JPS63191616A - Polyoxymethylene biaxially drawn sheet of film - Google Patents

Abstract

PURPOSE:To improve mechanical strength, thermal expansion coefficient and dimensional stability by adjusting density, degree of crystalline orientation and heat shrinking stress of a polyoxymethylene biaxially drawn sheet or film in a specific range. CONSTITUTION:A sheet or a film characterized by that it is composed of a polyoxymethylene whose main constituting unit is oxymethylene group-(CH2O)- and that the degree of crystallinity measured by means of density measurement is in the range of 55-75%, the both degrees of crystallinity measured from end and edge in two directions by means of X-ray diffractometry are in the range of 70-95%, and the heat shrinking stress at 130 deg.C is in the range of 5-100kg/cm<2>, has excellent mechanical properties such as tensile strength, tensile modulus and so on, and a low thermal expansion coefficient whose value in the range of 0-60 deg.C is -10X10<-6>-10X10<-6> cm/cm/ deg.C. It is more preferrable that the degree of crystallinity is 60-75%, the degree of crystalline orientation is 75-95% and the heat shrinking stress (130 deg.C) is 15-100kg/cm<2>. In this case, it is possible to obtain a sheet or a film having more balanced characteristics.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention is characterized in that the main structural unit is an oxymethylene group
-)- It relates to a biaxially oriented sheet or film formed from polyoxymethylene, more specifically, a polyoxymethylene biaxial sheet or film that has excellent mechanical strength, a small coefficient of thermal expansion, and excellent dimensional stability. It relates to stretched sheets or films.

(Prior art and its problems) Polyoxymethylene sheets or films are generally formed by melt pressing or melt extrusion followed by rapid cooling, but sheets or films obtained by these methods are
It is opaque or translucent and has poor mechanical properties. Biaxial stretching technology is being developed to improve these properties, but polyoxymethylene is difficult to handle due to its high crystallinity compared to other resins.
It has not yet been put to practical use industrially. Biaxial stretching of polyoxymethylene is disclosed in Japanese Patent Publication No. 40-21994 and Japanese Patent Application Laid-Open No. 61-252135. Japanese Patent Publication No. 40-21994 discloses a method of improving transparency and mechanical properties by stretching after rolling, and Japanese Patent Publication No. 61-252135 discloses a highly stretched polyoxymethylene film. ing.

It has been found that mechanical strengths such as tensile modulus and tensile strength can be significantly improved by these known techniques.

However, in order to use it as a film for magnetic recording media such as magnetic disks, in addition to mechanical properties, an even better and smaller coefficient of thermal expansion is required.

(Means and effects for solving the problem) In view of these facts, the present inventors have developed a polyoxymethylene biaxially stretched sheet or film that has excellent mechanical strength, a small coefficient of thermal expansion, and excellent dimensional stability. As a result of extensive research, we discovered that polyoxymethylene biaxially stretched sheets and films whose density, degree of crystal orientation, and heat shrinkage stress are adjusted to specific ranges have extremely good properties, and thus completed the present invention. did.

That is, the present invention consists of polyoxymethylene whose main structural unit is an oxymethylene group (100H2o-), has a crystallinity of 55 to 75% as measured by the density method, and has a crystallinity of 55 to 75% as determined by the X-ray diffraction method. Provided is a polyoxymethylene biaxially stretched sheet or film characterized by having a degree of crystal orientation measured from two directions of 70 to 95% and a heat shrinkage stress of 5 to 100 kg/cIjt2 at 130°C.

The polyoxymethylene sheet or film of the present invention includes:
Relatively high molecular weight, e.g. number average molecular weight of 35,000~
300,000 polyoxymethylene can be used. Furthermore, the main part of the main button is substantially oxymethylene groups, such as an acetal of polyoxymethylene, a reaction product thereof with incyanate, or a copolymer obtained by combining a small amount of a sixth component, for example. Polyoxymethylene composed of repeating units of (CH2O)- may also be used.

As a method for producing the polyoxymethylene biaxially stretched sheet or film of the present invention, known techniques such as roll tenter biaxial stretching, pantograph or tubular biaxial stretching, press biaxial stretching, etc. can be used.

When using press biaxial stretching, pressurize the unstretched polyoxymethylene sheet or film at a stretching temperature of 80 to 170°C and an area base yarn ratio of 2 to 50 times.
Accordingly, a sheet or film stretched in two axial directions can be obtained. Further, the sheet or Fi film obtained here may be heat treated at a temperature of 150 to 180°C, if necessary.

A polyoxymethylene biaxially stretched sheet or film with a degree of crystallinity exceeding 75% obtained by a known biaxial stretching technique other than press biaxial stretching is stretched at a temperature of 100 to 175°C.
You may further press 2111I in the 1c2 axial direction within the range of 2 to 40 times the area base height, and in addition to this, 150 to 40 times the height.
Heat treatment may be performed at a temperature of 180°C.

The polyoxymethylene biaxially stretched sheet or film obtained by the above production method has a degree of crystallinity of 55 to 75%, a degree of crystal orientation of 70 to 95%, and a heat shrinkage stress (160°C) of 5.
~100kl? /c! A sheet or film having the characteristics of IL2 has excellent mechanical properties such as tensile strength and tensile elasticity, and has a thermal expansion coefficient of 110X10-6 to 10X10 in the range of 0 to 60°C. −'α
It has a low coefficient of thermal expansion in the range of /an/°C. More preferably, the degree of crystallinity is 60 to 75%, the degree of crystal orientation is 75 to 95%, and the heat shrinkage stress (160°C) is 15 to 75%.
100 kg/cIrL2, and in this case, it is possible to obtain an excellent sheet or film in which the above properties are more balanced.

Also, the range of thermal expansion coefficient is 0 to 10 x 100-6a/c
To achieve rrv'°C, it is preferable to set the crystallinity, crystal orientation, and heat shrinkage stress within the range of the present invention, and set the stretching or heat treatment conditions to tp.

It is believed that the mechanical and thermal properties of polyoxymethylene sheets or films are characterized by the degree of orientation of the crystalline and amorphous portions of the polymer. That is, the crystal part,
By limiting the orientation ratio of the amorphous portion to a specific range, excellent mechanical and thermal properties can be exhibited. The present invention has found such a specific range.

That is, the ratio of the crystalline part to the amorphous part is characterized by the degree of crystallinity, the orientation ratio of the crystal part is characterized by the degree of crystal orientation, and the orientation ratio of the amorphous part is characterized by the heat shrinkage stress.

Biaxial stretching in the present invention refers to uniform stretching in two axial directions, but the stretching ratio and heat shrinkage stress in the two axial directions do not necessarily have to be the same, and a certain degree of anisotropy is required. may have. It also includes multiaxial stretching. That is, what is considered to be substantially biaxial stretching is included in the present invention.

The degree of crystallinity, degree of crystal orientation, and heat shrinkage stress in the present invention will be described below, including the method for measuring them.

Crystallinity: 26 by a solution consisting of normal heptane/carbon tetrachloride
The density (a) of the film was measured by the density gradient piping method at °C, and the crystallinity (D)'! Calculated as follows.

Here da is 1.506 f! /cc is the theoretical density of a completely crystallized polymer, and da is 1°25,9
/CO, which is the density of the fully amorphous polymer.

Crystal orientation degree End (E!nd) direction of the film shown in Figure 1 1
Alternatively, if Xi is incident from the edge direction 2, the polyoxymethylene (100)it(2θ-22°
~26.5°) is determined from the intensity distribution when scanning in the azimuth direction.

The end direction 1 of the film is parallel to the film surface and the machine direction (extrusion direction) of the film.
The edge direction 2 refers to a direction parallel to the film surface and also parallel to the width direction of the film.

For each sample, the thickness is 211% with the stretching direction aligned.
A rectangular molded product having a width of 1stms and a length of 10 inches was produced.

Cyanoacrylate adhesive was used to fix each film during molding. Next, this molded product was placed on the Shimadzu Imperial Universal Sample Stand (rotating sample stand) with the edge of the film (Kdg
It was installed so that X-rays could enter from the e) or end direction.

The X-ray generator uses Shimadzu Yosakusho #XD-3A type device.
3 Q KV -28mA with N1 filtered O
u-Kα ray? It was used as an XM source. The goniometer used was the same type #VG-108R manufactured by Shimadzu Kyosakusho, and was attached to the rotating sample stand. The slit thread is receiving slit (Receiving slit) 2txD, scattering pot slit (Scattering 5l)
it) 1 m 93'jr was adopted. Next, the diffraction angle was set to the (100) plane of polyoxymethylene (2θ-22° to 2
6.5°) and set the X1iiiit edge (Edge
) direction and En)-” (In, d) direction, the rotating sample stage was rotated at a rotation speed of 4°/min, and the diffraction intensity of the (100) plane was scanned in the azimuth direction. Chart speed is 10 m/
It was min. One of the results obtained by this measurement
An example 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 90°, the peak intensity factor is determined from the background r, and then the width (half width) W of the peak, which is intensity factor/2, is determined. Note that the background is determined prior to measurement. Next, the degree of crystal orientation A was calculated using the following formula.

A test piece with a length of 70 θm and @I Dtyi was attached to a support with a span interval of 50 m connected to a stress strain meter and a structure that could be immersed in a 130° OK silicone oil tank, and immersed in the silicone oil tank. , the shrinkage stress generated when the test piece was heated was measured. The stress generated at this time usually reaches an equilibrium value within a short time of 10 seconds after immersion, but for those that do not reach an equilibrium value within this time,
The value after 10 seconds was defined as the heat shrinkage stress.

Thermal expansion coefficient: A test piece with a length of 20xx and a width of 3111 was attached to a TMA-10 type thermal expansion coefficient measuring machine manufactured by Seiko Electronics Industries @), and was measured at a heating rate of 10°C/min. 6
The coefficient of thermal expansion ft in the range of 0°C was calculated.

(Examples) Next, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

Examples 1-6 ? with a number average molecular weight of about 63,000? Lioxymethylene is extruded through a slit die at a temperature of 200°C and a temperature of 160° is OK.
Rapidly cooled on a heated casting roll to a thickness of 600mm.
An original sheet of μ was obtained. The crystallinity of this fabric was 71% as determined by the density method. Next, this raw fabric f 5 Q ton
It was stretched using a press biaxial stretching machine at a stretching temperature of 150°C. The results are shown in Table 1. In the same table, each area times tA
Tensile physical properties results of stretched film at K and crystallinity,
The degree of crystal orientation, heat shrinkage stress at 130°C, and coefficient of thermal expansion are shown. In addition, the values for the original fabric are also listed in the same table for comparison.

Example 4 The stretched film obtained in Example 3 was subjected to constant length heat treatment at 170° C./1 m1n after identifying its vertical and horizontal dimensions. The physical properties of this film are also listed in Table 1.

From the results in the same table, it can be seen that the film of the present invention has excellent mechanical properties, a small coefficient of thermal expansion, and good dimensional stability.

(Effect of the invention) As explained above, the present invention provides oxymethylene 2
Axially stretched sheets or films have excellent mechanical properties, a small coefficient of thermal expansion, and good dimensional stability.
It can be used as a recording material for reef air discs, an optoelectronic material, a transparent FJA electrode material, etc. In addition to these applications, it can also be used for applications that require low strength, low coefficient of thermal expansion, and dimensional stability. For example, it has excellent effects in that it can be used in a wide range of fields, such as lamb skin used in musical instruments.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the direction of a sample for measuring the degree of crystal orientation by X-ray diffraction, and FIG. 2 is an explanatory diagram showing the method for calculating the degree of crystal orientation. Applicant: Asahi Kasei Kogyo Co., Ltd. (Figure 1, Figure 2)

Claims (1)

[Claims] The main structural unit is oxymethylene group -(CH_2O)-
It consists of polyoxymethylene, and the degree of crystallinity measured by the density method is 55 to 75%, and the degree of crystal orientation measured from the two directions of the end and edge by the X-ray diffraction method is both 70 to 95. %, a polyoxymethylene biaxially stretched sheet or film characterized by a heat shrinkage stress of 5 to 100 kg/cm^2 at 130°C.