Top layer of a printing blanket for the impression cylinder of a printing machine

Abstract

The top layer of the printing blanket for the impression cylinder of a printing machine comprises an outer printing surface intended to contact the substrate to be printed and is made of a material comprising a polyester-based thermoplastic polyurethane polymer including at least one diisocyanate, at least one chain extender, and at least one macrodiol.

Description

[0001] TOP LAYER OF A PRINTING BLANKET FOR THE IMPRESSION CYLINDER OF A

[0002] PRINTING MACHINE

[0003] DESCRIPTION

[0004] The present invention relates to the top layer of a printing blanket for the impression cylinder of a printing machine.

[0005] The typical, though not exclusive, reference sector is represented by printing machines of the Web Offset or Sheet Feed type (e.g., label printing machines).

[0006] As is well known to experts in the field, in these printing machines, the impression cylinder, made of metal and rotating around its own axis, is covered with a coating consisting of a printing blanket and an underblanket.

[0007] The printing blanket features a rubber top layer and a carcass.

[0008] The top layer of the printing blanket is equipped with an outer surface designed for printing on a substrate, typically paper or metal, and an inner surface facing the carcass.

[0009] The top layer of the printing blanket is traditionally made of nitrile / butyl rubber or EPDM. The underblanket, on the other hand, has a surface that covers the impression cylinder. The underblanket serves to achieve the overall required thickness of the coating.

[0010] The underblanket is often made of a sheet of cardboard, polyester, or TPU, which must be secured to the impression cylinder using adhesive.

[0011] One of the most common drawbacks of a commercially available rubber printing blanket top is its suboptimal resistance to abrasion caused by the substrate to be printed and the format edge marks. Another drawback is related to the quality and sharpness of the print delivered by the rubber printing blanket top, which sometimes does not meet the required specifications. An additional drawback is the potential difficulty in correctly mounting the rubber printing blanket in the gap of the impression cylinder due to its hardness. The aim of the present invention, therefore, is to provide a top layer for a printing blanket used on the impression cylinder of a printing machine that addresses and resolves the technical issues encountered with existing technologies.

[0012] In particular, an objective of the present invention is to provide a printing blanket top layer with improved abrasion resistance.

[0013] Another objective of the present invention is to provide a printing blanket top capable of offering improved print quality.

[0014] An additional objective of the present invention is to provide a printing blanket top with greater durability.

[0015] These objectives are achieved by a printing blanket top for the impression cylinder of a printing machine, comprising an outer printing surface intended to contact the substrate to be printed, characterized by the fact of being made of a material comprising an aromatic, polyester-based thermoplastic polyurethane polymer, including at least one diisocyanate, at least one chain extender, and at least one macrodiol.

[0016] Preferably, the at least one diisocyanate includes a 4,4 ’-dibenzyl diisocyanate (DBDI). In a preferred embodiment of the invention, the at least one chain extender includes ethylene glycol (EG) and / or 1,4-butanediol (BDI).

[0017] In another preferred embodiment, the at least one macrodiol includes polyethylene adipate (PEA). The conformational mobility of the selected diisocyanate provides an unusually wide range of mechanical, physical, and chemical properties.

[0018] Advantageously, the printing blanket top according to the invention has a hardness between 40 and 60 Shore A.

[0019] These hardness values are ideal for facilitating the proper mounting of the coating on the impression cylinder. The use of an aromatic, polyester-based thermoplastic polyurethane polymer for manufacturing the printing blanket top allows for highly effective cleaning of ink from the top layer, with reduced consumption of ketonic solvents compared to a traditional rubber printing blanket top.

[0020] Thanks to the use of an aromatic, polyester-based thermoplastic polyurethane polymer, the printing blanket top can be applied in both traditional and innovative printing technologies, such as UV printing technology.

[0021] The present invention also discloses a printing blanket that includes such a top layer, as well as a printing cylinder coating for a printing machine that includes this printing blanket in combination with an underblanket made of a material comprising a polyester-based thermoplastic polyurethane polymer.

[0022] The inclusion of an underblanket made of a polyester-based thermoplastic polyurethane polymer ensures, under both static and dynamic conditions, the maintenance of perfect adhesion of the coating to the impression cylinder and its easy removal from it.

[0023] The coating is fully capable of maintaining the correct tension on the impression cylinder, thereby ensuring print registration and, consequently, print quality.

[0024] The printing blanket can be conveniently manufactured not only by coating but also through bubble extrusion or 3D printing.

[0025] The printing blanket can be applied to the underblanket using permanent adhesive film technology or through calendering.

[0026] In terms of circular economy, sustainability, and ecology, the printing blanket is easy to dispose of, can be produced with low energy consumption — particularly because it does not require the highly energy-intensive vulcanization process necessary to provide abrasion resistance and durability to traditional rubber printing blankets — and significantly reduces ink consumption.

[0027] The invention will be more easily understood through the following description of an exemplary embodiment. The top layer of the printing blanket for an impression cylinder of a printing machine comprises, as mentioned, an outer printing surface intended to come into contact with the substrate to be printed.

[0028] The top layer of the printing blanket includes an aromatic, polyester-based thermoplastic polyurethane polymer comprising at least one diisocyanate, at least one chain extender, and at least one macrodiol.

[0029] Advantageously, the chain extender includes ethylene glycol (EG) and / or 1,4-butanediol (BDI). Additionally, the macrodiol advantageously includes polyethylene adipate (PEA).

[0030] The polyethylene adipate (PEA) has a molecular weight of 2000 ± 50 Da.

[0031] Finally, the diisocyanate advantageously includes at least one 4,4’-dibenzyl diisocyanate (DBDI). Alternatively, the diisocyanate may be a 4,4’ -methylene bis(phenyl isocyanate) (MDI).

[0032] In one embodiment, the aromatic, polyester-based thermoplastic polyurethane polymer includes a first chain extender, specifically monoethylene glycol (MEG), in combination with a second chain extender, particularly 1,4-butanediol (BDI).

[0033] Specifically, it has been found advantageous to use an aromatic, polyester-based thermoplastic polyurethane polymer with an MDI:BDO:MEG ratio of 1 :4:4.

[0034] More precisely, it has been found advantageous to use an aromatic, polyester-based thermoplastic polyurethane polymer with an MDI:BDO:ADI:MEG ratio of 1 :4:8:4, where ADI refers to a lipidic acid that forms a polyadipate in combination with one of the aforementioned chain extenders.

[0035] In one embodiment, the aromatic, polyester-based thermoplastic polyurethane polymer has a molecular weight of 147,000 ± 5,000 Da.

[0036] The top layer of the printing blanket made of the aromatic, polyester-based thermoplastic polyurethane polymer as defined above has a hardness between 40 and 60 Shore A, measured according to the current ASTM D-2240 standard. The top layer of the printing blanket made of the aromatic, polyester-based thermoplastic polyurethane polymer as defined above has a glass transition temperature of -40°C.

[0037] The top layer of the printing blanket is advantageously free from plasticizing agents and solvents. The top layer of the printing blanket advantageously contains an antistatic agent that prevents dust adhesion.

[0038] This agent can be incorporated through treatment with silicone-based release paper.

[0039] Such release paper, for example, but not limited to, release paper produced by Sappi or Favini, releases particles at temperature that penetrate the porosity of the printing blanket's top layer.

[0040] The outer surface of the top layer of the printing blanket may have a finish, and advantageously features a surface roughness between 0.4 and 1.4 microns.

[0041] The printing blanket comprises, in addition to the aforementioned top layer, a carcass that includes at least one fabric layer, such as a cotton canvas, and a polyurethane adhesive layer that bonds the fabric layer to the inner surface of the top layer.

[0042] Below are some examples of printing blankets according to the invention.

[0043] Example 1

[0044] The top layer of the printing blanket is a TPU film, ESTANE™ 54600 by Lubrizol, with a thickness of 3.50 mm. It is bonded to a cotton fabric layer with a thickness of 1.50 mm using a urethane adhesive film. The outer surface of the top layer is subsequently surface-finished using Sappi release paper.

[0045] The total thickness of the printing blanket is 2.35 mm, the surface roughness is 0.8 pm, and the hardness is 55 Shore A.

[0046] Example 2

[0047] The top layer of the printing blanket is a TPU film, ESTANE™ 5725 by Lubrizol, with a thickness of 3.50 mm. It is bonded to a cotton fabric layer with a thickness of 1.50 mm using a urethane adhesive film. The outer surface of the top layer is subsequently surface-finished using Sappi release paper.

[0048] The total thickness of the printing blanket is 4.45 mm, the surface roughness is 1.2 pm, and the hardness is 55 Shore A. The printing blanket, in combination with an underblanket, forms a printing coating for the impression cylinder of a printing machine.

[0049] The underblanket, in turn, is made of a single-layer or multi-layer material that includes a polyester-based thermoplastic polyurethane polymer.

[0050] The top layer of the printing blanket and the printing coating for printing machines, as conceived, have demonstrated excellent results in terms of sharpness and print quality, since they allow for achieving a significantly crisper halftone, a dot with much better coverage and definition, and solid areas with high clarity and resolution.

[0051] The top layer, the printing blanket, and the printing coating for printing machines, as conceived, are subject to numerous modifications and variations, all of which fall within the scope of the inventive concept. Additionally, all details can be replaced by technically equivalent elements.

[0052] In practice, the materials used, as well as the dimensions, can be adapted as needed based on requirements and the state of the art.

Claims

CLAIMS1. Top layer of a printing blanket for the impression cylinder of a printing machine, comprising an outer printing surface intended to contact the substrate to be printed, characterized by being made of a material comprising an aromatic, polyester-based thermoplastic polyurethane polymer including at least one diisocyanate, at least one chain extender, and at least one macrodiol.

2. Top layer of a printing blanket for the impression cylinder of a printing machine according to claim 1, characterized in that said at least one diisocyanate includes 4,4’-dibenzyl diisocyanate (DBDI).

3. Top layer of a printing blanket for the impression cylinder of a printing machine according to any preceding claim, characterized in that said at least one chain extender includes ethylene glycol (EG) and / or 1,4-butanediol (BDI).

4. Top layer of a printing blanket for the impression cylinder of a printing machine according to any preceding claim, characterized in that said at least one macrodiol includes polyethylene adipate (PEA).

5. Top layer of a printing blanket for the impression cylinder of a printing machine according to any of claims 1 to 3, characterized in that said at least one diisocyanate includes 4,4’- methylene bis(phenyl isocyanate) (MDI).

6. Top layer of a printing blanket for the impression cylinder of a printing machine according to any preceding claim, characterized in that said top layer has a hardness between 40 and 60 Shore A.

7. Top layer of a printing blanket for the impression cylinder of a printing machine according to any preceding claim, characterized in that said outer surface of said top layer has a finish with a roughness between 0.4 and 1.4 microns.

8. Top layer of a printing blanket for the impression cylinder of a printing machine according to any preceding claim, characterized in that said outer surface of said top layer has been treated with silicone-based release paper.

9. Printing blanket, comprising a top layer according to any preceding claim, characterized by comprising at least one fabric layer and a polyurethane adhesive layer that bonds said at least one fabric layer to said inner surface of the top layer.

10. Printing coating for the impression cylinder of a printing machine, comprising a printing blanket according to the preceding claim in combination with an underblanket made of a material including a polyester-based thermoplastic polyurethane polymer.