EP1313621B1 - Method for making a printing blanket and resulting blanket - Google Patents

Description

The invention relates to a method for manufacturing a printing blanket obtained by assembling a plurality of layers and a blanket thus obtained.

Blankets of this type, which are known, are manufactured by coating successive layers of elastomers on fabric reinforcements. These layers are dried, assembled and vulcanized. The materials used and the processes for producing these blankets involve the use of chemicals that are hazardous to humans and the environment, such as solvents, vulcanizers, plasticizers and decomposition products during curing and than carbon black. In fact, these products contain, in particular, substances that are carcinogenic or supposedly carcinogenic, such as plasticizers, carbon black and decomposition products, substances that are dangerous for reproduction and mutagenic substances such as vulcanizing agents, allergens harmful and flammable solvents and toxic and corrosive substances. In addition, the known blankets manufactured according to the known methods keep a residual solvent rate regardless of the drying precautions taken by the manufacturers. These residual solvents can cause porosity and nuisance subsidence in storage and service. It should be noted that subsidence is one of the serious functional defects of blankets. Known blankets still have the disadvantage of developing vapors and odors that can inconvenience users in case of confined storage. Finally, these blankets according to the state of the art can hardly be eliminated at the end of life because of their chlorine and sulfur content.

WO 93/09941 A , WO 97/00169 A , EP-A-0 914966 and EP-A-0 676 301 disclose printing blankets of multilayer structure, characterized in that the layers of the elastomers are thermoplastic in nature and do not contain crosslinking agents.

The object of the invention is to propose a process and blankets obtained according to this process, which make it possible to eliminate the danger for the environment and for the man of the abovementioned manufacturing processes and the blankets produced by these processes.

To achieve this goal, the method according to the invention. is characterized by the features of claim 1.

According to one characteristic of the invention, elastomers which do not contain thermal crosslinking agents and which are thermoplastic in nature are used for producing the layers.

According to another characteristic of the invention, the elastomers layers are produced by the dry route without the use of solvents, advantageously by extrusion.

According to another characteristic of the invention, in order to create a blanket in the form of a sleeve, a layer of thermoplastic material, of a predetermined length, is wound around a support sleeve, after having bevelled the ends of this layer. , superimposing the beveled ends and creates a tubular structure by assembling the ends by appropriate heating, the tubular structure thus obtained can serve as a support for the realization of another tubular layer.

According to one characteristic of the invention, the lithographic layer of a blanket in the form of a sleeve is crosslinked by radiation, and then, if necessary, ground and sanded.

According to another characteristic of the invention, a compressible tubular layer is made by conferring on it the possibility of expansion during the hot assembly of the ends, thanks to expandable microspheres previously incorporated in the layer.

• les figures 1 à 6 sont des vues en coupe de six modes de réalisation d'un blanchet selon l'invention, et
• la figure 7 est une vue schématique illustrant un procédé de réalisation d'un blanchet selon l'invention,

The invention will be better understood and other objects, characteristics, details and advantages thereof will appear more clearly in the following explanatory description made with reference to the accompanying schematic drawings given solely by way of example and in which:

• the Figures 1 to 6 are sectional views of six embodiments of a blanket according to the invention, and
• the figure 7 is a schematic view illustrating a method of producing a blanket according to the invention,

A multilayer blanket according to the invention which does not constitute a danger for man and the environment is advantageously produced by extrusion of successive layers of elastomers assembled with reinforcements and other layers of elastomers or polymers assembled in a calender downstream of the extruder. The fabrics used in the assembly of the layers are adhered to the elastomer layers by Corona treatment or ionization or flaming to avoid the use of solvents.

Solvent-free adhesives of the pressure-sensitive type may also be used.

The elastomers used in the context of the invention are mixed in the sheath of a extruder fed with the various ingredients of the formulation, or premixed by means known per se and fed into this sheath in the form of granules or the like.

The elastomers used in the context of the invention have the particularities that they do not contain thermal crosslinking agents. They are thermoplastic in nature with a suitable rheology and the various layers can be crosslinked by radiation after assembly of all or part of the blanket.

The elastomers layers are made by dry routes without the use of solvents and in particular by extrusion.

The materials used have the ability to become fluids at high temperature and thus allow the creation of thin films of good quality including extrusion.

By way of example of elastomers and reinforcements that can be used in the blankets in accordance with the invention, one could call formulations of elastomers or of polymers of the TPU type in combination with other polymers, dynamic vulcanization elastomers of the type based on PP, PAN and PVC, elastomers of the styrenic family, elastomer formulations of the family of olefins, olefin copolymers and functionalized olefins, elastomers of the family of acrylonitriles, EPDMs or MSCs or still ACM or AEM and combinations of elastomer modified or not, reinforcements aramid fibers or yarns, reinforcements with fibers or yarns of polyethylene or polypropylene type, reinforcements with fibers or yarns of polyester type or mixtures of such fibers or such yarns.

The materials without solvents and thus without risk for the environment and for man, used in the context of the invention, thanks to their thermoplastic implementation and therefore their property to merge by simple reheating at high temperature to create perfect junctions, allow to realize tubular blankets comprising one or more compressible layers, one or more reinforcing layers, a lithographic layer, associated, where appropriate, with a support layer, with other functional layers or with layers of filling.

Thus, for example, a tubular lithographic layer can be made from a lithographic layer obtained by extrusion and cut to the appropriate length and after bevelling the ends, by winding this layer on a support sleeve, by superimposing the beveled ends and heating them. This layer could be cross-linked by radiation, if necessary, then ground and sanded. The support sleeve in this case could be the blanket layer on which the lithographic layer rests. A compressible layer could be made in a similar manner with the additional possibility of expanding this layer during end joining by means of expandable microspheres previously incorporated into the layer forming materials. The extruded film intended to become a compressible layer could advantageously comprise fibers which will be oriented in the plane during extrusion to give the layer anisotropic properties. An extruded film with oriented fibers may also act as a layer of reinforcement or stabilization or paper flow control.

The tubular structure may also be obtained by direct extrusion of one or more successive concentric layers on the sleeve having an internal support and in progress. The direct extrusion may be of the ribbon type or of the annular type. Alternatively, coextrusion is also possible.

By producing the layer on the back, that is to say on the face opposite to the face comprising the lithographic layer, in a rectifiable polymeric material, the thickness of the blanket can be standardized by rectification of this layer on the back, while preserving or even improving the printing qualities of the blanket.

The rectification of the polymer layer on the back makes it possible to regulate the thickness in particular of ground and sanded lithographic blankets and blankets with a smoother surface obtained by molding and thus having an excellent print quality.

But, in general, the invention is applicable to all blankets whose thickness must be uniform, regardless of the means used to achieve a lithographic surface ensuring good print quality.

The invention thus makes it possible to obtain, with respect to the blanket without grinding, a precision gain of a factor 2, namely an overall thickness tolerance of +/- 0.01 mm against +/- 0.02 mm about the state of the art.

In addition to uniformizing the thickness of the blanket, the invention also makes it possible to obtain a reduction in the total thickness of the blanket. Indeed, in separating the different functions to be performed by the blanket, and by conferring these functions on specific layers, it is possible to establish an optimal blanket structure by assembling layers of fabric, compressible layers and the lithographic layer. It has been found that the use of a beam or a wire or a woven grid makes it possible to replace several fabrics and thus provides a reduction in thickness. The use of an aramid wire beam for example saves the relative thickness of at least one fold of tissue. The gain is at least 0.5 mm. The beam used in the context of the invention itself is of lower thickness than the tissues it replaces.

Since the beam replaces reinforcing fabrics that contribute to the compressibility of the blanket, this compressibility is maintained despite the removal of fabrics by making the polymer layer on the back compressible accordingly.

Thus, the invention makes it possible to produce a blanket with a substantially uniform thickness of 1.00 to 1.30 mm while preserving the breaking strength of the known blankets which are, for the most part, 1.7 to 2 mm thick. mm.

The invention allows the production of a blanket comprising, from inside to outside, the following layers: a slightly compressible polymer layer, an aramid beam or chain-like equivalent, a main compressible layer, a stabilizing fabric with for example, mono-filaments in weft and flexible-chain direction and a lithographic layer.

In a first variant, the stabilizing fabric may be replaced by a hard polymer layer optionally reinforced with fibers and, in a second variant, the compressible layer or layers can be made anisotropic by incorporation of oriented fibers in the plane of the blanket.

The Figures 1 to 6 show the structure of six advantageous embodiments of a blanket according to the invention having a reduced thickness. In these figures reference numeral 1 is a layer of slightly compressible polymer, the number 2 is a beam, the number 3 a compressible layer, the number 4 a stabilizing fabric or a reinforced hard layer, the number 5 a lithographic layer and the number 6 a layer of compact polymer.

The blanket shown on the figure 1 comprises, from the inside to the outside, a slightly compressible polymer layer 1, a compressible layer 3 to which the beam 2 is integrated, a stabilization fabric or reinforced hard layer 4, and a lithographic layer 5. The blanket a thickness of about 1.2 mm. In the blanket according to the figure 2 , the compact polymer layer 6 is removed relative to the blanket of the figure 1 which reduces the thickness of the blanket to about 1.1 mm. The figure 3 shows a blanket in which the beam 2 is integrated with the polymer layer 1 on the back of the blanket, the compact polymer layer 6 is also removed. The thickness of the blanket is about 1.2 mm. The blanket of the figure 4 corresponds to that of the figure 3 , with the difference however that the beam 2 is integrated into the compressible layer in the upper part thereof. The thickness of the blanket is 1.1 mm. The blanket shown on the figure 5 has an even smaller thickness of about 1 mm thanks to the fact that the layers 1 of compressible polymer and the layer 6 of compact polymer have been omitted, the assembly 2 being integrated with the compressible layer 3 in the upper part thereof. Finally, FIG. 8 shows a blanket comprising on the back a compressible layer 3 with the beam integrated in the upper part thereof, an anisotropic compressible layer 7 and a lithographic layer 5. The thickness of this blanket is also about 1 mm.

In the context of the invention, it has proved advantageous to embed in the lithographic layer of the blanket, on the surface, fine particles, for example glass microbeads or polymer or ceramic powders. Particular transfer surfaces having a specific micro-roughness and microheterogeneity are thus obtained. By using glass microbeads, a good property of spreading water on the surface is obtained. The encrustation of the particles may also be made on the surface of the layer on the back if it is made of a polymer material. This incrustation advantageously reduces and the coefficient of friction of this surface. A low coefficient of friction is very useful to facilitate attachment to the cylinder of the printing machine.

The embedded particles are preferably of a spherical nature and have diameters of preferably between 1 and 100 microns.

The figure 7 illustrates a method and an advantageous installation for implementing this incrustation. According to this figure, the polymer layer 8 is passed through the surface of which the particles must be embedded, downstream of the extruder die 9, with the blanket carcass shown in between two calender rolls 11 and 12. The calender roll which comes into contact with the surface to be treated 13, namely the lower roll 12, dips at its lower part into a container 15 containing fine particles, for example in the form of a powder. . The passage of the plunger through this tray causes the formation of a particle film indicated at 17 on the surface of the cylinder, which, by turning, transports and incrust in the surface 13 of the polymer layer 8. The The roughness of the surface of the plunger constitutes one of the parameters of the quantity of particles transported. The tray can be vibrated to ensure a smooth deposit on the surface of the calender roll.

A scraping device of the plunger can also be provided to measure the amount of particles deposited and embedded in the surface of the blanket.

In an alternative embodiment, the inlay described here can be made on the surface of a previously extruded polymeric film and, where appropriate, rectified by simply reheating the surface thereof by means known per se, such as infrared ramps, and passage of the blanket with its layer of polymer heated on the surface between the rolls of the calender of the figure 7 .

Alternatively, it is also conceivable to deposit a film of liquid product or pasty or pasty product which, driven by the plunger, freezes in contact with the hot polymer film on the surface of the blanket during the passage in the contact zone between the two cylinders of the calender ".

The invention provides many advantages. Thanks to the rectification of the polymer layer on the back of the blanket, the thickness of it is more precise and uniform. This has a direct impact on blanket performance. In fact, a controlled thickness improves the print quality and longevity of blankets. A smoother blanket thickness also extends the life of these by allowing a lower trim height limiting the mechanical forces on the blanket and thus delaying the possible occurrence of weak printing. The excellent print quality of a smooth and even very smooth printing surface can be maintained. Such a smooth surface makes it possible to print the details accurately and to generate a so-called "sharp" impression or "high fidelity" printing. It allows the use of a stochastic frame. The smooth surface can be characterized by a very low roughness (Ra: average roughness measured with the profilometer) lower than 0.4 μ against values of 0.8 to 1.5 μ for blankets of the state of the art. The deterioration of the thickness when it is desired to obtain a very smooth printing surface, for example by sanding this surface and the compromise made for the blankets known to be satisfied with less efficient sanding and therefore less surface area. smooth can be removed through the rectification of the layer on the back, as proposed by the invention. Reducing the thickness of the blankets provides a reduction in vibration by making it possible to design cylinders with a narrow groove for fastening the blanket and thus to minimize bouncing during high speed rolling. The invention also provides a cost reduction insofar as a thin blanket requires for its realization a lesser amount of material which is the most important item in the cost price. The invention makes it possible to obtain even a reduction in the quantities of waste. In fact, less thick blankets mean a quantity of waste to be eliminated less important. On the other hand, by embedding particles on the surface of the lithographic layer, or the layer on the back, one can obtain a desired surface microheterogeneity and / or reduce the friction of the blanket on the support. Finally, the invention makes it possible to achieve "ecological" blankets, that is to say not posing any risk to man and the environment.

Claims (14)

1. Method for manufacturing a printing blanket obtained by assembling a plurality of successive layers of elastomers assembled with reinforcements and layers of polymers, characterised in that, in order to produce the elastomer layers, elastomers that do not contain thermal crosslinking agents and are of a thermoplastic nature are used and in that the different layers are fixed to one another by Corona, ionisation or flame treatment.
2. Procedure according to claim 1, characterised in that, to create a muff-shaped blanket, a layer made of a thermoplastic material of a preset length is rolled around a muff forming a support, the two ends are connected and the ends are assembled by heating the latter to the melting temperature.
3. Method according to claim 2, characterised in that the ends are chiselled, superimposed and the ends are assembled by heating to the aforesaid melting temperature.
4. Method according to any one of claims 1 to 3, characterised in that the lithographic layer is subjected to crosslinking treatment by radiation and if necessary to grinding and sanding operations.
5. Method according to any one of claims 2 to 4, characterised in that a compressible tubular layer is made therein to enable it to expand during hot assembly of the ends, owing to expandable microspheres that are already incorporated in the layer.
6. Method according to any one of claims 1 to 5 characterised in that the layers of elastomers are produced dryly without using solvents, advantageously by extrusion.
7. Printing blanket of multilayer structure obtained according to the method of any one of claims 1 to 6.
8. Blanket according to claim 7, characterised in that the lithographic layer is ground and sanded.
9. Blanket according to one of claims 7 or 8, characterised in that it has the shape of a muff in which the ends of the layers in thermoplastic material are assembled by heating the ends to the melting temperature of the material.
10. Blanket according to claim 9 characterised in that one compressible tubular layer is obtained by expansion during hot assembly of the ends owing to expandable microspheres that were incorporated in the expandable layer.
11. Blanket according to one of claims 7 to 10, characterised in that the layer at the back is a layer in a polymer material.
12. Blanket according to claim 11, characterised in that the layer at the back is in a grindable polymer material and is ground.
13. Blanket according to one of claims 7 to 12, characterised in that the thickness thereof is reduced, forming a beam or thread or a woven scrim replacing several fabrics.
14. Blanket according to one of claims 7 to 13, characterised in that at least one of the outer layers has encrustations of particles on the surface.

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