JP3908424B2 - Manufacturing method of endless belt - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing an endless belt made of a polyimide resin, and more particularly to a method for uniformly dispersing a resistance control agent in a belt base material in order to prevent resistance variation of the endless belt.
As an application field of the present invention, a stirring method for preparing various liquids for producing belts can be mentioned. The endless belt manufactured according to the present invention can be effectively applied as an intermediate transfer belt for an image forming apparatus.
[0002]
[Prior art]
In image forming apparatuses such as copiers, facsimiles, and printers, there has recently been a growing demand for multi-color, especially full-color reconstructed images. As an image forming apparatus that can meet these demands, a transfer-type image using an intermediate transfer member. Forming devices are widespread. In the intermediate transfer method, there are cases where a roller is used as an intermediate transfer member and a belt is used.
[0003]
In the image forming method using the intermediate transfer method, the latent image formed on the photosensitive member is visualized with a charge carrier toner, and the photosensitive member is superimposed on the intermediate transfer member in the primary transfer step (transfer of the visualized image). After the primary transfer, the visualized image is secondarily transferred to a transfer target (copy paper) in a secondary transfer step. In this image forming method, it is necessary to apply a bias voltage between the photosensitive member and the intermediate transfer member in order to move and transfer the charge carrier (toner) when transferring to the intermediate transfer member. This bias voltage is adjusted so as to obtain an optimum image.
[0004]
By the way, when an endless belt is used for intermediate transfer type image formation, when this belt is not used (running stop state), a driving roller for driving the belt or a roller roller serving as an electrode for applying a bias. The shape follows the curvature of the diameter, and when the traveling is resumed, the shape is deformed according to the curvature, and a so-called curl phenomenon occurs. If the history remains, an image defect such as white spots caused by insufficient toner adhesion occurs at a portion curled during image formation or before and after the curled portion.
[0005]
This curl is related to the thermophysical properties of the belt base material, and is closely related to the melting point or softening temperature, and further to the glass transition temperature of thermoplastic resins. Has been found to be difficult.
[0006]
Polyimide resin belts are known to have good heat resistance, but this polyimide resin has the disadvantage that it is difficult to process due to its good heat resistance and chemical resistance. For this reason, at the time of belt forming, a production method is adopted in which a coating film is applied to a mold in the form of an unreacted precursor called varnish, and this coating film is reacted and cured after forming to form a belt film.
[0007]
That is, in the synthesis of the polyimide resin, polyamic acid is used as the precursor. This polyamic acid has a property of being dissolved in a specific solvent and a property of being changed to a polyimide resin by imide ring closure (imide conversion) by heat or a catalyst. As a method for producing an endless belt made of polyimide resin, a centrifugal molding method is generally known in which polyamic acid is injected and molded into a rotating cylindrical mold and then converted into an imide.
[0008]
By the way, in the intermediate transfer belt, it is necessary to apply an electric field application bias between the photosensitive member and the belt in order to perform good intermediate transfer. For this purpose, an appropriate surface resistance of 10 ⁸ Ω level is required for the belt. Is done. Therefore, in order to control the resistance of the belt, carbon black is mainly used as a resistance control agent in consideration of securing the mechanical strength of the belt and cost.
[0009]
[Problems to be solved by the invention]
However, in the conventional technology, even if a predetermined amount of carbon black is added and dispersed in order to bring the resistance of the belt to the target value, the resistance varies for each dispersion treatment batch. In addition, the batches that do not fit are discarded, which is not only cumbersome but also difficult to improve the yield of the belt, which makes it difficult to efficiently mass-produce high-quality belts. It was.
[0010]
Accordingly, an object of the present invention is to provide a method for efficiently producing an endless belt made of polyimide resin having uniform resistance throughout the belt by uniformly dispersing a resistance control agent in the belt base material. That is, in the case of preparing a raw material liquid (belt molding dispersion liquid) in which a resistance control agent is dispersed in a polyamic acid solvent solution, the present invention provides a belt having the same resistance when the resistance control agent is dispersed in the same amount. Presents a method for preparing a raw material solution that can be produced with good reproducibility.
[0011]
[Means for Solving the Problems]
The method for producing an endless belt according to the present invention is a method for producing an endless belt made of polyimide using a raw material liquid in which a resistance control agent is dispersed in a polyamic acid-containing solvent solution that is a polyimide precursor solution. A liquid having a moisture content including moisture absorption is less than 10 wt% of the solvent is used. As a molding method for producing the endless belt, known methods such as a centrifugal molding method and a dipping method are used. In the dipping method, the mold is immersed in the raw material liquid in the container and gradually pulled up.
[0012]
In the method of the present invention, the raw material liquid is prepared by mixing and stirring the resistance control agent dispersion obtained by adding and stirring the resistance control agent to the solvent in which the polyamic acid is dissolved, and the polyimide precursor solution. It is characterized by producing.
[0013]
In the method of the present invention, the raw material liquid can also be prepared by mixing and stirring a solvent capable of dissolving polyamic acid, a polyimide precursor solution, and a resistance control agent.
[0014]
Further, in the method of the present invention, a stirring operation for preparing the dispersion of the resistance control agent, a mixing stirring operation of the dispersion of the resistance control agent and the polyimide precursor solution (that is, the polyimide precursor solution with a solvent) At least one of the stirring / dilution operation is performed in a state where moisture in the outside air is blocked.
[0015]
In the method of the present invention, the mixing and stirring operation for preparing the raw material liquid is performed in a state where moisture in the outside air is shut off.
[0016]
In addition, as a method of performing the mixing and stirring operation in a moisture cut-off state, (1) putting the liquid to be stirred into a container having a volume as small as possible, sealing the container and performing the mixing and stirring operation, (2) nitrogen gas The liquid to be stirred is put into a container that has been replaced with an inert gas such as the above, and the container is sealed and the mixture is stirred.
[0017]
Method for producing an endless belt according to claim 2, at least one of mixing and stirring operation of the stirring operation for Dispersion Preparation before Symbol resistance control agent, a dispersion of the resistance control agent and the polyimide precursor solution Is performed by a centrifugal stirring method.
[0018]
In the method for producing an endless belt according to claim 3, the mixing and stirring operations for pre SL material solution prepared, and carrying out the centrifugal stirring method.
[0019]
A method for producing an endless belt according to claim 4 is the method according to claim 2 or 3 , wherein carbon black is used as the resistance control agent, and the stirring operation by the centrifugal stirring method is performed in the presence of a dispersion medium. Features.
[0020]
In the method for producing an endless belt according to the present invention, a material arbitrarily selected from carbon black, indium oxide (In ₂ O ₃ ) and the like can be used as the resistance control agent. Specific examples of carbon black include acetylene black, furnace black, thermal black, and channel black.
[0021]
The following has been found by the study of the present inventors. In a method for producing an endless belt using a dispersion liquid (the raw material liquid) in which a resistance control agent is dispersed in a polyamic acid solvent solution that is a polyimide precursor solution, the dispersion liquid preparation and the dispersion liquid dilution As the solvent, organic solvents such as dimethylacetamide (DMAC) and N-methylpyrrolidone (NMP) are used, but these organic solvents are highly hygroscopic, and the above precursor solution or diluted solution thereof can be used in the atmosphere. It was found that when left open, the moisture (moisture) in the atmosphere is absorbed and the weight increases, and a transparent liquid film is formed on the surface of the precursor solution or diluted solution. Thermal analysis of this transparent liquid film revealed that water was the main component.
[0022]
Moreover, when the weight increase by water absorption became 20 wt% or more, it was confirmed that the surface of the said raw material liquid became opaque, opaqueness progressed with the increase in water absorption amount, and finally the whole became opaque. When this was observed with a microscope, it was recognized that minute spherical substances were generated and grown. This is presumably because the raw material liquid was gelled or crystallized when the moisture content in the raw material liquid absorbed moisture in the atmosphere to reach a certain water content. For this reason, it is considered that the concentration distribution of the resistance control agent in the raw material liquid fluctuates and becomes non-uniform, which appears as resistance variation of the endless belt finally obtained.
[0023]
Based on the above examination results, the present inventors have developed a method for reducing the water absorption of the organic solvent as much as possible in order to prevent the gelation or crystallization and the resistance variation.
[0024]
【Example】
Examples of the present invention and comparative examples will be described below.
Example 1-1
By putting solvent DMAC, carbon black (furnace black) as a resistance control agent (conductive agent), and 1 mm diameter glass dispersion media into a plastic container, sealing the container, and mixing and stirring with a centrifugal stirrer A carbon black dispersion having an average particle size of carbon black of 1 μm or less and a concentration of 4 wt% (meaning that the ratio to 100 parts by weight of DMAC is 4 parts by weight, the same applies to the following examples and comparative examples) is prepared. did.
[0025]
Next, the above dispersion and a single lot of polyimide precursor solution (polyamic acid dissolved in a DMAC / NMP mixed solution) prepared in advance were poured into another container, and the container was sealed. In this case, the ratio of the carbon black to 100 parts by weight of the polyimide resin constituting the endless film obtained later was set to 20 parts by weight (carbon black resin solid content ratio was 20 wt%). And this container was set to the centrifugal stirrer, the carbon black was disperse | distributed and defoamed, and the raw material liquid for centrifuging (another name varnish) was produced.
[0026]
A part of this raw material solution was collected and injected and applied to a centrifugal mold, and then the coating film was dried and solidified. Next, this centrifugal mold was placed in a baking furnace and the dried and solidified film was heat-cured at 300 ° C. to obtain an endless film (polyimide film) having a thickness of 100 μm.
Similarly, a part of the raw material liquid was collected, and the above operation was repeated to produce a plurality of batches of endless films.
[0027]
Example 1-2
A plurality of batches of endless membranes were produced using the same procedures and conditions as in Example 1-1, using a plurality of lots of polyimide precursor solutions individually. In this case, the carbon black dispersion prepared in Example 1-1 was used as the carbon black dispersion.
[0028]
When the surface resistance of the polyimide film obtained in Example 1-1 and Example 1-2 was measured, the resistance value was within the range of 1 × 10 ^{8 to} 9 × 10 ⁸ Ω. In the plurality of centrifugal molding raw material liquids (mixed liquid of the polyimide precursor solution and the carbon black dispersion liquid), the water content was less than 10 wt% of the solvent DMAC (less than 10 parts by weight with respect to 100 parts by weight of DMAC). . That is, when a single lot of polyimide precursor solution is used, the resistance value is within a lot, and when multiple lots of polyimide precursor solution are used, the resistance value is small between the lots. A membrane was obtained.
[0029]
Example 2-1
The same operation as in Example 1-1 was performed. However, in this case, when producing the raw material liquid for centrifugal molding, in order to thoroughly block moisture, the inert gas replacement was performed as follows. Into a plastic container purged with nitrogen gas in advance, DMAC, carbon black (furnace black) as a resistance control agent, and 1 mm diameter glass dispersion media are added, and after nitrogen gas is introduced, it is sealed, By mixing and stirring with a centrifugal stirrer, a carbon black dispersion having an average particle size of carbon black of 1 μm or less and a concentration of 4 wt% was prepared.
[0030]
Next, this dispersion and a single lot of polyimide precursor solution (polyamic acid dissolved in a DMAC / NMP mixed solution) were injected into another container similarly purged with nitrogen, and nitrogen gas was sealed. . In this case, the ratio of carbon black to 100 parts by weight of polyimide resin constituting the endless film obtained later was set to 20 parts by weight. And the said container was sealed and set to the centrifugal stirrer, the dispersion | distribution and defoaming of carbon black were performed, and the raw material liquid for centrifugal molding was produced. A part of this raw material solution was collected and injected and applied to a centrifugal mold, and then the coating film was dried and solidified. Next, this centrifugal mold was placed in a baking furnace, and the dried and solidified film was heat-cured at 300 ° C. to obtain an endless film having a thickness of 100 μm. Similarly, a part of the raw material liquid was collected, and the above operation was repeated to produce a plurality of batches of endless films.
[0031]
Example 2-2
A plurality of batches of endless membranes were produced using the same procedures and conditions as in Example 2-1, using a plurality of lots of polyimide precursor solutions individually. In this case, the carbon black dispersion prepared in Example 2-1 was used as the carbon black dispersion.
[0032]
When the surface resistance of the polyimide film obtained in Example 2-1 and Example 2-2 was measured, the resistance value was within a range of 5 × 10 ^{8 to} 9 × 10 ⁸ Ω. In the plurality of centrifugal molding raw material liquids, the water content was less than 1 wt% of the solvent DMAC (less than 1 part by weight with respect to 100 parts by weight of DMAC). That is, when a single lot of polyimide precursor solution is used, the resistance value is within a lot, and when multiple lots of polyimide precursor solution are used, the resistance value is small between the lots. A membrane was obtained.
[0033]
Example 3-1.
In the same manner as in Example 2-1 and Example 2-2, a raw material solution for centrifugal molding was prepared using a container in which inert gas replacement was performed in order to thoroughly block moisture. In this case, DMAC, a polyimide precursor solution, and indium oxide (In ₂ O ₃ ) having an average particle size of 0.1 μm or less as a resistance control agent are charged into a plastic container purged with nitrogen gas in advance. After injecting nitrogen gas, the mixture was sealed, and mixed and stirred with a centrifugal stirrer to prepare a raw material liquid with a resin solid content ratio of indium oxide of 55 wt%.
[0034]
A part of this raw material solution was collected and injected and applied to a centrifugal mold, and then the coating film was dried and solidified. Next, this centrifugal mold was placed in a baking furnace, and the dried and solidified film was heat-cured at 300 ° C. to obtain an endless film having a thickness of 100 μm. Similarly, a part of the raw material liquid was collected, and the above operation was repeated to produce a plurality of batches of endless films.
[0035]
Example 3-2
A plurality of endless films were produced in the same procedure and conditions as in Example 3-1, except that a plurality of lots of solutions were individually used as the polyimide precursor solution.
[0036]
When the surface resistance of the polyimide film obtained in Example 3-1 and Example 3-2 was measured, the resistance value was within the range of 5 × 10 ^{8 to} 9 × 10 ⁸ Ω. In each of the plurality of centrifugal molding raw material liquids, the water content was less than 0.5 wt% of the solvent DMAC. That is, when a single lot of polyimide precursor solution is used, the resistance value is within a lot, and when multiple lots of polyimide precursor solution are used, the resistance value is small between the lots. A membrane was obtained.
[0037]
Comparative Example 1
In the preparation of the carbon black dispersions in Examples 1-1 and 1-2 and Examples 2-1 and 2-2, the raw material liquid obtained by centrifugally stirring without using the dispersion medium was fine but uncrushed. A carbon black aggregate was observed, and when a coating film of the raw material liquid was formed on the surface of the centrifugal mold, many bumps were generated on the film surface. Further, when an image was formed using the obtained intermediate transfer belt made of polyimide, an abnormal image of white spots was formed.
[0038]
By the way, in Examples 1-1 and 1-2 and Examples 2-1 and 2-2, a raw material liquid was prepared by mixing and stirring a resistance control agent dispersion prepared using a dispersion medium and a polyimide precursor solution. However, in Examples 3-1 and 3-2, the resistance control agent and the polyimide precursor solution were mixed with DMAC, which is a solvent for dissolving polyamic acid, to produce a raw material solution. is doing.
[0039]
Therefore, in Examples 3-1 and 3-2, an intermediate transfer belt made of a raw material liquid obtained by introducing a dispersion medium and performing centrifugal stirring, and an intermediate made of a raw material liquid centrifugally stirred without using the dispersion medium. When images were formed using the transfer belt separately, it was found that there was no great difference in image quality, and in Examples 3-1 and 3-2, there was no need for a dispersion medium.
[0040]
Comparative Example 2-1
DMAC and carbon black (furnace black) were charged into a container and mixed and stirred with a centrifugal stirrer to prepare a carbon black dispersion having an average particle size of carbon black of 1 μm or less and a concentration of 4 wt%. This dispersion and a single lot of polyimide precursor solution were poured into a bottle container and mechanically stirred with a homogenizer to prepare a raw material liquid having a carbon black resin solid content ratio of 20 wt%. A part of this raw material solution was applied to a centrifugal mold in the same manner as in Example 1-1, and then dried and cured to produce an endless film having a thickness of 100 μm. Similarly, a plurality of endless films were produced by repeating the above operation using a part of the raw material liquid.
[0041]
Comparative Example 2-2
A plurality of endless films were produced in the same procedure and conditions as in Comparative Example 2-1, except that a plurality of lots of polyimide precursor solutions were used individually. In this case, the carbon black dispersion prepared in Comparative Example 2-1 was used.
[0042]
When the surface resistance of the polyimide film obtained in Comparative Example 2-1 and Comparative Example 2-2 was measured, the resistance value varied widely in the range of 5 × 10 ^{6 to} 9 × 10 ¹⁰ Ω. That is, the resistance value of the polyimide film varied greatly within a single lot of the polyimide precursor solution and between a plurality of lots of the polyimide precursor solution. The amount of water in the carbon black dispersion liquid was 9 wt% of the solvent DMAC, and in each of the plurality of centrifugal molding raw material liquids, the water amount was 15% wt% of the solvent DMAC.
[0043]
In addition, as a result of performing the above raw material liquid preparation process in a room without temperature control and humidity in a high temperature and high humidity rainy season (average 28 ° C./90% RH), A transparent moisture layer appeared on the surface, and when the moisture content with respect to the solvent became 20 wt% or more, the raw material liquid became clouded. Moreover, the resistance value of the polyimide film obtained by this greatly fluctuated in the range of 1 × 10 ^{6 to} 9 × 10 ¹² Ω, and it was impossible to obtain a stable resistance value.
[0044]
Comparative Example 3-1
DMAC and 4% by weight of carbon black (furnace black) were charged into a container and dispersed by stirring with a sand mill to prepare a carbon black dispersion having an average particle size of 1 μm or less. This dispersion and a single lot of polyimide precursor solution prepared in advance are poured into a nitrogen purged container, and dispersed and defoamed with a centrifugal stirrer to obtain a raw material liquid having a carbon black resin solid content ratio of 20 wt%. Obtained. A part of this raw material solution was applied and dried on a centrifugal mold in the same manner as in Example 1-1, and then cured to prepare an endless film having a thickness of 100 μm. Similarly, a plurality of endless films were produced by repeating the above operation using a part of the raw material liquid.
[0045]
Comparative Example 3-2
A plurality of endless films were produced in the same procedure and conditions as in Comparative Example 3-1, except that a plurality of lots of polyimide precursor solutions were used individually. In this case, the carbon black dispersion prepared in Comparative Example 3-1 was used.
[0046]
When the surface resistance of the polyimide film obtained in Comparative Example 3-1 and Comparative Example 3-2 was measured, the resistance value was in the range of 1 × 10 ^{7 to} 5 × 10 ⁹ Ω, and the variation width was relatively small. However, a stable resistance value could not be obtained with good reproducibility. The water content of the raw material liquids used in these Comparative Examples 3-1 and 3-2 was 100 parts by weight of the solvent (DMAC in the carbon black dispersion and the solvent in the polyimide precursor solution) in the raw material liquid. It was around 12 wt%.
[0047]
As described above, it has been found that the moisture content of the solvent greatly affects the dispersion of the resistance value of the polyimide film obtained by molding the raw material liquid in which the resistance control agent is dispersed in the polyamic acid-containing solvent solution. It was.
[0048]
Dispersion of carbon black by the sand mill must be carried out with the container open for more than 1 hour, so it is inevitable to absorb moisture in the air during that time. Further, in the dispersion operation, the dispersion liquid is rotated at a rotational speed of 2000 rpm or more, so that bubbles are mixed into the dispersion liquid. And if this bubble contains water vapor in the atmosphere, it is absorbed by the solvent, but this absorbed moisture cannot be removed even after defoaming treatment, so the dispersion contains moisture, which is the cause of the above adverse effects It is considered that. In this way, in the polyimide film production process using the polyamide precursor solution containing the hygroscopic solvent, it is desirable to produce the polyimide film forming raw material liquid in a state where moisture in the external atmosphere is blocked. It became clear that it is important to obtain a polyimide film having the following characteristics.
[0049]
【The invention's effect】
As is apparent from the above description, the present invention provides the following effects.
(1) Effect of the invention of claim 1
In the present invention, a raw material liquid having a moisture content including moisture absorption is less than 10 wt% of the solvent. Thereby, the dispersion | variation in film resistance can be suppressed within one order (ratio of maximum value / minimum value is 10 or less). Therefore, in the image forming apparatus using the intermediate transfer belt made of the polyimide resin endless belt obtained by the present invention, it is possible to stably obtain a good quality image. When producing a polyimide film using a raw material solution containing a polyimide precursor solution, the moisture content of the solvent in the raw material solution increases and the moisture content increases. As a result, the precursor component is agglomerated or gelled. The resistance control agent fine particles are not uniformly dispersed in the raw material liquid. Therefore, the water absorption of the raw material liquid must be kept as low as possible.
[0050]
In the present invention, the raw material liquid preparation operations such as the stirring operation for dispersing the resistance control agent and the diluting stirring operation with the solvent of the polyimide precursor solution are performed in a state where moisture in the outside air is shut off. In order to suppress the above-described moisture absorption / water absorption, it is effective to reduce the humidity of the external environment and adopt a condition that does not absorb water during the stirring operation. For example, the container may be sealed or the atmosphere in the container may be replaced with an inert gas. By doing so, the effect of the present invention can be obtained.
[0051]
( 2 ) Effects of the Inventions of Claims 2 and 3 In these inventions, the stirring operation for dispersing the resistance control agent is performed by a centrifugal stirring method. Centrifugal stirring is the most suitable method for stirring the liquid in a sealed state. Further, defoaming can be performed in a sealed state simultaneously with stirring, and the appearance of the film surface due to the detachment of the contained bubbles by heating can be reduced.
[0052]
( 3 ) Effect of Invention of Claim 4 In the present invention, carbon black is used as a resistance control agent, and a stirring operation by a centrifugal stirring method is performed in the presence of a dispersion medium. Carbon black has strong cohesiveness, and aggregates are difficult to disperse completely by simple centrifugal stirring. For this reason, when a film is produced using a raw material liquid with poor dispersion, an uneven appearance or more appears on the film surface, and a good image cannot be formed. Therefore, it is necessary to improve the dispersibility of carbon black. To that end, if sand (media) is added at the same time as in the case of a sand mill, the agglomerates are crushed and dispersed as fine particles. A film having a good shape can be formed.

Claims (4)

In a method for producing an endless belt made of polyimide using a raw material liquid in which a resistance control agent is dispersed in a polyamic acid-containing solvent that is a polyimide precursor solution,
The raw material liquid uses a moisture content containing moisture absorption moisture that is less than 10 wt% of the solvent ,
As the solvent for dissolving the polyamic acid, the raw material liquid uses dimethylacetamide or a dimethylacetamide-containing solvent, a dispersion obtained by adding a resistance control agent to the solvent and stirring, and a polyimide precursor solution. , Obtained by mixing and stirring,
The stirring operation for adjusting the dispersion of the resistance control agent, or / and the stirring operation of mixing the polyimide precursor solution in the dispersion, performed in a state where moisture in the outside air is blocked, Alternatively, the raw material liquid is obtained by mixing and stirring a solvent capable of dissolving polyamic acid, a polyimide precursor solution, and a resistance control agent. The mixing and stirring step is performed by removing moisture in the outside air. A process for producing an endless belt, wherein the process is performed in a closed state .   The stirring operation for adjusting the dispersion of the resistance control agent and at least one of the mixing and stirring operation of the dispersion of the resistance control agent and the polyimide precursor solution are performed by a centrifugal stirring method. A process for producing an endless belt as described in 1.   The method for producing an endless belt according to claim 1, wherein the mixing and stirring operation for preparing the raw material liquid is performed by a centrifugal stirring method.   4. The method for producing an endless belt according to claim 2, wherein carbon resistance is used as the resistance control agent, and the centrifugal stirring is performed in the presence of a dispersion medium.