|
(11) | EP 0 980 032 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
| published in accordance with Art. 158(3) EPC |
|
|
|
|
|||||||||||||||||||||||||||
| (54) | SEAMLESS FILM BELT |
| (57) In a seamless film belt comprising a lamination of at least two layers, a modulus
of elasticity of the outermost layer is established to be larger than that of the
innermost layer. With this constitution, the seamless film belt which scarcely expands
and scarcely develops cracks can be provided. When this is used in an electrophotography
apparatus as an intermediate transfer belt, a high precision and uniform image can
be obtained stably for a long period of time. |
TECHNICAL FIELD
[0001] The present invention relates to a seamless film belt used for electrophotographic copying machines, printers, faxes and the like, particularly, to a scarcely expanding, scarcely cracking and highly durable seamless film belt.
BACKGROUND ART
[0002] Seamless film belts have long been used often for an intermediate transfer apparatus, transfer-separating apparatus or electrically charging apparatus of electrophotographic copying machines. These belts include an intermediate transfer belt, a transfer-carrying belt, a photosensitve belt and the like, and in view of cleaning of toner and the necessity of having a uniform electric resistance a seamless film belt which has no seam is most suitable for this purpose.
[0003] For example, a seamless film belt used as the intermediate transfer belt has to exhibit appropriate electric conductivity for electrostatic transfer of toner in addition to heat resistance. Moreover, in order to prevent toner adhesion on a surface of the belt, namely, a filming phenomenon, with use of the belt, compatibility between a material of the surface layer of the belt and the toner has to be considered. As a material satisfying such properties is typically used a material in which a thermally plasticizable resin such as polycarbonates and polyethylene terephthalate is used as an essential component and electric conductivity have been added thereto (Japanese Unexamined Patent Publication JP-A 63-311263 (1988)). The belt made of such materials, however, has a problem that although no expansion appears with use, cracking occurs from bending fatigue and therefore it can not withstand a prolonged use.
[0004] In order to solve this problem, a seamless tube which has a soft surface and sufficient strength, was synthesized by blending a thermoplastic polyalkylene terephthalate with a thermoplastic aromatic polycarbonate (Japanese Unexamined Patent Publication JP-A 4-313757 (1992)), but it was demonstrated that such seamless tube is improper for a seamless film belt because of the bending fatigue strength is not sufficiently enhanced. Moreover, Japanese Unexamined Patent Publication JP-A 5-200904 (1993) discloses a fluorinated resin as a belt material which is superior in durability to bending fatigue. The fluorinated resin, however, has a problem that, for example, a single-layer belt comprising a typical fluorinated resin, i.e., polytetrafluoroethylene resin has a so small tensile modulus of elasticity that the belt is expanded during operation to yield an uneven image.
[0005] Moreover, another seamless film belt has been proposed, which has a two-layer structure composed of an electrically conductive inner layer and a dielectric outer layer in order to provide an appropriate electric conductivity complementing the defects of a single-layer belt and prevent occurrence of filming phenomenon (JP-A 6-130830 (1994), JP-A 62-211678 (1987)). In the former belt, durability to bending is poor since both of the inner and outer layers of the belt are composed of a thermoplastic resin. In the latter belt, there is a drawback that interfacial exfoliation might readily occur since the lamination of the layers is made with an adhesive.
[0006] As for another example of the multi-layer belt, a three-layer structure consisting of a PVDF/MMA-BA co-polymer/PC-PBT blend has been proposed (Japanese Unexamined Patent Publication JP-A 5-105259 (1993)). In this three-layer structure, a polycarbonate is used in an innermost layer to suppress expansion and a fluorinated resin is used in an outermost layer to prevent adhesion of toner. The outermost layer, however, is fragile since the material is soft though it is superior in a mold-releasing property of toner at the early stage, and has a drawback that the toner- adhesion-proof feature can not be maintained over a long period of time.
[0007] As mentioned above, it is not possible to make an intended "scarcely expanding and scarcely cracking belt" in a seamless film belt of single-layer structure by means of merely blending a "hard" ingredient with a "soft" ingredient since they compensate each other for characteristics.
[0008] Moreover, in the belt of a lamination structure, a fluorinated soft material is layered on a polycarbonate hard material to greatly improve cracking caused by bending, but there is another problem such as wear and tight adhesion of toner caused thereby since the soft material is placed on the surface side.
[0009] The invention was made in view of these problems. The object of the invention is to provide a durable seamless film belt which scarcely expands and scarcely develops cracks, whereby tight adhesion of toner on a surface of the belt can be prevented over a long period of time.
DISCLOSURE OF THE INVENTION
[0010] According to the invention, a seamless film belt comprising a lamination of at least two layers is characterized in that an outermost layer has a larger modulus of elasticity than that of an innermost layer.
[0011] The aforementioned belt is characterized in that the outermost layer has a modulus of elasticity of 10,000 kgf/cm2 or more, and the innermost layer has a modulus of elasticity of 10,000 kgf/cm2 or less.
BRIEF DESCRIPTION OF DRAWINGS
[0012]
Fig. 1 shows a partially enlarged cross-sectional view of a seamless film belt of the invention.
Fig. 2 shows a plan view of an intermediate transfer apparatus using the seamless film belt of the invention.
BEST MODE FOR CARRYING OUT THE INVENTION
[0013] Fig. 1 shows a partially enlarged cross-sectional view of a seamless film belt of the invention. In Fig. 1, reference numerals 1, 2 and 3 show a seamless film belt, an outer layer and an inner layer, respectively. Fig. 2 shows a plan view of an intermediate transfer apparatus 10 using the seamless film belt 1 of the invention. Around a photosensitive drum 11, there are placed a charging device 12, an exposure optical system 13 equipped with a semiconductor laser as a light source, a developing device 14 for storing toner, cleaner 15 for removing residual toner, and an electrostatic transfer device 20. The photosensitive drum 11 rotates in the direction of an arrow in Fig. 2. An electrostatic image is formed on the photosensitive drum 11 by the exposure optical system 13, and developed by the developing device 14. The developed toner image is transferred onto the seamless film belt 1 of the invention used as an intermediate transfer belt by the electrostatic transfer device 20. The seamless film belt 1 is looped on three conveying rollers 17, 18 and 19 and rotates in the direction of the arrow. The toner image transferred on the seamless film belt 1 is then transferred on recording paper 21 between the conveying roller 19 and a pressure roller 22. The outer layer 2 of the seamless film belt 1 denotes a layer placed at a side of the belt where said layer contact with the photosensitive drum 11 and with the recording paper 21. The inner layer 3 denotes a layer placed at another side of the film where said layer contacts with the electrostatic transfer device 20 and with the conveying rollers 17, 18 and 19.
[0014] In an embodiment of the invention, as disclosed in JP-A 5-105259, an intermediate layer may be placed between the outer layer (surface layer) and the inner layer to form a seamless film belt of three layers.
[0015] As to the outer layer material for the seamless film belt of the invention, a thermoplastic resin is most suitable, especially including polypropylene, polyethylene, propylene ethylene block or random copolymer, styrene/butadiene, styrene/butadiene/styrene block copolymer or its hydrogen adduct, polybutadiene, polyisobutyrene, polyamide, polyacetal (POM), polyallylate, polycarbonate (PC), polyphenylene ether (PPE), polyethylene terephthalate (PET), polysulfone, polyether sulfone, polyphenylene sulfide (PPS), polybutyrene terephthalate (PBT), polyether ether ketone (PEEK), polyvinylidene fluoride (PVDF), ethylene tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polyvinyl fluoride, acryl, acrylic acid alkyl ester copolymer, polyether ester copolymer, polyether amide copolymer, polyurethane copolymer, and the like. Taking avoidance of the toner filming into consideration, a polycarbonate is preferably employed. In this invention, it is possible to use one of the aforementioned thermoplastic resins or a mixture of them as an outer layer material.
[0016] As to the inner layer material for the seamless film belt of the invention, a thermoplastic elastomer is most suitable, especially including polystyrene elastomer, polyolefine elastomer, polyvinyl chloride elastomer, polyurethane elastomer, polyamide elastomer, syndiotactic 1, 2BR, trans 1,4-IR, metal carboxylate ion cluster, crystalline polyethylene, fluorinated resin, and the like. Taking thermal resistance into consideration, polyurethane elastomer, polyestr elastomer and polyamide elastomer are preferably employed. Similarly in the case of the outer layer material, it is possible to use one of the aforementioned thermoplastic elastomers or a mixture of them as an inner layer material.
[0017] To each layer constituting the seamless film belt of the invention can be afforded an electric conductivity, if necessary, by blending an electric resistance regulator. As for the electric resistance regulator, a carbon black such as acetylene black, furnace black, channel black and the like are preferably used. The amount of the electric resistance regulator to be used may be determined according to the electric conductivity required for the respective layers.
[0018] Moreover, in the seamless film belt of the invention, a variety of additives may be blended in a range in which the effect would not be spoiled. Such additives include, for example, fillers, anti-oxidants, lubricants, antistatic agents, mold-releasing agents, and the like.
[0019] It has long been considered that it is desired to employ a material of lower modulus of elasticity for the outer layer and a material of higher modulus of elasticity for inner layer. For example, JP-A 5-105259 (1993) proposes the use of a polycarbonate as the inner layer and a polytetra-fluoroethylene resin as the outer layer (2nd column, lines 1 - 3). On the other hand, the seamless film belt of the invention comprises the outer layer 2 of higher modulus of elasticity and the inner layer 3 of lower modulus of elasticity.
[0020] Another feature of the invention is to make the outer layer 2 of a resin material having a modulus of elasticity of 10,000 kgf/cm2 or more and the inner layer 3 of a resin material having a modulus of elasticity of 10,000 kgf/cm2 or less. The reason is that a resin having a modulus of elasticity over 10,000 kgf/cm2 scarcely expands, while being too hard and fragile, and a resin having a modulus of elasticity under 10,000 kgf/cm2 scarcely develops cracks but easily expands. More preferably, the outer layer 2 has a modulus of elasticity in a range of 20,000 to 40,000 kgf/cm2 and the inner layer has a modulus of elasticity in a range of 400 to 5,000 kgf/cm2. According to the invention, the combination of such outer layer material and inner layer material affords the seamless film belt having both advantages, that is, scarcely expanding and scarcely cracking.
[0021] The ratio in thickness of the outer layer 2 to the inner layer 3 varies pursuant to the resin materials used. The ratio is preferably established so that the modulus of elasticity of the formed belt is 7,000 kgf/cm2 or more. When the modulus of elasticity modulus is less than 7,000 kgf/cm2, the belt used as an intermediate transfer belt is expanded to yield unclear and uneven images.
[0022] The thickness of the seamless film belt of the invention is in a range of 50 to 1,000 µm, preferably, 100 to 700 µm. When the thickness is less than 50µm, the seamless film belt becomes easily expanding to give such a problem as developing color unevenness, as mentioned above. Moreover, a sufficient voltage to give an electric charge required for the transfer cannot be applied due to insufficient charged voltage. On the other hand, when the, thickness is over 1,000µm, flexible deformation becomes difficult, and so the belt cannot move at a certain velocity on a roll small in diameter to generate a gap in the transferred image. In addition, since an electrostatic capacity becomes small, an electric charge required for the transfer cannot be afforded without application of high voltage, so the power supply apparatus not only increases in costs and in size, but also produces a problem of discharge between the parts of peripheral equipment.
[0023] The seamless film belt of the invention is preferably produced by concurrently and continuously extruding an outer layer material and an inner layer material from one die in a fused state by means of a coextrusion method for forming two layers. Injection molding and blow molding are discontinuous and intermittent molding methods, and so in the belt produced by these methods, the state of fused orientation of the longitudinal direction which crosses at right angles in the rotary direction becomes uneven to make the electric conductivity uneven. In this case, a film that is formed into a tube by the coextrusion method for forming two layers is cut sequentially in a prefixed length to produce seamless film belts.
[0024] The seamless film belt of the invention can be used mainly as an intermediate transfer belt in an electrophotography apparatus. Moreover, it can widely be used as other members (e.g., photosensitive belt, fixing belt, transfer-carrying belt) in said apparatus as well as a material for recording belt in a variety of printers such as office automation devices.
[0025] The invention will be explained by examples and comparative examples which are not intended as a limitation thereof.
Example 1
[0026] A polycarbonate (Panlite K-1300, product of Teijin Chemicals Ltd.) of 21,300 kgf/cm2 in modulus of elasticity as an outer thermoplastic resin and a poly-ester elastomer (Hytrel 4777, product of Toray End, and Du Pont) of 580 kgf/cm2 in modulus of elasticity as an inner thermoplastic elastomer were selected. These materials, respectively, were fused and extruded by a two-axle extruder equipped with a vent of 40 mm ⌀, then introduced into a two-layer co-extruding annular die of 170 mm ⌀, laminated in the die, extruded downward from the annular die in a form of tube, brought in contact with the outer surface of a cooling mandrel arranged coaxially to the annular die, and pulled out under cooling for hardening to yield a seamless tube. The seamless tube was adjusted by a core in the tube and an outside roll so as to have a ratio of 75/75 µm (outer layer/inner layer) (the sum of thickness: about 150µm). The resulting seamless tube, while maintaining a cylindrical form, was pulled out without creasing and cut into a prefixed length to yield a seamless film belt of the invention.
Example 2
[0027] A polyethylene terephthalate (DIAALLOY TW-90E, product of Mitsubishi Rayon Co.) of 28,000 kgf/cm2 in modulus of elasticity as an outer layer and a polyester elastomer (Pelprene S-2001, product of Toyobo Co.) of 1,150 kgf/cm2 in modulus of elasticity as an inner layer were selected. The ratio of the outer layer to the inner layer was made 50/100 µm. Otherwise, in the same manner as in Example 1, the seamless film belt of the invention was produced.
Example 3
[0028] A polycarbonate (Panlite K-1300, product of Teijin Chemicals Ltd.) of 21,300 kgf/cm2 in modulus of elasticity as an outer layer and a polyurethane elastomer (Resamine 2-8765, product of Dainichiseika Co.) of 800 kgf/cm2 in modulus of elasticity as an inner layer were selected. The ratio of the outer layer to the inner layer was made 70/80 µm. Otherwise, in the same manner as in Example 1, the seamless film belt of the invention was produced.
Example 4
[0029] A polycarbonate (Panlite K-1300, product of Teijin Chemicals Ltd.) of 21,300 kgf/cm2 in modulus of elasticity as an outer layer and a polyamide elastomer (Nylon 12 elastomer, product of Daicel-Huels Ltd.) of 2,100 kgf/cm2 in modulus of elasticity as an inner layer were selected. The ratio of the outer layer to the inner layer was made 60/90 µm. Otherwise, in the same manner as in Example 1, the seamless film belt of the invention was produced.
Comparative Example 1
[0030] The polycarbonate (Panlite K-1300, product of Teijin Chemicals Ltd.) of 21,300 kgf/cm2 in modulus of elasticity which was used as the outer layer in Example 1 was extruded from an extruder of 170 mm ⌀ and formed to a single-layer seamless film belt of 150 µm in thickness.
Comparative Example 2
[0031] The polyethylene terephthalate (DIAALLOY TW-90E, product of Mitsubishi Rayon Co.) of 28,000 kgf/cm2 in modulus of elasticity which was used as the outer layer in Example 2 was used. Otherwise, in the same manner as in Comparative Example 1, a single-layer seamless film belt was produced.
Comparative Example 3
[0032] The polyester elastomer (Hytrel 4777, product of Toray Ind. and Du Pont) of 580 kgf/cm2 in modulus of elasticity which was used as the inner layer in Example 1 was used. Otherwise, in the same manner as in Comparative Example 1, a single-layer seamless film belt was produced.
Test for Evaluation
[0033] In order to examine durability of the respective seamless film belts produced in Examples and Comparative Examples, they were disposed on a practical machine (40,000 copies were made with Ricoh Preter 550, Ricoh Co.) as an intermediate transfer belt for a predetermined long period of time. Thereafter, cracking, expansion and exfoliation of the interface (exfoliation between the outer layer and the inner layer) were observed. Table 1 shows the results.
Table 1
| Durability | |||
| Cracking | Expansion | Exfoliation | |
| Example 1 | ○ | ○ | ○ |
| Example 2 | ○ | ○ | ○ |
| Example 3 | ○ | ○ | ○ |
| Example 4 | ○ | ○ | ○ |
| Comp.Exam.1 | X | ○ | - |
| Comp.Exam.2 | X | ○ | - |
| Comp.Exam.3 | ○ | X | - |
[0034] The evaluation shown in Table 1 was entirely carried out visually on the belt after completion of the examination and the results were recorded. Symbol X indicates occurrence of abnormal cracks and interfacial exfoliation, and symbol ○ indicates no abnormality. As to expansion of the belt, occurrence of gaps in the printed image is indicated by symbol X, and no gap by symbol ○. In the seamless film belts of Comparative Examples 1 - 3, no interfacial exfoliation was observed since all of them were of single-layer type (indicated by symbol -).
[0035] The test results as shown in Table 1 demonstrate that the seamless film belt of the invention scarcely develops cracks and scarcely expands, but those produced in Comparative Examples had merely either of such characteristics.
INDUSTRIAL APPLICABILITY
[0036] According to the invention, as mentioned above, a seamless film belt which scarcely develops cracks due to expansion and bending fatigue can be provided by making a lamination of at least two layers in which the modulus of elasticity of the outer layer is larger than that of the inner layer. When the seamless film belt of the invention is used in an electrophotography apparatus for copying and printing as an intermediate transfer belt, a high precision and uniform image can be obtained stably for a long period of time without producing gaps in images due to expansion of the belt and development of cracks at the belt end.
1. A seamless film belt comprising a lamination of at least two layers wherein an outermost
one of the at least two layers has a modulus of elasticity larger than that of an
innermost one thereof.
2. The seamless film belt of claim 1, wherein the outermost layer has a modulus of elasticity
of 10,000 kgf/cm2 or more and the innermost layer has a modulus of elasticity of 10,000 kgf/cm2 or less.
3. The seamless film belt of claim 2, wherein the modulus of elasticity of the outermost
layer has a modulus of elasticity in a range of 20,000 to 40,000 kgf/cm2 and the innermost layer has a modulus of elasticity in a range of 400 to 5,000 kgf/cm2.