Hydrophobic lattices and coating compositions containing them

Details Hydrophobic lattices and coating compositions containing them Hydrophobic lattices and coating compositions containing them

2001-10-26

2004-01-27

Zalukaeva, Tatyana (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S078000, C526S079000, C526S080000, C526S307400, C526S318000, C526S319000, C524S501000, C524S591000, C525S162000, C428S461000, C428S463000, C428S520000, C427S388400

Reexamination Certificate

active

06683145

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to latex polymer dispersions and coating compositions containing such lattices, particularly automotive coatings.
BACKGROUND OF THE INVENTION
Increasing environmental concerns initiated an evolution in the automotive coatings industry in the last decades of the twentieth century. The push towards zero volatile organic compound-containing coatings brought more reliance on polymerization techniques limiting use of organic solvents, such as aqueous emulsion polymerization. Emulsion polymerization is carried out by addition polymerization of generally hydrophobic monomer in micelles stabilized by a surfactant in the water. The resulting polymer dispersion is referred to as a latex.
Common variations of the emulsion polymerization process include one-step (batch) and two-step polymerization techniques. In the one-step technique, all the monomers are combined and polymerized in a single step. In the two-step technique, two distinct monomer compositions are added sequentially, forming a first polymer and then polymerizing a second polymer in the presence of the first polymer. The product of the two-step emulsion polymer may be termed a two-stage polymer. A two-stage emulsion polymer offers more opportunity to tailor the emulsion particle properties as well as the properties of the coating obtained form the coating composition.
Coating compositions may be formulated with emulsion polymers, whether one-stage or two-stage, to achieve lower volatile organic content. Automotive coatings must meet rigorous performance requirements, and the polymer and other vehicle components must be able to provide the necessary application characteristics and film properties, including the rheology to achieve excellent appearance. It is important for the cured coating layers to provide a smooth surface so that the vehicle finish will have a mirror-like quality. One problem that has been encountered for automotive coatings made with emulsion polymers has been sagging when the composition is applied to the vehicle. Sagging causes unacceptable distortions of the vehicle finish.
It is believed that increased polymer hydrophobicity will reduce or eliminate sagging by increasing the rate of water release when the coating composition is applied by air-atomized spraying onto the vehicle. If the coating composition contains less water by the time it reaches the vehicle surface, then it will form a coating layer with less tendency to sag. It has been found that more hydrophobic monomers are more difficult to emulsify than more hydrophilic monomers. Mini-emulsion and micro-emulsion techniques, which use shear to form very small monomer droplets, have been employed for emulsion polymerization of more hydrophobic monomer mixtures. These techniques are explained in more detail in U.S. Pat. Nos. 5,969.030, 5,786,420, and 5,569,715, incorporated herein by reference. The mini-emulsion technique provides droplets in the range of 50 to 500 nanometers, while the micro-emulsion technique uses a co-surfactant to achieve monomer droplets in the range of 50 to 100 nm.
While the mini- and micro-emulsion techniques can produce more hydrophobic lattices, the increase in cost is substantial. The equipment for providing the high shear necessary to form the small droplet sizes of mini- and micro-emulsion is much more expensive than traditional emulsion polymerization equipment. The larger amount of surfactant and co-surfactant used in mini-emulsion and micro-emulsion techniques increase the cost of the emulsion polymer even more. Additionally, the added equipment and processing increases the opportunity for coagulum to form. Coagulum is a problem for a number of reasons. Coagulum must be filtered from the product polymer because the coagulated particles will cause imperfections in the coating layer. Coagulum reduces usable product. Coagulum also collects in the equipment so that eventually production must be stopped and the equipment cleaned, which is even more of a problem in mini- and micro-emulsion polymerizations because of additional equipment to clean.
It would be desirable, therefore, to have a method of preparing a more hydrophobic emulsion polymer that would not require the high shear and high surfactant/co-surfactant content necessary for the mini-emulsion and micro-emulsion techniques.
SUMMARY OF THE INVENTION
The invention provides a hydrophobic emulsion polymer prepared with up to about 20% by weight, based on total polymerizable monomers, of addition polymerizable esters of the glycidyl esters of tertiary acids having 9 or more carbon atoms, preferably up to 18 carbon atoms, and particularly having 9 to 11 carbon atoms. The emulsion polymerization process of the invention produces less coagulum without having to increase the amount of surfactant.
While “emulsion” generally refers to a liquid-in-liquid stable suspension and “dispersion” to a solid-in-liquid stable suspension, the products of emulsion polymerization have traditionally been called “emulsions” or “emulsion polymers” regardless of whether their glass transition temperature is such that they are in fact solids. “Emulsion” or “dispersion” will be used interchangeably to refer to dispersions and emulsions.
The invention further provides a coating composition containing the hydrophobic emulsion polymer described. The coating composition also provides better handling properties and better appearance (e.g., improved resistance to pinholing) because of its quicker release of water during application to the substrate.
The invention still further provides a coating formed by applying the coating composition to a substrate and, optionally, curing the applied coating to form a cured coating, and a composite coating having at least one layer formed by applying and optionally curing the coating composition of the invention. The coating composition advantageously contains less surfactant that would tend to increase water sensitivity in the coating prepared from it. The coating also has improved impact resistance and chip resistance.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.
Specific preferred addition polymerizable esters of the glycidyl esters of tertiary acids having 9 or more carbon atoms may be represented by the formula:
in which R
1
, R
2
, and R
3
are alkyl groups, preferably at least one of which is methyl, having a total of at least 8 carbon atoms, preferably up to about 16 carbon atoms preferably from 8 carbons to about 10 carbon atoms; and R
4
and R
5
are either both H or one of R
4
and R
5
is a methyl group and the other is H.
In one preferred embodiment, the polymerizable ester is the condensation product of a polymerizable acid and glycidyl esters of a mixture of tertiary acids having 9 to 11 carbon atoms having at least one methyl group on the &agr;-carbon (e.g., R
1
, R
2
, and R
3
of the above structure are alkyl groups having a total of from 8 carbons to 10 carbon atoms. at least one of which is a methyl group). Mixtures of tertiary acids having 9 to 11 carbon atoms having at least one methyl group on the &agr;-carbon are available under the trademark VERSATIC® acid, and the glycidyl ester of VERSATIC® acid (also commonly called neodecanoic acid) is available under the brand name CARDURA™ Resin E-10 from Resolution Performance Products, Houston, Tex. Examples of polymerizable acids include, without limitation, acrylic acid, methacrylic acid, and crotonic acid. The glycidyl esters may also be reacted with fumaric, maleic, and itaconic anhydrides, fumaric, maleic, and itaconic acids, and monoalkyl esters of these acids.
The emulsion polymer preferably includes crosslinkable functionality such as, without limitation, active hydrogen groups, oxirane groups, carbodiimide groups, and acetoacetoxy groups. The emulsion polymer may be polymerized from a monomer mixture that includes an active hydrogen-functional monomer and, when the active h

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