JPS58124617A - Polyester film - Google Patents

Abstract

PURPOSE:To provide a polyester film having multiple protruded points and multiple uneven units, each is composed of one of said points as its nucleus and a recess substantially in oval form, on its surface, of which surface is flat and friction coefficient is low, which is useful for the preparation of a magnetic tape excellent in operability, wear resistibility and durability. CONSTITUTION:After polyester such as polyethylene terephthalate, etc. containing clay, etc. is melted and extruded, it is caused to solidify by cooling it rapidly, and the film thus obtained is elongated horizontally and then vertically by heating it through a preheating roller and multiple protruded points 21 and uneven units, each is composed of one of those points as its nucleus and a recess 24, are formed on the surface of the film and by this method, an intended polyester film 23 is obtained. The longer diameter of this recess 24 along the longitudinal direction of the film is 2-50mu and the following relations exist between the longer diameter D(mu) and the frequency of occurrence of uneven unit, N(pcs/ mm.<2>), 200<=N<3,500 for 2<=D<5, 150<=N<2,000 for 5<=D<10, 50<=N<800 for 10<=D<30, and 0<=N<5 for 30<=D<50.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a polyester film having a flat surface and a low coefficient of friction.

Polyester films have a variety of uses, including magnetic tape applications and electrical applications. For tape applications, particularly video tape applications, a smooth film surface is required to improve electromagnetic conversion characteristics, and it is also necessary to improve the tape's runnability on decks, corrosion resistance, and durability. Therefore, a low coefficient of friction is required.

Conventionally, as a technology to reduce the coefficient of friction of film,
There is a known method for imparting irregularities to the six sides of a film by forming into a film a polymer to which inorganic particles have been added or a polymer in which insoluble catalyst residue particles have been formed.

This means provides protrusions on the film surface to reduce the contact area between the film and the object with which the skeleton film comes into contact, thereby reducing frictional resistance. All of these methods actively create protrusions on the surface of the film, and it is effective to create a large number of high protrusions on the film surface in order to reduce the coefficient of friction. However, in this case, although the coefficient of friction can be lowered as the number of tall projections increases, when magnetic coating is applied, the influence of the projections also appears on the coated surface, which tends to deteriorate the electromagnetic conversion characteristics.

As a result of extensive research into a base film that has excellent electromagnetic conversion characteristics and is suitable for slippery magnetic tapes with a low film friction coefficient, the present inventor has developed a polyester film having convex portions and concave portions on the surface thereof. The present invention was achieved based on the finding that this problem can be solved by forming a large number of fine uneven units and giving directionality to the wrinkle uneven units.

That is, the present invention provides a polyester film having a large number of uneven units consisting of protrusions and depressions with wrinkle protrusions as cores on the surface of the film, where the # depressions are formed in an elliptical shape around the protrusions, and the # depressions are formed in an elliptical shape around the protrusions. The long axis is from 2 microns to 50 microns, and the wrinkles are caused by inert inorganic compounds (additives) or catalyst residues present inside the film, and the long axis of the # depression is in the longitudinal direction (machine direction) of the film. This is an easily slippery polyester film having the uneven units along the surface.

The present invention is established. Conventional technology uses inert inorganic compounds 41 to obtain slippery films! (Example ★ means silica, clay,
Whereas protrusions (projections) are formed on the film surface by adding titania (11) or organic compounds (e.g. quasi-calcium terephthalate, high melting point polyester) or (and) using catalyst residues, the present invention The feature is that a pseudo-elliptical uneven unit consisting of a convex portion and a concave portion is formed in the film, and the major axis of this pseudo-ellipse is oriented in the longitudinal direction of the film. The film having protrusions and depressions as in the present invention has the advantage that the coefficient of friction is significantly lower and the slipping effect is increased compared to films that have only protrusions on the surface and cannot be obtained using conventional techniques. .

Polyesters to which the present invention can be applied include terephthalic acid,
It refers to a polymer or copolymer obtained by condensation polymerization of an aromatic dibasic acid such as isophthalene WI or naphthalene-2,6-dicalphone with a glycol such as ethylene glycol, tetramethylene glycol, or neopentyl glycol. Typical of these polymers are polyethylene terephthalate and polybutylene terephthalate.

Homoprimers such as polyethylene-2,6-naphthalene dicarboxylate, partially modified copolymers thereof,
Polyethylene Tele 7 Crate K [Engineering←Lentele 7 Talate/Polyethylene Glyfur] An example is a polymer blend in which a block copolymer is added.8 Of course, polymers and copolymers can be used as fillers, S colorants, and antioxidants. , a light stabilizer, etc. can also be added. Films obtained from these materials are included in the polyester film of the present invention.

The protrusions formed on the film surface of the present invention are due to the presence of particles of an inorganic compound added to the polymer; particles based on insoluble catalyst residues generated during polymerization of the polymer; or particles of both.

The pot formed around the protrusion according to the present invention is not a concave shape created by a conventional embossing mechanical stamp, but a concave shape created by the process of V-stretching the film.
- This is caused by the deformation of the film itself.

When an unstretched film containing particles is stretched in the width direction,
Since the polymer undergoes plastic deformation without deforming the particles, voids are created at the boundary between the polymer and the particles during large deformations (Ishin). When this film containing voids is then stretched in a direction approximately unilateral to the first axis stretching direction (machine direction) to form a biaxially oriented film, the voids that were generated during the second axis stretching are further deformed in the machine direction. , as shown in FIG. 1-11C (a void 22 is formed around the protrusion 21 in the shape of a dormitory. In this case, as shown in the cross-sectional view of FIG. The voids result in protrusions centered around the particles, but do not form depressions around the particles.

In the present invention, the above-mentioned voids are converted into depressions on the film surface. When stretching an unstretched film uniaxially (in the width direction), the film is preheated before stretching. By setting the magnification to a high degree or (and) by setting the earth magnification to a low value, the film after the first axial stretching has substantially no voids around the particles (external particles due to inorganic additives or internal particles containing protection residues). to prevent it from forming. Next, when the stretched film in this state is stretched in the machine direction, depressed portions (depressions) of the film with particles as cores are formed along the longitudinal direction.

The major axis of the elliptical depression is along the longitudinal direction.

Even if slight voids are formed around the grains during the helix-axis stretching, depressions are formed with these grains as cores.

The surface of the film after biaxial stretching is in a state as shown in Figure 2-1 (top view), and if the stretching conditions are such that stress is concentrated around the grains during the second axial stretching, the depressed portions will show the degree of stress concentration. There is a tendency for the groove to become deeply recessed and for the major axis to increase along the second axis direction. FIG. 2-2 (cross-sectional view) shows a cross section of the film near the surface, and the protrusions 21 containing particles and the depressions 24 formed around the protrusions 21 of the polyester film 2
VC occurs.

In the present invention, the depressions formed around the protrusions include those in the shape of a pseudo-finger circle that is eccentric in the direction of the biaxial axis.

In this case, if the long axis of the depression is referred to as the long culm, the long axis of the depression needs to have at least two directions from the viewpoint of improving the footability of the magnetic tape and improving the electromagnetic conversion characteristics.

Furthermore, if the major axis of the depression exceeds 50 μm, the drooping of the magnetic tape increases, making it undesirable as a base film for a magnetic tape.

According to the present invention, the long diameter D (μm) of the depression of the uneven unit on the surface of the polyester film and the occurrence frequency N (number/−) of the uneven unit are determined.
), 200≦N<3500°5 of 25D<5
5D<10 150SN<2000゜10≦
D<30 50≦N< 800゜30≦
When D<50 and the relationship 0≦N≦5, the material exhibits favorable slipperiness and has excellent magnetic conversion properties.

More preferably, when 2≦D<5, 350@N<2500°5
When ≦D<10 250≦N<1500゜10≦
According to the present invention, when D<30, to (1, N<500. and when 30≦D<50, 0<N≦3, the base film has excellent runnability and electromagnetic properties. It is understood that the depressions on the film surface reduce the frictional resistance by reducing the contact area.

The reason for the direction of Kubo is not clear, but II!
In relation to the frictional resistance with the tc metal pin, the frictional resistance is low when the longitudinal direction of the depression roughly matches the longitudinal direction of the film.

The concavo-convex unit in the present invention consists of one protrusion and a depression around the protrusion. The frequency of occurrence of the uneven unit size 9 can be controlled by the type of particles, the amount present in the polymer 2 and the stretching conditions of the film.

A specific method for producing the polyester film of the present invention will be explained. The average particle diameter of kaolin, silica, etc. is O, OS ~
When stretching an unstretched polyester film containing 0.01 to 2.0% by weight of fine particles of 5μ* (preferably 0.1 to 2.5μm) in the hexagonal direction,
Preheat to ℃. This unstretched film is about 90 to 12
When preheating to 0° C., a hard chromium-plated sole with a capped surface or a ceramic roll is preferable. The unstretched film can reach a predetermined preheating temperature without sticking to the roll surface (2) and without substantial crystallization. Of course, the unstretched film can be preheated in a non-contact manner.

The unstretched film is flame stretched at a temperature of 90 DEG to 135 DEG C. at a rotational stretching ratio of 3.5 times or less (preferably 2.6 to 3.4 times).

Next, the second stretching is carried out by cooling the m-oriented film to a temperature below the glass transition point or without cooling it to a temperature of 100 to 15
Preheat to the temperature of G'C, and further heat the temperature by 3.0 to 4.0 times (preferably 3.0 times) in the second axis direction at approximately the same temperature.
2 to 3.8 times). When the temperature of the second stretching is high, the boundary between the recessed portions of the concavo-convex units becomes clear, but at a low temperature, the boundary is often not clear. The stretching ratio in the second axis direction does not significantly affect the occurrence of uneven units s#L. However, if 3.8 times or more is selected as the second elongation magnification, 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 the so-called tensilization F.
It becomes a film, and the slipperiness of the film tends to decrease.

In the present invention, it is most preferable that the direction in which the first-axis stretching is performed is approximately perpendicular to the longitudinal direction of the film, and the direction in which the second-axis stretching is performed is in the longitudinal direction of the film. However, it is permissible to stretch at a low magnification in a direction different from the above-mentioned stretching direction before and after the second axial stretching and after the two-wheel stretching as long as the direction of the depressions is not disturbed.

The stretching conditions for the film to form such surface depressions are as follows:
This is because the film tends to have a relatively flat and smooth surface, resulting in improved electromagnetic characteristics as a magnetic tape.

That is, the polyester film of the present invention has the ability to be used as a base film for a magnetic tape, and does not cause dropouts or color noise even when a magnetic recording layer is provided because the film surface is relatively flat. Since the periphery of the protrusion has a depression, the contact area of the tape with the magnetic head, guide roll, and other film gradually decreases.Moreover, the major axis of the depression runs along the longitudinal direction of the film, which is perpendicular to the axial direction of the guide roll. Since it corresponds to the direction,
This has the advantage of further increasing the slipping effect. These smooth sliding effects cannot be obtained with a film having only ordinary protrusions, or a pseudo-digital shape in which the major axis of the recess runs along the width direction of the film even if it has concavo-convex units.

The method for measuring physical properties in the present invention is as follows.

(1) Measurement method for uneven parts: A film with a thin layer of aluminum vapor deposited on the film surface is photographed using a differential interference III calligraphy device (for example, a N1Kon differential interference microscope R11), and its size is measured on a scale. IIl is determined.

(2) Surface roughness CLA Surface roughness CLA (Cenlier Lin) referred to in the present invention
The value is measured by the following method.

Using a stylus-type surface roughness needle (8URFCOM 3B) manufactured by Tokyo Seimitsu Co., Ltd., for example, obtain a film roughness curve for the roughened film under the conditions of a needle radius of 2μ and a load of 70 da. When a part of measurement length L (reference length 2■) is extracted from K, the center line of this extracted part is X@, and 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-f t(x) dX O This measurement is performed on 8 samples, 3 are excluded from the large value, and the average value of 5 is expressed. Note that measurements are made in the vertical and horizontal directions, and the average value of both is used.

18-8 stainless steel SUE 3 with an outer diameter of 5 tll (at a room temperature of 25°C and an atmosphere of 60% relative latitude as shown in Figure 3)
A film cut into a 1/2 inch width was brought into contact with a fixed rod of No. 04 (upper surface roughness CLA = 0.030) at a winding angle of π radian, and moved and rubbed at a speed of 3.3 α/load. Adjust the tension controller 2 so that the inlet tension 〒1 (detected by inlet tension detection #!5) is 30.9.
The dynamic friction coefficient μk is calculated from the output tension Ttg (detected by the exit tension detector lO) using the following equation. In the present invention, the dynamic friction coefficient when running at 90 Wl is defined as μ.

Chroma 8/N magnetically coated tape is determined by the following method.

Lo to 50% white level signal using a commercially available home VTR
The signal on which the o% chroma level signal was superimposed was recorded, and the reproduced signal was filtered using a Shibaku Noise Meter 9250.
Determine. Note that the definition of chroma S/N is as follows according to Shibak's definition.

9 Rq 8/N = 20 log “”” (d
B) EN (rms) However, ES (p-p) = 0.7x4 V (p-p)E
N (rma) = AM noise effective value voltage (V) Also, the magnetic powder coating is prepared by the following method.

The magnetic powder coating shown below was applied using a gravure roll, and the magnetic coating layer was smoothed using a doctor knife to form a magnetic layer with a thickness of approximately 5 μm. While the magnetic paint is still dry, it is magnetically oriented by a conventional method and then introduced into an oven for dry curing. Further, the coated surface is calendered to create a tape having a uniform width of 1/2 inch.

Number of magnetic paints γ-Fe Snow Os powder 101001 ki parts Esletsukum (manufactured by Kensui Kagaku Co., Ltd., vinyl chloride/vinyl acetate copolymer) 16 Hiker 1432 J (manufactured by Nippon Zeon Co., Ltd., butadiene 7 nitrile copolymer) 11 〃Lecithin l 〃Carbon
8 〃 MEK 100 #MIBK
100 N Additive (lubricant, silicone resin) 0.15 # The present invention will be explained in more detail with reference to Examples below.

Examples 1 to 4 Tsubaki containing 0.24% clay with an average particle size of 0.7 μm and a limiting viscosity number of 0.62 dt/g (Ortsuk p-
Polyethylene terephthalate (measured at 35°C using phenol as a solvent) was dried at 160°C, melt-extruded at 280°C, and rapidly solidified on a casting drum held in SO'CK.
The same unstretched film was obtained.

Subsequently, this unstretched film was preheated to 80° C. with two preheating rollers, and then subjected to one step of stretching in the transverse direction by a conventional method while being heated with an infrared heater. Furthermore, this uniaxial stretched film was again preheated to 90°C with two preheating rollers, then stretched vertically to 3.3 times between two rollers while being heated with an infrared heater, and then heated to 190°C. Heat treatment was performed.

Here, the conditions of the infrared heater during horizontal stretching and the stretching ratio were changed to obtain films as shown in ***Stretching Table I.

The depressions present on the surface of the film of Example J were in the shape of a pseudo-finger circle with a major axis along the longitudinal direction of the film, that is, along the longitudinal direction of the film, as shown in FIG.

Comparative Examples 1 to 4 160μ obtained from the same raw materials and the same method as Examples 1 to 4
After preheating the unstretched film of 50 m to 80° C. using two preheating rollers, it was stretched one step in the longitudinal direction by a conventional method while heating with an infrared heater. This film was then stretched 3.3 times in the transverse direction at a temperature of 120°C, and then heat-treated at 190°C.

Films were formed by changing the heating φ of the infrared heater during longitudinal stretching and the stretching ratio to obtain films as shown in Table 3.

The depressions present on the surface of these films were pseudo-digital in shape, with the major axis extending in a direction approximately perpendicular to the longitudinal direction of the film, that is, along the horizontal direction.

Comparing Table I and Shishi ■, it can be seen that the type in Table ■ has a lower coefficient of friction against metal.

The chroma S/N standard is based on Example 4.

Comparative Example 5 An unstretched film of 210μ obtained using the same raw materials and the same method as Examples 1 to 4 was preheated to 80°C with two preheating rollers, and then heated to 90°C with an infrared heater. However, one step of stretching was carried out in the longitudinal direction by a factor of 3.6 using a conventional method.

Further, this film was stretched 3.9 times in the transverse direction at a temperature of 105°C, and then heat treated at +90'c.

On the surface of this film, there are no depressions as in Examples 1 to 4, but only convex protrusions, and there are approximately circular voids around the additive particles as shown in Figure 1. Met.

The surface roughness CLA of this film is 0.035μ Kai, which means that the surface is rougher than Examples 1 to 4, but the friction coefficient μ is 0.
．． 42, which was considerably higher than Examples 1-4.

Comparative Example 6 An unstretched film with a 310 μ blade obtained using the same raw materials and the same method as Examples 1 to 4 was preheated to 80°C with two preheating rollers, and then heated to 90°C with an infrared heater. Then, one step of stretching was carried out in the longitudinal direction by a factor of 3.0 using a conventional method of 1r.

Further, this film was stretched 3.4 times in the transverse direction at a temperature of 105°C, then further preheated to 80°C with two rollers, and then stretched 2 times in the machine direction while being heated to 100°C with an infrared heater. It was stretched 0 times and then heat treated at 190°C.

There are no depressions recognized in the present invention on the surface of this film, and there are mostly only convex protrusions, and around the additive particles there is a pseudo-digital shape in the longitudinal direction of the film with the additive particles as the center. Therefore, the shape of the protrusions on the surface of the film formed a convex portion having directionality along the longitudinal direction of the film.

The surface roughness of this film is CLA = 0.029μ, and when compared with Examples 1 to 4, the surface is rough, but the coefficient of friction is 0.4
4, which was considerably higher than Examples 1-4.

Comparative Examples 7-9 Examples! ~ 4, and the preheating stretching temperature at the time of stretching (stretching ratio 9
The outside was subjected to HM under the conditions of 1- and the results shown in Table 3 were obtained.

Compared to Examples 1 to 4, the friction coefficient and/or p-ma S/N
was found to be inferior.

[Brief explanation of the drawing]

FIG. 1 shows the state of voids created around particles when stretched by the conventional method, FIG. 1-1 is a plan view, and gill-2 is a cross-sectional view. FIG. 2 shows a polyester film of the present invention, in which projections containing particles and depressions are formed around the projections, FIG. 2-1 is a plan view, and FIG. 2-2 is a cross-sectional view. FIG. 3 is a schematic diagram of a tape pace inspection machine that measures the coefficient of dynamic friction μk of a rough film surface. FIG. 4 is a photograph of the surface of the polyester film according to the second example of the present invention (magnification: 900 times). Patent Applicant Teijin Limited Agent Patent Attorney Former 1) Jun Hiroshi 103

Claims (1)

[Scope of Claims] A polyester film in which a large number of uneven units consisting of protrusions and depressions having wrinkle protrusions as cores are formed on the film surface, and the depressions have eight major axes in the longitudinal direction of the film. It is pseudo-elliptical, and the major axis of the depression is in the range of 2 microns to 5 Gμ, and the distance K is between the major axis D (μ) and the frequency of occurrence N (number/-) of the unevenness unit. . When 2≦D<5, 200≦)! When <3500°5≦D<10 15G≦N<2000°10≦
When D<10 50≦N<800°30≦D≦S
A polyester film whose qlill is such that the relationship 0≦N≦5 is satisfied when O.