US3238002A - Insulated shipping container for biological materials - Google Patents

Description

2 Sheets-Sheet 1 A TTORNEV arch I, 1966 R. F. QcoNNELL ETAL INSULATED SHIPPING CONTAINER FOR BIOLOGICAL MATERIALS Filed June 26, 1963 March 1, 1956 R. F. o'coNNELL l-:TAL 3,238,002

INSULATED SHIPPING CONTAINER FOR BIOLOGICAL MATERIALS Filed June 26, 1963 2 Sheets-Sheet 2 INVENTORS WILFRIED HAUMAN N ROBERT F. OCONN ATTORNEY United States Patent O 3,238,002 INSULATED SHlPPING CONTAINER FOR BILGICAL MATERHALS Robert lF. OConnell and Wilfried Haumann, Indianapolis, Ind., assigner-s to Union Carbide Corporation, a

corporation of New York Filed June 26, 1963, Ser. No. 290,834 9 Claims. (Cl. 312--214) This invention relates to insulated containers and, in particular, to insulated containers that are especially adapted for shipment of biological materials.

Various biological lmaterials undergo undesirable changes unless maintained at extremely low temperatures. By Way of illustration, frozen bovine semen lose their viability unless maintained at a temperature below 129 C. To maintain biological materials at such low temperatures, it has become common practice to store the :materials in refrigerated containers employing liquid nitrogen as a refrigerant. However, satisfactory liquid nitrogen-refrigerated containers for shipping biological materials that must be maintained at extremely low temperatures by public carriers have not been available. The unavailability of suitable containers for shipping such materials is due in large measure to the tendency of the nitrogen refrigerant to escape from containers due to heat in-leak. The tendency of nitrogen to escape is aggravated by accidental tipping of the container in transit with the resulting flow of nitrogen from the conduit at the top of the container. Means for completely sealing the container against this leakage are not practical in such containers, particularly over a period of several days, such as is required for some shipments. Periodic replacement of the nitrogen from these containers as required during shipping is not feasible inasmuch as the personnel available on public carriers are generally not versed in the techniques of handling liquid nitrogen.

Other problems associated with the development of satisfactory liquid nitrogen-refrigerated shipping containers are the economic requirements that the containers be relatively light and compact.

It is, therefore, an object of the present invention to provide relatively light and compact liquid nitrogenrefrigerated shipping containers which do not require replenishment of the liquid nitrogen refrigerant during shipping.

Other objects, features and advantages of the present invention will be apparent from the following detailed description.

ln the drawings:

The FIGURE 1 is a front elevation view, partly in cross section, of an insulated container of this invention.

FIGURE 2 is a sectional front view of a portion of the container of FIGURE 1.

This invention provides double-wall containers suitable for transporting materials requiring refrigeration by liquid nitrogen having a composite opacied insulating ymaterial (hereinafter more specifically dened) in an evacuated space between the walls and containing a porous mass of a sand-lime ller (hereinafter more particularly defined) that is suitable for retaining absorbed liquid nitrogen and that is adapted with recesses for holding the material requiring refrigeration. More specifically, this invention provides containers for transporting materials requiring refrigeration by liquid nitrogen which containers comprise: (1) a rigid self-supporting outer shell, (2) an inner vessel enclosed by and spaced from the outer shell so as to define an intervening evacuable space, (3) a composite insulating material in the evacuable space composed of (a) a radiant heat reflecting component and (b) a low heat conducting component, said composite insulating material having a thermal conductivity no greater than about 3.2 10*5 B.t.u. per hour, F., square foot per foot, (4) a specimen holder composed of an integral mass of a sand-lime ller in the inner vessel comprising mainly calcium silicate in which the ratio of silica as silicon dioxide to calcium as calcium oxide is between l and 1.5, the filler also containing between 4% and 20% by Weight based on the total weight of the llers of an inert metal fiber and the iller having a porosity of 86% to 93%, said specimen holder having voids in the central portion thereof adapted for storing the materials requiring refrigeration, (5) an access means providing access to the inner vessel (e.g. for introducing the specimen holder into the inner vessel, and for introducing the objects requiring refrigeration into the voids in the specimen holder) and (6) sealing means for minimizing both heat in-leak through the conduit into the container and escape of liquid nitrogen from the inner vessel while providing passages for the escape of nitrogen vapor from the inner vessel. An optical feature of this invention contemplates the provision of a gas absorbent in the evacuable space between the outer shell and the inner vessel. Such gas adsorbents insure the maintenance of a vacuum in the evacuable space when the space is evacuated.

An illustration of a container of this invention is shown in FIGURE l showing container 1 having self-supporting outer wall 2 and inner vessel 3 disposed so as to provide an intervening evacuable space 4 occupied by an insulating material composed of alternating layers of a metallic radiant heat barrier substance 5 and a fibrous substance of low thermal conductivity 6 having a thermal conductivity of no greater than about 3.2 5 B.t.u. per hour, F., square foot per foot. Within inner vessel 3 there is provided specimen holder 7 composed of an integral mass of sand-lime filler having voids 3 in the central portion thereof adapted for storing the material to be refrigerated (not shown). The container `1 is fitted with a low heat conductive plug 9 which serves as a sealing means for preventing heat in-leak through the otherwise open top of the container 11 and which provides a conduit for introducing the specimen holder into the inner vessel and for introducing the material requiring Arefrigeration into the voids 8 in the specimen holder 7. In the preferred embodiment illustrated in FIGURE l, perforated disc 12 is attached to the outer surface of inner vessel 3 so as to provide a space for zeolitic molecular sieve gas adsorbent 13. Gasket 14 is provided between cap 15 and outer wall 2 to seal the inner vessel. Cap 15 (composed of aluminum or other suitable materials) provides protection for the sealing means and can, if desired, accommodate spring lock fasteners (not shown) for locking the cap `15 and, in turn, the plug 9 to the outer shell 2. Cap 15 and plug 9 can be integrally bonded together or they can be separate members.

FIGURE 2 depicts additional features of the plug 9 'and gasket 14. of the container of FIGURE l. Plug 9 is provided with gas escape passages and 21 which allow for the escape of vaporized liquid nitrogen from the inner vessel. Such escaping gas would pass between the inner vessel 3 and plug 9, into lower gas escape passages 20, then along upper gas escape passages 21 and out through openings `22 in gasket 14. The lower Lgas escape passages 20 preferably describe an angle of about with upper gas escape passages 21 so as to provide for maximum use of the cooling eect of escaping nitrogen gas on plug 9. Preferably, the plug 9 contains four lower gas escape passages 20 in a horizontal plane intersecting at right angles, and four upper gas escape passages 21 efach of which forms an angle of 45 with a lower gas escaping passage. These passages prevent excessive pressures building up in the container. In FIG- URE 2 the space between plug 9 and inner vessel 3 has been exaggerated for purposes of illustration. In actual practice, plug 9 would fit snugly against inner vessel 3 so as to minimize the tendency of liquid nitrogen to ow out of the container.

The materials of construction employed in the con- Itainers of this invention are not critical and, in general, any of the materials of construction normally used in liquid nitrogen refrigerated storage containers oan be employed. The outer shell can be composed of stainless steel, or plain carbon steel, but is preferably composed of aluminum for lightness in weight. The gasket can be composed of poly (tetrafiuoroethylene). The inner vessel can be composed of stainless steel or aluminum, but is preferably composed of a suitable reinforced plastic such as Synthane (a phenol aldehyde condensation resin). The container for the gas adsorbent (e.g. disc 12 in FIG- URE 1) can be composed of a metal screen, but is preferably composed of a glass cloth. The sealing means can be composed of cork but is preferably composed of a foam plastic (eg. polyurethane foam).

A critical feature of this invention is the use of .a specimen carrier composed of a filler having several essential low ltemperature properties. The filler must be capable of absorbing liquid nitrogen rapidly so as to minimie loss of liquid nitrogen while charging the filler with liquid nitrogen. The nature of the absorption must be such that the liquid nitrogen does not tend to flow Out of the filler appreciably under the influence of gravity or mild agitation. The latter property is particularly valuable when the container is accidentally inverted or shaken during shipment with the result that, if the liquid nitrogen were released from the filler, it would tend to escape to Some extent between the inner vessel and the sealing means. Moreover, the .absorption of the liquid nitrogen by the filler must be such that the vapor pressure of the liquid nitrogen is reduced so as to minimize the pressure in the inner vessel. On the other hand, the absorption must not be so strong as to unduly retard vaporization of the liquid nitrogen as required to cool the material requiring refrigeration. The porosity of the filler must be such fas to permit the absorption on a relatively small amount of the filler of sufficient liquid nitrogen to `achieve the amount of refrigeration required. If a filler is of insufiicient porosity, the amount required would be such that the volume and weight of the container would be excessive and hence economically unfeasible. The strength of the filler must be such that undesirable voids are not created and' the filler does not tend to settle when the container is subject to handling impacts or other forces during shipment. In addition, the filler must not undergo physical or chemical changes (e.g. crystalliz-ation) during cooling to liquid nitrogen temperatures or while at liquid nitrogen temperatures for la long period of time (e.g. several days) to the extent that any of the above-mentioned properties are seriously impaired.

A filler which has been found to possess the abovedescribed properties and which is, accordingly, uniquely suited for use in the containers of this invention is a sand-lime filler comprising mainly calcium silicate, in which the ratio of silica as silicon dioxide to calcium as calcium oxide is between l and 1.5, and between 4% land 20% by weight of an inert mineral fiber based on the total weight of the ller. Such fillers having a porosity of from 86% to 93%.

The sand-lime filler is formed into a specimen holder having the desired shape, such as the shape depicted in FIGURE l, by any convenient method. Thus, the sandlime filler can be produced in a mold such that the dimensions of the specimen holder will conform Ito those of the inner vessel of the container of this invention in which it is to be employed. The mold is placed at an autoclave since the filler is preferably produced under pressure. Thus, the fillers `are produced by providing an aqueous slurry containing fine particle size lime and having incorporated therein fine particle size reactive silica and a nonreactive mineral liber, the proportions of lime to silica being las l0 parts of calcium oxide to between l0 and 15 parts of silica by weight, the total amount of water being 6.7 to 18.7 pounds per pound of lime and the amount of mineral fiber being between 4% and 20% by weight of the total -dry solids. The mixture is stirred to provide complete mixing while keeping it cool. The mixture is maintained homogeneous during the subsequent steps of filling the suitably shaped mold and initial reaction of the ingredients in the mold. The mold is completely filled with such cooled mixture ,and provision is made for the escape of only enough liquid from the mold to avoid excessive pressure development due to hydraulic expansion. The mold and contents are heated to temperatures above 225 F. in an autoclave to promote reaction of the mixture therein while maintaining the internal pressure at a value at least about equal to the equilibrium pressure of steam corresponding to the temperature of heating until the mixture in 'the mold is set. The reaction is completed by heat and pressure and the filler is dried in the mold while allowing free escape of water vapor.

The mineral fiber used in producing the filler employed in the containers of this invention should be a material that is inert under the conditions of the manufacturing process so that it does not lose its fibrous character by substantial reaction with the other ingredients. Asbestos is a preferred mineral fiber and it should be in loosely shredded form. Commercial types of asbestos are quite satisfactory, such as chrysotile, and it has been found that when the type known as amosite is used, the smaller proportions thereof are preferable. The silica and lime used in producing the filler may contain minor impurities which may result in the presence of a small amount of alumina of the order of 1/2% or less in the final product due to such impurities, but when a preferred alumina-containing suspending agent is employed, such as bentonite or aluminum sulphate, the final product will have an appreciable content of aluminum compound measurable in alumina. On a dry basis, the finished filler mass will then contain aluminum compounds measurable as aluminum oxide in the amount of from 1% to 5% by weight. Various suspending agents may be used in producing the filler and examples of suitable inorganic suspending agents are: fresh aluminum and magnesium hydroxides, aluminum sulfate, sodium carbonate with a trace of sulfate, sodium aluminate, basic magnesium carbonate, phosphoric acid or a phosphate, `boric acid or a borate, and certain clays such as bentonite. Mixtures of these materials may also be used. The amount and type of suspending agent to be used should be merely suiiicient to keep the slurry from settling or stratifying before it becomes set, and also insufiicient to detract from the desired physical properties of the final filler structure.

The voids in the specimen holders employed in the insulated containers of this invention can be produced by any convenient method. By way of illustration, the above-described molds employed in producing the specimen holders can be fitted with removable cores whose dimensions correspond to the desired size of the voids. Alternately, voids of the desired dimensions can be drilled in a solid cylinder of the filler using 'a suitable drill (e.g. a fiat bottom drill).

As it is apparent, a variety of specimen holders each adapted with voids suitable for retaining an ampoule for biological material of particular dimensions can be employed with Va given container of this invention. The size of the plug employed can be adapted to suit the height of the specimen holder. In this connection, it should be noted that it is desirable that the plug be of sufiicient length so that its lower surface is close to the upper surface of the specimen holder, and/or the ampoules containing the specimen so as to prevent excessive movement of the holder and/or ampoule when the container is subjected to impacts.

The specimen holder can be saturated with Iabsorbed liquid nitrogen by any suitable method. Such suitable methods include a forced saturation method, a free float saturation method, and an installed position saturation method hereinafter described. The forced saturation method involves submerging the specimen holder in liquid nitrogen and maintaining it below the surface or liquid nitrogen for a time suicient to permit the holder to become saturated with liquid nitrogen. The liquid nitrogensaturated specimen holder can then be inserted in the inner vessel. The free flow saturation method involves placing the specimen holder in liquid nitrogen and allowing it to float freely on the liquid. The holder gradually absorbs liquid nitrogen and sinks below the liquid surface. After the holder has been Ibelow the surface of .the liquid for a sufhcient time to become saturated with liquid nitrogen, it is withdrawn and placed in the inner vessel. The installed position saturation method involves placing the specimen holder in the inner vessel and then pouring a liquid nitrogen into the holder. The liquid nitrogen level is maintained above the top of the specimen holder for a time sufiiciently long to permit the holder to become saturated with liquid nitrogen and then any non-absorbed liquid nitrogen is poured from the holder.

The use of the above-described sand-lime llers Ias contemplated in the containers of this invention constitutes a radically novel area of application for these fillers inasmuch as such llers have previously 'been employed in such non-analogous areas as ambient temperature absorbents for acetylene (as such or liqueed by absorption in acetone) in conventional gas storage cylinders.

By absorption of liquid nitrogen by the ller herein is meant retention of the liquid nitrogen by the filler by adsorption and capillarity as well as by absorption alone.

Another critical feature of this invention is the use of the composite opacified insulation hereinafter described. The composite insulation employed in the insulated containers of this invention comprises a radiant heat reflecting (ie. radiation-impervious) component and a low heat conducting component located in the space between the outer shell and the inner vessel. This space is maintained at a pressure less than 1 micron (preferably at a pressure less than 0.1 micron) when the container is in use. These low operating pressures are 'attained by conventional means and are preferably maintained by the above-described gas absorbents. The components in the insulation used in this invention cooperate to minimize the total heat leak into the inner vessel by radiation and conduction. The thermal conductivity of this insulation must be no greater :th-an about 3.2 B.t.u. per hour, F. square foot per foot. The use of such insulation has been found e-ssential in the insulated containers of this invention since, with other types of insulation (such as urethane foam insulation), an excessive loss of nitrogen from the container resulting from excessive heat in-leak across the evacuable space occurs.

The components of the insulation employed in the container of this invention can be in the form of particles (i.e., powder) or in the form of sheets and the components can be composed of any of a wide variety of materials. By way of illustration, suitable radiant heat reflecting components include particulate metals, metal oxides or metal-coated materials (e.g., particulate copper paint pigments, aluminum paint pigments, magnesium oxide, zinc oxide, iron oxide, titanium dioxide, carbon black above microns in size, copper-coated mica flakes and graphite) having particle sizes less than about 500 microns (preferably less than 50 microns). Suitable low heat conducting components include particulate silica, silicates (e.g., perlite), alumina, magnesia having particle sizes less than 420 microns (preferably less than 75 microns) and carbon black having particle sizes less than 0.1 micron. As further illustrated, suitable radiant heat reflecting components in sheet form include thin metal foil, such as aluminum, tin, silver, gold, copper and cadmium foil preferably having a thickness between 0.2 millimeter and 0.002 millimeter. Suitable low heat conducting components in sheet form include plastic sheets (e.g., polyethylene terephthalate and polytetrauoroethylene sheets) and fibrous sheets (e.g., glass fiber paper or web sheets) are preferably composed of fibers having ber glass diameters of less than 50 microns or more preferably of less than 10 or l microns. Insulation components in the form of sheets are disposed so that the sheets are substantially parallel to each other and substantially perpendicular to the direction of heat iiow across the evacuable space between the outer shell and the inner vessel.

The radiant heating reflecting component and the low heat conducting component used in the insulation employed in the insulated containers of this invention are so disposed in relation to each other that the latter component prevents transmission of heat across the evacuable space by conduction through the former component. By way of illustration, when both insulating components are in the form of sheets, they are arranged as alternating sequence. In the latter embodiment, the low heat conducting component sheets can serve as a spacing and supporting means for the radiant heat reflecting component sheets. As a further illustration, when both insulating components are in the form of particles (as in the insulation disclosed in ULS. Patent 2,967,152), the radiant heat reiiecting component particles are dispersed in a matrix of the low heat conducting component particles. In the latter embodiment, the radiant heat reiiecting component particles can constitute from 1% -to 80% by weight of the total weight of both component particles.

It should be recognized that combinations of sheet and particulate insulation components can be employed in the insulated containers of this invention. By way of illustration, a particulate low heat conducting component can be employed to fill the voids between the fibers of a fibrous low heat conducting component as disclosed in U.S. Patent 3,007,596. The latter embodiment serves to minimize the variations in the thermal conductivity of the insulation due to changes in pressure in the evacuable space. Moreover, the radiant heat reliecting component in the insulation employed in the insulated containers of this invention can, if desired, be bonded -to the low heat conducting component. By way of illustration, suitable insulation includes the metallized crinkled plastic or glassine sheets (e.g., crimped or crumpled polyethylene terephthalate or polytetrailuoroethylene sheets covered, preferably on only one side, with a thin film of aluminum, gold, silver or copper) disclosed in U.S. Patent 3,018,016. Preferably at least thirty layers of such sheets can be employed although fewer layers can be employed in some cases.

The above-mentioned insulation of U.S. Patent 3,018,016 can be more specifically described as metalcoated-non-metallic, iiexible plastic material, said plastic material being essentially free of any substance havingl an equilibrium vapor pressure at 20 C. of greater than 10 microns mercury absolute. There are between 12 and layers of flexible material per centimeter of thickness of insulation space occupied by the layers and the metal coating on the iiexible material has a thickness less than .25 micron and being sufficiently thick to have an emissivity less than .06. The flexible material has a low heat conductivity to give a low lateral heat conductivity to the metal-coated flexible material of less than 10 l06 watts per square degree K. at 300 K. the layers of flexible material are permanently deformed as by crumpling so that they are free of extensive areas of planar Contact while having numerous point contacts therebetween, the layers are essentially free of spacer elements therebetween and the major portions of the layers are held in spaced relation by the point contacts between layers. The apparent thermal conductivity of this insulation is less than about l microwatt/cm. degree K.

A typical insulation suitable for use in the insulated containers of this invention is composed of sheets of fibrous material, which are disposed alternately between sheets of metal foil material to provide alternate layer composite insulation. Such alternate layer composite insulation is broadly disclosed in U.S. Patent 3,007,576. One variety of such alternate layer composite insulation is disclosed in U.S. Patent 3,009,600 which relates to insulation comprising alternate layers (a) of fibrous material in the form of paper and (b) metal foil material. Another variety of such alternate layer composite insulation is disclosed in U.S. Patent 3,009,601 which relates to insulation comprising alternate layers of (a) fibrous material in the form of a web and (b) metal foil material. Such metal foil sheets function as the radiant heat reflecting component and fibrous sheets function at the low heat conducting component.

In general suitable fibrous-metal foil alternate layer composite insulation of U.S. Patent 3,007,576 can be more specifically described as external load-free insulation comprising low conductive fibrous sheet material layers composed of fibers `for reducing heat transfer by gaseous conduction and thin, flexible sheet radiation barrier layers. The radiation barrier layers being supportably carried in superimposed relation by .the fibrous sheet layers to provide a large number of radiation barrier layers in a limited space for reducing the transmission of radiant heat across said space without perceptively increasing the heat transmission by solid conduction thereacross. Each radiation barrier layer is disposed in contiguous relation on opposite sides with a layer of the fibrous sheet material, While the fibers of the fibrous sheet material all oriented substantially Iparallel to the radiation barrier layers and substantially perpendicular to the direction of heat in-leak across the space occupied by the layer. The fibrous sheet material is composed of fibers having diameters less than about 10 microns and the radiation barrier sheet having a thickness less than about 0.2 millimeter, the multilayered composite insulation being disposed in the space occupied by the layers `to provide more than 4 radiation barrier layers per inch of said composite insulation.

The above-mentioned insulation of U.S. Patent 3,009,600 can be more specifically described as a composite multi-layered, external load-free insulation in the space occupied by the layers comprising low conductive fibrous sheet material layers composed of fibers for reducing heat transfer by gaseous conduction and thin, flexible radiant heat reflecting shields. The radiant heat refleeting shields are supportably carried in superimposed relation by the fibrous sheet layers to provide a large number of radiant heat reflecting shields in a limited space for reducing the vtransmission of radiant heat across the space without perceptively increasing the heat transmission by solid conduction thereacross :and each radiant heat reflecting shield is disposed in contiguous relation on opposite sides with a layer of the fibrous sheet material. The fibers of the fibrous sheet material are oriented substantially parallel to the heat reflecting shields and substantially perpendicular to the direction of heat in-leak across the space. The fibrous sheet material is a permanently precompacted paper composed of unbonded fibers having a thickness less than about 0.2 millimeter. The multi-layered composite insulation is generally spirally wound in the space to provide more than 40 radiant heat reflecting shields per inch of said composite insulation.

The insulation of U.S. Patent 3,009,601 can be more specifically described as a composite multi-layered, external load-free insulation in the space occupied by the layers comprising low conductive fibrous sheet material layers composed of fibers for reducing heat transfer by gaseous conduction and thin, flexible radiant heat reflecting shields. The radiant heat reflecting shields are supportably carried in superimposed relation by the fibrous sheet layers to provide a large number of radiant heat reflecting shields in a limited space for reducing the transmission of radiant heat across the space without perceptively increasing the heat transmission by solid conduction thereacross and radiant heat reflecting shield is disposed in contiguous relation on opposite sides with a layer of the fibrous sheet material. The fibers of the fibrous sheet material are `oriented substantially perpendicular to the direction of heat in leak across the insulating space and the fibrous sheet material is an elastically compressible web composed of fibers having diameters between about 0.2 and 5 microns. The radiant heat reflecting shields have a thickness less than about 0.2 millimeter and can, if desired, be perforated lto provide flow paths through the shields. The multilayered composite insulation is generally spirally wound in the insulation space to provide more than 5 radiant lheat reflecting shields per inch of said composite insulation.

The containers of this invention preferably contain a gas absorbent that is in vapor communication with the evacuable space between the outer shell and the inner vessel. The absorbent can .be held in a perforated disc or blister or in a wire screen or glass cloth attached to the outer surface of the inner vessel. Such absorbents assist in maintaining a vacuum in .the evacuable space. Particularly suitable gas absorbents which can be placed between the outer shell and the inner vessel in the insulation containers of this invention are crystalline zeolitic molecular sieves such as zeolite A and zeolite X, which are more particularly described below.

Zeolite molecular' sieves have a three-dimensional framework of S104 and A104 tetrahedra. The tetrahedra are cross-linked by the sharing of oxygen atoms. The ectrovalence of the tetrahedra containing aluminum is -balanced by the inclusion in the crystal of a cation, for example sodium or calcium. The spaces between the tetrahedra are occupied by water molecules prior to dehydration or activation as by heating.

The general formula for zeolite A, disclosed in U.S. Patent No. 2,882,243, can be represented as follows:

In rthe latter formula M is a cation and n its valence.

The composition of calcium zeolite A, a preferred material `for use in the containers of the invention, expressed in terms of mol fractions of the oxide of the materials in the zeolite is as follows:

1.010.2CaO2Al2O3:1.851\0.5Si02:0 to 5H2O In addition to its composition, zeolite A can be identified by its X-ray powder diffraction pattern. In obtaining the X-ray powder diffraction pattern standard techniques were employed. The radiation was the Ka doublet of copper, and a Geiger counter spectrometer with a strip chart pen recorder was used. The most significant lines of the X-ray diffraction pattern zeolite A are given in Table A.

TABLE A d Value of reflection in A 12.2102 8.610,2 70510.15 40710.08 3.681007 33810.06 32610.05 2.961005 2.731005 2.601005 Zeolite X, disclosed in U.S. Patent 2,882,244, can be represented as follows:

0.910.2M2/nO1Al2O3:2.510.5Si021 0 to 8H2O In the latter `formula M represents a metal and n its valence. A typical composition for the sodium form of zeolite X is represented as follows:

0.9Na201A1203 i The more significant lines of the X-ray diffraction pattern of zeolite X are given in Table B.

TABLE B d Value of reflection in A Prior to use in the containers of this invention, the above-described zeolitic molecular sieve absorbents should be activated by heating to remove absorbed materials (eg. water vapor).

The containers of this invention are uniquely suited for shipping biological materials which must be maintained at temperatures below -l29 C. Such materials include bull semen, bone marrow, blood, pathogens and the like. Such materials are often admixed with various additives, extenders, solvents and the like. The biological materials are desirably in a frozen state before being .placed in the containers of this invention. These materials are generally placed in ampoules or vials of dimensions suitable for insertion in the voids in the specimen holders in the containers of this invention.

A specific container of this invention which has given excellent performance in the shipping of biological materials has the following specifications:

Height (from bottom of outer shell to top of cap) 16 inches. Outer diameter of outer shell 6.25 inches. Inside diameter of inner vessel 4.25 inches. Weight emptied (containing a holder but without liquid nitrogen and biological materials) pounds. Weight filled (with specimen holder saturated with liquid nitrogen) 8 pounds. Liquid nitrogen absorbed 1.6 liters.

Liquid nitrogen evaporation rate Holding time when holding two 50 cubic centimeter ampoules 5 days at a maximum temperature of 130 C.

The specimen holder employed in this container had an outer diameter of about 4.5 and a height of 73/8. It contained two voids having a depth of 6%. The diameter of the voids was l/s for the first inch below the top of the holder and /16 thereafter. The composite insulation material in the container was that disclosed in U.S. Patent 3,009,600.

What is claimed is:

l. An insulated container suitable for transporting materials requiring refrigeration by liquid nitrogen which container compri-ses (l) a rigid self-supporting outer shell, (2) an inner vessel enclosed by and spaced from the outer shell so as to define an intervening evacuable space, (3) a composite insulation material in the evacuable space composed of (a) a radiant heat reflecting component and (b) a low heat conducting component disposed in rlation to the radiant heat reflecting component so as to minimize the transfer of heat across the evacuable space through the radiant heat reflecting component by conduction, said composite insulating material serving to minimize heat transfer across the evacuable space by radi- 033 liters per day.

ation and conduction and said composite insulation material having a thermal conductivity no greater than about 3.2 l05 B.t.u. per hour, F. square foot per foot, (4) a specimen holder composed of an integral mass of a sand-lime filler in the inner vessel comprising mainly calcium silicate in which the ratio of silica as silicon dioxide to calcium as calcium oxide is between l and 1.5, the filler also containing between 4 percent and 20 percent by weight, based on the total weight of the filler, of an inert metal fiber and the filler having a porosity of 86 percent to 93 percent, said specimen holder having voids in the central portion thereof adapted for storing the materials requiring refrigeration, (5) access means for introducing the specimen holder into the inner vessel and for introducing the objects requiring refrigeration into the voids in the specimen holder and (6) sealing means for minimizing heat leak through the access means into the container and escape of liquid nitrogen from the inner vessel while providing passages for the escape of nitrogen vapor from the inner vessel.

2. The insulated container of claim 1 wherein the inrsulation material is a composite multi-layered, external load-free insulation comprising low conductive fibrous sheet material layers composed of fibers for reducing heat transfer by gaseous conduction and thin, fiexible sheet radiation barrier layers, said radiation barrier layers being supportably carried in superimposed relation by said fibrous -sheet layers to provide a large number of radiation barrier layers in a limited space for reducing the transmission of radiant heat across said space without perceptively increasing the heat transmission by solid conduction thereacross, each radiation barrier layer being disposed in contiguous relation on opposite sides with a layer of the fibrous sheet material, the fibers of said fibrous sheet material being oriented substantially parallel to the radiation barrier layers and substantially perpendicular to the direction of heat inleak across the space occupied by the layers, said fibrous sheet material being composed of fibers having diameters less than about l0 microns, said radiation barrier sheet having a thickness less than about 0.2 millimeter, and said multi-layered composite insulation being disposed in the space occupied by the layers to provide more than 4 radiation barrier layers per inch of said composite insulation.

3. The insulated container of claim ll wherein the insulating material is a composite multi-layered external load-free insulation in the space occupied by the layers comprising low conductive brous sheet material layers composed of fibers for reducing heat transfer by gaseous conduction and thin, flexible radiant heat reflecting shields, said radiant heat reflecting shields being supportably carried in superimposed relation by said fibrous sheet layers to provide a large number of radiant heat reliecting shields in a limited space for reducing the transmission of radiant heat across said space without perceptively increasing the heat transmission by solid conduction thereacross, each radiant heat reflecting shield being disposed in contiguous relation on opposite sides with a layer of the fibrous sheet material, the fibers of said fibrous sheet material being oriented substantially parallel to the heat reflecting shields and substantially perpendicular to the direction of heat inleak across the space, said fibrous sheet material being a permanently precompacted paper composed of unbonded fibers having a diameter less than 5 microns and a length of less than about 0.5 inch, said radiant heat reflecting shields having a thickness less than about 0.2 millimeter, and said multi-layered composite insulation being generally spirally wound in the space to provide more than 40 radiant heat reflecting shields per inch of said composite insulation.

4. The insulated container of claim 1 wherein the insulating material is a composite multi-layered, external load-free insulation in the evacuable space occupied by the layers comprising low conductive fibrous sheet material layers composed of fibers for reducing heat transfer by gaseous conduction and thin, flexible radiant heat reflecting shields, said radiant heat reflecting shields being supportably carried in superimposed relation by said fibrous sheet layers to provide a large number of radiant heat reflecting shields in a limited space for reducing the transmission of radiant heat across said space without perceptively increasing the heat transmission by solid conduction thereacross each radiant heat reflecting shield being disposed in contiguous relation on opposite sides with a layer of the fibrous sheet material, the fibers of said fibrous sheet material being oriented substantially perpendicular to the direction of heat inleak across the insulating space, said fibrous sheet material being an elastically compressible web composed of fibers having diameters between about 0.2 and microns, said radiant heat reflecting shields having a thickness less than about 0.2 millimeter and said multi-layered composite insulation being generally spirally wound in the insulation space to provide more than 5 radiant heat reflecting shields per inch of said composite insulation.

5. The insulated container of claim 1 wherein the insulating material is at least thirty of a metal-coated, nonmetallic, flexible plastic material, said plastic material being essentially free of any substance having an equilibrium vapor pressure at 20 C. of greater than l0 microns mercury absolute, there being between 12 and 120 layers of flexible material per centimeter of thickness of insulation space occupied by the layers, the metal coating on the flexible material having a thickness less than ,25 micron and being sufficiently thick to have an emissivity less than .06, the flexible material having a low heat conductivity to give a low lateral heat conductivity to the metal-coated flexible material of less than 106 watts per square per K at 300 K., the layers of flexible material being permanently deformed, as by crumpling, so that they are free of extensive areas of planar contact while having numerous point contacts therebetween, said layers being essentially free of spacer elements therebetween, the major portions of said layers being held in spaced relation by said point contacts between layers, the apparent thermal conductivity of the insulation being less than about 1 microwatt/cm. K.

6. The insulated container of claim 1 wherein the insulating material is characterized by a low rate of heat transfer by conduction and radiation, consisting essentially of finely divided low heat conductive particles of agglomerate sizes less than about 420 microns being selected from the group consisting of silica, perlite, alumina, magnesia and carbon black; and finely divided radiant heat reflecting bodies of sizes less than about 500 microns and having metallic surfaces, such radiant heat reflecting bodies constituting between about 1% and 80% by weight of said insulating material.

7. The insulated container of claim 1 wherein the insulating material is composed of a low heat conductive fibrous material and a multiplicity of radiation-impervious sheets supportably carried by said fibrous material, said radiation-impervious sheets being disposed in parallel spaced relation to each other, and said fibrous material having a fiber orientation substantially parallel to said sheets and substantially perpendicular to the direction of heat flow across said space, and a fine low-conductive powder in the voids between the fibers of said fibrous material, whereby said sheets and fibrous material are effective in reducing the transmission of radiant heat across said space without perceptibly increasing the heat transmission by conduction thereacross, and whereby said powder reduces the variation in thermal conductivity of said fibrous material and sheets due to changes in pressure conditions in said space.

8. The insulated container of claim 1 wherein a crystalline zeolitic molecular sieve gas absorbent is provided in the evacuable space.

9. An insulated container for transporting materials requiring refrigeration by liquid nitrogen which container comprises (l) a rigid self-supporting outer shell, (2) an inner vessel enclosed by and spaced from the outer shell so as to define an intervening evacuated space in which the pressure is less than 1 micron, (3) a composite insulating material in the evacuated space composed of (a) a radiant heat reflecting component and (b) a low heat conducting component disposed in relation to the radiant heat reflecting component so as to minimize the transfer of heat across the evacuable space through the radiant heat reflecting component by conduction, said composite insulating material serving to minimize heat transfer across the evacuated space by radiation and conduction and said composite insulating material having a thermal conductivity no greater than about 32x10-5 B.t.u. per hour, F., square foot per foot, (4) a specimen holder composed of an integral mass of a sand-lime filler in the inner vessel comprising mainly calcium silicate in which the ratio of silica as silicon dioxide to calcium as calcium oxide is between 1 and 1.5, the filler also containing between 4 percent and 20 percent by weight, based on the total weight of the filler, of an inert metal fiber and the filler having a porosity of 86 percent to 93 percent, said specimen holder having voids in the central portion thereof wherein are stored the materials requiring refrigeration and said specimen holder having liquid nitrogen absorbed thereon so as to saturate the filler therewith, (5) access means for introducing the specimen holder into the inner vessel and for introducing the objects requiring refrigeration into the voids in the specimen holder and (6) sealing means for minimizing heat in-leak through the access means into the container and escape of liquid nitrogen from the inner vessel while providing passages for the escape of nitrogen vapor from the inner vessel.

References Cited by the Examiner UNITED STATES PATENTS 3,007,596 l1/l96l Matsch 220-9 3,108,840 10/1963 Conrad 312-214 3,168,362 2/ 1965 Perkins 312-214 THERON E. CONDON, Primary Examiner.

G. E. LOWRANCE, Assistant Examiner.

Claims (1)

1. AN INSULATED CONTAINER FOR TRANSPORTING MATERIALS REQUIRING REFRIGERATION BY LIQUID NITROGEN WHICH CONTAINER COMPRISES (1) A RIGID SELF-SUPPORTING OUTER SHELL, (2) AN INNER VESSEL ENCLOSED BY AND SPACED FROM THE OUTER SHEEL SO AS TO DEFINE AN INTERVENING EVACUABLE SPACE, (3) A COMPSOSITE INSULATION MATERIAL IN THE EVACUABLE SPACE, COMPOSED OF (A) A RADIANT HEAT REFLECTING COMPONENT AND (B) A LOW HEAT CONDUCTING COMPONENT DISPSOED IN RELATION TO THE RADIANT HEAT REFLECTING COMPONENT SO AS TO MINIMIZE THE TRANSFER OF HEAT ACROSS THE EVACUABLE SPACE THROUGH THE RADIANT HEAT REFLECTING COMPONENT BY CONDUCTION, SAID COMPOSITE INSULATING MATERIAL SERVING TO MINIMIZE HEAT TRANSFER ACROSS THE EVACUABLE SPACE BY RADIATION AND CONDUCTION AND SAID COMPOSITE INSULATION MATERIAL HAVING A THERMAL CONDUCTIVITY NO GREATER THAN ABOUT 3.2X10-5 B.T.U. PER HOUR, *F. SQUARE FOOT PER FOOT, (4) A SPECIMEN HOLDER COMPOSED OF AN INTEGRAL MASS OF A SAND-LIME FILLER IN THE INNER VESSEL COMPRISING MAINLY CALCIUM SILICATE IN WHICH THE RATIO OF SILICA AS SILICON DIOXIDE TO CALCUIM AS CALCIUM OXIDE IS BETWEEN 1 AND 1.5, THE FILLER ALSO CONTANING BETWEEN 4 PERCENT AND 20 PERCENT BY WEIGHT, BASED ON THE TOTAL WEIGHT OF THE FILLER, OF AN INERT METAL FIBER AND THE FILLER HAVING A POROSITY OF 86 PERCENT TO 93 PERCENT, SAID SPECIMEN HOLDER HAVING VOIDS IN THE CENTRAL PORTION THEREOF ADAPTED FOR STORING THE MATEIRALS REQUIRING REFRIGERATION (5) ACCESS MEANS FOR INTRODUCING THE SPECIMEN HOLDER INTO THE INNER VESSEL AND FOR INTRODUCING THE OBJECTS REQUIRING REFRRIGERATION INTO THE VOIDS IN THE SPECIMENT HOLDER AND (6) SEALING MEANS FOR MINIMIZING HEAT LEAK THROUGH THE ACCESS MEANS INTO THE CONTAINER AND ESCPAE OF LIQUID NITROGEN FROM THE INNER VESSEL WHILE PROVIDING PASSAGES FOR THE ESCAPE OF NITROGEN VAPOR FROM THE INNER VESSEL.

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