US3508991A - Process of making bonded batts of microcellular filaments - Google Patents

Description

April 28, 1970 M. E. YUNAN 3,508,991

PROCESS OF MAKING BONDED BATTS OP MICROCELLULAR FILAMENTS Filed Dec. 28, 1966 INVENTOR MALAK E. YUNAN BY %Mm% ATTORNEY United States Patent 3,508,991 PROCESS OF MAKING BONDED BATTS OF MICROCELLULAR FILAMENTS Malak E. Yunan, Devonshire, Wilmington, DeL, assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Filed Dec. 28, 1966, Ser. No. 605,254 Int. 'Cl. B32b 5/02 US. Cl. 156209 3 Claims ABSTRACT OF THE DISCLOSURE A process for preparing consolidated reticulate batts of fully inflated microcellular filaments in which randomly deposited collapsed filaments are calendered to a compacted sheet, heated blades are drawn over the batt surface(s) to create a pattern of fused lines which solidify on cooling, and the unfused portions of filaments are subsequently fully inflated. Provides bonding and stable pre-loading of batts of pneumatic microcellular filaments for firm cushioning uses.

This invention relates to reticulate structures composed of microcellular filamentary material. It is more particularly directed to a process for making stably consolidated reticulate structures composed of randomly disposed, microcellular filamentary material. Structures made by the process of this invention, due to their consolidated condition, are useful in firm cushioning applications, for example, as carpet underlay.

Microcellular filamentary material as used herein refers to a homogeneously foamed polymeric material in filamentary form. The foam cells are polyhedral in shape, and at least a major proportion of them are completely enclosed by the cell-Walls which art thin, film-like, pliable elements of a high molecular weight film-forming thermoplastic polymer, ordinarily a synthetic organic polymer.

Excellent soft cushions for use in mattresses, chairs, and the like, can be made by depositing gas-inflated microcellular filamentary material in a random batt and stabilizing the resulting network by adhesive bonds at filament cross-over points. When a compressive load is applied to such a structure a cushioning effect results, due to compression of the gases confined within the cells at points of filament crossing.

As initially deposited in a batt, inflated filaments are much too turgid and too light to drape or bend around one another at crossings. Consequently, only point contacts between crossing filament-portions are made, and these are rather widely spaced. Unless forced into a consolidated state, the filaments occupy only a small fraction of the effective volume of the batt, this volume fraction usually being less than about 0.25. The unconsolidated structures are soft because the volume of gas compressed at filament crossing points when a load is initially applied is extremely small compared to the total volume of the batt.

Some cushioning materials, in particular carpet underlay, must support relatively large loads while retaining residual compressibility, must be initially more resistant to compression, and must be relatively thin, e.g., ordinarily between about 0.25 and about 0.75 inch (0.63 and 1.90 cm.) thick. Reticulate batts of randomly disposed, gas-inflated microcellular filamentary material can make excellent firm cushions if they are consolidated so that the turgid, pneumatic filamentary material is forced to conform around other filament portions, thus increasing the extent of contact area between filament portions and increasing the volume of gases, relative to the volume of the consolidated batt, which can resist compression. For firm-cushioning, the batt should be compacted to such an extent that the volume-fraction occupied by the microcellular filamentary material is greater than 0.4 but is less than 1.0. Consolidation should not eliminate the open, interconnected spaces between filament portions.

To be useful as commercial firm cushions, such consolidated batts must be stabilized in a consolidated state without continued application of an external force. Such stable consolidation is diflicult to achieve because:

(1) Pneumaticity of the inflated filaments causes them to rebound to the unconsolidated state unless the constraint provided is set before release of the consolidating pressure;

(2) Turgidity of the inflated filaments causes them to shatter if consolidating forces are too rapidly applied;

(3) Heating the inflated filaments to render them selfadhesive may cause loss of inflating gases;

(4) Localized thermal treatments sufficient to melt portions of the filaments readily cut through them because of their low density (i.e., ordinarily between 0.005 and 0.05 gm./cc.); and

(5) Prolonged thermal treatment can cause microscopic structural changes in the cell-walls to reduce their impermeability to gases.

According to the present invention a consolidated batt is formed of collapsed filamentary material, and is stabilized by melting and displacing polymer along spaced lines on at least one surface of the batt. Along these lines, adjacent filaments become fused and anchored together. Upon subsequent inflation of the foam (except along the melt lines, which are non-inflatable) the filaments in the untreated areas are forced by their anchored portions to conform around one another into a consolidated state.

The process of this invention comprises the following steps:

(1) Randomly depositing collapsed microcellular filamentary material into a reticulate batt with numerous crossings of portions of said filamentary material;

(2) Compacting said batt at temperatures below the polymer melt temperature of the polymer comprising said filamentary material to render the batt substantially uniformly thick Without appreciably altering the crosssectional sizes and shapes of said filamentary material;

(3) Heating at least one metal blade with an elongated surface to a temperature at least as high as said polymer melt temperature;

(4) Interposing between said batt and said elongated surface a film of release agent thermally stable at the temperature of said blades;

(5) Exerting pressure on a face of said batt with said elongated surface and maintaining relative motion between said batt and said surface in the direction of elongation of said surface, whereby polymer is melted and displaced along each of spaced parallel lines, relative motion of said elongated surface to said batt being such that less than of the thickness of said batt along each of said parallel lines is rendered molten;

(6) Resolidifying said molten polymer by cooling; and

(7) Inflating said collapsed filaments, except where fused along said parallel lines, by introducing inflatant gases to the closed cells of said microcellular filamentary material.

It should be observed that in the process of this invention, it is important that the microcellular filamentary material be collapsed at the outset. If melt-lines are formed in batts of inflated microcellular filaments, the small amounts of molten polymer formed are insufficient to bridge the large interfilament gaps. Batts of collapsed filaments are readily compacted to create small interfilament gaps.

In the drawings:

FIGURE 1 is a representation of a compacted reticulate batt of randomly disposed, collapsed microcellular filamerits.

FIGURE 2 is of a blade suitable for forming melt-lines on the face of the batt of FIGURE 1.

FIGURE 3 is a diagrammatic face-view of a batt showing one pattern of melt-lines.

FIGURE 4 represents the cross-section taken at 4-4 of FIGURE 3, drawn to a larger scale.

FIGURE 5 is a diagrammatic face-view of a batt showing a preferred pattern of melt-lines.

FIGURE 6 represents the cross-section taken at -66 of FIGURE 5, drawn to larger scale.

FIGURE 7 illustrates the change in the cross-section of FIGURE 6 when the collapsed filaments have been inflated.

Microcellular filaments are ordinarily prepared by direct extrusion of a foarnable composition which, on exit from the extrusion die, becomes fully expanded as each cellwall solidifies to a fixed area. If the inflating gases are lost from or removed from the cells, or if the gases condense within the cells, the microcellular filament collapses radially under the force of external atmospheric pressure, this collapse being characterized by a decrease in volume of each cell accompanied by wrinkling, folding, and buckling of the thin cell walls without change in their areas. Subsequent introduction to the cells of sufficient inflatant gases (suitable methods being described hereinafter) to create super-atmospheric pressure within the cells results in inflation of the filament to a volume which is substantially identical to its maximum volume attained at the time of cell-wall solidification immediately following extrusion. Collapsed microcellular filaments have volumes less than about of the maximum volume. Fully inflated filaments have volumes of at least about 95% of the maximum volume.

Microcellular filaments useful in this invention should additionally be yieldable such that substantial deformation results from externally applied compressive loading. Generally, this requirement is satisfied if the fully inflated filament is reduced in thickness by at least 10% under a load of 10 p.s.i. (0.70 kg./cm. based on an area computed from the length and original diameter of the filament, the load being maintained for one second, and if there is a thickness regain to at least and preferably to substantially 100%, of the original thickness on release of the load. Filaments which do not compress and regain thickness to this extent are too rigid to respond to available pressure differentials for post-inflation in this process.

Suitable microcellular filaments should have fully inflated densities in the range from about 0.005 to about 0.05 gm./cc. and collapsed densities ordinarily in the range from about 0.05 to about 0.5 gm./ cc. Useful diameter for a fully inflated filament is ordinarily in the range from about 0.01 to about 0.25 inch (0.25 to 6.35 mm.), but a diameter between 0.05 and 0.10 inch (1.27 and 2.54 mm.) is preferred.

A particularly desirable microcellular filament is ultramicrocellular as disclosed by Blades et al. in U.S. Patent No. 3,227,664. Ultramicrocellular filaments have cell walls less than about 2 microns thick in which the polymer exhibits uniplanar orientation and uniform texture as de scribed therein. The latter two properties provide the surprisingly great strength of the filaments and render their cell walls particularly impermeable to most gases.

A wide variety of both addition and condensation polymers can form microcellular filaments with the essential characteristics. Typical of such polymers are: polyhydrocarbons such as polyethylene, polypropylene, and polystyrene; polyethers such as polyformaldehyde, vinyl poly mers such as polyvinyl chloride and polyvinylidene fluoride; polyamides such as polycaprolactam, polyhexamethylene adipamide, and polymetaphenylene isophthalamide; polyurethanes 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.

Planar molecular orientation of the polymer in the cell 'walls contributes significantly to both strength and impermeability of the filaments. A preferred class of polymers is, therefore, one including those which respond to orienting operations by becoming substantially tougher and stronger. This class includes linear polyethylene, stereo-regular polypropylene, nylon-6, polyethylene terephthalate, polyvinyl chloride, and the like. Further preferred is the class of polymers known to be highly resistant to gas permeation, such as polyethylene terephthalate and polyvinyl chloride.

A portion of a random batt 1 of collapsed microcellular filaments 2 is shown in FIGURE 1, already compacted as described hereinafter. The filaments 2 can either be continuous or be cut into staple. Staple lengths should be relatively large compared to filament diameter (or other maximum transverse dimension); i.e., length-to-diameter ratio for the fully inflated staple preferably exceeds 20. Deposition of the collapsed filaments 2 in the form of a random batt can be by any convenient means. Thus, a previously formed supply of collapsed filaments 2 can be deposited either manually or mechanically. Preferably, however, they are collected on a moving belt immediately after they leave the extruder, being conveyed to the belt by, e.g., an oscillating duct. Regardless of the method of deposition, the thickness of the batt so formed should be As initially deposited, the batts are usually rather fluffy and non-uniform in absolute thickness. Collapsed microcellular filaments 2, are, however, not turgid and pneu matic as are fully inflated filaments; and they are readily compacted to a substantially uniformly thick batt by, for example, calendering between rolls exerting a compressive force of from about 1.0 to 20 pounds per linear inch (about 0.18 to 3.58 kg. per linear centimeter). The batts are preferably deposited and calendered as soon as possible after extrusion of filaments 2 while the outer surfaces of the filaments 2 are still sufiiciently plasticized that they can form fragile adhesive bonds at all crossing filament portions. Such bonds, though weak and easily broken, greatly facilitate subsequent processing of the batt. Most importantly, this calendering operation decreases the absolute thickness of the batt and brings all adjacent filament portions into close proximity.

A blade 3, such as shown in FIGURE 2, is provided with an elongated, substantially flat contact surface 4. It is attached to a holder 5 which can be a source of heat for raising the temperature of surface 4 to at least the polymer melt temperature of the polymer to be melted. Edges 6 of blade 3 can be rounded to prevent snagging. In use, blade 3 moves along a face of batt 1 in the direction indicated by arrow 7. Width 8 of the contact surface 4 is preferably minor compared to the length dimension along direction 7. Width 8 is usually less than about 0.125 inch (0.318 cm.), but this dimension is not limiting. Ordinarily blade 3 is of an oxidation-resistant rigid metal with high thermal conductivity.

When a bare heated blade contacts microcellular foam to melt it, molten polymer sticks to the metal with obvious disadvantages. Thus a film of release agent (i.e., a

material which does not stick to the molten polymer) should be interposed between blade 3 and batt 1. Although a separate film of release agent can cover the face of batt 1, it is preferred that the film be a permanently attached covering over the heated blade 3. It must, of course be thermally stable at the temperature of the blade. A preferred release agent is polytetrafluoroethylene. In the following description, it is assumed that the film of release agent covers and is integral with blade 3.

The polymer-melt temperature (PMT) as used herein is that temperature at which a polymer sample becomes molten and begins to leave a trail when moved across a hot metal surface under moderate pressure. Details of the measurement of PMT are given by W. R. Sorenson and T. W. Campbell in Preparative Methods of Polymer Chemistry, Interscience Publishers, Inc., New York, 1961, pp. 49 and 50.

In use, blade 3 is heated above the PMT and brought against a surface of batt 1. Simultaneously, relative motion between blade 3 and batt 1 along direction 7 is established. Velocity and contact pressure of surface 4 on a face of batt 1 are both adjusted so that less than 100% of the thickness of batt 1 along the line of contact is melted. Melting the Whole thickness simply cuts batt 1. Ordinarily, melting from 50 to 75% of the thickness of batt 1 is preferred. The relative motion of blade 3 to batt 1 displaces molten polymer along each melt-line to bridge interfilament gaps and to form secure interfilament bonds. Unless filaments 2 are both collapsed and compacted as described, the small amount of molten polymer available is insufficient to satisfactorily bridge interfilament gaps.

Following the formation of melt-lines by blade 3, the molten polymer is re-solidified. Cooling in the atmosphere or exposure to currents of cold fluids is satisfactory. In a preferred method of resolidifying the molten polymer, a cold blade physically similar to heated blade 3 is drawn along each melt-line.

Parallel melt-lines are formed over the whole face of batt 1, spaced as desired to create a given degree of consolidation after gas-inflation. Preferably, a plurality of blades 3 is employed simultaneously.

Alternatively, the blades can be heated fins extending radially from a cylindrical drum, the plane of each fin being perpendicular to the drum-axis and the fins being spaced apart along the axis. By drawing a batt 1 in contact with the fins in the direction of motion of the fins at the points of contact but slightly faster, parallel meltlines are formed continuously on the face of the batt.

FIGURE 3 illustrates a pattern of melt-lines 9 formed on batt 1. By treating the other face of the batt 1 similarly, the same pattern can be created on it, preferably without coincidence of melt-lines 9 on opposite faces, as indicated by a cross-section taken at 44 in FIGURE 3 and shown in FIGURE 4. In a preferred process according to this invention, two intersecting sets of parallel melt-lines 9 are formed on the same face to create a diamond pattern as shown in FIGURE 5, and by its crosssection 6-6 as shown in FIGURE 6. Alternative patterns of either straight or curved lines are immediately obvious.

Following the formation of stable melt-lines 9 as described, the unmelted portions of microcellular filaments 2 are inflated. The manner in which this inflation is accomplished depends on the gas content of the collapsed microcellular filaments. Thus, if they already contain a gas which permeates the cell walls more slowly than air, air will permeate the cell walls until its fugacity Within the cell equals its fugacity in the surrounding atmosphere. Ordinarily the internal partial pressure of air at equilibrium is substantially atmospheric, i.e., about 760 mm. Hg. This partial pressure coupled with the parital pressure of more slowly permeating gas already contained creates a superatmospheric pressure within the cells and causes inflation of the microcellular filaments. Attainment of or approach to this equilibrium state at commercially attractive rates occurs upon heating the surrounding air to temperatures below the polymer-melttemperature, but preferably above the glass-transition temperature, i.e., ordinarily between about and C. depending upon the kind of polymer.

Frequently, collapsed filaments 2 contain either no slowly permeating gas or less than required to produce full inflation. Slowly permeating gas is then introduced to the closed cells by immersing the batt 2 in a plasticizing fluid and, while the cell walls are still wet with and plasticized by plasticizing fluid, exposing the structure to a fluid which normally permeates the cell walls very slowly. Both the plasticizing fluid and the slowly permeating fluid can be either gaseous or liquid in this treatment, but the liquid phase is preferred.

Suitable plasticizing fluids are compounds which: (1) are easily volatilized, (2) have small molecules which readily permeate the cell Walls, i.e., much faster than air, (3) are chemically non-reactive with the microcellular material, (4) are non-solvents for the polymer at or below the fluids atmospheric boiling temperature, and (5) interact sufliciently with the polymer to plasticize, i.e., swell it. Methylene chloride frequently meets all these requirements, as do several chlorinated or fluorochlorinated methanes and ethanes. While plasticized, the cell walls are temporarily much less resistant to permeation, and normally slowly permeating fluids are readily introduced to the cells. On removal of the structure from these fluids, the plasticizing fluid is quickly volatilized by any convenient method to leave the slowly permeating gas trapped within the cells. Subsequent equilibration with air as described hereinbefore causes the filaments in the batt to become fully inflated, except where they have been melted.

Some slowly permeating gases permeate the cell walls so slowly that they are substantially permanently retained. These are referred to hereinafter as impermeant inflatants. Presence of an impermeant inflatant within closed cells results in several distinct benefits. First, it provides a permanent osmotic gradient for the inward permeation of air so that, even if air is subsequently lost during compression, a microcellular filament spontaneously re-inflates in air. Secondly, it guarantees that the equilibrium internal pressure is always superatmospheric so that the inflated filaments remain turgid and highly pneumatic. As is clearly obvious, presence of impermeant inflatant results in durable pneumaticity and indefinite retention of cushioning properties.

Candidates for impermeant inflatants should have vapor pressures at normal room temperature (i.e., greater than about 15 C.) of at least 50 mm. Hg and should be present Within the cells in suflicient quantity to provide an internal partial pressure of at least 50 mm. Hg. Preferred impermeant inflatants have atmospheric boiling points less than about 25 C.

The rate of permeation for an inflatant through a given polymer increases as its diffusivity and solubility increase. Accordingly, candidates for impermeant inflatants should have as large a molecular size as is consistent with the required vapor pressure, and they should have substantially no solvent power for the polymer. A preferred class of impermeant inflatants is exemplified by compounds whose molecules have chemical bonds different from those of the confining polymer, a low dipole moment, and a very small atomic polarizability.

Suitable impermeant inflatants are selected from the group consisting of sulfur hexafluoride and saturated aliphatic or cycloaliphatic compounds having at least one fluorine-to-carbon covalent bond and wherein the number of fluorine atoms preferably exceeds the number of carbon atoms. Preferably these impermeant inflatants are perhaloalkanes or perhalocycloalkanes in which at least 50% of the halogen atoms are fluorine. Although these inflatants may contain ether-oxygen linkages, they are preferably free from nitrogen atoms, carbon-to-carbon double bonds, and reactive functional groups. Specific examples of impermeant inflatants include sulfur hexafluoride, perlluorocyclobutane, 1,2-dichloro-1,1,2,2-tetrafluoroethane, perfluoro 1,3 dimethylcyclobutane, perfluorodimethylcyclobutane mixtures, 1,1,2-trichloro-1,2,2- trifluoroethane, CF CF CF OCFHCF chlorotrifluoromethane, dichlorodifluoromethane and chloropentafluoroethane. Particularly preferred because of its inertness, appreciable molecular size, very low permeability rate, and lack of toxicity are perfluorocyclobutane and chloropentafluoroethane with atmospheric boiling points of about 6 C. and about -39" C., respectively.

Linear dimensions of the faces of batt 1 are substantially unchanged by inflation; only the thickness changes. FIGURE 7 represents the change in cross-section of collapsed batt 1 in FIGURE 6 after post-inflation. Meltlines 9 (represented by heavier lines) remain stabilized in size and become submerged below the surface of the expanded batt 10. Frequently the protuberances 11 formed between melt-lines 9 bulge enough to contact above the melt-lines 9 and to at least partially obscure the openings 12 of the applied pattern.

Although the consolidated batt (e.g. batt 10 of FIG- URE 7) preferably comprises microcellular filaments containing impermeant inflatant, in some cases it is sufficient that the filaments be inflated only with air. To accomplish this the previously described post-inflation process is carried out as described except that slowly permeating inflatants, rather than impermeant inflatants, are used. Such temporary inflatants permeate the cell walls more slowly than air and remain in the cells long enough to produce full inflation; but temporary inflatants permeate the cell walls too rapidly to be permanently retained. Perhalogenated methanes and ethanes containing more chlorine than fluorine atoms are frequently good temporary inflatants, e.g., trichlorofluoromethane.

When fully inflated, microcellular filaments have their maximum volume, which is substantially the same maximum volume (or minimum density) attained immediately after their extrusion. This maximum volume is most easily computed by observing the maximum diameter after extrusion. Alternatively, the microcellular filament can be immersed in a boiling, refluxing bath composed of a plasticizing fluid and an impermeant inflatant, removed, and heated in an air oven until diameter increases no more. About minutes immersion in a 50:50 by volume bath of methylene chloride and 1,1,2-trichloro-1,2,2-trifluoroethane, followed by heating in air at about 80 C., is almost universally applicable.

Consolidated batts of inflated microcellular filaments as prepared by the process of this invention are excellent firm-cushioning materials, particularly useful as carpet underlay. At area weights from 4 to times less than those of commercially available carpet underlay (including known jute felt, hair felt, hair/jute felt, rubberized felts, and sponge-rubber underlays), these consolidated batts can provide at least equivalent cushioning properties. Additionally, they are excellent cushioning elements for packaging uses and serve for numerous thermal-insulation applications.

The following examples illustrate the process of this invention but are not intended as a limitation thereof except as provided by the appended claims. All parts and percentages are by weight unless otherwise specified.

EXAMPLE I Specimens of carpet underlay were formed according to the process of this invention.

Collapsed, continuous, ultramicrocellular filaments were prepared by extruding a 60% solution of polyethylene terephthalate in methylene chloride through a single orifice 0.015 inch (0.381 mm.) in both diameter and length. Relative viscosity (RV) of the polymer was 56.5, and it contained only about 58 ppm. of water. (Relative viscosity is the ratio of absolute viscosities of polymer solution and solvent, the solvent being itself a solution of parts of 2,4,6-trichlorophenol in parts of phenol and the polymer solution being 8.7% polyethylene terephthalate.) Extrusion pressure was 800 p.s.i.g. (56.3 kg./cm. gage) at a temperature of about 206208 C. The extruded filament became fully expanded immediately after extrusion but quickly collapsed to a stable density ranging from 0.076 to 0.110 gm./cc. Cross-sections of collapsed filaments were not round. When fully inflated by the process described later in this example, the round filaments had diameters ranging from 0.073 to 0.087 inch (1.85 to 2.21 mm.) and densities from 0.021 to 0.027 gm./cc.

A 10 foot (3.05 meter) long, 8 inch (20.3 cm.) diameter metal duct was swiveled near the extrusion die, its other downward end being automatically programmed to traverse the width of a conveyor belt while simultaneously moving in a complicated, perpendicular, zig-zag pattern. A downwardly directed jet of air from a 6090 p.s.i.g. (4.2-6.3 kg./cm. gage) supply, entering the duct about 3 feet (0.91 m.) below the orifice, carried the filament through the duct to randomly deposit it onto the moving conveyor belt. Area-weight of the collected batt was determined by the speed of the conveyor belt. Downstream from the collection area, the conveyor belt passed beneath a compaction roll exerting about 2 lbs./in. (358 gm./cm.) by which the loose batt was compacted into a weakly coherent, uniformly thick sheet capable of being wound onto a roll.

A portion of the above sheet was selected for processing according to this invention. It weighed about 4.9 oz./yd. (166 gun/m?) and was about 0.13 inch (0.33 cm.) thick. A 1 inch (2.5 cm.) high metal blade with a downwardly directed contact surface (4 of FIGURE 2) 2 inches (5 cm.) long and 0.125 inch (0.318 cm.) wide was coated with Teflon fluorocarbon resin (Teflon is a registered trademark of E. I. du Pont de Nemours & Co., Inc.) and suitably mounted to an electrically heated soldering gun. Heated by the soldering gun to about 300 C., the blade was moved in a straight line diagonally across a face of the batt at about 8 ft./ min. (2.44 m./min.) while exerting a force on the batt surface of about 10 p.s.i. (0.7 kg./cm. The hot blade melted foam along its path, and smeared molten polymer along the Walls of its path. Cooling in ambient air resolidified the melted polymer to securely bond together portions of adjacent foam filaments along the melt line. In identical fashion, melt lines spaced about 2 inches (5 cm.) apart were formed over the whole surface of the batt. Then the batt was turned over, and parallel melt lines spaced between those of the other face were formed. Each melt line penetrated about 0.07 inch (0.18 cm.) into the batt, corresponding to about 4 filament layers. Tensile strength at failure for this collapsed batt was about 10 lb./in. (1.79 kg./cm.) along the melt line direction, and about 7 lb./in. 1.24 kg./ cm.) perpendicularly.

The collapsed batt was immersed for 40 minutes in a. constant composition liquid bath boiling at about 6 C. at atmospheric pressure and containing about 91% methylene chloride and at least 9% perfiuorocyclobutane. Removed from this bath, it was quickly placed between two rigid metal screens spaced 0.5 inch (1.27 cm.) apart, the assembly being placed in an air-oven at C. for about 15 minutes. Removed from the oven and screens, the batt of inflated filaments was about 0.5 inch (1.3 cm.) thick and contained at least 8 gm. of perfluorocyclobutane per 100 gm. of polymer. Thickness along the melt lines was about 0.21 inch (0.533 cm.) indicating that approximately 40% of the microcellular material along the lines remained microcellular and postinfiatable. On standing in air, maximum batt thickness increased to about 0.7 inch (1.8 cm.) without change in the melt lines.

Another portion of the collapsed batt was similarly embossed and post-inflated, but the two sets of melt lines were formed on the same face to produce a repeated diamond-pattern with diagonals of about 2 and 4 inches (5 and cm.). Under a load of 25 p.s.i. (1.76 kg./ cm. this fully inflated batt decreased in thickness about 72.7% and returned to the original thickness immediately after removal of the load. This performance is characteristic of desirable carpet underlay.

EXAMPLE II This example demonstrates the feasibility of continuous line-melting.

A batt of collapsed microcellular filaments was formed, compacted, and rolled up substantially as described in Example I. On the average the batt was 3 filament layers thick. A portion of this batt was subsequently fastened to the conveyor belt formerly used to collect the filaments, and it was covered with an Armalon TFE-fluorocarbon-resin coated fabric (Armalon is a registered trademark of E. I. du Pont de Nemours & Co., Inc.). A 0.5 inch (1.27 cm.) brass blade with a 2 X 0.0625 inch (5.08 x 0.159 cm.) contact surface was mounted in an electrical soldering gun and heated thereby to about 290 C. Resting on the Armalon fabric, the weight of the soldering gun and its associated apparatus caused the contact surface to exert a pressure of about 8 lb./in. (0.56 kg./cm. While the soldering gun rested on the Armalon-covered batt, the conveyor belt moved the batt at a constant linear velocity of about 8 ft./min. (24 m./min.). A melt line was continuously formed penetrating about 50% of the batt thickness. On the average, 130 gm. of force on a filament was required to cause it to separate from adjacent filaments at the melt line.

The above was repeated except that an unheated blade 0.0625 inch (0.158 cm.) wide at its contact surface was mounted so as to follow the heated blade along each melt line. The film of resolidified fused polymer so formed in each melt line was visibly more uniform and provided improved bonding. A 2.5 inch (6.4 cm.) wide portion of this product with 3 parallel melt lines on one surface and 2 co-parallel non-coincident melt lines on the other surface was clamped at its ends and tensilely loaded along the melt line direction. A total load of about 12 lbs. (5.4 kg.) was required to tear the batt. This portion had previously been soaked for 5 minutes in methylene chloride, and it was thus shown that subsequent inflation treatment does not adversely affect the bonding along melt lines.

The invention claimed is:

1. A process comprising the steps: (1) randomly depositing collapsed microcellular filamentary material into a reticulate batt with numerous crossings of portions of said filamentary material; (2) compacting said batt at temperatures below the polymer melt temperature of the polymer comprising said filamentary material to render the batt substantially uniformly thick without appreciably altering the cross-sectional sizes and shapes of said filamentary material; (3) heating at least one metal blade with an elongated surface to a temperature at least as high as said polymer melt temperature; (4) interposing between said batt and said elongated surface a film of release agent thermally stable at the temperature of said blades; (5) exerting pressure on a face of said batt with said elongated surface and maintaining relative motion between said batt and said surface in the direction of elongation of said surface, whereby polymer is molten and spread along each of spaced parallel lines, relative motion of said elongated surface to said batt being such that less than of the thickness of said batt along each of said parallel lines is rendered :molten; (6) resolidifying said molten polymer by cooling; (7) inflating said collapsed filaments, except where fused along said parallel lines, by introducing inflatant gases to the closed cells of said microcellular filaments.

2. A process according to claim 1 wherein the film of release agent is 'a coating of polytetrafluoroethylene on said blades.

3. A process according to claim 1 wherein in step (7) inflatant gases are introduced by immersing the batt in a plasticizing fluid and while the cell walls of the microcellular filamentary material are still wet with plasticizing fluid exposing the structure to a fluid which normally permeates the cell walls very slowly, removing the structure from the fluids and exposing it to air.

References Cited UNITED STATES PATENTS 2,464,301 3/1949 Francis l61159X 3,043,733 7/1962 Harmon et al. 156-209 3,227,664 1/1966 Blades et al. 2602.5 3,278,954 10/1966 Barhite 16117O X 3,344,221 9/1967 Moody et al. 16ll59X 3,418,196 12/1968 Luc 156209X SAMUEL w. IENGLE, Primary Examiner US. Cl. X.R.

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