Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
1998-12-14
2001-05-22
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
C522S016000, C522S025000, C522S028000, C522S053000, C522S068000, C522S071000, C522S075000, C522S074000, C522S081000, C522S100000, C522S170000, C522S168000, C427S514000, C427S516000, C427S517000, C427S508000
Reexamination Certificate
active
06235807
ABSTRACT:
The present invention relates to a process for curing cationically polymerisable compounds.
In the case of cationically photocurable formulations which are subjected to additional thermal demands in the course of processing, e.g. by heat postcuring and the like, the photocured layer often yellows. This is not desirable, in particular not in white-pigmented formulations.
Surprisingly, it has now been found that the use of specific photoinitiators for cationically curing the UV-curable layers results in a bleaching effect during heating instead of yellowing, effectively suppressing the undesirable discolouration of the cured layer. In addition, the layers cured in this manner have good curing properties.
Diaryliodonium salts are known as catalysts for photochemically induced cationic polymerisations. EP-A 334 056, for example, discloses a coating process in which non-toxic diaryl-iodonium salts are used as photoinitiators for a cationically curable unpigmented composition based on epoxy resins.
EP-A 562 897 uses “onium” salts with (pentafluorophenyl)borate anions as photocuring agents in an unpigmented composition.
In Radtech Europe 95, A. Carroy describes the photocuring of, inter alia, pigmented systems. The chain transfer rate of the polymerisation was dependent on the type of anion. Accordingly, iodonium salt initiators containing specific anions, in particular tetrakis(penta-fluorophenyl)borate anions, as contrasted to customary sulfonium salt initiators containing e.g. SbF
6
anions, were suitable for curing pigmented systems. The performance of these compounds is further increased by the addition of sensitiser compounds such as thioxan-thones.
In RadTech North America '94, A. Carroy investigates the cationic photocuring of compositions having a very high TiO
2
content, using sulfonium salt compounds or iodonium salt compounds as initiators. The result shows that, without sensitising, none of the compounds give satisfactory results whereas very good curing results are obtained by sensitising additionally with thioxanthone or anthracene derivatives when using iodonium salt.
In RadTech North America '94, E. Donhowe describes a coating process for aluminium cans. In this instance, an ink and a radically or cationically polymerisable overvarnish is first applied to the external side of the can and cured with UV radiation. The internal side of the can is then coated with a heat-curing coating and is subsequently heat cured.
EP-A 667 381, EP-A 082 602 and U.S. Pat. No. 4,374,963 describe UV-crosslinkable epoxy resin compositions.
Coating substrates with, in particular, white radiation-curable formulations often results in a darkening or yellowing of the coated surfaces. Formulations are required wherein such effects are kept as low as possible or do not occur at all.
Surprisingly, it has now been found that when using specific iodonium salt photoinitiators containing SbF
6
or PF
6
anions in combination with sensitiser compounds in photocurable, in particular white-pigmented, formulations, these formulations do not show any yellowing during curing and subsequent heating, a bleaching of the formulation or coating taking place instead.
Accordingly, this invention relates to a curing process for cationically polymerisable resins, wherein
a composition comprising
(a) at least one cationically polymerisable compound,
(b) as photoinitiator at least one iodonium salt containing an SbF
6
, PF
6
or BF
4
anion,
(c) one pigment, and
(d) at least one sensitiser,
is applied to a substrate and is irradiated with light having a wavelength of 200-600 nm, which process comprises heat-treating the composition after the exposure to light, thereby producing a bleaching of the formulation.
This invention also relates to the use of a combination consisting of at least one iodonium salt containing an SbF
6
, PF
6
or BF
4
anion as photoinitiator and at least one sensitiser for curing and concommittantly bleaching pigmented cationically polymerisable compositions.
Compositions for the novel curing process comprise resins and compounds (as component (a)) which can be cationically polymerised using alkyl- or aryl-containing cations or protons. Typical examples are cyclic ethers, preferably epoxides, as well as vinyl ether and hydroxyl-containing compounds.
All customary epoxides may be used, such as aromatic, aliphatic or cycloaliphatic epoxy resins. These are compounds having at least one, preferably at least two, epoxy groups in the molecule. Typical examples are the glycidyl ethers and &bgr;-methylglycidyl ethers of aliphatic or cycloaliphatic diols or polyols, e.g. those of ethylene glycol, propane-1 ,2-diol, propane-1 ,3-diol, butane- ,4-diol, diethylene glycol, polyethylene glycol, polypropylene glycol, glycerol, trimethylolpropane or 1,4-dimethylolcyclohexane, or of 2,2-bis(4-hydroxycyclohexyl) propane and N,N-bis(2-hydroxyethyl)aniline; the glycidyl ethers of di- and polyphenols, typically of resorcinol, of 4,4′-dihydroxyphenyl-2,2-propane, of novolaks or of 1,1,2,2-tetrakis(4-hydroxyphenyl)ethane. Illustrative examples are phenyl glycidyl ether, p-tert-butyl glycidyl ether, o-icresyl glycidyl ether, polytetrahydrofuran glycidyl ether, n-butyl glycidyl ether, 2-ethylhexyl glycidyl ether, C,
12/15
alkyl glycidyl ether, cyclohexanedimethanol diglycidyl ether. Other examples are N-glycidyl compounds, typically the glycidyl compounds of ethylene urea, 1,3-propylene urea or 5-dimethylhydantoin or of 4,4′-methylene-5,5′-tetramethyidi-hydantoin, or e.g. triglycidyl isocyanurate.
Other technically important glycidyl compounds are the glycidyl esters of carboxylic acid, preferably di- and polycarboxylic acids. Typical examples are the glycidyl esters of succinic acid, adipic acid, azelaic acid, sebacic acid, phthalic acid, terephthalic acid, tetra- and hexa-hydrophthalic acid, isophthalic acid or trimellitic acid, or of dimerised fatty acids.
Illustrative examples of polyepoxides which are not glycidyl compounds are the epoxides of vinyl cyclohexane and dicyclopentadiene, 3-(3′, 4′-epoxicyclohexyl)-8,9-epoxy-2,4-dioxa- spiro [5.5]undecane, of the 3′, 4′-epoxycyclohexylmethyl ester of 3,4-epoxycyclohexane carboxylic acid, butadiene diepoxide or isoprene diepoxide, epoxidised linolic acid derivatives or epoxidised polybutadiene.
Other suitable epoxy resins are, for example, epoxy resins of bisphenol A and bisphenol F, e.g. Araldit® GY 250 (A), Araldit® GY 282 (F), Araldit® GY 285 (F) (supplied by Ciba Specialty Chemicals).
Further suitable cationically polymerisable components (a) can also be found, inter alia, in U.S. Pat. No. 4 299 938 and 4 339 567.
Of the group of the aliphatic epoxides, the monofunctional a-olefin epoxides having an unbranched chain consisting of 10, 12, 14 and 16 carbon atoms are particularly suitable.
As a large number of different epoxy resins is commercially available today, it is possible to substantially vary the properties of the binder in accordance with the curing process of this invention. Another possibility for variation consists in using mixtures of different epoxy resins and also in the addition of flexibilisers and reactive thinners.
To facilitate their application, the epoxy resins may be diluted with a solvent, for example when the application is carried out by spraying. Preferably, however, the epoxy resin is used in solvent-free state. Resins that are viscous to solid at room temperature can be applied hot.
All customary vinyl ethers may be used, such as aromatic, aliphatic or cycloaliphatic vinyl ethers. These are compounds having at least one, preferably at least two, vinyl ether groups in the molecule. Typical examples of vinyl ethers suitable for use according to this curing process are triethylene glycol divinyl ether, 1,4-cyclohexanedimethanol divinyl ether, 4hydroxybutyl vinyl ether, the propenyl ether of propylene carbonate, dodecyl vinyl ether, tert-butyl vinyl ether, tert-amyl vinyl ether, cyclohexyl vinyl ether, 2-ethylhexyl vinyl ether, ethylene glycol monovinyl ether, butanediol monoviny
Ciba Specialty Chemicals Corporation
Hall Luther A. R.
McClendon Sanza L.
Seidleck James J.
Stevenson Tyler A.
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