JPH0746534B2 - Conductive magnetic rubber sheet - Google Patents

Description

The present invention relates to a conductive magnetic rubber sheet. More specifically, it relates to a rubber sheet containing conductive magnetic particles.

[Conventional technology]

A rubber sheet (anisotropic conductive rubber sheet) containing conductive magnetic particles has been conventionally known. For example,
Japanese Patent No. 54-146873 discloses that a magnetic pole plate having an uneven surface is used for magnetic flux before or during crosslinking of a sheet of an insulating polymer elastic body containing two types of conductive magnetic particles having different particle size distributions. There is described a pressurized conductive rubber in which conductive magnetic particles are non-uniformly distributed in a sheet by applying a magnetic field whose lines are parallel to each other. Further, JP-A-58-152033 discloses that
Mainly composed of conductive magnetic particles and insulating polymer elastic material,
An anisotropic conductive rubber sheet obtained by subjecting an uncured composite containing an alkyl titanate crosslinking agent to a magnetic field treatment to be crosslinked is described.

However, these methods have the following drawbacks.

(1) As the conductive magnetic particles, metals such as iron, cobalt and nickel, alloys thereof or gold or silver plated products thereof are used, so that the specific gravity of the conductive magnetic rubber is increased to about 3.

(2) Metals often tend to interfere with the vulcanization reaction of rubber, and in sulfur vulcanization in particular, sulfur in the vulcanizing agent reacts with the metal and is consumed to form sulfides, and the rubber is vulcanized. Will not do. In addition, the conductivity also deteriorates, and it becomes difficult to obtain a product of constant quality.

(3) The adhesion between the matrix rubber and the conductive magnetic particles is poor, and the tensile strength is also small. For example, the nickel particle-filled silicone rubber has a tensile strength of about 15 to 17 kgf / cm ² .

(4) Especially when the nickel particles are dispersed in a low-viscosity rubber such as silicone rubber, if the nickel particles are left unstored in the storage state, the particles settle and the dispersion state is not uniform.

[Problems to be solved by the invention]

The inventors of the present invention have conducted various investigations in search of a conductive magnetic rubber sheet (anisotropic conductive rubber sheet) which does not have such defects found in the prior art, and as a result, have conducted a vulcanization molding in a sheet shape while applying a magnetic field. When forming the magnetic rubber composition,
By once blending both the conductive particles and the magnetic particles into a polymer substance and filling the resulting particulate conductive magnetic composition in a rubber compound, it is possible to effectively solve such problems. I found it.

[Means for solving problems]

Therefore, the present invention relates to a conductive magnetic rubber sheet, the conductive magnetic rubber sheet, the percentage is a volume percentage, the melting temperature 160 ° C. or higher or a polymer substance having a crosslinkable functional group 85-62%, conductive. A particulate conductive magnetic composition obtained by pulverizing a mixture of 5 to 30% of magnetic particles and 5 to 30% of magnetic particles is used in an amount of about 40 to 15% based on about 60 to 85% of a rubber compound.
The conductive magnetic rubber composition filled in the above ratio is vulcanized and molded while applying a magnetic field.

As the polymer substance, one having a melting temperature of 160 ° C. or higher or one having a crosslinkable functional group is used, which is obtained by dispersing this in a rubber compound as a particulate conductive composition mixed with conductive particles and molding it. This is in order to prevent the particulate composition from being deformed or flowing.

Examples of the polymer substance having a melting temperature of 160 ° C. or higher include aliphatic or aromatic polyamides or polyesters, polycarbonates, polyurethanes, polyureas, epoxy resin cured products, polyvinylidene fluoride and the like.

Further, as the polymer substance having a crosslinkable functional group, a carboxyl group, an epoxy group, a reactive halogen group, a hydroxyl group,
Monomers having crosslinkable functional groups such as amide groups and diene groups, such as acrylic acid, methacrylic acid, glycidyl acrylate, acrylic glycidyl ether, 2-chloroethyl vinyl ether, monochlorovinyl acetate, hydroxyalkyl acrylate, hydroxyalkyl methacrylate, acrylamide. , Methacrylamide, divinylbenzene, pentadiene and the like and about 99.9 to 90 mol% of at least one vinyl monomer such as alkyl acrylate, alkoxyalkyl acrylate, vinylidene chloride, acrylonitrile and styrene. A copolymer is mentioned. Further, a polyurethane prepolymer having a terminal isocyanate group can also be used.

As the conductive particles, ketjen black, conductive carbon black such as acetylene black, metal such as graphite, nickel, copper, zinc, aluminum, brass fiber, metal fiber such as aluminum fiber, carbon fiber, etc. Is a spherical one having a particle diameter of about 5 μm or less. The particles having a particle size within this range are used because the particles having a particle size larger than this range cause variations in conductivity and variations in anisotropic conductivity during magnetic field orientation. The preferred use of spherical particles is
This is because it is easy to flow under pressure.

Further, as magnetic particles, various ferrites, γ-Fe
₂ O ₃ , CrO ₂ , and metals such as iron, cobalt and nickel, M
An alloy such as nAl or FeCrCo having a grain size of about 5 μm or less is generally used. The particles having a particle diameter within this range are used because the particles having a particle diameter larger than this result in variations in magnetism and variations in anisotropic conductivity during magnetic field orientation.

Each of the above components is a volume percentage, and the polymer substance is 85 to 62% in percentage, and the conductive particles and magnetic particles forming the composite particles are both 5 to 30% and both of them. It is used in proportions such that the total amount is 15 to 38%. The role of the polymeric substance is to act as a binder for each particle, to give affinity to the composite particles and the matrix rubber, and to reduce the weight. From these effects, if the usage ratio is less than this, these effects are sufficient. If it is used more than this, the conductivity and magnetism will be impaired.

Mixing and pulverization of the polymer substance and the conductive and magnetic particles are performed by mixing using a mixing means such as a kneader or a roll mill, and at that time, a curing agent for the polymer substance, a vulcanizing agent, etc. are allowed to coexist, and the mixture is pulverized. It is easy to do, generally it is in a state of solidified by molding or foam molding into a simple shape such as roughly crushed bulk shape or preferably sheet shape, and then sufficiently solidified at room temperature or using dry ice etc. It is carried out by crushing after it is brought into a standing state. The pulverization is carried out until the particle diameter of the obtained particulate conductive magnetic material composition is about 30 to 150 μm. If a particle size larger than this is used, it becomes difficult to retain by dropping or peeling from the matrix with the rubber compound, while if the particle size is too small, the number of particles for conduction is very high. This is not desirable because it will have to increase.

The obtained particulate conductive magnetic material composition is filled in a rubber compound to form a matrix. The mixing ratio is
The volume ratio is about 40 to 15% of the particulate conductive magnetic material composition to about 60 to 85% of the rubber oriented material. This mixing ratio is selected so that a conductive path is formed by the contact of the composite particles when the rubber sheet is used. However,
If the composite particles are used in a proportion higher than this, they will always conduct, and the desired anisotropy and pressure conductivity will be lost, so the above range is selected.

Rubber compounds used here include natural rubber, polybutadiene, chloroprene rubber, urethane rubber, NBR, S
Various synthetic rubbers such as BR, EPDM, silicone rubber and the like, which are compounded with a compounding agent such as a vulcanizing agent and a vulcanization accelerator, a filler, a reinforcing agent, and a plasticizer, are used.

The mixing of the particulate conductive magnetic material composition and the rubber compound is performed by using a roll mill, a kneader or the like, in which case the particles react with the rubber at the particle interface so that the binding force is increased,
In the case of a combination of a compound having a reactive group, for example, a particle using an epoxy resin as a polymer substance and a rubber having a double bond such as EPDM or NBR, it is preferable to add and use allyl glycidyl ether.

The conductive magnetic rubber composition thus prepared,
It is vulcanized and molded into a sheet according to the vulcanization conditions of the rubber used, but a magnetic field is applied during vulcanization and molding. The application of the magnetic field is generally performed in a parallel magnetic field with a magnetic field strength of about 2000 to 20000 Gauss using a magnetic pole plate having a planar or conductive and magnetic particles having the same or larger size as the particle size of the magnetic particles. , Giving a magnetic field orientation to the vulcanized molded sheet.

[Operation] and [Effect of the Invention] The conductive magnetic rubber sheet according to the present invention is obtained as a rubber sheet having pressure-sensitive properties and anisotropic conductivity, and this rubber sheet is further characterized as follows. It has the characteristics of

(1) Small specific gravity. For example, the specific gravity of the particulate epoxy resin composition containing 10% of carbon black and 15% of ferrite is 1.83, which is significantly smaller than the specific gravity of nickel of 8.9, and 35% of this particulate epoxy resin composition and 65% of EPDM compound were used. The specific gravity of the conductive magnetic EPDM composition is 1.15.
Thus, the specific gravity of the conductive magnetic EPDM composition containing 35% nickel is significantly smaller than 3.65.

(2) Good conductivity and adhesiveness between magnetic particles and rubber. For example, the breaking strength of the rubber sheet obtained from the particulate phenolic resin composition and nitrile rubber is greater than that using nickel particles, and when the fracture surface is observed with a microscope, the rubber pieces torn off adhere to the particle surface. ing.

(3) The vulcanization rate is not reduced. For example, when the particulate epoxy resin composition of (1) above is mixed with a compound of NBR or EPDM using sulfur, which is a general-purpose vulcanizing agent, and vulcanization molded, the vulcanization rate shows almost no change. On the other hand, when nickel particles are used, the vulcanization rate is remarkably reduced.

(4) The tensile strength is not lowered so much. For example, 35% of the particulate epoxy resin composition of (1) above and EPDM compound 65
The tensile strength of the vulcanized rubber sheet is 72kgf /
In cm ^2, that of EPDM single rubber sheet 85 kgf / cm ² from 15%
Although only reduced to a certain extent, those using nickel particles show only a tensile strength of 30 kgf / cm ² .

(5) By subjecting the obtained rubber sheet to magnetic field orientation, variations in volume resistivity and pressure-sensitive characteristics of the rubber sheet are reduced.

〔Example〕

 Next, the present invention will be described with reference to examples.

[Preparation of particulate conductive magnetic material composition]

A: Epoxy resin (Oilized shell epoxy product Epon 828) 4
After mixing 00 cm ³ , ferrite fine particles 120 cm ³ and Ketjenblack (specific gravity 1.90) 140 cm ³ for 5 minutes in a kneader, add epoxy resin curing agent (Adeka Hardener EH531) 200 cm ³ and mix evenly for 3 minutes. Mixed. These mixtures were taken out of the kneader, cured at 100 ° C. for 1 hour, and then heat-treated at 160 ° C. for 1 hour.
The volume resistivity of the obtained cured product of the conductive magnetic material composition (specific gravity 1.71) was 4 Ω · cm.

B: Nitrile rubber (Goodrich Hiker 1042) 10
0 parts (weight, same below), 5 parts of zinc white, stearic acid 1
Parts, DOP 15 parts, sulfur 0.5 parts, vulcanization accelerator TT (tetramethylthiuram disulfide) 2 parts and CZ (n-cyclohexyl-2-benzothiazole sulfenamide) 1
Nitrile rubber blend 600 cm ³ with a composition of the parts, after mixing the ferrite fine powder 130 cm ³ and Ketjen black 140cm ³ roll mill, and vulcanizing to the 20 minutes sheet at 170 ° C., a further 160 ° C. Heat treatment was performed for 2 hours. The volume resistivity of the vulcanized sheet (specific gravity 1.82) of the obtained conductive magnetic composition was 7 Ω · cm. The conductive magnetic composition was pulverized in the state of A at room temperature, and in B, sufficiently cooled with dry ice and mixed with dry ice. The particle size range, average particle size, and volume resistivity (apparent) of the particulate conductive compositions a to b (corresponding to the conductive compositions A to B) obtained by pulverization were measured, and the results are The results are shown in Table 1 below.

Example 1 34 parts by volume of the particulate conductive magnetic composition a was added to 66 parts by volume of a nitrile rubber composition in which 15 parts by weight of SRF carbon black was further added to the composition of the above B, and they were mixed by a roll mill.

The mixture was vulcanized and molded under a parallel magnetic field of 10,000 gauss at 150 ° C for 20 minutes, and then heat-treated in an oven at 160 ° C for 1 hour to give a conductive magnetic rubber of 100 × 200 × 1 mm size. Got the sheet.

Example 2 In Example 1, instead of the nitrile rubber compound, EPDM
EPDM consisting of 100 parts (Japan synthetic rubber product EP22), carbon black (central carbon product HTC # S) 28 parts, zinc oxide 5 parts, process oil (Idemitsu Kosan PW-150) 10 parts and dicumyl peroxide 4 parts A formulation was used.

Example 3 In Example 1, the same b was used in place of the particulate conductive magnetic material composition a.

Example 4 In Example 2, the same b was used instead of the particulate conductive magnetic material composition a.

With respect to the vulcanized sheet obtained in each of the above examples, the physical property value and the electrical resistance (when the sheet having an area of 1 cm ² and a thickness of 1 mm is not pressed or pressed) are measured. The results obtained are shown in Table 2 below.

Claims (6)

[Claims] 1. All of the percentages are volume percentages and the melting temperature is
Polymer substances with a cross-linkable functional group of 160 ℃ or higher 85-6
A particulate conductive magnetic material composition obtained by pulverizing a mixture of 2%, conductive particles 5 to 30%, and magnetic material particles 5 to 30% is used in an amount of about 40 to about 40 to 85% for a rubber compound. A conductive magnetic rubber sheet obtained by vulcanization molding while applying a magnetic field to a conductive magnetic rubber composition filled at a rate of 15%. 2. A total of 15 to 38% of conductive particles and magnetic particles.
The conductive magnetic rubber sheet according to claim 1, which is used in a volume percentage of. 3. The conductive magnetic rubber sheet according to claim 1, wherein the conductive particles are Ketjen black. 4. The conductive magnetic rubber sheet according to claim 1, wherein the magnetic particles are ferrite. 5. The conductive magnetic rubber sheet according to claim 1, wherein both the conductive particles and the magnetic particles have a particle size of about 5 μm or less. 6. The particulate conductive magnetic material composition is about 30 to 150 μm.
The conductive magnetic rubber sheet according to claim 1, which has a particle diameter of m.