JPH05182246A - Optical tape - Google Patents

Abstract

PURPOSE:To improve recording and reproducing characteristics by providing an optical recording layer on one surface of a biaxially oriented polyester film having 2.5% thermal shrinkage in the longitudinal direction of the film subjected to a prescribed treatment and 45 to 55% rate of crystallization. CONSTITUTION:The base polyester film is treated for 30 minutes at 150 deg.C so as to obtain <=2.5% thermal shrinkage in the longitudinal direction of the film and 45 to 55% rate of crystallization of the film. The biaxially oriented polyester film is subjected to 0.2 to 20% slackening in the longitudinal direction in the cooling zone at the outlet of the heat treatment in order to obtain the desired thermal shrinkage. The desired rate of crystallization is obtd. by adequately selecting the heat treatment temp. Workability is good if slipperiness is imparted only to the side of the base where the optical recording layer is not provided at this time. The thermal shrinkage or rate of crystallization is changed if conditions, such as longitudinal and transverse stretching times, heat fixing temp. and slackening, are changed. As a result, the dealing with the various contents of the copolymer components and crystallization speeds is possible and good repetitive recording and reproducing are assured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical tape capable of recording / reproducing information by irradiating light. In particular, the present invention relates to an optical tape having repetitive recording characteristics significantly improved.

[0002]

2. Description of the Related Art Conventionally, a magnetic recording medium has been generally used as an information recording tape. In recent years, however, there has been an increasing demand for an improvement in information recording density, and an optical recording medium has been demanded to meet the demand. A method using a recording / reproducing system has been proposed. The structure of such an optical tape is as follows:
Those provided with a metal film of e-As-Se (JP-A-57-3
3447), Te on a polyimide tape substrate
-Se-based, Se-In-Sb-based and Ag-Sn-based alloys formed by RF-magnetron sputtering, and a protective layer formed thereon (JP-A-62-13).
2251) and other optical tapes have been reported. Various types of such optical tapes have been proposed, but their bases have advantages and disadvantages, and good ones have not been obtained. For example, a polyester film is suitable as such a support because it is excellent in chemical properties, mechanical properties, thermal properties, etc. and a flat film can be obtained relatively easily. However, an optical tape using a polyester film as a base material is not sufficient in terms of characteristics when repeatedly recorded as compared with an optical disk using a polycarbonate plate or the like as a base material.

[0003]

Means for Solving the Problems The inventors of the present invention have made extensive studies in view of the above problems, and as a result, found that a film having specific characteristics was useful as a base material for an optical tape, and completed the present invention. I arrived.

That is, the gist of the present invention is 3 at 150 ° C.
An optical recording layer is provided on one side of a biaxially oriented polyester film having a thermal shrinkage of 2.5% or less in the longitudinal direction of the film after treatment for 0 minutes and a crystallinity of 45 to 55% or a laminate thereof. Exists on optical tape.

The invention will be described in detail below. In the present invention, the recording layer formed on the base film,
A write-once type in which recording can be performed only once and a rewritable type in which recording and erasing can be performed any number of times can be adopted. Examples of rewritable media include a magneto-optical recording medium that utilizes the magneto-optical effect and a phase-change medium that utilizes reversible change in crystal state. These rewritable recording media generally have a layer structure of base film-dielectric layer-recording layer-dielectric layer-reflection layer when information is recorded and reproduced by irradiating a laser beam from the base film side. In addition, in the case of irradiating the laser beam from the recording layer side, generally, the constitution of the base film-reflection layer-dielectric layer-recording layer-dielectric layer is adopted. The dielectric layer is used for the purpose of protecting the recording layer that is easily oxidized from moisture and oxygen, preventing the deformation of the recording layer, and amplifying the signal by the interference effect of light, and is usually a transparent and highly heat-resistant metal. Compounds, metal nitrides, metal sulfides, inorganic carbides and the like are used.

As metal oxides, Al ₂ O ₃ , Ta ₂ O ₅ ,
SiO, metal oxides SiO ₂ alone or a mixture or a composite oxide such as Al-Ta-O thereof. Moreover, other elements such as Ti and Z can be added to these compounds.
r, Mo, Y, etc. are in the form of oxides alone or Al, Ta
It may form a complex with an oxide. Since these metal oxides have a dense structure, they prevent moisture and oxygen from entering from the outside, have high corrosion resistance, have low reactivity with the magneto-optical recording layer and the layer change recording layer, and have good adhesion with resin. Excellent and preferable. Specific examples of the metal nitride include nitrides of metals such as Si, Al, and Ge, composite nitrides of two or more kinds of these, or composite nitrides of these with Nb and Ta (for example, Si.
NbN, SiTaN, etc.). Among these, the nitride containing Si has a good effect. The metal nitride is dense and prevents moisture and oxygen from entering from the outside, and has high corrosion resistance itself. Examples of the metal sulfide include ZnS and the like, which can be used alone, but are often used as a mixture with the metal oxide or the metal nitride. SiC etc. are mentioned as an inorganic carbide. Especially in the present invention, tantalum oxide (Ta ₂ O ₅ ) and zinc sulfide (Zn
S) is suitable for use because it has small internal stress and few cracks.

The film thickness of these dielectric layers is preferably about 500 to 3000 Å on the dielectric layer on the side irradiated with laser light and about 100 to 3000 Å on the reflective layer side. As the recording layer, an alloy of a rare earth and a transition metal, such as TbFeC
o, GdTbFe, GdTbFeCo, GdDyFeC
o, magneto-optical recording material such as NdDyFeCo or Ge-
Phase change recording materials such as Te-based, Ge-Sb-Te-based, In-Sb-Te-based are used. The thickness of the recording layer is 10
The range of 0 to 2000Å is preferable. The thicknesses of the recording layer and the dielectric layer are set so that the absorption efficiency of the laser light is good and the amplitude of the recording signal, that is, the contrast between the recorded state and the unrecorded state is large in consideration of the interference effect due to the multilayer structure. To be elected. As the reflective layer, a metal thin film of Al, Au, Ag, Ni or the like having a high reflectance is usually used. The reflective layer also has an effect of promoting diffusion of heat energy absorbed by the recording layer. The thickness of the reflective layer is 200 to 3000A
Is preferred. In addition, a resin layer protective layer such as an ultraviolet curable resin may be provided on the reflective layer.

The recording layer, the dielectric layer, and the reflective layer are formed by a known thin film forming method in vacuum, such as a vacuum vapor deposition method, an ion plating method and a sputtering method. composition,
The sputtering method is particularly recommended because it is easy to control the film thickness. The thickness of the recording layer to be formed can be controlled by monitoring with a film thickness meter such as a crystal oscillator which is a known technique. The polyester of the polyester film that serves as the support of the optical tape of the present invention refers to polyethylene terephthalate in which 80 mol% or more of the constituent units is ethylene terephthalate. Examples of the copolymerization component other than the above-mentioned superior constituent components include diethylene glycol, propylene glycol, neopentyl glycol,
Diol components such as polyethylene glycol, polytetramethylene glycol and 1,4-cyclohexanedimethanol, dicarboxylic acid components such as isophthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, azelaic acid, sebacic acid and ester-forming derivatives thereof. An oxymonocarboxylic acid such as oxybenzoic acid and its ester-forming derivative can be used.

The thickness of the recording layer, the dielectric layer, and the reflective layer formed on the optical tape by a method such as sputtering is usually
Since it is less than 1 μm, the surface condition of the support film appears as unevenness of the recording layer, which causes noise during recording / reproduction by the optical recording / reproduction system. Therefore, the smoother the surface of the base polyester film is, the better. The center line average roughness (Ra) of the polyester film is preferably 5 nm or less, and more preferably Ra is 3 nm.
It is below. When the center line average roughness of the polyester film exceeds 5 nm, the optical recording characteristics are deteriorated, which is not preferable. In order to impart such film surface characteristics, added particles, precipitated particles, and other catalyst residues may be contained, but it is most preferable to use only polyester which forms an optically smooth surface. Further, as an additive other than the above-mentioned protrusion forming agent, if necessary, an antistatic agent, a stabilizer, a lubricant, an antiblocking agent, an antioxidant, a colorant, a light blocking agent, an ultraviolet absorber and the like are contained. May be. Further, other polymers such as polyamide, polyolefin, and polycarbonate can be blended in an amount of 10% by weight or less, but within a range that does not extremely reduce the crystallinity or extremely roughen the surface.

The biaxially oriented polyester film is produced by a known film forming method, for example, by using a polyester chip as a film forming raw material.
After melt extrusion into a film at 70 ° C to 320 ° C, 40
After cooling and solidification at -80 ° C to form an amorphous sheet, it is then stretched biaxially in the longitudinal and transverse directions sequentially or simultaneously to obtain 160-240.
It can be obtained by a method such as heat treatment at ℃. When recording and erasing signals, the optical tape irradiates the medium with laser light for a few tens of nanoseconds, and the optical recording layer has about 3
It reaches a high temperature of 00 ° C. The support polyester film does not directly absorb the laser light, and is not deteriorated by recording or erasing a few times. However, when recording is repeated 10 ⁴ times or more, the noise level gradually deteriorates.

The inventors of the present invention have found that the heat shrinkage of the support polyester film in the longitudinal direction of the film after treatment at 150 ° C. for 30 minutes is 2.5% or less, and the crystallinity of the film is 45.
It has been found that an optical tape having excellent repetitive recording characteristics can be obtained when the content is ˜55%. The longitudinal heat shrinkage is
More preferably 2.0% or less, still more preferably 1.5
% Or less. When the heat shrinkage in the longitudinal direction exceeds 2.5%, the repetitive recording characteristics are poor and unsuitable. Further, the crystallinity is more preferably 47 to 53%. If the crystallinity of the film is less than 45%, the repetitive recording characteristics will be poor and the workability of the polyester film will be poor, such being unsuitable. Further, if the crystallinity exceeds 55%, the repetitive recording characteristics will not be a problem, but the mechanical strength of the film will decrease. Further, the heat shrinkage in the lateral direction of the polyester film is preferably 5.0% or less.

In the present invention, in order to obtain a polyester film having a desired heat shrinkage ratio, in the cooling zone at the outlet of the heat treatment during the manufacturing process of the biaxially oriented polyester film, the longitudinal direction is relaxed by 0.2 to 20%. Is effective. The desired crystallinity can be obtained mainly by selecting an appropriate heat treatment temperature. However, these requirements of the present invention also depend on the conditions of the polyester raw material, for example, the content of the copolymerization component, the crystallization rate, etc., so that the requirements of the present invention can be satisfied by appropriately selecting these conditions. There must be. Since a polyester film having an extremely flat surface, such as the support of the optical tape of the present invention, generally has poor workability, it is preferable to impart slipperiness to the surface of the support polyester film on which the optical recording layer is not provided. .. As a means for imparting slipperiness, a method of forming a coating layer containing a lubricant on the running surface side of the film, or a method of co-extruding and co-stretching a film containing a lubricant is preferably used. Examples of the lubricant include particles, lubricants, protrusion forming resins and the like.

Particles used as a lubricant include inorganic particles such as alumina, silica, titanium oxide, kaolin and molybdenum sulfide, polyester, polyamide, polyarylate, polysulfone, polyphenylene oxide,
Polyimide, epoxy, cross-linked styrene, cross-linked acrylic,
Examples thereof include particles of polymer compounds such as crosslinked benzoguanamine and crosslinked melamine, carbon particles, and metal alkoxide hydrolyzate particles. Lubricants include anionic surfactants, cationic surfactants, amphoteric surfactants, nonionic surfactants, fluorochemical surfactants, organic carboxylic acids and their derivatives, higher aliphatic alcohols, paraffins, waxes, etc. Is mentioned. The protrusion-forming resin is a compound that is characterized by phase separation in the layer and stretching characteristics. A method for forming protrusions by applying a coating agent containing a water-soluble polymer represented by cellulose, gelatin, polyacrylic acid and its salts, polystyrene sulfonic acid and its salts, etc. in the polyester film manufacturing process and then stretching. However, the method is not limited to this method.

Although these lubricants may be dispersed alone in water or a solvent and applied, it is preferable that the resin binder and the lubricant are dispersed in water or a solvent and applied.

[0015]

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist. The evaluation methods in the examples are as follows. In Examples and Comparative Examples, "part" means "part by weight". (1) Surface Roughness Ra The surface roughness was measured using a surface roughness measuring device (SE-3F) manufactured by Kosaka Laboratory as follows. That is, a portion having a reference length L (2.5 mm) is extracted from the film cross-section curve in the direction of the center line, and the center line of the extracted portion is taken as the x-axis, and the longitudinal magnification direction is taken as the y-axis. When expressed by (x), the value given by the following equation is expressed by [μm]. The center line average roughness was obtained by obtaining 10 cross-section curves from the surface of the sample film and expressing the average value of the center line average roughness of the extracted portion obtained from these cross-section curves. The tip radius of the stylus is 2
μm, load 30 mg weight, cut-off value 0.08
mm.

[Number 1] Ra = (1 / L) ∫ L 0 | f (x) | dx (2) crystallinity chi _c (%) Film crystallinity calculating the density method of the (Mio Yokouchi, Nakamura Itariyaku " Polyester fiber ", p. 200, Corona Co., Ltd., issued January 10, 1945).

[0016]

[Equation 2] In the above formula, d is the measured density and d _k is the density of the perfect crystalline phase (1.455 g / cm ), D _a is the fully amorphous density (1.335 g / cm ) Represents.

(3) Thermal shrinkage (%) Heat shrinkage (%) was heat treated for 30 minutes in an atmosphere of 150 ° C., and the lengths of the samples before and after the heat treatment were measured and calculated by the following formula.

[0018]

[Equation 3]

Example 1 A transesterification reaction was carried out by a conventional method using 100 parts of dimethyl terephthalate, 69 parts of ethylene glycol, and 0.8 parts by weight of diethylene glycol, and 0.09 part of calcium acetate as a catalyst. Then, antimony trioxide 0.
01 parts, 0.3 parts by weight of lithium acetate, and 0.2 parts by weight of trimethyl phosphate were added, and polycondensation reaction was performed according to a conventional method to obtain polyethylene terephthalate (PET) having an intrinsic viscosity of 0.63. 28 after drying the obtained polyester
2. Melt extruded at 5 ° C., rapidly cooled and solidified on a casting drum to obtain an unstretched film, and first in the machine direction at 90 ° C.
After being stretched 5 times, 92 mol% of terephthalic acid, 8 mol% of sodium sulfoisophthalic acid as a dicarboxylic acid component, 75 mol% of ethylene glycol as a glycol component, and 25 mol% of diethylene glycol as a glycol component on the lower surface of the film.
95 parts of the water-based polyester, 5 parts of silica sol having an average particle diameter of 0.07 μm, and 1900 parts of water were applied. Further, it was stretched 4.0 times in the transverse direction at 105 ° C., heat-treated at 225 ° C., and then relaxed by 3% in the longitudinal direction in a cooling zone at the exit of the heat treatment to obtain a biaxially stretched polyester film having a thickness of 15 μm. Table 1 shows the center line average roughness (Ra) of the obtained polyester film on the flat surface side, the thermal shrinkage in the longitudinal direction, and the crystallinity.

On the flat surface of the obtained long polyester film having a thickness of 15 μm, an Al reflection layer of 1000 Å, a Ta ₂ O ₅ dielectric layer of 900 Å and Tb were formed by a sputtering method.
₂₂ Fe ₇₀ Co ₈ (atomic%) recording layer 400 Å, Ta ₂ O ₅
A dielectric layer 750Å was sequentially formed in the same chamber under vacuum to prepare a magneto-optical recording medium. The obtained magneto-optical recording medium did not deteriorate in noise level even after repeated recording test 10 ⁴ times, and showed good durability. Examples 2-3, Comparative Examples 1-2 Among the conditions of Example 1, the values of the crystallinity and the heat shrinkage are different by changing the longitudinal and transverse stretching ratios, the heat setting temperature and the relaxation conditions. Each 15 μm thick polyester film was made. An optical recording layer was formed on the obtained long polyester film in the same manner as in Example 1 and repeated recording test was repeated 10 ⁴ times. The optical tape outside the range specified in the present invention had a deteriorated noise level in the repeated recording test. The results of these evaluations are summarized in Table 1 below.

[0021]

[Table 1]

[0022]

INDUSTRIAL APPLICABILITY The optical tape of the present invention has excellent recording and reproducing characteristics, and its industrial value is high.

Claims (1)

[Claims] 1. A heat shrinkage ratio in the longitudinal direction of the film after treatment at 150 ° C. for 30 minutes is 2.5% or less and a crystallinity of 45.
An optical tape comprising an optical recording layer provided on one side of a biaxially oriented polyester film or a laminate of the biaxially oriented polyester film of ˜55%.