JPH0421491A - Image forming device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement of an image forming apparatus disclosed in Japanese Patent Application No. 63-36114.

[Prior Art] The image forming apparatus disclosed in Japanese Patent Application No. 63-36114 has a step of forming an image by a thermal transfer method and a step of recycling an ink sheet. The ink sheet consists of an insulating support and a conductive ink layer, and in the process of forming an image,
For example, an image is formed on the recording medium by transferring ink from an ink sheet to a recording medium according to an image signal using a thermal transfer method using a normal thermal head. In the process of forming an image, the insulating support is exposed in the areas where the ink has been peeled off, but in the next step of recycling the ink sheet, the areas where the ink has been peeled off are replenished with ink. . In the process of recycling an ink sheet, conductive powder ink held on a sleeve, which is a powder conveying member, is placed on the ink layer side of the ink sheet, and electrodes are placed on the insulating support side. is placed in contact with the Further, a predetermined voltage is applied between the sleeve and the electrode. When an ink layer supported on an insulating support passes through powder ink, the powder ink only serves as a path for charges, and the charges are injected into the ink layer, so there is no powder on the surface of the ink layer. Ink does not stick. When the peeled part of the ink layer passes through the powder ink, the powder ink comes into contact with the insulating support and charges are injected into the powder ink that is in contact with the insulating support. Electrostatic forces cause more powder ink to adhere to the insulating support. The reason why only the - layer is deposited is that the part other than the powder ink that is in contact with the support is only a path for the charge, and no charge is injected into it. Thereafter, the powder ink adhering to the insulating support is fixed onto the insulating support by a heat-pressure fixing means, and the ink sheet is recycled through zero or more steps of forming an ink layer.

[Problems to be Solved by the Invention] However, the image forming apparatus of Japanese Patent Application No. 63-36114 has problems caused strictly by the adhesive force of the surface of the powder ink, the adhesive force of the surface of the ink layer, and the poor conductivity of the powder ink. A small amount of powder ink adheres to the ink layer due to electrostatic force caused by frictional charging. The amount of adhesion is less than 2% of the total amount of the ink layer, which is a level that does not pose a problem.However, if ink transfer and ink sheet regeneration are carried out over a long period of time, variations in the thickness of the ink layer may occur in rare cases. However, there was a problem in that image density unevenness occurred.

The present invention has been developed to solve these conventional problems, and its purpose is to maintain a constant thickness of the ink layer on an ink sheet that is recycled over a long period of time, and to produce clear images without temperature unevenness. It's about getting.

[Means for Solving the Problems] An image forming apparatus of the present invention includes a step of forming an image using a thermal transfer method and a step of recycling an ink sheet. The member is characterized in that the surface magnetic flux density is 800G or more.

[Function] According to the above configuration of the present invention, since the surface magnetic flux density of the powder conveying member that conveys the powder ink is set to 800G or more,
The force of the powder conveying member to restrain the powder ink is improved, thereby making it possible to prevent the powder ink from adhering to the ink layer. Therefore, an ink sheet that retains an ink layer of constant thickness over a long period of time can be recycled.

Hereinafter, the present invention will be explained in detail with reference to Examples.

[Example 1 FIG. 1 is a schematic diagram of an image forming apparatus of the present invention.

Ink sheet 3 having an ink layer 2 on an insulating support 1
moves in the direction of the arrow 4, and by the thermal head 5,
One ink is transferred onto the recording medium 7 moving in the direction of the arrow 6,
An image is formed on the recording medium 7. (Step of forming an image using a thermal transfer method) By forming an image, a peeling part 8 of the ink layer and an adhesion part 9 of the ink layer are formed on the ink sheet 3.

The electrode 1 is placed in contact with the insulating support 1 of the ink sheet 3.
A powder conveying member 12 for conveying powder ink 11 is disposed on the opposite side of the electrode 10 with the ink sheet 3 interposed therebetween. In Example 1, the powder conveying member 12 is non-magnetic and conductive, and the powder ink 11 is transferred onto the powder conveying member 12 by magnetic force using the magnetic roller 13 built in the powder conveying member/'12. keeping. The surface magnetic flux density of the powder conveying member 12 is concentrated by the magnetic force of the magnetic roller 13, and in the present invention, the magnetic roller 13 is used so that the surface magnetic flux density of the powder conveying member 12 is 800 G or more. The reason why the magnetic flux density is set to 800G or more will be described later. The powder conveying member 12 supplies the powder ink 11 to the ink sheet 3 by rotating in the direction of the arrow 14 . Then, the powder ink 11 is supplied to the ink sheet 3 while a voltage is applied between the electrode 10 and the powder conveying member 12 by the power source 15.

Although not shown in the figure, the supply amount of the powder ink 11 is regulated by a blade.

The powder ink 11 that has come into contact with the peeled part 8 of the ink layer of the ink sheet 3 has an amount of charge proportional to the product of the peeled part 8 of the ink layer and the capacitance of the insulating support 1 because the peeled part 8 of the ink layer exhibits insulating properties. The injection receiver adheres to the insulating support 1 by electrostatic force.

The powder ink 11 in contact with the ink layer adhering portion 9 of the ink sheet 3 and the powder ink adhering to the insulating support 1 is theoretically conductive because the ink layer and the powder ink are conductive. The surface of the powder conveying member 12 merely acts as a path for electric charge and does not have any adhesive force.Actually, it may adhere due to the adhesive force of the ink layer or powder ink, but in the present invention, the surface magnetic flux density of the powder conveying member 12 By setting the force to 800G or more, the powder ink 11 is prevented from adhering to the ink layer 2. The reason is still under consideration, but I think it is as follows.

When the powder ink 11 comes into contact with the ink layer 2, the charge flows to the ink layer 2, so the electrostatic force due to the charge injection does not work.
A magnetic force Fm and an adhesive force Fn between the ink layer 2 (Fn also includes the electrostatic force generated by friction between the ink layer 2 and the ink layer 2) act. The magnetic force Fm is proportional to the product of the magnetization magnitude of the powder ink and the magnetic gradient. FIG. 2 is a diagram showing an example of an MH convex curve of a powder ink used in the image forming apparatus of the present invention. In the figure, the horizontal axis represents the magnetic field H, and the vertical axis represents the magnitude M of magnetization of the powder ink. As H increases, M also increases, but soon M becomes the saturation magnetization MS. Xs
The value of depends on the magnetic powder content of the powder ink, and the larger the magnetic powder content, the larger the value of Ms becomes. Note that since M normally has some hysteresis, the path of M when H increases and the path of M when 'H decreases are different.

In addition, a proportional relationship holds between the magnetic field H and the magnetic flux density B, and M
Since the magnetic flux density B when it becomes s is around 2000G,
The magnitude M of magnetization of the powder ink 11 held on the powder conveying member 12 does not reach Ms, and the powder conveying member 1
2 shows a value depending on the surface magnetic flux density. Furthermore, the greater the surface magnetic flux density of the powder conveying member 12, the greater the magnetic gradient near the surface of the powder conveying member. Therefore, as mentioned above, the magnetic force Fm acting on the powder ink 11 is proportional to the product of the magnitude of magnetization of the powder ink and the magnetic gradient. Fm can be increased by increasing the surface magnetic flux density of the member 12. Then, when Fm>Fn, it is possible to prevent the powder ink 11 from adhering to the ink layer 2 of the ink sheet 3. In other words, there are the following means to make Fm>Fn. 1) Increasing the magnetization magnitude M by increasing the magnetic powder content of the powder ink, 2) Surface magnetic flux density B of the powder conveying member
improve. By the way, if 1) is selected, it is not effective because the melt viscosity of the powder ink increases, which adversely affects the printing quality.From experiments, the magnetic powder content of the powder ink, considering printing quality, is limited to 50 wt%. I think that the.

Therefore, in the present invention, by selecting method 2), F
m>Fn.

FIG. 3 is a diagram showing the amount of powder ink 11 attached to the ink layer 2 with respect to the surface magnetic flux density of the powder conveying member 12. The measurement was performed using powder ink with a magnetic powder content of 50 wt%,
The test was carried out using a powder conveying member with a surface magnetic flux density of 500G to 1200G. The horizontal axis represents the surface magnetic flux density of the powder conveying member 12, and the vertical axis represents the amount of the powder ink 11 attached to the ink layer 2.

The amount of powder ink 11 attached to the ink layer 2 is expressed as a percentage of the total amount of the ink layer. At a surface magnetic flux density of 500G, the amount of adhesion is approximately 2%, but as the surface magnetic flux density increases, the amount of adhesion decreases, and when the surface magnetic flux density exceeds 800G, no adhesion occurs. The surface magnetic flux density of the conveying member 12 is 80
By setting it to 0G or more, the ink layer 2 of the ink sheet 3
Prevent powder ink from adhering to the ink sheet 3.
Powder ink can be replenished only to the ink layer peeling section 8 . The ink sheet 3 refilled with powder ink is fixed onto the ink sheet by the powder ink fixing means 16, and the ink sheet is regenerated.

The powder conveying member 12 used in the present invention is made of a non-magnetic and conductive material such as stainless steel, aluminum, or brass, and the magnet roller 13 is made of a known magnetic material such as a ferrite magnet or a rare earth magnet. can do. Furthermore, in the well-known electrophotographic method, the powder conveying member and the magnetic roller must be configured separately in order to triboelectrically charge the insulating developer, but in the image forming apparatus of the present invention, conductive powder is used as the developer. Since the powder ink is attached to the ink layer peeled part of the ink sheet by charge injection using body ink, the powder ink can be conveyed on the surface of the magnetic roller. In addition, since no other member is interposed between the magnetic roller and the powder ink, the surface charge density of the powder conveying member (in this case, the magnetic roller) can be easily increased. be able to.

As the insulating support 1 of the ink sheet 3 used in the present invention, a polymer film such as polyethylene terephthalate or aramid can be used. A stylus head used in this method can also be used, and in the case of an electrically conductive thermal transfer method, the structure of the ink sheet is such that an electrically conductive layer or the like is formed on the opposite side of the ink layer across the ink sheet.

As the recording medium 7, plain paper, OHP sheet, etc. are used. Further, as the powder ink fixing means 16, methods such as a heat roll fixing method, a flash fixing method, a pressure fixing method, etc., which are known in electrophotography, can be applied.

[Example 2] As the powder ink 11, polystyrene 16 wt% paraffin wax 30 wt% carnauba wax
10wt% carbon black 4wt%F
Powder ink 11 was prepared by producing base particles consisting of 40 wt % of eaOm by a dry pulverization method, and further adding carbon black externally around the base particles by a mechanochemical method. Further, in the image forming apparatus as shown in FIG. 1, the powder conveying member 12 is made of aluminum.
The magnetic roller 13 is formed of a samarium cobalt rare earth injection molded magnet, and the surface charge density of the powder conveying member is 10.
It was set to 0OG. When the ink sheet was actually recycled, no powder ink was observed adhering to the ink layer, and even if the ink sheet was recycled repeatedly, an ink sheet with a constant ink layer thickness was always obtained, and the density of the print was No unevenness occurred.

[Example 3] The powder ink used in Example 2 was used as the powder ink 11, and an ink sheet was actually recycled in an image forming apparatus having an ink sheet recycling section shown in FIG. FIG. 4 is a diagram showing an ink sheet recycling section of an image forming apparatus in Example 3. The numbers shown in FIG. 4 correspond to the numbers shown in FIG. 1, but in Example 3, the magnetic roller 13
plays the role of a powder conveying member, and the magnetic roller 1
3 rotates in the direction of arrow 14, powder ink 11
is transported. The magnetic roller 13 was made of an extruded ferrite magnet, and had a surface magnetic flux density of 950G. Although not shown in the figure, the supply amount of powder ink is regulated by a blade. As a result of recycling the ink sheet, no powder ink was observed adhering to the ink layer.
Even when the ink sheet was repeatedly recycled, an ink sheet with a constant ink layer thickness was always obtained, and no density unevenness occurred in the print.

[Example 4 Powder ink 11 includes: polystyrene 20wt% paraffin wax 30wt% carnauba wax 2
0wt%Fe30a 20w
Knead and crush 10 wt% of one of the following coloring agents: cyan dyes such as copper phthalocyanine, magenta dyes such as Carmiso 6B, and yellow dyes such as disazo yellow to obtain a matrix of cyan, magenta, and yellow with a volume average particle size of 10 μm. Particles were prepared. Furthermore, the particle size is 0.
5 parts of 1 μm ITO powder per 100 parts by weight of the base particles
The amount equivalent to parts by weight was placed in a super mixer to crush the ITO powder into primary particles, and then the base particles were mixed in the machine, and the ITO powder was attached and fixed around the base particles to create a powder ink. Furthermore, in the image forming apparatus shown in FIG. 1, the powder conveyance member 12 is made of aluminum, the magnet roller 13 is made of neodymium iron-based rare earth injection molded magnet, and the surface charge density of the powder conveyance member is 1200G. And so. When we actually recycled cyan, magenta, and yellow ink sheets, no powder ink was observed adhering to the ink layer, and even when the ink sheets were repeatedly recycled, the thickness of the ink layer was always constant. was obtained, and no density unevenness occurred in the print. Further, the color and turbidity of the produced ink were measured using a Macbeth thermometer and evaluated using the GATF color circle, and as a result, the hue error and turbidity were 5% or less. Furthermore, when color ink was made with 40 wt% of magnetic powder mixed in, the turbidity was 10% or more, so color reproducibility was improved by reducing the amount of magnetic powder mixed in powder ink. It turned out to be.

[Effects of the Invention] As described above, according to the present invention, in an image forming apparatus having a step of forming an image by a thermal transfer method and a step of recycling an ink sheet, a powder conveying member for conveying powder ink is provided. Since the surface magnetic flux density is set to 800 G or more, the force of restraining the powder ink of the powder conveying member is improved, thereby making it possible to prevent the powder ink from adhering to the ink layer.

Therefore, it has the effect that an ink sheet that retains an ink layer of a constant thickness over a long period of time can be recycled.

In addition, in the present invention, we have chosen a method of improving the surface magnetic flux density of the powder conveying member in order to make Fm>Fn, so it is possible to prevent the powder ink from adhering to the ink layer without impairing print quality. By increasing the surface magnetic flux density of the powder conveying member, the powder ink does not adhere to the ink layer even if the amount of magnetic powder added to the powder ink is reduced. It also has the effect of being able to improve color reproduction.

The image forming apparatus of the present invention can be widely applied to image output apparatuses such as facsimile machines, copying machines, and printers.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an image forming apparatus of the present invention, and FIG.
FIG. 3, which is a diagram showing an example of the MH curve of the powder ink used in the image forming apparatus of the present invention, shows the amount of the powder ink 11 attached to the ink layer 2 with respect to the surface magnetic flux density of the powder conveying member 12. FIG. 4 is a diagram showing an ink sheet recycling section of an image forming apparatus in Example 3. 1 ... Insulating support 2 ... Ink layer 3 ... Ink sheet 5 ... Thermal head 7 ... Recording medium 8 ... Peeling part of ink layer 9 ... Adhering part of ink layer 0 ... Electrode 1 ... Powder ink 2 ... Powder conveying member 3 ... Magnetic roller 5 ... Power supply 6 ... Powder ink fixing means Applicant Seiko Epson Co., Ltd. Agent Patent attorney Kizobe Suzuki (1st name) 11...Powder ink 12...Powder transport means 13...Magnetic roller 15...U Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] An image forming apparatus having a step of forming an image by a thermal transfer method and a step of recycling an ink sheet, characterized in that a powder conveying member that conveys powder ink has a surface magnetic flux density of 800 G or more. Device.