Patent ID: 12220923

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, a case where an embodiment of the present disclosure is applied to an inkjet printing apparatus1that performs printing on a medium M will be described by way of an example.

FIG.1is a schematic view describing an inkjet printing apparatus1.

FIG.2is a view showing a portion of a carriage3in an enlarged manner.

In each drawing, the reference sign “Y” means the main scanning direction, the reference sign “X” means the sub-scanning direction, and the reference sign “Z” means the vertical direction.

As shown inFIG.1, in the inkjet printing apparatus1, the carriage3is supported by a guide rail2arranged horizontally. The carriage3is provided to be movable forward and backward in the longitudinal direction (main scanning direction Y) of the guide rail2.

As shown inFIG.2, a plurality of inkjet heads30(30ato30d) and a UV irradiator32are mounted on the carriage3. In the following description, the inkjet heads30ato30dare also simply referred to as inkjet heads30when they are not distinguished.

The medium M is located below the carriage3. When printing is performed on the medium M, the carriage3moves on the guide rail2in the main scanning direction Y. At this time, ink droplets are ejected from the respective inkjet heads30(30ato30d) onto the surface of the medium M based on a command of a control device (not shown), and an image is formed on the surface of the medium M.

When the ink used for printing is an ultraviolet curable ink, the ink droplets landed on the medium M are irradiated with ultraviolet light from the UV irradiator32to solidify and fix the ink droplets.

FIG.3is a view schematically showing a cross-section of the inkjet head30.

The inkjet head30has a nozzle plate31at a portion facing the medium M.

In the nozzle plate31, nozzle rows formed by a plurality of nozzle holes31aare lined in the same direction.

A head port35having an ink supply port36is attached to an upper portion of the inkjet head30. An ink supply pipe11extending from the ink tank10is connected to the ink supply port36. The ink supply port36communicates with a filter chamber33. The ink in the ink tank10is supplied to the filter chamber33through the ink supply port36.

The ink supplied to the filter chamber33is supplied to an ink ejection chamber (not illustrated) through the head filter34. A piezoelectric element is provided in the ink ejection chamber. When the piezoelectric element is driven, the ink in the ink ejection chamber is ejected from the nozzle hole31atoward the medium M.

Here, the head filter34is provided in a direction along the horizontal line direction, and the ink supplied to the filter chamber33passes through the head filter34from the upper side to the lower side.

The horizontal line direction means a horizontal line direction based on an installation state with respect to an installation surface G (seeFIG.1) of the inkjet printing apparatus1.

The meshes (openings) of the head filter34used have different optimum apertures depending on the type of the inkjet head30. In the present embodiment, as an example, the head filter34having an opening of 5 to 8 μm is adopted.

Fine particles such as pigments and resins are dispersed in the ink. Therefore, fine particles and the like in the ink may aggregate to cause a phenomenon (bridging phenomenon) of crosslinking so as to cover the mesh of the head filter34. Then, the head filter34may be clogged by the aggregated particles or the like.

In the present embodiment, a rolling element (spherical body50) is disposed in the filter chamber33for the purpose of preventing clogging of the head filter34.

Specifically, at least one rolling element (spherical body50) is placed on the head filter34provided in a direction along the horizontal line.

In the present embodiment, a spherical body50having a circular outer shape in top view is placed on the head filter34. Here, the “spherical body” in the present specification merely needs to have roundness to such an extent that point contact can be made with the upper surface of the head filter34. Therefore, the spherical body50does not need to be a perfect circle. Therefore, even a spherical body having an elliptical outer shape in top view can be adopted as long as the spherical body can be in point contact with the upper surface of the head filter34.

In the present embodiment, the spherical body50rolls on the surface of the head filter34with a moment (acceleration) when the carriage3moves in the main scanning direction Y at the time of printing on the medium M.

In the present disclosure, it is considered that the rolling spherical body50produces the following action to suppress the occurrence of the bridging phenomenon.(a) The rolling spherical body50generates convection of ink on the surface of the head filter34to disperse the aggregated particles on the surface of the head filter34.(b) The rolling spherical body50moves while pushing away the particles aggregated on the surface of the head filter34, thereby dispersing the particles aggregated on the surface of the head filter34.(c) The rolling direction of the spherical body50is not limited to a specific direction. Therefore, as a result of the spherical body50moving randomly without being deviated to a specific region on the upper surface of the head filter34, the occurrence of the bridging phenomenon is suppressed over a wide range without being deviated only to the specific region of the head filter34.

Here, when the spherical body50sinks in the ink passing through the filter chamber33, buoyancy acts on the spherical body50. When the spherical body50is separated from the surface of the head filter34by the acting buoyancy, the spherical body50may not be able to roll on the surface of the head filter34at the time of printing, and the actions (a), (b), and (c) may not be exhibited.

For example, since a resin spherical body has a low specific gravity, there is a possibility that the spherical body floats from the surface of the head filter34when the spherical body sinks in the ink. Furthermore, the spherical body needs to have such a density that the spherical body can roll and move (roll) on the upper surface of the head filter34with the movement of the inkjet head30while physically coming into contact with the upper surface of the head filter34.

Therefore, in the present embodiment, a spherical body formed of a nonmagnetic metal material, specifically, a spherical body made of stainless steel having a high specific gravity and excellent durability is adopted.

The spherical body50is at least formed with a diameter larger than the mesh (opening) of the head filter34. In the present embodiment, a spherical body of 1 φ (diameter: 1 mm) is used as an example. This is because, if the diameter of the spherical body50is smaller than the mesh of the head filter34, the spherical body50may be clogged in the mesh of the head filter34, or the like, which may cause trouble in the rolling of the spherical body50.

FIG.4AtoFIG.4Care diagrams for explaining a relationship between a head filter34and a spherical body50.FIG.4Ais a schematic view showing the periphery of the filter chamber33in the inkjet head30in an enlarged manner.FIG.4Acorresponds to a cross-sectional view taken along line A-A inFIG.3.FIG.4Bis a view describing a projection area of the spherical body50with respect to an area of the head filter34.FIG.4Cis a view describing a projection area of a parallel pin50A with respect to an area of the head filter34.

InFIGS.4B and4C, the effective rolling range and the projection area of the spherical body50and the parallel pin50A are shown with hatching.

In the cross-sectional view, the filter chamber33has a substantially rectangular shape, and an opening on a lower side (nozzle plate31side) of the filter chamber33is covered with the head filter34. The ink supplied to the filter chamber33passes through the head filter34from the upper side to the lower side, and is supplied to the nozzle plate31side.

The usage area of the head filter34is substantially the same as the opening area of the filter chamber33in the cross-sectional view. The spherical body50is a spherical body in point contact with the upper surface of the head filter34, and has a circular outer shape in top view.

In the inkjet printing apparatus1, the inkjet head30moves in the main scanning direction Y at the time of printing on the medium M.

In the present embodiment, the total number and the diameter of the spherical bodies50arranged in the filter chamber33are determined so that the spherical bodies50can freely roll in the filter chamber33when the inkjet head30moves.

Specifically, the total number and the diameter of the spherical bodies are set such that the ratio (arrangement density of the spherical bodies) of the sum of the projection areas of each of the spherical bodies with respect to the area of the head filter34is greater than or equal to 3% and less than or equal to 30%.

Here, in a case where the diameter of each spherical body50is φ, the projection area R of one spherical body50is π(φ/2)2. Here, the projection area R of the spherical body50is a hatched circular region (R=π(φ/2)2) inFIG.4B.

The total number of spherical bodies50placed on the head filter34is N. The projection area R2 of the entire spherical body is N×π(φ/2)2(R2=N×π(φ/2)2).

Then, the ratio of the projection area R2 of all the spherical bodies with respect to the area R1 of the head filter34is R2/R1=(N×π(φ/2)2)/R1.

In the present embodiment, the arrangement density (R2/R1) and the diameter φ of the spherical bodies are set so that the ratio of the projection area R2 of all the spherical bodies with respect to the area R1 of the head filter34satisfies the following relationship of greater than or equal to 3% and less than or equal to 30%.
0.03≤arrangement density≤0.3  (1)

Therefore, for example, in a case where the area R1 of the head filter34is 20 mm2, and the diameters of the spherical bodies50are 1φ (1.0 mm), 1.5 φ(1.5 mm), and 2φ(2.0 mm), the values of the projection area and the arrangement density of the spherical bodies are as shown in the following table.

TABLE 1Diameter of spherical body (1 φ = 1 mm)Total number of spherical bodies123456789Projection area0.791.572.363.143.934.715.506.287.0Arrangement density0.040.080.120.160.200.240.270.310.35Diameter of spherical body (1.5 φ = 1.5 mm)Total number of spherical bodies123456789Projection area1.773.535.307.07Arrangement density0.090.180.260.35Diameter of spherical body (2 φ = 2 mm)Total number of spherical bodies123456789Projection area3.146.28Arrangement density0.150.31

Therefore, the total number N of spherical bodies satisfying the above equation (1) is 1 to 7 in the case of where the spherical bodies of lip (1 mm) are used.

When the spherical bodies of 1.5 φ(1.5 mm) are used, the total number is 1 to 4. When the spherical bodies of 2φ(2 mm) are used, the total number is 1 to 2.

When the arrangement density decreases, the suppression of the bridging phenomenon becomes insufficient, and there is a high possibility that the passing of the ink through the head filter34is inhibited.

Therefore, the ratio (arrangement density) of the projection area R2 of all the spherical bodies with respect to the area R1 of the head filter34is preferably greater than or equal to 3% and less than or equal to 30%, but preferably greater than or equal to 5% and less than or equal to 20%, or greater than or equal to 10% and less than or equal to 20%.

When the arrangement density exceeds 30%, the resistance when the ink passes through the head filter34increases. When the arrangement density is less than 3%, the suppression of the bridging phenomenon becomes insufficient.

Therefore, in a case where the condition of the arrangement density is greater than or equal to 5% and less than or equal to 20%, when the diameter of the spherical body50is 1φ(1 mm), the total number of spherical bodies is 2 to 5. When the diameter of the spherical body50is 1.5φ(1.5 mm), the total number of spherical bodies is 1 to 3. When the diameter of the spherical body50is 2φ(2 mm), the total number of spherical bodies is 1.

Therefore, in a case where the condition of the arrangement density is greater than or equal to 10% and less than or equal to 20%, when the diameter of the spherical body50is 1φ(1 mm), the total number of spherical bodies is 3 to 5. When the diameter of the spherical body50is 1.5φ(1.5 mm), the total number of spherical bodies is 2 or 3. When the diameter of the spherical body50is 2φ(2 mm), the total number of spherical bodies is 1.

Here, the degree of clogging of the head filter after passing the ink under the following conditions was verified for each of (A) a case where the rolling elements (spherical body50, parallel pin50A) were placed on the head filter34and (B) a case where the spherical bodies50were not placed on the head filter34.

Hereinafter, the verification conditions and the verification results will be described.

[Verification Condition]

<Head Filter>

A rectangular head filter having an area of 4 mm×5 mm was used.

In the verification, the head filter was disposed in a filter chamber having an opening of 4 mm×5 mm in the pseudo head, and the ink supplied to the filter chamber was caused to flow through the filter from the upper side to the lower side. The filter area in this case is 20 mm2.

<Rolling Element>

(A) Spherical Body

Five stainless steel spherical bodies50having a diameter of 1φ(diameter 1 mm) were placed on the head filter in the pseudo filter chamber (seeFIG.4B). In this case, the projection area R of the five spherical bodies with respect to the head filter40is 3.93 mm2.

(B) Parallel Pin

The parallel pin50A having a diameter of 2φ(2 mm) and a length of 4 mm was placed on the head filter in the pseudo filter chamber (seeFIG.4C). In this case, the projection area R′ of the parallel pin with respect to the head filter40is 8.0 mm2.

<Test Conditions>

In order to simulate the scanning of the carriage (inkjet head) at the time of printing, the pseudo head was moved at a speed of 466 mm/s and an acceleration of 0.43 G, and the SP ink was caused to pass through the head filter while flowing at a water head difference of 50 cm under a normal temperature environment.

The verification results under the above test conditions are shown in Table 2 ofFIG.5and in the following Tables.

Here, the surface image in Table 2 is an electron micrograph of the surface of the head filter40after the test. In the photomicrograph, the fewer the aggregates and foreign substances, the more the black color appears, and the aggregates and foreign substances appear in white color. In the area analysis, the region where the foreign substances are attached appears in red color.

Please refer toFIG.5for the verification results shown in Table 2.

TABLE 3After testWithoutstirringWith stirring bodyBefore testbodyParallel pinsSphereOcclusion rate50.28%76.13%64.51%66.31%Initial flow rate2.3 cc/min———Flow rate after test—0 cc/min1.47 cc/min2.1 cc/minFlow rate reduction—100%36.20%8.50%rate

In a case where the stirring body was not placed on the head filter, the occlusion rate of the head filter increased from 50.28% before the test to 76.13%. The reduction rate of the flow rate of the SP ink in the head filter was 100%.

In a case where one parallel pin serving as the stirring body was placed on the head filter, the occlusion rate of the filter increased from 50.28% before the test to 64.51%. The reduction rate of the flow rate of the SP ink was 36.20%.

In a case where five spherical bodies serving as the stirring body were placed on the head filter, the occlusion rate of the filter increased from 50.28% before the test to 66.31%. The reduction rate of the flow rate of the SP ink was 8.50%.

From the above, it was confirmed that when the rolling element was placed on the head filter, the decrease in the flow rate of the ink after the test was suppressed as compared with the case where the rolling element was not placed.

Furthermore, it was confirmed that when a spherical body was used as the stirring body, a decrease in the flow rate of the ink after the test was suppressed as compared with the case where the parallel pin was used.

As illustrated inFIG.4B, the spherical body50comes into contact (point contact) with the upper surface of head filter34at point C. Therefore, the effective rolling range of the spherical body50in the head filter34of 4 mm×5 mm is a range of 3 mm×4 mm.

As illustrated inFIG.4C, the parallel pin50A comes into contact (line contact) with the upper surface of head filter34at line C′. Therefore, the effective rolling range of the parallel pin50A in the head filter34of 4 mm×5 mm is a range of 2 mm×5 mm.

Therefore, as the rolling element, the spherical body50rolls in a wider range than the parallel pin50A.

When the rolling elements are disposed in the filter chamber33of the inkjet head30, the rolling elements are inserted from the ink supply port36.

When the parallel pin50A is placed on the head filter34, the parallel pin50A needs to be disposed in a direction in which the longitudinal direction of the parallel pin50A is orthogonal to the main scanning direction Y. However, when the parallel pin50A is inserted from the ink supply port36, the longitudinal direction of the parallel pin50A may not necessarily be in the direction orthogonal to the main scanning direction Y.

On the other hand, in the case of the spherical body50, it is not necessary to align the direction.

Therefore, in the present embodiment, the spherical body50is adopted as the rolling element due to the width of the effective rolling range and the ease of installation. However, the use of the parallel pin50A is not excluded.

When the plurality of spherical bodies50are placed on the head filter34, the moving direction of the spherical bodies50is not limited to a specific direction as with the parallel pin50A when the inkjet head30moves in the main scanning direction. Therefore, each of the spherical bodies50moves randomly (seeFIG.4A). As a result, the particles aggregated on the head filter34can be more reliably dispersed by the spherical bodies50passing through the region where the particles are aggregated. Thus, occurrence of the bridging phenomenon can be suppressed.

In the embodiment described above, the case where the ink passing through the head filter34in the filter chamber33is an ultraviolet curable ink has been exemplified. The ultraviolet curable ink has a high tendency to easily generate aggregates. Therefore, by placing a plurality of spherical bodies on the head filter34, the possibility of occurrence of clogging can be reduced in the head filter34using the ultraviolet curable ink.

When the printing apparatus is a shaping apparatus of a stereoscopic structural object, the present disclosure is preferably applied to a filter chamber of an inkjet head that ejects a support material ink.

Here, the support material ink is an ink composition used for shaping a region (support region) that supports a shaped object. An example of the support material ink is disclosed in Japanese Unexamined Patent Publication No. 2018-183890.

In the shaping of the stereoscopic structural object, the usage amount of the support material ink is larger than the usage amount of other inks for forming the shaped object. Therefore, in the inkjet head for the support material ink, clogging of the filter easily occurs as compared with other inkjet heads.

Therefore, in the inkjet head using the support material ink, the possibility of occurrence of clogging in the head filter34can be reduced by placing a plurality of spherical bodies on the head filter34.

In the embodiment described above, the case has been exemplified where the total number of spherical bodies to be placed is determined in consideration of the ratio of the sum R2 of the projection areas of the spherical bodies50with respect to the area R1 of the head filter34(see the above equation (1)).

Here, the total number and the diameter φ of the spherical bodies50may be set based on the area R1 of the head filter34.

For example, the total number and the diameter φ of the spherical bodies50may be set so as to satisfy the following relationship in which the sum R2 of the projection areas of the spherical bodies50is greater than or equal to 1/30 and less than or equal to ⅓ of the area R1 of the head filter34.
(R1/30)≤sum of projection areas of spherical bodiesR2≤(R⅓)  (2)

Therefore, for example, when the area R1 of the head filter34is 12 mm2, the total number and the diameter φ of spherical bodies are set so as to satisfy the relationship in which the sum R2 of the projection areas of the spherical bodies50placed on the head filter34is greater than or equal to 0.4 mm2and less than or equal to 4 mm2.

Referring to Table 1 described above, the total number N of spherical bodies satisfying the above equation (2) is 1 to 5 when the spherical bodies of 1φ(1 mm) are used.

When the spherical bodies of 1.5 φ(1.5 mm) are used, the total number is 1 to 2. When the spherical bodies of 2 φ(2 mm) are used, the total number is 1.

Furthermore, the total number of spherical bodies to be placed on the head filter34may be determined in consideration of the length L (seeFIG.4B) of the head filter34in the direction orthogonal to the main scanning direction Y of the inkjet head30and the diameter φ of the spherical body50.

For example, as illustrated inFIG.4B, when the head filter34has a length L (5 mm) in the direction orthogonal to the main scanning direction Y, and the spherical bodies50have a diameter φ(1 mm), at least five (5÷1=5) spherical bodies50can be lined in the direction orthogonal to the main scanning direction Y.

As shown inFIG.4A, the moving direction of the spherical body50when the inkjet head30moves is random. Thus, the spherical body50may be deviated to one part while the inkjet head30repeats the movement.

Therefore, it is preferable to set the total number of spherical bodies50so that (i) the number of spherical bodies that can be lined in more than at least one row in the orthogonal direction of the main scanning direction Y on the head filter34is set, and (ii) the ratio of the sum of the projection areas of the spherical bodies with respect to the area of the head filter34is set so as not to exceed 30% described above.

For example, when the total number of spherical bodies50having a diameter of 1 mm is set to 7, the conditions (i) and (ii) are satisfied. In this case, even if a bias occurs in the arrangement of some of the spherical bodies50, two spherical bodies exceeding 5 spherical bodies can fill the space formed by the bias. Thus, the spherical body50can roll in a wide range when the inkjet head30moves. When the condition (ii) is satisfied, the spherical body50is less likely to inhibit the flow of ink passing through the head filter34.

Instead of the condition (ii), (iii) a condition in which the sum R2 of the projection areas of the spherical bodies50is less than or equal to ⅓ of the area R1 of the head filter34may be adopted.

As described above, the inkjet printing apparatus1having the following configuration is disclosed in the embodiment.

(1) The inkjet printing apparatus1includes an inkjet head30that moves in a main scanning direction Y at the time of printing;a filter chamber33provided on a path for supplying ink to the nozzle hole31a(nozzle) in the inkjet head30; anda spherical body50placed on the head filter34(filter) in the filter chamber33.

The spherical body50has a diameter φ larger than the mesh of the head filter34.

The spherical body50is disposed on the head filter34so as to be rollable by the movement of the inkjet head30.

According to such configuration, when the inkjet head30is displaced at the time of printing, the spherical body50placed on the head filter34rolls on the head filter34. As a result, convection of the ink is generated on the surface of the head filter34by the rolling spherical body50, the aggregated particles are dispersed, and the occurrence of the bridging phenomenon can be suppressed.

In addition, since the rolling spherical body50comes into contact with the aggregates on the surface of the head filter34and diffuse the aggregates, the occurrence of the bridging phenomenon can be suppressed.

(2) The spherical body50is made of a nonmagnetic metal material (stainless steel).

If the spherical body50is lightweight, when the spherical body50sinks in the ink passing through the filter chamber34, the spherical body50may be lifted by buoyancy and move away from the head filter34. Then, the convection of the ink cannot be generated on the surface of the head filter34, and the occurrence of the bridging phenomenon may not be suppressed.

Therefore, by adopting the spherical body50formed of a nonmagnetic metal material, when the spherical body50sinks in the ink passing through the filter chamber33, the spherical body50can be prevented from separating from the surface of the head filter34by buoyancy. As a result, the spherical body50placed on the head filter34rolls on the head filter34at the time of printing, so that convection of the ink is generated on the surface of the head filter34by the rolling spherical body50, and the occurrence of the bridging phenomenon can be suppressed.

In addition, if the spherical body is made of resin, there is a possibility that the spherical body wears over time since the spherical body rolls on the upper surface of the head filter34. When the spherical body wears, there is a possibility that the suppression of the occurrence of the bridging phenomenon becomes insufficient. Furthermore, if the spherical body is damaged due to wear, the generated fragments or the like may become foreign substances and may cause an undesirable influence on the head filter34.

When formed of a material having magnetism, in a case where the spherical bodies are magnetized, there is a possibility that the spherical bodies gather by magnetic force or magnetically adhere to the wall constituting the filter chamber34and do not move. In such a case, as a result of the spherical body50not rolling on the upper surface of the head filter34, there is a possibility that the occurrence of the bridging phenomenon cannot be suppressed.

As described above, the occurrence of such a situation can be suitably prevented by forming the spherical body from stainless steel.

(3) A plurality of spherical bodies50are placed on the head filter34.

The spherical bodies50have an arrangement density at which the ratio of the sum R2 of the projection areas of the spherical bodies50with respect to the area R1 of the head filter34is greater than or equal to 3% and less than or equal to 30%.

When the arrangement density (R2/R1) of the spherical bodies50increases, the spherical bodies50collide with each other, and the rolling of the spherical bodies50on the head filter34becomes insufficient. Then, the range in which the spherical body50rolls in the head filter34is narrowed, and it becomes difficult to sufficiently generate the convection of the ink on the surface of the head filter34.

Furthermore, when the arrangement density (R2/R1) of the spherical bodies50increases, the spherical bodies50become a resistance to the flow of ink passing through the head filter34, and the flow rate of ink passing through the head filter34decreases.

Furthermore, when the arrangement density of the spherical bodies50decreases, the range in which the spherical bodies50in the head filter34actually roll becomes narrow, and it becomes difficult to sufficiently generate the convection of the ink on the surface of the head filter34.

When the arrangement density of the spherical bodies50is set within the above range, convection necessary for dispersing the aggregates can be generated on the surface of the head filter34. Therefore, the occurrence of the bridging phenomenon can be suppressed.

(4) A plurality of spherical bodies50are placed on the head filter34.

The total number50and the diameter of the spherical bodies50are set such that the sum R2 of the projection areas of the spherical bodies50with respect to the area of the head filter34is ⅓ to 1/30 of the area R1 of the head filter34.

With this configuration, convection necessary for dispersing the aggregates can be generated on the surface of the head filter34. Therefore, the occurrence of the bridging phenomenon can be suppressed.

(5) The ink is an ultraviolet curable ink.

The ultraviolet curable ink is likely to generate aggregates. Therefore, the occurrence of the bridging phenomenon can be suppressed by applying to the inkjet printing apparatus adopting the ultraviolet curable ink.

(6) The ink is a support material ink used for three-dimensional shaping.

Since the amount of the support material used for three-dimensional shaping is large, clogging of the nozzle tends to easily occur. Therefore, the occurrence of the bridging phenomenon can be suppressed by applying to the inkjet printing apparatus used for three-dimensional shaping.

The present disclosure of the present application is not limited to the mode of the above-described embodiment, and can be appropriately changed within the scope of the technical idea of the present disclosure of the present application.