Patent Publication Number: US-2016236499-A1

Title: Blanket for transferring a paste image from engraved plate to substrate

Description:
BACKGROUND 
     1. Technical Field 
     The disclosure relates to gravure offset printing, and in particular it relates to a blanket of the gravure offset printing. 
     2. Description of the Related Art 
     Printed electronic products possess great market potential. There is a continuing goal to miniaturize. To satisfy the design requirements of lighter, smaller, or thinner products, the volume of each component utilized in the product is strictly limited. Taking conductive wires—the most common component in printed electronic products—as an example, the line width thereof is reduced from the hundred-micron scale to a scale of just several microns. Screen printing is typically used in the manufacture of traditional conductive wires. However, the mass-producible line width is only down to 70 μm due to the intrinsic limitations of the screen. Obviously, such a process capability is insufficient for processing currently popular touch panels. To achieve fine wire production, most manufacturers rely on photolithographic technology. Although this process can produce wires with a line width less than 10 micron, the production cost is significantly higher than that of the printing process. Moreover, this process is not environmentally friendly because of the huge consumption of energy and materials. 
     To meet the production capacity of thin conductive paths and manufacturing cost considerations, gravure transfer (gravure offset printing) technology has seen a lot of research and trial production in industry in recent years, but the blanket of the gravure offset printing still needs to be improved. For example, the Tan δ of conventional blankets is overly high, and it may result in distortion of the printed line width, blanket aging, and the like. 
     Accordingly, a novel blanket to solve the above problems is called for. 
     BRIEF SUMMARY 
     One embodiment of the disclosure provides a blanket for transferring a paste image from an engraved plate to a substrate, comprising: a foam; a PET layer on the foam; and an paste transfer layer on the PET layer, wherein the blanket has a Tan δ value of 0.05 to 0.13. 
     A detailed description is given in the following embodiments with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
         FIG. 1  shows a flowchart of the gravure offset printing process in one embodiment of the disclosure; 
         FIG. 2A-2E  show schematic views of various stages of the gravure offset printing process in one embodiment of the disclosure; and 
         FIG. 3  shows a schematic view of the blanket in one embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. 
     In one embodiment, a gravure transfer process flow is provided as shown in  FIG. 1 . Process  100  begins at step  110 , in which an engraved plate  102  with an intaglio pattern  104  is provided. As shown in  FIG. 2A , the intaglio pattern  104  may have a line width between about 3 μm to about 100 μm, for example. The engraved plate  102  can be made of stainless steel, glass, ceramic, copper, or a combination thereof. Subsequently, a paste  106  is filled into the intaglio pattern  104  in step  120 . The excess paste  106  over the surface of the engraved plate  102  can be removed by a doctor blade, such that the top surface of the engraved plate  102  is flat, as shown in  FIG. 2B . In one embodiment, the paste  106  can be made of metal particles, polymer binder, and organic solvent. 
     Referring to  FIG. 2C , the process  100  proceeds to step  130 , in which the paste  106  in the intaglio pattern  104  is transferred to the surface of a blanket  108 . The blanket  108  may be a roller shape, for example, In one embodiment, the blanket  108  is a three-layered structure of a foam  301 , a PET layer  303  on the foam  301 , and an paste transfer layer  305  on the PET layer  303 , as shown in  FIG. 3 . The three-layered structure can be rolled as a roll (the blanket  108  in  FIG. 2C ), and the paste transfer layer  305  is the outermost layer to transfer the paste  106 . The blanket  108  has a Tan δ value of 0.05 to 0.13. A higher Tan δ value means that the blanket has a lower recovery ability when deformed by stress. When stress is applied to a viscoelastic body, the body will flow and deform. Even if the stress is removed, the deformed viscoelastic body cannot completely recover. The recovered part of the body is the so-called storage modulus (e.g. elastic part, E′), and the un-recovered part of the body is the so-called loss modulus (e.g. viscos part, E″). The loss modulus (E″) divided by the storage modulus (E′) is the Tan δ value. The lower Tan δ means the viscoelastic body is close to the ideal elastic body. A blanket with an overly high Tan δ value may have poor ability to recover to its original shape after the printing pressure being released, and its lifetime is decreased. A blanket with an overly low Tan δ value may have poor ability to absorb the solvent of the paste and lead to poor printing results. 
     In one embodiment, the foam  301  can be made of polyurethane, polyethylene, nitrile-butadiene rubber, silicone, or a combination thereof with a weight average molecular weight of 2,000 to 1,000,000. In one embodiment, the foam  301  has a thickness of 0.5 mm to 1.5 mm. Overly thick foam may lead little blanket engagement into gravure so that paste off ratio will be decreased. Overly thin foam may lead poor supporting ability so that the lifetime of blanket will be decreased. 
     In one embodiment, the PET in the PET layer  303  has a weight average molecular weight of 15000 to 40000. In one embodiment, the PET layer  303  has a thickness of 100 μm to 300 μm. An overly thick PET layer may lead overly high hardness of blanket. An overly thin PET layer may lead overly low supporting capacity of blanket. 
     In one embodiment, the paste transfer layer  305  can be made of silicone rubber, fluoro rubber, fluorosilicone rubber, a combination thereof, or a multi-layered structure thereof. The paste transfer layer  305  may have a Shore A hardness of 40 to 60. A paste transfer layer with an overly high Shore A hardness may lead the insufficiency of blanket engagement into gravure. A paste transfer layer with an overly low Shore A hardness may lead blanket without the ability to maintain the shape of printing pattern. In one embodiment, the paste transfer layer  305  has a thickness of 0.3 to 1.5 mm. An overly thick paste transfer layer  305  may lead too much strain remained in blanket so that printing shape will twist and distort. An overly thin paste transfer layer  305  may lead whole blanket composite is too hard to print moderately, which results from the hardness of PET dominate the hardness of the whole blanket. The surface of the paste transfer layer  305  and water may have a contact angle of 105° to 125°. An overly low contact angle means the paste transfer layer  305  is more hydrophilic, and it may keep too much paste on blanket and cannot get 100% paste transfer. An overly high contact angle means the paste transfer layer  305  is too hydrophobic, and it may have poor ability to take paste form gravure. Moreover, an adhesive (not shown) can be disposed between the foam  301  and the PET layer  303 , between the PET layer  303  and the paste transfer layer  305 , or a combination thereof. The adhesive may further enhance the adhesion between the layers in the blanket  108 , thereby eliminating the chance of delamination during the gravure transfer process. The adhesive can be made of silicone, epoxy, silane, or a combination thereof. 
     Referring to  FIG. 2D , the process  100  proceeds to step  140 , in which the paste  106  on the blanket  108  is transferred to a substrate  109 . Note that although the substrate  109  is shown as being planar, the disclosure is not limited thereto. For example, the substrate  109  can be curved. The substrate  109  can be made of a rigid substrate or a flexible-type substrate, i.e. glass, polyethylene terephthalate (polyethylene terephthalate; PET), polycarbonate (PC), or a combination thereof. 
     It should be understood that the yield of the gravure transfer process is determined on two critical points: (1) the yield of the paste  106  transferred from the engraved plate  102  to the blanket  108 , and (2) the yield of the paste  106  transferred from the blanket  108  to the substrate  109 . In other words, the paste  106  tends to attach to the substrate  109  rather than attach to the blanket  108 , and it also tends to attach to the blanket  108  rather than to the engraved plate  102 . The above attachment can be controlled by the pressure/temperature between the engraved plate  102  and the blanket  108  as well as between the blanket  108  and the substrate  109 . Furthermore, the Tan δ value (0.05 to 0.13) of the blanket  108  is critical for the product yield. While the gravure transfer process is a continuous process, a stable blanket  109  may prevent the distortion of the printed line width and blanket aging. 
     Below, exemplary embodiments will be described in detail with reference to the accompanying drawings so as to be easily realized by a person having ordinary knowledge in the art. The inventive concept may be embodied in various forms without being limited to the exemplary embodiments set forth herein. Descriptions of well-known parts are omitted for clarity, and like reference numerals refer to like elements throughout. 
     EXAMPLES 
     Comparative Example 1 
     A PET layer with a thickness of 250 μm and Mw of about 25000 (commercially available from ShinKong Materials Technology Co., Ltd.) was adhered on a foam (W-ADH-black-1.0, commercially available from Fujikura) by silicone (SL989, commercially available from STARSILICONE). A silicone layer with a thickness of 0.75 mm and a Shore A hardness of 50 (KE-951U, commercially available from Shin-Etsu Slicone Taiwan co.) was adhered on the PET layer by silicone (SL989, commercially available from STARSILICONE) to complete a blanket. The silicone layer served as a paste transfer layer of the blanket, and the surface of the silicone layer and water had a contact angle of 110°. The blanket had a Tan δ value of 0.13 to 0.2. 
     A paste made from silver particles, polymer binder, and organic solvent was filled into an intaglio pattern of an engraved plate of stainless-steel or nickel, and the intaglio pattern had a depth of 10 μm and a width of 15 μm. The blanket (on a roll) was pressed to the engraved plate by a pressure of 100N to transfer the paste from the intaglio pattern onto the blanket. The blanket was then pressed to a substrate made of poly(ethylene terephthalate) by a pressure of 180N to transfer the paste from the blanket onto the substrate. However, the paste pattern on the substrate was deformed compared to the intaglio pattern, especially in the corner part of the paste pattern. 
     Example 1 
     A PET layer with a thickness of 250 μm and Mw of about 25000 (commercially available from ShinKong Materials Technology Co., Ltd.) was adhered on a polyurethane foam with a thickness of 1.6 mm (AM60HD, commercially available from Adheso) by silicone (SL989, commercially available from STARSILICONE). A silicone layer with a thickness of 0.75 mm and a Shore A hardness of 50 (KE-951U, commercially available from Shin-Etsu Slicone Taiwan co.) was adhered on the PET layer by silicone (SL989, commercially available from STARSILICONE) to complete a blanket. The silicone layer served as a paste transfer layer of the blanket, and the surface of the silicone layer and water had a contact angle of 110°. The blanket had a Tan δ value of 0.08 to 0.1. 
     A paste made from silver particles, polymer binder, and organic solvent was filled into an intaglio pattern of an engraved plate of stainless-steel or nickel, and the intaglio pattern had a depth of 10 μm and a width of 15 μm. The blanket (on a roll) was pressed to the engraved plate by a pressure of 100N to transfer the paste from the intaglio pattern onto the blanket. The blanket was then pressed to a substrate poly(ethylene terephthalate) by a pressure of 180N to transfer the paste from the blanket onto the substrate. The paste pattern on the substrate was not deformed compared to the intaglio pattern. 
     Example 2 
     A PET layer with a thickness of 250 μm and Mw of about 25000 (commercially available from ShinKong Materials Technology Co., Ltd.) was adhered on a polyurethane foam with a thickness of 1.6 mm (AM60HD, commercially available from Adheso) by silicone (SL989, commercially available from STARSILICONE). A silicone layer with a thickness of 0.75 mm and a Shore A hardness of 40 (KET-8840, commercially available from Shin-Etsu Slicone Taiwan co.) was adhered on the PET layer by silicone (SL989, commercially available from STARSILICONE) to complete a blanket. The silicone layer served as a paste transfer layer of the blanket, and the surface of the silicone layer and water had a contact angle of 113°. The blanket had a Tan δ value of 0.07 to 0.11. 
     A paste made from silver particles, polymer binder, and organic solvent was filled into an intaglio pattern of an engraved plate of stainless-steel or nickel, and the intaglio pattern had a depth of 15 μm and a width of 15 μm. The blanket (on a roll) was pressed to the engraved plate by a pressure of 100N to transfer the paste from the intaglio pattern onto the blanket. The blanket was then pressed to a substrate poly(ethylene terephthalate) by a pressure of 180N to transfer the paste from the blanket onto the substrate. The paste pattern on the substrate was not deformed compared to the intaglio pattern. 
     Comparative Example 2 
     A PET layer with a thickness of 250 μm and Mw of about 25000 (commercially available from ShinKong Materials Technology Co., Ltd.) was adhered on a polyurethane foam with a thickness of 1.6 mm (AM60HD, commercially available from Adheso) by silicone (SL989, commercially available from STARSILICONE). A silicone mixture layer with a thickness of 0.75 mm and a Shore A hardness of 60 (mixture of KET-8540 and KET-8580, commercially available from Shin-Etsu Slicone Taiwan co.) was adhered on the PET layer by silicone (SL989, commercially available from STARSILICONE) to complete a blanket. The silicone mixture layer served as a paste transfer layer of the blanket, and the surface of the silicone layer and water had a contact angle of 110.7°. The blanket had a Tan δ value of 0.1 to 0.14. 
     A paste made from silver particles, polymer binder, and organic solvent was filled into an intaglio pattern of an engraved plate of stainless-steel or nickel, and the intaglio pattern had a depth of 15 μm and a width of 15 μm. The blanket (on a roll) was pressed to the engraved plate by a pressure of 100N to transfer the paste from the intaglio pattern onto the blanket. The blanket was then pressed to a substrate poly(ethylene terephthalate) by a pressure of 180N to transfer the paste from the blanket onto the substrate. The paste pattern on the substrate had a lot of bubbles in its corner. 
     Accordingly, the blanket with a Tan δ value out of 0.05 to 0.13 (i.e. Comparative Examples 1 and 2) would degrade the paste pattern. 
     While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.