JP7627634B2 - Conductive belt, image forming apparatus having the same, and method for manufacturing the conductive belt - Google Patents

Description

The present invention relates to a conductive belt for use in an image forming apparatus using an inkjet system or an electrophotographic system.

Conventionally, image forming devices such as electrophotographic and inkjet printers, copiers, and facsimiles have used rollers to transport paper, but as image formation speeds increase, problems with rollers during paper transport become more likely, so methods are being adopted in which the paper is securely supported and transported by a belt. Specifically, known methods include (1) a method in which a belt with suction holes is used to reduce pressure and suck the paper onto the belt, and (2) a method in which a belt made of a conductive base layer and an insulating surface layer is used, and the electrostatic attraction force generated by applying a voltage to the belt is used to attract the paper to the belt and transport it.

Of these, (1) the method of sucking the paper to the belt by reducing pressure requires a pressure reduction chamber and a pressure reduction device for reducing the pressure in the pressure reduction chamber, as described in Patent Documents 1 and 2, and the space between the driven belt and the pressure reduction chamber must be kept sealed at all times, making the structure of the image forming device complicated. On the other hand, (2) the method of using electrostatic attraction is simple, as the suction force can be controlled simply by adjusting the applied voltage if there is a member that applies voltage to the belt and a power source.

As a belt (paper transport belt) that utilizes electrostatic adsorption to attract and transport recording media such as paper, Patent Document 3 describes a paper transport belt in which both the inner layer and the outer layer are made of polyimide resin, and the volume resistivity of the inner layer is 1×10 ⁸ to 1×10 ¹⁴ Ω·cm, and the volume resistivity of the outer layer is 1×10 ¹⁴ to 1×10 ¹⁶ Ω·cm. However, the paper transport belt described in Patent Document 3 requires centrifugal molding (a process is required in which a solution of polyamic acid for the inner layer or outer layer is sprayed onto the front or back of a mold, the solvent is evaporated at high temperature, and then imidization is performed at high temperature in the absence of oxygen. In the case of a two-layer belt, this process is repeated twice), making the manufacturing process very complicated.

Patent Document 4 describes an inkjet paper transport belt having an inner layer made of conductive polyimide resin with a surface resistivity of 1×10 ⁴ to 1×10 ⁹ Ω/□ and an outer layer made of ethylene-tetrafluoroethylene copolymer (ETFE). This paper transport belt also requires a process of forming the inner layer by centrifugal molding, covering it with a preformed tubular ETFE, and melt-bonding it, making the manufacturing process very complicated.

On the other hand, some inks used in inkjet printers capable of printing at high speeds contain organic solvents, and when the ink adheres to the belt, depending on the type of resin used in the belt, the ink swells and causes unevenness on the belt surface. In view of such solvent resistance, it is desirable to use a fluororesin for the surface layer, but fluororesins have poor adhesion. Some fluororesins have a surface resistivity of less than 1× ¹⁰ Ω/□, which causes a problem of weak suction power.

JP 2019-131389 A JP 2019-127364 A JP 2008-94605 A JP 2011-73804 A

In view of this situation, in order to manufacture a multi-layer conductive belt by a co-extrusion method, a conductive belt was prototyped that had a base layer containing a polyamide resin and a conductive agent and having a surface resistivity of 1 x ¹⁰⁵ to 1 x ¹⁰⁸ Ω/□, and a surface layer containing an acid-modified ethylene-tetrafluoroethylene copolymer. However, a problem arose in which the ends of the conductive belt warped upon moisture absorption.
The present invention has been made in view of such problems, and has an object to provide a conductive belt in which the base layer exhibits semiconductivity in the medium resistance range (1×10 ⁵ to 1×10 ⁸ Ω/□), while the variation in surface resistivity is small, and the surface layer exhibits insulation, and which does not warp when absorbing moisture.

According to the present invention,
(1) A conductive belt comprising a substrate layer made of a composition containing a polyethylene resin, a polyamide resin, and a conductive agent, an adhesive layer made of a composition containing an epoxy group-containing polyethylene resin, and a surface layer made of a composition containing an acid-modified ethylene-tetrafluoroethylene copolymer;
(2) The conductive belt according to (1), wherein the composition for forming the base layer further contains a compatibilizer;
(3) The conductive belt according to (1) or (2), wherein the epoxy group-containing polyethylene resin is an ethylene-glycidyl methacrylate copolymer;
(4) The conductive belt according to any one of (1) to (3), wherein the conductive agent is an electronic conductive material;
(5) The conductive belt according to (4), wherein the electron conductive material is carbon black;
(6) The conductive belt according to any one of (1) to (5), characterized in that the surface resistivity of the base layer side at a temperature of 23° C. and a relative humidity of 50% RH is 1×10 ⁵ Ω/□ or more and 1×10 ⁸ Ω/□ or less;
(7) The conductive belt according to any one of (1) to (6), characterized in that the surface resistivity of the surface layer side at a temperature of 23° C. and a relative humidity of 50% RH is 1×10 ¹³ Ω/□ or more;
(8) The conductive belt according to any one of (1) to (7) above, which is used in an image forming apparatus;
(9) The conductive belt according to any one of (1) to (8), which is used in an inkjet type image forming apparatus;
(10) An image forming apparatus comprising the conductive belt according to any one of (1) to (9);
(11) The method for producing a conductive belt according to any one of (1) to (9), characterized in that a base layer-forming composition containing a polyethylene resin, a polyamide resin and a conductive agent, an adhesive layer-forming composition containing an epoxy group-containing polyethylene resin, and a surface layer-forming composition containing an acid-modified ethylene-tetrafluoroethylene copolymer are each fed into separate extruders, and co-extruded from a circular die so that the base layer is the inner layer, the adhesive layer is the middle layer, and the surface layer is the outer layer;
is provided.

The conductive belt of the present invention is a laminate of a base layer made of a composition containing a polyethylene resin, a polyamide resin, and a conductive agent, an adhesive layer made of a composition containing an epoxy group-containing polyethylene resin, and a surface layer made of a composition containing an acid-modified ethylene-tetrafluoroethylene copolymer, and has a high interlayer peel strength, a surface resistivity of the surface layer side of 1×10 ¹³ Ω/□ or more (insulating region), and a surface resistivity of the base layer side (side on which the surface layer is not formed) in the range of 1×10 ⁵ to 1×10 ⁸ Ω/□ (medium resistivity region). When such a belt is used as a paper transport belt, the surface layer has excellent insulating properties, so that the adsorption force of the recording medium (paper) is strong and the recording medium can be transported reliably.
Furthermore, the conductive belt of the present invention is unlikely to warp even under high humidity conditions, and can be suitably used as a paper transport belt. The conductive belt of the present invention can be manufactured more cheaply than a conventional multi-layer belt using a polyimide resin. The conductive belt of the present invention does not swell on its surface even when a solvent-type ink is attached thereto, and therefore can be suitably used as a paper transport belt in an inkjet system.

[Base layer]
The base layer of the present invention must be made of a composition containing a polyethylene resin, a polyamide resin, and a conductive agent. If necessary, other resins may be added to the composition within a range that does not impair the properties of the base layer.

The polyethylene resin used in the present invention is a polymer made of ethylene, and includes copolymers having polyethylene as a partial structure. Examples of polyethylene resins include high-density polyethylene (density: 0.942 to 0.96), medium-density polyethylene (density: 0.93 to 0.942), low-density polyethylene (density: 0.91 to 0.93), very low-density polyethylene (density: less than 0.91), linear low-density polyethylene, and the like. An example of a copolymer having polyethylene as a partial structure is ethylene-vinyl acetate copolymer (called EVA), which is a copolymer of ethylene and vinyl acetate.

Furthermore, the conductive belt for an image forming apparatus, which is one of the applications of the conductive belt of the present invention, is used by being stretched between rolls under a certain tension, but since the conductive belt is left stretched between rolls when the printer or the like is stopped, it will develop a bent shape. This causes a problem that the bent part will become convex when the printer or the like is started. If a film made of a thermoplastic resin is left in the same shape for a long time, it is inevitable that the bent part will develop a bent shape, but a conductive belt with a low tensile modulus of elasticity is stretched between rolls and tension is applied when the printer or the like is started, and the convex shape of the bent part will be alleviated. For this reason, it is preferable that the tensile modulus of elasticity of the polyethylene resin is 1100 MPa or less.
Furthermore, in recent years, with the increasing speed of printers, etc., if the tensile modulus of the conductive belt for an image forming apparatus falls below 400 MPa, the belt will stretch when driven, which is not preferable. As described above, there are various types of polyethylene resins, and low-density polyethylene, linear low-density polyethylene, and very low-density polyethylene have a tensile modulus of about 200 to 300 MPa, so that the tensile modulus can be adjusted by using high-density polyethylene in combination with low-density polyethylene, linear low-density polyethylene, very low-density polyethylene, etc., depending on the application.

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

In order to uniformly disperse the polyamide resin in the polyethylene resin, a compatibilizer may be added to the composition forming the base layer of the present invention. The compatibilizer is preferably a modified polyethylene resin containing an epoxy group, a carboxyl group, or an anhydride group. By using a modified polyethylene having an epoxy group, a carboxyl group, or an anhydride group that is reactive with the amino group that is the terminal group of the polyamide resin as the compatibilizer, a sea-island structure in which the polyamide resin is finely dispersed in the polyethylene resin matrix is formed. Carbon black and ion-conductive materials, which are conductive agents, are unevenly distributed in the polyamide resin to which they have a higher affinity, and as a result, the conductive agent can be uniformly dispersed in the polyethylene resin matrix.

Examples of the compatibilizer include terpolymers of ethylene-methyl acrylate-maleic anhydride, terpolymers of ethylene-ethyl acrylate-maleic anhydride, terpolymers of ethylene-butyl acrylate-maleic anhydride, copolymers of ethylene-glycidyl methacrylate, and terpolymers of ethylene-methyl acrylate-glycidyl methacrylate, and may contain structural units derived from other monomers. Examples of other monomers include α-olefins such as propylene and butene, styrene, vinyl acetate, (meth)acrylate, and (meth)acrylonitrile. The other monomers may be used alone or in combination of two or more. The content of the other monomers is 0 to 15 mol%, preferably 0 to 10 mol%, and more preferably 0 to 5 mol%. The number average molecular weight of the compatibilizer is preferably 3000 or more. If the number average molecular weight of the compatibilizer is less than 3000, the unreacted compatibilizer may bleed out to the surface of the base layer (bleed phenomenon). This bleeding phenomenon can cause contamination of paper and other parts in conductive belts for image forming devices, etc.

The tensile modulus of the base layer is preferably 500 MPa or more, and more preferably 700 MPa or more. In order to increase the tensile modulus of the belt, the high-density polyethylene content in the above-mentioned polyethylene resin can be increased, or a reinforcing material such as a plate-like filler or whiskers can be added. The thickness of the base layer is preferably 30 to 300 μm, and more preferably 40 to 200 μm, so as to satisfy the above performance. If the thickness is less than 30 μm, it is difficult to obtain a stable electrostatic adsorption force of the belt, and if the thickness exceeds 300 μm, the flexibility deteriorates.

In the conductive belt of the present invention, the surface resistivity of the substrate layer can be adjusted by blending a conductive agent in the substrate layer. The substrate layer preferably has a surface resistivity of 1×10 ⁵ to 1×10 ¹² Ω/□, and more preferably has a surface resistivity of 1×10 ⁵ to 1×10 ⁸ Ω/□, which is in the medium resistivity range. The conductive agent includes an electronic conductive material and an ion conductive material. In addition, when the substrate layer needs to have a lower resistivity range (for example, 1×10 ⁵ to 1×10 ⁶ Ω/□) within the medium resistivity range, it is preferable to use an electronic conductive material that can reduce the electrical resistance with a small amount of additive.

Examples of the electron conductive material 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 black 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 preferred because it can reduce electrical resistance with a small amount of carbon black. In addition, from the viewpoint of developing the structure of the carbon black and forming a conductive path, the DBP (Dibutyl Phthalate) oil absorption is preferably 100 to 500 ml/100 g, more preferably 100 to 300 ml/100 g, and more preferably 150 to 250 ml/100 g. In addition, from the viewpoint of electrical 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 to which a polymer having one or more functional groups selected from a carboxyl group, a hydroxyl group, an epoxy group, an amino group and an oxazoline group has been grafted, or carbon black surface-treated with a low molecular weight compound can also be used.

The amount of electronically conductive material is preferably 5 to 25 parts by weight, and more preferably 8 to 20 parts by weight, per 100 parts by weight of the total amount of the polyethylene resin and the polyamide resin. If the amount of conductive agent is less than 5 parts by weight, it may not be possible to obtain a composition that exhibits the desired semiconductivity, and if it exceeds 25 parts by weight, the melt viscosity will increase, making melt extrusion difficult.

Examples of ion-conductive materials include polyetheresteramide, polyetherester, polyetheramide, polyethylene oxide, polyethylene oxide copolymer, partially cross-linked polyethylene oxide copolymer, ionic electrolytes, etc., which can be used alone or in combination of two or more. As the ionic electrolyte, alkali metal thiocyanates, phosphates, sulfates, halogen-containing oxyacid salts, and tetraalkylammonium salts can be used alone or in combination of two or more. Among these, lithium perchlorate, sodium perchlorate, potassium perchlorate, lithium thiocyanate, sodium thiocyanate, and potassium thiocyanate are preferred.

When an ion-conductive material is used as the conductive agent, the amount of the conductive agent is preferably 1 to 50 parts by weight per 100 parts by weight of the total amount of the polyethylene resin and the polyamide resin. The amount is preferably 1 to 30 parts by weight, more preferably 2 to 25 parts by weight, and more preferably 15 to 25 parts by weight. If the amount of the ion-conductive material is less than 1 part by weight, it is not preferable because a composition exhibiting the desired conductivity cannot be obtained, and if it exceeds 50 parts by weight, it is not preferable because the hygroscopicity becomes high and the tensile modulus of elasticity becomes low.

The resin composition used in the base layer of the present invention may contain additives as necessary to the extent that the properties are not impaired. Examples of additives include antioxidants, heat stabilizers, organic and inorganic fillers, antiblocking agents, plasticizers, lubricants, processing aids, etc. These resins and additives can be used in appropriate amounts depending on the purpose.

There is no particular restriction on the composition ratio of each component of the composition forming the base layer of the present invention, but it is preferable that the polyethylene resin and polyamide resin are contained in a ratio of polyethylene resin: polyamide resin = 70 wt% to 92 wt%: 30 wt% to 8 wt%. The ratio of polyamide resin in a total amount of 100 wt% of polyethylene resin and polyamide resin is more preferably 10 wt% to 25 wt%, and even more preferably 12 wt% to 20 wt%. By setting the blending ratio of polyethylene resin and polyamide resin in the above range, a sea-island structure in which polyamide resin is finely dispersed in the polyethylene resin matrix is obtained, and thus the conductive agent is uniformly dispersed, resulting in excellent uniformity of electrical resistance. If the polyamide resin is less than 8 wt%, the spacing between the islands in the sea-island structure becomes large, which may result in poor uniformity of electrical resistance.

The amount of the compatibilizer is preferably 0.3 to 5.0 parts by weight, more preferably 0.5 to 2.0 parts by weight, per 100 parts by weight of the total amount of the polyethylene resin and the polyamide resin. By setting the amount of the compatibilizer in the above range, a sea-island structure in which the polyamide resin is finely dispersed in the polyethylene resin matrix is obtained, and the conductive agent is uniformly dispersed in the composition, resulting in excellent uniformity of electrical resistance. If the amount of the compatibilizer is less than 0.3 parts by weight, the size of the islands in the sea-island structure becomes large, making it difficult to obtain stable electrical resistance in the medium resistance range, and the breaking elongation of the film may decrease. On the other hand, if the amount of the compatibilizer is more than 5 parts by weight, the size of the islands in the sea-island structure may become too small, and the amount of conductive agent required to obtain electrical resistance in the medium resistance range increases, which is undesirable because the electrical resistance in the TD direction varies greatly when the film is formed into a belt shape. For these reasons, the size of the islands in the sea-island structure in the composition that forms the base layer is preferably 0.5 to 5.0 μm, and more preferably 0.8 to 3.0 μm.

[Adhesive layer]
The adhesive layer of the present invention is essential to be made of a composition containing an epoxy group-containing polyethylene resin. The composition may be made of only an epoxy group-containing polyethylene resin, or may contain other resins or additives as necessary within the range that does not impair the properties. When a conductive belt is produced by co-extrusion, which is made of a base layer containing a polyethylene resin, a polyamide resin, and a conductive material, and a surface layer containing an acid-modified ethylene-tetrafluoroethylene resin, the interlayer adhesive strength is weak and the belt is easily peeled off. The adhesive layer of the present invention is a layer necessary for bonding the base layer and the surface layer, and the presence of the adhesive layer allows the functional groups of the surface layer, such as carboxyl groups, to react with the epoxy groups of the adhesive layer, thereby firmly bonding the surface layer and the adhesive layer. Examples of epoxy group-containing polyethylene resins include copolymers of ethylene-glycidyl methacrylate, ternary copolymers of ethylene-glycidyl methacrylate-ethyl acrylate, and ternary copolymers of ethylene-glycidyl methacrylate-vinyl acetate.

The thickness of the adhesive layer is preferably 2 to 80 μm, more preferably 5 to 50 μm, to satisfy the above performance requirements. In the co-extrusion method, if the thickness of the specific layer (adhesive layer) is less than 2 μm, there is a risk of there being areas where the specific layer is not present, and if the thickness of the adhesive layer exceeds 80 μm, the thickness of the insulating layer (the total thickness of the adhesive layer and the surface layer) becomes too thick, reducing the electrostatic adsorption force.

[Surface layer]
The surface layer of the present invention is essentially made of a composition containing an acid-modified ethylene-tetrafluoroethylene copolymer. The composition may consist of only an acid-modified ethylene-tetrafluoroethylene copolymer, or may contain other resins and additives as necessary within a range that does not impair the properties of the composition. The acid-modified ethylene-tetrafluoroethylene copolymer is a copolymer that contains 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 polymerized units having an acid structure include unsaturated carboxylic anhydrides such as maleic anhydride, itaconic anhydride, citraconic anhydride, etc., and unsaturated carboxylic acids such as undecylenic acid, acrylic acid, methacrylic acid, maleic acid, etc. The content of the polymerized units having an acid structure is preferably 0.01 to 10 mol %, more preferably 0.1 to 5 mol %, based on the total polymerized units in the acid-modified ethylene-tetrafluoroethylene copolymer.

A surface layer made of a composition containing an acid-modified ethylene-tetrafluoroethylene copolymer and a base layer made of a composition containing a polyethylene resin, a polyamide resin, and a conductive agent have poor adhesion even when extruded as two layers by a co-extrusion method. However, by providing an adhesive layer made of a composition containing an epoxy group-containing polyethylene resin, the interlayer adhesive strength between the surface layer and the base layer is increased.
The surface resistivity of the surface layer side of the conductive belt of the present invention is preferably 1× ¹⁰ Ω/□ or more, more preferably 1× ¹⁰ Ω/□ or more, and among fluororesins, ethylene-tetrafluoroethylene copolymers and acid-modified ethylene-tetrafluoroethylene copolymers are particularly preferred because they have a surface resistivity of 1× ¹⁰ Ω/□ or more and are excellent in insulation. Furthermore, it has been found that the surface layer used in the present invention does not swell even if solvent ink adheres to the surface of the conductive belt, since a fluororesin is used for the surface layer.

[Method of manufacturing a belt for an image forming apparatus]
The method for producing the composition for forming the base layer of the present invention is not particularly limited, and examples thereof include a method in which a polyethylene-based resin, a polyamide-based resin, a conductive agent, and additives used as necessary are mixed and dry blended, and then melt-kneaded; a method in which a polyethylene-based resin and a conductive agent are melt-kneaded in advance to prepare a master batch, and then a polyamide-based resin and additives used as necessary are melt-kneaded into the master batch.

Examples of equipment for melt kneading include various known kneading machines, such as a batch kneader, a kneader, a co-kneader, a Banbury mixer, a roll mill, and a single-screw or twin-screw extruder. Among these, single-screw extruders and twin-screw extruders are preferably used because of their excellent kneading capacity and productivity.

The temperature during melt kneading can be appropriately selected depending on the type and melt viscosity of the polyethylene resin or polyamide resin used, but is usually in the range of 150 to 300°C, and preferably 170 to 280°C from the viewpoint of preventing deterioration of the resin.

The conductive belt of the present invention can be manufactured by extrusion molding, centrifugal molding, dipping, etc. Extrusion molding, particularly extrusion molding using an annular die, is preferred because it can produce a seamless belt. For the extrusion molding using an annular die, for example, an extrusion molding device can be used in which three extruders are arranged below the extruders, an annular die connected to the extruders is arranged below the annular die, and a mandrel is arranged below the annular die to support the molten resin extruded downward from the annular die on its outer periphery and cool and solidify it. A tubular molded body can be obtained by supplying a composition forming a base layer, a resin forming an adhesive layer, and a resin forming a surface layer to each extruder, co-extruding them from one annular die into a tubular shape, and cooling and solidifying them along the outer periphery of the mandrel. The obtained tubular molded body can then be cut to the desired width to produce a belt. Note that these explanations were for three layers, but when there are four or more layers, it is sufficient to prepare an extruder and a die according to the number of layers.

The conductive belt of the present invention can be suitably used as an intermediate transfer belt, a transfer conveyor belt, a paper conveyor belt, or other image forming device parts. In particular, the conductive belt of the present invention can be suitably used as a paper conveyor belt for inkjet printing that uses solvent ink, since the belt surface does not swell even if solvent ink adheres to the belt surface.

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 Corporation Koka type flow tester equipped with a die having a hole of 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 Co., Ltd.) 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) Interlayer Adhesion Between Base Layer and Surface Layer In the belts obtained in each of the Examples and Comparative Examples, whether the base layer and the surface layer were adhered to each other was confirmed, and evaluated based on the following evaluation criteria.
◯: The base layer and the surface layer are firmly bonded together (through the adhesive layer).
x: The base layer and the surface layer are adhered to each other but can be peeled off by hand, or the layers are easily peeled off from each other.
(4) Solvent Ink Resistance Solvent ink (a high boiling point petroleum-based solvent having a boiling point of 100° C. or higher) was dropped onto the surface layer of the belt obtained in each of the Examples and Comparative Examples, and the belt was left at 60° C. for 24 hours. The solvent ink was then wiped off, and the surface was observed and evaluated based on the following evaluation criteria.
A: The film surface did not swell or deform.
Δ: The film surface was slightly swollen and slightly deformed.
x: The film surface swelled and was obviously deformed.
(5) Warping of Belt Ends The belts obtained in the respective Examples and Comparative Examples were left for one day under high temperature and high humidity conditions (30°C x 70% RH), and then the warping of the belt ends was observed and evaluated based on the following evaluation criteria.
◯: No warping occurs at the belt end.
x: The belt end is warped toward the surface layer.

The following raw materials were used:
<Thermoplastic resin (A)>
High density polyethylene resin (A-1) [melting point: 132°C, melt viscosity: 9240 poise (measurement temperature: 200°C, load: 100 kg]
Low-density polyethylene resin (A-2) [melting point: 111°C, melt viscosity: 2300 poise (measurement temperature: 200°C, load: 100 kg]
Polyamide resin (A-3) [Melting point: 178°C, melt viscosity: 5000 poise (measurement temperature: 200°C, load: 100 kg]
Compatibilizer (A-4) [Ethylene-ethyl acrylate-maleic anhydride terpolymer (mixture ratio: ethylene:ethyl acrylate:maleic anhydride=92:5:3, melting point: 107° C., melt viscosity: 830 poise (measurement temperature: 200° C., load: 100 kg)]
Acid-modified ethylene-tetrafluoroethylene copolymer (A-5) [melting point: 190°C, melt viscosity: 6750 poise (measurement temperature: 220°C, load: 100 kg)]
Polyvinylidene fluoride (A-6) [Melting point: 168°C, melt viscosity: 4500 poise (measurement temperature: 200°C, load: 100 kg)]
Ethylene-glycidyl methacrylate copolymer (A-7) (mixture ratio: ethylene:glycidyl methacrylate = 88:12)
Ethylene-glycidyl methacrylate copolymer (A-8) (mixture ratio: ethylene:glycidyl methacrylate = 92:8)
<Conductive Agent (B)>
Carbon black (B-1) [DBP oil absorption: 190 ml/100 g, BET surface area: 70 m2/g]

[Base layer]
The polyethylene resin, polyamide resin, conductive agent, and compatibilizer were melt-kneaded using a twin-screw kneading extruder with a screw diameter of 38 Φmm so as to obtain the resin compositions for the base layer of Examples 1 and 2 and Comparative Examples 1 to 6, in the compounding ratios shown in Table 1.

[Examples and Comparative Examples]
Using an apparatus equipped with three extruders with a cylinder diameter of 50 mm and three-layer annular dies attached to the tips thereof, the resin composition for forming the base material layer shown in Table 1 was supplied to the extruder for the inner layer, the resin constituting the adhesive layer was supplied to the extruder for the intermediate layer, and the resin for forming the surface layer was supplied to the extruder for the surface layer. The resin was molded into a tubular shape by co-extrusion and then cut to a length of 350 mm to obtain a seamless belt having 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 evaluation results of the conductive belts produced in the examples and comparative examples are shown in Table 1.

As shown in Table 1, in Examples 1 and 2, which are conductive belts having a base layer made of a resin composition containing a polyethylene resin, a polyamide resin, and a conductive agent, an adhesive layer made of an epoxy group-containing polyethylene resin, and a surface layer made of an acid-modified ethylene-tetrafluoroethylene copolymer, the surface resistivity on the base layer side was 1×10 ⁶ to 1×10 ⁷ Ω/□, and the uniformity of the surface resistivity on the base layer side (less than one digit) was also excellent. The surface resistivity on the surface layer side was also 1×10 ¹⁴ Ω/□ or more, and excellent insulation properties were observed. In addition, the interlayer adhesion was good, the solvent ink resistance of the surface layer was good, and no warping of the belt ends occurred even when left under high temperature and high humidity.
In contrast, Comparative Example 1, which is a two-layer conductive belt having a base layer made of a resin composition containing a polyethylene resin, a polyamide resin, and a conductive agent and a surface layer made of an acid-modified ethylene-tetrafluoroethylene copolymer, had poor adhesion between the base layer and the surface layer, and the layers easily peeled off. Comparative Example 2, which is a two-layer conductive belt composed of a base layer made of a polyamide resin and a conductive agent and a surface layer made of an acid-modified ethylene-tetrafluoroethylene copolymer, had a warp at the belt end because the base layer was made of a polyamide resin, and was therefore unsuitable as a belt.

Comparative Examples 3 and 4, in which a polyamide-based resin or a polyethylene-based resin was used as the surface layer, had excellent uniformity in the surface resistivity of the base layer, but when a solvent ink was dropped onto the surface layer and left at 60° C. for 24 hours, swelling was observed, and the belt was particularly unsuitable as a paper transport belt for an inkjet system using a solvent ink. On the other hand, Comparative Example 5, in which a polyvinylidene fluoride was used as the surface layer, had good solvent ink resistance of the surface layer, but had poor adhesion to the base layer made of a resin composition containing a polyethylene-based resin, a polyamide-based resin, and a conductive agent, and peeled easily between the layers, and the surface resistivity of the surface layer side was in the range of 1×10 ¹³ to 1×10 ¹⁴ Ω/□, and the insulation was poor. In addition, Comparative Example 6, which is a conductive belt including a base layer made of a resin composition containing a polyethylene resin, a polyamide resin, and a conductive agent, an adhesive layer made of a polyamide resin, and a surface layer made of an acid-modified ethylene-tetrafluoroethylene copolymer, showed adhesion to the acid-modified ethylene-tetrafluoroethylene copolymer and had poor interlayer adhesion, even though the polyamide resin A-3 contained in the base layer was used as the adhesive layer.

Claims (11)

A conductive belt characterized by comprising a substrate layer made of a composition containing a polyethylene resin, a polyamide resin, and a conductive agent, an adhesive layer made of a composition containing an epoxy group-containing polyethylene resin, and a surface layer made of a composition containing an acid-modified ethylene-tetrafluoroethylene copolymer. The conductive belt according to claim 1, characterized in that the composition for forming the base layer further contains a compatibilizer. The conductive belt according to claim 1 or 2, characterized in that the epoxy group-containing polyethylene resin is an ethylene-glycidyl methacrylate copolymer. The conductive belt according to any one of claims 1 to 3, characterized in that the conductive agent is an electronically conductive material. The conductive belt according to claim 4, characterized in that the electronically conductive material is carbon black. 6. The conductive belt according to claim 1, wherein the surface resistivity of the base layer side at a temperature of 23° C. and a relative humidity of 50% RH is 1×10 ⁵ Ω/□ or more and 1×10 ⁸ Ω/□ or less. 7. The conductive belt according to claim 1, wherein the surface resistivity of the surface layer side at a temperature of 23° C. and a relative humidity of 50% RH is 1×10 ¹³ Ω/□ or more. The conductive belt according to any one of claims 1 to 7 is a conductive belt for use in an image forming device. The conductive belt according to any one of claims 1 to 8 is a conductive belt for use in an inkjet type image forming device. An image forming apparatus having a conductive belt according to any one of claims 1 to 9. 10. A method for producing a conductive belt according to claim 1, wherein a composition for forming a base layer containing a polyethylene resin, a polyamide resin and a conductive agent, a composition for forming an adhesive layer containing an epoxy group-containing polyethylene resin, and a composition for forming a surface layer containing an acid-modified ethylene-tetrafluoroethylene copolymer are each supplied to separate extruders, and are co-extruded from a circular die so that the base layer is the inner layer, the adhesive layer is the intermediate layer, and the surface layer is the outer layer.