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
1998-01-30
2001-07-24
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...
C525S108000
Reexamination Certificate
active
06265487
ABSTRACT:
The present invention relates to a powder coating hardener based on epoxide compounds having a molecular weight of no more than 1500, to a powder coating which contains said hardener and which is based on solid poly(meth)acrylic resins, i.e. on resins which are obtainable by polymerisation of monomers which contain acrylic and/or methacrylic monomers, as well as to the use of this powder coating as automotive lacquer.
Powder coating hardeners based on epoxide compounds having a molecular weight of no more than 1500 are known and are used, in particular, when the binder of the powder coating contains free carboxyl groups. A known powder coating is, for example, that by Johnson Wax Speciality Chemicals Product Application Bulletin, Powder Coatings, which comprises triglycidyl isocyanurate as hardener and a poly(meth)acrylic resin having free carboxyl groups as binder. However, one of the disadvantages of these powder coatings is that their flow is only sufficiently good at relatively high temperatures and said powder coatings are therefore not suitable for use in the temperature range from 140 to 150° C. which is required in the case of, for example, automotive lacquers.
It has now been found that powder coatings based on a binder having free carboxyl groups and comprising a hardener which is solid at room temperature (15° to 30° C.) and which is based on low-molecular epoxide compounds, the essential component of which is diglycidyl 1,4-cyclohexanedicarboxylate in the form of the pure trans-isomer or of a cis-/trans-isomer mixture having a melting point of above 70° C., have the desired good flow even when they are processed, i.e. applied and stoved, in the temperature range from 130 to 150° C.
Accordingly, this invention relates to a powder coating hardener which is solid at room temperature and which is based on epoxide compounds having a molecular weight of no more than 1500, the epoxide compounds consisting of 60 to 100% by weight of diglycidyl 1,4-cyclohexanedicarboxylate in the form of the pure trans-isomer or of a cis-/trans-isomer mixture having a melting point (defined as peak maximum of the DSC scan at a heating rate of 10° C. per minute) of above 70° C., and of 0 to 40% by weight of other epoxide compounds, and wherein 0 to 15% by weight of the entire amount of epoxide compounds can contain aromatic structural elements in the molecule.
The invention also relates to powder coatings based on one or more than one poly(meth)acrylic resin which contains the powder coating hardener of this invention, as well as to the use thereof as automotive lacquer.
In addition to the desired flow behavior, the powder coatings based on the hardener of this invention have good reactivity in the temperature range from 130 to 150° C. as well as very good storability in the range from room temperature to moderately elevated temperatures, e.g. in the range 40° C.; accordingly, they have a good reactivity/stability ratio. That form of diglycidyl 1,4-cyclohexanedicarboxylate which is intended as powder coating hardener according to this invention furthermore has hardly any plastifying action and shows no clotting tendency, which substantially facilitates processing the compositions to powder coatings, making it, in particular, easier to comminute the composition after it has been homogenised e.g. in an extruder, and prevents caking when stored.
Those forms of diglycidyl 1,4-cyclohexanedicarboxylate which can be used as hardeners according to this invention are obtainable in simple manner, e.g. by treating an isomer mixture of trans- and cis-1,4-cyclohexanedicarboxylic acid, such as is also commercially available, with water in the temperature range from about 80 to 95° C., at which the cis-isomer dissolves, giving a form of the 1,4-cyclohexanedicarboxylic acid which is sufficiently enriched with the trans-isomer. This form can then be glycidylised in customary manner by reaction with epichlorohydrin as is described, inter alia, in U.S. Pat. No. 3,859,314.
Although those novel powder coating hardeners are preferred in which the epoxide compounds consist to 100% by weight of diglycidyl 1,4-cyclohexanedicarboxylate in the form of a pure trans-isomer or of a cis-/trans-isomer mixture having a melting point of above 70° C., it is also possible that the epoxide compounds of the hardener consist of up to 30 to 40% by weight of other epoxide compounds, preferably of other diglycidyl or polyglycidyl esters.
Up to 15% by weight of the entire amount of epoxide compounds of a powder coating hardener of this invention can comprise aromatic structural elements; a higher proportion is not to be recommended because of the marked decrease of fastness to weathering. These epoxide compounds include, for example, the corresponding glycidyl esters which are mentioned in EP-A-0 506 617 and in EP-A-0 536 085, both descriptions of which are regarded as component of this description, as hardeners for powder coatings which are based on acid polyesters and which contain aromatic groups, in particular diglycidyl phthalate, diglycidyl isophthalate or diglycidyl terephthalate or triglycidyl trimesate or triglycidyl trimellitate.
In the case of aliphatic or cycloaliphatic epoxide compounds it is possible to use other epoxide compounds in amounts higher than 15% by weight or an additional proportion of other epoxide compounds exceeding this amount.
The aliphatic epoxide compounds are conveniently aliphatic polyglycidyl di- or polycarboxylates, preferably the aliphatic polyglycidyl polycarboxylates containing 2 to 50, more preferably 2 to 20, carbon atoms which may, in addition to the carboxyl groups, also contain other functional groups. Typical examples of suitable aliphatic polycarboxylic acids are oxalic acids, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, subaric acid, azelaic acid or sebacic acid. Hardeners which are also suitable for the purposes of this invention are aliphatic polyglycidyl esters of formula (I) given below, wherein X
1
, X
2
, X
3
, X
4
, X
5
and X
6
are each independently of one another a hydrogen atom, a C
1
-C
4
alkyl group or a group of formula (II) given below, and A in formula (II) is an alkylene group containing 2 to 4 carbon atoms, preferably an ethylene group, and Y is a hydrogen atom or a methyl group:
Polyglycidyl esters of formula (I) are disclosed, inter alia, in EP-A-0 506 617. Specific examples are glycidyl acetone-1,1,3,3-tetrapropionate and glycidyl pentanone-(3)-2,2,4,4-tetrapropionate.
Preferred aliphatic polyglycidyl polycarboxylates are diglycidyl oxalate, diglycidyl succinate, diglycidyl adipate, diglycidyl sebacate, diglycidyl azelate.
The cycloaliphatic epoxide compounds are conveniently cycloaliphatic polyglycidyl di- or polycarboxylates, i.e. polyglycidyl di- or polycarboxylates which are based on a carbon backbone containing one or more than one cycloaliphatic ring and which is free from C—C multiple bonds or of aromatic groups. The individual cycloaliphatic rings can contain one or more than one substituent, typically C
1
-C
6
alkyl, chloro, bromo or hydroxyl substituents and preferably contain 5 to 10 carbon atoms. If the polycarboxylic acid contains two or more cycloaliphatic rings, then these may be fused or linked via suitable atom groups, in particular via straight-chain or branched aliphatic groups of valency 2-6 having e.g. 1 to 30 carbon atoms which may also contain one or more than one hetero atom, typically a sulfur atom, nitrogen atom or, preferably, oxygen atom, as well as substituents, such as chloro, bromo or hydroxyl substituents. Typical examples of such linking groups are those of formula —CH
2
—, —C(CH
3
)
2
—, >CH—, >C(CH
3
)—, >C< or
wherein Q is an organic radical of valency 2-6 containing preferably 2 to 15 carbon atoms and which is free from C—C double bonds. Specific examples of cycloaliphatic polyglycidyl polycarboxylates which are suitable according to this invention are diglycidyl hexahydrophthalate, diglycidyl hexahydroisophthalate, diglycidyl hexahydroterephthalate, diglycidyl methylhexahydrophthalate, d
Lyon & Lyon LLP
Sellers Robert E. L.
Vantico Inc.
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