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
1999-11-30
2001-05-08
Nutter, Nathan M. (Department: 1711)
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...
C524S833000
Reexamination Certificate
active
06228935
ABSTRACT:
FIELD OF INVENTION
This invention relates to high solids, free radical polymerizations of acrylate and/or vinyl acetate monomers in a latex resulting in high solids (desirably greater than 50 wt. %, preferably 70-95 wt. %) dispersion of polymer particles. The monomer composition polymerized in the presence of the latex need not be similar to the composition of the monomers used to make the latex and may be chosen to modify the properties of dried films from the dispersion. The high solids makes the material economical to ship or store and when formulated into a caulking sealant results in a sealant with low modulus, high elongation and low shrinkage.
BACKGROUND
Traditionally, higher performance sealants and caulks have been formulated using solvent based polymer systems such as silicone and polyurethane polymers as the binder for the sealant formulation. These solvent based types of sealant formulations generally yield sealants with good application properties (thixotropy and viscosity) and in the cured form typically have the elastomeric properties and adhesion required for a high performance sealant or caulking material. However, in recent years, with increasing government regulation and heightened consumer awareness, the manufacturers of solvent based sealants are coming under increasing pressure to reduce the VOC (volatile organic content) of their product (i.e. organic solvent content).
Dispersions of polymer particles in water have been used extensively in water-based sealants such as coatings and caulking. Their low viscosity, low volatile organic emissions, and ease of application have been favorable factors for their use. However, irrespective of the polymer particle sizes there has been a barrier at from 40-65% solids (depending on emulsifier type and other conditions) above which dispersions of polymer particles are difficult to prepare. Therefore high solids sealants were made by adding fillers. The fillers dilute the polymer in the final application lowering elongation and increasing modulus. Polymers having low Tg values (such as below 0° C.) which are particularly useful in formulating sealants and caulks requiring low temperature flexibility are sticky.
One example of high solids polymerization is European Patent Publication No. 0 515 719 Al, which discloses a self-adhering acrylate copolymer, which can be used for the production of self-adhering surface layer formulations. This acrylate copolymer is produced by a combined suspension and emulsion polymerization. The solids content recited are 30-70 wt. % and the examples show 65 wt. % solids.
An article by Do Ik Lee in the Journal of Paint Technology, Vol. 42, No. 550 (1970) pp 579-587 discusses the packing of binary mixtures of spheres.
U.S. Pat. No. 4,130,523 to Hoy and Peterson discloses nearly 70 volume % solids. Their latex particles are desirably no larger than 1.5 microns in diameter.
It is the object of the current application to polymerize in the presence of a preformed latex additional monomers creating a high solids, low viscosity, thixotropic product especially useful in coatings and sealants.
SUMMARY OF THE INVENTION
It has been found that a latex dispersion of latex polymer particles, when used as the medium for a further polymerization, can result in high solids content (such as 70-95 wt. %) polymer particle dispersions with lower viscosities than achieved with traditional polymerization. The resulting dispersions show bimodal or multimodal particle size distributions with particle diameters ranging from around 0.05 to 100 microns. The resulting broad particle size distribution, and good mixing during polymerization are believed to be major factors allowing high solids contents to be achieved.
Upon removal of shear, the polymer particle dispersions thicken but are capable of being liquified. The large particles (above 4 &mgr;m) when formed are typically nonspherical, desirably having an average aspect ratio between the largest and smallest diameter of each particle of at least 1.5.
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“Ultra High Solids Copolymer Emulsion for Demanding Applications” by Mary L. Houseman, et al.,Adhesive Age, pp. 49-50, 54, 56-57, 59-60 (Oct. 1, 1995).
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Bidinger Gregory P.
Dunaway James H.
Hernandez Pamela K.
Calfee Halter & Griswold LLP
Nutter Nathan M.
Tremco Incorporated
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