Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-06-16
2002-12-10
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S158000, C524S166000, C524S201000, C524S322000, C524S377000, C524S394000, C524S458000, C524S556000, C524S565000, C524S571000
Reexamination Certificate
active
06492446
ABSTRACT:
TECHNICAL FIELDS OF THE INVENTION
The present invention relates to a latex compound for dip molding, particularly a latex compound for dip molding from which can be used for easily and efficiently producing a dip-molded product feeling soft and satisfying properties such as excellent oil resistance required for gloves used in medical fields and in a clean room for producing electronic parts, high mechanical strength and the absence of pinholes, as well as a dip-molded product obtained therefrom.
BACKGROUND OF THE INVENTION
Dip-molded products such as gloves and fingerstalls used in the fields of medicine, hygiene and production of electronic parts should be excellent in oil resistance and mechanical strength, free of pinholes and also excellent in close fitting thereof to the skin.
As the method of dip molding, there are known an anode coagulant dip process wherein a mold made of wood, glass, ceramics, metal or plastics is dipped in a coagulant and then dipped in natural latex or synthetic rubber latex, and a Teague coagulant dip process, wherein a mold is dipped in latex and then dipped in a coagulant. The molded products obtained by these dip processes are called as a dip-molded product.
The film thickness of a dip-molded product such as a glove, the occurrence of pinholes therein and the close fitting thereof to the skin depend mainly on the latex compound and a coagulant.
Most of latex used heretofore in the dip molding method is natural rubber latex or synthetic rubber latex, but for the reason of high resistance to oil and organic solvent, acrylonitrile butadiene rubber (NBR) latex is preferably used. Recently, the NBR latex has been used more and more owing to the development of allergy in those who use natural rubber latex gloves. However, molded products produced from NBR by dip molding, though being excellent in oil resistance, have high glass transition temperature (Tg), and thus they hardly give soft feeling to the skin.
Accordingly, there are methods wherein, for instance, a conjugated diene compound such as butadiene is used in a larger amount in production of NBR, or NBR is blended with natural rubber, and NBR are laminated on the natural rubber layer. In these cases, however, the resulting products are poor in oil resistance or chemical resistance.
Meanwhile, as the method of obtaining NBR film which is excellent in oil resistance and has soft feeling to the skin, there are proposed methods wherein e.g. the molecular weight of copolymer latex and the content of insolubles in methyl ethyl ketone therein are prescribed (JP-A 5-247266 and JP-A 6-182788), but it cannot be said that the object has been achieved satisfactorily.
Along with this soft feeling to the skin, the presence or absence of pinholes is important for the gloves. In particular, when the molded product is used for medical purposes such as a surgical gloves, the presence of pinholes is fatal. The pinhole is easily generated if bubbles are mixed in latex compound, the chemical stability of latex compound to a coagulant is high, or the wettability of latex compound on a mold is not satisfactory. Bubbles in latex compound occurs mainly due to stirring during synthesis of latex or during addition of other ingredients to latex. Once bubbles are mixed, they do not easily disappear owing to the action of an emulsifying agent etc. in latex compound, and pinholes in the molded product are generated. If the chemical stability of latex compound to a coagulant is high or the wettability of latex compound on a mold is not satisfactory, then the film thickness of the molded product may become uneven or pinholes may be generated.
It is also important for the molded products that the surface of the molded product is not sticky. This stickiness is a property permitting products produced by dip molding to adhere one another owing to the sticky surfaces of the molded products. Once the molded products assume stickiness, their qualities are lowered and, resulted in a significant reduction in their commercial value.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a latex compound for dip molding, which can be used for production of a dip-molded product that is excellent in oil resistance and mechanical strength, has uniform film thickness and soft feeling to the skin and no pinholes, and assumes no stickiness of the surface after molding.
As a result of their eager study for solving this object, the present inventors found that a specific amount of a bubble breaker consisting of a fatty acid containing 8 to 22 carbon atoms or a salt thereof, and preferably additionally a dialkylsulfosuccinate salt containing 5 to 12 carbon atoms for the respective alkyl groups and/or an alkyl benzene sulfonate whose alkyl group contains 13 to 20 carbon atoms, are blended with copolymer latex obtained by emulsion polymerization of a monomer mixture, whereby the bubble-breaking abilities of latex compound, the wettability of latex compound on the surface of a mold, the chemical stability of latex compound to a coagulant, and the anti-stickiness of the molded product are significantly improved, and on the basis of this finding, they extensively studied and completed the present invention.
That is, the present invention relates to:
(1) A latex compound for dip molding, which comprises a copolymer latex (L) obtained by emulsion polymerization of a monomer mixture and 0.05 to 5.0 parts by weight of a bubble breaker (A) consisting of a fatty acid containing 8 to 22 carbon atoms or a salt thereof per 100 parts by weight of the monomer mixture,
(2) The latex compound for dip molding according to item 1, which further comprises 0.1 to 5.0 parts by weight of a dialkylsulfosuccinate salt (B) represented by formula (1):
wherein R
1
and R
2
are the same or different and represent an alkyl group containing 5 to 12 carbon atoms and M is metal ion or ammonium ion, and/or 0.5 to 10.0 parts by weight of an alkyl benzene sulfonate (C) whose alkyl group contains 13 to 20 carbon atoms per 100 parts by weight of the monomer mixture;
(3) The latex compound for dip molding according to item 1 or 2, which further comprises 0.01 to 1.0 part by weight of a thickener per 100 parts by weight of the monomer mixture;
(4) The latex compound for dip molding according to item 1 or 2, wherein the emulsion polymerization of the monomer mixture is conducted in the presence of a polyhydroxy compound;
(5) The latex compound for dip molding according to item 4, wherein the polyhydroxy compound is a glycol;
(6) The latex compound for dip molding according to item 1 or 4, wherein the monomer mixture comprises 15 to 45 parts by weight of a vinyl cyanide monomer, 35 to 80 parts by weight of a conjugated diene monomer, 0.1 to 20 parts by weight of an ethylenically unsaturated carboxylic acid monomer, and 0 to 20 parts by weight of other ethylenically unsaturated monomers copolymerizable with the above monomers in 100 parts by weight of the monomer mixture;
(7) The latex compound for dip molding according to item 1, wherein the copolymer latex (L) has 51 to 90% by weight of gel content (methyl ethyl ketone-insolubles);
(8) The latex compound for dip molding according to item 1 or 6, wherein the copolymer latex (L) is obtained by emulsion polymerization of the monomer mixture in the presence of a seed polymer having an average particle diameter of 20 to 90 nm and glass transition temperature (Tg) of −50 to 50° C. obtained by emulsion polymerization between a vinyl cyanide monomer and an ethylenically unsaturated monomer copolymerizable therewith;
(9) The latex compound for dip molding according to item 1, wherein the bubble breaker (A) comprises 15 to 50% by weight of stearic acid or a salt thereof;
(10) A dip-molded product produced by dip molding from the latex compound for dip molding according to any one of items 1 to 9; and
(11) The dip-molded product according to item 10, which is a glove.
DETAILED DESCRIPTION OF THE INVENTION
The process for producing a latex component for dip molding according to the present invention is described below.
I
Ban Hiroshi
Kajiwara Yuichiro
Suetsugu Takashi
Suzuki Shigeo
Tsuji Masaaki
Egwim Kelechi C.
Takeda Chemical Industries Ltd.
Wenderoth , Lind & Ponack, L.L.P.
Wu David W.
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