JP2022127802A - Electrically conductive belt, image forming apparatus having the same, and method of manufacturing electrically conductive belt - Google Patents

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

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

Conventionally, image forming apparatuses such as electrophotographic and inkjet printers, copiers, and facsimiles have adopted a method of transporting paper using rollers. Since it becomes easier, a method of conveying paper with a belt is adopted. Specifically, (1) a method in which a belt having a suction port is used to vacuum-suck a paper sheet onto the belt, and (2) a belt consisting of a conductive base layer and an insulating surface layer is used. A method is known in which a sheet is conveyed by attracting the sheet to the belt using an electrostatic attraction force generated by applying a voltage to the belt.

Of these, (1) the method of sucking the paper onto the belt under reduced pressure requires a decompression chamber and a decompression device for decompressing the decompression chamber, as described in Patent Documents 1 and 2. Since the space between the driving belt and the decompression chamber must always be maintained in a sealed state, the structure of the image forming apparatus becomes complicated. On the other hand, (2) the method using the electrostatic attraction force is convenient because the attraction 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.

As a belt (paper conveying belt) for sucking and conveying a recording medium such as paper using 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 inner layer has a volume resistivity of 10. A paper transport belt is described with a volume resistivity of ⁸ to 10 ¹⁴ Ω·cm and an outer layer volume resistivity of 10 ¹⁴ to 10 ¹⁶ Ω·cm. However, the paper conveying belt described in Patent Document 3 is centrifugal molding (spraying a polyamic acid solution for the inner layer or the outer layer on the surface or back of the mold, volatilizing the solvent at high temperature, and then imidizing at high temperature in the absence of oxygen). In the case of two layers, this must be repeated twice), which makes the manufacturing process very complicated.

Further, Patent Document 4 discloses an ink-jet printer in which the inner layer is made of a conductive polyimide resin and has a surface resistivity of 1×10 ⁴ to 1×10 ⁹ Ω/□, and the outer layer is made of an ethylene-tetrafluoroethylene copolymer (ETFE). A paper transport belt is described. This paper conveying belt also requires a step of forming an inner layer by centrifugal molding, covering the inner layer with a preformed ETFE, and melting and adhering it, so the manufacturing process is very complicated.

On the other hand, some inks used in inkjet printers, which are capable of printing at high speed, use organic solvents. There is a problem that the portion swells and unevenness occurs on the belt surface. In view of solvent resistance, it is desired to use a fluorine-based resin for the surface layer, but the fluorine-based resin has poor adhesiveness. In addition, some of them have a surface resistivity of less than 10 ¹⁴ Ω/□, and there is also a problem that the attraction force becomes weak. Incidentally, 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. Laminated sheets and laminated hoses are only exemplified as specific uses of the laminate.

JP 2019-131389 A JP 2019-127364 A JP 2008-94605 A JP 2011-73804 A WO2016/195042

A multi-layered belt using polyimide resin can be produced by repeating centrifugal molding twice, or by melting and bonding a belt-shaped polyimide resin layer that has been pre-fabricated by centrifugal molding with a belt-shaped fluorine-based resin that has been molded in advance. It is expensive because it is manufactured through a complicated process.
The present invention has been made ^{in view} of such problems. An object of the present invention is to provide a conductive belt that exhibits insulating properties.

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

The conductive belt of the present invention comprises a substrate 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 substrate layer side (the side on which the surface layer is not formed) is 1×10 ⁵ A belt with a resistance in the range of ˜1×10 ⁸ Ω/□ (medium resistance region) is obtained. When such a belt is used as a paper transport belt, since the surface layer has excellent insulating properties, the adsorption force of the recording medium (paper) is strong, and the recording medium can be reliably transported.
In addition, the conductive belt of the present invention can be manufactured at a lower cost than conventional multi-layered belts using polyimide resin. The conductive belt of the present invention does not swell on the belt surface even when solvent-type ink adheres to it, so it can be suitably used particularly as a paper transport belt for an ink jet system.

[Base layer]
The substrate layer of the present invention must contain a thermoplastic resin and a conductive agent. Considering moldability, thermoplastic resins include, for example, fluorine-based resins, polyamide-based resins, polyester-based resins, polycarbonate-based resins, polyamide-imide-based resins, polyimide-based resins, polyolefin-based resins, and the like. More than one species can be blended or used in multiple layers. Among these, fluorine-based resins, unlike other resins, are flame-retardant in themselves, are easy to extrude, and have antifouling properties and releasability. It is suitable for use belts. Examples of such fluorine-based resins include polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, ethylene-tetrafluoroethylene copolymer, polyhexafluoropropylene, ethylene-vinylidene fluoride copolymer, and vinylidene fluoride. -tetrafluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, and the like can be employed.

A polyamide-based resin is a thermoplastic resin having a sufficient molecular weight obtained by polycondensation of diamine and dicarboxylic acid, polycondensation of α,ω-aminocarboxylic acid, ring-opening polymerization of lactams, or the like. 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 the m-xylylenediamine component), nylon 6,6T (T represents the terephthalic acid component), nylon 6,6I (I represents the isophthalic acid component), and the like. Among these, polyamide resins with low water absorption are preferred, and polyamide resins with low water absorption are excellent in the dispersibility of carbon black and in the stability of electrical resistance in high-humidity environments. The water absorption of the polyamide resin is preferably 1.5% or less, more preferably 1.0% or less. Polyamide resins with a water absorption of 1.5% or less include nylon 11, nylon 12, nylon 6,10, nylon 6,12, etc. 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.

In recent years, along with the speeding up of printers and the like, belts for image forming apparatuses are required to have a high elastic modulus. If the elastic modulus is low, the belt may stretch during driving, causing the transfer position to shift. The tensile modulus of the substrate layer is preferably 500 MPa or more, more preferably 800 MPa or more. In order to increase the tensile modulus of the belt, reinforcing materials such as flat fillers and whiskers can be added to the thermoplastic resin. The thickness of the substrate layer is preferably 50-300 μm, more preferably 75-200 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, flexibility deteriorates.

In the conductive belt of the present invention, the surface resistivity of the base layer is adjusted by containing a conductive agent in the base layer. The surface resistivity of the substrate layer is preferably 10 ⁵ to 10 ¹² Ω/square, and more preferably 10 ⁵ to 10 ⁸ Ω/square, which is in the medium resistance range. Conductive agents include electronically conductive materials and ionically conductive materials. In addition, when the substrate layer requires a lower resistance region (for example, 10 ⁵ to 10 ⁶ Ω/□) among the medium resistance regions, an electron conductive material capable of obtaining a low resistance region with a small amount of addition Materials are preferably used.

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; aluminum/zinc oxides, antimony/tin oxides, and indium/tin oxides. conductive inorganic particles such as inorganic particles surface-treated with carbon black or the like. Examples of carbon black include conductive carbon black such as furnace black, channel black, ketjen black, and acetylene black. In particular, a small amount of carbon black having an average particle size of 50 nm or less can reduce electrical resistance. It is preferable because it can be done. In addition, from the viewpoint of developing the structural structure of carbon black and forming a conductive path, the DBP (Dibutyl phthalate) oil absorption is preferably 100 to 500 ml/100 g, preferably 100 to 300 ml/100 g, and 150 to 250 ml/100 g. is more preferable. Carbon black having a BET surface area in the range of 30 to 1500 m ² /g is preferred from the viewpoint of conductivity. In the present invention, the surface is treated with a grafted carbon black in 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 is grafted, or a low molecular weight compound. Carbon blacks containing carbon black can also be used.

When an electronically conductive material is used as the conductive agent, the blending 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 blending amount is preferably 5 to 35 parts by weight, more preferably 15 to 30 parts by weight. If the amount of the electronically conductive material is less than 1 part by weight, a composition exhibiting the desired conductivity cannot be obtained. Become.

Examples of the ion conductive material include polyether ester amide, polyether ester, polyether amide, polyethylene oxide, polyethylene oxide copolymer, partially crosslinked polyethylene oxide copolymer, ion electrolyte, and the like. , or two or more types can be used in combination. As the ion electrolyte, alkali metal thiocyanates, phosphates, sulfates, halogen-containing oxates, and tetraalkylammonium salts can be used singly or in combination. 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 with respect to 100 parts by weight of the thermoplastic resin. The blending amount is preferably 1 to 30 parts by weight, preferably 2 to 25 parts by weight, more preferably 15 to 25 parts by weight. If the amount of the ion-conductive material is less than 1 part by weight, a composition exhibiting the desired conductivity cannot be obtained. I don't like it.

Additives may be blended into the resin composition used for the base layer of the present invention, if necessary, as long as the properties are not impaired. Examples of additives include antioxidants, heat stabilizers, organic fillers and inorganic fillers, antiblocking agents, plasticizers, lubricants, processing aids, and the like. These resins and additives can be used in appropriate amounts depending on the purpose.

[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 polymerized units based on ethylene, polymerized units based on tetrafluoroethylene, and polymerized units having an acid structure.
Polymerized units having an acid structure include unsaturated carboxylic 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. mentioned. The content of polymerized units having an acid structure is preferably 0.01 to 10 mol%, more preferably 0.1 to 5 mol%, relative to the total polymerized units in the acid-modified ethylene-tetrafluoroethylene copolymer. .

By containing the acid-modified ethylene-tetrafluoroethylene copolymer in the surface layer, the interlayer adhesion strength with the resin composition forming the substrate layer is increased, so coextrusion molding becomes possible.
Moreover, the surface layer used in the present invention has excellent insulating properties, and the surface resistivity is preferably 1×10 ¹³ Ω/□ or more, more preferably 1×10 ¹⁴ Ω/□ or more. Among fluorine-based resins, ethylene-tetrafluoroethylene copolymers and acid-modified ethylene-tetrafluoroethylene copolymers in particular have a surface resistivity of 1×10 ¹⁴ Ω/□ or more, and have high insulating properties. Do you get it. Furthermore, it was found that the surface layer used in the present invention does not swell even if the solvent ink adheres because the surface layer used in the present invention uses a fluororesin. In addition, the composition for forming the surface layer of the present invention may optionally contain other resins and additives within a range that does not impair the properties of the composition.

[Manufacturing method of image forming apparatus belt]
The method for producing the composition for forming the base material layer of the present invention is not particularly limited. a method of preliminarily melt-kneading a conductive agent into a thermoplastic resin to prepare a masterbatch, and a method of melt-kneading a thermoplastic resin and additives used as necessary.

Apparatuses for melt-kneading include various known kneaders such as batch-type kneaders, kneaders, co-kneaders, Banbury mixers, roll mills, and single-screw or twin-screw extruders. Among these, single-screw extruders and twin-screw extruders are preferably used from the viewpoint of excellent kneading ability and productivity.

The temperature during melt kneading can be appropriately selected depending on the type of thermoplastic resin to be used, the melt viscosity, etc., but it 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. be.

The conductive belt of the present invention can be produced by an extrusion molding method, a centrifugal molding method, a dipping method, or the like. Extrusion molding, particularly extrusion molding using an annular die, is preferred because it yields a seamless belt. As an extrusion molding method using an annular die, for example, two extruders are arranged, and an annular die is arranged below the extruder in communication with the extruder, and below the annular die, from the annular die An extrusion molding apparatus provided with a mandrel for cooling and solidifying a molten resin extruded downward can be used. The composition for forming the base layer and the composition for forming the surface layer are supplied to respective extruders, co-extruded into a tubular shape from one annular die, and cooled and solidified along the outer circumference of the mandrel to form a tube. A belt can be obtained by obtaining a tubular molded body and cutting the tubular molded body into a desired width. These descriptions are for the case of two layers, but when three or more layers are used, an extruder and a die corresponding to the number of layers may be prepared.

The conductive belt of the present invention can be suitably used as image forming apparatus parts such as intermediate transfer belts, transfer/transport belts, and paper transport belts, automobile-related parts, electronic/electrical parts, mechanical parts, semiconductor packaging films, and the like. can be done. In particular, the conductive belt of the present invention does not swell even when solvent ink adheres to the belt surface, so that it can be suitably used as a paper transport belt for an ink jet method using solvent ink.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples. Methods for measuring physical properties in Examples are as follows.
(1) Melt Viscosity Melt viscosity was measured using a Koka flow tester manufactured by Shimadzu Corporation equipped with a die having a length of 10 mm and a diameter of 1 mm.
(2) Surface resistivity The surface resistivity is measured using Hiresta UX (MCP-HT800, manufactured by Dia Instruments) equipped with a URS probe (load 2 kg) (applied voltage 10 V for the base layer, applied voltage 1000V).
Further, the uniformity (variation) of the surface resistivity was determined by the following formula.
Uniformity of surface resistivity [digit] = log10 (maximum value of surface resistivity / minimum value of surface resistivity)
(3) Solvent-ink resistance A solvent ink (high-boiling petroleum-based solvent) was dropped on the surface layer of the belt obtained in each of the examples and comparative examples, and the surface was observed after being left at 60°C for 24 hours. , was evaluated based on the following evaluation criteria.
◯: The film surface did not swell and was not deformed.
Δ: The film surface was slightly swollen and slightly deformed.
x: The film surface swelled and was clearly deformed.

The following materials were used as raw materials.
<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 to 15 nm, length: 10 μm or less, specific surface area: 180 to 250 m2/g]

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

As shown in Table 1, base layers 1 to 3 containing polyamide resin and carbon black as a conductive agent, and base layer 6 containing high-density polyethylene, polyamide resin and carbon black as a conductive agent have surface resistivities of It showed a value of 10 ⁵ to 10 ⁷ Ω/□, and was excellent in surface resistivity uniformity (within 0.5 digit) and film formability. The base layer 4 and the base layer 5, which contain polyamide resin and carbon nanotubes as a conductive agent, have a surface resistivity of 10 ⁶ to 10 ⁸ Ω/□, which is slightly higher than that of the base layers 1 to 3. The substrate layer 5 in which the blending ratio of the carbon nanotubes was increased in order to lower the resistivity had large thickness unevenness in the extrusion direction, and the uniformity of the surface resistivity was also poor.

[Example/Comparative example]
Using an apparatus equipped with two layers of annular dies at the tips of two extruders with a cylinder diameter of 50 mm, the resin composition forming the base layer and the resin composition forming the surface layer shown in Table 2 are co-extruded. After forming into a tubular shape, it was cut to a length of 400 mm to obtain a seamless belt having a circumference of 800 mm and a width of 350 mm, with the substrate layer as the inner layer and the surface layer as the outer layer.
The seamless belts produced in Examples and Comparative Examples were evaluated for the following items, and the results are shown in Table 2.

As shown in Table 2, in Examples 1 to 3 of belts in which the substrate layer 1 and the surface layer are made of an acid-modified ethylene-tetrafluoroethylene copolymer (A-4), the surface resistivity of the substrate layer side is showed a value of 10 ⁶ to 10 ⁷ Ω/□, and the uniformity of the surface resistivity (less than one digit) was also excellent. The surface resistivity of the surface layer also showed a value of 10 ¹⁴ Ω/□ or more, indicating excellent insulation. In addition, the solvent ink resistance of the surface layer was also good.
On the other hand, in Comparative Examples 1 and 2 in which the polyamide resin or high-density polyethylene was used as the surface layer, the uniformity of the surface resistivity of the substrate layer was excellent. Swelling was observed after standing for 24 hours. From this result, the belts of Comparative Examples 1 and 2 were particularly unsuitable as paper transport belts for an inkjet system using solvent ink. On the other hand, in Comparative Example 3, in which polyvinylidene fluoride was used as the surface layer, the solvent ink resistance of the surface layer was good, but the adhesion to the substrate layer 1 was poor, resulting in delamination, and the surface resistivity of the surface layer was also 10 ¹³ . It showed a range of ~10 ¹⁴ Ω/□ and was inferior in insulation.

Claims (10)

A conductive belt comprising a substrate 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 claim 1, wherein said thermoplastic resin is a polyamide resin. 3. The conductive belt according to claim 1, wherein said conductive agent is an electronically conductive material. 4. The conductive belt of claim 3, wherein said electronically conductive material is carbon black. 5. The surface resistivity of the substrate 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. conductive belt. 6. The conductive belt according to claim 1, wherein 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. A conductive belt according to any one of claims 1 to 6, which is a conductive belt for an image forming apparatus. 8. The conductive belt according to claim 7, wherein said conductive belt for an image forming apparatus is for conveying paper by an ink jet method. An image forming apparatus comprising the conductive belt according to claim 1 . 9. The method for producing a conductive belt according to any one of claims 1 to 8, wherein a composition for forming a base layer containing a thermoplastic resin and a conductive agent; and an acid-modified ethylene-tetrafluoroethylene copolymer. The composition forming the surface layer containing Method.