Method of making spun bond web from multicomponent filaments

Abstract

A spun bond mat, after collection on a perforated surface is consolidated by high velocity water jets and then subjected to heat treatment to crinkle or crimp the bicomponent or other multicomponent synthetic resin filaments.

Description

FIELD OF THE INVENTION

[0001] My present invention relates to a method of making a spun bond web of multicomponent filaments and, more particularly, to a method of making a filament web with increased filament bulk.

BACKGROUND OF THE INVENTION

[0002] When reference is made to multicomponent filaments here, I mean filaments which are composed of a plurality of different thermoplastic synthetic resin components and especially components with different properties like thermal coefficient of expansion, heat-induced shrinkage and like properties. These components can be of the same synthetic resin, for example, poly sters of different composition or polyethylenes or polypropylenes of different properties, or components of different synthetic resins, like, for example, a polypropylene component and a polyethylene component. A reference to a bicomponent filament is intended to mean a filament which has only two different thermoplastic synthetic resins.

[0003] A cross section through such filaments will show the two components, usually in a side-by-side relationship and the separation b twe n the two synth tic resins gen rally will ext nd over the entire length of the filament.

[0004] The reference to spun bond here is intended to mean webs which are formed from continuous filaments as well as webs which may be formed from less than continuous filaments, i.e. filam nts which may have various lengths and need not be continuous.

[0005] In the usual production of spun bond, i.e. webs formed from mats of such continuous or semicontinuous filaments, the mats or fleeces have the filaments thereof bonded together at cross-over points. One of the properties that is generally of importance in such webs is the bulk of the filaments. The bulkiness property in some cases leaves much to be desired.

[0006] In general, the filaments are extruded from a spinn ret, are stretched, generally by entrainment with air, and are collected on a foraminous surface on which the mat is formed and on which the filaments are bonded at their crossing points.

[0007] In conventional spun bond processes, the bulkiness may not b sufficient, the mechanical properties of the web may not b satisfactory and neither may be fully reproducible. As a consequence, in earlier processes, there may be an excessive r j ct rate.

OBJECTS OF THE INVENTION

[0008] It is the principal object of the present invention to provide an improved method of making a reproducible filament web with a high degree of bulkiness and surprisingly eff ctive mechanical properties.

[0009] Another object of the invention is to provide a method of making a filament web of high bulk, good mechanical properties and a high degree of reproducibility without drawbacks of prior art systems.

SUMMARY OF THE INVENTION

[0010] These objects are attained, in accordance with the invention in a method for the purposes described in which the spun bond web is made from multicomponent filaments whereby the multicomponent filaments are deposited upon a collecting surface or support and the mat thus formed by collecting the multicomponent filaments is bonded together or consolidated by a water jet system of the mat. Subsequently, a filament crinkling or crimping is introduced in the resulting web by a heat tr atment thereof to produce a high bulk spun bond web.

[0011] More particularly, the mat may comprise

[0012] (a) extruding multicomponent filaments consisting of at least two synthetic-resin components;

[0013] (b) depositing the multicomponent filaments in a mat upon a support;

[0014] (c) consolidating the mat of multicomponent filaments to a web by subjecting the mat to a water jet treatment; and

[0015] (d) heat treating the web to effect crinkling or crimping of the filaments thereof and bulking of the web.

[0016] As previously noted, the term “filament” is here us d to refer to endless filaments of thermoplastic synthetic resins as are commonly employed for spun bond although it can encompass, as far as the present invention is concerned, also shorter filaments and fibers which can benefit from being bonded in the w b by the application of the water jets and crimped or crinkled by the heat treatment.

[0017] I have found that the invention is especially effective when bicomponent filaments are used. The bicomponent filaments are comprised of only two different thermoplastic synthetic resins with different characteristics and especially different thermal expansion coefficients, different shrinkage properties and/or different mechanical or chemical properties in addition to th shrinkage and expansion.

[0018] The most highly preferred filaments are those which have two or more synthetic resin components in a side-by-side structure, i.e. the two components run next to one another to the full length of the filament. This applies especially to bicomponent filaments with a side-by-side structure. Along the length of the filament, a portion of the surface thereof is formed by the first polymer and the remainder by a second polymer in such bicomponent filaments. The use of the bicomponent filam nts in a side-by-side structure has been found to eliminate completely problems with earlier low-bulk webs and to provide surprising advantages with respect to high bulk webs.

[0019] The bicomponent filaments and, generally, multicomponent filaments ar produced by the individual extrusion nozzle of a spinneret adapted to handle two or more synthetic resin components. The extruded filament can be cooled, e.g. by contact with process air in a process air shaft and can be stretched in their passage downwardly along this shaft. The foraminous surface can be a perforated conveyor belt, i.e. a si ve belt which can be evacuated below he surface.

[0020] The water jet stabilization of the mat to produce the web can employ a multiplicity of fine very high speed water jets dir cted uniformly over the entire mat surface. The water jets pr ss the overlying filaments against underlying filaments to effect fusion between the filaments at the cross-over points.

[0021] Following the water jet treatment, the web is activated by a heat treatment and especially a heating in hot air at a temperature above 60° C. Because of different shrinkage and/or xpansion characteristics of the polymers in the filaments, a crinkling or crimping is produced which bulks the web. Indeed, the w b which results in accordance with the invention has especially high bulk and optimal mechanical characteristics which app ars to derive from the combination of water jet stabilization and subsequent heat treatment. In fact, without multicomponent and especially bicomponent filaments and both the water jet stabilization and heat treatment activation, an equivalent high bulk mechanically satisfactory web is not obtainable.

[0022] It has be n found, for xample, that the inv ntion provides a w b with esp cially long free filament segments, i.e. a high free filament length, in terms of the average length of filaments between two bonding or contact sizes with filaments at cross-overs. The high prefilament length means that the crimp, curling and in general bulking which is formed by the crinkling step, allows the development of a large number of loops, bends and other formations which extend transversely to the web and account for the bulk thereof. In addition, the bulking is esp cially reproducible.

BRIEF DESCRIPTION OF THE DRAWING

[0023] The above and other objects, features, and advantages will become more readily apparent from the following description, ref rence being made to the accompanying drawing in which:

[0024] FIG. 1 is a diagrammatic cross section of a bicomponent filament in accordance with the invention;

[0025] FIG. 2 is a schematic side view of the filament coll ction portion of the apparatus and the units downstream th reof in accordance with the invention;

[0026] FIG. 3 is a diagram illustrating the water jet stage of th invention; and

[0027] FIG. 4 is a diagram showing the hot air treatment stag.

SPECIFIC DESCRIPTION

[0028] FIG. 1 shows a cross section through a bicomponent filament in accordance with the invention and from this Figure it can be seen that the bicomponent filament comprises a polymer A making up half the cross section of the filament and a polymer B making up the other half of the cross section. The two polymers adjoin at an interface 1a and thus are in side-by-side relationship over the length of the filament.

[0029] Of course, either one of the components A or B can mak up a greater portion of the cross section than the other and can extend over a greater portion of the surface of the filaments than the other. The polymers A and B are for example two polymers which are compatible with one another and bond int grally to one another but have different heat shrinkage properties or different coefficients of thermal expansion.

[0030] FIG. 2 shows in highly schematic fashion the formation of the spun bond web in accordance with the invention. The filaments 1, collected from a spinneret from which the bicomponent filaments are extruded and a cooling and stretching shaft (not shown), gather on the endless sieve belt 2 into a mat 5 which is displaced in the direction of the arrow C. In a stabilizing station 3, the filament mat or fleece is subjected to a multiplicity of high velocity water jets as shown at 3a in FIG. 3, these water jets serving to bond crossing filaments 1 to one another at bonding points 1b where these filaments cross one another. A considerabl free length L may be provided between bonding points.

[0031] The water jets can be extremely fine water jets and preferably are of very high velocity. The water jets can be directed from nozzles having a diameter of from several millimeters to a fraction of a millimeter and at a pressure ranging from 2 bar to 1000 bar.

[0032] Subsequently the bonded filaments of the mats which now form a web 5a pass into a heat-treating station 4 in which hot air can be directed onto the web. The hot air flow is r pr sented at 4a in FIG. 4 and serves to cause crinkling or crimping at 1c of the filaments 1 between the fusion point 1b. Th result is a high bulk spun bond web. The apparatus of FIG. 2 has been shown in a highly simplified manner. It will be understood that other processing elements and apparatus components may be used where required or desirable.

Claims

1. A method of making a filament web, comprising the st ps of: (a) extruding multicomponent filaments consisting of at least two synthetic-resin components; (b) depositing said multicomponent filaments in a mat upon a support; (c) consolidating the mat of multicomponent filaments to a web by subjecting said mat to a water jet treatment; and (d) heat treating said web to effect crinkling of the filam nts thereof and bulking of the web.

2. The method defined in claim 1 wherein the multicomponent filaments produced in step (a) are bicomponent filam nts.

3. The method defined in claim 2 wherein said multicomponent filaments have the components thereof in side-by-side relationship.

4. The method defined in claim 3 wherein said h at tr ating of said web in step (d) is a treatment of said web with hot air.

5. The method defined in claim 1 wherein said multicomponent filaments have the components thereof in side-by-side relationship.

6. The method defined in claim 5 wherein said heat treating of said web in step (d) is a treatment of said web with hot air.

7. The method defined in claim 1 wherein said heat treating of said web in step (d) is a treatment of said web with hot air.