JPS628546B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel method for manufacturing a reticulated fiber sheet that is used as a fiber material for forming a nonwoven fabric with excellent drapability. The term "reticular fiber sheet" as used in the present invention refers to a sheet-like structure in which fibers are two-dimensionally or three-dimensionally branched and joined together in a network, arranged in the length direction.

A method for forming a reticulated web in which the fibers are two-dimensionally oriented by extending such a laminate of reticulated fiber sheets in the width direction was known prior to the filing of this application, as disclosed in Japanese Patent Publication No. 3458/1983.

The nonwoven fabric formed by this method has a so-called network structure in terms of fiber assembly structure, unlike the general random structure or orthogonal structure, and is basically flexible and tends to have excellent drape properties.
On the other hand, the thickness (denier) of the fibers is an important factor contributing to the drapeability of nonwoven fabrics, and it is clear both theoretically and empirically that the thinner the fibers, the better the drapeability.

Furthermore, as is well known, crimping of fibers is also an important factor.

Therefore, producing a thin, highly crimped reticulated fiber sheet directly leads to producing a nonwoven fabric with excellent drape properties.

Conventionally, foamable molten polymer is extruded through a slit die and drawn off with a draft.
The fact that it is possible to form morphologically similar reticulated fiber sheets is shown in Japanese Patent Publication No. 43-25960 and British Patent No.
It is known from the specification of No. 1165934.

However, since these known methods do not aim at forming a reticulated nonwoven fabric, no measures have been taken to make the fibers thinner, and only a structure of thick fibers that do not extend beyond the so-called split fiber region of the film can be obtained. do not have. In other words, the problem that the fibers inevitably become thicker in the conventional method is that the gas in the foamable molten polymer extruded from the slit rapidly expands and expands in the area directly below the outlet where the so-called balance effect occurs, causing the fibers to become large and thick. This is because the foam exhibits non-uniform foaming, and under such foaming phenomena, fine cracking does not occur even in a geometric sense.
Also, it is not possible to raise the draft because it is uneven.

On the other hand, for the purpose of forming a reticulated non-woven fabric, a method has been proposed in which a relatively thin reticular fiber sheet is formed by performing fine splitting (Japanese Patent Publication No. 36833/1983).
(Refer to Japanese Patent Publication No. 49-18508) These methods spray cooling gas from the outside immediately after the slit exit to prevent rapid expansion of the gas and maximize the degree of splitting, thereby forming a fine mesh. This method yields a thin fibrous structure, and has achieved some results. However, in these methods, since the foamed polymer at the exit of the slit is rapidly cooled and solidified, the flow area of the molten polymer is narrow, which limits the reduction in denier due to drafting and the stabilization of the fiber shape and molecular structure. That is, in these methods, contradictory results have been produced regarding the splitting effect and the draft effect due to cooling.

As a result of intensive research aimed at solving this problem, the present inventors have discovered that the bulge in foamable polymers ( This is achieved by forcibly applying a change in deformation speed to the foaming balance part while keeping at least the surface of the foaming balance part (tentatively called the foaming balance part) below the melting point of the polymer and the inside of the polymer being above the maximum crystallization speed temperature. We have discovered that the contradiction can be resolved, and have arrived at the present invention.

According to the present invention, a die having a structure in which a discharge slit for discharging a foamable molten polymer with an interval of 0.3 mm or less and an injection slit for injecting a heated gas intersect with each other at an acute angle at the exit is used,
The foamable molten polymer is discharged from the discharge slit at a draft rate of 50 times or more, and the melting point (absolute temperature) of the polymer is 0.7 from the injection slit.
There is provided a method for producing a reticulated fiber sheet, characterized in that heated gas heated to ~1.0 times the temperature (〓) is injected at a speed exceeding the discharge speed of the polymer at the outlet of a discharge slit, and the present invention provides a method for producing a reticulated fiber sheet, which A reticulated fiber sheet with high crimpability can be easily obtained.

The present invention will now be described in detail with reference to the accompanying drawings showing an enlarged cross-sectional view of the die tip used to carry out the method of the present invention.

In the accompanying drawings, a foamable molten polymer 1 is extruded quantitatively from discharge slits with a spacing d of 0.3 mm or less, and is continuously drawn off at a draft rate of 50 times or more. If you pick it up in this condition,
A foaming balance effect as shown by the dotted line 2 is produced directly below the discharge slit, but since there is no change in the deformation rate due to polymer flow due to draft tension in this area, splitting and fiber formation does not occur, and the foaming balance effect does not occur suddenly. Only a foaming phenomenon occurs, and only a coarse fibrous structure is obtained in the subsequent deformation rate change region (splitting portion).

In the present invention, as shown in the drawings, the heated gas 3 is injected and merged into the foaming ballast portion substantially parallel to the foaming ballast portion from the injection slit that intersects at an acute angle at the outlet with the discharge slit for the foamable molten polymer,
The gas injection force applies a shearing deformation rate change to this part, causing it to split. On this occasion,
An important requirement is the temperature of the injected gas, which must be below the melting point to prevent surface fusion of the shear split zone, and the external force of the injected gas and draft to ensure sufficient polymer flow. It must be at a temperature that can be maintained for a long time. When draft spinning is used in the general melt spinning method, the substantial change (reduction) in fiber diameter due to flow deformation after the ballast part occurs in the temperature range above the maximum crystallization rate temperature of the polymer, but foaming It can be considered that the same applies to the case of molten polymers. That is, in order to achieve the highest possible draft and form uniform and thin fibers, it is desirable to maintain the temperature of the polymer above this temperature for as long as possible. A general rule of thumb for thermoplastic crystalline polymers is that a molten polymer crystallizes at a maximum rate at a temperature approximately equal to 0.9 times its melting point (absolute temperature); In the case of the method of the invention, the temperature of the propellant gas is adjusted to below the melting point of the polymer.
It has been found that the objective can be achieved by setting the ratio to 0.7 times or more and 1.0 times or less. If the foamable molten polymer is a mixture of different polymers, the melting point of the mixture may be used, but it is convenient to calculate the melting point (absolute temperature) of each polymer by weighting it according to its melting point and amount. It can also be used as an average value. The temperature of the heated gas (absolute temperature K) in the method of the present invention is the temperature at the exit of the injection slit, and the optimum temperature varies depending on the type of polymer, etc., but is 0.7 to 8.5 of the polymer melting point (〓).
It is in the region of about 0.8 times, especially about 0.8 times.

In the present invention, the expandable melt polymer refers to a thermoplastic polymer (e.g. polyester, nylon,
polyethylene, polypropylene, polystyrene,
A gaseous substance (e.g., nitrogen, carbon dioxide, helium,
(butane, propane, etc.) are mixed and finely dispersed. In order to form thin fibrous materials, it is desirable that these gaseous substances be dispersed in as large a quantity as possible and as uniformly as possible.

In the present invention, the interval between the discharge slits is set to 0.3 mm.
The reason for the following is that if the thickness exceeds 0.3 mm, the discharge thickness of the foamable molten polymer will be too large, flow deformation due to the injection gas, and temperature uniformity will be difficult, making it difficult to perform fine cracking and drafting. This is because the effect of The preferred width of the discharge slit in this method is about 0.05 mm to 0.1 mm.

The width of the discharge slit should be selected to be the width of the desired reticulated fiber sheet, that is, the width necessary to form a reticulated web by spreading, but it is usually 10 cm or more.
Productivity should be increased. Further, a ring-shaped planar cross-sectional shape of the discharge slit may be selected.

In the present invention, the form in which the discharge slit and the injection slit intersect at an acute angle means that the angle θ formed by the adjacent inner walls of both slits ends at 90 degrees, as shown in the accompanying drawings. In particular, in the present invention, the angle θ is preferably in the range of 20 to 60 degrees. There is no need to set any particular restrictions on the spacing between the injection slits, but it is more efficient to make them as narrow as possible. The reason why the injection speed was set to exceed the discharge speed at the outlet of the discharge slit of the polymer taken up in the reticulated fiber sheet is that if it is less than this, there is almost no effect of causing polymer flow deformation in the foaming balance section, and the temperature of the polymer is also lowered. This is because it becomes unstable in the sense of uniformity. On the other hand, the upper limit of the injection speed is not uniquely determined and must be kept within a range that allows a continuous reticulated fiber sheet to be obtained. Further, the type of injection gas may be any gaseous substance such as air, water vapor, nitrogen gas, etc., but air is the most economical.

In the drawings, the ejection slit is provided with ejection slits from both sides, but in some cases, the ejection slit may be provided only on one side.

The draft rate in the present invention refers to the ratio of the forced take-up speed of the reticulated fiber sheet 4 to the linear velocity of the polymer at the exit of the discharge slit. The reason why the draft rate is 50 times or more in the present invention is that the draft rate is
This is because if it is less than 50 times, fine fibers that fully exhibit the effects of the present invention cannot be obtained.

Generally, draftability is called stringability, and it is closely related to the properties of the polymer, so it cannot be generalized, but the draft rate is improved by about 1.5 to 5 times compared to conventional methods.

In the method of the present invention, two or more different types of foamable molten polymers are introduced into the discharge slit from a plurality of extruders and are merged to form a laminar flow of different types of polymers, and then a reticular fiber sheet is formed in the same manner as described above. The immiscibility of different polymers gives good results during flow splitting of polymers, and not only can thin fibers be formed at any time, but also
Since composite fibers with irregular shapes are obtained, they have latent crimpability that is developed by heat treatment or the like.

In the present invention, different foamable molten polymers include not only polymers of completely different types, such as a combination of foamable molten nylon and foamable molten polyester, but also foamable molten polymers of 80% nylon and 20% polyester. mixture and nylon
Also meant are different blend ratios, such as a combination of 30% and 70% polyester foamable melt mixtures.

The method of the present invention will be described in detail below with reference to Examples. In the examples, "%" means "% by weight" unless otherwise specified.

Example 1 A mixture of 70% polypropylene chips with a melting point of 450〓 and 30% nylon-6 chips with a melting point of 495〓 was introduced into an extruder from a hopper, and while being melted, nitrogen gas was introduced under pressure and kneaded to form a foamable molten polymer. The polymer was extruded and introduced into a discharge slit with a die interval of 0.08 mm as shown in the attached drawing, and heated air of 370 mm was injected at a speed of 3000 m/min from the jet slit with a spray angle of 30 degrees, and the polymer was extruded at a speed of 120 m/min. A reticulated fiber sheet with an average denier of 0.2 denier was obtained.

Example 2 A 70% polyethylene terephthalate chip with a melting point of 540〓 and a polypropylene chip with a melting point of 450〓
Nylon with a melting point of 495〓 was introduced into an extruder.
6. A polypropylene lenticule with a melting point of 450% and a melting point of 450% was introduced into an extruder B, and while forming the foamable molten polymers A and B in the same manner as in Example 1, a die was inserted as shown in the attached drawing. Example 1 was introduced into the discharge slit separately to form a laminar flow.
A reticular fiber sheet having an average denier of 0.3 was obtained in the same manner as above. In addition, the discharge slit width in this case is 0.1
mm, injection air temperature 420K, injection speed 2500m/
minutes, the take-up speed was 100 m/min, and the draft rate was 180 times.

[Brief explanation of the drawing]

The accompanying drawing shows an example of an enlarged cross-sectional view of a die tip used in carrying out the method of the present invention.

Claims (1)

[Claims] 1. Interval for discharging expandable molten polymer
Using a die having a structure in which a discharge slit of 0.3 mm or less and an injection strip for injecting heated gas intersect with each other at an acute angle at the exit, the foamable molten polymer is discharged from the discharge slit at a draft rate of 50 times or more. At the same time, a heated gas heated to a temperature (〓) that is 0.7 to 1.0 times the melting point (absolute temperature〓) of the polymer is injected from the injection slit at a speed exceeding the discharge speed of the polymer at the outlet of the discharge slit. A method for producing a reticular fiber sheet characterized by: 2. The method for producing a reticulated fiber sheet according to claim 1, wherein at least two types of foamable molten polymers are merged before the outlet of the discharge slit and then discharged.