JPS5916771A - Electrostatic printing method - Google Patents

Abstract

PURPOSE:To enable to enhance clearness of printing result, by gradually augmenting an airflow by which electrically chargeable particulates constituting a desired segment form powder image formed on a screen are separated off in the direction toward a surface to be printed. CONSTITUTION:Electrically chargeable particulates are applied onto a screen through a stencil provided with 8-shaped 7-segment opening parts, thereby forming intermediate segment form power images S'1-S'n. Then, on-off valves 13 for nozzles 6 corresponding to unrequired segments are opened below a powder sucker 18 so that only the unrequired ones of the segment form powder images are removed by a high-pressure airflow fed through a high-pressure flow regulating valve VH, thereby forming dewired segment form powder images. Subsequently, a printing head 21 provided with the screen 4 is faced to, for example, the inside wall surface to be printed of a steel pipe 26, with a predetermined spacing therebetween, an electrostatic field is impressed between both of them, the on-off valves 13 for the nozzles 16 corresponding to the images are opened, and the pressure of the airflow is gradually changed from 0 to 0.5kg/cm<2> by an analog flow control valve VC, whereby the powder images are separated off from the screen 4 and are transferred. Accordingly, a clear transferred image is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a new method for electrostatic printing on a substrate without contact, and in particular to a new method for electrostatic printing that enables various types of electrostatic printing that can print desired print shapes even on the inner walls of steel pipes and the like. An electronic printing method is provided.

Conventional non-contact electrostatic printing methods first use a stencil with a printed shape defined by a large number of mesh holes, but this method allows the printed shape to be changed arbitrarily. However, by preparing a large number of stencils with various printing shapes and moving each stencil according to signals from computers etc., each stencil can be Some print shapes are combined arbitrarily to obtain a desired print shape, but although this has the advantage of being able to change the print shape arbitrarily, it has the disadvantage of increasing the size of the device.

Another method of printing on the printing material without pressure or contact is as shown in Japanese Patent Publication No. 52-37009, in which, for example, seven nozzles are arranged in a figure 8 shape, and the valves of each of these nozzles are There is a method in which only a predetermined nozzle outlet is fully opened by controlling the opening and closing of the nozzle, and powdered ink is ejected along with an air flow to print the entire desired print shape such as numbers. However, although this method is relatively simple, since the air flow and powder ink are ejected together from the nozzle outlet through a pipe and nozzle, the powder ink may stick inside the nozzle due to moisture and heat. It is difficult to maintain the printer because it can accumulate or become clogged, and the clarity of printing is also poor.

As an electrostatic printing method that eliminates all of these conventional drawbacks, there is a technique disclosed in Japanese Patent Publication No. 56-235. This electrostatic printing method is a technology to which the present invention belongs, and particularly includes a step of forming a predetermined intermediate cassegment-like powder image on a mesh body, and a step of charging unnecessary segments of the segment-like powder image. The present invention is characterized in that it includes a step of removing the powder particles by means of an air stream to obtain a final segmented powder image corresponding to the desired unit printing shape.

The electrostatic printing method of this patent publication No. 56-235 is described below as the first method.
The explanation will be made according to FIGS.

First, an example will be described in which an intermediate segmental powder image is entirely drawn on a mesh pore using charged powder particles.

Figure 1 shows an ordinary non-contact, pressureless electrostatic printing device, in which 1 is a hopper capable of supplying a predetermined amount of charged powder particles to a rolled printing brush 2; The stencil has seven segment openings corresponding to a segmented powder image, and the mesh of the openings is, for example, about 10.
It is 0 to 300 meshes. Reference numeral 4 denotes a mesh hole body like a wire mesh, which is provided with a large number of uniform mesh holes and is spaced apart from the stencil 6, and the size of each mesh hole is larger than the average particle size of the charged powder particles. is preferable, for example 400 to 500
In this case, the powder particles applied to the mesh pores hardly pass through the mesh pores. In addition, 5 is stencil 6
This is a DC high voltage power source for applying a high voltage between the mesh member 4 and the mesh member 4, and the mesh member is composed of a large number of mesh holes only in the portion where the segmented powder image described later is formed. It's okay.

In the apparatus configured as described above, as the printing brush 20 rotates or rotates, the brush comes into sliding contact with the surface of the stencil 3, so that the powder particles supplied to the brush 2 are transferred to the openings of the stencil 6. Stencil 6 through the mesh hole
The powder particles in the gap are moved into the electrostatic field formed between the stencil 6 and the mesh hole 4 and adhere to the mesh hole 4. The powder segments S1 as shown in FIG.
S2... is a segmented powder image in the shape of a figure 8 starting from 87. This powder image is an intermediate powder image, but in the case of numbers, it is the final image that should be transferred only when printing 8. It becomes a powder image.

Next, the process of obtaining the final segmented powder image will be explained.

FIG. 6 shows a nozzle 6n for ejecting a regulated air flow, the ejection opening 6n' of the core nozzle being about the size of each powder segment or slightly larger, such that seven nozzles 6a to 6g face each powder segment. will be placed in

The arrangement relationship between the nozzle and the powder segments 81 to s7 is shown in FIGS. 4A and B, and in order to remove unnecessary powder segments while maintaining this arrangement relationship, a Air is ejected from the nozzle. If the final segmented powder image, for example the number "2", is to be obtained from the intermediate segmented powder image, air streams are ejected or actuated from the nozzles 6b and 6f to form powder segments S2 and S6. It is sufficient to remove only the pores from the mesh 4.

Also, in the case of the number "!I", only the nozzles 6b and 60 are operated to remove the powder segments S2 and 85t, and in the case of the number "9", only the nozzles 6e and 6g are operated to remove the powder segments). S5 and S7 are removed from the mesh 4. Furthermore, part of the alphabet and katakana can also be obtained. For example, in the case of the alphabet "A", only the nozzle 6g is fully operated to remove the powder segment S7'z, and in the case of "E", the nozzles 6c and 6f are removed. The powder segments S6 and 86 are removed by operating only the nozzles 6a, (5c).

Powder segment S1 by operating 6f and 6gk.

S3. Remove S6 and S7.

Next, the formation of such a final segmented powder image will be specifically explained with reference to Fig. 5.

In the figure, 10 is a compressed air source, 11 is an opening/closing switching device, 12 is a valve switching device that performs all switching control of high and low pressure flow regulating valves VH+VL, and 1roa+13b.

16c, . . . are respective nozzles 6a', 6b',
On-off valves 14 are inserted in the channels connected to the on-off valves 6c', . . . , and a control panel 14 controls the opening and closing of these on-off valves. 16 is a computer that provides control signals to the control device 15; 17 is a measuring device that inputs measurement results such as the weight, length, or diameter of the printing material to the computer 16; 18 is a suction hood 18a, a cyclone 18b, and a buggy; Filter 18C
This powder suction device is fully equipped with a blower 18d, a cleaning nozzle 188, etc.

The apparatus having such a configuration is also used when transferring the final segmented powder image formed on the mesh body 4 to a printing medium and when cleaning the mesh body 4, as will be described later.

Next, the operation of this device will be explained. When the intermediate force 8-shaped powder image formed on the mesh hole body 4 and the nozzle device 6 are in a predetermined positional relationship as shown in FIG. Controlled FL board 14
The opening/closing switching device 11 opens in response to a control signal from the valve switching device 12 and connects the air source 10 to the valve switching device 12. On the other hand, at the same time, the valve switching device 12 also receives a signal from the control panel 14, and the high pressure flow rate regulating valve V sets the ejection meter of the nozzle device 6 to a high level.
Open H. Furthermore, on the other hand, the control panel 14 operates the on-off valves 13a, 13b based on the request from the computer 16.

Select 13c,..., and open/close valve 13bff.
iOpen.

Therefore, from the spout of nozzle 6b', another powder segment 1
-81', S3'... Bad shadow #'! A high-pressure airflow that does not cause damage is ejected for a predetermined short time,
As a result, the powder particles of the powder segment 82' are transferred to the mesh hole 4.
The particles are blown away from the powder and sucked into the powder suction device 18.

In this case, of course the other nozzles 6 a', 6 C'...
... does not eject all the airflow.

By removing only unnecessary powder segments in this manner, a desired segmented powder image is formed on the mesh 4.

This will be explained with reference to FIGS. 5 and 6. In response to a signal from the control panel 14, the opening/closing switching device 11 opens, and the valve switching device 12 opens only the low pressure flow regulating valve VL. -10,000 control panel 1
4 receives a signal from the computer 16 that is complementary to that at the time of forming the final segment powder image, and operates the on-off valves 13a, 1.
3c... is opened, and the valve 13b' is closed and maintained in good condition. Nozzle 6 connected to open valves 13a, 13c
a', 6 c'-..., the strength of the jetting causes the powder particles of the powder segment to float out of the wire mesh hole.

In other words, a small amount of breeze is blown out to the extent that it moves away. In this way, the powder segments Sl', S3', which ascend the fx jet airflow and leave the mesh hole 4, are connected to the mesh hole 4 and the printing surface 2.
Due to the action of the electrostatic field formed between the printing surface and the printing surface 20, the printing material moves toward the printing surface 20 and adheres to the printing surface.

Although the above description did not specifically explain the driving of the screen hole body 4, nozzle device 6, and related members (hereinafter referred to as the print head), in a practical device, the print head usually moves vertically and horizontally. It is constructed to be movable, and of course is equipped with a mechanism for detecting the gap between the printing surface and the mesh hole body, a mechanism for adjusting the gap, etc.

Next, an embodiment of the relationship between the print head and each unit will be described using a block diagram of an off-line diagram.

The print head 21 as described above is fixed to the tip of a hollow tube 24 that can freely reciprocate in the direction of the arrow by a guide 23 fixed to a frame 22. An airflow pipe, high lightning, pressure conductor, etc. (not shown) connected to each nozzle are inserted. The other end of the hollow tube 24 is connected to a driving device such as a cylinder or a motor.

First, the printing head 21 forms a segmented powder image in the shape of a figure 8 on the mesh in the powder image forming section 25 as shown in FIG. 1, which forms an intermediate segmented powder image. The powder suction device 18 is driven and stopped directly below the powder suction device 18. Here, as described above, only the unnecessary powder segments are removed from the entire mesh pore body to obtain a final segmented powder image, and then the printing head 21 is further driven and inserted into the hollow of the steel pipe 26 which is the printing target. It will be done. This steel pipe 26 is raised and lowered by a vertical movement device 27 disposed midway on a conveyor line (not shown) for conveying the steel pipe, and when the height of the print head 21 is constant, the inner wall surface of the steel pipe 26 to be printed is The vertical movement device R27 operates so that the gap between the surface of the print head 21 and the mesh hole body of the print head 21 becomes a predetermined size. It may be configured so that it can also move in the vertical direction along.

When the mesh hole body is positioned at a predetermined distance, for example, about 1 cm, from the inner wall surface of the steel pipe 26 to be printed, the print head 21 is stopped and the nozzles are selectively activated as described above to finish the printing process. The target cassegment-like powder image is transferred to the inner wall surface of the steel pipe 26. Thereafter, the print head 21 retreats again, and in the process, the mesh hole body is cleaned by the action of the cleaning nozzle in the powder suction device 18 and the operating force of the nozzle 60, and then it retreats further and returns directly below the powder image forming section 25. Prepare for the next print.

As mentioned above, such a conventional electrostatic printing method uses a low pressure flow adjustment valve V when transferring a desired segmented powder image onto the entire printing substrate.
Since L is open and a constant low level amount of breeze is used,
It has been found that the following problems may occur in actual printing.

First, due to the length of the air flow passage from the low pressure flow rate regulating valve vL to each nozzle, the characteristics of the on-off valves 13a, 13b, etc., the difference in the number of segmented characters, and the difference in the size of the opening of the valley nozzle, etc. , unless the air flow rate supplied to each nozzle is adjusted individually by the respective on-off valves 16, clear printing results cannot be obtained; Since they are not necessarily the same, the optimal air volume required for each nozzle is different, and the optimal air volume also differs due to changes in humidity, etc., and differences in the characteristics of charged powder particles, making adjustment of each on-off valve even more complicated and difficult. It must be done frequently. Therefore, as the number of printed characters increases, for example, the numerical index increases, it becomes extremely difficult to substantially improve the sharpness of the printed result.

In view of these drawbacks, the present invention relates to an improvement in the method of supplying airflow when transferring a desired segmented powder image to a printing substrate. Particle sound is also maintained over a substantial period of time, from a flow rate that does not substantially cause particles to separate from the wire mesh hole to a flow rate that causes substantially all of the segmented powder images to separate from the wire mesh hole.・It is characterized by increasing the amount.

An embodiment of the present invention will be fully described below with reference to FIG.

The present invention differs from the conventional art in that it uses an analog flow control valve Vc such as a servo valve that can continuously and automatically adjust the flow rate of the flowing air over a desired period in response to an external signal.
By using a valve control circuit Cv which increases the energization of the control valve VC over a period of time by applying a tilting voltage to the control valve Vc, the air flow is increased when the segmented powder image is transferred to the entire printing substrate. Since the purpose is to raise the level to 4th grade, this point will be explained in detail, and the rest will be omitted as they are almost the same as before.

The analog flow rate control valve VC used here is of a solenoid type, and the rate at which the valve opens increases in proportion to the current flowing through the solenoid. Therefore, by increasing the current flowing through the solenoid by a predetermined value of approximately zero over a predetermined period of time, the airflow flowing through the control valve Vck can be increased from zero to a predetermined flow rate in a predetermined period of time. The valve control circuit CV applies a hexagonal wave voltage to a control power supply, a CR time constant circuit including a variable resistor and a capacitor, an amplifier circuit, and the solenoid of the analog flow rate control valve Vc. This valve control circuit Cv valve switching device 1
Since the operation of the valve switching device 12 is exactly the same as that of the conventional valve switching device 12, the explanation thereof will be omitted.

Next, a specific example of the nozzle device 6 shown in FIG. 8 will be explained with reference to FIG. 9.

This nozzle device 6 is roughly divided into a base 6A, a segment plate 6B, a mesh hole body 4, a presser thin plate 6c, etc. The base 6A has through-holes 6E' communicating with the figure-8-shaped segment cavities 6D formed independently in the segment plates 6B. Each of the through holes 6E is provided with an attachment fitting so that the air hose 60 can be easily attached and detached. base 6A
A shallow recess is provided on the upper surface of the segment plate 6B to facilitate setting of the segment plate 6B, and the segment plate 6B is placed in this shallow recess. Here, if the segment plate 6B can cut a figure-8 segmented powder image for 7 characters,
The number of segments is 7X7=49, that is, 49 segment recesses 6D are required, and therefore the base 6A also has 49 through holes 6Ek. A mesh hole body 4 having a mesh of a predetermined size is stretched over the segment plate 6B, and a presser thin plate 6C having figure-8 segment openings is placed on top of the mesh body 4, and the base 6A is attached by a pole 8F. Fixed. With these various nozzle configurations, the entire nozzle device can be made considerably smaller and easier to handle than conventional ones.

In such an apparatus, the distance between the mesh hole body 4 and the inner wall surface of the steel pipe 26 to be printed is 5 mm to 10 mm! When the number of segmented characters is 7, the pressure at the outlet of the control valve Vc is increased from zero to 0.5' while changing the length of time from approximately 1 second, 2 seconds, 6 seconds, and 4 seconds. It was changed to d. During this process, the pressure at the outlet of the control valve Vc becomes 0 in either case.
．． 15~0.2kf/Cff! The charged powder particles forming each segmental powder image begin to separate from the mesh 4 at a rate of 0.3 to 0.4 kp/c++! Almost all the charged powder particles are removed. After that, when the pressure was further increased continuously, the charged powder particles once attached to the printing surface did not scatter up to about 2 kf/cyst. In addition, all experiments were carried out by changing several of the figure-8 segment characters, or by changing all of the segment characters, but the results were still similar to those described above.

Therefore, according to the electrostatic printing method according to the present invention, from the extent that the charged powder particles do not come off from the pressure wire mesh hole of the control valve to the point where most of the powder particles of the segmented powder image come off from the wire mesh hole, the electrostatic printing method continues. Therefore, there are various conditions such as differences in the length of the air hoses that supply the air flow to each segment, differences in the characteristics of each on-off valve, differences in the number of segmented characters, differences in the number of segmented characters, or changes in humidity. Even if there is a change, by increasing the air flow rate over time within a predetermined time, even if there is a slight time difference for each segment, the mesh hole can be adjusted without having to adjust the air flow individually. The segmented powder image on the body can be clearly transferred to the printing surface, and the practical effect is extremely large.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of a conventional apparatus for forming an intermediate segment-shaped powder image, and FIG. 2 is a diagram showing a mesh hole and an intermediate segment-shaped powder image formed on the mesh hole. , 6th
The figure shows a general nozzle, Figure 4 is a diagram showing the arrangement relationship between the conventional mesh porous body and the above-mentioned powder image, and the nozzle. Figures 5 to 5 are diagrams showing an example of an apparatus for carrying out all the conventional methods. FIG. 8 is a diagram showing an apparatus for implementing the method according to the present invention, and FIG. 9 is a diagram showing an example of a nozzle apparatus used for implementing the present invention. 4...Mesh pore S1-S7...Powder segment 6...Nozzle device 10...Compressed air source 1
1... Opening/closing switching device 12... Valve switching device Va.
...High pressure flow rate adjustment valve Vc...Analog? M, child control valve Cv...valve control circuit 16...open/close valve 14...
・Control panel 15... Nozzle control device 16...
・Computer 21... Print head 25... Powder image forming unit Patent applicant Origin Electric Co., Ltd. Figure 1 Figure 20 4 Figure-F16 Figure 7 Figure g

Claims (1)

[Claims] A predetermined intermediate segmental powder image is formed on the mesh body using charged powder particles, and the charged powder particles of unnecessary segments of the intermediate segmental powder image are formed in the mesh body by the entire air flow. After obtaining a desired segmented powder image on the mesh body, the charged powder particles of the desired segmented powder image are removed from the mesh body in the direction of the printing surface by an air flow, and then removed from the mesh hole. In an electrostatic printing method for printing on a substrate placed at a distance from a body, when the charged powder particles of the desired segmented powder image are separated from the mesh body by the entire airflow, this airflow is transferred to the charged powder Electrostatic printing characterized in that the flow rate is continuously increased over a substantial period of time from a flow rate at which particles do not substantially detach from the mesh pores to a flow rate at which most of the charged powder particles detach. Method.