Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1996-05-03
2001-09-11
Sellers, Robert E. L. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S212000, C524S588000
Reexamination Certificate
active
06288143
ABSTRACT:
The present invention relates to two-part room temperature vulcanizable (RTV) silicones. More particularly, the present invention relates to a method of treating fillers for use in RTV silicones. Most particularly, the present invention relates to an in-situ filler treating process for RTV silicones which provides improved physical properties.
BACKGROUND OF THE PRESENT INVENTION
Room temperature two-part vulcanizing silicone compositions are presently widely known. For example, Hyde, U.S. Pat. No. 2,571,039 discloses preparing an organosiloxane by compounding a readily deformable acid polymer comprising a polysiloxane and an acidic compound with a filler, and then reacting the compounded material with a silane of the formula R
n
Si(OR′)
4−n
where R is a monovalent hydrocarbon radical free of aliphatic unsaturation, R′ is an alkyl radical of less than 9 carbon atoms and n has a value of 0 to 1.
Berridge, United States Patent No. 2,843,555 discloses an organopolysiloxane composition convertible at room temperature to the cured, solid, elastic state comprising (a) a linear, fluid organopolysiloxane containing silicon-bonded hydroxy groups and having an average of about two organic groups per silicon atom, (b) an alkyl silicate, and (c) a metallic salt of an organic carboxylic acid.
The compositions are useful as sealants, electrical insulation, coatings, dental cement, caulking compounds, expansion joints, gaskets, shock absorbers, adhesives and in many other applications.
Presently, two-part condensation cure RTV's are typically comprised of an “A” component comprising (1) a dihydroxy or silanol terminated polydiorganosiloxane; (2) a semi-reinforcing filler such as CaCO
3
or ground quartz and a reinforcing filler such as fumed silica; and (3) water; and a “B” component comprising (1) a T or Q functional crosslinker; and (2) a condensation cure catalyst.
It is further known in the art to treat the fillers off site with organosilicones or silazanes prior to addition to the two component RTV mixture. See, for example, Lucas, U.S. Pat. Nos. 2,938,009; Lichtenwalner, 3,004,859; and Smith, 3,635,743.
More recently, Treco SRL has developed a low shear process for treating the filler in situ by preparing a filler/oil masterbatch and adding the treating agent to the masterbatch under low shear mixing conditions which do not rapidly break down aggregated filler particles. Although the Treco process has met with some success in the industry, the process requires unsuitable manufacturing times, on the order of at least about 3 to 5 days. Further, materials produced by the Treco process exhibit relatively low Shore A durometer and Die B Tear values.
It would therefore represent a notable advance in the state of the art if a novel method could be found which enabled a user to treat the filler in situ and formulate a two component RTV composition in a significantly shorter manufacturing time to produce a high Shore A durometer material which retained high Die B Tear values.
SUMMARY OF THE PRESENT INVENTION
To this end, the present inventors have now found an in-situ filler treating process for preparing RTV silicones which meet the shortcomings of the prior art processes.
According to the present invention, there is provided an in-situ method of preparing the first component of a two-component RTV silicone composition, the method comprising: (a) preparing a filler/oil masterbatch comprising (i) adding an unreactive silicone oil and untreated aggregated filler particles to a mixer; (ii) adding a filler treating agent to the unreactive silicone oil/filler mixture; and mixing the treating agent and unreactive silicone oil/filler mixture at mixing conditions sufficient to break down the aggregated filler particles to an average size of less than about 300 nm in diameter in a time period of less than about 24 hours; and (b) adding the filler/oil masterbatch to a reactive silicone oil.
According to the present invention there is also provided an in-situ method of preparing a two-component RTV silicone composition, the method comprising: (A) preparing a first component by a method comprising: (a) preparing a filler/oil masterbatch comprising (i) adding an unreactive silicone oil and untreated aggregated filler particles to a mixer; (ii) adding a filler treating agent to the unreactive silicone oil/filler mixture; and (iii) mixing the treating agent and silicone oil/filler mixture at mixing conditions sufficient to break down the aggregated filler particles to an average size of less than about 300 nm in diameter in a time period of less than about 24 hours; (b) adding the filler/oil masterbatch to a reactive silicone oil; and (c) adding a lower molecular weight silicone oil to the mixture of the filler/oil masterbatch and reactive silicone oil; (B) preparing a second component by admixing an effective amount of a condensation cure catalyst and an effective amount of a crosslinking agent; and (C) combining and reacting components (A) and (B) to effect curing of the polysiloxane.
Still further, according to the present invention there is provided a two-component RTV silicone composition having high Shore A durometer and Tear B strength values prepared by a process comprising: (A) preparing a first component by a method comprising: (a) preparing a filler/oil masterbatch comprising (i) adding an unreactive silicone oil and untreated aggregated filler particles to a mixer; (ii) adding a filler treating agent to the unreactive silicone oil/filler mixture; and (iii) mixing the treating agent and unreactive silicone oil/filler mixture at mixing conditions sufficient to break down the aggregated filler particles to an average size of less than about 300 nm in diameter in a time period of less than about 24 hours; and (b) adding the filler/oil masterbatch to a reactive silicone oil; (B) preparing a second component by admixing an effective amount of a condensation cure catalyst and an effective amount of a crosslinking agent; and (C) mixing and reacting components (A) and (B).
DETAILED DESCRIPTION OF THE PRESENT INVENTION
The present invention provides a novel two-part condensation cure RTV silicone and method of making same. The RTV's are typically comprised of an “A” component comprising (1) reactive silicone oils such as a dihydroxy or silanol terminated polydiorganosiloxane; (2) a filler/oil masterbatch comprising an unreactive silicone oil and a treated reinforcing filler such as, for example, fumed silica (90-325 m
2
/g surface area); and, optionally, (3) water; and a “B” component comprising (1) a T or Q functional crosslinker; and (2) a condensational cure catalyst.
The two-part condensation cure RTV's of the present invention are prepared by treating the filler in-situ at conditions sufficient to break down the aggregated filler particles to an average size of less than about 300 nm in diameter in less than about 24 hours, preferably less than about 14 hours, during compounding of the “A” component. The “A” and “B” components are then admixed at conditions to effect the curing of the polydiorganosiloxane. Preferably, the “A” and “B” components are admixed in a ratio of from about 80 to about 120 parts by weight of component “A”, to from about 1 to about 20 parts by weight of component “B”. More preferred is a weight ratio of from about 90 to about 110 parts by weight “A” to from about 2 to about 15 parts by weight “B”.
The reactive silicone oil for use in the present invention typically comprises silanol chain-stopped polydiorganosiloxanes and may be represented by the general formula:
wherein R
1
and R
2
are each organic radicals of up to 20, and preferably up to 8 carbon atoms, selected from hydrocarbyl, halohydrocarbyl and cyano lower alkyl and n is a number that varies generally from about 10 to about 15000, preferably from about 100 to about 3000, and more preferably from about 300 to about 1500.
The silanol chain-stopped polydiorganosiloxanes are well known in the art and they may be prepared by known methods, such as described in Beers, U.S. Pat. No.3,382,
Caradori Paul J.
Smith Robert Augustine
Zumbrum Michael Allen
General Electric Company
Sellers Robert E. L.
Wheelock Kenneth S.
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