Conductive Belt, Image Forming Apparatus Having the Same, and Method for Manufacturing Conductive Belt

Abstract

To provide a belt for an image forming apparatus that has a base material layer indicative of semiconductivity in a middle-resistance region (105-108 Ω / sq.), small variation in surface resistivity and a surface layer indicative of electric insulation, in which if such a belt is used as a paper-carrying belt, then a suction force of a recording medium (paper) is strong and the recording medium can be positively carried because the surface layer is excellent in electric insulation.SOLUTION: An electrically conductive belt comprises a base material layer consisting of a composition containing a thermoplastic resin and a conductive agent, and a surface layer consisting of a composition containing acid-modified ethylene-tetrafluoroethylene copolymer.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a conductive belt used in an image forming apparatus using an inkjet method or an electrophotographic method.

Background Art

[0002] Conventionally, image forming apparatuses such as printers, copiers, and facsimiles using the electrophotographic method or the inkjet method have adopted a method of conveying paper with rollers. However, when the image formation speed increases, troubles in paper conveyance are likely to occur with rollers. Therefore, a method of conveying paper with a belt is adopted. Specifically, (1) a method of sucking and conveying paper to the belt by vacuum suction using a belt having a suction port, or (2) a method of adsorbing and conveying paper to the belt by utilizing an electrostatic adsorption force generated by applying a voltage to a belt composed of a conductive base material layer and an insulating surface layer is known.

[0003] Among these, (1) the method of sucking paper to the belt by vacuum requires a vacuum chamber and a vacuum device for reducing the pressure in the vacuum chamber as described in Patent Document 1 and Patent Document 2, and furthermore, the structure of the image forming apparatus becomes complicated because the space between the driving belt and the vacuum chamber must always be kept airtight. On the other hand, (2) the method using an electrostatic adsorption force is simple because the adsorption force can be controlled only by adjusting the applied voltage if there is a member for applying a voltage to the belt and a power source.

[0004] As a belt (paper conveyance belt) for sucking and conveying a recording medium such as paper by utilizing an electrostatic adsorption force, Patent Document 3 discloses that both the inner layer and the outer layer are made of a polyimide resin, and the volume resistivity of the inner layer is 10 8 ~10 14 Ω·cm, and the volume resistivity of the outer layer is 10 14 ~10 16A paper transport belt with a resistivity of Ω·cm is described. However, the paper transport belt described in Patent Document 3 must be centrifugally formed (spraying a solution of polyamic acid for the inner layer or outer layer on the surface or back surface of the mold, volatilizing the solvent at high temperature, and then imidizing under high temperature and oxygen-free conditions. In the case of two layers, this is repeated twice), and the manufacturing process becomes very complicated.

[0005] In addition, Patent Document 4 describes an inkjet paper transport belt in which the inner layer is made of a conductive polyimide resin with a surface resistivity of 1×10 4 ~1×10 9 Ω / □, and the outer layer is made of an ethylene-tetrafluoroethylene copolymer (ETFE). This paper transport belt also requires a process of forming the inner layer by centrifugal forming and covering it with pre-formed ETFE and melting and bonding it, so the manufacturing process is very complicated.

[0006] On the other hand, some inks used in inkjet printers that can print at high speed use organic solvents. When the ink adheres to the belt, depending on the type of resin used in the belt, that part may swell and unevenness may occur on the belt surface. In view of solvent resistance, it is desirable to use a fluororesin on the surface layer, but fluororesins have poor adhesion. In addition, some have a surface resistivity of less than 10 14 Ω / □, and there is also a problem that the suction force becomes weak. Patent Document 5 describes a laminate having a first layer containing a fluorine-containing copolymer and a second layer containing a polyamide resin directly laminated on the first layer. However, only laminated sheets and laminated hoses are exemplified as specific uses of the laminate.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

[0008] A multilayer belt using a polyimide resin is expensive because it is manufactured through complicated processes such as repeating centrifugal molding twice or covering a belt-shaped polyimide resin layer prefabricated by the centrifugal molding method with a fluororesin preformed in a belt shape and then melt-bonding them. The present invention has been made in view of such problems, and an object of the present invention is to provide a conductive belt in which a base material layer exhibits semiconductive properties in a medium resistance region (10 5 ~10 8 Ω / □), has little variation in surface resistivity, and a surface layer exhibits insulating properties. [Means for Solving the Problems]

[0009] According to the present invention, (1) A conductive belt comprising a base material layer made of a composition containing a thermoplastic resin and a conductive agent, and a surface layer made of a composition containing an acid-modified ethylene-tetrafluoroethylene copolymer; (2) The conductive belt according to (1), wherein the thermoplastic resin is a polyamide-based resin; (3) The conductive belt according to either (1) or (2), wherein the conductive agent is an electron conductive material; (4) The conductive belt according to (3), wherein the electron conductive material is carbon black; (5) The surface resistivity of the base material layer at a temperature of 23°C and a relative humidity of 50% RH is 1×10 5 or more and 1×10 8 Ω / □ or less, and the conductive belt according to any one of (1) to (4); (6) The surface resistivity of the surface layer at a temperature of 23°C and a relative humidity of 50%RH is 1×10 13 Ω / □ or more, and the conductive belt according to any one of (1) to (5); (7) The conductive belt according to any one of (1) to (6), characterized in that it is a conductive belt for an image forming apparatus; (8) The conductive belt according to (7), characterized in that the conductive belt for an image forming apparatus is for paper conveyance by an inkjet method; (9) An image forming apparatus, characterized by having the conductive belt according to any one of (1) to (8); (10) In the method for manufacturing a conductive belt according to any one of (1) to (8), a composition for forming a base material layer containing a thermoplastic resin and a conductive agent, and a composition for forming a surface layer containing an acid-modified ethylene-tetrafluoroethylene copolymer are respectively supplied to separate extruders, and co-extruded from an annular die so that the base material layer is the inner layer and the surface layer is the outer layer. A method for manufacturing a conductive belt; is provided.

Effect of the Invention

[0010] The conductive belt of the present invention is a laminate of a base material layer made of a composition containing a thermoplastic resin and a conductive agent and a surface layer made of a composition containing an acid-modified ethylene-tetrafluoroethylene copolymer. The surface resistivity on the surface layer side is 1×10 14 Ω / □ or more (insulating region), and the surface resistivity on the base material layer side (the side where the surface layer is not formed) is 1×10 5 ~1×10 8 Ω / □ range (medium resistance region). When such a belt is used as a paper conveyance belt, since the surface layer is excellent in insulation, the adsorption force of the recording medium (paper) is strong, and the recording medium can be surely conveyed. In addition, the conductive belt of the present invention can be manufactured at a lower cost than a belt having a multilayer structure using a conventional polyimide resin. Since the surface of the belt of the present invention does not swell even when a solvent-type ink adheres thereto, it can be suitably used particularly as a paper conveyance belt for an inkjet system.

Mode for Carrying Out the Invention

[0011] [Base material layer] It is essential that the base material layer of the present invention contains a thermoplastic resin and a conductive agent. Considering the moldability, examples of the thermoplastic resin include fluororesins, polyamide resins, polyester resins, polycarbonate resins, polyamideimide resins, polyimide resins, polyolefin resins, etc., which can be used alone, blended with two or more kinds, or laminated. Among these, fluororesins are different from other resins in that they themselves have flame retardancy, are easy to extrude, and also have antifouling properties and mold release properties, so they are suitable for belts for image forming apparatuses. Examples of such fluororesins include polyvinylidene fluoride, vinylidene fluoride - hexafluoropropylene copolymer, ethylene - tetrafluoroethylene copolymer, polyhexafluoropropylene, ethylene - vinylidene fluoride copolymer, vinylidene fluoride - tetrafluoroethylene copolymer, vinylidene fluoride - hexafluoropropylene - tetrafluoroethylene copolymer, etc., which can be adopted.

[0012] Polyamide resins are thermoplastic resins obtained by polycondensation of diamines and dicarboxylic acids, polycondensation of α,ω-aminocarboxylic acids, ring-opening polymerization of lactams, etc., and have a sufficient molecular weight. Examples of polyamide resins include nylon 6, nylon 4, nylon 6,6, nylon 11, nylon 12, nylon 6,10, nylon 6,12, nylon 6 / 6,6, nylon 6 / 6,6 / 12, nylon 6,MXD (MXD represents an m-xylylenediamine component), nylon 6,6T (T represents a terephthalic acid component), nylon 6,6I (I represents an isophthalic acid component), and the like. Among these, polyamide resins with low water absorption are preferred. Polyamide resins with low water absorption are excellent in the dispersibility of carbon black and also excellent in the stability of electrical resistance in a high-humidity environment. The water absorption of the polyamide resin is preferably 1.5% or less, and more preferably 1.0% or less. Examples of polyamide resins with a water absorption of 1.5% or less include nylon 11, nylon 12, nylon 6,10, nylon 6,12, etc., and examples of polyamide resins with a water absorption of 1.0% or less include nylon 11 and nylon 12. These polyamides may be used alone or in combination of two or more.

[0013] In recent years, with the increase in speed of printers and the like, a high elastic modulus has been required for the belt for an image forming apparatus. If the elastic modulus is low, the belt may stretch during driving and the transfer position may shift. The tensile elastic modulus of the base material layer is preferably 500 MPa or more, and more preferably 800 MPa or more. In order to increase the tensile elastic modulus of the belt, reinforcing materials such as plate-like fillers and whiskers can also be added to the above-mentioned thermoplastic resin. Also, the thickness of the base material layer is preferably 50 to 300 μm, and more preferably 75 to 200 μm so as to satisfy the above performance. If the thickness is less than 50 μm, it is difficult to obtain sufficient tensile strength, and if the thickness exceeds 300 μm, the flexibility deteriorates.

[0014] The conductive belt of the present invention adjusts the surface resistivity of the base material layer by containing a conductive agent in the base material layer. The surface resistivity of the base material layer is 10 5 ~10 12It is preferably Ω / □, particularly 10 in the medium resistance region 5 ~10 8 Ω / □ is preferred. Conductive agents include electron-conductive materials and ion-conductive materials. Further, when the base material layer needs to be in a lower resistance region (for example, 10 5 ~10 6 Ω / □) even in the medium resistance region, it is preferable to use an electron-conductive material that can obtain a low resistance region with a small addition amount.

[0015] Examples of electron-conductive materials include carbon-based materials such as carbon black, graphite, and carbon nanotubes, conductive polymers such as polyaniline, polythiophene, and polyacetylene, and conductive inorganic particles such as inorganic particles surface-treated with aluminum-zinc oxide, antimony-tin oxide, indium-tin oxide, and carbon black. Examples of carbon black include conductive carbon blacks such as furnace black, channel black, ketjen black, and acetylene black. In particular, carbon black with an average particle size of 50 nm or less is preferable because it can reduce the electrical resistance with a small amount of blending. Also, from the viewpoint of developing the structure of carbon black and forming a conductive path, the DBP (Dibutyl phthalate) oil absorption amount is preferably 100 to 500 ml / 100 g, preferably 100 to 300 ml / 100 g, and more preferably 150 to 250 ml / 100 g. Also, from the viewpoint of conductivity, carbon black with a BET surface area in the range of 30 to 1500 m 2 / g is preferred. In the present invention, grafted carbon black grafted with a polymer having one or more functional groups selected from carboxyl group, hydroxyl group, epoxy group, amino group, oxazoline group, or carbon black surface-treated with a low molecular weight compound can also be used.

[0016] When an electron conductive material is used as the conductive agent, the compounding amount of the conductive agent is preferably 1 to 50 parts by weight with respect to 100 parts by weight of the thermoplastic resin. The compounding amount is preferably 5 to 35 parts by weight, more preferably 15 to 30 parts by weight. If the compounding amount of the electron conductive material is less than 1 part by weight, a composition showing a predetermined conductivity cannot be obtained, which is not preferable. If it exceeds 50 parts by weight, the melt viscosity of the composition becomes high and extrusion molding becomes difficult.

[0017] Examples of the ion conductive material include polyetheresteramide, polyetherester, polyetheramide, polyethylene oxide, polyethylene oxide copolymer, partially crosslinked polyethylene oxide copolymer, ion electrolyte, etc. These can be used alone or in combination of two or more. In addition, as the ion electrolyte, thiocyanates, phosphates, sulfates, halogen-containing oxygen acid salts, and tetraalkylammonium salts of alkali metals can be used alone or in combination of a plurality of types. Among these, lithium perchlorate, sodium perchlorate, potassium perchlorate, lithium thiocyanate, sodium thiocyanate, and potassium thiocyanate are preferable.

[0018] When an ion conductive material is used as the conductive agent, the compounding amount of the conductive agent is preferably 1 to 50 parts by weight with respect to 100 parts by weight of the thermoplastic resin. The compounding amount is preferably 1 to 30 parts by weight, preferably 2 to 25 parts by weight, and more preferably 15 to 25 parts by weight. If the compounding amount of the ion conductive material is less than 1 part by weight, a composition showing a predetermined conductivity cannot be obtained, which is not preferable. If it exceeds 50 parts by weight, the hygroscopicity becomes high and the tensile elastic modulus becomes low, which is not preferable.

[0019] Additives may be compounded in the resin composition used for the base material layer of the present invention as long as the properties are not impaired as necessary. Examples of the additives include antioxidants, heat stabilizers, organic fillers and inorganic fillers, antiblocking agents, plasticizers, lubricants, processing aids, etc. These resins and additives can be used in appropriate amounts according to the purpose.

[0020] [Surface layer] It is essential that the surface layer of the present invention contains an acid-modified ethylene-tetrafluoroethylene copolymer. The acid-modified ethylene-tetrafluoroethylene copolymer is a copolymer containing at least a polymerization unit based on ethylene, a polymerization unit based on tetrafluoroethylene, and a polymerization unit having an acid structure. Examples of the polymerization unit having an acid structure include unsaturated carboxylic acid anhydrides such as maleic anhydride, itaconic anhydride, and citraconic anhydride, and unsaturated carboxylic acids such as undecylenic acid, acrylic acid, methacrylic acid, and maleic acid. The content of the polymerization unit having an acid structure is preferably 0.01 to 10 mol%, more preferably 0.1 to 5 mol%, based on all the polymerization units in the acid-modified ethylene-tetrafluoroethylene copolymer.

[0021] By containing an acid-modified ethylene-tetrafluoroethylene copolymer in the surface layer, the interlayer adhesion strength with the resin composition forming the base layer is increased, enabling coextrusion molding. In addition, the surface layer used in the present invention is excellent in insulation properties, and the surface resistivity is preferably 1×10 13 Ω / □ or more, more preferably 1×10 14 Ω / □ or more. Among fluororesins, in particular, ethylene-tetrafluoroethylene copolymers and acid-modified ethylene-tetrafluoroethylene copolymers have been found to have a surface resistivity of 1×10 14 Ω / □ or more and high insulation properties. Furthermore, since the surface layer used in the present invention uses a fluororesin, it has been found that even if solvent ink adheres, its surface does not swell. Also, the composition for forming the surface layer of the present invention may be blended with other resins and additives as necessary within a range that does not impair its properties.

[0022] [Method for manufacturing a belt for an image forming apparatus] The manufacturing method of the composition for forming the base material layer of the present invention is not particularly limited. For example, a method of blending a thermoplastic resin, a conductive agent, and additives used as necessary, followed by dry blending and then melt kneading; a method of previously melt kneading a conductive agent with a thermoplastic resin to prepare a masterbatch, and then melt kneading a thermoplastic resin and additives used as necessary into this masterbatch, etc. can be mentioned.

[0023] Examples of the apparatus for melt kneading include various known kneaders such as batch kneaders, kneaders, conical kneaders, Banbury mixers, roll mills, single-screw or twin-screw extruders, etc. Among these, single-screw extruders and twin-screw extruders are preferably used because of their excellent kneading ability and productivity.

[0024] The temperature during melt kneading can be appropriately selected according to the type of thermoplastic resin used, the melt viscosity, etc. Usually, it is in the range of 150 to 300 °C, and preferably 170 to 280 °C from the viewpoint of preventing resin deterioration.

[0025] The conductive belt of the present invention can be manufactured by an extrusion molding method, a centrifugal molding method, a dipping method, etc. The extrusion molding method, particularly the extrusion molding method using an annular die, is preferable because a seamless belt can be obtained. As the extrusion molding method using an annular die, for example, two extruders are used, an annular die is arranged below the extruders in communication with the extruders, and below the annular die, a mandrel for supporting the molten resin extruded downward from the annular die on its outer periphery and cooling and solidifying it is provided. The composition for forming the base material layer and the composition for forming the surface layer are supplied to the respective extruders, co-extruded in a tube shape from one annular die, and cooled and solidified along the outer periphery of the mandrel to obtain a tube-shaped molded body, and the tube-shaped molded body can be made into a belt by cutting it to a desired width. Note that these explanations are for the case of two layers, but when there are three or more layers, extruders and dies corresponding to the number of layers may be prepared.

[0026] The conductive belt of the present invention can be suitably used as parts for image forming devices such as intermediate transfer belts, transfer transport belts, and paper transport belts, as well as automobile-related parts, electronic and electrical parts, machine parts, semiconductor packaging films, etc. In particular, the conductive belt of the present invention can be suitably used as a paper transport belt for inkjet systems that use solvent inks, since the belt surface does not swell even if a solvent ink adheres to the belt surface. EXAMPLES

[0027] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples. The physical properties in the examples were measured as follows. (1) Melt Viscosity The melt viscosity was measured using a Shimadzu Koka type flow tester equipped with a die measuring 10 mm in length and 1 mm in diameter. (2)Surface resistivity The surface resistivity was measured using a Hiresta UX (MCP-HT800, manufactured by Dia Instruments) equipped with a URS probe (load 2 kg) (applied voltage of 10 V for the substrate layer and 1000 V for the surface layer). The uniformity (variation) of the surface resistivity was calculated using the following formula. Uniformity of surface resistivity [digits] = log10 (maximum surface resistivity / minimum surface resistivity) (3) Solvent-resistant ink Solvent ink (high boiling point petroleum-based solvent) was dropped onto the surface layer of the belt obtained in each of the Examples and Comparative Examples and left at 60°C for 24 hours, after which the surface was observed and evaluated based on the following criteria. ◯: The film surface did not swell or deform. Δ: The film surface was slightly swollen and slightly deformed. ×: The film surface swelled and was obviously deformed.

[0028] The following raw materials were used: <Thermoplastic resin (A)> Polyamide 12 (A-1) [Melting point: 178°C, Melt viscosity: 1100 poise (measurement temperature: 200°C, load: 100 kg)] Polyamide 12 (A-2) [Melting point: 178°C, Melt viscosity: 5440 poise (measurement temperature: 200°C, load: 100 kg)] High density polyethylene (A-3) [Melting point: 132°C, Melt viscosity: 7500 poise (measurement temperature: 200°C, load: 100 kg)] Acid-modified ethylene-tetrafluoroethylene copolymer (A-4) [Melting point: 190°C, melt viscosity: 6750 poise (measurement temperature: 220°C, load: 100 kg)] Polyvinylidene fluoride (A-5) [Melting point: 168°C, melt viscosity: 4500 poise (measurement temperature: 200°C, load: 100 kg)] <Conductive agent (B)> Carbon black (B-1) [DBP oil absorption: 190ml / 100g, BET surface area: 70m2 / g] Carbon nanotubes (B-2) [average diameter: 10-15 nm, length: 10 μm or less, specific surface area: 180-250 m2 / g]

[0029] [Base material layer] A compound was obtained by melt-kneading polyamide resin or high-density polyethylene and a conductive agent using a twin-screw kneading extruder with a screw diameter of 38Φmm so as to obtain the compounding ratio shown in Table 1. The compound obtained was then fed to a single-screw extruder (extrusion diameter: 50Φmm) equipped with an annular die, and extruded in a molten state into a tube to obtain a tubular film. The surface resistance of the obtained film was measured at 20 points every 50 mm in the extrusion direction, and the uniformity is shown in Table 1.

[0030] [Table 1]

[0031] As shown in Table 1, the substrate layers 1 to 3, which are made by blending polyamide resin and carbon black as a conductive agent, and the substrate layer 6, which is made by blending high-density polyethylene, polyamide resin, and carbon black as a conductive agent, have a surface resistivity of 105 ~10 7 Ω / sq, indicating excellent uniformity (within 0.5 digits) of surface resistivity and film formability. The base material layers 4 and 5, which were compounded with polyamide resin and carbon nanotubes as a conductive agent, had a slightly higher surface resistivity than those of the base material layers 1 to 3, showing a value of 10 6 ~10 8 Ω / sq, and the base material layer 5 with an increased compounding ratio of carbon nanotubes to reduce the surface resistivity had a large thickness unevenness in the extrusion direction and poor uniformity of surface resistivity.

[0032] [Examples and Comparative Examples] Using an apparatus with a two-layer annular die attached to the tips of two extruders with a cylinder diameter of 50 mm, the resin composition for forming the base material layer shown in Table 2 and the resin composition for forming the surface layer were co-extruded and formed into a tube shape, then cut to a length of 400 mm to obtain a seamless belt with a circumference of 800 mm and a width of 350 mm, with the base material layer as the inner layer and the surface layer as the outer layer. The seamless belts produced in the examples and comparative examples were evaluated for the following items, and the results are shown in Table 2.

[0033]

Table 2

[0034] As shown in Table 2, in Examples 1 to 3 of the belt in which the base material layer 1 and the surface layer were made of an acid-modified ethylene-tetrafluoroethylene copolymer (A-4), the surface resistivity on the base material layer side showed a value of 10 6 ~10 7 Ω / sq, and the uniformity of surface resistivity (less than one order of magnitude) was also excellent. The surface resistivity of the surface layer also showed a value of 10 14 Ω / sq or more, indicating excellent insulation. Also, the solvent ink resistance of the surface layer was good. On the other hand, although Comparative Example 1 and Comparative Example 2 with a polyamide resin or high-density polyethylene as the surface layer are excellent in the uniformity of the surface resistivity of the base material layer, swelling was observed when solvent ink was dropped on the surface layer and left in an environment of 60 °C for 24 hours. From this result, the belts of Comparative Example 1 and Comparative Example 2 were unsuitable as an inkjet paper conveyance belt, especially when using solvent ink. On the other hand, although Comparative Example 3 with polyvinylidene fluoride as the surface layer has good solvent ink resistance of the surface layer, the adhesiveness with the base material layer 1 is poor and delamination occurs, and the surface resistivity on the surface layer side also shows a range of 10 13 ~10 14 Ω / sq, indicating poor insulation.

Claims

1. It comprises a base material layer made of a composition containing a thermoplastic resin and a conductive agent, and a surface layer made of a composition containing an acid-modified ethylene-tetrafluoroethylene copolymer, The thermoplastic resin of the base material layer includes a polyamide-based resin, The polyamide-based resin is nylon 6, nylon 4, nylon 6,6, nylon 11, nylon 12, nylon 6,10, nylon 6,12, nylon 6 / 6,6, nylon 6 / 6,6 / 12, nylon 6,MXD (MXD represents an m-xylylenediamine component), nylon 6,6T (T represents a terephthalic acid component), nylon 6,6I (I represents an isophthalic acid component), either alone or in combination of two or more, and is characterized by a conductive belt.

2. The conductive belt according to claim 1, wherein the conductive agent is an electron conductive material.

3. The conductive belt according to claim 2, wherein the electron conductive material is carbon black.

4. The surface resistivity of the base material layer at a temperature of 23°C and a relative humidity of 50% RH is 1×10 ５ or more and 1×10 ８ Ω / □ or less, and is characterized by the conductive belt according to any one of claims 1 to 3.

5. The surface resistivity of the surface layer at a temperature of 23°C and a relative humidity of 50% RH is 1×10 １３ Ω / □ or more, and is characterized by the conductive belt according to any one of claims 1 to 4.

6. The conductive belt according to any one of claims 1 to 5, which is a conductive belt for an image forming apparatus.

7. The conductive belt according to claim 6, wherein the conductive belt for an image forming apparatus is for inkjet paper conveyance.

8. An image forming apparatus comprising the conductive belt according to any one of claims 1 to 7.

9. In a method for manufacturing a conductive belt according to any one of claims 1 to 7, a composition for forming a base material layer containing a thermoplastic resin containing the polyamide-based resin and a conductive agent, and a composition for forming a surface layer containing an acid-modified ethylene-tetrafluoroethylene copolymer are respectively supplied to separate extruders, and co-extruded from an annular die such that the base material layer is the inner layer and the surface layer is the outer layer. A method for manufacturing a conductive belt, characterized by the above.

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