EP2197677B1 - Sleeve for flexo printing - Google Patents

Abstract

Use of a sleeve for flexographic printing, comprising: a base sleeve; an intermediate layer enlarging the printing length, provided on the base sleeve and having a thickness of from 2 to 20 mm; a laser-engravable layer of a radiation-cured polymer; for enlarging the repeat.

Description

The present invention relates to a sleeve for flexographic printing and method for its production.

Flexographic printing is a printing process that is used extensively for printing on packaging materials made of plastics, paper, cardboard or cardboard.

On the one hand, printing plates are used which are clamped onto a printing cylinder or mounting sleeve. This technology has the disadvantage that a seam remains after assembly, which interferes with the printing process.

There are also seamless printing forms in which the printing form is produced seamlessly on a roller. Usually, sleeves are used here whose outer side represents the printing layer, i. only the roll covers are changed and transported, not the cores.

Typical materials for the printing layer of the sleeves in flexographic printing consist of rubber or photopolymers.

The technology of photopolymer polymerization has found a wide range of applications. In this case, an existing image is exposed on the photopolymer surface of the roller or plate, thereby hardening in the exposed areas of the photopolymer. Unexposed areas are washed off. After drying, this creates the printing plate.

An alternative to this is direct laser engraving. The unnecessary areas of the printing form are removed by using a laser, the remaining and the removed areas then give the printing form. This is possible with both rubber-coated sleeves and sleeves, in which a layer of a photopolymer is applied to a sleeve and polymerized. The direct laser engraving is particularly advantageous because nowadays the required information is generally already available digitally and can be saved by the direct engraving step over the analog exposure system.

Due to the fact that the photopolymer is applied directly to the sleeve, the circumference of the printing form is specified in narrow ranges. In order to achieve an enlarged outer circumference (= printing length) for a given inner diameter of the sleeve, a large amount of photopolymer would have to be applied, which is very expensive on the one hand, and, on the other hand, hardening of the photopolymer becomes more difficult as the thickness increases. For larger layer thicknesses, the printing plate can be mechanically unstable due to the low hardness, which adversely affects the printing result.

The circumference of the roller or the sleeve determines the printable with the roller printing length, so the repeat, i. the length after which the print pattern repeats.

It was an object of the present invention to provide a sleeve coated with a photopolymer at a low cost, even with a greater total wall thickness and correspondingly greater pressure perimeters / lengths while maintaining the same internal diameter.

• eine Hülse
• eine auf der Hülse befindliche, drucklängenvergrößernde Zwischenschicht mit einer Stärke von 2 bis 20 mm mit einer Härte von ≥ 80 shore A
• eine lasergravierbare Schicht eines strahlungsgehärteten Polymers zur Vergrößerung des Rapports bzw. der Drucklänge.

The problem is solved by the use of a sleeve for flexographic printing comprehensively

• a sleeve
• an intermediate layer with a thickness of 2 to 20 mm and a hardness of ≥ 80 shore A located on the sleeve
• a laser-engravable layer of a radiation cured polymer to increase the repeat or print length.

The sleeve according to the invention has on the sleeve on a Umfangsvergrößernde intermediate layer. This has a thickness of 2 to 20 mm, preferably 2 to 15 mm.

In some embodiments, it is preferred that the thickness of the intermediate layer is> 5 mm or> 8 mm or> 10 mm.

This intermediate layer increases the distance of the outer printing layer from the central axis, so that the printing length increases and larger motifs can be printed. This increases the repeat.

The outer layer is a radiation-cured polymer, in particular a photopolymer, as has hitherto been used in the prior art for corresponding sleeves.

The sleeve of the sleeve is typically made of a glass fiber reinforced plastic. However, it is also possible, for example, to use carbon fiber-reinforced plastics or other sleeve materials used in flexographic printing.

Natural rubber or synthetic rubber, but also polyurethane, is suitable in particular as a pressure-length-increasing intermediate layer. It is important that the intermediate layer has a certain mechanical and geometric stability in order to be used as part of the printing plate in flexographic printing can. A hardness of the material ≥ 80 Shore A has proven to be particularly suitable.

Between the pressure-length-increasing intermediate layer and the laser-engravable layer, in one embodiment, a further compressible layer may be present, for example, a porous polyurethane.

Radiation-curable polymers which can be engraved by means of a laser are known to the person skilled in the art, for example from US Pat EP 1 710 093 A1 or the EP 1 424 210 A1 , in which further suitable materials are described.

The invention further relates to the use of the sleeve according to the invention, which has a motif produced by laser engraving.

• Bereitstellen einer Hülse
• Aufbringen einer drucklängenvergrößernde Zwischenschicht
• Gegebenenfalls Oberflächenbearbeitung der Zwischenschicht
• Aufbringen eines strahlungshärtbaren Polymers
• Aushärtung des strahlungshärtbaren Polymers durch Strahlung.

The sleeves according to the invention can be produced by a method having the following steps:

• Providing a sleeve
• Applying a printing length-increasing intermediate layer
• If necessary, surface treatment of the intermediate layer
• Applying a radiation-curable polymer
• Curing of the radiation-curable polymer by radiation.

In a particularly preferred embodiment, the radiation-curable polymer is polymers which are liquid at room temperature. These allow a particularly advantageous application on the intermediate layer.

The print length-increasing intermediate layer can be produced in various ways. For example, if it is a natural or synthetic rubber, the partially finished sleeve must first be vulcanized. As a rule, this will be followed by a surface treatment of the intermediate layer before the radiation-curable polymer is applied.

If polyurethane is used as the pressure-length-increasing intermediate layer, this can basically also be applied directly to the sleeve. It is also possible to surround the sleeve with an outer sleeve and to introduce the polyurethane layer between the two sleeves and then to remove the outer sleeve. It may also leave the outer sleeve and be coated with the photopolymer.

The applied radiation-curable polymer is then subsequently cured. In a photopolymer, this is done by exposure, for example, with UV light.

Surprisingly, it turns out that although the cured polymer has sufficient adhesion to the printing length-increasing intermediate layer, the layer of the cured polymer in a relatively simple manner again can be removed, for example by scratching and tearing. As a result, the print length-increasing intermediate layer is exposed again and can - if necessary after a surface treatment - be coated again with a radiation-curable polymer. In this way, the inner sleeve can be repeatedly reused with the pressure-length-increasing intermediate layer.

The invention also provides for the use of a print length-increasing intermediate layer having a thickness of 2 to 20 nm with a hardness of ≥ 80 shore A for a sleeve with a sleeve and a laser-engravable layer of a radiation-cured polymer for increasing the repeat of the sleeve.

• eine Hülse
• eine auf der Hülse befindliche, drucklängenvergrößernde Zwischenschicht mit einer Stärke von 2 bis 20 mm mit einer Härte von ≥ 80 ShoreA
• eine lasergravierbare Schicht eines strahlungsgehärteten Polymers zur Vergrößerung des Rapports des Sleeves.

Another subject is a sleeve for flexographic printing comprising

• a sleeve
• an on the sleeve located, pressure length increasing intermediate layer with a thickness of 2 to 20 mm with a hardness of ≥ 80 ShoreA
• a laser-engravable layer of a radiation-cured polymer to increase the repeat of the sleeve.

The invention also provides the use of the sleeve according to the invention in a method for laser direct engraving or the use of a sleeve with an applied motif in flexographic printing.

FIG. 1 shows schematically the structure according to the invention. On a sleeve 1 made of a glass fiber reinforced plastic is a drucklängenvergrößemde Intermediate layer 2, on which a layer of a cured photopolymer 3 is located. The cured photopolymer can then be laser engraved with a motif for flexographic printing.

FIG. 2 shows a corresponding structure with a stronger intermediate layer. 2

example

• Die Druckmaschine ist mit einer Aufnahme für Sleeves mit einem Innendurchmesser von 136,989 mm ausgerüstet. Damit könnte mit dem normalen Aufbau (Hülse + Beschichtung = 3,125 mm) ein Druckumfang von 450 mm erreicht werden.

A corresponding application is available, for example, in the present case:

• The printing machine is equipped with a receptacle for sleeves with an inner diameter of 136.989 mm. This could be achieved with the normal structure (sleeve + coating = 3.125 mm) a pressure of 450 mm.

However, if a motif with a length of 480 mm is to be printed, an intermediate layer of an 80 Shore A hard intermediate rubber is additionally installed between the sleeve and the functional layer, so that a total layer thickness of 7.90 mm and thus an outer diameter of 152.79 mm are formed , With this additional hard liner, a larger print size is achieved cost and at the same time the mechanical stability of the printing plate is maintained.

Claims (11)

1. Use of a sleeve for flexographic printing, comprising:

   - a base sleeve (1);

   - an intermediate layer (2) enlarging the printing length, provided on the base sleeve and having a thickness of from 2 to 20 mm and a hardness of ≥ 80 Shore A;

   - a laser-engravable layer of a radiation-cured polymer (3);
   for enlarging the repeat.
2. The use according to claim 1, characterized in that said base sleeve (1) consists of a plastic material reinforced by glass fibers or of a plastic material reinforced by carbon fibers.
3. The use according to claim 1 or 2, characterized in that said intermediate layer (2) is selected from synthetic rubber, natural rubber, polyurethane or mixtures thereof.
4. The use according to at least one of claims 1 to 3, characterized in that said radiation-cured polymer is a cured photopolymer.
5. The use according to at least one of claims 1 to 4, characterized in that a compressible layer is provided between the intermediate layer (2) enlarging the printing length and the laser-engravable layer (3).
6. The use according to at least one of claims 1 to 5, characterized in that said laser-engravable layer (3) has a pattern produced by laser engraving.
7. Use of an intermediate layer (2) enlarging the printing length having a thickness of from 2 to 20 mm and a hardness of ≥ 80 Shore A in a sleeve comprising a base sleeve and a laser-engravable layer of a radiation-cured polymer (3) for enlarging the repeat of the sleeve.
8. A sleeve for flexographic printing, comprising:

   - a base sleeve (1);

   - an intermediate layer (2) enlarging the printing length, provided on the base sleeve and having a thickness of from 2 to 20 mm and a hardness of ≥ 80 Shore A;

   - a laser-engravable layer of a radiation-cured polymer (3);
   for enlarging the repeat of the sleeve.
9. A process for preparing a sleeve according to claim 8 comprising the following steps:

   - providing a base sleeve (1);

   - applying an intermediate layer (2) enlarging the printing length;

   - optionally finishing the surface of the intermediate layer (2);

   - applying a radiation-curable polymer;

   - curing said radiation-curable polymer by means of radiation.
10. A process for recycling a sleeve according to claim 8 comprising the following steps:

    - removing the radiation-cured polymer layer (3);

    - optionally finishing the surface of the exposed intermediate layer (2);

    - applying a radiation-curable polymer;

    - curing said radiation-curable polymer by means of radiation.
11. Use of a sleeve according to claim 8 in a method for laser direct engraving.

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