Stock material or miscellaneous articles – Composite – Of polycarbonate
Reexamination Certificate
1999-12-20
2002-03-05
Boykin, Terressa M. (Department: 1711)
Stock material or miscellaneous articles
Composite
Of polycarbonate
Reexamination Certificate
active
06352778
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to weatherable compositions, and more particularly to weatherable coating compositions for application to thermoplastic substrates.
It has long been conventional to apply protective coating compositions to abrasion-susceptible substrates such as polycarbonates and poly(methyl methacrylate) in sheet form, to improve their resistance to degradation of various kinds, including abrasion and degradation. Among the coating compositions employed for this purpose are those derived from a polymeric polyol, sometimes in combination with a low molecular weight diol, and an aminoplast.
Polymeric articles thus coated frequently have a problem of long term color instability. This causes yellowing of the polymeric substrate, detracting from its transparency and attractiveness. Loss of gloss can also be an undesirable long term phenomenon.
Yellowing of polymers is often caused by the action of ultraviolet radiation, which is why such yellowing is frequently designated “photoyellowing”. It is particularly vexing when the polymeric article is to be used outdoors, in direct exposure to sunlight.
Numerous means for suppressing photoyellowing have been employed and proposed. Many of these involve incorporating in the coating composition an ultraviolet absorbing compound (UVA). Among the commercially available UVA's of particular interest are hydroxybenzophenones, hydroxyphenylbenzotriazoles, hydroxyphenyltriazines, cyanoacrylates and polyaroylresorcinols. It is frequently found, however, that these UVA's do not provide adequate protection against weathering.
A class of UVA's which has been found particularly useful in many environments for protection against weathering in outdoor exposure situations, is the silylated diaroylresorcinols disclosed in U.S. Pat. Nos. 5,391,795, 5,679,820 and 5,990,188. They are disclosed as being useful in and compatible with silicone hardcoat compositions and silicon-containing ultraviolet-cured coating compositions comprising acrylic monomers. Their use in polyol-aminoplast coating compositions is, however, not disclosed.
It is of interest, therefore, to develop protective coating compositions capable of improved protection of a substrate against weathering as evidenced by photoyellowing and the like.
SUMMARY OF THE INVENTION
The present invention is based on the discovery that silylated diaroylresorcinols are particularly effective as WVA's in polyol-aminoplast protective coating compositions, especially in combination with hindered amine light stabilizers (HALS).
In one of its aspects, the invention includes thermally curable compositions comprising the following and any uncured reaction products thereof:
(A) at least one polymeric polyol,
(B) at least one alkanediol,
(C) at least one reactive aminoplast and
(D) at least one silylated substituted resorcinol of the formula
wherein:
each A is independently an unsubstituted or substituted aromatic radical,
R
1
is a divalent C
1-10
aliphatic hydrocarbon radical,
each R
2
and R
3
is independently a C
1-12
alkyl radical, and
n is 0-3.
In another aspect of the invention, said thermally curable compositions further contain at least one hindered amine light stabilizer.
Another aspect of the invention is a method for producing a cured coating on a thermoplastic substrate which comprises:
(I) coating said substrate with a thermally curable composition prepared by blending the constituents described above, and
(II) heating the coated substrate thus formed at a temperature effective to thermally cure said composition.
Still another aspect of the invention is coated resinous articles prepared by the above-described method.
DETAILED DESCRIPTION; PREFERRED EMBODIMENTS
It is immaterial from the standpoint of the invention, and not entirely certain in any event, whether any chemical reaction takes place between the various components as defined hereinafter, with the proviso that no curing reaction has taken place at the time the curable compositions are employed as coatings. Thus, the invention includes simple physical mixtures of said components and also uncured reaction products thereof.
Component A in the compositions of the invention is at least one polymeric polyol. By “polymeric polyol” is meant a polymer, usually of low to medium molecular weight (e.g., a number average molecular weight in the range of about 200-5,000), containing two or more hydroxy groups. For the most part, two hydroxy groups are present as end groups.
Various types of polymeric polyols are known in the art, and any of them may be used in the invention. Illustrations are polyether-, polyester-, polycarbonate- and polyurethane-polyols as well as the polycaprolactone-polyols disclosed in the aforementioned U.S. Pat. No.4,552,936. The polyester-polyols are often preferred by reason of their particular suitability and relatively low cost. They may be illustrated by the “RUCOFLEX” hydroxy-terminated polyesters of Ruco Chemical Company, which are generally prepared by the reaction of at least one aliphatic diol, or mixture thereof with at least one triol and/or polyhydroxy compound of higher functionality, with at least one aliphatic and/or aromatic dicarboxylic acid or functional derivative thereof. Examples of diols are ethylene glycol, diethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, 2-methyl-1,3-propanediol and 2,2-dimethyl-1,3-propanediol; higher polyols include 1,1,1-tris(hydroxymethyl)propane and glycerol. Examples of dicarboxylic acids are adipic acid, succinic anhydride, 1,12-dodecanedioic acid, phthalic anhydride, isophthalic acid and terephthalic acid. Most preferred in many instances are polyester-polyols prepared from adipic acid and a mixture of 1,6-hexanediol and 2,2-dimethyl-1,3-propanediol, as illustrated by the product sold under the trade name “RUCOFLEX S-1015”.
Component B is at least one alkanediol, preferably containing about 1-6 carbon atoms. Illustrative alkanediols are ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol and 2,2-dimethyl-1,3-propanediol. 1,4-Butanediol is usually preferred.
Component C is at least one reactive aminoplast. As used herein, the term “aminoplast” means a thermosetting amine-aldehyde or amide-aldehyde condensation product, which may be monomeric or polymeric. Exemplary of the aminoplast compositions that may be employed are the urea formaldehydes, e.g., propylene urea formaldehyde and dimethylol urea formaldehyde; melamine formaldehydes, e.g., tetramethylolmelamine, pentamethylolmelamine and hexamethylolmelamine; ethylene ureas, e.g., dimethylol ethylene urea, dihydroxydimethylol ethylene urea, ethylene urea formaldehyde and hydroxyethylene urea formaldehyde; carbamates, e.g., alkyl carbamate formaldehydes; formaldehyde-acrolein condensation products; formaldehyde-acetone condensation products; alkylolamides, e.g., N-methylolformamide, N-methylolacetamide, N-methylolacrylamide, N-methylolmethacrylamide, N-methylol-N-methylacrylamide and N-methylol methylene bis(acrylamide); haloethyleneacrylamide; diureas, e.g., trimethylol acetylene diurea and tetramethylol acetylene diurea; triazones, e.g., dimethylol-N-ethyl triazone, N,N′-thylenebis(dimethylol)triazone and halo triazones; haloacetamides, e.g. N-methylol-N-methylchloroacetamide; and urons, e.g., dimethylol uron and dihydroxy dimethylol uron. Also useful, and often preferred, are derivatives of the above compounds wherein the methylol or other hydroxyalkyl groups therein are replaced by lower alkoxyalkyl groups (e.g., hexamethoxymethylmelamine), as well as analogous thioureas, thioamides and the like. Particularly preferred are the melamine derivatives and especially hexamethoxymethylmelamine, which is commercially available from Cytec Industries under the trade name “CYMEL 301”.
Component D, the silylated substituted resorcinol, has formula I in which the A value may be any unsubstituted or substituted aromatic radical, illustrations being phenyl, p-chlorophenyl, p-tolyl, 1-naphthyl and 2-naphthyl; phenyl is generally prefe
Gillette Gregory Ronald
Patel Gautam Ambalal
Boykin Terressa M.
Brown S. Bruce
General Electric Company
Johnson Noreen C.
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