Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
1999-07-28
2001-02-13
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...
C522S025000, C522S081000, C522S083000, C522S146000, C522S170000, C522S908000, C523S116000, C523S117000
Reexamination Certificate
active
06187833
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to photocurable, addition polymerizable compositions that contain an epoxy resin, a hydroxyl containing material, and optionally a free radically polymerizable material. The compositions contain a ternary photoinitiator system that is activated on exposure to actinic radiation in the visible spectrum. The invention is additionally directed to methods of curing addition polymerizable compositions using the ternary photoinitiator system.
BACKGROUND OF THE INVENTION
Epoxy containing compounds are known to be curable using various cationic initiator systems. Smith, in U.S. Pat. No. 4,256,828, describes photopolymerizable compositions that contain epoxides, an organic compound with hydroxyl functionality, and a photosensitive aromatic sulfonium or iodonium salt of a halogen containing complex ion. Hayase et al., U.S. Pat. No. 4,835,193, describes photopolymerizable epoxy resin compositions that comprise an epoxy resin and a heteropoly-acid aromatic sulfonium salt as the photocuring catalyst. In WO 95/14716 Neckers et al. describe photohardenable compositions that comprise a cationically polymerizable compound, a xanthene or fluorone dye, a hydrogen donor, and an onium salt. Palazzotto et al., U.S. Pat. No. 5,545,676, describes addition polymerization of free-radically polymerizable materials. The photoinitiator system described in that patent comprises an aryliodonium salt, a sensitizer, and an electron donor having an oxidation potential less than or equal to that of p-dimethoxybenzene.
PCT published application No. WO 96/13538 describes a system for curing epoxy compounds by exposure to visible light by use of a system comprising an aryliodonium salt and a sensitizer. Comparative Example 34 of this disclosure describes the use of one of the initiator systems of Palazzotto et al., U.S. Pat. No. 5,545,676 in an epoxy/polyol resin system. N, N-dimethylbenzylamine is used as the electron donor. The results of this experiment indicated that the use of this amine donor tended to retard the cure of the resin system.
Suppliers of cationically cured resins expressly warn against using organic amines in photoinitiated epoxy resins. An example of such a warning is found in Union Carbide literature regarding Cyracure® cycloaliphatic epoxides.
SUMMARY OF THE INVENTION
We have discovered, and the invention provides, a photopolymerizable composition that contains an epoxy resin, a hydroxyl-functional compound and a photoinitiator system containing an iodonium salt, a visible light sensitizer, and an electron donor compound, wherein the photoinitiator system has a photoinduced potential greater than or equal to that of 3-dimethylamino benzoic acid in a standard solution of 2.9×10
−5
moles/g diphenyl iodonium hexafluoroantimonate and 1.5×10
−5
moles/g camphorquinone in 2-butanone. Generally, 3-dimethylamino benzoic acid in this standard exhibits a photoinduced potential of at least about 115 mV relative to a standard solution of 2.9×10
−5
moles/g diphenyl iodonium hexafluoroantimonate and 1.5×10
−5
moles/g camphorquinone in 2-butanone.
These compositions are curable on exposure to light having a wavelength of about 400 to 1000 nm, and the invention provides a method of addition photopolymerization comprising the step of irradiating a photopolymerizable composition with light having a wavelength of about 400 to 1000 nm until the composition gels or hardens, the composition containing an epoxy resin, a hydroxyl-containing material and a photoinitiator system containing an iodonium salt, a visible light sensitizer, and an electron donor compound wherein the photoinitiator system has a photoinduced potential of at least about 100 mV relative to a standard solution of 2.9×10
−5
moles/g diphenyl iodonium hexafluoroantimonate and 1.5×10
−5
moles/g camphorquinone in 2-butanone.
In this application “polyol” and “hydroxyl-containing material” are used interchangeably.
The initiator systems of the invention allow efficient cationic polymerization under conditions of room temperature and standard pressure. In addition, the initiator systems can, under appropriate conditions, initiate both cationic and free-radical polymerization. This property permits their use with a variety of photopolymerizable compositions, including systems that contain acrylate or methacrylate functionality. Use of the initiator systems of the invention can provide a substantial reduction in the time required for an epoxy and hydroxyl containing resin composition to cure to a tack-free gel or solid. This reduction in gel time can represent about a 30 to 70% decrease in the time required for a resin composition to harden to a tack-free gel or solid.
DETAILED DESCRIPTION OF THE INVENTION
The photopolymerizable compositions of the invention are sensitive throughout the visible spectral region and photocure without the need to introduce substantial heat to the system to initiate cure, although an incidental amount of heat can be present. The term “visible light” is used throughout this application to refer to light having a wavelength of about 400 to 1000 nanometers (nm). Photopolymerization of the compositions takes place on exposure of the compositions to a source of actinic radiation having a wavelength within this spectral region.
The cationically polymerizable epoxy resins useful in the compositions of the invention are organic compounds having an oxirane ring, i.e., a up of the formula
which is polymerizable by ring opening. Such materials, broadly called epoxides, include monomeric epoxy compounds and epoxides of the polymeric type and can be aliphatic, cycloaliphatic, aromatic or heterocyclic. These materials generally have, on the average, at least 1 polymerizable epoxy group per molecule, preferably at least about 1.5 and more preferably at least about 2 polymerizable epoxy groups per molecule. The polymeric epoxides include linear polymers having terminal epoxy groups (e.g., a diglycidyl ether of a polyoxyalkylene glycol), polymers having skeletal oxirane units (e.g., polybutadiene polyepoxide), and polymers having pendent epoxy groups (e.g., a glycidyl methacrylate polymer or copolymer). The epoxides may be pure compounds or may be mixtures of compounds containing one, two, or more epoxy groups per molecule. The “average” number of epoxy groups per molecule is determined by dividing the total number of epoxy groups in the epoxy-containing material by the total number of epoxy-containing molecules present.
These epoxy-containing materials may vary from low molecular weight monomeric materials to high molecular weight polymers and may vary greatly in the nature of their backbone and substituent groups. For example, the backbone may be of any type and substituent groups thereon can be any group that does not substantially interfere with cationic cure at room temperature. Illustrative of permissible substituent groups include halogens, ester groups, ethers, sulfonate groups, siloxane groups, nitro groups, phosphate groups, and the like. The molecular weight of the epoxy-containing materials may vary from about 58 to about 100,000 or more.
Useful epoxy-containing materials include those which contain cyclohexene oxide groups such as epoxycyclohexanecarboxylates, typified by 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, 3,4-epoxy-2-methylcyclohexylmethyl-3,4-epoxy-2-methylcyclohexane carboxylate, and bis(3,4-epoxy-6-methylcyclohexylmethyl) adipate. For a more detailed list of useful epoxides of this nature, reference is made to the U.S. Pat. No. 3,117,099, which is incorporated herein by reference.
Further epoxy-containing materials which are useful in the compositions of this invention include glycidyl ether monomers of the formula
where R′ is alkyl or aryl and n is an integer of 1 to 6. Examples are glycidyl ethers of polyhydric phenols obtained by reacting a polyhydric phenol with an excess of chlorohydrin such as epichlorohydrin (e.g., the diglycidyl ether of 2,2-bis-(2,3-epoxypropoxyphe
Jacobs Dwight W.
Oxman Joel D.
3M Innovative Properties Company
Berman Susan W.
LandOfFree
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