JP6192554B2 - Manufacturing method of vacuum insulation - Google Patents

Description

The present invention relates to a manufacturing method of vacuum insulation material.

  As a conventional vacuum heat insulating material used as a heat insulating material for a heat insulating box such as a refrigerator, a core material formed of an aggregate of glass fibers is covered with an outer packaging material having a gas barrier property, and the inside of the outer packaging material is decompressed. And sealed (see, for example, Patent Document 1).

  In this way, the vacuum heat insulating material in which the inside of the outer packaging material is depressurized is thinned by covering the bulky glass fiber aggregate with the outer packaging material and sealing under reduced pressure, and the convection and heat conduction of the gas inside the outer packaging material are reduced. The effect is reduced to improve the heat insulation performance. In general, the heat transfer mechanism of a heat insulating material is caused by heat conduction, radiation, and convection of solid and gas components. On the other hand, the vacuum heat insulating material whose inside of the outer packaging material is sealed under reduced pressure has little effect on the heat conduction and convection of the gas component. Further, there is almost no influence of radiation when used in a temperature range below room temperature. Therefore, in a vacuum heat insulating material applied to a refrigerator or the like used in a temperature range below room temperature, it is important to suppress the heat conduction of the solid component. Therefore, various forms of fibers have been reported as vacuum insulation core materials having excellent heat insulation performance. In recent years, due to fierce energy-saving competition, there is a strong demand for a vacuum heat insulating material with excellent heat insulating performance even when it is thin, in particular, a fiber assembly having high heat insulating properties as a core material.

  As a method of reducing the thermal conductivity of the vacuum heat insulating material, there is one in which heat transfer by the glass fiber is suppressed by orienting the glass fiber constituting the vacuum heat insulating material in a direction perpendicular to the heat insulating direction (for example, patents) Reference 2).

  In addition, glass fibers are heated and pressed by a dry method using a binder, and the glass fibers are not only oriented perpendicular to the heat transfer direction, but also contain 40 to 70% of short fibers with a length of 100 μm or less. As a result, the heat transmitted through the fibers is interrupted to reduce the solid thermal conductivity (for example, see Patent Document 3).

  Further, in a dry method that does not use a binder, the glass fiber has an average fiber diameter of 2 to 5 μm, the shot (dama) mixing rate is 0.5 mass% or less, and the average particle diameter of the shot is 150 μm or less. In addition, there is a vacuum heat insulating material excellent in heat insulating properties using a glass fiber laminate in which the ratio of glass fibers having a fiber length of 500 μm or more is 80% or more (see, for example, Patent Document 4).

Japanese Patent No. 3580315 (Summary, FIG. 1) Japanese Patent Laid-Open No. 9-4785 (Summary) Japanese Patent No. 3513143 (paragraph [0006]) JP 2009-155172 A (summary)

  As a method for reducing the thermal conductivity of the vacuum heat insulating material, there is a method in which the glass fibers constituting the vacuum heat insulating material are oriented and laminated in a direction perpendicular to the heat insulating direction, but the glass fibers are perpendicular to the heat insulating direction. If the layers are simply oriented and laminated, the heat transmitted through the glass fiber is present, so that the solid thermal conductivity is increased, and there is a limit to the reduction of the initial thermal conductivity in the vacuum heat insulating material.

  In addition, the method of binding glass fibers by heat and pressure molding using a binder increases not only the power cost for heating and the material cost of the binder, but also the vacuum heat insulating material cannot be obtained at a low cost. There was a problem that the thermal conductivity was greatly deteriorated. This is because when a vacuum heat insulating material is used, a low molecular gas component is released from the binder in vacuum, and the degree of vacuum is lowered.

  Moreover, in the dry method which does not use a binder, even if the length of the glass fiber and the weight ratio of the short fiber can be controlled, there is a problem that the fiber angle in a state where the vacuum heat insulating material is used cannot be controlled.

The present invention has been made in order to solve the above problems, the weight ratio of the short fibers, and can control the average fiber angle and its standard deviation, to provide a method for producing a vacuum insulation material having excellent heat insulating performance Objective.

The method for producing a vacuum heat insulating material according to the present invention is a method of repeatedly compressing an aggregate of glass fibers 50 to 1000 times in the thickness direction at a pressure of 0.02 to 0.07 MPa by a compression mechanism capable of controlling the load. A step of creating a core material in which a weight ratio of fibers of 1.85 mm or less is 11 wt% or less, a step of inserting the core material into an outer packaging material, and depressurizing the inside of the outer packaging material to a preset vacuum degree; And the step of sealing the opening in a state where the outer packaging material is decompressed .

In the vacuum heat insulating material according to the present invention, since the weight ratio of the fiber having a fiber length of 1.85 mm or less is 11 wt% or less of the core material, the heat path path in the heat insulating direction of the core material is shortened and the heat insulating performance. The influence of a fiber having a fiber length of 1.85 mm or less, which is a factor that deteriorates the resistance, can be minimized. For this reason, high heat insulation performance can be obtained.
In addition, by setting the weight ratio of the fibers having a fiber length of 1.85 mm or less to 11 wt% or less of the core material, the fibers having a fiber length of 1.85 mm or more can be easily oriented perpendicular to the heat insulating direction of the core material. The influence of fibers having a fiber length of 1.85 mm or less, which is a factor that is oriented in the heat insulating direction of the material and deteriorates the heat insulating performance, can be minimized. For this reason, the vacuum heat insulating material excellent in heat insulation performance can be obtained.
And by applying the vacuum heat insulating material of the present invention to a heat insulation box such as a refrigerator, the heat insulation effect of the product is improved, the thickness of the product wall can be reduced, and the internal volume is increased in a limited space of the product. can do.

It is a graph which shows the relationship between the weight ratio of the fiber with a fiber length of 1.85 mm or less of the core material of the vacuum heat insulating material which concerns on Embodiment 1 of this invention, and thermal conductivity. It is an optical microscope photograph in the measurement of the average fiber length of the core material of the vacuum heat insulating material which concerns on Embodiment 1 of this invention. It is an optical microscope photograph in the measurement of the average fiber angle of the core material of the vacuum heat insulating material which concerns on Embodiment 1 of this invention. It is a graph which shows the relationship between the average fiber angle of the core material of the vacuum heat insulating material which concerns on Embodiment 1 of this invention, and thermal conductivity. It is a graph which shows the relationship between the fiber angle standard deviation of the core material of the vacuum heat insulating material which concerns on Embodiment 1 of this invention, and thermal conductivity. It is sectional drawing which shows the vacuum heat insulating material which concerns on Embodiment 1 of this invention. It is a schematic diagram which shows the manufacturing method of the vacuum heat insulating material which concerns on Embodiment 1 of this invention. It is a schematic diagram which shows the heat insulation box which concerns on Embodiment 2 of this invention.

Embodiment 1. FIG.
The vacuum heat insulating material according to Embodiment 1 of the present invention is such that the weight ratio of fibers having a fiber length of 1.85 mm or less (hereinafter sometimes referred to as “short fibers”) in the fiber assembly serving as the core is the core. It is 11 wt% or less of the material, and preferably 8 wt% or less of the core material. Here, the weight ratio of fibers (short fibers) having a fiber length of 1.85 mm or less means a measured value measured by the following method.

(Short fiber weight ratio measurement method)
100 mL of the weighed fiber was put in a beaker, 50 mL of distilled water was added, and the mixture was diffused with an ultrasonic cleaner for 5 minutes. Thereafter, all of the aggregated fibers in contact with two or more fibers were removed with precision tweezers within 1 minute, and the remaining fibers (short fibers) that could not be picked with precision tweezers were filtered and dried. The short fibers remaining on the filter paper were weighed and divided by the initial fiber amount to obtain the weight ratio.

FIG. 1 is a graph showing the relationship between the weight ratio of fibers having a fiber length of 1.85 mm or less and the thermal conductivity of the core material of the vacuum heat insulating material according to Embodiment 1 of the present invention, and the vertical axis represents the thermal conductivity [mW / M · K], and the horizontal axis represents the weight ratio [wt%] of fibers having a fiber length of 1.85 mm or less.
As is clear from this result, the thermal conductivity was almost constant at 2.0 mW / m · K or less in the range where the weight ratio of the fiber having a fiber length of 1.85 mm or less was 11 wt% or less of the core material. On the other hand, when the weight ratio of fibers having a fiber length of 1.85 mm or less exceeds 11 wt% of the core material, the thermal conductivity increases to 2.0 mW / m · K or more.
From the above results, the weight ratio of the fibers having a fiber length of 1.85 mm or less constituting the vacuum heat insulating material having a thermal conductivity of 2.0 mW / m · K or less is 11 wt% or less of the core material.
The average fiber length of the short fibers in the measurement method was determined by the following method.

(Measurement method of average fiber length)
Several drops of several mg of short fibers dispersed in water were dropped on the petri dish, and the water was evaporated in a high-temperature bath at 110 ° C. The dried fiber was observed with an optical microscope (20 to 100 times), the length of 20 fibers at any one place was measured to the nearest 0.01 mm, this measurement was performed at 5 places, and a total of 100 fibers. The average value of the lengths was taken as the average fiber length.

FIG. 2 is an optical micrograph in the measurement of the average fiber length of the core material of the vacuum heat insulating material according to Embodiment 1 of the present invention.
As a result of measuring the average fiber length of the short fibers in the weight ratio measurement by this measurement method, it was found that the average fiber length was 0.50 mm and the standard deviation σ was 0.45 mm. That is, the core material constituting the vacuum heat insulating material having a thermal conductivity of 2.0 mW / m · K or less has an average short fiber length + 3σ of fiber length of 1.85 mm or less, and the weight ratio of the core material is 11 wt% or less. It is. The standard deviation σ is one measure for looking at the spread width (variation) of the data distribution. 99.73% of the total length data of the collected short fibers is distributed within the range of the fiber length that is 1.85 mm long as the average short fiber length + 3σ.

  In the fiber assembly serving as the core material of the vacuum heat insulating material according to Embodiment 1 of the present invention, the average value of the fiber angle φ with respect to the plane perpendicular to the heat insulating direction of the core material is 14 ° or less. Here, the average value (average fiber angle) of the fiber angle φ with respect to the plane perpendicular to the heat insulating direction of the core means a measured value measured by the following method.

(Measurement method of average fiber angle)
FIG. 3 is an optical micrograph in the measurement of the average fiber angle of the core material of the vacuum heat insulating material according to Embodiment 1 of the present invention, and a measurement example is shown in the figure.
That is, in order to maintain the thickness of the vacuum heat insulating material, the outside of the vacuum heat insulating material was hardened with an epoxy resin, and then the epoxy resin was poured into the core material under vacuum to be cured. After curing, the central part of the vacuum heat insulating material is cut by a horizontal surface along the heat insulating direction, the cut surface is polished, and the surface perpendicular to the heat insulating direction of the core material is used as a horizontal plane (0 °) as a reference for the angle. Observed with an optical microscope. Assuming that the cross section of the fiber is all elliptical, the long axis length a [μm] and the short axis length b of all the fibers on the screen at any one location except the range of the peripheral width of 1 mm of the cut cross section. [μm] and the angle θ [°] between the major axis and the horizontal plane that is the reference of the angle are measured to 0.01 μm, 0.01 μm, and 0.01 ° units, respectively, and the measurement result is expressed by the following formula (1 The fiber angle φ [°] was calculated by substituting in (), and this measurement was performed at two locations. The average value of a total of 200 fiber angles φ was taken as the average fiber angle. Here, the angle θ is an angle between the major axis of the ellipse and the horizontal plane, whereas the fiber angle φ is an angle including the angle between the major axis of the ellipse and the horizontal plane and the angle formed with the cut surface. is there.

FIG. 4 is a graph showing the relationship between the average fiber angle of the core material of the vacuum heat insulating material according to Embodiment 1 of the present invention and the thermal conductivity, and the vertical axis represents the thermal conductivity [mW / m · K], The horizontal axis shows the average fiber angle [°].
As is apparent from the results, the thermal conductivity was almost constant at 2.0 mW / m · K or less in the range where the average fiber angle was 14 ° or less. In contrast, it has been found that when the average fiber angle exceeds 14 °, the thermal conductivity increases to 2.0 mW / m · K or more.
From the above results, the average fiber angle of the core material constituting the vacuum heat insulating material having a thermal conductivity of 2.0 mW / m · K or less is 14 ° or less.

FIG. 5 is a graph showing the relationship between the fiber angle standard deviation of the core material of the vacuum heat insulating material according to Embodiment 1 of the present invention and the thermal conductivity, and the vertical axis represents the thermal conductivity [mW / m · K]. The horizontal axis is the fiber angle standard deviation [°].
As is clear from this result, in the range where the standard deviation of the fiber angle is 12 ° or less, the thermal conductivity was almost constant at 2.0 mW / m · K or less. On the other hand, when it exceeded 12 degrees, it turned out that it increases to 2.0 mW / m * K or more.
From the above results, the standard deviation of the fiber angle of the core material constituting the vacuum heat insulating material of 2.0 mW / m · K or less is 12 ° or less.

  The relationship between the weight ratio of fibers having a fiber length of 1.85 mm or less, the average fiber angle and fiber angle standard deviation, and the thermal conductivity can be explained by percolation theory. For example, consider the weight ratio of fibers with a fiber length of 1.85 mm or less. One of the factors that deteriorate the heat insulation performance of VIP (Vacuum Insulation Panel) is fiber oriented in the heat insulation direction of VIP. The shorter the fibers, the higher the probability that they will be oriented in the heat insulating direction of VIP. Therefore, it is considered that the heat insulating performance is higher when there are fewer short fibers. However, if a plurality of fibers oriented in the heat insulation direction overlap and the heat path path in the heat insulation direction is not connected, the influence on the heat insulation performance is small.

In the present invention, fibers having a fiber length of 1.85 mm or less are defined as short fibers, and it is considered that the heat insulation is higher when the number of short fibers is smaller. As a result of the experiment, when the weight ratio of the short fibers is 11 wt% or less of the core material, the thermal conductivity is constant, and when the weight ratio of the short fibers exceeds 11 wt% of the core material, the thermal conductivity increases rapidly. found. This is because the weight ratio of the fiber having a fiber length of 1.85 mm or less is 11 wt% of the core material, and a plurality of fibers oriented in the heat insulation direction overlap, and the connection of the heat path path in the heat insulation direction increases rapidly. This suggests that the point is a critical point (percolation critical point).
For the above reasons, it is considered that there is an inflection point in the relationship between the weight ratio of fibers having a fiber length of 1.85 mm or less and the thermal conductivity. Furthermore, regarding the relationship between the average fiber angle, the fiber angle standard deviation, and the thermal conductivity, it can be similarly considered that each has an inflection point.

FIG. 6 is a cross-sectional view showing a vacuum heat insulating material according to Embodiment 1 of the present invention.
In FIG. 6, the vacuum heat insulating material 1 is deteriorated with time by adsorbing a core material 2 composed of a fiber assembly, a gas barrier outer packaging material 3 covering the core material 2, and moisture inside the outer packaging material 3. And a moisture adsorbent 4 to be suppressed. The inside of the outer packaging material 3 is sealed by, for example, a heat-sealing welding seal portion 5 in a state where the pressure is reduced to a vacuum degree of 1 to 3 Pa (Pascal).

  As the core material 2, glass fiber, alumina fiber, silica alumina fiber, silica fiber, rock wool, silicon carbide fiber, or nonwoven fabric can be used, and is not particularly specified.

The outer packaging material 3 has at least a gas barrier layer and a heat welding layer, and may be provided with a surface protective layer as necessary. As the gas barrier layer, a metal film, a metal oxide, or a plastic film or metal foil on which diamond-like carbon is deposited can be used as long as it can be used for the purpose of reducing gas permeation, and is not particularly specified. .
Further, silica or alumina can be used as a material for metal oxide vapor deposition on the plastic film, and is not particularly specified.

  The heat welding layer of the outer packaging material 3 is a portion having the highest gas permeability in the film constituting the outer packaging material 3, and the property of the heat welding layer greatly affects the heat insulation performance of the vacuum heat insulating material over time. The thickness of the heat-welded layer is the stability of the sealing quality in the reduced-pressure sealing process, the suppression of gas intrusion from the end face of the heat-welded part, and the heat from the surface due to heat conduction when a metal foil is used as the gas barrier layer. In consideration of the leak, 25 μm to 60 μm is suitable.

  As the material for the heat-welded layer, an unstretched polypropylene film, a high-density polyethylene film, or a linear low-density polyethylene film can be used, and is not particularly specified.

  It is also possible to further provide a surface protective layer outside the gas barrier layer. As the surface protective layer, a stretched product of a polyethylene terephthalate film, a polypropylene film, or a nylon film can be used. Further, when a nylon film is used on the outer side, the bending resistance and the puncture resistance are improved.

  The bag shape of the outer packaging material 3 includes a four-side seal bag, a gusset bag, a three-side seal bag, a pillow bag, and a center tape seal bag, but is not particularly specified.

  The moisture adsorbent 4 is, for example, calcium oxide (CaO) inserted into a bag having good air permeability. The moisture adsorbent 4 is not limited to CaO, and is not particularly limited as long as it has moisture adsorption properties such as zeolite.

Next, the manufacturing method of the vacuum heat insulating material 1 which concerns on Embodiment 1 of this invention is demonstrated.
The core material 2 used for the vacuum heat insulating material 1 of this embodiment is comprised with the glass fiber aggregate manufactured by the dry method which does not use a binder, for example. The core material 2 composed of this glass fiber aggregate has a low bulk density and poor handling properties when inserting the vacuum heat insulating material 1 and insertability into the outer packaging material 3. Therefore, in order to handle as the core material 2, it is necessary to increase the bulk density by processing.

FIG. 7 is a schematic view showing a method for manufacturing a vacuum heat insulating material according to Embodiment 1 of the present invention.
The processing device 6 includes a compression mechanism 7 that compresses the core material 2. The core material 2 is installed in the processing device 6 after being aligned with the width and length necessary for the vacuum heat insulating material 1. At this time, the thickness of the core material 2 is 10 times or more that of the vacuum heat insulating material 1.

  Next, the core material 2 is repeatedly compressed by the compression mechanism 7. The pressure when compressing is preferably 0.02 to 0.07 MPa, and more preferably 0.02 to 0.04 MPa. The number of compressions is preferably 50 to 1000 times. By compressing under the above conditions, the weight ratio of fibers with a fiber length of 1.85 mm or less keeps the state before compression, and the fibers gradually shift and repeat rearrangement, and perpendicular to the heat insulation direction of the core material 2. A core material 2 having an average value of the fiber angle φ with respect to a smooth surface of 14 ° or less and a standard deviation of 12 ° or less is obtained.

  When the pressure when compressed 50 to 1000 times exceeds 0.07 MPa, the fiber breaks, the weight ratio of the fiber having a fiber length of 1.85 mm or less becomes 11 wt% or more of the core material 2, and vacuum insulation with excellent heat insulation performance The material is not obtained. The cause is that short fibers are filled between the main fibers or entangled between the main fibers, causing heat conduction between the fibers, and heat conduction along the thickness direction of the core material. It is considered that the heat insulation performance is lowered by causing

  On the other hand, when the pressure when compressed 50 to 1000 times is less than 0.02 MPa, rearrangement due to fiber displacement is less likely to occur, and the average value of the fiber angle φ with respect to the plane perpendicular to the heat insulating direction of the core material 2 Cannot be controlled to 14 ° or less, and a vacuum heat insulating material excellent in heat insulating performance cannot be obtained. Further, the bulk density does not increase, the handling property and the insertion property into the outer packaging material 3 are not improved, and the vacuum heat insulating material cannot be produced efficiently.

Next, the core material 2 processed with a high bulk density is inserted into the outer packaging material 3, and after passing through a drying process for removing moisture, the moisture adsorbent 4 is inserted, and the interior of the outer packaging material 3 is 1 to 3 Pa ( The vacuum heat insulating material 1 is obtained by sealing the opening by heat sealing in a state where the pressure is reduced to Pascal). In the drying process, for example, heating may be performed at 100 ° C. for 2 hours, which is a condition capable of removing moisture from the core material 2 and the outer packaging material 3 covering the core material 2, but the heating condition is limited to this. The core material 2 and the outer packaging material 3 covering the core material 2 may be removed under any conditions.
Further, the moisture adsorbent 4 is not limited to being inserted after the drying process, but compresses the core material 2 and the outer packaging material 3 covering the core material 2 before the drying process or by the processing device 6. It may be inserted before.

  About the vacuum heat insulating material 1 which concerns on Embodiment 1 of this invention, thermal conductivity, the weight ratio of the fiber of 1.85 mm or less of fiber length, the average value of fiber angle (phi) with respect to a surface perpendicular | vertical with respect to the heat insulation direction of the core material 2, and The standard deviation was evaluated. The thermal conductivity was measured with a thermal conductivity meter by a steady method. The measurement conditions were a high temperature side of 37.7 ° C., a low temperature side of 10 ° C., and an average temperature of 23.85 ° C. The weight ratio of the fibers having a fiber length of 1.85 mm or less is 11 wt% or less of the core material 2, the average value of the fiber angle φ with respect to the plane perpendicular to the heat insulation direction of the core material 2 is 14 ° or less, and the standard deviation is 12 °. Below, the thermal conductivity was 2.0 mW / m · K or less. From the above results, it was found that the vacuum heat insulating material satisfying the above conditions processed by the method of the present embodiment was excellent in heat insulating performance.

Embodiment 2. FIG.
Although the said vacuum insulation material 1 and its manufacturing method were demonstrated in the said embodiment, the heat insulation box of a refrigerator with small power consumption can be provided by using this vacuum heat insulation material 1. FIG.
FIG. 8 is a schematic view showing a heat insulation box according to the second embodiment of the present invention (in this embodiment, a heat insulation box of a refrigerator). In the figure, parts corresponding to those of the first embodiment are denoted by the same reference numerals. Is attached.
In FIG. 8, the heat insulating box 8 includes an inner box 9 made of ABS resin, an outer box 10 made of a steel plate, and one side of the space between the inner box 9 and the outer box 10 (inner box 9 side). And a urethane foam heat insulating material 11 filled in a space other than the vacuum heat insulating material 1 between the inner box 9 and the outer box 10. The inner box 9 and the outer box 10 each have an opening (not shown) formed on a common surface, and an opening / closing door (not shown) is provided in the opening. Other parts are the same as the heat insulation box used in a general refrigerator, and thus illustration and description thereof are omitted.

  In the heat insulating box 8 of the refrigerator, the range in which the vacuum heat insulating material 1 is disposed is not limited, and may be the entire space formed between the inner box 9 and the outer box 10, or It may be a part, and may be arranged inside the opening / closing door.

  The refrigerator heat insulating box 8 configured as described above uses the vacuum heat insulating material 1 of the present invention embedded in the urethane foam heat insulating material 11 and uses it in combination. An effect is obtained.

  DESCRIPTION OF SYMBOLS 1 Vacuum heat insulating material, 2 core material, 3 outer packaging material, 4 moisture adsorption agent, 5 welding seal part, 6 processing apparatus, 7 compression mechanism, 8 heat insulation box, 9 inner box, 10 outer box, 11 urethane foam heat insulating material.

Claims (1)

The weight ratio of fibers having a fiber length of 1.85 mm or less is 11 wt% by repeatedly compressing the aggregate of glass fibers 50 to 1000 times in the thickness direction at a pressure of 0.02 to 0.07 MPa by a compression mechanism capable of controlling the load. Creating a core material that is:
Inserting the core material into an outer packaging material, and depressurizing the interior of the outer packaging material to a preset vacuum degree;
And a step of sealing the opening in a state where the outer packaging material is depressurized.

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