JPH0314840A - Biaxially cold-stretched vinylidene fluoride polymer film and its preparation - Google Patents

Abstract

PURPOSE:To prepare a biaxially cold-stretched vinylidene fluoride polymer film excellent in the mechanical strengths at a low cost by biaxially cold- stretching a specific vinylidene fluoride polymer by the inflation process. CONSTITUTION:A vinylidene fluoride polymer having an inherent viscosity of 0.8-1.6dl/g and a ratio of the wt.-average mol.wt. to the number-average mol.wt. of 10-20, or a polymer mixture comprising at least 30wt.% above- mentioned vinylidene fluoride polymer and 70wt.% or lower vinylidene fluoride polymer having a ratio of the wt.-average mol.wt. to the number-average mol.wt. of 10 or lower is biaxially cold-stretched pref. in a stretching ratio of at lest 1.5 in both the longitudinal and transverse directions by the inflation process.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a biaxially stretched film made of a vinylidene fluoride polymer and a method for producing the same. [Prior art] Vinylidene fluoride polymers have excellent weather resistance, chemical resistance, piezoelectricity, pyroelectricity, dielectricity, flame retardancy, etc., but their decomposition temperature is much higher than their melting and softening temperature. Another important feature is that it is easy to extrude, unlike polytetrafluoroethylene and polyvinyl fluoride, which are expensive. On the other hand, vinylidene fluoride-based polymers have extremely strong crystallinity, which makes it difficult to stretch a sheet-like material for molecular orientation due to its strong crystallinity. In particular, biaxial cold-stretched films had not been obtained by the inflation method. For this reason, vinylidene fluoride polymers can be stretched by blending polyacrylate as a crystallization inhibitor (Japanese Unexamined Patent Publication No. 60-67133), or by laminating them with other easily stretchable films. A method has also been proposed in which the film is stretched while avoiding excessive stress concentration on the crystal parts scattered within the polymer film (Japanese Patent Laid-Open No. 57-1562).
No. 24). However, in the former method, since the vinylidene fluoride polymer is not used alone, depending on the intended use, for example, when used as a film for a capacitor, there may be disadvantages such as a decrease in dielectric constant. In the latter case, the increase in costs cannot be ignored. [Problems to be Solved by the Invention] In view of the above-mentioned circumstances, the main object of the present invention is to produce a biaxial cold-stretched film of vinylidene fluoride polymer with excellent mechanical strength using an inflation method with particularly high production efficiency. The goal is to develop manufacturing technology based on Furthermore, the present invention
By setting the conditions of the inflation method and selecting the composition of the raw vinylidene fluoride polymer, it is possible to provide not only a smooth film but also a roughened vinylidene fluoride polymer biaxially cold-stretched film. The purpose is to [Means for Solving the Problems] The present inventors have produced a film with a reduced tan δ (tangent of dielectric loss angle) by manufacturing a film using the direct blow one-type inflation method disclosed in Japanese Patent Application Laid-open No. 62-286720. However, they discovered that by selecting a raw material resin and further cold-stretching the film that had been cooled after direct blowing, it was possible to obtain a vinylidene fluoride polymer film with less uneven thickness and improved strength. Here, cold stretching refers to stretching at a temperature below the crystal melting temperature of the raw resin. Furthermore, by selecting a vinylidene fluoride polymer with high strand melt tension as a film forming raw material and setting the conditions, fine irregularities are created during inflation, and the irregularities are maintained even during subsequent cold stretching, making it virtually triaxially stretched. A roughened film was obtained. That is, the vinylidene fluoride polymer film of the present invention has an independent viscosity (hereinafter simply referred to as "inherent viscosity") measured as a dimethylforma-based solution at a concentration of 0.4 g/dj2 and a temperature of 30°C. It is made of a vinylidene fluoride polymer with an IL/g range of 0.8 to 1.6 d IL/g, and is characterized by being biaxially cold stretched by an inflation method. According to another aspect, the method for producing a vinylidene fluoride polymer biaxially cold-stretched film by the inflation method of the present invention has an overall independent viscocity of 0.8 to t. It is in the range of 6du/g, and M W /
A vinylidene fluoride polymer having an Mn ratio of 10 to 2o alone or a mixture of the polymer containing the polymer in an amount of 301i% or more and a vinylidene fluoride polymer having an Mw/Mn ratio of less than 10, The molten parison is obtained by melt extrusion from an annular die, the parison is expanded and then cooled to obtain a raw fabric tube, the raw fabric tube is heated again, air is blown into the tube, and the circumferential speed ratio of the upper and lower nip rolls is adjusted. This method is characterized by simultaneous biaxial cold stretching by controlling the Furthermore, according to a preferred embodiment of the present invention, the biaxial cold-stretched film of vinylidene fluoride-based polymer is cold-stretched by 1.5 times or more in each of the vertical and horizontal biaxial directions, and has a zero depth on one side. It can also be obtained as a roughened film in which grooves extending in the horizontal direction of .2 to 1.0 μm are continuously formed at intervals of 10 mm or less in the vertical direction. The details of the vinylidene fluoride polymer biaxially cold stretched film of the present invention and the method for producing the same will be explained below.

The vinylidene fluoride-based polymer constituting the film of the present invention includes not only vinylidene fluoride homopolymer but also vinylidene fluoride in an amount of 50 mol% or more, preferably 75 mol%.
A copolymer containing the above, preferably a copolymer with a fluorine-containing monomer, may also be used. Examples of comonomers that can be copolymerized with vinylidene fluoride include ethylene tetrafluoride, propylene hexafluoride, ethylene trifluoride, ethylene chloride trifluoride, and vinyl fluoride. The vinylidene fluoride polymer used in the present invention has an independent viscosity of 0.8 to 1.6 d It/g, preferably 0.9 to 1.3 d It/g, and even more preferably 0. 9 to 1.15 dbu/g is used. If a polymer with an independent viscosity of less than 0.8 dJ2/g is used, the melt viscosity decreases significantly and bubbles cannot be stably formed and maintained in the melt inflation process, which is not preferable.

Furthermore, if a polymer exceeding 1.6 du/g is used, the melt viscosity will be too high, making it impossible to stably extrude the plasticized resin using an extruder during actual purchase, or making cold stretching impossible. .

In order to enable biaxial cold stretching by the inflation method, it is important to control the Mw/Mn (Il weight average molecular weight/number average molecular weight) ratio, which indicates the molecular weight distribution of the raw vinylidene fluoride polymer. That is, according to the present invention, the raw material vinylidene fluoride polymer is a vinylidene fluoride polymer (hereinafter referred to as "highly dispersed polymer") having a Mw/Mn ratio in the range of 10 to 2o, preferably in the range of 12 to 16.
) is used alone, or a polymer containing such a polymer in an amount of 30% or more and M w / M
70% by weight of vinylidene fluoride polymer with an n ratio of less than 10 (hereinafter sometimes referred to as "low dispersion polymer")
Mixtures with:

The M w / M n ratio was determined using a 7.8 mmφ x 30 cm mixed gel column (TSK geILGMH manufactured by Tosoh Corporation).
XL) 2 pieces and 7.5mmφ x 7.5cm guard column (TSK guardcolumn Ha)
It can be determined from the molecular weight distribution curve measured by GPC (gel perfusion column chromatography) using a differential refractometer (Model Rl-8012 manufactured by Tosoh Corporation) as a detector. The measurement was carried out using DMF (N.N'-
Using a 0.2% by weight sample polymer solution in (dimethylformamide) solvent, temperature 40°C, flow rate 0.8 mj2/min,
It can be performed with an injection volume of 0.5 mIL. In the above vinylidene fluoride polymer, M W
/Mn ratio in the range of 10 to 20 is to control the high crystallinity of the vinylidene fluoride polymer by the entanglement of molecular chains in the manufacturing process of the raw tube from melt extrusion to inflation prior to cold stretching. bring about an effect. As a result, the degree of crystallinity is suppressed, and the crystal orientation is also suppressed at the same time, allowing the next cold drawing process (
That is, the crystalline melting temperature of the polymer (e.g. Metll
er3000 Systaa+ At a temperature below the temperature that gives a peak or shoulder in the endothermic curve measured at a heating rate of 10°C/min with DSC (in other words, in a stretching process in which no endothermic reaction occurs), large deformation energy is generated. Since the film is stretched without the need for film breakage, film breakage is avoided. On the other hand, if only a low-dispersion polymer with a Mw/Mn ratio of less than 10 is used, the crystallization of the molecular chain alone, that is, intramolecular crystallization, will proceed as the molecular weight decreases. Due to the increase in crystal size, increased crystallization, and strengthened crystal orientation, it becomes difficult to stretch during subsequent cold stretching. In addition, vinylidene fluoride polymers with M W / M n exceeding 20 are not preferable because the high molecular weight components create a large resistance to melt flow within the above range of inherent viscosity, making extrusion almost impossible. .

On the other hand, the state in which crystalline polymers originally try to become stable,
In other words, when an unstable morphology is forcibly created by using a highly dispersed polymer as described above in order to prevent the crystalline lamellar morphology, the resulting physical properties are those that are particularly weak both thermally and mechanically. They usually exhibit large changes due to intermolecular forces that constantly try to return to their original state from an unnatural state. Therefore, if necessary to provide stable crystals in the film after cold stretching, M w
/Mn is 10 or less (inherent viscosity is similarly 0.8 to 1.6 dIL/
(preferably in the range of g) may be blended within 70% by weight. However, if the blend ratio exceeds 70% by weight, it becomes highly crystalline and stable cold stretching becomes difficult again. The content of the low dispersion polymer is preferably 50% by weight or less. Next, the method of the present invention using the vinylidene fluoride polymer as described above (hereinafter, unless otherwise specified, the term is used to include a high dispersion polymer alone and a mixed system with a low dispersion polymer) is carried out using a preferred apparatus. This will be explained with reference to FIG. 1, which is a schematic diagram of an example.

(A) Melt extrusion process The above vinylidene fluoride polymer is heated in an extruder 1,
It is plasticized at a temperature below its decomposition temperature (generally below 300 t) and is melt-extruded through an annular die 2 to form a thick-walled molten parison 5a. (B) Primary fabric tube forming process Air ring 3 is attached to the extruded thick inner melted parison 5a.
Cooling air is blown from the air to the bubble support 4, from where it is blown into a tube shape to form medium-sized bubbles 5b, and while being crystallized by the cooling air, this bubble-shaped raw fabric tube 5b is transferred to a pair of nip rolls 6. Pick it up. At this time, the blow ratio (tube final diameter/die diameter) is 3 times or less, especially 2.5 times or less, and the drawdown ratio (tube withdrawal speed/die exit speed) is 100 or less, further 60 or less, especially 40 or less, It is preferable that the following conditions are adopted.

In this raw fabric tube forming process, especially in the vicinity of the bubble support 4, after the start of C% expansion (1) as shown in FIG. While changing the speed in the tube circumferential direction (TD (horizontal) direction) and tube thickness direction (HD direction) (point (2) at (I1) and (m) in Figure 2), and (3
) is solidified by the cooling air from the external air ring 3, and its rate of change becomes zero at the position shown in Figure 2 (3). In other words, this point can be considered the crystallization line. In the raw tube forming process of the present invention, the rate of change (strain rate) in the tube withdrawal (MD) direction once decreases (M sum) in the process from the start of expansion until reaching the maximum strain rate. It is preferable that this occurs, and it is one of its characteristics (see, for example, Figure 4).

In order to cause such relaxation of strain rate in the MD direction,
It is understood that the selection of the raw material polymer and the settings of the blow ratio and drawdown ratio mentioned above have important effects. More specifically, the relaxation phenomenon of the strain rate in the MD direction is closely related to the melt elasticity of the raw material polymer used in the present invention, and the necessary melt elasticity is achieved by the combination of abundant molecular chains in the raw material polymer. Conceivable. It is thought that the relaxation of the strain rate during this process also leads to the relaxation of the molecular chains that have been oriented once, and also contributes to the ease of stretching in the subsequent cold stretching process. In fact, a wide-angle X-ray photograph of the original tube obtained as described above (e.g. 's5
Figure) shows Depay annular scattering and is an almost random collection of characteristic crystals, indicating poor crystal conformity.

Furthermore, if the blowing ratio exceeds 3 times, bubble stability is basically lacking and a uniform primary fabric tube cannot be formed. If the drawdown ratio exceeds 100, tube breakage will occur. Similarly, when the drawdown ratio exceeds 60, the relaxation of strain rate becomes slight. Furthermore, in order to obtain a roughened film, which is a preferred embodiment of the present invention, the blow ratio (lateral radial direction) and drawdown ratio (vertical take-up direction) are adjusted according to the third As shown in figure (a), the middle part (core type) 2a
The extruded molten parison is selected so that the extruded molten parison appropriately contacts the circumferential tip of the exit circumference of the inner ring 2a of the circular die 2 consisting of the inner ring 2a and the outer ring 2b. That is, the space in the die is not completely filled with molten polymer at the circumferential tip of the outlet, but a space is created at the tip of the outlet, and the die is operated in a state in which it slightly contacts the outer surface of the intermediate 2a. More specifically, the constriction angle (neck-in angle) θ of the molten parison 5a is 01 to 100, more preferably 4 to 100, as shown in FIG. 3(a).
Select a range of 9°. The surface roughening effect cannot be obtained in the shape R of FIG. 3(b) (ordinary shape 7!I in the normal inflation method) in which the molten parison 5a and the intermediate 2a are constantly out of contact and θ is negative. , and a third case in which the molten parison 5a and the intermediate 2a are in constant contact and θ is excessively large.
In the state shown in Figure (c), a good raw material tube cannot be obtained. Under such a condition that the constriction angle θ of the molten parison 5a is 0 to 10 degrees, fine wind pressure fluctuations of the cooling air and large fluctuations of the polymer, which can be arbitrarily controlled by the outlet opening and air volume of the air blown from the air ring 3, occur. The crystallization line of the tube 5b moves up and down due to the melt elasticity. As a result, the internal pressure of the tube 5b and the diameter of the parison 5a before inflation vary slightly, so the degree of solidification on the inside and outside of the tube differs, and periodicity occurs in the draft tension, causing an annular striped pattern on the inside of the parison. The annular striped pattern generated on the inside of the parison 5a, and thus on the inside of the tube 5b, is maintained as fine irregularities even after the subsequent cold drawing process or annealing process, and the vinylidene fluoride surface is finally roughened. A polymer film is obtained. In order to obtain this roughened film, it is particularly preferable to use a vinylidene fluoride-based polymer containing a highly dispersed polymer of 70ii% or more.

In addition, in order to suppress the crystallinity of the vinylidene fluoride polymer and obtain a cold-stretched film by the inflation method, and in particular to impart the above-mentioned annular Mm shape to the inside of the parison, it is necessary to make the molten parison 5a a strong elastic body. It is necessary that there be. In order to provide such conditions, vinylidene fluoride polymers are used using a cavillary rheometer (for example, Toyo Seiki Co., Ltd.) equipped with a nozzle of 15 mm in length and 4 mm in diameter.
The shear rate was 20 sec-
', the temperature at which the apparent melt viscosity becomes 2X10' poise (
Vinylidene fluoride polymers having an inherent viscocity within the above range are usually 240 to 27
The force (melt tension) on the molten strand at 0℃) is 3
00-800g/cm', more preferably 40
0 to 700 g/cm2, particularly preferably 500 to ao
0 g/cm" is used. In this way, rather than the absolute temperature, the present invention focuses on controlling the melt tension at the resin mobilization temperature for each vinylidene fluoride polymer used. This is one of the characteristics of the inflation method.The melt tension referred to here refers to the molten strand extruded downward from the nozzle using the above-mentioned capillary rheometer at a room temperature of 20 to 25°C and a humidity of 50 to 60%. This is the tension when taken in an unweathered state, and is the value of tension per unit cross-sectional area of the strand nozzle used.

If a vinylidene fluoride-based polymer with a melt tension lower than the above value is used, the formation of bubbles (tubular film) in the above step (B) will become unstable, and good bubbles will not be formed during the subsequent re-cooling stretching. This results in insufficient film strength or uneven thickness, resulting in a film that cannot be used for practical purposes. In the worst case scenario, the bubble may even burst. In addition, if the melt tension is higher than 800 Kg/cm', the stringiness of the molten resin is insufficient and stretching during melting cannot be carried out promptly, making stable film formation of the original fabric impossible. ．． In order to achieve such melt tension conditions, as the raw material vinylidene fluoride polymer, M w / M n is 10 to 10.
The amount of highly dispersed polymer in the range of 20% by weight or more is 30% by weight or more, preferably 50% by weight or more, more preferably 70% by weight or more, especially 85% by weight or more.
When the content of the highly dispersed polymer is less than 70% by weight, the elasticity is insufficient and periodic striped patterns cannot be produced, resulting in M w
/Mn is 3 highly dispersed polymers in the range of 10 to 20
When the content is 0 to 70% by weight, bubbles with smooth surfaces can be obtained.

(c) Cold stretching process Next, the medium-thickness tubular film 5b taken up by a pair of nip rolls 6 is further supplied with hot air from a hot air heater 8 at a temperature below the crystal melting temperature, and air is again supplied thereto. By doing so, the bubble 5C is expanded, and at the same time, the circumferential speed ratio of the feed nip roll 1 and the take-up nip roll 9 is controlled in the take-off direction to simultaneously perform longitudinal and lateral stretching, and the thin-walled tubular film 5c is taken off by the nip roll 9. The stretching ratio in the longitudinal and lateral directions is 1.5 times or more. If the stretching ratio is less than 1.5 times, it is not preferable because it may cause uneven stretching. (D) Thermal relaxation treatment process The thin tubular film 5C obtained in this way is again heated with a hot air heater 10 and a nip roll! 1 and 12) at a temperature lower than the stretching temperature in step (C) above) 1! I
After the heat treatment, the product film 5d is wound onto a winding roll 13. Of course, depending on the intended use of the heat-shrinkable film, for example, it may be possible to wind it onto the take-up roll 13 without applying the relaxing heat treatment. (E) Post-processing process The product film wound onto the roll 13 may be It is wound onto a bobbin (not shown) while slitting both ends accordingly. As mentioned above, in the present invention, a suitable biaxially oriented film is produced using only vinylidene fluoride polymer as a raw material, but inorganic and organic compounds may be added as necessary to the extent that they do not affect the inflation method. Mixing is also allowed. [Example] Large @ 1-1 Inherent viscocity is 1.0 and Mw/Mn is 1
6. 270℃ using a capillograph equipped with a 4mm diameter nozzle.
Vinylidene fluoride homopolymer (trade name: Kynar #460,
Made by Pennwalt, heated to 270°C (crystal melting point = 168°C), diameter 50mmφ, lip clearance 1.0
Melt extrusion into a tube through an annular die of 200 mm
g/min), then taken off with a constriction angle of 6°, and inflation molded under the conditions of a blow ratio of 2.0 and a drawdown ratio of 22 to form a raw tubular film with a final thickness of 20 μm (corresponding to Fig. ) was obtained. As shown in FIG. 4, the strain rate in the raw tube forming process (step (B) above) once showed a large relaxation after the tube (bubble) started expanding. (In addition, the measurement of strain rate is [ (SENI GAκκAISHI.I/ol.4
1 P74. No. 1 (1985)] The following procedure was performed according to the method of Fuji et al. That is, we marked the bubble during molding with a fine oil pen, captured the entire bubble image on an 8 m/m video, and measured the bubble diameter as well as the bubble flow direction speed at 1/30 second frame rate to calculate the strain rate. Calculated. ) A wide-angle X-ray scattering photograph of this original film is shown in Figure 5, and it showed -circular scattering and poor crystal conformation. Next, the raw film was rolled at 13 m/min by blowing air again at a transverse stretching ratio (stretching bubble diameter/raw fabric bubble diameter) of 2.7 times, a longitudinal stretching ratio of 1.7 times, and a stretching temperature of 145°C. Biaxial cold stretching was easily possible at the drawing speed. Subsequently, a relaxation treatment was performed under hot air at 135° C., and a biaxially stretched film with a thickness of 5.4 μm was obtained at a winding speed of 12.9 m/min.

The obtained film exhibited excellent thickness uniformity and breaking strength as shown in Table 2 below. Also, this film
As shown in Figure 6 (a polarized photograph taken using a MH32 It exhibited a continuous groove pattern of 4 μm. Changes in physical properties due to differences in raw material composition are summarized in Table 1 below, along with the following Examples and Comparative Examples. 1 insect, 1 raw, Inherent viscocity is 1.0, Mw/Mn is 2
A vinylidene fluoride homopolymer having a melt tension of 220 g/cm2 was melt-extruded under the same conditions as in Example 1 to produce an unstretched raw film. As shown in Figure 7, the strain rate during molding at this time was immediately after the tube expansion start point and did not show any relaxation. In addition, as shown in Figure 8 (wide-angle X-ray scattering photograph), the original film had advanced crystal orientation and a large scattering intensity. As a result, during the subsequent cold stretching, even if the same conditions as in Example 1 and various conditions were changed, the film only broke, and stretching was virtually impossible. The vinylidene fluoride polymer used in Example 1-1 and the vinylidene fluoride polymer used in Comparative Example 1 were blended at a weight fraction of 70/30, respectively. (The melt tension is 4
60 g/cm”) Example 1-
Melt extrusion was performed in the same manner as in 1 to obtain a raw film with a thickness of 20 μm. Subsequently, biaxial cold stretching and thermal relaxation treatment were performed under the same conditions as in Example 1-1 to obtain a roughened film with a groove pattern having a thickness of 5.4 μm. - Same as Example 1-2 except that the weight fractions of the vinylidene fluoride polymer used in Example 1-1 and the vinylidene fluoride polymer used in Comparative Example 1 were 30/70, respectively. A biaxial cold-stretched film with a thickness of 5.4 μm was obtained, but both sides were smooth and no 7111 pattern was observed. Example 1 The vinylidene fluoride polymer used in Example 1-1 and the vinylidene fluoride polymer used in Comparative Example 1 were blended at a weight fraction of 20/80 (%), respectively. −
Using the same equipment as in 1, melt extrusion was performed at 260 ° C. and t50 g/min to create a 20 μm thick raw tube under the conditions of blow ratio 2.01 and drawdown ratio 22.
Subsequently, cold stretching was attempted, but the film frequently broke.
Stable stretching film formation was not possible.

Summarizing the differences in film physical properties as a result of the differences in raw material composition of Examples 1-1 to 1-3 and Comparative Examples 1 and 2,
It is shown in Table 1 below. Looking at the results in Table 1 above, the films obtained in Examples 1-1 to 1-3, excluding Comparative Examples 1 and 2 in which it was impossible to form stable films, had roughened surfaces. The greater the degree of dispersion, the better the handling properties are, and as the amount of low-dispersion polymer increases, the surface becomes rougher and becomes more difficult, but the mechanical properties tend to improve. During the thermal relaxation treatment, some differences were observed between Examples 1-1 to 1-3, but when comparing the dimensional stability after heating at 100°C for 5 minutes after the relaxation treatment, all differences were less than 1%. was not recognized. The vinylidene fluoride polymer used in Example 1-1 and the vinylidene fluoride polymer used in Comparative Example 1 were blended at a weight fraction of 30/To (%), and the melt tension was 35.
A mixture of 0g/cm' was obtained. This is an example! Melt extrusion was performed using the same equipment as in -1 at 260° C. and 150 g/min to obtain a raw film with a thickness of 6.5 μm at a blow ratio of 2.0 and a drawdown ratio of 68.

At this time, as shown in Figure 9, the strain rate in the take-off direction at the time of formation showed a relatively small but clear relaxation after the start of expansion. In addition, this original film is shown in Figure 10 (wide-angle X-ray photograph).
As shown in Figure 2, some had poor crystal orientation. As a result, as in Example 1-1, the stretching temperature was 160°C, the stretching ratio was 1.5 times in the longitudinal direction, 3.1 times in the transverse direction, and the winding speed was 2.
In the subsequent cold stretching step under the condition of 0 m/min, biaxial cold stretching was easily achieved. Subsequently, a relaxation treatment was performed under 120' cpIAffl to obtain a biaxially stretched film with a thickness of 1.6 μm. The thickness uniformity and breaking strength/elongation data of the obtained film are shown in Table 2 below, along with the results of Examples 1-1 and 1-3. It can be seen that in terms of strength and elongation data, superior results were obtained compared to the film of Example 1-1. However, as shown in FIG. 11 (polarized light photograph), regular grooves as seen in the film of Example 1-1 were not formed. Table 2 x1: Thickness was measured using a 171,000 mm needle dial gauge, with 10 films stacked, and 32 pieces measured at 10 mm intervals, and the value divided by 10 was used. x2: Breaking strength and elongation are sample length/trial width = 100/20 (mm
) in an atmosphere of 25°C at a tensile speed of 300 mm/min. Lai 10 Raw 1 Polyvinylidene fluoride (Product name: Kynar #4601 manufactured by Pennwalt Co., Ltd.: Inherent Viscocity: 1.O
dl/g, Mw/Mn-1 6, Strand melt tension:
550g/cm" crystal melting point 168℃), 270℃
Heated to diameter 50mmφ, lip clearance 1.
Extruded into a tube shape from a 0 mm annular die in a molten state,
Air was introduced into the tube from the outside through the die hole to form a bubble. At this time, the extrusion rate was 200 g/min, and the blow ratio and take-up speed (drawdown ratio) were changed as shown in Table 3 below so that the obtained film thickness was approximately 20 μm. (corresponding to Fig. 1 5b) was obtained. Table 3 Figures 12(a), (b), and (C) show the thickness distribution of the raw film obtained under each condition in the tube drawing direction.
(The thickness distribution was obtained using a capacitive continuous thickness meter CL-230 manufactured by Ono Sokki Co., Ltd. under the conditions of a film feed speed of 10 m/min and a measurement sensitivity of AV = 0.3.) As a result, as shown in FIG. 12(b), grooves with remarkable periodicity were observed under the conditions of Example 3-2. Next, air was blown into the original film of Example 3-2 again,
Lateral stretching ratio (stretching bubble diameter/original bubble diameter) 2.7 times,
13.0 m at a longitudinal stretching ratio of 1.7 times and a stretching temperature of 145°C.
Biaxial stretching was performed at a winding speed of /min. Continued to 135℃
Relaxation treatment was performed under hot air at a winding speed of 12.9 m/min. Figure 13 shows the thickness distribution in the take-up direction of the obtained film (corresponding to the 13 rolled state in Figure 1) under the same conditions as in Figure 12.
X0.30 {Polarized photograph obtained using a li light plate (xt/
3) is shown in FIG.

That is, the average thickness of the film obtained as described above was 5.9 μm, and clearly periodic irregularities were observed as seen in Figures 5J13 and 14.

In addition, a film with a trial length of 100 mm and a trial width of 20 mm was pulled at a speed of 30 mm using a Tensilon manufactured by Toyo Baldwin Co., Ltd.
The mechanical strength and elongation properties measured at 0 mm/min are the 15th
As shown in the figure, it had sufficient values. [Effects of the Invention] As described above, according to the present invention, a biaxial cold-stretched film of a vinylidene fluoride polymer, which has not been obtained conventionally, can be obtained by the inflation method. The thus obtained biaxially stretched film of the present invention is composed only of vinylidene fluoride polymer, has high mechanical strength by cold stretching (stretching below the crystal melting point), and can be easily formed into a thin film. It is characterized by being able to obtain a film at a low cost and having extremely few large thickness irregularities that are characteristic of inflation, allowing the expensive vinylidene fluoride biaxially stretched film to be supplied to the market at a low price, and its industrial significance. is very large. Further, according to a preferred embodiment, a biaxially stretched film of vinylidene fluoride polymer having one surface roughened can be achieved with almost no decrease in strength by improving the inflation method. The roughened film thus obtained not only becomes an oil-immersed capacitor film that combines the excellent dielectric properties of vinylidene fluoride-based polymers with properties improved by roughening, but also serves as an oil-immersed capacitor film that is even more effective as a composite film material. It is expected to improve the functionality of the product, and it will also have improved handling due to its close contact with the roll. In addition, in order to use it for applications such as metallized capacitors, a metal vapor deposited film of, for example, 200 to 500 sizes is provided on one surface (if one surface is roughened, usually the surface opposite to the rough surface). Things are good. The roughened surface improves affinity with oil, ensuring long-term reliability of the capacitor.

[Brief explanation of drawings]

FIG. 1 is a schematic flowchart of an inflation device suitable for remanufacturing the film of the present invention, FIG. 2 is an enlarged view showing the velocity changes in three directions near the expansion point (1) of the molten parison, and Figures 3 (a), (b), and (C) are enlarged views of the vicinity of the circular die under various conditions. Figures 4 and 7
9 and 9 are strain rate diagrams showing strain rate changes in the take-off direction in the melt inflation process obtained in Example 1-1, Comparative Example 1, and Example 2, respectively; Figures 8 and 10 show Example 1-1, respectively.
, wide-angle X-ray scattering photographs of films before cold stretching obtained by the melt inflation process according to Comparative Example 1 and Example 2; This is a polarized photograph of the stretched film (the scale is as shown with the vernier scale in cm in the photograph),
The presence or absence of a fine and regular uneven structure formed on the surface of these films can be visually recognized by detecting the phase difference of transmitted light. Moreover, FIGS. 12(a), (b), and (c) are measurement charts of thickness changes in the tube take-off direction that occurred in the original film before cold stretching due to inflation under various conditions. Figure 13 is a measurement chart of the thickness change in the take-off direction that occurred in the film after cold stretching.
Figure 4 is a polarized photograph of the same film (the scale is in centimeters as shown in the photograph). FIG. 15 is a graph showing the strength and elongation characteristics of the film after cold stretching. 1... Extruder, 2... Circular die (2a... Middle part)
, 5...Polymer film during inflation (5
a... Melt extrusion state, 5b... After inflation B, 5C, 5 d... During cold stretching), 6, 7, 9, 11
, 12... Nip roll, 8, 1o... Heat ffl heater 13... Product film winding roll. Fig. 7 tr > lm (a) Fig. 3 (k)) -425- Fig. 2 (C) Fig. 6 Expanded angle →M [) Figure 9 Figure 13 Pick-up direction Figure 8 G prisoner

Claims (1)

[Claims] 1. Inherent viscocity is 0.8 to 1.6 dl
/g of vinylidene fluoride-based polymer,
A vinylidene fluoride polymer film that is biaxially cold-stretched using the inflation method. 2. The film according to claim 1, which is stretched by 1.5 times or more in each of the vertical and horizontal biaxial directions. 3. The vinylidene fluoride polymer has an Mw/Mn (weight average molecular weight/number average molecular weight) ratio in the range of 10 to 20, or a vinylidene fluoride polymer alone or a polymer containing 30% by weight or more of the polymer and Mw The film according to claim 1 or 2, comprising a mixture with a vinylidene fluoride polymer having a /Mn ratio of less than 10. 4. The film according to claim 3, which contains 70% by weight or more of a vinylidene fluoride polymer having an Mw/Mn ratio in the range of 10 to 20. 5. The shear rate is 20 sec^-^1 by a capillary rheometer with a nozzle of length 15 mm and diameter 4 mm.
The melt tension of the strand at the temperature where the apparent melt viscosity is 2 x 10^5 poise is 300 to 800 g/cm^2.
Claims 1 to 4 are made of a vinylidene fluoride polymer.
The film described in any of the above. 6. Stretched by 1.5 times or more in both vertical and horizontal biaxial directions, and grooves extending in the horizontal direction with a depth of 0.2 to 1.0 μm on one side are continuous at intervals of 10 mm or less in the vertical direction. 6. The film according to claim 1, wherein the film is provided with: 7. Inherent viscocity as a whole is 0.8~
1.6d,/g, and the Mw/Mn ratio is 10 to 2.
0 vinylidene fluoride polymer alone or the polymer containing 30% by weight or more of the polymer and Mw/Mn
A mixture of vinylidene fluoride and a certain polymer having a ratio of less than 10 is melt-extruded through an annular die to obtain a molten parison, the parison is expanded and then cooled to obtain a raw tube, and the raw tube is heated again. A method for producing a vinylidene fluoride-based polymer biaxially cold-stretched film using an inflation method, in which simultaneous biaxial cold-stretching is performed by blowing air into the tube and adjusting the circumferential speed ratio of upper and lower nip rolls. 8. Claim 7: The strain rate due to expansion of the molten parison formed by melt extrusion in an annular die is temporarily relaxed after the expansion starts.
The method described in. 9. In the raw tube manufacturing process, the blow ratio (final tube diameter/annular die diameter) is 3 or less, the drawdown ratio (
9. The method according to claim 7, wherein the tube withdrawal speed/die exit speed) is 100 or less. 10. The concave angle of the molten parison extruded through an annular die is 0 to 10 degrees, and the grooves extending in the transverse direction after cold stretching are
10. The method according to claim 7, wherein a roughened film is obtained that is continuous in the machine direction. 11. The proportion of vinylidene fluoride polymer with Mw/Mn in the range of 10 to 20 in the melt extrusion raw material is 70% by weight
The method according to claim 10, which is the above. 12. In the raw tube manufacturing process, the crystallization line of the tube is moved up and down by adjusting the cooling air blown onto the molten parison from the outside, thereby imparting irregularities to the inner surface of the tube. Method. 13. In the cold stretching process, 1.5 in each of the vertical and horizontal biaxial directions
13. Any one of claims 10 to 12, wherein the film is stretched at least twice as long to obtain a film in which grooves extending in the horizontal direction and having a depth of 0.2 to 1.0 μm are continuously provided on one side at intervals of 10 mm or less in the vertical direction. Method described in Crab. 14. The method according to any one of claims 7 to 13, further comprising the step of performing relaxation heat treatment after biaxial cold stretching.