JP3963541B2 - Solar irradiation type air cleaning sheet and air purification method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a solar irradiation type air cleaning sheet and an air purification method using the air cleaning sheet , and is particularly useful for deodorization in an automobile.
[0002]
[Prior art]
When photocatalyst fine particles such as titanium oxide, which is an oxide semiconductor, are irradiated with light having energy greater than the band gap, electrons and holes are generated by excitation, and organic substances and microorganisms close to the surface are decomposed by oxidation, resulting in inorganic oxidation. In the product, it is oxidized to the final oxide.
Therefore, it has been proposed that indoor air is brought into contact with a photocatalyst body carrying the photocatalyst fine particles with a binder to decompose odorous components in the air to perform deodorization or air purification. In this case, there are a case of using sunlight and a case of using an ultraviolet generator such as black light as an ultraviolet ray source for exciting (activating) the photocatalyst fine particles. It is convenient to use sunlight for purifying indoor air.
[0003]
In order to support the photocatalyst fine particles on the support, a method of fixing the photocatalyst fine particles to the support through a binder is usually used, and the binder is decomposed and degraded by the activated photocatalyst fine particles. Stability is required.
Therefore, many prior arts have been proposed. For example, a fluorine-based polymer such as a silicone-based polymer, a vinyl ether-fluoroolefin copolymer, or a vinyl ester-fluoroolefin copolymer is used as a binder. Has been proposed (Japanese Patent Laid-Open No. 7-171408).
In addition, since the air purification is based on a contact reaction on the surface of the photocatalyst, it is required to increase the contact area as much as possible, for example, a sheet-like photocatalyst is stacked with a gap, It has been proposed to condense a cylindrical photocatalyst body and use the gap as an air passage (Japanese Patent Laid-Open No. 7-251028).
[0004]
[Problems to be solved by the invention]
In automobiles, the so-called new car odor caused by the volatile gas from the interior material is disliked in the case of a new car. In the case of a car in use, the smell of tobacco adsorbed inside the interior material or the air conditioner is a problem. ing.
Conventionally, deodorizing materials mainly composed of an adsorbent such as activated carbon, zeolite, silica gel, and alumina have been used for deodorization of automobile interiors. However, the life of the deodorizing material is short and needs to be replaced with considerable frequency. It is awkward.
Thus, although it has been proposed to deodorize the cigarette odor with the above-mentioned photocatalyst (Japanese Patent Laid-Open No. 7-251028), the conventional photocatalyst has a small area of air contact per unit volume. -It is necessary to stack G-shaped photocatalysts with a gap, or to focus the cylindrical photocatalysts and use the gap as an air passage. In such a gap structure, air flows through the gap. In addition, a fan is required, and the cost of equipment is inevitably increased.
[0005]
In addition, when sunlight is used for the activation of the photocatalyst, the arrangement of the photocatalyst is limited to the vicinity of the window, and thus the installation space is necessarily limited. For example, in the case of an automobile, it is limited to a space between a windshield and a back mirror or in the vicinity of a rear window and that does not substantially obstruct the field of view, and the usable space is a vertical plane area of about 200 mm × 200 mm. Within range. However, with the conventional photocatalyst, it is difficult to satisfactorily deodorize the interior of the vehicle under the irradiation of sunlight with such a limited space.
[0006]
Therefore, as a result of intensive studies to make it possible to perform deodorization in an automobile with a photocatalyst under the use of sunlight, the present inventor has obtained a dispersion between polytetrafluoroethylene powder and photocatalyst fine particles. It was found that the photocatalyst layer obtained by applying and firing the applied layer exhibited a remarkably excellent deodorizing performance, and the inside of the vehicle can be effectively deodorized even in the small installation space. In order to elucidate the cause of this high deodorizing performance, when the structure of the photocatalyst layer was observed with a microscope, an air layer was present between the photocatalyst fine particles and the resin, and this air layer was connected to form a communication path. I knew that In this photocatalyst layer, voids are formed at the interface between the photocatalyst fine particles and the polytetrafluoroethylene resin. The reason is that there is a significant difference in thermal shrinkage between the polytetrafluoroethylene and the photocatalytic titanium oxide fine particles and the non-adhesion of the polytetrafluoroethylene. It is presumed that due to the non-adhesiveness of the interface, interfacial delamination occurs due to the large tensile stress due to the non-adhesiveness of the interface when cooling by firing heating.
[0007]
Conventionally, as a method for producing a photocatalyst, a solvent solution of a fluorine-based polymer such as vinyl ether-fluoroolefin copolymer or vinyl ester-fluoroolefin copolymer, a crosslinking agent such as an isocyanate curing agent, and photocatalyst fine particles is used. It is coated on a support and the coated layer is cured by a crosslinking reaction (Japanese Patent Laid-Open No. 7-171408), or a mixture of polytetrafluoroethylene particles, titanium dioxide and activated carbon is rolled into a sheet shape (special feature). No. 6-3156) is known, but in these, there is no process of generating shrinkage stress at the interface between the photocatalyst fine particles and the resin, and void generation at the interface cannot be expected at all.
[0008]
The object of the present invention is based on the findings of the above examination results, using sunlight with a photocatalyst in the interior of an automobile, and capable of deodorizing satisfactorily without disturbing the visibility of drivers and the like. An object of the present invention is to provide an air cleaning element and a method for purifying air.
[0009]
[Means for Solving the Problems]
The solar radiation-type air cleaning sheet according to the present invention is formed by applying a dispersion containing polytetrafluoroethylene powder and photocatalyst fine particles onto a support substrate and firing the resulting product to sinter the polytetrafluoroethylene powder. It has a porous photocatalyst layer, and the porosity of the porous photocatalyst layer is 7% or more due to interfacial delamination based on the difference in thermal expansion and shrinkage between the polytetrafluoroethylene powder and the photocatalyst fine particles. it has a structure, wherein, activated carbon, zeolites, or copper carboxymethyl cellulose - it is possible to stack the bets - deodorizing sheet mainly scan of one or more kinds.
The air purification method according to the present invention has a configuration characterized in that these solar light irradiation type air cleaning sheets are disposed indoors and irradiated with sunlight.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a sectional view of an air cleaning sheet A according to the present invention.
In FIG. 1, 1 is a support substrate. Reference numeral 2 denotes a photocatalyst layer provided on the support substrate 1, in which the photocatalyst fine particles are dispersed in the fired layer of the sintered polytetrafluoroethylene powder, and microvoids are formed between the resin and the photocatalyst fine particles. A gap between the joined polytetrafluoroethylene powders is connected to the air layer to form a multi-gap communication structure.
The thickness of the gap between the polytetrafluoroethylene resin and the photocatalyst fine particles is a fine gap of several nanometers to several microns, and the passage of water or the like does not occur due to the hydrophobicity of polytetrafluoroethylene. Air can flow in and out sufficiently.
[0011]
To produce an air cleaning sheet according to the present invention, a dispersion containing polytetrafluoroethylene powder and photocatalyst fine particles is applied to a support substrate, and the solvent in the coating layer is evaporated and removed by heating. The polytetrafluoroethylene particles are sintered by heating and baking (heating temperature is 330 ° C. or higher). Upon cooling after this sintering, the photocatalyst fine particles and the polytetrafluoroethylene resin are bonded to each other due to thermal contraction greater than that of the photocatalytic fine particles of the polytetrafluoroethylene resin and non-fusibility of the polytetrafluoroethylene resin to the photocatalytic fine particles. An air layer is formed between them.
In addition, since the polytetrafluoroethylene powder at the time of firing has a high melt viscosity (10 poise or more) and does not flow, the particle shape is maintained and the firing is performed without pressure. Sufficient gaps remain between the powders.
Therefore, the photocatalyst layer becomes a breathable multi-gap structure.
The particle diameter of the polytetrafluoroethylene powder is 0.1 to 1 μm, and the particle diameter of the photocatalyst fine particles is 200 nm or less, preferably 50 nm or less.
The porosity of the photocatalyst layer is 7% or more, preferably 10% or more. The porosity x is expressed as follows: ρ is the true specific gravity of the photocatalyst layer, and w is the weight of the volume v of the photocatalyst layer.
x = 1- [w / (vρ)]
Given in. When the porosity is less than 7%, the effect of improving the contact degree between the air and the photocatalyst fine particles due to the multi-pore structure is low, and it is difficult to satisfactorily deodorize the interior of the automobile, as will be apparent from the comparative examples described later. However, the mechanical strength is preferably 30% or less.
Moreover, it is preferable that the thickness of a photocatalyst layer shall be 3 micrometers-30 micrometers. If it is less than 3 μm, the volume of the photocatalyst layer is small and the deodorizing performance is low, and if it exceeds 30 μm, the gas diffusion efficiency is lowered and the layer thickness becomes thicker than necessary.
If the amount of the photocatalyst fine particles in the dispersion is too large, the binding strength between the photocatalyst fine particles by polytetrafluoroethylene becomes insufficient, so the content of the photocatalyst fine particles is preferably 5 to 60%.
[0012]
As the photocatalyst fine particles, it is preferable to use anatase-type titanium oxide fine particles exhibiting excellent photocatalytic activity. Further, alkali metal ions can be supported in order to increase the activity of the photocatalyst fine particles.
As the support substrate, a material having heat resistance that does not deform even when heated during firing is used. For example, metal foil such as aluminum and stainless steel, ceramic plate, inorganic plate such as glass plate, polyimide, A glass fiber or polyamide fiber fabric impregnated with a heat-resistant plastic film such as tetrafluoroethylene or a heat-resistant plastic such as polytetrafluoroethylene, or a felt-like material made of glass fiber, ceramic fiber, metal fiber, or carbon fiber alone or in combination. Glass fibers, ceramic fibers, metal fibers, carbon fibers alone or a mixture of nets can be used.
For applying the dispersion to the support substrate, a method of applying with a roll coater, a method of immersing and lifting the support substrate in the dispersion, a method of spraying the dispersion, a disperser A method of brushing John, a method of casting disperse, and the like can be used.
The concentration of the dispersion is set according to the coating method, but is usually 40% to 60%. It is also possible to appropriately add an additive for increasing the porosity of the fired layer, an additive for improving the strength, and a gas adsorbent that can withstand the firing temperature to the dispersion.
[0013]
In the air cleaning sheet according to the present invention, there is a gap between the photocatalyst fine particles and the resin binder, and air diffuses and circulates through the gap, so that the air almost contacts the outer surface of the photocatalyst fine particles. Passing through, the deodorizing component in the air is efficiently oxidized and deodorized by the activated photocatalyst fine particles.
In addition, since polytetrafluoroethylene carrying the photocatalyst fine particles is hardly decomposable, the resin binder can be stably held for a long time without collapsing, and the photocatalyst fine particles are wrapped through the voids of the resin layer. The photocatalyst fine particles can be stably supported over a long period of time.
Therefore, the deodorizing component in the air can be efficiently oxidized and deodorized over a long period of time.
The air cleaning sheet according to the present invention has a flat plate shape such as a rectangle or an ellipse, and can be used with a fastener such as a hook attached to both ends thereof. In order to increase the surface area, as shown in FIG. It can also be used after being processed into a honeycomb. In FIG. 2, 3 indicates a hook.
Moreover, it can also be used by laminating | stacking with the deodorizing sheet | seat which has 1 type, or 2 or more types of activated carbon, a zeolite, or copper carboxyl methyl cellulose as a main component.
[0014]
The air cleaning sheet according to the present invention can be suitably used for deodorization in the interior of an automobile (deodorization of a new car odor, deodorization of cigarette odor). As shown in FIG. Between the rear view mirror 42 and the rear window 43, the driver's field of view is arranged so as not to obstruct the driver's field of view. The photocatalyst layer of the air cleaning sheet A can be activated to deodorize the room.
[0015]
【Example】
[Example 1]
For dispersion, an aqueous dispersion of polytetrafluoroethylene powder (particle size 0.3 μm, specific gravity 2.20) having a content of 40% by weight of photocatalytic titanium oxide fine particles (particle size 7 nm, specific gravity 3.84) is used. The supporting substrate was an aluminum foil having a thickness of 60 μm. This aluminum foil is immersed in a dispersion, pulled up, dried at 100 ° C., and then fired at 390 ° C. for 2 minutes. The photocatalytic layer has a porosity of 12.2% and a thickness of 7 μm. A photocatalyst was obtained.
This sheet-like photocatalyst was cut into 10 cm × 100 cm, processed into an outer dimension of 10 cm × 10 cm, and hooks were attached to both ends to form an air cleaning sheet .
This air cleaning element was disposed between the windshield and the back mirror of a new passenger car (2000 cc class sedan type), and deodorized by parking outdoors in sunlight.
The new car odor disappeared in 5 hours after the air cleaning sheet was installed. When the air cleaning seat was removed on the third day, a new car odor was detected again after a day and night. When the air cleaning seat was placed again, the new car odor disappeared 5 hours after the re-installation. Was not perceived.
[0016]
[Example 2]
A sheet-like photocatalyst was obtained in the same manner as in Example 1 except that a carbon fiber felt having a thickness of 0.6 mm and a basis weight of 30 g / m ² was used as the support substrate. A deodorizing sheet (clean sky made by Kojin Co., Ltd.) mainly composed of copper carboxymethyl cellulose is laminated, and this is cut into 10 cm x 100 cm and processed into a 10 cm x 10 cm outer dimension bleat. Then, hooks were attached to both ends to obtain an air cleaning sheet .
This air-cleaning seat is placed between the windshield and the back mirror of a passenger car (2000cc class sedan type) that has a cigarette odor adsorbed in the interior of the car or inside the air conditioner. And deodorized.
After the air cleaning sheet was installed, the cigarette odor disappeared after 6 hours, and the permanent odor due to the detachment of the cigarette odor from the adsorbent was completely eliminated.
[0017]
[Comparative Example 1]
A sheet-like photocatalyst having a photocatalyst layer porosity of 3.1% and a thickness of 7 μm was obtained with respect to Example 1, and an air cleaning sheet was produced in the same manner as in Example 1.
When an attempt was made to deodorize a new car odor in the same manner as in Example 1, satisfactory deodorization could not be performed.
[Comparative Example 2]
Example 1 was the same as Example 1 except that polytetrafluoroethylene in the water dispersion was replaced with a perfluoroalkylvinyl ether-tetrafluoroethylene copolymer having a melt viscosity of 10 poise. . The porosity of the photocatalyst layer was 1%.
When an attempt was made to deodorize a new car odor in the same manner as in Example 1, satisfactory deodorization could not be performed.
[0018]
Thus, Comparative Example 2 is inferior in deodorization performance compared to Example 1 because the perfluoroalkylvinyl ether-tetrafluoroethylene copolymer is well heat-sealed to the photocatalyst fine particles, and the surface of the photocatalyst fine particles is large. The part is covered with a perfluoroalkyl vinyl ether-tetrafluoroethylene copolymer, and the melt viscosity of the perfluoroalkyl vinyl ether-tetrafluoroethylene copolymer is low, making it difficult to maintain the powder form during firing. It is presumed that this is because gaps hardly remain between the sintered powders.
[0019]
【The invention's effect】
In the air cleaning sheet according to the present invention, there are fine voids between the photocatalyst fine particles and the binder-resin, and external air flows through the voids in contact with almost the entire surface of the photocatalyst fine particles. The oxidative deodorization efficiency of the active photocatalyst fine particles for the medium deodorizing component can be improved. Further, since the photocatalyst fine particles are embraced in the resin binder and the resin itself is hardly decomposable, the photocatalyst fine particles can be stably supported.
Therefore, it can be deodorized for a long time with a relatively small outer dimension, and is disposed between the windshield and the back mirror of an automobile or in the vicinity of the rear window without substantially impeding the visibility, and the activity of the photocatalyst particles by the irradiation of sunlight. The new car odor and cigarette odor can be deodorized satisfactorily.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a solar light irradiation type air cleaning sheet according to the present invention.
FIG. 2 is a view showing an example of a solar irradiation type air cleaning sheet according to the present invention.
FIG. 3 is a view showing a usage state of a solar irradiation type air cleaning sheet according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Support base material 2 Photocatalyst layer A Solar irradiation type air cleaning sheet

Claims (5)

A polytetrafluoroethylene powder and a photocatalyst having a porous photocatalyst layer in which a dispersion containing polytetrafluoroethylene powder and photocatalyst fine particles is applied and fired on a support substrate to sinter the polytetrafluoroethylene powder. The solar photoirradiation type air purifier, wherein the porosity of the porous photocatalyst layer is 7% or more by interfacial delamination based on the difference in thermal expansion / shrinkage ratio between the two with fine particles. Sheet . The solar radiation-type air cleaning sheet according to claim 1, wherein a deodorizing sheet mainly composed of activated carbon, zeolite, or copper carboxylmethyl cellulose is laminated. A method for purifying air, wherein the solar irradiation type air cleaning sheet according to claim 1 is disposed indoors and irradiated with sunlight. A method for purifying air, wherein the solar irradiation type air cleaning sheet according to claim 2 is disposed indoors and irradiated with sunlight. The method for purifying air according to claim 3 or 4, wherein the room is inside a car.

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