Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Ethylenically unsaturated reactant admixed with either...
Reexamination Certificate
2000-03-08
2001-09-18
Michl, Paul R. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Ethylenically unsaturated reactant admixed with either...
C523S526000
Reexamination Certificate
active
06291581
ABSTRACT:
The invention relates to a powder paint binder composition and to a radiation curable powder paint formulation comprising this binder composition.
As is evident from Powder Coatings Bulletin, 1996, 10, pp. 6-8, there is a market demand for radiation-curable powder paint formulations that can be cured on metal.
It is the object of the invention to provide a radiation-curable powder paint binder composition, which comprises a polymer and optionally a crosslinker, that results in a powder coating with good properties, such as for instance a good storage stability and a viscosity at a relatively low curing temperature that is so low that a good flow can be obtained, and that also results in a powder paint binder formulation that can be cured on metal.
The invention is characterized in that the powder paint composition comprises:
a) a polymer with an amount of unsaturation of between 300 and 1800 g per mole of unsaturated group (WPU) and with a molecular weight (Mn) of between 800 and 5000 g per mole and
b) a crosslinker comprising units of a prepolymer having a molecular weight (Mn) higher than 400 and units of a vinyl ether or an unsaturated alcohol, the number of polymerizable unsaturations of the crosslinker being higher than or equal to 2.
The compounds a) and b) are solid at 20° C.
The powder paint binder composition according to the invention results in a powder paint having sufficient adhesion and flexibility for application on metal substrates and exhibits very good storage or powder stability, processing properties and good flow properties.
Other required properties, such as, for instance, chemical resistance, toughness, color stability and scratch resistance, are also obtained.
A powder paint formulation comprising the binder composition according to the invention can also be applied on other substrates such as for instance wood, chipboard, MDF (medium density fiber board), paper and plastic.
A major practical advantage of the binder composition according to the invention is the combination of fast curing and the absence of emissions of volatile organic compounds.
Another major advantage of the composition according to the invention is the possibility of using powder paint on a metal object that because of its size cannot entirely be heated at a high temperature in one operation. Consequently it is possible to coat very large metal substrates and assembled objects (containing metal as well as for example plastic).
Generally the degree of polymerizable unsaturation in the polymer a)—expressed as WPU—ranges from about 145 to about 3000 grams per mole of unsaturated group (WPU), and preferably from about 300 to about 1800 grams of polymer per mole of unsaturated group. The unsaturated groups may be positioned both within the chain and at the end of the chain.
The molecular weight (Mn) generally ranges from 800 to 5000 and preferably from 2000 to 4500. Mn is determined by means of gel permeation chromatography (GPC) using a polystyrene standard.
Preferably, the polymer (a) is an unsaturated polyester and/or an unsaturated polyacrylate.
If the polymer is an unsaturated polyester, the amount of unsaturation is preferably between 300 and 1800 grams per mole of unsaturated group (WPU) and the molecular weight (Mn) is preferably between 800 and 5000 grams per mole.
The polymer a) and the crosslinker b) can be either (semi)crystalline or amorphous. Depending on the required application, a mixture of crystalline and amorphous compounds can be selected in which the optimum balance of flow and processing properties can be obtained through the choice of the weight ratio.
The glass transition temperature (Tg) of an amorphous polyester generally ranges between 25° C. and 100° C., and preferably between about 30° C. and about 80° C.
The melting point of a crystalline unsaturated polyester and of a crystalline crosslinker generally lies between 35° C. and 180° C., preferably between 50° C. and 120° C.
A general description of powder coatings on the basis of unsaturated polyesters can be found on pages 167-170 of Powder Coatings, Chemistry and Technology, by Misev (Wiley; 1991).
The preparation of the unsaturated polyester can for instance take place in one step, with (un)saturated acids and glycols being heated at, for instance, between about 180° C. and about 230° C. for, between about, 6 and about 15 hours.
Preparation by means of a two-step process, with saturated glycols and acids being esterified at, for instance, 230-250° C. for, for instance, 2 to 8 hours in the first step, and saturated compounds and/or unsaturated glycols and acids being esterified at, for instance, 180-220° C. for, for instance, 2 to 8 hours in the second step, is also possible.
The unsaturated polyester is generally composed of one or more aliphatic and/or cycloaliphatic, mono-, di- and/or polyhydric alcohols and one or more aliphatic, cycloaliphatic and/or aromatic di- or polycarboxylic acids and, if desirable, monocarboxylic acids and/or esters derived therefrom.
Examples of suitable alcohols are benzyl alcohol, ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, neopentyl glycol, butane diol, hexane diol, dimethylol cyclohexane, diethylene glycol, glycerol, trimethylol propane, pentaerythritol and/or dipentaerythritol.
Instead of or besides the alcohol compound(s) one or several epoxy compounds such as, for instance, ethylene oxide, propylene oxide, epoxides (for instance Cardura™), triglycidyl isocyanurate, carbonates such as, for instance, ethylene carbonate and propylene carbonate and/or allyl glycidyl ether can be used.
Examples of suitable di- or polycarboxylic acids are maleic acid, fumaric acid, itaconic acid, citraconic acid, malonic acid, succinic acid, glutaric acid, adipic acid, sebacic acid, 1,4-cyclohexane dicarboxylic acid, hexahydrophthalic acid, hexachloroendomethylene tetrahydrophthalic acid, dichlorophthalic acid, isophthalic acid, terephthalic acid and/or trimellitic acid. The carboxylic acid can also be used in the form of an anhydride, for instance tetrahydrophthalic anhydride, maleic anhydride or phthalic anhydride.
If desired the unsaturated polyester may also contain saturated or unsaturated monocarboxylic acids, such as synthetic and/or natural fatty acids with 2 to 36 carbon acids or esters prepared from these carboxylic acids and polyhydric alcohols such as glycerol. Examples of suitable monocarboxylic acids are lauric acid, stearic acid, oleic acid, linolic acid, benzoic acid, acrylic acid and/or methacrylic acid. The unsaturated polyester may also contain dicyclopentadiene.
As unsaturated carboxylic acid use is preferably made of fumaric acid and/or maleic acid.
For the preparation of polyesters having a sufficient degree of crystallinity it is desirable, though not necessary, for the (di) acids and (di) ols used in the polycondensation to contain an even number of carbon atoms. Aromatic and/or aliphatic cyclic diacids and diols in which the functional groups are parapositioned relative to each other, such as, for instance, terephthalic acid, cyclohexane dicarboxylic acid and dimethyl cyclohexane generally promote the crystallinity.
The monomers for the synthesis of (semi)crystalline polyesters preferably comprise diols and diacids with an even number of carbon atoms, such as, for instance, terephthalic acid, isophthalic acid, adipic acid and cyclohexane dicarboxylic acid, hexane diol, butane diol, ester diol and dimethylol cyclohexane.
The preparation of (semi)crystalline polyesters is described in, for instance, WO-A-91-14745.
Hydroxyl-functional unsaturated polyesters usually have a hydroxyl number between 5 mg KOH/gram of resin and 75 mg KOH/gram of resin and preferably a hydroxyl number of between 25 mg KOH/gram of resin and 60 mg KOH/gram of resin. The acid number is as a rule lower than 10 mg KOH/gram of resin and is preferably chosen as low as possible.
Acid-functional unsaturated polyesters usually have an acid number of between 15 mg KOH/gram of resin and 75 mg KOH/gram of resin, and preferably an acid number of between 25 mg KOH/gram of resin and 45 mg KOH/gr
Bayards Richard A.
De Jong Evert S
Udding-Louwrier Saskia
DSM N.V.
Michl Paul R.
Pillsbury & Winthrop LLP
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