This Example explains the molding example using the upper and lower molds of Fig. 3 with which a molded article having a plane view of Fig. 4 is formed and which are set in a pressing machine having a clamping force of 300 tons. As a skin material, was used an embossed polyvinyl chloride sheet having a thickness of 0.4 mm (manufactured by Kyowa Leather Co., Ltd.) which was lined by a polypropylene foam having a thickness of 3.0 mm (manufactured by Toray; an expansion ratio of 15) with an adhesive. As a thermoplastic resin, was used polypropylene containing 15 % of talc (Sumitomo Noblen BPZ 5077 manufactured by Sumitomo Chemical Co., Ltd.; Melt flow index of 40 g/10 min.). This resin was molten and supplied in the molds as a resin melt 8 and molded. The upper and lower molds were maintained at 50°C and 40°C, respectively. The skin material was set on the lower mold with matching its edge to the protruded part 3, and the edge of the skin material 8 was sucked via the gap having a width of 0.05 to 0.1 mm which opened at the protruded part through a suction hole 6, whereby the skin material was absorbed on the lower mold 2. An edge of the skin material which was present outside the article surface was held with a pin 10. The lower mold 2 was lifted at a rate of 200 mm/sec. When the cavity clearance reached 50 mm, the lifting speed of the lower mold was decreased to 5 mm/sec. and the above thermoplastic resin which had been heated and molten at 190°C was supplied between the skin material and the upper mold through a resin conduit 7 provided in the upper mold (Fig. 3A). The resin supply was stopped when the clearance reached 25 mm. When the lower mold 2 was further lifted up, the molten resin was flowed to fill the mold cavity (Fig. 3B). Then, the resin melt was compressed and formed. The final clearance between the upper and lower molds was 3.0 mm. After compressing and cooling the rein for 40 seconds, the molds were opened and the molded multilayer article was removed from the molds. The skin material had no wrinkle or breakage and soft and high quality feeling, and the edges of the skin material were embedded in the grooves of the molded article so that the article had good appearance.

Claims: A method for producing a multilayer molded article comprising a thermoplastic resin body and a skin material laminated on a part of said resin body, which method comprises the steps of: a) supplying a skin material (9) between unclosed upper and lower molds (1, 2), b) fixing said skin material (9) to the lower mold (2) by sucking, c) supplying a melt of a thermoplastic resin (8) between said skin material (9) and said upper mold (1), d) closing said upper and lower molds (1, 2), and e) pressing said molds (1, 2) while cooling to mold said article, wherein said skin material (9) is supplied so that edges of said skin material (9) match protruded parts (3) which are formed on a surface of said lower mold (2) and said edges of said skin material (9) are sucked via gaps (4) which open at said protruded parts (3) or their root parts. The method according to claim 1, characterized in that each of the protruded parts (3) has a width of 1 to 10 mm at its root part, and an upstand edge of which has a slope of at least three degrees from the plane of said lower mold (2).

Inventors: FUJITA HIROMU, HARA TAKAHISA, KAMIJI YUJI, MATSUMOTO MASAHITO, NAKATSUKA HIROMASA, FUJITA, HIROMU, HARA, TAKAHISA, KAMIJI, YUJI, MATSUMOTO, MASAHITO, NAKATSUKA, HIROMASA
Applicants: NISSEN KAGAKU KK, SUMITOMO CHEMICAL CO, NISSEN CHEMITEC CORPORATION, SUMITOMO CHEMICAL COMPANY, LIMITED
Application year: 1992
Main classification: B29C33
IPC codes: B29C33, B29C70