ES2364889T3 - HOSE FOR FLEXOGRAPHIC PRINTING. - Google Patents

Abstract

Use of a sleeve for flexographic printing comprising - a sleeve (1) - an intermediate layer (2) located on the sleeve, which increases the length of printing, with a thickness of 2 to 20 mm and with a hardness of> = 80 Shore A - a layer that can be etched by laser, of a polymer (3) hardened by radiation to increase the repetition of the cuff.

Description

The present invention relates to a sleeve for flexographic printing and the method of its manufacture.

Flexographic printing is a printing process that is widely used to print plastic, paper, cardboard or cardboard packaging media.

On one hand, printing plates are tensioned on a printing cylinder or on a mounting sleeve. This technology has the disadvantage that after assembly there is a seam that is annoying in the printing process.

There are also seamless printing molds in which the seamless printing mold is manufactured on a roller. Generally, sleeves are used in this case whose outer face represents the layer that performs the printing, that is, only the roller liners are changed and transported and not the cores.

Typical materials for the sleeve layer that performs flexographic printing are rubber or photopolymers.

The polymerization technology of photopolymers has found a wide range of application. For this, an existing image is exposed on the surface of the cylinder or plate photopolymer, thereby hardening the photopolymer in the areas that have been exposed. Areas that have not been exposed are removed by washing. After drying, the printing mold is thus obtained.

An alternative of this is direct laser engraving. The areas of the printing mold that are not to be used are removed by the use of a laser, and the remaining areas and the removed areas then give rise to the printing mold. This is possible both in rubber-coated sleeves and also in sleeves in which a layer of a photopolymer is applied and polymerized on a bushing. Direct laser engraving is especially advantageous due to the fact that today the required information usually already exists in digital form, and through direct engraving the passage through the analog exposure system can be saved.

Due to the fact that the photopolymer is applied directly to the sleeve, the perimeter of the printing mold is predetermined within very narrow limits. To achieve a larger outer perimeter (= print length) for a given inner diameter of the sleeve, a large amount of photopolymer would have to be applied, which on the one hand implies a high cost and on the other, increasing the thickness becomes more difficult hardening of the photopolymer. In the event that there are some important layer thicknesses, the printing mold may have mechanical instability due to its reduced hardness, which negatively impacts the printing result.

The perimeter of the cylinder or sleeve is what determines the printing length that can be printed with the cylinder, that is, the repetition, which is the length after which the print pattern is repeated.

The objective of the present invention is to economically provide a sleeve coated with a photopolymer also with a greater total wall thickness and therefore greater print perimeters / print lengths, while maintaining the inside diameter.

This objective is solved by means of a sleeve for flexographic printing comprising

-a cap

-a middle layer located on the sleeve to increase the printing length, with a thickness of 2 to 20 mm and a hardness of ≥ 80 Shore A

-a layer that can be laser etched from a radiation-hardened polymer to increase repetition or print length.

The sleeve according to the invention has an intermediate layer on the bushing to increase the perimeter. This layer 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.

Thanks to this intermediate layer, the separation between the outer printing layer and the central axis increases, thereby increasing the printing length and larger patterns can be printed. This increases the repetition.

The outer layer is a radiation-hardened polymer, in particular a photopolymer, as has been used so far in the state of the art for the corresponding sleeves.

The sleeve bushing is normally made of a fiberglass reinforced plastic. But for example, carbon fiber reinforced plastics or other cap materials used in flexographic printing can also be used.

As an intermediate layer to increase the printing length, natural or synthetic rubber, but also polyurethane, is particularly suitable. The important thing is that the intermediate layer has a certain mechanical and geometric stability in order to be used as a component of the printing mold for flexographic printing. A material hardness ≥ 80 Shore A. has been particularly suitable.

Between the intermediate layer that increases the printing length and the layer that can be etched by the laser there may be in another embodiment another compressible layer, for example of a porous polyurethane.

Radiation curable polymers that can be etched by a laser are known to the specialist, for example from EP 1 710 093 A 1 or EP 1 424 210 A1, in which other suitable materials are described.

The object of the invention is also the use of the sleeve according to the invention which has a motif produced by means of laser engraving.

The sleeves according to the invention can be produced by a process comprising the following steps:

-preparation of a cap

-application of an intermediate layer to increase the print length

-eventually, surface treatment of the intermediate layer

-application of a radiation-curable polymer

- hardening of the polymer curable by radiation, by radiation.

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

The intermediate layer that extends the printing length can be produced in various ways. If it is, for example, a natural or synthetic rubber, it is necessary that the semi-manufactured sleeve be vulcanized first. A surface treatment of the intermediate layer will generally follow before applying the radiation-hardening polymer.

If polyurethane is used as an intermediate layer to extend the printing length, it can also be applied directly on the sleeve in principle. But there is also the possibility of surrounding the bushing of an outer bushing and introducing the polyurethane layer between the two bushes, then removing the outer bushing. You can also leave the outer cap to coat it with the photopolymer.

The radiation curable polymer that has been applied is then cured. In the case of a photopolymer this is done by exposure, for example with UV light.

Surprisingly, it has been found that, although the hardened polymer has sufficient adhesion on the intermediate layer that extends the printing length, the hardened polymer layer can instead be removed relatively easily, for example by tearing and tearing. In this way the intermediate layer that extends the printing length is exposed again, and it can be coated again with a radiation-curable polymer, possibly after a surface treatment. In this way, the inner sleeve can be reused many times with the intermediate layer that extends the printing length.

The object of the invention is also the use of an intermediate layer that increases the printing length having a thickness of 2 to 20 mm and a hardness of ≥ 80 Shore A in a sleeve with a cap and a layer that can be engraved by laser, of a polymer hardened by radiation, in order to increase the length of repetition of the sleeve.

Another object of the invention is a sleeve for flexographic printing, comprising -a cap

-a middle layer located on the cap, which increases the printing length, with a thickness of 2 to 20 mm and with a hardness of ≥ 80 Shore A

-a layer that can be etched by laser, of a polymer hardened by radiation to increase the repetition of the sleeve.

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

Figure 1 schematically shows the structure according to the invention. On a bushing 1 of a glass fiber reinforced plastic material there is an intermediate layer 2 for extending the printing length, on which there is a layer of a hardened photopolymer 3. The hardened photopolymer can then be provided by engraving Laser of a motif for flexographic printing.

Figure 2 shows the corresponding structure with a thicker intermediate layer 2.

Example

A corresponding application is obtained for example in the present case:

The printing machine is equipped with a sleeve housing with an inner diameter of 136,989 mm. With this, a printing perimeter of 450 mm could be achieved with the normal structure (bushing + coating = 3,125 mm).

But if it is desired to print a pattern with a length of 480 mm, an intermediate layer of an intermediate rubber with a hardness 80 Shore A is installed according to the invention additionally, so that a total thickness is obtained of the sleeve of 7.90 mm and therefore an outside diameter of 152.79 mm. With this additional hard intermediate layer, a greater printing perimeter is economically achieved and at the same time the mechanical stability of the printing mold is maintained.

Claims (11)

one.

Use of a sleeve for flexographic printing comprising -a cap (1) -a intermediate layer (2) located on the cap, which increases the length of printing, with a thickness of 2

at 20 mm and with a hardness of ≥ 80 Shore A - a layer that can be etched by laser, of a polymer (3) hardened by radiation to increase the repetition of the cuff.

2.

Use according to claim 1,

 characterized because The bushing (1) is made of a fiberglass reinforced plastic or a carbon fiber reinforced plastic. 3. Use according to claim 1 or 2,  characterized because The intermediate layer (2) is chosen from synthetic rubber, natural rubber, polyurethane or mixtures thereof. 4. Use according to at least one of claims 1 to 3,  characterized because The radiation hardened polymer is a hardened photopolymer. 5. Use according to at least one of claims 1 to 4,  characterized because Between the intermediate layer (2) that extends the printing length and the layer (3) that can be laser engraved, there is a compressible layer. 6. Use according to at least one of claims 1 to 5,  characterized because The layer (3) that can be laser engraved has a motif obtained by laser engraving.

7.

Use of an intermediate layer (2) that extends the printing length, with a thickness of 2 to 20 mm and a hardness of ≥ 80 Shore A for a sleeve with a bushing and a layer of a radiation-hardened polymer (3) that can be laser engraved to increase cuff repetition.

8.

Sleeve for flexographic printing comprising -a cap (1) -a intermediate layer (2) located on the cap, which increases the printing length, with a thickness of 2

at 20 mm and with a hardness of ≥ 80 Shore A - a layer that can be etched by laser, of a polymer (3) hardened by radiation to increase the repetition of the cuff.

9.

Process for manufacturing a sleeve according to claim 8, with the following steps: -preparation of a bushing (1) -application of an intermediate layer (2) to increase the print length -eventually, surface treatment of the intermediate layer (2)

-application of a radiation-curable polymer - hardening of the polymer curable by radiation, by radiation. 5 10. Method for reusing a sleeve according to claim 8, the steps comprising: - elimination of the radiation-hardened polymer layer (3) 10 -eventually surface treatment of the intermediate layer (2) that has been discovered -application of a polymer that can be hardened by radiation-hardening of the polymer that can be hardened by radiation, by radiation. fifteen 11. Use of a sleeve according to claim 8 in a method for direct laser recording.