Stock material or miscellaneous articles – Composite – Of silicon containing
Reexamination Certificate
2002-04-18
2004-09-14
Tucker, Philip (Department: 1712)
Stock material or miscellaneous articles
Composite
Of silicon containing
C525S523000, C528S038000, C528S103000, C528S425000
Reexamination Certificate
active
06790532
ABSTRACT:
The present invention relates to a coating composition comprising organically modified inorganic condensates based on hydrolysable silanes containing at least one epoxide group, to a process for preparing the coating composition, to the use thereof for coating substrates, especially glass, and to substrates coated therewith.
The fracture strength of glass is drastically reduced by surface microcracks, so that the actual strength is lower by several orders of magnitude than the theoretical strength. These microcracks come about as a result of mechanical, thermal and/or chemical attack on the surface of the glass during production and processing, but also in the course of use.
It is known that the fracture strength of damaged glass can be increased further by coating, filling the microcracks with a transparent glasslike sol-gel material and/or using the coating process to produce a zone of compressive strain in the near-surface region of the glass. Studies are also known which use glass ceramic coats, metal oxide coats or else ceramic coats for increasing the strength. In general, however, these coats lack glasslike transparency, which limits their use.
It has also been found to be the case that, although these glasslike or ceramic-like coats are able to increase the fracture strength, they are unable to protect the glass against renewed damage, since their brittle fracture properties are similar to those of the underlying glass surface to which they are firmly bonded chemically via oxygen bridges. As a result, under external attack, similar damage is produced in the coating and can propagate into the glass. The same applies to applied coats of an SiO
2
sol-gel, irrespective of whether the coats used are thick or thin, in the &mgr;m range.
One widespread protection for glass in terms of the strength properties is that known as cold end coating with waxes, fatty acids or fatty acid esters, which is described, for example, in U.S. Pat. No. 4,232,065. Further possible treatments include the application of thin polymer coats with thicknesses of about 8 &mgr;m, as described in WO 93/6054, or the use of polysiloxane-containing wax, fatty acid or fatty acid ester coats, which are disclosed in WO 98/45217.
In order both to retard the rapid drop in strength mentioned at the outset and to obtain protection against mechanical damage in combination with sufficient slip properties, WO 97/41966 proposed coating the glass with organic polymer coats. This is done by applying polymer coats with a thickness of 80-100 &mgr;m using, for example, a powder coating material. Protection against stress cracking corrosion, however, is difficult owing to the high water permeability. Water diffuses to the polymer/glass interface where, owing to the weak attachment of the polymer, it causes the known, strength-lowering corrosion phenomena. A further grave disadvantage when using thick polymer coats is that recovery of the glass necessitates a very cumbersome procedure to separate glass from polymer, in order not to disrupt the redox equilibrium in the glass melting furnace. With polymer-coated bottles, for instance, the shards are ground to a particle size within the range of the polymer coat thickness (50 &mgr;m-100 &mgr;m) and the polymer fraction is separated off by agitation.
The object on which the invention was based was therefore to provide a coating having a high strength-maintaining effect without adversely affecting the recyclability of glass. A further requirement was, on the one hand, to achieve effective adhesion to the glass while, on the other hand, avoiding the brittleness of ceramic materials and at the same time obtaining sufficient abrasion strength.
The object according to the invention, with the diverse and divergent requirements, has surprisingly been achieved by means of a coating composition comprising a polycondensate obtainable by reacting
a) a prehydrolysate based on at least one hydrolysable silane having at least one nonhydrolysable substituent, the silane containing one or more epoxide groups on at least one non-hydrolysable substituent;
b) at least one amine component selected from (1) prehydrolysates based on at least one hydrolysable silane having at least one nonhydrolysable substituent, the silane containing one or more amino groups on at least one nonhydrolysable substituent, and (2) amine compounds containing at least two amino groups, and
c) an amino protective group reagent.
The invention provides coating compositions which can be used to increase the fracture strength of glass, especially damaged glass. At the same time, high abrasion-resistant coatings are obtained which, moreover, adhere effectively to glass. Nor do any problems arise with regard to the recovery of the glass.
The prehydrolysate used as component a) is based on at least one hydrolysable silane having at least one nonhydrolysable substituent, the silane containing an epoxide group on at least one nonhydrolysable substituent. This silane is a silicon compound having from 1 to 3, preferably 2 or 3, with particular preference 3, hydrolysable radicals and 1, 2 or 3, preferably 1 or 2, with particular preference one, nonhydrolysable radical(s). At least one of the nonhydrolysable radicals possesses at least one epoxide group.
Examples of nonhydrolysable radicals R containing epoxide group are in particular those which possess a glycidyl or glycidyloxy group. They can be linked to the silicon atom by way of an alkylene group, e.g. a C
1
-C
6
alkylene, such as methylene, ethylene, propylene or butylene. Specific examples of hydrolysable silanes that can be used in accordance with the invention can be found, for example, in EP-A-195493. Examples of nonhydrolysable radicals without epoxide groups are the examples of the radical R″ that are listed below for the general formula (III). Examples of hydrolysable radicals are the examples of the radical X that are listed below for the general formula (I).
Hydrolysable silanes with epoxide group that are particularly preferred in accordance with the invention are those of the general formula (I):
X
3
SiR (I)
in which the radicals X, the same as or different from one another (preferably identical), stand for a hydrolysable group and are, for example, a halogen (F, Cl, Br and I, especially Cl and Br), alkoxy (especially C
1-4
alkoxy, such as methoxy, ethoxy, n-propoxy, isopropoxy and butoxy), aryloxy (especially C
6-10
aryloxy, e.g. phenoxy), acyloxy (especially C
1-4
acyloxy, such as acetoxy and propionyloxy) and alkylcarbonyl (e.g. acetyl), and R is a nonhydrolysable group containing at least one epoxide group, e.g. an aliphatic, cycloaliphatic or aromatic group, in particular an alkylene group, e.g. a C
1
-C
6
alkylene, such as methylene, ethylene, propylene and butylene, containing at least one epoxide group. The radical X is preferably C
1-4
alkoxy and with particular preference methoxy and ethoxy, and R is preferably a glycidyloxy-(C
1-6
)-alkylene radical.
Owing to its ready availability, &ggr;-glycidyloxypropyltrimethoxysilane (abbreviated below to GPTS) is used with particular preference. Further examples are glycidyloxypropyltriethoxysilane, glycidyloxypropylmethyldiethoxysilane and glycidyloxypropylmethyldimethoxysilane.
Component b) comprises at least one amine component selected from (1) prehydrolysates based on at least one hydrolysable silane having at least one nonhydrolysable substituent, the silane containing an amino group on at least one nonhydrolysable substituent, and (2) amine compounds containing at least two amino groups. Components (1) and (2) can be used alone or in a mixture. Component b) is preferably composed at least in part of component (1); for example, at least 20 mol % or at least 40 mol %, preferably at least 60 mol %, of component b) are component (1). With particular preference, component b) consists only of component (1).
Component (1) comprises prehydrolysates based on at least one hydrolysable silane having at least one nonhydrolysable substituent, the silane containing one or more amino groups on at lea
Gier Andreas
Mennig Martin
Schmidt Helmut
Aylward D.
Greenblum & Bernstein P.L.C.
Institut Fuer Neue Materialien gemeinnuetzige GmbH
Tucker Philip
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