US 3459627 A
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Description (OCR text may contain errors)
g 1969 w. e. VOSBURGH, SR 3,459,627
NONWOVEN FABRIC WITH COLUMNAR BONDS 2 Sheets-Sheet 1 Filed June 12, 1864 INVENTOR WILLIAM GEORGE VOSBURGH, SR.
ATTORNEY Aug. 5, 1969 W. G. VOSBURGH, SR
NONWOVEN FABRIC WITH COLUMNAH BONDS 2 Sheets-Sheet 2 Filed June 12, 1964 FIG. 4
SELF- BOND AREAS/ INVENTOR mum GEORGE 'vosauncu, sn.
500 SELF-BOND AREAS IN.
. W M if.
ti; x Edmrizfi 1 iii .0 m
1/ BY M ATTORNEY 3,459,627 NONWOVEN FABRIC WITH COLUMNAR BONDS William George Vosburgh, Sn, West Chester, Pa., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Filed June 12, 1964, Ser. No. 374,704 The portion of the term of the patent subsequent to Feb. 13, 1985, has been disclaimed Int. Cl. D0411 1/06; B32b 7/14 US. Cl. 161-448 4 Claims ABSTRACT OF THE DISCLOSURE DETAILED DESCRIPTION OF THE INVENTION This invention relates to nonwoven fabrics, in particular to nonwoven fabrics which have an unusual combination of properties.
Nonwoven fibrous materials are Well known and products having a broad spectrum of properties are now available in the market place. In most cases, however, the combination of properties obtainable in any one product is very limited. Thus, while individual nonwoven products may be strong, conformable, tear-resistant, delamination-resistant, abrasion-resistant or may have low gas-permeability, heretofore a single product has not had all of these properties to a sufiicient extent to qualify it for replacement of woven fabrics in such applications as tenting materials, tarpaulins, tire chafers, shoeliners, etc. Another requirement for any nonwoven product to fit into these markets is that it be competitive from the cost standpoint with the woven fabrics now used. For the new product to have the most impact on the market place, it should, however, also offer salable property advantages over competitive materials. In addition to the properties listed above, particularly desired properties, especially in a nonwoven fabric to be used as protective coverings are resistance to mildew and rot and high tear strength at reduced fabric weight.
It is an object of this invention to provide a conformable nonwoven fabric which exhibits high tear and tensile strength, and resistance to delamination and abrasion.
A still further object is a nonwoven fabric with a low level of gas-permeability.
Another object is a nonwoven fabric which is a resistant to mildew and rot.
These and other objects of this invention are obtained by providing a nonwoven fabric of continuous synthetic organic filaments having at least 25 crimps per inch (10 crimps per centimeter) of unextended length, the fabric being bonded by a combination of (1) a synthetic organic binder distributed randomly throughout the fabric as granule bonds that constitute between 1 and 20% by weight of the fabric, and (2) from 500 to 1000 discrete self-bond areas per square inch (defined below) (80 to 160 per square centimeters) of the fabric surface, the self-bond areas being uniformly distributed over the fabric surface and covering between 2 and 12% of the surface area of the fabric.
The invention will be more readily understood by reference to the drawings in which:
atent O FIGURE 1 is a schematic representation of an apparatus assembly which can be utilized to prepare continuous filament nonwoven webs;
FIGURE 2 shows schematically in longitudinal section the nozzle portion of an aspirating jet which may be used with the apparatus of FIGURE 1;
FIGURE 3 is a schematic representation of a bonding apparatus which is suitable for use with these nonwoven fabrics produced by the apparatus in FIGURE 1;
FIGURE 4 is a graph showing the effect of number of self-bond areas per square inch on the air-permeability of a series of bonded nonwoven fabrics; and
FIGURE 5 is a graph which demonstrates the relationship between tenacity x conformability of a nonwoven fabric and the number of self-bond areas per square inch of fabric surface.
FIGURE 6 is an enlarged schematic plan view of a bonded fabric 19 of the invention having crimped filaments 20, self-bond areas 21, and granule bonds 22.
Continuous synthetic organic filaments are used in the nonwoven fabrics of this invention. The fabrics can be made economically in a process which integrates spinning, orientation of the filaments, and laydown of the filaments in the form of a random nonwoven web which is essentially free from filament aggregates. Such a process, which involves electrostatic charging of the filaments and then permitting the filaments to separate due to the applied electrostatic charge, is described in British Patent 932,482 and illustrated schematically in FIGURE 1. This process when used to produce a nonwoven fabric of poly(hexamethylene adipamide) or other polyamide filaments can be so operated that it inherently gives filaments with the level of crimp required for the fabric to be conformable. In the case of poly(ethylene terephthalate) filaments, a heat-relaxation step according to Kitson and Reese, US. Patent 2,952,879 can be effected during or subsequent to the web-laydown process to provide fibers which are spontaneously elongatable. Subsequent heating of the filaments, for example, during the bonding operation, causes the filaments to elongate and form crimps.
The concept of filament crimp is well understood in the art. Crimps can be measured by direct observation using a microscope with a scaled eyepiece, or by projection. A procedure which can be utilized with the bonded nonwoven fabrics of this invention involves making a photomicrograph of the fabric surface. A magnification of 65 X will usually be suitable. A transparent sheet material, e.g., cellophane, is then placed over the photomicrograph. Several filaments (e.g., 50) are then traced on the transparent sheet. For a filament whose general contour is straight, a straight line between the ends of the filaments is drawn and measured. The number of times the filament crosses the straight line is counted. Dividing this number number by two gives the number of crimps. For a curved filament, a sufiicient number of lines is drawn to provide an approximation of the curved contour of the filament. The total length of the straight line segments is measured, and the number of times the filament crosses the segments is divided by 2 to give the number of crimps. The number of crimps per inch of unextended length (c.p.i.) is calculated as follows: i
N XM G.p.l.- -L- where: N=total number of crimps in the sketched filaments M=magnification of the photomicrograph L=total length of the straight lines and straight line segments for the sketched filaments In this invention a filament crimp is one in which the amplitude of the departure from a straight line or a straight line segment is less than three times the radius of curvature of the crimp, the latter always being less than 0.5 inch (1.3 cm.).
Since, as indicated above, poly(hexamethylene adipamide) and poly(ethylene terephthalate) filaments can be readily formed into a web with crimped filaments and moreover, because these synthetic filaments yield nonwoven fabrics which are mildewand rot-resistant, they are preferred for use in this invention. The most preferred species is po1y(ethylene terephthalate). Other continuous synthetic filaments, e.g., polypropylene, which can be formed into nonwoven webs having crimped filaments can also be used, however; and this invention is not limited to either the specific polymers above or to products made by the above-described web-laydown process. For example, crimp in continuous filaments can also be obtained by the use of two-component fibers as disclosed in Breen, U.S. Patent 2,931,091; and such side-by-side spun filaments as poly(ethylene terephthalate)/poly(propylene terephthalate) and poly(ethylene terephthalate)/ poly(hexamethylene adipamide) can be used in the nonwoven fabrics of this invention. Crimped filaments can also be prepared by the process of Kilian, US. Patent 3,118,012.
A convenient and effective way to distribute the binder uniformly throughout the nonwoven fabric is by cospinning it with the matrix filaments of the fabric. In order to be readily melt-spinnable, the initial tensile modulus of the binder should be g.p.d. or higher. With this limitation on the modulus of the binder, it is necessary in order to obtain the desired level of conformability in the nonwoven fabric, not to use more than about 20% binder based on the total fabric. The minimum level of binder, 1%, is the amount which will give the bonded nonwoven fabric sufiicient strength for subsequent coating operations such as are used in the preparation of tenting materials or chafer fabrics. In other applications where the nonwoven fabric is not coated, such as in shoe liners, a higher level of binder, e.g., 13%, is used to obtain the desired abrasion resistance.
Conformability, referred to hereinabove, may be defined as the ability of a fabric to undergo area deformation and thereby mold itself to a curved-tl1reedimensional surface, such as a sphere, when stretched thereover. This property, which is essential to satisfactory performance of a tenting material and is also required in tire chafer fabrics and shoe liners, can be conveniently measured in the laboratory by placing an 8-inch (20 cm.) diameter circular sample of the fabric over the top of a 3-inch (7.6 cm.) diameter steel sphere. The level of conformability may then be expressed as the area of the surface of the sphere covered by the sample without breaks or folds. The area of the conforming surface is determined by (1) drawing the largest circle which just excludes the first breaks or folds that are formed on the surface of the fabric, (2) measuring the diameter of the circle, and (3) calculating the area by the following equation:
I) where A=conformability D=diameter of sphere d=diameter of largest circle.
A soft, drapable, textile-like nonwoven fabric will, merely under its own weight, conform over a significant area of the sphere. The nonwoven fabrics of this invention, however, are relatively stiff and do not conform under their own weight. They can be forced to conform by attaching weights to the edges of the fabric sample. In this respect they differ from papery materials which, when forced to conform to a spherical surface, form sharp bends. whi h may intersect with each o h r o gi e h rp breaks, abrupt changes in slope, and sharp edges. These characteristic attributes of a papery break occur because paper does not readily undergo area deformation. The fabrics of this invention exhibit a conformability of 0.5 in. (3.2 cm?) or greater under a total load of 500 g.//- oz./yd. (14.7 g.//g./m. applied to the edges of the fabric at 8 equidistant points.
In addition to the binder amount and modulus, and the level of crimp in the constituent filaments, another factor affecting the conformability of the nonwoven fabrics of this invention is the number of discrete self-bond areas per square inch of the fabric. If the number exceeds 1,000 per square inch (160 per square centimeters), or if these bond areas cover more than 12% of the surface area of the fabric or if the areas are not discrete, the conformability rapidly decreases to a value of less than 0.5m. (3.2 cm.
The minimum number of self-bond areas in the nonwoven fabrics of this invention is determined by the requirement that the fabrics be resistant to delamination and abrasion and have a certain maximum level of airpermeability, namely less than about 250 cubic feet per square foot per minute (76 m. /m. /min.) at a pressure differential of 0.5 inch (1.3 cm.) water. It has been found that the required resistance to delamination and abrasion and level of permeability are obtained if there are at least 500 self-bond areas per square inch (80 square centimeter) and if at least 2% of the surface area of the fabric is covered by the self-bond areas. Other factors such as filament denier and degree of freedom from filament aggregates also have an effect on the air-permeability of the nonwoven fabrics of this invention. It has been found, however, that if these factors are held constant, the permeability increases markedly with fewer than 500 self-bond areas per square inch (80 per square centimeter). As low a permeability as possible consistent with maintenance of the desired level on conformability is preferred because this property correlates directly with the amount of coating required to obtain a waterproof tenting material.
The self-bond areas can be formed by passing the nonwoven fabric between heated embossing rolls under pressure. Under these conditions the fibers in sections of fabric compressed between raised portions of the rolls are consolidated as discrete columns extending through the thickness of the fabric in a direction generally perpendicular to the plane of the fabric. The columns, which are arranged in a predetermined pattern, comprise matrix filaments that are adhered to each other and may additionally contain binder material of the type randomly disposed throughout the remainder of the bonded fabric of the invention. The terminals of the columns at the faces'of the fabric constitute the self-bond areas.
The temperature and pressure required to produce self-bond areas through use of embossing rolls will depend on the nature of the matrix filaments in the nonwoven fabric. For instance, with filaments of poly(ethylene terepthalate), having a density of 1.37 or less a pressure of 50 p.s.i. (3.5 kg./cm. and a temperature of C. or greater are suitable. Higher-density po1y(ethylene terephthalate) fibers will require a higher temperature. The embossing rolls which are used may have matching surface patterns with raised areas corresponding to the desired number and size of the self-bond areas. It is, however, difiicult with paired rolls of this type to obtain the exact and complete registry which is required to form distinct self-bond areas. It is especially difficult because of the large number and small size of the self-bond areas. Thus the raised areas on the embossing rolls must number 500 to 1,000 per square inch (80 to per square centimeter) and have a size of 0.00002 to 0.00016 square inch (0.0013 to 0.0010 cm. While it is possible to use the foregoing type of embossing rolls, it is preferred to use grooved rolls, one roll having parallel grooves run-. ning circumferentially around the roll and the other of the roll. As the fabric passes between these two rolls, it receives the maximum pressure between the rolls only at the locations where the raised areas between the grooves on the two rolls cross, thus only at these locations will self-bond areas be formed. Typical rolls for use in making the nonwoven fabrics of this invention have 24 grooves per inch (9.5 per centimeter) with the raised areas between grooves being 0.008 inch (0.02 cm.) wide. Use of two such rolls gives 576 self-bond areas per square inch (89 per square centimeter) and the self-bond areas cover 4% of the surface of the fabric.
The denier of the matrix filaments of the nonwoven fabrics affects the permeability characteristics. Since permeability decreases with decreasing filament diameter, it is generally preferred that the filaments in the nonwoven fabrics of this invention have a denier of 9 or less. The binder filaments normally are spun at about the same denier as the matrix filaments to aid in obtaining uniform distribution throughout the nonwoven fabric.
As indicated previously, the binders used in this invention are high-modulus materials. This is required in order that they can be incorporated into the nonwoven fabric by cospinning with the matrix filaments. The binder should be chosen so that its melting point is at least 10 C., and preferably at least 25 C., below the melting point of the matrix filaments. Preferred binders for use with poly(hexamethylene adipamide) filaments include polycaproamide and copolymers thereof with poly (hexamethylene adipamide). Preferred binders for use with poly(ethylene terephthalate) include poly(ethylene terephthalate)/poly(ethylene isophthalate), poly(ethylene terephthalate)/poly(ethylene sebacate), and similar copolyesters. The heating operation in which the binder filaments are activated to form the granule bonds is usually carried out after the embossing operation which forms the self-bond areas. The temperature used is, of course, dependent on the nature of the binder. Typical temperatures used when an 80/20 copolymer of poly (ethylene terephthalate)/poly(ethylene isophthalate) is used as the binder are in the range of 190 to 230 C.
The invention will be further illustrated by the following examples:
Example 1 This example describes the preparation of bonded nonwoven product of this invention which is useful in making a coated tenting material. The apparatus assembly used in this example is shown schematically in FIGURE 1, wherein the filaments pass directly, as indicated by the dotted lines, from the spinnerets 1 and 2 to the target bar of corona discharge device 3. Poly(ethylene terephthalate) (27 relative viscosity) is spun through spinneret 1 having 17 holes (0.009 in. diameter x 0.012 in. long) (0.023 cm. x 0.031 cm.) at a total throughput of 20.0 g./ min. while an 80/20 copolymer of poly(ethylene terephthalate)/poly(ethylene isophthalate) (29 relative 'viscosity) is spun through spinneret 2 having 10 holes (0.009 in. diameter x 0.012 in. long) (0.023 cm. x 0.031 cm.) at a total throughput of 9.0 g./min. The spinneret temperatures are 285 C. and 258 C., respectively. Three of the copolyester filaments are used and the other 7 are spun to waste. The filaments are quenched in the ambient air at 27 C. before entrance into a draw jet 4 located about 65 in. (165 cm.) below the spinnerets. The 20 filaments from the two spinnerets are combined into a filament bundle at the target bar of corona discharge device 3 which is located about 6 inches (15 cm.) from the jet inlet.
The corona discharge device consists of a 4-point electrode positioned 0.63 inch (1.6 cm.) from a grounded, 1.25-inch (3.2 cm.) diameter, chrome-plated target bar rotating at 10 r.p.m. A negative voltage of 35 kv. (200 microamperes) is applied to the corona points. The filament bundle passes between the target bar and electrode and makes light contact with the target bar.
The filaments are drawn and forwarded toward the laydown belt 7 by aspirating jet 4 having a nozzle section as shown in FIGURE 2 and having the following dimensions:
Inches Over-all jet length (61 cm.) 24 Filament inlet diameter 9 (0.158 cm.) 0.062
Filament passageway diameter 10 (0.254 cm.) 0.100 Metering annulus 11:
Inner diameter (0.190 cm.) 0.0750 Outer diameter (0.236 cm.) 0.0930 Length (0.051 cm.) 0.020 Filament inlet length 12 (1.40 cm.) 0.55
Air at a pressure of 49.5 p.s.i.g. (3.5 kg./cm. is supplied to the jet through inlet 13. The jet under these conditions applies about 13.5 grams total tension to the filament bundle. Attached to the bottom of the jet is a relaxing chamber 6 (9.5 in. long; 0.375 in. inside diameter) (24 cm.; 0.95 cm.) which is provided with an annular nozzle for supplying additional air to the relaxing cham ber. Hot air (about 300 C.) is supplied to the relaxing chamber at a rate of 4.5 standard cu. ft./min. (127 liters/ min.), or sutficient to give an air temperature of 225 C. at the exit of the relaxing chamber. This raises the filament temperature to an estimated C. at the exit Filaments spun without hot air in the relaxing chamber will have a linear shrinkage of about 25% when treated in 75 C. water. Filaments processed with hot air in the relaxing chamber will show a linear shrinkage of less than 2% in 75 C. water, and will show spontaneous elongation (SE) as exhibited by a linear elongation of about 15% when heated relaxed in dry air at 200 C.
The jet-relaxing chamber unit is positioned at an angle of 82 with the plane of laydown belt and is moved by a traversing mechanism 5 so that it generates a portion of the surface of a cone, while the output from the relaxing chamber forms an arc on the laydown belt 7 having a chord length of 36 inches (91 cm.). The traverse speed is 20 passes (10 cycles) per minute. The distance from the exit of the relaxing chamber to the laydown belt is approximately 30 inches (76 cm.). The laydown belt moves at a speed of 7.8 inches (20 cm.) per minute. Plate 8 located beneath the belt is charged at +35 kv. to attract and hold the filaments to the laydown belt.
A typical unbonded web prepared by this procedure will have the following properties: unit Weight 3.5 oz./yd. (119 g./rn. homopolymer filaments 3.8 d.p.f.; copolymer binder filaments 3.7 d.p.f.; amount of copolymer binder, 12% by weight.
A web prepared by the above process is next embossed in a hot-calendering operation. Embossing is carried out with a conventional calender stack equipped with two steel rolls each 16 in. (41 cm.) in diameter. The top roll of the pair is patterned with raised areas and grooves machined parallel to the axis of the roll, at a frequency of 24 raised areas/in. (approximately 10/cm.). Each raised area is 0.0075 in. (0.0190 cm.) wide and each .groove is 0.019 in. (0.048 cm.) deep. The bottom roll has raised areas and grooves of the same size and frequency set perpendicular to the axis of the rolls. Embossing of the web is carried out at 4 yds./min. (3.7 m./min.) with both rolls heated to a temperature of C., and under a pressure of 50 lbs/linear in. (8.9 kg./cm.). The selfbond areas so formed cover 3.2% of the surface of the web.
Bonding of the embossed web is accomplished by restraining the web between a belt and a metal drum while heating the web to a temperature sufiicient to melt the binder filaments. The bonding unit is shown schematically in FIGURE 3. This consists of a 20m. (51 cm.) diameter steel drum 14 wrapped tightly with a Woven wire screen having 30 x 28 wires per inch (11 x 12 per cm.). This drum is motor-driven and has provision for internal oil heating. An endless flexible wire screen 15 is held in contact with the drum by guiding over suitable Webs are bonded at 215 C., but do not contain the selfrollers 16, to provide a drum-to belt contact of 31.4 in. bond areas of the fabric of this invention. (80 cm.), and tensioned sufiiciently to provide a unit pressure of about 0.40.5 1bs./ sq. in. (0.030.04 kg./cm. Tongue Tear" SIB Percent against the drum. The entire assembly is enclosed in an 5 Bonded web Binder Lb, Kg FL Kg insulated box 17 which can be heated with hot air and I 12 5 3 9 4 22 0 030 is provided with entrance and exit slots for the web 18. 'f V 9 i 0:014 The embossed Web from about is bonded by a passing a I g I through this unit at 4 ydsjminl m /min with (gigging gggesiotlilbtamed with samples tested 111 the machine and both the drum and air temperature inside the box being 10 held at 200 C.; Residence time in the box is about 28 seconds and residence time under restraint is about 13 The use of discrete self-bond areas according to this invention improves delamination-resistance and lowers permeability with no loss in tear. Additional binder imseconds.
proves the delammation-resistance but at the ex ense of Typical properties of the sheet bonded by the above tear Strength, and, moreover, it does not g any described Process ale as follows: 15 significant change in the permeability. Thus, to obtain Unit Wei the desired combination of high tear strength, delamina- 3 5 i2) d 2 (110 w /m tion-resistance, and reduced air-permeability, it is neces- Thickllessf y sary for the nonwoven fabric to contain self-bond areas 0024 in (01061 in acocrdance with this invention. Strip tensile strength: Example 3 5.9 lbs./in.//oz./yd. (31 g./cm.//g./m. Tongue tear:
2.1 lbs.//oz./yd. (28 g.//g./m.
This example establishes the lower and upper limits on the number of self-bond areas required to obtain the' optimum level of air-permeability consistent with the conformablhfyi strength. and conformability required in the nonwoven 1 cm-z) fabrics. A graph of air-permeability against the number Penneablhty2 of discrete self-bond areas is shown in FIGURE 4. Air- 225 fts/fl-z/mlfh (at mch of Watt) permeability is measured with a Gurley Permeometer at (69 (at 0f Water) a pressure differential of 0.5 inch (1.3 cm.) of water.
Fliament cnmpfl 30 With fewer than 500 self-bonds per square inch (80 per P Inch of unextended length square centimeter), the permeability increases markedly. 2046 P of unextended length A graph of tenacity x conformability against the number of discrete self-bond areas is shown in FIGURE 5. The web samples used in this study are prepared by the same general procedure as in Example 1. The binder content is 13% and the matrix filaments have a high level of spontaneous elongation before embossing and bonding. The webs are simultaneously embossed and bonded in a laboratory press at 156 lb./in. (10.0 kg./cm. 225 C., for seconds between various cross-lined plates. After bonding, the crimp levels in the matrix filaments is about per inch of unextended lengths (28 per centimeter). It is noted from FIGURE 5 that the numerical value obtained by multiplying the conformability times the' tenacity drops sharply when the selfbond density exceeds 1,000 per square inch (160 per square centimeter).
Example 2 This example demonstrates the beneficial effect of discrete self-bond areas on delamination resistance as measured by the Scott Internal Bond (SIB) test and air permeability as determined with a Gurley Permeometer (ASTM D-737) at a pressure differential of 0.5 in. (1.3 40 cm.) water. Webs A and B are prepared by the procedure described in Example 1. Both webs consist of 88% poly(ethylene terephthalate) filaments and 12% binder [/20 poly(ethylene terephthalate)/poly(ethylene isophthalate) copolyester] filaments. The matrix filaments of 45 the webs are capable of elongating 5% in length during the embossing and/or bonding operations. Web A is bonded at 215 C. Web B is embossed between crosslined rolls as in Example 1 to give 576 discrete self-bond Example 4 0 I u areas P Square Inch P Square Centlmetel') P This example lllustrates the effect of binder content on to bonding at 200 C. The results are summarized conformability of the nonwoven fabrics of this invention. below: Unbonded webs having various levels of copolyester binder Unit Weight Grab Tensile* Tongue Tear SIB Air Permeability Bonded Web OzJyd. G.j'n1. Lb. Kg. Lb. Kg. Ft. lb. Kg. m. Fti litfilmin. MfilnL lmin.
A s. e 122 82 37 6.9 3.1 0. 16 0. 022 247 75 B 3. 4 75 34 7. 4 3. 4 0. 25 0. 035 14s 45 *Average of values obtained with samples tested in the machine and cross-machine directions.
It is readily apparent from these results that the presare prepared following the general procedure outlined ence of discrete self-bond areas within the number range in Example 1. The matrix filaments are poly(ethylene specified for the nonwoven fabrics of this invention proterephthalate) and the copolyester filaments are polyvides a significant increase in delamination-resistance (ethylene terephthalate)/ po1y( y n i ph h l e). The (higher SIB value) and a significant decrease in air- 70 Webs are embossed and bonded in a single operation by permeability, both without a loss in tensile strength or being held between lined plates (lines in top plate pertear strength. An increase in the binder concentration pendicular to lines in bottom plate) at 210 C. for 30 secwill also improve the delamination-resistance of a nononds at a pressure of 78 lbs/in. (5 .5 kg./cm. Two pairs woven fabric, but this leads to a reduction in tear of lined plates are used, one giving 576 self-bond areas per strength. Some data with webs similar to A and B is pre- 75 square'inch (89 per cm?) and the other, 900 per square sented below to substantiate these conclusions. These inch (139 per cm. The percentages of the fabric sur- Self-Bond Areas Coniormability- Percent Binder No./in. NoJem. In. Cm.
The results indicate the amount of binder has a significant effect on conformability. In order to have a conformability of at least 0.5 in. (3.2 cm. the binder level is maintained below 20%, based on the total weight of the fabric. The results further indicate that within the number of self-bond areas specified for the nonwoven fabrics of this invention, conformability is not significantly affected by the number of self-bond areas.
Example 5 This example demonstrates the effect of crimp level on conformability. Nonwoven webs are prepared, bonded and embossed as in Example 4. The table below summarizes the results.
Self-B nd Areas Crimp Level Conformability Percent Binder NoJin. NoJem. No./in. No./cm. In Cm.
At a crimp level below crimps per inch (10 per cm.) of unextended length, the conformability drops below the desired level of 0.5 in. (3.2 cm.
Example 6 This example shows the effect of number of self-bond areas and the total area of the fabric surface covered by those areas on the abrasion resistance of nonwoven fabrics. A nonwoven web is prepared following the general procedure of Example 1. The matrix filaments are poly- (ethylene terephthalate) and show a spontaneous elongation of about 20% when heated during the embossing and bonding operation. The binder filaments of poly(ethylene terephthalate)/poly(ethylene isophthalate) are present in an amount of 13% by weight based on the fabric. The nonwoven web is simultaneously embossed and bonded following the procedure of Example 4 using crosslined plates to give the number of self-bond areas indicated in the table below. The percentage of the fabric surface covered by the self-bond areas is determined by microscopic examination of the bonded fabrics. The fabrics are evaluated for abrasion resistance with the abrasion tester described in ASTM D-1242, Procedure B, by measuring the number of abrasion cycles to failure.
Self-Bond Areas Percent Surface Area Abraslon-Resistance No./in. No./em. Covered Cycles to Failure These results indicate that abrasion-resistance increases as the number of self-bond areas and the total area covered by the areas increase. Crimps in the matrix filaments of the products of this invention also contribute to abrasion resistance. In order to obtain the level of abrasion resistance required in applications such as shoe liners, it is desired that the fabrics can tolerate at least 90 abrasion cycles in the above test. With fewer than 500 self-bond areas per square inch per cm. the abrasion resistance is below this level.
Example 7 This example demonstrates the application of a weatherresistant, water-repellent coating to the nonwoven fabrics of this invention to give a product with the required strength, conformability and breathability (passage of air and water vapor) for superior performance as a tenting material. The coating formulation is as follows:
Cure accelerators Titanium dioxide Phthalooyanine blue 17 Pigments. Carbon black Alkylated phenol 2 Antioxidant. Xylene 750-1, 000 Solvent.
1 Combination of 1.5 parts tetramethylthiuram disulfide; 1.5 parts zinc dimethyl dithiocarbamate; 1 part Zinc salt of 2mercaptobenzothiazole; and 1 part piperidinium pentamethylenedithiocarbamate.
The coating formulation is prepared by mixing the solid ingredients in a rubber mill or Banbury mixer, and then mixing with the xylene, which is a solvent for the butyl rubber and ethylene/propylene rubber, to give a composition containing 1520% solids. The coating formulation is then applied to a nonwoven fabric of this invention, for example, the nonwoven fabric of Example 1, by conventional coating techniques such as a dip coatingknife scraping operation. The coating is dried by heating in an oven and vulcanization of the elastomeric components of the coating is effected by heating at l50-l75 C.
In the above formulation, the butyl rubber contributes softness and drape while the ethylene/propylene rubber provides resistance to weather. Although conventional butyl rubbers work satisfactorily, a butyl rubber containing about 1.2% chlorine is preferred because of its more rapid curing rate. The antioxidant improves the weatherresistance of the coating and prevents its softening.
Satisfactory coatings for tents and tarpaulins can also be obtained by application of two separate coating compositions on the nonwoven fabrics of this invention. Thus a soft butyl-rubber-coating formulation may be applied first followed by an ethylene/ propylene rubber-coating formulation for weather-resistance. The combination coating containing both the butyl and ethylene/ propylene rubbers is preferred, however, because of the obvious simplicity in using a single coating.
The nonwoven fabrics of this invention are characterized by a tensile strength of at least 5 lb./in.//oz./yd. (26 g./cm.//g./cm. a tear strength of at least 1.5 lb./ oz./yd. (20 g./g./m. a conformability of at least 0.5 in. (3.2 cm. high delaminationand abrasion-resistance and the minimum air-permeability consistent with these properties. This combination of properties in a nonwoven fabric is unique and it enables the products of this invention to be used in applications which have previously been closed to nonwoven fabrics.
What is claimed is:
1. A nonwoven fabric comprising continuous synthetic organic fibers having at least 25 crimps per inch of unex tended length, said fabric having randomly distributed therethrough as granule bonds, a synthetic organic binder in an amount between about 1 and 20% by weight of the fabric and from about 500 to 1000 discrete, self-bond 3,459,627 1 1 12 I areas per square inch of the fabric surface, said self-bond References Cited areas covering between about 2 and 12% of the surface area of the fabric, with the self-bonds extending as discrete UNITED STATES PATENTS columns through the thickness of the fabric. 3,117,055 1/1964 GuaPdique et 161170 2. The fabric of claim 1 wherein the synthetic fibers 2,774,129 12/1959 m 161'170 X are poly(ethy1ene terephthalatey 5 2,774,128 12/1956 Secnst 161-170 X 3. The fabric of claim 1 wherein the organic binder has an initial tensile modulus of at least 5 grams per ROBERT BURNETT Primary Examine:
denier. M. A. LITMAN, Assistant Examiner 4. The fabric of claim 3 wherein the organic binder U S C] X R is a copolymer of poly(ethylene terephthalate) and poly- 10 (ethylene isophthalate). 156-181, 209; 161150, 170