JP7536730B2 - Sponge Roller - Google Patents

Description

The present invention relates to a sponge roller.

Printers such as laser printers and video printers, copiers, facsimiles, and all-in-one machines employ various image forming devices that utilize electrophotography. Image forming devices that utilize electrophotography are equipped with various printing sponge rollers, such as cleaning rollers, charging rollers, developing rollers, transfer rollers, secondary transfer rollers, pressure rollers, paper feed rollers, and fixing rollers, each of which has a shaft body and an elastic layer formed on its outer circumferential surface.

Among these rollers, conductive rollers such as transfer rollers and secondary transfer rollers are required to have excellent charging characteristics so that when they are installed in an image forming device, they can transfer developer from an image carrier carrying developer, a secondary transfer belt, etc., to a recording medium and form a high-quality image on the recording medium.

On the other hand, in recent years, with the trend towards higher resolution, toner has become finer, and there is a demand for fine and uniform cell diameters. For example, it is widely known that in order to adjust the cell diameter to a desired range, a foamed elastic layer is formed by using unexpanded microballoons in combination with a chemical foaming agent (see Patent Document 1).

JP 2018-031850 A

However, in adjusting the cell diameter, the variation in the electrical resistance of the foamed elastic layer may become large depending on the foaming balance. Furthermore, the resistance of the conductive sponge roller is adjusted mainly by carbon black, but the foamed elastic layer made of carbon conductivity has a problem that the resistance increases when electricity is passed through it. The increase in the resistance when electricity is passed through the conductive sponge roller may adversely affect the image quality, so it is required to have stable electrical characteristics.
The present invention has been made in consideration of the above circumstances, and has an object to provide a sponge roller in which an increase in resistance value when electricity is passed therethrough is suppressed.

The inventors discovered that by further incorporating conductive particles other than carbon black into a foamed elastic layer containing carbon black, a chemical foaming agent, and unexpanded microballoons, it is possible to suppress an increase in resistance value after passing a current through the layer, and obtain stable electrical characteristics, and thus arrived at the present invention.
In other words, the present invention is a sponge roller comprising a shaft body and a foamed elastic layer provided on the outer periphery of the shaft body, wherein the foamed elastic layer contains base rubber, carbon black, a chemical foaming agent, unexpanded microballoons, and conductive particles other than carbon black, and the increase in resistance value of the foamed elastic layer after passing an electric current of 1 kV for 15 hours is 10% or less.

The conductive particles are zinc oxide particles, and the zinc oxide particles are preferably contained in an amount of 15 parts by mass or more and 50 parts by mass or less per 100 parts by mass of the resin composition for the foamed elastic layer that forms the foamed elastic layer.

The foamed elastic layer preferably contains silicone rubber.

The cell diameter of the foamed elastic layer is preferably 30 μm or more and 150 μm or less.

The sponge roller of the present invention may be a transfer roller.

The present invention provides a sponge roller that suppresses the increase in resistance value when electricity is applied.

1 is a perspective view showing an embodiment of a sponge roller of the present invention. FIG. 2 is a schematic front view showing an apparatus for measuring the surface resistance of a sponge roller.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.
[Sponge roller]
As shown in Fig. 1, a sponge roller 1 of the present invention includes a shaft 2 and a foamed elastic layer 3 provided on the outer periphery of the shaft 2. The foamed elastic layer 3 contains a base rubber, carbon black, a chemical foaming agent, unexpanded microballoons, and conductive particles other than carbon black, and the increase rate of the resistance value of the foamed elastic layer after passing a current of 1 kV for 15 hours is 10% or less.
The details of each component will be described below.

<Shaft body>
The shaft body 2 may preferably be a shaft body having conductive properties and used in a conventionally known sponge roller. The shaft body 2 is preferably made of at least one metal selected from the group consisting of iron, aluminum, stainless steel, and brass. Such a shaft body 2 is generally also known as a "core metal."

The shaft body 2 may contain an insulating resin. The insulating resin may be, for example, a thermoplastic resin or a thermosetting resin. The shaft body 2 may include, for example, a core body made of an insulating resin and a plating layer provided on the core body. Such a shaft body 2 can be obtained, for example, by plating a core body made of an insulating resin to make it conductive.
The shaft body 2 is preferably a core bar in order to obtain good electrical conductivity characteristics.

The shape of the shaft body 2 is preferably, for example, rod-like or tubular. The cross-sectional shape of the shaft body 2 may be, for example, circular or elliptical, or may be non-circular, such as polygonal. The outer peripheral surface of the shaft body 2 may be subjected to a cleaning treatment, a degreasing treatment, a primer treatment, or the like.

The axial length of the shaft body 2 is not particularly limited, and may be adjusted as appropriate depending on the type of the image forming device in which it is installed. The diameter of the shaft body 2 (diameter of the circumscribed circle) is also not particularly limited, and may be adjusted as appropriate depending on the type of the image forming device in which it is installed.

<Foamed Elastic Layer>
The foamed elastic layer 3 is provided to impart to the sponge roller 1 hardness and elasticity that enables it to be pressed against the photosensitive member with an appropriate nip width and nip pressure so that toner can be supplied to the electrostatic latent image formed on the surface of the photosensitive member without excess or deficiency.
The foamed elastic layer 3 can be formed by foaming and crosslinking a resin composition for a foamed elastic layer.

Various rubbers can be used as the base rubber of the foamed elastic layer 3. Examples of rubber include ethylene-propylene-diene copolymer rubber (EPDM), acrylonitrile-butadiene rubber (NBR), chloroprene rubber (CR), natural rubber (NR), isoprene rubber (IR), styrene-butadiene rubber (SBR), fluororubber, silicone rubber, epichlorohydrin rubber, NBR hydride, and urethane rubber. These can be used alone or in combination of two or more. Among these, silicone rubber is preferred because it has a small compressive stress distortion due to pressure. Examples of silicone rubber include polydimethylsiloxane, polymethyltrifluoropropylsiloxane, polymethylvinylsiloxane, polyphenylvinylsiloxane, and copolymers of these siloxanes.

The foamed elastic layer 3 can be formed by heating and crosslinking the resin composition for the foamed elastic layer. In the case of silicone rubber, the resin composition for the foamed elastic layer can contain, for example, (a) organopolysiloxane as a base rubber, (b) carbon black, (c) a chemical foaming agent, (d) unexpanded microballoons, and (e) conductive particles other than carbon black.
Hereinafter, (a) the base rubber, (b) the carbon black, and (e) the material containing conductive particles other than the carbon black may be referred to as the "base material."

(a) Organopolysiloxane The organopolysiloxane is preferably an organopolysiloxane having a degree of polymerization of 100 or more and represented by the following average composition formula (I).
R ¹ _a SiO _(4-a)/2 (I)
(In the formula, ^R1 represents the same or different unsubstituted or substituted monovalent hydrocarbon groups, and a is a positive number of 1.95 to 2.05.)

Examples of ^R1 include alkyl groups such as methyl, ethyl, propyl, butyl, hexyl, and dodecyl groups, cycloalkyl groups such as cyclohexyl groups, alkenyl groups such as vinyl, allyl, butenyl, and hexenyl groups, aryl groups such as phenyl and tolyl groups, and aralkyl groups such as β-phenylpropyl groups. ^R1 may also be a group in which some or all of the hydrogen atoms of these hydrocarbon groups have been substituted with a substituent. The substituent may be, for example, a halogen atom or a cyano group. Examples of the hydrocarbon group having a substituent include a chloromethyl group, a trifluoropropyl group, and a cyanoethyl group.

It is preferable that the molecular chain terminals of the organopolysiloxane are blocked with a trialkylsilyl group such as a trimethylsilyl group, a dialkylaralkylsilyl group such as a dimethylvinylsilyl group, a dialkylhydroxysilyl group such as a dimethylhydroxysilyl group, or a triarylalkylsilyl group such as a trivinylsilyl group.

The organopolysiloxane preferably has two or more alkenyl groups in the molecule. The organopolysiloxane preferably has 0.001 mol % or more and 5 mol % or less (more preferably 0.01 mol % or more and 0.5 mol % or less) of alkenyl groups in ^R1 . The alkenyl group in the organopolysiloxane is particularly preferably a vinyl group.

Organopolysiloxanes can be obtained, for example, by cohydrolytic condensation of one or more organohalosilanes, or by ring-opening polymerization of cyclic polysiloxanes such as siloxane trimers or tetramers. The organopolysiloxane may basically be a linear diorganopolysiloxane, or may be partially branched. The organopolysiloxane may also be a mixture of two or more types having different molecular structures.

The organopolysiloxane preferably has a kinematic viscosity at 25°C of 100 cSt or more, and more preferably 100,000 cSt or more and 10,000,000 cSt or less. The degree of polymerization of the organopolysiloxane is preferably, for example, 100 cSt or more, and more preferably 3,000 cSt or more and 10,000 cSt or less.

(b) Carbon Black Examples of carbon black include furnace black such as Ketjen Black (registered trademark), acetylene black, channel black, and thermal black.

(c) Chemical Foaming Agent The chemical foaming agent may be either an inorganic foaming agent or an organic foaming agent. Examples of inorganic foaming agents include sodium bicarbonate and ammonium carbonate, and examples of organic foaming agents include organic azo compounds such as diazoamino derivatives, azonitrile derivatives, and azodicarboxylic acid derivatives. Among the organic azo compounds, azodicarboxylic acid amide and azobis-isobutyronitrile are preferably used. In particular, azobis-isobutyronitrile is preferably used.

(d) Unexpanded Microballoons As the unexpanded microballoons, resin microballoons can be mentioned. As the resin microballoons, those using a thermoplastic resin for the outer shell are preferably used. As the thermoplastic resin constituting the outer shell, vinylidene chloride/acrylonitrile copolymer, methyl methacrylate/acrylonitrile copolymer, methacrylonitrile/acrylonitrile copolymer, etc. can be mentioned. It is preferable to use resin microballoons whose shell resin has a softening temperature within an appropriate range according to the curing temperature of the silicone rubber. In addition, as the evaporative substance to be encapsulated, hydrocarbons such as butane and isobutane can be mentioned.
The average particle size of the unexpanded microballoons is preferably 5 μm or more and 50 μm or less, and more preferably 5 μm or more and 25 μm or less.

Unexpanded microballoons suitable for the present invention are commercially available as "Matsumoto Microsphere F Series" (manufactured by Matsumoto Yushi Seiyaku Co., Ltd.), "Expansel Series" (manufactured by Expansel Co., Ltd.), etc. Unexpanded resin microballoons suitable for the present invention are selected from resin microballoons that have the function of expanding at a temperature higher than the decomposition temperature of the chemical foaming agent used to form the elastic layer.
The amount of the foaming agent to be added is preferably 0.5% by mass or more and 6% by mass or less, from the viewpoint of obtaining cells of uniform size while having a low specific gravity relative to 100 parts by mass of the resin composition for foamed elastic layer.

(e) Conductive particles other than carbon black As the conductive particles, zinc oxide particles and tin oxide particles are preferred, and zinc oxide particles are more preferred. These particles may be used alone or in combination of two or more. The conductive particles are preferably 15 parts by mass or more and 50 parts by mass or less, more preferably 17 parts by mass or more and 40 parts by mass or less, and even more preferably 17 parts by mass or more and 30 parts by mass or less, per 100 parts by mass of the resin composition for the foamed elastic layer. By the content of the conductive particles being within the above range, the rate of increase in the resistance value after energization can be reduced, and high-quality images can be provided for a long period of time.

(Other ingredients)
The resin composition for the foamed elastic layer may contain a crosslinking agent. Examples of the crosslinking agent include an addition reaction crosslinking agent and an organic peroxide crosslinking agent.
As an addition reaction crosslinking agent, for example, organohydrogenpolysiloxane, which is known as an addition reaction type crosslinking agent having two or more SiH groups (SiH bonds) in one molecule, can be preferably used. The addition reaction crosslinking agents can be used alone or in combination of two or more.
The amount of the addition reaction crosslinking agent is usually 0.1 parts by mass or more and 7 parts by mass or less based on 100 parts by mass of the resin composition for the foamed elastic layer.

When an addition reaction crosslinking agent is used, the organic peroxide crosslinking agent can crosslink the millable silicone rubber by itself, but when used in combination as an auxiliary crosslinking agent for the addition reaction crosslinking agent, the physical properties such as strength and distortion of the obtained toner supply roller can be further improved. Examples of the organic peroxide crosslinking agent include benzoyl peroxide, bis-2,4-dichlorobenzoyl peroxide, dicumyl peroxide, di-t-butyl peroxide, 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane, etc.
The amount of the organic peroxide crosslinking agent is usually 0.1 parts by mass or more and 7 parts by mass or less based on 100 parts by mass of the resin composition for the foamed elastic layer. The organic peroxide crosslinking agent may be used alone or in combination of two or more kinds.

It is preferable to use an addition reaction catalyst in combination with the addition reaction crosslinking agent. Examples of addition reaction catalysts include platinum black, platinic chloride, chloroplatinic acid, reaction products of chloroplatinic acid and monohydric alcohols, complexes of chloroplatinic acid and olefins, platinum bisacetoacetate, palladium catalysts, and rhodium catalysts. The amount of addition reaction catalyst used can be a catalytic amount.

The resin composition for the foamed elastic layer may also contain various additives. Examples of the various additives include auxiliary agents such as chain extenders, catalysts, dispersants, antiaging agents, antioxidants, and fillers other than silica-based materials such as glass beads, pigments, colorants, processing aids, softeners, plasticizers, emulsifiers, heat resistance improvers, flame retardant improvers, acid acceptors, thermal conductivity improvers, release agents, and solvents. These various additives may be additives that are commonly used, or may be additives that are specially used depending on the application.

The foamed elastic layer 3 is formed on the outer circumferential surface of the shaft body 2 by simultaneously or successively performing heat curing and molding using a known molding method. The resin composition for the foamed elastic layer may be cured by any method that can apply the heat required for hardening the rubber composition. The molding method for the foamed elastic layer 3 is not particularly limited and may include continuous vulcanization by extrusion molding, pressing, mold molding by injection, etc. For example, extrusion molding may be selected. The foamed elastic layer 3 formed on the shaft body 2 may also be ground or polished.

The heating temperature when vulcanizing the resin composition for the foamed elastic layer is preferably 100°C or higher and 500°C or lower, more preferably 120°C or higher and 300°C or lower. The heating time is preferably several seconds to 1 hour, more preferably 10 seconds to 35 minutes. In addition, secondary vulcanization may be performed as necessary. Furthermore, tertiary vulcanization may be performed at 180 to 280°C, particularly 200 to 250°C, for 1 to 15 minutes. By heating multiple times in this way, it is possible to control the expansion of unexpanded microballoons, the hardening of the millable type silicone rubber, the elimination of residual low molecular weight siloxane, and the thermal contraction of the expanded microballoons as necessary, which is preferable. By performing multiple heating operations in this way, the unexpanded microballoons expand and the millable type silicone rubber hardens at the same time to form cell walls, and then only the expanded microballoons are thermally contracted, and the average cell diameter can be adjusted to 150 μm or less. In addition, the rubber composition can be foamed and hardened by a known method to easily form a foamed elastic layer 3 having bubbles.

The sponge roller thus obtained may be further subjected to a polishing process. The polishing process is a process for adjusting the shape of the sponge roller formed on the outer peripheral surface of the shaft body to a shape in which the thickness of the sponge roller in the axial direction of the shaft body gradually increases toward the center of the shaft body and gradually decreases from the center of the shaft body toward the tip of the shaft body, i.e., an inverted crown shape, or a shape in which the thickness of the sponge roller increases from the center of the shaft body toward both ends of the shaft body, i.e., an inverted crown shape.

(cell diameter)
The cell diameter of the foamed elastic layer 3 is preferably 30 μm or more and 150 μm or less, more preferably 30 μm or more and 110 μm or less, and even more preferably 30 μm or more and 100 μm or less.

(Resistance value)
The surface resistance of the foamed elastic layer 3 is preferably 3.0 (log Ω) to 9.0 (log Ω), and more preferably 4.0 (log Ω) to 9.0 (log Ω). The resistance can be adjusted by a conductivity imparting agent such as carbon and conductive particles.

(Rate of increase in resistance after current is passed)
The foamed elastic layer 3 of the sponge roller 1 of the present invention has a resistance value increase rate of 10% or less, preferably 5% or less, and more preferably 1% or less after passing a current of 1 kV for 15 hours.
By keeping the rate of increase in resistance value after energization to 10% or less, stable electrical characteristics can be obtained, making it possible to provide high-quality images over a long period of time.
The resistance value is measured by the method described later in the Examples.

The sponge roller of the present invention can be incorporated into an image forming device, for example as a transfer roller in a fixing device, and has stable electrical characteristics, contributing to the provision of high-quality images.

The present invention will be described in detail below with reference to examples. Note that the present invention is not limited to the examples shown below.

[Example 1]
The sponge roller of Example 1 was produced by the following procedure.
(Formation of primer layer)
An electroless nickel-plated shaft (made of SUM23, diameter 10 mm, length 274.2 mm) was washed with ethanol, and its surface was coated with a silicone-based primer (product name "Primer No. 16", made by Shin-Etsu Chemical Co., Ltd.). The primer-treated shaft was baked in a gear oven at 150°C for 10 minutes and then cooled at room temperature for 30 minutes or more to form a primer layer on the outer circumferential surface of the shaft.

(Formation of foamed elastic layer)
A foamed elastic layer made of a rubber material was formed on the outer circumferential surface of the shaft by extrusion molding using a resin composition for foamed elastic layer containing the materials shown in Table 1. In the extrusion molding, the resin composition was heated at 270°C for 5 minutes using an infrared heating oven (IR oven), and further heated at 200°C for 4 hours using a gear oven to harden it. As a result, a foamed elastic layer made of silicone rubber was formed on the outer circumferential surface of the shaft treated with the primer. The thickness of the foamed elastic layer was 4 mm.

Details of the resin composition for the foamed elastic layer are as follows.
(1) Base material: KE87C-40PU (conductive agent, manufactured by Shin-Etsu Chemical Co., Ltd.)
65 parts by mass KE-78VBS (silicone raw rubber, manufactured by Shin-Etsu Chemical Co., Ltd.) 17.5 parts by mass Zinc oxide particles 17.5 parts by mass (2) Crosslinking agent, catalyst and foaming agent C-3 (crosslinking agent, manufactured by Shin-Etsu Chemical Co., Ltd.) 5 parts by mass C-25B (crosslinking agent, manufactured by Shin-Etsu Chemical Co., Ltd.) 2 parts by mass C-25A (platinum catalyst, manufactured by Shin-Etsu Chemical Co., Ltd.) 2 parts by mass F-35D (unexpanded microballoons, manufactured by Matsumoto Yushi Seiyaku Co., Ltd.) 0.6 parts by mass AIBN (chemical foaming agent, manufactured by Otsuka Chemical Co., Ltd.) 0.4 parts by mass

[Example 2, Comparative Examples 1 to 4]
A sponge roller was produced in the same manner as in Example 1, except that a foamed elastic layer was formed with the composition shown in Table 1.

[evaluation]
The following evaluations were carried out for the above-mentioned Examples and Comparative Examples. The evaluation results are shown in Table 1.

(Method of measuring cell diameter)
The cut surface of the foamed elastic layer of the sponge roller was observed under an optical microscope at 50 to 200 times magnification, and the cell diameters of 10 randomly selected cells were measured. The average value was taken as the "cell diameter of the foamed elastic layer."

(Rate of increase in resistance value of foamed elastic layer)
The resistance value increase rate of the foamed elastic layer of the sponge roller was measured for the above-mentioned Examples and Comparative Examples. FIG. 2 shows a schematic front view of the measuring device.
As shown in Fig. 2, the sponge roller 1 was placed on a gold-plated plate 51, and weights 52 weighing 500 g were hung on both ends. The resistance values of the shaft 53 and the gold-plated plate 51 were measured at an applied voltage of 1 kV using an ultra-high resistance/microammeter "5450" (manufactured by ADC Corporation) 54. The rate of increase (%) in the resistance value was calculated using the following formula.
Resistance increase rate (%) = (resistance after energization - initial resistance) / initial resistance x 100

As shown in Table 1, Examples 1 and 2, in which the foamed elastic layer further contains zinc oxide particles in addition to the base rubber, carbon black, chemical foaming agent, and unexpanded microballoons, show a significantly reduced rate of increase in resistance value compared to Comparative Example 1, which does not contain zinc oxide particles.

REFERENCE SIGNS LIST 1 sponge roller 2 shaft body 3 elastic layer 51 gold-plated plate 52 weight 53 shaft 54 ultra-high resistance/microcurrent meter

Claims (4)

A sponge roller comprising a shaft body and a foamed elastic layer provided on an outer periphery of the shaft body,
the foamed elastic layer comprises a base rubber, carbon black, a chemical foaming agent, unexpanded microballoons, and conductive particles other than the carbon black;
A sponge roller serving as a transfer roller, wherein the resistance value of the foamed elastic layer increases by 10% or less after a current of 1 kV is passed therethrough for 15 hours. the conductive particles are zinc oxide particles,
2. The sponge roller according to claim 1, wherein the zinc oxide particles are contained in an amount of 15 parts by mass or more and 50 parts by mass or less based on 100 parts by mass of a resin composition for forming the foamed elastic layer. The sponge roller according to claim 1 or 2, wherein the foamed elastic layer contains silicone rubber. 4. The sponge roller according to claim 1, wherein the cell diameter of the foamed elastic layer is 30 [mu]m or more and 150 [mu]m or less.