JP2887341B2 - Reinforcing silica filler - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a reinforcing silica filler, particularly a reinforcing silica filler which is capable of preventing viscosity increase at the time of compounding without deteriorating elastomer properties, thereby improving processability. It relates to the agent.

[0002]

2. Description of the Related Art Silica fillers are said to be made by hydrolysis of alkoxysilanes, flame hydrolysis of silicon compounds such as silicon tetrachloride and trichlorosilane, etc. Although there are some differences depending on the number of hydrophilic silanol groups (≡S
It is known that i-OH) has an extremely strong affinity with polar substances such as water due to the binding.

[0003] For this reason, several methods of converting silanol groups on the silica surface into hydrophobic silica are known for this silica, and Estersil (US Patent No. 2,6
No. 57,149), which is widely used because of its extremely good dispersibility in organic substances. In addition, a method of converting silanol groups into organosiloxy groups by bringing organochlorosilane vapor into contact with the silica is also known.
No. -22129) and a method of reacting with silazanes (see US Pat. No. 789,352).

[0004]

However, when the silica filler thus treated is used as a filler for a fluorine-containing silicone, the composition thus obtained is used for the dimethyl silicone. Since the viscosity is significantly increased as compared with the obtained composition, there is a disadvantage that it is difficult to prepare a low-viscosity composition.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a reinforcing silica filler which can be used for a fluorine-containing silicone which has solved such disadvantages, and which comprises absorbing water at least.
0.2 to 25% by weight of particulate silica containing 0.2% by weight and having a surface area of at least 50 m ² / g.
Weight% of the general formula (1)

Embedded image Or the general formula (2)

Embedded image (Where R ¹ is a divalent organic group, R ² is a monovalent hydrocarbon group,
R ³ , R ⁴ and R ^{5 each} represent a hydrogen atom or a monovalent hydrocarbon group;
and f is a silylation agent which is contacted with a silylating agent represented by a perfluoroalkyl group or a perfluoroalkyl ether group).

That is, as a result of various studies to develop a silica filler which does not increase in viscosity even when added to a fluorine-containing silicone, the present invention contains at least 0.2% by weight of absorbed water and has a surface area of at least 0.2%. When 50 m ² / g of fine-grained silica is used, and this is contacted with a silylating agent comprising a fluorinated silazane represented by the above general formula (1) or (2) at 20 to 50 ° C. This is particularly useful as a filler for a fluorosilicone rubber composition which is cured by cross-linking a fluorosilicone with a polyfunctional crosslinker. It has been found that the viscosity does not increase, so that a low-viscosity fluorine-containing silicone composition can be easily prepared, The present invention was completed by confirming that a fluorine-containing silicone rubber composition having excellent workability and the like could be produced. This is described in more detail below.

[0007]

The present invention relates to a reinforcing silica filler, and more particularly to a reinforcing silica filler which does not cause an increase in viscosity even when added to a fluorine-containing silicone. However, this silica absorbs water at least by contact with atmospheric moisture or by adding water from the outside to effectively promote the reaction between the contacting silylating agent and the silanol group on the silica surface.
It must contain 0.2% by weight, preferably 0.2 to 2% by weight, which also has a surface area of at least 50 m ² / g, preferably 150 m ² / g, since it is for reinforcement of the fluorosilicone composition. 500500 m ² / g is required.

[0008] However, even if it has this water absorption and surface area, when it is added as a reinforcing agent for the fluorine-containing silicone, the fluorine-containing silicone composition is thickened to produce a low-viscosity composition. Is difficult, and this is based on the general formula (1) described above according to the present invention.

Embedded image Or the general formula (2)

Embedded image Is required to be brought into contact with a silylating agent comprising a fluorinated silazane represented by the formula (1) to silylate it.

In the silylating agent represented by the general formula (1) or (2), R ¹ is a divalent organic group, which may be a lower alkylene group or an arylene which may have oxygen interposed therebetween. Groups usually having 1 to 1 carbon atoms represented by groups such as-(CH ₂ ) _n- (n = integer of 2 to 6),-(CH ₂ ) _n -O-CH _2- (n = integer of 2 to 4) 6, preferably 2 to 4, R ²
Is a methyl group, an ethyl group, a propyl group, an isopropyl group,
Monovalent having 1 to 8 carbon atoms, preferably 1 to 6 carbon atoms, typically exemplified by lower alkyl groups such as butyl group, hexyl group and cyclohexyl group, alkenyl groups such as vinyl group and allyl group, and aryl groups such as phenyl group. Hydrocarbon group, R ³ , R
⁴ and R ⁵ are a hydrogen atom or a monovalent hydrocarbon group similar to those exemplified above for R ² , but R ³ is preferably a hydrogen atom, and R ⁴ and R ⁵ are preferably a methyl group or an ethyl group. Wherein Rf is a perfluoroalkyl group or a perfluoroalkyl ether group,

Embedded image

Embedded image C _m F _{2m + 1} - are those (n = 1 to 12 integer) in what is shown is illustrative, as the silylating agent, there are exemplified those described below.

Embedded image

Embedded image

The reinforcing silica filler of the present invention is obtained by contacting fine particle silica containing at least 0.2% by weight of the above-mentioned absorbed water and having a surface area of at least 50 m ² / g with the silylating agent to obtain a silylation agent. However, the silylation can be carried out by contacting the finely divided silica with the silylating agent at 20 to 150 ° C., and the treatment time does not need to be strictly regulated. And it is sufficient. If the amount of the silylating agent used here is less than 3% by weight based on the weight of silica, the effect due to this silylation is poor, and if the amount is more than 25% by weight, the effect becomes more significant. Is not expected, so the content may be in the range of 3 to 25% by weight, but the preferred range is 10 to 20% by weight.

The reinforcing silica filler of the present invention thus treated is assumed to be silylated by the silylating agent. The silylating agent is represented by the general formulas (1) and (2). Since it is a fluorinated silazane compound as described above, even if it is added to a fluorinated silicone composition which is cross-linked and cured by the addition of a polyfunctional cross-linking agent, its viscosity is not increased, so that For example, it is possible to easily produce a low-viscosity fluorine-containing silicone composition, which is advantageous in that it can be used as a composition having excellent processability.

[0012]

Next, examples of the present invention and comparative examples will be described. Example 1 A silica filler containing 3% by weight of absorbed water and having a surface area of 300 m ² / g was mixed with a 20% by weight formula.

Embedded image Add the silylating agent shown in
C. for 3 hours and then dried at 180.degree. C. for 24 hours to produce a silica filler silylated with this silylating agent.

Next, the equation

Embedded image By mixing 15 parts by weight of this silylated silica filler with 100 parts by weight of a vinyl group-terminated fluorine-containing polysiloxane having a viscosity of 18,000 centipoise at 25 ° C., a composition having a viscosity of 37,000 centipoise at 25 ° C. Obtained.

Comparative Example 1 The same silica filler as used in Example 1 was silylated in the same manner as in Example 1 except that hexamethyldisilazane was used in place of the fluorinated silazane used in Example 1. Was added to 100 parts by weight of the vinyl-terminated fluorinated polysiloxane used in Example 1 to give a composition having a high viscosity of 85,000 centipoise at 25 ° C.

[0015]

The present invention relates to a reinforcing silica filler which, as described above, has a water absorption of at least 0.2%.
Contacting particulate silica having a surface area of at least 50 m ² / g with a silylating agent represented by the general formula (1) or (2) in an amount of 3 to 25% by weight based on the weight of the silica. However, since the silylating agent is a fluorinated silazane compound, even if it is added to the fluorinated silicone composition, the viscosity increases during compounding. , So that a fluorine-containing silicone composition having a low viscosity can be obtained.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-2-45539 (JP, A) JP-A-56-41263 (JP, A) JP-B-49-20739 (JP, B1) (58) Field (Int.Cl. ⁶ , DB name) C09C 1/00-3/12 C08K 3/00-13/08

Claims (1)

(57) [Claims] 1. A particulate silica containing at least 0.2% by weight of absorbed water and having a surface area of at least 50 m ² / g is converted from 3 to 25% by weight, based on the weight of silica, of the general formula: Or (Where R ¹ is a divalent organic group, R ² is a monovalent hydrocarbon group,
R ³ , R ⁴ and R ^{5 each} represent a hydrogen atom or a monovalent hydrocarbon group;
f is a perfluoroalkyl group or a perfluoroalkyl ether group), and is a silylating agent;