Process For Texturizing Fibers Obtained By Splitting Synthetic Foils And Products Made Therefrom

Abstract

Fibers obtained by splitting synthetic foils and the resulting products are texturized by subjecting the foil or the fibers obtained after splitting and prior to their separation to a cross-sectionally differential modifying action, and thereafter contacting the modified foil or fibers with a shrinking agent, or subjecting the foil or fibers to stretching.

Description

BACKGROUND OF THE INVENTION

The invention relates to a process for texturizing fibers obtained by splitting synthetic foils. It also relates to texturizing the resulting products, such as filaments, non-woven fabrics, and similar sheet fabrics.

Processes are known for texturizing filaments wherein the texturizing is for instance effected by compression in compression chambers, by applying pinions to the thread, followed by fixation of the resulting impressions, or by tangling the initial threads by means of an air current. These processes have the shortcoming that they are suited for the old type of fiber materials, but do not sufficiently account for the specific properties of fibers obtained by splitting synthetic foils.

A process is also known for texturizing filaments wherein texturizing effects are obtained by using materials having different shrink characteristics. The shortcoming of these processes is that they require at least two fiber components which have different shrinking properties.

It is an object of the present invention to provide for a process for texturizing filaments which avoids the shortcomings of the prior-art processes, and in particular does not require the use of two fiber components with different shrinking properties.

SUMMARY OF THE INVENTION

The invention resides in a process wherein the foil or the fibers, after splitting the foil but prior to their separation, are subjected to a cross-sectionally differential modifying action, whereupon the modified foil or fibers are then contacted with a shrinking agent or subjected to stretching to obtain a texturizing effect.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its structure and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description of specific embodiments when read in connection with the drawing.

BRIEF DESCRIPTION OF THE DRAWING

The three FIGURES illustrate, in diagrammatic form, different embodiments of the process of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention relates to various kinds of synthetic fibers and foils from which fibers may be obtained by a splitting action. It is particularly applicable to polyolefins such as polyethylene but also to polyamides, polyesters and cellulosic textiles. Preferably, the foil is subjected to an initial unidirectional stretching action before the modifying treatment of the invention is applied. The amount of stretching depends on the type of polymer and will affect particularly the degree of texturizing obtained in the subsequent treatment.

The shrinking action applied to the modified foil or fibers can be effected with hot air, steam or other shrinking agents.

The modifying action itself may be carried out in various manners. For instance, the foil or not-yet-separated fibers may be subjected to a cross-sectionally differential cross-linking, degrading or grafting of monomeric compounds, preferably vinyl monomers, by means of high-energy radiation. Preferably, the radiation is an electron radiation. The radiation dose depends on the material. For polyolefins it is at about 10.sup.7 rad, for polyesters at about 5.multidot.10.sup.7 rad. The dose depends also on the ultimate objective. To form free radicals for grafting, a lower dose is sufficient than would be sufficient for cross-linking.

Several of these effects may be combined, such as cross-linking plus grafting or degrading plus grafting.

The differential limitation of the modifying action may for instance be accomplished by limiting the radiation dose so as to prevent complete penetration of the cross-section. In another embodiment, the entire cross-section may be penetrated by the radiation, but the action may be modified by heating and cooling opposed faces of the foil or fibers. The penetration depth will depend on the energy of the radiation.

The texturized fibers and sheet materials may for instance be in the form of non-woven fabrics. These may be made from the fibers obtained by splitting foils, without the aid of additional binding agents, by applying a thermal treatment to the non-woven fabric so as to heat the fibers to a point close to their softening point and cause them to become bonded to each other at points of contact. The heat employed in this step can at the same time be used to effect the shrinking which causes the texturizing effect.

The temperature of the heat treatment should preferably be a few degrees below the initial melting range of the material.

The grafting may be effected with acrylic acid or derivatives thereof, such as the sodium salt of acrylic acid, and other suitable monomers conventionally used for grafting operations. The type of graft polymer obtained may affect also other properties, such as the melting range, water adsorption, antistatic properties, etc.

The following examples will further explain the invention. Reference is made to the attached drawings.

EXAMPLE 1

This example illustrates the making of a texturized filament from fibers obtained by splitting wherein the modification is obtained by unilateral radiation of a polyethylene foil in a vacuum chamber.

With particular reference to FIG. 1, it will be noted that reference numeral 1 designates a foil of polyethylene which had been subjected to a unidirectional stretching in the direction of movement. The foil was passed through an air lock 2 into vacuum chamber 5 with which the scanner 3 of an electron acclerator 4 was associated. The foil was treated in the vacuum chamber by radiation with the electron beam 6. The speed of movement of the foil and the energy of the electron current produced by the electron accelerator 4 were adjusted so that the foil 1 absorbed radiation in a dose of 3.multidot.10.sup.7 rad. The energy of the electrons of the beam 6 was selected to provide for a maximum range of the electrons in the polyethylene foil corresponding to exactly one half the thickness of the foil. With a foil of a mass equal to 50 g/m.sup.2 an electron energy of 50 KeV was applied. In this manner the polyethylene foil was cross-linked only on the side facing the scanner. After passing through a second air lock 7, the foil entered a splitting device 8 wherein the individual fibers were separated. In the device 9 filaments were spun from the individual fibers which were then exposed to heat in the zone 10. This caused a shrinking which affected the foil and fibers which had been crosslinked by chemical radiation in a manner different from the foil or fibers that had not been so treated. Thus, a texturizing of the filament was obtained. The texturized filaments 11 were finally collected on a spool 12.

EXAMPLE 2

This example illustrates the making of a texturized filament from fibers obtained by foil splitting by means of radiation of one major face of a polyethylene foil in a vacuum chamber and subsequent unilateral grafting of the polyethylene with acrylic acid.

With particular reference to FIG. 2, it will be noted that the parts indicated by the same numbers as in FIG. 1 have the same function. Accordingly, a polyethylene foil 1 which has been subjected to unidirectional stretching in the direction of movement was subjected to radiation in the same manner as described in EXample 1. The radiation caused the formation of free radicals. Before these free radicals disintegrated, the foil was passed into a vessel 13 wherein it was subjected to graft copolymerization with acrylic acid.

It will be understood that the radiation treatment could also be applied subsequent to the grafting step. All other steps were the same as in Example 1. The texturized filaments produced by this process have the specific advantage that, because of the grafting of the acrylic acid, they are amenable to easy dyeing in specific areas. Thus, specific color effects can be obtained.

With an acrylic acid concentration in aqueous solution of 20 percent, a treatment time of 15 minutes and a temperature of 28.degree.C an increase of the mass was obtained indicating the degree of grafting to be of 8.5 percent.

EXAMPLE 3

This example illustrates the making of a texturized filament from fibers obtained by splitting of a foil, the process being characterized in this example by homogeneous radiation of the entire cross-section of a polyethylene foil and a differential heating or cooling treatment of the two major faces of the foil during or after radiation.

With specific reference to FIG. 3, it will again be noted that parts having the same reference numerals as in FIG. 1 have the same function. Accordingly, a polyethylene foil which had been subjected to unidirectional stretching in the direction of movement as indicated at 1 was passed under the scanner 3 of an electron accelerator 4 and was radiated in the open air with electrons 6. No air locks were used in this case. The speed of movement of the foil and the energy of the beam produced by the electron accelerator were adjusted so that the foil absorbed a dose of 2.multidot.10.sup.7 rad.

Contrary to the process of Examples 1 and 2, the electron energy in this case was of a magnitude sufficient to cause a homogeneous irradiation of the foil throughout its cross-section. Thus, with a foil of a mass equal to 50 g/m.sup.2 an electron energy of 200 KeV was applied. However, a differential modification of the cross-section was obtained by exposing the foil, prior to, during or after the irradiation to a cooling gas 14 at its underside and to a heating gas 15 at its top face. Thus, the irradiation on the side facing the scanner 3 resulted in a different structure than on the opposite face. All other steps were the same as in Example 1.

All of the processes of the above Examples can also be carried out with the same results using other textiles, such as polypropylene, polyamide (Nylon 6), polyester or cellulosic foils.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

Claims

What is claimed as new and desired to be protected by Letters Patent is set

1. In a process for making crimped fibers and products of the latter wherein the fibers are obtained by fibrillation of synthetic foils, the steps of irradiating a foil, or the fibers obtained by fibrillation of the same but prior to their separation, so as to cause differential modification of the structure of said foil or said fibers through the cross section thereof; and treating the irradiated foil or fibers so as to

2. A process as defined in claim 1, wherein said foil or fibers are

3. A process as defined in claim 1, and further comprising the step of subjecting said foil or fibers to unidirectional stretching prior to the

4. A process as defined in claim 1, wherein said foil or fibers are composed of a synthetic polymer which undergoes differential crosslinking

5. A process as defined in claim 1, wherein said foil or fibers are composed of a synthetic polymer which undergoes differential degradation

6. A process as defined in claim 1, wherein said foil or fibers are composed of a synthetic polymer which undergoes differential grafting

7. A process as defined in claim 1, wherein the step of irradiating said foil or fibers comprises adjusting the magnitude of high-energy radiation so that the effects of the same extend substantially throughout the entire cross sections of said foil or fibers; and further comprising the step of heating one major surface of the foil or the unseparated fibers and cooling the other major surface of said foil or unseparated fibers to thereby cause differential modification of the structure of said foil or

8. A process as defined in claim 1, wherein the step of irradiating said foil or fibers comprises adjusting the magnitude of high-energy radiation so as to limit the effects of the same to only a portion of the total

9. A process as defined in claim 1, wherein the step of treating said

10. A process as defined in claim 1, wherein the step of treating said irradiated fibers comprises heating the same to a temperature sufficient to cause shrinkage of said fibers and simultaneous bonding of the same to

11. A process as defined in claim 1, wherein said foil or fibers are composed of a synthetic polymer which undergoes differential cross-linking

12. A process as defined in claim 1, wherein said foil or fibers are composed of a synthetic polymer which undergoes differential cross-linking

13. A process as defined in claim 1, wherein said foil or fibers are composed of a synthetic polymer which undergoes differential degradation

14. A process as defined in claim 1, wherein said foil or fibers are composed of a synthetic polymer which undergoes differential cross-linking, differential degradation and differential grafting during said process.