JPH0341833B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a cleaning blade for an electrophotographic copying machine. In general, electrophotographic copying machines, especially electrophotographic copying machines that use plain paper as recording paper, develop the latent image formed on the photoreceptor with toner and transfer the toner image to the recording paper, thereby repeatedly printing the photoreceptor. Therefore, as a final step in a single electrophotographic process, it is necessary to clean the photoreceptor to remove residual toner adhering to it. As an example of such a cleaning method, a blade cleaning method is known in which a cleaning blade made of an elastic material is brought into contact with the photoreceptor and rubbed against the photoreceptor, and this method has the advantage of being very simple in structure. It's advantageous. Conventionally, known materials for blades used in this blade cleaning method include urethane rubber, silicone rubber, fluorine rubber, chloroprene rubber, butadiene rubber, etc. Among these, urethane rubber is more expensive than other rubbers. , its mechanical properties,
In particular, it is extremely useful in terms of its excellent wear resistance. Conventionally, in the cleaning blade, for example, urethane rubber obtained by reacting polyethylene adipate ester, polyoxypropylene glycol, caprolactone ester, etc. with polyisocyanate can be used as a material, as disclosed in JP-A-54-104840. Are listed. However, not all substances belonging to this group of substances are suitable as cleaning blades, regardless of their structure, molecular weight, etc. In fact, research conducted by the present inventors has confirmed that there are many products that do not necessarily provide good cleaning effects in terms of temperature stability, mechanical strength, moisture resistance, etc., and are therefore not suitable for practical use. has been done. Due to these circumstances, the cleaning blades currently in practical use are made from polyethylene adipate ester,
Polyisocyanate raw materials such as 4'-dimethylene diisocyanate and 1,5-naphthylene diisocyanate are used, which are reaction-cured by the action of a glycol such as 1,4-butanediol as a curing agent. This conventional cleaning blade (hereinafter referred to as "conventional blade") has the following drawbacks. The first drawback is that the characteristics of conventional blades change significantly due to changes in ambient temperature.
Inside an ordinary electrophotographic copying machine, a considerable amount of heat is emitted from the heat source for fixing, the lamp for exposing documents, the motor for driving the device, etc., and the cleaning blade itself generates heat due to friction with the photoreceptor. Therefore, the cleaning blade may be about 10 to 20 degrees Celsius higher than the environmental temperature outside the copying machine, while the environmental temperature usually changes within a temperature range of about 0 to 35 degrees Celsius, and the cleaning blade must not be cleaned when the copying machine is first used. In many cases, the blade is also at a temperature substantially equal to the environmental temperature, and as a result, the cleaning blade ends up cleaning within a relatively wide temperature range of, for example, 5 to 50°C. It is necessary to have a stable cleaning effect regardless of the temperature state, but urethane rubber, which is the material for conventional blades, has low temperature stability and has poor hardness, tensile strength, impact resilience, etc. It is subject to large temperature changes, and therefore cannot always provide a good cleaning effect. That is, in order to obtain a good cleaning effect in the blade cleaning method, the characteristics of the photoreceptor,
In relation to the characteristics of the developing toner and other process conditions, the cleaning blade has specific physical properties such as hardness (preferably 60 to 95 degrees on the JISK6301A scale hardness), tensile strength (preferably
Value according to JISK6301 is 250Kg/cm ² or more, more preferably 300Kg/cm ² or more), impact resilience (preferably
The blade must have physical properties such as 20% or more according to JISK6301, and the blade must meet certain conditions such as thickness, shape, and pressure against the photoreceptor during installation. If even one of the above physical property values changes significantly due to temperature change, the balance with other conditions will be disrupted, and the temperature conditions under which a good cleaning effect can be obtained will be limited, making it impossible to always perform the desired cleaning. It may also damage the photoreceptor. A second drawback is that conventional blades suffer from significant deterioration of their properties over time. For this reason, when the conventional plate is used after being stored for a long period of time after its commercialization, or when it is incorporated into a copying machine that makes fewer copies, the number of copies it can be used for is significantly limited. It has been determined that this deterioration of conventional blades over time is mainly caused by the progress of hydrolysis and crystallization of the urethane rubber material. The higher the humidity and temperature of the atmosphere surrounding the cleaning blade, the faster the hydrolysis progresses, and the more easily crystallization occurs due to hydrolysis. As this hydrolysis progresses, the physical properties of the urethane rubber decrease, and the strength as an elastic body decreases. When such development occurs, the cleaning blade becomes soft compared to when it is initially installed, so the actual contact area with the photoreceptor increases, and as a result, the pressing force per unit area against the photoreceptor decreases. It is believed that this reduces the force for scraping off the residual toner on the photoreceptor, causing poor cleaning. Additionally, if the urethane rubber of a conventional blade has undergone advanced hydrolysis, crystallization of the urethane rubber will progress if the conventional blade is used at a relatively low temperature, and as a result, the urethane rubber will become harder. It loses its flexibility and becomes brittle. If such a situation occurs, it will not be possible to achieve the condition in which the tip edge of the blade contacts the entire width of the photoreceptor with a uniform pressing force, which is essential in the blade cleaning method, and as a result, it will not be possible to perform good cleaning. It disappears. The present invention reduces and eliminates the above-mentioned drawbacks of conventional blades, has high stability against temperature changes and high thermal durability, and provides an electrophotographic copying machine that can stably perform good cleaning over a long period of time. The purpose is to provide cleaning blades. The above purpose is to use a cleaning blade for an electrophotographic copying machine that cleans the surface of a photoreceptor by rubbing it with the polycaprolactone ester containing a caprolactone ester component of 30% by weight or more and having an average molecular weight of 1000 to 4000. This is achieved by a cleaning blade for an electrophotographic copying machine made of urethane rubber obtained by reaction-curing with polyisocyanate. A feature of the urethane rubber that is the material of the cleaning blade of the present invention is that it is made of polycaprolactone ester containing a specific amount (30% by weight or more) of a caprolactone ester component. A cleaning blade made of urethane rubber having such characteristics has good physical properties, and has excellent physical properties such as temperature stability, hydrolysis resistance, and change over time during storage. The reason for this is not clear, but it is believed that the high reaction energy of the caprolactone ring results in the formation of urethane rubber with excellent properties as a cleaning blade. According to the research conducted by the present inventors, if the proportion of caprolactone ester component in the polycaprolactone ester is too low, the desired effect cannot be obtained, and it is necessary to use a polycaprolactone ester containing at least 30% by weight or more. A simple urethane bond obtained by reacting the polycaprolactone ester with a polyisocyanate often does not necessarily have excellent properties, and urethane rubber cured with a curing agent is preferable, especially its physical properties such as JISK6301A Hardness by scale is 60~
Urethane rubber with a tensile strength of 250 Kg/cm ² or more, more preferably 300 Kg/cm ² or more according to JISK6301, and a rebound resilience of 20% or more according to JISK6301 at 95 degrees is desirable. Polycaprolactone ester, which is a raw material for the urethane rubber that is the material of the cleaning blade of the present invention, has an average molecular weight in the range of 1,000 to 4,000. The average molecular weight is measured by adding an acetylating reagent consisting of acetic anhydride and pyridine to polycaprolactone ester, acetylating it at a specified reaction temperature and for a certain period of time, and then determining the amount of potassium hydroxide required to neutralize the acetic acid produced. This value is obtained by quantifying the terminal OH group and measuring the number average molecular weight. In addition, since polycaprolactone ester is actually obtained as a mixture of various components with different bonding states, it is not necessarily appropriate to define it by a specific structural formula, but if the polycaprolactone ester is represented by the general formula [] Then, it can be considered as something like the following. General formula [] HO-[X ₁ ] _-n R-[X ₂ ] _-o OH In the formula, X ₁ and X ₂ are cleavage residues of the caprolactone ring and may be the same or different, m, The sum of n is in the range of 2 to 35, and m:n is in the range of 1:3 to 3:1. R is a linking group for X ₁ and X ₂ and is a divalent organic group having about 300 or less carbon atoms. Further, the average molecular weight (molecular weight based on the above measurement method) of the compound represented by the general formula [] is 1000 to 4000, and the content of the caprolactone ester component (X ₁ +X ₂ ) is 30% by weight or more. In order to produce the polycaprolactone ester represented by the above general formula [], 1 mole of polymerization initiator is added to 2 to 35 moles of the same or different kind of caprolactone compound, and the polymerization is initiated at a temperature of 150 to 300°C. Cycloaddition polymerization is performed to obtain a polycaprolactone ester having an average molecular weight of 1000 to 4000. As the polymerization initiator, an organic compound having at least two active hydrogen groups such as -OH group, _-NH2 group, or -SH group is used. The caprolactone compound for forming the caprolactone ring-cleaved residue in the above general formula [] has a 3- to 7-membered lactone ring and has 6 carbon atoms, but the carbon atoms constituting the lactone ring further contain Also included are those to which a lower alkyl group such as a methyl group or an ethyl group is bonded. Specific examples of such caprolactone compounds include the following. Further, examples of the polymerization initiator for forming the linking group R in the general formula [] include the following compounds.

【table】

[Table] As commercially available polycaprolactone esters that can be advantageously used in the cleaning blade of the present invention, there are, for example, those with the following trade names. "NIAXPCP 0240" (manufactured by Union Carbide) "CATA 220" (manufactured by LaPolde) "ODX-640" (manufactured by Dainippon Ink) The above polycaprolactone esters react with polyisocyanate in the presence of a curing agent. The urethane rubber which is the material of the cleaning blade of the present invention is provided, and the following polyisocyanates can be mentioned as suitable examples.

【table】

[Front] Manufactured by DuPont

【table】

[Table] Specific examples of curing agents include the following. In order to manufacture the cleaning blade of the present invention made of urethane rubber using the above-mentioned polycaprolactone ester, polyisocyanate, and curing agent, it is preferable to proceed as follows. That is, polycaprolactone ester that has been dehydrated and polyisocyanate are mixed and heated at a temperature of 70 to 150°C for 10 minutes.
A urethane prepolymer is prepared by reacting for ~120 minutes, and the number of moles of isocyanate groups from the polyisocyanate and the number of moles of isocyanate groups from the polyester and curing agent and/or
Alternatively, make a liquid rubber composition by adding a curing agent at a ratio such that the ratio to the number of moles of amino groups is 1.00 to 1.30, and then inject this rubber composition into a centrifugal casting machine kept at a temperature of, for example, about 140°C. do. Figure 1 shows an example of a centrifugal casting machine, in which 1 is a heating chamber, 2 is a heating fluid flow path for heating the heating chamber 1, 3 is a heat insulating material layer, 4 is an opening/closing door, and 5 is a cylindrical rotor. , 6 is a drive shaft, and 7 is a motor. The rubber composition is injected into the rotor 5 which is rotating at high speed, and is uniformly spread over the casting surface by the inner peripheral surface of the rotor 5 due to the centrifugal force caused by the rotation. A cylindrical membrane-like body 8 is spread out to a thickness of
(indicated by a chain line) is formed. This film-like body 8 is solidified as the crosslinking by the curing agent progresses, and the thus formed solidified urethane rubber layer is peeled off from the casting surface, and then heat-treated and aged for several days to form a rubber plate for a blade. This rubber plate is cut to meet the specifications of the intended electrophotographic copying machine to produce a cleaning blade. The physical properties of the rubber plate obtained in this way, namely the hardness, are
60-95 degrees on JISK6301A scale, tensile strength is
JISK6301: 250Kg/cm ² or more, preferably 300Kg/
cm ² or more, and rebound resilience is preferably 20% or more according to JISK6301. In addition to the above-mentioned centrifugal casting method, there are other methods, such as injecting and solidifying into a mold in the shape of a cleaning blade, or press-forming with such a mold.
Any of these methods can advantageously produce the cleaning blade of the present invention made of urethane rubber. As mentioned above, in comparison with conventional blades, the cleaning blade of the present invention has a urethane rubber obtained by using polycaprolactone ester instead of polyethylene dipate ester, etc., which is a polyol raw material for urethane rubber, which is the material of conventional blades. It is made of rubber, and as is clear from the explanation of the examples below, it has good physical properties as a cleaning blade, and has small changes in physical properties such as elasticity due to temperature changes, so it is temperature stable. It is large in size, has great durability in a high-humidity, high-temperature atmosphere, and exhibits little deterioration over time, so that it can be used as a cleaning blade for electrophotographic copying machines to stably perform good photoreceptor cleaning over a long period of time. The kneading blade of the present invention is used, for example, in the following manner. That is, in a repeat transfer type electrophotographic copying machine,
For example, a rotating selenium photoreceptor drum is charged and exposed to form an electrostatic charge image, and this is developed with toner to form a toner image, which is then electrostatically transferred to transfer paper, for example, to form a transferred image. Form. On the other hand, since residual toner adheres to the selenium photoreceptor drum, after erasing the charge on the drum that causes this toner to adhere, a cleaning blade is brought into contact with the selenium photoreceptor drum surface to clean the residual toner. Then, the next image forming cycle is performed. The cleaning blade is held by a holding member and preferably faces the selenium photoreceptor drum surface with a pressing force of, for example, 15 to 25 g/cm so as to face upstream. It may be brought into contact with. EXAMPLES The present invention will be specifically explained below with reference to Examples, but the embodiments of the present invention are not limited thereto. Example According to what is shown in Table 1, caprolactone and a polymerization initiator were measured and mixed, and the mixture was heated at a temperature of 150 to 350°C.
A total of 10 types of polycaprolactone esters PLE1 to PLE10 were synthesized by addition polymerization for 30 to 180 minutes.

【table】

[Table] For these 10 types of polycaprolactone ester and polyethylene adipate ester,
According to what is shown in Table 2, polyisocyanate was added and reacted at a temperature of about 70°C for 100 minutes to synthesize a polyurethane prepolymer, and a required amount of crosslinking agent was further added thereto and reacted at a temperature of 120°C for 2 minutes, Note that the rubber composition that is in a liquid state is
It is injected into the rotor of the centrifugal casting machine shown in the figure, which is kept at a temperature of around 140°C, and the rotor is rotated at approximately 1000 revolutions per minute, continuing to rotate for 20 to 120 minutes to form a solidified rubber layer. was peeled off, taken out, heat treated in a heating furnace at a temperature of approximately 140°C for 180 minutes, and then aged for 6 to 8 days at room temperature, resulting in a total of 11 types of urethane rubber plates UR1 to UR11 in a cylindrical shape with an inner diameter of 204 mm. .

【table】

[Table] When the thickness distribution of these urethane rubber plates was investigated, the errors were all within ±15 μm. These urethane rubber plates thus obtained were cut according to the specifications of an electrophotographic copying machine "U-Bix3000" (manufactured by Konishiroku Photo Industry Co., Ltd.) to obtain a total of 11 types of cleaning blades CB1 to CB11. Among the above 11 types of cleaning blades,
CB2, CB3, CB6 to CB10 are according to the present invention, but CB1 has an average molecular weight of polycaprolactone ester PLE1 of its urethane rubber UR1.
800 is too small, CB4 is too large at 4500,
CB5 is the polycaprolactone ester PLE5 of the urethane rubber UR5 whose caprolactone ester component content is as low as 25% by weight, CB
Material No. 11 is made of urethane rubber obtained using polyethylene adipate ester "Desmofene 2000M" (manufactured by Bayer), which has been put into practical use. Each of these cleaning blades CB1 to CB1
1 was subjected to forced deterioration for 25 days at a temperature of 70°C and a relative humidity of 100%.
Bix3000" was installed and copy operations were performed under conditions of a temperature of 20°C and a relative humidity of 60%, and the cleaning performance was investigated. The results are shown in Table 3.

【table】

[Table] Also cleaning blades CB1 to CB6, CB
Copying operations were performed using CB 8 to CB 11 under various environmental conditions shown in Table 4 to examine the cleaning performance. The results are also shown in Table 4. The attachment of each cleaning blade to the electrophotographic copying machine is as shown in FIG.
The angle made with the surface of 1 is 160 with respect to the upstream surface.
This was carried out by holding it in the holder 20 so that the pressing force F was 25 g/cm. In FIG. 2, 12 is a charging device, 13 is a document light image exposure mechanism, 14 is a developer, 15 is a paper feed roller, P is a transfer paper path, 16 is a transfer electrode, 17 is a separation electrode, and 18 is a charger. The erasing exposure mechanism and 21 indicate a toner collection container. From the above results, it can be seen that when the cleaning blade of the present invention is attached to a repetitive transfer type electrophotographic copying machine and used for image formation, it is particularly excellent in terms of aging, heat resistance, moisture resistance, etc. Next, the cleaning blades CB1 to CB6,
For each of CB8 to CB11, heat them at a temperature of 70
Changes in hardness and tensile strength over time when stored under conditions of 100% relative humidity and 100% were examined at three stages: initially, after 15 days, and after 25 days.
The results are shown in Tables 5 and 6.

【table】

【table】

[Table] Next, the cleaning blades CB1 to CB3,
For each of CB6, CB8 to CB11, these were heated at a relative humidity of 60% and a temperature of 5℃, 20℃, 35℃ and 50℃.
Changes in impact resilience were examined when stored for 1 hour under each condition. The results are shown in Table 7.

[Table] From Table 5 above, it can be seen that the cleaning blade using caprolactone ester has a smaller change in hardness over time compared to the conventional cleaning blade CB11 using polyethylene adipate ester, especially this conventional cleaning blade CB11. It can be seen that the hardness after 25 days was 56 degrees, which is below the lower limit of 60 degrees of hardness normally required for cleaning blades, making it impractical. Furthermore, from Table 6, even if the cleaning blade uses caprolactone ester, the average molecular weight of the caprolactone ester is less than 1,000 (Cleaning Blade CB1), the cleaning blade (CB4) is more than 4,000, and the caprolactone ester component in the polycaprolactone ester is 30% by weight. Cleaning blades with a tensile strength of less than 250 kg/cm 2 are already insufficient in tensile strength at the initial stage, and may fall below the lower limit of 250 kg/cm ² normally required for cleaning blades, making them unsuitable for practical use. I can see that it is something. In contrast, the cleaning blade of the present invention
It can be seen that CB2, CB3, CB6, CB8 to CB10 have excellent physical properties with little change in tensile strength over time even after 25 days at high temperature and high humidity, and can be suitably used for practical use. Also, conventional cleaning blades using polyethylene adipate ester
It can be seen that although CB11 had sufficient tensile strength at the initial stage, it significantly decreased after 25 days and could not be put to practical use. Also, from Table 7, cleaning blade CB with an average molecular weight of caprolactone ester of less than 1000
1 and the conventional cleaning blade CB11 using polyethylene adipate ester, the impact resilience changes significantly with temperature changes, and at a temperature of 5°C, the impact resilience is far above the lower limit of 20 kg/cm ² normally required for cleaning blades. It can be seen that the result is too low to be of practical use. On the other hand, the cleaning blades CB2, CB3 of the present invention,
It can be seen that CB6, CB8 to CB10 can be suitably used for practical use even at a low temperature of 5°C, although there are some changes in rebound resilience with respect to temperature changes.

[Brief explanation of drawings]

FIG. 1 is an explanatory sectional view of a centrifugal casting machine that can be suitably used for manufacturing the cleaning blade of the present invention, and FIG. 2 is an explanatory view showing a mode of use of the cleaning blade. DESCRIPTION OF SYMBOLS 1...Heating chamber, 2...Heating fluid flow path, 3...Insulating material layer, 4...Opening/closing door, 5...Cylindrical rotor, 6
... Drive shaft, 7 ... Motor, 11 ... Photosensitive drum, 12 ... Charging device, 13 ... Original light image exposure mechanism, 14 ... Developing device, 15 ... Paper feed roller, P
... Passageway, 16 ... Transfer electrode, 17 ... Separation electrode, 18 ... Exposure mechanism for charge erasing, 19 ... Cleaning blade, 20 ... Holder, 21 ...
Toner collection container.

Claims (1)

[Claims] 1. In a cleaning blade for an electrophotographic copying machine that cleans the surface of a photoconductor by rubbing it against the surface, a polycaprolactone ester containing a caprolactone ester component of 30% by weight or more and having an average molecular weight of 1000 to 4000 and a polyisocyanate are used. A cleaning blade for an electrophotographic copying machine, characterized in that it is made of urethane rubber obtained by reaction curing.