JPH01247162A - Base film for high density recording medium - Google Patents

Abstract

PURPOSE:To obtain a film capable of satisfying both of a surface property and runnability, by a method wherein the surface of one of the layers of the film has specific RPA (center line depth) and the surface of the other layer thereof has specific RPB (center line depth) and specific RaB (center line average roughness) and projections each having a height of a specific value or more. CONSTITUTION:A film composed of aromatic polyamide and aromatic polyimide consists of two layers A, B and the surface of the layer A provided with a magnetic layer has RPA of 10-200Angstrom and, when RPA is smaller than 10Angstrom , surface becomes excessively smooth and is easily damaged at the time of the preparation of a magnetic recording medium and, contrarily, when RPA is larger than 200Angstrom , an electromagnetic conversion characteristic becomes inferior. With respect to the surface properties of the layer B (called a B-surface) on a side provided with no magnetic layer, it is necessary that RPB is within a range of formula (1) and, when RPB is smaller than RPA+50, the B-surface is too smooth to contribute to the improvement in the runnability of the film and, when RPB is larger than 1500Angstrom , runnability is well but the smoothness of the film or magnetic layer is lost. The RaB of the B-surface is 20-200Angstrom and it is necessary that 30 or more projections having a height of 50Angstrom or more are present per 1mm.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a base film for high-density recording media.

[Prior Art] A metal thin film type magnetic recording medium in which Co, Nr, Cr, Fe, or an alloy thereof is formed on a film substrate by a method such as vacuum evaporation, sputtering, or ion blating has a high recording density. Polyester films are often used as substrates.

However, polyester films do not have sufficient heat resistance, which limits the conditions for forming metal thin films, and the use of aromatic polyimide films or aromatic polyamide films as substrates for perpendicular magnetic recording media is being considered. Regarding the surface forming method of these heat-resistant films, please refer to JP-A-60-12
Various proposals have been made in No. 7523 and Japanese Unexamined Patent Publication No. 116637/1983.

[Problems to be Solved by the Invention] However, in JP-A-60-127523, the tape width is narrow, so runnability in a VTR is not a problem, but manufacturing of a wide tape is not an issue. During the process, the surface was too smooth and wrinkled easily during running or winding, leading to problems such as low production yields and an inability to increase manufacturing speed.

In response to the demand for improving runnability while maintaining the surface properties of the side on which the magnetic layer is provided to be extremely smooth to withstand use in vapor-deposited tapes, it is no longer possible to have the same surface properties on both sides. This is not possible and we have no choice but to use a method that changes the surface properties of the front and back sides of the film. JP-A-62-1
16637 is a film that has this kind of surface quality, but because one side is too scraped, when the film is wound into a roll, the unevenness is transferred to the opposite side (the side on which the lactic layer is provided), causing bleed-through. There was a problem in that this phenomenon occurred and the surface properties on the magnetic layer side were impaired.

On the other hand, the coextrusion method used in the production of polyester films and cellulose acetate films (e.g., JP-A-56-162617) is a good method for changing the surface properties between the front and back sides, but the film thickness is extremely high. When making a thin film using the solution casting method, 2 times during drying of the solvent.
There is a problem that the liquid may be mixed partially or completely.
A thin film with a very smooth surface on one side and a rough surface on the other has never been produced by solution casting.

The object of the present invention is to solve these problems and provide a film that has both surface properties and runnability.

[Means for Solving the Problems] The present invention provides a film made of aromatic polyamide or aromatic polyimide, the film comprising at least two
Consisting of layers, one layer (layer A) has a surface R, A (center line depth) of 10 to 200, and the other layer (B layer) has a surface R6, (center line depth) as follows. (1) is within the range of formula,
This is a base film for a high-density recording medium, which has an Ra (center line average roughness) of 20 to 200 Å and 30 or more protrusions with a height of 50 Å or more per 1 mm.

R+50≦RPB≦1.500 (contains) (1)A The aromatic polyamide of the present invention is preferably a polymer containing 50 mol% or more of repeating units represented by the general formula %), More preferably, it is 70 mol% or more.

Here, Ar1. Ar;> contains at least one aromatic ring and may be the same or different, and representative examples thereof include the following.

In addition, some of the hydrogens on the aromatic rings are halogen groups (especially chlorine), nitro groups, 01 to C3 alkyl groups (
In particular, those substituted with substituents such as methyl group) and C1-C3 alkoxy groups are also included. Also, X is partially , CH2+, 302, S
, Go-, etc. These may be included alone or in copolymerized form.

Particularly for applications such as thin magnetic tapes, from the viewpoint of mechanical properties and dimensional stability against environmental changes (temperature, humidity), it is preferable to use a material mainly consisting of para-bonds, and a material in which chlorine is roughly introduced into the aromatic ring is preferable. More preferred.

for example, (Here p, qG, to~3) Examples include those containing 50 mol% or more.

The aromatic polyimide in the present invention is one containing one or more aromatic rings and one or more imide rings in the repeating units of the polymer, preferably one containing 50 mol% or more of repeating units represented by the general formula, and more preferably Preferably it is 70 mol% or more.

Here, Ar3 and Ar5 contain at least one aromatic ring, and the two carbonyl groups forming the imide ring are bonded to adjacent carbon atoms on the aromatic ring.

This Ars is derived from aromatic tetracarboxylic acid or its anhydride. Representative examples include the following:

Here, Y is -0, Co, -CH2-.

-3-, -302-, etc.

Furthermore, Ars is derived from tricarboxylic anhydride or its halide.

Arc and Are contain at least one aromatic ring and are derived from aromatic diamines and aromatic diisocyanates. Further, it may contain an amide bond, a urethane bond, or the like. A
r4. Representative examples of Are include the following.

Here, some of the hydrogens on the aromatic rings are halogen groups, nitro groups, C1-C3 alkyl groups, 01-C3
It also includes those substituted with substituents such as alkoxy groups.

Z is O+, -CH2-.

-3-, -30>-, -Co-, etc. These may be included alone or in copolymerized form.

Furthermore, the aromatic polyamide and aromatic polyimide of the present invention may be blended with lubricants, antioxidants, other additives, and other polymers to the extent that the physical properties of the film are not impaired.

The film of the present invention consists of at least two layers, layer A and layer B, and these two layers are preferably made of polymers with the same structure, but may be different.

In the film of the present invention, the magnetic layer is provided on the surface of the A layer, but
The surface property of this A layer (the surface is called the A surface) has an RPA of 1
0 to 200 people are required. Preferably 20 to 150 people.

Here, RPA is called centerline depth, and is the distance from the highest peak of the cut-off portion to the centerline after cutting off the roughness curve by a reference length.

If the RPA is less than 10, the surface will be too smooth, the coefficient of friction will increase, and scratches will easily occur during the manufacture of magnetic recording media. On the other hand, if there are more than 200 people, the spacing loss between the magnetic layer and the head will increase, and the electromagnetic conversion characteristics will deteriorate.

Further, the surface properties of the B layer (the surface is referred to as the B surface) on the side on which no magnetic layer is provided must have an RPB in the range of formula (1), preferably 220 to 1,000. R,A
If it is less than +50, the B side will be too smooth and will not contribute to improving the runnability of the film. On the other hand, if the film is larger than 1.500, the runnability is good, but if the film is wound into a roll or a film with a magnetic layer formed is stored in a roll, the transfer of unevenness due to bleed-through becomes large. As a result, the smoothness of the film or magnetic layer required for high-density recording is impaired, making it unusable.

Also, R6B (center line average roughness) of this B side is 20 to 20
There is a need for 0 people. Preferably it is 25 to 150 people.

If it is less than 20 people, the running performance cannot be improved, and if it is more than 200 people, the film will be scratched.

Roughly speaking, it is necessary that 30 or more protrusions with a height of 50 Å or more exist per 1 mm on this B surface.

The number of protrusions is preferably 50 or more, and more preferably 5 or more with a height of 100 people or more. Here, the height of the protrusion is the distance from the center line of the cut-out part to the peak of the protrusion by cutting out the standard length from the roughness curve, and drawing the roughness curve on the chart. film 1mm
The number of protrusions is determined from the roughness curve corresponding to the contact. If the height of the protrusions is less than 50, or if the number of protrusions with a height of 50 or more is less than 30, no improvement in running performance can be expected.

In order to produce a film in which the B side has a rougher surface than the A side according to the present invention, particles must first be present in the B layer. There are organic and inorganic particles,
Inorganic materials are more preferred from the viewpoint of heat resistance. For example, S
i02. T i 02. ZnO.

AI 203. Ca5Oa, Ba5O7I, C
Examples include aCO3, carbon black, zeolite, and other fine metal powders. The particle size is preferably 0.02 to 2 μm, and the amount added is preferably 0.1 to 1Qwt% per polymer. More preferably, particles having a particle size of 0.05 to 1 μm are used. Moreover, two or more types may be used.

Layer A does not need to contain any particles, but particles smaller than those in layer B may be added, or a small amount of small particles may be added. As for particles, the particle size is 0.00
The thickness is preferably 5 to 0.3 μm, and the amount added is preferably 0 to 5 wt% based on the polymer. Colloidal particles with uniform particle sizes are particularly preferred, and silica sol, alumina sol, titanium oxide sol, etc. are particularly preferred.

The thickness of the film of the present invention is preferably 1 to 15 μm, more preferably 2 to 10 μm. The thinner the film, the greater the effect of the present invention.

Regarding the thickness of layer A and layer B, it is preferable that layer A be at least 10 times as thick as RPB (center line depth of plane B).

For example, if the RPB is 500 people, the thickness of layer A is 0.5 μm or more. In solution casting, it is necessary to dry the solvent when forming a film, but at this time the layers mix at the interface between the two layers. Since the surface of layer A (A side) must be sufficiently smooth even if the two layers are mixed, the minimum value of its thickness is determined in relation to layer B. On the other hand, the requirements for layer B are not as strict as for layer A, but it is preferably 0.5 μm rather than 0.1 μm1.
A thickness of m or more is preferable. In this way, the A layer and B layer maintain the minimum thickness, and the thickness ratio is A layer/B layer =
It is preferable to adjust it within the range of 0.1 to 10. More preferably it is 0.2-5.

Furthermore, the A side of the film of the present invention has a center line average roughness Ra
Preferably, the number of participants is 2 to 20 people. Also 0.01μm
The presence of 10 3 to 10 8 microprotrusions/mm 2 of diameter or larger is effective in improving the durability of the magnetic layer and is preferred, but the presence of microprotrusions may be omitted. Moreover, the B side of the present invention is RPB
and R3, the ratio RpB/RaB is preferably 3-20, more preferably 4-15.

The film of the present invention has a Young's modulus of 4 in at least one direction.
00 layer Mmm2 or more is preferable, more preferably 800
kMII 1 m2 or more. Further, the humidity engraving coefficient in at least one direction is preferably 30x10-81/%RH or less, more preferably 20x10-1i1/%RH or less.

Furthermore, the coefficient of dynamic friction between the A side and the B side is preferably 1 or less, more preferably 0.8 or less. This friction coefficient is 2
This is a value measured in an atmosphere of 5°C and 155%RH.

Next, the manufacturing method of the present invention will be explained, but it is not limited thereto.

First, aromatic polyamide is made from acid chloride and diamine, N-methylpyrrolidone (NMP>
The polymer solution is synthesized by solution polymerization in an aprotic organic polar solvent such as dimethylacetamide (DMAC) or dimethylformamide (DMF) or by interfacial polymerization using an aqueous medium. When using chloride and diamine, hydrogen chloride is produced as a by-product. To neutralize this, inorganic neutralizers such as calcium hydroxide, calcium carbonate, and lithium carbonate, or organic neutralizers such as ethylene oxide, ammonia, and triethylamine are used. Add agent.

Further, the reaction between isocyanate and carboxylic acid is carried out in an aprotic organic polar solvent in the presence of a catalyst. These polymer solutions may be used directly as a film-forming stock solution to form a film, or the polymer may be isolated once and then redissolved in the above-mentioned solvent to prepare a film-forming stock solution. Inorganic salts such as calcium chloride, magnesium chloride, lithium chloride, etc. may be added to the membrane forming stock solution as a solubilizing agent.

! ! ! The polymer concentration in the membrane solution is preferably about 2 to 4 Qwt%.

On the other hand, a solution of aromatic polyimide or polyamic acid can be obtained as follows. That is, polyamic acids include N-methylpyrrolidone (NMP>), dimethylacetamide (
DMAC>, dimethylformamide (DMF>) can be prepared by reacting a tetracarboxylic dianhydride with an aromatic diamine in an aprotic organic polar solvent such as dimethylformamide (DMF). Polyimide powder (q) can be prepared by heating a solution containing pyridine or adding an imidizing agent such as pyridine, and dissolving this again in a solvent.The polymer concentration in the film forming stock solution is 5 to 4.
Approximately 0 wt% is preferable.

The membrane forming stock solution prepared as described above is formed into a film by a so-called solution casting method. Solution film forming methods include a wet-dry method, a dry method, and a wet method, and the wet-dry method and dry method are preferable for producing a film with good surface properties.

When forming a film by a wet method, the stock solution is directly extruded from a die into a film forming bath, or it is first extruded onto a support such as a drum and then introduced into a wet bath together with the support. . This bath generally consists of an aqueous medium, and may contain an organic solvent, an inorganic salt, etc. in addition to water. Salts, organic solvents, imidizing agents, etc. contained in the film are extracted by passing it through a wet bath, but the time it takes to pass through the entire wet bath is 10 seconds to 30 seconds, depending on the thickness of the film.
It's a minute. Stretching is carried out roughly in the longitudinal direction of the film. Next, drying, lateral stretching, and heat treatment are performed, but these treatments are generally performed at 100 to 500°C for a total of 1 second to 30°C.
It's a minute.

When forming a film by a wet-dry method, the stock solution is extruded from a die onto a support such as a drum or an endless belt to form a thin film, and then the solvent is scattered from the thin film layer and the film is dried until it has self-retention properties. Drying conditions are room temperature to 300°C16
The range is within 0 minutes.

After the first dry process, the film is peeled off from the support and introduced into the first wet process, where it undergoes desalting, solvent removal, etc. in the same way as the wet process described above, and is roughly stretched, dried, and heat treated to form a film. becomes.

When a dry process is employed, the self-retaining film is dried on a drum, endless belt, etc., and then peeled off from the support and stretched in the longitudinal direction of the film. Drying, stretching, and heat treatment are performed to roughly remove residual solvent, and these treatments are performed at 100 to 500° C. for 1 second to 30 minutes.

The film formed as described above is stretched during the film forming process, and the stretching ratio is 0.8 to 5.0 in area ratio.
(The areal magnification is defined as the value obtained by dividing the area of the film after stretching by the area of the film before stretching. 1 or less means relaxed.) It is preferably within the range of 1.1 to 1.1. It is 3.0.

In order to form the laminated film of the present invention, two types of film forming stock solution, a film forming stock solution corresponding to the A layer side and a film forming stock solution corresponding to the 8th layer side, are used.
It can be formed by a known method, for example, by laminating in a confluence pipe as in JP-A-56-162617, or by laminating in a mouthpiece. When casting, it is better to place the B layer on the support side.
This is preferable in that the surface properties of the A-side can be maintained smooth. Alternatively, a self-retaining film may be formed using one of the membrane-forming stock solutions, and then the other film-forming stock solution may be cast onto the film to remove the solvent, thereby forming a laminated film. In particular, when laminating in a confluence pipe or a mouthpiece, it is preferable to adjust the viscosity of the stock solution to 100 to 10,000 poise. If it is smaller than this range, the two liquids will tend to mix before the stock liquid comes out of the nozzle, and in the case of a thin film, the A side will become rough even with very slight mixing. On the other hand, if it is larger than this range, mixing of the two liquids becomes difficult to occur, but melt fracture occurs and the film surface tends to become rough, which is not preferable.

Further, it is preferable that the two liquids have the same viscosity, but there may be some viscosity difference, and there is no problem as long as the viscosity of the high viscosity side is within 100% of the low viscosity side.

Furthermore, when a dry method or a wet-dry method is employed, the two liquids may mix during the drying process. The viscosity of the stock solution cast onto the support decreases once when it is heated, and then increases again as the solvent evaporates. However, when the viscosity decreases below 10 poise, the two liquids become easier to mix. It is necessary to adjust the drying conditions sufficiently so that the viscosity does not drop below Poise.

For example, a method can be adopted in which the drying temperature is increased in at least two stages.

The film of the present invention is produced as described above, but the adhesion and durability of the magnetic layer can be improved by performing glow discharge treatment or corona discharge treatment as a pretreatment before attaching the magnetic layer etc. to the rough surface. More preferred.

[Effects of the Invention] In the film of the present invention, the characteristics required for each of the front and back surfaces are separated. Therefore, although the surface properties of the A side required for base films for high-density magnetic recording such as vapor-deposited tapes are kept very smooth, if the surface properties of the 8th side are within the range of the surface properties of the present invention, No show-through phenomenon,
In addition, when manufacturing vapor-deposited tapes, etc., it is necessary to have good runnability even in wide widths.
It has good winding properties and can improve productivity and quality. Furthermore, since the film of the present invention has good heat resistance, a magnetic layer can be provided at high temperatures, and the magnetic properties can be improved. The magnetic recording method does not matter whether horizontal magnetization or perpendicular magnetization is used.

The film of the present invention can also be used in the continuous production of optical recording or magneto-optical recording media in the same way as in the case of magnetic recording.

[Method for Measuring Characteristics and Evaluating Effects] Methods for measuring characteristic values and evaluating effects of the present invention are as follows.

(1) Ra (center line average roughness), Rp (center line depth),
Using a thin film step measuring device (ET-10> manufactured by the Protrusion Number and Plate Research Institute,
Measurement was carried out 10 times under the conditions of stylus tip radius of 0.5 μm, stylus load of 5 m'j, cutoff values o, ooamm, and measurement length Q of 5 mm, and Ra and Rp were expressed as the average values.

The number of protrusions was determined by drawing a chart under the above conditions, counting the number of protrusions having a distance of 50 Å or more from the center line of the roughness curve to the top of the protrusion, and expressing the number of protrusions per 1 mm of film.

The definitions of Ra and Rp can be found, for example, in "Surface Roughness Measurement and Evaluation Method" by Jibu Nara (General Technology Center, 19B3).
).

(2) The running film was slit into a width of 3Qcm and loaded into a vapor deposition machine, and the A side was glow-treated in an Ar atmosphere of 10-2 Torr, then evacuated to 10-5 Torr and heated to 100'C. Along the drum, Co is deposited by electron beam evaporation.
-Ni alloy (Co80%, Ni2O%) 100% on A side
0 people were deposited. Runnability was evaluated by observing the appearance of wrinkles on the drum and guide roll during these treatments and the winding appearance of the film roll after treatment.

(3) Electromagnetic conversion characteristics The vapor-deposited film is slit into 2-inch width per layer, and VT
It was incorporated into an R cassette and used as a VTR tape. A 100% chroma signal was recorded on this tape using a Shibaku TV test waveform generator (TG7/U706) using a home VTR, and the chroma signal was measured using a Shibaku color video noise measuring device (925D/1) from the playback signal. /N was measured.

Evaluation was made using a commercially available tape as a standard.

[Examples] The present invention will be described below based on Examples. However, the present invention is not limited to these examples.

Example 1 70 mol% 2-chloroparaphenylenediamine and 4.4
Polymerization was carried out in NMP using 30 mol % of °-diaminodiphenylsulfone as an amine component and 100 mol % of terephthalic acid chloride as an acid component, and the polymer solution was neutralized with lithium hydroxide to give 1 q of polymer solution. The intrinsic viscosity is 2.5. This was divided into two parts, and 0.08 μm was previously dispersed in NMP.
0.1 wt% of spherical silica was added to the polymer solution forming the A layer based on the polymer. Separately, silica with an average particle size of 0.2 μm, which was dispersed in NMP, was added to the polymer solution that would become the B layer at 1 wt% per polymer, and both polymer solutions were roughly heated to 1000 poise at 30'C. It was adjusted and used as a film forming stock solution.

Put these stock solutions into the cap and make the final film with layer A of 5 μm.
Layer B is laminated in two layers with a thickness of 3 μm, and heated roughly at 30°C.
1 barley, 12 barley and dried for 2 minutes at 80℃.
The temperature was raised stepwise from 0°C to 150°C and dried for a total of 10 minutes to obtain a self-retaining gel film. Note that the film was formed with layer B facing the belt side. This gel film was continuously peeled off from the belt and introduced into a water tank, where it was desolventized and desalted, and then dried in a tenter and subjected to heat treatment to obtain 1 q of 8 μm final film. During this time, the film was expanded by 1.3 times in the longitudinal direction in a water tank and by 1.3 times in the width direction in a tenter.
It was stretched 3 times, and the heat treatment conditions were 300' for 0.5 minutes.

As shown in Table 1, the properties of the 1q film were that the A side was very smooth and the 8th side was rougher than the A side.

This film also has a Young's modulus of 1 in both the MD and TD force directions.
, 000 kg/mm2, strength of 53 kg/mm2, and elongation of 55%, and the humidity expansion coefficient was as small as 6X10-61/%RH.

Next, 1000 people vapor-deposited Co--Ni on the A side of this film, but there were no wrinkles on the drum or guide roll during vapor deposition, and the wound appearance of the film roll was very good.

This was roughly slit to make a magnetic tape, and its electromagnetic conversion characteristics were evaluated, and it was found to be very excellent.

Example 2 The same polymer as in Example 1 was used, and the layer A had a thickness of 0°08 μm.
0.5wt% of silica per polymer, 0.2% on the B layer side
2 wt% of silica was added to the polymer, and the final film was laminated so that both layers A and B had a thickness of 4 μm, and the film was formed in the same manner as in Example 1 to obtain a film of 8 μm.

A magnetic layer is deposited on this film to produce a magnetic tape.
An evaluation was conducted, and the running properties during the manufacturing process and the electromagnetic conversion characteristics of the tape were very good.

Example 3 80 mol% of 2-chloroparaphenylenediamine; 4.
Polymerization was carried out in NMP using 20 mol % of 4°-diaminodiphenyl ether as an amine component and 100 mol % of 2-chloroterephthalic acid chloride as an acid component, and neutralized with calcium carbonate to obtain a polymer solution. This was divided into two parts, and on the A layer side, 0.05 μm silica was added to Q, 2 wt% per polymer, and B
On the layer side, 0.2 μm silica is added at 2.5 wt% per polymer.
The final film was laminated using a convergence tube so that layer A had a thickness of 3 μm and layer B had a thickness of 1 μm, and the film was cast onto a 30'C metal belt. The viscosity of the polymer solution is 3000 poise at 30°C. As in Example 1, this was dried by raising the temperature stepwise until it had self-retention properties, and then passed through a water tank and a tenter to obtain a 4 μm film.

The stretching ratio is the same as in Example 1.

The obtained film had a Young's modulus of 1 in both the MD and TD force directions.
, 200k (1/mm2), strength 58kMmm2, elongation 50%, and the surface properties are as shown in Table 1.

This film was then vapor-deposited, and although it was very thin, there were no problems with running properties, and the rolled film had a good appearance. This was roughly evaluated as a magnetic tape, and the electromagnetic conversion characteristics were very good.

Example 4 4.50 mol% of 4°-diaminodiphenyl ether,
50 mol% of paraphenylenediamine is used as an amine component,
1100 mol% of anhydrous pyromellit was polymerized in DMAC to obtain 1 q of polyamic acid solution.

This was divided into two parts, 0.05 wt% of 0.05 μm silica per polymer was added to the A layer side, and 0.8 wt% of average particle size was added to the B layer side.
A silica powder having a thickness of 100 μm was added in an amount of +wt% per polymer, and the final film was laminated on a metal belt at 30° C. using two ferrules so that both layers A and B had a thickness of 5 μm. The viscosity of each polymer solution is 500 voices at 30°C. This was dried at elevated temperatures of 60°C, 100°C, and 130°C until it had self-retention properties, and then peeled off from the belt and heated to 420°C.
Heat treatment was performed in a tenter at ℃. Stretching ratio is MD, T
D force direction is also 1.0 times, thickness is 10 μm, Young's modulus is 4
(20 kmMmm2, surface properties are shown in Table 1) The A side through which it was passed was very smooth.

Next, vapor deposition was performed on this film, and although the A side was very smooth, the running properties were good and the roll appearance was also good. Furthermore, it was evaluated as a magnetic tape,
It showed good electromagnetic conversion characteristics.

Comparative Examples 1 to 5 Using the same polymer as in Example 1, the particles added to the A layer side were 0.08 μm silica as in Example 1, and the silica particles added to the 8th layer side were various as shown in Table 2. However, a film was formed in the same manner as in Example 1, and 1q of 8 μm film was produced. The thickness of AM was 5 μm, and the thickness of the 8 layers was 3 μm. Table 1 shows the surface properties, running properties, and electromagnetic conversion characteristics of these films.

In Comparative Examples 1 to 3, even when three layers were tried to be deposited in a width of cm, wrinkles appeared on the deposition drum and heat loss of the film was observed. Furthermore, wrinkles appeared on the guide roll, making it impossible to wind the film smoothly, and the appearance of the film roll after being wound was very poor. Therefore, when the film was made to have a width of 5 cm and was deposited in the same manner, the deposition was completed without any problem with cracking. A magnetic tape was prepared using this material, and its electromagnetic conversion characteristics were evaluated and found to be good. As will be seen, in Comparative Examples 1 to 3, the surface of the B side was too smooth, and the running performance over a wide width was extremely poor.

In Comparative Example 4, running properties were good at the start of vapor deposition, but as time went by, scraped powder from the film began to adhere to the drum and guide roll, and the film slipped on the drum, causing wrinkles in the MD force direction. It was recognized that the film had lost heat. In addition, because the film easily slipped on the guide roll, the film began to meander and could not be wound smoothly. Furthermore, the electromagnetic conversion characteristics were also poor due to the influence of adhesion of scraping powder on the film.

Comparative Example 5 had good runnability due to its large RPB, but there was large show-through, the surface of the produced magnetic tape was undulated in an orange skin shape, and the electromagnetic conversion characteristics were very poor. .

Comparative Example 6 A film of 8 μm was formed in the same manner as in Example 1 except that the temperature of the belt during casting and the drying temperature were 190°C.
obtained the film. As shown in Table 1, almost the same surface properties were obtained on both sides A and B, and the electromagnetic conversion characteristics were poor.

When we investigated the viscosity behavior of the stock solution cast onto the belt at the initial stage of drying, we found that the viscosity had decreased to 8 poise, and the viscosity was reduced to 8 poise.
It was found that IB was mixed by convection and did not form two layers.

Claims (1)

[Claims] A film made of aromatic polyamide or aromatic polyimide, the film consists of at least two layers, one layer (layer A) having a surface R_P_A (center line depth).
is 10 to 200 Å, and the other layer (B layer) has a surface R_
P_B (center line depth) is within the range of formula (1) below, and R
__a_B (center line average roughness) is 20 to 200 Å, 50 Å
A base film for a high-density recording medium, characterized in that there are 30 or more protrusions per mm with a height of 30 or more. R_P_A+50≦R_P_B≦1,500 (Å)...
・(1)