JP7223557B2 - Thermal insulation structure and manufacturing method thereof - Google Patents

Description

TECHNICAL FIELD The present invention relates to a heat insulating structure using a porous structure such as airgel and a method for manufacturing the same.

Automobiles are equipped with various pipes for transporting fluids, such as cooling water hoses and air conditioner ducts. In piping intended to transport heat, it is desirable that the temperature of the fluid does not change as much as possible during transportation. For this reason, it is important to reduce heat loss during transportation by increasing the thermal insulation of piping. Further, when the temperature of the fluid is low and there is a temperature difference between the inside and outside of the pipe, dew condensation may occur on the surface of the pipe. If the condensed water droplets (condensed water) drip, there is a risk of causing failures in electronic components, wiring, etc. arranged around the piping, so it is also important to suppress the occurrence of condensation and the dripping of condensed water.

Insulation may be placed around the piping to reduce heat loss during fluid transport. Specifically, there are methods such as winding slab urethane around the pipe and integrally molding the pipe and foam. In addition, the development of heat insulating materials using silica airgel or the like, which has high heat insulating properties, is also progressing (see Patent Documents 1 to 3, for example). As a countermeasure against condensation on the piping, in addition to the method of wrapping slab urethane around the piping to insulate it, thin ridges are formed on the surface of the piping in a mesh pattern to make it difficult for condensed water to collect and prevent dripping of condensed water. Suppression methods are known.

Japanese translation of PCT publication No. 2013-534958 JP 2017-36745 A JP 2015-197662 A

However, the method of winding slab urethane requires manpower and man-hours, resulting in high cost. Since many of the pipes are curved and have complicated shapes, it is not easy to wind the pipes around them. In addition, according to the method of integrally molding the pipe and the foam by blow molding, air is blown into the foam during molding and high pressure is applied to the foam, which crushes the cells of the foam and makes it thinner. Therefore, there is a problem that a desired heat insulating effect cannot be obtained. Further, according to the method of forming the ridges on the surface of the pipe, the effect of suppressing dripping of condensed water can be obtained to some extent, but it cannot be said that it is sufficient as a countermeasure against condensation.

As a heat insulating material using silica airgel or the like, Patent Document 1 describes an article containing silica airgel bound by a water-soluble polyurethane binder. However, in the article of Patent Document 1, the binding force of the binder may not be sufficient, and when used alone, the silica airgel may fall off (so-called powder falling off).

In Patent Document 2, a first composite layer in which silica airgel is supported on first fibers and a second composite layer in which silica airgel is supported on second fibers having a basis weight larger than that of the first fibers are laminated. thermal insulation is described. According to the heat insulating material of Patent Literature 2, by laminating two layers having different fiber basis weights, silica airgel is suppressed from coming off. However, since the outer second composite layer also contains silica airgel, it cannot be said that there is no falling off.

Patent Literature 3 describes a heat insulating sound absorbing material having a flexible structure and a heat insulating layer. Here, the heat insulating layer contains airgel particles and a binder, is formed into a sheet and is adhered to the flexible structure. Since the heat insulating and sound absorbing material of Patent Document 3 is intended to improve the sound absorbing property, a flexible structure having a thickness of 1 to 10 mm is arranged between the base material, which is the member to be heat-insulated, and the heat-insulating layer. be. Therefore, the thickness of the entire heat insulating and sound absorbing material is increased. Patent document 3 also describes a form in which a reinforcing layer is arranged on the outer surface of the heat insulating layer (the surface opposite to the flexible structure). However, in the heat insulating sound absorbing material of Patent Document 3, suppression of dew condensation is not assumed. Therefore, no consideration is given to the hydrophilicity of the reinforcing layer, and paper, resin, woven fabric, non-woven fabric, and metal foil are mentioned as materials for the reinforcing layer. Also, the preferred thickness of the reinforcing layer is described as 0.1 mm to 5 mm. When the reinforcing layer is made of a thick resin film, a large stress is generated when the reinforcing layer expands and contracts due to temperature changes, and cracks are likely to occur in the heat insulating layer.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a heat insulating structure that is resistant to powder falling off, has excellent heat insulating properties, and is resistant to dripping of condensed water, and a method for manufacturing the same.

(1) In order to solve the above problems, the heat insulating structure of the present invention includes a base material, a heat insulating layer arranged on the surface of the base material, and a protective layer laminated on the heat insulating layer, The heat insulating layer has a porous structure in which a plurality of particles are connected to form a skeleton, has pores inside, and has a hydrophobic site on at least the surface of the surface and the inside, and a first aqueous binder. , the protective layer has a second aqueous binder, and the thickness of the protective layer is 10 μm or more and less than 100 μm.

(2) The method for producing a heat insulating material structure of the present invention includes a surface treatment step of surface treating a base material, and a first coating having a porous structure and a first aqueous binder is applied to the surface of the base material. a heat-insulating layer forming step of forming a heat-insulating layer by applying it to the surface of the heat-insulating layer; and a protective layer-forming step of applying a second paint having a second aqueous binder to the surface of the heat-insulating layer to form a protective layer. characterized by having

(1) In the heat insulating structure of the present invention, a heat insulating layer is arranged on the surface of the substrate, which is the member to be heat insulated. The thermal insulation layer has a porous structure and a first aqueous binder. Among them, the porous structure has a skeleton formed by connecting a plurality of particles, has pores inside, and has hydrophobic sites on at least the surface of the surface and the inside. The size of pores formed between skeletons of the porous structure is about 10 to 50 nm, and most of the pores are so-called mesopores of 50 nm or less. Since the mesopores are smaller than the mean free path of air, heat transfer is impeded. Therefore, by having a porous structure, the heat insulating layer exhibits an excellent heat insulating effect. As a result, heat transfer through the base material is reduced, so if the base material is a pipe, for example, the temperature of the fluid flowing through the pipe is less likely to change. In addition, since the temperature difference with the outside becomes small, it is possible to suppress dew condensation that conventionally occurs on the surface of the base material.

Both the first aqueous binder for the heat-insulating layer and the second aqueous binder for the protective layer are water-based binders. The heat insulating layer and protective layer containing the binder have hydrophilicity. Therefore, the contact angle of the surface of the protective layer is small, and even if dew condensation occurs on the surface, water droplets are unlikely to form. Therefore, dripping of condensed water can be suppressed. In addition, the porous structure included in the heat insulating layer has a hydrophobic portion on at least the surface of the surface and the inside so that moisture or the like does not enter inside and crush the pores. Therefore, the first aqueous binder is less likely to enter the pores of the porous structure and less likely to impair the heat insulating properties.

In the heat insulating structure of the present invention, the surface of the heat insulating layer is covered with the protective layer. Therefore, the porous structure included in the heat insulating layer is less likely to come off. That is, in the heat insulating structure of the present invention, less powder falls off.

For example, when the heat insulating layer and the protective layer expand and contract due to temperature changes, stress is generated inside. The stress increases as the thickness of the protective layer increases. In the heat-insulating layer, the porous structures are bound together by the first aqueous binder, and cracks tend to occur between the porous structures when the stress exceeds the binding force of the binder. In addition, when the porous structure is silica airgel, the silica airgel exhibits a white color and reflects infrared rays, so the heat insulating layer exhibits a heat shielding effect. Here, if the protective layer is too thick, the heat shielding property of the heat insulating layer may be impaired. In this regard, according to the heat insulating structure of the present invention, the thickness of the protective layer is 10 μm or more and less than 100 μm. By limiting the thickness of the protective layer to this range, it is possible to prevent the porous structure from coming off (powder falling off) and to maintain the heat shielding properties of the heat insulating layer and achieve durability.

(2) According to the method for manufacturing a heat insulating structure of the present invention, a base material is surface-treated in advance to form a heat insulating layer on the surface. As a result, when the first coating material (heat insulating layer forming coating material) having the first aqueous binder is applied, repelling of the first coating material is suppressed and wettability is improved. Therefore, the heat insulating layer can be formed evenly and uniformly, and the adhesion between the substrate and the heat insulating layer can be improved. Further, in the heat insulating layer forming step, the first paint is applied to form the heat insulating layer, and in the protective layer forming step, the second paint is applied to form the protective layer. Therefore, the process can be simplified and the cost can be reduced compared to the method of attaching a sheet-like member.

It is a sectional view of piping which is one embodiment of the heat insulation structure of the present invention.

<Heat insulation structure>
First, an embodiment of the heat insulation structure of the present invention will be described. In this embodiment, the insulation structure of the present invention is embodied as piping. FIG. 1 shows a cross-sectional view of a pipe to which the heat insulating structure of the present invention is applied. As shown in FIG. 1, the pipe 1 includes a pipe main body 10, a heat insulating layer 20, and a protective layer 30. As shown in FIG. The pipe main body 10 is made of polyethylene. The surface (outer peripheral surface) of the pipe body 10 is subjected to flame treatment. The pipe main body 10 is included in the concept of the base material in the present invention. The heat insulating layer 20 covers the surface of the pipe body 10 . The heat insulating layer 20 has silica airgel having hydrophobic sites on the surface and inside, and urethane resin as the first aqueous binder. The silica airgel is included in the concept of porous structure in the present invention. The thickness of the heat insulating layer 20 is 0.5 mm. The protective layer 30 is laminated on the heat insulating layer 20 and covers the surface of the heat insulating layer 20 . The protective layer 30 has a urethane resin as a second aqueous binder. The thickness of the protective layer 30 is 50 μm.

Since the heat insulating layer 20 contains silica airgel, it has excellent heat insulating properties and heat shielding properties. Therefore, according to this embodiment, heat transfer through the pipe body 10 is reduced, and the temperature of the fluid flowing through the pipe body 10 is less likely to change. Also, since the temperature difference between the inside and outside of the pipe body 10 is small, dew condensation is less likely to occur.

A surface of the heat insulating layer 20 is covered with a protective layer 30 . Therefore, the silica airgel contained in the heat insulating layer 20 is less likely to come off. The protective layer 30 contains urethane resin, which has a high affinity for water. Therefore, the contact angle of the surface of the protective layer 30 is small, and even if dew condensation occurs on the surface, water droplets are unlikely to form. Therefore, the condensed water is less likely to drip. In addition, the silica airgel contained in the heat insulating layer 20 has hydrophobic sites on its surface and inside. Therefore, the hydrophilic urethane resin hardly penetrates into the pores of the silica airgel and does not inhibit the heat insulating effect of the silica airgel. Moreover, the thickness of the protective layer 30 is 50 μm. Since the protective layer 30 is thin, stress due to expansion and contraction is less likely to act on the heat insulating layer 20 even if temperature changes occur. As a result, cracks are less likely to occur in the heat insulating layer 20, and the durability of the pipe 1 is improved. In addition, when the protective layer 30 is thin, the heat shielding property of the heat insulating layer 20 is less likely to be impaired. Thus, according to the pipe 1 (insulating structure), reduction of heat transfer through the pipe main body 10, suppression of dew condensation, and suppression of dropout of silica airgel can be realized.

Further, the surface of the pipe main body 10 is preliminarily subjected to flame treatment, and functional groups are introduced to impart hydrophilicity. Therefore, when the first paint (heat insulation layer forming paint) having a urethane resin is applied to the surface of the pipe body 10, repelling can be suppressed, and the first paint is evenly and uniformly applied to the surface of the pipe body 10. be able to. As a result, the adhesion between the pipe main body 10 and the heat insulating layer 20 is increased, and the durability of the pipe 1 is improved.

Although one embodiment of the heat insulating structure of the present invention has been described above, the heat insulating structure of the present invention is not limited to the above-described form, and can be performed by those skilled in the art without departing from the gist of the present invention. It can be embodied in various forms with modifications, improvements, and the like. A heat insulating structure of the present invention includes a base material, a heat insulating layer arranged on the surface of the base material, and a protective layer laminated on the heat insulating layer.

[Base material]
The material, shape, etc. of the base material are appropriately selected according to the type of the member to be insulated. Examples of materials include resins such as polyethylene, polypropylene, and nylon, as well as metals such as aluminum alloys, stainless steel, and iron. For example, when the base material is made of a material having a high thermal conductivity such as an aluminum alloy, the heat insulating effect and dew condensation suppressing effect of the present invention are fully exhibited. The shape of the substrate is not particularly limited, and may be plate-like, tubular, or the like.

From the viewpoint of enhancing the adhesion with the heat insulating layer, it is desirable that the surface of the substrate on which the heat insulating layer is arranged is subjected to surface treatment. As the surface treatment, a treatment for cleaning and activating the surface, and a treatment for introducing a functional group such as a hydroxyl group, a carboxyl group, or a carbonyl group to the surface are suitable. Examples of surface treatment include flame treatment, plasma treatment, ultraviolet irradiation treatment, and corona treatment. One or more selected from these treatments may be appropriately selected and performed.

[Insulation layer]
A thermal insulation layer is disposed on the surface of the substrate and has a porous structure and a first aqueous binder. The porous structure has a skeleton formed by connecting a plurality of particles, has pores inside, and has hydrophobic sites on at least the surface of the surface and the inside. It is desirable that the diameter of the particles (primary particles) forming the skeleton is about 2 to 5 nm, and the size of the pores formed between the skeletons is about 10 to 50 nm. Many of the pores are so-called mesopores of 50 nm or less. The shape of the porous structure is not particularly limited, and may be a spherical shape, an irregular block shape, or the like. When the maximum length of the porous structure is defined as the particle size, the average particle size of the porous structure is desirably about 1 to 200 μm. The larger the particle diameter of the porous structure, the smaller the surface area and the larger the pore (void) volume. For example, those having an average particle size of 10 μm or more are suitable. On the other hand, considering the stability of the paint for forming the heat insulating layer, the ease of coating, and the suppression of falling off of the porous structure, those having an average particle size of 100 μm or less are preferable. In addition, when two or more types with different particle sizes are used together, the small-diameter porous structure enters the gap between the large-diameter porous structures, so the filling amount can be increased, and the effect of improving the heat insulation is large. Become.

Porous structures include hydrophilic ones having hydrophilic sites on the surface or inside. However, hydrophilic porous structures are fragile and easily crumbled. Therefore, in the heat insulating structure of the present invention, the one having at least the hydrophobic part on the surface or the inside is employed.

The type of porous structure is not particularly limited. Examples of primary particles include silica, alumina, zirconia, and titania. Among them, from the viewpoint of excellent chemical stability, a silica airgel in which the primary particles are silica, that is, a silica airgel in which a plurality of silica particles are linked to form a skeleton is desirable.

Silica airgel having a hydrophobic site on at least the surface of the surface and the interior can be produced by subjecting it to a hydrophobizing treatment such as imparting a hydrophobic group during the production process. If at least the surface has a hydrophobic site, it is possible to suppress penetration of moisture and the like, so that the pore structure is maintained and the heat insulating property is less likely to be impaired. The method for producing silica airgel is not particularly limited, and the drying process may be carried out under normal pressure or under supercritical conditions. For example, if the hydrophobizing treatment is performed before the drying step, the need for supercritical drying is eliminated, that is, the drying can be performed under normal pressure, which facilitates production at low cost.

A method for producing spherical silica airgel by drying at normal pressure includes, for example, the method described in Japanese Patent No. 4960534. According to this publication, silica airgel can be produced through the following steps: aqueous silica sol preparation step→emulsion formation step→gelation step→solvent replacement step→hydrophobic treatment step→drying step. In the emulsion forming step, the aqueous silica sol obtained in the preceding step is dispersed in a hydrophobic solvent to form a W/O emulsion (an emulsion in which water droplets are dispersed in a hydrophobic solvent). As a result, silica sol, which is a dispersoid, becomes spherical due to surface tension or the like, and by gelling it in a post-process, a spherical gel can be obtained.

The content of the porous structure in the heat insulating layer may be appropriately determined in consideration of the thermal conductivity, hardness, mechanical strength, etc. of the heat insulating layer. For example, from the viewpoint of reducing thermal conductivity, the content of the porous structure is desirably 40 mass % or more when the mass of the entire heat insulating layer is 100 mass %. More preferably, it is 50% by mass or more and 65% by mass or more. On the other hand, if there are too many porous structures, the insulating layer may easily fall off, or the heat insulating layer may become hard, resulting in a decrease in mechanical strength. Therefore, the content of the porous structure is desirably 75 mass % or less when the mass of the entire heat insulating layer is 100 mass %.

The first aqueous binder is a binder in which water is used as a solvent. Among them, an emulsion binder (aqueous emulsion binder) is preferable. Aqueous emulsion binders are emulsified by introducing surfactants or hydrophilic groups. According to the aqueous emulsion type binder, it is considered that the surfactant and the hydrophilic group volatilize during drying, resulting in a decrease in hydrophilicity and difficulty in dissolving in water. The emulsification method may be a forced emulsification type using a surfactant as an emulsifier or a self-emulsification type in which a hydrophilic group is introduced.

The binder component may be resin or rubber. For example, in the case of an aqueous emulsion binder, it may be a resin emulsion or a rubber emulsion. Examples of resins include acrylic resins, urethane resins, mixtures of acrylic resins and urethane resins, and the like. Examples of rubber include styrene-butadiene rubber (SBR), nitrile rubber, silicone rubber, urethane rubber, and acrylic rubber. Urethane resin, styrene-butadiene rubber, and the like are suitable from the viewpoint of making the heat insulating layer flexible. From the viewpoint of increasing the strength of the binder portion and improving the strength of the heat insulating layer, a cross-linking agent or the like may be used in combination to cross-link the binder component.

The heat insulating layer desirably contains a polysaccharide in addition to the porous structure and the first aqueous binder. Polysaccharides are glycosidic bonds of one or more monosaccharides and have high viscosity. As will be described later, when the porous structure is added to the dispersion of the first aqueous binder in water to prepare the first paint (heat insulation layer-forming paint), the addition of polysaccharide causes the viscosity of the first paint to becomes high, and the porous structure becomes difficult to separate from the dispersion medium. Therefore, the dispersibility of the porous structure is improved, and the porous structure can be stably retained in the first paint. In addition, when the viscosity of the first paint increases, it becomes difficult for the first paint to drip, so that the first paint can be easily applied to the base material. Polysaccharide suppresses the separation of the porous structure by thickening due to the entanglement of molecular chains. Therefore, even if a polysaccharide is blended, a heat transfer path is unlikely to be formed, and the heat insulating properties are unlikely to deteriorate.

For example, when a polysaccharide having both a hydrophilic site and a hydrophobic site is blended, the hydrophobic site selectively binds to the hydrophobic site of the porous structure, and the hydrophilic site is arranged so as to surround the porous structure. This creates a protective colloid-like state. This action also suppresses the separation of the porous structure from the dispersion medium and improves the dispersibility of the porous structure. As a result, the time required for dispersion can be shortened, making it easier to make a paint. In addition, polysaccharides having hydrophilic moieties are less likely to enter the pores of the porous structure.

Polysaccharides include carboxymethylcellulose, carboxyethylcellulose, carboxypropylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, xanthan gum, agarose, carrageenan and the like. In particular, those with a long main chain and no or short side chains have more entanglement of the molecular chains. As a result, since the retention of the porous structure is enhanced, it is possible to prevent the porous structure from coming off from the heat insulating layer. For example, carboxymethylcellulose is suitable.

In addition, from the viewpoint that it is difficult to penetrate into the pores of the porous structure, it is desirable to have a high compatibility with water. For example, the solubility parameter (SP value) is 21 or more, which is close to the SP value of water. It is desirable to adopt A polysaccharide whose SP value is close to that of water is highly compatible with water (easy to dissolve in water). According to the simulation software described later, the SP value of water is estimated to be 29.7. Therefore, polysaccharides having an SP value of 21 or more are highly hydrophilic and have low affinity for hydrophobic pores, so that they are less likely to penetrate into the pores of the porous structure. More preferably, the SP value of the polysaccharide is 34 or more. On the other hand, the SP value of polysaccharides is desirably 50 or less. In this specification, as the solubility parameter, a value calculated by JSOL's material property simulation software "J-OCTA (registered trademark)" is adopted. In the simulation, the SP value is estimated using the atomic group contribution method. As explained above, the heat insulating layer may contain other components such as a cross-linking agent and a polysaccharide in addition to the porous structure and the first aqueous binder.

The thickness of the heat insulating layer may be appropriately determined in consideration of heat insulating properties, durability, and the like. If the heat insulating layer is too thin, the desired heat insulating effect cannot be obtained. Therefore, it is desirable that the thickness of the heat insulating layer is 0.5 mm or more. On the other hand, if the heat insulating layer is too thick, it not only increases the cost, but also reduces the strength, making it brittle and likely to crack. Therefore, the thickness of the heat insulating layer is preferably 5 mm or less, 3 mm or less, or 1 mm or less.

[Protective layer]
The protective layer is laminated on the heat insulating layer and has a thickness of 10 μm or more and less than 100 μm. If the thickness is less than 10 μm, the effect of preventing the porous structure from falling off from the heat insulating layer is reduced. A suitable thickness of the protective layer is 30 μm or more, further 50 μm or more. On the other hand, if the thickness is 100 μm or more, cracks are likely to occur in the heat insulating layer because the stress generated during expansion and contraction due to temperature change increases. In addition, when the porous structure exhibits white color, there is a possibility that the heat shielding property due to it is impaired. A suitable thickness of the protective layer is 95 μm or less, or even 90 μm or less.

The protective layer has a second aqueous binder. The second aqueous binder is a binder in which water is used as a solvent, and is preferably an emulsion-like binder (aqueous emulsion-based binder) like the first aqueous binder of the heat insulating layer. The binder component of the second aqueous binder may be resin or rubber, and preferred examples thereof are the same as those of the first aqueous binder. The binder component of the second aqueous binder may be the same or different than the binder component of the first aqueous binder. From the viewpoint of improving the adhesion between the heat insulating layer and the protective layer, it is desirable that the heat insulating layer and the protective layer have the same binder component. The protective layer may contain other ingredients such as a cross-linking agent in addition to the second aqueous binder.

<Method for manufacturing heat insulating structure>
The heat-insulating structure of the present invention may be manufactured by forming a heat-insulating layer and a protective layer on the surface of a base material, and the forming method is not particularly limited. For example, from the viewpoint of improving the adhesion between the substrate and the heat insulating layer, the manufacturing method of the present invention described below is suitable. A method for manufacturing a heat insulating structure of the present invention includes a surface treatment step, a heat insulating layer forming step, and a protective layer forming step.

[Surface treatment process]
This process is a process of surface-treating a base material. The material and shape of the substrate are as described above. The surface treatment may be appropriately selected according to the material of the substrate. Surface treatments include treatments for cleaning and activating the surface, and treatments for introducing functional groups such as hydroxyl groups, carboxyl groups, and carbonyl groups onto the surface. Specific examples include flame treatment, plasma treatment, and ultraviolet irradiation treatment. , corona treatment, etc.

[Heat insulation layer forming step]
This step is a step of applying a first paint having a porous structure and a first aqueous binder to the surface-treated surface of the substrate to form a heat insulating layer. The first paint may be prepared by adding other components such as a porous structure, a first aqueous binder, and optionally a polysaccharide and a cross-linking agent to water and stirring. It should be noted that a porous structure having hydrophobic sites on its surface or inside does not easily absorb water. On the other hand, when the specific gravity is small, it tends to float in water and is difficult to disperse. Therefore, considering the dispersibility of the porous structure, etc., when blending polysaccharides in the first paint, the first aqueous binder and polysaccharides are added to the water to increase the viscosity of the liquid, and then the porous structure is formed. A structure may be added. Polysaccharides are as described above. The agitation may be impeller agitation, or positive shearing force or ultrasonic waves may be applied. A rotation/revolution stirring device or a media-type stirring device may be used. A coater such as a bar coater, a die coater, a comma coater (registered trademark), a roll coater, or a spray may be used to apply the first coating material. Alternatively, the substrate may be dipped into the first paint.

In this step, the coating film of the first paint applied to the substrate may or may not be dried. Drying may be performed at a temperature of 80 to 120° C. for several minutes to several tens of minutes. In this step, when the coating film of the first paint is dried to complete the heat insulating layer, in the next protective layer forming step, the second paint is applied to the surface of the heat insulating layer and dried to complete the protective layer. (2-coat 2-bake method). If the coating film of the first coating material is not dried in this step, the next step of forming the protective layer is performed as it is, and the second coating material is applied to the surface of the coating film of the first coating material. Then, the coating film of the first paint and the coating film of the second paint are collectively dried to complete the heat-insulating layer and the protective layer (two-coat, one-bake method). Thus, the "heat insulating layer" formed in this step and the "heat insulating layer" in the next step are concepts that include not only the state after drying but also the state of the coating film before drying.

[Protective layer forming step]
This step is a step of applying a second paint having a second aqueous binder to the surface of the heat insulating layer to form a protective layer. The second paint may be prepared by adding a second water-based binder and, if necessary, other components such as a cross-linking agent to water and stirring. Stirring, application and drying of the second paint may be carried out in the same manner as the first paint in the heat insulating layer forming step.

EXAMPLES Next, the present invention will be described more specifically with reference to Examples.

<Dripping of condensed water>
[Production of samples]
(1) Surface Treatment of Base Material A flame of a burner was applied to the entire surface of a polyethylene pipe (tubular base material) for flame treatment.

(2) Preparation of the first paint In water, a urethane resin emulsion ("Permaline (registered trademark) UA-368" manufactured by Sanyo Chemical Industries, Ltd., solid content 50% by mass) as a first aqueous binder, and a polysaccharide of carboxymethyl cellulose (CMC: SP value 34.4, molecular weight 380,000) was added and stirred. Spherical silica airgel (average particle size 10 μm) was added thereto and stirred to prepare a first paint. Silica airgel is manufactured according to the method described in the above-mentioned Japanese Patent No. 4960534, and has hydrophobic sites on the surface and inside.

(3) Preparation of Second Coating A urethane resin emulsion (same as above) as a second aqueous binder was added to water and stirred to prepare a second coating. The binder for the second paint is the same as the binder for the first paint.

(4) Application to base material First, the first paint was applied to the entire surface of the flame-treated pipe by spraying, and then dried at 100 ° C. for 20 minutes to form a heat insulating layer with a thickness of 0.5 mm. . Next, the surface of the formed heat insulating layer was sprayed with a second paint and then dried at 100° C. for 20 minutes to form a protective layer with a thickness of 0.05 mm (50 μm). The pipe manufactured in this manner is referred to as Example 1 pipe. The piping of Example 1 is included in the concept of the thermal insulation structure of the present invention. The content of silica airgel in the heat insulating layer is 72.2% by mass.

[experimental method]
The inside of the pipe of Example 1 was filled with a refrigerant cooled to 0° C. or less, and the opening at the end was plugged. In this state, the pipe was placed in a constant temperature bath at 40° C. and relative humidity of 80% for 1 hour. At this time, a saucer was placed under the same pipe to check for dripping of condensed water. For comparison, the pipe (corresponding to the base material used in Example 1, hereinafter referred to as the pipe of Comparative Example 1) was not subjected to flame treatment and was not formed with a heat insulating layer and a protective layer. After standing in a constant temperature bath under the same conditions, the presence or absence of dripping of condensed water was examined.

[Experimental result]
Regarding the piping of Example 1, no dripping of condensed water was observed, whereas dripping of condensed water was confirmed for the piping of Comparative Example 1. As a result, it was confirmed that the piping of Example 1 has high heat insulating properties, and dripping of condensed water is suppressed.

<Presence or absence of powder drop>
[Production of samples]
(1) Sample of Example 2 First, the entire surface of a plate material (base material) made of polypropylene was subjected to flame treatment by applying a burner flame to the entire surface. Next, the first paint used in the manufacture of the piping of Example 1 was applied by spraying to the entire surface of the flame-treated plate material and dried at 100°C for 20 minutes to form a heat insulating layer with a thickness of 0.5 mm. formed. Subsequently, on the surface of the formed heat insulating layer, the second paint used in the manufacture of the pipe in Example 1 is sprayed and dried at 100 ° C for 20 minutes to protect the thickness of 0.095 mm (95 μm). formed a layer. A sample consisting of "substrate/insulating layer/protective layer" thus produced is referred to as Example 2 sample. The sample of Example 2 is included in the concept of the insulating structure of the present invention.

(2) Sample of Comparative Example 2 The entire surface (flame-treated) of the same plate material as the sample of Example 2 was sprayed with the first paint used for manufacturing the pipe of Example 1, and then heated at 100°C for 20 minutes at 100°C. It was dried for a minute to form a heat insulating layer with a thickness of 0.5 mm. A sample consisting of "substrate/thermal insulation layer" thus produced is referred to as Comparative Example 2 sample.

[experimental method]
A black non-woven fabric made of polyethylene terephthalate (PET) was rubbed on the surface of the protective layer of the sample of Example 2 and the surface of the heat insulating layer of the sample of Comparative Example 2, and the presence or absence of powder falling (falling off of silica airgel) was examined. rice field.

[Experimental result]
The sample of Example 2 did not have powder falling off, while the sample of Comparative Example 2 had powder falling off. As a result, it was confirmed that in the sample of Example 2, since the heat insulating layer was covered with the protective layer, powder fall-off was suppressed.

<Relationship between protective layer thickness and cracks>
[experimental method]
First, a flame of a burner was applied to the entire surface of a plate material (base material) made of polypropylene to perform flame treatment. Next, the first paint used in the manufacture of the piping of Example 1 was applied by spraying to the entire surface of the flame-treated plate material and dried at 100°C for 20 minutes to form a heat insulating layer with a thickness of 0.5 mm. formed. Subsequently, the surface of the formed heat insulating layer was spray-coated with the second paint used in the manufacture of the pipe of Example 1 and dried at 100° C. for 20 minutes to form a protective layer. At this time, four types of samples with different thicknesses of the protective layer were produced by changing the coating amount, and after drying at 100 ° C. (after forming the protective layer), whether cracks occurred in the heat insulating layer. I checked whether

[Experimental result]
Table 1 shows the presence or absence of cracks with respect to the thickness of the protective layer. As shown in Table 1, no cracks were observed when the thickness of the protective layer was less than 100 μm, whereas cracks were observed when the thickness was 150 μm and 200 μm, which was greater than 100 μm.

The heat insulating structure of the present invention is suitable for automotive piping such as cooling water hoses and air conditioner ducts.

1: Piping (heat insulating structure), 10: Pipe main body (base material), 20: Heat insulating layer, 30: Protective layer.

Claims (10)

A base material, a heat insulating layer arranged on the surface of the base material, and a protective layer laminated on the surface of the heat insulating layer opposite to the base material side and covering the heat insulating layer ,
The heat insulating layer is a non-foamed body having a porous structure in which a plurality of particles are connected to form a skeleton, a first aqueous binder, and carboxymethyl cellulose ,
The porous structure has pores formed between the skeletons inside, and has a hydrophobic site on at least the surface of the surface and the inside,
A heat insulating structure, wherein the protective layer contains a second aqueous binder and has a thickness of 10 μm or more and less than 100 μm. The heat insulating structure according to claim 1, wherein the heat insulating layer has a thickness of 0.5 mm or more and 5 mm or less. 3. The heat insulating structure according to claim 1, wherein said first aqueous binder and said second aqueous binder are emulsion binders having resin or rubber as a binder component. 4. The heat insulating structure according to claim 1, wherein the binder component of said first aqueous binder and the binder component of said second aqueous binder are the same. 5. The heat insulating structure according to any one of claims 1 to 4, wherein said second aqueous binder is a urethane resin emulsion. 6. The heat insulating structure according to any one of claims 1 to 5 , wherein said porous structure is silica airgel . The base material is a tubular body made of resin or metal,
7. The heat insulating structure according to any one of claims 1 to 6, wherein the heat insulating layer is arranged on the outer surface of the tubular body . The heat insulating structure according to any one of claims 1 to 7, wherein the surface of the base material on which the heat insulating layer is arranged is surface-treated. A method for manufacturing the thermal insulation structure according to claim 1,
A surface treatment step of performing surface treatment of the base material;
Forming a heat insulating layer by applying a first paint containing water, a porous structure , a first aqueous binder , and carboxymethyl cellulose and having no foaming agent to the surface of the surface-treated substrate to form a heat insulating layer. process and
A protective layer forming step of applying a second paint having a second aqueous binder to the surface of the heat insulating layer to form a protective layer;
A method for manufacturing a heat insulating structure, comprising: 10. The method of manufacturing a heat insulating structure according to claim 9, wherein the surface treatment is one or more selected from flame treatment, plasma treatment, ultraviolet irradiation treatment, and corona treatment.

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