JPS61252135A - High-rigidity polyoxymethylene film - Google Patents

Abstract

PURPOSE:To obtain the polyoxymethylene polymer film having high rigidity and high dimensional stability by specifying the degree of crystallinity of the film as well as the degree of orientation of the crystal thereof. CONSTITUTION:The biaxially orientated film is formed by employing polyoxymethylene polymer, in which the principal part of the backbone chain thereof is constituted of the repeated unit of oxymethylene base-(CH2-O). The degree of crystallinity of the film, which is measured by density method, is 75-95% and the degree of orientation of crystal, which is measured by X-ray deffractometry from two directions of end and edge, is 85-95% respectively. When the degree of crystallinity is less than 75%, the rigidity and dimensional stability are reduced. When the same exceeds 95%, formation of the film is very hard. When the degree of orientation of crystal is less than 85%, the orientation of the crystal is insufficient and the high rigidity of the film can not be obtained, however, when the same exceeds 95%, the formation of the film is very hard. Accordingly, the polymerized film, satisfying these important conditions, may obtain the tensile elasticity of 550kg/mm<2> or more in respective directions of axes respectively.

Description

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

[Prior Art] In recent years, with the increasing density and miniaturization of electronic devices, and the speeding up of signal processing, films used as magnetic recording media films such as video tapes, audio tapes, floppy disks, etc. have become increasingly popular in recent years. In recent years, there has been a growing demand for extremely thin walls and high dimensional stability. To meet this demand, it is essential to develop high-performance films with superior rigidity and dimensional stability. The present invention focuses on a polyoxymethylene polymer film as a film that satisfies such requirements,
A biaxially oriented polyoxymethylene polymer film having high rigidity and high dimensional stability is provided.

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, various methods have been tried in the past to improve this transparency and mechanical properties, and as a result, films with improved transparency and mechanical properties to some extent have been obtained. There is. However, since polyoxymethylene film is extremely difficult to handle compared to ordinary films, the excellent properties of this film, namely the excellent rigidity and dimensional stability of this film as a biaxially oriented film, have not been discovered until now. It had reached this point.

One reason why polyoxymethylene film is difficult to handle
One reason is said to be due to relatively large spherulites present in the crystal structure. In Japanese Patent Publication No. 40-2191114, a crystallized polyoxymethylene polymer film, which is translucent to opaque due to the presence of spherulites, is processed until the film becomes substantially transparent and almost no spherulites can be detected by a visible light microscope. The transparency and mechanical properties are improved by rolling at a roll temperature of 120°C or less, and then stretching the rolled film by 25% or more in at least one axis at a temperature in the range of 120 to 180°C. A method for producing a polyoxymethylene film is disclosed.

This method is characterized by improving the transparency of the film and making it easier to orient the crystals by rolling.As a result, the film is more transparent than the film obtained by the conventional method. The properties and mechanical properties were improved.

Generally, the rigidity of a film is said to be proportional to its tensile modulus, and the higher the modulus of elasticity, the greater the rigidity. To give an example of the rate, the maximum rate was about 530 kg/m Oboro2. However, this level of improvement in rigidity is extremely insufficient for a highly rigid, high-performance film, and is not the purpose of the present invention.

This known technique does not suggest the possibility of further increasing this value or any measures or means for further increasing it.

[Problems to be Solved by the Invention] In the case of polyoxymethylene polymer films, it is extremely difficult to highly orient the crystals by ordinary orientation means because of the spherulites present in the crystal structure as described above. It was considered difficult. Although this has been made possible to some extent by the above-mentioned known technology, it has not been possible to achieve the characteristics aimed at by the present inventors. It was considered to be the limit of its characteristics.

[Means and effects for solving the problems] The present inventors focused on the high crystallinity property of polyoxymethylene polymers, and conducted extensive research to make the most of this property.
The present invention was achieved as a result of numerous repeated studies including more precise control of processing conditions such as orientation conditions. That is, we have completed a polyoxymethylene polymer film with a higher degree of crystallinity and a highly oriented film, and have also demonstrated that the film has a high tensile modulus and excellent dimensional stability. I found it. And, it far exceeds the characteristics that were previously considered to be the limit.
A polyoxymethylene polymer film having high rigidity and high dimensional stability has been obtained.

In the present invention, the main part of the main chain is substantially oxymethylene group H.
A biaxially oriented film made of a polyoxymethylene polymer composed of repeating units of cH2-0)-, which has a crystallinity of 75 to 85% as measured by the density method, and End (End) and Edge (
This polyoxymethylene polymer film is characterized in that the degree of crystal orientation measured from two directions (edge) is 85 to 95% in both directions.

The film in the present invention has the following structural parameters:
The degree of crystallinity and the degree of orientation of its crystals must satisfy the following conditions. First of all, the degree of crystallinity was calculated by the formula from the value of the density (d) of the film measured by the density gradient tube method. It is necessary that the crystallization (D) is 75-85%. Here, dc is 1.506 g/ec, which is the theoretical density of a completely crystallized polymer, and da
is 1.25 g/cc, the density of the completely amorphous polymer. When the degree of crystallinity is less than 75%, even if the degree of orientation of the crystals is sufficiently high, the influence of the amorphous portion appears significantly, reducing the rigidity and dimensional stability of the film. Also, films that exceed 95%.

The properties of polyoxymethylene polymers make their formation extremely difficult.

Next, the second parameter is the degree of crystal orientation, which is determined by the (100) Surface (2θ; 22° to 23.5°)
The diffraction intensity can be determined from the intensity distribution when scanning in the azimuth direction. The end direction of the film is a direction that is parallel to the film surface and also parallel to the machine direction (extrusion direction) of the film.
) direction refers to a direction parallel to the film surface and also parallel to the width direction of the film. In the present invention, the half width (W) of the diffraction peak centered at an azimuth angle of 80° is measured.

The calculated value (A) was taken as the degree of crystal orientation.

In the present invention, the end (End) and the edge (Edga)
The degree of crystal orientation measured from two directions is 85.
~95% is required. When the crystal orientation degree is less than 85%, the crystal orientation is insufficient, and even if the crystallinity degree satisfies the above conditions, a highly rigid film cannot be expected as a biaxially oriented film. Due to the properties of polyoxymethylene polymer, films exceeding
Its formation is extremely difficult.

It is an essential requirement of the present invention to simultaneously satisfy the above two structural parameters and parameters, and a polyoxymethylene polymer film that satisfies these requirements has excellent characteristics of high rigidity and high dimensional stability. Specifically, its tensile modulus in each axial direction is 550 kg/m2 or more, which is a high modulus that exceeds conventional limits.

Furthermore, in order to obtain a film with more excellent properties, the crystallinity is preferably 78 to 85% and the crystal orientation is 80 to 95%. At this time, the tensile modulus in each axial direction becomes an extremely high value of 700 kg/m2 or more.

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.
It is derived from 0 or more polyoxymethylenes. In the case of a film with high rigidity and high dimensional stability as in the present invention, polyoxymethylene with a relatively high molecular weight is preferred, and polyoxymethylene heptacetals, or their reaction products with incyanates, or e.g. The main part of the main chain is substantially composed of oxymethylene groups -(GHz-
It can also be applied to polyoxymethylene polymers composed of repeating units of 0).

Next, a specific method for producing a film that satisfies each parameter of the present invention will be exemplified below.

First, a sheet or film (hereinafter referred to as "original fabric") of the polymer is formed by conventional means, such as melt pressing or melt extrusion followed by rapid cooling. The degree of crystallinity of the original fabric at this time varies depending on formal conditions such as cooling conditions after melting, but is usually 60 to 72%.

Next, this original fabric is stretched at least 5 times or more in each axial direction. That is, the film of the present invention could only be discovered by stretching the original film to a high magnification of at least 5 times or more. More preferably, more excellent properties can be obtained by stretching the film by a factor of 8 or more.

For this stretching, special attention must be paid to the stretching temperature.
lorimetry/DSC) at a temperature 25°C lower than the peak temperature of the crystal melting curve of the original fabric,
The temperature range is 5° C. higher than the peak temperature.

At temperatures lower than this temperature range, not only is it difficult to whiten the crystal molecules, but there is also a risk that the film will whiten or break. Further, at a temperature higher than this temperature range, the melting of crystal molecules becomes dominant, and the effect of crystal orientation is hardly expected, and in some cases, there is a possibility that the film may be fused. And preferably 1 from the peak temperature.
The temperature range is 5° C. lower 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.

In addition, in the case of the film of the present invention, since the stress during stretching is relatively large compared to ordinary films, it is preferable that the stretching be performed at a relatively low speed. 50-3000%/intestine i of length
n, preferably 100 to 1000%/win.

By stretching the raw fabric at least 5 times or more in each axial direction at the above stretching temperature and stretching speed, the biaxially oriented polyoxymethylene molecules of the present invention are highly crystallized and highly oriented. An oxymethylene polymer film can be obtained. The film thus obtained had a tensile modulus of elasticity of 550 kg/m in each axial direction.
It has a high value north of m2 and has excellent dimensional stability due to its high crystallinity.

The film of the present invention is characterized by crystallinity and crystal orientation, which are structural parameters, and the relationship between its properties, tensile modulus and stretching ratio, depends on the crystallinity of the original film or the conditions during stretching. etc., and is not necessarily determined uniquely, but in order to obtain a film with a higher elastic modulus, it is sufficient to stretch at a higher magnification under the above stretching conditions. If the stretching ratio is 8 times or more, the tensile modulus is 700 kg/■
A film with an extremely high value of 112 or more can be obtained. This value is more than 3 times that of a normal raw film, making it an extremely high rigidity film.

Further, if necessary, stretching can be performed with anisotropy in the elastic modulus in each axial direction. That is, by providing a difference in the stretching ratio in each axial direction, this can be easily carried out. For example, stretching can be performed with a stretching ratio of 10 times or more in the longitudinal direction and 5 times or more in the transverse direction.

Further, the film obtained here is subjected to heat treatment, if necessary. The temperature and time in this case are not particularly limited, but it is carried out at a temperature near the stretching temperature for a relatively short time, for example, 1 to 120 seconds.

In the method for producing the above-mentioned film, conventional means can be applied to the stretching method.9 For example, longitudinal-horizontal or transverse-longitudinal sequential biaxial stretching method or simultaneous biaxial stretching method can be applied. In the case of polyoxymethylene polymers, when an attempt is made to reorient crystals that have been oriented in a particular direction in a different direction, due to the characteristics of the crystal structure, some of the crystal molecules break, resulting in There is a risk that the film will break during stretching. Therefore, a simultaneous biaxial stretching method in which stretching is performed simultaneously in the z-axis direction is a more preferable method, but when adopting a sequential biaxial stretching method, for example, first stretching is performed in the transverse direction using a tenter, and then a relatively easy roll A preferred method is a transverse-longitudinal sequential biaxial stretching method in which stretching is performed in the longitudinal direction.

In obtaining the film of the present invention, some of the above-mentioned known techniques can also be used in combination in order to more easily orient the crystals in the raw film. That is, prior to stretching, the original fabric is rolled using a roll mill or the like, and then stretched under the above-mentioned stretching conditions. In this case, rolling is performed in at least one axial direction, that is, in the roll direction, until the length becomes approximately 1.1 to 3 times the length of the original fabric, but in the subsequent stretching step, In order to make it easier to orient the crystals in both directions, if this rolling operation is performed in the roll direction and in the direction perpendicular to this, that is, in the width direction, a more uniform stretched film can be obtained in the stretching process. I can do it.

Also, if rolling is performed prior to stretching in this way, the original fabric will be stretched to a certain extent during rolling.

The stretching ratio in the stretching process is considered to be already included in the stretching ratio during rolling.For example, when obtaining a 10 times stretched film, if it is stretched to 2 times in the rolling process, it will be 5 times in the actual stretching process. Stretching may be performed. That is, the stretching ratio in the present invention is based on the original fabric.

Furthermore, the method exemplified below can also be applied as a method for making it easier to orient the crystals in the original fabric. First, the original fabric is preheated to an appropriate temperature of 100 to 150°C, and then the original fabric is pressurized. The pressurizing operation in this case can be easily performed using, for example, a compression molding machine. By this operation, the crystals in the original fabric are preliminarily oriented to some extent in the biaxial directions. This is a method in which the preliminarily oriented original fabric is then highly oriented and crystallized under the stretching conditions according to the present invention. In the above pressurizing operation, a suitable resin having better fluidity than polyoxymethylene polymer, such as polymethyl methacrylate (PM) [A], is used, and the original fabric is sandwiched between the resins. By pressurizing the original fabric together with the resin, the original fabric can be more easily oriented.

As described above, various methods can be employed to obtain the film of the present invention. The film thus obtained has excellent properties of high rigidity and high dimensional stability.

Therefore, the film of the present invention can be applied to a wide variety of applications that utilize such properties, such as base films for magnetic recording materials such as magnetic tapes and floppy disks.

The density of the film in the present invention is normal heptane/
This is a value measured using a density gradient tube at 23° C. using a solution consisting of carbon tetrachloride.

Next, a method for measuring the degree of crystal orientation using X-ray diffraction will be described. For each sample, the thickness is 2 cm with the stretching direction aligned.
A rectangular molded product with a width of 1 cm and a length of 101 mm was produced. Each film was fixed during molding using a cyanoacrylate adhesive.Then, the molded product was placed on a universal sample stand (rotating sample stand) manufactured by Shimadzu Corporation with the edge of the film.
) or so that X-rays can enter from the end direction.

The X-ray generator is an XD-3A model manufactured by Shimadzu Corporation.
30KV-28mA -1: Cu-Ka rays passed through a Ni'74 router were used as the X-ray source. The goniometer used was also a VC-108R model manufactured by Shimadzu Corporation, which was attached to the rotating sample stand. The slit system is receiving slit (Receiving 5lit) 2+u*φ, scattering/talling slit (Scattering
5lit) 1 amφ was adopted. Next, the diffraction angle was set to the (100) plane of polyoxymethylene (2θ = 22° ~
23.5°) and incident X-rays from the edge direction and the end direction,
Rotate the sample stage twice at a rotation speed of 4°/win,
0) The diffraction intensity of the plane was scanned in the azimuthal direction. The chart speed of the recorder was 10 mm/ll1n. An example of the results obtained by this measurement is shown in Figure 2.
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 80°, the peak intensity I from the background is determined, and then the width (half width) W of the peak, which is 1/2 the intensity, is determined. Note that the background was determined prior to the measurement, and the degree of crystal orientation A was then calculated using the following formula.

The differential calorimeter (OSC) is a DS manufactured by Seiko Electronics.
C-20 type, sample weight 10 mg, heating rate 101
Measurements were made with 7 layers in and recorded at a chart speed of 2 cm/sin. An example of measurement at this time is shown in FIG.

[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.

The various properties of the films shown in the following examples were measured using the following test methods.

(1) Tensile properties For a test piece with a length of 100 m+s and a width of 10 mm, the chuck distance is 601 mm, and the chuck speed is 30 Cao Qian/intestine.
The zero elastic modulus measured at a temperature of 23° C. and a humidity of 50% was calculated from the initial slope of the stress-strain curve obtained at this time.

(2) Dimensional stability According to JIS C-2318, length 150mm, width 20mm
■150℃/2h for samples with 100mm between gauge lines
The heat shrinkage rate (%) after r was determined, and this value was shown as the thermal dimensional stability (%).

Example 1 Pelletized polyoxymethylene (Tenac 3010 manufactured by Asahi Kasei Corporation) with a number average molecular weight of about 57,000 was
The material was melted and pressed at a temperature of 200° C. for 2 minutes under a pressure of 0 kg/cir2, and then immediately cooled in water at a temperature of about lθ° C. to obtain a raw sheet with a thickness of 300 W. The crystallinity of this original fabric was 87% by the density method, and the peak temperature of the crystal melting curve by DSC was 175°C.

Next, this original fabric was subjected to simultaneous biaxial stretching at a temperature of 175° C. and a stretching speed of 170%/inch using a biaxial stretching machine (tenter type) manufactured by Karamoto Seisakusho. Although this stretching resulted in necking stretching and some unevenly stretched parts were generated, a biaxially stretched film with a size of 6×6 times was obtained. Table 1 shows the tensile properties of this film, the degree of crystallinity determined by the density method, and the degree of crystal orientation determined by the X-ray diffraction method, compared with the original film.

The biaxially stretched film obtained here had equivalent physical properties in each direction, and Table 1 shows the results in one direction.

This result shows that this film is highly oriented and crystallized, and also shows that it has higher rigidity than conventional polyoxymethylene films.

Example 2 The same polyoxymethylene as in Example 1 was extruded from a slit die at a temperature of 200°C and rapidly cooled on a casting roll heated to 120°C to obtain a raw sheet with a thickness of 500 l. The crystallinity of this raw fabric by the density method is 71%, DS
The peak temperature of the crystal melting curve according to C was 176°C.

Next, this original fabric was sandwiched between two sheets of polymethyl methacrylate resin having a thickness of 10 layers, preheated to a temperature of 130° C., then pressurized at about 1000 kg/cs+2, and then cooled. Through this operation, the original fabric was stretched 2×2 times.

Next, the original fabric stretched to 2×2 times was stretched at a stretching temperature of 180 to 177°C using a biaxial stretching machine as in Example 1.
Simultaneous biaxial stretching was performed at a stretching rate of 100 to 400%/win to obtain a uniform stretched film. Table 2 shows the stretching conditions, stretching ratio, and physical properties of the film after stretching.

The stretching ratios in the table are based on the original fabric, and the anisotropic stretching ratios were obtained by varying the stretching speed in each direction. , Experiment No. 7 was subjected to heat treatment at 170° C./1 ain after stretching.

The results in Table 2 show that the films of the present invention have extremely high stiffness and also have excellent dimensional stability.

Example 3 The raw sheet obtained in Example 2 was rolled using a two-high rolling mill consisting of two rolls with a length of 300° C. and a diameter of 2501 mm. Rolling was performed at a roll temperature of 70°C and a rolling speed of 1.
．． 2 m/inch, and by rolling, the length in the roll direction and in the direction perpendicular to this is 2
Rolling was repeated alternately in the direction of the rolls and in the direction perpendicular to this until the size doubled.

Next, this original film stretched to 2×2 times was subjected to simultaneous biaxial stretching using a biaxial stretching machine in the same manner as in Example 1 to obtain a uniform stretched film. Table 3 summarizes the stretching conditions, stretching ratio, and physical properties of the film after stretching.

Note that the stretching ratios in the table are based on the original fabric.

Example 4 The raw sheet obtained in Example 2 was rolled using the same rolling mill used in Example 3 at a roll temperature of 70°C and a rolling speed of 1.2.
Roll rolling was performed in the layer/win to obtain rolled products with stretching ratios of 1X2 times, 1X3 times, and 1.5X2 times.Next, these stretched original fabrics were stretched using a biaxial stretching machine. . As the stretching method at this time, a sequential biaxial stretching method was adopted in which stretching was first carried out in the direction of a low stretching ratio and then stretching was carried out in the direction of a high stretching ratio. Table 4 lists the stretching conditions, stretching ratio, and physical properties of the film after stretching for each rolled product. Note that the stretching ratios in the table are based on the original fabric.

Comparative Example 1 The original fabric stretched 2×2 times by rolling in Example 3 was stretched 100% in one direction at a temperature of 170°C and a stretching speed of 300%/win using the same stretching machine as in the example. A stretched film having a stretching ratio of 2×4 times that of the original film was obtained. The physical properties of this stretched film are shown in Table 5. This comparative example was made based on the example described in Japanese Patent Publication No. 40-21994. The results in Table 5 show that this film is highly oriented in the biaxial direction and is not crystallized, and the obtained physical properties are also at an extremely low level compared to the film of the present invention, i.e., the film of the present invention. For the first time, a polyoxymethylene polymer film having excellent rigidity and dimensional stability was discovered as a biaxially oriented film.

Comparative Example 2 The original fabric stretched 2×2 times by rolling in Example 3 was stretched at a temperature of 173°C and a stretching speed of 3 using the same stretching machine as in the Example.
00%/win, simultaneous biaxial stretching was performed in two directions to obtain a stretched film with a stretching ratio of 3×3 times that of the original film. The physical properties of this stretched film are shown in Table 5. This result shows that although the crystallinity of this film satisfies the requirements of the present invention, sufficient physical properties cannot be obtained due to the low crystal orientation.

Comparative Example 3 The original film stretched to 2×2 times by the pressure operation in Example 2 was further repeated in the same manner to obtain a biaxially oriented film with a stretching ratio of 5×5 times compared to the original film. The physical properties of this oriented film are also shown in Table 5. This result shows that even if the degree of crystal orientation satisfies the requirements of the present invention, a film with a low degree of crystallinity cannot be expected to have sufficient physical properties.

[Effects of the Invention] The polyoxymethylene film of the present invention is highly oriented and crystallized, has high rigidity and high dimensional stability, and can be made extremely thin. Therefore, the film of the present invention:
These properties are used in a wide variety of applications, such as base films for magnetic recording materials such as magnetic tapes and floppy disks, and have great industrial significance.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram showing the direction of the sample for measuring the degree of crystal orientation by X-ray diffraction, Figure 2 is an explanatory diagram showing the method for calculating the degree of crystal orientation, and Figure 3 is an explanatory diagram showing the direction of the sample for measuring the degree of crystal orientation using the X-ray diffraction method. 3 is a graph showing a DSC curve of a measurement example of DSC).

Claims (1)

[Claims] (1) The main part of the main chain is substantially an oxymethylene group -(C
A biaxially oriented film made of a polyoxymethylene polymer composed of repeating units of H_2-O)-, which has a crystallinity of 75 to 85% as measured by the density method and A polyoxymethylene polymer film characterized in that the degree of crystal orientation measured from two directions, end and edge, is 85 to 95%.