Simplified screen printing machine

Abstract: A simplified type screen printing machine (1) including a base member (2) mounted with an object to be pressed (4), a framed stencil sheet assembly (15) at least constituted by stencil sheet (18) comprising a porous support and a resin film laminated to the support and a frame member (19) laminated with the stencil sheet (18), pressing means (11) attachably and detachably attached with the framed stencil sheet assembly (15), pressing the framed stencil sheet assembly (15) to the base member (2) to be brought into contact with the object to be pressed (4) and fixing with tense the framed stencil sheet assembly (15) and image forming means (21) for making image forming material pass though the framed stencil sheet assembly (15) which is fixed with tense.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a screen printing machine for printing an object to be pressed mounted on a print base by using a framed stencil sheet assembly, and to a screen printing machine for easily exerting tension to a framed stencil sheet assembly and providing distinct picture. 2. Description of the Related Art Screen printing is suitable for a print face the surface of which is smooth and a print face which absorbs ink with difficulty. According to such a screen printing method, as is well known, there is used a screen 53 formed by laminating together a thermoplastic resin film 51 and a porous support 52 as shown by Figs. 12(a), 12(b), 12(c) and 12(d). The screen 53 is perforated and four peripheries thereof are fixed to a plate frame 54 with tension. As shown by Fig. 12(a), the screen 53 is opposed to a print base member 56 on which an object to be printed 55 is mounted (spaced apart therefrom by a predetermined interval) and is fixed thereto with a predetermined tension. Further when, as shown by Fig. 12(b), screen printing ink 57 is placed on the screen 53 and while pressing a surface of the screen 53 (porous support 52) by a squeegee 58, the rear face of the screen 53 (thermoplastic resin film 51) is brought into contact with the object to be printed 55 when then squeegeed, as shown by Fig. 12(c), the ink 57 passes through opening portions of the plate where the thermoplastic resin film 51 is not present from the porous support 52 and is extruded onto the object to be printed 55. When the squeegee operation is finished, as shown by Fig. 12(d), the screen 53 recovers to its original state by virtue of the tension of the screen 53. However, according to the above-described printing, the screen 53 needs to be fixed with tension by being held up from the print face of the object to be printed 55 by the predetermined interval. Further, the squeegee 58 is partially depressed onto the screen 53 which fixed with a strain and, therefore, adjustment of the force exerted on the squeegee 58 is difficult and differs between operators. Therefore, considerable skill is needed to uniformly squeegee the surface of the screen 53 by pertinent depressing force. Further, some degree of rigidity is needed for the plate frame 54 and, therefore, it is difficult to use a frame member having weak rigidity such as a frame member made of paper. US-A-5,355,791 and EP-A-0,588,580 are prior art documents to the present invention. US-A-4,896,597 discloses a screen printing apparatus having the features of the preamble of claim 1. The present invention is characterized by the features of the characterizing portion of claim 1. Optional features are recited in the dependent claims. Embodiments of the present invention remove the above-described drawbacks by exerting, in use, a predetermined tension to a framed stencil sheet assembly over an entire face of an object to be pressed by pressing the stencil sheet assembly to a base member to be brought into contact with the object to be pressed and fixing the framed stencil sheet assembly with tension. The also make a image forming material pass through a framed stencil sheet assembly by image forming means in a state of exerting predetermined tension to the framed stencil sheet assembly to thereby form image having a uniform distinctness over an entire face of an object to be pressed constituting an object to be pressed even when pressure applied on the framed stencil sheet assembly by the image forming means is not uniform. Perforations may be formed which have a uniform distinctness by uniformly irradiating light over an entire face of the draft constituting an object to be pressed by providing attachably and detachably a light irradiating apparatus for irradiating light to perforate a framed stencil sheet. Uniform tension of a framed stencil sheet assembly may be achieved by relievably fixing pressing means to a base member in a state in which the framed stencil sheet assembly is fixed with tense to an object to be pressed on a base member. Further distinct perforations may be provided in perforating operation and further distinct images may be provided in printing operation. Screen printing and plane press type printing may be carried out by a single printing machine according to the present invention by interchangeably constituting pressing means and pressing means with transparent plate provided with a transparent plate at an opening portion. In a perforating operation, firstly, the light irradiating apparatus is mounted to the opening portion of the pressing means. The pressing means is pressed to the base member, the framed stencil sheet assembly is brought into contact with an original and the framed stencil sheet assembly is fixed with tension. At this point at least a portion of the print base provided at the base member is disposed inside of the opening portion of the pressing means. Further, a pivotal end of the pressing means and the base member are brought into contact with each other, electricity is conducted to the light irradiating apparatus and light is irradiated to the stencil sheet of the framed stencil sheet assembly which has been fixed with tension. The stencil sheet is formed with desired perforated image in accordance with an original image. In a printing operation, the light irradiating apparatus is removed. The pressing means is pressed to the base member, the framed stencil sheet assembly which has been perforated is brought into contact with an object to be printed and the framed stencil sheet assembly is fixed with tension. At this point at least a portion of the print base provided at the base member is disposed inside of the opening portion of the pressing means. From this state, the image forming material is made to pass through the perforated stencil sheet by the image forming means. The image forming material which has passed therethrough reaches the object to be printed and the desired image is formed. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a disassembled perspective view of a screen printing machine according to a first embodiment; Fig. 2 is a view showing the screen printing machine according to the first embodiment and a light irradiating apparatus; Fig. 3(a) is a side sectional view showing a state before pressing in a perforating stage of the screen printing machine according to the first embodiment; Fig. 3(b) is a side sectional view showing pressing in the perforating stage of the screen printing machine according to the first embodiment; Fig. 4(a) is a side sectional view showing the state before pressing in a printing stage of the screen printing machine according to the first embodiment; Fig. 4(b) is a side sectional view showing a the state of pressing in the printing stage of the screen printing machine according to the first embodiment; Fig. 4(c) is a side sectional view showing squeeging in the printing stage of the screen printing machine according to the first embodiment; Fig. 4(d) is a side sectional view showing taking out an object to be printed in the printing stage of the screen printing machine according to the first embodiment; Fig. 5(a) is a side sectional view showing a state before pressing when a fixing means is provided to the screen printing machine according to the first embodiment; Fig. 5(b) is a side sectional view showing a state in pressing when the fixing means is provided to the screen printing machine according to the first embodiment; Fig. 5(c) is a partial enlarged side sectional view of the fixing means; Fig. 6 is a disassembled perspective view of a screen printing machine according to a second embodiment; Fig. 7(a) is a side sectional view showing a state before pressing in a perforating stage of the screen printing machine according to the second embodiment; Fig. 7(b) is a side sectional view showing pressing in the perforating stage of the screen printing machine according to the second embodiment; Fig. 8(a) is a side sectional view showing a the state before pressing in a printing stage of the screen printing machine according to the second embodiment; Fig. 8(b) is a side sectional view showing a the state of pressing in the printing stage of the screen printing machine according to the second embodiment; Fig. 8(c) is a side sectional view showing squeegeeing in the printing stage of the screen printing machine according to the second embodiment; Fig. 8(d) is a side sectional view showing taking out an object to be printed in the printing stage of the screen printing machine according to the second embodiment; Fig. 9(a) is a side sectional view showing a state before pressing when a fixing means is provided to the screen printing machine according to the second embodiment; Fig. 9(b) is a side sectional view showing a state in pressing when the fixing means is provided to the screen printing machine according to the second embodiment; Fig. 9(c) is a partial, enlarged side sectional view of the fixing means; Fig. 10 is an outline view of a screen printing machine according to the present invention provided with a press plate having a transparent plate; Fig. 11 is a view showing a framed stencil sheet assembly useful with a screen printing machine according to the present invention provided with the press plate having the transparent plate; Fig. 12(a) is an outline view showing a state before squeegeeing of a conventional screen printing machine; Fig. 12(b) is an outline view showing the start of squeegeeing of the conventional screen printing machine; Fig. 12(c) is an outline view showing finishing squeegeeing of the conventional screen printing machine; and Fig. 12(d) is an outline view showing the state after finishing printing with the conventional screen printing machine. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown by Fig. 1 and Fig. 2, a screen printing machine 1 according to an embodiment of the present invention is generally constituted by a base member 2, a press plate 11 constituting pressing means and a framed stencil sheet assembly 15. As shown by Fig. 1, a recess portion 3 of a rectangular shape is formed at an upper face of the base member 2. In the recess portion 3 there is a print base 5 for mounting an object to be pressed such as an object to be printed (for example, printing paper) or an original which is axially supported pivotably within a predetermined angular range. The print base 5 is constituted by a base plate 6 axially supported within the recess portion 3 of the base member 2. An elastic pad 7 is provided on the base plate 6. Pivot shafts 8 project from left and right end faces of the base plate 6 and are pivotably engaged with bearings 9 formed adjacent the recess portion 3. The pad 7 is formed by soft polyurethane foam which has the property that the pressure state thereof stays substantially constant when an amount of displacement thereof falls in a predetermined range. At one end portion of the base member 2, there is provided a pivotal shaft 10 to which the press plate 11 is pivotably attached. The press plate 11 is provided with an opening portion 12. The opening portion 12 is formed slightly larger than a mounting face 7a (the top surface of pad 7) of the print base 5 on which an object to be pressed such as a printing paper or an original, not illustrated, is mounted. When the press plate 11 is pressed in a direction of the print base 5, the mounting face is disposed inside the opening portion 12. On a side of a face of the press plate 11 opposed to the base member 2, there are provided holding members 13 to which the framed stencil sheet assembly 15 is fitted. As shown by Fig. 2, a light irradiating apparatus 47 is provided which is attachable and detachable to and from the opening portion 12 of the press plate 11. The light irradiating apparatus 47 is provided with a cabinet 48 substantially in the shape of a quadrangular prism and flash bulbs 49 as light emitting means at inside thereof. Further, a reflecting mirror, not illustrated, is provided at an inner face of the cabinet 48. As shown by Figs. 3(a) and 3(b), the framed stencil sheet assembly 15 is constituted by a heat-sensitive framed stencil sheet 18 constituted by laminating together a thermoplastic resin film 16 such as a plastic film and a porous support 17 in a mesh-like shape and a frame member 19 made of paper, wood or aluminum for fixing four peripheries of the stencil sheet 18. In this case, the frame member 19 for supporting the stencil sheet 18 is fitted to the holding members 13 provided on the side of the base member 2 of the press plate 11. Further, the base member 2 is built with a power source, not illustrated, which is conducted to the light irradiating apparatus 47 mounted to the opening portion 12 by being brought into contact with a pivotal end of the press plate 11. Next, an explanation will be given of operation of the embodiment in reference to Figs. 3(a) and 3(b) and Figs. 4(a), 4(b), 4(c) and 4(d). As shown by Fig. 3(a), firstly, the light irradiating apparatus 47 is mounted to the opening portion 12 of the press plate 11. The framed stencil sheet assembly 15 is fitted to the holding members 13 of the press plate 11. Further, an original 4a as an object to be pressed 4 is mounted on the pad 7. The press plate 11 is pivoted toward the print base 5 and the framed stencil sheet assembly 15 is brought into close contact with the surface of the original 4a on the pad 7. Further, when the press plate 11 is pressed down as shown by Fig. 3(b), the framed stencil sheet assembly 15 is pressed by the print base 5 from a side with which the an original 4a is brought into close contact and is fixed by a predetermined tension. At this point, a portion of the print base 5 mounted with the original 4a is disposed inside the opening portion 12 of the press plate 11. Further, the pivotal end of the press plate 11 and the base member 2 are brought into contact with each other to thereby conduct electricity to the light irradiating apparatus 47, light is irradiated to the stencil sheet 18 of the framed stencil sheet assembly 15 which is fixed with tension and an image of the the original 4a generates heat. The thermoplastic resin film 16 of the stencil sheet 18 is formed with desired perforated image in accordance with an original image. Next, in the printing operation, the light irradiating apparatus 47 is firstly removed. Further, as shown by Fig. 4(a), a sheet of printing paper 4b as the object to be pressed 4 is mounted on the print base 5. The press plate 11 is pivoted toward the print base 5 and the framed stencil sheet assembly 15 is brought into close contact with the surface of the printing paper 4b on the print base 5. Further, when the press plate 11 is pressed down (as shown by Fig. 4(b), the framed stencil sheet assembly 15 is pressed by the print base 5 from a side thereof with which the printing paper 4b is brought into close contact and is fixed by a predetermined tension. At this point, a portion of the print base 5 mounted with the printing paper 4b is disposed inside the opening portion 12 of the press plate 11. Under the state, as shown by Fig. 4(c), the framed stencil sheet assembly 15 is then squeegeed by a squeegee 21 constituting image forming means from a side of the porous support 17. Screen printing ink 22 constituting an image forming material passes from the porous support 17 to the side of the resin film 16 and is printed on a printed face of the printing paper 4b. Then, as shown by Fig. 4(d), the press plate 11 is pushed up and the printing paper 4b which has been printed is taken out. Therefore, according to the screen printing machine 1 constituted in this way, a predetermined tension can be exerted simply to the framed stencil sheet assembly 15 even by manual operation and a distinct image can be provided over the entire printed face of the printing paper 4b even when force exerted to the squeegee 21 is not uniform. Further, as shown by Figs. 5(a), 5(b) and 5(c), the pivotal end 11a of the press plate 11 according to the embodiment may be provided with engaging means 24 for engaging with the base member 2 and may be engaged with an engaging hole 26 provided at a corresponding position of the base member 2. The engaging means 24 is constituted by an engaging piece 25 engaged with the engaging hole 26, a shaft 27 axially supporting pivotably the engaging piece 25, a spring member 28 for urging the engaging piece 25 to a notched side and a release piece 29 connected to the engaging piece 25. In this case, as shown by Figs. 5(b) and 5(c), when the press plate 11 is pivoted to the side of the print base 5 and the framed stencil sheet assembly 15 is fixed with tension by the predetermined tension, the engaging piece 25 is engaged with the engaging hole 26 of the base member 2. Thereby, the tension of the framed stencil sheet assembly 15 can be made always constant. Particularly, in a perforating operation, further distinct perforated images can be provided and in a printing operation, further distinct images can be provided. Further, when released, by depressing the release piece 29, the engaging piece 25 is pivoted centering on the shaft 27 and a notched portion 25a of the engaging piece 25 is separated from a notched hole 26a of the engaging hole 26. Next, an explanation will be given of a screen printing machine 30 according to a second embodiment of the present invention. As shown by Fig. 6, a simplified screen printing machine 30 according to this embodiment is an example in which a base member 32 and a press plate 31 are constituted as separate members. The base member 32 is built with a power source, not illustrated, and the power source is conducted to the light irradiating apparatus 47 mounted to the opening portion 12 of the press plate 31 by being brought into contact with an end edge of the press plate 31. Further, portions the same as those in the first embodiment are attached with the same numerals and an explanation thereof will be omitted. Operation of the embodiment is as follows. In the perforating operation, as shown by Fig. 7(a), firstly, the light irradiating apparatus 47 is mounted to the opening portion 12 of the press plate 31. The framed stencil sheet assembly 15 is fitted to the holding members 13 of the press plate 31. Further, the original 4a is mounted on the pad 7. The press plate 31 is pivoted toward the print base 5 and the framed stencil sheet assembly 15 is brought into face contact with the surface of the original 4a on the pad 7. Further, when the press plate 31 is pressed in as shown by Fig. 7(b), the framed stencil sheet assembly 15 is pressed by the print base 5 from the side with which the an original 4a is brought into face contact and is fixed by a predetermined tension. Further, a pivotal end of the press plate 31 and the base member 32 are brought into contact with each other, electricity is conducted to the light irradiating apparatus 47 and light is irradiated to the stencil sheet 18 of the framed stencil sheet assembly 15 which is fixed with tension. The desired perforated image in accordance with an original image is formed at the stencil sheet 18. In the printing operation, the light irradiating apparatus 47 is firstly removed. Further, as shown by Fig. 8(a), the printing paper 4b is mounted on the print base 5. Further, the framed stencil sheet assembly 15 is brought into face contact with the surface of the printing paper 4b on the print base 5. Thereafter, when the press plate 31 is pressed in as shown by Fig. 8(b), the framed stencil sheet assembly 15 is pressed by the print base 5 from a side with which the printing paper 4b is brought into face contact and is fixed by a predetermined tension. Under the state, as shown by Fig. 8(c), by the squeegee 21 constituting image forming means, the framed stencil sheet assembly 15 is squeegeed from the side of the porous support 17. The screen printing ink 22 constituting image forming material passes from the porous support 17 to the side of the resin film 16 and is printed on the printed face of the printing paper 4b. Then as shown by Fig. 8(d), the press plate 31 is pushed up and the printing paper 4b which has been printed is taken out. Therefore, according to the screen printing machine 30 constituted in this way, there can be achieved an operation and effect similar to those in the above-described first embodiment. Further, as shown by Figs. 9(a), 9(b) and 9(c), the engaging means 24 explained in the first embodiment may be provided at least two opposed end edges of the press plate 31 and may be engaged with the engaging holes 26. Thereby, the tension of the framed stencil sheet assembly 15 can be made always constant. Particularly, in perforating operation, further distinct perforated images can be provided and in printing operation, further distinct images can be provided. Further, in the above-described first embodiment, the press plate 11 having the opening portion 12 and a press plate 41 with transparent plate provided with a glass plate 43 as transparent plate at the opening portion 42 as shown by Fig. 10, may interchangeably be constituted and screen printing and plane press type printing for planely pressing the stencil sheet of the framed stencil sheet assembly 44, may be carried out by a single printing machine. In this case, as shown by Fig. 11, a framed stencil sheet assembly 40 is provided with a frame member 44 substantially of a rectangular shape having predetermined thickness and rigidity. One face of the frame member 44 is laminated with stencil sheet 45 before perforating. The stencil sheet 45 is heat-sensitive stencil sheet constituted by laminating together a thermoplastic resin film and a porous support. Further, other face of the frame member 44 is fixed with an ink-unpermeable back sheet 46. The back sheet 46 is constituted by an outer shape substantially the same as that of the frame member 44. According to the back sheet 46, one short edge side thereof is fixed to corresponding one short edge side of the frame member 44. According thereto, in the case of changing from the screen printing to the plane press type printing, the press plate 11 is interchanged by the press plate 41 having the transparent plate provided with the glass plate 43 at the opening portion 42. In the perforating operation, the light irradiating apparatus 47 is mounted to the opening portion 42, an original 4a is mounted on the print base 5 and the stencil sheet assembly 40 is mounted to a lower face of the glass plate 43. Further, when the press plate 41 is pressed to the direction of the print base 5, the heat-sensitive stencil sheet 45 is brought into close contact with the original 4a and at the same time, the light irradiating apparatus 47 is operated by closing a switch mechanism, not illustrated. The flash bulbs 49 emit flashes which passes through the transparent plate 43 and the heat sensitive stencil sheet 45 and make an image of the original 4a by the generated heat. A perforated image in correspondence with image of the original 4a is formed at the resin film of the heat-sensitive stencil sheet 45. Thereafter, the back sheet 46 of the framed stencil sheet assembly 40 which has been perforated is opened, ink is mounted on the porous support and the back sheet 46 is closed again. Further, the framed stencil sheet assembly 40 which has been perforated is mounted to the press plate 41 having transparent plate with the heat-sensitive stencil sheet 45 directed downwardly. When the print sheet 4b is mounted on the print base 5 and the press plate 41 having transparent plate is pressed to the side of the print base 5, the heat-sensitive stencil sheet 45 is pressed to the print sheet 4b and stencil printing is carried out to the print sheet 4b. Further, although in Fig. 10, there is shown the screen printing machine according to the first embodiment, the same goes with the screen printing machine according to the second embodiment. As has been explained, according to the screen printing machine of the present invention, the predetermined tension can be exerted to the framed stencil sheet assembly over the entire face of the object to be pressed by pressing the framed stencil sheet assembly to the base member into contact with the object to be pressed and stretching and fixing the stencil sheet assembly. Further, images having a uniform distinctness can be formed over the entire face of the object to be printed (constituting the object to be pressed) by making the image forming material pass through the framed stencil sheet assembly by the image forming means while exerting the predetermined tension to the framed stencil sheet assembly even when pressure applied on the framed stencil sheet assembly by the image forming means is not uniform. Further, perforated images having a uniform distinctness can be formed by uniformly irradiating light over the entire face of an original (constituting the object to be pressed) by attachably and detachably providing the light irradiating apparatus for irradiating light to the stencil sheet while exerting the predetermined tension to the framed stencil sheet assembly. Further, the tension of the framed stencil sheet assembly can be made always constant by fixing the pressing means relievably to the base member in the state in which the framed stencil sheet assembly is fixed to the object to be printed on the base member with the predetermined tension. Particularly, in a perforating operation, further distinct perforated images can be provided and in a printing operation, further distinct images can be provided. Further, the screen printing and the plane press type printing can be carried out by a single printing machine by interchangeably constituting the pressing means and the pressing means having transparent plate provided with the transparent plate at the opening portion.

Claims: A screen printing machine comprising: a base member (2) for mounting an object to be pressed; a framed stencil sheet assembly (15) at least constituted by a stencil sheet (18) comprising a porous support (17) and a resin film (16) laminated to the support (17) and a frame member (19) laminated with the stencil sheet (18); and a pressing means (11) attachably and detachably attached to the framed stencil sheet assembly (15) for pressing the framed stencil sheet assembly (15) to the base member (2) with the framed stencil sheet assembly (15) under tension; characterized in that : the base member (2) has a print base (5) with an elastic member (7); and by said pressing means (11) having an opening (12) for receiving at least a part of the print base (5) therein so that when the pressing means (11) assembled with the stencil sheet assembly (15) is disposed on the print base (5) with the object to be pressed thereon, the print base (5) with the object to be pressed is at least partly located in the opening (12) to thereby stretch the framed stencil sheet assembly (15) and tension it. The screen printing machine according to claim 1, further comprising: an image forming means (21) for making an image forming material (22) pass through the framed stencil sheet assembly (15) while under tension. The screen printing machine according to claim 1, further comprising: a light irradiating apparatus (47) attachably and detachably mounted to the pressing means (11) for irradiating light to the framed stencil sheet (18) of the framed stencil sheet assembly (15) while under tension. The screen printing machine according to claim 1 wherein the pressing means (11) is openably and closably pivotally supported by the base member (2) and attachably and detachably assembled with the framed stencil sheet assembly (15). The screen printing machine according to claim 1 wherein the pressing means (11) is provided to the base member (2) as a separate member. The screen printing machine according to claim 1, further comprising: engaging means for relievably fixing the pressing means (11) to the base member (2) with a predetermined tension. The screen printing machine according to claim 1, wherein the base member (2) includes two bearings (9), and said print base (5) includes two pivot shafts (8) disposed in the two bearings (9) so that the print base (5) is pivotally supported on the base member (2).

Inventors: TANAKA TOSHIO, TANAKA, TOSHIO, Tanaka, Toshio, c/o Riso Kagaku Corp. R &amp; D Center
Applicants: RISO KAGAKU CORP, RISO KAGAKU CORPORATION
Application year: 2000
Main classification: B41F15
IPC codes: B41F15, B41C1, B41L13, H05K3