JPS61167531A - Polyester film for magnetic sheet - Google Patents

Abstract

PURPOSE:To obtain the titled film which is superior in flat and easily sliding properties, by a method wherein a difference between a shrinkage factor in a longitudinal direction and that in a widthward direction at a nonreversible process under specific terms satisfies a specific expression, in the film wherein R to be obtained through polarized light and fluorescent strength of a polyester film is shown by a specific expression. CONSTITUTION:A polyester raw material containing particles is dried by a conventional device, melted and extruded through an extruding machine and unoriented polyester sheet is molded by cooling and curing. The same is oriented in a longitudinal direction and after orientation further in the longitudinal direction the same is oriented in a crosswise direction in the next place, reoriented longitudinally so that 0.95<=R(45 deg.)<=1.05 is given again in the longitudinal direction and then fixed thermally according to necessity. Then calendering treatment is applied to said film for 72hr under terms of the temperature of 53 deg.C and the humidity of 90% and a target film whose difference between a shrinkage factor alphaMD in the longitudinal direction and that alphaTD in a widthward direction at a nonreversible process is shown by an expression is obtained. EFFECT:The titled sheet is superior in anisotropy within the surface, the anisotropy within the surface of a dimensional variation at a nonreversible process and flat and easily sliding properties.

Description

[Detailed description of the invention] The present invention has excellent flat smoothness and small in-plane optical anisotropy, and at the same time, the in-plane anisotropy of the film due to dimensional changes due to severe thermal treatment is small. The present invention relates to a biaxially oriented polyester film suitable for magnetic sheet films such as small floppy disks and electrophotographic base films.

Biaxially oriented polyester films are used in various industrial applications due to their excellent properties, and are particularly useful as base films for magnetic sheets for floppy disks and electrophotography.

The first condition for magnetic sheets used in magnetic disks and electrophotography is to be flat and smooth, but due to the demand for higher densities, properties related to dimensional changes such as linear expansion coefficient, humidity expansion coefficient, and thermal contraction rate are changing. , it is desired that the film be oriented in the same direction in all directions within the plane of the film. If these properties are not in the same direction, the track position will deviate from the head position under different environments, making recording and playback impossible. Therefore, a problem arises in that the track density cannot be increased.

Until now, films that meet these properties have been characterized by small in-plane birefringence anisotropy of biaxially stretched polyester films before coating with a magnetic layer, and in-plane dimensional changes due to irreversible changes after harsh moist heat treatment. It has been proposed to provide a film with small anisotropy (Japanese Patent Application Laid-Open No. 139131/1983).
issue).

The above-mentioned film was effective in the magnetic tape production process without a calendering process, but in the case of magnetic sheets for floppy disks, electrophotography, etc. that require a calendering process, before the magnetic layer is coated, It is true that the in-plane anisotropy is good, but since non-recurrence processes such as moist heat treatment are performed after the magnetic layer is applied and the product is made, the anisotropy of the in-plane dimensional change that accompanies this process is extremely large. Therefore, it did not contribute to higher density.

Here, irreversible dimensional change is assumed to be the harshest use, storage and transportation environment for magnetic disks and magnetic sheets for electrophotography, such as when subjected to moist heat treatment at 53°C, 190% humidity, and 72 hours. This is the expansion and contraction of the film seen in later films.

The present inventor has discovered that the film has excellent smoothness when flattened, and the anisotropy of the in-plane orientation after forming into a magnetic sheet and the anisotropy of the in-plane shrinkage rate upon irreversible change. As a result of intensive studies to obtain a film with a small The present invention was achieved based on the new knowledge that shows changes.

In other words, the present invention is a film in which R(45''), which is determined from the polarized fluorescence intensity of a polyester film, satisfies the formula 0, and the longitudinal direction of the film after being treated for 72 hours at 53°C and 90% humidity in an irreversible process. Shrinkage rate (payment M
D) and a polyester film for magnetic sheets where the difference in shrinkage rate (cATo) in the width direction satisfies the formula 0, 0.95≦R (45°)≦1.05...■Payment rD
d'=MO≧15(P)・・・■ and its manufacturing method.

Here, R (45°) is the value from the polarized fluorescence intensity of the polyester film, and "l-1c)" and "P" are the irreversible values of the film after being processed for 72 hours at 53°C and 90% humidity. These are the shrinkage rate in the longitudinal direction and the shrinkage rate in the width direction during the process.

The polyester referred to in the present invention refers to aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, and naphthalene-2,6-dicarboxylic acid or esters thereof, and diols such as ethylene glycol, diethylene glycol, tetramethylene glycol, and neopentyl glycol. It is a polymer that can be obtained by polycondensation.

The polyester can be obtained by direct polycondensation of aromatic dicarboxylic acid and glycol, or can be obtained by single polycondensation after transesterification of aromatic dicarboxylic acid dialkyl ester and glycol, or by monopolycondensation of aromatic dicarboxylic acid dialkyl ester and glycol, or by polycondensation of aromatic dicarboxylic acid dialkyl ester and glycol. It can also be obtained by methods such as polycondensation of esters.

Typical examples of such polymers include polyethylene terephthalate and polyethylene-2,6 naphthalene dicarpoxylate.

The polymer may be a non-copolymerized homopolymer, and up to 15 mol% of the dicarboxylic acid component is a non-aromatic dicarboxylic acid component, and/or up to 15 mol% of the diol component, as long as its properties are not impaired. It may be a copolymerized polyester in which is a diol component other than aliphatic glycol. In particular, it is preferable to copolymerize a polyalkylene glycol such as polyethylene glycol or polytetramethylene glycol as a diol component that improves adhesiveness with the magnetic layer.

Furthermore, it may be a polymer blend of the polyester and another polymer, and examples of blendable polymers include polyamide, polyolefin, and other types of polyesters (including polycarbonate).

The polyester film of the present invention must have an R(45°) value of 95≦R(45°)≦1.05, which is determined from the polarized fluorescence intensity of the film after biaxial stretching and heat setting. The value of R (45°) is an index related to the temperature-humidity expansion coefficient and does not change before and after calendering, so it is sufficient that it is satisfied in the film before calendering (condition 1).On the other hand, irreversible change The in-plane anisotropy of the dimensional change due to the calendering process shows an extremely large change before and after the calendering process. For example, when a film without in-plane anisotropy in dimensional changes due to irreversible changes in the film before calendering is calendered, the anisotropy increases to a greater or lesser extent, although the amount of change varies depending on the calendering conditions. In other words, the dimensions in the irreversible process in the longitudinal direction show contraction, whereas the dimensions in the irreversible process in the width direction expand, resulting in extremely large in-plane anisotropy. Although the reason for this appearance is not clear, it is probably because tension is applied in the longitudinal direction at a high temperature close to or higher than the Tg of the film during calendering, causing the film to shrink in the longitudinal direction after processing.

By the way, in the irreversible dimensional change of the film before calendering, the dimensional change in the width direction shows shrinkage, and by producing a film whose shrinkage in the width direction is larger than that in the longitudinal direction, the non-reversible process of the film after calendering can be improved. It was found that the in-plane anisotropy of the dimensional change during the reversible process can be suppressed to a low level. The degree of shrinkage in the longitudinal and width directions of the film before calendering varies depending on the calendering conditions and cannot be absolutely determined, but the in-plane anisotropy of the film due to dimensional changes due to severe thermal treatment is In order to obtain a film with low elasticity, at least the difference between the shrinkage rate in the width direction (tightness TD) and the shrinkage rate in the longitudinal direction (penetration 0) in the irreversible process defined below, cl = 0 - weighted PID. is 1
It is necessary to have 5P or more (condition 2).

The film of the present invention is a film that simultaneously satisfies Conditions 1 and 2 described above.9 Films that satisfy Conditions 1 and 2 individually have been known, but no film that satisfies them at the same time has been known. For example, in order to obtain a film that satisfies condition 1, it is sufficient to balance the longitudinal and lateral stretching, but it is often not possible to obtain a film that satisfies condition 2 with such a film. On the other hand, if, for example, the width is increased during heat setting or the lateral stretching ratio is increased in order to satisfy condition 2, the anisotropy of the in-plane refractive index increases, and condition 1 is no longer satisfied.

Hereinafter, a method for producing a film of the present invention that satisfies Conditions 1 and 2 will be described.

The polyester raw material containing the particles is dried by a conventional method, melt-extruded through an extruder, and cooled and solidified on a rotating cooling drum to form an unstretched polyester sheet. The unstretched film thus obtained was first
Stretched at a temperature of ℃ to 130℃ so that Δn becomes 0.015 to 0.055, and further stretched 1.1 to 2.0 times in the longitudinal direction at a temperature range of 90℃ to 150℃. The birefringence Δn after stretching is set to 0.085 or less, preferably 0.060 or less, and then stretched 3 to 4.5 times in the transverse direction, and again in the longitudinal direction 0.95≦R (45°)≦ The film is longitudinally stretched again by 1.05 to 1.5 times at 120° C. to 200° C. so that the film has a diameter of 1.05, and heat setting is performed as necessary. In addition, in the longitudinal stretching again, after stretching to R (45°)>1°05, further in the transverse direction at 15.0°C to 210°C, 0.95≦R(45°)
It is also preferable to re-transversely stretch the film by 1.05 to 1.5 times so that ≦1.05.

In the stretching recipe, it is important that the first stage longitudinal stretching temperature be at or above super draw. By performing such stretching, the shrinkage rate in the longitudinal direction after heat setting can be lowered.

Furthermore, in order to improve the smoothness of the finished magnetic sheet when it is flattened, the length of the protrusions and the major axis of the protrusions must be at least 0.
Film surface area of a concavo-convex unit consisting of a depression of 5 Pm 1
It is preferable that the film has a number A per mm2 (numbers/mm2) of 0≦A≦5000.If the number is 5000 or more, it is not preferable because it has excellent flatness but poor slipperiness.

In order to obtain such a film (: a CO3+
A1203 g BaSO4 (') average particle size 0.
It is obtained by forming a film of polyester containing 0.01 to 1.5% of added particles of 1 to 10P or particles precipitated by transesterification catalyst residue under the above-mentioned stretching conditions, where A is the particle amount and the transverse stretching. It depends on the birefringence Δn after the previous longitudinal stretching.

Furthermore, it has been found that when drawing at or above the super draw of the present invention, the higher the viscosity, the higher the drawing ratio when obtaining the same Δn. In other words, since the overall stretching ratio in the radial contraction direction where the film viscosity is high is improved, productivity can be improved and costs can be reduced. Therefore, in the stretching of the present invention, the higher the film viscosity, the better, and it is 0.60 or more, preferably 0.63 or more.

A1 Jisu 1 fruit Above 1, the film of the present invention is a floppy disk.

In-plane anisotropy occurs in films that require high density magnetic sheets for calendar processing, such as electrophotography.

This film has excellent in-plane anisotropy of dimensional changes during irreversible processes and smooth flatness.

EXAMPLES The present invention will be explained in more detail with reference to Examples below, but it goes without saying that the present invention is not limited to these Examples.

The evaluation method for each physical property of the film is shown below.

(1) Birefringence Retardation was measured using a polarizing microscope manufactured by Carl Zeiss, and birefringence (Δn) was determined using the following formula.

Δn=R However, R: Retardation d: Film thickness 2) Coefficient of friction (,”) A film is brought into contact with a fixed hard chrome-plated metal roll (diameter 6 mm) at a winding angle of 135° (θ), 53
A load of g (T2) was applied to one end and the vehicle was run at a speed of 1 m/min, the resistance force (T+ (g)) at the other end was measured, and the coefficient of friction during running was determined using the following equation.

,,,=1/ρ l n (T+ /T2)=0.4
24 in (T+ 153) (3) Center line average surface roughness Ra) It was determined as follows using a surface roughness meter (SE-3FK) manufactured by Koita Research Institute. The tip radius of the stylus was 2 Pm, and the load was 30 mg. A section of standard length L (2.5 mm) is extracted from the film cross-sectional curve in the direction of its center line, and the roughness curve y=f( x) When expressed as f, the value given by the following formula is expressed in %m. However, the cutoff value is 80
It is Pm. For Ra, the average value of a total of 10 points, 5 points in the vertical direction and 5 points in the horizontal direction, was determined.

(4) Number of uneven units (propellers) with depressions around the protrusions (A) The surface of the aluminum-deposited film was photographed at a magnification of 750 times using a Carl Zeiss differential interference microscope. 1 total 1 m
The major axis of the protrusion per m2 film surface area is at least 0.5. - Number A of uneven units consisting of m depressions (pieces/m
m2) was counted.

(5) R (45°) A film sample was immersed in a water bath containing a fluorescent agent, air-dried, and the JASCO fJiF M-1 polarized fluorescence intensity was determined using the sample. demand.

1 (0°): Vertical polarized fluorescence intensity ■ (90°)
: Polarized fluorescence intensity I in the longitudinal direction and perpendicular direction (45°): Polarized fluorescence intensity in the longitudinal direction and the 45° direction (6) Film viscosity 200 mg of sample was mixed with phenol/tetrachloroethane = 5
The mixture was added to 20 ml of a mixed solution of 0150 and heated to dissolve at about 110° C. for 1 hour, and then measured at 30° C.

(7) Heat treatment and dimensional change measurement method after treatment Cut out a sample 10 mm wide and 50 mm long (811 direction) along the measurement direction, cut it in half along the longitudinal direction, and heat one half at 53°C. Place the free end in an oven adjusted to 90 parts humidity. The untreated sample and the treated sample were placed in close contact with each other, and the deviation at both ends was read using a microscope. Measurements were made every 10 degrees over 180 degrees within the film plane, and the absolute value of the difference between the maximum and minimum deviation values was expressed as a percentage of the original length (50 mm), and was taken as the in-plane dimensional change rate of the film.

In addition, extension was expressed as a minus sign, and contraction was expressed as a plus sign. In this example, the direction in which the maximum and minimum dimensional changes were obtained coincided with the longitudinal or lateral direction of the film for all samples.

(8) Linear expansion coefficient Constant load elongation measuring device manufactured by Japan Automatic Control Co., Ltd. (Model/TL
2), a tension of 27 g/mm2 was applied to a sample film with a width of 12.7 mm and a length of 250 mm (measurement direction), and the temperature was raised at a rate of 15°C/min.
Two points at ~50°C were connected with a straight line, and the slope was determined.

Drift Goto (Production method of polyester) 100 parts of dimethyl terephthalate, 70 parts of ethylene glycol, 0.10 parts of calcium acetate hydrate, and 0.17 parts of lithium acetate dihydrate were charged into a reactor, and the temperature was raised while heating. Methanol was distilled off to perform a transesterification reaction, and it took about 4 hours after the start of the reaction to reach 230°C.
The transesterification reaction was substantially completed.

Next, add 0.35% of triethyl phosphate to this reaction product.
of antimony dioxide as a polycondensation catalyst.
．． After adding 05 parts, polymerization was carried out according to a conventional method to obtain a polyester. The polyester contains particles with a particle size of approximately 0.5 to
A large number of precipitated particles containing calcium, lithium, and phosphorus elements were observed to be as uniform as IP. The polyester A had a weight ratio of 0.65.

Separately, polyester B ((yJ) = 0.65) containing almost no such internal precipitated particles is produced and mixed with the previous polyester at a ratio of A/B = 1/1 (weight ratio). It was used as a raw material for membranes.

(Film forming method) The above raw material was dried by a conventional method, extruded into a sheet form from an extruder at 285°C, and rapidly cooled to form an amorphous sheet.

The amorphous sheet was stretched 3.6 times in the longitudinal direction at 110°C and Δ
After setting the ntt to 0.040, it was further heated at 90°C in the longitudinal direction for 1.
It was stretched 45 times. The thus obtained film was stretched in the transverse direction by a tenter at 100° C. by a factor of 4.3 and heat-set at 207° C. to obtain the film 15)-. Film viscosity is 0.6
It was 3. A magnetic layer was applied to the film in a conventional manner, and 1
Seven-stage calender treatment was performed at 10° C. and a linear pressure of 300 Kg/cm to form a magnetic sheet. Table 1 shows the properties of the film before applying the magnetic layer and the magnetic sheet after calendaring.

Comparative Examples 1 and 2 Films were formed and evaluated in the same manner as in Example 1, except that the longitudinal stretching ratio in the second stage was 1.3 times and 1.55 times.

Since the film of Comparative Example 1 has a lower orientation in the longitudinal direction than in the lateral direction, R (45°) is 0.95 or less. Comparative example 2
The film has a higher orientation in the longitudinal direction than in the lateral direction, so R
(45°) is as high as 1.20, and the difference in shrinkage rate in the horizontal and vertical directions is small.

Comparative Example 3 3.75 at 85°C using the same unstretched sheet as in Example 1
Double longitudinal stretching, then 3.8x stretching in the transverse direction at 100°C, 4.
The film was stretched 3 times and heat-set at 207°C to obtain the film 15)-, and the same evaluation as in Example 1 was performed.

The film is R (45°) with balanced vertical and horizontal orientation.
is between 0.95 and 1.05, but since the shrinkage rate in the longitudinal direction is high, the difference in shrinkage rates in the transverse direction and the longitudinal direction is small.

Example 2 Using an amorphous sheet similar to Example 1, 3.
After stretching 0 times and setting Δn to 0.025, it was stretched to 1.0 times at ioo°C.
The longitudinally stretched film thus obtained was then stretched 4.2 times in the transverse direction at 140°C with a stenter, heat treated at 140°C, and stretched 1.25 times at 150°C. Stretch longitudinally and heat set at 207°C to obtain 1
A 5P film was obtained. The same evaluation as in Example 1 was performed on this film.

Example 3 In Example 2, the transverse stretching ratio was set to 3.8 times, and at the end of heat setting, the film was expanded by 0.3% in the width direction and longitudinally relaxed by 0.2% in the machine direction, and 15 films were obtained and evaluated. did.

Comparative Example 4 The same unstretched film as in Example 1 was first heated at 85°C for 2.4
After double longitudinal stretching and setting Δn to 0.040, 1.
After stretching 25 times and longitudinally stretching, Δn is set to 0°065, and then 1
Transversely stretched 3.9 times at 40°C and heat-set at 207°C 15. I
- films were obtained and evaluated.

The film has a low longitudinal orientation and an R (45°) of 0.9.
Not only is it smaller than 5, but the vertical shrinkage rate is high, so 6e1)
'Mp is also a small film.

Comparative Example 5 The transversely stretched film of Comparative Example 4 was further longitudinally stretched by 1.2 times and then heat-set at 207°C. 15. -obtain a film of
evaluated.

Since the film was longitudinally stretched again from Comparative Example 4, it had an R(45
°) is between 0.95 and 1.05, but this is because the shrinkage rate in the vertical direction is higher than that of Comparative Example 4.
HO has become even smaller.

These results are shown in Table 1.

From the results in Table 1, R (45°) and Bear. It can be seen that only the films whose bare MCI satisfies the provisions of the claims of the present invention have extremely good magnetic sheet properties, in-plane dimensional change rate, and the difference between the maximum and minimum values of the coefficient of linear expansion.

Claims (1)

[Claims] (1) In a film in which R (45°) determined from the polarized fluorescence intensity of the polyester film satisfies the formula [1], 5
The shrinkage rate in the longitudinal direction (α_M_D
) and shrinkage rate (α_T_D) in the width direction that satisfy two formulas. 0.95≦R(45°)≦1.05...[1]α_T
_D-α_M_D≧15(μ)... [2] (2) Number A of uneven units per 1 mm^2 film surface area consisting of a protrusion and a depression with a major axis of at least 0 and 5 mm centered on the protrusion The polyester film for a magnetic sheet according to claim 1, which has excellent flat lubricity and has a polyester film/mm^2) in the range of formula 3 below. 0≦A≦5000...[3] (3) Polyester unstretched film at 100°C or higher13
Birefringence Δn is 0.015 to 0.05 at a temperature below 0°C
Stretched in the longitudinal direction so that the
Stretched again in the longitudinal direction by 1.1 to 2.0 times in the temperature range of 50 ° C., the birefringence index before and after the longitudinal stretching is 0.085 or less, then stretched in the transverse direction, and as necessary. The following [[
1] and [2] A method for producing a polyester film for a magnetic sheet that satisfies formulas. 0.95≦R(45°)≦1.05...[1] α_T
_D−α_M_D≧15(μ)...[2] (However,
R (45°) is the value from the polarized fluorescence intensity of the polyester film, and α_M_D and α_T_D are each 5
These are the shrinkage percentage in the longitudinal direction and the shrinkage percentage in the width direction in the irreversible process of the film after processing for 72 hours at 3° C. and 90% humidity. )