JPS63356A - Silicone rubber composition - Google Patents

Abstract

PURPOSE:To provide the title compsn. which gives cured products having excellent resistance to electricity and no microvoid, consisting of a specified organopolysiloxane, a pulverized silica filler and an org. peroxide such as o- methylbenzoyl peroxide, etc. CONSTITUTION:100pts.wt. organosiloxane (A) having a degree of polymn. of not lower than 3,000 and 0.02-2.0mol% of an alkenyl group per molecule, represented by formula II [wherein R<2> is a (substd.) monovalent hydrocarbon group; and b is a number of 1.95-2.05] wherein both terminals of its molecular chain are blocked with a divinylorganosiloxy or trivinylsiloxy group of formula I (wherein R<1> is CH3, C2H5 or phenyl; and a is 2 or 3) is blended with 20-100 pts.wt. pulverized silica filler (B) having a specific surface area of 100-400m<2>/g and an average particle size of 1-20mu and 0.3-3pts.wt. org. peroxide (C) of formula III [wherein X is CH3, C2H5, methoxy, ethoxy, a group of formula IV or V (wherein R<3> is H, CH3 or alkoxy) or Cl; and n is 1 or 2] (e.g., o- methylbenzoyl peroxide).

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention provides silicone rubber compositions, particularly extruded products of unsaturated group-containing silicone rubber, etc., by continuous normal pressure hot air treatment without generating voids or surface tack. The present invention relates to a silicone rubber composition that can be made into a cured silicone rubber product by vulcanization.

(Conventional technology) Silicone rubber is widely used in various fields due to its excellent heat resistance, cold resistance, and seven-dimensional properties.
Regarding the processing process, various methods have been implemented depending on the application.

Various methods are used to vulcanize silicone rubber, depending on the type of rubber and the physical properties required of the cured product, but in general, heat treatment in the presence of an organic peroxide is widely used. Examples of the organic peroxides include benzoyl peroxide, p-gloropenzoyl peroxide, 2゜4-L/glolopenzoyl peroxide, digmyl peroxide, di-butyl peroxide, and 2.5-L/gloropenzoyl peroxide. Dimethyl-2,5-di(t-butylperoxinehexane, t-butylperbenzoate,
Examples include t-butylcumyl peroxide,
2 is a vulcanizing agent for obtaining good molded products such as tubes and underlay sheets by extrusion continuous hot air vulcanization.
．． 4-dichlorobenzoyl peroxide is the only one known to be -.

However, the silicone rubber obtained by this normal pressure hot air vulcanization is a silicone rubber compound released from an extruder.
When placed in a high-temperature vulcanization furnace of ~500°C, volatile substances such as low-molecular-weight xylochitin in the compacted material gasify in the air and expand, which can be observed with the naked eye in the silicone rubber cured product obtained by C2 vulcanization. microvoids are generated,
This has the disadvantage that the withstand voltage is 10 to 30% lower than that of a sheet obtained by press vulcanization of the same rubber compound. However, although the initial physical properties and surface tackiness are improved by this secondary vulcanization, the surface tackiness is not improved by the rolling of the extruded product and the rolling process (twice a month). This may cause problems in the working environment and in post-processing.

(Structure of the Invention) The present invention relates to a silicone rubber composition that can be cured by normal pressure hot air vulcanization and solves the above-mentioned disadvantages.
'3-aS i○0.5 (wherein R1 is a methyl group, ethyl group or phenyl group, a is 2 or 3) are the same or different unsubstituted or substituted monovalent hydrocarbon groups, b
is 1.95 to 2.053, contains 0.02 to 2.0 mol% of alkenyl groups in one molecule, and has a polymerization degree of 3.
．． 100 parts by weight of an organoborin loxane of 000 or more,
2] 20 to 100 parts by weight of a fine powder filler, 3 structural formulas (5: (is a methyl group, an ethyl group, a methoxy group, an ethoxy group, a formula -3iR, -CH2SiRζ (R3) or a chlorine atom, and n is 3 to 3 parts by weight of an organic peroxide represented by ] or 2.

That is, the present inventors have conducted various studies on methods for obtaining cured silicone rubber products that do not generate microvoids and therefore have excellent electrical resistance, and have found that this silicone rubber composition Both chain ends are blocked with divinylorganosilyl group or trivinylsilyl group, with 0.02 to 240 alkenyl groups in one molecule.
Assuming that it is composed of a high molecular weight organopolysilochitin containing mol%, finely powdered silica, and an organic peroxide represented by the above structural formula, this material can be cured by hot air vulcanization at normal pressure, This vulcanization progresses faster than the gasification of volatile substances in organopolysilochitin and the generation of microvoids due to expansion, making it possible to obtain a hard silicone rubber without microvoids, and as a result, withstand voltage We have discovered that an excellent product can be obtained, and that the molded product thus obtained is free of tack even without secondary vulcanization, and therefore can be made non-tacky without powdering. According to the method, the vulcanization speed is significantly improved compared to the conventional technology (for example, when electric wires and tubes are extruded using a known vulcanization tower, the extrusion speed can be increased; When constructing a new sulfur tower, it can be made smaller and cheaper than before, which improves productivity and lowers costs, thereby improving the electrical customization of the target product. The present invention was completed by confirming that it was also possible to achieve this goal, and proceeding with research on the types and amounts of each of these components.

The organopolysiloxane as component 1) constituting the composition of the present invention may be one whose main chain is substantially composed of diorganopolysiloxane units such as those used in ordinary silicone rubber (2). a divinylorganosiloxy group in which both ends of the molecular chain are represented by the formula (CH=CHJ R5iOa3-aQ, 5 , R1 is a methyl group, ethyl group or phenyl group, and a is 2 or 3;
It is required to be capped with a trivinylsiloxy group. Additionally, this organopolysiloxane has the formula
Rb 310 2, and this R2 is an alkyl group such as a methyl group, an ethyl group, a propyl group, a butyl group, an alkenyl group such as a vinyl group or an allyl group, an aryl group such as a phenyl group or a tolyl group, or a nochlorohexyl group. From cycloalkyl groups, or glolomethyl groups, 3,3,3-trifluoropropyl groups, cyanoethyl groups, etc. in which part or all of the hydrogen atoms bonded to the carbon atoms of these groups are substituted with halogen atoms, cyano groups, etc. selected same or different unsubstituted or substituted monovalent hydrocarbon groups, b is 1.9
It is assumed to be a positive number from 5 to 2.05, and usually 50% or more of the above-mentioned R2 is a methyl group. As mentioned above, this product is substantially composed of diorganopolysiloxane units, but it may also contain small amounts of triorganosiloxane units, monoorganosiloxane units, and 810 units. , which requires that 0602 to 2 mole percent of the total organic groups contain alkenyl groups such as vinyl groups.

In addition, since this organopolysiloxane is the main material of silicone rubber compositions, it is said to have a relatively high molecular weight, but if the degree of polymerization is not reduced, microvoids will occur during extrusion processing, and Since the obtained cured product will have poor physical properties, it is necessary to have a degree of polymerization of 3.000 or more.

Next, the fine powder adhesive filler 41 as the component 2 in the composition of the present invention may be a known material used for reinforcing silicone rubber, and these 12 may include humutonica,
Examples include 1' formula silica and calcined silica, which may be used as they are, or may be surface-treated with organochloroduran, organopolysiloxane, organozoladen, etc. may be surface-treated by mixing with the organopolysiloxane described above in 1) 5 to 2 minutes and then heating and kneading. In addition, this material usually has a specific surface area of 100 to 400 m2/P and an average particle size of 1 to 2 by the BET method.
Although it is said to be about 0 mμ, these may be used in combination with quartz powder, celite, calcium carbonate, alumina, zinc white, iron oxide, graphite, etc. as semi-reinforcing fillers. Note that if the amount of this fine powder silica filler is less than 20 parts by weight and more than 100 parts by weight based on 100 parts by weight of the above-mentioned organoborin loxane, the physical properties of the cured silicone rubber obtained from it will be inferior. 20-10
A range of 0 parts by weight is required.

Further, the organic peroxide as component 3) in the composition of the present invention has the structural formula Xn
n, and X is a methyl group, ethyl group, methoxy group, ethoxy group, formula -3iR-, -0H2SiR; (R3
is a group selected from a hydrogen atom, a methyl group or an alkoxy group, or a chlorine atom, n is 1 or 2, and this includes O-monochlorobenzoyl peroxide, ○-methylbenzoyl peroxide, 2,4-dichloro Convex benzoyl peroxide, 2゜4-dimethylbenzoyl peroxide, P-monochlorobenzoyl peroxide, bis(orthocherpenzoyl peroxide),
Examples include bis(orthomethoxybenzoyl) peroxide and bis(orthoethoxybenzoyl coperoxide).

The amount of this compound added is 1) If it is less than 0.3 parts by weight per 100 parts by weight of organoborisicoxane as a component, the vulcanization of this composition will not be sufficiently carried out, and if it is more than 3 parts by weight, vulcanization will not occur. Since the physical properties of the obtained silicone rubber are adversely affected by this, it is necessary to set the amount in the range of 0.3 to 3 parts by weight.

The composition of the present invention can be obtained by uniformly mixing predetermined amounts of the above-mentioned components 1) to 3 (2).
A silicone rubber compound is prepared by mixing a glue filler for y, and heating if necessary, and then adding an organic peroxide for 3) 5SE to this, and using a two-roll, kneader, etc. You can try kneading it, but
At this time, it is optional to add a low molecular weight organosiloxane having a C diacid group or an alkoxy group at the molecular chain end or a coloring agent as a processing aid.

The composition of the present invention thus obtained is made into a ballistic cured product by heating and vulcanizing, but since this composition contains the above-mentioned organic peroxide, it cannot be heated under normal pressure. Can be continuously cured by vulcanization. This vulcanization can be carried out, for example, by extrusion molding the composition to form a tube C2 or coating it on an electric wire, and then calendering it to form a sheet or the like. Vulcanization is sufficient, but if the temperature is below 200°C, vulcanization will be delayed and microvoids will occur, and if it is above 550"C, overvulcanization will occur and surface cracks will occur, so please adjust the temperature of the heating furnace. The temperature is 200550°C, and the residence time is preferably in the range of 5 to 50 seconds.
It has the same industrial advantages in that it is easy to obtain molded products that do not require dusting because it has no surface tack and does not require dusting.

Next, examples of the present invention will be given. The parts in the examples show important parts, and the viscosity shows the measured value at 25°C. The measured values in the examples show the measurement results by the following method. It is something that

[Vulcanization properties]

120 using a disc rheometer [manufactured by Toyo Seiki]
℃, and the torque was measured at a deflection angle of ±3°.

[Presence or absence of microvoids]

A silicone rubber composition as a sample was extruded into a rod with a diameter of 6 TOmφ using an extruder with a diameter of 40 mm, and the rod was passed through a 380° C. vulcanization furnace for a residence time of 13 seconds to be vulcanized in hot air at normal pressure. The cross section of the obtained cured product was magnified 100 times with an optical microscope to confirm the presence or absence of microvoids.

[Dielectric breakdown strength]

Using a silicone rubber assembly 5'i as a sample, a tin-plated annealed copper wire with a diameter of 0.6 mm was made using an extruder with a diameter of 40 mm. °C230
Ten samples were made from this and subjected to a dielectric strength test in water using the method of J.E.C. SC-3004 (double method).

Examples 1 to 2, Comparative Example 1 Both ends of the molecular chain were blocked with (CH22CHn, 5ino,, units, (CH312SiO units 99.68 mol%)
, CH3CCH2=CH)SiO unit 0.3 mol%, (
100 parts of organopolysiloxane with a degree of polymerization s, ooo consisting of 0.02 mol% of OH2=OH)3Sin65 units, 53 parts of fumed silica with a specific surface area of 200 dl, 3 parts of diphenylsilanediol, and α with a viscosity of 20C8.
, adding 6 parts of ω-dimethylborinoxanediol,
After homogeneously kneading in a kneader, a silicone rubber compound was prepared by heat treatment at 160°C for 3 hours, and then 100 parts of this compound (2, 1 part of 50% silicone oil paste of 2,4-diglolopenzoyl peroxide) was added.
5 parts were added and kneaded using two rolls to prepare silicone rubber composition-I.

In addition, organopolysiloxane with the same composition except that both ends of the molecular chain are blocked by units of (CH2=CH], 0H8s1oo, and contains 0.02 mol% of the above organopolysiloxane) This is treated in the same manner as above to prepare a silicone rubber composition-t[, and for comparison, both ends of the molecular chain are (CH,)2(OH
2=CH)SiOo,,blocked in units,ICH5)
2SiO units 99.64 mol%, CH3(OH2=OH
)8 parts 0 units α34 mol%, (CI(3)2(CH2=
Using CHJSin (organopolysiloxane with a polymerization degree of 8.00 and consisting of 0.02 mol % per part unit), this was treated with C2 in the same manner as above to form a silicone rubber composition -■
made.

Next, this silicone rubber composition r~■ was extruded into two rods ζ with a diameter of 6 m x φ using an extruder with a diameter of 40 mm.
When this was cured by hot air vulcanization at normal pressure at 380° C. for 13 seconds, the results as shown in Table 1 were obtained regarding the vulcanization characteristics and the presence or absence of microvoids.

Table 1 Example 3 The silicone rubber compositions M products M to ■ made in Example 1.2 and Comparative Example 1 were prepared using an extruder with a diameter of 40 mm to form a plated mild steel plated with a diameter of 0.6 mm. The outer diameter of the wire is 1.
Make an electric wire of 2 diameter diameter, vulcanization temperature 450℃, residence time 30
The silicone rubber composition was cured by hot air vulcanization at normal pressure for 2 seconds, and a withstand voltage test was conducted on two of the wires obtained in this way, and the results were as shown in Table 2. It was confirmed that the silicone rubber composition of the present invention had a higher withstand voltage than that of the comparative example.

When the wire-processed molded product thus obtained was wound up and rewound, it was found that in the case of the product made from silicone rubber composition-I, the wires stuck to each other during unwinding, making the winding difficult. It was necessary to apply dusting powder for unrolling, but those made from silicone rubber compositions (1) and (2) could be easily undone without applying dusting powder.

Table 82 Example 4, Comparative Example 2 Organic peroxide (50% silicone oil paste of 2,4-diglolopenzoyl peroxide) in Composition I and ■ as Example 1 and Comparative Example 1 described above)1. 5 parts was changed to 1.5 parts of 50% silicone oil paste of ○-methylbenzoyl peroxide. When the dielectric breakdown strength was examined, the results shown in Table 3 below were obtained.

Table 3

Claims (1)

[Claims] 1, 1) Both ends of the molecular chain are (CH_2=CH)_aR^1
_3_-_aSiO_0_. Formula R^2_bSiO(_4_
-_b_/_2) (here, R^2 is the same or different unsubstituted or substituted monovalent hydrocarbon group, b is 1.95 to 2.0
5), 0.02 to 0.02 alkenyl groups in one molecule
100 parts by weight of organopolysiloxane containing 2.0 mol% and having a degree of polymerization of 3.000 or more, 2) 20 to 100 parts by weight of fine powder silica filler, 3) Structural formula ▲ Numerical formulas, chemical formulas, tables, etc. are available ▼ (Here, X is a methyl group, ethyl group, methoxy group, ethoxy group, formula -SiR^3_3, -CH_2SiR^3_3
(R^3 is a hydrogen atom, a methyl group, or an alkoxy group), or a chlorine atom, and n is 1 or 2. 0.3 to 3 parts by weight of an organic peroxide A silicone rubber composition. 2. The silicone rubber composition according to claim 1, wherein the organopolysiloxane is dimethylpolysiloxane crude rubber whose molecular chain ends are capped with trivinylsilyl groups.