EP0097618A1 - Method of dividing a thermoplastic filament or a textile fibre by means of a laser beam - Google Patents

Abstract

The method provides for the formation of frayed ends on textile fibers (9) comprised of thermoplastic material by heating them sufficiently by means of a laser beam (12') so as to bring the fiber material to a visco-elastic state, while simultaneously submitting those fibers to a tensile stress so that the breaking of said fibers is preceded by an important striction. The method allows to manufacture particularly velvet and synthetic fur.

Description

The subject of the present invention is a method for cutting, by laser, a filament or a textile fiber made of thermoplastic material.

It has already been proposed, in the patents CH 586 769 and CH 609 736, to manufacture velvet by a process according to which strands of thread are divided, distributed on the surface of a fabric, using a laser beam focused, whose focus is placed successively in the presence of a portion of each of the strands, for a period of time sufficient to cause the combustion of at least a portion of the fibers forming these strands.

Furthermore, patent CH 560 772 discloses a process for converting textile filaments according to which a ribbon of textile filaments to be converted is tensioned while subjecting it to the action of a radiant energy source.

According to the methods described, the textile fibers are cut either by the combustion of a natural fiber, or by the melting of a thermoplastic material. In the latter case, a pseudospheric surface is formed at the ends thus cut, the diameter of which is greater than that of the fibers. This surface results from the surface tension of the thermoplastic material following its fusion during the cutting of the fibers.

The shape of the ends of these fibers clearly constitutes a disadvantage of this thermal cutting method with respect to conventional mechanical cutting. Indeed, in the case of cutting synthetic velvet from a thermoplastic material such as acrylic, the formation of such droplets gives a less velvety velvet and therefore a sensation less pleasant to the touch.

The use of laser radiation for the improvement of thermoplastic wires, in particular for creating corrugations, is, moreover, known from patent CH 471,915.

The object of the present invention is not only to remedy to address the shortcomings of known thermal cutting processes, but it also makes it possible to form tapered ends on the cut elements and, therefore, to make these ends more pleasant to the touch.

To this end, the subject of the present invention is a method for cutting, by laser, a filament or a textile fiber of thermoplastic material, in which this filament or fiber is subjected to the radiation of a laser focused on the area of the filament or fiber desired for sectioning, characterized in that a tensile stress is applied to this filament or fiber and that, by the laser, thermal energy is supplied to said zone of the filament or fiber in sufficient quantity to bring it only in a viscoelastic state, the whole so that, thanks to the combined action of the tensile stress and the thermal energy brought to said zone of the filament or fiber, a stretching of this zone is produced, subdividing the filament or fiber in two sections whose opposite ends receive a shape that tapers gradually, by stretching the thermoplastic material, to become pointed at the end of this tapering and separate by the top of their po respective inte.

The replacement of at least part of the ends of fibers comprising droplets by tapered points makes it possible to increase the value of the product obtained: in fact, obtaining tapered points, otherwise impossible by using a mechanical cutting means, allows you to get closer to the appearance of animal hair appearing in particular on the surface of natural fur, which results in a velvety sensation pleasant to the touch. The present invention can therefore not only be advantageously applied to the manufacture of velvet but, in addition, to the production of synthetic furs.

• La figure 1 est une vue en élévation d'un dispositif expér imen- tal de mise en oeuvre;
• Les figures 2 à 4 sont des diagrammes explicatifs;
• Les figures 5 et 6 illustrent l'application du procédé selon l'invention dans la fabrication de velours.

The attached drawing illustrates, schematically and by way of example, how the method according to the invention can be implemented:

• Figure 1 is an elevational view of an experimental implementation device;
• Figures 2 to 4 are explanatory diagrams;
• Figures 5 and 6 illustrate the application of the method according to the invention in the manufacture of velvet.

Figure 1 shows a variable speed motor 1 whose shaft 2 is rotatably mounted between two bearings 3, 4 and carries a disc 5. This disc is equipped with pairs of pins 6, 7, only one of which is visible in the drawing, arranged radially around the axis 2. One of the pins of each pair receives the end of a spring 8 while the other is used to fix one end of a wire 9, of thermoplastic material, the second end of which is attached to the free end of the spring 8 the latter thus stretching the wire between the two pins. The device also carries a laser source 10 capable of generating a focused beam of light 12 by means of an optical system, represented schematically by a simple lens 11, and directing this beam perpendicular to the upper face of the disc 5.

To cut the wire 9 while forming tapered fiber ends, this wire is exerted a determined traction using the spring 8 and the disk 5 is rotated by the motor 1 so that, by turning, each wire 9, distributed on the disk successively cut the beam 12 focused by the lens 11. the rotational speed _V. of the disc 5 is chosen such that the wire 9 cuts the laser beam for a sufficient time so that the thermoplastic material of the wire is heated so as to take on a viscoelastic consistency. Therefore, and under the effect of the traction which is applied to the wire by the spring 8, this wire stretches in the impact zone of the laser. It is the diameter f of the cross section of the laser beam through which the wire passes which determines the length of this area. The appearance of the tapered portions of the fibers essentially depends, on the one hand, on the diameter of the laser beam and, on the other hand, on the tensile force applied to the wire 9 by the spring 8. Furthermore, to a lesser extent , this aspect also depends on the temperature reached by the fibers, and therefore on the thermal energy transmitted to these fibers.

In the diagram of FIG. 2, the ordinate N represents the proportion of tapered fibers relative to the total number of fibers cut according to the stress resulting from the tensile force applied to the wire 9 by the spring 8, for a constant power P of the laser beam and a constant speed V _o of displacement of the wire relative to the laser beam 12. Diagram 2 shows that there is a relationship between the stress resulting from the for this traction applied to the wire 9 by the spring 8 and the proportion of tapered points. The stress σ min is the maximum stress for which 100% droplet-shaped ends are obtained (N = o). By increasing the value of the stress applied to the fibers, the droplets are gradually replaced by tapered points until 100% of fibers with tapered points (N = 1) are obtained, when the stress reaches the cpt value. If the opt stress is exceeded, the tapered ends are gradually replaced by torn ends, until 100% torn ends are obtained (N = o), when the stress reaches the value σ max. Thus, curve V delimits the zones A (100% of droplet-shaped points), B (100% of tapered points), and C (100% of torn points). It is possible to set a minimum proportion N _o of tapered tips by choosing the width of the interval D _o delimited by the constraints σ o ₁ and σ o ₂ . In other words, for any stress applied to the fibers, and comprised between σo ₁ and σo ₂ , it is possible to obtain at least a proportion N _o of fibers whose ends are tapered. The value of the stresses σ min and σ max depends on the nature of the wire and the thermal energy transmitted, as we will see later.

.n où S représente la section normale du fil (S =

φ² avec φ diamètre du fil) et n représente l'efficacité du système optique. Les droites d₁ et d₂ ont été obtenues par une "régression linéaire" faisant intervenir la valeur des contraintes σ_i1 et σ_i2 constituant les limites des intervalles D_i correspondant à des proportions Ni données de pointes effilées. La position des intervalles D_i dépend de la valeur de la puissance spécifique q_i si la vitesse de déplacement V_I est fixée. Ces droites sont sensiblement parallèles entre elles. Une variation de la vitesse V₁ de déplacement du fil 9 par rapport au faisceau laser 12 implique une variation inver- sément proportionnelle de l'énergie reçue du faisceau 12 par ce fil. Une diminution de la vitesse de V₁ à V₂ a, pour conséquence, une augmentation de l'énergie transmise au fil, donc une diminution des contraintes σ_i1 et σ_i2, ce qui se traduit, dans le diagramme de la figure 3, par un rapprochement des droites d₁ et d₂ de l'origine du système d'axes σ-q (droites d'₁ et d'₂) .The diagram of FIG. 3 shows the variation of the value of the constraints constituting the upper and lower limits of an interval D _i , corresponding to the interval D _i of the diagram of FIG. 2, as a function of the variations of the specific power q _i transmitted to the wire by the laser beam 12 of power P _i and defined by the relation q̇ _i =

.n where S represents the normal section of the wire (S =

φ ² with φ wire diameter) and n represents the efficiency of the optical system. The lines d ₁ and d ₂ were obtained by a "linear regression" involving the value of the stresses σ _i1 and σ _i2 constituting the limits of the intervals D _i corresponding to given proportions Ni of tapered points. The position of the intervals D _i depends on the value of the specific power q _i if the speed of movement V _I is fixed. These lines are substantially parallel to each other. A variation in the speed V ₁ of displacement of the wire 9 with respect to the laser beam 12 implies an inversely proportional variation in the energy received from the beam 12 by this wire. A decrease in the speed from V ₁ to V ₂ results in an increase mentation of the energy transmitted to the wire, therefore a reduction in the stresses σ _i1 and σ _i2 , which results, in the diagram of figure 3, by a bringing together of the lines d ₁ and d ₂ of the origin of the system d 'axes σ-q (lines of ₁ and ₂ ).

By implementing the invention, the acrylic yarns of 30 and 107 Tex were cut, subjected to a tensile force producing a stress between 2 and 5 N / Tex, by means of a laser with a power varying between 140 and 450 W. The efficiency of the optical system was 0.88. The numerical values corresponding to obtaining a majority of tapered tips have been summarized in the table below:

. q̇ ϕ V , où q̇ est la puissance spécifique, _V la vites- se de déplacement du fil par rapport au faisceau laser et ϕ le diamètre du faisceau laser. L'énergie spécifique q permet d'exprimer les droites dans un diagramne énergie spécifique/contrainte, avec l'avantage de ne pas faire intervenir explicitement le paramètre vitesse. L'ensemble des paires de droites d'₁, d'₂ correspondant chacune à une vitesse V_o (fig. 3) peut ainsi être remplacé (fig. 4) par une seule paire de droites L₃, L₄ parallèles entre elles, d'équation ^q ₃ = - 2,2.10⁶.σ+ 1,85.10⁵, respectivement q₄ = - 2,2.10⁶.σ+ 2,3.10⁵, correspondant aux valeurs minimale et maximale de l'énergie spécifique à fournir à des fils d'acrylique en fonction de la contrainte qui leur est appliquée, pour obtenir une majorité de fibres à pointes effilées. Les droites L_I et L₂ correspondent aux contraintes fmin. respectivement σ max. définies précédemment en relation avec le diagramme de la figure 2.These numerical values made it possible to define the surface delimited by the lines L ₁ to L ₄ in the diagram of FIG. 4 which represents the relation linking the specific energy to be supplied to acrylic threads and the tensile force to which these threads must be submitted so that a majority of the cut fibers have tapered tips. The specific energy is defined by the ratio between the total energy supplied to a textile thread and the surface S of the thread having been in contact with the laser beam (S = φ · ϕ where φ represents the diameter of the thread and ϕ the diameter of the laser beam). The specific energy is expressed, from the specific power defined above, by the relation ^q =

. q̇ ϕ V, where q̇ is the specific power, _V the speed of displacement of the wire with respect to the laser beam and ϕ the dia laser beam meter. The specific energy q makes it possible to express the lines in a specific energy / stress diagram, with the advantage of not explicitly involving the speed parameter. The set of pairs of lines of ₁ , of ₂ each corresponding to a speed V _o (fig. 3) can thus be replaced (fig. 4) by a single pair of lines L ₃ , L ₄ parallel to each other, of equation ^q ₃ = - 2.2.10 ⁶ .σ + 1.85.10 ⁵ , respectively q ₄ = - 2.2.10 ⁶ .σ + 2.3.10 ⁵ , corresponding to the minimum and maximum values of the specific energy to be supplied to acrylic yarns depending on the stress applied to them, to obtain a majority of fibers with tapered points. The lines L _I and L ₂ correspond to the constraints fmin. respectively σ max. defined above in relation to the diagram in Figure 2.

By way of example of industrial use of the process described above, FIGS. 5 and 6 show partial views, one in perspective, the other in section, of a circular knitting machine in which a diagrammatic representation is shown. thread guide 30, felling plates 21 engaged with a cam 24, a needle bed 20 on which needles 25 are slidably mounted, a segment of a bottom thread 28 of a bottom knit, not shown, and a loop wire 29. The tensioning member for the wire loops 29 is constituted by a projection 23 situated at the upper end of the plate spout 22 (FIG. 6). This member makes it possible to drive the portion of the wire 29, constituting a loop 31, in the recoil movement of the plate 21 consecutive to the formation of this loop and, by this recoil movement, to subject this wire to a traction force. . The laser beam, coming from the source 27, is directed by the optical system 26 on the loop portion in contact with the tensioning member 23 as soon as, by its new recoil, the plate has reached the position in which the tension in the thread becomes sufficient to obtain fibers with tapered points.

In Figure 6, the various organs of the loom have been shown during taper. This operation can only take place when the two ends of the loop intended to be tapered are made integral with the base knit. This condition is considered satisfied as soon as the needle 25 reaches the point dead low. It is therefore necessary that, at this instant, the loop wire bearing on the member 23 has been tensioned by the recoil movement of the plate 21 usually intended to release the loop once it has formed. A laser source control device, not shown, allows the synchronization of the energy supply with the movements of the needle 25 and of the plate 21.

The manufacturing method described above is capable of replacing the shaving operation, involved in the production of knitted velvet, thanks to a loop cutting operation which is integrated into the knitting process. It makes it possible to remedy the loss of material occurring during shaving, while improving the quality of the product obtained by the creation of tapered tips.

Claims (2)

1. Method for cutting, by laser, a filament or a textile fiber made of thermoplastic material, in which this filament or fiber is subjected to the radiation of a laser focused on the area of the filament or fiber desired for sectioning, characterized by the fact that a tensile stress is applied to this filament or fiber and that, by the laser, thermal energy in sufficient quantity is brought to said zone of the filament or fiber to bring it only in a viscoelastic state, the everything so that, thanks to the combined action of the tensile stress and the thermal energy brought to said zone of the filament or fiber, a stretching of this zone is produced, subdividing the filament or fiber into two sections whose ends opposite receive a shape gradually tapering, by stretching the thermoplastic material, to become pointed at the end of this tapering and separated by the top of their respective tip. 2. Method according to claim 1, characterized in that said tensile stress is of value between 2.10- ² _{N / T} ex and 5.10- ² _{N / T} ex, the power and the section of the laser beam being such that l thermal energy supplied is between 1.41.10 ⁵ J / m ² and 1.86.10 ⁵ J / m ² for a value of the tensile stress of 2.10- ² N / Tex, respectively 0.75.10 ⁵ J / m ² and 1.2.10 ⁵ J / m ² , for a tensile stress of value 5.10 ^-2 N / Tèx.

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