IL31993A - Process for the production of non-woven fabric from polyamide filaments - Google Patents

Description

PROCESS FOR THE PRODUCTION OF NON-WOVEN FABRIC FROM POLYAMIDS FILAMENTS A continuous process for producing non-woven fabric from polyamide filaments includes the forming of a mass of randomly disposed filaments and contacting the filaments with a liquid which is comprised of an activating gas having been dissolved in an organic liquid solvent carrier in which the gas remains substantially unionized with the liquid carrier being inert to the polyamide filaments. The removal of the dissolved gas from the filaments causes cohered adjacent filament to bond to each other to form a non-woven sheet of randomly disposed and interconnected polyamide filaments.

This invention relates to the production of non-woven fabrics and, more specifically, to a process for forming a non-woven sheet from polyamide filaments by bonding touching filaments together at the points of intersection by contacting the filaments with a gas, dissolved in an organic liquid carrier, which disrupts the interchain hydrogen bonding between adjacent amide groups without breaking the covalent bonds within polyamide chains so that upon removal of the gas from the polyamide filaments, hydrogen bonding occurs between the molecu- ar chains comprising the different filaments.

The production of non-woven fabrics is an old art; however, the bonding of the known non-woven fabrics has been accomplished by the addition of external binders or by softening of the fiber with heat, solvents or plast icizers.

While external binders may be applied as a powder, solution, emulsion or even in the form of fibers, the resulting products suffer from several disadvantages. For example, the use of those of the binder. Thus, if a filament with a relatively low melting point is used as a binding material, the temperature conditions to which the web or resulting fabric may be subjected are limited by the melting point of the binder fibers.

Solvent bonding by the prior art methods is not easily controlled and frequently tends to alter the aesthetic properties of the resulting web. In solvent bonding, it is difficult to achieve adequate adhesiveness between the fibers without dissolving the entire web or, at least, without signi-ficantly impairing the physical properties of the web. Furthermore, the bonds between the touching filaments frequently have a swollen appearance or evidence redeposition of the polymer which is generally referred to as polymer migration. In most instances, these swollen areas around the bonds do not possess the same dye acceptance level because of changes in the crystalline structure which is localized at the bond site thereby causing non-uniform dyeing.

In a process for forming a non-woven fabric from a batt of polyamide filaments, the filaments, which may be either con-tinuous or staple, are contacted with a liquid which is comprised of a gas having been dissolved in a non-ionizing organic liquid solvent. The liquid solvent is chemically inert to the polyamide filaments and serves as a carrier for the gas. However, the molecules of the dissolved gas disrupt the interchain hydrogen bonding between adjacent amide groups without breaking the covalent bonds within the polyamide chains so that upon removal of the gas from the polyamide filaments, the inter contiguous and touching filaments as well as between the molecular chains comprising the body of the filaments.

The batt of non-woven filaments may be formed in a variety of ways. If the filaments are in staple form, a batt may easily be made by means of a Rando-Webber or by means of a conventional textile carding system. Alternatively, if the filaments are of very short lengths, webs may be formed from a dispersion in water as in paper making processes. If the batt is to be comprised of continuous polyamide filaments, the batt may be formed by the known method of passing the filaments through an aspirator jet which forces the filaments downwardly and onto a conveyor belt. The aspirator jet randomly disposes the filaments on the belt so that there is substantially no difference in the machine, transverse and bias directions in regard to the physical properties of the batt.

Once the batt is formed, it is ready to be immersed in or contacted with the bond-inducing liquid of this invention. The activating gases which may be dissolved in a suitable solvent to form the bond-inducing liquid include hydrogen chloride, hydrogen bromide, boron trifluoride, boron trichloride, chlorine, sulfur trioxide, nitrogen trioxide, nitrogen dioxide, and other related gases which do not significantly degrade the fiber but, while in contact with the fiber, disrupt the interchain hydrogen bonds between the adjacent amide groups. Solvent carriers as used herein relate to solvents for the activating gases and include acetone, ether, chloroform, carbon tetrachloride, benzene, pentane, heptane, trichlorofluoro- mains substantially unionized and which are chemically inert to polyamide f laments. The- bonding liquid may be prepared by bubbling the gas into the organic liquid solvent carrier for a selected interval of time.

The bonding of adjacent filaments is initiated by immersing the batt into the bonding liquid. As the gas concentration in the liquid carrier increases, the web strength increases as stronger and possibly more bonds are formed until fiber breakage begins to play a significant part in the fabric rupture mechanism.

Upon withdrawing the batt from the bonding liquid, the inter-filament bonds are stabilized by removing the activating gas from the batt which may be accomplished either by evaporating the liquid from the batt or by washing the batt in water or the like.

The process of this invention is applicable to substantially all nylons or polyamide articles including nylon 66, nylon 6, nylon 11 and the like.

Figure 1 is a graph showing fabric tenacity plotted against the concentration of hydrogen chloride in the solvent; Figure 2 is a graph showing the "performance ratio", which is the ratio of breaking strength to bending length plotted against the concentrat on of the hydrogen chloride gas in the liquid solvent; Figure 3 is a graph showing zero span tenacity plotted against the concentration of the hydrogen chloride gas in the liquid solvent; plotted against the concentration of the hydrogen chloride gas in the liquid solvent; Figure 5 is a graph showing the bending length of the fabric plotted against the concentration of the hydrogen chloride gas in the liquid solvent; Figure 6 is a graph showing the initial modulus of the fabric plotted against the concentration of the hydrogen chloride gas in the liquid solvent; Figure 7 is a graph showing the bonding efficiency, which is the ratio of normal span tenacity to zero span tenacity expressed as percent, plotted against the concentration of the hydrogen chloride gas in the liquid solvent; and Figure 8 is a graph showing the percent elongation of the fabric plotted against the concentration of the hydrogen chloride gas in the liquid solvent.

The invention as herein set forth includes a process for bonding touching synthetic linear aliphatic polyamide articles which may be in the form of filaments, pellicles, granules and the like along their contiguous surfaces. Synthetic linear polyamides have in their structure recurring -NHCO- groups.

The mechanism of bonding is that the gases which have been absorbed in the solvent liquid form complexes with the -NHCO-groups which disrupt the hydrogen bonds between the polymer chains. In the polymer art, it is well known that many of the physical properties of polyamides depend to a great extent on the intermolecular hydrogen bonding between the -CO- and the -NH- groups in adjacent polymer chains. The bonds form cross properties as melting point and tensile strength. Therefore, when these bonds are disrupted by the action of the activating dissolved gases, the polymer chains v/ithin the structure and especially along the surface thereof become more flexible and tend to shift to relieve the stresses caused by tension or pressure on the structure. The complex formation is reversible and when the hydrogen chloride is desorbed, the hydrogen bonds reform. In the shifted position of the polymer chains, many of the new bonds formed are between the -CO- and the -NH- groups of different structures, such as, between adjacent granules and the like.

In determining the effectiveness of the bonding system of this invention, a standard batt which is comprised of a randomly disposed collection of polyamide continuous filaments having zero twist and having been stretched is cut into 9 inch (22.86 cm) squares. The bonding liquid is prepared by bubbling into 1,000 cc. of chloroform for about 45 seconds hydrogen chloride at a rate of 450 cc. per minute, the resulting liquid having a hydrogen chloride concentration of 0.045 N. Bonding is effected by saturating the batt with the bonding liquid, passing the saturated batt through a wringer to remove excess liquid, removing the bonding liquid from the batt by contacting the batt with hot nitrogen while the batt is held between two wire screens and removing the residual hydrogen chloride from the batt by washing in water. A concentration of 0.045N hydrogen chloride in chloroform gives excellent bonding, the fabric properties being set forth in Table I.

TABLE I Fabric as Bonded Weight Thickness (mils) 17 3 Density (g/cm ) 0.17 Bending Length (ins.) 2.28 (cms) 5.8 Tenacity (lbs./in./o^./yd ) 11.4 (kg/cm/gm/m ) 0.06 Bonding Efficiency (%) 75 Performance Ratio (lbs./in ) 11 (kg/cm ) 0.7 A review of the test results indicates that the fabric properties are substantially influenced by the normality of the bonding liquid. The molar concentration of the parti¬ cular gas in the liquid solvent is primarily determined by the length of time the gas is allowed to bubble through the liquid solvent. Using hydrogen chloride as the activating gas and chloroform as the liquid solvent, for example, the effect upon the degree of bonding and the resulting fabric properties are set forth in Figures 1 - 8. Six fabric samples being sub¬ stantially identical in weight, density and the like are treated in the exact same manner as herein set forth the ex¬ ception being the variance of the molar concentration of the hydrogen chloride in the chloroform. Six fabric samples are immersed respectively in concentrations of 0.01N, to 0.02N, 0.03N, 0.045N, 0.06N and 0.12N. In Figure 1, tenacity which 2 2 is measured in lbs./in./oz./yd (kg/cm/gra/m ) reached a maximum the combination of the bond strength and the fiber strength and it can be seen that at low molar concentrations, there is little bonding so that the resulting tenacity is quite low.

As the strength of the bonds increases, the tenacity increases to a maximum at a molar concentration of about 0.045. Molar concentrations greater than 0.05 while probably increasing slightly the strength of the bonds cause slight fiber degradation so that the fibers themselves are weakened and, resultingly, lower the overall fabric tenacity.

In reference to Figure 5, it can be seen that the molar concentration has relatively little effect upon the fabric bending length. This is not surprising since both fabric initial modulus and thickness which to a large extent determine this parameter are effectively constant throughout.

Figures 2 and 4 show the performance ratio and quality ratio, respectively, plotted against the molar concentration.

The performance ratio which is breaking strength measured in pounds per inch (kgs per cm) divided by the bending length of the fabric in inches (centimeters) is slightly biased in favor of heavy fabrics and will generally increase as the weight in¬ creases. The quality ratio while including the pounds per inch (kgs per cm) of the performance ratio divided by the bend¬ ing length in inches (centimeters) also includes the weight of 2 the fabric in ounces per square yard (gm/m ) . Therefore, where the weight of the fabric is increased, the quality ratio accounts for it and the ratio will thus be slightly biased to light weight fabrics. tenacity in lbs. /in./oz./yd (kg/cm/gm/m ), fiber degradation is measured and can be seen to slightly increase with an increase in molar concentration of the hydrogen chloride gas in the chloroform. Zero span tenacity is measured by placing a sample of fabric in the jaws of two touching clamps which are then pulled outwardly and away from each other. By testing tenacity in this manner, the bonds which are formed by the immersion of the batt in the bonding liquid has no substantial effect on fabric strength and only the fiber strength is examined.

Bonding efficiency which is set forth in Figure 7 is a ratio of the normal tenacity, measured at a span of five inches (12.70 cms), of the fabric as set forth in Figure 1 and the zero span tenacity of the fabric which is set forth in Figure 3. The results show a slight increase in bonding efficiency after a concentration of 0.045N which is most likely due to the combination of stronger bonds being formed and to fiber degradation, fiber breakage playing a significant part in the rupture of the fabric beyond the optimum molar concentration.

While other activating gases such as hydrogen bromide, boron trifluoride, boron trichloride, chlorine, sulfur trioxide, nitrogen dioxide, nitrogen trioxide and the like may form bonds best at different molar concentrations, the properties of the resulting fabrics function substantially as set forth herein with reference to hydrogen chloride gas dissolved in a suitable substantially gas non-ionizing organic solvent such as chloroform. In other words, the performance concentration of the activating gas to a maximum whereupon the addition or increase in molar concentration of the activating gas in the liquid solvent has little effect upon the bonding efficiency of the system.

In the following examples, which are merely illustrative of the present invention, all parts are by weight unless otherwise designated.

EXAMPLE I A random web of drawn continuous filament nylon im¬ mersed in, for about 5 seconds, a bonding medium prepared by bubbling gaseous hydrogen chloride into 1,000 cc. chloroform for 45 seconds at a rate of 450 cc./min. The web was passed through a manually operated roll type wringer to remove excess liquid after which it was placed between wire screens (21 ends/ in.) (8.3 ends/cm) and held under a pressure of 35 psig (2.46 2 kg/cm ) while nitrogen at a temperature of 60°C. was passed through the sample to evaporate the chloroform. The sample was subsequently washed with water to remove any residual traces of hydrogen chloride. Properties of the resulting fabric are as follows: Fabric as Bonded Weight (oz./^d ) (gm m ) Thickness (mils) 3 Density (g/cm ) Bending Length (ins.) (cms) 2 Tenacity (lbs./in./oz^/yd ) (kgs/cm/gm/m ) Bonding Efficiency {%) EXAMPLE II A web prepared from drawn continuous filament nylon was placed between two pieces of wire screen and immersed in acetone into which gaseous hydrogen chloride had been bubbled.

The sample assembly was withdrawn from the bonding medium, shaken to remove excess solution, and placed in a press where, 2 while under a pressure of 35 psig (2.46 kg/cm ), heated nitrogen (60°C.) was passed through the web for a period of 3 - 4 minutes. The web was then removed from the press, washed in water to remove any residual hydrogen chloride and dried. The resulting product was strongly bonded, and was not discolored.

EXAMPLE III A web of drawn continuous filament nylon was treated in the same manner as in Example II except that a solution of hydrogen chloride in benzene was substituted for the solution of hydrogen chloride in acetone. The resulting product was strongly bonded and was not discolored.

EXAMPLE IV A sample of a web of non-woven drawn continuous fila- ment nylon supported between two pieces of wire screen (21 ends per inch) (8.3 ends per centimeter) was immersed in a solution of chloroform into which boron trifluoride had been bubbled.

The saturated web was then placed in a press and subjected to 2 a pressure of 35 psig (2.46 kg/cm ) while heated nitrogen was passed through the sample to remove the liquid. The web was then washed to remove any residual boron trifluoride and dried.

Physical properties of the resulting product are as follows: Fabric as Bonded Weight (oz./yd ) 1.9 (gm/m ) 64.3 Thickness (mils) 19 Density (g/cm3) 0.13 Bending Length (ins.) 2.2 (cms) 5*6 2 Tenacity ( lbs./in./o^./yd ) 8.8 (kg/cm/gm/m ) 0.046 Bonding Efficiency (%) 67 2 Performance Ratio (lbs./in ) 7.6 (kg/crn ) 0.53 EXAMPLE V Using the same procedure as in Example IV a web of continuous filament nylon was bonded using a solution of boron trichloride in chloroform. Physical properties of the result¬ ing product are as follows: Fabric as Bonded Weight (oz./gd2) 1.9 (gm/m ) 64.3 Thickness (mils) 21 3 Density (g/cm ) 0.12 Bending Length (ins.) 2.6 (cms) 6.6 Tenacity (lbs./in./oz,./yd2) 10.5 (kg/cm/gm/m ) 0.055 Bonding Efficiency {%) 76 2 Performance Ratio (lbs./in ) 7.8 (kg/cm ) 0.55 EXAMPLE VI Using the same procedure as in Example IV a web of gen dioxide in chloroform. Physical properties of the result ing product are as follows: Fabric as Bonded Weight (oz./^d") 1.7 (gm/m ) 57.6 Thickness (mils) 21 Density (g/cm^) 0.11 Bending Length (ins.) 1.8 (cms) 4.57 2 Tenacity (l s./in./og./yd ) 7.2 (kg/cm/gm/m ) 0.038 2 Performance Ratio (lbs./in ) 6.8 (kg/cm ) 0.48 EXAMPLE VII Using the same procedure as in Example IV a web of continuous filament nylon was bonded using a solution of nitro gen trioxide in chloroform. Physical properties of the result ing product are as follows: Fabric as Bonded Weight (02./yd ) 2.0 (gm/rn ) 67.7 Thickness (mils) 21 3 Density (g/cm ) 0.13 Bending Length (ins.) 1.9 (cms) 4.83 2 Tenacity (lbs./in./oz,./yd ) 7.5 (kg/cm/gm/m ) 0.0396 Bonding Efficiency (%) 66 2 Performance Ratio (lbs./in ) 8.2 (kg/cm ) 0.576 EXAMPLE VIII continuous filament nylon was bonded using a solution of chlorine in chloroform. Physical properties of the resulting product are as follows: Fabric as Bonded Weight (oz./^d ) 1.3 (gm/m ) 44 Thickness (mils) 18 3 Density (g/cm ) 0e10 Bending Length (ins.) 1.7 (cms) 4.31 2 Tenacity (Ibs./in./og./yd ) 7.4 (kg/cm/gm/m ) 0.039 Bonding Efficiency (%) 51 2 Performance Ratio (lbs./in ) 5.4 (kg/cm ) 0.38 EXAMPLE IX A web of drawn continuous filament nylon was treated in the same manner as in Example II except that solution of sulfur trioxide in trxchlorofluoromethane (Freon-11) was sub¬ stituted for the solution of hydrogen chloride in acetone. The resulting product was strongly bonded and was not discol¬ ored. The fabric was heat treated in air at 110°C. to remove any residual traces of sulfur trioxide gas remaining in the polyamide filaments.

Claims (10)

1. A process for mutually bonding synthetic linear polymeric articles along their contiguous surfaces, said poly- EE 0 meric articles having -N - C- linkages characterized by con¬ tacting said articles with a medium, said medium being comprised of a gas having been dissolved in an organic liquid carrier in which said gas remains substantially unionized, said liquid carrier being inert to said polymeric articles while the molecules of said dissolved gas disrupt the inter- H 0 molecular hydrogen bonds between adjacent linkages without appreciably disrupting covalent bonds within the poly¬ meric chains and removing said dissolved gas from said articles while adjacent articles are in contact to bond said articles along said contiguous surfaces.

2. The process of Claim 1 for bonding touching syn¬ thetic linear polymeric articles, characterized in that said article is a polyamide in the form of filaments, pellicles or granules.

3. The process of Claim 2 for forming a non-woven fabric from a batt, characterized by: (a) contacting said mass with a liquid, said liquid being comprised of a gas having been dissolved in an organic liquid carrier in which said gas remains substantially unionized, said liquid carrier being inert to said polyamide articles while the molecules of said dissolved gas dis¬ rupt the interchain hydrogen bonding between turbing the covalent bonds within the polyamide chains; (b) removing excessive amounts of said liquid from said batt; (c) pressing said batt to insure contact between overlapping filaments; and (d) removing said dissolved gas from said batt to bond permanently said filaments together at their points of contact.

4. The process of Claim 3, characterized in that said gas is selected from the group consisting of hydrogen chloride, hydrogen bromide, boron trifluoride, boron trichlorid chlorine, sulfur trioxide, nitrogen trioxide, and nitrogen dioxide.

5. The process of Claim 3, characterized in that said non-ionic organic liquid carrier is selected from the group consisting of acetone, ether, chloroform, carbon tetrachloride, benzene, pentane, trichlorofluoromethane and heptane.

6. The process of Claim 4, characterized in that said gas is hydrogen chloride.

7. The process of Claim 6, characterized in that said hydrogen chloride having been dissolved in said organic liquid carrier is removed from said batt by evaporation.

8. The process of Claim 7, characterized in that said evaporation is effected by a heated gaseous atmosphere, said gaseous atmosphere chemically being inert to said polyamide filaments.

9. The process of Claim 8, characterized in that said bonded fabric is washed in water subsequent to said evaporation to remove the residual amounts of said hydrogen chloride gas remaining in said polyamide filaments.

10. The process of Claim 8, characterized in that said bonded fabric is heated to temperatures in excess of l00eC. to remove any residual amounts of said hydrogen chloride gas remaining in said pol amide filaments. Δ. Ε MULFORD Attorney for Applicants