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Image forming materialRelated Patent Categories: Radiation Imagery Chemistry: Process, Composition, Or Product Thereof, Imaging Affecting Physical Property Of Radiation Sensitive Material, Or Producing Nonplanar Or Printing Surface - Process, Composition, Or Product, Radiation Sensitive Composition Or Product Or Process Of MakingImage forming material description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070122738, Image forming material. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATION [0001] This application claims priority under 35 USC 119 from Japanese patent Application Nos. 2003-15905 and 2003-24499, the disclosures of which are incorporated by reference herein. BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention relates to an image forming material, and, more particularly, to a positive image forming material useful as a positive planographic printing plate precursor suitable for a so-called "direct plate-making" by an infrared laser, by which direct plate-making a plate can be made directly from a digital signal in particular such as from a computer. [0004] 2. Description of the Related Art [0005] In recent years, laser technology has rapidly progressed; in particular, higher output and smaller size solid lasers and semiconductor lasers that have an emission region from near infrared to infrared are readily available. These lasers are very useful as an exposure light source when a planographic plate is directly made from digital data such as from computers. [0006] A known positive photosensitive image forming material for use in a direct plate-making by an infrared laser includes a novolac resin or the like as a resin soluble in an aqueous alkali solution. For example, a positive photosensitive image forming material is known which includes a resin that has a phenolic hydroxyl group and is soluble in an aqueous alkali solution such as a novolac resin, a substance that absorbs light to generate heat, and a positive photosensitive compound such as an onium salts, quinone diazide compounds are added (Japanese Patent Application Laid-open (JP-A) No. 7-285275). In the above positive photosensitive image forming material, the positive photosensitive compound, in an image portion, works as a dissolution inhibitor that substantially decreases the solubility of the resin soluble in an aqueous alkali solution. Meanwhile, in a non-image portion, owing to heat, the positive photosensitive compound does not exhibit the dissolution inhibiting effect and the resin soluble in an aqueous alkali solution can be removed by development. In this way, an image is formed. [0007] Furthermore, a positive photosensitive image forming material is disclosed (International Publication WO97/39894 and European Patent Application Laid-open (EP-A) No. 0,823,327). This positive photosensitive image forming material includes a substance that absorbs light to generate heat and a resin whose solubility in an aqueous alkali solution is changed by heat. In this positive photosensitive image forming material, an image portion has low solubility in an aqueous alkali solution, and a solubility of a non-image portion in an aqueous alkali solution is increased by heat. In this way, the non-image portion becomes able to be removed by development to form an image. [0008] In a conventional planographic printing plate precursor, a novolac resin is preferably used since the novolac resin interacts strongly with a dissolution inhibitor, the difference in solubility between the novolac resin in an exposed region and the novolac resin in a non-exposed region is large, and the novolac resin has excellent ink-receiving property. A novolac resin is used also in a positive photosensitive image forming material suitable for infrared laser exposure, for similar reasons. As the novolac resin, in particular, novolac resins obtained by polymerizing phenols such as phenol, cresol, and xylenol with formaldehyde under acidic condition are generally used. [0009] As the dissolution inhibitor, although a variety of compounds are under study, it is known that in particular onium salt type dissolution inhibitors exhibit very strong dissolution inhibiting effect. However, when a general onium salt compound is added, although an improvement in the alkali-resistance in a non-exposed portion can be achieved owing to the strong dissolution inhibiting effect of the onium salt, there exists a problem that the sensitivity is lowered. In order to overcome this problem, a novel photosensitive material that uses a specific onium salt is disclosed. For instance, onium salts disclosed in JP-A No. 2002-278050 and quaternary ammonium salts disclosed in JP-A No. 2003-107688 are known to have excellent characteristics in which high dissolution inhibiting power and high sensitivity are compatible. [0010] However, it has become apparent that there is a problem that as time passes after the exposure, developability of a photosensitive material that uses the above onium-salt type dissolution inhibitor declines and development failure is caused. Such decline in the developability with time lapse after the exposure is problematic in a plate making process and an improvement in the stability of the developability is required. (Hereinafter, the magnitude of developability change after the exposure is expressed by the storability after exposure, and larger decrease in developability is referred to as "worse storability after exposure".) SUMMARY OF THE INVENTION [0011] Accordingly, an object of the invention is to provide an image forming material that can be used for a heat-example type positive planographic printing plate precursor, is excellent in the difference (solubility discrimination) in the solubility in a developer between an exposed portion and a non-exposed portion, and has small degree of change of the developability with time after the exposure (excellent in the storability after the exposure). [0012] The present inventors found that when a combination of a novolac-type phenolic resin containing phenol as a structural unit and a specific ammonium compound or a specific onium salt is contained in an image forming layer, the storability after the exposure can be largely improved without decline in the sensitivity and in the development latitude. Thereby, the invention has been accomplished. [0013] A first image forming material according to the present invention comprises, on a substrate, an image forming layer that contains at least (A) a novolac type phenolic resin that contains phenol as a structural unit (hereinafter appropriately referred to as "particular novolac resin"), (B) a photo-thermal converting agent, and (C) a compound represented by the following general formula (1-1) (hereinafter appropriately referred to as "particular ammonium compound"). [0014] In the general formula (1-1), R.sup.1 represents a residue that forms a ring structure containing a N.sup.1 atom. R.sup.2 and R.sup.3 each independently represent an organic group and may combine with each other to form a ring structure. Furthermore, at least one of R.sup.2 and R.sup.3 may combine with R.sup.1 to form a ring structure. X.sup.- represents a conjugate base of an organic acid or inorganic acid. [0015] Furthermore, a second image forming material according to the invention comprises, on a substrate, an image forming layer that contains at least (A) a novolac type phenolic resin that contains phenol as a structural unit (the particular novolac resin), (B) a photo-thermal converting agent, and (C) an onium salt represented by the following general formula (1-2) (hereinafter appropriately referred to as "particular onium salt"). X.sup.-M.sup.+ General formula (1-2) [0016] (In the general formula (1-2), X.sup.- represents an anion having at least one substituent group having an alkali dissociative proton. M.sup.+ represents a counter cation selected from sulfonium, iodonium, ammonium, phosphonium and oxonium.) [0017] In general, when the development latitude is sacrificed, the storability after the exposure can be secured. However, surprisingly, in the invention, by adopting the above constitution, in addition to making both the sensitivity and the development latitude compatible, improvement in the storability after the exposure becomes also possible. [0018] In the invention, "heat-example type" means that an image forming material can be recorded by the heat-example exposure. [0019] The definition of the heat-example exposure in the invention will be detailed. As described in Hans-Joachim Timpe, IS & Ts NIP 15:1999 International Conference on Digital Printing Technologies, p 209, it is known that there are two examples, when largely divided, in a process from photo-excitation to chemical or physical change of a light absorbing substance when the light absorbing substance (for instance dye) in a photosensitive material is excited by light and forms an image through the chemical or physical change. One example is a so-called photon-example in which an optically excited light absorbing substance undergoes a certain photochemical interaction (for instance, energy transfer, electron transfer) with another reactive substance in the photosensitive material and is deactivated, then the resultant activated reactive substance causes the chemical or physical change necessary for the image formation. The other example is a so-called heat-example in which an optically excited light absorbing substance generates heat and is deactivated, and by utilizing the generated heat, a reactive substance causes the chemical or physical change necessary for the image formation. Other than the above-mentioned examples, there are special examples such as an ablation process in which a substance explosively scatters owing to a locally concentrated light energy and a multi-photon absorption process in which one molecule absorbs a lot of photons at one time. However, these special examples are omitted herein. [0020] Exposure processes that make use of the above respective examples are called a photon-example exposure and a heat-example exposure. The technical difference between the photon-example exposure and the heat-example exposure exists in whether or not energy amounts of several photons can be summed up for providing the energy required for a target reaction. For instance, a case is supposed where a certain reaction is caused by n photons. In the photon-example exposure, since a photochemical interaction is utilized, energy amounts of respective photons cannot be summed up due to the requirement of energy conservation law of quantum and momentum conservation law of quantum. That is, in order to cause a certain reaction, it is necessary to satisfy the relation: "amount of energy of single photon.gtoreq.amount of energy of reaction". On the other hand, in the heat-example exposure, since heat is generated after the photo-excitation, that is, since the optical energy is converted to heat and utilized, energy amounts of photons can summed up. Accordingly, in order to cause the reaction, it is sufficient to satisfy the relation: "amount of energy of n photons.gtoreq.amount of energy of reaction". However, the summation of amounts of energy is restricted by the heat diffusion. That is, if a subsequent photoexcitation-deactivation process is caused and heat is generated before heat diffuses from a given exposure portion (reaction point) according to the thermal diffusion, heat is certainly accumulated and a temperature in this portion rises. However, when subsequent heat generation is delayed, the heat diffuses and is not accumulated. That is, in the heat-example exposure, even when the total exposure energy is the same, the results are different between a case where light having high energy amount is irradiated for a short period and a case where light having low energy amount is irradiated for a long period. And shorter irradiation is advantageous to the accumulation of heat. [0021] Of course, in some cases, a similar phenomenon may occur even in the photon-example exposure owing to an influence of the diffusion of a subsequent reaction species. However, in principle, such a phenomenon does not occur. Continue reading about Image forming material... Full patent description for Image forming material Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Image forming material patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. 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