JP2001106793A - Method for granulating filler-containing polytetrafluoroethylene powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a granular polytetrafluoroethylene(PTFE) powder having a high apparent density and high fluidity without deteriorating physical properties of a molding product at a low production cost. SOLUTION: This method for granulating the PTFE powder comprises a step for uniformly mixing the PTFE powder having <=100 μm average particle diameter with at least one or more kinds of fillers and a step for applying rolling and pulverizing actions to the resultant mixed powder while dropping or spraying a binder on the mixed powder in the method for granulating the PTFE powder containing at least the one or more kinds of the fillers compounded therein. The binder is an organic solvent having 90-150 deg.C boiling point.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for granulating a polytetrafluoroethylene powder containing a filler, and more particularly to a method for granulating a powder containing a predetermined organic solvent as a binder.

[0002]

2. Description of the Related Art Polytetrafluoroethylene (hereinafter referred to as P)
Because TFE is very high in melt viscosity, it is formed by compression molding or ram extrusion. In compression molding or ram extrusion molding, the PTFE powder obtained by the suspension polymerization method is used to smoothly fill the PTFE powder into the mold.
It is necessary to granulate the TFE powder into granules of 500 μm or more. However, depending on the quality of the PTFE granulated powder,
Based on this, it greatly affects the physical properties of the compact and the filling (flowability) of the PTFE granulated powder into the mold. That is, the properties required for the PTFE granulated powder that can obtain favorable results as a molded article and a molded article of PTFE are listed below. 1) uniform particle size; 2) good fluidity for automation such as filling into molds; 3) compact size of compression molds and increased molding speed during ram extrusion molding. High apparent density, 4) mechanical properties such as tensile strength and tensile elongation at break of the molded body do not decrease, and the particle hardness is low to prevent poor fusion between particles during molding. Is soft.

[0003] Granulation methods of PTFE powder include, for example, a method using a binder composed of water and an organic solvent (JP-A-52-38565), and an average particle size of perfluorovinyl ether-modified PTFE obtained by a suspension polymerization method. Diameter
A method of granulating by stirring a powder of 100 to 300 μm in an aqueous medium (JP-A-9-52955);
Surface tension at 20 ℃ including colloidal particles 25 × 10 ^-5 N /
There is known a method of granulating the granular PTFE powder by spraying a binder comprising an aqueous solution of a surfactant having a particle size of not more than 1 cm to give a rolling action and a crushing action (JP-A-9-241387).

[0004]

However, when an organic solvent is used as a binder, there is a problem that the apparent density and the fluidity are reduced. In addition, when a mixed solution of an organic solvent and water is used as a binder, a step of separating water and the organic solvent is required, and there is a problem that the production cost increases. In addition, PT obtained by the suspension polymerization method
When FE powder is used, there is a problem that the physical properties of the molded body such as creep resistance may be reduced. Furthermore, when used as a binder composed of an aqueous solution of a surfactant, there is a problem that the production cost also rises because the surfactant is expensive.

The present invention has been made to address such a problem, and can form a uniform particle size at a low production cost, has a high apparent density and a high fluidity, and has a further improved physical property of a molded product. An object of the present invention is to provide a granulation method for obtaining a granular PTFE powder that does not decrease.

[0006]

According to the present invention, there is provided a method for granulating a polytetrafluoroethylene powder containing at least one or more fillers, the method comprising the steps of: A step of uniformly mixing the above filler, and a step of granulating by applying a tumbling and pulverizing action while dripping or spraying a binder to the mixed powder, wherein the binder has a boiling point of 90 to 150 ° C. Characterized as an organic solvent

Conventionally, in the method using only the organic liquid, the apparent density and the fluidity of the granular PTFE powder obtained by granulation have been reduced. However, the apparent density and the fluidity are improved by limiting the organic liquid. I found to do. The present invention is based on such knowledge, and as a binder,
Without adding a third component such as a surfactant or a solid binder, a binder is used on a rotating disk while pulverizing the particles having a larger particle size with a chopper attached to the inner wall of the granulation layer using a predetermined organic solvent. By rolling the wetted powder, it is possible to prevent a reduction in production cost and a reduction in physical properties of the compact.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The average particle size used in the present invention is 100.
The PTFE powder of μm or less will be described. The PTFE powder is a homopolymer of tetrafluoroethylene or a copolymer of tetrafluoroethylene with 1.0% by weight or less of a copolymerizable monomer (for example, hexafluoropropylene-perfluoroalkylvinylether, etc.), and both are suspended. Obtained by polymerization. The PTFE powder is finely pulverized and has an average particle size of 100 μm or less. Preferably, the average particle size is 5 to 100 μm. Such PTFE powder can include various fillers. The type of the filler is not particularly limited, and a filler usually mixed with PTFE can be used.
For example, fine powder or fibrous powder such as glass, carbon, graphite, mica, bronze, polyimide, molybdenum disulfide, tungsten disulfide, and iron oxide can be exemplified. The filler is mixed with PTFE and then finely pulverized to an average particle size of 5 to 100 μm. The mixing ratio of the filler is preferably 0 to 50% by weight. By using the PTFE powder containing the filler in this range, the average particle diameter is 700 to 1, using only a predetermined organic solvent, by the rolling and pulverizing actions.
It can be granulated to 000 μm.

The binder used in the present invention has a boiling point of
Use an organic solvent at 90 to 150 ° C. In the case of an organic solvent having a boiling point of less than 90 ° C., the organic solvent evaporates before granulation cannot be performed, and it is impossible to granulate to an average particle diameter of 700 to 1,000 μm. On the other hand, when the boiling point exceeds 150 ° C., the granules are not sufficiently dried. In addition, this organic solvent is a PT
It is preferable that the surface tension is low enough to sufficiently wet the FE powder, and it is particularly preferable that the surface tension is 15 × 10 ⁻³ N / m or less.

Examples of the binder include alcohols such as isobutanol and 1-propanol, and aromatic hydrocarbons such as toluene and xylene.

An apparatus for granulating the filled PTFE powder by imparting a rolling and pulverizing action to the powder will be described with reference to FIG. FIG. 1 is a diagram showing an outline of a granulation tank. The granulation tank 1 has a cylindrical shape and is provided in the lower part of the tank and provides a rotating disk 2 for rolling operation, and a chopper 3 provided on the side wall inner surface 5 and rotates at high speed to provide a pulverizing action. And a spray 4 for dripping or spraying the binder. Using this granulation tank 1, filled PTFE
A method for granulating the powder will be described. First, the average particle size
A PTFE fine powder having a size of 100 μm or less is charged, and a specific amount of a binder capable of sufficiently wetting the fine powder and enabling a long-time granulation operation is dropped or sprayed. At this time, the fine powder is crushed by the high-speed rotating chopper 3 attached to the inner surface 5 of the side wall of the granulation tank 1 while being rolled on the rotating disk 2 and further scattered toward the center of the tank. In general, the particle size of the granulated powder is proportional to the amount of the binder added during granulation, so the amount of the binder to be added is such that the average particle size can be 700 to 1,000 μm, for example, fine powder 100
10 to 70 parts by weight based on parts by weight. Further, during the granulation operation, the liquid crosslinking force is increased by keeping the viscosity of the binder high, and the binding force between the primary particles is kept high, and the loss of the binding force between the primary particles due to the evaporation of the binder is prevented. Because the atmosphere and powder temperature in the tank are low,
For example, it is controlled at about 22 ° C.

When the granulation operation is started in the granulation tank 1 controlled as described above, the granulated particles formed in the initial stage are formed along the inner surface 5 of the cylindrical side wall by the centrifugal force on the outer periphery of the rotating disk 2. It rises, then falls toward the center, moves again to the outer periphery of the rotating disk 2 by centrifugal force, and repeats the above movement. For this reason, the granulated particles move on the inner surface 5 of the cylindrical side wall in a portion other than the chopper 3 while drawing a screw-like locus. At this time, in the chopper 3 rotating at a high speed, the granulated particles are pulverized to have an average particle diameter of 100 to 2,000 μm and scatter to the center of the rotating disk 2. By repeating such a movement for 20 to 40 minutes, the granulated particles are formed into a spherical shape with an average particle diameter of 700 to 1,000 μm, and the granulated particles are sized, and the apparent density is improved.

[0013]

【Example】

Examples 1 to 3 and Comparative Examples 1 to 2 PTFE fine powder containing glass fiber (glass fiber 25% by weight, average particle diameter 30 μm) was charged into a granulating tank 1, and a rotating disk 2 and a chopper 3 were rotated. After stirring for 1 minute, the aggregated fine powder is pulverized, and then tumbled, mixed and stirred for 3 minutes while dropping the binder shown in Table 1. Thereafter, the number of rotations of the chopper 3 was reduced to about half and rolling and pulverization were performed for the granulation time shown in Table 1 to perform granulation. The amount of the binder added was 33 parts by weight based on 100 parts by weight of the PTFE fine powder containing glass fibers.

The average particle diameter, angle of repose, and apparent density of the obtained granulated powder were measured. Further, molding was performed by a ram extrusion molding method, and the moldability was evaluated. The ram extrudability was evaluated as good when the granulated powder did not stay in the supply path during automatic filling in the mold, and poor when the granulated powder stayed even slightly. Table 1 shows the results. The angle of repose and apparent density were measured according to ASTM D1457.

[0015]

[Table 1]

As shown in Table 1, in each of the examples, granulated powder having a large average particle size, a small angle of repose, and a large apparent density was obtained. As a result, the ram extrudability was excellent. In addition, the mechanical properties of the molded product obtained by the ram extrusion were also excellent. On the other hand, in the comparative example using a binder having a boiling point of less than 90 ° C., the granulation time could not be extended, and only a granulated powder having a small average particle size, a large angle of repose, and a small apparent density could be obtained. Was.

[0017]

According to the present invention, there is provided a method for granulating a filled PTFE powder, comprising the steps of uniformly mixing a polytetrafluoroethylene powder having an average particle diameter of 100 μm or less and at least one or more fillers; A process of giving a rolling and pulverizing action while dropping or spraying a binder to granulate, and since the binder uses a predetermined organic solvent, a surfactant, a solid binder and the like are used as compared with the related art. do not do. The finished granulated powder has an average particle size of 700
1,0001,000μm, and particle size variation is small. As a result, the manufacturing cost can be reduced, and a granulated powder having a high apparent density can be obtained. In addition, since the boiling point of the organic solvent is 90 to 150 ° C., the granulation time can be secured and separation after granulation is easy. As a result, it is excellent in moldability, and does not adversely affect the molded body during and after molding, such as a decrease in physical properties.

[Brief description of the drawings]

FIG. 1 is a diagram showing an outline of a granulation tank.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Granulation tank 2 Rotating disk 3 Chopper 4 Spray 5 Side wall inner surface

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4F070 AA24 AC28 AC36 AE01 AE22 DA03 DA06 DC05 DC07 4J002 BD151 CM041 DA026 DA036 DC006 DE116 DG026 DJ056 DL006 FD012 FD016 GT00

Claims (1)

[Claims] 1. A method for granulating a polytetrafluoroethylene powder containing at least one filler, wherein a polytetrafluoroethylene powder having an average particle diameter of 100 μm or less and at least one filler are uniformly mixed. And a step of granulating by applying rolling and pulverizing action while dripping or spraying a binder onto the mixed powder, wherein the binder is an organic solvent having a boiling point of 90 to 150 ° C. For granulating polytetrafluoroethylene powder with a filler.