JPH059521B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a split yarn made of vinylidene fluoride resin and a method for producing the same.

BACKGROUND ART Although yarns made from continuous fibers of vinylidene fluoride resins, ie, filament yarns, have been industrialized, yarns made from staple fibers, ie, split yarns, have not yet been industrially obtained. do not have.

Split threads are difficult to obtain with many resins, not just vinylidene fluoride resins. Split yarns known up to now include polypropylene yarns, which are obtained by cold-stretching polypropylene at a high draw ratio of around 10 times and then splitting it. Split yarns have not been obtained from the resin. The reason is that polypropylene has a high degree of crystallinity,
It is thought that this is because the intermolecular cohesive force is weak, making it easy to split, making it easy to apply the above method.

Therefore, it was thought that it would be difficult to obtain split yarns using the splitting method described above for vinylidene fluoride resins, which have a lower degree of crystallinity and greater intermolecular cohesive force than polypropylene. It is.

OBJECTS OF THE INVENTION The main object of the present invention is to provide a split yarn made of vinylidene fluoride resin and a method for producing the same in view of the current situation.

Summary of the Invention According to the research conducted by the present inventors, it has been found that vinylidene fluoride resin split threads can be obtained by treating vinylidene fluoride resin having an appropriate molecular weight under appropriate conditions, and that a vinylidene fluoride resin split yarn can be obtained in this manner. It has been found that the vinylidene fluoride resin split thread has a characteristic crystal melting point and crystal size.

The vinylidene fluoride resin split yarn of the present invention is based on such knowledge, and more specifically, it is characterized by satisfying the following requirements (a) to (b).

(a) It has a crystal melting point of approximately 182°C or higher when heated in a nitrogen atmosphere at a heating rate of 10°C/min using a differential scanning calorimeter, and (b) The average crystal width size is approximately 200 Å. Consisting of crystals that are the above.

The method for producing vinylidene fluoride resin split yarn of the present invention is characterized by including the following steps (a) to (d) in this order.

(b) Use dimethylacetamide as the solvent and adjust the concentration to
Inherent viscocity is 0.8 to 1.4 dl/g under conditions of 0.4 g/dl and concentration at 30°C.
A step of melt-extruding a vinylidene fluoride resin into a sheet or tube shape, (b) cooling and solidifying it while draft stretching in the melt-extruded state to form a film having a birefringence of 25×10 ^-3 or more. (c) a step of heat-treating the film at a temperature of 80 to 180°C; and (d) a step of splitting the film.

The present invention will be explained in more detail below.

Detailed Description of the Invention In the present invention, "vinylidene fluoride resin" refers to a vinylidene fluoride homopolymer, 70 mol% or more of vinylidene fluoride as a structural unit, and one monomer copolymerizable with the vinylidene fluoride homopolymer. The term "vinylidene fluoride resin composition" includes a species or a copolymer consisting of two or more species, and a vinylidene fluoride resin composition containing at least 80% by weight of at least one of these species.

Components other than the vinylidene fluoride alone or copolymer constituting the composition include other polymers, plasticizers, processing aids, and additives such as ultraviolet absorbers. Examples of other polymers include polymers, etc. Inside are polyethylene, polypropylene, polyvinyl acetate,
Examples include polymethyl methacrylate, polyethyl methacrylate, polystyrene, fatty acid polyester, aromatic polyester, polyamide, and fluorine-based polymers excluding vinylidene fluoride.

In the present invention, among the vinylidene fluoride resins mentioned above, vinylidene fluoride homopolymer or vinylidene fluoride is used as a constituent unit in an amount of 70 mol%.
In particular, a copolymer of vinylidene fluoride and perfluoroolefin containing 80 mol% or more, particularly a copolymer of vinylidene fluoride and ethylene tetrafluoride, is preferably used.

The vinylidene fluoride resin split yarn of the present invention is determined mainly by the state after drafting during its manufacturing process, but it is determined by a differential scanning calorimeter (DSC) that the yarn is heated with nitrogen at a heating rate of 10°C/min. It has a melting point of about 182°C or higher when heated in an atmosphere. Here, the crystal melting point refers to the endothermic peak of DSC.

Among them, resins with a larger proportion of the endothermic area based on the melting endothermic peak of 182°C or higher in the DSC endothermic area are more likely to form split yarns. For example, when splitting a film to make a split yarn, the yarn will be easily split and will have a large Young's modulus. Therefore, in the endothermic area of DSC,
The ratio of the endothermic area based on the melting endothermic peak at about 182° C. or higher is preferably 5% or more, more preferably 20% or more, even more preferably 45% or more.

Also, for the same reason, it is preferable to have a crystal melting point at a higher temperature, preferably 185°C or higher, and even more preferably 190°C or higher. Moreover, it is preferable that the proportion of the endothermic area based on the melting endothermic peak at the temperature above the above-mentioned temperature increases in the endothermic area of the DSC measurement chart, and it is even more preferable that the proportion is the same as that described above for temperatures above 182°C. .

The baseline for determining the endothermic area of the DSC measurement chart explained above is determined as follows.

First, measure the measurement sample under the measurement conditions already described.
Raise the temperature to 220℃ and obtain the melting curve of the crystal. At this time, the temperature was continuously maintained at 220°C for 30 seconds, and then the temperature was lowered at a rate of 10°C/min to crystallize and cool to room temperature. The melted recrystallized product thus obtained is heated again under the same conditions to obtain a crystal melting curve. The first crystal melting end point of the obtained crystal melting curve, that is, the point at which the exothermic peak ends (Tmid) is determined (see FIG. 1, which was determined for Examples described later).

Locate the melting peak of the melting curve of the measurement sample at this point.
Tmid, while there is no heat balance at the highest and lowest temperature sides of the melting curve (Tmax and
Tmin) are connected to the point Tmid to form the baseline.

Note that both ends with no heat balance are obtained with no sample included, assuming all other conditions are the same.
Its position is determined by superimposing the DSC measurement chart.

In addition, the split yarn of the present invention is made of crystals with an average crystal width size of approximately 200 Å or more, and is usually 250 Å or more.
It is about ~350 Å. Here, the average crystal width size is determined by X-ray diffraction. That is, a sample is a collection of split yarns aligned approximately in the draft direction and hardened into a film with an amorphous adhesive. With the draft direction of this sample in the vertical direction,
The X-ray reflection intensity in the horizontal direction on the film surface, that is, the diffraction intensity is recorded on a chart. In determining the average crystal width size from the obtained chart, we focus on the diffraction peak of the (110) plane. That is, the diffraction intensity of the (110) plane is read on a chart, and the half width of the peak is determined. On the other hand, using a silicone single crystal powder, the mechanical broadening under the measurement conditions (that is, the broadening of the diffraction peak specific to the measuring machine) is determined. The value obtained by subtracting the half-width value of mechanical expansion from the half-width value of the half-width value of the measurement sample is defined as the true half-width value (βw (radians)) of the sample. Using this true half-width value, the crystal width (L) is determined from Schierer's equation L=k·λ/βw·cosθ.

where θ is the measured diffraction surface (i.e. (110)
The Bragg reflection angle of the surface), k is a constant (=1.0), and λ is the wavelength of the X-ray Cukα (1.542 Å).
(For details on such measurement methods, see, for example, p. 569 of "Fundamentals of X-ray Crystallography", co-translated by Hirabayashi and Iwasaki, Maruzen (published August 30, 1972)). The measured values in this specification were taken using an X-ray diffraction device manufactured by Rigaku Corporation, and the voltage-current was 40KV-20mA. The condition is 1°, and the scanning speed is 2θ of 1°/
It was determined under the conditions of . Also, X-rays
It was made monochromatic with a Ni filter.

Such a vinylidene fluoride resin split yarn of the present invention can be obtained, for example, by the following method.

That is, first, the coherent viscocity of a solution in dimethylacetamide with a concentration of 0.4 g/dl at a temperature of 30°C is 0.85 to 1.4 dl/dl.
The vinylidene fluoride resin (g) is melt-extruded into a sheet or tube shape. If the inherent viscocity is smaller than this range, unevenness in thickness is likely to occur during drafting, which will be described later, making it difficult to obtain a substantially high draft rate, leading to a decrease in mechanical strength.
Furthermore, if the inherent viscocity is larger than this range, molding becomes difficult and thermal decomposition tends to occur when molded at high temperatures. Preferably, the inherent viscocity based on the above criteria is 0.9 to 1.3.
dl/g, more preferably 1.0 to 1.2 dl/g.

As the extrusion method, known methods such as T-die method and inflation are employed. Preferably, a method is employed in which the film is produced by extrusion using a circular inflation die and then by an inflation method. The reason for this is that the width shrinkage is large in the T-die method, so that if a high draft is subsequently applied, both ends of the film will be insufficiently oriented, which is undesirable.

After melt extrusion, the product is cooled and solidified into a film while being draft stretched at a high draft rate.
The draft rate at this time is selected so that the birefringence of the film after cooling and solidification is 25×10 ⁻³ or more.

To explain this point in more detail, after melt-extruding the vinylidene fluoride resin, the temperature that indicates the maximum crystallization rate of the main resin constituting the vinylidene fluoride resin (hereinafter abbreviated as "maximum crystallization rate temperature") When winding a film at the following ambient temperature and pinch roll temperature below the maximum crystallization rate temperature, a film with oriented polymers can be obtained if the film is wound at a high draft rate higher than a certain draft rate. At this time, the draft rate varies depending on the melt viscosity of the resin, ambient temperature, cooling air volume, etc., but it is wound at a high draft rate so that the birefringence Δn of the obtained film is about 25 × 10 ^-3 or more. The obtained film has crystals with a high melting point of 182° C. or higher, unlike films with a birefringence lower than that, and the Young's modulus increases rapidly, as shown in FIG. 2. (Figure 2 shows a vinylidene fluoride homopolymer with an inherent viscocity of 1.1 dl/g, a die temperature of 240°C, and a die diameter of 50 mm.
The graph shows the relationship between Δn and Young's modulus obtained by extruding from a circular die with a lip clearance of 2 mm and winding at various winding speeds at a blow-up ratio of 1.2). The process of winding a material having high melting point crystals at a draft rate greater than the draft rate at which the Young's modulus begins to rapidly increase is herein referred to as draft stretching.

An appropriate draft rate depends on the melt viscosity of the resin, but is usually about 50 to 5,000. When the melt viscosity of the resin is low, the draft ratio must be set to a relatively large value in order to achieve a birefringence of 25×10 ⁻³ or higher after cooling and solidification. Preferably, the birefringence is 30×10 ^-3 or more, more preferably 35
Choose a draft rate so that it is at least ×10 ^-3 . This is because the splitting process described later becomes easier.

In the case of the inflation method, the draft ratio and the blow-up ratio, which is the stretching ratio in the width direction, are selected as appropriate, and are usually in the range of 0.7 to 2.5, preferably in the range of 0.8 to 1.5.

A known method is used for cooling and solidifying, but
For example, in the case of an inflation method, the material may be extruded upward, cooled with air, and then wound up, or extruded downward, and typically cooled with a coolant such as water.

The film thus obtained was heated to 80 to 180℃.
heat treated at a temperature of

This heat treatment is carried out to promote crystallization, and it is efficient to carry out the heat treatment at around the maximum crystallization rate temperature of the main resin constituting the vinylidene fluoride resin. Therefore, preferably the temperature does not fall below 60°C below the maximum crystallization rate temperature and does not exceed 60°C above the maximum crystallization rate temperature, even more preferably does not fall below 40°C below the maximum crystallization rate temperature and the maximum crystallization rate temperature This is done at a temperature not exceeding 40°C above the speed temperature.

The longer the heat treatment time, the better, but it is usually carried out at the maximum crystallization rate temperature for at least 2 hours,
More preferably, it is carried out for 24 hours or more.

Although it is not necessary to keep the film in a constant length state during heat treatment like a cold stretched film, it is desirable that the film be in a constant length state. By such heat treatment, the crystal structure of the vinylidene fluoride resin constituting the film is transformed from a structure mainly consisting of an α-type structure to a structure mainly consisting of a γ-type structure.

It is preferable that the film is cold-stretched after or together with the heat treatment to transform the crystal structure into one mainly having a β-type structure. This is because the film has higher elasticity and is more likely to become split yarn.

The stretching ratio at this time is about 1.1 to 5.0 times.

The film thus obtained is split into split yarns having a rectangular cross section with an average short side of 1 to 10 μm and an average long side of 2 to 100 μm, for example.

The film is split by using, for example, a needle roll as disclosed in JP-A-58-180621 and rotating the roll in contact with the film along the transport direction.

The split yarn thus obtained has a higher Young's modulus than the known polypropylene split yarn. This is surprising in comparison with the fact that the Young's modulus of polyvinylidene fluoride filaments known up to now is smaller than that of polypropylene filaments. In addition, although it is common to conventional vinylidene fluoride resin, the split yarn of the present invention
It has excellent weather resistance, chemical resistance, etc., which is not found in polypropylene sprit yarn.

Effects of the Invention As explained in detail above, according to the present invention, by treating vinylidene fluoride resin having an appropriate molecular weight through a specific process bond, vinylidene fluoride resin A resin split yarn was obtained, and the split yarn thus obtained was superior in chemical properties such as weather resistance and chemical resistance compared to polypropylene yarn, which was almost the only synthetic resin split yarn available in the past. This results in a split yarn with a higher Young's modulus.

Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example A vinylidene fluoride homopolymer with an inherent viscocity of 1.1 dl/g (measured at 30°C and a concentration of 0.4 g/dl using dimethylformamide as a solvent) was obtained by suspension polymerization at 25°C. , 50mmφ,
It was extruded upward using an extruder having a circular die with a lip clearance of 3.0 mm at an extrusion temperature of 240°C and an extrusion rate of 60 g/min.

Inflation was performed at a blow-up ratio of 1.5 and a winding speed of 50 m/min while cooling with air at an air volume of 0.01 m ³ /min from an air ring installed approximately 10 cm above the die. Therefore, the draft rate (R ₁ )
is 670, and the birefringence of the obtained film is 36
It was ×10 ^-3 .

In this way, the blown film was wound up into a paper tube and kept at 90°C for 20 minutes.
Heat treated in a gear oven for 1 day.

Furthermore, the average width size of the crystals determined from X-ray diffraction was 320 Å. 10 in nitrogen atmosphere with further DSC
When looking at the melting behavior of the crystal at a heating rate of ℃/min, the crystal melting point shows a double peak at 175℃ and 195℃ as shown in Figure 1, and the ratio of the endothermic area based on the melting endothermic peak at 195℃ is was 50%.

This film was further stretched 1.3 times at 150°C.
As a result of splitting the 1.3 times stretched film using a planted needle type splitting device, finer split yarns were obtained. The average crystal width size and DSC melting endotherm peak measured for the resulting split yarns were substantially the same as the results for the above film.

The Young's modulus of the resulting split yarn is considered to be the same as that of the film since there is essentially no change in the microstructure before and after splitting, and it is estimated that the Young's modulus of the resulting split yarn is 500 Kg/mm ² or more.

[Brief explanation of the drawing]

FIG. 1 shows an example of a melting curve in a differential scanning calorimeter, and FIG. 2 shows the relationship between draft ratio and birefringence to explain draft stretching.

Claims (1)

[Scope of Claims] 1. A vinylidene fluoride resin split yarn characterized by satisfying the following requirements (a) to (b). (a) It has a crystal melting point of approximately 182°C or higher when heated in a nitrogen atmosphere at a heating rate of 10°C/min using a differential scanning calorimeter, and (b) The average crystal width size is approximately 200 Å. Consisting of crystals that are the above. 2. A method for producing vinylidene fluoride resin split yarn, which comprises the following steps (a) to (d) in this order. (b) Use dimethylacetamide as the solvent and adjust the concentration to
Inherent viscocity is 0.8 to 1.4 dl/g at a temperature of 0.4 g/dl and a temperature of 30°C.
A step of melt-extruding a vinylidene fluoride resin into a sheet or tube shape, (b) cooling and solidifying it while draft stretching in the melt-extruded state to form a film having a birefringence of 25×10 ^-3 or more. (c) a step of heat-treating the film at a temperature of 80 to 180°C; and (d) a step of splitting the film.