Patent Application
20120103216
The invention relates to a multilayer sheet in the form of a printing blanket or of a printing plate for flexographic printing and letterpress printing with:
This type of sheet is disclosed by way of example in the following literature: U.S. Pat. No. 6,019,042; U.S. Pat. No. 6,935,236; EP 2 070 717 A1; WO 02/096648 A1; U.S. Pat. No. 5,798,202; and, U.S. Pat. No. 5,804,353; as well as Technik des Flexodruckes [Flexographic printing technology], p. 173 ff., 4th edition, 1999, Coating Verlag, St. Gallen (CH).
In the current prior art, in the context of flexographic and letterpress printing, the printing layer of the generic type of sheet with laser engraving is in most cases composed of a photopolymer. By way of example, the printing layer in U.S. Pat. No. 6,935,236 is composed of an elastomeric binder, of a polymerizable compound, of a photoinitiator or of a photoinitiator system, and also of a fine-particle filler, for example of a fumed oxide (silicon oxide, titanium oxide, aluminum oxide). The crosslinking of the entire area of the printing layer is achieved here via irradiation with light, for example with actinic light. Finally, a printing relief is engraved by means of a laser into the crosslinked printing layer. After the laser treatment, the printing layer is then also termed relief layer or printing plate.
However, a printing layer made of a photopolymer with laser engraving has the following attendant disadvantages:
A feature of the sheet of the invention with a view to eliminating the abovementioned disadvantages is that the polymeric material of the printing layer is a vulcanizate.
Vulcanizate is the term used for products or product components—in this case the printing layer—produced via vulcanization of a vulcanizable polymer mixture. The polymer mixture here comprises one or more rubber components. A vulcanizate is characterized by its elastic properties. Depending on the type of rubber used, crosslinking occurs using sulfur (e.g. in the case of NR) or peroxides (e.g. in the case of EPDM). A particularly important process is thermal vulcanization at temperatures of from 130 to 200° C. It is also possible to use cold vulcanization or radiation vulcanization.
For the vulcanizate, the following two variants are used in particular:
The vulcanizate is a vulcanized thermoplastic—free rubber mixture comprising at least one rubber component, and also mixing ingredients. Particular rubber components that may be mentioned are:
ethylene-propylene rubber (EPM)
ethylene-propylene-diene rubber (EPDM)
nitrile rubber (NBR)
(partially) hydrogenated nitrile rubber (HNBR)
fluororubber (FKM)
chloroprene rubber (CR)
natural rubber (NR)
styrene-butadiene rubber (SBR)
isoprene rubber (IR)
butyl rubber (IIR)
bromobutyl rubber (BIIR)
chlorobutyl rubber (CIIR)
butadiene rubber (BR)
chlorinated polyethylene (CM)
chlorosulfonated polyethylene (CSM)
polyepichlorohydrin (ECO)
ethylene-vinyl acetate rubber (EVA)
acrylate rubber (ACM)
ethylene-acrylate rubber (AEM)
silicone rubber (VMQ)
fluorinated methylsilicone rubber (MFQ)
perfluorinated propylene rubber (FFPM)
perfluorocarbon rubber (FFKM) polyurethane (PU)
The abovementioned types of rubber can be unblended. It is also possible to use a blend, in particular in conjunction with one of the abovementioned types of rubber, for example an NR/BR blend, or a BR/SBR blend.
The following are of particular importance: EPM, EPDM, SBR, BR, CR, NR, or NBR.
Typical mixing ingredients encompass at least one crosslinking agent or one crosslinking agent system (crosslinking agent and accelerator). Other mixing ingredients are typically a filler and/or a processing aid, and/or a plasticizer, and/or an antioxidant, and also optionally further additional materials (e.g. color pigments). Reference is made in this regard to the general prior art of rubber mixture technology.
The vulcanizate is a the thermoplastic vulcanizate comprising at least one thermoplastic component, at least one rubber component, which has been at least partially crosslinked, and also mixing ingredients.
The preferred thermoplastic components are polyethylene (PE), polypropylene (PP), polystyrene (PS), polyamide (PA) or polyester (PES).
Particular rubber components that may be mentioned are EPM, EPDM, SBR, BR, CR, NR or NBR, in particular in unblended form.
With respect to the mixing ingredients, reference is made to the abovementioned mixture technology, in particular to the teaching of U.S. Pat. No. 6,774,162.
In conjunction with the novel material for the printing layer, it is advantageous that the printing layer is in direct contact with a compressible layer, in contrast to a design in U.S. Pat. No. 6,019,042, in which the printing layer is in immediate contact with a reinforcement layer.
In a preferred layer structure, the compressible layer, which is in direct contact with the printing layer, is applied directly onto a reinforcement layer, so that the underlying structure is as follows, independently of the number of layers:
Based on this underlying structure there can be additional layers, in particular in terms of further compressible layers and reinforcement layers.
The compressible layer—also termed compression layer—serves for avoidance of flexing through volume reduction in the printing zone, and for compensation of impression differences. A decisive factor for the compressible layer is that it does not expand during compression, i.e., that its volume actually becomes smaller during compression, thus avoiding any lateral propagation of misalignment. By way of example, microbeads made from plastic can be used here in a rubber mixture, or a microporous cellular structure with gas inclusions can be used (foams). The relevant materials here are in particular polyurethanes, crosslinked polyethylenes, polypropylenes, NBR, neoprenes, and EPM. The modulus of elasticity is typically in the range from 1 MPa to 1000 MPa. With regard to further details relating to the compressible layer, reference is made to the literature cited in the introduction, in particular U.S. Pat. No. 6,019,042 and EP 2 070 717 A1.
The reinforcement layer used can comprise a textile structure, for example a woven material, or a foil, for example a polymer foil (e.g. polyamide foil) or metal foil. In the case of a sheet with many layers and at least two reinforcement layers, it is also possible to use a combination of a textile structure and a foil or a foil composite. By way of example, U.S. Pat. No. 6,019,042 describes a six-layer sheet with three woven layers and with a foil layer (polymer foil or metal foil).
The novel multilayer sheet in the form of a printing blanket or of a printing plate is delivered to customers in the form of roll product. The customer mounts the roll product onto a sleeve (adapter, printing cylinder) and then exposes the printing layer to a laser, with a subsequent cleaning process. By using modern laser technology, an engraved pattern using points with various depths and shapes within a grid can be introduced into the novel printing layer made of a vulcanizate. The engraved pattern is formed rapidly and cleanly, and without solvent. 100% registration accuracy and reproducibility is ensured here. A fact of great economic importance is that the process requires the customer to perform markedly fewer steps to produce the printing plate.
The multilayer sheet can also be supplied in the form of self-adhesive composite.
A comparative experiment and the results thereof are presented in the table below. In each case, the comparison relates to a three-layer printing plate with a layer sequence of printing layer, compressible layer, and reinforcement layer. The printing layer is composed in the first case, according to the prior art, of a photopolymer and in the second case, according to the invention, of a thermoplastic-free vulcanizate based on a peroxidically crosslinked EPDM. Test criteria in each case here are the most important technical printing data, namely the data for tonal value range, color intensity, and dynamic positional adjustment.
The following further comments relate to this comparative experiment and also to supplementary studies:
Inventive examples will now be used to illustrate the invention with reference to the drawings wherein:
In the case of a sheet as in
The multilayer sheets in the inventive examples of
It is understood that the foregoing description is that of the preferred embodiments of the invention and that various changes and modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2009 003 817.5 | Apr 2009 | DE | national |
This application is a continuation application of international patent application PCT/EP 2010/054168, filed Mar. 30, 2010, designating the United States and claiming priority from German application 10 2009 003 817.5, filed Apr. 23, 2009, and the entire content of both applications is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2010/054168 | Mar 2010 | US |
| Child | 13278468 | US |
