JPH05298672A - Audio tape - Google Patents

Abstract

PURPOSE:To prevent the generation of tape hiss while maintaining excellent characteristics as a magnetic tape by imparting a laminated structure consisting of two or more layers to a base film, incorporating particles into a layer of the base film opposite to the magnetic face to satisfy specified relation between the average particle diameter of the particles and the thickness of the outermost layer and specifying the thermal shrinkage of the base film in the longitudinal direction. CONSTITUTION:When a base film is coated with a magnetic layer to obtain a magnetic tape, a polyester film having a laminated structure consisting of two or more coextruded layers and having 0.5-2% thermal shrinkage at 80 deg.C in the longitudinal direction is used as the base film. The polyester film contains particles in a layer opposite to the magnetic face and the relation between the average particle diameter (d) (nm) of the particles and the thickness (t) (nm) of the outermost layer satisfies 0.2<=t/d<=10. The resulting magnetic tape is used for digital signal recording.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic tape having a support film provided with a coating type magnetic layer, and more particularly to an audio tape in which signals are digitally recorded.

[0002]

2. Description of the Related Art A support film of a magnetic tape having a support film provided with a coating type magnetic layer is a biaxially oriented laminated film, for example, polyester containing substantially spherical silica particles derived from colloidal silica. A biaxially oriented laminated polyester film is known (for example, JP-A-59-171623).

However, with the increase in the process speed of the film processing process, particularly the magnetic layer coating / calendering / winding process in a magnetic medium application, the cassette assembling process, etc., the film surface, especially minute irregularities, is formed on the film by the contacting rolls or guides. There was a drawback that the film surface was easily scraped off. Further, especially in audio tapes whose signals are digitally recorded, strict tape traveling position regulation is required, but with conventional tapes, this requirement cannot be sufficiently satisfied due to insufficient traveling performance. However, there was a drawback that a "quick" sound (tape squeaking) sometimes occurred when running.

In order to eliminate the above-mentioned defects relating to abrasion resistance, the outermost layer of the laminated film is made thin, and particles having a relatively large particle diameter relative to the layer thickness are contained, and the layer thickness and the particle diameter of the particles are A biaxially oriented laminated film is proposed in which minute protrusions that are difficult to be scraped off are formed on the surface of the film by making the above specific relationship (Japanese Patent Laid-Open No. 2-77431).
Publication).

[0005]

DISCLOSURE OF INVENTION Problems to be Solved by the Invention
To further improve the technology proposed in Japanese Patent No. 77431,
An object of the present invention is to prevent squeaking of a tape particularly in a digital audio tape while improving the abrasion resistance.

[0006]

The audio tape of the present invention for this purpose is a magnetic tape comprising a support film and a coating type magnetic layer, wherein at least two layers of the support film are coextruded. A polyester film having a structure and a thermal shrinkage at 80 ° C. in the longitudinal direction of 0.5 to 2%, which contains particles in a layer opposite to a magnetic surface,
Average particle diameter d (nm) of the particles and layer thickness t (nm) of the layer
And 0.2 <t / d <10, and the signal is digitally recorded.

First, in the audio tape of the present invention, the support film of the magnetic tape must have a laminated structure of at least two layers. As long as there are two or more layers, three layers or four layers may be used. However, since a single-layer film cannot maintain good running properties, the target tape squeal prevention cannot be obtained.

The laminated structure of two or more layers is formed by coextrusion. That is, so that the predetermined thickness ratio,
Two or more layers of polymer are laminated with a polymer merging block or a die, and the polymer is discharged into a sheet and then formed into a film.

Next, in the support film of the present invention, it is preferable that at least one of the layers constituting the support film is biaxially oriented. It is particularly preferable that all layers in a laminated structure of two or more layers are biaxially oriented. It is difficult to satisfy the characteristics of the present invention when all layers are non-oriented or uniaxially oriented.

The polymer constituting the support film of the present invention is polyester, and the polyester is not particularly limited, but ethylene terephthalate, ethylene α, β-bis (2-chlorophenoxy) ethane-4,
It is particularly preferable when at least one structural unit selected from 4'-dicarboxylate and ethylene 2,6-naphthalate units is the main constituent. Of these, polyesters containing ethylene terephthalate as a main constituent are particularly preferable. Incidentally, within the range that does not inhibit the present invention,
Two or more kinds of polyesters may be mixed, or a copolymer polymer may be used.

In the layer on the side opposite to the magnetic surface of the support film having a laminated structure of two or more layers, particles have an average particle diameter d (nm) of the particles and a layer thickness t (nm) of the outermost layer. It is contained so that the relationship with is 0.2d ≦ t ≦ 10d. If t is less than 0.2d, the target running property and the prevention of tape squeaking cannot be obtained, and if t is greater than 10d, the electromagnetic conversion characteristics and sound quality of an audio tape are deteriorated.

In the support film having this laminated structure, the heat shrinkage ratio at 80 ° C. in the longitudinal direction is controlled within the range of 0.5 to 2%. If the heat shrinkage ratio is out of this range, especially if it is larger than this range, the tracking characteristics become poor and the quality of the digital audio tape becomes poor.

Then, a magnetic tape is prepared by providing a coating type magnetic layer on the support film. When it comes to magnetic tape, especially digital audio tape,
As mentioned above, strict tape traveling position regulation is required,
Tape squealing prevention characteristics are required. In order to satisfy such a strict tape traveling position regulation, good tape traveling property is required. In the present invention, basically, the relationship between the average particle diameter of the contained particles and the particle-containing layer is as described above. It is achieved by having a specific relationship. In order to achieve it more reliably, it is preferable to control the number of protrusions on the surface opposite to the magnetic surface within a predetermined range.
The range is preferably from 0 ^{3 to} 2 × 10 ⁶ pieces / mm ² .

In the support film of the present invention, when the support film has a laminated structure of three or more layers,
In the laminated structure of three or more layers, the intermediate layer preferably contains inorganic particles. By doing so, the projection forming action of the intermediate layer-containing inorganic particles also appears in the outermost layer of the thin layer, and the projections formed by the outermost layer-containing particles are further added to the projection forming surface of the inorganic particles. Desired protrusions that are formed and are less likely to be scraped off and that can exhibit better running properties are formed. As a result, the tape squeal occurrence preventing characteristic is further improved.

Thus, in addition to the outermost layer-containing particles, the intermediate layer-containing inorganic particles also have the effect of forming protrusions. As a result, in the support film of the present invention, the number of protrusions on the diamagnetic surface side of the film surface is within a desired range, that is, It is easily controlled to 3 × 10 ^{3 to} 2 × 10 ⁶ pieces / mm ² .

When the number of projections on the diamagnetic surface side film surface is less than the above range, the coefficient of friction becomes high, and it is difficult to obtain good running properties, and the tape squealing prevention characteristic is deteriorated. On the contrary, when the number of protrusions is larger than the above range, the film surface becomes brittle and is easily scraped.

The inorganic particles contained in the intermediate layer are not particularly limited, but are preferably at least one kind selected from calcium carbonate, silica, alumina, zirconia and titanium oxide.

When the intermediate layer-containing inorganic particles are calcium carbonate, the crystal form thereof is preferably calcite type or vaterite type. When the inorganic particles are silica, it is preferably colloidal silica. Further, when the inorganic particles are alumina,
The crystal form is preferably δ type, γ type, θ type, or η type.

In the support film of the present invention, different polymers may be blended within the range not impairing the object of the present invention, and an antioxidant, a heat stabilizer, a lubricant, an ultraviolet absorber. Organic additives such as may be added to the extent that they are usually added.

A magnetic tape is prepared by providing a coating type magnetic layer on such a support film and used as a digital audio tape. The thickness of the coating type magnetic layer is 0.1 to 5 depending on the output characteristics as a magnetic tape and the electromagnetic conversion characteristics.
About μm is preferable.

The magnetic powder used in the magnetic layer is not particularly limited, but among them, Fe, Co, Fe-Co, Fe-C.
Metals or alloys such as o-Ni, Co-Ni, etc., and A
Alloys with l, Cr, Si and the like are preferably used.

The magnetic powder can be made into a magnetic paint by using various binders, but in general, thermosetting resin binders and high energy ray curable binders are preferable, and other additives such as dispersants, lubricants and antistatic agents. The agent may be used according to a conventional method. For example, a binder made of vinyl chloride / vinyl acetate / vinyl alcohol copolymer, polyurethane prepolymer and polyisocyanate can be used.

Next, a method of manufacturing the support film and the digital audio tape according to the present invention will be described. First, as a method for incorporating particles into the polyester, for example, a method is preferred in which particles are dispersed in a predetermined ratio in ethylene glycol, which is a diol component, and the ethylene glycol is polymerized with a predetermined dicarboxylic acid component. When adding particles, for example,
When the water sol or alcohol sol obtained at the time of synthesis is added without being dried, the dispersibility of the particles is very good, and the high-speed abrasion property and the electromagnetic conversion characteristics can be improved. Further, a method in which an aqueous slurry of particles is directly mixed with a predetermined polyester pellet and supplied to a vent type twin-screw kneading extruder and kneaded into polyester is also very effective in further improving the effect of the present invention. Content of particles,
As a method for adjusting the number of particles, it is effective to prepare a high-concentration particle master by the above method, and dilute it with a polyester that does not substantially contain particles during film formation to adjust the content of particles. ..

Next, the polyester pellets are used to prepare a polyester film having a laminated structure of two or more layers. The polyester pellets obtained by the above method are mixed at a predetermined ratio, dried and then fed to a known melt laminating extruder, extruded into a sheet from a slit die, and solidified by cooling on a casting roll. At the very least make an unstretched film. That is, by using two or more extruders, two or more layers of manifolds or a merging block (for example, a merging block having a square merging portion), the film layers forming the respective layers are laminated, and two or more sheets are formed from the die. Extruded and cooled on a casting roll to make an unstretched film. In this case, a static mixer in the polymer channel,
The method of installing a gear pump is effective. Further, it is effective to lower the melting temperature of the extruder for extruding the polymer on the outermost layer laminated portion side by 5 to 10 ° C. lower than that on the base layer portion side.

Next, this unstretched film is biaxially stretched to be biaxially oriented. As a stretching method, a sequential biaxial stretching method or a simultaneous biaxial stretching method can be used. However, a sequential biaxial stretching method of first stretching in the longitudinal direction and then in the width direction is used, stretching in the longitudinal direction is divided into three or more stages, and the total longitudinal stretching ratio is 3.5 to 6.5 times. The method is particularly preferred. The stretching temperature in the longitudinal direction varies depending on the type of polyester and cannot be generally stated, but usually the first step is 50 to 1
It is effective to set the temperature to 30 ° C. and raise the temperature from the second stage onward. The longitudinal stretching speed is 5000 to 50000% /
The range of minutes is preferred. As a stretching method in the width direction, a method using a stenter is generally used. The draw ratio is 3.0
The range of up to 5.0 times is appropriate. The stretching speed in the width direction is
The range of 1000 to 20000% / min and the temperature of 80 to 160 ° C are suitable. Next, this stretched film is heat-treated. The heat treatment temperature in this case is 170 to 220 ° C., especially 1
The range of 80 to 200 ° C. and the time of 0.2 to 20 seconds are suitable.

Next, a predetermined magnetic layer is applied to this film. The method of applying the magnetic layer can be performed by a known method, and the temperature of the drying step after application is preferably 90 to 120 ° C. At this time, apply a process tension of 1 to 1
Setting it to 5 kg / m, preferably 10 kg / m or less is effective for obtaining the heat shrinkage ratio within the range of the present invention.

The calendering step is performed at a temperature range of 25 to 90 ° C., particularly 40 to 70 ° C., using polyamide or polyester for the elastic roll, and the process tension at that time is 13 kg / m, preferably 8 kg / m or less. Is desirable. Further, after curing the magnetic layer of this film, the original material (wide width) is rolled for 40 to 90 minutes.
It is effective to obtain a heat shrinkage ratio within the range of the present invention by leaving it in the temperature range of ° C for 24 to 96 hours. Then, the tape is slit to a predetermined tape width to obtain a magnetic tape, which is wound to obtain the digital audio tape of the present invention.

[Physical property measuring method and effect evaluating method] The characteristic value measuring method and effect evaluating method of the present invention are as follows. (1) Average particle size and number of particles The polymer is removed from the film by a plasma low temperature ashing method to expose the particles. The processing conditions are such that the polymer is incinerated but the particles are not damaged as much as possible. The particles are observed with a scanning electron microscope (SEM), and the particle image is processed with an image analyzer. The magnification of the SEM is approximately 2000 to 10,000 times, and the visual field for one measurement is appropriately selected from approximately 10 to 50 μm on each side. The volume average diameter d is obtained from the particle diameter and its volume fraction with the number of particles of 5000 or more by changing the observation location. d = Σd _i · Nv _i where d _i is the particle size and Nv _i is the volume fraction thereof. The number of particles is calculated from the volume fraction and converted per mm ² for those satisfying the relationship between the laminated thickness and the average particle diameter. When the particles are organic particles or the like and are significantly damaged by the plasma low temperature ashing method, the following method may be used. Using a transmission electron microscope (TEM), the film cross section is 30
Observe at 00-100,000 times. The section thickness of the TEM is set to about 1000Å, the location is changed and 500 or more visual fields are measured, and the volume average diameter d is obtained from the above formula.

(2) Thickness of laminated polyester layer (thickness of outermost layer: t) Using a secondary ion mass spectrometer (SIMS), the highest thickness among particles in the film in the range of 3000 nm from the surface layer to the depth The concentration ratio (M ⁺ / C ⁺ ) of the element due to the concentration of particles and the carbon element of polyester is defined as the particle concentration, and the analysis is performed in the thickness direction from the surface to a depth of 3000 nm. In the surface layer, the particle concentration is low due to the interface of the surface, and the particle concentration increases as the distance from the surface increases. In the case of the film of the present invention, the particle concentration once reaching the maximum value starts to decrease again. Based on this concentration distribution curve, the depth at which the surface layer particle concentration becomes ½ of the maximum value (this depth is deeper than the maximum value) was determined and used as the laminated thickness. The conditions are as follows. Measuring instrument Secondary ion mass spectrometer (SIMS) A-DIDA3000 manufactured by ATOMIKA, West Germany Measuring conditions Primary ion species: O ₂ ⁺ Primary ion accelerating voltage: 12KV Primary ion current: 200nA Raster area: 400μm □ Analysis area: Gate 30% Measured vacuum degree: 6.0 × 10 ^-9 Torr E-GUN: 0.5KV-3.0A If the most contained particles in the depth range from the surface layer to 3000 nm are organic polymer particles, SIMS Since it is difficult to measure with XPS (XPS (X
The layer thickness may be obtained by measuring a depth profile similar to the above by line photoelectron spectroscopy), IR (infrared spectroscopy), or the like, or by observing a cross section with an electron microscope or the like, the state of change in particle concentration or polymer It is also possible to recognize the interface from the difference in contrast due to the difference and obtain the laminated thickness. Furthermore, after peeling the laminated polymer, the laminated thickness can be obtained using a thin film step measuring machine.

(3) Number of projections on the film surface A two-detector scanning electron microscope [ESM-3200, manufactured by Elionix Co., Ltd.] and a cross-section measuring device [PMS-1, manufactured by Elionix Co., Ltd.] were used to measure the film surface. The measurement value of the height of the projection when scanning is performed with the height of the flat surface set to 0 is sent to an image processing apparatus [IBAS2000, manufactured by Carl Zeiss Co., Ltd.] to reconstruct a film surface projection image on the image processing apparatus. Next, the highest value among the individual projections obtained by binarizing the projections in this surface projection image is taken as the height of the projection, and this is calculated for each projection. This measurement was repeated 500 times at different places, and the number of protrusions was determined using protrusions having a height of 20 nm or more. The magnification of the scanning electron microscope is selected to be 1000 to 8000 times. In some cases, a high-precision optical interference type three-dimensional surface analyzer (WY
KO TOPO-3D, objective lens: 40-200
The height information obtained by using a double high-resolution camera is effective) may be used instead of the value of the SEM.

(4) Heat shrinkage rate of the tape Mark lines are inserted at intervals of about 200 mm in the longitudinal direction of the tape, and the length between them is precisely measured (A). Next, the sample is
After being left in an oven at ℃ for 30 minutes, the distance between the marked lines was precisely measured (B), and the value obtained by the following formula was defined as the heat shrinkage ratio in the longitudinal direction of the tape. 100 x (A-B) / A (%)

(5) Tape squeal A digital audio tape is put on a commercially available digital audio tape recorder, and reproduction and rewind are repeated 100 times in an atmosphere of 40 ° C. and 80% RH. Evaluate sound generation. The evaluation was done by listening to the ear, and if a tape squeal was generated, it was judged as defective, and if the tape squeal was inaudible,
It was good.

[0033]

EXAMPLES Next, the embodiments of the present invention will be described based on examples. Examples 1 to 4 and Comparative Examples 1 to 4 Several kinds of particles having different particle diameters were dispersed in ethylene glycol in the form of a slurry, transesterified with dimethyl terephthalate, and then polycondensed to give a predetermined amount of the particles. The contained polyethylene terephthalate (hereinafter abbreviated as PET) was prepared. In addition, PET was produced by a conventional method without containing substantially inert particles. These polymers were mixed in appropriate amounts to adjust the particle concentration, and dried under reduced pressure (3 Torr) at 180 ° C. for 3 hours. The combination shown in Table 1 was supplied to two extruders and melted at 290 ° C.
Or rectangular confluence block (feed block) for 3 layers
Layered together at a surface temperature of 3 using the electrostatic cast method.
The film was wound around a casting drum at 0 ° C. and cooled and solidified to prepare an unstretched film having a 2-3 layer structure. At this time,
The discharge amount of each extruder was adjusted to control the total thickness and the thickness of the polyester A layer. This unstretched film is heated to a temperature of 8
It was stretched 4.5 times in the longitudinal direction at 0 ° C. This stretching was performed by the difference in peripheral speed between the two sets of rolls. This uniaxially stretched film was stretched 4.0 times in the width direction at 100 ° C. at a stretching speed of 2000% / min using a stenter and heat-treated at 200 ° C. for 5 seconds under a constant length to give a biaxial film having a total thickness of 14 μm. An oriented laminated polyester film was obtained. The layered structure of Example 4 is A layer / B layer / A
The layer has a three-layer structure, and the other layers have a two-layer structure of A layer / B layer.

A magnetic paint is applied to this film by a gravure roll. The composition of the magnetic paint was adjusted as follows.・ Fe 100 parts Average particle size Length: 0.3 μm Needle ratio: 10/1 Coercive force 2000 Oe ・ Polyurethane resin 15 parts ・ Vinyl chloride / vinyl acetate copolymer 5 parts ・ Nitrocellulose resin 5 parts ・ Aluminum oxide Powder 3 parts Average particle size: 0.3 μm Carbon black 1 part Lecithin 2 parts Methyl ethyl ketone 100 parts Methyl isobutyl ketone 100 parts Toluene 100 parts Stearic acid 2 parts

After the above composition was mixed and dispersed by a ball mill for 48 hours, 6 parts of a curing agent was added and the resulting kneaded product was filtered through a filter to prepare a magnetic coating solution, which was coated on the above film and magnetic field oriented. And dried at 110 ° C (process tension up to this point is 10 kg / m), and then calendered (steel roll / nylon roll, 5 steps) at temperature 70 ° C, linear pressure 200 kg / cm 2, process tension 7 kg / m. After calendering, it was wound into a roll and cured at 70 ° C. for 24 hours to obtain a raw magnetic recording tape having a width of 1 m. This raw fabric was slit with a micro slitter and incorporated into a tape having a width of 3.8 mm to prepare a cassette tape. The tape squeal of these tapes is as shown in Table 1, and those satisfying the requirements of the present invention were good, but those not satisfying the requirements were poor.

[0036]

[Table 1]

[0037]

According to the audio tape of the present invention, the relationship between the specific particle average particle diameter and the layer thickness of the outermost layer in the layer opposite to the magnetic surface of the support film having a laminated structure of at least two layers. Since particles are included so as to satisfy the above condition and the heat shrinkage ratio in the longitudinal direction is set to a specific range, it is possible to prevent the occurrence of tape squeaking while maintaining excellent characteristics as a magnetic tape in digital audio tape applications. You can

Claims (4)

[Claims] 1. A magnetic tape comprising a support film provided with a coating type magnetic layer, wherein the support film has a laminated structure of at least two layers in which the support film is coextruded.
A polyester film having a heat shrinkage of 0.5 to 2% at 0 ° C., containing particles in a layer on the side opposite to the magnetic surface, and having an average particle diameter d (nm) of the particles and a layer thickness of the layer. An audio tape characterized in that the relationship with t (nm) is 0.2 ≦ t / d ≦ 10 and the signal is digitally recorded. ^2. The audio tape according to claim 1, wherein the number of protrusions on the surface opposite to the magnetic surface of the magnetic tape is 3 × 10 ³ to 2 × 10 ⁶ pieces / mm ² . 3. The audio tape according to claim 1, wherein the support film of the magnetic tape is a film having a laminated structure of three or more layers, and the intermediate layer contains inorganic particles. 4. The audio tape according to claim 3, wherein the inorganic particles in the intermediate layer are at least one selected from calcium carbonate, silica, alumina, zirconia, and titanium oxide.