GB2451614A

GB2451614A - Vacuum insulating structure

Info

Publication number: GB2451614A
Application number: GB0812583A
Authority: GB
Inventors: Kyoko Nomura; Syuichi Iwata; Tsukasa Takagi; Sho Hanaoka; Masanori Tsujihara
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2007-08-06
Filing date: 2008-07-09
Publication date: 2009-02-11
Anticipated expiration: 2028-07-09
Also published as: GB2451614B; JP2009041592A; CN101363566B; CN101363566A; BE1018383A5; JP4789886B2; GB0812583D0

Abstract

A vacuum thermal insulating structure for a thermal insulating case comprises a gas barrier container (outer jacket) having air-impermeability and a core material 5 and optionally a gas adsorbent 6, which are enclosed in the outer jacket under a pressure reduced to a predetermined vacuum level. The core material 5 has a layered structure in which a plurality of sheet-like organic fiber assemblies (fiber assemblies) 1 are laminated. The fiber assemblies may be composed of a first set of organic fibers arranged at a predetermined interval and a second set of organic fibers arranged perpendicularly to the first set and at a predetermined interval. The organic fibers assembly may be formed in a sheet by pressing and welding continuous organic fibers together. The core may be formed by folded first and second organic fibers assemblies (1x and 1y) laminated so as to cross each other. The organic fibers may be polyester, polypropylene, polylactic, aramid and LCP (liquid crystal polymer). A thermal insulation wall 12 for a refrigerator comprises the thermal insulation structure 7, spacer 8 and polyurethane foam 11. The thermal insulation structure has improved handling and thermal insulation properties and recyclability.

Description

VACUUM THERMAL INSULATING

STRUCTURE PND THERMAL INSULATING CASE

[0001] The present invention relates to a vacuum thermal insulating structure and a thermal insulating case, in particular, to a vacuum thermal insulating structure and a thermal insulating case suitable for constituting a cooling or heating apparatus.

[0002] Hitherto, urethanes have been used as thermal insulating materials. However, recently, vacuum thermal insulating structures having more excellent thermal insulation capabilities than urethanes have been used together with existing urethanes. Such vacuum thermal insulating structures are used for cooling or heating apparatuses such as attemperators, air conditioners of cars, and hot water suppliers, in addition to refrigerators.

[0003] A vacuum thermal insulating structure is constituted by an outer jacket made of gas barrier (i.e., air-impermeable) aluminum foil in which powder, foamed material, fibrous material, or the like is contained as a core material and the pressure inside the outer jacket is maintained at several Pa.

An example of factors lowering the thermal insulation capability of the vacuum thermal insulating structure is release of gas from the core material or existence of moisture in the core material, other than penetration of air or moisture from outside the vacuum thermal insulating structure. In order to adsorb such gas and moisture, an adsorbent is provided in the outer jacket.

Examples of the core material of the vacuum thermal insulating structures include silica powder, urethane foam, and glass fibers. Under the present circumstances, the most commonly used core material is a fibrous material having the highest thermal insulation capability.

(0004] Fibrous materials are roughly classified into two types of fibers, that is, inorganic fibers and organic fibers.

Inorganic fibers include glass fibers and carbon fibers (for example, refer to Patent Documents 1 and 8).

Organic fibers include polypropylene fibers, polylactic fibers, aramid fibers, LCP (liquid crystalline polymer) fibers, polyethylene terephthalate fibers, polyester fibers, polyethylene fibers, and cellulose fibers (for example, refer to Patent Documents 2 and 7).

[0005] Examples of the type of the fibrous material include a flocculent type configuration and a laminated-sheet type configuration (for example, refer to Patent DocumentS 3 and 4) Furthermore, examples of the type of the fibrous material also include sheets which are laminated in such a manner that, in each of the sheets, an orientation direction of fibers therein is perpendicular to that of adjacent sheets (refer to Patent Documents S and 6).

[0006] [Patent Document 1] Japanese Unexamined Patent Application Publication No. 8-028776 (pages 2 and 3) [Patent Document 2) Japanese Unexamined Patent Application Publication No. 2002-188791 (pages 4 to 6, Fig. 1) [Patent Document 3] Japanese Unexamined Patent Application Publication No. 2005-344832 (pages 3 and 4, Fig. 1) (Patent Document 4] Japanese Unexamined Patent Application Publication No. 2006-307924 (pages 5 and 6, Fig. 2) [Patent Document 5] Japanese Unexamined Patent Application Publication No. 2006-017151 (page 3, Fig. 1) [Patent Document 6] Japanese Examined Patent Application Publication No. 7-103955 (page 2, Fig. 2) (Patent Document 7] Japanese Unexamined Patent Application Publication No. 2006-283817 (pages 7 and 8) (Patent Document 8) Japanese Unexamined Patent Application Publication No. 2005-344870 (page 7, Fig. 2) [0007) In conventional vacuum thermal insulating structure, glass fibers and polyester fibers have been used as a core material.

Glass fibers are hard and fragile and lead to dust particles being scattered therefrom in a manufacturing step.

Therefore, handling and workability are problems because the scattered dust particles may cause irritation of skin, mucosa, or the like of operators. Furthermore, when recycling is considered, for example, when refrigerators are broken into pieces in a recycling factory, glass fibers contained in urethane chaff and the like are subjected to thermal recycling. This glass fibers disadvantageously lower combustion efficiency and remain as residual waste which leads to lowering of recyclability.

(0008] In contrast to this, organic fibers such as polyester are advantageous in terms of handleability and recyclability.

However, thermal conductivity, which represents the thermal -4-.

insulation efficiency of the organic fibers is 0.0030 W/rnK (refer to Patent Document 7) while that of glass fiber is 0.0013 W/mK (refer to Patent Document 8). This makes the organic fibers disadvantageous in terms of thermal insulation capability.

(0009] The present invention has been developed to solve the above-mentioned problems and provides a vacuum thermal insulating structure having advantages in terms of handling and thermal insulation capability and provides a thermal insulating case including the vacuum thermal insulating structure.

[0010] The vacuum thermal insulating structure of the present invention is constituted by a gas barrier container and a core material accommodated therein, wherein the pressure therein is maintained at a low pressure.

The core material has a layered structure of organic fiber assemblies each of which is formed in a sheet composed of organic fibers.

(Advantages] [0011] As mentioned above, the vacuum thermal insulating structure of the present invention has an advantage in terms I.' of handling and recyclability and has an excellent thermal insulation capability because the vacuum thermal insulating structure of the present invention is constituted by laminated sheet-like organic fiber assembies.

The invention will now be described by way of non-limiting examples, with reference to the accompanying drawings, in which: (Fig. 1] Fig. 1 is a perspective view showing laminated core material thin layers constituting a vacuum thermal insulating structure of the first embodiment of the present invention.

[Fig. 2) Fig. 2 is a side view showing direction of fibers in a sheet in vacuum thermal insulating structure shown in Fig. 1.

[Fig. 3] Fig. 3 is a side view showing direction of fibers in a thick sheet in vacuum thermal insulating structure shown in Fig. 1.

[Fig. 4) Fig. 4 is an exploded perspective view showing a configuration of a vacuum thermal insulating structure.

(Fig. 5] Fig. 5 is a graph indicating the thermal insulation capability of the vacuum thermal insulating structure according to the first embodiment.

[Fig. 6] Fig. 6 is a perspective view which schematically shows the method for laminating the core material constituting the vacuum thermal insulating structure of a second embodiment of the present invention.

[Fig. 7) Fig. 7 is a perspective view which schematically shows the method for laminating the core material constituting the vacuum thermal insulating structure of the second embodiment of the present invention.

(Fig. 8) Fig. 8 is a cross-sectional view schematically showing a thermal insulating case (refrigerator) of a third embodiment of the present invention.

Figs. 1 to 4 show schematic views of the vacuum thermal insulating structure according to a first embodiment of the present invention. Fig. 1 is a perspective view of laminated layers forming a thin core material. Fig. 2 is a side view of a sheet showing direction of fibers. Fig. 3 is a side view of a thick sheet showing direction of fibers.

Fig. 4 is an exploded perspective view showing a configuration of the vacuum thermal insulating structure.

In Fig. 4, a vacuum thermal insulating structure 7 includes a gas barrier container (hereinafter referred to as an "outer jacket") 4 having air-impermeability and a core material 5 and a gas adsorbent 6, which are enclosed in the outer jacket 4. The pressure inside the outer jacket 4 is reduced to a predetermined vacuum level.

(0013) (Layered structure) As shown in Fig. 1, the core material 5 has a layered structure in which a plurality of sheet-like organic fiber assemblies (hereinafter referred to as a "fiber assembly") 1 are laminated.

As shown in Fig. 2, the fiber assembly 1 is composed of a plurality of organic fibers 2x arranged at a predetermined interval and a plurality of organic fibers 2y arranged perpendicularly to the organic fibers 2x and at a predetermined interval. The organic fibers 2x and the organic fibers 2y are in point-contact with each other.

Furthermore, since the fiber assembly 1 is formed to be thin, the amount of fibers arranged in the heat-transferring direction is reduced and this results in the thermal conductivity thereof being lowered.

Although, in the above-mentioned case, the organic fibers 2x and the organic fibers 2y perpendicularly cross each other, the present invention is not limited to this case and these fibers may cross each other at an angle other than a right angle.

[0014] (Organic fibers) In the first embodiment, polyester is used for organic fibers 2 constituting the core material 5 of the vacuum thermal insulating structure 7. Examples of the material for the organic fibers 2 include polypropylene, polylactic, aramid, and LCP (liquid crystalline polymer) other than polyester. p1

If polypropylene is used, the productivity of the organic fibers can be improved because polypropylene has a low hygroscopic property, which results in reduction of drawing time for vacuum and drying time, and enhancement of the thermal insulation capability of the vacuum thermal insulating structure is expected because polypropylene has low solid thermal conductivity.

If polylactic is used, removed and classified core materials of used products can be used for reclaiming land because polylactic is biodegradable.

If aramid or LCP is used, since aramid and LCP have high rigidity, sufficient shape-keeping capability of a vacuum package is exhibited under atmospheric pressure and a high vacant space rate of the core material can be achieved, which may result in enhancement of the thermal insulation capability of the vacuum thermal insulating structure.

[0015] (Fiber assembly) The fiber assembly (i.e., organic fiber assembly or sheet assembly) 1 constituting the core material 5 is manufactured by withdrawing a molten polyester resin by a free-fall method onto a conveyer from many nozzles aligned in a line having a desired length, by pressing the fallen polyester resin with a roller while moving the conveyer at a predetermined speed, and by coiling the resultant.

A volume density of the fiber assembly 1 is controlled by the amount of discharge of the molten resin and the speed of the conveyer, and then fiber assemblies having various thicknesses can be obtained.

[0016] Note that the fiber assembly 1 obtained using the above-mentioned method occasionally has a problem in terms of handling required to manufacture the vacuum thermal insulating structure because the organic fibers 2 are not bound together. Therefore, the organic fibers 2 are preferably welded together by heating when a pressing treatment is performed. In this welding step, an excessive pressure or excessive heating may increase a contact area between the organic fibers 2, which leads to undesirable increase of heat transfer. Therefore, it is preferable that the contact area be decreased as much as possible and the ratio of the contact area to the entire area is preferably suppressed to 5% or lower.

(0017] Next, the obtained fiber assembly 1 was cut into A4 size sheets and 25 sheets were laminated so as to form the core material 5. The number of sheets to be laminated may be freely determined on the basis of the thicknesses of the obtained fiber assembly 1 and desired vacuum thermal insulating structure 7. In the first embodiment, a diameter -10 -of the fibers included in the fiber assembly 1 was adjusted to about 15 pm by changing the diameter of the nozzles used in the forming step. When the thermal insulation capability is considered, the diameter of the fibers is preferably small. Theoretically, the diameter of the fibers is preferably 10 pm or smaller.

[0018] (Outer jacket) For the outer jacket 4 of the vacuum thermal insulating structure 7, a gas barrier plastic laminate film was used which was constituted by nylon (6 pm), aluminum deposited PET (10 pin), aluminum foil (6 jun), and high-density polyethylene (50 pm).

If a laminate film having a structure, in which a polypropylene film, a polyvinyl-alcohol film, and another polypropylene film are laminated without an aluminum foil is used, the reduction of the thermal insulation capability caused by heat bridging can be mitigated. Note that three of the four sides of the outer jacket are sealed by heating using a seal packaging machine.

[0019] (Method for manufacturing) The vacuum thermal insulating structure 7 was manufactured by inserting the core material 5 into the outer jacket 4 serving as a case, by fixing the case with one side -11 -thereof being open, and by drying the case in a constant-temperature oven at a temperature of 105°C for half a day (about 12 hours), and then inserting the gas adsorbent 6 into the film case in order to adsorb gas remaining after conducting packaging under a reduced pressure, gas released from the core material 5 with time, and gas that had penetrated through a seal layer of the outer jacket 4. By using a KA.SHIWAGI vacuum packaging machine (NPC Incorporated; KT-650), the chamber was evacuated to a pressure of about 1 to 10 Pa and the open side of the film case, which was set in the chamber, was sealed by heating so as to obtain a plate- like vacuum thermal insulating structure 7.

[0020) (Thermal insulation capability) Next, effects of the thickness of the fiber assembly 1 on the thermal insulation capability are described with respect to the fiber assemblies 1 of EXPNPLES 1 to 4 of the present invention and A COMPARATIVE EXAMPLE.

For the COMPARATIVE EXAMPLE, flocculent polyester fibers with the same diameter as those (about 15 run) used in EXAMPLES 1 to 4 were used as a core material and a vacuum thermal insulating structure was obtained using the same method as that mentioned above.

The vacuum thermal insulating structures obtained in -12 -EXAMPLES 1 to 4 and the CONPABATIVE EXAMPLE were measured with respect to thermal conductivity, which is exhibited between a portion with an upper temperature of 37.7°C and a portion with a lower temperature of 10.0°C. This measurement was conducted after one day had passed since the evacuating step, using a thermal conductivity measurement apparatus "Auto A HC-073 (EKO INSTRUMENTS CO., LTD)" (00211 The thickness of each fiber assembly 1 is determined by dividing the thickness of the vacuum thermal insulating structure 7 minus two times the thickness of the outer jacket 4 by the number of laminated fiber assemblies 1. The average diameter of fibers is defined to be an average value of 100 values measured with a microscope. The results, which were calculated by dividing the thickness of a fiber assembly measured after evacuation by the average diameter of fibers, are shown in Table 1.

(00221

[Table 1]

Thickness of Sheet/Average Diameter of Fibers

EXAMPLE 1 4

EXAMPLE 2 8

EXAMPLE 3 14

EXAMPLE 4 18

COMPARATIVE 369

EXAMPLE

-13 -[0023] Fig. 5 is a graph indicating the thermal insulation capability of the vacuum thermal insulating structure according to the first embodiment of the present invention.

The abscissa shows values of a thickness of the fiber assembly 1 divided by an average diameter of fibers, and the ordinate shows a ratio of thermal insulation capability.

Note that the ratio of the thermal insulation capability is a value which is calculated by dividing the thermal conductivities of the COMPARATIVE EXAMPLE by the thermal conductivitieS of EXAMPLES 1 to 4 (i.e., each value is a reciprocal of the value calculated by dividing the thermal conductivity of one of EXAMPLES 1 to 4 by the thermal conductivity of the COMPARATIVE EXAMPLE.) With respect to Fig. 5, it is found that if the thickness of the fiber assembly 1 becomes less than 18 times the average diameter of fibers, the thermal insulation capability is improved compared with that in the COMPARATIVE EXAMPLE in which flocculent fibers serves as a core material.

This is because the smaller the thickness of the fiber assembly 1 becomes, the more easily the fibers can be aligned in the direction parallel to the surface, the direction being perpendicular to a thermally insulating direction. That is, it can be thought that since the path of heat transfer along the thermally insulating direction -14 -can be lengthened in the vacuum thermal insulating structure 7, the thermal insulation capability thereof can also be improved.

Furthermore, it is found that the thickness of the fiber assembly 1 may preferably be 1 to 18 times the diameter of the fibers therein because the closer the thickness of the fiber assembly 1 becomes to the average diameter of the fibers, the more the thermal insulation capability improves.

Note that the thickness of the fiber assembly may preferably be 1 to 8 times the average diameter of the fibers because the thermal insulation capability significantly improves in the case where the thickness of the fiber assembly 1 becomes 8 times or less the diameter of the fibers.

(0024) Figs. 6 and 7 are perspective views schematically showing the method for laminating layers of the core material constituting the vacuum thermal insulating structure of a second embodiment of the present invention.

As shown in Fig. 6, the core material 5 is composed of a fiber assembly 1 having a continuous sheet-like form folded without being cut so as to form a layered structure.

-15 -r As shown in Fig. 7, by using a first fiber assembly lx having a continuous sheet-like form without being cut and a second fiber assembly ly having a continuous sheet-like form without being cut (hereinafter they are also referred to as "fiber assemblies 1"), the assemblies are disposed so as to cross each other so that areas of the assemblies divided by pleat lines can be alternately laminated by folding each of the assemblies so that the other assembly is positioned between layers thereof.

[0025] That is, by folding the fiber assemblies 1 so as to laminate them, a cutting step can be omitted, so that the core material 5 or the vacuum thermal insulating structure 7 can be efficiently manufactured.

Since the fiber assembly 1 used in the present embodiment was formed by the above-mentioned manufacturing method, the organic fibers 2 are oriented along the longitudinal direction. Considering the above, if the fiber assemblies 1 are alternately laminated so as to cross each other, they come into point-contact with each other, resulting in the thermal insulation capability being further improved.

(0026] Fig. 8 is a cross-sectional elevated view schematically r showing a refrigerator and describes a thermal insulating case shown in the third embodiment of the present invention.

Note that the same reference numerals will be used to denote common components of the first embodiment and the second

embodiment, and redundant description is avoided.

As shown in Fig. 8, a refrigerator 100 includes an outer case 9, an inner case 10 housed inside the outer case 9, a vacuum thermal insulating structure 7 and polyurethane foam 11 disposed in a gap between the outer case 9 and the inner case 10, and a freezer unit (not shown in the drawing) to supply a cold source into the inner case 10. The outer case 9 and the inner case 10 have openings on a common face side and a door is provided thereat (the openings and the door are not shown in drawings).

(00271 In the present embodiment, since the outer jacket 4 of the vacuum thermal insulating structure 7 includes aluminum foil, this aluminum foil may serve as heat bridging in which thermal conduction occurs. In order to suppress thermal conduction through heat bridging, the vacuum thermal insulating structure 7 is placed at a position away from a coated steel panel of the outer case 9 with intervention of a spacer 8 composed of molded resin. Note that the spacer 8 may have holes therein, if required, so that the spacer can prevent formation of voids in polyurethane foam and -17 -( facilitate flow of the polyurethane foam which is to be provided into the gap of a thermal insulation wall in a step to be performed later.

That is, the refrigerator 100 has a thermal insulation wall 12 constituted by the vacuum thermal insulating structure 7, the spacer 8, and the polyurethane foam 11.

The region where the thermal insulation wall 12 is provided is not limited and may be the entirety of or a part of the gap formed between the outer case 9 and the inner case 10 and also may be in the above-mentioned door.

[0028] Once use of the refrigerator 100 has finished, it is to be dismantled and recycled at a recycling plant according to the Home Appliance Recycling Law. Since the refrigerator of the present invention has the vacuum thermal insulating structure 7 including the core material 5 composed of the fiber assembly 1 (formed of the organic fibers 2), the refrigerator can be subjected to a fracturing treatment without removing the vacuum thermal insulating structure 7. Therefore, in thermal recycling, reduction of the combustion efficiency does not occur and remnants of the combustion are not formed. This shows the high recyclability of the refrigerator 100 of the present invention.

In contrast to this, in the case where a refrigerator -18 -r is provided with a vacuum thermal insulating structure having an inorganic powder as a core material thereof, the inorganic powder will be scattered when the panel is fractured. Therefore, the refrigerator cannot be subjected to a fracturing treatment without dismounting the vacuum thermal insulating structure from the body of the refrigerator. This is a troublesome operation.

[0029) In the case that the vacuum thermal insulating panel has glass fibers as a core material, the refrigerator can be subjected to a fracturing treatment without dismounting operation. However, when fractured glass fibers mixed with pieces of fractured polyurethane foam are to be subjected to thermal recycling, the fractured glass fibers lower combustion efficiency or remain as a residue after combustion, so that the recyclability of the refrigerator is lowered.

Note that the above-mentioned embodiment shows an example of a refrigerator as a thermal insulating case.

However, the present invention is not limited to this. The present invention may be used for cooling or heating apparatuses such as attemperators, air conditioners of cars, hot water suppliers, and furthermore, thermal insulating bags (thermal insulating containers) including transformable outer bags and inner bags instead of thermal insulating -19 -( cases having a predetermined shape.

[0030] As mentioned above, since the vacuum thermal insulating structure and the thermal insulating case of the present invention have an advantage in terms of handling, thermal insulation capability, and recyclability, they can be widely used as a vacuum thermal insulating structure in various instruments and as a thermal insulating case or thermal insulating bag in various applications.

(Reference Numerals] (0032] 1: fiber assembly (sheet-like organic fiber assembly), 2: organic fiber, 2x: organic fiber, 2y: organic fiber, 3: gap, 4: outer jacket, 5: core material, 6: gas adsorbent, 7: vacuum thermal insulating structure, 8: spacer, 9: outer case, 10: inner case, 11: polyurethane foam, 12: thermal insulation wall, 100: refrigerator -20 -(

Claims

1. A vacuum thermal insulating structure comprising: a gas barrier container including a core material accommodated therein, wherein the pressure in the gas barrier container (4) is maintained at a low pressure and the core material (5) has a layered structure of organic fiber assemblies (1) each of which is formed in a sheet composed of organic fibers.

2. The vacuum thermal insulating structure according to Claim 1, wherein the thickness of the organic fiber assembly (1) accomodated in the gas barrier container (4) under the low pressure is 1 to 18 times the diameter of the organic fibers.

3. The vacuum thermal insulating structure according to Claim 1 or 2, wherein the organic fiber assembly (1) is formed in a sheet by pressing and welding continuous organic fibers together.

4. The vacuum thermal insulating structure according to any one of Claims 1 to 3, wherein the core material (5) has the layered structure including the organic fiber assemblies -21 -

I

(1) which are folded, so as to constitute the layered structure.

5. The vacuum thermal insulating structure according to Claim 4, wherein the core material (5) is composed of a first organic fiber assembly folded so as to constitute the layered structure and a second organic fiber assembly folded so as to constitute the layered structure, and the first organic fiber assembly and the second organic fiber assembly are laminated in such a manner as to cross each other.

6. A thermal insulating case comprising: an outer case (9); an inner case (10) housed in the outer case (9); and a vacuum thermal insulating structure (7) according to any one of Claims 1 to 5 disposed in the entirety of or a part of a gap formed between the outer case (9) and the inner case (8) 7, A thermal insulating case according to claim 6, wherein a thermal insulating material is disposed between the outer case and the vacuum thermal insulating structure and/or between the inner case and the vacuum thermal insulating structure.

-22 -r 8. A thermal insulating case according to claim 6 or 7, further comprising temperature controlling means for controlling the temperature of the inside of the inner case.

-23 -