JPH07228822A - Production of article having water-repellent fluororesin surface - Google Patents

Abstract

PURPOSE:To obtain the subject article excellent in water repellency with water droplets and concomitant stains less apt to stick thereto, and high in the adhesive strength to base; material articles. CONSTITUTION:This article consists of an undefined porous form >=8mm in the maximum IPA diffusion diameter built by mutual stacking fluororesin particles <=40mu m in average diameter and has the tangent value of contact angle of <=50/500. This porous form can be obtained by mutual surface fusing of the fluororesin particles at a temperature between the melting initiation temperature and the melting termination temperature both determined by differential scanning colorimetry(DSC) for the fluororesin under such a status as to enable mutual contact of the fluororesin particles. By this method, the porous form constituted of undefined fluororesin structure and voids can be obtained.

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 an 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, an attempt has been made to increase the apparent contact angle with water by making the actual surface area larger than the apparent surface area due to the fine protrusions present 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 view of such a situation, the inventors of the present invention heat-treat high molecular weight fluorine-containing resin particles having a specific particle diameter at a specific temperature to cause surface fusion, and the non-adhesion of these particles causes non-adhesion. It has been found that a shaped porous body is formed and an article having excellent water repellency can be obtained.

Therefore, it is an object of the present invention to provide a method for producing an article having a fluorine-containing resin surface, which has dramatically improved water repellency and antifouling property as compared with the prior art.

[0010]

DISCLOSURE OF THE INVENTION The present invention provides a method for producing a fluororesin containing D-containing fluororesin particles under the condition that they can contact each other.
Maximum IPA diffusion diameter formed by stacking fluorine-containing resin particles having an average particle diameter of 40 μm or less, which consists of surface-fusing fluorine-containing resin particles to each other at a temperature not lower than the melting start temperature and not higher than the melting end temperature measured by SC. Is 8m
Provided is a method for producing an article having a water-repellent fluororesin surface, which is composed of an amorphous porous body having a diameter of m or more and has a tangent value of a water transfer angle of 50/500 or less.

The method for bringing the fluororesin particles into contact with each other is not particularly limited, and the article is spray-coated with water, an organic liquid or a mixed dispersion thereof containing the fluororesin particles having an average particle diameter of 40 μm or less. The fluororesin particles may be applied to the surface by a method such as the above or a method of electrostatically coating 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 the molecule, such as polytetrafluoroethylene (PTFE) resin and tetrafluoroethylene.
Perfluoro resins such as hexafluoropropylene copolymer (FEP) resin and tetrafluoroethylene / perfluoro (alkyl vinyl ether) copolymer (PFA, C _{1 to} C ₅ 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 characteristic of the amorphous porous body produced by the production method of the present invention that individual fluorine-containing resin particles having an average particle diameter of 40 μm or less in a state of surface heat-sealing can be observed in the structure. On the other hand, since the fluorine-containing resin particles are entirely fused on the surface of the article obtained by fusing the fluorine-containing resin particles to each other at a temperature equal to or higher than the melting end temperature (FIG. 3), such voids should be present. No porous body is formed.

(Average Particle Diameter) In such a fluororesin porous material, the fluororesin particles forming the porous material must have an average particle diameter (d ₅₀ ) of 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. The more preferable particle size suitable for stacking varies depending on the coating method, but is 0.1 to 0.1 in spray coating.
20 μm particle size, 20 to 30 in electrostatic coating
A particle size of μm is preferred. 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 directly obtained 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 refers to adhering the fluorine-containing resin particles or a dispersion liquid containing the fluorine-containing resin particles onto the surface of an article by a method used for paints. Examples of the method for coating the surface of the article with the fluorine-containing resin particles having an average particle size of 40 μm or less include spray coating, electrostatic coating and dipping. 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. Further, after aggregating agent such as ethanol is added to the aqueous dispersion to agglomerate the particles, spray coating may be performed, or powder coating of PFA or FEP having an average particle diameter of about 25 μm may be electrostatically coated as it is. .

(Dispersion medium) In the method for producing a water-repellent article of the present invention, colloidal particles directly obtained from emulsion polymerization, and further aggregated particles obtained by aggregating these with ethanol or 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 an amount to be used as an emulsifier when the resin is produced by emulsion polymerization.

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

(Surface fusion temperature) An amorphous porous body can be obtained by mutually surface-adhesing the fluorine-containing resin particles applied to the surface of the article, but the fluorine-containing resin particles having an average particle diameter of 40 μm or less It is necessary to strictly control the heat treatment temperature in order to form a porous body by the surface fusion and to increase the strength of the film itself and the adhesion strength with the article.

After the dispersion containing the fluororesin particles is sprayed and applied to the article and the temperature is raised, the dispersion medium is evaporated and the residual fluororesin particles are piled up to form an amorphous porous article on the article. The body is formed. Below the melting start temperature measured by DSC, the particles are not yet surface-fused to each other, so that the porosity is large and the water repellency is high, but the strength is weak. However, when the temperature exceeds the melting start temperature, the surfaces of the particles are fused to each other, the porosity is gradually reduced, and the water repellency is slightly reduced as compared with that before the surface fusion, but the strength is increased. However, if the temperature is further raised and heated at a temperature higher than the melting end temperature for a long time, the fluorine-containing resin particles are entirely fused and the porous body disappears, the surface becomes smooth, and the water repellency is remarkably lowered. In the method of the present invention in which the heat treatment is carried out at a temperature not lower than the melting start temperature and not higher than the melting end temperature, the fluorine-containing resin particles are surface-fused to each other, have an appropriate porosity, and have a sufficiently large fusion strength. A body is obtained. It is usually sufficient that the time for surface fusion of the particles is 10 minutes or more, particularly 15 to 2
About 0 minutes is desirable.

In order to retain the porous material, two or more kinds of fluorine-containing resin particles, for example, a PTFE resin as the pore-forming particles and a heat-melting PFA resin or FEP resin as an auxiliary material can be used. The surface fusion is carried out at a temperature not lower than the melting start temperature of the PTFE resin and not higher than the melting end temperature, based on the PTFE resin having a high melting end temperature.

(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 substrate, and 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 material of the present invention has a fluorinated resin 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 layer.
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 water repellency on the surface of a highly water repellent article as in 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 cutting film made of PTFE measures about 110 degrees by the contact angle method, but 120 /
A value of 500 is shown. The water transfer angle of the article surface of the present invention is 50 /
It shows 500 or less.

(Substrate Article) When the surface of the water-repellent fluororesin is formed by the production 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, and a substrate article. 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 fluororesin particles, generally a temperature of 100 ° C. or higher. Then, after forming an adhesive layer or a primer layer on these base materials as a pretreatment, the fluororesin particles may be stacked.

[0030]

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 The fluorine-containing resin used as a raw material is shown in Table 1. Where T
1: melting start temperature, Tpeak: melting peak temperature, T2: melting end temperature (° C).

[0032]

[Table 1]

<Average particle size> Average particle size 5 to 300 μm
Microtrac method: LEEDS & NORTHRUP Microtrac Particle Size Analyzer model 7991-
Measured by 01. For particles with an average particle size of 0.5 μm or less, the turbidity method: measured with a Shimadzu Multipurpose 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
The aluminum plate having a thickness of 2 mm, a width of 50 mm, and a length of 100 mm was spray-coated with the air pressure. <Electrostatic coating> Electrostatic coating machine (GX by Onoda Cement Co., Ltd.)
-200T) and electrostatic powder coating gun (GX-107 manufactured by Onoda Cement Co., Ltd.) were used to coat the powder with a voltage of 10
Electrostatic spraying was applied to an aluminum plate having a thickness of 2 mm, a width of 50 mm, and a length of 100 mm, which was grounded at a distance of 25 cm at a discharge rate of about 50 g / min and a Kv (negative).

(4) Method of measuring water divergence angle An aluminum plate having a length of 550 mm and a porous body formed thereon by raising one of the plates (width 5)
(0 mm length 100 mm), and a drop of 0.05 g of distilled water is dropped from the nozzle on this surface 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 (Maximum Isopropyl Alcohol Diffusion Diameter Test) 0.01 ml of IPA is dropped onto an amorphous porous body using a microsyringe, and the maximum diffusion diameter (mm) of the liquid is measured. In the case of a porous material, IPA penetrates into the coating film and diffuses from the diameter at the time of dropping to a diameter of about 20 mm.
For TFE cut sheets, the initial diameter remains about 5.0 mm.

Example 1 PFA obtained from emulsion polymerization
The aqueous dispersion (average particle size 0.17 μm) was spray-coated on an aluminum plate. This was dried at 120 ° C. for 20 minutes and then heat-treated at 310 ° C. for 20 minutes to obtain an article having a water repellent PFA resin surface. An electron micrograph of the surface of the obtained article is as shown in FIG. 1, in which PFA resin particles having a fine particle diameter are surface-fused and stacked on each other, and voids are formed between the resin particles, resulting in an irregularly shaped porous material. It has become a body.
The water transfer angle of this surface was 1/500. The maximum isopropyl alcohol diffusion diameter was 23 mm.

When water droplets are dropped on the thus produced amorphous porous body, the water droplets are in contact with the fluorine-containing resin only at the protrusions of the amorphous porous body, so that they have extremely high water repellency and are wet with water. The angle was about 150 degrees or more. The results are shown in Table 2 together with the results of 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 size 0.16 μm), and the mixture was thoroughly ultrasonically mixed and coagulated.
Spray painted on aluminum plate. 20 at 120 ℃
After drying for 1 minute, it was heat-treated at 260 ° C. for 20 minutes to obtain an article having a water-repellent FEP resin surface. The water transfer angle of this surface was 3/500. The maximum isopropyl alcohol diffusion diameter was 20 mm.

Example 3 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 wt%. This was spray-painted on an aluminum plate. This was dried at 120 ° C. for 20 minutes and then further heat-treated at 340 ° C. for 20 minutes to obtain an article having a water-repellent PTFE resin surface. The diversion angle of this surface is 1/50
It was 0. Maximum isopropyl alcohol diffusion diameter is 16
It was mm.

Example 4 PFA obtained from emulsion polymerization
1 g of aqueous dispersion (average particle size 0.17 μm) and PTFE
1 g of molding powder (average particle size 26 μm) was dispersed and mixed in 5 g of ethanol, and spray-coated on an aluminum plate. This was dried at 120 ° C. for 20 minutes and then heat-treated at 350 ° C. for 20 minutes to obtain an article having a water-repellent fluororesin surface. The water transfer angle of this surface was 12/500. The maximum isopropyl alcohol diffusion diameter was 8 mm.

In this experiment, since two kinds of fluorine-containing resin particles having different melting points were used as raw materials and heat-treated at 350 ° C., the PFA resin was melted, but the high melting point PTFE was used.
Since it was below the melting end temperature of the resin, a porous PTFE body was formed, and an article having a surface excellent in strength and water repellency was obtained.

[Example 5] PFA powder coating (average particle size: 2)
5 μm) was electrostatically coated on an aluminum plate and baked at 310 ° C. for 20 minutes to obtain an article having a water repellent PFA resin surface. As shown in FIG. 2, an electron micrograph of the surface of the obtained article shows that PFA resin particles having a fine particle diameter are surface-fused and stacked on each other to form a porous body having voids between the resin particles. The water transfer angle of this surface was 7/500.
The maximum isopropyl alcohol diffusion diameter was 20 mm.

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 this surface was 23/500. The maximum isopropyl alcohol diffusion diameter was 16 mm.

Comparative Example 2 PFA obtained from emulsion polymerization
The aqueous dispersion (average particle size 0.17 μm) was spray-coated on an aluminum plate. After drying at 120 ℃ for 20 minutes, heat treatment at 360 ℃ above melting end temperature for 20 minutes to PFA
An article having a resin surface was obtained. Since the heat treatment was performed at a temperature higher than the melting end temperature of PFA, the electron micrograph of the surface of the obtained article showed that 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 size 0.22 µm) containing 3.6% of a surfactant based on the weight of particles was diluted with water to a solid content of 20% by weight, 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 film having a thickness of 0.1 mm was cut from a billet obtained by compression-molding PTFE molding powder (average particle size: 26 µm) and firing it. The water transfer angle of this film was 120/500. The maximum isopropyl alcohol diffusion diameter was 5.0 mm.

[0051]

[Table 2]

[0052]

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

[Brief description of drawings]

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.

2 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 5. FIG.

FIG. 3 is an electron micrograph of a fluororesin surface of an article obtained by the method of Comparative Example 2.

Claims (6)

[Claims] 1. Surface fusion of fluororesin particles to each other at a temperature not lower than the melting start temperature and not higher than the melting end temperature measured by DSC of the fluororesin under the condition that the fluororesin particles can contact each other. Which is composed of an amorphous porous body having a maximum IPA diffusion diameter of 8 mm or more, which is formed by stacking fluororesins having an average particle diameter of 40 μm or less, and has a tangent value of a water transfer angle of 50/500 or less. Which is a water-repellent fluororesin surface. 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. An article is coated with water, an organic liquid, or a mixed dispersion thereof containing fluorine-containing resin particles having an average particle diameter of 40 μm or less, and the fluorine-containing resin particles are surface-fused to each other. A method for producing an article having a water-repellent fluororesin surface according to claim 1. 5. Fluorine-containing resin particles having an average particle diameter of 40 μm or less are aggregated, and then water, an organic liquid or a mixed dispersion thereof containing the fluorine-containing resin aggregated particles is applied to an article to form fluorine-containing resin particles. The method for producing an article having a water-repellent fluororesin surface according to any one of claims 1 to 4, wherein the surfaces are fused with each other. 6. The water-repellent fluororesin surface according to claim 1, wherein the fluororesin particles having an average particle diameter of 40 μm or less are electrostatically coated and the fluororesin particles are surface-fused to each other. Method for manufacturing possessed article