US3507943A - Method for rolling nonwoven fabrics - Google Patents

Description

April 21, 1970 J. J. SUCH ET L METHOD FOR ROLLING NONWOVEN IABRICS 3 Sheets-Sheet 1 Filed Feb. 5, 1966 April 21, 1970 J. J. SUCH ET 3,507,943

METHOD FOR ROLLING NONWOVEN FABRICS Filed Feb. 5, 1966 3 Sheets-Sheet 2 April 21, 1970 J. J. SUCH ET AL 3,507,943

METHOD FOR ROLLING NONWOVEN FABRICS Filed Feb. 3, 1966 3 Sheets-Sheet 5 United States Patent 3,507,943 METHOD FOR ROLLING NONWOVEN FABRICS John J. Such, Wrentham, and Arthur R. Olson, Walpole, Mass., assignors to The Kendall Company, Boston, Mass., a corporation of Massachusetts Continuation-impart of application Ser. No. 492,644, Oct. 4, 1965. This application Feb. 3, 1966, Ser. No. 524,931

Int. Cl. D04h 1/64; B29g /00; 132% 7/14 US. Cl. 264-103 25 Claims ABSTRACT OF THE DISCLOSURE A method directed to forming unwoven sheets of deformable textile materials by rolling is described. The unsynchronized non-meshing pair of rolls are engraved in a pattern of lands and grooves; the desired pattern is reproduced in the material without registry between the roll patterns. Impregnation, heated rolls, aperture formation, lamination, felting and plying are included among the embodiments.

This application is a continuation-in-part of our copending application Ser. No. 492,644, filed on Oct. 4, 1965, now abandoned.

This invention relates to methods of reforming sheets of deformable textile fibrous material by permanently displacing and rearranging at least a part of the fibrous substance to provide a set of discrete, spaced-apart rearranged areas, and to certain products produced by such methods. Illustrative of deformable textile fibrous sheet materials are fibrous webs, particularly those with a certain percentage of thermoplastic fibers; fibrous webs containing a plastic bonding material in either set or unset condition; and woven or knitted fabrics, including fabrics treated or coated with organic polymeric material, such as artificial leather or adhesive tape. Various embodiments of such textile materials may be used alone, or in laminated combination with other sheet materials such as polymeric organic films or paper.

It is known to emboss textile fabrics and films by passing them between a metal roll patterned in raised and depressed areas, and a solid backup roll. Processes are also known where the pattern to be applied to the fabric or film is divided between the two rolls. An extension of this type of embossing is found in US. Patent 2,464,301, to Francis. In general, prior art pressure-embossing processes, on non-woven fibrous sheets for example, have been carried out in one of three ways. Both embossing rolls may be engraved with an identical pattern of areas in relief and areas in intaglio, so that a relief or raised area on one roll matches and opposes a relief area on the other roll, creating an area of high pressure. Conversely, a raised area on one roll may be designed to register with an intaglio or depressed area on the other roll. In both such cases, proper and exact synchronization of both rolls is essential to provide proper registry of the pattern, which is difficult and expensive to maintain. It is common practice in the commercial embossing art, therefore, to reproduce all of the desired pattern on just one roll, and to process the sheet material between such a roll and a plain, non-patterned roll, such a plain roll varying in hardness from rubber to metal depending on the particular pattern to be embossed. This chief disadvantage of such a process is that the pattern, being impressed by one roll, appears prominent and well-defined only on one face of the material.

We have found that novel and useful results may be realized by processing deformable material between a pair of rolls which are both engraved in a pattern of lands and grooves, as explained more fully below. Such a roll system we have found to have novel advantages in the rearrangement of fibers contained in deformable textile sheet material, including the printing in relief of a displacement pattern simultaneously on both faces of the sheet, spot-bonding of sheets containing pressure-sensitive or thermoplastic material, and to be particularly suitable for spot-aperturing of both woven and nonwoven fabrics.

It is a primary object of this invention therefore to provide a new and useful process for rearranging the fibers in a deformable textile fibrous sheet material. It is also an object of this invention to provide novel products made according to said process.

The invention will be more clearly understood by reference to the following specification and drawings, in which FIGURE 1 is a view, partly broken away, of a preferred apparatus suitable for carrying out the process of this invention.

FIGURE 2 is a stylized representation of the type of pattern produced by the apparatus of FIGURE 1.

FIGURE 3 is an alternative pair of rolls for carrying out the process of the invention, explained in detail below.

FIGURE 4 is a rearrangement by rotation of the rolls of FIGURE 3.

FIGURE 5 is a partly broken-away view of another pair of embossing rolls useful in the practice of this invention, in which the angular pitch and direction of both rolls is the same, but the land and groove width on one roll is twice the land and groove width on the other roll, and both rolls have their lands and grooves arranged in our preferred helical pattern.

FIGURE 6 represent the stylized pressure-pattern produced by the rolls of FIGURE 3.

FIGURE 7 is a partly broken-away view of another pair of rolls suitable for use in this invention, with an upper helically-engraved roll and a lower roll with circumferential lands and grooves.

FIGURE 8 represents the stylized pressure-pattern produced by the rolls of FIGURE 5.

FIGURE 9 is a partly broken-away view of still another pair of rolls useful in the practice of this invention.

FIGURE 10 represents the stylized pressure-pattern produced by the rolls of FIGURE 7.

FIGURE 11 is a view of either surface of one product of this invention.

FIGURE 12 is a cross-sectional view of the product of FIGURE 9.

FIGURE 13 is a view of the surface of a spot-bonded nonwoven fabric made according to the process of this invention.

FIGURE 14 is a view of the bottom surface of a piece of fabric-backed adhesive tape apertured by the process of this invention.

FIGURE 15 is a view of an apertured nonwoven fabric, also made according to the process of this invention.

By the term stylized in the references to FIGURES 2, 6, 8, and 10, it is meant that these are idealized tracings of the pressure areas as made by passing a sheet of paper and carbon paper through the apparatus. In dealing with the aperturing of nonwoven fabrics, for instance, it will be appreciated that the apertures may be somewhat oval in nature, due to plastic flow and plastic memory inherent in the fibrous sheet.

Basically, this invention resides in the pressure-deformation and rearrangement of deformable textile sheet material as set forth above through a pair of rolls each of which is engraved in a series of lands and grooves, preferably with at least one of the pair of rolls bearing a land-groove pattern in the form of a series of helices forming a pattern of continuous lands and grooves. In this manner, there is imposed on the sheet material a repeating pattern of pressure areas wherein the fibers are permanently displaced, such areas varying from condensed areas to actual apertures, of a generally quadrilateral configuration, formed by the traverse of a land area on one roll over a land area of the other roll, as the rolls are caused to rotate. The shape and spacing of the pressure areas will vary with the configuration of the rolls, as set forth more fully hereinbelow.

Referring to what may be regarded as a basic design of apparatus, reference is made to FIGURE 1 which comprises a pair of metal rolls and 12 each engraved with what we herein term a helical pattern of lands 14 and grooves 16. Rolls 10 and 12 are provided with journals 18 and 20, and are also preferably provided with heavy backup rolls 22 and 24, for equalizing the pressure distribution and for minimizing bowing. The journals 26 and 28 of the backup rolls, as well as the journals 18 and of the embossing rolls, are preferentially equipped with roller bearings, not shown. Pressure may conveniently be applied by an air cylinder or similar device 36, transmitted to the journals by pillow- blocks 30 and 32, the latter resting on a solid bedplate 34. Journals and pillow blocks will be contained in a vertical casing, not shown. Also, provision may be made for conventional heating of the embossing rolls 10 and 12, as by the insertion of electrical heating elements disposed in cores drilled through said rolls, or by oil, by gas firing, or the like.

When a deformable textile sheet material is passed through the nip 17 between rolls 10 and 12 of FIGURE 1, a series of pressure-areas 52 of FIGURE 2 is formed. In general, the overall character of the fiber-displacement pattern will comprise three components: a highly compacted area 52 where a land has traversed a land: more lightly compressed areas 50 and 51 where a land on one roll has traversed a groove on the other roll; and a substantially unaffected area 48 where a groove on one roll has traversed a groove on the other roll. The degree to which these areas are permanently impressed onto the deformable sheet material processed between such rolls will depend on the thickness of the sheet material, its nature, and the pressures and temperatures used in processing. At moderate pressures of not more than about 100 pounds per inch of nip width, thin fibrous webs usually show a pattern of unconnected quadrilateral impressions which may be thinned out areas, or may be actual apertures, usually bordered by a ridge or grommet of film substance. Such considerations pertain to the processing of nonwoven fabrics of the order of up to 0.005 inch in thickness and of generally light weight, up to 30 grams per square yard, as set forth in Examples 2 and 4 below.

On bulkier deformable fibrous sheet material, especially when weighing in excess of 50 grams per square yard and over 0.005 inch in thickness, and employing moderate pressures of not more than about 100 pounds per inch of nip width, the customarily expected pattern is one of heavily depressed areas lying within a trough of less depressed material, said troughs running diagonally across the deformed sheet and being separated by ridges of relatively undisplaced material, as shown in FIGURES 11 and 12 and explained in Example 1, If the fibrous sheet contains thermoplastic fibers or thermoplastic material dispersed therein, and if there is a temperature differential between the rolls 10 and 12, then there may be a difference in depth and in degree of permanence between a heated land on one roll traversing a groove on the other roll, and a cool land on the other roll traversing a groove on the one roll. That is, the semi-affected quadrilaterallyshaped areas 50 and 51 may differ slightly in nature. Such differences are also noticed in the processing of plastic masses laminated to fibrous sheet material, such as adhesive tapes, where various patterned or apertured pressure-sensitive adhesive tapes can be produced by the process of this invention, with the apertures either isolated and discrete, or connected by channels which facilitate the transmission of moisture and moisture vapor from aperture to apertur Especially in the case of adhesive tapes, the pattern impressed onto the product will vary not only with the physical variables of the apparatus, such as design, pressure and temperature, but with the properties of both the adhesive mass and of the backing, such as resilience, elastic memory, etc.

Using a fibrous sheet containing a proportion of thermoplastic fibers, with pressures in excess of about pounds per inch of nip width and with fiber sheets weighing from 60 to 100 grams per square yard, the nature and degree of fiber displacement will vary with the nature of the fibers used. At pressures of pounds per inch of nip width, blends of nylon with a minor proportion of polypropylene give a pattern of heavily depressed areas interconnected by troughs of less heavily depressed material, as mentioned above. Other fibers of lower moduls of resilience, such as cotton, viscose rayon, or modified acrylics, blended with polypropylene, will under the same pressures yield a product wherein the heavily depressed areas are actual apertures. The preparation of such apertured nonwoven felts is set forth in Example 7, below.

Considerable latitude may be exercised in the design of the rearranging rolls, as shown in FIGURES 1, 3, 5, 7 and 9, provided that both rolls bear a land and groove pattern, so arranged that maximum pressure is exerted only intermittently and in a set pattern of quadrilaterallyshaped areas.

In FIGURE 1, both upper roll 10 and lower roll 12 bear a pattern of lands and grooves in helical arrangement. In FIGURE 3, the lands 15 on upper and lower rolls 11 and 13 are shown as a spacer set of parallel ellipsoids extending equidistant from the axes of the rolls and in a plane which is inclined relative to the roll axes. So long as the register of the lands remains as shown in FIGURE 3, the desired intermittent pattern of pressure areas will be obtained. However, if either of the rolls 11 or 13 is rotated through the allipsoidal discs forming the lands on that roll will now be inclined in opposition to the other roll, as shown in FIG. 4. In such a case, the lands 23 on both rolls 19 and 21 will mate continuously as the rolls revolve at uniform speeds, provided that the rolls are of the same diameter. Instead of maximum pressure being developed intermittently at a set of spaced-apart points, the continuous mating of lands 23 and grooves 25 will result in maximum pressure being delivered in a series of curved lines running the length of the fabric, which is undesirable. Therefore, we prefer to employ helically-disposed lands and grooves as shown in FIGURES 1, 5, 7 and 9, since the slippage of one roll relative to another has little or no effect on the desired intermittent pattern of pressure areas. This is a unique advantge of the helical configuration, which additionally seems to distribute roll pressure and roll wear better than separated lands in the form of inclined ellipsoids.

FIGURE 5 represents a partly broken-away pair of rolls with the same helical pitch of 20 (20 lead), but with the lands 60 on the upper roll 62 twice the width of the lands 64 on the lower roll 66. FIGURE 6 represents the displacement pattern created by passing a sheet of deformable material between the rolls of FIGURE 5, under pressure. The elongated and skewed compressed areas thus obtained are the solid black areas 67 of maximum pressure, where a land on one roll has made a transient crossing of a land on the other roll: the lessseverely displaced dotted areas 68, where a land has crossed a groove; and the unshaded areas 69, where the material has been substantially unaffected by a groove crossing a groove.

FIGURE 7 represents a suitable pair of rolls where the upper roll 70 has lands 72 angularly oriented at a 45 pitch to the roll axis, to make contact with a lower roll 74 in which the lands 76 are circumferential, being oriented perpendicular to the roll axis, and are not connected, instead of being helically oriented. In FIGURE 8, the pressure-pattern diagram of FIGURE 7, the

dark areas 77, dotted areas 78, and unshaded areas 79 again represent the areas of maximum, intermediate, and minimum pressure, respectively.

In FIGURE 9, the top roll 80 has lands 82 running at a 45 pitch in a northeast-southwest direction while the lands 86 of the bottom roll 84 are pitched at 26 in a northwest-southeast direction, the lands on the top roll being three times the width of the lands on the bottom roll.

FIGURE represents the displacement pattern produced by the rolls of FIGURE 9, wherein the particular angles and land-widths of the rolls gives rise to a set of elongated quadrilateral maximum pressure points 87, similar areas of unshaded minimum pressure 88, and areas of stippled intermediate pressure 89 the quadrilateral areas of maximum pressure 87 being bounded fully on each of their four sides by the quadrilateral areas 89 of intermediately compacted fibers and being contiguous at each of their apices with quadrilateral areas 88 of substantially uncompacted fibers. From the description of the rolls of FIGURES 1, 3, 5, 7 and 9 and from their displacement patterns of FIGURES 2, 6, 8 and 10, it will be apparent that the patterns may vary from squares oriented at 45 to narrow, elongated slits. The pitch angle of the lands on one roll should not be equal and opposite to the pitch angle of the lands on the other roll in order to avoid the special case where the lands on one roll mesh with the grooves on the other roll, or the possibility that a land on one roll will remain in such prolonged contact with a land on the other roll that a maximum pressure area of substantially continuous length is evolved. When the helical pitch on one roll is opposed to the helical pitch on the other, therefore, the pitch of the lands on one roll should be selected in relation to the pitch of the lands on the other roll so that on the material being treated, the lines formed by one set of lands will intersect with the lines formed by the other set of lands at an acute angle which is at least In general, the surfaces of the lands in a pair of the grooved rolls of this invention may be considered to define the surfaces of a pair of coacting cylinders in which the sum of the radii of such cylinders is at no time greater than the distance between the centers of the cylinder axes.

The process of the invention will be illustrated by the following examples. In each example, the apparatus of FIGURE 1 was used, in which rolls 10 and 12 and pressure rolls 22 and 24 were of steel and were 3 /2 inches in diameter. Pattern rolls 10 and 12 were helically grooved in identical patterns, with lands 14 0.035 inchwide and grooves 16 0.040 inch wide. The depth of the grooves was 0.025 inch, and the helical pitch or lead was 30.

EXAMPLE 1 A felted nonwoven fabric was prepared according to the procedure set-forth in US. Patent 2,774,128, consisting of a batt of eight superimposed card webs, the second and seventh card webs being composed of 85% bleached absorbent cotton fibers and 15% of 1% inch 1.5 denier polypropylene staple fibers. All other card webs were composed of 100% bleached absorbent cotton fibers. After shrinking the layered batt to an extent of 60% in refrigerated caustic, according to US. Patent 2,774,128, the result was a nonwoven felt weighing 120 grams per square yard, with all-cotton surfaces and center, but with a layer of blended cotton and polypropylene immediately underlying each cotton surface. In this form, such a product may be used as a lithographic or general purpose wiping pad, like its all-cotton counterpart. However, the material is smooth-faced, and lacks gripping action: it tends to ball up when used wet; and is has a dry crosswise tensile strength of only about 0.2 to 0.3 pound per inch-wide strip.

Felts consisting solely of cotton fibers may be processed under pressure to form a patterned or textured surface, but due to the rapid swelling which cotton fibers undergo when wet, an impressed pattern disappears rapidly when such a pad is wet out with water.

The dry felt containing polypropylene fibers thus prepared was therefore processed according to this invention by passing it through therolls of FIGURE 1, with both rolls heated to 440 F. A pressure corresponding to 94 pounds per inch of nip width was employed. The result was a lithographic wiping pad of the general configuration shown in FIGURE 11 and in cross-section in FIGURE 12, both magnified about 11 times, wherein diagonal ribs of uncompressed cotton fibers 58 are alternated with trough-like grooves 56, the general pattern being unified by the high pressure areas 61. In FIGURE 11, the machine direction is from left to right. These areas 61 represent the spots 52 of FIGURE 2, where maximum pressure was exerted by the lands of the heated rolls crossing each other. Due to the combination of heat and maximum pressure in these areas, the polypropylene fibers are fused together within the interior of the felt, thus serving to render the alternating ridge-and-trough pattern insensitive to water. That is, when patterns of this sort are developed by pressure alone on pure cotton felts, the pattern is clear and prominent on the dry material, but disappears when the swelling action of water disrupts the transient cellulose-to-cellulose bonds thus established. For many types of lithographic work, and for general application, distribution, and removal of aqueous and other solutions, a certain degree of surface roughness or corrugated pattern is desirable. The practice of this invention on a mixed-fiber felt of the type set forth above results in a wiping pad which consists in dominant proportion of absorbent fibers, is soft, conformable, and lintfree, yet possesses a functional corrugated surface which maintains its character even when wet out with swelling agents. The dry cross strength of the embossed product is about 1.4 pounds per inch-wide strip, or about six times the strength of the unembossed felt.

As an alternative to the above procedure of Example 1, a layer of thermoplastic fiber may be sandwiched between two layers of all-cotton felt made in accordance with US. Patent 2,528,793, and the sandwiched passed through the procedure of Example 1.

Useful products similar in appearance to FIGURE 11 may also be made from batts of fibers, such as nylon or polyester fibers, which are not normally regarded as thermoplastic, as illustrated by the following example.

EXAMPLE 2 A batt of 3 denier 1 /2 inch nylon staple fibers was processed through the apparatus of FIGURE 1 at a pressure of 125 pounds per inch width of nip, and with both rolls heated to 420 F. The resulting product was similar to FIGURE 11, with the quadrilateral areas 61 of maximum pressure converted to unbroken but translucent windows of fused fiber substance. The presence of over of these fused spots per square inch serves to unify the nylon batt without the use of extraneous binder material, making a nylon felt of this character useful as a battery separator in alkaline batteries. Greater strength and decreased porosity may be achieved, if desired, by placing a film of cellophane or other film-forming material in the interior of the nylon batt prior to passing the assembly between the rolls.

Essentially similar results are obtained when polyester fibers are used instead of nylon.

EXAMPLE 3 Using the same pair of rolls as in Example 1, a card web consisting of 3 denier polypropylene fibers 1% inches long, weighing about 10 grams per square yard, was processed at a pressure of 94 pounds per inch of nip width, with the top roll heated to about 340 F. and the bottom roll heated to 240 F. The result was the spot-bonded, open, porous nonwoven fabric of FIGURE 13, which is magnified about 35 times. In FIGURE 13, the polypropylene fibers 71 are fused together locally in a set of discrete spaced-apart areas 73, which in the actual fabric, using the roll specifications set forth above, were about inch apart. In a light, thin web of this nature, the process of this invention in general effects a pattern only in a set of such unified areas where a land on one roll crosses a land on the other roll, the land-groove and groove-groove combinations being substantially ineffective in altering the inter-fiber relationships. The fiber segments lying between the bonded areas 73 are therefore in a soft, flexible and unfused condition, except for the intermittent appearance of fused fiber nodes 75, appearing on one surface of the web.

Such nodes are formed because although the fibers 71 in FIGURE 13 are represented as being disposed in a two-dimensional plane, actually there is a minor but definite third dimension of thickness in any carded web of fibers. Certain fiber segments and fiber ends may be considered as being oriented in a path which carries them above and below the two-dimensional plane of FIGURE 13. It has been our experience that when one roll is heated sufficiently to fuse the fibers, with the other roll below the fusion point, as in this example, those segments of the thermosensitive fibers which protrude appreciably out of the plane of the web toward the more strongly heated roll are fused into small nodes or nodules 75. Not all fibers are thus affected, nor is more than a quite minor part of the length of any one thermosensitive fiber involved, but the summation of the effects of such nodes, considering that FIGURE 13 represents about one onehundredth of a square inch, is to impart a distinctly harsh, rasping and dragging hand or feel to the face of the web which has been processed next to the hotter roll, while the face which was against the cooler roll remains soft and smooth to the touch.

Such an unexpected effect renders products of this sort especially valuable as coverings for dressings and absorbent articles in general, such as hospital sponges, pads, sanitary napkins and the like. The nonwoven fabric thus produced has one surface of smooth soft fiber segments lying between spaced-apart discrete areas, extending substantially through the entire thickness of the fabric, where the intercrossing thermosensitive fibers are fused together, while the other face of the fabric is additionally characterized by a randomly-spaced set of nodes or nodules of fused fiber substance, amounting to over one hundred of such minute points per square inch, which impart a harsh and rasping hand thereto, and a high degree of frictional engagement toward other fabrics or fibrous assemblies. Although esthetically undesirable for contact with the human body, such a harsh hand frictionally anchors such a nonwoven fabric on the surface of layers of cellulose wadding, cotton, wood pulp, or other absorbent fillers which commonly constitute the major absorbent in pads and napkins. Not only does the frictional engagement of one face of the nonwoven fabrics of this invention facilitate the wrapping operations involved in the preparation of combination dressings, but in the final dressing it prevents shifting or displacement of the absorbent contents, a common source of complaint in combination dressings employing a cover made from a nonwoven fabric which is smooth-surfaced on both faces. To the extent that close contact is maintained between a cover produced according to this invention and the absorbent filler enlosed by such a cover, transfer of fluid exudate to the absorbent filler is facilitated, lessening the degree of saturation of the cover and encouraging a dryer and healthier wound site.

Although the above specific example was made from polypropylene fibers, it will be obvious that other thermoplastic fibers can be employed, such as polyethylene, vinyl fibers, plasticized cellulose acetate, and other synthetic fibers which can be thermally bonded to each other or to other fibers at temperatures below their decomposition points. I11 addition to the above example, we have made spot-bonded nonwoven fabrics by the process of this invention which contain 25%, 50%, or thermoplastic fibers, the balance being, for example, viscose fibers, or any other fiber selected for a particular property in the final nonwoven fabric. Fibrous webs containing thermoplastic fibers can, by the process of this invention, be laminated to films, to paper, to fabrics, to other nonwoven fabrics, or a multiplicity of such fibrous webs, of varying composition if desired, may be bonded together.

EXAMPLE 4 A further example of the utility of the process of this invention is in the preparation of porous pressure-sensitive adhesive tapes, capable of transmitting moisture vapor therethrough and thereby diminishing the skin maceration which frequently accompanies the use of occlusive, moisture-impervious tapes. The gravity of dermal reactions to impervious tapes is evidenced by the numerous attempts which have been made to render tapes permeable, as by perforating the tape mechanically with a series of relatively large holes; or by printing the adhesive onto a porous backing in the form of disconnected spots as in US. Patent 2,940,868; by coating With adhesive a perforated film as in U.S. Patent 3,073,303; or by embossing a tape on the adhesive side with a patterned roll which carries a set of raised areas which displace the adhesive under pressure, as in US. Patent 3,073,304.

We have found that a novel porous adhesive tape of an unusual and advantageous configuration in the adhesive mass may be produced by passing a suitable tape through the rolls of FIGURE 1 as follows:

A pressure-sensitive adhesive tape was made employing an acetate satin fabric base, 225 ends and 78 warp yarns per inch, weighing 3.57 yards per pound. This fabric was solvent-coated with a heptane solution of a commercial pressure-sensitive adhesive mass comprising pale crepe rubber, tackifier resins, fillers, and age-resistors.

The tape thus prepared was passed through the nip created by the patterned rolls 10 and 12 of FIGURE 1, at a pressure of 94 pounds per inch width of nip. The adhesive face of the tape was exposed to the top roll, heated to 425 F., while the cloth face pressed against the bottom roll, heated to 440 F.

The adhesive face of the resulting product is shown in FIGURE 14, the machine direction again being from left to right. Apparently due to the continuous traversing and shearing action of the helically-grooved lands 14 of the set of rolls, the adhesive mass has been displaced into a set of continuous transverse ridges 81, about 0.010 inch thick, running diagonally and uninterruptedly from one selvage edge of the fabric to the other. In regular alternation with these ridges, and similarly spaced and oriented, is a set of grooves 83, in which the mass is about 0.005 inch thick. Regularly spaced in these grooves or troughs 83 is a set of quadrilaterally-shaped aperture 85, corresponding to a land on one roll crossing a land on the other roll as at 52 of FIGURE 2, in which apertures the acetate backing fabric has been crushed and moved aside so that there is no substance therein, under the particular pressures employed.

Porous adhesive tapes prepared in this manner have several advantages over prior-art tapes. First, they are characterized by a series of continuous diagonal ridges of adhesive mass, the continuity of said ridges providing a greater holding power than prior art patterns in which the adhesive is printed in a pattern of isolated spots or areas which are completely surrounded by areas containing no adhesive. Second, the actual apertures 86 are interconnected, along any one trough, by areas in which the adhesive is only about one-half as thick as the adhesive on the ridges, thus providing auxiliary paths for moisture vapor from the skin to be transmitted to the air. Such an interconnection of apertures through a channeled adhesive mass allows fewer apertures to vent more moisture than is the case where individual apertures are underlaid by an encircling grommet of adhesive mass, and thereby allows the preservation of a higher proportion of the tensile strength of the backing material.

In cases where the backing of the adhesive is porous, as in the case of the acetate fabric above, it is not necessary actually to perforate the backing. The use of lower pressure and less drastic processing conditions will displace the adhesive mass from the quadrilaterally-shaped areas 85 without cutting through the fabric, but still allowing moisture-vapor transpiration therethrough due to the channels 83.

Although the above example was set forth in terms of an acetate fabric, the general procedure is equally applicable to adhesive tapes employing a backing of film, or of a variety of woven or nonwoven fabrics.

EXAMPLE The process of this invention also finds particular utility in the preparation of novel apertured nonwoven fabrics, as well as in the aperturing of prebonded nonwoven fabrics. Apertured nonwoven fabrics are those in which a portion of the fibers of an unspun and unwoven web, comprising textile-length fibers, are displaced from their normal overlapping and intermingled relationship to form a spaced set of apertures or areas which are essentially devoid of fibers, thus lending to the nonwoven fabric the appearance of certain woven fabrics. Such apertured nonwoven fabrics are described in U.S. Patents 3,137,893 and 3,150,416, among others, and are of recognized utility as pad covering materials, surgical dressings, disposable towels, and the like.

An unbonded card web of 3 denier inch viscose rayon fibers was saturated with an acrylic binder solution of 12% concentration and the wet pickup adjusted to 150%. The wet web Was then passed through the rolls of FIGURE 1 at a pressure of 94 pounds per inch width of nip, with the both rolls heated to 430 F. Final drying was accomplished by passing the moist apertured nonwoven fabric over a steam-heated dry can.

The final product is represented by FIGURE 15, magnified about times, wherein the apertured nonwoven fabric 90 consists of a web of rayon fibers 92, marked by a pattern of generally quadrilaterally-shaped apertures 94-, said apertures being essentially devoid of fiber substance. The apertures occur where a land on the top roll traverses a land on the bottom roll, corresponding to the areas 52 of FIGURE 2. As mentioned above, in thin and lightweight materials of this character, the land-groove coaction 50 of FIGURE 2 is not apparent, and the apertured nonwoven product is essentially planar and unmarked by transverse ridges or grooves.

The apertures 94 of FIGURE 15 are characterized by a rim or grommet of displaced fiber segments 96, apparently due to the shearing action of the traverse of land over land having aggregated said fiber segments. Such a traverse is initiated at a point, proceeds to its maximum width, and then recedes to a point again as the characteristic quadrilateral shape is generated. Especially when wet, textile fibers are somewhat plastic and are displaced to one side to form the reinforcing fibrous rims 96. This effect is a local displacement confined to the peripheries of the apertures, and the characteristic card web configuration of the fibers lying between the apertures is essentially undisturbed. Each reinforcing fibrous rim surrounding an aperture is therefore independent, and the rims defining the apertures are interconnected only by unrearranged fiber segments.

It is also possible according to this invention to produce comparable apertured nonwoven fabrics from textile webs which have been prebonded: that is, bonded and dried in a separate operation, in distinction to the above example where bonding and apertures were done simultaneously. This is illustrated 'by the following example.

10 EXAMPLE 6 A card web of 1.5 denier inch viscose rayon, weighing 12. grams per square yard, was saturated with 25% of its weight of an acrylic binder and dried, in the conventional manner used for preparing bonded nonwoven fabrics. The bonded material was then wet out with water, adjusted to about 200% water pickup, and then run through the apparatus of FIGURE 1 at a nip pressure of 125 pounds per inch of nip width with both rolls heated to 430 F. The result was an apertured nonwoven fabric resembling the material of Example 4 made from rayon fibers run through the apparatus while wet with binder solution.

In addition to nonwoven fabrics bonded by liquid binders in the form of latices or emulsions, so-called mixed fiber webs can also be apertured by the process of this invention: that is, webs which contain a certain proportion of themo'plastic binder fibers such as polypropylene, vinyl fibers, or plasticized acetate fibers, mixed with nonbinder fibers. Not only are the apertured felts thus produced of interesting surface texture, with a twill-like structure, but the mechanical integrity and resistance to rupture of the product is of a very high order in view of the essentially soft and conformable nature of the material. The preparation of such an apertured felt is set forth in the following example.

EXAMPLE 7 A blend of bleached absorbent cotton fibers with 25% 1.5 denier 1.5 inch polypropylene fibers was carded to give a fibrous batt weighing grams per square yard. This fibrous batt was then passed through the apparatus of FIGURE 1, with both rolls heated to 450 F. and under a pressure of pounds per inch of nip. The resulting apertured felt resembled the product of FIGURE 11, wherein the quadrilateral areas 61 were actual apertures devoid of fibers, interconnected by diagonal trough-like depressed areas 56, and with the depressed areas 56 separated by soft, uncondensed ribbed diagonal stripes 58, so that a twill effect was prominent.

An especially useful characteristic is the high loft and low bulk density of the structure: the measured thickness of 60 thousandths of an inch represents a bulk density, for this weight of web, of 1.1 grams per cubic inch or 0.070 gram per cubic centimeter. This open structure enables the fabric to take up relatively large amounts of liquid, as high as 11 to 12 times its own weight, as determined in a standard test in which the product is immersed in water for 2 minutes, drained for 2 minutes, and weighed.

Another feature of considerable utility and interest is the manner in which the tensile properties of the structure are unaffected by the presence of water or other swelling agent therein. The fabric of this example showed a measured machine direction tensile strength of 2.57 pounds per inch of Width and about one-fifth of this in the cross direction. When wet with water these values did not change significantly, measuring 2.20 pounds per inch width in the machine direction and 050* pound crosswidth.

The high absorbency and softness that is characteristic of this material makes it especially useful for many hospital product applications such as sponges, pads, rolls, etc. Its intrinsic softness on both sides results from the special feature of this process which locates the apertures, representing the bonding points of the structure, at approximately the mid-point of the cross section in deep pockets of bulked fiber.

Carded structures of blended fibers similar to the above have been made in a range of Weights from 40 to 12.0 grams .per square yard and with binder fiber fractions from 0.10 to 0.50, and non-binder fibers other than bleached cotton, including viscose rayon, and Dynel (Union Carbides modified acrylic fiber). Especially when synthetic fibers are used, or coarse deniers of viscose, the resulting apertured felts have a combination softness, conformability and resilience which makes them suitable for interlining use.

The size and spacing of the aperture made by the process of this invention may readily be varied by changing the dimensions, spacing, and orientation of the lands and grooves on the forming rolls. In general, an acceptable range of aperture size seems to be from 0.03 to 0.125 inch in the long diameter of the aperture, at a spacing of from 0.25 and 0.50 inch on centers. Customarily, using textile-length fibers of from 1 to 2 inches in length, the average fiber length is at least eight times the maximum width of an aperture, though products of a special nature may demand departure from these dimensional characteristics.

Having thus described our invention, we claim:

1. The method of reforming an unspun and unwoven sheet of nonwoven deformable textile material comprising intermingled fibers of textile length, characterized by passing said sheet between a pair of non-meshing and non-interpenetrating rigid rolls rotating in opposite directions, said rolls being engraved in a pattern of land and grooves, the sum of the radii of said rolls being at no time greater than the distance between their axes, the lands and grooves on at least one roll being angularly disposed to the central axis of the roll at an angle of less than 90, a segment only of any land area on one of said rolls transiently traversing a segment of a land area on the other of said rolls, without synchronization of the lands and grooves of the opposing rolls, whereby maximum pressure is exerted on said deformable textile material at a set of discrete and spaced-apart points, intermediate pressure is exerted where a land on one roll has traversed a groove on another roll, and minimum pressure is exerted where a groove on one roll has traversed a groove on the other roll, thereby producing a fabric having a set of uniformly spaced-apart quadrilateral areas bounded fully on each of their four sides by an area of lightly-compacted fibers, and each such quadrilateral area being contiguous at each of its four apices to an area of substantially uncompacted fibers.

2. The method according to claim 1 in which the pattern of lands and grooves on at least one of said rolls is helical.

3. The method according to claim 1 in which both rolls bear a helical pattern of lands and grooves of identical dimensions and of the same angle and orientation of pitch.

4. The method according to claim 1 in which One roll has a helical pattern of lands and grooves angularly disposed to the roll axis at less than 90, and the other roll a pattern of lands and grooves which are perpendicular to the roll axis.

5. The method according to claim 1 in which the lands and grooves on one roll differ in width from the lands and grooves on the other roll.

6. The method according to claim 1 in which the lands and grooves on one roll are helically oriented in a righthand sense, and the lands and grooves on the other roll are helically oriented in a left-hand sense, the lands on one roll being of greater width than the grooves on the other roll.

7. The method of producing an absorbent wiping pad of improved gripping action and resistance to collapse when wet which comprises felting together a fibrous mixture comprising absorbent fibers and thermoplastic fibers,

and subjecting the felted mixture to the process of claim 1,

in which process at least one of the rolls is heated sufiiciently to activate the thermoplastic fibers.

8. The method of producing a spot-bonded nonwoven fabric which comprises subjecting an unspun and intermingled array of textile-length fibers comprising thermoplastic fibers to the process of claim 1,

in which at least one of the rolls is heated sufiiciently to activate the thermoplastic fibers.

9. The method according to claim 8 in which the intermingled array of textile-length fibers comprises 25% to 100% thermoplastic fibers and to 0% absorbent fibers.

10. The method according to claim 8 in which the thermoplastic fibers are polypropylene and the absorbent fibers are viscose rayon.

11. The method of producing a laminated textile article which comprises forming at least one sheet of unspun and unwoven intermingled fibers of textile length, comprising thermoplastic fibers, plying at least one sheet of said fibers with at least one substrate layer, passing the assembly between a pair of non-meshing and non-interpenetrating rigid rolls rotating in opposite directions, at least one of said rolls being heated, said rolls being engraved in a pattern of land and grooves, the sum of the radii of said rolls being at no time greater than the distance between their axes, the lands and grooves on at least one roll being angularly disposed to the central axis of the roll at an angle of less than a segment only of any land area on one of said rolls transiently traversing a segment of a land area on the other of said rolls, without synchronization of the lands and grooves of the opposing rolls, whereby maximum pressure is exerted on said assembly at a set of discrete and spaced-apart points, intermediate pressure is exerted where a land on one roll has traversed a groove on another roll, and minimum pressure is exerted where a groove on one roll has traversed a groove on the other roll, thereby producing a laminated article having a set of uniformly spaced-apart quadrilateral areas bounded fully on each of their four sides by an area of lightly-compacted fibers, and each such quadrilateral area being contiguous at each of its four apices to an area of substantially uncompacted fibers.

12. The method according to claim 11 in which the pattern of lands and grooves on at least one of said rolls is helical.

13. The method according to claim 11 in which both rolls bear a helical pattern of lands and grooves of identical dimensions and of the same angle and orientation of pitch.

14. The method according to claim substrate is a woven fabric.

15. The method according to claim substrate is a film.

16. The method according to claim substrate is a paper.

17. The method according to claim substrate is a bonded nonwoven fabric.

18. The method according to claim substrate is an unbonded fibrous fleece.

19. The method according to claim 11 in which the deformable sheet material is a pressure-sensitive adhesive tape.

20. The method of aperturing an unspun and unwoven sheet of nonwoven deformable textile material comprising intermingled fibers of textile length which comprises applying to the unwoven sheet a liquid bonding medium, passing said sheet between a pair of non-meshing and non-interpenetrating rigid rolls rotating in opposite directions, at least one of said rolls being engarved in a pattern of land and grooves, the sum of the radii of said rolls being at no time greater than the distance between their axes, the lands and grooves on at least one roll being angularly disposed to the central axis of the roll at an angle of less than 90, a segment only of any land area on one of said rolls transiently traversing a segment of a land area on the other of said rolls, without synchronization of the lands and grooves of the opposing rolls, where by maximum pressure is exerted on said deformable 11 in which the 11 in which the 11 in which the 11 in which the 11 in which the textile material at a set of discrete and spaced-apart points, intermediate pressure is exerted where a land on one roll has traversed a groove on another roll, and minimum pressure is exerted where a groove on one roll has traversed a groove on the other roll, thereby producing a fabric having a set of uniformly spaced-apart quadrilateral areas bounded fully on each of their four sides by an area of lightly-compacted fibers, and each such quadrilateral area being contiguous at each of its four apices to an area of substantially uncompacted fibers.

21. The method according to claim 20 in which the pattern of lands and grooves on at least one of said rolls is helical.

22. The method according to claim 20 in which both rolls bear a helical pattern of lands and grooves of identical dimensions and of the same angle and orientation of pitch.

23. The method of producing an apertured nonwoven fabric which comprises moistening with water a prebonded nonwoven fabric comprising textile-length fibers unified by means of a polymeric binder, passing said sheet between a pair of non-meshing and non-interpenetrating rigid rolls rotating in opposite directions, at least one of said rolls being heated, said rolls being engraved in a pattern of land and grooves, the sum of the radii of said rolls being at no time greater than the distance between their axes, the lands and grooves on at least one roll being angularly disposed to the central axis of the roll at an angle of less than 90, a segment only of any land area on one of said rolls transiently traversing a segment of a land area on the other of said rolls, without synchronization of the lands and grooves of the opposing rolls, whereby maximum pressure is exerted on said nonwoven fabric at a set of discrete and spaced-apart points, intermediate pressure is exerted where a land on one roll has traversed a groove on another roll, and minimum pressure is exerted where a groove on one roll has traversed a groove on the other roll, thereby producing a fabric having a set of uniformly spaced-apart quadrilateral areas bounded fully on each of their four sides by an area of lightlycompacted fibers, and each such quadrilateral area being contiguous at each of its four apices to an areas of substantially uncompacted fibers.

24. The method according to claim 23 in which the pattern of lands and grooves on at least one of said rolls is helical.

25. The method according to claim 23 in which both rolls bear a helical pattern of lands and grooves of identical dimensions and of the same angle and orientation of pitch.

References Cited UNITED STATES PATENTS 1,962,683 6/1934 Dreyfus 264284 2,154,940 4/1939 Ives.

2,464,301 3/1949 Francis 264284 XR 2,591,385 4/1952 Sunderhauf 264322 XR 2,957,780 10/1960 Stephens 264-284 XR 3,137,893 6/1964 Gelpke 26493 3,150,416 9/1964 Such 264119 XR 3,351,693 11/1967 Feather 264320 XR 3,130,412 4/1964 Fox et a1.

ROBERT F. WHITE, Primary Examiner R. R. KUCIA, Assistant Examiner U.S. C1.X.R.

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