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
2000-02-24
2004-01-06
Baxter, Janet (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
C430S259000, C430S281100, C430S286100, C430S944000
Reexamination Certificate
active
06673509
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention involves a photopolymerizable recording element and a process for preparing flexographic printing forms. The photopolymerizable recording element comprises at least one support, at least one photopolymerizable layer containing at least one polymeric binder, at least one ethylenically unsaturated, copolymerizable, organic compound and at least one photoinitiator or photoinitiator system, and a layer sensitive to infrared radiation and opaque to actinic radiation.
2. Description of Related Art
The use of photopolymerizable recording elements for preparing flexographic printing forms is known. The printing surface is produced by exposing a photopolymerizable layer imagewise to actinic radiation and subsequently removing unexposed unphotopolymerized areas. Examples are found in U.S. Pat. Nos. 4,323,637; 4,427,759; and 4,894,315. Such photopolymerizable recording elements usually comprise a support, optionally an adhesive or other underlayer, one or more photopolymerizable layers containing at least one polymeric binder, at least one monomer, at least one photoinitiator, and optionally, an elastomeric intermediate layer and a cover layer.
The photopolymerizable recording elements are usually exposed imagewise by superposing a photographic original, removing air through a vacuum frame, and exposing overall. The photographic original is usually a mask, mostly a photographic negative, having areas opaque to actinic radiation and those that are transparent to actinic radiation. The transparent areas permit photopolymerization by actinic irradiation of the underlying areas of the photopolymerizable layer. The opaque areas of the mask prevent photo-polymerization of the underlying areas of the photopolymerizable layer, so that these can be removed during development. Photographic originals having separating or slip layers containing wax are disclosed in U.S. Pat. No. 4,711,834. German Patent DE-C 39 41 493 describes color proof recording materials with wax layers between the color-imparting pigment layer and the imagewise exposed layer of the recording material.
The disclosed photographic originals have many disadvantages, such as, for example, sensitivity to temperature and moisture or complicated and time-consuming correction possibilities. Therefore, digital methods and associated materials that do not require a photographic negative have been developed. Such recording materials comprise a conventional recording element, as previously described, and additionally an integrated mask. These are described in WO 94/03838, WO 94/03839, WO 96/16356, and EP-A 0 767 407. The integrated mask is a layer sensitive to infrared and opaque to actinic radiation. This infrared-sensitive layer is imaged digitally, whereby the infrared-sensitive material is vaporized or transferred onto a superposed film. Subsequent overall exposure of the photopolymerizable element through the resulting mask, washing off unpolymerized areas and the remaining areas of the infrared-sensitive layer, and drying the element yield a flexographic printing form. These recording materials can also contain various auxiliary layers between the photo-polymerizable layer and the infrared-sensitive layer.
However, such prior art recording elements have some disadvantages. One is that the adhesion of the infrared-sensitive layer on the photopolymerizable layer or optionally on intermediate auxiliary layers is frequently inadequate, resulting in faulty release of the infrared-sensitive layer. In addition, these infrared-sensitive layers are extremely fragile and are very easily damaged mechanically during handling in production operation.
Therefore, the problem involved in the present invention is to make available photopolymerizable recording elements for preparing flexographic printing forms, which do not show the disadvantages of prior art materials, and do not adversely affect other essential properties of the photopolymerizable recording elements or the flexographic printing forms prepared therefrom.
SUMMARY OF THE INVENTION
The problem was solved by the present invention which provides a photopolymerizable recording element comprising a support, at least one photopolymerizable layer containing at least one polymeric binder, at least one ethylenically unsaturated, copolymerizable, organic compound, and at least one photoinitiator or photoinitiator system, and a layer sensitive to infrared radiation and opaque to actinic radiation, characterized by the presence of an adhesive wax layer between the photopolymerizable layer and the infrared-sensitive layer. The present invention further includes a process for preparing flexographic printing forms by using such recording elements.
DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
The present invention is a photopolymerizable recording element which includes a support, at least one photopolymerizable layer containing at least one polymeric binder, at least one ethylenically unsaturated, copolymerizable, organic compound, and at least one photoinitiator or photoinitiator system, and a layer sensitive to infrared radiation and opaque to actinic radiation, characterized by the presence of an adhesive wax layer between the photopolymerizable layer and the infrared-sensitive layer.
Surprisingly, the wax layer increases the adhesion of the infrared-sensitive layer to the photopolymerizable layer. This was all the more astonishing, as wax is customarily used as a separating or slip layer, as is described in DE-C 39 41 493 for color proof printing and in U.S. Pat. No. 4,711,834 for conventional photo originals. Another advantage of the present invention is that the mechanical sensitivity of the infrared-sensitive layer can be largely eliminated by the added wax layer. In addition, laser exposure requires about 15% less energy than with the use of infrared layers without a wax layer.
The wax layer of the present invention is 0.02-1.0 micron thick, preferably 0.05-0.5 micron. Suitable waxes are all natural and synthetic waxes, in particular polyolefin waxes, paraffin waxes, camauba waxes, montan waxes, and stearin and/or steramide waxes. Preferred waxes have a softening temperature ≧70° C., preferably 80-160° C., particularly preferred 90-150° C. In particular, polyethylene waxes having a softening temperature above 90° C. are suitable for preparing the adhesive wax layer (which may also be identified as the adhesive layer or wax layer) of the present invention.
The wax layer of the present invention can be prepared by conventional methods, such as, for example, casting, printing, or spraying dispersions in suitable solvents and subsequent drying. Additives such as surfactants, coating aids, etc. can be used. The wax layer is applied preferably by gravure printing either on the infrared-sensitive layer or on the photopolymerizable recording element. In particular, application on the infrared-sensitive layer is preferred.
The preferred infrared-sensitive layer is soluble or dispersible in the developer, opaque to ultraviolet or visible light, that is, has an optical density ≧2.5, and can be imaged with an infrared laser. This layer contains material having high infrared absorption in the wavelength range between 750 and 20,000 nm, such as, for example, polysubstituted phthalocyanine compounds, cyanine dyes, merocyanine dyes, etc., inorganic pigments, such as, for example, carbon black, graphite, chromium dioxide, etc., or metals, such as aluminum, copper, etc. The quantity of infrared absorbing material is usually 0.1-40% by weight, relative to the total weight of the layer. To achieve the optical density ≧2.5 with actinic radiation, the infrared-sensitive layer contains a material that prevents the transmission of actinic radiation, such as, for example, dyes or pigments, in particular the aforesaid inorganic pigments. The quantity of this material is usually 1-70% by weight relative to the total weight of the layer. This layer contains optionally a polymeric binder, such as, for example, nitrocellulose, homopolymers or copo
Baxter Janet
E. I. du Pont de Nemours and Company
Magee Thomas H.
Thornton Yvette C.
LandOfFree
Photopolymerizable recording element and process for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Photopolymerizable recording element and process for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Photopolymerizable recording element and process for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3233125