JPH1195542A - Resistance against oxidation and ageing of surface oxidized roller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain excellent printing performance and to prolong the effective life of a roller by using an antioxidant such as a hindered phenol. SOLUTION: This roller consists of an injection molded urethane conductive rubber roller having a surface layer of high electric resistivity and is prepared by blending a polydiene such as polyisoprene as the prepolymer of polyol or urethane with a second prepolymer of polyurethane and conductive additive such as iron (III) chloride. The surface of the hardened roller is oxidized to form a surface layer of a material having high electric resistivity. The roller is hardened by baking at a rather high temp. in air for several hours. By the reaction of oxygen and polybutadiene with iron (III) chloride as a catalyst, the surface of the roller is oxidized. To suppress further oxidation of the roller in the functional life to the min. as possible, an antioxidant such as hindered phenol is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001] This application is a continuation of US Patent Application Serial No. 60 / 046,884, filed May 14, 1997. US patent application Ser. No. 08 / 629,855, filed Apr. 9, 1996, relates to a roller modified according to the present invention for oxidation aging resistance. U.S. patent application Ser. No. 08 / 870,782, filed Jun. 6, 1997, is incorporated herein by reference.
No. 855, which relates to the scope of the method. A corresponding part of U.S. patent application Ser. No. 08 / 423,481, filed Apr. 19, 1995, is filed by British patent application No. 23 / Oct.
Although disclosed in US Pat. No. 0,050, as shown in the embodiments of the present application, this U.S. patent application is directed to a developing roller having a polycaprolactone ester body and ferric chloride.

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing roller for use in electrophotography, and more particularly, to a roller having a layer having a high electric resistivity on its surface and a method for producing the same.

[0003]

2. Description of the Related Art According to a functional developing roller used for contact electrophotographic printing and having a high-resistance surface layer on a semiconductive core, excellent performance can be obtained irrespective of the moving speed (process speed) of a printing member. Printing characteristics are obtained. The present invention improves upon the general method of fabricating a semiconductive core and then coating the core with a high resistance material in a separate step such as spray coating or dip coating.

[0004]

The above-mentioned application No. 08
With the novel combination of materials described in US Pat. No. 6,629,855, a high resistance surface layer can be formed on a more conductive core by simply oxidizing the surface of the roller. . This eliminates the need to coat the conductive roller with a resistive layer in a separate step. This step improves the general method of fabricating the semiconductive core and then coating the core with a resistive material in a separate step such as spray coating or dip coating. Baking is more cost effective than spray coating and dip coating and produces rollers with less defects. The baked polydiene based roller of the present invention has properties similar to the electrical properties of the coated roller,
Provides excellent printing performance over a wide range of process speeds.

[0005] However, during the life of the functionality of the roller, this set of materials is susceptible to further oxidation, known as aging or aging due to oxidation, which has a detrimental effect on the properties of the roller.

[0006]

According to the present invention, an antioxidant such as hindered phenol is used to minimize further oxidation of the roller during its functional life. The antioxidant extends the useful life of the roller by a factor of about 10 or more while providing excellent printing performance.

The roller of the present invention is a cast urethane conductive rubber roller having a surface layer having a high electric resistivity. The electrical properties of this roller are similar to those of a coated roller. The roller is composed of a polydiene such as polyisoprene, more specifically, a blend of polybutadiene as a polyol or urethane prepolymer with a second polyurethane prepolymer and a conductive additive such as ferric chloride. ing. The bulk resistivity of the roller is about 1 × 10 at a temperature of 22 ° C. and a relative humidity of 50%.
8 ohm-cm. The cured roller surface is oxidized to form a surface layer of a high electrical resistivity material. Oxidation of the rollers is accomplished by baking the rollers in air at fairly high temperatures (above 80 ° C.) for several hours.
The surface of the roller is oxidized by a reaction between oxygen and polybutadiene using ferric chloride as a catalyst. The oxide layer has a very high resistance. Manufacturing costs are low.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In electrophotography, the function of the developing roller is to develop a toner layer on a photoconductor drum charged to an image pattern. A fixed amount of toner per volt of development bias, determined by the photoconductor, toner, and dielectric thickness of the development roller, will be developed on the roller with the two layers applied. This development characteristic does not depend on the process speed within limits. In contrast, a single resistance homogeneous roller develops a toner quantity based on the dielectric constant of the photoconductor and toner, as well as the resistance of the roller in the photoconductor nip. This depends on the process speed. Further, a two-layer roller has a larger time constant than a homogeneous roller. A material with a large time constant places a higher effective surface potential on the developer roll at the entrance of the photoconductor nip. This improves the single pel dot printing performance of the roller.

Therefore, the printing performance of a two-layer roller is superior to a homogeneous roller over a wide range of process speeds and is less susceptible to office environments. Desirable electrical properties of the two-layer roller during normal operation include a core resistivity of less than 1.times.10@9 ohm-cm, preferably less than 3.times.10@8 ohm-cm at a temperature of 22 DEG C. and 50% relative humidity (RH). The resistivity of the coating is 5.times.10@9 ohm-c at 22 DEG C. and 50% RH.
m to 2 × 10 12 ohm-cm, preferably 1 × 10 11 ohm-cm, coating thickness 22 ° C., 50%
RH is about 50-150 microns, preferably about 100 microns. The time constant is about 5 at 22 ° C and 50% RH.
It should be ０００2000 ms, preferably about 100 ms.

[0010] A common method of producing a semi-conductive roller having a resistive layer is to form the core using any standard rubber molding method, such as casting liquid urethane or transfer molding rubber. The core is then ground to size and the resistive material is spray coated or dip coated to the desired thickness. The coating is typically applied in several layers to a desired thickness of 100 microns. The problem with this method is that the costs are high due to the multiple coating steps and that the surface layer is defective during the coating steps.

With the unique combination of materials described herein, a resistive surface layer can be formed on cast urethane rollers simply by baking at high temperatures in air. When polybutadiene is oxidized in the presence of ferric chloride, a high-resistance layer can be formed on the surface. The thickness and resistivity of this layer can be controlled by varying the amount of polybutadiene, amount of ferric chloride, baking time, baking temperature, and oxygen concentration. However, the material remaining on the roller after this controlled oxidation process to form a resistive surface layer makes the roller more susceptible to oxidation, which oxidation may affect the life of the printer prior to use or its functional life. Accelerated at higher temperatures that may be encountered in both storages in between.

In the present invention, the urethane prepolymer is
Includes the use of polybutadienes of the diol or urethane prepolymer type, as well as blends with ferric chloride as a conductivity modifier. After the blended material is cured into the shape of a roller, it is baked at elevated temperature (≥80 ° C.) for various times to oxidize the surface of the roller. This oxidation forms a layer of high resistance material on the surface of the roller.

Urethane prepolymers of polycaprolactone, such as Vibrathane 6060 (a product of Uniroyal Chemical Corporation) are preferred as base urethanes because of their stable electrical resistivity to changes in temperature and humidity. Vibrathane 6060 is a polycaprolactone ester toluene-diisocyanate prepolymer. Ferric chloride is added to the urethane to reduce the electrical resistivity of the roller core to less than 1 × 10 9 ohm-cm. The combination of polycaprolactone urethane and ferric chloride forms a single resistivity roller from the roller surface to the center or core. To form a roller with a high surface layer resistance, a polydiene must be included in the formulation.

The polybutadiene diol (PBD) is reacted with toluene diisocyanate (TDI) to form a polybutadiene prepolymer. This PBD-TD
The I prepolymer can be blended in various proportions with the caprolactone prepolymer. A suitable polybutadiene prepolymer is a pilot product of Uniroyal Chemical. A blend of these prepolymers is made into Voran, a trifunctional polyether polyol.
234-630 (a product of Dow Chemical Co., Ltd.). A typical blend ratio of polycaprolactone / polybutadiene is from 95/5 parts by weight to 6 parts by weight based on 100 parts by weight of the whole rubber containing polycaprolactone and polybutadiene.
0/40 parts by weight.

As an alternative formulation, polycaprolactone / urethane is a polybutadiene diol (Elf)
A-chem product R-45HT registered trademark p
oly bd) and Voranol 234-630
It can be cured using a combination with a trifunctional curing agent such as Trademark poly bd R-45H
T-polybutadiene has a molecular weight Mn of 2800 and cis-1,4-polybutadiene 20%, tran
It has a microstructure consisting of 60% s-1,4-polybutadiene and 20% 1,2-polybutadiene. Vor
nanol 234-630 is a polyether polyol with a functionality of 3. In this case, the polybutadiene diol functions as a urethane polymer chain extender. Typical weight ratios of Voranol to the trademark polybd R-45HT range from 1/0 to 1/7.

[0016] Polybutadiene prepolymer is a very high resistance material. Even if a powdery conductive additive such as copper (II) chloride or ferric chloride is added at a high concentration, the electrical resistivity of this material does not decrease. In contrast, when 0.1 part by weight of ferric chloride powder is added to 100 parts by weight of polycaprolactone / urethane per 100 parts by weight of rubber, the electrical resistivity is 5 × 10 10 ohm-cm. From the range to 1.5 × 10 8 ohm-cm. Ferric chloride is insoluble in the polybutadiene prepolymer.

Ferric chloride is added to the polybutadiene / polycaprolactone / urethane blend, and the bulk resistivity of the blend is 1 × 10 9 ohm-c.
m. Typical concentrations of ferric chloride are 0.05 to 0.30 parts by weight per 100 parts by weight of rubber. Other powdered conductive additives, such as ferrous chloride, calcium chloride, and cobalt hexafluoroacetylacetonate, can be used as a replacement for ferric chloride.

The urethane formulation is then cast into a mold around a central metal shaft and then combined with in-mold cure, removal, and post-cure in an oven at about 100 ° C.
And cure for 16 hours. Next, the rollers are polished to regular dimensions. This roller has no resistance layer on the surface. The resistance layer is formed by baking the polished roller in air at a high temperature for a predetermined time. This baking oxidizes ferric chloride and polybutadiene. Polybutadiene is highly unsaturated and is therefore very susceptible to oxidation. The presence of ferric chloride is necessary to function as a catalyst in this oxidation process. Example 1 illustrates the composition and manufacturing conditions using such a combination of materials. Since copper (II) chloride does not function sufficiently as a catalyst for an oxidation reaction forming a high-resistance surface layer, a high-resistance layer is not formed in the presence of copper (II) chloride.

Oxidation of polybutadiene in the presence of ferric chloride forms a high resistance surface layer. The thickness and electrical resistivity of the surface layer can be controlled by changing the concentration of ferric chloride, the concentration of polybutadiene, the baking temperature, the amount of oxygen, and the baking time.

After processing the rollers, further oxidation can occur even at room temperature (22 ° C.). Without antioxidants,
The thickness of the resistive surface layer, which changes the printing performance of the roller during the life of the roller, can increase. Therefore, it is necessary to add an antioxidant to the roller in order to extend the useful life of the roller, and such a life increases not only the functional life but also the storage life before use.

The antioxidant is selected from the main types of antioxidants which meet the standards of the rubber industry, for example, aromatic amines such as diphenylamine or dihydroquinoline; phenols such as substituted phenols; Hydroperoxide decomposers such as salts or sulfides;
Adding an antioxidant during the casting process requires modification of the bake process to form a resistive surface layer by requiring higher oxidation bake temperatures and / or longer bake times. . For example, 2,6-di-tert-butyl-4-methyl-phenol, also known as BTH, or 2,2'-methylenebis (4-methyl-6-tert-butyl), also known as Cytec Industries' CYANOX2246. Antioxidants such as hindered phenols of phenol can be used. Post-treatment by pre-blending with the polybutadiene diol or prepolymer raw material and then casting the roller using the standard type of process described above, or by tipping or spray coating a dilute solution of antioxidant on the roller surface The antioxidant can be added to the roller by applying using a process and diffusing the antioxidant into the rubber roller. The concentration of antioxidant may be varied depending on the type of antioxidant used and the method of adding to the roller. For example, the BHT used can be between 0.05% by weight (w / w) and 1.0% (w / w) when added to the rollers during casting of the mixed urethane raw material.
w), preferably 0.08% (w / w) to 0.40%
(W / w). Also, CYANOX2
246 is 2.0% to 28.0% (w / w), preferably 1% when added to the rollers in a post-treatment process such as tip coating by dissolving in a solvent.
The range may be 0.0% to 20.0% (w / w).
Examples 2 and 3 illustrate the formulations and processing conditions for using such materials and processes.

The rollers are characterized by various electrical methods. The roller is usually cleaned with isopropyl alcohol, and a conductive carbon paint is applied in a 10 mm band below the roller. Alternatively, a conductive carbon tape piece may be arranged below the roller. The painted surface is brought into electrical contact with the roller shaft to form a circuit.
The DC resistivity of the roller at 100 V is measured, the AC resistivity at 1 kHz, and the time constant. To measure the time constant, apply a bias of 100 V to the roller, remove this voltage,
This is performed by measuring the time until the voltage on the roller decreases to 1 / e (37%) of the original value. This time constant is related to the thickness and resistivity of the surface layer of the roller. Roller is 2
It is modeled as a series connection of two parallel circuits. One RC circuit represents the core and the second RC circuit represents the coating. Based on this model, the following equation is applied. τ = R × C = rhoc × Kc × ε0 rhoc = τ / (Kc × ε0) T = R × A / rhoc where τ = time constant rhoc = resistivity of coating C = capacitance Kc = dielectric constant of coating ε0 = 8.85 × 10 −12 coulomb 2 / Newton × meter 2 (dielectric constant of free space) T = thickness of resistive layer R = DC resistance of roller A = surface area of roller

Thus, the thickness and resistivity of the coating can be calculated from the measured time constant and DC resistance. The dielectric constant of the coating is estimated to be 10, which is a typical value for polyurethane rubber.

Experimental observations have shown that the addition of antioxidants to the rollers dramatically improves roller performance, which was only 43 ° C. for rollers without antioxidants. Those showing an unacceptable thickness after 39 days of aging, while those with the addition of the above antioxidant show acceptable electrical properties even after 140 days of aging at 43 ° C. Applying the antioxidant to the rollers using a tip coating process shows a dramatic improvement, as compared to 1 day aging at 80 ° C. for rollers without added antioxidant. The addition of the above antioxidants shows acceptable electrical properties even after aging at 80 ° C. for 11 days, showing an improvement of over 11 times.

[0025] Increasing the amount of polybutadiene increases the resistivity of the coating. Increasing the baking time and temperature increases the thickness of the coating and the electrical resistivity of the coating. By properly combining the amount of polybutadiene and the baking conditions, the resistivity measured at a temperature of 22 ° C. and a relative humidity of 50% is 5 × 10 9 ohm-cm to 2 × 10 12 ohm-cm, and the thickness of the surface layer is about 50 to 150. A roller having a micron surface layer is formed.

The resistive surface layer created by the oxidation process is permanent. The rollers to which the antioxidant was added were analyzed for months at 22 ° C. and at higher temperatures such as 43 ° C. and 80 ° C. for shorter periods of time without significant changes in electrical properties.

According to the printing test results of an oxidized polybutadiene roller containing an antioxidant, this roller shows excellent printing performance over a wide speed range. Their performance is similar to that of a conductive roller coated with a resistive material in a separation process.

In an office environment, high humidity is not uncommon, and printers, especially developing rollers in printers, are often exposed to high temperatures (> 40 ° C.) during operation. Polyurethanes degrade when exposed to relative humidities as high as 80% for extended periods of time, and at elevated temperatures accelerates the degradation of urethane rubber. Acid sources also promote degradation. When ferric chloride, a highly acidic material, is added to polyurethane,
Urethane degradation is promoted. The term “deterioration” refers to a decrease in durometer hardness over time. Here, it refers to a decrease in durometer hardness when exposed to a high-temperature and high-humidity environment such as 60 ° C. and 80% relative humidity for a specified time. In various environments, maintaining the physical and electrical properties of the roller over an extended period of time requires a hydrolysis stabilizer. TIPA
The addition of (registered trademark of Dow Chemical Company) (chemically triisopropanolamine 99) stabilizes the urethane-based developing roller against hydrolysis.

[0029] Specific implemented applications of the present invention include the following.

[0030]

[Table 1]

[0031]

[Table 2]

[0032]

[Table 3]

Modifications are obvious and predictable. We claim patent protection conferred by law, with particular reference to the claims.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Jean Marie Massy United States 40509 Kentucky, Lexington, Gingermill Lane 583 (72) Inventor Johnny Dale Massy Second United States 40509 Kentucky, Lexington, Gingermill Lane 583 (72) Inventor Ronald Lloyd Low United States 40515 Kentucky, Lexington, Woodglen Court 932

Claims (12)

[Claims] 1. An endless developing member comprising a body of polycaprolactone / ester / toluene / diisocyanate / polyurethane, a conductive filler, a lower alkane polydiene, and an antioxidant, wherein the antioxidant electrically charges the developing member. An endless developing member having an outer surface made of the oxidized lower alkane polydiene, which is to be stably stabilized. 2. The developing member according to claim 1, wherein said conductive filler is ferric chloride. 3. The developing member according to claim 2, wherein the antioxidant is only on the outer surface. 4. The developing member according to claim 3, wherein said antioxidant is 2,2′-methylenebis (4-methyl-6-tert-butyl) phenol. 5. The developing member according to claim 1, wherein said polydiene is polybutadiene. 6. The developing member according to claim 2, wherein said polydiene is polybutadiene. 7. The developing member according to claim 3, wherein said polydiene is polybutadiene. 8. The developing member according to claim 4, wherein said polydiene is polybutadiene. 9. The developing member according to claim 1, wherein said antioxidant is 2,6-di-tert-butyl-4-methyl-phenol. 10. The method according to claim 2, wherein said antioxidant is 2,6-di-tert-butyl-4-methyl-phenol.
5. The developing member according to item 1. 11. The developing member according to claim 9, wherein said polydiene is polybutadiene. 12. The developing member according to claim 10, wherein said polydiene is polybutadiene.