JPH10142990A - Fixing roller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing roller having excellent release property and wear resistance which can sufficiently respond to realizing faster copying processes and full-color images. SOLUTION: This fixing roller is produced by forming a fluorocarbon resin layer, with a rubber layer interposed if desired, on the outer surface of a roller base body. The fluorocarbon resin layer consists of a fluorocarbon resin mixture containing (A) 20 to 97wt.% tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) having 1 to 15μm average particle size and (B) 3 to 80wt.% polytetrafluoroethylene (PTFE) having <=1μm average particle size.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing roller used in a fixing step of fixing a toner on a transfer material such as transfer paper in an image forming apparatus such as an electrophotographic copying machine. The present invention relates to a fixing roller provided with a fluororesin layer and having excellent releasability and abrasion resistance.

[0002]

2. Description of the Related Art In an image forming apparatus such as an electrophotographic copying machine, generally, a charging step for uniformly and uniformly charging a photosensitive drum, an exposure step for forming an electrostatic latent image on the photosensitive drum by exposure, and a toner (Developing agent) for developing the electrostatic latent image into a visible image, transferring the toner image on the photosensitive drum to the transfer material, fixing the toner image on the transfer material, and after the transfer process An image is formed by a cleaning process for cleaning the toner remaining on the photosensitive drum.

In the fixing step, a toner image is fixed on a transfer material by using various methods such as heating, pressurizing, and solvent vapor. Usually, a fixing roller having a built-in heat source and a pressing roller are used. The transfer material is passed through the gap, and the toner on the transfer material is heated and melted and fixed. As the fixing roller, a roller having a structure in which a fluororesin layer is formed directly or via a rubber layer on the outer surface of a roller-shaped substrate to prevent offset (for example, Japanese Patent Application Laid-Open No. 57-89785). No.). As the fluororesin, tetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkylvinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP) and the like are used. The fluororesin layer is usually formed by applying and baking a dispersion (paint) containing these fluororesins. As a rubber material forming the rubber layer, fluorine rubber, silicone rubber, or the like is used. A fixing roller having a fluororesin layer formed on its surface generally has good releasability and abrasion resistance, prevents contamination of the roller surface, and has excellent fixability. However, in recent years, with the speeding up of copying and full-color images, it has been required to lower the melting point of toner, and toner components have been changed. As a result, in a conventional fixing roller having a fluororesin layer formed thereon, the releasability is insufficient and an offset phenomenon frequently occurs, or the abrasion resistance is insufficient and a problem occurs in durability.

[0004] The toner used for developing an electrostatic image is generally colored fine particles in which a coloring agent, a charge controlling agent, an offset preventing agent, and the like are uniformly dispersed in a thermoplastic resin. By being pressed, it is fused and fixed on the transfer material. In order to meet the demand for high-speed copying, it is necessary to reduce the melting point while preventing blocking between toners, and to heat and melt the toner quickly in the fixing process. Further, in order to make an image full-color, it is necessary to uniformly melt and mix toner particles of each color in a fixing step, and it is also required to lower the melting point of the toner. However, when the melting point of the toner is lowered, the toner easily adheres to the surface of the fixing roller, and the offset phenomenon easily occurs. Further, the speed of copying increases the load on the fixing roller, and the fluorine resin layer is easily worn. As a result, the fixing roller provided with the PTFE layer has an insufficient releasability, and the offset phenomenon has frequently occurred. In addition, conventional PF
It has been found that the fixing roller provided with the layer A has a large amount of wear and is inferior in wear resistance.

Conventionally, as a fixing roller having a PFA layer formed thereon, (1) a PFA having an average particle diameter of 5 to 75 μm is used.
A fixing roller having a layer on which FA particles are electrostatically coated (Japanese Patent Publication No. Sho 62-10429); and (2) an average particle diameter of 5 μm.
A fixing roller having a layer formed by applying and baking a fluororesin paint in which PFA particles having a particle size of m or more and PFA particles having an average particle size of 1 μm or less are dispersed in a liquid dispersion medium (Japanese Patent Publication No. 4-168)
No. 170) is known. However, PFA
In a conventional fixing roller using particles, further improvement in abrasion resistance is required as copying speeds up.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a fixing roller having excellent releasability and abrasion resistance which can sufficiently cope with high-speed copying and full-color images. It is in. The present inventors have conducted intensive studies to overcome the problems of the prior art, and as a result, on the outer surface of the roller-shaped substrate, via a rubber layer if desired, a fixing roller formed by forming a fluororesin layer, Average particle size 1-15μ
By forming a fluororesin layer using a fluororesin mixture containing PFA of m and PTFE having an average particle diameter of 1 μm or less, the releasability and abrasion resistance are highly balanced, and high-speed copying and full color printing are achieved. It has been found that a fixing roller capable of withstanding the above conditions can be obtained. As the PFA, those having a relatively high molecular weight of 500,000 or more are preferable. In addition, the fluororesin layer can be easily formed by applying and firing a fluororesin mixture paint in which PFA and PTFE are dispersed in a liquid medium, on the outer surface of the roller-shaped base material via a rubber layer, if desired. it can. The present invention
It has been completed based on these findings.

[0007]

According to the present invention, in a fixing roller in which a fluororesin layer is formed on the outer surface of a roller-like base material via a rubber layer if desired, the fluororesin layer is formed by (A) A) 20-97% by weight of a tetrafluoroethylene-perfluoroalkylvinyl ether copolymer (PFA) having an average particle diameter of 1 to 15 µm, and (B) an average particle diameter of 1 µm.
m or less of polytetrafluoroethylene (PTFE) 3 to
A fixing roller is provided, which is formed of a fluororesin mixture containing 80% by weight.

[0008]

DETAILED DESCRIPTION OF THE INVENTION In the present invention, PF having an average particle diameter of 1 to 15 .mu.m is used as a fluororesin for forming a fluororesin layer.
A fluororesin mixture containing A and PTFE having an average particle size of 1 μm or less is used. By using such a fluororesin mixture, it is possible to form a fluororesin layer in which high releasability of PFA and high wear resistance of PTFE are compatible. The reason is that the PTFE particles adhere around the PFA particles, so that the coating film surface becomes PFA and PTFE.
This is presumed to be covered by the fluororesin mixture having a composition according to the mixing ratio with the above.

The PFA used in the present invention is a powder having a relatively large particle diameter having an average particle diameter of 1 to 15 μm, preferably 2 to 13 μm, more preferably 3 to 10 μm. Such PFA is a resin powder generally used for electrostatic coating. Since the average particle diameter of PFA is large, when a wet paint is used, the control of the film thickness becomes easy. For example, a coating film having an arbitrary film thickness of about several μm to about several tens μm and having no defect can be used. It can be formed by a single coating process. However, if the average particle diameter of PFA is too large, P
When used in combination with TFE, the releasability of the fluororesin layer is undesirably reduced. If PFA having an average particle diameter that is too large is used, it is presumed that unevenness due to large particles remains on the surface of the coating film, so that the releasability is reduced.

[0010] The molecular weight of PFA is preferably 300,000 or more, more preferably 400,000 or more, and most preferably 500,000 or more. The upper limit of the molecular weight of PFA is not particularly limited, but is preferably 1.5 million, more preferably 1.2 million, and most preferably 1 from the viewpoint of availability and physical properties.
One million. Having a specific range of average particle size, and
By using PFA having a large molecular weight, the wear resistance of the fluororesin layer is remarkably improved, and the releasability is also excellent. In the present invention, the molecular weight of PFA refers to ASTM
Melt flow rate (MFR) is measured according to D3307 and is a weight average molecular weight calculated from a known “relation between molecular weight and MFR”.

In order to form a coating film having a uniform thickness and no defect, it is preferable to use PFA particles as a wet paint. In general, a wet coating material in which PFA particles are dispersed in a liquid medium such as water using a surfactant uses PFA particles having an average particle diameter of less than 1 μm, so that the cohesive force between the particles is weak, and defects are generated. It is difficult to obtain a small number of coating films, especially when trying to form a coating film with a thickness of 20 μm or more in a single film-forming process, cracks are generated or concave defects are generated by being repelled on the base material. Cheap. On the other hand, PFA particles having a large particle diameter used for electrostatic coating have good film-forming properties, and form a film having a large thickness and no defect in a single film-forming process. be able to. But,
A coating material in which PFA particles having a large particle diameter are dispersed in a liquid medium,
Since the cohesive force between the particles is strong, the particles settle in a short time, and easily cause irreversible aggregation that cannot be easily redispersed by simple stirring or the like.

On the other hand, by forming a wet paint by combining PFA particles with PTFE particles having an average particle diameter of 1 μm or less, instead of using the PFA particles alone as a wet paint, the cohesive force between particles is weak. It is possible to obtain a wet paint that can be easily redispersed without preserving the properties and controlling the film thickness and without causing non-aggregation even when precipitated. It is presumed that the reason is that a large number of PTFE particles adhere around the PFA particles having a large particle diameter, thereby preventing irreversible aggregation of the PFA particles in the wet paint. The average particle diameter of PTFE is preferably 0.5 μm or less from the viewpoint of the effect of preventing aggregation. Such PTFE can be easily obtained as a commercially available PTFE dispersion. P
The molecular weight of TFE is not particularly limited, but is preferably 1
It is at least one million, more preferably at least 1.5 million.

In the present invention, (A) the average particle diameter is 1 to 15 μm.
20 to 97% by weight of PFA, preferably 30 to 95% by weight, more preferably 60 to 90% by weight, and (B) 3 to 80% by weight, preferably 5 to 70% by weight of PTFE having an average particle diameter of 1 μm or less. It is preferably formed using a fluororesin mixture containing 10 to 40% by weight. If the blending ratio of PFA is too small, the releasability decreases, while if it is too large, the abrasion resistance decreases. If the blending ratio of PTFE is too small, the effect of preventing irreversible aggregation of PFA particles in a wet coating is reduced, in addition to the reduction of abrasion resistance. From the viewpoint of achieving a high balance between release properties and wear resistance, PFA6
The mixing ratio of 0 to 90% by weight and 40 to 10% by weight of PTFE, therefore, the weight ratio of PFA / PTFE is 1.5 to
It is particularly preferred that it is in the range of 9.0.

In view of the above, preferred in the present invention are (A) a molecular weight of 400,000 or more and an average particle diameter of 2
A fluororesin layer is formed using a fluororesin mixture (PFA / PTFE = 0.4 to 19.0) of 30 to 95% by weight of PFA having a particle size of 1 to 13 μm and (B) 5 to 70% by weight of PTFE having an average particle diameter of 1 μm or less. This is the fixing roller. Also,
Particularly preferred in the present invention are (A) 60 to 90% by weight of PFA having a molecular weight of 500,000 or more and an average particle diameter of 3 to 10 μm, and (B) PTFE 10 having an average particle diameter of 0.5 μm or less.
~ 40% by weight of a fluororesin mixture (PFA / PTFE)
= 1.5 to 9.0) to form a fixing roller having a fluororesin layer formed thereon.

In the present invention, PFA and PT
A fluororesin mixture paint in which FE is dispersed in a liquid medium is prepared, and the fluororesin layer is formed by applying and calcining the paint on the outer surface of the roller-shaped base material via a rubber layer if necessary. As the liquid dispersion medium, water is usually used, but an organic solvent may be used if desired, or a mixture of water and a polar organic solvent such as alcohol is used to facilitate drying after coating. You can also. PFA
A surfactant is usually used to disperse the particles in the liquid medium. As the surfactant, an anionic surfactant and a nonionic surfactant are preferable. These surfactants can be used alone or in combination of two or more. Among these, nonionic surfactants are particularly preferred. The surfactant is used in such a ratio that the PFA particles can be dispersed. PFA
The procedure for preparing a wet paint containing PTFE and PTFE is not particularly limited.
A dispersion in which FA particles are dispersed is prepared, and this is mixed with PTFE.
Is preferred to be mixed with a dispersion containing

Various additives such as pigments and fillers can be blended in order to improve the coating film strength, thermal conductivity, abrasion resistance and the like or to color. Specifically, pigments for coloring, for example, carbon black, titanium white, mica, colored mica coated with titanium oxide and iron oxide, and other inorganic pigments can be added. In addition, various adhesives such as engineering plastics such as polyamideimide (PAI), polyimide (PI), and polyethersulfone (PES), and organic metal complexes can be added as an adhesion aid to the base material. When a non-aqueous solvent is used as a liquid medium, a silane coupling agent or the like can be used as an adhesion aid.

As the material of the roller-shaped substrate, a metal such as aluminum or stainless steel having good thermal conductivity, or ceramics is usually used. The fluororesin layer is formed directly on the outer surface of the roller-shaped base material or formed via a rubber layer. Examples of the material of the rubber layer include silicone rubbers such as methyl silicone rubber, vinyl methyl silicone rubber, phenyl methyl silicone rubber, and fluorosilicone rubber; vinylidene fluoride rubber, tetrafluoroethylene-propylene rubber, and tetrafluoroethylene-par. Fluoro rubbers such as fluoromethyl vinyl ether rubber, phosphazene-based fluoro rubber, and fluoropolyether can be exemplified. These can be used alone or in combination of two or more.
The rubber layer can be formed not only in one layer but also in two or more layers as desired. The thickness of the rubber layer is usually 0.
It is about 1 to 1 mm, preferably about 0.15 to 0.5 mm.

The rubber layer may optionally contain an inorganic filler. As the inorganic filler, for example, carbon black, talc, mica, kaolin, titanium oxide, iron oxide, chromium oxide, calcium carbonate, calcium silicate, calcium sulfate, barium sulfate, magnesium carbonate, magnesium phosphate, graphite, silicon nitride , Boron nitride, titanium nitride, molybdenum disulfide, hydrotalcite, metal powder and the like. As organic fillers, natural resins and synthetic resins (PAI, PI, PES, etc.)
May be added. The mixing ratio of the filler is 100 parts by weight or less, preferably 80 parts by weight or less based on 100 parts by weight of the rubber.

The method for producing the fixing roller of the present invention is as follows. (1) The outer surface of the roller-shaped base material is subjected to a roughening treatment with a sandplast or the like, and a primer is coated thereon if necessary, and then a fluororesin is applied. A wet paint containing the mixture is applied by a spray coating method or the like, dried, and then fired. (2) The outer surface of the roller-shaped base material is subjected to a roughening treatment with sandplast or the like, and the desired After applying a heat-resistant adhesive, the rubber is coated and vulcanized, then, if necessary, formed into a required shape (for example, grinding into an inverted crown shape), and then containing a fluororesin mixture. A method in which a wet paint is applied by a spray coating method or the like, dried, and then baked is used. The thickness of the fluororesin layer is usually 0.1 to 50 μm, preferably 5 to 30 μm. If the thickness of the fluororesin layer is too large, the thermal conductivity is reduced, and if it is too small, the fluororesin layer is worn due to long-term use and the durability is deteriorated.

[0020]

The present invention will be described below more specifically with reference to examples and comparative examples.

Example 1 An average particle diameter of about 7 μm and a molecular weight of about 500,000 (MF measured according to ASTM D3307)
60 g of PFA powder (TW3507 manufactured by Asahi Glass Co., Ltd.) of 50 g of water and 50 g of a surfactant (Octapol 80 manufactured by Sanyo Chemical Co., Ltd.) of R value calculated from 14 to 19 g / 10 min.
Is dispersed in a liquid medium obtained by mixing PTFE, and the resulting dispersion contains PTFE containing PTFE having an average particle diameter of 0.2 μm.
E dispersion (D-1F, manufactured by Daikin Industries, Ltd.) was added in an amount such that the solid content concentration (PTFE component) became 40 g, and the mixture was thoroughly mixed to prepare a fluororesin mixture paint. The composition of the paint is shown in Table 1. The rubber layer of a rubber roller (diameter 50 mmφ, roll length 320 mm) obtained by bonding silicone rubber to an aluminum roller and vulcanizing was ground to a thickness of 0.2 mm, and the surface was polished with # 320 sandpaper. It was roughened. On top of this, apply a fluororesin mixed paint,
After drying at 250 ° C. for 10 minutes, baking was performed at 350 ° C. for 20 minutes to obtain a fixing roller coated with a 20 μm-thick fluororesin layer. The obtained fixing roller was excellent in releasing property and abrasion resistance.

Examples 2 to 5 PFA powder and PTFE
A fixing roller was prepared in the same manner as in Example 1 except that the usage ratio of (solid content) was changed as shown in Table 1. All of the obtained fixing rollers were excellent in releasing property and abrasion resistance.

Example 6 PFA powder having an average particle diameter of about 7 μm and a molecular weight of about 500,000 was used. PFA powder having an average particle diameter of about 7 μm and a molecular weight of about 700,000 (MFR = 4 to 6 g / 10 min) (Asahi Glass Co., Ltd.) A fixing roller was prepared in the same manner as in Example 1, except that TW5507) was used. The obtained fixing roller was excellent in releasing property and abrasion resistance.

Example 7 PFA powder having an average particle diameter of about 7 μm and a molecular weight of about 500,000 was used. PFA powder having an average particle diameter of about 7 μm and a molecular weight of about 900,000 (MFR = 1 to 3 g / 10 min) (Asahi Glass Co., Ltd.) A fixing roller was prepared in the same manner as in Example 1, except that TW6507) was used. The obtained fixing roller was excellent in releasing property and abrasion resistance.

Comparative Example 1 A PFA powder having an average particle diameter of about 7 μm and a molecular weight of about 500,000 was replaced with a PFA powder having an average particle diameter of about 20 μm and a molecular weight of about 500,000 (MP-10 manufactured by Mitsui Dupont, Inc.).
A fixing roller was prepared in the same manner as in Example 1 except that the method was changed to 2). The obtained fixing roller was excellent in abrasion resistance but inferior in releasability.

Comparative Example 2 As a PFA dispersion, a dispersion containing PFA particles having an average particle diameter of about 0.4 μm and a molecular weight of about 200,000 (MP-102; PFA4 manufactured by Daikin Industries, Ltd.)
A fixing roller was prepared in the same manner as in Example 1, except that 7% by weight, 6% by weight of a surfactant, and 47% by weight of water) were used in an amount to give a solid content of 60 g. The obtained fixing roller was excellent in abrasion resistance but inferior in releasability.

Comparative Example 3 A dispersion containing PFA particles having an average particle diameter of about 0.4 μm and a molecular weight of about 200,000 as a fluororesin (MP-102; PFA47 manufactured by Daikin Industries, Ltd.)
% Of a surfactant, 6% by weight of a surfactant, and 47% by weight of water) were used alone to prepare a fixing roller in the same manner as in Example 1. The obtained fixing roller was excellent in releasability but poor in abrasion resistance.

<Evaluation Test of Releasability> The respective fixing rollers obtained in each of the above Examples and Comparative Examples were set in a fixing unit of a copying machine NP-4335 manufactured by Canon Inc., and 2 mm wide and 1 cm square on A4 paper. Made 100,000 copies of the paper on which the lattice pattern was drawn. Whether the toner adhered to the surface of the fixing roller to cause an offset in the fixed image or whether the toner adhered to the surface of the roller and became dirty was examined, and the releasability was evaluated in the following three stages. Table 1 shows the results. ：: No offset, no roller dirt. ：: No offset, roller dirt. ×: Offset, roller dirt.

<Evaluation Test for Abrasion Resistance> In the above-mentioned evaluation test for releasability, the decrease in the thickness of the fluororesin layer after 100,000 copies were made was measured. The smaller the decrease, the better the wear resistance. If the wear amount is 3.0 μm or less,
The wear resistance is remarkably excellent, exceeding 3.0 μm and 5.0 μm
When it is less than m, there is no problem in practical performance, and when it exceeds 5 μm, it is evaluated that abrasion resistance is insufficient. The results are shown in Table 1.

[0030]

[Table 1]

As is clear from the results shown in Table 1, by using a mixture of PFA and PTFE having a specific average particle size (Examples 1 to 7), a fixing roller having excellent wear resistance and durability was obtained. It is understood that it is possible. In particular, when a mixture in which the molecular weight of PFA is 500,000 or more and the ratio (weight ratio) of PFA / PTFE is in the range of 1.5 to 9.0 is used (Examples 1 to 3, and 6 to 7). It can be seen that a fixing roller having a highly balanced release property and abrasion resistance can be obtained. On the other hand, when the average particle diameter of PFA is too large (Comparative Example 1) or too small (Comparative Example 2), the releasability is poor, and when PFA alone is used (Comparative Example 3). , Poor wear resistance.

[0032]

According to the present invention, there is provided a fixing roller having excellent releasability and abrasion resistance which can sufficiently cope with high-speed copying and full-color images.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI // B29K 27:18 B29L 9:00 23:00

Claims (3)

[Claims] In a fixing roller having a fluororesin layer formed on the outer surface of a roller-like base material via a rubber layer if desired, the fluororesin layer may have (A) an average particle diameter of 1 to 15 μm.
m-tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) 20-97% by weight;
(B) A fixing roller comprising a fluororesin mixture containing 3 to 80% by weight of polytetrafluoroethylene (PTFE) having an average particle diameter of 1 μm or less. 2. The fixing roller according to claim 1, wherein the molecular weight of PFA is 500,000 or more. 3. A fluororesin layer in which (A) PFA and (B) PTFE are dispersed and dispersed in a liquid medium, and a fluororesin mixture paint is applied and fired on the outer surface of the roller-like substrate via a rubber layer if desired. 3. The fixing roller according to claim 1, wherein the fixing roller is formed.