JP4591197B2 - Vacuum insulation - Google Patents

Description

  The present invention relates to a vacuum heat insulating material having excellent heat insulating performance.

  As the core material used for the vacuum heat insulating material, an inorganic compound having a small thermal conductivity and less gas generation is suitable. In particular, it is known that a vacuum heat insulating material using a glass fiber laminate as a core material has excellent heat insulating performance, and an example of a core material constituting the vacuum heat insulating material is shown in FIG. There is something.

  FIG. 6 shows that the inorganic fine-diameter fibers 1a and 1b have their length directions perpendicular to the heat transfer direction, and the perpendicular directions of the small-diameter fibers 1a and 1b cross each other. Randomly laminated and point-contacted with each other, and provided with penetration fibers 1c constituting the high-density inorganic fine fiber mat 1 that are driven into the laminated thin fibers 1a and 1b in parallel with the heat transfer direction. It has been proposed to form a core material 3 by superimposing a plurality of inorganic fine fiber mats 1 (see, for example, Patent Document 1).

  In the conventional vacuum heat insulating material configured as described above, since the inorganic thin fibers 1a and 1b are randomly arranged at right angles to the heat transfer direction, the fibers 1a and 1b are in point contact with each other. Therefore, the contact thermal resistance at the contact point is large, and the amount of heat transfer in the thickness direction of the core material 3 is small.

  However, with only the fibers 1a and 1b arranged perpendicular to the heat transfer direction, the compression resistance against the atmospheric pressure acting in the heat transfer direction is reduced, and the core material 3 is compressed by the atmospheric pressure acting after the vacuum packaging and the thickness is reduced. Therefore, the penetration fibers 1c are partially arranged parallel to the heat transfer direction.

However, since the heat insulation performance is lowered by the penetration fibers 1c, the core material 3 is formed by superimposing a plurality of inorganic fine fiber mats 1 to reduce the amount of heat transferred by the penetration fibers 1c.
Japanese Examined Patent Publication No. 7-103955

  However, in the above conventional configuration, since the contribution of heat conduction by fibers parallel to the heat transfer direction is large, even when a plurality of inorganic thin fiber mats are stacked, it is difficult to sufficiently reduce heat conduction, There was a problem that the heat conduction of the solid component was increased.

  On the other hand, in a core material formed by laminating glass fibers, which is a kind of inorganic fine fiber, only in the direction perpendicular to the heat transfer direction, the heat conduction of the solid component increases due to the following factors.

  A compressive force is applied to the glass fiber through the jacket material. Glass fibers are intertwined in a core made of glass fibers, and when a compressive force is applied by atmospheric pressure, tensile stress and bending stress are applied to the glass fibers to cause distortion.

  If the tensile strength at break of the glass fiber is small, the glass fiber breaks with a slight tensile force, the space held by the presence of this fiber disappears, and heat is easily transferred by the fibers that are not in contact with each other. Become. Furthermore, heat is easily transferred also when the broken portion of the fiber comes into contact with the nearby fiber.

  The present invention solves the above-mentioned conventional problems, and aims to provide a vacuum heat insulating material that suppresses heat conduction of a solid component caused by fibers in the heat transfer direction and the horizontal direction and has low heat conductivity. To do.

In order to achieve the above object, the vacuum heat insulating material of the present invention is a vacuum heat insulating material formed by covering a core material made of short glass fiber aggregates with a covering material made of a laminate film and reducing the pressure inside the covering material. And the said core material taken out from the said vacuum heat insulating material is that the tensile fracture strength of the orthogonal | vertical direction with respect to a heat transfer direction is 65 N / cm < ² > or more .

  The tensile strength at break of glass fibers is increased, so that even if compressed by atmospheric pressure, the fibers are not broken and the surrounding space is maintained, the surrounding fibers are difficult to contact each other, and the heat conduction of the solid component is increased. It is suppressed.

  In addition, since the core material is composed of a very large number of fine glass fibers, the characteristics of the scale using the vacuum heat insulating material can be attributed to both the contribution from unbroken glass fibers and the contribution from broken glass fibers. It depends on the average of the broken part and the unbroken part of the glass fiber. That is, in the core material, the higher the proportion of the glass fiber that is not broken, the better the heat insulation performance.

  Therefore, a vacuum heat insulating material in which the heat conduction of the solid component is kept low can be obtained by using a core material having a high tensile breaking strength due to a large proportion of glass fibers having a high tensile breaking strength.

  The vacuum heat insulating material of the present invention has a more excellent heat insulating performance than a vacuum heat insulating material manufactured using a core material manufactured using glass having the same thermal conductivity.

The invention of the vacuum heat insulating material according to claim 1 is a vacuum heat insulating material formed by covering a core material made of a short glass fiber assembly with a covering material made of a laminate film and reducing the pressure inside the covering material. The core material taken out from the vacuum heat insulating material has a tensile breaking strength in the direction perpendicular to the heat transfer direction of 65 N / cm ² or more.

According to the present invention, since the glass fiber has a high tensile breaking strength, the tensile strength is 65 N / cm ² or more in the direction perpendicular to the heat transfer direction of the core material.

  The tensile strength at break of glass fibers is increased, so that even if compressed by atmospheric pressure, the fibers are not broken and the surrounding space is maintained, the surrounding fibers are difficult to contact each other, and the heat conduction of the solid component is increased. It is suppressed. In addition, an increase in the heat transfer point due to contact with surrounding fibers can be suppressed by the broken portion being a free end. Since the core material is composed of a very large number of fine glass fibers, the characteristics of the scale using the vacuum heat insulating material consist of both the contribution from the unbroken glass fiber and the contribution from the broken glass fiber, Depends on the average of the broken and unbroken portions of the glass fiber. That is, in the core material, the higher the proportion of the glass fiber that is not broken, the better the heat insulation performance.

  The invention of the vacuum heat insulating material according to claim 2 is such that the porosity of the core material in the invention according to claim 1 is 85% or more, and the tensile breaking strength of the core material is a portion other than the void of the core material. This is the force caused by the breakage of the short glass fibers.

  According to the present invention, since the space occupied in the core material is large, heat is hardly transmitted. Therefore, the vacuum heat insulating material which reduced heat conductivity can be obtained by suppressing the increase in the contact of a fiber by the fracture | rupture of glass fiber.

The invention according to claim 1 or 2, wherein the sample for measuring the tensile strength of the core material is obtained by cutting the core material into a rectangular parallelepiped in a direction perpendicular to the heat transfer direction, and a method for measuring the tensile rupture strength. However, the sample attaching part of the tensile breaking strength measuring device is attached adjacent to the sample, and the sample supporting part is broken by increasing the distance.

According to the method for measuring the tensile breaking strength, by adjoining the sample mounting portions, it becomes difficult to break the core material due to the unraveling of the glass fiber, and the tensile breaking strength due to the breaking of the glass fiber is reduced. It can be measured accurately. Since the tensile strength at break of the glass fiber is large, heat transfer due to the breakage of the glass fiber inside the core material is suppressed, and a vacuum heat insulating material having better heat insulating performance can be obtained.

3. The invention according to claim 1, wherein the sample mounting portion has plate-like support portions parallel to each other, and the sample is fixed and pulled by compressing the sample by reducing the distance between the plate-like support portions. Measures breaking strength.

According to the measurement method, when the core material is sandwiched between the parallel plates, the glass fibers inside the core material are pressed to each other, and when a tensile force is applied to the core material, the frictional force between the glass fibers is the tensile force of the glass fiber. When the force is exceeded, the core material breaks when the glass fiber breaks. Therefore, it is possible to accurately measure the tensile breaking strength due to the breaking of the glass fiber. Since the tensile strength at break of the glass fiber is large, heat transfer due to the breakage of the glass fiber inside the core material is suppressed, and a vacuum heat insulating material having better heat insulating performance can be obtained.

The invention of the vacuum heat insulating material according to claim 3 is such that the core material in the invention according to claim 1 or 2 does not contain a binder that binds the glass fibers to each other.

  According to the present invention, since the increase in heat conduction by the binder can be suppressed by not including the binder that binds the glass fibers to each other, it is possible to obtain a vacuum heat insulating material with further reduced thermal conductivity.

The invention of the vacuum heat insulating material according to claim 4 is formed by binding the core material in the invention according to claim 1 or 2 with a binder.

  According to the present invention, by using a binder, a core material can be created even for glass fibers that are difficult to collect.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment 1)
FIG. 1 is a cross-sectional view of the vacuum heat insulating material in the first embodiment. FIG. 2 is a schematic diagram of a cross-section of the core material in the first embodiment. FIG. 3 is a schematic diagram of a cross section of a tensile strength measurement test piece in the first embodiment. FIG. 4 is a schematic diagram of test piece mounting in the first embodiment.

  In FIG. 1, the vacuum heat insulating material 2 is composed of a core material 3, a jacket material 4, and an adsorbent 5. In FIG. 2, 1a is a glass fiber arranged substantially horizontally on the cross section of the core material, and 1b is a glass fiber arranged substantially perpendicular to the cross section of the core material. The core material 3 is formed by forming a glass fiber aggregate into a plate shape, and the jacket material 4 is configured using linear low density polyethylene as a sealant layer, aluminum as a metal foil, and nylon as an outermost layer. It is a laminated film.

  In FIG. 3, what is shown by the code | symbol 6 is a tensile strength measurement test piece. In FIG. 4, what is denoted by reference numeral 7 is a core material attaching portion.

  The adsorbent 5 is calcium oxide. The glass fiber aggregate constituting the core material 3 is obtained by increasing the proportion of fibers having a high tensile strength at break by the production process.

  The glass fiber was fiberized by exiting from a fiberizing device rotating at high speed.

  In order to increase the proportion of fibers having a high tensile breaking strength, the temperature of the air for stretching the glass fibers was set to −30 ° C. in order to reduce the occurrence of Griffith cracks on the surface. By doing in this way, the glass fiber aggregate | flour with many ratios of the glass fiber with a reduced surface Griffith crack and large tensile strength can be obtained.

  A core material 3 was produced by thermoforming a collection of the glass fibers. The core material produced in this way was inserted into the jacket material 4 which was made in advance by a three-side seal, and then the pressure was reduced to 13 Pa and sealed to produce a vacuum heat insulating material 2. As shown in FIG. 2, the glass fiber 1 a oriented substantially horizontally in the cross section is in contact only through the glass fiber 1 b oriented substantially perpendicular to the cross section.

  When atmospheric pressure is applied to the core material, tensile force acts on the fibers that are entangled inside. However, because the tensile strength at break of the fibers is increased, the fibers are compressed by atmospheric pressure, and tensile force acts on the fibers. The fibers are not broken, the surrounding space is maintained, and the surrounding fibers are not in contact with each other. Furthermore, the contact with the surrounding glass fiber by a broken part becoming a free end is suppressed. Therefore, the heat conduction by the glass fiber is reduced around the unbroken fiber.

  The scale in actual use of the vacuum heat insulating material is significantly larger than the scale of the heat transfer point between the glass fibers. Therefore, the thermal conductivity in actual use of the vacuum heat insulating material depends on the average of these heat conductions. Therefore, a core material having a high tensile fracture strength and a large proportion of fibers has low heat conduction. By using such a core material, a vacuum heat insulating material with excellent heat insulating performance can be obtained.

  Thus, the heat conductivity of the vacuum heat insulating material produced was 0.0015 W / mK.

  The vacuum heat insulating material was disassembled, the core material was taken out, and the tensile strength was measured. The measurement test piece was cut out to 100 mm × 25 mm. Since the thickness depends on the applied pressure, it is necessary to regulate the thickness under a certain pressure, so compression was performed at 1013 hPa.

The compression method was performed in the process of reducing the distance of a flat jig attached in parallel to a compression tester (not shown). The thickness of the core material under this condition was 10 mm. Therefore, the cross-sectional area of the core material was 2.5 cm ² .

The tensile strength at break of this test piece was 300N. Therefore, the tensile strength at break of the core material was 120 N / cm ² .

Further, since the density under 1013 hPa is 250 kg / cm and the density of the glass is 2500 kg / cm ³ , the ratio of the glass to the cross-sectional area is 10%. Accordingly, the tensile strength at break when the area of the glass occupying the cross section is 1200 N / cm ² .

  This is because the ratio of glass fibers having a high tensile breaking strength increases as the tensile breaking strength of the glass fibers increases.

  Since the core material is an aggregate of glass fibers, there are two types of breakage of the core material: a break due to the breakage of the glass fiber and a break due to the unraveling of the glass fiber.

  The force for unraveling the glass fibers is smaller than the force for breaking the glass fibers. For this reason, the force required for the breakage of the core material due to the unraveling of the glass fibers is smaller than the force necessary for the breakage of the core material due to the breakage of the glass fibers. Therefore, when the glass fiber aggregate is broken and broken, the tensile breaking strength of the core material is estimated to be small. Therefore, it is necessary to break the core material by breaking most of the glass fibers.

  For this purpose, the measurement of the tensile strength of the core material requires an appropriate measurement method. Therefore, optimization was performed as shown below.

  As shown in FIG. 3, the test piece has fibers that are substantially horizontal to the cross-sectional direction, and the sum of the forces that break when these fibers are pulled is the tensile breaking strength of the core material.

  For this reason, as shown in FIG. 4, when attaching the core material 3 to a tensile testing machine, the core material attaching part 7 is attached in proximity to the core material, and pressure is applied to the core material to fix it. By doing in this way, the core material 3 is fractured | ruptured on the surface substantially the same as the surface where the core material attachment part 7 is contacting, and a cross section becomes planar shape.

  Even in the case of the measurement as described above, a part of the breakage may be a breakage due to the fiber assembly being unwound. For this reason, the tensile breaking strength when the core material is broken by breaking all the fibers is equal to or higher than the measured value. Therefore, the tensile strength at break of the core material is tested 10 times and the maximum value is used.

  Moreover, when the core material is molded using a binder, the tensile strength at break of the core material increases. This is because, when the tensile strength of the core material is measured, the aggregate of fibers is difficult to be unwound, so that the proportion of fibers that break is increased.

For example, the tensile strength at break of a cotton-like glass fiber aggregate obtained by binding glass fibers produced by a method equivalent to the above using a phenol resin was 125 N / cm ² . Moreover, the heat conductivity of the vacuum heat insulating material produced using this glass fiber aggregate as a core material is 0.0018 W / mK, which is larger by 0.0003 W / mK than when no binder is used. This is because the phenol resin at the contact between the glass fibers contributes to heat transfer.

(Embodiment 2)
FIG. 5 is a schematic diagram of a cross-section of the core material in the present embodiment.

  The glass fiber 1 is produced by rapidly cooling glass fiber discharged from a glass fiber producing apparatus rotating at a high speed by blowing air at −10 ° C. Since it is strengthened by blowing air at −10 ° C., when this glass fiber is collected, a glass fiber aggregate having a large proportion of glass fiber having a high tensile breaking strength can be obtained.

The glass fiber assembly thus produced was molded to produce a core material, and a vacuum heat insulating material was produced. The vacuum heat insulating material had a thickness of 10 mm and a density of 240 kg / m ³ . The thermal conductivity was measured and found to be 0.0015 W / mK. The heat transfer rate was 0.15 W / m ² K. The tensile strength at break of the core material was 120 N / cm.

When this vacuum heat insulating material was compressed to a thickness of 8 mm, the density was adjusted to 300 kg / m ³ , the material was disassembled, and the tensile strength at break of the core material was measured to be 113 N / cm ² . Although the tensile strength at break is reduced by compression, there is a glass fiber that breaks due to the tensile force acting on the glass fiber in the core material by compressing the core material. This is because it does not contribute to the tensile strength at break.

The heat flow rate after compression was 0.18 W / m ² K. This is because the fibers broken by compression contribute to heat transfer. On the other hand, since the thermal conductivity is the product of the thermal transmissivity and the thickness, it was calculated as 0.00144 W / mK, and the measured value was 0.0014 W / mK.

  As in the present embodiment, when the decrease in thickness is greater than the increase in thermal conductivity due to compression, the thermal conductivity can be reduced by compression.

  A method for producing a vacuum heat insulating material, such as a method for producing a core material from a glass fiber assembly, a bag making method for a jacket material, and a method for measuring each physical property are the same as those in the first embodiment.

  In the glass fiber assembly, as a technique for increasing the ratio of fibers having a high tensile breaking strength, a technique for decreasing the temperature of the cooling air that stretches the glass fibers was used. However, the present invention is not limited to this, and Griffith cracks may be removed by treating the surface of the glass fiber with a chemical.

  In the embodiment, the method for increasing the ratio of fibers having a high tensile breaking strength was changed and examined. The vacuum heat insulating material was produced using the core material produced by shape | molding the glass fiber aggregate obtained on each condition. Examples 1 to 7 show the physical properties and thermal conductivity of the core material under the respective production conditions. Moreover, the case where rapid cooling is not performed is shown in Comparative Example 1. The production method of the vacuum heat insulating material is the same in each case.

(Example 1)
When the glass fiber was rapidly cooled at 50 ° C., the thermal conductivity of the vacuum heat insulating material was 0.0018 W / mK. The tensile strength at break of the core material was 70 N / cm ² .

(Example 2)
When the glass fiber was rapidly cooled at 30 ° C., the thermal conductivity of the vacuum heat insulating material was 0.0017 W / mK. The tensile strength at break of the core material was 85 N / cm ² .

Example 3
When the glass fiber was quenched at 10 ° C., the thermal conductivity of the vacuum heat insulating material was 0.0016 W / mK. The tensile strength at break of the core material was 100 N / cm ² .

Example 4
When the glass fiber was quenched at −10 ° C., the thermal conductivity of the vacuum heat insulating material was 0.0015 W / mK. The tensile strength at break of the core material was 120 N / cm ² .

(Example 5)
When the glass fiber was rapidly cooled at −30 ° C., the thermal conductivity of the vacuum heat insulating material was 0.0015 W / mK. The tensile strength at break of the core material was 120 N / cm ² .

Example 6
When the glass fiber was reinforced by ion exchange, the thermal conductivity of the vacuum heat insulating material was 0.0015 W / mK. The tensile strength at break of the core material was 115 N / cm ² .

(Example 7)
When glass fiber was reinforced with hydrofluoric acid, the thermal conductivity of the vacuum heat insulating material was 0.0015 W / mK. The tensile strength at break of the core material was 110 N / cm ² .

  Table 1 shows the relationship between the thermal conductivity of the vacuum heat insulating material using the glass fiber reinforced under each condition as a constituent element of the core material, and the physical properties of the fiber and the core material.

ガラス繊維の冷却温度を２００℃とした場合の真空断熱材の熱伝導率と芯材の引張り破断強度を比較例に示す。

The comparative example shows the thermal conductivity of the vacuum heat insulating material and the tensile breaking strength of the core material when the glass fiber cooling temperature is 200 ° C.

(Comparative Example 1)
The heat conductivity of the vacuum heat insulating material was 0.0020 W / mK. The tensile strength at break of the core material was 60 N / cm ² .

As shown in (Table 1), the thermal conductivity decreases as the tensile strength of the core increases, and the thermal conductivity decreases when the tensile strength of the core is 65 N / cm ² or more. I understand that.

  Also, when the ratio of glass fibers with high strength is increased by lowering the temperature of the cooling air, and when the proportion of glass fibers with high strength is increased by reducing Griffith cracks by surface treatment, the tension of the core material is increased. The thermal conductivity decreases as the breaking strength increases.

  Therefore, it can be seen that when the tensile strength at break of the core material is large, the thermal conductivity is reduced regardless of the glass fiber preparation conditions.

  As mentioned above, since the vacuum heat insulating material concerning this invention has the outstanding heat insulation performance, high heat insulation performance is obtained by thinner thickness. Therefore, in addition to uses such as a refrigerator and a cooler box, the present invention can be applied to uses that require high heat insulation performance in a narrow space such as a liquid crystal projector, a copy machine, and a notebook computer.

Sectional drawing of the vacuum heat insulating material in Embodiment 1 of this invention Schematic diagram of a core cross-section of the vacuum heat insulating material in Embodiment 1 of the present invention Schematic diagram of cross section of test piece for measuring tensile strength of core material of vacuum heat insulating material in Embodiment 1 of the present invention The schematic diagram which shows the state of the test piece attachment of the core material of the vacuum heat insulating material in Embodiment 1 of this invention. Schematic diagram of the core material cross-section of the vacuum heat insulating material in Embodiment 2 of the present invention Schematic diagram of the cross-section of the core material of a conventional vacuum heat insulating material

Explanation of symbols

1, 1a, 1b Glass fiber 2 Vacuum heat insulating material 3 Core material 4 Jacket material

Claims (4)

A vacuum heat insulating material obtained by covering a core material made of short glass fiber aggregates with a cover material made of a laminate film and reducing the pressure inside the cover material, wherein the core material taken out from the vacuum heat insulating material is A vacuum heat insulating material having a tensile breaking strength in the direction perpendicular to the heat transfer direction of 65 N / cm ² or more.   2. The vacuum heat insulation according to claim 1, wherein the core material has a porosity of 85% or more, and the tensile strength at break of the core material is a force caused by breakage of short glass fibers occupying a portion other than the space of the core material. Wood. The vacuum heat insulating material according to claim 1 or 2 , wherein the core material does not contain a binder that binds the glass fibers to each other. The vacuum heat insulating material according to claim 1 or 2 , wherein the core material is formed by binding with a binder.

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