Stabilized nonwoven web and method of preparation

• US 3,912,567 A
• Filed: 05/14/1973
• Issued: 10/14/1975
• Est. Priority Date: 05/14/1973
• Status: Expired due to Term

• Current Assignee: Robert J. Schwartz
• Original Assignee: Robert J. Schwartz
• Inventors: Schwartz, Robert J.
• Primary Examiner(s): Lesmes, George F.
• Assistant Examiner(s): Robinson, Ellis P.
• Application Number:
  US05/359,673
• Time in Patent Office: 883 Days
• Field of Search: 156/167,290,306,324,181,180 161/148,150
• US Class Current: 156/167
• CPC Class Codes: D04H 3/16 with bonds between thermoplastic filaments produced in association with filament formation, e.g. immediately following extrusion

Abstract

A process is described for the intermittent autogenous bonding of a continuous filament web wherein the filaments have a low degree of crystallinity. In one embodiment, the process involves passing the web directly through a nip formed by a smooth hard surfaced roll and a roll containing raised points on its surface with both rolls being maintained at a temperature near the softening point of the filaments. The speed of the web through the nip, the roll size and the configuration of the raised points are coordinated such that the surface temperature of the web is not substantially increased before maximum pressure has been developed in the nip, but then is rapidly raised to a point where surface fusion is effected before a significant increase in filament crystallinity occurs. Webs prepared as illustrated possess a desirable combination of surface abrasion resistance and strength.

Claims

1. A PROCESS FOR STABILIZING A NONWOVEN WEB OF MOLECULARLY ORIENTED CRYSTALLIZABLE THERMOPLASTIC FIBERS, SAID WEB HAVING A BASIS WEIGHT OF AT LEAST ABOUT 1 OZ./YD.2 AND CONTAINING FIBERS HAVING A CRYSTALLINITY BELOW THE EQUILIBRIUM VALUE, SAID PROCESS CONSISTING ESSENTIALLY OF COMPRESSING IN THE ABSENCE OF ANY PREHEATIG STEP SAID WEB IN INTERMITTEN REGIONS UNDER A PRESSURE OF AT LEAST ABOUT 200 PSI. TO EFFECT FIBER DEFORMATION WITHIN SAID REGIONS AND SUBSTANTIALLY INSTANTANEOUSLY RAISING THE TEMPERATURE OF THE AREAS OF THE WEB DEFINING THE SURFACES OF THE COMPRESSED REGIONS TO EFFECT FIBER FUSION OF THE SURFACE FIBERS BEFORE CRYSTALLINITY IS SUBSTANTIALLY INCREASED, TO COMBINED EFFECTS OF FIBER DEFORMATION WITHIN THE COMPRESSED REGIONS OF THE WEB AND FIBER FUSION ON THE SURFACES THEREOF PROVIDING DESIRABLE TWO-SIDED ABRASION RESISTANCE AND STRENGTH CHARACTERISTICS.

2. The process of claim 1 wherein the fibers are polypropylene.

3. The process of claim 2 wherein the nonwoven web is a continuous filament web having a basis weight of about 1.25-2.5 oz./yd2.

4. The process of claim 3 wherein the filaments in the continuous filament web have a crystallinity of less than about 45 percent.

5. IN A PROCESS FOR PREPARING A CONTINUOUS FILAMENT HAVING A CRYSTALLINITY BELOW ABOUT 45 PERCENT WEB OF POLYPROPLENE FILAMEENTS COMPRISING EXTURDING POLYPROPLENE THROUGH A MULTIPLE NUMBER OF DOWNWARDLY DIRECTED SPINNING NOZZLES IN THE FORM FILAMENTS PNEUMATICALLY MELT DRAWING THE FILAMENTS AT A VELOCITY OF AT LEAST 300 METERS/MIN. FOLLOWED BY RAPID QUENCHING AND COLLECTION AS A CONTINUOUS FILAMENT WEB HAVING A BASIC WEIGHT OF AT LEAST ABOUT 1 OZ./YD.2, TTHE IMPROVEMENT WHEREIN THE CONTINUOUS FILAMENT WEB IS THEREAFTER STABILIZED BY COMPRESSING IN THE ABSENCE OF ANY PREHEATING STEP SAID WEB IN INTERMITTEN REGIONS UNDER A PRESSURE OF AT LEAST ABOUT 200 PSI. TO EFFECT FILAMENT DEFORMATION WITHIN SAID REGIONS AND SUBSTANTIALLY INSTANTANEOUSLY RAISING THE TEMPERATURE F THE AREAS OF THE WEB DEFINING THE SURFACE OF THE COMPRESSED REGIONS TO EFFECT FILAMENT FUSION OF THE SURFACE FILAMENT BEFORE CRYSTALLINITY IS SUBSTANTIALLY INCREASED THE COMBINED EFFECTS OF FILAMENT DEFORMATION WITHIN THE COMPRESSED REGIONS OF THE WEB AND FILAMENT FUSION ON THE SURFACE THEREOF PROVIDING DESIRABLE TWO-SIDED ABRASION RESISTANCE AND STRENGTH CHARACTERISTICS.

6. The process of claim 5 wherein the continuous filament web is stabilized by being passed directly through a nip formed by hard surfaced rolls maintained at a temperature near the softening point of the filaments with at least one of the rolls having raised intermittent regions on the surface thereof and with the nip pressure on the raised regions being at least 2000 psi.

7. The process of claim 6 wherein the continuous filament web has a basis weight of about 1.25-2.5 oz./yd.2.

8. The process of claim 7 wherein at least one of the hard surfaced rolls is so configured such that the stabilized web contains compressed regions in a density of about 50-3200/in.2 which occupy about 5-50% of the web surface area.

9. The process of claim 7 wherein at least one of the hard surfaced rolls is so configured such that the stabilized web contains compressed regions in a density of 100-500/in.2 which occupy about 10-25 percent of the web surface area.

10. The process of claim 9 wherein the temperature of the hard surfaced rolls is about 145* C. and the nip pressure is about 3500 psc.