JPH0310108B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a novel image forming apparatus for developing a latent image and fixing the resulting unfixed image by a fixing method such as heat or pressure to obtain an image. 2. Description of the Related Art Conventionally, various methods and devices have been developed for fixing toner images on paper or the like in fixing devices such as electrophotographic copying machines. 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 phenomenon 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. However, the present inventor discovered the following phenomenon that cannot be explained only 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 to plain paper. Let N be the unfixed image obtained. The same toner is also 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.

[Table] ○: Good △: Slightly good ×: Poor When the plain paper used for the fixing test is passed through the fixing device, the plain paper is positively charged, and the two rollers are both negatively charged with respect to the plain paper. Considering this fact and the results of the above-mentioned fixation test, the present inventor makes the following conclusion. In other words, as a result of the charging experiment, the transfer paper is positively charged during fixing, so if the toner on the image is positively charged, the toner will move away from the paper and transfer to the fixing roller. This makes it difficult for the paper to adhere to the paper and easily offset to the roller. On the other hand, if the toner on the image is negatively charged, it will easily adhere to the paper and will be difficult to offset. Therefore, image N has excellent fixing properties and offset resistance, but image P has poor fixing properties and offset resistance despite using the same toner. Note in Table 1 that image P has poor offset properties at low temperatures (150-170°C). It is thought that if the temperature of the fixing roller is high (190° C. to 200° C.), the toner melts sufficiently and comes into close contact with the paper, so that the influence of the electric force is almost eliminated. Under these circumstances, efforts were made to develop an image forming method in which a negative latent image or the like is developed and a toner image is fixed using a hot roll fixing method or the like. That is, the present invention has been made to solve the above problems, and includes a first rotating body, a second rotating body that is in pressure contact with the first rotating body, and a first rotating body and a second rotating body that are in pressure contact with the first rotating body.
In the fixing device, the guide member includes a guide member provided immediately before the pressure contact portion of the rotating body and guides the support material supporting the unfixed image into the pressure contact portion, the guide member having a guide member that is opposite to the unfixed image. It is characterized in that a polar voltage is applied. In the above explanation, an electrically negative latent image means a latent image that is electrically negative with respect to the developing electrode, and not only a latent image with a negative charge but also a latent image with a positive charge can be reversed. If development is carried out, 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 photoconductor having three layers (layer - P-type photoconductor - conductive substrate) is negatively charged, then positively charged or AC neutralized at the same time as image exposure, and then the entire surface is exposed. . 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. In the following examples, the toner image is passed between at least one pair of heated rollers to fix the toner image on the toner support, for example,
A fixing roller whose surface is coated with a fluorine-based resin or silicone rubber and which has a heat source inside and a pressure roller whose surface is coated with a fluorine-based resin or silicone rubber and which has a heat source inside as necessary are placed almost parallel to each other. There is a method of thermally fixing the image passing between the two rollers by applying a linear pressure of about 0.01 to 10 kg/cm between the two rollers.
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 remaining toner on the latent image carrier.
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. Carbon black, iron black,
Graphite, Nigrosine, Ultramarine Phthalocyanine Blue, Penzidine Yellow, Hansa Yellow,
Quinacridone metal complex dyes, various lake pigments, etc. may be used. Furthermore, if necessary, for purposes such as positive charge control, prevention of aggregation, and improvement of 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, bisamides, higher fatty acids and their metal salts, 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 an image forming method according to the present invention can be applied. Reference numeral 1 denotes 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. (Here, the linear speed is 100mm/
sec) 2 is a well-known charging device that discharges a -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 ps at 140°C, 2 parts by weight of nigrosine dye, 60 parts by weight of magnetic powder,
This is a positively charged magnetic toner made of 2 parts by weight of colloidal silica, and is produced by rotating a SUS developing sleeve 4b having a magnet 4c fixed inside at approximately the same linear speed as the photoreceptor 1 in the direction of the arrow. ,
It passes through the gap between the iron blade 4d and the sleeve 4b, which is set to 250μ, and is coated onto the sleeve 4b. 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 according to the pattern of the latent image at the minimum gap between the sleeve 4b and the photoreceptor 1. Here, the gap between the sleeve 4b and the photoreceptor 1 is set to 250μ, and a DC bias of -150V and an AC bias of 1.2KV to 1.5KV are applied to the sleeve 4b. Subsequently, the positively charged toner image on the photoreceptor 1 is transferred to a transfer paper 7 by a -7KV charging device 6.
transferred on top. 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 from the photoreceptor 1 by the cleaner 8 . FIG. 2 is a sectional view of a main part of an embodiment of the present invention, showing an outline of the fixing device used. An iron roller 9a that contacts the image surface of the transfer paper 7 has a halogen lamp 9b inside and a polytetrafluoroethylene coating layer 9c on its surface. The iron roller 9d that comes into contact with the back side of the image plane is hollow inside and has a coating layer 9 of a silicone rubber roller on its surface.
It has e. A counter electrode 9f made of aluminum is located at a position where the transfer paper 7 comes into contact with the back surface of the toner image holding sheet immediately before it enters between the pair of fixing rollers, and guides the transfer paper to enter the pressure contact area between the fixing rollers. A fixing roller 9a and a counter electrode 9f are provided.
A bias voltage 9g of about -0.5 to 5 KV, which is negative with respect to the fixing roller 9a and opposite in polarity to the unfixed toner image, is applied between the counter electrode 9f and the fixing roller 9a. The images obtained were clear and no offset was observed. On the other hand, when the same procedure as above was performed except that the bias voltage of 9 g was not applied, an offset was observed. As described above, according to the present invention, a voltage of opposite polarity to that of the unfixed image is applied to the guide provided immediately before the pressure contact portion between the pair of fixing rollers, which guides the entry of the unfixed image support material, so that a clear image can be obtained. The resulting image solves various problems such as image scattering and offset that have conventionally occurred, has a high degree of separability, and is extremely effective in preventing offset. 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 to this, and if the latent image is of a positive polarity and a negatively charged toner is used, It is only necessary to apply a positive voltage to the guide member immediately before the press-contact portion, and an excellent offset prevention effect can be achieved regardless of the material of the rotating body or other members.

[Brief explanation of the drawing]

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 iron rollers, 9f
is the counter electrode, and 9g is the bias potential.

Claims (1)

[Claims] 1. A first rotating body, a second rotating body that is in pressure contact with the first rotating body, and an undetermined component provided immediately before the pressure contact portion of the first and second rotating body pair. a guide member that guides the support material that supports the printed image to enter the press-contact portion;
In a fixing device in which an unfixed image is fixed by the sliding supporting material on the guide member entering the pressure contact portion, a voltage having a polarity opposite to that of the unfixed image is applied to the guide member. A fixing device characterized by: 2. The fixing device according to claim 1, wherein the voltage is a bias voltage of 0.3 to 5 KV.