EP0517628B1 - Process for the production of polyamide filaments with better productivity - Google Patents

Abstract

An improved output efficient polyamide-based preoriented yarn spun at a speed of at least 4000 m/min and obtained by introducing, before the spinning, of a quantity of 0.05 to 1% by weight of pyrogenic silica of particle size of between 5 and 15 nm into the molten polymer in the form of dispersion in a master mix of the same polyamide as that intended to be processed, the filaments after spinning being then cooled by means of a gas stream at room temperature and then sized and wound at a speed of between 4200 and 5800 m/min. The preoriented yarns thus prepared exhibit a delay in the orientation and are obtained with a gain in output efficiency of at least 10%, generally at least 15%.

Description

The present invention relates to a method for obtaining non-stretched polyamide based (PA) filaments with better productivity.

It also relates to modified non-stretched yarns based on polyamide suitable for false stretch-texturing texturing torsion.

Polyamide based yarn generally not drawn used for false twist stretch-texturing operation must have orientation and crystallinity properties weak, in order to better orient the macromolecules then to crystallize and thus fix the orientation during the process stretch-texturing without degrading or breaking the filaments during thermal fixing of the wire.

In particular, it is known according to the patent application French published under No. 2,274,710 to prepare PA yarns usable directly in stretch-texturing processes by false twist, by melt spinning of polyhexamethylene adipamide, cooling, treatment in a vapor atmosphere of water and under pressure to obtain the desired properties of yarn, and preferably slight overstretching of the threads before rewinding. It is performed at speeds generally between 2700 and 4000 m / min.

To increase spinning speed without significantly changing the crystallinity and orientation properties of POY yarns not stretched, it has also been proposed in the European patent application published under No. 08274 (A) to introduce into the melted PA of polyethylene or polypropylene then forming microfibrils in the filaments obtained.

But the addition of polymer in the form of fine particles has drawbacks during industrial production: particular, it requires very sophisticated technology to obtaining mixtures with finesse and stability over time sufficient to allow reliable spinning without breakage of strands. Of made such a technique is not usable industrially.

It is also known to improve the productivity of yarns PA not oriented, suitable for texturing by false-twist, by introduction into the polymer chains of 0.01 to 1 mol% of an agent connection such as bishexamethylene triamine, or acid trimesic, or 4-aminomethyl diamino octane-1,8. But such compounds modify the rheology of the polymer by increasing its viscoelasticity by so that the spinning of such copolymers becomes very delicate and presents significant risks of breakage of strands.

Furthermore, it is also known, according to French patent application published under No. 1,428,439, to prepare resinous compositions of PA containing silica in the form of particles <10 μm of specific conductance <5.10 ^-4 mho / cm .

But the use of such compositions relates to plastics applications.

It is also known according to French Patent No. 1,169,578 to prepare PA compositions for compression and injection molding having more extensive softening and melting zones, making it possible to maintain a viscous flow and to avoid gels by incorporating PA mineral charges such as SiO ₂ with a particle size of 1 to 40 µm.

It is also known according to French patent no. 951 371 a process for manufacturing (filaments and) yarns based on, between others, of polyhexamethyleneadipamide, in which process one incorporates into the polymer, before its spinning conventional in the molten state, an inert substance in an amount of 0.005% to 0.05%, an inert substance which, even preferably being titanium dioxide, nevertheless may also consist of silica. However, this known method is at low speed and the wires obtained are drawn.

The present invention relates to the preparation of yarns for base of unstretched PA, preoriented, with improved productivity.

More particularly, it relates to a method according to claim 1, designed to improve the productivity during the spinning of a preoriented polyamide-based yarn, at a speed of at least 4000 m / min, by introduction into the molten polymer before spinning , in an amount of 0.05 to 1%, preferably 0.05 to 0.5% by weight of combustion silica, of particle size between 5 and 15 nm, in the form of a dispersion in a masterbatch of the same PA as that intended to be conformed. The mean interparticle distance of the SiO ₂ aggregates in the final polymer is between 0.2 and 0.7 μm, the maximum value between 2 aggregates being ≤ 3 μm.

After spinning, the filaments are cooled using a gas stream at room temperature then sized and returned to a speed between 4200 and 5800 m / min, the filaments preferably being intertwined before being returned.

The productivity gain obtained is greater than 10%, more usually more than 15% or even more.

The present invention also relates to wires according to claim 4. They are wires pre-oriented unstretched PA-based, containing 0.05 to 1%, preferably 0.05 to 0.5% by weight of particulate combustion silica between 5 and 15 nm (50 to 150 Å) evenly distributed in the PA, having a delay in crystallization and orientation.

In the description, polyamide means polyhexamethylene adipamide, or copolyamides containing 85% or more hexamethylene adipamide units and up to 15% of other units obtained by replacing, for example, the starting adipic acid with a other diacid such as terephthalic acid, sebacic acid, and or replacing the two monomers with caprolactam for example.

The starting polyamides may also contain known additives such as matting agents, stabilization with regard to light, heat and oxidation, additives intended to reduce the accumulation of static charges or modify the suitability for dyeing, etc.

The polyamide used according to the present invention has a relative viscosity measured on a solution at 8.4% by weight by volume in 90% formic acid between 38 and 52, preferably 40 about.

The expression combustion silica is understood to mean silicon dioxide obtained by combustion of an organosilicon compound and commercially available under different brands such as the Aerosil 300 type from the Degussa company, or a silicon dioxide treated on the surface of known manner to avoid re-agglomerations. Silicas are ultrafine fillers in the form of aggregates consisting of elementary particles with a specific surface of between 100 and 450 m ² / g, the size of which is between 5 and 15 nm (50 to 150 Å), more generally of the order of a hundred Å and gathered in linear chains.

According to the invention the combustion silica is mixed with PA identical to PA to be conformed in a phase mixing apparatus fondue such as a twin screw extruder or any suitable device, in proportions such as a master mix of 1-10% silica, preferably 2-5% is obtained in the form of granules at 260-280 ° C, preferably about 260-270 ° C.

The masterbatch granules thus obtained contain very uniformly distributed silica. Distribution in the final polymer is evaluated by the mean interparticle distance of the aggregates.

According to the invention, the interparticle distance average of the aggregates in the final polymer is between 0.2 and 0.7 µm, the maximum value between two silica aggregates being ≦ 3 µm. This assessment is made from photographs taken in electron microscopy, the photographs then being processed in image analysis in order to know the number of particles and calculate the interparticle distance of each aggregate.

The interparticle distance obviously depends on the rate of introduced silica: the higher the silica, the lower the distance interparticle. Furthermore, the dispersion of silica in the polyamide depends in part on the type of silica used, certain silicas coated disperses better than uncoated silica.

If the silica content is> 1%, this will affect the rheological behavior of the polymer and in particular the spinning risk to be disturbed by broken strands.

If the silica content is less than 0.05%, the distance mean interparticle becomes too high, the silica level introduced is insufficient to modify the structure of the polyamide of so that the desired effect is not obtained.

Masterbatches are introduced in proportions various depending on the desired silica content, in the polyamide which can be either in the molten state or in the state of granules, before spinning by example using a twin screw mixer extruder heated between 260-270 ° C or any other suitable means.

According to the invention the desired level of silica on wire is between 0.05 and 1%, preferably 0.05 and 0.5% by weight.

The spinning is carried out at the usual temperatures for the polyamide between 280 and 295 ° C, preferably close to 285 ° C and the filaments are cooled under the die by a gas stream of cooling then sized and rewound at speeds between 4200 and 5800 m / min. Cooling conditions may vary by depending on the cooling device used, the precise speed the spinning, the title and the number of filaments, these settings being spring of the skilled person.

Preferably, the filaments are intertwined and / or intertwined before rewinding for better subsequent rewinding.

The method according to the invention, surprisingly and unexpected, allows to obtain unstretched, preoriented filaments, with improved productivity greater than 10%, generally greater than 15% or even more, due to a delay in the orientation of the filaments: that is to say that for the same level of orientation of the filaments, the winding speed is greater than 10% or even 15% or more.

Scientific studies show that when obtaining direct PA wires not drawn from very low speeds (500 to 1000 m / min) up to at least more than 6000 m / min, we first observe a strong orientation of crystalline and amorphous areas, then a weaker orientation, the orientation being developed essentially by the spinning constraint which is mainly a function of the speed and title of filaments. The orientation state of the material, in particularly the orientation of the amorphous phase, the organization of the phases crystalline and amorphous, the interface between the crystalline phases and amorphous, for a given polyamide, is clearly highlighted by the elongation at break of the wires from this material. This one, in effect, decreases significantly from spinning speeds from 1000 m to 4000 m / min, then significantly lower by 4000 to 6000 m / min and beyond. This makes it difficult to obtain non-stretched pre-oriented polyamide yarns, suitable for stretch-texturing processes used to date at speeds greater than 4000 m / min.

According to the present invention, it has been found, so surprisingly, that the introduction of 0.05 to 1% preferably 0.05% to 0.5% of combustion silica caused a delay in the reduction of the elongation at break or close to break of the filaments in function of the spinning speed, delay which corresponds to a delay at the orientation of the filaments along the spinning path. This delayed orientation provides pre-oriented, unstretched yarn having characteristics identical to those of the wires obtained at at least 10% lower speeds, more generally at least 15%, calculated in relation to the values of their elongation at rupture, or their elongation corresponding to the same stress, close to breaking.

According to the invention, the values of elongations at break or at a given stress are measured with a known normal dynamoneter commercially under the brand Instron 1122 connected to a calcuter; each value represents the average over 20 measurements.

Elongation at a reference stress: lc - lo / lo × 100
lc = length corresponding to the reference or rupture stress,
lo = initial length.

Figure 1 shows the offset of the elongation values at the breakage as a function of the spinning speed by loaded wires respectively 0.05 and 0.5% by weight of silica relative to a uncharged control polymer and for speeds greater than 4000 m / min. The value of elongations on unstretched polyamide yarn control, spun at speeds below 4000 m / min is also indicated with reference.

The delay in the orientation of the modified yarns according to the invention is confirmed by the values of the sonic and birefringence module which are measured as follows.

Sonic module = we measure the phase change caused by variations in mechanical wavelength longitudinal of a wire which passes between a frequency transmitting probe 6750 cycles / sec and a receiving probe. Phase changes, for example a simple relationship, directly represent the changes in the speed of sound which are, by well known changes, the image of module changes. The sonic or dynamic module is directly proportional to the square of the speed of sound in the sample by the density of matter.

Birefringence = measured on circular strand only.

The birefringence of a filament testifies to the macromolecular orientation of its material. It is equal to the difference of the refractive indices in the directions parallel and perpendicular to the axis of the filament: Δη = η // - η ⊥

The refractive indices are obtained by a method compensation optics (polarized light and Berek compensator) on individual filament kept taut under low tension in dispersion in petroleum jelly oil.

The present invention therefore makes it possible to produce at speeds of spinning above 4000 m / min of pre-oriented polyamide yarns, not stretched with a delayed orientation corresponding to those of yarn obtained at speeds lower by at least 10%, more usually 15% or even more. Such threads having an orientation have the mechanical characteristics of wires obtained at lower speeds which allows their false texturing torsion under good conditions by the texturing stretching processes simultaneous, skewer or friction. They can also be used for all textile transformations such as weaving, hosiery or the manufacture of non-woven tablecloths.

Furthermore, the introduction of silica does not alter the mechanical properties of the wires necessary for their use later; moreover, the combustion silica is inexpensive and does not no significant modification of industrial installations required of spinning.

The examples which follow are given as an indication but nonlimiting to illustrate the invention.

Examples 1 to 3

A 5% silica masterbatch is produced using an extruder fully meshed corotative double screw, known commercially as the Leistreitz LSM 30/34 brand, working at a rotational speed average of 300 rpm and at a temperature varying from 260-270 ° C.

The combustion silica used is an ultrafine commercial filler of the A 300 type from the Degussa company. It is in the form of aggregates made up of elementary particles with a specific surface of 300 m ² / g, with an apparent density of 0.05 to 0.06, the particle size being between 5 and 15 nm (50 to 150 Å). The master mixture of 5% silica is then introduced in various proportions, according to the final desired silica content, into the polyamide in the molten state before spinning, by means of a twin-screw kneader extruder heated to an increasing temperature. from 260 to 270 ° C and with a rotation speed of 300 rpm.

The temperature profile allows the material to melt polyamide before the addition of the filler which is therefore done in the middle molten. A vacuum zone is established on part of the extruder in order to ensure the drying of the polyamide.

The final silica content and the average interparticle distance between aggregates in the final polymer are as follows:

Polyamide loaded with silica is spun through a plate die maintained at 283 ° C with 2 times 7 round section orifices 0.34 mm in diameter and the hole height is 4 times its diameter. Spinning is carried out at a constant flow rate per orifice of 1.68 g / min. The filaments are cooled by a stream of air transverse at room temperature in the presence of humidity (RH = 60%), sent at a speed of 50 m / min. The filaments are converged and simultaneously sized and then interlaced by means of a pneumatic nozzle, (air pressure 2 bar) and rewound at different speeds: 4200 - 5000 - 5800 m / min.

The control wire is obtained in an identical manner but lower spinning speeds were achieved for the evaluation of the productivity gain from elongation at break values.

The characteristics of the wires are gathered in the following table:

From the above values we notice that the best productivity gains are obtained with the highest loads in silica. Such threads are intended for texturing on the machines of usual false twist.

Examples 4 and 5

The process used in Examples 1 to 3 is reproduced in using combustion silica with the same specific surface area and density, surface treated with octamethylcyclotetrasilaxone in gas phase to avoid re-agglomerations.

A master mixture is prepared with 5% of treated silica of the as indicated in Examples 1 to 3. The masterbatch is introduced in the form of granules at the same time as the polyamide to conform in a twin screw mixer extruder heated to a increasing temperature between 260 and 270 ° C and with a speed of rotation of 300 rpm. A vacuum zone ensures the drying of the polymer in the last part of the extruder.

The final silica content and the average interparticle distance in the final polymer are as follows: Ex. Silica content by weight Average interparticle distance between aggregates Aggregate size 4 0.5% 0.7 µm 0.1 µm 5 1% 0.6 µm 0.1 µm

Polyamide loaded with silica is spun through a plate die maintained at 282 ° C comprising twice 10 orifices of round section 0.39 mm in diameter and the height of the orifice is 4 times its diameter. The spinning is carried out on a constant basis. The filaments are cooled by a transverse air stream at temperature ambient in the presence of humidity (RH = 60%), sent at a speed of 48 m / min. The filaments are converged and sized simultaneously then interlaced by means of a pneumatic nozzle (air pressure 2.2 bars) and rewound at different speeds: 4800 - 5500 m / min.

The control thread is obtained in an identical manner (but lower spinning speeds were achieved for the evaluation of the productivity gain from elongation values).

For reasons of homogeneity of the different tests, the elongation values were measured for a stress of 45.6 cN / tex, identical for all tests.

The wire elongation values are collated in the following table: Speed m / min % SiO2 Elongation% Productivity gain % 4800 0 66.6 - 4800 0.5 73.9 17 4800 1 76.1 21.5 5500 0 56.7 - 5500 0.5 64.2 11 5500 1 67.4 15.9

Claims (5)

1. Process for manufacturing a polyamide-based undrawn preoriented yarn at a speed of at least 4000 m/min, characterized in that, before the spinning, a quantity of 0.05 to 1 % by weight of pyrogenic silica of particle size of between 5 and 15 nm is introduced into the molten polymer in the form of dispersion in a masterbatch of the same polyamide as that intended to be processed, the filaments after spinning being then cooled by means of a gas stream at room temperature and then sized and wound at a speed of between 4200 and 5800 m/min.
2. Process according to Claim 1, characterized in that the gain in output efficiency is at least 10 % based on the measurement of the elongation.
3. Process according to Claim 1, characterized in that the gain in output efficiency is at least 15 % based on the measurement of the elongation.
4. Undrawn preoriented polyamide yarns obtained by the process according to Claim 1, characterized in that they contain from 0.05 to 1 % by weight of pyrogenic silica of particle size of between 5 and 15 nm and that they exhibit a delay in the orientation.
5. Yarns according to Claim 4, characterized in that the mean interparticular distance between the silica aggregates is between 0.2 and 0.7 µm, the maximum value between 2 silica aggregates being ≤ 3 µm.

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