EP0844100B1 - Blanket for offset printing - Google Patents

Abstract

The continuously-produced offset lithographic printing cloth comprises a lithographic surface (6), compressive or resilient layer (3) and reinforcing layer (1) of low expansibility. There is a fabric layer (2) on the back of the reinforcement. The compressive layer is located between the lithographic surface and the reinforcing layer.

Description

The invention relates to a printing blanket for offset printing according to the preamble of Claim 1.

Printing blankets that are attached to the printing cylinder of an offset printing press, serve to print what is, for example, on a metal printing plate Image of the material to be printed, for example paper, cardboard or metal, which is in Form of sheets or rolls can be transferred. Thereby are essentially known three types of printing blankets. The first type, which is the present one Invention is so-called. continuously produced printing blankets that are continuous produced on a roll and then according to the dimensions of the impression cylinder be cut to where they will be used. The second and third Art are individually manufactured printing blankets, each specially for the one to be used Printing cylinders are manufactured and on the one hand like a sleeve ("sleeve printing blanket") can be pushed over the pressure cylinder or traditionally with one Clamping device can be clamped individually. The second type of blanket has the advantage that it is not like conventional printing blankets by means of a Cylinder surface trained groove must be attached to the pressure cylinder. Consequently there are no imbalances when the printing cylinder rotates and a higher one Rotation and thus printing speed is made possible. The disadvantage of such sleeve-shaped printing blankets, however, is that the printing press specifically for this must be designed and is very expensive due to the concept, the sleeve-shaped Printing blankets are also very expensive.

As mentioned above, the continuously produced printing blankets are each cut according to the dimensions of the impression cylinder. In the past, Attach the respective blanket to the printing cylinder clamping rails attached to the blanket, for example by means of screws, whereupon the Clamping rails on a groove of the impression cylinder formed in the cylinder surface were clamped. However, this technique is outdated and is becoming current Disposable rails are used, which are clamped to the printing blanket and glued at the same time become. If the printing blanket is worn, it will be together with the disposable rail disposed of. In comparison to the previously used multi-purpose clamping rails is therefore It is important in today's technology that the printing blanket is constructed in such a way that the one-way clamping rails can be easily glued to it.

In Japanese Patent Application No. 58-84294, Patents Abstracts of Japan, 1985 Vol. 9 / no. 80, a printing blanket is known which has a lithographic surface on its Has top and a metal layer on its underside. Between the Metal layer and the lithographic surface is a compression layer arranged. Such a compression layer serves to avoid a Process through volume reduction in the pressure zone and to compensate for Indentation differences. It is crucial that the compression layer is itself does not expand when compressed, i.e. that their volume at Squeezing actually shrinks so that no laterally spreading Faults arise. There are some known techniques for this, e.g. the Use of plastic microspheres in a rubber compound or the Use of a microporous cell structure with enclosed gas chambers. The printing blanket disclosed in the Japanese patent application has the great disadvantage that that its lower layer is formed from the reinforcing layer, which is made of metal here is, so that the disposable clamping rails used today for fastening the Printing blanket on the printing cylinder can not be reliably attached to this printing blanket can. The metal such as Aluminum existing one-way clamping rails can be glued to the metal layer only with difficulty, so that a reliable It is not possible to clamp this blanket on the printing cylinder. Another The disadvantage of the metal layer arranged on the underside of the printing blanket is that Moisture that is between the blanket and the printing cylinder during the Printing process forms or gets there, neither absorbed by the printing blanket be able to step out laterally between the printing blanket and printing cylinder and thus can cause corrosion of the printing cylinder. The same disadvantages apply of course also for printing blankets that have a polymer or on their underside Have polyester film, because the disposable clamping rails hardly on these materials are glued and no liquid is absorbed by them, but is included.

Some of the known printing blankets without a reinforcing layer have the disadvantage that the stabilizing layer (or several Stabilizing layers) made of fabric material, for example cotton fabric material, have a comparatively high static elongation. This leads to the fact that Printing blankets on the printing cylinder often have to be retensioned and the Print quality is affected by blurring of the individual halftone dots. Especially when used for four-color printing, four for four colors in a row arranged pressure cylinder can be used, an uneven expansion of the four printing blankets used in succession for printing on the same sheet of paper lead to a false register of colors and thus image blur.

Furthermore, in some conventional printing blankets, the stretch in the weft direction is Fabric much higher than in the warp direction, so that this only on a pressure cylinder with the warp direction (longitudinal direction) in the circumferential direction of the cylinder can. Clamping the printing blankets on the printing cylinder in the weft direction (Transverse direction) is not possible due to the high elongation.

From Japanese Patent Application No. 64-273158, Patents Abstracts of Japan, 1991, Vol. 15 / No. 339 a printing blanket is known which has a lithographic surface, a Reinforcement layer made of metal, a compression layer and a fabric layer has, which is arranged on the lower layer of the printing blanket. The one on the bottom arranged fabric layer is on the underside of the compression layer arranged, which is attached to the reinforcing layer on its upper side. The Print layer with the lithographic surface is by means of a primer or a Adhesive layer attached to the metal layer. So are on this known printing blanket Although the disposable clamping rails used nowadays can be easily attached, as its Underside is formed by a layer of fabric, however, it has other serious Disadvantages. The first disadvantage is that the metal reinforcement layer, the according to their purpose, to stretch the blanket lengthways and crossways avoid a slight stretch and when opening the printing blanket a compression cylinder strongly compresses the underlying compression layer. The results from the fact that the individual layers of the printing blanket as plane during manufacture Surfaces are glued together and the blanket in during the printing process Shape of a pitch circle is clamped on the impression cylinder. Because the compression layer is placed under the metal reinforcement layer, it has a smaller one Circumferential radius than the metal layer. When clamping the printing blanket through the much less elongation of the metal layer the compression layer compressed and can perform its actual function during the printing process, namely the avoidance of a flexing process and the compensation of Do not exert indentation differences or only to a very limited extent therefore pointless. Furthermore, due to the loss of thickness of the printing blanket, printing is only possible in possible to a limited extent, for example in the case of rubber-to-rubber web offset printing adjustment is not possible.

Another disadvantage of this known printing blanket is that it is not a printing blanket for the Printing on varnishes can be used. When printing varnish usually cut out parts of the lithographic surface manually or with a plotter, that correspond to those parts of the object to be printed that do not have varnish should be printed. The remaining uncut parts of the lithographic surface take up the varnish and print it on the corresponding sections of the respective object to be painted. For the quality of the varnish print and in particular also the period of use of the printing blanket used the relief depth is crucial. The deeper the relief depth is, the better it can be prevented be that paint accumulates in the cut out parts and accumulates and itself then transfers to the respective object to be printed (substrate), which is a Decrease in quality and cause an undesired machine downtime can. The printing blanket known from the above Japanese patent application however, the metal layer just below that forming the lithographic surface Print layer. If this printing blanket is to be used for varnish printing, the maximum relief depth only correspond to the thickness of the print layer, since no further than can be cut to the hard metal layer. So this is known Printing blanket difficult to use for varnish printing because the relief depth is too small. The cut out parts of the printing blanket create an insufficient relief depth and lead after a short printing time for the accumulation of paint in the recessed areas. This known printing blanket is therefore not for printing varnish over a longer period Suitable period.

DE-A-2244766 discloses a printing blanket with a lithographic layer, one compressible layer, a thermoplastic layer and one Reinforcement layer 1 in this order. DE-A-1940852 discloses printing blankets with at least one compressible layer in different variations.

Starting from the Japanese patent application discussed in detail above No. 64-273158 is the object of the present invention, a continuously produced Printing blanket for offset printing with a lithographic surface, one Compression layer, a reinforcement layer with a low stretch and one on the side of the reinforcement layer facing away from the lithographic surface Arranged fabric layer to provide improved print quality in particular through a better distribution of the pressure during the printing process enables and that is still suitable for coating printing.

This task is accomplished through a continuously produced blanket for offset printing solved with the features of claim 1, which is characterized in that the Compression layer between the lithographic surface and the Reinforcement layer is arranged.

By placing the compression layer between the lithographic surface and the reinforcement layer ensures that the compression layer after the Clamping the blanket on a printing cylinder is not compressed, no Starch loss occurs and avoidance during printing Walk processes and a compensation of indentation differences in maximum Way is enabled. When using the printing blanket according to the invention Varnish printing is due to the arrangement of the compression layer between the Reinforcement layer and the lithographic surface a maximum relief enables. Since the incision is ideally down to the hard reinforcement layer is carried out, both the entire thickness of the printing blanket according to the invention the print layer as well as the entire thickness of the compression layer including if necessary. existing tissue layers are available for cutting out, so that relatively deep Cut-outs are created that prevent the accumulation of paint. Hereby the duration of use of the printing blanket during coating printing is significantly extended and also increases the print quality when printing on varnish.

The fabric layer which is arranged on the side of the reinforcement layer which is from the facing away from the lithographic surface enables a safe and reliable Attachment of the one-way clamping rails to the printing blanket. The usually made of metal Existing disposable clamping rails can be easily glued to the fabric become. Another advantage of this fabric layer is that it can be used during the Liquid produced between the reinforcing layer and the printing process Soak up the pressure cylinder and discharge it as a result of wicking, so that this Liquid can evaporate and cause no corrosion.

Advantageous embodiments of the present invention are in the respective Subclaims specified.

The fabric layer is advantageously on that of the lithographic surface opposite side of the reinforcement layer attached. By this measure is ensures that the reinforcement layer avoid stretching the blanket should have its effect in the maximum way, since it can only be Layer of fabric is removed from the impression cylinder, and on the other hand, that the printing blanket can be easily and securely clamped onto a pressure cylinder, because during clamping not additional layers between the reinforcement layer and the Pressure cylinders are compressed.

It can furthermore be advantageous to interpose at least one further compression layer to arrange the lithographic surface and the reinforcing layer. This allows for example, one or between the first and a second compression layer several layers of tissue can be arranged. It can also be advantageous, at least another reinforcement layer between that on the lithographic surface facing away from the reinforcing layer and the fabric layer Arrange reinforcement layer. Here too, the first reinforcement layer and a second reinforcement layer, for example through one or more fabric layers be separated.

Furthermore, it is advantageous if the or one of the reinforcement layers consists of one Polymer film, a polyester film or a metal foil. Especially for the Using the printing blanket according to the invention for coating printing, it is advantageous that when cutting the printing forms right up to the hard reinforcement film can be cut out without being injured.

An exemplary embodiment of the printing blanket according to the invention is described below 1, in which such a blanket is shown schematically in cross section is shown.

The printing blanket according to the exemplary embodiment has a lithographic layer 5, which is provided with a lithographic surface 6 for transferring the printed image. Under the lithographic layer 5 is a tissue intermediate layer 4 and one compressible layer 3 arranged, for example, contains microspheres. Means a further intermediate layer 7 of fabric is underneath the stabilizing layer 1 consisting for example of a polymer film or a metal foil. Below this is again a textile finishing layer 2, the better one Connection of the printing blanket with a disposable clamping rail is used in the Printing cylinder is clamped. The layers are known per se Bonding techniques linked together. It should be noted that in the shown Embodiment the textile layers 4, 7 for reasons of simpler Producibility are provided, but can also be omitted without the To leave the framework of the teaching according to the invention.

The static elongation of the blanket was measured as follows: A blanket sample 25 mm wide and 300 mm long is clamped and a tensile load of 250 N exposed for 10 minutes. The relative stretch of the blanket is measured on a reference length of 100 mm.

According to the invention, the reinforcement layer 1 is like this trained that the stretch of the blanket with a static load of 10 Newton per mm for 10 minutes in the longitudinal and transverse directions at most 3% is. The printing blanket can advantageously be designed so that the static expansion in Lengthways and crossways maximum 2%, maximum 1% or maximum 0.5% is. The difference between the static elongation in the longitudinal direction and the static elongation in the transverse direction can be at most 1%, preferably at most 0.5% be.

According to an embodiment of the invention, the elongation is Blanket with a static load of 10 Newtons per mm for 10 minutes Duration in at least one direction at most 0.6%. With the blanket according to this In one embodiment, offset printing of particularly high resolution is possible.

The possibly still existing fabric layers only serve to simplify the connection of the Layers among themselves. Therefore, an inexpensive material can be used for the fabric layers High stretch fabrics are used because their stretch properties are not of Meaning.

One or more reinforcement layers made of polymer foil or metal foil have the Advantage that the stretching properties are isotropic in contrast to fabric material the blanket therefore in both the longitudinal and transverse directions on the printing cylinder can be spanned. Thus, the printing blanket can be used both lengthways and in Transverse direction, and if necessary also in any other direction from the roll can be cut, with a given roll width a larger number of Printing cylinder widths can be supplied without unnecessary waste. Thereby for the manufacturer of the printing blankets, the necessary number of different blanket widths and for the user the need for each To keep a blanket roll of the appropriate width in stock. Furthermore, damaged at one point by contamination or the like Printing blankets (a so-called "winder") after removing the damaged area in Transverse direction again clamped on a printing cylinder of a smaller format and thus continue to be used.

The reinforcement layer made of a polymer or metal foil also has absolutely one significantly less elongation than known printing blankets according to the prior art with a reinforcing layer of textile fabric material, so that a distortion or an increase in the pressure points ("dot gain") is reduced. This is one It is possible to improve the resolution that can be achieved with the printing blanket. The print template, which by means of a rigid plastic film (film) or directly on the likewise rigid Pressure plate is applied, is in the described embodiment by means of the also rigid printing blanket on the rigid substrate (paper, cardboard, metal, Plastic). It therefore only occurs at every step of the printing process a very low elongation of the image-transmitting medium, in contrast to known printing blankets with reinforcing layers made of textile fabric.

With the slight stretching of the printing blanket, there is also a variation in the stretching of the Printing blanket low. This is especially true for four-color printing (or Multi-color printing) is advantageous where the material to be printed is stacked several times different colors is printed to form the finished color print image. Each less the spread of stretch of the different on the four (or more) Printing blankets used, the more exact the colors are to each other aligned and the better the quality of the printed color image.

The printing blanket according to the invention also has the advantage that at a lower Stretching a frequent tensioning of the printing blanket on the printing cylinder as with conventional printing blankets is not required. Besides, the loss of strength is that caused by the stretching of the printing blanket, less.

Furthermore, the printing blanket according to the embodiment has a low plastic Stretch of the printing blanket, i.e. with repeated use with interruption the blanket has returned to its original stretched state, so to speak "Memory". This is particularly advantageous when parts are cut out in the printing blanket not to print at the cut out areas. This procedure will be like Used above to use only parts of a printed image with an additional one To provide a layer of paint, but to leave other parts unpainted.

When cutting out parts of the printing blanket for varnish printing, as mentioned, cut out manually or by means of a plotter to the reinforcement layer in order to to create a sufficiently deep relief so that an accumulation of lacquer in the recessed areas is avoided. Therefore, it is advantageous to ensure the adhesion of the layers above, i.e. towards the lithographic surface, with the reinforcing layer to make less than the adhesion between the reinforcing layer 1 and the underlying fabric layer 2. This will make it easier to detach the allows cut out parts from the printing blanket. A relatively strong connection between the fabric layer 2 and the reinforcement layer 1 is also in terms of Fastening of the disposable clamping rails is necessary, as these are attached to the fabric layer 2 is stuck on. The adhesion between the reinforcement layer is advantageously and the overlying layers between 0.3 and 1kg / cm, whereas the adhesion between the reinforcement layer 1 and the underlying fabric layer 2 is preferably greater than 1kg / cm. It is particularly advantageous to be precise predefined target separation value that specifies the separability of the above Reinforcement layer 1 layers from the reinforcement layer 1 precisely specifies for a simple detachment of the corresponding parts of the printing blanket for coating printing to enable.

If the reinforcement layer 1 is a polyester film, it is particularly advantageous to use the adhesive or primer intermediate layer, which of course between the individual in the Blanket provided layers are present to secure them together, made from an antistatic rubber compound. Because the polyester film is hydrophobic and is dielectric and does not absorb water, static electricity can build up on it occur. Through the use of antistatic rubber compounds for the adhesive or intermediate layers becomes a static charge on the entire printing blanket avoided. The effect of avoiding static build-up of the printing blanket is further supports if the reinforcement layer 1 has a static elongation of less than 0.4%.

Claims (8)

1. Continuously manufactured offset printing blanket, with a lithographic surface (6), a compressible layer (3), a reinforcing layer (1) with low elongation characteristics and a fabric layer (2) on the side of the reinforcing layer (1), which is opposite to the lithographic printing surface (6), whereby
   the compressible layer (3) is located between the lithographic surface (6) and the reinforcing layer (1), and the elongation exhibited by the blanket, when subjected to a static load of 10 Newtons per mm in both the length and cross direction for a period of 10 minutes, is not greater than 3%.
2. Continuously manufactured offset printing blanket according to claim 1, characterised in,
   that the fabric layer (2) is attached on the side of the reinforcing layer (1), which is opposite to the lithographic surface (6).
3. Continuously manufactured offset printing blanket according to claim 1 or 2, characterised in,
   that at least one additional compressible layer is located between the lithographic surface and the reinforcing layer (1).
4. Continuously manufactured offset printing blanket according to claim 1, 2 or 3, characterised in,
   that at least one additional reinforcing layer is located between the textile layer (2) and the reinforcing layer (1).
5. Continuously manufactured offset printing blanket according to one of the preceding claims,
   characterised in,
   that the one or more reinforcing layers (1) is made from a polymeric or a metallic foil.
6. Continuously manufactured offset printing blanket according to one of the preceding claims,
   characterised in, that the difference between the static elongation in the length direction and that in the cross direction is no greater than 1 % or more preferably 0.5%.
7. Continuously manufactured offset printing blanket according to one of the preceding claims,
   characterised in,
   that the reinforcing layer (1) is made from polyester foil.
8. Continuously manufactured offset printing blanket according to one of the preceding claims,
   characterised in,
   that the overall gauge of the blanket is between 1.00 and 3.00 mm.

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