FIELD OF THE INVENTION
The present inventions relates to a method for manufacturing a beautiful and quality key pad assuring a good durability to be used for portable phone, portable information terminal, remote control of various home electric apparatuses, card remote control or various keyboards.
BACKGROUND OF THE INVENTION
Silicon rubber or the like are primarily used for the conventional key pad, because of their excellent low temperature resistance, heat resistance, precise formability and electric insulation. As key top, soft rubber is used for disposing graphics composed of character, numeral, symbol or picture on its surface or light masking portion is arranged to dispose graphics formed by cutting out a character, numeral, symbol or picture.
However, as silicone base coating is used, in every case, as material of graphics to be formed on theses surfaces, they are worn or broken by finger pressure or friction with clothing resulting in the deterioration of 20 visual recognition or appearance.
Therefore, Japanese Utility Model Laid-Open Shouwa 48-15161, Japanese Patent 2627692 or Japanese Patent Publication Heisei 7-95411 have proposed methods 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 double side adhesive tape or the like.
Concerning the addition of different material to silicone rubber, it is also known to treat the surface as described in Japanese Patent Publication Heisei 7-282687 or Japanese Patent Publication Heisei 7-296676.
It should be noted that they all concerns the formation of coating layer and not the adhesion of rigid resin key top with silicone key pad.
SUMMARY AND OBJECTS OF THE INVENTION
As silicone rubber is less adhesive, generally silicone base adhesives have been used or the surface was treated with substrate for adhering them and there was no other solution. However, as these silicone base adhesives have weak retention force and exfoliate easily after adhesion, it has been often necessary to dispose additional anti-detachment collar or the like on the key top part to be used in practice.
Moreover, as silicone base adhesives are slow in hardening, it is necessary to heat 100° C. or more. As the consequence, it was difficult to use resins of low softening point represented by ABS as key to material.
What is more, as silicone rubber presents a high linear dilatation coefficient of 2 to 3×10−4/°C., heating expands the key top part enormously and key pitch or the like vary; consequently it has been necessary to fix the key top part and the base key pad portion until the adhesion completion, increasing the time of adhesion process and the number of affixing jigs, and resulting in low productivity and less economy.
The present Invention concerns a method for manufacturing a key pad with rigid resin key top, solving these problems.
It concerns a method for manufacturing a high productivity key pad, comprising the steps for surface-modifying the adhesion surface of a key pad key top or a portion thereof by at least one method selected from the group including short wavelength ultraviolet irradiation treatment, corona discharge treatment, flame treatment and plasma treatment and adhering the key top molded with rigid resin with reactive hardening resin such as urethane base resin, epoxy base resin, amino base resin, cyanoacrylate base resin, photo reactive hardening resin or the like, thereby assuring more hard adhesion between the silicone rubber key pad and the key top, characterized by that low softening point rigid resins represented by ABS may also be used and that the adhesion operation can be completed more rapidly, without dislocation during the adhesion.
Namely, the present Invention concerns a method for manufacturing a key pad with rigid resin key top, comprising steps for surface-modifying the adhesion surface of a silicone rubber key pad for push-button, applying reactive hardening resin and, thereafter, adhering the key top molded with rigid resin.
Members composing a key pad are preferably made of silicone rubber, because of its excellent low temperature resistance, heat resistance, weather resistance, precise formability and electric insulation. Graphics composed of character, number, symbol or picture 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.
Silicone rubber, key top member is weakly adhesive, however, the rigid resin key top is so made to be attached firmly with photo reactive hardening resin, by surface treating using at least one method selected from the group including short wavelength ultraviolet irradiation treatment, corona discharge treatment, flame treatment, plasma treatment or substrate treatment.
The short wavelength ultraviolet irradiation treatment used for the Invention consists in irradiating the key pad surface with short wavelength ultraviolet irradiation at a constant illumination, by a constant total light quantity to alter the surface. To be more precise, 184.9 nm and 253.7 nm radiation irradiated from a mercury lamp wherein mercury in contained under the pressure of about 10−1 mmHg generates ozone under the presence of oxygen, the ozone oxidizes the surface of an object to be treated, generates active groups such as carboxyl group or silanol group and, thereby, improving the adhesion and compatibility of printing inks or paintings.
Corona discharge treatment consists in applying a high tension between electrodes in the atmosphere to provoke dielectric breakdown and discharge, and introducing an object to be treated there-between, thereby oxidizing polymer of the surface layer and introducing active group into the surface to bring out the similar effect.
Flame treatment consists in passing an object to be treated through a strong oxidizing flame to bring out an effect similar to the corona treatment.
Plasma treatment consists in ionizing gas molecular by provoking glow discharge in low pressure inactive gas, oxygen, halogen gas or the like, generating plasma and activating the surface using its chemical activity.
Being dry process, short wavelength ultraviolet irradiation treatment, corona discharge treatment, flame treatment or plasma treatment are simpler in terms of process than the method using surface treatment agent; however, short wavelength ultraviolet irradiation treatment or corona treatment are preferable, because plasma treatment requires vacuum status or expensive equipment and flame treatment is necessarily dangerous.
To obtain a higher holding power, additional surface treatment may also be executed, after this surface-modification, using well-known silane, titanium or aluminum base various coupling agents.
The composition of the reactive hardening resin is not limited and at least one resin selected from the group including urethane base resin, epoxy base resin, amino base resin, acrylic resin and cyanoacrylate base resin.
The color is not particularly limited; however, if the key top part is to be illuminated, the reactive hardening resin should be translucent.
The hardening method of the reactive hardening resin is not particularly limited, but the use of heat reactive hardening resin or photo reactive hardening resin can reduce the adhesion process. As for heat reactive hardening resin allowing to reduce the adhesion time and increase the holding power, urethane base resin or cyanoacrylate base resin are preferable and, particularly , cyanoacrylate base resin would permit to obtain the adhesion within several seconds and reduce the manufacturing time. Photo reactive hardening resin also allows to obtain the adhesion within several seconds and reduce further the adhesion process, and moreover, assures a good stability during application work or conservation and a good workability. On the other hand, as visible ray reactive hardening resin would react even to an ordinary work light, UV hardening type resin is preferable in terms of workability.
If photo reactive hardening resin is used as reactive hardening resin and light is irradiated from the key pad side, at least members of the key pad member where photo reactive hardening resin is applied should be composed of semi-translucent or translucent member allowing to pass the light having the wavelength in the range of 200 to 600 nm where the applied photo reactive hardening resin hardens.
If light is irradiated from the key top side, members of at least the portion, among the rigid resin key top members, where photo reactive hardening resin is applied should be at least composed of semi-translucent or translucent member allowing to pass the light having the wavelength in the range of 200 to 600 nm where the applied photo reactive hardening resin hardens.
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 mould 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, elasticity, color of the rigid resin key top are not particularly limited, but as indication, polycarbonate resin, polymethyl methacrylate resin, styrene base resin, acrylic base co-polymerized resin, polyolefine base resin, ABS resin, polyester base resin, epoxy base resin, polyurethane base resin, polyamide resin, silicone base resin or the like are included.
Graphics composed of character, number, symbol or picture may be disposed on the surface or back of the rigid resin key top, or light masking may be arranged to dispose graphics formed by cutting out a character, number, symbol or picture. Moreover, coating layer may be prepared over these graphics.
The form of the rigid resin key top adhesion portion may not be flat and may have irregularities arranged for positioning with the object to be adhesived.
If the key top is to be illuminated, graphics disposed on the back of the resin key top is to be configured to be recognized through the rigid resin key top or, moreover, these graphics are to be illuminated, the rigid resin key top color should be semi-translucent or translucent.
If translucent resin is used as reactive hardening resin and at least a part of the rigid resin key top member is made of translucent member, 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 light masking portion and cutting out characters, numerals, symbols, pictures or the like, the color or the others.
For applying the reactive hardening resin, in addition to screen printing method, dispenser method, potting method, pad printing method, spray method or transfer method may also be used without particular specification.
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.
If cyanoacrylate base resin is used as reactive hardening resin, the key pad and the rigid resin key pad are adhered by compression, heating and humidification. Photo reactive hardening resin can be adhered by light irradiation. The other adhesives are adhered by various other hardening conditions. As photo reactive hardening resin and cyanoacrylate base resin harden rapidly at a low temperature, it is unnecessary to heat the key pad composed of silicone rubber and dislocation would not be provoked by heat dilatation. As the consequence, it is enough to position the rigid resin key top at the adhesion, dispensing with fixing both rigid resin key top and key pad.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is illustrated.