Classifications

• • D—TEXTILES; PAPER
  • D04—BRAIDING; LACE-MAKING; KNITTING; TRIMMINGS; NON-WOVEN FABRICS
  • D04H—MAKING TEXTILE FABRICS, e.g. FROM FIBRES OR FILAMENTARY MATERIAL; FABRICS MADE BY SUCH PROCESSES OR APPARATUS, e.g. FELTS, NON-WOVEN FABRICS; COTTON-WOOL; WADDING ; NON-WOVEN FABRICS FROM STAPLE FIBRES, FILAMENTS OR YARNS, BONDED WITH AT LEAST ONE WEB-LIKE MATERIAL DURING THEIR CONSOLIDATION
  • D04H3/00—Non-woven fabrics formed wholly or mainly of yarns or like filamentary material of substantial length
  • D04H3/08—Non-woven fabrics formed wholly or mainly of yarns or like filamentary material of substantial length characterised by the method of strengthening or consolidating
  • D04H3/14—Non-woven fabrics formed wholly or mainly of yarns or like filamentary material of substantial length characterised by the method of strengthening or consolidating with bonds between thermoplastic yarns or filaments produced by welding
• • D—TEXTILES; PAPER
  • D04—BRAIDING; LACE-MAKING; KNITTING; TRIMMINGS; NON-WOVEN FABRICS
  • D04H—MAKING TEXTILE FABRICS, e.g. FROM FIBRES OR FILAMENTARY MATERIAL; FABRICS MADE BY SUCH PROCESSES OR APPARATUS, e.g. FELTS, NON-WOVEN FABRICS; COTTON-WOOL; WADDING ; NON-WOVEN FABRICS FROM STAPLE FIBRES, FILAMENTS OR YARNS, BONDED WITH AT LEAST ONE WEB-LIKE MATERIAL DURING THEIR CONSOLIDATION
  • D04H1/00—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres
  • D04H1/40—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties
  • D04H1/54—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties by welding together the fibres, e.g. by partially melting or dissolving
  • D04H1/542—Adhesive fibres

Definitions

• This invention relates to processes for bonding nonwoven webs of organic fibers to form nonwoven fabrics. More specifically, the invention relates to such processes wherein the web is preferentially bonded in spaced, discrete areas.
• Nonwoven fabrics and numerous uses thereof are well known to those skilled in the art. Such fabrics are prepared by forming a web of continuous filament and/or staple fibers and bonding the fibers at points of fiber-to-fiber contact to provide a fabric of requisite strength.
• nonwoven fabrics bonded by autogenous fiber-to-fiber fusion are desired. Bonding of this type is in some instances obtained by the application of heat to soften or plasticize the fibers and render them cohesive. In such thermal bonding technques the web can be subjected to mechanical compression to increase contact of the thermally softened fibers and provide bonds of required strength.
• nonwoven fabric When web fibers are bonded at essentially all points of fiber-to-fiber contact, for example, by overall compression of the web in the presence of heat, the resultant nonwoven fabric tends to be stiff and boardy and characterized by low elongation and tear resistance. That is, such overall bonded fabrics are frequently more similar to paper than to conventional textile fabrics.
• nonwoven "point-bonded" fabrics In order to more closely simulate the properties of conventional textiles, nonwoven "point-bonded" fabrics have been prepared by processes tending to effect preferential bonding in spaced, discrete areas (primary bond sites). In order to provide point-bonded nonwoven fabrics of adequate strength, it is generally necessary that bonding of the web in the primary bond sites be accompanied by mechanical compression.
• the compression means are generally heated sufficiently to effect thermal bonding.
• bonding is not limited to the primary bond sites produced in the areas compressed. Varying degrees of secondary or “tack” bonding are generally observed between the primary bond sites. Such "tack” bonding probably results from the fact that techniques employed for preparing point-bonded nonwoven fabrics expose areas of the web between the areas being compressed to heat sufficient to effect some softening and tack bonding of fibers at points of contact. The strength and number of the tack bonds formed may vary widely with the properties of the fiber utilized in the web as well as the conditions employed for effecting bonding in the primary bond sites. Desired fabric properties such as softness are progressively impaired as the degree of tack bonding is increased. There is, therefore, a need in the art for processes capable of providing softer nonwoven fabrics.
• the process of the invention is one for making point-bonded nonwoven fabrics, said process being characterised by simultaneously heating and compressing spaced, discrete areas of a nonwoven web of thermally bondable organic fibers said web containing an attenuating liquid and the quantity of attenuating liquid, the temperature, the compressive force, and the time of exposure of the web thereto being correlated to effect bonding of web fibers in the heated and compressed areas and to provide a point-bonded nonwoven fabric having a bending modulus at least 20% lower than that.of a fabric prepared without the use of said attenuating liquid under otherwise equivalent conditions.
• the practice of the invention will be understood from the following description of the preferred embodiments.
• thermoly bondable organic fibers is used herein in the specification and claims to denote fibers which can be bonded at points of fiber-to-fiber contact by the application of heat and compression.
• thermoplastic polymer essentially any thermoplastic polymer can be utilized.
• the fibers may be in the form of continuous filaments or staples or mixtures thereof.
• bondable fibers suitable for use in the practice of this invention include polyamide fibers such as nylon 6 and nylon 66; and polyester polymer fibers.
• Composite fibers such as fibers having a sheath of one polymer and a core of another polymer or side-by-side polycomponent fibers can be utilized.
• multicomponent fibers it is not essential that all polymer components thereof be bondable under the process conditions hereinafter described.:It. is sufficient that such multicomponent fibers have bondable surface portions. If desired, the fibers can be crimped or textured to provide elasticity or other desired characteristics to the finished fabric.
• the thermally bondable fibers are processed in the form of nonwoven webs.
• the nonwoven webs of bondable organic fibers nmay be composed entirely of bondable fibers or, alternatively. may consist of bondable fibers interspersed with other fibers.
• the art of preparing nonwoven webs is well understood and the manner of web formation is not critical. Generally webs are formed by deposition of fibers on a moving belt in either random or aligned orientation to provide a web having a weight of from 4 to 400 grams per square meter, preferably 10 to 150 grams per square meter. Particularly useful methods for web formation are disclosed in United States Patent No. 3,542,615.
• a selected quantity of attenuating liquid is applied to the web and the web is simultaneously heated and compressed in spaced discrete areas to effect bonding of the fibers in such areas.
• the attenuating liquid can be any liquid whose presence in the web in quantities of 1000% or less of the web weight does not, under the bonding conditions employed, provide a fabric having higher strip tenacity (strength) than would be obtained in the absence of such liquid under otherwise equivalent conditions and which provides a fabric having at least a 20% lower bending modulus than that of a fabric obtained in the absence of such liquid under otherwise identical conditions.
• a key element of the present invention is this unexpected discovery that utilization of an attenuating liquid in sufficient quantity will provide a reduction in fabric bending modulus (i.e., an increase in fabric "'softness") as compared to that of fabrics prepared using no liquid under otherwise equivalent conditions.
• a quantity is employed to reduce bending modulus by at least 20%.
• the actual amount of attenuating liquid used may be any quantity sufficient to effect such reduction. Generally, there is no theoretical objection to use of very large quantities of liquid..
• the amount of liquid be chosen such that in addition to reducing bending modulus by at least 20% a higher ratio of strip tenacity to bending modulus (as compared to that obtained using no liquid) is obtained. That is, the maximum quantity utilized is preferably chosen so as not to reduce fabric strength disproportionately to improvements in softness obtained.
• a particular liquid will function as an attenuating bonding liquid will depend on the nature of the nonwoven web to be bonded, the properties of the fibers constituting the web and the manner in which the web is heated and compressed. Therefore, it is not practical to exhaustively list all combinations of liquids, fibrous webs and conditions of temperature and compression suitable for the practice of the present invention. For example, water will effectively improve the bonding of a web of nylon fibers highly compressed in spaced discrete areas at temperatures below that required to cohesively soften an otherwise identi--cal dry web. Thus, under such conditions water is considered a bonding agent rather than an attenuating liquid. However, under low compressive force and temperatures sufficiently high to effect thermal bonding, water may function as an attenuating liquid. The effectiveness of a particular liquid as an'attenuating liquid under given bonding conditions can readily be determined by routine tests.
• Attenuating liquids provide softening by limiting (for example by evaporative cooling, heat capacity, etc.) the temperatures attained in the web in areas not being simultaneously heated and compressed as hereinafter described.
• the heat attenuation provided by the liquid is believed to limit or prevent tack bonding outside the discrete, spaced areas which are heated and compressed, thereby providing a softer fabric.
• preference may be given to those which have relatively low boiling points as compared to fiber softening points and / or those having high heat capacities.
• any liquid which is not a bonding agent and has a boiling point below the fiber softening point will be an effective attenuating liquid.
• liquids contemplated to be suitable attentuating liquids for polyamide fibers include water and hexane; examples of suitable attenuating liquids for polyester fibers include water and carbon tetrachloride.
• the nonwoven web containing the attenuating liquid is simultaneously heated and compressed in spaced, discrete areas (points) to effect fiber bonding in such areas thereby forming the web into a point-bonded fabric.
• Simultaneous heating and compression of the web in spaced, discrete areas can readily be accomplished by compressing the webs between a pair of compressing means such as rolls or platens at least one of which compression means is heated. Further, one or both of the compression means will have bosses or a land and groove design or combinations thereof such that compression of the web will be effected in spaced discrete areas rather than overall. In order to provide adequate overall physical properties it is generally desirable that from 2% to 80%, preferably 3% to 50%, most preferably 5% to 30%, of the total surface area of the web be subjected to compression. Further, the number of spaced, discrete bond sites per square centimeter generally should be from 1 to 250, preferably from 16 to 64.
• the compressive force, the temperature, and the time of exposure of the web to compression and heating will depend on the nature and quantity of the attenuating liquid utilized and the nature of the fibers being processed. Therefore, for a particular nonwoven web and a particular attenuating liquid, the compressive force, the temperature, and the time of exposure of the web to the compressive force and heating will be correlated to effect bonding of the web fibers in the heated, compressed areas.
• the heating and compression will be correlated to effect a degree of bonding sufficient to provide a wash stable fabric as hereinafter defined.
• increases in bonding will be observed with increased temperature until a temperature is attained beyond which further increases will have little, if any, beneficial effect.
• the heat attenuation characteristics of the liquid may not be adequate to provide requisite improvements in fabric softness.
• the use of increasing quantities of attenuating liquid may require increased compressive force and/or temperature to provide wash stable fabrics.
• the optimum correlation of temperature and compressive force can, of course, be empirically determined by routine tests.
• Strip Tenacity is used as an indicator of fabric strength and is determined by dividing the breaking load of a cut fabric strip (as determined by American Society of Testing Materials procedure D-1682-64) by the fabric basis weight. Strip Tenacity is expressed as g/cm/g/m 2 . Values reported are an average of tenacities in the machine and transverse directions of the fabric. (The machine direction corresponds to the direction of feed to the heating and compressing means and the transverse direction is the planar direction at a right angle thereto,)
• Bending Modulus is used as a measure of fabric softness and is determined in accordance with techniques as described in U.S. Patent 3,613,445.
• a test fabric is forced vertically downward through a slot at a constant speed.
• a signal is generated in proportional response to the load incurred in moving the fabric into and through the slot.
• a load-extension curve is generated by plotting the signal as a function of the distance.
• Hand, drape and bending modulus are determined by analyzing the load-extension curve. Hand is represented by the maximum . point on the load-extension curve.
• Drape is represented by the slope of the load-deflection curve and bending modulus is determined by dividing the drape value by the cube of fabric thickness.
• Bending Modulus as determined on a 10.6 x 10.6 cm sample, is expressed in gm/cm 4 and values reported are an average of fabric face up and face down machine and transverse direction measurements.
• Wash stability is determined as follows: Nonwoven fabric samples are mixed with at least 10 pieces of hemmed cotton sheeting each measuring about 91 cm x 91 cm. The number and size of the nonwoven fabric samples are subject to the following constraints:
• the total weight of the cotton sheeting plus the nonwoven samples should not exceed about 1.8 kg. (These constraints assure comparable results.)
• the load is washed in a Kenmore Model 76431100 washing machine (marketed by Sears Roebuck & Co.) using the "normal" cycle (14 min.) "Hi” water level (55 l) , HOT WASH, WARM RINSE (water temperatures of 60°C. + 3°, 49°C. + 3°) and 90 g of American Association of Textile Colorists and Chemists Standard Detergent 124.
• the wash load is then dried in a Kenmore electric dryer, Model 6308603 (marketed by Sears, Roebuck and Co.) for at least 30 minutes (or longer if required to dry the entire load).
• the test specimens are then evaluated by visual observation to determine the number of pills formed.
• a pill is a visually discernible (usually roughly spherical) tangle of fiber, or fiber plus extraneous material, extending above the surface of a fabric and connected to the body of the fabric by one or more filaments.
• a fabric is considered to fail the test when 5 or more pills are observed in any 929 square centimeters surface area or when more severe physical deterioration is visually discernible. Fabrics passing the above test are considered "wash-stable".
• the pills are predominantly formed by fibers which were not bonded in the process of which, in test procedure, were freed from bond sites.
• the degree of pilling provides a measure of the efficacy of the process for forming bonds and a measure of the resulting bond integrity.
• more severe fabric deviation than pilling, e.g., complete disintegration may be observed.
• fabrics which do not pass the test even if not totally or partially disintegrated in the test) will not withstand substantial physical stress or repeated washings without excessive deterioration.
• Nonwoven webs composed of continuous filament. 24% crystalline polyethyleneterephthalate fibers and having web weights of 5 gms/meter 2 and wetted with water to the add-on percentages shown in Table 1 below are simultaneously heated and compressed in spaced discrete areas by passage at a speed of .6 meters/minute between a pair of metal rolls. One roll is smooth while the other has 28 square boss sites/cm 2 aligned in a square pattern covering about 18% of the surface area of the roll. The pressure at the roll nip is calculated as 65.0 kg/cm (assuming all pressure to be applied only to the boss sites). Both rolls are heated to a temperature of 230°C. Properties of the fabrics obtained are shown in Table 1 below. The above tests in general (test 3 is anomalous and may reflect inaccurate measuring or sampling) show that the use of water as described enables the preparation of point-bonded polyester fabrics of improved softness.
• Nonwoven webs composed of continuous filament crystalline polyethylene terephthalate fibers are passed (either wet with about 1000% add-on carbon tetrachloride or dry) through the nip of a pair of rolls at a speed of 6 meters/min.
• Each roll bears a helical land and groove pattern (508 micron land width; 1270 micron groove width) with the lands and grooves disposed at 45° angles to the roll axis and cooperating to produce a pattern of diamond shaped depressions covering abc 8% of the web surface.
• the rolls exert a nip pressure of 130 kg/cm (calculated as in Example 1).
• Nonwoven webs of continuous filament nylon 6,6 were processed at 225°C. with and without about 700% add-on hexane using the same roll pattern and pressure as in Example II.
• the use of hexane provided a fabric having about a 40% lower bending modulus and a substantially higher ratio of strip tenacity to bending modulus than that obtained without the use of hexane.

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• Engineering & Computer Science (AREA)
• Textile Engineering (AREA)
• Nonwoven Fabrics (AREA)

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Citations (7)

• 1979
  • 1979-12-19 EP EP79302958A patent/EP0013125B1/fr not_active Expired
  • 1979-12-19 DE DE7979302958T patent/DE2965649D1/de not_active Expired
  • 1979-12-20 CA CA000342390A patent/CA1145213A/fr not_active Expired
  • 1979-12-20 JP JP16491079A patent/JPS5584462A/ja active Pending
  • 1979-12-20 BR BR7908369A patent/BR7908369A/pt unknown

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