JP2010202741A - Low-molecular-weight polytetrafluoroethylene powder, manufacturing method thereof, low-molecular-weight polytetrafluoroethylene gelled powder and paint for fixing member - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low-molecular-weight polytetrafluoroethylene powder capable of forming a coating film excellent in smoothness when used as an additive in a paint, a manufacturing method thereof, a low-molecular-weight polytetrafluoroethylene gelled powder, and a paint for a fixing member. <P>SOLUTION: The low-molecular-weight polytetrafluoroethylene powder has a 50% average particle size of ≤3 μm determined by a dry laser method, contains a powder with a particle size of ≤1 μm, has a melt viscosity of ≤2,500 Pa s determined at 340°C using a flow tester and is obtained by suspension polymerization. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to a low molecular weight polytetrafluoroethylene powder and a production method thereof, a low molecular weight polytetrafluoroethylene gelled powder, and a fixing member coating.

Low-molecular-weight polytetrafluoroethylene is used for the purpose of reducing friction on the surface of the counterpart material and improving the slipperiness, for example, by mixing it with the counterpart material of ink, cosmetics, etc. It has been used for the purpose of improving the texture. Low molecular weight polytetrafluoroethylene is used in a coating material for a fixing member of an electrophotographic apparatus (see, for example, Patent Document 1, Patent Document 2, Patent Document 3, and Patent Document 4).

The low molecular weight polytetrafluoroethylene is obtained by emulsion polymerization (for example, see Patent Document 5 and Patent Document 6), or obtained by thermally decomposing high molecular weight polytetrafluoroethylene (for example, Patent Document). 7, Patent Document 8, Patent Document 9, Patent Document 10 and Patent Document 11), and those obtained by irradiating a molded body such as high molecular weight polytetrafluoroethylene powder or scrap (for example, (See Patent Document 12, Patent Document 13, Patent Document 14, and Patent Document 15.)

The low molecular weight polytetrafluoroethylene is obtained directly by polymerization from the viewpoint of simplification of the process and narrowing of the molecular weight distribution, and preferably it does not require a post-process for reducing the molecular weight. An emulsion polymerization method is known as a method obtained directly by polymerization (see, for example, Patent Document 6).

Moreover, a method for obtaining low molecular weight polytetrafluoroethylene by suspension polymerization using a chain transfer agent is also disclosed (for example, see Patent Document 16).

As a low molecular weight polytetrafluoroethylene obtained by polymerization, a powder having a specific surface area of 7 to ²⁰ m ² / g is known (for example, see Patent Document 17).

Furthermore, recent research results have revealed concerns about the environmental impact of perfluorooctanoic acid [PFOA]. On April 14, 2003, the EPA (US Environmental Protection Agency) conducted a chemical survey on PFOA. (For example, refer nonpatent literature 1).

JP-A-5-45920 JP 2000-292957 A JP 2000-275889 A JP 2008-165018 A Japanese Patent Laid-Open No. 51-41085 JP-A-7-165828 JP 49-39642 A Japanese Patent Publication No. 7-5744 Japanese Patent Publication No. 50-15506 JP 61-118331 A JP 61-162503 A Japanese Patent Publication No.52-25419 Japanese Patent Publication No. 49-48671 JP-T-2001-513529 US Pat. No. 3,766,031 International Publication No. 2004/075539 Pamphlet Japanese Patent Laid-Open No. 10-1476176

EPA report "PRELIMINARY RISK ASSESSMENT OF THE DEVELOPMENTAL TOXICITY ASSOCIATED WITH EXPOSURE TO PERFLUOROCOCANTOIC ACID AND ITS SALT", Internet <URL: http: // www. epa. gov / optintr / pfoa / pfoaara. pfd>).

Conventional low molecular weight polytetrafluoroethylene, for example, lubron obtained by suspension polymerization produced in Patent Document 16 and the like has been used in coating materials for fixing members so far, but has a large particle size and is not necessarily a coating film. It is not optimal as polytetrafluoroethylene for forming a coating, and even if it is used as an additive for paints, there is a possibility that a film having excellent smoothness may not be obtained, and there is room for further improvement. was there.

In view of the above situation, the present invention is a low molecular weight polytetrafluoroethylene powder and a method for producing the same, which can form a coating film having excellent smoothness when used as an additive for paints, and a low molecular weight polytetrafluoroethylene gel. Another object of the present invention is to provide a powder and a coating material for a fixing member.

The present invention includes a powder having a 50% average particle size of 3 μm or less measured by a dry laser and a particle size of 1 μm or less, and a melt viscosity measured by a flow tester method at 340 ° C. of 2500 Pa · s or less. It is a low molecular weight polytetrafluoroethylene powder (hereinafter also referred to as “low molecular weight PTFE powder (A)”) characterized by being obtained by suspension polymerization.

The present invention is a low molecular weight polytetrafluoroethylene gelled powder obtained by a heat treatment in which the low molecular weight polytetrafluoroethylene powder is heated at 250 ° C. or higher and lower than 340 ° C.

The present invention is a method for producing a low molecular weight polytetrafluoroethylene powder comprising producing the above low molecular weight polytetrafluoroethylene powder by suspension polymerization using a chain transfer agent, the 50% average measured by a dry laser A method for producing a low molecular weight polytetrafluoroethylene powder comprising a step of pulverizing a low molecular weight polytetrafluoroethylene powder having a particle diameter of 0.5 to 20 μm.

The present invention is a coating material for a fixing member comprising the low molecular weight polytetrafluoroethylene powder or the low molecular weight polytetrafluoroethylene gelled powder.
The present invention is described in detail below.

The low molecular weight polytetrafluoroethylene powder (A) of the present invention is obtained from low molecular weight polytetrafluoroethylene (hereinafter also referred to as “low molecular weight PTFE”).
The low molecular weight PTFE has a number average molecular weight of 600,000 or less. If it exceeds 600,000, the fibrillation characteristics are manifested and it tends to agglomerate, so it may be inferior in fine dispersibility. If the number average molecular weight of the said low molecular weight PTFE is in the said range, a preferable minimum can be made into 10,000, for example. If it is less than 10,000, it is highly volatile at high temperatures and may not be suitable for heat-resistant paints such as paints that require baking.
The number average molecular weight of the low molecular weight PTFE is a value calculated from the melt viscosity obtained by measurement using a flow tester method.

The low molecular weight PTFE has a number average molecular weight of 600,000 or less, and is obtained by the polymerization method of low molecular weight PTFE described later, or obtained by thermally decomposing high molecular weight polytetrafluoroethylene. Any of those obtained by irradiating high molecular weight polytetrafluoroethylene with radiation may be used.

The low molecular weight PTFE is tetrafluoroethylene homopolymer [TFE homopolymer] and / or modified polytetrafluoroethylene [modified PTFE].
In the present specification, the “TFE homopolymer and / or modified PTFE” means a TFE homopolymer that does not contain a modified PTFE, a modified PTFE that does not contain a TFE homopolymer, or a TFE homopolymer and a modified PTFE. It means any one of PTFE.

“Polytetrafluoroethylene” in the term “low molecular weight PTFE” may generally represent the above TFE homopolymer, but in the present specification, the “low molecular weight PTFE” is a TFE homopolymer and / or a modified PTFE. As is clear from the above, it is not limited to the TFE homopolymer, but only a part of the term “low molecular weight PTFE”. The “low molecular weight PTFE” as a whole refers to a TFE homopolymer and / or modified PTFE as a whole.

The TFE homopolymer is obtained by polymerizing only tetrafluoroethylene [TFE] as a monomer.
The modified PTFE means a polymer obtained from TFE and a modifying agent.

The modifying agent in the modified PTFE is not particularly limited as long as it can be copolymerized with TFE. For example, perfluoroolefin such as hexafluoropropene [HFP]; chlorofluoro such as chlorotrifluoroethylene [CTFE] Examples thereof include olefins; hydrogen-containing fluoroolefins such as trifluoroethylene; and perfluorovinyl ethers.

The perfluorovinyl ether is not particularly limited, and for example, the following general formula (I)
_{CF 2 = CF-ORf (I} )
(Wherein Rf represents a perfluoro organic group), and the like. In the present specification, the “perfluoro organic group” means an organic group in which all hydrogen atoms bonded to carbon atoms are substituted with fluorine atoms. The perfluoro organic group may have ether oxygen.

Examples of the perfluorovinyl ether include perfluoro (alkyl vinyl ether) [PAVE] in which Rf represents a perfluoroalkyl group having 1 to 10 carbon atoms in the general formula (I). The perfluoroalkyl group preferably has 1 to 5 carbon atoms.

Examples of the perfluoroalkyl group in the PAVE include a perfluoromethyl group, a perfluoroethyl group, a perfluoropropyl group, a perfluorobutyl group, a perfluoropentyl group, and a perfluorohexyl group. Groups are preferred.

As the perfluorovinyl ether, in the general formula (I), Rf is a perfluoro (alkoxyalkyl) group having 4 to 9 carbon atoms, the following formula:

(Wherein m represents an integer of 0 or 1 to 4), an organic group represented by the following formula

(In the formula, n represents an integer of 1 to 4.) Perfluoro (alkoxyalkyl vinyl ether) or perfluoro (alkyl polyoxyalkylene vinyl ether) which represents an organic group represented by
As the modifier in the modified PTFE, perfluorovinyl ether and chlorotrifluoroethylene are preferable, and as the perfluorovinyl ether, PAVE is preferable.

In the modified PTFE, the proportion of the modifier in the total amount of the modifier and TFE (% by mass) is preferably 1% by mass or less when the perfluorovinyl ether is used as the modifier, for example. 0.001-1 mass% is more preferable.

As said modified PTFE, you may use 1 type, or 2 or more types from which a number average molecular weight, a copolymerization composition, etc. differ, for example, as said TFE homopolymer, 1 type or 2 from which a number average molecular weight differs, for example More than one species may be used.
The polymerization method of the low molecular weight PTFE is not particularly limited, and examples thereof include emulsion polymerization and suspension polymerization.

A chain transfer agent may be used for the polymerization of the low molecular weight PTFE. By using the chain transfer agent, the molecular weight of the low molecular weight PTFE obtained can be adjusted, and the dispersibility can be improved as an additive to the counterpart material.
The chain transfer agent is not particularly limited as long as it is hydrogen, a lower saturated hydrocarbon or a lower alcohol. Examples of the lower saturated hydrocarbon include linear or cyclic alkanes having 1 to 6 carbon atoms such as methane, ethane, propane, butane, hexane, and cyclohexane. Examples of the lower alcohol include methanol, Examples thereof include alcohols having 1 to 3 carbon atoms such as ethanol.

During the polymerization of the low molecular weight PTFE, an unstable terminal group derived from the chemical structure of the polymerization initiator and the chain transfer agent described later may be generated at the molecular chain terminal of the low molecular weight PTFE. There are no particular restrictions regarding the unstable terminal groups, for _{example, -CH 2 OH, -COOH, -COOCH} 3 , and the like.
The low molecular weight PTFE may be one obtained by stabilizing an unstable end group. The method for stabilizing the unstable terminal group is not particularly limited, and examples thereof include a method of changing the terminal to a trifluoromethyl group [—CF ₃ ] by exposure to a fluorine-containing gas.

The low molecular weight PTFE may also be subjected to terminal amidation.
The terminal amidation method is not particularly limited. For example, as disclosed in JP-A-4-20507, a fluorocarbonyl group [—COF obtained by exposure to the above-mentioned fluorine-containing gas, etc.] And the like are brought into contact with ammonia gas.
When the low molecular weight PTFE is obtained by stabilizing the above-mentioned unstable terminal group or terminal amidation, the resulting low molecular weight PTFE powder of the present invention is used as an additive for a partner material such as ink, paint, and cosmetics. When used, it is easy to become familiar with the counterpart material and the dispersibility can be improved.

The low molecular weight PTFE powder (A) is a powdery solid composed of low molecular weight PTFE.
The low molecular weight PTFE powder (A) preferably has a specific surface area of less than 7 m ² / g and a melt viscosity measured using a flow tester method at 340 ° C. of 2500 Pa · s or less. In the present specification, the low molecular weight PTFE powder (A) having a specific surface area and melt viscosity within the above range is hereinafter referred to as “low molecular weight PTFE powder (B)”.
The low molecular weight PTFE powder (B) has a relatively small specific surface area, and can reduce the powder behavior and adhesion to the hopper. The preferable upper limit of the specific surface area of the low molecular weight PTFE powder (B) is 6 m ² / g, the more preferable upper limit is 5 m ² / g, and the preferable lower limit is 1 m ² / g.
In the present specification, the specific surface area is a value obtained by measurement using a surface analyzer according to the BET method.
Since the low molecular weight PTFE powder (B) has a melt viscosity at 340 ° C. within the above range, the number average molecular weight of the low molecular weight PTFE is about 100,000 or less. The number average molecular weight can be, for example, 40000 or less.
In the present specification, the melt viscosity is a value obtained by a flow tester method at 340 ° C. in accordance with ASTM D 1238.
The low molecular weight PTFE powder (B) preferably has a melt viscosity within the above range, a specific surface area within the above range, and is obtained by suspension polymerization.
In the present specification, when the term “low molecular weight PTFE powder” is used without referring to (A), (B) or (C) described later, the low molecular weight PTFE powder (A), the low molecular weight PTFE powder ( The low molecular weight PTFE powder (A), the low molecular weight PTFE powder (B) and the low molecular weight PTFE powder (B) and the low molecular weight PTFE powder (C) described later and the low molecular weight PTFE powder other than these are not distinguished. This refers to the entire low molecular weight PTFE powder that may contain C).

In the present specification, the term “low molecular weight PTFE powder” means a low molecular weight PTFE powder having an average particle diameter of 0.5 to 20 μm.
In the present specification, the average particle size of the low molecular weight PTFE powder is calculated by measuring the particle size distribution using a laser diffraction type particle size distribution measuring method, and is calculated as being equal to the particle size corresponding to 50% of the obtained particle size distribution integration. Value.

The low molecular weight PTFE powder (A) preferably has a melt viscosity of 2500 Pa · s or less measured using a flow tester method at 340 ° C. In the present specification, the low molecular weight PTFE powder (A) having a melt viscosity within the above range is hereinafter referred to as “low molecular weight PTFE powder (C)”.

The low molecular weight PTFE powder (C) can be easily obtained by suspension polymerization. As suspension polymerization for obtaining the low molecular weight PTFE powder (C) of the present invention, it is preferable to use the low molecular weight PTFE powder production method of the present invention described later.

The low molecular weight PTFE powder (C) preferably has a melt viscosity within the above range and a specific surface area of less than 7 m ² / g. A more preferable upper limit of the specific surface area of the low molecular weight PTFE powder (C) is 6 m ² / g, a still more preferable upper limit is 5 m ² / g, and a more preferable lower limit is 1 m ² / g.
The low molecular weight PTFE powder (C) has a melt viscosity within the above range, a specific surface area within the same range as the low molecular weight PTFE powder (B), and is obtained by suspension polymerization. It is preferable that By using suspension polymerization, a low molecular weight PTFE powder having both the melt viscosity within the above range and the specific surface area within the above range can be easily obtained.

The low molecular weight PTFE powder (A) includes a powder having a 50% average particle size of 3 μm or less and a particle size of 1 μm or less as measured with a dry laser. When the powder has a small particle size, for example, when used as an additive for paints, a coating film having better surface smoothness can be formed.
The 50% average particle size of the low molecular weight PTFE powder (A) is preferably 2.5 μm or less, and more preferably 2.0 μm or less.
The low molecular weight PTFE powder (A) is preferably obtained by suspension polymerization. That is, the present invention includes a powder having a 50% average particle size of 3 μm or less measured by a dry laser and a particle size of 1 μm or less, and a melt viscosity measured by a flow tester method at 340 ° C. is 2500 Pa · It is also a low molecular weight polytetrafluoroethylene powder obtained by suspension polymerization.

The present invention is also a finely divided low molecular weight PTFE powder.

The fine pulverization method is not particularly limited, and examples thereof include a pulverization method. In addition, a method of pulverizing with a pulverizer after irradiating the low molecular weight polytetrafluoroethylene powder with radiation is also a preferable method.

Examples of the pulverizer include an impact type such as a hammer mill, a pin mill, and a jet mill, and a grinding type such as a cutter mill in which a rotating blade and an outer peripheral stator are pulverized by a shearing force caused by unevenness. The pulverization temperature is preferably −200 to 100 ° C. In the freeze pulverization, the temperature is usually -200 to -100 ° C, but may be pulverized at room temperature (10 to 30 ° C). Liquid nitrogen is generally used for freeze pulverization, but the equipment is enormous and the pulverization cost is high. It is appropriate to grind at room temperature (10 ° C.) to 100 ° C., preferably at a temperature close to room temperature (10 ° C. to 30 ° C.) in that the process becomes simple and the grinding cost can be suppressed.

Examples of the radiation include γ-rays, electron beams, and X-rays. For example, γ-rays and electron beams are preferable. The radiation dose is preferably 10 kGy or more. More preferably, it is 100 kGy or more. Although the upper limit of the irradiation amount of a radiation is not specifically limited, For example, it is 1000 kGy.

After the fine pulverization, fine particles and fibrous particles may be removed by airflow classification, and then coarse particles may be further removed by classification.

In airflow classification, the pulverized particles are sent to a cylindrical classification chamber by reduced pressure air, dispersed by a swirling airflow in the room, and fine particles are classified by centrifugal force. Fine particles are collected from the center to the cyclone and bag filter. In the classification chamber, a rotating body such as a conical cone or a rotor is installed so that the pulverized particles and the air can perform a swirl motion uniformly.

When using a classification cone, the classification point is adjusted by adjusting the air volume of the secondary air and the gap between the classification cones. When using a rotor, adjust the air volume in the classification chamber according to the number of rotations of the rotor.

Examples of the method for removing coarse particles include air classification using a mesh, vibrating sieve, ultrasonic sieve, and the like, and air classification is preferred.

The low molecular weight polytetrafluoroethylene gelled powder of the present invention (hereinafter referred to as “low molecular weight PTFE gelled powder”) is a heat treatment in which the low molecular weight PTFE powder (A) is heated at 250 ° C. or higher and lower than 340 ° C. It is obtained through the process.
In the heat treatment, the lower limit of the preferable temperature is 300 ° C., and the upper limit of the preferable temperature is the melting point of the low molecular weight PTFE, for example, 330 ° C.

The low molecular weight PTFE gelled powder of the present invention was “completely gelled” completely for all the particles of the low molecular weight PTFE powder (A), and was performed for some particles or part of one particle. It may be in any state of “semi-gelation”.
By the heat treatment, the particles of the low molecular weight PTFE powder (A) are fused to each other by point contact, and as a whole, a lump is formed that is bonded together with a weak bonding force.
As a result of the heat treatment, and as a result of the polymer chains increasing in momentum and entangled with each other in the individual particles of the low molecular weight PTFE powder (A), the individual particles tend to shrink in a small size and a dense structure. It is in. The apparent density of the individual particles obtained by the heat treatment is generally higher than that of the low molecular weight PTFE powder (A), which is the powder before the heat treatment, so that the powder is less affected and the powder flowability is low. By improving, the filling property to a hopper can be improved.
You may grind | pulverize to the desired magnitude | size with respect to the lump obtained by the said heat processing. The pulverization treatment is preferably performed so as to be divided into individual particles of the low molecular weight PTFE gelled powder. Further, the pulverization process may be performed by the fine pulverization method described above.

The low molecular weight polytetrafluoroethylene powder production method of the present invention (hereinafter referred to as “low molecular weight PTFE powder production method”) produces the above low molecular weight PTFE powder (A) by suspension polymerization using a chain transfer agent. Is made up of.
The low molecular weight PTFE powder production method of the present invention employs suspension polymerization, and is superior in that coagulation is unnecessary as compared with the case of production by an emulsion polymerization method. The low molecular weight PTFE powder production method of the present invention is suitable for the production of the low molecular weight PTFE powder (C) of the present invention described above, but is also suitable for the production of the above low molecular weight PTFE powder (B).

The chain transfer agent is the same as that described in the description regarding the polymerization of the low molecular weight polytetrafluoroethylene.
The chain transfer agent is preferably used in an amount of 0.01 to 0.5 mol% with respect to 100 mol% of the polymerization monomer in the gas phase portion at the start of polymerization. The gas phase polymerization monomer is, for example, a gas phase polymerization monomer charged in a polymerization tank.

When the suspension polymerization is performed at a liquid temperature of 40 ° C. or higher and lower than 100 ° C., the polymerization initiator used preferably contains a persulfate or sulfite and an organic peroxide.
As the polymerization initiator, the “persulfate and sulfite” is referred to as group a, the “organic peroxide” is referred to as group b, and at least one type is selected from each of group a and group b. If present, other reagents having a polymerization initiating action may be used. The persulfate and the sulfite have a short half-life and act as a polymerization initiator from the start of polymerization, whereas the organic peroxide has a relatively long half-life, and the persulfate as a polymerization initiator. And begins to work slower than sulfite. Therefore, by combining the two, the molecular weight distribution can be made small and sharp.
The persulfate is not particularly limited, and examples thereof include ammonium persulfate and potassium persulfate. The sulfite is not particularly limited and includes, for example, ammonium sulfite and potassium sulfite. The product is not particularly limited, and examples thereof include benzoyl peroxide, disuccinic acid peroxide, and diglutaric acid peroxide.
In addition to the polymerization initiator described above, a redox catalyst described later may be used.
The “liquid temperature” is the temperature of the polymerization reaction liquid.

When the suspension polymerization is carried out at a liquid temperature of 5 ° C. or higher and lower than 40 ° C., the polymerization initiator used preferably contains a persulfate or sulfite and / or an organic peroxide and a redox catalyst. By including a redox catalyst, the reaction can proceed even at a low temperature of 5 ° C. or higher and lower than 40 ° C.
The above-mentioned “persulfate or sulfite and / or organic peroxide and redox catalyst” includes persulfate and redox catalyst, sulfite and redox catalyst, organic peroxide and redox catalyst, persulfate and organic peroxide. Any combination of the following five types may be used: a product, a redox catalyst, a sulfite, an organic peroxide, and a redox catalyst.
Two or more of the persulfates, sulfites, organic peroxides, and redox catalysts may be used.
As the persulfate, sulfite and organic peroxide, those described above can be used.
The redox catalyst is not particularly limited, and examples thereof include a metal carbonyl-carbon tetrachloride mixture, a peroxide-iron (II) compound mixture, and the like.

The method for producing a low molecular weight PTFE powder of the present invention comprises a step of finely grinding a low molecular weight polytetrafluoroethylene powder having a 50% average particle diameter of 0.5 to 20 μm measured by a dry laser. By finely pulverizing the low molecular weight PTFE powder, it can be suitably used for paints and the like. Examples of the method for pulverizing the low molecular weight PTFE powder include the same methods as described above.

An additive containing the low molecular weight PTFE powder (A) or the low molecular weight PTFE gelled powder can also be prepared.
The additive may be the low molecular weight PTFE powder (A) itself, or the low molecular weight PTFE gelled powder itself, or may be a composite additive to which, for example, a wax or the like is added in addition to these. Good. The composite additive formed by adding the wax is used for ink applications, for example.

The additive is blended with various counterpart materials according to the purpose. Examples of the counterpart material include engineering plastics such as polyoxybenzoyl polyester, polyimide, polyamide, polyamideimide, polyacetal, polycarbonate, polyphenylene sulfide, and other molding materials. Ink, paint, and the like.
The use of the additive is not particularly limited, and can be used for the purpose of improving the slipperiness of cosmetics such as paints such as inks, varnishes and paints, and foundations. Also used to improve the texture of engineering plastic moldings such as furniture surface sheets, automobile dashboards, covers for household appliances, light load bearings, gears, cams, buttons for push phones, projectors, camera parts, sliding materials, etc. It is also suitable for applications that improve the slipperiness and wear resistance of mechanical parts that generate mechanical friction, applications that improve oil repellency or water repellency such as wax, and processing aids for engineering plastics.

Moreover, the said additive can be used suitably also for the coating material for fixing members of an electrophotographic apparatus (a laser printer, a copier, etc.). For example, the non-adhesiveness / sliding property of the copy roll can be improved, and the non-adhesiveness / cleaning property of the surface of the photoconductor can be improved by blending with the coating material for the photoconductor, resulting in the suppression of image quality defects. Further, by blending with toner, effects such as a charge adjusting agent, a fluidity improver, and a spacer are generated, and as a result, generation of image quality defects can be suppressed.

That is, this invention is also the coating material for fixing members containing the said low molecular weight PTFE powder (A) or the low molecular weight PTFE gelled powder of this invention. The coating material for a fixing member of the present invention is excellent in glossiness and transparency because the molecular weight of PTFE is low. The relationship between the molecular weight, gloss and transparency has not been known so far, and the use of low molecular weight PTFE as an additive is also one of the technical significance of the present invention.
Moreover, since the coating material for a fixing member of the present invention contains a low molecular weight PTFE powder having a small particle diameter, it is possible to suppress the occurrence of flaws in the formed film. Furthermore, it has sufficient durability at a practical level.

The fixing member coating material is a low molecular weight PTFE powder (A) and a low molecular weight PTFE gelled powder. The 50% average particle size measured by a dry laser is 3 μm or less, and the particle size is 1 μm or less. It is preferable that it is included. According to this, the coating film which has the more excellent surface smoothness can be obtained.

The fixing member coating material preferably contains the low molecular weight PTFE powder (A) and / or the low molecular weight PTFE gelled powder, and water and / or an organic solvent.

When the fixing member coating material contains an organic solvent and a low molecular weight PTFE powder (A) and / or a low molecular weight PTFE gelled powder, the organic solvent preferably contains a resin. The resin may be appropriately selected according to the characteristics of the film obtained by applying the fixing member coating material. For example, acrylic resin, polycarbonate resin, urethane resin, and the like are preferable.

Although the said organic solvent will not be specifically limited if it is an organic solvent which can dissolve resin to be used, For example, polar solvents, such as alcohol, a ketone, and ether, Nonpolar solvents, such as toluene and benzene, can be used.

The fixing member coating material preferably contains 1 to 30% by mass of the low molecular weight PTFE powder (A) and / or the low molecular weight PTFE gelled powder with respect to 100% by mass in total of the resin and the organic solvent. . In addition, when using together low molecular weight PTFE powder (A) and the said low molecular weight PTFE gelled powder, the total amount should just be the said range. If it exceeds 30% by mass, the dispersion stability may decrease, and if it is less than 1% by mass, the non-adhesive effect may not be sufficiently obtained. A more preferable upper limit is 25% by mass. A more preferred lower limit is 2% by mass.

When the fixing member coating material contains the low molecular weight PTFE powder (A) and / or the low molecular weight PTFE gelled powder and water, the water may contain a water-soluble organic solvent. Examples of the water-soluble organic solvent include polar solvents such as alcohol, ketone, and ether.

When the water contains a water-soluble organic solvent, the mass ratio of the water-soluble organic solvent and water may be appropriately selected in consideration of the desired properties of the paint.

When the fixing member paint contains water, or when the water contains a water-soluble organic solvent, the water content in the fixing member paint and the mass ratio of the water-soluble organic solvent and water are as desired. These may be selected as appropriate in consideration of the above characteristics.

When the fixing member coating contains water, the fixing member coating is preferably a low molecular weight polytetrafluoroethylene aqueous dispersion containing a surfactant. The form of the low molecular weight polytetrafluoroethylene aqueous dispersion may be a form after polymerization produced by suspension polymerization or the like and not dried, or the dispersion after polymerization may be powdered by drying or the like. After taking out, it may be dispersed in water again.

The fixing member has at least a base material and a film formed by the fixing member coating material of the present invention. As long as the fixing member has a film formed of at least a base material and a coating material for the fixing member, another layer (for example, an elastic layer provided between the base material and the coating film) is provided as necessary. You may have. Examples of the fixing member include, but are not particularly limited to, a fixing roll, a fixing belt, or a fixing film for an electrophotographic apparatus, a pressing roll, a pressing belt, or a pressing film. For example, it may be a fixing member in general office automation equipment (hereinafter also referred to as “OA equipment”). Examples of the OA equipment include image forming apparatuses such as a printing machine and a copying machine. Examples of the fixing member include a roll for OA equipment, a belt for OA equipment, or a film for OA equipment.
Examples of the roll for OA equipment, the belt for OA equipment or the film for OA equipment include a fixing roll, a fixing belt or a fixing film, a pressing roll, a pressing belt or a pressing film.

The fixing member coating material is preferably for forming a fixing member by applying a coating material in which the above-described low molecular weight PTFE powder is dispersed in a liquid medium to a base material. The present invention is also a method for manufacturing a fixing member including a step of applying a dispersion containing the low molecular weight PTFE powder (A) and / or the low molecular weight PTFE gelled powder to a substrate.

The base material can be applied without limitation as long as it is suitable for the application. For example, a polymer film, a metal film, a ceramic film, a glass fiber film, or a combination of two or more of these is used. The composite film etc. which were obtained by using can be used.

As the polymer film, a heat resistant resin material is desirable. Examples of the heat resistant resin material include polyimide resins, polybenzimidazole resins, polyamide resins, and polyamideimide resins. In addition, thermal conductivity improvers such as granular, needle-like, and fibrous carbon black, graphite, alumina, silicone, carbide, boron nitride, and the like may be added to the inside. Additives such as an inhibitor, a release agent, and a reinforcing agent may be added. It is also possible to laminate a metal such as nickel or copper, or a heat resistant elastomer such as silicone rubber or fluorine rubber on the outer peripheral surface of the heat resistant resin.

Examples of the metal film include SUS, nickel, and copper. It is also possible to laminate a heat resistant resin, a heat resistant elastomer such as silicone rubber or fluoro rubber, or other metal material on the outer peripheral surface of the metal film.

Examples of the base material include conductive powders such as graphite and metal powder, organic compounds having conductivity, barium sulfate, mica, titanium oxide, iron oxide, aluminum oxide, silicon carbide, silicon nitride for improving wear resistance. In addition, powders of inorganic compounds such as silicate compounds may be blended.

The low molecular weight PTFE powder (A) or the low molecular weight PTFE gelled powder can also be used as a molding material for obtaining a molded product. The molded article may contain a filler and / or oil. The filler is not particularly limited. For example, engineering plastics such as polyoxybenzoyl polyester, polyimide, polyamide, polyamideimide, polyacetal, polycarbonate, and polyphenylene sulfide; carbon fiber; glass fiber; bronze powder; graphite powder; calcium carbonate; Calcium; molybdenum disulfide; silicate minerals such as chlorite, talc and mica; metal oxides; soft metal powders and the like.

Since the low molecular weight PTFE powder, the low molecular weight PTFE gelled powder and the low molecular weight PTFE powder of the present invention have the above-mentioned configuration, they are suitable as additives for paints, etc. The surface smoothness of the coating can be made excellent. The paint exhibits particularly excellent effects when used as a coating for fixing members.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited only to these examples.

[Polymerization of low molecular weight PTFE powder]
Polymerization example 1
70 L of deionized water was charged into a 150 L stainless steel polymerization tank equipped with a stirring cone blade and sealed. After removing the air in the tank, 100 g of ethane was charged. The TFE monomer was charged to a tank internal pressure of 0.5 MPa, and the temperature was raised to 85 ° C. When the temperature in the tank reached 85 ° C., TFE monomer was added again to adjust the pressure to 0.8 MPa. As soon as 250 ppm / H ₂ O ammonium persulfate and 250 ppm / H ₂ O disuccinic acid peroxide were charged as polymerization initiators in the form of an aqueous solution, consumption of the TFE monomer in the tank started. When the pressure inside the tank is consumed up to 0.7 MPa during the polymerization, the operation of additionally adding TFE to 0.85 MPa is repeated, and when the TFE supply amount reaches 12 kg, the polymerization reaction is terminated, and the pressure inside the tank is reduced to normal pressure. Opened up. After the start of the polymerization reaction, the temperature in the tank was kept at 84.5 to 85.5 ° C throughout. After cooling the inside of the tank to room temperature, the obtained particles were washed with deionized water, filtered, and dried in a hot air circulating drier at 170 ° C. for 12 hours to obtain a low molecular weight PTFE powder.

Polymerization example 2
A low molecular weight PTFE powder was obtained in the same manner as in Polymerization Example 1 except that the amount of ethane charged was 140 g.

Polymerization example 3
A low molecular weight PTFE powder was obtained in the same manner as in Polymerization Example 1 except that the amount of ethane charged was 160 g.

Polymerization example 4
A low molecular weight PTFE powder was obtained in the same manner as in Polymerization Example 1 except that the amount of ethane charged was 200 g.

Polymerization example 5
A low molecular weight PTFE powder was obtained in the same manner as in Polymerization Example 1 except that the amount of ethane charged was 60 g.

Polymerization Example 6
A low molecular weight PTFE powder was obtained in the same manner as in Polymerization Example 1 except that the amount of ethane charged was 75 g.

The following physical property evaluation was performed on the obtained low molecular weight PTFE powder.
Apparent density Measured according to JIS K 6891-5.3.
Average particle size and particle size distribution Using a laser diffraction particle size distribution measuring device (manufactured by JEOL Ltd.), measuring the particle size distribution at a pressure of 0.1 MPa and a measurement time of 3 seconds without using a cascade, and obtaining the obtained particle size distribution To a particle size corresponding to 50%.
A hot-air circulating electric furnace in which 10 g of a sample (expressed as A gram in the following formula) is placed in a high-temperature volatility aluminum cup (capacity 50 ml, upper diameter 61 mm, lower diameter 42 mm, depth 33 mm) and adjusted to the heating temperature in advance. After holding for 1 hour in a nitrogen atmosphere at 300 ± 2 ° C., the mass was measured, and the following formula high temperature volatility (% by mass) = [{A-mass after heat treatment (g)} × 100] / A
Was used to calculate the high temperature volatility.
Using a 2φ-8L die with a melt viscosity flow tester (manufactured by Shimadzu Corporation), a 2 g sample heated in advance at a temperature of 340 ° C for 5 minutes was measured at 340 ° C under a load of 0.7 MPa.
The specific surface area was measured by a BET method using a surface analyzer (trade name: MONOSORB, manufactured by QUANTA CHROME). A mixed gas of 30% nitrogen and 70% helium was used as the carrier gas, and cooling was performed with liquid nitrogen.
The results are shown in Table 1.

From Table 1, it was found that the melt viscosity decreases when the addition amount of ethane, which is a chain transfer agent, is increased.

[Gelification of low molecular weight PTFE powder]
Gelation experiment example 1
The dried low molecular weight PTFE powder obtained in Polymerization Example 2 was spread on a stainless steel tray so as not to exceed a thickness of 20 mm, and then placed in a hot-air circulating electric furnace heated to 250 ° C. and heat-treated for 30 minutes. It was. After 30 minutes, the tray was immediately taken out into the room and allowed to cool to obtain a low molecular weight PTFE gelled powder.

Gelation experiment example 2
A low molecular weight PTFE gelled powder was obtained in the same manner as in Gelation Experimental Example 1 except that the temperature of the hot air circulating electric furnace was set to 300 ° C.

Gelation experiment example 3
A low molecular weight PTFE gelled powder was obtained in the same manner as in Gelation Experimental Example 1 except that the temperature of the hot air circulating electric furnace was 320 ° C.

Gelation experiment example 4
A low molecular weight PTFE gelled powder was obtained in the same manner as in Gelation Experimental Example 1 except that the temperature of the hot air circulating electric furnace was changed to 330 ° C.

Gelation experiment example 5
A low molecular weight PTFE gelled powder was obtained in the same manner as in Gelation Experimental Example 1 except that the temperature of the hot air circulating electric furnace was changed to 340 ° C.

Gelation experiment example 6
A low molecular weight PTFE gelled powder was obtained in the same manner as in Gelation Experimental Example 1 except that the temperature of the hot air circulating electric furnace was 200 ° C.

In addition to the above-mentioned apparent density, average particle diameter, and melt viscosity measurement, the following physical property measurements were performed on the obtained low molecular weight PTFE gelled powder.
The area of the melting peak was measured using a differential scanning calorimeter (trade name: DSC-50, manufactured by Shimadzu Corporation).
Sensory test of powder dancing Evaluation was made by visual observation as follows.
◎… No dancing was observed. ○… No dancing was observed. △… Several amount of dancing was observed. ×… A large amount of dancing was observed.

From Table 2, it was found that, in the gelation experiment example, the higher the gelation temperature, the larger the apparent density and the average particle size, and the more the powder is suppressed.

Grinding example 1
The PTFE obtained in Polymerization Example 5 was finely pulverized with a pulverizer to obtain a powder having a 50% average particle size of 2.0 μm. The obtained powder contained a powder having a particle size of 1 μm or less.
As a pulverizer, Hosokawa Micron Air Jet Mill 100AFG equipped with a classifier 50ATP was used. The classification rotor of the classifier 50ATP was rotated at about 22000 rpm.

Grinding example 2
The PTFE obtained in Polymerization Example 5 irradiated with 200 kGy of γ-rays was pulverized under the same conditions as in Crushing Example 1 to obtain a 1.2 μm powder. The obtained powder contained a powder having a particle size of 1 μm or less.

Grinding example 3
The PTFE obtained in Polymerization Example 4 was finely pulverized under the same conditions as in Grinding Example 1 to obtain a 1.2 μm powder. The obtained powder contained a powder having a particle size of 1 μm or less.
Table 3 shows the powders obtained in the pulverization examples 1 to 3.

Paint test 1
A paint blended with PTFE obtained in pulverization example 1 was prepared, applied to a glass plate, and air dried. After drying, when the number of visible spots in an arbitrary place 25 cm ² on the coating film surface was counted, none was found. The coating and application were performed by the following method.
Acryloid A-11 made by ROHM & HAAS dissolved in MEK was used, and the resin concentration was 25% by mass. PTFE was blended in an amount of 10% by mass with respect to the total mass of MEK and resin to obtain a paint.
The dispersion was performed for 2 hours using a sand mill. During the dispersion, the paint was adjusted to 18 to 28 ° C. Application was performed manually with a 1 mill applicator and air dried.

Paint test 2
The test was performed in the same manner as in the coating test 1 except that the PTFE obtained in pulverization example 2 was used. There was no stuff.

Paint test 3
The test was performed in the same manner as in the paint preparation test 1 except that the PTFE obtained in pulverization example 3 was used. There was no stuff.

Paint Comparison Example 1
The test was performed in the same manner as in the coating test 1 except that Lubron L-2 (manufactured by Daikin Industries, Ltd.) was used for PTFE. The 50% average particle size of L-2 is 3.5 μm. There were 4 items.
The above results are shown in Table 4 below.

Since the low molecular weight PTFE powder of the present invention has the above-described configuration, it can be suitably used as a coating material for forming a coating film having excellent smoothness.

Claims (5)

The 50% average particle size measured with a dry laser is 3 μm or less, the powder includes a powder with a particle size of 1 μm or less, and the melt viscosity measured using the flow tester method at 340 ° C. is 2500 Pa · s or less. A low molecular weight polytetrafluoroethylene powder obtained by turbid polymerization. 2. The low molecular weight polytetrafluoroethylene powder according to claim 1, which is finely pulverized. A low molecular weight polytetrafluoroethylene gelled powder obtained by a heat treatment in which the low molecular weight polytetrafluoroethylene powder according to claim 1 or 2 is heated at 250 ° C or higher and lower than 340 ° C. A low molecular weight polytetrafluoroethylene powder production method comprising producing the low molecular weight polytetrafluoroethylene powder according to claim 1 or 2 by suspension polymerization using a chain transfer agent,
A method for producing a low molecular weight polytetrafluoroethylene powder, comprising a step of pulverizing a low molecular weight polytetrafluoroethylene powder having a 50% average particle diameter of 0.5 to 20 μm measured by a dry laser. A coating material for a fixing member comprising the low molecular weight polytetrafluoroethylene powder according to claim 1 or 2 or the low molecular weight polytetrafluoroethylene gelled powder according to claim 3.