Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From silicon reactant having at least one...
Reexamination Certificate
2001-07-19
2003-03-04
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From silicon reactant having at least one...
C525S476000, C528S029000
Reexamination Certificate
active
06528607
ABSTRACT:
RELATED APPLICATIONS
This application claims priority to German application 100 35 755.5, filed on Jul. 22, 2000, herein incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention describes a silicone epoxy resin, its preparation, and the use in corrosion-inhibiting, heat-stable coatings.
2. Background of the Invention
Crosslinked silicone resins containing T groups are highly heat-stable and have excellent film-forming properties. For these reasons they are used, for example, as electrical insulating materials, as heat-stable coatings and paints, as protective coating materials, as performance enhancers in organic binders, and as copolymers in conjunction with organic monomers or with organic resins. As silicone combination resins from this group, silicone epoxy resins are described in a large number of publications and patents. For the preparation of these resins a large number of synthesis routes are taken.
For the preparation of silicone resins containing epoxide groups, a large number of patents describe cohydrolysis of trialkoxysilanes containing epoxide groups, such as 3-glycidyloxypropyltrialkoxysilane, for example, with organotrialkoxysilanes and/or diorganodialkoxysilanes and/or triorganomonoalkoxysilanes. An overview is given by U.S. Pat. No. 5,516,858.
A disadvantage of this synthesis route is that only a maximum of one epoxide group per Si is attached; the resultant resins possess no carbinol (COH) functionality which is capable of crosslinking with SiOR. Accordingly, it is necessary to add heat-labile crosslinkers for the crosslinking reaction. The heat-labile crosslinkers critically reduce the heat stability of the resultant anticorrosion coating.
U.S. Pat. No. 4,250,074 describes the formation of an interpenetrating polymer network (IPN) of epoxy-polyamine and polysiloxane. Owing to the incompatibility of epoxy resin and silicone resin, only a small amount of silicone resin (about 2-4% of the formulation) can be used. Corresponding formulations exhibit no heat stability at temperatures above 200° C.
Epoxysilane formulations wherein said silanes act as adhesion promoters are described, for example, in EP 0 556 023 A1. The low concentrations in which the epoxysilanes are used do not make it possible to formulate heat-stable systems.
Other patents describe simple mixtures of silicones and epoxides for the preparation of coatings:
The Japanese patents JP 04176368 A2 and JP 04135674 A2 describe mixtures of various epoxides, OH-functional polydimethylsiloxanes, and titanates. Owing to the lack of attachment of silicone and epoxide and to the use of linear polydimethylsiloxanes, which only effect chain extension, the coatings obtained are not heat-stable. The coatings merely exhibit good resistance to boiling water in conjunction with high flexibility and weathering stability.
The Japanese patent JP 61258871 A2 describes a mixture of silicone resin and epoxy resin. By formulating with various inorganic pigments, heat-stable formulations are obtained. Since the epoxy resin is not stabilized by chemical reaction with silicones, the formulations described require very high silicone fractions in order to achieve temperature stability; the epoxide fraction in the formulation is, accordingly, only about 10% by weight. Correspondingly, the formulations are highly priced; the large silicone fraction impairs the anticorrosion effect owing to the increased water vapor permeability.
Mixtures of epoxy resins with linear polydimethylsiloxanes, as described in the Japanese patent JP 2132165 A2, achieve only corrosion-protecting but not heat-stable properties, owing to the absence of chemical attachment.
The curing of epoxides by organosilicone curing agents is described by Vasiléva et al. in Lakokras. Mater. Ikh Primen. 4 (1967), 18-20. The high amine content of the formulation and the lack of attachment of epoxide and silicone do not permit heat stability for the corrosion-protecting formulation.
Formulations comprising glycidyl-containing trialkoxysilanes, silicone resins and epoxides are described in WO 97/19764. The application is directed to heat-deflecting coatings. The principal binder is a silicone-modified polyether. Owing to the thermolabile polyether substituents, these formulations cannot be used for heat-stable corrosion protection.
Modification of epoxy resins with silicones is described in the Japanese patent JP 52040535 A. The reaction of methoxy- or hydroxy-functional siloxanes with epoxy resins and organic acids or anhydrides is described here. The curing agent used is a reaction product of phenyl glycidyl ether, dicyanamide and benzyltriammonium chloride. Owing to the use of this curing agent, which is not heat-stable, the resultant coatings cannot be used at elevated temperatures.
JP 50153063 A describes the modification of epoxy resin with a methylphenyl silicone resin. In a second step, the transparent silicone epoxy resin is reacted with phthalic anhydride. The carboxylic acid groups formed in the reaction with phthalic anhydride have an adverse effect on the storage stability of the silicone epoxy resin. The hydrolysis-labile Si-OR bonds, in particular, are not stable on storage in the presence of acidic groups, such as carboxylic acids (—COOH), for example.
DT 11 29 704 and DT 954 456 describe the reaction of epoxides with silanes or with silane mixtures. A disadvantage of this process is the reaction of the trialkoxyfunctional silanes, which proceeds irreproducibly. Depending on the reaction regime, insoluble silicone gels are formed. Accordingly, only small amounts of trifunctional silanes (T units) can be used; the major fraction of the silicone is formed of difunctional units (D units). This leads to coatings which, although flexible, lack sufficient hardness.
OBJECT OF THE INVENTION
It is an object of the present invention to provide a heat-stable silicone epoxy resin which is thermally curable even at relatively low temperatures below 200° C. without the use of curing agents and whose coatings possess an anticorrosion effect even after long-term temperature exposure at high temperatures above 200° C.
SUMMARY OF THE INVENTION
The present invention provides for a process for preparing silicone epoxy resins and their use for anticorrosion temperature-stable coating.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides for a process for preparing silicone resins which comprises reacting:
I) siloxanes of the general formula
R
a
Si(OR′)
b
O
(4−a−b)/2
in which
OR′ is an alkoxy group with primary or secondary aliphatic alcohols, preferably having from 1 to 8 carbon atoms,
R is identical or different and is an alkyl group, preferably having from 1 to 8 carbon atoms or an aromatic group, preferably having from 6 to 20 carbon atoms,
a is from 0.1 to 2.0, and
b is from 0.1 to 1.0, with
II) one or more low molecular mass polyhydric alcohols/polyols and
III) one or more resins containing epoxide groups, containing at least two 1,2-epoxide
groups per molecule, at temperatures in the range from about 100 to about 160° C. with removal of the alcohol HOR′ to a degree of conversion of from about 20 to about 80% and terminating the reaction by cooling to a temperature <about 100° C.
A sufficient conversion may be determined, for example, by withdrawing a portion of the reaction mixture, drying it on a glass plate and determining the transparency of the coating on the glass plate. A transparent film indicates sufficient conversion. Furthermore, the conversion may be determined precisely from the amount of ethanol distilled off.
The present invention further provides for a coating produced therewith, comprising the silicone resin of the invention, and its use.
It has surprisingly been found that using one or more low molecular mass polyhydric alcohols/polyols the modification reaction of silicone resin and epoxy resin is easier and quicker to carry out. In contrast to the reaction without alcohol/polyol, it is possible in accordance with the invention to react even epoxides
Dawson Robert
Frommer & Lawrence & Haug LLP
Goldschmidt AG
Zimmer Marc S.
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