Electrification adjustment apparatus and image forming apparatus

An electrification adjustment apparatus includes a first electrification adjuster facing the recording material conveyed for supplying charges each with one polarity, and a second electrification adjuster facing the recording material downstream of the first electrification adjuster in a conveying direction for supplying charges each with opposite polarity to that of the charge supplied by the first electrification adjuster. In the electrification adjustment apparatus, an electrostatic capacity between the recording material surface facing the second electrification adjuster, and an electrode partially or entirely formed from the conveyor member is smaller than the one between the recording material surface facing the first electrification adjuster and an electrode partially or entirely formed from the conveyor member. Either front or back surface of the recording material is in contact with the conveyor member in a region between the first and the second electrification adjusters.

CROSS-REFERENCE TO RELATED APPLICATIONS

The entire disclosure of Japanese Patent Application No. 2018-57684, filed on Mar. 26, 2018, is incorporated herein by reference in its entirety.

BACKGROUND ART

Technological Field

The present invention relates to an electrification adjustment apparatus and an image forming apparatus.

Description of the Related Art

Charges on a sheet recording material (hereinafter referred to as a “recording material”) with high insulation property such as a resin film and a synthetic paper are electrified by the frictional electrification, the separation discharge, and the corona discharge in the process of manufacturing the recording material, the surface treatment process such as the corona process, and the conveyance process, and remain on the surface without being attenuated. In most cases, those electrified charges are in the non-uniform state with uneven distribution on the recording material surface, for example, locally electrified with both positive and negative polarities. It has been known that the ink-jet (IJ) printing onto the above-described high insulating recording material generates an image noise owing to electrification of the recording material as described below.

When the recording material is electrified, the electric field formed between the electrified charge and the ink-jet head influences the flying characteristic of the ink droplet, thus changing the flying speed and the flying direction. This may cause the problem that the ink droplet reaches an unintended landing point on the recording material rather than the expected one. Especially as the small droplet is susceptible to the electric field because of large deceleration owing to air resistance, the following problems will occur. For example, the misted ink droplets (sub-droplets) are returned toward the ink-jet head side and adhering thereto by the electric field, and the ink droplets adhere to the unintended point on the recording material, resulting in scumming. The sub-droplet may be referred to as a satellite.

FIGS. 1A and 1Bshow a relationship between electrification of the recording material and the image noise in the ink-jet type image forming processing.FIG. 1Arepresents an example of a flying ink droplet injected from an ink-jet head.FIG. 1Brepresents an example of a state in which the ink droplet has reached the landing point.

FIG. 1Arepresents how the flying ink droplet is influenced. Referring toFIG. 1A, the ink droplet injected from an ink-jet head10includes a main droplet11with a large volume, and a sub-droplet11a(mist) generated in the process of generating the main droplet11. Focusing on the sub-droplet11awith high air resistance as shown inFIG. 1A, it is assumed that the sub-droplet11ahas a positive charge. A recording material20is positively electrified relatively uniformly. At the location where the vertical electric field is formed as shown inFIG. 1A, the sub-droplet11areceives the electrostatic force directed toward the ink-jet head10in the direction opposite the flying direction (center part ofFIG. 1A).

At the location where the horizontal electric field is formed by electrification non-uniformity of the recording material20(left side and right side ofFIG. 1A), as a sub-droplet12abecomes proximate to the surface of the recording material20, it receives the lateral electrostatic force. The above-described electrostatic force changes the speed and direction of the ink droplet. As a result, the sub-droplet12areaches the different landing position from the originally intended position, resulting in the image noise. If the sub-droplet11ais adhering to the ink-jet head10under the electrostatic force, the ink-jet head10will be stained. Especially when the sub-droplet11ais adhering to the position near the nozzle, such malfunction as injection bending and the like will occur.

It has been known that the electrified charge on the recording material20or the like influences the ink droplets immediately after they reach the landing points. For example, asFIG. 1Bshows, under the electric field in the planar direction as a result of electrification non-uniformity of the recording material20, the electrostatic induction occurs in a landed ink droplet13. The electrostatic force acts in the electric field direction, causing the problem of fluctuating the dot shape. The size of the dot shape fluctuation (deformation) may be affected depending on what extent the planar electric field is cancelled by movement of the electrostatically induced charge accompanied with the dot deformation. Therefore, it is necessary to reduce the non-uniformity in the charge density of the recording material20so as to suppress fluctuation of the dot shape. Especially when the recording material is thin, the electrostatic capacity between the recording material surface in the presence of the electrified charges, and the electrode at the back surface side of the recording material is large. Even if the electrified potential is relatively small, the charge density may be large. In order to suppress the dot shape fluctuation, it is important to reduce the charge density non-uniformity.

There has been known a destaticizer for destaticizing the recording material with a plurality of destaticizing units as described below. Japanese Unexamined Patent Application Publication No. 8-64384 (Patent Literature 1) discloses the technology for bringing the point of the insulating web, which is to be destaticized into tight contact with the point of the grounding conductive roller facing the charging electrode to which the DC voltage is applied so that the charge is supplied to the surface of the point to be destaticized. The point to be destaticized is separated from the grounding conductive roller surface while being rotated so as to eliminate the charge at the point to be destaticized by the destaticizing electrode disposed at the same side as that of the charging electrode, downstream with respect to the insulating web surface.

Japanese Unexamined Patent Application Publication No. 2002-289394 (Patent Literature 2) discloses the technology for the destaticizing process to one surface of the insulation sheet so as to uniformize the electrification polarity on the one surface, and the electrification neutralizing process (destaticizing) from the same surface at the downstream side so that the electrification pattern on the processed surface is destaticized.

CITATION LIST

Patent Literature

Patent Literature 2: Japanese Unexamined Patent Application Publication No. 2002-289394

SUMMARY

In Patent Literature 1, the charging electrode at the upstream side supplies charges each with one polarity so as to reduce electrification non-uniformity, and the destaticizing electrode at the downstream side (separation part) neutralizes the entire charges. It is not possible to increase the amount of charge from the charging electrode for the purpose of suppressing the separation discharge at the separation part. Therefore, the large electrification non-uniformity cannot be sufficiently eliminated. The technology disclosed in Patent Literature 1 fails to supply the destaticizing charges to the line of electric force closed by the electrification non-uniformity of the recording material at the separation part (near the destaticizing electrode) because of large residual electrification non-uniformity.

In Patent Literature 2, at the upstream side, the charges each with one polarity are supplied to reduce the electrification non-uniformity, and at the downstream side (separation part), the entire charges are neutralized. In the case of executing the electrification neutralizing process (destaticizing) to the thin recording material with high electrostatic capacity (specific dielectric constant), the charge density of the recording material cannot be uniformized sufficiently even if the electrified potential non-uniformity is reduced. It is difficult to execute the control for eliminating the electrified potential non-uniformity to zero. In the case of large electrostatic capacity of the recording material, the potential generated by electrification on the recording material (Q=CV) becomes small. The electric field for suction of the charge supplied by the ionizer becomes small. As a result of superposing the recording material after destaticizing on the member with small electrostatic capacity, or moving the recording material apart from the conductive conveyor roller21(electrode), the synthetic capacity between the surface of the recording material at the ionizer side, and the electrode becomes small. Then the electrified potential non-uniformity and the potential become large.

It is preferable to have no electrification non-uniformity on the recording material surface (electrified potential non-uniformity, electrified charge non-uniformity) in another image forming process such as electrographic type for the purpose of maintaining the image quality.

It is an object of the present invention to eliminate the electrification non-uniformity on the recording material surface as a factor that affects the image quality, and to suppress unnecessary influence of the electric field.

To achieve the above-described object, according to an aspect of the present invention, an electrification adjustment apparatus reflecting one aspect of the present invention includes a conveyor member for conveying a recording material, a first electrification adjuster disposed to face the recording material being conveyed for supplying a charge with one polarity, a second electrification adjuster disposed to face the recording material at a downstream side of the first electrification adjuster in a conveying direction for supplying a charge with opposite polarity to the polarity of the charge supplied by the first electrification adjuster, a first DC power supply for a DC power supply to the first electrification adjuster, and a second DC power supply for a DC power supply having a polarity opposite to the polarity of the first DC power supply to the second electrification adjuster. In the electrification adjustment apparatus, an electrostatic capacity between a surface of the recording material, which faces the second electrification adjuster and an electrode partially or entirely formed from the conveyor member is smaller than an electrostatic capacity between a surface of the recording material, which faces the first electrification adjuster and an electrode partially or entirely formed from the conveyor member, and any one of the surface and a back surface of the recording material is in contact with (not separated from) the conveyor member in a region between the first electrification adjuster and the second electrification adjuster.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, an example of one or more modes for carrying out the present invention (hereinafter referred to as “embodiments”) will be described referring to the attached drawings. However, the scope of the invention is not limited to the disclosed embodiments. In the specification and the drawings, components with substantially the same functions or the same structures will be designated with the same codes, and explanations thereof, thus will be omitted.

First Embodiment

Structure of Electrification Adjustment Apparatus

A structure example of an electrification adjustment apparatus according to a first embodiment of the present invention will be described.

FIG. 2is an explanatory view showing an example of the electrification adjustment apparatus according to the first embodiment of the present invention.

An electrification adjustment apparatus30as shown inFIG. 2is exemplified as the electrification adjustment apparatus to be disposed on a conveying path of an ink-jet recording apparatus, for example. The electrification adjustment apparatus30includes a first guide member120, a second guide member140, an intermediate guide member130, a first electrification adjuster27, a second electrification adjuster28, a first DC power supply271, and a second DC power supply281.

Each of the first guide member120, the second guide member140, and the intermediate guide member130is structured to have a surface in contact with the conveyed recording material20. The second guide member140is disposed at the downstream side of the first guide member120in the conveying direction. The intermediate guide member130is disposed between the first guide member120and the second guide member140so as to be in abutment with both members via the recording material20. Each of the first guide member120, the second guide member140, and the intermediate guide member130as an example of the conveyor member is constituted by a rotary body such as a roller having a rotary axis perpendicular to the conveying direction.

The first guide member120is formed as a metal roller121(example of a conductive roller with low resistance) made of aluminum, for example, and grounded. The second guide member140is formed as a metal roller141made of aluminum having its surface coated with an insulation layer142, and grounded. The metal rollers121,141are exemplified as electrodes each constituted from the conveyor member either partially or entirely. The insulation layer142is made of an insulating resin, for example. The insulation layer142functions as a heat insulation layer for suppressing fluctuation of the temperature of the second guide member140owing to heat generated upon ultraviolet ray curing in a fixing unit25.

The insulating recording material20subjected to the electrification adjustment is conveyed while being wound on the respective surfaces of the first guide member120, the intermediate guide member130, and the second guide member140sequentially. The intermediate guide member130regulates the conveying path for the recording material20kept in a tensed state.

The first DC power supply271is a power supply circuit for supplying DC voltage (first DC power supply) to the first electrification adjuster27. The second DC power supply281is a power supply circuit for supplying DC voltage (second DC power supply) with opposite polarity to that of the first DC power supply271to the second electrification adjuster28.

The first electrification adjuster27is disposed to face the surface of the first guide member120. As the recording material20is conveyed to the first guide member120, the first electrification adjuster27is positioned to face the surface of the recording material20, which is not in contact with the first guide member120. Upon reception of the DC voltage applied from the first DC power supply271, the first electrification adjuster27generates the charge with one polarity so as to be supplied to the first guide member120. The electric field is formed between the voltage applied to the first electrification adjuster27and the grounded first guide member120so that the charge is supplied to the recording material20which is wound on the surface of the first guide member120.

The second electrification adjuster28is disposed to face the surface of the second guide member140. As the recording material20is conveyed to the second guide member140, the second electrification adjuster28is positioned to face the surface of the recording material20, which is not in contact with the second guide member140. Upon reception of the DC voltage applied from the second DC power supply281, the second electrification adjuster28generates the charge with opposite polarity to that of the charge supplied form the first electrification adjuster27so that the generated charge with the opposite polarity is supplied to the second guide member140. The electric field is generated between the potential of the second electrification adjuster28in accordance with the applied DC voltage and the electrified charge of the recording material20on the grounded second guide member140so that the charge with the opposite polarity is supplied to the recording material20wound on the surface (insulation layer142) of the second guide member140.

The corona electrifier and the roller electrifier may be employed for the first electrification adjuster27and the second electrification adjuster28. The present embodiment is configured to employ the scorotron electrifier (a kind of the corona electrifier) having a grid electrode27b(28b) disposed between a wire-like corona discharge electrode27a(28a) extending in a main scanning direction and an electrification body (the recording material20in the present embodiment). The scorotron electrifier adjusts the charge amount to be supplied to the recording material20via the grid electrode27butilizing the voltage to be applied to the grid electrode27b. Specifically, it is possible to provide two separate functions, that is, the function for generating charges by the corona discharge electrode27a(28a), and the function for forming the electric field by the grid electrode27b(28b) so as to secure the charge supply amount in accordance with the electrostatic capacity of the recording material20. The scorotron electrifier allows the grid electrode27b(28b) for forming the electric field to be disposed adjacent to the recording material20. Accordingly, it is preferable to employ the scorotron electrifier in terms of uniformizing the electrification non-uniformity, and adjusting the electrified amount.

The intermediate guide member130is a conductive roller (for example, the metal roller) disposed in abutment with both the first guide member120and the second guide member140. It is preferable to form the intermediate guide member130as the roller with the surface onto which an elastic member is applied for securing the contact with both the first guide member120and the second guide member140. As the intermediate guide member130is interposed between the first guide member120and the second guide member140, the recording material20electrified by the first electrification adjuster27is conveyed to the second electrification adjuster28while having its surface either front or back surface constantly kept in contact with any one of the first guide member120, the intermediate guide member130, and the second guide member140.

Each of the first guide member120, the second guide member140, and the intermediate guide member130may be formed as the fixed member instead of the rotatable roller. The use of the roller may suppress wear on the surface of the recording material20.

In the present embodiment, the recording material20subjected to the electrification adjustment is assumed to be a resin film, and the recording material with electrically high resistance. The synthetic paper and the coated paper may be the high resistance paper. In the case of low humidity, the resistance of the paper becomes higher than that of the paper at the normal humidity. The above-described paper may also be the one to be subjected to the electrification adjustment.

Electrification Adjustment Operation

An electrification adjustment performed by the electrification adjustment apparatus30(the process for uniformly destaticizing the non-uniform electrification state) will be described referring toFIG. 3. Each of graphs (1) to (8) shown inFIG. 3represents an example of the electrified charge and the electrified potential at each position on the recording material20located at the respective parts of the electrification adjustment apparatus30. Each x-axis of the graphs (1) to (8) shown inFIG. 3represents the position on the recording material20, each y-axis shown inFIG. 3(corresponding to odd numbers) represents the charge density, and each y-axis shown inFIG. 3(corresponding to even number) represents the electrified potential.

As the graph (1) of Fi.3shows, in the presence of electrified charges with non-uniformity on the surface of the insulating recording material20, the electrified potential in accordance with the charge density non-uniformity is formed on the surface around the region as described above (solid line in the graph (2) ofFIG. 3). However, as the left and right sides ofFIG. 1Ashow, the charges with opposite polarities around the surface of the recording material20may close the electric line of force. Therefore, as the distance from the surface becomes farther, the electrified potential affected by the charge density with non-uniformity is averaged (see broken line of the graph (2) ofFIG. 3). The ion generator (electrifier) generally employed for destaticizing purpose allows suction of the generated charges at the electrified potential formed by the electrified charges (see broken line of the graph (2) ofFIG. 3). Upon neutralization of the electrified charges through averaging, the electrostatic force directed to the recording material20does not act on the charge with either polarity, thus failing to sufficiently destaticize the non-uniform electrification on the surface of the recording material20as described above.

The first electrification adjuster27is configured to generate the charge with one polarity (negative charge in this case), and form the electric field that ensures sufficient supply of charges between the first electrification adjuster27and the first guide member120so that the recording material20is entirely electrified with the polarity. This makes it possible to supply the charge to the region with the closed electric line of force on the surface of the recording material20(seeFIG. 1A). As a result, the charge moves along the electric line of force in accordance with the electrification non-uniformity, thus reducing the electrification non-uniformity (see graphs (3), (4) ofFIG. 3). In the above-described case, preferably, the first electrification adjuster27supplies sufficient charge amount compared with the one which causes the electrification non-uniformity on the surface of the recording material20(electrification with one polarity).

Increase in the electrostatic capacity of the recording material20to be electrified may reduce the extent of increase in the electrified potential by the supplied charge so as to reduce the electric field formed by the first electrification adjuster27(possible to supply sufficient charge at low voltage). It is preferable to maximize the electrostatic capacity on the surface of the first guide member120by employing the conductive roller as the first guide member120having its surface in contact with the recording material20(on the back surface of the recording material20). In the present embodiment, the metal roller121is used for the first guide member120.

The second guide member140has its surface applied with the insulation layer142, on which the recording material20is superposed. AsFIG. 4shows, in the region covered by the second electrification adjuster28, a synthetic electrostatic capacity C2of an electrostatic capacity C1of the recording material20and an electrostatic capacity CO of the insulation layer142(the electrostatic capacity on the surface of the second guide member140) is smaller than the electrostatic capacity in the region covered by the first electrification adjuster27. The region covered by the first electrification adjuster27refers to the range influenced by the charge generated by the first electrification adjuster27(electrification adjustable area). The region covered by the second electrification adjuster28may also be defined correspondingly. The electrified potential of the second electrification adjuster28becomes higher than the one derived from the charge (see graph (5) ofFIG. 3) electrified by the first electrification adjuster27by the amount corresponding to a potential difference g (see graph (6) ofFIG. 3). As described above, in the region covered by the second electrification adjuster28, the electrostatic capacity is small, and the electrified potential largely changes relative to the electrified charge amount.

The second electrification adjuster28supplies appropriate amount of charges each with opposite polarity to that of the charge supplied by the first electrification adjuster27by utilizing the electrified potential as shown in the graph (6) ofFIG. 3so that the electrified amount of the recording material20reaches the required level (level zero in the embodiment). The second electrification adjuster28adjusts the electrified potential of the recording material20conveyed on the second guide member140to be approximated to 0V (see graph (8) ofFIG. 3). This makes it possible to approximate the charge amount electrified on the recording material20to the target value (preferably, 0) (see graph (7) ofFIG. 3).

For uniformization of the electrification non-uniformity as described above, the first electrification adjuster27supplies sufficient amount of charges to the region with electrification non-uniformity of the recording material20(by increasing the electrostatic capacity of the first electrification adjuster27), and the second electrification adjuster28with less electrostatic capacity adjusts the charge amount on the surface of the recording material20. For example, the charge amount to be supplied by the first electrification adjuster27is determined based on the empirically obtained value, and the value preliminarily derived from the experiment, and the determined value is registered in a storage unit44(to be described later referring toFIG. 11). It is preferable to provide the intermediate guide member130in contact with both the first guide member120and the second guide member140so as not to generate the separation discharge when conveying the recording material20from the first guide member120to the second guide member140. The embodiment is configured to change the electrostatic capacity on the region covered between the first electrification adjuster27and the electrification adjuster28while having the recording material20to be conveyed being in contact with the intermediate guide member130.

Function of Intermediate Guide Member

A function of the intermediate guide member130will be described referring toFIGS. 5 and 6.FIG. 5is an explanatory view showing an example of a generally employed electrification adjuster. Referring toFIG. 5, an electrification adjuster15supplies the charge with one polarity to the recording material20to be conveyed by the first guide member120as the conductive roller. The electrification adjuster15is a corona electrifier with no grid electrode.FIG. 6is a graph showing results of calculating a gap potential difference with respect to a gap distance between the guide member and the recording material20.

Referring toFIG. 5, upon separation of the recording material20from the first guide member120having its surface electrified, a gap (gap A) is formed between the first guide member120and the recording material20. A gap potential difference of the gap is obtained for comparative purpose so as to explain how the intermediate guide member130functions. Furthermore, referring toFIG. 2, a gap potential difference at an inlet B of a nip part between the second guide member140and the intermediate guide member130, and a gap potential difference at an outlet C of a nip part between the intermediate guide member130and the second guide member140are obtained.

FIG. 6shows results of calculating each gap potential difference with respect to the gap distance, where the recording material20has the electrified charge density of 200 μC/m2, the thickness of 10 μm, the specific dielectric constant of 2, and the insulation layer142on the surface of the second guide member140has the thickness of 100 μm, and the specific dielectric constant of 2.FIG. 6also shows the calculation result of an approximate equation (Vth=312+6.2 d (d: gap distance, unit: μm)) for an insulation breakdown voltage Vth of an air layer in accordance with Paschen's law. Upon separation of the electrified recording material20from the first guide member120, discharge occurred in the structure shown inFIG. 5at the position around the region with the gap distance in excess of 10 μm. Compared with the above-described structure inFIG. 5, the structure as shown inFIG. 2having the intermediate guide member130is capable of suppressing the gap potential difference to the low level as well as the separation discharge.

As described above, the first embodiment includes the first electrification adjuster27disposed at the upstream side of the direction for conveying the recording material20, and the second electrification adjuster28disposed at the downstream side. The charge supplied by the first electrification adjuster27has an opposite polarity to that of the charge supplied by the second electrification adjuster28. In the present embodiment, the electrostatic capacity between the surface (non-contact surface) of the recording material20in contact with the second guide member140and the electrode of the second guide member140is smaller than the electrostatic capacity between the surface (non-contact surface) of the recording material20in contact with the first guide member120and the electrode of the first guide member120. In other words, the electrostatic capacity between the surface of the recording material20facing the second electrification adjuster28and the electrode of the second guide member140is smaller than the electrostatic capacity between the surface of the recording material20facing the first electrification adjuster27and the electrode of the first guide member120.

In the above described embodiment, as the electrostatic capacity at the side of the first electrification adjuster27is large, fluctuation in the potential on the surface of the recording material20(electrified potential) owing to the electrified charge non-uniformity is small, and the charge may be easily supplied to the recording material20. It is therefore possible to reduce the electrification non-uniformity by electrifying the recording material20to one polarity in spite of the electrified potential non-uniformity on the recording material20. Meanwhile, as the electrostatic capacity at the side of the second electrification adjuster28is small, it is possible to further reduce the charge density non-uniformity on the recording material20subjected to uniformization of the potential on the surface thereof.

The embodiment employs the intermediate guide member130which allows either the front surface or the back surface of the recording material20to be in contact with the first guide member120or the second guide member140for the purpose of suppressing the separation discharge considered as a risk which may occur when switching the electrostatic capacity in the region covered between the first electrification adjuster27and the second electrification adjuster28. This makes it possible to extend the upper limit of the charge amount supplied by the first electrification adjuster27, as well as to eliminate larger electrification non-uniformity on the recording material20.

Second Embodiment

In a second embodiment, another structure is described for obtaining the effect of the present invention by suppressing the separation discharge as an example in which arrangement of the second electrification adjuster28according to the first embodiment is changed.

FIG. 7is an explanatory view of an example of the electrification adjustment apparatus according to the second embodiment.

In the above-described first embodiment, the gap potential difference at the outlet C of the nip part formed between the intermediate guide member130and the second guide member140becomes large, which may cause the separation discharge. An electrification adjustment apparatus30A as shown inFIG. 7is configured to arrange a second electrification adjuster28A to face the outlet C of the nip part between the intermediate guide member130and the second guide member140.

The second electrification adjuster28A is disposed near the outlet C of the nip part so as to intensify the electric field formed between the grid electrode28band the recording material20on the second guide member140positioned at the outlet C of the nip part. The charge may be supplied to the outlet C of the nip part between the intermediate guide member130and the second guide member140, suppressing increase in the gap potential difference at the outlet C of the nip part. In this case, it is preferable not only to dispose the second electrification adjuster28A to face the nip part between the second guide member140and the intermediate guide member130, but also to dispose the grid electrode28bproximally to the surface of the second guide member140from the perspective of appropriate charge supply to the recording material20.

Third Embodiment

In a third embodiment, another structure is described for obtaining the effect of the present invention by suppressing the separation discharge as an example in which a voltage is applied to the intermediate guide member130according to the first embodiment.

FIG. 8is an explanatory view of an example of an electrification adjustment apparatus according to the third embodiment.

An electrification adjustment apparatus30B as shown inFIG. 8includes a third DC power supply131(power supply circuit) for applying the DC voltage with the same polarity as that of the charge supplied by the first electrification adjuster27to the intermediate guide member130. As described above, the third DC power supply131applies the voltage with the same polarity as that of the charge supplied by the first electrification adjuster27to the intermediate guide member130. As a result, increase in the gap potential difference may be slowed down, and the separation discharge may be prevented.

Fourth Embodiment

In a fourth embodiment, another structure is described for obtaining the effect of the present invention by suppressing the separation discharge as an example in which the first guide member120and the second guide member140according to the first embodiment are integrally structured.

FIG. 9is an explanatory view showing an example of an electrification adjustment apparatus according to the fourth embodiment.

An electrification adjustment apparatus30C as shown inFIG. 9includes a guide member160(an example of a conveyor member) formed by integrating a first guide161having a surface in contact with the recording material20, which faces the first electrification adjuster27, and a second guide162having a surface in contact with the recording material20, which faces the second electrification adjuster28while being contiguous to each other. The guide member160on which the recording material20is wound has the function for guiding the recording material20while being conveyed.

The first guide161has a cylindrical shape (having an annular cross section (substantially semicircular shape inFIG. 9)) with a center axis in an orthogonal direction (main scanning direction) to the rotating direction of the recording material20. A notch161awith a depth corresponding to the thickness of the second guide162is formed from an arbitrary part (the highest point inFIG. 9) to the end at the downstream side on an outer circumferential surface of the first guide161. The second guide162is formed in contact with the surface of the notch161aof the first guide161. Surfaces of the first guide161and the second guide162, which are brought into contact with the recording material20form a single contiguous smooth surface with no stepped part.

For example, the first guide161is formed as a curved conductor (metal and the like), and the second guide162is formed as a curved insulating resin. In the present embodiment, the above-described structure and the selected material allow the electrostatic capacity at the second guide side to be smaller than the electrostatic capacity at the first guide side. The guide member160constituted by the first guide161and the second guide162is an example of the electrode constituted partially or entirely from the conveyor member.

AsFIG. 9shows, four head units24(seeFIG. 11to be described later) corresponding to yellow (Y), magenta (M), cyan (C), and black (B) are disposed to face the second guide162, and the fixing unit25is disposed at the downstream side of the head units24(seeFIG. 11to be described later).

In the case of the above-structured fourth embodiment, upon switching of the electrostatic capacity in the region covered between the first electrification adjuster27and the second electrification adjuster28, the recording material20is conveyed while having its back surface in contact with the first guide161and the second guide162of the guide member160. Therefore, the gap where the separation discharge occurs is not formed. This structure eliminates the intermediate guide member130, thus securing the compact electrification adjustment apparatus.

Fifth Embodiment

Structure of Ink-Jet Recording Apparatus

In a fifth embodiment, a structure example of an ink-jet recording apparatus with the electrification adjustment apparatus is described. The present embodiment will be described with respect to the ink-jet recording apparatus with the electrification adjustment apparatus30according to the first embodiment as an example. It is possible to employ the electrification adjustment apparatus according to another embodiment for the ink-jet recording apparatus.

FIG. 10is an explanatory view showing a structure example of an ink-jet recording apparatus with the electrification adjustment apparatus30as shown inFIG. 2. An ink-jet recording apparatus200as shown inFIG. 10is an example of the image forming apparatus to which the present invention is applied.

AsFIG. 10shows, the ink-jet recording apparatus200includes a feed roll110on which the recording material20is wound, the electrification adjustment apparatus30, an image forming unit35including head units24corresponding to the respective basic colors, and a winding roll150for winding the recording material20on which the image has been formed. The ink-jet recording apparatus200includes a conveyor mechanism constituted by a conveyor roller and a driven roller for conveying the recording material20fed from the feed roll110to the winding roll150via the electrification adjustment apparatus30and the image forming unit35. Referring to the example shown inFIG. 10, a driven roller111, a conveyor roller pair112, and a driven roller113are disposed between the feed roll110and the electrification adjustment apparatus30(first guide member120). A driven roller151, a conveyor roller pair152, and a driven roller153are disposed between the image forming unit35(second guide member140) and the winding roll150.

The electrification adjustment apparatus30uniformizes the electrification non-uniformity on the recording material20, having its image forming surface on which an image is formed in the ink-jet process executed by the image forming unit35disposed at the downstream side. Specifically, the image is formed on the recording material20by means of ink-jet heads242(seeFIG. 11) each provided with ultraviolet-curable type ink (hereinafter simply referred to as “ink”) corresponding to yellow, magenta, cyan, and black, respectively. The ink is cured by a light source for UV irradiation (UV lamp) of the fixing unit25at the downstream side, providing the fixed image.

It is possible to form a predetermined electric field between the ink-jet head242and the recording material20through adjustment of the electrified potential of the recording material20performed by the second electrification adjuster28in accordance with the electrification characteristic (electrified polarity) of the ink droplet. Even in the case that the recording material20is electrified to the predetermined electrified potential by the second electrification adjuster28, it is preferable to form images in the ink-jet process, and to perform the UV curing process on the second guide member140which faces the second electrification adjuster28. This makes it possible to form the image under the appropriate control of the electric field between the ink-jet head242and the recording material20without having the electrified potential adjusted by the second electrification adjuster28, and the image formed in the ink-jet process being disturbed by the separation discharge.

In the present embodiment, the ink-jet recording apparatus200using the ultraviolet-curable type ink has been described as an example. However, the image forming method is not limited to the one as described above. It is possible to use the aqueous ink, the solvent-base ink and the like for forming images. Arbitrary types, or arbitrary number of colors may be used for forming the image without being limited to those described above.

Control System for Ink-Jet Recording Apparatus

The structure of the control system for the ink-jet recording apparatus200will be described referring toFIG. 11.FIG. 11is a block diagram showing a structure example of the control system for the ink-jet recording apparatus200.

AsFIG. 11shows, the ink-jet recording apparatus200includes a control unit40. The control unit40includes a CPU (Central Processing Unit)41, a RAM (Random Access Memory)42used as a work area for the CPU41, and a ROM (Read Only Memory)43for storing the program and the like to be executed by the CPU41, for example. The control unit40further includes a storage unit44as a mass storage device such as a hard disk drive (HDD). The storage unit44stores image data read by an image reader26, the information for executing the electrification adjustment, the test chart for detecting the discharge fault of the nozzle of the ink-jet head242, and the information for detecting the discharge fault of the nozzle.

The ink-jet recording apparatus200includes a conveyance drive unit51for driving the conveyor system, for example, a not shown image forming drum, a paper ejection unit, a paper reversing unit and the like, an operation display unit52, and an I/O interface53.

The CPU41of the control unit40is connected to a heater23, the head unit24, the fixing unit25, the image reader26, the RAM42, the ROM43, and the storage unit44via a system bus54so as to control the entire apparatus. The CPU41is connected to the conveyance drive unit51, the operation display unit52, and the I/O interface53via the system bus54.

The operation display unit52is a touch panel constituted as a display, for example, a liquid crystal display (LCD) or an organic ELD (Electro Luminescence Display). The operation display unit52displays an instruction menu for the user, and information relating to the nozzle discharge detection operation, and the acquired image data. Furthermore, the operation display unit52includes a plurality of keys functioning as an input unit for receiving inputs of data such as various instructions, characters, and figures through the user's key operation.

The I/O interface53is communicably connected to an external apparatus4. The I/O interface53receives a print job (image data, output setting) from the external apparatus4. The I/O interface53outputs the received image data to the control unit40. The control unit40subjects the image data received from the I/O interface53to image processing. The control unit40may be configured to execute the image processing to the received image data as needed, for example, the shading correction, the image density adjustment, and the image compression.

The head unit24receives the image data which have been processed by the control unit40so as to form a predetermined image on the recording material20based on the image data. Specifically, the head unit24drives a head driver241to allow the ink-jet head242to discharge the ink to the predetermined position. The heater23for heat generation is disposed at the upstream side of the head unit24so that the recording material20passing therearound has the predetermined temperature under the control of the control unit40.

The four head units24are disposed corresponding to colors of yellow (Y), magenta (M), cyan (C), and black (K), respectively. The four head units24corresponding to yellow, magenta, cyan, black are arranged sequentially in order from the upstream side in the direction for conveying the recording material20.

The head unit24is set to have a length (width) sufficient to entirely cover the recording material20in the direction orthogonal to the one for conveying the recording material20(main scanning direction). In other words, the ink-jet recording apparatus200is of line head type as a one-pass system. Each of the four head units24has the same structure except the color of the ink to be discharged.

In the present embodiment, prior to the image formation by the head units24onto the recording material20, the control unit40controls the first DC power supply271and the second DC power supply281so that charges supplied from the first electrification adjuster27and the second electrification adjuster28are regulated to adjust electrification of the recording material20(seeFIG. 2). Based on the information relating to the kind of the recording material20(for example, the information about resistance, specific dielectric constant, and thickness), and image forming conditions (for example, density of image, and printing area rate), the control unit40adjusts the amount of charge supplied from the first electrification adjuster27and the second electrification adjuster28.

The image formed on the recording material20by the head units24is read by the image reader26. The read image data are transmitted to the control unit40. Upon detection of the nozzle discharge fault, the control unit40identifies the nozzle having the discharge fault based on the image data transmitted from the image reader26. The control unit40executes the correction process to the head unit24by increasing the discharge amount of the ink from the nozzle adjacent to the one having the discharge fault.

Measurement Results

Effects of the electrification adjustment performed by the respective embodiments have been confirmed using structures of examples and comparative examples, and confirmation results will be described referring toFIGS. 12 and 13.

FIG. 12is a table showing measurement results derived from the first to the fourth examples, and the first and the second comparative examples.

FIG. 13is a table showing measurement results derived from the fifth example and the third comparative example.

First Example

The first example employed the electrification adjustment apparatus30(each of the electrification adjusters27,28was a scorotron electrifier) as shown inFIG. 2. A PET (polyethylene terephthalate) layer with thickness of 100 μm functioning as the insulation layer142was formed on the surface of the second guide member140.

Second Example

The second example employed the electrification adjustment apparatus30B (each of the electrification adjusters27,28was the scorotron electrifier) as shown inFIG. 8. The PET layer with thickness of 100 μm functioning as the insulation layer142was formed on the surface of the second guide member140. The voltage of −300 V was applied to the intermediate guide member130.

Third Example

The third example employed the electrification adjustment apparatus30A (each of the electrification adjusters27,28was the scorotron electrifier) as shown inFIG. 7. The PET layer with thickness of 100 μm functioning as the insulation layer142was formed on the surface of the second guide member140.

Fourth Example

The fourth example employed the electrification adjustment apparatus30C (each of the electrification adjusters27,28is the scorotron electrifier) as shown inFIG. 9. The PET layer (insulation layer) with thickness of 100 μm was formed as the second guide162of the guide member160in the region covered by the second electrification adjuster28.

First Comparative Example

The first comparative example employed the structure derived from removing the intermediate guide member130from the electrification adjustment apparatus30as shown inFIG. 2(each of the electrification adjusters27,28was the scorotron electrifier). The PET layer with thickness of 100 μm functioning as the insulation layer142was formed on the surface of the second guide member140.

Second Comparative Example

The second comparative example employed the electrification adjustment apparatus30(each of the electrification adjusters27,28was the scorotron electrifier) as shown inFIG. 2. The second electrification adjuster28was disposed on the first guide member120instead of the second guide member140. The PET layer with thickness of 100 μm functioning as the insulation layer142was formed on the surface of the second guide member140.

Evaluations have been made using the recording material made of the PET with thickness of 12 μm (hereinafter referred to as “PET recording material”) as the recording material20to be subjected to the electrification adjustment. The electrification adjustment was made (target: 0 V) for the respective structures under conditions where the voltage with negative polarity (−7 kV) was applied to the corona discharge electrode27aof the first electrification adjuster27, the grid voltage was set to −50 V, −100 V, and −150 V, the voltage with positive polarity (7 kV) was applied to the corona discharge electrode28aof the second electrification adjuster28, and the grid voltage was set to 0 V.

After the electrification adjustment, the toner for copy (negative electrification toner) was sprinkled over the PET recording material on the second guide member140so as to visualize the electrification non-uniformity. The PET recording material was patted to visually evaluate the toner adhesion state. In the case of no toner adhesion to the recording material, the mark “◯” was recorded. In the case of slight toner adhesion to the recording material, the mark “Δ” was recorded. In the case of the toner adhesion to the recording material, the mark “x” was recorded. Confirmation whether or not the separation discharge has occurred was made based on the discharge sound.

Table 1 ofFIG. 12shows the respective measurement results derived from the first to the fourth examples, and the first and the second comparative examples. As Table 1 shows, in each case of the examples, at the low grid voltage of the first electrification adjuster27set to −50 V, the toner adhesion was observed as a result of failing to eliminate the electrification non-uniformity. In the case of the first comparative example, the discharge sound was confirmed, and the separation discharge occurred. At the grid voltage of the first electrification adjuster27set to −100 V, the toner adhesion was not observed in the first to the fourth examples, succeeding in elimination of the electrification non-uniformity. On the contrary, the toner adhesion was observed in the first and the second comparative examples. In the first comparative example, the discharge sound was also confirmed. Even in the case of the structure according to the first example, the discharge sound accompanied with the separation discharge was confirmed as a result of raising the grid voltage to −150 V, causing the toner adhesion. The discharge sound was not confirmed in the second to the fourth examples and the second comparative example.

Findings from the above-described results will be described as follows.

(1) The first electrification adjuster27is required to supply sufficient charges relative to the electrification non-uniformity on the recording material. That is, at the grid voltage of −50 V (charge density: about 110 μC/m2) in the first to the fourth examples, the amount of supplied charges is insufficient.
(2) Continuous increase in the amount of charge supplied by the first electrification adjuster27caused the separation discharge in the first example. It is therefore necessary to employ the structure that prevents increase in the gap potential difference shown inFIG. 6(for example, structures ofFIGS. 7 to 9).
(3) In the second comparative example, the second electrification adjustment (charge supply by the second electrification adjuster28) was performed on the first guide member120with large electrostatic capacity. If the electrostatic capacity is fluctuated as a result of the process for conveying the recording material to the second guide member140, the electrification non-uniformity on the recording material will be increased.

From the above-described measurement results, it is confirmed that the respective examples according to the embodiments of the present invention are capable of eliminating the electrification non-uniformity on the recording material surface while suppressing the separation discharge between the guide member and the recording material.

It was verified that the ink-jet recording apparatus200shown inFIG. 10employed as the image forming apparatus with the electrification adjustment apparatus according to the respective embodiments generated no image failure (hereinafter referred to as “image non-uniformity”) owing to the electrification non-uniformity.

Fifth Example

The fifth example employed the electrification adjustment apparatus30A (seeFIG. 7) as the structure used for the third example. The PET layer with thickness of 100 μm functioning as the insulation layer142was formed on the surface of the second guide member140. The grid voltage of the first electrification adjuster27was set to −300 V, and the grid voltage of the second electrification adjuster28was set to 0 V and −100 V.

Third Comparative Example

Likewise the second comparative example, the third comparative example employed the electrification adjustment apparatus30(seeFIG. 2), and the second electrification adjuster28was disposed on the first guide member120instead of the second guide member140. The PET layer with thickness of 100 μm functioning as the insulation layer142was formed on the surface of the second guide member140. The grid voltage of the first electrification adjuster27was set to −300 V, and the grid voltage of the second electrification adjuster28was set to 0 V and −100 V.

The evaluation was made by using the OPP (oriented polypropylene) recording material with thickness of 30 μm as the recording material20so that the half-tone (isolate dot) image was output by the ink-jet recording apparatus. The uniformity of the output image was visually evaluated. In the case of the image with uniformity, the mark “◯” was recorded. In the case of the image with non-uniformity, the mark “x” was recorded. The ink adhesion state to the ink-jet head242after outputting the image was observed. If the ink adhesion was hardly observed, the mark “◯” was recorded. If the ink adhesion was slightly observed, the mark “Δ” was recorded. If more ink adhesion was observed, the mark “x” was recorded.

Table 2 ofFIG. 13shows measurement results derived from the fifth example and the third comparative example. As Table 2 shows, the fifth example provides the uniform image. Meanwhile, the image derived from the third comparative example exhibits non-uniformity and an irregular outline (recorded as “x”, indicating lack of image uniformity). Observing the enlarged part of the image with non-uniformity and the outline as described above, disorder of the dot shape, that is, elliptical shape was confirmed.

The degree of stain of the ink-jet head242became the lowest when the grid voltage of the second electrification adjuster28according to the fifth example was set to −100 V. The above-described result is considered to be related to the appropriate value for the electric field between the ink-jet head242and the recording material. Meanwhile, in the third comparative example, the stain of the ink-jet head242was worsened when the grid voltage of the second electrification adjuster28was set to −100 V. The above-described result is considered to be attributable to inappropriate control of the electric field between the ink-jet head242and the recording material resulting from the second electrification adjustment performed on the first guide member120having the electrostatic capacity increased, and the image formation in the ink-jet process on the second guide member140having the electrostatic capacity decreased.

From the above-described measurement results, it is confirmed that the examples according to the embodiments of the present invention are capable of eliminating the image noise owing to the electrification non-uniformity on the recording material surface. In other words, the image quality may be improved by those examples according to the embodiments of the present invention.

Effects of Embodiments

According to the first to the fifth embodiments as described above, it is possible to sufficiently reduce not only the apparent non-uniformity of the electrified potential owing to the charge density non-uniformity on the recording material such as the resin film, but also the charge density non-uniformity. This makes it possible to suppress the unnecessary influence of the electric field owing to the electrification non-uniformity in the image forming process for adhesion of the pigment (ink or toner) to the recording material. For example, it is possible to appropriately control flying of the ink droplets by eliminating the electrification non-uniformity on the recording material, which may influence flying of ink droplets, and shape of the landed droplet in the ink-jet type image forming process. It is therefore possible to suppress the unnecessary influence of the electric field upon flying of the ink droplets, and to further suppress dot deformation as a result of electrostatic induction of the droplet landed on the recording material.

Sixth Embodiment

In most cases, the image forming apparatus of electrographic type has been employed for forming a toner image on the paper recording material (that is, a plain paper). However, the paper recording material with high resistance tends to be easily electrified likewise the resin recording material. Therefore, the electrification adjustment apparatus according to the respective embodiments may be applied to any other image forming apparatus such as electrographic type so that improvement in the image quality is expected by eliminating the image noise owing to the electrification non-uniformity on the recording material surface.

Structure of Electrographic Image Forming Apparatus

An explanation will be made with respect to a structure example of the electrographic image forming apparatus as the sixth embodiment, which is provided with the electrification adjustment apparatus according to the embodiments. In the present embodiment, the image forming apparatus with the electrification adjustment apparatus30(seeFIG. 2) according to the first embodiment will be described as an example.

FIG. 14is an explanatory view showing a structure example of the image forming apparatus provided with the electrification adjustment apparatus30as shown inFIG. 2. An image forming apparatus200A as shown inFIG. 14is configured as the structure of the ink-jet recording apparatus200in which the ink-jet type image forming unit35provided with the head units24is replaced with an electrographic type image forming unit35A.

The image forming unit35A is disposed at the downstream side of the electrification adjustment apparatus30, and provided with four image forming units170Y,170M,170C,170K corresponding to yellow (Y), magenta (M), cyan (C), black (K), respectively. The four image forming units170Y to170K are arranged sequentially in the order of yellow, magenta, cyan, and black from the upstream side with respect to the rotating direction of an intermediate transfer belt171. The image forming unit170Y is constituted by an electrification unit, an exposure unit, a development unit, and a photosensitive drum Y having a toner image developed on its surface. Each of the image forming units170M to170K is structured similarly to the image forming unit170Y.

The toner images formed on the photosensitive drums by the respective image forming units170Y to170K based on the image data under the control of the control unit40are superposed through a primary transfer on the intermediate transfer belt171sequentially in accordance with the timing so that the color toner image (color image) is formed. The color image formed on the intermediate transfer belt171is subjected to a secondary transfer to the recording material20by a secondary transfer unit172, and further subjected to the fixing process by a fixing unit170.

Measurement Results

The electrographic image forming apparatus200A as shown inFIG. 14was employed as the image forming apparatus provided with the electrification adjustment apparatus according to the above-described embodiment so as to verify that no image failure owing to the electrification non-uniformity on the recording material surface occurred.

FIG. 15is a table representing measurement results derived from a sixth example and a fourth comparative example.

Sixth Example

The sixth example employed the electrification adjustment apparatus30A (seeFIG. 7) with the structure according to the third example. The grid voltage of the first electrification adjuster27was set to −300 V, and the grid voltage of the second electrification adjuster28was set to 0 V.

Fourth Comparative Example

The fourth comparative example includes the electrification adjustment apparatus30(seeFIG. 2) with the structure according to the second comparative example. The grid voltage of the first electrification adjuster27was set to −300 V, and the grid voltage of the second electrification adjuster was set to 0 V.

The evaluation was made using the OPP (oriented polypropylene) recording material with thickness of 30 μm as the recording material20, and the image forming apparatus200A for outputting a solid image by changing the output level of a secondary transfer voltage. The uniformity of the output image was visually evaluated. In the case of the image with uniformity, the mark “◯” was recorded. In the case of the image with non-uniformity, the mark “x” was recorded. If the density of the solid image was sufficient, the mark “◯” was recorded. If the density of the solid image was insufficient, the mark “x” was recorded.

Table 3 ofFIG. 15shows measurement results derived from the sixth example and the fourth comparative example. As Table 3 shows, the structure according to the sixth example provided the image with uniformity and sufficient density at the secondary transfer voltage of 1750 V. In spite of the region of the structure according to the fourth comparative example where the density was secured at the secondary transfer voltage of 1750 V, the image with non-uniformity and partially insufficient density was confirmed. Furthermore, the region with insufficient density was not corrected unless the secondary transfer voltage was increased to 2000 V. At the secondary transfer voltage lower than 2000 V, the structure failed to provide the image with uniformity. The above-described phenomenon is considered to be attributable to the difference in the transfer characteristic on the recording material surface with electrification non-uniformity between a non-electrified part and the electrified part.

In the case of using the negatively electrified toner, it is drawn to the positively electrified region of the recording material by not only the secondary transfer voltage but also the electrified recording material, resulting in the high toner transcription property. Meanwhile, in the negatively electrified part of the recording material, electrification of the recording material may serve to cancel the secondary transfer voltage, resulting in the low toner transcription property.

In the sixth embodiment, as the secondary transfer voltage becomes as high as 1750 V, the electrification non-uniformity on the recording material no longer exists (image uniformity “◯”). Therefore, the secondary transfer characteristic hardly fluctuates depending on the location. The secondary transfer voltage to be applied may be arbitrarily set so long as the density is secured. In the fourth comparative example, the electrified state is variable depending on the position of the recording material. Even if the secondary transfer voltage is applied to the non-electrified part where the density may be secured, the negatively electrified part will act to cancel the secondary transfer voltage. This may fail to secure the density. As a result, it is necessary to apply the secondary transfer voltage which overtakes the canceling action of the transfer voltage in the negatively electrified part for the purpose of obtaining the uniform image.

If the secondary transfer voltage exceeds 2500 V, the secondary transfer unit172generates noise owing to discharge (Table 3 does not show the result). The need of setting the secondary transfer voltage to the high value for eliminating the electrification non-uniformity on the recording material may lead to the loss of the margin for setting the voltage.

The present invention is not limited to the above-described embodiments, but may be arbitrarily applied and modified in various forms so long as they do not deviate from the scope of the present invention.

For example, the embodiments have been described in detail for readily understanding of the present invention with respect to structures of the apparatus and the system, which are not necessarily limited to the one equipped with all components as described above. It is possible to replace a part of the structure of one embodiment with the component of another embodiment. The one embodiment may be provided with an additional component of another embodiment. It is further possible to add, remove, and replace the other component to, from and with a part of the structure of the respective embodiments.

It is also possible to implement the respective components, functions and processing units partially or entirely through hardware by designing integrated circuits, for example.

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