US3535181A

US3535181A - Process for making consolidated batts of microcellular filamentary material

Info

Publication number: US3535181A
Authority: US
Inventors: Malak E Yunan
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1966-12-28
Filing date: 1966-12-28
Publication date: 1970-10-20
Anticipated expiration: 1987-10-20
Also published as: NL6717494A; DE1635606A1; FR1559730A; GB1203279A

Description

Oct. 20, 1970 YUNAN 3,535,181

PROCESS FOR MAKING CONSOLIDATED BATTS OF MICROGELLULAR FILAMENTARY MATERIAL Filed Dec. 28. .1966

PROVIDE ULTRAIII CROCELLULAR FILAHENTS commune IHPERHEANT IHFLATANT TREAT VIITH THERMOPLASTIC ADHESIVE AND RANDOHLY DEPOSIT INTO A BATT HEAT T0 ACTIVATE THERHOPLAST IC ADHESIVE COIIPRESS T0 CONSOLIDATE am AND COOL T0 STABILIZE CONSOLIDATED sum:

INVENTOR HALAK E. YUNAN BY ym ATTORNEY United States Patent US. Cl. 156-181 Claims ABSTRACT OF THE DISCLOSURE A process for making stably-consolidated batts of polymeric foam filaments for firm cushioning applications such as carpet underlay. The filaments are randomly deposted to form a reticulate batt. Before or after batt formation, an adhesive binder is deposited on the filaments. The batt is heated to activate the binder. The filaments may be fully expanded originally, or they may be partially collapsed and contain an impermeant inflatant, in which case they will be fully expanded during the heating step. After or simultaneously with heating, the batt is compressed. Finally, the batt is cooled while compressed to deactivate the adhesive and stabilize the batt in its consolidated condition.

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 fully inflated, randomly disposed, microcellular filamentary material. Structures made by the process of this invention, due to to their consolidated conditions, 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 are completely enclosed by walls which are 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, the inflated filaments are much too turgid and too light to drape or bend around one another. 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 to a consolidated state without continued application of external force. Turgidity of the inflated filamentary material will cause the batt to revert to the unconsolidated state unless the constraint provided is set before release of the consolidating pressure. The usual thermal bonding methods used in making non-woven sheets of dense fibrous thermoplastic materials are generally not suitable for stably-consolidating batts of fully inflated microcellular filaments. Generalized thermal treatments sufficient to render the filamentary material self-adhesive can cause microscopic structural changes in the cell-walls, thereby reducing their impermea-bility to gases and resulting in loss of inflatants. Localized thermal treatments suflicient to melt portions of the inflated filamentary material result in cutting or tearing of the material due to its low density.

According to this invention there is provided a process for making stably-consolidated reticulate structures composed of microcellular filamentary material. The process comprises the steps:

(A) Providing a reticulate batt of fully inflated, randomly disposed microcellular filamentary material, the outer surfaces of said filamentary material having deposited thereon a binder comprising a normally solid thermoplastic adhesive activatable at a temperature below the polymer-melt temperature of the polymer comprising said filamentary material, the batt being heated to a temperature below said polymer melt temperature suflicient to activate said adhesive; and

(B) Compressing to consolidate the batt and cooling it while maintaining the compression to deactivate the adhesive and thereby stabilize the batt in its consolidated state, the volume fraction of the filamentary material in the consolidated batt being at least 0.4.

A preferred process of the invention comprises the steps:

(A) Providing a supply of ultramicrocellular filamentary material, the filamentary material containing within the closed cells thereof between about 6 and 40 grams of an impermeant inflatant per grams of polymer;

(B) Randomly depositing the filamentary material into a recticulate batt and depositing a binder on the surfaces of the filamentary material, the binder comprising a normally solid thermoplastic adhesive activatable at a temperature below the polymer melt temperature of the polymer comprising the filamentary materials;

(C) Heating the batt to a temperature below the polymer melt temperature suflicient to activate the adhesive;

(D) Compressing to consolidate the batt and cooling it while maintaining the compression to deactivate the adhesive and thereby stabilize the batt in its consolidated state, the volume fraction of the filamentary material in the consolidated batt being at least 0.4.

The drawing which accompanies this specification is a flow sheet of the above defined preferred process.

It should be observed that numerous variations in the process of this invention are possible. Thus ordinarily fully expanded microcellular filaments will be used as starting materials; however it is possible to start with collapsed or partially collapsed filaments provided that they become fully expanded prior to cooling the batt to stabilize it in its consolidated state. The filamentary material can be made in fully expanded form in the first instance, in which case it need neither contain an impermeant inflatant nor be post-inflated; or it can be made in collapsed or partially collapsed form with a slowly permeating inflatant in the cells; or a slowly permeating inflatant can be inserted at any time prior to deposition of the thermoplastic adhesive. Where a collapsed filamentary material containing slowly permeating inflatant is used, it will become fully inflated no later than upon heating the batt to dry or activate the thermoplastic adhesive. Known methods for inserting inflatants into the closed cells of microcellular foams either weaken or dissolve the adhesive bonds if carried out after adhesive application. Application of the thermoplastic adhesive can be either before or after deposition of the heat. The batt can be heated to activate the adhesive and then compressed between cold surfaces to consolidate and stabilize it; or the compression and heating can be carried out simultaneously, as in Example 1, provided that the compression is maintained until the batt is cooled and the adhesive is deactivated sufliciently to retain the consolidated condition upon removal of the restraint. These and other variations in the process, e.g. lamination of the batt with other materials and application of dyes, lubricants, and the like will be more fully discussed in the description which follows.

Microcellular filaments are ordinarily prepared by direct extrusion of a foamable composition which, on exit from the extrusion die, becomes fully expanded as each cell wall solidifies to a fixed area. If the inflating gases are subsequently 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 suflicient 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. Fully inflated filaments have volumes of at least about 95% of the maximum volume.

Suitable microcellular filaments should have fully inflated densities in the range from about 0.005 to about 0.05 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. Microcellular filaments useful in this invention should additionally be pliable 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 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 50%, and preferably to substantially 100%, of the original thickness on release of the load.

A particularly desirable microcellular filament is the ultramicrocellular material as disclosed by Blades et al. in US. Pat. No. 3,227,664. Ultramicrocellular filaments have cell walls less than about 2 microns thick in which the polymer is crystalline and exhibits uniplanar orientation and uniform texture as described 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 polymers such as polyvinyl chloride and polyvinylidene fluoride; polyamides such as polyeaprolactam, 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, stereoregular 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.

Fully inflated microcellular filaments can be used either in continuous or in staple form, but staple length of a fully inflated filament should be at least about 20 times its diameter (or other maximum transverse dimension).

The foam-cells of suitable microcellular filaments must be substantially of the closed type in order to remain gas-inflated. Ordinarily, the predominance of closed cells is determined either visually or microscopically. Alternatively, a gas-displacement method may be employed to determine the closed-cell content, such as that described by Remington and Pariser in Rubber World, May 1958, p. 261, modified to operate at the lowest possible pressure differentials.

Whether or not a microcellular filament remains or spontaneously becomes fully inflated after extrusion depends on the rate of permeation of the gases in the cells relative to air (or other ambient gases). If the contained gases permeate the cell walls more slowly than does air, an osmotic gradient for air exists which causes its inward permeation until the filaments become fully inflated. Otherwise, it is necessary to introduce slowly permeating gases to the cells in order to cause full reinflation.

Slowly permeating inflatant gases can be introduced to the closed cells by immersing the microcellular filaments 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 other halogenated methanes and ethanes, especially chlorinated ones but also fluorochlorinated ones having more chlorine than fluorine atoms. 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 slowly permeating gas trapped within the cells. Subsequent equilibration with air causes the filaments to become fully inflated. Ordinarily the internal partial pressure of air at equilibrium is substantially atmospheric, i.e., about 760 mm. Hg. This partial pressure coupled with the partial pressure of more slowly permeating gas already contained creates a super-atmospheric pressure within the cells which causes full inflation. Attainment of or approach to this equilibrium state at commercially attractive rates occurs upon heating the surrounding air to temperatures below the polymer-melt temperature, but preferably above its glass-transition temperature, i.e., ordinarily between about 80 and 175 C. depending on kind of polymer.

'Some 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 super-atmospheric 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 temperatures (i.e., between about and 40 C.) of at least 50 mm. Hg and should be present within the cells in sufficient quantity to provide an internal partial pressure of at least 50 mm. Hg. Preferred impermeant inflatants have atmospheric boiling points less than about 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 infiantants include sulfur hexafluoride, perfluorocyclobutane, 1,2-dichloro-1,1,2,2-tetrafluoroethane, perfluoro-1,3-dimethy1cyclobutane, perfluorodimethylcyclobutane mixtures, 1,1,2 trichloro1,2,2-trifluoroethane, CF CF CF OCFHCF chlorotrifluoromethane, and dichlorodifluoromethane and chloropentafluorethane. Particularly preferred because of inertness, appreciable molecular size, very low permeability rate, and lack of toxicity are perfluorocyclobutadene and chloropentafluorethane with atmospheric boiling points of about -6 C. and about 39 C. respectively.

The presence of impermeant inflatant gas within the foam cells guarantees full inflation of the filaments by providing an osmotic gradient for the inward permeation of air until internal pressures are super-atmospheric. If some air is lost during compression, the filaments thereby spontaneously re-inflate after removal of the load. Foam-filaments containing impermeant inflatant are seen to be durably pneumatic, as opposed to those inflated only with air or with rapidly permeating foaming agents. In practice, a certain minimum concentration of impermeant inflatant is required to provide these advantages. From about 6 to about 40 grams of impermeant inflatant per 100 grams of polymer has proved effective for use in carpet-underlay.

The determination of quantity of confined impermeant inflatant is readily carried out. A foam-filament with impermeant inflatant in its cells and at osmotic equilibrium with air has an internal partial pressure for air of about one atmosphere. Total internal cell pressure exceeds atmospheric by about the partial pressure of the impermeant inflatant. With these conditions, air buoyancy corrections to Weights in air are, at best, only second order. Weight in air, W of an inflated sample is measured. The sample is then reduced between heated platens to a solid, non-foamed film, after which its Weight in air, W is measured. Platen temperatures must, of course, be low enough that no weight change attributable to polymer degradation can occur. Impermeant inflatant content, I, in grams per 100 grams of polymer is then readily computed using Equation 1.

W2 Other physical methods, such as gas chromatography or infrared spectroscopy, can also be used to determine concentration of impermeant inflatant.

Although the consolidated batt preferably comprises microcellular filaments containing impermeant inflatant, in some cases it is sufficient that the filaments only be inflated 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 filamentary material is at or near its maximum volume, which is substantially the same maximum volume (or minimum density) attained immediately after extrusion. For the purpose of this invention, the term fully-inflated is used to indicate that the microcellular filamentary material is inflated to a volume of at least about 95% of the maximum attainable volume. 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 5 minutes immersion in a 50:50 by volume bath of methylene chloride and l,1,Z-trichloro-l,2,2,-trifluoroethane, followed by heating in air at about C., is almost universally applicable.

Fully inflated foam-filaments useful in the construction of the products of this invention have major crosssectional dimensions in the range of 0.01 to 0.25 inch (0.25 to 6.35 mm.) but are preferably in the range from 0.05 to 0.10 inch (1.27 to 2.54 mm.). Although various cross-sectional shapes can be formed, circular ones are usually preferred for which the circular extrusion orifices are easily made.

Before or after the filaments are exposed to thermoplastic adhesive as required, the microcellular filaments are randomly deposited to form a reticulate batt. It has been found that the preferred uniformity of area-weight of microcellular filaments results only when the batt is at least three filament-layers thick, and preferably four or more. In such unconsolidated batts, the microcellular filaments physically occupy less than about 25% of the volume of the batt.

Application of thermoplastic adhesive to the filaments is ordinarily by dipping, spraying, or the like. Dilute liquid solutions or dispersions of the adhesive in a volatile carrier are normally employed in order to satisfactorily distribute the adhesive over all the surfaces of the filaments without excessive pick-up of adhesive solids. Depending on the adhesive and on the diameter of the fully inflated filaments, adhesive-solids pick-ups of from about to 200% of the weight of the microcellular filaments are found satisfactory, and levels of from about to about 50% are preferred. Alternatively, powdered solid thermoplastic adhesive can be dusted onto the filaments.

Before further processing, the filaments are dried by evaporating the volatile carrier. When the adhesive is applied to filaments already deposited in the form of a batt, drying frequently is accomplished simultaneously with the step in which the adhering themoplastic adhesive is activated by heat. Likewise, if the filaments contain inflatant gases but have not been equilibrated in air sufiiciently to attain their fully inflated volumes, this heating step should also result in air-reinfiation to the maximum volumes. Any suitable means of heating may be used, including radiant heaters and circulated hot air. The temperature reached must be high enough to activate the thermoplastic adhesive, but below the polymer-melt temperature of the microcellular material.

With the thermoplastic adhesive activated and the filaments fully inflated, the batt is held sufliciently consolidated between cold surfaces that the filaments are forced to conform around one another, thus greatly increasing the area of interfilament contact. The cold surfaces cause the melted thermoplastic adhesive to resolidify, thus stabilizing the batt in its consolidated state. Obviously, the speed with which stable consolidation is so obtained depends on several factors including: (1) the increment in temperature of the thermoplastic adhesive above its solidification temperature, (2) the temperature of the cold surfaces, (3) the thickness of the batt. As will be apparent, the word cold is used herein to describe the temperature of the consolidating surfaces relative to the temperature of the batt prior to consolidation. Actually, the surfaces can frequently be at or above ambient temperature.

Numerous means for satisfactorily effecting consolidation and cooling exist. The simplest of these involves compressing the batt between smooth, flat, cold, and parallel surfaces. Alternatively, either or both of these surfaces can be deeply engraved to provide a raised pattern of intersecting lines, e.g., diamond-shapes. This disCOn tinuous, step-wise process is useful when one or both surfaces has at least one deeply recessed pattern serving as a mold to produce toys, e.g., molded stufiings for toy animals. Likewise, it is adaptable to consolidating a batt as a layer around items requiring cushioning protection. Preferably, however, the batt is continuously consolidated to an endless sheet-like structure. When short residence times create suflicient cooling, e.g., for thin structures, passage through the nip of cooperating, cold, calender rolls is effective. Longer residence times result on passage through the nip between a conveyor belt and a cold roll wherein the belt is held tightly against a large portion of the roll-surface, which may be smooth or deeply engraved. Still more preferably, passage is through the uniformly thick elongated nip between extended portions of two endless conveyor belts. Supplementary backing of these belts along their nip is ordinarily required for providing sufficient pressure for consolidation While maintaining constant nip-thickness. While smooth belts are effective, preferably either or both is composed of links of deeply engraved or grid-like metal sections.

Suitable thermoplastic adhesives should: (1) adhere to the microcellular material to form elastic bonds; (2) be flexible and non-brittle at normal room temperatures, i.e., from about 15 to about 40 C.; (3) be normally solid, i.e., at temperatures below about 50 C.; and (4) be activated at temperatures above the temperature for use of the cushioning structure but below the polymermelt temperature of the microcellular material.

Numerous materials are satisfactory thermoplastic adhesives. Among them are synthetic organic polymers, such as the well-known dispersions of vinyl resins, including ethylene/vinyl acetate copolymers, ethylene/meth acrylic acid copolymers, and the like. Polyesters, polyolefins, and polyamides of suitable melting point (below the polymer melt temperature of the microcellular filaments) can also be used. Dispersions or solutions of elastomers are particularly effective, these elastomers including certain neoprenes, polyurethanes, and the like. Natural resins which are thermoplastic and of acceptable melt temperature are also suitable.

The specific adhesive employed can be compounded with customary additives including plasticizers, finely divided inert solid extenders, fire-proofing agents, antioxidants, and the like, as are well known.

Particularly preferred for eflicient application of the desired amounts of adhesive are aqueous dispersions containing about 5 to about 40% (preferably 15 to 25%) by weight of adhesive-solids. Dispersions or solutions in non-aqueous volatile carriers are satisfactory provided either that the carrier is not a plasticizing fluid for the polymer or that it is evaporated before it plasticizes the microcellular filaments. Prolonged plasticization results in the loss of some or all of the contained inflating gases.

The process of this invention requires that the microcellular filaments be fully inflated before consolidation. Particularly the plasticizing fluids, but also the impermeant inflatants in some cases, either dissolve or weaken the thermoplastic adhesives. Attempts to introduce inflatants to the filaments of batts constrained to a consolidated state by thermoplastic adhesives, therefore, diminish or remove the constraint. Also, unless the microcellular filaments are fully inflated before consolidation, the filaments are readily collapsed and stabilized by adhesive in the collapsed state. Thereafter, the filaments cannot expand to their full volume and the consolidated batt is denser and less effective as a cushion per unit weight of microcellular material.

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.

A thermoplastic adhesive, as intended herein, is one which can be activated repeatedly simply by heating. An adhesive is activated when it has softened enough to fuse with another contacting portion of adhesive so that, when cooled, a strong adhesive bond results.

A particularly useful aspect of the process of this inven tion is that the product has adjustable degrees of consolidation. By simply heating the batt at a later time, the thermoplastic adhesive becomes reactivated. Thus, the batt can be heated to reactivate the adhesive, expanded to a new, greater thickness (lower density), then cooled to deactivate the adhesive and stabilize the batt at the new thickness. Resolidification can then occur at a new stable batt-thickness. Highly consolidated batts in which the volume fraction of microcellular material is greater than, e.g., 0.8, can be shipped less expensively, to be expanded to a desired greater thickness at the point of use.

Cushioning structures prepared as described herein frequently produce rustling or squeaking noises when cyclically compressed, these noises arising from dynamic interfilament frictional contact. Where required, minor amounts of various silencers effectively overcome the noisiness. Inert, solid powders, such as talc, can be dusted throughout the batt; or the batt can be dipped in or sprayed with lubricants, such as detergentor siliconecontaining liquids, followed by drying. Preferably the talc, lubricant, wax, or other suitable silencer is dispersed with the adhesive before its application to the microcellular filamentary material.

Although this invention has been described primarily as a process for forming sheet-likecushioning structures, molds can be used for consolidation to form molded structures of any shape.

Frequently it is desirable to adhesively bond layers of other materials to either or both surfaces of cushioning structures prepared according to this invention. Such layers include knit, non-Woven, closely woven, and notlike fabrics, foam-foils, metallic foils and continuous polymeric films. Bonding of these layers can be in a separate post-treatment, but advantageously they are applied to the batt-surfaces While the thermoplastic adhesive is activated, and then passed with the batt through the consolidation step so as to become securely bonded to the batt surfaces.

Alternatively, the consolidated batt of this invention can have doctored onto either or both of its faces a foamable composition or an incompletely cured froth of a polymeric elastomer. In this way, self-bonded layers of polyurethane, neoprene, or natural rubber sponges are provided.

By providing a means for stabilizing batts of turgid, pneumatic, microcellular filaments in a consolidated state, the process of this invention makes possible the production of outstanding firm-cushioning structures from said filaments. Such structures are particularly useful as carpet underlay, but are by no means so restricted. Thus, they may be used to construct cushioning containers or cushioning interliners for items easily damaged in shipment. Moreover, the structures are excellent thermal insulators useful in the walls of refrigeration equipment, residential dwellings, cold-weather clothing and the like. Even further, their low density and waterproofness are sueful in constructing buoyancy devices.

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

EXAMPLE I A carpet underlay specimen was constructed according to the teachings of this invention.

The ultramicrocellular polyethylene terephthalate filaments were prepared by extrusion of a uniform foamable solution from a 3-liter cylindrical pressure vessel, through an orifice 0.012 inch (0.305 mm.) in diameter and 0.006 inch (0.152 mm.) long, into the ambient atmosphere. Charged to the pressure vessel were:

Dried polyethylene terephthalate (RV =50) gm 1485 Dry methylene chloride (-25 C.) ml.. 942 Dry 1,1,2-trichloro-1,2,2-trifluoroethane (-25 C.)

Relative viscosity (RV) is the ratio at 25 C. of absolute v-iscosities of polymer solution and solvent. The solvent is a solution of 70 pat-ts of 2,4,6-trichlorophenol in 100 parts of phenol. The polymer solution is 8.7% polyethylene terephthalaite in the solvent,

The solution in the pressure vessel was maintained at about 190 C. under 525 p.s.i.g. (36.9 kg./cm. gage) during extrusion through the orifice. A rotating blade mounted downstream from the extrusion orifice cut the extruded filaments into 5 :1 inch (12.7- L2.5 cm.) staple lengths.

Full inflation was accomplished by immersing the staple for several minutes in a constant-boiling bath composed of methylene chloride and at least 9% perfiuorocyclobutane. his bath boiled at 6 C. under one atmosphere of pressure removed from this bath, the staple was heated for about minutes in an air-oven at 125 It became fully inflated with a diameter of about 0.075 inch (1.90 mm.), a density of about 0.015 gm./cc., and a perfiuorocyclobutane impermeant inflatant content of about 14 grams per 100 grams of polymer (Tmpermeant inflatant level, as given herein, is determined by weighing a fully inflated specimen, by compressing it to a solid film between heated platens, and

by weighing the solid film. The weight of solid film is polymer content, and different between the two weights is content of impermeant inflatant) A dispersion of thermoplastic binder was prepared by mixing Wet parts 51.5% dispersion in water of a 72/28 ethylene/vinyl acetate copolymer with softening point by ASTM E28 (ring and ball) of 310 F. (154.4 C.) 100 Talc (60% solids in water) 100 Extra water 245 This binder-dispersion was finely sprayed onto the staple, the staple was placed in a box with a 15 x 25 inch (38.1 x 63.5 cm.) open top, and the box was placed in an oven at 125 C. until the water in the binder composition had evaporated This treatment also fused the thermoplastic binder so that, when cooled, the staple filaments were bonded at their crossings The cooled Batt was sandwiched between two flexible 0.5 oz./yd. (l7 gm/m?) foils of polypropylene foam. Placed on a metal embossing plate, the assembly was positioned between the fiat plates of a hydraulic press. The embossing plate was constructed with nested diamond-shaped patterns with 1 x 2 inch (2.5 x 5.0 cm.) diagonals which were recessed about 0.5 inch (1.27 cm.) into the plate. The raised embossing lines defining the patterns were about 0.0625 inch (1.59 mm.) wide. The plates of the press were internally steam-heated to a temperature of about 125 C. Holding the uncompressed batt between the plates reactivated the adhesive, whereupon the plates were closed on the batt to a pres-sure of 40 p.s.i.g. (2.8 kg./cm. the steam was turned off, and cold water was circulated Within the plates until their surface temperature reached about 50 C. On removal of the sandwich, it was found to be stably consolidated and to retain the embossed pattern. The foam-foils were securely bonded to both faces, the one on the embossed face conforming precisely to the embossed pattern.

Area-weight of the consolidated carpet-underlay specimen was about 6 oz./yd. (204 gm./m. of which both the ultramicrocellular staple and the binder contributed about 2.5 oz./yd. gm./m. each. Maximum thickness of the rounded humps of the diamond-shaped patterns was about 0.36 inch (0.91 cm.), and minimum thickness along the embossed lines was about 0.07 inch (0.18 cm.). These thicknesses corresponded to densities of about 1.4 lb./ft. (0.022 g-m./cc.) and 7.2 lb./ft. (.115 gm./cc.) respectively.

EXAMPLE II Ultramicrocellular polyethylene terephthalate staple was used to prepare another carpet-underlay specimen. All operations and characterizations were as described in Example I except that:

(1) The post-inflated filaments contained about 15 gm. of perfiuorocyclobutane per gm. of polymer;

(2) Components of the binder composition were Wet parts 50% dispersion in water of a 67/33 ethylene/vinyl acetate copolymer with softening point by ASTM E 28 (ring and ball) of 240 F. (115.6 C.) 390 Talc (60% solids in water) 332 Extra water 1300 (3) Neither face was covered with a foam-foil; and

(4) Consolidation was between the flat plates of the hydraulic press without an inserted embossing plate.

The stably consolidated flat product was about 0.363 inch (0.922 cm.) thick with a density of about 0.84 lb./ft. (0.0135 gm./cc.) of which about 57% was contributed by foam-filaments and 43% by the binder. The specimen was about 13.5 inches (34.3 cm.) wide and 22 inches (55.9 cm.) long. A number of flat carpet-underlay specimens were similarly constructed with their faces bonded to surfacing layers including kraft paper, polymeric films, foam-foils, net-like fabrics, non-woven fabrics, and carpeting.

EXAMPLE III This example illustrates that a cushioning structure prepared according to this invention can later be re-expanded to a greater thickness by a simple heat treatment.

Materials and procedures used in this example were as described in Eample II. The specimen prepared was 13.25 inches (33.6 cm.) 'Wld6 and 21.5 inches (54.6 cm.) long. It-s consolidated thickness was 0.237 inch (0.602 cm.) at a density of about 1.88 lb./ft. (0.030 gm./cc.), of which about 55.6% was contributed by foam-filaments and 44.4% by binder. Two rigid expanded-metal plates were clamped over spacers to provide an opening of about 0.75 inch (1.90 cm.), and the specimen was slipped into the space between the plates. Heating the assembly in an air-oven at 125 C. activated the thermoplastic adhensive and allowed the batt to fill the available space. Rebonding occurred on cooling to room temperature, and the specimen finally obtained was stably consolidated at a thickness of about 0.75 inch (1.90 cm.) and at a density of about 0.595 lb./ft. (0.0096 gm./cc.).

EXAMPLE IV Fully inflated, staple filaments as described in Example I were sprayed with an adhesive dispersion, laid down by hand into a random batt 3 inches (7.6 cm.) wide and 2 feet (61 cm.) long, and dried. Total area-weight of the dried batt was about 3.5 oz./yd. (187 gm./m. of which the adhesive solids contributed about 1.0 oz./yd. (34 gm./m.

The adhesive dispersion employed contained the following components:

Wet parts 42% emulsion in water of an ethylene/methacrylic acid/vinyl acetate (83/6.9/10.l) terpolymer partially neutralized with caustic to an ionomer 476 33% emulsion in water of ethylene-bis-stearamide (melting point, l42144 C.) 45 Talc (60% dispersion in water) 166 Extra water 576 The bonded batt was stably consolidated and embossed on passage through the nip of a roll-belt embossing unit. The l-foot (30.5 cm.) diameter roll had attached to its surface two sets each of 8 parallel helical fins extending about 0.31 inch (0.79 cm.) radially and being about 0.062 inch (0.16 cm.) wide. The two sets of fins intersected to provide a nested diamond pattern with 8 rows of diamonds having about 2 x 1 inch x 2.5 cm.) diagonals. The roll was at room temperature, and the moving belt was mounted to form a nip around one-half of the circumference of the roll.

Just before being fed to the nip of the roll-belt unit, the batt was heated by air ejected from a hot-air gun, thus activating the thermoplastic adhesive. Peripheral speed of the roll was about 20 ft./min. (6.1 m./min.) giving a contact time in the nip of about 5 secs. Passage through the nip resulted not only in stable consolidation of the batt but also produced a stable, deeply embossed, diamond pattern on its surface.

EXAMPLE V Staple, fully inflated, microcellular filaments substantially as described in Example I were further cut into staple lengths of about 1.0 inch (2.5 cm.). They were sprayed with the adhesive dispersion of Example IV modified only by the addition of 4 parts of a blue dye. Filament-to-adhesive solids weight ratio was about 10:1. A layer of adhesive wet filaments was placed over the bottom of a cardboard box, an Erlenmeyer flask, a bottle,

and a metal cone were set on this layer, the box was stuffed full of the remaining wet filaments, and the top was closed. The closed box was placed in an air oven at 125 C. until all the water had evaporated, simultaneous- 1y rendering the adhesive activated. On cooling, the batt had formed a stable cushioning block with the inner shape of the box. Removal of the glass and metal objects showed the batt had conformed exactly to them. This demonstrates the utility of the invention in forming molded life jackets, toys, pillows, packages, etc.

EXAMPLE VI A highly consolidated bonded batt prepared with the materials and methods described in Example II was about 0.32 inch (0.82 cm.) thick with an area-weight of about 2.75 oZ./yd. (93.3 gnm/m?) of which about 0.75 oz./yd. (25 gm./m. was adhesive solids. It was placed between a net-like scrim fabric and an ordinary cotton fabric and sewed over its whole face with intersecting stitch-lines forming diamonds with 2 x 2 inch (5 x 5 cm.) diagonals. Heated in air at 125 C. for about 1 minute, the batt bulged in the areas between stitch-lines to create a quilted effect, thickness remaining substantially unchanged along the stitch-lines.

What is claimed is:

1. A process for making a structure useful as a firm cushioning material which comprises the steps:

(A) randomly depositing microcellular filamentary material to form a reticulate batt, the filamentary material containing within the closed cells thereof between about 6 and 40 grams of an impermeant inflatant per grams of polymer, and depositing a binder on the surfaces of the filamentary material, the binder comprising a normally solid thermoplastic adhesive activatable at a temperature below the polymer melt temperature of the polymer comprising the filamentary material;

(B) heating the batt to a temperature below the polymer melt temperature sufiicient to activate the adhesive and to assure full inflation of the filamentary material;

(C) compressing to consolidate the batt and cooling it while maintaining the compression to deactivate the adhesive and thereby stabilize the batt in its consolidated state, the volume fraction of the filamentary material in the consolidated batt being at least 0.4.

2. A process as defined in claim 1 wherein at least one layer of another material is applied to at least one surface of the batt while the adhesive is activated and is passed with the batt through the consolidation step, whereby the other material becomes securely bonded to the batt surfaces, the other material being selected from knit, nonwoven, closely woven and net-like fabrics, foam-foils, metallic foils and continuous polymeric film.

3. A process as defined in claim 1 wherein the volume fraction of filamentary material in the consolidated batt is at least 0.8.

4. A process as defined in claim 1 followed by the steps of:

(E) reheating the batt to a temperature below the polymer melt temperature to reactivate the ahersive;

(F) expanding the batt to a new, lower density; and

(G) cooling to deactivate the adhesive and re-stabilize the batt at the lower density.

5. A process as defined in claim 1 followed by the step of adhesively applying at least one layer of another material to at least one surface of the stabilized batt, the other material being selected from knit, non-woven, closely woven and net-like fabrics, foam-foils, metallic foils and continuous polymeric film.

6. A process as defined in claim 1 followed by the step of coating at least one surface of the batt with a poly- {neric elastomer froth then curing to form a self-bonded ayer.

7. A process as defined in claim 1 wherein the binder is deposited on the filamentary material before formation of the batt.

8. A process as defined in claim 1 wherein the binder is deposited on the filamentary material after formation of the batt.

13 14 9. A process as defined in claim 1 wherein the batt is dated state, the volume fraction of the filamentary embossed at the same time it is compressed. material in the consolidated batt being at least 0.4.

10. A process for making a structure useful as a firm cushioning material which comprises the following steps: RefereIlQeS Cited (A) randomly depositing inflated microcellular fila- 5 UNITED STATES PATENTS mentary material in the form of a reticulate batt and depositing a binder on the surfaces of the filamentary gl g 5% material, the binder comprising a normally solid ther- 3179551 4/1965 d mon 156 209 X moplastic adhesive activatable at a temperature be- 3180778 4/1965 P T'j-T 311 low the polymer melt temperature of the polymer m erspac er 6 a 10 3,227,664 1/1966 Blades et al. 26()2.5 comprising the filamentary material,

3,278,954 10/1966 Barhlte l6ll70 X (B) heating the batt to a temperature below the poly- 3 344 221 9/1967 M d t l 161 159 X mer melt temperature sufficient to activate the ad- 00 y e a lliezsiiitelsiaaind to assure full inflation of the filamentary SAMUEL ENGLE Primary Examiner (C) compressing to consolidate the batt and cooling it Us CL while maintaining the compression to deactivate the adhesive and thereby stabilize the batt in its consoli- 156' 209= 311; 161159: 178