EP0316597A2 - Process for sealing cavities and/or interstices in printing plates fixed on cylinders - Google Patents

Abstract

A process for sealing cavities or interstices which are formed on fixing printing plates to a cylinder. The process employs a pasty, light-curable sealing compound composed of at least one photopolymerisable, ethylenically unsaturated low-molecular-weight compound (a), at least one polymeric binder (b) which is compatible with the photopolymerisable low-molecular-weight compounds of the component (a), at least one photopolymerisation initiator (c) and at least one finely divided oxidic filler (d) which, when mixed with the components (a) to (c), yields mixtures which are transparent to long wave UV light. Said sealing compound is cured after being applied by exposure to light and can be finally processed mechanically.

Description

The invention relates to a method for closing and / or sealing openings, cavities or gaps, such as result from the application of printing plates to forme cylinders, in particular in the region of the end or edge sections of the printing plates, by means of a sealing or sealing compound. The method according to the invention is particularly suitable for closing and / or sealing such openings, cavities or gaps in intaglio printing plates applied to forme cylinders.

For the production of rotary printing forms, it is known to wrap form cylinders with flat printing plates and to fasten them to the form cylinders in a suitable manner, for example by gluing, magnetically or mechanically by means of suitable holding and clamping elements. Here, only one printing plate or several printing plates can be applied one behind the other and / or next to one another on the surface of a forme cylinder. This method for producing rotary printing forms is becoming increasingly important, especially in rotogravure printing, because of the simple and cost-saving production and handling of gravure winding plates. The intaglio printing plates are preferably applied to the form cylinder by folding one or both of their end sections and hooking these folded areas into a groove of the forme cylinder provided for this purpose while simultaneously tensioning the intaglio plate.

When flat printing plates are applied to a forme cylinder, this results between the opposite, possibly folded, ends or end regions of a printing plate or, if several printing plates are applied on a forme cylinder one behind the other and / or next to one another, between the abutting edges of the end and / or Side areas of the printing plates an interruption of the printing surface on the forme cylinder in the form of columns, clamping slots or other gaps or cavities. Such openings or gaps which form when applying printing plates to forme cylinders have to be closed in a suitable manner in order to prevent penetration of printing ink, which may result, for example, in detaching the adhesive of the printing plate on the forme cylinder or, in particular in gravure printing, injecting the printing ink and unwanted impression of the column can lead, and also to ensure a smooth squeegee run and thereby prevent damage to the squeegee and printing form surface. Also on the Forme cylinder end faces, between the form cylinder surface and the side areas of the applied printing plate or between the printing form surface and the printing cylinder, which laterally provide metal rings that delimit the printing surface, as is usually the case in rotogravure printing, openings and gaps are created to avoid problems during printing against penetration must be sealed by printing ink or for other reasons.

It has already been proposed to seal the gaps or tensioning slots formed during the mechanical clamping of gravure winding plates on forme cylinders by means of sealing strips, tapes or cords made of elastic or plastically deformable materials (see, for example, US Pat. No. 2,056,991, US Pat. 2 285 116, DE-A-25 45 124 or DE-A-26 33 445). This method of gap closure can only be used to a limited extent, is complex in terms of its design and, moreover, frequently causes greater difficulties because of the adaptation of the sealing profile strips to the shape of the opening or joint to be closed and any subsequent surface treatment which may be necessary.

Furthermore, it is known that the gaps, clamping slots or other openings and spaces which are formed when printing plates are applied to forme cylinders, by filling with materials which only reach the state required for their function by chemical reaction, heat, drying or the like, for example To seal adhesives, thermoplastics, hot melt adhesives, thermosetting or light-curing reactive resins or foams or liquid photopolymerizable compositions. The use of such sealing compounds for printing plates mounted on forme cylinders is described, for example, in Deutscher Drucker, No. 41 (1975), pages 17-22, DE-A-25 45 618, EP-A-118 866, EP-A-174 568, EP-A-175 189 or GB-A-2 160 882. These sealing compounds generally pose no problems with regard to shape adaptation, but often have only insufficient resistance to the printing ink solvents and / or show mechanical weaknesses under the stresses of the printing process, in particular under the action of impression cylinders, printing material and, in the case of gravure printing, also the doctor blade. Some of these known closure materials tend to become brittle, so that after a short time small cracks form in the gap area which can fill with paint. It is precisely the combined action of printing ink solvents and mechanical forces that often cause damage or even destruction of these filler or sealing compounds. But even if these sealing compounds have a chemical and mechanical resistance that meets the requirements, their application and the setting of the required properties is in as a rule laborious and time-consuming and their use is restricted primarily to the closing of relatively wide or large gaps, openings or other cavities or gaps.

The present invention has for its object the openings and gaps that form when applying and fixing printing plates to forme cylinders, such as e.g. Gaps, joints, holes, cavities and the like. Sealing and / or sealing quickly and effectively with little effort, while avoiding the disadvantages known from the prior art, so that an all-round uninterrupted printing form surface is obtained which corresponds to the mechanical and withstands chemical stresses.

Another object of the invention is to provide a method which makes it possible to adapt the sealing or sealing compound to different plate types, the adhesion of these compounds in the cured state in the gap of the plate being sufficiently large to ensure that they function during the printing process fulfill. Another object of the invention is to provide a method for sealing the plate gap and other openings to be sealed, which allows the sealing and sealing compound to be removed from the plate cleanly and without residue after printing, without damaging the printing plate.

It has now surprisingly been found that this object can be achieved in a very advantageous manner by a method in which pasty light-curing sealing or sealing compounds are used at room temperature.

• a) 10 bis 90 Gew.% mindestens einer photopolymerisierbaren, ethylenisch ungesättigten niedermolekularen Verbindung,
• b) 5 bis 75 Gew.% mindestens eines polymeren Bindemittels, das mit den photopolymerisierbaren niedermolekularen Verbindungen der Komponente (a) verträglich ist,
• c) 0,01 bis 10 Gew.% mindestens eines Photopolymerisationsinitiators, sowie
• d) 3 bis 40 Gew.% mindestens eines feinteiligen oxidischen Füllstoffs, der im Gemisch mit den Komponenten (a) bis (c) für langwelliges UV-Licht transparente Mischungen ergibt,
  mit der Maßgabe, daß die Summe der unter (a) bis (d) genannten Prozentzahlen 100 ist,

besteht, eingesetzt wird, die nach Applikation in und auf die zu ver­schließenden oder abzudichtenden Öffnungen, Hohl- oder Zwischenräume durch Belichtung ausgehärtet und gegebenenfalls anschließend mechanisch nach­bearbeitet wird.The invention relates to a method for closing and / or sealing openings, cavities or spaces which are formed when printing plates are applied to a forme cylinder by means of a sealing or sealing compound, which is characterized in that a sealing or sealing compound At room temperature, viscous, pasty, light-curable mass, which consists essentially of a photopolymerizable mixture

• a) 10 to 90% by weight of at least one photopolymerizable, ethylenically unsaturated low-molecular compound,
• b) 5 to 75% by weight of at least one polymeric binder which is compatible with the photopolymerizable low molecular weight compounds of component (a),
• c) 0.01 to 10% by weight of at least one photopolymerization initiator, and
• d) 3 to 40% by weight of at least one finely divided oxidic filler which, when mixed with components (a) to (c), gives transparent mixtures for long-wave UV light,
  with the proviso that the sum of the percentages mentioned under (a) to (d) is 100,

exists, is used, which after application is cured in and onto the openings, cavities or interstices to be closed or sealed, and then optionally mechanically reworked.

The sealing or sealing compound can additionally contain a polymerization inhibitor and an additive of 0.1 to 2% by weight, based on the total amount of components (a) to (b), of a paraffin.

Component (a) includes, for example, vinyl and / or acrylic compounds which may optionally contain further functional groups such as hydroxyl, carboxyl or amino groups, in particular vinyl aromatics such as styrene and / or esters of α, β-ethylenically unsaturated carboxylic acids with mono- or polyhydric alcohols, such as the esters of acrylic acid or methacrylic acid with a polyhydric alcohol.

For example, styrene / maleic acid half-ester copolymers and / or one or more unsaturated polyesters can be used as component (b).

A preferred embodiment of the invention consists in that as component (b) a mixture of (b1) a styrene / maleic acid half-ester copolymer, (b2) a "hard" unsaturated polyester based on phthalic acid / maleic acid / ethylene glycol / propylene glycol and (b3) one Use "soft" unsaturated polyester based on adipic acid / phthalic acid / maleic acid / dipropylene glycol / propylene glycol.

Preferred finely divided oxidic fillers (d) are silicic acid (silicon dioxide) and aluminum hydroxide with particle diameters between 0.01 and 10, preferably 0.01 and 5 μm.

Even if the method according to the invention can be used with printing plates of all types applied to forme cylinders, for example high-pressure and flexographic printing plates, it has proven to be particularly favorable and advantageous for gravure printing plates applied to forme cylinders. Through the use of the sealing or sealing compounds to be used according to the invention, that too Prevention of even thin liquid printing ink in the openings, voids or gaps mentioned while avoiding the resulting disadvantages. The adhesion of the sealing and sealing compounds used according to the invention in the hardened state in the gap of the plate ensures trouble-free printing. After printing, the sealing and sealing compound can also be removed from the plate cleanly and without residue, without damaging it. It was also surprising that the openings, voids or gaps closed and / or sealed by the process according to the invention are outstandingly chemically and mechanically stable and durable under the requirements and stresses during printing, show no weaknesses and that those produced by the process according to the invention Rotogravure printing forms allow the squeegee to slide smoothly, smoothly and smoothly on the printing form surface without damaging it. The method according to the invention is particularly advantageous since it can be used universally. The sealing or sealing compound to be used according to the invention is simple and easy to process in the method according to the invention. On the one hand, it can be distributed uniformly in the gap cavity, on the other hand, the sealing of the gap cavity on the end faces of the cylinder is possible without additional expensive measures having to be taken. Although the method according to the invention is suitable for closing and / or sealing any kind of openings, cavities or gaps in the case of printing plates mounted on forme cylinders, it is particularly suitable and can be used without problems and advantageously when closing and / or sealing small or narrow gaps, joints, other openings, spaces and the like.

The customary photopolymerizable ethylenically unsaturated, low molecular weight compounds, in particular those with boiling points above 100 ° C., are suitable for the process according to the invention, for example vinyl aromatics, such as styrene, acrylic and methacrylic compounds, which may contain further functional groups such as hydroxyl, carboxyl or amino groups contain, or allyl compounds, such as allyl alcohol or esters, α, β-ethylenically unsaturated carboxylic acids, such as esters of corresponding mono- or dicarboxylic acids, such as acrylic acid, methacrylic acid, maleic acid, itaconic acid with monoalcohols having 1 to 12, in particular 1 to 8, carbon atoms Component (a) into consideration, as they are known as such. Preferred monomers are those whose photopolymerizable ethylenic double bonds are activated by conjugation or proximity to O, N or S atoms. The photopolymerizable, ethylenically unsaturated, low molecular weight compounds to be used according to the invention can be both monofunctional and multifunctional, ie they can contain one or more photopolymerizable, ethylenic double bonds in the molecule.

The photopolymerizable, ethylenically unsaturated low molecular weight compounds to be used according to the invention as component (a) of the sealing compounds include, inter alia, the N-vinyl compounds and the α, β-olefinically unsaturated mono- or dicarboxylic acids and corresponding derivatives thereof. An example of the N-vinyl monomers are the N-vinyl lactams, in particular N-vinyl pyrrolidone and N-vinyl caprolactam. In the case of the α, β-olefinically unsaturated carboxylic acids, acrylic acid and methacrylic acid are particularly important. Derivatives of α, β-olefinically unsaturated carboxylic acids, in particular derivatives of acrylic or methacrylic acid, such as hydroxyalkyl (meth) acrylates, (meth) acrylamide or derivatives of (meth) acrylamide, are also particularly advantageous as photopolymerizable monomers. Examples of the hydroxyalkyl (meth) acrylates, which preferably contain 2 to about 20 C atoms, and in particular 2 to 8 C atoms, in the alkyl radical are 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth ) acrylate, 3-hydroxypropyl (meth) acrylate, 1,4-butanediol mono- (meth) acrylate or hexanediol mono- (meth) acrylate. Mono- (meth) acrylates of polyalkylene glycols, e.g. Di-, tri- or tetraethylene glycol mono- (meth) acrylate. Examples of the derivatives of (meth) acrylamide which are also suitable according to the invention as monomers are N-methylol- (meth) acrylamide and its diether with diols, such as the reaction product of 2 moles of N-methylol- (meth) acrylamide with one mole of ethylene glycol. Preferred component (s) are hydroxyalkyl (meth) acrylates of the type mentioned above and their mixtures with styrene.

The selection of the photopolymerizable low molecular weight compounds used as component (a) depends, inter alia, on the type of polymeric binder used as component (b) with which the photopolymerizable low molecular weight compounds are to be compatible, and also on the desired properties of the cured sealing compound. The photopolymerizable low molecular weight compounds can be used alone or in a mixture with one another. For example, it is possible to vary the mechanical properties of the hardened sealing compound and thus sealed gaps and to adjust them to the desired extent via the type and amount of the monomers used or, if monomer mixtures are used, also via the mixing ratio of the monomers with one another. The pasty sealing compounds to be set for the process according to the invention generally contain 10 to 90% by weight, in particular 20 to 50% by weight, based on the total sealing compound, of the photopolymerizable low molecular weight compounds (a). The viscosity of the sealing compound can also be adjusted and varied via the amount of the photopolymerizable low molecular weight compounds (a).

In addition, the sealing compounds to be used for the process according to the invention contain at least one polymeric binder as component (b) which is compatible with the photopolymerizable low molecular weight compounds of component (a). The polymeric binder is selected so that it is resistant to the toluene-, gasoline-, ketone- and / or ester-containing printing ink solvents commonly used and customary in gravure printing. One class of very suitable polymeric binders are the styrene / maleic acid half-ester copolymers. These copolymers often contain the styrene and maleic acid half-ester comonomers in a molar ratio of about 1: 1. However, other comonomer ratios are also possible; In addition, the copolymers may also contain other comonomers, such as maleic anhydride and / or (meth) acrylates, in copolymerized form. The styrene / maleic acid half-ester copolymers generally have a softening point above 150 ° C., in particular above 180 ° C., and an average molecular weight in the range from 5,000 to 50,000. Another class of very suitable polymeric binders for the sealing compounds to be used according to the invention are the linear synthetic polyamides, in particular the linear soluble copolyamides, with recurring amide groups in the main molecular chain, such as are known as such as polymeric binders for photopolymerizable recording materials and, inter alia, in FR-PS 15 20 856 and DE-A-22 02 357 are described. Particularly suitable copolyamides are those which have been prepared by mixed condensation of a mixture of one or more lactams, in particular caprolactam, and at least one dicarboxylic acid / diamine salt, for example from ε-caprolactam, hexamethylene diammonium adipate and the 4,4′-diaminodicyclohexylmethane / Adipic acid salt. The polyamides used according to the invention preferably have a K value (according to Fikentscher, Cellulose-Chemie, 13 , 58 (1932)) in the range from 20 to 80, in particular in the range from 30 to 70.

Unsaturated polyesters have also proven useful as polymeric binders (b) which are particularly advantageous for the process according to the invention.

Unsaturated polyesters can usually be prepared by polycondensation of α-unsaturated polybasic carboxylic acids, in particular dicarboxylic acids or their anhydrides, with polyhydric, preferably dihydric alcohols. Some of the α-unsaturated dicarboxylic acids can be replaced by aromatic and / or saturated dicarboxylic acids. Examples of suitable unsaturated dicarboxylic acids are: maleic acid, fumaric acid, itaconic acid, citraconic acid or mesaconic acid. Examples of aromatic dicarboxylic acids are phthalic acid, isophthalic acid and terephthalic acid. As saturated dicarboxylic acids, for example Succinic acid, glutaric acid, α-methylglutaric acid, adipic acid or sebacic acid can also be used.

The usual dihydric alcohols, such as e.g. Ethylene glycol, 1,2-propylene glycol, 1,3-butylene glycol, 1,4-butanediol, 1,6-hexanediol, diethylene glycol, dipropylene glycol, triethylene glycol or 2,2-dimethylene-1,3-propanediol and, in certain quantities, also higher-functional alcohols, such as e.g. Glycerin, pentaerythritol or trimethylolpropane.

Particularly preferred unsaturated polyesters are those based on phthalic acid / maleic acid / ethylene glycol / propylene glycol, which are commercially available, for example, in styrene solution (with about 35% by weight of styrene) and, after the polymerization, tear strengths of about 70 N / mm², a bending E Module of approx. 4,000 N / mm² and a glass transition temperature of approx. 95 ° C.

Such standard polyester resins can be blended with other polyester resins, for example those based on adipic acid / phthalic acid / maleic acid / dipropylene glycol / propylene glycol, which are also commercially available in styrenic solution (for example with about 25% by weight of styrene) and after the polymerization for significantly lower tensile strengths and glass transition temperatures which are below room temperature result in elasticization or flexibilization, which is familiar to the person skilled in the art. Mixtures of these two types of polyester are preferred. These mixtures can advantageously also be combined with styrene / maleic acid half-ester copolymers.

Preferably used as component (b) are those polymeric binders which are soluble in the photopolymerizable, ethylenically unsaturated low molecular weight compounds used as component (a). However, it is also possible to use as component (b) those polymeric binders which are only dispersible in the photopolymerizable low molecular weight compounds of component (a), as long as the photopolymerizable low molecular weight compounds and the polymeric binders are compatible with one another and can be processed into a homogeneously flowable mixture . The proportion of polymeric binders (component (b)) in the sealing compounds according to the invention is generally in the range from 5 to 75% by weight, in particular in the range from 25 to 50% by weight, based on the total sealing compound.

In addition to the photopolymerizable, low molecular weight compounds of the type in question and the polymeric binders, the sealing compounds to be used for the process according to the invention contain as Component (c) one or more photopolymerization initiators, in particular in an amount of 0.01 to 10% by weight, preferably 0.1 to 2% by weight, based on the total sealing compound. According to the invention, the compounds which are customary and known per se as photoinitiators for light-curable compositions are suitable for this purpose. These include in particular benzoin and benzoin derivatives, such as benzoin alkyl ether, in particular with 1 to 8 carbon atoms in the alkyl radical, for example benzoin monomethyl ether or benzoin isopropyl ether, α-hydroxymethylbenzoin and its alkyl ether, such as α-hydroxymethylbenzoin methyl ether or α-methylbenzoin and its ether; Benzil and benzil derivatives, in particular benzil monoketals, such as benzil dimethyl ketal, benzil methyl ethyl ketal or benzil methyl benzyl ketal; the acylphosphine compounds which act as photoinitiators, as described, for example, in DE-OSes 28 30 927, 29 09 994, 30 20 092, 30 34 697, 31 14 314 and 31 33 419 and for which 2,4, 6-trimethylbenzoyldiphenylphosphine oxide, the 2,4,6-trimethylbenzoylphenylphosphinic acid ethyl ester and the 2,4,6-trimethylbenzoylphenylphosphinic acid ethyl ester and the 2,4,6-trimethylbenzoylbis (o-toluyl) phosphine oxide; Derivatives of α-hydroxyacetophenone, such as 1-phenyl-2-hydroxy-2-methyl-1-propanone, 1- (p-isopropylphenyl) -2-hydroxy-2-methyl-1-propanone and 1-hydroxy-1- benzoyl cyclohexane; furthermore benzophenone, Michler's ketone, fluorenone, anthraquinone, xanthone, thioxanthone and acridone, and the derivatives of these compounds known and customary as photoinitiators. The photopolymerization initiators can be contained alone or as a mixture with one another in the sealing compositions according to the invention; they can also be used together with the activators known per se for these photoinitiators, the activators being primarily amine compounds.

As component (d) for the process according to the invention, at least one finely divided oxidic filler is used which, when mixed with components (a) to (c), gives transparent mixtures for long-wave UV light. The particle size of these fillers is generally between 0.01 and 10, preferably 0.01 to 5 μm. Examples of such fillers are colloidal or hydrophobized silicon dioxide, microtalkum, micro-mica, kaolin, aluminum oxides and aluminum hydroxides. Silica (such as Aerosil ^®. From Degussa) and aluminum hydroxide (eg Martinal ^® from. Martinswerk) and mixtures thereof are particularly preferred.

For the process according to the invention, the use of aluminum hydroxide of the hydrargillite type is particularly advantageous as component (d), for example if it has grain sizes (80%) of between 0.2 and 3.0 μm or platelet structure. Apart from the fact that this reduces the shrinkage of polymerization and increases the strength, the result is smooth Surfaces and significantly reduced tendency to crack during hardening. In addition, there are only slight differences between the refractive index of the aluminum hydroxide and that of the resin component (b) or its mixture with component (a).

The addition of highly disperse silicon dioxide also contributes to the thickening and thixotropy of the mixture of components (a) + (b), serves as a sedimentation inhibitor for other fillers and results in an increase in strength when hardened. Particularly advantageous are hydrophilic and hydrophobic, highly disperse types of silicon dioxide which, for example, have particle sizes of approximately 12 and 14 nm, respectively. The hydrophobic highly disperse types of silica are generally preferred for unsaturated polyester resins.

Component (d) is contained in the compositions to be used according to the invention in amounts of 3 to 40, preferably 5 to 30,% by weight.

Further auxiliaries and additives can be added to the compositions to be used according to the invention, e.g. Paraffin (for example a paraffin with a solidification point between 56 to 58% by weight), generally in amounts of 0.1 to 2% by weight, based on the total amount of components (a) + (b), or polymerization inhibitors, for example so-called thermal polymerization inhibitors, such as hydroquinone, hydroquinone derivatives, 2,6-di-tert-butyl-p-cresol, nitrophenols, N-nitrosoamines, such as N-nitrosodiphenylamine, or the salts, in particular the alkali and aluminum salts, of the N- Nitrosocyclohexylhydroxylamine. Pigments and dyes can be helpful for visual observation during gap filling and the assessment of the gap closure. By adding plasticizers, the viscosity and the flow behavior of the light-curable sealing compounds according to the invention can be varied and controlled, and mechanical properties of the cured gap filling, such as e.g. Toughness and elasticity can be influenced. In particular, low-molecular compounds such as e.g. the known phthalic acid esters, or compounds containing hydroxyl groups, e.g. Glycerin, ethylene glycol and the like, which are compatible with components (a) and (b) of the sealing compounds according to the invention.

An example of very suitable sealing compounds to be used according to the invention are those homogeneous photopolymerizable mixtures which, in addition to photoinitiators (c) and finely divided oxidic filler of the type mentioned above (d), are a styrene / maleic acid half-ester copolymer and as a polymeric binder (component (b)) photopolymerizable, ethylenically unsaturated low molecular weight Compound (component (a)) contain hydroxyalkyl acrylates and / or hydroxyalkyl methacrylates in the proportions given above for these components. These very advantageous sealing compounds to be used according to the invention with styrene / maleic acid half-ester copolymers as polymeric binders contain, as component (a), in particular a mixture of hydroxyalkyl acrylates and hydroxyalkyl methacrylates, for example a mixture of 2-hydroxyethyl acrylate and 2-hydroxyethyl methacrylate.

Another example of sealing compounds to be used according to the invention, with which very advantageous results have likewise been achieved, are those homogeneous mixtures which, in addition to photopolymerization initiators (c) and finely divided oxidic fillers of the type mentioned above (d), are a soluble copolyamide as polymeric binder (b) and contain as photopolymerizable, ethylenically unsaturated low molecular compound (a) (meth) acrylic acid and / or hydroxyalkyl (meth) acrylates. Suitable copolyamides are in particular the mixed polyamides mentioned above, which have been prepared by mixed condensation of a mixture of one or more lactams, in particular caprolactam, and at least one dicarboxylic acid / diamine salt; a mixture of (meth) acrylic acid and hydroxyalkyl (meth) acrylates, for example of acrylic acid and 2-hydroxyethyl methacrylate, is advantageously used as the photopolymerizable, low molecular weight compound, the proportion of hydroxyalkyl (meth) acrylate in these monomer mixtures in general predominates and is, for example, in the range from about 50 to 80% by weight, based on the monomer mixture. In the case of these sealing compound mixtures, too, the amounts in which the individual mixture components are contained in the sealing compound are preferably in the ranges generally specified above for these components.

In general, it has been shown that in the cases in which very good adhesion of the hardened sealing compounds to the intaglio printing plates is sought, sealing compounds are particularly favorable in which either the photopolymerizable, ethylenically unsaturated low-molecular compounds of component (a) or as a component (b) the polymeric binder used contain free carboxyl groups. In the preferred mixtures, the proportion of free COOH groups in component (a) and / or component (b) is in the range from about 0.5 to 10% by weight, based on the sum of components (a) + ( b), the weight of the free carboxyl groups being set at 45.

It is essential that the components used for the process according to the invention are coordinated with one another in terms of quantity within the limits specified above such that the light-curable sealing or sealing compound has a pasty consistency at room temperature, i.e. that it does not flow under its own weight.

The paste-like, light-curable sealing compounds to be used for the process according to the invention are suitable for the gap closure in all intaglio printing plates that can be clamped onto the forme cylinder of a sheet-fed or roller rotogravure printing machine, such as, for example, the conventional intaglio printing plates made of metal with Ballard skin or of solid copper, whereby the printing surface can be chrome-plated in the usual way. However, the closure compositions according to the invention are particularly advantageous for the gap closure in gravure printing plates with plastic printing layers clamped on forme cylinders. In the case of gravure printing plates with plastic printing layers, a plastic layer is applied to a suitable printing layer support, into which the ink-absorbing depressions (cells) are made. These cells may have been formed in the plastic printing layer by mechanical engraving or laser engraving (see, for example, DE-A-27 52 500 or DE-A-30 28 098) or, in the case of photopolymer gravure printing plates, by imagewise exposure and development have been introduced into the photosensitive plastic printing layer (cf. DE-A-20 61 287, DE-A-31 28 949 and DE-A-31 28 951). The light-curable pasty sealing compound to be used according to the invention is very advantageously suitable for gravure winding plates for closing the gap, as is formed when these winding plates are clamped onto a form cylinder between the ends of the gravure plate. However, it is equally suitable for closing the gaps which result when several intaglio plates are applied one behind the other and / or next to one another on a single forme cylinder, for example by means of suitable and known saddle constructions, between the end regions and / or side edges of the individual intaglio plates. A particular advantage of the light-curable pasty sealing compounds to be used according to the invention is also to be seen in the fact that this allows wide and deep gaps, which can result when the intaglio printing plates are clamped onto a forme cylinder, between the abutting edge regions of the intaglio printing plate, to be closed easily and very permanently. In the context of this invention, intaglio printing plates are understood to mean the finished intaglio printing plates in which the ink-guiding depressions have already been introduced, as well as the intaglio printing plate blanks in which the cells have not yet been formed. This means that it is also possible to clamp a finished rotogravure plate onto the forme cylinder and then the plate itself to fill the resulting column with the sealing compound to be used according to the invention, or first to clamp rotogravure plate blanks onto the forme cylinder, then to fill in the resulting column with the sealing compound and only then to insert the cells into the printing layer of the printing plates. Clamping the gravure printing plates onto the forme cylinders is known as such and is carried out, for example, via permanent magnets or mechanical means for fastening and clamping the printing plates. In general, form cylinders are used for this purpose, in which the intaglio printing plates are fastened and tensioned by hanging and anchoring at least one, but preferably both, plate ends bent over for this purpose in a hanging groove or cylinder channel.

In the method according to the invention, the sealing compound for closing the gaps which result when the intaglio printing plates are clamped onto the forme cylinders can be introduced into the gap by any suitable methods or processes suitable for pasty masses, provided this ensures a uniform and complete filling of the gap cavity.

The application of the viscoplastic, light-curable pasty masses to be used in the process according to the invention as sealing or sealing masses can, for example, in a very simple manner by simply applying the viscous, pasty masses, for example from a tube, cartridge or similar metering device, to the areas to be sealed Printing plates and / or forme cylinders and simple mechanical pressing and tightening or pressing into the openings or cavities to be closed, for example by means of a spatula, scraper or the like. Excess sealing material can then be easily removed by simply wiping off the printing form surface or the end faces of the printing form cylinder thus obtained. Thus, according to the invention, there are no special devices or expenses for closing and / or sealing the openings and gaps. Post-processing can often be omitted; As a rule, however, it is expedient to smooth the surface of the hardened mass by mechanical finishing, for example by grinding, milling and / or polishing, and to adapt it to the contour of the cylinder. No special devices or expenditure are required to remove the printing plates from the forme cylinder. The extent of adhesion (gap sealing compound pressure plate) can be controlled by changing the proportions of components (a) and (b), preferably the different polymer proportions of components (b). This is also a particular advantage of the method according to the invention. Inserted printing plates can be reused without restriction.

After the gaps have been filled, the pasty, light-curable sealing compound is irradiated with actinic light for curing. For this purpose, all known light sources which are able to emit light in the wavelength range actinic for the sealing compounds, in particular in a wavelength range of approximately 250 to 450 nm, can be used, e.g. Carbon arc lamps, actinic or superactinic fluorescent tubes, low, medium or high pressure mercury lamps, which can optionally be doped, xenon lamps or lasers with a high UV component.

example 1

The homogeneous mixture of 240 g of a copolymer of styrene / maleic acid half-ester (average molecular weight 10,000), 560 g of hydroxyethyl acrylate, 1 g of the potassium salt of N-nitrosocyclohexylhydroxylamine and 2 g of the photoinitiator trimethylbenzoyl-diphenylphosphine oxide is stirred vigorously with 200 g of a finely divided aluminum hydroxide and then mixed with 35 g of a highly disperse silicon dioxide. All operations are carried out in the absence of UV light. After thorough homogenization with gentle heating, the batch is degassed in the stirred tank under reduced pressure.

The pasty mass is introduced by means of a tube into the inwardly sealed gap between the ends of a pressure plate fixed on a cylinder. After smoothing, the mass is cured by exposure to ultraviolet light.

The mechanical properties and the adhesion of the gap closure produced in this way are so good that it can withstand long print runs without interference. To remove the plate, it must be opened mechanically.

Example 2

A mixture of 100 g of a copolymer of styrene / maleic acid half-ester (average molecular weight 10,000), 232 g of hydroxyethyl acrylate and 0.4 g of the potassium salt of N-nitrosocyclohexylhydroxylamine is mixed with a second mixture of 140 g of a styrene-containing (approx. 35% by weight styrene) Polyester resin (o-phthalic acid / maleic acid / ethylene glycol / propylene glycol), viscosity at 23 ° C 700-800 mPa · s, 60 g of a "soft" styrene-containing (approx. 25 wt.% Styrene) polyester resin (adipic acid / o-phthalic acid, maleic acid , Dipropylene glycol / propylene glycol), viscosity at 23 ° C 1100-1300 mPa · s, and 1.4 g of trimethylbenzoyldiphenylphosphine oxide, 0.1 g of benzil dimethyl ketal and 0.02 g of hydroquinone monomethyl ether in the warm homogenized. Then 254 g of a finely divided aluminum hydroxide and 30 g of a highly disperse silicon dioxide are added and stirred in evenly. The mixture is then degassed under reduced pressure.

The gap between the ends of the pressure plate is closed as in Example 1. The closure also shows practically the same properties. When the plate is removed, however, it detaches more easily from the plate ends, so that it can be removed completely without damaging the plate.

Example 3

Similar to Example 2, a mixture of 80 g of the styrene / maleic acid half ester copolymer, 186 g of hydroxyethyl acrylate and 0.25 g of the potassium salt of the N-nitrosocyclohexylhydroxylamine with the mixture of 172 g of the "hard" polyester resin (Example 2) is 74 g the "soft" polyester resin (Example 2), 0.9 g of trimethylbenzoyldiphenylphosphine oxide, 0.1 g of benzil dimethyl ketal and 0.025 g of hydroquinone monomethyl ether were homogenized in the heat. Then 245 g of a finely divided aluminum hydroxide and then 30 g of a highly disperse silicon dioxide are stirred in homogeneously.

The mass obtained in this way is further treated as in the previous example and processed into a well-functioning gap closure. When the pressure plate is removed, the sealing compound is largely detached from the plate ends under the mechanical action; for the later re-use of the plate, the few remaining residues of the sealing compound can easily be removed mechanically.

Claims (11)

1. A method for closing and / or sealing openings, cavities or gaps which are formed when printing plates are applied to a forme cylinder by means of a sealing or sealing compound, characterized in that a sealing plastic or sealing compound is tough at room temperature, pasty, light-curable mass, which consists essentially of a photopolymerizable mixture
a) 10 to 90% by weight of at least one photopolymerizable, ethylenically unsaturated low-molecular compound,
b) 5 to 75% by weight of at least one polymeric binder which is compatible with the photopolymerizable low molecular weight compounds of component (a),
c) 0.01 to 10% by weight of at least one photopolymerization initiator, and
d) 3 to 40% by weight of at least one finely divided oxidic filler which, when mixed with components (a) to (c), gives transparent mixtures for long-wave UV light,
with the proviso that the sum of the percentages mentioned under (a) to (d) is 100,
exists, is used, which after application is cured in and onto the openings, cavities or interstices to be closed or sealed, and then optionally mechanically reworked. 2. The method according to claim 1, characterized in that the sealing or sealing compound additionally contains a polymerization inhibitor. 3. The method according to claim 1 or 2, characterized in that the sealing or sealing compound contains an addition of 0.1 to 2 wt.%, Based on the total amount of components (a) + (b), of a paraffin. 4. The method according to any one of the preceding claims, characterized in that as component (a) at least one vinyl and / or (meth) acrylic compound, which optionally contains further functional groups, such as hydroxyl, carboxyl or amino groups, is used. 5. The method according to any one of the preceding claims, characterized in that a vinyl aromatic and / or an ester of an α, β-ethylenically unsaturated carboxylic acid with mono- or polyhydric alcohols is used as component (a). 6. The method according to claim 5, characterized in that styrene and / or an ester of acrylic acid or methacrylic acid with a polyhydric alcohol is used as component (a). 7. The method according to any one of the preceding claims, characterized in that a styrene / maleic acid half-ester copolymer is used as component (b). 8. The method according to any one of claims 1 to 6, characterized in that one or more unsaturated polyesters are used as component (b). 9. The method according to any one of claims 1 to 6, characterized in that a mixture of a styrene / maleic acid half-ester copolymer and one or more unsaturated polyesters is used as component (b). 10. The method according to claim 9, characterized in that as component (b) a mixture of
b₁) a styrene / maleic acid half-ester copolymer
b₂) a "hard" unsaturated polyester based on phthalic acid / maleic acid / ethylene glycol / propylene glycol, and
b₃) a "soft" unsaturated polyester based on adipic acid / phthalic acid / maleic acid / dipropylene glycol / propylene glycol
is used. 11. The method according to any one of the preceding claims, characterized in that aluminum hydroxide and / or silica are used as finely divided oxidic fillers.