JPH0156657B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a polyester film having a large number of irregularities consisting of minute protrusions and depressions on the surface of the film, and an improved technique for manufacturing the same. It is known that when a fine organic or inorganic compound is added to a polyester polymer, protrusions appear on the film surface due to the influence of the fine compound. It is also known that the presence of minute protrusions on a film makes it slippery. A similar lubricity effect can also be achieved by precipitating insoluble catalyst residues in the polyester polymer.
Insoluble catalyst residues have the property of forming fine protrusions on the surface of a polymer film. JP-A-57-66936 discloses a method of forming protrusions and depressions on the film as an improvement on these conventional techniques for making polyester films slippery. While the conventional technique produces only protrusions on the film surface, the improved technique described in this publication has many fine irregularities on the surface, each consisting of protrusions and depressions, and therefore The effective area of contact with other films, etc. is reduced, and the slipperiness is further improved. As specified in the publication, the cause of the formation of depressions in this improved technology is the deformation of voids that tend to occur around fine particles (additives or insoluble catalyst residues) during stretching, and the formation of hollows around fine particles with the fine particles as the center core. It is assumed that the surface caved in, creating a depression. Polyester films are used in various industrial materials including magnetic tapes and capacitors. In particular, for magnetic tape applications, especially video tape applications, an extremely smooth and flat film surface is required in order to improve electromagnetic conversion characteristics. Improvement is also required. The latter property requires the presence of fine protrusions in the film, which often result in a reduction in electromagnetic properties. In contrast to these contradictory surface characteristics of films, the film provided with projections and depressions of the present invention has extremely high slipperiness, and even if the height and number of projections are limited, the film of the prior art will not run as easily. It is excellent in that it surpasses sexuality. The present invention provides a polyester film that has novel surface properties that combine longitudinal (longitudinal) strength, low coefficient of friction, and surface smoothness and flatness required for magnetic tapes. While the conventional film has a low coefficient of friction due to protrusions on its surface, the film of the present invention has protrusions and depressions on the film surface, and these uneven units improve the smoothness and smoothness of the film surface. It satisfies the surface characteristics of a magnetic tape by being sufficiently fine and having an appropriate shape so as not to impair flatness. The present invention provides: 1) A polyester film having a large number of concavo-convex units on the film surface consisting of fine protrusions and depressions surrounding the protrusions, wherein the ratio of the major axis to the minor axis of the depressions is 1:1 to 1:1. 1.8:1 polyester film having a surface roughness in the range of 1.8:1;
Stretching at a stretching ratio of 2.9 times or more and 3.2 times or less at a temperature of ~150°C, and then stretching on a second axis approximately perpendicular to the first axis at a temperature of 3.0 to slightly higher than the stretching temperature in the first axis direction. Stretched at a stretching ratio of 4.5 times, if necessary, subjected to intermediate heat treatment at a temperature range of 140 to 200°C, and further stretched to a stretching ratio of 1.2 to 2.5 times in the first axis direction at a temperature of 120 to 170°C. The film surface is subjected to stretching, and the surface of the film is provided with a large number of uneven units consisting of fine protrusions and depressions around the protrusions, and the ratio of the major axis to the minor axis of the depressions is 1:1 to 1.8:1. Method of manufacturing polyester film in the range. The present invention will be explained. The polyester to which the present invention can be applied is a combination of an aromatic dibasic acid component such as terephthalic acid, isophthalic acid, naphthalene-2,6-dicarboxylic acid, etc. and a glycol component such as ethylene glycol, tetramethylene glycol, neopentyl glycol, etc. A polymer or copolymer obtained by condensation polymerization. Representative polymers include homopolymers such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene-2,6-naphthalene dicarboxylate, partially modified copolymers of these, and polyethylene terephthalate (ethylene terephthalate, polyethylene glycol).
Examples include polymer blends to which block copolymers are added. Of course, fillers, pigment colorants, antioxidants, light stabilizers, etc. can also be added to the polymers and copolymers. Films obtained from these materials are included in the polyester film of the present invention. The protrusions formed on the surface of the film of the present invention are due to the presence of inorganic particles added to the polymer, particles based on insoluble catalyst residues generated during polymerization of the polymer, or particles of both. In the present invention, a depression formed around a protrusion with the protrusion as a core is not a depression formed by a mechanical stamp such as a conventional embossing, but is formed by deformation of the film itself during the process of stretching the film. It is something that occurs. When an unstretched film containing particles is stretched in a uniaxial direction, the polymer is plastically deformed without deforming the particles, so that voids are generated at the boundary between the polymer and the particles during large deformation (stretching). When this film containing voids is then stretched in a direction substantially perpendicular to the uniaxial stretching direction (second axial direction) to form a biaxially oriented film,
The voids generated during the uniaxial stretching are further deformed in the second axial direction, and voids 22 are formed in an elliptical shape around the projections 21 as shown in FIG. 1-1. Furthermore, even if the film is re-stretched in the first axis direction, this void remains in an elliptical shape. In this case, as shown in the cross-sectional view of Figure 1-2, the particles existing in a shallow area near the film surface and the voids around them produce protrusions with the particles as the nucleus, but depressions are formed around the particles. There isn't. In the present invention, the above voids are changed to depressions on the film surface. When unstretched film is uniaxially stretched, the film is preheated to 90°C before stretching.
By setting the temperature to a high temperature of ℃ or higher and the stretching ratio to a low value, the film after the first axial stretching will have voids around the particles (external particles due to the addition of inorganic compounds or internal particles containing insoluble catalyst residues). substantially prevent it from forming. The conditions for the first axial stretching are a temperature of 100 to 150°C, preferably 100 to 120°C, and a stretching ratio of about 3.2 times or less, preferably about 3.0 times or less. The lower limit of the stretching ratio is preferably 2.9 times. When increasing the stretching speed, it is preferable to set a higher stretching temperature. Next, second axis stretching is performed in a direction perpendicular to the first axis.
This second axial stretching is performed by first cooling the uniaxially oriented film below its glass transition point, or by preheating it to a temperature of 100 to 150°C without cooling, and then stretching it again at approximately the same or slightly higher temperature. biaxially
Stretch 3.0 to 4.5 times (preferably 3.2 to 3.8 times).
When the temperature of the second axis stretching is high, the boundaries between the concave portions of the concave and convex units become clear, but at low temperatures, the boundaries are often not clear. The stretching ratio in the second axis direction does not significantly affect the frequency of occurrence of uneven units. If a stretching ratio of 3.8 times or more is selected as the second axis stretching ratio, the mechanical strength in the second axis direction (Young's modulus) will be higher than the mechanical strength in the first axis direction, resulting in a so-called tensilized film. The slipperiness of the film tends to decrease. The biaxially oriented film that has undergone second axial stretching can be heat set (intermediate heat setting) for 0.1 to several seconds at a temperature slightly higher than the second axial stretching temperature. This heat setting relaxes the biaxial orientation and makes re-stretching smoother, but is not essential. This intermediate heat setting temperature is preferably selected to be at least 10°C higher than the second axial stretching temperature in the temperature range of 140 to 200°C, more preferably 140 to 180°C. The biaxially oriented film is stretched again in the first axial direction. This stretching condition is 120 to 170℃ as the stretching temperature.
Select a stretching ratio of 1.2 to 2.5 times, preferably 1.2
Set ~2.0x. By stretching the film in the first axial direction again, a wide range of films can be selected from balanced films to tensilized films. The biaxially stretched film after re-stretching is 180~240℃,
Preferably, heat setting can be performed at a temperature of 190 to 220°C for about 0.2 to 30 seconds. By such a method, the ratio of the major axis to the minor axis of the depression of the present invention is in the range of 1 to 1.8,
A film with a high Young's modulus can be obtained. The film of the present invention has the advantage that the film-to-roll and film-to-film contact area is further reduced by having the protrusions in the recesses and the core portions, thereby increasing the sliding effect. Incidentally, with the recent development of the information industry, there is a demand for thinner films serving as the base of magnetic recording media. The conventional strength of these thin films is insufficient and it is necessary to increase the strength of these thin films. The Young's modulus in the longitudinal direction of a normal biaxially stretched polyester film is around 500 Kg/mm ² , but as a base film aimed at thinning, the Young's modulus in the longitudinal direction is 600 Kg/mm ² or more, preferably 700 Kg/mm ² or more. Something is desired. As a method for producing such a high-strength film, it is known to re-stretch a biaxially stretched film. In the present invention, by re-stretching the film in the longitudinal direction, a film having a Young's modulus in the longitudinal direction of 600 Kg/mm ² or more and a depression having a protrusion at the center of an elliptical shape 24 as shown in FIG. 2-1 is produced. is obtained. The ratio of the major axis to the minor axis of the pseudo-elliptical shape of this depression is in the range of 1.0 to 1.8. The standard deviation of this ratio is about 0.2 for a one-level film. Further, this pseudo-elliptical shape includes an elliptical shape as shown in FIG. 2-1, and a shape in which the elliptical depression 24 is symmetrical about the protrusion 21 as shown in FIG. 2-3. The thus-obtained high-strength film with depressions has a sufficient sliding effect. In addition, in order to obtain a film with high mechanical strength in the longitudinal direction, the first stage may be stretched at a high stretching ratio, but this method tends to cause voids to be formed in the film, and the film provided with the dimples of the present invention It's hard to get. The size of this depression can be determined by depositing a thin layer of aluminum on the surface of the stretched film and using a differential interference microscope (e.g. Nikon differential interference microscope R type, magnification 900x).
can be used to take and observe photographs. The present invention will be specifically explained below using Examples.
The method for measuring physical properties in the present invention is as follows. (1) Measuring method for uneven parts A photograph of a film surface with a thin layer of aluminum vapor deposited is taken using a Nikon differential interference microscope (R type), and its size is measured using a scale. (2) Surface roughness CLA Surface roughness CLA (Center Line
Average) value is measured by the following method. Using a stylus-type surface roughness meter (SURFCOM3B) made by Tokyo Seimitsu Co., Ltd., for example, obtain the film roughness curve of the roughened film under the conditions of a needle radius of 2 μm and a load of 70 mg, and from this, calculate the measurement length. L
(Reference length 2 mm) is extracted, the center line of this extracted portion is the X-ray, the vertical magnification direction is the Y axis, and the roughness curve is expressed as Y=f(x).
The value given by the following formula is expressed in μ. CLA=1/L∫ ^L _O |f(x)|dx This measurement was performed on 8 samples,
Three of the highest values are excluded and the average value of the five values is expressed. Note that the measurement is performed in the vertical direction and the horizontal direction, and the average value of both is used. (3) Young's modulus Cut the film into a sample width of 10 mm and length of 150 mm.
The chuck distance is 100mm, and the pulling speed is 10mm/min.
The material was tensile tested using an Instron-type universal tensile testing device. Young's modulus was calculated from the tangent to the rising part of the obtained load-elongation curve. (4) Coefficient of static friction A fixed glass plate is placed below two stacked films, and the film in contact with the lower stacked glass plate is moved at a constant speed (10 to 15 per minute).
mm), the detection end is fixed to one end of the upper film (in the opposite direction to the direction in which the lower film is taken), and the tensile force between the films is detected. The weight of the thread used for this measurement is 1
Kg, and the area of the lower film is in the range of 10 to 100 ^cm2 . Example 1 Intrinsic viscosity number 0.65 dl/g containing 0.25% by weight of kaolin with an average particle size of 0.6 μm (value measured at 25°C using orthochlorophenol as a solvent)
Polyethylene terephthalate was dried at 160°C for 3 hours, then melt-extruded at 280°C and rapidly solidified on a casting drum kept at 50°C.
An unstretched film of 160 μm was obtained. This was stretched 3.2 times in the machine direction at a film temperature of 100°C, then stretched 3.7 times in the transverse direction at 120°C, and further heat-set at 160°C. Next, re-stretching was continued, and the film was re-stretched 1.8 times in the machine direction at a film temperature of 140°C, and heat-set at 225°C.
The film speed at this time was 22 m/min after the first stage of stretching. Example 2 A film was obtained in the same manner as in Example 1 up to transverse stretching, then longitudinally stretched again by 1.5 times at 140°C, and heat-set at 205°C. Example 3 A film was obtained in the same manner as in Example 1 up to transverse stretching, then longitudinally stretched again by a factor of 1.3 at 140°C, and heat-set at 205°C. Example 4 An unstretched film similar to Example 1 was stretched in the longitudinal direction.
Stretched 2.9 times at 100℃, then 115℃ in the transverse direction
It was stretched 3.7 times and further heat-set at 160°C. Next, it was longitudinally stretched again by 1.5 times in the machine direction and heat-set at 205°C. Example 5 Polyethylene terephthalate was produced by a conventional method using ²⁰⁰ parts of calcium acetate as a transesterification catalyst, 150 parts of lithium acetate as a transesterification catalyst, 450 parts of antimony trioxide as a polymerization catalyst, and 1450 parts of trimethyl phosphate as a stabilizer per 10 6 parts of polyethylene terephthalate. Polymerized. This polymer contained many internally precipitated particles and had an intrinsic viscosity of 0.65 dl/g in an orthochlorophenol solution at 25°C. This polyethylene terephthalate was stretched in two stages as in Example 1, then longitudinally stretched again by 1.6 times at a film temperature of 140°C, and heat-set at 220°C. The film speed after the first stage stretching was 22 m/min. Comparative Example 1 The same unstretched film as in Example 1 was heated to 80°C for 3.3
It was longitudinally stretched twice, then transversely stretched at 100°C and 3.5 times, then heat-set at 170°C, longitudinally stretched again at 150°C and 1.6 times, and then heat-set at 220°C. Comparative Example 2 The same unstretched film as in Example 1 was heated to 3.4°C at 100°C.
After longitudinal stretching, it was stretched horizontally at 120°C and 3.7 times, and then heat-set at 205°C (longitudinal stretching was not performed again). Comparative Example 3 A two-stage stretched film obtained under the same conditions as Example 1 was
It was longitudinally stretched again by 1.2 times at 140°C and heat-set at 225°C. Characteristics of the films obtained in Examples 1 to 5 and Comparative Examples 1 to 3 are displayed.

[Table] These results are summarized as follows. (1) In Examples 1 to 5, the Young's modulus in the longitudinal direction of the film was 600 Kg/mm ² or more, the surface was flat, the coefficient of friction was low, the Young's modulus in the longitudinal direction was high, and the electromagnetic conversion A magnetic tape film with excellent properties and slipperiness was obtained. (2) Comparative Examples 1 to 3 Although Comparative Example 1 has a high Young's modulus in the longitudinal direction, there are almost no depressions on the film surface. This comparative example has a higher coefficient of friction than Examples 1 to 5 despite having a rougher surface, and cannot be said to have a desirable quality. Although Comparative Examples 2 and 3 have depressions on the surface and a low coefficient of friction, their surfaces are rougher than those of Examples 1 to 5, and the Young's modulus in the longitudinal direction is 600 Kg/mm ² The following are unfavorable.
The shape ratio of the major axis and minor axis of the depressions in Comparative Examples 2 and 3 is as follows:
They were high at 3.0 and 2.4, respectively.

[Brief explanation of drawings]

Figure 1 shows the state of voids created around particles when stretched using the conventional method, and Figure 1-1 is a plan view;
1-2 is a cross-sectional view. Figure 2 shows the polyester film of the present invention, which has protrusions containing particles and depressions formed around them. Figures 2-1 and 2-3 are plan views, and Figure 2-2 is a cross-sectional view. be. Figure 3
is a micrograph of the surface of the polyester film of Example 1 of the present invention (magnification: 900 times).

Claims (1)

[Scope of Claims] 1. A polyester film having a large number of concavo-convex units on the film surface consisting of fine protrusions and depressions surrounding the protrusions, wherein the ratio of the major axis to the minor axis of the depressions is 1:1. A polyester film having an uneven surface, characterized in that the ratio is in the range of 1.8:1 to 1.8:1. 2 The polyester film is 100~
Stretched at a temperature of 150°C with a stretching ratio of 2.9 times or more and 3.2 times or less, and then stretched on a second axis approximately perpendicular to the first axis at a temperature of 3.0 to 4.5 at a temperature that is about the same or slightly higher than the stretching temperature in the first axis direction. If necessary, perform intermediate heat treatment at a temperature range of 140 to 200°C, and then re-stretch in the first axis direction at a stretching ratio of 1.2 to 2.5 times at a temperature of 120 to 170°C. The film surface has many uneven units consisting of fine protrusions and depressions around the protrusions, and the ratio of the major axis to the minor axis of the depressions is in the range of 1:1 to 1.8:1. A method for manufacturing polyester film.