JPH0126065B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention involves attaching toner to an electrostatic latent image formed on a latent image carrier (photoreceptor) of an electrophotographic copying machine,
This relates to a blade used to clean toner remaining on the surface of a photoreceptor after being transferred to a sheet such as paper by rubbing against the surface of the photoreceptor. Properties required of a cleaning blade include high mechanical strength, small changes in various properties due to temperature, excellent hydrolysis resistance, and excellent ozone resistance. Polyethylene adipate ester is currently used as a polyol raw material for polyurethane used in cleaning blades, but it is difficult to say that polyurethane using this polyol fully satisfies the above-mentioned properties. In particular, the large temperature dependence and poor hydrolysis resistance cause considerable problems. Inside an electrophotographic copying machine, a large amount of heat is emitted from the exposure lamp, fixing device, etc.
It is normal to have a high temperature of 20℃, and the environmental temperature varies from 0 to 35℃, from low humidity and low temperature in winter to high humidity and high temperature in summer, so these changes in temperature and humidity will affect the characteristics of the blade. It is a practical problem if the value changes significantly. Polyurethane rubber is significantly different from other general rubbers in that its mechanical and physical properties are mainly determined by intermolecular cohesive forces, so its properties change significantly when the temperature changes. In particular, the temperature dependence is largely controlled by the type of polyol forming the soft segment. The present invention solves the above problems by using polyurethane containing 1,6-hexanediol and neopentyl glycol in a molar ratio of 9/1 to 5/5 as polyol raw materials for polyurethane rubber. This is what I did. The polyurethane rubbers used in the following tests were polyethylene adipate, adipate of 1,6-hexanediol and neopentyl glycol, and diphenylmethane-4,4'- as the isocyanate.
Diisocyanate was used as the main raw material, and 1,4-butanediol and trimethylolpropane were used as curing agents.

[Table] As shown in the table above, polyurethane rubber based on polyethylene adipate has a large change in impact resilience and Young's modulus depending on temperature. At 0°C, elasticity is extremely low and adhesion with the photoreceptor becomes a problem. Young's modulus is much higher than at room temperature, so the plate pressing pressure becomes higher and the contact angle becomes larger than the designed value, causing abnormal noise. This can lead to poor cleaning. At 50 degrees Celsius, the repulsion elasticity becomes too high, causing bounce phenomena and abnormal noises.A decrease in Young's modulus is caused by a decrease in the contact pressure between the cleaning blade and the photoconductor, which reduces the back force, which causes the toner to contact the cleaning blade. It becomes easier to pass between the photoreceptors. On the other hand, in the polyurethane rubber of the present invention using 1,6-hexanediol and neopentyl glycol in a molar ratio of 9/1 to 5/5, the impact resilience and Young's modulus change with temperature compared to that of the polyethylene adipate-based polyurethane rubber. It is considerably smaller than polyurethane rubber, and almost satisfactory results can be obtained in the range of 0 to 50°C. However, when 1,6-hexanediol and neopentyl glycol were used in a molar ratio of 3:7, the impact resilience at 50°C was high and an abnormal noise was generated. Furthermore, due to the increased number of methyl groups, the physical properties are poor and it is unsuitable for blades. When only 1,6-hexanediol is used, it has a strong tendency to crystallize and therefore has a sufficiently high mechanical strength, but its low temperature properties deteriorate. 1,6-
By using neopentyl glycol in combination with hexanediol, the crystallization effect of the methyl group is produced, improving low-temperature properties and reducing changes in properties due to temperature. Another disadvantage of polyurethane rubber is its poor water resistance. For urethane rubber based on polyethylene adipate ester, it has been observed that hydrolysis has progressed in cleaning blades that have been manufactured for 2 to 4 years, although this varies depending on the usage conditions. Ru. This is mainly due to the molecular cleavage of ester bonds, which progresses gradually at first, but once it has progressed to a certain extent, the organic acid produced by hydrolysis acts as an accelerator, leading to rapid deterioration. Those that have undergone advanced hydrolysis become soft in the summer and lack firmness, making it impossible to obtain a sufficient cleaning effect, and in the winter, the elasticity decreases due to crystallization, resulting in insufficient cleaning. In order to compare hydrolysis resistance, a small amount of water was placed at the bottom of a sealed container, the sample was hung above it so as not to come into direct contact with the water, and the sample was kept at 70℃ for 35 days.The physical properties obtained were as follows: The changes in are shown in the table below.

[Table] As shown in the above table, 1,6-hexanediol and neopentyl glycol in a ratio of 9:1 has much better hydrolysis resistance than polyurethane rubber based on polyethylene glycol adipate ester. The reason for this is thought to be that the concentration of ester bonds is lower in the present invention and steric hindrance is caused by the methyl group of neopentyl glycol. Conventionally, injection molding is a common processing method for manufacturing cleaning blades, and
It is obtained by adding a curing agent to a prepolymer made by reacting polyester with polyisocyanate that has been dehydrated at 140°C and carrying out a crosslinking reaction. In this case, if the molecular weight of the polyester is less than 1000, the reaction rate in the crosslinking reaction with the addition of a curing agent will be too fast and injection molding will not be completed completely, and if the molecular weight of the polyester is more than 4000, the viscosity of the polyester will be too high. In addition, the crosslinking reaction is too slow, resulting in slow curing, and the defoaming is insufficient, resulting in bubble defects on the blade surface. As described above, according to the present invention, it is possible to provide a durable cleaning blade whose physical properties change little due to temperature.

Claims (1)

[Claims] 1 From urethane rubber, which is the reaction product of polyisocyanate and polyester with an average molecular weight of 1000 to 4000, consisting of glycol and adipic acid with a molar ratio of 1,6-hexanediol to neopentyl glycol of 9/1 to 5/5. A cleaning blade for electrophotographic copying machines used to rub and clean the surface of a photoreceptor.