JP2003005555A - Fixing belt - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing belt which hardly gives rise to an electrostatic offset in fixing of fine toners by high-speed passing of paper, makes a well fixed image obtainable and is high in durability. SOLUTION: This fixing belt is constituted by forming a fluororesin layer 3 which contains carbon black and contains a fluororesin at >=95 wt.% through a primer layer 2 not containing the carbon black on the surface of a polyimide belt 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing belt used for fixing in an image forming apparatus such as a copying machine, a facsimile and a printer.

[0002]

2. Description of the Related Art Among the image fixing methods for transfer paper in the electrophotographic image forming apparatus as described above, the belt fixing method which has been recently proposed has a structure in which a roller and a belt are arranged to face each other. The toner is fixed by feeding the paper between them. In this case, basic functions such as pressurization, heating, driving, and releasing are necessary as in the heat roller fixing method, but these functions may be provided on the roll side or the belt side. By thus using the belt on one side, it is possible to increase the contact area between the two and increase the sheet passing speed while ensuring the heating time. As such a fixing belt, a base belt made of polyimide provided with a release layer such as a fluororesin is used.

However, when the paper feeding speed is increased, the fixing belt is easily charged, and the static electricity tends to cause an electrostatic offset in which the toner immediately before fixing is offset and an image bleeding occurs. Also, in order to deform the belt to increase the contact area and drive it at a higher speed,
If the adhesion between the fluororesin layer and the base material belt is not high, peeling will occur. On the other hand, regarding image quality, in order to make it clearer, the size of the toner is made smaller and the fusing temperature is made higher, but the belt surface (the surface of the release layer)
If the value is rough, the toner is not released from the mold uniformly, and problems such as white spots occur.

By the way, as to the problem of image resolution due to electrostatic offset of the fixing belt, Japanese Patent No. 30540 has been proposed.
In No. 10, a fluororesin layer is applied on the conductive primer layer to which carbon black or the like is added to deal with it. As a result, the content of carbon black in the fluororesin layer is set to zero or a small amount while preventing the fixing belt from being charged.

[0005]

However, in the above fixing belt, since the conductive primer layer contains carbon black, the adhesion between the fluororesin layer and the base material belt is significantly reduced. However, when it is used in a fixing device that is large in size and can be driven at a higher speed, the fluororesin layer peels off.

Further, Japanese Patent Laid-Open No. 2001-125404 discloses a fixing belt in which a fluororesin layer containing an inorganic semiconductive substance and carbon black is formed on the surface of a polyimide belt via a primer layer. Proposed. However, since the content of the inorganic semiconductive substance is large (20 to 40% by weight in the examples), there is a problem that the fluororesin layer is easily peeled off as in the above case.

The present invention has been made in view of such circumstances, and even in the fixing of fine toner by high-speed paper passing,
An object of the present invention is to provide a fixing belt in which electrostatic offset hardly occurs, a good fixed image can be obtained, and which has high durability.

[0008]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies to achieve the above object, and found that a fluororesin layer containing a small amount of carbon black is formed through a polyimide-based primer layer containing no carbon black. By doing so, they have found that the above object can be achieved, and completed the present invention.

That is, in the fixing belt of the present invention, a fluororesin layer containing carbon black and having a fluororesin content of 95% by weight or more is provided on the surface of the polyimide belt via a polyimide primer layer containing no carbon black. Is formed.

In the above, the fluororesin layer has a surface roughness Ra of 1 μm or less and a surface resistivity of 10 ⁸ Ω /
□ or less, the peel strength is preferably 1 N / cm or more.

The fluororesin layer is preferably composed of tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) and Ketjen black.

At this time, the fluororesin layer contains 1.5 to 2.3 wt% of carbon black with respect to the resin solid content and is dispersed so that the median diameter is 0.7 μm or less. It is preferably formed by.

Further, in the polyimide-based primer layer,
It is preferable that PFA particles are included.

[Operation and Effect] According to the fixing belt of the present invention, the primer layer does not contain carbon black and the fluororesin content of the fluororesin layer is 95% by weight or more. The peel strength is high, the surface is smooth, and a sufficient antistatic effect is obtained. As a result, it is possible to provide a fixing belt in which electrostatic offset is unlikely to occur even when fixing fine toner by high-speed paper passing, a good fixed image is obtained, and durability is high.

The surface roughness of the fluororesin layer is Ra.
1 μm or less, surface resistivity of 10 ⁸ Ω / □ or less, and peel strength of 1 N / cm or more, electrostatic offset does not easily occur even when fixing fine toner by high-speed paper passing, and a good fixed image can be obtained. In addition, the effect of high durability can be obtained more reliably.

When the fluororesin layer is composed of PFA and Ketjen black, PFA has high heat resistance, and it is easy to obtain a smooth fluororesin layer due to fusion of particles and the like. The desired conductivity can be easily obtained even by containing a small amount of black.

At this time, the carbon black content is 1.5 to 2.3 wt% with respect to the resin solid content, and the median diameter is 0.7.
When the fluororesin layer is formed by applying a dispersion liquid dispersed to have a particle size of not more than μm and then heating, a sufficient antistatic effect can be more reliably obtained while enhancing the smoothness of the surface.

PFA is added to the polyimide primer layer.
When the particles of No. 1 are contained, the adhesion with the fluororesin such as PFA becomes high, so that the fixing belt having higher durability can be obtained.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing an example of the fixing belt of the present invention.

As shown in FIG. 1, the fixing belt of the present invention has a structure in which a fluororesin layer 3 is formed on the surface of a polyimide belt 1 which is a base material belt with a polyimide primer layer 2 interposed therebetween.

Although the thickness of each layer of the fixing belt can be set arbitrarily, the thickness of the polyimide belt 1 is 5 to 200 μm.
It is preferable to set in the range of. If it is less than 5 μm, buckling is likely to occur, and if it exceeds 200 μm, the separation angle from the fed paper tends to be small, and the releasability of the toner tends to deteriorate.

The thickness of the polyimide primer layer 2 is preferably 0.3 to 10 μm. If it is less than 0.3 μm, the peel strength of the polyimide belt and the fluororesin layer will be low
If it exceeds 10 μm, the roughness tends to increase, depending on the thickness of the outermost fluororesin layer 3.

The fluororesin layer 3 preferably has a thickness of 5 to 50 μm, more preferably 20 to 40 μm. 5μ
If it is less than m, it will follow the irregularities of the base primer layer,
The surface roughness tends to increase and the surface resistivity tends to increase depending on the amount of carbon added to the fluororesin. 5
If it exceeds 0 μm, the fluororesin tends to be cracked.

The polyimide belt 1 is a belt mainly composed of a polyimide resin, and a seamless belt is preferable. The polyimide resin may contain fluororesin, carbon black, boron nitride, etc. within a range that does not impair the physical properties of the base material belt.

For the polyimide resin, for example, tetracarboxylic dianhydride which is an acid component and approximately equimolar amount of diamine which is an amine component are dissolved and reacted in a suitable solvent to prepare a polyamic acid solution, and the solvent is removed. Although it can be obtained by polymerizing (imide conversion) at a higher temperature later, in the present invention, a seamless belt can be formed by applying the polyamic acid solution seamlessly.

As the tetracarboxylic acid dianhydride, aromatic tetracarboxylic acid dianhydrides are preferable, and specifically, pyromellitic acid dianhydride and 3,3 ', 4,4'-benzophenonetetracarboxylic acid. Acid dianhydride, 3,3 ′,
4,4'-biphenyltetracarboxylic dianhydride, 2,
3,3 ′, 4-biphenyltetracarboxylic dianhydride,
2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, etc. To be A particularly suitable acid dianhydride component is
Biphenyltetracarboxylic dianhydride and pyromellitic dianhydride. These acid anhydride components may be used alone or in combination of two or more.

As the diamine, aromatic diamines are preferable, and 4,4'-diaminodiphenyl ether,
4,4'-diaminodiphenylmethane, 3,3'-diaminodiphenylmethane, 3,3'-dichlorobenzidine, 4,4'-diaminodiphenyl sulfide, 3,
3'-diaminodiphenyl sulfone, 1,5-diaminonaphthalene, m-phenylenediamine, p-phenylenediamine, 3,3'-dimethyl 4,4'-biphenyldiamine, benzidine, 3,3'-dimethylbenzidine, 3, Examples include 3'-dimethoxybenzidine, 4,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenylpropane and the like.

When reacting and polymerizing the above raw material compounds, known organic solvents can be appropriately selected and used. Specifically, N, N-dimethylformamide, N, N-dimethylacetamide, N, N-diethylformamide,
N, N-dialkylamides such as N, N-diethylacetamide, N, N-dimethylmethoxyacetamide, dimethyl sulfoxide, hexamethylphosphortriamide, N-methyl-2-pyrrolidone, pyridine, tetramethylene sulfone, dimethyltetramethylene The use of highly polar organic solvents such as sulfones is preferred.

A polyimide precursor solution is obtained by reacting the above-mentioned acid dianhydride and equimolar diamine in an organic polar solvent. The reaction is carried out by the method and conditions generally used in the technical field of polyimide synthesis. The monomer concentration in the organic polar solvent can be appropriately set according to various conditions, but is usually 5 to 30% by weight, preferably 10 to 25% by weight. The temperature during the reaction is preferably set to 80 ° C or lower, and particularly preferably 5 to 50 ° C.

The polyimide primer layer 2 in the present invention does not contain carbon black, and preferably does not contain an inorganic filler. The polyimide-based primer is one that enhances adhesiveness with a polyimide by containing a polyimide component in the chemical structure or as a mixed component, and in general, a component that enhances adhesiveness with a fluororesin is included in the chemical structure. Or as a mixed component. In the present invention, any type of polyimide-based primer can be used. The raw material for applying such a primer generally contains a polyimide precursor (polyamic acid).

However, for the reasons described above, it is preferable that the polyimide primer layer 2 contains fluororesin particles, particularly PFA particles. The fluororesin particles preferably have an average particle size (primary particles) of 2 μm or less. Average particle size is 2
If it exceeds μm, the surface roughness tends to increase. Also,
The content of PFA particles is preferably 25 to 95% by weight from the viewpoint of the effect of improving the adhesiveness.

The fluororesin layer 3 in the present invention contains carbon black and has a fluororesin content of 95% by weight or more, preferably 97% by weight or more. If the fluororesin content is less than 95% by weight, the adhesive strength with the polyimide-based primer layer 2 will decrease,
Further, the amount of wear per unit time increases, and the durability of the belt deteriorates.

Examples of the fluororesin include polytetrafluoroethylene (PTFE) or its modified product, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-
Ethylene copolymer (ETFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-vinylidene fluoride copolymer (T
FE / VdF), tetrafluoroethylene-hexafluoropropylene-perfluoroalkyl vinyl ether copolymer (EPA), polychlorotrifluoroethylene (PCTFE), chlorotrifluoroethylene-ethylene copolymer (ECTFE), chlorotrifluoroethylene -Vinylidene fluoride copolymer (CTFE / VdF),
Examples thereof include polyvinylidene fluoride (PVdF) and polyvinyl fluoride (PVF). Among them, PFA is preferably used.

As the carbon black, in order to maintain the smoothness of the surface of the fluororesin layer 3, it is preferable that the surface resistivity be 10 ⁸ Ω / □ or less even if the addition amount is small. From this viewpoint, the average particle diameter is 100 to 500 nm.
Carbon black is preferable, and the dibutyl phthalate (DBP) oil absorption is 300 to 500 cc / 100 g.
Are preferred. Here, the DBP oil absorption is JIS
It is measured according to the A method of K 6221. Examples of such carbon black include Ketjen black, acetylene black, graphite and the like.

In the present invention, the fluororesin layer 3 is preferably composed of PFA and the above carbon black, and particularly preferably composed of PFA and Ketjen black.

The fluororesin layer 3 is formed by applying the dispersion liquid to the polyimide primer layer 2 using a dispersion liquid containing fluororesin particles and carbon black, and then heating it at a temperature above the melting point of the fluororesin. Can be formed with. At that time, the amount of carbon black added to the PFA dispersion was 1.
It is preferably set to 5 to 2.3 wt%. If it is less than 1.5 wt%, the surface resistivity tends to be high, and if it exceeds 2.3 wt%, the surface roughness tends to be high and the peel strength tends to be low. Further, since the peel strength is reduced by half from 1.9 wt% to 2 wt%, less than 2 wt% is preferable.

The median diameter in the dispersion of PFA particles and carbon particles for forming the fluororesin layer 3 is preferably 0.7 μm or less. If it is larger than 0.7 μm, the surface roughness Ra exceeds 1 μm, which is not preferable. Examples of the method for dispersing the PFA particles and the carbon particles in the dispersion to a median diameter of 0.7 μm or less include a method using a homogenizer, a collision type nanomizer, or the like. In addition to these operations, the median diameter can be further reduced by diluting with water or the like to reduce the viscosity of the dispersion. Further, as a method of coating these on the belt, either a spray method or a dipping method may be applied.

In the production of the fixing belt of the present invention, for example, a belt surface of a polyimide precursor is coated with an insulating primer composed of a polyimide precursor solution and PFA powder by spraying or the like, and PFA and carbon are dispersed thereon. It can be carried out by coating the dispersion, removing water and solvent by heating and drying, and then heating. The heating temperature at that time is preferably equal to or higher than the melting point of the fluororesin such as PFA, but when PFA is used, it is preferably 340 to 430 ° C. If the temperature is lower than 340 ° C., the PFA particles are insufficiently melted during coating, and it tends to be difficult to obtain a smooth film. Four
If it exceeds 30 ° C, the surface resistivity tends to be too high. Also, depending on the heating temperature, when the temperature is 400 ± 10 ° C., the heating time is preferably 0.5 to 1.5 h, 0.5 h
If it is below, the surface roughness tends to be large, and if it exceeds 1.5 hours, the surface resistivity tends to be too high.

The fixing belt of the present invention obtained as described above has a surface roughness Ra of 1 μm or less and a surface resistivity of 1.
It is preferable to have a fluororesin layer having a peel strength of 0 ⁸ Ω / □ or less and a peel strength of 1 N / cm or more. More preferably,
The surface roughness Ra is 0.1 to 0.8 μm, and the surface resistivity is 1
It is 0 ⁴ to 10 ⁷ Ω / □, and the peel strength is 3 to 12 N / cm.

[0040]

EXAMPLES Examples and the like specifically showing the constitution and effects of the present invention will be described below. The physical properties in the examples and the like were evaluated as follows.

(1) Median Diameter of Dispersion Using LB500 manufactured by HORIBA, Ltd., measurement was carried out at a measurement temperature of 25 ° C. on a sample diluted with pure water as a dispersion medium so as to be 50 times the weight of the dispersion. .

(2) Surface roughness measuring device: Surfcom 554A, pickup: E-DT
-S01A, probe: 5 μm R cone, measurement length:
The arithmetic average roughness Ra was measured at 2.5 mm, cutoff wavelength: 0.32 mm, moving speed: 0.12 mm / s, and magnification: 5000 times. The arithmetic average roughness Ra was an average of 5 points in the circumferential direction.

(3) Surface resistivity measuring device: Advantest R8340A, probe: Mitsubishi Kagaku Hiresta UR-SS, the probe was pressed against the belt surface at a measuring voltage of 100 V, and the display after 10 seconds was read.

(4) Peel Strength When using ORIENTEC UTM1000 Tensilon, peeling was performed at a peeling speed of 50 mm / min. As a sample, FEP film with a standard thickness of 500 μm is used as the P
After placing it on the FA side, thermocompression-bond it at 305 ± 5 ° C * 3min,
The adhered product and the FEP film punched out to a width of 1 cm were used.

(Example 1) 3,3'4 as an acid component
4′-biphenyltetocarboxylic dianhydride was dissolved in N-methyl-2-pyrrolidone (NMP) in an approximately equimolar amount of p-phenylenediamine as an amine component (monomer concentration 2
0% by weight) and reacted at 20 ° C. for 6 hours to give a rotational viscosity of 33
A polyamic acid solution having 000 poise (temperature: 20 ° C., measured by B-type viscometer) and logarithmic viscosity of 2.6 was prepared. Then 7
The viscosity of the polyamic acid solution was adjusted to 1500 poise by heating to 0 ° C. This polyamic acid solution has an inner diameter of 30.61
mm hot mold, then apply hot air at 150 ℃ for 10 min
It was put into a solid state. Further, this mold was heated until it reached 220 ° C., and after returning to room temperature, the polyimide belt was released from the mold to form a polyimide precursor belt.

Next, a PFA dispersion liquid having a viscosity of 200 cp (Mitsui DuPont 510CL, average particle size of 0.
Ketjen Black (Lion, W311)
N, average particle size 0.3 μm) to PFA solid content of 1.
Add 9 wt% so that it is 300 with a homogenizer.
Stir at 0 rpm 10mim / L and set the median diameter to 0.6
μm. A polyimide primer (Mitsui DuPont Fluorochemicals, K001-02) was applied to the surface of the polyimide precursor belt heated to 80 ° C. by using a spray, and then the above dispersion was applied. Then, it was replaced with a cylindrical aluminum pipe and heated at 400 ° C. for 1 hour to obtain a fixing belt having a polyimide layer of 80 μm, a primer layer of 2 μm, and a carbon-containing fluororesin layer of 30 μm.

The belt obtained has a peel strength of 2 N / c.
m, surface roughness Ra 0.8 μm, surface resistivity 7 × 10 ⁵ Ω
It became / □. Even when this belt is mounted on a commercially available copying machine of the belt fixing type and the toner is actually fixed, there is no offset, the image resolution is excellent, and the durability is also eliminated by the abrasion of the fluororesin layer 30 μm. Do 1
It was possible to operate up to the passage of 0,000 sheets without peeling the fluororesin layer and the polyimide belt.

(Example 2) A belt was prepared in the same manner as in Example 1 except that the liquid obtained by diluting Ketjenblack of Example 1 with water was added to a PFA dispersion liquid having a viscosity of 200 cp to make 100 cp, and the mixture was stirred with a homogenizer. It was made.
At this time, the median diameter of the dispersion containing PFA and Ketjenblack was 0.5 μm.

The belt obtained has a peel strength of 2 N / c.
m, surface roughness Ra 0.6 μm, surface resistivity 1 × 10 ⁶ Ω
It became / □. Further, when the toner is fixed in the same manner, there is no offset, the image resolution is excellent, and even in durability, the fluororesin layer 30 μm is worn out and disappears until 100,000 sheets of paper are passed, and the fluororesin layer and the polyimide are removed. It was possible to operate without peeling the belt.

Example 3 The primer of Example 2 was prepared by adding PFA particles (average particle size 0.5 μm) in a polyimide precursor.
A belt was produced in the same manner as in Example 1 except that a mixed solution containing 50% by weight of m) was used (Mitsui DuPont Fluorochemical, developed product 047-4). The obtained belt has a peel strength of 7 N / cm, a surface roughness Ra of 0.6 μm, and a surface resistivity of 1 ×.
It became 10 ⁶ Ω / □. Further, when the toner is fixed in the same manner, there is no offset, the image resolution is excellent, and even in durability, the fluororesin layer 30 μm is worn out and disappears until 100,000 sheets of paper are passed, and the fluororesin layer and the polyimide are removed. It was possible to operate without peeling the belt.

(Comparative Example 1) A polyimide-based primer (Mitsui DuPont Fluorochemical, K001-02) and carbon (Lion, W3) so that the solid content ratio was 25 wt%.
A belt was produced in the same manner as in Example 1 except that a liquid containing 11N and an average particle diameter of 0.3 μm was mixed. The obtained belt has a peel strength of 0.3 N / cm and a surface roughness Ra.
The surface resistivity was 0.8 μm and the surface resistivity was 7 × 10 ⁵ Ω / □. When a paper feed operation was performed using this belt, the fluororesin layer and the polyimide belt were peeled off after 10,000 sheets were printed.

(Comparative Example 2) Carbon (lion, W311N, average particle size of 0. 20%) was added to the primer of Example 3 such that the total amount of solids of polyimide and PFA was 2 wt%.
A belt was produced in the same manner as in Example 3 except that 3 μm) was mixed. The belt obtained has a peel strength of 0.9 N /
cm, surface roughness Ra 0.6 μm, surface resistivity 1 × 10 ⁶
Became Ω / □. When a paper feed operation was performed using this belt, the fluororesin layer and the polyimide belt were peeled off after 40,000 sheets were printed.

(Comparative Example 3) 2.5 wt% of carbon was added to the PFA solid content of the PFA dispersion liquid of Example 1.
%, And 5% by weight of titanium oxide (average particle size 0.3 μm) was added to the PFA solid content in Example 1
A belt was produced in the same manner as in. Peel strength 0.7N /
cm, surface roughness Ra 1.2 μm, surface resistivity 5 × 10 ⁴
Became Ω / □. The toner thus fixed entered the irregularities on the surface of the fluorine, and caused an offset due to defective release. In addition, a paper feed operation (fixing temperature 21
At 0 ° C., the fluororesin layer and the polyimide belt were peeled off after passing 30,000 sheets of paper.

Reference Example 1 Dispersion of the PFA dispersion liquid of Example 1 and Ketjen Black at 200 rpm3
A belt was produced in the same manner as in Example 1 except that the h / L blade was stirred. The median diameter was 0.75 μm. The obtained belt has a peel strength of 2 N / cm and a surface roughness Ra.
The surface resistance was 1.3 μm and the surface resistivity was 5 × 10 ⁵ Ω / □. When a paper feed operation was performed using this belt, the belt had satisfactory durability and antistatic effect, but white spots occurred in the image due to defective toner release.

Reference Example 2 1.25 w of carbon was added to the PFA solid content of the PFA dispersion liquid of Example 1.
A belt was produced in the same manner as in Example 1 except that t% was set. Peel strength 4 N / cm, surface assembly Ra 0.8 μm,
The surface resistivity was 1 × 10 ⁹ Ω / □. When a paper feed operation was performed using this belt, the durability and releasability of the belt were sufficient, but the image was distorted like dust due to electrostatic offset.

[Brief description of drawings]

FIG. 1 is a sectional view showing an example of a fixing belt of the present invention.

[Explanation of symbols]

1 Polyimide belt 2 Polyimide-based primer layer 3 Fluororesin layer

Continued front page    F term (reference) 2H033 AA11 AA23 AA32 BA02 BA17                       BB03 BB05 BB08 BB13 BB14                       BB15 BE03                 4F006 AA39 AB19 AB38 AB72 BA01                       BA07                 4F100 AA37A AK17A AK17B AK49B                       AK49C BA03 BA07 BA10A                       DA20 DE01B JA20A JD20A                       JG03 JG04A JK06 JK06A                       JL00 YY00A

Claims (5)

[Claims] 1. A polyimide-based primer layer containing no carbon black on the surface of a polyimide belt,
A fixing belt having a fluororesin layer containing carbon black and having a fluororesin content of 95% by weight or more. 2. The surface roughness of the fluororesin layer is R.
The fixing belt according to claim 1, wherein a is 1 μm or less, surface resistivity is 10 ⁸ Ω / □ or less, and peel strength is 1 N / cm or more. 3. The fixing belt according to claim 1, wherein the fluororesin layer is composed of a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer and Ketjen black. 4. A dispersion liquid in which the fluororesin layer contains 1.5 to 2.3 wt% of carbon black with respect to the resin solid content and is dispersed so that the median diameter is 0.7 μm or less, and the dispersion liquid is heated after coating. The fixing belt according to claim 3, which is formed by the following method. 5. The fixing belt according to claim 1, wherein the polyimide-based primer layer contains particles of a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer.