Cushioning material

Abstract: A cushioning material is disclosed which includes two laminated films between which a plurality of air tight cells are formed. Each of the films is composed of an intermediate layer formed of a polyamide resin and two surface layers formed of a polyolefin resin and provided on both sides of the intermediate layer.

Description: This invention relates to a cushioning material according to the preamble of claim 1 (US-A-4314865). Cushioning material such as a cushioning sheet composed of two laminated films and having a plurality of air-tight cells therebetween is well known and is widely used in, for example, packaging products or padding furnitures. Conventional cushioning materials, which are generally formed of a polyolefin such as a low density polyethylene, have a problem because they are relatively poor gas barrier materials. Thus, for example, when such cushioning materials are used under pressurized conditions, air entrapped in the cells is gradually got out of the cells so that the cushioning property is deteriorated. This is especially so when the pressed cushioning materials are also subjected to a great change of temperature. US-A-4314865 proposes, as a solution to the problem of reducing the escape of air from cushioning material of this type, that each film forming the laminate should be a composite material comprising an intermediate layer of relatively high density, high melting plastic and a surface layer bonded to each side of the intermediate layer and formed of relatively low density, relatively low melting point thermoplastic. It is preferred that the intermediate layer is a nylon which is substantially impervious to the passage of gases therethrough and that the surface layers are of polyethylene. US-A-3843479 is concerned with the problem of improving the heat seal strength of polyamides obtained by polycondensation of m-xylylenediamine with aliphatic dicarboxylic acids such as adipic acid, without deleteriously affecting their good gas barrier properties, and to this end it proposes that one or both sides of the polyamide should be coated with a thermoplastic resin coating layer. A large number of thermoplastic resins are said to be suitable for this purpose, including polymers of α-olefin compounds. The resulting composite material is said to be useful as a packaging material. The present invention has been made in consideration of the problem of air loss from the conventional cushioning material. In accordance with the present invention there is provided a cushioning material which, like the cushioning material of US-A-4314865, supra , comprises two, first and second composite films each including an intermediate layer formed of a polyamide resin and two surface layers laminated one on each side of said intermediate layer and each formed of a polyolefin resin, at least one of said first and second composite films being formed to provide one or more discrete embossments, and said first and second composite films being bonded to form a substantially unitary structure and to seal said embossments so that one or more air-tight cells are defined between said first and second composite films. The present invention is characterized in that the polyamide resin of the intermediate layer comprises a polyamide obtained by polycondensation of m-xylylenediamine with a dicarboxylic acid. The cushioning material according to the present invention can have excellent gas and moisture vapor barrier properties and, moreover, exhibit excellent resistance to water, oil and heat. It also can have a high mechanical strength. The present invention will now be described in detail below with reference to the accompanying drawings in which: Fig. 1 is a perspective view diagrammatically showing one embodiment of cushioning material according to the present invention; Fig. 2 is an enlarged, cross-sectional view taken along line II-II in Fig. 1; Fig. 3 is a sectional view similar to Fig. 2 showing another embodiment according to the present invention; Fig. 4 is a perspective view diagrammatically showing a further embodiment according to the present invention; and Fig. 5 is a schematic illustration showing an apparatus for fabricating cushioning material of the present invention. Figs. 1 and 2 depict a cushioning material in the form of a sheet. The cushioning material is formed from two, first and second composite films 10 and 11. The first composite film 10 is composed of an intermediate layer 2 sandwiched between two overlying surface layers 1 and 3 and so formed as to provide a plurality of discrete embossments 8. The second composite film, too, is composed of an intermediate layer 5 sandwiched between two overlying surface layers 4 and 6. The first and second films 10 and 11 are laminated to form a substantially unitary sheet and to seal the embossments 8 of the first film 10. The sealed embossments 8 define air-tight cells 7. The surface layers 1, 3, 4 and 6 of the first and second films 10 and 11 are each formed of a polyolefin resin such as a polyethylene, a polypropylene or an ethylene-vinyl acetate copolymer. Polymers obtained by modifying these polyolefins with a graft-polymerizable monomer such as acrylic acid or maleic anhydride may also be used for the surface layers 1, 3, 4 and 6. The surface layers 1, 3, 4 and 6 preferably have a thickness (before embossing) of 5 - 500 µm, more preferably 10 - 250 µm. The intermediate layers 2 and 5 of the first and second films 10 and 11 are each formed of a polyamide resin which, in accordance with this invention comprises a polyamide obtained by polycondensing m-xylylenediamine with a dicarboxylic acid, preferably an aliphatic dicarboxylic acid such as adipic acid. In a specific embodiment the polyamide is a product obtained by polycondensing m-xylylenediamine with a mixture of dicarboxylic acids composed of 55-70 mol % of an aliphatic dicarboxylic acid, 20-30 mol % of isophthalic acid and 5-20 mol % of terephthalic acid, wherein the total amount of the isophthalic acid and terephthalic acid in the mixture is in the range of 30-45 mol %. In another embodiment, the polyamide resin is a blend of 40-60% by weight of the polyamide just defined with 60-40% by weight of a second polyamide obtained by polycondensing m-xylylenediamine with an aliphatic dicarboxylic acid. The aliphatic dicarboxylic acid may be, for example, adipic acid. The intermediate layer preferably has a thickness (before embossing) of 5-250 µm, more preferably 10-100 µm. Fig. 3 depicts the cell structure of another example of cushioning material of this invention, in which two embossed composite films 10 and 11 are laminated to provide a unitary sheet. The embossments 8 which are hemicircular in shape are combined in back-to-back fashion to form hermetically sealed cells 7. In the present invention, the shape or configuration and the arrangement of the cells 8 are not limited to the above-described specific embodiments. On the contrary, the cushioning sheet may have any desired cell configuration and arrangement. The cushioning material of this invention is not limited to a sheet form only. As shown in Fig. 4, the cushioning material may be in the form of an "air cap". The "air cap" type cushioning material shown in Fig. 4 may be obtained by simply severing the cushioning sheet of Fig. 1 at its sealed portions into pieces 8 each having one air-tight cell. The cushioning material of the present invention may be prepared in any known manner. Fig. 5 illustrates one example of an apparatus, which is known per se, useful for producing the cushioning material. The first composite film 10 is continuously fed to a heat roller 14 where it is heated to a suitable temperature. The heated film 10 is then fed on an embossing cylinder 16 having a plurality of depressions 17 of any desired configuration distributed on its circumference. The depressions 17 are connected to a vacuum means (not shown) so that the heated film 10 on the embossing cylinder 16 is embossed. The embossed film 21 is then brought into pressure contact with the second composite film 11 during its passage through a nip and heat roller 15 so that the two films are bonded to form a unitary sheet having a plurality of sealed embossments 8. The laminate is then passed about a cooling roller 18 and is guided onto a spool 19. The composite films 10 and 11 may be prepared in any known manner such as by co-extrusion, bonding with a suitable adhesive resin, e.g. polyethylene, polypropylene, ethylene-acrylate copolymer, polybutadinene or polyisoprene, or fuse bonding without using any adhesive. The cushioning material according to the present invention, which is composed of laminated composite films each having the intermediate polyamide layer, has excellent gas barrier properties, heat resistance and mechanical strength. Whilst the polyamide layer has a tendency to absorb moisture vapor, the presence of the polyolefin layers on both sides thereof can protect the cushioning material from being deteriorated in cushioning properties. Further, though the polyamide resin is relatively expensive, the overlying polyolefin layers permits the use of a very thin polyamide layer. This is advantageous from the stand point of economy.

Claims: A cushioning material comprising two, first and second composite films each including an intermediate layer formed of a polyamide resin and two surface layers laminated one on each side of said intermediate layer and each formed of a polyolefin resin, at least one of said first and second composite films being formed to provide one or more discrete embossments, and said first and second composite films being bonded to form a substantially unitary structure and to seal said embossments so that one or more air-tight cells are defined between said first and second composite films, characterized in that: said polyamide resin of said intermediate layer comprises a polyamide obtained by polycondensation of m-xylylenediamine with dicarboxylic acid. A cushioning material according to Claim 1, wherein said dicarboxylic acid is an aliphatic dicarboxylic acid. A cushioning material according to Claim 2, wherein said aliphatic dicarboxylic acid is adipic acid. A cushioning material according to Claim 1, wherein said polyamide resin is a product obtained by polycondensation of m-xylylenediamine with a mixture of dicarboxylic acids composed of 55-70% mol % of an aliphatic dicarboxylic acid, 20-30 mol % of isophthalic acid and 5-20 mol % of terephthalic acid, the total amount of the isophthalic acid and terephthalic acid in said mixture being in the range of 30-45 mol %. A cushioning material according to Claim 4, wherein said aliphatic dicarboxylic acid is adipic acid. A cushioning material according to claim 1, wherein said polyamide resin is a blend of (a) 40-60 % by weight of a first polyamide obtained by polycondensation of m-xylylenediamine with a mixture of dicarboxylic acids composed of 55-70 mol % of a first aliphatic dicarboxylic acid, 20-30 mol % of isophthalic acid and 5-20 mol % of terephthalic acid, the total amount of the isophthalic acid and terephthalic acid in said mixture being in the range of 30-45 mol % and (b) 60-40 % by weight of a second polyamide obtained by polycondensing m-xylylenediamine with a second aliphatic dicarboxylic acid. A cushioning material according to claim 6, wherein said first and second aliphatic dicarboxylic acids are each adipic acid.

Inventors: AKIYAMA HIROYUKI, AKIYAMA, HIROYUKI
Applicants: JAPAN STYRENE PAPER CORP, JAPAN STYRENE PAPER CORPORATION
Application year: 1987
Main classification: B65D81
IPC codes: B32B3, B32B27, B65D81