JPH0420555A - Preparation of filled polytetrafluoroethylene particle - Google Patents

Abstract

PURPOSE:To effectively prevent the separation of filler by mixing a polytetrafluoroethylene powder with a (semi)hydrophilic filler in a specific two- phase liq. medium. CONSTITUTION:A polytetrafluoroethylene powder having a mean particle diame ter of 100mum or lower is mixed homogeneously with 5-40wt.% (semi)hydrophilic filler surface-treated with 0.001-10wt.% aminated org. silane or silicone resin (e.g. gamma-aminopropyltriethoxysilane) and having a particle size of 200 mesh or lower (e.g. a bronze powder) in a two-phase liq. medium comprising 2-10l of water and 0.2-2.0l of at least one halogenated hydrocarbon selected from the group consisting of 2,2-dichloro-1,1,1-trifluoroethane,1,1-dichloro-1-fluoroethane, 1,1-dichloro-1,2,2,3,3-pentafluoropropane, and 1,3-dichloro-1, 1, 2,2, 3- pentafluoropropane.

Description

[Detailed description of the invention] [Industrial application field] The present invention uses polytetrafluoroethylene (PTFE).

The present invention relates to a method for producing a filler-containing granulated powder (the same applies hereinafter).

[Prior Art] PTPE molding powder is obtained by finely pulverizing coarse powder obtained by suspension polymerization, and is used for molding by compression molding or ram extrusion. The particle size after pulverization (-formed particle size) is at most 5 particles or more, up to about 1000 particles at most, but usually 100 particles or less.

Filled PTPE molding powder, which is obtained by uniformly blending a hydrophilic or semi-hydrophilic filler with this molding powder, is used because it is more effective than PTFE itself in improving the wear resistance, hardness, etc. of molded products.

Uniform mixing of filler into PTFE can be achieved using special mixing equipment, but in recent years, as emphasis has been placed on automation of molding, powder handling properties, especially powder flowability, have been improved and high Agglomerated and granulated type powders have come to be manufactured and used as filler-containing compacted powders having an apparent density.

Such agglomeration and granulation methods can be broadly classified into dry methods and wet methods. Of these, the former refers to a method that does not use water;
The latter method refers to a method using water. As a typical example of the latter method, a method is known in which a mixture of PTPE, filler and organic liquid is stirred in water. Although this wet method requires additional steps such as separation and drying of water after treatment compared to the dry method, it is superior in that it is relatively easy to automate the production process.

However, since this method uses water, hydrophilic or semi-hydrophilic fillers such as glass powder easily migrate into the water phase.
It is difficult to mix uniformly with PTFE, that is, all of the hydrophilic filler used is not converted into the agglomerated powder mixed with PTFE, and some of it remains in the treated water. This phenomenon is called filler separation. Further, even in the obtained granulated powder, the filler may be detached during handling of the powder.

To deal with this problem, the hydrophilic or semi-hydrophilic filler can be subjected to a hydrophobic surface treatment in advance to bring its surface activity down to the surface activity of PTFE before stirring in water, or during stirring. A method is employed in which a substance having such an effect is added to an aqueous medium and stirred.

Organic silanes or silicone resins containing amino functional groups are known as silicon compounds used in this type of method (Japanese Patent Publication No. 47269/1983, Japanese Patent Publication No. 54/1983).
40099, Japanese Patent Publication No. 57-7164, Japanese Patent Publication No. 8O-2LH4).

On the other hand, it is said that it is appropriate for the organic liquid used in this wet method to have a surface tension of about 35 dynes/cfl or less at 25°C and a boiling point of about 30 to 150°C (Japanese Patent Publication No. 44-22619 No. Publication, Special Publication No. 54-400
No. 99, Japanese Unexamined Patent Publication No. 18730/1983).

Specific examples of such organic liquids include aliphatic hydrocarbons, aromatic hydrocarbons, and fluorinated chlorinated hydrocarbons. Such fluorinated chlorinated hydrocarbons include trichlorotrifluoroethane, monofluorotrichloromethane, difluorotetrachloroethane, C1(CF2 CF(J
) ncI, ) dichloropentafluoropropane and other perhalogenated hydrocarbons are exemplified, and perhalogenated hydrocarbons are mainly used in actual granulation.

[Problems to be Solved by the Invention] Perhalogenated hydrocarbons are preferable as organic liquids used in wet granulation methods in terms of nonflammability, solvent recovery efficiency, etc., but generally have a boiling point of high <(80 to 130°C), When collecting organic liquid, the temperature becomes high and the granulated powder is exposed to too much heat, which makes the particles hard.As a result, the surface of the molded product becomes rough, and the tensile strength, elongation, gas permeability, electrical insulation, etc. decreases. In addition, energy cost is required for recovery, which is also disadvantageous. Furthermore, perhalogenated hydrocarbons are said to contribute to the depletion of the ozone layer, making their use undesirable.

The present invention is a PTFE filler-containing structure that does not cause separation of the filler, the filler is uniformly dispersed in the resulting granulated powder, has less impact on the ozone layer, and has improved physical properties of the granulated powder and molded product. A method for producing granular powder is provided.

[Means for Solving the Problems] That is, the present invention provides PTFE with an average particle size of 100 mm or less.
The powder and a hydrophilic or semi-hydrophilic filler whose surface has been treated with an organic silane or silicone resin containing an amino functional group (hereinafter referred to as a (semi) hydrophilic filler) are mixed with water and 2.
2-dichloro-1,1,1 trifluoroethane, l, ■
, 1-dichloro-1-fluoroethane, 1,1-dichloro-2,2,3,3,3-pentafluoropropane and 1,3-dichloro-1,1,2,23-pentafluoropropane Production of a PTFE filler-containing granulated powder characterized in that it is uniformly mixed in a two-phase liquid medium consisting of at least one halogenated hydrocarbon selected from (hereinafter referred to as specific halogenated hydrocarbon) Regarding the law.

[Function and Examples] In the production method of the present invention, PTFE powder, a (semi-)hydrophilic filler, an organic silane or silicone resin containing an amino functional group, a specific halogenated hydrocarbon, water, and other substances as necessary. Additives are used.

As the PTPE powder used in the present invention, for example, a homopolymer of tetrafluoroethylene (TFE, hereinafter the same),
TFE modified with 2% by weight or less of a copolymerizable monomer
Contains an O copolymer. Examples of the modifier include perfluoroalkenes having 3 to 6 carbon atoms (e.g. hexafluoropropylene), perfluoro(alkyl vinyl ethers) having 3 to 6 carbon atoms (e.g. perfluoro(
Propyl vinyl ether)), chlorotrifluoroethylene, etc., and copolymers modified with these are P
Like TFE, it does not have melt processability. These polymers have an average particle size of 100A! It is used as a powder crushed to less than m. In addition to the above-mentioned PTPE powder, a PTFE colloidal dispersion with an average particle size of 0.1 to 0.5 times can be used in the method of the present invention, and its use can be used to prevent filler separation. It is particularly effective when the filler content is high.

The amount of colloidal PTFE to be used is 0.00% relative to the PTFE powder.
1 to 5% by weight is preferred. Moreover, it is appropriate to add it before adding a specific halogenated hydrocarbon.

The (semi)hydrophilic filler used in the present invention includes powdered glass fiber, glass beads, fused silica powder, crystalline silica powder, white carbon powder, alumina powder,
Hydrophilic fillers such as bronze powder and semi-hydrophilic fillers such as potassium titanate fiber powder, talc powder, calcium carbonate powder, zinc oxide powder, tin oxide powder, boron trinitride powder, carbon fiber powder, molybdenum disulfide powder, graphite powder, etc. It is a powder with a particle size of 200 mesh or less that is generally used as a filler for PTFE, such as a filler. The loading amount of the (semi)hydrophilic filler to the PTFE powder is 5 to 40% by weight, preferably 15 to 25% by weight. If the filling amount is less than 5% by weight, the effect of improving the abrasion resistance, creep resistance, etc. of the molded product will be small;
If it exceeds % by weight, the physical properties of the molded article such as tensile strength and elongation will be too low. In addition, in the present invention, bronze powder,
It is particularly useful when colored powders such as carbon fiber powder, molybdenum disulfide powder, and graphite powder are used as fillers.

Examples of the surface treatment agent for the filler used in the present invention include γ-aminopropyltriethoxysilane, m- or p-aminophenyltriethoxysilane, γ-ureidopropyltriethoxysilane, γ-anilinopropyltrimethoxysilane, and γ-aminopropyltriethoxysilane. -(2-aminoethyl)aminopropyltrimethoxysilane, γ-(2-aminoethyl)
Examples include organic silanes containing amino functional groups such as aminopropylmethyldimethoxysilane, water-soluble silicone resins such as dimethylsiloxane, phenylmethylsiloxane, monophenylsiloxane, and propylphenylsiloxane. The amount of these surface treatment agents used is not particularly limited, and is usually 0.001 to 0.001 to (semi)hydrophilic filler.
10% by weight, preferably 0.1-10% by weight.

Certain halogenated hydrocarbons have less impact on the ozone layer, have boiling points that are neither too high nor too low, and have a low surface tension (
25°C) or less than about 35 dynes/cm. Specifically, 2,2-dichloro-1,1,1-trifluoroethane has a surface tension of 17 dynes/cm and a boiling point of 27°C.
1.1-dichloro-1-fluoroethane is 20 dynes/
32°C at mouth, 1,1-dichloro-2,23,3,3-pentafluoropropane at 51°C at 16 dynes/CW+,
1,3-dichloro-1,1,2,2,3-pentafluoropropane at 18 dynes/cm at 56°C. Among these, dichloropentafluoropropane is particularly preferred because it further improves the economy of solvent recovery, powder properties, and various physical properties of molded products. When the boiling point becomes high, the granulated powder becomes hard as described above, while when the boiling point becomes too low, the aggregation becomes incomplete and tends to be easily broken by a small external force. A particularly preferred boiling point range is 40 to 60°C. These specific halogenated hydrocarbons are one or two types.
Used in combination of more than one species.

Further, other conventionally used organic liquids may be used in combination, if necessary.

Certain halogenated hydrocarbons form two-phase liquid media with water. The mixing ratio with water varies depending on the type of specific halogenated hydrocarbon and the target average particle size, but usually water/specific halogenated hydrocarbon (weight ratio)
is 20/1 to 3/1, preferably 10/1 to 5/1.

This two-phase liquid medium consists of a total amount of PTPE powder and filler of 1
per kg, about 2 to 2 foils of water and about 0.2 to 2 grams of certain halogenated hydrocarbons. OIll! use

In the method of the present invention, hydrophobic fillers other than those described above, such as carbon black, can be co-existed as appropriate, and these do not pose any hindrance to the purpose of the present invention.

As the solvent for surface treatment of the (semi)hydrophilic filler in the present invention, polar solvents such as ketones, alcohols, and water are preferable. Various methods can be used for surface treatment, but for example, a (semi-)hydrophilic filler is immersed in an aqueous solution of organic silane containing an amino functional group and then pulled up, preferably subjected to centrifugal dehydration treatment, and then heated at 100°C. As mentioned above, a method of drying at about 110 to 180° C. and heating at the same time is preferably employed. The concentration of the aqueous solution of organosilane or silicone resin containing an amino functional group is approximately 0.
．． A suitable amount is about 0.001 to 10% by weight, preferably about 0.1 to 1.0% by weight.

In a preferred embodiment of the production method of the present invention, the raw materials thus prepared are blended and mixed according to the following procedure to produce granulated powder.

First, PTFE powder and surface-treated (semi-)hydrophilic filler are uniformly mixed. This mixed powder is stirred and mixed in a two-phase liquid medium consisting of water and a specific halogenated hydrocarbon to form a slurry, which is then agglomerated and granulated. For such a mixed granulation method, a conventionally known method can be adopted as a procedure. For example, such a method is as follows:
Publication No. 19, Special Publication No. 47-1549, Special Publication No. 1977
Examples include methods described in Japanese Patent Application Laid-open No. 47-34936 and Japanese Patent Application Laid-Open No. 47-34936.

The PTFE filler-containing granulated powder thus obtained is
The average particle size is approximately 200 to 80, with filler mixed evenly.
It has an apparent density of 0.50 to 1.00 g/cc, and is easy to handle with excellent powder flowability.

Molded articles obtained using this granulated powder also have excellent mechanical properties such as tensile strength and elongation.

Next, the manufacturing method and granulated powder of the present invention will be explained based on Examples and Comparative Examples, but the present invention is not limited only to these Examples.

Examples 1 to 5 and Comparative Examples 1 to 2 (Surface treatment of filler) The (semi)hydrophilic filler shown in Table 1 was treated with an organic silane or silicone resin containing an amino functional group shown in Table 1.
It was immersed in a wt% aqueous solution, thoroughly stirred and left to stand, and the precipitated filler was collected by filtration.
Dry for 2 hours to obtain a surface-treated (semi-)hydrophilic filler.

(Production of granulated powder with PTFE filler) Capacity: 3g
baffle plate 2 with a flat plate two-blade agitator in the center;
A mixed solution of water in the amount shown in Table 1 and the organic medium shown in the same table is placed in a stainless steel cylindrical granulation tank with a plate. moreover,
Granular type PTFε powder with an average particle size of 35 items (
Powder fluidity: 1) mixed powder with surface-treated (semi-)hydrophilic filler (weight ratio + 80/20) 600 g
was placed in a granulation tank and stirred for 5 minutes at a rotation speed of 1200 rpm, then the rotation speed was reduced to 600 rpm and stirred for an additional 30 minutes to coagulate and granulate the PTFE powder and filler.

After stirring, the granulated product is filtered through a 60-mesh wire mesh, and the filtered solid is directly dried in a drying oven at 150° C. for 16 hours to obtain a granulated powder.

The average particle size, apparent density, and powder fluidity of the resulting granulated powder were examined. In addition, the coloring, tensile strength, and elongation of the molded products produced using each granulated powder were examined. In addition, in order to investigate the degree of separation of the (semi)hydrophilic filler during granulation, the granules were filtered through a 60-mesh wire mesh, the filtrate was filtered through a filter paper, and the filter paper was dried and added to the filtrate. The weight of the liberated filler was determined, and the value (%) obtained by dividing the amount by the total weight of the filler used (referred to as filler separation degree) was determined.

These results are shown in Table 1. Moreover, the above test was measured in the following manner.

Average particle size: Layer 10, 20, 32, 48, 60 and 80 mesh standard sieves in order from the top, place the powder on the 10 mesh sieve and sieve, calculate the weight of the powder remaining on each sieve, and based on this weight. 50 on log probability paper
The % particle size is defined as the average particle size (ts).

Apparent density: According to JIS K-6891 (inner volume 1
The weight (g) of a sample dropped from a damper into a 00ee stainless steel cylindrical container and scraped off with a flat plate is calculated as the internal volume (cc
) is defined as the apparent density (g/ce).

Powder fluidity: Measured and evaluated by the method described in detail in Japanese Patent Publication No. 80-21694. The second method is to install two hoppers, one above the other, drop the powder from the upper hopper to the lower hopper, and then test the fluidity of the powder by dropping the powder from the lower hopper.

The larger the amount of PTFE, the more difficult it becomes to flow, so the larger the amount of PTFE that falls from the hopper, the better the fluidity. In this measurement method, it is expressed as a number from 0 to 7 (exceeding 7 is expressed as 8), and the higher the number, the better the fluidity is.

Coloring of the molded product: First, it was preformed under a pressure of 500 kg/c-, fired at 380°C for 24 hours, and then left to cool outside the furnace.The resulting product had a diameter of 256 mm and a height of 250 m.
Slice the m cylindrical molded product into rounds near the center, and visually judge the state of coloring or discoloration at the center of the cut surface (〇-
No coloration or discoloration; △ - Slight coloration or discoloration; × - Significant coloration or discoloration).

Tensile strength and elongation 7 500 kg / (!-) Preformed under pressure, fired at 380°C for 3 hours, and left to cool outside the furnace to obtain a sheet with a thickness of 1.5 cm JIS K- The tensile strength (kg/cj) and elongation (%) are the measured values of the strength and elongation at break of a sample punched with a dumbbell type No. 3 specified in 6031.
It is determined that

Margin below L [Effect of the invention] According to the method for producing PTFE filler-containing granulated powder of the present invention, it is possible to efficiently prevent separation of the (semi-)hydrophilic filler during granulation, and it also has a negative impact on the ozone layer. There are few things,
It can be effectively and uniformly contained in the resulting granulated powder and even in the molded product. As a result, the resulting PTFE molded product has excellent not only mechanical properties but also excellent appearance.

Special permission

Claims (1)

[Claims] 1 Polytetrafluoroethylene powder with an average particle size of 100 μm or less and a hydrophilic or semi-hydrophilic filler surface-treated with an organic silane or silicone resin containing an amino functional group are mixed with water and 2,2-dichloro-1,1 , 1-trifluoroethane, 1,1-dichloro-1-fluoroethane, 1,1-dichloro-2,2,3,3,3-pentafluoropropane and 1,3-dichloro-1,1,2, 2
, 3-pentafluoropropane, and at least one halogenated hydrocarbon selected from the group consisting of 3-pentafluoropropane. Law.