JP5797439B2 - Cleaning blade for image forming apparatus - Google Patents

Description

  The present invention relates to a cleaning blade for removing residual toner on the surface of a photosensitive member in an electrostatic image forming apparatus such as a plain paper copying machine, a plain paper facsimile machine, and a laser beam printer.

  As an elastic blade used in an image forming apparatus, a cleaning blade using a polyurethane elastomer is generally used. In recent years, spherical polymerization toners with small particle diameters have been used for high-quality image formation, and the purpose is to improve blade wear resistance and ensure cleaning properties when toners with such small spherical particle diameters are used. Such cleaning blades are known (Patent Documents 1 to 3, etc.).

  Patent Documents 1 and 2 aim to provide a cleaning blade having excellent wear resistance when a toner having a small spherical particle diameter is used, and a single layer made of polyurethane having a molecular weight between crosslinks adjusted to a specific range. A cleaning blade is disclosed. Patent Document 3 discloses a cleaning blade having a two-layer structure for the purpose of ensuring cleaning properties when a toner having a small spherical particle diameter is used, and the polyurethane constituting the edge layer has a certain range of hardness and resilience. A cleaning blade made of a polyurethane elastomer having elasticity is disclosed.

JP 2005-345637 A JP 2001-345651 A WO2008 / 078461 Publication

  However, as described in Patent Document 3, a single-layer cleaning blade having a relatively low molecular weight between crosslinks as disclosed in Patent Documents 1 and 2 and thus a cleaning blade having a high resilience is required in recent years. It is not possible to sufficiently meet the demand for further improvement in wear resistance due to the longer service life. The cleaning blade disclosed in Patent Document 3 has a large molecular weight between crosslinks of the edge layer-constituting polyurethane, and there is room for improvement in wear resistance. Photosensitivity by heat cycle (repeating high temperature and high humidity conditions and low temperature and low humidity conditions). There is room for improvement in the reduction of linear pressure in contact with the body.

  In view of the above-mentioned problems of the prior art, the present invention provides a cleaning blade that is excellent in wear resistance and cleanability in a low-temperature environment when polymerized toner is used, and in which the reduction in contact linear pressure with a photoreceptor due to heat cycle is improved. The purpose is to provide.

The cleaning blade of the present invention has a two-layer structure consisting of an edge layer that contacts and cleans the edge of the photosensitive member and a base material layer laminated integrally with the edge layer,
The polyurethane constituting the edge layer is selected from polycaprolactone polyol, polyethylene adipate, polybutylene adipate as a polyol compound, and at least one bifunctional polyester polyol having an average molecular weight (end group determination method) of 1500 to 3500, a chain extender. 1,4-butanediol, trimethylolpropane as the crosslinking agent, the diisocyanate compound is diphenylmethane diisocyanate (MDI), and the molecular weight Mc between crosslinks according to (Formula 1) is 2000 ≦ Mc ≦ 4500
And
The polyurethane constituting the base layer is a bifunctional polycaprolactone polyol having an average molecular weight (end group determination method) of 1500 to 3500 as a polyol compound, 1,4-butanediol (BD) as a chain extender, and trimethylol as a crosslinking agent. Propane (TMP) is used, the diisocyanate compound is diphenylmethane diisocyanate (MDI), and the molecular weight Mc between crosslinks according to (Formula 1) is 8000 ≦ Mc ≦ 15000
It is characterized by being.
(Formula 1) Mc = (total amount of polyurethane) / (Wt / Mt)
(Mt is the molecular weight of the crosslinking agent, Wt is the blending amount of the crosslinking agent)

  The cleaning blade having such a configuration is a cleaning blade that is excellent in wear resistance and cleanability in a low-temperature environment when polymerized toner is used, and in which the reduction in contact linear pressure with the photoreceptor due to heat cycle is improved.

  In the above invention, it is preferable that the polyurethane constituting the edge layer further contains a low molecular weight bifunctional polyester polyol having a molecular weight of 400 to 800 in an amount of 5 to 20% by weight of the total polyol compound.

  The cleaning blade having such a configuration is also a cleaning blade that is excellent in wear resistance and cleanability in a low-temperature environment when polymerized toner is used, and in which a decrease in contact linear pressure with the photoreceptor due to heat cycle is improved.

  The polyol compound constituting the edge layer of the elastomer blade made of polyurethane elastomer for the image forming apparatus of the present invention is selected from polycaprolactone polyol, polyethylene adipate, and polybutylene adipate, and has an average molecular weight (end group determination method) of 1500 to 500. 3500 at least one bifunctional polyester polyol is used. Moreover, the polyurethane which comprises a base material layer uses the bifunctional polycaprolactone polyol whose average molecular weight (end group quantitative method) is 1500-3500 as a polyol compound. These polyols all preferably have an average molecular weight of 3000 or less. Polyester polyol is used as the low molecular weight bifunctional polyol which is additionally used as the polyol compound constituting the edge layer constituting polyurethane. The molecular weight of the low molecular weight bifunctional polyol is 400 to 800, more preferably 500 to 700.

  In the edge layer, the ratio of the chain extender and the crosslinker that achieves the molecular weight between the crosslinks is preferably 1 to 4 in the weight ratio, and in the base material layer. It is preferable that the weight ratio of the crosslinking agent / chain extender is 0.2 to 0.4.

  The hardness of the polyurethane constituting the blade is 60 to 65, preferably 60 to less than 65 (Shore A) for the two-layer edge layer, and 65 to 75 (Shore A) for the base material layer. Further, the resilience of polyurethane constituting the blade is preferably 10% to 35% in the edge layer and 25% to 50% in the base material layer. In the cleaning blade of the present invention, the thickness of the edge layer is preferably 0.3 to 1.0 mm, and the thickness of the base material layer is preferably 1.0 to 2.0 mm.

  As a method of forming a polyurethane elastomer using the above-mentioned polyurethane elastomer raw material, both the edge layer and the base material layer can be produced by a prepolymer method or a pseudo prepolymer method. In the pseudo-prepolymer method, a part of the polyol compound (polyol P1) of the prepolymer component is reacted with an isocyanate component in advance to prepare a prepolymer (prepolymer production step), and the remaining polyol compound, if necessary. A polyol compound (polyol P2) containing a low molecular weight bifunctional polyol, a chain extender and a crosslinking agent are mixed to form a polyol composition (polyol composition production process), and the prepolymer and the polyol composition are mixed (mixing process). It is preferable to adopt a pseudo prepolymer method in which a reaction stock solution composition is prepared and the reaction stock solution composition is reaction-cured. The NCO / OH equivalent ratio (NCO index) in the curing reaction of the reaction stock solution composition is preferably 1.05 to 1.30.

  In the pseudo prepolymer method, a polyol P1 which is a part of a polyol compound is previously reacted with an isocyanate component to prepare a prepolymer, and the remaining polyol component (polyol P2) is mixed with a crosslinking agent and a chain extender. A polyol composition. The NCO / OH equivalent ratio in the prepolymer production process of the pseudo prepolymer method of the present invention is preferably 5-12. The ratio of the polyol P1 and the polyol P2 is 1.5 to 4.5, more preferably 2.0 to 4.0, in terms of a polyol P1 / polyol P2 molar ratio.

The blade for an image forming apparatus can be manufactured, for example, by a manufacturing method having the following molding process.
<1> Sheet Forming Method 1) Two kinds of reaction stock solution compositions are sequentially cast into a sheet shape and reacted and cured to form a raw sheet, which is cut (cutting step) into a blade. In sheet forming, a centrifugal forming method is generally used.
2) A blade is mounted on a base material (metal fitting) for mounting the blade on the image forming apparatus by bonding or the like.
<2> Direct molding method A base material (metal fittings, etc.) for mounting the blade on the image forming apparatus is arranged in the mold having the cavity of the shape of the blade to be molded as required, and reacts to the molding cavity. The stock solution composition is cast to form a blade or a blade unit in which the blade and the substrate are integrated. In this case, when the first layer is formed, a thin mold is used, or a predetermined mold is used to form a member having the same shape as the second layer with a polyurethane and a material having good releasability such as silicon resin. The first layer is formed by forming and accommodating this in a mold. After the first layer material is cured, the releasable member is removed, and the second layer forming raw material is injected and molded into this portion.

<Example of polyurethane elastomer sheet production>
(Examples 1-4, Comparative Examples 1 and 2)
MDI, which is a diisocyanate compound, and a polyol compound were reacted in a conventional manner at a blending ratio (numerical values are parts by weight) described in the column “Prepolymer” in Table 1 to obtain a prepolymer (pseudo prepolymer). Further, a polyol composition was prepared by mixing a polyol compound, a crosslinking agent, and a chain extender at a blending ratio described in the “Polyol composition” column of Table 1. This prepolymer and a polyol composition were mixed to obtain a reaction stock solution composition, a polyurethane elastomer sheet was prepared by centrifugal molding, and post-cure and aging were performed. Molding is performed by first forming a sheet having a thickness of 1.3 mm using the reaction stock solution composition for forming the base layer, and using the reaction stock solution composition for forming the edge layer when fluidity is lost. A sheet having a thickness of 0.5 mm was formed to obtain a two-layered sheet having a total thickness of 1.8 mm.

The polyurethane raw materials used are as follows.
PEA2000: Polyethylene adipate (average molecular weight 2000; number of functional groups f = 2)
PCL2000: Polycaprolactone diol with a linear glycol as an initiator (average molecular weight 2000; Daicel Chemical Industries)
PBA2000: polybutylene adipate (average molecular weight 2000; number of functional groups f = 2)
PCL1000: polycaprolactone diol with a linear glycol as an initiator (average molecular weight 1000; Daicel Chemical Industries)
PCL4000: polycaprolactone diol with side chain-containing glycol as an initiator (average molecular weight 4000; Daicel Chemical Industries)
PCL205: Polycaprolactone diol with a linear glycol as an initiator (average molecular weight 525; Daicel Chemical Industries)
PBA600: Polybutylene adipate (average molecular weight 600)
BD: 1,4-butanediol (chain extender)
TMP: Trimethylolpropane (crosslinking agent)
MDI: 4,4′-diphenylmethane diisocyanate

<Evaluation>
The polyurethane elastomer sheet produced above was cut to produce a cleaning blade having a width of 12.5 mm and a length of 326 mm, and adhered to a predetermined metal fitting to form a cleaning member. This cleaning member is mounted on IPSIO SPC821 (manufactured by Ricoh Co., Ltd.) which is a full-color printer / copier combined machine of electrostatic transfer process type using polymerized toner, and a certain test pattern is printed to provide abrasion resistance. Evaluation was performed.

  Abrasion resistance was evaluated by continuously forming 20,000 images in an N / N environment (23 ° C., 54% RH), and then continuously 20,000 in an L / L environment (10 ° C., 20% RH). After the sheet image was formed, the cleaning blade was removed and the edge portion was evaluated by the following method to determine the maximum wear depth (μm). The results are shown in the lower part of Table 1. The low-temperature cleaning property was visually evaluated based on the image after 20,000 continuous images were formed in an L / L environment. The evaluation results of the low-temperature cleaning property are indicated by ◯, those that are not practically used but are inferior in performance but are indicated by Δ, and those that are defective and cannot be practically used are indicated by ×.

(Measurement of wear cross section, maximum wear depth)
After the evaluation, the cleaning blade was cut in the width direction so that the cross section of the contact portion with the photosensitive member could be seen at both ends and the central portion, and the cross section was observed with a digital microscope VHX100 (Keyence). . The maximum wear depth is Y (μm) in FIG. t is the thickness of the entire cleaning blade, and the result in Table 1 is the maximum of the three measured values.

(Hardness / Rebound resilience)
The hardness was measured according to JIS K 6253, and the Shore A hardness at 23 ° C. was measured using a durometer hardness meter, and the resilience was measured at 23 ° C. according to JIS K 6255 (Lupke type). The measurement was performed on a sample obtained by stacking six polyurethane elastic sheets having a thickness of 1.8 mm obtained in the production example.
(Heat cycle test)
A strip-shaped sample is cut out from the polyurethane elastomer sheet prepared in Example 1, and a 50 mm marked line is put on it and set in an extension jig to extend 50%. In this state, it is held at 30 ° C. and 80% RH state (HH) for 12 hours from a normal temperature environment, and then held at 10 ° C. and 15% RH state (LL) for 8 hours over 2 hours. Thereafter, the temperature is changed to 30 ° C. and 80% RH over 2 hours. This HH-LL cycle of 24 hours for one cycle was repeated three times, then left for 24 hours in a room temperature environment, the sample was released from the extension jig, and the permanent elongation after 4 hours was measured.

<Evaluation results>
From the results shown in Table 1, the cleaning blades of Examples 1 to 4 had a small maximum wear depth, and therefore excellent abrasion resistance when using polymerized toner, and a clear image could be maintained for a long time. Also, it had excellent cleaning performance even in a low temperature environment. On the other hand, the cleaning blade of Comparative Example 1 corresponding to the example of Patent Document 1 was inferior to the cleaning blade of the present invention in both wear resistance and low temperature cleaning properties. In addition, the single-layer cleaning blade made of the polyurethane material of Example 1 of the present invention also has problems in wear resistance and low temperature cleaning properties when using the polymerized toner, and in particular, the low temperature cleaning properties are insufficient. there were. Further, the heat cycle test result of the sample of Example 1 was as excellent as a permanent elongation of 3.3%, and the change in cleaning property due to repeated heat shock at low temperature and high temperature was small.

Cross section showing maximum wear depth of cleaning blade after wear resistance evaluation

Claims (2)

A cleaning blade having a two-layer structure comprising an edge layer that contacts and cleans an edge with a photoreceptor and a base material layer laminated integrally with the edge layer,
The polyurethane constituting the edge layer is selected from polycaprolactone polyol, polyethylene adipate, polybutylene adipate as a polyol compound, and at least one bifunctional polyester polyol having an average molecular weight (end group determination method) of 1500 to 3500, a chain extender. 1,4-butanediol, trimethylolpropane as the crosslinking agent, the diisocyanate compound is diphenylmethane diisocyanate (MDI), and the ratio of the chain extender to the crosslinking agent is a crosslinking agent / chain extension by weight ratio. Agent = 1 to 4,
The molecular weight Mc between crosslinks according to (Formula 1) is 2000 ≦ Mc ≦ 4500.
And
The polyurethane constituting the substrate layer uses a bifunctional polycaprolactone polyol having an average molecular weight (end group determination method) of 1500 to 3500 as a polyol compound, 1,4-butanediol as a chain extender, and trimethylolpropane as a crosslinking agent. The diisocyanate compound is diphenylmethane diisocyanate (MDI), and the molecular weight Mc between crosslinks according to (Formula 1) is 8000 ≦ Mc ≦ 15000.
The cleaning blade characterized by being.
(Formula 1) Mc = (total amount of polyurethane) / (Wt / Mt)
(Mt is the molecular weight of the crosslinking agent, Wt is the blending amount of the crosslinking agent)   2. The cleaning blade according to claim 1, wherein the polyurethane constituting the edge layer further contains 5 to 20 wt% of a low molecular weight bifunctional polyester polyol having a molecular weight of 400 to 800 with respect to the total polyol compound.

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