JPH0337189B2 - - 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,
It relates to a blade used to clean toner remaining on the surface of a photoreceptor of a transfer machine by rubbing it against the surface of the photoreceptor on a sheet such as paper. 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, problems arise due to the large temperature dependence and poor hydrolysis resistance. Inside an electrophotographic copying machine, a large amount of heat is emitted from the exposure lamp, fixing device, etc.
The temperature of Ontsu is 20℃, and the environmental temperature ranges from low and humid in winter to high and humid in summer.
Since the temperature changes from 0° to 35°C, it would be a practical problem if the characteristics of the blade changed significantly due to such changes in temperature and humidity. Especially recently, electrophotographic copying machines have become widespread,
When devices are installed in ordinary homes, the above-mentioned problems become impossible to ignore. In other words, due to the fact that ordinary homes are not necessarily air-conditioned in the same way as offices,
Temperature dependence is considered to be an important property. In addition, if the copy polyurethane is small, the blade will wear less, so there is a greater possibility that the blade will be used for a long period of time without being replaced. For this reason, in blades using conventional polyethylene glycol adipate, the lifespan due to progress of hydrolysis tends to be longer than the lifespan due to wear. Polyurethane rubber is significantly different from other general rubbers in that its mechanical and physical properties depend primarily on intermolecular collective 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 can solve the above problems by using a polyurethane rubber using glycol with a molar ratio of 1,6 hexanediol and 1,4 butanediol of 9/1 to 1/9 as a polyol raw material for the polyurethane rubber. This is what I did. The polyurethane rubber used in the following tests was mainly made of polyethylene adipate, adipate of 1,6-hexanediol and 1,4-butanediol, and diphenylmethane-4,4'-diisocyanate as the isocyanate, and 1,
The hardness was adjusted to a desired level by using a combination of 4-butadiol and trimethylolpropane.

[Table] Table 1 shows the temperature dependence of rebound resilience and Young's modulus. As can be seen from Table 1, the impact resilience and Young's modulus of urethane rubber made of polyethylene adipate vary greatly with temperature. For example, at 0° C., the rebound resilience is extremely low and the Young's modulus is much higher than at room temperature, which causes the blade and photoreceptor to come into too close contact and the blade pressing pressure to become high, causing abnormalities and poor cleaning. or. At 50°C, the rebound resilience is higher than at room temperature, which also causes abnormal noise and poor cleaning. On the other hand, the molar ratio of 1,6-hexanediol and 1,4-butadiol of the present invention is from 9/1 to
For the urethane rubber used in the range of 1/9, the change in impact resilience and Young's modulus due to temperature is considerably smaller than that of polyurethane rubber based on polyethylene adipate, and almost satisfactory results can be obtained in the range of 0° to 50°C. When only 1,6-hexanediol and 1,4-butanediol are used, crystallization is strong;
Therefore, although the mechanical strength is sufficiently high, the temperature change characteristics are deteriorated. Another disadvantage of polyurethane rubber is its poor water resistance. For urethane rubber based on polyethylene adipate ester, it is observed that hydrolysis has progressed when 2 to 4 years have passed since the cleaning blade was manufactured, although this varies depending on the usage conditions. . 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,
Due to lack of elasticity, sufficient cleaning action cannot be obtained, and in winter, elasticity decreases due to crystallization, resulting in insufficient cleaning. In order to compare the 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. Changes in physical properties are shown in the table below.

[Table] As can be seen from Table 2, the ratio of 1,6-hexanediol to 1,4-butanediol of 9/1 is extremely resistant to hydrolysis compared to polyurethane rubber based on polyethylene glycol adipate ester. It can be seen that the reason for this is that the ester bond concentration according to the present invention is lower. Traditionally, injection molding is the most common processing method used to manufacture cleaning blades.
It is obtained by adding a curing agent to a prepolymer made by reacting polyester that has been dehydrated at 140°C with polyisocyanate 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.If the molecular weight of the polyester is more than 4000, the viscosity of the prepolymer will increase. If the temperature is too high, the crosslinking reaction is too slow, curing is slow, 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 are less likely to change due to temperature.

Claims (1)

[Claims] 1 Consists of urethane rubber which is a reaction product of polyester and polyisocyanate with an average molecular weight of 1000 to 4000, consisting of glycol and adipic acid in which the molar ratio of 1,6 hexanediol to 1,4 butadiol is 9/1 to 1/9. A cleaning blade for electrophotographic copying machines used to rub and clean the surface of a photoreceptor.