JP2010007683A - Vacuum thermal insulating material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a vacuum thermal insulating material capable of enhancing the thermal insulating performance. <P>SOLUTION: A core material is constituted by laminating a plurality of fibrous sheets made of a plurality of fibers having different fiber diameter, and the core material is vacuum-sealed and covered by an outer covering material to constitute a vacuum thermal insulating material. The fiber longitudinal direction can be brought close to orthogonal with respect to the heat transferring direction by the fiber having the large fiber diameter and the long fiber length. Thus, the solid heat conduction moving through the fiber itself can be suppressed. Further, the strength of the fibrous sheet can be ensured by the fiber having the small diameter. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a vacuum heat insulating material.

  Conventionally, in order to improve the heat insulation performance of a vacuum heat insulating material, a vacuum heat insulating material has been proposed in which a large number of fiber sheets laminated in the heat transfer direction are arranged in a panel and the inside is sealed with a high vacuum. Yes. In this vacuum heat insulating material, the fiber sheet is composed of an inorganic fiber material having a fiber diameter distribution peak value of 1 μm or less and 0.1 μm or more, thereby suppressing heat conduction from the fibers and improving heat insulation. (For example, refer to Patent Document 1).

  Further, as another vacuum heat insulating material, a vacuum heat insulating material has been proposed in which the breaking strain limit is increased and the length direction and the heat transfer direction are made substantially perpendicular to the glass fiber that is difficult to break against deformation due to external force. In this vacuum heat insulating material, high-performance is achieved by preventing fiber breakage by laminating glass fibers whose strength is increased by spinning conditions so that the glass fibers intersect in the heat transfer direction. (For example, refer to Patent Document 2).

Japanese Patent Laid-Open No. 2002-81596 (page 3, FIG. 2) Japanese Patent Laying-Open No. 2006-307921 (page 3, FIG. 3)

  However, in a vacuum heat insulating material composed of inorganic fibers having a diameter smaller than 1 μm, the fiber length is limited due to the manufacturing method, and it is difficult to produce a sheet with long fibers. Therefore, the short fiber tends to have a large fiber angle between the longitudinal direction of the fiber and the plane direction forming the sheet, and the heat transfer direction and the fiber direction are directed in the same direction. As a result, the heat conduction in the heat transfer direction is increased, so that the heat insulating performance of the vacuum heat insulating material is deteriorated.

  In addition, in the vacuum heat insulating material in which the length direction and the heat transfer direction are made substantially perpendicular to the glass fiber, although there is a description about the production conditions at the time of spinning in order to increase the fiber strength, it is layered so that the fibers cross each other. No mention is made of the specific method of stacking. Furthermore, when laminated in an intersecting layer, a space penetrating in the heat transfer direction is likely to exist inside the vacuum heat insulating material, and the spatial distance in the heat transfer direction is greater than the mean free path of gas molecules remaining inside the jacket material. become longer. As a result, there has been a problem that gas conduction increases and rather the heat insulation performance deteriorates. And when it produced with the textile manufacturing method, productivity worsened, and when it speeded up, there existed a problem that a fiber will be easy to fracture | rupture and a performance will fall further.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to obtain a vacuum heat insulating material capable of improving the heat insulating performance.

  In the vacuum heat insulating material according to the present invention, a fiber sheet composed of a plurality of fibers having different fiber diameters and a core material obtained by laminating a plurality of fiber sheets are vacuum-sealed and covered with a jacket material.

  In the vacuum heat insulating material according to the present invention, since the fiber sheet is composed of a plurality of fibers having different fiber diameters, a thick fiber is obtained while ensuring the tensile strength of the fiber sheet formed of fibers having a thin fiber diameter. The fiber having a diameter makes it possible to make the inclination angle in the heat transfer direction and the fiber length direction close to a right angle. For this reason, it is possible to suppress the heat conduction of the solid moving through the fiber itself, and to improve the heat insulating performance of the vacuum heat insulating material.

Embodiment 1 FIG.
FIG. 1 is a schematic cross-sectional view showing a vacuum heat insulating material in Embodiment 1 for carrying out the present invention. The vacuum heat insulating material 1 includes a core material 3 configured by laminating fiber sheets 2 and an outer cover material 4 that covers and seals the core material 3. FIG. 2 is an enlarged schematic cross-sectional view of the fiber sheet 2 in the present embodiment. In FIG. 2, the fiber sheet is configured by mixing a large diameter fiber 5 and a small diameter fiber 6 having a fiber diameter smaller than the fiber diameter of the large diameter fiber.

  Next, the manufacturing method of the vacuum heat insulating material 1 in this Embodiment is demonstrated. First, regarding the method for producing the fiber sheet 2, for example, the large-diameter fibers 5 and the small-diameter fibers 6 are dispersed in water, made into a sheet by making paper with an automatic feed paper machine, and then into a roll through a drying process. A wound sheet roll is produced. Next, the sheet is pulled out from the sheet roll and cut into a required size to obtain a fiber sheet 2, and a core material 3 in which a plurality of the fiber sheets 2 are stacked is produced. Thereafter, the core material 3 is covered with two or one outer cover material 4 which is folded, and the core material 3 covered with the outer cover material 4 is disposed in the vacuum chamber. After that, by reducing the pressure in the vacuum chamber, the space covered with the jacket material 4 is reduced to make the space covered with the jacket material 4 in a vacuum state. Then, after sealing the outer periphery of the jacket material 4 in a state where the space covered with the jacket material 4 is at a predetermined pressure, for example, a vacuum pressure of about 0.1 to 3 Pa, the pressure in the vacuum chamber Return to atmospheric pressure. Thereby, the vacuum heat insulating material 1 is completed. The internal space of the completed vacuum heat insulating material 1 is kept in a vacuum state, and the jacket material 4 and the core material 3 receive a compressive force due to a pressure difference with the outside. Further, an appropriate gas adsorbent is inserted into the space covered with the jacket material 4 as necessary.

  In addition, about the water | moisture content contained in the fiber sheet 2, you may provide the process of decompressing, heating the fiber sheet 2 before and behind cutting, etc. separately from the drying process at the time of papermaking, and may remove this water | moisture content. Further, in a state where the core material 3 covered with the jacket material 4 is decompressed in the vacuum chamber, a mechanism for heating the inside of the vacuum chamber is provided so that the fiber sheet 2 itself has heat such as heat shrinkage and thermal decomposition. The moisture of the fiber sheet 2 may be removed by setting appropriate conditions, for example, by setting the pressure at a temperature at which no load is applied and not inducing vacuum discharge.

  In addition, constituent materials in the present embodiment will be described. Glass fiber can be used for the large diameter fiber and small diameter fiber which are used for a fiber sheet, for example. The fiber diameter of the large fiber can be set to, for example, about φ6 μm, and the fiber diameter of the thin fiber can be set to, for example, about φ1 μm. Further, as the jacket material, for example, an aluminum laminate sheet can be used.

  Next, the effect of mixing fibers with different fiber diameters in the fiber sheet in the vacuum heat insulating material of the present embodiment will be described. FIG. 3 is a characteristic diagram that simulates the relationship between the fiber diameter of a fiber and the thermal conductivity of a vacuum heat insulating material that forms a fiber sheet with only the fiber. FIG. 3 is a model in which single fibers are in contact with each other unlike the present embodiment, which corresponds to a fiber sheet configured with a constant core material filling rate, and the thermal conductivity is the thickness of the vacuum heat insulating material. The thermal conductivity in the direction is calculated. In FIG. 3, the difference in thermal conductivity on the vertical axis represents the difference in thermal conductivity from the reference value with the thermal conductivity of the vacuum heat insulating material when the fiber diameter is φ4 μm as the reference value. FIG. 3 shows that the heat insulation performance of a vacuum heat insulation sheet improves, so that a fiber diameter becomes thin. This is because the thermal resistance increases as the fiber diameter decreases. However, when the numerical influence was examined, it was found that, for example, the difference in thermal conductivity between the fibers of φ10 μm and φ1 μm was not significantly different on the order of 0.0001 W / (m · K).

FIG. 4 is a characteristic diagram simulating the relationship between the fiber inclination angle and the thermal conductivity of the vacuum heat insulating material with the fiber diameter and the filling rate being constant. Here, the fiber inclination angle is an angle between the planar direction of the fiber sheet and the longitudinal direction of the fiber, and since this angle has a certain distribution, it is expressed as an average value. In FIG. 4, the difference in thermal conductivity on the vertical axis represents the difference in thermal conductivity from the reference value with the thermal conductivity of the vacuum heat insulating material when the fiber tilt angle is 10 degrees as the reference value.
From FIG. 4, it became clear that the increase rate of the thermal conductivity becomes more remarkable when the fiber inclination angle becomes larger than 10 degrees. Therefore, it was found that the heat insulation performance can be improved by setting the fiber inclination angle to about 10 degrees or less. That is, from FIG. 3 and FIG. 4, the knowledge that the heat insulation performance is remarkably improved by reducing the fiber inclination angle to 10 degrees or less rather than reducing the fiber diameter can be obtained. It is a thing.

  FIG. 5 is a schematic diagram showing a state of the large-diameter fiber inside the fiber sheet. For example, as shown in FIG. 5, when the fiber length (L) of the large diameter fiber 5 having a diameter of 6 μm is set to 6 mm and the thickness (t) of the fiber sheet 2 is set to 0.4 mm, the state where the large diameter fiber rises most. That is, the theoretical fiber inclination angle θ in a state where one end of the large diameter fiber reaches one surface of the fiber sheet and the other end of the large diameter fiber reaches the other surface of the fiber sheet is sin θ = 0.4 / 6. Therefore, the maximum fiber inclination angle is 4 degrees, and the fiber inclination angle of the large diameter fiber is 4 degrees or less. On the other hand, with regard to the fine fiber, for example, if the fine fiber having a diameter of about 1 μm is a glass fiber, the fiber length is usually about 1 mm in order to produce the fiber by the flame method. Therefore, when the fiber inclination angle of only the fiber of about φ1 μm × length of 1 μm is calculated in the same manner, the maximum fiber inclination angle is about 24 degrees. Therefore, the fiber inclination angle of a glass fiber having a fiber length of 1 mm is 0 to 24 degrees. Actually, this glass fiber has many different fiber lengths less than 1 mm, and is affected by the fiber strength, orientation, and the like. As is clear from the above, the fiber inclination angle within this range becomes a factor that hinders performance improvement. On the other hand, it is recognized that the large diameter and long fibers can realize the suppression of the inclination angle.

  4 and 5, if the relationship between the fiber length (L) and the sheet thickness (t) is t / L <sin (10 °), the heat insulation performance is remarkably improved. Since sin (10 °) is about 0.174, when t / L is smaller than 0.174, the heat insulation performance is remarkably improved.

  In order to demonstrate that, as an example, a glass fiber having a fiber diameter of φ1 μm × fiber length of 1 mm as a thin fiber is 50 wt%, and a glass chop having a fiber diameter of φ6 μm × fiber length of 6 mm as a thick fiber is a ratio of 50 wt%. A fiber sheet having a thickness of 0.4 mm was made as a prototype.

  Here, for fiber sheet production, for example, when an automatic paper machine is used, it is impossible to roll and unwind from the roll unless an appropriate tensile strength is secured in the flow direction of the sheet roll serving as the fiber sheet. become. In particular, when no binder such as a binder is added at all so as not to deteriorate the heat insulation performance, there is a limit to thinning the sheet. When mass production is assumed, the current 0.4 mm is close to this value. About 30 sheets of the produced fiber sheets are laminated to form a core material, which is inserted into an aluminum laminated sheet (nylon 15 μm + polyethylene terephthalate 12 μm + aluminum sheet 6 μm + polyethylene 50 μm) with an adsorbent and up to about 1 Pa in a vacuum chamber. The vacuum was applied to seal the opening of the outer cover material by heat sealing, and a vacuum heat insulating material was produced. Here, the adsorbent retains the degree of vacuum by adsorbing moisture, external gas, or outgas generated from the core material that penetrates into the interior through defects such as the sealing material of the jacket material or the aluminum laminate sheet itself. There are CaO type, activated carbon type, zeolite type, and those in which Li or Ba is mixed.

  As a result of measuring the thermal conductivity λ of the vacuum heat insulating material of this example, λ = 0.417 W / (m · K) was obtained. On the other hand, as a comparative example, the result of measuring the thermal conductivity by manufacturing a vacuum heat insulating material under the same conditions as in the Examples using only glass fiber having a fiber diameter of 1 μm × fiber length of 1 mm is λ = 0.0002 W / It was found that the heat insulation performance was inferior to (m · K) and the above examples. When the cross-section of the core material was observed by simulating the vacuum state at this time, in the examples, the fiber inclination angle of the large-diameter fiber was almost less than 10 degrees. On the other hand, in comparative examples using only small-diameter fibers, fibers having a fiber inclination angle exceeding 10 degrees were often observed, and those having a large fiber inclination angle were observed at around 20 degrees. Therefore, by mixing the large-diameter long fibers, the longitudinal direction of the fibers can be made to be perpendicular to the heat transfer direction, the thermal conductivity can be reduced, and a high-performance heat insulating material can be obtained.

  The method of observing the cross section of the core material by simulating the vacuum state is that the vacuum heat insulating material before being put in the vacuum chamber is compressed from both sides with a pressure equivalent to 1 atm, and this is solidified with resin and then the cross section is This is a method of observing with an electron microscope.

  On the other hand, performance evaluation was performed when the fiber sheet was composed of all thick fibers. As a result of trial production of a fiber sheet using only fibers having a fiber diameter of φ6 μm without adding a binder such as a binder that lowers the heat insulation performance, it is impossible to unwind the sheet roll that becomes the fiber sheet, making handling difficult. A manufacturing problem occurred. Further, as a result of measuring the thermal conductivity by forcibly forming a core material in the form of incising the roll sheet that was forcibly wound, and using this as a vacuum heat insulating material in the same manner as described above, λ = 0.0019 W / (m · K) and the heat insulation performance were inferior to those of the above examples. This is because the fiber sheet stacking boundary becomes uncertain, the large-diameter fibers are inclined beyond the fiber sheets, the fiber inclination angle is increased, and further, the fiber-to-fiber spacing is increased. Therefore, it is presumed that gas molecules inside the jacket material are easily moved and gas heat conduction is promoted.

  In the present embodiment, glass fibers are used as the large diameter fibers and the small diameter fibers used in the fiber sheet, but inorganic fibers such as ceramic fibers made of an inorganic material other than glass fibers are used. You can also.

  In this embodiment, a wet method using a papermaking method is used as a method for producing a fiber sheet. However, the method is not limited to this, and a dry sheet or the like can be used as long as the fiber sheet can be formed. The following manufacturing method may be used.

Embodiment 2. FIG.
FIG. 6 is an enlarged schematic cross-sectional view of a fiber sheet used for the vacuum heat insulating sheet in the second embodiment. In FIG. 6, the fiber sheet includes a large-diameter fiber 5, a small-diameter fiber 6 having a fiber diameter smaller than the fiber diameter of the large-diameter fiber, and a finer fiber 6 that is smaller than the fiber diameter of the large-diameter fiber 5. The medium diameter fiber 7 having a fiber diameter larger than the fiber diameter is mixed. As for the configuration of these fibers, for example, a large diameter fiber has a fiber diameter of φ10 μm and a fiber length of 10 mm, a thin fiber has a fiber diameter of φ1 μm and a fiber length of 1 mm, and the medium diameter fiber has a fiber diameter of 10 mm. The length is 4 mm and the length is about 4 mm. A trial production of a fiber sheet was attempted using 50% by weight of these fibers, 25% by weight of medium diameter fibers, and 25% by weight of large diameter fibers. As a result, the sheet thickness was reduced to 0.2 mm.

In the present embodiment, when the fiber inclination angle described with reference to FIG. 5 of Embodiment 1 is calculated, the fiber inclination angle of the medium diameter fiber is about 3 degrees, the fiber inclination angle of the large diameter fiber is about 1 degree, The fiber inclination angle of the fine fiber is about 12 degrees.
About 60 sheets of each of these fiber sheets were laminated, a vacuum heat insulating material was produced in the same manner as in the example of Embodiment 1, and the thermal conductivity (λ) was measured. As a result, λ = 0.014 W / (m · K) Met. Further, when a cross-sectional observation simulating the vacuum state of this vacuum heat insulating material was performed, the fiber inclination angle of the large-diameter fiber was less than 5 degrees, and the fiber inclination angle of the medium-diameter fiber was less than 10 degrees. A very small amount of the fiber inclination angle of the diameter fiber was observed with a maximum inclination of about 15 degrees, but most of the inclination angle was about 10 degrees and some were about 1 degree.

  As a comparative example, as a result of producing a vacuum heat insulating material comprising a fiber sheet with only small-diameter fibers and measuring the thermal conductivity (λ), λ = 0.0019 W / (m · K), which is more than the above example. It was found that the heat insulation performance was inferior. Moreover, when cross-sectional observation which simulated the vacuum state of the vacuum heat insulating material of this comparative example was implemented, there were many fiber inclination angles 12-15 degree | times.

  As in the present embodiment, by mixing medium diameter fibers, the tensile strength of the fiber sheet can be increased, thereby making the fiber sheet thinner. As a result, it is possible to make the longitudinal direction of the mixed large-diameter long fibers and medium-diameter fibers closer to a right angle with respect to the heat transfer direction, thereby obtaining a vacuum heat insulating material with further improved heat insulating performance as compared with the first embodiment. It was.

  In the present embodiment, the fiber sheet is configured using three types of fibers having different fiber diameters, but four or more types of fibers having different fiber diameters may be used. In that case, if the fiber length of at least one kind of fiber other than the fiber with the smallest fiber diameter is longer than the fiber length of the fiber with the smallest fiber diameter, the same effect can be obtained.

Embodiment 3 FIG.
In Embodiment 1, glass fibers are used as the large-diameter fiber and the small-diameter fiber used in the fiber sheet. However, in Embodiment 3, organic fibers are used.

  In this embodiment, polyethylene terephthalate fibers are used as the large diameter fibers and the small diameter fibers used in the fiber sheet. The fiber diameter of the large fiber was about φ11 μm, and the fiber diameter of the small fiber was about φ3 μm. The configuration other than the fiber material is the same as that of the first embodiment.

  In the thus configured vacuum heat insulating material, the result of measuring the thermal conductivity (λ) was λ = 0.018 W / (m · K). For comparison, in a vacuum heat insulating material using a fiber sheet composed only of small-diameter fibers, the result of measuring the thermal conductivity (λ) is λ = 0.0023 W / (m · K), which was carried out. Similarly to Form 1, by forming a fiber sheet with large diameter fibers and small diameter fibers, the heat insulation performance of the vacuum heat insulating material can be improved.

  In this embodiment, polyethylene terephthalate fiber is used as the fiber material. However, polyester-based or other organic fibers such as polypropylene, polystyrene, polyethylene, and the like can also be used. Further, it is clear that the same effect can be obtained even if inorganic fibers and organic fibers are mixed, and it is possible to appropriately select a fiber material from the viewpoint of the manufacturing method and cost.

It is a cross-sectional schematic diagram which shows the vacuum heat insulating material of Embodiment 1 of this invention. It is an expanded sectional schematic diagram of the fiber sheet in Embodiment 1 of this invention. It is the characteristic view which showed the relationship between the fiber diameter in Embodiment 1 of this invention, and the heat conductivity of a vacuum heat insulating material. It is the characteristic view which showed the relationship between the fiber inclination angle in Embodiment 1 of this invention, and the thermal conductivity of a vacuum heat insulating material. It is the schematic diagram which showed the relationship between the fiber length in Embodiment 1 of this invention, and the thickness of a fiber sheet. It is an expanded sectional schematic diagram of the fiber sheet in Embodiment 2 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Vacuum heat insulating material 2 Fiber sheet 3 Core material 4 Cover material 5 Large diameter fiber 6 Small diameter fiber 7 Medium diameter fiber

Claims (6)

A vacuum heat insulating material comprising: a fiber sheet composed of a plurality of fibers having different fiber diameters; and a jacket material that covers a core material in which a plurality of fiber sheets are laminated in a vacuum-sealed manner. The vacuum heat insulating material according to claim 1, wherein the plurality of fibers having different fiber diameters include a fiber having a fiber length longer than that of a fiber having a minimum fiber diameter. 2. The fiber length L of at least one fiber of a plurality of fibers having different fiber diameters is such that the value of t / L is smaller than 0.174 in relation to the thickness t of the fiber sheet. Vacuum insulation material. The vacuum heat insulating material according to claim 1, wherein the plurality of fibers having different fiber diameters are inorganic fibers. The vacuum heat insulating material according to claim 1, wherein the plurality of fibers having different fiber diameters are organic fibers. The vacuum heat insulating material according to claim 1, wherein a plurality of fibers having different fiber diameters are a mixture of inorganic fibers and organic fibers.

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