Film-forming method

Abstract: A flexographic apparatus including a plate having a prescribed relief pattern for printing on a substrate to be printed is provided with a temperature control means for controlling the substrate, preferably embedded within a stage for supporting the substrate to be printed. The substrate to be printed may be controlled at a temperature above 30 o C. As a result, an organic polymer film or an inorganic oxide film may be formed with improved thickness uniformity and evenness by applying a solution of the organic polymer or an inorganic oxide precursor by using the flexographic apparatus.

Description: FIELD OF THE INVENTION AND RELATED ART The present invention relates to a method of printing by a flexographic apparatus for forming a film of an organic polymer or an inorganic oxide thereby, wherein the temperature of the substrate to be printed is controlled. A conventional flexographic apparatus roughly has an arrangement, as shown in Figure 3, including a stage 1 to which a substrate (to be printed) 11 is fixed, a cylinder 2, a relief plate 3 having a printing pattern and fastened to the cylinder 2, an extension plate 8, a nozzle 5 for supplying to the extension plate 8 a printing liquid 4 fed from a tank 6, and a doctor blade 7 for extending or spreading the printing liquid on the extension plate 8. A commercially available example of such a flexographic apparatus is "Angstromer" (trade name, available from Nihon Shashin Insatsu K.K.). DE-A 17 86 295 discloses a printing method with control device for controlling the substrate and printing color, in which the substrate is kept at room temperature and the temperature of the ink is cooled to a value(e.g. 14°C to 19°C) below the temperature of the substrate. US-A 2,614,493 discloses a printing method in which the substrate, e.g. sheet or web, is heated to a temperature between 107°C to 204°C in order to permit second side printing without offset. Further EP-A 0 257 103 discloses a thin film forming apparatus for printing and forming various thin films, which can precisely print and form a thin film of a given pattern with a specified thickness. This object is achieved by a thin film forming apparatus comprising an intaglio plate, which is constructed in the form of a cylindrical body. That is, according to this document, films of uniform thickness are obtained by applying a specific kind of intaglio plate However, there is no teaching to control the substrate to be printed at a temperature above 30°C but insufficient to cause a dryness of the printing liquid due to evaporation of the solvent, so as to provide the printing liquid on the substrate with an improved fluidity and an improved smoothness. However, when an organic polymer solution or an inorganic oxide solution is applied on a substrate by using a conventional flexographic apparatus as described above, the resultant organic polymer or inorganic oxide film is sometimes accompanied with an ununiform thickness distribution or poor smoothness (undulation), which results in adverse effects to the properties of the film. SUMMARY OF THE INVENTION In view of the above-mentioned problem of a conventional flexographic apparatus, an object of the present invention is to provide a method of printing by a flexographic apparatus for film-forming, whereby a liquid containing an organic polymer, an inorganic oxide precursor, etc., may be applied to provide a film with an improved uniformity of thickness distribution, an improved smoothness and an improved reproducibility of these factors. According to the present invention, there is provided a method of printing by a flexographic apparatus comprising: providing a printing liquid comprising a solution of an organic polymer or an inorganic oxide precursor in a solvent, applying the printing liquid on a plate having a prescribed relief pattern, and printing the printing liquid on the plate onto a substrate to be printed while controlling the substrate to be printed at a temperature which is above 30°C but insufficient to cause a dryness of the printing liquid due to evaporation of the solvent during the printing. This and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a front view showing an outline of a flexographic apparatus used in the present invention. Figure 2 is a plan view showing a stage supporting a substrate to be printed used in the apparatus shown in Figure 1. Figure 3 is a front view showing a conventional flexographic apparatus. DESCRIPTION OF THE PREFERRED EMBODIMENTS The temperature control means used in the present invention may for example be embodied as a temperature control mechanism for keeping at a constant temperature a stage for supporting or fastening a substrate to be printed in a flexographic apparatus. In a preferred embodiment, a liquid, preferably a solution, containing an organic polymer or an inorganic oxide precursor may be applied onto a substrate to be printed which is supported on the stage and controlled at a temperature above 30 °C within an accuracy of ±5 °C, thereby forming a film of such an organic polymer or inorganic oxide. Examples of such an organic polymer film may include: color filters comprising colored resins of, e.g., polyamides, and protective films thereon; films of photoresists, such as photosensitive phenol-novolak resin; alignment films for liquid crystal devices, comprising, e.g., polyimide resins; and sealants for liquid crystal devices, comprising e.g., epoxy-type adhesives. Further, the inorganic oxide film thus formed may for example be an insulating film for liquid crystal devices. A conventional flexographic apparatus is not equipped with a temperature control mechanism so that the temperature of the substrate to be printed is affected by the environment. In other words, the flexographic printing has been possible only in the neighborhood of room temperature. In case where a solution of an organic polymer or an inorganic oxide precursor is applied by flexography under such a condition, the resultant organic polymer or inorganic oxide film is liable to be accompanied with an ununiformity of thickness distribution and/or surface undulation, which results in adverse effects to the final properties of the film. According to the present invention, a solution of an organic polymer or an inorganic oxide precursor is applied to a substrate to be printed while the substrate to be printed is temperature-controlled at a constant temperature above 30 °C within an accuracy of ±5 °C by equipping a flexographic apparatus with a temperature control means for keeping a stage for supporting the substrate at a constant temperature, so that the resultant film is provided with improved uniformity of film thickness, surface flatness and reproducibility thereof. Hereinbelow, some embodiments of the present invention will be described with reference to the drawings. Figures 1 and 2 illustrate principal features of an embodiment of the flexographic apparatus used in the present invention. The flexographic apparatus includes a stage 1 for supporting a substrate to be printed 11, a cylinder 2, a plate (rubber relief plate) 3 having a printing pattern, a supply nozzle 5 for supplying a printing liquid 4 supplied from a tank 6, an extension plate 8, and a doctor blade 7 for extending the printing liquid 4 on the extension plate 8. Example 1 In a specific example, the stage 1 was formed of a metal (e.g., stainless steel) having a smoothened surface, and the surface temperature thereof was controlled at a temperature of 20 - 50 °C within an accuracy of ±1.0 °C by circulating a constant-temperature water controlled at a temperature of 20 - 50 °C ± 0.5 °C within the stage 1 along a circulating path 10. Correspondingly, a substrate 11 fastened to and in intimate contact with the stage 1 by vacuum generated in vacuum grooves 13 leading to a vacuum pump was heated by conduction to a temperature of 20 - 50 °C ± 2.0 °C within ten and several seconds. Generally, the substrate-to-be-printed should preferably be controlled within an accuracy of ±5 °C, particularly ±3 °C, according to measurement at, e.g., 9 points of the substrate by CA thermocouples directly applied to the substrate. On the above-mentioned stage controlled at five constant temperatures of 20 °C, 30 °C, 35 °C, 40 °C and 50 °C, respectively, several glass plates (each measuring 300 mm x 320 mm x 1.1 mm-t) were successively placed, and a color filter ink containing a color filter resin comprising a photosensitive polyamide resin colored with a red colorant dispersed therein ("PA-1012R" (trade name), available from Ube Kosan K.K.) diluted to a viscosity of 500 centipoise with N-methylpyrrolidone (solvent) and extended on the extension plate 8 of SUS (stainless steel) having 36 µm-deep grooves (a groove widths of 27 µm and a convexity spacing of 25 µm between grooves), was applied onto the glass plates by a plate of a rubber ("CYREL" (trade name) available from E.I. Du Pont) having a rectangular relief pattern of 280 mm x 300 mm under a plate impression of 0.15 mm. The color filter films printed on the glass substrates at various temperatures showed properties as shown in the following Table 1. Sample Substrate temp. Thickness Undulation Temp. range No. 1 20 °C 765±53 nm (7650±530 Å) 41 nm (410Å)/8mm ±2 °C No. 2 30 °C 793±51 nm (7930±510 Å) 39 nm (390Å)/8mm ±2 °C No. 3 35 °C 832±31 nm (8320±310 Å) 18 nm (180Å)/8mm ±2 °C No. 4 40 °C 850±23 nm (8500±230 Å) 16 nm (160Å)/8mm ±2 °C No. 5 50 °C 938±43 nm (9380±430 Å) 19 nm (190Å)/8mm ±2 °C The thickness and the undulation of each film sample were measured at several points and pairs of 8 mm-distant points for each of the several points, respectively, by partly peeling the film in a width of 8 mm at the several points and measuring the thicknesses of the sides of the remaining films by a contacting needle-type surface roughness meter ("Surfcoder ET-30" (trade name) available from Kosaka Kenkyuso K.K.). As is understood from the above Table 1, Sample Nos. 1 and 2 printed at 20 - 30 °C provided a fluctuation in thickness exceeding ±7 % and undulations of 39 nm (390 Å) or larger. In contrast thereto, Sample No. 3 printed at 35 °C provided a remarkably smaller fluctuation in thickness of within ±4 % and a smaller undulation of 18 nm (180 Å) or less, and Sample No. 4 printed at 40 °C provided a fluctuation of within ±3 % and an undulation of 16 nm (160 Å) or less. Sample No. 5 printed at 50 °C gave a thickness fluctuation of ±5 % and an undulation of 19 nm (190 Å) which were not inferior to the results of Samples Nos. 3 and 4. However, Sample No. 5 showed some dryness due to evaporation of the solvent in the ink during the printing as the printing was continued on a large number of glass plates, and gradually provided inferior films. The above results are considered to show that an elevated temperature exceeding 30 °C of the substrate promoted leveling of the printing liquid applied on the substrate but an excessively high temperature caused too high a drying speed, thus being liable to provide inferior film properties. However, the latter difficulty can be alleviated by using a solvent having a higher boiling point, while a temperature up to 50 °C is generally preferred. As is understood from the above results, by using the above-mentioned flexographic apparatus to control the substrate to be printed at a constant temperature, a color filter film having a good thickness distributions and good surface roughness was formed on the glass plates. Then, each color filter film was exposed through a photomask to ultraviolet rays at an intensity of 300 mJ/cm 2 to photocure the prescribed parts of the film, which was then developed with a prescribed developer liquid to remove the uncured part of the film by dissolution and then subjected to further curing in a clean oven at 200 °C for 1 hour to form a good red color filter pattern on the glass plate. Example 2 Similarly as in Example 1, on the above-mentioned stage controlled at five constant temperature of 20 °C, 30 °C, 35 °C, 40 °C and 50 °C, respectively, several glass plates (each measuring 300 mm x 320 mm x 1.1 mm-t) were successively placed, and a solution of a transparent polyamide resin ("PA-1000C" (trade name) available from Ube Kosan K.K.) which may be used to form, e.g., a protective film on a color filter, diluted to a viscosity of 500 mPa·s (500 centipoise) with a mixture solvent of N-methylpyrrolidone/n-butylcellosolve and extended on the extension plate 8 of SUS having 30 µm-deep groove (a groove width of 275 µm and a convexity spacing of 25 µm between grooves), was applied onto the glass plates by a plate of EPT (ethylene-propylene terpolymer) having a rectangular relief pattern of 280 mm x 300 µm under a plate impression of 0.15 mm. The clear films printed on the glass substrates at various temperatures showed properties as shown in the following Table 2. Sample Substrate temp. Thickness Undulation Temp. range No. 1 20 °C 1022±40 nm (10220±400 Å) 39 nm (390Å)/8mm ±2 °C No. 2 30 °C 1070±25 nm (10700±250 Å) 29 nm (290Å)/8mm ±2 °C No. 3 35 °C 1103±19 nm (11030±190 Å) 16 nm (160Å)/8mm ±2 °C No. 4 40 °C 1120±16 nm (11200±160 Å) 15 nm (150Å)/8mm ±2 °C No. 5 50 °C 1232±23 nm (12320±230 Å) 22 nm (220Å)/8mm ±2 °C As is understood from the above Table 2, Sample Nos. 3, 4 and 5 printed at 35 - 50 °C provided fluctuations in thickness of within ±1.5 - 2.0 % and undulations of 15 ± 22 nm (150 - 220 Å) or smaller. In contrast thereto, Sample No. 1 printed at 20 °C showed inferior thickness distribution and smoothness (undulation) presumably because of insufficient leveling of the ink on the substrate. Further, Sample No. 2 printed at 30 °C showed a thickness distribution and a smoothness (undulation) which were better than those of Sample No. 1 but inferior to those of Samples Nos. 3 - 5 printed at 35 - 50 °C. As the organic polymer material applicable in the present invention, it is also possible to use polyimides which may be used for forming alignment films principally used in liquid crystal devices, phenol-novolak resins having photosensitivity, high-temperature curable epoxy-type sealants for, e.g., liquid crystal devices. It is also possible to use, for application, a solution of an inorganic oxide precursor, examples of which may include hydroxides and organo-oxides of metals or metalloids such as silicon, titanium, tantalum, and zirconium. These inorganic oxide precursors may, for example, be heated after the printing, to form a (patterned) film which may be used as an insulating film, a protective film, or a spacer member. It has been confirmed that the effect of temperature control of the substrate to be printed at a temperature above 30 °C is effective for forming a film having a uniform thickness and an improved flatness (less undulation) also of these materials. As described above, by equipping a stage for supporting a substrate to be printed of a flexographic apparatus with a temperature control means, the substrate can be controlled at a temperature exceeding 30 °C, preferably by 3 °C or more, within an accuracy of ±5 °C, preferably ±3 °C, further preferably ±2 °C, whereby an organic polymer film or an inorganic oxide film can be stably formed at an improved thickness uniformity and a better flatness and with a good reproducibility by application of a solution of the organic polymer or an inorganic oxide precursor.

Claims: A method of printing by a flexographic apparatus comprising: providing a printing liquid(4) comprising a solution of an organic polymer or an inorganic oxide precursor in a solvent, applying the printing liquid(4) on a plate(3) having a prescribed relief pattern, and printing the printing liquid(4) on the plate(3) onto a substrate(11) to be printed while controlling the substrate(11) to be printed at a temperature which is above 30°C but insufficient to cause a dryness of the printing liquid(4) due to evaporation of the solvent during the printing. A method according to claim 1. wherein the temperature of the substrate(11) is controlled within an accuracy of ±5°C at a temperature of 33-50°C. A method according to claim 1, wherein the polymer is a polyamide. A method according to claim 1, wherein the polymer is a polyimide. A method according to claim 1, wherein the polymer is an epoxy adhesive. A method according to claim 1, wherein the printing liquid comprises a pigment and a polymer. A method according to claim 1, wherein the polymer is a photosensitive phenol-novolak resin.

Inventors: SUZUKI MASAAKI, WATANABE YASUYUKI, YOSHIOKA MAYUMI, SUZUKI, MASAAKI, WATANABE, YASUYUKI, YOSHIOKA, MAYUMI, SUZUKI, MASAAKI, C/O CANON KABUSHIKI KAISHA, Watanabe, Yasuyuki, c/o Canon Kabushiki Kaisha, Yoshioka, Mayumi, c/o Canon Kabushiki Kaisha
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1992
Main classification: B41F5
IPC codes: G02B5, B41F23, B41F3, B41F31, B41M1, B41F5, G02F1