JP2002140811A - Polyester film for magnetic recording medium and its film roll - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester film wherein the generation of blocking and discharge trace can be suppressed even though the static charge level of the film cannot be satisfactorily lowered and which is effective for efficiently manufacturing a high performance DVC tape and to provide its film roll. SOLUTION: In the polyester film for a magnetic recording medium, plural layers consisting of a layer A and a layer B are laminated by co-extrusion method, the surface of the layer A is coated with a discontinuous coating film containing polar polymer, the outer surface (a) on the side of the discontinuous coating film has 1-5 nm surface roughness value SRa, the outer surface (b) on the side of the layer B laminated on the opposite side to the surface (a) has 5-30 nm surface roughness value SRa and 0.10-0.60 wt.% wax is mixed in the layer B. The film roll which is wound up has -2.0-2.0 kV static charge potential.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester film for a magnetic recording medium. More particularly, the present invention relates to a polyester film for a magnetic recording medium which is optimal for efficiently producing a high-quality magnetic recording medium for recording a large amount of digital data, such as a digital video cassette tape or a data storage tape.

[0002]

2. Description of the Related Art The world's first digital video cassette tape for home use (hereinafter referred to as DVC tape) put into practical use in 1995 is formed by vacuum-depositing a metal magnetic thin film of cobalt on a polyester film having a thickness of 6 to 7 μm. Further, the surface is coated with a diamond-like carbon film.

[0003] A polyester film layer A containing fine particles having a particle size of 10 to 300 nm and having fine projections having a height of 5 to 90 nm formed by the fine particles is used as a base film. Consisting of a discontinuous film with a thickness of 5 to 50 nm adhered to the surface,
The discontinuous film is mainly composed of a polar polymer, and includes a polyester film (for example, JP-A-6-51401) in which the fine projections appear on the surface.

On the surface b of the film layer A, which is opposite to the surface a on one side, a layer B containing larger fine particles in contact with the base layer for the purpose of imparting runnability as a magnetic recording medium. Are laminated and co-extruded.

[0005] This DVC tape has a large recording capacity in spite of its small size, the image quality and sound quality are not deteriorated even after a long period of time, and since no noise is generated, the high quality and high sound quality can be enjoyed. It does not degrade the sound quality and has received high praise from the market.

[0006]

However, when a DVC tape is manufactured from a conventional polyester film as shown in JP-A-6-51401 or the like, when the DVC tape is put into a post-process of vacuum deposition of a magnetic layer, It may be difficult to increase productivity because a blocking phenomenon occurs in which the upper and lower films laminated inside the roll are stuck to each other, and in some cases, a discharge mark appears to significantly impair the performance of the product. I understand. During film formation, when the film is charged by contacting or rubbing with various transport system rolls, when it is wound around a cylindrical core to form a rolled product, it does not contain a polar polymer. The surface a covered with the continuous film and the surface b on which the layer B is laminated easily adhere to each other. In addition, SRa for both sides a and b
The value is small and smooth, and the film itself is extremely thin. These factors cause blocking or discharge marks.

For this reason, it is essential that a static eliminator is installed at the winding portion of the film roll and the like, so that the charging level of the inner layer of the roll and the surface layer film is kept low, so that blocking and discharge marks are hardly generated. Have been. However, in practice, it is very difficult to maintain a desirable state in which the charging potential is almost 0, because the distance between the film and the static eliminator is not constant and it is difficult to uniformly eliminate the static electricity. there were.

[0008] The present invention solves the above problem, and can suppress the occurrence of blocking and discharge marks even if the charge level of the film cannot be sufficiently reduced, and can efficiently produce a high-performance DVC tape. An object of the present invention is to provide a polyester film and a film roll which are effective for the above.

[0009]

In order to achieve the above object, the polyester film for a magnetic recording medium of the present invention comprises a plurality of layers consisting of a layer A and a layer B which are laminated by co-extrusion. The surface is coated with a discontinuous film containing a polar polymer, the surface a of the outer surface a on the side of the discontinuous film has a surface roughness SRa value of 1 to 5 nm, and a layer B laminated on the side opposite to the a surface. The surface roughness SRa value of the outer surface b surface on the side is 5 to 3
0 nm and the amount of wax added in layer B is 0.1
It is characterized by being blended at 0 to 0.60% by weight.

[0010] Further, a film roll formed by winding the polyester film, wherein the charged potential of the film is -2.0 to 2.0 kV, is a polyester film roll for a magnetic recording medium.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The polyester film to be used in the present invention is a general plastic material comprising a polyester raw material from which the contained particles have been removed as much as possible, and comprising melting, molding, biaxial stretching, heat setting and winding. It is manufactured by a film manufacturing process. At that time, in both the stretching and heat-setting steps, the film is usually stretched 2.7 to 5.5 times and 3.5 to 7.0 times in the vertical and horizontal directions at 90 to 140 ° C. The conditions for heat setting are taken. Biaxial stretching can be performed by sequential biaxial stretching or simultaneous biaxial stretching, and can be further stretched in the vertical or horizontal direction or in both the vertical and horizontal directions before heat setting to increase the strength.

The polyester used in the present invention may be any polyester capable of forming a high-strength film by molecular orientation accompanying stretching, and is preferably polyethylene terephthalate or polyethylene-2,6-naphthalate.
These may be polyester copolymers, but it is preferable that 80% or more of the constituent components be ethylene terephthalate or ethylene-2,6-naphthalate. Other polyester copolymer components include diol components such as diethylene glycol, propylene glycol, neopentyl glycol, polyethylene glycol, p-xylene glycol, 1,4-cyclohexanedimethanol, or adipic acid,
Examples include dicarboxylic acid components such as sebacic acid, phthalic acid, isophthalic acid, and 5-sodium sulfoisophthalic acid, or polyfunctional dicarboxylic acid components such as trimellitic acid and pyromellitic acid, and p-hydroxyethoxybenzoic acid.

[0013] In addition, the polyester shown above may not contain more than 5% of at least one of alkali metal salt derivatives of sulfonic acid which is not reactive with the polyester or polyalkylene glycol insoluble in the polyester. If necessary, they may be mixed.

The thickness of the polyester film of the present invention is preferably from 3.0 to 8.0 μm, more preferably 4.0.
６6.5 μm is preferred. If the thickness is less than 3.0 μm, the rigidity of the film is significantly reduced, the contact between the magnetic tape and the magnetic head of the recorder becomes poor, and the output performance of the magnetic tape is undesirably reduced. On the other hand, when the thickness is 8.0 μm or more, the winding length of the film roll becomes short, and the productivity is undesirably reduced.

[0015] The polyester film of the present invention comprises a plurality of film layers in which a plurality of layers consisting of a layer A and a layer B are laminated by co-extrusion, and a discontinuous film formed on the surface of the layer A.

In this polyester film, one side surface (referred to as surface a) on which a metal magnetic layer is formed by vapor deposition.
Is an outer surface in which the surface of the layer A is covered with a discontinuous film containing a polar polymer, which requires smoothness for magnetic layer deposition, and has a surface roughness (SRa value) of 1 to 1. 5
nm, preferably 2 to 4 nm. SRa value is 1nm
If it is less than 1, the magnetic thin film formed outside the a-plane becomes too smooth, and when used as a magnetic recording medium, the magnetic thin film tends to be worn by the head during recording / reproducing. Also,
If the SRa value exceeds 5 nm, the magnetic thin film formed outside the a-plane becomes too coarse, and the output characteristics deteriorate when used as a magnetic recording medium.

The discontinuous film covering the surface of the layer A contains fine particles having an average particle size of 5 to 30 nm, preferably 8 to 30 nm, in an amount of 0.5 to 12.0% by weight, preferably 0.6 to 10%.
It can be formed by a method in which a resin coating solution containing a polar polymer containing 0% by weight is applied to a film that has been stretched in one direction.

In order to increase the durability of the magnetic layer,
The average particle size in the layer A is 30 to 150 nm, preferably 40
It is preferable to form surface protrusions by containing 0.01 to 1.0% by weight, preferably 0.02 to 0.8% by weight of fine particles having a size of 100 nm to 100 nm.

As the fine particles, silica, calcium carbonate, alumina, titanium oxide, polyacrylic acid, polystyrene, kaolin, calcium phosphate, barium sulfate, talc, lithium fluoride, zirconia, zeolite and the like can be used. Further, as the polar polymer, polyvinyl alcohol, tragacanth rubber, casein, gelatin, cellulose derivative, water-soluble polyester, polyurethane and the like can be used, and a mixture thereof is also used. Neither is limited to these. The height and number of protrusions on the surface can be controlled by adjusting the type, average particle size, or amount of the fine particles described above.

On the other hand, on the surface of the layer A opposite to the side on which the discontinuous film is formed, the layer B is composited by coextrusion. This layer B is a film layer containing larger fine particles for the purpose of imparting runnability as a magnetic recording medium, and is formed by lamination by melt co-extrusion from the viewpoint of ease of production. desirable. The fine particles used here include silica, calcium carbonate,
Alumina, or cross-linked polystyrene and the like,
The average particle size is 100 to 1000 nm, preferably 150 to
900 nm, the content is 0.05 to 1.0% by weight, preferably 0.08 to 0.8% by weight.

The surface roughness (SRa value) of the outer surface b of the layer B of the polyester film is 5 to 30 nm, preferably 5 to 30 nm.
２５25 nm is preferred. If the SRa value is less than 5 nm, the friction between the a-side and the b-side becomes too large, so that the slip is difficult, and wrinkles or blocking occurs when wound up in a roll. On the other hand, if the SRa value exceeds 30 nm, when the magnetic thin film is deposited and wound into a roll, the surface protrusions on the b surface are transferred to the a surface, and undulating deformation occurs in the magnetic thin film layer.

The produced polyester film is charged by being in contact with or rubbing with various transport system rolls and guide rolls in the course of being wound into a roll. In addition, both sides a and b are S
Since the Ra value is small and smooth, and the film itself is extremely thin, when the product is wound into a cylindrical core to form a roll, the surface a covered with the discontinuous film and the surface b on the layer B side have Easy to adhere. Due to these factors, when the film is unwound after the magnetic layer is deposited and fed into the back coat process, a blocking phenomenon occurs in which the upper and lower films laminated inside the roll are stuck to each other. Will occur.

In order to prevent such a phenomenon, in the present invention, 0.10 to 0.60% by weight, preferably 0.30 to 0.50% by weight of wax is added to the layer B.
Thereby, lubricity is imparted, and the level of contact charging and frictional charging can be improved. The amount of wax added is 0.
If it is less than 10% by weight, the effect of improving the slipperiness is not recognized. If the added amount of the wax exceeds 0.60% by weight, the wax component easily bleeds out and the film surface is contaminated.

Examples of the wax contained in the layer B in the present invention include carnauba wax, candelilla wax, olicury wax, wood wax, cinnawa wax, whale wax, beeswax, and sugarcane wax.

Further, in order to obtain a desired effect,
The charge potential of the film of the inner layer and the surface layer of the roll is controlled, and is in the range of -2.0 to +2.0 kV, particularly-
It is preferable to keep it within the range of 1.5 to +1.5 kV. Charge potential is less than -2.0kV or + 2.0k
If it exceeds V, the blocking phenomenon may not be sufficiently prevented when the film is put into the back coat step after forming the magnetic layer by vacuum deposition, which is not preferable for productivity.

In order to set the charging potential of the inner layer of the roll and the surface film to -2.0 to +2.0 kV, each of the heat fixing and winding steps in the film forming step, particularly, the winding step of the film intermediate spool. In each of the roll winding steps for slitting to the product width, a method of installing an ion generator for neutralizing static electricity and applying ions to neutralize the charge on the film surface may be adopted. The support of this ion generator has a sensor that senses the distance between the product and the product.The sensor sends a signal indicating the surface position of the product to the control device, and the signal is received by the support. It is preferable to use an ion generator for neutralizing static electricity which moves so that the distance between the ion generator and the wound product becomes equal (for example, JP-A-6-50680). A voltage application type static eliminator using an ion generator of a type that promotes acceleration is preferable. By adjusting the distance between the electrode of the static eliminator and the film surface, adjusting the amount of generated ions, and adjusting the air pressure of the static eliminator, it is possible to obtain a desired film charging potential without unevenness from the beginning to the end of winding.

Using the polyester film of the present invention as a base film, a ferromagnetic metal thin film layer having a thickness of 100 to 300 nm is formed on one side surface a by vacuum evaporation, and a diamond-like carbon film having a thickness of about 10 nm is formed thereon. By coating and further applying lubricant,
Magnetic recording tapes can be manufactured. The metal thin film provided here is preferably made of a ferromagnetic material such as iron, cobalt, nickel, or an alloy thereof. In addition, it is not necessarily limited to these.

A backcoat layer having a thickness of about 0.5 to 1.5 μm is provided on one surface b of the base film. The backcoat layer is formed by dissolving fine particles, a lubricant and a binder in an organic solvent. It is preferable to apply the dried solution to the surface b and dry it. Fine particles include carbon black, alumina and the like, lubricants include silicones and fluorine compounds, and binders include polyurethane and epoxy resins. In addition, it is not necessarily limited to these.

The polyester film of the present invention exhibits excellent performance when used as a base film for a magnetic recording medium, particularly when used as a base film for a DVC tape. It also demonstrates excellent performance on high-quality magnetic recording media for recording large volumes of digital data, such as for data storage applications.

[0030]

EXAMPLE The measuring method used in this example will be described. (1) Surface roughness (SRa value) Optical stylus type (critical angle focus error detection method) manufactured by Kosaka Laboratory
Was measured using a three-dimensional roughness meter (ET-30HK). The SRa value is a center line average roughness corresponding to Ra in JIS B0601. Aluminum was deposited on the measurement surface of the film test piece. The measurement direction is the width direction, the cutoff value is 0.08 mm, and the measurement length is 0.1 to
0.25 mm, the feed pitch was 0.2 μm, the measurement speed was 20 μm / s, the number of measurement lines was 100, and the average value was calculated for each of the a-plane and the b-plane.

(2) Charge potential of the inner layer of the roll and the surface film The measurement was carried out using an electrostatic potential meter SV-10 manufactured by Kasuga Electric. Roll winding length 3000m, 6000m, 90
The charging potential was measured every time the distance reached 00 m or 12000 m (when the film was rolled up). The distance between the sensor of the measuring device and the surface of the film roll was 100 mm. Five points in the width direction were measured for each small slit product, and the average value was determined.

(3) Blocking Resistance of Film The outer surface a of the composite film layer A on the discontinuous coating side,
500 g is obtained by superposing the outer surface b surface on the layer B side laminated on the side opposite to the surface (overlap area: 3 cm × 4 cm).
/ 12cm ² at 60 ° C / 80% RH with a load of 7
After standing for 2 hours, the shear stress of the overlapped part was measured by an Orientec Tensilon tensile tester AMF / RTA-1.
It was measured at a pulling speed of 20 cm / min by using 00, and judged according to the following criteria. ◎ ・ ○ is a level that can be put to practical use. ◎: 0 kg / cm ² (no blocking at all) ○: 0 kg / cm ² or more and less than 1 kg / cm ² △: 1 kg / cm ² or more and less than 3 kg / cm ² ×: 3 kg / cm ² or more

(4) Suitability of DVC Tape for Vapor Deposition A cobalt-oxygen thin film having a thickness of 150 nm was formed on the polyester film surface by vacuum vapor deposition. Next, a diamond-like carbon film was formed to a thickness of 10 nm on the thin film by a sputtering method, and a fluorine-containing fatty acid ester-based lubricant was applied to a thickness of 3 nm. Finally, a back coat layer made of carbon black, polyurethane, and silicone was formed by a method of applying a methyl ethyl ketone solution to a thickness of 500 nm and drying. The obtained DVC tape was observed and ranked according to the following criteria. Rank A is a level that can be put to practical use.

Rank A: No problem at all. Rank B: A discharge mark was observed on the DVC tape. Rank C: A case in which a blocking phenomenon was observed when the composition was put into the back coat step after vacuum deposition, and the back coat layer could not be applied.

Next, the present invention will be described based on examples.

Example 1 Polyethylene terephthalate containing 0.030% by weight of silica having an average particle size of 60 nm, 0.35% by weight of a mixture of silica and alumina, and 0.30% by weight of polystyrene having an average particle size of 300 nm %, And polyethylene terephthalate containing 0.40% by weight of carnauba wax at a composite ratio of 15 parts by weight to 100 parts by weight of the former, and coextruded with a cooling drum to form a sheet. The film was longitudinally stretched 3.1 times by a roll stretching method.

In the process after the longitudinal stretching, a mixed aqueous solution having the following composition was applied to one surface. Hydroxypropyl methylcellulose: 0.110% by weight Water-soluble polyester resin (1: 1 copolymer of 70 mol% of terephthalic acid, 30 mol% of 5-sodium sulfisophthalic acid and ethylene glycol): 0. 330 wt% of colloidal silica (SiO ₂ ratio 40 wt%): 0.010 wt% amino-modified silicone emulsion: 0.002 wt%

Thereafter, the film is stretched 4.38 times in the transverse direction by a tenter method at 102 ° C., heat-fixed at 207 ° C., wound up on an intermediate spool, slit into a small width with a slitter, and wound up in a roll into a cylindrical core. , Thickness 6.3 μm, width 620
mm, and a polyester film roll having a winding length of 12000 m was obtained. The SRa values of the films a-side and b-side were 2.8 nm and 16.7 nm, respectively.

At this time, an air type static eliminator is installed at the winding portion of the intermediate spool, the neutralizing voltage is set to 8.5 kV, the static elimination air pressure is set to 1.0 kg / cm ² , and ions for neutralizing static electricity are generated. went. A similar static eliminator was also installed at the winding portion of the slitter, and the static eliminator was moved in accordance with the increase in the winding diameter of the film, and static elimination was performed so that the distance between the static eliminator sensor and the surface of the roll became equal. The static elimination air pressure was 1.0 kg / cm ² . The charging characteristics and blocking resistance of the obtained film roll were as shown in Table 1.

Using this polyester film, a cobalt-oxygen thin film was formed on the film surface by vacuum evaporation.
It was formed with a thickness of 0 nm. Next, a diamond-like carbon film was formed on this thin film by sputtering to a thickness of 10 nm.
And a fluorine-containing fatty acid ester-based lubricant was further applied to a thickness of 3 nm. Finally, a back coat layer made of carbon black, polyurethane, and silicone is formed by a method of applying a 500 nm thick methyl ethyl ketone solution, followed by drying, slitting to a width of 6.35 mm, winding on a reel, and forming a magnetic tape (DVC tape). Produced. Table 1 shows the deposition suitability of the obtained DVC tape.

Example 2 In the production of the base film of Example 1, the content of carnauba wax was reduced to 0.30%.
Changed to Other conditions were the same as in Example 1 to obtain a polyester film roll having a thickness of 6.3 μm, a width of 520 mm, and a winding length of 12,000 m. The SRa values of the a-plane and the b-plane of the obtained polyester film are each 3.1 n.
m, 16.2 nm. Table 1 shows the charging characteristics and the blocking resistance.

A magnetic tape was produced in the same manner as in Example 1. Table 1 shows the deposition aptitude of the obtained magnetic tape.

Example 3 In the production of the base film of Example 1, the content of carnauba wax was reduced to 0.50%.
Changed to The other conditions were the same as in Experimental Example 1 to obtain a polyester film roll having a thickness of 6.3 μm, a width of 520 mm, and a winding length of 12,000 m. The SRa values of the a-side and the b-side of the obtained polyester film were each 2.9 n.
m, 16.4 nm. Table 1 shows the charging characteristics and the blocking resistance.

A magnetic tape was produced in the same manner as in Example 1. Table 1 shows the deposition aptitude of the obtained magnetic tape.

Example 4 In Example 1, the main component of the polyester copolymer was polyethylene-2,6-naphthalate. The other conditions were the same as in Experimental Example 1 to obtain a polyester film roll having a thickness of 6.3 μm, a width of 520 mm, and a winding length of 12,000 m. The SRa values of the a-plane and the b-plane of the obtained polyester film were respectively 3.
1 nm and 17.1 nm. Table 1 shows the charging characteristics and the blocking resistance.

A magnetic tape was produced in the same manner as in Example 1. Table 1 shows the deposition aptitude of the obtained magnetic tape.

Comparative Example In the production of the base film of Example 1, the content of carnauba wax was changed to 0%. Other conditions were the same as in Experimental Example 1, and the thickness was 6.3 μm.
m, a width of 520 mm, and a roll length of 12000 m were obtained. The SRa values of the a-plane and the b-plane of the obtained polyester film were 3.0 nm and 1 nm, respectively.
It was 6.8 nm. Table 1 shows the charging characteristics and the blocking resistance.

A magnetic tape was produced in the same manner as in Example 1. Table 1 shows the appropriateness of vapor deposition of the obtained magnetic tape.

[0049]

[Table 1]

[0050]

According to the polyester film or film roll of the present invention, even if the charge level of the film cannot be reduced sufficiently, the occurrence of blocking and discharge marks can be suppressed, and therefore a high quality digital video cassette can be obtained. Tapes or various magnetic recording media can be efficiently produced.

 ────────────────────────────────────────────────── ─── Continued on the front page F term (reference) 4F100 AJ11C AJ11H AK01B AK41A AK41C BA03 BA10B BA10C BA15 EH20 JA20 JK15B JL00 YY00 YY00B YY00C YY00H 5D006 CB01 CB05 CB07 CB08

Claims (4)

[Claims] 1. A plurality of layers comprising a layer A and a layer B are laminated by co-extrusion, and the surface of the layer A is covered with a discontinuous film containing a polar polymer, and the outer surface a on the side of the discontinuous film. Has a surface roughness SRa value of 1 to 5 nm, a surface roughness SRa value of the outer surface b surface of the layer B side laminated on the side opposite to the a surface is 5 to 30 nm, and A polyester film for a magnetic recording medium, wherein a wax is added in an amount of 0.10 to 0.60% by weight. 2. The polyester film for a magnetic recording medium according to claim 1, wherein the film thickness is 3.0 to 8.0 μm. 3. A film according to claim 1, wherein a metal magnetic layer is formed by vacuum evaporation on the a-surface, which is one surface of the film.
The polyester film for a magnetic recording medium according to the above. 4. A film roll formed by winding the polyester film according to claim 1, 2, or 3,
A polyester film roll for a magnetic recording medium, wherein the charged potential of the film is -2.0 to 2.0 kV.