Key pad with rigid resin key top

Abstract: A key pad with a rigid key top, preventing key top detachment or dislocation, and allowing omission of key detachment prevention means such as a collar to simplify the structure, and adhering to a silicone rubber key pad (1) with silicone base adhesive (3), by providing a urethane base adhesion substrate layer (7) on a back of a key top made of rigid resin (4).

Description: The present invention relates to a key pad with a rigid resin key top, to be used for portable phones, portable information terminals, remote controls for various home electrical apparatuses, card remote controls or various keyboards. Silicon rubber or the like has been conventionally used as an element for a conventional key pad, because of its excellent low temperature resistance, heat resistance, weather resistance, precise formability and electric insulation. As a key top, soft rubber has been used for disposing graphics composed of characters, numbers, symbols, or pictures on its surface or a light masking portion has been arranged to dispose graphics formed by cutting out a character, number, symbol or picture. However, as silicone base coating has been used, in every case, as material of graphics to be formed on these surfaces, they become worn or broken by finger pressure or friction with clothing resulting in the deterioration of visual recognition or appearance. Therefore, Japanese Utility Model Laid-Open No. 48-15161, Japanese Patent Publication No. 7-095411 or Japanese Patent No. 2627692 have proposed a method wherein a key top part is formed separately with rigid resin for printing its surface or back or elsewhere and then integrated by engaging with a silicone key pad or adhering with adhesive or both faces with adhesive tape or the like. However, as silicone rubber is less adhesive, silicone base adhesives have been used generally for adhering them. Silicone base adhesives include additional reaction type and condensation reaction type, and relatively high strength silicone adhesives are of condensation reaction type. On the other hand, adhesives of condensation reaction type take several hours to several days for hardening, lowering their productivity; if a higher productivity is required, it has been necessary to use those of additional reaction type having faster reaction. However, silicone base adhesives of additional reaction type are less adhesive with resin or printing ink or other organic compounds used for key tops, peeling easily after the adhesion. It has been necessary in practice to arrange a collar or the like on the key top part in order to avoid its detachment. Moreover, the adhesion portion can be treated with primer, but this increases the number of process steps, resulting in low productivity. On the other hand, Japanese Patent 2627692 does not describe clearly these points. The invention provides a key pad with a rigid resin key top, comprising: a silicone rubber key pad with an adhesion portion; a silicone base adhesive on said silicone rubber key pad adhesion portion; a rigid resin key top with a back; and an adhesive substrate layer on said back of said rigid resin key top, said adhesive substrate layer having a urethane base adhesion substrate layer on a portion to be adhered to said silicone base adhesive on said key pad. The key pad with rigid resin key top of the present invention is manufactured by a method comprising steps of preparing urethane base adhesive substrate on the back face of a key top made of rigid resin and adhering with a silicone rubber made key pad, by enhancing the adhesive strength of silicone base adhesives to be used, such that the key top does not detach nor become dislocated, allowing a collar or other means for preventing key detachment to be omitted and to simplify its structure. The invention will be further described with reference to the accompanying drawings, wherein: Fig. 1 is a vertical cross-portion showing a first embodiment of the invention, denoted as example 1; Fig. 2 is a vertical cross-portion showing a second embodiment of the invention, denoted as example 2; Fig. 3 shows the arrangement of a third embodiment of the invention, denoted as example 3; Fig. 4 shows the arrangement of a comparative example 1; and Fig. 5 shows the arrangement of a comparative example 2. As keypad material, silicone rubber is used for its excellent low temperature resistance, heat resistance, precise formability and electric insulation. Graphics composed of characters, numbers, symbols, or pictures may be disposed on its surface or light masking may be arranged to dispose graphics formed by cutting out a character, number, symbol or picture. The key top is made of rigid resin, and urethane base adhesive substrate is prepared on the adhesion surface of silicone base adhesive, to enhance the adhesive strength of silicone base adhesives. The rigid resin key top used for the invention is a molded resin key top or a ground resin key top. The molded resin key top can be manufactured by using a mold of desired key top configuration, charging heat melt resin or liquid non hardened resin into the resin and hardening it by injection molding, compression molding, transfer molding or rotation molding. Composition, kind, elastici ty, and colour of the rigid resin key top are not particularly limited, but polycarbonate resin, acrylic resin, ABS resin or other thermoplastic resins are largely used for their formability, cost and appearance. Graphics composed of characters, numbers, symbols or pictures may be disposed on its surface or back, or light masking may be arranged to dispose graphics formed by cutting out a character, number, symbol or picture. Moreover, a coating layer may be prepared over these graphics. Ink for printing graphics to be disposed on the back of rigid resin key tops is not particularly limited; however, for instance, acrylic base or polyester base, PVC base or urethane base ink may be used. The form of the rigid resin key top adhesion portion need not be flat and may have irregularities arranged for positioning with the object to be adhered. Urethane base adhesive substrate layer used for the invention is suitably an organic resin having urethane links in a polymer. To be more specific, it is obtained by the reaction between organic compounds having isocyanate group and organic compounds having active hydrogen group such as hydroxyl group or amino group and their polymerization. Organic compounds having isocyanate group include, for instance, tolylenediisocyanate, xylylenediisocyanate, methylcyclohexylene-2,4-diisocyanate, hexamethylenediisocyanate, isophoroneisocyanate, lysineisocyanate methylester, or doublets and triplets of these isocyanates or those partially degenerated by polyhydric alcohol. Organic compounds having active hydrogen group such as hydroxyl group or amino group include polyester polyol, polyurethane polyol, polyether polyol, polycarbonate polyol, polyether polyamine or the like. They may be mixed, applied, reacted and polymerized to obtain a reaction type coating, or they may also be polymerized beforehand, then diluted by solvent or the like to obtain solvent evaporation type painting. Their viscosi ty shall be adjusted appropriately by solvent or the like, and charge, colourant, catalyst or others are added as necessary before use. Hardening method or elastic modulus is not limited, but as for colour, semi-translucent or translucent member should be used if the key top part is to be illuminated. For applying the adhesive substrate layer, in addition to a screen printing method, a dispenser method, potting method, pad-printing method, spray method or transfer method may also be used without particular specification. The thickness of the adhesive substrate layer is not particularly limited; preferably it is between 0.1µm and 100 µm. Less than 0.1µm, the adhesive substrate layer resistance is insufficient and more than 100µm, the application becomes difficult. On the other hand, if urethane base ink is used for printing graphics to be disposed on the back of the rigid resin key top, the graphics printing layer would act as an adhesive substrate layer, dispensing with a new layer as adhesive substrate layer, resulting in reduction of printing steps. If the key top is to be illuminated, graphics disposed on the back of the res in key top are to be configured to be recognized through the rigid resin key top or, moreover, if these graphics are to be illuminated, the rigid resin key top member, graphics print portion to be realized on the back of the key top, the adhesive substrate layer and silicone adhesive should be semi-translucent or translucent. If translucent silicone adhesive is applied to the rigid resin key top, the urethane base adhesive layer is also translucent and at least a part of the rigid resin key top member is made of a translucent member, and it can naturally be composed to allow to recognize through them characters, numerals, symbols, pictures or the like realized on the key pad surface, graphics made by disposing a light masking portion and cutting out characters, numerals, symbols, pictures or the like, colour or other. To position the rigid resin key top for adhesion, irregularities for fitting may be disposed on either or both of key pad and rigid resin key top, or a jig may be used to embrace the key pad and the rigid resin key top from outside. Silicone base adhesive is applied to the keypad or the rigid resin key top, then they are applied the one to the other; the adhesive is heated for its hardening adhesion. The silicone base adhesive used for the invention is not limited as for its hardening method, elastic modulus or the like; however, preferably, heat hardening additional reaction type presents shorter hardening time and higher resistance and moreover is more practical. As for the colour, if the key top part is to be illuminated, a semi-translucent or translucent member should be used. For applying adhesive, in addition to a screen printing method, a dispenser method, potting method, pad-printing method, spray method or transfer method may also be used without particular specification. According to the Invention, the rigid resin key top sticks securely with silicone base adhesive, by disposing urethane base adhesive substrate layer on the back of the rigid resin key top. It may be the result of an effective interaction between urethane links contained in the urethane base adhesive substrate layer and OH-groups or CN-groups contained in the silicone base adhesive at the adhesion interface. The invention will be further described referring to examples and comparative examples, but it should be noted that the invention is not limited to such examples. Example 1 As shown in Fig. 1, a key pad 1 is formed wi th silicone rubber compound (SH861 supplied by TORAY-Dow Corning Silicone Co., Ltd.) by disposing irregularities for the rigid resin key top positioning. Silicone base adhesive (TSE3221 supplied by Toshiba Silicone Co., Ltd.) 3 is applied to an adhesion portion 2 of a key top by screen printing method. Separately, a graphic printing 5 is made with polyester base printing ink (PC-8000 supplied by Jujo Kako Co., Ltd.) on the surface of a rigid resin key top 4 formed with polycarbonate resin (Panlite L1225L supplied by Teijin Kasei Co., Ltd.) and hard coated with UV hardening type hard coat agent (3070 supplied by Three Bond Co., Ltd.), then urethane base ink (SG410 supplied by Seiko Advance Co., Ltd.) 7 is applied as adhesive substrate layer by the dispenser on a key pad adhesion portion 6 of the key top 4, hardened and dried, then the key top and the key pad are assembled by fitting the irregularities defined on their adhesion portion, and heated at 120°C for 10 minutes for hardening adhesion. In the key detachment test of this key pad with rigid resin key top, only the portion A in the figure is fixed, the portion B is pulled in the direction shown by the arrow by the traction rate of 50mm/min to measure the exfoliation resistance, obtaining, as a result, 1.1 Kg. At this moment, a part of the keypad was destroyed from the portion C in the figure. Example 2 As shown in Fig. 2, to an adhesion portion 8 of a key top of a key pad 1 formed with silicone rubber compound (SH861 supplied by TORAY-Dow Corning Silicone Co., Ltd.), silicone base adhesive (TSE3221 supplied by Toshiba Silicone Co., Ltd.) 9 is applied by screen printing method. Character printing 11 is made with printing ink (PC-8000 supplied by Jujo Kako Co., Ltd.) on the back of a rigid resin key top 10 formed with translucent polycarbonate resin (Panlite L1225L supplied by Teij in Kasei Co., Ltd.), then translucent urethane base ink (SG410 supplied by Seiko Advance Co., Ltd.) 12 is printed thereon as adhesive substrate layer, then this rigid resin key top 10 and the adhesion portion 8 of the key top is assembled, and heated at 120°C for 10 minutes for hardening adhesion. As in the example 1, the exfoliation resistance of this keypad with rigid resin key top was measured and found to be 1.0 Kg. At this moment, a part of the keypad was destroyed from the portion C in the figure. Example 3 As shown in Fig. 3, to an adhesion portion 14 of a key top of a key pad 13 formed with silicone rubber compound (SH861 supplied by TORAY-Dow Corning Silicone Co., Ltd.), silicone base adhesive (TSE3221 supplied by Toshiba Silicone Co., Ltd.) 15 is applied by screen printing method. Character printing 17 is made with coloured printing ink (SG410 supplied by Seiko Advance Co., Ltd.) on the back of a rigid resin key top 16 formed with translucent polycarbonate resin (Panlite L1225L supplied by Teijin Kasei Co., Ltd.), then this rigid resin key top 16 and the key top adhesion portion 14 are assembled, and heated at 120 °C for 10 minutes for hardening adhesion. The exfoliation resistance of this keypad with rigid resin key top was measured and found to be 1.0 Kg. At this moment, a part of the keypad was destroyed from the portion C in the figure. Comparative example 1 As shown in Fig. 4, a key pad 18 is formed with silicone rubber compound (SH861 supplied by TORAY-Dow Corning Silicone Co., Ltd.) by disposing convex irregularities for a rigid resin key top positioning. Silicone base adhesive (TSE3221 supplied by Toshiba Silicone Co., Ltd.) 20 is applied to an adhesion portion 1a of a key top 9 by clean printing method. Separately, a graphic printing 22 is made wi th printing ink (PC-8000 supplied by Jujo Kako Co., Ltd.) on the surface of a rigid resin key top 21 formed with polycarbonate resin (Panlite supplied by Teijin Kasei Co., Ltd.). This key top is adhered by fitting into the irregularities defined on the adhesion portion 19 of the key top, and heated at 120°C for 10 minutes for hardening adhesion. As in the example 1, the exfoliation resistance of this keypad with rigid resin key top was measured and found to be 0.3 Kg. At this moment, the part D of the figure was exfoliated at the interface between the key top and the silicone base adhesive layer. Comparative example 2 As shown in Fig. 5, to an adhesion portion 24 of a key top of a key pad 23 formed with silicone rubber compound (SH861 supplied by TORAY-Dow Corning Silicone Co., Ltd.), silicone base adhesive (TSE3221 supplied by Toshiba Silicone Co., Ltd.) 25 is applied by screen printing method. Character printing 27 is made with printing ink (PC-8000 supplied by Jujo Kako Co., Ltd.) on the back of a rigid resin key top 26 formed with translucent polycarbonate resin (Panlite L1225L supplied by Teijin Kasei Co., Ltd.). This rigid resin key top 26 and the key top adhesion portion 24 are assembled together, and heated at 120°C for 10 minutes for hardening adhesion. As in the example 1, the exfoliation resistance of this key pad with rigid resin key top was measured and found to be 0.2 Kg. At this moment, the part D of the figure was exfoliated at the interface between the printing ink layer of the key top and the adhesive layer of the silicone base. The adhesion resistance of the rigid resin key top of keypads with rigid resin key top shown in examples 1, 2 and 3 was satisfactory. On the other hand, the adhesion resistance of the rigid resin key top of key pads with rigid resin key top of comparative examples 1 and 2 are insufficient, so exfoliation was observed at the interface between the rigid resin key top and the silicone base adhesive layer in the comparative example 1, and at the interface between the ink face printed to the rigid resin key top and the silicone base adhesive layer in the comparative example 2. As described before, the key pad with rigid resin key top of the present invention provides an advantage of realizing a high productivity key pad, preventing key top detachment or dislocation, and allowing to omit key detachment prevention means such as a collar and to simplify its structure, through the improvement of the adhesion resistance of silicone base adhesive, by preparing urethane base adhesive substrate layer on the back of the key top made of rigid resin.

Claims: A key pad with a rigid resin key top, comprising: a silicone rubber key pad (1) with an adhesion portion (2); a silicone base adhesive (3) on said silicone rubber key pad adhesion portion; a rigid resin key top (4) with a back; and an adhesive substrate layer (7) on said back of said rigid resin key top, said adhesive substrate layer having a urethane base adhesion substrate layer on a portion to be adhered to said silicone base adhesive on said key pad. A key pad with a rigid resin key top as claimed in claim 1, characterized in that the adhesive substrate layer includes a graphic printed urethane base ink layer.

Inventors: NISHI KENGO, NISHI, KENGO
Applicants: POLYMATECH CO LTD, POLYMATECH CO., LTD.
Application year: 1999
Main classification: C08J5
IPC codes: H01H13, H01H11, C08J5