Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-07-19
2002-05-28
Lipman, Bernard (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S246000, C525S288000, C525S326500, C525S353000
Reexamination Certificate
active
06395837
ABSTRACT:
FIELD OF INVENTION
The present invention is directed to a crosslinkable polymer composition comprising an alkoxysilane functional polyolefin and an alkylated aryl disulfonic acid as a crosslinking catalyst. More particularly, the present invention is directed to a silane functional polyolefin and an alkylated aryl disulfonic acid wherein the aryl moiety is naphthalene or biphenyl or two benzene rings covalently bonded through a divalent moiety and wherein the aryl moiety is substituted with 1-4 alkyl groups and each alkyl group is a hydrocarbon chain with 6 to 16 carbons, preferably 9 to 12 carbons with the total number of carbons in the alkyl substituents being in the range of 9 to 64 carbons. The catalysts of the present invention also include derivatives of the alkylated aryl disulfonic acids that can be hydrolyzed to the corresponding acids.
The useful alkylated aryl disulfonic acid catalysts in the present invention are highly active crosslinking catalysts being effective at a very low concentration in the silane functional polyolefin composition. Because of the low concentration of the alkylated aryl disulfonic acid catalyst required, it is anticipated that the electrical resistance of resulting crosslinked polymeric compositions will be excellent. The resulting crosslinked polymeric compositions are desirable for use as coatings for electrical cables and wires.
BACKGROUND OF THE INVENTION
Thermoplastic polyolefins such as polyethylene have long been known as excellent dielectric materials for use as insulation in the manufacture of power cables. The major drawback of thermoplastic polyethylene is the relatively low temperature at which it softens and flows. The upper temperature at which thermoplastic polyethylene is useful is 75° C., which is rather low. This temperature may be increased by crosslinking. However, polyethylene is a linear polymer with no functional groups along the chain for crosslinking. Thus, to crosslink polyethylene, the polymer chain needs to be activated or provided with functional groups. Although polyethylene is described here, the present discussion is applicable generally to polyolefins.
One way to crosslink polyethylene is to incorporate a peroxide crosslinking agent to provide a source of free radicals when heated to a temperature higher than its decomposition temperature. The free radical extracts a hydrogen from the polyethylene backbone to produce alkyl radicals which combine to crosslink the linear polyethylene. However, polyethylene tends to scorch at a low temperature, which limits the temperature at which the polyethylene can be heated to provide crosslinking and to produce an extruded coated wire. For this reason, wires produced by using peroxide to crosslink polyethylene require a specialized extruder equipped with a high pressure continuous vulcanization (CV) tube. However, this extruder is very expensive and costly to operate.
Another way to crosslink polyethylene is to use electron beam irradiation to form free radicals. This process avoids the use of the high pressure continuous vulcanization extruder. However, the use of electron beam radiation prevents the use of carbon black commonly used as a pigment in coated wires. Further, it was found that where a thicker coating material is desired, the thickness of the material prevents penetration by the electron beam leading to non-uniformity of the resulting coating, thereby posing challenging engineering problems. Moreover, the equipment to produce high energy radiation and the necessary special shielding is also very expensive.
A third way of crosslinking polyethylene is to incorporate a second component, an unsaturated silane compound, such as vinyl alkoxysilane into the polyethylene. A small amount of a vinyl alkoxysilane, preferably vinyl trimethoxysilane (VTMS), at a level of 0.5% to 5%, preferably 2%, is incorporated into the backbone of the polyethylene chain and moisture cured.
Suitable unsaturated silanes would be of general structure, CH
2
═CH—Si—(OR)
3
, wherein R is any alkyl group of 1-4 carbons. Examples of unsaturated silane compounds would be vinyltrimethoxysilane, vinyltriethoxysilane, and vinyldimethoxyethoxysilane. The most preferred is vinyltrimethoxysilane (VTMS).
The crosslinking of polyethylene using VTMS is a two step process. The first step involves hydrolysis of the methoxy group to a hydroxy group with the liberation of methanol. The second step is a condensation step to release H
2
O to crosslink or cure the polymer. The hydrolysis step requires the presence of water and the catalyst used must not be soluble in water or affected thereby. The rate of cure of silane functionalized polyethylene is controlled by silane concentration, silane structure, catalyst concentration and type, resin crystallinity, coating thickness, the rate at which water penetrates into the inner layers of the polymer, the cure temperature, and the relative humidity.
There are many advantages to this process. It is a single line process. That is, the VTMS modified polyethylene can go directly from the reactor to the extruder without going through grafting and/or compounding. This process also provides a product that is very clean with uniform density and molecular weight distribution.
Methods of incorporating hydrolyzable silane groups into a polyethylene followed by crosslinking of the resulting silane functional polymer are known.
Shinkai et al., U.S. Pat. No. 4,160,072 and Hosokawa et al., U.S. Pat. No. 4,252,906, disclosed zinc carboxylates as the crosslinking catalyst for foamable and crosslinkable silane functional polyethylene.
Akutsu et al., U.S. Pat. No. 4,297,310 disclosed a process for producing moisture crosslinkable polymer by copolymerization of ethylene and an unsaturated silane compound. Metal salts of carboxylic acids, organic bases, inorganic acids and organic acids were disclosed as suitable crosslinking catalysts for this system. Toluene sulfonic acid was among one of the organic acids listed.
Isaka et al., U.S. Pat. No. 4,413,066, described a copolymer of ethylene and an ethylenically unsaturated silane in combination with a crosslinking catalyst. The copolymer may further comprise a monomer copolymerizable with the ethylene and the ethyleneically unsaturated silane compound. The catalysts include metal carboxylate salts, organic bases, inorganic acids and organic acids as the crosslinking catalysts. Although toluene sulfonic acid was disclosed as being a suitable crosslinking catalyst, the preferred catalysts are the carboxylates of tin.
Doi et al., U.S. Pat. No. 4,446,283, described a copolymer consisting essentially of ethylene and a specific unsaturated silane compound having a (meth)acrylate group as a copolymerizable group and a methoxy group as a hydrolyzable group, and an effective amount of a silanol crosslinking catalyst. The catalysts useful for crosslinking are the same as those previously described. Umpleby, U.S. Pat. No. 4,753,992, discloses a crosslinkable composition comprising a silyl polymer and a silanol crosslinking catalyst which is a polymeric tin compound. However, the electro-conductivity of tin or metal salts of the carboxylic acids, and the inorganic acids disclosed by Isaka et al. are relatively high. It is not desirable to incorporate such compounds in a wire coating that should be an insulation material. In addition, the metal carboxylates and inorganic metal salts provide a slower rate of cure than the catalysts useful in the present invention.
Another process for crosslinking polyethylene was described in Konno et al., U.S. Pat. No. 5,393,823. Konno et al. disclosed a paint composition wherein a vinyl polymer is obtained by copolymerizing a vinyl monomer with a siloxy group and a polyisocyanate compound in the presence of a radical generator. The vinyl siloxy monomer with a radical generator and a curing agent are mixed with a siloxy dissociating catalyst. The compounds suitable as the dissociation catalyst include phosphoric acid and its salts, organic phosphates and phosphites. Also included as dissociation catalysts are to
Abramshe Richard A.
Blank Werner J.
Hessell Edward T.
KIng Industries, Inc.
Lipman Bernard
Morgan & Finnegan , LLP
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