Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
2000-07-31
2002-09-17
Cooney, Jr., John M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C521S086000, C521S091000, C521S099000, C521S110000, C521S122000, C521S134000, C521S142000, C521S154000
Reexamination Certificate
active
06451866
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a cured rubber body having a cellular structure and useful in a variety of applications not only in various general-purpose applications requiring a so-called spongy rubber such as puffs for spreading cosmetic compositions over the human skin but also in office-automation machines equipped with a spongy rubber roller such as laser beam printers and photocopying machines including development rollers, electrostatic charging rollers, toner-carrying rollers, toner-transfer rollers, cleaning rollers for photosensitive drums, referred to simply as cleaning rollers hereinafter, and the like. The spongy rubber of the invention is particularly suitable as a material for forming the rubber layer of a cleaning roller.
Following is a description of the background situations leading to the use of a spongy rubber roller in office-automation machines. In a laser beam printer or a photocopying machine, namely, it is always the case in toner transfer in the image-forming unit that not all of the toner particles are transferred onto the paper sheet but a substantial amount of the toner particles are left untransferred on the photosensitive drum necessitating provision of a recovery system for the remaining toner particles. If the toner-recovery system works incompletely, the printed matter obtained by a succeeding printing run is necessarily contaminated with the toner particles remaining on the photosensitive drum in the preceding run leading to blur of the printed images not to give a printed matter of high quality.
In view of this problem, it is conventional that a spongy rubber is employed for the rubber layer of a rubber roller such as cleaning rollers, development rollers, toner-transfer rollers and the like working smoothly for removal of the remaining toner particles deposited on the photosensitive drum, for development with fresh toner particles onto the photosensitive drum and transfer of the toner particles onto a paper sheet. The spongy rubber roller here implied is an integral elongated body consisting of a shaft of an electroconductive material including metals and alloys such as iron, aluminum, copper, stainless steels, zinc and brass or a shaft having a plating layer of these metals or alloys on the surface of an insulating rod and a layer of a spongy rubber coaxially formed on and around the shaft.
It is sometimes the case that, in these spongy rubber rollers, the rubber layer is required to have semiconductivity which is imparted to the rubber by compounding a rubber compound or, in particular, silicone rubber compound with a substantial amount of a conductivity-imparting agent such as carbon blacks. Since carbon blacks in general have an activity to inhibit curing of a silicone rubber curable with an organic peroxide as a curing agent, it is desirable that the silicone rubber compound is of the type which is free from the inhibitive effect of carbon blacks on curing such as those curable by the crosslinking mechanism involving the hydrosilation addition reaction. The most conventional blowing agent for forming the foamed cellular structure of the spongy rubber is azobisisobutyronitrile (AIBN). A spongy rubber body is obtained by heating the silicone rubber composition compounded with the curing agent and blowing agent in a hot-air oven, infrared oven, high-frequency induction heating oven and the like to effect simultaneous curing and foaming of the rubber composition under normal pressure.
As a major current in recent years, many of the office-automation machines are designed for the use of a toner having a decreased average particle diameter such as so-called polymerization toners. As a result of this shift toward finer toner particles, a new problem has arisen in conventional cleaning rollers currently under use that the average cell diameter of the spongy rubber layer of the roller, which is 20 &mgr;m or larger, is too large to comply with the decrease in the toner particle diameter so that cleaning of the photosensitive drum cannot be complete leaving some toner particles thereon unremoved adversely affecting the quality of the next printed matter. The “cell” of a spongy rubber here implied is the pore of the spongy rubber appearing on the surface and the average cell diameter, referred to simply as the cell diameter hereinafter, is calculated for 10 cells taken at random determining the cell diameter as the diameter of the largest circumcircle to the cell contour. Similarly, another problem is encountered in transfer rollers that the electric field on the spongy rubber layer is dependent on the cell diameter so that, when the cell diameter is too large, the image of the cells is transferred to the printed pattern.
With regard to development rollers, furthermore, the rubber layer on and around the metal shaft in a conventional development roller is formed not from a spongy rubber but from a solid, i.e. non-spongy, rubber in view of the duty of the development roller to put the toner particles uniformly onto the photosensitive drum. In order to comply with the demand for higher quality of printing and increase in the printing velocity, it is a requirement that the rubber layer of development rollers is formed from a rubber having a decreased rubber hardness. If the matter concerned is the rubber hardness alone, the problem can easily be solved by using a solid rubber of an inherently low rubber hardness but another problem must be solved in a development roller made from a low-hardness solid rubber that low-hardness rubbers in general exhibit a large permanent compression set resulting in a decrease in the durability of the rubber roller adversely affecting the printing quality in the long run.
Although it is possible even in the prior art method that a low-hardness spongy rubber having a cell diameter of about 150 &mgr;m can be prepared by adequately controlling the curing velocity and foaming velocity, it is a difficult matter to obtain a low-hardness spongy rubber having a rubber hardness not exceeding 40° Hs required for standard products of development rollers if not to mention that such a modification of the process conditions involves a serious disadvantage of a decrease in the productivity.
As regard to the application of spongy rubbers in the general industrial field, on the other hand, or, in particular, in relation to spongy rubber puffs used in cosmetic makeup for spreading a cosmetic composition over the skin, greatly diversified spongy rubbers are employed as the material of cosmetic puffs depending on the formulation and properties of the cosmetic compositions and preference of the respective users while a common problem must be solved in the spongy rubber materials for puffs in general. When the cell diameter of the spongy rubber puffs for spreading of a powdery foundation is too large, for example, a large bit of the foundation particles is held in a single pore of the spongy puff which cannot be spread over the skin with full smoothness and uniformity unless the foundation is spread to form a layer of a large thickness disregarding the unhealthy influences on the skin. Needless to say, a spongy cosmetic puff having cells of too coarse cell diameters is not preferred by consumers in respect of unpleasant touch feeling to the skin.
From the standpoint of giving a solution to the above described problems, spongy rubbers are required to have a cell diameter not exceeding 200 &mgr;m or, preferably, not exceeding 100 &mgr;m and a rubber hardness in the range from 10 to 40° Hs. In particular, the spongy rubber forming the rubber layer of development rollers is required to have a cell diameter not exceeding 50 &mgr;m.
SUMMARY OF THE INVENTION
The present invention accordingly has an object to provide a novel and improved spongy rubber having a cellular structure and free from the above described problems and disadvantages encountered in the prior art when the spongy rubber is used as a material of spongy rubber puffs for cosmetic makeup or as a material of spongy rubber rollers used in photocopying m
Kanai Takashi
Sakyo Yasuyuki
Cooney Jr. John M.
Shin-Etsu Polymer Co. Ltd.
Wenderoth Lind & Ponack LLP
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