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.

1 . 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 CaCl 2  (determined for a total solids content of the latex of 0.1% at pH 10).  
   
   
       2 . The polymer latex of  claim 1 , wherein the total amount of hard phase segments is between 5 and 30 wt-% and the total amount of the soft phase segments is between 70 and 95 wt-%, the weight percentages being based on the total weight of the polymer particles.  
   
   
       3 . The polymer latex of  claim 1 , wherein the total amount of hard phase segments is 10 to 25 wt-% and the total amount of the soft phase segments is 75 to 90 wt-%, the weight percentages being based on the total weight of the polymer particles.  
   
   
       4 . The polymer latex of  claim 1 , wherein the soft phase segments contain independently from each other structural units derived from monomers selected from the group consisting of conjugated dienes; ethylenically unsaturated mono-carboxylic acids; ethylenically unsaturated di-carboxylic acids, anhydrides, mono-esters and mono-amides thereof; (meth)acryl nitrile; styrene; substituted styrenes; alpha-methyl styrene; C1 to C10 esters of (meth)acrylic acid; amides of (meth)acrylic acid; ethylenically unsaturated compounds comprising N-methylol amide groups, and ester and ether derivatives thereof.  
   
   
       5 . The polymer latex of  claim 1 , wherein the hard phase segments contain independently from each other structural units derived from monomers selected from the group consisting of ethylenically unsaturated mono-carboxylic acids; unsaturated di-carboxylic acids, anhydrides, mono-esters and mono-amides thereof; ethylenically unsaturated compounds comprising N-methylol amide groups, and ester and ether derivatives thereof; and mixtures thereof; (meth)acryl nitrile; styrene; substituted styrenes; alpha-methyl styrene; C1 to C8 esters of (meth)acrylic acid; amides of (meth)acrylic acid; and mixtures thereof.  
   
   
       6 . The polymer latex of claims  1  having an electrolyte stability determined as critical coagulation concentration of less than 25 mmol/l CaCl 2  determined for a total solids content of the latex of 0.1% at pH 10.  
   
   
       7 . The polymer latex of  claim 6 , having an electrolyte stability determined as critical coagulation concentration of less than 20 mmol/l CaCl 2  determined for a total solids content of the latex of 0.1% at pH 10.  
   
   
       8 . The polymer latex of  claim 1 , wherein the polymer particles comprise groups that are capable of self-crosslinking.  
   
   
       9 . Polymer latex of  claim 8 , wherein the groups capable of self-crosslinking are selected from N-methylol amide groups and their ester and ether derivatives thereof; and mixtures thereof.  
   
   
       10 . The polymer latex of  claim 9 , wherein said groups capable of self-crosslinking are selected from N-methylol acrylamide, N-methylol methacrylamide, N-methoxymethyl-(meth)acrylamide, N-n-butoxy-methyl-(meth)acrylamide, N-acetoxymethyl-(meth)acrylamide, and N(-2,2-dimethoxy-1-hydroxyethyl)acrylamide.  
   
   
       11 . The polymer latex of  claim 1 , wherein said polymer latex is carboxylated.  
   
   
       12 . The polymer latex of  claim 11 , wherein the soft phase segment or the hard phase segment or both are carboxylated.  
   
   
       13 . The carboxylated polymer latex of  claim 11 , wherein the polymer particles comprise groups that are capable of self-crosslinking.  
   
   
       14 . The polymer latex of  claim 13 , wherein said groups capable of self-crosslinking are selected from N-methylol amide groups and their ester and ether derivatives thereof; and mixtures thereof,  
   
   
       15 . The polymer latex of  claim 14 , wherein said groups capable of self-crosslinking are selected from N-methylol acrylamide, N-methylol methacrylamide, N-methoxymethyl-(meth)acrylamide, N-n-butoxy-methyl-(meth)acrylamide, N-acetoxymethyl-(meth)acrylamide, and N(-2,2-dimethoxy-1-hydroxyethyl) acrylamide.  
   
   
       16 . A compounded polymer latex composition suitable for the production of dip molded articles comprising the polymer latex of  claim 1 .  
   
   
       17 . The compounded polymer latex composition of  claim 16  being free of sulfur and accelerators for the sulfur vulcanization.  
   
   
       18 . The compounded polymer latex composition of  claim 17  being substantially free of polyvalent cations and cross-linkers.  
   
   
       19 . A compounded polymer latex composition suitable for the production of dip molded articles comprising the carboxylated polymer latex of  claim 11 .  
   
   
       20 . The compounded polymer latex composition of  claim 19  being free of sulfur and accelerators for the sulfur vulcanization.  
   
   
       21 . The compounded polymer latex composition of  claim 20  being substantially free of polyvalent cations and cross-linkers.  
   
   
       22 . A compounded polymer latex composition suitable for the production of dip molded articles comprising the carboxylated polymer latex of  claim 13 .  
   
   
       23 . The compounded polymer latex composition of  claim 22  being free of sulfur and accelerators for the sulfur vulcanization.  
   
   
       24 . The compounded polymer latex composition of  claim 23  being substantially free of polyvalent cations and cross-linkers.  
   
   
       25 . A method for making dip molded latex films comprising: 
 (a) immersing a mold having the desired shape of the final article in a coagulant bath comprising a solution of a metal salt;    (b) removing the mold from the bath and optionally drying the mold;    (c) immersing the mold as treated in step (a) and (b) in the compounded latex composition of claims  16  or  19 ;    (d) removing the mold from the latex composition and optionally immersing the latex coated mold in a water bath;    (e) heat treating the latex coated mold obtained from step (d) at a temperature of 80 to 180° C.; and    (f) removing the latex article from the mold.    
   
   
       26 . A film made from a polymer latex of  claim 1 .  
   
   
       27 . The film according to  claim 26  exhibiting an increase in tensile strength of at least 2 MPa after heat treatment at 120° C. for 30 minutes compared to the identical polymer latex film kept at 25° C.  
   
   
       28 . The film according to  claim 26  being heat treated and having a tensile strength of at least about 7 MPa and an elongation at break of at least about 300% measured according to ISO 37:1994.  
   
   
       29 . A film made from a carboxylated polymer latex of  claim 11 .  
   
   
       30 . The film according to  claim 29  exhibiting an increase in tensile strength of at least 2 MPa after heat treatment at 120° C. for 30 minutes compared to the identical polymer latex film kept at 25° C.  
   
   
       31 . The film according to  claim 29  being heat treated and having a tensile strength of at least about 7 MPa and an elongation at break of at least about 300% measured according to ISO 37:1994.  
   
   
       32 . A film made from a polymer latex of  claim 13 , wherein the polymer particles comprise groups that are capable of self-crosslinking.  
   
   
       33 . The film according to  claim 32  exhibiting an increase in tensile strength of at least 2 MPa after heat treatment at 120° C. for 30 minutes compared to the identical polymer latex film kept at 25° C.  
   
   
       34 . The film according to  claim 32  being heat treated and having a tensile strength of at least about 7 MPa and an elongation at break of at least about 300% measured according to ISO 37:1994.  
   
   
       35 . A latex article comprising a latex film according to claims  26  or  29  being selected from surgical gloves, examination gloves, condoms, catheters and industrial and household gloves.  
   
   
       36 . A method for making a polymer latex comprising 
 polymerizing in an emulsion polymerization process in presence of a free-radical initiator, stabilizers and water a first ethylenically unsaturated monomer or mixture of monomers that results in a hard phase segment having a glass transition temperature (Tg) of at least 50° C., and    thereafter polymerizing a second monomer or mixture of monomers that results in a soft phase segment having a glass transition temperature (Tg) of 10° C. at most or vice versa in amounts so that the total amount of hard phase segments is 2 to 40 wt-% and the total amount of the soft phase segments is 60 to 98 wt-% based on the total weight of the polymer, whereby the Tg is measured by DSC according to ASTM D3418-03 with the proviso that at least one conjugated diene is employed in the polymerization process and the amount of stabilizers is adjusted to obtain an electrolyte stability determined as critical coagulation concentration of less than 30 mmol/l CaCl 2  determined for a total solids content of the latex of 0.1% at pH 10.    
   
   
       37 . The method of  claim 36 , further comprising polymerizing at least one hard phase and/or soft phase segment.  
   
   
       38 . The method of  claim 37 , wherein the first segment is polymerized in the presence of a seed latex for adjusting the particle size.  
   
   
       39 . A method for making an impregnated substrate comprising impregnating a substrate with the polymer latex according to claims  1 ,  11 , or  13 .  
   
   
       40 . A method for making a coated substrate comprising coating a substrate with the polymer latex according to claims  1 ,  11 , or  13 .  
   
   
       41 . Article comprising a substrate coated or impregnated by the polymer latex according to claims  1 ,  11 , or  13 .  
   
   
       42 . Article according to  claim 41  wherein the substrate is a textile material.