JPH08108139A - Production of article having surface of water-repellent fluorine-containing resin - Google Patents

Abstract

PURPOSE: To produce an article having the surface of a fluorine-containing resin which places emphasis on water repellency by applying water incorporating fluorine-containing resin particles to the article and drying the dispersion liquid at the temperature not exceeding the fusion starting temperature through DSC measurement of the fluorine-containing resin and mutually fixing the fluorine-containing resin particles on the surface of the article. CONSTITUTION: Water, an organic liquid or a mixed dispersion liquid thereof incorporating fluorine-containing resin particles is applied to an article. The dispersion liquid is dried at the temperature not exceeding the fusion starting temperature through DSC measurement of the fluorine-containing resin under a state in which fluorine-containing resin particles are brought into contact with each other. Thereby, fluorine-containing resin particles are mutually fixed on the surface of the article in a nonfused state. Hereupon, the article having the surface of water-repellent fluorine-containing resin is constituted of an amorphous porous body which is formed of accumulation of mutual fluorine-containing resin particles having average particle diameter of at most 40μm and has the maximum IPA diffusion diameter of at least 8mm. Tangent value of an angle of water rolling is regulated to be at most 50/500. Thereby, the fluorine-containing resin layer having high water repellency is formed on the surface of the article by a simple installation and operation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a water-repellent article having a fluorine-containing resin surface which is excellent in water repellency and is less likely to have water droplets and dirt attached thereto.

[0002]

2. Description of the Related Art It has been required to impart properties such as water repellency, weather resistance and antifouling property to the surface of industrial equipment and household equipment. In order to have such surface properties, conventional article surfaces are roughened by blasting or etching, treated with a primer, etc., and then fluorine-containing resin particles such as polytetrafluoroethylene (PTFE) having excellent non-adhesiveness are added. Apply paint such as enamel contained, and after drying 350-400
A method in which a fluorinated resin is applied to the surface of an article by performing a baking treatment at ℃ has been widely used.

By the way, it is known that the water repellency of an article is greatly affected not only by the water repellency of the forming material but also by the surface condition. Therefore, in recent years, in order to obtain higher water repellency of an article, it has been attempted to increase the apparent contact angle with water by making the actual surface area larger than the apparent surface area by means of minute projections existing on the article surface.

For example, in Japanese Unexamined Patent Publication (Kokai) No. 4-239633, a layer having irregularities in which fine particles and silicate glass are mixed and a polymer film layer containing a fluorocarbon group and a siloxane group are chemically bonded by a siloxane bond to form an irregular surface. A method of forming a water and oil repellent film is disclosed.

Further, in Japanese Patent Laid-Open No. 4-283268,
A polytetrafluoroethylene oligomer having a molecular weight of about 8000 to 10000 is dispersed in a plating solution and the oligomer is co-deposited on the plating film to form a water-repellent metal composite.

Japanese Unexamined Patent Publication (Kokai) No. 6-122838 discloses a water-repellent coating material and a coating method in which a low molecular weight polytetrafluoroethylene powder having a molecular weight of about 500 to 20,000 is mixed and dispersed in an acrylic silicone resin.

[0007]

However, the method using the siloxane bond requires a step of forming a water-repellent film by the siloxane bond after once forming an uneven layer, and the plating method requires plating as an article for forming the water-repellent film. There was a drawback that it was limited to those that could work. Furthermore, the method of mixing and dispersing low molecular weight PTFE in acrylic silicone resin also requires a special low molecular weight PTFE fluorinated up to the end.

In order to solve these problems, the inventor previously composed of an amorphous porous body having a maximum IPA diffusion diameter of 8 mm or more formed by stacking fluorine-containing resin particles having an average particle diameter of 40 μm or less, And an article having a water-repellent fluororesin surface characterized by having a tangent value of a water transfer angle of 50/500 or less, and such an article having the following conditions: It was proposed that the fluororesin particles are manufactured by surface-fusing the fluororesin particles to each other at a temperature not lower than the melting start temperature and not higher than the melting end temperature of the fluororesin measured by DSC.

The heat treatment temperature at the time of heat treating the fluororesin particles applied to the surface of the article has a great influence on the porosity and strength of the resulting porous body. The above proposal of heat treatment at a temperature not lower than the melting start temperature and not higher than the melting end temperature by DSC measurement provides an article having a surface with sufficient strength, an appropriately high porosity, and high water repellency. Although it is an excellent method, heat treatment at a low temperature is more preferable in order to form an amorphous porous body having a higher porosity by focusing on water repellency. In view of such circumstances, the inventors of the present invention have investigated a method for obtaining an article having a fluororesin surface having a high degree of water repellency, and as a result, contain high molecular weight fluororesin particles having a specific particle diameter. By coating the dispersion and drying at a specific temperature, the fluororesin particles are fixed to the article surface in a non-molten state, and the fluororesin particles are piled up with each other to form an amorphous porous body having a high porosity. It has been found that an article having excellent water repellency can be obtained.

Accordingly, it is an object of the present invention to provide a method for producing an article having a fluorine-containing resin surface, with particular emphasis on water repellency.

[0011]

According to the present invention, water, an organic liquid or a mixed dispersion thereof containing fluorine-containing resin particles is applied to an article so that the fluorine-containing resin particles can come into contact with each other. Fluorine-containing resin particles having an average particle diameter of 40 μm or less, which are obtained by drying the dispersion liquid at a temperature not higher than the melting start temperature measured by DSC of the fluorine-containing resin to fix the fluorine-containing resin particles to the article surface in a non-molten state. It is composed of an amorphous porous body having a maximum IPA diffusion diameter of 8 mm or more formed by mutual stacking, and has a tangent value of a water transfer angle of 50.
The method for producing an article having a water-repellent fluorine-containing resin surface is characterized by being / 500 or less.

The method for bringing the fluorine-containing resin particles into contact with each other is not particularly limited, and water, an organic liquid or a mixed dispersion thereof containing the fluorine-containing resin particles having an average particle diameter of 40 μm or less is spray-coated on the article. The fluororesin particles may be applied to the surface by a method such as a spraying method or after aggregating the fluororesin particles.

(Fluorine-Containing Resin Particles) The fluorine-containing resin of the present invention is a thermoplastic resin containing at least one fluorine atom in its molecule, such as polytetrafluoroethylene (PTFE) resin and tetrafluoroethylene.
Perfluoro resins such as a hexafluoropropylene copolymer (FEP) resin and a tetrafluoroethylene / perfluoro (alkyl vinyl ether) copolymer (PFA: C1 to C5 as a perfluoroalkyl group) resin are preferable.

Among the perfluoro resins, a resin having a molecular weight of 100,000 or more is more preferable. It is economically advantageous to use commercially available general-purpose resins as these resins.

(Amorphous porous material) The surface of the fluororesin is
In order to exhibit water repellency higher than the water repellency inherent to the fluororesin which is the forming substance, it is preferable to have a surface structure that makes the contact area with water droplets smaller. For this reason, in the article of the present invention, it is necessary that the surface of the article is covered with a porous body having micron-order voids formed by stacking fluorine-containing resin particles having an average particle diameter of 40 μm or less.

The porous body produced by the production method of the present invention does not have a fixed shape, but the fluorine-containing resin particles are irregularly stacked, and as a result, shown in electron micrographs (FIGS. 1 and 2). Thus, it is composed of an amorphous fluororesin structure and voids. Further, it is a feature of the amorphous porous body of the present invention that individual fluorine-containing resin particles having an average particle diameter of 40 μm or less can be observed in the structure. On the other hand, the surface of the article (FIG. 3) obtained by fusing at a temperature equal to or higher than the melting end temperature of the fluororesin does not have such voids because the fluororesin particles are entirely fused. The porous body is not formed.

(Average Particle Diameter) In such a fluororesin porous material, it is necessary that the average particle diameter (d ₅₀ ) of the fluororesin particles forming the porous body is 40 μm or less.
That is, the fluorine-containing resin may be primary particles having an average particle diameter of 40 μm or less, or agglomerated particles of these primary particles. If the primary particle size is larger than this, the pores of the formed porous body are large and water easily penetrates into the voids, and air and water are replaced, so that the porous body is not suitable for water repellency. Further, a more preferable particle size suitable for stacking varies depending on the coating method, but in spray coating, a particle size of 0.1 to 20 μm is preferable. The size of the voids in the porous body can be controlled by selecting the diameter of the fluororesin particles and the diameter of the agglomerated particles to be used.

As the particles to be specifically used, colloidal particles having an average particle size of about 0.2 μm obtained directly from emulsion polymerization, agglomerated particles which are so-called secondary particles obtained by aggregating the colloidal particles with ethanol, etc. The particles which have been dried and pulverized again or particles having a diameter of more than 40 μm obtained by suspension polymerization may be pulverized as long as the primary particle diameter is 40 μm or less.

(Coating) Coating means applying a dispersion containing fluorine-containing resin particles onto the surface of an article by a method used for paints. Average particle size of 40μ on article surface
Examples of the method of applying the fluorine-containing resin particles having a particle size of m or less include spray coating. More specifically, a method of spray coating a fluororesin dispersion obtained by emulsion polymerization having an average particle size of about 0.2 μm can be mentioned. In the process of spray coating, the fluororesin particles are stacked on each other to form a porous body, and the size of the voids can be controlled by the coating conditions. In addition, the particles may be aggregated by adding an aggregating agent such as ethanol to the aqueous dispersion and then spray coating.

(Dispersion medium) In the method for producing a water-repellent article of the present invention, colloidal particles directly obtained from emulsion polymerization, agglomerated particles obtained by aggregating the colloidal particles with ethanol, and particles obtained from suspension polymerization are ground. Used particles are used. In order to form an amorphous porous body using these particles, it is preferable that the particles are dispersed in the liquid at the time of applying to the article.

When a large amount of a surfactant is contained in a non-shaped porous body formed of fluorine-containing resin particles, water droplets are easily absorbed in the porous body and water repellency is not exhibited. Therefore, in the present invention, when a dispersion containing fluorine-containing resin particles is applied by spray coating or the like, it is preferable that the dispersion medium does not contain a surfactant, but since it does not substantially affect the water repellency, fluorine-containing. The surfactant may be contained in the same amount as that used as an emulsifier when the resin is produced by emulsion polymerization. (Processing temperature)

After the dispersion is applied to an article, the fluororesin particles are adhered in a non-molten state to form a porous body having a high porosity, and the temperature is below the melting start temperature of the fluororesin measured by DSC. It is necessary to dry at the temperature of. The dispersion medium may be dried at a temperature not higher than the melting start temperature of the fluororesin measured by DSC, but is preferably 50 ° C. or higher from the viewpoint of the drying time until the fluororesin particles adhere to each other.

In order to form a porous body, two or more kinds of fluorine-containing resin particles, for example, a PTFE resin as a porous forming particle and a heat-melting PFA resin or FEP resin as an auxiliary material can be used. The drying temperature of is not higher than the melting start temperature of the fluorine-containing resin having the higher melting start temperature. When a heat-meltable fluorine-containing resin is used as an auxiliary material, it acts as a film-forming auxiliary agent by selecting the type, particle size and drying temperature, and the fluorine-containing resin particles are fixed on the article surface in a non-melting state. The water-repellent fluororesin surface having excellent strength can be obtained by adhering each other.

Specifically, the dispersion medium is preferably water from the viewpoint of non-flammability and environmental hygiene. In this case, the fluorine-containing resin particles can be aggregated by adding ethanol.

(Thickness) If the porous body existing on the surface of the article is too thin, water droplets may come into contact with the surface of the base material and the water repellency may not be exhibited. Strength is low, which is not desirable for practical use as an article. Therefore, it is usually 0.5 μm as an amorphous porous material.
A thickness of ~ 500 μm is suitable.

(Maximum IPA Diffusion Diameter) The porous article of the present invention has a fluororesin surface with isopropyl alcohol (IP
It can be compared by dropping one drop of A) and measuring the maximum diameter of the IPA diffused and permeated into the porous body.
In the case of a PTFE non-porous cutting sheet, the diameter at the time of dropping remains the same, whereas in the porous body according to the production method of the present invention, IPA penetrates into the porous body so that the diameter of IPA becomes smaller than that at the time of dropping. Expanding. The water-repellent article of the present invention is characterized by having a maximum IPA diffusion diameter of 8 mm or more, preferably 16 mm or more, more preferably 20 mm or more.

(Water repellency) Since the surface of the article of the present invention is covered with a porous body, it exhibits excellent water repellency. For example, even with PTFE, which is a water-repellent material, the contact angle with water is about 110 degrees in the case of a cutting film, whereas the contact angle with water of the water-repellent article of the present invention is usually 150 degrees or more. Is.

(Water Transfer Angle) It is difficult to compare the water repellency on the surface of a highly water repellent article produced by the manufacturing method of the present invention by conventional contact angle measurement. Therefore, the water transfer angle, that is, the minimum angle of the article surface where the water droplet rolls on the surface when the water droplet is dropped on the surface of the article, is measured by the method described later, and the tangent value (tangent) is taken as this It was expressed as and used as a measure of water repellency. For example, a PTFE cutting film shows a value of about 120/500 at the water transfer angle, although about 110 degrees is measured by the contact angle method. The water transfer angle of the surface of the article of the present invention is 50/500 or less.

(Substrate Article) When a water-repellent fluororesin surface is formed by the production method of the present invention, the substrate article may be a metal plate such as iron or aluminum which has been conventionally coated with a fluororesin, Various plastics, woods, papers and other materials can be selected as long as they can withstand the processing temperature for drying the dispersion containing the fluorine-containing resin particles, generally 100 ° C. or higher.

As a pre-treatment, an adhesive layer or a primer layer may be formed on these base materials and then the fluorine-containing resin particles may be stacked.

[0031]

EXAMPLES The present invention will be specifically described with reference to Examples and Comparative Examples below. The types of the raw material fluorine-containing resin particles used in the examples, the temperature measuring method, the coating method, the physical property measuring method of the product, etc. are as follows.

(1) Raw Material Fluorine-Containing Resin Particles Table 1 shows the fluorine-containing resin used as a raw material. Where T
1: melting start temperature, Tpeak: melting peak temperature, T2: melting end temperature (° C).

[0033]

[Table 1]

<Average particle size> Powder having an average particle size of 5 to 300 μm Microtrack method: Microtrack particle size analyzer model 79911-made by LEEDS & NORTHRUP
Measured by 01.・ Particles with an average particle size of 0.5 μm or less Turbidity method: Measured with a Shimadzu multi-purpose auto-spectrophotometer (halogen lamp).

(2) DSC Melting Temperature Measuring Method A DSC7 type differential scanning calorimeter manufactured by Perkin Elmer was used. A 5 mg sample is weighed and placed in a special aluminum pan, crimped by a special crimper, and then stored in the DSC main body to start heating. The temperature was raised from 200 ° C. to 380 ° C. at a rate of 10 ° C./minute, and from the melting curves obtained at this time, the melting start temperature (T1), the melting peak temperature (Tpeak) and the melting end temperature (T2) were determined.

(3) Coating method <Spray coating> 3 kg / cm ^{2 with} a nozzle having a diameter of 0.6 mm
2 mm thickness x 50 mm width x 100 mm length with G air pressure
Spray painted on the aluminum plate.

(4) Method of measuring water divergence angle An aluminum plate (width: 50 m) having a slope formed by raising one of the plates having a length of 550 mm and having a coating film formed thereon (width: 50 m)
m length 100 mm), 0.05 g of distilled water is dropped from the nozzle on the membrane 8 mm. The minimum slope at which the water drop does not stop and then rolls along the slope after falling onto the surface is represented by a distance (mm) increased with respect to a horizontal distance of 500 mm, that is, a tangent value of the slope angle.

(5) Porosity Measuring Method (Isopropyl Alcohol Diffusion Test) 0.01 ml of IPA is dropped onto an amorphous porous body using a microsyringe to measure the maximum diffusion diameter of the liquid. In the porous material, IPA penetrates into the porous material and diffuses from the diameter at the time of dropping to about 20 mm in diameter, while PTFE
With the cutting sheet of No. 3, the initial diameter remains 5.0 mm.

(6) Evaluation of Water Resistance of Porous Body From a height of 1.5 m, water of 15 to 20 ° C. is supplied at 100 mm / min with a gardening sprinkler (Toyox nozzle: 0.3 mm × 445 holes). Let it dry for 10 minutes and then air dry,
The residual weight% of the porous body was calculated from the weight change before and after the shower to evaluate the water resistance of the porous body.

[Example 1] PTF obtained from emulsion polymerization
Water was added to the aqueous dispersion E (average particle size 0.22 μm) to dilute it to a solid content of 23% by weight, and the dispersion was spray-coated on an aluminum plate. This was dried at 120 ° C. for 20 minutes to obtain an article having a water repellent PTFE resin surface. The electron micrograph of the surface of the obtained article is as shown in FIG. 1, in which the PTFE resin particles having a fine particle diameter are stacked in a non-melted state,
Voids are formed between the resin particles to form an irregularly shaped porous body. The water transfer angle of this surface was 1/500. The maximum isopropyl alcohol diffusion diameter is 20 mm.
Met.

When water droplets are dropped on the porous body of the present invention having the projections thus produced, the water droplets come into contact with the fluorine-containing resin film only at the protruding portions of the fluorine-containing resin, so that the water repellency is extremely high, The wetting angle with respect to water was about 150 degrees or more. The results are shown in Table 2 together with other examples and comparative examples.

Example 2 FEP obtained from emulsion polymerization
2 g of water and 2 g of ethanol were added to 3 g of the aqueous dispersion (average particle diameter of 0.16 μm), and the mixture was ultrasonically mixed and coagulated, and then spray coated on an aluminum plate. This was dried at 120 ° C. for 20 minutes to obtain an article having a water-repellent FEP resin surface. The water transfer angle of this surface was 1/500. The maximum isopropyl alcohol diffusion diameter was 20 mm.

Example 3 PFA obtained from emulsion polymerization
Water was added to the aqueous dispersion (average particle size of 0.17 μm) to dilute it to a solid content of 14 wt%. The dispersion liquid obtained by adding 10 wt% of ethanol to this and aggregating was spray-coated on an aluminum plate. Water-repellent PF
An article having an A resin surface was obtained. The electron micrograph of the surface of the obtained article is as shown in FIG.
The resin particles A are stacked in a non-melted state, and voids are formed between the resin particles to form a porous body having an irregular shape. The water transfer angle of the surface of this article, the measurement result of the maximum isopropyl alcohol diffusion diameter and the water resistance evaluation result are shown in Table 2.
It is

[Examples 4 to 5] Example 4 except that the heat treatment temperature in Example 3 was changed to 150 ° C and 250 ° C.
An article having a water-repellent fluorine-containing resin surface was obtained in the same manner as in. The water transfer angle of the surface of this article, the measurement result of the maximum isopropyl alcohol diffusion diameter, and the water resistance evaluation result are shown in Table 2.

[Examples 6 to 8] P obtained from emulsion polymerization
Water was added to the TFE aqueous dispersion (average particle size 0.22 μm) to dilute it to a solid content of 14 wt%. This was spray-painted on an aluminum plate. The dispersion liquid obtained by adding 10 wt% of ethanol to this and aggregating was spray-coated on an aluminum plate. This was heat-treated at the temperature shown in Table 2 for 30 minutes to obtain an article having a water-repellent PTFE resin surface. Table 2 shows the measurement results of the water transfer angle of the surface, the maximum isopropyl alcohol diffusion diameter, and the water resistance evaluation result.

Comparative Example 1 PFA powder coating (average particle size 6
3 μm) was electrostatically coated on an aluminum plate and baked at 310 ° C. for 20 minutes to obtain an article having a PFA resin surface. The water transfer angle of the surface of this article was 23/500. The maximum isopropyl alcohol diffusion diameter was 16 mm.

Comparative Example 2 PFA obtained from emulsion polymerization
Water was added to the aqueous dispersion (average particle size of 0.17 μm) to dilute it to a solid content of 14 wt%, and this was spray-coated on an aluminum plate. This was dried at 120 ° C. for 20 minutes and then heat-treated at 360 ° C., which is the melting end temperature or higher, for 20 minutes to obtain an article having a PFA resin surface. An electron micrograph of the surface of the obtained article was heat-treated at a temperature equal to or higher than the melting end temperature of PFA. Therefore, as shown in FIG. 3, the PFA resin particles were entirely melted and there were no voids between the resin particles, resulting in a porous body. is not. The water transfer angle of this surface was 150/500. The maximum isopropyl alcohol diffusion diameter was 5.0 mm.

[Comparative Example 3] An aqueous PTFE dispersion (average particle diameter 0.22 µm) containing 3.6% of a surfactant by weight was diluted with water to a solid content of 20 wt%, and an aluminum plate was obtained. Spray painted. This was dried at 120 ° C. for 20 minutes to obtain an article having a PTFE resin surface. The water transfer angle of this surface could not be measured because water droplets were absorbed by the film.

Comparative Example 4 PFA obtained from emulsion polymerization
2 g of water and 2 g of ethanol were mixed with 3 g of the aqueous dispersion (average particle size of 0.17 μm) to coagulate, and then spray coated on an aluminum plate. After drying this at 120 ° C. for 20 minutes,
A product having a PFA resin surface was obtained by baking at 360 ° C. for 20 minutes. The water transfer angle of this surface was 115/500. Maximum isopropyl alcohol diffusion diameter is 5.0 mm
Met.

[Comparative Example 5] PFA powder coating (average particle size: 2)
5 μm) was electrostatically coated on an aluminum plate and baked at 360 ° C. for 20 minutes to obtain an article having a PFA resin surface. The water transfer angle of this surface was 115/500. The maximum isopropyl alcohol diffusion diameter was 5.0 mm.

Comparative Example 6 A 0.1 mm-thick film was cut from a billet obtained by compression-molding and molding PTFE molding powder (average particle size 26 μm). The water transfer angle of this film was 120/500. The maximum isopropyl alcohol diffusion diameter was 5.0 mm.

[0052]

[Table 2]

[0053]

According to the production method of the present invention, a fluorine-containing resin layer having a particularly high water repellency can be formed on the surface of an article by simple equipment or operation. It can be widely used for industrial applications such as water, and for construction and civil engineering applications to prevent stains on electric wires, insulators and building tiles, and prevent snow damage, icing and salt damage.

[Brief description of drawings]

FIG. 1 is an electron micrograph of the surface of a water-repellent fluororesin of the article of the present invention obtained by the method of Example 1. FIG. 1 shows the structure of particles and is a photograph replacing a drawing.

2 is an electron micrograph of the surface of the water-repellent fluororesin of the article of the present invention obtained by the method of Example 3. FIG. FIG. 2 shows the structure of particles and is a photograph as a drawing substitute.

FIG. 3 is an electron micrograph of a fluororesin surface of an article obtained by the method of Comparative Example 2. FIG. 3 shows the structure of particles and is a photograph as a drawing substitute.

Claims (4)

[Claims] 1. A DS of a fluororesin under the condition that water, an organic liquid or a mixed dispersion thereof containing the fluororesin particles is applied to an article so that the fluororesin particles can contact each other.
Formed by stacking of fluorine-containing resin particles having an average particle diameter of 40 μm or less, which comprises drying the dispersion liquid at a temperature not higher than the melting start temperature measured by C to fix the fluorine-containing resin particles to the article surface in a non-melted state. Maximum I
A method for producing an article having a water-repellent fluororesin surface, which is characterized by comprising a non-shaped porous body having a PA diffusion diameter of 8 mm or more and having a tangent value of a water transfer angle of 50/500 or less. 2. The fluorine-containing resin particles are polytetrafluoroethylene (PTFE) resin, tetrafluoroethylene.
Perfluoro (alkyl vinyl ether) copolymer (P
FA) resin or tetrafluoroethylene / hexafluoropropylene copolymer (FEP) resin. The method for producing an article having a water-repellent fluororesin surface according to claim 1. 3. The method for producing an article having a water-repellent fluororesin surface according to claim 1, wherein the fluororesin particles have a molecular weight of 100,000 or more. 4. A fluororesin particle having an average particle diameter of 40 μm or less is aggregated, and water, an organic liquid or a mixed dispersion liquid thereof containing the fluororesin agglomerate particle is applied to an article. A method for producing an article having a water-repellent fluororesin surface according to claim 1.