Polymer latex suitable for the preparation of dip-molded articles

Abstract

The present invention relates to a polymer latex made by free-radical emulsion polymerization comprising polymer particles containing structural units derived from at least one conjugated diene component, whereby said polymer particles comprise at least one hard phase segment having a glass transition temperature (Tg) of at least 50° C. and at least one soft phase segment having a glass transition temperature (Tg) of 10° C. at most, the total amount of hard phase segments being 2 to 40 wt-% and the total amount of the soft phase segments being 60 to 98 wt-% based on the total weight of the polymer particles, whereby the Tg is measured by DSC according to ASTM D3418-03 and said polymer latex having an electrolyte stability determined as critical coagulation concentration of less than 30 mmol / l CaCl2 (determined for a total solids content of the latex of 0.1% at pH 10) that is particularly suitable for the production of dip-molded articles. Furthermore, the present invention relates to a process for making such a polymer latex, to the use of said polymer latex for the production of dip-molded articles, to a compounded polymer latex composition that is suitable for the production of dip-molded articles, to a method for making dip-molded latex articles, as well as to the latex articles obtained thereby.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application claims the benefit of US Provisional patent Application No. 60 / 609,094, filed Sep. 9, 2004, the entire disclosure of which is hereby expressly incorporated by reference.BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention relates to a polymer latex that is particularly suitable for the production of dip-molded articles. Furthermore, the present invention relates to a process for making such a polymer latex, to the use of said polymer latex for the production of dip-molded articles, to a compounded polymer latex composition that is suitable for the production of dip-molded articles, to a method for making dip-molded latex articles, as well as to the latex articles obtained thereby. [0004] 2. Description of the Related Art [0005] Thin wall extensible articles, such as gloves and other medical products have long been made from a natural latex polymer. Typically such articles are formed ...

AI Technical Summary

Benefits of technology

[0051] Although according to the present invention single soft phase and / or hard phase segments may be constituted by homo-polymer blocks it is preferred that at least the soft phase segment(s) is(are) constituted by copolymer blocks, particularly copolymer blocks that contain in addition to structural units derived from at least one conjugated diene structural units that are derived from at least one other ethylenically unsaturated co-monomer. In a particularly preferred embodiment the soft phase and the hard phase segments are constituted by copolymer blocks. Most preferably, if copolymer blocks are present either as soft phase segment or hard phase segment or both these copolymer blocks are random copolymer blocks. These copolymer blocks can be easily prepared by free-radical emulsion polymerization in a great versatility. Thus, it is a particular advantage of the present invention that the latex polymer can by easily tailored to the specific needs of the particular end use.

[0052] It is well known to a person skilled in the art how to adjust the Tg of the hard phase segment or the soft phase segment by selecting a monomer or a mixture of monomers that result in the desired Tg in the polymerization process. For example, the Tg's of the homopolymers of a wide range of monomers are disclosed in J. Brandrup, E. H. Immergut (eds.), Polymer Handbook, Second Edition, Wiley, New York,1975

[0053] For random copolymers the Tg depends on the weight fractions of the component monomers and the Tg's of the component homopolymers. A rough correlation is described by the Fox equation: 1 / Tg=w / Tg1+w2 / Tg2+ . . .

[0054] where w1, w2, . . . are the weight fractions of the component monomers and Tg1, Tg2, . . . are the Tg's of the component homopolymers in ° K. The Fox equation allows a first orientation for the Tg of a copolymer. For the resulting real Tg's also further parameters of the used monomers and the process have an important influence. Therefore physical methods for the determination of the Tg like the DSC method are still necessary.

[0055] It is within the routine of a person skilled in the art to select in the copolymerization process, as will be discussed below, certain monomers or mixture of monomers that give rise to a hard segment or a soft segment in the appropriate amounts in order to obtain a polymer particle within the ranges of Tg for the hard segments and the soft segments as well as the relative amounts of both segments, as specified above for the present invention.

[0056] The polymer particles of the present invention contain structural units derived from conjugated dienes.

Problems solved by technology

However, diene monomers can be used as long as sulfur vulcanization is not applied for crosslinking the resultant rubber.

But nevertheless external crosslinkers are necessary that have a potential not to be bound to the polymer and therefore to bloom out to the surface of the polymer in the final product, and therefore in itself may cause health risks, especially in view of the selections of crosslinking agents disclosed in that reference.

Thus the rubber compositions still have to be compounded with the crosslinking agent which results in a complicated process for making the latex compound.

In this process the relative amounts have to be carefully adjusted in order to achieve the desired crosslinking density, and if possible to bind all the additional crosslinkers into the final molecule to avoid blooming out of crosslinker component that in itself again may create a health risk.

Furthermore, especially when using polyvalent metal ions as crosslinking agent latex instability during the compounding process may occur which makes the compounding process particularly difficult.

Furthermore the crosslinking agents, especially the polyvalent ions, reduce the stability of the latex compound and therefore the ability to store the already compounded latex composition prior to its use in a dip-molding process for making the medical care product.

Furthermore, especially the introduction of polyvalent metal ions as crosslinking system in rubber compositions may increase environmental hazards.

Consequently the elastomeric polymers to be used or making medical care products according to the teaching of both latter prior art documents have the disadvantage that still crosslinking is necessary.

Either a complex radiation curing has to be employed which in itself is a health hazard, or traditional vulcanization systems that suffer from the drawbacks as discussed above, have to be applied.

Finally conventional dip-molding processes cannot be applied using these polymer systems in order to make the desired products.

Due to the anionic polymerization process the number of monomers which can be used for block copolymerization is very limited.

The limited versatility in respect of suitable monomers for the anionic block copolymerization process is another disadvantage of the teaching in U.S. Pat. No. 5,500,469.

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