Composite structure and production method thereof

Abstract

A composite structure comprising a metallic sheet and two thermoplastic material layers of a layer (A) and a layer (B) which are placed in turn and integrated with each other, characterized in that the layer (A) comprises a thermoplastic material capable of being thermally fusedly adhered to the thermoplastic material in the layer (B), the metallic sheet and the layer (A) are adhered to each other, and the layers (A) and (B) are thermally fusedly adhered to each other; and a process for producing a composite structure which comprises installing, on a metallic sheet by coating, a layer (A) comprising a thermoplastic material capable of being thermally fusedly adhered to a thermoplastic material in a layer (B) to be placed thereon, and further installing the layer (B) on the layer (A) by thermally fusedly adhering a desirable thermoplastic material on the (A).

Description

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a composite structure which comprises a metallic sheet and thermoplastic materials and a process for the production of said composite structure. More particularly, the present invention is concerned with a composite structure which is well suited for use in a gasketed cover and the like to be used for housing electronic equipment, etc. and in which an injection molded thermoplastic material is integrated with a metallic sheet with favorable adhesivity by coating the metallic sheet in advance, with an adhesive; and a process for readily and efficiently producing said composite structure.

[0003] 2. Description of the Related Arts

[0004] The development of electronic equipment in recent years really amazes the persons concerned. The aforesaid equipment, which is subjected to printed circuit on a substrate by the use of integrated circuits utilizing semiconductors, is directed to compactified lightweight equipment, and is prone to be readily damaged by moisture or dampness in particular. Accordingly, the hermetically sealing properties of a case housing electronic equipment is a factor of importance for the performance and durability of the electronic equipment.

[0005] The case housing electronic equipment is constituted of a box body and a cover body, which are integrated by interposing on the jointing surface thereof, a gasket made of vulcanized rubber, a urethane foam and a thermoplastic material or the like. The gasket is usually in the form of a gasket which is fitted to a cover body and thus fixed to the cover, but there is unavailable a favorable method of adhesively bonding the gasket to the cover body. Accordingly, the fixation is carried out by a (1) method comprising fixing the gasket on the cover body by means of a double-coated tape, a (2) method comprising making holes in the cover body and fixing a gasket material from both sides of the cover body through the holes or the like method. The gasketed cover body is fixed on a box body by means of screws and accordingly, the fixing job is markedly facilitated by the adhesion of the gasket to the cover body.

[0006] As the above-mentioned (1) method comprising fixing the gasket on the cover body by means of a double-coated tape, there is usually adopted a method in which a sheet like gasket material to which a double-coated tape is adhered, is punched into a shape of gasket, and the resultant gasket is fixed to the cover body. However, said method is involved in such problems that most of the sheet-like gasket material after punching remains as waste material and besides, the production process is made intricate or troublesome, thus inevitably increasing the production cost, since the gasket is fixed to the cover body after the gasket material has been punched into a shape of gasket.

[0007] In addition, in the (2) method comprising making holes in the cover body and fixing a gasket material through the holes, since the gasket material is exposed on the upper side of the cover body, the gasket material exposed thereon is sometimes upturned or curled when the cover body is inserted into the space of an electronic equipment main body, said space being narrowed accompanying the recent compactified electronic equipment part items. Thus, there is caused the problem that such upturning or curling is responsible for defective sealing properties.

[0008] Moreover, in the case where the gasket which is fitted to a cover body and which is produced by such a method, is used in a hard disc unit, there is caused the problem that it is impossible to suppress the vibration due to the rotation of the hard disc.

[0009] On the one hand, the adhesion between a thermoplastic material and a metallic sheet as the cover body, is usually carried out by a method in which the thermoplastic material is subjected to adhesion treatment on the surface thereof by corona discharge or the like, and thereafter is stuck to the metallic sheet by using an epoxy-based or a urethane-based adhesive. Nevertheless, the job in said method is intricate and troublesome, and is involved in gas generation problem, whereby the method is inapplicable to a gasket for use in electronic equipment.

[0010] In order to simplify and facilitate the aforesaid job, consideration is given to a method comprising injection molding an adhesive thermoplastic material for the purpose of direct adhesion. However, such a thermoplastic material, even when being made rather hard, is enlarged upon injection molding, thereby making it impossible to employ the molded product as such as a gasket. Therefore, said method has not been adopted to the production of a gasket for a cover body in a hard disc.

SUMMARY OF THE INVENTION

[0011] Under such circumstances, it is a general object of the present invention to provide a composite structure which comprises a metallic sheet and a thermoplastic material that are integrated in good adhesion by injection molding, and which is excellent in such a performance as vibration-damping properties and is well suited for usage in a gasket fitted to a cover body to be used for housing electronic equipment and the like.

[0012] Other objects of the present invention will be obvious from the text of the specification hereinafter disclosed.

[0013] In view of the foregoing, intensive extensive research and investigation were accumulated by the present inventors in order to develop the above-mentioned composite structure having favorable properties. As a result, it has been found that the general object can been achieved by the composite structure which is equipped, on a metallic sheet by coating, with a layer comprising a thermoplastic material capable of being thermally fusedly adhered to a thermoplastic material to be placed thereon, and further equipped on said layer with a layer comprising a desirable thermoplastic material by means of thermal fusion adhesion. It being so, the present invention has been accomplished on the basis of the above-mentioned findings and information.

[0014] Specifically, the present invention provides a composite structure comprising a metallic sheet and two thermoplastic material layers of a layer (A) and a layer (B) which are placed in turn and integrated with each other, characterized in that said layer (A) comprises a thermoplastic material capable of being thermally fusedly adhered to the thermoplastic material in the layer (B), said metallic sheet and said layer (A) are adhered to each other by coating, and said layers (A) and (B) are thermally fusedly adhered to each other. The present invention further provides a process or producing a composite structure which comprises installing, on a metallic sheet by coating, a layer (A) comprising a thermoplastic material capable of being thermally fusedly adhered to a thermoplastic material in a layer (B) to be placed thereon, and further installing the layer (B) on said layer (A) by thermally fusedly adhering a desirable thermoplastic material on said layer (A).

BRIEF DESCRIPTION OF THE DRAWING

[0015] FIG. 1 is a perspective illustration which shows one example of a gasket fitted to a cover body according to the present invention, wherein the symbols 1 and 2 denote gasket and cover body, respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The composite structure according to the present invention comprises a metallic sheet and two thermoplastic material layers of a layer (A) and a layer (B) which are placed in turn and integrated with each other.

[0017] The above-mentioned metallic sheet is not specifically limited, but can be properly selected for use according to the purpose of use of the composite structure, from cold rolled steel sheets, galvanized steel sheets, aluminum/zinc alloy plated steel sheets, stainless steel sheets, aluminum sheets, aluminum alloy sheets, magnesium sheets and magnesium alloy sheets, and the like.

[0018] There is preferably usable a metallic sheet which is treated with non-electrolytic nickel plating for its being inexpensive and excellent in corrosion resistance. As a method for non-electrolytic nickel plating, there is usable any of well known methods that have heretofore been applied to metallic raw materials, for instance, a method which comprises immersing a metallic sheet to be treated in a non-electrolytic nickel plating bath comprising an aqueous solution at a pH of approximately 4.0 to 5.0 and at a temperature of approximately 85 to 95° C. which contains nickel sulfate, sodium hypochlolite, lactic acid, propionic acid and the like each in a proper proportion.

[0019] The thickness of the metallic sheet to be employed in the the present invention is properly selected for use according to the purpose of use of the composite structure, and is in the range of usually from 0.1 to 2 mm, preferably from 0.2 to 1 mm.

[0020] The layer (A) is a layer comprising a layer capable of being thermally fusedly adhered to the thermoplastic material in the layer (B) to be equipped thereon. The thermoplastic material in the layer (A) is properly selected for use according to the type of the thermoplastic material to be used in the layer (B), for instance, from polyolefinic resin, polystyrenic resin, acrylic resin and the like. In the case where a styrenic thermoplastic elastomer is used in the layer (B), it is advantageous to use a modified polyolefinic resin as a thermoplastic material in the layer (A). In this case, the polyolefinic resin is exemplified by a homopolymer of an &agr;-olefin such as ethylene; propylene; butene-1; 3-methylpentene-1; and 4-methylpentene-1, a copolymer of at least two in these, and a copolymer of any of these and an other polymerizable unsaturated monomer. Typical examples thereof include ethylenic polymer such as high density, intermediate density and low density polyethylenes, straight-chain low density polyethylene, ethylene/vinyl acetate copolymer and ethylene/ethyl acrylate copolymer, propylenic polymer such as propylenic homopolymer, propylene/ethylene block or random copolymer, propylene/ethylene/diene compound copolymer, polybutene-1; and poly 4-methylpentene-1.

[0021] In order to enhance the adhesivity to the metal, there are effectively usable the above-mentioned resins incorporated with an acid anhydride, a functional group such as carboxyl group, carboxylic acid ester group or chlorosulfonate group, or a halogen.

[0022] The layer (A) in the present invention is installed onto the metallic sheet in good adhesion by means of coating. In this case, the coating is carried out usually at a temperature close to the softening point or melting point of the thermoplastic material to be used. The thickness of the layer (A) is selected in the range of usually from 3 to 100 &mgr;m, preferably from 5 to 30 &mgr;m.

[0023] In the composite structure according to the present invention, a thermoplastic material layer as the layer (B) is formed on the layer (A) by means of thermal fusion adhesion. The thermoplastic material which constitutes the layer (B) is not specifically limited, but can be properly selected for use from various materials according to the purpose of use of the composite structure.

[0024] In the case where, for instance, the composite structure is used as a sealing member, and the gasket portion is the layer (B), the thermoplastic material which constitutes the layer (B) is preferably a thermoplastic material having a low hardness of less than 60 degrees in terms of JIS hardness A. Examples of said thermoplastic material having a low hardness include thermoplastic elastomers of styrenic base, olefinic base, urethane based and acrylic base, respectively. In particular, with regard to a case for housing electronic equipment, it is preferable to use such a material that surely interrupts moisture and air and besides does not generate a halogen base gas or an acidic gas. From the viewpoint of adhesivity to the box body of a case and tackiness, it is preferable to use a material having a JIS hardness being less than 60 degrees, especially being in the range of 15 to 45 degrees. The above-mentioned thermoplastic material is preferably a thermoplastic elastomer of styrenic base, which is exemplified by styrene/butadiene/styrene block copolymer (SBS), hydrogenated styrene/butadiene/styrene block copolymer (SEBS), styrene/isoprene block copolymer (SIR), styrene/isoprene/styrene block copolymer (SIS) and hydrogenated styrene/isoprene/styrene block copolymer (SEPS).

[0025] Specific examples of the foregoing styrenic thermoplastic elastomer include “Rubberon” manufactured by Mitsubishi Chemical Industries Co., Ltd., specifically exemplified by “Rubberon MJ4300B” (trade name) having a JIS hardness A of 45 degrees and “Rubberon T320C” (trade name) having a JIS hardness A of 15 degrees, “Septon” manufactured by Kuraray Co., Ltd., specifically exemplified by “Septon 2063” (trade name) having a JIS hardness A of 36 degrees, and “Elastomer AR” manufactured by Aron Kasei Co., Ltd. Different from EPDM and butyl rubber, the styrenic thermoplastic elastomer need not vulcanization and can be recycled, thereby greatly contributing to cost curtailment. Specific examples of the olefinic thermoplastic elastomer include “Santprene” manufactured by A. E. S. Japan Inc. (trade name) having a JIS hardness A of 45 degrees.

[0026] The thermoplastic material which constitutes the layer (B) may be used alone or in combination with at least one other.

[0027] With respect to the composite structure according to the present invention, the thickness of the layer (B) to be placed on the aforesaid layer (A) by means of thermal fusion adhesion is not specifically limited, but can be properly selected for use in accordance with the purpose of use of the composite structure, and it is in the range of usually 0.1 to 5 mm, preferably 0.2 to 2 mm.

[0028] It is possible in the present invention that the thermoplastic material layer as the layer (B) be incorporated, as desired and to the extent that the objects of the present invention are not impaired, with such additives as an antioxidants (age resisters), ultraviolet absorbers, light stabilizers and a variety of fillers specifically exemplified by carbon black, talc, barium sulfite, calcium carbonate, magnesium carbonate, metal oxide, mica, graphite, aluminum hydroxide, various metallic powders, wood chipping, glass powder, ceramic powder, granular or powdery polymer, glass fiber, metallic fiber, and organic fiber.

[0029] Particularly preferably usable composite structure in the present invention, is that comprising a styrenic thermoplastic elastomer as the layer (B) and a polyolefinic thermoplastic elastomer as the layer (A).

[0030] The process for producing the composite structure according to the present invention is not specifically limited, provided that said process is capable of producing the composite structure imparted with the above-mentioned properties. According to the simplified process of the present invention as described hereunder, it is made possible to efficiently produce a desirable composite structure.

[0031] In the process according to the present invention, first of all, the layer (A) is formed on a metallic sheet which has been preferably subjected to non-electrolytic nickel plating by coating the metallic sheet with a thermoplastic material (hereinafter sometimes referred to as “thermoplastic material I”) capable of being thermally fusedly adhered to the thermoplastic material in the layer (B) (hereinafter sometimes referred to as “thermoplastic material II”) to be placed on the layer (A). The metallic sheet or the metallic sheet which has been subjected to non-electrolytic nickel plating may be subjected at need, to a surface treatment such as plasto-treatment, treatment by hair line, etching, crack plating, oxidation, anodic oxidation, corona discharge, plasma or primer coating.

[0032] The layer (A) may be formed by the use of an aqueous emulsion of the thermoplastic material I from the standpoint of environmental concern or suppression of gas generation. Specifically in this case, the layer (A) may be formed by pulverizing the thermoplastic material I such as polyolefinic resin and emulsifying the resultant pulverized material with an emulsifier according to a previously well known method to prepare an aqueous emulsion containing the thermoplastic material I, and applying coating of the resultant emulsion. In this case, an adhesive component with good adhesivity of urethane base or epoxy base may be added thereto as required, to the extent that the objects of the present invention are not impaired thereby.

[0033] Subsequently, by applying the solution of the modified adhesive polyolefinic resin onto the metallic sheet so that the thickness of the resultant coating comes to be a desired value by a well known method such as brush coating, padding coating, spray coating, roller coating and flow coating, followed by drying, the layer (A) is formed adhesively onto the metallic sheet.

[0034] It is preferable to apply the solution of the modified adhesive polyolefinic resin only to the portion where the gasket material is adhered by means of a dispenser, pat printing, screen printing or the like from the viewpoint of preventing gas generation and curtailing the manufacturing cost.

[0035] Subsequently, by thermally fusedly adhering a desired thermoplastic material II, for instance, styrenic thermoplastic elastomer or the like onto the layer (A) so as to form the layer (B). In the formation of the layer (B), there is preferably used injection insertion method, whereby for instance, a metallic sheet equipped with the layer (A) is arranged in a mold, and the thermoplastic material II is injectedly poured onto said layer (A) so that the thermoplastic material II and the thermoplastic material I are thermally fusedly adhered to each other to form the layer (B) having a desired thickness on the layer (A). Alternatively, there is usable a method in which the layer (B) is formed onto the layer (A) by thermally fusedly adhering the layers by means of pressing method.

[0036] The thermal fusion adhesion temperature is properly selected according to the types of the thermoplastic material I and the thermoplastic material II. In the case, for instance, where polypropylene is used as the thermoplastic material I and SEBS or SEPS, that is, styrenic thermoplastic elastomer is used as the thermoplastic material II, said temperature is in the range of approximately 170 to 200° C.

[0037] In such a manner as described hereinbefore, there is obtainable the composite structure according to the present invention wherein the metallic sheet and the thermoplastic materials are integrated with one another.

[0038] According to the process of the present invention, it is made possible to readily integrate the thermoplastic material for a gasket and the metallic sheet through injection molding only-by applying in advance, the solution of an adhesive resin without deteriorating the physical properties of the thermoplastic material. Further, the composite structure according to the present invention is excellent in vibration-damping properties, since the metallic sheet is laminated with the thermoplastic material I, and it is well suited for usage in the gasket fitted to a cover body to be used in sealing members, particularly electronic equipment.

[0039] Moreover according to the present invention, it is made possible to prevent the adhesion of dirt such as dust and the leak of electromagnetic wave by mixing an electroconductive material in the thermoplastic material I and/or the thermoplastic material II, and besides to prevent heat accumulation in a hard disc by by mixing a material having high heat releasabity in the thermoplastic material I so as to enable to release internally generated heat to the outside.

[0040] As described hereinbefore, the composite structure according to the present invention, wherein the metallic sheet and thermoplastic materials are integrated with one another in good adhesivity by applying in advance the adhesive resin onto the metallic sheet, and then injection molding the thermoplastic gasket material, is excellent in vibration-damping properties, and is is well suited for usage in the gasket fitted to a cover body to be used in electronic equipment and the like.

[0041] Furthermore, the production process according to the present invention enables to efficiently produce the composite structure, dispensing with intricate or troublesome steps.

[0042] In what follows, the present invention will be described in further detail with reference to comparative examples and working examples, which however shall never limit the present invention thereto.

EXAMPLE 1

[0043] An aluminum sheet which had a thickness of 0.5 mm and which was equipped with non-electrolytic nickel-plated film of 5 &mgr;m in thickness was coated thereon with a solution of a modified adhesive polyolefinic resin (maleic acid-modified copolymer of propylene, ethylene and butene, manufactured by Mitsubishi Chemical Industries Ltd. under the trade name “Unistol P-802”), and the resultant coated sheet was heat treated at 50° C. to prepare an aluminum sheet having the coated film of 30 &mgr;m in thickness.

[0044] Subsequently, onto the resultant adhesive polyolefinic resin coat formed on the aluminum sheet, there was insertion molded a styrenic thermoplastic elastomer having a JIS hardness A of 45 degrees (manufactured by Mitsubishi Chemical Industries Ltd. under the trade name “Rubberon MJ 4300B”) in a thickness of 0.5 mm by the use of an injection molding machine under the temperature conditions of the nozzle and cylinder at 180° C. and the insert aluminum sheet at room temperature to prepare a composite structure.

[0045] The composite structure thus obtained was subjected to peel test for styrenic thermoplastic elastomer in accordance with JIS Z 0237. As a result, there were found the destruction of the material of the thermoplastic elastomer itself along with the delamination on the interface between the aluminum sheet and the adhesive polyolefinic resin coat. However, the peeling strength at the time of delamination was at least 1.6 kg/25 mm, thus showing sufficient adhesion strength for fixing the composite structure to the main body by means of screws.

COMPARATIVE EXAMPLE 1

[0046] The procedure in Example 1 was repeated except that the adhesive polyolefinic resin coat was not formed on the aluminum sheet subjected to non-electrolytic nickel plating, namely the styrenic thermoplastic elastomer was directly insertion molded onto the aluminum sheet. As a result, because of failure in adhesion, the elastomer was separated from the aluminum sheet at the time of taking out thereof.

EXAMPLE 2

[0047] FIG.1 is a perspective illustration which shows a gasket fitted to a cover to be used for a case housing a hard disc drive unit as one embodiment of the composite structure according to the present invention, and which is viewed from the sealing surface side, wherein a gasket 1 is adhered to the surface of a metallic cover body 2 as a cover for the case housing a hard disc drive unit. Such equipment and machinery as a magnetic disc, a magnetic head and an actuator are arranged in the box body side of the case housing a hard disc drive unit, closed with said box body (not illustrated on the drawing) and said gasket fitted to the cover, and are housed in said case.

[0048] As the cover body 2, use was made of an aluminum sheet which had a thickness of 0.5 mm and which was equipped with non-electrolytic nickel-plated film of 5 &mgr;m in thickness, was coated thereon with a solution of a modified adhesive polyolefinic resin (maleic acid-modified adhesive polypropylene, manufactured by Mitsubishi Chemical Industries Ltd. under the trade name “Unistol R-300”), and the resultant coated sheet was heat treated in the same manner as in Example 1 to prepare an aluminum sheet with the coated film of 30 &mgr;m in thickness.

[0049] Subsequently, onto the resultant polypropylene coat formed on the aluminum sheet, there was insertion molded a styrenic thermoplastic elastomer in a thickness of 0.5 mm in the same manner as in Example 1 to form the gasket 1 and prepare a gasket fitted to a cover. As the result of peel test in accordance with JIS Z 0237, the peeling strength at the time of delamination was at least 1.4 kg/25 mm, thus showing sufficient adhesion strength for fixing said gasket to the main body by means of screws.

[0050] The gasket fitted to a cover thus prepared was used as the cover of the case housing a hard disc drive unit for a period of 30 days so that the gasket portion faced the box body, and thereafter visual observation was made of the gasket portion. As a result, the dust preventive properties during the service was satisfactory without observable sagging on the gasket portion. Further observation was made of the vibration-damping performance of the gasket fitted to a cover in the hard disc drive unit. As a result, resonance due to the hard disc was not observed.

COMPARATIVE EXAMPLE 2

[0051] The procedure in Example 2 was repeated except that the modified adhesive polyolefinic resin coat was not formed on the aluminum sheet. Thus, there was prepared a gasket fitted to a cover by injection molding a styrenic thermoplastic elastomer onto a cover body having holes for fixing said elastomer. Then, observation was made of the vibration-damping performance of the gasket fitted to a cover in the hard disc drive unit. As a result, resonance due to the hard disc was observed.

[0052] As is obvious from the foregoing results of evaluations, the gasket fitted to a cover as one of the embodiments of the present invention, can readily be produced, exhibits favorable dust preventive properties owing to good adhesion between the gasket and the cover body when used as a cover of a case housing a hard disc drive unit, and besides is free from any deformation even after a long time of service because of the gasket being constituted of a material having a low hardness.

Claims

1. A composite structure comprising a metallic sheet and two thermoplastic material layers of a layer (A) and a layer (B) which are placed in turn and integrated with each other, characterized in that said layer (A) comprises a thermoplastic material capable of being thermally fusedly adhered to the thermoplastic material in the layer (B), said metallic sheet and said layer (A) are adhered to each other, and said layers (A) and (B) are thermally fusedly adhered to each other.

2. The composite structure according to claim 1, wherein the layer (A) comprises a modified polyolefinic resin, and the layer (B) comprises a styrenic thermoplastic elastomer.

3. The composite structure according to claim 1, wherein the metallic sheet is that subjected to non-electrolytic nickel plating.

4. The composite structure according to claim 1, which is used as a sealing member.

5. The composite structure according to claim 4, wherein the sealing member is a gasket fitted to a cover for a hard disc drive.

6. A process for producing a composite structure which comprises installing, on a metallic sheet by coating, a layer (A) comprising a thermoplastic material capable of being thermally fusedly adhered to a thermoplastic material in a layer (B) to be placed thereon, and further installing the layer (B) on said layer (A) by thermally fusedly adhering a desirable thermoplastic material on said layer (A).