JPH0314858B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a base film for magnetic recording media, and more particularly to a base film for magnetic recording media with excellent wear resistance. [Prior Art] Biaxially oriented polyethylene terephthalate films are known as base films for magnetic recording media (for example, Japanese Patent Publication No. 40929/1983). [Problems to be Solved by the Invention] However, the above-mentioned conventional base film for magnetic recording media does not have sufficient wear resistance, especially in the recent 8
Because the recording wavelength of millimeter video tapes is short, less than 1 μm, the powder generated when the film surface is scraped is
This is causing a major problem in the output characteristics of the tape. It is an object of the present invention to solve these problems and provide a base film for magnetic recording media with excellent wear resistance. [Means for solving the problems] The present invention uses a composition consisting of 4 to 50% by weight of polyester (B) and 96 to 50% by weight of polyester (A) whose main repeating unit is ethylene terephthalate as the main components. A biaxially oriented base film for magnetic recording media, wherein inert inorganic particles with an average particle size of 0.03 to 2.5 μm are added to the polyester (B) in a proportion of 0.1 to 2.5 μm.
5.0% by weight, and the square of the glass transition point (Tg ² ) and crystallization parameter (△
Tcg) (Tg ² /△Tcg) is 118 to 1000, and the cohesive energy density of the polyester (B) is 120
~175 Cal/cc, and furthermore, the product (φ・μs) of the inert inorganic particle content φ (weight %) and the static friction coefficient μs in the base film for magnetic recording media is 0.02~
The present invention relates to a base film for magnetic recording media, characterized in that the magnetic recording medium has a hardness of 0.6. Polyester A in the present invention is a polyester whose main repeating unit is ethylene terephthalate. However, other components may be copolymerized within a range that does not impede the present invention, preferably within 5 mol%. Also, polyester B
It is necessary that the ratio of the square of the glass transition point Tg ² to the crystallization parameter ΔTcg, Tg ² /Tcg, is in the range of 118 to 1000, preferably 120 to 760, more preferably 120 to 600. Even if Tg ² /ΔTcg is smaller or larger than the above range, it is not preferable because the abrasion resistance of the film will be poor. The cohesive energy density of polyester B is 120~
It is necessary that it is 175 Cal/cc, preferably 130 to 165 Cal/cc. It is not preferable if the cohesive energy is smaller than the above range or larger than the above range because the abrasion resistance of the film becomes poor. Polyesters whose Tg ₂ /ΔTcg and cohesive energy density satisfy the above ranges include polybutylene terephthalate, polyethylene-2,6-naphthalate, polyethylene-α, β-bis(2-chlorophenoxy)ethane 4,4′- Examples include dicarboxylate, polyethylene-α, β-bis(phenoxy)ethane 4,4'-dicarboxylate, and particularly preferred is polybutylene terephthalate. The film of the present invention has the above-mentioned polyesters A and B as main components, and the ratio thereof is 96 to 50% by weight of polyester A and 4 to 50% by weight of polyester B, preferably,
Polyester A93-60% by weight, Polyester B7
~40% by weight, more preferably polyester
A content of 85 to 70% by weight and polyester B of 15 to 30% by weight are required. If the proportion of polyester B is smaller than the above range, the abrasion resistance of the film will be poor, which is not preferable. Moreover, if the ratio of polyester B is larger than the above range, the abrasion resistance of the film will be poor, which is not preferable. The film of the present invention has an average particle size of 0.03 to 2.5 μm,
Preferably 0.1 to 2.0 μm, more preferably 0.1 to 2.0 μm
1.0μm inert inorganic particles to polyester B
It is necessary that the content be 0.1 to 5.0% by weight, preferably 0.3 to 3.0% by weight, and more preferably 0.7 to 2.0% by weight. If the average particle diameter of the inert inorganic particles is smaller than the above range, the abrasion resistance of the film will be poor, making it undesirable as a base film for magnetic recording media. Furthermore, if the average particle size is larger than the above range, the abrasion resistance of the film will be poor, which is not preferable. If the content of inert inorganic particles in polyester B is less than the above range, the abrasion resistance of the film will be poor, which is not preferable. Further, if the content is greater than the above range, the abrasion resistance of the film will be poor, which is not preferable. The inert inorganic particles in the present invention are not particularly limited as long as they are inactive to polyester, but
_SiO2 , _CaCO3 , MgO, ZnO, _MgCO3 , _{Al2O3 ,}
It is particularly desirable that the film be selected from TiO ₂ because the abrasion resistance of the film will be even better. Further, two or more types of inert inorganic particles may be used, but in that case, the total content of each must be within the above range. The film of the present invention has the above-mentioned composition as a main component, but other polymers may be blended within the range that does not impede the purpose of the present invention, and antioxidants, heat stabilizers, lubricants, ultraviolet absorbers, etc. agent, nucleating agent,
Inorganic or organic additives such as these may be added to the extent that they are normally added. The film of the present invention is a film in which the above-mentioned composition is biaxially oriented, and the inert inorganic particle content φ (weight %) in the film and the static friction coefficient μs of the film are
It is necessary that the product (φ·μs) is 0.6 or less, preferably 0.4 or less, and more preferably 0.35 or less. If φ·μs is larger than the above range, the abrasion resistance of the film will be poor, which is not preferable.
The lower limit of φ·μs is not particularly limited, but about 0.02 is the manufacturing limit. In addition, the melt viscosity of polyester A constituting the film of the present invention is 700 to 5000, and the melt viscosity of polyester B is 1000.
It is particularly desirable that the melt viscosity of polyester A is lower than that of B at 10,000 poise because the abrasion resistance of the film will be even better. Furthermore, the refractive index in the thickness direction of the film of the present invention is 1.55.
Below, it is particularly desirable that the abrasion resistance of the film becomes even better when it is preferably 1.50 or less. Further, the Young's modulus (sum of longitudinal direction and width direction) of the film of the present invention is 700 Kg/mm ² , preferably 800 Kg/mm ²
The above is particularly desirable since the abrasion resistance of the film becomes even better. Furthermore, it is particularly desirable when the matrix closest to the inert inorganic particles forming the protrusions on the surface of the film of the present invention is polyester B, since the abrasion resistance of the film is further improved. Whether the matrix closest to the inert inorganic particles is polyester B can be determined by ESCA (X-ray photoelectron spectroscopy) or SIMS.
This can be confirmed using analysis methods that use electromagnetic waves, such as (secondary ion mass spectrometry) and MOLE (Raman microprobe). Next, a method for manufacturing a base film for magnetic recording media according to the present invention will be explained. First, as a method for incorporating inert inorganic particles, particles with a primary average particle size of 0.03 to 2.5 μm are added to the diol component of polyester B in the form of a slurry.
The method of mixing and dispersing in a predetermined amount is such that the product of the inert inorganic particle ratio φ (wt%) in the film and the static friction coefficient μs of the film, φ・μs, is within the range of the present invention,
It is extremely effective in improving the abrasion resistance of the film. Next, this polyester B and polyester A are mixed in a predetermined ratio. Mixing can be done by a known method, but after thoroughly mixing both pellets using a Henschel mixer, etc., pelletize the mixture using a melt extruder in advance to make pellets of the mixture, and feed the pellets to the melt extruder. The general method is to form a film using a Henschel Mexer or the like, or to directly feed a mixture of both pellets into a melt extruder to form a film. Also,
In order to obtain the φ·μs of the film of the present invention, the melt mixing conditions of the present invention are such that the mixture does not become a completely random copolymer. Randomness in this case is, for example,
It can be measured by sequence distribution using 13CNMR at 100MHZ. After sufficiently drying the pellets of the mixture of both or the mixture of pellets of both thus obtained,
The pellets are fed to a known melt extruder at a temperature above the temperature at which the pellets melt and below the temperature at which the polymer decomposes.
It is melt-extruded into a sheet through a slit-shaped die, cooled and solidified to produce an unstretched film. Next, this unstretched film is biaxially stretched and oriented. As the stretching method, a sequential biaxial stretching method or a simultaneous biaxial stretching method can be used, but a sequential biaxial stretching method is particularly preferred. In this case, suitable stretching conditions include stretching 3.0 to 4.0 times in the longitudinal direction at 60 to 90°C and then stretching 3.2 to 4.2 times in the width direction at 70 to 100°C. In addition, this stretched film
A method of further stretching in at least one direction is effective for improving the abrasion resistance of the film. Next, the stretched film is heat-treated, and the heat treatment conditions in this case include heat treatment at a temperature of 190°C to 240°C, more preferably 200°C to 220°C, for 0.5 to 60 seconds. This is effective in keeping μs within the range of the present invention. Furthermore, it is effective to carry out the heat treatment under a constant length condition in order to keep the φ·μs of the film within the range of the present invention. [Method for Measuring Physical Properties and Evaluating Effects] Methods for measuring characteristic values and evaluating effects of the present invention are as follows. (1) Average particle size of inert particles Capture an image of the particles using a scanning electron microscope, connect the light shading produced by the particles to an image analyzer (for example, QTM900: manufactured by Cambridge Instruments), This is the number average diameter φn obtained by the following numerical processing. Σdn/Σn=φn where n is the number and d is the effective diameter. (2) Amount of inert inorganic particles Measurement of amount of precipitated particles: O-
After adding 1.0 l of chlorphenol and heating at 120°C for 3 hours, use an ultracentrifuge 55-P-72 manufactured by Hitachi Koki Co., Ltd.
The particles obtained by centrifugation at 30,000 γpm for 40 minutes are vacuum dried at 100°C. When the fine particles are measured using a scanning differential calorimeter, if a destruction peak corresponding to the polymer is observed, the fine particles are heated and cooled with o-chlorophenol and then centrifuged again. When the melting peak is no longer observed, the fine particles are considered to be precipitated particles. Normally, two centrifugation operations are sufficient. (3) Glass transition point Tg, cold crystallization temperature Tcc Measured using a DSC (differential scanning calorimeter) manufactured by PerkinElmer. The DSC measurement conditions are as follows. i.e. 10mg of sample film
is placed in a DSC apparatus, melted for 5 minutes at a temperature of (melting point + 30°C), and then rapidly cooled in liquid nitrogen. This rapidly cooled sample was heated at a rate of 10°C/min to reach the glass transition point Tg.
Detect. As the temperature continues to rise further, the exothermic peak temperature of crystallization from the glass state is reached, and the temperature reaches the cold crystallization temperature.
It was set as Tcc. (4) Crystallization parameter △Tcg The difference between Tg and Tcc above (Tcc − Tg)
Tcg. In addition, for polymers in which Tcc was not observed, ΔTcg was set to 100°C. (5) Cohesive energy density The cohesive energy density (molar evaporation energy/molar volume) per repeating unit of the polymer was calculated using Fedors' method (atomic group contribution method).
For Fedors' method, see Polym.eng.sci.
14147 (1947) or Jitsugaku Kobunshi p.73 (1981) (Kodansha Scientific). Note that the value at 25°C was calculated without considering correction based on the glass transition point of the polymer. (6) Static friction coefficient Using a slip tester manufactured by Toyo Testa,
Measured according to ASTM-D-1894. (7) Melt viscosity Measured using a Koka type flow tester at a temperature of 290°C and a shear rate of 200sec ^-1 . (8) Refractive index Measured at 25° C. and 65% RH using an Atsupé refractometer using sodium D line (wavelength 589 nm) as a light source. Note that a methylene iodide solution was used as the mounting solution. (9) Young's modulus Measured at 25° C. and 65% RH using an Instron tensile tester according to ASTM-D-882. (10) Abrasion resistance The sample film and “Mylar” PB (polyester film manufactured by Dupont) were rubbed together 200 times (load: 2 kg, rotation speed).
60γpm). Next, apply Al to “Mylar” to a thickness of approximately 1000 mm.
Deposited with Å and analyzed using an image analyzing computer (manufactured by Cambridge Instruments).
The area fraction (%) of protrusions with a size of 50 μm or more was defined as a white powder index (magnification: 5×8 times, reflection method). When this white powder index was less than 0.001%, it was determined that the abrasion resistance was good, and when it was 0.001% or more, it was determined that the abrasion resistance was poor. [Example] The present invention will be described based on an example. Examples 1 to 3, Comparative Examples 1 to 7 Dimethyl bis α・β-(2-chlorophenoxy)ethane 4,4′-dicarboxylate (melting point 194 to 196
30 parts of ethylene glycol, 11.2 parts of ethylene glycol, and 0.01 part of tetrabutyl titanate are heated to the boiling point of ethylene glycol under normal pressure, and reacted for 2 hours while distilling off the methanol produced. Then, the reaction temperature is gradually raised to 240°C to distill off excess ethylene glycol. Next, the temperature was raised to 280°C, 0.01 part of trimethyl phosphate was added, the pressure was gradually reduced, and the reaction mixture was polycondensed for 3 hours at 0.5 to 1.0 mmHg with thorough stirring. -chlorophenoxy)ethane 4,4' dicarboxylate was obtained. Incidentally, various types of silica (SiO ₂ ) having different average particle sizes were added to the above-mentioned ethylene glycol in the form of a slurry in the amounts shown in Table 1 relative to the above-mentioned polyester. These pellets and polyethylene terephthalate pellets were blended in a Henschel mixer at different mixing weight ratios. This mixed pellet was dried under reduced pressure (3 Torr) at 180°C for 3 hours.
The pellets were fed into an extruder and melted and extruded at 300°C, then wound around a casting drum with a surface temperature of 30°C using an electrostatic casting method, and cooled and solidified to produce an unstretched film with a thickness of approximately 150 μm. . This unstretched film was stretched 3.4 times in the longitudinal direction at 90°C. This stretching is performed using a difference in peripheral speed between two sets of rolls,
The stretching speed was 10,000%/min. This uniaxial film was stretched to 100% using a stenter at a stretching speed of 2000%/min.
Stretched 3.6 times in the width direction at ℃ and stretched 5 times at 210℃ under constant length.
Heat treatment was performed for seconds to obtain a film with a thickness of 12 μm. The average particle size of inorganic particles (SiO ₂ ) in this film is as shown in Table 1, and the content is polyethylene-α, β-bis(2-chlorophenoxy)ethane 4,4'-dicarboxylic The rates were as shown in Table 1. Further, the product of the inert inorganic particle content φ (weight %) in the film and the static friction coefficient μs of the film, φ·μs, was as shown in Table 1. As can be seen from Table 1, in the case of the present invention, the content of inert inorganic particles, the average particle size, the mixing ratio of the two types of polyester, or the above φ/μs, the wear resistance is excellent. Films were obtained (Examples 1 to 3), but when those characteristic values were outside the range of the present invention, films with excellent abrasion resistance were not obtained (Comparative Examples 1 to 7). Examples 4 to 6, Comparative Examples 8 to 11 Similarly to Example 1, calcium carbonate (CaCO ₃ ) with an average particle size of 0.24 μm was added during polymerization of various polyesters, and the content was 1.0% by weight based on the polyester. made polymer pellets. This polyester B and polyethylene terephthalate A
were mixed using a Henschel mixer at a weight ratio of A/B=80/20. Using this mixed pellet, a biaxially oriented film with a thickness of 7 μm was produced in the same manner as in Example 1. As a result of evaluating the abrasion resistance of these films, as shown in Table 2, the abrasion resistance was good when the properties of Polymer B were within the range of the present invention, but the properties of Polymer B were within the range of the present invention. In other cases, no matter how the φ and μs of the film were adjusted, a film with excellent abrasion resistance could not be obtained. [Effects of the Invention] The present invention provides a base film for magnetic recording media with excellent wear resistance by combining polyester with specific thermal properties and inert inorganic particles and limiting the surface parameters (φ・μs). It is something that The base film for magnetic recording media of the present invention can be used for various recording media, but it is particularly preferable to use it as a base film for video tapes and computer tapes, taking advantage of its excellent abrasion resistance. In addition, the film of the present invention may be subjected to a known corona discharge treatment (in air, nitrogen, carbon dioxide, etc.), and may also be subjected to a known corona discharge treatment (in air, nitrogen, carbon dioxide, etc.), or for the purpose of imparting adhesiveness, moisture resistance, heat sealability, slipperiness, etc. It may also be used in the form of a laminate of other types of polymers or in the form of a coating with other organic or inorganic compositions.

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Claims (1)

[Claims] 1. A biaxially oriented base film for magnetic recording media, the main component of which is a composition consisting of 4 to 50% by weight of polyester (B) and 96 to 50% by weight of polyester (A) whose main repeating unit is ethylene terephthalate. containing 0.1 to 5.0% by weight of inert inorganic particles with an average particle size of 0.03 to 2.5 μm based on the polyester (B), and having a
The ratio (Tg ² /△Tcg) of the power (Tg ² ) to the crystallization parameter (△Tcg) is 118 to 1000, and the cohesive energy density of the polyester (B) is 120 to 175 Cal/cc, and the above magnetic A base film for a magnetic recording medium, characterized in that the product (φ·μs) of the inert inorganic particle content φ (weight %) and the coefficient of static friction μs is 0.02 to 0.6.