JPH0618072B2 - Polyester film for magnetic recording media - Google Patents

Description

TECHNICAL FIELD The present invention relates to a polyester film for a magnetic recording medium,
More specifically, the present invention relates to a polyester film for a magnetic recording medium, which has excellent runnability and abrasion resistance, and is a single-layer film having different surface roughnesses on the front and back sides and having a light-shielding property.

[Problems to be Solved with Prior Art] Video tapes, audio tapes, computer tapes, etc. are known and widely used as magnetic recording media based on polyester film.

In recent years, demands for high-density recording and high quality have been increasing in these fields of application, and along with this, the base polyester film has a flat surface and excellent slipperiness.
In addition, there is an increasing demand for excellent durability and wear resistance.

Further, the ferromagnetic powder used in these magnetic tapes is becoming finer and finer. This fine powder makes it difficult for the long-wavelength light to be scattered by the magnetic powder, and increases the light transmittance. Therefore, it is necessary to lower the light transmittance of the magnetic recording layer in the magnetic recording medium in which the end detection is performed by utilizing the difference in light transmittance between the non-magnetic support and the magnetic recording layer. Conventionally, the magnetic recording layer has been made to contain colored fine powder such as carbon or abrasives to reduce the light transmittance, but this method has limitations in terms of electromagnetic conversion characteristics, head wear and the like.

In order to meet these demands, for example, in addition to the magnetic recording layer surface of a magnetic tape, a back coat is applied to the diamagnetic layer surface, and pigments, carbon black, etc. are mixed in the back coat layer to improve the light shielding property. However, recently, non-back coat has been promoted in response to a demand for cost reduction, and it is desired to deal with the base film.

Heretofore, as a method for improving slipperiness, a method of adding inorganic particles to polyester or a method of precipitating fine particles during synthesis has been proposed.

There has been proposed a means of adding carbon black in addition to the inert particles in order to impart light-shielding properties to these (JP-A-61-237622). However, since this film has the same surface property on both sides, there is a limit to the improvement, and it cannot be said to be a satisfactory level. Then, some front and back different surface films in which one exposed surface has excellent slipperiness and the other exposed surface is flat are proposed, and a laminated film is proposed as a means for this. However, the laminated film has a problem of high cost.

[Object of the Invention] The present inventors have conducted extensive studies to develop a single-layer film having low light transmittance in addition to excellent running properties and abrasion resistance.
We have found that this problem can be solved all at once by adding a specific substance to polyester and making the both surfaces (front and back) of the polyester film have a temperature difference during stretching in the machine direction, and arrived at the present invention. Is.

Therefore, an object of the present invention is to provide a flat surface that does not cause noise such as dropout and does not deteriorate electromagnetic conversion characteristics, has a small friction coefficient during repeated running, and is a part of a magnetic recording medium processing step and a magnetic recording / reproducing apparatus. For magnetic recording media, which has extremely little scraping property of the film due to contact with it, has excellent durability in continuous use, and has excellent light-shielding properties, and therefore can withstand high-density recording, high quality, and repeated use. It is to provide a polyester film.

[Constitution of Invention] The present invention relates to carbonaceous fine particles having an average particle diameter of 0.01 to 0.60 μm.
A biaxially stretched film made of an aromatic polyester in which 0.05 to 2% by weight and 0.007 to 2% by weight of other inert particles having an average particle size of 0.045 to 1.0 μm are dispersed and the light having a wavelength of 900 nm is transmitted through the film. Of the film having a thickness of 15 μm is 40% or less, the surface roughness (Ra) of one side of the film is 0.011 to 0.06 μm, and the surface roughness (R) of the other side is (R).
a) is 0.005 to 0.015 μm, and the difference in surface roughness between both surfaces is 0.005 μm or more, which is a polyester film for magnetic recording media.

The aromatic polyester in the present invention is a polyester having 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, especially film formation by melt molding. Examples of the aromatic dicarboxylic acid include terephthalic acid, naphthalenedicarboxylic acid, isophthalic acid, diphenoxyethanedicarboxylic acid, diphenyldicarboxylic acid, diphenyletherdicarboxylic acid, diphenylsulfonedicarboxylic acid, diphenylketonedicarboxylic acid, anthracene. A dicarboxylic acid etc. can be mentioned. As an aliphatic glycol,
For example, ethylene glycol, trimethylene glycol,
Examples thereof include polymethylene glycol having 2 to 10 carbon atoms such as tetramethylene glycol, pentamethylene glycol, hexamethylene glycol and decamethylene glycol, and alicyclic diols such as cyclohexanedimethanol.

In the present invention, as the aromatic polyester, for example, one having alkylene terephthalate and / or alkylene naphthalate as a main constituent component is preferable.

Among such aromatic polyesters, for example, polyethylene terephthalate, polyethylene-2,6-naphthalate, as well as, for example, 80 mol% or more of all dicarboxylic acid components are terephthalic acid and / or 2,6-naphthalenedicarboxylic acid, A copolymer in which 80 mol% or more of the glycol component is ethylene glycol is particularly preferable. 20 mol% or less of the total acid component of the dicarboxylic acid may be the above-mentioned aromatic dicarboxylic acid other than terephthalic acid and / or 2,6-naphthalenedicarboxylic acid, and fatty acids such as adipic acid and sebacic acid. Group dicarboxylic acids; alicyclic dicarboxylic acids such as cyclohexane-1,4-dicarboxylic acid and the like. Also, of all glycol components
20 mol% or less can be the above glycols other than ethylene glycol, or aromatic diols such as hydroquinone, resorcinol, 2,2-bis (4-hydroxyphenyl) propane; 1,4-dihydroxymethyl It may be an aliphatic diol containing an aromatic ring such as benzene; a polyalkylene glycol (polyoxyalkylene glycol) such as polyethylene glycol, polypropylene glycol, polytetramethylene glycol and the like.

The aromatic polyester is known per se and can be produced by a known method. As the aromatic polyester, a solution in O-chlorophenol is used.
It is preferable that the intrinsic viscosity measured at 35 ° C. is about 0.4 to about 0.9.

The aromatic polyester of the present invention contains inorganic or organic inactive fine particles or organic polymer inactive fine particles dispersed therein in order to improve the slipperiness of the film. Examples of the inorganic inert fine particles include MgO, ZnO, MgCO ₃ , CaCO ₃ , CaSO ₄ , B
Examples include aSO ₄ , Al ₂ O ₃ , SiO ₂ and TiO ₂ . Typical examples thereof include silica, titanium oxide, alumina, and the like. Examples of the organic inert fine particles include sorbitan cycloid and cataloid. Examples of the organic polymer inert fine particles include fine particles of tetrafluoroethylene and polyethylene.

The average particle size of such inert fine particles is 0.045 to 10 μm, preferably 0.08 to 2 μm, and more preferably 0.1 to 1 μm. The content of the inert fine particles is 0.007 to 2% by weight, preferably 0.01 to 1% by weight, based on the aromatic polyester.
It is more preferably 0.05 to 0.5% by weight. This content is
If it is less than 0.007% by weight, the effect of imparting slipperiness is not sufficient, and if it exceeds 2% by weight, the number of coarse particles in the film is too large and the film surface is too rough, which is not preferable.

The aromatic polyester of the present invention contains carbonaceous fine particles as a light-shielding agent. The light-shielding agent is preferably used in combination with a dispersant in order to improve the dispersibility. Examples of such carbonaceous fine particles include carbon black and activated carbon, but carbon black is particularly preferable. Further, specific examples of carbon black include lamp black, thermal black, furnace black, acetylene black and the like.

The average particle size of the carbonaceous fine particles is 0.01 to 0.60 μm, preferably
The thickness is 0.01 to 0.5 μm, and more preferably 0.01 to 0.4 μm.
Furthermore, the content of carbonaceous fine particles relative to the aromatic polyester
The amount is 0.05 to 2% by weight, preferably 0.1 to 2% by weight, and more preferably 0.3 to 2% by weight. This content is 0.05% by weight
When it is less than 2, the light-shielding property is low, and when it exceeds 2% by weight, coarse particles in the film are too much and the surface of the film is too rough, which is not preferable.

The method of dispersing and containing the carbonaceous fine particles and other inert fine particles in the aromatic polyester can be carried out by a method conventionally known as a method for containing fine particles. For example, inert fine particles and carbonaceous fine particles can be added before, during, or after the reaction in the reaction system for polyester production.

In the present invention, when only the inert fine particles are contained, the light-shielding property of the film is poor, and when only carbon black is contained, the friction coefficient of the film with respect to the metal is high and the running property is poor.

The polyester film of the present invention has a transmittance (light transmittance) of light having a wavelength of 900 nm of 4 in a film having a thickness of 15 μm.
It is 0% or less, preferably 30% or less, more preferably 25% or less. Furthermore, the polyester film is a single-layer film having a surface roughness (Ra) of 0.011 to 0.0
6 μm, preferably 0.011 to 0.03 μm, the surface roughness (Ra) of the other surface is 0.005 to 0.015 μm, and the difference in surface roughness between both surfaces is 0.005 μm or more.

The polyester film of the present invention can be preferably produced by the following method.

Carbonaceous fine particles and other inert fine particles having a predetermined particle diameter and amount are added, and the polyester mixed and contained is extruded in a sheet form by a melt extruder and brought into close contact with a rotary cooling drum to be rapidly cooled. An amorphous, unstretched film is obtained. Then, this unstretched film is brought into contact with the surface of the heated mirror-finishing roll to heat it from both sides to a uniform temperature,
Only one side of the unstretched film is heated by a rod-shaped infrared heater installed in a direction perpendicular to the running direction of the film. At this time, the film surface heated by the infrared heater is set to be higher than the preheating temperature by 10 ° C. or more. The film heated to such a temperature is immediately stretched in the vertical direction at a known stretching ratio. In the uniaxially stretched film thus obtained, the surface of the strongly heated film has a smaller surface roughness than the surface on the opposite side.

In this uniaxial stretching, the temperature (T
₁ ) is (Tg + 5) to (Tg + 20) ° C (where Tg is the glass transition temperature of the aromatic polyester), and the temperature (T ₂ ) of the other surface is (T ₁ +10) ° C or higher. It is preferable to set the temperature to. This uniaxially stretched film is subsequently stretched by a stenter method at a known temperature and a stretching ratio, and heat-treated under tension.
The difference in surface roughness between the front and back of the film of the present invention is substantially formed in the vertical stretching step. As a method of making the film temperature different between the front and back in the vertical stretching step, one side of the uniformly preheated film may be heated or cooled in a non-contact or contact manner so that the temperature difference is 10 ° C. or more. Among these, a method in which a film that has been uniformly preheated with a heating roll is heated in a non-contact manner with an infrared heater on only one side to give a temperature difference is preferable. Even in these methods, the addition of only inert fine particles makes it impossible to impart a temperature difference between the front surface and the back surface during stretching and orientation of the film, so that a film having a difference in surface roughness between the front surface and the back surface cannot be obtained. Only when a combination of inert particles and carbonaceous particles is used, it is possible to obtain excellent light-shielding properties, scratch resistance, and running properties.

The polyester film of the present invention has different surface roughnesses on the front and back surfaces, but when a magnetic layer is provided on the film,
It is preferable to provide the magnetic layer on a surface having a small surface roughness. For forming the magnetic layer, conventionally known means and methods can be used. For example, known magnetic paints containing ferromagnetic powder can be used. For example, a ferromagnetic powder such as α-Fe ₂ O ₃ , barium ferrite, cellulose acetate butyrate, epoxy resin lecithin, silicone oil, etc. dissolved or dispersed in a solvent such as methyl isobutyl ketone, toluene etc. is applied. it can. Known means and conditions can be applied to the drying of the magnetic paint. Also, known means and known processing conditions can be applied to the calendering treatment for smoothing the magnetic layer.

[Examples] The present invention is described in detail below with reference to Examples. The characteristic values were measured according to the following methods.

1) Light transmittance The light transmittance at a wavelength of 900 nm of a film (thickness 15 μm) is measured using a Shimadzu Multipurpose Autograph Spectrophotometer (MPS-5000).

2) Coefficient of friction A film cut into a width of 1/2 inch is brought into contact with a fixed hard chrome-plated metal roll at a constant wrap angle, a load is applied to one end and the product is run at a constant speed, and the resistance force at the other end is measured. . More specifically, the measuring device and method are measured according to the method described in JP-A-61-237622.

The surface on which the coefficient of friction is measured is not the flat surface of the film (the surface to which the magnetic material is applied) but the rougher surface (traveling surface) of the opposite surface.

3) Film surface roughness (Ra) This is a value defined by JIS-B0601 as the center line average roughness (Ra), and in the present invention, a stylus surface roughness meter (SURFCORDER SE- of Kosaka Laboratory Ltd.) 30C). The measurement conditions are as follows.

(a) Stylus tip radius: 2 μm (b) Measuring pressure: 30 mg (c) Cut-off: 0.25 mm (d) Measuring length: 2.5 mm (e) Data compilation method The largest value was obtained by repeating the same measurement five times. 1
Except for one, the average value of the remaining four data is rounded off to the fourth decimal place and displayed up to the third decimal place.

4) Scratch resistance film is slit to 1/2 inch width and made of stainless steel SUS.
The film is applied to a 304 fixed rod (outer diameter 5 mm) at an angle of 150 °, and is run for 10 m at a film speed of 20 cm / sec.
After repeating this 50 times, the thickness, depth, number, etc. of the scratches on the surface of the film are comprehensively judged according to the following 5 grades.

The surface for determining the scratch resistance is not the flat surface on which the magnetic layer is provided, but the surface (running surface) on the rougher side of the film that is involved in running durability.

<Five-step judgment> ◎: No scratch is recognized on the film ○: Almost no scratch is recognized on the film △: Scratch is recognized on the film (some) ×: Some thick scratches are recognized on the film XX: A large number of thick and deep scratches are recognized on the entire surface of the film. 5) Signal trouble Based on polyester film, magnetic tape was formed by a conventional method, and no signal detection trouble occurred with a commercially available VHS video recorder (Yes), Yes (X ) To evaluate.

6) Average particle size Stokes equation Where ρp is the density of the sample particles, ρo is the density of the medium, η is the viscosity of the medium, g is the acceleration of gravity, ν is the settling velocity of the sample particles, and Dp is the average diameter of the sample particles. Diameter of
Expressed by the value of Dp.

Example 1 Polyethylene terephthalate added with 1.0% by weight of carbon black having an average particle size of 0.35 μm and 0.009% by weight of calcium carbonate having an average particle size of 0.6 μm was melted by a conventional method, extruded on a cooled mirror surface drum, and cooled. An unstretched film was obtained. This unstretched film was run on a hard chrome plated mirror surface roll heated to 80 ° C. and sufficiently heated from both sides. The surface temperature of the unstretched film heated by this roll is measured by a non-contact type radiation thermometer,
It was 77-79 ℃ on both sides. Subsequently, only one side of this unstretched film was heated by an infrared heater arranged so as to cross the running direction of the film, and stretched 3.6 times in the machine direction. The film temperature just before stretching is
The temperature was 95 ° C and the surface not heated by infrared rays was 77 ° C. This uniaxially stretched film is stretched in a transverse direction with a stenter (115 ° C,
(3.7 times), followed by heat setting at 220 ° C. for 30 seconds. Thus, a 15 μm biaxially stretched polyester film was obtained. The surface roughness of this polyester film was smaller on the surface heated by infrared rays (the surface having a higher temperature during stretching) than on the surface not heated (the surface having a lower temperature during stretching).

The results of various characteristics of the magnetic tape based on this film are as shown in Table 1.

The film had a small coefficient of friction, and had good scratch resistance and light-shielding properties. No signal troubles occurred.

Example 2 A biaxially stretched polyester film was obtained in the same manner as in Example 1 except that 1.0% by weight of carbon black having an average particle size of 0.50 μm and 1.5% by weight of titanium oxide having an average particle size of 0.3 μm were used. . The results of various properties of this film as a base film are as shown in Table 1 and were excellent.

Comparative Example 1 In the film production of Example 1, only the amount of calcium carbonate added was reduced to 0.005% by weight. The results are shown in Table 1.

The obtained film was good in scratch resistance and light-shielding property, but was greatly worn and poor in running property.

Comparative Examples 2 and 3 Carbon black 1.0 having an average particle size of 0.35 μm as an additive
Add wt% alone (Comparative Example 2) or average particle size
A biaxially stretched polyester film was obtained in the same manner as in Example 1 except that 0.009% by weight of calcium carbonate (0.000% by weight) was added alone (Comparative Example 3). The results of various properties based on this film are shown in Table 1.

The film containing carbon black alone (Comparative Example 2) had poor running properties and insufficient properties, whereas the film containing calcium carbonate alone had poor light-shielding properties and insufficient scratch resistance.

[Effects of the Invention] The polyester film of the present invention has both excellent running properties and durability and excellent light-shielding properties. Therefore, when this film is used as a base film of a magnetic recording medium, it has excellent electromagnetic conversion characteristics, running properties, wear resistance, durability, etc.
Moreover, it is possible to manufacture a magnetic recording medium having optical characteristics capable of detecting the end without performing a specific process. Particularly, it is useful for producing a magnetic recording medium for video audio.

When a magnetic recording tape is manufactured using the base film of the present invention, since the base film has both light-shielding properties and running durability, it is not necessary to provide a back coat layer on the surface opposite to the magnetic recording layer. There is an advantage that you can.

Claims (2)

[Claims] 1. Carbonaceous fine particles having an average particle diameter of 0.01 to 0.60 μm.
A biaxially stretched film made of an aromatic polyester containing 05-2% by weight and 0.007-2% by weight of another inert particle having an average particle size of 0.045-1.0 μm dispersed therein, the film transmitting light having a wavelength of 900 nm. 4 for film with a thickness of 15 μm
0% or less, the surface roughness (Ra) of one side of the film is 0.011 to 0.06 μm, and the surface roughness (Ra) of the other side.
Is 0.005 to 0.015 μm, and the difference in surface roughness on both sides is
Polyester film for magnetic recording media having a thickness of 0.005 μm or more. 2. The biaxially stretched film has an unstretched film whose surface temperature (T ₁ ) on _one side is (Tg + 5) to (Tg + 20).
℃ (however, Tg is the glass transition temperature of polyester), the surface temperature (T ₂ ) of the other surface is heated to (T ₁ +10) ℃ or more and stretched in the longitudinal direction, then in the transverse direction with a stenter. The polyester film for a magnetic recording medium according to claim 1, wherein the polyester film is stretched into a sheet and then heat set under tension.