Fibrous products and process for making them

March 14, 1950 c. s. francis, jr 2,500,282

FIBROUS PRODUCTS AND PROCESS FOR MAKING THEM

Filed June 8, 1944

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ATTORNEY

Patented Mar. 14, 1950

2,500,282

UNITED STATES PATENT OFFICE

2,500,282

FIBROUS PRODUCTS AND PROCESS FOR MAKING THEM

Carleton S. Francis, Jr., West Harwich, Mass., assignor to American Viscose Corporation, Wilmington, Del., a corporation of Delaware

Application June 8,1944, Serial No. 539,287

Claims.

This invention relates to felt-like fibrous products having improved properties and comprising mixtures of at least two types of fibers, one of which is activatable by heat with or without pressure, and/or with or without the assistance of fluids.

Fibrous webs, bats, mats, or the like of considerable thickness have been prepared previously by superimposing relatively thin carded webs or layers comprising heat-activatable and non-activatable fibers upon one another, subjecting the composite product to the influence of heat to render the activatable fibers more or less adhesive, and deactivating the activated material. Such webs or the like have valuable properties and are suitable for use for many purposes. However, the difficulty arises, especially in the case of very thick bats made up of numerous individual thinner webs or layers, that the activatable fibers within the body of the structure are not activated, or are not activated to a state of adhesiveness or tackiness in which they coalesce with adjoining fibers, by the heat treatment which is sufficient to convert the activatable fibers comprising the layers at or near the surfaces of the bat to the softened state, and indeed this difficulty is not wholly absent when the bat is less bulky and comprises only a relatively few thinner layers or webs. In order to insure penetration of the heat to the activatable fibers occurring internally of the final structure, and effectively activate or soften the same, it is necessary to utilize temperatures which are detrimental to the fibers occurring at the outer portions, or to subject the product to the heat for such a prolonged period that even at lowei· temperatures the outer fibers are rendered too soft. High temperatures or exposure of the bat to heat for prolonged periods results in excessive distortion of the outer fibers, the structure of which may be totally destroyed so that they are caused to flow, with concomitant acquisition of an undesirable surface gloss by the product, and a loss in flexibility, bulk, hand, and porosity. Further, if the surface fibers are rendered too soft and tacky by the heat treatment required to activate the inner fibers, and the product is subjected to compacting, as by passing the same through squeezing or pressure rolls or the like, the outer surfaces of the bat tend to stick or adhere to the rolls or the like from which they must be manually dislodged, which interferes with continuous processing of the bats and disturbs the arrangement of the surface fibers thereof and a glazed impermeable surface film is (Cl. 154—101) formed. Such bats, in which the fibers within the body are not activated, or are insufficiently activated, are not characterized by a high degree of internal cohesion and tend to come apart or 5 separate into layers quite readily when subjected to high tensile, compressive, or impact stress, since the interiorly positioned fibers and layers comprising the same, are not firmly bonded or interfelted together with other fibers and layers 10 in the product to form a structure which is completely integrated throughout. In many instances, the final bats obtained have been found to contain activatable fibers and layers of fibers within the body thereof which are substantially 15 unaffected by the activating treatment, whereas the fibers at the surfaces have been heated and activated to an objectionable amount.

In accordance with the present invention, fibrous webs, mats, bats, or the like, which 20 possess good internal cohesion and uniformity throughout, are obtained by assembling and super-imposing upon one another a multiple of relatively thin webs or layers comprising heatactivatable fibers and non-activatable fibers, in 25 which, however, the heat-activatable fibers in the web or webs farthest removed from the point at which heat is applied thereto, (which may be the web or webs at the intermediate portion or portions of the composite product when heat is 30 applied to both of the exposed surfaces thereof, or the web or webs at one or the other of the exposed surfaces thereof when heat is applied to only one of the exposed surfaces) have a lower thermal softening point than those in the 35 webs which are closer to the point of application of heat, by reason of which differences the fibers in the webs away from the point of heat application become tacky and adhesive at substantially lower temperatures, or within substantially lower 40 temperature ranges, so that when the product is heated to activate the fibers, such fibers, being more susceptible to softening under the influence of heat, are adequately activated by heating the product to a temperature and for a period of time ⁴⁵ which is insufficient to deleteriously affect the fibers in the web or webs nearer the application of heat. In this manner very thick composite bats or the like may be obtained in which after activation of the activatable fibers and deactiva50 tion thereof, the fibers and layers of fibers throughout the entire structure are firmly bonded or interlocked together, all of the fibers being sufficiently activated during the activation treatment to achieve this result. Any number of 65 layers comprising heat-activatable and non2,600,282 activatable fibers may be assembled and superimposed upon one another in accordance with the invention to form webs, bats, mats, or like products of any desired degree of thickness or density, in which all of the activatable fibers in the final composite product, after subjection thereof to the influence of heat, are uniformly heat-activated throughout.

The felted fibrous product may consist of one or more layers comprising thermoplastic fibers, or thermosetting fibers in the thermoplastic state, which fibers are of relatively low thermal softening point, and which constitute a core enveloped by one or more layers comprising thermoplastic fibers, or thermosetting fibers in the thermoplastic state, which fibers are of higher thermal softening point. Alternatively, products may be obtained by superimposing upon one another a plurality of relatively thin webs or layers, each one or more of which comprises heat-activatable fibers of different degrees of heat-sensitivity, as compared to that of one or more of the other webs, the webs being so disposed that the softening points of the activatable fibers contained therein decrease progressively from the outer to the inner portions of the structures, one or more thin webs containing fibers of the same melting or softening point being present, if desired.

Products may also be obtained by winding relatively thin fibrous webs one upon the other about a suitable mandrel, which mandrel may be shaped in the form of a cylinder, cone, sphere, or rectangular body, or may have an irregular shape, if desired. The fibrous webs may be wound upon the mandrel in helical or spiral manner, and may be built up thereon in such a way that the webs comprising the more readily heatactivated fibers occur at the central or inner part of the mat, or at the outer part thereof, depending upon the maimer in which heat is applied. The mats or bats finally obtained, which may be used as pipe insulators or the like, for example, may be of any desired thickness.

In the composite product obtained by assembling and superimposing the comparatively thin webs or layers upon each other, the activatability or heat-sensitivity of the activatable fibers is graduated throughout, and such gradation may be from a lesser to a greater extent from the outside surfaces or boundaries inwardly to an intermediate point, or it may be from a lesser to a greater extent from one surface or boundary to the other, depending upon the manner in which the individual layers are assembled and whether heat is to be applied to both surfaces of the final mat or to only one surface thereof. The products are heat-treated to activate the activatable fibers without damage to the non-activatable fibers, all of the fibers at all parts of the assembled webs being activated. When so treated, the fibers are anchored at their points of contact wherever the activatable fibers occur throughout the entire structure and at all parts thereof.

The products are characterized by greatly improved Internal cohesion and sturdiness, excellent resistance against compressive, tensile, and heating stress or strain applied in any direction and to any part thereof, and are reinforced at all parts thereof against separation or tearing under the wear and tear of hard usage. Further, when the less heat-sensitive fibers are at the surfaces of the composite mats and the mats are compacted while the activatable fibers are in the activated state, which compacting step is optional but may be desirable for some purposes, no difficulty is encountered due to sticking of the surface fibers to the pressure rolls or other squeezing devices.

By “heat-activatable” is meant those fibers which are capable of being rendered adhesive upon the application of heat either alone or in conjunction with swelling or solvent agents. By non-activatable or non-adhesive fibers is meant any which are not rendered adhesive by the treatment used in activating the heat-activatable fibers.

The activatable fibers may be composed of a wide variety of materials, and may comprise any material capable of being formed into fibers which have an inherent tackiness upon heating to temperatures below that at which the nonactivatable fibers are damaged or rendered tacky and which are non-tacky at room temperature. Examples of the heat-activatable fibers include thermoplastic fibers, such as those of cellulose acetate or other cellulose esters and ethers or mixed esters, mixed ester-ethers and mixed ethers, such as cellulose acetate propionate, cellulose acetate butyrate, or the ethyl ether of cellulose acetate, in plasticized condition; also, resins, either permanently thermoplastic or thermosetting but in the thermoplastic state, formed by the polymerization or condensation of various organic compounds such as coumarone, indene or related hydrocarbons, vinyl compounds, styrene, sterols, phenol-aldehyde resins either unmodified or modified with oils, urea-aldehyde resins, sulfonamide-aldehyde resins, polyhydric alcoholpolybasic acid resins, drying oil-modified alkyd resins, resins formed from acrylic acid, its homologues and their derivatives, sulfurolefine resins, resins formed from dicarboxylic acids and diamines (nylon type); synthetic rubbers and rubber substitutes, herein called resins,” such for example as polymerized butadiene, olefine polysulfides, iso-butylene polymers, chloroprene polymers; and fibers formed from a resin comprising the product of copolymerizing two or more resins, such as copolymers of vinyl halide and an acrylic acid derivative; and also a mixture of resins, such as a mixture of vinyl resins and acrylic acid resins or methacrylic acid resins, a mixture of polyolefine resins and phenol-aldehyde resins, or a mixture of two or more resins from the different classes just named. There may be employed also fibers made from rubber latex, crepe rubber, gutta percha, balata, and the like.

Further, the heat-activatable fibers may be mixtures of the cellulose derivatives with resins or rubber, such for example, as a mixture of cellulose nitrate and an acrylic acid resin, or a mixture of benzyl cellulose and a vinyl resin, or. a mixture of ethyl cellulose and shellac.

A preferred class of vinyl resins from which the fibers may be formed are the copolymers of vinyl chloride with vinyl acetate or vinyl cyanide and after-chlorinated copolymers of vinyl chloride and vinyl acetate.

The resins above mentioned may be classified as:

(a) Heat non-convertible resins such for example as glycol polybasic acid resins, vinyl resins (particularly those of the preferred class above) and the acid type phenolaldehyde resins, and the like.

(b) Heat-convertible or thermosetting resins such for example as glycerol-polybasic acid resins, polyolefine resins, phenol aldehyde resins and the like.

(e) An element-convertible resin (which be2,600,282 comes infusible through the action of certain elements, such as oxygen and sulfur) such for example as glycerol-polybasic acid-drying oil resins and olefine-sulfur resins.

The difference in the thermal softening point of the activatable fibers in the various layers of the present product may be obtained in a number of different ways, of which the following will be given by way of example but not by way of limiting the invention:

(a) By selecting or forming the different activatable fibers so that they will differ in chemical constitution. Thus, the fibers nearer the point of heat application may be formed from a highmelting vinyl chloride polymer, while the more remote fibers may be formed of a low-melting vinyl acetate polymer.

(b) The different activatable fibers may be formed from resins which are chemically identical, but differ in their degrees of polymerization. For example, both of the fibers may be formed of a copolymer of vinyl chloride and vinyl acetate, but the resin used for the more remote fibers may have a lower degree of polymerization whereby they have a lower thermal softening point than that of the other fibers.

(c) The different activatable fibers may be formed from copolymers of the same two or more resin-forming compounds, but the ratio of the monomeric components in the copolymer are varied so that the more remote fibers have a lower thermal softening point. For example, the more remote fibers may be formed of a copolymer of vinyl chloride and vinyl acetate comprising 83% vinyl chloride, while the other activatable fibers are formed of the same copolymer except that it comprises 87% vinyl chloride. The increased proportion of vinyl acetate in the more remote fibers impart to them a lower thermal softening point.

(d) Both types of fibers may be formed of the same or different chemical compounds, but the more remote fibers have a higher percentage of plasticizer than the other activatable fibers, whereby the former fibers have a lower thermal softening point.

Among the non-activatable fibers which may be, used are wood pulp fibers, cotton, flax, jute, kapok, silk and the like, or synthetic fibers of cellulosic composition, such as a cellulose or regenerated cellulose, cellulose derivatives, such as cellulose esters, mixed cellulose esters, cellulose ethers, mixed cellulose ester-ethers, mixed cellulose ethers, cellulose hydroxy-ethers, cellulose carboxy-ethers, cellulose ether-xanthates, cellulose xanthofatty acids, cellulose thiourethanes; natural and synthetic rubber and derivatives thereof; alginic acid, gelatine, casein; mineral fibers such as spun glass, asbestos, mineral wool and the like; fibers made of natural and synthetic resins which should be of such type that they are not rendered tacky when the activatable fibers are rendered tacky by heating; and the fibers made by slitting, cutting or shredding non-fibrous films, such as waste cellophane.

Relatively thin layers or webs comprising one or more types of the heat-activatable fibers may be felted together in accordance with the invention, the only limitation being that the webs or layers are assembled in such manner that the heat-activatable fibers comprising at least the relatively thin webs farthest removed from the heating source are more readily activated when the structure is subjected to heat, either alone or in conjunction with swelling or solvent agents.

The fibers which comprise the layers to be superimposed and bonded together in accordance with the invention may be obtained in any suitable manner. Thus, either type of fiber may be obtained by cutting previously formed continuous filaments to the desired length, or, in the case of the activatable fibers, and in the case of the non-activatable fibers, when they are formed of a plastic fiber-forming material, either or both types of fibers may be obtained by dispersing the fiber-forming material while in flowable condition, that is, in solution, plastic, or molten condition, under sufficient pressure to form a multiplicity of fibers, into a setting fluid, e. g„ a liquid or a gaseous atmosphere, as disclosed in my copending application Serial No. 381,292, filed March 1, 1941, now Patent No. 2,357,392, Sept. 5, 1944.

The fiber-forming material may contain added agents for obtaining special effects. For example, the parent fiber-forming material for the activatable fibers may contain hardening agents in the case of resins, for instance; while the fiberforming material for either the activatable or the non-activatable fibers may contain dyes, pigments, mothproofing agents, fireproofing agents, waterproofing agents, and the like.

In the relatively thin webs or layers which are assembled and anchored or bonded together to produce the composite products of the invention, the mixed fibers may be interlaced together in unarranged haphazard distribution with relatively little if any distribution of the fibers in exact parallelism or in side-by-side relation, or the fibers in the various thin webs or layers may have a certain amount of accidental or intentional parallelism, such as that existing in carded webs, for example. The fibers comprising the thin webs to be bound together may be of any suitable length, and may be blown together into a common depositing chamber without resort to mixing and carding and/or combing operations, or they may be precarded and/or combed either individually or in admixture, and then blown together, as disclosed in my co-pending application Serial No. 530,953, filed April 14, 1944, now abandoned, and in this case the thick bat or final product may be obtained by successively blowing mixtures of fibers in which the activatable fibers have different degrees of activatability, and permitting the different mixtures to settle out on one another without producing and superimposing separate webs or layers upon one another. On the other hand, the thin webs coming from a carding and/or combing machine may be superimposed upon one another and bonded together. Fibers of spinnable, carding, or paper-making length may be utilized in preparing the relatively thin webs which comprise the composite product of this invention. The fibers may be of such short length that they are not feltable by conventional methods, such as the extremely short fibers existing in waste of the type of sheer flock, leather dust, etc. The layers which are assembled and subjected to activating treatment in the assembled condition may be of the same or different thicknesses.

In order to effect a binding together of the mixed fibers, and of the various layers of mixed fibers comprising the product, to form an integral reticulated web structure, the assembled, superimposed thin webs are subjected to heat to cause at least a partial adhesion between the fibers and, due to the thermal softening point differential as between the activatable fibers occurring at different parts of the product, all of the fibers

2,600,282 ate activated throughout the entire structure, both at the surfaces and at the innermost portions thereof, and abnormally high temperatures, or prolonged heating periods, are not required in order to insure thorough and uniform activation. The fibers may be activated by subjecting the product to dry hot air, steam, contact with heated metal surfaces, irradiation, high frequency electric current, etc.

A plasticizer may be applied to the fibers and layers of fibers, and/or to the composite product comprising the assembled layers, before activation. The plasticizer may function to increase the flexibility of the fibers, and is particularly useful when applied to thermoplastic fibers positioned away from the heating source, since it serves to lower the thermal softening point. The fibers farthest removed from the heating source may be such that they have a softening point which is inherently lower than the softening point of the remaining fibers, or they may have such lower thermal softening point as the result of treatment thereof with a plasticizing agent. The plasticizer may be allowed to remain in the product, or it may be removed by suitable treatment, such as washing and extraction, thus again elevating the thermal softening point of the thermoplastic material and preventing reactivation upon ironing.

During or after activation, the composite product may be compacted, if it is desired to produce a bat of increased density, and the compacting may be effected in any suitable manner, as by pressing, squeezing, and tensioning. For example, mechanically applied pressure exerted on the activated material during and/or after activation, and/or during calendering, embossing, printing or dyeing will effect compacting of the fibers. Also the fibrous mat or bat in. activated condition may be passed between pressure rolls to compress the mixed fibers, or it may be subjected to tension in one or both directions.

After activation and compacting, if the latter is employed, the activated fibers comprising the superimposed thin webs or layers, are deactivated to render the same non-tacky, so as to fix the new relationship of the mixed fibers and layers. Deactivation may be effected by cooling; or by heating the product for a prolonged period, or to a higher temperature in the case of thermosetting resins.

The properties of the finished composite product depend upon various factors, including the number of comparatively thin webs or layers which have been assembled and bound or felted together, the proportion of the activatable fibers present in the various layers, the extent to which the fibers have been activated, whether or not the product is compacted by pressure or the like, and if so compacted, the adhesive or softened state of the various fibers during compacting, and all such factors may be preselected and controlled for the production of products of any degree of pliability, firmness, density, or porosity as may be desired.

The proportion of activatable fiber in the product may vary widely, depending on the properties end the purposes for which the products are destined, but in general a minor proportion, preferably from about 3% to 35% of the activatable fiber will be employed. Where a greater degree of strength or closer binding of the fibers is desided, the percentage will be relatively high. The proportion of activatable fiber in each of the original webs from which the product is obtained may be different from that in the other webs, in order to vary the texture from one surface to the other of the product or from the two exposed surfaces to the interior thereof. Thus, by providing a larger proportion of activatable fibers in the exterior webs, the product will have its exposed surfaces somewhat more resistant to deformation, to snagging, to tearing, and to wear in general, thereby constituting a protective armor to the product. On the other hand, an interior web may have a large proportion of activatable fibers, in order to produce at any desired plane in the product an impermeable or less permeable zone or a stiffer zone therein than the other zone of the product.

Flat felts per se, such as webs, mats, bats, etc., are obtained, which products may be used as such or subsequently shaped into any desired form.

Although the final mats or bats are obtained by assembling and superimposing individual thin webs or layers upon each other, such final products, due to the uniform activation of the activatable fibers are well-integrated composite products which are unitary throughout and, when cut through, show a transverse cross section which does not have the appearance of a laminated structure.

The individual thin webs formed by carding and/or combing the mixed heat-activatable and non-activatable fibers together, or by blowing or otherwise commingling the same into a felt-like structure, may be treated to partially activate the heat-activatable fibers prior to assembling and superimposing the same upon one another, in order to effect an initial binding together of the fibers and assist in handling the individual thin webs or layers without damaging the same.

The composite products of the invention comprising activatable fibers of varying degrees of heat-sensitivity, and in which the most heatsensitive fibers are farthest removed from the point at which heat is applied to the product, may at any time be embossed, calendered, molded, or otherwise shaped, in whole or in part, to deform the surface while the activatable fibers are still tacky or in a softened state, and then subsequently treated to deactivate the fibers to set the product in the desired form or surface condition to produce effects such as grain, lustre, smoothness or design, by suitable means, used hot or cold, and with or without the aid of agents which soften, swell, or plasticize the material acted on.

Further, the products may be colored before, during, or after activation, compaction, and/or deactivation, by dyeing, printing for example with inks containing pigments or dyestuffs which are resistant to the activating, compacting, and deactivating treatments.

In the accompanying drawing illustrative of the invention—

Figure 1 is a diagrammatic view showing one form of apparatus which may be used in obtaining products according to the invention;

Figure 2 is a perspective view of one embodiment of means for carrying out the invention in the fabrication of hollow cylindrical products;

Figure 3 Is a perspective view of a second means for producing a shaped felt-like product in accordance with the invention; and

Figure 4 is a cross-section through a product of the present invention.

In the drawing, relatively thin webs 2, 3, 4 and

5, taken from cards 6, 1, 8 and 9, by doffer rolls

10, II, 12 and 13 respectively, are carried on endless aprons 14, 15, 16, and the fixed apron 17, and

2, δοο, 282 deposited in superimposed relation upon an endless belt 18. In the arrangement shown, the web 5 comprises heat-activatable fibers of relatively high thermal softening point. That web is deposited on belt 18 to form one surface of the final product. Webs 3 and ¢, which comprise heatactivatable fibers of relatively low thermal softening point, are deposited one on top of the other upon web 5. Web 2, which again comprises heatactivatable fibers of the same softening point as those contained in web 2, or at any rate heatactivatable fibers the softening point of which is higher than.those in webs 3 and 4, is superimposed upon web 4. The superimposed thin webs, comprising thick bat 19, are carried on endless belt 18 through a rotary press comprising the heated drum 20 and the heated plate 20a, at which point the activatable fibers are activated and rendered adhesive and the product is simultaneously subjected to compaction, the activated fibers being deactivated when the bat 19 passes from the rotary press and becomes cool. Instead of utilizing the heated rotary press, the apparatus may be modified to include means for blowing hot air through bat 19 from both sides as it is carried on endless belt 18, and means for blowing cool air through the bat may also be provided for deactivating the activated fibers. Any desired number of cards or other source of thin web may be utilized to provide any desired number of thin webs to be assembled and superimposed and bound or felted together in the manner described herein and in accordance with the principles of the invention, to form a product of any desired degree of thickness. Extremely thick, integrated final composite structures may thus be obtained.

When utilizing the apparatus shown in Figure 2, a plurality of thin fibrous webs 21 (two being shown) may be wound helically about the pipe or cylindrical mandrel 22, being superimposed upon one another by winding the same alternately in reverse directions. The webs comprising the heat-activatable fibers which are least sensitive to heat are wound directly upon the pipe or mandrel. After the fibrous bat has been built up to the required thickness, the structure is subjected to heat and pressure to activate the heat-activatable fibers in the bat and fix the structure. In this case, it is desirable to be able to heat the mandrel 22, and this may be accomplished by using a hollow mandrel and passing hot air or hot water into the interior as by means of the pipe 23. When it is not feasible to slip the shaped mat or bat from the mandrel, it may be slit longitudinally.

In Figure 3 there is shown another embodiment of means for activating and applying pressure to the mat 24 for activating the activatable fibers. In that case, the mat comprising a plurality of relatively thin fibrous webs containing heat-activatable fibers and in which the activatable fibers in the outer or surface webs are less sensitive to heat than the fibers comprising the inner webs, is supported on the mandrel 25, and inserted in a cylindrical heating oven 26 which is divided lengthwise into two parts having a hinge joint 27 on one side and a spring clasp 28 on the other. The heater may be supplied by means of electrical resistance coils 29. If the unpressed body of the mat is larger than the diameter of the cavity 38, the closing of the heater will apply pressure to the fibrous material while the heat will activate the fibers. After activation, the heater is opened and the mandrel 25 is withdrawn to give a hollow bat or mat in which the activatable fibers have been activated uniformly throughout to bind fibers in the product.

By way of illustration but not of limitation, there are given the following examples of products produced in accordance with the invention.

Example I

A thin fibrous web in which 90% of the fibers consisted of cotton linters and 10% consisted of a copolymer of vinyl acetate and vinyl chloride which becomes tacky at about 245° to 255° F. was interposed between two fibrous webs each of which contained 30% of cellulose acetate fibers plasticized to become tacky at about 265 to 275°

F. and 70% of viscose rayon staple. The laminate was subjected to two heating surfaces at a temperature of about 275° F. While in the heatedsoftened condition the thermoplastic copolymer and cellulose acetate fibers become adhered to the other fibers surrounding them, causing the fibers and layers of fibers to cling together. At the indicated temperature, all of the activatable fibers including those at the innermost part of the structure, were thoroughly activated. On cooling, the activated fibers become solid and non-tacky, although still adhering to the fibers surrounding them. The product is illustrated in Figure 4, in which the inner zone A is bonded between the outer zones B and B' and the fibers are adhesively bonded throughout the thickness of the product.

Example II

Upon a thin web (I) comprising 90% viscose rayon staple and 10% of cellulose acetate fibers (plasticized to soften at about 285° to 300° F.) were placed successively, a thin web (2) comprising 90% of cotton linters and 10% fibers consisting of an after-chlorinated vinyl acetatevinyl chloride copolymer having a content of 64.6% chlorine and softening point of about 265 to 275° F. a molecular weight of 31,000; a web (3) comprising 70% wool flock and 30% of fibers consisting of an after-chlorinated vinyl acetatevinyl chloride copolymer having a content of 62% of chlorine, a molecular weight of 40,000; and softening point of about 240 to 250° F. and two webs (4 and 5) each comprising 90% of viscose rayon staple and 10% of fibers obtained by spraying a solution of 25 parts of polyvinyl acetate (softening point, 220 to 230° F.) in 75 parts of acetone into a gaseous atmosphere under pressure. Thin webs of the same composition as webs 3, 2 and 1 were then placed upon the structure, in that order, and the product was subjected to the heat of calender rolls whose surfaces were maintained at a temperature of about 295° F. sufficiently long to render the activatable fibers adhesive, after which the product was cooled to deactivate the activated fibers. The resultant product was a unitary structure in which all of the non-activatable fibers were firmly bound or anchored by the activatable fibers.

Example ΠΙ

Using the apparatus shown in Figure 2, a thin web (I) comprising 94% cotton fibers and 6% cellulose ether fibers was wound helically upon the mandrel 22. Another thin web (2) of the same composition was wound on the mandrel, over web (1). Then a third web, comprising 80% of rayon staple and 20% of fibers comprising a vinyl acetate-vinyl chloride copolymer was wound over web (2), after which a thin web (4) com2,600,982 prising 70% of wool flock and 30% of fibers consisting of a polyvinyl acetate resin was wound on the mandrel, over the other webs. Heat was applied to the product, through mandrel 22, and a final product obtained in which the activatable fibers were uniformly activated.

Since many changes and modifications may be made in the invention without departing from its scope, it is intended that the above description shall be interpreted as illustrative and not limited except as defined by the appended claims.