JP2001089624A - Polytetrafluoroethylene aqueous dispersion composition and preparation of coating film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polytetrafluoroethylene (PTFE) aqueous dispersion composition which prevents occurrence of cracks in thick coating films and has good still standing stability, and a method of preparing coating films. SOLUTION: This polytetrafluoroethylene aqueous dispersion composition contains, as the essential components, 20-65 wt.% PTFE fine particles having an average particle diameter of 0.2-0.4 μm, 9-12 wt.%, based on PTFE, heat decomposable component having, as the major component, a specific polyoxyethylene alkylphenyl ether based or polyoxyalkylene alkyl ether based surface active agent, and water.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aqueous dispersion composition containing polytetrafluoroethylene (hereinafter, referred to as PTFE) fine particles and a method for producing a coating film using the same.

[0002]

2. Description of the Related Art Generally, PTFE prepared by an emulsion polymerization method is prepared by stirring a mixture of water, a peroxide-based polymerization initiator, an anionic dispersant, and a higher stabilizer such as a higher paraffin as a polymerization stabilizer. Ethylene (hereinafter referred to as TFE) monomer is injected under pressure and polymerized to produce PTFE fine particles having an average particle diameter of 0.1 to 0.6 μm.
It is obtained as an aqueous dispersion dispersed at a concentration of around 0% by weight or less. When high-grade paraffin and the like are removed from the aqueous dispersion, they tend to aggregate and become unstable. After stabilizing by adding a nonionic surfactant, the solid content of PTFE is reduced to 40% by a known method such as an electric concentration method or a phase separation method. ~ 65
Concentrated to weight%. Then, to this concentrated aqueous dispersion, a surfactant is added as necessary for storage stability and viscosity adjustment, and further, water, ammonia, a coloring agent, a filler, a thickener, and the like, if necessary. By adding and dissolving or dispersing the above components, the PTFE concentration becomes 20 to 6
A PTFE aqueous dispersion composition containing 5% by weight and containing about 5 to 8.5% by weight of a nonionic surfactant as a thermal decomposition component based on PTFE is obtained.

As an application of these PTFE aqueous dispersion compositions, they are impregnated into glass fiber cloth and fired to be used as a roof material for a membrane structure building or a high-frequency circuit board material, or coated on a metal plate and fired. In addition, there are applications such as peeling to obtain a film and using it as an insulating film for a capacitor or an electronic component, and coating the surface of a cooking utensil. Such PTFE
In the application process of the aqueous dispersion composition, the PTFE aqueous dispersion composition is applied to a heat-resistant substrate, dried at, for example, 120 ° C. to remove moisture, and then heated and fired at a temperature higher than the melting point of PTFE, for example, 380 ° C. At the same time, a surfactant, which is a thermal decomposition component, is removed, and a PTFE film is formed at the same time.

[0004]

However, when the PTFE aqueous dispersion composition is applied to a thickness greater than the film thickness called a crack limit thickness, a crack called a mud crack occurs, and the coating film becomes defective. There was a problem that impaired quality. In addition, when thick film processing is required, there is a problem that the production cost increases because recoating is required.
With respect to the crack limit thickness, a document describing that the crack limit thickness becomes a constant value when the surfactant concentration with respect to PTFE is around 4% (Coloring Material, 1975, 48 volumes,
513), but no further description is given of the higher concentration of the surfactant. Also, Japanese Patent Application Laid-Open No. 5-337
439, PTFE having an average particle size of 0.3 to 0.6 μm
It is described that the occurrence of mud cracks is prevented by using large particles, but the crack limit thickness is not satisfactory because the amount of surfactant is too small.
The large E particles tend to settle out in the liquid, and have a problem of poor standing stability. The present invention increases the crack limit thickness, and a high-quality coating film in which cracks hardly occur even when thickly applied is obtained,
Another object of the present invention is to provide a PTFE aqueous dispersion composition having excellent standing stability and a method for producing a coating film using the same.

[0005]

Means for Solving the Problems As a result of repeated studies to solve the above-mentioned problems, the present inventors have found that PTFE fine particles having a specific average particle diameter are reduced to 20 to 65% by weight, and specific non-fine particles are reduced. PTF for thermal decomposition component consisting of ionic surfactant
By making the PTFE aqueous dispersion composition blended with 9 to 12% by weight based on E, cracks are hardly generated specifically, and it has been found that the static value stability is excellent, and the present invention has been completed. . That is, according to the present invention, 20 to 65% by weight of PTFE fine particles having an average particle diameter of 0.2 to 0.4 μm, and at least 70% by weight of the non-ionic surfactant represented by the general formulas (1) and (2) At least one of the thermal decomposition components selected from
To 12% by weight and water as an essential component.

[0006]

Embedded image R—C ₆ H ₄ —O—A—H (1) (wherein, R is a linear or branched alkyl group having 4 to 12 carbon atoms, and A is an oxyethylene group having 5 to 20 carbon atoms)
It is a polyoxyethylene chain composed of )

[0007]

R'-OA'-H (2) wherein R 'is a linear or branched alkyl group having 8 to 18 carbon atoms or an unsaturated aliphatic hydrocarbon group;
A ′ is a polyoxyalkylene chain composed of 5 to 20 oxyethylene groups and 0 to 2 oxypropylene groups. Further, the present invention provides the PTFE aqueous dispersion composition, wherein the PTFE fine particles have an average particle diameter of 0.3 to 0.4 μm. Further, the present invention provides a method for producing a coating film, which comprises applying the above aqueous PTFE dispersion composition on a heat-resistant substrate, followed by drying and baking.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The PTFE fine particles used in the aqueous PTFE dispersion composition of the present invention can be obtained as fine particles having an average particle diameter of 0.2 to 0.4 μm by an emulsion polymerization method. Can be manufactured. Among them, those having an average particle size of 0.3 to 0.4 μm can provide a particularly large crack limit thickness. However, PTFE fine particles are liable to settle due to gravity, and the static stability is slightly lowered. It can be arbitrarily selected. P
When the average particle size of the TFE fine particles is smaller than the range of the present invention, there is a problem that the crack limit thickness becomes small. On the contrary, when the average particle size is larger than the range of the present invention, the stability at rest decreases. The average molecular weight of PTFE is 1,000,000 to 3
The range of 10,000,000 is suitable, and particularly preferably 1,000,000 to 25,000,000, but can be arbitrarily selected according to the mechanical properties required for the coating film. The average molecular weight is
Using the heat of crystallization determined by differential thermal analysis, Suwa et al. (Jo
urnal of Applied Polymer
Science, 17, 3253 (1973)).

In the present invention, PTFE means not only homopolymers of TFE, but also trace amounts of halogenated ethylene such as chlorotrifluoroethylene, halogenated propylene such as hexafluoropropylene, and fluorocarbon such as perfluoro (alkyl vinyl ether). TF such as vinyl ether
So-called modified PTFE, which contains a polymerized unit based on a component copolymerizable with E and cannot be substantially melt-processed, is also included. In the PTFE aqueous dispersion composition of the present invention, PT
The content of the FE fine particles is 20 to 65% by weight, preferably 40 to 60% by weight. When the viscosity is lower than the above range, the stability at rest is inferior due to low viscosity, and when the viscosity is higher than the above range, it becomes difficult to handle due to high viscosity. The content of the PTFE fine particles was 20 to 40% by weight.
In the case of (1), the viscosity of the liquid can be increased by using a thickener or the like, and the stationary stability can be obtained. The aqueous PTFE dispersion composition of the present invention contains the thermal decomposition component in an amount of 9 to 12% by weight, preferably 9.4 to 11.5% by weight, based on the PTFE. When the concentration of the thermal decomposition component is 9 to 12% by weight with respect to PTFE, the crack limit thickness becomes extremely large. On the other hand, when the concentration of the thermal decomposition component is less than 9% by weight with respect to PTFE, the crack limit thickness is reduced and mud cracks are remarkably generated. On the other hand, when the concentration of the thermal decomposition component is more than 12% by weight with respect to PTFE, fine cracks are easily generated and the crack limit thickness is reduced. Although the reason for this is not clear, when the concentration of the thermal decomposition component is less than 9% by weight with respect to PTFE, the PTFE fine particles generate clearance and shrinkage in the coating film from which water and the like have been removed by drying. When the thermal decomposition component is more than 12% by weight based on PTFE, cracks are not easily formed after drying, but the amount of the thermal decomposition component is too large. It is presumed that a contraction force is generated and a crack is generated. On the other hand, when the concentration of the thermal decomposition component is in the range of 9 to 12% by weight based on PTFE, PT
Since the thermal decomposition component is added in such an amount as to just fill the gap of the FE fine particles, it is presumed that cracks are unlikely to occur specifically and the crack limit thickness becomes large.

The content of at least one selected from the nonionic surfactants of the general formulas (1) and (2) in the pyrolysis component is at least 70% by weight, preferably at least 80% by weight. And particularly preferably at least 85% by weight. The polyoxyethylene alkyl phenyl ether-based nonionic surfactant of the general formula (1) or the polyoxyalkylene alkyl ether-based nonionic surfactant of the general formula (2) is PT
It plays a role in stabilizing the FE fine particles in water. When the amount of the nonionic surfactant component represented by the general formulas (1) and (2) is less than 70% by weight of the pyrolysis component, the stability of the aqueous PTFE dispersion composition is reduced, or the crack limit thickness is reduced. Occurs.

In the general formula (1), R which is a hydrophobic group is
Alkyl group, but the alkyl group has 4 to 12 carbon atoms.
The box is effective for the present invention, preferably 6 to 10.
If the alkyl group is too small, the PTFE aqueous dispersion composition will
Surface tension increases, wettability decreases, and conversely, alkyl groups
If it is too large, the stationary stability of the dispersion is likely to be impaired. Ma
In addition, A which is a hydrophilic group is a polyoxyethylene group having 5 to 20 groups.
Lioxyethylene chains are effective in the present invention, especially 7-1
The range of 2 is preferred in terms of viscosity and stability. General formula
Specific examples of the nonionic surfactant (1) include
For example, C₉H₁₉C₆H₄O (C₂H₄O)
_9-10H, C₈H₁₇C₆H₄O (C₂H₄O)
_9-10H and the like. Non-ion of general formula (1)
Surfactants may be used alone or in combination of two or more.
Can be

In the general formula (2), R ′, which is a hydrophobic group, is an alkyl group or an unsaturated aliphatic hydrocarbon group, preferably an alkyl group. The alkyl group or unsaturated aliphatic hydrocarbon group having 8 to 18 carbon atoms is effective in the present invention, and preferably has 10 to 16 carbon atoms. If the alkyl group or the unsaturated aliphatic hydrocarbon group is too small, the wettability of the PTFE aqueous dispersion composition will be reduced. Conversely, if the alkyl group or the unsaturated aliphatic hydrocarbon group is too large, the dispersion will remain stable. Is easily damaged. The unsaturated group of the unsaturated aliphatic hydrocarbon group is preferably an ethylene group. Further, A ′ which is a hydrophilic group has 5 to 20 oxyethylene groups and 0 to oxypropylene groups.
2 is a polyoxyalkylene chain. The polyoxyalkylene chain may have a block structure or a random structure. Those having a polyoxyalkylene chain having 7 to 12 oxyethylene groups and 0 to 2 oxypropylene groups are preferred in view of viscosity and stability. In particular, the number of oxypropylene groups in the hydrophilic group A ′ is set to 0.1.
When the content is 5 to 1.5, the bubble elimination property becomes good, and it is more preferable.

[0013] The nonionic surfactant of the general formula (2)
As a body example, for example, C₁₃H ₂₇O (C₂H
₄O)_9-10H, C₁₀H₂₁CH (CH₃) CH₂
O (C₂H₄O)₁₀H, C₁₀H₂₁CH (CH₃)
CH₂O (C₂H₄O)_9-10OC₃H₆OH, C
₁₂H₂₅O (C₂H₄O)₁₀H, C₁₆H₃₃O
(C₂H₄O)_10-11H, C₁₆H₂₅O (C₂H
₄O)_6-7Surfactants having a molecular structure such as H
Can be The nonionic surfactant of the general formula (2) is used alone
Alternatively, two or more kinds can be used as a mixture. What
Note that nonionic surfactants are not usually single compounds.
Because it is a mixture of multiple substances with a certain distribution,
The structure shall be treated as the mean of such a distribution. You
That is, the alkyl group or unsaturated aliphatic carbon in the molecular structure
The number of carbon atoms in the hydride group,
The number of ethylene and oxypropylene groups are not used.
Should be treated as the average chemical structure of the surfactant
You. In addition, non-ionic compounds represented by general formulas (1) and (2)
When two or more surfactants are used as a mixture,
The effects of the present invention can be obtained.

In the PTFE aqueous dispersion composition of the present invention, a thermal decomposition component other than the nonionic surfactants of the general formulas (1) and (2) can be added or used in combination. Other thermal decomposition components other than the nonionic surfactants of the general formula (1) and the general formula (2) are components which are not usually removed by drying at 120 ° C. and do not remain after firing, and Examples thereof include nonionic surfactants other than the general formulas (1) and (2), polyoxyethylene alkyl ester type surfactants, fluorine surfactants such as perfluoroalkyl polyoxyethylene adducts, and silicone-based surfactants. Surfactant, anionic surfactant, polyethylene glycol,
Examples include polyethylene oxide, water-soluble polyurethane-based thickeners, polymers such as ethylene glycol propylene glycol copolymer, thixotropy-imparting agents, leveling agents, organic coloring agents, and other known water-soluble organic substances. Water used as an essential component in the present invention is PT
Water used in the FE polymerization may be used as it is, or may be water newly added in the process, but water containing less impurities is desirable.

The PTFE aqueous dispersion composition of the present invention includes:
If necessary, preservatives such as ammonia, various salts, water-soluble organic solvents such as alcohols and ketones, water-insoluble organic solvents such as toluene and xylene, and other known components may be appropriately used in combination. . Further, the PTFE aqueous dispersion composition of the present invention, if necessary, titanium oxide cadmium oxide pigment, iron oxide pigment, chromium oxide pigment, cobalt blue, carbon black, glass powder, hollow glass beads, graphite fine particles, Inorganic coloring agents such as titanium oxide fine particles, mica or titanium oxide-coated mica powder, polyimide resin powder, polyether sulfone resin powder, polysulfone resin powder, polyether ether ketone resin powder, polyphenylene sulfide resin powder, and aramid resin powder, and heat resistance. One or more filler components may be appropriately added. If necessary, an aqueous dispersion of a TFE-perfluoro (alkyl vinyl ether) copolymer, an aqueous dispersion of a TFE-hexafluoropropylene copolymer, and a polystyrene may be added to the PTFE aqueous dispersion composition of the present invention. A so-called meltable fluororesin such as an aqueous dispersion of chlorotrifluoroethylene may be used in combination.

The method for producing a coating film of the present invention comprises the above-mentioned PTFE
An aqueous dispersion composition is used, applied to a heat-resistant substrate, dried and fired to form a PTFE film. The heat-resistant substrate may be any substrate that can withstand the firing temperature of PTFE,
Specific examples include heat-resistant materials such as glass fiber cloth, carbon fiber cloth, metal fiber cloth, and metal plate. When adhesion to a base is required when applying to a metal plate or the like, it is desirable to roughen the substrate surface in advance by etching or sandblasting. As a coating method, a known method such as a spin coating method, a dipping method, a spray method, a bar coating method, and a roll coating method can be used. The term “drying” as used herein refers to a stage or process in which low-boiling components such as water as a dispersion medium are dried and removed. The drying temperature is preferably 100 ° C. or higher and the firing temperature or lower. In the present invention, firing refers to a step or step of heating at a temperature equal to or higher than the melting point of PTFE to form a film of PTFE. The firing temperature is preferably 400 ° C. or lower. Since the thermal decomposition component used in the present invention is generally an organic substance, it is usually thermally decomposed and volatilized at about 200 to 400 ° C. in a drying to baking stage. The drying, thermal decomposition, and baking processes after the application may be independent processes, or may be a process in which drying, thermal decomposition, and baking are performed simultaneously by continuous treatment or rapid heating. The coating film may have only one layer, or may have a plurality of layers in order to obtain a predetermined function or strength. The thickness of the obtained coating film may be appropriately selected depending on the application properties, but it can be set within a range of 1 to 50 μm in which mud cracks do not occur per application, and can be optionally determined by overcoating. It can be as thick as the film thickness.

The obtained coating film may be used as it is as a surface-treated film on a heat-resistant substrate, or may be used by peeling off only the PTFE coating film to form a film. PTF of the present invention
The E aqueous dispersion composition can be particularly suitably used for coating applications. In other words, it is used for impregnating and firing glass fiber cloth or carbon fiber cloth, etc. to process it into roof materials for membrane structures or high-frequency printed circuit boards, etc. A PTFE film is obtained by coating and baking on a substrate and peeling off only the coating layer, and can be used as a capacitor dielectric or an electrical insulating material. In such applications, cracks in the coating film become serious defects and impair the commercial value, but the use of the present invention can prevent the occurrence of cracks. Further, the aqueous PTFE dispersion composition of the present invention is prepared by adding a viscose, sodium alginate, polyvinyl alcohol, or the like, spinning under pressure into a coagulation bath to form a fibrous body, and heating and calcining and stretching the PTFE fiber to form a PTFE fiber. Use for manufacturing, kneading with soil improver such as chemical fertilizer and lime, and powder of civil engineering material such as cement to capture fine powder to prevent dust generation, manganese dioxide and nickel hydroxide used in battery manufacturing The active substance powder such as carbon and carbon is kneaded with the diluent of the aqueous PTFE dispersion composition,
Application to apply paste obtained by fibrillating TFE to electrode plate, Application to obtain eutectoid of PTFE aqueous dispersion and filler such as lead, and then process to oilless bearing, PTF
Various binders utilizing fibrillation of E, use of adding PTFE dispersion to plastic powder to prevent dripping during burning of plastic, other conventional PTFE
It can also be used in many applications where dispersions have been utilized.

[0018]

The present invention will be described in more detail with reference to the following Examples and Comparative Examples, which do not limit the present invention in any way. Examples are Examples 1 to 6, and Examples 13 and 15, and Comparative Examples are Examples 7 to 12, Example 14, and Example 16.
It is. Tables 1 and 2 collectively describe the formulations and results of Examples 1 to 6 and Examples 7 to 12. The thermal decomposition components (a) to (f), which are additives used in each example, are summarized in Table 3. The method for preparing the sample and the method for evaluating each item are described below. (A) Average particle size of PTFE fine particles:
The measured mode diameter was measured using a laser light scattering particle size analyzer, and the obtained mode diameter was defined as the average particle diameter. (B) PTFE fine particle concentration and pyrolysis component concentration: 7 g of the PTFE aqueous dispersion composition was placed in an aluminum dish (weight W ₁ ) weighed in advance, weighed (weight W ₂ ), and dried in an oven at 120 ° C. for 1 hour for precision. (Weight W ₃ ), 380
After calcination at 35 ° C. for 35 minutes, the mixture was cooled, weighed (weight W ₄ ), and calculated by the following equation.

[0019]

## EQU1 ## PTFE fine particle concentration (wt%) = (W ₄ −
W ₁ ) × 100 / (W ₂ −W ₁ ) Thermal decomposition component concentration (wt% based on PTFE) = (W ₃ −
W ₄ ) × 100 / (W ₄ −W ₁ )

(C) pH: Digital pH manufactured by Iuchi Seieido
It was measured using a meter. (D) Viscosity: # 1 using a Brookfield viscometer
PTF at 23 rpm at 60 rpm using spindle
The viscosity of the E aqueous dispersion composition was measured. (E) Limit thickness of crack: 0.5 cm in thickness of 10 cm square
2 cc of the PTFE aqueous dispersion composition was dropped on a smooth and clean aluminum plate having a coating gap of 0 μm on one side and a reverse side of 2 μm.
12 μm and a coating thickness of 12 to 200 μm.
After drying at 0 ° C. for 1 hour, baking was performed at 380 ° C. for 35 minutes. Cracks occur at places where the coating was applied thickly and disappear as the coating becomes thinner. The thickness of the places where the cracks disappear was measured at five places using a permascope, and the average value was determined to be the crack limit thickness. (F) Static stability: 10% aqueous PTFE dispersion composition
It was placed in a 0 ml graduated cylinder and allowed to stand at room temperature, and the thickness of the supernatant layer generated after one week and one month was measured. In addition, if these values are 8 mm or less after one month, there is no problem in practical use by performing periodic stirring. (G) Coating test: Bar coater # 18 manufactured by Tester Sangyo
On a 20cm square aluminum plate surface with a thickness of 0.5mm
The FE aqueous dispersion composition was applied, dried at 120 ° C. for 10 minutes, and then baked at 380 ° C. for 10 minutes to obtain a coating film having a thickness of about 18 μm.

Example 1 An aqueous dispersion having an average particle size of PTFE fine particles of 0.25 μm, an average molecular weight of PTFE of 3,000,000, and a concentration of PTFE fine particles of 20% by weight was obtained by an emulsion polymerization method. . After dissolving the pyrolysis component (a) corresponding to the general formula (1) at a ratio of 5% by weight with respect to PTFE, the solution is concentrated by an electroconcentration method, and the supernatant is removed. 2.5% by weight of PT based on the ionic surfactant (a) based on PTFE
An FE concentrate was obtained. Add 8% of this concentrate to PTFE
% By weight of pyrolysis component (a), add water and 200 p
pm of ammonia was added to obtain a PTFE aqueous dispersion composition shown as Formulation (1) in Table 1. The PTFE aqueous dispersion composition had a PTFE fine particle concentration of 57% by weight, a thermal decomposition component was 10.5% by weight based on PTFE, a crack limit thickness was as excellent as 30 μm, and the stationary stability was good. Was. A coating test was carried out on an aluminum foil using this PTFE aqueous dispersion composition. As a result, no cracks were observed in the coating film and the appearance was good.

Example 2 The same PTFE concentrate as in Example 1 was added with P
9% by weight of TFE, water and 200 ppm of ammonia were added to obtain a PTFE aqueous dispersion composition shown in Table 1 as formulation (2). The PTFE fine particle concentration of this PTFE aqueous dispersion composition is 5
7% by weight, the thermal decomposition component was 11.5% by weight of PTFE.
% By weight, good performances such as crack limit thickness and standing stability, and no cracks occurred in the coating test.

Example 3 PT was prepared by the same emulsion polymerization method as in Example 1.
After obtaining an aqueous dispersion of FE fine particles, the pyrolysis component (b) corresponding to the general formula (2) is added to the PTFE at a ratio of 4% by weight to perform primary stabilization. After concentration, the supernatant is removed, and PTFE fine particles 66
% By weight of the surfactant (b) was obtained at 2.3% by weight based on PTFE. To this concentrated liquid, 7.2% by weight of the pyrolysis component (b) based on PTFE, 200 ppm of ammonia and water were added and dissolved by stirring for 1 hour, and the pyrolysis component shown in Table 1 as formulation (3) was added. Was 9.5% by weight with respect to the PTFE weight to obtain an aqueous PTFE dispersion composition.
The dispersion composition had good performances such as crack limit thickness and standing stability, and no cracks were generated in a coating test.

Example 4 The same PTFE concentrate as in Example 1 was added with P
2.5% by weight, based on TFE, of the pyrolysis component (a), P
After adding 5% by weight of the thermally decomposable component (b), 200 ppm of water and ammonia to TFE and stirring and dissolving, the powder of the thermally decomposable component (d), which is a thickener, was further stirred and dissolved little by little. To obtain a PTFE aqueous dispersion composition represented by Formulation (4). The evaluation results of the obtained PTFE aqueous dispersion composition are shown in Table 1 in the same manner as in Example 1, and each physical property was good.

Example 5 PT was prepared by the same emulsion polymerization method as in Example 1.
After obtaining an aqueous dispersion of FE fine particles, the thermal decomposition component (c)
Was added to the PTFE at a ratio of 4% by weight to perform primary stabilization, followed by concentration by an electroconcentration method, removing the supernatant, 66% by weight of PTFE fine particles, and a pyrolysis component of PT.
A 2.4% by weight concentrate based on FE was obtained. To this concentrated liquid were added 6.1% by weight of the pyrolysis component (c) based on PTFE, 1% by weight of the pyrolysis component (e) based on PTFE, 200 ppm of ammonia and water, and dissolved by stirring. The thermal decomposition component shown as blending (5) in 1 is P
An aqueous PTFE dispersion composition of 9.5% by weight based on the weight of TFE was obtained. Each physical property of this dispersion composition was good.

Example 6 The average particle size of the PTFE fine particles was 0.35 μm by lengthening the polymerization time in the emulsion polymerization method.
m, the average molecular weight of PTFE is 4.5 million,
An aqueous dispersion having a TFE fine particle concentration of 20% by weight was obtained. After thermal decomposition component (a) was added to the PTFE at a ratio of 5% by weight to primary stabilization, concentration was performed by an electroconcentration method, the supernatant was removed, 68% by weight of PTFE fine particles, Component (a) is 2.
A 5% by weight PTFE concentrate was obtained. PT
8.5% by weight of the FE, the pyrolysis component (a), the pyrolysis component (d), water and 200 ppm of ammonia were added to obtain a PTFE aqueous dispersion composition shown as formulation (6) in Table 1. Was. PTF of this PTFE aqueous dispersion composition
The E particle concentration was 58% by weight, the pyrolysis component was 11.1% by weight based on PTFE, and the crack limit thickness was 38 μm.
m, and the static stability was within the allowable range.

Example 7 An aqueous PTFE dispersion composition (formulation (7)) was obtained in the same manner as in Example 1, except that the pyrolysis component (a) was 6.5% by weight based on PTFE. Table 2 shows the evaluation results.
As shown in the figure, the crack limit thickness was as low as 13 μm, and a remarkable crack was recognized in the coating film in the coating test, which was not preferable.

Example 8 An aqueous PTFE dispersion composition was obtained in the same manner as in Example 1 except that the amount of the thermally decomposed component (a) was 13% by weight based on PTFE. The evaluation results are shown in Table 2, but the crack limit thickness was insufficient at 20 μm, and a minute crack was observed in the coating test, which was not preferable.

Example 9 The same PTFE concentrate as in Example 1 was added with P
4% by weight, based on TFE, of pyrolysis component (b), PTF
3% by weight of E, 200 ppm of water and ammonia were added and dissolved by stirring to obtain a PTFE aqueous dispersion composition shown in Table 1 as formulation (9). The thermal decomposition component of this dispersion composition was 9.5 with respect to PTFE.
% By weight, of which the ratio of the surfactant component is 6%.
It was as low as 8.5% by weight. As shown in Table 2, the evaluation results of the PTFE aqueous dispersion composition were such that the crack limit thickness was insufficient, and the coating test was unfavorable because cracks occurred.

[Example 10] By shortening the polymerization time in the emulsion polymerization method, the average particle diameter of the PTFE fine particles was 0.15.
μm, the average molecular weight of PTFE is 1,000,000,
An aqueous dispersion having a PTFE fine particle concentration of 11% by weight was obtained. 6% by weight of the pyrolysis component (a) based on PTFE
, And dissolved in the same manner as in Example 1 by electroconcentration.
After the FE concentrate was obtained, each component was added to obtain a PTFE aqueous dispersion composition shown in Table 1 as formulation (10).
As shown in Table 2, this PTFE aqueous dispersion composition
The concentration of the FE fine particles was 55% by weight, and the amount of the pyrolysis component was 10% by weight based on PTFE.
μm, and many cracks occurred in the coating test, which was not preferable.

Example 11 As in Example 6, the average particle size was 0.3
A PTFE aqueous dispersion composition having a particle size of 5 μm was prepared in which the concentration of the thermal decomposition component (a) was 3% by weight based on PTFE. Its crack limit thickness is 2
It was slightly low at 2 μm, had some cracks even in the coating test, and had poor standing stability.

Example 12 By extending the polymerization time in the emulsion polymerization method, the average particle size of the PTFE fine particles was 0.45.
μm, the average molecular weight of PTFE is 8 million,
An aqueous dispersion having a PTFE fine particle concentration of 30% by weight was obtained. After the thermal decomposition component (a) was dissolved in PTFE at a ratio of 5% by weight, a PTFE aqueous dispersion composition shown in Table 2 was prepared in the same manner as in Example 6. This had poor standing stability because the particle size was too large.

[Example 13] 1000 parts by weight of the PTFE aqueous dispersion composition (formulation (1)) prepared in Example 1 was used, and 20 parts of a carbon black dispersion (Carbon Paste EP1731 manufactured by Dainichi Seika Co., Ltd.) was added thereto. , 20 parts of mica powder (Magnapearl 1000 manufactured by Engelhard Co.), 10%
The mixture was stirred for 30 minutes while sequentially adding 50 parts by weight of an aqueous solution of sodium lauryl sulfate and 100 parts of water to obtain a blended composition. The concentration of the PTFE fine particles in this composition was 47.9% by weight, and the content of the pyrolysis component was 11.7% by weight based on PTFE. This was spin-coated on an aluminum plate having a diameter of 40 cm and a thickness of 0.8 mm, which had been previously sandblasted, dried at 120 ° C. for 30 minutes, and baked at 380 ° C. for 20 minutes to obtain a 20 μm-thick good crack-free coating film.

Example 14 A composition was obtained in the same manner as in Example 13 except that the composition (7) prepared in Example 7 was used as the aqueous PTFE dispersion composition. The calculated value of the PTFE fine particle concentration of this compounded composition was 50.4% by weight, and the measured value of the pyrolysis component was 7.7% by weight based on PTFE. Example 13
The coating was applied to an aluminum plate in the same manner as described above, but cracks occurred at the center of the coating film, which was not preferable.

[Example 15] Using the composition (5) prepared in Example 5 as a PTFE aqueous dispersion composition, a PTFE aqueous dispersion composition was formed on a 0.5 mm thick aluminum plate by a bar coater # 18 manufactured by Tester Sangyo. The product is applied, dried at 120 ° C. for 10 minutes, baked at 380 ° C. for 10 minutes, and further coated with an aqueous PTFE dispersion composition on this coating film, dried and baked,
After obtaining a coating film of 36 μm in total, the coating film was peeled off from the aluminum plate to obtain a PTFE sheet without cracks.

Example 16 A PTFE sheet was obtained in the same manner as in Example 15 except that the formulation (7) prepared in Example 7 was used as the aqueous PTFE dispersion composition. However, many cracks were generated. The film broke when peeled from the aluminum plate.

[0037]

[Table 1]

[0038]

[Table 2]

[0039]

[Table 3]

[0040]

The PTFE aqueous dispersion composition of the present invention comprises:
When used for forming a coating film, the crack limit thickness of the coating film can be increased, the occurrence of defects in the coating film can be prevented, and the standing stability is excellent.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C09D 127/18 C08L 71:02) // (C08L 27/18 C08J 3/03 CEW 71:02) F-term (Reference) 4F070 AA24 AC38 AC84 AE14 CA01 CB01 CB13 4J002 BD151 CH022 ED036 ED066 GH01 GL00 GQ00 GQ05 HA06 4J038 CD121 DF022 HA156 KA09 MA02 MA08 MA10 MA14 NA01 NA11 NA12 NA26 PA19 PB09 PC01 PC02 PC03

Claims (3)

[Claims] 1. A non-ionic polytetrafluoroethylene fine particle having an average particle diameter of 0.2 to 0.4 μm is 20 to 65% by weight, and at least 70% by weight is a nonionic type represented by the general formulas (1) and (2) An aqueous dispersion of polytetrafluoroethylene, characterized in that at least one pyrolytic component selected from surfactants is contained in an amount of 9 to 12% by weight based on polytetrafluoroethylene, and water as an essential component. Composition. Embedded image R—C ₆ H ₄ —OAH (1) (wherein, R is a linear or branched alkyl group having 4 to 12 carbon atoms, and A is an oxyethylene group having 5 to 20 carbon atoms)
It is a polyoxyethylene chain composed of R′-OA′-H (2) (wherein, R ′ is a linear or branched alkyl group having 8 to 18 carbon atoms or an unsaturated aliphatic hydrocarbon group,
A ′ is a polyoxyalkylene chain composed of 5 to 20 oxyethylene groups and 0 to 2 oxypropylene groups. ) 2. The aqueous polytetrafluoroethylene dispersion composition according to claim 1, wherein the average particle size of the polytetrafluoroethylene fine particles is 0.3 to 0.4 μm. 3. A method for producing a coating film, which comprises applying the polytetrafluoroethylene aqueous dispersion composition according to claim 1 on a heat-resistant substrate, drying and firing.