JPH0430977B2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a biaxially stretched polyester film for magnetic recording, and more specifically, it has excellent electromagnetic conversion properties, surface flatness, and runnability, as well as low light transmittance. This invention relates to a biaxially stretched polyester film for magnetic recording. <Prior Art> Polyester films are used in various applications such as magnetic tape applications and electrical applications. In recent years, in magnetic tape applications, especially video tape applications,
Suitable for high-density recording, a smooth film surface is required to improve electromagnetic conversion characteristics, and a low coefficient of friction is required to improve tape runnability, abrasion resistance, and durability on decks. ing. At the same time, the ferromagnetic powder used in these magnetic tapes is becoming increasingly finer. When the magnetic powder is pulverized, light with a long wavelength is less likely to be scattered by the magnetic powder, resulting in higher light transmittance.
For this reason, in a magnetic recording medium in which termination is detected using the difference in light transmittance between the nonmagnetic support and the magnetic recording layer, it is necessary to lower the light transmittance. Conventionally, colored inorganic fine powders such as antistatic agents and abrasives were included in the magnetic recording layer to reduce light transmittance, but this method had limitations in terms of electromagnetic conversion characteristics, head wear, etc. It was hot. Therefore, attempts have been made to lower the light transmittance of the base film, and it has been proposed to incorporate a light shielding agent such as carbon black into the polyester film. However, if a sufficient amount of carbon black is used to lower the light transmittance, the surface of the polyester film will become rough, and this roughening will cause the surface after applying the magnetic paint to become rough, resulting in electromagnetic conversion characteristics. New problems arise, such as the tendency for conditions to worsen. As a method to improve this problem, dispersants for improving the dispersion of carbon black are being studied. However, at present, no film has yet been found that can satisfy the flatness of the film surface. <Purpose of the Invention> As a result of research to obtain a biaxially oriented polyester film with further improved surface flatness and excellent light-shielding properties, the present inventor has developed a carbon black with a specific primary particle size that has high light absorption ability. We discovered that when used in combination with inert solid fine particles with a high optical refractive index, sufficient light-shielding properties can be expressed even with a small amount of carbon black due to their synergistic effect.
We have arrived at the present invention. An object of the present invention is to provide a biaxially stretched polyester film for magnetic recording that has excellent electromagnetic characteristics, surface flatness, and runnability, as well as low light transmittance. <Structures and Effects of the Invention> According to the present invention, an object of the present invention is to combine 0.5 to 2.5% by weight of carbon black (A) with an average primary particle size of 0.04 to 0.2 μm and an optical Refractive index 1.8
A biaxially stretched polyester film containing 0.05 to 2.0% by weight of the above inert fixed fine particles (B) dispersed therein, the film has a light transmittance of 30% or less at a wavelength of 900 nm and a surface roughness of 0.007.
This is achieved by a biaxially stretched polyester film for magnetic recording, which is characterized by a thickness of ~0.024 μm. The polyester in the present invention is a polyester containing an aromatic dicarboxylic acid as a main acid component and an aliphatic glycol as a main glycol component. Such polyester is substantially linear;
It also has film-forming properties, particularly film-forming properties by melt molding. Examples of aromatic dicarboxylic acids include terephthalic acid, naphthalenedicarboxylic acid, isophthalic acid, diphenylethanedicarboxylic acid, diphenyldicarboxylic acid, diphenyl ether dicarboxylic acid, diphenylsulfonedicarboxylic acid, diphenylketonedicarboxylic acid, and anthracene. Examples include dicarboxylic acids. Examples of aliphatic glycols include polymethylene glycols having 2 to 10 carbon atoms such as ethylene glycol, trimethylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol, and decamethylene glycol, or alicyclic diols such as cyclohexanedimethanol. etc. can be given. In the present invention, polyesters containing, for example, alkylene terephthalate and/or alkylene naphthalate as main constituents are preferably used. Among such polyesters, for example, polyethylene terephthalate, polyethylene naphthalate, etc.
Particularly preferred are copolymers in which 80 mol% or more of the glycol component is terephthalic acid and/or naphthalene dicarboxylic acid, and 80 mol% or more of the total glycol component is ethylene glycol. In this case, the dicarboxylic acids accounting for up to 20 mol% of the total acid component can be the above-mentioned aromatic dicarboxylic acids; for example, aliphatic dicarboxylic acids such as adipic acid and sebacic acid; cyclohexane-1,
It can be an alicyclic dicarboxylic acid such as 4-dicarboxylic acid. In addition, 20% of the total glycol content
Up to mol% can be of the above glycols other than ethylene glycol, or of aromatic diols such as hydroquinone, resorcinol, 2,2-bis(4-hydroxyphenyl)propane; of 1,4-dihydroxymethylbenzene. Aliphatic diols containing an aromatic ring such as; polyalkylene glycols (polyoxyalkylene glycols) such as polyethylene glycol, polypropylene glycol, and polytetramethylene glycol can also be used. In addition, the polyester in the present invention includes, for example, an aromatic oxyacid such as hydroxybenzoic acid;
Also included are those containing a component derived from an oxycarboxylic acid such as an aliphatic oxyacid such as -hydroxycaproic acid in an amount of 20 mol % or less based on the total amount of the dicarboxylic acid component and the oxycarboxylic acid component. Furthermore, the polyester in the present invention contains a trifunctional or higher functional polycarboxylic acid or a polyhydroxy compound, such as trimellitic acid, in an amount within a substantially linear range, for example, an amount of 2 mol % or less based on the total acid components.
Copolymerized products such as pentaerythritol are also included. Such a polyester preferably has an intrinsic viscosity of 0.4 to 0.8 as measured at 35° C. as a solution in O-chlorophenol. In the present invention, carbon black (A) with an average primary particle size of 0.04 to 0.2 μm is added to polyester from 0.5 to 0.5 μm.
2.5% by weight, and a refractive index with an average particle size of 0.1-0.5μm
0.05-2.0% by weight of inert solid fine particles (B) of 1.8 or more
Uniformly disperse and contain. Thereby, sufficient light-shielding properties can be obtained even when the carbon black content is small. The reason for this sufficient light-shielding ability is not clear, but it is thought that inert solid particles with a high optical refractive index have a high light-scattering ability, and this is due to a synergistic effect between this and carbon black, which has a high light-absorbing ability. . This carbon black (A) may be used, but is not limited to, buttocket black, thermal black,
Channel black, furnace black, acetylene black, etc. are preferred. Furthermore, since carbon black tends to aggregate easily, it is preferable to add a dispersant and uniformly disperse it using a ball mill, sand mill, etc. before use. Polyvinylpyrrolidone is preferably used as the dispersant. If the average primary particle size of the carbon black exceeds 0.2 .mu.m, the surface of the film will become extremely rough due to the carbon black, which is undesirable. Furthermore, if the average primary particle size of carbon black is smaller than 0.04 μm, agglomeration tends to occur even if a dispersant is used, which is undesirable because surface roughness occurs. From these points, it is preferable that the average primary particle size of carbon black is 0.06 to 0.2 μm. In addition, the amount of carbon black added is 0.5% by weight.
If the amount is less, the light shielding property will be insufficient, and
If it exceeds 2.5% by weight, agglomeration will occur, and the surface will become rough due to unevenness, which is not preferable. The amount of carbon black added is 0.7~
2.0% by weight is preferred, and 0.8-1.5% by weight is particularly preferred. Furthermore, the inert solid fine particles (B) having an optical refractive index of 1.8 or higher include, but are not particularly limited to, titanium dioxide, black iron oxide (triiron tetroxide), zinc oxide,
Preferred examples include cadmium yellow, lithopone (zinc sulfide and pallium sulfate co-precipitated mixture), and the like. The average particle size of such inert solid fine particles is 0.10~
It is preferably in the range of 0.50 μm, more preferably in the range of 0.15 to 0.40 μm, particularly in the range of 0.20 to 0.35 μm. If the average particle size of the inert solid particles is too large,
This is undesirable because the surface roughness of the film becomes large, which deteriorates the electromagnetic conversion characteristics when used as a magnetic tape, and the synergistic effect with carbon black does not sufficiently improve light-shielding properties. Furthermore, if the average particle size is too small, agglomeration tends to occur, resulting in coarse protrusions, which may cause dropouts (missing signals) when used as a tape, for example, which is undesirable. In the present invention, the ratio of the content of inert solid fine particles (B) having an optical refractive index of 1.8 or more to the content of carbon black (A) (weight ratio: B/A) is expressed by the following formula: 0.05≦(B/A )≦0.8. This weight ratio (B/
Even if A) becomes too large or too small, sufficient light-shielding properties can be obtained, probably because the interaction between the inert solid fine particles (B), which has a high optical refractive index, and the carbon black (A) becomes small. Therefore, the total content of (A+B) increases, which is undesirable because the surface becomes rough. The weight ratio (B/A) is preferably 0.1 or more and 0.6 or less, more preferably 0.15 or more and 0.4 or less. In the present invention, in the polyester film,
In addition to carbon black (A) and inert solid fine particles (B) with an optical refractive index of 1.8 or more, inert particles (C ) is preferably included. Such inert particles preferably have an average particle diameter of 0.1 to 1.2 μm, and the amount thereof is preferably 0.03 to 1% by weight. The “inert particles” mentioned here are carbon black.
(A) and inert solid fine particles with an optical refractive index of 1.8 or more
It means things other than (B) that are solid at room temperature, such as metal salts of organic acids, inorganic substances, etc. Preferred inert particles (C)
As silicon dioxide (hydrate, diatomaceous earth,
(including silica sand, quartz, etc.), alumina, silicates containing 30% by weight or more of _SiO2 (e.g., amorphous or crystalline clay minerals, aluminosilicate compounds (including calcined products and hydrates), warm asbestos, zircon, fly ash, etc.), oxides of Mg, Zn and Zr, sulfates of Ca and Ba, Li, Na and Ca
phosphates (including monohydrogen salts and dihydrogen salts), Li,
Benzoate of Na and K, Ca, Ba, Zn and Mn
Terephthalates, Mg, Ca, Ba, Zn, Cd,
Pb, Sr, Mn, Fe, Co and Ni titanates,
Ba and Pb chromate, Ca and Mg carbonate,
glass (e.g. glass powder, glass beads, etc.),
Examples include fluorite and ZnS. Particularly preferably used are anhydrous silicic acid, hydrated silicic acid, aluminum oxide, aluminum silicate (including calcined products, hydrates, etc.), monolithium phosphate, trilithium phosphate, sodium phosphate, calcium phosphate, barium sulfate, Sodium benzoate, double salts of these compounds (including hydrates), glass powder, clay (including kaolin, bentonite, clay, etc.),
Examples include talc and diatomaceous earth. Inclusion of inert particles (C), carbon black (A), and inert solid fine particles (B) can be carried out by methods conventionally known as methods for containing fine particles. For example, inert particles (C), carbon black (A) and inert solid fine particles (B) can be added to the reaction system for producing the respective polyester, for example before, during or after the reaction. The biaxially stretched polyester film of the present invention needs to have a surface roughness (Ra) of 0.007 to 0.024 μm. If the surface roughness (Ra) exceeds 0.024 μm, the electromagnetic conversion characteristics when used as a magnetic tape will deteriorate, which is undesirable. On the other hand, if it becomes less than 0.007 μm, the surface roughness will become too flat, resulting in poor slipperiness and Wrinkles may occur during winding and processing, which is undesirable. The surface roughness (Ra) of the film is preferably 0.018 μm or less and 0.008 μm or more,
Particularly preferred is 0.014 μm or less and 0.009 μm or more. The biaxially stretched polyester film in the present invention must have a light transmittance of 30% or less at a wavelength of 900 nm. If the light transmittance of the film increases and its light shielding properties deteriorate, the light transmittance will also increase when it is used to make a magnetic tape, and as a result, the light transmittance between the nonmagnetic support and the magnetic recording layer will decrease. In the method of detecting the end using the difference, the difference in light transmittance is small, and detection troubles are likely to occur when detecting the end. The light transmittance at a wavelength of 900 nm is preferably 20% or less, particularly preferably 10% or less. The biaxially stretched polyester film of the present invention can be manufactured according to conventional manufacturing methods. For example, a polyester containing predetermined amounts of carbon black (A), inert solid particles (B), and inert particles (C) is melted and formed into an amorphous unstretched film, and then the unstretched film is It can be produced by biaxially stretching, heat setting, and if necessary, relaxation heat treatment. that time,
Film surface properties are, for example, inert solid particles.
They vary depending on the shape, particle size, amount, etc. of (B), inert particles (C), etc., and also depending on the stretching conditions, so they are selected appropriately. For example, the stretching temperature is such that the first stage stretching temperature (for example, longitudinal stretching temperature: T ₁ ) is (Tg−10) to (Tg
+45)°C (however, Tg: glass transition temperature of polyester), the second-stage stretching temperature (for example, transverse stretching temperature: T ₂ ) is (T ₁ +10) to (T ₁ +40)
It is recommended to select from the range of ℃. Further, the stretching ratio is preferably selected from a range in which the stretching ratio in the longitudinal direction is 3.0 times or more, particularly 3.5 times or more, and the area magnification is 10 times or more, especially 12 times or more. Furthermore, the heat fixing temperature is
It is preferable to select from the range of 180 to 250°C, more preferably 200 to 230°C. The biaxially stretched polyester film of the present invention has excellent properties for use in magnetic recording media, especially high-grade magnetic tapes. <Examples> The present invention will be further explained below with reference to Examples. Note that various physical property values and characteristics in the present invention were measured and defined as follows. (1) Average particle size of particles (1-1) Average primary particle size of carbon black Add chloroform to carbon black powder, disperse it by vibration with an ultrasonic cleaner, then place it on a mesh and examine it under a transmission electron microscope. Observe at a magnification of 80,000 times, read the primary particle size, and calculate the average value. (1-2) Average particle size of particles other than carbon black Measured using a Shimadzu CP-50 Centrifugal particle size analyzer. From the cumulative curve of particles of each particle size and their abundance calculated based on the obtained centrifugal sedimentation curve, 50 mass percent (mass
persent), and this value was taken as the above average particle size ("Particle Size Measurement Technology").
Published by Nikkan Kogyo Shimbun, 1975, pp. 242-247). (2) Light transmittance Shimadzu multi-purpose self-recording spectrophotometer (MPS)
-5000) and base film wavelength 900n.
The light transmittance at m was measured. (3) Film surface roughness (Ra) Center line average roughness: JIS as Ra (unit: μm)
- This is the value defined in B0601. Kosaka Laboratory Co., Ltd.'s stylus-type surface roughness meter (SURFCORDER SE-
30C), draw a film surface roughness curve under the conditions of stylus radius: 2 (μm, measurement pressure: 0.03g, cutoff value: 0.25mm), and calculate the center line from the film surface roughness curve. When a part of measurement length L is extracted in the direction, the center line of this extracted part is taken as the X axis, the direction of vertical magnification is taken as the Y axis, and the roughness curve is expressed as Y=f(x), the following formula is used. The given value (Ra: μm) is defined as the film surface roughness. Ra=1/L∫ ^L ₀ ｜f(x)｜dx In the present invention, the reference length is 2.5 mm, and 5 pieces are measured. (4) Electromagnetic conversion characteristics of magnetic coating film (chroma S/N) 100 parts by weight of Co-containing iron oxide powder with the following composition was applied on the film. Sekisui Chemical (vinyl chloride-vinyl acetate copolymer) 10 parts by weight Nituporan 2304 (polyurethane elastomer manufactured by Nippon Polyurethane) 10 parts by weight Coronate L (polyisocyanate manufactured by Nippon Polyurethane) 5 parts by weight lecithin 1 part by weight methyl ethyl ketone 75 parts by weight methyl isobutyl ketone 75 parts by weight Toluene 75 parts by weight Additives (lubricant, silicone resin) 0.15 parts by weight Carbon black A predetermined amount of magnetic powder paint is applied separately using a gravure roll, and the magnetic paint layer is smoothed with a doctor knife to remove any remaining magnetic paint. While it is still drying, it is magnetically oriented using a conventional method, and then brought to an oven for dry curing.Furthermore, it is calendered to make it uniform on the coated surface, and then slit to form a 1/2 inch wide magnetic layer with a thickness of about 5μ. A coating tape is prepared.The electromagnetic conversion characteristics (chroma S/N) of this magnetic coating tape are measured using the following method.Using a commercially available home VTR, a 50% white level signal (100% white level signal is the peak; 2; the peak voltage is 0.714 volts), record the signal with a 100% chroma level signal, and measure the playback signal using a noise meter: Type 925R.
Perform measurements using The definition of chroma S/N is as follows according to Shibasoku's definition. Chroma S/N (dB) = 20log {ES (p-p) / EN (rms)} Here, ES (p-p) is the peak-to-peak voltage difference (p-p) of the reproduced signal of the white level signal. be. RS (p-p) = 0.714V (p-p) EN (rms) is the square root value of the peak voltage of the reproduced signal of the chroma level signal. EN (rms) = AM noise effective value voltage (V) (5) Dropout Apply the tape (1/2 inch width) coated with magnetic powder paint in (4) above to a commercially available dropout counter (for example, Shibasoku VHO1BZ). type)
Count the dropout of 5 μsec x 10 dB and calculate 1
The number of counts per minute was calculated. (6) Signal troubles Polyester film is used as a base, and it is made into a magnetic tape using conventional methods, and it is possible to detect signal and detection troubles using a commercially available VHS video recorder.
It was evaluated as (○) and none (x). (7) Running properties The electromagnetic conversion characteristics of the tape prepared in (4) above were evaluated using the method described therein, and at the same time, the tape and running conditions were observed. ○...Running condition is good and there are no problems. △...There are some irregularities in the running condition and the tension is high, but it can be used somehow. ×... The running condition is poor and the tension is too high to withstand running. Example 1 Ethylene glycol (hereinafter abbreviated as EG) 85
After adding 15 parts by weight of calcium carbonate having an average particle size of 0.58 μm to the parts by weight, mixing and stirring were performed to obtain a slurry. Next, 100 parts by weight of dimethyl terephthalate and EG70
The weight part was transesterified in a conventional manner using 0.035 weight part of manganese acetate tetrahydrate as a catalyst. At that time, the calcium carbonate slurry obtained above was added under stirring. After the transesterification reaction is complete, trimethyl phosphate heated under reflux in the presence of ethylene glycol is mixed with dimethyl terephthalate.
0.015 mol % was added, and further, 0.030 mol % of antimony trioxide was added to dimethyl terephthalate, and a polycondensation reaction was carried out under a high vacuum of 1 Torr or less. After the polycondensation reaction was completed, the polymer was cooled with water and cut to obtain polyethylene terephthalate pellets containing calcium carbonate particles dispersed therein (hereinafter referred to as polyester). In addition, the transesterification reaction and polycondensation reaction were carried out in the same manner as above, except that a previously prepared ethylene glycol slurry of titanium dioxide particles was added instead of the ethylene glycol slurry of calcium carbonate particles, and titanium dioxide particles were Dispersed polyethylene terephthalate pellets were obtained (hereinafter referred to as polyester). Furthermore, in the method for producing polyester, transesterification and polycondensation reactions were carried out without adding inert particles to obtain polyethylene terephthalate pellets to which no externally active particles were added (hereinafter referred to as polyester). Furthermore, transesterification and polycondensation were carried out in the same manner as above, except that instead of the ethylene glycol slurry of calcium carbonate, an ethylene glycol slurry of carbon black with an average primary particle size (hereinafter simply referred to as average particle size) of 0.06 μm was added. The reaction was carried out to obtain polyethylene terephthalate pellets in which carbon black particles were dispersed [hereinafter referred to as
called polyester]. Polyester, polyester, polyester and polyester with a carbon black content of 1.4% by weight and a calcium carbonate particle content of
0.20% by weight, and titanium dioxide particle content 0.06
Blend A was obtained by mixing in such a manner as to achieve the same weight percentage. The obtained blend A was melt-extruded by a conventional method to obtain an unstretched film, and this unstretched film was sequentially stretched at a longitudinal stretching temperature of 105°C, a longitudinal stretching ratio of 3.4 times, a transverse stretching temperature of 110°C, and a transverse stretching ratio of 3.6 times. Biaxial stretching was performed and further heat treatment was performed at 215°C. Table 1 shows the properties of the 14 μm thick polyester film thus obtained. Using this biaxially oriented polyester film as a base film, a 1/2 inch wide video tape was prepared by the method described above. Its characteristics are shown in Table-1. As is clear from Table 1, the light transmittance of the base film at a wavelength of 900 nm is low, and no signal detection trouble occurred after tape formation. Furthermore, the surface roughness of the base film was low, the electromagnetic conversion characteristics of the tape were good, there were few dropouts, and the overall evaluation was good. Examples 2 and 3 The content of carbon black and the content of titanium dioxide (TiO ₂ ) were changed as shown in Table 1,
Furthermore, a biaxially stretched polyester film having a thickness of 14 μm was obtained in the same manner as in Example 1, except that kaolin clay having an average particle size of 0.55 μm was used instead of calcium carbonate, and a magnetic recording tape for video was also obtained. This characteristic is shown in Table-1. As is clear from Table 1, the base film has low light transmittance, low surface roughness, good electrical conversion characteristics as a magnetic tape, little drop-out, good runnability, and has a good overall evaluation. Ta. Comparative Examples 1 and 2 A thickness of 14 μm was prepared in the same manner as in Example 1 except for changing the mixing ratio of polyester.
A biaxially stretched polyester film was obtained, and a video magnetic recording tape was also obtained. This characteristic is shown in Table-1
Shown below. As is clear from Table 1, in Comparative Example 1, which does not use inert solid particles with a high optical refractive index, the light transmittance decreases by increasing the carbon black content, but the surface roughness of the base film decreases. The tape became rough, had poor electromagnetic characteristics as a tape, had many dropouts, and received a poor overall evaluation. In addition, the ratio of the amount of carbon black to TiO ₂ , which is an inert solid fine particle with a high optical refractive index, was set at 1.33.
In Comparative Example 2, which had a high surface roughness, the surface roughness of the base film was low, but the light transmittance was high, and the electromagnetic conversion characteristics as a tape caused many signal troubles.
The overall evaluation was poor. Example 4 As inert solid fine particles with high optical refractive index
Zinc oxide was used instead of _TiO2 , and calcium carbonate and kaolin clay were added as inert particles.
The thickness was measured in the same manner as in Example 2 except for using the type.
A 14 μm biaxially stretched polyester film was obtained, and a 1/2 inch wide magnetic recording tape was also obtained. This characteristic is shown in Table-1. As is clear from Table 1, the light transmittance of the base film was low, the surface roughness was also at a low level, the tape had good electromagnetic conversion characteristics, few signal troubles, and the overall evaluation was good. 【table】

Claims (1)

[Claims] 1. 0.5 to 2.5% by weight of carbon black (A) with an average primary particle size of 0.04 to 0.2 μm and inert solid fine particles (B) with an optical refractive index of 1.8 or more and an average particle size of 0.1 to 0.5 μm. 0.05～
A biaxially oriented polyester film containing 2.0% by weight dispersed, the film having a wavelength of 900n.
A biaxially stretched polyester film for magnetic recording, characterized in that it has a light transmittance in m of 30% or less and a surface roughness of 0.007 to 0.024 μm. 2 Optical refractive index for carbon black (A)
Weight ratio (B/A) of inert solid fine particles (B) of 1.8 or more
The polyester film according to claim 1, wherein 0.05 to 0.8. 3 Inert solid fine particles with an optical refractive index of 1.8 or more (B)
The polyester film according to claim 1, wherein is titanium dioxide. 4 Inert solid fine particles with an optical refractive index of 1.8 or more (B)
The polyester film according to claim 1, wherein is any one of black iron oxide, zinc oxide, and lithopone.