Coating processes – Direct application of electrical – magnetic – wave – or... – Polymerization of coating utilizing direct application of...
Reexamination Certificate
2001-02-07
2003-10-14
Short, Patricia A. (Department: 1712)
Coating processes
Direct application of electrical, magnetic, wave, or...
Polymerization of coating utilizing direct application of...
C427S508000, C427S385500, C525S044000, C525S445000, C525S454000, C525S455000, C525S530000, C525S531000, C522S090000, C522S100000, C522S101000, C522S102000, C522S103000, C522S104000, C522S106000, C522S107000
Reexamination Certificate
active
06632481
ABSTRACT:
The invention relates to a binder, preferably for coating materials, which is curable thermally and/or by high-energy radiation, to a process for preparing it, to a formulation comprising the binder, and to a procedure relating to the formulation.
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, lamps with very high energy density, and accelerated curing by means of amine coinitiators, are required. 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 levelling 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 levelling, 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 also 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. No. 4,129,488 and U.S. Pat. No. 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 arranged 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 copolymers 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 a crosslinker component 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 dicyclopentadiene, and a crosslinking agent which has vinyl ether groups, vinyl ester groups or (meth)acrylic groups.
DE-A 42 26 520 discloses liquid compositions comprising unsaturated polymers, 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 monomeric photoinitiators added and 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.
WO 97/25724 discloses a process for coating wound and profiled wires with solvent-free polyester resins, polyesterimide resins or polyurethane resins which comprise monomeric or polymeric dicyclopentadiene structural units.
A process for coating articles with UV-curable powder coating materials is disclosed by WO 97/25157. There, the binder of the powder coating materials used comprises copolymers formed from a monomer which has at least one (meth)acrylic group, and special dicyclopentadiene derivatives.
WO 97/25387 discloses, as low-emission binders for coatings, the use of monomer-free saturated and unsaturated polyester resins or mixtures of saturated and unsaturated polyester resins which contain monomeric or polymeric dicyclopentadiene structural units. Also, WO 97/25362 discloses the use of the same compounds as impregnating, casting and coating compositions for components in electrical engineering and electronics and for support materials for sheetlike insulating substances.
Against the background of this prior art, it is an object of the present invention to provide a binder which is curable with high reactivity thermally and/or by high-energy radiation and can be employed preferably, but not exclusively, for coating materials, especially powder coating materials, without oxygen inhibition of the 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 which comprises a mixture of substances comprising (a), as one component, monomers or polymers which have at least one vinyl ether, vinyl ester, (meth)acrylic and/or allyl group and (b), as a further component, saturated polymers and/or unsaturated polymers different from component (a), with the proviso that at least one of components (a) and (b) has structural units of the formulae (I) and/or (II)
and the further component (b) has structural units of the formulae (I) and/or (II) at least when it contains saturated polymers.
These binders of the invention are surprisingly crosslinkable with high reactivity under high-energy radiation, preferably under UV light, and show no oxygen inhibition of the surface even without the use of coinitiators.
In one preferred embodiment component (a) is formed from starting compounds which are selected from the group consisting of vinyl ethers of mono- and polyfunctional (poly)hydroxy compounds, (poly)urethane vinyl ethers and vinyl ether-terminated polyesters and also mixtures of two or more of these compounds.
Alternatively, component (a) can also be formed from starting compounds which are selected from the group consisting of (meth)acrylates of mono- and polyfunctional (poly)hydroxy compounds and (poly)urethane (meth)acrylates, (meth)acrylate-terminated polyesters, (meth)acrylate-fuctionalized epoxy compounds, and also mixtures of two or more of these compounds.
In a further preferred embodiment, components (a) and/or (b) can possess copolymerically bonded groups which in the triplet-excited state are capable of abstracting hydrogen. Groups of this kind are known as Norrish II-type photoinitiators. A particular advantage with the binders of the invention is that it is possible completely to forego the addition of monomeric photoinitiators if these copolymeric photoinitiators are present.
The binder can contain components (a) and (b) in a ratio of from 99.5:0.5 to 0.5:99.5. In this context, preference is given to mixing ratios of from 90:10 to 10:90 and particular preference to those from 70:30 to 30:70.
The invention additionally provides a process for preparing the binder of the invention, in which, in components (a) and, if desired, (b), the structural units of the formulae (I) and (II) are introduced by way of esters of dihydrodicyclopentadienol, of the formula (III)
with monomeric or polymeric carboxylic acids and/or by way of
Blum Rainer
Prieto Rodriguez Jorge
Reich Wolfgang
BASF Coatings AG
Keil & Weinkauf
Short Patricia A.
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