JPH0155986B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a polyester film having a smooth surface and a low coefficient of friction. Polyester films have a variety of uses, including magnetic tape applications and electrical applications. In magnetic tape applications, particularly video tape applications, a smooth film surface is required to improve electromagnetic conversion characteristics, and a smooth film surface is required to improve the tape's runnability on a deck, abrasion resistance, and durability. A low coefficient is required. Conventionally, as a technique for reducing the coefficient of friction of a film, there has been known a method of imparting irregularities to the surface of the film by forming a polymer containing inorganic particles or a polymer in which inactive catalyst residue particles are formed into a film. It is being This means provides protrusions on the film surface to reduce the contact area between the film and the object with which it 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 protrusions increases, there is a strong possibility that when magnetically coated, the protrusions will have an effect on the coated surface, deteriorating 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 its surface. It was discovered that this problem could be solved by forming a large number of fine uneven units. Furthermore, as a result of intensive research into a method for efficiently manufacturing this film, the present invention was arrived at. That is, in the present invention, an unstretched polyester film containing inert additive particles or/and catalyst residue particles having an average particle size of 0.05 to 1.2 μm is heated at a film temperature of 105 μm.
℃ or higher and lower than 130℃, stretching ratio 3.3 times or less, stretching speed
Stretched in the longitudinal direction under conditions of 50 to 150 m/min, then stretched the longitudinally stretched film 3 to 4 times in the transverse direction,
A biaxially stretched polyester film in which a large number of uneven units consisting of protrusions and depressions with the protrusions as cores are formed on the film surface, and the protrusions are caused by the inert additive particles or (and) catalyst residue particles. The depression is in the form of an ellipse with a major axis along the lateral stretching direction of the film, and the major axis of the depression is in the range of 2 μm to 50 μm, and the major axis D
(μm) and the occurrence frequency N (pieces/mm ² ) of uneven units: 2≦D<5 200≦N<3500, 5≦D<10 150≦N<2000, 10≦D< 30 50≦N<800, 30≦D<50 0≦N≦5 This is a method for producing a polyester film characterized by producing a biaxially stretched film that satisfies the following relationships. The present invention will be explained. In the prior art, inert inorganic particles (e.g. silica,
While protrusions (protrusions) are formed on the film surface by adding clay, titania, etc.), organic particles (e.g. calcium terephthalate, high melting point polyester), or (and) using catalyst residue, the present invention The feature is that convex portions and concave portions (depressions) are formed on the surface of the film. A film having protrusions and depressions as in the present invention has an advantage in that it has a significantly lower coefficient of friction and a smoother slipping effect than a film obtained by the prior art having only protrusions on its surface. The polyester to which the present invention can be applied refers to the condensation polymerization of aromatic dibasic acids such as terephthalic acid, isophthalic acid, and naphthalene-2,6-dicarboxylic acid with glycols such as ethylene glycol, tetramethylene glycol, neopentyl glycol, etc. refers to the polymer or copolymer obtained in this manner. Typical examples of these polymers include polyethylene terephthalate, polybutylene terephthalate, and polyethylene.
Examples include homopolymers such as 2,6-naphthalene dicarboxylate, partially modified copolymers thereof, and polymer blends such as polyethylene terephthalate to which a [ethylene terephthalate/polyethylene glycol] block copolymer is 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 particles of an inorganic compound added to the polymer; particles based on insoluble catalyst residues produced during polymerization of the polymer; or particles of both. In the present invention, the depressions that can be generated around the protrusions with the protrusions as the nucleus are not concave-shaped depressions caused by mechanical stamps such as conventional embossing, but are caused by deformation of the film itself during the process of stretching the film. This is caused by. 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). If this film containing voids is then stretched in a direction approximately perpendicular to the uniaxial stretching direction (second axial direction), it becomes 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 a quasi-circular shape around the projections 21, as shown in FIG. 1-1. In this case, as shown in the cross-sectional view of Figure 1-2, the particles existing in the shallow part near the film surface and the voids around them produce protrusions with the particles as the nucleus, but no depressions are formed around the particles. . In the present invention, the above voids are changed to depressions on the film surface. When stretching an unstretched film in the longitudinal direction, longitudinal stretching can be achieved by setting the preheating of the film before stretching to a high temperature to raise the film temperature during stretching, and setting the stretching ratio low. The film that has undergone this process is made so that substantially no voids are formed around the particles (external particles due to inorganic additives or internal particles containing catalyst residues). Next, when the stretched film in this state is stretched in the transverse direction, depressions (depressions) of the film with particles as nuclei are formed along the transverse axis direction. The major axis of the elliptical depression is along the horizontal direction. Even if slight voids are formed around the particles during longitudinal stretching, depressions are formed with these particles as the nucleus. 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 lateral stretching, the depressed portions will change depending on the degree of stress concentration. It tends to be deeply recessed and its major axis becomes larger in the lateral direction. FIG. 2-2 (cross-sectional view) shows a cross section of the film near the surface, in which protrusions 21 containing particles and depressions 24 formed around the protrusions 21 are formed in the polyester film 23. In the present invention, the depressions formed around the protrusions include pseudo-ellipsoidal depressions that are biased in the horizontal axis direction. In this case, if the most eccentric long axis of the depression is referred to as the major axis, it is necessary that the major axis of the depression be at least 2 μm from the viewpoint of improving the running properties of the magnetic tape and improving the electromagnetic conversion characteristics. Furthermore, if the major axis of the depression exceeds 50 μm, dropout of the magnetic tape increases, making it undesirable as a base film for a magnetic tape. According to the present invention, between the long diameter D (μm) of the depression of the uneven unit on the surface of the polyester film and the occurrence frequency N (pieces/mm ² ) of the uneven unit, 2≦D<5 200≦N<3500 , 5≦D<10 150≦N<2000, 10≦D<30 50≦N<800, 30≦D<50 0≦N≦5. The electromagnetic conversion characteristics are also excellent. More preferably, 2≦D<5, 350≦N<2500, 5≦D<10, 250≦N<1500, 10≦D<30, 100≦N<500, 30≦D<50. When the condition of 0<N≦3 is satisfied, the base film has excellent running properties and electromagnetic properties. According to the present invention, it is understood that the depressions on the film surface reduce frictional resistance by reducing the contact area. The concavo-convex unit in the present invention consists of one protrusion and a depression around the protrusion. The size and frequency of occurrence of these uneven units can be controlled by the type of particles, the amount present in the polymer, and film stretching conditions. A specific method for stretching the polyester film of the present invention will be explained. When stretching in the longitudinal direction an unstretched polyester film containing 0.01 to 2.0% by weight of fine particles such as kaolin and silica with an average particle diameter of 0.05 to 1.2 μm (preferably 0.3 to 1.0 μm),
Preferably, it is preheated to 90-120°C. When this unstretched film is preheated to about 90 DEG to 120 DEG C., a hard chromium-plated roll or a ceramic roll with a matte surface is preferred. The unstretched film can reach a predetermined preheating temperature without sticking to the roll surface and without substantial crystallization. Of course, the unstretched film can be preheated in a non-contact manner. Unstretched film: 105℃ or higher 130
3.3 times or less (preferably 2.6-3.2
Stretched at a stretching ratio of Although it is preferable that the stretching speed is relatively slow, a stretching speed of usually 50 to 150 m/min, preferably 50 to 100 m/min is selected,
In the case of low speed, the stretching temperature can be moved to a slightly lower temperature side. Next, for horizontal stretching, the longitudinally stretched film is cooled to below the glass transition point, or without cooling.
It is preheated to a temperature of 100 to 150°C, and then stretched 3.0 to 4.0 times (preferably 3.2 to 3.8 times) in the transverse direction at approximately the same temperature. When the transverse stretching temperature is high, the boundaries of the depressions in the unevenness units become clear;
At low temperatures, boundaries are often not obvious. The stretching ratio in the lateral direction does not significantly affect the frequency of occurrence of uneven units. Just as the horizontal stretching ratio
If 3.8 times or more is selected, the mechanical strength in the transverse direction (Young's modulus) becomes higher than the mechanical strength in the longitudinal direction, resulting in a so-called tensilized film, and the slipperiness of the film tends to decrease. . If the mechanical strength in the longitudinal direction is insufficient, the biaxially stretched film may be further
A balanced film can also be obtained by re-stretching the film by about 1.2 to 1.6 times at a temperature of about 170°C. The biaxially oriented polyester film, which has been subjected to two-stage stretching and, if necessary, three-stage stretching, is heated at 180 to 240°C (preferably
Heat setting can be performed at a temperature of 190 to 210°C for about 0.2 to 30 seconds. In addition, the third stage in the three-stage stretching
Stage (first axial direction) re-stretching can also be carried out on a film that has undergone heat setting. By appropriately combining the above stretching conditions,
A slippery polyester film having an appropriate frequency of uneven units can be produced. In the present invention, the direction in which the first axial stretching is applied may be either the machine direction or the width direction of the film. Further, the second axial stretching direction is preferably approximately perpendicular to the first axial direction. Of course, high-stage (multi-stage) stretching in which stretching is further performed in the first axial direction and/or the second axial direction can be performed. In this case as well, the protrusions and depressions on the film surface remain as they are even if the shape of the uneven unit is slightly deformed. friction coefficient) is maintained. The film stretching conditions that form such surface depressions tend to make the film surface relatively smooth, 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 without causing dropouts or color noise when a magnetic recording layer is provided due to the film surface being relatively flat; Since there are depressions around the protrusions, the tape has the advantage that the contact area with the magnetic head, guide roll, and other films is further reduced, and the low protrusions on the film surface also enhance the sliding effect. . Since the surface of the polyester film of the present invention has depressions in addition to protrusions, the electromagnetic conversion characteristics can be maintained at a high level compared to the conventional film that has only protrusions on the surface, and the adverse effects caused by some excessive unevenness units can be avoided. It has the advantage of being avoided. The method for measuring physical properties in the present invention is as follows. (1) Measuring method for uneven parts A film surface with a thin layer of aluminum vapor deposited is photographed using a differential interference microscope device (for example, Nikon differential interference microscope R type), and its size is measured on a scale. (2) Surface roughness CLA Surface roughness CLA (Center Line
Average) value is measured by the following method. The roughened film is measured using a stylus surface roughness tester (SURFCOM 3B) manufactured by Tokyo Seimitsu Co., Ltd., with a needle radius of 2 μm and a load of 70 mg.
Determine the film roughness curve, extract a part of measurement length L (reference length 2 mm), take the center line of this extracted part as the X-ray, and take the direction of vertical magnification as the Y axis, and calculate the roughness curve as Y=f( When expressed as 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,
The three with the largest values are excluded and the average value of the five is expressed. Note that measurements are made in the vertical and horizontal directions, and the average value of both is used. (3) Coefficient of friction As shown in Figure 4, 18-8 stainless steel with an outer diameter of 5 mmφ was measured at a room temperature of 25°C and a relative humidity of 60%.
1/ to SUS304 fixing rod (surface roughness CLA=0.030)
Wrap the film cut to 2 inches wide at an angle of π
They are brought into contact with each other in radians and moved at a speed of 3.3 cm/sec. When the tension controller 2 is adjusted so that the inlet tension T ₁ (detected by the inlet tension detector 5) is 30 g, the outlet tension T ₂ g (detected by the outlet tension detector 10)
The dynamic friction coefficient μk is calculated using the following formula. In the present invention, the coefficient of dynamic friction when traveling 90 m is defined as μk. μk=1/πlnT ₂ /T ₁ (4) Chroma S/N The magnetic coating tape is measured by the following method. A commercially available home VTR is used to record a signal in which a 100% chroma level signal is superimposed on an 80% white level signal, and the reproduced signal is measured using a Shibasoku noise meter 925C. In addition, Chroma S/
The definition of N is as follows according to Shibasoku's definition. Chroma S/N = 20log ES (p-p) / EN (rms) (dB) However, ES (p-p) = 0.714V (p-p) EN (rms) = AM noise effective value voltage (V) Also magnetic The powder coating is created in the following way. The magnetic powder coating shown below is applied using a gravure roll, and the magnetic coating layer is smoothed using a doctor knife to form a magnetic layer of about 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. Furthermore, it is calendered to make the coating surface uniform and create a 1/2 inch wide tape. Composition of magnetic paint γ-Fe ₂ O ₃ powder 100 parts by weight Eslec A (Sekisui Chemical Co., Ltd., vinyl chloride-vinyl acetate copolymer) 16 Hiker 1432J (Nippon Zeon Co., Ltd., butadiene acrylonitrile copolymer) 11 Lecithin 1 Carbon 8 〃 MEK 100 〃 MIBK 100 〃 Additive (lubricant, silicone resin) 0.15 〃 The present invention will be explained in more detail with reference to Examples below. Examples 1 to 5, Comparative Examples 1 to 4 Polyethylene terephthalate containing 0.25% by weight of kaolin and having an intrinsic viscosity of 0.65 dl/g (measured at 35°C using orthochlorophenol as a solvent) was dried at 160°C. The mixture was melt extruded at 280°C and rapidly solidified on a casting drum maintained at 50°C to obtain an unstretched film of 160 μm. Subsequently, the unstretched film was stretched 4 as shown in FIG.
After preheating with real heating rollers 31, 32, 33, and 34, the film was stretched one step in the longitudinal direction between rollers 34 and 35 while being heated with an infrared heater 38. Further, the film was stretched 3.6 times in the transverse direction at a temperature of 105°C, and then heat-treated at 210°C. In addition, the stretching speed at this time is
It was 55m/min. Here, while changing the preheating temperature of the heating rollers 31 to 34 during longitudinal stretching and the conditions of the infrared heater 38, the film temperature just before the roller 35 and the stretching ratio were changed to form a film and stretch it as shown in Table 1. I got it.

[Table] In Examples 1 to 5 and Comparative Examples 1, 2, and 4,
Even when the same polymer is used, the frequency of uneven units having depressions on the film surface can be changed by changing the stretching conditions. In this case, if the uneven units according to the present invention are formed on the film surface, the friction coefficient will be greatly improved even though the surface is flat, and the electromagnetic conversion characteristics will be Chroma S/
N gets better. In addition, in Comparative Example 3, it was observed that under conditions where the stretching temperature was very high, the frequency of uneven units with relatively large major diameters of depressions increased, which is a typical value of electromagnetic variation characteristics when used as a magnetic tape. Chroma S/
An increase in M and an increase in dropout are observed, which is not desirable. Examples 6 to 8 and Comparative Examples 5 to 6 Same conditions as Example 1, only the type and amount of particles added were changed, and the film temperature during longitudinal stretching was 120 ° C.
It was stretched at a longitudinal stretching ratio of 3.0 times, and the results shown in Table 2 were obtained.

[Table] As can be seen from Table 2, the frequency of occurrence of uneven units on the film surface and the resulting overall evaluation were the same for Examples 1 to 5 and Comparative Examples 1 to 4, even though the types of particles were different.
Similar results were obtained as described in . In addition, the frequency of occurrence of uneven units on the film surface varies depending on the size and number of particles present in the film, so as in Comparative Example 5, the average particle diameter is 0.02 μm.
and when the average particle size is 2.0 μ as in Comparative Example 6.
When m is large, the frequency of occurrence of uneven units decreases. As in Examples 1 to 8, it can be seen that a large number of uneven units occur when the average particle size is 0.3 to 1.0 μm. Example 7 uses a mixed powder of barium sulfate with an average particle size of 0.25 μm and calcium carbonate with an average particle size of 0.8 μm. Further, the reference tape for chroma S/N was the tape of Example 4. Examples 9-10, Comparative Examples 7-8 Polyethylene terephthalate was polymerized by a conventional method using calcium acetate and lithium acetate as transesterification catalysts, antimony trioxide as a polymerization catalyst, and trimethyl phosphate as a stabilizer. At this time, the amount of catalyst added was varied to obtain the particle size and amount of internally precipitated particles as shown in Table 3. The intrinsic viscosity of the polymer (measured at 35°C using orthochlorophenol as a solvent) was 0.65 dl/g. This polyethylene terephthalate was formed into a film under the same conditions as in Examples 6 to 8, and the results shown in Table 3 were obtained. Even when the unevenness on the film surface was generated by internal particles, the same results as in Examples 1 to 8 and Comparative Examples 1 to 6 were obtained.

【table】 [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. 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 stretching machine used in an example of the present invention. Figure-
4 is a schematic diagram of a tape base inspection machine that measures the dynamic friction coefficient μk of a film rough surface. FIG. 5 is a microscopic photograph showing the surface of a polyester film according to the prior art, and FIG. 6 is a microscopic photograph of the surface of the polyester film of the present invention. (All magnifications are 900x).

Claims (1)

[Claims] 1. An unstretched polyester film containing inert additive particles or (and) catalyst residue particles with an average particle diameter of 0.05 to 1.2 μm is stretched at a film temperature of 105°C or higher and lower than 130°C and a stretching ratio of 3.3 times or lower. Speed 50~150m/
The longitudinally stretched film is stretched in the longitudinal direction under the conditions of min. In the axially stretched polyester film, the protrusions are caused by the inert additive particles and/or catalyst residue particles, and the depressions are elliptical in shape with a major axis along the transverse stretching direction of the film. and the major axis of the depression is 2 μm
In the range of 50 μm to 50 μm, the difference between the major axis D (μm) and the occurrence frequency N (pieces/mm ² ) of unevenness units is 2≦D<5 200≦N<3500, 5≦D<10 A biaxially stretched polyester film satisfying the following relationships: 150≦N<2000, 10≦D<30 50≦N<800, 30≦D<50 0≦N≦5 Production method.