JPH0670146B2 - Polyester film - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a polyester film, and more particularly to a polyester film having a flat surface and excellent slipperiness and abrasion resistance.

2. Description of the Related Art Polyester films have various applications such as magnetic tape applications and electrical applications. In magnetic tape applications, especially video tape applications, a smooth film surface is required to improve electromagnetic conversion characteristics, and friction to improve tape running, abrasion resistance and durability on the deck. A low coefficient is required.

Conventionally, as a technique to reduce the friction coefficient of the film,
There is known a means for forming protrusions on the surface of a film by molding a polymer to which inorganic particles are added or a polymer in which insoluble catalyst residue particles are produced in the polymer into a film.

This means reduces the frictional resistance by reducing the contact area between the film and the object with which the film contacts by providing a projection on the film surface. All of these methods positively form convex portions on the surface of the film, and it is effective to generate a large number of high protrusions on the surface of the film in order to reduce the friction coefficient. However, in this case, although the friction coefficient can be lowered as the number of high protrusions increases, the influence of the protrusions also appears on the coating surface when magnetically coating, and the electromagnetic conversion characteristics are likely to deteriorate.

Therefore, for example, in JP-A-57-66936, 57-167216, etc., it has been proposed to form a large number of fine concave-convex units having convex portions and concave portions on the surface of a polyester film. However, although this means is effective in reducing the friction coefficient of the film, it has not yet been sufficiently effective in improving the wear resistance.

SUMMARY OF THE INVENTION In view of the above situation, the inventors of the present invention have earnestly studied a film having a flat film surface, slipperiness, and excellent wear resistance, and as a result, found that a large number of irregularities of a specific shape were formed on the film surface. The inventors have found that the problem can be solved and arrived at the present invention.

An object of the present invention is to provide a polyester film which has a flat surface and is excellent in slipperiness and abrasion resistance, and particularly useful for a magnetic recording medium.

According to the present invention, the object of the present invention is to provide anisotropic protrusions on the surface of the film, which are caused by fine fibrous substances, and dents adjacent to the minor axis of the protrusions and having a major axis of at least 2μ. irregularity units consisting of is achieved by a polyester film, characterized by being formed 400 / mm ² or more.

The polyester referred to in the present invention may be any polyester as long as it can form a biaxially oriented film, for example, polyethylene terephthalate, polytetramethylene terephthalate, polyethylene-p-oxybenzoate, poly-1,4-cyclohexene. Examples include cilendimethylene terephthalate and polyethylene-2,6-naphthalene dicarboxylate. Of course, these polyesters may be homopolyesters or copolyesters, and examples of the copolymer component include diethylene glycol, neopentyl glycol, polyalkylene glycol (for example, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, etc.). ) And other diol components, adipic acid, sebacic acid, phthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, 5-sodium sulfoisophthalic acid and other dicarboxylic acid components; an amount range in which the polymer remains substantially linear Examples thereof include polyfunctional carboxylic acid components such as trimellitic acid and pyromellitic acid. The copolyester may be a random copolymer or a block copolymer.

If necessary, the polyester may contain additives such as pigments, dyes, ultraviolet absorbers, heat stabilizers, antioxidants, and light stabilizers.

The fibrous substance referred to in the present invention is not particularly limited as long as it is insoluble in polyester and does not substantially deform during melting and stretching of the polyester, and may be an organic substance or an inorganic substance. Specific examples of fibrous substances include potassium titanate, calcium carbonate, offretite / erionite type zeolite, halloysite, attapulgite, iron oxide,
Preferable examples include silicon nitride, alumina, titanium dioxide and the like, and particularly preferable examples include potassium titanate, calcium carbonate, offretite / erionite type zeolite, halloysite, iron oxide and the like. These are the availability
It is preferable from the viewpoint of dispersibility in polyester.

The fibrous substance is a fine substance, and it is preferable that the shape has an average fiber diameter (d) of 0.5 μ or less, an average fiber length (l) of 5 μ or less, and l / d of 3 to 10. . The lower limit of the average fiber length is preferably 0.1 μ. The addition amount of the fibrous substance is the following formula (1) 0.005 ≦ d × l × w ≦ 1 with respect to the polyester (1) where, d: average fiber diameter of the fibrous substance (μ) l: fibrous It is preferable to satisfy the average fiber length (μ) w of the substance: the addition amount (% by weight) of the fibrous substance. A more preferable amount of addition is in a range that satisfies the condition of the following formula (2).

0.006 ≦ d × l × w ≦ 0.5 (2) [However, d, l, w are the same as defined above] If the fibrous substance is less than 3 in l / d, for example, spherical or lumpy particles The obtained polyester film is not preferable in abrasion resistance and transparency, and when l / d exceeds 10, the abrasion resistance of the film is insufficient, which is not preferable. Further, if the average fiber diameter exceeds 0.5μ, the unevenness of the film surface becomes too large, and the electromagnetic conversion specification deteriorates in applications such as magnetic tape, and if the average fiber length exceeds 5μ, the orientation in the plane direction during stretching of the film. Becomes difficult,
It is not preferable because the film tends to be broken before reaching a desired draw ratio, and the unevenness of the film surface becomes too large, which deteriorates the electromagnetic conversion characteristics. Also, the value of (d × l × w) is 0.
When it is less than 005, the slipperiness of the polyester film is insufficient, and the effect of improving the abrasion resistance is also insufficient. On the other hand, when the value of (d × l × w) exceeds 1, the effect of imparting slipperiness and There is no further improvement in wear resistance,
On the contrary, the electromagnetic conversion characteristics are deteriorated, which causes adverse effects such as a shortened filter life during film formation, which is not preferable.

The method of incorporating the fine fibrous substance into the polyester may be performed at any time by any method, but it is preferable to add it as a glycol slurry before the polymerization reaction of the polyester reaction, particularly before the completion of transesterification or esterification reaction. .

The polyester film of the present invention is produced using polyester containing a fine fibrous substance. The film has an anisotropic projection on the surface thereof, which is caused by the fibrous substance, and a major axis of at least 2 which is adjacent to the short axis of the projection.
400 or more concave / convex units composed of μ depressions / mm ² are formed. This depression is not a concave shape formed by a conventional mechanical stamp such as embossing, but is generated by the deformation of the film itself in the process of stretching the film.

Generally, when an unstretched film containing particles is stretched uniaxially, the particles are not deformed and the polymer is plastically deformed, so that voids occur at the boundary between the polymer and the particles during large deformation (stretching). When the film containing the 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. , As shown in Figure 1-1,
A void 22 is formed in a pseudo circular shape around the protrusion 21. In this case, as shown in the cross-sectional view of FIG. 1-2, the particles existing in the shallow portion near the film surface and the voids around the particles bring about protrusions having the particles as cores, but form cavities around the particles. There is no such thing.

The depression in the present invention can be said to be a depression (deformation) of at least a part of the void portion. When axially stretching the unstretched polyester film containing fine fibrous material in the machine axial direction, preheating of the film before stretching is set to a high temperature or (and) a low stretching ratio. , So that voids are not substantially formed around the fibrous substance of the film that has been uniaxially stretched. Since the fibrous substance has the property of aligning in the flow direction by the force when the molten polymer is extruded from the die, the fibrous substance in the unstretched film usually has its fiber length direction (long axis direction) It exists almost parallel to the machine axis direction. Next, when the uniaxially stretched film in this state is stretched in the second axial direction (direction perpendicular to the first axial stretching direction), the minor axis side (direction) of the fibrous substance, that is, the different direction, is stretched along the second axial direction. A depressed portion (concave) of the film is formed on the minor axis side (direction) of the directional protrusion.

During the uniaxial stretching, even if a slight void is formed around the fibrous substance, a depression is formed around this fibrous substance.

The film surface that has been biaxially stretched is in a state as shown in Fig. 2-1 (plan view), and "the more" the depressed portion is deeper under the condition that the stress is concentrated around the fibrous substance in the second axial stretching. It tends to be recessed and elongated along the second axial direction. Second-
FIG. 2 (cross section) shows a cross section of the film in the vicinity of the surface, and anisotropic projections 21 containing fibrous substances and depressions 24 formed in the periphery thereof are formed in the polyester film 23.

In the present invention, the depressions formed around the anisotropic protrusion include a pseudo-elliptical shape that is eccentric in the second axis direction. At this time, if the longest axis of the recess is referred to as the major axis, the major axis of the recess must be at least 2 μ in order to prevent the dropout of the magnetic tape. In other words, the depressions on the surface of the film having a major axis of less than 2 μ cannot eliminate the drawback of the electromagnetic conversion characteristics of the protrusions of the film. As described above, the second axial stretching direction is substantially perpendicular to the first axial stretching direction. Needless to say, high-stage (multi-stage) stretching in which stretching is performed in the first axial stretching direction and / or the second axial stretching direction can also be performed. Also in this case, the effect of the present invention is maintained because the shape of the unevenness unit formed by the projections and the depressions on the film surface is slightly deformed and remains as it is.

The concavo-convex unit referred to in the present invention is composed of one anisotropic protrusion and a recess around it. The size and frequency of occurrence of the uneven unit can be controlled by the fibrous substance, the amount of the polymer present in the polymer, and the film stretching conditions.

In order to maintain the runnability as a magnetic tape, the size of the hollow portion needs to be 2 μ or more, preferably 4 μ or more in terms of major axis (see FIG. 2). The size of the recess is 30μ considering the signal dropout as a video tape.
It is preferable that the number of m or more is as small as possible.

The number of concavo-convex units must be 400 pieces / mm ² or more, preferably 6
00 pieces / mm ² or more. The average surface roughness (Ra) of the film is
It is preferably 0.005 to 0.05 μ, and more preferably 0.08 to 0.02 μ.

The size of this recess and the frequency of occurrence of uneven units are determined by depositing thin aluminum on the surface of the stretched film and then using a differential interference microscope (for example, Nikon differential interference microscope apparatus R type, magnification 900 times).
You can take a picture and observe it.

Since the polyester film of the present invention has a large number of concave and convex units composed of anisotropic projections and depressions adjacent to each other on the minor axis side on the surface thereof, it is possible to reduce the contact area between the film or the equipment that comes into contact with the film, and thus the flatness It also has an excellent sliding effect. Further, it has an advantage that the abrasion resistance is enhanced as compared with the conventional polyester film having a large number of concave and convex units composed of protrusions and depressions due to particles having different film surfaces. In addition, as long as the effect of the present invention is not impaired, externally added particles insoluble in polyester having a normal spherical shape, a lump shape, a plate shape, and / or protrusions caused by internal particles precipitated during polyester synthesis It does not matter even if the concavo-convex unit having recesses having the particles as cores is mixed on the surface of the polyester film.

INDUSTRIAL APPLICABILITY The polyester film of the present invention has various advantages such as a flat surface, excellent slipperiness, and excellent abrasion resistance as compared with conventional polyester films, and thus can be used for various applications. In particular, it can be preferably used in the magnetic tape field and the like where abrasion resistance is required.

[Examples] Examples will be specifically described below. In addition, "part" in an Example means a weight part. Further, the measurement of each characteristic value in the examples was carried out according to the following methods.

(1) Average fiber diameter and average fiber length of fibrous substance It was measured by a microscope. That is, the average fiber diameter and the average fiber length were obtained by measuring the diameter and the fiber length of the fibrous substance after calculating the number average by measuring the diameter and fiber length of the fibrous substance after passing through the film containing the fibrous substance or the film containing the fibrous substance. .

(2) Film surface roughness (Ra) It was measured according to JIS B 0601. Use a stylus surface roughness meter (SURFCOM3B) manufactured by Tokyo Seimitsu Co., Ltd.
A chart (film surface roughness curve) was drawn under the conditions of μ and load of 0.07 g. From the film surface roughness curve, a portion of the measurement length L is extracted in the direction of the center line, the center line of the extracted portion is taken as the X axis, and the longitudinal magnification direction is taken as the Y axis.
When the roughness curve is represented by Y = f (x), the value (Ra: μm) given by the following equation is defined as the film surface roughness.

In the present invention, 8 pieces were measured with a reference length of 0.25 mm, and Ra was expressed as an average value of 5 pieces excluding 3 pieces having the larger values.

(3) Friction coefficient of film (μk) The friction coefficient was measured as follows using the apparatus shown in FIG. In Fig. 3, 1 is an unwind reel, 2 is a tension controller, 3, 4, 6, 8, 9, and 11 are free rollers, 5 is a tension detector (inlet), and 7 is a fixed rod made of stainless steel SUS 304. (Outer diameter 5 mmφ), 10 is a tension detector (outlet), 12 is a guide roller, and 13 is a take-up reel.

The film was cut into 1/2 inch width in an environment of temperature 20 ° C and humidity 60%, and the angle θ was applied to 7 fixed rods (surface roughness 0.3 μm).
= (152/180) π radians (152 °) and contact at 20 per minute
Move (rub) at a speed of 0 cm. Inlet tension T ₁ is 3
Outlet tension when adjusting the tension controller 2 so as to 5g (T _2: g) a is film detected by the outlet tension detector into After parallel 90m, and calculates the running friction coefficient μk by the following equation.

μk = (2.303 / θ) log (T 2 / t 1) = 0.8681 log (T 2/35) (4) Wear resistance evaluation -I 1/2 inch 5mmφ Sutenren made fixing pin the film surface of the width (surface roughness 0.58) at an angle of 150 ° and reciprocates about 15 cm at a speed of 2 m / min and rubs (at this time, the entrance side tension T ₁ is 60 g).

After repeating this operation 40 times reciprocatingly, the degree of scratches on the face is visually judged.

At this time, those with almost no scratches are ◎, those with few scratches are ○, those with a large number of scratches are ×, scratches are in the middle of the former two, △,
And judge in four stages.

(5) Evaluation of Wearability-II The abrasion resistance of the running surface of the base film was evaluated using a 5-stage mini super calendar. The calender was a five-stage calender consisting of a nylon roll and a steel roll, and was run at a processing temperature of 80 ° C., a linear pressure applied to the film of 200 kg / cm, and a film speed of 50 m / min. Running film length 40
The scraping property of the base film was evaluated by the dirt attached to the top roller of the calender when it was run for 00 m.

<Four-level judgment> ◎ Nylon roll is not soiled at all ○ Nylon roll is barely soiled △ Nylon roll is soiled × Nylon roll is soiled very much Example-1 Fibrous material having an average fiber diameter of 0.3 µ and an average fiber length of 1.2 µ Polyethylene terephthalate with an intrinsic viscosity (orthochlorophenol, 35 ° C) of 0.65dl / g containing 0.25% by weight of calcium carbonate was dried at 180 ° C, then melt extruded at 290 ° C, and 50 ° C.
An unstretched film was obtained by rapidly cooling and solidifying on the casting drum held in the above.

Subsequently, the unstretched film was preheated to 90 ° C. with a heating roller and then stretched 3.3 times in the machine direction while being heated with an infrared heater. Subsequently, the film was stretched 3.4 times in the transverse direction at a temperature of 105 ° C. and then heat-treated at 200 ° C. to obtain a film having a thickness of 15 μ.

Major axis adjacent the anisotropic protrusion and projecting short shaft of the electromotive force due to calcium carbonate of at least consists 2μ of depression and irregularity units were present ² 1500 Ke / mm on the surface of the biaxially oriented film. Table 1 shows the surface roughness, friction coefficient, and abrasion resistance evaluation results of the film. Despite the low surface roughness Ra, the abrasion coefficient is low and the abrasion resistance is good.

Comparative Example-1 In Example-1, exactly the same as in Example-1, except that the unstretched film was preheated to 70 ° C. with a heating roller and then stretched 3.6 times in the machine direction while being heated with an infrared heater. To get the film. The characteristics of the obtained film are shown in Table 1, and the unit price of unevenness composed of anisotropic projections and depressions adjacent to the short axis side of the projections is smaller than that of Example-1, and the friction coefficient, Example 1 for body wear
It was inferior to.

Comparative Examples-2 and-3 In Example-1 and Comparative Example-1, the same procedure as in Example-1 and Comparative Example-1 was carried out except that the fibrous calcium carbonate was changed into normal agglomerated particles. I got a film. The surface projections of the obtained film had no anisotropy. The properties of the obtained film are shown in Table 1, but the properties were inferior in all cases.

Example-2, Comparative Example-4 Example-1 and Comparative Example-1 except that fibrous calcium carbonate in Example-1 and Comparative Example-1 was changed to potassium titanate having an average fiber diameter of 0.2μ and an average fiber length of 1.0μ, respectively. Example-1
The same procedure was performed to obtain a film. The characteristics of the obtained film are shown in Table 1. The film of Example-2 was good, but the film of Comparative Example-4 was inferior.

Examples-3, -4 Except for using fibrous calcium carbonate in Example-1 as an offretite / erionite zeolite having an average fiber diameter and an average fiber length shown in Table 1 and halloysite, the same as in Example-3. I went and got a film. The properties of the obtained film are shown in Table 1, and all of them were excellent.

[Brief description of drawings]

FIG. 1 shows a void state formed around a normal particle, FIG. 1-1 is a plan view, and FIG. 1-2 is a sectional view.
FIG. 2 shows the polyester film of the present invention in which anisotropic projections due to the fibrous substance are formed and depressions are formed in contact with the projections and in the minor axis direction. FIG. 2-1 is a plan view and FIG. 2-2 is a sectional view. FIG. 3 is a schematic view of an apparatus for measuring the dynamic friction coefficient μk of the film.

Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical display area C08K 3/34 7/04 C08L 67/00 KJR 8933-4J KJS 8933-4J KKF 8933-4J B29K 67:00 B29L 7:00 4F

Claims (3)

[Claims] 1. Concavo-convex units of 400 / mm ² or more on the surface of the film, each of which is composed of an anisotropic protrusion due to a fine fibrous substance and a recess adjacent to the minor axis of the protrusion and having a major axis of at least 2 μ. A polyester film characterized by being formed. 2. The polyester according to claim 1, wherein the fine fibrous substance is at least one selected from the group consisting of potassium titanate, calcium carbonate, offretite / erionite zeolite, halloysite and iron oxide. Film. 3. The polyester film according to claim 1 or 2, wherein the polyester film is a film for a magnetic recording medium.