Coatings for printing press blanket cylinders

Abstract

A coating for a blanket cylinder of a printing press has a multi-layer structure comprising a blanket layer (1) and an elastomeric layer (2) having a first surface firmly connected to said blanket layer and a second surface in contact with said cylinder, the blanket layer (1) comprising at least one printing sublayer (6) made of a polymeric material and at least one fabric sublayer (3, 4, 5), the elastomeric layer (2) having a tensile stress at 100% elongation comprised between 4.3 MPa and 1 MPa according to the ASTM D-412 standard.

Description

[Technical Field]

[0001] This invention relates to coatings for blanket cylinders in printing presses, particularly, but not exclusively, offset or sheet-fed printing presses. [Background technology]

[0002] As known to those skilled in the art, in these printing presses, a coating sheet (known in the industry simply as a "blanket" or printing blanket; hereafter the term blanket will be used) having a base layer of rubberized material is attached to a metal printing cylinder that is rotatable about its own axis and covers the side of the cylinder.

[0003] The blanket layer has, on two opposite sides, respective metal bars with a U-shaped cross section, usually made of aluminum or steel, which fit onto the corresponding edges of the blanket and can then be fixed there. The two metal bars serve to fix the blanket to the cylinder. Traditionally, the blanket layer includes at least two sublayers, namely a fabric sublayer and a rubber sublayer, but blanket layers with more complex structures have also been produced in the past, including two or more fabric sublayers and two or more rubber sublayers. The fabric is, for example, a cotton fabric or a PES fabric, but can also be made of metal (in particular an alloy of aluminum and steel). The rubber, on the other hand, is, for example, a nitrile / butyl type rubber.

[0004] For each model of offset printing press, the manufacturer indicates the total thickness of the coating covering the blanket cylinder, which can also be achieved by using an undercoating (forming the so-called underblanket) in addition to the blanket layer (actual coating) mentioned above.

[0005] The underblanket is often made of a sheet of cardboard or polyester and must be secured to the blanket cylinder by adhesive.

[0006] Sheet-fed presses typically use a cardboard underblanket attached by a fixed bar, while offset presses use a sheet of polyester that must be secured onto the blanket cylinder by adhesive.

[0007] In order to avoid the inconveniences associated with the complexity of the operations required to remove and replace the coating, a layer of elastomeric material is proposed as an underblanket, which has self-leveling capabilities and a thickness which, combined with the thickness of the blanket layer described above, allows the desired overall thickness of the coating to be maintained.

[0008] The layer of elastomeric material of the type described above has the ability to directly adhere to the blanket cylinder without the need for an additional adhesive product, and the degree of adhesion is at least sufficient to ensure, on the one hand, the maintenance of perfect adhesion to the blanket cylinder and, on the other hand, easy removal therefrom under the static and dynamic conditions of the cylinder described above.

[0009] However, it has been found that with underblankets made from known types of elastomeric materials, the coating can gradually suffer a loss of tension on the blanket cylinder, particularly in offset printing presses.

[0010] Loss of tension manifests itself as loss of print registration and a resulting degradation of print quality.

[0011] To return to the optimum print settings, the printing process must be stopped, the coating tension adjusted, and then the printing process restarted - and as you can imagine, all of the productivity benefits are lost.

[0012] It has also been observed that underblankets made from known types of elastomeric materials can experience concentrated tension in the area of ​​the gap in the blanket cylinder where the coating, following the contours of the blanket cylinder, forms an acute angle.

[0013] These tensions, in turn, can cause additional resistance to tension in the blanket, resulting in loss of performance.

[0014] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a coating for a blanket cylinder of a printing press, which makes it possible to eliminate the aforementioned technical drawbacks of the prior art.

[0015] In particular, one object of the present invention is to provide a coating for a printing press blanket cylinder that ensures perfect adhesion to the blanket cylinder without complicating removal and replacement procedures.

[0016] Another object of the present invention is to provide a long-lasting coating for a blanket cylinder of a printing press. Summary of the Invention

[0017] These objects are achieved by a coating for a blanket cylinder of a printing press, the coating having a multilayer structure including a blanket layer and an elastomeric layer, the elastomeric layer having a first surface rigidly connected to the blanket layer and a second surface adhesive to the cylinder, the blanket layer including at least one polymer printing sublayer and at least one fabric sublayer, the elastomeric layer being characterized in that it has a tensile stress at 100% elongation comprised between 4.3 MPa and 1 MPa according to ASTM D-412 standard.

[0018] In one embodiment, the at least one printed sub-layer is made from a cross-linked elastomeric polymer.

[0019] In one embodiment, the multi-layer structure described above includes at least one compressible sub-layer made from an expanded cross-linked elastomeric polymer.

[0020] The elastomer layer has a hardness comprised between 70 Shore A and 45 Shore A according to the ASTM D-2240 standard (ISO 868).

[0021] Preferably, the elastomer layer is made from a material containing at least a thermoplastic polyurethane.

[0022] The elastomeric layer maintains a thickness that allows for self-leveling capabilities and, in combination with the thickness of the blanket layer, allows the desired overall thickness of the coating to be maintained.

[0023] The elastomeric layer also has an improved ability to adhere directly to the blanket cylinder without the need for an additional intervening adhesive product. The properties of the elastomeric layer ensure that the coating both maintains full adhesion to the blanket cylinder under static and dynamic conditions and is easily removed.

[0024] The coating is perfectly capable of maintaining the correct tension on the blanket cylinder, ensuring proper print registration and, therefore, print quality.

[0025] If the printing process is subject to only a few short interruptions, the productivity of the printing press is increased.

[0026] In fact, thanks to the properties of the elastomeric layer, the elastic restoring forces that may contribute to the aforementioned loss of tension in coatings of known types are reduced.

[0027] Furthermore, due to the properties of the elastomeric layer, loss of adhesion of the coating is avoided in the area of ​​the gap in the blanket cylinder.

[0028] Additionally, the elastomeric layer significantly reduces penetration of cleaning solutions into the blanket sheet, which over time can lead to separation of the coating layers, lateral swelling and consequent loss of print registration, and damage to the support sheet and resulting structural collapse.

[0029] The intimate bond between the elastomer layer and the surface of the blanket cylinder provides the blanket cylinder with protection against corrosion of the cylinder.

[0030] The elastomeric layer is applied to the inner surface of the blanket layer by a process of known type to obtain a thickness specified by the machine manufacturer or, in any case, desired by the user (so that the user can have a coating of a thickness tailored to his or her specific needs). The process for bonding the elastomeric layer to the blanket layer may be of the mechanical, physical, and / or chemical type, for example by a flat head extrusion process, calendering, spreading, or another process.

[0031] The elastomeric layer can be applied to the blanket layer as it is being manufactured, or it can be bonded to the blanket layer after it is manufactured.

[0032] It has been possible to verify that thicknesses of the aforementioned elastomer layers comprised between 0.05 mm and 1.50 mm are in fact capable of covering all market demands.

[0033] Preferably, for a coating according to the invention, the blanket layer has physicochemical properties such that the static coefficient of friction μs is greater than 0.1 and the dynamic coefficient of friction μk is greater than 0.1 according to the ASTM D1894 standard. These properties are for elastomer / steel surfaces. [Brief explanation of the drawings]

[0034] The present invention will be more readily understood from the following description of exemplary embodiments thereof.

[0035] In this description, reference is made to the accompanying drawings.

[0036] [Figure 1] 1 shows a schematic cross section of a portion of a coating according to the invention. [Figure 2] 1 shows the coating applied to the blanket cylinder. [Figure 3] An enlarged detail of FIG. 2 is shown. DETAILED DESCRIPTION OF THE INVENTION

[0037] As can be seen, coating 100 includes a conventional blanket layer 1 and an elastomeric layer 2 applied to the inner surface (the surface facing toward blanket cylinder 10) of blanket layer 1. In the specific example shown, blanket layer 1 is composed of a series of sublayers.

[0038] The blanket layer 1 includes, inter alia, at least one polymeric printed sublayer 6 and at least one fabric sublayer 3, 4, 5.

[0039] In one embodiment, the polymeric print sublayer 6 is made from a cross-linked elastomeric polymer.

[0040] Additionally, the multi-layer structure may include at least one compressible sub-layer made from an expanded cross-linked elastomeric polymer 9 .

[0041] In the illustrated case, the blanket layer 1 comprises three cotton fiber-based fabrics 3, 4, 5 (but as already mentioned, they can also be made from PES fiber or carbon fiber or a metal substrate), an outer printing sublayer 6 formed from conventional nitrile / butyl rubber (which constitutes the face of the blanket layer opposite the surface of the blanket cylinder 10), one or more intermediate sublayers 7, 8 of rubber with known, variable formulations, and a compressible sublayer 9 made from an expanded, closed-cell cross-linked elastomeric polymer formed from nitrile / butyl rubber, modified by the addition of a blowing agent.

[0042] The composition and structure of the blanket layer 1 may obviously differ from that described above depending on the type of printing press.

[0043] Assuming that a Roland Colorman or Uniman press for newspapers, or a Lithoman press for commercial printing, or a Heidelberg Speedmaster 102 sheet-fed press is used, the thickness of the blanket layer 1 is 1.70 to 1.95 mm, depending on the press model.

[0044] In particular, a 48 page Lithoman machine using a 1.70 mm Vulcan Alto model blanket layer 1 and a 2 to 0.20 mm elastomer layer 2 having the properties described above results in a coating having a total thickness of 1.90 mm.

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

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

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

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

[0049] The elastomer layer 2 is made from a material that includes at least a thermoplastic polyurethane.

[0050] Preferably, the elastomer layer 2 is made from a material that contains at least an aromatic polyester-based thermoplastic polyurethane. In particular, the use of caprolactone-modified thermoplastic polyurethane has been found to be advantageous.

[0051] The material of the elastomer layer 2 can advantageously have silicone added to it to improve its abrasion resistance and processability, in particular the suitability of the material for extrusion.

[0052] The material of the elastomer layer 2 is plasticizer-free, which reduces the risk of product degradation over time.

[0053] The elastomer layer 2 further contains a thermoplastic elastomer, which is present in an amount of 1% by weight to 15% by weight.

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

[0055] The above additives improve the manufacturing process and reduce surface friction, thereby improving the slip characteristics of the coating on the surface of the blanket cylinder.

[0056] As mentioned above, the elastomer layer 2 has a thickness comprised between 0.05 and 1.50 mm with a tolerance of ±0.01 mm.

[0057] According to the invention, the elastic recovery force of the coating has been limited by the specific characteristics of the elastomeric layer 2, defined by the initial choice of its elastic elongation and, secondarily, its hardness value.

[0058] As an example, tensile tests were performed on two standard specimens consisting of the same blanket layer but different elastomer layers.

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

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

[0061] The elastomer layer of the second standard specimen has a tensile stress at 100% elongation of greater than 4.3 MPa according to ASTM D-412 (ISO 527) and a hardness of greater than 70 Shore A according to ASTM D-2240 (ISO 868).

[0062] The tests were carried out at room temperature (23°C) using standard specimens with 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] The long side was chosen to be parallel to the direction of positioning of the coating on the blanket cylinder.

[0064] The following results were obtained (average of three tests) and are expressed as % elongation under a given stress: [Table 1]

[0065] The results of the instrumental test show that the first standard sample has a greater elongation than the second standard sample.

[0066] It has been found that the deformability of the elastomeric layer 2 affects the tension generated in the gap region 11 of the blanket cylinder 10 , ie, the region where the coating 100 is mechanically secured to the blanket cylinder 10 .

[0067] In order to significantly reduce the tension in the aforementioned gap region, it has proven advantageous to choose an elastomer layer 2 having a hardness, measured according to the ASTM D-2240 standard, comprised between 70 and 45 Shore A, preferably between 60 and 45 Shore A.

[0068] Once the coating 100 is secured inside the gap region 11, the coating 100 can conform to the surface of the blanket cylinder 10 all the way around.

[0069] In particular, at the exit 12 of the gap region 11 where an acute angle Δ is formed between the concave surface 13 of the blanket cylinder 10 and the cylindrical surface 14 of the blanket cylinder 10 , the coating 100 can follow the contours of the surfaces 13 , 14 of the blanket cylinder 10 .

[0070] The characteristic deformability and low hardness of the elastomeric layer 2 improves the adhesion of the coating to the blanket cylinder 10 .

[0071] The increased adhesion prevents the cleaning product from penetrating between the coating and the blanket cylinder 10, thus improving protection against aggressive chemicals.

[0072] Elastomeric layer 2 still has self-leveling capabilities and a thickness that, in combination with the thickness of blanket layer 1, allows the desired overall thickness of the multilayer structure to be maintained. The second surface of elastomer layer 2 still has direct adhesion capabilities to the blanket cylinder without the need for an additional adhesive product, and the degree of adhesion under the static and dynamic conditions of the cylinder is at least sufficient to ensure, on the one hand, the maintenance of complete adhesion to the blanket cylinder and, on the other hand, easy removal from the blanket cylinder. Furthermore, thanks to the special properties of elastomer layer 2, coating 100 also has the ability to accurately replicate surfaces 13, 14 of blanket cylinder 10, even when an acute angle Δ is present.

[0073] The printing press coating so conceived is susceptible to numerous modifications and variations, all of which are within the scope of the inventive concept, and all details may be substituted by technically equivalent elements. The materials and dimensions used may in fact be any arbitrary materials and dimensions according to the needs and the state of the art.

Claims

1. 1. A coating (100) for a blanket cylinder (10) of a printing press, the coating (100) having a multilayer structure including a blanket layer (1) and an elastomeric layer (2) having a first surface firmly connected to the blanket layer and a second surface adhered to the blanket cylinder (10), the blanket layer (1) including at least one printing sublayer (6) made of a polymer material and at least one fabric sublayer (3, 4, 5), the elastomeric layer (2) having a tensile stress at 100% elongation comprised between 4.3 MPa and 1 MPa according to ASTM D-412 standard (ISO 527).

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

3. 3. A coating (100) for a blanket cylinder (10) of a printing press according to claim 1 or 2, characterized in that the elastomeric layer (2) has a hardness comprised between 70 Shore A and 45 Shore A according to the ASTM D-2240 standard.

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

5. 5. A coating (100) for a blanket cylinder (10) of a printing press according to any one of claims 1 to 4, characterized in that the elastomeric layer (2) is made from a material that contains silicone but does not contain plasticizers.

6. A coating (100) for a blanket cylinder (10) of a printing press according to any one of claims 1 to 5, characterized in that the elastomeric layer (2) is made from a material comprising at least a thermoplastic polyurethane.

7. 7. A coating (100) for a blanket cylinder (10) of a printing press according to claim 6, characterized in that the elastomer layer (2) is made from a material containing at least an aromatic polyester-based thermoplastic polyurethane.

8. The elastomer layer (2) is made of a material containing a thermoplastic elastomer, 8. The coating (100) for a blanket cylinder (10) of a printing press according to claim 6 or 7, characterized in that the thermoplastic elastomer is contained in the elastomer layer (2) in an amount of 1% to 15% by weight.

9. 9. The coating (100) for a blanket cylinder (10) of a printing press according to claim 8, wherein the thermoplastic elastomer is contained in the elastomer layer (2) in an amount of 8% to 12% by weight.

10. 10. A coating (100) for a blanket cylinder (10) of a printing press according to one or more of the preceding claims, characterized in that the elastomeric layer has a thickness comprised between 0.05 and 1.50 mm with a tolerance of ±0.01 mm.

11. 11. A coating (100) for a blanket cylinder (10) of a printing press according to one or more of claims 1 to 10, characterized in that the elastomeric layer (2) has a thickness such that it allows for self-leveling ability and maintaining a desired overall thickness of the multilayer structure in combination with the thickness of the blanket layer (1).

12. 12. A coating (100) for a blanket cylinder (10) of a printing press according to claim 11, characterized in that the second surface of the elastomer layer (2) has the ability to adhere directly to the blanket cylinder (10) without the need for an additional adhesive product for adhesion thereto, with a degree of adhesion under static and dynamic conditions at least sufficient to ensure, on the one hand, the maintenance of perfect adhesion to the blanket cylinder (10) and, on the other hand, easy removal from the blanket cylinder (10).

13. 13. A coating (100) for a blanket cylinder (10) of a printing press according to one or more of claims 1 to 12, characterized in that the elastomer layer (2) has the ability to follow the concave surface (13) and the cylindrical surface (14) of the blanket cylinder (10) at the outlet (12) of the gap region (11) of the blanket cylinder (10), where an acute angle (Δ) is formed between the concave surface (13) of the blanket cylinder (10) and the cylindrical surface (14) of the blanket cylinder (10).

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