Highly functional polymer latex

Details Highly functional polymer latex Highly functional polymer latex

2001-03-30

2003-05-13

Sanders, Kriellion A. (Department: 1714)

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

active

06562892

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to high ethylene ethylene-vinyl acetate (EVA) emulsions comprising a water dispersible copolymer which is non-dispersible in aqueous solutions containing 0.5 weight percent or more of an inorganic salt. The invention also relates to ethylene-vinyl acetate emulsions containing at least 55 percent by weight of ethylene, and a process for producing said high ethylene EVA emulsions. The invention also relates to emulsions comprising a water dispersible polymer which is non-dispersible in aqueous solutions containing 0.5 weight percent or more of an inorganic salt, where the polymer has a Tg of less than 25° C.
BACKGROUND OF THE INVENTION
Ethylene-vinyl acetate (EVA) polymers provide useful properties at relatively low cost in many industrial applications. Ethylene monomer is a low-cost monomer and therefore incorporation of as much ethylene as possible into an ethylene-vinyl acetate polymer allows one to take advantage of cost and performance benefits.
U.S. Pat. No. 3,644,262 discloses a process for increasing the ethylene content of an EVA emulsion. An ethylene content of 5 to 40 percent is targeted in the patent, and examples of copolymers containing 11 to 21 percent ethylene are cited.
EP 0 990 688 describes an EVA pressure sensitive adhesive containing carboxyl monomer. Said PSA has an ethylene content of greater than 45 percent, and most preferably from 45 to 55 percent.
Salt sensitive polymers are dispersible in water, but non-dispersible in salt solutions. Said polymers are useful in applications where a film is desired which will dissolve or disperse in water. Such applications include polymer products which can be disposed of in water, where the film will disperse.
U.S. Pat. No. 5,312,883 discloses a composition of a water-soluble polymer that is insoluble in 0.5% salt solutions. The composition requires 30 to 75% acrylic acid, 5 to 30 percent of a C
8
to C
12
alkyl (meth)acrylate, and 20 to 40 percent of a C
2
to C
4
alkyl (meth)acrylate. The disclosure is limited to acrylic acid copolymers and specific (meth)acrylates. Also, the disclosed process for preparing these polymers is costly and time consuming.
WO 00/38751 discloses an ion-sensitive polymer which is insoluble in a neutral salt solution containing at least 0.3 weight percent salt, and is soluble in tap water containing 15 ppm to 500 ppm of one or more multivalent ions. Said polymers are formed as solution polymers.
U.S. patent application Ser. No. 09/540,033 describes salt sensitive aqueous emulsions which are non-dispersible in aqueous solutions containing 0.5% or more of an inorganic salt which contain a copolymer of an 10 to 90 percent of an acid monomer and a second monomer.
Surprisingly, it has been found that EVA emulsion polymers containing a high level of ethylene can be produced without a carboxyl-containing monomer. Said polymers, using other functional comonomers, produce better properties than carboxyl-containing EVAs. It has also been found that stable EVA emulsion polymers, having an ethylene content of greater than 55 percent by weight, can be obtained. Also, it has been found that emulsions can be produced which form flexible films that are dispersible in water but not in an aqueous solution containing 0.5 percent or more of an inorganic salt. The combination of these two findings yields a high ethylene content ethylene-vinyl acetate emulsion polymer capable of forming a film which is redispersible in water but non-redispersible in a 0.5 percent or greater inorganic salt solution.
SUMMARY OF THE INVENTION
The present invention is directed to an ethylene-vinyl acetate emulsion polymer comprising:
a) a copolymer of ethylene and vinyl acetate having greater than 55 percent by weight ethylene; and
b) a hydrophilic polymeric colloid stabilizer
wherein said hydrophobic colloid comprises from 1 to 100 percent by weight of an acidic ethylenically unsaturated monomer; wherein said ethylene-vinyl acetate copolymer is water-dispersible, and wherein said ethylene-vinyl acetate copolymer is non-dispersible in an aqueous solution containing 0.5 weight percent or more of an inorganic salt.
In a second embodiment, the present invention is directed to an aqueous emulsion comprising a water-dispersible polymer which is non-dispersible in aqueous solutions containing 0.5 weight percent or more of an inorganic salt, wherein said water-dispersible polymer comprises from 1 to 100 percent by weight of a hydrophilic monomer and from 0 to 99 percent by weight of at least one non-hydrophilic monomer, wherein a film formed from said polymer has a Tg of less than 25° C.
In a third embodiment, the present invention is directed to a high ethylene, ethylene-vinyl acetate emulsion polymer comprising greater than 55 percent by weight of ethylene, and to a process for producing said high ethylene content EVA polymer.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is directed to salt-sensitive emulsion polymers containing a water-dispersible polymer which is non-dispersible in aqueous solutions containing 0.5 weight percent or more of an inorganic salt. The invention is also directed to an ethylene-vinyl acetate emulsion polymer having at least 55 percent by weight of ethylene, and a process for producing said emulsion polymer. The invention is also directed to a combination of the above two concepts producing a high ethylene content EVA emulsion polymer which is water-dispersible, yet non-dispersible in an aqueous solution containing 0.5 percent or more of an inorganic salt.
Salt Sensitive Emulsion Polymers
Salt sensitive emulsion polymers are polymers which are formed by an emulsion polymerization process, and which form films that are dispersible in tap water, yet are non-dispersible in water containing at least 0.5 percent by weight of an inorganic monovalent, divalent, or trivalent salt, or mixtures thereof The polymer is dispersible, rather than soluble, in water. Dispersible, as used herein, means that in tap water, a film formed from the polymer breaks into small discrete pieces or particles that can be filtered out. These pieces are capable of being filtered from the water. While not being bound to a theory, it is believed that the dispersion of the polymer film is related to the fact that a film forms from an emulsion by coalescence of polymer particles, forming weak bonds between particles. In water, some bonds between the particles will break, resulting in clusters of polymer particles. This is different from a solution polymer in which polymer chains mix and entangle during film formation, and this film dissolves into individual polymer chains, which cannot be filtered. Since the polymer contains a high level of hydrophilic monomer(s), when the emulsion dries to a film, the particles are easily dispersed in water.
The emulsion polymers of the present invention consist of a polymer which is stabilized by a hydrophilic polymeric colloid. The polymer itself is not salt sensitive. The colloid may or may not be salt sensitive. However, the colloid-stabilized polymer particle is salt sensitive.
The polymer colloid contains at least one monomer, and ideally two or more monomers. At least one of the monomers is a hydrophilic monomer.
The hydrophilic monomer may be an acidic monomer containing a carboxylic acid, a dicarboxylic acid, a sulfonic acid, or a phosphonic acid group, or a mixture thereof. Examples of carboxylic acid monomers include, but are not limited to, acrylic acid, methacrylic acid, maleic acid, maleic acid half esters, maleic anhydride, itaconic acid, and crotonic acid. Preferred carboxylic acids include acrylic acid and methacrylic acid. Sulfonic acid monomers include, but are not limited to styrene sulfonic acid, 2-acrylamido-2-methyl-1-propanesulfonic acid, vinylsulfonic acid, and the salts of these acids. Examples of monomers containing a phophonic acid group include, but are not limited to styrene phosphonic acid, sodium vinyl phosphonate, vinylphosphoric acid, and CH
2
=C(CH
3
)COO(CH
2
)
n
OPO
3
H, where n is from 2 to 4. A preferre

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