JP6934593B2 - Insulation material and its manufacturing method - Google Patents

Description

The present invention relates to a heat insulating material and a method for producing the same. In particular, it relates to a heat insulating material used in a high temperature environment and a method for manufacturing the heat insulating material.

(Some parts have been deleted because it is preferable to be short)
Unlike general-purpose heat insulating materials such as urethane foam (PU), expanded polystyrene (EPS), and vacuum heat insulating material (VIP), silica airgel has almost no change over time in its heat insulating performance. Further, silica airgel is attracting attention as a next-generation heat insulating material because it has a heat resistance of 400 ° C. or higher.

Silica airgel is superior to existing heat insulating materials in terms of aging deterioration and heat resistance, and has an excellent thermal conductivity of about 15 mW / mK. However, the silica airgel forms a bead-like network structure in which silica particles on the order of several tens of nm are connected by point contact. For this reason, silica airgel does not have much mechanical strength. Therefore, in order to overcome the brittleness, studies have been made to improve the strength of silica airgel by combining it with fibers, non-woven fabrics, resins and the like.

In a high temperature environment where the heat insulating material of silica airgel exceeds 100 ° C., this heat insulating material tends to generate radiant heat on the surface of silica particles having a high emissivity (emissivity 0.95).

As a result, the influence of radiant heat transfer becomes large on the heat insulating property obtained by the pores of the silica particles, and the heat insulating property tends to be lost (the apparent thermal conductivity of the heat insulating material becomes large). That is, it absorbs infrared rays from the outside and emits them to the outside. This transfers heat.

Patent Document 1 is a conventional technique for this. At least a part of the surface of a base material having a silica airgel having a silica skeleton attached to a non-woven fabric or a matte fiber material is coated with a coating layer made of alumina (low radiance). This coating layer suppresses the influence of radiant heat transfer.

Japanese Patent No. 38546445

However, Patent Document 1 does not disclose how to coat the filler with a coating layer and keep it in a heat insulating material. If the coating layer is not good, the filler can be easily attached and detached, reducing the effect of radiation prevention.

Therefore, an object of the present invention is to provide a heat insulating material that prevents radiation and a method for producing the same, without causing a decrease in heat insulating property or dropping of a member, and by effectively blending a radiation preventing material.

In order to achieve the above object, a third heat insulating layer containing a first silica xerogel and a first radiation inhibitor, a third insulating layer containing a third silica xerogel and a second fiber, and laminated with the first heat insulating layer. A heat insulating material having a heat insulating layer is used.

The heat insulating material uses an electronic device in which the first heat insulating layer is arranged toward a heat generating component.

A solification step using water glass or an aqueous silicate solution as a sol, an impregnation step of inserting the sol containing a radiation inhibitor and the sol not containing a radiation inhibitor into a non-woven fiber, and the radiation inhibitor. A gelling step of gelling the sol containing the sol and the sol not containing the radiation inhibitor, a curing step of curing the gel, a dipping step of immersing the gel in an acidic aqueous solution, and a hydrophobicity of making the gel hydrophobic. A method for producing a heat insulating material is used, which includes a chemical conversion step and a drying step of drying the gel.

According to the present invention, a radiation preventing material is added to the surface layer of the heat insulating material on the heat source side so as not to reduce the heat insulating property of the heat insulating material or cause the member to fall off. As a result, infrared scattering is generated in the surface layer portion, and infrared rays do not penetrate to the inside. As a result, the heat insulating material of the present invention effectively suppresses heat transfer, has a radiation prevention function, and has high heat insulating performance.

Cross-sectional structural view of the heat insulating material having the radiation prevention function of the embodiment The figure which shows the surface observation photograph by the scanning electron microscope of the 1st insulation layer of embodiment The figure which shows the surface observation photograph by the scanning electron microscope of the 2nd insulation layer of embodiment The figure which shows the surface observation photograph by the scanning electron microscope of the 3rd insulation layer of embodiment The figure which shows the temperature comparison result of Example 1 and Comparative Example 1. Cross-sectional view of an electronic device showing an example in which the heat insulating material of the embodiment is applied to an electronic device.

Hereinafter, embodiments will be described with reference to the drawings.

(Structure of heat insulating material 100)
FIG. 1 is a cross-sectional view of the heat insulating material 100 having a radiation prevention function according to the first embodiment. The heat insulating material 100 has a three-layer structure. Table 1 shows the contents of each layer.

The first heat insulating layer 101 contains silica xerogel 104 and a radiation preventing material 105.

The second heat insulating layer 102 contains silica xerogel 104, a radiation inhibitor 105, and fibers 106. The third heat insulating layer 103 contains silica xerogel 104 and fibers 106.

The third heat insulating layer 103 is the main body (center) of the heat insulating material 100, and the first heat insulating layer 101 and the second heat insulating layer 102 are layers that suppress the radiation of infrared rays from the third heat insulating layer 103.

<First heat insulating layer 101>
The first heat insulating layer 101 contains a radiation preventing material 105 in a network structure of silica xerogel in which silica particles on the order of 10 nm are connected by point contact. The thickness of the first heat insulating layer 101 may be 1 μm or more. It is preferable to increase the thickness of the first heat insulating layer 101, but the strength is weak. When the thickness is 100 μm or less, there is no desorption and it is preferable. When infrared rays are incident on the heat insulating material 100, the radiation preventing material 105 of the first heat insulating layer 101 first scatters the infrared rays to prevent heat transfer.

The first heat insulating layer 101 does not contain fibers 106. This is because the presence of the fiber 106 improves the thermal conductivity and deteriorates the heat insulating performance. This is also because the fibers 106 absorb and emit infrared rays.

<Second heat insulating layer 102>
The second heat insulating layer 102 has a thickness of 0.1 mm or more and 5 mm or less, and together with the first heat insulating layer 101, prevents infrared rays from being emitted. The difference from the first heat insulating layer 101 is that it contains fibers 106. Due to the fibers 106, the second heat insulating layer 102 has high strength.

If the thickness is increased, the amount of the radiation preventing material 105 required is also increased, and the cost is increased.

On the other hand, the fibers 106 are present in the second heat insulating layer 102, and a certain amount of infrared rays are absorbed by the fibers 106. Therefore, in order to scatter more infrared rays, the first heat insulating layer 101 that does not contain the fibers 106 is provided.

The second heat insulating layer 102 mechanically joins the first heat insulating layer 101 and the third heat insulating layer 103. Moreover, the second heat insulating layer 102 also suppresses the absorption and radiation of infrared rays within a certain range.
The second heat insulating layer 102 is not essential, but is preferable. The heat insulating property can be ensured by the third heat insulating layer 103, and the prevention of infrared scattering and heat transfer can be ensured by the first heat insulating layer 101. The second heat insulating layer 102 can further improve their functions and can firmly join the first heat insulating layer 101 and the third heat insulating layer 103.

<Third heat insulating layer 103>
The third heat insulating layer 103 is the main body of the heat insulating material 100. The thickness is calculated from the thermal conductivity of solids other than radiation and the thermal conductivity of gas convection required for the heat insulating material 100, and ranges from 0.1 mm to several mm.

<Insulation material 100>
The silica xerogel 104 of the first heat insulating layer 101, the second heat insulating layer 102, and the third heat insulating layer 103 may be of different types, but the same silica xerogel is preferable.

The radiation prevention material 105 of the first heat insulating layer 101 and the second heat insulating layer 102 may be different from each other, but the same one is preferable.
The fibers 106 of the second heat insulating layer 102 and the third heat insulating layer 103 may be different, but the same one is preferable.

It is preferable that the thickness is thicker in the order of the first heat insulating layer 101, the second heat insulating layer 102, and the third heat insulating layer 103. This is because the first heat insulating layer 101 cannot be made thick as described above, and it is necessary to secure the heat insulating property in the third heat insulating layer 103.

<Silica xerogel 104>
Silica xerogel 104 is composed of a dehydration condensate produced by adding a base to a silicate aqueous solution obtained by using water glass (sodium silicate aqueous solution) as a raw material and ion-exchange it with an ion exchange resin or an electrodialysis method to remove sodium. Alternatively, as a raw material, it is composed of a dehydration condensate produced by adding an acid to a high molar silicic acid aqueous solution having a particle size intermediate between water glass and colloidal silica (1 to 10 nm).

Silica xerogel 104 has an average pore size of 10 to 55 nm and a pore volume of 3.0 to 10 cc / g. The average pore size is preferably from 10 to 55 nm. When the average pore size is smaller than 10 nm, the bulk density of the xerogel increases, and as a result, the proportion of the heat conductive component of the solid (silica particles) increases. Therefore, the value of thermal conductivity becomes large. If the average pore size is larger than 55 nm, the bulk density of the xerogel will decrease and the thermal conductivity component of the solid will decrease, but the air (nitrogen molecule) convection will have a stronger effect due to the increase in the void ratio of the xerogel, resulting in heat conduction. The value of the rate becomes large.

The pore volume is preferably 2.5 to 10 cc / g. When the pore volume is less than 2.5 cc / g, the ratio of the solid heat conductive component increases as in the case where the average pore is less than 10 nm, so that the value of the thermal conductivity becomes large. When the pore volume is larger than 10 cc / g, the thermal conductivity component of the solid decreases, but the effect of convection increases due to the increase in the void ratio of the xerogel, so that the value of the thermal conductivity increases.

When the average pores and the pore volume of the silica xerogel 104 are in the above range, the heat insulating property is excellent, so that the silica xerogel 104 is suitable as the heat insulating material 100.

In order to control the average pores and pore volume of silica xerogel 104, the silicic acid concentration of water glass as a raw material and the type of basic colloidal silica used at the time of solification (pH, dispersion medium, particle size, particle shape). , Particle concentration), amount of addition, gelation condition (temperature, time) of sol, curing condition (temperature, time) and the like can be easily controlled.

Water glass (aqueous solution of sodium silicate) is used as a starting material for producing silica xerogel 104, and the preparation is the silicic acid concentration of water glass, the type and concentration of acid used during gelation, and gelation conditions (temperature, time, It can be controlled by adjusting pH). Further, the hydrophobization condition can be controlled by adjusting the amount of the silylating agent, the amount of the solvent, the temperature, and the time. The drying conditions can be controlled by adjusting the drying temperature, time, and the like.

<Radiation prevention material 105>
As the form of the radiation preventing material 105, a filler having a high refractive index and a high infrared reflectance, such as titanium oxide, is used. In the case of titanium oxide, the primary average particle size is preferably 1 μm in order to shield infrared rays having a wavelength of 2 μm or less.

<Fiber 106>
As the form of the fiber 106, glass wool, rock wool and alumina fibers are preferable from the viewpoint of heat insulation, heat resistance, flame retardancy and dimensional stability. Carbon fibers are not preferable because they have high thermal conductivity and poor heat insulating properties. The fiber diameter of glass wool, rock wool and alumina fibers is 1 to 20 um, and the fiber length is 3 to 25 mm. Fibers in this range have low thermal conductivity and are preferable. Further, the fibers having a fiber diameter and a fiber length in this range have a thermal conductivity in the range of 0.03 to 0.05 W / mK as a single non-woven fabric.

When the fiber diameter is 20 um or the fiber length is larger than 25 mm, the solid heat conductive component of the inorganic fiber increases, and the thermal conductivity becomes larger than 0.05 W / mK. As a result, even if the fiber contains silica xerogel 104, the thermal conductivity of the final heat insulating material exceeds 0.025 W / mK, which is not preferable.

Fibers having a fiber diameter of less than 1 mm and a fiber length of less than 3 mm are not preferable because the entanglement between the fibers is significantly reduced and the form as a sheet cannot be maintained.

<As a whole of heat insulating material 100>
It is preferable that the concentrations of the radiation preventing material 105 in the first heat insulating layer 101 and the second heat insulating layer 102 are the same.

The weight concentration of the second heat insulating layer 102 is as follows. Silica airgel: radiation inhibitor: fiber = 35-60: 5-20: 20-55.

The weight concentration of the third heat insulating layer 103 is as follows. Silica airgel: fiber = 40-75: 25-60.

The weight concentration of the first heat insulating layer 101 is as follows. Silica airgel: radiation inhibitor = 70 to 95: 5 to 30.

The radiation-preventing material is effective at 5% or more. If it is 30% or more, the solid thermal conductivity increases, which is not good, preferably 10% to 20%.

It is preferable that the silica xerogel is the same in the second heat insulating layer 102 and the third heat insulating layer 103. It is preferable that the weight ratio of silica xerogel: fiber is the same in the second heat insulating layer 102 and the third heat insulating layer 103.

(Manufacturing method of heat insulating material 100)
The method for manufacturing the heat insulating sheet comprises the seven steps (1) to (7). Seven steps: (1) sol preparation step, (2) impregnation step, (3) gelation step, (4) curing step, (5) acidic aqueous solution dipping step, (6) hydrophobic step, and (7) drying step. It is a process. Each will be described below.

(1) Sol preparation step In the sol preparation step, there are cases where water glass is used as a raw material and cases where a high molar silicic acid aqueous solution is used. When water glass is used, sodium in the water glass is removed by an ion exchange resin or an electrodialysis method, acidified to form a sol, and then a base is added as a catalyst to carry out polycondensation to obtain a hydrogel. When high molar silicate sodium is used, an acid is added as a catalyst to the high molar silicate aqueous solution and polycondensed to obtain a hydrogel.

To prepare the first heat insulating layer 101 and the second heat insulating layer 102, the radiation inhibitor 105 is added to the water glass or the high molar silicic acid aqueous solution. The addition ratio is preferably 5% by weight to 40% by weight with respect to the weight of the silicic acid concentration. If the addition ratio is less than 5% by weight, the effect of scattering infrared rays becomes small, and the effect of preventing the influence of radiation becomes small. On the other hand, if the addition ratio is larger than 40% by weight, the solid thermal conductivity increases due to the influence of the added radiation inhibitor.

(2) Impregnation step A sol solution prepared in (1) is poured into a non-woven fabric such as glass wool or rock wool having a thickness of 0.2 to 1.0 mm in an amount of 6.5 to 10 times the weight of the non-woven fabric, and the sol solution is applied to the non-woven fabric. Impregnate.

First, in order to prepare the first heat insulating layer 101 and the second heat insulating layer 102, the non-woven fabric is impregnated with a sol solution to which the radiation preventing material 105 is added (first impregnation step). The impregnation method is to spread the sol solution on a film or the like in advance to a certain thickness, and then cover the non-woven fabric from above to allow the sol solution to permeate the non-woven fabric. Further, in order to prepare the third heat insulating layer 103, a sol solution to which the radiation preventing material 105 is not added is impregnated on the third heat insulating layer 103 (second impregnation step).

If the total thickness of the first heat insulating layer 101 and the second heat insulating layer 102 is 10% of the heat insulating material 100, the ratio of the sol solution to which the radiation preventing material 105 is added and the sol solution to which the radiation preventing material 105 is not added is 10 : 90. If you want to set it to 20%, set the ratio to 20:80.

As a result, a part of the sol solution to which the radiation preventing material 105 is added under the heat insulating material 100 goes out not only to the fibers 106 but to the outside. The first heat insulating layer 101 can be produced from the sol solution that has come out to the outside (coating step). On the other hand, the second heat insulating layer 102 can be produced in the portion where the sol solution to which the radiation preventing material 105 is added remains permeated into the fibers 106. A third heat insulating layer 103 is formed on the sol solution to which the radiation preventing material 105 is not added.

When the heat insulating material 100 without the second heat insulating layer 102 is manufactured, it can be manufactured by slightly immersing one surface of the third heat insulating layer 103 in the sol solution prepared in (1). In this case, the process is the same thereafter.

(3) Gelation step After (2), the sol is gelled. The gelation temperature of the sol is preferably 20 to 90 ° C. If the gelation temperature is less than 20 ° C., the heat required for the silicic acid monomer, which is the active species of the reaction, is not transferred. Therefore, the growth of silica particles is not promoted. As a result, it takes time for the gelation of the sol to proceed sufficiently. On top of that, the strength of the produced gel (hydrogel) is low, and it may shrink significantly when dried, and a hydrogel of the desired strength may not be obtained.

Further, when the gelation temperature exceeds 90 ° C., the growth of silica particles is remarkably promoted. As a result, water volatilizes rapidly, and a phenomenon is observed in which water and hydrogel separate. As a result, the volume of the obtained hydrogel may be reduced, and the desired silica xerogel 104 may not be obtained.

The gelling time varies depending on the gelling temperature and the curing time after gelation described later, but the total of the gelling time and the curing time described later is preferably 0.1 to 12 hours, and the performance (heat conduction) is preferable. From the viewpoint of achieving both rate) and production tact, 0.1 to 1 hour is more preferable.

If the gelation time is longer than 12 hours, the silica network is sufficiently strengthened, but if the curing time is longer, not only the productivity is impaired, but also the gel shrinks and the bulk density increases. There is a problem that the thermal conductivity increases.

By gelling and curing in this way, the strength and rigidity of the wall of the hydrogel is improved, and a hydrogel that does not easily shrink when dried can be obtained.

(4) Curing step The curing step is a step of converting the silica skeleton into a strengthened skeleton-enhanced hydrogel after gelation. The curing temperature is preferably 50 to 100 ° C. When the curing temperature is less than 50 ° C., the dehydration condensation reaction becomes relatively slow, and it becomes difficult to sufficiently strengthen the silica network within the target tact time when productivity is taken into consideration.

When the curing temperature is higher than 100 ° C., the water content in the gel evaporates remarkably, so that the gel shrinks and dries, and the thermal conductivity increases.

The curing time is preferably 0.1 to 12 hours, and more preferably 0.1 to 1 hour from the viewpoint of achieving both performance (thermal conductivity) and production tact.

If the curing time is longer than 12 hours, the silica network is sufficiently strengthened, but if the curing time is longer, not only the productivity is impaired, but also the gel shrinks and the bulk density increases, resulting in heat. There is a problem that the conductivity increases.

By curing the curing time in the range of 0.1 to 6 hours, it is possible to sufficiently strengthen the network of silica particles while ensuring productivity.

(5) Acid Aqueous Solution Immersion Step After immersing the gel sheet in hydrochloric acid (specified in 6 to 12), leave it at room temperature of 23 ° C. for 45 minutes or more to incorporate hydrochloric acid into the gel sheet.

(6) Hydrophobicization Step The gel sheet is immersed in, for example, a mixed solution of octamethyltrisiloxane as a silylating agent and 2-propanol (IPA) as an alcohol, placed in a constant temperature bath at 55 ° C., and reacted for 2 hours. When the trimethylsiloxane bond begins to be formed, hydrochloric acid water is discharged from the gel sheet, and the two liquids are separated (siloxane in the upper layer and hydrochloric acid water in the lower layer).

(7) Drying The gel sheet is transferred to a constant temperature bath at 150 ° C. and dried for 2 hours.

<Example 1>
A high molar silicic acid aqueous solution (Toso Sangyo Co., Ltd.) was used as the sol solution, and the ratio of the sol solution to which titanium oxide (manufactured by Teika Co., Ltd.) was added as the radiation prevention material 105 to the sol solution to which the radiation prevention material 105 was not added was 1: 1. As No. 2, the first heat insulating layer 101, the second heat insulating layer 102, and the third heat insulating layer 103 were produced by the above method. The addition ratio of the radiation preventing material 105 was 30 parts by weight of the silicic acid concentration.
The weight concentration of the second heat insulating layer 102 is as follows. Silica airgel: radiation inhibitor: fiber = 55:18:27.

The weight concentration of the third heat insulating layer 103 is as follows. Silica airgel: fiber = 67:33.

A surface observation photograph of the first heat insulating layer 101 with a scanning electron microscope is shown in FIG. 2 (magnification: 1500 times). It can be seen that titanium oxide, which is a radiation preventing material 105, is scattered in white on the silica xerogel 104.

A surface observation photograph of the second heat insulating layer 102 with a scanning electron microscope is shown in FIG. 3 (magnification: 2000 times). It can be seen that the silica xerogel 104 is dotted with titanium oxide, which is the radiation preventing material 105, in white, and the fibers 106 are further present.

A surface observation photograph of the third heat insulating layer 103 with a scanning electron microscope is shown in FIG. 4 (magnification: 2000 times). In FIG. 4, it can be seen that the fibers 106 are present in the silica xerogel 104, but the titanium oxide that was present in white in FIGS. 2 and 3 is not present.

<Comparative example 1>
A sol solution using a high molar silicate aqueous solution (Toso Sangyo Co., Ltd.) as a sol solution, and a sol solution containing titanium oxide (Tayca Corporation) as a radiation inhibitor 105 and a heat insulating material (layer structure) to which the radiation inhibitor 105 is uniformly added. It was created. The ratio of the radiation preventing material 105 added was 10 parts by weight of the silicic acid concentration, and the same amount of titanium oxide as in Example 1 was used.

(Effect of heat insulating material 100)
In order to compare the heat insulating performance, the heat insulating materials of Example 1 and Comparative Example 1 were heated on a hot plate, the temperatures of the front surface and the back surface were measured with a thermocouple, and the temperature difference was confirmed. The heat insulating material of Example 1 had the structure of FIG. 1, and the first heat insulating layer 101 was brought into contact with the hot plate.

The result is shown in FIG. From FIG. 5, it can be seen that the heat insulating effect of Example 1 is higher.

That is, by encapsulating the radiation prevention material 105 in the silica xerogel 104 according to the structure of FIG. 1, it is possible to prevent the radiation prevention material 105 from being attached or detached. By adding the radiation preventing material 105 to the surface layer (first heat insulating layer) of the heat insulating material on the heat source side, the scattering of infrared rays can be prevented at the surface layer portion. As a result, since infrared rays do not penetrate into the heat insulating material, heat transfer by the heat insulating material can be effectively suppressed and a radiation prevention function can be provided. As a result, the heat insulating material 100 can obtain high heat insulating performance.

(Application to electronic device 109)
An example in which the heat insulating material 100 is used for the electronic device 109 will be described with reference to FIG. FIG. 6 is an electronic device 109 of the embodiment. There is a heat generating component 107 mounted on the circuit board 108. The heat insulating material 100 is located on the heat generating component 107. The heat insulating material 100 does not transfer the heat of the heat generating component 107 to the outer frame 110 of the electronic device 109. Even if a person touches the outer frame 110 for a long time, there is no harm such as low temperature burns.

In the heat insulating material 100, the first heat insulating layer 101 is located on the heat generating component 107 side. The heat insulating material 100 is preferably used by wrapping it in a thin resin film 111. When the heat insulating material 100 is wrapped with the film 111, the handleability is good.

(as a whole)
The heat insulating material 100 is arranged in the electronic device so that the first heat insulating layer 101 comes to the heat generating component side.

The heat insulating material of the present invention is widely used as a heat insulating material. In particular, it is used in a temperature range of 100 ° C. or higher, where radiant heat transfer is dominant. It is used for heat insulation of all kinds of equipment.

100 Insulation material 101 First insulation layer 102 Second insulation layer 103 Third insulation layer 104 Silica xerogel 105 Radiation prevention material 106 Fiber 107 Heat generation component 108 Circuit board 109 Electronic equipment 110 Outer frame 111 Film

Claims (9)

A first heat insulating layer containing a first silica xerogel and a first radiation inhibitor,
A third heat insulating layer containing a third silica xerogel and a second fiber and laminated with the first heat insulating layer,
Insulation material with. The heat insulating material according to claim 1, further comprising a second heat insulating layer arranged between the first heat insulating layer and the third heat insulating layer and containing a second silica xerogel, a second radiation preventing material, and a first fiber. The first insulation layer, heat-insulating material according to claim 1, wherein not including textiles. The heat insulating material according to claim 2, wherein the first fiber and the second fiber are the same fibers. The heat insulating material according to claim 2 or 4, wherein the first radiation preventing material and the second radiation preventing material are the same radiation preventing material. The heat insulating material according to any one of claims 2, 4, and 5, wherein the first heat insulating layer and the second heat insulating layer are thinner than the third heat insulating layer. The heat insulating material according to any one of claims 2, 4, 5, and 6, wherein the first heat insulating layer, the second heat insulating layer, and the third heat insulating layer are thicker in this order. An electronic device in which the heat insulating material according to any one of claims 1 to 7 is arranged so that the first heat insulating layer faces a heat generating component. A solification process using water glass or an aqueous solution of silicic acid as a sol,
An impregnation step of inserting the sol containing a radiation inhibitor and the sol not containing a radiation inhibitor into the non-woven fiber.
A gelling step of gelling the sol containing the anti-radiation material and the sol not containing the anti-radiation material.
The curing process for curing the gel and
A dipping step of immersing the gel in an acidic aqueous solution and
The hydrophobizing step of hydrophobizing the gel and
Including a drying step of drying the gel.
The method for producing a heat insulating material according to any one of claims 1 to 8.

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