JPS60723B2 - Manufacturing method of foamed pressure-sensitive resistor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a highly sensitive pressure sensitive resistor mainly consisting of liquid silicone rubber and conductive metal particles.

Conventionally, metal particles of about 0.01 to 200 mm in size obtained by chemical reduction methods, forging methods, mechanical crushing, etc. are mixed with plastics, rubbers, etc., molded, crosslinked, and electrically compressed by pressure. Pressure-sensitive resistors whose resistance value changes within a large range are known (Tsubaki Sekisho 46-6173, Japanese Patent Application Laid-Open No. 49-114).
7 Suction〆 Tokka Showa 50-1116990 Hakama Kosho 40-2406
1, Tokusekki 1975-5159 entry, etc.).

The purpose of the present invention is to achieve a volume resistivity of 10 at lower pressures.
To provide a high-sensitivity pressure-sensitive resistor that can be changed from an insulator of 7Q. The purpose of this invention is to reduce the change in physical properties, reduce the amount of metal particles used compared to the amount required to obtain a pressure-sensitive resistor from solid silicone rubber and metal particles, and improve cost and performance. As a result of intensive studies by the present inventors to obtain a pressure-sensitive resistor that meets these objectives, we found that: i) Pressure force P
is added to the pressure-sensitive resistor, and the pressure required to make the volume resistivity pv 1 piQ/skin is P* (k9/ground). The amount can be made smaller when using liquid rubber than when using solid rubber, and ii) When using the same liquid rubber, P* can be made smaller by increasing the particle size of the conductive metal particles. , iii) However, when the particle size of the metal particles is increased, it is necessary to increase the amount of conductive metal particles mixed in order to obtain a pressure-sensitive resistor with the same P*, and as a result, the hardness of the pressure-sensitive resistor increases. It was found that the rubber properties were damaged and the durability against repeated pressure was reduced.

As a result of further research based on the above facts, the present inventors
We have found a method to obtain a highly sensitive pressure-sensitive resistor that has rubber-like properties and excellent durability against repeated pressurization by using liquid silicone rubber and foaming the matrix.

That is, the present invention provides a pressure-sensitive resistor with an average particle diameter of 10 to 200, which is mainly composed of a main integral ratio (%) of skin conductive metal particles 15 to 5 and a main integral ratio (%) of liquid silicone rubber 85 to 5. When manufacturing the body, N is added to the liquid silicone rubber.
- A method for producing a pressure-sensitive resistor in which the foaming ratio is adjusted from 1.05 to 1.5 times by mixing and heating an organic foaming agent having a nitroso group. Conventionally, organic blowing agents such as nitroso compounds, azo-diazo compounds, and sulfonic acid hydrazide compounds have been used in solid silicone rubber compounds with hardnesses of 30 and 60.

The amount of addition is 1 to 5 parts per 100 parts of the compound, and penzoyl peroxide, 2,4-
Dichlorobenzoyl peroxide "T-butyl peroxide is commonly used (Journal of the Japan Rubber Association, Vol. 46, April issue, p. 92 (1973), Special Publication No. 45-1267
5). In addition, as a method for foaming liquid silicone rubber, there is also a method in which a dehydrogenation reaction is performed during crosslinking to cause foaming (Special Publications Publication No. 4).
2-17115), but a good pressure-sensitive resistor cannot be obtained by this method. On the other hand, organic tin compounds and compounds containing platinum are usually used as crosslinking catalysts for liquid silicone rubber, but ``compounds containing nitrogen, phosphorus, and sulfur are known to act as catalyst poisons for the aforementioned catalysts'' (Nippon Rubber Co., Ltd. Association magazine 4 Mother To, April issue, page 46 (1973)).

In addition, when an organic tin compound and a peroxide are mixed, crosslinking is not sufficiently carried out (Tokusei Sho 49-1147 issue). RTV silicone rubber foam can be made by using hydrogen gas, which is produced as a by-product of the dehydrogenation condensation reaction, as a foaming agent and by balancing the dehydrogenation reaction rate and curing rate (Japan Rubber Association Journal 4) 332 (1973)), it was found that the blowing agents normally used in solid rubbers are not applicable to liquid silicone rubber in most cases.However, surprisingly, blowing agents consisting mainly of conductive metal particles and liquid silicone rubber were found to be ineffective in most cases. When obtaining a pressure-sensitive resistor, a good foam is obtained by mixing 0.1% to 5% by weight of an organic foam having an N-nitroso group to liquid silicone rubber and heating it. By adjusting the magnification to 1.05 to 1.5, "the sensitivity of the pressure-sensitive resistor increases compared to a non-foamed material," and the electrical properties of the pressure-sensitive resistor hardly change even after repeated deformation. It was found that it has advantages.

Furthermore, by using liquid silicone rubber, the dispersibility and processability of metal particles and fillers are excellent. The conductive metals that can be used in the present invention include iron, chromium, stainless steel, silver, nickel, aluminum, zinc, etc., and may be flaky, spherical, or irregularly shaped.

In addition, the particle size of these metals may be about 0.1 to 200 microns, but it is preferably about 10 to 200 microns in order to reduce the P* of the pressure-sensitive resistor.
If the particle size is larger than 200 microns, it is undesirable because it tends to fall off from the rubber due to mechanical stimulation. In order to obtain the high-sensitivity resistor of the present invention, the conductive metal particles are used at an integral ratio of 15% and 5%.

Even if the particle size of the conductive metal particles is about 10 mm, if the mixed amount is less than 1 kalpa integral ratio (%), it will usually become an insulator.
Even if the particle size of the conductive metal particles is about 200 degrees Fahrenheit, if the mixed amount exceeds the main integral ratio (%) of 5, it becomes a normal conductor. Organic blowing agents having an N-nitroso group that can be used in the present invention include L, such as N.N'-dimethyl-N.

N'-dinitrosoterephthalamide, dinitrosobentamethylenetetramine, and blowing agents containing these as main ingredients can be mentioned. The pressure-sensitive resistor obtained by the method of the present invention changes from a high-resistance material to a conductor with small deformation or small pressure, has small pressure-resistance hysteresis during pressurization and depressurization, and has low electrical characteristics due to repeated pressurization. Since the change is small, it can be applied to many industrial applications such as switches, signal input boards, and pressure-sensitive elements.

Next, the present invention will be further explained with reference to examples, but the present invention is not limited to the examples only.

Example 1 Nickel powder with a particle size of 40 mm obtained from nickel carbonyl 255 mm (43 volume fraction %), condensation type silicone rubber (KEI Wave TV manufactured by Shin-Etsu Chemical Co., Ltd.) 50 mm (57 volume fraction %) and K
N/N as a crosslinking agent for EI wave TV and a foaming agent
1.5 hours of dinitrosobentamethylenetetramine was mixed in a Brabender for 10 minutes.

Transfer the mixture to a stainless steel mold of 10 skins x 10 arcs x 2 skins, mold, and heat in a heat press for 2 minutes at 125°C.

After that, reduce the pressure to zero and continue foaming until the specified thickness.
A crosslinking reaction was carried out for 8 minutes. The foaming ratio obtained in this way is 1
．． Regarding the double sample and the comparison sample obtained without foaming,
Changes in volume resistivity pv due to pressure P were measured. The measurement results are shown in Table 1-1, and the attached drawing shows the horizontal axis as log
P shows the results of plotting each measurement data with the vertical axis as logpv. Table - I Z In the drawing, the volume resistivity pv is expressed as 1 pi○・skin (log
If the force required to achieve pv=3) is P*, then the smaller P* is, the higher the sensitivity to pressing force is.

As shown in the figure, the foamed sample (foaming ratio: 1.2 times) has a smaller value of P* and better sensitivity than the unfoamed sample of the comparative example. Next, foamed samples having different expansion ratios from 1.0 to 1.6 were prepared, and for each sample, P* was determined in the same manner as described above, and is shown in Table 1-2.

Table 1-2 Expansion ratio 1.0 1.05 1.2 1
．． 4 1.6P* 8 4 2 6
9 As shown in Table 1-2, it was found that a highly sensitive pressure sensitive resistor can be obtained even when the expansion ratio is 1.05 or 1.5.

Example 2 Particle size 1-3 peak obtained from nickel carbonyl (1), 1
Nickel powder of 0-12 pu skin (0) and particle size 70-10
Copper powder with a volume fraction (%) of 284,347 m and 130 to 170 m, respectively, and 8 m of additive silicone rubber (KE130 plate TV manufactured by Shin-Etsu Chemical), respectively.
72 "57, 53 volume fraction (%), several drops of crosslinking catalyst in an amount that can control crosslinking time to about 2 hours, and N/N weighed to be 2% by weight based on silicone rubber.
'-dimethyl-N.N'nitrosoterephthalamide are kneaded in a Brabender for 5 minutes.

The mixture was formed into a sheet of 10 skins x 10 arcs x 0.2 skins in a mold, and after being left for 1 hour, it was inserted into a press at 190°C and pressed to 200k9/base for 1 minute. After pressurization, a substrate was inserted between the presses, the foaming ratio was controlled to 1.1 times, and a crosslinking reaction was carried out at 1°C for 19 minutes. The resulting sample was pressurized, and the force P* (k9' swim) required to reduce its volume resistivity pv to 1 pi*skin was measured and is shown in Table 2.

As shown in Table 2, it can be seen that the use of metal powder with a larger particle size results in lower P* (higher sensitivity), but the JISK 301 type A hardness is higher. Furthermore, the pressure that reaches P* is increased to 1
The addition was repeated 00,000 times, and P* after deterioration was measured. Table 2 shows samples prepared in Example 2 without foaming as comparative examples. Table 2. Metal sample 10 m. W (comparative example) p* (abbreviation) 14 9 5
3 Hardness 42 51 63 67.1 million times
20 14 11 P* after 9 pressure (Example) p
*(k2 ground) 11 6 2 0.7 hardness 38 45 55 59.1 million turns low 9
8 4 P* after 1.4 pressure Example 3 Particle size 70-100 Particle size 35 volume fraction (%) of iron powder and additive silicone rubber (Toray Silicon SH9555) 54.
2 volume fraction (%) of the crosslinking agent for the rubber, 10.8 volume fraction (%) of the crosslinking agent for the rubber, and 3% by weight of the blowing agent shown in Table 3 based on the total of the rubber and the crosslinking agent, and and mixed for 1 minute.

Transfer this mixture to a 10 x 10 x 0.2 mold, heat it for 2 minutes in a 125q○ press (at a pressure of 100k9'), remove the pressure, and place only the lid of the 1.5k9 mold on the sample. It was placed and crosslinked at 125qC for 28 minutes, and the foaming status was observed.

The results are shown in Table 3. Table 3 Additives Foaming status Notes Azoisobutyronitrile Does not form a foam Comparative example J Ammonium carbonate No crosslinking, inhibits crosslinking) Azodicarbonamide No crosslinking, Diazoaminobenzene No crosslinking, benzene round Lefodyl hydrazide No crosslinking Toluene-2,4- without Nylhydrazide crosslinking
Dizlephonyl Not crosslinked Comparative example hydrazide N
,N''dimetre-N,N-dinito Good foam Example 3 Rosoterephthalamide

[Brief explanation of drawings]

The drawings are diagrams showing volume resistivity-pressure curves in examples of the present invention and comparative examples.

Claims (1)

[Claims] 1. Conductive metal particles 1 having an average particle diameter of 10 to 200 μm
When producing a pressure sensitive resistor mainly consisting of 5 to 50 volume fraction (%) and liquid silicone rubber 85 to 50 volume fraction (%), an organic blowing agent having an N-nitroso group is mixed with liquid silicone rubber. , heating to increase foaming ratio to 1.0
A method for manufacturing a pressure-sensitive resistor, characterized in that the adjustment is performed by a factor of 5 to 1.5. 2 As an organic blowing agent having an N-nitroso group, N.N.
The method according to claim 1, characterized in that '-dimethyl-N.N'-dinitrosoterephthalamide or dinitrosopentamethylenetetramine is used.