Powder paint binder composition

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Reexamination Certificate

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C428S480000, C528S272000, C528S296000, C528S297000, C528S298000, C528S300000, C528S302000, C528S303000, C528S304000, C528S306000, C528S307000, C528S308000, C528S308600

Reexamination Certificate

active

06337137

ABSTRACT:

The invention relates to a powder paint binder composition comprising a polymer that contains endomethylene tetrahydrophthalic acid (HIMIC) units.
A powder paint binder composition based on such a polymer is described in U.S. Pat. No. 3,956,228. This patent discloses the esterification of a mixture, consisting of 10-50 mol % endomethylene tetrahydrophthalic acid (HIMIC) and dibasic acids with a glycol after which curing to yield a coating takes place by means of air drying. The coatings based on these compositions exhibit poor mechanical properties such as impact resistance.
Furthermore these compositions do not result in colorless or light-colored powder coatings.
It is an object of the present invention to provide a powder paint binder composition comprising HIMIC-units which composition results in powder coatings having a good impact resistance.
The powder paint binder composition according to the invention comprises a polymer that contains endomethylene tetrahydrophthalic acid units and a crosslinker.
This binder composition has a good storage stability and a good reactivity and after curing results in a powder coating with a combination of desirable properties such as, for example, good flow, hardness, scratch resistance, chemical resistance and mechanical properties.
Furthermore, in spite of the presence of HIMIC double bonds in the curable polymer a light coloured powder coating can be obtained.
According to a preferred embodiment of the invention the acid or hydroxyl functional polymer containing HIMIC units is obtained by first preparing an unsaturated polymer which is subsequently reacted with cyclopentadiene (CPD) at a temperature between about 160° C. to about 220° C.
Generally, prior art two-step methods for the preparation of polyesters are difficult to control due to several exothermic reactions resulting from HIMIC being prepared in the first step followed by the combination with other monomers in a second step and subsequent esterification of the polymer. Said exothermic reactions can lead to high pressures and to high temperatures.
The two step procedure according to the present invention provides a safe process.
According to another preferred embodiment of the invention the polymer contains at least 10 wt. % HIMIC but less than 100 wt. % (relative to the monomers), and preferably between about 35 and about 80 wt. %, as a result of which the good impact resistance is obtained.
The HIMIC-units in the polymer can (in contrast to the HIMIC-units in the polymer according to U.S. Pat. No. 3,956,228) act as functional acid end groups which can react with the crosslinkers.
It is a further advantage that the less reactive, compared with for example fumaric acid, HIMIC need not be incorporated and is not obtained until the reaction over the acid groups has taken place, so that the overall reaction time can be shortened and a well defined product can be obtained.
Preferably the unsaturated polymer is an unsaturated polyester.
The unsaturated polester prepared in the the first step is generally formulated from one or more aliphatic and/or cycloaliphatic mono-, di- and/or polyvalent alcohols and one or more aliphatic, cycloaliphatic and/or aromatic di- or polyvalent carboxylic acids and/or esters derived therefrom. If desired also monocarboxylic acids can be applied.
Examples of suitable alcohols include benzyl alcohol, ethylene glycol, propylene glycol, neopentyl glycol, butane diol, hexane diol, dimethylol cyclohexane, diethylene glycol, glycerol, trimethylol propane, pentaerythritol, dipentaerythritol, hydrated bisphenol-A, 2,2-bis-(2-hydroxyethoxy)phenylpropane and/or 2,2-bis-2-hydroxypropoxy phenylpropane. Instead of or in addition to the alcohol compound(s) one or more epoxy compounds, such as for example ethylene oxide, propylene oxide and/or allylglycidyl ether or dicyclopentadiene can be used.
Examples of suitable di- or polyvalent carboxylic acids include 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 or esters thereof. The carboxylic acid can also be used in the form of an anhydride, for example tetrahydrophthalic anhydride, endomethylene tetrahydrophthalic anhydride, hexahydrophthalic anhydride, maleic anhydride or phthalic anhydride.
For the acid component fumaric acid in combination with isophthalic acid and/or terephthalic acid can be used. Optionally, saturated or unsaturated monocarboxylic acids, such as synthetic and/or natural fatty acids with 2 to 36 carbon atoms or esters prepared from these carboxylic acids and polyvalent alcohols such as glycerol can also be used. Examples of suitable monocarboxylic acids are lauric acid, stearic acid, oleic acid, linolic acid, benzoic acid, acrylic acid and/or methacrylic acid.
According to a preferred embodiment of the invention the unsaturated polymer is an unsaturated is polyester containing fumaric acid, maleic acid (anhydride) and/or terephthalic acid as acid units.
The alcohol component of the unsaturated polyester is preferably ethylene glycol, propylene glycol and/or neopentyl glycol.
The unsaturated polyester may be both crystalline and amorphous.
The amount of double bonds in the unsaturated polyester is usually between about 120 and about 2000 grams per unsaturated group and preferably between about 125 and about 1500.
The molecular weight M
n
(number average molecular weight) of the unsaturated polyester is usually between about 500 and about 6000, preferably between about 1000 and about 4500.
Acid functional polyesters usually have an acid number between about 25 mg KOH/grams resin and about 145 mg KOH/grams resin, preferably an acid number between about 30 mg KOH/grams resin and about 120 mg KOH/grams resin.
Hydroxyl-functional polyesters usually have a hydroxyl number between about 25 mg KOH/grams resin and about 145 mg KOH/grams resin, preferably a hydroxyl number between about 30 mg KOH/grams resin and about 120 mg KOH/grams resin.
The functionality is generally between about 1.5 and about 4 and is preferably between 1.9 and 3.5.
The polymerization reaction in the preparation of the unsaturated polyester generally takes place in the presence of catalysts and inhibitors.
Suitable catalysts include for example tetrabutyl titanate and dibutyl tin oxide.
Suitable inhibitors include for example butyl alcohol and hydroquinone.
In the formation of the unsaturated polyester catalysts and inhibitors are generally used in amounts between about 0.005 and about 1 wt. % relative to the monomers.
The preparation of the unsaturated polyester can take place via a one-step process or via a multistep process.
If the unsaturated polyester preparation takes place via a one-step process, glycols, acids, catalysts and optionally inhibitors can be esterified to the desired acid number or hydroxyl number at a temperature lower than 220° C. To remove low-molecular material or to obtain the desired acid number or hydroxyl number, optionally a vacuum can be applied at reduced temperature.
If the unsaturated polyester preparation takes place in two steps, in the first step saturated acids, glycols, catalysts and inhibitors can be esterified at temperatures between, for example, about 210° C. to about 260° C. during for a period of about 2-10 hours, and in the second step the unsaturated compounds, acids and glycols can be esterified at temperatures between, for example, about 180° C. to about 220° C. for a period of about 5-16 hours. The monomers and the reaction conditions can be varied depending on the desired properties.
After the unsaturated polyester has been obtained dicyclopentadiene (DCPD) is added to the unsaturated polyester at temperatures between about 160° C. and about 220° C. resulting in a retro Diels-Alder reaction forming CPD.
Next the cyclopentadiene (CPD) and the fumaric acid or maleic acid groups in the unsaturated polyester react by

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