Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2000-08-11
2001-10-23
Cameron, Erma (Department: 1762)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S286000, C526S289000, C526S314000, C526S318300
Reexamination Certificate
active
06306991
ABSTRACT:
FIELD OF THE INVENTION
This invention generally relates to a method of crosslinking polymers and more particularly relates to catalytic crosslinking of polymers having oxidatively crosslinkable functional groups. “Crosslinkable” and “crosslinking” refer to the formation of new chemical bonds between existing polymer chains.
BACKGROUND OF THE INVENTION
A number of polymers are capable of being crosslinked in the presence of a catalyst. A significant improvement in physical and chemical properties of such polymers occurs when such polymers are subjected to a crosslinking process. However, crosslinked polymers become highly viscous as a result of their increased molecular weight, which occurs due to the crosslinking process. As a result, crosslinked polymers are typically incapable of being molded into desired shapes or are incapable of being readily applied over substrate surfaces as a layer.
Thus, a catalyst is stored separately from a polymer or a polymeric component of a coating composition, which contains the polymer. Just before use the catalyst is mixed with the polymeric component to form a pot mix which can then be readily applied as a layer by conventional means, such as by brushing or spraying, over the surfaces of substrates or can be readily shaped into an article by conventional means, such as molding. The polymers in the layer then crosslink in the presence of the catalyst to form a coating on the surface having improved physical and chemical properties, such as durability, water and solvent resistance, mar resistance, block resistance compared to the uncrosslinked polymer.
Several types of catalysts are known to crosslink a polymer. For example, it is conventional to use a heavy metal catalyst, such as a tin compound, for crosslinking polymers having oxidatively crosslinkable functionalities. However, these metal catalysts tend to have a low catalytic activity. As a result, a significantly higher quantity of such catalysts, generally in amounts exceeding 5000 parts per million (ppm) or in excess of 0.5 weight percent based on the total polymer solids weight, have to be added to the polymer for achieving a desired degree of crosslinking of the polymer. Moreover, these metal catalysts have adverse impact on the environment because they are hazardous to human, animal and plant habitat. Furthermore, these heavy metal catalysts cannot be readily degraded into harmless compounds. Thus, articles made from polymers containing these heavy metal catalysts or articles coated with coating compositions containing these heavy metal catalysts cannot be safely disposed of in typical land fills or other disposal sites, unless such catalysts are removed or rendered harmless before disposal. The present invention solves this problem by providing for an oxidative catalyst that has no substantially adverse impact on the environment and it readily undergoes biodegradation upon disposal. As a result, the catalyst of the present invention can be safely disposed of in conventional landfills or disposal sites without any significant impact on the environment. Furthermore, as the catalyst of the present invention is catalytically more active than conventional heavy metal catalysts, smaller amounts of the catalyst of the present invention are needed to achieve the same degree of crosslinking that is accomplished by utilizing higher amounts of conventional heavy metal catalysts.
STATEMENT OF THE INVENTION
The present invention is directed to a method of crosslinking an oxidative polymer having oxidatively crosslinkable functional groups, said method comprising:
contacting said oxidative polymer with a catalytic amount of an oxidizing enzyme; and
crosslinking said oxidatively crosslinkable functional groups on said oxidative polymer.
The present invention is also directed to a method of applying a coating on a substrate comprising:
contacting a polymeric component of a coating composition with a crosslinking component of said coating composition to form a pot mix, said polymeric component comprising an oxidative polymer having oxidatively crosslinkable functional groups and said crosslinking component comprising a catalytic amount of an oxidizing enzyme;
applying a layer of said pot mix over said substrate; and
crosslinking said oxidatively crosslinkable functional groups on said oxidative polymer to form said coating on said substrate.
The present invention is further directed to a two-pack coating composition comprising:
a first container containing a polymeric component, which comprises an oxidative polymer having oxidatively crosslinkable functional groups; and
a second container containing a catalytic component, which comprises a catalytic amount of an oxidizing enzyme sufficient to crosslink said oxidatively crosslinkable functional groups on said oxidative polymer, when said polymeric component is mixed with said catalytic component.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
As defined herein:
“Polymer” means a dispersed, solubilized or a sequential polymer, defined below, all provided with oxidatively crosslinkable functional groups.
“Dispersed polymer” means particles of polymer colloidally dispersed and stabilized in an aqueous medium.
“Solubilized polymer” includes “Water soluble polymer”, “Water reducible polymer” or a mixture thereof. Water soluble polymer means a polymer dissolved in an aqueous medium. Water reducible polymer means a polymer dissolved in water and water miscible solvent. Solubilized polymer results in a polymer solution characterized by having the self-crowding constant (K) of the Mooney equation [1/ln
&eegr;rel
=1/BC−K/2.5] equal to zero. By contrast, dispersed polymer has (K) equal to 1.9. The details of Mooney equation are disclosed in an article entitled “Physical Characterization of Water Dispersed and Soluble Acrylic Polymers” by Brendley et al., in “Nonpolluting Coatings and Coating Processes” published by Plenum Press, 1973 and edited by Gordon and Prane.
“Sequential polymer” means particles of a polymer colloidally dispersed and stabilized in an aqueous medium having a core/shell morphology, wherein reactable group(s) are located on the shell or on the relatively more hydrophilic portion of the sequential polymer.
“Polymer particle size” means the diameter of the polymer particles measured by using a Brookhaven Model BI-90 Particle Sizer supplied by Brookhaven Instruments Corporation, Holtsville, N.Y., which employs a quasi-elastic light scattering technique to measure the size of the polymer particles. The intensity of the scattering is a function of particle size. The diameter based on an intensity weighted average is used. This technique is described in Chapter 3, pages 48-61, entitled
Uses and Abuses of Photon Correlation Spectroscopy in Particle Sizing
by Weiner et al. in 1987 edition of American Chemical Society Symposium series. To measure the particle diameter, 0.1 to 0.2 grams of a sample of the polymer was diluted to a total of 40 milliliters (mLs) with distilled water. A two mLs portion was delivered into an acrylic cell, which was then capped. The particle size in nanometers was measured for 1000 cycles. The measurement was repeated three times and an average was reported.
“Tg of a polymer” is a measure of the hardness and melt flow of the polymer. The higher the Tg, the lesser will be the melt flow and the harder will be the coating. Tg is described in
Principles of Polymer Chemistry
(1953), Cornell University Press. The Tg can be actually measured or it can be calculated as described by Fox in
Bull. Amer. Physics Soc.,
1, 3, page 123 (1956). Tg, as used herein, refers to actually measured values.
“GPC weight average molecular weight” means the weight average molecular weight determined by gel permeation chromatography (GPC) which is described on page 4, Chapter I of
The Characterization of Polymers
published by Rohm and Haas Company, Philadelphia, Pa. in 1976, utilizing polymethyl methacrylate as the standard. The GPC weight average molecular weight can be estimated by calculating a theory weight avera
Fischer Gordon Charles
Larson Gary Robert
Cameron Erma
Falk Stephen T.
Rohm and Haas Company
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