JPH0618901B2 - Polyester film - Google Patents

Description

TECHNICAL FIELD The present invention relates to a polyester film, and more particularly to a polyester film having a flat surface, excellent slipperiness, abrasion resistance and dimensional stability in the longitudinal direction of the film.

Conventional technology Polyester film has 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 is required 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 means for forming protrusions on the surface of a film by forming a polymer on which inorganic particles are added or a polymer in which catalyst residual particles insoluble in the polymer are formed, on the 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 and 57-167216, it has been proposed to form a large number of fine concave-convex units having convex portions and concave portions (concave portions) on the surface of a polyester film. However, although this means is effective in reducing the film friction coefficient, it has not yet been sufficiently effective in improving the wear resistance. Further, a film provided with such a concave portion (concavity) usually has a low F-5 value in the longitudinal direction of the film, and has a problem that it has poor dimensional stability when the film becomes thin.

SUMMARY OF THE INVENTION In consideration of the above-mentioned circumstances, the present inventors have developed a polyester film which has high strength in the longitudinal direction (longitudinal direction) of the film, has a flat film surface, and is excellent in slipperiness and abrasion resistance. As a result of intensive investigations, they have found that this problem can be solved by forming a large number of irregularities of a specific shape on the film surface, and arrived at the present invention.

The object of the present invention is a polyester film having a flat surface, excellent slipperiness and abrasion resistance, high strength in the longitudinal direction (longitudinal direction) of the film, and excellent dimensional stability, particularly useful for magnetic recording media. To provide a special polyester film.

According to the present invention, an object of the present invention is to provide anisotropic protrusions caused by fine fibrous substances on the surface of the film and dents adjacent to the major axis of the protrusions and having a major axis of at least 2μ. It is achieved by a polyester film, characterized in that the irregularities units are formed 200 pieces / mm ² or more made of a.

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 copolymerization component include diethylene glycol, neopentylene glycol, polyalkylene glycol (eg, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, etc.). ) And other diol components, dicarboxylic acid components such as adipic acid, sebacic acid, phthalic acid, isophthalic acid, and 5-sodium sulfoisophthalic acid; Examples thereof include polyfunctional carboxylic acid components such as acids. 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 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 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 linear material is fine, and this shape has an average fiber diameter (d).
Is 0.5 μm or less, the average fiber length (l) is 5 μm or less, and l / d is a value of 3 to 10. The lower limit of the average fiber length is preferably 0.1μ. The addition amount of the fibrous substance is the following formula (1) 0.005 ≦ d × l × w ≦ 1 with respect to polyester (1) where d: average fiber diameter of the fibrous substance (μ) l: fibrous Average fiber length (μ) of substance w: It is preferable to satisfy 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] The fibrous substance is less than 3 in l / d, for example, spherical or lumpy particles. If so, the obtained polyester film is unsatisfactory in abrasion resistance and transparency, and if l / d exceeds 10, the abrasion resistance of the film becomes insufficient, which is not preferable. Further, if the average fiber diameter exceeds 0.5 μ, the irregularities on the film surface become too large, and the electromagnetic conversion characteristics deteriorate in applications such as magnetic tape, and if the average fiber length exceeds 5 μ, the orientation in the plane direction during film stretching. 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 abrasion resistance is also insufficient. On the other hand, when the value of (d × l × w) exceeds 1, the effect of imparting slipperiness and The effect of improving wear resistance is not further exerted, and on the contrary, electromagnetic conversion characteristics are deteriorated, which causes adverse effects such as shortening of filter life during film formation, which is not preferable.

The method for incorporating the fine fibrous substance into the polyester may be performed at any time and by any method, but a method of adding it as a glycol slurry before the polymerization reaction of the polyester reaction, particularly before the ester exchange or the ester reaction is preferable.

The polyester film of the present invention is produced using polyester containing a fine fibrous substance. Then, the film has an anisotropic protrusion due to the fibrous substance on the surface thereof, and a major axis of at least 2 which is adjacent to the major axis side of the protrusion.
More than 200 concave / convex units consisting 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 in a uniaxial direction (first axial direction), the particles are not deformed and the polymer is plastically deformed. Therefore, during large deformation (stretching), voids are generated at the boundary between the polymer and the particles. Occurs. 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. , 1-1
As shown in the drawing, 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 them bring about projections with the particles as cores, but it is not possible to form depressions around the particles. Absent.

The depression in the present invention can be said to be a depression (deformation) of at least a part of the void portion. When uniaxially stretching the unstretched polyester film containing fine fibrous substances in the machine axial direction (longitudinal direction of the film), the preheating of the film before stretching is set to a low temperature, and the stretching ratio is set to a high value. By performing the second axial stretching (stretching in the film width direction), it is possible to form the anisotropic protrusion due to the fibrous substance and the depression adjacent to the major axis side of the protrusion. 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 in a state almost parallel to the machine axis direction. Then
When the film stretched in this state in a uniaxial direction at a high magnification is stretched in the second axial direction (the direction perpendicular to the first axial stretching direction), the long axis side of the fibrous substance, that is, the long axis of the anisotropic protrusions. A depressed portion (concave: concave portion) of the film is formed on the side.

During the uniaxial stretching, even if a void is formed around the fibrous substance, a recess 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 under conditions where the uniaxial stretching concentrates stress mainly on the fibrous substance, the "depression" is deeper. It tends to be recessed and elongated along the uniaxial direction. No. 2-2
The figure (cross section) shows a film cross section 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 recesses formed around the anisotropic projection include a pseudo-elliptical shape which is eccentric in the first 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 may be 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. Even in this case, the effect of the present invention can be maintained because the shape of the unevenness unit formed by the projections and the depressions on the film surface is slightly deformed and still exists.

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 200 / mm ² or more, preferably
400 pieces / mm ² or more. Average surface roughness of film (Ra)
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 unevenness 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 device R type, magnification 900 times).
Can be used to take a picture and observe.

The polyester film having such an uneven unit can be prepared based on a method in which polyester is melt-extruded, rapidly cooled to obtain an unstretched film, and then the unstretched film is sequentially biaxially stretched.

For example, a polyester containing a fibrous substance is melt extruded from a die, rapidly cooled on a casting drum to obtain an unstretched film, and then the unstretched film is sequentially stretched biaxially to be heat treated. The film-forming conditions are set so that the above-mentioned characteristics are obtained.
It is selected from the range of 4.5 times, the stretching ratio in the width direction of 3.0 to 3.8 times, the stretching temperature of 80 to 100 ° C. and the heat setting temperature of 150 to 240 ° C., respectively. Further, the heat shrinkage ratio in the width direction can be set to a desired value by relaxing or tensioning in the width direction.

Biaxially oriented polyester film is 4-35μ, and further 6
A thickness of up to 25μ is preferred. Further, the F-5 value in the longitudinal direction of the film is 13 kg / mm ² or more, and the F-5 value in the width direction is
It is preferably greater than 5 values. The F-5 value in the longitudinal direction is particularly preferably 15 kg / mm ² or more.

Since the polyester film of the present invention has a large number of concave and convex units consisting of anisotropic protrusions and depressions adjacent to the major axis side on the surface thereof, the contact area with the film or equipment contacting the film can be reduced and the film can be flattened. It also has an excellent sliding effect. Further, there is an advantage that the abrasion resistance is enhanced as compared with the conventional polyester film having a large number of concave and convex units consisting of protrusions and depressions formed by simple particles on the surface of the film. In addition, as long as the effect of the present invention is not impaired, the external points insoluble in the polyester having a usual spherical, lumpy, plate-like shape are caused by the particles and / or the internal particles precipitated during the polyester synthesis. There is no problem even if the unevenness unit having the projections and the depressions having the particles as the core 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) The average fiber diameter and the average fiber length of the fibrous substance were measured by a microscope. That is, after taking a photograph through a fibrous substance or a film containing a fibrous substance, measuring the diameter and fiber length of the fibrous substance, and calculating the number average value,
The average fiber diameter and average fiber length were determined.

(2) Film surface roughness (Ra) This is a value defined by JIS-B0601 as the center line average roughness (Ra). In the present invention, a stylus surface roughness meter (SURFCORDER SE of Kosaka Laboratory Ltd.) is used in the present invention. -30C). The measurement conditions are as follows.

(a) Stylus tip radius: 2μ (b) Measuring pressure: 30mg (c) Cut-off: 0.25mm (d) Measuring length: 0.5mm (e) Data compilation method The same sample was repeatedly measured 5 times, and the largest Value 1
Except one, the remaining four data are represented by the average value.

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

A film cut into a width of 1/2 inch in an environment of temperature 20 ° C and humidity 60% is attached to 7 fixed rods (surface roughness 0.3 μm) at an angle θ = (152/180) π radian (152 °). Contact and move (rub) at a speed of 200 cm per minute. The film adjusts the exit tension (T ₂ : g) when adjusting the tension controller 2 so that the entrance tension T ₁ becomes 35 g.
After traveling 0 m, it is detected by the exit tension detector, and the traveling friction coefficient μk is calculated by the following formula.

μk = (2.303 / θ) log (T 2 / T 1) = 0.8681 log (T 2/35) (4) Wear resistance evaluation -I 1/2 inch 5mmφ stainless steel fixing pin the film surface of the width (surface roughness 0.58) contact at an angle of 150 °, 2 per minute
It moves back and forth about 15 cm at a speed of m and rubs (at this time, the entrance side tension T _{1 is set} to 60 g).

After repeating this operation 40 times back and forth, the degree of scratches on the friction surface is visually determined.

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 abrasion resistance-II The abrasion resistance of the running surface of the film was evaluated using a 5-stage mini super calender. The calender is a 5-stage calender consisting of nylon roll and steel roll, and the processing temperature is 80.
C, the linear pressure applied to the film was 200 kg / cm, and the film speed was 50 m / min. Running film length 4000
The scrapability of the film was evaluated by the dirt attached to the top roller of the calendar when the film was run for m.

<Four-level judgment> ◎ Nylon roll is not soiled at all ○ Nylon roll is barely soiled △ Nylon roll is soiled × Nylon roll is heavily soiled (6) F-5 value A film with a width of 10 mm is 100 mm between chucks and a pulling speed of 100 mm /
In minutes, pull with an Instron type universal tensile tester,
The load of 5% elongation of the obtained load elongation curve was divided by the initial cross-sectional area to obtain F-5 value.

(7) Durability during repeated running Test with the abrasion resistance evaluation-I described in (4) above, and evaluate the damage based on the edge of the sample according to the following criteria.

⊚: The edge of the tape is almost unchanged from before running ◯: The edge of the tape is slightly damaged ×: The edge of the tape is greatly damaged Example-1 Average fiber diameter 0.3 μm, average Polyethylene terephthalate having an intrinsic viscosity of 0.65 dl / g (orthochlorophenol, 35 ° C) containing 0.25% by weight of fibrous calcium carbonate having a fiber length of 1.2μ was dried at 160 ° C, and then melt-extruded at 290 ° C.
An unstretched film was obtained by rapid cooling and solidification on a casting drum kept at 40 ° C.

Subsequently, the unstretched film was preheated to 60 ° C. with a heating roller, and then 4.6 mm in the longitudinal direction while being heated with an infrared heater.
It was stretched by a factor of 2. Then, the film was transversely stretched 3.4 times at a temperature of 90 ° C., and then heat-treated at 200 ° C. to obtain a film having a thickness of 15 μm.

Major axis adjacent the anisotropic protrusion and projecting the long shaft of the electromotive force due to calcium carbonate of at least consists 2μ of depression and irregularity units were present 500 / mm ² 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 friction coefficient is low and the abrasion resistance is good.

Comparative Example-1 In Example-1, except that the unstretched film was preheated to 70 ° C. with a heating roller and then stretched by 3.6 times in the machine direction while being heated with an infrared heater. The same procedure was followed to obtain a film. The characteristics of the obtained film are shown in Table 1. The unevenness unit consisting of the anisotropic projections and the depressions adjacent to the major axis of the projections is smaller than that in Example-1, and the friction coefficient is The wear resistance was inferior to that of Example-1.

Comparative Examples-2 and-3 In Examples-1 and Comparative Example-1, the film was prepared in exactly the same manner as in Example-1 and Comparative Example-1, except that the fibrous calcium carbonate was changed to ordinary lump particles. Obtained. 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 In Example-1 and Comparative Example-1, the fibrous calcium carbonate was added with an average fiber diameter of 0.2 µ and an average fiber length of 1.0, respectively.
A film was obtained in the same manner as in Example-1 and Comparative Example-1 except that the amount of potassium titanate was changed. 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 and-4 Exactly the same as Example-1 except that the fibrous calcium carbonate in Example-1 is changed to an offretite / erionite type zeolite having the average fiber diameter and average fiber length shown in Table 1 and halloysite. To get the 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 a polyester film of the present invention in which anisotropic projections due to a fibrous substance are formed and depressions are formed in contact with the projections and in the major 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 location C08L 67:00 (72) Inventor Takatoshi Kuratsuji 77 Kitayoshida-cho, Matsuyama-shi, Ehime Teijin Limited Matsuyama Factory (56) Reference JP-A-49-71036 (JP, A)

Claims (4)

[Claims] 1. Concavo-convex units of 200 / mm ² or more on the surface of the film, each of which is composed of an anisotropic projection caused by a fine fibrous substance and a dent adjacent to the major axis of the projection 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 F-5 value in the longitudinal direction of the film is 13 kg /
The polyester film according to claim 1, which has a size of not less than mm ² and is larger than the F-5 value in the width direction. 4. The polyester film according to claim 1 or 3, wherein the film is a base film of a magnetic recording medium.