JP2007239931A - Vacuum heat insulation material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a vacuum heat insulation material with high uniformity in heat insulation characteristics, easily manufacturable by a normal paper making device and method, having a structure not having particular orientation in fiber orientation in a sheet horizontal direction, and providing efficient removal of a very small amount of adsorbed moisture on an inorganic fiber surface, in regard to a vacuum heat insulation material using multiple layers of wet type papermaking sheets mainly composed of inorganic fiber with very small diameters as a vacuum heat insulation material core material. <P>SOLUTION: The vacuum heat insulation material is composed by using plurally laminated inorganic sheets formed by carrying out wet type paper making on mainly inorganic fiber with an average fiber diameter of 4 μm or less. It is characterized by that a percentage content of particulate matter with a particle size of 30 μm or more and fibrous matter with a diameter of 10 μm or more in the inorganic fiber is 0.1 wt.% or less, thickness of the inorganic fiber sheet is 0.2 mm or less, and the inorganic fiber in the core material is arranged in a vertical direction with respect to a laminated direction of the inorganic fiber. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a vacuum heat insulating material in which a nonwoven fabric sheet mainly composed of inorganic fibers is laminated as a core material.

  Conventionally, a vacuum heat insulating material is generally used in which a core material formed of an inorganic fiber, such as a needling mat, felt, wool, etc., is stored in a heat insulating container and then vacuumed and sealed. ing.

  In order to improve the heat insulation of the core material for vacuum heat insulating materials made of such inorganic fibers, conventionally, the content of shots (non-fibrous granules) in the inorganic fibers is reduced, or the inorganic fibers are moved in the heat transfer direction. On the other hand, a method has been proposed in which the thermal conductivity is lowered by arranging in the vertical direction.

If the shots in the inorganic fiber are large in size and large in number, the size and number of voids in the core for vacuum heat insulating material increase, and heat conductivity is increased by heat transfer due to air convection in the large voids. It has been found that it increases and the thermal insulation decreases.
In addition, it is known that the thinner the inorganic fiber, the smaller the joint area between the fibers, which complicates the heat transfer path and improves the heat insulation.

  For this reason, recently, as disclosed in Patent Document 1, a multilayered wet paper sheet made of inorganic fibers having a fine diameter of 2 μm or less without using a binder or the like is used for a vacuum heat insulating material. It has also been proposed to use it as a core material. In this case, the shot content is substantially zero, and since the heat transfer path can be lengthened by the fine-diameter inorganic fibers as described above, a vacuum heat insulating material having high heat insulating performance. Is obtained.

  In addition, if the core for vacuum insulation is made up of only inorganic fibers without using a binder, there will be no extra gas generation other than moisture during decompression. The amount of the gas adsorbent used for maintaining the degree of vacuum of the heat insulating material can be reduced, resulting in characteristic and cost advantages.

  In addition, when the vacuum heat insulating material core is composed of a wet papermaking sheet, since the sheet thickness is uniform, there are no irregularities on the outer surface of the vacuum heat insulating material core, and there is no space between the exterior material and the core material. Therefore, thermal convection is reduced, resulting in improved thermal insulation performance and uniformity of thermal insulation characteristics.

  In addition, when a wet paper-making sheet is laminated in multiple layers to form a vacuum heat insulating material core material, it is certainly a vacuum heat insulating material core material that is not a multilayer structure in which inorganic fiber raw cotton is accumulated as in Patent Document 2. Compared with the core material as a whole, the fibers are arranged in a direction relatively perpendicular to the lamination direction of the core material, but the thickness per wet papermaking sheet is usually about 2 mm, which is special during wet papermaking. If the control is not performed, the fibers in the wet papermaking sheet are not necessarily arranged in the horizontal direction. Therefore, when the wet papermaking sheet having a thickness of about 2 mm is viewed as a single piece, the degree of fiber arrangement in the horizontal direction is never high. I can not say.

In view of this, the applicant previously used a special paper machine (such as a sealed inclined paper machine with a pound regulator) that can easily adjust the jet / wire ratio during wet paper making. By setting the ratio to a specific value of 0.5 to 0.8 to obtain a wet papermaking sheet, fibers oriented in the thickness direction of the core material are eliminated, and the degree of alignment of the fibers in the horizontal direction is remarkably increased. The vacuum heat insulating material which improved and improved the heat insulation effect was proposed (patent document 3).
JP 7-139691 A JP 7-167376 A JP 2005-265038 A

  However, the vacuum insulating material core material disclosed in Patent Document 3 can certainly increase the degree of alignment of the fibers in the horizontal direction, but cannot be manufactured without using a special paper machine or a special control device. In addition, the resulting wet papermaking sheet is also arranged in the MD direction (the length direction of the wet papermaking sheet formed on the continuous sheet) by pulling the fibers on the forming wire and forcing the fibers in the horizontal direction. ) In which the fibers are oriented. In wet papermaking sheets with fibers oriented in the MD direction, the mechanical strength in the CD direction (the direction perpendicular to the MD direction, the width direction of the wet papermaking sheet) is extremely weak, which hinders handling in the vacuum insulation material manufacturing process, etc. In addition, the heat conduction in the horizontal direction of the core (perpendicular to the sheet stacking direction) is concentrated in one direction when used as a core for vacuum insulation. It may interfere with the design.

  In addition, when a wet paper-making sheet made of inorganic fibers with an average fiber diameter of 2 μm or less is laminated in multiple layers as a core material for a vacuum heat insulating material, it certainly has high heat insulating performance and uniform heat insulating properties. There are also the following disadvantages. The core material for a vacuum heat insulating material made of a wet papermaking sheet of inorganic fibers is supplied and used as a dry sheet, but since inorganic fibers have a high affinity with water (contact angle is 0 degree), they are supplied. The core material for a vacuum heat insulating material made of a wet papermaking sheet of inorganic fibers has a problem that moisture in the air is gradually adsorbed (absorbed) until it is assembled as a vacuum heat insulating material. If the fiber diameter of the inorganic fiber is reduced, the surface area of the inorganic fiber is increased, so that the amount of moisture absorbed by the wet papermaking sheet having a constant mass is also increased. Usually, in the case of a vacuum heat insulating material using a vacuum heat insulating material core composed of a wet papermaking sheet mainly composed of inorganic fibers having an average fiber diameter of 2 μm or less, about 0.5% by mass until the vacuum heat insulating material is assembled. Moisture is adsorbed on the fiber surface.

  If the vacuum insulation core material has moisture, the vacuum degree of the vacuum insulation material cannot be increased, so it is necessary to remove moisture in advance before assembling the vacuum insulation material.・ Dry processing by external heating methods such as far-infrared heating, contact drying, and hot air drying is performed. However, this drying method has a problem that the inorganic fibers on the surface partially reflect heat, and the inorganic fibers are fine. Therefore, the thicker the core material, the worse the heat conduction. Therefore, it usually takes about 10 hours for drying at 120 ° C., which increases the cost.

  Therefore, in view of the above-mentioned conventional problems, the present invention provides a vacuum heat insulating material in which a wet paper-making sheet mainly composed of fine-diameter inorganic fibers is laminated as a core material for a vacuum heat insulating material. The sheet can be easily manufactured by a normal paper making apparatus and a paper making method that does not use a special device or special control, and the degree of arrangement of the inorganic fibers in the horizontal direction of the sheet is extremely high. Provides a vacuum insulation with high heat insulation performance and high uniformity of heat insulation properties, which has a structure that does not have a specific orientation in the fiber orientation, and that can efficiently remove trace moisture adsorbed on the surface of inorganic fibers The purpose is to do.

As a result of intensive studies to achieve the above-mentioned object, the inventors of the present invention, in the inorganic fiber sheet obtained by the wet papermaking method, the smaller the thickness, the more the fibers constituting the sheet are oriented in the same direction as the thickness direction. It has become difficult to do, and it has been found that it will be arranged in a substantially horizontal direction. The vacuum heat insulating material of the present invention is an invention made on the basis of such knowledge, and as described in claim 1, a plurality of inorganic fiber sheets obtained by wet papermaking mainly composed of inorganic fibers having an average fiber diameter of 4 μm or less are laminated. It is a vacuum heat insulating material using a thing as a core material, Comprising: The content rate of the granular material with a particle size of 30 micrometers or more in the said inorganic fiber and the fibrous material with a diameter of 10 micrometers or more is 0.1 mass% or less, The said inorganic The fiber sheet has a thickness of 0.2 mm or less, and the inorganic fibers in the core material are arranged in a direction perpendicular to the stacking direction of the inorganic fiber sheets.
The vacuum heat insulating material according to claim 2 is characterized in that, in the vacuum heat insulating material according to claim 1, the inorganic fibers in the inorganic fiber sheet do not have a specific orientation in the horizontal direction of the sheet. .
The vacuum heat insulating material according to claim 3 is the vacuum heat insulating material according to claim 1 or 2, wherein the inorganic fiber sheet is composed of only inorganic fibers.
Moreover, the vacuum heat insulating material of Claim 4 is a vacuum heat insulating material in any one of Claims 1 thru | or 3, The said inorganic fiber is glass fiber, It is characterized by the above-mentioned.
Moreover, the vacuum heat insulating material according to claim 5 is the vacuum heat insulating material according to any one of claims 1 to 4, wherein an average fiber diameter of the inorganic fibers is 0.2 to 2 μm.
The vacuum heat insulating material according to claim 6 is characterized in that, in the vacuum heat insulating material according to claim 5, an average fiber diameter of the inorganic fibers is 0.2 to 1 μm.
In addition, “the content of the granular material having a particle size of 30 μm or more and the fibrous material having a diameter of 10 μm or more in the inorganic fiber is 0.1% by mass or less” in claim 1 is the particle size contained in the inorganic fiber. It means that the total amount of the granular material having a diameter of 30 μm or more and the fibrous material having a diameter of 10 μm or more is 0.1% by mass or less.

  The vacuum heat insulating material of the present invention is an inorganic fiber sheet formed by wet papermaking mainly using inorganic fibers as the minimum unit fiber layer constituting the core material, in particular, an inorganic fiber sheet having a thickness set to be very thin as 0.2 mm or less. It is characterized by being used as a core material by laminating it in multiple layers. That is, according to the present invention, in the inorganic fiber sheet obtained by the wet papermaking method, the thinner the thickness, the more difficult it is for the fibers constituting the sheet to be oriented in the same direction as the thickness direction. The inorganic fiber has an extremely high degree of alignment of the inorganic fibers in the horizontal direction of the sheet by a normal papermaking apparatus and a papermaking method that do not require special equipment or special control. In the fiber sheet, the fiber orientation in the horizontal direction of the sheet is aligned in one direction and does not adversely affect the mechanical strength and heat conduction characteristics of the core material. It is possible to easily obtain an inorganic fiber sheet that does not have, and if the inorganic fiber sheet is laminated in multiple layers to form a core material, a vacuum heat insulating material with high heat insulating performance and high uniformity of heat insulating properties can be accommodated. It is possible to provide.

  In addition, when the trace moisture of inorganic fibers constituting the core material is removed by heat drying before packing and vacuuming the exterior material, the heat conduction is worse as the minimum unit fiber layer constituting the core material is thicker. However, in the vacuum heat insulating material of the present invention, the inorganic fiber sheet whose thickness is set as thin as 0.2 mm or less is used as the minimum unit fiber layer constituting the core material, and this is laminated in multiple layers. Therefore, the evaporation of moisture from both sides of the thin inorganic fiber sheet is facilitated, and the drying time can be shortened by efficient moisture removal, which contributes to the improvement of the productivity of the vacuum heat insulating material.

  The inorganic fiber sheet constituting the core material is a sheet made by wet papermaking mainly composed of inorganic fibers, excellent in accuracy of thickness and density, and when such an inorganic fiber sheet is laminated in multiple layers as a core material, Compared to a core material formed by compressing a cotton collection laminate made of inorganic fiber wool, it is superior in accuracy of thickness and density, and stable quality can be obtained.

  The core material has a structure in which inorganic fiber sheets having a very thin thickness of 0.2 mm or less are laminated in multiple layers, and inorganic fibers in the horizontal direction of the core material (perpendicular to the sheet lamination direction) Because of the extremely high degree of arrangement, the inorganic fibers aligned in the horizontal direction with respect to the heat conduction block the heat conduction, making the heat transfer path complicated and maze, thereby extending the heat conduction time and insulating. It becomes possible to improve the property.

  As described above, the average fiber diameter of the inorganic fibers needs to be 4 μm or less. This is because if the average fiber diameter of the inorganic fibers is more than 4 μm, a very thin inorganic fiber sheet having a thickness of 0.2 mm or less is not used by wet papermaking, and in particular, a secondary material such as a binder other than inorganic fibers is not used. This is because it becomes difficult to form a sheet alone.

  Further, if the average fiber diameter of the inorganic fiber is less than 0.2 μm, it is possible to form a sheet by wet papermaking, but the manufacturing cost is high, and there is a disadvantage that it is not suitable for practical use as an industrial product. The average fiber diameter of the inorganic fibers is preferably 0.2 μm or more.

  In addition, as described above, in the case of a core material composed of inorganic fibers, the thinner the inorganic fibers, the smaller the joint area between the fibers, the more complicated the heat transfer path, and the better the heat insulation. From this viewpoint, the average fiber diameter of the inorganic fibers constituting the core material is preferably 2 μm or less, more preferably 1 μm or less.

  As the inorganic fiber, glass fiber, ceramic fiber, slag wool fiber, rock wool fiber or the like can be used, but glass fiber is preferable in that a fine fiber having an average fiber diameter of 4 μm or less is easily obtained industrially. .

  As the glass fiber, for example, a short glass fiber obtained by melting and spinning an acid-resistant C glass and then applying energy by a flame of a burner and blowing it, or a long glass fiber spun after melting the C glass is suitable. Used for. Glass fiber obtained by such a flame method or other methods such as centrifugation is formed in a columnar shape with a small surface area and is not branched (fibrillated) like pulp fibers. Even when the fiber in the papermaking raw material liquid is pulled by a forming wire that travels in a certain direction during wet papermaking, there is no inconvenience that the fiber is caught and the surface of the sheet collapses or a hole is opened.

  In the case of the short glass fiber, if the burner flame energy is uneven or insufficient, it is mixed with the original short glass fiber, and the fiber ends are attached with a teardrop-like lump. In some cases, a small amount of a granular material or a fibrous material having a relatively large size with respect to the original short glass fiber, such as a thickened fiber or a thick fiber before being blown off by a burner, may remain. In the present invention, in order to eliminate the surface irregularities and the like and perform wet papermaking, for example, a papermaking raw material liquid (papermaking slurry) in which glass fibers are dispersed in a dispersion medium is centrifuged and passed through a screen filter. The granular material having a particle size of 30 μm or more in the sheet made by removing the content of the granular material having a particle size of 30 μm or more and the fibrous material having a diameter of 10 μm or more in the papermaking raw material liquid to substantially 0%. And the content rate of the fibrous material with a diameter of 10 micrometers or more can be reduced to 0.1 mass% or less.

  In addition to inorganic fibers, the inorganic fiber sheet includes binder materials such as organic binders, inorganic binders, and organic fibers, organic powders, inorganic powders, and other microcapsule granules. Although it is possible to mix a secondary material having an effect of improving strength, uniformity, and handleability, from the viewpoint of eliminating extra gas generation other than moisture during decompression or vacuum, the inorganic fiber sheet is It is preferable that the material is composed only of inorganic fibers.

Next, the manufacturing method of the said inorganic fiber sheet is demonstrated. The inorganic fiber sheet does not require a special papermaking apparatus or papermaking method as in Patent Document 3, and can be easily manufactured by a normal papermaking apparatus and papermaking method. It can be manufactured using a net paper machine. An example will be described below. In the following examples, glass fibers are used as the inorganic fibers, but the same applies when other inorganic fibers are used.
(1) As a raw material, for example, a predetermined amount of fine glass fibers having an average fiber diameter of 1 μm are weighed, and the fibers are uniformly dispersed and mixed in water by a separator such as a mixer or a pulper. Since glass fiber is not fibrillated unlike pulp, it is broken into powder when using a beating machine equipped with a blade such as a beater, so a pulper is used. This papermaking raw material liquid is transported and stored in a storage tank.
(2) Next, the glass fiber in the papermaking raw material liquid is presumed to contain a small amount of granular materials and fibrous materials having a relatively large size with respect to the original glass fiber. After centrifuging the papermaking raw material liquid with a centrifuge, it passes through a screen filter, and the content of the granular material having a particle size of 30 μm or more and the fibrous material having a diameter of 10 μm or more in the papermaking raw material liquid is substantially close to 0%. Reduce.
(3) Next, the supply amount of the papermaking raw material liquid is controlled by the seed valve and the white water valve, and the papermaking raw material liquid is ejected from the head box via a step diffuser and deposited on the traveling forming wire. After dehydrating and forming into a wet paper glass fiber sheet having a thickness of 0.2 mm or less, a dryer is passed through to sufficiently dry the water to obtain a dry paper glass fiber sheet.
(4) Next, the glass fiber sheet, which is a wide continuous sheet, is cut into a predetermined dimension in the length direction, and a predetermined number of sheets are laminated in accordance with the heat insulating performance and thickness required as a vacuum insulating material core material. The core material for vacuum heat insulating material.
(5) Next, the core material is cut into a predetermined size, and after heat treatment to evaporate and remove the adsorbed trace moisture, the core material is immediately inserted into the exterior material while preventing re-adsorption of moisture, and evacuation (0.04 torr, 10 minutes) and heat sealed to obtain a vacuum heat insulating material.

Next, examples of the present invention will be described in detail together with comparative examples and conventional examples.
Example 1
From the raw material of 100% by mass of C glass short fibers having an average fiber diameter of 0.7 μm, wet papermaking is performed by the above method, and after drying with hot air, a glass fiber sheet having a thickness of 0.20 mm and a density of 0.16 g / cm ³ is obtained. It was. Next, the sheet is cut into a specified size, heat-treated at 180 ° C. for 10 hours with a dryer, and then immediately laminated 50 sheets to form a core material having a thickness of 10 mm, which is a bag of gas barrier laminate made of aluminum foil and PET film. And vacuum-sealed at 0.04 torr for 10 minutes and then heat-sealed to obtain a vacuum heat insulating material. The appearance of the obtained vacuum heat insulating material was observed, the thickness was measured, and the density change of the core material was determined. The thermal conductivity measured at room temperature was 0.0015 W / m · K.

(Example 2)
From the raw material of 100% by mass of short C glass fibers having an average fiber diameter of 0.7 μm, wet papermaking is performed by the above method, and after drying with hot air, a glass fiber sheet having a thickness of 0.10 mm and a density of 0.16 g / cm ³ is obtained. It was. Next, the sheet is cut to a specified size and heat-treated at 180 ° C. for 1 hour with a dryer, and then immediately laminated 100 sheets to form a core material having a thickness of 10 mm, and a gas barrier laminate bag shape made of aluminum foil and PET film. And vacuum-sealed at 0.04 torr for 10 minutes and then heat-sealed to obtain a vacuum heat insulating material. The appearance of the obtained vacuum heat insulating material was observed, the thickness was measured, and the density change of the core material was determined. The thermal conductivity measured at room temperature was 0.0014 W / m · K.

(Example 3)
From the raw material of 100% by mass of short C glass fibers having an average fiber diameter of 0.7 μm, wet papermaking is performed by the above method, and after drying with hot air, a glass fiber sheet having a thickness of 0.10 mm and a density of 0.16 g / cm ³ is obtained. It was. Next, the sheet is cut into a specified size, heat-treated at 180 ° C. for 6 minutes with a dryer, and then immediately laminated with 100 sheets to form a core material having a thickness of 10 mm, which is a bag of gas barrier laminate made of aluminum foil and PET film. And vacuum-sealed at 0.04 torr for 10 minutes and then heat-sealed to obtain a vacuum heat insulating material. The appearance of the obtained vacuum heat insulating material was observed, the thickness was measured, and the density change of the core material was determined. The thermal conductivity measured at room temperature was 0.0020 W / m · K.

(Comparative example)
From the raw material of 100% by mass of short C glass fibers having an average fiber diameter of 0.7 μm, wet papermaking is performed by the above method, and after drying with hot air, a glass fiber sheet having a thickness of 0.50 mm and a density of 0.16 g / cm ³ is obtained. It was. Next, the sheet is cut into a specified size, heat-treated at 180 ° C. for 10 hours with a dryer, and then immediately laminated with 20 sheets to form a core material having a thickness of 10 mm, which is made of a gas barrier laminate made of aluminum foil and PET film. And vacuum-sealed at 0.04 torr for 10 minutes and then heat-sealed to obtain a vacuum heat insulating material. The appearance of the obtained vacuum heat insulating material was observed, the thickness was measured, and the density change of the core material was determined. The thermal conductivity measured at room temperature was 0.0025 W / m · K.

(Conventional example)
From the raw material of 100% by mass of C glass short fibers having an average fiber diameter of 0.7 μm, wet papermaking is performed by the above method, and after hot air drying, a glass fiber sheet having a thickness of 2.0 mm and a density of 0.16 g / cm ³ is obtained. It was. Next, the sheet is cut to a specified size and heat-treated at 180 ° C. for 10 hours with a dryer, and then immediately laminated to form a core material having a thickness of 10 mm, which is made of a gas barrier laminate made of aluminum foil and PET film. And vacuum-sealed at 0.04 torr for 10 minutes and then heat-sealed to obtain a vacuum heat insulating material. The appearance of the obtained vacuum heat insulating material was observed, the thickness was measured, and the density change of the core material was determined. The thermal conductivity measured at room temperature was 0.0032 W / m · K.

  Table 1 shows the results of measuring the heating conditions, thickness, density, and thermal conductivity of Examples 1 to 3, Comparative Example, and Conventional Example.

From the results in Table 1, the following was found.
(1) The vacuum heat insulating material used as a core material by laminating 50 glass fiber sheets having a thickness of 0.2 mm in Example 1 is a glass in a horizontal direction of the core material (a direction perpendicular to the stacking direction of the sheets). The degree of fiber alignment is extremely high, and the effect of inhibiting heat transfer from the front surface to the back surface of the vacuum heat insulating material is high. Also, the glass fiber sheet, which is the minimum unit fiber layer that forms the core material, is thin, so that the glass is heated by heat treatment. Since the moisture removal efficiency at the time of removing a small amount of moisture adsorbed on the fiber was good, the thermal conductivity was 0.0015 W / m · K, which was about 53% better than the conventional example.
(2) The vacuum heat insulating material obtained by laminating 100 glass fiber sheets having a thickness of 0.1 mm in Example 2 as a core material has a glass fiber sheet thickness that is 1/2 thickness thinner than that in Example 1. The degree of glass fiber alignment in the horizontal direction of the core material (perpendicular to the sheet stacking direction) is further enhanced to further improve the heat transfer inhibiting effect, and further improve the moisture removal efficiency. Although the heat treatment time was shortened to 1 hour and 1/10 of Example 1, the thermal conductivity was 0.0014 W / m · K, which was 7% better than Example 1.
(3) The vacuum heat insulating material of Example 3 was obtained by shortening the heat treatment time to 0.1 hour (6 minutes) and 1/10 of that of Example 2 with respect to the vacuum heat insulating material of Example 2. However, the thermal conductivity was 0.0020 W / m · K, which was about 43% worse than Example 2 but about 38% better than the conventional example. Therefore, as in Example 3, the vacuum heat insulating material used as a core material by laminating 100 glass fiber sheets having a thickness of 0.1 mm is 5 glass fiber sheets having a thickness of 2.0 mm as in the conventional example. Compared to the vacuum heat insulating material that is made by laminating the sheets, the heat treatment time is improved by about 38% even if the heat treatment time is reduced to 1/100, which is only 0.1 hour (6 minutes). It is possible to achieve both a significant improvement in productivity and a significant improvement in heat insulation performance.
(4) The vacuum heat insulating material of the comparative example is a vacuum heat insulating material in which 20 glass fiber sheets having a thickness of 0.5 mm in which the thickness of the glass fiber sheet is ¼ thinner than that of the conventional example are laminated to form a core material. However, the thermal conductivity is 0.0032 W / m · K to 0.0025 W / m · K despite the fact that the thickness of the glass fiber sheet is significantly reduced from 2.0 mm to 0.5 mm to ¼. However, it is only about 22% improvement.
(5) That is, when the thickness of the inorganic fiber sheet constituting the core material is reduced without changing the thickness of the vacuum heat insulating core material (laminated body of inorganic fiber sheets), the inorganic fiber Even if the sheet thickness is reduced by 75% from 2.0 mm to 0.5 mm, the thermal conductivity (heat insulation performance) remains only about 22%, whereas the inorganic fiber sheet thickness is reduced from 0.5 mm to 0.00 mm. It was found that the thermal conductivity (heat insulation performance) was improved by 40% when reduced to 2 mm by 60%.

Claims (6)

  A vacuum heat insulating material using, as a core material, a laminate of a plurality of inorganic fiber sheets that are wet-made mainly with inorganic fibers having an average fiber diameter of 4 μm or less, and a granular material having a particle size of 30 μm or more in the inorganic fibers And the content rate of the fibrous material with a diameter of 10 micrometers or more is 0.1 mass% or less, the said inorganic fiber sheet is 0.2 mm or less in thickness, and the said inorganic fiber in the said core material is lamination | stacking of the said inorganic fiber sheet. A vacuum heat insulating material arranged in a direction perpendicular to the direction.   The vacuum heat insulating material according to claim 1, wherein the inorganic fibers in the inorganic fiber sheet do not have a specific orientation in a horizontal direction of the sheet.   The vacuum heat insulating material according to claim 1 or 2, wherein the inorganic fiber sheet is composed of only inorganic fibers.   The vacuum heat insulating material according to any one of claims 1 to 3, wherein the inorganic fiber is a glass fiber.   The vacuum heat insulating material according to any one of claims 1 to 4, wherein the inorganic fiber has an average fiber diameter of 0.2 to 2 µm.   The vacuum heat insulating material according to claim 5, wherein an average fiber diameter of the inorganic fibers is 0.2 to 1 μm.