US3471610A - Process for making a firm cushioning structure - Google Patents

Description

Oct. 7, 1969 F. s. SADEK 3,471,610

' PROCESS FOR MAKING A FIRM CUSHIONING STRUCTURE Filed Feb. 20. 1967 DEPOSIT PARTIALLY EXPANDED NICROCELLIILAR FILANENTARY NATERIAL TO FORM A BATT "m OPPOSIIG ENBOSSING SURFACES T0 mm 20% 0F POLYMER um TEMPERATURE CONSOLIDATE BOND, AND ENBOSS BATT BY CONPRESSINC BETWEEN ENBDSSINC SURFACES RENOVE AND COOL STABLY CONSOLIDATED. ENBOSSED BATT FULLY IN FLATE BATT BY INTRODUCING CASEDUS INFLATANT INTO CLOSED CELLS INVENTOR mm s SADEK ATTORNEY 3,471,610 PROCESS FOR MAKING A Fll CUSHTONING STRUCTURE Fawzy S. Sadek, Green Acres, Wilmington, DeL, as-

signor to E. 1. du Pont de Nemours and Company, Wilmington, DeL, a corporation of Delaware Filed Feb. 20, 1967, Ser. No. 617,319 Int. Cl. 132% 27/00 U.S. Cl. 264321 7 Claims ABSTRACT OF THE DISCLOSURE A process for making structures suitable for firm cushioning applications, such as carpet underlay, is disclosed. Partially expanded microcellular filaments are randomly deposited into a reticulate batt. The batt is then thermally embossed and consolidated by pressing it between opposing embossing surfaces heated to approximately the polymer-melt temperature. The batt is removed and cooled, then inflated by introducing an inflatant into the cells of the filaments.

BACKGROUND OF THE INVENTION This invention relates to cushioning structures composed of randomly disposed pneumatic microcellular filamentary material and more particularly to a novel process for preparing these structures which involves consolidating, embossing, and thermally bonding a reticulate batt of randomly disposed, partially inflated microcellular filamentary material, and thereafter fully infiating the filamentary material.

A microcellular filament is a predominantly closedcell foam in filament form. It is substantially homogeneously foamed throughout to provide polyhedral-shaped foam-cells enclosed by cell walls which are thin, filmlike elements of a high molecular weight, film-forming, thermoplastic polymer, ordinarily a synthetic organic polymer. Although the outer surface of a microcellular filament is smooth and substantially continuous, close examination reveals that it is composed of cell walls and is not a separately identifiable skin or casing of dense, unexpanded polymer. On the average, the maximum transverse dimension of foam cells in a microcellular filament should not exceed about 1000 microns, and cellwall thickness should be less than about 2 microns.

Microcellular filaments are preferably prepared by direct extrusion of a foama-ble composition through filament-forming orifices under conditions such that the cell walls solidify to subsequently fixed areas while the cells are fully expanded. A particularly preferred process is that disclosed by Blades and White in US. Patent No. 3,227,784, but this invention is in no way restricted to any one method for preparing suitable microcellular filaments. After cell-wall solidification, the density of a microcellular filament is largely determined by how much inflatant gas is retained within its closed cells. A fully expanded filament contains within its cells sufficient inflatant gases at at least atmospheric pressure to make the cell walls taut and to provide a filament-volume which is at least 95% of its maximum attainable volume, i.e., the volume at the point of cell-wall solidification during filament preparation. As inflatant gases are lost from or removed from the cells internal pressures decrease until the force of the external atmosphere is great enough to decrease filament volume by wrinkling and folding of the cell Walls. A microcellular filament is said to be collapsed if its volume is less than 25 of its maximum attainable volume. Varying degrees of partial collapse or partial expansion are represented by filament volumes between 25 and 95% of the maximum attainable volume,

nited States Patent and, for the purposes of this invention, volumes between about 25% and about of the maximum are preferred.

Fully expanded microcellular filaments are turgid and pneumatic, and they exhibit excellent resilient cushioning properties. These properties derive almost totally from the compressible gases within the closed cells since the densities of the filaments and their cell wall thicknesses are too low to provide significant load support from the polymer. Excellent soft cushions result when fully expanded microcellular filaments are deposited in the form of a random batt with numerous crossings of filament portions, particularly if adhesive bonds are created at the points of interfilament contact to prevent their spontaneous rearrangement during repeated compressive loadings. Such cushioning structures are ideally suited to upholstery cushioning such as in chairs, mattresses, and the like. They are soft because only the very small quantity of gases at the widely scattered points of filament crossings is initially compressed. Since the turgid, pneumatic filaments are too stifi and too light to drape or bend around one another, the microcellular filaments usually occupy less than 25 of the volume of the batt.

Some cushioning materials, in particular carpet underlays, must support relatively large loads while retaining residual compressibility; and they must simultaneously be relatively thin, e.g., between about 0.25 and 0.75 inch (0.63 and 1.90 cm.) thick. When fully expanded microcellular filaments are randomly deposited into a batt and consolidated until the volume of microcellular material exceeds about 40% of the volume of the structure, the consolidated structure exhibits firm-cushioning properties ideally suited to, for example, carpet underlay. Consolidation forces the turgid filaments to conform around one another, thus increasing the extent of interfilament contacts and the volume of gases, relative to the volume of the consolidated batt, which can resist further compression.

It is necessary not only to consolidate the batt but also to provide a mechanism for constraining it in the consolidated state after removing the consolidating force. This is difficult to achieve because: (1) pneumaticity of fully expanded filaments re-expands the consolidated structure unless the constraint is set before release of the consolidating pressure; (2) heating the filaments to render them self-adhesive can cause the loss of inflatant gases; (3) turgid, fully expanded filaments are shattered or cut by too rapidly or too severely applied forces of consolidation; (4) localized thermal treatments sufficient to melt portions of the filaments readily cut through them due to their very low density (i.e., between about 0.005 and 0.05 gm./cc.); and (5) prolonged thermal treatment can decrease or destroy the ability of the closed cells to retain inflatant gases.

SUMMARY OF THE INVENTION This invention provides a process for manufacturing stably consolidated reticulate batts comprising randomlydisposed, fully expanded microcellular filamentary material. This process effectively overcomes the problems of constraining the turgid pneumatic filaments in a consolidated state wherein less than but more than 40% of the volume of the batt is occupied by the microcellular filaments.

The novel process of this invention comprises the following steps:

(1) Randomly depositing partially expanded microcellular filamentary material into a reticulate batt, said filamentary material being expanded to more than about 25% but less than about 85% of its maximum attainable volumes;

(2) Heating to within about :20" C. of the polymermelt temperature of the polymer of which the microcellular filamentary material is comprised at least one of two opposing surfaces arranged to consolidate said batt, at least one of said surfaces being deeply engraved to provide raised line elements surrounding deeply recessed geometric shapes;

(3) Consolidating said batt by compressing it between said opposing surfaces until the density of filamentary material along said line elements is at least 50% of the density of said non-expanded solid polymer, the consolidated batt having a maximum thickness, in areas corresponding to the centers of said deeply recessed geometric shapes, at least times greater than along said line elements;

(4) Maintaining the consolidated state of step (3) until the filament portions contacted by said raised line elements fuse sufficiently to retain their reduced thickness;

(5) Removing said batt and cooling it to solidify the polymer along the lines of fusion; and

(6) Introducing to the closed cells of the portions of microcellular filaments surrounded by lines of fusion sufficient normally gaseous infiatant to provide at least atmospheric pressure within the cells and to render said portions fully expanded.

BRIEF DESCRIPTION OF THE DRAWING FIGURE 1 is a schematic representation of the process of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The basic discovery of this invention is that partial expansion of microcellular filaments is necessary to successful thermal embossing, as described. If collapsed microcellular filaments are employed during thermal embossing, cell walls are so close together and resistance to heat flow is so low that sufficient fusion along the embossed line elements also causes fusion Within the geometric shapes and prevents subsequent full expansion of the filament portions therein. On the other hand, fully expanded filaments are so turgid that the embossing lines shatter and tear the filaments along those lines. Partially expanded filaments contain enough infiatant gases to prevent polymer fusion within the geometric shapes by improving thermal insulation and by physically separating adjacent cell walls, but they are not so turgid as to shatter when subjected to severe compression during embossing.

Microcellular filaments useful in the process of this invention should, in addition to requirements given hereinbefore, be resilient such that substantial deformation occurs under externally applied compressive loading. Generally, this requirement is satisfied if the fully expanded filament is reduced in thickness by at least 10% under a load directed perpendicular to the filament axis and selected to exert 10 p.s.i. (0.70 kg./cm. on the area computed from length and diameter of the uncompressed filament, the load being maintained for one second. Additionally, there should be an immediate thickness-regain to at least 50%, and preferably to 100%, of the original thickness on removal of the load. Filaments less resilient than this are too rigid to respond to available pressure differentials causing full expansion.

Suitable microcellular filaments should also have densities from about 0.005 to about 0.05 gm./ cc. in the fully expanded state. Useful diameter for such fully expanded filaments is generally in the range from about 0.01 to about 0.25 inch (0.25 to 6.35 mm), but diameters between 0.05 and 0.10 inch (1.27 and 2.54 mm.) are preferred. A particularly desirable type of microcellular filament is ultramicrocellular as described in US. Patent No. 3,227,664. Not only do ultramicrocellular filaments possess all the above preferred properties, but also their cell Walls exhibit uniplanar orientation and uniform texture as described in the patent. These two properties provide the surprisingly great strength of the filaments and render them particularly impermeable to most gases.

A wide variety of both addition and condensation polymers can form cellular structures 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 polycaprolactam, polyhexamethylene adipamide, and polymetaphenylene isophthalamid; polyurethanes such as the polymer from ethylene bischloroformate and ethylene diamine; polyesters such as polyhydroxypivalic acid and polyethylene terephthalate; and copolymers such as polyethylene terephthalateisophthalate.

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.

Ordinarly the easiestway to determine the maximum attainable volume of a microcellular filament is to observe its diameter at the point of maximum size immediately following its extrusion. Alternatively, it may be immersed in a boiling refluxing liquid bath composed of a plasticizing fluid and an impermeant inflatant (both as defined hereinafter), removed, and heated in air until diameter increases no further. About 5 minutes immersion in such a bath composed of methylene chloride and 1,1,2-trichloro-1,2,2-trifluoroethane (50:50 volume) followed by heating in air at about C. is almost universally applicable.

Partially expanded microcellular filaments, regardless of how they are obtained, are randomly deposited by any convenient method into a reticulate batt. Numerous crossings of filament portions exist in such a batt. Either continuous or staple filament may be employed, but staplelengths should preferably be at least 20 times filament diameter. In order to provide the desired uniformity in area weight of microcellular material, the batt should be at least three filaments thick, regardless of the degree of consolidation.

The two surfaces between which the batt is to be consolidated can be parallel, broad, and generally plane. When relatively low rotational speeds are acceptable, the nip between two cooperating rolls can also be employed for consolidation according to this invention. At least one of the two surfaces is deeply engraved to provide a raised pattern of intersecting lines surrounding deeply recessed geometric shapes, e.g., diamonds, triangles, rectangles, hexagons, etc. If the shapes are too small, all of the batt becomes over-consolidated; if too large, the constraint along the lines is insufficient to hold the centers of the shapes consolidated. Generally, the size requirements of the geometric shapes are satisfied if each line element defining a geometric shape and measured between its intersections with two other line elements is at least about 5 but no greater than about 30 times the diameter of the fully expanded filaments. When both of the surfaces are deeply engraved, their patterns should be identical and in register line-to-line and shape-to-shape. In use, the two surfaces are brought close enough together that the microcellular material along the embossed lines is raised to a density of at least 50% of that of the non-foamed solid polymer. Maximum batt thickness at the centers of the outlined patterns should be at least 5 times the minimum thickness along the embosed lines, and it is pre- T. W. Campbell in Preparative Methods of Polymer Chemistry, Interscience Publishers, Inc., New York, 1961, pp. 49 and 50.

The heated surfaces are closed to produce the degree of consolidation previously described, and the consolidated state is maintained until the polymer along the line elements has fused not only along the outer surfaces of the filaments but also at wall-to-wall contacts of their inner cells so that those portions remain compressed and non-expandable. Temperature of the consolidating surface is critical in this step. If higher than the value specified, the material along the line elements becomes so fluid that it is displaced, resulting in cutting along the lines rather than just consolidation. Simultaneously, excessive temperatures cause melting of polymer within the geometric shapes so that those filament portions cannot later become fully inflated. If temperature of the consolidating surface is too low, microcellular material along the line elements is insufficiently fused to remain consolidated during subsequent inflation or use. Heating and consolidation should be continued only about the minimum time necessary to cause the batt to remain consolidated on removal of the consolidating force, Thereafter, the consolidated batt is removed and cooled by any convenient method.

The process of this invention is completed when sufficient inflatant gases have been introducd to the closed cells to render the microcellular filaments fully expanded with at least atmospheric pressure Within their cells. Those filament portions along the fused lines are, of course, non-expandable; and the lines of fusion tie down filament portions passing through the thicker geometric shapes so that their expansion causes them to bend, drape, and buckle around one another into a consolidated state characterized by a volume of fully expanded microcellular material which is at least 40% of the volume of the batt. Some filament portions immediately adjacent the embossed lines may not reach full expansion, but at least a major part of the filamentary material in the final structure is fully expanded however much of its cross-sectional shape may be distorted.

Preferably, the fully expanded microcellular filaments in the cushioning products prepared according to this invention contain in their inflatant gases from about 6 to about 40 grams of impermeant inflatant per 100 grams of polymer. The remaining inflatant gas is ordinarily that of the surrounding atmosphere, i.e., air. An impermeant inflatant is a normally gaseous compound which permeates the cell walls so slowly as compared to air that it is substantially permanently retained within the closed cells.

Presence of an impermeant inflatant within the closed cells results in several distinct benefits. First, it provides an osmotic gradient for the inward permeation of air so that, even if air diffuses out during compression, at microcellular filament spontaneously re-expands in air. Secondly, air permeates into a closed cell containing impermeant inflatant until, at equilibrium, the partial pressure of air is substantially the same as the air pressure in the surrounding atmosphere. The total equilibrium gas pressure within the cell then exceeds atmospheric pressure by about the partial pressure of the contained impermeant inflatant, and the combined super-atmospheric pressure not only fully expands the filament but also contributes turgidity and high pneumaticity. As is clear, presence of impermeant inflatant provides durable pneumaticity and essentially indefinite retention of the excellent cushioning properties.

Candidates for impermeant inflatants should have vapor presures at normal room temperatures of at least about 50 mm. Hg. Preferred impermeant inflatants have atmospheric boiling points less than about 25 C. Full expansion and durable cushioning properties result generally from impermeant inflatant contents in the range from about 6 to about 40 grams per grams of polymer.

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 sulfurhexafluoride, perfluorocyclobutane, 1,2-dichloro-l,1,2,2-tetrafluoroethane, perfluoro-1,3-dimethylcyclobutane, perfluorodimethylcyclobutane mixtures, l,l,2-trichloro-l,2,2- trifluoroethane, chloropentafluoroethane,

chlorotrifluoromethane, and dichlorodifluoromethane. Particularly preferred because of inertness, appreciable molecular size, very low permeability rate, and lack of toxicity are perfluorocyclobutane with an atmospheric boiling point of about 6 C. and chloropentafluoroethane with an atmospheric boiling point of about 39 C.

Normally gaseous inflatants which permeate cell-walls more slowly than air but too quickly to be substantially permanently retained withi nthe cells are called temporary inflatants. Suitable temporary inflatants are chemically similar to impermeant inflatants but generally: (1) are not necessarily perhalogenated, (2) have more chlorine than fluorine atoms in their molecules, and/ or (3) have more carbon than fluorine atoms. They can be introduced to the cells of microcellular filaments exactly as are impermeant inflatants. Because temporary inflatants permeate out from the cells more slowly than air permeates inward, their presence causes the necessary osmotic gradient for full expansion of the filament 0n equilibration with air. They are subsequently lost by permeation in times short with respect to the life of, for example, a carpet underlay and do not provide for spontaneous reinfiation in use or for the indefinite retention of cushioning properties. Thus, while temporary inflatants are satisfactory for the practice of this invention, impermeant inflatants are preferred.

If the partially expanded microcellular filaments used in preparing consolidated batts already contain the desired 6 to 40 gm. of impermeant or temporary inflatant, a simple air-exposure step causes the filaments to fully expand. Otherwise, it is necessary first to introduce impermeant or temporary inflatant to the closed cells. [Hereinafter temporary inflatants are also intended when only impermeant inflatant is specified] Introduction of impermeant inflatant results when the batt is exposed to a plasticizing fluid and, while the cell-walls are still with and plasticized by plasticizing fluid, is treated with impermeant inflatant. Both plasticizing fluid and impermeant inflatant can be either gaseous or liquid in this treatment, but the liquid phase is preferred. So treated, the filaments become fully inflated after equilibration with air. Temperature of the air during equilibration must be well below the polymer-melt temperature but preferably above the glass-transition temperature. Depending on the polymer, lair-temperatures from about 80 to about 175 C. are effective. Even more rapid inflation results if the heated air passes over the filament surfaces at velocities of from about 100 to about 2000 ft./min. (30.5 to 610 m./min.).

A plasticizing fluid is a compound which: (1) is readily volatilized; (2) has small molecules which permeate cell walls much faster than air; (3) is chemically nonreactive with the microcellular filament; (4) is a nonsolvent for the polymer at or below fluids atmospheric boiling temperature; and (5) interacts sufliciently with the polymer to plasticize (i.e., swell) it. Methylene chloride frequently meets all of these requirements. While plasticized, the cell-walls are temporarily much less resistant to permeation, and impermeant inflatants are readily introduced to the cells. On removal of the batt from these fluids, plasticizing fluid is quickly volatilized by any convenient method to leave impermeant inflatant trapped within the cells; and air-equilibration causes full expansion.

Various alternative additional process steps can be added to the basic process of this invention for producing firm-cushioning products with particular properties or utility. For instance, thermoplastic webs, films, and fabrics, or thermoplastic foam-foils can be layered over one or both faces of the batt before consolidation, being fused to the batt at the subsequently imposed embossed lines. Any of these layers can be adhesively bonded to the faces of the fully expanded product; or various froths of elastomeric polymers, e.g., polyurethanes, neoprene, natural rubber, etc., can be spread onto one or both faces and then cured into a self-adhering, open-celled, sponge layer. Moreover, the fully expanded cushioning structure can be flocked with carpet pile or adhesively bonded to the under-surface of a carpet.

Sometimes batts produced by this invention are noisy in use; i.e., interfilament frictional contacts cause squeaky sounds. Immersion of the batt in various silencers overcomes this difliculty, such silencers including dispersions or solutions of detergents, silicones, and the like. A particularly effective silencing treatment is that of dipping the batt in, or spraying it with, an aqueous dispersion of elastic adhesive. Adhesives so applied must not fill the interfilament openings of the batt but should coat at least the areas causing noises. Waxes and dry powders can be compounded with the adhesive for further improved silencing. Moreover, it is advantageous to compound dyes with the adhesive in order to create cushioning structures with various colors. Additional post-treatments are apparent to one skilled in the art.

Although cushioning structures prepared according to this invention are particularly useful as carpet underlay, many other cushioning applications are served, for example, as walls or interlayers in packages for shipping fragile items. In addition to cushioning, the batts are also excellent thermal insulators of use in refrigerated containers or in the walls of residential construction. Other uses are immediately apparent.

The following examples are intended to illustrate the invention but are not intended to limit it, except as provided by the appended claims. All parts and percentages are by weight unless specified otherwise.

Example I Ultramicrocellullar polyethylene terephthalate filaments 8 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 trephthalate (RV =50) .gm. 1485 Dry methylene chloride (-25 C.) ml. 942

Dry 1,1,2 trichloro 1,2,2 trifluoroethane (-25C.) ml. 162

Relative viscosity (RV) is the ratio at 25 C. of absolute viseosities of polymer solution and solvent. The solvent is a solution 0,: 70 parts of 2,4,6-trichlorophenol in 100 parts of plllielnol. The polymer solution is 8.7% polyethylene terepht a ate.

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. The extruded filaments retained about 8 to 9 gm. of l,1,2-trichloro-1,2,2-trifluoroethane per 100 gm. of polymer in their closed cells, which level of impermeant inflatant prevented extreme collapse. Density of the extruded filaments was in the range from 0.05 to 0.07 gm./cc. A portion heated for several minutes at about 125 C. in air became fully expanded to a diameter of about 0.070 inch (1.78 mm.) at a density of about 0.020 gm./cc. Ratios of these densities show the extruded filaments had a volume of between 30 and 40% of the maximum attainable volume, i.e., were partially expanded. The fully expanded filament had a smooth surface, a round cross-section, and no skin of dense polymer other than that in exposed thin cell walls. The average transverse dimension of the foam-cells was about 22 microns.

The partially expanded ultramicrocellular filaments were collected randomly but uniformly on a moving screen belt. Velocity of the belt was varied to produce batt-lengths of differing area-weight. On the belt, the batt passed continuously through the nip of a roll exerting about 2.0 lb./in. (0.36 kg./cm.) of width. The lightly consolidated batt was rolled up between layers of kraft paper, held about 25 minutes, and then thermally embossed.

Embossing was between the plates of a flat-bed press. To one of the plates was fastened a deeply engraved embossing plate having a repetitive, nested, diamond design with 2x1 inch (5.08X2.54 cm.) diagonals and extending to 0.5 inch (1.27 cm.) deep into the plate. Separating adjacent diamond-shaped openings were raised line elements nominally 0.0625 inch (0.159 cm.) wide. The other plate of the press was plane-surfaced. Both plates were pro-heated to about 250 C. The plates were closed on the batt to a pressure (averaged over the whole area of the batt) of 45 p.s.i. (3.2 kg./cm. and held closed for a time depending on area-weight of the batt. At 2.5-3.0 oz./yd. (-102 gm./m. about 15 sec. was optimum, increasing to 30 sec. at 5.0 oz./yd. (170 gm./ m. Successful deep embossing and permanent consolidation resulted over a press-plate temperature range of 250:20 C., i.e., near the polymer-melt temperature of the foamed polymer.

Samples of a range of area-weights were cut from the above thermally consolidated products, each 11 x 16 inches (27.9 x 40.6 cm.). These samples were placed in a large autoclave containing 2 liters of methylene chloride. Eight pounds (3.63 kg.) of perfluorocyclobutane were then transferred to the closed autoclave. Heated to 55:2 C., autoclave pressures rose to :5 p.s.i.g. (6.3 to 7.0 kg./cm. gage). Liquid level was below the samples, but a circulating pump showered the mixed liquid over the samples for 5 minutes. The liquids were then blown from the autoclave, and the samples were removed. Heating for 15 minutes in an air-circulating oven at 125 C. caused the filament portions within the diamond shapes to fully inflate, and these were found to contain 15:2 grams of perfluorocyclobutane impermeant inflatant per gms. of polymer.

To silence the noise of these carpet underlay samples, they were dipped in a silencer solution, drained, and

in thickness. The values shown in Column 8 were computed by multiplying the 4 in. load by (50/4).

TABLE I.THERMALLY CONSOLIDATED AND EMBOSSED UNDERPAYMENT Area Weight [z./yd. (gm. /m. Percent Compression Sample Silencer Thlckness at 25 p.s.i. or Number Color Total Filament and Latex [inch-(cm.)] at 1.76 kg./(:1.r1. R.M.A.

Golden Yellow--- 6.7 (227) 4.2 (142) 2.5 (85) .51 (1.29) 63 161 d 6. 2 (210) 4. 0 (136) 2. 2 (75) 46 (1. 17) 65 167 5. 5 (187) 3. 5 (119) 2.0 (68) .49 (1.2 70 79 7. 1 (241) 4. 6 (156) 2. 5 (85) 57 (1. 45) 56 225 5.9 (200) 4.0 (136) 1.9 (64) 43 (1.09 61 152 5. 8 (197) 3. 8 (129) 2. 0 (68) 48 (1. 22) 67 121 5.3 (180) 3. 5 (119) 1.8 (61) 46 (1.17 68 144 3.7 (126) 3.0 (102) 0.7 (24) 43 (1.09) 79 71 4.4 (149) 3.5 (119) 0.9 (31) 43 (1.35) 72 73 5.6 (190) 3. 1 (105) 2. 5 (85) 55 (1.40) 68 141 4.0 (136) 2.2 (75) 1. 8 (61) 47 (1. 19) 76 70 4.5 (153) 2.4 (81) 2.1 (71) 47 (1.19) 60 163 dried for 30 minutes in an air-clrculatlng oven at 125 C. Example 11 Such samples are denoted 11 and 11a in Table I. The silencer solution was composed of 9 parts of a 40% emulsion in water of approximately equal parts of poly-(dimethylsiloxane) and poly-(methylsiloxane), 1 part of Dow corning Catalyst 21 (apparently a mixture of dibutyltindilaureate and of the zinc salt of 2-ethyl hexoate) and 90 parts of distilled water.

Alternatively, the thermally consolidated structures were immersed in a latex dispersion, dried minutes at 125 C. in air, and then given the above silencing treatment. Less of the expensive silencer was picked up this way, and pigment dispersed in the latex dispersions imparted deep coloration to the otherwise white samples. Samples 10, 10a-f, 12, 12a, and 12b of Table I were so prepared. In no case was latex pick-up .sufiicient to significantly decrease the volume of interfilament openings in the samples. The latex dispersion was a preparation containing 3 components obtained from the Alco Chemical C0.

Parts Foamtol BGL-9002 latex dispersion (58% in water of a mixture of 70 parts of natural rubber and parts of butadiene/ styrene (75/25 co These three components were dispersed in '900 parts of a surfactant solution prepared from 100 parts of Du Pont Aquarex ME surfactant (sodium salts of sulfate monoesters of mixed higher fatty acids), 10 parts of Dewey & Almey -Co.s Daxad l1 dispersion agent (polymerized sodium salts of alkyl aryl and aryl alkyl sulfonic acids), and 890 parts of distilled water.

Although not represented by entries in Table I, a particularly elfective silencing of these structures results if they are sprayed with or dipped in dilute water dispersion of ethylene/vinyl acetate copolymer resins and talc.

Column 1 of Table I lists the sample numbers as previously referred to. Column 2 lists colors obtained by incorporation of dyes in the latex dispersons. Columns 3, 4 and 5 present area-weights in the units shown. Values in parentheses are for the units shown in parentheses. Column 6 lists effective thickness, i.e., maximum thickness near centers of the thick geometric shapes. Column 7 is the percent reduction in thickness of an area held compressed by a 100 lb. (45.4 kg.) load applied by a 4 in. (25.8 cm?) round indentor. R.M.A. is a traderecognized abbreviation for the load in pounds on a 50 in. (322.6 cm?) indentor to produce a 25% decrease Ultramicrocellular polyethylene terephthalate filaments were prepared by extrusion of a uniform solution of the polymer in methylene chloride through an orifice, 0.020 inch (0.51 mm.) in diameter and 0.040 inch (1.02 mm.) in length, into the ambient atmosphere. The dried polymer (RV=63.9) constituted about 70% of the extruded solution. Solution temperature was about 220 C., and it was under a pressure of about 700 p.s.i.g. (49.2 kg./cm. gage). Immediately adjacent the exit surface of the extrusion orifice, the filaments were fully expanded and solidified by rapid vaporization of the methylene chloride. Thereafter, the filaments collapsed, as methylene chloride permeated out much faster than air could permeate in, to a volume of from 15 to 20% of the maximum attainable volume.

Batts of collapsed filaments were laid down on a wire mesh screen and covered by a flat aluminum plate for light consolidation. Area-weights of filaments were in the range shown in Table 1. One batt was consolidated by embossing between the plates of apress, each plate heated to about 270 C. The upper plate was deeply engraved as described in Example I, and the flat aluminum cover plate was removed before the upper press-plate was closed onto the top surface of the batt. Embossing was for 45 seconds at p.s.i. (12.0 kg./cm. Removed from the press-plates and cooled, the batt was treated in a pressure autoclave containing methylene chloride and perfluorocyclobutane, as described in Example I. Subsequent heating as in Example I did not cause significant expansion of the filaments. Analysis of the treated filaments showed they retained only 4% of perfluorocyclobutane as contrasted with about 15% retention in the same filaments not subjected to embossing. Microscopic examination of cross-sections of embossed products, in areas between the embossed lines, showed that many cell-walls had fused together thus preventing both adequate imbibition of impermeant inflatant and full re-expansion.

A number of batts were treated as described above, using initially collapsed filaments. Press-plate temperatures ranged from 230 to 270 C., pressures from 45 to 170 p.s.i. (3.2 to 12.0 kg./cm. and times from 15 to 45 seconds. None were improved over the example given in detail.

Since excess fusion in areas other than the deeply embossed lines was found responsible for this decrease in filament expansion, strips of asbestos insulating tape were fastened over the recessed areas of the embossing plate to reduce heat transfer, and the example was repeated. As expected, some improvement was detected, but the products did not expand nearly as much as, and were not 'as pneumatic as, those of Example I wherein the initial microcellular filaments were partially expanded.

1 1 Example III Ultramicrocellular polyethylene terephthalate filaments were prepared as described in Example I. Before assembly into batts, they were treated in the autoclave with perfluorocyclobutane and methylene chloride, removed, and heated in air (as described in Example I). About 22 gm. of perfiuorocyclobutane per 100 gm. of polymer were retained. Immediately thereafter the filament-volume was 90% of the maximum attainable volume and was still increasing rather rapidly. Thus, the series of batts to be embossed as in either of the previous examples was composed of fully expanded microcellular filaments.

A variety of embossing conditions was employed. Pressplate temperatures range from 230 C. to 280 C. Pressplate pressures ranged from 25 to 300 psi. (1.75 to 21.1 kg./cm. Times of temperature-pressure application were from to 90 seconds. The best conditions employed Were 270 C., 45 p.s.i. 3.16 kg./cm. and 10 sec. All of these products were shattered, torn, or cut along the embossed lines. The filaments in the thicker portions between embossing lines were fully expanded and highly pneumatic, but the final products were weak and easily separated along the embossed lines. This is in contrast to the products of Example I which were prepared starting with partially expanded microcellular filaments.

The time elapsed between extrusion of microcellular filaments and their being consolidated by thermal embossing as in this invention can be significant in determining whether or not the filaments are collapsed, partially expanded, or fully expanded. Filaments prepared as in Examples I and III have impermanent inflatant (1,1,2-trichloro-l,2,2-trifluoroethane in the examples) in their cells. If kept from contact with air, they remain collapsed, as defined, even though they contain some gas. If left for days in contact with ambient air, they can become fully expanded. Carefully monitored exposure to air can provide any desired degree of partial inflation. Even the filaments prepared with any impermanent inflatant in the foamable solution, as in Example II, can expand somewhat on continued exposure to air, especially if heated. In example II, however, the time elapsed between extrusion and embossing never exceeded 10 minutes, a time too short for detectable increase in filament volume.

Finally, although only static embossing between generally fiat plates is shown in the examples, it is clear that the teachings of these examples will enable one skilled in the art to obtain equivalent results in a continuous process using embossing rolls rather than flat plates.

What is claimed is:

1. A process for making a firm cushioning structure suitable as a carpet underlay which comprises the steps:

(I) randomly depositing partially expanded microcellular filamentary material into a reticulate batt, said filamentary material being expanded to more than about 25% but less than about 85% of its maximum attainable volumes;

(2) heating to within about 120 C. of the polymermelt temperature of the polymer of which the microcellular filamentary material is comprised at least one of two opposing surfaces arranged to consolidate said batt, at least one of said surfaces being deeply engraved to provide raised line elements surrounding deeply recessed geometric shapes;

(3) consolidating said batt by compressing it between said opposing surfaces until the density of filamentary material along said line elements is at least 50% 0f the density of said non-expanded solid polymer, the consolidated batt having a maximum thickness, in areas corresponding to the centers of said deeply recessed geometric shapes, at least 5 times greater than along said line elements;

(4) maintaining the consolidated state of step (3) until the filament portions contacted by said raised line elements fuse sufiiciently to retain their reduced thickness;

(5) removing said batt and cooling it to solidify the polymer along the lines of fusion; and

(6) introducing to the closed cells of the portions of microcellular filaments surrounded by lines of fusion sufiicient normally gaseous infiatant to provide at least atmospheric pressure within the cells and to render said portions fully expanded.

2. A process as defined in claim 1 wherein both surfaces used to compress that batt are engraved and heated.

3. A method as defined in claim 1 wherein the filamentary material is ultramicrocellular.

4, A method as described in claim 3 wherein the partially expanded filamentary material as deposited in step 1 already contains within its closed cells between about 6 and 40 grams of impermeant infiatant per grams of polymer and wherein the consolidated cooled batt is fully expanded as in step 6 by exposure of said batt to air at temperatures below the polymer melt temperature.

5. A method as defined in claim 4 wherein the polymer of which the filamentary material is composed is polyethylene terephthalate.

6. A method as defined in claim 3 wherein the consolidated cooled batt is fully expanded as in step 6 by (a) exposure of said batt to a plasticizing fiuid and an impermeant inflatant whereby to provide within its closed cells between about 6 and 40 grams of impermeant inflatant per 100 grams of polymer, and (b) exposure of said batt to air at temperatures below the polymer-melt temperature.

7. A method as defined in claim 6 wherein the polymer of which the filamentary material is composed is polyethyleneterephthalate and the plasticizing fluid is methylene chloride at or below its normal boiling point.

References Cited UNITED STATES PATENTS 3,344,221 9/1967 Moody et a1 264-321 3,384,531 5/1968 Parrish 264-321 XR 3,389,446 6/1968 Parrish 264-321 XR PHILIP E. ANDERSON, Primary Examiner US. Cl. X.R.

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