JPH0762241A - Electrically-conductive silicone rubber composition - Google Patents

Abstract

PURPOSE:To obtain the subject composition having high electrical conductivity and excellent viscosity and processability. CONSTITUTION:This electrically-conductive silicone rubber composition is obtained by blending a polyorganosiloxane composition with furnace black having 40-150ml/100g DELTADBP and 250-400nm Dmod diameter (aggregate mode diameter) as an electrically-conductive filler.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a conductive silicone rubber composition.

[0002]

2. Description of the Related Art Conventionally, a silicone composition which is cured to give a silicone rubber has been well known.
It is widely used as a potting material for electric and electronic parts, a coating material, a molding material for molding, etc. by utilizing its excellent properties such as heat resistance, cold resistance and electric insulation. In addition, a silicone composition, which is originally an insulating material, is also used by imparting conductivity.

As a method of imparting conductivity to the silicone composition as described above, a method of blending conductive carbon black is generally used. That is, as such carbon black, acetylene black, Ketjen black, etc. are mainly used.
It has the advantages of being lighter and cheaper than metal.

[0004]

However, in a system containing these carbon blacks, if a large amount is added in order to obtain high conductivity, the viscosity becomes too high and the workability is remarkably lowered. Due to the strong surface activity of carbon black, the crosslinking agent does not act effectively and it becomes difficult to obtain a stable vulcanized product. Even if an attempt was made to obtain higher conductivity, there was a physical upper limit to the amount of carbon black compounded, and there was a limit to the volume resistivity obtained. There is a difficulty.

[0005]

Therefore, the present inventors have
In order to solve the above problems, various studies have been made and the present invention has been achieved. That is, the present invention provides a polyorganosiloxane composition with a conductive filler of ΔDBP 40 to 150 m.
1/100 g, Dmod diameter (aggregate mode diameter) 250 to
The gist is a conductive silicone rubber composition containing 400 nm furnace black.

The present invention will be described in detail below. First, the polyorganosiloxane composition in the present invention becomes a rubber elastic body by curing at room temperature or by heating, and comprises (a) a polyorganosiloxane base polymer, (b) a curing agent, and if necessary. And various additives and the like are uniformly dispersed. Among various components used in such a composition, the (a) polyorganosiloxane base polymer and (b) curing agent are appropriately selected according to the reaction mechanism for obtaining the rubber elastic body. As the reaction mechanism, (1) a crosslinking method using an organic peroxide vulcanizing agent, (2) a condensation reaction method, (3) an addition reaction method, etc. are known, and depending on the reaction mechanism, (a) It is well known that the preferred combination of component and component (b), i.e. the curing catalyst or crosslinking agent, is determined.

The organic group in the polyorganosiloxane as the base polymer of the component (a) used in such various reaction mechanisms is a monovalent substituted or unsubstituted hydrocarbon group, such as a methyl group, an ethyl group, Propyl group, butyl group, hexyl group, alkyl group such as dodecyl group, aryl group such as phenyl group, β-phenylethyl group, unsubstituted hydrocarbon group such as aralkyl group such as β-phenylpropyl group and , Chloromethyl group, 3,3
Substituted hydrocarbon groups such as a 3-trifluoropropyl group are exemplified. Incidentally, a methyl group is generally used because of its easiness of synthesis.

The (a) polyorganosiloxane base polymer and the (b) curing agent in the respective reaction mechanisms (1) to (3) will be described below. First, in the case of applying the crosslinking method of (1) above, usually,
As the base polymer of the component (a), a polyorganosiloxane in which at least two of the organic groups bonded to silicon atoms in one molecule are alkenyl groups such as vinyl, propenyl, butenyl, and hexenyl are used. Of these groups, the vinyl group is particularly preferred because it is easy to synthesize and the raw materials are easily available. Further, as the curing agent of the component (b), benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, dicumyl peroxide, cumyl-
t-butyl peroxide, 2,5-dimethyl-2,5-
Various organic peroxide vulcanizing agents such as di-t-butylperoxyhexane and di-t-butylperoxide are used,
Since it gives a particularly low compression set, dicumyl peroxide, cumyl-t-butyl peroxide, 2,5-
Dimethyl-2,5-di-t-butylperoxyhexane and di-t-butylperoxide are preferred. In addition, these organic peroxide vulcanizing agents are used as one kind or as a mixture of two or more kinds.

The blending amount of the organic peroxide which is the curing agent of the component (b) is preferably 0.05 to 15 parts by weight with respect to 100 parts by weight of the polyorganosiloxane base polymer of the component (a). If the content of the organic peroxide is less than 0.05 parts by weight, the vulcanization is not carried out sufficiently, and if it is more than 15 parts by weight, there is no further remarkable effect, and the silicone rubber obtained is This is because the physical properties may be adversely affected.

When the condensation reaction of the above (2) is applied, a polyorganosiloxane having hydroxyl groups at both ends is used as the base polymer of the component (a). As the curing agent of the component (b), first, as a cross-linking agent, ethyl silicate, propyl silicate, methyltrimethoxysilane, vinyltrimethoxysilane, methyltriethoxysilane, vinyltriethoxysilane, methyltris (methoxyethoxy) silane, vinyltris ( Alkoxy type such as methoxyethoxy) silane and methyltripropenoxysilane; acetoxy type such as methyltriacetoxysilane and vinyltriacetoxysilane; methyltri (acetoneoxime) silane, vinyltri (acetoneoxime) silane, methyltri (methylethylketoxime) silane, Examples thereof include vinyltri (methylethylketoxime) silane and the like, and partial hydrolysates thereof. Hexamethyl-bis (diethylaminoxy)
Cyclotetrasiloxane, tetramethyldibutyl-bis (diethylaminoxy) cyclotetrasiloxane, heptamethyl (diethylaminoxy) cyclotetrasiloxane, pentamethyl-tris (diethylaminoxy) cyclotetrasiloxane, hexamethyl-bis (methylethylaminoxy) cyclotetrasiloxane, Cyclic siloxanes such as tetramethyl-bis (diethylaminoxy) -mono (methylethylaminoxy) cyclotetrasiloxane are also exemplified. As described above, the cross-linking agent may have a silane or siloxane structure, and the siloxane structure may have a linear, branched or cyclic structure. Furthermore, when these are used, it is not necessary to be limited to one type, and two or more types can be used in combination.

Further, among the curing agents of the component (b), the curing catalyst includes iron octoate, cobalt octoate, manganese octoate, tin naphthenate, tin caprylate, tin oleate, and other carboxylic acid metal salts; Organics such as oleate, dimethyltin dilaurate, dibutyltin diacetate, dibutyltin dioctoate, dibutyltin dilaurate, dibutyltin dioleate, diphenyltin diacetate, dibutyltin oxide, dibutyltin dimethoxide, dibutylbis (triethoxysiloxy) tin, dioctyltin dilaurate Tin compounds are used.

In the curing agent of component (b), the amount of the cross-linking agent is preferably 0.1 to 20 parts by weight per 100 parts by weight of the base polymer of component (a). If the amount of the cross-linking agent used is less than 0.1 parts by weight, the cured rubber will not have sufficient strength, and if it exceeds 20 parts by weight, the resulting rubber will be brittle, and any of them will not be practically usable. Further, the compounding amount of the curing catalyst is preferably 0.01 to 5 parts by weight with respect to 100 parts by weight of the base polymer as the component (a). If the amount is less than this, it is insufficient as a curing catalyst, and it takes a long time to cure, and the curing in the interior far from the contact surface with air becomes poor. On the other hand, if the amount is larger than this, the storage stability will decrease. As a more preferable range of blending amount,
It is in the range of 0.1 to 3 parts by weight.

As the base polymer of the component (a) in the case of applying the addition reaction of the above (3), the same base polymer as that in the above (1) is used. Also,
As the curing agent of the component (b), a platinum catalyst such as chloroplatinic acid, a platinum olefin complex, a platinum vinyl siloxane complex, platinum black, or a platinum triphenylphosphine complex is used as a curing catalyst. A polyorganosiloxane having an average number of hydrogen atoms bonded to atoms of at least 2 in one molecule is used.

In the curing agent as the component (b), the compounding amount of the curing catalyst is preferably such that the amount of platinum element is in the range of 1 to 1000 ppm with respect to the base polymer as the component (a). When the compounding amount of the curing catalyst is less than 1 ppm as the amount of platinum element, the curing does not proceed sufficiently, and even when it exceeds 1000 ppm, the improvement of the curing rate or the like cannot be expected. In addition, the amount of the cross-linking agent blended is such that the hydrogen atom bonded to the silicon atom in the cross-linking agent is 0.5 with respect to one alkenyl group in the component (a).
The amount is preferably about 4.0, more preferably about 1.0 to 3.0. When the amount of hydrogen atoms is less than 0.5, curing of the composition does not proceed sufficiently and the hardness of the composition after curing becomes low, and the amount of hydrogen atoms is 4.0. If it exceeds, the physical properties and heat resistance of the composition after curing will deteriorate.

In the conductive silicone rubber composition of the present invention, the curing mechanism and the polysiloxane base polymer are not particularly limited, but from the viewpoint of conductive properties, the addition reaction of (3) or the addition reaction of (1) is performed. It is preferable to use organic peroxide vulcanization, and it is preferable that the polysiloxane base polymer has a degree of polymerization of 1000 or more, that is, a so-called millable type. It is presumed that this is because the shearing stress during mixing is appropriate, and therefore the above-mentioned effects are more exerted by mixing.

Next, in the conductive silicone rubber composition of the present invention, ΔDBP 40 to 150 ml / 1 is added to such a polyorganosiloxane composition as a conductive sufficient agent.
Furnace black having a Dmod of 250 to 400 nm is blended. Here, ΔDBP is the DBP (dibutyl phthalate) absorption amount (JIS K-6221-198).
It means the difference between 2) and the amount of DBP absorption after compression, which is 24M ₄ DBP absorption (ASTM D3493). This Δ
DBP is selected from the range of 40 to 150 ml / 100 g, preferably 45 to 100 ml / 100 g, and more preferably 50 to 80 ml / 100 g.

The structure formed by the connection of particles is a permanently fused primary structure (aggregate).
And a secondary structure (agglomerate) aggregated by the interaction of van der Waals forces. DB here
The amount of P absorption is a value that evaluates the degree of this aggregate and the whole agglomerate, while 24M ₄ DBP is
It may be considered as a method of evaluating only aggregates.

Therefore, the difference between the two, so-called ΔDBP, can be said to be an index for evaluating the degree of agglomeration. Generally, a carbon black having a higher DBP absorption has a higher conductivity when compounded with a resin or rubber, but the viscosity of the compound becomes higher, resulting in poor processability.

As the carbon black satisfying these requirements, it is preferable to use a carbon black which has a high DBP and is apt to loosen agglomerates during kneading. Therefore, in the present invention, it is necessary to select ΔDBP from the above range. If ΔDBP is less than 40 ml / 100 g, it is difficult to obtain desired conductivity, and ΔDBP is 150 ml / 100.
If it exceeds g, the viscosity of the compound increases, which is not suitable.

Further, the Dmod of the furnace black in the present invention needs to be selected from 250 to 400 nm, preferably 270 to 320 nm. Dmod
Is a mode diameter of an aggregate (aggregate) by a centrifugal sedimentation method in a water dispersion system. The measurement is by the following method.

5 mg of dried sample was mixed with a small amount of activator and 2
Add 50 cc of 0% aqueous ethanol solution. This is dispersed by an ultrasonic disperser for 6 minutes to obtain a measurement sample. Aggregate size measuring device by centrifugal sedimentation method (UK Joyes Loebl
Manufactured by K.K.) is set at 6000 rpm, 10 ml of a spin solution (ion exchanged water) is added, and then 1 ml of a buffer solution (20% aqueous ethanol solution) is injected. Next, measurement sample solution 0.5
Add ml with a syringe to start the measurement. The maximum frequency diameter (Dmod) in the obtained aggregate distribution curve is determined.

Dm of furnace black in the present invention
If the od is less than 250 nm, the dispersibility is poor and the viscosity becomes too high, while if it exceeds 400 nm, the conductivity is lowered, which is inconvenient. As described above, the furnace black used in the present invention has ΔDBP of 40-15.
It is necessary that 0 ml / 100 g and Dmod are 250 to 400 nm, but those having the following physical property values are preferably selected.

(I) DBP absorption amount Considering viscosity, processability, conductivity and dispersibility, it is preferably 50 to 200 ml / 100 g, and optimally 100 to 100 ml.
It is 150 ml / 100 g. (Ii) Nitrogen adsorption specific surface area (N ₂ SA) (ASTMD30
37) Considering dispersibility and workability, preferably 100 m ² / g
Or less, more preferably 50 m ² / g or less, most preferably 30
m ² / g or less.

(Iii) UV Absorbance (Measurement is According to the Method Described Later) Carbon black is a carbon material which is infinitely nearly pure, but when analyzed in detail, substances that are considered to be precursors such as pyrene, naphthalene and fluoranthene are particles. Present on the surface and inside particles. UV absorbance is a measuring method for knowing the abundance of these substances, and the higher the value, the greater the amount of precursor. In the present invention, the UV absorbance is preferably 0.5 or less, and most preferably 0.1 or less, in consideration of coloring of rubber and conductivity. (Iv) True specific gravity is preferably 1.80 or more, and most preferably 1.82 or more.

The furnace black of the present invention is obtained, for example, by the following method. That is, it is possible to manufacture in a horizontal furnace, which is usually used, and in any vertical furnace black method manufacturing furnace, but preferably, a so-called vertical furnace having a cylindrical reaction furnace is used to center the hot gas in which the furnace black is suspended. It is preferable to manufacture it under the condition that it is circulated from the section toward the furnace wall.

The circulation ratio of the hot gas can be adjusted by changing the ratio of the inner air and the outer air charged circumferentially from the furnace bottom, and generally, the amount of air on the inner middle side is increased. The higher the frequency, the more frequent the circulation and the longer the residence time in the furnace. Further, the furnace black of the present invention is a furnace black obtained by using a furnace furnace for producing air, CO ₂ ,
It can also be obtained by heat treatment in an oxidizing atmosphere such as steam or an inert atmosphere such as argon.

The heat treatment may be carried out in the reaction stagnant zone in the latter stage of the manufacturing furnace, or may be a system in which the furnace black recovered from the manufacturing furnace is carried out by another apparatus. The temperature is generally 300 ° C. or higher and is not particularly limited. However, if the temperature is too high, problems such as hard agglomerates and development of grain surface roughness may occur. It is below ℃. On the other hand, the treatment time is determined in combination with the temperature so as to keep the specific surface area within a desired range, but as a rough guideline, 300 to 600 ° C. is on the order of hours, 700 to 10 ° C.
00 ° C is on the order of minutes, and 1000 to 1300 ° C is on the order of seconds to milliseconds.

In the present invention, when the furnace black is blended with the polyorganosiloxane composition, a kneader such as a kneader, Banbury mixer or open roll, which is commonly used, can be used. The blending amount of the furnace black is arbitrarily selected depending on the degree of polymerization of the polysiloxane base polymer and the characteristics of the silicone rubber to be obtained, and is not particularly limited,
Generally, 1 to 300 parts by weight per 100 parts by weight of the polyorganosiloxane base polymer of the component (a) described above,
It is preferably used in the range of 10 to 150 parts by weight.

The conductive silicone rubber composition of the present invention may optionally contain various additives such as a reinforcing filler, a heat resistance improver, a flame retardant and a foaming agent. Examples of such fillers are usually fumed silica, precipitated silica, reinforcing filler such as diatomaceous earth, aluminum oxide,
Examples thereof include mica, clay, zinc carbonate, glass beads, polydimethylsiloxane, alkenyl group-containing polysiloxane, polysilsesquioxane and the like.

[0030]

EXAMPLES The present invention will now be described in more detail with reference to Examples and Reference Examples. In addition, "part" shows a "weight part."
The UV absorbance, Williams plasticity and volume resistivity are measured by the following methods.

(I) UV Absorbance The sample is dried in a constant temperature oven (105 ± 2 ° C) for 1 hour and cooled to room temperature in a desiccator. 3.00g sample in 100ml Erlenmeyer flask with no stopper
Weigh out. 30 ml of toluene into the Erlenmeyer flask containing the sample
In addition, stopper the flask and immediately shake vigorously by hand for 60 seconds. Filter through filter paper that has been dried at 105 ° C. (For filter paper, two types specified in JIS P3801 are used.) The absorbance of the filtrate is measured. The absorbance is the value obtained by performing the operations in (1) to (Blank test) without using a sample. After checking 0-100%, the filtrate is put into a flow cell and the absorbance is measured. Read absorbance to 0.001. The absorbance at a measurement wavelength of 336 mμ of the spectrophotometer is measured. (Device used "Hitachi U-1100") Absorbance records up to 0.01.

(II) Williams Plasticity The method is shown in JIS K6300 "Unvulcanized Rubber Physical Test Method". However, the test temperature is room temperature, and no preheating is performed.

(III) Volume resistivity The resistance value was calculated by measuring the voltage value by the constant current application method. As a tester, "Digital Multimeter R6871E" manufactured by Advantest Corporation was used.

Reference Examples 1 and 2 (Production of furnace blacks A and B) Using a vertical furnace having a cylindrical reaction furnace, furnace blacks were formed under the conditions shown in Table 1, and the conditions shown in Table 1 from the furnace bottom. Furnace blacks A and B were obtained by introducing air into the furnace and rotating it from the center toward the furnace wall. The characteristic values of the obtained furnace blacks A and B are also shown in Table 1.

Reference Example 3 1 kg of the furnace black A obtained in Reference Example-1 was filled in a SUS drum having an inner diameter of 400 mm and a length of 700 mm, and was rotated while flowing CO ₂ of 1 m ³ / min.
It was treated at 0 ° C. for 16 hours. The characteristic values of the obtained furnace black C are shown in Table 1.

[0036]

[Table 1]

Examples 1 to 3 and Comparative Examples 1 to 4 Vinyl group-containing polydimethylsiloxane 100 having dimethylvinylsilyl groups at both ends and containing 0.30 mol% of methylvinylsiloxane units and an average degree of polymerization of about 6500.
Part of any of the furnace blacks A to G (characteristic values of the furnace blacks D to G used as comparative examples are shown in Table 1) was charged in a kneader at a ratio of 70 parts and kneaded, and then, as a crosslinking agent, 2,5 -Dimethyl-2,5-di-t
-Butyl peroxyhexane 1.5 parts was charged and uniformly mixed to obtain a silicone rubber composition. First, measure the Williams plasticity (normal temperature) of this compound, then
A sheeting property test was performed to compare the processability of each compound.

The electrical conductivity was also evaluated by measuring the volume resistivity of a 1 mm thick sample sheet made from each silicone rubber composition. The sample sheet was prepared by press-vulcanizing at 170 ° C. for 10 minutes after forming the sheet and then performing hot air vulcanization at 200 ° C. for 4 hours as secondary vulcanization. The results of these measurements are shown in Table 2 together with the composition of each composition.

[0039]

[Table 2]

1) Polydimethylsiloxane having a vinyl group content of 0.30 mol% and an average degree of polymerization of 6500 2) 2,5-dimethyl-2,5-di-t-butylperoxyhexane 3) 8 of the compound obtained Inch, wrapped around a two-roll roll, shrinking the gap, and noted the thinnest sheet thickness at which sheeting was possible. The roll was not heated and cooled. The gap adjustment was tested by shrinking in units of 0.5 [mm] up to 1.0 [mm], and shrinking in units of 0.05 [mm] from 1.0 [mm].

Examples 4 to 6 and Comparative Examples 5 to 8 In a universal stirrer having a volume of 3 liters, 100 parts of polymethylvinylsiloxane having dimethylvinylsilyl groups at both ends and a viscosity of 10,000 cp at 25 ° C., furnace black Composition A was prepared by adding 30 parts of any of A to G and 200 parts of toluene and stirring for 2 hours. These were measured with a tube gauge to confirm the dispersed state of carbon.

Next, with respect to 100 parts of this composition A, trimethylsilyl groups were used at both ends, and the viscosity at 25 ° C. was 2
A silicone ink was prepared by mixing 1 part of 0 cp of methylhydrogenpolysiloxane and a solution of chloroplatinic acid in isopropyl alcohol so that the amount of platinum atom was 5 ppm and uniformly dispersing the mixture. To check the conductive performance,
Each ink has a dry coating thickness of about 50 μm on PET film
Was applied so that 20 in an oven at 80 ° C
After pre-drying for 1 minute, it was placed in an oven at 200 ° C. for 1 hour to complete crosslinking. Then, after standing, the volume resistivity was measured at room temperature. The results are shown in Table 3.

[0043]

[Table 3]

[0044]

According to the present invention, high conductivity is maintained,
Moreover, it is possible to obtain a conductive silicone rubber composition having good viscosity and processability. Such conductive silicone rubber compositions are used for rubber switching of liquid crystal elements, calculators, remote control transmitters, etc., conductive rollers for OA equipment such as copiers, facsimiles, laser beam printers, static elimination blades, EMI shield parts, conductive inks. It is also useful as a material such as a conductive adhesive, a top coat conductive paint for a roller, and the like.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Katsuharu Honda 370 Enzo, Chigasaki City, Kanagawa Mitsubishi Kasei Co., Ltd. Chigasaki Plant

Claims (1)

[Claims] 1. A polyorganosiloxane composition containing 40 to 150 ml / 100 g of ΔDBP as a conductive filler.
A conductive silicone rubber composition prepared by blending furnace black having a Dmod diameter (aggregate mode diameter) of 250 to 400 nm.