FINGER TOUCH MEMBER OF AN ILLUMINATED SWITCH

Abstract: The invention is related to a multicomponent rubber material for the cover piece of finger touch members of illuminated switches, comprising, in the uncures condition, a composition composed of, as essential components, 90 - 70% by weight of EPDM and 5 - 30% by weight of a lower polymerized butadiene rubber which is liquid under ordinary condition.

Description: FIELD OF THE INVENTION The present invention relates to finger touch members of illuminated switches to be employed especially in dark sites in electric instruments such as, on-vehicle telephones, portable telephones, wireless devices, and car audio instruments, as well as to a rubber material employed in the light-transmissible cover pieces of such finger touch members (denoted hereinafter as finger touch cover) of such illuminated switches, which is transparent and has a high affinity to the printing ink to be applied thereto together with a superior processibility. BACKGROUND OF THE INVENTION Heretofore, for the material of the light-transmissible finger touch covers for illuminated switches mentioned above, exclusively silicone rubber has found practical use due to its light permeability and excellence in heat resistance, weatherability and electric isolation performance. The inks to be printed on such finger touch cover have been limited only to those having film-forming components based on silicone because of their better compatibility with the silicone rubber for attaining a firm fixation on the cover. Such inks should reveal a high light-blocking ability, in order to attain a high relief contrast of the illuminated pattern and, therefore, are pigmented usually in black or dark gray color. Usually, carbon black is employed as coloring pigment in an amount of 10 - 20 % or even more, based on the weight of the film-forming component (base polymer) of the ink. While there have been used in practice inks based on silicone for printing the light-transmissible finger touch covers, as mentioned above, such inks have disadvantages of inferior wear-resistance and low oil-resistant property. In particular, in case of using carbon black for obtaining black or dark gray colored ink, the amount of the base polymer per unit surface area of the printing layer is reduced correspondingly, resulting in a reduction in the wear-resistance so that the print may easily be worn out by rubbing with a finger upon repeated finger touches on the switch or by contact with other materials, such as clothes. Moreover, the highly stuffed carbon black may easily be rubbed off and stain the finger. Under these circumstances, employment of other rubber materials including an ethylene-propylene rubber (EPDM), which exhibit also a superior transparency, as material for finger touch covers may be considered. Thus, attempts had been made for realizing such a possibility. However, no satisfactory durability of printing layer with any ink was attained. As another approach for solving these problems, the inventors have attempted to develop (a modified material for) a finger touch cover, the material property of which is improved such that the bonding between the ink printing layer and the substrate finger touch cover made thereof is high enough to insure a high durability of the printing layer. The inventors have dissovered that a multicomponent rubber material based on EPDM combined with another elastomeric component based on butadiene rubber reveals a high bonding performance to a printing layer of various inks. EP-A-0188097 gives an overview over several rubber compositions with varying compositions of ethylene-a-olefin copolymer rubber and/or an isobutylenebutylene-isopropene rubber as well as liquid polybutadiene rubber and /or polyisopropene rubber with an additional sulphur component. However, this document does not give any indication about the use of rubber composition materials in the process of preparing finger touch members of illuminated switches. SUMMARY OF THE INVENTION Thus, according to the present invention, a finger touch member of an illuminated switch is prepared by printing or coating an ink of contemplated color on a cover piece made of a multicomponent rubber material exhibiting high bonding performance to the printing layer is provided, which comprises, in the uncured condition, a composition composed of, as essential components, 90-70 % by weight of EPDM and 5 - 30 % by weight of an oligomerized butadiene rubber which is liquid under normal conditions, and requisite additives such as filler and curing agent, covering the entire top face of the printed or coated cover piece with a light blocking layer and irradiating the so covered top face of the cover piece with a laser beam to cut out the coating layer in a contemplated pattern. Alternatively a multicomponent rubber material comprises, in the uncured condition, a composition composed of, as essential components, 90 - 65 % by weight of EPDM and 5 - 25 % by weight of a liquid oligomerized butadiene rubber and 5 - 10% by weight of an oligomerized butadiene. The finger touch cover according to the present invention provides a high durability of printing applied thereon with inks containing carbon black and various base polyners. BRIEF DESCRIPTION OF THE DRAWING The sole drawing is a schematic vertical section of an embodiment of a cover piece of a finger touch member of an illuminated switch according to the present invention. DETAILED DESCRIPTION OF THE INVENTION The multicomponent modified rubber material based on EPDM used in the finger touch member according to the present invention is obtained by kneading a raw mixture composed of EPDM, the liquid oligomer of butadiene and requisite additives such as a curing agent and filler, in an adequate proportion, with, if pertinent, addition of another butadiene oligomer, on a kneader and molding the so-kneaded mass in a mold into a cured cover piece for finger touch member of an illuminated switch. On the cured finger touch cover prepared as above, an indication mark is printed with an ink containing, in particular, carbon black. Here, the carbon black content may preferably be restricted to 10 % by weight or below, in order to prevent possible wearing-off of carbon black. A matting agent based on silica may be incorporated in the ink composition for assisting further shading of the illuminated light. Ink compositions based on polyurethane are particularly suitable due to their high affinity to the EPDM-based modified rubber material according to the present invention. According to the present invention, cover pieces for the finger touch members for illuminated switches are provided, by which it is able to attain a higher wear-resistance of indication patterns printed thereon with various inks without necessitating use of expensive silicone rubber. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Below, the present invention will be described in more detail by way of Examples. Example 1 To 100 parts by weight of an ethylene-propylene rubber (EPT-4045, a product of EPDM of Mitsui Petrochemical Industries, Ltd.), there were added 20 parts by weight of an oligomerized butadiene (R45-HT, a product of Idemitsu Petrochemical Co., Ltd) and 35 parts by weight of a commercial filler product (Nipseal® LP, made by Nippon Silika Industrial Co., Ltd.) together with each requisite amount of adjuvants including coupling agent and strengthening agent, and the resulting mixture was kneaded on an open roller kneader to prepare a premix, which was molded in a heated mold into a cover piece of a finger touch member for an illuminated switch. Test pieces were prepared by printing on the so molded finger touch cover a pattern with either one inks based on polyester, polyurethane, polyvinyl chloride and fluororesin. On these test pieces, a rubbing peel-off test for the printing layer was carried out by rubbing the printed patern with the nail of a human finger. As a blank test, a finger touch cover molded with a rubber premix of corresponding composition but without the butadiene component was employed. In addition, a comparative test piece was prepared also in the same manner with the exception that the elastomer components of the premix according to the present invention were replaced by a silicone rubber (SE1187U, a product of Toray Industries, Inc.) The printing layer on the test piece for the blank test was peeled off from the interface between it and the substrate test piece when rubbed intensely with a finger nail. The printing layer on the comparative testpiece was peeled off from the interface even by rubbing with the finger. The experimental result of a checkerboard pattern cross-cutting peel off test for the silicone rubber test piece with either one of the inks was found to be 80/100 in proportion of the number of retained squares per 100 squares. All the test pieces according to the present invention revealed a result of the nail rubbing peel off test in which the printing layer was found to be so firmly bound to the substrate cover piece that the printing layer persisted until the internal cover piece was broken up upon scratching out with excessively intense force. The checkerboard pattern cross-cutting peel test for all the test pieces also resulted in a value of 100/100. Thus, it was confirmed that the multicomponent rubber material according to the present invetion has a superior ability of bonding the printing layer of various inks firmly thereto. As an additional experiment, similar test pieces were prepared using a rubber premix having a composition corresponding to that of the first-said rubber premix according to the present invention with an exception that another kind of oligomerized butadiene rubber (JSR ®) BR-01 was added in an amount of 5 parts by weight. The test results for these test pieces showed that the resiliency of the rubber material became higher and the bonding of the printing layer to the substrate was further increased. Thus, a multicomponent rubber which is more suitable for the finger touch cover was obtained. Example 2 An illuminated switch was prepared with a finger touch member having a cover piece as shown in the appended Drawing by the numeral (1) which was prepared by applying onto the cover piece (1) produced as in Example 1 a printing layer (2) with an ink of contemplated color based on polyester or polyurethane and covering then the entire surfase of the cover piece (1) with a light-blocking coating layer (3), followed by irradiating a beam of a laser onto the top face of the cover piece to cut out the coating layer (3) in a contemplated pattern (4) for visual display upon illumination from inside. The ink contained a heat resistance promoting agent for preventing possible deterioration of the printing layer by the irradiation by the laser beam. The carbon black content of the light-blocking layer (3) was restricted to at highest 10 %, based on the weight of the base polymer thereof, in order to reduce wear-off of carbon black. The lightblocking layer (3) contained also a matting agent based on silica. According to the present invention, it is now made possible to provide finger touch covers for illuminated switches superior in the wear resistance and in the oil-resistance, since a higher bonding performance between the finger touch cover and the printing layer applied thereto can be attained as compared with known prior art products. Especially, by choosing the printing ink, a combination of highermost bonding performance to the substrate finger touch cover with a highermost oil-resistance can be attained. In addition, it is now made possible by the multicomponent rubber material used in the finger touch covers according to the present invention to eliminate the existing disadvantage of dust staining on the finger touch cover during the preparation process through the printing, coating and drying, by adhering the dust floating in the air due to facilitated static charge when using a silicone rubber for the finger touch cover as in the conventional process, whereby an increase in the productivity is achieved by the increase in the production yield. Another advantage of the present invention exists in the reduction of the production cost due to the exclusion of expensive silicone rubber. By the decrease of the amount of worn-off carbon black, undesirable staining of the finger becomes excluded. When a coating layer based on polyurethane is employed, a higher mechanical strength of the coating layer which is as high as 10 fold of that based on silicone can be realized, whereby illuminated switches having high reliability are realized.

Claims: A finger touch member of an illuminated switch prepared by a process comprising printing or coating of a cover piece (1) made of a multicomponent rubber material which comprises, in the uncured condition, a composition composed of, as essential components, 90 - 70 % by weight of EPDM (ethylene-propylene rubber) and 5 - 30% by weight of a liquid oligomerized butadiene rubber, and requisite additives such as filler and curing agent, with an ink of contemplated color, covering the entire top face of the printed or coated cover piece (1) with a light blocking coating layer (3), and irradiating the so covered top face of the cover piece (1) with a laser beam to cut out the coating layer (3) in a contemplated pattern (4). A finger touch member of an illuminated switch prepared by a process comprising printing or coating of a cover piece (1) made of a multicomponent rubber material which comprises, in the uncured condition, a composition composed of, as essential components, 90 - 65 % by weight of EPDM (ethylene-propylene rubber) and 5 - 25 % by weight of a liquid oligomerized butadiene rubber and 5 - 10 % by weight of an oligomerized butadiene, and requisite additives such as filler and curing agent, with an ink of contemplated color, covering the entire top face of the printed or coated cover piece (1) with a light blocking coating layer (3), and irradiating the so covered top face of the cover piece (1) with a laser beam to cut out the coating layer (3) in a contemplated pattern (4). A finger touch member according to claim 1 or 2, wherein the ink is based on a polyester or polyurethane. A finger touch member according to claim 1 or 2 or 3, wherein the coating material for the light blocking coating(3) is based on a polyurethane.

Inventors: FUJIGAKI MASAHISA, HARIKAE KEIKO, KIMURA YASUKO, FUJIGAKI, MASAHISA, HARIKAE, KEIKO, KIMURA, YASUKO
Applicants: FUJI POLYMERTECH CO LTD, FUJI POLYMERTECH CO., LTD
Application year: 1993
Main classification: C08L23
IPC codes: B32B25, H01H13, H01H3, C08L23, H01H9