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
2000-06-28
2002-02-26
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...
C523S427000, C525S438000, C525S524000, C525S526000, C525S934000, C528S093000, C528S094000
Reexamination Certificate
active
06350825
ABSTRACT:
The present invention relates to a powder coating composition based on an epoxy resin mixture, and to a preferred process for the preparation of an epoxy resin mixture suitable for such coating compositions.
A large number of powder coating compositions based on epoxy resins and free-carboxyl-group-containing polyesters as the main curing components are already known for a wide variety of purposes.
EP-A-O 299 421, for example, describes powder coating compositions based on solid epoxy resins and free-carboxyl-group-containing polyesters for decorative purposes, there being used as epoxy resin a reaction product of a solid epoxy resin having on average more than one terminal epoxy group per molecule, for example a condensation product of the diglycidyl ether of bisphenol A with bisphenol A, and the monoimide of a dicarboxylic acid. The epoxy resins have a relatively high Mettler softening point of at least 85° C., which has an advantageous effect on the storage stability of the powder coating compositions produced with them. At the same time, the said epoxy resins have a low melt viscosity and exhibit a good flow behaviour, so that especially uniform powder coating surfaces are formed and no so-called orange-peel effect occurs.
Also known, from EP-A 0 119 164, are powder coating compositions that comprise:
(A) a solid epoxy resin mixture that comprises at least one epoxy resin component (A1) and one epoxy resin component (A2), and
(B) a free-carboxyl-group-containing polyester in an amount sufficient for the full cure of the composition,
the epoxy resin component (A1) consisting of epoxy resin having a mean epoxy functionality that is greater than 2, and
the epoxy resin component (A2) consisting of epoxy resin having a maximum mean epoxy functionality of 2.
There is used as component (A2) of the epoxy resin mixture (A), for example, a diglycidyl ether based on bisphenol A (mean epoxy functionality of 2). The said powder resin coatings are used for coating the interior of metal containers. Those powder coating compositions are less suitable for decorative purposes, however, since their flow behaviour is unsatisfactory. The present invention relates to a powder coating composition that has been improved especially in the above respect comprising
(A) a solid epoxy resin mixture comprising at least one epoxy resin component (A1) and one epoxy resin component (A2), and
1
(B) a free-carboxyl-group-containing polyester in an amount sufficient for the full cure of the composition,
in which the epoxy resin component (A1) consists of one or more epoxy resins and has overall a mean epoxy functionality that is greater than 2,
in which powder coating composition the epoxy resin component (A2) consists of one or more advanced epoxy resins, each of which has a mean epoxy functionality of at least 1.2 but less than 1.95, and is the product of a reaction in which (i) at least one diglycidyl compound is simultaneously reacted with (ii) at least one bisphenol compound and (iii) at least one monophenol as starting materials, and wherein furthermore the difference between the mean epoxy functionality of the epoxy resin mixture (A) and the mean epoxy functionality of component (A2) of the mixture is at least 0.05 but less than 0.8.
At room temperature (15 to 25° C.), the advanced epoxy resins forming the epoxy resin component (A2) are solid products, ideally of a chain-like molecular structure, that can be obtained by the reaction of one or more diglycidyl compounds with one or more bisphenol compounds in the presence of one or more monophenols and a suitable advancement catalyst. As is generally necessary in the case of advancement reactions of epoxy resins, the glycidyl groups of the diglycidyl component must in this reaction be present in a stoichiometric excess relative to the phenolic hydroxyl groups. The monophenol in the reaction mixture results in chain reaction terminations during the advancement reaction so that when diglycidyl compounds, such as, for example, diglycidyl ethers of bisphenols (mean epoxy functionality of 2), are used as starting materials, advanced epoxy resins having a mean epoxy functionality of less than 2 are obtained. Of course, the epoxy resins advanced in that manner are in reality mixtures that consist of several different epoxy compounds, that is to say especially di- and mono-glycidyl compounds. The above numerical values for the mean epoxy functionality thus represent theoretical mean values for the number of epoxy groups contained in a molecule of the advanced epoxy resin but give, in particular, no indication of the precise number and nature of the different epoxy compounds in such a mixture. For the purposes of this Application, the mean epoxy functionality (f
(AvaH)
) of an epoxy resin advanced using monophenol can be calculated using equation (
1):
f
(AvaH)
=2 −(2 n
(MoPh)
/d) (1),
wherein n
(MoPh)
corresponds to the number of moles of monophenol used for the preparation of the advanced epoxy resin and d is the difference between the number of epoxy equivalents, which corresponds to the amount of diglycidyl compound (i) used for the advancement, and the number of hydroxyl equivalents, which corresponds to the amount of bisphenol compound (ii) used. Preferably, the lower limit for the mean epoxy functionality of the advanced epoxy resins in the epoxy component (A2) is 1.4 and the upper limit is 1.9. Advanced epoxy resins having a mean epoxy functionality of from 1.5 to 1.8, especially from 1.55 to 1.65, are especially suitable. Since those values for the mean epoxy functionalities are theoretical mean values, experimentally determined values for the epoxy functionalities will in practice naturally differ from those values within certain limits. Some of the values found in practice are up to approximately 15% lower, but this has no significant effect on the effectiveness of the present invention in practice.
Especially preferred are powder coating compositions according to the invention in which the advanced epoxy resins in the epoxy resin component (A2) are the product of the reaction of one or more diglycidyl compounds of formula (I):
wherein R corresponds to the formula
X in each of the groups R corresponds independently of the others to >CH
2
or >C(CH
3
)
2
, and m is a number from 0 to approximately 1, which corresponds to half of the average number of structural repeating units
in the molecules of the diglycidyl ether.
More especially preferred diglycidyl compounds of formula (I) are pure diglycidyl ethers of bisphenol A and diglycidyl ethers of bisphenol F, especially those in which m is 0 or approximately 0, for example in the range from 0 up to and including 0.1.
The bisphenol compounds (ii) employed are preferably bisphenol A and bisphenol F.
In the advancement, the diglycidyl ethers of formula (I) and the bisphenol compounds are preferably used in a stoichiometric ratio of from 2:1 to 1.3:1 when m is 0 or approximately 0. If m is 1 or approximately 1, the lower limit for the said stochiometric ratio is preferably approximately 2:1. If mixtures of diglycidyl ethers having a variety of the values mentioned for m are used, the lower limits for the stoichiometric ratio of diglycidyl ethers and bisphenol compounds advantageously lie between those indicated above for each of the values of m. For example, an epoxy resin mixture consisting of approximately 33 mol % of a diglycidyl ether of formula (I) wherein m=1 and approximately 66 mol % of a further diglycidyl ether of formula (I) wherein m=0 could be used satisfactorily with bisphenol compounds in a stoichiometric ratio of from 2:1 to 1.5:1.
Preferred monophenols (iii) for the advancement are especially phenols containing one or more, for example two, C
1
-C
12
alkyl substituents, or a C
6
-C
10
aryl substituent, for example ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, tert-pentyl, neopentyl, n-hexyl, isohexyl and corresponding heptyl and octyl substituents, especially tert-octyl, nonyl, dodecyl or phenyl. Sp
Finter Jürgen
Frischinger Isabelle
Poget Christine
Lyon & Lyon LLP
Neuman Kristin H.
Sellers Robert E. L.
Shalek James H.
Vantico Inc.
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