WO2004066026A2

WO2004066026A2 - Imageable elements and compositions for imaging by means of uv irradiation

Info

Publication number: WO2004066026A2
Application number: PCT/EP2004/000457
Authority: WO
Inventors: Hans-Joachim Timpe
Original assignee: Kodak Polychrome Graphics Gmbh
Priority date: 2003-01-21
Filing date: 2004-01-21
Publication date: 2004-08-05
Also published as: WO2004066026A3; DE10302111A1

Abstract

A process is described for imaging imageable elements by means of UV light with a wavelength selected from the range of 220 to 310 nm, wherein the imageable elements comprise a coating on a substrate which coating consists of a phenolic resin capable of forming a multiple centered hydrogen bonding and optionally one or more additives.

Description

Imageable elements and compositions for imaging by means of UV irradiation

The present invention relates to a process for imaging positive working elements by irradiating them with light of a wavelength of 220 to at most 310 nm, as well as to the use of functionalized phenolic resins for coating the imageable elements.

During the production of electronic components such as e.g. printed circuits and also printing plate precursors, in particular precursors of lithographic printing plates, a radiation- sensitive composition is applied to a substrate and modified image- wise by means of image- wise exposure to suitable radiation so that (possibly only after a subsequent developing step) an image (also referred to as "pattern") is generated. If the exposed portion of the coating is either removed directly by ablation due to the radiation or rendered so soluble that it is removed during developing, the coating is referred to as positive working. On the other hand, a coating is referred to as negative working if the exposed portion of the coating is hardened by the radiation and the unexposed portions are removed during developing.

Alkali-soluble phenolic resins together with naphthoquinone diazide derivatives are often used in positive working coatings that can be imaged with near UN light (about 330 to 430 nm). In this case, irradiation is carried out through an appropriately designed image mask.

Recent developments in the field of electronic components and lithographic printing plate precursors provide radiation-sensitive compositions allowing imaging with lasers or laser diodes in a wavelength range of about 150 nm to about 1,200 nm. This allows the generation of an image without the use of a film, as common in conventional processes.

Some of the described radiation-sensitive compositions comprise so-called light-heat converters as an essential component, which absorb the light emitted by the laser or laser diode and convert it to heat. The heat thus generated can be used e.g. to form reactive intermediates (free radicals, acids, nitrenes etc.) or to modify the solubility properties of the compositions.

Such compositions for IR-sensitive printing plate precursors are e.g. described in EP-A-0 823 327. In addition to an DR. absorber that functions as a light-heat converter and a polymer such as for example novolak, the radiation-sensitive coating used in this document comprises a substance that reversibly decreases the solubility of the composition in an alkaline developer. Amongst others, sulfonic acid esters, phosphoric acid esters, aromatic carboxylic acid esters, carboxylic acid anhydrides, aromatic ketones and aldehydes, aromatic amines and aromatic ethers are mentioned as such "insolubilizers". These radiation-sensitive layers show a high degree of IR sensitivity and are stable vis-a-vis white light.

Thermally imageable elements whose coating comprises a polymer with a reversibly decreased solubility in an alkaline developer are also described in WO 02/053626 and WO 02/053627. The "supramolecular polymers" used therein form multiple centered hydrogen bonding (which decreases the solubility of the polymers) that are cleaved by heat, which re-establishes the solubility in the alkaline developer. For generating this heat, these compositions contain a light-heat converter.

In the production of printing plate precursors and in particular of electronic components, increasing importance is attached to the resolution of the radiation-sensitive layer, i.e. the goal is the generation of especially precise patterns. This way, increasing amounts of information can be stored on any given surface, a characteristic which is especially sought after in the case of electronic components.

According to the Rayleigh equation

Res = k > λ / NA

(k = process factor; λ = wavelength of the radiation source; NA = numeric aperture of the lens), the resolution (Res) is directly proportional to the wavelength, i.e. the lower the applied wavelength, the finer the resolution.

As research and development progress in the field of lasers and particularly excimer lasers, such as ArF lasers and KrF lasers with an emission of light in the far UN range, their use for imaging radiation-sensitive elements becomes more and more interesting.

EP-A-0 824 223, EP-A-0 829 766, EP-A-1 078 945, EP-A-1 091 250 and WO 01/85811 describe photoresist compositions suitable for imaging with UN radiation of less than 300 nm. The resist compositions each comprise a specific copolymer and a photo-acid former. In such systems, which are referred to as "chemically reinforced", the light absorption is followed by reactions such as e.g. cross-linking reactions or abstraction of blocking groups that are catalyzed by the acid formed in the process. This requires compositions consisting of several components and necessitates the exclusion of compounds that scavenge the acid (such as e.g. water, certain organic solvents, amines) both in the compositions and during their processing.

It is the object of the present invention to provide a process for imaging elements with radiation wavelengths between 220 and 310 nm which results in imaged elements with a very high resolution, wherein the radiation-sensitive compositions used only consist of one essential component and wherein no further chemical reactions are necessary after exposure of the elements.

It has surprisingly been found that the phenolic resins which are used in IR-sensitive elements and are functionalized such that they are capable of forming a multiple centered hydrogen bonding are also suitable for elements imaged with UN light in the range of 220 to 310 nm. According to the above-mentioned Rayleigh equation, a high resolution can be obtained this way.

According to one aspect of the present invention, a process for imaging an imageable element is provided, said process comprising the following process steps: (a) providing an imageable element comprising a substrate and a coating applied thereon, said coating comprising at least one functionalized phenolic resin capable of forming a multiple centered hydrogen bonding and optionally an additive selected from colorants, plasticizers, stabilizers, surfactants, polymers different from the phenolic resin and mixtures thereof;

(b) image- wise exposing the imageable element to UN light of a wavelength selected from a range of 220 to 310 nm;

(c) developing the irradiated element with an alkaline developer and

(d) drying the developed element,

wherein the functionalized phenolic resin exhibits an extinction coefficient of 1 to 25 l/(g ^• cm), measured in methanol, at the wavelength selected in step (b).

According to another aspect of the invention, an imageable element is provided comprising a coating applied to a substrate, said coating consisting of at least one functionalized phenolic resin capable of forming a multiple centered hydrogen bonding and optionally an additive selected from colorants, plasticizers, stabilizers, surfactants, polymers different from the phenolic resin and mixtures thereof.

According to another aspect, the invention is directed to the use of such an element for producing electronic components and printing plates by means of irradiation with UN light of a wavelength in the range of 220 to 310 nm.

The imageable element used in the process according to the present invention comprises a substrate and a coating applied thereon, which is characterized in that it consists of at least one phenolic resin functionalized such that it is capable of forming a mutiple centered hydrogen bond and optionally an additive selected from colorants, plasticizers, stabilizers, surfactants, polymers different from the phenolic resin and mixtures thereof. The functionalized phenolic resin is preferably a functionalized novolak (especially preferred a phenol/cresol novolak), a functionalized poly vinyl phenol polymer or copolymer, a vinylphenol hydrocarbyl acrylate copolymer or a pyrogallol/acetone polymer.

This functionalized phenolic resin comprises substituents which allow a multiple centered hydrogen bonding, preferably a two- or four-centered hydrogen bonding (especially preferred a quadruple hydrogen bonding), between the polymer molecules. This causes a decrease in the aqueous alkaline developer solubility of the underlying phenolic resin (such as e.g. novolak). Upon application of heat, these hydrogen bonds are broken and the phenolic resin becomes soluble in the developer.

Substituents in the above sense are all the groups described in WO 98/14504 and WO 02/053626. This particularly includes substituents comprising 6-membered 2- pyrimidone, 2,6-diamino-l,2,4-triazine, 2,6-diamino-l,3,4-triazine and 2-amino-pyrimidone rings.

Functionalized novolaks of the following formula (I) are an especially preferred group of functionalized phenolic resins that can be used in the present invention:

wherein R and R' are independently selected from a hydrogen atom, an optionally substituted cyclic or straight or branched saturated or unsaturated hydrocarbon group with preferably 1 to 22 carbon atoms or an optionally substituted aromatic group (preferably a substituted phenyl ring with one or more substituents selected from Ci-C₈ alkyl, Cι-C₈ alkoxy, nitro, cyano, halogen or carboxy-Cι-C₈ alkyl), R" is a phenolic group derived from a novolak R"(OH) , Y is an optionally substituted divalent cyclic or straight or branched saturated or unsaturated hydrocarbon group with preferably 1 to 22 carbon atoms derived from a diisocyanate of the formula Y(NCO)₂ (e.g. isophorone diisocyanate, toluene- 1,2- diisocyanate, methylene-bis-phenyl diisocyanate, hexamethylene diisocyanate, tetramethyl xylylene diisocyanate, 3-isocyanatomethyl-l-methylcyclo-hexylisocyanate, dimers thereof and adducts with diols), m is at least 1 and k is at least 1; preferably, m is 1, 2 or 3. It is especially preferred that R and R' are hydrogen atoms, Ci-C₄ alkyl and substituted phenyl rings.

Within the framework of the present invention, the term "cyclic or straight or branched saturated or unsaturated hydrocarbon group" indicates cyclic, straight-chain and branched alkyl groups which can optionally comprise one or more C-C double and/or triple bonds, i.e. including alkenyl groups, alkdienyl groups, alkinyl groups etc. The saturated or unsaturated hydrocarbon groups can optionally comprise one or more substituents independently selected from nitro groups, cyano groups, halogen atoms and alkoxy groups (preferably d- ^' C₄). Preferably, the number of carbon atoms of the saturated or unsaturated hydrocarbon groups is 1 to 22, especially preferred 1 to 12 and particularly preferred 1 to 4 (wherein carbon atoms of optional substituents are not counted). The same applies analogously to divalent hydrocarbon groups.

The term "aromatic group" as used in the present invention refers to a carbocyclic aromatic comprising a ring (preferably a 6-membered ring) or two or more benzofused rings (e.g. a naphthalene ring); preferably, it is a phenyl group. The aromatic group can optionally comprise one or more (preferably 1 to 3) substituents independently selected from alkyl (preferably Cι-C₈), alkoxy (preferably CrC₈), nitro groups, cyano groups, halogen atoms and carboxyalkyl groups (wherein the alkyl unit preferably comprises 1 to 8 carbon atoms).

The novolaks used according to a preferred embodiment with an isocytosine unit bonded via a diisocyanate (see also formula I) are capable of forming a quadruple hydrogen bonding, as is illustrated by Schematic I with formulas and by Schematic II in a simplified schematic depiction: Schematic I

quadruple hydrogen bonding

Schematic II

The keto-enol tautomerism of isocytosine derivatives, their synthesis and supramolecular polymers are described in detail in WO 98/14504.

The synthesis of units that are suitable for forming a quadruple hydrogen bonding (also referred to as QHB in short; quadruple hydrogen bonding) as well as the functionalization of phenolic resins such as e.g. novolaks or polyvinyl phenols with such units is described in detail in WO 02/053627. For example, one mole of isocytosine is reacted with one mole of diisocyanate and the obtained product is bonded to novolak. The degree of functionalization of the phenolic resins has a decisive influence on their solubility in developers. Molecules of phenolic resins with 2 QHB units are subject to a chain prolongation reaction, while phenolic resins with 3 or more QHB units per molecule will cross-link. According to a preferred embodiment, functionalized phenolic resins with about 2 QHB units per polymer molecule of the phenolic resins are used. This guarantees a sufficient decrease in solubility on the one hand and a sufficient radiation-sensitivity on the other hand. While a higher degree of functionalization causes a decrease in the developer solubility of the resins (which would be quite welcome for the developing process), the radiation-sensitivity of the resins can decrease; that is, higher exposure energy or a longer exposure time may be required.

Another prerequisite for the use of the functionalized phenolic resins in the sense of the present invention is their absorption in the range of 220 to 310 nm. The extinction coefficient (measured by means of standard methods in methanol) of the phenolic resins has to be 1 to 25 l (g ' cm), preferably 2 to 10 l/(g ' cm), and especially preferred 3 to 6 l/(g ' cm) at the wavelength selected for imaging. If the extinction coefficient were too low, the coating would absorb too little radiation energy at the layer thicknesses used in practical applications. If the extinction coefficient were too high, too large a gradient of the absorbed radiation energy would occur in the coating; i.e. the hydrogen bonding would not be broken to the same extent throughout the layer.

According to a preferred embodiment, exposure is carried out by means of UN light of a wavelength selected from the range of 240 to 260 nm; for this wavelength range, functionalized novolaks are especially suitable.

Novolak resins suitable for the production of functionalized novolaks that can be used in the present invention are condensation products of suitable phenols, e.g. phenol itself, C-alkyl- substituted phenols (including m-cresol, p-cresol, m-ethylphenol, p-ethylphenol, 2,5-xylenol, 3,5-xylenol, p-tert-butylphenol, p-phenylphenol and nonylphenols), and of multivalent phenols (e.g. bisphenol-A, resorcin and pyrogallol), with suitable aldehydes such as formaldehyde, acetaldehyde, propionaldehyde and furfuraldehyde. The type of catalyst and the molar ratio of the reactants (mixtures of the listed phenols may be used as well) determine the molecular structure and thus the physical properties of the resin. An aldehyde/phenol ratio of about 0.5:1 to 1:1, preferably 0.5:1 to 0.8:1, and an acid catalyst are used in order to produce those phenolic resins known as "novolaks" which have a thermoplastic character. The average molecular weight (measured by means of gel permeation chromatography and polystyrene as standard) of these novolaks is preferably between 1,000 und 15,000, especially preferred between 1,500 and 10,000. As used in the present application, however, the term "novolak resin" should also encompass the phenolic resins known as "resols" which are obtained at higher aldehyde/phenol ratios and in the presence of alkaline catalysts.

Poly vinyl phenols suitable for the production of functionalized polyvinyl phenols that can be used in the present invention are polymers of a hydroxystyrene (o-hydroxystyrene, m- hydroxystyrene, p-hydroxystyrene), a substituted hydroxystyrene (preferred substituents are C1-C4 alkyl groups), a hydroxyphenylpropylene (e.g. 2-(p-hydroxyphenyl) propylene, 2-(m- hydroxyphenyl)propylene) or copolymers of several hydroxystyrenes or of the mentioned hydroxystyrenes with (meth)acrylates (e.g. (meth)acrylic acid, (meth)acrylic acid methyl- ester; as used in the present application, the term "(meth)" indicates that derivatives of both acrylic acid and methacrylic acid are meant). The polyvinylphenols are usually prepared by polymerization in the presence of free-radical or cationic polymerization initiators. Such polyvinylphenols can also be partially hydrated, or part of the phenolic OH groups can be substituted with known blocking groups (e.g. t-butoxycarbonyl, pyranyl and furanyl groups). The average molecular weight (measured by means of gel permeation chromatography and polystyrene as standard) of these polyvinyl phenols is preferably between 1,000 and 100,000, especially preferred between 1,500 und 50,000.

Of the phenolic resins described above, novolaks are especially preferred.

The functionalized phenolic resin is the only essential compound for the coating of the imageable elements; it functions as a light-heat converter and modifies its solubility when subjected to heat. Optionally, additives selected from polymeric binders, colorants, plasticizers, surfactants, stabilizers and mixtures thereof may be present; however, none of the optional additives is capable of functioning as a light-heat converter, i.e. independent whether or not additives are present the functionalized phenolic resin is the only light-heat converter of the coating.

Optionally, the radiation-sensitive coating of the present invention can also comprise one or more polymeric binders. These binders are preferably selected from polyvinyl acetals, acrylic polymers and polyurethanes. It is preferred that these polymers contain acid groups, especially preferred carboxyl groups. Most preferred are acrylic polymers. Polymers with acid groups preferably have acid numbers in the range of 20 to 180 mg KOH g polymer. Optionally, the additional polymer can comprise unsaturated groups in the main chain or the side chains. Such unsaturated bonds are capable of undergoing a free-radical photo- polymerization reaction or another photoreaction such as e.g. a 2+2-photocycloaddition.

Another important criterion in the selection of the polymeric binder to be added is its UN absorption at the wavelength used for imaging which is selected from the range of 220 to 310 nm. Too high an optical density in this wavelength range would lead to a filtering effect with respect to the light absorption of the functionalized phenolic resin. This in turn would decrease the radiation-sensitivity of the coating in the above-mentioned wavelength range. Therefore, extinction coefficients (measured in methanol) of < 5 l/(g " cm) are preferred, especially preferred are those < 3 l/(g ' cm) in the wavelength range desired for imaging.

The polymeric binders are preferably present in an amount of 0 to 20 wt.-%, based on the dry layer weight, especially preferred 0 to 10 wt.- .

Furthermore, the radiation-sensitive coating of the present invention can comprise dyes or pigments for coloring the layer. Examples of colorants include e.g. phthalocyanine pigments, azo pigments, carbon black and titanium dioxide, ethyl violet, crystal violet, azo dyes and anthraquinone dyes. Dyes are preferred over pigments. If pigments are used, they should preferably not exceed a particle size of 0.5 μm. The amount of colorant is preferably 0 to 10 wt.-%, based on the dry layer weight, especially preferred 0.5 to 2 wt.-%. Regarding the selection of dyes or pigments and the amounts in which they are added, it is also important that their addition does not lead to a pronounced filtering effect with respect to the light absorption of the functionalized phenolic resin (i.e. their extinction coefficient at the wavelength used for imaging should be below 5 l/(g ' cm)).

For improving the physical properties of the hardened layer, the radiation-sensitive coating of the present invention can additionally comprise further additives such as plasticizers. Suitable plasticizers include e.g. dibutyl phthalate, dioctyl phthalate, didodecyl phthalate, dioctyl adipate, dibutyl sebacate, triacetyl glycerin and tricresyl phosphate. The amount of plasticizer is not particularly restricted if they possess the absorption properties described above with respect to the polymeric binders; however, it is preferably 0 to 5 wt.-%, based on the dry layer weight, especially preferred 0.25 to 2.5 wt.-%. Other optional components are stabilizers such as e.g. organic mercapto compounds (e.g. 3- mercapto-l,2,4-triazole, 2-mercaptobenzimidazole, 2-mercaptobenzoxazol, 2-mercapto- benzothiazole, 5-mercapto- 1 -phenyl- 1 H-tetrazole, 2-mercapto- 1 -methylimidazole), phosphites (e.g. triphenylphosphite, tri-(p-cresyl)phosphite) or phenolic stabilizers (e.g. 4- methoxyphenol, 2,6-di-tert.-butyl-4-methylphenol), which improve the storage stability of the imageable and imaged elements. As long as they exhibit an extinction coefficient of < 5 l/(g ' cm), measured in methanol, at the wavelength selected for imaging, their amount is not particularly restricted, however, it is preferably 0 to 5 wt.-%, based on the dry layer weight, especially preferred 1 to 2.5 wt-%.

Additionally, the radiation-sensitive coating can comprise surfactants. Suitable surfactants include siloxane-containing polymers, fluorine-containing polymers and polymers with ethylene oxide and/or propylene oxide groups. They are preferably present in an amount of 0 to 10 wt.-%, based on the dry layer weight, especially preferred 0.2 to 3 wt.-%.

In addition to the functionalized phenolic resin, which functions as light-heat converter itself, the coating does not comprise another light-heat converter. A coating composition comprising at least on functionalized phenolic resin as described above, a solvent and optionally one or more of the additives listed above is applied to a substrate by means of common processes such as e.g. spray coating, coating by means of doctor blades, dip coating and centrifugal coating.

All solvents can be used that are usually used for novolaks. Examples of such solvents include alcohols such as methanol, n- and iso-propanol, n- and iso-butanol; ketonee, such as methyl ethyl ketone, methyl propyl ketone, cyclohexanone; multifunctional alcohols and their derivatives such as ethylene glycol monomethyl ether and monoethyl ether, propylene glycol monomethyl ether and monoethyl ether; esters such as methyl acetate, ethyl acetate and methyl lactate; ethers such as tetrahydrofuran and dioxolane; and mixtures thereof.

The solids content of the solution to be applied depends on the coating method and is usually in the range of 5 to 30 wt.-%. A dimensionally stable plate or foil-shaped material is preferably used as a substrate. Examples of such substrates include paper, paper coated with plastic materials (such as polyethylene, polypropylene, polystyrene), a metal plate or foil, such as e.g. aluminum (including aluminum alloys), zinc and copper plates, plastic films made e.g. from cellulose diacetate, cellulose triacetate, cellulose propionate, cellulose acetate, cellulose acetate- butyrate, cellulose nitrate, polyethylene terephthalate, polyethylene, polystyrene, polypropylene, polycarbonate and polyvinyl acetate, and a laminated material made from paper or a plastic film and one of the above-mentioned metals, or a paper/plastic film that has been metallized by vapor deposition.

In the production of a printing plate precursor, an aluminum plate or foil is especially preferred since it shows a remarkable degree of dimensional stability; is inexpensive and furthermore exhibits excellent adhesion to the coating. Furthermore, a composite film can be used wherein an aluminum foil has been laminated onto a polyethylene terephthalate film.

A metal substrate, in particular an aluminum substrate, can be subjected to a surface treatment, e.g. graining by brushing in a dry state or brushing with abrasive suspensions, or electrochemical graining, e.g. by means of a hydrochloric acid electrolyte, and optionally to anodizing.

Especially in the production of printing plate precursors, in order to improve the hydrophilic properties of the surface of the metal substrate that has been roughened and optionally anodized in sulfuric acid or phosphoric acid, the metal substrate can be subjected to an aftertreatment with an aqueous solution of e.g. sodium silicate, calcium zirconium fluoride, polyvinylphosphonic acid or phosphoric acid. Within the framework of the present invention, the term "substrate" also encompasses an optionally pretreated substrate exhibiting, for example, a hydrophilizing layer on its surface.

The details of the above-mentioned substrate pretreatment are known to the person skilled in the art.

In the production of electronic components such as e.g. microprocessors and integrated circuits, silicone wafers and silicone wafers coated with silicon dioxide can be used. Also, aluminum/aluminum oxide substrates, gallium arsenide substrate, ceramic substrates, quartz substrates, copper plates and glass substrates can be used.

However, substrates that are suitable for the production of liquid crystal displays, such as e.g. different glass substrates or indium tinoxide substrates, can be used as well.

After application of the coating solution on the substrate, the element is heated as usual for removing the solvents used for dissolving the components of the layer. For this purpose, temperatures of between 60 and 120°C are usually applied. The drying conditions strongly depend on the solvent or solvent mixture used. After drying, the solvent content of the layer should preferably not exceed 5 wt.-% (based on the total layer weight).

The dry layer weight of the coating is usually between 0.5 and 2.0 g/m².

Imaging of the elements is carried out by means of UN radiation of a wavelength selected from the range of 220 to 310 nm. Exposure with a wavelength between 240 and 260 nm is preferred, and a wavelength of 245 to 250 nm is especially preferred. Exposure can be carried out either digitally by means of a laser or an equivalent radiation source, or non- digitally by means of a photomask. Suitable radiation sources for the elements according to the present invention include a xenon chloride (XeCl) laser (emitted wavelength: 308 nm), a krypton fluoride (KrF) laser (emitted wavelength: 248 nm) and a krypton chloride (KrCl) laser (emitted wavelength: 222 nm); a KrF laser is preferred; however, irradiation is not limited to this radiation source. This excimer laser can be used both for digital exposure and for non-digital exposure in optical steppers.

The laser energy is usually 15 to 170 mJ per pulse, especially preferred 15 to 150 m per pulse. The number of pulses directed to a certain point of the coating is not particularly restricted; however, it is preferably in the range of 1 to 10, more preferably 1 to 5.

After irradiation, the element is treated with a commercially available alkaline developer that usually has a pH value in the range of 12.5 to 14 and the irradiated portions of the coating are removed. If desired, the developed element can be subjected to further treatments. For instance, selective chemical etching or electrochemical coating can be carried out according to common methods, and eventually the photoresist coating can be removed entirely if an electronic component is to be produced. If the intended use for the element is as a lithographic printing plate, its copying performance can be increased by so-called baking at a temperature of about 150 to 250°C. The details of this process are sufficiently well-known to the person skilled in the art.

For improving the durability of the imageable elements, a protective overcoat can be applied on the layer of the functionalized phenolic resin.

The polymers suitable for the overcoat include, inter alia, polyvinyl alcohol, polyvinyl alcohol/polyvinyl acetate copolymers, polyvinyl pyrrolidone, polyvinyl pyrrolidone/poly- vinyl acetate copolymers and gelatin. The layer weight of the overcoat can e.g. be 0.1 to 4 g/m², especially preferred 0.3 to 2 g/m².

If the overcoat is permeable to UN light with a wavelength of 220 to 310 nm, it can remain on the element during image-wise irradiation; however, this often affects resolution. It is also possible to remove an overcoat prior to irradiation (e.g. by washing it off with a suitable solvent).

In the present invention, the term "imageable element" also encompasses an element wherein a radiation-sensitive coating (and optionally an overcoat) is provided on both sides of the substrate. However, a one-sided coating is preferred.

The invention will be explained in more detail in the following examples. Preparation Example 1

This example describes the preparation of a novolak resin that is QHB -functionalized to a degree of 4.0 mole-%.

35 g dry dimethylacetamide (DMA) and 4.9 g dry 6-methylisocytosine (from Aldrich) were mixed in a 100 ml flask. 9 g isophorone diisocyanate (from Aldrich) were added to this mixture and the flask was sealed with a plug in order to keep out atmospheric moisture. The mixture was stirred for 2.5 days at 30°C.

124 g solid cresol formaldehyde novolak resin Alnovol SPN 584 (40:60 m-cresol/p-cresol) (from Clariant, Wiesbaden) and 3 g triethylamine were dissolved in 300 g dry DMA in a 1- liter flask and the above mixture was added within 1 hour under stirring. Stirring was continued at room temperature for another day, under the exclusion of moisture. Then the mixture was slowly poured in a thin stream into 2 liters of vigorously stirred water, which caused the product to precipitate as fine grains. The fine precipitate was isolated by filtration, thoroughly washed with water and dried for 2 days at about 45°C in a drying chamber. The yield was 94.5%, based on the novolak originally used.

Preparation Example 2

According to the process of Preparation Example 1, a novolak resin functionalized to a degree of 3.3 mole-% was prepared from a cresol/formaldehyde novolak resin PD 140 (75:25 m-cresol/p-cresol) (available from Borden Chemical, Columbus, Ohio).

Example 1

A coating formulation was prepared by dissolving 5.2 g of the functionalized novolak resin of Preparation Example 1, 0.15 g crystal violet arid 0.05 g Byk 307 (available from Byk Chemie) in 30 g of a solvent mixture of Dowanol PM and methyl ethyl ketone (weight ratio 1:1). This solution was applied to an electrolytically grained, anodized aluminum substrate treated with polyvinylphosphonic acid using a wire- wound doctor blade and dried in an oven for 4 minutes at 90°C, which resulted in a printing plate precursor with a coating weight of 1.6 g/m².

After one day of storage at 50°C in dry air, the precursor was exposed using different number of pulses with a krypton fluoride laser (Lambda Physics, Gδttingen) emitting light of the wavelength 248 nm, with a laser energy of 140 m per pulse. A photomask with comblike elements of 75 μm lines and 85 μm gaps, which is commonly used for evaluating the copying quality, was used for imaging. Shortly after imaging, developing was carried out with a 4030 developer (available from Kodak Polychrome Graphics GmbH), and a good positive image with a clean background was obtained in those instances when exposure was carried out with 5 pulses. Both lines and gaps were reproduced well under these conditions. When fewer pulses were used, the background was not clean, and more than 10 pulses led to an ablation of the coating.

Example 2

Example 1 was repeated, but instead of the functionalized novolak resin of Preparation Example 1, the functionalized novolak resin obtained in Preparation Example 2 was used. The exposure energy was 130 mJ per pulse. A good positive image with a clean background was obtained with 4 pulses. Both lines and gaps were reproduced well under these conditions.

Example 3

A coating formulation was prepared by dissolving 4.1 g of functionalized novolak resin obtained in Preparation Example 1, 0.15 g 3-mercapto-l,2,4-triazole, 0.18 g N-benzyl- quinolinium bromide, 0.15 g crystal violet and 0.05 g Byk 307 (available from Byk Chemie) in 36 g of a solvent mixture of Dowanol PM and methyl ethyl ketone (weight ratio 1:1). This solution was applied to an electrolytically roughened, anodized aluminum substrate sealed with polyvinylphosphonic acid using a wire-wound doctor blade and dried in an oven for 4 minutes at 90°C; a printing plate precursor with a coating weight of 1.5 g/m was obtained. The precursor was then stored for 1 day at 50°C in dry air. Exposure was carried out as described in Example 1, and Goldstar Plus (available from Kodak Polychrome Graphics GmbH) was used as developer. A good positive image with a clean background was obtained with 5 pulses. Both lines and gaps were reproduced well under these conditions.

Claims

1. Process for imaging an imageable element, said process comprising the following process steps:

(a) providing an imageable element comprising a substrate and a coating applied thereon, said coating comprising at least one functionalized phenolic resin capable of forming a multiple centered hydrogen bonding and optionally an additive selected from colorants, plasticizers, stabilizers, surfactants, polymers different from the phenolic resin and mixtures thereof;

(b) image-wise irradiation of the imageable element with UN light of a wavelength selected from a range of 220 to 310 nm;

(c) developing the irradiated element with an alkaline developer and

(d) drying the developed element,

2. Process according to claim 1, wherein a KrF laser is used for the image- wise irradiation in step (b).

3. Process according to claim 2, wherein irradiation is carried out with an energy of 15 to 170 m per pulse and a number of pulses in the range of 1 to 10.

4. Process according to any of claims 1 to 3, wherein the functionalized phenolic resin is a phenol/cresol novolak, a polyvinylphenol polymer or copolymer, a vinlylphenol/hydro- carbylacrylate copolymer, a pyrogallol/acetone polymer or a mixture thereof, which have been functionalized such that a multiple centered hydrogen bonding can be formed.

5. Process according to any of claims 1 to 4, wherein the functionalized phenolic resin is a resin of formula (I)

wherein R and R' are independently selected from a hydrogen atom, an optionally substituted cyclic or straight or branched saturated or unsaturated hydrocarbon group or an optionally substituted aromatic group, R" is a phenolic group derived from a novolak R"(OH)_k, Y is an optionally substituted divalent cyclic or straight or branched saturated or unsaturated hydrocarbon group derived from a diisocyanate of the formula Y(NCO)₂, m is at least 1 and k is at least 1.

6. Process according to any of claims 1 to 5, wherein the coating only consists of the functionalized phenolic resin.

7. Imageable element comprising a substrate and a coating applied thereon, said coating comprising at least one functionalized phenolic resin capable of forming a multiple centered hydrogen bonding and optionally an additive selected from colorants, plasticizers, stabilizers, surfactants, polymers different from the phenolic resin and mixtures thereof.

8. Imageable element according to claim 7, wherein the coating only consists of the at least one functionalized phenolic resin capable of forming a multiple centered hydrogen bonding.

9. Imageable element according to claim 7 or 8, wherein the functionalized phenolic resin is a functionalized novolak capable of forming a multiple centered hydrogen bonding and exhibiting an extinction coefficient of 1 to 25 l/(g " cm), measured in methanol, at 248 nm.

10. Use of an imageable element as defined in any of claims 7 to 9, for producing electronic components or printing plates, wherein the desired image is generated by means of irradiation with UN light of a wavelength selected from the range of 220 to 310 nm and subsequent alkaline development.

11. Imaged element obtainable from the process according to any of claims 1 to 6.