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
2000-10-25
2002-08-20
Sellers, Robert E. L. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S438000, C549S368000, C549S453000, C549S525000, C549S561000
Reexamination Certificate
active
06437045
ABSTRACT:
The invention relates to a powder coating composition comprising a binder selected from carboxyl-group-containing polyesters, carboxyl-group-containing poly(meth)acrylates and mixtures of the said substances, and one or more epoxy compounds as thermal hardeners, and also to a preferred preparation process for one type of the epoxy compounds that are to be used.
Powder coating compositions as referred to at the outset are used in a wide variety of forms. Triglycidyl isocyanurate (TGIC) has been successful as an epoxy hardener in such compositions, especially for external paints, which must have a high weather resistance. Its solid consistency, inter alia, has resulted in TGIC being considered today as the standard hardener for powder coating compositions based on carboxyl-group-containing polyesters as binders (see, e.g. Ullmann's Encyclopedia of Industrial Chemistry, 5th Ed., Vol A9, p. 559) and on carboxyl-group-containing poly(meth)acrylates (see, e.g., Johnson Wax Speciality Chemicals Product Application Bulletin, Powder Coatings).
There have also been known for some time, however, powder coating compositions stable to outside weathering that are based on a TGIC-free, solid mixture of epoxy resins as hardener (see, e.g., EP-A-0 536 085), where substantial amounts of a liquid, higher-functional epoxy resin, e.g. Trimellitic acid triglycidyl ester, are incorporated into a solid epoxy resin, e.g. diglycidyl terephthalate, without the total mixture of epoxy resins taking on a liquid consistency as a result. In industrial practice, however, virtually the only solid resins available hitherto for such hardener mixtures have been difunctional glycidyl esters. Furthermore, the solid resin makes up the majority of such a mixture, so that a significant disadvantage of such hardener mixtures is that their epoxy functionality is appreciably reduced in comparison with TGIC. In addition, clean glycidylisation of 1,2-dicarboxylic acids is not easy on an industrial scale.
Accordingly there is still a need for new powder coating compositions with properties comparable to those of the above-mentioned powder coating compositions from a surface-coating technology standpoint, that is to say, for powder coating compositions that, especially, have good flow behaviour and high reactivity and with which it is possible to produce coatings having a high crosslinking density and a high level of stability towards weathering and UV. The present invention provides such new powder coating compositions.
The invention relates especially to powder coating compositions that comprise a binder selected from carboxyl-group-containing polyesters, carboxyl-group-containing poly(meth)acrylates and mixtures of the said substances, and one or more epoxy compounds, wherein the epoxy compounds comprise at least one compound of formula (I) that is solid at 25° C.:
wherein
A corresponds to a group of formula (II), (III), (IV) or (VI):
in which
B is an x-valent organic radical that is derived from a polyol having x or more hydroxyl groups by the removal of x hydroxyl groups;
E is a (2x)-valent organic radical that is derived from a polyol having (2x) or more hydroxyl groups by the removal of (2x) hydroxyl groups; and
D is a (y+2z)-valent radical that is derived from a polyol having (y+2z) or more hydroxyl groups by the removal of (y+2z) hydroxyl groups;
R
1
and R
5
are each independently of the other hydrogen, halogen, C
1
-C
4
alkyl or C
1
-C
4
alkoxy or are together a methylene group; and
R
2
, R
3
, R
4
, R
6
, R
7
, R
8
and R
9
are each independently of the others hydrogen, halogen, C
1
-C
4
alkyl or C
1
-C
4
alkoxy; and
x is an integer of at least 3;
y is an integer from 1 to (x−1) and
z is (x−y).
The powder coating compositions according to the present invention are distinguished, inter alia, by a very good flow behaviour, and yield a cured material that has a high crosslinking density, a high degree of fastness to weathering and a high gloss. Epoxy resins of formula (I) are, in addition, toxicologically less harmful than glycidyl compounds such as are normally used for powder coating compositions.
When one of the radicals R
1
, R
2
, R
3
, R
4
, R
5
, R
6
, R
7
, R
8
and R
9
in formula (I) is halogen, it is preferably, for example, chlorine or bromine; when one of those radicals is C
1
-C
4
alkyl or C
1
-C
4
alkoxy, it is, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl or tert-butyl or an alkoxy group corresponding to one of those alkyl groups.
Preferably, the radicals R
1
, R
2
, R
3
, R
4
, R
5
, R
6
, R
7
, R
8
and R
9
are C
1
-C
4
alkyl or, especially, hydrogen.
At least some of the compounds of formula (I) are known or are obtainable in known manner or in a manner analogous thereto.
Compounds of formula (I) wherein A corresponds to a group of formula (II) can be obtained, for example, from a polyol of formula B(OH)
x
wherein x is as defined hereinbefore, by esterifying the x hydroxyl groups of the polyol with cyclohexene-3-carboxylic acid and then epoxidising the carbon double bonds of the resulting polyester compound in customary manner, for example by means of an organic peracid, such as, for example, peracetic acid.
An especially preferred process for the preparation of compounds of formula (I) wherein A corresponds to a group of formula (II) comprises the transesterification of a cyclohexene-3-carboxylic acid ester, especially a cyclohexene-3-carboxylic acid C
1
-C
4
alkyl ester, such as methyl 3-cyclohexenecarboxylate, with a polyol of formula B(OH)
x
, wherein x is as defined hereinbefore, in the presence of LiNH
2
as transesterification catalyst, and with continuous removal from the reaction mixture of the alcohol freed from the cyclohexene-3-carboxylic acid ester, the transesterification being followed by the epoxidation of the carbon double bonds of the resulting transesterification product, which is carried out in customary manner, for example by means of an organic peracid, such as, for example, peracetic acid. The use of LiNH
2
as catalyst results, inter alia, in especially good yields and a high degree of product purity. The said process can also be used for epoxy compounds of formula (I) wherein A corresponds to a group of formula (II) and x is 1 or 2, and the present invention relates also thereto.
Compounds of formula (I) wherein A corresponds to a group of formula (III) can be prepared, for example, in accordance with British Patent No. 870 696, by reacting a polyol of formula B(OH)
x
, wherein x is as defined hereinbefore, with an aldehyde of formula (V)
wherein R
1
and R
5
, as well as R
2
, R
3
, R
4
, R
6
, R
7
, R
8
and R
9
, are likewise as defined hereinbefore, in the presence of a suitable catalyst, such as, for example, p-toluenesulfonic acid, and epoxidising the carbon double bonds of the resulting product in customary manner, for example by means of an organic peracid.
Compounds of formula (I) wherein A corresponds to a group of formula (IV) can be obtained, for example, in accordance with SU-A-1 792 956, by trimerising an aldehyde of the above-mentioned formula (V) in the presence of an acid, for example phosphoric acid or nitric acid, and epoxidising the double bonds of the resulting product, again in customary manner.
Compounds of formula (I) wherein A corresponds to a group of formula (VI) are likewise known, for example from Batog, A. E.; Pet'ko, I. P.; Kozlova, L. V.; Pandazi, I. F.; Plast. Massy (1979); (10), p. 9-10, where, for example, a compound of the above-mentioned formula (I) is described in which A corresponds to the group set out below and D is a tetravalent radical derived from pentaerythritol by the removal of 4 hydroxyl groups:
Preference is given to powder coating compositions according to the invention wherein A corresponds to a group of formula (II), especially where x is from 3 to 6 and, preferably, is 4.
B in formula (II) is preferably a radical that is derived from an aliphatic polyol having from 3 to 20 carbon atoms, from a cycloaliphatic polyol having from 5 to 20 carbon atoms
Francois Jacques
Rickert Christoph
Tena Mireille
Turpin François
Lyon & Lyon LLP
Neuman Kristin H.
Sellers Robert E. L.
Shalek James H.
Vantico Inc.
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