Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2001-02-13
2003-05-06
Wilson, D. R. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S212000, C526S219200, C526S219600, C526S227000, C526S230500, C525S330600, C524S379000, C524S391000
Reexamination Certificate
active
06559254
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to a technology of producing vinyl acetate polymers and saponification products thereof and more particularly to a process for producing an ethylene-vinyl acetate copolymer and a process for producing a saponified ethylene-vinyl acetate copolymer.
BACKGROUND OF THE INVENTION
The saponified ethylene-vinyl acetate copolymer has excellent gas-barrier properties, mechanical strength and other useful characteristics and, as such, is broadly used in various applications such as films, sheets, bags and fibers.
The saponified ethylene-vinyl acetate copolymer is produced by copolymerizing ethylene and vinyl acetate in a solvent and then saponifying the resulting copolymer. This copolymerization of ethylene and vinyl acetate is usually carried out in an alcohol solvent, such as methanol, in the presence of a catalyst, such as a peroxide or an azo compound.
JP Kokai H9-316110 discloses a technology of producing vinyl acetate polymers by way of homopolymerization of vinyl acetate monomer or copolymerization of vinyl acetate monomer and one or more other monomers copolymerizable therewith characterized in that an organic peroxide having a half-life of 10-110 minutes at 60° C. is used as a polymerization initiator and that the polymerization reaction is carried out in the presence of at least one carboxylic acid selected from the group consisting of hydroxycarboxylic acids and polycarboxylic acids or a salt thereof.
According to the above patent literature, the object of the invention disclosed is to provide a method of producing a vinyl acetate polymer which is conducive to a reduced amount of dissolved polymer in the waste liquor in the stage of saponification of a vinyl acetate polymer, a reduced amount of undissolved vinyl alcohol polymer in a solvent in the preparation of a solution of the vinyl alcohol polymer obtained by saponification of a vinyl acetate polymer, an improved clarity of the vinyl alcohol polymer solution obtained by the saponification of the vinyl acetate polymer, and a reduced odor of the vinyl alcohol polymer produced by the saponification of the vinyl acetate polymer.
As examples of said hydroxycarboxylic acids and polycarboxylic acids, the above literature mentions glycolic acid, lactic acid, glyceric acid, malic acid, tartaric acid, citric acid, salicyclic acid, malonic acid, succinic acid, maleic acid, phthalic acid, oxalic acid and glutaric acid. It is stated that the preferred, among these, are aliphatic saturated hydroxycarboxylic acids, particularly aliphatic saturated hydroxypolycarboxylic acids.
As said other monomer or monomers copolymerizable with vinyl acetate monomer, the same literature mentions olefins (ethylene, propylene, etc.), hydroxyolefins, (meth)acrylic acid esters, allyl compounds, nonionic monomers, anionic monomers and cationic monomers, but in view of the statement that these comonomers preferably constitute a minor component and the use of vinyl acetate monomer alone is particularly preferred, it is logical to assume that, even when a copolymer is indicated, the invention envisages only copolymers representing minor modifications of polyvinyl acetate.
The above invention disclosed in JP Kokai H9-316110 does not specifically refer to an ethylene-vinyl acetate copolymer with a comparatively high ethylene content.
The inventors of the present invention analyzed the rationale of using a hydroxycarboxylic acid and an organic peroxide in the polymerization system for producing an ethylene-vinyl acetate copolymer with a reasonably high ethylene content and found that when pellets of the saponification product of the ethylene-vinyl acetate copolymer so obtained was melt-formed into a film and the film was evaluated for the degree of discoloration of pellets, emanation of an odor at molding, the degree of transparency of the resulting film, and fish-eyes in the film, the product was not satisfactory enough in any of the above quality parameters.
OBJECT AND SUMMARY OF THE INVENTION
In the above state of the art, the present invention has for its primary object to provide a process for producing a saponified vinyl acetate polymer (a saponified ethylene-vinyl acetate copolymer in particular) with a minimum of pellet discoloration, a sufficient suppression of an odor in the melt-molding of pellets, high transparency of the film obtained, and a low incidence of film fish-eyes and a process for producing a vinyl acetate polymer (an ethylene-vinyl acetate copolymer in particular) for use as a raw material for said saponified polymer which is conducive to said desirable qualities.
The process for producing a vinyl acetate polymer according to the present invention is characterized in that, in the presence of a hydroxylactone compound and a polymerization catalyst, vinyl acetate is polymerized alone or copolymerized with one or more other copolymerizable monomers.
The process for producing a saponified vinyl acetate polymer according to the present invention is characterized in that, in the presence of a hydroxylactone compound and a polymerization catalyst, vinyl acetate is polymerized alone or copolymerized with one or more other copolymerizable monomers and the resulting vinyl acetate polymer is saponified.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is now described in detail. It should be understood that the polymer with which the present invention is concerned is not limited to an ethylene-vinyl acetate copolymer inclusive of its saponification product but since this polymer is particularly important, the following description will be mainly directed to the ethylene-vinyl acetate polymer.
In producing an ethylene-vinyl acetate copolymer in accordance with the invention, ethylene and vinyl acetate are copolymerized. The method for this polymerization includes solution polymerization, bulk polymerization, suspension polymerization and emulsion polymerization. The preferred is solution polymerization or bulk polymerization. The mode of copolymerization may be continuous or batchwise, and suitable conditions, such as those described below, can be selectively used according to the specific polymerization technique selected.
According to the solution polymerization technique or bulk polymerization technique, the copolymerization of ethylene and vinyl acetate is conducted in the presence of a polymerization catalyst. The most outstanding feature of the present invention residues in that this copolymerization is carried out in the presence of a hydroxylactone compound described later herein.
The solvent for use in a solution polymerization process is not particularly restricted but any of the solvents which are conventionally used in the production of ethylene-vinyl acetate copolymers can be employed. For example, alcohols containing up to 4 carbon atoms, aliphatic hydrocarbons, aromatic hydrocarbons, fatty acid esters, and mixtures thereof can be mentioned. The alcohols mentioned above include methanol, ethanol and propanol, among others. A mixture of water with such an alcohol can also be employed.
The proportion of the solvent to be used in carrying out this copolymerization reaction is not particularly restricted but the preferred proportion is not more than 1000 parts by weight (more preferably not more than 100 parts by weight, particularly not more than 50 parts by weight) based on 100 parts by weight of vinyl acetate. Use of the solvent in excess of 1000 parts by weight is undesirable, for the molecular weight of the product copolymer will then be not as high as desired.
The polymerization catalyst may be virtually any radical initiator. Thus, use may be made of, for example, azo compounds such as 2,2′-azobis(2,4-dimethylvaleronitrile), 2,2′-azobis(2,4,4-trimethylvaleronitrile), 2,2′-azobisisobutyronitrile, 2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2′-azobisisobutyrate, etc.; peroxy esters such as t-butyl peroxyneodecanoate, t-butyl peroxypivalate, t-butyl peroxy-2-ethylhexanoate, &agr;,&agr;′-bis(neodecanoylperoxy)diisopropyl
Harao Akio
Kato Kenji
Nagao Yoshiharu
Ninomiya Kenji
Armstrong Westerman & Hattori, LLP
Nippon Gohsei Kagaku Kogyo Kabushiki Kaisha
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