JPS61286115A - Manufacture of high rigidity polyoxymethylene film - Google Patents

Abstract

PURPOSE:To improve the transparency and facilitate the following orientation of the title film by a method wherein the film is rolled before being oriented. CONSTITUTION:In order to manufacture a biaxially oriented film made of polyoxymethylene polymer, the principal part in the main chain of which consists of a repeated unit of oxymethylene group -(CH2-O)-, firstly, a molten and solidified raw fabric sheet or film is longitudinally rolled so as to realize the rolling reduction (r) satisfying the following formula: 1.2<=1(1-r)<=4, r=1-t/to in which, to represents the thickness of film or sheet before rolling and (t) represents that after rolling. Secondly, the resultant sheet or film is laterally oriented by the draw ratio of 5 times or more and, finally, longitudinally oriented by the draw ratio of 5(1-r) times or more.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing a polyoxymethylene polymer film, particularly a biaxially oriented polyoxymethylene polymer film that is highly oriented and crystallized and has high rigidity.

[Prior Art] In recent years, with the increasing density and miniaturization of electronic devices, for example, films used as magnetic recording media such as video tapes, audio tapes, and floppy disks have been There is a growing demand for thinner walls. In order to meet this requirement, it is essential to develop a high-performance film with excellent rigidity.The present invention focuses on a polyoxymethylene polymer film as a film that satisfies this requirement. A method for producing an axial polyoxymethylene polymer film is provided.

Conventional unoriented polyoxymethylene films are generally formed by melt pressing or melt extrusion followed by rapid cooling, but the films obtained by these methods are not only opaque or translucent but also have poor mechanical properties. Inferior. Therefore, an attempt was made to improve these properties by biaxially stretching this film. We have discovered and filed an application for a highly rigid, biaxially aligned polyoxymethylene polymer film that is highly oriented and crystallized. When a polyoxymethylene film is biaxially stretched using conventional stretching techniques, the stretching results in non-uniform necking stretching due to the presence of spherulites in the crystal structure, or breaks occur before the desired stretching ratio is reached. Therefore, in order to obtain a uniform stretched film, extremely precise control of the stretching temperature, etc. was required, and this was a major barrier to the industrialization of this film.

Therefore, prior to stretching, methods to make this stretching easier were researched. For example, Japanese Patent Publication No. 40-21994 describes a crystallized polyoxymethylene film that is translucent to opaque due to the presence of spherulites, but the film becomes substantially transparent and almost no spherulites can be detected using a visible light microscope. A method for producing a polyoxymethylene film is disclosed, which comprises rolling at a roll temperature of up to 120°C and then stretching at a temperature of 120 to 180°C. This method is characterized in that by rolling the film prior to stretching, it improves transparency and facilitates subsequent stretching.

That is, it was attempted to facilitate stretching by destroying or greatly deforming the spherulites by rolling.

[Problems to be solved by the invention] When a film is rolled, the crystal orientation and deformation state are completely different in the rolling direction and the direction perpendicular to this, and the stretching behavior in each axial direction is also completely different. It's coming. Particularly in the case of a biaxially oriented film that requires a high degree of stretching in two axial directions as in the present invention, this anisotropy is a major obstacle. In order to eliminate this anisotropy, a method can be considered, for example, to roll the film in two axial directions, that is, in the longitudinal direction of the film and in the width direction orthogonal thereto. However, although biaxial rolling technology is used in some industrial applications for rolling metals, the technology has not yet been established in the field of polymers, as in the present invention, and it is extremely difficult to apply it to industrial processes.

Furthermore, the above-mentioned known techniques do not provide detailed explanations about the method of stretching the film after rolling, especially the method of biaxial stretching. In particular, when biaxially stretching a highly crystalline polymer such as the film of the present invention, the crystalline state changes significantly due to the stretching, so the method requires more detailed analysis and more advanced technology.

For example, the orientation and deformation state of crystals during stretching are significantly different4 between a simultaneous biaxial stretching method in which longitudinal and horizontal stretching is performed simultaneously and a sequential biaxial stretching method in which each is performed separately. etc. will also be different. Therefore, a stretching method that matches the characteristics of the object to be stretched must be adopted.

[Means and effects for solving the problems] Therefore, the present inventors have continued their intensive research in order to overcome the above-mentioned barriers to industrialization and to find a biaxial stretching method that suits the characteristics of polyoxymethylene. Ta. First, we begin with a detailed analysis of the orientation and deformation state of the crystals caused by rolling, repeat tensile property tests in the rolling direction and in the direction orthogonal to this to evaluate the stretching performance, and then perform various tests on this rolled film. A stretching method was adopted, and the conditions for each method were examined in detail, and the behavior of the crystals during stretching was analyzed in detail. As a result, by applying normal uniaxial rolling, that is, rolling in the longitudinal direction of the film, without going through biaxial rolling, which is considered to be extremely difficult industrially, we were able to achieve a high degree of biaxial rolling in the primary stretching process. We have discovered a method that makes stretching possible. Through this stretching, an excellent method for producing a highly rigid polyoxymethylene film in which polyoxymethylene is highly oriented and crystallized in biaxial directions was established, and the present invention was accomplished.

In the present invention, the main part of the main chain is substantially oxymethylene group-
In producing a biaxially oriented film made of a polyoxymethylene polymer composed of repeating units of +CH2-0+-, the rolling reduction ratio r of the melt-solidified raw sheet or film is expressed by the formula where to: before rolling. Thickness t of film or sheet: After rolling in the machine direction until it reaches the thickness of the film or sheet after rolling, it is stretched at least 5 times in the transverse direction, and then stretched by 5 times in the machine direction (
1-r) It is characterized by stretching on the position.

The present invention will be explained in detail below. First, a polyoxymethylene polymer sheet or film (hereinafter referred to as "original fabric") is formed by conventional means, such as melt pressing or melt extrusion followed by rapid cooling. The crystallinity of the original fabric at this time varies depending on the forming conditions such as the cooling conditions after melting, but 1
Usually it is 60-73%.

Next, this original fabric is rolled. A normal roll mill can be used for this rolling. Depending on the purpose of the roll rolling mill,
There are two-high rolling mills, four-high rolling mills, and other multi-high rolling mills, but in the present invention, a two-high rolling mill or a four-high rolling mill can sufficiently achieve the purpose. By this rolling, the original fabric is rolled in the longitudinal direction, that is, in the machine direction, and the rolling ratio at this time is preferably 1.2 to 4 times. If the rolling ratio is lower than 1.2 times, the effect of rolling is small, and At higher magnifications, the film tends to tear in the machine direction during the subsequent stretching process, making it difficult to operate. More preferably, it is 165 to 3.5 times.

In addition, if the rolling at this time is expressed using the formula: to: thickness of the film or sheet before rolling, t: thickness of the film or sheet after rolling, rolling within the following range is preferable, and more Preferably.

The temperature of the film or sheet during rolling is preferably in the range of room temperature or higher and 40° C. lower than the peak temperature of the crystal melting curve of the original film measured by a differential calorimeter. More preferably, the temperature range is at least room temperature and at most 55° C. lower than the peak temperature. In terms of rolling efficiency, it is preferable that the temperature of the film or sheet during rolling be high, but if the temperature exceeds a temperature that is 40°C lower than the peak temperature of the crystal melting curve, there is a tendency for the stretchability to decrease in the subsequent stretching process. be.

Further, the raw material may be preheated prior to rolling, and furthermore, the rolling may be repeated several times without rolling to a desired rolling ratio in one rolling.

By this rolling, some of the polyoxymethylene spherulites present in the crystal structure of the original fabric are destroyed and deformed so that they are preferentially oriented in the rolling direction. That is, by rolling, a decrease in crystallinity due to spherulite fracture and orientation of crystals in the rolling direction occur simultaneously. The present inventors reflected and utilized this phenomenon in the subsequent stretching process. That is, in the transverse stretching process, the drawability is improved by reducing the degree of crystallinity, resulting in a high degree of transverse stretching, and in the subsequent longitudinal stretching process, some of the crystals oriented during rolling retain their orientation. Therefore, stretching in that direction is made easier.

If the degree of rolling increases, the decrease in crystallinity will increase accordingly, but beyond the scope of the present invention, the rate of this decrease will not only decrease, but also cause deterioration of the rolled element itself and to the direction of rolling. The orientation of the crystals becomes more preferential, and as a result, in the subsequent transverse stretching process, fractures in the rolling direction, that is, the longitudinal direction, become noticeable, making it difficult to apply the method of the present invention.

The present invention was discovered by making full use of the anisotropy caused by the preferential orientation of crystals in the rolling direction due to rolling, and by combining this with another change: a decrease in crystallinity. .

The rolled film or sheet is then subjected to a subsequent stretching process.
Stretched along the axis. This stretching process consists of a horizontal stretching process in which the film is first stretched in the width direction, and then a longitudinal stretching process in which the film is stretched in the longitudinal direction.

That is, the stretching method of the present invention employs a sequential biaxial stretching method in the horizontal and vertical directions. By this stretching, a highly rigid polyoxymethylene film in which polyoxymethylene is highly oriented and crystallized in biaxial directions can be obtained.

As mentioned above, the present inventors discovered this process by conducting a detailed analysis of the rolling conditions during rolling and the crystal structure based on the rolling conditions. That is, it is characterized by being stretched in the transverse direction and then in the rolling direction, that is, in the longitudinal direction.

The transverse stretching is usually carried out using a transverse stretching machine called a tenter, and the rolled film or sheet is stretched in the width direction. In this case, the stretching ratio is at least 5
That's more than double that. At lower magnifications, the resulting film has insufficient rigidity. Moreover, in order to obtain a film with higher rigidity, this magnification may be made higher, for example, 8 times or more.

Next, two longitudinal stretchings are generally carried out using a roll stretching machine. By this stretching, the transversely stretched film is stretched in the longitudinal direction. In this case, the stretching ratio is at least 5 times or more in the longitudinal direction based on the original film or sheet before rolling. Therefore, if the rolling ratio during rolling is high,
Accordingly, the magnification during stretching can be lowered. for example,
When the magnification during rolling is 2 times and 2.5 times, the stretching magnification during longitudinal stretching is 2.5 times or more and 2 times or more, respectively. That is, when expressed using the rolling reduction r defined above, the stretching ratio in longitudinal stretching is at least 5(1-r) higher. Similarly, by increasing this magnification even higher,
A film with higher rigidity can be obtained.

In the above stretching process, the stretching temperature is a particularly important condition, and special attention must be paid to the stretching temperature.
Scanning Calarimstry/DSC
) is within a temperature range of 25°C lower than the peak temperature of the crystal melting curve of the original fabric and 5°C higher than the peak temperature. At temperatures lower than this temperature range, not only is it difficult to orient crystal molecules, but there is also a risk that the film will whiten or break. Furthermore, at temperatures higher than this temperature range, melting of crystal molecules becomes dominant,
Not only will the effect of crystal orientation be almost impossible to expect, but in some cases there is a risk that the film will melt. The temperature range is preferably 15° C. lower than the peak temperature or higher and lower than the peak temperature, and a more uniform stretched film can be obtained at this time.

Note that the peak temperature of the crystal melting curve measured by a differential calorimeter varies depending on the molecular weight, crystallinity, formation conditions, etc. of the original fabric, but is usually 173 to 178°C.

The polyoxymethylene film of the present invention has a relatively high molecular weight, for example, a number average molecular weight of 35,000 to 100.00.
Zero or more polyoxymethylenes are derived.

In the case of a film with high rigidity as in the present invention, polyoxymethylene with a relatively high molecular weight is preferred, and polyoxymethylene acetalized products, or their reaction products with isocyanates, or copolymerized products with, for example, a small amount of a third component, are preferred. It can also be applied to polyoxymethylene polymers, such as copolymers, in which the main part of the main chain is substantially composed of oxymethylene groups, -(GHz-0)- repeating units.

Next, the present invention will be explained in more detail based on FIG. 1, which illustrates the method of the present invention.

The polyoxymethylene exiting the extruder 1 is cooled by a cooling roll 2 to form a raw fabric. Next, this original fabric is introduced into a rolling mill 3 and rolled. This rolled film or sheet is then guided to a transverse stretching machine 4. After being preheated to the stretching temperature in step 4a, it is laterally stretched in step 4b. 4C is a heat treatment zone, which is applied as necessary. The transversely stretched film is preheated again to the stretching temperature by heating rolls 5 and 6, and then longitudinally stretched by stretching rolls 7.8.

The rotational speeds of the stretching rolls 7.8 are set to Vl and V2, respectively, and the longitudinal stretching ratio is determined by this speed ratio V2/Vl. The film is then cooled by cooling rolls 9, 10 and then wound up by winding rolls 11. Although not shown in the figure, the longitudinally stretched film is subjected to heat treatment, if necessary, before being cooled to improve its thermal stability.

According to the method of the present invention, the degree of crystallinity measured by the density method is 75 to 85%, and the degree of crystal orientation measured from two directions, end and edge, by the X-ray diffraction method. It is possible to obtain a highly oriented and crystallized biaxially oriented polyoxymethylene film in which each of This biaxially oriented polyoxymethylene film has a high tensile modulus of 550 to 1500 kg/am'' and exhibits high dimensional stability due to its high degree of crystallinity.

Note that the crystallinity and crystal orientation are measured as follows.

Crystallinity: 23 with a solution consisting of normal heptane/carbon tetrachloride
The density (d) of the film is measured at °C by the density gradient piping method, and the degree of crystallinity CD) is calculated by the following formula.

Here, da is 1.508 g/cc, which is the theoretical density of a completely crystallized polymer, and da is 1.25 g/cc.
is the density of the completely amorphous polymer.

[Grading] For each sample, the stretching direction is aligned and the thickness is 2 mm.
A rectangular molded product having a width of 1t+i and a length of 10 mm was produced.

Cyanoacrylate adhesive was used to fix each film during molding. Next, this molded product was placed on a universal sample stand (rotating sample stand) manufactured by Shimadzu Corporation with the edge of the film
e) It was installed so that X-rays could enter from the end direction. The direction of the sample is shown in Figure 2.

x&! The generator used was a Shimadzu XD-3A type device, with 30KV-28mA -C through an rNi filter.
U-Ka radiation was used as the X-ray source. The goniometer used was a model VG-108R manufactured by Shimadzu Corporation, which was attached to the rotating sample stand. The slit type is the receiving slit (
Receiving slit) 2 mmφ, ski? -/Scattering Slit
5lit) 1 mmφ was adopted. Next, the diffraction angle was set to the (100) plane of polyoxymethylene (2θ = 22° to 23
．． 5°), incident X-rays from the edge direction and the end direction, and rotated the sample stage twice at a rotation speed of 4°/win to measure the diffraction intensity of the (100) plane. Scanned in the angular direction. The chart speed of the recorder was 10 mm/win. An example of the results obtained by this measurement is shown in FIG. Next, a method for calculating the degree of crystal orientation will be explained with reference to the same figure. For the peak at an azimuth angle of 90'', calculate the peak intensity factor from the background, and then calculate the width of the peak (which is 1/2 the intensity) (
Find half price @)W. Note that the background is determined prior to measurement. Next, the degree of crystal orientation A was calculated using the following formula.

[Examples] The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited to these Examples.

In the measurement of various properties of films or sheets shown in the examples below, the crystal melting curve was measured using a differential calorimeter (DSC-20 model) manufactured by Seiko Electronics Co., Ltd., with a sample weight of 10 mg and a heating rate of 10°. C/win and recorded at a chart speed of 2 am/win. An example of measurement at this time is shown in FIG. In addition, the tensile properties are 100mm in length.
+, 80m between chucks for a 10mm wide test piece
m, chi'r-/kusubido 30mm/win, temperature 2
Measured at 3°C and 50% humidity. The elastic modulus, which is a measure of the stiffness of the film, was calculated from the initial slope of the stress-strain curve obtained at this time.

Example 1 Polyoxymethylene (with a number average molecular weight of about 57,000)
Tenac 3010 manufactured by Asahi Kasei Corporation was extruded through a slit die at a temperature of 200°C, rapidly cooled with a casting roll heated to 120°C, and the thickness was 700 mm and the width was 150 mm.
An original fabric sheet was obtained. The crystallinity of this raw fabric is 70% by the density method, and the peak temperature of the crystal melting curve by DSG is 1.
The temperature was 76°C. 1 Next, roll this raw fabric with a roll diameter of 50! III, roll width 40
The material was rolled at a temperature of 70°C using a four-high rolling mill consisting of a 0+++m work roll and a backup roll with a roll diameter of 100 mm and a roll width of 400 mm. The rolling ratio at this time was 2 times, and the rolling reduction ratio was 0.5. Moreover, the degree of crystallinity after rolling was 67%.

Next, this rolled sheet was introduced into a tenter transverse stretching machine whose stretching temperature was maintained at 172° C., and transversely stretched 8 times in the width direction at a stretching speed of 200%/win. Next, this film was introduced into a roll longitudinal stretching machine and longitudinally stretched. At this time, the film was preheated to the stretching temperature of 174° C. by a heating roll, and then stretched 4 times by a subsequent stretching roll. The rotation speed of the stretching roll is V l = 0.4 m/sin, V
2 = 1.8m/ff1in. Through the above steps, it was possible to obtain a polyoxymethylene film that was uniformly stretched 8×8 times in the biaxial directions. The biaxially stretched film thus obtained had an average thickness of 11 g, and its tensile properties, crystallinity degree determined by density method, and crystal orientation degree determined by X-ray diffraction method were as shown in Table 1.

The degree of crystal orientation in the table is expressed by the value measured from the edge direction of the film in the MD direction, and the value measured from the end direction in the TD direction.

From this result, the biaxially stretched film obtained by the present invention has an extremely high elastic modulus compared to a normal film,
It also shows that the film is highly oriented and crystallized, indicating that it is an excellent film with high rigidity.

Example 2 The raw sheet of Example 1 was rolled using the same rolling mill as in Example 1 at a temperature of 110° C. with a rolling ratio of 3 times and a rolling reduction of 0.87. The crystallinity after rolling was C4%. Next, this rolled sheet was rolled at a rolling temperature of 175°C and a stretching speed of 20°C.
Transverse stretching was performed 10 times in the width direction at 0%/win. Next, this film was stretched by a roll longitudinal stretching machine at a stretching temperature of 17
Stretching was carried out 4 times in the machine direction at 6°C. The rotational speed of the stretching rolls at this time was the same as in Example 1. Through the above steps, a polyoxymethylene film uniformly stretched 12 times by 10 times in the biaxial directions was obtained. 2 obtained here
The axially stretched film had an average thickness of 6 mm, and its tensile properties, degree of crystallinity determined by the density method, and degree of crystal orientation determined by the X-ray diffraction method were as shown in Table 2.

Table 1 MD: Longitudinal direction (machine direction) of film TD:
Width direction Table 2 Example 3 The raw sheet of Example 1 was rolled at a temperature of 100°C using the same rolling mill as in Example 1, and the rolling ratio was 1.
．． 2.1.5.2.2.5.3.3.5.4.4.5 times the rolled sheet was obtained. Next, each rolled sheet was subjected to 5-fold transverse stretching in the width direction at a stretching temperature of 175°C and a stretching rate of 200%/win. Next, the transversely stretched sample was stretched at a stretching temperature of 178°C using a roll longitudinal stretching machine.
Longitudinal stretching was performed at °C. The stretching ratio at this time was set such that the stretching ratio after stretching was 5 times that of the original fabric, taking into account the stretching ratio during rolling. Therefore, the rotational speed of the stretching roll is V 2
= 1.8 m/sin, and Vl was set to match each stretching ratio. Through the above process, 5
A polyoxymethylene film stretched by a factor of X5 was obtained.

Table 3 summarizes the rolling ratio, rolling reduction, crystallinity after rolling, and stretching performance during each stretching. This result shows that a uniformly stretched biaxially oriented polyoxymethylene film can be obtained within the rolling range of the present invention.

Table 3 0: Good Δ: Slightly difficult (breakage occurred in some parts) ×:! ! [Effects of the Invention] The present invention is based on uniaxial rolling, which is an industrially established technology, and is a method that can be fully applied industrially. The film obtained by the present invention has excellent rigidity not found in other conventional films, and this property can be used in various applications such as base films for magnetic recording materials such as magnetic tapes and floppy disks. applied to the field.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing an example of the film manufacturing method of the present invention, Fig. 2 is an explanatory diagram showing the direction of the sample for measuring the degree of crystal orientation by X-ray diffraction method, and Fig. 3 is a diagram showing the direction of the sample for measuring the degree of crystal orientation by X-ray diffraction method. FIG. 2 is an explanatory diagram showing a calculation method. Figure 4 shows the differential calorimeter (OS
It is a figure which shows an example of the crystal melting curve measured by C). l... Extruder, 2... Cooling roll, 3... Rolling machine, 4... Lateral stretching machine, 4a... Preheating zone, 4b...
・Stretching zone, 4C... Heat treatment zone, 5.6...
Heating roll, 7, 8... Stretching roll, 9.10...
Cooling roll, 11... winding roll.

Claims (3)

[Claims] (1) The main part of the main chain is substantially an oxymethylene group -(C
In producing a biaxially oriented film made of a polyoxymethylene polymer composed of repeating units of H_2-O)-, the rolling reduction ratio r of the melt-solidified raw sheet or film is determined by the formula 1.2≦1/ (1-r)≦4 r=1-(t/t_0) where t_0: Thickness of film or sheet before rolling t:
A high-rigid polyoxy which is characterized by being rolled in the machine direction until it reaches the thickness of the rolled film or sheet, then stretched 5 times or more in the transverse direction, and then stretched 5 (1-r) times or more in the machine direction. Method for manufacturing methylene film. (2) The highly rigid polyoxymethylene film according to claim 1, wherein the rolling temperature is at least room temperature and at most 40°C lower than the peak temperature of the crystal melting curve of the original film measured by a differential calorimeter. Production method. (3) The stretching temperature is at least 25°C lower than the peak temperature of the crystal melting curve of the original fabric measured by a differential calorimeter,
The method for producing a highly rigid polyoxymethylene film according to claim 1, wherein the temperature range is 5° C. higher than the peak temperature.