Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
2000-08-16
2003-04-29
Seidleck, James J. (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, C522S173000, C522S111000, C522S112000, C528S068000
Reexamination Certificate
active
06555597
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to pulverulent binders containing specific oligo- and polyurethanes having (meth)acryloyl groups which may be applied to a substrate, melted by heating and cured by means of high energy radiation, especially UV radiation; to a process for their preparation; and to their use as a component of powder coating compositions.
2. Description of the Prior Art
Particularly high quality coatings from pulverulent binders are obtained using oligo or polyurethanes. Such compounds are described e.g. in EP-A 410242. They are prepared by reacting at least one organic polyisocyanate with at least one monohydric alcohol having (meth)acryloyl groups, and at least one isocyanate-reactive compound free from (meth)acryloyl groups.
These compounds must be prepared in an organic solvent. A solventless preparation is not possible due to the viscosities of urethane acrylates, which are known to be high at temperatures up to 120° C. Increasing the preparation temperature beyond 100 to 120° C. involves the risk, familiar to those skilled in the art, of a spontaneous undesirable polymerization of the compounds having (meth)acryloyl groups. Thus the disadvantage of the binders described in EP-A 410242 is that they must be prepared in an organic solvent, which has to be removed at high cost at the end of the preparation. Even small solvent residues strongly influence the melting behavior, which is critical to the application of the powder coatings.
To lower the melt viscosity of powder coatings based on unsaturated polyesters or polyacrylates with acryloyl functional groups, the powders are first prepared and then, according to EP-A 636 669, mixed with a low molecular weight crosslinking agent having vinyl ether, vinyl ester or (meth)acrylate functional groups. In the cited patent application, the polyacrylates with acryloyl functional groups and the crosslinking agent are also prepared in organic solvents, which subsequently have to be removed. Furthermore, mixtures of vinyl ethers or esters with unsaturated (meth)acrylates involve a considerably higher risk of an undesirable spontaneous polymerization (copolymerization of electron-rich and electron-deficient double bonds) than e.g. in the case of pure (meth)acrylate systems.
In Journal of Coatings Technology, vol. 70, no. 884, Sept. 1998, 57-62, A. Hult et al. describe radiation-curable powder coatings based on mixtures of amorphous polymers having methacrylate functional groups (polyacrylate) and crystalline (meth)acrylate monomers. Again, the polymers and monomers must be separately prepared using organic solvents, which have to be removed at high cost after the preparation.
An object of the present invention is to provide oligo- and polyurethanes having (meth)acryloyl groups, which are suitable as binders for powder coatings and which have a greatly reduced residual organic solvent content than prior art binders.
It has now been found that oligo- and polyurethanes having (meth)acryloyl groups can be prepared as binders for powder coatings without using solvents so that the residual organic solvent content is extremely low.
SUMMARY OF THE INVENTION
The present invention relates to pulverent binders for powder coating compositions which contain oligo- and polyurethanes having (meth)acryloyl groups, are curable by means of high energy radiation and have an organic solvent content of less than 1 wt. %.
The present invention also relates to a process for preparing pulverent binders for powder coating compositions containing oligo- and polyurethanes having (meth)acryloyl groups and curable by means of high energy radiation by reacting in the absence of an organic solvent
A) a monoisocyanate or diisocyanate having 4 to 20 carbon atoms and
B) a diisocyanate and/or a polyisocyanate that may be the same as A) or different from A) with
C) a monohydroxyalkyl (meth)acrylate having 2 to 12 carbons in the alkyl chain,
D) at least one alcohol having (meth)acryloyl groups that may be the same as C) or different from C) and
E) a compound which is free of (meth)acryloyl groups and contains two or more isocyanate-reactive groups,
wherein
i) the equivalents of OH groups in C) corresponds to the equivalents of isocyanate groups in A),
ii) the sum of the equivalents of OH groups in D) and the equivalents of isocyanate-reactive groups in E) corresponds to the equivalents of isocyanate groups in B) and
iii) the amount of the reaction product of A) and C), based on the total weight of oligo- and polyurethanes having (meth)acryloyl groups, is 10 to 95 wt. %.
The present invention further relates to the use of the binders in powder coating compositions for coating wood, metal, plastic, mineral and/or preprimed substrates.
DETAILED DESCRIPTION OF THE INVENTION
The binders according to the present invention preferably contain 10 to 95 wt. % of the reaction product of component A) with component C) and 5 to 90 wt. % of the reaction product of component B) with components D) and E), wherein the percentages are based on the total weight of oligo- and polyurethanes having (meth)acryloyl groups. Preferably, the percentages of the reaction products add up to 100.
Suitable mono- or diisocyanates A) include aliphatic or aromatic isocyanates such as cyclohexyl isocyanate, butylene diisocyanate, hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), 3(4)-isocyanatomethylcyclohexyl isocyanate (IMCI), trimethylhexamethylene diisocyanate (2,2,4- and/or 2,4,4-trimethylhexamethylene diisocyanate), the isomeric bis(4,4′-isocyanatocyclohexyl)methanes, 1,4-cyclohexylene diisocyanate, phenyl isocyanate, toluyl isocyanate, 1,4-phenylene diisocyanate, 2,4- and/or 2,6-toluylene diisocyanate (TDI), 1,5-naphthylene diisocyanate, 2,4′- and/or 4,4′-diphenylmethane diisocyanate (MDI) and derivatives of the preceding isocyanates containing urethane, isocyanurate, allophanate, biuret, uretdione and/or iminooxadiazinedione groups, provided that these derivatives contain one or two free NCO groups. HDI, IPDI, TDI, MDI, the isomeric bis(4,4′-isocyanatocyclohexyl)-methanes, and mixtures thereof are preferred. IPDI, HDI and mixtures thereof are particularly preferred.
Component B) is selected from polyisocyanates having a functionality of at least 2. Suitable polyisocyanates include the known organic polyisocyanates from polyurethane chemistry, which have aliphatically, cycloaliphatically and/or aromatically bound isocyanate groups and a molecular weight of 144 to 1000, preferably 168 to 300. Examples include butylene diisocyanate, hexamethylene dilsocyanate (HDI), isophorone diisocyanate (IPDI), 3(4)-isocyanatomethylmethylcyclohexyl isocyanate (IMCI), trimethylhexamethylene diisocyanate (2,2,4- and/or 2,4,4-trimethylhexamethylene diisocyanate), the isomeric bis(4,4′-isocyanato-cyclohexyl)methanes, isocyanatomethyl-1,8-octane diisocyanate, 1,4-cyclohexylene diisocyanate, 1,4-phenylene diisocyanate, 2,4- and/or 2,6-toluylene diisocyanate (TDI), 1,5-naphthylene diisocyanate, 2,4′- and/or 4,4′-diphenylmethane diisocyanate (MDI), 4,4′,4″-triphenylmethane triisocyanate, derivatives of these polyisocyanates containing urethane, isocyanurate, allophanate, biuret, uretdione and/or iminooxadiazinedione groups, and mixtures of the preceding polyisocyanates. The derivatives preferably have a molecular weight of up to approx. 1000 and may be prepared in accordance with U.S. Pat. Nos. 3,124,605, 3,183,112, 3,919,218, 4,324,879 and EPA 798 299.
HDI, IPDI, TDI, MDI and/or polyisocyanates obtained by the trimerization of HDI, TDI or IPDI are preferably used as component B). HDI, IPDI and mixtures thereof are particularly preferred.
Monohydroxyalkyl (meth)acrylates C) are selected from hydroxyalkyl esters of acrylic acid or methacrylic acid having 2 to 12 carbon atoms, preferably 2 to 4 carbon atoms, in the hydroxyalkyl ester group. Examples include hydroxyethyl (meth)acrylate, 2- or 3-hydroxypropyl (meth)acrylate and 2-, 3- or 4-hydroxybutyl (meth)acrylate. 2-Hydroxyethyl acrylate is
Fischer Wolfgang
Thometzek Peter
Weikard Jan
Zwiener Christian
Bayer Aktiengesellschaft
Gil Joseph C.
McClendon Sanza L.
Roy Thomas W.
Seidleck James J.
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