JPS5952177B2 - Polytetrafluoroethylene molding powder and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to polytetrafluoroethylene molding powders.

There are generally two types of polytetrafluoroethylene (PT).
FE), i.e. ordinary molding powder (MoldlngpOwde)
A granular type called R) and a fine powder type obtained by aqueous dispersion polymerization are commercially available.

Both types are made by pressurized injection of tetrafluoroethylene under polymerization conditions into a stirred aqueous solution containing a free radical polymerization initiator. In aqueous dispersion polymerization, stirring should be slow enough and a sufficient amount of dispersant should be present so that when the polymerization is stopped, the PTFE is dispersed in the dispersion medium in a colloidal size smaller than 1 μm in diameter. . When the particles are coagulated and dried, fine powder type PTFE is obtained. In particulate polymerization, agitation is fast enough to coagulate the polymer particles during polymerization.

Dispersants are generally not present in amounts other than perhaps less than dispersion stabilizing amounts for different purposes, such as those described in Anders On et al., US Pat. No. 3,245,972. When the polymerization is stopped, the particulate polymer obtained is in the form of relatively coarse particles, ie several thousand microns or more in size. Usually, the polymer is coarsely or finely ground to form a commercially available molded powder. These two types of PTFE are completely different and have mutually opposing molding properties.

The ratio of PTFE fine powder to oil lubricant is approximately 80:20.
They are blended in parts by weight and the resulting paste-like mass is generally processed by extrusion at room temperature. This method is called paste extrusion method. PTFE molding (a) sintering the preform obtained after pressing in a mold without applying pressure; or (b) extruding the powder through a heated orifice, thereby placing the powder under pressure. Processed by either sintering or ram extrusion methods. PTFE fine powders cannot be processed except in small quantities (generally 309 or less) by preforming/free accretion methods or ram extrusion methods. Conversely, PTFE molding powder cannot be subjected to paste extrusion. These two industries are separated and independent from each other because the two types of PTFE are manufactured using different methods, and the two types of molded products obtained by different processing methods are used in different fields.

The only exception to this is Mathews
) and Roberts (U.S. Patent No. 3)
No. 087921 describes a method for producing a PTFE molding powder with good handling properties and high apparent density. i.e. the previously obtained PTFE molding powder or PT
FE fine powder (a) at a temperature of 50 to 300°C;
Pressure 70~211kg/c! Densification to a density of at least 2151<9/CC under 11 pressing conditions (COMpac
t), (b) cool the densified polymer, and (c) cool the densified and cooled polymer to 1000μ or less, preferably 2
It is produced by a process of grinding to particles with an average diameter of 0.00 to 500 μm. (The wet sieve D5O particle size of 350-650 microns for non-densified fine powder is the particle size of the loose coagulum made by coagulating colloidal polymer particles). Through this treatment, the fluidity of the fine powder changes from almost no flow to 17.
9/sec, and the apparent density is 400-600f! /
However, the tensile strength of the PTFE molding powder made from fine powder is only 116 kg/Cd, which is higher than ASTM type high quality PTFE.
FE molding powder tensile strength standard lower limit 280kg/Clll
・It's worse than I. According to the present invention, a high quality tetrafluoroethylene molding powder is provided which can be obtained from a fine powder or from a special method used for current PTFE molding powders.

More specifically, according to the invention, the specific surface area is at least 1.
5i/9, the average particle size is smaller than 100μ, the apparent density is at least 5009/l, and the formula apparent density≧500+3.
00(△SG5-1)・・・・・・(1) However, ΔSG5
-1 is 1000pSi (70kg/d) and 5000p
This is 1000 times the difference in specific gravity of the sintered molded product made with preforming pressure at si (352 kg/Cd), and △SG5-
A polyteiraethylene molding powder is provided which is characterized by a combination of a high degree of moldability and a high apparent density, expressed by 1 is not greater than 75.

The method for measuring ΔSG5- will be explained later.

70kg/(-JmoVi and 352'K9/Cd) The larger the difference in specific gravity between Vi and 352'K9/Cd, in other words, the larger the value of △SG5-1, the more voids there will be in the sintered product made from the low-pressure preform. will increase.

These voids reduce the tensile strength and dielectric strength, thus impairing the quality of the sintered product. In industrial applications, the use of high preforming pressures often prevents the formation of highly voided sintered products, but this requires the use of large and therefore expensive preforming equipment. That is, △SG, . , the smaller the amount of voids and the better the quality of the sintered product. That is, a small value of ΔSG5-1 indicates that the quality of the molded product made from the molding powder is good, and in other words, it means that the moldability is high. ΔSG,l is also referred to herein as the formability coefficient. (value of -1 unless otherwise specified). The preferred moldability factor for the molding powder of the invention is not greater than 60. The low moldability coefficient exhibited by the molding powder of the invention in combination with the small particle size corresponds to a high tensile strength of the products made therefrom, which is at least 245 kg/(-J Mo
Vi) Preferably at least 280 kg/(-JMoVf).

Standard tensile tests were conducted on sintered products formed at a preforming pressure of 352 kg/Cd.

Due to the low moldability coefficient of the molding powder of the present invention, such a tensile strength can be achieved with a preforming pressure of only 70 kg/Clll. For comparison, a densified dispersion polymer made from a densified granular polymer (2150p
The moldability coefficient of Mayuse and Roberts molding powders, which have higher tensile strength than molding powders made from molding powders made from molding powders made from molding powders from Roberts and Anderson (Anders On, U.S. Pat. No. 3,766,133, Example 8) It was 89, as if it were there.

Such high formability coefficient is 2000-5000psi
This is obtained when the difference in specific gravity at preforming pressures that are close to each other is larger than that used in the present invention. At the 1000 and 5000 psi preforming pressures used in the present invention, the formability factor of the Mayuse and Roberts product is much higher than 89. For example, Anderson
Edens and LarsOn
The lower moldability coefficient reported for the high apparent density molding powder (5659/l) of U.S. Pat. No. 3,245,972 of ΔSG5-1)
It was hot. At preforming pressures of 1000 and 5000 psi, this formability factor (15) increases to about 75.

A molding powder with a moldability factor (5-1) of 75 has a very high apparent density, at least 700 g/l. The characters shown in Figure 1 are high quality PTFE finely pulverized powder (Fineg) made using the conventional method.
rOundPTFEmOldingpOwder) with respect to apparent density and ΔSG,−1.
The molding powder is as follows. A “Alcofron (AlgO)
flOn)" F-2 [Montecateini Edison (
MOntecatiniEdisOn)] B "HastaflOn" TF-17 [FarbwerkeHOechst] C "POlyflOn" Ml2 (Daikin Industries) D
"FluOn" Gl63 [1. C. I. E "HalOn" G-80 [Allied Chemi-Ca
l) U.S. Patent No. 3,640,984 F “Teflon”
7A [DuPont] G "Teflon" 7B [DuPont] H U.S. Patent No. 3,690,569 Example 11 U.S. Pat. is 10 to 100μ.

Anderson, Edens and Larson molding powders are not included in this graph. This is because it is not pulverized. Due to coarse grinding, the average particle size is approximately 40
It is 0 to 500μ. Finely pulverized molding powder can be preformed,
They are advantageous over coarse powders because they can be free-synthesized to produce molded parts with improved mechanical and electrical properties.
Further, since the finely pulverized molding powder has advantageous properties when mixed with a granular filler, it is particularly suitable for making filled molded products that are widely used in applications requiring wear resistance. The data points indicated by numbers and letters on the graph are approximately midpoint between the respective numbers and letters.

Curve 1 in FIG. 1 is expressed by the above equation (1).

Curve 2 in Figure 1 is expressed by the formula AD≧600+3.00(ΔSG5−
1) The line shown in (2) and the lower boundary of the preferred AD versus ΔSG,l.

Curve 3 in Figure 1 is expressed by the formula AD≧400+3.00(ΔSG5−
,) ・・・・・・・・・ This is the line shown in (3).

As seen from curve 1, U.S. Patent No. 3,690,569
All lettered molding powders fall below curve 3, with the exception of molding powder l, which is considered undesirable in the No. far enough away.

The slope of curve 3 indicates an improvement in formability that reduces the apparent density (
(low ΔSG54 value), that is, corresponds to the effect of fine pulverization. The smaller the average particle size of these molded powders, the lower their apparent density. This is Kometani (KOmetani)
) et al., US Pat. No. 3,726,483. In FIG. 2, the molding powder used to make the cutting tape is "Halon" G-80. The bright spots in these figures are voids in the tape, which make it unsuitable for applications such as covering wires and cables. In Figure 3, this molding powder is representative of the molding powder of Example 25 before stirring with water, and the advantageous effect of its molding quality (low ΔSG5l) is demonstrated by the absence of voids in the tape. There is.

The molding powder of the present invention can be obtained from various raw materials, namely the aqueous dispersion or fine powder of polytetrafluoroethylene and the granular powder of polytetrafluoroethylene can be obtained from the molding powder.

Regarding aqueous dispersions of PTFE as raw materials, this raw material is well known in the art and is described, for example, in the aforementioned Mayuse and Roberts patent, and in particular in Berry U.S. Pat. No. 2,559,752. There is.

This type of PTFE is often referred to as "fine powder" and is used in coagulated form. The first step of converting this coagulated aqueous dispersion of PTFE into mature cedar powder is to densify the PTFE by applying high pressure in a pressure device, such as a forming press or densification roll, at room temperature, e.g. 20-30°C. This is a method of Pressure is 562kg/Cd~3513
kg/(1771) can be used.The aqueous dispersion of coagulated PTFE can be wet, i.e. it can contain some aqueous polymerization medium in it, or can be dry. The second step is to partially crush the densified particles (DecOmpac
t) to make the particles have an average particle size of 100μ or less.

This crushing process cannot be considered as crushing because the densified particles are much smaller than the particles obtained by crushing, but this crushing can be carried out using conventional crushing equipment.
Such equipment includes high-speed cutter mills that operate underwater, such as the Taylor Styles Cutter Mill, which performs underwater crushing.
Sha and Mill (TaylOrStilesGia
ntMill) (Taylor Stiles'first; and fluid energy mills that crush densified materials in a dry state, such as the Micronizer (MicrOnizer).
Sturteyant Mill
l) manufactured by the company].

Before the densified product is fed to such a mill, it must be made into a mass of a size that can be fed to the mill. If a wet mill operation is performed, drying is then performed. The partially crushed material obtained is the molded powder of the invention. The molding powder of the present invention produced by this method of densifying and partially crushing fine powder differs from the raw material in several respects.

Firstly, in the product of the invention, the preforming pressure is 70 kg/
The porosity of the preform when Cd is 0.20 or less, preferably 0.17 or less. In fact, many molding powders obtained from this method have a porosity of 0.15 or less and exhibit excellent low-pressure preformability. In contrast, raw fine powder 1 has a porosity significantly greater than 0.20, indicating poor low pressure preformability. The significance of this difference in porosity is that while fine powder cannot be sintered into large molded parts without cracking, the molded powder obtained therefrom according to the present invention can be sintered without cracking. I can do it. Second, the raw material fine powder is 1000 psi.
Molding shrinkage rate (%S(1000)) at premolding pressure of
is greater than 8,0, while %S(100
0) is 8.0 or less, preferably 7.2 or less. This low shrinkage rate is advantageous in that there is less difficulty in designing a mold to make a product of a given size. Third, the molding shrinkage (%S(5000)) of Fine Powder 1 at a preforming pressure of 5000 psi is significantly reduced in molding powders made therefrom. Generally, the %S(5000) of fine powder is greater than 3.7, and the %S(5000) of the molding powder of the present invention obtained therefrom is 3.7 or less. Finally, although the products of the present invention can be molded by molding powder methods, fine powders tend to stick to molds and crack when preformed or sintered. As mentioned above, the typical molding powder of the present invention made from fine powder has been widely molded, and the results show that the typical molding powder is equivalent to high quality finely ground molding powder,
It shows that it is superior in some respects.

Commercially available fine powders are not suitable for shaping by preform sintering operations because they stick to the mold and cause aggressive cracking. Several hundred cylinders with diameters of 5.72C-ITL, 7.62 (V7L and 10.15crfL) were made from the molding powder of the present invention made from fine powder, but no adhesion to the mold was observed.10 The resulting sintered cylinder containing a .15 cm cylinder (weighing 0.908 kg) was made from a previously obtained high quality PTFE finely ground molding powder (molding powder,
That is, it does not crack like the control product made from granular tree stamps.

No cracks were observed in the 5.72CTrL or 7.62cTn cylinders.

Molded articles made from molding powders of the present invention made from fine powder have very smooth surfaces, and tapes cut from these molded articles have the uniform void-free appearance shown in FIG.

This molding powder sinters into a clear, self-supporting melt, whereas the finely divided particulate resin obtained by conventional methods gives a cloudy melt. A transparent melt is preferred. This is because the user can look into the furnace to see if sintering is complete, ie the melt is transparent, and then begin the cooling process. The high quality of the cut tape is demonstrated by the dielectric strength of a 127μ thick sample made using the method described above being 700K.
This is indicated by V/Cm or more. The good mechanical and electrical properties of the molding powder of the present invention made from fine powder were shown to be 2 to 3 after sintering at 380°C for 5 hours.
The molded powder has a tensile strength of 320 kg/d), an elongation of 320%, and a dielectric strength of 740 KV/Cln, as measured on a 127 μm tape made from a solid billet of diameter 5.72 Cln cooled at 0°C/min. . A comparison of elongation and dielectric strength with other typical PTFE molding powders is as follows. Billet preforming is 176kg/C! I did it on 7L.

When the preforming pressure is only 70 V/ClfL, the molded powder still exhibits a better dielectric strength than the commercially pulverized molded powder, which is observed for example when comparing the tape of FIG. 3 with the tape of FIG. 2. This is because the physical uniformity of the tape has been improved. More specifically, at a preforming pressure of 70 kg/Cd, a 127μ thick tape cut from a sintered preform of the molding powder of the present invention has a dielectric strength of 768 KV.
/CTn, whereas molding powder B is 433KV/C
-FfL, molding powder A is 295KV/me. Regarding the granular PTFE as raw material for the molding powder of the present invention, the granular type PTFE consists of two parts, one of which is soft and the other part is hard, which are tightly bonded to each other.

In this specification, the soft portion is referred to as α resin, and the hard portion is referred to as β resin. As part of this invention, the crude (freshly polymerized) particulate resin consists of alpha and beta resins, the proportions of which depend on the polymerization conditions. For example, by increasing the solids content when carrying out the polymerization, the proportion of β moieties can be increased.
In industrial milling operations of granular PTFE, the two parts tend to separate from each other into separate particles.

More specifically, alpha resins are crushed more quickly than beta resins, about 10 times faster, so that when the grinding mill is shut down after an extended period of operation, the resin in the circulation line is primarily beta resin. This resin in the circulation line is called the mill residue after stopping the mill and is a very small portion of the total amount fed to the mill, the proportion depending on the total operating time of the mill. Traditionally, mill residues have been discarded because they have a coarse particle size relative to the average particle size present in the desired product of the mill. This residue obtained from the production of conventionally main finely pulverized molded powder has the following characteristics. The molding powder of the invention, broadly defined, differs from mill residues in that it has a high specific surface area and a high tensile strength.

The mill residues have a very low specific surface area, while the molded powder produced in the milling operation that produces these mill residues has a relatively high specific surface area. The maximum specific surface area of mill residue is 1.2
4 to the lowest value of 1.577z''/9 for the molding powder of the present invention is at least a 25% increase. This corresponds to a minimum reduction in particle size of at least that proportion. The pulverized powder is mainly β resin with some α resin.To make the molding powder of the present invention, (a) the β resin is first separated from the mixture of β resin and α resin, and (b) the β resin is separated from the mixture of β resin and α resin. The resulting β-resin is further ground into an improved molding powder having the desired combination of properties described above. Step (a)
The better the degree of separation, the higher the apparent density for a given degree of grinding in step (b). Mill residue represents the type of separation in which a very small proportion of separated β-resin is obtained in industrial mill operations, but this separation reduces the pulverized molding powder to approximately α and β parts. It is economical to do this by dividing.

This classification is possible because the β portion, which is difficult to grind, has a larger average particle size than the α portion after a certain grinding time. After the alpha part has been sufficiently ground and leaves the mill, only the beta part remains, thus separating the alpha part from the beta part. The β parts obtained by this classification are too coarse and do not themselves have good formability, as in the case of mill residues.

This separated β portion or mill residue of β resin is further pulverized to increase its surface area and tensile strength. This results in the product of the invention. Contrary to common experience, finely pulverized β-resin molding powders, like the molding powders of the present invention described above, have high apparent densities. This is made possible by the absence or presence of only a small amount of alpha resin in the finely ground beta resin. Examples of mills that can be used for fine grinding are "Micronizer I" and "Hurricane Mill".
ricane Mill)” [Micro Cyclomatsu (
MicroOcycleOmat)] [U.S. Patent No. 2,
No. 936,301] and “Ginit-o-Maiza I”
(U.S. Pat. No. 3,640,984).

The finely ground molding powder and the resulting mill residue containing significant amounts of both beta and alpha resins cannot be milled into the apparent density/forming factor region of the present invention. This is because the apparent density of the alpha portion is initially relatively low, and pulverization causes excessive milling of the alpha resin present, thereby reducing the overall apparent density of the molded powder. The effect of fine milling on creating low apparent densities is seen for molding powders A-G in FIG. 1, where the low apparent density results from the alpha resin content of these molding powders. In addition to the relative hardness that distinguishes alpha and beta resin particles, beta resin particles are distinguished by their shape.

That is, the particles of fine powder β resin have a smooth surface and the general shape of a flattened sphere, but the fine powder α
The resin particles have a fluffy appearance. Furthermore, the individual particles of the molded powder of the present invention, which consists of finely powdered β-resin, exhibit a characteristic Maltese cross-shaped birefringence typical of single crystals when viewed under a microscope under polarized light. Alpha particles, on the other hand, do not exhibit this characteristic appearance. The particles of the molding powder of the present invention made from fine powder also exhibit this birefringence. In addition to low AD force and ΔSG,-1, the finely pulverized molded powder of β resin has low anisotropic behavior during molding. This means that the powder preform shrinks in a relatively uniform manner in all directions when sintered. This facilitates designing molds and using them to create sintered parts of desired dimensions. The anisotropic behavior is measured as (S). The desired low anisotropic behavior is achieved when the absolute value of (S) is 0.0 for the molding powder of the present invention.
8 or less (between −0.8 and +0.8), preferably 0.5 or less (between −0.5 and +0.5). The closer the (S) value is to o, the better the molding powder is in this respect. Other finely ground granular resins are larger (
S) value, for example −1.23 to −1.0. Even if the molding powder of the present invention is made from fine powder,
or even made from coarse β-resin, ThOma
s) and Wallade U.S. Pat.
Somewhat better flowability than the finely ground resin of No. 36,301 (
powder flow).

Powder flow uses water, an organic wetting liquid or an immiscible mixture thereof as an agglomeration medium to form agglomerates of shaped powder, e.g.
Improvement is achieved by creating agglomerates with an average particle size of ~1000μ. The molding powder of the present invention preferably has a moldability coefficient (ΔSG5-1) of 30 or less and an average particle size of 60 μm or less.

The finely pulverized β-resin molding powder has a ΔSG,, of 15 or less, and an average particle size of 20 μ or less. Some of these molding powders have ΔSG54 of O, which means that the molding powder is 1
000PS1 (70k9/d) means that it has extremely good sinterability. Such molding powder of the present invention has a minimum pressure of 500 psi (35 kg/CTIL) or 200 p
It can be preformed even at s1 (14 kg/Cl7L) and can be sintered into a dense and strong molded product. Preferably the molding powder of the invention has an average particle size of at least 10 microns. The molding powders of the present invention are comprised of high molecular weight PTFE, which means that these molding powders can be processed using non-melt processing methods used for conventional PTFE molding powders. One measure of high molecular weight means that the molding powder of the present invention has an apparent melt viscosity of at least 1.times.10@9 poise at 380.degree. The PTFE from which the molding powder of the invention is made may also contain small amounts of terminally unsaturated fluorinated monomers, for example from 0.01 to 0.5% by weight, based on the total weight of the copolymer.

Suitable copolymerizable monomers are perfluoroalkenes or perfluoro(alkyl vinyl ethers) having 3 to 8 carbon atoms, respectively. The monomer imparts a high degree of toughness and high bending life to the molding powder. Test Method The test results described herein are determined by the following test method.

Apparent density (AD) is the unpressed apparent density of the powder, which can be measured using ASTM D-1 without separating and reconstituting the sample.
457-69.

Theoretically, the maximum apparent density of the molded powder obtained when the particle shape is spheres of different sizes giving the maximum packing density is 194
It is 29/l. Calculated AD The calculated apparent bulk density is determined by measuring the volume occupied by the void-free powder of polymer 1d contained in the sample tube used in the sub-sieve test.

This volume is called the bulk factor. Calculated value of AD = 2285/
bulk factor. The unit of apparent density is 9/l. The values obtained in this measurement are always close to, but need not necessarily correspond to, the values of apparent density determined by the ASTM I457 method. The reason for not using the ASTM method using the calculated value of AD is that it requires a sample of 2,285 g instead of the maximum amount of 2,009. Specific Surface Area (SSA) The specific surface area of a powder sample is the surface area (in square meters) of the polymer 19 measured by the nitrogen adsorption method. All measurements of this parameter were performed by a modified gas chromatography method.
In this case, polytetrafluoroethylene was used to calibrate the device, and its surface area was determined by Instrument Publishing Company 1.
Published in 949 by Barr and Anhorn.
Scientific and Industrial Glass Blowing Ink and Laboratory Techniques (HOrn)
ustrialGlassblOwingandLab
OratOryTechniques)] Measured by the standard BET method described in Chapter 12. All molding powders in the examples below have an SSA of at least 1.5 i/9.
The raw PTFE fine powder has an SSA of at least 9 I/9, and even after the densification and crushing process, the SSA is still 1.5 I/9.
It is 9 or more. Subsieve size
SSS (SSS) - This value is called the subsive size.
It is a numerical value in μ determined by a device manufactured by HerScientific.

This method is substantially the same as that described in ASTM Standard B-330-58T using a sample of 2.28 g of unfilled resin and a porosity in the determination of 0.55.
SSS is a measure of air permeability, which is a function of particle size and porosity. For a series of samples where porosity does not change, SSS is a measure of average particle size. SSG-standard specific gravity C is measured on preformed samples at 5000 ps1 (352 kg/Cd).

The test method is described in ASTM D1457-69, but the preforming die used had a diameter of 2.86 cm.
m and using a polymer charge of 12.09.

The sintering process involves forcing the sample from 30,009 to 380°C at a rate of 2°C/min. This is the process of After heating at 380°C for the specified 30 minutes, the furnace was cooled at 1°C/min to 295°C and held at this temperature for 25 minutes, after which time the sample was removed, cooled to room temperature, and the standard specific gravity determined using Dl457-69. decide.

SG (1000) has a specific gravity of 500 in the SSG method.
Means measured on a sintered preform formed at 1000 PS1 rather than 0 psi. SSG increases with crystallization rate, and (at least for homogeneous polymers) crystallization rate decreases with increasing molecular weight.

That is, the measurement of SSG before and after one process serves as a guide to the change in molecular weight due to that process. Changes in ΔSG54-specific gravity (forming coefficient 5-1) are determined by measuring the specific gravity of a sintered sample made in the same manner as the SSG method.
The preforming pressure used is 1000psi (70kg/c!
l).

△SG,l = 1000 x (SSG (preforming pressure at 5000 psi) - SG (preforming pressure at 1000 ps1))
It is. When using the term formability coefficient for △SG5-2, such a formability coefficient is 1000 x (5
Defined as specific gravity molded at preforming pressures of 0.000 psi and 2000 psi. %S(5000) The percentage shrinkage is the percentage decrease in diameter between the final sintered sample and the preform of the sample used to determine the SSG, and the measurement is perpendicular to the direction of applying the preform pressure. direction (lateral change).

The values obtained for %S vary considerably with preforming pressure and also on the precise method of applying the preforming pressure. %S(1000) is 5000psi (3521<g/
It is the value obtained by preforming at 1000 psi (70 kg/d) instead of d). (S) is a constant in the equation used to predict the change in lateral and axial dimensions during sintering. (S
)teeth. It is a measure of the fibrous or elastic memory of polymer particles,
It has been experimentally shown that the preforming pressure is essentially constant, instead of varying widely as the percentage shrinkage. If the void volume of the preform is known, then (S) . ' can be used to calculate the dimensional changes in both the lateral and axial directions of the molded article. The value of (S) is 352kg/CfIL
It is determined from %S shown in the following formula (5) using a preforming pressure of . The closer (S) is to O, the more the sample behavior approaches isotropy.

Equation (4a)... Calculated value of change in lateral direction'
Formula (4b)・・・・・・・・・Calculated value of change in axial direction/
Calculated value of formula (5) (S), 7 Guideline for elastic memory of molded particles'' Porosity - Porosity is the sample for the measurement of SG (1000) as defined above. This is the value of porosity (void Cd)/(total volume d) of the preform used for.

This is a measure of the preformability of the resin. Tensile strength - The tensile strength is the original cross-sectional area of the sample specified by ASTM D-1457-69 method made at 50000s1 (352kg/c!l) and the sample sintered by the method described in the SSG section. Breaking stress (Kg/(V7I).A
EF (anisotropic expansion factor) is a measure of the dimensional change obtained by sintering.

This value is obtained as follows. Weigh 12 g of powder into a 2.86 (177!) diameter mold, compress to 352 kg/c!11 within 1 minute, hold for 2 minutes, then release the pressure.

The diameter and height of the preform are measured and the preform is sintered using the same sintering process as for SSG. Next, measure the sintered thickness and diameter, and calculate the anisotropic expansion factor using the following formula: Ts/Tp+Ds/Dp where Ts and Tp are the thicknesses of the sintered resin and the preform, and Ds and Dp are the diameters of the sintered body and the preform.

%E - Percentage of elongation at break of tensile strength (TS) measurement sample.
Height 22.8C using powder flowable monopolymer sample! ILs
Fill a vertical polytetrafluoroethylene pipe with a diameter of 5.08 CfL and a 6-mesh screen at the bottom.

Pipe frequency 675 cycles/min, amplitude 0.762c
Gives wL vibration. Continuously weigh and record the amount of powder flowing through the screen. From the obtained curve 9/
Calculate the powder flow rate in seconds. Unless otherwise specified, the particle size described herein is the weight average particle size (D5O) of the molded powder determined by the wet sieving method described in US Pat. No. 2,936,301.

Standard sieves smaller than 37μ are not readily available for wet sieving, and wet sieving cannot be applied to very small particles. The weight average particle size of particles smaller than 37μ is determined by the MicroMerograph described in U.S. Pat. No. 3,265,679 unless otherwise stated. The result is in d(μ)×V ten thousand units.

In the string, ρ is the density of particles. This density is not known, but is believed to vary depending on particle size and type (α or β resin). This density is expected to vary between about 0.8 and 2.28. handle! The value of 7 is approximately 0.9-1.5
and thus the average particle size (μ) varies between the reported DV
It is usually somewhat smaller than the value of i. In most cases the particle size values obtained by one of these tests were confirmed quantitatively by optical microscopy. The average particle size D5O of the agglomerated powder is determined by the wet sieving method of ASTM D-11457-69 and is determined by the International Standards Organization (International Standards Organization).
Choose a set of sieves with double square root units starting from 1000μ as recommended by ndardsOrganizationOn).

The basic or primary particles of the PTFE fine powder are determined by observation with an electron microscope. The apparent melt viscosity is calculated by measuring the tensile creep of a sintered piece held at 380°C. More specifically, 129 molding powder is placed in a 7.6 CfL diameter mold between a 0.152 (177!) rubber membrane and a paper screen. The mold is heated to 100° C. for 1 hour.

Pressure is then slowly applied to the mold until a value of 140.6 kg/Cd is obtained. Hold this pressure for 5 minutes,
The sample disk was then removed from the mold and separated from the rubber membrane and paper screen by gradually releasing the pressure.
Sinter at 380° C. for 0 minutes.

The furnace is then cooled to 290°C at a rate of about 1°C/min and the sample is removed. Cut a crack-free rectangular sliver with the following dimensions: Accurately measure the width 0.152-0.165 cfn, thickness 0.152-0.165 cfn and length at least 6 cfn0 and calculate the cross-sectional area. The intermediate end of the sample sliver is attached to a quartz rod by wrapping a silver-coated wire. The distance between the wraps is 4.00 In.
Place the quartz rod sample assembly in a cylindrical furnace and bring the test length (in this case 7n) to a temperature of 380±2°C.A weight is attached to the bottom of the quartz rod, and a total of about 4g of The weight is suspended from the sliver of the sample.

Measurements of elongation versus time are obtained and the best average value for the creep curve between 30 and 60 minutes is determined. Specific melt viscosity, often referred to as apparent melt viscosity, is calculated from the following equation: Examples of the molding powder of the present invention are as follows.

(All percentages are by weight unless otherwise noted). Example 1 In this experiment, the diameter was 20.3C! A FL stainless steel micronizer air mill was used.

This is Palmyra, New Chassis, USA.
ra) Jet-Pulv
It is a model 08-5057 manufactured by Elizer.

This is done adiabatically, that is, without heat going in and out, at -25℃, 6
．． It is operated with 67 kg/min of filtered compressed air introduced at 71 L. The feed polymer is
It was Teflon 7A fluorocarbon resin (1967).

During a period of 4 minutes, 200 f1 of feed resin is gradually introduced into the mill at a uniform feed rate of 509/min.

This feed rate is determined experimentally to maximize separation of the beta resin from the alpha resin. Once the polymer feed is complete, run the mill for 1 minute without polymer feed to remove most of the remaining alpha resin as effluent. The total effluent and residue removed from the micronizer chamber after cutting the mill were approximately the same weight. Repeat this experiment several times and the residue (coarse β)
were combined and fed to other experiments on the same device.

In this case the polymer feed rate was 30 f1/min. The resulting effluent (finely pulverized molded powder of the β-resin of the present invention) was about 70% of the co-feed amount, weighed 3549 kg, and was the molded powder of the present invention. Table 1 shows the characteristics of this product. The molding powder of the present invention produced in this example still has a high apparent density, and △SG
、． It has much better formability, indicated by l being O, which has a tensile strength of 4000 psi (280 k
g/Cd) or more.

In fact, the specific gravity of a sintered molded product made by preforming at 1000 ps1 (70 kg/Cd) is 0.00079/Cd compared to one made with a preforming pressure of 5000 psi (352 kg/Cd).
CC is high, which probably represents the experimental precision of the test method. The meaning that ΔSG,−, is O means that this molded product is preformed at a very low pressure to create a preformed product.
This means that it can be sintered into high-quality molded parts. For example, to obtain a positive value of ΔSG,
The low pressure preforming pressure may be reduced to, for example, 700-500 psi. This low pressure preformability is unique in the molding powder industry. The high degree of densification of the preform is 70
kg/(177i). This porosity value is much smaller than that for Fine Powder 1, and similar to the porosity value of other PTFE finely ground molding powders, but , △SG5-1 is O, which is much better than other finely ground molding powders with similarly high apparent densities. The value of shrinkage, S(1000) is 6.32%
, S(5000) of 2.94% and AEF of 1.124 compared with commercially available PTFE finely pulverized molded powder.
The particles of the molded powder produced in this example exhibit birefringence when viewed under a polarizing microscope.

Example 2 A. Example 1 was repeated to obtain 1.46 kg of molding powder of the present invention made from pulverized β-resin.

The results are shown in Table 2. The 70% alpha resin effluent is the product obtained by separating the alpha resin from the coarse beta resin.

This coarse beta resin is pulverized to form the final effluent. This is a molded powder of the finely pulverized β-resin of the present invention. The 70% alpha resin effluent exhibits excellent formability characterized by a low ΔSG5 of 2.7, but this improvement is due to a decrease in apparent density and an increase in particle fibrousness ((S) (increase in value), obtained by increasing shrinkage.

In contrast, the final effluent obtained by pulverizing coarse β-resin has somewhat better moldability than that obtained from Teflon 7A moldings, has a somewhat higher apparent density, and has a fibrous nature of the particles. is reduced without significantly sacrificing contractility. Example 2A
The particles of the molded article of the present invention made from the above exhibit birefringence when viewed under a polarizing microscope.

B. This experiment was conducted using the polytetrafluoroethylene resin feed described in Example 1 and a fluid energy mill.

During a period of 4 minutes, the 2009 resin feed is introduced into the mill at a uniform feed rate of 50 g/min.

When the polymer feed is finished, the air flow to the mill is cut off and run for 2 minutes without adding feed, then the run is stopped. Start the mill, run for 2 minutes without adding feed, then shut down. The product receiver was changed and the mill was run again for 2 minutes, yielding uniformly shaped particles 18.59 having a particle size of approximately 15 microns and exhibiting polarized light when viewed under a polarizing microscope. C. In this experiment,
The micronizer was operated as in B above until the 2009 feed polymer was introduced into the mill.

The air flow is then turned off and the product portions are separated. Open the mill and remove the mill residue. Repeat this operation three times. The three parts, totaling 2029 products, are combined and fed to a new mill.

This feed material has already passed through the mill once and has an 80
% alpha and 20% beta resin. Once the milled material has been introduced into the mill, turn off the mill, change the product receiver and run the mill for 4 minutes. Open the mill 13.2
9 resins were recovered. This material is the ground beta resin of the present invention. This one has a subsieve size of 6.0 and a calculated apparent density of 671f! It was hot at /l. According to a polarizing microscope, it consists of small homogeneous particles (average particle size about 10 μm) exhibiting birefringence. Example 3~
4 This example shows the production of molding powders of the present invention from various raw materials Fine Powder 1 (Fine Powder 1E was used in Examples 21 and 26).

All these raw materials are small elementary particles (0.13~0
．． 5μ) and large aggregates (D,O4OO~600μ).

Raw material fine powder (coagulated and dried aqueous dispersion PT)
FE) is densified in a laboratory press at 25° C. and various pressures.

Is the diameter of the mold 5.72? The number of fillers of Huasun powder in the cylinder was 109. Partial crushing is performed using a Waring Blender 3.7851 unless otherwise specified.
Blender (Type CB-5), a high-speed airfoil mixing device with 12.1° diameter blades, 6.35 m wide and 3.5 m thick.
This was done using a 17111t leading edge attached.

The broad plane of the blade moves in a plane perpendicular to the vertical shaft.
The temperature during finishing is measured with a thermocouple in the slurry and controlled by passing ice water or hot water through the jacket of the compounder. This device was used in Examples 3 to 8, 12, 13 and 1.
4 and its control experiments were used at high speed. In some experiments, a Waring blender fitted with standard blades was used in place of the flat blades (Examples 9 and 10).
and 11 and its control material.

In other experiments, the 0.947
A No. 1 Waring blender was used. (Example 8 and its control experiment). The data table indicates whether the compounder was used at high or low speed. 12.1 When using my own feathers,
Peripheral speed is 76.3 m/s at high speed and 45.8 m/s at low speed.
Seconds.

In each partial crushing process, one cylinder of 30°C water and densified fine powder was filled into a blender,
Enough water was used to obtain a solids content of 0-20%.

The time of partial disruption is shown for each experiment. The molded powder was separated and dried at 120°C for 16 hours. The details and results of this experiment are shown in Table 3. Although raw fine powders A, B, C and D all exhibit low ΔSG5-1 values, these materials tend to stick to the preform mold and crack when the preform is sintered, making it difficult to use molding powder technology. It cannot be processed.

This poor formability is due to the high porosity of the fine powder preform (0.24 or more), the high shrinkage of the sintered fine powder (%SlOOOO is 9.0 or more), and (S)
The cause is that the absolute value of is higher than 1.0. On the other hand, the examples shown in Table 3 are good to excellent molding powders, with preform porosity greater than 0.20 and in most cases 0.17.
Therefore, in most cases it is lower than 0.15, the absolute value of (S) is smaller than 0.8, and the AEF is also small.

Additionally, all of these molded powders have significantly higher apparent densities than conventionally pulverized molded powders. Examples 8 to 14 conducted under other partial crushing conditions generally show that the more intense and widespread the crushing, the smaller the ΔSG,-1 value (the moldability is improved). Example 1
5 and 16 In this example, Fine Powder 1A was used as the raw material, and Table 4 shows the effect of changing the densification pressure in the method used in Example 3.

The control molding powder A, which is not a conventional molding powder, is inferior due to its lower apparent density.

densification pressure) increases to 352 kg/(1-J mo Vf,
Then, as the weight increases above 562 kg/d, the apparent density increases, the formability improves, and properties such as porosity and anisotropic expansion factor improve. Table 5 shows the effect of varying the partial grinding temperature according to the method used in Example 3.

These experiments show that various partial crushing temperatures can be used.

In the case of control B molding powder, high densification pressures or short partial crushing times give high AD molding powders upon partial crushing. Examples 19-20 In these experiments, the method of Example 3 was repeated, but as shown in Table 6 below, the Fine Powder A was not dried after coagulation, and during densification, the Fine Powder A was mixed with 30% by weight. It contained water.

Examples 21-23 These examples demonstrate that there is no need to use a Waring blender for partial crushing.

In these examples, each raw material fine powder was heated at 25°C in a press with a temperature of 5621<9/C! Densify in il. E is the fine powder used in Example 21, and D is the fine powder used in Examples 22 and 23. The densified fine powder E used in Example 21 and the D used in Examples 22 and 23 were mixed with water to prepare a Taylor Stiles cutter-T having a rotating blade of 15.2 crlL.
The S-06 was continuously fed and operated at a rotation speed of 9600 rpm with a screen installed across the cutter output. For Examples 21 and 22, the screen was a 30p screen (manufacturer's name) and the screen thickness was 0.21 mL. The minimum pore diameter is O. 33
7 nm and has an aperture area of 14.5010. The holes have a profile that starts at about 0.83μ on one side of the screen and then reduces to the minimum shown on the opposite side. For Example 23, the screen is a 60R VERO screen (manufacturer's name). This screen has a thickness of O. 2011, the diameter of the lowest hole is 0.13n, and the open area is 8%. The pore has a rounded profile, with a diameter of approximately 0.4211 on one side, then reaches a minimum value, then increases again outwards. The feed slurry at 8° C. is passed through the cutter at a water flow rate of 1360 l/hr and a polymer feed rate of 22.7 kg/hr.

This product is separated from water by the flotation method and a new 10
of water and stirred in a slurry tank for 30 minutes at room temperature according to US Pat. No. 3,690,569.

The slurry tank is fitted with vertical baffles to increase agitation and to control temperature with a jacket. The diameter of the tank was 45.7 (11 cm) and the height was 45.7 cm.The blades of the stirrer were rectangular and there were 4 in number, each of which had a diameter of 22.9 cm and a height of 5.1 cm. .45°
It had a pitch. The stirrer speed was 400 rpm. The details and results of the experiment are shown in Table 7. Although the control fine powders 1 in the table have high apparent densities and low ΔSG5-1, these fine powders 1 cannot be molded by normal mold powder processing methods.

One cause is the stickiness of Fine Powder Type 1 PTFE, and other causes are the high (S) value and porosity. It is.
The molding powder obtained from these fine powders is PTF.
It can be molded in the same way as E molding powder. Examples 24 and 2
5 These examples use the same feed resin (Fine Powder 1A) in Table 8, partial crushing in a Waring blender after preforming at 562 kg/CIL (Example 24), and by stirring the aqueous solution. After partial crushing by Taylor Styles 17601<g/C!
It is shown that equivalent results can be obtained when pre-densifying with IL (Example 25).

Examples 26 and 27 These examples show in Table 9 that the pre-densified fine powders can also be partially crushed by water.

20.3C1r described in U.S. Patent No. 3,726,484
A L fluid energy mill was used. The pre-densified resin was crushed in a cutter and passed through a screen with 6.3511 holes so that the resin could be fed into an air mill. Example 28 In this example, fine powder 1A was used and 25
°C pressure 562kg/C! The following data were obtained for the resulting molded powder of the present invention after a series of densifications and various degrees of partial crushing were carried out in 1.

5 This data shows the general relationship that moldability increases as particle size decreases.

These data are plotted in FIG. The region with high D5O in the string was plotted using the following experimentally determined information. △SG5-, (1168
It was hot.

ΔSG5-1 was 147 when D5O was 170μ. When D5O is 90, △SG5-1 (ma 115). Determine △SG5-1 for the molding powder from FIG.
, O can be determined. For example, Example 3~
In ΔSG5lO~75 containing No. 27, the D5O particle size of the molding powder of the present invention was about 30-70μ. Example 2
9-34 Coagulation The finely ground β-polymer molded powder of the present invention was coagulated by stirring in a glass resin pot of No. 21 for about 15 minutes using tetrachloroethylene and water.

The sintering kettle was equipped with four 0.5-inch baffles and an agitator, and the agitator was operated at 2000 rpm with four blades pointing downward at an angle of 45 mm. The solvent:PTFE ratio (dsolvent:9PTFE) is shown in Table 10, and the PTFE:water ratio was about 1:10. Pulverized β-resin 1009 was used in each experiment. After separation and drying, the product has the following properties shown in Table 10. The properties of the finely ground resin used as a raw material are shown in the control section. Example 35 Typical molding powders obtained from Coagulum Fine Powder 1A were coagulated in the 45.7 cTn stirred tank of Examples 21-23.

The charges were 4.54 kg of polymer, 38.14 kg of water, and 1200 CC of tetrachlorethylene, which were stirred at 860 rpm for 30 minutes at 25°C. After separation and drying, the product had good sinterability and excellent AD and powder flow properties as shown below. Example 36 Coagulated product 6.82 kg of product obtained by partially crushing densified resin F using the same equipment as in Example 35, 38.11
l! of water and 3000 ml of tetrachlorethylene were charged.

The mixture is stirred at 860 rpm for 30 minutes at 25° C., separated and dried. It showed the following properties.

[Brief explanation of drawings]

Figure 1 shows the apparent density ΔSG5-1 (1000 psi (70
kg/Cd) and the value calculated from a preform pressed at 5000 ps1 (352 kf!/d)), and the values plotted in the graph correspond to the molding powder of the previous example. 2 and 3 are micrographs at 100x magnification of a cross section of a cutting tape cut from a billet of sintered molding powder.

Claims (1)

[Claims] 1. Item 1: surface area of at least 1.5 m^2/g, average particle size of 100
μ, and the apparent density is at least 500 g/l, and the formula apparent density ≥ 500 + 3.00 (△SG_5_-_1), where △SG_5_-_1 is 1000 psi (70 kg/cm
^2) and 10 of the difference in specific gravity of the sintered molded parts made with a preforming pressure of 5000 psi (352 kg/cm^2).
Polytetrafluoroethylene molding powder, characterized in that it has at least an apparent density calculated as: 00 times, and ΔSG_5_-_1 is not greater than 75. 2nd term: temperature approximately 20~30℃, pressure 8000psi (562kg
/cm^2) ~ 50.000psi (3513kg/c
In m^2), a fine powder of tetrafluoroethylene is densified, and the resulting densified product is partially crushed to produce a molded powder with an average particle size of less than 100μ, which has a specific surface area of at least 1 .5m^2/g, average particle size smaller than 100μ, apparent density at least 500μ
In g/l, the formula apparent density ≥ 500 + 3.00 (△SG_5_
-_1) However, △SG_5_-_1 is 1000psi (7
0kg/cm^2) and 5000psi (352kg/
This is 1000 times the difference in specific gravity of the sintered molded product made with a preforming pressure of cm^2), and △SG_5_-_1 is 75
A method for producing a polytetrafluoroethylene fine powder having an apparent density of at least not greater than . Section 3 (a) β from a mixture of β granular resin and α granular resin
separating the particulate resin, and (b) crushing the separated β particulate resin in the absence of the α particulate resin to increase its specific surface area and tensile strength, with a specific surface area of at least 1.5 m
^2/g, the average particle size is smaller than 100 μ, the apparent density is at least 500 g/l, and the formula apparent density ≧ 500 + 3.00
(△SG_5_-_1) However, △SG_5_1 is 1000
psi (70kg/cm^2) and 5000psi (3
This is 1000 times the difference in specific gravity of the sintered molded product made with a preforming pressure of 52 kg/cm^2), and △SG_5_-
A method for producing a polytetrafluoroethylene molding powder from a polytetrafluoroethylene granular resin having at least an apparent density calculated by _1 not greater than 75.