PROCESS FOR PRODUCING CUSHIONING LAMINATE

Abstract: A process for producing a cushioning laminate is de­ scribed, comprising melting a laminated sheet comprising (a) a thermoplastic resin substrate sheet and (b) a thermo­ plastic resin adhesive layer having a heat distortion temper­ ature at least 25°C lower than that of the thermoplastic resin which constitutes the substrate sheet (a); moving the lami­ nated sheet below an upper mold in such a manner that the substrate sheet (a) faces the upper mold; vacuum molding the laminated sheet using the upper mold to produce a molded article having a desired irregular surface; and then bonding a plate-shaped member, such as a cardboard and a metallic or plastic plate, to the adhesive layer (b) of the lam­ inated sheet while the above-molded article is brought into close contact with the upper mold, thereby producing the cushioning laminate having enclosed air rooms. This cush­ ioning laminate is useful as a cushioning material for wrap­ ping.

Description: The present invention relates to a process for preparing a set-up box from a cushioning laminate. It is known that cushioning materials are produced by integrally bonding a paper or rigid resin plate and a vacuum molded article of a resin sheet. Japenese Patent Publication No. 47335/83 and U.S. Patent 3,674,109 disclose a method for producing a container with a cover or a cushioning material which comprises superposing an air-impermeable sheet made of a thermoplastic resin and a paper having microholes and with a synthetic resin film laminated thereon or rigid resin plate which comprising bringing the air-impermeable sheet into contact with a mold, heating the assembly at a temperature higher than the heat distortion temperature of the air-impermeable sheet, and then vacuum molding only the air-impermeable sheet along the mold. In producing a box using the cushioning material produced by the above vacuum molding method, however, the paper with printing applied thereon appears outside and the microholes of the paper give a singular feeling to the consumer. DE-A-22 27 690 discloses a process for producing a cushioning laminate by heat-melting a flexible thermoplastic resin film, vacuum forming the melt by means of embossing rolls or vacuum cylinder rolls to form embossments or projections, and melt adhering a web or film material on the embossed film. The thus formed air cap is flexible, the height of the projections is uniform, and the air cap per se can be wound into a roll form. US-A-3 142 599 discloses a method for making laminated cushioning material which does not employ adhesives. It is the problem of the present invention to provide a process for preparing a set-up box from a cushioning laminate using a paper which does not have microholes. This problem is solved according to the present invention by a process which comprises the following steps: (1) heat-melting a laminated sheet (1) comprising a thermoplastic resin foamed polystyrene substrate sheet (a) having a thickness of 0.3 to 4mm and a thermoplastic resin adhesive layer (b) having a heat distortion temperature at least 25°C lower than that of the thermoplastic resin which constitutes the substrate sheet (a); (2) moving the laminated sheet (1) below a mold in such a manner that the substrate sheet (a) is positioned so as to face the mold (4a); (3) vacuum-molding the laminated sheet (1) using the mold (4a) to produce a molded article having a desired irregular surface; (4) bonding a cardboard plate-shaped member (2) having a high stiffness to the adhesive layer (b) of the laminated sheet (1) while the above-molded article is brought into close contact with the mold (4a) by vertically raising said cardboard plate-shaped member (2) to contact the adhesive layer (b), thereby producing the cushioning laminate having closed air pockets; and (5) trimming said cushioning laminate (5) to obtain the desired product. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a cross-sectional view of a laminated sheet which is used in the present invention; Figure 2 is a top plan view of the laminated sheet; Figure 3 is a diagrammatic illustration of an apparatus for use in the practice of the process of the present invention; Figure 4 is an enlarged view of a unit of the apparatus shown in Figure 3; Figure 5 is a partial cross-sectional view of a wrapping material; Figure 6 is a top plan view of the wrapping material shown in Figure 5; and Figure 7 is 1 perspective view of a wrapping container (set-up box) prepared from the cushioning material according to the present invention Examples of the thermoplastic resin which can be used in the preparation of the adhesive layer (b) include low density polyethylene, low molecular weight soluble linear polyesters, a vinyl chloride/vinyl acetate copolymer, polyvinyl acetate, an ethylene/vinyl acetate copolymer (ethylene content: 55-85 wt%), chlorinated polypropylene, chlorinated polyethylene, an ethylene/ (meth)acrylic acid copolymer or its metal salts (Na, Li, X, Zn), and an ethylene/(meth)acrylic acid lower ester copolymer. The heat distortion temperature of the thermoplastic resin for the adhesive layer (b) must be at least 25°C lower than that of the thermoplastic resin for the substrate sheet (a). The reason for this is that the laminated sheet after vacuum molding is bonded to a cardboard plate-shaped member haying a high stiffness, and the adhesive layer of the laminated sheet which is softened or melted serves as an adhesive for this adhesion. The laminated sheet comprising a polystyrene foamed sheet and an ethylene/vinyl acetate copolymer film is preferred. The laminated sheet can be produced by a method wherein thermoplastic resins for the substrate sheet (a) and the adhesive layer (b) are fed to a die through different extruders and then co-extruded or a method wherein an anchor coating agent is coated on the surface of a substrate sheet which has been extrusion molded and a film made of the resin for the adhesive layer is melt laminated thereon. Prior to vacuum molding, the laminated sheet is passed through a heating chamber and moved below the upper mold by means of, for example, a chain. Therefore, in order to prevent the molten resin for the adhesive layer from attaching to the chain, it is desirable that the width of the adhesive layer (b) be made narrower than that of the substrate sheet (a) as shown in Figure 1. In addition, the laminated sheet can be produced by coating an aqueous emulsion or organic solvent solution of the resin for the adhesive layer (b) on the surface of the substrate sheet (a) and then drying. Such an aqueous emulsion can be prepared by the methods described in Japanese Patent Application (OPI) Nos. 2149/81, 76049/82 and 120655/83 and Japanese Patent Application Nos. 113229/82 and 188536/82 (the term "OPI" as used herein refers to a "published unexamined Japenese patent application"). When the liquid adhesive is used, it is not necessary to coat on the whole surface of the substrate sheet. From a viewpoint of production costs, it is advantageous that the liquid adhesive be partially coated as shown in figure 2 using, for example, a gravure printing roll or a flexo printing roll, thereby producing a laminated sheet with areas (a₁, a₂, a₃) where the adhesive layer is not provided. In Figure 2, b₁, b₂, b₃, b₄, .... indicate partially coated adhesive layers each being prepared by one shot; a₂ indicates boundaries between the partially coated adhesive layers, i.e., with no adhesive layer coated thereon; and a₃ indicates areas with no adhesive layer coated thereon and which are clamped with the chain. The liquid adhesive is usually controlled so that the resin content is from 1 to 60% by weight and preferably from 5 to 50% by weight and the Brookfield viscosity is from 1 to 100 Pa.s (10 to 1,000 poises). The amount of the liquid adhesive coated on the laminated sheet is from 0.1 to 10 g/m² as the resin solids content. The thickness of the substrate sheet is from 0.3 to 4 mm (density:0.02-0.01 g/cm³ ), and the thickness of the adhesive layer is preferably from 1. to 60µm. The process for producing a cushioning laminate according to the present invention will hereinafter be explained by reference to the apparatus shown in Figure 3. A laminated sheet 1 is transferred to a heating chamber 3 by a chain (not shown) where a substrate sheet and an adhesive layer of the laminated sheet 1 are melted. The molten laminated sheet 1 is positioned below an upper mold 4a by moving the chain by a distance corresponding. to one shot. The pressure in the chamber of the upper mold 4a is reduced by means of a pipe 4c connected to a vacuum pump (not shown), and the laminated sheet is shaped into a desired form by vacuum molding (see Figure 4). A paper-feeding unit 4b is placed below the upper mold 4a and designed to move upwardly and downwardly by means of an air cylinder. A cardboard 2 is placed on the paper-feeding unit 4b. While the laminated sheet is brought into close contact with the upper mold 4a, the paper-feeding unit 4b is raised and the cardboard 2 is bonded to the laminated sheet 1 molded into the desired form (see Figure 4). This adhesion results in the formation of air rooms 6 in the cushioning material 5, enclosed by the cardboard 2 and the laminated sheet 1 molded in the desired form. These enclosed air rooms provide the cushioning material 5 with cushioning properties. After the laminated sheet 1 and the cardboard 2 are bonded together, the resulting cushioning material 5 is cooled by jetting air from a cooling air-spraying device 7a in a cooling chamber 7 provided if desired and necessary and then trimmed by means of a cutter knife 9a and two plateweights 8-8 in a trimming chamber 9 by one shot. An embodiment in which the above-produced cushioning material is used as a wrapping material for set-up boxes will be explained hereinafter. Figure 5 is a partial cross-sectional view of a wrapping material 5 and the top plan view of the wrapping material 5 is shown in Figure 6. A stiff cardboard 2 is provided with a printing coating 15 on the surface thereof. An adhesive layer a is an ethylene/vinyl acetate copolymer film having a thickness of 30µm. A vacuum molded product 1 of a polystyrene foamed sheet (thickness: 2µm) having a bulk density of from 0.03 to 0.5 g/cm³ is bonded to the cardboard 2 through the adhesive layer b A polyolefin sheet 10 made of an ethylene/vinyl acetate copolymer and having a thickness of about 100µm is bonded to the polystyrene foamed sheet 1, thereby constituting an outer, lustrous layer. Enclosed air rooms 6 are formed by the cardboard 2 and projections 12 of the molded sheet 1, 10. After an article A is placed on the cardboard, the wrapping material is folded along lines 13 in such a manner that the cardboard 2 appears outside and the polyolefin sheet 10 appears inside, and then a sealing label 14 is attached (see Figure 7). The article A is protected by the polystyrene foamed material and air rooms. The present invention is described in greater detail by reference to the following examples. PREPARATION EXAMPLE Preparation of Aqueous Dispersion of Ethylene/Vinyl Acetate Copolymer An ethylene/vinyl acetate copolymer (vinyl acetate content: 28% by weight) was fed at a rate of 100 parts by weight per hour from a hopper of a corotating, intermeshing-type twin-screw extruder. An aqueous solution of an N,N-dimethylaminoethyl methacrylate/ butyl methacrylate/lauryl methacrylate (0.4:0.5:0.1 by mol) which had been neutralized with formic acid (solids content: 35%) was continuously introduced at a rate of 22.9 parts by weight per hour from the first inlet, and water was continuously introduced at a rate of 147.1 parts by weight per hour from the second inlet. The mixture was then extruded at a temperature of 130°C to produce a milky white aqueous dispersion (solids content: 50% by weight). EXAMPLE 1 A laminated sheet of a foamed polystyrene paper (density: 0.08 g/cm³, thickness: 2.5 mm) and an ethylene/ vinyl acetate copolymer film (thickness: 30µm) was introduced into a heating chamber maintained at 200°C and melted by heating with an infrared ray heater. The molten laminated sheet was vacuum molded using an upper mold ((degree of reduction in pressure: -60kPa (-450 mmHg)). While the above-molded laminated sheet was brought into close contact with the upper mold, a paper-feeding unit was moved upwardly by means of an air cylinder to thereby bond the uppermost cardboard and the laminated sheet. The paper-feeding unit was lowered while on the other hand the upper mold was raised to remove the resulting cushioning material from the upper mold. The cushioning material was then cooled and trimmed to obtain the desired product. EXAMPLE 2 A cushioning material was produced in the same manner as in Example 1 except that a partially coated polypropylene sheet produced by coating a 600µm thick polypropylene sheet with the aqueous emulsion prepared in Preparation Example as shown in Figure 2 was used as the laminated sheet.

Claims: A process for preparing a set-up box from a cushioning laminate which comprises the following steps: (1) heat-melting a laminated sheet (1) comprising a thermoplastic resin foamed polystyrene substrate sheet (a) having a thickness of 0.3 to 4 mm and a thermoplastic resin adhesive layer (b) having a heat distortion temperature at least 25°C lower than that of the thermoplastic resin which constitutes the substrate sheet (a); (2) moving the laminated sheet (1) below a mold (4a) in such a manner that the substrate sheet (a) is positioned so as to face the mold (4a); (3) vacuum molding the laminated sheet (1) using the mold (4a) to produce a molded article having a desired irregular surface; (4) bonding a cardboard plate-shaped member (2) having a high stiffness to the adhesive layer (b) of the laminated sheet (1) while the above-molded article is brought into close contact with the mold (4a) by vertically raising said cardboard plate-shaped member (2) to contact the adhesive layer (b), thereby producing the cushioning laminate (5) having closed air pockets; and (5) trimming said cushioning laminate (5) to obtain the desired product. The process of claim 1, wherein the thickness of the adhesive layer (b) is 1 to 60µm. The process of claim 1, wherein the thermoplastic resin for the adhesive layer (b) is selected from the group consisting of low density polyethylene, low molecular weight soluble linear polyesters, a vinyl chloride/vinyl acetate copolymer, polyvinyl acetate, an ethylene/vinyl acetate copolymer, chlorinated polypropylene, chlorinated polyethylene, an ethylene/(meth)acrylic acid copolymer or its metal salts, and an ethylene/(meth)acrylic acid lower ester copolymer. The process of claim 1, wherein the laminated sheet (1) comprises a polystyrene foamed sheet and an ethylene/vinyl acetate copolymer film. The process of claim 1, wherein the laminated sheet (1) is prepared by feeding the thermoplastic resins for the substrate sheet (a) and the adhesive layer (b) to a die through different extruders and coextruding. The process of claim 1, wherein the laminated sheet (1) is prepared by coating an anchor coating agent on the surface of an extrusion molded substrate sheet and melt laminating a resin film for the adhesive layer. The process of claim 1 wherein the laminated sheet (1) is prepared by coating an aqueous emulsion or organic solvent solution of a resin for the adhesive layer (b) on the surface of the substrate sheet (a) and drying.

Inventors: MAEDA, ATSUSHI MITSUBISHI YUKA BADISCHE CO., LTD.
Applicants: MITSUBISHI YUKA BADISCHE CO., LTD.
Application year: 1985
Main classification: B29C51
IPC codes: B29C65, B29C51, B32B3, B29C69, B29L31, B29K105