Note: Descriptions are shown in the official language in which they were submitted.
I ~7B394
-Z 0050/3509~
Curable coating compositions and the production of mar-
- . resistan-t coatings on plastics
The present invention relates to ~urable coat-
- ing compositions based on olefinically unsaturated poly-
siloxanes, processes for the produc~ion of ~ar-
- resistant coatings from these compositions on plastics,
and plastics coated by these processes.
German Pu~lished Application DAS 1,957,357 dis-
closes reaction products of unsaturated siloxanes with
olefinically unsaturated epoxy resins and/or olefinically
unsaturated diurethanes, and a method for hardening these
with e7ectron beams.
Further, German Published Application DAS
1,957S358 describes a system which may be hardened simi-
larly and which comprises an olefinically unsaturated
siloxane and an a,~-olefinically unsaturated polyester.
The films obtained are fully hardened and are weather-
resistant, but their abrasion resistance and .-mar- -
resistance are far from satisfactory Thus, ~hehardened
films are requiredto have, inter alia, a pencil hardness of
9 ~ and, as Example 1 of German Published Application
DAS 1,957,358 shows ~pencil hardness H), the prior art
coatings fall ~ar short of this requirement.
German Patent Application P 29 46 474.2 also
proposes .curable coating compositions based on olefini-
cally unsaturated polysiloxanes.
It is an object of the present in~ention to pro-
vide coating compositions, especially for plastics such
as polymethyl methacrylate, polycarbonates, polystyrene,
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styrene/acryloni-trile copolymers and polyvinyl chloride,
which in addition to exhibiting good adhesionl trans-
parency and good leveling give a further improvement in
abrasion and mar resistanca~omp~red-to
the prior artO The coatings are intended to improve
the mechanical stress resistance of the surface of the
plastic sufficiently to allow transparent plastics to be
used as a substitute ~or glass, especially in the auto-
motive industry.
We have ~ound that this object is achieved by
~ ur~ble . coating compositions based on olefinicallyunsaturated polysiloxanes, wherein the said siloxane is
a polycondensate of
a) from 50 to 95 mole~ of an olefinically unsaturated
silane of the general formula
Rl - si (oR2 ) ~5 .
where Rl is vinyl or a C2-C8-alkyl acrylate or methacryl-
ate radical bonded to the Si atom via a C-Si bond and R2
is hydrogen or a saturated hydrocarbon radical of l to 4
carbon atoms,
b) from 5 to 50 mole% of a saturated silane of the
general formula
R4
R3 - Si - oR2
oR2
where R2 has the abo~e meanings and R3 and R4 are iden-
tical or different and each is a saturated hydrocarbon
radical of 1 to 6 carbon atoms or an unsubstituted or
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Cl-C4-alkyl-substituted aromatic hydrocarbon radical,
and
c) 0 to 25 mole% of an epoxide-containing silane
with 2 or more hydroxyl or alkoxy groups,
~ith the proviso that the sum of the percentages of a),
b) and c) is lO0, and by curable .coating compositions
of the same type which however additionally contain up
to an 8-fold excess, basedon the amountby weightof thepoly-
condensate, of an olefinically unsaturated reaction pro-
duct o~ acrylic acid or methacrylic acid and a poly-
alcohol or polyether-polyol.
The present invention additionally provides a
process for producing ~ar-resistant coatings ~n
plastics surfaces, wherein the novel -curable coating
composition is applied i~ aconventional mannerto thes~i~sur-
~ace and is hardened by means of ionizing radiation or
by exposure to ultraviolet light in the presence of a
conventional photoinitiator.
The invention further provides articles made of
a plastic and coated by the above process.
Using the novel coating compositions it is ~ound,
surprisingly, that after hardening by ionizing radiation
or ultraviolet radiation, transparent, well-adhering
very hard coatings having excellent abrasion resistance
an~ ._ mar resistance are produced on plastics.
The ~ollowing details may be noted concerning
the components from ~hich the novel coating compositions
are synthesized:
The olefinically unsaturated polysiloxane is a
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polycondensate o~ components (a3 and (b), with or with-
out (c).
a) Examples of suitable olefinically unsaturated
silanes of the general ~ormula
Rl-Si~OR2)3
where Rl is vinyl or a C2-C8-alkyl acrylate or methacryl-
ate radical bonded to the Si atom via a C-Si bond and R2
is hydrogen or a saturated hydrocarbon radical of 1 to 4 -
c~rbon atoms are vinyltrimethoxysilane, vinyltriethoxy-
silane, Y~methaoryloxypropyl.trimethoxysilane and Y-
methacryloxypropyltriethoxysilane, amongst which vinyl-
triethoxysilane. and Y-methacryloxypropyltrimethoxysilane
are preferred.
Component (a) is used, in the preparation of the
novel polycondensate 9 in amounts of from 50 to 95, pre-
ferably from 65 to 94, mole%, based on the sum o~ the
percentages of (a) + (b) ~ (c).
b) Examples of suitable saturated silanes of the
general formula
R4
R3_si_oR2
R2
where R2 has the abovemeanings and R3 and R4 are iden-
tical or different and eash is a saturated hydrocarbon
radical of 1 to 6 carbon atoms or an unsubstituted or
Cl-C4-alkyl-substituted aromatic hydrocarbon radical are
dimethyldimethoxysilane, dimethyldiethoxysilane, dimethyldi-
butoxysilane, diphenyldimethoxysilane, diphenyldie-thoxy-
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_ 5 _ O.Z. 0050/35~91
silane and diphenyldibutoxysilane, amongst which di-
methyldibutoxysilane is particularly ~referred. Com-
_. ponent (b), becau~e of its bifunctional charao~er,
results in a deliberate linear structure of the novel
polycondensate and is employed in an amount of ~rom 5
to 50, preferably from 6 to 35, mole%, based on the sum
of the percentages of (a) + (b) ~ (c),
c) Examples of suitable expoxide-containing silanes
with 2 or more hydroxyl or alkoxy groups are Y glycidoxy-
propyltrialkoxysilanes, where alkoxy is of 1 to 4 carbon
atoms, eg~ Y-glycidoxypropyltrimethoxysilane, Y-glycid-
oxypropyltriethoxysilane and Y-glycidoxypropyltributoxy-
silane, ~-(3,4-epoxycyclohexyl)-ethyltrialkoxysilanes 9
~here alkoxy is of 1 to 4 carbon atoms, eg ~-(3,4-èpoxy-
cyclohexyl)-ethyltrimethoxysilane, --triethoxysilane and
-tributoxysilane, and mixtures of these compounds.
The preferred component (c) is Y-glycidoxypropylt~
methox~silane.
In the preparation of the novel polycondensates,
component (c) is used in an amou~t of from 0 to 25, pre-
ferably from 5 to 15, mole~, based on the sum of the per-
centages of (a) + (~) + (c) The use of component (c)
improves the adhesion of the ooatings to the substrate.
To prepare the novel coating compositions, com-
ponents (a), ~b) and (c) are co-condensed using an acid
catalyst 9 advantageously in the presence of not less than
a 5-fold molar excess of water; first, the whole reac-
tion mixture is heated for from 1 to 8 hours at 50-80C,
and thereafter the alcohol ~ormed is distilled off as an
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alcohol/water azeotrope, partly under atmospheric pres-
sure and partly under reduced pressure,
Suitable acid catalysts ar~ the organic and
inorganic compounds conven~ionally used for condensation
reactions, eg. p-toluenesulfonic acid, hypophosphorous-
acid, vanadium pentoxide, antimony trioxide, hydrochloric
acid or sulfuric acid, ..
The novel polysiloxanes contain units of the
~ollowing ~ormulae:
Rl R3
0-Si-o- and -0-Si-0- with or without
0 R4
R5-Si_o_
. o
where Rl, R3 and R4 have the above meanings and R5 is an
epoxide-containing organic ether radical with a glycidyl group
an alkoxy radica~ 2 to-8 ca~hQn atoms..
The novel polycondensates in general have mole-
cularweights of from500 to 10,000, preferably from 800 to
3,000,
Crosslinkingcomponents which can beaddedto the
novel polysiloxanes are poly-olefinically unsaturated
monomers, for example those obtained by reacting acrylic
acid or methacrylic acid with a polyol or polyether-
polyol; Preferred monomers of this type are thediacrylates and dimethacrylates of ethylene glycol,
propanediol, butanediol, diethylene glycol, triethylene
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- 7 - o.Z. 0050/35091
glycol and tetraethylene glycol; butanediol diacrylate
a~d tetraethylene glycol diacrylate are particularly
_ preferred;
These additional crssslinking components can be
combined with the novel olefinically unsaturated poly-
siloxanes in up to eight-fold excess, pre~erably l-fold
to 6-fold excess, based on polysiloxane.
The novel coating compositions may be used to
produce scratch-resistant coatings on plastics
surfaces~ eg on polymethyl-methacrylate,polycarbonate,
polystyrene, styrene/acrylonitrile copolymers and poly-
vinyl chloride.
The coating compositions are applied to the sub-
str~te by conventional methods such as spraying, knife-
coating or dipping; for economic reasons, the coatings
should not be more than 50 um thick
The coating ~ilms are preferably hardened by
means of ionizing radiation, preferably in the form of
electron beams having an average energy of ~rom lO0,000
to 250,000 electron volts. The total dosage o~
this radiation is in general from 3 to 20 Mrad.
Suitable radiation sources are those conven-
tionally used for electron beam hardening of sur~ace
coatings.
High-energy light (ultraviolet radiation), in
combination with conven-tional photoinitiators such as
benzophenone, benzil dimethyl ketal, 2-hydroxy-2-methyl-
propiophenone, thioxanthone and its derivatives, benzoin
alkyl ethers or combinations of these photoinitiators
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with synergistic agents (eg tertiary amines)~can also
initiate the crosslinking reaction, so as to harden the
novel coatings.
Advantageously, the surface of the plastic is
thoroughly cleaned and dried before coating. For ex-
ample, sheets to be coated may first be washed with
detergent-containing water, then freed from organic
contaminants by means of an alcohol or other organic
solvent which does not attack the surface of the plastic,
and thereafter dried for ~0 minutes at 50C. The
sheets cleaned in this way are advantageously stored in-
a desiccator or similar container until the coating pro-
cess is to be carried out.
In the Examples, parts and percentages are by
weight.
EXAMPLES 1 T0 4
The silanes shown in Table 1 are stirred, in the
presence of a 10-molar excess of fully demineralized
water and o~ 0.5~ by weight of p-toluenesulfonic acid,
at 50C for the time shown in the Table The alco-
hol formed9 toge-ther with the excess water, is then
distilled off as an azeotrope at a bath temperature of
110C, using reduced pressure towards the end o~ the
reaction.
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TABLE 1
Ex- MEM0l) DMDB02) Condensation Viscosity
ample time ~23C~
No. [mole~] [mole~] Ch] ~mPasJ
l 80 20 5 7,332
2 50 50 3 9l5
3 68 32 2 2,84~
4 9l 9 2 16,050
=
)Y~Metha~yloylox~Tpropyltrimethoxysilane (= MEMO~
2)Dimethyldibutoxysilane (~ DMD~0)
EXAMPLE5 5 T0 8
The binders described in Examples 1 to ~ were
mixed undiluted with tetraethylene glycol diacrylate (=
TEGDA), in the ratios shown in Table 2. Each mixture
was knife-coated onto a thoroughlycleaned sheet of poly-
methyl methacrylate (= PMMA), the zverage coating thick-
ness being ~rom 8 to l0 um. Hardening was effected
in a nitrogen atmosphere, using electron beams in a
total dose of l0.6 MradO
The : mar resistance of the coating films was
tested by the falling abrasive method of ASTM-D
673 (2l000 g of No. 80 ~ilicon carbide).
The mar resistance was determined by measur-
ing the cloudiness, according to ASTM-D 1003, on a
Gardner AUX-l0 apparatus; To do this, the marred
surface coating film, on the substrate, was introduced
into the path of a parallel light beam and the percent~
age of light scattered at an angle of more than 4 ~rom .
the horizontal was used, after deduction o~ the blank
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value, as a measure o~ the mar resistance.
The adhesion was determined by the DIN 53,151
cross-hatch method, but, as a modifîcation of the method,
the hatched squares were additionally covered with sel~-
adhesive tape, which was abruptly ~ d off
again. Adhesion = O means that the coating film
remained completely on the subs-trate, and adhesion = 4
means that the film can be pulled off entirely.
The measured adhesion and mar resistance are
shown in Table 2.
1 ~7~39~
O . Z . 0050/3509 1
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Table 3 shows7by way of comparison, the cloudi-
ness of uncoated polymethyl methacrylate (P~MA) and
gl~ss, resulting in the falling abrasive test.
TABLE 3
Su~strate Falling abrasive test
~% cloudiness
~ . . . . .
PMMA 36
Glass 5.8
,__ . . . ~ .
- After 24 hours~ exposure to organic solvents
such as toluene, acetone, butyl acetate, butanol and
. universal spirit, the hardened coating films remained
unattacked.
