JPH0358580B2 - - Google Patents

Description

[Detailed description of the invention]

Industrial Application Fields The present invention has excellent flatness and smoothness, adhesion with the magnetic layer, and multi-time running performance, and generates little white powder even when worn with the guide part, and does not cause scratches on the film. The present invention relates to a biaxially oriented polyester film which is particularly useful as a base film for magnetic recording media because it is difficult and has few coarse particles. Conventional technology and problems to be solved Biaxially stretched polyester film has excellent heat resistance, mechanical properties, chemical resistance, etc., and is used for magnetic recording media, especially magnetic tapes for audio and video, and floppy disks. Demand for magnetic sheets is rapidly increasing. In recent years, these magnetic recording media have been trending toward higher quality and higher density, and there is a demand for better flatness and slipperiness of the base film, better adhesion with the magnetic layer, and better multi-run performance. . Furthermore, magnetic recording media are manufactured by applying a binder containing magnetic powder onto a base film using a combination of a coaching roll and a doctor knife, for example.
Even if the coaching roll is a driving roll, an idle roll, or a fixed stationary roll, the friction and abrasion between the polyester film and the roll surface are severe, and the surface of the film itself is scraped, causing white powder-like substances to precipitate, and even dropouts. It causes. Furthermore, when a tape or sheet coated with the magnetic material is used for recording, recording, etc., the film is scratched due to friction and abrasion at the guide portion, white powder is generated, and slipperiness deteriorates after many runs. Also, if there are many coarse particles, the filter life of the extruder will be shortened and dropouts will occur. A base film that satisfies all of these characteristics has not yet been perfected, and there has been a strong demand from film manufacturers. Means for Solving the Problems The present inventor has developed a film that maintains its flatness, slipperiness, and adhesion with the magnetic layer, has few coarse spots, has abrasion resistance, scratch resistance, and a large number of scratches. As a result of intensive studies aimed at developing a film with improved running properties, the inventors discovered that the problem could be solved by adjusting the physical properties of the polyester film to a certain range and mixing appropriate particles therein, resulting in the present invention. That is, the present invention has a refractive index n〓 of 1.492 or more in the thickness direction of the film, and the number A (number of concavo-convex units per mm ² of the film surface area) consisting of a protrusion and a depression having a major axis of at least 0.5 μm with the protrusion as the core. / ^mm2 )
satisfies the formula, (A) 0.01 to 1.0% by weight of internal particles containing lithium element, calcium element, and phosphorus element, and (B) an inorganic salt consisting of calcium oxide or inorganic salt with an average particle size of 0.1 μm to 10.0 μm. A biaxially oriented polyester film for magnetic recording media containing 0.001 to 0.7% by weight of active external particles. This relates to 0≦A≦10000. The polyester referred to in the present invention is a product obtained by polycondensing aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, and naphthalene-2,6-dicarboxylic acid or their esters with diols such as ethylene glycol, diethylene glycol, tetramethylene glycol, and neopentyl glycol. It is a crystalline aromatic polyester that can be obtained by The polyester can be obtained by direct polycondensation of aromatic dicarboxylic acid and glycol, or by polycondensation after transesterification of aromatic dicarboxylic acid dialkyl ester and glycol, or by polycondensation of aromatic dicarboxylic acid dialkyl ester and glycol. It can also be obtained by methods such as condensation. Typical examples of such polymers include polyethylene terephthalate, polyethylene-2.6-naphthalate, polytetramethylene terephthalate, and polytetramethylene-2.6-naphthalate. Not only polyester in which 2.6-dicarboxylic acid and ethylene glycol are bonded, but also 80 mol% or more of the repeating units are ethylene terephthalate or ethylene-2,6-naphthalate units, and 20 mol% or less of the repeating units are other components. It may be a copolymerized polyester or a mixed polyester obtained by adding and mixing other polymers to these polyesters.
In particular, it is preferable to copolymerize a polyalkylene glycol such as polyethylene glycol or polytetramethylene glycol as a diol component in order to improve adhesion to the magnetic layer. When adding or mixing other polymers to polyester, it is necessary to do so within a range that does not essentially change the properties of the polyester.
15 polycarbonate, other polyester, etc.
It can be added in a proportion of less than % by weight. In the present invention, in order to impart flatness and slipperiness to the film, it is necessary that the refractive index n in the direction of the thickness of the film satisfies the formula, preferably 1.493 or more, and that the protrusions and the protrusions are It is necessary that the number A (pieces/mm ² ) of concavo-convex units, each consisting of a depression and a core having a major axis of at least 0.5 μm, per 1 mm ² of the film surface area satisfies the formula. n〓≧1.492...0≦A≦10000...Although A may be zero, it is preferable that at least the uneven unit exists. On the other hand, if the number exceeds 10,000, although the flatness is excellent, the slipperiness, especially the runnability when running many times, is poor, so it is not suitable. Thus, a film that satisfies the formula has better flatness and slipperiness than a film that does not satisfy this formula using the same raw material, has the effect of reducing the amount of coarse particles, and is also effective in reducing the amount of coarse particles used in the magnetic layer coating process. It has the effect of reducing the generation of white powder due to friction and wear with guide pins when used as a magnetic tape. However, it has been found that the degree of the effect varies depending on the raw materials used. Currently, there is a strong demand for higher density and higher quality magnetic recording media, and higher performance films are required.
, even among films that satisfy the formula, there is a need to select raw materials that provide higher performance characteristics. The present invention selects raw materials that satisfy the following formula and provide even higher performance characteristics. In the production of polyester films, a conventional method has been to produce a film from a polyester composition containing particles obtained by adding inert fine particles such as silica, titanium dioxide, kaolin, charcoal, and barium sulfate during or after polymerization. particle addition method). Many methods have been proposed (internal particle generation method) of forming a film from a particle-containing polyester composition obtained by precipitating part or all of the catalyst, color inhibitor, etc. used during polyester synthesis during the reaction process. However, in the case of the external particle addition method, the kaolin normally used has flat particles, so the slipperiness cannot be improved even in a film that satisfies the above requirements.
In addition, with BaSO ₄ , particles are easily crushed during calendering during the magnetic tape manufacturing process, and slipperiness is extremely poor. Furthermore, titanium dioxide has a low ability to form surface irregularities, and if it is included only in sufficient amounts, a large amount of white powder will be generated, making it unsuitable. Also,
When using talc, calcium carbonate, silica, etc., it is unavoidable that coarse particles will be introduced, and grinding and grinding are necessary to keep the average particle size constant.
In the classification process, coarsening occurs due to agglomeration, clogging the filter of the extruder, not only hindering production, but also causing the problem of dropouts. As described above, various problems occurred with the external particle addition method, and it was extremely difficult to use it as a raw material. However, as mentioned above, polyester compositions containing internal particles containing lithium elements, calcium elements, and phosphorus elements When a film that satisfies the formula is manufactured using
Coarse particles were extremely effectively reduced. The internal particles contain 0.03 to 5% by weight of lithium element, 0.03 to 5% by weight of calcium element, and 0.03 to 5% by weight of phosphorus element.
Favorable results were obtained when the content was 0.03 to 10% by weight (both relative to internal particles). Examples of methods for producing polyesters containing such precipitated particles that are particularly suitable for use in the present invention are described in more detail below. That is, the polyester containing such particles is prepared by, for example, carrying out a transesterification reaction in the presence of a lithium compound and a calcium compound, and after the transesterification reaction is completed, a polyester selected from the group consisting of phosphoric acid, phosphorous acid, or an alkyl or aryl ester thereof. It can be obtained by adding one or more of these compounds in an amount of 0.6 to 3 times the total amount of these metal compounds, and then performing a polycondensation reaction. The lithium compound used in this case may be one that is soluble in the esterification or transesterification reaction product, such as salts of aliphatic carboxylic acids such as acetic acid, propionic acid, and butyric acid, and aromatic compounds such as benzoic acid and P-methylbenzoic acid. Mention may be made of salts of carboxylic acids, as well as lithium glycolates such as ethylene glycol and propylene glycol. Among these, lithium aliphatic carboxylates, particularly lithium acetate, are preferred. The amount is 0.03 to 0.4 mol%, especially 0.1 mol% based on the aromatic dicarboxylic acid component.
~0.3 mol% is preferably used. There are no particular restrictions on the calcium compound as long as it is soluble in the esterification or transesterification reaction product, such as salts of aliphatic carboxylic acids such as acetic acid, propionic acid, and butyric acid, benzoic acid, and P-methylbenzoic acid. Examples thereof include salts of aromatic carboxylic acids such as ethylene glycol, propylene glycol, and calcium glycolates. Among these, calcium aliphatic carboxylates, particularly calcium acetate, are preferably used.
The amount of the calcium compound used is preferably 0.05 to 0.3 mol%, particularly 0.08 to 0.15 mol%, based on the aromatic dicarboxylic acid component. The phosphorus compound may be any compound as long as it can react with the above-mentioned metal compound and convert part or all of it into a phosphate or phosphite derivative, but especially phosphoric acid and trialkyl phosphoric acid. ester, partial alkyl ester of phosphoric acid,
Phosphous acid, trialkyl esters of phosphorous acid, and partial alkyl esters of phosphorous acid are preferably used. The amount of these phosphorus compounds added is 0.6 to 3 times equivalent, preferably 0.8 to 2 times equivalent, and more preferably 0.9 to 1.5 times equivalent relative to the total amount of the metal compounds. The equivalent ratio of the phosphorus compound to the metal compound is expressed by the following formula: P/Ca+1/2Li (where P, Ca, and Li are each a phosphorus compound,
The number of moles of calcium compounds and lithium compounds is shown. ). By using a metal compound and a phosphorus compound in combination as described above, precipitated particles containing the metal element and phosphorus element used in the particles can be obtained. Of course, part or all of the lithium compound or calcium compound may be added after the transesterification reaction is completed. In order to achieve the object of the present invention, the amount of particles containing lithium, calcium, and phosphorus elements precipitated in this polyester is 0.01 to 1.0% by weight, preferably 0.03 to 0.5% by weight based on the polyester film.
% by weight, more preferably from 0.06 to 0.18% by weight. In this case, the amount of precipitated particles is determined as follows. (Quantification of precipitated particles in polyester film:
1.0 O-chlorophenol per 100g of polyester
After heating at 120°C for 3 hours, centrifugation was performed at 30,000 rpm for 40 minutes using a Beckman ultracentrifuge L _3-50 , and the resulting particles were vacuum dried at 100°C.
When the particles are measured using a scanning differential calorimeter, if a melting peak corresponding to the polymer is observed, O-chlorophenol is added to the particles, and after heating and cooling, centrifugation is performed again. When the melting peak is no longer observed, the particles are treated as precipitated particles, and the weight ratio to the polyester is calculated. ) In this way, we were able to obtain a film with excellent flatness and smoothness, and an extremely small amount of coarse particles.
This product still had insufficient wear resistance. Therefore, in order to improve the abrasion resistance, as a result of further investigation, by including a specific amount of specific inert external particles in a specific amount of fine internal particles made of a specific metal element in a film that satisfies the formula, It was found that it was significantly improved. That is, among inorganic inert external particles, particles made of oxides or inorganic salts of calcium, such as CaCO ₃ , CaSO ₄ , Ca(H ₂ PO ₄ ) ₂ , CaHPO ₄ ,
Average particle size of particles such as Ca ₃ (PO ₄ ) ₂ 0.1 μm ~
By combining 0.001 to 0.7% by weight of particles of 10.0 .mu.m, preferably 0.5 .mu.m to 10 .mu.m, more preferably 1.0 .mu.m to 10 .mu.m, with the internally precipitated particles, a remarkable effect can be obtained. Although the reason is not clear, it is thought that it is distinguished from other particles by the fact that the particle diameter is close to that of a sphere and the particle hardness is appropriate. The particle size of the particles exceeds 10.0 μm or the particle amount is 0.7% by weight
If it exceeds 50%, coarse particles become noticeable and it is unsuitable. Also, the average particle size is less than 0.1μm, and the content is 0.001% by weight.
If it is less than that, it is not suitable because the effect of reducing the generation of white powder, which is the objective of the present invention, cannot be achieved. The particles may be added before polyester polymerization, during the polymerization reaction, or kneaded in an extruder during pelletization after polymerization. Furthermore, it may be added during melt extrusion into a sheet, dispersed in an extruder, and extruded. In this way, we were able to obtain a film with excellent flatness, slip resistance, abrasion resistance, and multi-run performance.In addition, we were able to obtain a film with excellent scratch resistance, that is, resistance to scratching of the tape due to friction and abrasion during magnetic tape recording and playback. There is also a need to improve scratch resistance. As a result of intensive studies regarding this issue, it has been found that it is better to lower the refractive index in the longitudinal direction. In other words, the difference between the horizontal refractive index n _TD and the vertical refractive index n _MD
It became possible to improve the scratch resistance by making n _TD − n _MD satisfy the following equation. n _TD −n _MD ≧0.030 Preferably, n _TD −n _MD is 0.050 or less. 0.03
If it is less than that, the film will be easily damaged when running in a cassette deck after being made into a magnetic tape, that is, the scratch resistance will be poor, which is undesirable. or,
If it exceeds 0.050, the strength in the longitudinal direction decreases too much, which is not preferable. Thus, the present invention has made it possible to provide a polyester film that satisfies the various properties required for a magnetic tape. Next, the method for forming a polyester film of the present invention will be specifically explained. A polymer resin containing the required amount of internal precipitated particles and inert external particles consisting of calcium oxide or inorganic salt with an average particle size of 0.1 μm to 10.0 μm, a mixed resin thereof, or a resin added during extrusion is prepared by a conventional method. The polyester material is dried, melt-extruded through an extruder, and cooled and solidified on a rotating cooling drum to form an unstretched polyester sheet. At this time, it is preferable to employ a known contact method such as an electrostatic application cooling method. The unstretched film thus obtained is first stretched in one step or in multiple steps in the first axial direction, usually in the longitudinal direction, with rolls until Δn is 0.080 or less, and then in the direction perpendicular to the first axial direction in one step or in multiple steps. n _TD − at temperatures between °C and 150 °C
Stretch 2.5 to 5.0 times so that n _MD = 0.030, create a biaxially stretched film, and stretch at 200℃ to 250℃ for 1 second to 10
Heat set for a minute. However, if necessary, it is particularly preferable to further longitudinally and/or transversely stretch the film after biaxial stretching within a range that satisfies n _TD −n _MD ≧0.030. In this way, a film is obtained in which n〓 is 1.492 or more and has concavo-convex units consisting of concavities and concavities with particles as nuclei. As described above, by keeping Δn low after longitudinal stretching, n〓 becomes high and uneven units with grains as the nucleus are formed.The reason for this is not certain, but it is thought to be as follows. In other words, by keeping the birefringence (△n) low after longitudinal stretching, the plane orientation of the benzene rings in the polyethylene terephthalate skeleton toward the film surface decreases, and the refractive index n〓 in the thickness direction increases accordingly. . It is also believed that when the birefringence after longitudinal stretching is low, a difference in orientation occurs around the particles, and when this is laterally stretched, depressions are formed with the particles as the nucleus. In the film thus obtained, the particles of the film are uniform and dense, and have steep edges without voids around the particles, resulting in an extremely flat and easily slippery film. In the present invention, first axial stretching is usually carried out after longitudinal stretching.
It is essential that n be 0.080 or less. △n is
If it is not 0.080 or less, not only is the flatness and slipperiness inferior, but even if n _TD −n _MD ≧0.030 is satisfied, no improvement in scratch resistance is observed. In particular, it is preferable to carry out multi-stage stretching in the first axis direction in order to improve thickness unevenness, and it is also preferable to use super draw or near super draw drawing in order to increase the longitudinal stretching ratio. Examples Examples will be described in more detail below. The method for measuring each physical property of the film will be described below. (1) Coefficient of friction (μ) Fixed hard chrome-plated metal roll (diameter 6
mm) with a wrapping angle of 135° (θ), and a load of 53 g (T ₂ ) was applied to one end at 1 m/min.
The resistance force at the other end (T ₁
(g)) was measured, and the coefficient of friction during running was determined using the following formula. μ = 1/θln (T ₁ / T ₂ ) = 0.424ln (T ₁ / 53) (2) Center line average surface roughness (Ra) Surface roughness measuring instrument manufactured by Kosaka Laboratory Co., Ltd. (SE-3FK)
It was calculated as follows. The tip radius of the stylus is
2μm, load is 30mg. A part of standard length L (2.5 mm) is extracted from the film cross-sectional curve in the direction of its center line, and the roughness curve y=f(x )
When expressed as , the value given by the following formula is expressed in μm. However, the cutoff value is 80 μm. Ra
The average value was calculated for a total of 10 points, 5 points in the vertical direction and 5 points in the horizontal direction. 1/L∫ ^L ₀ ｜f(x)｜dX (3) Refractive index Using Atsube's refractometer (manufactured by Atago, a nuclear company)
The value for the Na-D line measured at 25°C was determined. (4) Concave and convex unit with depressions around protrusions (propeller)
Number of pieces (A) Photograph the surface of the aluminum-deposited film using a Carl Zeiss differential interference microscope at 750x magnification to determine the number of concave-convex units consisting of depressions with protrusions as cores and depressions with a major axis of at least 0.5 μm per 1 mm ² of total film surface area. The number A (pieces/mm ² ) was counted. (5) Number of coarse projections (L ₅ ) Observe the film under polarized light at 10x magnification, mark the part that shines as a fish eye, and measure the height of the marked part using the two-beam method.
The number of protrusions with a height of 1.35 μm or more was measured for 200 cm ² and was defined as the number of coarse protrusions with a height of L ₅ or more. (6) Multi-run performance, abrasion resistance, and scratch resistance The film was slit into thin strips, placed on a winder, rubbed against a metal guide roll installed in the middle, and run back and forth at high speed 200 times. The amount of white powder generated at this time was measured, and the wear resistance was ranked as follows. Rank: 1st grade: Good 2nd grade: Fair 3rd grade: Poor 4th grade: Extremely poor At that time, the scratch resistance on the film surface was observed through photographic observation, and the scratch resistance was ranked as follows. Rank 1st grade Good 2nd grade Fair 3rd grade Bad 4th grade Extremely bad Example 1 (Polyester manufacturing method) React 100 parts of dimethyl terephthalate, 70 parts of ethylene glycol, 0.10 parts of calcium acetate hydrate, and 0.17 parts of lithium acetate dihydrate. The transesterification reaction is carried out by charging the mixture into a container, heating it to raise the temperature, and distilling off the methanol, which takes about 4 hours after the start of the reaction.
The temperature was reached to 230°C, and the transesterification was substantially completed. This reaction product is then treated with triethyl phosphate.
After adding 0.35 part of antimony trioxide and further adding 0.05 part of antimony trioxide as a polycondensation catalyst, polymerization was carried out according to a conventional method to obtain a polyester. In the polyester, many uniform and fine precipitated particles containing calcium, lithium, and phosphorus elements with a particle size of about 0.5 to 1 μm were observed. The polyester A has [η]=0.65
It was hot. The amount of precipitated particles was quantified using the method described above for polyester A.
It was 0.3wt%. Separately, polyester B ([η]=0.65) containing no internally precipitated particles or inert externally added particles was produced.
On the other hand, polyester C contains 0.4% by weight of charcoal with an average particle size of 1.4 μm as external particles in polyester B.
[η]=0.65 was produced. (Film forming method) Polyester A, polyester B, and polyester C were blended in a ratio of A:B:C=50:45:5, dried by a conventional method, extruded at 285°C, and rapidly cooled to form an amorphous sheet. The amorphous sheet was stretched 3.2 times at 100℃ to obtain △n.
0.043 and then stretched 1.2 times at 98℃ to △n=0.062
And so. The thus obtained longitudinally stretched film was then stretched 3.9 times in the transverse direction at 140°C using a tenter, and then stretched at 217°C.
Heat fixation was performed to obtain a 15 μm film. Comparative Example 1 Using an amorphous film prepared in the same manner as in Example 1, the amorphous film was stretched 3.7 times in the longitudinal direction at 85°C, then stretched 3.9 times in the transverse direction at 100°C, and heat-set at 217°C. A 15 μm film was obtained. The film of the comparative example was longitudinally stretched at a low temperature and high magnification, so that n〓 was low and there were no uneven units having depressions. Example 2, Comparative Example 2 In Example 1, the second longitudinal stretch ratio was 1.3 times,
Polymerization film formation was carried out in the same manner as in Example 1, except that the film was stretched 1.4 times and Δn was changed to 0.072 (Example 2) and 0.083 (Comparative Example 2) to obtain a 15 μm film. The film of Comparative Example 2 had a high △n and n〓 after longitudinal stretching in two-stage stretching.
This is an example of a film in which there are no uneven units having depressions and depressions of 1.4920 or less. Example 3 The film after longitudinal and transverse biaxial stretching in Example 1 was further stretched 1.07 times in the longitudinal direction (Example 3).
Heat-fixed at 217°C. Comparative Example 3 Polyester and polyester C each containing 0.30% by weight of externally added particles of silica with an average particle size of 0.75 μm were blended in a ratio of 95:5 instead of the internally precipitated particles of Example 1, and a film was formed in the same manner as in Example 1. . The film combines two types of external particles instead of a combination of internal particles and external particles. Comparative Example 4 A film was formed in the same manner as in Example 1 except that alumina was used instead of the externally precipitated particles of Example 1. The film is exemplified using particles that do not contain Ca oxide or inorganic salt as external particles. Comparative Example 5 Polymerization and film formation were carried out in the same manner as in Example 1 and Comparative Example 1, except that polyester A and polyester B were blended at a ratio of 1:1. The film was exemplified as a film made of only internal particles and containing no external particles. Example 4 Using the same unstretched film as in Example 1, film formation was carried out in the same manner as in Example 1, except that the transverse stretching ratio was 4.2 times, to obtain a 15 μm film. The above results are shown in Table 1. From Table 1, using Ca-Li-P type particles as precipitated particles and calcium carbonate as added particles, n〓
It can be seen that films containing uneven units with grain cores of 1.492 or higher have excellent flatness, easy slippage, firm eye, abrasion resistance, and scratch resistance.

[Table] Effects of the invention As described above, the refractive index n〓 is set to 1.492 or more,
The number A (pieces/mm ² ) is 0 to 10000, and Li-Ca-P
0.01 to 1.0% by weight of internal precipitated particles containing Ca, and 0.001 to 0.7% by weight of inert external particles consisting of an oxide or inorganic salt of Ca with an average particle size of 0.1 μm to 10.0 μm, and a refractive index in the transverse direction. By setting the difference between n _TD and the longitudinal refractive index n _MD to 0.030 or more, it has excellent flatness, easy running performance, wear resistance (less generation of white powder), and scratch resistance. A biaxially oriented polyester film useful as a base film for magnetic recording media with a small amount of oxidation can be obtained.

Claims (1)

[Claims] 1. The refractive index n〓 in the thickness direction of the film is 1.492 or more, and the length of the protrusion and the major axis of the protrusion are at least
The number A (pieces/mm ² ) of uneven units consisting of 0.5 μm depressions per 1 mm ² of film surface area satisfies the formula,
(A) 0.01 to 1.0% by weight of internal particles containing lithium, calcium, and phosphorus elements; and (B) 0.001 to 1.0% of inert external particles made of calcium oxide or inorganic salt with an average particle size of 0.1 to 10.0 μm. A biaxially stretched polyester film for magnetic recording media containing 0.7% by weight. 0≦A≦10000... 2 Difference between refractive index n _TD in the transverse direction of the film and refractive index n _MD in the longitudinal direction n _TD −n _MD ≧0.030, which is the excellent scratch resistance described in claim 1 Biaxially stretched polyester film for magnetic recording media.