HK1133669B

HK1133669B - Carbon-black-dispersed polyamic acid solution composition, and process for producing semiconductive polyimide resin belt therewith

Info

Publication number: HK1133669B
Application number: HK10101093.2A
Authority: HK
Inventors: 西浦直树; 鞍冈隆志; 村上彻
Original assignee: 郡是株式会社; Ube 株式会社
Priority date: 2006-09-19
Filing date: 2007-09-18
Publication date: 2012-11-09

Description

Carbon black-dispersed polyamic acid solution composition and method for producing semiconductive polyimide resin belt using same

Technical Field

The present invention relates to a carbon black-dispersed polyamic acid solution composition which is a raw material of a semiconductive polyimide belt, and a method for producing a semiconductive polyimide belt using the same. The semiconductive polyimide belt obtained by the production method can be used as an intermediate transfer belt for electrophotographic copiers, printers, facsimiles, complex machines thereof, digital printers, and the like, each equipped with a color image forming apparatus.

Background

In recent years, office automation equipment has been rapidly developed to increase the speed and image quality, and precise semiconductivity control is indispensable for the intermediate transfer belt in order to achieve optimum transfer efficiency. Among them, it is an important technique to precisely control the resistance of the intermediate transfer belt.

The carbon black-dispersed polyamic acid solution composition as a raw material of the intermediate transfer belt is generally prepared by adding carbon black to a polyamic acid solution obtained by polymerizing tetracarboxylic dianhydride and diamine, and dispersing and mixing the resulting mixture. Generally, polyamic acid is a solution having a weight average molecular weight of 30000 or more and a high molecular weight, from the viewpoint of film-forming properties of a tape. Therefore, the polyamic acid resin has a limited solubility in an organic polar solvent, and has a disadvantage that a high concentration cannot be obtained (for example, at most, 20% by weight or less based on the concentration of the solid content in the solution).

Further, if carbon black is added to the polyamic acid solution, the viscosity increase rate is high, and it is difficult to pulverize the carbon black even by impact force between balls in a dispersing machine such as a bead mill. When carbon black is added and uniformly dispersed in a polyamic acid solution, there is inevitably accompanied an interfacial phenomenon such as "wetting" of the carbon black dispersed and pulverized by a dispersing machine due to a solvent liquid. Therefore, at present, a method of uniformly dispersing carbon black by adding a large amount of an organic polar solvent together with carbon black is employed. As a result, only a polyamic acid solution composition containing carbon black at a high concentration, usually at a solid content concentration of about 15 to 20% by weight, can be obtained.

It is difficult to form a band having a large film thickness at a time by using such a polyamic acid solution having a low solid content concentration, and it takes a long time to evaporate and remove a large amount of organic polar solvent. As a result, time and cost required for the entire process are wasted, and there is room for improvement from the viewpoint of efficiency and economy.

Patent document 1 exemplifies a conductive polyimide seamless belt in which conductive carbon black having a low powder resistance, such as acetylene black or ketjen black, is dispersed in a polyimide resin.

However, since the adsorption and retention of the polyamic acid and the solvent of the conductive carbon black are significantly increased, the viscosity is increased and the dispersibility is deteriorated, which causes problems such as poor dispersion stability and low processability. Further, even when the volume resistivity of the intermediate transfer belt filled with the conductive carbon black is set to a predetermined range, there is a problem that unevenness occurs in an image to be formed. This is considered to be because, when the conductive carbon black is dispersed in a polyimide resin, the formation of a structure by primary aggregation and the formation of a conductive chain by secondary aggregation significantly affect an image.

Patent document 2 discloses a semiconductive belt obtained by mixing 1 to 30 parts by weight of one or two or more carbon blacks each having a volatile content of 2% or more and less than 30% with respect to 100 parts by weight of a binder resin. It is also described that when the amount of carbon black is more than 30 parts by weight, the molded semiconductive tape becomes brittle, and the mechanical properties (toughness herein) inherent in the binder resin are lost, so that it is not preferable that the amount of carbon black is more than 30 parts by weight.

Patent document 3 discloses a semiconductive polyimide belt using conductive carbon black containing 10 to 25% of a volatile component mainly comprising a volatile acid component. It is also described that when the volatile content of carbon black is less than 10%, the dispersibility of carbon black is poor, and as a result, the resistance value cannot be satisfied.

Further, since the channel black is produced in air at a low temperature, the surface thereof contains many oxygen-containing functional groups such as carboxyl groups, phenolic hydroxyl groups, quinone groups, lactone groups, and the like. Therefore, it is known that the dispersibility into the polyamic acid solution becomes good. However, the volatile components of the channel black contain many sulfur compounds and impurities such as undecomposed raw material hydrocarbon (PAH) in addition to hydrogen and oxygen. Among these, the use of channel black is not preferable from the viewpoint of safety and environmental suitability because the undecomposed raw material hydrocarbon (PAH) reacts with nitrogen oxide to form a nitro compound and the nitro compound is converted to a polycyclic aromatic nitro compound having high carcinogenicity.

On the other hand, oil furnace carbon black is preferably produced by thermally decomposing hydrocarbons in a reducing atmosphere in a high-temperature gas of 1400 ℃ or higher in which fuel is burned, because oxygen content and impurities in the inside or on the surface of the particles are extremely small and crystallites are developed. However, they have disadvantages such as poor dispersibility in a polyamic acid solution and aggregation of carbon black due to storage.

Patent documents 4 to 7 report various oxidation methods for modifying oil furnace carbon black to impart an oxygen functional group to the surface thereof, for the purpose of producing carbon black suitable for applications such as liquid toners, inks, and paints.

Patent document 1: japanese laid-open patent publication No. 5-77252

Patent document 2: japanese patent laid-open No. 2000-309712

Patent document 3: japanese patent laid-open No. 2001 and 47451

Patent document 4: japanese laid-open patent publication No. 11-181326

Patent document 5: japanese laid-open patent publication No. 2000-7937

Patent document 6: japanese patent laid-open publication No. 2000-290529

Patent document 7: japanese patent laid-open publication No. 2001-40240

Disclosure of Invention

In view of the problems of the prior art described above, an object of the present invention is to provide a carbon black-dispersed polyamic acid solution composition which uses carbon black having excellent safety and environmental suitability, is excellent in fluidity and dispersion stability of carbon black dispersed in a polyamic acid solution, and has a high solid content concentration and a high carbon black concentration.

Further, an intermediate transfer belt made of polyimide is provided which can obtain a high-quality transferred image in a color image forming apparatus using the polyamic acid solution composition.

In order to achieve precise semiconductivity control in the intermediate transfer belt, the present inventors paid attention to the dispersibility of carbon black in a polyimide resin as a base of the intermediate transfer belt.

For example, in the conductivity model of carbon black in the resin shown in fig. 1, there are 3 types considered: partially continuous carbon black (a), discontinuous carbon black (B), and continuous carbon black (C). As is clear from the equivalent circuit shown on the right, the conductivity of the polyimide tape is exhibited by a combination of the chain effect (R: resistance) and the tunnel effect (C: capacitance) of carbon black. Fig. 2 is a photomicrograph showing the states of (a) to (C). (A) In the above-described image forming method, carbon black is agglomerated to cause microscopic level resistance unevenness, thereby causing image defects. (B) Among them, semiconductivity can be controlled by uniform dispersion, but resistivity varies due to mechanical stress or electrical stress. (C) In (b), stable conductivity is exhibited, and the conductivity is almost determined by the powder resistance of carbon black.

Therefore, as shown in fig. 1, it is necessary to disperse the carbon black continuously and uniformly as much as possible, rather than to disperse the carbon black partially continuously or discontinuously in the resin, and therefore it is considered important to increase the filling degree of the carbon black in the resin, that is, to increase the carbon black concentration in the solid content of the carbon black-dispersed polyamic acid solution composition.

Then, the present inventors have found that carbon black obtained by an oil furnace method is oxidized to obtain carbon black having a high powder resistance with a volatile content in a range of 2 to 6%, and a polyamic acid solution composition in which the carbon black is dispersed can be uniformly dispersed at a high concentration (about 20 to 30% by weight in a solid content). Further, it was found that when a belt obtained by rotational molding using the polyamic acid solution composition was used for an intermediate transfer belt, the desired uniform semiconductivity (surface resistivity of 10) was exhibited⁹～10¹⁴Ω/□ or so) to obtain a high-quality transferred image. Based on such knowledge, further studies have been repeated, and the present invention has been finally completed.

That is, the present invention provides the following carbon black-dispersed polyamic acid solution composition and a semiconductive polyimide resin belt obtained using the polyamic acid solution composition.

A carbon black-dispersed polyamic acid solution composition comprising a polyamic acid solution obtained by reacting biphenyltetracarboxylic dianhydride and an aromatic diamine in substantially equimolar amounts, and carbon black having a volatile content of 2 to 6% produced by an oil furnace method, wherein the solution composition has a solid content concentration of 23% by weight or more and the solid content has a carbon black concentration of 20 to 30% by weight.

Item 2 the carbon black-dispersed polyamic acid solution composition according to item 1, wherein the carbon black has a pH of 2 to 3 and a nitrogen-adsorbing specific surface area of 60 to 150m²The DBP absorption amount is 40-120 ml/100g, and the extraction amount of undecomposed raw material hydrocarbon (PAH) is 10ppm or less.

The carbon black-dispersed polyamic acid solution composition according to item 1 or 2, wherein the carbon black is a carbon black obtained by oxidation treatment with an oxidizing agent containing ozone.

Item 4 the carbon black-dispersed polyamic acid solution composition according to item 1, wherein the polyamic acid solution is a polyamic acid solution in which the weight-average molecular weight of the polyamic acid is 30000 or less.

The carbon black-dispersed polyamic acid solution composition according to claim 1, wherein the biphenyltetracarboxylic dianhydride comprises about 10 to 80 mol% of asymmetric 2, 3, 3, ' 4 ' -biphenyltetracarboxylic dianhydride, and the aromatic diamine is 4, 4 ' -diaminodiphenyl ether.

The item 6 is a method for producing a semiconductive polyimide resin belt, wherein the carbon black-dispersed polyamic acid solution composition described in any one of items 1 to 4 is formed into a tubular article by a rotational molding method, and the article is heat-treated to imidize the article, the method comprising the steps of:

(1) a step of coating the carbon black-dispersed polyamic acid solution composition onto the inner peripheral surface of a cylindrical mold rotating at a centrifugal acceleration of about 0.5 to 8 times the gravitational acceleration, in a uniform thickness;

(2) heating the cylindrical mold at a temperature of about 100 to 140 ℃ while rotating the cylindrical mold at a centrifugal acceleration of about 0.5 to 8 times the gravitational acceleration to form a self-supporting (no flow of the coating) coating; and

(3) and heating the cylindrical mold at a temperature of about 300 ℃ or higher in a state where the film is adhered to the inner peripheral surface of the cylindrical mold, thereby imidizing the film.

Item 7. a semiconductive polyimide resin tape produced by the production method described in item 6.

Item 8 is a semiconductive polyimide resin tape having uniformly dispersed therein carbon black having a volatile component of 2 to 6% produced by an oil furnace process, which contains 70 to 80% by weight of the polyimide resin and 20 to 30% by weight of the carbon black, and has a surface resistivity of 10⁹～10¹⁴Ω/□。

The semiconductive polyimide resin tape according to the item 8, wherein the average film thickness is 50 μm to 150 μm.

An intermediate transfer belt for an electrophotographic apparatus according to item 10, which is formed of the semiconductive polyimide resin belt according to any one of items 7 to 9.

The present invention will be described in detail below.

The carbon black-dispersed polyamic acid solution composition is characterized by containing a polyamic acid solution and carbon black having a volatile content of 2-6% obtained by oxidizing carbon black obtained by an oil furnace method, wherein the solid content concentration of the solution composition is 23 wt% or more, and the carbon black concentration in the solid content is 20-30 wt%. The solution composition has a high solid content, and the carbon black is uniformly dispersed in the polyamic acid solution. The "solid content concentration" used herein means a concentration measured by the method described in the examples.

1. Carbon black having 2-6% volatile component

The carbon black used in the present invention is prepared by further subjecting carbon black produced by an oil furnace method to oxidation treatment to obtain carbon black having a volatile content of 2 to 6%.

The production method of carbon black by the oil furnace method is superior in yield and productivity as compared with the tank method, and does not pollute the environment during production, and therefore, it is currently the mainstream of carbon black. However, since the channel black contains a large amount of volatile components (usually 10.0 or more), it has excellent fusion ability with the polyamic acid solution and excellent dispersibility, whereas the oil furnace black has a significantly smaller amount of volatile components (usually 1.5% or less) than the channel black, and therefore has disadvantages such as poor dispersibility in the polyamic acid solution and aggregation of the carbon black during storage. This is because oil furnace black is produced by thermally decomposing hydrocarbons in a reducing atmosphere in a high-temperature gas in which fuel is burned, and therefore volatile components are significantly reduced as compared with channel black produced in air at a low temperature.

In the present invention, the volatile content is increased to a range of 2 to 6% by modifying (oxidizing) the oil furnace black.

In the oxidation treatment, the type of the oxidizing agent used for the oxidation is particularly important, and as the oxidizing agent, an oxidizing agent such as nitric oxide, ozone, hypochlorites, or sulfuric acid gas can be used. In particular, an oxidizing agent containing ozone, particularly ozone, can be preferably used in view of the fact that the amount of the raw material oxidizing agent remaining in the carbon black after the treatment is small and the raw material hydrocarbon (PAH) is not decomposed. It is preferable that the amount of undecomposed hydrocarbon feedstock (PAH) is as small as possible, specifically, 10ppm or less.

It is important that the volatile content of the carbon black obtained by the oil furnace method is in the range of 2 to 6%, preferably about 2.5 to 5% by the oxidation treatment.

Since the surface of carbon black having a volatile content of 2 to 6% contains an oxygen functional group (particularly, a carboxyl group) such as a phenolic hydroxyl group, a carbonyl group, or a carboxyl group, fluidity and dispersion stability in a polyamic acid solution are improved, and affinity with a polyimide resin is also improved.

In addition, if carbon black having the same specific surface area and dibutyl phthalate absorption amount (DBP absorption amount) is produced by the oil furnace method, the volatile matter amount and powder resistance are roughly in a proportional relationship. Since the oxygen functional group, which is a volatile component on the surface of the carbon black, functions as an insulator that blocks the flow of pi electrons, the powder resistance of the carbon black after oxidation treatment is higher than that of the carbon black obtained by an oil furnace method without oxidation treatment, and by setting the volatile component in the above range, the powder resistance of the carbon black can be adjusted to a high value of about 3 to 30 Ω · cm.

Therefore, the surface resistivity of the polyimide resin tape is set to a desired range (10)⁹～10¹⁴Ω/□), the polyimide resin can be highly filled with the carbon black (the concentration of the carbon black in the polyimide resin is 20 to 30 wt%). This makes it possible to obtain a polyimide resin tape which is provided with conductivity based on chains of carbon black and has stable electrical characteristics which are not easily affected by the external environment and applied voltage. In other words, the carbon black concentration in the solid content of the carbon black-dispersed polyamic acid solution composition can be adjusted to a high concentration of 20 to 30 wt%.

Further, when the filling amount (concentration) of carbon black in the polyimide resin is increased, the relationship between the surface resistivity of the polyimide resin and the filling amount of carbon black is shown in the figure, and the slope thereof becomes gentle (for example, see example 4 and fig. 3). That is, the amount of change in the surface resistivity of the polyimide resin with respect to the amount of change in the carbon black loading is reduced. Therefore, when the belt is manufactured, the surface resistivity can be prevented from being greatly changed due to a slight change in the carbon black loading amount, and the control of the surface resistivity of the belt becomes easy.

The volatile content of carbon black was measured by the method described in examples.

Carbon black having a volatile content of less than 2% (for example, mitsubishi carbon black "MA 11" and "MA 100" manufactured by mitsubishi chemical, "Printex 95" and "Printex L6" manufactured by Degussa) has a problem of affinity with a polyamic acid solution, and tends to form secondary aggregates by van der waals force after dispersion.

Carbon blacks having a volatile content of more than 6% (for example, "Color Black fw 200", "Special Black 5", "Special Black 4", "Printex 150T" manufactured by Degussa) are almost all channel Black, and contain a large amount of impurities such as sulfur and undecomposed raw material hydrocarbon (PAH) in addition to hydrogen and oxygen, and the impurities deteriorate the mechanical properties inherent in a binder resin such as a polyimide resin. Further, when the oil furnace black is oxidized to a volatile content of more than 6%, the powder resistance is significantly increased (to be changed to insulating carbon black), and thus the surface resistivity of 10, which is necessary as an intermediate transfer belt, cannot be realized⁹～10¹⁴Ω/□。

The carbon black used in the present invention preferably has a nitrogen adsorption specific surface area (JIS K6217) of 60 to 150m²A total of 80 to 130m²(ii) a range of/g. Generally, when carbon black is oxidized by various methods, the larger the specific surface area is, the more oxygen functional groups are imparted. However, the powder resistance of carbon black and the physical properties of carbon black mixed with various materials are related to the number of oxygen functional groups provided per unit surface, not the absolute amount of oxygen functional groups.

The specific surface area is less than 60m²At the time of the reaction,/g, the affinity with the polyamic acid solution cannot be obtained, and the powder resistance does not reach a sufficiently high value. And a specific surface area exceeding 150m²In the case of the specific surface area per gram, carbon black having a small primary particle size or having micropores even if the primary particle size is the same, the powder resistance of the carbon black is not increased even if an oxygen functional group is added. Therefore, a semiconductive polyimide resin tape having a high carbon black concentration in the solid content (for example, filled at a high concentration of 20 wt% or more) cannot be obtained. That is, only semiconductive polyimide resin tapes with a low carbon black loading can be obtained.

The carbon black used in the present invention has a pH of 2 to 4, preferably 2 to 3.

Further, the dibutyl phthalate absorption amount (DBP absorption amount) of the carbon black used in the present invention is preferably in the range of 40 to 120ml/100g, more preferably 50 to 90ml/100 g. When the DBP absorption exceeds 120ml/100g, the powder resistance of the carbon black does not increase even if the oxidation treatment is carried out. Therefore, a semiconductive polyimide resin tape having a high carbon black concentration of 20 wt% or more in the solid content cannot be obtained. When the DBP absorption is less than 40ml/100g, the powder resistance becomes too high, and therefore, carbon black cannot be filled in such a manner that the carbon black concentration in the solid content exceeds 30% by weight, and thus a semiconductive polyimide resin tape cannot be obtained.

Further, it is preferable that the amount of the undecomposed raw material hydrocarbon (PAH) is as small as possible, specifically, when the amount of the undecomposed raw material hydrocarbon is 10ppm or less, the amount of the reaction with nitrogen oxides is small, and the nitro compound formed is negligible. The undecomposed raw material hydrocarbon (PAH) can be decomposed by an oxidation treatment, particularly an oxidation treatment with ozone.

2. Carbon black dispersed polyamic acid solution composition

The carbon black-dispersed polyamic acid solution composition is prepared by dispersing carbon black having a volatile content of 2-6% in a polyamic acid solution obtained by reacting biphenyl tetracarboxylic dianhydride and an aromatic diamine in an approximately equimolar amount in an organic polar solvent.

Specific examples of the biphenyltetracarboxylic dianhydride include 2, 3, 3 ', 4' -biphenyltetracarboxylic dianhydride (a-BPDA), 3, 3 ', 4, 4' -biphenyltetracarboxylic dianhydride (s-BPDA), 2 ', 3, 3' -biphenyltetracarboxylic dianhydride (i-BPDA), and biphenyltetracarboxylic dianhydrides obtained by mixing two or more of the above biphenyltetracarboxylic dianhydrides.

Examples of the aromatic diamine include diaminodiphenyl ether, and specific examples thereof include 4, 4 ' -diaminodiphenyl ether, 3 ' -diaminodiphenyl ether, and 3, 4 ' -diaminodiphenyl ether.

The organic polar solvent is preferably an aprotic organic polar solvent, and examples thereof include N-methyl-2-pyrrolidone (hereinafter referred to as "NMP"), N-dimethylformamide, N-diethylformamide, N-dimethylacetamide, dimethyl sulfoxide, hexamethylphosphoramide, and 1, 3-dimethyl-2-imidazolidinone. One or a mixed solvent of two or more of these solvents may be used. NMP is particularly preferred.

Further, a typical example of the polyamic acid solution of the present invention is a polyamic acid solution obtained by reacting two or more kinds of biphenyltetracarboxylic acid dianhydride and an aromatic diamine in an organic polar solvent. Among them, the biphenyltetracarboxylic dianhydride preferably contains both of a symmetric and an asymmetric biphenyltetracarboxylic dianhydride. More preferably, the composition contains 10 to 80 mol% (particularly 15 to 50 mol%) of asymmetric 2, 3, 3 ', 4' -biphenyltetracarboxylic dianhydride and 90 to 20 mol% (particularly 85 to 50 mol%) of symmetric biphenyltetracarboxylic dianhydride, and further more preferably contains 20 to 30 mol% of asymmetric 2, 3, 3 ', 4' -biphenyltetracarboxylic dianhydride and 80 to 70 mol% of 3, 3 ', 4, 4' -biphenyltetracarboxylic dianhydride.

The upper limit of the weight average molecular weight of the polyamic acid in the polyamic acid solution is 30000, preferably 25000 or less. The lower limit is 3000, preferably 6000 or more. Molecules in an oligomer state having a weight average molecular weight of less than 3000 do not have an effect of entangling (entangling) with internal molecules, resulting in formation of a brittle layer on the surface of the semiconductive polyimide resin belt.

The molecular weight of the polyamic acid can be adjusted by any known method. For example, the molecular weight adjustment can be well performed by the following method: a method in which a polyamic acid having a predetermined molecular weight is formed by polymerization at a molar ratio of biphenyltetracarboxylic dianhydride to aromatic diamine of 0.5 to 0.95, and biphenyltetracarboxylic acid is added as necessary so that the molar ratio of biphenyltetracarboxylic acid to aromatic diamine is substantially equal (see, for example, Japanese patent publication (Kokoku) No. 1-22290); and a method of reacting biphenyltetracarboxylic dianhydride with an aromatic diamine in an approximately equimolar amount, in which a compound for suppressing the increase in molecular weight such as a predetermined amount of water is made to coexist (see, for example, Japanese patent publication No. 2-3820).

Particularly, in the case of a polyamic acid solution containing both of the above-described symmetric and asymmetric biphenyltetracarboxylic dianhydrides, the solubility of the polyamic acid in the organic polar solvent can be improved, and the solid content concentration of the polyamic acid solution can be made high at 23% by weight or more, particularly 25 to 50% by weight. The reason why the solid content can be made high in this way is that polyamic acid is not increased in molecular weight and is easily dissolved in a solvent. Therefore, a certain band having a film thickness of 100 μm or more can be easily produced, and the amount of solvent used is small, so that the cost is controlled and the solvent is easily evaporated and removed.

In addition, when the amount of the solvent to be evaporated is large, the buoyancy and surface tension causing temperature convection and evaporation convection during drying, viscosity change due to solvent evaporation, density change, and the like are large, and a "floating phenomenon" occurs, which causes the dispersion state of the carbon black to be uneven. However, the polyamic acid solution composition of the present invention has a small amount of solvent, and therefore such a problem can be suppressed as much as possible.

The method for mixing the carbon black in the polyamic acid solution is not particularly limited as long as the carbon black is uniformly mixed and dispersed in the polyamic acid solution. For example, a method using a sand mill, a bead mill, an ultrasonic mill, a triple roll, or the like can be used. The average particle diameter of the carbon black after mixing and dispersing is usually about 0.1 to 0.5. mu.m, preferably about 0.2 to 0.4. mu.m.

The amount of carbon black added to the polyamic acid solution is set so that the carbon black is 20 to 30% by weight of the solid content of the polyamic acid solution composition. When the lower limit is 20 wt% or more, for example, in the case of using as an intermediate transfer belt of a color image forming apparatus or the like, since it is possible to remove electricity appropriately while securing charging stability of electric charge, and it is stable for a long period of time, and a high-quality transfer image can be obtained, it is necessary to set the lower limit to 20 wt% or more, and it is necessary to set carbon black to 30 wt% or less in order to maintain strength as an intermediate transfer belt, and there is no problem such as breakage of an intermediate transfer member even in long-term use.

In addition, additives such as imidazole compounds (2-methylimidazole, 1, 2-dimethylimidazole, 2-methyl-4-methylimidazole, 2-ethyl-4-ethylimidazole, 2-phenylimidazole), surfactants (fluorine-based surfactants, etc.) may be added to the composition within a range not to adversely affect the effects of the present invention.

Thus, a polyamic acid solution composition in which carbon black is uniformly dispersed in a solid content of 20 to 30% by weight can be produced.

When the viscosity of the polyamic acid solution composition containing carbon black dispersed therein is, for example, 0.5 to 50 pas, preferably 1 to 10 pas, deterioration in dispersion of carbon black can be minimized. The carbon black in the solution preferably has an average particle diameter in the range of 0.1 to 0.5 μm and a maximum particle diameter of 1 μm or less.

3. Method for producing semiconductive polyimide tape

The semiconductive polyimide belt of the present invention is produced by molding the carbon black-dispersed polyamic acid solution composition into a tubular article by a rotational molding method and subjecting the tubular article to a heat treatment.

In particular, the manufacturing method is characterized by comprising the following steps: (1) a step of coating the polyamic acid solution composition in which carbon black is uniformly dispersed, with a uniform thickness, on the inner peripheral surface of a cylindrical mold that rotates at a low speed at a centrifugal acceleration that is 0.5 to 8 times the gravitational acceleration; (2) heating the cylindrical mold at a temperature of 100 to 140 ℃ while the cylindrical mold is rotating at a low speed at a centrifugal acceleration of 0.5 to 8 times the gravitational acceleration, thereby volatilizing the solvent to form a self-supporting (film-free flow) film; and (3) heating at a temperature of about 300 ℃ or higher in a state where the film is adhered to the inner peripheral surface of the cylindrical mold, thereby imidizing the film.

Hereinafter, a method for producing a semiconductive polyimide tape using the carbon black-dispersed polyamic acid solution composition (hereinafter, also simply referred to as "liquid raw material") will be described.

The liquid material is coated on the inner peripheral surface of a cylindrical mold rotating at a low speed at a centrifugal acceleration of 0.5 to 8 times the gravitational acceleration in a uniform thickness. That is, by supplying the liquid raw material under low-speed rotation at a centrifugal acceleration of 0.5 to 8 times the gravitational acceleration, the shearing force applied in the rotation direction is small, and the orientation of the molecular chain and the structural orientation of the filler such as carbon black can be suppressed. When the centrifugal acceleration is less than 0.5 times the gravitational acceleration, the supplied liquid raw material may not be closely attached to the inner peripheral surface of the cylindrical mold and may flow down (fall down). On the other hand, when the centrifugal acceleration is more than 8 times the gravitational acceleration, not only the molecular chain orientation and the structural orientation of the filler such as carbon black are caused by the shear force in the rotational direction received at the time of supply, but also the flow of the liquid raw material is caused by the centrifugal force.

The centrifugal acceleration (G) used in the present invention is derived from the following equation.

G(m/s²)＝ρ·ω²＝ρ·(2·π·v)²

Here, r represents the radius (m) of the cylindrical die, ω represents the angular velocity (rad/s), and n represents the number of revolutions for 1 second (the number of revolutions for 60s is r.p.m). The acceleration of gravity (g) for comparison was 9.8 (m/s)²)。

The liquid material supply mechanism is configured to apply the liquid material to the inner peripheral surface of the cylindrical die in a uniform thickness by moving the liquid material in the direction of the rotation axis of the rotating cylindrical die while discharging the liquid material by a nozzle method or a spray method. The shape of the coating head is not particularly limited, and a circular shape, a rectangular shape, or the like can be used as appropriate. The size of the coating head is not particularly limited, and may be designed in accordance with the viscosity of the liquid material to be discharged. The mode of the output pressure is not particularly limited, and compressed air, a screw pump (mohno pump) corresponding to a high viscosity liquid, a gear pump, or the like can be used.

When the liquid material is applied to the inner peripheral surface of the cylindrical die in a uniform thickness, the liquid material is made to flow by the high-speed rotation of the cylindrical die, that is, by the centrifugal force, and it is not necessary to make the thickness of the coating film uniform. In the rotational molding using a centrifugal force, after the raw material is supplied, the liquid raw material is uniformly cast on the inner surface of the cylindrical mold by the centrifugal force. Then, the carbon black particles are aligned in the flow direction by the flow generated by the centrifugal force action and are formed into a certain structure. Therefore, the electrical characteristics of the polyimide intermediate transfer belt may be adversely affected. In contrast, the method of the present invention, which does not rotate at high speed, hardly causes such a problem.

The inner peripheral surface of the cylindrical mold is preferably coated with a release agent so that the polyimide resin does not adhere to the inner peripheral surface. The kind of the mold release material is not particularly limited as long as it is a material into which a solvent of a liquid raw material and steam or the like generated from the resin during the heating reaction do not enter.

In the film forming step of the liquid resin, the solvent is volatilized at a temperature of 100 to 140 ℃ in a state of being rotated at a low speed at a centrifugal acceleration of 0.5 to 8 times the gravitational acceleration so that the solid content concentration becomes 40 wt% or more, thereby forming a self-supporting film on the inner peripheral surface of the cylindrical mold, whereby the film forming step can be completed.

The polyimide resin film forming step is performed by increasing the temperature to about 250 ℃ for 60 to 120 minutes in a state of being adhered to the inner peripheral surface of the cylindrical mold, depending on the kind of the polyimide resin. Then, the film is heated at a temperature of, for example, 300 to 350 ℃ for 30 to 90 minutes to complete the imidization, whereby a polyimide resin film can be formed. By forming the coating film in a state of adhering to the inner peripheral surface of the cylindrical mold, shrinkage due to imidization reaction and solvent volatilization can be suppressed, and the polymer chains can be uniformly oriented in the in-plane direction by the stress.

As described above, the carbon black-dispersed polyamic acid solution composition has a high solid content concentration and a high carbon black concentration in the solid content. Furthermore, the semiconductive polyimide resin tape molded using the composition has a high carbon black concentration and sufficiently maintains the original mechanical properties (toughness and the like) of the polyimide resin.

The average film thickness of the obtained semiconductive polyimide tape is usually adjusted to about 50 to 150 μm, preferably about 60 to 120 μm.

And, the surface resistivity is usually adjusted to 10⁹～10¹⁴Omega/□ of about 10 is preferred¹⁰～10¹³And omega/□.

When the thus produced semiconductive polyimide belt is used as an intermediate transfer belt of a color image forming apparatus such as an electrophotographic machine, for example, it can be used to remove electricity appropriately while ensuring charge stability of electric charge, and can provide a high-quality transferred image stably for a long period of time.

With the carbon black-dispersed polyamic acid solution composition of the present invention, carbon black in the solution is excellent in fluidity and dispersion stability, has a high solid content concentration in which the solvent is reduced as much as possible, and has a high carbon black concentration in the solid content. The carbon black used has an extremely low impurity content and is excellent in safety and environmental suitability. Further, when a polyimide resin belt produced using the polyamic acid solution composition is used as an intermediate transfer belt or the like, accurate transfer can be achieved in a color image forming apparatus, and a high-quality transfer image can be obtained stably for a long period of time.

Drawings

FIG. 1 shows a conductivity model of carbon black in a resin.

Fig. 2 is a photomicrograph showing the state of (a) to (C) in fig. 1. (A) The carbon black is partially continuous, and is agglomerated, and the resistance is not uniform at a microscopic level, resulting in image defects. (B) The carbon black is uniformly dispersed for discontinuity, and semiconductivity can be controlled, but the resistivity varies due to mechanical and electrical stress. (C) The chain effect is a continuous (ideal model) and the conductivity is exhibited only by the chain effect due to the high filling of the carbon black, and the conductivity is determined by the powder resistance of the carbon black.

FIG. 3 shows the relationship between the carbon black loading of the semiconductive polyimide resin tape and the surface resistivity of the tape, which were measured in example 4.

Detailed Description

The present invention will be described in more detail below with reference to comparative examples and examples, but the present invention is not limited to these examples.

The physical property values described in the present specification were measured as follows.

(1) Nitrogen adsorption surface area

The nitrogen adsorption surface area was measured based on JIS K6217 (low-temperature nitrogen adsorption method). Alternatively, reference is made to the characteristic data of commercial carbons.

(2) DBP absorption

The DBP absorption was measured in accordance with JIS K6217. Alternatively, reference is made to the characteristic data of commercial carbons.

(3) Volatile component of carbon black

The volatile matter was measured in accordance with JIS K6221, and the weight loss of the carbon black after heating at 950 ℃ for 7 minutes was measured, and the weight loss was expressed in percentage (% by weight) relative to the weight of the carbon black before heating.

(4) pH of carbon Black

The pH was measured using a glass electrode meter for a mixture of carbon black and distilled water.

(5) Extraction of undecomposed feedstock hydrocarbons (PAH) of carbon black

5g of carbon black dried at 80 ℃ for 24 hours was put on a cylindrical glass filter paper, and Soxhlet extraction was carried out for 48 hours using 180cc of monochlorobenzene as a solvent. The extract was concentrated, and the amount of extraction was quantified by liquid chromatography, and divided by the weight of carbon black to obtain the content. The liquid chromatography analyzer is implemented as follows: LC-6A flow control device manufactured by Shimadzu corporation, model SCL-6A Detector manufactured by Shimadzu corporation, Watera490E, manufactured by Millipore corporation, injection quantity was 5. mu.L.

(6) Particle size of carbon black

The particle size of the carbon black in the solution was measured by using a LA-920 type laser diffraction-scattering particle size distribution measuring apparatus manufactured by HORIBA.

(7) Solid component in polyamic acid solution composition and concentration thereof

The solid content concentration of the carbon black-dispersed polyamic acid solution composition was a value calculated as follows. The sample is precisely weighed in a heat-resistant container such as a metal cup, and the weight of the sample at this time is defined as A (g). The heat-resistant container containing the sample was placed in an electric oven, and heated and dried while sequentially raising the temperature for 120 ℃x15 minutes, 180 ℃x15 minutes, 260 ℃x30 minutes, and 300 ℃x30 minutes, and the weight of the obtained solid content (solid content weight) was set to b (g). The values of a and B (n is 5) were measured for the same sample of 5 samples, and the solid content concentration was obtained by substituting the following equation. The average value of the 5 samples was used as the solid content concentration.

Solid content concentration ═ B/A × 100 (%)

(8) Weight average molecular weight of Polyamic acid

The weight average molecular weight in the present specification is a value measured by GPC (solvent: NMP, in terms of polyethylene oxide).

(9) Surface resistivity of semiconductive tape

In the measurement of the Surface Resistivity (SR), the obtained semiconductive tape was cut into a length of 400mm, and the sample was measured using a resistance measuring instrument "high resistivity instrument IP · UR probe" manufactured by mitsubishi chemical corporation, in which 3 places and 4 places in the longitudinal (circumferential) direction at equal intervals in the width direction were counted to 12 places in total, and the surface resistivity was expressed as the average value of the whole. The Surface Resistivity (SR) was measured after 10 seconds under the application of 500V.

Production example 1

Ethylene tar was used as the feedstock oil, and 3 kinds of carbon blacks were produced by a normal oil furnace method using coke oven gas at the time of combustion. As the reaction stop water, pure water treated with an ion exchange resin was used.

800g of the above carbon black was charged into a cylindrical kiln having an inner diameter of 50cm and a length of 80cm, and a gas having an ozone concentration of 10 wt% was allowed to contact and react with the carbon black from the bottom thereof. The gas was generated by an ozone generator manufactured by PCI corporation, 100% oxygen was used as a raw material gas) and the amount of nitrogen oxide in the ozone gas was 0 ppm. The properties of the obtained carbon black (CB 1-3) are shown in Table 1.

Further, the characteristics of commercially available carbon Black "MA 100" manufactured by Mitsubishi chemical and carbon Black "Special Black 4(SB 4)" manufactured by Degussa are also given.

[ Table 1]

	CB1	CB2	CB3	MA-100	SB4
						Manufacturing method	Oil furnace method	Oil furnace method	Oil furnace method	Oil furnace method	Trough method
PH	2.7	2.4	2.3	3.5	3.0
						Volatile component (%)	2.6	3.3	5.1	1.5	14.0
Specific surface area (m)²/g)	98	118	122	110	180
						DBP absorption (ml/100g)	91	75	68	100	230
PAH extraction amount (ppm)	1.0	0.8	0.6	1.1	16.0

Example 1

50kg of a polyamic acid solution (weight-average molecular weight 29000) synthesized from 3, 3 ', 4, 4 ' -biphenyltetracarboxylic dianhydride and 4, 4 ' -diaminodiphenyl ether in NMP solution was prepared. The viscosity of the solution was 3.0 pas, and the solid content concentration was 18.0 wt%. To 10kg of this solution were added carbon black of CB1 and an NMP solution, and the carbon black was uniformly dispersed by a sand mill. The dispersion conditions are set so that the average particle diameter of the carbon black in the solution is 0.5 μm or less, respectively, for the purpose of uniform dispersion. The characteristics of the obtained carbon black-dispersed polyamic acid solution composition are shown in table 2.

Example 2

A carbon black-dispersed polyamic acid solution composition was prepared using CB2 in place of CB1 of example 1. The properties are shown in Table 2.

Example 3

A carbon black-dispersed polyamic acid solution composition was prepared using CB3 in place of CB1 of example 1. The properties are shown in Table 2.

Comparative example 1

A carbon black-dispersed polyamic acid solution composition was prepared using "MA 100" manufactured by mitsubishi chemical, instead of CB1 of example 1. In order to uniformly disperse the carbon black in the solution to an average particle diameter of 0.5 μm or less, a large amount of NMP solution must be added, and the volatile content concentration is lowered. The properties are shown in Table 2.

Comparative example 2

Instead of CB1 of example 1, a carbon Black-dispersed polyamic acid solution composition was prepared using "Special Black 4" manufactured by Degussa. In order to uniformly disperse the carbon black in the solution to an average particle diameter of 0.5 μm or less, a large amount of NMP solution must be added, and the solid content concentration is low. The properties are shown in Table 2.

[ Table 2]

Example 4 (production of semiconductive polyimide resin tape by rotational Molding)

A plurality of liquid materials adjusted to various carbon black concentrations were prepared using the carbon black-dispersed polyamic acid solution compositions (solutions 1 to 5) of examples 1, 2, and 3 and comparative examples 1 and 2.

While a cylindrical die having an outer diameter of 324mm, an inner diameter of 300mm and a length of 500mm was rotated at a centrifugal acceleration of 4.0 times the acceleration of gravity, each liquid material was uniformly applied to the inner peripheral surface of the cylindrical die at a width of 480mm by a spraying method. The coating thickness was calculated from the solid component concentration, and was set so that the thickness of the intermediate transfer member was 100 μm. Thereafter, the cylindrical mold was rotated at a centrifugal acceleration 4.0 times the acceleration of gravity, and the temperature was raised to 120 ℃ for 60 minutes, followed by drying at 120 ℃ for 90 minutes.

Then, the film was put into a high-temperature heating furnace with the film adhered to the inner peripheral surface of the cylindrical mold, and the temperature was raised to 320 ℃ over 120 minutes, and the film was heated at 320 ℃ for 60 minutes, thereby completing the conversion into polyimide. Thereafter, the temperature was cooled to room temperature, and the semiconductive polyimide tape was taken out from the mold.

Fig. 3 shows the relationship between the carbon black loading and the surface resistivity of the semiconductive polyimide tape thus obtained.

As can be seen from fig. 3, with regard to "MA 100" and "SB 4", when the concentration of carbon black filled in the polyimide resin reached 20 wt%, high conductivity was exhibited due to the chain effect of the carbon black, and the range of semiconductivity required for the intermediate transfer belt could not be controlled (10)⁹～10¹⁴Omega/□ or so). Specifically, the surface resistivity became 1 × 10⁸Omega/□ or less (under range).

On the other hand, it is found that CB1, CB2, and CB3 can be filled with the carbon black at a concentration of 20 wt% or more. This can impart conductivity to the carbon black-based chain, and has stable electrical characteristics that are not easily affected by the external environment and applied voltage. Further, the relationship between the surface resistivity and the carbon black loading of the polyimide resin is gentle in the slope. Therefore, when the belt is manufactured, the surface resistivity can be prevented from greatly varying due to a slight change in the amount of carbon black filled, and the control of the resistance can be simplified.

Example 5

10kg of a polyamic acid solution (weight-average molecular weight 24000) synthesized from 3, 3 ', 4, 4 ' -biphenyltetracarboxylic dianhydride and 4, 4 ' -diaminodiphenyl ether in an NMP solution was prepared. The viscosity of the solution was 3.0 pas, and the solid content concentration was 19% by weight. To the solution, 570g of CB1 and 100g of NMP were added, and the carbon black was uniformly dispersed by a sand mill.

The carbon black-dispersed polyamic acid solution composition had a solid content of 23.15 wt% and a carbon black content of 23.1 wt%. The average particle diameter of carbon black in the solution was 0.243. mu.m, and the maximum particle diameter was 0.421. mu.m.

Using the carbon black-dispersed polyamic acid solution composition, a semiconductive polyimide belt was produced by the rotational molding method shown in example 4. The surface state, surface resistivity and thickness of the semiconductive polyimide belt are shown in table 3.

Example 6

After dissolving 4, 4 ' -diaminodiphenyl ether in 100 mol% in NMP solution, 20 mol% of 2, 3, 3 ', 4 ' -biphenyltetracarboxylic dianhydride and 80 mol% of 3, 3 ', 4, 4 ' -biphenyltetracarboxylic dianhydride were added, and water was added thereto to synthesize a polyamic acid solution (weight-average molecular weight 12000) based on japanese examined patent publication No. 2-3820, and 5kg of this solution was prepared. The viscosity of the solution was 5.5 pas, and the solid content concentration was 30.0 wt%. To the solution were added 510g of CB2 and 1000g of NMP, and the carbon black was uniformly dispersed by a sand mill.

The carbon black-dispersed polyamic acid solution composition had a solid content of 30.87 wt% and a carbon black content of 25.4 wt%. The average particle diameter of carbon black in the solution was 0.281. mu.m, and the maximum particle diameter was 0.51. mu.m.

Example 7

After dissolving 4, 4 ' -diaminodiphenyl ether in 100 mol% in NMP solution, 50 mol% of 2, 3, 3 ', 4 ' -biphenyltetracarboxylic dianhydride and 50 mol% of 3, 3 ', 4, 4 ' -biphenyltetracarboxylic dianhydride were added to synthesize a polyamic acid solution (weight average molecular weight 7000), and 5kg of this solution was prepared. The viscosity of the solution was 6.5 pas, and the solid content concentration was 38.0 wt%. To the solution were added 750g of CB3 and 1200g of NMP, and the carbon black was uniformly dispersed with a sand mill.

The solid content concentration of the carbon black-dispersed polyamic acid solution composition was 38.13 wt%, and the carbon black concentration of the solid content was 28.3 wt%. The average particle size of the carbon black in the solution was 0.253. mu.m, and the maximum particle size was 0.45. mu.m.

Comparative example 3

10kg of a polyamic acid solution (weight-average molecular weight 32000) prepared by synthesizing 3, 3 ', 4, 4 ' -biphenyltetracarboxylic dianhydride and 4, 4 ' -diaminodiphenyl ether in a NMP solution was prepared. The viscosity of the solution was 5.0 pas, and the solid content concentration was 18.0 wt%. To the solution were added 320g of Mitsubishi chemical "MA 100" and 3000g of NMP, and the carbon black was uniformly dispersed with a sand mill. The reason why the amount of NMP added is 3000g is that the solution viscosity is high and it is difficult to uniformly disperse the carbon black.

The carbon black-dispersed polyamic acid solution composition had a solid content concentration of 15.92% by weight and a carbon black content in the solid content of 15.09% by weight. The average particle size of the carbon black in the solution was 0.51 μm, and the maximum particle size was 3.26. mu.m.

Using the carbon black-dispersed polyamic acid solution composition, a semiconductive polyimide belt was produced by the rotational molding method shown in example 4. The surface state, surface resistivity and thickness (average film thickness) of the semiconductive polyimide belt are shown in table 3.

[ Table 3]

	Solid content concentration (% by weight)	CB concentration (% by weight)	Surface state	Surface resistivity (omega/□)	Thickness (μm)
						Example 5	23.15	23.1	Good effect	6.4×10¹¹	98～103
Example 6	30.87	25.4	Good effect	2.1×10¹¹	98～102
						Example 7	38.13	28.3	Good effect	1.3×10¹²	98～102
Comparative example 3	15.92	15.09	Scaly pattern	2.0×10¹¹	96～103

As is clear from table 3, the concentration of carbon black in the polyimide resin can be increased by increasing the concentration of the volatile component of carbon black.

In comparative example 3, the solid content concentration of the liquid material was low, and it took a long time to volatilize a large amount of the organic polar solvent, and the production efficiency was very poor. In addition, the "Floating phenomenon" (Floating) in which the dispersion state of carbon black is not uniform occurs due to the influence of buoyancy and surface tension of convection caused by temperature convection and evaporation convection during drying by the spin molding method, viscosity change due to evaporation of a solvent, density change, and the like, and a scaly pattern is formed.

When the semiconductive polyimide belts of examples 5, 6, and 7 were used as an intermediate transfer belt in a color image forming apparatus, the charge stability of the charge was ensured, the charge was appropriately removed, the belt was stable for a long period of time, and a high-quality transferred image was obtained.

Claims

1. A carbon black-dispersed polyamic acid solution composition comprising a polyamic acid solution obtained by reacting biphenyltetracarboxylic dianhydride and an aromatic diamine in equimolar amounts, and carbon black produced by an oil furnace method, wherein the carbon black has a volatile content of 2 to 6%, a pH of 2 to 4, and a nitrogen adsorption specific surface area of 60 to 150m²(ii)/g, DBP absorption of 40 to 120ml/100g, and the amount of extraction of undecomposed raw material hydrocarbon PAH of 10ppm or less, the concentration of the solid content in the solution composition being 23 wt% or more, and the concentration of the carbon black in the solid content being 20 to 30 wt%.

2. The carbon black-dispersed polyamic acid solution composition according to claim 1, wherein said carbon black is a carbon black obtained by oxidation treatment with an oxidizing agent containing ozone.

3. The carbon black-dispersed polyamic acid solution composition according to claim 1, wherein the polyamic acid solution is a polyamic acid solution having a weight-average molecular weight of polyamic acid of 30000 or less.

4. The carbon black-dispersed polyamic acid solution composition according to claim 1, wherein the biphenyltetracarboxylic dianhydride comprises 10 to 80 mol% of asymmetric 2, 3, 3 ', 4 ' -biphenyltetracarboxylic dianhydride, and the aromatic diamine is 4, 4 ' -diaminodiphenyl ether.

5. A process for producing a semiconductive polyimide resin belt, which comprises forming the carbon black-dispersed polyamic acid solution composition according to any one of claims 1 to 4 into a tubular article by a rotational molding method and heat-treating the article to imidize the article, the process comprising the steps of:

(1) a step of coating the carbon black-dispersed polyamic acid solution composition onto the inner peripheral surface of a cylindrical mold rotating at a centrifugal acceleration of 0.5 to 8 times the gravitational acceleration, in a uniform thickness;

(2) heating the cylindrical mold at a temperature of 100 to 140 ℃ while rotating the cylindrical mold at a centrifugal acceleration of 0.5 to 8 times the gravitational acceleration to form a self-supporting coating; and

(3) and heating the cylindrical mold at a temperature of 300 ℃ or higher in a state where the film is adhered to the inner peripheral surface of the cylindrical mold, thereby imidizing the film.

6. A semiconductive polyimide resin tape produced by the production method according to claim 5.

7. A semiconductive polyimide resin tape comprising a polyimide resin and carbon black produced by an oil furnace method uniformly dispersed therein, wherein the semiconductive polyimide resin tape contains 70 to 80 wt% of the polyimide resin and 20 to 30 wt% of the carbon black and has a surface resistivity of 10⁹Ω/□～10¹⁴Omega/□, wherein the carbon black has volatile components of 2-6%, pH of 2-4, and nitrogen adsorption specific surface area of 60-150 m²(iv) a DBP absorption of 40 to 120ml/100g and an extraction amount of undecomposed raw material hydrocarbon (PAH) of 10ppm or less.

8. The semiconductive polyimide resin tape according to claim 7, wherein the average film thickness is 50 to 150 μm.

9. An intermediate transfer belt for an electrophotographic machine, which is formed from the semiconductive polyimide resin belt according to any one of claims 6 to 8.