Squeegee doctor printing mechanism

Abstract

 Disclosed is a squeegee doctor printing or coating mechanism, which comprises a squeegee doctor (5) arranged on the upper side of a substrate (1) to be printed or coated, a pressing member (6) formed of a magnetic material and mounted on the squeegee doctor (5), and an electromagnet (8) arranged on the lower side of the substrate (1) at a position confronting the squeegee doctor (5), wherein the squeegee doctor (5) is pressed to the substrate (1) by the pressing member (6) when the pressing member (6) is attracted by the electromagnet (8).

Description

Background of the Invention

(1) Field of the Invention

[0001] The present invention relates to a printing mechanism. More particularly, the present invention relates to a squeegee doctor printing or coating mechanism, according to which the entire surface of a substrate to be printed can be uniformly printed very easily with a good reproducibility.

(2) Description of the Prior Art

[0002] In printing or coating mechanisms such as coating apparatus and printing apparatus, there have been heretofore adopted (1) means in which a squeegee doctor member composed of an elastic material such as a rubber or thin metal sheet is used, the squeegee doctor is pressed to a substrate to be printed by applying a pressure to both the ends of a supporting member having the squeegee doctor attached thereto and a printing ink is coated on the substrate, and (2) means in which a squeegee roller composed of a magnetic material is used, the squeegee roller is attracted by an electromagnet arranged on the lower side of a substrate to press the squeegee roller to the substrate and a printing ink is coated on the substrate.

[0003] However, these means have merits and demerits and they fail to simultaneously satisfy all of requirements concerning reduction of the coating amount, increase of the printing accuracy, increase of the sharpness of a printed pattern, increase of the deepness of the color of a print, increase of the easiness in controlling the printing step and enhancement of the reproducibility with respect to a variety of substrates, and they are practically adopted only in a very narrow range.

[0004] More specifically, the means (1) using an elastic squeegee doctor member is advantageous in that (A) the coating amount is small and fine printing is possible and (B) a fine print having a sharp contour can be obtained, but the means (1) is defective in the following points.

(a) Since the force of pressing the squeegee doctor is controlled by adjusting the pressure applied to both the ends of the supporting member for the squeegee doctor and the relation between the pressure to be applied to both the ends of the supporting member and the pressing force to be applied to the squeegee doctor is not uniform but is influenced by the properties of the printing ink or substrate and other conditions, in order to adjust the force of pressing the squeegee doctor to a desired level, a delicate analogue technique and a high skill are required.

(b) Since the pressure is applied only to both the end portions of the supporting member, the supporting member is inevitably bent or curved by a reaction force from the squeegee doctor, and it is very difficult to coat the entire surface of the substrate uniformly.

(c) If the length of the squeegee doctor is increased to print a substrate having a broad width, the pressing force should be increased and the toughness of the supporting member should be therefore increased, with the result that the weight of the supporting member is increased and the operation adaptability is degraded.

[0005] The means (2) using a squeegee roller composed of a magnetic material is advantageous in that (Aʹ) the pressing force of the squeegee roller can be digitally adjusted very easily by controlling the size of the roller and the voltage supplied to the electromagnet, (Bʹ) since the pressing force acts uniformly on the entire width of the substrate, an excellent coating accuracy or level dyeing can be obtained and (Cʹ) since there is no risk of bending of the supporting member, the weight can be reduced. However, the means (2) is defective in the following points.

(aʹ) Since application of a coating liquid depends on the action of casting the coating liquid to the substrate by kinetic friction between the roller surface and the coating liquid, which is due to the pressing rotation of the squeegee roller, the coating amount is increased.

(bʹ) Accordingly, delicate coating or formation of a sharp and delicate print is difficult.

Summary of the Invention

[0006] It is a primary object of the present invention to provide a printing or coating mechanism which can be applied to a variety of substrates and makes it possible to uniformly print and coat the entire surface of a substrate with a good reproducibility.

[0007] Another object of the present invention is to provide a printing or coating mechanism which can form high-quality prints on various substrates by using coating liquids differing in the permeation degree in a broad range in coating amounts ranging from a very small amount to a large amount.

[0008] Still another object of the present invention is to provide a printing or coating mechanism which can be easily operated by any person without a troublesome adjusting operation or a high skill.

[0009] A further object of the present invention is to provide a printing or coating mechanism in which the weight of the squeegee-supporting member is much reduced, a response characteristic is improved, a delicate operation is easily performed and the operation adaptability is improved.

[0010] In accordance with the present invention, there is provided a squeegee doctor printing or coating mechanism, which comprises a squeegee doctor arranged on the upper side of a substrate to be printed or coated, a pressing member formed of a magnetic material and mounted on the squeegee doctor, and an electromagnet arranged on the lower side of the substrate at a position confronting the squeegee doctor, wherein the squeegee doctor is pressed to the substrate by the pressing member when the pressing member is attracted by the electromagnet.

[0011] The printing or coating mechanism of the present invention exerts the following prominent effects.

(a) A variety of substrates can be printed or coated, and the entire surface of a substrate can be uniformly printed and coated.

(b) Since the pressing force of the squeegee doctor can be digitally adjusted by adjusting the weight of the squeegee doctor-pressing member and the voltage applied to the electromagnet in combination, the adjustment is easy and printing can be performed with a good reproducibility.

(c) Since no pressing force is applied to the squeegee doctor-supporting member, there is no risk of bending of the supporting member during the printing operation, and therefore, the weight can be reduced and a delicate operation can be performed easily with a good response characteristics.

(d) By adjusting the angle between the squeegee doctor and the substrate as well as the weight of the pressing member and the voltage to be applied to the electromagnet, sharp prints and other high-quality prints can be formed on various substrates by using a variety of coating liquids differing in the permeation degree in a broad range in coating amounts ranging from a very small amount to a large amount.

(e) A troublesome adjustment or a high skill is not required for the operation, and any person can operate the printing or coating mechanism very easily and the operation adaptability is highly improved.

Brief Description of the Drawings

[0012] 

Fig. 1 is a sectional partial view illustrating an embodiment of a squeegee doctor printing or coating mechanism for directly printing or coating a substrate.

Fig. 2 is a sectional partial view illustrating an embodiment of a squeegee doctor printing or coating mechanism for printing or coating a substrate through a screen.

detailed Description of the Preferred Embodiments

[0013] The present invention will now be described in detail with reference to embodiments illustrated in the accompanying drawings.

[0014] In the instant specification and appended claims, the term "printing" is defined to mean not only direct coating of a coating liquid on a substrate but also printing of a coating liquid on a substrate through a flat screen or rotary screen.

[0015] Referring to Fig. 1, a substrate 1 is spread on the top face of an endless belt 2 and is moved to the left. Above the substrate 1, a squeegee doctor-supporting member 3 is arranged so that the axial direction of the member 3 is orthogonal to the direction of advance of the substrate 1. A squeegee doctor-attaching member 4 is fixed to the lower side of the supporting member 3, and a squeegee doctor 5 is fixed to the top end portion of the attaching member 4 so that an acute angle is formed between the squeegee doctor 5 and the substrate 1 with respect to a direction reverse to the direction of advance of the substrate 1. Each of the supporting member 3, the attaching member 4 and the squeegee doctor 3 has a length which is equal to or larger than the width of the substrate 1. The supporting member 3 is arranged so that the supporting member 3 can conduct a circular movement with the orthogonal line between the vertical plane passing through the central axis of the supporting member 3 and the surface of the substrate being as the central axis. A pressing member 6 composed of a magnetic material is disposed on the squeegee doctor 5 and is prevented from departing from the position on the squeegee doctor 5 by an anchoring member 7 fixed to the attaching member 4. The pressing member 6 has a length equal to or larger than the width of the substrate 1, but the anchoring member 7 need not extend along the entire width of the substrate, so far as the pressing member 6 is prevented from departing from the position on the squeegee doctor 5. The pressing member 6 does not move in the width direction of the substrate but is movable in the region surrounded by the attaching member 4, the squeegee doctor 5 and the anchoring member 7. An electromagnet 8 is disposed on the lower side of the endless belt 2 at the position confronting the squeegee doctor 5 and pressing member 6. When the electromagnet 8 is energized by an electric current, the pressing member 6 is attracted to the electromagnet 8 and a pressing force is applied to the squeegee doctor 5 by this attracting force and the weight of the pressing member 6. A coating liquid 9 is supplied between the squeegee doctor 5 and the substrate 1 below the squeegee doctor 5 and is coated on the substrate 1 by the squeegee doctor 5.

[0016] The squeegee doctor 5 is formed of a thin sheet of a metal such as a stainless steel or phosphor broze, a plate of a resin such as a thermoplastic resin, a thermosetting resin or a thermoplastic or thermosetting resin reinforced with a glass fiber or the like, or a plate of a rubber. As the thermoplastic resin, there can be mentioned a vinyl chloride resin, high-density polyethylene, crystalline polypropylene, a polyamide, a polyacetal and a polycarbonate. As the thermosetting resin, there can be mentioned an epoxy resin, a melamine resin, a urea resin and an unsaturated polyester resin. It is generally preferred that the thickness of the thin metal sheet be 0.1 to 1.0 mm and the thickness of the resin plate be 0.2 to 3.0 mm. A laminate formed by piling or bonding the thin metal sheet and the resin plate can be used as the squeegee doctor 5.

[0017] The pressing member 6 is a rod-shaped body formed of a magnetic material. The pressing member 6 may be formed of a magnetic material and a non-magnetic material, and an iron rod having the surface plated or coated with a resin is advantageously used as the pressing member 6. The sectional shape of the pressing member 6 may be a circular shape as shown in Fig. 1 or an ellipsoidal, polygonal or other optional shape. The size and weight of the pressing member 6 may be optionally selected, so far as the above-mentioned function is exerted. However, in case of a pressing member having a circular section, it is generally preferred that the diameter be about 5 to about 50 mm.

[0018] A known supporting member can be used as the supporting member 3. In the known squeegee doctor printing or coating mechanism, since it is necessary to press the squeegee doctor by applying a pressure to both the end portions of the supporting member, the supporting member should be so tough that the supporting member can resist a reaction force from the squeegee doctor and deformation is prevented. In contrast, in the present invention, it is sufficient if only the squeegee doctor is supported, and the supporting member may have a lower strength and a lighter weight than the known supporting member.

[0019] The shapes of the attaching member 4 and anchoring member 7 are not particularly critical, so far as the above-mentioned functions are exerted. For example, the anchoring member 7 may be fixed to the supporting member 3.

[0020] A known electromagnet can be used as the electromagnet 8, and the attracting force to the pressing member 6 can be adjusted by adjusting the voltage to be applied to the electromagnet 8, whereby the pressing force to the squeegee doctor 5 can be adjusted. The pressing force to the squeegee doctor 5 should be appropriately changed according to the properties of the substrate 1 and coating liquid 9, the amount of the coating liquid coated on the substrate 1 and the moving speed of the substrate 1. As pointed out hereinbefore, the pressing force to the squeegee doctor 5 is given by the sum of the weight of the pressing member 6 and the force of attracting the pressing member 6 to the electromagnet 8. Accordingly, there can be adopted a method in which the necessary minimum pressing force of the pressing force to the squeegee doctor 5 is given by the weight of the pressing member 6 and a variable portion of the pressing force to the squeegee doctor 5 is given by the attracting force of the electromagnet 8. Since the attracting force to the pressing member 6 is changed according to the kind and weight of the pressing member 6, the distance from the electromagnet 8 and the size of the electromagnet 8, the range of the voltage to be applied to the electromagnet 8 cannot be specified, but it is generally preferred that the voltage be selected so that an attracting force of 10 to 3000 g/cm is given to the pressing member 6. It also is preferred that the above-mentioned factors having influences on the attracting force be adjusted so that the attracting force within the above-mentioned range can be given to the pressing member 6 while the voltage to be applied to the electromagnet 8 is 10 to 150 volts. The voltage applied to the electromagnet 8 can be digitally displayed. The voltage may be adjusted steplessly and continuously, or there may be adopted a method in which a plurality of voltages are set in advance and an appropriate voltage is selected by switching.

[0021] It is preferred that the attaching member 4 and squeegee doctor 5 be arranged so that the top end of the squeegee doctor 5 is located just below the central axis of the suppporting member 3 with respect to the vertical direction. If this arrangement is adopted, by the circular movement with the orthogonal line between the vertical plane passing through the central axis of the supporting member 3 and the surface of the substrate being as the center axis, the angle ϑ formed between the squeegee doctor 5 and the substrate 1 on the upstream side of the squeegee doctor 5 can be changed while the top end of the squeegee doctor 5 is kept in contact with the surface of the substrate 1. The amount of the coating liquid coated on the substrate 1 can be adjusted by thus changing the above-mentioned angle ϑ.

[0022] The supporting member 3 (the squeegee doctor 5 supported thereby) and the electromagnet 8 may be arranged so that they can be moved to the left and right while the positional relation between them is maintained.

[0023] In the embodiment illustrated in Fig. 1, the endless belt 2 may be omitted.

[0024] In an embodiment shown in Fig. 2, a rotary screen 10 is arranged on the upper surface of a substrate 1 spread on the upper surface of the endless belt 2, and a supporting member 3, an attaching member 4, a squeegee doctor 5, a pressing member 6 and an anchoring member 7 are arranged within the rotary screen 10. An electromagnet 8 is disposed below the endless belt 2. The structures, materials and functions of the supporting member 3, attaching member 4, squeegee doctor 5, pressing member 6, anchoring member 7 and electromagnet 8 are the same as described hereinbefore with reference to the embodiment shown in Fig. 1.

[0025] A coating liquid 9 is supplied between the squeegee doctor 5 and the rotary screen 10 below the squeegee doctor 5, and the coating liquid 9 is printed on the substrate 1 through the rotary screen 10 by the squeegee doctor 5. Printing through the rotary screen is performed according to known procedures.

[0026] A flat screen can be used instead of the rotary screen.

[0027] The supporting member 3 (the squeegee doctor 5 supported thereby), the rotary screen and the electromagnet 8 may be arranged so that they can be moved to the left and right or in the width direction of the substrate 1 in Fig. 2 while the positional relation among them is maintained. In the case where these members are moved in the width direction of the substrate 1, known means such as a screen frame should be adopted.

Claims

1. A squeegee doctor printing or coating mechanism, which comprises a squeegee doctor arranged on the supper side of a substrate to be printed or coated, a pressing member formed of a magnetic material and mounted on the squeegee doctor, and an electromagnet arranged on the lower side of the substrate at a position confronting the squeegee doctor, wherein the squeegee doctor is pressed to the substrate by the pressing member when the pressing member is attracted by the electromagnet.

2. A printing or coating mechanisms as set forth in claim 1, wherein a screen is arranged between the squeegee doctor and the substrate.

3. A printing or coating mechanism as set forth in claim 2, wherein the screen is a flat screen or a rotary screen.

4. A printing or coating mechanism as set forth in claim 1, wherein the pressing member has a length substantially equal to the lateral length of the squeegee doctor.

5. A printing or coating mechanism as set forth in claim 1, wherein the pressing member is mounted on the squeegee doctor so that the pressing member is not moved in the width direction of the substrate but is movable in the direction vertical to the width direction of the substrate.

6. A printing or coating mechanism as set forth in claim 1, wherein the squeegee doctor is a plate formed of at least one member selected from the group consisting of metals, thermoplastic resins, thermosetting resins, fiber-reinforced resins and rubbers.

7. A printing or coating mechanism as set forth in claim 1, wherein the pressing member is a rod-shaped body formed of a magnetic material or a magnetic material and a non-magnetic material.

8. A printing or coating mechanism as set forth in claim 1, wherein the electromagnet has an attracting force of 10 to 3000 g/cm to the pressing member.

9. A squeegee doctor printing or coating mechanism, which comprises an endless belt movable in one horizontal direction, on the top surface of which a substrate is spread, a squeegee doctor-supporting member disposed above the endless belt so that the axial direction of the supporting member is orthogonal to the direction of advance of the endless belt, a squeegee doctor attached to the supporting member through an attaching member so that an acute angle is formed between the squeegee doctor and the endless belt with respect to the direction reverse to the direction of advance of the endless belt, a pressing member formed of a magnetic material, which is mounted on the squeegee doctor so that the pressing member does not move in the width direction of the endless belt but is movable in the direction vertical to the width direction of the endless belt, an anchoring member fixed to the supporting member to prevent the pressing member from departing from the position on the squeegee doctor, and an electromagnet disposed below the endless belt at the position confronting the pressing member.

10. A printing machine comprising a supporting member for a substrate to be printed, a stencil having a pattern to be printed and a squeegee mechanism located on the stencil to apply a printing ink onto the substrate through the pattern of the stencil, wherein the squeegee mechanism a flexible squeegee doctor located above the stencil, a pressing member formed of a magnetic material, which is mounted on the squeegee doctor movably in the vertical direction and an electromagnet arranged below the substrate at the position confronting the squeegee doctor, and the respective members of the squeegee mechanism are relatively arranged so that when the pressing member is attracted by the electromagnet, the pressing member presses the squeegee doctor to the substrate.

11. A squeegee doctor printing or coating mechanism, which comprises an endless belt movable in one horizontal direction, on the top surface of which a substrate is spread, a squeegee doctor-supporting member disposed above the endless belt so that the axial direction of the supporting member is orthogonal to the direction of advance of the endless belt, a squeegee doctor attached to the supporting member through an attaching member so that an acute angle is formed between the squeegee doctor and the endless belt with respect to the direction reverse to the direction of advance of the endless belt, a pressing member formed of a magnetic material, which is mounted on the squeegee doctor so that the pressing member does not move in the width direction of the endless belt but is movable in the direction vertical to the width direction of the endless belt, an anchoring member fixed to the supporting member to prevent the pressing member from departing from the position on the squeegee doctor, a rotary screen which is arranged so that a part of the screen is located between the squeegee doctor and the endless belt and the supporting member and squeegee doctor are located within the screen, and an electromagnet disposed below the endless belt at the position confronting the pressing member.

Drawing