Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
2001-02-07
2003-04-01
Berman, Susan W. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
C522S090000, C522S098000, C522S099000, C522S100000, C522S104000, C522S170000, C522S172000, C522S173000, C522S179000, C522S181000, C522S182000, C522S183000, C528S025000, C528S026000, C528S065000, C528S075000, C528S220000, C528S272000, C528S298000
Reexamination Certificate
active
06541535
ABSTRACT:
The invention relates to a binder for powder coating materials curable thermally and/or by high-energy radiation, to the powder coating material comprising the binder, itself, and to its use in accordance with the invention.
UV-curable coating materials for use in liquid form, and powder coating materials, are continually acquiring more fields of use on the grounds of reduced solvent consumption. A major problem with known UV coating materials, however, is the inhibiting effect of atmospheric oxygen on curing at the film surface. To overcome this inhibition requires lamps with very high energy density, and accelerated curing by means of amine coinitiators. These amines are frequently the cause of odor nuisance.
In the case of UV powder coating materials, in addition, further problems arise from the contradictory requirements for good blocking resistance of the powders on storage and good leveling of the melted coating film. For good blocking resistance, the glass transition temperature and melting point should be as high as possible, whereas for good leveling, and to permit use on heat-sensitive substrates, they should be as low as possible, in order to prevent a curing reaction before optimum surface smoothness has developed and in order to prevent substrate damage. Likewise for the purpose of improving the surface smoothness, the melt should have a low viscosity and the reaction should set in only after a delay period. These concepts are difficult to realize with powder coating materials whose curing is based on one of the known, thermally activated reactions between resin and hardener, e.g., polyepoxy resin and dicarboxylic acid hardener, since a viscosity-increasing reaction sets in simultaneously with the melting process. In the case of radiation-curable powder coating materials, on the other hand, it should be possible to separate the melting process from crosslinking. In order to meet this requirement, various attempts have been disclosed in the prior art.
U.S. Pat. Nos. 4,129,488 and 4,163,810 disclose UV-curable powder coating materials having specific spatial arrangements of ethylenically unsaturated polymers. Here, the binder consists of an epoxy-polyester polymer in which the epoxy adduct is arranged spatially such that by means of a linear polymer chain it is at a distance from the polyester adduct. In addition, the polymer comprises a chemically bonded photoinitiator.
EP-A 0 650 978, EP-A 0 650 979 and EP-A 0 650 985 disclose copolymers whose essential constituent is a relatively high fraction of monomers having the structural unit of methacrylic acid. These monomers can be used as binders for UV-curable powder coating materials, and feature a relatively narrow molecular weight distribution.
EP-A 0 410 242 discloses binders for UV-curable powder coating materials, consisting of polyurethanes which have specific (meth)acryloyl groups, can be crosslinked without crosslinker components or peroxides, and are therefore stable on storage. Crosslinking by UV irradiation requires the addition of photoinitiators.
EP-A 0 636 669, furthermore, discloses a UV-curable binder for powder coating materials which consists of unsaturated polymers, which can include cyclopentadiene, and a crosslinking agent which has vinyl ether groups, vinyl ester groups or (meth)acrylic groups.
WO-A-93/25596 discloses polyacrylates, for use as automotive topcoats, which are functionalized with double bonds in a wide variety of ways.
DE-A 42 26 520 discloses liquid compositions comprising unsaturated polymer, in the form of unsaturated polyesters, and compounds containing (meth)acryloyl groups and/or vinyl ether groups. These compositions can be crosslinked both by means of free-radical initiators and by means of radiation curing, and are used as binders for coating materials. In the case of crosslinking by UV radiation it is necessary to add photoinitiators.
With the UV coating materials of the cited prior art, problems arise as a result of the need to employ coinitiators, generally amines, in order to provide high photosensitivity and to overcome the known oxygen inhibition of the surface. The elimination products of these photoinitiators remain in the cured coatings and are the cause of odor nuisance.
In addition, EP-A-0 322 808 has disclosed a prior art which reveals a liquid binder, curable by means of high-energy radiation, which consists of a mixture of an ethylenically unsaturated polyester component, which may also include an ethylenically unsaturated polyester oligomer, and a nonpolymerized vinyl ether component. In this case, the vinyl ether component is selected such that per molecule of the vinyl ether component it contains on average at least two vinyl ether groups which are able to react with the ethylenic double bonds of the polyester component.
Against the background of this prior art, it is an object of the present invention to provide a binder for powder coating materials which are curable thermally and/or by means of high-energy radiation and which when used is unaccompanied by oxygen inhibition of the film surface, so that it is possible to forego the use of malodorous amines and other coinitiators.
We have found that this object is achieved by a binder having in each case terminally and/or laterally at least one vinyl ether group a) and at least one, preferably copolymerizable group b) which is different from the vinyl ether groups a) but is coreactive with the groups a), there being on average at least one vinyl ether group a) and one coreactive group b) per oligomer or polymer molecule.
Powder coating materials which comprise such a binder surprisingly show high UV reactivity and no oxygen inhibition of the surface when cured in air. This has the advantage that it is possible to forego the use of amines and other coinitiators.
Also possible is curing to a B-stage, i.e., to a partially cured state in which the curing is interrupted and can be started again later.
In connection with the binder of the invention, mention should be made of the problem, known per se to the skilled worker, that in the course of the customary polymer synthesis, which takes place under statistical reaction conditions, and/or in the case of polymer-analogous functionalization, it is also possible for polymer molecules to be formed which are functionalized only in one way, e.g., with the vinyl ether groups a), or which are not functionalized at all. Since such polymeric substructures with little functionalization or none whatsoever may adversely effect the properties of the polymers of the invention, it is preferred to direct the preparation process such that minimal fractions of such minimally functionalized or completely unfunctionalized polymeric substructures are formed. Methods suitable for this purpose are known to the person skilled in the art of polymers. They include the use of excesses of substances which if unreacted can be separated off again later, or, if desired, the residence of the excess in the finished coating binder. It has been found that any residual fractions which nevertheless remain have essentially no adverse effect on the success of the invention when using the claimed binders.
The outstandingly high UV reactivity which is observed when the binder of the invention is used in powder coating materials curable thermally and/or by means of high-energy radiation, which is unaccompanied by oxygen inhibition of the surface, is attributed to the fact that functionalization of the polymeric substructure in the binders of the invention permits self-crosslinking to take place, whereas in the prior art the binder compositions are mixtures of substances which must only be crosslinked with one another.
The schematic structural principle of the binders of the invention can be illustrated as follows:
In accordance with the structural principle depicted, the functional groups a) and b) can be linked to the polymeric substructure at the same point and/or different points, and they may arbitrarily terminate this substructure. The functional groups a) and b) may also be present more than once
Blum Rainer
Prieto Rodriguez Jorge
BASF Coatings AG
Berman Susan W.
Keil & Weinkauf
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