Electrostatic screen printer

An electrostatic screen printer includes: an electrically conductive screen arranged in non-contact with a printing medium; sponges for rubbing a powder into the screen; and a direct current power source for applying a voltage to the printing medium and the powder, wherein the powder rubbed into the screen is adhered to the printing medium by electrostatic induction. The electrostatic screen printer includes a rotation mechanism for rotating the sponges, a parent revolution mechanism for parent revolution of the sponges, and a child revolution mechanism for child revolution of the sponges. The revolution speed ratio of the child revolution to the parent revolution may preferably be 4.0 or greater, a scraper is provided on the parent revolution mechanism so as to be interlocked with the revolution of the sponges, and the scraper is arranged so as to scrape the powder on the screen toward an axis of the parent revolution because of the interlocking.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is the U.S. National Stage of PCT/JP2015/068453, filed Jun. 26, 2015, which in turn claims priority to Japanese Application No. 2014-138198, filed Jul. 4, 2014, the entire contents of all applications are incorporated herein by reference in their entireties.

TECHNICAL FIELD

The present invention relates to an electrostatic screen printer.

BACKGROUND

Electrostatic screen printing is widely used for fragile printing media (such as food) because in electrostatic screen printing, a printing medium on which to adhere or deposit printing powder is not pressed. In recent years, there has been an increasing demand for all-solid secondary batteries with the development of electronic instruments, and it has been proposed to use electrostatic screen printing to form a powder layer in all-solid secondary batteries (see, e.g., Patent Literature 1).

All-solid secondary batteries need to have a powder layer having a strictly even thickness. However, in the method of Patent Literature 1, the thickness of the powder layer (such as an electrode layer or an electrolyte layer) is not more even than in conventional electrostatic screen printing.

By contrast, there has been provided an electrostatic screen printer that can uniform the thickness of the powder adhered and deposited on a printing medium (e.g., Patent Literature 2). In the electrostatic screen printer described in Patent Literature 2, a powder is rubbed into a screen with a roller, thereby adhering the powder to the printing medium somewhat evenly.

RELEVANT REFERENCES

Patent Literature

Patent Literature 1: Japanese Patent Application Publication No. 2012-140016

Patent Literature 2: Japanese Patent Application Publication No. 2011-243402

SUMMARY

However, even with the electrostatic screen printer described in Patent Literature 2, when the amount of powder placed on the screen is uneven in the axial direction of the roller, the powder is unevenly rubbed into the screen. Therefore, in this case, there is a problem that the powder unevenly adheres to the printing medium.

An object of the present invention is to provide an electrostatic screen printer that can adhere a powder to a printing medium more evenly.

Solution to Problem

To address the above problem, an electrostatic screen printer according to a first aspect comprises: an electrically conductive screen arranged in non-contact with a printing medium; at least one rubbing member configured to rub a powder into the screen; and a direct current power source configured to apply a voltage to the printing medium and the powder, wherein the powder rubbed into the screen is adhered to the printing medium by electrostatic induction, and wherein the electrostatic screen printer includes a rotation mechanism configured to rotate the at least one rubbing member and a revolution mechanism configured to revolve the at least one rubbing member.

The electrostatic screen printer according to a second aspect is fabricated by configuring the electrostatic screen printer according to the first aspect such that a scraper is provided on the revolution mechanism so as to be interlocked with the revolution of the at least one rubbing member, and the scraper is arranged so as to scrape the powder on the screen toward an axis of the revolution because of the interlocking.

The electrostatic screen printer according to a third aspect is fabricated by configuring the electrostatic screen printer according to the first or second aspect such that the at least one rubbing member comprises a plurality of rubbing members, and the distance from an axis of the revolution of the plurality of rubbing members to an axis of the rotation of each of the plurality of rubbing members is different.

The electrostatic screen printer according to a fourth aspect is fabricated by configuring the electrostatic screen printer according to the first or second aspect such that the revolution of the at least one rubbing member includes two stages, i.e., parent revolution and child revolution, and a revolution speed ratio of the child revolution to the parent revolution is 4.0 or greater.

The electrostatic screen printer according to a fifth aspect is fabricated by configuring the electrostatic screen printer according to the first or second aspect such that the rotation mechanism is configured to rotate the at least one rubbing member in a direction opposite to a direction of the revolution.

The electrostatic screen printer according to a sixth aspect is fabricated by configuring the electrostatic screen printer according to the second aspect so as to further include a powder feeding unit configured to feed to the scraper the powder to be rubbed into the screen.

The electrostatic screen printer according to a seventh aspect is fabricated by configuring the electrostatic screen printer according to the third aspect such that the plurality of rubbing members are configured to rotate such that trajectories of contact surfaces thereof with the screen overlap with each other, and rotate so as not to contact with each other.

The electrostatic screen printer according to an eighth aspect is fabricated by configuring the electrostatic screen printer according to the first or second aspect such that the at least one rubbing member includes an elastic member and a wear-resistant layer covering the elastic member and capable of contacting with the screen.

The electrostatic screen printer according to a ninth aspect is fabricated by configuring the electrostatic screen printer according to the first or second aspect so as to further include a screen vibrating unit configured to vibrate the screen.

Advantages

The above electrostatic screen printer can adhere a powder to a printing medium more evenly.

DESCRIPTION OF EMBODIMENTS

An electrostatic screen printer according to Embodiment 1 of the present invention will now be described.

First, an outline of conventional electrostatic screen printing will be described with reference toFIG. 1.

In conventional electrostatic screen printing, as shown inFIG. 1, a powder7is rubbed by a sponge12into a screen6including a mesh net connected to the negative electrode of a direct current power source DC, thereby to charge the powder7and pass the powder7through the screen6. Then, the charged powder7adheres to the printing medium SE by electrostatic induction. The printing medium SE is connected to the positive electrode of the direct current power source DC via the pedestal B.

The electrostatic screen printer of the present invention performs the above-described electrostatic screen printing with improved arrangement and movement (rubbing method) of the sponge12that enables the powder7to be adhered to the printing medium SE to an extreme evenness.

Next, the electrostatic screen printer according to Embodiment 1 of the present invention will now be described with reference to the drawings. In the following description, “rotation” involves an axis thereof located inside the rotating object, whereas “revolution” involves an axis thereof located outside the revolving object.

As shown inFIGS. 2a, 2b, and3, the electrostatic screen printer includes a screen6through which the powder7is to be passed, and sponges1and2(an example of rubbing members) for rubbing the powder7into the screen6. As shown inFIG. 3, these two sponges1,2rotate and revolve around axes t1, t2, Op, Oc that are orthogonal to the screen6, such that the powder7is rubbed into the screen6to an extreme evenness. That is, the electrostatic screen printer10includes a rotation mechanism5for rotating the two sponges1and2, a parent revolution mechanism3for revolving the sponges1and2(at a revolution speed ωp), and a child revolution mechanism4for further revolving the sponges1and2(at a revolution speed ωc). Although not shown, the electrostatic screen printer10further includes a pedestal disposed below the screen6and configured to carry a printing medium, and a direct current power supply for electrically connecting the screen6and the pedestal. As in the conventional electrostatic screen printing shown inFIG. 1, the direct current power source applies a negative voltage to the powder7via the screen6, and also applies a positive voltage to the printing medium via the pedestal. In the following description, the revolution caused by the parent revolution mechanism3(at a revolution speed ωp) will be referred to as “parent revolution,” and the revolution caused by the child revolution mechanism4(at a revolution speed ωc) will be referred to as “child revolution.” These two revolutions, the parent revolution and the child revolution, will be simply referred to as “revolutions.”

As shown inFIGS. 2a, 2b, and3, the screen6is disposed horizontally and included a mesh net, and when the powder7placed on the upper surface of the screen6is rubbed in, the screen6passes the powder7to the lower surface thereof. The screen6is made of an electrically conductive material and charges the powder7to be passed through by applying a high voltage from the direct current power supply. Furthermore, as in the conventional electrostatic screen printing shown inFIG. 1, the screen6is essentially arranged so as not to contact with the printing medium. As shown inFIGS. 2aand 2b, a screen frame16is arranged on the periphery of the screen6.

The sponges1,2are made of a material advantageous for rubbing the powder7into the screen6and charging the powder7. Examples of such materials include polyurethane, nylon or the like made elastic (for example, spongy). In addition, the two sponges1,2may preferably have different sizes in order to rub the powder7evenly into the screen6. In the following description, the smaller one of these two sponges1,2will be referred to as “a first sponge1” and the larger one as “a second sponge2”.

The rotation mechanism5include a first rotation shaft51providing the rotation axis t1of the first sponge1, a first rotation pulley53(not shown inFIG. 3) connected to the first rotation shaft51on the screen6side, a second rotation shaft52providing the rotation axis t2of the second sponge2, and a second rotation pulley54(not shown inFIG. 3) connected to the second rotation shaft52on the screen6side. On the screen6side of the first rotation pulley53and the second rotation pulley54, there are provided cylindrical bodies15for supporting the first sponge1and the second sponge2. Further, as shown inFIGS. 2aand 2b, the rotation mechanism5includes a rotation drive unit55connected to one of the first rotation shaft51and the second rotation shaft52(the first rotation shaft51inFIGS. 2aand 2b), and a power transmission unit56that transmits the driving force of the rotation drive unit55to the other of the first rotation shaft51and the second rotation shaft52(the second rotation shaft52inFIGS. 2aand 2b).

As shown inFIGS. 2a, 2b, and3, the parent revolution mechanism3includes a parent revolution shaft31providing the parent revolution axis Op, a parent revolution arm33connected to the parent revolution shaft31on the screen6side so as to be parallel with the screen6, and a parent revolution drive unit (not shown) disposed on the top plate18shown inFIGS. 2aand 2band connected to the parent revolution shaft31. On one end of the parent revolution arm33, there are provided a rod32(e.g., a stud bolt) and a scraper34. The rod32is arranged toward the screen6, and the scraper34is arranged such that the upper end thereof is fixed on the rod32on the screen6side and the lower edge thereof contacts with the screen6.

As shown inFIGS. 2a, 2b, and3, the child revolution mechanism4includes a child revolution shaft41disposed on the other end of the parent revolution arm33and providing the child revolution axis Oc, a child revolution arm43connected to the child revolution shaft41on the screen6side so as to be parallel with the screen6, and a child revolution drive unit45(not shown inFIG. 3) connected to the child revolution shaft41. On both ends of the child revolution arm43, there are provided the first rotation shaft51and the second rotation shaft52, respectively.

The parent revolution drive unit, which is connected to the upper end of the parent revolution shaft31and thus is not shown, is constituted by, for example, an electric motor and configured to drive the parent revolution shaft31. As shown inFIGS. 2aand 2b, the child revolution drive unit45is, for example, a child revolution gear45configured to mesh with a non-rotating spur gear36provided on the parent revolution shaft31. The spur gear36on the parent revolution shaft31and the child revolution gear45meshing therewith interlock the child revolution with the parent revolution in the forward direction. The rotation drive unit55is, for example, a rotation gear55configured to mesh with a non-rotating spur gear46provided on the child revolution shaft41. The spur gear46on the child revolution shaft41and the rotation gear55meshing therewith interlock the rotation with the child revolution in the forward direction. The power transmission unit56is, for example, a timing belt56stretched around the first rotation pulley53and the second rotation pulley54. The timing belt56interlock the rotation of one of the first sponge1and the second sponge2with the other in the forward direction.

In the configuration of the electrostatic screen printer10as shown inFIG. 3, the distance between the parent revolution axis Op and the child revolution axis Oc is referred to as “sponge parent revolution radius Ro,” the distance between the parent revolution axis Op and the axis s of the rod32is referred to as “scraper parent revolution radius Rs,” the distance between the child revolution axis Oc and the rotation axis t1of the first sponge1is referred to as “first child revolution radius r1,” the distance between the child revolution axis Oc and the rotation axis t2of the second sponge2is referred to as “second child revolution radius r2,” the diameter of the contact surface (having a circular shape) between the first sponge1and the screen6is referred to as “first contact diameter d1,” and the diameter of the contact surface (having a circular shape) between the second sponge2and the screen6is referred to as “second contact diameter d2.”

Here, the trajectories of the first sponge1and the second sponge2on the screen6will be described in detail. InFIG. 4, for simplicity, the trajectory of the rotation axis t1of the first sponge1represents the trajectory of the first sponge1, and the trajectory of the rotation axis t2of the second sponge2represents the trajectory of the second sponge2. In addition, to facilitate understanding of the trajectories of the first sponge1and the second sponge2, the trajectory of the child revolution axis Oc is also shown inFIG. 4.

As shown inFIG. 4, both the trajectories of the rotation axes t1, t2of the first sponge1and the second sponge2swing in and out (make the child revolution) around the trajectory of the child revolution axis Oc making the parent revolution. Naturally, the trajectory of the child revolution axis Oc constitutes the circumference of the sponge parent revolution radius Ro, the swing width of the first sponge1is double the first child revolution radius r1, and the swing width of the second sponge2is double the second child revolution radius r2. In addition, the density (closeness) of the trajectories of the first sponge1and the second sponge2is proportional to the revolution speed ratio of the child revolution to the parent revolution (ωc/ωp). In other words, the trajectories of the first sponge1and the second sponge2are determined by the sponge parent revolution radius Ro, the first child revolution radius r1, the second child revolution radius r2, and the revolution speed ratio of the child revolution to the parent revolution (ωc/ωp). Furthermore, the distribution of the powder7adhering to the printing medium varies depending on the first contact diameter d1and the second contact diameter d2.

The sponge parent revolution radius Ro may preferably be equal to or less than 140% of the distance from the parent revolution axis Op to the edge of the screen6. Thus, the first sponge1and the second sponge2reach the vicinity of the parent revolution axis Op on the screen6, such that the area of the screen6where the powder7is not rubbed in can be minimized. It may be preferable that the first child revolution radius r1and the second child revolution radius r2are different. Thus, the overlapping area between the trajectory of the first sponge1and the trajectory of the second sponge2is reduced, such that the powder7can be rubbed into the screen6to an extreme evenness. The second contact diameter/the second child revolution radius (d2/r2) may preferably be 70 to 120% of the first child revolution radius/the first contact diameter (r1/d1). Thus, the trajectories of the first sponge1and the second sponge2are not excessively sparse, such that the powder7can be rubbed into the screen6to an extreme evenness. The revolution speed ratio of the child revolution to the parent revolution (ωc/ωp) may preferably be 4.0 or greater. Thus, the trajectories of the first sponge1and the second sponge2are dense, that is, these trajectories are close to each other, such that the powder7can be rubbed into the screen6to an extreme evenness. It may be more preferable that the revolution speed ratio of the child revolution to the parent revolution (ωc/ωp) is not an integer. Thus, the first sponge1and the second sponge2do not return to the respective original positions after one parent revolution, such that the powder7can be rubbed into the screen6to an extreme evenness.

The scraper34is disposed at such a position that it can scrape the powder7close to the parent revolution axis Op on the screen6by the parent revolution. More specifically, as shown inFIG. 5, the angle θ formed on the screen6between the line of the scraper parent revolution radius Rs and the lower edge34uof the scraper34(the contact line between the screen6and the scraper34) is set at 40 to 70°. With the angle θ equal to or greater than 40°, the powder7can be smoothly scraped close to the parent revolution axis Op on the screen6by the parent revolution, that is, the powder7can be smoothly scraped to an area reachable to the first sponge1and the second sponge2. Further, with the angle θ equal to or less than 70°, the powder7can be scraped from a larger area. In addition, the scraper34is disposed so as to extend to the outside of the trajectories of the first sponge1and the second sponge2. Thus, even if the powder7is pushed to the outside of the trajectories by the first sponge1and the second sponge2, the powder7is scraped to the inside of the trajectories by the scraper34.

The operation of the electrostatic screen printer10will be hereinafter described.

First, a printing medium is placed on the pedestal, and the powder7is placed on the screen6. Then, the parent revolution drive unit drives the parent revolution shaft31(that is, cause the parent revolution), the child revolution shaft41, which is interlocked with the parent revolution shaft31, is driven (that is, make the child revolution), and the first sponge1and the second sponge2rotate. As a result, the powder7is rubbed into the screen6to an extreme evenness. The portion of the powder7which has not been rubbed into the screen6is scraped by the scraper34to the area reachable to the first sponge1and the second sponge2, and eventually rubbed into the screen6to an extreme evenness.

The powder7rubbed into the screen6is charged negatively by the direct current power supply and passes through the screen6to adhere by electrostatic induction to the printing medium charged positively via the pedestal.

As described above, in the electrostatic screen printer10, the powder7is rubbed into the screen6to an extreme evenness, and therefore, it is possible to adhere the powder7to the printing medium to an extreme evenness.

Further, since the scraper34scrapes the powder7to the area reachable to the first sponge1and the second sponge2, the powder7can be adhered to the printing medium without waste.

To explain the advantages of the electrostatic screen printer10, the measurement results of Comparative Example and Examples 1 to 5 are shown in Table 1 andFIGS. 6 to 11. In Comparative Example, the sponge was manually moved such that the powder7was rubbed into the screen6and adhered to the printing medium, instead of using the electrostatic screen printer10. The sponge used in Comparative Example was a rectangular parallelepiped having a size of 100 mm×50 mm in a plan view. On the other hand, in Examples 1 to 5, the powder7was adhered to the printing medium using the electrostatic screen printer10. In the electrostatic screen printer10of Examples 1 to 5, the revolution speed ratio of the child revolution to the parent revolution (ωc/ωp) was 53/12, the sponge parent revolution radius Ro was 33 mm, the first child revolution radius r1was 25 mm, the second child revolution radius r2was 15 mm, the first contact diameter d1was 28 mm, and the second contact diameter d2was 36 mm.

In addition, all of Comparative Example and Examples 1 to 5 satisfied the following conditions.

(1) The screen6included a mesh net having a size of 70 mm square.

(2) A mask having a 50 mm square hole was placed on the printing medium constituted by aluminum foil.

(3) 0.7 g of powder was placed on the screen6.

(4) The powder adhered and deposited on the printing medium was compressed at 0.25 GPa or 1.00 GPa to form a film.

(5) The film formed on the printing medium was divided into a lattice (10 mm square) having five rows and five columns, and the film thickness of the divisions were measured with a micrometer.

The measurement results of Comparative Example and Examples 1 to 5 are shown in Table 1 andFIGS. 6 to 11.

As shown in Table 1 andFIGS. 6 to 11, the film thicknesses of Examples 1 to 5 had a standard deviation about one-fifth of that of the film thickness of Comparative Example, indicating a higher evenness.

The electrostatic screen printer10according to Embodiment 2 of the present invention is fabricated by configuring the electrostatic screen printer10of Embodiment 1 such that the direction in which the first sponge1and the second sponge2rotate is opposite to the direction of the parent revolution and the child revolution.

As shown inFIG. 12, in the electrostatic screen printer10according to Embodiment 2 of the present invention, the rotation mechanism5is configured such that the rotation is reversely interlocked with the child revolution. More specifically, in the rotation mechanism5of Embodiment 2 of the present invention, for example, a reverse gear (not shown) is provided between the spur gear46and the rotation gear55of Embodiment 1 so as to mesh with these gears46,55. Since the rotation mechanism5makes the direction of the rotation opposite to that of the child revolution, the powder7scraped by the first sponge1, the second sponge2, and the scraper34are less likely to concentrate at the parent revolution axis Op.

As described above, in the electrostatic screen printer10according to Embodiment 2 of the present invention, the powder7is less likely to concentrate at the parent revolution axis Op, and therefore, the powder7can be adhered to the printing medium more evenly than in the electrostatic screen printer10according to Embodiment 1.

As shown inFIG. 13, the electrostatic screen printer10according to Embodiment 3 of the present invention is fabricated by omitting the portions related to the child revolution, the second sponge2, and the scraper34from the electrostatic screen printer10according to Embodiment 1, so as to have an extremely simple configuration.

The following description will be focused on the portions different from those in Embodiment 1. The same elements as in Embodiment 1 will be denoted by the same reference numerals and the description thereof will be omitted.

As shown inFIG. 13, the electrostatic screen printer10according to Embodiment 3 of the present invention includes, on one end of the parent revolution arm33, the first sponge1and the rotation mechanism5for the portions related to the first sponge1, instead of the child revolution mechanism4as in Embodiments 1 and 2. Therefore, the electrostatic screen printer10may have an extremely simple configuration, in which the powder7can be rubbed into the screen6more evenly by the revolution and the rotation of the first sponge1.

As described above, in the electrostatic screen printer10according to Embodiment 3 of the present invention, the powder7is rubbed into the screen6move evenly, such that the powder7can be adhered to the printing medium more evenly, and the extremely simple configuration can lower the initial costs extremely.

As shown inFIG. 14, the electrostatic screen printer10according to Embodiment 4 of the present invention is fabricated by providing the electrostatic screen printer10according to Embodiment 3 with the rod32and the scraper34on the other end of the parent revolution arm33. Therefore, the electrostatic screen printer10according to Embodiment 4 of the present invention has a sufficiently simple configuration, in which the powder7can be rubbed into the screen6more evenly by the revolution and the rotation of the first sponge1. In addition, the scraper34scrapes the powder7to an area reachable to the first sponge1.

As described above, in the electrostatic screen printer10according to Embodiment 4 of the present invention, the powder7is rubbed into the screen6move evenly, such that the powder7can be adhered to the printing medium more evenly, and the sufficiently simple configuration can lower the initial costs sufficiently.

Further, since the scraper34scrapes the powder7to the area reachable to the first sponge1, the powder7can be adhered to the printing medium without waste.

As shown inFIG. 15, the electrostatic screen printer10according to Embodiment 5 of the present invention is fabricated by providing the electrostatic screen printer10according to Embodiment 4 with the second sponge2and the rotation mechanism5for the portions related to the second sponge2on the other end of the parent revolution arm33, instead of the rod32and the scraper34as in Embodiment 4. Therefore, the electrostatic screen printer10according to Embodiment 5 of the present invention has a simple configuration, in which the powder7can be rubbed into the screen6to a high evenness by the revolution and the rotation of the first sponge1and the second sponge2.

As described above, in the electrostatic screen printer10according to Embodiment 5 of the present invention, the powder7is rubbed into the screen6move evenly, such that the powder7can be adhered to the printing medium to a high evenness, and the simple configuration can lower the initial costs.

As shown inFIG. 16, the electrostatic screen printer10according to Embodiment 6 of the present invention is fabricated by configuring the electrostatic screen printer10according to Embodiment 1 such that the disintegrated powder7is supplied to the scraper34, the powder7is rubbed into the screen6much more evenly, and the screen6into which the powder7is rubbed is vibrated. The vibration herein includes intermittent or continuous shock motions.

The following description will be focused on the portions different from those in Embodiment 1. The same elements as in Embodiment 1 will be denoted by the same reference numerals and the description thereof will be omitted.

As shown inFIG. 16, the electrostatic screen printer10according to Embodiment 6 of the present invention is fabricated by adding, to the electrostatic screen printer10according to Embodiment 1, a powder feeding unit84to86for feeding the disintegrated powder7to the scraper34, a first sponge8, a second sponge9, and elliptical columns18,19for rubbing the powder7into the screen6much more evenly, and screen vibrating unit93to95for vibrating the screen6into which the powder7is rubbed.

The powder feeding unit84to86include a downstream hopper86extending from above the top plate18through the interior of the parent revolution shaft31and having a lower end thereof oriented toward the scraper34, a material feeder85for feeding the powder7to the downstream hopper86from above, and an upstream hopper84for feeding the powder7to the material feeder85from above. Since the downstream hopper86rotates together with the parent revolution shaft31, the downstream hopper86disintegrates the powder7passing therethrough by the centrifugal force and feed it to the scraper34. The material feeder85and the upstream hopper84is configured to feed a predetermined amount of powder7to the downstream hopper86, using vibration generating elements92,91provided thereon. The powder7may preferably be fed continuously, or else it may preferably be fed intermittently at a rate of a plurality of times per one parent revolution.

The parent revolution shaft31through which the downstream hopper86extends is driven by the parent revolution drive unit81to83. The parent revolution drive unit81to83include an electric motor81disposed on the top plate18, a motor-side gear82connected to a shaft of the electric motor81, and a shaft-side gear83connected to the parent revolution shaft31. The motor-side gear82and the shaft-side gear83may be replaced with other elements such as a screw gear and a pulley as long as they transmit the rotation of the electric motor81to the parent revolution shaft31.

As shown inFIG. 17, the first sponge8, the second sponge9, and the elliptical columns18,19are configured that the contact surface between the first sponge8and the screen6(hereinafter referred to as “the small contact surface80”) and the contact surface between the second sponge9and the screen6(hereinafter referred to as “the large contact surface90”) have ellipse shapes centered at the respective rotation axes t1, t2. The small contact surface80and the large contact surface90have ellipse shapes with major diameters D8, D9and minor diameters d8, d9. In addition, for the small contact surface80and the large contact surface90, the sum of the major diameters D8, D9is greater than the sum of the first revolution radius r1and the second revolution radius r2, and the sum of the major diameter D8or D9of one of the contact surfaces and the minor diameter d9or d8of the other is kept small. Furthermore, the first sponge8and the second sponge9rotate so as not to contact with each other. For example, as shown inFIGS. 17 and 18, when one of the contact surfaces orients its major diameter D8or D9toward the child revolution axis Oc, the other orients its minor diameter d9or d8toward the child revolution axis Oc. In other words, the first sponge8, the second sponge9, and the elliptical columns18,19rotate such that the trajectories180,190of the contact surfaces80,90with the screen6overlap at the portion189, and rotate so as not to contact with each other. As long as this configuration is maintained, the small contact surface80and the large contact surface90may have other shapes than an ellipse such as oblong, ovoid, or oval shapes.

As shown inFIG. 16, the screen vibrating unit93to95include an upper vibration generating element93provided on a screen frame16, a vibration absorbing member94for vibratably supporting the screen6on a fixing base60, and a lower vibration generating element95provided under the screen6. The lower vibration generating element95is arranged circumferentially around Op in a plan view. The upper vibration generating element93and the vibration absorbing member94vibrate the screen6from the peripheral thereof, and the lower vibration generating element95vibrates the screen6from the lower portion thereof. It may also be possible that the screen vibrating unit93to95includes only the upper vibration generating element93and the vibration absorbing member94or includes only the lower vibration generating element95.

As described above, in the electrostatic screen printer10according to Embodiment 6 of the present invention, the disintegrated powder7is fed to the scraper34, the powder7is rubbed into the screen6much more evenly, and the screen6into which the powder7is rubbed is vibrated, so as to adhere the powder7to the printing medium much more evenly.

As shown inFIG. 19, the electrostatic screen printer10according to Embodiment 7 of the present invention is fabricated by simplifying the powder feeding unit87,88in the electrostatic screen printer10according to Embodiment 6.

The following description will be focused on the portions different from those in Embodiment 6. The same elements as in Embodiment 6 will be denoted by the same reference numerals and the description thereof will be omitted.

The powder feeding unit87,88in the electrostatic screen printer10according to Embodiment 7 includes a large hopper87for feeding to the scraper34the powder7put in through the powder inlet80formed in the top plate18, and a fixture88for fixing the large hopper87to the parent revolution shaft31. As shown inFIG. 20, the large hopper87rotates together with the parent revolution shaft31and is vibrated by a vibration generating element96provided on the lower surface of the top plate18.

As shown inFIG. 19, the powder7put in through the powder inlet80formed in the top plate18is disintegrated by falling into the large hopper87which is rotating and vibrating and is fed to the scraper34.

As described above, the electrostatic screen printer10according to Embodiment 7 can be simpler than that of Embodiment 6.

As shown inFIG. 21, the electrostatic screen printer10according to Embodiment 8 of the present invention is fabricated by simplifying the configuration to vibrate the large hopper87in the electrostatic screen printer10according to Embodiment 7.

The following description will be focused on the portions different from those in Embodiment 7. The same elements as in Embodiment 7 will be denoted by the same reference numerals and the description thereof will be omitted.

The large hopper87in the electrostatic screen printer10according to Embodiment 8 is vibrated not by the vibration generating element96shown inFIGS. 19 and 20, but by a plurality of projections89provided on the outer edge of the large hopper87at a constant pitch in a plan view and a collision member97provided on the lower surface of the top plate18and configured to collide with the projections89by rotation of the large hopper87as shown inFIGS. 21 and 22. Either or both of the projections89and the collision member97may be made of an elastic material (such as rubber or sponge), such that the large hopper87can be vibrated properly by the collision without hindering the rotation of the large hopper87and the parent revolution shaft31.

As described above, the electrostatic screen printer10according to Embodiment 8 can be simpler than that of Embodiment 7.

In Embodiments 1 to 8, the first sponge (and the second sponge) has been described as an example of the rubbing member, but the present invention is not limited thereto. That is, the rubbing member is required only to rub the powder7into the screen6, and more than two rubbing members may be included. As another example, the rubbing member may include an elastic member made of a sponge or carpet and a wear-resistant layer such as a nonwoven fabric covering the elastic member and capable of contacting with the screen6.

Further, in Embodiment 5, the scraper34has been described as provided on the parent revolution mechanism3, but it may also be possible that the scraper34is provided on the child revolution mechanism4.

Furthermore, in Embodiments 1 to 8, the screen6has been simply described as made of a mesh net, but it may be also possible that the screen6has a form having less tendency to pass the powder7in a region where the powder7tends to be concentrated.

In addition, in Embodiments 1 to 5, it has been described that the sponges1,2are moved on the fixed screen6so as to rub the powder7into the screen6, but the screen6may also be moved.

If the contact surfaces between the sponges1,2and the screen6are circular, the rotation axes t1, t2of the sponges1,2may preferably be eccentric such that the powder7can be adhered to the printing medium more evenly. If the contact surfaces80,90between the sponges8,9and the screen6are elliptical as in Embodiments 6 to 8, the same advantages can be produced as with the sponges1,2having circular contact surfaces and eccentric axes t1, t2.

Further, a mesh net having an appropriate coarseness may be selected for screen6depending on the desired amount of the powder7to be adhered to and deposited on the printing medium.

The sponges1,2may be provided with a brush for sweeping the outer periphery of the contact diameters d1, d2on the screen6, such that the powder7can be adhered to the printing medium more evenly.