JPS6294901A - pressure sensitive resistor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field to which the Invention Pertains] The present invention relates to a pressure-sensitive resistor made of pressurized conductive rubber that has high mechanical strength and can be molded at relatively low temperatures.

[Prior art and its problems]

It is known that the resistance value of a composite rubber made by mixing and molding conductive metal particles into an elastic polymer and crosslinking changes greatly when pressurized, and such pressurized conductive rubber can be used as a pressure-sensitive resistor. Connector now.

Widely used in switching devices, coordinate input devices, variable resistors, pressure sensors, etc.

For example, when using this pressure sensitive resistor as a connector,
The following characteristics are required.

(1) Figure 6 shows a partial cross-sectional view of a printed circuit board connected via a connector, for example.
In this state, a pressurized conductive rubber sheet 2 as a connector is sandwiched and tightened between steel foils 1.1a on two printed circuit boards. At this time, the pressurized conductive rubber sheet 2 must have anisotropy such that it shows conduction only in the thickness direction, and the dimension l must be 0.51!1 or less and a withstand voltage of 400V or more. (2) Show a low resistance value with the lowest possible pressing force. For example, Fig. 7 is a pressure-resistance diagram of pressurized conductive rubber, showing two types of materials, A and B, in which the solid line is pressurized and the two-dot line is depressurized. It can be seen that A has smaller hysteresis and better press resistance characteristics than B. Preferably, the resistance value is 100-α or less at a pressing force of 1 kg or less.

(3) Even if pressurization is continued for a long time, the above (1) and (2)
The pressure-sensitive resistor must have low permanent deformation strain due to compression, that is, compression creep, so that its characteristics do not change.

(4) If the lid deforms due to pressure is small, the contact resistance with the connected conductor becomes worse, so the pressure-sensitive resistor must have a lid that deforms sufficiently even with a low pressing force. The relationship between pressing force and strain is closely related to rubber hardness, and it is preferable that the rubber hardness is 70 or less as defined by the Japanese Industrial Standards.

On the other hand, a rubber resistor whose resistance value changes when pressurized can be used by integrally molding it with polyethylene T#A or plastic parts, for example.
It is necessary that it can be molded in 3 to 20 minutes at a low temperature of 8 degrees, and that it also has the properties (1) to (4) above.

On the other hand, the polymer elastic materials conventionally used in pressure-sensitive resistors include natural rubber, synthetic rubber, thermoplastic 11. Although elastomers can be used, it is known that it is better to use crosslinked rubbers such as ethylene-propylene rubber, silicone rubber, polyunitane rubber, butylene rubber, etc. from the viewpoint of air characteristics and heat resistance. The particles include a mixture of carbon black with a volume fraction of 5 to 20% and conductive metal particles of 25 to 50 cm, and other pressure-sensitive particles containing a combination of conductive carbon, semiconductive oxide, and conductive metal particles. Resistors are known. In addition, the method for producing a pressure-sensitive resistor is mainly a method in which a composition consisting of liquid rubber and magnetic conductive metal particles such as Ni is cured at room temperature while being oriented in a magnetic field in a mold. is published in Japanese Unexamined Patent Application Publication No. 53-14
This is disclosed in Publication No. 772 and the like.

However, the above pressure sensitive resistor and its manufacturing method have the following drawbacks.

1) Pressure-sensitive resistors using polymer elastic bodies other than silicone rubber cannot be used for switches, crimp-type connectors, etc. because they have large compression set strains at high temperatures.

2) The composition of putty-like silicone rubber mixed with peroxide and metal particles requires kneading with rolls, and the curing conditions are 1.
After press forming at 50℃ for 20 minutes or more, press molding at 200℃ or higher
The production time is long because the heat treatment is performed for ~4 hours.

3) When carbon black and graphite are mixed into addition reaction type liquid silicone rubber to the extent that it becomes conductive, the addition reaction progresses and curing becomes insufficient.
Molded products with good physical properties cannot be obtained.

4) A composition in which conductive particles such as metal, semiconductor, and carbon are individually mixed and dispersed has a large hysteresis in pressure-resistance characteristics.

5) A method in which magnetic conductive metal particles are dispersed in liquid silicone rubber and cured in a mold while being oriented in a magnetic field generally takes 2 to 24 hours to cause a room temperature curing reaction.

As mentioned above, conventional pressure-sensitive resistors require high-temperature molding.
Not being able to be integrally molded with other plastic molded objects;
They have various drawbacks, such as not being able to obtain sufficient pressure-sensitive characteristics and being expensive if they require a long manufacturing process.

[Purpose of the invention]

The present invention has been made in view of the above points, and its objectives are to be able to be molded at relatively low temperatures and in a short time, to have low compression set, low hysteresis in the pressure-resistance diagram, and to have high tensile strength. The object of the present invention is to provide a sensitive resistor having sufficient rubber physical properties such as high .

[Key points of the invention]

The pressure-sensitive resistor of the present invention has a JISA hardness of 40 to 70 and has the following material composition, which is molded at 120°C or lower using a compression molding method or a transfer molding method. (1) Addition reaction silicon that cures at room temperature. Rubber; 60-80
Volume fraction CH (2) Metal particles with a particle size of 40 to 200 μm: 15 to 25 Volume fraction CH (3) Graphite particles with a particle size of 10 to 200 μm: 2 to 10 Volume fraction CH (4) Particle size 100 to 300 μm Fine powder silica: 2-5
Volume Fraction CH [Embodiments of the Invention] The present invention will be described below based on Examples.

First, knowledge obtained from preliminary experiments regarding the constituent materials of the pressure-sensitive resistor of the present invention will be described.

The rubber used in the present invention is an addition reaction type liquid silicone resin. This addition reaction type silicone resin is a room temperature curing type and is usually molded at 100-120'C for 10-20 minutes, but when other rubbers are used, it is molded at 150°C.
This is because it requires a molding temperature higher than that, making it difficult to mold integrally with the soft plastic that covers electric wires and the like. Of course, it is possible to mold the silicone rubber first and then perform integral molding with the plastic, but in this case it is not preferable because the adhesiveness between the silicone rubber and the plastic deteriorates.

Particle size 40~ as the main conductive particle for imparting conductivity
Using 100 μm Ni powder, the mixing amount is 11 parts of 200-350M per 100 parts by weight of resin, and the volume fraction is 15-2.
5%. Volume fraction of conductive metal particles is 15-25%
The reason is that when more than 25% is mixed, it becomes a pressure-sensitive resistor, but the tensile strength decreases, and the hardness and compressive deformation strain also deteriorate, making it unsuitable for practical use.On the other hand, if it is less than 15%, the addition effect is not This is because the conductivity during pressurization is low and it cannot be used as a pressure-sensitive resistor.For particle size 0, if Ni particles of 40 fim or less are used, the particle arrangement becomes discontinuous and a conductive path is not formed sufficiently, resulting in poor pressure-sensitive characteristics. If the particle size exceeds 200 μm, there will be a local shortage of binder and particle bonding will not be sufficient (
The tensile strength of the pressure sensitive resistor decreases.

In addition to Ni, graphite is also used as the conductive particles, and the addition of graphite powder plays the role of keeping the hysteresis small without reducing the withstand voltage of the pressure-sensitive resistor.
5 to 25 parts by weight of 200 μm, 9 parts by weight, 2 to 1
0% mixed 0 Therefore, as conductive particles 17-3
5 volume fractions will be mixed. The amount of graphite mixed is 2
ts or less, and the withstand voltage also decreases. 10 for particle size
When using graphite particles of μm or less, the resistance when no pressure is applied is 106
It tends to be less than 0α.

Figure 1 is a diagram showing the relationship between the amount of graphite powder mixed and the volume resistance of the pressure-sensitive resistor when no pressure is applied.When the volume fraction of graphite powder exceeds 10 cm, the resistance decreases rapidly. It shows that it becomes possible to do.

Furthermore, in the present invention, the reinforcing material of addition reaction type silicone rubber is also important.
Semi-average particle size 100-300 suitable for compression molding method such as 200
mμm, and the mixing amount is preferably 10 to 200 to 20 parts by weight, 9 to 5%. Mixed amount is 2 volume fraction -
Below 20 parts by weight (5 parts by weight) the tensile strength of the pressure sensitive resistor decreases.
If the volume fraction exceeds 1), the rubber hardness will be high and the compression permanent deformation strain will be large, resulting in unfavorable rubber physical properties.

FIG. 2 is a diagram showing the relationship between the amount of finely divided silica mixed and the tensile strength and hardness of the pressure-sensitive resistor, with the solid line representing the tensile strength and the dotted line representing the strength.

It can also be seen from FIG. 2 that in order to keep the tensile strength at an appropriate value and the rubber hardness in a good range of 40 to 70, it is preferable to limit the amount of finely divided silica mixed to 5% by volume.

The constituent materials added to the addition reaction type liquid silicone rubber used in the present invention have been described above, and from the above it can be seen that the amount of addition reaction type liquid silicone rubber blended is preferably 60 to 80 volume fraction. . When addition reaction type liquid silicone rubber is used, it contains about 5 parts by weight of a platinum compound catalyst to accelerate curing.

Next, a pressure-sensitive resistor actually molded according to the above material structure will be described. First, after kneading for 15 minutes using a mixing machine, a predetermined amount of this kneaded material was sandwiched between two iron plates and compression molded for 10 minutes using a hot plate heated to 100°C to form a product with a thickness of 0.5 Two types of sheets were made: ``Kan'' and ``2.4 Dragon.'' The characteristics of the pressure sensitive resistor were determined using these two types of sheets.
The tensile strength, compression permanent deformation strain, etc. were measured according to the method of 2013, and for the 0.5 mm thick one, the pressure P1 and the pressure at which the resistance becomes 1030-α or less when the pressure applied to the pressure-sensitive resistor increases are determined. The pressure P2 at which the resistance of the pressure-sensitive resistor becomes 10''Ω-α or higher when lowering, that is, the hysteresis due to pressurization and depressurization, and the withstand voltage were determined.

FIG. 3 shows two examples of the composition and characteristic values of the pressure-sensitive resistor according to the present invention. For comparison, FIG. 3 also shows a pressure-sensitive resistor having a composition different from that of the present invention. Figure 3 shows the case where the Ni powder and graphite powder used both have a relatively small particle size. In FIG. 3, Example 1 shows a composition range in which the pressure-sensitive resistor exhibits good characteristics, but Example 2 has more Ni powder added and less graphite powder than Example 1. Therefore, the tensile strength and withstand voltage are low, and the compression permanent deformation strain is large, but it is fully usable as a pressure-sensitive resistor. Comparative Example 1 is a case where a putty-like silicone resin is used as the polymeric elastomer, and peroxide is added to the catalyst, but both the molding temperature and the post-heating temperature have to be higher than those for addition reaction type liquid silicone resin. In addition, the processing time becomes longer and the hysteresis of the molded product becomes very thick. In Comparative Example 2, the Ni powder was added and no graphite powder was added. In this case, the physical properties of the pressure-sensitive resistor were The values are worse for most items. Comparative Example 3 uses Ni powder with a particle size of 40 μm or less, and the hysteresis characteristics of pressure reduction are extremely poor. Comparative Example 4 uses graphite powder with a particle size of 10 μm or less. It uses
Volume resistance and withstand voltage when no pressure is applied are significantly reduced. Rubber hardness refers to the type of rubber.

Although the hardness varies depending on the curing conditions, the type and amount of filler added, etc., as mentioned above, a hardness of 40 to 70 is good; if the hardness is over 70, the contact area will be small, the contact resistance will increase, and the rubber If the hardness is less than '40, mechanical strength may be insufficient and the pressure sensitive resistor may be damaged during handling.

The method of measuring the withstand voltage in Figure 3 is as follows. In other words, Figure 4 shows a conceptual diagram of the surroundings of the sample to explain the measurement method.
．． Electrodes 4a and 4b are arranged symmetrically across the pressure-sensitive resistor 3, and electrodes 4a and 4b are arranged on the upper surface of the pressure-sensitive resistor 3 and electrodes 4c and 4d are arranged on the lower surface, respectively, between the electrodes 4a and 4b and between the electrodes 4c and 4d. insert insulating spacers 5a and 5b of 0.5 mm each, and
a and 4c.

4b and 4d are pressurized to 95 cm, which is the thickness of the pressure sensitive resistor 3.
Conductive state between a and 4c and between 4b and 4d, and 4a and 4b
This is a measurement of the withstand voltage between.

Furthermore, a non-contact switch using a vinyl chloride electric wire was fabricated using the pressure sensitive resistor of the present invention. FIG. 5 shows its structural concept. As shown in FIG. 5, in this non-contact switch, the ends of vinyl chloride electric wires 7, 7a are integrally molded from one symmetrical side surface of a pressure-sensitive resistor 6 so as to be parallel to each other at a predetermined distance. , the vinyl chloride coatings 8, 8a are removed from the ends of the electric wires 7, 7&, and the copper wires 9, 9a are exposed. In this way, when the pressure sensitive resistor 6 is pressurized in a direction perpendicular to both chamber wires 7, 7a, conduction can be established between the copper wires 9, 9a. In this way, since the pressure sensitive resistor of the present invention has relatively low molding temperature and post-heating temperature as described above,
While it is possible to integrally mold with soft plastics such as vinyl chloride and polyethylene, for example, when using a pressure sensitive resistor using putty-like silicone resin shown in Comparative Example 1, the vinyl chloride coating will melt and deteriorate. However, discoloration was observed and a sound integrally molded product could not be obtained. This means that a commercially available, inexpensive pressure-sensitive conductor can be easily molded using the pressure-sensitive resistor of the present invention, and this is due to the effect of using an addition reaction type silicone resin.

As mentioned above, when comparing the example shown in FIG. 3 with the comparative example, it is clear that in the present invention, an addition reaction type liquid silicone resin that is easy to mold is used and various additives are mixed therein. In order to impart rubber physical properties with excellent functions as a pressure-sensitive resistor, setting an appropriate blending amount of additives has a great effect.

〔Effect of the invention〕

Addition reaction type liquid silicone resin as a pressure sensitive resistor of pressurized conductive rubber with a volume fraction of 60 to 80% including catalyst, 9 particle size 40
~200/l m Ni powder 1~2~10 volume fraction 1, fine powder silica 2~5 volume fraction 1
Since the molding was carried out at a temperature of 20° C. or lower, the resulting pressure-sensitive resistor has the following advantages.

(1) Raw materials can be easily kneaded in a short time without using a special kneading machine such as a roll during production.

(2) It can be molded at a relatively low temperature in a short time of 20 minutes or less.

(3) Because low-temperature molding is possible, it is easy to integrally mold with other soft plastic molded products such as vinyl chloride-coated electric wires, expanding the range of applications.0 (4) High strength and low compression set. 0(5) which has both good mechanical properties and high elastic properties such as N as a conductive particle.
Hysteresis in pressure-resistance characteristics is extremely small due to the combination of I powder and graphite powder.

[Brief explanation of drawings]

Figure 1 is a relationship diagram between the amount of graphite powder mixed and the volume resistivity of the pressure sensitive resistor of the present invention, and Figure 2 is the same (the relationship between the amount of mixed silica and the tensile strength, (iil! degrees). Figure 3 is a characteristic comparison diagram of the composition of the pressure-sensitive resistor of the present invention and pressure-sensitive resistors with different compositions, Figure 4 is a conceptual diagram of a method for measuring withstand voltage of a pressure-sensitive resistor, and Figure 5 Figure 6 is a schematic diagram of a switch in which a PVC electric wire and a pressure-sensitive resistor are integrally molded, Figure 6 is a diagram of a switch in which a pressure-sensitive resistor is used as a connector, and Figure 7 is the pressure force of a conventional pressure-sensitive resistor. 2) 3.6-Pressure sensitive resistor, 4a, 4b, 4c.4 d = electrode, 5a, 5b-insulating spacer, 7,7
a Vinyl chloride electric wire, 8, 8a... Suspected vinyl chloride, 9, 9a... Copper wire. sie kt (vo9 坏) Sai 1 (2) T2 (2) 21 Si Hi Hi Ale 1 [Gohan
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Claims (1)

[Claims] 1) The molding material is an addition reaction liquid silicone resin 60 to 80
% by volume, 17-35% by volume of conductive particles, and 2-5% by volume of fine powder silica, capable of being molded at 120°C or less, and having a JISA hardness of 40-70 after molding. A pressure-sensitive resistor featuring: 2) Nickel powder 15 with a particle size of 40 to 200 μm as conductive particles in the pressure sensitive resistor according to claim 1
Graphite powder with a volume fraction of ~25% and a particle size of 10-200 μm2~
10% by volume. 3) A pressure-sensitive resistor according to claim 1 or 2, characterized in that fine powder silica having a particle size of 100 to 300 mμm is used. 4) A pressure-sensitive resistor according to any one of claims 1 to 3, characterized in that a compression molding method or a transfer molding method is used.