Note: Descriptions are shown in the official language in which they were submitted.
1 ~Z~7~
PHOTOCURING COMPOSITION FOR COATING SUBSTRATES WITH
AN ABRASION-RESISTANT TRANSPARENT OR TRANSLUCENT FILM
Field of the invention
The present invention relates to scratch-resistant sur-
faces and more particularly concerns a photopolymerizable
composition to be applied on a substrate so as to produce
thereon a translucent or transparent coating resisting cor-
rosion and abrasion. This coating is intended to protect
said substrate against shocks, bruises and other mechanical
accidents as well as against wear resulting from normal
use. Such composition is very useful in all industrial
fields where it is desirable to avoid, as much as possible,
that sensitive objects exposed to shock and wear be progres-
sively damaged. This is particularly important when dealing
with transparent articles such as optical goods the surface
of which must be protected by all means against scratches so
as not to lose its desirable optical properties.
It has been definitely established by now that the manu-
facture of high performance optical ware by using transparent
organic materials is possible, the working of which by cast-
ing or any other machining means, is much easier and more
economical than with corresponding articles of ordinary
glasses from metal oxides. On the other hand, such articles
of "organic glass" are relatively soft and poorly resist
abrasion, wear and corrosion by external agents. Thus, it is
desirable to cover such articles with an anti-abrasion and
anti-corrosion protective film but thin enough for not sig-
nificantly altering the optical properties of the substrate.
The prior art
Very many coating compositions and application methods
have already been proposed for achieving the aforementioned
objectives, this being with variable success.
Among all these compositions of the prior art, some are
particularIy relevant that owe their properties to the pres-
ence of compounds from elements other than the usual con-
stitutents of organic matter and, in particular, to aluminum
and silicon in the form of specific mineral or organic com-
pounds. With reference to silicon, for instance, some of the
techniques used involve the buildup of a protective coating
on substrate, this coating being obtained from the vapor
phase deposition of glass or silica evaporated under vacuum.
Polysiloxane based protective coatings can also be obtained,
2 :~2~7~3;2
the structure of which resembles to some extent that of
crosslinked polysilicic acid, by the in situ polymerization
of organo-silicon compounds previously partly hydrolyzed.
During the hardening (curing) of such coatings, polymeriza-
tion occurs, either due to the formation of Si-O-Si bridges
(by the dehydration of silanol functions), or due to the
participation of polymerizable organic groups belonging to
substituents possibly present on the silicon atoms (olefins,
epoxy-, amino- groups, etc.), or by a combination of the said
two polymerization modes. From the references illustrating
such techniques, the followings can be cited: A.J. REEDY,
Res. Discl. 1978, 171-6; Patents USP 4,006,271; 4,098,840;
4,186,026; 4,197,335; JP (Kokai) 77, 101,235; 112,698;
152,426; 154,837; 79, 60,335; 62,267; 119,597; 119,599;
129,095 to 129,099; 133,600; 144,5G0; 148,100; 80, 05,924;
and DOS 2,803,942; 2,805,552; 2,820,391; 2,831,220;
2,917,440. However, despite the protection they impart to
the substrate on which they are applied, these coatings have
some drawbacks. One of such disadvantages is related to the
relatively high temperatures needed for curing polysilicic
type coatings which can lead to substrate deformation. An-
other drawback is inherent to the expansion coefficient of
the polysiloxane coatings which is often sufficiently differ-
ent from that of the substrate for causing the development of
adhesion problems (for instance in the case of polycarbonate
or polymethacrylate organic glasses) and of cracks or crazing
after alternating hot and cold periods (particularly in the
case of articles subjected to weathering like automobile
headlights). Adhesion problems were partially solved by
interposing an intermedlate bonding sublayer between the
coating and the substrate but, more generally, it has been
sought to remedy the above-mentioned drawbacks by replacing
the coatings from polymerized silicon compounds by composi-
tions comprising, dispersed within an organic or silico-
organic matrix, fine particles of silica or alumina. Thus,
there were used in this context aqueous mixtures of silicon
compounds, colloidal silica and hydrocompatible solvents
(alcohols, glycols, etc.), with or without polymerizable or-
ganic monomers. Examples of such uses can bè found in the
following ~eferences: Belgian Patents Nos. 821.403; 877.372;
USP 4,027,073; 4,188,451; 4,177,315; GB 2,018,621; 2~018,622;
DOS 2.811.072 and JP (Kokai) 79, 157,187. However, colloidal
silica being essentially hydrophilic, as are also the other
types of silica such as amorphous, crystalline, microcrystal-
line, precipitated and pyrogenic silicas, it is well compati-
ble, in general, only with hydrophilic polymers, for instance
organosilicon polymer, whereas it is much less or not
3 ~ 7~3Z
miscible with typical hydrophobic resins such as polyolefins,
which very strongly restricts its use as a filler in the film
forming thermosetting or photocuring compositions. rloreQverl
adding hydrophilic silica to organic polymerizable monomers
leads to the formation, with relatively low concentrations of
solids, e.g., about 5 to 10% by weight, of highly thixotropic
masses (non-Newtonian rheologic behaviour) which are very
difficult to apply as thin layers on substrates. Hence,
attempts were made to remedy this disadvantage, i.e., to
increase the level of silica in organic resin coatings, while
overcoming such application problems, by treating the
particles so as to make them organophilic. It should be re-
marked at this stage that methods for imparting hydrophobic
organophilic properties to alumina or silica particles are
already known, per se; however, it does not appear that there
exist, up to now, methods for giving to silica or alumina
particles sufficient organophllic properties to enable them
to be incorporated at high levels (of more than about 40~ by
weight) into polymeric resin films, while maintaining suit-
able rheological properties for application and nearly com-
plete transparency of the films formed. Yet, ensuring proper
transparency of the protective coatings of optical goods is a
fundamental requirement, as will be seen hereinafter in the
description of the present invention. As pertinent refer-
ences regarding the methods for "treating" silica or alumina
particles for rendering them organophilic, South African Pat-
ent No. 72,5180 and Japanese Patent (Kokai) No. 77, 138,154
can be cited. In the first of these references~ silica par-
ticles are treated with trimethylchlorosilane which, by reac-
tion with the silanol groups of said particles, generates hy-
drophobic groups of formula -Si-O-Si~e3, whereby said par-
ticles are rendered compatible with a mixture of olefinic
monomers (ethylenic and acrylic monomers). These particles
are then incorporated, to a level of about 5 - 10% by weight
and together with a proportion of alumina about 10 to 20
times greater, into a mixture of polymerizable resins which,
after curing, provides insulators for high electric voltages.
Such materials are, however, opaque and their resistance to
abEasion is not indicated. In the second of the two refer-
ences cited above, particles of alumina are coated with y-
(glycidyloxy)-propyl-trimethoxysilane and a mixture contain-
ing about 25% by weight of such treated alumina and an epoxy
resin is used for coating a polycarbonate article so as to
obtain, after polymerization, a translucent abrasion-resis-
tant film. rloreover, in the following references, there are
described methods for attaching organic groups such as vinyl,
methacryl, epoxyr glycidoxy to hydrophilic silica so as to
4 ~ 3~
impart thereto hydrophobic properties: L.P. ZIEMJANSKI et
al, Rubber ~orld 163, 1 (1970); rl.w. RANEY et al, Meeting of
the Div. of Rubber Chem., Paper No. 71, ACS ~eeting, Cieve-
land, Ohio (1971); M.W. RANEY et al, Meeting of the Div. of
Rubber Chem., ACS, Miami, Fla (1971); and Rubher Chem. and
Tech. 44, 1080-142 (1971); HI-SIL Bulletin 41, Jan. 1971, PPG
Industries.
In addition to the above mentioned prior art, some fur-
ther United States Patent references can be cited in connec-
tion with the following subjects pertinent to the invention:
1. SiO2: 3,986,997; 4,177,315; 4,188,451; 4,242,403.
lA. Treated SiO2, e.g., to make it hydrophobic:
2,610,167; 2,818,385; 3,652,379; 4,001,128.
2. Forming SiO2 in situ, e.g., hydrolyzing organic
silicates: 2,404,357; 2,4~4,426; 3,971,872; 4,049,868;
4,120,992; 4~186J026.
3.Using siloxanes and/or silanes and the like:
2,610,167; 3,389,11~; 3,801,361; 3,953,115; 3,986,997;
4,001,128; 4,006,271; 4,~26,826; 4,027,073; 4,029,842;
4,049,868; 4,177,315; 4,186,026; 4,188,451; 4,1g7,335;
4,242,403.
4. Combination of any of the above items with:
4A. Polymers: 2,404,357; 2,404,426; 2,610,167;
3,652,379; 3,801,361; 3,971,872; 4,001,128; 4,026,826;
4,049,868; 4,098,840; 4,120,992; 4,197,335; 4,242,403
4B. Prepolymers (oligomers or monomers): 3,819,562;
4,029,842; 4,197,~35.
4Bl~ Photopolymerizable monomers: 3,968,305;
3,968,309; 4,188,451.
4C. Other chemicals, e.g., solvents, fillers cross-
linking agents, to obtain transparent abrasion-resistant
coatings (as single or composite systems): 3,986,997 (acidic
alcohol H2O solution); 4,001,128 (A12O3); 4,006,271 (sol-
vent); 4,027,073 (acidic alcohol water solution); 4,049~868;
4,186,026 and 4,120,992 (crosslinks with formaldehyde);
4,120,992.
5. Miscellaneous routes to such coatings: thus USP
3,645,779 provides a vacuum vapor deposited coating of B2O3-
SiO2 on organic glass; USP 4,051,297 discloses a sputtered
film of chromium silicide on smooth surfaces; in USP
4,242,403, there is disclosed a polyethylene terephthalate
sheet covered with an intermediate layer of ~-(3,4-epoxycy-
clohexyl)-ethyltrimethoxysilane and an upper layer of silica
reinforced organopolysiloxane resin.
In spite of the progress achieved by the above mentioned
techniques, it was still desirable to have at hand a quick
setting composition for providing thin translucent or
_ 5 _ ~Z~7~3~
transparent films very resistan-t to abrasion by virtue of a
high level therein of hydrophobic silica. Thus, a first object
of the invention was to provide a composition for depositing
transparent protective films on substrates, such films being
sufficiently mechanically resistant to withstand normal wear or
accidental abuses without impairment of the surface proper-
ties.
A second object of the invention was to provide a
composition for coating protective transparent films on optical
goods, the optical properties of which will not be significant-
ly modified by this film and which will keep such proper-ties
for a significant period of time under adverse conditions.
Another object of the invention is to provide a com-
position for depositing thin well-adhering Eilms on subs-trate,
such adhesion not being affected by weathering conditions even
after a prolonged period of exposure.
Another object of the invention is to provide a film
forming composition that will strongly adhe~e to organic glass
substrate and which can be cured at room temperature, i.e.,
much below the softening temperatures of the substrate.
Another object of the invention is to provide a com-
position for making transparent scratch-resistant films, such
films being coated on substrates as one layer films, i.e.,
without the need oE an intermediate bonding layer.
Still another object of the invention is to provide a
composition that can be stored for prolonged periods at room
temperature without hardening and which can be cured on the
substrates in a matter of seconds without the use of elevated
temperatures.
Another object of the invention is to provide indus-
trial optical articles made of relatively soft and easy mold-
able organic glasses protected with a scratch-resistant film
that will withstand prolonged use under severe weathering con-
ditions without discoloration, crazing, or significant adhesion
losses.
Other objects of the present invention will become
apparent to people skilled in the art from the description of
the invention that follows and from the disclosed preferred
embodiments thereof.
. ~'
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Summary of the Invention
The present invention enables achievement of the
aforementioned objects. Indeed, the invention provides a
photo-polymerizable composition comprising one or more pho-to-
polymerizable monomers, at least one photo-initiator and parti-
cles of pyrogenic or precipitated SiO2 or
~.~..,
6 ~l2~93Z
A12O3 particles having, grafted on some of the oxygen atoms
thereof, substituents of the formulae Al (I) or siAlA2A3 (II)
wherein Al represents R or OR groups, R being a saturated or
unsaturated substituted or unsubstituted hydrocarbon radical
and A2 and A3 either represent oxygen atoms for connecting
the Si atom in formula (II) to neighboring silicon or alumi-
num atoms of the silica or alumina particle, or they have the
same definition as for Al. Naturally when, by virtue of the
aforesaid definition, the Si atom in ~II) bears more than one
or OR groups, the R's can be the same or they can be dif-
ferent. The detailed nature of the R's will be explained in
a moment.
One distinctive feature of the composition of the inven-
tion is that the total number of carbon atoms which are in-
cluded in formulae (I) or (II), i.e., in Al, or in Al plus A2
and/or A3 in case more than one of the A's on the Si atom of
(II) are R and/or OR groups, should always be four or more in
order to obtain rheological properties of the coating compo-
sitions containing high concentrations of coated particles
that allow satisfactory practical application of the composi-
tions to organic glass substrates. For example, as will be
cited later, suitable coatings were not obtained with compo-
sitions containing silica treated with silicon compounds hav-
ing less than four carbon atoms, while other compositions in-
volving four or more carbon atoms gave satisfactory results
Table VIIa vs those in Tables VI and VII).
Another distinctive feature of the composition is that
the refraction index "n" of the organic phase of the composi-
tion should be as near as possible to that of the particles
used. If the refraction index in the protective film of the
organic matrix which is composed of the various organic con-
stituents of the composition is not near that of the mineral
particles, then said pxotective film is not perfectly clear
but only translucent, this effect being particularly signifi-
cant with high levels of mineral fillers, for instance of the
order o 10 or 20 to 40% by weight. Thus, it was noticed
that if the index "n" of the organic mixture is between 1.45
and 1.48, there is obtained with for instance a pyrogenic
silica of index "n" = 1.475, even at high concentration
levels, excellent clear coatings even for thicknesses thereof
of the order of several microns. In the case of alumina (n =
1.70 - 1.76), such index values for the organic phase are
nowadays impossible to achieve and, for this reason, the
coatings containing high proportions of alumina are translu-
cent and not transparent. In general, it is preferred within
the scope of the invention to use partlcles with refractive
-- 7
~7~3;2
index values between 1.40 and 1.50 and an organic phase the "n"
of which lies in the same range.
The inven-tion also comprises a process for producing
a UV-cured photopolymerizable composition for applying onto
substrates to provide thereon a transparent abrasion resistant
coating. The process comprises: hydrolyzing a trialkoxysilane
in an aqueous acidic solution; dispersing the hydrolyzed trial-
koxysilane into intimate contact with finely divided pyrogenic
or precipitated silica or alumina having a particle size of
less than 0.1 microns to form a dispersion; chemisorbing the
hydrolyzed trialXoxysilane on-to the finely divided pyrogenic or
precipitated silica or alumina by effecting dehydration of the
dispersion by heating to 80-110C to yeild organophillic parti-
cles; and dispersing the organophillic particles into intimate
contact wi-th one or more photopolymerizable monomers and one or
more photoinitiators.
_ eferred Embodiments of the Invention
It should be noted that the size of the particles is
important with respect to the optical properties of the present
protective coating. Thus, using relatively large particles,
i.e., having a diameter of about the same order of magnitude as
that of the thickness of the film, produces at the surface
thereof microscopic prominences not visible with the eye but
being detrimental to the optical properties thereof (undesir-
able light reflection and diffraction effects) and may impart
thereto a milky appearance. To be perfectly clear, the film
should have a flawless, smooth, mirror-like surface. Conse-
quently, there will preferably be used particles of a size
about one order of magnitude less than the coating thick-
ness. Thus, for instance, with coa-tings having a thickness of
the order of one micron or less, there are advantageously used
particle sizes of 0.007 to 0.05 ~ (pyrogenic SiO2: AEROSIL*
(Deguc,sa, Germany), CAB-O-SIL* (Cabot Corp. USA); precipitated
silica: Hi-SIL* (PPG Industries, USA), etc.). For thicker
coatings, larger size particles are possible, for instance 0.02
to 0.1 ~L (precipitated silica). The same is true for alumina,
* Trade Mark
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corresponding requiremen-ts for this mineral filler being
however less, since films loaded with ~12O3 are usually not
transparent per se. As suitable alumina for the present compo-
sition, there can be mentioned a product called ALON (Alcan,
Canada), the particles of which have a size approximately
0.006~. The silicas used or tried within the limits of this
invention are the following:
Name and type Specific area Particle size
of silica (m2/g) s~/m)
_
10 Pyrogenic silica
CAB-O-SIL*EH-5 390 + 40 0.007
H-5 325 + 25 0.007
M-5 200 + 25 0.012
L-5 50 0.05
AEROSIL*-380 380 + 30 0.007
-300 300 ~ 30 0.007
-200 200 + 25 0.012
~130 130 + 25 0.016
Precipitated silica
~li-SIL* 233 -- --
215 150 0.02
SILENE* EF 90 0-03
Organophillic silica*
~EROSIL* R-972 120 + 30 0.016
*This silica was made organophillic by reacting with
trimethylchlorosilane, the number of carbon atoms per grafted
silicon atom is thus only three which does not correspond to
the standards required for embodying the invention. Indeed,
under testing, this hydrophobic silica did not provide composi-
tions with properties suitable for achieving protective
coatings according to the invention, as shown in Table IIIa.
Regarding the photopolymerizable monomers that fit
the requirements of the present invention, one can use most
monomers or mixtures of monomers generally known to photopoly-
* Trade Mark
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merize and the photopolymerization of which is fas-t enough
under usual conditions to be completed shortly (i.e., with
exposure times from about a few seconds to a few minutes) and
the "n" indexes of which fall within the aforementioned limits.
Examples of such monomers (olefinic and preferably acrylic) can
be found in the following reference: ~V Curing by S. Peter
PAPPAS, Science & Technology, Technology Marketing Corp., USA
(1978).
Among the monomers usable in the present invention,
there can be mentioned also some olefinic prepolymers with a
photopolymerizable function which possess, at the start, a
significant intrinsic viscosity. This feature is valuable
when it is wished to deposit with the present composition a
relatively thick film but with sufficient flow stability during
the period before the photopolymerization not to collapse and
spread out or run away from the substrate before curing. Such
prepolymers are known in practice most often under generic
commercial names such as UVITHANE* (Thiokol Corp.), EB~RYL*
~Union Chimique Belge), UCAR-X* (Union Carbide), SETAROL*
(Kunstharsfabrick Syntehse MV, Holland). The structure of such
prepolymers which fit well in the invention, provided they have
the proper refraction indexes, are generally not disclosed
publicly except for the fact that they are mainly
polyol-acrylates (polyesterglycols) or polyurethane-glycols.
In practising the invention, one should use either monomers the
"n" index of which is intrinsically close to that of the
mineral filler used or, and this is the most frequent case,
mixtures of photopolymerizable monomers and/or prepolymers the
mixture index of which comes as near as possible to that of
said mineral filler. By suitably varying the proportions of
the two or more monomeric constituents the respective indexes
of which are above and below the desired value, the latter can
be approximated close enough for eventually obtaining, with the
composition according to the invention, a practically
transparent protective film with silica contents of up to 40%
* Trade Mark
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- 9a 1;~ ~7~432
by weight or more. As non-limiting examples, Tables I and II
below give a list of such possible monomeric ingredients in the
form of individual constituents or of mixtures (proportions
of cons-tituents in the mixtures are given), the refraction
indexes thereof as well as viscosities under standard
conditions.
2~ .~J,: ...
3L%~7~13;~
TABLE I
~lonomer Refractive
index Viscosity
nD20 cP
.. . . ..
~5ethyl acrylate 1.4040 max. 10
Methyl methacrylate 1.4142 max. 10
Ethylene glycol diacrylate
(EGDA) 1.4550 max. 10
1-6-Hexanediol diacrylate
(HDDA) 1.4574 max. 10
1,4-Butanediol diacrylate
(BUDA) 1.4567 max. 10
Neopentylglycol diacrylate
(NPGDA) 1.4515 max. 10
Diethyleneglycol diacrylate
(DEGDA) 1.4621 max. 10
Tripropyleneglycol diacrylate
(TPGDA) 1.4495 max. 10
Tetraethyleneglycol diacrylate
(TEGDA) 1.4616 max. 10
Bisphenol A diacrylate
(EBECRYL-150) 1.5415 1000 + 20%
Trimethylolpropane triacrylate
(TMPTA) 1.4738 70 ~ 20%
Pentaerythritol triacrylate
(PETIA) 1.4871 650 ~ 20%
Pentaerythritol t~traacrylate
(PETEA) 1.4855 800 + 20%
Dipentaerythritol pentaacrylate 1.4932 4400 + 20%
EBECRYL 210 (Acrylic prepolymer) 1.4980 25.10 + 20%
" 220 ( " " ) 1.5030 18.10 + 10%
" 230 ( " " ) 1.4646 6.10 + 30%
" 240 ( " " ) 1.4743 3.10 + 50%
" 270 ( " " ) 1.4755 15.10 + 13%
VVITHANE 782 ( " " ) 1.5024 paste
" 783 ( " " ) 1.5264 'paste
" 788 ~ " " ) 1.5085 paste
~CAR X 117 ( " " )1.4816 135.10 + 1%
" X 118 ( " " ) 1.4898 17.10 + 5%
" X 125 ( " " ) 1.4978 106.10 + 1
EBECRYL 600 (epoxy-acrylate)1.53 4-8.10
(60C)
n 601 ( " " ) 1.55 2.10 + 10~
" 830 (acrylic polyester) 1.5005 45.10 + 10%
" 810 ( " " ) 1.4675 500 + 40
~%q}~3~
11
TARLE I (Cont.)
SETAROL 3625 (olefinic polyester) -- solid
Ethylene glycol dimethacrylate
(EDGMA) 1.4527 max. 10 .
(25C)
Diethylene glycol dimethacrylate
(DEGDMA) 1.4580 max. 10
(25C)
Triethylene glycol dimethacrylate
(TRIGDMA) 1.4595 max. 10
Tetraethylene glycol dimethacrylate
(TEGDMA) 1.4609 max. 10
Bis~phenol-A dimethacrylate 1.5412 1600 i 20%
1.6-Hexanediol dimethacrylate
(HDDMA) -- maxO 10
Trimethylolpropane trimethacrylate
(TMPTMA3 1.4700 35 ~ 20%
(25C)
Pentaerythritol tetramethacrylate solid M.P. 52-55C
12 ~ z~7~3Z
TABLE II
Monomers or mixtures IndexViscosity cP
(% by weight) "nD20"
Trimethylol-propane triacrylate 1.474075 ~ 15
( 100 ~
Pentaerythritol triacrylate (50)
Diethylene glycol diacrylate (50) 1.4742 70 + 15
UCAR X 118 (49,2)
Diethylene-glycol diacrylate (50,8) 1.4748 290 i 10
UCAR X 118 (11,0)
Diethylene-glycol diacrylate (89.0) 1.4670 max. 30
UCAR X 118 (18)
Diethylene-glycol diacrylate (82) 1.4670 45 ~ 5
EBECRYL 600 (33,3)
Diethylene-glycol diacrylate (66,6) 1,4915 75 + 5
EBERCRYL 600 (16,7)
Diethylene-glycol diacrylate (83,3) 1.4765 max. 30
EBECRYL 830 (33,3)
Diethylene-glycol diacrylate (66,6) 1.4742 65 i 5
SETAROL 3625 (16,7)
Diethylene-glycol diacrylate (83,3) 1.4735 100 i 10
r~ethyl methacrylate (38,46)
Pentaerythritol triacrylate (38,46)
EBECRYL 600 (23,08) 1.4732max~ 30
7~32
There is further noted that, especially for some
applications to be described hereinafter, the adhesion of the
film toward glass substrates should preferably be weak or nil
and, in such cases, the mixture of photopolymerizable monomers
will include no hydrophillic monomer such as acrylic acid or
glycol acrylates and methacrylates.
~ s photopolymerization initiators, there can be used
in the present composition most substances generally suitable
for this purpose and being compatible with the contemplated
monomers and fillers. For example, the following photo-initi-
ators suitable for the present invention can be; benzophenone,
Michler's ketone, ethyl 4-dimethylamino-benzoate, benzil, 2-
ethylanthraquinone, diethoxyacetophenone, (DEAP, Union Carbide)
UVECRYL*P-36 (U.C.B.), IRGACURE* 651 (Ciba), SANDORAY*1000
(Sandoz), FI-4 (Eastman Kodak), Vicure*10 and 30 (Stauffer
Chemicals), TRIGONAL* 14 and P-l (Noury), UV-Harter Nos. 1113
and 1116 (Merck), 2-chlorothioxanthone, etc. Using diethoxy-
acetophenone is appreciated as, being a liquid, it dissolves
particularly well in the present photo-polymerizable composi-
tion. Another excellent photo-initiator is UV-HARTER No. 1116
(Merck). Generally, there can be used advantageously from 0.5
to 5% by weight of the ~hoto-initiator depending on the
selected mixture, on the amount of filler and on the polymeri-
zation rates which are desired. Using 1 to 2% by weight of
diacetophenone or o-ther initiators is advantageous.
The nature of the radical R in -the formulae (I) and
(II) can be much varied and its ranye is essentially dictated
by the requirement of mutual compatibility with the organic
phase components. In general, alkyl, alkenyl, cycloalkyl, and
cycloalkenyl of about 1 to about 12 carbon atoms are suitable,
provided of course that the total number of C's in (I) or (II)
is 4 or more, i.e., for instance, if only one organic radical
per grafting site i9 involved then it should be at least a
four-carbon radical while if more than one organic radical is
* Trade Mark
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involved, say three for instance, two of such radicals can be
methyl and the third be ethyl or the like. The organic radi-
cals can be unsubstituted or substituted with functions
containing oxygen or heteroatoms (N, S, etc.). Oxygen
functions can be hydroxy, keto, ester, ether functions, and the
like. Unsubstituted radicals can include photopolymerizable
functions that will participate to the overall photopolymeriza-
tion of -the composition and provide thus photocopolymers in
which some of the copolymerized groups will actually bond to
the silica particles by vir-tue of the fact that the photopoly-
merizable R was included in the compounds of formulae (I) or
(II~ for grafting to said silica
14
7~3~
particles. Other definitions for the R radicals will appear
from further details hereinafter. Preferably, for optimal
properties of the scratch-resistant coatings of this inven-
tion, the weight of the organic substituents used for graft-
ing the silica particles relative to the weight of the SiO2
of said particles should be at least 20%~
The methods which can be advantageously used for render-
ing organophilic the particles of the mineral fillers that
are incorporated into the composition of the invention are
selected among the known methods the references of which are
listed in the introduction. Among these methods, the four
methods (A to D? described hereinafter suit the invention to
various extents~ In the following schemes the structure -Si-
OH represents one of the peripheral silicon atoms (with a
silanol function) of a hydrophilic silica particle which is
to be made hydrophobic. It will remain understood that the
free Si bonds represented in the schemes mean that this Si
atom is bonded to the general polysilicic acid network of the
particle as follows:
-o-s i-o-s i-oH
-Si-o-Si-oH
-Si-oH
It should be further remarked that the particles of sil-
ica thus treated, even the smallest, each has a relatively
large number of oxygen and silicon atoms. For instance, a
particle of 0.02 ~ diameter has a weiyht of about 10 17 g
assuming a value of 2.3 for the average density which corre-
sponds to about 10 18/6 mole of SiO2. Since the number of
molecules in a mole is 6.1023, said particle will have about
105 atoms of Si. The particles are therefore aggregates of
relatively high molecular weight and the mi~tures therefrom
in liquid media are indeed micellar dispersions or colloidal
solutions and not true solutions of organo-silicon compounds
as in the majority of prior art compositions mentioned here-
inbefore. It is thus all the more remarkable that the compo-
sition of the invention does provide, in the case of silica
particles, transparent films even with very high levels of
such mineral fillers.
In the case of alumina particles, the above discussion
will apply by analogy since peripheral alumina molecules also
bear reactive OH functions.
The grafting methods which were experimented with in the
scope of the invention are listed below schematically~ They
~ 2~t~ 3 z
are given for illustration and evldently they do not limit
the invention as other methods could be contemplated or even
preferred as far as they may be more economical or more
efficient.
A. The conversion of some OH functions of the mineral
particles (silanol functions in the case of silica particles)
into reactive functions; e.g., by chlorination as in the
schemes below:
~ iOH + soC12 . ~ iCl + HCl + SO2
2. -liOH + SiC14 ~ -$iO-SiC13 + HCl
Then alkyla ion of the intermediate product thus ob-
tained:
3. -SiCl + ROH ~ -SioR + HCL
4. -SiO-SiC13 + 3ROH ~ slo-si(oR)3 + 3HC1
B. A reaction with organosubstituted halogenosilanes:
Cl
5. -SioH ~ C12SiRR' ~ SiO-Si~R + HCl
R'
Then alkylation of the silicon atom with elimination of
the chlorine atom:
Cl R"
6. -SiO-Si-R ~ R''OH D -Sio-si-R + HC1
R' R'
In the above schemes, R' and R" (organic radicals) can
be the same as R or be different from R. They can have
~taken individually) less than four carbon atoms since for
having the grafting conditions within the scope of the inven-
tion to be satisfied, it is sufficient to have only one of
the organic substituents brought up during grafting at one
site with at least four C atoms or, otherwise, the total of
the carbon atoms of substituents R, R' and R'' put together
in accordance with the definition of the aforesaid formula
tII) should be at least four.
C. The condensation promoted by heat with silanols (R-
Si(OH)3):
16 ~ 7~
o~
7. -SiOH + (HO)3SiR - D -SlO-Si-R + H20
OH
It should be noted with regard to reaction 7 that the
remaining OH functions can still react after grafting by
further dehydration with other silanol molecules tchain ex-
tension by grafting) or with an OH on a neighbor Si atom in
the polysilicic acid backbone of the particle under reaction
(cross-link bridges). It should also be noted that the sila-
nols used generally result from the hydrolysis of trialkoxy-
silanes according to reaction 8:
8. RSi(OMe)3 ~ 3H20 ~ RSi(OH)3 + 3~1eOH
D. ~ reaction of "physisorption" with trialkoxysilanes.
This route is a "complexation" reaction providing a product
in which the bonds to the silicon atom to be grafted are not
covalent. It is carried out by boiling in an organic solvent
like xylene:
I ~ I
9. -SioH ~ tMeo)3siR - ~ -sioH.(rleo)3siR
It should be remarked that the "complex" thus obtained
(electrostatic type of bonds) is not very stable and that a
dispersion made from particles grafted as such has character-
istics different from those of dispersions made from parti-
cles grafted by methods A to C above. In particular, disper-
sions obtained from particles treated according to 9 have a
rheologic behavior that is sometimes non-Newtonian in charac-
ter and are more difficult to use in the present composition.
In the above described grafting methods, the group R
will preferably be a radical such as n-butyl, n-hexyl, n-
heptyl, n-octyl, oleyl, 3-butenyl, decanyl, etc. Also func-
tional groups are suitable that result from the use, when
alkylating activated mineral particles, of glycol acrylates
or methacrylates. Thus, in the substituent formulae R can be
-(CH2~nOCO-CH=CH2 where n can be for instance an integer
between l and 6. ~hen the group R has an olefinic moiety,
that function can copolymerize with the other monomers of the
composition when under irradiation, in which case the parti-
cles are then immobilized by chemical bonds within the coat-
ing organic matrix.
Grafting method C is preferred in the methods described
hereinabove because it is relatively simple and because no
halogenated intermediates are necessary, the handling and the
disposal of which are undesirable regarding safety and
17 ~LZ~37~3Z
environmental problems. Further, compounds of the formula R-
Si(OR')3 where R' is an easily hydrolyzable lower alkyl are
¢ommercially available, the range of the various usable R
groups being relatively large.
For instance, the R with reactive functions can be the
following: '
CH2-C(CH3)-COO-(CH2)3 (methacryloylpropyl radical)
CH2-cH-cH2-o-(cH2)3 (glycidoxypropyl radical)
O~ .
O -(CH2)2 ~3,4-epo~ycyclohexyl-ethyl radical)
In the case where R contains a reactive function, such
as the oxirane function as above, it is evident that the lat-
ter can contribute by its own polymerization reaction to the
overall curing of the protective film of the invention.
On the practical aspect, for achieving the composition
of the invention, the mineral particles made organophilic as
mentioned above are dispersed into the photopolymerizable
monomer or the mixture of monomers and the photo-initiator.
This dispersion is carried out by usual means (blender, ul-
trasonics, mixer, ball-mill r etc.) until the composition is
suitably homogeneous. Then, after the mixture is allowed to
stand for escape of the alr bubbles (or gas bubbles if the
operation is done under an inert gas), it is applied to a
substrate to be coated so as to form a thin film thereon.
Generally, standard tools and methods can be used such as
brush, rod, doctor blade, spraying, dipping, etc~ However,
for the protection of the all important optical goods, lens-
es, mirrors, etc., the following procedure is preferably fol-
lowed- on the surface to be protected, there is put a few
drops of the photopolymerizable composition, after which
there is applied thereon, in order to wel'l spread it and make
it even, a negative counter-plate or mold made of optical
glass, the uncured protective layer being squeezed (and mold-
ed) between it and the substrate and consecutive spreading of
the mixture taking place leading to the formation of a regu-
lar film over said substrate. The surface of the mold has a
finish which is such as to confer well defined optical prop-
erties to the outside surface of the coating such properties
being that, in facsimile, of said mold (replica molding).
After irradiation of the piece and photosetting of the coat-
ing, the mold is removed which step is effected with no
effort as the adhesion between'the mold and the film is weak
- 18 -
7~3;:
or practically negligible. This unexpected result is due -to
the hydrophobic properties oE the coating and of the particles
therein; indeed, the monomers used are not hydrophillic (they
contain no significant amount of hydrocompatible carboxylic or
hydroxy groups such as those of acrylic acid or the hydroxyac-
rylates) and also the mineral particles have no more affinity
for the glass after being grafted with organic radicals as
described above. In this connection, it should be said that
if, instead oE the composition of the invention, another compo-
sition were used having the same organic component but contain-
ing in lieu of 20 - 40% hydrophobic silica, only 2 - 3~ of
ordinary (non grafted) pyrogenic or precipitated silica, there
is obtained a film that strongly adheres to a glass subs-trate
so that it is difficult, if not impossible, to remove it there-
from.
With regard to photocuring of the film on the sub-
strate to be protected, usual means are employed, i.e.,
subjecting the film on the substrate to a suitable irradiation
operation, such irradiation taking place either directly on the
film or through a transparent layer applied over the coating
(plastic membrane for avoiding dust falling on the fresh film
or negative glass counter-form as described above). Also, .
the substrate can be turned upside down relative to the
irradiation source, the exposure being done -through the
transparent body of the substrate itself if desired. As an
irradiation source, one preferably uses a commercial type UV
light giving fluxes of about 10 - 100 W/cm and suitable for
photo-polymerizing a film at a distance of 5 - 30 cm for 2 to
60 seconds at room temperature. Other means and techniques for
photopolymerization known to those skilled in the art may be
used in photocuring the coating.
The photopolymerized film thus obtained is in the
foxm of a thin smooth layer perfectly transparent in the case
where hydrophobic silica is present and translucent if
hydrophobic alumina is present. When clear, this thin layer
does not significantly modify the optical properties of the
substrate and it offers an exceptional resistance to abrasion,
weathering, and accidental abuses as seen hereinafter in the
special part of this disclosure. It can thus be used advan-
,~-t
- 18a - ~2~7~32
tageously for coating optical apparatus lenses made of organic
glasses such as PVC, polycarbonates and polymethacrylates as
well as many other transparent articles such as clear panels,
headlights, and other lighting appliances.
In summary, the resulting advantages from embodying
the present invention are as listed below:
19 ~7~3~
a) Thin layers (from about O.S to 20 or 50 ~m), smooth,
transparent (with SiO2) and very resistant to wear by abra-
sion (the composition of the invention lends itself however
to the preparation of thicker layers in special cases).
b) Solventless compositions requiring no evaporation
step when curing the coating. The absence of solvents also
removes the risks that the substrate be attacked (organic
glass) by such solvents.
c) Very quick hardening of the film at room temperature
which is technically and economically advantageous, the pro-
duction rate being high and the risks of damaging the coating
before curing being strongly reduced.
d) Low cost of the raw materials by virtue of the fact
that the mineral fillers and the monomers are easily availa-
ble and relatively cheap and that the fillers load percent is
quite high.
e) Excellent physical properties such as abrasion re-
sistance and very low friction index. This last property is
mostly unexpected in connection with such a high proportion
of mineral filler and constitutes a highly surprising element
of the present invention.
f) Simple application techniques and well experimented
and economical implementation methods, non-standard equipment
being unnecessary.
The coatings of the invention, as far as described up to
now, contain no stabilizers against weathering and against
degradation by daylight exposure. If such stabilizers (a de-
scription of which will be found hereinafter in section II)
are incorporated in the composition of the invention at con-
centration of about 0.5 to 5% by weight of composition, the
resistance against oxidation, discoloration, and other dam-
ages caused by external exposure conditions is greatly in-
creased. This will be described in section II of this
disclosure.
There will be now described in detail in the experimen-
tal part that follows how the invention can be put to appli-
cation practically,
Reduction to practice of the invention
1. Preparation of hydrophobic silica and alumina
A. Chlorination of silica then alkylation of the chlo-
rinated product:
In a 1 liter flask were placed 500 ml of anhydrous ben-
zene, 240 ml of thionyl chloride and 30 g of pyrogenic silica
~2~793;~
~AEROSIL 380). The mixture was refluxed for 5 hrs after
which the solvent and excess of SOC12 were distilled off.
The residue was further left for 2 hrs at 50C under 10 Torr
(13.3 mbar) so as to complete the evaporation and 31~3 g of
chlorinated silica were collected. Ten g of this were then
alkylated by boiling 2 hrs with 60 g of n-butanol (actually,
temperatures of 60 - 90C were already sufficient for 2 hrs
reaction periods). The HCl formed was removed under reduced
pressure (20 - 28 mbar) and dry ether was added. The suspen-
sion w~s centrifugated and, after separating the liquid
phase, the solid was washed twice with ether. There were
thus obtained 11.1 g of silica the particles of which bore,
grafted on the silicon atoms, n-butoxy radicals.
The same procedure was followed but replacing in the
above preparation the n-butanol by equivalents of the follow-
ing alcohols: n-hexanol, n-heptanol, n-octanol, oleyl alco-
hol, and 1,2-propanediol monoacrylate. There were thus
obtained silica products with corresponding grafted
substituents.
A'. Treating with tetrachlorosilane then alkylation of
the obtained chlorinated product:
This reaction corresponds to the following scheme:
-lioH + SiC14 ~ -liO-SiC13 ~ -SiO-Si(OR)3
In a 1 liter flask there was boiled for 5 hrs a mixture
of 500 ml of anhydrous benzene, 240 ml o~ SiC14 and 30 g of
AEROSIL 380 (Degussa). Then, the solvent and the excess
SiC14 were distilled off and evaporation was completed by
heating 2 hrs at 50C under 14 mbar for fully removing vola-
tile materials. Then 70 g of n decanol were added to 10 g of
the silica thus modified and, after 2 - 3 hrs at 70 - 90C,
the pressure was dropped to 20 - 30 mbar to completely expel
the HCl formed. After cooling, ether was added as described
beore (see under part A~ and the product was centrifugated
and washed twice with ether. After drying in air, 10.7 g of
grafted silica were collected.
With n-hexyl and oleyl alcohols, corresponding results
were obtained.
B. Reaction with chlorosilanes: '
Twenty-five g of AEROSIL 380 were heated to reflux for 5
hrs with 500 ml of anhydrous chloroform and 25 ml of tri-
chlorovinylsilane or dichloromethylvinylsilane. Then, the
solvents and excess volatile reagents were evaporated under
~Z~793Z
vacuum. Alkylation of the residue was achieved by heating
for 2 hrs with 200 ml of ethanol. Then the reaction mixture
was centrifugated and the residue was purified by extracting
with ether (5 hrs). This method provided a grafted silica of
excellent whiteness. Analogous results were obtained by re-
placing trichlorovinylsilane by trichloromethylsilane.
C. Condensation with silanols:
Forty g of y-methacryloxypropyl-trimethoxysilane (prod-
uct A-174, Union Carbide) were stirred at room temperature in
one liter of water acidified with dilute acetic acid to pH
3.5. An emulsion which first appeared in the flask dissolved
progressively during hydrolysis. After 1 - 2 hrs stirring,
there were added! when the solution became clear, 40 g of
silica (AEROSIL 380) and the mixture was stirred for an addi-
tional 15 hrs at room temperature. The suspension which had
become thicker with time was centrifugated and the solid was
dried overnight at ~0 - 100C under vacuum. Then the modi-
fied silica was processed in a Waring blender and heated an-
other 2 hrs at 110C under 14 - 20 mbar in order to complete
dehydration and condensation of the remaining free silanol
groups of the grafts with neighbour silanol groups of the
particle network. The organic content of the grafted silica
was determined thermogravimetrically to be 33 parts by weight
of organic matter for 100 ppw of silica, i.e., 33%.
This grafting process is the preferred method in the
present invention~ It was used successfully to provide or-
ganophilic silica from the following grades: AEROSILS 130,
200, 300, and 380, and CAB-O-SIL rl-5 and H-5. By this
method, 40 g of starting silica furnished 54 - 57 g of silica
grafted with oxy-silico-y-methacryloxypropyl groups. The
organic content of said grafted silica lots varied between
about 25~ and 33%.
In the above preparation, the following trialkoxysilanes
were also used: y-methacryloxypropyl-ethoxy-dimethoxysilane
tNo. A-175, Union Carbide); y-glycidoxypropyl-trimethoxy-
silane ~No. A-lB7, Union Carbide); (3,4-epoxy-cyclohexyl)-
ethyl-trimethoxysilane (No~ A-186, Union Carbide); isobutyl-
trimethoxysilane (DYNASILANE, IBIMO) and octyl-triethoxy-
silane (DYNASILANE, OCTEO).
D. "Physisorption" with trialkoxysilanes:
In a 1 liter flask, there was heated 5 hrs to the boil a
mixture of pyrogenic silica (AEROSIL-380) (25 g), A-174
(Union Carbide) (25 ml) and anhydrous xylene (500 ml). The
22
~Z~7~3~,
mixture was centrifugated and the solid residue was taken
into fresh xylene and again centrifugated. After repeating
once more such purification step, the resulting powder was
collected and dried in air.
The above procedure was also carried out with the fol-
lowing trialkoxysilane products (defined above): A-175,
A-186, and A-187, as well as with ~-aminopropyltriethoxy-
silane (A-llO0) all from Union Carbide. Results were similar
except for the color of the treated silica--brown with A-175
and pale yellow with A-llO0. The other modified silicas were
colorless.
A sample of silica modified with A-174 (methycryloxy-
propyl group) (10 g) was mixed with 3 9 of methyl methacry-
late, 60 g of xylene and 0.05 g of lauroyl peroxide after
which ~he mixture was refluxed for 4 hrs. Thereafter, the
doubly modified silica was purified by successively centrifu-
gating with xylene three times.
2._ Preparation of compositions according to the
invention
A. By means of silica grafted by chlorination and alky-
lation: '
Several types of organophilic silica were used, obtained
according to the procedure described hereinbefore under para-
graph l.A. which were dispersed as indicated earlier in this
specification, to various solid concentrations into tri-
methylol-propane triacrylate (TMPTA) containing 2% of di-
ethoxyacetophenone (D~AP). Compositions having different
viscosities were obtained the rheological properties of which
were either Newtonian or thixotropic depending on the cases.
The data about such compositions are gathered in Table III
below. In this table, the following data are provided: the
type of alkylating alcohol used, the concentration of the
silica in parts by weight relative to the TMPTA (the total of
the parts being 100), the refraction index of the organic
mixture of the compositions, the viscosities, and the rheo-
logical properties.
~793~
TABLE III
Silica
(A-380) Rheo-
Composi- (parts Viscosity logical
tion No. Alcohol by weight) "nD20" (cP) properties
. .
1 Butanol 20 1.4705 670-710 Thixotropic
2 Heptanol 20 1.4691 340-360 Newtonian
3 Glycidyl
acrylate 20 -- -- Thixotropic
4 Octanol 20 -- -- Thixotropic
Decanol 20 ~ Thixotropic
6 Hexanol 16 1.4708 240-250 Newtonian
7 " 20 1.4701 320-325 Newtonian
8 " 25 -- 810-950 Fluid
9 " 27 -- 950-1450 Fluid
Table IV gives information similar to that of Table III
regarding silica activated by SiCl~ then alkylated by method
A' or by means of silica grafted with tetrachlorosilane then
alkylation of the chlorinated intermediate.
TABLE IV
Silica
(A-380) Rheo-
Composi- (parts Viscosity logical
tion No. Alcohol by weight) "nD20" (cP) Properties
_ ................. . . .
1 Decanol 16 1.4715 830-930 Fluid
2 . Oleyl
alcohol 13 -- -- Thixotropic
B. By means of silica grafted with chlorosilanes then
alkylation of the chlorinated intermediate:
The procedure used was as disclosed in paragraph 2.A.
and compositions were prepared by mixing various lots of sil-
ica (made hydrophobic by method l.B) in TMPTA with 2% DEAP.
Table V summarizes the tested compositions and indicates, in
turn, the type of chlorosilane used for modifying the silica,
the alkylating alcohol, the levels of silica fillers in the
compositions, the refraction index, viscosities, and rheolog-
ical properties of the compositions~
24 ~LZC~793 ~
TABLE V
Rheo-
SilicaVi5- logical
Composi- Chloro- (partscosity proper-
tion No. silanes Alcohol by weight) "nD20" (cP) ties
. . . . . . _ _
1 Trichloro~ ethanol A 380 (40) 1.4525 260-270 Fluid
vinyl
silane
2 Trichloro-ethanol A 380 ~33) 1.4634 1150-1490 Fluid
vinyl
silane water
3 Trichloro-ethanol A 200 1.4730 1150-1600 Fluid
vinyl ~ (18.4)
silane water
4 Dichloro-ethanol A 380 (20) 1.4636 240 280 Fluid
methyl
vinyl
silane .
C. Silica treated by condensing with silanols:
Several types of silica were used and made organophilic
by the method described above under paragraph l.C with
hydrolyzed y-methacryloxypropyl-trimethoxysilane (A~174).
Table VI summarizes the various parameters relative to such
compositions and indicates the type of monomer or monomer
mixture used, the amount of silica filler in parts by weight
(the total of said parts and the parts of monomers being 100
parts), the refraction index "n", and the rheological proper-
ties of the compositions which also contained 2% by weight of
diethoxyacetophenone photo-initiator. The first three compo-
sitions of this table distinguish themselves from each other
by the hydrophilic modification conditions: Composition 1
contains a silica treated with a 1% aqueous solution of A-
174, Composition 2 contains a silica treated with a 4% aque-
ous solution of A-174 after 18 hrs of hydrolysis, and Compo-
sition 3 a similarly treated silica except that hydrolysis
was for only 20 minutes.
793Z
TABLE VI
Silica type
Composi- Monomer or (parts by Viscosity Rheolo~ical
tion No. mixture weight)"nD20" (cP) properties
1 TMPTA A-380 (20)1.4735 -- Thixotropic
2 " " (20)1.4740 530-535 Newtonian
3 ~ n ( 20)1.4743 990-1040 Newtonian
4 " A-300 (20)1.4738 445-455 Newtonian
" A-200 (20)1.4739 570-590 Newtonian
6 " H-5 (20)1.4738 425-440 Newtonian
7 " M-5 (20)1.4736 520-570 Newtonian
8 . " H-5 (28.5)1.4758 1020-1050 Newtonian
9 UCAR X-118
(49.2) H-5 (13.6)1.4748 -- Pseudo-
DEGDA (50.8) plastic
UCAR ~-118
(18)
DEGDA (82) H-~ (20)1.4698 230-228 Newtonian
11 UCAR X-118
.' (11) 1
DEGDA (89) H-5 (20)1.4682 150-155 Ne~tonian
12 EBECRYL 830
(33.3)
DEGDA (66.7) H-5 (20) 1.4745 430-450 Newtonian
13 E~ECRYL 600
(16.7)
DEGDA (83.3) H-5 (20) 1.4762 210-215 Newtonian
14 Methyl ~-5 (20)1.4755 140 Newtonian
methacrylate
(38.5)
PETEA (38.5)
EBECRYL 600
(23)
Methyl H-5 (43.7) -- -- Very fluid
methacrylate and
Newtonian
16 Butyl H-5 ~43.7) -- -- Very fluid
acrylate and
Newtonian
D. Silica grafted by "physisorption":
Preparation of the corresponding composition was carried
out exactly as for the previous compositions of Tables III to
VI. The various parameters pertaining to these compositions
26 ~2~7932
are grouped in Table VXI. These parameters comprise, in
turn, the types of organosilanes used for the "physisorp-
tion", the amount of sllica (A-380) used in the compositions
(parts by weight in relation to the weight of the organic
matter, the total of the ingredients being 100 parts), the
types of monomers or mixtures o~ monomers used, the refrac-
tion index "n", the viscosity of the mixture and its rheolog-
ical behavior. All the compositions also contained 2% by
weight of diethoxyacetophenone as the photo-initiator.
The first ~our compositions of Table VII differ from
each other by the following points: In the first (No. 1),
silica has been made organophilic simply by the indicated
treatment (all the other samples starting from the fifth were
also trea~ed similarly). Composition No. 2 contains silica
which, after physisorption, was ~ubjected to a second acti-
vating modification by thermal copolymerization with methyl
methacrylate as indicated in the last paragraph of section
l.D hereinabove. Compositions 3 and 4 contained silica
products that were similarly doubly modified with the A-174
monomer and butyl acrylate, respectively.
TABLE VII
.,
Silica
Composi- Silane (parts Monomers Viscosity Rheological
tion No. used by weight) used (%) "nD20" (cP) properties
.
1 A-174 20 TMPTA1.4730 650-800 Fluid
2 " " " 1.47741100-1200 Fluid
3 " " " 1.47422000-2400 Fluid
4 " " " 1.47502250-2750 Fluid
" " HDDA 1.4595 205-207 Newtonian
6 " " DEGDA1.4S84 205-210 Newtonian
7 " " DEGDA1~4732 510-570 Fluid
(50)
PETRIA
(50)
8 " 24.5 DEGDA1.4732 800-900 Fluid
(50)
PETRIA
(50)
9 A-174 + 17 T~lPTA -- -- Thixotropic
1~ SOC12
A-175 20 " 1.47341300-1700 --
11 A-1120 20 " 1.4775 Thixotropic
~Zg:~793Z
Compositions represented in Tables III to VII have, de-
pending on the cases, a Newtonian (fluid) or thixotropic be-
havior. For embodying the invention, composition with New-
tonian properties are preferred since they more easily form
thin films with well-controlled characteristics. Generally,
the smaller the silica par~icles ~or alumina particles) and
the greater the organophilic properties thereof (in propor-
tion to the de~ree of grafting and to the length and the num-
ber of carbon atoms of the grafted radicals), the more the
composition will behave as a Newtonian liquid and the easier
it can be handled. Moreover, the overall viscosity of the
compositions increases with increasing size of the particles
and increasing solid concentration in the mixture.
With respect to the clarity of the compositions contain-
ing organophilic silica, it is advantageous to use mixtures
of monomers with an index of refraction as near as possible
to that of said silica. It should be pointed out in this
connection that the organophilic modifying treatments used in
this invention do not necessarily always lead to silica prod-
ucts with the same refraction index. However, this index
remains most of the time reasonably close to the 1.4740 -
1.4750 range. Thus, it may be useful to adapt, from case to
case, the refraction of the organic mixture to that of `the
selected silica. In this regard, it is to be remembered that
if the difference between the indices (that of the organic
phase and that of the silica) becomes too great, the composi-
tion becomes milky and the coatings obtained therefrom are
not perfectly clear. For example, if one uses 20 parts by
weight of organophilic silica (n = 1.4746) with 80 parts by
weight of TMPTA (n = 1.4732) or a 1:1 mixture of PETIA and
DEGDA (n = 1.4746), one obtains a clear mixture. Contrari-
wise, in the same conditions but with either pure HDDA (n =
1.4574) or DEGDA (1.4621), translucent mixture will be ob-
tained.
The results in Table VIIa obtained with the use of a
silica, A-972, treated with a silicone coating compound con-
taining less than four carbon akoms show that this silica
treatment does not give satisfactory coating application be-
havior, even with low silica loading.
28
~Z~793~
TABLE VIIa
Composition Concentration
No. of A-972 Polymer Viscosity and Observations
12 11 TMPTA 89 Strongly thixotropic mass
121 8 TMPTA 92 550-840, liquid, developed
thixotropy after storage
for a day
7.4 DEGDA 92.6 195-205, nD20 1.4615 slow-
ly developed thixotropic
properties
3. Compositions with alumina
.
If, in the various methods for treating silica described
in the prior art and in the methods for preparing the coating
compositions of the present invention with said organophilic
particles, the silica particles are replaced by alumina of
equivalent mesh sizel similar results are experienced except
for the transparency parameter as already explained.
4~ Preparation of abrasion resisting coatings
For the coating experiments, organic glass plates (2 x
10 cm) of polymethylmethacrylate (PMMa), polycarbonate (PC),
polyvinyl chloride (PVC), and CR-39~ (poly(diethyleneglycol)-
bis-allylcarbonate) were used as substrates. The plates were
first washed with isopropanol, then, thin layers (thickness 1
to 50 ~m) of the compositions listed in Tables III to VII
were applied on the plates by the means already mentioned
previously. Then, the samples were irradiated with a 80 w/cm
W source for periods o~ 5 to 30 sec or more. Best optical
properties were obtained by pressing on the freshly coated
plates a perfectly smooth glass plate, i.e., by performing a
"replica molding" of the coating by means of a glass mold.
In this case, the exposure is done through the glass, the
latter being eventually easily detached from the hardened
film after cooling to room temperature.
5. Measurements of the optical properties
The optical properties of the coatings (obtained by
"replica molding" as above) from the various compositions
listed in Tables III to VII were measured. Coatings with
about 15 25 ~m thickness were selected. The measured
29 ~ 75~3~
parameters were the percent transmission and reflectance
(relative to a corresponding non-coated plate) between 800
and 400 nm measured with a PYE-UNICAM spectrophotometer. Re-
sults are provided in the following tables: Table VIII for
the PC substrates (MAKROLON~); Table IX for the P~lMa sub-
strates (PLEXIGLAS~) and Table X for the PVC substrates
(TAKIRON~). In the tablesr there are provided, successively,
the following data: a control sample uncoated, then samples
identified by the number given to the corresponding composi-
-tion from Tables III to VII, the percent of transmission at
800 ~ 590 ~ and 400 nm for said coatings (plus the substrate),
respectively, and the gain or the loss relative to said con-
trol sample.
- TABLE VIII
Composition Transmission (%) at nm Gain or loss (%) at
No. 800 590 400 590 nm
. .
Control
(MAKROLON) 89~7 86.5 74~4 0
III 2 92 ~ 2 86. 8 76 ~ 8+ 0 ~ 35
III 5 91.5 88~2 76~8 + la96
III 6 94 ~ 2 87 ~ 5 73 ~ 4 ~ 1.16
VI 2 89~7 86~7 74~4 + 0~02
VI 3 89 ~ 5 86 ~ 5 73 0
VII 1 93~4 86~4 76~8 ~ 0~01
VII 7 88~2 84~2 70~0 ~ 2~54
Table IX further lists a samplel X, coated with a trans-
lucent film containing alumina. This film was prepared with
a composition containing TMPTA and 16 parts by weight of
A12O3 (total 100 p.b.w.), the latter having been made organo-
philic by the process disclosed under section A.l + hexanol
(analogous to Composition III-6); viscosity: 255 ~ 277 cP~
A similar behavior was observed for a corresponding sample
containing silica activated by the process described under
section C.
~2~7~3Z
TABLE IX
Composition Transmission (%) at nmLoss (%) at nm
No. 400 590 800 590
Control
(PLEXIGLAS) 93.2 91.7 88.2 o
III 2 93.5 91.0 85.5 0.76
III 5 93.2 90.4 84.5 1.4
III 6 93.2 91.0 87.0 0.76
VI 2 92.0 89.7 83.5 2.18
VI 3 90.0 87.0 79.0 5.12
VII l 91.8 89.5 84.0 2.4
VII 5 91.0 88.0 83.5 4.03
VII 6 88.5 84.5 76~0 7.85
VII 7 92.8 89.5 84.0 2.40
X (A12O3) 75.0 66.5 49.5 27.5
TABLE X
Composition Transmission (%)
No. at 590 nm Gain or loss `(%)
Control
PVC TAKIRON~ 83.2 - 83.3 0
VI 2 83.8 - 83~9 ~ 0.6
VI 4 82.5 - 82.6 - 0.6
VI 5 84.1 - 84.2 ~ 0.7
VI 6 83.6 - 83.7 + 0.4
VI 7 83.3 - 83.4 + 0.1
It is interesting to note from the results of Tables
VIII and IX that the clarity of the coatings containing sil-
ica rendered organophilic by "chemisorption" r i.e., by the
techniques described in sections A to C is better than the
clarity of the coating containing silica modified by "Physi-
sorption".
6 Measurements of abrasion resistance
_
For the abrasion resistance measurements, the same
plates were used which are described in Section 4 with a pro-
tective coating according to the invention. The abrading de-
vice (Creusot-Loire Instrumentation, Adamel-Lhomargy, France)
31 12~793~
comprised a rubbing shoe (1 x 1 cm; 2 kg) moving alternative-
ly forward and backward on the sample by means of a crank-
drive and the rubbing surface of which was provided with a
patch of steel wool (Tampon GEX). The operating parameters
of this testing were: displacement amplitude: 4 cm; fre-
quency: 1.4 HZ; number of cycles: up to 500. Table XI
provides the results obtained for samples of polycarbonate
(MAKROLON~), PMMa (~LEXIGLAS~), CR-39~ (PPG), Polyurethane
(SECURIFLEX~ of St. Gobain) and FLOAT glass as well as for
the coatings of the invention applied on some of the above
substrates (thicknesses 5 - 20 ~m). The abrasion effect is
expressed as the loss of optical transmission (loss of gloss)
after a number of abrading cycles.
32 ~z~793;:
TABLE XI
~ ~ = ....
Loss of
Coated sample Coating compo- Cycles transmission
or substrate sition No. ~number of) at 590 nm (%)
MAKROhON~ (1 mm) - O O.O
" - 100 34.1
" III 2, 5 and 6 " 0.67
" VI 2 and 3 " 0.67
" VII 1 and 7 " 0.67
" X (A1203) " -
PLEXIGLAS~ (1 mm) - O O.O
" - 50 29.0
" - 100 32.9
" III 2 " 0.52
" III 5 " 0.67
" VI 2 " 0.52
" VI 9 " 8.0
" VI 10 " 1.0
" VI 11 " 0.6
VI 12 " 0-5
" VI 13 " 1.7
" X (A12O3 " 0.0
" VII 1, 5 and 6 " 0.52
" VII 7 " 0.57
PLEXIGLAS0 (1 mm) III 2 500 0.80
" III 5 500 0.80
" VI 2 500 0.80
SECURIFLEX~ - 0 0.0
" - 100 5.4
" - 200 9.1
CR-39~ PPG - 0 0.0
" - 50 7.8
" - 100 8.9
" - 200 10.8
Glass ~1 mm) - 100 0.O
33 ~2~793~
The results of Table XI show that, with the exception of
composition VI-9, all coatings according to the invention
provide an excellent protection against scratches. The pro-
tection offered by the coating containing alumina (sample X
A12O3) is even better since no optical transmission loss was
evidenced after 100 rubbing cycles. However, account should
be taken that silica hardness is only 820 Knoop whereas that
of alumina is 2,100 Knoop.
7. Resistance to organic solvents
For testing the resistance of the present coatings to
solvent attack, the steel wool used in the device of the pre-
vious test was replaced with a porous plug soaked in the 501-
vent to be tried. After 100 rubbing cycles, the possible
transmission loss of the sample was compared to that of the
same coating sample not subjected to an attack by the sol-
vent. The following solvents were tried and none had any
effect on a PLEXIGLAS~ sample protected by films from the
compositions III-2 and 5, VI-2 and VII-l, 5, 6, and 7. In
contrast, a noncoated PLEXIGLAS~ plate suffered a 47.6~ loss
under the same conditions when subjected to chloroform. Sol-
vents tried heptane/toluene (70/30); toluene, aceto'ne,
chloroform; tetrachloroethylene/trichloroethylene (60~40);
heptane/trichlorethylene/toluene (15/50/35).
8. Resistance to surfactants solutions
.
Samples to be tested were immersed for various periods
in 1~ aqueous TEEPOL~ (an alkyl-aryl-sulfonate) at 20 - 30C,
then they were left to dry in air after which they were
cleaned with a moist cloth. It was noted that the same sam-
ples mentioned above under section 7 had only a 0.8~ optical
transmission loss after 864 hrs of immersion and that the
films had no tendency to loosen from the substrate.
9. Resistance to heat
For this 'test, the sample was subjected to conditions
reproducing normal operating conditions for vehicle head-
lights cover glasses: 1 day in a moist atmosphere at 18 -
28C and 16 hrs in a dry atmosphere at 115C. In the present
case a polycarbonate projector glass (type E-2, SEV Marchal)
was protected with a film from composition VII-l. After 16
hrs in the oven at 115C the coating was not cracked, nor
flaked off and had no visible deformation.
~LZ~;P79;~2
10. Resistance to shock
-
A steel ball (13.6 g, 0 15 mm) was dropped from a height
of 9 m on a projector glass protected as described in the
previous section. The velocity at the hitting point was
13.28 m/sec. After the shock, the coating did not crack or
peel off (composition VII-l).
11. Resistance to weathering
A photopolymerizable anti-abrasive composition was pre-
pared by mixing together 333 parts of EBECRYL~ 220 (see Table
I) and 666 parts of diethylene glycol diacrylate (DEGDA). To
this mixture were added, and all ingredients were milled to-
gether overnight in a glass jar with glass beads, various
amounts of grafted silica (prepared according to the method
described under section l.C), various amounts of a photo-
initiator (UV-Harter-1116 from Merck) and various quantities
of W stabilizersO Such stabilizers were selected rom com-
mercially available stabilizers as listed below: th~
TINUVIN~ stabilizers made by the CIBA-GEIGY Company and in-
cluding the TINUVIN~-900, -P, ~328. The WIN~L~ stabilizers
sold by the BASF-Wyandotte Company; the UVINUL~ stabiliz'ers
are mostly benzophenone derivatives and are detailed in a
data sheet from the BASF-Wyandotte Corp., Parsippany, N.J.
07054 called "UVINUL~ UV Absorbers for Cosmetics, Plastics,
Coatings and Textiles". The absorbers tested included the
following types of WINUL~: N-539; D-49. Phenyl salicylate
was also included in the W absorbers tested. The respective
quantities of grafted silica, photo-initiator and the various
stabilizers are given in % by weight with respect to the
above composition.
After filtering the composition on a nickel mesh (25 ~),
films of such compositions (10 - 50 ~ thick) were applied on
standard polycarbonate plates (7.5 x 15 cm) and irradiated
with a 60 W~cm W light source placed 30 cm from the film.
During irradiation cure, a 4 mm thick glass plate was inter-
posed between the source and the sample plates to evenly dis-
tribute the light energy. Irradiation times were 30 sec (Tl)
and 60 sec (T2).
The coated samples were then subjected to an accelerated
weathering test in a "Q-UV Accelerated Weathering Tester"
(the Q-Panel Company, Cleveland, Ohio). This test consists
in subjecting the samples to very strong W irradiation from
fluorescent W lamps under alternating conditions of dry and
humid heat (1 cycle = 8 hrs under W at 70C dry followed by
4 hrs W at 50C under condensating humidity conditions 100
~lZ~793z
relative humid'ty). After intervals, the samples were
examined for the advent or formation of crazing (cracks),
dewetting (separation of the film from substrate), chalking
and other general degradation signs. The "cross-hatch"
testing was applied to determine the residual adhesion of the
film over the substrate. This test consists in cross-cutting
the film at right angles with a sharp knife so as to provide
criss-cross stripes about 1 mm wide thus defining a plurality
of little film squares like a checkerboard; then a piece of
scotch adhesive tape is pressed over the test area and there-
after lifted whereby some of the little squares will be
removed if adhesion of the film on the substrate is low. The
conditions for passing the above weathering test were that no
trace of any deficiency (in connection with th.e aforesaid
criteria) is found; for instance, in the cross-hatch test,
the lifting of even one of the little squares is failing.
In the weathering test none of the samples had failed at
the end o~ the 168-hour exposure period. The first column of
the weathering test data (Table XII) shows an X for each
coating that was rated failed at the end of the 336-hour per-
iod, the second column similarly shows which coatings were
rated failed at the end of the 504-hour period, and the third
column likewise shows those rated failed at the end of 'the
672-hour period. Only one coating was considered to have
passed the 672-hour test--No. 658gg'T2. The other columns of
the table pertain to other aforedescribed composition
parameters.
TABLE XII
Sample SiO2 Photo-initiator Stabilizer Weathering test
(No) (%) (%) type and (%) 1 2 3
Cure(T)
.. . . _ _ _ _ _
,
TINUVIN~9OQ
658 c Tl 20 1 0.5 X
658 c T2 " " " X
658 d T2 " " 1 X
658 Tl " 2 0.5 X
658 T2 " " " X
658 a Tl " " 1 X
658 a T2 " " " X
658 b Tl " 4 0.5 X
658 b T2 " 4 " X
658 kkTl 27.7 2 " X
658 kkT2 " " " X
36
~2~7~
_ BLE XII (Cont)
l 2 3
UVINUL~N-539
658 bb'T2 27.i l l X
658cc''T2 " " 2 X
658 aaTl " 2 0.5 X
658 aaT2 " " " X
658 bbTl " " 1 X
658 llTl ~ 1- 0.5 X
658 llT2 " " " X
658 ll'T2 " " 2 X
658 bbT220 2UVINUL~-539 X
658 ccT2 " " 2 X
658 cc'T2 " " 3 X
658 ddTl " 4 1 X
658 ddT2 " " l X
658 S T235 2 2 X
658 V T2 lS " " X
UVINUL~D-49
658 iiT2 " 1 l X
658 eeTl " 2 0.5 X
658 eeT2 " " " X
658 ffTl " " l X
658 ffT2 " " " X
658 ggT2 " " Z X
658 gg'T2 " " 3 *
658 hhTl " " l X
658 hhT2 " " " X
658 mmTl27.7 " 0.5 X
658 mmT2 " " " X
658 mm'T2 " " 2 X
TINUVIN~-P
658 p T220 " 2 X
TINUVIN~-328
658 g T2 " " 2 X
Phenyl saly-
658 r T2 " " cylate 2 X
D-49 /N-539
658 xlT2 " " (l:l) 2 X
D-50 N-35
658 x2T2 " " (l:l) 2 X
UVINULæ ~1-40/
658 x3T2 " "TIN~-328 (l:) 2 X
~2e~7~3;~
TABLE XII (Cont)
,_
1 2 3
TIN~-P/Phenyl
658 x4T2 " "salicylate(l:l) X
;*Coating considered to have passed the 672~hour test.
... i,- .. , . . . \
The data of Table XII show that the best results were
` ~ obtained with films containing 20% grafted silica and the
UVINUL0 W stabilizers.
- 12 Comparative testin~s
-
Further tests were done with films (about 5 ~ to 30 ~
thick) of the composition disclosed in the previous Example
deposited on polymethacrylate (PMMA) and polycarbonate (PC)
organic glasses. The composition contained 20% by weight of
the grafted silica, 2% of the photo-initiator (UV-H-arter-
1116) and 2% of a UVINUL~ weathering stabilizer. The tests
to which the samples were submitted are listed below. ~
i: Adhesion after curing; cross-hatch scotch-tape test
(technique and passing criteria were described in the pre-
vious Example),
ii: Pencil hardness: pencil lines are drawn by hand on
the sample by holding the pencil at 45 angle and pushing
forward. Pencil hardness grades 2 H to 9 H were used. No
mark should be visible for passing,
iii: Flexion (GTB test): In this test, the sample (150
x 25 mm) is supported horizontally on two blocks twith
rounded corners) separated by a distance of 125 mm~ Then a
force is applied in the center of the sample that produces a
bending the central extent of which (relative to the hori-
zontal) is measured. The 25 mm and 50 mm deformation are
recorded in terms of the coating aspect after returning to
horizontal, i.e., the inspection for creases, crazing, peel-
off, opalescence, etc. No such defect should be visible for
passing.
iv: Heat resistance: the sample is heated in an oven
for one hour at 115C. Then surface examination is done as
in iii above.
38
~2~7~3Z
v: Thermoforming: A coated plate sample (75 x 140 mm,
1 mm thick) is heated in an oven to its softening point
(glass transition temperature), then it is bent until forming
a cylinder with the opposite shorter edges touching. After
cooling, the surface of the rigid cylinder is examined for
any of the defects outlined under iii. No defect should be
visible for passing.
vi: Scratch width (French standards): A flat sample is
placed on the table and a diamond point with a 270 g load is
fixedly applied on it by its own weight. The sample is then
gently pulled so that the point will dig a groove in the
sample surface the width of which is inversely proportional
to the surface resistance to scratching. The width of the
groove is recorded in ~m.
vii: Taber abrasion test (ASTM): The test sample is
placed on a horizontal turntable and two free spinning flat
edge abrasive rollers held on a fixed horizontal axle are
applied on the sample in a manner such that~ upon rotation of
the table, the rollers will be driven to spin by friction
with the sample surface. The rollers are loaded with a 500 g
weight and since they are radially symmetrically disp~sed
with regard to the turntable center, they will provide an
annular abraded zone on the sample after some time of opera-
tion. The number of cycles is 500 after which the loss of
transparency of the abraded area is measured in an apparatus
for measuring diffusion of light and expressed as a percent
attenuation of visibility by diffusion.
viii: GTB abrasion test: In this test, a seven inch
diameter organic glass lens protected by a scratch-resistant
coating to be tested (such as a lens is used in automotive
light equipment) is subjected to rubbing with an alterna-
tively moving shoe applying on the horizontally layed anti-
scratch surface. The contact surface of the shoe is provided
with a cloth dusted with quartz powder (UTAC powder)~ The
load on the shoe is 2N/cm2 and the number of rubbing cycles
is 100. The abraded area is then examined for diffusion (~D)
and light transmission (~T) as above. Results are expressed
in "digit units"; the lower the "digits" value, the more
abrasion resistant the sample is.
ix: Water immersion test: The samples were immersed in
1% TEEPOL aqueous solution at 65C. They were removed at
intervals and tested for adhesion (cross-hatch). The number
39 ~Z¢~7932
of hours before failure is recorded as the merit index in
this test.
x: Accelerated weathering resistance: This is the QUV
~est described in the previous Example.
.
The aforedescribed tests were applied to the samples of
the invention and, simultaneously, to samples of PC protected
by a commercially available anti-scratch composition labelled
GE/SHC-1000. The data pertaining to that comparable material
and to the samples of the invention as well as the results to
the aforementioned tests are recorded in Table XIII. In the
middle column, the results are for both coated PMMA and PC
unless separately mentioned.
- TABLE XIII
Data & tests Coatings of GE/SHC-1000
the invention on PC
.
Composition before curing
resin content 80~ 20% ~
solvent none methanol-isobutanol
flash-point >130C 26C ~Penske-Markens)
density tg/cm3) 1.1 - 1.3 0.91
pH -- neutral to mildly
alkaline
shelf-life >6 months at 2 months at 4C
23C in the dark
viscosity lO0 - 200 cP 4 - 10 cStokes
handling care fluid (no vapor) flammable liquid
toxicity skin irritant skin and eye irritant
Application procedure
primer none primer SHP-200 dip,
flow or spray air
drying 30 min
scratch-resistant spray, brush, dip, flow, spray
layer roll, doctor air drying 20 min
blade replica
coating
curing 30 - 60 sec W 60 min 120 - 125C
no heat
40 ~2q~793;~ ~
TABLE XIII (Cont)
Film data
density 1.2 - 1.5 g/cm 1.45 g/cm3
thickness 5 - 30 ~ 5.1
Tests
i passed passed
ii PC <6H <6H
ii pMrlA >8H <9H >6H
iii ~25) pass pass
(50) pass pass
iv PC pass pass
v prlrlA pass ?
vi PC 50-75 ~ 150 - 200 ~ .
vii 18 - 19 20 - 21 .
viii ~D = 30 - 40 ~D = 50 - 80
~T = 8 - 16 QT = ~70 .
ix PC ~600 hrs PC passed 500 hrs
x 500 - 672 hrs up to 500 hrs
The xesults of Table XIII show that the scratch-
resistant films obtained from the composition behave equally
or better than a comparable commercially available material.
However, being applicable as a one layer coatin~ the composi- .
tion of the invention is more simple to use than two layers .
commercial composition.
