JPS5936863B2 - Manufacturing method of rubber molded body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a new and improved method of manufacturing a rubber molded article.

Conventionally, in order to manufacture rubber molded bodies such as rubber switches for keyboards or switch covers that are incorporated into various electronic devices, compression molding using molds, injection molding, injection molding, etc. have been used. In either case, the unvulcanized rubber is exposed to heat for a long time during the molding cycle, so if the molded product to be manufactured is particularly thin, the so-called scorching phenomenon is likely to occur. Therefore, it is difficult to manufacture relatively thin (and large-area) molded products or to perform multi-cavity molding, and the use of unvulcanized rubber dough with low plasticity as the rubber material. In this case, there are disadvantages and drawbacks such as difficulty in handling and difficulty in making the thickness of the molded product uniform.

On the other hand, in the case where rubber molded bodies are required to have high functional reliability, such as parts incorporated into various electronic devices as mentioned above, it is desirable to have high inspection accuracy, and in recent years, it has become necessary to As standards tend to become higher and higher,
There is a problem in that the cost required for the above-mentioned inspection process and finishing process is becoming the largest proportion of the cost of such a rubber molded body.

The present invention provides a new and improved method for manufacturing a rubber molded article that can solve the disadvantages, shortcomings, and problems of the conventional methods described above, and this invention provides a method for manufacturing a rubber molded article, which is capable of solving the above-mentioned disadvantages, shortcomings, and problems of the conventional method. and a mold half having a substantially smooth molding surface, two sheets, at least one of which is made of a thermoplastic material. After inserting a composite sheet with at least one unvulcanized rubber layer sandwiched therebetween, the gap between the peripheral protrusion of one mold half and the smooth molding surface of the other mold half. The method is characterized in that both halves of the molds are pressed to such an extent that the two sheets remain but substantially no unvulcanized rubber layer remains.

In the method of the present invention described above, by sandwiching the unvulcanized rubber layer between two sheets, it is possible to easily and quickly charge the unvulcanized rubber into the mold, and the unvulcanized rubber can be placed in a mold under high temperature. Since the exposure is mostly only during the time when it is pressed against the molding surface and can be kept to the minimum necessary, it is possible to reliably suppress the occurrence of the scorching phenomenon in the rubber molded product, and therefore, according to the invention theory. For example, it is extremely easy to manufacture a rubber molded body that is relatively thin and has a large area.

Furthermore, according to the present invention, the desired rubber molded body and flash can be obtained in a state where they are sandwiched between two sheets, so when the rubber molded body is relatively small piece-like or thin, It has excellent effects such as no separation from the flash, no damage during molding, vulcanization, and mold release, high yield (and extremely easy handling in subsequent product inspections, etc.).

Furthermore, according to the present invention, problems such as mold release treatment during molding and vulcanization of rubber, staining of the mold surface, and cleaning of the mold surface due to the presence of the two sheets ("Applied Rubber Processing Technology Lecture 12")
Another advantage is that there is no need to take into account all the considerations for "Middle Volume, Written by Hideo Kaneko," published by Taiseisha Co., Ltd., 2nd edition, June 20, 1971, pages 158-159.

The method of the present invention will be described in detail below according to its steps. In the method of the present invention, in the first step, one or more unvulcanized rubber layers are provided between two sheets.

There are no particular limitations on the method of forming the unvulcanized rubber layer between these two sheets, or it may be possible, for example, to form an unvulcanized rubber layer on one sheet by a topping method, which is relatively easy to control the thickness of the layer. After providing the rubber layer, another sheet is laminated on the rubber layer.

Regarding the above two sheets used in the present invention,
At least one of them shall be made of a thermoplastic resin material, and this material shall be selected from materials that are difficult to melt, soften, or nearly melt and adhere to the surface of the mold when subjected to pressure heating within the mold. However, the material is not particularly limited.

Further, at least the surface of the sheet that comes into contact with the unvulcanized rubber layer may have a glossy surface, a matte surface, a textured surface, a mesh surface, or any other embossed surface. If necessary, it is possible to perform partial mold release treatment or primer treatment for integration, and the sheet that needs to be integrated with the rubber molded product after the molding of the rubber molded product has a letter in advance. , symbols, numbers, and other symbols may be added.

Furthermore, the above-mentioned sheets include not only single sheets, but also composite laminated sheets, painted sheets, metallized sheets, etc., as well as various forms of thermoplastic resin sheets such as woven fabrics, non-woven fabrics, and those reinforced with paper. can do.

On the other hand, as sheets other than sheets made of thermoplastic resin materials, woven fabrics or non-woven fabrics made of crow cloth, natural fibers, synthetic fibers, etc., or various sheets reinforced with these can be used. Similar to the sheet made of the thermoplastic resin material described above, various treatments can be applied to the surface in contact with the unvulcanized rubber layer.

In addition, regarding rubber materials applicable to the method of the present invention,
Any of them may be used, such as insulating rubber, conductive rubber, porous comb, foam rubber, conductive foam rubber, pressure-sensitive conductive rubber, etc.
Although not particularly limited, in addition to the vulcanizing agent, known fillers and additives may be added as necessary, such as extenders, reinforcing fillers, pigments, conductivity imparting agents, stabilizers, blowing agents, internal release agents, etc. One or more types of molding agent etc. can be included, and those having a rubber hardness (JI, S' K6301) of 80 or less after vulcanization are suitable.

As mentioned above, the composite sheet-like body in which the unvulcanized rubber layer is sandwiched between two sheets is then introduced into a compression mold, and the unvulcanized rubber is then heated under pressure in the mold. The layer is vulcanized.

The mold used in the present invention has a cavity corresponding to a desired molded product, a mold half having a knife-like protrusion around the cavity, and a substantially smooth molding surface. It consists of a mold half.

Strictly speaking, the cavity in the former half of the mold is the shape of the rubber molded product to be manufactured plus the thickness equivalent to the thickness of the sheet made of thermoplastic resin material. If necessary, an overflow groove or depression is provided on the outside of the protrusion.

Note that this overflow groove or recess may be provided in the latter half of the mold.

Furthermore, the mold used in the present invention can be provided with a guide bin around the cavity or at the edge of the mold for positioning the composite sheet. A guide hole is provided that takes into account the coefficient of thermal expansion.

The compression molding mold described above is heated to a temperature sufficient to vulcanize the unvulcanized rubber layer, and between the two mold halves,
A sheet of at least the thermoplastic material described above is placed in contact with the mold half having the cavity and pressed.

At this time, both mold halves are made of unvulcanized rubber, although two sheets remain between the peripheral protrusion of one mold half and the smooth molding surface of the other mold half. The pressure is applied to such an extent that no layer remains, in other words, the peripheral protrusions are pressed to the extent that they reach the molding surface of the other half of the mold through the two sheets.

Note that the protrusions around the cavity described above are not limited to knife-like ones, but may have a structure that clearly separates the desired rubber molded body from the flash portion when the mold is pressed. Of course, it is a good thing to have.

After the unvulcanized rubber layer is completely vulcanized in the mold under pressure heating, the composite sheet is also removed from the mold.

Between the two sheets of the composite sheet-like body taken out in this way, the desired rubber molded body is placed in the other part, that is, the flash part is a groove-like hoop line formed corresponding to the above-mentioned peripheral protrusion. It is obtained in a clearly demarcated state.

Therefore, when the flash portion and one end of one sheet are pinched and peeled off from the other sheet, the entire flash portion can be peeled off at once while leaving the desired rubber molded body on the other sheet.

Further, the desired rubber molded body is peeled off from the other sheet as necessary.

In addition, when the rubber molded article to be manufactured is thin or very small in the form of small pieces, in the method of the present invention, the rubber molded article can be handled while remaining on one sheet. Therefore, handling of the product, such as subsequent product inspection, can be easily carried out.

Further, the particularly advantageous shape of the rubber molded article obtained by the method of the present invention is a small piece or thin article, and it is particularly suitable for rubber contacts and rubber covers for keyboards in desktop electronic calculators, telephones, computers, electronic musical instruments, etc., as well as radios, It is useful for operation switch parts, keyboard parts, and panel control parts for televisions, measuring instruments, microwave ovens, electronic ovens, cheap record cords, cassette cords, video cords, electronic watches, etc.

Claims (1)

[Claims] 1. At least one of the mold halves has a cavity corresponding to the desired molded product and a protrusion around the cavity, and a mold half having a substantially smooth molding surface. After inserting a composite sheet formed by sandwiching at least one unvulcanized rubber layer between two sheets of thermoplastic material, the peripheral protrusion of one half of the mold and the other mold are inserted. Production of a rubber molded article characterized in that both mold halves are pressed to such an extent that the two sheets remain between the two halves and the smooth molded surface, but substantially no unvulcanized rubber layer remains. Method.