阅读说明：本技术 气凝胶结构体及其制造方法 (Aerogel structure and method for producing same ) 是由 鹤田崇 岩崎里佳子 于 2021-05-19 设计创作，主要内容包括：本发明的气凝胶结构体具备：在纤维材料之间保持有气凝胶的复合层(101)；以及设于复合层(101)的至少一侧的面上,由气凝胶形成的气凝胶层(102),气凝胶层(102)具有从与复合层(101)相反侧的面突出的凸部(103),凸部(103)处的气凝胶的密度比凸部(103)以外的气凝胶层(102)(平坦部(104))处的气凝胶的密度高0.1％以上且3.0％以下。由此,可以提供尺寸稳定性和绝热性优异、且能够生产率良好地制造的气凝胶结构体及制造方法。(The aerogel structure of the present invention comprises: a composite layer (101) in which aerogel is held between fiber materials; and an aerogel layer (102) formed of aerogel and provided on at least one surface of the composite layer (101), wherein the aerogel layer (102) has a projection (103) projecting from the surface on the opposite side of the composite layer (101), and the density of aerogel at the projection (103) is higher by 0.1% to 3.0% than the density of aerogel at the aerogel layer (102) (flat portion (104)) other than the projection (103). Thus, an aerogel structure and a method for producing the same can be provided, which are excellent in dimensional stability and thermal insulation properties and can be produced with high productivity.)

1. An aerogel structure, comprising:

a composite layer of aerogel is held between the fibrous materials; and

an aerogel layer formed of the aerogel and provided on at least one side surface of the composite layer,

the aerogel layer has a convex portion protruding from a surface opposite to the composite layer,

the density of the aerogel at the convex portions is higher than the density of the aerogel in the aerogel layer other than the convex portions by 0.1% or more and 3.0% or less.

2. The aerogel structure according to claim 1, wherein a compression ratio after applying a pressure of 1.0MPa or more and 5.0MPa or less to the protrusions is lower by 0.1% or more and 20% or less than a compression ratio after applying a pressure of 1.0MPa or more and 5.0MPa or less to the aerogel layer other than the protrusions.

3. The aerogel structure of claim 1 or claim 2, wherein the protrusions are elliptical in shape in plan view.

4. The aerogel structure of any of claims 1-3, wherein the average diameter of the fiber material is 0.1 μm or more and 10 μm or less,

the porosity of the composite layer is more than 90%.

5. The aerogel structure of claim 1, wherein the raised portions have a higher tone than the aerogel structure other than the raised portions.

6. The aerogel structure of claim 1, wherein the aerogel is a network structure in which particles of silica aerogel are connected by point contact.

7. The aerogel structure of claim 1, wherein the protrusions can be visually confirmed when the aerogel structure is covered with light.

8. The aerogel structure of claim 1, wherein the thermal conductivity of the aerogel structure (110) is 0.02W/(m-K) or more and 0.06W/(m-K) or less.

9. The aerogel structure of claim 1, wherein the compressibility of the aerogel structure after being pressurized at 5MPa is 40% or less.

10. A method of manufacturing an aerogel structure, comprising:

a composite-producing step of discharging a sol from a nozzle that moves discontinuously in a direction intersecting a direction in which a fiber material is conveyed, toward the continuously conveyed fiber material, and impregnating the fiber material with the sol to produce a composite of the fiber material and a hydrogel;

a surface modification step of performing surface modification on the complex; and

a drying step of drying the composite.

11. The method of manufacturing an aerogel structure according to claim 10, wherein, in the composite body generation step, the fiber material containing the sol is pressurized.

Technical Field

The present invention relates to an aerogel structure and a method for producing the same.

Background

As a heat insulating material having high heat insulating performance, an aerogel structure is known in which aerogel or xerogel (hereinafter, collectively referred to as "aerogel") is held on fibers such as nonwoven fabric. The aerogel has fine pores smaller than the mean free path of air of 68nm, heat conduction of solid and heat conduction caused by convection are small, and has high hydrophobicity. It is known that the aerogel structure has more excellent heat insulation effect than air due to such a structure.

In addition, aerogels are characterized by low mechanical strength and high manufacturing costs. Therefore, in the case where a thick-film heat insulator having a large area is not required, but the heat insulator is installed in a narrow space, particularly, in the case where the heat insulator is sandwiched between small parts, the heat insulator containing aerogel is preferably used. Preferably, the thermal insulation material provided in such a narrow space has small variations in size (thickness).

For example, japanese patent laid-open publication No. 2019-181809 (hereinafter referred to as "patent document 1") discloses a method of providing a heat insulating material excellent in dimensional stability and heat insulating properties.

Patent document 1 discloses a method for producing a heat insulator including the following steps. That is, the method for manufacturing a heat insulator disclosed in patent document 1 includes: a step of adjusting an aerogel precursor (raw material mixing step), a step of impregnating a nonwoven fabric with a raw material and forming a composite (impregnation step), and a step of sandwiching a composite between films (film sandwiching step). Further, a method for manufacturing a heat insulator includes: a step of locally heating the composite to promote the gelation reaction (heating step), a step of pressurizing the composite (pressurizing step), and a step of promoting the growth of the skeleton of the silica particles (curing step). Further, a method for producing a heat insulator including a film peeling step, a hydrophobizing step, and a drying step is disclosed.

According to the method for producing a heat insulator, a heat insulator having excellent compressibility and a sufficient heat insulating effect even in a narrow space in a case of an electronic device or the like can be produced.

In addition, the heat insulator manufactured by the method of patent document 1 intentionally forms a ridge portion and a flat portion. It was confirmed that when a desired compressive force is applied to the heat insulator, the ridge portion is crushed preferentially, and the heat insulating structure of the remaining flat portion is preserved.

However, in recent years, a method of producing an aerogel structure excellent in dimensional stability and thermal insulation with better productivity has been demanded.

Disclosure of Invention

The invention provides an aerogel structure and a manufacturing method thereof, wherein the aerogel structure has excellent dimensional stability and heat insulation performance and can be manufactured with high productivity.

The aerogel structure of the present invention comprises: a composite layer of aerogel is held between the fibrous materials; and an aerogel layer formed by aerogel and arranged on at least one side surface of the composite layer. The aerogel layer has a convex portion protruding from a surface opposite to the composite layer. The density of the aerogel in the convex portion is higher by 0.1% to 3.0% than the density of the aerogel in the aerogel layer other than the convex portion.

The method for producing an aerogel structure of the present invention includes a composite-producing step of discharging a sol from a nozzle that moves discontinuously in a direction intersecting the direction of conveyance of a fiber material toward the continuously conveyed fiber material, and impregnating the fiber material with the sol to produce a composite of the fiber material and a hydrogel. The method for producing an aerogel structure includes a surface modification step of modifying the surface of the composite, and a step of drying the composite.

According to the present invention, an aerogel structure and a method for producing the same can be provided, which are excellent in dimensional stability and thermal insulation properties and can be produced with high productivity.

Drawings

Fig. 1A is a schematic view of an aerogel structure according to an embodiment of the present disclosure.

Fig. 1B is a schematic view of an aerogel structure according to an embodiment of the present disclosure.

Fig. 2 is a step diagram of a method of manufacturing an aerogel structure.

Fig. 3 is a diagram for explaining the distribution of the sol in the nonwoven fabric continuously conveyed in the conveying direction.

Fig. 4A is a diagram illustrating a state in which the sol is impregnated in the nonwoven fabric.

Fig. 4B is a diagram illustrating a state in which the sol is impregnated in the nonwoven fabric.

Fig. 5A is a view showing an appearance of an aerogel structure.

Fig. 5B is a view showing the appearance of the aerogel structure.

Detailed Description

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

(embodiment mode)

An aerogel structure 110 according to an embodiment of the present invention will be described in detail with reference to fig. 1A and 1B.

Fig. 1A and 1B are schematic views of an aerogel structure 110 according to an embodiment of the present invention. In detail, fig. 1A is a schematic perspective view of an aerogel structure 110. Fig. 1B is a schematic sectional view (1B-1B section) of the aerogel structure 110. The aerogel structure of the present embodiment can be used as a heat insulator, for example.

< Structure of aerogel Structure 110 >

First, the structure of the aerogel structure 110 of the present embodiment will be described.

As shown in fig. 1A and 1B, the aerogel structure 110 includes: a composite layer 101 composed of a fiber material and aerogel, and aerogel layers 102 located on the upper and lower surfaces of the composite layer 101. The aerogel layer 102 is disposed on at least one side of the composite layer 101. In a plan view of the aerogel structure 110, the aerogel layer 102 has a plurality of protrusions 103 protruding toward the opposite side of the composite layer 101. Here, the shape of the convex portion 103 in a plan view is a substantially elliptical shape (including an elliptical shape).

The raised portions 103 have a higher color tone than the regions of the aerogel layer 102 other than the raised portions 103 (hereinafter referred to as flat portions 104), and therefore appear bright and white. The reason is presumed to be, for example, that the projection 103 easily transmits light. Therefore, when the aerogel structure 110 is covered with light, the convex portions 103 can be easily visually confirmed. In this case, the intensity of light (emission intensity) when the aerogel structure 110 is covered with light may be, for example, 1cd or more. Therefore, the convex portion 103 can be easily confirmed by using a general fluorescent lamp or a general LED lighting as a light source. The aerogel has a network structure in which particles of silica aerogel are connected by point contact.

(thickness of aerogel structure 110)

The thickness of the aerogel structure 110 is preferably in the range of 0.1mm to 3.0 mm. Further, the thickness of the aerogel structure 110 is more preferably in the range of 0.5mm or more and 1.5mm or less. The reason is as follows: when the aerogel structure 110 is used as a heat insulator, if the thickness of the aerogel structure 110 is less than 0.1mm, it is difficult to obtain sufficient heat insulating performance in the thickness direction. If the thickness of the aerogel structure 110 exceeds 3.0mm, it becomes difficult to incorporate the aerogel structure into a thin and small device. Therefore, the thickness of the aerogel structure 110 is preferably within the above range.

(Density of aerogel Structure 110)

The density of the aerogel structure 110 is preferably 0.3g/cm³Above and 0.6g/cm³The following.

That is, the preferred density range of the aerogel structure 110 is set from both the viewpoint of the thermal insulation performance and the mechanical strength that the aerogel structure 110 should have.

In terms of thermal insulation performance, when the density of the aerogel structure 110 is increased, the average pore size of the aerogel particles is decreased, and the proportion of the solid heat conductive component is increased, thereby decreasing the thermal insulation performance. On the other hand, if the density of the aerogel structure 110 is decreased, the proportion of the solid heat conductive component is decreased, and the proportion of the voids of the aerogel is increased. Therefore, in the aerogel structure 110, the influence of air convection becomes strong, and it becomes difficult to obtain high-performance heat insulation performance.

In addition, in view of mechanical strength, if the density of the aerogel structure 110 is increased, the rigidity is increased. On the other hand, if the density of the aerogel structure 110 decreases, the rigidity decreases. Therefore, if the density is decreased, the aerogel structure 110 becomes difficult to withstand the fastening force when it is incorporated into the heat-insulated unit including the aerogel structure 110 as the heat insulator.

Therefore, in consideration of the use in a thermal insulator, the aerogel structure 110 of the present embodiment is set to the above-described density range in order to achieve both thermal insulation performance and mechanical strength.

(thermal conductivity of aerogel structure 110)

The thermal conductivity of the aerogel structure 110 is preferably 0.02W/(m · K) or more and 0.06W/(m · K) or less.

Here, the thermal conductivity of the nonwoven fabric, which is an example of the fiber material, is 0.03W/(m · K) to 0.06W/(m · K). In addition, the thermal conductivity of the aerogel is 0.01W/(mK) to 0.025W/(mK).

As described above, the aerogel structure 110 of the present embodiment is configured.

(compression ratio of aerogel structure 110)

The compressibility of the aerogel structure 110 after being pressurized at 5MPa is 40% or less, and more preferably 30% or less.

< composite layer 101>

Next, the composite layer 101 of the aerogel structure 110 will be explained.

The composite layer 101 is a main constituent element of the aerogel structure 110, and includes a fiber material and aerogel.

In the present embodiment, the composite layer 101 uses a nonwoven fabric as a fiber material, and aerogel is arranged between fibers of the nonwoven fabric.

(thickness of nonwoven Fabric)

Generally, nonwoven fabrics vary depending on the production method, but have large variations in thickness.

Therefore, in the composite layer 101 of the present embodiment, first, aerogel is filled in a space volume in the nonwoven fabric, and the aerogel layer 102 and the convex portion 103 are formed on the upper surface and the lower surface of the composite layer 101. This absorbs and reduces the variation in thickness of the nonwoven fabric.

Therefore, as the thickness of the nonwoven fabric for forming the composite layer 101, it is preferable to select a nonwoven fabric having a thickness in the range of 60% to 99% with respect to the preferable thickness of the aerogel structure 110 (0.1mm or more and 3.0mm or less, more preferably 0.5mm or more and 1.5mm or less). By setting the thickness of the nonwoven fabric within this range, variations in the thickness of the nonwoven fabric can be absorbed and alleviated while maintaining the flexibility peculiar to the nonwoven fabric.

(bulk Density of nonwoven Fabric)

The bulk density of the nonwoven fabric is preferably 100kg/m³Above and 500kg/m³Within the following ranges. By using the nonwoven fabric having the above bulk density, the content of the aerogel in the aerogel structure 110 can be increased, and the thermal conductivity can be reduced. Further, by using a bulk density of 100kg/m³The nonwoven fabric described above can ensure mechanical strength as a continuous body. In this case, the porosity of the nonwoven fabric is preferably 85% or more, more preferably 90% or more.

(Material of nonwoven Fabric)

As the material of the nonwoven fabric used for the composite layer 101, glass wool or rock wool of inorganic fiber system can be used; organic fiber-based PolyEthylene Terephthalate (PET: PolyEthylene Terephthalate), PolyPhenylene Sulfide (PPS: PolyPhenylene Sulfide), PolyPropylene (PP: PolyPropylene), PolyTetraFluoroEthylene (PTFE: PolyTetrafluoroethylene); natural wool, cellulose, and the like. Among these, nonwoven fabrics of inorganic fibers are particularly preferable.

(average diameter of fiber of nonwoven Fabric)

The average diameter of the fibers used in the nonwoven fabric is preferably 0.1 μm or more and 10 μm or less. The average diameter of the fibers is more preferably 0.3 μm or more and 5 μm or less.

The reason why the above range is preferable is as follows.

If the average diameter of the fibers is less than 0.1 μm, the fibers may be difficult to manufacture and handle, and thus the economical efficiency may be lowered. When the average fiber diameter exceeds 10 μm, the porosity in the case of producing a nonwoven fabric is lowered. Therefore, there is a concern that preferable heat insulating performance of the aerogel structure 110 cannot be secured.

As described above, the composite layer 101 of the aerogel structure 110 of the present embodiment is configured.

< aerogel layer 102>

Next, the aerogel layer 102 of the aerogel structure 110 will be explained.

The aerogel layer 102 is formed on both surfaces of the composite layer 101 to a thickness of at least 0.01mm or more. The aerogel layer 102 is a single layer formed of aerogel only.

The aerogel layer 102 has a network structure in which aerogel particles of several tens of nm are connected.

When the aerogel layer 102 is made thicker, the thermal insulation performance is improved, but the possibility that the aerogel layer 102 peels off from the composite layer 101 is also increased. Therefore, the thickness of the aerogel layer 102 is preferably 0.2mm or less. That is, in the present embodiment, the thickness of the aerogel layer is preferably 0.01mm to 0.2 mm. The aerogel layer 102 is preferably free of fibers and preferably consists of aerogel alone.

< convex part 103>

As described above, the convex portion 103 is a portion of the aerogel layer 102 protruding from the surface opposite to the composite layer 101. Like the aerogel layer 102, the projections 103 are composed of only aerogel.

The thickness of the convex portions 103 is 10 μm to 30 μm thicker than the flat portions 104 in the periphery of the aerogel layer 102.

With respect to the convex portions 103, the aerogel particles forming the convex portions 103 are connected by a network structure continuous with the aerogel particles of the aerogel layer 102.

< method for producing aerogel structure 110 >

An example of a method for producing the aerogel structure 110 will be described below with reference to fig. 2.

Fig. 2 is a step diagram of a method of manufacturing the aerogel structure 110. The method for producing the aerogel structure 110 includes (a) a raw material adjustment step, (b) a composite body formation step, (c) a surface modification step, and (d) a drying step, which are described below.

(a) Raw material adjusting step

Hereinafter, the production method will be described by taking a case of using silica aerogel as the aerogel as an example.

As the silica aerogel, a general-purpose silica raw material such as alkoxysilane or water glass is used as a raw material. In particular, in order to produce silica aerogel having a high-density porous structure, water glass is used in many cases. In the present embodiment, a dispersion or solution obtained by dispersing or dissolving a silica raw material in water is used so that the silica concentration falls within a desired range. In order to synthesize a high-density aerogel, the higher the silica concentration in the dispersion or solution, the more preferable is 14% by weight or more and 22% by weight or less.

In the present embodiment, carbonate is used as a gelling agent for gelling a dispersion or a solution in the silica raw material. Carbonates are known to hydrolyze to carbonic acid and alcohol under alkaline conditions. Therefore, in the present embodiment, the carbonic acid generated by the hydrolysis is used for gelation.

Specific examples of the carbonate include dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethylmethyl carbonate, ethylene carbonate, and propylene carbonate. In particular, from the viewpoint of solubility of the carbonate in water and the hydrolysis reaction rate, it is preferable to use dimethyl carbonate or ethylene carbonate having a short alkyl chain and being relatively easily soluble in water.

The amount of the carbonate added is preferably 1.0 part by weight or more and 10.0 parts by weight or less, and preferably 3.0 parts by weight or more and 6.0 parts by weight or less, based on 100 parts by weight of the total amount of the silica raw material (water glass composition). By this addition amount, a uniform gel can be formed. The carbonate may be mixed with the raw material dispersion or solution in a state of being dissolved or dispersed in water. This improves the compressibility of the produced thermal insulation material.

(b) Complex Generation step

The composite production step is a step of impregnating a nonwoven fabric with an alkaline sol (hereinafter, referred to as "sol") produced by mixing a carbonate with a water glass composition, and gelling the impregnated nonwoven fabric.

In the present embodiment, the composite producing step produces a composite by a roll-to-roll method in consideration of productivity.

Here, the roll-to-roll method is a method in which the nonwoven fabric placed on the film is continuously conveyed, and the nozzle that continuously discharges the sol is oscillated in the width direction of the nonwoven fabric. Then, the sol is dropped from the oscillating nozzle from the upper side onto the nonwoven fabric to impregnate the nonwoven fabric with the sol. In the present embodiment, in order to stably run the impregnated nonwoven fabric, the film is combined with the open surface side after the sol drops, and the film is laminated by a roller (the impregnated nonwoven fabric is sandwiched by the film from both sides). This makes it possible to stably run the nonwoven fabric, to easily adjust and uniformize the thickness, and to prevent contamination of the production equipment.

As an example of the swing pattern of the nozzle, an operation of discontinuously moving between 2 or more stop points set in a direction intersecting the conveyance direction of the nonwoven fabric is employed. The discontinuous movement means an operation in which the nozzle is intermittently moved between stop points and is suspended at the stop points. The nozzle is mechanically oscillated by, for example, an oscillation mechanism not shown. In the present embodiment, three points, i.e., the left and right end portions and the central portion in the width direction of the nonwoven fabric, are set as the stopping points.

By the operation of the nozzle, the 1 st region and the 2 nd region are formed in the nonwoven fabric continuously conveyed in the predetermined conveying direction. The 1 st region is a region where the sol ejected from the nozzle drops at the stop point. The 2 nd region is a region other than the 1 st region.

That is, as described above, in the 1 st region, there is a sol continuously ejected in a state where the nozzle is suspended. Therefore, the amount of sol existing in the 1 st region is larger than that in the 2 nd region where the sol is discharged while the nozzle moves between the stopping points.

The supply amount of the sol discharged from the nozzle is fixed, and is set to, for example, the 1 st supply amount. That is, even in the 2 nd region where the amount of the sol is small, the supply amount is set to the 1 st supply amount exceeding the standard amount that can sufficiently impregnate the nonwoven fabric. The above setting is to impregnate the nonwoven fabric with an excessive amount of sol, thereby obtaining a state in which the sol is allowed to bleed out in the thickness direction of the nonwoven fabric.

In the aerogel structure thus produced, aerogel layers 102 disposed on both sides of the composite layer 101 are formed as shown in fig. 1A and 1B in the composite body production step. The reference amount of the sol that can sufficiently impregnate the nonwoven fabric is preferably set based on a theoretical spatial volume in the nonwoven fabric calculated from the bulk density of the nonwoven fabric.

Next, in the composite-body producing step, the distribution of the sol in the nonwoven fabric 201 continuously conveyed in the conveying direction will be described with reference to fig. 3.

Fig. 3 is a diagram for explaining the distribution of the sol in the nonwoven fabric 201 continuously conveyed in the conveying direction.

As described above, the sol is dropped onto the nonwoven fabric being continuously conveyed by using the nozzle moving in the direction intersecting the width direction of the nonwoven fabric. In this case, the movement of the nozzle as viewed from the nonwoven fabric is shown by arrow a in fig. 3. In fig. 3, the following case is illustrated as an example: the nozzle was repeatedly moved in the order of left, center, right, and left … at 3 stopping points set to left, center, and right, with respect to the direction of conveyance of the nonwoven fabric.

By such an operation of the nozzle, the 1 st region 202 in which the amount of the sol is large and the 2 nd region 203 in which the amount of the sol is small are formed on the nonwoven fabric 201. The 1 st region is a region where the sol ejected from the nozzle that was suspended at any of the 3 stopping points is present. The 2 nd region is a region where the sol discharged from the nozzle on the way between the stopping points is present.

As described above, in the composite body producing step, the sol is excessively supplied in the vicinity of the 1 st region where the sol discharged while the nozzle is suspended at the stop point is present. Therefore, the excessive sol that cannot be completely absorbed in the voids inside the nonwoven fabric is superimposed in the thickness direction, or overflows to the outside from the end faces of the nonwoven fabric.

That is, in the aerogel structure 110 of the present embodiment, the convex portions 103 shown in fig. 1A and 1B are portions where the above-described excessive sols are superimposed in the thickness direction. Therefore, the convex portion 103 becomes thicker than other regions.

The reason why the protruding portions 103 have a substantially elliptical shape as described above is considered to be that the sol spreads out due to the pressing action on the sol when the film is attached to the composite.

In the following, an example of a state in which the nonwoven fabric 201 is impregnated with the sol in the composite producing step will be described with reference to fig. 4A and 4B.

Fig. 4A and 4B are diagrams illustrating a state in which the sol is impregnated in the nonwoven fabric. Specifically, fig. 4A is a photograph showing a state in which the sol is impregnated in the nonwoven fabric. FIG. 4B is a schematic view showing a state in which the sol is impregnated in the nonwoven fabric.

That is, fig. 4A and 4B show a state in which the region impregnated with the sol is expanded.

As shown in fig. 4A and 4B, the vicinity of the boundary between the region impregnated with the sol and the region not impregnated with the sol includes a region divided into a 3 rd region 301, a 4 th region 302, and a 5 th region 303. The 3 rd region 301 is a region where both surfaces of the nonwoven fabric are sufficiently impregnated with the sol. The 4 th region 302 is a region which is impregnated with a gel to a greater or lesser extent but is not impregnated sufficiently to both surfaces of the nonwoven fabric. The 5 th region 303 is a region not impregnated with the gel.

Specifically, when the sol is dropped onto a nonwoven fabric provided on a film, not shown, the gel spreads in each of the planar direction and the thickness direction. More specifically, when the sol is dropped onto the nonwoven fabric, the sol spreads in the planar direction and also spreads in the thickness direction due to a capillary phenomenon caused by the fibers of the nonwoven fabric. Then, the sol that has once seeped out to the back surface spreads in the planar direction along the film disposed on the lower side of the nonwoven fabric.

Therefore, it is important to dispose the film at least on the lower side of the nonwoven fabric, preferably also on the upper surface of the nonwoven fabric, and to supply the sol in a sufficient amount. This allows the sol to be sufficiently impregnated in the plane direction of the nonwoven fabric.

Therefore, after a suitable amount of sol is impregnated into the nonwoven fabric, the film is placed from the upper side of the composite of the nonwoven fabric and the sol. Thus, the both surfaces of the composite are sandwiched by the films so that the sol impregnated into the nonwoven fabric does not flow down. Then, the composite sandwiched by the films undergoes gelation during conveyance. At this time, the thickness is regulated by using a twin roll or the like at an appropriate timing. This enables a more homogeneous composite to be produced.

(c) Surface modification step

Mixing the hydrogel/nonwoven fabric composite produced in the composite production step (b) with a silylating agent to perform surface modification. As the silylation method and silylation agent, known methods and known materials can be used. In particular, the following method is preferable because the silylation treatment can be performed rapidly. That is, first, the hydrogel/nonwoven fabric composite is immersed in an aqueous hydrochloric acid solution. Thereafter, the composite impregnated with the aqueous hydrochloric acid solution is treated with a mixed solution of siloxane and alcohol. This enables the complex to be silylated quickly.

(d) Drying step

Removing the liquid contained in the surface-modified hydrogel/nonwoven fabric composite obtained in the surface modification step (c) by drying under conditions of a critical temperature of the liquid and a pressure lower than the critical pressure of the liquid. Thereby, the aerogel structure 110 of the present embodiment is obtained.

When a carbonate is added as a gelling agent to the water glass composition in the complex formation step (b), sodium carbonate is formed along with dehydration condensation of silicic acid. Therefore, there are cases where sodium carbonate is incorporated into the gel to enable a very basic hydrogel to be obtained. In this case, when the hydrogel having a very strong basicity is immersed in hydrochloric acid in the surface modification step (c), a neutralization reaction between the hydrochloric acid and sodium carbonate occurs, and carbon dioxide gas is rapidly generated. At this time, when a nonwoven fabric fiber such as a cellophane in which entanglement of fibers is small is used, there are cases in which: due to the generation of the carbon dioxide gas, a large number of bubbles are generated in the fiber sheet. Therefore, before the surface modification step (c) of immersing in hydrochloric acid, water washing may be performed to remove sodium carbonate in the hydrogel in advance.

As described above, the aerogel structure 110 of the present embodiment is manufactured.

(examples)

Next, an example of the aerogel structure manufactured by the manufacturing method according to the above embodiment will be described with reference to fig. 5A and 5B. The following examples are only examples, and the present invention is not limited to these examples.

In addition, regarding the aerogel structure in the example, in the manufacturing method of the above embodiment, the raw material was adjusted so that the silica concentration became 20 wt%, and was performed under the air. Further, the aerogel structures of examples were produced by adjusting various parameters such as the thickness, bulk density, material, average fiber diameter, thickness of the aerogel layer, and thickness of the convex portion of the nonwoven fabric to values within the preferable ranges.

Fig. 5A and 5B are views showing the appearance of the aerogel structure according to the example produced under the above conditions. In detail, fig. 5A is an appearance photograph of the aerogel structure. Fig. 5B is a schematic view of an aerogel structure.

As shown in fig. 5A and 5B, the convex portions 103 are formed so as to protrude from the flat portions 104 of the aerogel layer 102 in a direction perpendicular to the paper surface of fig. 5A and 5B. The convex portion 103 corresponds to the 1 st region 202 (see fig. 3) formed at the stop point of the nozzle.

The appearance, thickness, density, compressibility, thermal conductivity, and thermal resistance of the obtained aerogel structure were evaluated as follows.

< evaluation of appearance >

The appearance evaluation of the aerogel structure of the example manufactured by the manufacturing method of the present embodiment was performed by transmitting illumination light from the back surface of the aerogel structure in a dark room. In addition, the method is not limited to the above method, and in an indoor environment under general fluorescent lamp illumination, illumination (LED illumination or the like) having a higher emission intensity than ambient illumination may be transmitted from the back surface to perform appearance evaluation.

As a result, the convex portions protruding from the aerogel layers on both surfaces of the aerogel structure have a higher color tone (are brighter and whiter) than the peripheral regions thereof. As a result, as described above, it can be easily determined whether or not the convex portions are properly formed after the aerogel structure is manufactured.

< evaluation of thickness, density, compressibility, thermal conductivity, thermal resistance >

The thickness was evaluated by using Digimatic Indicator H0530 (manufactured by Mitutoyo Co., Ltd.).

At this time, the measurement pressure was set to 7.4 kPa. As for the measurement position, first, 13 points are selected in the vicinity of the center of the convex portion in the plane of the aerogel structure, and 10 points are selected in the vicinity of the center of the flat portion which is the portion around the convex portion of the aerogel layer. Then, each of the selected measurement positions was cut into a size of 20mm square, and the thickness was evaluated.

As a result of the measurement, the thickness (average value) of the convex portion was 1.148mm, and the thickness (average value) of the flat portion was 1.126 mm. That is, the projections were 0.022mm thicker than the peripheral flat portions thereof, and about 2.0% thicker.

In addition, for each thickness, when compared with each other at the minimum value, the convex portion is 0.9% thicker than the flat portion, and when compared with each other at the maximum value, the convex portion is 2.6% thicker than the flat portion. That is, it is understood that the convex portion can be formed to be sufficiently thicker than the flat portion.

As described above, the convex portion protrudes from the flat portion. Therefore, when a compressive force is applied to the aerogel structure, the convex portions receive the compressive force concentratedly. As a result, the compressive force can be made difficult to be applied to the flat portion. Even when a compression force of a predetermined value or more is applied, the structure of the flat portion can be ensured by first crushing from the convex portion.

On the other hand, when the aerogel structure is used as a heat insulating material, a plurality of aerogel structures are arranged so as to be sandwiched between the heat-insulated cells. Therefore, the increase in the thickness of the projection is preferably not excessively large.

In the aerogel structure manufactured by the manufacturing method of the present embodiment, the convex portions are formed to be thicker than the flat portions, and the increase in thickness of the convex portions can be suppressed within an appropriate range. Therefore, the structure securing performance of the aerogel structure and the performance of incorporating the aerogel structure into the heat-insulated unit can be achieved at the same time.

In addition, the density evaluation was calculated by dividing the weight of each of the above cut pieces by the volume, and the average value thereof was evaluated. As a result of the calculation, the density of the convex portion was 0.465g/cm³The density of the flat part is 0.458g/cm³. That is, when comparing the density of the convex portions and the flat portions, the density of the convex portions is higher by about 1.5%.

In addition, when the densities are compared with each other at the respective minimum values, the convex portions are higher than the flat portions by 0.03%, and when the densities are compared with each other at the maximum values, the convex portions are higher than the flat portions by 2.1%. That is, it is found that the convex portions can be formed at a sufficiently higher density than the flat portions.

In the aerogel structure, the density of the convex portions is preferably higher than that of the flat portions by 0.1% to 3.0%. When the density of the projections is higher than 3.0%, the thickness of the projections is excessively increased, and there is a possibility that the assembling property is impaired. When the difference between the density of the convex portions and the density of the flat portions is less than 0.1%, the density of the convex portions and the flat portions hardly changes. Therefore, there is a possibility that the projections may not sufficiently secure the structure of the aerogel structure.

The compression ratio was evaluated by averaging the changes in compression behavior of the aerogel structure according to a fastening force of 1 to 5MPa, a load, and the like. The fastening force and the load are values close to the actual use environment of the aerogel structure. That is, the fastening force required for assembling the unit to be insulated is 1MPa, and the maximum load in use is 5 MPa. The above-described dicing sheet was used for the sample specimen. A universal tensile tester AUTOGRAPH-AGS-X (manufactured by Shimadzu corporation) was used as the measuring device.

As a result of evaluation of the compressibility, the convex portion was 3.39%, and the flat portion was 3.56%. That is, when the compressibility of the convex portion was compared with that of the flat portion, the convex portion was lower by about 5.1%. In addition, for the respective compression ratios, the convex portion was lower than the flat portion by 0.6% when compared with each other at the minimum value, and the convex portion was lower than the flat portion by 15.1% when compared with each other at the maximum value. That is, it is found that the convex portion can be formed by sufficiently reducing the compression ratio as compared with the flat portion.

In the aerogel structure, the compression rate is preferably 0.1% or more and 20% or less lower at the convex portion than at the flat portion. When the protrusions are lower by more than 20%, the void portions of the aerogel cannot be formed in the protrusions. Therefore, there are cases where sufficient heat insulating performance cannot be ensured in the entire aerogel structure. In addition, when the difference in the compression ratios of the convex portions and the flat portions is less than 0.1%, the compression ratios of the convex portions and the flat portions hardly change. Therefore, when a compressive force is applied to the aerogel structure, it is difficult to withstand the applied compressive force at the convex portions. That is, with respect to the compression ratio, the above range is preferable.

The aerogel structure of the present embodiment is produced using a raw material having a silica concentration of 20 wt%. This can achieve both the reactivity and the suppression of compressive strain during the production of the aerogel. That is, the compressive strain of the aerogel structure according to the present embodiment is suppressed to 5% or less.

In addition, the thermal conductivity was measured at arbitrary 6 points of the aerogel structure including the convex portions and the flat portions before cutting, not the cut piece, and the average value was calculated and evaluated. The thermal flowmeter HFM436Lamda (NETZSCH) was used for the measuring instrument. The evaluation result was 49.18 mW/(m.K).

In addition, the thermal resistance value was evaluated by calculating the thermal resistance value by dividing the average value of the thicknesses when the above-described dicing sheets were pressed at 5MPa by the thermal conductivity. As a result, the number of projections was 0.022m²K/W, flat part of 0.021m²K/W。

< summary of evaluation >

Hereinafter, the evaluation results of the convex portions and the flat portions of the aerogel structure according to the above-described example are shown in table 1.

[ Table 1]

< action, Effect >

As described above, the aerogel structure 110 of the present invention includes: a composite layer 101 in which aerogel is held between fiber materials; and an aerogel layer 102 formed of aerogel and provided on at least one surface of the composite layer 101. The aerogel layer 102 has a projection 103 projecting from the surface opposite to the composite layer 101. The density of the aerogel in the convex portions 103 is higher by 0.1% to 3.0% than the density of the aerogel in the aerogel layers 102 (flat portions 104) other than the convex portions.

According to this configuration, the aerogel structure 110 according to the present invention has a structure in which the aerogel having high thermal insulation properties is held in the fiber material. Therefore, it is useful as a heat insulator. The convex portion 103 is thicker than the flat portion 104, and is also excellent in compression characteristics. Therefore, in an environment where the aerogel structure 110 is sandwiched in a narrow space and compressive stress acts, the convex portions 103 are crushed, so that damage to the flat portion 104 is favorably reduced. The density of the aerogel in the convex portions 103 is higher than the density of the aerogel in the flat portions 104 by 0.1% to 3.0%. Therefore, even if stress is applied to the aerogel structure 110 from the outside, the convex portions can sufficiently secure the structure of the aerogel structure. Thereby, high dimensional stability of the aerogel structure 110 can be ensured. In addition, the thickness of the convex portion 103 is not excessively thickened compared to the flat portion 104. Therefore, when the aerogel structure 110 is incorporated as a heat insulator into the heat-insulated unit, sufficient assemblability can be ensured.

Further, the aerogel structure 110 is provided with a plurality of convex portions that are provided on the surface and that have a higher color tone (brighter and whiter) than the flat portions 104. Therefore, image recognition becomes easy, and such an effect on appearance that the appearance authentication is improved is also obtained. The image recognition is performed to recognize the produced aerogel structure in the production stage and the inspection stage of the aerogel structure 110.

In addition, the method for producing an aerogel structure of the present invention includes: a composite body production step of applying and impregnating a sol into a fiber material continuously conveyed in a conveyance direction to produce a composite body of the fiber material and a hydrogel; a surface modification step of performing surface modification on the complex; and a drying step of drying the composite to produce the aerogel structure 110. In the composite body producing step, the fiber material is coated with the sol discharged from the nozzle discontinuously moving in the direction intersecting the conveying direction of the fiber material.

According to this method, the aerogel structure 110 can be produced by a continuous production method such as a roll-to-roll method. Thereby, the productivity of the aerogel structure 110 can be improved.