Abstract: Polyvinyl alcohol is modified by reaction with a stilbazol quaternary salt acetal to produce a water soluble polymer capable of photodimerizing on exposure to active radiation to yield water-soluble photoresist materials.

Abstract: A light-sensitive composition comprises a light-sensitive diazo resin, a polymer binder and a fluorine atom-containing surfactant, wherein the polymer binder is a polyurethane resin having acidic hydrogen atom-containing substituents and comprising structural units derived from a diol represented by the following general formula (I); and the fluorine atom-containing surfactant is a copolymer of (i) an acrylate or methacrylate having a fluoroaliphatic group which has a carbon atom number of 3 to 20 and a fluorine atom content of not less than 30% by weight and in which at least three terminal carbon atoms are completely fluorinated, with (ii) poly(oxyalkylene) acrylate or poly(oxyalkylene)methacrylate, the copolymer containing the fluoroaliphatic group-containing acrylate or methacrylate units in an amount ranging from 35 to 50% by weight on the basis of the weight of the copolymer and the copolymer having has a molecular weight ranging from 20,000 to 100,000:HO--(CH.sub.2 CH.sub.2 O).sub.

Abstract: A radiation-sensitive mixture which contains a polymeric binder having acid-labile side groups and a compound which generates a strong acid on irradiation wherein the binder is a polymer built up from novel amides of .alpha.,.beta.-unsaturated carboxylic acids, is highly sensitive in the shortwave uv region and useful in the production of recording material.

Abstract: A radiation-sensitive mixture is disclosed that contains a polymeric binder having acid-cleavable side groups and a compound which forms a strong acid on irradiation. Novel amides of .alpha.,.beta.-unsaturated carboxylic acids with which the polymers used as binders are synthesized are also disclosed. A positive- or negative-working radiation-sensitive recording material comprising a base and a layer of the radiation-sensitive mixture according to the invention is also disclosed.

Abstract: A photosensitive composition comprising a sensitizing amount of light-sensitive diazonium compound and a polyurethane resin binder in an amount sufficient to improve physical property of the composition, wherein said polyurethane resin has at least one group selected from a phosphonic acid group, a phosphoric acid group and ester groups thereof in an amount sufficient to improve adhesion to a support. The photosensitive composition of the present invention provides an excellent adhesion to a support, an excellent developability with an aqueous alkali developer, and a high printing durability.

Abstract: A photosensitive polymer containing a repeating unit represented by the following formula (I) and having a logarithmic viscosity number of from 0.1 to 5 dl/g as measured in a solvent at a temperature of 30.degree..+-.0.01.degree. C. at a concentration of 0.5 g/dl: ##STR1## (wherein R.sup.1 is a trivalent or tetravalent carbocyclic aromatic group or heterocyclic group, R.sup.2 is an aliphatic group having at least two carbon atoms, an alicyclic group, an aromatic aliphatic group, a carbocyclic aromatic group, a heterocyclic group or a polysiloxane group, R.sup.3 is a divalent organic group, R.sup.4 is ##STR2## a hydrogen atom or a monovalent organic group, R.sup.5 is a hydrogen atom or a monovalent organic group, m is independently 1 or 2, n is independently 0 or 1, and m and n meet 1.ltoreq.m+n.ltoreq.

Abstract: A composition containing novolak polymer, and/or poly(p-vinylphenol), an organometallic material, an amino polymer a cationic photocatalyst. The composition can also include a cosensitizer material which makes a composition sensitive to near U.V. radiation.

Abstract: A photopolymerizable recording material is diclosed comprising a base material, a photopolymerizable layer and a cover layer which comprises a water-soluble polymer which is substantially impermeable to atmospheric oxygen, and a polymer which binds atmospheric oxygen and is virtually completely soluble in water at 20.degree. C. The material displays reduced sensitivity to atmospheric oxygen, even on prolonged storage and at elevated ambient temperatures and elevated atmospheric humidity.

Abstract: A photosensitizer composition comprising a diazo fluorinated ester containing the hexafluoroisopropylidene group, said photosensitizer selected from hexafluoro-bis-phenols having the following formula: ##STR1## where R is selected from hydrogen, methyl, ethyl and phenyl; and bis-hexafluoroethers having the following formula: ##STR2## wherein R' is selected from hydrogen, methyl, ethyl and phenyl.

Abstract: Disclosed is a photosensitive composition comprising a diazo resin and a polymeric compound containing a structural unit represented by the following formula (I) in the molecule: ##STR1## wherein J represents a divalent linking group and n is 0 or 1. Disclosed is also a photosensitive lithographic printing using the photosensitive composition.

Abstract: A radiation sensitive material suitable for the production of radiation sensitive plates for lithographic printing plate manufacture comprises a polymer having appendent azide-substituted aromatic ester groups and sulphonyl urethane groups. The radiation sensitive compound is produced by a process in which some hydroxyl and/or epoxide groups of a polymer are reacted with an azide substituted carboxylic acid or ester forming derivative thereof, and some hydroxyl groups are reacted with a sulphonyl isocyanate.

Abstract: The present invention relates to a photosensitive composition comprising an o-quinonediazide compound and a polyurethane resin having a phosphonic acid group, a phosphoric acid group or its ester group. The photosensitive composition of the present invention provides an excellent adhesion to the support, an excellent developability with an aqueous alkali developer, and a high printing durability.

Abstract: A photosensitive mixture is disclosed that contains a photocurable compound, for example, a diazonium salt polycondensation product, or a photocurable combination of compounds, for example, a photopolymerizable mixture, and a polymeric binder, which binder is a graft copolymer with a polyurethane graft backbone onto which chains containing vinyl alcohol units and vinyl acetal units derived from hydroxyaldehydes are grafted. The mixture is suitable for use in the production of printing plates and photoresists, can be developed with purely aqueous solutions, and gives printing plates distinguished by high resistance to mechanical and chemical attacks.

Abstract: A photopolymerizable mixture is disclosed which contains:a) a graft copolymer having a polyurethane as the graft backbone, onto chains containing vinyl alcohol units and vinyl acetal units are grafted,b) a free-radically polymerizable compound possessing at least one terminal ethylenically unsaturated group and having a boiling point of more than 100.degree. C. at normal pressure, andc) a compound or a combination of compounds which under the action of actinic light is capable of initiating the polymerization of compound b).The mixture is suitable for use in the production of printing plates and photoresists. It is distinguished by high photospeed and can be developed with aqueous solutions. It yields printing plates producing large print runs.

Abstract: The present invention is concerned with a photosensitive polymer composition for a water-developable, flexographic printing plate, having a phase separating structure in a sea-and-islands state, the phase separating structure comprising island phases and a sea phase, the island phase comprising a thermoplastic elastomer component having a glass transition temperature lower than 25.degree. C., and the sea phase comprising a gelled, ethylenically unsaturated compound component.The photosensitive polymer composition of the present invention affords a printing plate capable of being developed with neutral water and suitable for flexographic printing using a water-based ink.

Abstract: The present invention provides a photosensitive resin composition which comprises, as essential components:(A) a polyamic acid having a recurring unit represented by the following formula [I]: ##STR1## wherein R.sub.1 and R.sub.2 each represents an organic group selected from the group consisting of an aromatic group, an alicyclic group, an aliphatic group, and a heterocyclic group and m is 1 or 2,(B) an amide compound having carbon-carbon double bond, and(C) a photosensitizer.

Abstract: The present invention relates to a photopolymerizable resin composition developable with an aqueous weak alkaine solution and suitable for a printed circuit board.The photopolymerizable resin composition of the present invention is mainly composed of:(a) a linear acrylic copolymer,(b) an ethylenically unsaturated compound, and(c) a photopolymerization initiator,wherein said linear acrylic copolymer comprises as indispensable comonomers:i) at least one compound represented by the general formula: ##STR1## wherein X is a hydrogen atom or a methyl group, Y is an oxygen atom or an imino group and Z is an alkylene group having 1 to 5 carbon atoms, andii) an ethylenically unsaturated compound having a carboxyl group.the photopolymerizable resin composition of the present invention can afford a resist film having excellent flexibility and adhesion through the use of the above-described particular linear acrylic copolymer.

Abstract: A positive type photosensitive resinous composition comprising a binder resin and a quinone diazide compound, the binder resin being a copolymer of(a) at least one phosphoric acid ester monomer represented by the formula: ##STR1## (b) at least one acid group containing .alpha.,.beta.-ethylenically unsaturated monomer, and(c) other copolymerizable .alpha.,.beta.-ethylenically unsaturated monomers than (a) and (b), which is specifically useful for the formation of resist coating in the preparation of printed circuit board.

Abstract: A photopolymerizable mixture is disclosed that contains a polymer binder, a polymerizable compound having at least one terminal ethylene double bond and a boiling point above 100.degree. C. at normal pressure, a hexaarylbisimidazole and a 1,3-diarylpyrazoline or a 1-aryl-3-aralkenyl-pyrazoline. The mixture is suitable for the preparation of printing plates and photoresists and is distinguished by high photosensitivity and low sensitivity towards acid solutions.

Abstract: A water-less PS plate for use in making a water-less lithographic printing plate comprises, on a substrate, a photopolymerizable light-sensitive layer and a silicone rubber layer in this order, wherein the light-sensitive layer is formed from a photopolymerizable light-sensitive composition which contains an urea bond-containing polyurethane as a binder. According to the present invention, there is obtained a water-less PS plate having good resistance to scratch and high printing durability. Moreover, the resulting light-sensitive layer does not get sticky, the light-sensitive layer of the non-image portions is not peeled off during the printing operations, and the lithographic plate shows good dyeability and plate-examination property.

Abstract: The present invention relates to photosensitive negative and positive tone compositions for imagewise deposition of polyimide on a substrate.

Abstract: A photocurable elastomeric mixture is described which comprises a compound which contains at least one terminal ethylenically unsaturated group and is polymerizable by free radical polymerization, a photopolymerization initiator and, as binder, a graft polymer which is soluble or dispersible in water or an aqueous solution, the graft base of which is a polymer of diol components and diisocyanate components having at least 2 urethane groups in the molecule, onto which polymer carboxylic acid vinyl ester units having 3 to 20 carbon atoms, or their saponification products, are grafted. The mixture is suitable for the production of relief printing plates, in particular flexographic printing plates, and can be developed with water or aqueous solutions.

Abstract: A photosensitive resin composition which is excellent in flexibility and impact resilience, which is less affected by humidity is provided. This composition comprises a soluble synthetic polymer, a photo-polymerizable unsaturated compound, and a photo-polymerization initiator, wherein the soluble synthetic polymer comprises an addition polymer obtained by the reaction between a diamine compound having amino groups selected from primary and secondary amino groups and having no amide bonds in its molecule and a diisocyanate compound; and the addition polymer contains a polyoxyalkylene glycol component in an amount of 20 to 80% by weight.

Abstract: A photocurable mixture is disclosed that contains a diazonium salt polycondensation product or an organic azido compound as the photosensitive compound and a high-molecular weight polymer as the binder, the polymer being a graft copolymer with a polyurethane as the graft backbone, onto which chains containing vinyl alcohol units are grafted. The mixture is suitable for use in the production of printing plates and photoresists, which can be developed with aqueous solutions. It yields printing plates having a good ink acceptance and long shelf life that produce large print runs.

Abstract: A light-sensitive composition comprises (A) a polymer comprising structural units represented by the following general formula (I): ##STR1## (wherein R.sup.1 represents a hydrogen atom or a methyl group; R.sup.2 represents a hydrogen atom, an alkyl group or an aryl group; and Z represents a bivalent connecting group having at least 3 non-metallic atoms in the main chain); (B) a monomer or an oligomer having at least two polymerizable ethylenically unsaturatred double bonds; and (C) a photopolymerization initiator. The light-sensitive composition has high sensitivity and is excellent in stability of sensitivities such as storage stability, temperature dependency and latent image sensitization.

Abstract: An alkaline-solution-developable liquid image-producing composition useful as a permanent protective layer for printed circuit boards is disclosed comprising at least: (1) an acrylic copolymer with hyroxy group, carboxyl group and branched unsaturated carbon double bond. Its number average molecular weight is 3,000 to 10,000 and its acid value is at least 30 mg KOH/g; (2) a photo reactive monomer with hydroxy group, the number of the unsaturated carbon double bond functional groups should be not less than 2; (3) a melamine compound; and (4) a free radical photo initiator.

Abstract: A photocurable composition suitable for flexible photosensitive articles is prepared by reacting an acid-containing copolymer and a nitrogen-containing compound having polymerizable ethylenically unsaturated groups. The resulting composition can be used "as is" or can be formulated with ethylenically unsaturated monomers and photoinitiators to prepare the flexible photosensitive articles, e.g. flexographic printing plates. The plates prepared from the photocurable composition are aqueous developable and sufficiently flexible and soft to be used for printing on flexible packaging surfaces.

Abstract: A photosensitive composition is described, wherein it comprises a high-molecular compound having sulfonamide group to be insoluble in water, but soluble in an aqueous alkaline solution and a positive working photosensitive compound. The photosensitive composition is excellent in coatability and in developability when the composition is used for photosensitive lithographic printing plates.

Abstract: An electrophotographic copying material is disclosed containing, in the photoconductive film, a high-molecular-weight polymer binder which is a graft polymer having a polyurethane as grafting base and grafted-on chains which contain vinyl alcohol units. The material is suitable, in particular, for the production of printing plates and printed circuits which are highly photosensitive and laminatable even at fairly large film thickness. The films can be treated with mild and toxicologically safe stripper solutions.

Abstract: A curable composition which comprises a homogeneous blend of (a) a solvent soluble polyimidesiloxane containing about 0.2-30 weight percent silicon and (b) an ethylenically unsaturated multifunctional monomer. The siloxane units in the polyimide-siloxane have from 10 to about 200 ##STR1## linkages per unit, more preferably from about 15 to about 100 linkages, and most preferably from about 40 to about 60 ##STR2## linkages per siloxane unit. Another embodiment provides the composition produced by curing the above-described composition. The curable compositions of this invention can be cured by either actinic radiation, e.g., uv light, or thermal radiation. In the cured composition, the polymer produced upon polymerization of the monomer, and the polyimide portion of the polyimide-siloxane form a homogeneous blend, in which the siloxane portion of the polyimide-siloxane is phase separated.

Abstract: A base developable negative acting photoresist composition which is thermally stable, provides high resolution at short exposure times and is capable of development by means of conventional aqueous alkaline developers. The present compositions comprise an alkali soluble hydroxylated polyamide and/or polyimide binder material, a photopolymerizable compound containing at least two ethylenically-unsaturated double bonds, and a light-sensitive photoinitiator.

Abstract: The invention relates to positive working photoresists for producing relief structures of high-temperature resistant polyimide prepolymers, which photoresists can be developed in aqueous-alkaline medium and which contain, in an organic solvent, essentially at leasta) one prepolymer which is convertible into a polyimide,b) one radiation-sensitive quinonediazide compound, and further optional components, said prepolymer being a completely esterified polyamic acid polymer.

Abstract: An image-receiving sheet material to be used for the formation of a transferred image by transferring a transferable image formed on an image-forming layer of a photo-sensitive material onto the image-receiving sheet material and then retransferring the image onto a permanent substrate, as well as a process for the formation of a transferred image with the use of the image-receiving sheet material are disclosed.

Abstract: The invention provides photosensitive mixtures consisting of a polymer and a photoactive component which meet the requirements placed on photoresists. The polymer has carboxylic acid anhydride groups or phenolic hydroxyl groups and the photoactive component is an N-alkylated or N-arylated 1.4-dihydropyridine or a 1.4- dihydropyridine derivative of the following structure: ##STR1## where the R group is a (substituted) aryl group, which, in the ortho position to the bond with the dihydropyridine ring, carries a NO.sub.2 group; and R.sup.3 is alkyl, cyclohexyl or phenyl.

Abstract: A photopolymerizable mixture is disclosed that comprises,a) a polymeric binder,b) an acrylate or alkacrylate of a polyhydric alcohol containing one or more urea groups and one or more urethane groups,c) a photoreducible dye as photoinitiator,d) a trihalomethyl compound which can be cleaved by irradiation, ande) an acridine or phenazine compound which is active as a photoinitiator.The mixture is suitable for the production of printing plates and photoresists and is distinguished by an increased shelf life.

Abstract: A radiation-polymerizable mixture is described which comprisesa) a saturated polyurethane containing carboxyl groups and repeating urea groups as binder,b) a radical-polymerizable compound containing at least one terminal olefinic double bond and having a boiling point above 100.degree. C. at normal pressure, andc) a compound or combination of compounds capable of initiating the polymerization of compound (b) on exposure to actinic radiation.The mixture can be developed with purely aqueous developers and yields lithographic printing plates with high photosensitivity, low stickiness and high print runs.

Abstract: (I) A photosensitive resin composition comprising(i) a thermoplastic elastomer selected from(A) a poly(amide-imide) ester produced by reacting a polyamide-forming monomer with either an aromatic carboxylic acid or its anhydride and either a polyalkylene glycol or an .alpha.,.omega.-dihydroxy hydrocarbon,(B) a poly(amide-imide) urethane produced by reacting the above poly(amide-imide) ester with a diisocyanate compound, and(C) a poly(amide-imide) urethane produced by reacting the above diisocyanate compound with a mixture of polymer diol and a poly(amide-imide) ester obtained from a Chthd 2-C.sub.4 alkylene glycol and a polyamide-forming monomer, and(ii) an ethylenic unsaturated compound, and(iii) a photopolymerization initiator,(II) a photosensitive sheet for printing plate formation which comprises a resin layer formed of the above composition, and(III) the above defined thermoplastic elastomer.

Abstract: A photocurable elastomeric mixture is described which contains a photopolymerization initiator; as binder, a graft polymer which is soluble or dispersible in water or an aqueous solution, the graft backbone of which is a polymer of diol components and diisocyanate components having at least 2 urethane groups in the molecule, onto which polymer chains of units of carboxylic acid vinyl esters having about 3 to 20 carbon atoms or their saponification products and optionally of further ethylenically unsaturated monomers or their saponification products are grafted; and at least one compound which is polymerizable by a free-radical polymerization and corresponds to the general formula ##STR1## wherein R.sub.1 denotes hydrogen or alkyl,X denotes ethylene or propylene,R.sub.2 denotes alkyl andn is a number from 1 to 4.

Abstract: The optical image properties of gelatin holograms are improved by reducing uneven shrinkage during chemical development. This is accomplished by introducing from 2 to 10 weight percent of a water soluble sizing agent into the gelatin. Suitable sizing agents include polyvinylpyrrolidone homopolymer and polyvinylpyrrolidone-vinyl acetate copolymers.

Abstract: The present invention relates to compositions comprising(a) a titanocene photoinitiator of the formula I ##STR1## (b) a 3-ketocoumarin of the formula II ##STR2## in which both R.sup.1, R.sup.2 and R.sup.3 are as defined in claim 1, R.sup.4 is a radical of the formula V ##STR3## R.sup.5 is C.sub.1 -C.sub.20 alkyl, cycloalkyl having 5-7 ring carbon atoms, phenyl or naphthyl which are unsubstituted or substituted by one to three C.sub.1 -C.sub.6 alkyl groups, C.sub.1 -C.sub.6 alkoxy groups or halogen atoms or by one diphenylamino or C.sub.1 -C.sub.6 dialkylamino group, or is C.sub.7 -C.sub.9 aralkyl, a radical --(CH.dbd.CH).sub.a --C.sub.6 H.sub.5 or a radical of the formula V, a is 1 or 2, preferably 1, and R.sup.10, R.sup.11, R.sup.12, R.sup.13 and R.sup.14 independently of one another are hydrogen, C.sub.1 -C.sub.6 alkyl, C.sub.1 -C.sub.6 alkoxy, phenyl, tolyl, xylyl or benzyl, and R.sup.11 can additionally also be a group --NR.sup.15 R.sup.16 or --OR.sup.15, wherein R.sup.15 and R.sup.

Abstract: The invention relates to a polyacetylenic recording film of improved resistance to degradation by UV light and increased sensitivity to ionizing radiation and to the process for producing said film which comprises dissolving polyacetylenic imaging crystals in n-butanol before forming a dispersion in a binder material and before coating on a polyester film base.

Abstract: A photosensitive resin composition suitable for a water-developing type photosensitive resin plate as a patrix of a matrix for a rubber plate which comprises a basic nitrogen containing polyamide; a monomer having polymeric unsaturated bond; a compound of the formula (I): ##STR1## wherein R.sub.1 and R.sub.2 are the same or different and are hydrogen, alkyl, aryl or a derivative thereof; m and n are integers of 0 to 2 and the sum of m and n is 1 to 3; and M is an alkaline metal, an alkaline earth metal or a transition metal, and a N-nitrosoamine compound of the formula (II) of the formula: ##STR2## wherein R.sub.3 and R.sub.4 are the same or different and are halogen, hydroxyl, carboxyl, alkyl, cycloalkyl, optionally substituted aryl or acyl group; X and Y are carbonyl or --O--; and p and q are 1 or 0, or a salt thereof.

Abstract: Photopolymerizable compositions for image recording, containing, among other components, addition-polymerizable, ethylenically unsaturated compounds and polymeric binders, wherein at least one of these binders is a copolymer of the formula (I) containing 5 to 50 percent by weight of one or more different structural units C1, C2, or combinations thereof containing carboxyl groups.

Abstract: A polymerizable composition comprises a polymeric precursor selected from the group consisting of (1) at least one ethylenically-unsaturated monomer, optionally in combination with an epoxy monomer or polyurethane precursors, or (2) at least one epoxy monomer, or (3) polyurethane precursors, and a curing agent comprising an organometallic salt and an onium salt.

Abstract: A light image forming material comprising a support having provided thereon a layer comprising microcapsules containing a leuco dye capable of developing a color through oxidation and a photo oxidizing agent, a reducing agent provided outside the microcapsules, and the layer further comprising carboxy-modified polyvinyl alcohol and epoxidated polyamide resin for imparting high water resistivity.

Abstract: Multilayer, photosensitive recording materials which can be developed with aqueous media contain one or more layers of a mixture which is crosslinkable by photopolymerization, soluble or dispersible in aqueous media and based on polymer containing hydroxyl and/or amide groups, as binders, compatible photopolymerizable monomers and photopolymerization initiators, which mixture contains from 0.1 to 10% by weight, based on its total amount, of an aldehyde of the general formula I ##STR1## where R is hydrogen, hydroxyl, C.sub.1 -C.sub.6 -alkyl, C.sub.1 -C.sub.6 -alkoxy, C.sub.6 -C.sub.10 -aryl or C.sub.6 -C.sub.10 -aryloxy.

Abstract: This invention relates to positive working color proofing sheet construction which, upon exposure to an actinic radiation source through a screened image, can accuratley reprouce said image. The construction is useful as a color proofing film which can be employed to accurately predict the image quality from a lithographic printing process. The image is produced by forming a composite of a receiver base, diazo or diazide layer, photopolymerizable layer and cover sheet. Upon imagewise exposure, a positive image appears on the receiver base after dry peel apart development.

Abstract: A light-sensitive composition comprises at least one water-insoluble and aqueous alkaline-soluble polyurethane resin having N-sulfonylamido, N-sulfonylureido or N-aminosulfonylamido groups. The light-sensitive composition is excellent in developing properties in an aqueous alkaline developer and coating properties. In addition, the images obtained from the composition are good in wear resistance and exhibit high adhesion to the substrate. Thus, the composition is very suitable for use in making IC circuits, photomasks and PS plates which provide lithographic printing plates exhibiting high printing durability.

Abstract: The present invention relates to a photosensitive composition containing at least one compound selected from the group consisting of N-acyl amino acid derivatives, hydroxycarboxylic acids and their derivatives, condensates of an aliphatic or aromatic aldehyde with a polyhydric alcohol, acylated polysaccharides and metallic soaps. From the photosensitive composition of the present invention, moldings having excellent shape retentivity and/or compatibility of the components thereof with one another can be produced. Therefore, the production of moldings from a composition which has been heretofore impossible is made possible. Particularly a composition having a good moldability during the molding operation can be employed. The composition is useful for the preparation of printing plate materials having a good developability and printing plates, particularly flexible printing plates and flexographic printing plates, having an improved ink solvent resistance.

Abstract: Orifices, cavities or spaces which are formed when printing plates are mounted on a plate cylinder are closed and/or sealed by means of a pasty, photocurable sealing or closing compound consisting of one or more photopolymerizable, ethylenically unsaturated low molecular weight compounds (a), one or more polymeric binder (b) which are compatible with the said compounds of component (a), one or more photopolymerization initiators (c) and one or more finely divided oxidic fillers (d) which, when mixed with components (a) to (c), give mixtures which are transparent to long-wavelength UV light. After it has been applied, this sealing or closing compound is cured by exposure and can then be mechanically processed. The process is particularly suitable for closing and/or sealing orifices, cavities or spaces in gravure printing plates mounted on plate cylinders.