JPH09104772A - Form with water-repellent fluororesin surface - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a highly water-repellent surface on a foam to inhibit water from permeating into the foam and from icing on its surface in cold districts. SOLUTION: This foam has a water-repellent fluororesin surface which comprises an amorphous porous body having an uneven surface and formed by heaping fluororesin particles having an average particle size of 1μm or lower. The surface has a tangent value of a water-rolling angle (the smallest inclination of a surface causing water droplets to roll down there along) of 50/500 or lower and is formed by dispersing fluororesin particles in a medium comprising water, an org. solvent, or their mixture contg. 0.5wt.% or lower (based on the particles) surfactant, applying the resultant dispersion to the surface of a foam, and drying the foam at a temp. lower than the fusion-starting temp. of the particles in such a state that the particles can be in contact with each other, thus fixing the particles to the surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a foam having a superhydrophobic surface, and more particularly to a foam applicable to industrial fields such as electrical, mechanical, chemical and various household appliances and equipment. The present invention relates to a foam having an aqueous fluororesin surface.

[0002]

2. Description of the Related Art Foams such as synthetic resin foams and elastic foams are used as heat insulating materials, electric insulating materials, soundproofing materials, buoyancy materials, weight reducing materials, shock absorbing materials, etc. Widely used in equipment. However, there is a problem that these performances are lost when water penetrates into the bubbles of the foam.

Therefore, in order to prevent such performance deterioration due to water penetration, a compound having a fluorinated alkyl, a silicon compound, and a compound having a long-chain alkyl group are often fixed to the surface of the foam to thereby fix the surface of the foam. Have been made to have water repellency or waterproofness (Japanese Patent Publication No. 4-74392, JP-A-3-14923).
No. 5 publication). However, the contact angle of water on the surface of the foam obtained by such a method is usually in the range of 100 to 110 degrees, and the water repellency was not sufficient for the above purpose of preventing water from entering.

Further, there are problems that the water repellent treatment agent is decomposed by light or invasion of water, and mold is generated. Furthermore, when used in extremely cold regions, water droplets adhering to the surface of the foam may have a problem of freezing, so there has been a demand for a method of imparting high water repellency such that the water droplets roll off the surface of the foam before freezing. .

[0005]

On the other hand, the inventor of the present invention has previously found that a fluororesin comprising an amorphous porous body having an irregular surface formed by stacking fluororesin particles having an average particle diameter of 40 μm or less with each other. It was found that an article having a high water repellency can be obtained by forming the surface on the article surface, and the article and the manufacturing method thereof were proposed. The application of the application method was examined.

As a result, when fluorine-containing resin particles having a smaller average particle diameter are used in the above method and applied to foams such as synthetic resin foams and foamed elastic bodies, excellent effects are exhibited. The inventors have found a method for preventing the freezing of water droplets adhering to the surface of a foam and imparting super-water repellency to the foam by a synergistic effect with the heat insulating property of the foam in use in an extremely cold region, and arrived at the present invention. Therefore, the object of the present invention is not only to further enhance the effect of preventing permeation of water into the inside of the foam, which is the above-mentioned problem, by imparting superhydrophobicity to the foam, but also to newly add a foam of water droplets in an extremely cold region. It is an object of the present invention to provide a foam capable of preventing the formation of ice on the surface and a method for producing the foam.

[0007]

Means for Solving the Problems The foam of the present invention comprises an amorphous porous body having an irregular surface formed by mutual stacking of fluorine-containing resin particles having an average particle diameter of 1 μm or less. The present invention relates to a foam having a surface of a water-repellent fluororesin having a tangent value of 50/500 or less. The present invention also relates to fluororesin particles obtained by dispersing fluororesin particles in a dispersion medium composed of water, an organic liquid or a mixture thereof containing 0.5% by weight or less of a surfactant based on the weight of the fluororesin particles. The above water-repellent agent is formed by applying the dispersion liquid to a foam and drying and fixing the fluororesin particles on the surface of the foam at a temperature not higher than the melting start temperature of the fluororesin under the condition that they can contact each other. Provided is a method for producing a foam having a fluororesin surface.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION

(Fluorine-containing resin particles) The fluorine-containing resin particles used in the present invention are particles of a thermoplastic resin containing at least one fluorine atom in the molecule, and specifically, tetrafluoroethylene, chlorotrifluoro Refers to particles of homopolymers or copolymers of ethylene and vinylidene fluoride. Examples of preferable fluorine-containing resin particles include polytetrafluoroethylene (PTFE) resin, tetrafluoroethylene / hexafluoropropylene copolymer (FEP) resin, tetrafluoroethylene / perfluoro (alkyl vinyl ether) copolymer (PFA: perfluoroethylene). Examples of the fluoroalkyl group include perfluoro resins such as C _{1 to} C ₅ ) resins and tetrafluoroethylene / ethylene copolymer (ETFE).

(Average Particle Diameter) Further, the above-mentioned fluorine-containing resin particles have an average particle diameter of 1 μm or less. Such fine particles of fluorine-containing resin are usually present only in a liquid medium, and when they are in a dry state, they become aggregates in which the particles are stacked on each other. The fluorine-containing resin particles thus obtained form a highly water-repellent surface made of an amorphous porous body. The present invention utilizes such a principle. On the other hand, in the fluorine-containing resin particles having an average particle diameter of more than 1 μm, it becomes difficult for the particles to agglomerate with each other, or even if they agglomerate, the aggregating force is weak, so that the obtained porous body is easily disintegrated. However, the water-repellent surface firmly fixed to the foam object of the present invention cannot be obtained.

Specific examples of the fluorine-containing resin particles used include an average particle diameter of 0.1 to 0.5 μm obtained by emulsion polymerization.
m colloidal particles and aggregated particles of the colloidal particles,
Further, particles obtained by deagglomerating aggregated particles in an organic liquid may be mentioned.

(Dispersion Medium) In order to produce a foam having a surface of the water-repellent fluororesin of the present invention, first, a dispersion liquid in which fluororesin particles are dispersed in a dispersion medium is prepared. As the dispersion medium, water, an organic liquid, or a mixture thereof can be used, but it is preferable to use water as the dispersion medium in terms of flammability and environmental hygiene. For example, an aqueous dispersion of a fluorine-containing resin produced by an emulsion polymerization method as described in US Pat. No. 2,559,752 can be exemplified as a particularly preferable one.

A surfactant such as P-alkylphenyl polyethylene glycol ether may be added for the purpose of stabilizing the above-mentioned dispersion liquid, but if a large amount of this is added, the water repellency of the foam of the present invention is lowered. Therefore, it is not preferable. In order to prepare a stable dispersion liquid without substantially lowering the water repellency, the amount of the surfactant added is preferably 0.5% by weight or less based on the weight of the fluororesin particles.

(Film forming auxiliary agent) The fluorine-containing resin dispersion is
A film forming auxiliary agent for forming a stronger film of the amorphous porous body may be contained. The film-forming auxiliary is dissolved or dispersed in the fluororesin dispersion and applied to the foam. What is used as a film-forming auxiliary is not particularly limited as long as it has film-forming properties at a temperature below the melting start temperature of the fluororesin, and various organic film-forming compounds or inorganic film-forming compounds are used. To be

Examples of the organic film-forming compound include acrylic resin, polyimide precursor, aminosilane, tetrafluoroethylene / vinyl acetate copolymer, alkyd resin,
Organic polymers such as epoxy resin, polyamide resin, polyimide resin, polysulfonic acid resin, silicone resin, acrylic silicone resin, and polyester resin are used.

Examples of the inorganic film-forming compound include colloidal silica, lithium silicate, alumina sol and zirconia sol. These organic film-forming compounds or inorganic film-forming compounds may be used alone, or two or more kinds of film-forming auxiliary agents may be mixed and used.

When a film-forming auxiliary agent is used, the amount of the film-forming auxiliary agent used varies depending on the type of the film-forming auxiliary agent, but the amount of the film-forming auxiliary agent is preferably 150% by weight or less based on the weight of the fluororesin particles.

(Fungicide and UV Absorber) The fluororesin dispersion liquid may contain various fungicides and / or various UV absorbers depending on the application. The bactericidal agent and / or the film forming auxiliary agent is dissolved or dispersed in the fluororesin dispersion liquid and applied to the foam. A foam with a water-repellent fluorine-containing resin surface consisting of an amorphic porous body containing a bactericide prevents bacteria from growing, reduces water repellency and prevents dirt from adhering, and has an amorphous porous shape containing an ultraviolet absorber. A foam having a water-repellent fluororesin surface composed of a body is particularly effective as a building material because the foam is prevented from deterioration and the usable period is extended. There is no particular limitation on what is used as the bactericidal agent and the ultraviolet absorber as long as the effect is not lost at a temperature below the melting start temperature of the fluororesin.

(Foam) The foam used as the substrate of the present invention is a synthetic resin foam or a foamed elastic material, and synthetic resin foams such as polyolefin, polystyrene and polyvinyl chloride, or polyurethane, natural rubber, and synthetic rubber. A foamed elastic body such as rubber can be used. Either closed cells or open cells may be used, but closed cells having a pore diameter of 5 to 500 μm are preferable. It is more preferable that the pore size distribution of the foam is narrow. A foam having an average pore size of more than 500 μm has large irregularities in the foam, so that water droplets easily accumulate in the recesses regardless of the surface condition of the water-repellent fluororesin surface, and the water repellency and stain resistance of the foam surface are less likely to be exhibited. Tends to become.

(Coating of Dispersion Liquid) The fluorine-containing resin is laminated on each other by spray coating, electrostatic coating or dipping of water, an organic liquid or a dispersion liquid of fluorine-containing resin particles having an average particle diameter of 1.0 μm or less. And the like, and the fluororesin particles are dried and fixed in a non-molten state. The coating method is not particularly limited, and any method may be used as long as it can form a structure in which the fluorine-containing resins are stacked in layers.

(Drying Method) It is necessary to fix the fluororesin particles in a non-molten state on the foam surface in order to form a structure by stacking the fluororesin particles on the foam surface. Therefore, under the condition that the fluororesin particles can contact each other, the melting start temperature (T
₁ ) Dry and fix on the foam surface at the following temperature. When the heat treatment is performed at a temperature higher than the melting start temperature, the surface of the fluorine-containing resin particles is fused, the porosity is reduced, the amorphous porous material disappears, the surface becomes smooth, and the water repellency is reduced, which is not preferable. Further, since the foamed material which is the base material generally has lower heat resistance than the fluororesin, the foamed material may be melted or thermally decomposed at a temperature higher than the melting start temperature of the fluororesin. In the present invention, the particle diameter of the fluororesin particles is 0.1 μm or less, and in the case of the dispersion liquid of the fluororesin particles of the present invention having such a fine particle diameter, it is dried at a temperature not higher than the melting start temperature. The fluororesin particles can be fixed to the surface of the foam only by itself.

As shown in FIGS. 1 and 2 which are electron micrographs of the surface of the porous body manufactured by such a method, the porous body is composed of an amorphous fluororesin structure and micron-order voids. It is something. In FIG. 1, an uneven surface (white portions are convex portions, black portions are concave portions) is observed, and in the enlarged FIG. 2, it can be observed that individual fluorine-containing resin particles that are not easily removed are stacked as white spherical particles.

(Water repellency) The surface of the foam of the present invention exhibits extremely excellent water repellency. For example, the contact angle with water is usually 150 degrees or more. Since the foam of the present invention has high water repellency as described above, it is difficult to compare the water repellency by a commonly used contact angle measuring method. Therefore, by the method described below,
That is, when a water drop is dropped on the surface of a foam, the water drop does not adhere to the surface and the water rolls on the surface. The minimum angle of the foam surface is measured, and the angle (water transfer angle) is expressed as a tangent value (tangent). It was used as a scale.

For example, a cutting film made of PTFE shows a value of about 120/500 at the water transfer angle, although about 110 degrees is measured by the contact angle measuring method. The water transfer angle of the foam of the present invention is 50/500 (angle about 5.7 degrees) or less.

The foam having the surface of the fluororesin of the present invention has such excellent water repellency and therefore can prevent the icing of water droplets in cold and extremely cold regions. That is, when the foam surface comes into contact with water droplets in cold and extremely cold regions, due to the effect of the excellent water repellency and the heat insulating property of the foam, the water droplets are not allowed to adhere to the surface of the foam before the water droplets are frozen on the surface of the foam. It is because it can be excluded from. This is an excellent advantage of the present invention, the water-repellent effect of the fluorine-containing resin surface consisting of an amorphous porous body, by applying to the foam,
Particularly remarkable.

[0025]

EXAMPLES The present invention will be specifically described with reference to Examples and Comparative Examples below. The physical properties, coating method, and water transfer angle measuring method of the raw material fluorine-containing resins used in Examples and Comparative Examples are as follows.

1. Fluorine-Containing Resin Particles Table 1 shows the types of fluororesin particles used in the present invention and their physical properties. Of the DSC melting temperatures, T ₁ is the melting start temperature, Tpeak is the melting peak temperature, and T ₂ is the melting end temperature (° C.).

[0027]

[Table 1]

(1) Method of measuring average particle size The average particle size was measured by a turbidity method (Shimadzu multipurpose self-spectrophotometer (halogen lamp)).

(2) DSC melting temperature measuring method A DSC7 type differential scanning calorimeter manufactured by Perkin Elmer was used. A 5 g sample is weighed and placed in a dedicated aluminum pan, crimped by a dedicated crimper, and then stored in the DSC body to start heating. From 200 ℃ to 380 ℃ 10 ℃
The temperature was raised at a heating rate of 1 / min, and the melting start temperature (T ₁ ), melting peak temperature (Tpeak) and melting end temperature (T ₂ ) were determined from the melting curves obtained at this time.

2. Coating method (1) Spray coating: Thickness 2 mm x width 50 mm x length 1
3 mm with a nozzle of 0.6 mm in diameter on a foam of 00 mm
The fluoropolymer aqueous emulsion was spray coated at an air pressure of g / cm ² G.

(2) Immersion: A foam having a thickness of 2 mm, a width of 50 mm, and a length of 100 mm was immersed in an aqueous fluoropolymer emulsion held at 5 ° C., and then an excessive aqueous fluoropolymer emulsion was squeezed out. .

3. Method of Measuring Water Transfer Angle A slope is created by raising one of the plates having a length of 500 mm, a test piece is placed on this, and 0.05 g of distilled water is dropped from 8 mm above the test piece using a syringe. When this water drop falls on the test piece,
The minimum slope that does not adhere to the test piece and rolls along the slope is represented by the distance (mm) increased with respect to the horizontal distance of 500 mm, that is, the tangent value of the slope angle.

[Example 1] A PFA aqueous emulsion having a solid content of 14% by weight (average particle diameter 0.17 µm) obtained by emulsion polymerization was mixed with an average cell pore size of natural rubber 25
A 0 μm foam (trade name: Crocel made by Shinoda Rubber) was spray-painted. The foam was dried at 30 ° C. for 20 minutes, and the water repellency was measured. The water transfer angle of this foam is 1/5
00. It is shown in Table 2 together with the results of other examples. 1 and 2 are electron micrographs of the surface of the foam.
It can be seen from FIGS. 1 and 2 that an amorphous porous body having an uneven surface (white portions are convex portions and black portions are concave portions) is formed. Further, in FIG. 2 which is magnified by about 2 times, it is clearly observed that the fluororesin particles are fixed on the surface of the foam as white spherical particles.

Example 2 An aqueous PFA emulsion having a solid content of 14% by weight (average particle size 0.17 μm) obtained by emulsion polymerization was added to a film-forming reinforcing agent in an amount of 10% by weight of tetrafluoroethylene based on the weight of PFA. A vinyl acetate copolymer (hereinafter referred to as FV polymer) was mixed and spray-painted on a foam made of natural rubber having an average pore size of 250 μm (trade name: Crocel made by Shinoda Rubber). The foam was dried at 30 ° C. for 20 minutes, and the water repellency was measured. The water transfer angle of this foam was 1/500. It is shown in Table 2 together with the results of other examples.

Example 3 The same PFA obtained by emulsion polymerization as used in Example 1 was coagulated and dried, and then the PFA organosol having a solid content of 14% by weight dispersed in an organic solvent was used to prepare an average pore diameter of natural rubber. A 250 μm foam (trade name: Crocel made by Shinoda Rubber) was spray-painted. The foam was dried at 30 ° C. for 20 minutes, and the water repellency was measured. The water transfer angle of this foam was 1/500. It is shown in Table 2 together with the results of other examples.

Example 4 An aqueous PTFE emulsion having a solid content of 23% by weight (average particle size 0.22 μm) obtained by emulsion polymerization was added to an average pore size 250 μm of natural rubber.
m foam (trade name: Crocel made by Shinoda Rubber) was spray-painted. The foam was dried at 30 ° C. for 20 minutes, and the water repellency was measured. The water transfer angle of this foam was 1/500. It is shown in Table 2 together with the results of other examples.

Example 5 A PFA aqueous emulsion having a solid content of 23% by weight (average particle diameter 0.17 μm) obtained by emulsion polymerization was added as a stabilizer in an amount of 0.4% by weight of TRITON X-based on the weight of PTFE. 100 (Rohm
& Hass Triton X-100) are mixed,
A foam made of silicone rubber and having an average pore size of 100 μm (SE-200 manufactured by Sun Polymer) was spray-coated. The foam was dried at 30 ° C. for 20 minutes, and the water repellency was measured. The water transfer angle of this foam was 1/500.
It shows in Table 3 with the result of a comparative example.

Comparative Example 1 A PTFE aqueous emulsion having a solid content of 23% by weight (average particle size 0.17 μm) obtained by emulsion polymerization was added as a stabilizer with 2.0% by weight of TRITON X-based on the weight of PTFE. 100 (Rohm
& Hass Triton X-100) are mixed,
A foam made of soft urethane and having an average pore size of 500 μm (manufactured by Toyo Tire & Rubber) was immersed in the PTFE aqueous emulsion at 5 ° C. The foam was dried at 30 ° C. for 20 minutes, and the water repellency was measured. Since a large amount of the stabilizer was used, the water repellency was insufficient and the foam contained water droplets. The water transfer angle of this foam could not be measured. The results are shown in Table 3 together with the results of other comparative examples.

[Comparative Example 2] A foam made of the natural rubber used in Example 1 and having an average pore size of 250 μm (made by Shinoda Rubber).
The water repellency of the surface was measured without carrying out the fluorine-containing resin surface forming treatment of the present invention as it is (trade name: Crocel). The water transfer angle of this foam could not be measured, and the foam contained water droplets. Table 3 shows the results.

[Comparative Example 3] The foam made of silicone rubber having an average pore size of 100 µm (SE-200 manufactured by Sun Polymer) used in Example 5 was used as it was without the fluorine-containing resin surface forming treatment of the present invention. Was measured for water repellency. The water transfer angle of this foam could not be measured, and the foam contained water droplets. Table 3 shows the results.

[0041]

[Table 2]

[0042]

[Table 3]

[0043]

INDUSTRIAL APPLICABILITY According to the present invention, a highly water-repellent surface can be formed on the surface of a foam, so that it has a great effect of preventing water from penetrating into the inside of the foam, and the surface of the foam of water drops in extremely cold regions. The effect of preventing icing on the ice is particularly remarkable,
It can be used for industrial fields such as electricity, machinery, and chemistry, and various household appliances and devices.

[Brief description of the drawings]

FIG. 1 is an electron micrograph of the surface of a foam having a water-repellent fluororesin surface of the present invention.

FIG. 2 is an electron micrograph obtained by further enlarging FIG.

Claims (4)

[Claims] 1. A non-shaped porous body having an irregular surface formed by stacking fluorine-containing resin particles having an average particle diameter of 1 μm or less, and having a tangent value of a water transfer angle of 50/50.
A foam having a water-repellent fluororesin surface of 0 or less. 2. The fluororesin particles are polytetrafluoroethylene resin, polytetrafluoroethylene / perfluoro (alkyl vinyl ether) copolymer resin or polytetrafluoroethylene / hexafluoropropylene copolymer resin. A foam having the surface of the water-repellent fluororesin according to claim 1. 3. A fluororesin in which the fluororesin particles are dispersed in a dispersion medium composed of water, an organic liquid or a mixture thereof containing 0.5% by weight or less of a surfactant based on the weight of the fluororesin particles. A method in which the particle dispersion is applied to a foam, and the fluororesin particles are dried and fixed on the surface of the foam at a temperature not higher than the melting start temperature of the fluororesin under the condition that they can contact each other. 2) A method for producing a foam having a surface of a water-repellent fluororesin according to 2). 4. The water-repellent fluororesin surface according to claim 3, wherein the fluororesin particle dispersion contains 150% by weight or less of a film-forming auxiliary agent based on the weight of the fluororesin particles. Method for producing foam.