JPH0367867B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention relates to a biaxially oriented laminated polyester film, and more specifically, it has excellent light-shielding properties and surface flatness, provides particularly excellent electromagnetic conversion characteristics, D/O characteristics, and has excellent runnability and durability. In addition to being abrasive, it has low light transmittance and is useful as a base film for magnetic recording media.
This invention relates to a biaxially stretched laminated polyester film. <Prior Art> Polyester films are used for various purposes including magnetic tapes. In recent years, magnetic tapes, especially video tapes, are required to have a flat film surface to improve electromagnetic conversion characteristics for high-density recording, as well as to improve tape runnability, abrasion resistance, and durability on decks. Therefore, a low coefficient of friction is required. 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 devise ways 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, there is a need to lower the light transmittance of the base film, and light-shielding films are being considered. Conventionally, as a method to obtain a light-shielding film,
Single-layer films containing light-shielding agents such as carbon black are being considered. However, in this method, if carbon black or the like is contained in the film in a sufficient amount to satisfy the light-shielding property, the surface of the film becomes uneven due to aggregated coarse particles such as carbon black, resulting in a rough surface. The surface of the magnetic agent applied to the magnetic material also became rough, resulting in a decrease in magnetic output and other drawbacks, such as deterioration of electromagnetic conversion characteristics. As a method to improve this problem, a laminated film consisting of a layer containing a light shielding material and a layer not containing a light shielding material has been studied.
A biaxially stretched laminated film is disclosed in which a layer of polyethylene terephthalate mixed with carbon black and a layer of polyethylene terephthalate without mixed carbon black are laminated and stretched, and in a specific example, the thickness composition ratio is higher than that of the layer mixed with carbon black. A biaxially oriented laminated film with a thickened layer is shown. However, even in this case, the roughness of the film surface caused by coarse agglomeration has not been sufficiently reduced. In other words, in a laminated film consisting of a layer containing carbon black and a layer not containing carbon black, if you want to have the same thickness as a single layer film and obtain the same light shielding properties as a single layer film, the carbon black content in the core layer film will increase. (wt%) needs to be increased. On the other hand, carbon black has the property of being extremely prone to agglomeration, and this aggregation becomes more pronounced as the carbon black content increases, and even if various dispersants, anti-aggregation agents, etc. difficult to prevent. For this reason, the inner film contains many agglomerated carbon black particles, but the large unevenness caused by these agglomerated particles cannot be completely prevented by the outer film layer, and the surface of the laminated film is impact and roughen the surface. Therefore, when a magnetic tape is made using this laminated film, even if the electromagnetic conversion characteristics are reasonably good, there is a problem in that the D/O increases due to large irregularities caused by carbon black aggregation. <Object of the Invention> As a result of intensive studies to develop a film free of such problems, the present inventors have developed a polyester film layer containing more carbon black and a polyester film layer containing less carbon black. We have discovered that by laminating layers in a specific combination, it is possible to obtain a biaxially stretched laminated film that provides a magnetic recording medium with good electromagnetic characteristics and low dropout (D/O), and has arrived at the present invention. An object of the present invention is to provide the above-mentioned biaxially stretched laminated polyester film. <Configuration/Effects of the Invention> According to the present invention, an object of the present invention is to provide a film-forming aromatic polyester having an aromatic dicarboxylic acid as a main acid component and an aliphatic glycol as a main glycol component, and having an average particle size of 0.02〜
Light rays at a wavelength of 900 nm obtained by laminating a polyester film layer (core layer) containing 2 to 20% by weight of 1.0 μm carbon black dispersed thereon and a polyester film layer (surface layer) containing a smaller amount of carbon black than the above carbon black content on both sides. A biaxially stretched laminated polyester film having a transmittance of 30% or less, wherein the exposed surface of the film has a surface roughness Ra of 0.025 μm or less and 0.004 μm or more. will be achieved. The aromatic 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 polyesters are substantially linear and have film-forming properties, particularly by melt molding. Examples of aromatic dicarboxylic acids include terephthalic acid, naphthalene dicarboxylic acid, isophthalic acid, diphenoxyethane dicarboxylic acid, diphenyl dicarboxylic acid, diphenyl ether dicarboxylic acid, diphenyl sulfone dicarboxylic acid, diphenyl ketone dicarboxylic 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 aliphatic diols such as cyclohexanedimethanol. 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, up to 20 mol % of the total acid composition of other dicarboxylic acids can be the above-mentioned aromatic dicarboxylic acids, and also aliphatic dicarboxylic acids such as adipic acid, sebacic acid; cyclohexane-
It can be an alicyclic dicarboxylic acid such as 1,4-dicarboxylic acid. In addition, up to 20 mol% of the total glycol component can be the above-mentioned glycols other than ethylene glycol, or, for example, hydroquinone, resorcinol, 2,2-bis(4
-Aromatic diols such as (hydroxyphenyl)propane; aliphatic diols containing aromatic rings such as 1,4-dihydroxymethylbenzene; polyalkylene glycols (polyoxyalkylene glycols) such as polyethylene glycol, polypropylene glycol, and polytetramethylene glycol. etc. In addition, the aromatic polyester used in the present invention includes a dicarboxylic acid component and a component derived from an oxycarboxylic acid such as an aromatic oxyacid such as hydroxybenzoic acid; an aliphatic oxyacid such as ω-hydroxycaproic acid; It also includes those containing 20 mol% or less based on the total amount of oxycarboxylic acid components. Furthermore, the aromatic polyester in the present invention contains a trifunctional or higher functional polycarboxylic acid or a polyhydroxy compound, such as trimellitic acid, in a substantially linear amount, for example, 2 mol % or less based on the total acid components. Copolymerized pentaerythritol is also included. The above-mentioned aromatic polyester preferably has an intrinsic viscosity of 0.4 to 0.8 measured as a solution in O-chlorophenol at 35°C. In the present invention, preferred carbon blacks to be included in the aromatic polyester include, for example, ketone black, thermal black, channel black, furnace black, acetylene black, and the like. Such carbon black must have an average particle size of 0.02 to 1.0 μm, preferably 0.04 to 0.6 μm, and more preferably 0.06 to 0.2 μm. If the average particle diameter of the carbon black exceeds 1.0 μm, the effect of unevenness due to the carbon black will extend to the surface of the laminated film, making it undesirable. Also, the average particle size of carbon black is
If it is smaller than 0.02 μm, agglomeration tends to occur even if a dispersant is used, and this causes unevenness, which is not preferable. Carbon black is usually used in a state dispersed in a solvent, but since carbon black tends to aggregate, it is preferable to use a dispersant to disperse it using a ball mill, sand mill, etc. Glycols, particularly ethylene glycol, are preferably used as the solvent. Further, as a dispersant, polyvinylpyrrolidone or the like is preferably used. Furthermore, titanium oxide or the like may be added at the same time to supplement light shielding properties. In the present invention, carbon black can be added by a method conventionally known as a method for adding fine particles. For example, carbon black can be added to the reaction system of polyester production, for example before, during or after the reaction. The carbon black content (D _B : wt%) contained in the polyester film layer (core layer) to contain a larger amount of carbon black is preferably 2 to 20 wt%. The amount of carbon black added is 2wt.
If it is less than %, the light shielding properties will be insufficient, which is not preferable. Moreover, if it exceeds 20 wt%, large agglomeration will occur, and non-uniform stretching will likely occur during film forming and stretching, which is not preferable. From these points, the amount of carbon black added is preferably 2 to 10 wt%, particularly preferably 3 to 9 wt%. On the other hand, the carbon black content (D _A , D _C : wt%) contained in the polyester film layer (surface layer) that contains less carbon black is
It is preferable that the amount is less than 2wt% and further satisfies the following formulas (1) and (2). 0.01≦D _A (wt%)/D _B (wt%)≦0.4 …(1) 0.01≦D _C (wt%)/D _B (wt%)≦0.4 …(2) D _A (wt%), D As _C (wt%) increases, the A-plane layer,
Surface roughness of exposed surface of C-plane layer (RaA, RaC)
is undesirable because it becomes rough and the electromagnetic conversion characteristics when used as a magnetic recording medium deteriorate.On the other hand, if these become too low, RaA and RaC become low and flat, but light shielding properties become insufficient, which is undesirable. From these points, D _A (wt%) and D _C (wt%) are respectively
0.1 to 1.8 wt% is preferred, and 0.3 to 1.3 wt% is particularly preferred. A larger value of D _A (wt%)/D _B (wt%), D _C (wt%)/D _B (wt%) means that the carbon black content of the A, C and B layers increases. As the difference between the This is not preferable because it causes roughness and poor electromagnetic conversion characteristics. Also
When the values of D _A (wt%) / D _B (wt%) and D _C (wt%) / D _B (wt%) become small, if the core layer D _B (wt
%), but if D _B (wt%) is increased, large agglomeration of carbon black will occur and the D/O in the magnetic tape will increase, which is not preferable. From these points, D _A (wt%)/D _B (wt%), D _C (wt%
)/D _B (wt%) is preferably in the range of 0.04 to 0.30, more preferably in the range of 0.07 to 0.20. In addition, the average particle diameter (R _A , R _C ) of carbon black contained in the polyester film layer (surface layer) containing less carbon black is:
It is preferable that the average particle diameter (R _B ) of the carbon black contained in the polyester film layer (core layer) containing more carbon black is smaller than that, and it is more preferable that the following formulas (3) and (4) are satisfied. preferable. 1.5≦R _B /R _A ≦5.0 …(3) 1.5≦R _B /R _C ≦5.0 …(4) Furthermore, the ratios of R _B /R _A and R _B /R _C are each from 1.7 to
A range of 4.0 is preferred, especially a range of 2.0 to 3.0. The laminated film of the present invention has a light transmittance at a wavelength of 900 nm of 30% or less, preferably 20% or less, preferably 20% or less, and more preferably 10% or less. If the light transmittance exceeds 30%, it will no longer be possible to satisfy the characteristics required for use as a base film for magnetic recording media. The carbon black content in the polyester forming the core layer, the carbon black content in the polyester forming the surface layer, and the ratio of these amounts are selected from the viewpoint of light transmittance. In the present invention, exposed surfaces (A side, C side)
In addition to carbon black, the polyester layer forming the polyester layer preferably contains 0.03 to 1% by weight of one or more types of inert particles having an average particle size of 0.1 to 1.2 μm. The inclusion of the inert particles facilitates adjustment of the surface roughness of the laminated film. The term "inert particles" used herein refers to particles other than carbon black that are solid at room temperature, such as metal salts of organic acids, inorganic substances, and the like. Preferred inert particles include silicon dioxide (including hydrates, diatomaceous earth, silica sand, quartz, etc.), alumina, _SiO2 , etc.
Silicates containing 30% or more by weight (e.g. amorphous or crystalline clay minerals, aluminosilicate compounds (including calcined products and hydrates), warm asbestos, zircon, fly ash, etc.), Mg, Zn, Zr and oxides of Ti, sulfates of Ca and Ba, phosphates of Li, Na and Ca (including monohydrogen salts and dihydrogen salts), Li,
Benzoate of Na and K, Ca, Ba, Zn and Mn
terephthalate, Mg, Ca, Ba, Zn, Cd,
Pb, Mn, Fe, Co and Ni titanates, Ba and Pb chromates, Ca and Mg carbonates,
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,
Examples include barium sulfate, titanium oxide, calcium carbonate, lithium benzoate, double salts of these compounds (including hydrates), glass powder, clay (including kaolin, bentonite, clay, etc.), talc, diatomaceous earth, etc. be done. The biaxially stretched laminated film of the present invention has surface roughness RaA, RaC of its exposed surfaces (A side and C side).
is 0.025 μm or less and 0.004 μm or less. If this surface roughness exceeds 0.025 μm, it is not preferable because the electromagnetic conversion characteristics when used as a magnetic tape deteriorate.
If it is smaller than 0.004 μm, it becomes too flat and has poor slip properties, and wrinkles may occur during winding and processing of the base film, which is not preferable. From these points, the surface roughness is preferably 0.020 μm or less and 0.004 μm or more, more preferably 0.015 μm or less and 0.006 μm or more, and particularly preferably 0.010 μm or less and 0.0006 μm or more. Further, the surface roughness of the A side and the C side may be the same or different. When surface roughness is different between the A side and the C side, it is preferable to form the magnetic layer on a flatter surface because better electromagnetic conversion characteristics can be obtained. The biaxially oriented laminated film of the present invention usually has a
The film layer has a thickness of 23 μm, and the thickness of the core layer (layer B) containing a larger amount of carbon black dispersed is approximately 1 to 7 μm, and the thickness of the core layer (layer B) containing a larger amount of carbon black dispersed is approximately 1 to 7 μm. (Layer B) preferably has a thickness ratio of 5 to 45%. If the thickness ratio of the core layer (B layer) is small and the thickness of the core layer is too thin, the light transmittance will be insufficient even if the carbon black content is increased, which is not preferable, and the carbon black content will become high. If it is too much, large agglomerations will occur, which is not preferable. On the other hand, if the thickness ratio of the core layer (B layer) is large and the thickness of the core layer is too thick,
The surface layer and the C-plane layer become thinner, and the surface flatness of the laminated film deteriorates due to the influence of carbon black, which is not preferable. From these points of view, the thickness ratio of the film layer (layer B) containing dispersed carbon black is preferably 5 to 35%, more preferably 15 to 30%, and particularly preferably 20 to 30%. The biaxially oriented laminated polyester film of the present invention can be produced by conventionally accumulated laminated films. For example, a polyester layer forming the surface A, a polyester layer forming the core layer (layer B), and a polyester layer forming the surface C can be laminated in a molten state or a cooled and solidified state. More specifically, for example, coextrusion
It can be manufactured by methods such as extrusion coating. The film laminated by the above method is sequentially biaxially stretched or simultaneously biaxially stretched in accordance with the conventional method of manufacturing biaxially stretched films,
Further heat treatment is performed. At this time, the film surface characteristics vary depending on the shape, particle size, amount, etc. of the solid fine particles, and also depending on the stretching conditions, so they are appropriately selected from conventional stretching conditions. For example, the stretching temperature is such that the first stage stretching temperature (e.g. longitudinal stretching temperature: T ₁ ) is (Tg-
10) - (Tg + 45) °C (however, Tg: glass transition temperature of polyester), the second-stage stretching temperature (for example, transverse direction stretching temperature: T ₂ ) is (T ₁ + 15) -
It is recommended to select from the range of (T ₁ +40)°C. Also,
The stretching ratio is preferably selected from a range in which the uniaxial stretching ratio is 2.5 or more, particularly 3 or more times, and the area magnification is 8 or more, particularly 10 or more times. Furthermore, the heat setting temperature is preferably selected from the range of 180 to 250°C, more preferably 200 to 230°C. The biaxially stretched laminated polyester film of the present invention has excellent light shielding properties, significantly improves surface roughness caused by agglomerated carbon black particles, and has a specific surface roughness, and is suitable for use in magnetic recording media.
It has excellent properties especially for use in 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 inert solid particles Measured using a Shimadzu CP-50 Centrifugal Particle Size Analyzer. The particle size corresponding to 50 mass percent was read from the cumulative curve of particles of each particle size and their abundance calculated from the centrifugal sedimentation curve obtained, 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 900nm.
The light transmittance was measured. (3) Film surface roughness (Ra) Center line average roughness: Ra (unit: μm) JIS
- This is the value defined in B0601. In the present invention, a stylus-type surface roughness meter (SURFCORDER SE-30C) manufactured by Kosaka Laboratory Co., Ltd. is used.Stylus radius: 2μm, measurement pressure: 0.03g, cutoff value:
A film surface roughness curve is drawn under the condition of 0.25 mm, and a part of measurement length L is extracted from the film surface roughness curve in the direction of its center line. When the roughness curve is expressed as Y=f(x) with the direction of , the value (Ra: μm) given by the following equation is defined as the film surface roughness. Ra=1/L∫ ^L _O |f(x)|dx In the present invention, five measurements were taken using a reference length of 2.5 mm, and Ra was expressed as the average value of the four measurements, excluding the one with the largest value. (4) Electromagnetic conversion characteristics of magnetic coating film (chroma S/N) Co-containing iron oxide powder with the following composition: 100 parts by weight Eslec A (Sekisui Chemical's vinyl chloride-vinyl acetate copolymer) 10〃 Nitsuporan 2304 ( Polyurethane elastomer manufactured by Nippon Polyurethane) 10 parts by weight Coronate L (Polyisocyanate manufactured by Nippon Polyurethane) 5 Lecithin 1 Carbon black (average particle size 40 mμ)
Magnetic powder paint containing the following specified amounts of methyl ethyl ketone 75 parts by weight Methyl isobutyl ketone 75〃 Toluene 75〃 Additives (lubricant, silicone resin) 0.15 parts by weight was applied using a gravure roll, and the magnetic paint layer was smoothed using a doctor knife. While the magnetic paint is still dry, it is magnetically oriented by a conventional method and then introduced into an oven for dry curing. Furthermore, it is calendered to make the coating surface uniform, and then slit to approximately 5μ.
Form a magnetic layer and create a 1/2 inch wide magnetic coating tape. The amount of carbon black mentioned above is 0.1 parts by weight when a back coat layer is provided, and 5 parts by weight when not provided. The electromagnetic conversion characteristics (chroma S/N) of this magnetic coating tape are measured by the following method. Using a commercially available home VTR, record a signal in which a 100% chroma level signal is superimposed on a 50% white level signal (the 100% white level signal has a peak voltage of 0.714 volts) and play it back. Signal noise meter; type 925 R
Measurement is performed 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) where ES (p-p) is the peak-to-peak voltage difference (p-p) of the reproduced signal of the white level signal
It is. ES (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 Use the tape (1/2 inch width) coated with magnetic powder paint as described in (4) above with a commercially available dropout counter (for example, Shibasoku VH01BZ). type)
Count the dropout of 5 μsec x 10 dB and
Calculate the number of counts per minute. (6) Signal Troubles Using a laminated polyester film as a base, it was made into a magnetic tape using a conventional method, and evaluated using a commercially available VHS video recorder as having signal and detection trouble (○) or not (x). (7) Average particle size of carbon black After adding chloroform to carbon black powder and dispersing it by vibration with an ultrasonic cleaner, place it on a mesh and observe it with a transmission electron microscope at 80,000x magnification to determine the particle size. Read it. 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
Parts by weight were transesterified in a conventional manner using 0.035 parts by weight 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 completed,
Trimethyl phosphate heated under reflux in the presence of ethylene glycol was added to the reaction product in an amount of 0.015 mol% relative to dimethyl terephthalate, and antimony trioxide was further added to dimethyl terephthalate.
0.030 mol% was added, and the polycondensation reaction was carried out under high vacuum of 1 Torr or less. After the polycondensation reaction was completed, the polymer was water-cooled and cut to obtain polyethylene terephthalate pellets containing calcium carbonate particles dispersed therein (hereinafter referred to as polyester). In addition, transesterification and polycondensation reactions 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, and polyethylene terephthalate pellets without external inert particles were obtained (hereinafter referred to as polyester). Furthermore, transesterification and polycondensation reactions were carried out in the same manner as above except that an ethylene glycol slurry of carbon black with an average particle size of 0.1 μm was added instead of calcium carbonate in the polyester manufacturing method, and carbon black particles were dispersed. Polyethylene terephthalate pellets (hereinafter referred to as polyester) were obtained. Polyester, polyester, polyester and polyester with a calcium carbonate particle content of 0.20% by weight and a titanium dioxide particle content of 0.20% by weight.
0.10% by weight and the carbon black particle content is 0.8% by weight to obtain blend A.
I got it. In addition, polyester, polyester and polyester with a content of titanium dioxide particles
0.25% by weight and carbon black particle content
Blend C was obtained by mixing at a concentration of 0.8% by weight. Furthermore, a blend B was obtained by mixing polyester and polyester so that the carbon black particle content was 6% by weight. Blend A is the layer that forms the A side of the laminated film, Blend C is the layer that forms the C side, and Blend B is the layer that forms the middle between A and C ( The core layer is supplied to separate extruders of the film forming machine so that the thickness of each layer is A:
A laminated unstretched film was obtained by extrusion from a die so that B:C=5:4:5. This unstretched film was stretched at a longitudinal stretching temperature of 100°C, a longitudinal stretching ratio of 3.5 times, a transverse stretching temperature of 110°C, and a transverse stretching ratio of 3.7.
Biaxial stretching was carried out sequentially at 200° C. and heat treatment was performed at 210° C. Table 1 shows the properties of the 14 μm thick laminated polyester film thus obtained. In addition,
The symbol A means the A side, and the symbol C means the C side. This film has different front and back sides, and has good abrasion resistance on the easily slippery side (side A), with few scratches.
The electromagnetic conversion characteristics and dropout characteristics of the tape after the magnetic layer was applied to the flat surface (C surface) were also good. Furthermore, the light transmittance of the base film at 900 nm was low, and there were no problems with signal detection after the tape was made. Example 2 In Example 1, the blend C was used to form both the layer forming the A side and the layer forming the C side, and the blend B was further used to form the layer forming the A side layer and the layer C side. The layers forming the intervening core layer are fed to separate extruders of the film forming machine, and the thickness ratio of each layer is A:
A biaxially stretched laminated polyester film having a thickness of 14 μm was obtained in the same manner as in Example 1 except that it was extruded from the die so that B:C=5:4:5. Furthermore, a magnetic layer similar to that in Example 1 was applied to the C side of this film, and the following coating liquid was applied to the A side using a conventional method to improve running properties.
A 0.8 μm back coat layer was provided to obtain a magnetic recording tape. Coating liquid for back coat layer: Carbon black (average particle size 60 μm) 25 parts by weight Nitrocellulose 40 parts by weight Polyurethane resin 30 Polyisocyanate (product name: Coronate L)
30 〃 Methyl ethyl ketone 600 〃 The properties of this laminated polyester film are shown in Table-1.
Shown below. The light transmittance of the base film at 900 nm was as low as 8%, and its surface was also flat. Furthermore, the electromagnetic conversion characteristics as a tape were good and there were no signal troubles. Comparative Example 1 A biaxially stretched polyester film having a thickness of 14 μm and substantially a single layer was prepared in the same manner as in Example 2, except that the blend C was also supplied to the B layer forming the core layer in Example 2. I got it. Furthermore, a magnetic tape was obtained using this film in the same manner as in Example 2. The characteristics are shown in Table 1. Although the biaxially stretched polyester film had a flat surface, it had a high light transmittance. For this reason, although the magnetic tape had good electromagnetic conversion characteristics, signal detection troubles occurred and it could not be put to practical use. Comparative Example 2 In Example 2, polyester, polyester, and polyester were mixed so that the content of titanium dioxide particles was 0.25% by weight and the content of carbon black was 1.2% by weight to produce blend D.
Blend E was obtained by mixing polyester and polyester so that the content of carbon black particles was 2.4% by weight. Each blend was placed in a separate extruder of the film-forming machine so that Blend D was the layer forming the A side and C side, and Blend E was the layer forming the core layer (B layer). and the thickness was adjusted in the same manner as in Example 2.
A 14 μm biaxially stretched laminated polyester film was obtained. Furthermore, a magnetic tape was obtained in the same manner as in Example 2. These characteristics are shown in Table-1. Although the light transmittance of this film at 900nm is low,
Since D _A /D _B and D _C /D _B were high, the surface roughness of the A side and B side was high, resulting in a rough film. For this reason, although the tape was good with few signal troubles and few dropouts, it had poor electromagnetic conversion characteristics and was not usable. Comparative Example 3 In Example 2, polyester, polyester, and polyester were mixed so that the titanium dioxide content was 0.25% by weight and the carbon black content was 0.1% by weight to obtain blend F,
Blend C was also obtained by mixing polyester and polyester so that the content of carbon black particles was 12% by weight. Each blend is placed in a separate extruder of the film-forming machine so that the blend F becomes the layer forming the A side and the C side, and the blend G becomes the layer forming the core layer (B layer). The thickness was adjusted in the same manner as in Example 2.
A 14 μm biaxially stretched laminated polyester film was obtained. Furthermore, a magnetic tape was obtained in the same manner as in Example 2. These characteristics are shown in Table-1. The light transmittance of this film at 900 nm was low, and the surface roughness of sides A and C was also low, but large aggregation of carbon black was observed in the core layer (layer B). For this reason, the tape has good electromagnetic conversion characteristics and no signal problems, but there are many dropouts and
It was unusable.

【table】

[Table] Example 3 After adding 15 parts by weight of calcium carbonate having an average particle size of 0.58 μm to 85 parts by weight of EG, mixing and stirring were performed to obtain a slurry. Next, 100 parts by weight of dimethyl terephthalate and EG70
A transesterification reaction was carried out in a conventional manner using 0.035 parts by weight 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. Furthermore, 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 is completed, the polymer is water-cooled and cut.
Polyethylene terephthalate pellets containing calcium carbonate particles dispersed therein were obtained (hereinafter referred to as polyester'). Transesterification and polycondensation reactions were carried out in the same manner as above, except that the ethylene glycol slurry of titanium dioxide particles prepared in advance was added instead of the ethylene glycol slurry of calcium carbonate particles, and the titanium dioxide particles were dispersed. Polyethylene terephthalate pellets were obtained [hereinafter referred to as
It is called polyester. Next, in the process for producing polyester', transesterification and polycondensation reactions were carried out without adding any inert particles, to obtain polyethylene terephthalate pellets to which no external inert particles were added (hereinafter referred to as polyester'). Next, in the method for producing polyester', transesterification and polycondensation reactions were carried out in the same manner as above, except that instead of calcium carbonate, ethylene glycol slurry of carbon black with various average particle sizes shown in Table 2 was added. Polyethylene terephthalate pellets in which carbon black particles were dispersed were obtained (hereinafter referred to as polyester'). Polyester', polyester', polyester' and polyester' were mixed such that the content of calcium carbonate particles was 0.20% by weight, the content of titanium dioxide particles was 0.10% by weight, and the content of carbon black particles was 0.5% by weight. A blend A' was obtained, and a blend C' was obtained by mixing polyester', polyester', and polyester' so that the content of titanium dioxide particles was 0.25% by weight and the content of carbon black particles was 0.5% by weight. Obtained. Further, polyester' and polyester' were mixed so that the carbon black particle content was 5% by weight to obtain blend B'. Then, blend A' becomes a layer forming side A, blend C' becomes a layer forming side B, and blend B' forms an intermediate layer between layer A and layer B. The core layer is fed to separate extruders of the film forming machine, and the thickness ratio of each layer is A:B:
A laminated unstretched film was obtained by extrusion from a die so that C=5:4:5. This unstretched film was stretched at a longitudinal stretching temperature of 100°C, a longitudinal stretching ratio of 3.5 times, a transverse stretching temperature of 110°C, and a transverse stretching ratio of 3.7.
Biaxial stretching was carried out successively at 200° C. and heat treatment was performed at 210° C. Table 2 shows the properties of the 14 μm thick laminated polyester film thus obtained. Note that the symbol A means the A side, and the symbol C means the C side. This film has different front and back sides, and has an easy-slip surface (side A).
The tape has good abrasion resistance and few scratches, and the electromagnetic characteristics of the tape after the magnetic layer is applied to the flat surface (C surface).
Dropout characteristics were also good. Furthermore, the light transmittance of the base film at 900 nm was low, and the light transmittance after tape formation was 0.08%, and no signal detection problems occurred. Example 4 The thickness was changed in the same manner as in Example 1, except that the particle type, average particle size, and addition amount of each layer of the A-plane layer, C-plane layer, and B layer were changed as shown in Table 2. A 14 μm biaxially stretched laminated polyester film was obtained. This film had a low light transmittance at 900 nm as the base film, and after being made into a tape, the light transmittance was 0.10, and no signal detection problems occurred. In addition, the electromagnetic conversion characteristics and drop amt characteristics of the tape were also good.

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Claims (1)

[Scope of Claims] 1. 2 to 20% by weight of carbon black consisting of a film-forming aromatic polyester containing aromatic dicarboxylic acid as the main acid component and aliphatic glycol as the main glycol component, and having an average particle size of 0.02 to 1.0 μm. A polyester film layer (core layer) containing dispersed carbon black and a polyester film layer (surface layer) containing a carbon black amount smaller than the above carbon black content are laminated on both sides, and the light transmittance at a wavelength of 900 nm is 30% or less. 1. A biaxially stretched laminated polyester film, characterized in that the exposed surface of the film has a surface roughness Ra of 0.025 μm or less and 0.004 μm or more. 2 The ratio of the amount of carbon black contained in the polyester film of the core layer (D _B : wt%) to the amount of carbon black contained in the polyester films of both surface layers (D _A , D _C : wt%) is , the following formula
(1), (2) 0.01≦D _A (wt%)/D _B (wt%)≦0.4 …(1) 0.01≦D _C (wt%)/D _B (wt%)≦0.4 …(2) A biaxially oriented laminated polyester film according to claim 1. 3 The average particle size of carbon black contained in the polyester film of the core layer (R _B ) and the average particle size of carbon black contained in the polyester films of both surface layers (R _A , R _C ) are calculated by the following formula (3). ), (4) 1.5≦R _B /R _A ≦5.0 …(3) 1.5≦R _B /R _C ≦5.0 …(4) The biaxial stretching described in claim 1 or 2 satisfies the following. Laminated polyester film.