JP5489773B2 - Polyester film for photoreceptor belt - Google Patents

Description

  The present invention relates to a polyester film which is used as an electrophotographic photosensitive belt (photosensitive layer coating film) used in an electrophotographic copying machine, a printer, a facsimile machine or the like, and has excellent image forming performance. It relates to film.

  Conventionally, a photosensitive belt for electrophotography, which is a system that performs line scanning with a laser beam, has a particular problem that an interference fringe pattern appears in an image formed using laser light. This kind of interference fringe is caused by the fact that transmitted light that has not been absorbed in the photosensitive layer causes multiple reflections of the laser beam in the photosensitive layer coated on the belt substrate, and incident light on the surface of the photosensitive layer. This is attributed to the occurrence of interference.

  As a countermeasure against such interference fringes, it has been proposed to roughen the surface of the belt base material. For example, a method based on a method of performing sandblasting on a substrate surface (Patent Document 1) or a method of performing etching processing on a substrate surface (Patent Document 2) is disclosed. By providing irregularities on the belt base material surface by these methods, it is possible to suppress interference between incident light and reflected light, and to prevent occurrence of interference fringes. However, the above-described conventional method for producing an electrophotographic photoreceptor has the following problems in adopting the above-described method for preventing interference fringes.

  In other words, when roughening the surface of the substrate, there is a limit to reducing the particle size of the blast material, etc., so that the size of the unevenness of the scraped trace is the same as or larger than that of the developing toner. The resolution is lowered, which causes so-called black spots and white spots during image formation. In addition, when sandblasting is performed, a sandblasting material mainly composed of abrasive grains of alumina-based material is blown onto the base material with air or the like, so that the blasting material bites into the surface of the base material. Therefore, it is difficult to remove the blasting material that has digged into the base material even after washing, and the remaining blasting material is not preferable because it causes defects in the copy image. On the other hand, in the case of etching processing, it becomes a factor of high cost by a processing process. In any of the methods, it is difficult to uniformly roughen the surface of the belt base material, and there is a problem that black spots and white spots of an image, which are different from interference fringes, are generated and resolution is lowered. . Furthermore, since the surface of the belt base material needs to be cleaned in a separate step after the surface treatment, it is not preferable.

JP-A-2-87154 JP-A-6-10268

  The present invention has been made in view of the above circumstances, and its solution is to prevent interference fringes at the time of image formation and to obtain good image quality without occurrence of black spots and white spots. The object is to provide a photoreceptor belt.

  As a result of intensive studies in view of the above problems, the present inventors have found that the above problems can be easily solved by a polyester film having a specific configuration, and have completed the present invention.

That is, the gist of the present invention is that two or more kinds of amorphous silica particles including at least amorphous silica particles having a large average particle diameter of 4 to 7 μm and amorphous silica particles having an average particle diameter of 1 to 3 μm. It is a polyester film containing regular silica particles and has an air leakage index in the range of 1000 to 2000 seconds.

  According to the present invention, by blending two or more kinds of amorphous silica particles having different particle diameters, a film having surface irregularities such that the air leakage index is in a certain range is provided, and this is photosensitive. By using it as a body belt, it is possible to obtain a photoconductor that eliminates the crystallization of the conductive support, does not increase the residual potential, and eliminates interference fringes, black spots, and white spots that appear during image formation. The industrial value is very large.

  Hereinafter, the present invention will be described in detail.

  Specifically, the polyester film of the present invention is used as a substrate for a photoreceptor belt after a surface of a metal such as aluminum or titanium or an alloy thereof is formed by vacuum deposition. The polyester film for a photosensitive drum of the present invention has a smoothness according to JIS P 8119: 1998 on almost the entire surface of the film in order to prevent black spots and white spots in the image due to interference fringes on the image and coarse protrusions on the surface. In the measurement, the air leakage index needs to be 1000 to 2000 seconds. When the air leakage index is less than 1000 seconds, black spots and white spots in the image due to coarse protrusions on the film surface are generated. When the air leakage index exceeds 2000 seconds, interference fringes cannot be prevented.

  In order to satisfy that the air leakage index is 1000 to 2000 seconds as described above, the surface of the uniformly roughened film is usually subjected to vacuum deposition of aluminum (aluminum film thickness = 50 to 100 nm), A photosensitive layer is formed.

  If desired, an undercoat layer is formed on the surface of the deposited layer of the film. The undercoat layer is formed using a known resin, but the film thickness is usually set in the range of 4 to 10 μm, particularly in the range of 4 to 6 μm. In the case of a laminated photoreceptor, a charge generator and a charge transport layer containing a binder resin are provided on the undercoat layer in this order or in the reverse order. The film thickness of the charge generation layer is usually preferably set in the range of 0.3 to 1 μm, particularly in the range of 0.3 to 0.7 μm. Moreover, what is necessary is just to form the film thickness of a charge transport layer with a film thickness of 20-40 micrometers. A coating solution in which a charge transport agent, a charge generator, a binder resin, and an organic solvent are mixed is applied to the surface of the photoreceptor belt base material thus surface-treated by a dipping method to form a photosensitive layer having a thickness of 30 μm. It can be formed to produce an electrophotographic photosensitive belt.

  The polyester constituting the electrophotographic polyester film of the present invention typically includes, for example, polyethylene terephthalate in which 80 mol% or more of the structural unit is ethylene terephthalate, and 80 mol% or more of the structural unit is ethylene-2,6. -Polyethylene-2,6-naphthalate which is naphthalate, poly-1,4-cyclohexanedimethylene terephthalate in which 80 mol% or more of the structural unit is 1,4-cyclohexanedimethylene terephthalate, and the like. Other examples include polyethylene isophthalate and polybutylene terephthalate.

  Examples of copolymer components other than the above-described dominant components include diol components such as diethylene glycol, propylene glycol, neopentyl glycol, polyethylene glycol, and polytetramethylene glycol, isophthalic acid, 2,7-naphthalenedicarboxylic acid, and 5-sodium dicarboxylic acid. Ester-forming derivatives such as diasulfoisophthalic acid, adipic acid, azelaic acid, sebacic acid and oxymonocarboxylic acid can be used. Further, as the polyester, in addition to a homopolymer or a copolymer, a small proportion of a blend with another resin can also be used.

  The polyester film for a photoreceptor belt of the present invention can contain general-purpose fine particles in the film in order to improve running performance. Examples of the fine particles to be contained include silica (silicon oxide), lithium fluoride, kaolin, clay, calcium carbonate, silicon oxide, calcium terephthalate, ammonium oxide, calcium phosphate, titanium oxide, etc. Inactive particles consisting of salts or oxides containing elements selected from Group II, Group III, Group IV, etc., inert particles such as cross-linked polymers, or metal compound catalysts used during polyester synthesis, such as alkali metals Examples thereof include particles formed inside the polymer during the production of the polyester by a compound, an alkaline earth metal compound, or the like.

  In the present invention, it is necessary to contain two or more kinds of amorphous silica particles having different average particle diameters as the inert additive particles, in particular, in order to impart image forming performance as a photoreceptor belt. The average particle diameter of the amorphous silica particles added here is usually in the range of 1 to 10 μm, and preferably in the range of 2 to 7 μm.

  In the present invention, the amorphous silica particles are used because they have the same refractive index as that of polyethylene terephthalate and are less likely to cause voids during film stretching. When amorphous silica particles are used, the most preferable form is a so-called bimortal system of large particles and medium particles, specifically, large particles having an average particle size of 4 to 7 μm and medium particles having an average particle size of 1 to 3 μm. It is preferably bimodal and both are amorphous silica. In this case, the content of large particles in the film is usually in the range of 2000 to 4000 ppm, and the content of medium particles is usually in the range of 2000 to 8000 ppm. If the average particle size of the added large particles is less than 4 μm, the contribution to the formation of irregularities in the film tends to be small. Conversely, if the average particle size exceeds 7 μm, coarse protrusions are formed on the film surface, and It can be a cause. On the other hand, if the content of large particles is less than 2000 ppm, the resulting film has less tendency to form irregularities. On the other hand, if it exceeds 4000 ppm, coarse protrusions occur on the film surface, causing black spots and white spots in the image. May be. In addition, only the addition of medium particles having a small particle size tends to result in insufficient surface unevenness formation of the resulting film.

  The glossiness of the polyester film of the present invention is usually 50 to 80%, preferably 60 to 70%, and the haze is usually 45 to 70%, preferably 55 to 65%. When the glossiness exceeds 80% or the haze is less than 45%, the occurrence of interference fringes may not be suppressed. Further, when the glossiness is less than 50% or the haze exceeds 70%, there is a tendency for black spots and white spots in the image due to the unevenness on the surface of the photoreceptor belt.

  Next, although an example at the time of using biaxial stretching is demonstrated in detail, unless the summary of this invention is exceeded, this invention is not limited to the following examples.

  First, the raw material which comprises a polyester film is supplied to an extruder, and is extruded after melt-kneading. In the case of a laminated film, raw polymer melt polymers supplied from different extruders are laminated in a slit shape in a T-die and then extruded. Next, the molten sheet extruded from the die is rapidly cooled and solidified on the rotary cooling drum so that the temperature is equal to or lower than the glass transition temperature, thereby obtaining a substantially amorphous unoriented sheet. In this case, in order to improve the planar uniformity and cooling effect of the sheet, it is preferable to improve the adhesion between the sheet and the rotary cooling drum, and in the present invention, an electrostatic application adhesion method is preferably employed. Next, the obtained sheet is stretched in a biaxial direction to form a film. First, the unstretched sheet is stretched under the conditions of a stretching temperature of usually 70 to 150 ° C., preferably 75 to 130 ° C., usually 2.0 to 6.0 times, preferably 2.5 to 5.0 times. Stretch in one direction (longitudinal direction). A roll and tenter type stretching machine can be used for such stretching. Next, at a stretching temperature of usually 75 to 150 ° C., preferably 80 to 140 ° C., orthogonal to the first stage under the conditions of a stretching ratio of usually 2.0 to 6.0 times, preferably 2.5 to 5.0 times. The film is stretched in the direction (transverse direction) to obtain a biaxially oriented film. For such stretching, a tenter type stretching machine can be used.

  A method of performing the above-mentioned unidirectional stretching in two or more stages can also be adopted, but in this case as well, it is preferable that the final stretching ratio falls within the above-described range. Next, heat treatment in the tenter is usually performed at 180 to 245 ° C., preferably 200 to 240 ° C., for 1 second to 5 minutes. In this heat treatment step, relaxation of 0.1 to 20% in the transverse direction and / or the longitudinal direction is performed in the zone of the highest temperature of the heat treatment and / or the cooling zone immediately before the heat treatment outlet, in order to impart thermal dimensional stability. Is preferable.

  Hereinafter, the configuration and effects of the present invention will be specifically described with reference to examples. However, the present invention is not limited to the following examples unless it exceeds the gist. Various physical properties and characteristics are measured or defined as follows.

(1) Measurement of Intrinsic Viscosity of Polyester 1 g of polyester was accurately weighed and dissolved by adding 100 ml of a mixed solvent of phenol / tetrachloroethane = 50/50 (weight ratio), and measured at 30 ° C.

(2) Average particle diameter of filler (fine particles) used for polyester film (d50: μm)
The value of 50% integration (volume basis) in the equivalent spherical distribution measured using a centrifugal sedimentation type particle size distribution measuring apparatus (SA-CP3 type manufactured by Shimadzu Corporation) was defined as the average particle diameter.

(3) Air leakage index (G)
It measured according to JIS8119: 1998 using the Toyo Seiki make and a Digibeck smoothness tester. First, the film was set so as to be at the center of the sample stage, a rubber press plate and a pressure plate were placed on the film, and a pressure of 100 kPa was applied by a pressure device. After selecting a large vacuum container with a volume of 380 ml and reducing the pressure in the container to less than 50.7 kPa, the time for 10 ml of air to flow, that is, the time until the pressure in the container changes from 50.7 kPa to 48.0 kPa Was measured in seconds.

(4) Film glossiness (G60 °)
Using a VG-2000 gloss meter made by Nippon Denshoku Industries Co., Ltd., the 60 ° specular gloss (60 °) was measured according to JISZ8741. That is, the reflectance of the sample was determined based on the reflectance of the black standard plate at an incident angle and a reflection angle of 60 degrees, and was used as the glossiness.

(5) Film haze The turbidity of the film was measured by Nippon Denshoku Industries Co., Ltd. according to JISK6714 using a NDH-2000 type turbidimeter manufactured by Nippon Denshoku Industries Co., Ltd.

(6) Evaluation of image forming performance Coating liquid in which an aluminum vapor deposition layer having a thickness of 70 nm is provided on a film in a vacuum vapor deposition process, and a charge transport agent, a charge generator, a binder resin, and an organic solvent are mixed on the vapor deposition layer surface. Was applied by a dipping method to form a photosensitive layer having a thickness of 30 μm. The produced electrophotographic photosensitive belt was attached to a copying machine AF1000 manufactured by Kyocera Mita Co., Ltd., and an image was printed on a transfer paper with a gray original, and interference fringes and white spots / black spots on the image were evaluated.
A: The most excellent image was formed. ○: An excellent image was formed. Δ: The image was somewhat difficult but usable. ×: There were many image defects and the image could not be used.

Example 1:
280 of polyethylene terephthalate containing 3000 ppm of amorphous silica particles (A) having an average particle diameter of 4.1 μm and 4000 ppm of amorphous silica particles (B) having an average particle diameter of 3.2 μm using a twin screw extruder with a vent An amorphous film was obtained by melt extrusion at a temperature of from C to 300C and casting on a cooling drum while using an electrostatic adhesion method. This film was stretched 3.3 times in the longitudinal direction at 82 ° C., further stretched 3.9 times in the transverse direction at 120 ° C., and heat treated at 230 ° C. to obtain a 75 μm thick polyester film.

Example 2:
A biaxially stretched film having a thickness of 75 μm was obtained in the same manner as in Example 1 except that polyethylene terephthalate containing 3000 ppm of silica particles (A) and 5000 ppm of silica particles (B) was used.

Example 3:
A biaxially stretched film having a thickness of 75 μm was obtained in the same manner as in Example 1 except that polyethylene terephthalate containing 3000 ppm of silica particles (A) and 3000 ppm of silica particles (B) was used.

Example 4:
A biaxially stretched film having a thickness of 75 μm was obtained in the same manner as in Example 1, except that polyethylene terephthalate containing 3000 ppm of silica particles (A) and 1000 ppm of silica particles (B) was used.

Comparative Example 1:
A biaxially stretched film having a thickness of 75 μm was obtained in the same manner as in Example 1 except that polyethylene terephthalate containing 3000 ppm of silica particles (A) and not containing silica particles (B) was used.

Comparative Example 2:
A biaxially stretched film having a thickness of 75 μm was obtained in the same manner as in Example 1 except that polyethylene terephthalate containing 4000 ppm of silica particles (B) and not containing silica particles (A) was used.

Comparative Example 3:
A biaxially stretched film having a thickness of 75 μm was obtained in the same manner as in Example 1 except that polyethylene terephthalate containing 10,000 ppm of silica particles (A) and not containing silica particles (B) was used.
The characteristics evaluation of the obtained film are summarized in Table 1 below.

  The polyester film of the present invention can be suitably used as, for example, a base material for a photoreceptor belt for superelectrophotography.

Claims (1)

Polyester film containing two or more kinds of amorphous silica particles including at least amorphous silica particles having a large average particle diameter of 4 to 7 μm and amorphous silica particles having an average particle diameter of 1 to 3 μm. A polyester film for a photoreceptor belt, wherein the air leakage index is in the range of 1000 to 2000 seconds.