JPH05301283A - Laminated biaxially-oriented polyester film for magnetic recording medium - Google Patents

Abstract

PURPOSE:To constitute a film so that it possesses surface properties superior in sliding properties, cutting resistance, scratch resistance and electromagnetic conversion properties and is low cost and useful for resource saving. CONSTITUTION:This is a laminated biaxially-oriented polyester film comprised of three layers, which is a laminated biaxially-oriented polyester film wherein a core layer contains inert particulates having a mean particle diameter of at the most 1.0mum, a thickness of a surface layer is at least two times as big as the mean particle diameter of the inert particulates contained into the core layer and the surface layer contains inert particulates having a mean particle diameter of at least the mean particle diameter of the inert particulates contained in the core layer so that the same becomes at least 20% of volume of the whole inert particulates contained into the surface layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated biaxially oriented polyester film for a magnetic recording medium, and more particularly to a laminated biaxially oriented polyester film composed of three layers, which comprises fine inert particles added to the film. Laminated biaxial orientation for magnetic recording media, which is useful for low cost and resource saving while maintaining surface properties such as surface roughness, slipperiness, abrasion resistance and scratch resistance imparted by fine projections on the formed film surface. Regarding polyester film.

[0002]

2. Description of the Related Art Biaxially oriented polyester film represented by polyethylene terephthalate film is widely used as a base film for magnetic recording media such as magnetic tape and floppy disk because of its excellent physical and chemical properties. .

In such a biaxially oriented polyester film, its slipperiness and abrasion resistance are major factors that affect the workability of the film manufacturing process and the processing process in various applications, and further the quality of the product. ing. If these are insufficient, for example, when a magnetic layer is coated on the polyester film surface and is used as a magnetic tape, friction between the coating roll and the film surface during coating of the magnetic layer is severe, and the film surface is also greatly worn. In extreme cases, wrinkles, slip scratches, etc. on the film surface occur. In addition, even after slitting the film after coating the magnetic layer and processing it into audio, video or computer tape, etc., when it is pulled out from the reel or cassette, rolled up and other operations, many guide parts, playback heads etc. Abrasion occurs remarkably between the two, and scratches and distortions are generated, and further, white powder is generated due to abrasion of the surface of the polyester film and the like, which often causes a large loss of the magnetic recording signal, that is, dropout.

Generally, in order to improve the slipperiness of a polyester film, (i) a method of precipitating inactive fine particles from a catalyst residue in a production process of a raw material polymer, or (ii) a method of adding inactive fine particles For example, a method has been adopted in which unevenness is imparted to the film surface by such means as to reduce the contact area with a guide roll or the like. Generally, the larger the size of the fine particles in these films, the greater the improvement in the slipperiness.

On the other hand, in the base film for magnetic recording media, the surface of the base film is required to be as flat as possible from the viewpoint of improving electromagnetic conversion characteristics.

To meet the contradictory requirements of improving the slipperiness and improving the electromagnetic conversion characteristics, for example, coarse projections on the film caused by coarse particles present in the fine particles to be added may cause abrasion powder. Focusing on the fact that even after coating the magnetic layer, it sticks out to the magnetic surface and becomes a factor that deteriorates the electromagnetic conversion characteristics, various improvements such as strengthening classification of fine particles and originally using synthetic particles having a sharp particle size distribution have been proposed. There is.

However, although such a method imparts excellent characteristics to the film, it also causes a significant increase in cost. That is, when the classification of the fine particles is strengthened, the cut portion cannot be used and the total cost is increased. In the case of synthetic particles having a sharp particle size distribution, the particle size is generally uniform because the starting raw material for the synthesis is high in purity, and the particles are often extremely expensive.

As a countermeasure against this, a method has been proposed in which additive particles for forming protrusions on the surface of the film are unevenly distributed only on the surface of the film, that is, a laminated film. This method forms a thin layer containing particles on the outside of a core layer containing no particles, thereby achieving the same film surface formation as a single layer, while reducing the amount of added particles as a whole film. This can lead to reduction of film manufacturing cost. However, in general, in the method for producing a biaxially oriented polyester film, a molten polyester extruded into a sheet is cooled and solidified to obtain an unstretched film, which is then subjected to simultaneous biaxial stretching or sequential biaxial stretching to obtain a desired machine. Has acquired the characteristic. At this time, in order to stretch the film in the lateral direction, it is common to grasp the edge portion of the film with a chuck and move it on a rail installed so that the width gradually increases at a predetermined temperature. In order to prevent breakage at the chuck portion, it is customary to make the thickness of the edge portion thicker than the thickness of the central portion. This edge portion cannot be the final product and is discarded, which is a problem from the viewpoint of resource saving.

[0009]

DISCLOSURE OF THE INVENTION The inventors of the present invention satisfy the above-mentioned problems, that is, the contradictory requirements of improving the slipperiness of the film surface and improving the electromagnetic conversion characteristics, and at the same time, to save resources and save resources. As a result of conducting research on how to do so, even if particles are contained in the core layer, the particle size of the particles, the thickness of the surface layer, the particle size of the particles contained in the surface layer, and the addition amount are appropriate. Within the range, a laminated biaxial that can be manufactured at low cost and has excellent slip properties and abrasion resistance in a form that helps save resources, has excellent electromagnetic conversion characteristics when used for magnetic recording media, and has few dropouts The inventors have found that an oriented polyester film can be obtained and have reached the present invention.

[0010]

That is, the present invention has three features.
A laminated biaxially oriented polyester film comprising layers, wherein the core layer contains inert fine particles having an average particle size of 1.0 μm or less, and the surface layer has a thickness of 2 times the average particle size of the particles contained in the core layer.
The amount of the inert fine particles having the average particle diameter equal to or larger than the average particle diameter of the inert fine particles contained in the core layer is 20% or more of the volume of all the inert fine particles contained in the surface layer. A laminated biaxially oriented polyester film for a magnetic recording medium, which is characterized by containing.

The 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, 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 dicarboxylic acid. You can Examples of the aliphatic glycol include polymethylene glycol having 2 to 10 carbon atoms such as ethylene glycol, trimethylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol and decamethylene glycol, and alicyclic compounds such as cyclohexanedimethanol. Examples thereof include diols.

In the present invention, as the polyester, those having alkylene terephthalate and / or alkylene naphthalate as a main constituent are preferably used.

Among such polyesters, especially polyethylene terephthalate, polyethylene-2,6-naphthalate, etc., for example, 8 of all dicarboxylic acid components are used.
A copolymer in which 0 mol% or more is terephthalic acid and / or 2,6-naphthalenedicarboxylic acid and 80 mol% or more of all glycol components is ethylene glycol is preferable. 20 mol% or less of the total acid component may be the above-mentioned aromatic dicarboxylic acids other than terephthalic acid and / or 2,6-naphthalenedicarboxylic acid, and aliphatic dicarboxylic acids such as adipic acid and sebacic acid. An alicyclic dicarboxylic acid such as cyclohexane-1,4-dicarboxylic acid can be used. Also, 20 mol% or less of the total glycol component may be the above-mentioned glycol other than ethylene glycol, or an aromatic diol such as hydroquinone, resorcin, 2,2-bis (4-hydroxyphenyl) propane, etc .; 1 An aliphatic diol having an aromatic ring such as 1,4-dihydroxydimethylbenzene; a polyalkylene glycol (polyoxyalkylene glycol) such as polyethylene glycol, polypropylene glycol, polytetramethylene glycol and the like can also be used.

The polyester of the present invention includes
Aromatic oxyacids such as hydroxybenzoic acid, ω-
Also included are those in which a component derived from an oxycarboxylic acid such as an aliphatic oxyacid such as hydroxycaproic acid is copolymerized or bonded at 20 mol% or less based on the total amount of the dicarboxylic acid component and the oxycarboxylic acid component.

Further, in the polyester of the present invention,
Amounts in a range that is substantially linear, eg, 2 based on total acid component.
It also includes a copolymerized polycarboxylic acid or polyhydroxy compound having a functionality of 3 or more, such as trimellitic acid and pentaerythritol, in an amount of not more than mol%.

The above-mentioned polyester is known per se, and can be produced by a method known per se.
The polyester has an intrinsic viscosity of about 0.4 when measured at 35 ° C. as a solution in o-chlorophenol.
Of about 0.9 are preferred.

The polyester constituting each layer in the laminated biaxially oriented polyester film of the present invention comprises the above polyester, but the polymer in each layer may be the same or different. Among them, it is preferable that they are the same.

The laminated biaxially oriented polyester film of the present invention comprises three layers, and each layer, that is, the core layer and both surface layers, contains inert fine particles. Examples of the inert fine particles include (1) silicon dioxide (including hydrates, silica sand, quartz, etc.); (2) alumina in various crystal forms; (3) SiO ₂
Silicates containing 30% by weight or more (eg, amorphous or crystalline clay minerals, aluminosilicates (including calcined products and hydrates), warm asbestos, zircon, fly ash, etc.); (4) Mg Oxides of Zn, Zr, and Ti;
(5) Ca and Ba sulfates; (6) Li, Ba, and Ca phosphates (including monohydrogen salts and dihydrogen salts):
(7) Li, Na, and K benzoates; (8) Ca,
Terephthalates of Ba, Zn, and Mn; (9) Mg,
Ca, Ba, Zn, Cd, Pb, Sr, Mn, Fe, C
o and Ni titanates; (10) Ba and Pb chromates; (11) carbon (eg carbon black,
(Graphite etc.); (12) glass (eg glass powder,
Glass beads, etc.); (13) Ca and Mg carbonates;
(14) Fluorite; (15) ZnS; (16) Heat-resistant polymer particles (for example, silicone resin particles, crosslinked acrylic particles, crosslinked polystyrene particles, crosslinked styrene-acrylic particles, crosslinked polyester particles, Teflon particles, polyimide particles, polyimide -Amide particles, melamine resin particles, etc.)
And the like are preferable.

The inert fine particles contained in the core layer in the present invention are fine particles having an average particle diameter of 1.0 μm or less.
When the average particle size exceeds 1.0 μm, protrusion of the fine particles to the film surface appears largely through the surface layer,
It becomes difficult to obtain the homogeneity of the film surface, which is not preferable.

The amount of the inert fine particles contained in the core layer must be less than the amount of the inert fine particles contained in the surface layer. When the amount of the inert fine particles contained in the core layer exceeds the amount of the inert fine particles contained in the surface layer, a large number of protrusions by the particles to the film surface appear through the surface layer, and the flatness of the film surface, especially the background portion is obtained. Is difficult and not preferable.

In the present invention, the surface layer has an average particle size not less than twice the average particle size of the fine particles contained in the core layer and not less than the average particle size of the inert particles contained in the core layer. It is important that the content of the inert fine particles is 20% or more of the total volume of the inert fine particles contained in the surface layer. When the thickness of the surface layer is less than twice the average particle diameter of the fine particles contained in the core layer, the protrusion of the projections on the film surface by the fine particles contained in the core layer significantly affects the surface property, which is not preferable. Further, the inert fine particles contained in the surface layer mainly constitute the protrusions on the film surface, but 20% or more of the total volume of the inert fine particles contained in the surface layer is the average particle size of the inert fine particles contained in the core layer. Unless the particles have the above average particle diameter, the effect of the protrusions due to the protrusion of the particles in the core layer on the surface property of the film formed by the particles of the surface layer (when the magnetic tape is used due to the increased surface roughness) It is not preferable because the electromagnetic conversion characteristics are deteriorated). It is important that this value is 20% or more, more preferably 30% or more, and further preferably 50% or more.

The laminated biaxially oriented polyester film of the present invention preferably has a thickness of 10 to 25 μm.

The laminated biaxially oriented polyester film of the present invention can be obtained by a method conventionally known or accumulated in the art. For example, it can be obtained by first producing a laminated unstretched film and then biaxially orienting the film. This laminated unstretched film can be manufactured by a conventionally accumulated manufacturing method of a laminated film. For example, a method of laminating a film layer forming a surface and a film layer forming a core layer in a melted state or a cooled and solidified state can be used. More specifically, it can be produced by, for example, a method such as coextrusion or extrusion laminating.

The unstretched film laminated by the above-mentioned method can be made into a biaxially oriented film according to the conventional accumulated manufacturing method of a biaxially oriented film. For example, the laminated unstretched film is uniaxially (longitudinal or transverse) at a temperature of (Tg-10) to (Tg + 70) ° C. (however, Tg: glass transition temperature of polyester) of 2.5 to
The film is stretched at a draw ratio of 5.0 times, and then in a direction perpendicular to the above-described stretching direction (when the first stage stretching is the longitudinal direction, the second stage stretching is the transverse direction), Tg (° C)-(Tg + 70) ° C. It can be produced by stretching at a temperature of 2.5 to 5.0 times.
In this case, the area draw ratio is 9 to 22 times, and further 12 to 2
It is preferably doubled. The stretching means may be simultaneous biaxial stretching or sequential biaxial stretching. Further, the biaxially oriented film can be heat-set at a temperature of (Tg + 70) ° C. to Tm (° C.). For example, laminated polyethylene terephthalate film is preferably heat set at 190 to 230 ° C. The heat setting time is, for example, 1 to 60 seconds.

The laminated biaxially oriented polyester film of the present invention can be used as a polymer for the core layer in a simple device such as an edge portion of a biaxially stretched film which cannot be a final product until now if it is satisfied with the above-mentioned conditions. To provide a laminated biaxially oriented polyester film which can be reused, and as a result, has excellent surface properties, that is, excellent slidability and abrasion resistance, and excellent electromagnetic conversion properties when formed into a magnetic tape, at low cost. It has the characteristic of being able to

Various physical properties and characteristics in the present invention are measured and defined as follows.

(1) Average particle size (DP) CP-50 type Centrifugal particle size analyzer (Centrifugal Particle S) manufactured by Shimadzu Corporation
ize Analyzer). The particle diameter corresponding to 50 mass% is read from the integrated curve of particles of each particle diameter calculated based on the obtained centrifugal sedimentation curve and the abundance thereof, and this value is taken as the above average particle diameter (Book Technology ”, Nikkan Kogyo Shimbun, 1975, pp. 242-247).

(2) Specific surface area of powder BE, using Autosorb-1 manufactured by Kantachrome Co., Ltd.
The specific surface area is measured by the T method.

(3) Coefficient of running friction of film (μk) It is measured as follows using the apparatus shown in FIG.
In FIG. 1, 1 is an unwind reel, 2 is a tension controller, 3, 5, 6, 8, 9 and 11 are free rollers, 4
Is a tension detector (inlet), 7 is stainless steel SUS
304 fixed rod (outer diameter 5mmφ, surface roughness Ra = 0.02)
μm), 10 is a tension detector (outlet), 12 is a guide roller, and 13 is a take-up reel.

At a temperature of 20 ° C. and a humidity of 60%, the width is 1 /
The film cut into 2 inches is attached to a fixed rod of 7 at an angle θ =
It is brought into contact with (152/180) π radian (152 °) and moved (rubbed) at a speed of 200 cm per minute. When the tension controller 2 is adjusted so that the inlet tension T ₁ becomes 35 g, the outlet tension (T ₂ : g) is detected by the outlet tension detector after the film has run 90 m, and the running friction coefficient μk is calculated by the following formula. calculate.

[0031]

[Number 1] μk = (2.303 / θ) log (T 2 / T 1) = 0.868log (T 2/35)

(4) Flatness of film surface Ra (center line average roughness) is measured according to JIS B 0601. Using a stylus type surface roughness meter (SURFCOM3B) manufactured by Tokyo Seimitsu Co., Ltd., the radius of the needle is 2 μm and the load is 0.0
A chart (film surface roughness curve) is applied under the condition of 7 g, a portion of the measurement length L is extracted from the obtained film surface roughness curve in the direction of its center line, and the center line of this extracted portion is taken as the X axis. When the roughness curve Y = f (x) is expressed with the direction of longitudinal magnification as the Y axis, the value (Ra: μm) given by the following equation is defined as the flatness of the film surface.

[0033]

[Equation 2]

In the present invention, the reference length is 0.25 mm and 8
Ra is expressed as an average value of 5 pieces obtained by measuring 3 pieces from the largest value.

(5) High-speed scratch resistance and abrasion resistance In the same apparatus as that used in FIG. 1 used for measuring the running friction coefficient μk, the surface roughness Ra obtained by bending the fixing rod 7 into a cylindrical shape of a SUS sintered plate has a surface roughness Ra of 0.15 μm. In place of the tape guide, the winding angle is 30 degrees and the inlet tension is 5 at a speed of 300 m / min.
Run 200m so that it will be 0g. The shavings adhering to the tape guide after running and the scratches of the tape after running are evaluated.

<Judgment of shavings> ◎ No shavings are observed. ○ A slight amount of shavings can be seen. △ The existence of shavings can be seen at a glance. × Shavings are badly attached.

<Scratch Judgment> ◎ No scratch is observed. ○ 1 to 5 scratches can be seen. Δ 6 to 15 scratches are seen. × 16 or more scratches can be seen.

[0038]

EXAMPLES The present invention will be further described below with reference to examples.

[0039]

Comparative Example 1 Dimethyl terephthalate and ethylene glycol, manganese acetate as a transesterification catalyst, antimony trioxide as a polymerization catalyst, phosphorous acid as a stabilizer, and calcium carbonate fine particles having an average particle size of 0.60 μm as a lubricant. Addition and polymerization were carried out by a conventional method to obtain polyethylene terephthalate having an intrinsic viscosity of 0.62 (orthochlorophenol, 35 ° C.). The amount of calcium carbonate fine particles added was adjusted to 0.3% by weight.

1 of the obtained polyethylene terephthalate was used.
After drying at 70 ° C. for 3 hours, it was supplied to an extruder, extruded into a sheet form from a die, and cooled to obtain an unstretched film.

The unstretched film thus obtained is preheated at 75 ° C., and further 15 mm between low speed and high speed rolls.
It was heated from above by one IR heater having a surface temperature of 900 ° C., stretched 3.6 times, rapidly cooled, then supplied to a stenter and stretched laterally 3.9 times at 105 ° C. The obtained biaxially oriented film was heat set at a temperature of 205 ° C. for 5 seconds to obtain a heat set biaxially oriented film having a thickness of 15 μm in the central portion.

Then, portions (both end portions) having different thicknesses, which were grasped by the stenter clip, were cut with a leather blade, the central portion was wound as a product film, and both end portions were wound as unused portions. The weight of the unused portion was 32% based on the weight of the product film. The characteristics of the product film in the central portion are shown in Table 1.

[0043]

[Example 1 and Comparative Example 2] Both ends, which were wound as unused portions in Comparative Example 1, were flaked using a crusher. The obtained flakes were melted by an extruder, extruded in a strand shape, and then cut into pellets to produce recovered pellets.

In the production of a three-layer laminated biaxially oriented polyester film, the polyester for the core layer is a mixture of the above-mentioned recovered pellets and polyethylene terephthalate containing no inert fine particles in half, and the polyester for the surface layer is The polyethylene terephthalate polymerized in Comparative Example 1 was used.

Both the polyester for the core layer and the polyester for the surface layer were dried at 170 ° C. for 3 hours in the same manner as in Comparative Example 1, and then fed to different extruders of the coextrusion film-forming machine, and the thickness ratio of surface layer / core layer / surface layer was changed. A laminated unstretched film was obtained by extruding from a three-layer die so that the ratio was 2.5 / 10 / 2.5 in Example 1 and 1.0 / 13 / 1.0 in Comparative Example 2, and then cooling. Subsequently, the product film was obtained by stretching and winding in the same manner as in Comparative Example 1. The properties of the obtained central product film are also shown in Table 1.

[0046]

[Comparative Example 3] In addition to using 0.3% by weight of calcium carbonate fine particles having an average particle size of 0.60 μm as a lubricant, a specific surface area of 80
m ² / g θ-crystal alumina fine particles (Crushing treatment is performed so that the average particle size of primary particle aggregates is 0.15 μm)
Polyethylene terephthalate was obtained in the same manner as in Comparative Example 1 except that 0.2% by weight of was added.

A film was formed from this polyethylene terephthalate in the same manner as in Comparative Example 1 to obtain a roll for the product film and a film for collecting pellets of unused parts at both ends. The unused portion was made into a recovered pellet by the same method as in Example 1 and Comparative Example 2. The characteristics of the product film are shown in Table 2.

[0048]

Example 2 and Comparative Example 4 Using the polyethylene terephthalate containing calcium carbonate fine particles and theta crystalline alumina fine particles and the recovered pellets obtained in Comparative Example 3, the laminated biaxial was prepared in the same manner as in Example 1 and Comparative Example 2. An oriented polyester film was obtained. However, the thickness constitution of the surface layer / core layer / surface layer was changed to 2.0 / 11.0 / 2.0 in Example 2 and 0.5 / 14.0 / 0.5 in Comparative Example 4. The properties of the obtained product film are also shown in Table 2.

[0049]

[Table 1]

[0050]

[Table 2]

As is clear from Tables 1 and 2, the core material of the present invention is used as a core layer component by passing a film, which has not been used in the past, at both ends in a biaxial stretching process which has not been used in the past, through a simple process. Despite its use, it shows the same surface characteristics as a single layer film. Further, in the films of Comparative Examples 2 and 4 in which the thickness of the surface layer does not satisfy the conditions of the present invention, the surface of the laminated biaxially oriented polyester film is roughened by the core layer component, and when the film is used as a magnetic recording medium, electromagnetic conversion is performed. There is a concern about deterioration of characteristics.

[0052]

According to the present invention, it is possible to provide a laminated biaxially oriented polyester film having excellent surface properties, slipperiness, and abrasion resistance at a low cost and in a form useful for resource saving.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an apparatus for measuring a coefficient of dynamic friction for evaluating film running property.

[Explanation of symbols]

 1 Feeding reel 2 Tension controller 3,5,6,8,9,11 Free roller 4 Tension detector (entrance) 7 Fixing pin 10 Tension detector (outgoing side) 12 Guide roller 13 Take-up reel

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Claims (2)

[Claims] 1. A laminated biaxially oriented polyester film comprising three layers, wherein the core layer contains inert fine particles having an average particle size of 1.0 μm or less, and the surface layer has an average particle size of particles contained in the core layer. Inactive fine particles having a diameter not less than twice the average diameter and the surface layer having an average particle diameter not less than the average particle diameter of the inert fine particles contained in the core layer are 20 times the volume of all the inert fine particles contained in the surface layer.
% Of the biaxially oriented polyester film for a magnetic recording medium. 2. The laminate for magnetic recording media according to claim 1, wherein the amount of all the inert particles contained in the surface layer is equal to or larger than the amount of all the inert particles contained in the core layer. Biaxially oriented polyester film.