Stock material or miscellaneous articles – Composite – Of silicon containing
Reexamination Certificate
2001-02-23
2002-11-19
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Composite
Of silicon containing
C264S522000, C427S387000
Reexamination Certificate
active
06482525
ABSTRACT:
The invention relates to a method for producing a substrate coated with a sol-gel coating material, in which the substrate coated with the sol-gel coating material is shaped thermally and the complete curing of the sol-gel coating material does not take place until during and/or after the thermal shaping.
Sol-gel working materials and sol-gel coating materials are characterized by their conversion into three-dimensionally crosslinked structures by a condensation step. Since the condensation reaction proceeds spontaneously, it can certainly be accelerated by catalysts, for example, but is very difficult to stop. The crosslinking generally produces gels which are extremely brittle and fractious and permit thermal shapability only above the melting point. If parts of the inorganic bonds are replaced by organic bonds, then the three-dimensional crosslinking is maintained but becomes weaker. This does not in general lead to a state of thermal shapability, unless compounds are incorporated, such as bifunctional silanes, for example, which are able to break down linear chains and weaken the network to an extent where the three-dimensional character is barely present.
For instance, DE 3011761 describes silicic acid heteropolycondensates which have thermoshapable characteristics. These characteristics, however, are tied essentially to phenylsilanes, since these not only reduce the degree of crosslinking but also keep the molecular weight correspondingly low, in order to provide thermoshapable characteristics. There have been virtually no observations of such characteristics outside the phenylsilanes. The silicic acid heteropolycondensates described in DE 3011761 are used to bond substrates by heat sealing.
EP-A-588 508 describes coating compositions comprising a polyfunctional acrylic monomer, an amino-functional silane, colloidal silica and a polyalkylene oxide with a terminal acrylate group. When this coating composition is applied to a substrate and completely cured, the substrate thus coated can be subsequently embossed without the coating fracturing, i.e. the material is a thermoplastic. In this case, only stretching of at least 5% at room temperature is made possible; thermal shaping is not described. However, especially in the case of thermal shaping, the tensile strength is unsatisfactory.
The object of the present invention, then, was to provide a method for producing a substrate coated with a sol-gel coating material, in which a crack-free and hard coating is obtained despite thermal shaping of the substrate coated with the sol-gel coating material.
This object has surprisingly been achieved by a method for producing a thermally shaped substrate coated with a sol-gel coating material, in which the sol-gel coating material comprises one or more hydrolysable silanes, which may have been hydrolysed to form a precondensate, and, if desired, a crosslinking agent, at least some of the hydrolysable silanes containing on a non-hydrolysable substituent a functional group by way of which crosslinking is possible, and in which
A) the sol-gel coating material is applied to a thermally shapable substrate,
B) the applied sol-gel coating material is partially precrosslinked and/or dried,
C) the coated substrate is subsequently shaped thermally, and
D) during and/or after the thermal shaping the sol-gel coating material is cured completely by means of thermal and/or photochemical crosslinking.
In one preferred embodiment, the complete curing of the sol-gel coating material takes place by means of thermal and/or photochemical crosslinking (step D) after the thermal shaping.
The method of the invention surprisingly gives substrates coated with sol-gel coating material which, despite thermal shaping beforehand, remain without fractures, cracks or splinters in the coating and which nevertheless have a hard surface.
A sol-gel coating material is a coating material prepared using the sol-gel method.
The sol-gel coating material comprises one or more hydrolysable silanes and, if desired, a crosslinking agent. The method of the invention uses sol-gel coating materials in which, for example, at least 25 mol%, preferably at least 50 mol%, with particular preference at least 75 mol%, with very particular preference 100 mol% of the hydrolysable silanes present therein contain one or more non-hydrolysable substituents having a functional group by way of which crosslinking is possible.
The crosslinking in question comprises inorganic crosslinking by way of siloxane bridges (sol-gel crosslinking) and/or organic crosslinking by way of the functional groups. The organic crosslinking may take place by way of addition polymerization, polyaddition or polycondensation reactions, preference being given to polyaddition reactions and addition polymerization reactions on account of the fact that, unlike polycondensation reactions, they do not lead to elimination products such as water or alcohols. The functional groups are selected so that crosslinking can be performed by way of the—catalysed or uncatalysed—addition polymerization, polyaddition or poly-condensation reactions.
It is possible to choose functional groups which are able to enter into the abovementioned reactions with themselves and which in so doing form the organic crosslinking.
Examples of such functional groups are epoxy-containing groups and reactive carbon-carbon multiple bonds (especially double bonds). Concrete and preferred examples of such functional groups are glycidyloxy and (meth)acryloyloxy radicals.
Additionally, the functional groups in question may comprise groups which are able to enter into—catalysed or uncatalysed—addition polymerization, polyaddition or polycondensation reactions with other functional groups (so-called corresponding functional groups) . In that case it is possible to use silanes containing both functional groups, or mixtures of silanes containing the respective corresponding functional groups. If only one functional group is present in the sol-gel coating material, the corresponding functional group may be present in the crosslinking agent to be used in this case if desired. For example, a functional group with a carbon-carbon multiple bond and an SH group may enter into an addition reaction at elevated temperatures and, if desired, with catalysis. Epoxides may react, for example, with amines, alcoholic compounds such as phenols or derivatives thereof or carboxylic acids or derivatives thereof. Further preferred corresponding functional group pairings are methacryloyloxy/amine, allyl/amine or amine/carboxylic acid. If blocked isocyanates are employed, it is also possible to use amine/isocyanate, isocyanate/alcohol or isocyanate/phenol as corresponding functional groups.
It is of course also possible to use a crosslinking agent if the functional group of the silane is able to react with itself or if corresponding functional groups are present in the silanes of the sol-gel coating material. For example, in the case of silanes containing methacryloyloxy groups, it is possible to use as crosslinking agent a compound which likewise contains reactive double bonds.
The functional group is located on a non-hydrolysable substituent of the silane. A non-hydrolysable substituent is a substituent which cannot be eliminated hydrolytically from the silicon atom, and which on hydrolysis of the silane remains linked to the silicon atom of the silane.
The hydrolysable silanes preferably comprise silanes of the general formula R
n
SiX
4−n
. The group or groups X, which may be identical or different but are preferably identical, are hydrolysable radicals. The radicals X are preferably selected from halogen atoms (especially chlorine and bromine), alkoxy groups, alkylcarbonyl groups and acyloxy groups, particular preference being given to alkoxy groups, especially C
1−4
alkoxy groups such as methoxy and ethoxy. n may adopt the values 1, 2 or 3, preferably 1 or 2 and with particular preference 1.
The hydrolysable silanes used may also comprise fully hydrolysable silanes of the above formula in which n is 0, preferably in a
Kasemann Reiner
Kunze Nora
Schmidt Helmut
Sepeur Stefan
Dawson Robert
Feely Michael J
Heller Ehrman White & McAuliffe LLP
Institut für Neue Materialien gemeinnützige GmbH
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