Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1999-10-19
2001-02-13
Acquah, Samuel A. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C528S271000, C528S272000, C528S297000, C528S300000, C528S302000, C528S307000, C528S308000, C528S361000, C525S437000
Reexamination Certificate
active
06187875
ABSTRACT:
The present invention relates to carboxyl functional polyester resins, to powder coating compositions comprising them, to cured coating compositions and to a process for their preparation.
Powder coating compositions based on acid functional polyesters and epoxy resins are known from e.g. U.S. Pat. Nos. 4,094,721 and 5,262,510 and the International Patent Application WO 95/25762.
U.S. Pat. No. 4,094,721 relates to linear saturated crystalline polyesters of an acid moiety and a moiety of a dihydric alcohol, at least 40 mol percent of the acid moiety being a terephthalic acid moiety, said polyester containing moieties of 1,4-butanediol and
1,6-hexanediol, the ratio of the 1,4-butanediol moieties to 1,6-hexanediol moieties being 10:90-90:10, said polyester being further characterized by
(a) a glass transition temperature of −10° C. to +30° C.;
(b) a melting point in the range of from 40 to 130° C.;
(c) a difference between the glass transition temperature and the melting point being equal to or less than 100° C.;
(d) a reduced viscosity, measured on a 1 wt % solution in a 60-40 mixture of phenol and 1,1,2,2-tetrachloroethane of 0.5 to 1.5.
According to preferred embodiments, in addition to terephthalic acid moieties of isophthalic acid, azelaic acid, adipic acid, sebacic acid had been included, while the molar ratio of 1,4-butanediol to 1,6-hexanediol is 80:20 to 40:60 and additional dihydric alcohols could be included such as ethylene glycol, propanediol-1,3; pentanediol-1,5 and neopentyl glycol.
U.S. Pat. No. 5,262,510 disclose a process for preparing polyester resins, which comprised (1) reacting a mixture of organic carboxylic acid monomers, having at least two reactive carboxyl groups with a mixture composed of at least two aliphatic alcohols, having at least two hydroxyl groups to form a prepolymer, and (2) reacting the prepolymer with a mixture composed of pyromellitic dianhydride and adipic acid or azelaic acid to form polyester resins. Said polyester resins could be combined with epoxy resins into powder coating compositions, which could be cured at temperatures of about 160° C. in a short time of about 10 minutes, and could overcome the disadvantages of conventional mixed powder coatings, which required a high temperature (180° C.) cure.
WO 95/25762 relates to semi-crystalline polyglycidylesters obtainable by glycidation of the acid groups of a semi-crystalline acid functional polyester the latter being a reaction product of at least compound(s) A and compound(s) B, wherein compound A is a straight chain aliphatic alpha,omega-dicarboxylic acid having at least 6 carbon atoms, and wherein compound B is a straight chain aliphatic alpha,omega-primary diol having at least 4 carbon atoms, said reaction product having an acid content of from ≧1.6 meq/g to ≦4.0 meq/g, a number average molecular weight of at least 500, a melting temperature (Tm) by Differential Scanning Calorimetry of ≧25° C., an average acid functionality of 2 or more and essentially no reactive groups other than carboxyl groups.
A was preferably adipic-, pimelic-, suberic-, azelaic-, sebacic- or 1,10-decanedicarboxylic acid, while B was 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol.
However, the coated layers had to be baked at temperatures in the range of from 150 to 225° C.
On the other hand, powder coatings have become during the last decade more and more popular in the coating industry, due to the absence of solvent in the coating formulations.
This absence of solvent will become more and more important due to increasing pressure from environmental and health authorities.
However the conventional powder coating systems for indoor decorative applications have been based up to now on “hybrid” formulations, which consisted of an epoxy resin cured by an acid functional polyester. Typical curing temperatures for said systems are higher than 160° C.
It will be appreciated that there is still a growing need in powder coating formulations, which will be able to cure at temperatures lower than 140° C. in combination with other sufficiently attractive physical properties of the powder coating and of the cured coatings derived therefrom. Such compositions must be very reactive and lead to very short curing times and shall on the other hand show an acceptable storage stability under temperatures of 40° C. Moreover, said powder coating compositions will have to be applied and cured on heat sensitive substrates, such as wood and thermoplastic polymers.
In general, the resins used for powder coatings were amorphous and had therefore, a high melting viscosity. Said high melting viscosity restricted the flow of the coatings and degraded the appearance and smoothness of the films. Therefore high curing temperatures were required in order to overcome the aforementioned disadvantages.
Therefore, it is an object of the present invention to provide improved polyester resins, which can be cured at low temperatures and which, when included in powder coating compositions, cannot deteriorate the appearance of the final coating films and other relevant coating properties such as an acceptable storage stability under 40° C.
It is another object of the present invention to provide powder coating compositions containing the above polyester resins in combination with at least one epoxy resin, which can be cured at low temperatures (<140° C.), which can provide attractive coating properties and which shows an acceptable storage stability under 40° C.
It is still another object of the present invention to provide a process for the preparation of said polyester resins.
More in particular the present invention relates to linear carboxyl functional polyester resins derived from dicarboxylic acids and dialcohols, to powder coating compositions comprising said polyesters and at least one epoxy resin, and which are curable at lower temperatures than the conventional compositions and more in particular at temperatures below 140° C.
Accordingly the invention relates to linear carboxylic acid functional polyester resins, obtainable by reaction of:
(a) at least one aromatic and/or cycloaliphatic dicarboxylic acid compound A, comprising two aromatic and/or secondary aliphatic carboxyl groups in the 1,2-position, or anhydride thereof;
(b) at least one hydroxyl monocarboxylic acid B
1
, comprising two aliphatic hydroxyl groups, which groups each independently may be primary or secondary hydroxyl groups and wherein the carboxylic acid group is a tertiary carboxyl group, mixed with a cycloaliphatic diol B
2
, in an amount of at least 5 wt %, relative to the weight of B
1
and B
2
together;
(c) optionally an aliphatic dicarboxylic acid C, comprising an alkylene group having from 3 to 8 carbon atoms and having two terminal aliphatic carboxyl groups; and
(d) optionally an aromatic monocarboxylic acid D, the molar ratio of the compounds A:B
1
+B
2
:C:D being X:Y+X+Z
1
:Y:Z
2
, wherein X ranges from 1 to 8, Y ranges from 0 to 8, Z
1
ranges from −3 to +3 and Z
2
ranges from 0 to 2 until at least 90% of all the hydroxyl groups as supplied into the reaction mixture have been reacted.
It will be appreciated that another aspect of the present invention is formed by a process for the preparation of the hereinbefore specified linear carboxylic acid functional polyester resins.
Accordingly the invention relates to a process for the preparation of linear carboxylic acid functional polyester resins, comprising the reaction of:
(a) at least one aromatic and/or cycloaliphatic dicarboxylic acid compound A, comprising two aromatic and/or secondary aliphatic carboxyl groups in the 1,2-position, or anhydride thereof;
(b) at least one hydroxyl monocarboxylic acid B, comprising two aliphatic hydroxyl groups, which groups each independently may be primary or secondary hydroxyl groups and wherein the carboxylic acid group is a tertiary carboxyl group;
(c) optionally an aliphatic dicarboxylic acid C, comprising an alkylene group having from 3 to 8 carbon atoms
Bergmans Ann Elise Germaine Christiane
Bertens Jean-Marc Jacques Eric
De Cock Christian Jean Charles
Kooijmans Petrus Gerardus
Rans Marc Jozef
Acquah Samuel A.
Shell Oil Company
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