JPH0845375A - Keypad - Google Patents

Abstract

PURPOSE:To provide a keypad that is excellent in both the light touch of a key and a definite clicking feel by using an elastic material composed chiefly of a styrene thermoplastic elastomer or 1,2-polybutadiene. CONSTITUTION:An elastic material composed chiefly of a styrene thermoplastic elastomer or 1, 2-polybutadiene is molded into a keypad shape having a hollow mesa elastic body 3, and the material is crosslinked by irradiation of radioactive rays to form a keypad. Preferably, the molecular weight of the styrene elastomer is in the range 5,000 to 500,000, and that of the 1,2-polybutadiene in the range 10,000 to 500,000. The radioactive rays used are preferably electron beams.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a keypad having excellent mechanical strength, heat resistance, flexibility and creep characteristics at room temperature and high temperature.

[0002]

2. Description of the Related Art In recent years, vulcanized rubber moldings have been used in various fields such as electric appliances, automobiles, and industrial fields by taking advantage of excellent properties such as rubber elasticity, flexibility, creep resistance and flexibility. Is used for. However, the vulcanized rubber has a drawback that it requires a vulcanization process and has a low production efficiency.

There is a keypad for a push button as the above-mentioned vulcanized rubber molded product, for example, a remote control device for a television, a video, etc.,
It is used as a spring part for push buttons such as operation parts for telephones, facsimiles, input operation keys for calculators, and operation keys for personal computer keyboards. The structure of the push-button keypad molded body includes a hollow mesa-type elastic body 3 as shown in FIG. Further, the keypad molded body 1 has a thin portion having a thickness of about 100 to 150 μm called a skirt portion 2, and a deformation of the skirt portion 2 due to an operation load and a buckling phenomenon generate a feeling of pressing pressure and a feeling of click. .

For measuring the operating load of keypad moldings
Thus, the stress-strain curve as shown in FIG. 1 can be obtained. Figure
P for each peak value in₁Point, P₂Point, P₃point,
P_FourIt is a point. P₁The point is the maximum value of the operating load.
Align the shapes of the keypad moldings to
This maximum load P
₁Mainly reflects the flexibility of the keypad material
Can be understood as. Generally P if the material is flexible₁
The point load becomes smaller and becomes harder, P₁Point load is large
It Further, in FIG. 1, (P₁−P₂) / P₁× 10
0 (%) is a numerical value generally called click rate (A)
However, a good click feeling, that is, a clear push feeling is generated.
For the present, it is preferable that this number be large. further
The switch can be restored with moderate elasticity.
It is said that it is good, but (P₁−P_Four) / P₁× 10
The smaller the click rate (B) indicated by 0 (%),
preferable.

The click feeling is expressed by the numerical values of the click rate (A) and the click rate (B) as described above. However, in order to obtain a clear click feeling, the buckling deformation of the skirt portion is sharp. It needs to happen.

In order to obtain a light pressing force, a softer material is used as the keypad molded body, and
Two methods are conceivable: to make the wall thickness of the thin portion called the skirt portion of the keypad thinner.
It is not realistic to design the skirt part of the skirt part to have an ultra-thin thickness of 100 μm or less from the viewpoint of the material strength of the elastomer material and the precision required for molding.
It is the preferred method to utilize a more flexible material.

Silicone rubber, natural rubber, synthetic rubber, etc. are mainly used as the material of the keypad for the push button, but conventionally, the most widely used silicone is one of the vulcanized rubbers. It is rubber. The silicone rubber has the advantages of being excellent in dimensional stability and heat resistance and being inexpensive, but extrusion and injection molding cannot be performed, and the keypad for push buttons is manufactured by heat curing by press molding. Therefore, the time required for molding is long and there is a problem in productivity.

On the other hand, it is possible to perform thermoforming such as extrusion molding and injection molding at a high temperature like a general resin and does not require a vulcanization step, so that it is excellent in productivity, energy saving and recyclability, and rubber at room temperature. Thermoplastic elastomers exhibiting good physical properties have been attracting attention as materials, but in general, molded products obtained by molding thermoplastic elastomers have flexibility, creep resistance, and high-temperature mechanical properties compared to vulcanized rubber molded products. It had drawbacks such as poor characteristics.

The thermoplastic elastomer is promising as a material for the keypad for extrusion because it can be subjected to thermoforming such as extrusion molding and injection molding as described above and has excellent productivity without requiring a vulcanization step. In recent years, polyester-based thermoplastic elastomers and the like have been used as a substitute for silicone rubber, and are used as remote control devices for televisions and video devices, telephones, and keypads for extruding operation portions of facsimiles. However, the thermoplastic polyester-based elastomer has a limit of flexibility, and the JIS-A hardness is 75 to 8
About 0 is the most flexible material on the market.

Accordingly, among push buttons of a remote controller, a telephone, etc., a relatively light touch is required, and an application requiring a lighter touch, that is, a smaller operation load, such as an input operation key for a calculator and an operation key of a keyboard of a personal computer. However, it is not appropriate to use a conventional polyester-based thermoplastic elastomer because the material has a problem in flexibility. For example, JP-A-4-351813 discloses a method for producing a keypad having excellent durability by electron beam crosslinking in a keypad molded product of a resin composition comprising a polyester thermoplastic elastomer and a polyfunctional monomer. However, it was difficult to realize the same good click feeling as that of the vulcanized rubber due to the lack of flexibility of the material.

Further, a thermoplastic elastomer which merely satisfies the condition of being flexible cannot achieve a good click feeling as a keypad. For example, JP-A-4-83619 and JP-A-64-393.
No. 0 discloses a method for producing a keypad for a push button by molding a styrene-based thermoplastic elastomer, but all of them are inferior in click feeling to a keypad using silicone rubber. There was a problem.

Up to now, the thermoplastic elastomer used for the keypad has a light key touch feeling (small operating load maximum value P ₁ ) and a good click rate for expressing a clear click feeling. There was no excellent material for both, and there was a strong demand for a material that simultaneously satisfies these conditions.

[0013]

SUMMARY OF THE INVENTION In view of the above, an object of the present invention is to provide a keypad excellent in both a light key touch feeling and a clear click feeling.

[0014]

SUMMARY OF THE INVENTION According to the present invention, a key in which an elastic material containing a styrene thermoplastic elastomer as a main component is molded into a keypad having a hollow mesa type elastic body, irradiated with radiation and crosslinked. It is a pad.

The styrene thermoplastic elastomer is
A polymer consisting of a hard segment responsible for physical crosslinking and a soft segment expressing entropy elasticity, such as polystyrene as the hard segment, poebutadiene as the soft segment, polyisoprene, a block made of a hydrogenated product thereof or a copolymer thereof or the like. It is a copolymer.

Generally, as the soft segment, one using polybutadiene is called SBS, one using polyisoprene is called SIS, and one using hydrogenated product is called SEBS. These polymers are commercially available from various manufacturers. As the SBS, for example, JS manufactured by Japan Synthetic Rubber Co., Ltd.
R-TR, etc., and various composition grades are available.
For example, TR2825 has a styrene / soft segment ratio of 23/77. As the SIS, for example,
JIS-SIS manufactured by Japan Synthetic Rubber Co., Ltd. and the like are listed, and there are grades of various compositions. For example, SIS5000 has a styrene / soft segment ratio of 15/85 and SIS500.
No. 2 has a styrene / soft segment ratio of 22/78. Examples of SEBS include Sumitomo TPE-SB manufactured by Sumitomo Chemical Co., Ltd., Lavalon manufactured by Mitsubishi Petrochemical Co., Ltd., and grades of various compositions such as SB-2610.

The styrene thermoplastic elastomer is
At room temperature, it is lower than the glass transition temperature of polystyrene, so the frozen phase of polystyrene becomes a cross-linking part and a good rubber develops.At high temperatures, it is higher than the glass transition temperature of polystyrene, so polystyrene melts and extrusion molding and injection molding are possible. It will be possible.

The molecular weight of the styrene thermoplastic elastomer is preferably in the range of 5,000 to 500,000. When the molecular weight is less than 5,000, it is difficult to maintain the shape of the molded product, and when the molecular weight exceeds 500000, the fluidity is lowered and molding becomes difficult, which is not preferable.

The elastic material may be preliminarily blended with a crosslinking aid for promoting the crosslinking reaction. For example, triallyl cyanate, triallyl isocyanurate, trimethylol propane methacrylate, trimethylol ethane methacrylate, and triethyl ethane methacrylate. Examples thereof include polyfunctional monomers such as methylolpropane triacrylate, trimethylolethane triacrylate, and tetramethylolmethane tetraacrylate.

The type and addition amount of the above-mentioned cross-linking auxiliary agent are appropriately selected and adjusted by the irradiation amount, and the addition amount is 0.1% based on 100 parts by weight of the styrene-based thermoplastic elastomer.
1 to 10 parts by weight is preferable. If the amount is less than 0.1 parts by weight, the effect of the crosslinking aid is not observed, and if it exceeds 10 parts by weight, the crosslinking aid bleeds, which is not preferable.

In the elastic material, various rubber components can be used in combination with the styrene-based thermoplastic elastomer within a range in which it can be melt-molded for the purpose of improving various physical properties, and examples thereof include silicone rubber, nitrile rubber, acrylic rubber, and fluorine. Examples thereof include rubber, ethylene-propylene-diene terpolymer rubber, styrene-butadiene rubber, butyl rubber, isoprene rubber, chloroprene rubber, butadiene rubber, epichlorohydrin rubber, polysulfide rubber and natural rubber.

The amount of the rubber component added is preferably 20 parts by weight or more and 75 parts by weight or less based on 100 parts by weight of the styrene-based thermoplastic elastomer. If it is less than 20 parts by weight, the effect of the rubber component is not observed, and if it exceeds 75 parts by weight, molding is difficult, which is not preferable.

The keypad of the present invention can be obtained by molding the above elastic material into a keypad having a hollow mesa-type elastic body and then irradiating with radiation.

The keypad may be formed by press-molding, injection-molding or the like after melt-kneading the styrene-based thermoplastic elastomer, but the thermoplastic elastomer is previously molded into a sheet by extrusion molding or the like. Then, it may be molded by vacuum molding or compression molding, and in the case of injection molding or extrusion molding, it may be prepared by blending by dry blending without melt-kneading, and it is necessary to prepare the final product. A two-color molding method or the like may be adopted accordingly.

Examples of the radiation include gamma rays,
An electron beam and the like can be mentioned, but it is preferable to use an electron beam. The irradiation dose of the electron beam varies depending on the shape of the molded product, but is preferably 0.1 to 50 Mrad. Irradiation amount is 0.1 Mr
If it is less than ad, the degree of cross-linking of the styrene-based thermoplastic elastomer does not increase, so the mechanical properties such as creep resistance are insufficient. It is inferior and is not preferable.

Although it is not clear why the irradiation of radiation causes a light pressing feeling and a good clicking sensation, the irradiation causes the soft segment of the styrenic thermoplastic elastomer to be crosslinked and the hard segment The freezing of the hard segment is mitigated by the cross-linking of the portions, so that a light pressing feeling and a good clicking feeling are achieved.

The present invention 2 is the one in which the styrene-based thermoplastic elastomer of the present invention 1 is replaced with 1,2-polybutadiene. The molecular weight of the above 1,2-polybutadiene is preferably in the range of 10,000 to 500,000. When the molecular weight is less than 10,000, it is difficult to maintain the shape when formed into a molded product, and when the molecular weight exceeds 500,000, fluidity is lowered and molding becomes difficult, which is not preferable.

[0028]

In the present invention, after molding the above elastic material, the molded article is irradiated with radiation to crosslink a part of the molecular chains of the material, thereby imparting durability more than that of crosslinked rubber such as silicone rubber. The keystroke durability of the keypad can be significantly improved.

[0029]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Example 1 Styrenic thermoplastic elastomer (T manufactured by Japan Synthetic Rubber Co., Ltd.
R2825) pelletized resin sample dried (70 ° C
X 3 hours), and then injection molding to JISK 630
Based on No. 1, a dumbbell No. 3 and a keypad molded product as shown in FIG. 3 were prepared. The injection molding conditions were as follows. Injection molding machine: Toshiba Machine Co., Ltd. EPN-IS30 (30
t) Molding temperature: Cylinder / Nozzle / Mold = 180 ° C./16
5 ℃ / 20 ℃

5 Mra on molded No. 3 dumbbell sample
The electron beam irradiation of d was performed, and the permanent elongation was evaluated. The results are shown in Table 1. On the other hand, a keypad molded product is similarly irradiated with an electron beam of 5 Mrad, and a micro load measuring device (MO
(DEL 1305D, manufactured by Aiko Engineering)
Was used to measure the operating load. The results are shown in Table 2. In addition, as an evaluation of keystroke durability, the above load measuring machine was used in a constant temperature bath of 60 ° C., and a push button portion of a keypad molded article was acted with a force of 1 kgf per stroke in a stroke of 3 mm, and an action speed was 20 rpm ( The pressing test was stopped for 1 second), and the number of durability tests was 20,000. The retention rate of P ₁ at that time is shown in Table 2.

Example 2 The same molding and evaluation were performed under the same conditions as in Example 1 except that the electron beam was changed to 20 Mrad. The results are shown in Table 1.
And shown in Table 2.

Example 3 Same as Example 1 except that 3 parts by weight of triallyl isocyanurate was added as a cross-linking aid to 100 parts by weight of styrene-based thermoplastic elastomer and the electron beam irradiation amount was set to 0.5 Mrad. The same molding and evaluation were performed under the conditions of. The results are shown in Tables 1 and 2.

Example 4 The same molding was carried out under the same conditions as in Example 1 except that SIS5002 manufactured by Japan Synthetic Rubber Co., Ltd. was used as the styrene-based thermoplastic elastomer and the electron beam irradiation amount was 1 Mrad.
An evaluation was made. The results are shown in Tables 1 and 2.

Example 5 SIS 5000 manufactured by Japan Synthetic Rubber Co., Ltd. was used as the styrene thermoplastic elastomer, and 5 parts by weight of triallyl isocyanurate was added as a crosslinking aid to 100 parts by weight of the styrene thermoplastic elastomer. The same molding and evaluation were performed under the same conditions as in Example 4. The results are shown in Tables 1 and 2.

Example 6 The same molding and evaluation were carried out under the same conditions as in Example 4 except that SB-2610 manufactured by Sumitomo Chemical Co., Ltd. was used as the styrene thermoplastic elastomer. The results are shown in Tables 1 and 2.

Comparative Example 1 The same molding and evaluation were carried out under the same conditions as in Example 1 except that the electron beam irradiation amount was 0.01 Mrad. The results are shown in Tables 1 and 2.

Comparative Example 2 Example 1 except that the electron beam irradiation amount was set to 60 Mrad.
The same molding and evaluation were carried out under the same conditions as above, but the molded keypad was insufficient in strength due to disassembly and did not function as a button. The evaluation results are shown in Table 1 and Table 2.
It was shown to.

Comparative Example 3 Hytrel 4047 (manufactured by DuPont Toray) was used as the ester thermoplastic elastomer instead of the styrene thermoplastic elastomer, and the electron beam irradiation dose was 10 Mrad.
The same molding (molding temperature: cylinder / nozzle / die = 240 ° C./2) under the same conditions as in Example 3 except that
(20 ° C / 20 ° C) was evaluated. The results are shown in Tables 1 and 2.

Example 7 Under the same conditions as in Example 1 except that 1,2-polybutadiene (JSR805 manufactured by Japan Synthetic Rubber Co., Ltd.) was used in place of the styrene thermoplastic elastomer, the same molding (molding temperature: cylinder) was carried out. / Nozzle / Mold = 125 ° C / 125
(° C / 20 ° C) was evaluated. The results are shown in Table 1 and Table 2.
It was shown to.

Example 8 The same molding and evaluation were carried out under the same conditions as in Example 7 except that the electron beam was changed to 20 Mrad. The results are shown in Table 1.
And shown in Table 2.

Example 9 The same as Example 7 except that 5 parts by weight of triallyl isocyanurate was added as a crosslinking aid to 100 parts by weight of 1,2-polybutadiene and the electron beam irradiation amount was 0.3 Mrad. The same molding and evaluation were performed under the conditions of. The results are shown in Tables 1 and 2.

Comparative Example 4 The same molding and evaluation were carried out under the same conditions as in Example 7 except that the electron beam irradiation amount was 0.05 Mrad. The results are shown in Tables 1 and 2.

Comparative Example 5 Example 7 except that the electron beam irradiation amount was set to 60 Mrad.
The same molding and evaluation were performed under the same conditions as, but the molded keypad lacked flexibility and did not function as a button. The evaluation results are shown in Tables 1 and 2.

In Table 2, the click rate (A) is (P ₁ -P
₂ ) / P ₁ × 100 (%), and click rate (B)
Represents (P ₁ -P ₄ ) / P ₁ × 100 (%).

[0046]

[Table 1]

[0047]

[Table 2]

[0048]

INDUSTRIAL APPLICABILITY According to the present invention, by irradiating a molded article molded from a styrene-based thermoplastic elastomer or an elastic material containing 1,2-polybutadiene as a main component with radiation, flexibility and creep resistance can be obtained. A keypad having excellent mechanical properties can be easily obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a keypad molded body including a hollow mesa-type elastic body.

FIG. 2 is a graph of the operating load measurement (stress-strain curve) of the keypad. The vertical axis represents the operating load, and the horizontal axis represents the stroke.

FIG. 3 is a diagram showing an evaluation keypad.

[Explanation of symbols]

 1 Keypad peripheral part 2 Skirt part 3 Key top

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Claims (2)

[Claims] 1. A keypad characterized in that an elastic material containing a styrene-based thermoplastic elastomer as a main component is molded into a keypad having a hollow mesa-type elastic body, irradiated with radiation, and crosslinked. 2. A keypad, wherein an elastic material containing 1,2-polybutadiene as a main component is molded into a keypad having a hollow mesa-type elastic body, irradiated with radiation, and crosslinked.