Surface-active photoinitiators

Details Surface-active photoinitiators Surface-active photoinitiators

2001-12-21

2004-02-17

Berman, Susan W. (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Compositions to be polymerized by wave energy wherein said...

C522S035000, C522S039000, C522S042000, C522S044000, C522S096000, C522S117000, C522S126000, C522S135000, C522S137000, C526S194000

Reexamination Certificate

active

06693141

ABSTRACT:

The invention relates to a process for the preparation of scratch-resistant durable coatings in which siloxane-containing photoinitiators are used as surface-active initiators, and to new surface-active photoinitiators.
In order to improve the miscibility of photoinitiators with silicone-containing substrates (compatibility) that are to be photochemically crosslinked, WO 97/49768, U.S. Pat. No. 5,776,658, U.S. Pat No. 4,391,963 and EP 88842, for example, propose photoinitiators, e.g. of the hydroxy-ketone, aminoketone, benzoin ether, benzophenone or thioxanthone type, that have been modified with silyl radicals, especially with polymeric silyl radicals. Patent Specifications U.S. Pat No. 4,536,265, U.S. Pat No. 4,534,838 and EP 162572 also describe a wide variety of photoinitiator structures provided with organopolysiloxane radicals. Those compounds are derived, for example, from dialkoxyacetophenones and have enhanced solubility in silicone substrates. U.S. Pat No. 4,507,187 discloses silyl-group-containing diketo photoinitiators as photoinitiators that are readily soluble in silicone polymers, and also the polymers obtained with those initiators. U.S. Pat. No. 4,477,326 describes self-polymerising siloxane polymers that contain photoinitiator units as groups that trigger the polymerisation reaction. Polymeric photoinitiators containing siloxane radicals are described in U.S. Pat. No. 4,587,276.
In J.M.S. Pure Appl. Chem. A31(3) (1994), 305-318, A. Kolar, H. F. Gruber and G. Greber describe reactive silyl-derived &agr;-hydroxyketone photoinitiators. The literature references mentioned are concerned especially with solving the problem of improving the miscibility of the photoinitiators with the substrate to be polymerised, that is to say distributing the initiator in the substrate as homogeneously as possible. WO 98/00456 proposes certain coating compositions, and a curing process by means of which the properties of the coating surface can be improved.
New energy-saving curing mechanisms and applications that result in as few emissions as possible are sought by the coatings industry in order to produce durable, scratch-resistant coatings. There is especially a need to improve the surface of coatings, especially in respect of hardness, durability and gloss properties.
It has now been found that the desired properties can be obtained using certain photoinitiators in the coatings that are to be cured. For that purpose, the photoinitiator is not distributed as homogeneously as possible in the formulation to be cured but is concentrated in targeted manner at the surface of the coating to be cured; the initiator is thus oriented in targeted manner towards the surface of the formulation. For that purpose it is necessary to use photoinitiators that have been designed in a particular manner.
The invention relates to a process for the preparation of coatings having scratch-resistant durable surfaces, in which
(I) a photocurable formulation comprising
(A) an ethylenically unsaturated polymerisable compound; and
(B) a photoinitiator;
is prepared;
(II) that formulation is applied to a support; and
(III) the formulation is cured either solely by irradiation with electromagnetic radiation of a wavelength of from 200 to 600 nm, or by irradiation with electromagnetic radiation of a wavelength of from 200 to 600 nm and by prior, simultaneous and/or subsequent action of heat;
in which process the formulation comprises as photoinitiator (B) at least one surface-active photoinitiator that is concentrated at the surface of the formulation.
A surface-active photoinitiator is used as photoinitiator (B). Photoinitiator (B) is a photoinitiator compound that is incompatible with the formulation to be cured, that is to say has poor miscibility therewith, and is therefore able to concentrate at the surface of the formulation.
A suitable surface-active photoinitiator (B) in the process described above is a compound comprising
a customary photocleavable photoinitiator molecule moiety (b1) and
a molecule moiety (b2) that is incompatible with the formulation to be cured.
Customary photocleavable molecule moieties are known to the person skilled in the art, and are, for example, &agr;-cleaving radicals. Of special interest are compounds in which the photocleavable photoinitiator molecule moiety (b1) contains a group
The molecule moiety (b2) having poor compatibility with the formulation to be cured is a siloxane radical.
Suitable photoinitiators (B) are especially compounds of formula I
wherein the units of formulae Ia, Ib and/or Ic
are arranged randomly or in blocks, and wherein
n is a number from 1 to 1000, or, when the siloxane starting material is a mixture of oligomeric siloxanes, n may also be less than 1, but greater than 0;
m is a number from 0 to 100;
p is a number from 0 to 10 000;
x is the number 1 or 2;
A
1
is C
1
-C
18
alkyl or a radical of formula
A
2
is C
1
-C18alkyl or a radical of formula
or A
1
and A
2
together are a single bond;
R
1
, R
2
, R
3
, R
5
, R
6
, R
7
, R
8
, R
9
and R
10
are each independently of the others C
1
-C
18
alkyl, phenyl, C
2
-C
6
hydroxyalkyl, C
2
-C
6
aminoalkyl or C
5
-C
8
cycloalkyl;
R
4
is C
1
-C
18
alkyl; C
1
-C
18
alkyl substituted by hydroxy, C
1
-C
12
alkoxy, halogen, C
3
-C
8
-cycloalkyl and/or by N(R
11
)(R
12
); or R
4
is phenyl; phenyl substituted by C
1
-C
12
alkyl, C
1
-C
12
-alkoxy, halogen, hydroxy and/or by N(R
11
)(R
12
); or R
4
is C
5
-C
8
cycloalkyl;
R
11
and R
12
are each independently of the other hydrogen, C
1
-C
12
alkyl or C
1
-C
12
hydroxyalkyl, or R
11
and R
12
together are C
2
-C
8
alkylene, which may be interrupted by an oxygen atom;
IN when x is 1, is a radical of formula
IN when x is 2, is a radical of formula
R
13
and R
14
are each independently of the other C
1
-C
12
alkyl, C
2
-C
8
alkenyl, C
5
-C
8
cycloalkyl, phenyl-C
1
-C
3
alkyl; or R
13
and R
14
together are C
2
-C
8
alkylene, C
3
-C
9
oxaalkylene or C
3
-C
9
-azaalkylene;
Y is —(CH
2
)
a
—, —(CH
2
)
a
—O—, —O—(CH
2
)
a
—O—, —(CH
2
)
b
—O—(CH
2
)
a
—, —(CH
2
)
b
—O—(CH
2
)
a
—O—, —(CH
2
)
a
—N(R
12
)— —(CH
2
)
b
—O—(CH
2
)
a
—N(R
12
)—, —(C
2
-C
10
alkenylene)—O—, —(C
2
-C
10
alkenylene)—N(R
12
)—, —(C
2
-C
10
alkenylene)—O—(CH
2
)
a
—O— or —(C
2
-C
10
alkenylene)—O—(CH
2
)
a
—N(R
12
)—;
a and b are each independently of the other a number from 0 to 10;
X is OR
15
or N(R
16
)(R
17
);
R
15
is hydrogen, C
1
-C
4
alkyl, C
2
-C
8
alkenyl or C
1
-C
4
alkanoyl;
R
16
and R
17
are each independently of the other hydrogen, C
1
-C
12
alkyl or C
2
-C
6
alkenyl; or R
16
and R
17
together are C
4
-C
5
alkylene and, together with the nitrogen atom to which they are bonded, form a 5- or 6-membered ring, which may be interrupted by O or by N(R
12
); and
X
1
is a radical —O—, —O—(CH
2
)
a
— or —N(R
12
)—(CH
2
)
a
—.
A number of compounds of formula I are novel and form part of the subject matter of the present Application.
C
1
-C
18
Alkyl is linear or branched and is, for example, C
1
-C
12
-, C
1
-C
8
-, C
1
-C
6
- or C
1
-C
4
-alkyl. Examples thereof are methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, pentyl, hexyl, heptyl, 2,4,4-trimethylpentyl, 2-ethylhexyl, octyl, nonyl, decyl, undecyl, dodecyl, hexadecyl and octadecyl. For example, R
1
, R
2
, R
3
, R
4
, R
5
, R
6
, R
7
, R
8
, R
9
and R
10
are C
1
-C
8
alkyl, especially C
1
-C
6
alkyl, preferably C
1
-C
4
alkyl, such as methyl or butyl, especially methyl.
C
1
-C
12
Alkyl, C
1
-C
10
alkyl and C
1
-C
8
alkyl are also linear or branched and have, for example, the meanings given above up to the corresponding number of carbon atoms.
Substituted alkyl is, for example, mono- to penta-substituted, mono- to tri-substituted or mono- or di-substituted.
Alkyl substituted by halogen is substituted, for example, by fluorine, chlorine, bromine or iodine.
Alkyl substituted by OH is mono- or poly-substituted, especially mono-substituted, by OH. Examples thereof are 2-hydroxyeth-1-yl, 3-hydroxyprop-1-yl and hydroxymethyl.
C
2
-C
6
Hydroxyalkyl is hydroxy-substituted C
2
-C
6
alkyl, wherein the a

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