Coating for blanket rollers in printing presses

Abstract

A coating for a rubber blanket roller of a printing press, the coating having a multilayer structure including a rubber blanket layer (1) and an elastic layer (2), the elastic layer having a first side firmly attached to the rubber blanket layer and a second side in contact with the roller, wherein the rubber blanket layer (1) includes at least one printing sublayer (6) made of a polymer material and at least one fabric sublayer (3, 4, 5), and the elastic layer (2) having a tensile stress between 4.3 MPa and 1 MPa at 100% elongation according to standard ASTM D-412.

Description

Technical Field

[0001] This invention relates to a coating for a blanket cylinder of a printing press, particularly, but not limited to, a coating for a web offset printing press or a sheet offset printing press. Those skilled in the art know that in these printing presses, a coated sheet having a base of rubber material—commonly referred to in the industry as a “blank” or printing blanket (hereinafter the term “blank”)—is mounted on the printing cylinder, is made of metal and is rotatable about its own axis, and covers the side surfaces of the cylinder. Background Technology

[0002] The rubber blanket layer has corresponding metal rods on its two opposite sides. These metal rods are typically made of aluminum or steel and have a U-shaped cross-section, allowing them to be fitted and secured to the corresponding edges of the rubber blanket. The two metal rods are used to secure the rubber blanket to the aforementioned cylinder. Traditionally, the rubber blanket layer comprises at least two sublayers (a fabric sublayer and a rubber sublayer), but more complex rubber blanket layers have been produced that also include multiple fabric sublayers and multiple rubber sublayers. The fabric is, for example, cotton or PES fabric, or even made of metal (especially aluminum and steel alloys), while the rubber is, for example, an acrylonitrile / butyl type.

[0003] For each model of offset printing machine, the manufacturer specifies the total thickness of the coating covering the blanket cylinder. This total thickness is achieved in addition to the blanket layer (the actual coating) mentioned above, by using an undercoat layer (forming what is called the undercoat).

[0004] The bottom rubber blanket is often composed of a cardboard sheet or a polyester fiber sheet, which must be fixed to the rubber blanket roller by adhesive.

[0005] Sheet-fed presses typically use a cardboard bottom blanket applied via a fastening rod. Web offset presses use polyester sheets, which must be adhesively attached to the blanket cylinder.

[0006] To avoid the inconvenience caused by the complexity of operations required to remove and replace the coating, it has been proposed to use an elastic material layer as the base rubber blanket; which has self-leveling capabilities and thickness, thereby combining with the thickness of the rubber blanket layer to enable the maintenance of the desired total coating thickness.

[0007] The elastic material layer of the above type has direct adhesion capability, eliminating the need for additional adhesive products to bond the blanket roller, and has at least sufficient adhesion under both static and dynamic conditions to ensure, on the one hand, perfect adhesion to the blanket roller, and on the other hand, easy removal from it.

[0008] However, it has been found that when using a bottom blanket made of a known type of elastic material, the coating (especially in the case of web offset printing presses) may gradually suffer from tension loss on the blanket rollers.

[0009] Tension loss manifests as a loss of print registration and a subsequent decline in print quality.

[0010] To restore optimal printing settings, the printing process needs to be stopped and the coating tension adjusted before restarting. It's easy to imagine the loss of all productivity advantages in this situation.

[0011] It has also been observed that bottom rubber blankets made of known types of elastic materials may generate tension concentrated in the gap region of the rubber blanket roller, where the coating following the contour of the rubber blanket roller forms an acute angle.

[0012] These tensions, in turn, can create further resistance to the tension of the rubber blanket, leading to a loss of performance.

[0013] Therefore, the objective of this invention is to provide a coating for a rubber blanket roller in a printing press that enables the elimination of the aforementioned technical defects in the prior art. Summary of the Invention

[0014] Specifically, one object of the present invention is to provide a coating for a blanket roller of a printing press that ensures perfect adhesion to the blanket roller without complicating disassembly and replacement operations.

[0015] Another object of the present invention is to provide a long-lasting coating for a rubber blanket roller for a printing press.

[0016] These objectives are achieved by a coating for a rubber blanket roller of a printing press having a multilayer structure comprising a rubber blanket layer and an elastic layer having a first side firmly attached to the rubber blanket layer and a second side adhered to the roller, wherein the rubber blanket layer comprises at least one polymer printing sublayer and at least one fabric sublayer, characterized in that the elastic layer has a tensile stress between 4.3 MPa and 1 MPa at 100% elongation according to standard ASTM D-412.

[0017] In one embodiment, the at least one printed sublayer is made of a cross-linked elastic polymer.

[0018] In one embodiment, the multilayer structure includes at least one compressible sublayer made of an expanded cross-linked elastic polymer.

[0019] According to standard ASTM D-2240 (ISO 868), the elastic layer has a hardness between 70 Shore A and 45 Shore A.

[0020] Preferably, the elastic layer is made of a material comprising at least thermoplastic polyurethane.

[0021] The elastic layer maintains its self-leveling capability and thickness, which, combined with the thickness of the rubber sheet layer, enables the maintenance of the required total coating thickness.

[0022] The elastic layer also offers superior direct adhesion to the blanket roller without the need for additional adhesive products. The properties of the elastic layer ensure that the coating remains perfectly adhered to the blanket roller under both static and dynamic conditions and is easy to remove.

[0023] The coating perfectly maintains the correct tension on the blanket roller, thus ensuring proper print registration and consequently print quality.

[0024] Because the printing process only experienced a few brief interruptions, the productivity of the printing press was increased.

[0025] In fact, due to the properties of the elastic layer, the elastic restoring force that may contribute to the tension loss of the aforementioned known types of coatings is reduced.

[0026] Furthermore, due to the properties of the elastic layer, adhesion loss of the coating is avoided in the area between the rubber blanket and the roller.

[0027] Furthermore, the elastic layer significantly reduces the penetration of cleaning solvents into the blanket sheet. Over time, the penetration of cleaning solvents can cause the layers constituting the coating to separate and laterally expand, leading to loss of print registration, damage to the support sheet, and ultimately structural failure.

[0028] Because the elastic layer is tightly bonded to the surface of the rubber blanket roller, the surface of the rubber blanket roller protects the roller from corrosion.

[0029] An elastomer layer is applied to the inner surface of a rubber blanket layer using a known type of process to achieve the thickness specified by the machine manufacturer and, in any case, the thickness required by the user (thus, the user can obtain a coating thickness customized to their specific needs). The process of bonding the elastomer layer to the rubber blanket layer can be of mechanical, physical, and / or chemical type, such as by a flat-end extrusion process, calendering, spreading, or other processes.

[0030] An elastomer layer can be produced and simultaneously applied to a rubber sheet layer, or an elastic layer can be produced and then bonded to a rubber sheet layer.

[0031] It can be verified that using the above-mentioned elastomer layer with a thickness between 0.05mm and 1.50mm can actually meet all market demands.

[0032] Preferably, for the coating according to the invention, the rubber blanket layer has the following physicochemical properties according to standard ASTM D 1894: static friction coefficient µ s > 0.1; coefficient of kinetic friction µk > 0.1.

[0033] These properties refer to the elastomer / steel surface. The invention will be more readily understood through the following description of exemplary embodiments thereof. Attached Figure Description

[0034] Reference will be made to the accompanying drawings in this specification, wherein:

[0035] Figure 1 A cross-section of a portion of the coating according to the invention is shown schematically;

[0036] Figure 2 The coating applied to the rubber blanket roller is shown, and magnified details are also shown. Detailed Implementation

[0037] As can be seen from the figure, coating 100 includes a conventional rubber blanket layer 1 and an elastomer layer 2 applied to the inner surface of rubber blanket layer 1 (the surface facing rubber blanket roller 10). In the specific case shown, rubber blanket layer 1 consists of a series of sublayers.

[0038] The rubber sheet layer 1 specifically includes at least one polymer printing sublayer 6 and at least one fabric sublayer 3, 4, 5.

[0039] In one embodiment, the polymer printed sublayer 6 is made of a crosslinked elastic polymer.

[0040] Furthermore, the multilayer structure may include at least one compressible sublayer made of an expanded crosslinked elastic polymer 9.

[0041] In the illustrated case, the rubber blanket layer 1 comprises three cotton fiber-based fabrics 3, 4, 5 (but as previously mentioned, they may also be made of PES fibers or carbon fibers or metal substrates), an outer printed sublayer 6 formed of conventional nitrile / butyl rubber (forming the side of the rubber blanket layer opposite to the surface of the rubber blanket roller 10), one or more intermediate rubber sublayers 7, 8 having known and variable formulations, and a compressible sublayer 9 made of an expanded closed-cell crosslinked elastic polymer formed of nitrile / butyl rubber modified with a foaming agent.

[0042] The composition and structure of the blanket layer 1 can obviously differ from those just described, depending on the type of printing press.

[0043] Assuming newspaper printing is done using a Roland Colorman or Uniman machine, commercial printing using a Lithoman machine, or a Heidelberg Speedmaster 102 sheetfed printing press, the thickness of blanket layer 1 is 1.70 mm to 1.95 mm, depending on the press model.

[0044] Specifically, for a 48-page Lithoman machine, a coating with a total thickness of 1.90 mm can be obtained by using a 1.70 mm Vulcan Alto type rubber blanket layer 1 and an elastomer layer 2 with the aforementioned properties ranging from 2 to 0.20 mm.

[0045] Advantageously, the elastic layer 2 has a tensile stress between 4.3 MPa and 1 MPa at 100% elongation, according to standard ASTM D-412 (ISO 527).

[0046] Preferably, the elastic layer 2 has a tensile stress between 2.5 MPa and 1 MPa at 100% elongation according to standard ASTM D-412 (ISO 527).

[0047] Furthermore, according to standard ASTM D-2240, the elastic layer 2 has a hardness between 70 Shore A and 45 Shore A.

[0048] Preferably, according to standard ASTM D-2240, the elastic layer 2 has a hardness between 60 Shore A and 45 Shore A.

[0049] The elastic layer 2 is made of a material comprising at least thermoplastic polyurethane.

[0050] Preferably, the elastic layer 2 is made of a material comprising at least an aromatic polyester-based thermoplastic polyurethane. Specifically, it has been found advantageous to use caprolactone-modified thermoplastic polyurethane.

[0051] The material of the elastic layer 2 can be advantageously incorporating silicone resin to improve abrasion resistance and processability, specifically the extrusion suitability of the material.

[0052] The material of elastic layer 2 does not contain plasticizers, thereby reducing the risk of product degradation over time.

[0053] The elastic layer 2 also contains a thermoplastic elastomer, which is present in an amount between 1% and 15% by weight.

[0054] Preferably, the thermoplastic elastomer added to the elastic layer 2 is present in an amount between 8% and 12% by weight.

[0055] The additive improves the production process and reduces surface friction, thereby increasing the slidability of the coating on the surface of the rubber blanket roller.

[0056] As described above, the thickness of the elastic layer 2 is between 0.05 mm and 1.50 mm, with a tolerance of + / - 0.01 mm.

[0057] According to the present invention, the elastic recovery force of the coating is limited by the specific characteristics of the elastic layer 2, which are defined by the initial selection of its elastic elongation and its hardness value.

[0058] For example, tensile tests were performed on two reference samples consisting of the same rubber sheet layer and different elastic layers.

[0059] The reference rubber blanket layer thickness is 1.95 ± 0.02 mm. The reference rubber blanket layer is manufactured by Trelleborg and is called Rollin Metro.

[0060] Advantageously, the elastic layer of the first reference sample has a tensile stress between 4.3 MPa and 1 MPa at 100% elongation according to standard ASTM D-412 (ISO 527). According to standard ASTM D-2240 (ISO 868), the elastic layer has a hardness between 70 Shore A and 45 Shore A.

[0061] Advantageously, the elastic layer of the second reference sample has a tensile stress greater than 4.3 MPa at 100% elongation according to standard ASTM D-412 (ISO 527). According to standard ASTM D-2240 (ISO 868), the elastic layer has a hardness greater than 70 Shore A.

[0062] The test was conducted at room temperature (23℃). The reference sample had a length of 10.0 ± 0.1 cm, a width of 2.5 ± 0.1 cm, and a thickness of 2.80 ± 0.05 mm.

[0063] Choose the long side that is parallel to the coating positioning direction on the rubber blanket roller.

[0064] The following results were obtained (average of three tests), expressed as a percentage of elongation at a given stress:

[0065] # A B C D Stress (N) 113 226 544 1600 Elongation of the first reference sample 1.66% 2.04% 2.93% 6.64% Elongation of the second reference sample 1.61% 1.91% 2.60% 5.30%

[0066] Instrument test results show that the elongation of the first reference sample is greater than that of the second reference sample.

[0067] It was found that the deformability of the elastic layer 2 affects the tension generated in the gap region 11 of the rubber blanket roller 10 (i.e., the region where the coating 100 is mechanically fixed to the rubber blanket roller 10).

[0068] It was found that selecting an elastic layer 2 with a hardness between 70 Shore A and 45 Shore A, preferably between 60 Shore A and 45 Shore A, is convenient (measured according to standard ASTM D-2240) in order to significantly reduce tension in the gap region.

[0069] Once the coating 100 is fixed to the interior of the gap region 11, it can follow the surface of the rubber blanket roller 10 throughout its periphery.

[0070] Specifically, at the outlet 12 of the gap region 11, an acute angle ∆ is created between the recessed surface 13 of the rubber blanket roller 10 and the cylindrical surface 14 of the rubber blanket roller 10, and the coating 100 is able to follow the contours of the surfaces 13 and 14 of the rubber blanket roller 10.

[0071] The deformability and low hardness of the elastic layer 2 improve the adhesion of the coating to the rubber blanket roller 10.

[0072] Improved adhesion prevents cleaning products from penetrating between the coating and the rubber blanket roller 10, thereby enhancing protection against corrosive chemicals.

[0073] The elastomer layer 2 maintains its self-leveling capability and thickness, thus combining with the thickness of the blanket layer 1 to maintain the required total thickness of the multilayer structure. The second surface of the elastomer layer 2 retains direct adhesion capability, eliminating the need for additional adhesive products to bond the blanket roller, and exhibits at least sufficient adhesion under both static and dynamic conditions to ensure perfect adhesion to the blanket roller on the one hand, and easy removal from it on the other. Furthermore, due to the special properties of the elastomer layer 2, the coating 100 has the ability to accurately replicate the surfaces 13, 14 of the blanket roller 10, even in the presence of acute angles ∆.

[0074] The coating conceived for use in printing presses is readily modified and varied, all of which fall within the scope of the inventive concept; furthermore, all details can be replaced with technically equivalent elements. The materials used and the dimensions can be determined as needed and based on existing technology during implementation.

Claims

1. A coating (100) for a rubber blanket roller (10) of a printing press, the coating having a multilayer structure including a rubber blanket layer (1) and an elastic layer (2), the elastic layer having a first side firmly attached to the rubber blanket layer and a second side adhered to the roller, wherein the rubber blanket layer (1) includes at least one printing sublayer (6) made of a polymer material and at least one fabric sublayer (3, 4, 5). The elastic layer (2) has self-leveling capability and thickness, which, combined with the thickness of the rubber sheet layer (1), enables the maintenance of the required total thickness of the multilayer structure. The second side of the elastic layer (2) has the ability to adhere directly to the rubber blanket roller (10) without the need for additional adhesive products, and the degree of adhesion under both static and dynamic conditions is sufficient to ensure, on the one hand, perfect adhesion to the rubber blanket roller (10), and on the other hand, easy removal from it. Furthermore, the elastic layer (2) has a tensile stress between 4.3 MPa and 1 MPa at 100% elongation according to standard ASTM D-412 (ISO 527), and a hardness between 70 Shore A and 45 Shore A according to standard ASTM D-2240. The coating (100) is able to follow the surface (13, 14) of the rubber blanket roller (10) at the outlet (12) of the gap region (11), wherein an acute angle (∆) is created between the recessed surface (13) of the rubber blanket roller (10) and the cylindrical surface (14).

2. The coating (100) of a blanket cylinder (10) for a printing press according to claim 1, characterized in that The elastic layer (2) has a tensile stress between 2.5 MPa and 1 MPa at 100% elongation according to standard ASTM D-412 (ISO 527).

3. The coating (100) of a blanket cylinder (10) for a printing press according to claim 1, characterized in that The elastic layer (2) has a hardness between 60 Shore A and 45 Shore A according to standard ASTM D-2240.

4. The coating (100) of a blanket cylinder (10) for a printing press according to claim 1, characterized in that The elastic layer (2) is made of a material containing siloxanes but without plasticizers.

5. The coating (100) of a blanket cylinder (10) for a printing press according to claim 1, characterized in that The elastic layer (2) is made of a material comprising at least thermoplastic polyurethane.

6. The coating (100) of a blanket cylinder (10) for a printing press according to claim 5, characterized in that The elastic layer (2) is made of a material comprising at least aromatic polyester-based thermoplastic polyurethane.

7. The coating (100) of a blanket cylinder (10) for a printing press according to claim 5 or 6, characterized in that The elastic layer (2) is made of a material containing additives, the additives including thermoplastic elastomers present in amounts between 1% and 15% by weight.

8. The coating (100) for the blanket roller (10) of a printing press according to claim 7, characterized in that... The thermoplastic elastomer is present in an amount between 8% and 12% by weight.

9. The coating (100) for the blanket roller (10) of a printing press according to claim 1, characterized in that... The thickness of the elastic layer is between 0.05 mm and 1.50 mm, with a tolerance of + / - 0.01 mm.

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