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
2000-12-29
2003-07-22
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
C430S287100, C430S905000, C430S906000, C430S907000, C430S909000, C430S910000, C430S195000, C430S271100, C430S278100, C430S302000, C430S944000, C526S266000, C525S061000
Reexamination Certificate
active
06596460
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to binders and radiation-sensitive compositions comprising such binders. More particularly, this invention relates to polyvinyl acetal copolymer compounds having azido groups, and the use of such compounds as binders in radiation sensitive compositions which are suitable for the production of lithographic printing plates.
2. Background Information
It is well know that radiation-sensitive compositions useable particularly for high-performance lithographic plates must fulfill high requirements.
To improve the properties of radiation-sensitive compositions and corresponding lithographic plates, essentially two different techniques are available. The first technique deals with the improvement of the properties of the radiation-sensitive components in the compositions (frequently negative diazo resins, photo polymers etc.). The second technique is the search for novel polymeric compounds (i.e. binders), which are used to control the physical properties of the radiation-sensitive layers. In particular the second technique is decisive for lithographic plates because the behavior in the developing and printing processes (such as developability, ink receptivity, scratch resistance, and consistency in the number of prints produced) is decisively influenced by the polymeric binders. Also shelf life and radiation-sensitivity of the materials are strongly influenced by such polymeric compounds.
The polymeric binders, therefore, exhibit various structural elements for satisfying the extensive requirements, which may have different effects on individual properties. For instance, hydrophilic structural elements such as carboxyl groups, hydroxyl groups and the like generally promote the developability of the radiation-sensitive compositions in aqueous alkaline developers and partly ensure sufficient adhesion to polar substrates. Hydrophobic structural elements, on the other hand, reduce the capability of being developed in the above-mentioned developers, but ensure good ink receptivity used in the printing process, which is indispensable in lithographic plates.
The latest developments in the field of printing plates deal with radiation-sensitive compositions which can be imaged by lasers. In this type of imaging, the use of films as an intermediate information carrier may be omitted since lasers can be controlled by computers.
High-performance lasers or laser diodes which are used in commercially available image-setters emit light in the wavelength ranges of between 800 to 850 nm and between 1060 and 1120 nm, respectively. Therefore,, printing plate precursors, or initiator systems contained therein, which are to be imagewise exposed using such image-setters have to be sensitive in the near IR range. Such printing plate precursors can then basically be handled under daylight conditions which significantly facilitates their production and processing. There are two different possibilities of producing radiation-sensitive compositions for such printing plates: (1) For negative printing plates, radiation-sensitive compositions are used wherein after an imagewise exposure the exposed areas are cured. In the developing step only the non-exposed areas are removed from the substrate. (2) For positive printing plates, radiation-sensitive compositions are used wherein exposed areas dissolve faster in a given developing agent than the non-exposed areas. This process is referred to as photosolubilization.
However, with respect to the radiation-sensitive compositions in positive systems, there is a certain dilemma since for a high number of copies crosslinked polymers are needed. However, such polymers are insoluble in the solvents or solvent mixtures suitable for the plate coating, thereby requiring noncrosslinked or only slightly crosslinked starting products. The necessary crosslinking can then be achieved by preheating steps which can be carried out at various stages of the plate processing.
A positive system is described in EP-A-0 819 980 where it is assumed that the non-image areas are formed by a reaction of the formed acid with carbon black. The image areas are only formed during a preheating step; for a high number of copies the image areas have to be baked.
Another positive system is described in U.S. Pat. No. 5,658,708. The necessary crosslinking of the layer is already carried out during the drying step of the coating. However, for that purpose the system has to be treated at 120° C. for 10 minutes whereby chemical processes take place which eventually lead to crosslinking. However, the required relatively long heating periods at such high temperatures represent an unacceptable waste of time in today's typical fully automated plate production lines. Baking does not lead to an increase in the number of copies since the crosslinking is partly undone.
EP-A-0 823 327, WO 99/11456 and WO 97/39894 also describe positive compositions. As is the case with many positive systems, they entail the disadvantage that a complicated conditioning step is necessary to ensure a sufficient shelf-life of the plates. Furthermore, a baking step is required to obtain high numbers of copies and a good solvent resistance. Moreover, these printing plates require the use of highly alkaline developers which are prone to reactions with atmospheric carbon dioxide, thereby necessitating the use of sealed, specialized processing equipment.
Plates which can be imagewise exposed with IR lasers are furthermore known from EP-A-0 672 544, EP-A-0 672 954 as well as U.S. Pat. No. 5,491,046, WO 00/48836 and EP-A-0 819 985. These plates are negativeworking, and after imagewise exposure they require a preheating step within a very narrow temperature range which only causes a partial crosslinking of the image layer. To meet the highest requirements regarding the number of copies and to show sufficient resistance to press room chemicals an additional heating step—what is referred to as preheating—is carried out during which these layers are further crosslinked.
U.S. Pat. No. 5,741,619 is an example of a negative working printing plate containing an IR sensitive composition of an acrylic resin, a diazonium compound and carbon black. However, such formulations require high energy IR exposure to yield an image. High energies are also needed for those compositions described in WO 98/31545.
The use of azide compounds both low-molecular weight or polymer bonded, in printing plates designed for imaging with either ultraviolet light (U.S. Pat. No. 4,940,646 and U.S. Pat. No. 5,254,431) or infrared light exposure is well known. For later applications it is believed that heating of the azides results in the elimination of nitrogen gas and the formation of reactive nitrene intermediates. They can be used to crosslink polymers containing C═C bonds (U.S. Pat. No. 5,705,309, JP 10161304) to improve the network formation. These formulations consist of a mixture of low-molecular multifunctional azides and a polymeric binder or combinations of polymers. Therefore, problems with layering during coating of these formulations onto substrates and consecutive drying can occur.
In a different context, the nitrogen gas evolution during heating of polymers with pendant azide groups assists in the ablative transfer or removal of materials during imaging (U.S. Pat. No. 5,278,023, U.S. Pat. No. 6,037,085, EP-B 562,952). However, such compositions require special caution for the exposure units to avoid deposition of ablated materials.
There is a continuing need for lithographic printing plates that can be imaged in the near infrared region using moderate light power, and that can be processed under simple processing conditions.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide polymers for radiation-sensitive compositions which ensure a good adhesion to normal aluminum substrates and thus lead to an acceptable number of prints produced without affecting ink receptivity. It is another object of the present invention to provide polymers enabling com
Müller Ursula
Timpe Hans-Joachim
Baxter Janet
Faegre & Benson LLP
Kodak Polychrome Graphics LLC
Lee Sin J.
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