JPS58168526A - Polyester film with near infrared ray absorbing property - Google Patents

Abstract

PURPOSE:To obtain the titled film used in magnetic disc or the like by a process wherein said light screening film with omnidirectional homogeneous solid state property is provided with near infrared ray absorption property and the difference between the surface roughness of the front and back sides of said film is eliminated and further its linear expansion coefficient due to temperature or humidity is made small. CONSTITUTION:Polyester such as polyethylene terephthalate or the like is added with pigment such as carbon black or the like and thoroughly kneaded and, after that, molten at an extrusion former. Next, the polyester is orientated longitudinally at the temperature of 95-100 deg.C and, after that, further orientated crosswise under the condition so as to give said orientated polyester film the same degree of orientation as that given in the longitudinal orientation. Furthermore, the crosswise orientated film is cooled below the transition point of glass and then heat-treated under the state being kept stretched, resulting in obtaining the desired biaxially orientated film, which has the absorptivity of near infrared rays, the wave lengths of which are 800-900mmu, of more than 90%, the difference between the central line mean roughnesses of the front and the back sides of the film of less than 0.005mu and yet the isotropy index of the film plane formulated in the formula (where A represents the maximum value of linear expansion coefficient due to temperature or humidity and B represents the minimum value at the time when A is employed as the maximum value) of within 10%.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a biaxially oriented thermoplastic polyester film having near-infrared absorption ability.

More specifically, the present invention provides an isotropic balanced film in which there is almost no difference in roughness between the front and back surfaces of the film, and the film is oriented approximately equally in any direction on the plane of the film. This invention relates to a polyester film endowed with near-infrared absorbing properties.

BACKGROUND OF THE INVENTION Biaxially oriented polyester films are used in a variety of industrial applications. Among these applications, for magnetic disks and masking for copying, it is desirable that the film have the same and uniform physical properties in all directions; for example, it is desirable that the film has anisotropic thermal expansion coefficient, humidity expansion coefficient, and thermal contraction coefficient It is preferable that there is no such thing. Furthermore, in magnetic disks, it is necessary to provide the film itself with light-shielding properties so that the light does not leak except through the index hole. However, a film that satisfies all of these quality requirements has not yet been obtained.

As a result of intensive research to obtain a light-shielding film with substantially homogeneous physical properties in all directions, the inventors of the present invention discovered that it absorbs near-infrared rays, and there is virtually no difference between the front and back sides regarding unevenness on the film surface. The inventors have discovered that a film that is free from temperature and humidity and has a small difference in expansion coefficient with respect to temperature or humidity is the most suitable film for magnetic disks, etc., and has thus arrived at the present invention.
Ta.

That is, the present invention has an absorption coefficient of near infrared rays of 800 to 900 mμ of 90 coefficient or more, and a center line average roughness of JIS BO60.
1-1976) is less than 0.005μ, and the maximum and minimum values of the coefficient of temperature expansion and the coefficient of humidity expansion in all directions at any position on the plane of the film are medium. It is a thermoplastic biaxially oriented near-infrared absorbing polyester film that satisfies the indicators.

The present invention will be explained.

As the thermoplastic polyester film, polyethylene terephthalate, polybutylene terephthalate, polyethylene-2,6-naphthalene dicarboxylate, etc. can be used. In addition, copolymerized polyesters are also included, and the above-mentioned polynisder includes those to which 15% by weight or less of organic or inorganic compounds or other polymers are added.

When using the film of the present invention for e&ki discs, it is important that near-infrared rays do not pass through areas other than the index holes, and when measured with a visible/infrared spectrometer, the near-infrared absorption rate is 800 to 900 mμ. It is best if the light intensity is within 90%.

It is even better if this absorption rate is 93% or more. As a means of obtaining such characteristics, it is common to add pigments with low brightness to the film, such as carbon black and iron oxide pigments.

It is obtained by mixing molybdenum disulfide or the like with raw polyester and extruding it. Near-infrared absorption varies depending on the thickness, so thicker films require less cooling. An appropriate near-infrared absorption rate can be selected by trial and error.

The fewer the surface protrusions of the film, the better, and the smaller the difference in roughness between the front and back surfaces, the better. In the present invention, the center line average roughness is expressed as JIS BO601-19.
According to the measurement method described in 76. For example, a stylus type surface roughness meter (SURFCOM 3 B) manufactured by Tokyo Seimitsu Co., Ltd.
), draw a chart of the film surface roughness curve under the conditions of a needle tip radius of 2μ and a load of 70 da, and extract a part of measurement length L (o, 2s dragon) in the direction of its center line. When the center line of the part is the X axis, the direction perpendicular to the X axis is the Y axis, and the roughness curve is expressed as Y = f(X), the roughness average Y is 5- Also, the center line average roughness RCLA It can be displayed with .

This measurement was performed on 8 samples, and the average value of the 5 Oki 1 constant values, excluding the 3 largest measured values, was used as the RC.
Let's call it LA.

In the present invention, the center line average roughness of the front and back surfaces of the film in which pigments are mixed or which has been subjected to stretching heat treatment is 0.005 μm or more, more preferably 0.003 μm.
Make it as follows.

To achieve this condition, it is necessary to sufficiently cross-wire the polyester containing pigment, and to heat and cool the front and back surfaces of the film to substantially the same temperature during the film-forming and stretching heat treatment. It is. Further, it is advantageous to use fine particles of the pigment to obtain a film with few surface protrusions.

6- From this point of view, it is preferable to use a filter with an average opening of about 15 to 30 μm when melt-extruding polyester containing a pigment. Here, the average mouth opening is the pressure I in the region where the air pressure is constant with respect to the air flow condition when the filter is submerged in ethanol and bubbles are generated through compressed air.
This refers to the case where the following relationship holds true between and mouth opening (d).

r where r: surface tension of ethanol h: depth of filter in ethanol po: viscosity of air p: viscosity of ethanol y: gravitational acceleration When the opening exceeds 30μ, coarse particles will mix into polyester, Differences in the protrusions on the front and back sides of the film tend to occur. In addition, if apertures smaller than 15μ are selected, the service life will be shortened due to clogging of the filter, which is inconvenient.There are many methods for reducing the temperature difference between the front and back sides of the film during stretching of 3° film. It is also effective to provide a preheating roll and arrange it so that the front and back sides are in contact with the roll surface alternately.

Materials used as magnetic disks or copy masking must have a uniform expansion coefficient with respect to temperature and humidity. In particular, it is essential that the thermal shrinkage rate is low in absolute value and has no directionality. To obtain such a film, the tenth step is to reduce the difference in physical properties in the width direction during production.

For example, when stretching in the longitudinal direction, in the case of polyethylene terephthalate, selecting a stretching temperature of 95 to 100°C can reduce differences in physical properties. In films that absorb near-infrared rays, such as the film of the present invention, so
Longitudinal stretching can be achieved in a suitable manner by heating the stretched section using an infrared heater with a surface temperature above o'c.

As is well known, when the surface temperature of a heating element becomes high (the wavelength of the radiant energy peak becomes shorter and shifts from far infrared to near infrared to visible range), most thermoplastic polyesters live in the visible range.・It transmits light in the near-infrared region.Therefore, even if the surface temperature of the infrared heater is raised, the thermal efficiency tends to decrease.However, the film of the present invention has good near-infrared and visible heat absorption. Therefore, rapid heating with an infrared heater is possible, the drawn wire is stabilized, and the stretched portion can be limited to a narrow range, so the subsequent stretchability in the width direction is not impaired, and roll heating, etc. When the film temperature is raised, the adhesiveness between the roll and the film may cause uneven thickness, the drawing line tends to move easily, width fluctuations occur, and process stability is often poor.

As mentioned above, when stretching a film that has been stretched in the longitudinal direction at a relatively high temperature in the width direction, the temperature conditions are set so that the degree of orientation is approximately the same as in the longitudinal direction.

Select the stretching ratio. Measurement of temperature expansion coefficient or humidity expansion coefficient is effective as an index of the degree of orientation. When the degree of orientation is biased in one direction, the coefficient of linear (temperature) expansion in the direction 9- where the degree of orientation is high decreases, and the coefficient of linear expansion in the direction orthogonal thereto increases. It is important to adjust the difference between the maximum and minimum values of these coefficients of linear expansion at each position of the film in each direction so that the maximum value (divided by the direction) is within 10%.

This adjustment is performed by measuring the temperature expansion coefficient (humidity expansion coefficient, R3 refraction index) in each direction of the film while appropriately changing the stretching ratio and stretching temperature in the longitudinal direction and width direction, and setting the film to suitable conditions. Complete by doing. Note that in order to obtain a film with little difference in expansion coefficient in each direction, it is not sufficient to have the same degree of orientation in the longitudinal direction and in the width direction; it is necessary to reduce the difference in physical properties in the width direction. . As a means for this purpose, there is a method in which the temperature of the film after stretching in the width direction is once cooled to below the glass transition point and then a tension heat treatment is performed, or a method in which the film is subjected to a tension heat treatment at a relatively low temperature of 100°C to 150'C and then passed through a denter. Furthermore, it is possible to select a means for heat treatment using a heating roll.

In the film stretched in the longitudinal direction, in the width direction of the film
10- Draw a virtual straight line and stretch it in the horizontal (width) direction,
Furthermore, when a tension heat treatment is applied, the above-mentioned imaginary curve tends to bend and exhibit so-called bowing. With this invention (sai,
By reducing this bowing, a film with small differences in physical properties in the width direction can be obtained. As mentioned above, if the stretching temperature is set higher than the stretching temperature in the longitudinal direction, the bowing will be reduced or it will be relatively easy to obtain the film of the present invention.

In addition, physical properties (refractive index, shrinkage rate, temperature expansion coefficient.

Since it is complicated to measure the humidity expansion coefficient, etc.) at every position and in every direction, it is actually difficult to measure the humidity at several locations along the width of the film, including near the center and near both ends. By measuring 6 to 12 points at intervals of 15 to 30 degrees as representative values for each orientation, the differences in physical properties can be generally estimated. Even if the isotropy index is ≦10 near the center, there is a tendency for it to increase to a single subdivision as it shifts to both sides.

The film of the present invention has extremely small differences in physical properties on the front and back sides of the film, in its position, and in its direction. Therefore, for film applications that require isotropy,
It is preferably used for those with near-infrared absorption ability. A typical application for this is magnetic disks, which are characterized by excellent performance and high dimensional stability even under environmental changes.

Next, it will be further explained by examples.

[Example 1] Polyethylene terephthalate chips without carbon black and 4-layer carbon black.

The amount of carphone black that is mixed with polyethylene terephthalate chips containing polyethylene terephthalate and tarnished throughout is 0.5% by weight.
The mixture was kneaded and melted using an extruder, and then extruded through a T-die while filtering through Nijin's IOC grade (average mesh size 25 μm) filter, and formed into a film on the surface of a quenching drum. The film was heated with a preheat roll at 75°C, and between this roll and another roll with a different circumferential speed, the film was rapidly heated from solid to self with a silicon carbide heating element heated to a surface temperature of 1000°C, increasing the temperature by 3.6 times. The film was stretched in the longitudinal direction at a stretching ratio of , and then stretched 3.9 times in the width direction at a temperature of 105° C. to obtain a biaxially stretched film of 75 μm. Afterwards, the surface temperature of the film immediately after width stretching was cooled down to -80℃ by blowing cold air [7. Next, it was heat treated in an atmosphere of 230℃, and then brought to an atmosphere of 215℃ and tensed by 10% in the width direction. Stretched, heat treated, and subjected to relaxation heat treatment in an atmosphere of 100°C to obtain a biaxially stretched film, which was further run on three rolls at a relatively low tension while being reheated to 130°C. The sample was cooled to near room temperature and wound up to provide a sample for an example. The resulting physical property values were as shown.

[Comparative Example 1] A 75μ biaxially stretched film was obtained in the same manner as in Example 1 except that the surface temperature of the infrared heater was 750°C and the longitudinal stretching ratio was 3.4 times. Ta.

[Comparative Example 2] In Example 1, 0.3% by weight of fine silica powder (average particle size 1.θμ) was added without intertwining carbon black, and Nijin Co., Ltd. 15G filter (average mesh size 4) was added.
7 in the same manner as in Example 1 except that 0/I) was used.
A 5μ biaxially stretched film was obtained. A comparison of these physical properties is shown in the table below.

The near-infrared (800 to 900 mμ) absorption rates of the films of Example 1 and Comparative Example 1.2 were both 95 cm.

14- The film of Example 1 of the present invention had a small isotropy index of 4%, had almost no difference in texture between the front and back sides, and was found to be of high quality as a magnetic disk.

15- Procedural amendment dated November g, 1981 Mr. Commissioner of the Patent Office 1, Indication of the case Patent Application No. 1987-50976 2, Name of the invention Near-infrared absorbing polyester film 3 Person making the amendment Relationship with the case Special ♂ [Applicant 1-11 Minamihonmachi, Higashi-ku, Osaka (300) Teijin Ltd. Representative Tomio Toku +11 Mei 11IfI9II, page 6, line 1O, ``
"Average roughness" is corrected as 1 minus the difference in average roughness of 1. −(2
1, page 7, line 12, "viscosity of air" is corrected to "density of the liquid used in the manometer."

(3) Same, same page, line 13, correct "viscosity of ethanol" to "density of 1 ethanol".

(4) Same, page 9, line 11, “Between film”
is corrected to ``1 film''.

(5) Same, 12th Tei, line 14, “Evening falls on the whole.”
is corrected to "account for the whole."

that's all 2-

Claims (1)

[Claims] Absorption rate of near infrared rays of 800 to 900 mμ is 90 chi or more,
A biaxially oriented near-infrared absorbing polyester film having a difference in centerline average roughness between the front and back surfaces of o, o o sμ or less and an isotropy index of the film plane within 10%. Here,
The isotropic index (I) is when there is a direction showing the maximum value (5) of the temperature expansion coefficient or humidity expansion coefficient and a direction showing the minimum value CB+ of the temperature expansion coefficient or humidity expansion coefficient in the film plane, -B ■=-X100 (%).