US2746892A

US2746892A - Multi-layer heat insulating material

Info

Publication number: US2746892A
Application number: US318628A
Authority: US
Inventors: Thore M Elfving
Original assignee: Isoflex Corp
Current assignee: Isoflex Corp
Priority date: 1952-11-04
Filing date: 1952-11-04
Publication date: 1956-05-22
Anticipated expiration: 1973-05-22
Also published as: GB784526A; FR1117503A; BE534019A; CH332722A

Description

May 22, 1956 T. M. ELFVING MULTI-LAYER HEAT INSULATING MATERIAL Filed Nov. 4, 1952 IN VEN TOR.

T110192 M Eur/ma. B Y

MULTI-LAYER HEAT INSULATING MATERIAL Thore M. Elfving, San Mateo, Calif., assignor to lsoflex Corporation, Redwood City, Calif.

Application November 4, 1952, Serial No. 318,628

6 Claims. (Cl. 154-45) My present invention relates to heat insulating board of the multi-layer type and more particularly to an improved heat insulation comprising a plurality of aluminum foils of hard and bright finish laminated in a board with a light Weight pervious spacing element which can be easily handled and used in complicated structures such as refrigerated railway cars and trucks, aeroplanes and the like.

The principal object of my invention is to provide an insulating board of light weight suitable for the use in the low temperature field and especially in the refrigeration transportation field where moisture migration by diffusion from the warm side of the refrigerated structure often causes serious trouble.

A further object of the invention is to provide a light weight insulation board of multi-layer aluminum foil in which direct metal conductivity is prevented by interspaced low conductive material.

Another object of the invention is to provide a light weight heat insulation board-like structure in which heat radiation is effectively restricted by a plurality of double acting aluminum foils and in which convection fiow is restricted by a large number of layers and moisture migration by diffusion in a transversal direction is practically prevented by impervious metallic vapor barriers.

In the operation of air conditioned or refrigerated railway cars or trucks considerable difiiculty is experienced in eliminating condensed water within the insulation space or water entering the insulation from the commodity space. Unless proper drainage is provided, moisture will accumulate and reduce the efficiency of the insulation. At low temperatures even ice can be formed within the insulating material with a detrimental increase of the heat transfer as a result. It is therefore a further object of the invention to provide a light weight insulation board with self draining properties so that Water entering within its structure can not seriously affect its insulation properties.

Other objects and advantages of the invention will be in part evident to those skilled in the art and in part pointed out herein often in connection with the accompanying drawing wherein there is shown by way of illustration and not of limitation several preferred embodiments thereof.

In the drawing:

Figure l is a fragmentary perspective view of a heat insulation board constructed in accordance with my invention,

Figure 2 is a fragmentary perspective view showing a modification of the heat insulation board, and

Figure 3 is a fragmentary perspective view showing another modification of the heat insulating board.

In Figures 2 and 3 of the drawing, the aluminum foils are shown as separated by a low conductivity material, but it is to be understood that an insulating board made in accordance with the invention, may comprise any number of foils and intervening layers of low conductive nited States Patent O 2 material depending upon the desired thickness of the board.

For a more detailed description of the invention reference is now had to Figure lot the accompanying drawing where the numerals 11 and 13 designate two bright and hard corrugated aluminum foils which, according to the invention, may vary from .0003 to .003 inch in thickness. These aluminum foils are separated by a similarly corrugated plastic film 12, the corrugations extending substantially between two parallel imaginary surfaces. The film may be of cellulose acetate, poly vinyl chloride or silicone plastic; This plastic film material like the aluminum foil is quite thin and may vary from .001 to .003 inch in thickness. 1

The upper crests or ridges of the three corrugated foils as shown are respectively designated by the numerals 14, 16 and 18, and the lower ridges are designated by the

numerals

15, 17 and 19 respectively, the opposite sides of the ridges being considered as valleys. At the points where the ridges cross and contact each other the corrugated sheets are secured together in any conventional or convenient way as with a suitable cement or glue.

The gluing of the corrugated foils offers particular difficulties because of the different nature of contacting surfaces. The metal foils have to be glued to a nonmetallic or plastic film material with a waterproof and strong bond. According to the invention, this gluing can be executed by using a copolymer consisting of 87% vinyl chloride, 12% vinyl acetate and 1% maleic acid. To one part of copolymer is added five parts of isopropyl acetate or normal propyl acetate but other solvents may also be used. The presence of maleic acid causes an attack on the metal foils and results in a bond between the plastic and the metal that will not be affected by water.

The corrugation or valley depth of the aluminum foils may, according to my invention, vary from A; to of i an inch and the corrugations of the plastic film may vary from a minimum of /s of an inch inch in depth.

The plastic film material should preferably be of a non-inflammable character, as indicated by the materials mentioned above. In the use of a cellulose acetate film material, the plasticizing agent, if such a material is used, should be triphenyl phosphate and/or, tri-cresyl phosphate in order to render the material non-inflammable to the greatest possible degree.

When the thicknesses of the plastic film materials are between .001 to .003 inch, as set forth above, they will be pervious to long wave heat rays. For this reason an 2.1- plastic insulation board of corrugated film material having said thickness cannot be successfully used without incorporating in the plastic material a finely divided blocking substance such as graphite, usually in the amount of 35% by weight.

With an insulation board constructed according to this invention, no such blocking agent for the heat rays is required in the film material even though the plastic film between two layers of corrugated aluminum foils is pervious to heat rays. it is a special feature of this invention that the interspaced low conductive non-metallic material between the reflective layers of metallic foil allows heat radiation to pass through without being wholly absorbed. The penetration of heat rays in the range corresponding to temperatures from 40 F. to F. varies for the plastic materials mentioned above from 5 to 50% according to the particular material and thickness of the film used and the heat wave length.

As an example of an application of the invention, with a cellulose acetate film material, having a thickness of .00135 inch and corrugated to aheight of inch, the heat ray penetration through such a film is less than 10% to a maximum of one for heat rays in the above mentioned range of temperature. it has been demonstrated by numerous tests that an insulation board using clear transparent plastic film of the above type and dimensions as a spacing material between aluminum foils corrugated to a height of A" gives an sulation board with an approximately 25% lower k-factor than a board of exactly the same structure of aluminum foils and plastic film in which the film material has been made impervious to heat rays by the incorporation of approximately 3% of finely dispersed graphite in the film material. The reason for this superiority of the clear pervious material as a spacer between the reflective metal foils is believed to be partly explained by the lower heat conductivity of the film material. In other words, the incorporation of graphite in the plastic film increases the conduction of heat in the material considerably and thereby also increases the heat transmission through the whole insulation board. The problem of heat transfer through multilayer insulation board according to the invention is, however, extremely complex. It involves not only an exchange of radiation between adjacent layers of different foil and film material, but also in case the film material is pervious to heat rays, an exchange of radiation between the reflective foils themselves through the interspacing pervious material and the influence of the perviousness of the spacing material. Repeated tests, however, have shown that the incorporation of blocking material in the film leads to an inferior product.

Reference is now made to Figure 2 of the drawing where there is shown another embodiment of the invention. In this showing the board is illustrated as of two corrugated aluminum foils 2t and 21, separated by an interposed blanket 22 of fiber glass or similar material, the blanket having yielding fibrous surfaces and, although fibrous, it is of approximately uniform thickness throughout. The number of alternate layers of foil and fiber glass of which the board may be constructed is immaterial.

In this instance, the corrugated metallic aluminum foils are cemented or glued to the non-metallic, pervious spacing material in any conventional or convenient way along the ridges 23 and 24. This leaves the intervening valleys formed by the corrugations of the aluminum foil substantially free of the spacing material. The glue material already described above will be found suitable.v The range of thickness'of the aluminum foil is the same as mentioned above with the arrangement of Figure l and a suitable thickness of hard and bright aluminum foil is approximately .00065 of an inch. The corrugation height of the aluminum foils may in this modification of the invention vary from A2 of an inch to /4 of an inch.

The fiber glass spacing material 22 should have a thickness not less than Mr inch and should not exceed 1 inch. The fiber glass blanket 22 should also be light in weight and have a weight per unit volume of not less than .5

lb./cu. ft. and not exceeding 5 lbQ/cu; ft. Such materials are penetrated by long wave heat rays to a considerable depth varying from 1 inch to over 4 inches depending upon compactness and weight of the material. The fiber glass spacing material used in a heat insulating board, according to the invention is therefore to a great extent also pervious to heat rays. The incorporation of a blocking material within the fiber glass increases the k-factor of the multi-layer insulation board and this perviousness of the spacing material is therefore one of the characteristics of my invention.

In this particular embodiment of the invention it will In Figure 3 of the drawing 1 have shown an arrangement wherein the metallic foils and 21 are alternately disposed between a plurality of the fiber glass blankets 22 with the corrugations of the

foils

20 and 21 extending at right angles to each other. By this particular structure I provide a substantially uniform stiffness for the unit in directions at right angles to each other. In these latter embodiments, the fiber glass spacing members or blankets 22 are of a softness of texture or density of mass which will yieldingly support the aluminum foils in space relation under all conditions of handling and operation unduly subjecting the corrugations of the foils to distortion due to shocks or jars. In other words, the fiber glass foil spacing means or blanket 22 has a softness or resiliency of texture of a sufficiently light mass so that it will yield and then spring back in order to absorb pressures applied normally to the insulating board. I

An insulation board of this type is completely noncombustible and has a k-factor which is lower than that of an all-fiber glass insulation. Moisture migration by diffusion of water vapor in the transverse direction is practically inhibited by the numerous layers of metal foils and internal convection and radiation of heat is for the same reason minimized.

Whereas self drainage is practically complete in the first described board consisting of interspaced plastic film material because of the absence of capillarities. the drainbe noted, as shown in Figure 2 of the drawing, that the corrugations of the several superimposed aluminum foils may be disposed parallel with each other as in the case of the first described embodiment. The folds of the corrugations should preferably be sharp and by closely spacing these corrugations irrespective of varying depths it is possible greatly to increase the compressive strength ofthe several foils without materially reducing the heat insulating characteristic thereof.

age of the latter described modifications, utilizing fiber glass blanket material as spacing material, is superior to fiber glass alone as the whole insulation space never can be completely soaked with water. The spaces defined by the corrugations in the aluminum foils are not occupied by fiber glass and therefore constitute air layers which will always maintain a high insulation ethciency and also form drainage channels that will carry away and prevent the accumulation of moisture.

The light weight heat insulation board of the character described has an extremely low k-factor when in a dry condition. The factor is comparatively little affected by a rise in the mean temperatures of the insulation and is less influenced by moisture migration than are other hitherto known light weight insulation boards. An insulating board, constructed in the manner described, is also resilient, as to the fiber glass portion'while remaining relatively stiff as to the foil portion and is easy to handle and cut and can therefore be applied in complicated structures.

While my present invention may find many and varied uses it is for the purposes of this application described as primarily designed for use in the refrigeration transporf tation field where a minimum of weight combined with the qualities pointed out above are of paramount importance.

While I have, for the sake of clearness and in order to disclose the invention so that the same can be readily understood, described and illustrated several specific forms and arrangements, it is to be understood that the invention is not limited to the specific forms described, but may be embodied in other forms that will suggest themselves topersons skilled in the art. It is believed that this invention is new and it is desired to claim it so that all such changes as come within the scope of the appended claims are to be considered as part of this invention.

Having thus described my invention, what I claim and .desire to secure by Letters Patent is:

1. In a multi-layer heat insulating board, the combina- ;-tion of a plurality of spaced impervious sheets of reflective metal foil each having corrugations extending paral- ,lel to each other, said sheets forming vapor, convection and radiation barriers, and a blanket of insulating material of substantial thickness disposed between said sheets and secured directly-to the apexesof the corrugatio ns and serving to provide insulation between foils, said corrugations being open and unobstructed whereby to provide drainage channels between the foil and the insulating material.

2. A multi-layer heat insulating board as in claim 1 wherein said blanket of insulating material is formed of a glass fiber blanket.

3. A multi-layer heat insulating board as in claim 1 wherein said glass fiber blanket is of a density of from .5 lb. to 5.0 lbs. per cubic foot so that it is pervious to long wave heat rays.

4. In a multi-layer heat insulating board, the combination of a plurality of spaced impervious sheets of reflective metal foil each having corrugations extending parallel to each other, said sheets forming vapor, convection and radiation barriers, and a plurality of blankets of insulating material of substantial thickness disposed between said foils and secured directly to the apexes thereof and serving to provide insulation between the foils, said corrugations being open and unobstructed whereby to provide drainage channels for moisture condensed thereon.

5. A multi-layer heat insulating board as in claim 4 wherein said blanket of insulating material is formed of a glass fiber blanket.

6. A multi-layer heat insulating board as in claim 4 wherein said glass fiber blanket is of a density of from .5 lb. to 5.0 lbs. per cubic foot so that it is pervious to long wave heat rays.

References Cited in the file of this patent UNITED STATES PATENTS 1,020,567 MOeller Mar. 19, 1912 2,029,679 Seving et al. Feb. 4, 1936 2,037,813 Munters Apr. 21, 1936 2,206,059 Slayter July 2, 1940 2,221,309 Gazelle Nov. 12, 1940 2,329,456 Campbell Sept. 14, 1943 2,330,941 Acuif Oct. 5, 1943 2,406,815 Elfving Sept. 3, 1946 2,514,170 Walter et al. July 4, 1950 FOREIGN PATENTS 448,543 Great Britain June 10, 1936 459,574 Great Britain June 17, 1936 482,809 Great Britain Apr. 5, 1938

Claims

1. IN A MULTI-LAYER HEAT INSULATING BOARD, THE COMBINATION OF A PLURALITY OF SPACRD IMPERVIOUS SHEETS OF REFLECTIVE METAL FOIL EACH HAVING CORRUGATIONS EXTENDING PARALLEL TO EACH OTHER, SAID SHEETS FORMING VAPOR, CONVECTION AND RADIATION BARRIERS, AND A BLANKET OF INSULATING MATERIAL OF SUBSTANTIAL THICKNESS DISPOSED BETWEEN SAID SHEETS AND SECURED DIRECTLY TO THE APEXES OF THE CORRUGATIONS AND SERVING TO PROVIDE INSULATION BETWEEN FOILS, SAID CORRUGATIONS BEING OPEN AND UNOBSTRUCTED WHEREBY TO PROVIDE DRAINAGE CHANNELS BETWEEN THE FOIL AND THE INSULATING MATERIAL.