Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2000-01-28
2002-08-27
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S081000, C528S008000, C528S013000, C528S025000, C528S033000, C264S142000
Reexamination Certificate
active
06441086
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a pelletizing additive for silicone rubber compositions, to a process for preparing the additive, to a pelletized silicone rubber material containing the additive, and to a process for preparing the pelletized material.
2. Description of the Related Art
There has been a longfelt need to provide pelletized silicone rubber. Such products are important, for example, for use in automated extrusion or injection molding processes. A problem is that it has not been possible to pelletize untreated silicone rubber since the untreated rubber clogs the pelletizing die or the knife.
U.S. Pat. No. 4,172,871 discloses the production of silicone rubber pellets, but the silicone rubber pellets adhere to one another in the untreated state. This adherence problem is solved by the '871 patentee by coating the pellets, for example with mica or talc.
BRIEF SUMMARY OF THE INVENTION
An object of the present invention is to improve upon the prior art silicone rubber pellets, and in particular to provide a pelletized material which has free-flowing properties and does not require surface-treatment with substances which, in some circumstances, could cause processing or performance difficulties. These and other objects are achieved by the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The invention provides a pelletizing additive composition which is prepared from at least one polyorganosiloxane, boric acid and water, and silicone rubber formulations containing such a composition as a pelletizing additive.
The polyorganosiloxanes are preferably linear polyorganosiloxanes, such as dimethylpolysiloxanes, phenylmethylpolysiloxanes, trifluoropropylpolysiloxanes or ethylpropylpolysiloxanes having a viscosity of from 10,000 to 9×10
6
mPa·s, preferably from 100,000 to 8×10
6
mPa·s and in particular from 6×10
6
mPa·s to 8×10
6
mPa·s. The polyorganosiloxane(s) preferably comprise from 30 to 90% by weight, more preferably from 40 to 80% by weight, and most preferably from 60 to 70% by weight, of the composition.
Boric acid preferably comprises from 2 to 20% by weight, more preferably from 3 to 14% by weight, and most preferably from 8 to 9% by weight, of the composition.
Preferably, the novel composition further comprises fatty acid salts. The fatty acid salts are preferably salts of the metals Al, Ba, Ca, Cd, Co, Cr, Cu, Fe, Li, Mg, Mn, Ni, Pb, Sn, Sr, or Zn with higher fatty acids, resin acids or naphthenic acids, for example stearates, palmitates, oleates, linoleates, resinates, laurates, octanoates, ricinolates, 12-hydroxystearates, naphthenates, tallates and the like. Preference is given to fatty acids having from greater than 12 to 30 carbon atoms, particularly to fatty acids having from greater than 16 to 26 carbon atoms, and most preferably stearates, especially calcium stearate. The composition preferably contains 1 to 10% by weight, more preferably from 2 to 6% by weight, and most preferably from 3 to 4% by weight, of the fatty acid salts.
The invention also provides a process for preparing the novel composition, where the components polyorganosiloxane, boric acid and water are mixed. In this aspect of the invention, the abovementioned components polyorganosiloxane, boric acid and preferably deionized water, and, if desired, from 8 to 60% by weight, preferably from 15 to 50% by weight, and more preferably from 25 to 40% by weight, of silica produced pyrogenically in the gas phase and having a surface area of from 150 to 300 m
2
/g, or precipitated silicic acid, are mixed together. Kneading is preferably carried out for from 2 to 4 hours, preferably at a temperature of from 120 to 190° C., and preferably under an atmosphere of nitrogen. The water which serves here as solvent for the boric acid is drawn off as a vapor.
The resultant composition serves as an additive for producing a pelletized material made from silicone rubber. This silicone rubber may be a peroxidically crosslinking or an addition-crosslinking silicone rubber. Surprisingly, this additive allows production of a pelletized silicone rubber material which has full free-flowing properties. The amounts of this additive added to the silicone rubber are preferably from 0.1 to 4% by weight, more preferably from 0.4 to 2% by weight, and most preferably from 0.8 to 1.2% by weight.
The novel silicone rubber is preferably a peroxidically crosslinking polyorganosiloxane material, which preferably comprises the following components.
Polyorganosiloxanes made of units of the general formula
R
r
SiO
4
-
r
2
,
(
I
)
where
R is identical or different and is an unsubstituted or substituted hydrocarbon radical and
r is 0, 1, 2 or 3 and has an average numerical value of from 1.9 to 2.1.
Examples of hydrocarbon radicals R are alkyl radicals such as the methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, neopentyl and tert-pentyl radicals; hexyl radicals such as the n-hexyl radical, heptyl radicals such as the n-heptyl radical; octyl radicals such as the n-octyl radical, and isooctyl radicals, such as the 2,2,4-trimethylpentyl radical; nonyl radicals such as the n-nonyl radical; decyl radicals such as the n-decyl radical; dodecyl radicals such as the n-dodecyl radical; octadecyl radicals such as the n-octadecyl radical; cycloalkyl radicals such as cyclopentyl, cyclohexyl and cycloheptyl radicals and methylcyclohexyl radicals; aryl radicals such as the phenyl, biphenyl, naphthyl, anthryl and phenanthryl radicals; and alkaryl radicals such as o-, m-, and p-tolyl radicals, xylyl radicals and ethylphenyl radicals; aralkyl radicals, such as the benzyl radical and the &agr;- and &bgr;-phenylethyl radicals.
Examples of substituted hydrocarbon radicals R are halogenated alkyl radicals such as the 3-chloropropyl radical, the 3,3,3-trifluoropropyl radical, and the perfluorohexylethyl radical, and halogenated aryl radicals such as the p-chlorophenyl radical and the p-chlorobenzyl radical.
The radicals R are preferably hydrocarbon radicals having from 1 to 8 carbon atoms, most preferably the methyl radical. Other examples of radicals R are the vinyl, allyl, methallyl, 1-propenyl, 1-butenyl and 1-pentenyl radicals, the 5-hexenyl, butadienyl, hexadienyl, cyclopentenyl, cyclopentadienyl, cyclohexenyl, ethynyl, propargyl and 1-propynyl radicals. The radicals R are preferably alkenyl radicals having from 2 to 8 carbon atoms, most preferably the vinyl radical. Among unsubstituted or substituted hydrocarbon radicals having from 1 to 8 carbon atoms, particular preference is given to the methyl, vinyl, phenyl and 3,3,3-trifluoropropyl radicals.
There are preferably alkyl radicals, most preferably methyl radicals, bonded to at least 70 mol % of the Si atoms present in the polyorganosiloxane (A) made of units of the formula (I). If the polyorganosiloxanes contain, besides Si-bonded methyl and/or 3,3,3-trifluoropropyl radicals, Si-bonded vinyl and/or phenyl radicals, the amounts of the latter are preferably from 0.001 to 30 mol %.
The polyorganosiloxanes (A) are preferably composed predominantly of diorganosiloxane units. The end groups of the polyorganosiloxanes may be trialkylsiloxy groups, in particular the trimethylsiloxy radical or the dimethylvinylsiloxy radical. However, it is also possible for one or more of these alkyl groups to have been replaced by hydroxyl groups or by alkoxy groups, such as methoxy or ethoxy radicals. The polyorganosiloxanes (A) may be liquids or highly viscous substances. The viscosity of the polyorganosiloxanes (A) is preferably from 10
3
to 10
8
MPa·s at 25° C. It is possible to use either just one type of polyorganosiloxane (A) or a mixture of at least two different types of polyorganosiloxanes (A).
The crosslinking agents preferably used in the novel silicone rubber materials are peroxides, such as dibenzoyl peroxide, bis(2,4-dichlorobenzoyl) peroxide, dicumyl peroxide or 2,5-bis(tert-butylperoxy)-2,5-dimethylhexane, or mixtures of these, preferably a mixture of bis(2,4-dichlorobenzoyl)
Marsch Wilhelm
Wolfer Dietrich
Brooks & Kushman P.C.
Dawson Robert
Keehan Christopher M.
Wacker - Chemie GmbH
LandOfFree
Silicone rubber does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Silicone rubber, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Silicone rubber will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2887698