JP2003281969A - Tact switch and adhesive tape therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an adhesive tape for a tact switch which meets the thinned tact switch and in which a malfunction does not occur. <P>SOLUTION: The adhesive tape for the tact switch, where an adhesive layer is provided on a supporting substrate, is characterized in that the supporting substrate is formed by making a fluorine resin a sheet by casting process. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an adhesive tape applied to a tact switch operated by a click action. Furthermore, the present invention relates to a tact switch using the adhesive tape.

[0002]

2. Description of the Related Art As a tact switch used for a keyboard switch or the like, as shown in FIG. 1, a fixed contact 2 is provided on the bottom surface of a housing 1, a movable contact material 3 is provided on the fixed contact 2, and a housing opening is provided. It is known that a frame 6 is sealed with an adhesive tape 5, a frame 6 is attached to the housing 1, and a stem 7 is slidably fitted in the frame 6.

FIG. 2 shows the relationship between the load of the stem and the amount of movement in the tact switch. When a certain load f ₁ (operating force) is reached, the movable contact member 3 reacts and the load is smaller than the load up to that point. The movement progresses, and the stem is pushed down by a certain load f ₂ (restoring force), and thereafter, the stem does not substantially move even if the load is increased.

In the load-movement amount diagram of the tact switch, the load depends on the deformation rigidity of the member which resists the movement of the stem, mainly on the bending rigidity. Maximum load f ₁
When the (operating force) is large, the feel is hard-touch, and when the maximum load is small, the feel is soft-touch.

In the tact switch, it is necessary to set the shape of the movable contact 3 so as to cause the reversal operation. Usually, the shape of the movable contact member 3 is a dome shape, and the lower end of the dome shape is instructed to locally contact the electrodes 4 and 4. Therefore, the space between the fixed contact 2 and the movable contact 3 communicates with the space outside the movable contact 3.

A reflow soldering method is used to mount the tact switch on the circuit board. The housing opening is sealed with an adhesive tape or the like in order to prevent the flux from entering between the fixed contact and the movable contact in the process of applying the flux in this soldering to ensure good contact contact property. Is essential.

The sealing of the housing opening with an adhesive tape or the like also prevents dust from entering the gap between the housing 1 and the frame 6 and causing contact failure between the fixed contact 2 and the movable contact 3 due to the dust. There is.

The adhesive tape must be adhered to the upper end surface of the opening of the housing 1 and must flexibly follow the vertical movement of the stem 7. Therefore, the base material of the adhesive tape is required to have flexibility, and a fluororesin sheet is generally used. In particular, polytetrafluoroethylene is used as the fluororesin.

Further, the tact switch has been made smaller and thinner, and accordingly, the adhesive tape is also required to be thinner. However, when the device is made thinner, the parts become smaller and further accuracy is required. In this case,
If the thickness accuracy of the adhesive tape is poor, problems occur such as a gap being formed when the housing 1 and the frame 6 are assembled, or the stem 7 is tilted because it cannot be made parallel.

The pressure-sensitive adhesive tape comprises a supporting base material and a pressure-sensitive adhesive layer. Even when the pressure-sensitive adhesive layer is made thin, the thickness is usually about 5 to 50 μm. In order to exert the necessary adhesive strength, the pressure-sensitive adhesive layer cannot be made thinner than this, and the thickness reduction of the pressure-sensitive adhesive layer has already reached its limit. On the other hand, the fluororesin sheet used as a supporting base material has heretofore been obtained by cutting a molded product. However, the tolerance of the fluororesin sheet obtained by this method is ± 5
It is 10 μm, and accuracy is insufficient when the thickness is reduced to 22 μm or less. With this method, the thickness of the fluororesin sheet cannot be substantially cut to 15 μm or less, and there is a limit to thinning.

[0011]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an adhesive tape for a tact switch, which can cope with a reduction in the thickness of the tact switch and does not cause any trouble. Furthermore, it aims at providing the tact switch using the said adhesive tape.

[0012]

As a result of intensive studies to solve the above problems, the present inventors have found that the above-mentioned object can be achieved by the adhesive tape shown below, and have completed the present invention. .

That is, the present invention provides a pressure-sensitive adhesive tape for a tact switch in which a pressure-sensitive adhesive layer is provided on a supporting base material, wherein the supporting base material is a fluororesin sheet formed by a casting method. The present invention relates to a characteristic tact switch adhesive tape.

Fluorine resin is used as a supporting base material for the adhesive tape for tact switch because it has flexibility and heat resistance against heat of reflow soldering. In addition, the sheet made of fluororesin by the casting method is suitable for thinning of the tactile switch, and even if the adhesive tape is thinned, it is possible to obtain the adhesive tape for the tactile switch with good thickness accuracy and no trouble. .

The fluororesin used for the supporting base material of the adhesive tape for tact switch is preferably one containing polytetrafluoroethylene.

In the pressure-sensitive adhesive tape for a tact switch, it is preferable that the support base material has an average thickness of 22 μm or less and a tolerance of ± 3 μm or less. The supporting base material of the fluororesin sheet obtained by the casting method is
Corresponding to thinner thickness, the average thickness is 22 μm or less,
Furthermore, even if it is 16 μm or less, the tolerance is ± 3 μm
After that, it is possible to obtain the one having an accuracy of ± 2 μm or less, and no trouble occurs. In addition, the thickness average value is JIS
It is a value obtained by a 1/1000 dial gauge according to C2107, and the tolerance is a value obtained by ± 3σ from the standard deviation σ of the thickness measurement value.

Further, according to the present invention, a fixed contact is provided on the inner bottom surface of the housing, a movable contact material is provided on the fixed contact, the housing opening is sealed with an adhesive tape, and a stem is provided on the adhesive tape. In the tact switch that presses the adhesive tape together with the movable contact material by the operation of the stem to bring the movable contact into contact with the fixed contact and releases the movable contact by releasing the pressure, the adhesive tape is used as the adhesive for the tact switch. The present invention relates to a tact switch characterized by using a tape.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION The pressure-sensitive adhesive tape for a tact switch according to the present invention has a pressure-sensitive adhesive layer provided on a supporting substrate. The supporting base material is a fluororesin formed into a sheet by a casting method.

As the fluororesin, polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA),
Tetrafluoroethylene-hexafluoropropylene copolymer (FEP), ethylene-tetrafluoroethylene copolymer (ETFE), polyvinylidene fluoride (PVD)
F) and the like. Among these, polytetrafluoroethylene (PTFE) is preferable. As the fluororesin, a dispersion obtained by emulsion polymerization is used.

The method of forming the fluororesin into a sheet by the casting method includes, for example, a method of applying a dispersion of the fluororesin on a heat resistant carrier sheet and firing the dispersion at a temperature higher than the melting point of the fluororesin. The fluororesin sheet is obtained by peeling the obtained fired sheet from the heat resistant carrier sheet.

As the heat resistant carrier sheet, a material that can withstand the firing temperature of the fluororesin dispersion can be used without particular limitation. For example, a polyimide film, a polyether ether ketone film, a polyether sulfone film or a metal foil is used. In addition, the heat-resistant carrier sheet may be coated with a release agent such as a silicone-based release agent in order to remove the baked sheet more smoothly.

Examples of the dispersion medium used for the dispersion of the fluororesin include water. From the viewpoint of workability, the solid content concentration of the fluororesin dispersion is 20 to 80% by weight, preferably 40 to 60% by weight. Dispersion can be applied by dipping, spraying,
It can be performed by various methods such as a brush coating method.

The firing method is not particularly limited. The firing can be performed in one step by heating at one stage, but first heating at the evaporation temperature of the dispersion medium used for the dispersion of the fluororesin, a part or most of the dispersion medium is removed by evaporation, and then It is preferable to perform multi-step heating in which the melting point of the fluororesin is abnormally heated and then baked.

The thickness of the supporting substrate can be produced within a range of 100 μm or less by repeating coating and baking. In order to cope with the reduction in thickness, as described above, the average thickness value is preferably 22 μm or less. If the thickness of the supporting base material is too thin, the strength of the supporting base material will be insufficient, and it may be difficult to apply the adhesive, cut it for incorporation into the tact switch, and punch it out. Is preferably 8 μm or more. In order to cope with the reduction in thickness, it is preferable that the average thickness of the supporting base material is 8 to 22 μm. Further, the support base material having an average thickness value of 8 to 22 μm can be produced by a single application of a fluororesin dispersion. Thus, according to the casting method,
Since it is produced by applying a dispersion of a fluororesin on a heat-resistant carrier sheet, a supporting base material having a more accurate thickness than the conventional method of cutting a molded product can be obtained, and the average thickness of the supporting base material is obtained. Even when the value is 22 μm or less, the tolerance is ± 3 μm or less.

The supporting base material of the fluororesin sheet is usually
It is preferable to perform a surface treatment for the purpose of improving the adhesiveness. As the surface treatment, a wet treatment such as alkali etching and a dry treatment such as sputter etching can be used.

In forming the pressure-sensitive adhesive layer provided on the above-mentioned supporting substrate, a pressure-sensitive adhesive that does not cause peeling or misalignment upon use of the pressure-sensitive adhesive tape is preferably used. The pressure-sensitive adhesive is not particularly limited, but since the pressure-sensitive adhesive tape is used in the vicinity of electrical contacts, a silicone-based pressure-sensitive adhesive that causes contact failure is not preferable. Examples of the pressure-sensitive adhesive include rubber-based pressure-sensitive adhesives and acrylic pressure-sensitive adhesives. Among these, an acrylic pressure-sensitive adhesive having good heat resistance is preferable.

The base polymer of the acrylic pressure-sensitive adhesive is a copolymer of alkyl acrylate and a carboxyl group-containing monomer and has a weight average molecular weight of 1
It is preferably 1,000,000 or more. The weight average molecular weight of the copolymer is usually about 1,000,000 to 4,000,000, and preferably 1,000,000 to 2,000,000.

As the acrylic acid alkyl ester which is a component of the above copolymer, the number of carbon atoms of the alkyl group such as butyl acrylate, propyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate and innonyl acrylate is 3 It is preferable to use those of 10 to 10. Examples of the carboxyl group-containing monomer include acrylic acid, methacrylic acid, fumaric acid, maleic acid and itaconic acid. Among these,
Acrylic acid and methacrylic acid are preferable, and acrylic acid is particularly preferable.

The weight ratio of the alkyl acrylate ester to the carboxyl group-containing monomer in the copolymer is 80 to 99.5% by weight for the former and 0.5 to 20 for the latter.
% By weight. Preferably, the former is 88 to 97% by weight,
The latter is 3 to 12% by weight. In addition to the above-mentioned monomers, the base polymer copolymer may be a monomer having a functional group such as a hydroxyl group-containing monomer, an N element-containing monomer, an epoxy group-containing monomer, and further vinyl acetate, styrene, etc. for the purpose of the present invention. It can also be used within a range that does not impair it.

The above copolymer is prepared by, for example, mixing a flask equipped with a stirrer, a thermometer, a condenser and a nitrogen introducing tube with an alkyl acrylate ester, a carboxyl group-containing monomer and an organic solvent (eg toluene). It can be obtained by a method in which the inside of the flask is replaced with nitrogen, and the mixture is heated at a predetermined temperature and then polymerized in the presence of a polymerization initiator (for example, benzoyl peroxide, azobisisobutyronitrile, etc.). The heating temperature and the polymerization time are not particularly limited, but the heating temperature is usually 5
It is preferable that the polymerization time is about 0 to 70 ° C. and the polymerization time is about 5 to 7 hours.

Various tackifiers may be added to the acrylic copolymer. In order to form a pressure-sensitive adhesive layer that has heat resistance and does not shift or peel off during the process or after the process, the acrylic copolymer has two types of high softening point resin and low softening point resin. It is preferable to use a pressure-sensitive adhesive containing the tackifier resin. The pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition containing such a tackifier can form a pressure-sensitive adhesive layer that has a large adhesive force both initially and after heating, and further has a small deviation in holding force.

The softening point of the high softening point resin is 100 to 150 ° C.
The softening point of the low softening point resin is about 60 to 110 ° C. However, the high softening point resin has a softening point higher by 10 ° C. or more than the low softening point resin. The blending amount of the high softening point resin is 8 to 60 parts by weight based on 100 parts by weight (solid content) of the copolymer,
It is preferably 20 to 50 parts by weight. On the other hand, the blending amount of the low softening point resin is 100 parts by weight of the copolymer (solid content).
On the other hand, it is 5 to 40 parts by weight, preferably 15 to 30 parts by weight. Further, the compounding ratio of the high-softening point resin and the low-softening point resin is such that the weight ratio of the low-softening point resin to the high-softening point resin is 1: in order to balance the characteristics of the adhesive force and the holding force at the initial stage and after the heating. It is preferable to mix them in a ratio of 1 to 2.

As the high softening point resin and the low softening point resin, resins conventionally used as tackifying resins can be used without particular limitation. For example terpene resin,
Examples thereof include terpene phenol resin, petroleum resin, coumarone-indene resin, rosin resin, (alkyl) phenol resin, xylene resin, and hydrogenated products thereof. Of these, those having the above softening point are selected and used.

Further, a crosslinking agent can be added to the pressure-sensitive adhesive composition of the present invention. The amount of the crosslinking agent blended is preferably about 0.05 to 5 parts by weight with respect to 100 parts by weight of the copolymer. The type of cross-linking agent is not particularly limited, and those conventionally used for pressure-sensitive adhesives can be used. Specific examples thereof include isocyanate-based crosslinking agents such as hexamethylene diisocyanate, amine-based crosslinking agents such as bisamine,
An epoxy-based cross-linking agent such as ethylene glycol diglycidyl ether can be used. In addition, it is optional to add various additives.

In the method for producing the pressure-sensitive adhesive tape for a tact switch of the present invention, the pressure-sensitive adhesive solution is applied to one surface of the supporting substrate and dried. The drying temperature and time are not particularly limited, but usually about 100 to 180 ° C. and about 2 to 10 minutes. The thickness of the adhesive layer is not particularly limited, but is 5 to 5 in terms of solid content.
It is about 0 μm, and is preferably 8 to 20 μm from the viewpoint of thinning and clicking feeling.

[0036]

EXAMPLES Examples and the like showing the effects of the present invention will be described below, but the present invention is not limited to these examples.

Example 1 (Preparation of supporting substrate) PTFE powder (average particle size 0.25
90 μm) of an aqueous dispersion having a solid content concentration of 60% by weight is applied to the polyimide carrier sheet by dip coating.
Water was removed by heating at a temperature of 2 ° C. for 2 minutes. Then
12 μm thick PTFE by baking at 360 ° C for 2 minutes
A sheet was prepared. This PTFE sheet was used as a supporting substrate by subjecting one side of the PTFE sheet to sputter etching.
When the thickness of the supporting base material was measured with a 1/1000 digital dial gauge, the average value was 12.2 μm, and the tolerance was ±
It was 1.8 μm.

(Preparation of adhesive composition) Stirrer, thermometer,
90 g of butyl acrylate, 1 acrylic acid in a flask (capacity 1 liter) equipped with a condenser and a nitrogen introducing tube.
Mix 0 g and 150 g of toluene and stir 1
The atmosphere was replaced with nitrogen. Next, 0.1 g of benzoyl peroxide was added, and polymerization was carried out at a temperature of 60 ° C. for 6 hours to obtain a copolymer solution of butyl acrylate and acrylic acid. The weight average molecular weight of this copolymer was measured by HPLC (high performance liquid chromatography) to find that it was 1.4 million.

With respect to 100 parts by weight of the above copolymer solution (solid content), a phenolic resin (Sumilite Resin PR-51732, manufactured by Sumitomo Dures Co., Ltd.) having a softening point of 130 ° C. 32
20 parts by weight of a terpene resin (YS-Hara Chemical Co., YS resin PX800) having a softening point of 80 ° C. and 3 parts by weight of hexamethylene diisocyanate (Coronate L, manufactured by Nippon Polyurethane Co.) as a cross-linking agent, and then solidified with toluene. The pressure-sensitive adhesive composition (solution) was obtained by diluting so as to be 14% by weight on a minute basis.

(Preparation of Adhesive Tape) The adhesive composition was applied on the surface-treated surface of the above-mentioned supporting substrate so that the solid content thickness was 15 μm, and the hot air dryer was dried at 130 ° C. for 5 minutes. It was dried and cured to obtain an adhesive tape.

Comparative Example 1 In Example 1, except that a PTFE sheet obtained by cutting a molded and fired product of PTFE molding powder to a thickness of 22 μm and subjecting one side to an alkali etching treatment was used as the supporting substrate. An adhesive tape was produced in the same manner as in Example 1. The thickness of the supporting substrate is 1/1000.
Average value of 2 when measured with a digital dial gauge
It was 2.5 μm and the tolerance was ± 7.1 μm.

The adhesive tapes obtained in Examples and Comparative Examples were adhered to a tact switch having an operating force of 13N and a restoring force of 6N without adhering the adhesive tapes to confirm the sealing property. In the pressure-sensitive adhesive tape of Example 1, floating or displacement of the pressure-sensitive adhesive tape was not seen. In the pressure-sensitive adhesive tape of Comparative Example 1, floating and displacement of the pressure-sensitive adhesive tape were observed.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a general structure of a tact switch.

FIG. 2 is an explanatory diagram showing a load-movement amount diagram of a tact switch.

[Explanation of symbols]

1 housing 2 fixed contacts 3 movable contacts 5 Adhesive tape 6 frames 7 stem

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 4J004 AA05 AA10 AB01 CA05 CC02                       FA05                 4J040 CA001 DF041 JA09 JB09                       LA01 NA19                 5G006 AA02 AB25 AC01 BA01 BA02                       BB03 BC04 DB03 FB39 LG02                       LG07 LG08

Claims (4)

[Claims] 1. A pressure-sensitive adhesive tape for a tact switch in which a pressure-sensitive adhesive layer is provided on a supporting base material, wherein the supporting base material is a fluororesin formed into a sheet by a casting method. Adhesive tape for tact switch. 2. The adhesive tape for a tact switch according to claim 1, wherein the fluororesin contains polytetrafluoroethylene. 3. The pressure-sensitive adhesive tape for a tact switch according to claim 1, wherein the average thickness of the supporting base material is 22 μm or less and the tolerance is ± 3 μm or less. 4. A fixed contact is provided on the inner bottom surface of the housing, a movable contact material is provided on the fixed contact, a housing opening is sealed with an adhesive tape, and a stem is provided on the adhesive tape. In the tact switch that presses the adhesive tape together with the movable contact material to bring the movable contact into contact with the fixed contact by the operation of
A tact switch, wherein the tact switch adhesive tape according to any one of claims 1 to 3 is used as the adhesive tape.