Radiation imagery chemistry: process – composition – or product th – Diazo reproduction – process – composition – or product – Composition or product which contains radiation sensitive...
Reexamination Certificate
2000-06-07
2003-04-29
Chu, John S. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Diazo reproduction, process, composition, or product
Composition or product which contains radiation sensitive...
C430S272100, C430S281100, C430S303000, C430S394000
Reexamination Certificate
active
06555283
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an imageable element that can be employed to make a waterless lithographic printing plate. More particularly, this invention relates to an imageable element having a substrate and a radiation sensitive imageable composition applied thereon. The radiation sensitive imageable composition comprises a first layer having a photosensitive composition which undergoes a decrease in solubility in a developer upon absorption of actinic radiation by the first layer, and an inhibitor which may be activated to retard the decrease in solubility, or deactivated to avoid retarding the decrease in solubility.
2. Background Information
Waterless printing plates have existed since 1970 and have the advantage of not requiring fountain solution for offset printing. Most waterless printing plates involve an ink repellent layer such as silicone overlying a light absorbing imageable layer. Imaging is typically achieved by exposing the imageable layer to an ultraviolet radiation source then selectively removing the ink repellent coating.
For positive-working waterless plates, the imageable layer is a light absorbing layer typically containing a negative-working diazo resin, as described for example in U.S. Pat. Nos. 3,511,178; 3,677,178; and 4,775,607; or a light absorbing layer containing a photopolymerizable compound, as described for example in U.S. Pat. Nos. 3,894,873; 5,232,813, and 5,503,074. For negative-working waterless plates, imaging is achieved by solubilizing, via ultraviolet radiation, the imageable layer which typically contains diazonaphthoquinones, as described for example in U.S. Pat. Nos. 4,342,820 and 4,358,522; or imaging a layer that undergoes light-induced acid-catalyzed hydrolysis, as described for example in U.S. Pat. No. 4,842,990. Further, U.S. Pat. No. 3,933,495 describes a dual-tone waterless plate in which the solubility of the imageable layer is either enhanced or reduced by the developer in the developing step, depending upon which developer is used.
The majority of the plate manufacturing processes described above require a photographic film used as a mask for imaging the plate, which is expensive and tedious to make. However, recent advances in computer-to-plate (CTP) technologies have created the need to develop new waterless plates that can be imaged without the need of photographic film mask.
One method of adapting waterless plate-making technology to CTP applications is to generate a contact mask on a photosensitive waterless plate. The mask may be produced, for example, via a digital device such as an ink jet printer, electrographic printer, or any other apparatus employing a digitally controlled laser. The mask may also be produced by laser ablation, laser ablative transfer, laser induced color change techniques in a photochromic top layer or in a laser-induced solubilized or insolubilized opaque top layer. However, masked printing plates are also more costly and time-consuming to manufacture because they require an additional layer to form the mask.
For example, U.S. Pat. No. 5,339,737 describes physically transforming an infrared-absorbing layer by laser ablation using high doses of laser energy to remove the overlying silicone layer. However, this process is time consuming, and to circumvent the problem, U.S. Pat. No. 5,353,705 describes adding an ablatable, but non-infrared absorbing, layer, below the infrared absorbing layer. Another approach, described in U.S. Pat. No. 5,379,698, involves using a metallic or metal oxide thin film as the imageable layer.
In another example, European Pat. Publication 738 930 describes coating a polyester substrate with a layer comprising a component A which absorbs light in the infrared to visible region and thereby bleaches a second component B, which absorbs in the ultraviolet to visible region. This layer is used as a mask for a second image-forming photosensitive layer, so that imagewise IR exposure of component A, followed overall UV exposure of component B, followed by development, results in the image.
To avoid use of a mask layer, U.S. Pat. No. 5,955,238 describes a digital, negative-working, waterless plate precursor comprising a laser light-sensitive layer on a support which is over-coated with an ink repellent surface. The laser-sensitive layer contains an acid generator, an acid labile polymer, and a photothermal converter. The plate precursor is overall exposed to UV radiation, which generates acid, followed by imagewise IR laser exposure, which selectively solubilizes the acid labile polymer by a thermally induced, acid-catalyzed reaction. Aqueous development selectively removes the thermally exposed portions.
In another example, WIPO Publication WO 97/07430 describes a waterless plate precursor prepared by coating on a support a layer comprising a mixture of an ink-repellent component and photo-reactive component, which is imagewise exposed to heat or light to harden the imagewise-exposed areas.
A positive-working waterless plate that is imaged by imagewise exposure to actinic radiation is described in U.S. Pat. No. 4,775,607, and comprises a specific class of diazo resin condensates over-coated with a cross-linked silicone elastomer. The photosensitive layer is not suitable for digital imaging by exposure to long wavelength visible or IR radiation.
Thus, there is a need for an imageable element that may be used to prepare a waterless CTP printing plate which avoids the costly and time-consuming use of a mask layer. Further, there is a need for an imageable element for a waterless CTP printing plate which has dual tone, so that it may be digitally imaged by, for example, imagewise exposure to infrared laser, or analog imaged by, for example, imagewise exposure to actinic radiation. There is also a need for an imageable element that may be used to prepare printing plates having negative-working and positive-working embodiments. It is an object of this invention to provide such an imageable element and waterless printing plate. The imageable element and printing plate of this invention overcome the disadvantage of requiring a mask layer, and may be employed in negative-working and positive-working embodiments.
SUMMARY OF THE INVENTION
The limitations of current technology described above are overcome by this invention, which relates to the control of chemical reactions which affect the solubility in a developer of a photosensitive composition. Embodiments of this invention may comprise any photosensitive material that undergoes such a chemical reaction, and which can be affected by an intervening molecule such as inhibitors of the chemical reaction, which may affect the chemical reaction either directly or indirectly.
In one embodiment of this invention, an imageable element comprises: (A) a substrate; and (B) a radiation sensitive imageable composition applied on the substrate. The radiation sensitive imageable composition comprises: (a) a first layer, comprising (i) a photosensitive composition which undergoes a decrease in solubility in a developer upon absorption of actinic radiation by the first layer, and (ii) an inhibitor which is activated by heat or radiation of longer wavelength than the actinic radiation to retard the decrease in solubility of the photosensitive composition of the first layer upon absorption of actinic radiation, and (b) a second layer contiguous to the first layer comprising an ink repellent polymeric material which is transparent to both the actinic radiation and the longer wavelength radiation.
In this embodiment, the photosensitive composition of the first layer preferably comprises a condensate of an aryldiazonium salt or a mixture of aryldiazonium salts with a condensable compound. The inhibitor is preferably a dye or pigment which absorbs infrared radiation and is transparent to the actinic radiation, such as a cyanine dye. The ink repellent polymeric material of the second layer preferably comprises a crosslinked polydiorganosiloxane. This embodiment may be used to prepare a digital negative-worki
Huang Jianbing
Pappas S. Peter
Zhong Xing-Fu
Chu John S.
Faegre & Benson LLP
Kodak Polychrome Graphics LLC
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