The above aspects and features of the present invention will be more apparent by describing certain exemplary embodiments of the present invention with reference to the accompanying drawings, in which:
Certain exemplary embodiments of the present invention will now be described in greater detail with reference to the accompanying drawings.
The matters defined in the description such as a detailed construction and elements are provided to assist in a comprehensive understanding of the embodiments of the invention and are merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. Also, descriptions of well-known functions and constructions are omitted for clarity and conciseness.
The conductive resilient member 13b in one preferred embodiment has a density of about 60 kg/m3 to 120 kg/m3, and an outer diameter of about 8.0 mm to 10.0 mm.
The conductive resilient member 13b as prepared is formed or cut into a cylindrical shape to have a desired outer diameter. In order to insert the shaft 13a into the conductive resilient member 13b, a shaft-shaped hole is formed in the center of the conductive resilient member 13b. The shaft 13a desirably has an outer diameter of about 4.0 mm to 6.0 mm, and thus the shape of the hole should correspond to the outer diameter of the shaft 13a.
When the hole is formed, the shaft 13a is pushed into and through the conductive resilient member 13b, and the supply roller 13 is manufactured following predetermined steps.
The shaft 13a may be any shaft usable in manufacturing the roller, but desirably has an outer diameter of about 4.0 mm to 6.0 mm.
The shaft 13a is desirably made of metal, and metal alloy containing metals such as aluminum, iron and/or nickel.
The conductive resilient member 13b is formed from a molding composition which comprises a polyurethane, a conductive additive, a blowing agent, and a surfactant. In one embodiment of the invention the conductive resilient member is produced by molding a composition comprising polyurethane-forming monomer components, at least one conductive additive additive, a blowing agent and a surfactant. The composition is reacted to a polyurethane foam containing the conductive additive.
In this exemplary embodiment of the present invention, the polyurethane is obtained by mixing a compound containing at least two active hydrogens and a compound containing at least two isocyanate groups with additives in the presence of a catalyst, and a blowing, and curing the mixture to harden the composition and form the conductive resilient product.
For the compound containing the at least two active hydrogens, a polyol may be used. Examples of suitable polyols include a polyether polyol, a polyester polyol, and a polyetherester polyol having a terminal hydroxyl group on its end, but are not necessarily limited thereto. Additionally, a denatured polyol such as an acryl-denatured polyol or a silicone-denatured polyol can be used as the polyurethane used in the supply roller.
For the compound containing the at least two isocyanate groups, a polyisocyanate may be used. Examples of suitable polyisocyanates include toluene dilsocyanate (TDI), 4,4-diphenylmethane diisocyanate (MDI) and mixtures thereof, but are not necessarily limited thereto. Additionally, a denatured polyisocyanate can be used as the polyisocyanate.
The polyurethane is desirably prepared by reacting the polyol and the polyisocyanate in the presence of the catalyst. The catalyst is desirably selected from among organometallic compounds, amine-based compounds, and mixtures thereof.
The type and amount of the catalyst used are decided by taking into consideration the blowing properties, reaction time, increase in the ventilation rate of a polyurethane foam, and minimization of the density deviation.
The organometallic compounds used as the catalyst comprise at least one metal selected from the group consisting of tin, lead, iron, and titanium. It is preferable that the amine-based compounds used as the catalyst comprise a tertiary amine.
More desirably, the catalyst is selected from among a tertiary amine and a tin catalyst.
The conductive additive desirably comprises a compound having a terminal hydroxyl group on its end, and a polyalkylene glycol. In addition to the polyalkylene glycol, the conductive additive further comprises at least one salt selected from the group consisting of alkali metal salts and alkaline earth metal salts.
The polyalkylene glycol may comprise condensates of a linear or branched ethylene glycol, a propylene glycol, a tetramethylene glycol, 1,3-butadiol, 1,4-butadiol, neopentyl glycol, 1,6-hexanediol, and bisphenol A. In other words, the polyalkylene glycol may comprise a polyethylene glycol, a polypropylene glycol, a polytetramethylene glycol, a polyethylene glycol-polypropylene glycol copolymer, a ring-opening adduct of bisphenol A ethylene oxide, and a ring-opening adduct of bisphenol A propylene oxide.
Additionally, a polyester diol such as a polyadipate diol, a polycarbonate diol, and a polycaprolactone diol may be used as the compound having a hydroxyl group on its end.
The polyalkylene glycol or the polyalkylene diol desirably has a molecular weight of about 300 to 3,000. If the molecular weight is less than 300, the unreacted materials in the resulting polyurethane foam migrate to the surface, and if the molecular weight is equal to or higher than 3,000, the high viscosity of the polyalkylene glycol may inhibit the formation of the polyurethane foam.
The metal salts usable as the conductive additive according to the exemplary embodiment of the present invention may include perchlorate, chlorate, hydrochlorate, bromate, oxo acid salt, fluoroborate, sulfate, ethylsulfate, carboxylate, and sulfonate of the alkali metals and the alkaline earth metals, but are not necessarily limited thereto. Desirably, the metal salts may be lithium perchlorate.
Examples of the alkali metal salt are selected from the group consisting of lithium, sodium, potassium, rubidium, and cesium salts, but are not necessarily limited thereto. Desirably, lithium salts may be used.
Additionally, examples of the alkaline earth metal salts are selected from the group consisting of beryllium, magnesium, calcium, strontium, barium and radium salts, but are not necessarily limited thereto.
In the exemplary embodiments of the present invention, the amount of the conductive additive having a terminal hydroxyl group on its end to be added is about 3 phr (parts per hundred rubber) to about 100 phr based on the amount of the polyol. If the amount is equal to or lower than 3 phr, sufficient conductivity is not provided to the resulting polyurethane. If the amount is equal to or higher than 100 phr, the resulting polyurethane foam disintegrates and the cells are irregularly formed.
The blowing agent forms bubbles in the polyurethane, which helps to form the foam. The blowing agent usable in the exemplary embodiment of the present invention may comprise any blowing agent usable in blowing the polyurethane.
The blowing agent may be either water or a low-boiling point material such as a halogenated alkane. Examples of the halogenated alkane may include trichlorofluoromethane, but desirably water is used as the blowing agent.
The surfactant improves miscibility by reducing surface tension, causes the bubbles generated by the blowing agent to be of a uniform size, and stabilizes the blowing agent by controlling the cell structure of the polyurethane foam.
Desirably, a silicon surfactant can be used as the surfactant.
The surfactant is desirably added in an amount in the range of about 0.1 phr to about 5 phr based on the amount of polyol added in order to form the polyurethane. When the amount of the surfactant is equal to or less than 0.1 phr, the proper functioning of the surfactant cannot be guaranteed, and when the amount of the surfactant is equal to or higher than 5 phr, properties such as its compression set, may be reduced.
In the exemplary embodiments of the present invention, a method of manufacturing a supply roller of a developing device for an image forming apparatus comprises preparing a conductive resilient member comprising a polyurethane, a conductive additive, a blowing agent and a surfactant; cutting the conductive resilient member into a cylindrical shape, and forming a shaft-shaped hole in the center of the conductive resilient member; and pushing a shaft into and through the hole, heating, and adhering the conductive resilient member and the shaft.
The conductive resilient member prepared by the manufacturing method according to the exemplary embodiment of the present invention has a density of about 60 kg/m3 to about 120 kg/m3 and an outer diameter of about 8.0 mm to about 10.0 mm.
Additionally, the shaft has an outer diameter of about 4.0 mm to about 6.0 mm.
First, a conductive resilient member was prepared. GP-3000 (manufactured by KOREA POLYOL Co., Ltd., containing 54 mgKOH/g of a hydroxy group) and KE-848 (manufactured by KOREA POLYOL Co., Ltd, containing 30 mgKOH/g of a hydroxyl group) as a polyester polyol, were combined with water as a blowing agent, a silicone surfactant as a surfactant, a catalyst, and a compound containing polyethylene glycol and lithium perchlorate as a conductive additive having a terminal hydroxyl group on its end, to obtain a pre-mixed polyol.
The conductive additive having a terminal hydroxyl group on its end was obtained in the following manner. To a methyl ethyl ketone solvent, were added 100 g of a polyethylene glycol having a molecular weight of 500 and 10 g of lithium perchlorate, and the resulting mixture was reacted at a temperature of 50° C. to 80° C. for 16 to 20 hours. This reaction was monitored using a Fourier Transform-Infrared Spectroscope (FT-IR), and the methyl ethyl ketone solvent was distilled off under a reduced pressure of 30 to 5 mmHg to obtain a conductive additive.
Toluene diisocyanate (TDI) as a polyisocyanate was added to the prepared pre-mixed polyol, and then agitated at 2000 rpm. The resulting mixture was injected into a mold, and then dried in a forced air convection oven at 60° C. for 20 minutes to prepare a conductive resilient member.
The prepared conductive resilient member was cut into a cylindrical shape, and a shaft-shaped hole was then formed longitudinally in the center of the cylindrical column. A metal shaft, wound with a hot melt sheet, was pushed into the hole. The conductive resilient member and the shaft were attached to each other by heating in a forced air convection oven at 120° C. for 30 minutes. The adhered conductive resilient member was polished by a polisher, and both ends of the conductive resilient member were then cut. By this process, a supply roller was manufactured.
A supply roller was prepared in the supply roller manufacturing method described above, using the following quantities of each component.
The volume resistance and density of the supply roller manufactured in Example 1 were measured as follows.
(1) Resistance: the supply roller was mounted in a Jig, conductive shafts of 200 g were put on both ends of an upper part of the supply roller, −100 V of a direct current (DC) voltage was applied to the shaft, and the roller was rotated at a certain speed (for example, 30 rpm) to measure the electric current. The measured current value was converted to a resistance value using the following Equation.
Resistance (Ω)=Voltage (V)/Electric current (A)
(2) Density: the weight of the conductive resilient member having a width of 300 mm, a length of 300 mm, and a thickness of 50 mm was measured.
Density (kg/m3)=Weight (kg)/Volume (m3)
The supply roller manufactured in Example 1 had a volume resistance of 0.5 MΩ and a density of 100 kg/m3.
Supply rollers were manufactured by changing the outer diameter of the supply roller, the outer diameter of the shaft and the density of the conductive resilient member, and images were formed using each of the manufactured supply rollers to measure image quality.
(1) Outer Diameter of Supply Roller
When a supply roller having a volume resistance of 0.5 MΩ was manufactured in which the density of the conductive resilient member was 100 kg/m3 and the outer diameter of the shaft was 6.0 mm, the outer diameter of the supply roller was changed to 7.0 mm, 8.0 mm, 9.0 mm, 10.0 mm, and 12.0 mm to measure image quality.
When the supply properties of the supply roller and the ghost phenomenon occurring on images were evaluated by the naked eye as the criteria for the image quality, the results were recorded using ◯ to represent “Excellent”, Δ to represent “Good”, and × to represent “Poor.” A toner was inserted into a gap of the conductive resilient member to block the gap when printing images for a long time period, so that the supply properties of the supply roller were reduced. The ghost phenomenon occurs when a residual image is generated on a formed image due to a difference in the charge amount of the toner. Accordingly, the image quality was evaluated by the naked eye by determining whether the ghost phenomenon occurred or whether the supply properties were reduced.
The results of the evaluation are shown in Table 1.
(2) Outer Diameter of Shaft
When a supply roller having a volume resistance of 0.5 MΩ and an outer diameter of 9.0 mm was manufactured, in which the conductive resilient member had the density of 100 kg/m3, shafts with an outer diameter of 3.0 mm, 4.0 mm, 5.0 mm, 6.0 mm, and 7.0 mm were used to measure the image quality.
When the supply properties of the supply roller and the ghost phenomenon occurring on images were evaluated by the naked eye as the criteria for the image quality, the results were recorded using ◯ to represent “Excellent”, Δ to represent “Good”, and × to represent “Poor.” The results of the evaluation are shown in Table 2.
(3) Density of Conductive Resilient Member
When a supply roller having a volume resistance of 0.5 MΩ was manufactured to have a shaft with an outer diameter of 6.0 mm, and a supply roller with an outer diameter of 9.0 mm, the density of the conductive resilient member was set at 40 kg/m3, 60 kg/m3, 80 kg/m3, 100 kg/m3, 120 kg/m3, and 140 kg/m3 using a method such as changing the content of the composition, and the image quality was then measured. In order to change the density, a method was used in which the contents of a polyol and a polyisocyanate were changed, or an amount of the mixture injected into a mold was varied while maintaining the ratio of the total content of the composition.
When the supply properties of the supply roller and the ghost phenomenon occurring on images were evaluated by the naked eye as the criteria for the image quality, the results were recorded using ◯ to represent “Excellent”, Δ to represent “Good”, and × to represent “Poor.” The results of the evaluation are shown in Table 3.
Referring to Table 1, a greater outer diameter of the supply roller corresponded to superior supply properties and prevention of the ghost phenomenon. However, if the outer diameter of the supply roller is too large, it is difficult to miniaturize the image forming apparatus.
Accordingly, when the outer diameter of the supply roller was 7.0 mm, the supply properties were reduced and the ghost phenomenon was obvious. When the outer diameter of the supply roller was 12.0 mm, the ghost phenomenon was less obvious. The ghost phenomenon occurred due to a difference in the charge amount of the toner by increasing the nip portion between the developing roller and the supply roller to increase the toner stress. The increased nip portion allowed the load of a toner cartridge to be increased, resulting in image deviations caused by such factors as jitter. Additionally, as it is necessary to miniaturize the image forming apparatus, particularly the developing device, high quality images can be formed using a small supply roller having an outer diameter of 8.0 mm to 10.0 mm.
Referring to Table 2, when the outer diameter of the shaft was 3.0 mm, the quality of the formed image was reduced when the above test was observed. In this case, the diameter of the shaft was very small, the shaft was bent, and thus the toner supply properties were reduced and the ghost phenomenon was obvious.
However, when the outer diameter of the shaft was in the range of 4.0 mm to 5.0 mm, the quality of the formed image was excellent as observed in the above test. When the outer diameter of the shaft was in the range of more than 6.0 mm to 7.0 mm, the outer diameter of the shaft was increased to reduce the thickness of the conductive resilient member because the outer diameter of the supply roller remained constant. Accordingly, the toner supply properties were reduced due to the occurrence of the toner filming phenomenon. Therefore, when the outer diameter of the supply roller remained constant, it was most desirable that the outer diameter of the shaft was in the range of 4.0 mm to 6.0 mm.
Referring to Table 3, when the conductive resilient member had a density of 40 kg/m3, the image quality was reduced due to the ghost phenomenon occurring on images. When the conductive resilient member had a density of 140 kg/m3, the supply properties were reduced due to the occurrence of the toner filming phenomenon. Therefore, it was most suitable that the density of the conductive resilient member was in the range of 60 kg/m3 to 120 kg/m3.
As described above, the exemplary embodiments of the present invention provide a supply roller of a developing device for an image forming apparatus, which can be manufactured in a compact size and which exhibits excellent toner supply properties while preventing occurrence of ghost phenomenon and toner-filming phenomenon causing deterioration in image quality.
Additionally, since the toner-filming phenomenon is prevented, the lifespan of the supply roller can be guaranteed to be longer.
The foregoing embodiments and advantages are merely exemplary and are not to be construed as limiting the present invention. The present teaching can be readily applied to other types of apparatuses. Also, the description of the embodiments of the present invention is intended to be illustrative, and not to limit the scope of the claims, and many alternatives, modifications, and variations will be apparent to those skilled in the art.
Number | Date | Country | Kind |
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10-2006-0079806 | Aug 2006 | KR | national |