WO2013191440A1

WO2013191440A1 - Seamless belt

Info

Publication number: WO2013191440A1
Application number: PCT/KR2013/005354
Authority: WO
Inventors: Sang Kyun Kim; Sang Min Song; Ki Nam Kwak
Original assignee: Kolon Industries, Inc.
Priority date: 2012-06-18
Filing date: 2013-06-18
Publication date: 2013-12-27
Also published as: KR20130141928A; TW201402694A

Abstract

This invention relates to a seamless belt, including a single-layer substrate including a polyimide resin and carbon nanotubes dispersed in the polyimide resin, wherein the polyimide resin is obtained by imidizing an aromatic dianhydride and an aromatic diamine, and the aromatic diamine includes 40 ~ 100 mol% of 1,4-phenylenediamine (1,4-PDA) based on the total amount of the aromatic diamine, and the carbon nanotubes have a diameter of 5 ~ 20 nm and are contained in an amount of 0.1 ~ 2.0 parts by weight based on 100 parts by weight of the polyimide resin.

Description

SEAMLESS BELT

The present invention relates to a seamless belt, which is useful as an intermediate transfer belt for an imaging device.

Typically, belts are used in a variety of fields, and have been utilized as main parts which replace gears in apparatuses or devices using rotary shafts and motors, such as electronic appliances, automobiles or conveyors. Particularly, belts have been used in electronic appliances, such as copiers, laser beam printers, facsimiles, etc., to fix and transfer a toner image formed on copy paper or transfer paper, and examples thereof include fuser belts, intermediate transfer belts or conveyor belts.

Because belts easily generate an electrostatic phenomenon while they rotate, they should have antistatic performance. In order to attain antistatic performance, semiconductivity may be utilized as a physical property for toner transfer in electronic appliances.

Such belts include small-size belts having a diameter of about 20 mm and large-size belts having a diameter of ones of meters, based on tubular belts. However, most of the belts are seam belts resulting from jointing flat belts or V belts to each other, and are problematic because the surface characteristics of the seam are different from those of the periphery thereof due to the uneven seam. Moreover, in an electronic appliance using an even plane of a belt, especially in a color laser printer, surface unevenness of an intermediate transfer belt may damage an optical drum or may deteriorate quality of a printed image. Also, in the case where the seam becomes slightly warped, linearity of a tubular belt may be decreased, undesirably causing the belt to stray from an intended path during rotation. The case where a belt is detached from a driving roll due to the straying of the belt may incur a problem wherein the electronic appliance itself is damaged.

Thus, when a tubular belt has no seam, maximal durability of the belt material may be obtained. Further, because there is no unevenness, the belt or an object in contact with the belt may be prevented from bouncing during rotation, and linearity of the belt may be easily ensured.

In particular, a fuser belt, an intermediate transfer belt, etc., for use in electronic appliances such as printers, copiers, complex machines, facsimiles, etc. should be superior in terms of antifouling performance, heat resistance, heat dissipation performance, elastic modulus, antistatic properties, durability, water repellency, and oil repellency, and should have appropriate surface resistivity to achieve a toner transfer function. In the case where the actual surface resistivity of the belt used is higher or lower than the required surface resistivity, properties of the belt such as antistatic properties, transfer performance, imaging properties, releasibility and antifouling performance may deteriorate, and thereby the printed image may become poor.

Upon manufacturing a fuser belt, an intermediate transfer belt, etc., polycarbonate, polyvinylidene fluoride, polyamideimide, a polyimide resin or rubber is used, and a conductive additive such as carbon black, etc., is mixed and dispersed therein. However, in order to achieve rapid printing, a polyimide resin is preferably used because the transfer belt requires that the color overlap and discrepancy thereof due to the deformation thereof during its traveling do not occur, because it requires high strength to such an extent that it may be repetitively used, and because it requires flame retardance. As a conductive filler, a conductive additive such as carbon black is used. In this case, it is possible to sufficiently ensure electrical conductivity of a semiconductive resin only in the presence of a considerably large amount of the conductive additive. Further, in order to ensure uniformity of surface resistivity, a large amount of dispersant should be added, undesirably deteriorating durability of the belt.

In regard to seamless belts including a polyimide resin and a conductive filler, Korean Unexamined Patent Publication No. 2011-0032917 discloses a seamless belt, which includes a polyimide or polyamideimide resin, with a 5% weight reduction initiation temperature of 300℃ or more as measured by thermogravimetric analysis, a surface resistivity of 10⁷ ~ 10¹³ Ω/sq, and a surface resistivity deviation of 10¹ or less as defined by a difference between the maximum value and the minimum value of the surface resistivity at ten random positions in a single product. However, the above seamless belt makes it difficult to control the degree of dispersion of the carbon nanotubes, and is still problematic in durability, etc. upon serving as an intermediate transfer belt.

Accordingly, the present invention is intended to provide a seamless belt, which is improved in durability and has superior uniformity of surface resistivity.

According to a preferred first embodiment of the present invention, a seamless belt is provided, which comprises a single-layer substrate comprising a polyimide resin and carbon nanotubes dispersed in the polyimide resin, wherein the polyimide resin is obtained by imidizing an aromatic dianhydride and an aromatic diamine, and the aromatic diamine comprises 40 ~ 100 mol% of 1,4-phenylenediamine (1,4-PDA) based on the total amount of the aromatic diamine, and the carbon nanotubes have a diameter of 5 ~ 20 nm and are contained in an amount of 0.1 ~ 2.0 parts by weight based on 100 parts by weight of the polyimide resin.

In the above embodiment, the carbon nanotubes may be dispersed in a solvent and then dispersed in the polyimide resin, and the carbon nanotubes dispersed in the solvent may have a particle size of 0.02 ~ 10 ㎛.

In the above embodiment, the aromatic dianhydride may be biphenyltetracarboxylic dianhydride (BPDA).

In the above embodiment, the aromatic diamine may further include one or more selected from the group consisting of 1,3-phenylenediamine (1,3-PDA), 4,4'-methylenedianiline (MDA), 4,4'-oxydianiline (ODA) and 4,4'-oxyphenylenediamine (OPDA).

In the above embodiment, the seamless belt may have a surface resistivity of 10⁸ ~ 10¹³ Ω/sq.

In the above embodiment, the seamless belt may have a common logarithm of surface resistivity deviation of 1.0 or less.

In the above embodiment, the seamless belt may have a tensile modulus of 4000 MPa or more.

In the above embodiment, the seamless belt may have a folding endurance of 1000 times or more.

According to the present invention, a seamless belt can have uniformity of surface resistivity and improved durability, and thus can exhibit properties adapted for an intermediate transfer belt requiring reliability.

FIG. 1 is a transmission electron microscope (TEM) image illustrating the diameter of carbon nanotubes according to the present invention;

FIG. 2 is a graph illustrating the results of measurement of particle size of a carbon nanotube dispersion solution according to an embodiment of the present invention (Example 1); and

FIG. 3 is a graph illustrating the results of measurement of particle size of a carbon nanotube dispersion solution according to a comparative embodiment of the present invention (Comparative Example 6).

Hereinafter, a detailed description will be given of the present invention.

This invention pertains to a seamless belt, which is manufactured by dispersing carbon nanotubes in a polyamic acid solution prepared from a dianhydride and a diamine, thus obtaining a semiconductive polyamic acid solution, which is then imidized. The seamless belt comprises a single-layer substrate comprising a polyimide resin and carbon nanotubes dispersed in the polyimide resin, wherein the polyimide resin is obtained by imidizing an aromatic dianhydride and an aromatic diamine, and the aromatic diamine contains 1,4-phenylenediamine (1,4-PDA) in an amount of 40 ~ 100 mol% based on the total amount thereof, and the carbon nanotubes have a diameter of 5 ~ 20 nm and are contained in an amount of 0.1 ~ 2.0 parts by weight based on 100 parts by weight of the polyimide resin.

As used herein, the term “diameter” means a cylindrical diameter of a single carbon nanotube strand having a cylindrical long carbon structure.

As also used herein, the term “particle size” means a size of carbon nanotbues which are agglomerated and provided in the form of a bundle, due to a tendency of mutually entangling carbon nanotubes which are originally long in a longitudinal direction and due to agglomeration based on a van der Waals force.

Conventionally, the use of carbon black as a filler to impart conductivity to a seamless belt for an imaging device is being known. However, 10 wt% or more of carbon black should be added in order to increase conductivity of a polyimide resin having insulating properties to the extent that a toner may be electrically charged. When carbon black is added in a large amount in this way, original superior mechanical properties of the polyimide resin may undesirably deteriorate.

In the present invention, carbon nanotubes are used as a conductive filler. Since the carbon nanotubes were first found by Iijima [S. Iijima, Nature Vol. 354, P.56 (1991)], thorough research thereto has been carried out. The carbon nanotubes have latent properties, for example, a high elastic modulus of about 1.0 ~ 1.8 TPa which cannot be obtained from conventional materials, high heat resistance up to 2800℃ in a vacuum, high thermal conductivity about two times that of diamond, a high ability to transport a current about 1000 times that of copper. Therefore, such carbon nanotubes are evaluated to be very applicable in a variety of fields including nanoscale electric devices, nanoscale electronic devices, nanosensors, photoelectronic devices, high functional composites, etc.

The carbon nanotubes are provided in the form of a graphite sheet that is rolled to a nano-sized diameter, and refer to a material, the diameter of which is very small and measurable in nanometers.

The carbon nanotubes are largely classified into, depending on the structure thereof, single-wall carbon nanotubes having a single layer, and multi-wall carbon nanotubes configured in a plurality of concentric layers. The single-wall carbon nanotubes have a diameter of 1.0 nm, and the multi-wall carbon nanotubes have a diameter of 2 ~ 100 nm depending on the number of walls. The single-wall carbon nanotubes have very superior electrical conductivity, whereas the multi-wall carbon nanotubes are decreased in electrical conductivity in proportion to an increase in the diameter thereof.

According to the present invention, the carbon nanotubes may have a diameter of 5 ~ 20 nm. If the diameter of the carbon nanotubes is less than 5 nm, electrical conductivity thereof is very high, and thus, in order to satisfy electrical properties required of a semiconductive seamless belt for an imaging device, the carbon nanotubes should be added in a very small amount, making it difficult to handle the process and to control the surface resistivity deviation in the seamless belt. In contrast, if the diameter of the carbon nanotubes exceeds 20 nm, electrical conductivity of such carbon nanotubes may be low, and thus a large amount of carbon nanotubes should be added to satisfy electrical properties required of a seamless belt for an imaging device, which is regarded as disadvantageous as in the use of carbon black. The diameter of the carbon nanotubes is measured using TEM. The results are shown in FIG. 1.

In the seamless belt according to an embodiment of the present invention, the carbon nanotubes are not used in the form of original powder, but may be used in a dispersion phase in which the carbon nanotubes are added to a solvent so that they are uniformly distributed in the polyimide resin. As the solvent, an organic solvent may include, for example, methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, butanol, ethylene glycol, N,N-dimethylformamide, dimethylacetamide, methylethylketone, ethyl acetate, butyl acetate, acetone, toluene, etc. In particular, a high-polar aprotic solvent such as N,N-dimethylformamide, dimethylacetamide, N-methylpyrrolidione, etc., may be used. As such, the particle size of the carbon nanotubes dispersed in the solvent may be 0.02 ~ 10 ㎛, and preferably 0.1 ~ 8 ㎛. When the carbon nanotubes are added to the solvent and dispersed using milling and ultrasonic waves, the particle size thereof may decrease. When the initial particle size of the carbon nanotubes after addition to the solvent before dispersion is measured, the carbon nanotubes do not individually exist but are provided in the form of a bundle, and thus the initial particle size thereof is about 1000 ㎛, and the particle size of the carbon nanotubes is decreased due to an external force as the dispersion processes is repeated. If the particle size of the carbon nanotubes dispersed in the solvent exceeds 10 ㎛, the agglomerated lumps of the carbon nanotubes dispersed in the solvent are large, and thus binding force of the substrate resin may be weakened, undesirably causing cracking from the positions of the carbon nanotubes dispersed in the solvent, resulting in poor folding endurance. The solvent may be dimethylformamide (DMF).

Also, the amount of the carbon nanotubes may be 0.1 ~ 2.0 parts by weight based on 100 parts by weight of the polyimide resin. If the amount of the carbon nanotubes is less than 0.1 parts by weight, resistivity is higher than the required level. In contrast, if the amount of the carbon nanotubes exceeds 2.0 parts by weight, resistivity is lower than the required level. The seamless belt for an imaging device functions to transfer a toner from a drum to paper, and thus should have a resistivity in the semiconductive range. However, because the polyimide resin itself has insulating properties, that is, it is not electrically conductive, a conductive material such as carbon nanotubes may be added, whereby the resulting polyimide resin may have resistivity in the semiconductive range. Hence, the use of carbon nanotubes in an appropriate amount is preferable.

In the seamless belt according to the present invention, the polyimide resin is obtained by imidizing biphenyltetracarboxylic dianhydride (BPDA) and an aromatic diamine, and the aromatic diamine may contain 40 ~ 100 mol% of 1,4'-phenylene diamine (1,4-PDA) based on the total amount of the aromatic diamine.

As the dianhydride useful in the preparation of the polyimide resin, biphenyltetracarboxylic dianhydride is polymerized along with 1,4'-phenylenediamine as the diamine, thus obtaining a polyimide, from which a hard and elastic polyimide resin may be prepared, resulting in a seamless belt having good durability. As such, 1,4'-phenylenediamine has a structure which is the shortest and hardest among diamines, and the seamless belt manufactured by using 40 mol% or more of 1,4'-phenylenediamine based on the total amount of the diamine may have high tensile modulus. On the other hand, when the other aromatic diamine except for 1,4'-phenylenediamine is used in an amount of 60 mol% or more, tensile modulus is decreased, and thus the belt may slacken when used for long-term printing, and durability may deteriorate.

In addition to 1,4-phenylenediamine (1,4-PDA), the aromatic diamine may further include one or more selected from the group consisting of 1,3-phenylenediamine (1,3-PDA), 4,4'-methylenedianiline (MDA), 4,4'-oxydianiline (ODA) and 4,4'-oxyphenylenediamine (OPDA). The dianhydride may include 1,2,4,5-benzenetetracarboxylic dianhydride (PMDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 4,4'-oxydiphthalic anhydride (ODPA), 4,4'-hexafluoroisopropylidene diphthalic anhydride, etc. Preferably useful is 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA). The diamine and the dianhydride are typically used in equimolar amounts.

Particularly, in the case where BPDA is used as the dianhydride, superior tensile modulus and folding endurance may be exhibited compared to when using the other dianhydrides.

In the present invention, the molecular weight of the polyimide resin may be adjusted depending on the kind of dianhydride or diamine and the polymerization conditions, and is preferably controlled by adjusting the molar ratio of the dianhydride and the diamine. Specifically, the molar ratio of dianhydride/diamine is preferably set to 100/100 ~ 90, or 100 ~ 90/100. If the molar ratio falls outside of the above range, the molecular weight of the resin is lowered, mechanical strength of the formed belt is decreased, and the conductive filler dispersed in the semiconductive polyamic acid may reagglomerate, thus increasing non-uniformity of the surface resistivity of the formed belt.

The solvent used to prepare the polyimide resin according to the present invention may include amide-based polar solvents, such as N-methyl-2-pyrrolidone, N,N-dimethyl acetamide, N,N-dimethyl formamide, N,N-diethyl acetamide, N,N-diethyl formamide, N-methyl caprolactam, etc. which may be used alone or in mixtures of two or more.

The seamless belt is preferably manufactured so as to be seamless, and the manufacturing method thereof is not particularly limited. In the present invention, the seamless belt may be manufactured in such a manner that, for example, the surface of a cylindrical mold is coated with a polyimide resin in a solution phase using a dispenser and then thermally treated. The thermal treatment is stepwisely performed at 50 ~ 400℃, and pre-baking is performed at 50 ~ 100℃ for 10 ~ 120 min, thus primarily removing the solvent and moisture from the surface of the cylindrical mold coated with the polyimide resin. Subsequently, while the heating rate of 2 ~ 10℃ per minute is maintained, post-curing is performed up to 350 ~ 400℃, so that the solvent and moisture are thoroughly removed from the surface of the cylindrical mold coated with the polyimide resin, and the imidization is performed and completed, and simultaneously a solid seamless belt is manufactured.

When manufacturing the seamless belt, if the belt is excessively thinned to improve thermal conductivity thereof, strength of the belt is drastically decreased, whereby the belt may crack or may be distorted due to repeated rotation stress during printing. The appropriate thickness of the seamless belt is 30 ~ 300 ㎛.

The seamless belt according to the present invention may have a surface resistivity of 10⁸ ~ 10¹³ Ω/sq, and the seamless belt has a uniform surface resistivity the deviation of which is 1.0 or less in any zone thereof, and has a tensile modulus of 4000 MPa or more and a folding endurance of 1000 times or more, thus exhibiting superior mechanical properties. The resulting seamless belt may be effectively employed as an intermediate transfer belt having durability.

A better understanding of the present invention may be obtained through the following examples which are set forth to illustrate, but are not to be construed as limiting, the present invention.

Example 1

A seamless belt was manufactured from the composition shown in Table 1 below using the following method.

1460 g of dimethylformamide (DMF) was placed in a 2L double jacket reactor equipped with a mechanical stirrer, a reflux condenser and a nitrogen inlet. The temperature was set to 30℃, and 67.7 g of 4,4'-oxydianiline (ODA) and 24.4 g of 1,4'-phenylenediamine (PDA) were added as diamines in a nitrogen atmosphere. The mixture was stirred for about 30 min, and completely dissolved, after which 165.7 g of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added. Thereafter, the mixture was stirred for 3 hr while the temperature was maintained. After completion of the reaction, the resulting polyamic acid solution was mixed with 0.1 parts by weight of carbon nanotubes (CNTs) subjected to dispersion treatment, based on the solid content of the polyimide. The carbon nanotubes used had a diameter of 5 nm, and the minimum particle size of the carbon nanotube dispersion solution was 0.2 ㎛ and the maximum particle size thereof was 6 ㎛. The results of measurement of the particle size of the carbon nanotube dispersion solution are graphed in FIG. 2.

The semiconductive polyamic acid thus prepared was a black solution in a uniform phase, and had a viscosity of 200 poises.

A seamless mold made of chromium plated SUS 304 and having a diameter of 300 mm, a thickness of 5 mm and a width of 500 mm was spray coated with a releasing agent (), rotated on a rotary molding machine, and uniformly coated with the semiconductive polyamic acid solution prepared as above using a dispensing coater. Subsequently, the mold was placed in a dry oven, heated at a heating rate of 10℃/min, allowed to stand for 30 min at each of 100℃, 200℃ and 300℃, thus simultaneously completing an imidization reaction and thoroughly removing the solvent and moisture, followed by performing cooling to obtain a polyimide film from the SUS belt, thereby manufacturing a seamless belt having a thickness of 65 ㎛, after which both ends of the seamless belt were cut to have a width of 300 mm.

Example 2

1290 g of dimethylformamide (DMF) was placed in a 2L double jacket reactor equipped with a mechanical stirrer, a reflux condenser and a nitrogen inlet. The temperature was set to 30℃, and 61.0 g of 1,4'-phenylenediamine (PDA) was added as a diamine in a nitrogen atmosphere. The mixture was stirred for about 30 min, and completely dissolved, after which 165.7 g of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added. Thereafter, the mixture was stirred for 3 hr while the temperature was maintained. After completion of the reaction, the resulting polyamic acid solution was mixed with 2.0 parts by weight of carbon nanotubes (CNTs) subjected to dispersion treatment, based on the solid content of the polyimide. The carbon nanotubes used had a diameter of 20 nm, and the minimum particle size of the carbon nanotube dispersion solution was 100 nm (0.1 ㎛) and the maximum particle size thereof was 7 ㎛.

Using the semiconductive polyamic acid thus prepared, a seamless belt was obtained in the manner as in Example 1.

Comparative Example 1

1490 g of dimethylformamide (DMF) was placed in a 2L double jacket reactor equipped with a mechanical stirrer, a reflux condenser and a nitrogen inlet. The temperature was set to 30℃, and 79.0 g of 4,4'-oxydianiline (ODA) and 18.3 g of 1,4'-phenylenediamine (PDA) were added as diamines in a nitrogen atmosphere. The mixture was stirred for about 30 min, and completely dissolved, after which 165.7 g of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added. Thereafter, the mixture was stirred for 3 hr while the temperature was maintained. After completion of the reaction, the resulting polyamic acid solution was mixed with 0.5 parts by weight of carbon nanotubes (CNTs) subjected to dispersion treatment, based on the solid content of the polyimide. The carbon nanotubes used had a diameter of 20 nm, and the minimum particle size of the carbon nanotube dispersion solution was 20 nm (0.02 ㎛) and the maximum particle size thereof was 3 ㎛.

Comparative Example 2

1460 g of dimethylformamide (DMF) was placed in a 2L double jacket reactor equipped with a mechanical stirrer, a reflux condenser and a nitrogen inlet. The temperature was set to 30℃, and 67.7 g of 4,4'-oxydianiline (ODA) and 24.4 g of 1,4'-phenylenediamine (PDA) were added as diamines in a nitrogen atmosphere. The mixture was stirred for about 30 min, and completely dissolved, after which 165.7 g of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added. Thereafter, the mixture was stirred for 3 hr while the temperature was maintained. After completion of the reaction, the resulting polyamic acid solution was mixed with 0.1 parts by weight of carbon nanotubes (CNTs) subjected to dispersion treatment, based on the solid content of the polyimide. The carbon nanotubes used had a diameter of 2 nm, and the minimum particle size of the carbon nanotube dispersion solution was 20 nm (0.02 ㎛) and the maximum particle size thereof was 3 ㎛.

Comparative Example 3

1460 g of dimethylformamide (DMF) was placed in a 2L double jacket reactor equipped with a mechanical stirrer, a reflux condenser and a nitrogen inlet. The temperature was set to 30℃, and 67.7 g of 4,4'-oxydianiline (ODA) and 24.4 g of 1,4'-phenylenediamine (PDA) were added as diamines in a nitrogen atmosphere. The mixture was stirred for about 30 min, and completely dissolved, after which 165.7 g of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added. Thereafter, the mixture was stirred for 3 hr while the temperature was maintained. After completion of the reaction, the resulting polyamic acid solution was mixed with 2.0 parts by weight of carbon nanotubes (CNTs) subjected to dispersion treatment, based on the solid content of the polyimide. The carbon nanotubes used had a diameter of 30 nm, and the minimum particle size of the carbon nanotube dispersion solution was 150 nm (0.15 ㎛) and the maximum particle size thereof was 10 ㎛.

Comparative Example 4

1460 g of dimethylformamide (DMF) was placed in a 2L double jacket reactor equipped with a mechanical stirrer, a reflux condenser and a nitrogen inlet. The temperature was set to 30℃, and 67.7 g of 4,4'-oxydianiline (ODA) and 24.4 g of 1,4'-phenylenediamine (PDA) were added as diamines in a nitrogen atmosphere. The mixture was stirred for about 30 min, and completely dissolved, after which 165.7 g of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added. Thereafter, the mixture was stirred for 3 hr while the temperature was maintained. After completion of the reaction, the resulting polyamic acid solution was mixed with 0.05 parts by weight of carbon nanotubes (CNTs) subjected to dispersion treatment, based on the solid content of the polyimide. The carbon nanotubes used had a diameter of 20 nm, and the minimum particle size of the carbon nanotube dispersion solution was 100 nm (0.1 ㎛) and the maximum particle size thereof was 5 ㎛.

Comparative Example 5

1460 g of dimethylformamide (DMF) was placed in a 2L double jacket reactor equipped with a mechanical stirrer, a reflux condenser and a nitrogen inlet. The temperature was set to 30℃, and 67.7 g of 4,4'-oxydianiline (ODA) and 24.4 g of 1,4'-phenylenediamine (PDA) were added as diamines in a nitrogen atmosphere. The mixture was stirred for about 30 min, and completely dissolved, after which 165.7 g of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added. Thereafter, the mixture was stirred for 3 hr while the temperature was maintained. After completion of the reaction, the resulting polyamic acid solution was mixed with 2.5 parts by weight of carbon nanotubes (CNTs) subjected to dispersion treatment, based on the solid content of the polyimide. The carbon nanotubes used had a diameter of 20 nm, and the minimum particle size of the carbon nanotube dispersion solution was 130 nm (0.13 ㎛) and the maximum particle size thereof was 8 ㎛.

Comparative Example 6

1460 g of dimethylformamide (DMF) was placed in a 2L double jacket reactor equipped with a mechanical stirrer, a reflux condenser and a nitrogen inlet. The temperature was set to 30℃, and 67.7 g of 4,4'-oxydianiline (ODA) and 24.4 g of 1,4'-phenylenediamine (PDA) were added as diamines in a nitrogen atmosphere. The mixture was stirred for about 30 min, and completely dissolved, after which 165.7 g of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added. Thereafter, the mixture was stirred for 3 hr while the temperature was maintained. After completion of the reaction, the resulting polyamic acid solution was mixed with 1.0 part by weight of carbon nanotubes (CNTs) subjected to dispersion treatment, based on the solid content of the polyimide. The carbon nanotubes used had a diameter of 20 nm, and the minimum particle size of the carbon nanotube dispersion solution was 1.7 ㎛ and the maximum particle size thereof was 63 ㎛. The results of measurement of the particle size of the carbon nanotube dispersion solution are graphed in FIG. 3.

The seamless belts manufactured in the examples and comparative examples were measured in terms of surface resistivity, common logarithm of surface resistivity deviation, the particle size of carbon nanotubes, tensile modulus and folding endurance using the following methods. The results are shown in Table 2 below.

(1) Surface resistivity

The seamless belts manufactured in the examples and comparative examples were cut in a width direction to be unfolded in the form of a two-dimensional film. Five random points were chosen from each of the inner/outer surfaces of the seamless belt. At the chosen ten points, surface resistivity was measured under an applied voltage of 100 V for 10 sec using a Hiresta UP resistivity meter (available from Mitsubishi Chemical) provided with a UR-100 probe. The average of the ten measured surface resitivity values was determined.

(2) Common logarithm of surface resistivity deviation

The seamless belts manufactured in the examples and comparative examples were cut in a width direction to be unfolded in the form of a two-dimensional film. Five random points were chosen from each of the inner/outer surfaces of the seamless belt. At the chosen ten points, surface resistivity was measured under an applied voltage of 100 V for 10 sec using a Hiresta UP resistivity meter (available from Mitsubishi Chemical) provided with a UR-100 probe. The common logarithms of the maximum and minimum values of the ten measured surface resistivity values were obtained, and the difference thereof was calculated.

(3) Particle size of carbon nanotubes dispersed in solvent

The dispersion solution of carbon nanotubes subjected to dispersion treatment was analyzed using a particle size meter, Microtrac S3500 (available from ). This particle size was based on the volume average particle size.

(4) Tensile modulus

Five samples having a width of 15 mm x a length of 100 mm were taken from one of the seamless belts, and placed on an Instron tester (Instron 3365SER). According to ASTM D 882, tensile modulus was measured.

(5) Folding endurance

Ten samples having a width of 15 mm x a length of 100 mm were taken from one of the seamless belts, and placed on an MIT tester. Under conditions of R=2, a refraction angle of 135°, and a rate of 175 rpm, the number of foldings was measured up to break of the test samples.

	Solvent (g)	Dianhydride (g)	Diamine (g)		CNT
	DMF	BPDA	ODA	1,4-PDA	CNT Diameter (nm)	CNT Amount (parts by weight)	Min. Particle size of CNTs dispersed in Solvent (㎛)	Max. Particle size of CNTs dispersed in Solvent (㎛)
Ex.1	1460	165.7	67.7	24.4	5	0.1	0.2	6
Ex.2	1290	165.7	-	61.0	20	2.0	0.1	7
C.Ex.1	1490	165.7	79.0	18.3	20	0.5	0.02	3
C.Ex.2	1460	165.7	67.7	24.4	2	0.1	0.02	3
C.Ex.3	1460	165.7	67.7	24.4	30	2.0	0.15	10
C.Ex.4	1460	165.7	67.7	24.4	20	0.05	0.1	5
C.Ex.5	1460	165.7	67.7	24.4	20	2.5	0.13	8
C.Ex.6	1460	165.7	67.7	24.4	20	1.0	1.7	63

	Surface resistivity (Ω/sq)	Common logarithm of surface resistivity deviation (log /sq)	Tensile modulus (MPa)	Folding endurance (times)
Ex.1	108	0.6	4,500	20,000
Ex.2	1012	0.7	8,000	1,000
C.Ex.1	1010	0.6	3,500	18,000
C.Ex.2	105	0.5	4,300	45,000
C.Ex.3	1014	1.0	4,600	8,000
C.Ex.4	1014	1.2	4,500	32,000
C.Ex.5	107	0.9	4,400	7,000
C.Ex.6	1010	1.3	7,200	500

As is apparent from the results of Table 2, the seamless belts according to the embodiment of the present invention, including 0.1 ~ 2.0 parts by weight of carbon nanotubes having a diameter of 5 ~ 20 nm with a minimum particle size of the carbon nanotubes of 0.02 ㎛ or more and a maximum particle size thereof of 10 ㎛ or less, and including a polyimide resin containing 40 ~ 100 mol% of 1,4-PDA based on the total amount of the aromatic diamine, can be seen to exhibit a surface resistivity of 10⁸ ~ 10¹³ Ω/sq, a surface resistivity deviation of 1.0 or less, a high tensile modulus of 4000 MPa or more, and a high folding endurance of 1000 times or more, thus actually improving durability.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

A seamless belt, comprising a single-layer substrate comprising a polyimide resin and carbon nanotubes dispersed in the polyimide resin,
wherein the polyimide resin is obtained by imidizing an aromatic dianhydride and an aromatic diamine, and the aromatic diamine comprises 40 ~ 100 mol% of 1,4-phenylenediamine (1,4-PDA) based on a total amount of the aromatic diamine, and
the carbon nanotubes have a diameter of 5 ~ 20 nm and are contained in an amount of 0.1 ~ 2.0 parts by weight based on 100 parts by weight of the polyimide resin.
The seamless belt of claim 1, wherein the carbon nanotubes are dispersed in a solvent and then dispersed in the polyimide resin, and the carbon nanotubes dispersed in the solvent have a particle size of 0.02 ~ 10 ㎛.
The seamless belt of claim 1, wherein the aromatic dianhydride is biphenyltetracarboxylic dianhydride (BPDA).
The seamless belt of claim 1, wherein the aromatic diamine further includes one or more selected from the group consisting of 1,3-phenylenediamine (1,3-PDA), 4,4'-methylenedianiline (MDA), 4,4'-oxydianiline (ODA) and 4,4'-oxyphenylenediamine (OPDA).
The seamless belt of claim 1, which has a surface resistivity of 10⁸ ~ 10¹³ Ω/sq.
The seamless belt of claim 1, which has a common logarithm of surface resistivity deviation of 1.0 or less.
The seamless belt of claim 1, which has a tensile modulus of 4000 MPa or more.
The seamless belt of claim 1, which has a folding endurance of 1000 times or more.