US3344221A - Method for inflating or deflating closed cell foams - Google Patents

Method for inflating or deflating closed cell foams Download PDF

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US3344221A
US3344221A US302495A US30249563A US3344221A US 3344221 A US3344221 A US 3344221A US 302495 A US302495 A US 302495A US 30249563 A US30249563 A US 30249563A US 3344221 A US3344221 A US 3344221A
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agent
cells
density
foam
walls
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US302495A
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Moody Frank Baldwin
Parrish Robert Guy
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EIDP Inc
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EI Du Pont de Nemours and Co
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Priority to US302495A priority Critical patent/US3344221A/en
Priority to LU46773D priority patent/LU46773A1/xx
Priority to GB33576/64A priority patent/GB1062086A/en
Priority to DE1504716A priority patent/DE1504716C3/de
Priority to FR22969A priority patent/FR1484626A/fr
Priority to CH207866A priority patent/CH489563A/de
Priority to NL6601868A priority patent/NL6601868A/xx
Priority to BE682064D priority patent/BE682064A/xx
Priority to US615883A priority patent/US3375211A/en
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Publication of US3344221A publication Critical patent/US3344221A/en
Priority to US735926*A priority patent/US3584090A/en
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C67/00—Shaping techniques not covered by groups B29C39/00 - B29C65/00, B29C70/00 or B29C73/00
    • B29C67/20—Shaping techniques not covered by groups B29C39/00 - B29C65/00, B29C70/00 or B29C73/00 for porous or cellular articles, e.g. of foam plastics, coarse-pored
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C44/00—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles
    • B29C44/34—Auxiliary operations
    • B29C44/36—Feeding the material to be shaped
    • B29C44/46—Feeding the material to be shaped into an open space or onto moving surfaces, i.e. to make articles of indefinite length
    • B29C44/50—Feeding the material to be shaped into an open space or onto moving surfaces, i.e. to make articles of indefinite length using pressure difference, e.g. by extrusion or by spraying
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
    • C08J9/04—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof using blowing gases generated by a previously added blowing agent
    • C08J9/12—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof using blowing gases generated by a previously added blowing agent by a physical blowing agent
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S521/00—Synthetic resins or natural rubbers -- part of the class 520 series
    • Y10S521/91—Plural blowing agents for producing nonpolyurethane cellular products

Definitions

  • An object of the present invention is to provide a method for readily effecting a change in the gas content, i.e. regulated inflation or deflation, of yieldable cellular structures.
  • a further object of the invention is a method by which the volume and density of such cellular structures can be reversibly lowered and raised.
  • Another object of the invention is a method for deflating foams without the need for employing mechanical compression, subatmospheric pressure, or condensable gases.
  • Still another object of the invention is a method for consecutively denited States Patent 0 flating and inflating cellular foam materials.
  • Another object of the invention is :a method for restoring the pneumaticity of foams which have been deflated by compression. Further objects of the invention include foamed products of unique composition and/or structure. Other objects will be apparent from the remainder of the specification and claims.
  • the cellular structures employed have a major proportion of closed cells defined by gas permeable walls.
  • These cells constitute a structure which in expanded condition is reversibly yieldable such that substantial deformation occurs under internal-external pressure differentials.
  • the cellular structure is immersed, at a pressure no less than about atmospheric, in a fluid permeating agent which is capable of permeating the cell walls, i.e. by osmotic diffusion of permeating agent molecules therethrough. Accordingly, difiusion is effe ted of the permeating agent through the wall and into the cells to establish an internal partial pressure of the agent.
  • the original gas contained in the cells will likewise diffuse outwardly, as when the internal partial pressure of that gas (inside the cel s) exceeds its external partial pressure (outside the cells or the environment).
  • the introduction of enough permeating agent to establish an internal partial pressure thereof which is about 5% of the total pressure (usually about atmospheric depending upon the degree of resilience of the structure) is normally the minimum amount necessary to effect sufficient changes in the density of the structure.
  • the thusly treated structure having an appreciable content of the agent is subjected to a gaseous atmosphere which is also capable of permeating the cell walls but which has a different permeability rate through the cell walls than does the permeating ag nt.
  • the gaseous atmosphere is so selected as to be more permeant to the walls than is the permeating agent and the external partial pressure of the gaseous atmosphere is greater than the internal partial pressure of that atmosphere, then a portion of the atmosphere will diffuse into the cells, at least partially expand and inflate the cells, and give rise to an overall decrease in density.
  • the gaseous atmosphere is less permeant to the walls than is the permeating agent and the external partial pressure of the agent is lower than its internal partial pressure, then at least a portion of the permeating agent will diffuse out of the cells, atleast partially contract and collapse the cells and give rise to an overall increase in density.
  • FIGURE 1 illustrates equilibrium expansion of polypropylene foam filaments inflated in fluorotrichloromethane/rnethylene chloride baths in accordance with this invention
  • FIGURE 2 is a flow diagram of the process of this invention.
  • the invention involves controlled utilization of osmotic pressure differentials to inflate or deflate :a cellular structure of the described character.
  • the net change in density can be slight or incremental as for purposes of product control or can be great, i.e. an order of magnitude or more.
  • the invention affords a great number of significant advantages and virtues. Several of these will be mentioned hereinafter al- U. though the list is not exhaustive and many others will be apparent to those skilled in the art.
  • deflated foams to fashion a material, e.g. a textile, followed by inflation permits the production of products which could not be obtained by fabricating a fully inflated foam.
  • the process of the invention also makes possible the restoration of the pneumaticity of foams which have been damaged by collapse, e.g. under sustained loading such that the gaseous component has largely been removed.
  • the process of the invention can be performed simply, even continuously, without the necessity of pressurized or vacuum systems, compression devices, and the like.
  • the process of the invention is based upon the finding that the bulk density, or simply density, of a closed-cell yieldable foam may be adjusted at will by varying the volume of the individual cells, and that this may be accomplished by filling the cells with suitable fluid permeating agents or inflatants (e.g. gases or volatile liquids) fulfilling certain permeability conditions.
  • suitable fluid permeating agents or inflatants e.g. gases or volatile liquids
  • the cells are filled with a substance which permeates the walls faster than does air (or whatever gaseous atmosphere in which the sample is to be used).
  • the inflatant will diffuse out of the cells faster than air diffuses in to take its place, so that a partially collapsed structure of higher density is produced.
  • the degree of collapse and density increase can be varied at will, the more permeative and larger the quantity of inflatant, the greater the degree of collapse.
  • a gas less permeative than air is introduced into the cells, an osmotic driving force will cause air to enter the cells faster than the inflatant gas diffuses out, and a net increase in volume or decrease in density will be observed.
  • air as the gaseous atmosphere is particularly preferred because of its availability and its normally suitable permeabilitycoeflicient, there are numerous instances where it is desirable to provide another gas in the final product, e.g. for insulation purposes, one having a lower thermal conductivity.
  • Inflation of collapsed foams according to the invention is accomplished by introducing into the cell a quantity of a gas or volatile liquid, i.e. a fluid permeating agent, having a rate of permeation through the cell walls lower than that of the gaseous atmosphere (usually air) in which the foam is subsequently exposed.
  • a gas or volatile liquid i.e. a fluid permeating agent
  • the exterior atmosphere will diffuse into and inflate the cells until its internal and external fugacities, or apparent partial pressures, are equal.
  • the foam containing the permeating agent is subjected to a gaseous atmosphere having a pressure of about 14.7 pounds per square inch, the internal total pressure, if allowed to come to equilibrium, i.e.
  • substantially equal internal and external fugacities will also be about one atmosphere or more depending upon the quantity of inflatant gas retained in the cells.
  • intermediate degrees of inflation can also be achieved as by selecting the original inflatant of proper permeation and quantity so that its concentration will have decreased to zero by outward diffusion when the desired degree of inflation has been reached.'It is also possible to achieve intermediate degrees of inflation or deflation by charging the cells with a judicious mixture of fast and slow permeating gases or liquids.
  • the inflation technique can be performed upon almost totally deflated or collapsed cellular structures, i.e. those having a density of about 75% of the polymer itself, or upon products of relatively lower density, i.e. to as little as 1% of the polymer, where simply a greater degree of bulk is required.
  • a structure having at least a minor residual quantity of gas is necessary to create an osmotic driving force for permeating agent to enter the cells.
  • Inflation of collapsed foams as described in this invention is to be distinguished from primary blowing processes which are employed to form and blow the cells of the foam.
  • This invention is not concerned with forming new cells nor with appreciable stretching of the walls beyond their original dimensions.
  • the maximum volume of the inflated foams is substantially that of the foam in its initial state, plus perhaps a minor increase from the slight distention as occasioned when the final internal pressure in the cells is superatmospheric, as when a quantity of impermeant inflatant remains in the cell in addition to the gaseous atmosphere which diffuses into the cells.
  • an especially desirable system in accordance with the invention is obtained when the inflatant gas has substantially zero permeation through the cell walls.
  • air can be allowed to diffuse into the cells until the fugacity of air is equal inside and outside the cells, i.e., until the partial air pressure inside the cells is essentially one atmosphere.
  • the total internal gas pressure may, therefore, be greater than one atmosphere, and the foam will be fully inflated.
  • the invention is particularly advantageous in the preparation of deflated cellular products such as filaments.
  • deflated cellular products such as filaments.
  • such products have special utility as postexpandable stuffing materials (as in life jackets, sleeping bags, etc.) and textile yarns.
  • postexpandable stuffing materials as in life jackets, sleeping bags, etc.
  • textile yarns Although the strength of an inflated cellular filament, for example, is adequate for power weaving operations, its high surface friction makes the operation diflicult, and its extremely high bulk means that only a relatively few yards of yarn can be held on conventional bobbins, beams or shuttles.
  • a collapsed cellular yarn is used, not only are these problems effectively overcome but also a very open scrim-like fabric, i.e.
  • loosely woven can be economically prepared which, on subsequent inflation of the filaments, expands to a tight, highly opaque, pneumatic, bulky fabric.
  • the resultant fibers without fusion or permanent adherence to one another can therefore constitute a more tightly woven fabric than could be produced by the weaving of an expanded filament.
  • a technique suitable for deflating preformed foams is to immerse the sample in a highly permeant gas or volatile liquid, i.e., permeating agent, which will replace the previous or original gas content since the latter diffuses out of the cells as a result of the osmotic pressure difference caused when its'external partial pressure is less than its internal partial pressure. Since the highly permeant material can enter the cells faster than the original diffuses out, the structure may temporarily be super-inflated or turgid.
  • the structure can be partially deflated by exposure to a less permeant atmos phere.
  • the degree of deflation is governed by how fast the concentration of the highly permeant substance drops which depends on its permeation rate and original concentration. If allowed to proceed to a concentration of about zero, the internal partial pressure of the inflatant will also be about zero. In any event an increase of the density of the structure by 50% or more will normally be desired.
  • a preferred plasticizing agent has a high diffusion coefiicient and high volatility so that when the desired quantity of exchange material has penetrated the cells, the plasticizer may be rapidly removed (as by a heat treatment) and the exchange material locked in the cells.
  • This technique is particularly useful for introducing impermeant gases into cellular structures.
  • the action of the plasticizing agent may be assisted by operating at elevated temperatures.
  • the step of immersing the initial foam structure in the fluid permeating agent should be effected at pressures no less than about one atmosphere with a large excess of the agent in order to achieve diffusion into the cells in practical periods of time. Then too this eliminates the need for special equipment.
  • the subsequent exposure to a gaseous atmosphere is also desirably conductedat no less than about one atmosphere of pressure.
  • the time required for completion of the process of this invention is frequently of the order of a few minutes, as will be apparent from the specific examples hereinafter.
  • the speed of sample inflation is governed principally by the speed of inward air diffusion, and sample deflation must, of course, occur faster than this rate.
  • the time required for complete gas equilibrium will, therefore, depend on many factors: sample size, cell wall thickness, permeability coefiicient of original gas, permeating agent, or gaseous atmosphere in the polymer in question, temperature, presence of plasticizing agent, etc.
  • the cellular structures employed in accordance with the invention require certain essential characteristics and properties.
  • a particularly essential characteristic of a suitable foam is that it has a major proportion, by number, of closed cells since open cells do not confine liquids and would not afford osmotic pressure differentials.
  • mere visual or microscopic examination will often readily reveal whether or not a particular cellular structure predominates in closed or open cells. Particularly this is true in the case when the identity of the polymer and the conditions of foam formation are known. Otherwise the closed-cell content of a yieldable foam sample may be determined by the gas displacement method of Remington and Pariser, Rubber World, May 1958, p. 261, modified by operating at as low a pressure differential as possible to minimize volume changes of the yieldable closed cells.
  • the cell walls must be gas permeable in the sense that they must be capable of being permeated by at least some gases, although not all.
  • certain gas molecules or inordinately large size could be virtually incapable of permeating the walls. Also such large molecules would frequently be unsuitable because of unduly low vapor pressures.
  • a further essential characteristic of the foams to be employed in the process of the invention is that they be yieldable, i.e., resilient such that substantial deformation occurs under internal-external pressure differentials, meaning differences, of one atmosphere or less (since this is the order of magnitude of the pressure differentials available for collapse and inflation).
  • substantial deformation is meant that the cellular structure in expanded condition, i.e., having an internal pressure of about one atmosphere with few if any buckles and wrinkles in the walls, is yieldable such that its volume can be compressed by at least about 10% under a load of 10 lbs. per square inch sustained for a period of 1 second with recovery of at least about 50% of its original volume on release of the load.
  • Foams which do not compress to that extent are entirely too rigid and hence do not afford a sufficient degree of resiliency to respond to pressure differentials. Moreover if the foam does not sufficiently recover after release of the load, then it is not sufliciently flexible to resist fracturing and rupturing of the cell walls.
  • the wall portions of cellular structures are composed of a synthetic, high molecular weight polymer, usually organic polymers. These may be a wide variety of addition or condensation polymers, provided, of course, that in the form of a cellular structure they possess the described essential characteristics. Typical of such polymers are the polyolefins such as polyethylenes, linear or branched, polypropylene, polyamides such as nylon 6 or polyesters such as polyethylene terephthalate, halohydrocarbon polymers such as polychlorotrifluoroethylene, etc.
  • a highly suitable class of cellular structures is that wherein substantially all of the polymer is present as filmy elements of thickness less than 2 microns, since the walls are extremely thin and diffusion of gases through the cell walls is easily facilitated.
  • a particularly desirable type of cellular material is the ultramicrocellular structure described in copending US application, Ser. No. 170,187, filed Jan. 31, 1962, now US. Patent 3,227,664, issued Ian. 4, 1966, wherein additionally the structure is a crystalline organic polymer having thin walls exhibiting uniplanar orientation and a uniform texture.
  • These preferred cellular structures contain at least 10 cells per/cc. and the average transverse dimension of the cells in expanded condition is under 1000 microns.
  • substantially all of the polymer is present as filmy elements whose thickness is less than 2 microns and preferably under 0.5 micron.
  • the thickness of a cell wall, bounded by intersections with other walls, will ordinarily not vary by more than Adjacent walls commonly will have nearly equal thicknesses, usually within a factor of 3.
  • the polymer in the cell walls exhibits uniplanar orientation and a uniform texture.
  • such an ultramicrocellular structure will have a tenacity of at least 0.1 g.p.d.
  • the microcellular sheets have in general, a tenacity of at least 5 lbS./in./'oz./yd. in the machine direction and a TAPPI opacity of at least 70% at 1 oz./yd.
  • the apparent density of these ultramicrocellular products (p) in expanded condition is between 0.5 and 0.005 g./cc.
  • the number of cells per cc. (f), is at least 10 wherein t is the wall thickness in cm., and ,0 is the bulk polymer density.
  • the wall thickness and transverse cell dimensions are determined by microscopic examination of cross sections cut perpendicular to the machine direction. Thus 20-60 micron thick sections may be cut from a frozen sample with a razor blade. Large cell 50 microns) samples are frozen directly in liquid nitrogen. Smaller celled samples are preferably imbedded in water containing a detergent, and then frozen and sectioned.
  • the transverse dimension of one or more cells can be readily measured by the freezing and sectioning technique mentioned above Which at least partially inflates the cells. The cells will then exhibit a general polyhedral shape similar to the shape of the internal bubbles in a foam of soap suds.
  • the average transverse dimension of the cells is less than 1000 microns, and that the mutually perpendicular transverse dimensions of a single cell in a fully inflated condition do not vary by more than a factor of three. In the preferred structures the average transverse dimension is under 100 microns.
  • the ratio of the cell volume to the cube of the wall thickness can be calculated and exceeds about 200.
  • the wall thickness is preferably measured with an interferometer microscope. A layer of the sample is peeled off by contact with Scotch Tape. The layer is freed from the tape by immersion in chloroform and subsequently placed on the stage of the microscope for measurement.
  • Axial orientation refers to the perfection with which the crystalline axis parallel to the molecular chain axis in a sample is aligned with respect to a given direction, or axis, in the sample.
  • Axial orientation refers to the perfection with which the crystalline axis parallel to the molecular chain axis in a sample is aligned with respect to a given direction, or axis, in the sample.
  • prior art materials which have been drawn in one direction only e.g., fibers or one-way stretched films
  • Planar orientation refers to the perfection with which the crystalline axis parallel to the molecular chain axis is oriented parallel to a surface of the sample.
  • Electron diffraction furnishes a convenient technique for observing the presence of uniplanar orientation in the ultramicrocellular structures.
  • a single cell wall is placed perpendicular to the electron beam. Since the Bragg angle for electron diffraction is so small, only crystalline planes essentially parallel to the beam (perpendicular to the Wall surface) will exhibit diffraction. If the sample does in fact have perfect uniplanar orientation, there is some crystalline plane which occurs only parallel to the film surface and, therefore, will be unable to contribute to the diffraction pattern. Thus, the observed pattern will lack at least one of the equatorial diifractions normally observed for an axially oriented sample of the same polymer.
  • a sample is considered to have uniplanar orientation when at least one of the equatorial diffractions appears with less than one-half its normal relative intensity as determined on a randomly oriented sample of the same polymer.
  • uniform texture applied to the polymer in the cell walls means that the orientation, density, and thickness of the polymer is substantially uniform over the whole area of a cell wall, examined with a resolution of approximately /2 micron. This is best determined by observin the optical birefringence in the plane of a wall of a cell removed from the sample.
  • the individual cell walls will also normally exhibit an axial orientation in addition to the required unipanar orientation. In the birefringence test, such products will show a uniform extinction over the whole area of the cell wall. Samples with no net axial orientation must show a uniform lack of birefringence over their whole area rather than numerous small patches of orientation with each patch oriented at random with respect to the others. Lacy or cobweb-like cell walls, of course, do not have uniform birefringence over the whole area of a cell wall, and such products are readily distinguished from the uniform text-ured products preferred in this invention.
  • the polymers suitable for the preferred ultramicrocellular structures in accordance with this invention are members of the class of synthetic crystallizable, organic polymers which includes polyhydrocarbons such as linear polyethylene, stereo-regular polypropylene or polystyrene; polyethers such as polyformaldehyde; vinyl polymers such as polyvinylidene fluoride; polyamides both aliphatic and aromatic, such as polyhexamethylene adipamide and polymetaphenylene isophthalamide; polyurethanes, both aliphatic and aromatic, such as the polymer from ethylene bischloroformate and ethylene diamine; polyesters such as polyhydroxypivalic acid and polyethylene terephthalate; copolymers such as polyethylene terephthalate-isophthalate, and equivalents.
  • polyhydrocarbons such as linear polyethylene, stereo-regular polypropylene or polystyrene
  • polyethers such as polyformaldehyde
  • vinyl polymers such as polyvinyliden
  • the polymers should be of at least film-forming molecular weight.
  • One of the features of the ultramicrocellular structures is the high degree of orientation of the polymer in the cell Walls, which contributes to the unique strength of these structures. Therefore, a preferred class of polymers from which to make these objects is that class of polymers which responds to an orienting operation (e.g., drawing of fiber or films) by becoming substantially tougher and stronger.
  • This class of polymers is well known to one skilled in the art and includes, for example, linear polyethylene, polypropylene, 66 nylon, and polyethylene terephthalate.
  • Another feature of the preferred predominantly closed cell ultramicrocellular structures is their very high degree of pneumaticity resulting directly from their uinque structure, which may be looked upon as numerous tiny bubbles of gas enclosed in thin polymer skins. Retention of this gas, and hence of the structures pneumaticity depends on a low rate of gas diffusion through the polymer walls. Therefore, another preferred class of polymers particularly for preparing microcellular structures where pneumaticity is important, is that class of polymers with low permeability coefficients for gases, such as polyethylene terephthalate. Polymer properties such as solubility, melting point, etc., are usually reflected in the properties of the ultramicrocellular product.
  • various polymer additives such as dyes, pigments, antioxidants, delusterants, antistatic agents, reinforcing particles, adhesion promoters, removable particles, ion exchange materials, U.V. stabilizers and the like may be mixed with the polymer solution prior to formation of the original foam.
  • the nature of the fluid permeating agent will largely depend upon the permeability of the cell walls of the cellular structure and whether inflation or deflation is desired. Both gaseous and liquid materials are contemplated by the term although in the case of the latter those liquids having a high vapor pressure are preferred. Such materials should be essentially inert, a non-solvent for the polymer and have a boiling point below the softening temperature of the polymer.
  • the permeating agent may be composed of a single substance or a mixture of two or more materials. For purposes of deflation and for use as a plasticizer with less permeative materials, methylene chloride is particularly suitable.
  • the perhaloalkanes and perhalocycloalkanes of 1 to 4 carbon atoms constitute a highly useful class of such materials whether used alone, in combination, or with other components such as methylene chloride.
  • Example I This example describes the preparation of a deflated ultramicrocellular crystalline polymeric structure for use in accordance with the invention.
  • 400 grams of polyethylene terephthalate (relative viscosity of 50, vacuum dried in an oven at 120 C. for 24 hours) and 250 ml. of methylene chloride (dried over calcium hydride) are charged into a one liter pressure vessel, heated at 210 C. While the vessel is being rotated, held at 210 C. for minutes, cooled to 201 C., held minutes, positioned vertically, and connected to a source of nitrogen pressure at 1,000 p.s.i.g. just prior to extrusion through a cylindrical orifice 0.014 inch diameter by 0.028 inch long.
  • the extruded strand has a denier of 1,400 and an estimated density of 0.02 g./cc. but within a few seconds most of the methylene chloride vapor diffuses out of the cells, leaving a highly collapsed strand of 0.13 g./ cc. density.
  • the cell walls are composed of filmy elements less than 1 micron in thickness and essentially all of the polymer is present in the walls. The polymer in the cell walls exhibits uniplanar orientation and a uniform texture.
  • Example II Another deflated structure is prepared for purposes of subsequent inflation in accordance with the invention.
  • Example I is repeated, except that grams of carbon dioxide is added to the mixture, and the extrusion temperature is 191 C.
  • the carbon dioxide serves to assist bubble nucleation so that approximately 10 cells per cc. are now produced.
  • carbon dioxide like methylene chloride, will difluse out of the cells fairly rapidly so that the 900 denier strand produced is again observed to collapse within a few seconds to a density of 0.08 g./ cc. The collapsed yarn will not re-inflate on simple heating.
  • Example III Portions of the collapsed yarn prepared in Example I are partially inflated by being immersed in several liquid permeating agents at their normal boiling points for periods of time as indicated in Table I.
  • the samples are observed to inflate to some extent in the baths, but collapse immediately on removal from the bath and exposure to the room atmosphere owing to condensation of the F Ethyl chloride internal inflatant on adiabatic cooling when rapid evaporation of residual surface inflatant occurs.
  • the samples rapidly reinflate as they warm up to room temperature and the internal inflatant is converted back to the vapor state, this process being substantially complete in 1-2 minutes.
  • the equilibrium degree of inflation is shown to be dependent upon 1) the quantity of inflatant introduced into cells during the immersion in the liquid bath and (2) the relative rates of diffusion of air into the cells and inflatant vapor out of the cells. After standing in air the gaseous content of the cells is largely composed of air.
  • partially collapsed 6-nyl0n cellular samples are post-inflated with various agents.
  • partially collapsed 6-nylon foam filaments of density 0.087 g./ cc. are placed in a refluxing 50/50 volume mixture of fluorotrichloromethane/methanol for about 1% hrs., removed and placed in an air oven at '80-100" C. to complete the inflation to a stable density of about 0.013 g./cc.
  • the initially partially collapsed filaments may be placed in a boiling methanol bath for two minutes (which presumably plasticizes the polymer to an appropriate degree), then transferred directly to a boiling fluorotrichloromethane bath for 15 minutes, followed by the warm oven drying to achieve the same degree of inflation.
  • Another portion of the 6-nylon filaments is sealed in a pressure vessel with a 50/50 volume mixture of perfluorocyclobutane/ethanol and heated two hours at about 110 C. After the vessel is cooled and vented, the foam filaments are removed and placed in the warm air oven to generate a fully inflated, stable, pneumatic, perfluorocyclobutane-containing sample of density 0.013 g./cc. This sample likewise shows exceptional stability and recovery under sustained load.
  • Pneumatic polyethyleneterephthalate foams or 6-nylon foams containing inflatant such as perfluorocyclobutane In each case a large volume excess of permeating agent was provrded and the exposure period extended to promote the introduction of a maximum quantity of the agent.
  • this fabric is dipped in a 1,1,2-trichloro-1,2,2-trifluoroethane/methylene chloride (50/50 volume mixture) bath at the boil and dried for a few minutes at 100 C., the foam yarns are inflated to a density of 0.02 g./ cc.
  • woven or non-woven fabrics can be constructed from blends of foam yarns and normal dense synthetic or natural textile fibers.
  • these fabrics may be used in constructing an all-weather garment, using the techniques of this invention to collapse the foam to provide an open, breathable fabric for summer wear, and to expand the yarn to provide a tight insulating fabric for winter wear. It is to be noted in this regard that many common drycleaning solvents are suitable inflatants for certain closedcell foam yarns.
  • Example VII A sample of fully inflated ultramicrocellular polyethylene terephthalate foam yarn having a denier of 41 and density of 0.022 g./cc. is immersed in a methylene chloride bath at its atmospheric boiling point (40 C.) for 15 minutes. The sample is observed to collapse during the first two minutes or so, as the air diffuses out of the cells. The sample remains collapsed on removal from the bath, since the methylene chloride in the cells diffuses out faster than air diffuses in. The density of the collapsed yarn is 0.55 g./cc. (an increase of 25 times) while its denier remains unchanged at 41. Similar samples collapsed in methylene chloride may be inflated temporarily by taking the yarn from the bath directly into a 1009 C.
  • the fast permeation rate of methylene chloride in polyethylene terephthalate is related to its plasticizing action on the polymer.
  • any tendency of the strands to develop tacky surfaces can readily be overcome by the addition of 10 parts by volume of DC-55O silicone oil (a heat-stable, methylphenyl siloxane polymer, colorless to light straw colored, with a viscosity of 100-150 centistokes and a flash point of 575 F.) for each 750 parts by volume of methylene chloride completely inhibits the sticking problem while still permitting collapse of the yarn to a density of 0.29 g./ cc.
  • DC-55O silicone oil a heat-stable, methylphenyl siloxane polymer, colorless to light straw colored, with a viscosity of 100-150 centistokes and a flash point of 575 F.
  • Example VIII Although all the preceding examples have dealt with polyethylene terephthalate foams in order that the various features of the invention may more readily be intercompared, gas permeable cellular structures of other polymers such as linear polyethylene, branched polyethylene,
  • polypropylene, polychlorotrifluoroethylene, etc. may also be employed in accordance with the invention.
  • portions of a closed-cell foam of crystalline ultramicrocellular polypropylene in sheet form, wall thickness less than 1 micron are immersed for several minutes in baths respectively of fiuorotrichloromethane, 1,1,2-trichloro-1,2,2-trifluoroethane, and methylene chloride at their atmospheric boiling points. Evolution of gas bubbles is observed as air diffuses out of the cells to be replaced by the respective organic vapors.
  • the foam samples collapse on removal from the baths (due to condensation of the organic vapors), but within a minute or two the first two samples reinflate while the third remains permanently collapsed.
  • the two fluorinated compounds permeate polypropylene slower than air does, while methylene chloride permeates fastest of all and diffuses out before an equal volume of air can enter.
  • Example IX The preceding example demonstrates that trichlorofluoromethane permeates polypropylene foam slower than air while methylene chloride permeates faster than air. This example illustrates controlled intermediate degrees of expansion achieveable with mixtures of these two liquids.
  • Closed-cell yieldable polypropylene foam filaments are prepared by extruding a mixture of 1,000 grams polypropylene of melt index 0.7 (Hercules Powder Companys Profax), 1,000 grams methylene chloride, 5 grams Santocel (Monsanto trademark for silica aerogel) nucleating agent and 300 grams 1,l,2-trichloro-2,2,1- trifluoroethane heated to 150 C. for 16 hours in a three liter pressure vessel.
  • the autogenous pressure of 255 p.s.i. was increased to 300 p.s.i. by connecting the pressure vessel to a source of nitrogen gas just prior to extrusion through a 20 mil orifice into air.
  • These ultramicrocellular filaments self-inflate to an equilibrium diameter of 1.8 mm.
  • Example X Ultramicrocellular polypropylene foam filaments of 0.72 .p.d. tenacity, 563 denier, wall thicknes less than 1 micron, are collapsed in methylene chloride prior to being woven into a fabric of 14 ends and 8 picks per inch. This loosely-woven fabric is expanded by a 30 seconds immersion in fiuorotrichloromethane at room temperature. It shrinks momentarily on removal from the bath, but reexpands within 15 seconds at room temperature to a tight, opaque fabric of 1.7 oz./yd.
  • this fabric is partially collapsed under load of 1.5 p.s.i. applied overnight.
  • the loaded area remains depressed even when the load is removed, indicating that the original fluorotrichloromethane infiatant has diffused out of the cells and that there is no osmotic driving force for air to reinflate the fabric.
  • the damaged fabric is completely restored by re-immersing the sample in fluorotrichloromethane for 20 seconds followed by a 30 seconds room temperature air drying whereupon the 1 -3 whole fabric is reinfiated to its previous state with no residual evidence of the compression damaged areas.
  • Example XI Although fluo-rotrichloromethane permeates ploypropylene foams slowly enough to be a good infiatant the cell walls are not completely impermeable thereto as illustrated in Example X.
  • Perfluorocyclobutane employed in this example is an infiatant with a much lower permeability rate.
  • Polypropylene filaments are prepared as in Example 1X, except that 82 ml. of perfluorocyclobutane is substituted for the 300 gram trichlorotrifluoroethane and the spinning pressure is 465 p.s.i. Osmotic pressure drives air into these foam filaments, and, since no appreciable quantity of the perfluorocyclobutane diffuses out, the total internal pressure developed in the cells is appreciably greater than one atmosphere, making these filaments quite turgid. The low permeation of this infiatant is further evidenced by the fact that samples of these filaments remain inflated even after being stored for many months under the appreciable pressure generated in a closed bound, laboratory record book.
  • Example XII Pneumatic closed-cell synthetic polymer foam filaments are excellent stufiing materials for buoyancy devices, such as life jackets, because of their conformability, high specific buoyancy and water insensitivity.
  • buoyancy devices such as life jackets
  • water insensitivity By employing the post-expansion techniques of this invention, one may avoid to a considerable extent the difficulties of inserting inflated foam filaments into irregular shapes such as are found, for example, in life jackets.
  • Example XIII Part (a) of Example V describes a technique for introducing perfluorocyclobutane into polyethylene terephthalate ultramicrocellular structures which requires heating the sample in a sealed tube containing perfluorocyclobutane and methylene chloride. Superatmospheric pressure was utilized since perfluorocyclobutane is not miscible with methylene chloride at room temperature and atmospheric pressure. The present example describes two emthods for achieving the introduction of perfluorocyclobutane at atmospheric pressure.
  • Methylene chloride and perfluorocyclobutane may be made miscible at room temperature by addition of a suitable third component.
  • a suitable third component 100 ml. of liquid perfluorocyclobutane (measured at 7 C.) are added to 100 ml. of methylene chloride and 65 ml. of 1,'1,2-trifiuoro-1,2,2- trichloroethane to form a miscible liquid system.
  • a portion of collapsed polyethylene terephthalate ultramicrocellular 25 denier yarn of density about 0.2 g./cc. is placed in the refluxing (at atmospheric pressure) liquid for 30 minutes and subsequently removed and dried 15 15 minutes at 120 C. in an air oven.
  • the yarn inflates permanently to a density, measured at room temperature, of 0.02 6 g./cc., and contains 6.3 ml./g. of perfluorocyclobutane measured as a gas at room temperature and pressure by standard vapor chromatography techniques.
  • a plasticizing agent miscible with perfluorocyclobutane is chosen.
  • a 50/50 volume mixture of perfluorocyclobutane/fluorodichloromethane is miscible at room temperature.
  • a portion of partially collapsed polyethylene terephthalate ultramicrocellular yarn of density 0.064 g./ cc. is immersed for 15 minutes in the refluxing mixture, removed and dried 10 minutes at 120 C.
  • the yarn inflates immediately, and after cooling has a density of 0.018 g./cc.
  • the perfluorocyclobutane content is determined to be 1.2 ml. of gas at room temperature and pressure per gram of foam. When the immersion time is increased to one hour, the perfluorocyclobutane content increases to 4 ml./ g.
  • step (a) is conducted at a temperature near the boiling point of the "agent.
  • the ultramicrocellular structure has at least cells/cc. and wherein the 15 average transverse dimension of the cells in expanded condition is under 1000 microns.
  • polymeric cellular foam structure is composed of polyethylene terephthalate and said agent is methylene chloride.
US302495A 1963-08-16 1963-08-16 Method for inflating or deflating closed cell foams Expired - Lifetime US3344221A (en)

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Application Number Priority Date Filing Date Title
US302495A US3344221A (en) 1963-08-16 1963-08-16 Method for inflating or deflating closed cell foams
LU46773D LU46773A1 (de) 1963-08-16 1964-08-14
DE1504716A DE1504716C3 (de) 1963-08-16 1964-08-17 Ultramikrozellenförmiges Erzeugnis und Verfahren zur Herstellung desselben
GB33576/64A GB1062086A (en) 1963-08-16 1964-08-17 Improvements in or relating to ultramicrocellular structures
FR22969A FR1484626A (fr) 1963-08-16 1965-06-30 Perfectionnements aux structures ultramicrocellulaires et procédé de préparation de telles structures
CH207866A CH489563A (de) 1963-08-16 1966-02-14 Verfahren zur Herstellung eines zur Selbstaufblähung fähigen, aus Ultramikrozellen aufgebauten Körpers
NL6601868A NL6601868A (de) 1963-08-16 1966-02-14
BE682064D BE682064A (de) 1963-08-16 1966-06-03
US615883A US3375211A (en) 1963-08-16 1967-02-14 Ultramicrocellular polymeric structures containing an inflatant
US735926*A US3584090A (en) 1963-08-16 1968-01-08 Process for producing an ultramicrocellular structure by extruding a crystalline polymer solution containing an inflatant

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Cited By (23)

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US3381077A (en) * 1966-01-26 1968-04-30 Du Pont Method for inflating closed cell foams
US3389446A (en) * 1966-01-25 1968-06-25 Du Pont Process for producing foam fabrics
US3461026A (en) * 1966-06-23 1969-08-12 Du Pont Laminated fibrous batt
US3471610A (en) * 1967-02-20 1969-10-07 Du Pont Process for making a firm cushioning structure
US3485711A (en) * 1966-06-23 1969-12-23 Du Pont Low-density web-like cushioning structure of cellular filamentary material
US3503840A (en) * 1968-04-24 1970-03-31 Du Pont Composite cellular cushioning structures
US3505248A (en) * 1964-11-16 1970-04-07 Dow Chemical Co Process for producing expandable styrene polymer particles
US3505249A (en) * 1964-11-16 1970-04-07 Dow Chemical Co Fabricating expandable thermoplastic resinous material
US3508991A (en) * 1966-12-28 1970-04-28 Du Pont Process of making bonded batts of microcellular filaments
US3535181A (en) * 1966-12-28 1970-10-20 Du Pont Process for making consolidated batts of microcellular filamentary material
US3607596A (en) * 1968-07-10 1971-09-21 Fmc Corp Cellular article
US3900433A (en) * 1973-12-17 1975-08-19 Allied Chem Expandable polystyrene beads
US3914191A (en) * 1974-07-31 1975-10-21 Union Carbide Corp Methyl format E-trichloromonofluoromethane blowing agent for polystyrene
FR2377166A1 (fr) * 1977-01-14 1978-08-11 Rudy M F Semelle intercalaire pneumatique, telle qu'une premiere de chaussure
FR2406520A2 (fr) * 1977-10-20 1979-05-18 Rudy M F Dispositif elastomere de rembourrage
FR2425007A2 (fr) * 1978-05-05 1979-11-30 Rudy M F Dispositif se gonflant automatiquement par penetration de l'air exterieur par diffusion
US4179540A (en) * 1974-12-23 1979-12-18 Union Carbide Corporation Fabrication of foamed articles
FR2429567A2 (fr) * 1978-06-26 1980-01-25 Rudy M F Dispositif gonflable tel qu'une semelle intercalaire faisant partie d'une chaussure
US4351911A (en) * 1973-07-02 1982-09-28 General Electric Company Foamable polyester composition
US4360484A (en) * 1981-04-03 1982-11-23 The Dow Chemical Company Pressurization and storage of thermoplastic resin foams prior to secondary expansion
US5532284A (en) * 1990-03-23 1996-07-02 E. I. Du Pont De Nemours And Company Polymer foams containing gas barrier resins
US20070105970A1 (en) * 2005-11-10 2007-05-10 Kenneth Warnshuis Energy absorbing flexible foam
US20070105969A1 (en) * 2005-11-10 2007-05-10 Kenneth Warnshuis Multi-density flexible foam

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US5160674A (en) * 1987-07-29 1992-11-03 Massachusetts Institute Of Technology Microcellular foams of semi-crystaline polymeric materials
WO1989000918A2 (en) * 1987-07-29 1989-02-09 Massachusetts Institute Of Technology A method of producing microcellular foams and microcellular foams of semi-crystalline polymeric materials

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US2746088A (en) * 1951-11-10 1956-05-22 Lindemann Herbert Cellular thermoplastic bodies
US2795008A (en) * 1952-11-04 1957-06-11 Lonza Ag Method of producing cellular resin bodies
US3126432A (en) * 1961-05-18 1964-03-24 Particles of thermoplastic polymer
US3189669A (en) * 1962-11-01 1965-06-15 Goldfein Solomon Process for shipping flexible polyurethane foam
US3192300A (en) * 1962-03-14 1965-06-29 Lonza Ag Method of improving deformability of cellular bodies
US3202998A (en) * 1962-05-16 1965-08-24 Edward L Hoffman Flexible foam erectable space structures
US3227784A (en) * 1961-12-07 1966-01-04 Du Pont Process for producing molecularly oriented structures by extrusion of a polymer solution

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US2659935A (en) * 1950-03-18 1953-11-24 Christopher L Wilson Method of making compressed sponges
US2746088A (en) * 1951-11-10 1956-05-22 Lindemann Herbert Cellular thermoplastic bodies
US2795008A (en) * 1952-11-04 1957-06-11 Lonza Ag Method of producing cellular resin bodies
GB891943A (de) * 1957-06-11
US3126432A (en) * 1961-05-18 1964-03-24 Particles of thermoplastic polymer
US3227784A (en) * 1961-12-07 1966-01-04 Du Pont Process for producing molecularly oriented structures by extrusion of a polymer solution
US3192300A (en) * 1962-03-14 1965-06-29 Lonza Ag Method of improving deformability of cellular bodies
US3202998A (en) * 1962-05-16 1965-08-24 Edward L Hoffman Flexible foam erectable space structures
US3189669A (en) * 1962-11-01 1965-06-15 Goldfein Solomon Process for shipping flexible polyurethane foam

Cited By (25)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3505248A (en) * 1964-11-16 1970-04-07 Dow Chemical Co Process for producing expandable styrene polymer particles
US3505249A (en) * 1964-11-16 1970-04-07 Dow Chemical Co Fabricating expandable thermoplastic resinous material
US3389446A (en) * 1966-01-25 1968-06-25 Du Pont Process for producing foam fabrics
US3381077A (en) * 1966-01-26 1968-04-30 Du Pont Method for inflating closed cell foams
US3630823A (en) * 1966-06-23 1971-12-28 Du Pont Cocarded blend of microcellular and conventional fibers
US3485711A (en) * 1966-06-23 1969-12-23 Du Pont Low-density web-like cushioning structure of cellular filamentary material
US3521328A (en) * 1966-06-23 1970-07-21 Du Pont Process for carding microcellular fibers
US3461026A (en) * 1966-06-23 1969-08-12 Du Pont Laminated fibrous batt
US3508991A (en) * 1966-12-28 1970-04-28 Du Pont Process of making bonded batts of microcellular filaments
US3535181A (en) * 1966-12-28 1970-10-20 Du Pont Process for making consolidated batts of microcellular filamentary material
US3471610A (en) * 1967-02-20 1969-10-07 Du Pont Process for making a firm cushioning structure
US3503840A (en) * 1968-04-24 1970-03-31 Du Pont Composite cellular cushioning structures
US3607596A (en) * 1968-07-10 1971-09-21 Fmc Corp Cellular article
US4351911A (en) * 1973-07-02 1982-09-28 General Electric Company Foamable polyester composition
US3900433A (en) * 1973-12-17 1975-08-19 Allied Chem Expandable polystyrene beads
US3914191A (en) * 1974-07-31 1975-10-21 Union Carbide Corp Methyl format E-trichloromonofluoromethane blowing agent for polystyrene
US4179540A (en) * 1974-12-23 1979-12-18 Union Carbide Corporation Fabrication of foamed articles
FR2377166A1 (fr) * 1977-01-14 1978-08-11 Rudy M F Semelle intercalaire pneumatique, telle qu'une premiere de chaussure
FR2406520A2 (fr) * 1977-10-20 1979-05-18 Rudy M F Dispositif elastomere de rembourrage
FR2425007A2 (fr) * 1978-05-05 1979-11-30 Rudy M F Dispositif se gonflant automatiquement par penetration de l'air exterieur par diffusion
FR2429567A2 (fr) * 1978-06-26 1980-01-25 Rudy M F Dispositif gonflable tel qu'une semelle intercalaire faisant partie d'une chaussure
US4360484A (en) * 1981-04-03 1982-11-23 The Dow Chemical Company Pressurization and storage of thermoplastic resin foams prior to secondary expansion
US5532284A (en) * 1990-03-23 1996-07-02 E. I. Du Pont De Nemours And Company Polymer foams containing gas barrier resins
US20070105970A1 (en) * 2005-11-10 2007-05-10 Kenneth Warnshuis Energy absorbing flexible foam
US20070105969A1 (en) * 2005-11-10 2007-05-10 Kenneth Warnshuis Multi-density flexible foam

Also Published As

Publication number Publication date
DE1504716A1 (de) 1969-09-25
BE682064A (de) 1966-11-14
DE1504716C3 (de) 1975-11-20
CH489563A (de) 1970-04-30
NL6601868A (de) 1967-08-15
DE1504716B2 (de) 1972-02-10
LU46773A1 (de) 1966-02-14

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