US3607543A

US3607543A - Process for forming lightweight nylon nonwoven web

Info

Publication number: US3607543A
Authority: US
Inventors: Philip J Stevenson; Robert P Teulings
Original assignee: ROBERT P TEULINGS
Current assignee: ROBERT P TEULINGS; Georgia Pacific Consumer Products LP
Priority date: 1969-03-21
Filing date: 1969-03-21
Publication date: 1971-09-21
Anticipated expiration: 1988-09-21
Also published as: IL34131A; FR2035156A7; CA941570A; NL7004000A; IL34131A0; DE2013529A1; BE747762A; US3630818A; GB1284236A

Abstract

A method of forming a lightweight nonwoven bonded web of nylon comprises collecting nylon filaments on a moving foraminous belt at a rate to form a web which weighs less than 1 oz/yd2, providing a vacuum beneath the belt, contacting the web while on the belt with an activating gas to lightly bond the filaments together at filament crossover points, and removing the web from the belt prior to the belt''s entering an arc around a beltsupporting roller.

Description

United States Patent Inventors Philip J. Stevenson 2624 McDowell Road; Robert P. Teulings, Hudson Road, both of Durham, NC. 27705 Assignee Monsanto Company, St. Louis, Missouri,

a Corporation of Delaware Appl. No. 809,319 Filed Mar. 21, 1969 Patented Sept. 21, 1971 PROCESS FOR FORMING LIGHTWEIGHT NYLON NONWOVEN WEB 9 Claims, 1 Drawing Fig.

US. Cl 156/306, 161/150 Int. Cl C09] 7/00 Field 01 Search... 156/306;

[56] References Cited UNITED STATES PATENTS 3,368,934 2/1968 Vosburgh, Sr 161/150 3,420,724 1/1969 Saunders... 156/306 X 3,485,428 12/1969 Jackson 226/97 3,509,009 4/1970 l-lartmann 161/150 3,516,900 6/1970 Mallonee et a1. 156/306 Primary Examiner-Reuben Epstein Attorneys-J. Bowen Ross, .lr., Russell E. Weinkauf and John D. Upham ABSTRACT: A method of forming a lightweight nonwoven bonded web of nylon comprises collecting nylon filaments on a moving foraminous belt at a rate to form a web which weighs less than 1 oz/yd, providing a vacuum beneath the belt, contacting the web while on the belt with an activating gas to lightly bond the filaments together at filament crossover points, and removing the web from the belt prior to the belt's entering an are around a belt-supporting roller.

PATENTEU SEPZI 197! mvsmons PHIL/P J. STEVENSON ROBERT P. TEULINGS ATTORNEY PROCESS FOR FORMING LIGHTWEIGHT NYLON NONWOVEN WEB BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a nonwoven web and, more specifically, to a lightweight web which is comprised of continuous nylon filaments being autogenously bonded together at a substantial number of filament crossover points.

2. Description of the Prior Art Bonded nonwoven fabrics are old in the art; however, the concept of manufacturing nonwoven webs from continuous synthetic filaments is relatively new. It was not until the 1960 s that processes were developed which were capable of attenuating freshly extruded filaments and laying them down on a moving belt to form a nonwoven web (U.S. Pat. No. 3,341,394, 3,338,992 and 3,276,944). These patents deal primarily with polyester and polyolefinic filaments although the use of nylon filaments is casually mentioned. Bonding is accomplished by heat, solvents or adhesives. The reason continuous filament nylon webs are only referred to in the mentioned patents and in the prior art is that nylon is not readily bondable by these techniques. While nylon is a thermoplastic, heating nylon filaments to the melting points destroys substantially all molecular orientation thus weakening the filament to the point of uselessness. Solvent bonding of nylon filaments is impractical since the solvating rate is uncontrollable. The use of adhesive binders renders the resulting fabrics too boardy to be of any practical value.

In producing light weight webs, the use of adhesive binders to form the bonded web is further not practical because the weight of the adhesive which is generally about 40 percent of the total fabric weight replaces the equivalent weight of filaments thus leaving the web with too few filaments to provide adequate strength. The use of solvents for bonding tends to destroy the web for the bonding rate is uncontrollable. In either case, the web would be subjected to a liquid or water treatment bath which would destroy the web geometry since the web does not have the integrity to withstand the liquid.

In the manufacture of lightweight nonwoven webs, i.e., webs weighing less than 1 oz./yd. the technique to date has been either to deposit olefinic fibrous materials on a belt with bonding being carried out by a heat process or by means of depositing submicron organic fibrils onto a collection surface as set forth in U.S. Department of Commerce, Office of Technical Services, publication number PB] 1 1437. While nonwoven fabrics can be made from nylon in accordance with the publication, the fibers are not continuous and the resulting web has little strength.

SUMMARY OF THE INVENTION In its broadest aspects, the present invention comprehends the formation of a nonwoven web weighing less than 1 oz./yd. and being comprised on continuous filament nylon preferably of less than denier per filament with the filaments being autogenously bonded together at a substantial number of filament crossover points. The filaments comprising the web may be arranged in an orderless manner, that is, without any preferred orientation or they may be directionalized especially in the machine direction in order to build up strength therealong.

Autogenous bonding of nylon filaments can be accomplished in accordance with the method set forth in U.S. Pat. No. 3,516,900 filed June 17, 1968, by William C. Mallonee et al. By autogenous bonding, it is meant that bonds are formed between touching filaments without visible polymer migration at the bond points and in the absence of external bonding agents. As disclosed in detail in the above-identified application, gaseous hydrogen chloride or like activating gases contacts and is absorbed by the nylon filaments at least along the surfaces thereof. The hydrogen chloride molecule in the nylon causes the interchain hydrogen bonds which exist between adjacent amide groups to break and upon removal or desorption of the hydrogen chloride from the nylon, the interchain hydrogen bonds reform, some of which reform between amide groups of different filaments (at crossover points) to form bonds therebetween.

In reference to the process for forming the lightweight nonwoven nylon webs of this invention, the general procedure is set forth in U.S. Pat. No. 3,542,615 filed June 16, 1967 by EJ. Dobo et a1. However, lightweight webs must be handled more delicately than the webs of the mentioned application or the prior art. The webs of this invention should be lifted from the belt while the belt is flat or planar and prior to the belt 5 entering an arc around a belt-supporting roller. Such a procedure prevents the web filaments from following the belt around the roller and furthermore prevents the web filaments from being trapped between the foraminous collection belt and the roller. In order that the web has sufficient strength to maintain its integrity while being lifted from the belt, the web is prepressed while moving along the belt by means of aligned rolls or is contacted with a small amount of the activating gas while it remains on the belt so as to lightly bond selected touching filaments.

Therefore, an object of this invention is to provide a lightweight nonwoven bonded nylon web.

Another object of this invention is to provide a nonwoven web weighing less than 1 oz./yd. which is comprised of continuous nylon filaments directionalized during laydown which are bonded together at a substantial number of filament crossover points.

A further object is to provide a process for forming a nonwoven web weighing less than 1 oz./yd. and being comprised of continuous filament nylon.

A still further object is to provide a lightweight nonwoven web comprised of continuous nylon filaments being au togenously bonded together at a substantial number of filament crossover points.

Other objects and advantages of the present invention and their means of attainment will be apparent from the following description and accompanyingdrawing.

DESCRIPTION OF THE DRAWING The figure is a schematic diagram of the apparatus used for making the lightweight nonwoven web of this invention and for carrying out the process of this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT With reference to the Figure, extruder 10 is of the general type used for spinning continuous nylon filaments l1. Filaments 1] are drawn downwardly and attenuated by aspirator l2. Aspirator 12 forwards filaments l1 downwardly toward the laydown zone by means of compressed air which is fed into aspirator 12 by a supply line (not shown).

The laydown zone is comprised of an endless foraminous belt 14 which is supported and moved along a defined path by

rollers

15 and 16, one of which is positively driven. While the particular path assumed by belt 14 may be varied, it is contemplated that such path will include at least one planar surface which is to receive filaments l1 forwarded to it by means of aspirator 12. The planar surface is to include the area at which filaments 11 are deposited on belt 14 and the location at which filaments 11 in the form of web 17 are lifted from belt 14. While certain undulations along that length are permissible, web 17 must be lifted from belt 14 prior to the portion of belt 14 which carries web 17 reaching roller 16 and assuming the arcuated path therearound. The laydown zone also includes vacuum source 18 which is in the shape of an openended box and has exhaust means 19. Vacuum source 18 is positioned directly beneath aspirator l2 and below belt 14 so as to maintain filaments 11 on belt 14 upon the deposition of the same. The length of vacuum source 18 in the direction of roller 16 should be sufficient to firmly position the filaments on belt 14. Depending upon the operating conditions, a

second vacuum source of reduced suction (not shown) may be Tenacity -l -1 desirable which would be located substantially adjacent 48 Tongue tear (lbs) 0.19 vacuum source 18 in the direction of roller 16. weigh, (Dz/yd." M 8 ln order that web 17 has the integrity to withstand the tension required to lift it from belt 14 at a second location which can be said to be included along the planar surface, web 17 EXAMPLE and {hat P of belt 14 supporting the web y be Passed The procedure as set forth in example I was followed with a P of Press mus and winch compact web 17 the exception that nylon 6,6 flake was extruded. Web properand increase filament cohesion. Alternatively, web 17 may be ties were as f ll lightly bonded by means of an activating gas applicator 22 which directs an activating gas such as hydrogen chloride into web 17. Sufficient bonding will occur at filament crossover Thickness (mils) 4.4 points allow the web to be lifted from belt 14. While only one Density (8 [cm a) 0408 of these web takeoff aiding methods is generally required, it is Bending law}, (in) 1,0 possible that more than one may be desired. Such an occasion Tenacity (lbs./i'n./oz.lyd.) 5.8 may arise when the relative humidity is extremely low thus 58 kin it difficult for an static electric char e on the fila- Tang mambs') ma g Y 8 Weight (ca/yd?) 0.26 ments to be dissipated.

Web 17 is lifted from belt 14 at a second location by means of a guide bar 24, is passed over guide bar 24 and is passed EXAMPLE Iv through

rolls

26 and 27 whlch forwards web 17 cage The procedure as set forth in example 1 was followed and 29. While in gas cage 29, the nylon filaments comprising web the resulting web properties were: 17 absorbs the hydrogen chloride gas or come like activating gas. Web 17 is then removed from gas cage 29 by means of guide rolls 30 and 31 and is passed through a heater 34 where g desorption is effected and as a result permanent bonding ocf g Aft d t. b 17 d ll Density (g./cm. 0.l2 curs. er esorp 10', we is rawn over gui e r0 5 Bending (m) 0.9 and 37 whereupon it proceeds to an appropriate take up Tenacity (lbs/inJoL/yd?) 6.6 mechanism (not shown). If required additional gas desorption 30 Elongation (i 46 ongue tear s.) can be achieved by a subsequent water wash. weigh! (CL/yd?) 0'30 EXAMPLE] Nylon 6 flake was extruded through a 14 hole spinnerette, EXAMPLE v at a rate of 2.6 g./min. Two reciprocating aspirators were used Th procedure as Set f h i example 1 was f ll d d which were supplied compressed air having an input pressure h resulting b properties were; of 64 p.s.i.g. The aspirators attenuated the filaments to a finished denier of from 2.0 to 2.5 and were positioned about 16 inches above the foraminous belt. The belt speed was 8.6 bk 5 0 ft./min. and the weight of the web deposited on the belt was L I' Z L ,L J 0.09 oz./yd. The unbonded web was pressed by a pair of Bending lengthfins.) 1.0 prepress rolls while remaining on the belt. Ambient conditions 'lenacit (llzginjozJydfj 2,5

o ongation during web laydown were 76 F. and a relative humidity of 40 Tongue ear (um 0.80 P 5 Weight (ca/yd?) 0.41 The web was lifted from the belt by means of being pulled 4 over a lift bar and was passed through a gas chamber filled with gaseous hydrogen chloride. After being exposed to the EXAMPLE VI gaseous hydrogen chloride for approximately 6 Seconds the The procedure as set forth in example I was followed and web was passed through a heated area which was comprised of the resulting web properties were; two opposed Fostoria heat lamps where the hydrogen chloride having been absorbed by the nylon filaments was desorbed. The web was exposed for 25 seconds to a temperature in ex- Th, k 1 cess of 200 F. The heat treatment reduced the hydrogen f g ilfigfi g chloride content in the web to a residual level of about 0.2 Bendinglenglh(in5 1 percent by weight. Tenacity (lbsJinJozJyd) 1 L2 The web properties are as follows: Emgam" Tongue tear (lbs) 2.00 Weight (ozlyd?) 0.75

Thickness (mils) 2.0 Density (g-lcmfl 0.06 By certain process modifications the filaments comprising f the webs of this invention can be directionalized so that the Tenacity (lbsJinJOL/yd?) 5.0 Elongadon 45 webs have greater strength, for example, in the machine Tongue tear(lbs.) 0.|2 direction than in the transverse direction. A web having differential strengths find utility where tension is applied in only EXAMPLE ZLZfiifiiilififli Ll? 21 .3%; "123.1113226 1123353)? The procedure as set forth in example I was followed with a savings in web weight or a stronger web per unit weight can the exception that nylon 6,6 flake was extruded. Web properbe in by rr nging most of the filaments in the i were as f ll preferred direction so that they become the load-bearing members.

While any one of several methods may be used to compare the strengths in the given directions, the preferred method is a Thickness (mils) 4.2 Density 16mg) I 006 correlation between the zero span tenacities of the two Bending length n. 0,5 directions. In zero span tenacity, the measured rupture load is dependent upon the component filament strength and filament orientation only since opposed clamps which receive the fabric are positioned adjacent each other and are pulled in opposite directions to rupture the web. It has been found that the ratio of the zero span tenacity in the high strength direction to the zero span tenacity in low strength direction (DH/DL) generally should be at least 1.50 for there to be useful realization of the unidirectional strength characteristics of the web.

EXAMPLE VII The general procedure as set forth in example I was followed with the exception that nylon 6.6 was used and aspirator 12 was sloped at an angle of 30 from the vertical in the machine direction. Spinnerette l0 and aspirator 12 were positioned to direct filaments 11 onto belt 14 in the area above vacuum source 18. By sloping aspirator l2, filaments 11 were laid on belt 14 with the preferred orientation being in the machine direction. The resulting web properties were:

1. A process for producing a lightweight nonwoven web of continuous nylon filaments comprising the steps of:

a. forwarding a plurality of said nylon filaments toward a laydown zone, said laydown zone including a foraminous belt moving along an endless path, said belt being planar for a given length along said path;

b. collecting said filaments onsaid belt at a first location along said planar length to form a web having a weight being less than 1 oz./yd.

c. including a vacuum beneath said planar length to maintain said filaments on said belt during and subsequent to collection;

d. contacting said web while on said belt with an activating gas to lightly bond said filaments together at selected filament crossover points whereby web integrity is increased; and

e. removing said web from said belt at a second location along said planar length.

2. The process of claim 1 wherein said filaments are autogenously bonded together at a substantial number of filament crossover points.

3. The process of claim 2 wherein said autogenously bonding said filaments include the steps of subjecting said web to an activating gas, said gas being at least partially absorbed by said filaments and desorbing said gas from said filaments to permanently bond said filaments together at a substantial number of said crossover points.

4. The process of claim 3 wherein said desorbing is substantially completed by subjecting said web to heat.

5. The process of claim 4 wherein said web is calendered while on said belt prior to said web removal by means of press rolls spaced in alignment on either side of said belt.

6. The process of claim 5 wherein said filaments of said web are lightly bonded together at selected filament crossover points prior to said web removal from said belt.

7. The process of claim 4 wherein said filaments are less than 10 dpf.

8. The process of claim 4 wherein said filaments are preferentially arranged in a first selected direction within said fabric to increase the fabric tenacity in said first selected direction relative a second selected direction.

9. The process of claim 8 wherein the ratio of said first selected direction tenacity to said second selected direction tenacity is greater than 1.50.

Claims

2. The process of claim 1 wherein said filaments are autogenously bonded together at a substantial number of filament crossover points.
3. The process of claim 2 wherein said autogenously bonding said filaments include the steps of subjecting said web to an activating gas, said gas being at least partially absorbed by said filaments and desorbing said gas from said filaments to permanently bond said filaments together at a substantial number of said crossover points.
4. The process of claim 3 wherein said desorbing is substantially completed by subjecting said web to heat.
5. The process of claim 4 wherein said web is calendered while on said belt prior to said web removal by means of press rolls spaced in alignment on either side of said belt.
6. The process of claim 4 wherein said filaments of said web are lightly bonded together at selected filament crossover points prior to said web removal from said belt.
7. The process of claim 4 wherein said filaments are less than 10 dpf.
8. The process of claim 4 wherein said filaments are preferentially arranged in a first selected direction within said fabric to increase the fabric tenacity in said first selected direction relative a second selected direction.
9. The process of claim 8 wherein the ratio of said first selected direction tenacity to said second selected direction tenacity is greater than 1.50.