JPH0698663B2 - Polytetrafluoroethylene resin molding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a polytetrafluoroethylene resin molding method.

[Prior Art] Even if polytetrafluoroethylene (hereinafter abbreviated as PTFE) is heated to a temperature higher than its melting point, ordinary melt extrusion cannot be performed because the melt viscosity is extremely high. In addition, since it is easy to form fibers, there are many rules regarding molding conditions. Therefore, in order to obtain PTFE tubes, fine rods, sheets, etc., they are formed by the method described in Japanese Examined Patent Publication No. 61-54578 or ICI's full-on PTFE fine powder molding technical data.
That is, tetrafluoroethylene (hereinafter abbreviated as TFE)
Was obtained by emulsion polymerization, a polymer obtained by aggregating and drying the PTFE aqueous dispersion, so-called fine powder, with processing aids such as naphtha and white kerosene added, preformed into a sleeve, and then cylinder metal Fill a mold, pressurize with a ram and extrude through a nozzle suitable for the shape of tubes, rods, sheets, etc. After plastic deformation of PTFE, volatilize the processing aid and fire to obtain a product A paste extrusion molding method is known.

[Problems to be Solved by the Invention] In the conventional PTFE paste extrusion molding method, as described above, PTFE and a processing aid are mixed and then preformed into a sleeve shape, which is intermittently filled into a cylinder die and pressed. It is a way to put it out.
Therefore, the amount of extrusion per one time depends on the sleeve shape and is discontinuous.

On the other hand, when the usual melt extrusion molding was carried out in PTFE, the extrusion pressure was remarkably increased and the molding was extremely difficult. Even if an extrudate was obtained, it was severely cracked and the desired shape could not be obtained. Accordingly, there are problems that continuous molding cannot be performed, continuous molded products cannot be obtained by the conventional paste extrusion molding method and melt extrusion molding method, and labor saving is difficult, resulting in high cost.

In addition, the conventional paste extrusion method is a molded product with strong mechanical anisotropy such that PTFE fibers are generated in the extrusion direction and the extrudate has high strength in the extrusion direction and low strength in the direction perpendicular to the extrusion direction. However, there is a problem that the strength is insufficient in practical use.

[Means for Solving the Problems] The present invention has been made to solve the above-mentioned problems, and the processing aids 20 to 70 are added to 100 parts by volume of the polytetrafluoroethylene resin powder that is difficult to melt and flow. In the presence of the volume part, extrusion molding temperature 25 ~ using a screw extruder
The present invention provides a polytetrafluoroethylene resin molding method characterized by continuously performing extrusion molding at 100 ° C. and an extrusion pressure of 20 to 100 kg / cm ² .

As the polytetrafluoroethylene in the present invention,
Not only a homopolymer of tetrafluoroethylene, but a small amount that does not reach the melt fluidity (for example,
It also includes those modified by copolymerizing other comonomers (about 0.5 mol% or less). As such a copolymer,
Hexafluoropropylene, chlorotrifluoroethylene, perfluoro (alkyl vinyl ether), trifluoroethylene, (perfluoroalkyl) ethylene and the like are exemplified. Further, if the molecular weight is too low, it is not preferable because it becomes liquid or gel, and preferably 50% or more of solid having a molecular weight of 10 ⁶ or more calculated from standard specific gravity is contained. Further, such a PTFE is preferably obtained by emulsion polymerization, since it is easy to fiberize as described later, but PT obtained by emulsion polymerization is preferable.
A finely pulverized product of PTFE obtained by another polymerization method may be mixed with FE.

The polytetrafluoroethylene resin used in the molding method of the present invention may be polytetrafluoroethylene alone or may contain a filler. Here, as the filler, carbonaceous powder, carbonaceous fiber, inorganic powder, inorganic fiber, metal powder, alloy powder, organic powder, organic fiber or the like is adopted. Specifically, carbon black, carbon fiber, carbonaceous powder or fiber such as graphite, feldspar, silica, alumina,
Oxide powder of titanium oxide, iron oxide, etc., silicon nitride, carbon nitride, aluminum nitride, boron nitride, zirconium carbide, silicon carbide, tungsten carbide, nickel carbide, zirconium sulfate, barium sulfate, kaolin, clay, glass beads, glass balloon Inorganic powder such as, glass fiber, alumina fiber, potassium titanate fiber, silica fiber and other inorganic fibers, copper alloy, zinc white, molybdenum disulfide, aluminum, aluminum alloy and other metal or alloy powder, tetrafluoroethylene-perfluoro (Alkyl vinyl ether) copolymer resin, tetrafluoroethylene-hexafluoropropylene copolymer resin, polychlorotrifluoroethylene resin, polyamideimide resin, polyethersulfone resin, polyimide resin, polyphenylene oxide resin, oki Benzoyl polyester resins, such as organic powder or fiber such as a liquid crystal polymer and the like. It is preferable to employ a powdery filler, particularly a finely powdered filler.

Further, the addition amount of these fillers is preferably 95 vol% or less. If the proportion of the filler is too large, the extrusion pressure will increase significantly, making extrusion impossible, or the extrudate obtained will be a very brittle molded product due to insufficient strength.
Not desirable.

In producing a composition of PTFE and a filler, a method of adding a predetermined amount of a filler to a PTFE dispersion and co-coagulating it and then drying, or stirring and mixing the PTFE powder and the filler. Any method can be adopted.

In the present invention, the processing aid is one that can appropriately perform fiberization and plastic deformation of PTFE, and any liquid can be used as long as it is a liquid that easily wets PTFE and can be easily removed from the extrudate. . Specifically, solvent naphtha, white oil, petroleum ether, isopropyl alcohol, liquid paraffin, ethylene glycol, glycerin, polyalkylene glycol and other aliphatic or aromatic compounds that have been conventionally used as a processing aid for extrusion molding of PTFE. Examples of hydrocarbon alcohols include Further, a processing aid having a boiling point of about 50 to 400 ° C., which does not easily cause discoloration during firing of PTFE, is preferably used. Further, as a processing aid, it is also possible to use a fluoropolymer aqueous dispersion such as a PTFE aqueous dispersion.

The processing aid is preferably used in an amount of about 20 to 70 parts by volume based on 100 parts by volume of PTFE or the composition of PTFE and the filler. If the amount of the processing aid is too small, the fluidity becomes insufficient and extrusion molding becomes difficult. If the amount is too large, the extrusion pressure does not increase, the fiberization of PTFE is not sufficiently achieved, and the processing aid is leached during extrusion, which is uneconomical.

The method of adding and mixing the processing aid to the composition of PTFE or PTFE and the filler is preferably carried out under the condition that the fiberization of PTFE is minimized. As a method, use a mixer (such as an omni-mixer) that is hard to apply mechanical shearing force.
It is preferable to adopt a method of grading the mixing conditions such as using PTFE or the composition powder with the filler in a dry state.

It is important to use a screw extruder in the molding method of the present invention. Such a screw extruder has a screw having a linear groove cut in the barrel of the extruder to rotate and knead while rotating PTFE in the barrel for resin, rubber , A screw extruder for building materials and the like.

As the screw extruder, either a single-screw extruder or a multi-screw extruder can be adopted. As the screw shape, various shapes such as a full flight screw, a variable pitch screw, and a screw with mixing can be adopted, but a full flight screw whose extrusion pressure can be easily adjusted is preferably used. Further, it is preferable to adopt 1.0 to 3.0 as the screw compression ratio. In particular,
1.0 to 2.0 is preferable. If the screw compression ratio is too small, the fiberization of PTFE will be insufficient, the strength of the extrudate will decrease, and in some cases it will be difficult to maintain the shape of the extrudate. Further, if the screw compression ratio is too large, the extrusion pressure becomes high, which may make extrusion molding difficult.
Here, the screw compression ratio is a value obtained by dividing the cross-sectional area between the inside of the barrel at the tip of the screw and the screw root diameter by the same cross-sectional area at the screw root.

Further, the extrusion temperature and the extrusion pressure have a great influence on the fiberization of PTFE. If the extrusion temperature is too low or the extrusion pressure is too low, the fiberization of PTFE is not achieved well, the strength of the extrudate is reduced, and in some cases, the extrudate cannot retain its shape. Further, if the extrusion temperature is too high or the extrusion pressure is too high, the fiberization of PTFE proceeds excessively, and the extrudate may have many cracks or the extrusion molding may become difficult. Generally, it is preferable to set the extrusion temperature within the range of 5 to 300 ° C.
In particular, it is preferably within the range of 25 to 100 ° C. The extrusion pressure is preferably set within the range of 5 to 300 kg / cm ² . In particular, it is preferably in the range of ^{20 to} 100 kg / cm ² .

According to the molding method of the present invention, a cylindrical, rod-shaped, sheet-shaped, or other continuous body can be molded. In particular, the method of the invention is suitable for extruding in a tubular shape. Further, the cylindrically extruded product can be easily made into a sheet by cutting it open. In the present invention, when a tubular object is extruded, the ratio of the outer diameter of the tubular object to the inner diameter of the cylinder is 0.1 to 20.
It is preferably within the range of 0. If this ratio is too large, extrusion becomes difficult or the extrudate tends to shrink, and it tends to be difficult to obtain a sheet having a uniform thickness when the tubular product is cut open to form a sheet, which is not preferable.
Also, if the ratio is too small, extrusion becomes difficult, and PTFE
This is not preferable because the direction of fiberization becomes uneven.

Further, the tubular article formed by the method of the present invention has PTFE fiberized along the circumferential direction. Therefore,
Sheets having various orientations can be obtained by the method of cutting open the tubular material. For example, when a tubular product is cut open in parallel with the extrusion direction, a sheet in which PTFE is made into fibers in a direction perpendicular to the longitudinal direction is obtained. Further, when cut open in a spiral shape, a sheet in which PTFE is made into fibers is obtained at an angle. In addition, by cutting the tubular object into slices and then opening it, PTFE can be cut in the longitudinal direction.
It is also possible to obtain a fiberized sheet. Considering the easiness of work, the productivity, the relationship with the rolling step described later, and the like, the method of slitting in parallel with the extrusion direction is the most preferable.

According to the molding method of the present invention, it is possible to continuously manufacture molded products. Therefore, when the post-treatment process is included, the post-treatment process can be continuously performed. For example, by further rolling the sheet obtained by the method of the present invention, in the case of obtaining a rolled film, to a rolling device such as a rolling roll, by continuously supplying the sheet by the method of the present invention, continuous A rolled film can be obtained.

Further, when a rolled film is obtained, a tubular product is formed by screw extrusion, the tubular product is cut open parallel to the extrusion direction into a sheet, and this sheet is further fed to the rolling roll device in the same direction as the extrusion direction. Most preferably, it is made into a rolled film. According to this method, the seat is laterally PT
FE is fiberized, and further rolling causes fiberization of PTFE in the longitudinal direction of the film. Therefore, the rolled sheet obtained by this method becomes a film having small mechanical anisotropy. Furthermore, with this method, it is possible to continuously produce a rolled film.

Further, the molded article produced by the present invention may or may not be fired as required. The conditions such as temperature for firing can be the same as those for firing ordinary PTFE. For example, a condition of about 10 seconds to 1 week at a temperature of about 350 to 450 ° C. is exemplified. Further, such firing may be carried out using a batch type firing furnace or a continuous type firing furnace. The firing furnace can be appropriately selected depending on the shape of the molded product, desired physical properties, and the like. However, if a continuous firing furnace is used, productivity can be expected to be improved.

[Examples] Examples 1 and 2 In the proportions shown in Table 1, PTFE powder (emulsion polymerized product), clay, silica, and processing aid Isopar M (manufactured by Exxon Chemical Co., Ltd.) were mixed by an omni mixer. This mixture was mixed with a single-screw extruder with a cylinder inner diameter of 40 mm and a full flight screw with a screw compression ratio of 1.6 and dimensions of 87 mmφ-6.
According to the extrusion conditions shown in Table 1 using a 7 mmφ nozzle,
A tubular extrudate was obtained. This extrudate was cut open in parallel with the extrusion direction, and then rolled with a rolling roll in the same direction as the extrusion direction to obtain a sheet having a thickness of 0.4 mm. This sheet at 350 ℃
Baked for 30 minutes. Regarding this baked sheet, JIS-K6891
Table 1 shows the results of measuring the tensile strengths in the extrusion direction and in the direction perpendicular to the extrusion direction.

Comparative Example 1 PTFE having the same composition as in Example 1 and a processing aid were mixed by an omni mixer. This composition was preformed into a sleeve, and the paste was extruded using an extruder having a cylinder-nozzle cross-sectional area ratio of 200 to obtain a sheet having a thickness of 10 mm. This sheet material was rolled by a rolling roll in the same direction as the extrusion direction to obtain a rolled sheet having a thickness of 0.4 mm. This rolled sheet was baked at 350 ° C. for 30 minutes. Table 1 shows the results of measuring the tensile strength of this fired sheet according to JIS-K6891 in the extrusion direction and the direction perpendicular thereto.

[Advantages of the Invention] The present invention has an excellent effect that an extruded product of PTFE can be continuously and inexpensively molded, and in particular, a sheet obtained by extruding a tubular product into an extruded shape and then cutting and rolling the extruded product. The film has an effect of obtaining a molded product having less mechanical anisotropy. Further, it has an excellent effect that it can be continuously operated from the extrusion of PTFE to the extruder to the extrusion, slitting of a tubular product, and rolling into a rolled sheet, which can greatly reduce the cost.

It is also recognized that the addition of various fillers to PTFE makes it possible to inexpensively produce a continuous extrudate of a molded product having excellent physical properties such as high elasticity and high strength.

 ─────────────────────────────────────────────────── --- Continuation of the front page (56) Reference JP-A-54-110271 (JP, A) JP-A-1-135855 (JP, A) JP-A-1-135854 (JP, A) JP-A-64- 40550 (JP, A) JP 58-57209 (JP, A) JP 52-134657 (JP, A) JP 54-110271 (JP, A)

Claims (8)

[Claims] 1. Extrusion molding temperature of 25 to 100 ° C. using a screw extruder in the presence of 20 to 70 parts by volume of a processing aid to 100 parts by volume of polytetrafluoroethylene resin powder which is difficult to melt and flow. A polytetrafluoroethylene resin molding method, which comprises continuously extruding at a pressure of 20 to 100 kg / cm ² . 2. The screw compression ratio of claim 1 according to claim 1.
Molding method performed at ~ 3.0. 3. The molding method according to claim 1, wherein the polytetrafluoroethylene resin powder obtained by emulsion polymerization is used. 4. The molding method according to claim 1, wherein a polytetrafluoroethylene resin powder containing a filler is used as the polytetrafluoroethylene resin powder. 5. A carbonaceous powder, a carbonaceous fiber, an inorganic powder, an inorganic fiber, a metal powder as a filler according to claim 4.
A molding method using at least one selected from alloy powder, organic powder and organic fiber. 6. The filler according to claim 4, wherein the proportion of the filler is 95 vol.
%, A molding method performed using a polytetrafluoroethylene resin containing a filler. 7. An extrusion molding temperature of 25 to 100 ° C. using a screw extruder in the presence of 20 to 70 parts by volume of a processing aid with respect to 100 parts by volume of polytetrafluoroethylene resin powder which is difficult to melt and flow. A molding method comprising continuously extruding at a pressure of 20 to 100 kg / cm ² and rolling the obtained extruded product in the same direction as the extrusion direction to form a sheet. 8. The extruded product according to claim 7, which is a tubular product. The tubular product is cut open parallel to the extrusion direction, fed to a rolling roll in the same direction as the extrusion direction, and rolled to obtain a rolled film. Molding method to obtain.