JPS6178865A - Silicone rubber composition - Google Patents

Abstract

PURPOSE:To obtain a silicone rubber compsn. which is pure white and is not yellowed, by blending an organopolysiloxane, a reinforcing silica filler, a white pigment, an oxazole fluorescent brightener and an org. peroxide. CONSTITUTION:A silicone rubber compsn. consists of 100pts.wt. organo polysiloxane (A) of the formula (wherein R is an unsubstituted or substd. mono- valent hydrocarbon groups ; a is 1.90-2.05), 5-100pts.wt. reinforcing silica filler (B) having a specific surface area of 50m<2>/g or above, 0.1-50pts.wt. while pigment (C), 0-0.02pts.wt. blue pigment (D), 0.005-0.5pts.wt. oxazole fluorescent brightener (E) and 0.1-5pts.wt. org. peroxide (F). The blue pigment has an effect of improving the effect of the white pigment, and is an optional compo nent and used in an amount of 0.02pts.wt. or below per 100pts.wt. component A. Examples of the blue pigments are ultramarine and cobalt blue.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a silicone rubber composition, and particularly to a silicone rubber composition that provides pure white silicone rubber molded articles that do not yellow.

(Prior Art) Silicone rubber molded products are tasteless, odorless, nontoxic, and inert, and are therefore widely used in foods, cosmetics, medical products, and the like. In addition, silicone rubber uses silica-based fillers, so it has the advantage of being able to be colored freely.

In recent years, swimming caps, underwater glasses, and goggles have become popular due to their excellent water and weather resistance.

It is also being widely applied to leisure goods such as golf grips. There is a strong demand for white molded products for the above various types of 1 m, and this is generally met by adding titanium oxide, but pure white products cannot be obtained from silicone rubber using organic peroxide as a catalyst. Moreover, even if it is obtained, there are many problems such as yellowing afterward.

Therefore, the type of organic peroxide used as a curing catalyst, which is said to be the main cause of yellowing, is selected and the amount used is reduced, and vulcanization is performed by a platinum addition reaction. Methods such as adding a small amount of blue pigment and lowering the temperature of the post-dP equipment have been used.

None of these methods give satisfactory results.Especially in the air in the low-temperature post, a new problem of harmful decomposition residue remains, and the platinum addition reaction has a limited pot life, which is disadvantageous to processability. There is.

(Structure of the Invention) The present invention relates to a silicone rubber composition cured by organic peroxide vulcanization which solves the above-mentioned disadvantages and gives a pure white silicone rubber molded article, which has the general formula -Bib, -a (where ζ is R & Engineering Jll [or a different unsubstituted or substituted monovalent hydrocarbon group, a is 1.9
Organopolysiloxane 10 represented by 0 to 2.05)
01 [Okibe, B) 5 to 100 parts by weight of reinforcing silica filler with a specific surface area of 50 tt//N or more, a) White colorant 0
．． 1 to 50 parts by weight, D) 0 to 0.02 parts by weight of blue colorant, E) 0.005 to 0.5 part of oxazole fluorescent whitening agent
Weight part.

? ) 0.1 to 5 parts by weight of an organic peroxide.

Namely, as a result of various studies on methods for obtaining pure white silicone rubber molded products that do not yellow even when vulcanized with commonly used organic peroxides, the present inventors found that titanium oxide and zinc oxide were used as white pigments. If you use a known product such as Hana, Lead White, or Litopon, and also use an oxazo-y type fluorescent whitening agent, the molded product will not only have the properties of silicone rubber, but also water and weather resistance tests. They found that the whiteness of these components was maintained, and completed the present invention by conducting research on the amount of nitrogen and blending amount of each of these components.

The organopolysiloxane as component A, which constitutes the composition of the present invention, is the main material of the present composition, and is represented by the general formula RSiO.

a4-a! This R is an alkyl group such as a methyl group, an ethyl group, a globyl group or 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, a cycloalkyl group such as a cyclohexyl group, or a cycloalkyl group such as a cyclohexyl group. Carbon atoms of the group (chloromethyl group in which part or all of the bonded hydrogen atoms are substituted with halogen atoms, cyano groups, etc., 3
,3. ) Same or different unsubstituted or substituted monovalent hydrocarbon groups selected from trifluoroglobyl group, cyanomethyl group, etc. -a is a positive number from 1.90 to 2.05, but -m sulfur Since the summer of improving efficiency and improving physical properties, this R
contains 0.025 to 3 mol % of vinyl groups, and preferably 50 mol % or more of methyl groups. This organopolysiloxane is well known to those skilled in the art as a raw material for silicone rubber, and can be easily obtained by combining acid and alkali with the corresponding cyclic low-molecular-weight siloxane.
There is no particular limit to this viscosity, but at 25°C IX10
It is preferable to use 0Bj2 as the upper gum-like material.

B] The reinforcing silica filler as a component may also be one known in the art, and representative examples include fumed silica and precipitated silica.

From the viewpoint of reinforcing effect, the specific surface area needs to have a value measured by the BET method of Sod/1 or more. Although the amount added can be varied within a wide range depending on the purpose, it is generally 5 to 100 parts by weight per 100 parts by weight of the above-mentioned ingredients.

Preferably it is 20 to 60 parts by weight.

In addition, as component a), the white pigment is considered to be an essential component since the present invention is a silicone rubber composition that provides a M white silicone rubber molded product.
Examples of this include anatase-type or rutile-type defeated titanium, zinc white, lead white, lithopone, etc., which have been conventionally added to silicone rubber, and the amount added is A] component 10.
0.1 to 50 parts by weight, preferably 1 to 20 parts by weight
is considered to be the place of residence.

D) The blue pigment as the component is used to further improve the effect of the white pigment as the O) component. However, it is not an essential component and may be added as needed in an amount of 0.02 part or less per 100 parts by weight of the component.

The oxazole-based fluorescent brightener as component E) is an essential component that is added to keep the silicone rubber molded product obtained from the composition of the present invention pure white. Illustrated. The silicone rubber composition to which this oxazole fluorescent brightener has been added can maintain its original whiteness without causing any damage during polishing, water resistance, and weather resistance tests. The amount of component E) to be added may be very small (one person) in the range of 0.005 to 0.5 part per 100 parts by weight of the component, preferably 0.0
The amount may be in the range of 1 to 0.2 parts.

In addition,? Organic peroxide as a component of
1. Any type of rubber commonly used may be used, including benzoyl peroxide, 2.4
-dichlorobenzoyl peroxide, dichlorobenzoyl peroxide, di-tert-butyl peroxide, 2.
An example is 5-dimethyl-2,5-di(t-butylperoxy)hexane, which is used in an amount of 0.1 to 5 parts by weight based on the oott part of the AJ acid component.

The composition of the present invention can be obtained by mixing predetermined amounts of the above-mentioned ingredients and kneading them uniformly. agent, flame retardant agent, fungicide.

Known additives such as adhesion improvers may optionally be added.

Next, an example of the present invention will be described. The part in one example shows the iW part, and this whiteness was measured using a digital colorimeter C.
P6-1001DP (product name developed by Nippon Denshoku Kogyo Co., Ltd.) was used for measurement, and from the values obtained, the formula % formula %) proposed by Hunter in the 1958 US JOBA January 0 issue was calculated. , b is displayed digitally on the above measuring instrument]
This is what I asked for.

Example 1 100 parts of dimethylpolysiloxane raw rubber containing 0.2 mol% of vinyl groups, 35 parts of fumed silica with a specific surface of fi200//i, and 3 parts of diphenylsilanediol as a silica dispersant! Add 0.3 parts of titanium chloride and kneader
Heat mix the base compound (referred to as base person) in
along with adjusting.

100 parts of the above dimethylpolysiloxane raw rubber.

40 parts of precipitated silica with a specific surface area of 180rd/If, 4 parts of dimethylpolysiloxane with a 2.5 i part of hydroxyl base, and 0.3 parts of fermented titanium were heated and kneaded in a kneader to form a base compound ( Base B and 5) were adjusted.

Tsuki VC, 100 copies each of this Base A and Pace B, and only 1.5 copies of Pennzoil Pao Medium Side? 0.02 part of benzoxazole and 1.5 parts of benzoyl peroxide were added thereto to produce a composition of the present invention.

Press vulcanize these at 120℃ for 10 minutes to a thickness of 2s+
I made a sheet of T and spent 4 hours on Kzooc.

Alternatively, the sheet was post-cured at 250C for 4 parts, and the whiteness (W) of this sheet was measured.

The IJ results shown in Table 1 were obtained.

Example 2 Add 4!0 benzoxazole to base A prepared in Example 1.
．． 005 part, 0.01! It, 0.05 part, 0.1
Department.

A sheet was prepared in the same manner as in Example 1 from a composition in which 0.5 parts of benzoyl peroxide was added and 1.5 parts of benzoyl peroxide was added, and the whiteness of the sheet was subjected to Bostairing at 200°C for 4 hours. (W) was measured and found to be as shown in Table 2. 2 parts of Azovy-based tyronitrile was added to Base A prepared in Example 1 to form a foamable composition (W).
Make a base O) and add to it the amount of benzoxazole shown in Table 3. lj suitable peroxide 2QQ"C1 was added, and this was foamed and vulcanized in an open air at 10°C for 1 hour to explode a silicone rubber sponge about 3 cm thick,
When we measured the whiteness (CW) of these, we found that
The results shown in the table were obtained.

Example 5 100 parts of Pace made in Example 1 with 0.001 part of Nine Ultramarine added thereto was used as Base D, and sheets were made in the same manner as in Example 1 by adding various organic peroxyacids to this. A comparison of the whiteness (W) of molded products with and without the addition of benzoxazole upon post-vulcanization resulted in the results shown in Table 4.

In addition, 2,5-dimethyl-2,5-di(t
-butylperoxy)hexane and vulcanization, 20
When the whiteness (W) of a sheet that had been vulcanized at 0°C for 74 hours and exposed to a Sunshine Queza-Ometer for 200 hours was measured, the whiteness (W) of the sheet without benzoxazole was 81.5. The item is 85.
It showed a value of 1.

Claims (1)

[Claims] 1. A) with the general formula R_aSiO_4_-_a^/^2 (wherein R is the same or different unsubstituted or substituted monovalent hydrocarbon group, and a is 1.90 to 2.05); 100 parts by weight of the indicated organopolysiloxane B) 5 to 100 parts by weight of a reinforcing silica filler with a specific surface area of 50 m^2/g or more C) 0.1 to 50 parts by weight of a white colorant D) 0 parts by weight of a blue colorant ~0.02 parts by weight E) 0.005 to 0.5 parts by weight of an oxazole fluorescent brightener F) 0.1 to 5 parts by weight of an organic peroxide.