Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
2001-11-26
2004-06-08
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...
C522S093000, C522S096000, C522S111000, C522S173000, C522S097000, C525S437000, C525S445000, C525S453000, C525S455000, C427S496000, C427S500000, C427S508000, C427S514000, C427S195000, C526S301000, C526S302000
Reexamination Certificate
active
06747070
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a UV curable powder coating composition that crosslinks to form a light-stable and weather-stable paint film possessing excellent gloss.
2. Discussion of the Background
Thermally crosslinkable powder coatings are known and are frequently used in the paint industry.
For instance, DE-C-27 35 497 describes PUR powder coatings possessing excellent weathering and heat stability. The crosslinkers, the preparation of which is described in DE-C-27 12 931, consist of &egr;-caprolactam blocked isophorone diisocyanate containing isocyanurate groups. Also known are polyisocyanates containing urethane, biuret or urea groups having blocked isocyanate groups.
The disadvantage of these systems is the detachment of the blocking agent during the thermal crosslinking reaction. Since the blocking agent may thus be emitted into the environment, special precautions have to be taken for ecological and occupational hygiene reasons to clean the exit air and/or recover the blocking agent. In addition, the reactivity of the crosslinkers is low. Curing temperatures above 170° C. are required.
Both disadvantages, emission of blocking agent and curing at high temperatures, can be circumvented by powder coatings which are cured by radiation, known as UV powder coatings. Such UV powder coatings are known and described for example in U.S. Pat. No. 3,485,732, EP-A-0 407 826 and U.S. Pat. No. 5,639,560.
U.S. Pat. No. 5,639,560 describes UV curable powder compositions with specific crystalline polyesters which also have methacryloyl end groups, as binders. These powder compositions optionally contain ethylenically unsaturated oligomers, including urethane acrylates. The amount of ethylenically unsaturated oligomer is minor, preferably up to 10 percent by weight. But the UV powder coating formulations disclosed in this patent have significant disadvantages. They are only grindable at minus 80° C. and generally the resulting coatings are either not stable to outdoor weather or are not flexible. A particularly serious disadvantage is a very low König pendulum hardness of below 120 s.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a UV powder coating composition which is storage stable at 35° C. After curing of the paint films, the composition is required to lead to coatings which are hard, flexible, and stable to outdoor weather. Moreover, the powder coatings should be grindable using little, if any, cryogen.
This and other objects have been achieved by the present invention, the first embodiment of which includes a UV curable powder coating composition, comprising:
I. a binder comprising
A) 60-90% by weight of at least one amorphous urethane acrylate; and
B) 10-40% by weight of at least one crystalline urethane acrylate;
provided that a Tg of a mixture of A and B is at least 35° C.; and
II. an auxiliary.
In another embodiment the present invention relates to a polymer containing a urethane group and a terminal acrylate group, comprising:
A) 60-90% by weight of at least one amorphous urethane acrylate; and
B) 10-40% by weight of at least one crystalline urethane acrylate;
provided that a Tg of a mixture of A and B is at least 35° C.; and
wherein said amorphous urethane acrylate A is formed by reaction of the following components:
A1) at least one amorphous hydroxyl-containing polyester having a Tg of 35 to 80° C.;
A2) at least one polyisocyanate;
A3) at least one compound having at least one alcohol group and at least one polymerizable acrylate group; and
wherein said crystalline urethane acrylate B is formed by reaction of the following components;
B1) at least one crystalline hydroxyl-containing polyester;
B2) at least one polyisocyanate; and
B3) at least one compound having at least one alcohol group and at least one polymerizable acrylate group.
Yet another embodiment of the present invention relates to a coating, obtained from the above powder coating composition; wherein said coating is opaque or transparent.
The present invention also relates to a method of producing a coating, comprising:
coating a substrate with the powder coating composition according to claim
1
.
DETAILED DESCRIPTION OF THE INVENTION
The object of the present invention is surprisingly achieved by a radiation curable powder coating composition which includes a binder comprising a mixture of at least one amorphous urethane acrylate and at least one crystalline urethane acrylate, said mixture having a glass transition point (Tg) of at least 35° C., preferably at least 45° C. and most preferably at least 55° C.
The invention provides a UV curable powder coating composition comprising
I. a binder comprising
A) 60-90% by weight of at least one amorphous urethane acrylate, and
B) 10-40% by weight of at least one crystalline urethane acrylate,
subject to the proviso that the Tg of the mixture of A and B is at least 35° C.; and
II. an auxiliary and/or an additive material.
The amount of component A includes all values and subvalues therebetween, especially including 65, 70, 75, 80 and 85% by weight. The amount of component B includes all values and subvalues therebetween, especially including 15, 20, 25, 30 and 35% by weight.
The urethane acrylate for the purpose of this invention consist of a hydroxyl-containing polyester to which a urethane group and an acrylate group are attached by reaction with a polyisocyanate and an acrylate-containing alcohol.
The amorphous urethane acrylate of the invention is prepared from an amorphous hydroxyl-containing polyester (A1) having a Tg of 35-80° C. by reaction with a polyisocyanate (A2) and a compound which contains both at least one alcohol group and at least one polymerizable acrylate group (A3). The amorphous urethane acrylate possesses a urethane group and a terminal acrylate group.
A1. An amorphous hydroxyl-containing polyester having a Tg of 35-80° C. is prepared by polycondensation of a dicarboxylic acid and a diol. The Tg of polyester (A1) includes all values and subvalues therebetween, especially including 40, 45, 50, 55, 60, 65, 70 and 75° C. The condensation is effected in an inert gas atmosphere at temperatures of 100 to 260° C., preferably 130 to 220° C., in the melt or azeotropically, as described, for example, in Methoden der Organischen Chemie (Houben-Weyl); vol. 14/2, pages 1 to 5, 21 to 23, 40 to 44, Georg Thieme Verlag, Stuttgart, 1963, or in C. R. Martens, Alkyd Resins, pages 51 to 59, Reinhold Plastics Appl. Series, Reinhold Publishing Comp., New York, 1961.
Preferred carboxylic acids for preparing polyesters can be aliphatic, cycloaliphatic, aromatic and/or heterocyclic in nature and can be optionally halogen substituted and/or unsaturated. Preferred examples are succinic acid, adipic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid, terephthalic acid, isophthalic acid, trimellitic acid, pyromellitic acid, tetrahydrophthalic acid, hexahydrophthalic acid, hexahydroterephthalic acid, dichlorophthalic acid, tetrachlorophthalic acid, endomethylenetetrahydrophthalic acid, glutaric acid and, if available, their anhydrides, dimethyl terephthalate, bisglycol terephthalate. Isophthalic acid is particularly preferred.
Useful polyols include, for example, monoethylene glycol, 1,2- and 1,3-propylene glycol, 1,4- and 2,3-butylene glycol, di-&bgr;-hydroxyethylbutanediol, 1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, decanediol, dodecanediol, neopentylglycol, cyclohexanediol, 3(4),8(9)-bis(hydroxymethyl)tricyclo[5.2.1.0
2,6
]decane (dicidol), bis(1,4-hydroxymethyl)cyclohexane, 2,2-bis(4-hydroxycyclohexyl)propane, 2,2-bis[4-(&bgr;-hydroxyethoxy)phenyl]propane, 2-methyl-1,3-propanediol, 2-methyl-1,5-pentanediol, 2,2,4(2,4,4)-trimethyl-1,6-hexanediol, glycerol, trimethylolpropane, trimethylolethane, 1,2,6-hexanetiol, 1,2,4-butanetriol, tris([&bgr;-hydroxy-ethyl) isocyanurate, pentaerythritol, mannitol and sorbitol and also diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, polypropylene glycols, polybutyle
Franzmann Giselher
Spyrou Emmanouil
Wenning Andreas
Berman Susan W.
Degussa - AG
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