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
1999-05-26
2004-03-16
Mulcahy, Peter D. (Department: 1713)
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...
C524S110000
Reexamination Certificate
active
06706792
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to improved adhesion of water-based inks and paints to articles made from heat stabilized halogen-containing resins. It relates particularly to articles of manufacture such as flexible film and semi-rigid tubing that are prepared from heat-stabilized vinyl chloride polymers.
BACKGROUND OF THE INVENTION
Changes in heat stabilizers and in printing inks over the years has resulted in a loss of printability of flexible poly(vinyl chloride) substrates. The curtailment of heavy metals (e.g. cadmium) in stabilizers and of volatile solvents in both stabilizers and printing inks has been held responsible for the loss of printability. Thus, there has arisen a need for a way to enhance the wettability of such present day PVC substrates.
A patent application by Witco Corporation published under the number WO96/15186 teaches that the wettability of heat-stabilized PVC film to water-based inks and the adherence of such inks to the film are improved by the incorporation of oxidized polyethylene in the PVC composition. The heat stabilizer is a mixture of barium and zinc carboxylates having up to 20 carbon atoms in combination with organic phosphites.
The surface tension of a heavy metal-containing PVC has been found to be from 25 to 33% higher than that of a traditionally plasticized PVC according to E. R. Napoleon in “Journal of Vinyl & Additive Technology”, 3, No. 2, 145 (June 1997).
As taught in co-pending, commonly assigned patent application Serial No. 09/133,605, filed August 13, 1998, the teachings of which are incorporated herein by reference, the degradation products of a blocked or latent mercaptan present during processing of the halogen-containing resin at an elevated temperature enhance the activity of metal-based heat stabilizers such as organotin carboxylates and mercaptides in the composition. Vinyl chloride resin compositions and articles made thereof are stabilized particularly well by a combination of very low levels of zinc carboxylates and latent mercaptans selected from the group consisting of 2-S-(hydroxyalkylthio)tetrahydropyran, 5-S-(hydroxyalkylthio)tetrahydrofuran, 6-S-(2-formylhydroxyalkylthio)tetrahydropyran, the carboxylic acid esters of said alcohols, and mixtures of said alcohols and esters. Said latent mercaptans are also referred to as 2-S-(tetrahydropyranyl)-thioalkanol; 2-S-(tetrahydropyranyl)thioalkyl carboxylate; 6-S-(2-formyl-tetrahydropyranyl)thioalkanol and carboxylates thereof, and their furanyl homologs, i.e., 5-S-(tetrahydrofuranyl)thioalkanol, and 5-S-(tetrahydrofuranyl)thioalkyl carboxylate.
SUMMARY OF THE INVENTION
It has now been found that a combination of such a latent mercaptan and a zinc salt of oxidized polyethylene is particularly valuable in that it imparts improved hydrophilicity to the surfaces of articles made from vinyl chloride resins as well as thermal stability during high temperature processing during fabrication of such articles. The zinc salt is the only metal-containing stabilizer present during the high temperature processing.
It is an object of this invention, therefore, to provide a heat stabilizer composition which is free from metals other than zinc and which also improves the wettability of vinyl chloride resins by water-based inks and paints.
It is another object of this invention to provide a heavy metal-free, heat stabilized halogen-containing resin having a surface tension which is amenable to coating with a water-based ink or paint.
It is a related object of this invention to provide heat stabilized flexible, semi-rigid, and rigid PVC resin articles which have improved receptivity to water-based inks and paints.
It is a related object of this invention to provide novel latent mercaptans which are useful, alone or in combination with other additives, in heat stabilizer compositions.
These and other objects of the invention which will become apparent from the following description are achieved by adding a heavy metal-free heat stabilizer comprising a latent mercaptan and a synergistic amount of a zinc salt of oxidized polyethylene as the sole metal-containing stabilizer to a vinyl chloride resin and processing the resulting composition at the incipient resin decomposition temperature whereupon a small but hydrophilically effective amount of oxidized polyethylene is split from the zinc salt by liberated hydrogen chloride and the latent mercaptan degrades to liberate a free mercaptan. Examples of the latent mercaptan include, without limitation, 2-S-(tetrahydropyranyl)thioalkanol, a carboxylate thereof, a 2-S-(tetrahydropyranyl)thiocarboxylic acid or ester thereof, furanyl homologs of each, and mixtures thereof.
For the purposes of this invention, the terms blocked mercaptan and latent mercaptan are used interchangeably to mean a thioether which degrades during processing of the composition at an elevated temperature to liberate a free mercaptan.
Other products of the degradation of the blocked mercaptan are believed to include carbocations of the blocking moiety which are stabilized by a molecular structure in which the electron deficiency is shared by several groups. Resonance stabilization and neighboring group stabilization are two of the possible mechanisms by which the carbocations may be stabilized. The carbocations act as intermediates in the formation of stable compounds early in the hot processing of halogen-containing polymers. Although such mechanisms and the resultant carbocations are believed to be an impetus for the liberation of the active free mercaptan, this invention is in no way limited by the foregoing attempt to explain the working of the invention. Those skilled in the art will see the resonance stabilization and neighboring group stabilization that are possible in the following structures of the blocked mercaptan; other mechanisms may be at work in other blocked mercaptans represented by these structures that also liberate an active free mercaptan upon thermal and/or chemical degradation during processing of polymeric compositions containing such blocked mercaptans.
DETAILED DESCRIPTION OF THE INVENTION
The vinyl chloride resins, also referred to hereinafter as PVC resins, are made from monomers consisting of vinyl chloride alone or a mixture of monomers comprising, preferably, at least about 70% by weight of vinyl chloride, based on the total monomer weight. Examples of the copolymers include those made from vinyl chloride and from about 1 to about 30% of a copolymerizable ethylenically unsaturated material such as vinyl acetate, vinyl butyrate, vinyl benzoate, vinylidene chloride, diethyl fumarate, diethyl maleate, other alkyl fumarates and maleates, vinyl propionate, methyl acrylate, 2-ethylhexyl acrylate, butyl acrylate and other alkyl acrylates, methyl methacrylate, ethyl methacrylate, butyl methacrylate and other alkyl methacrylates, methyl alpha-chloroacrylate, styrene, trichloroethylene, vinyl ketones such as vinyl methyl ketone and vinyl phenyl ketone, 1-fluoro-2-chloroethylene, acrylonitrile, chloroacrylonitrile, allylidene diacetate, chloroallylidene diacetate, and vinyl ethers such as vinyl ethyl ether, vinyl chloroethyl ether, vinyl phenyl ether, and the vinyl ether of ethoxytetrahydropyran prepared by the reaction of one mole of acrolein with one mole of ethylene glycol divinyl ether. Typical copolymers include vinyl chloride-vinyl acetate (96:4 sold commercially as VYNW), vinyl chloride-vinyl acetate (87:13), vinyl chloride-vinyl acetate-maleic anhydride (86:13:1), vinyl chloride-vinylidene chloride (95:5); vinyl chloride-diethyl fumarate (95:5), and vinyl chloride 2-ethylhexyl acrylate (80:20).
As used herein, the term PVC composition means a composition comprising a vinyl chloride resin. A rigid PVC composition is one which does not contain a plasticizer. A semi-rigid PVC composition is one which contains from 1 to about 25 parts of a plasticizer per 100 parts by weight of the vinyl chloride resin. A flexible PVC composition contains from about 25 to about 100 parts per 100 parts by weight (phr) of the vinyl chloride resin. Alkyl este
Carpenter Jefferey L.
Duvall Tod C.
Mulcahy Peter D.
Rohm and Haas Company
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