Note: Descriptions are shown in the official language in which they were submitted.
BACKGROUND O~ .r'[E I~ NTION
I~ Descr~tion of the Prior ~rt
Thermoplastic and thermoset polymers can be
improved as to abrasion resistance by siloxane- and silicone-
~ased abrasion resistant coatings su^h as tho.æ disclosed in
U.S. Patent 3,986,997 to Clark and u.S. Patent 3,894,881
to Suzuki et al.
However, such coating co~positions9 when applied
.0 direct'y to polycarbonate substrates 9 do not adhere adequately.
Japanese Patent Application 81928/73 published
. l~ovember 1, 1973 and assigned to Toray Industries, Inc. teaches
the advantage of a primer coating whose binder is a polymer of
methyl methacrylate prior to applying a siloxane abrasion re
sistant coating, but in all cases when polymers of methyl
nethacrylate are used in the tie coating 7 the tie coating was
baked on prior to applying the abrasion resistant coating.
The object of my invention is to provide a primer
coating system which improves the adhesion of silicone- and
siloxane-type abrasion resistant coatings to thermoplastic
and thermoset substrates.
, Another object is to provide a method of improving
the adhesion.of such coatings to such substrates.
A further object is to provide substrates having
a first primer coating an~ a second abrasion resistant coating~
II. Summar~ of the Inve_tion
These objects and others which will become apparent
from the following disclosure are achieved by the present in-
vention which comprises in one as~ect a process for applying
--2--
and adhering a silicone or siloxane based abrasion-resistant
coating to a thermoplastic or a thermoset polycarbonate sub-
strate cemprising applying a tie coatin~ composltion comprising
a thermoplastic polymer of an alkyl me~hacrylate or a thermo-
plastic copolymer polymerized from a monomer mixture comprised
of at least 50 weight percent of at least one alkyl methacrylate
and a flow improver dissolved in one or more organic solvents,
and drying at a temperature of about 20-30C prior to applying
said abrasion-resistant coating.
In another aspect the invention comprises articles
produced by the above-described process.
This invention then, in another aspect, resides in
coated polycarbonate articles having improved
abrasion resistance comprising a polycarbonate substrate
having deposited on the surface thereof (i) an adhesion-
promoting primer layer comprising (a) a thermoplastlc polymer
of an alkyl methacrylate ox a thermoplastic copolymer
polymerized from a monomer mixture comprised of at least
50 weight percent of at least one alkyl methacrylate or a
mixture of such polymers, and (b) a flow improver, said
primer layer having been air dried at 20-30C; and (ii) an
abrasion-resistant silicone- or siloxane-based top coat disposed
on said primer layex, said top coat being firmly adhered to
said polycarbona~e substrate by means of said primer layer.
-3
DETAILED DESCRIPTION OF THE INVENTION
A~ THE_PRE~RRED EMBODIMENTS
The polycarbonate substrates used in this invention
can be in sheet, rod, tube, shaped article~ or any other form~
After application of the coating~ the articles are useful for
flat or curved enclosures such as windows~ skylights, wind
shields, plastic lenses, furniture, and the like. Examples
of suitable polycarbonates are poly(diphenylolpropane carbonate),
poly(diethylene glycol bis(al~yl carbonate)) 9 and the like.
The tie coating composition comprises a polymer of
alkyl methacrylate, a flow modifier~ and one or more organic
solvents. The alkyl methacrylate polymer is polymerized from
a monomer mixture comprised of at least 50 weight percent o~
at least one alkyl methacrylate. Methyl methacrylate is the
preferred methacrylate~ but other Cl to C6 alkyl methacrylates
are also quite useful. Comonomers can be any copolymerizable
monoethylenically unsaturated type~ for example Cl to C6 alkyl
acrylates such as ethyl acrylate~ acrylic acids such as acrylic
or methacrylic acid~ other me-thacrylates such as glycidyl meth-
acrylate, isobornyl methacrylate, etc., styrene~ acrylonitrile,
-3a-
and the like. The methyl methacrylate polymer used can be
imidized via the imide reaction with a~onia or an amine as
taught in Kopchik British Patent No. 1,559,132, granted
March 3, 1980. A mixture of the above polymers may also be
used in the present invention.
Preferred flow modifiers include fluoroaliphatic
oligomers such as those described in U. S~ Patent 3,737,351,
for example 2 (N-butylperfluoroockanesulfonamide) ethyl acrylate-
polyethylene-polypropylene glycol acrylate copolymer. 0-ther0 flow modifiers suitable are commercially available silicone
a~
~low improvers used in paints such as Raybo-3 (Ra~ Chemical Co.),
" "2 " "3 "
DC~7 and DC-3 (Dow Corning Co.)and SF-1023 (General Electric Co.).
The organic solvent system can be any capable of
dissolving -the alkyl methacrylate polymer. Suitable systems
~ ,,~
include toluene~ isopropanol~ butanol~ ~ellosolve acetate,
butyl acetate, and the like. A pre~erred system is a mix-ture
of toluene and isopropanol in about a 1/l weight ratio.
The preferred weight ratio of alkyl methacrylate
polymer -to solvent is about 6:9L~ to 10:90. S'ightly higher and
lower ratios can also be used, depe~ding on fac-tors such as
p~lymer molecular weight and composition, solvent system7 and
speed of application desired
The preferred weigh-t ratio of flow modifier to solvent
is about 0O' 100 to l:100.
In addition7 005 to lO percent of a UV absorber, e.g
benzotriazole-type can be added~ based on pol~mer weight.
The tie or primer coat is applied to tne substrate by anJ
suitable means, e.g., spraying, brushing, dipping~ spinning etc
followed by air drying ak room temperature ~or 5-20 minutes de-
pending o~ the solvent system~ Room temperature is about 20-30 C~
1. Trademark
2. Trademark -4-
3. Trademark
4. Trademark
, *Trademark~ "Cellosolve" aceta~e is ethylene glycol monoethyl
ether acetateO
Next~ the abrasion resistant coating is applied bJ
any suitable means, e.g., those means mentioned for the tie
coat, and cure~ at eleva-ted temperature, preferably about
50 t~ 150 C.
The resultant articles are unexpectedly improved as
compared to articles prepared withou~ the tie coat.
The abrasion resistant coating has superior adhesion
and abrasion resistance because of the tie coat. It is
surprising that no dilute acid etching of the tie coat is
necessary as it usually is when applying the same siloxane
coatings directly to poly~ethyl methacrylate substrates.
The following non-limiting examples illustrate a few
embodiments of the invention.
EXAMPLES
EXAMPLE 1
The following polymers o~ an alkyl methacr~rlate were
prepared by conventional bulk molding procedures:
A. Polymethyl methacrylate, number average molecular
weight of 50,000.
B. Poly(methyl methacrylate/methacrylic acid)
(97O7/~3)~ viscosity average molecular weight of 50jO00.
C. Poly(methyl methacrylate/isobutyl methacrylate/
glycidyl methacrylate) (75/23/2) number average molecular
weight of 50~000.
D. Poly(methyl methacrylate/ethyl acrylate) (99/l),
post imidized with methyl amine to 23% CH3 ~ glutarimide
functionality, according to the procedure of ~opchik, as
described in sritish Patent No. 1,559,132, granted March 3, 1980.
~5~
. ,,
.
E. Poly(methyl ~ethacrylate/butyl rmethacr-ylate/
isobutyl methacrylate) (60/15/25) number average molecular
weight of 507000.
EXAM~PLE 2
The following solvent systems were prepared
A. Toluene/isopropanol (1:1)
A. A mixture of
33.3 parts water
0~62 parts NaOAc.3~I20
50.0 parts colloidal silica, 60 millimicron
2~5 parts glacial acetic acid
46.7 parts methyl ~rimethoxysilane
4.8 parts dimethyl dimethoxysilane
was diluted to 20% solids with isopropanol and aged 6 days before
application.
B. A coating solution was prepared in accordance
~ith U. S. Patent 3,986,997, Example VII.
EXAMPLE 4
, Primer coatings were prepared by
A. Dissolving the polymer of lA in the solvent
system of system of Example 2A at a ratio of 6:94 (polymer
solvent) and adàing 0.01 part 2-(N~butylperfluoro-octanesulfon-
amide) ethyl acrylate-polyethylene-polypropy]ene glycol acrylate
copolymer as flow modifier. 7.5 percent~ based on polyme~9 of
2-(2-hydroxy-5-t-octylphenyl)-benzotriazole was added as U~J
abs~rber.
,, .. ,.. . . . .. ;~
~1~
B. Example ~ ~as repeated except using the polymer
of Example lB instead of lA.
C~ Example ~ was repeated except using the polymer
of Example lC.
D. Example ~A was repeated except using the polymer
of Example lD.
E.~ Example ~ was repeated except using (l/l)
combina-tion of polymers of Example lA and lCo
EXAMPLE 5
The tie coating of Examples 4A, B, C, D, and E
were applied to poly(diphenylpropane carbonate) sheets and
to poly(d ethylene glycol bis(allyl carbonate)) sheets by
cascading -the solutions on the sheets, air dried for ten
minutes, then coated with the silicone abrasion resistant
coating mix~ures of Examples 3A and 3B. The silicone coating
was cured for t~ hours at 100 C.
Clear~ level~ abrasion resistant coatings with
eXcellent adhesion are obtained without the need for solvent
washing of the polycarbonate substrates prior to coating.
~he cross-hatch tape-peel test wais used to test for adhesion.
The coating did not delaminate when immersed in 140 F. water
for 30 days.
~ ~
The silicone abrasion resistant coating of Example
3A was applied to a sheet of poly(diphenyl propane carbonate)
without first applying the primer-coating of the invention~
The abrasion-resistant coating had poor adhesion
and scraped off with a finger nail.
'~,
- compa~ a v_
This E~yample shows the importance of not baking
the tie coating prior to appl:ication of the silicone abrasion
coating
The -tie coating of Example 4A was applied to
poly(diphenyl propane carbona-te), but rather than simply air
drying for ten minutes before appl~Ting the silicone abrasion
resistan-t coating~ as in Example 5, the primer coating ~s
~akcd at lO0~ C. for 20 minutes, and then the silicone coating
of Example 3A was applied and then cured for two hours at
100 C~ as in Example 5~
After two days immersion in 140 F. water, the
coating delaminated.
