JPH052148B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a cleaning blade for an electrophotographic copying machine that uses plain paper as a recording paper, and that cleans the surface of a photoreceptor by rubbing the same. (Prior Art) According to an electrostatic electrophotographic copying machine that uses plain paper as recording paper, an electrostatic latent image is generally created by applying an electrostatic charge to the surface of a photoreceptor by discharging and then exposing an image thereon. Next, toner with opposite polarity is attached to the electrostatic latent image and developed, and the toner image is transferred to recording paper.Finally, the recording paper to which the toner image has been transferred is heated, and the toner image is transferred to the recording paper. Copying is done by fixing the image onto recording paper. Therefore, in order to sequentially copy onto multiple sheets of recording paper, in the above steps,
After the toner image is transferred from the photoconductor to the recording paper, it is necessary to remove the toner remaining on the surface of the photoconductor, and one known method for removing this is the blade cleaning method, which cleans the photoconductor by rubbing it. ing. Various rubbers have been used for the blade material for this blade cleaning method, but urethane rubber is particularly preferred because it has excellent mechanical strength such as abrasion resistance. . Such urethane rubber is generally a combination of commercially available polyols, such as polyester polyols such as polyethylene adipate ester polyol, polyethylene butylene adipate ester polyol, and caprolactone ester polyol, or polyether polyols such as polyoxypropylene glycol, and polyisocyanate. Manufactured by reaction. However, the urethane rubbers produced from these commercially available polyols cannot be said to have sufficient properties such as temperature stability, heat and humidity resistance, and mechanical strength. In particular, the temperature inside the electrophotographic copying machine where the cleaning blade is installed is large. For example, when the environmental temperature changes in the range of -5 to 30°C, the temperature inside the electrophotographic copying machine is usually 10 to 20°C higher than the ambient temperature. Therefore, the cleaning blade is substantially exposed to temperature changes of 5 to 50°C. For this reason, with conventionally used urethane rubber, its physical properties such as hardness and elasticity decrease with temperature changes, making it difficult to maintain constant physical properties over a wide temperature range. In addition, because conventional urethane rubber does not have sufficient heat and humidity resistance, it undergoes hydrolysis in high-temperature, high-humidity environments, and crystallization progresses as a result, resulting in the hardness, tensile strength, and elasticity required for cleaning blades. The cleaning blade will no longer be able to perform its functions satisfactorily. Such changes are accelerated as temperature and humidity become higher, and progress over time regardless of whether or not an electrophotographic copying machine is used. In order to solve the above problems, for example,
No. 59-30574 uses a specific polycaprolactone ester as the polyol, and JP-A No. 59-9147 uses a polyol obtained from adipic acid and a mixture of hexanediol and neopentyl glycol in specified proportions. It is disclosed that the durability of the cleaning blade, such as temperature stability and heat-and-moisture resistance, can be improved by doing so. (Objective of the Invention) Unlike these cleaning blades in which the type of polyol is limited, the present inventors have developed a polyol with a ratio of weight average molecular weight (Mw) to number average molecular weight (Mn) (Mw/Mn). By using a substance with a defined molecular weight distribution (hereinafter sometimes simply referred to as molecular weight distribution) of 2 or less,
It was discovered that a cleaning blade with good temperature stability and little deterioration over time can be obtained, leading to the present invention. (Structure of the Invention) The cleaning blade for an electrophotographic copying machine of the present invention comprises a polyol and a polyisocyanate having a molecular weight distribution in which the ratio of weight average molecular weight (Mw) to number average molecular weight (Mn) (Mw/Mn) is 2 or less. It is characterized by being made of urethane rubber made by reacting with. Polyols used in the present invention include ethylene glycol, butylene glycol,
Polyester polyols consisting of glycols such as diethylene glycol, 1,5-pentanediol, 1,6-hexanediol, or neopentyl glycol alone or in mixtures and divalent organic acids having 2 to 6 carbon atoms, such as polyethylene adipate ester polyols. , polyethylene butylene adipate ester polyol, polycaprolactone ester polyol obtained by ring-opening polymerization of caprolactone, polycarbonate ester polyol,
Polyether polyols such as poly(oxytetramethylene) glycol, polyoxypropylene glycol and the like can be mentioned. In the present invention, the above polyol needs to have a molecular weight distribution of 2 or less, preferably in the range of 1.4 to 1.8. The molecular weight distribution of this polyol can be calculated, for example, from molecular weight measurement using the GPC method. The polyisocyanate to be reacted with the polyol is not particularly limited, but includes tolylene diisocyanate, diphenylmethane-4,4'-diisocyanate, naphthalene-1,5-diisocyanate,
Representative examples include hexamethylene diisocyanate and isophorone diisocyanate. The cleaning blade according to the present invention is made of polyurethane obtained from the above-mentioned polyol and polyisocyanate, but in order to impart the necessary hardness to the cleaning blade, a curing agent is further used in the reaction between the above-mentioned polyol and polyisocyanate. It will be done. As a curing agent, ethylene glycol, 1,4-butanediol,
2,3-butanediol, 1,1,1-trimethylolpropane, triisopropanolamine,
3,3'-dichloro-4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, hydroquinone-bis(β-hydroxylethyl) ether, and the like are used. The cleaning blade according to the present invention is manufactured using a polyol, a polyisocyanate, and a curing agent as described above according to a conventional method. Prior to reacting the polymer with the curing agent, it may be subjected to an annealing treatment, which, depending on the polyol used, provides better durability and better cleaning performance. Next, a preferred example of the method for manufacturing the cleaning blade of the present invention will be described. First, a dehydrated polyol with a molecular weight distribution of 2 or less, preferably 1.4 to 1.8, and a polyisocyanate are mixed, and a polyisocyanate with a molecular weight distribution of 70 to 150 is mixed.
React for 10-180 minutes at a temperature of °C. Next, a curing agent is added to the obtained urethane prepolymer to prepare a liquid rubber composition. The curing agent is blended with the urethane prepolymer so that the ratio of the number of moles of isocyanate groups in the polyisocyanate to the number of moles of hydroxyl groups or amino groups in the polyol and curing agent is 1.00 to 1.50. The liquid rubber composition thus obtained is formed into a plate shape by, for example, injection molding, extrusion molding, centrifugal casting, or by casting into a desired mold, and then heat-treated and aged. and use it as rubber for cleaning blades. The plate-shaped cleaning blade rubber thus obtained is cut to meet the specifications of the electrophotographic copying machine used and used as a cleaning blade. Furthermore, as mentioned above, depending on the polyol used, it is preferable to subject the urethane prepolymer to an annealing treatment. Afterwards, a curing agent is added and reacted. For example, annealing treatment can be applied to urethane prepolymer
At 100-150°C, usually for several hours, e.g. 1-6
This is done by holding it for a while. Through such annealing treatment, the cleaning performance of the cleaning blade obtained depends on the number of copies.
Improved by about 20%. (Effects of the Invention) As described above, the cleaning blade of the present invention is made of urethane rubber manufactured using a polyol with a molecular weight distribution of 2 or less, and when a polyol with a molecular weight distribution outside the range of the present invention is used. In comparison, it has excellent mechanical properties, temperature stability, and resistance to changes in physical properties over time, and therefore provides stable cleaning performance when installed in an electrophotographic copying machine.
The number of copies made until the cleaning blade is replaced is also significantly increased. (Example) Examples of the present invention are shown below. Example (1) Preparation of polyol Table 1 shows the type, number average molecular weight, and molecular weight distribution (Mw/
Mn). Polyols other than Po1, 7, 9, 10, and 11 were specially prepared in the present invention. (2) Preparation of urethane rubber and production of cleaning blade Polyisocyanate was added to each of the above polyols in the proportions shown in Table 2, and reacted at 80°C for 120 minutes to obtain a urethane prepolymer.
Add the specified amount of curing agent as shown in the table and heat to 110℃.
The mixture was mixed for 2 minutes to react. The obtained liquid rubber composition was injected into a mold that had been preheated to about 150°C, and after 2 hours, the solidified rubber plate was taken out of the mold and heat treated in a heating furnace at a temperature of 120°C for 8 hours.
After aging at room temperature for 7 days, urethane rubber plates Pu1 to Pu13 with a thickness of 3.0 mm were obtained. Each urethane rubber plate was cut according to the specifications of an electrophotographic copying machine "Ricoh FT-4060" (Ricoh Co., Ltd.) to obtain cleaning blades FT1 to FT13. (3) Changes in the physical properties of cleaning blades over time For FT1 to FT13 obtained as described above, changes in tear strength and permanent elongation over time when stored at a temperature of 50℃ and a relative humidity of 85% are initialized. , after 28 days and after 56 days. Tear strength was determined using JIS B type dumbbells, and permanent elongation was determined using JIS No. 1 dumbbells.
It was measured according to the vulcanized rubber physical test method specified in JISK6301. The results are shown in Tables 3 and 4. For example, when the polyol is polyethylene adipate, a cleaning blade having a molecular weight distribution according to the present invention is FT2 to FT5, which is clearly compared to a comparative product FT1 using a commercially available polyol whose molecular weight distribution is outside the range of the present invention. Even after 56 days had passed, the rate of change over time in both tear strength and permanent elongation was small. Similar trends are observed for other polyols as well. (4) Cleaning performance of cleaning blades Next, each of the cleaning blades FT1 to FT13 was cleaned under the environmental conditions of a temperature of 35℃ and a relative humidity of 85%.
The cleaning performance was evaluated by the number of copies made until a defect occurred by attaching it to a Ricoh FT-4060 and performing copying operations. Rating is 40000
Based on the number of copies, if the defect occurred before 40,000 copies, mark it as ×, if the defect occurred between 40,000 and 70,000 copies, mark △, if the defect occurred after 70,000 copies, mark ○, and if it was good until 80,000 copies. stopped copying at that point. The results are shown in Table 5. For example, when the polyol is polyethylene adipate, cleaning blades FT2 to FT5 using polyols having a molecular weight distribution according to the present invention all have excellent cleaning performance, but cleaning blade FT1 whose polyol molecular weight distribution is outside the range of the present invention. has poor cleaning performance. Similarly, when polyethylene butylene adipate is used as the polyol, the cleaning performance of the inventive product FT6 is significantly improved compared to the comparative product FT7.

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[Table] Poly-ε-
Even when caprolactone is used, the cleaning performance of the product FT8 of the present invention is significantly improved compared to the comparative product FT9. When using poly(oxytetramethylene) glycol as the polyol, depending on the type of polyisocyanate and curing agent used,
Comparative product FT10, although cleaning performance is slightly different.
The cleaning performance is significantly improved in the product FT12 of the present invention and the product FT13 of the present invention as compared to the comparison product FT11.

Claims (1)

[Claims] 1. An electron characterized by being made of a urethane rubber made by reacting a polyol with a polyisocyanate having a molecular weight distribution in which the ratio of weight average molecular weight (Mw) to number average molecular weight (Mn) (Mw/Mn) is 2 or less Cleaning blade for photocopy machines.