Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Radiation sensitive composition or product or process of making
Reexamination Certificate
1998-11-10
2001-10-02
Ashton, Rosemary E. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Radiation sensitive composition or product or process of making
C522S033000, C522S034000, C522S036000, C522S046000, C522S096000
Reexamination Certificate
active
06296986
ABSTRACT:
The present invention relates to a photoinitiator for curable compositions and in particular, for photo-curable coating compositions.
Such compositions are any which are cured by exposure to ultraviolet light and include for example, lacquers which may be applied to wood, metal or similar substrates by suitable techniques such as roll coating or curtain coating. They may also be formulated as inks, for example to be applied by techniques such as letterpress, offset lithography, rotogravure printing, silk screen printing or flexographic printing. Printing, depending on the particular printing technique, is applicable to a wide range of substrates which include paper, board, glass, plastics materials or metals.
There is an increasing appreciation of a need to minimise migration and/or extraction of residual photoinitiator components from the cured product. For example, inks used in printing on plastics food packaging should ideally meet the stringent standards for minimisation of extractables from the coated and/or printed plastics. Such contamination can cause problems of taint and odour of the foodstuff. Moreover, for other coating compositions, it is important to minimise migration of reactive materials which may cause other undesirable effects such as loss of adhesion to the substrate, yellowing, or other undesirable effects.
One approach to reduce the concentration of residual photoinitiator components in the cured product and hence migratables and/or extractables is to use photoinitiators which contain an ethylenically unsaturated moiety, for example, 4(2-acryloyloxyethoxy)-phenyl-(2-hydroxy-2-propyl) ketone as described in U.S. Pat. No. 4,922 004. The ethylenically unsaturated group enables the photointiator to become incorporated into the polymeric structure, during the curing process.
An alternative approach is to use photoinitiators of increased molecular size to reduce the level of migratable and/or extractable residual photoinitiator components in a cured coating or ink composition. Such polymeric photoinitiators are disclosed in EP-A-0 161 463 and include a commercially available compound, Fratelli-Lamberti's KIP 100. Examples of polymeric benzophenones have also been described (C. Carlini et. al., Polymer 24, 599 (1983)). It is possible to combine the advantages of greater molecular size and ethylenic unsaturation in the same compound by incorporating a photoinitiator moiety into an ethylenically unsaturated vehicle such as a urethane acrylate, as disclosed in GB-A-2 280 905.
The present invention is aimed at providing multi-functional photoinitiators (i.e. photoinitiators which are multifunctional with respect to photoactive groups) with reduced levels of migratable and/or extractable residual photoinitiator components, compared with monofunctional photoinitiators.
Thus the present invention provides a multifunctional photoinitiator which is obtainable as the reaction product of a multifunctional core material containing two or more reactive groups and a photoinitiator or a derivative thereof, which photoinitiator or its derivative has a reactive group capable of reacting with said reactive groups of the multifunctional core.
Although not wishing to be bound by any particular theory or explanation, the applicants have conjectured that the advantage over known monofunctional photoinitiators is a consequence of the increased likelihood of any particular photoinitiator molecule initiating the polymerisation of ethylenically unsaturated materials. Thus, any multifunctional photoinitiator molecule will have an increased probability of becoming bound into a cured coating, resulting in reduced levels of migratable and/or extractable photoinitiator components from the cured coating.
The multifunctional photoinitiators of the present invention preferably have a relatively small “core” between the functional groups, preferably so that the average percentage molecular weight of functional groups per total molecular weight of the multi-functional photoinitiator is at least 30%, more preferably at least 40%. A difunctional photoinitiator according to the present invention should preferably have a core having a molecular weight less than 500. The core of a tetrafunctional photoinitiator according to the invention should preferably have a core having molecular weight less than 1000 and a hexafunctional photoinitiator according to the invention should preferably have a core having a molecular weight less than 1500.
A preferred embodiment of a photoinitiator according to the present invention comprises a multifunctional photoinitiator which is obtainable as the reaction product of a multifunctional core material containing two or more reactive groups and a photoinitiator or a derivative thereof, which photoinitiator or its derivative has a reactive group capable of reacting with said reactive groups of the multifunctional core.
Multifunctional photoinitiators according to the present invention not only show good photoinitiating properties but in addition, possess one or more advantages over the photoinitiators described in U.S. Pat. No. 4,922,004 or EP-A-0 161 463. For example, compared to the ethylenically unsaturated materials, or indeed compared with any monofunctional material they result in cured compositions having higher molecular weights and increased hardness. This is attributable to their polyfunctional nature.
Compared with polymeric photoinitiators, such as those disclosed in EP-A-0 161 463, examples of the present invention give significantly lower viscosity compositions due to their more highly branched nature resulting from the attachment of a suitably reactive photoinitiator to a compact, multifunctional reactive core. This gives a viscosity advantage over the polymeric multifunctional materials which is very beneficial in many applications, for example flexographic printing, because it makes the compositions more easy to apply and endows them with better wetting capabilities etc. Moreover, this low viscosity means that less diluent is required in the compositions, which also minimises migration of components from the cured product.
The multifunctional photoinitiators of the present invention also meet the primary aim of minimizing migration of the photoinitiators themselves, from the finally cured composition.
Some commercially available photoinitiators themselves have a reactive group capable of reacting with suitable reactive groups on a multifunctional core material. For example, the ethylenically unsaturated materials described in U.S. Pat. No. 4,922,004 can advantageously react with multifunctional amines. However, in some cases, it may be necessary first to modify a commercially available photoinitiator to endow it with a reactive group capable of reacting with the reactive groups of the multifunctional core materials.
One preferred class of material according to the present invention comprises those materials which are obtainable by reaction of a photoinitiator having an ethylenically unsaturated group together with a multifunctional amine, for example a tetrafunctional photoinitiator can be prepared by the action of 4-(2-acryloyloxyethoxy)-phenyl-(2-hydroxy-2-propyl)-ketone on 1,4-diaminobutane (Michael addition of amine to ethylenic unsaturation).
Other suitable polyfunctional amines include N,N′-dimethylethylenediamine which will result in a difunctional material; hexylamine which, again, will produce a difunctional material; ethylenediamine which will produce a tetrafunctional material; 1,4-diaminobutane which will result in a tetrafunctional material; and N,N′-bis(3-aminopropyl)ethylenediamine which produces a hexafunctional material.
In any event, Type I (i.e. cleavage-type) photoinitiators or Type II (hydrogen abstractive-type) photoinitiators may be used in their primary or modified form, depending on whether or not they are already capable of reacting with suitable reactive groups of the multifunctional core material.
Suitable Type I photoinitiators include any of those described in U.S. Pat. No. 4,922,004, those described in JP-A
Burrows Roger Edward
Davidson Robert Stephen
Dias Aylvin Angelo
Illsley Derek Ronald
Ashton Rosemary E.
Coates Brothers PLC
Ostrolenk Faber Gerb & Soffen, LLP
LandOfFree
Photoinitiator does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Photoinitiator, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Photoinitiator will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2603077