JP2869554B2 - High modulus film for magnetic tape and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high elastic modulus film for a magnetic tape, and more particularly to a base for a high-density recording magnetic tape which can be applied stably when a magnetic material is applied by a die coater. It is about a film.

[0002]

2. Description of the Related Art The spread of computers and the progress of computerization have been remarkable, and the storage capacity of a hard disk that complements a memory has been steadily increasing. The need for hard disk backup is also increasing, and efforts are being made to increase the recording capacity of magnetic tapes as backup media. In order to increase the capacity of the magnetic tape per cassette, use a highly crystalline film such as aramid as the base film and have a high elastic modulus, reduce the tape thickness and increase the tape length per cassette, and The signal wavelength has been shortened, the fineness of the magnetic powder has been reduced and the coating thickness has been reduced even with a coating type magnetic tape, and a metal thin film type magnetic tape in which metal is deposited or sputtered is used. Attempts have been made.

[0003] A magnetic tape coated with magnetic powder is preferable in terms of durability and reliability of the magnetic tape against repeated recording and reproduction of data, but from the viewpoint of shortening the signal wavelength,
There is a demand for a thinner magnetic layer, and a method has been proposed in which a thin magnetic layer is formed uniformly by using a die coater instead of a conventional gravure coater and applying the magnetic layer on the nonmagnetic layer in a superimposed manner ( Electric Materials Magazine, March 1996,
Pages 135-140). However, there are some difficulties in processing a base film having a high elastic modulus such as aramid into a magnetic tape using a die coater. That is, in the die coater, the base film is pressed against the slit of the die and run, and the dispersion of the magnetic powder extruded from the slit is applied. This causes uneven pressure bonding to the die, resulting in uneven coating thickness of the magnetic layer and unstable running of the film.

Since a conventional polyester film has a low elastic modulus, a slight partial slack is eliminated by elongation of the film due to tension at the time of coating, but a partial elastic slack is eliminated in a film having a high elastic modulus such as aramid. Does not reach. Further, if a large tension is applied so as to eliminate the partial slack of the aramid film, the film is liable to be cut during running, the friction with a guide or the like increases, and problems such as scratches occur.

[0005]

Since a synthetic resin film such as aramid which can realize a high elastic modulus is not subjected to a molecular orientation treatment at a high stretching ratio unlike a conventional film such as polyester, so-called bowing is used. Despite the non-uniform alignment in the width direction as in the phenomenon, nevertheless, for example, both ends of the film are longer than the center, and the film hangs or floats on the roll in the coating process. It has been found that a partial slack occurs in the width direction, such as a loose ear state such as running up or a loose state in the center. An object of the present invention is to provide a film having a high elastic modulus, such as an aramid film, which exhibits favorable mechanical properties and can reduce the thickness of a magnetic tape. To provide a possible film.

[0006]

The present inventors have made a film having an average thickness of 2 to 8 μm, an elastic modulus in any direction of the film of 1000 to 2500 kg / mm ² , and an average particle size of 5 nm. Containing 150-150% by weight of inactive fine particles of 150-150 nm, and the center plane average roughness (SRa) of the film surface as determined by the resolution of an optical surface roughness meter.
Is 0.5 to 10 nm, and the amount of partial slack of the film is 2
It has been found that the above problem can be solved by a high elastic modulus film for a magnetic tape characterized in that the supporting distance is 5 mm or less with respect to the supporting distance of m , and the present invention has been completed.

[0007] In the film of the present invention, the central portion of the generated location film width direction of a portion slack, even anywhere ears, slack amount 5 m m or less relative to the support distance 2m, preferably 3 mm or less, and if the slack is more than that, there is a problem in that the running of the film becomes unstable and the coating thickness of the magnetic layer becomes uneven during coating by the die coater. In practicing the present invention, the slipperiness between each part of the coating machine and the film is also an important factor, and the surface of the film is subjected to photoelectric conversion with a horizontal resolution of 1 μ or less in an interference phase contrast microscope, data processing, and surface processing. SRa measured at a cutoff wavelength of 80 μm is 0.5
10 nm, preferably 1-6 nm, and SRa is 1
If the surface roughness exceeds 0 nm, especially on the surface on which the magnetic layer is formed, the surface roughness of the base film is also reflected on the surface of the magnetic tape, and data errors are likely to occur and should be avoided.

The film of the present invention contains 0.01 to 1.0% by weight, preferably 0.0% by weight of fine particles in the film as a so-called lubricant in order to control the surface roughness and the like.
It must be contained in an amount of 2 to 0.5% by weight. If the amount of the fine particles is less than 0.01% by weight, the film slips in the film manufacturing process or the magnetic tape manufacturing process is poor, and stable running may be impaired or wrinkles may occur. Should. Fine particles should be present independently in the film, but it is known that ultrafine particles are likely to associate and agglomerate. It is preferable that the state of aggregation is as low as 20 or less in average aggregation degree.

As the fine particles, it is necessary to use a solvent, a finishing agent or the like to be used, or an inert particle which does not cause denaturation or deterioration due to the environment used as the tape. Usually, for example, SiO ₂ , TiO ₂ , ZnO, Al ₂ O
₃ , fine particles of inorganic compounds such as CaSO ₄ , BaSO ₄ , CaCO ₃ , carbon black, zeolite, and other metal powders, and organic compounds such as carbon, carbon fluoride, and fluororesin.

Fine particles are finely dispersed in a solvent using various dispersers. From the viewpoint of dispersibility, the fine particles dispersed in a liquid in a colloidal state are diluted with the solvent or replaced with a solvent. It is also recommended to use it. Those satisfying these conditions include colloidal silica (S
iO ₂ ) is commercially available and can be suitably used, but any other material than silica may be used in the practice of the present invention as long as it satisfies the above conditions. Further, as the colloidal silica, those which are usually stabilized in the range of pH 8 to 11 are used, but there are also those which are stabilized at pH 2 to 4 as an acidic type. Is preferably used.

The average particle size of the lubricant particles is 5n.
m to 150 nm, preferably 20 nm to 110 nm. If the particle size is too small, it is difficult to disperse the particles. Even colloidal silica is easily aggregated. This is out of the intended range of the invention, which is not preferable. In practicing the present invention, it is important to reduce the thickness of the magnetic tape in order to increase the recording capacity per magnetic tape cassette,
The thickness of the film suitable for the purpose of the present invention is 2
A range of not less than μm and not more than 8 μm is selected. In making the base film thin, workability in the manufacturing process of magnetic tape,
It is preferable that the elastic modulus and strength of the base film be high in view of the running property and electromagnetic conversion characteristics of the magnetic tape.

For example, the elastic modulus in any direction of the film is preferably 1000 kg / mm ² or more, more preferably 1300 kg / mm ² or more. The upper limit of the elastic modulus is not particularly limited, but the achievable elastic modulus of the aramid film having excellent mechanical properties is about 2500 kg / mm ² . Similarly, the strength is 20 kg / mm ² or more, more preferably 30 k / mm ^2.
g / mm ² or more is preferable. Although there is no particular limitation on the upper limit of the strength for carrying out the present invention, even an aramid film having excellent mechanical properties is usually about 60 kg / mm ^{2 in} strength that can be realized.

The properties of these films should be satisfied both in the length direction and in the width direction, but they do not necessarily have to be the same, and it is possible to enhance either property according to the purpose. This may be performed by any of a so-called balanced type in which the characteristics in the length direction and the width direction are almost equal, and a uniaxial tension type in which the tension is applied in either direction. As a resin capable of realizing the provision of the high elastic modulus film of the present invention, such as an aramid resin, it is necessary to have a high crystallinity, and these resins are characterized by a high melting point and are also known as heat-resistant resins. . The property of high heat resistance is preferable for use in a magnetic tape because dimensional stability during heat treatment in the manufacturing process and environmental conditions for use of the tape are widened.

As a film satisfying these characteristics, a part of a film made of an aramid resin or a polyimide resin can be used. The aramid resin used in the present invention is substantially composed of units selected from the group consisting of the following structural units. —NH—Ar ₁ —NH— (1) —CO—Ar ₂ —CO— (2) —NH—Ar ₃ —CO— (3) where Ar ₁ , Ar ₂ and Ar ₃ are at least one aromatic ring And may be the same or different. Representative examples of these include the following chemical formula 1.

[0015]

Embedded image Wherein X _{is, -O -, - CH 2 -} , - SO 2 -, - CO
-And the like.

Further, those in which a part of hydrogen on the ring of these aromatic rings is substituted with a halogen group, a nitro group, an alkyl group, an alkoxy group or the like are also included. In particular, an aramid resin in which 80 mol% or more of all the aromatic rings are bonded in a rose position is preferable for producing a film used in the present invention. As the polyimide resin used in the present invention,
The polymer contains at least one aromatic ring and at least one imide group in the repeating unit of the polymer, and contains the repeating unit represented by the general formula (2) or (3).

[0017]

Embedded image

[0018]

Embedded image Here, Ar ₄ and Ar ₆ contain at least one aromatic ring, and two carbonyl groups forming an imide ring are bonded to adjacent carbon atoms on the aromatic ring. This Ar ₄ is derived from an aromatic tetracarboxylic acid or its anhydride. As a representative example, Chemical formula 4 is given.

[0019]

Embedded image Wherein Y is, -O -, - CO -, - CH 2 -, - S-,
—SO ₂ — and the like. Ar ₆ is derived from tricarboxylic anhydride or its halide. Ar ₅ ,
Ar ₇ contains at least one aromatic ring and is derived from an aromatic diamine and an aromatic isocyanate. A typical example of Ar ₅ or Ar ₇ is Chemical Formula ₅ .

[0020]

Embedded image

Here, Z represents —O—, —CH ₂ —, —S
_{-, - SO 2 -, -} CO- , and the like. These include those in which some of the hydrogen atoms on these aromatic rings are substituted with halogen groups, nitro groups, alkyl groups, alkoxy groups, and the like.
In particular, a polyimide resin in which 80% or more of Ar ₅ and Ar ₇ are aromatic rings bonded in a loose position is preferable for producing a film used in the present invention. Further, in practicing the present invention, the aramid resin or the polyimide resin used for producing the film, in addition to the aforementioned lubricant, as long as the physical properties of the film are not impaired or the purpose of the present invention is not adversely affected,
Antioxidants, other additives, and other polymers may be included.

The film also contains a coloring agent such as a dye or a pigment, a flame retardant, an antistatic agent, an antioxidant, and other modifiers, as long as they do not contradict the object of the present invention. You may. The method for producing the film of the present invention is not particularly limited, and a production method suitable for each resin may be employed. First, with respect to aramid resins, those soluble in organic solvents are either polymerized directly in a solvent or formed into a solution by once re-dissolving the polymer after isolation, and then formed into a film by a dry method or a wet method. ,Also,
Those hardly soluble in organic solvents such as polyparaphenylene terephthalamide (PPTA) are dissolved in concentrated sulfuric acid or the like to form a solution, and then formed into a film by a wet method.

On the other hand, with respect to the polyimide resin, a tetracarboxylic anhydride is reacted with an aromatic diamine in an organic solvent to obtain a polyamic acid. The solution is obtained by dissolving, and they are formed into a film by a dry method or a wet method. In the dry method, the solution is extruded from a die, cast on a support such as a metal drum or an endless belt, and the drying or imidization reaction proceeds until the cast solution forms a self-supporting film. In the wet method, the solution is extruded directly from a die into a coagulating liquid, or cast on a metal drum or an endless belt as in the dry method, and then guided into the coagulating liquid and solidified.

Next, these films are washed with a solvent or an inorganic salt in the films, and then subjected to treatments such as stretching, drying and heat treatment. Surface smoothness film of the present invention, aramid resin or polyimide or a polyamide acid solution which is a precursor of polyimide, mixed with a lubricant fine particles adjusted to a specific aggregation state, to form a film of this solution It is manufactured by

In order to obtain the flat surface film of the present invention, the dispersion of fine particles is important. Fine particles cannot be achieved in a sufficiently dispersed state by directly adding only the fine particles to the resin solution and should be avoided. The fine particles are preferably dispersed in a low-viscosity liquid, and are pre-dispersed in a solvent used for the polymerization of the resin, or when the resin is redissolved, are pre-dispersed in a solution used for dissolution, or a solvent. , A part of the mixture is taken out, fine particles are dispersed, and then added to a solution and mixed.

As a method for dispersing the fine particles, it is preferable to use various homogenizers. In particular, an ultrasonic homogenizer is recommended because of its excellent dispersing power. As a method of improving the dispersion state of the fine particles, a method of decomposing an organic silicon compound in an organic solvent to form a fine particle sol or colloidal fine particles has also been proposed. It should be noted that the intended effect may be difficult to achieve. In a preferred embodiment, the fine particle dispersion liquid previously dispersed in a low-viscosity solvent is subjected to filtration of undispersed or aggregated fine particles before being used for polymerization, dissolution of a resin, or the like. Further, the fine particles once finely dispersed often aggregate with time, and it is preferable to use the fine particles immediately after the dispersion.

The film which has been subjected to the washing treatment is subjected to stretching treatment in either the length direction or the width direction, if necessary, and then subjected to drying and heat treatment characteristic of the present invention. What is important in producing the film of the present invention is a drying and heat treatment step. The drying and heat treatment of the film are performed by installing gripping rolls across the entire width of the film at the processing machine inlet and the processing machine outlet, and by gripping both ears of the film between the gripping rolls, in the width and length directions of the film. It is necessary to implement while restraining both. It is also a preferred embodiment of the present invention that after gripping both ears of the film, the film is widened and stretched in the width direction prior to or while drying. Even if drying and heat treatment are performed continuously while being gripped by the same ear gripping equipment, a gripping roll is installed between the dryer and heat treatment machine, and after drying, the ear gripping is released once and another gripping is performed. The heat treatment may be performed by holding the ear portion again by using the equipment. Performing a stretching treatment between drying and heat treatment is also an embodiment of the present invention.

In the above drying and heat treatment,
The temperature of the film after processing is 150 ° C., preferably 100 ° C.
It is necessary to release the grip on the ear after maintaining the grip on the ear until the temperature drops to below ℃, remove the ear if necessary, and then pull out the film with a grip roll. Film temperature is 15
If the ear grip is released at a temperature exceeding 0 ° C., the effect of the present invention may not be obtained. The method of gripping the ear is not particularly limited, and a clip-type gripper is usually used. Also, the gripping roll is not particularly limited, and is not a driven type used in a normal film manufacturing apparatus, but a driving device capable of overcoming the tension generated in the processing machine and capable of sufficiently restraining the film. What is necessary is that the film is fed at a uniform speed over the entire width without slipping.

<Method of measuring characteristics> The method of measuring characteristic values according to the present invention is as follows. (1) Method of Measuring Film Thickness, Strength, Elongation and Elastic Modulus The film thickness is measured with a dial gauge having a measuring surface of 2 mm in diameter. Strength, elongation, elastic modulus, using a constant extension rate type strength and elongation measuring machine, measuring length 100 mm, a tensile rate of 5
It was measured at 0 mm / min. (2) Measurement method of center plane average roughness (SRa) by optical microscopy The definition of SRa is, for example, the one shown in Jiro Nara, "Method of measuring and evaluating surface roughness" (General Technology Center, 1983). A method of calculating and obtaining an interference image of an interference phase contrast microscope was used. That is, New V manufactured by ZYGO
Using an item 100 type surface roughness measuring device, the objective lens magnification was 40 times, the camera resolution was 550 μm, and the cutoff was 25.
In μm, SRa was measured at any three points of the film and expressed as an average.

(3) Method for Measuring the Average Aggregation Degree of Fine Particles A thin sample having a thickness of about 100 nm was cut out from a film by a conventional method and observed at a magnification of 50,000 times with a JEOL JEM200FX transmission microscope. 50 of fine particle aggregates (including those that exist alone)
The number of the fine particles constituting each of the particles or the individual particles or the particles dispersed and dispersed were counted and expressed as an average value. (4) Method of measuring partial slack of film A sample film roll supporting device and a winding device are installed so that the axes are horizontal and parallel at intervals of 2 m, and the tension is 10 kg.
After winding the sample film to a take-up device for 10 m or more while unwinding the sample film so as to be / mm ² , the film is stopped while maintaining its tension, and the film is loosened from a reference line horizontally set at the intermediate point in the width direction. The amount is measured, and the difference between the minimum value and the maximum value is defined as the slack amount.

[0031]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to examples and the like, but the present invention is not limited to these examples. In the examples,% that is not particularly indicated is% by weight.
It is.

Example 1 A colloidal silica dispersion containing 40% of spherical silica having an average particle size of about 80 nm in water was diluted with distilled water to a concentration of 5%, and stirred with 101% concentrated sulfuric acid. While adding concentrated sulfuric acid having a silica concentration of 0.035%. PPT using the obtained silica-dispersed concentrated sulfuric acid
A is dissolved so that the polymer concentration becomes 12.5%, and P
PTA dope was adjusted. The dope irregularly reflected light during stirring, and was observed under an optical microscope, and was found to be in a liquid crystal state, such as exhibiting optical anisotropy that makes the dark field of a crossed Nicol of a polarizing microscope a bright field.

After the PPTA dope was filtered through a 5 μm-cut stainless steel nonwoven fabric filter, it was cast from a die onto an endless belt at a draft rate of 1.2. Next, the dope is heated and absorbed simultaneously with moisture to convert the dope from a liquid crystal phase to an isotropic phase. The dope is coagulated in 30% sulfuric acid at 10 ° C., neutralized and washed with water. After being stretched by one time, five mirror-finished stainless steel rolls are sent out from a set of gripping rolls, and both ears of the film are gripped by clips, and then stretched by a factor of 1.1 in the lateral direction. While holding it at a fixed length, drying with hot air, heat-treating at 430 ° C, cooling the film by blowing air at room temperature, confirming that the temperature of the film is 80 ° C or less, After releasing the grip of the ear and slitting out about 30 mm of both ears, it was pulled out with a gripping roll having the same structure as described above, and 500
The film was wound by a winder as a film having a width of mm. The obtained PPTA film has a thickness of 4.5 μm, and the physical properties of the film are strength 42, 4 in the length direction and width direction, respectively.
3 kg / mm ² , elongation 14, 12%, elastic modulus 1510,
1510 kg / mm ² , the average cohesion of silica is 2.4,
SRa was 2.0 nm. The amount of film slack is 2 m
m.

Comparative Example 1 In the same manner as in Example 1, except that the film holding roll was changed to a freely rotating driven roll as in the conventional film manufacturing apparatus,
A TA film was manufactured. The thickness and physical properties of the obtained PPTA film were almost the same as those in Example 1, but the central portion of the film was not loose, the both ears were loose, and the amount of slack was 15 mm.

(Comparative Example 2) In Example 1, cooling by air blowing after the heat treatment was omitted, and the film temperature was reduced to about 2
Both ears were released at 50 degrees, and a PPTA film was produced in the same manner. The thickness and physical properties of the obtained PPTA film were almost the same as those in Example 1, but the ears were loosened and the amount of slack was 7 mm as in Comparative Example 2.

Example 2 Example 1, Comparative Examples 1 and 2
Using the PPTA film obtained in the above, a coating test was carried out using a test die coater. As a result, the film of Example 1 did not show any coating unevenness and could be smoothly coated. In each of Examples 1 and 2, the running of the film was unstable, the thickness of the applied magnetic layer was not uniform, and the shape of the rolled up roll was a so-called gauge band.

[0037]

According to the present invention, a flat high elastic modulus film having no partial slack in the width direction is provided, and a thin film magnetic layer is stably coated by a die coater suitable for producing a high-density magnetic tape. it can. Therefore, a thinner magnetic layer can be realized with a coating type magnetic tape that is advantageous in terms of durability and reliability against repeated recording and reproduction, and magnetic recording with high recording capacity using short wavelength signals, which is increasingly required in the future, will be realized. Becomes possible,
A magnetic tape useful for recording information such as multimedia, recording high-definition television images such as digital high-definition television, and backing up computer information recording in an advanced information society can be provided.

Continuation of the front page (51) Int.Cl. ⁶ identification code FI G11B5 / 842 G11B5 / 842Z (58) Investigation field (Int.Cl. ⁶ , DB name) G11B5 / 704 B29C 41/24 B29C 71 / 02 B29D 7/00 C08J 5/18 CFG G11B 5/842 G11B 5/66

Claims (4)

(57) [Claims] 1. The film has an average thickness of 2 to 8 μm and an elastic modulus of 1000 to 2500 kg in any direction of the film.
A film / mm ^2, an average particle diameter of 5 n m~15
0-inactive fine particles are contained in an amount of 0.01 to 1.0% by weight, and a center plane average roughness (SRa) of the film surface is 0.5 to 10 nm as viewed with a resolution of an optical surface roughness meter; A high elastic modulus film for a magnetic tape, wherein a partial slack amount of the film is 5 mm or less for a supporting distance of 2 m. 2. The high elastic modulus film for a magnetic tape according to claim 1, wherein the high elastic modulus film has a strength of 20 to 60 kg / mm ² in any direction of the film. 3. The high elastic modulus film for a magnetic tape according to claim 1, wherein the resin forming the film is an aramid resin or a polyimide resin. 4. A film is prepared by a dry method or a wet method from a solution of an aromatic polyamide resin or a polyimide resin containing 0.01 to 1.0% by weight of inert fine particles having an average particle diameter of 5 to 150 nm based on the resin. In forming, washing, stretching, drying, and heat-treating to produce a heat-resistant film having an average thickness of 12 μm or less, drying and heat-treating are performed while holding both ears of the film, and at the entrance of the processing machine and at the exit of the processing machine. A gripping roll is installed on the side to perform processing under constraints in both the width direction and the length direction, and release the grip after maintaining the grip of the ear of the film until the film temperature is cooled to 150 ° C. or less. Characteristic method for producing high elastic modulus film for magnetic tape.