JPH0377515B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field of the Invention] The present invention relates to a fixing device that fixes an electrostatically formed unfixed image using heat, pressure, or the like. In particular, the present invention relates to a fixing device that fixes an unfixed image by passing a support material supporting the unfixed image between a pair of rotating bodies. [Prior Art] In image forming apparatuses such as electrophotographic copying machines, various methods and devices have been developed for the process of fixing toner images on paper or the like. Currently, the most common method is the so-called hot roll fixing method, which applies heat and pressure at the same time.This method fixes the toner image onto the image-receiving sheet by bringing the image-receiving sheet carrying the toner image into contact with a heated roller. It's a method. However, when such a fixing method is used, problems such as so-called offset tend to occur. Offset is an undesirable development in which a portion of the toner image carried on the image receiving sheet is transferred to the roller surface, and is a major problem in developing a hot roll fixing system. In the currently commonly used hot roll fixing devices, the roller that comes into contact with the toner image usually has at least a surface layer formed of silicone rubber or fluorine resin with good release properties, but there is no offset prevention layer on the surface. In many cases, a release oil such as silicone oil is applied to the roller surface to prevent fatigue. However, the method of applying oil has problems such as that the fixing device becomes complicated due to the provision of the oil application system and that the evaporation of the oil causes discomfort to the user. Therefore, it is not desirable to try to prevent offset by coating with oil, but rather the development of a toner with good offset resistance over a wide fixing temperature range is currently desired. It is true that in the development of a hot roll fixing system, it is not appropriate to require excessive release properties from the roll material and release oil, which are limited in terms of materials, in terms of fixing system design. Developing offset-free toners is important for creating inexpensive and compact fusers. Conventionally, important points for developing offset-free toners have been the viscosity and releasability of the toner when it is melted. In other words, the toner has an appropriate viscosity with little change in viscosity due to changes in temperature during melting,
Furthermore, it is important to design the toner composition so that it has releasability against a hot roll. In short, these are problems with the thermal and physical properties of the toner. [Problems to be Solved by the Invention] However, the present inventors have discovered the following development that cannot be explained solely by the thermal and physical properties of the toner. A toner was prepared consisting of 100 parts by weight of styrene-butyl methacrylate copolymer, 10 parts by weight of low molecular weight polypropylene, and 6 parts by weight of carbon black.
This toner is mixed with carrier iron powder to form a negatively charged toner, and a positive latent image is developed and transferred onto plain paper. Let N be the unfixed image obtained. Further, the same toner is mixed with surface-coated carrier iron powder to form a positively charged toner, and a negative latent image is developed and transferred onto plain paper. Let P be the unfixed image obtained. Next, images N and P are transferred using a fixing device having a fixing roller whose surface is coated with polytetrafluoroethylene and has a halogen lamp inside, and a pressure roller whose surface is coated with silicone rubber.
We conducted a retention test. The results were as shown in Table 1 below.

[Means for solving problems]

The present invention, which solves the above-mentioned problems, includes: a first rotating body that is in contact with an unfixed toner image and has a conductive base material;
In a fixing device that performs fixing by sandwiching and conveying a supporting material supporting an unfixed toner image between the first rotating body and a second rotating body having a conductive base material in pressure contact with the first rotating body, the first rotating body The base material of the body is grounded, and the base material of the second rotary body is applied with a potential of opposite polarity to that of the unfixed toner image. [Embodiments of the Invention] In the following explanation, an electrically negative latent image means a latent image that is electrically negative with respect to the developing electrode, and includes not only a latent image with a negative charge but also a latent image with a positive charge. Even if it is an image, if reversal development is performed, it is included in the present invention. The process of forming the electrically negative latent image etc. includes, for example, the Carlson method, in which a negative charge is imparted to an N-type photoconductor such as a zinc oxide photoreceptor, various organic photoconductors, and imagewise exposed; There are well-known methods such as the NP method, in which a photoreceptor having three layers (layer, P-type photoconductor, and conductive substrate) is negatively charged, and simultaneously with image exposure, positive charging or AC discharging is performed, and then the entire surface is exposed. be. Examples of methods for developing an electrically negative latent image include the magnetic brush method described in U.S. Pat. No. 2,874,063, the cascade development method described in U.S. Pat. −42141,
Examples include a method using an insulating magnetic toner described in JP-A-Sho, a powder cloud method, an impression method, and a method using a high-resistance magnetic toner. The toner image is passed between at least one pair of heated rollers used in the following examples to fix the toner image on the toner support, for example, the surface of which has a heat source inside is made of fluorine-based resin or silicone rubber. A fixing roller coated with a heat source and a pressure roller coated with a fluororesin or silicone rubber having an internal heat source as needed are arranged approximately parallel to each other, and there is approximately a gap between the two rollers.
There is a method of thermally fixing the image passing between both rollers by applying a linear pressure of about 0.01 to 10 kg/cm. In this step, a roller for supplying thermal energy, a cleaner for removing offset toner, a means for applying oil, etc. may be provided as necessary. The method also includes a step of transferring the developed image on the latent image carrier onto a transfer member, if necessary, and for this purpose, a corona transfer method, a bias roll transfer method, a magnetic transfer method, etc. can be used. In this case, it is usually necessary to clean the residual toner on the latent image holder, and for this purpose, a blade cleaning method, a fur brush cleaning method, a magnetic brush cleaning method, etc. can be used. The toner for developing the electrically negative latent image is made of polymers such as styrene polymers, acrylic polymers, polyesters, epoxy resins, and polyamides that have a relatively wide molecular weight distribution and are suitable for hot roll fixing. As the coloring resin, carbon black, iron black, graphite, nigrosine, ultramarine phthalocyanine blue, benzidine yellow, Hansa yellow, quinacridone metal complex dye, various lake pigments, etc. may be used as the coloring agent. Furthermore, positive charge control and
For the purpose of preventing agglomeration and improving mold release properties, nigrosine-substituted quaternary ammonium salts, dimethylaminoethyl methacrylate polymers, vinylpyridine polymers, acrylamide polymers, basic dyes and their lakes, colloidal silica, Low molecular weight polyethylene, low molecular weight polypropylene, bisamide, higher fatty acids and metal salts thereof, etc. may be added. In addition, in order to make the toner described above a magnetic toner, ferromagnetic elements and alloys and compounds containing these are used, such as iron such as magnetite, hematite, and ferrite, alloys and compounds of cobalt, nickel, manganese, etc. Substances conventionally known as magnetic materials such as ferromagnetic alloys may be added. Furthermore, if necessary, it may be mixed with carrier particles such as iron powder, glass beads, nickel powder, ferride powder, etc., and used as a developer for electrical latent images. An abrasive such as colloidal silica powder or cerium oxide may be added to prevent toner from sticking. The present invention will be described in detail below with reference to Examples, but the present invention is of course not limited thereto. FIG. 1 shows an embodiment of a copying device or a recording device to which a fixing device according to the present invention can be applied. 1 is a zinc oxide photoreceptor, which consists of a zinc oxide binder layer and a grounded conductive substrate, and rotates at a constant speed in the direction of the arrow (in this case, the linear speed is 100 mm/
sec). Reference numeral 2 denotes a well-known charging device, which discharges -7 KV negative polarity corona to apply a negative charge onto the photoreceptor 1. Reference numeral 3 denotes a light image irradiation device that projects an original image, a light image, or a light beam modulated by an image signal, thereby forming a negative latent image on the photoreceptor 1. The formed negative latent image is developed using the developing device 4. The toner 4a in the developing device contains 100 parts by weight of styrene-butyl methacrylate copolymer;
Polypropylene with a melt viscosity of 280 cps at 140°C, 2 parts by weight of nigrosine dye, 60 parts by weight of magnetic powder,
The developing sleeve 4b, which is a positively charged magnetic toner made of 2 parts by weight of colloidal silica and is made of SUS stainless steel and has a magnet 4c fixed inside, rotates in the direction of the arrow at approximately the same linear speed as the photoreceptor 1. Therefore, iron blade 4 set to 250μ
d and the sleeve 4b and pass through the sleeve 4b.
coated on top. The coated toner is applied to the photoreceptor 1 and the sleeve 4b.
The latent image is transferred from the sleeve 4b to the photoreceptor 1 in accordance with the pattern of the latent image at the minimum distance between the two. Here, the distance between the sleeve 4b and the photoreceptor 1 is set to 250μ, and a DC bias of -150V and an AC bias of 1.2KHz and 1.5KV are applied to the sleeve 4b. Subsequently, the positively charged toner image on the photoreceptor 1 is transferred onto a transfer paper 7 by a -7 KV charging device 6. Next, the image is fixed by the fixing device 9. On the other hand, the remaining toner on the photoreceptor 1 that has not been transferred is removed by the cleaner 8. FIG. 2 is a sectional view of a fixing device according to an embodiment of the present invention. The roller that comes into contact with the unfixed image surface of the transfer paper 7 has an iron core 9a that is the base material of the roller, a halogen lamp inside the core 9a, and a polytetrafluoroethylene coating on the roller surface. It has layer 9c. The roller that comes into contact with the back surface of the unfixed image surface of the transfer paper 7 has an iron core 9d that is a base material of the roller having a hollow interior, and a coating layer 9e made of silicone rubber that covers the core 9d. and has. By applying a bias voltage of 9 g between the fixing rollers, especially between the core bars 9a and 9d, so that the roller on the side that does not come into contact with the unfixed image becomes electrically negative with respect to the roller on the side that comes into contact with the unfixed image. A potential difference is applied between both rollers. That is, due to this potential difference, the positively charged toner is electrically pulled in a negative direction, that is, toward the roller on the side not in contact with the unfixed image, so that the offset is reduced or eliminated. The images actually obtained were clear and no offset was observed. On the other hand, the bias voltage 9
When the same procedure as above was performed except that g was not applied, an offset was observed. In the above embodiment, a potential difference is applied between the roller that contacts the image surface and the roller that does not contact the image surface among at least one pair of heated fixing rollers, and in particular, the roller that does not contact the image surface becomes electrically negative. Although a potential difference is applied as described above, it is also a more preferable embodiment to use it in a pressure fixing device or the like that does not use heat. Additionally, 10 pairs of conveyor rollers
This is a more preferable embodiment in which the effect is doubled if it is provided on both the fixing roller and the fixing roller. Furthermore, although the above embodiments show examples in which a negative latent image and a positively charged toner are used, the present invention is not limited thereto. It is sufficient to apply a potential difference between the core metals of the rollers so that the member such as a rotating body such as a roller or belt that is in contact with the toner image is electrically negative with respect to the rotating body that is not in contact with the toner image. . [Effects of the Invention] As described above, according to the present invention, various problems such as image scattering and offset that have conventionally occurred can be solved, and the image has a high degree of separability and is extremely effective in preventing offset.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an embodiment of a copying apparatus to which the present invention can be applied, and FIG. 2 is a sectional view of essential parts of an embodiment of the present invention. 1 is a photoreceptor, 2 and 6 are charging devices, 4 is a developing device, 4a is a toner, 5 is a toner image, 7 is a transfer paper,
9 is a fixing device, 9a and 9d are core metals, and 9g is a bias voltage.

Claims (1)

[Scope of Claims] 1. A first rotating body that is in contact with an unfixed toner image and has a conductive base material, and a second rotating body that is in pressure contact with the first rotary body and has a conductive base material. , in a fixing device that performs fixing by nipping and conveying a support material supporting an unfixed toner image, the base material of the first rotating body is grounded, and the base material of the first rotating body is grounded;
A fixing device characterized in that a base material of a rotating body is applied with a potential of opposite polarity to that of an unfixed toner image.