JPH0781075B2 - Silicone rubber composition, method for producing the same, and cured product thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention requires that the silicone rubber composition, particularly the product itself, not be yellowed, so that the product itself is transparent or white. The present invention relates to a silicone rubber composition, a method for producing the same, and a cured product thereof, which are useful for rubber contacts in desktop electronic calculators, illuminated touch-tone phones, as well as underwater eyeglass pads and nipples.

[Prior Art] Silicone rubber has excellent properties such as electric insulation, heat resistance, cold resistance, weather resistance, compression set, rubber elasticity, etc., and is non-toxic. It is used in a wide range of fields such as office equipment, automobiles, aircraft, food materials, medical materials, and leisure products. In addition to static applications, they are also widely used for dynamic applications such as rubber contacts in calculators and touch-tone phones, keyboards, automobile constant velocity joint cover boots, diaphragms, medical pump tubes, and the like.

[Problems to be Solved by the Invention] However, conventionally known silicone rubbers include dialkyl peroxides such as 2,5-bis (t-
Butylperoxy) -2,5-dimethylhexane, di-t
-If butyl peroxide, t-butyl cumyl peroxide, etc. are used, the rubber molded product will turn yellow after post-curing after molding, so use it for applications requiring transparency or whiteness. There is a disadvantage in that it is not possible, and this improvement is required.

In addition, Japanese Patent Publication No. 62-19652 describes a silica-containing organopolysiloxane having excellent storage stability.
This refers to the stability of the compounded composition and nothing to the rubber composition to be vulcanized.

[Means for Solving the Problems] The present invention relates to a silicone rubber composition, a method for producing the same, and a cured product thereof, in which such disadvantages are solved. (Wherein R is the same or different and is an unsubstituted or substituted monovalent hydrocarbon group having 1 to 10 carbon atoms, a is a number of 1.95 to 2.05), and the average degree of polymerization is in the range of 3,000 to 30,000. 100 parts by weight of organopolysiloxane, B) Reinforcing filler 10-1
00 parts by weight, C) 0.5 to 5 parts by weight of dialkyl peroxide, D) 0.1 to 15 parts by weight of an alkaline agent, and a silicone rubber composition, and A), B),
After heat treating the mixture of component D) at 100 to 200 ° C,
The gist is a method for producing a silicone rubber composition obtained by adding the component C), and a cured product obtained by curing the composition.

That is, as a result of various investigations by the present inventors on various measures for preventing yellowing after molding of a silicone rubber composition containing a dialkyl peroxide, the above A), B), and C) containing dialkyl peroxide as a curing agent When an alkaline agent such as the above-mentioned component D) is added to the known silicone rubber composition to neutralize the acidity in the system, the by-product of the conjugated compound which has been conventionally the cause of yellowing is prevented. Therefore, it was found that yellowing of the silicone rubber composition after molding was prevented, and the present invention was completed by conducting research on the constitution of the component D) used here.

This will be described in more detail below.

[Operation] The present invention relates to a silicone rubber composition which prevents yellowing after molding of a silicone rubber composition containing a dialkyl peroxide as a curing agent, a method for producing the same, and a cured product thereof.

The silicone rubber composition of the present invention neutralizes the acidity in the silicone rubber by the addition of an alkaline agent in order to prevent yellowing after molding. As the component A) constituting the silicone rubber composition, The average composition formula of diorganopolysiloxane is And R is a methyl group, an ethyl group, a propyl group,
Alkyl group such as butyl group, alkenyl group such as vinyl group, allyl group, butenyl group, aryl group such as phenyl group and tolyl group, some or all of hydrogen atoms bonded to carbon atoms of these groups are halogen atoms, A chloromethyl group substituted with a cyano group or the like, a chloropropyl group, a 3,3,3-trifluoropropyl group, a 2-cyanoethyl group, or the like having the same or different carbon number of 1 to 10, preferably 1 ~ 8 unsubstituted or substituted monovalent hydrocarbon groups, 98 mol% or more of which is an alkyl group having 1 to 4 carbon atoms, especially a methyl group, and groups other than such alkyl groups include vinyl groups and phenyl groups. A 1,3,3,3-trifluoropropyl group is preferable, and a is 1.95 to 2.05. This diorganopolysiloxane preferably has a linear molecular structure, but it may partially contain a branched molecular structure, and this product has a degree of polymerization of 3,00
The degree of polymerization is preferably in the range of 0 to 30,000, but the degree of polymerization is preferably in the range of 4,000 to 10,000 from the viewpoint of processability.

Next, the reinforcing filler as the component B) which constitutes the silicone rubber composition of the present invention may be a known filler which has been conventionally used for reinforcing a silicone rubber. Silica, silica aerogel, etc. are exemplified, but it is preferable that they have a specific surface area of at least 50 m ² / g because of their reinforcing properties. The surface of the reinforcing filler is trimethylsilyl group [(CH
₃ ) ₃ SiO _0.5 ], dimethylsilyl group [(CH ₃ ) ₂ SiO], monomethylsilyl group [CH ₃ SiO _1.5 ], diphenylmethylsilyl group [(C ₆ H ₅ ) ₂ (CH ₃ ) SiO _0.5 ], etc. It may be treated with the contained silane, siloxane, silazane or the like.

The amount of the reinforcing filler added was 10 parts by weight based on 100 parts by weight of the diorganopolysiloxane as the component A).
If it is less than part by weight, it is too small and the reinforcing effect is not sufficient,
If the amount is more than 100 parts by weight, the processability of the obtained rubber composition will be poor, so the range of 10 to 100 parts by weight is preferable.

Further, the dialkyl peroxide as the component C) constituting the silicone rubber composition of the present invention is used as a curing agent for curing the silicone rubber composition, which can generate acetone upon decomposition. And di-t-butyl peroxide, t-butyl cumyl peroxide, 2,2'-bis (t-butylperoxy-m-isopropyl) benzene, 2,5-dimethyl-2,5 -Di (t-butylperoxy) hexane, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane and the like are exemplified, but these can be used alone or in combination of two or more kinds. . The compounding amount of these substances may be in a generally known range, and therefore, it may be in a range of 0.5 to 5 parts by weight with respect to 100 parts by weight of the diorganopolysiloxane as the component A).

Component D) which constitutes the silicone rubber composition of the present invention is for making the composition of the present invention alkaline to prevent yellowing after molding, which is an alkaline substance. However, this may be a dispersion liquid of an inorganic salt machine, an organic base or a filler treated with an alkali.

The inorganic base is sodium hydroxide, potassium hydroxide or an aqueous solution thereof, and the organic base is alkali metal silanolates such as sodium silanolate and potassium silanolate, and alkali metal alcoholates such as sodium methylate and sodium ethylate. As an example of the filler dispersion, a silica-based filler which has been conventionally used as a reinforcing filler for silicone rubber is treated with a sodium hydroxide solution or silazane, or the surface thereof is treated with an amine. For example, a dispersion prepared by mixing alkaline with water to make a dispersion of which 4% of the pH is 7 or more is exemplified.
For the dispersion of this filler, Nipsil NA, Nipsil ES,
It may be commercially available under the trade name of NIPSIL G-300 [all are trade names manufactured by Nippon Silica Industry Co., Ltd.].

The amount of the alkaline agent added is 100 g of the diorganopolysiloxane as the component A) and an alkali OH.
It is in the range of 1.0 × 10 ^{-4 to} 2.0 × 10 ^-1 mol, preferably 1.
Since it may be in the range of 0 × 10 ^{−3 to} 2.0 × 10 ⁻² mol, if the range is 0.1 to 15 parts by weight with respect to 100 parts by weight of the diorganopolysiloxane as the component (A). Good.

The silicone rubber composition of the present invention can be obtained by uniformly mixing the predetermined amounts of the above-mentioned components A) to D), and a low molecular weight siloxane having a polymerization degree of 100 or less and a silanol group-containing silane. , Dispersants such as alkoxy group-containing silanes, heat resistance improvers such as iron oxide, cerium oxide, iron octylate and titanium oxide, pigments for coloring, flame retardant auxiliaries such as platinum compounds and palladium compounds, and the like Various additives that are usually added to the silicone rubber composition can be added arbitrarily.

The production of this silicone rubber composition is facilitated by uniformly kneading a predetermined amount of the components A) to D) using a kneading device such as a two-roll, kneader, pressure kneader, Banbury mixer or continuous kneader. Although it can be carried out, in this production, the components A), B) and D) and the components optionally blended as described above are uniformly kneaded by using the above-mentioned apparatus, and then this is mixed with 100 ~ 200 ° C
It is preferable to heat-treat for about 5 minutes to 4 hours, and then add a curing agent as the component C) to and mix with it, which is advantageous in that the effect of adding the component D) is sufficiently exhibited. Is given.

It is also possible to knead a predetermined amount of the components A) and B) in the above apparatus first, heat-treat them, and then add and mix the components C) and D).

The silicone rubber composition of the present invention thus produced contains a dialkyl peroxide as a component C). This dialkyl peroxide is decomposed during vulcanization of the silicone rubber to produce acetone as a by-product. This is aldol-condensed to a condensate by using the filler in the silicone rubber as a catalyst, and when this system is acidic due to the influence of silica, it is dehydrated and becomes a conjugated compound. Although it is believed that this occurs, the silicone rubber composition of the present invention contains an alkaline substance as component D), which neutralizes the system, so that there is no formation of a conjugated compound due to this dehydration. Therefore, it is presumed that the occurrence of yellowing is prevented, but this yellowing is caused by the use of precipitated silica as a reinforcing filler. Since there is a particularly remarkable when the effect of the present invention is markedly observed when using precipitated silica as a reinforcing filler.

[Examples] Next, examples of the present invention and comparative examples will be given. The parts in the examples are parts by weight, and the physical properties of the silicone rubber elastic body obtained in the examples are in accordance with JIS K-6301. It shows the measurement results by the method according to the above.

Examples 1 to 4, Comparative Example 1 (CH ₃ ) ₂ SiO unit 99.85 mol%, CH ₃ (CH ₂ = CH) SiO unit 0.
It is composed of 15 mol% and the molecular chain end is (CH ₂ = CH) (CH ₃ ) ₂ S
100 parts of methyl vinyl polysiloxane raw rubber with a degree of polymerization of about 5,000 blocked with _0.5 unit of iO, 40 parts of wet silica / Nipsil LP [trade name of Nippon Silica Industry Co., Ltd.], both molecular chains as a dispersant 3 parts of a dimethylpolysiloxane containing a hydroxyl group at the end and having a degree of polymerization of 18 and 0.5 part of 1N-NaOH as an alkaline agent were added and uniformly mixed in a kneader, followed by heat treatment at 150 ° C. for 2 hours to give a silicone rubber composition. While making the product I, 2N-N instead of 0.5 part of this 1N-NaoH
Add 0.1 part of aOH to add Silicone Rubber Composition II to Mg (O
H) _2. Kisuma 5AN (trade name of Kyowa Chemical Co., Ltd.) is added to 3 parts to obtain Silicone rubber composition III, and the average structural formula is Silicone rubber composition IV was prepared by adding 1.0 part of sodium silanolate / Na-T silanolate (trade name, manufactured by Shin-Etsu Chemical Co., Ltd.) containing a T unit represented by (n = 3 to 20), and further for comparison. A silicone rubber composition V was prepared in the same manner as above except that no alkaline agent was used.

Then, the silicone rubber compositions I to V were added with 2.5-bis (t-butylperoxy) -2,5-dimethylhexane 0.5.
After adding 1 part, these compositions were press-cured under the condition of 170 ° C. for 10 minutes to form a sheet with a thickness of 2 mm, and 200 ° C.
After post-curing for 4 hours, the physical properties of this sheet were examined, and the yellowing of this sheet was also examined visually, and the results shown in Table 1 were obtained.

Examples 5 to 8 and Comparative Example 2 (CH ₃ ) ₂ SiO unit 100 mol%, both ends of the molecular chain were blocked with (CH ₃ ) ₃ SiO _0.5 units, and the degree of polymerization was about 5,000. and 50 parts, are blocked with (CH _{3) 2} SiO units 99.5 mol% and _{(CH 3) (CH 2 =} CH) consists of SiO unit 0.5 mol%, both ends of the molecular chain (CH _{3) 3} SiO _0.5 units Also, 50 parts of methyl vinyl polysiloxane raw rubber with a degree of polymerization of about 5,000 and wet silica Nipsyl LP [above] 40
Part, 9 parts of dimethylpolysiloxane having a degree of polymerization of 18 and having a hydroxyl group at both ends of the molecular chain as a dispersant, and 2.36 parts of 2N-NaOH as an alkaline agent are added and uniformly mixed in a kneader at 150 ° C. A silicone rubber composition VI was prepared by heat treatment for 2 hours, and 1.6 parts of sodium silanolate having an average degree of polymerization of 4 and both ends of the molecular chain blocked with Na was added to the silicone rubber composition instead of 2N-NaOH. VII,
A silicone rubber composition VIII was prepared by adding 0.25 part of sodium methylate, and 5 parts of the above 40 parts of the nip seal LP were treated with alkali as Nipsil G-300 to prepare a silicone rubber composition IX. Silicone rubber composition X was prepared in the same manner as described above except that the above was not used at all.

Then, the silicone rubber compositions VI to X were added with 2.5-bis (t-butylperoxy) -2,5-dimethylhexane 0.5.
Parts and Examples 1 to 1 described above for these compositions.
A sheet having a thickness of 2 mm was prepared in the same manner as in Example 4, and the yellowing degree and physical properties of this sheet were examined. The results shown in Table 2 were obtained.

[Effects of the Invention] The present invention relates to a silicone rubber composition capable of preventing yellowing after molding, a method for producing the same, and a cured product thereof. As described above, the silicone rubber composition is A) diorganopolysiloxane. , B) Reinforcing filler,
It consists of C) dialkyl peroxide and D) alkaline agent, but since this composition contains an alkaline agent as component D), even if acetone is generated by the decomposition of dialkyl peroxide, this is aldol. Since it does not condense and dehydrate to form a conjugated compound and the molded article does not yellow even after molding the silicone rubber composition, a transparent or white molded article can be easily obtained. It is given an advantage, and therefore, it is useful for underwater eyeglass pads and nipples where transparency and whiteness are required, as well as for desktop computer, rubber contact in illuminated touch-tone phone, etc. Industrial benefits are given.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display area C08K 5/54 C08L 83/07 LRT

Claims (3)

[Claims] 1. A) Average composition formula (Wherein R is the same or different and is an unsubstituted or substituted monovalent hydrocarbon group having 1 to 10 carbon atoms, and a is a number from 1.95 to 2.05) and has an average degree of polymerization of 3,000 to 30,000. Silicone rubber composition comprising 100 parts by weight of polysiloxane, B) 10 to 100 parts by weight of reinforcing filler, C) 0.5 to 5 parts by weight of dialkyl peroxide, and D) 0.1 to 15 parts by weight of alkaline agent. . 2. The method according to claim 1, wherein the composition comprising the components A), B), and D) in claim 1 is heat-treated at 100 to 200 ° C., and then the component C) is added. Method for producing silicone rubber composition. 3. A silicone rubber cured product obtained by curing the silicone rubber composition according to claim 1.