Stock material or miscellaneous articles – Composite – Of silicon containing
Reexamination Certificate
1999-12-02
2001-10-23
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Composite
Of silicon containing
C524S091000, C524S430000, C524S431000, C524S437000, C528S027000, C548S110000, C556S437000
Reexamination Certificate
active
06306512
ABSTRACT:
The present invention relates to non-volatile UV-stabilising mixtures for siloxane lacquer systems, which mixtures have certain hydroxybenzotriazoles as the UV-stabilising active structure and which are thus particularly suitable for the UV-stabilisation of thermoplastics, in particular of aromatic polycarbonates.
Materials are frequently protected from the harmful influences of the environment by providing them with a protective surface. Siloxane-based lacquers have proved particularly suitable for this purpose, inter alia providing the materials with a scratch-resistant surface.
These lacquers may contain so-called UV-stabilising substances in order to protect the lacquer itself and the underlying material, the so-called substrate, from harmful UV radiation. Apart from providing long-term UV protection, one requirement placed upon these substances is, inter alia, that they are not volatile so that they remain homogeneously distributed within the lacquer layer and do not escape from the lacquer layer either during curing or during subsequent use of the laquer. The UV-stabilising substances must furthermore not decompose rapidly, must be durably homogeneously miscible with the lacquers and the lacquer containing the UV-stabilising substances should be transparent
U.S. Pat. Nos. 4,278,804 and 4,051,161 relate to UV-stabilising active substances and lacquers containing them. The substances disclosed therein, however, exhibit the disadvantage that they provide inadequate UV protection, they decompose too rapidly and/or the siloxane system containing the stabilisers has a yellow tinge.
U.S. Pat. No. 5,438,142 furthermore discloses the UV-stabilising active substance, 1-(3′-(benzotriazol-2″-yl)-4′-hydroxyphenyl)ethane. This active substance, however, exhibits the disadvantage that it is not durably miscible with siloxane-based lacquers.
This object thus arises of providing a UV-stabiliser system which does not exhibit the above-stated disadvantages.
This object is achieved according to the invention by the provision of UV-stabilising mixtures containing hydroxybenzotriazoles of the general formula (I) below and hydrolysable silanes containing epoxy groups.
R
1
: H, C
1-
C
18
alkyl, C
5-
C
6
cycloalkyl, C
6-
C
12
aryl,
R
2
: H, halogen, preferably C1, or C
1-
C
12
alkyl,
R
3
: a single bond, C
1-
C
12
alkylene, C
5-
C
6
cycloalkylene or phenylene,
R
4
: H, alkali metal, ammonium, alkaline earth metal, C
1-
C
12
alkyl,
The present invention furthermore provides UV-stabilising mixtures having a molar ratio of epoxy groups of the silane to the hydroxybenzotriazole of the general formula (1) which is greater than 1.4, preferably greater than 2, particularly preferably greater than 8. The molar ratio of epoxy units of the silane to the hydroxybenzotriazole of the general formula (1) should not, however, exceed 1:100.
The mixtures according to the invention are suitable for the UV-stabilisation of siloxane systems, in particular of scratch- and abrasion-resistant siloxane coating materials. Such UV-stabilised coating materials, preferably lacquers, may be used for coating materials of all kinds, such as for example wood, textiles, paper, stone articles, but preferably for coating plastics, metals, glass and ceramics, particularly preferably for coating thermoplastics and very particularly preferably for coating polycarbonates.
The hydroxybenzotriazoles used for the non-volatile, UV-stabilising mixtures according to the invention are compounds of the general formula (1).
Preferred compounds of the formula (1) are:
The compounds of the formula (1) are either known from the literature or obtainable using processes known from the literature, for example in accordance with the reaction scheme disclosed on page 7 of EP-0 057 160. This patent application is introduced as a reference and is accordingly part of the disclosure of the present invention.
Silanes containing epoxy groups are generally taken to mean compounds which, on the one hand, possess at least one epoxy ring and simultaneously have groups which form silanol structures under hydrolysing conditions.
Epoxysilanes as are preferably used according to the invention are described, for example, in U.S. Pat. No. 2,946,701. They are compounds of the formulae (2) or (3):
R
5
is a divalent hydrocarbon residue having at most 9 carbon atoms or a divalent residue having at most 9 carbon atoms consisting of C, H and O atoms, wherein the O atom is present as an ether bond residue. R
5
is preferably —CH
2
OCH
2
CH
2
CH
2
—.
R
6
is an aliphatic hydrocarbon residue having at most 4 carbon atoms, an acyl residue having at most 4 carbon atoms or a residue of the formula (CH
2
CH
2
O)
n
Z, in which n is at least 1 and Z means an aliphatic hydrocarbon residue having at most 4 carbon atoms; m is 0 or 1.
Production of these epoxysilanes is also described in U.S. Pat. No. 2,946,701. This patent is accordingly introduced as a reference. Particularly preferred epoxysilanes are those compounds in which R
6
is methyl. They are commercially available, inter alia from the companies Union Carbide and Hüls AG as:
A-187 or Dynasilan
3-glycidyloxypropyltrimethoxysilane
Glymo
A-186
2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane.
Production of the UV-stabilising Mixtures
The UV-stabilising components are produced by homogeneously mixing compounds of the general formula (1) with the hydrolysable silanes containing epoxy groups and heating this mixture. Heating should be performed for at least 30 minutes at at least 90° C. The temperature should preferably be above 120° C. during heating. It has proved particularly favourable to use a mixing ratio at which stoichiometrically more epoxy groups are present than the —R
3
—CO—OR
4
—groups of the hydroxybenzotriazole of the general formula 1. The molar ratio of epoxy units of the silane to the hydroxybenzotriazole of the general formula (1) should thus be greater than 1.4, preferably greater than 2, particularly preferably greater than 8.
The UV-stabilising components need not necessarily be produced separately so that they may subsequently be added to the siloxane system to be stabilised, but may also be synthesised in situ as a sub-stage during synthesis of the siloxane systems/siloxane coating materials.
Siloxane systems/siloxane Coating Materials
The siloxane systems are substantially thermally curing systems which preferably crosslink by a condensation reaction to yield —Si—O—Si—linkages. Other crosslinking mechanisms may proceed in parallel. Such systems are described, for example, in U.S. Pat. Nos. 3,790,527, 3,865,755, 3,887,514, 4,243,720, 4,278,804, 4,680,232, 4,006,271, 4,476,281, in DE-A 4 011 045, 4 122 743, 4 020 316, 3 917 535, 3 706 714, 3 407 087, 3 836 815, 2 914 427, 3 135 241, 3 134 777, 3 100 532, 3 151 350, in DE-A 3 005 541, 3 014 411, 2 834 606, 2 947 879, 3 016 021, 2 914 427 and 4 338 361 and should be considered part of the present disclosure.
The present invention accordingly also provides siloxane systems UV-stabilised according to the invention.
Preferably used siloxane systems are those containing particulate material selected from among oxides, oxide hydrates, nitrides and carbides of Si, Al, Sb and B and of transition metals, preferably Ti, Ce, Fe and Zr, and having a particle size in the range from 1 to 100 nm, preferably from 2 to 50 nm.
The UV-stabilising mixture according to the invention should be added to the siloxane system in such a quantity, relative to the solids content of the siloxane system, that the proportion of hydroxybenzotriazole, relative to the solids content of the siloxane system, is 0.3 to 20, preferably 3 to 15, particularly preferably 5 to 10 wt %.
Reference is made to DE-A 2 914 427 and DE-A 4 338 361 with regard to the production of siloxane-based scratch-resistant coating systems and components thereof and these documents are thus part of the present description.
Substrates, materials
The siloxane systems provided with the UV-stabilising mixture according to the invention may be used as bulk materials and as coating materials. There are
Bayer Aktiengesellschaft
Dawson Robert
Gil Joseph C.
Preis Aron
Zimmer Marc S.
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