Phosphine oxide photoinitiator systems and curable...

Details Phosphine oxide photoinitiator systems and curable... Phosphine oxide photoinitiator systems and curable...

2000-12-05

2002-11-26

Berman, Susan (Department: 1711)

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

Synthetic resins

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

C522S064000, C522S081000, C522S083000, C522S084000, C522S092000, C522S093000, C522S096000, C522S107000, C523S300000, C430S002000, C430S281100, C430S286100

Reexamination Certificate

active

06486226

ABSTRACT:

The present invention relates to a novel process for curing ethylenically unsaturated polymerizable compounds with acylphosphine oxide photoinitiators concomitantly with low color formation, to novel acylphosphine oxide photoinitiator compositions, and to the method of use of compositions which are curable with the novel photoinitiator composition.
Mono-, bis- and trisacylphosphine oxide compounds are well known photoinitiators. U.S. Pat. Nos. 4,792,632, 4,737,593 and 5,534,559 and GB-A-2310855 disclose bisacylphosphine oxide photoinitiators. Mono- and bisacylphosphine oxide photoinitiators are disclosed in U.S. Pat. No. 5,218,009. U.S. Pat. No. 5,942,290 discloses molecular complexes of mono-, bis- and trisacylphosphine oxides with &agr;-hydroxyketone compounds as photoinitiators. Alkylbisacylphosphine oxides are disclosed in GB-A-2259704. Alkoxyphenyl-substituted bisacylphosphine oxide photoinitiators are described in GB-A-2292740. Dimeric bisacylphosphine oxide photoinitiators are revealed in U.S. Pat. No. 5,723,512.
U.S. Pat. No. 5,667,856 teaches ultraviolet radiation curable compositions comprising a curable component and a pigment selected from the group consisting of pyrrolopyrrol and isoindolinone, red and yellow pigments respectively. Ketone based and onium salt photoinitiators may be present.
Acylphosphine oxide compounds are very effective photoinitiators for ethylenically unsaturated compounds. However, a disadvantage of the use of photoinitiators of this class is that they are to varying degrees inherently yellow. Not all of the photoinitiator is consumed upon curing and therefore the cured substrate often has an undesired yellow color. This is considered “yellowing upon curing” or “initial yellowing.” This is a particular problem for the curing of clear and white pigmented systems, for instance clear and white pigmented coatings on wood, metal, plastic, glass, etc., especially thick coatings. A solution to this problem would be beneficial for instance for gel coat and powder coating applications. Yellowing upon curing with acylphosphine oxides is also a particular problem in printing inks of all types including screen print, flexographic, gravure and off-set printing inks. This yellowing is also a problem for the curing of plastic lenses and lens coatings.
The undesired yellow color is a particular problem when photoinitiators of the class of bisacylphosphine oxides are employed. Currently, many practitioners, in certain applications, intentionally “over-irradiate” the curable substrate in order to purposely photo-bleach away any residual yellow color. This process is destructive to the formed article and is not economical. Surprisingly, it has now been found that photocuring a composition with an acylphosphine oxide photoinitiator in the presence of certain red, blue and violet pigments at low levels prevents the undesired yellow color of the cured substrate.
Accordingly, the invention relates to a process for curing ethylenically unsaturated polymerizable compounds, wherein minimal yellowing occurs upon curing, which comprises
adding to said compounds
(a) at least one acylphosphine oxide photoinitiator, and
(b) one or more lightfast red, blue or violet organic pigments
wherein the weight ratio of component (b) to component (a) is from about 10 parts per million to about 10,000 parts per million,
and irradiating the mixture so obtained with ultraviolet radiation or daylight or with light sources equivalent to daylight.
The acylphosphine oxide photoinitiators of component (a) may be formulated together with the pigment or pigments of component (b) to form a novel acylphosphine oxide photoinitiator system that does not result in yellow color formation when employed in a curing process of ethylenically unsaturated polymerizable compounds. Accordingly, it is also an object of this invention to provide a photoinitiator system comprising
(a) at least one acylphosphine oxide photoinitiator, and
(b) one or more lightfast red, blue or violet organic pigments
wherein the weight ratio of component (b) to component (a) is from about 10 parts per million to about 10,000 parts per million.
The invention also relates to compositions which have minimal yellow color upon curing with ultraviolet radiation or daylight or with light sources equivalent to daylight comprising
at least one ethylenically unsaturated polymerizable compound, and
(a) at least one acylphosphine oxide photoinitiator, and
(b) one or more lightfast red, blue or violet organic pigments
wherein the weight ratio of component (b) to component (a) is from about 10 parts per million to about 10,000 parts per million.
The processes and compositions according to this invention comprise any acylphosphine oxide photoinitiator that is inherently yellow in color. Descriptions of mono-, bis- and trisacylphosphine oxide photoinitiators and which may be employed according to the present invention are found in U.S. Pat. No. 5,942,290, incorporated herein by reference.
Preferably, the acylphosphine oxide photoinitiators of component (a) are of formula (I)
in which
R
1
and R
2
independently of one another are C
1
-C
12
alkyl, benzyl, phenyl which is unsubstituted or substituted from one to four times by halogen, C
1
-C
8
alkyl and/or C
1
-C
8
alkoxy, or are cyclohexyl or a group COR
3
; or
R
1
is —OR
4
, or a group
R
3
is phenyl which is unsubstituted or substituted from one to four times by C
1
-C
8
alkyl, C
1
-C
8
alkoxy, C
1
-C
8
alkylthio and/or halogen, or is a group
R
4
is C
1
-C
8
alkyl, phenyl or benzyl;
Y is phenylene, C
1
-C
12
alkylene or cyclohexylene; and
X is C
1
-C
18
alkylene or a group
Most preferably, component (a) is at least one bisacylphosphine oxide class of formula (Ia)
wherein
R
1
is C
1
-C
12
alkyl, cyclohexyl or phenyl which is unsubstituted or substituted from one to four times by halogen and/or C
1
-C
8
alkyl,
R
5
and R
6
are each independently of the other C
1
-C
8
alkyl,
R
7
is hydrogen or C
1
-C
8
alkyl, and
R
8
is hydrogen or methyl, preferably R
8
is hydrogen.
A preferred process is one wherein R
1
in the compounds of formula (Ia) is C
2
-C
10
alkyl, cyclohexyl or phenyl which is unsubstituted or substituted one to four times by C
1
-C
4
alkyl, Cl and/or Br.
An interesting process is also that wherein R
1
in the compounds of formula (Ia) is C
3
-C
8
alkyl, cyclohexyl or phenyl which is unsubstituted or substituted in the 2-, 3-, 4- or 2,5-positions by C
1
-C
4
alkyl.
A particularly preferred process is that wherein R
1
in the compounds of formula (Ia) is C
4
-C
12
alkyl or cyclohexyl, R
5
and R
6
are each independently of the other C
1
-C
8
alkyl and R
7
is hydrogen or C
1
-C
8
alkyl.
A preferred process is that wherein R
5
and R
6
in the compounds of formula (Ia) are C
1
-C
4
alkyl and R
7
is hydrogen or C
1
-C
4
alkyl.
A particularly preferred process is that wherein R
5
and R
6
in the compounds of formula (Ia) are methyl and R
7
is hydrogen or methyl.
A further interesting process is that wherein R
5
, R
6
and R
7
in the compounds of formula (Ia) are methyl.
A further preferred process is that wherein R
5
, R
6
and R
7
in the compounds of formula (Ia) are methyl and R
8
is hydrogen.
A process meriting special mention is that wherein R
1
in the compounds of formula (Ia) is C
3
-C
8
alkyl.
A particularly preferred process is that wherein R
1
in the compounds of formula (Ia) is isobutyl.
A very particularly preferred process is that wherein R
1
in the compounds of formula (Ia) is phenyl.
A most preferred process is that wherein the compound of formula (Ia) is Irgacure® 819, available from Ciba Specialty Chemicals:
C
1
-C
12
alkyl can be linear or branched and is, for example, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl, isopentyl, hexyl, heptyl, octyl, nonyl, decyl or dodecyl. Preference is given to C
1
-C
12
, for example C
1
-C
8
or C
1
-C
6
, especially C
1
-C
4
alkyl, which have the same definitions as indicated above up to the appropriate number of C atoms.
C
1
-C
8
alkoxy can be linear o

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