JPH044652B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a polyester film for magnetic recording media. More specifically, the present invention relates to a biaxially stretched polyester film for use in magnetic recording media that is flat, easily slippery, and has excellent adhesion to a magnetic layer. Biaxially oriented polyester film has excellent mechanical, thermal, and electrical properties and is widely used in a variety of applications.In particular, it is used as a base film for magnetic recording media because it has many of the required properties. In order to satisfy this demand, production volume has increased significantly in recent years. Base films for magnetic recording media must satisfy various required properties, and among these, it is important for base films for magnetic tapes to have excellent running properties and electrical properties. For base films, runnability refers to the slipperiness between the film and stretching rolls during the film forming process,
Regarding the film after forming the magnetic layer, this refers to the slipperiness with the magnetic layer or the polyester film on the back side of the magnetic layer during winding, or the slipperiness when used as a magnetic recording medium. Conventionally, a method has been used in which a roughening substance is added to the base film to appropriately roughen the film surface. However, if the surface roughness is increased using this method, the electrical characteristics of the magnetic tape will deteriorate. Therefore,
It is extremely difficult to satisfy both running performance and electrical characteristics at the same time, and quality design is currently being done while balancing both characteristics. However, in recent years there has been a growing demand for higher quality video tapes, that is, higher recording density and higher image quality, and it is necessary to minimize the spacing loss between the magnetic layer and the magnetic head, so the base film has become flatter. is moving in the direction of However, when the surface of the base film is made flat, various problems arise due to poor slippage during the film manufacturing process. For example, problems such as scratches on the film caused by various rolls during the film manufacturing process, wrinkles and uneven edges when winding the film onto rolls, and even bulge-like defects on the film surface occur. This significantly reduces film production yield. On the other hand, when manufacturing magnetic tape using such a flat base film, it is not only difficult to rewind smoothly due to poor slippage of the base film, it is difficult to pass through the process, and the product yield is low. When I put it on a video deck, it causes poor running. In order to improve running properties, a solution is generally provided by providing a back coat layer on the diamagnetic layer side. However, implementing this method increases the number of steps and requires new equipment, which increases costs.
A flat and smooth base film with excellent runnability even without a back coat is desired. Furthermore, it is thought that these magnetic tapes will be used outdoors more frequently in the future, and it is required that the slipperiness of the tapes does not deteriorate even under harsh environments such as high temperature and high humidity than ever before. Furthermore, one of the properties required for a base film for magnetic recording media is excellent adhesion to magnetic paints. The present inventors have completed the present invention as a result of extensive research into a polyester base film for magnetic recording media that is flat, easily slippery, and has excellent adhesion to magnetic coatings. That is, in the present invention, the numbers H ₁ and H ₂ (number/mm ² ) of first-order and second-order interference fringes measured by multiple interferometry satisfy the following formulas (1), (2), and (3). , 1≦H ₁ ≦150 …(1) 0≦H ₂ ≦70 …(2) H ₂ /H ₁ ≦1 …(3) and a bisamide represented by the following general formula (4) or (5) A biaxially stretched polyester film for magnetic recording media containing 0.005 to 1.0% by weight of a compound. In the above formula, R ₁ represents an alkylene group having 1 to 12 carbon atoms, R ₂ and R ₃ represent an alkyl group having 8 to 30 carbon atoms, R ₄ represents hydrogen or a methyl group, and R ₅ represents a carbon number Represents a divalent hydrocarbon residue containing 1 to 12 alkylene groups or aromatic or aliphatic rings. The present invention will be explained in more detail below. The polyester forming the polyester film as used in the present invention refers to a polyester obtained using terephthalic acid or 2,6-naphthalene dicarboxylic acid or an alkyl ester thereof as an acid component and ethylene glycol as the main starting materials, but other third materials may also be used. The ingredients may be used as part of the raw materials. The third component includes one or more aromatic dicarboxylic acid components such as isophthalic acid, phthalic acid, or alkyl esters thereof, and the glycol component includes propylene glycol, tetramethylene glycol, and cyclohexanedimethanol (1,4). , polyethylene glycol, polytetramethylene glycol, etc., or two or more thereof can be used. In any case, the polyester of the present invention refers to a polyester in which at least 80% of the repeating structural units are ethylene terephthalate units or ethylene naphthalate units. In the present invention, the number of n-th interference fringes Hn (number/
mm ² ) within the specified ranges mentioned above. If the number of H ₁ is less than one, even if a bisamide compound is added, the sliding properties will be insufficient, which is not preferable. H ₁ is over 150 or
If H ₂ exceeds 70, it is undesirable because H ₃ which inevitably affects dropout increases. Furthermore, if H ₂ /H ₁ exceeds 1, it is not preferable because the video output decreases. Methods for imparting roughness to the surface of such a polyester film include a method using insoluble fine particles based on the catalyst residue used in producing polyester (precipitation method), a method using silica, alumina, which is a compound insoluble in polyester, calcination, or water. Examples include a method (addition method) of adding fine powder (average particle size 0.01 to 5 μm) of aluminum silicate, cowsium carbonate, talc, calcium fluoride, cowsium terephthalate, and the like. Further, the surface of the film can also be roughened by adding an insoluble organic compound to the polyester. These organic compounds include fine particles of high melting point aromatic polyamides, fluororesins, polyphenylene sulfide resins, polysulfone resins, and crosslinked polymers, such as copolymers of divinylbenzene and methacrylic acid. In the present invention, by containing a small amount of a bisamide compound, the slipperiness of the film is greatly improved without affecting the surface roughness of the film, and the adhesion to the magnetic paint is also improved. The bisamide compound used in the present invention is represented by the above general formula (4) or (5), where R ₁ represents an alkylene group having 1 to 12 carbon atoms, and specifically, , methylene group, ethylene group, trimethylene group, tetramethylene group, hexamethylene group, octamethylene group, decamethylene group, dodecamethylene group, and the like. Preferably, R ₁ is an alkylene group having 1 to 6 carbon atoms. R ₂ and R ₃ represent an alkyl group having 8 to 30 carbon atoms, specifically octyl group, nonyl group, decyl group, undecyl group, dodecyl group, tridecyl group,
Examples include a tetradecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group, an octadecyl group, a nonadecyl group, an eicosyl group, a heneicosyl group, a docosyl group, a heptacyl group, a triaconcyl group, and the like. Preferably R ₂ and R ₃ have 12 carbon atoms
~30 alkyl groups. These R ₁ to R ₃ may have a branched chain. R ₄ represents hydrogen or a methyl group. The bisamide compound represented by the above general formula (4) includes alkylene diamines such as ethylenediamine, propylene diamine, butylene diamine, hexamethylene diamine, octamethylene diamine, decamethylene diamine, and dodecamethylene diamine, stearic acid, capric acid, decanoic acid, It can be obtained by reaction with fatty acids such as lauric acid, myristic acid, palmitic acid, arachidic acid, behenic acid, oleic acid, elaidic acid, montanic acid, and carnaubic acid, but representative compounds include N,
N'-methylene bisstearamide, N,
N'-ethylene bisstearamide, N,
N'-butylene bisstearamide, N,
N'-butylene bismyristic acid amide, N,
Examples include N'-hexamethylene bisbehenic acid amide. In the above general formula (5), R ₅ represents an alkylene group having 1 to 12 carbon atoms or a divalent hydrocarbon residue containing an aromatic ring or an aliphatic ring. Specifically, arylene groups such as phenylene groups and naphthylene groups; arylene groups such as xylylene groups in which two hydrogen atoms of an aromatic hydrocarbon are replaced with two alkylene groups; or diphenylene groups. Diarylene realkylene groups such as rimethylene groups, aryl-substituted alkylene groups, cyclopropenylene groups,
Preferred examples include cycloalkylene groups having 6 or more carbon atoms, such as cyclohexylene groups and cyclopentylene groups. These may have a substituent. The bisamide compound represented by the general formula (5) includes octylamine, decylamine, pentadecylamine, heptadecylamine, ortadecylamine,
Alkyl monoamines such as dodecylamine, cyclohexanedicarboxylic acid, succinic acid, adipic acid, sebacic acid, terephthalic acid, isophthalic acid,
It can be obtained by reaction with phenylethyldicarboxylic acid, phenylethanedicarboxylic acid, naphthalene dicarboxylic acid, biphenyldicarboxylic acid, etc.
Representative examples include N,N'-diheptadecyl adipic acid amide, N,N'-diheptadecyl sebacic acid amide, N,N'-diheptadecyl terephthalic acid amide, and N,N'-dihenyl adipic acid amide. Examples include eicosyl terephthalic acid amide. These bisamide compounds, regardless of the compounds represented by general formulas (4) and (5), may be used alone or as a mixture. The amount of the bisamide represented by formula (4) or (5) added is 0.005 to 1.0% by weight, preferably 0.01 to 0.5% by weight. If the amount added is less than 0.005% by weight, the effect will be insufficient. Even if it is used in an amount exceeding 1.0% by weight, no further improvement effect can be seen; on the contrary, it becomes difficult to uniformly disperse it in the polyester, and the rate of decrease in the degree of polymerization increases, which is not preferable. In producing the polyester film of the present invention, the bisamide is preferably added at a stage after producing the polyester resin and before extrusion molding. For example, it can be directly dispersed and mixed into polyester resin before extrusion molding, or a highly concentrated masterbatch resin can be prepared in advance, and this and polyester homopolymer can be diluted and mixed to a predetermined concentration, and then extrusion molded to form a film. It is also possible to adopt the method of In addition to the kneading method, for example, a method of adding after the completion of the polycondensation reaction is also possible. The method for producing the polyester film of the present invention is not particularly limited, but may be performed using a conventional polyester film production method such as a T-die method or an I-die method.
A method such as melt-extruding an amorphous sheet into a film at ~295°C, sequentially or simultaneously biaxially stretching in the longitudinal and transverse directions, and heat-treating at a predetermined temperature can be employed. It is preferable to bleed out the bisamide by heat treating the film so that the bisamide forms a suitable film on the surface of the polyester film. For this purpose, it is necessary to heat-treat the film. The heat treatment temperature is preferably 170 to 250°C.
The water droplet contact angle of the film thus obtained is 60~
Preferably, the angle is in the range of 80°. If the angle is less than 60°, the effect of improving running properties and adhesion to the magnetic layer is insufficient. Even if the angle exceeds 80°, no further improvement effect is shown. The biaxially stretched polyester film of the present invention preferably has a density in the range of 1.375 to 1.401 g/cm ³ . If the density is lower than 1.375g/ ^cm3 ,
The resulting polyester film has poor thermal properties and poor adhesion. On the other hand, the density is 1.401
If it exceeds g/cm ³ , mechanical properties deteriorate, which is not preferable. The magnetic coating material as used in the present invention refers to a coating material containing magnetic iron oxide and a binder resin, and in which a plasticizer, lubricant, dispersant, antistatic agent, etc. are mixed and dispersed as necessary. Binder resins include vinyl resins, cellulose resins, urethane resins, epoxy resins, phenoxy resins, etc., but the polyester film of the present invention is particularly suitable for magnetic paints for video tapes that use urethane resins as a binder. It is valid. The thickness of the polyester film is preferably in the range of 5 to 100 μm. The polyester film of the present invention exhibits excellent adhesion to magnetic paints, but may be subjected to other surface treatments such as ultraviolet irradiation, electron beam irradiation, corona discharge treatment, plasma or arc discharge treatment, if necessary. Next, a magnetic coating prepared by a known method (see, for example, Japanese Patent Laid-Open No. 52-43405) is coated on the polyester film, dried and aged to form a magnetic layer on the film. Magnetic paint is made by mixing magnetic iron oxide, such as γ-Fe ₂ O ₃ , doped with cobalt, or pure iron and additives such as binder resin, dispersant, and lubricant, and then adding an appropriate solvent. It is prepared by The thickness of the magnetic layer after drying is about 2 to 5 μm. The thus obtained magnetic recording material has excellent adhesion between the magnetic layer and the polyester film, and is easy to flatten and slide, so it has good electrical properties and runnability, and is suitable for magnetic applications such as audio and video applications. In addition to tapes, it is also suitably used as a magnetic recording medium for floppies and the like. Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples unless the gist thereof is exceeded. In addition, "part" and "%" in the examples indicate "part by weight" and "% by weight", respectively. The measurement method and evaluation method of the main characteristics in the present invention are shown below. (1) Measurement of surface roughness using multiple interference method After aluminum is deposited on the film surface, interference fringes are produced at a measurement wavelength of 0.54μ using multiple interference method, and the interference fringes are photographed to calculate the number of n-order interference fringes. Count and convert to 1 mm ² . The measuring instrument used was a Surf Eighth Finish Microscope manufactured by Nippon Kogaku Co., Ltd. The mirror reflectance was 65% and the microscope magnification was 200 times. (2) Coefficient of friction (μ) A film is wrapped around a fixed hard chrome-plated metal roll (diameter 6 mm) and brought into contact at an angle of 135° (θ), and a load of 53 g (T ₂ ) is applied to one end.
This was run at a speed of m/min, the resistance force (T ₂ (g)) at the other end was measured, and the coefficient of friction during running was determined using the following equation. μ=1/θln(T ₁ /T ₂ )=0.424ln(T ₁ /T ₂ ) (3) Constant temperature and humidity treatment test Using a constant temperature and humidity chamber manufactured by Tabai Seisakusho, 50℃, 80℃
% relative humidity, and after holding for 6 days, the coefficient of friction was measured. (4) Adhesion with magnetic paint A magnetic paint with the following composition was prepared. Composition part γ-Fe ₂ O ₃ 371 Polyurethane resin 65 Nitrocellulose 20 Polyvinyl chloride-polyvinyl acetate copolymer 30 Carbon black 12 Lecithin 4 Solvent (methyl ethyl ketone: toluene: methyl isobutyl ketone = 1:1:1) 90 Each of the above The ingredients are stirred and dispersed together in a sand grinder for 24 hours, then the isocyanate
5.6 parts were added and treated with a sand grinder for another 20 minutes to obtain a magnetic paint. This magnetic paint is applied to a biaxially stretched polyester film with a dry film thickness of approximately 5 μm.
It was coated with a coater so that it had a thickness of m, dried at 80°C for 1 minute, and then aged at 80°C for 20 hours. Thereafter, this coated film was cut into 12.7 mm width along the length direction, and the adhesive strength was measured. That is, a double-sided adhesive tape is pasted on a stainless steel plate with a thickness of 1 mm, and a magnetic recording body is pasted thereon so that the magnetic layer surface of the magnetic recording body is in contact with the adhesive tape. After that, the polyester film was peeled off from the magnetic layer at an angle of 180°, and the peeling resistance was measured using a tensile tester at 1000 mm/min.
Measure at a speed of (5) Contact angle of film The contact angle of the film with distilled water was measured at 20°C and 65% humidity using a goniometer manufactured by Elma Optical.
The diameter of the water droplet is approximately 2 mm. (6) Intrinsic viscosity [η] 1 g of polymer was dissolved in 100 ml of a mixed solvent of phenol/tetrachloroethane = 50/50 (weight ratio) and measured at 30°C. (7) Solution haze Dissolve 2.7 g of polymer in 20 ml of mixed solvent of phenol/tetrachloroethane = 60/40 (weight ratio), and measure 1 cm using a Nippon Denshoku turbidity meter (SR type).
Measured using a cell. Example 1 100 parts of dimethyl terephthalate, 70 parts of ethylene glycol, 0.08 parts of calcium acetate monohydrate, and 0.018 parts of lithium acetate dihydrate were placed in a reactor, heated to raise the temperature, and methanol was distilled off to carry out the transesterification reaction. It took 4 hours from the start of the reaction to raise the temperature to 230°C to substantially complete the transesterification reaction. Next, 0.05 part of phosphoric acid, 0.19 part of triethyl phosphate,
After adding 0.04 part of antimony trioxide, a polycondensation reaction was carried out according to a conventional method. After 3.5 hours, the reaction was stopped and the pressure in the system was restored with nitrogen to obtain a polyester resin with [η] 0.66 and solution haze 12%. After adding 0.1 part of fine powder of N,N'-hexamethylene bisstearic acid amide to 100 parts of polyester resin containing fine particles based on this catalyst residue and mixing uniformly, the mixture was melted at 290°C, and then melted in a T-die. After extrusion and quenching, the film was stretched 4 times in the longitudinal direction at 95°C, 3.5 times in the transverse direction at 105°C, and heat set at 220°C to obtain a biaxially stretched film with a thickness of 15 μm.
The number of protrusions on the surface of the obtained film, coefficient of friction, adhesive strength with magnetic paint, slippage after constant temperature and humidity treatment,
The contact angle of water droplets etc. were evaluated. The results are shown in Table 1 together with the results of the following Examples and Comparative Examples. Example 2 A film was obtained and evaluated in the same manner as in Example 1, except that the amount of N,N'-hexamethylene bisstearamide was changed to 0.03 part. Comparative Example 1 A film was obtained and evaluated in the same manner as in Example 1 except that N,N'-hexamethylene bisstearamide was not added. Example 3 98 parts of a polyethylene terephthalate resin containing almost no particles that would roughen the film surface was vacuum-dried in advance at 180° C. for 6 hours. After cooling the resin, 2 parts of fine powder of N,N'-hexamethylene bisstearamide was added and mixed, and then kneaded at 280°C using an extruder to give a 2%
A masterbatch resin containing N,N'-hexamethylene bisstearamide was prepared. 97.5 parts of the polyester resin obtained in Example 1 before addition of N,N'-hexamethylene bisstearamide and 2.5 parts of the above masterbatch resin were dry blended, and after vacuum drying at 180°C for 6 hours, the mixture of Example 1 and Similarly, melt extrusion, stretching, and heat setting were performed to obtain a biaxially stretched film with a thickness of 15 μm, which was then evaluated. Example 4 and Comparative Example 2 Transesterification was carried out in the same manner as in Example 1, and then 0.20 part of triethyl phosphate, 0.02 part of phosphoric acid, and 0.04 part of antimony trioxide were added to the transesterification product, and then The polycondensation reaction was carried out according to the method. The obtained polymer had a [η] of 0.66 and a solution haze of 25%. Next, this polyester resin
0.05 part of N,N'-hexamethylene bisbehenic acid amide was added and mixed to 100 parts, and the mixture was made into a film in the same manner as in Example 1 to obtain a biaxially stretched polyester film with a thickness of 15 μm, and evaluation was performed. . For comparison, the case where N,N'-hexamethylene bisbehenic acid amide was not added was also evaluated (Comparative Example 2). Example 5 and Comparative Example 3 100 parts of dimethyl terephthalate, 70 parts of ethylene glycol and 0.08 parts of calcium acetate monohydrate were placed in a reactor to carry out a transesterification reaction. 0.22 parts of calcium acetate, 0.29 parts of triethyl phosphite, 0.065 parts of triethyl phosphite, and 0.045 parts of antimony trioxide were added to the transesterification product, and a polycondensation reaction was carried out to obtain a polyethylene terephthalate resin with [η] 0.64. . Solution haze is 22
It was %. 0.05 part of N,N'-hexamethylene bisbehenic acid amide was added and mixed to 100 parts of this polyester resin, and the mixture was extruded and stretched in the same manner as in Example 1 to obtain a thickness.
A biaxially stretched polyester film of 15 μm was obtained and evaluated. For comparison, the case where N,N'-hexamethylene bisbehenic acid amide was not added was also evaluated (Comparative Example 3). Example 6 and Comparative Example 4 100 parts of dimethyl terephthalate, 70 parts of ethylene glycol and 0.08 parts of calcium acetate monohydrate were placed in a reactor to carry out a transesterification reaction. After completion of the transesterification reaction, 0.037 parts of phosphoric acid, average particle size of 0.9μ
0.2 parts of kaolin of m and 0.035 parts of antimony trioxide were added to carry out a polycondensation reaction to obtain polyethylene terephthalate of [η] of 0.65. Solution haze is 11%
It was hot. N to 100 parts of this polyethylene terephthalate,
A biaxially stretched film having a thickness of 15 μm was obtained in the same manner as in Example 1 by adding 0.2 part of N'-diheptadecyl terephthalic acid amide, and evaluated. For comparison, a case in which N,N'-diheptadecyl terephthalic acid amide was not added was also evaluated (Comparative Example 4).

[Table] As is clear from the above results, the biaxially stretched polyester film of the present invention has extremely good slip properties, and even when subjected to constant temperature and humidity treatment, the slip properties do not deteriorate, and water droplets The contact angle is within a preferable range, and the film has excellent adhesion to magnetic paints, making it extremely desirable as a base film for magnetic recording media.

Claims (1)

[Claims] 1. The numbers H ₁ and H ₂ (number/mm ² ) of primary and secondary interference fringes measured by multiple interferometry satisfy the following formulas (1), (2), and (3). 1≦H ₁ ≦150 …(1) 0≦H ₂ ≦70 …(2) H ₂ /H ₁ ≦1 …(3) and expressed by the following general formula (4) or (5) A biaxially stretched polyester film for magnetic recording media containing 0.005 to 1.0% by weight of a bisamide compound. In the above formula, R ₁ represents an alkylene group having 1 to 12 carbon atoms, R ₂ and R ₃ represent an alkyl group having 8 to 30 carbon atoms, R ₄ represents hydrogen or a methyl group, and R ₅ represents a carbon number Represents a divalent hydrocarbon residue containing 1 to 12 alkylene groups or aromatic or aliphatic rings. 2. The biaxially stretched polyester film for magnetic recording media according to claim 1, wherein the contact angle of water droplets on the film surface is in the range of 60° to 80°.