JPS63247913A - Polyester film for magnetic recording medium - Google Patents

Abstract

PURPOSE:To permit provision of excellent handling workability and wear resistance by forming a titled film in such a manner as to contain silica particles satisfying specific conditions at a specific ratio and to have specific values in the average refractive index of the film and the refractive index in the thickness direction thereof. CONSTITUTION:The grain size distribution B, volumetric shape factor phiV and specific surface area ratio R of the polyester film for a magnetic recording medium satisfy the equations I-III. The film contains 0.01-3.0wt.% silica particles having 0.05-2mum average grain size. The average refractive index-n of the film and the refractive index nalpha in the thickness direction thereof satisfy the equations IV, V. In the equations, B and R are defined by B=(particle size when the integrated volume of the particles is 25%)/(particle size when the integrated volume of the particles is 75%), R=(the specific surface area value determined by a BET method)/(the specific surface area value in terms of equiv. sphere). The excellent handling workability and wear resistance as the base film for the magnetic recording medium for which high-density recording is required as well as the good electrical characteristics when the film is made into a magnetic tape are thereby obtd.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention has excellent film handling properties, and has few drawbacks such as playback output fluctuations and dropouts when used as a magnetic tape. This invention relates to a biaxially stretched polyester film that generates extremely little abrasion powder during the tape forming process.

[Prior art and problems to be solved by the invention] Polyester films have excellent physical and chemical properties and are widely used in industry. In particular, biaxially oriented polyethylene terephthalate is now indispensable as a base material for magnetic recording media because it is particularly superior in flatness, mechanical strength, and dimensional stability compared to other films. On the other hand, in recent years, improvements in magnetic recording media have been made at a rapid pace, and along with this, the demands on PACE 7 film have become more severe.

For example, in applications requiring high-density recording, such as videotapes, a flatter base film surface is required. However, as is well known, when the surface of the film becomes flat, the wear between the film and the base material increases, and the resulting abrasion powder causes various problems.

For example, if abrasion powder is generated in the process before the magnetic layer coating process, including the film manufacturing process, droplets may occur when the magnetic layer is applied, causing drop-acts, and the magnetic layer surface treatment that is performed after magnetic N coating and drying. Abrasion powder generated during the so-called calendering process adheres to the calendering roll, roughens the surface of the magnetic layer, and significantly deteriorates the properties of the magnetic tape. Furthermore, if the abrasion resistance is poor, abrasion powder can be seen adhering to the calendering roll from an early stage, and the roll must be cleaned each time.
This will significantly reduce productivity.

On the other hand, in order to improve the handling efficiency of the film in the film manufacturing process and magnetic layer coating process, it is necessary to reduce the coefficient of friction of the film1). It is known that it is sufficient to blend inorganic or organic fine particles to impart appropriate unevenness to the film surface. The unevenness of the film surface not only reduces the coefficient of friction but also contributes to improving wear resistance to some extent, but in order to improve this, it is necessary to increase the amount of these fine particles or incorporate large particles. A need arises. In such cases, the average roughness of the film surface increases, and coarse protrusions often increase due to the mixture of coarse particles and the generation of coarse particles due to agglomeration of particles. This is contradictory to flattening the surface.

It is known that inert inorganic compound particles are added to polyester, such as talc, kaolin, silica, calcium carbonate, titanium dioxide, graphite, and carbon black, to give unevenness to the film surface. It is being However, these inorganic particles are usually ground natural minerals or synthesized. If these coarse particles are contained in the polyester, the properties during the film forming process or when made into a product will be significantly deteriorated. For example, in the film-forming process, when polyester is melt-extruded using an extruder, the filter provided to remove coarse foreign matter becomes severely clogged, and the film frequently breaks when stretched.

Furthermore, if the resulting film contains coarse particles either singly or agglomerated, they will cause so-called fish eyes, which will cause dropouts when made into a magnetic tape.

Furthermore, in order to flatten and make the film surface uniform, it is necessary to make the particles finer. For this purpose, a method has been proposed in which inert inorganic particles are crushed and classified in advance to remove coarse particles. For example, a method is known in which a powder obtained by pulverizing a natural raw stone or a powder obtained by synthesis is further subjected to dry or wet pulverization and classification treatment.

However, although this method can remove and homogenize coarse particles to some extent, it is not sufficient.On the other hand, another factor that contributes to abrasion resistance is the affinity between the particles blended into the film and the polyester. There is. When particles with poor affinity are made into a film, voids occur at the interface between the polyester and the particles, and the particles may be damaged by contact with various rolls or other external forces during the film forming process, winding process, magnetic tape forming process, etc. They fall off and cause various problems. For this reason, a method is used in which the particle surface is treated with an organic compound such as organic silane or acrylic acid in order to improve the affinity with polyester. however,
At present, sufficient improvements have not been made in such surface treatments because either sufficient affinity cannot be obtained or interactions between particles become stronger, resulting in aggregation and coarse particles.

Among the inorganic particles to be mixed into the polyester described above, silica particles are commercially available in various products with different average particle sizes. However, even when such silica particles are blended with polyester to form a tightening film, it has not been possible to fully satisfy the above-mentioned strict required properties. That is, fine particles such as silica particles, which have a relatively high optical surface activity, tend to form secondary agglomerated particles, making it difficult to completely disperse them in a dispersion medium. In addition, there is a problem that agglomeration often increases during the polyester polymerization reaction, resulting in coarse particles in the polyester, forming coarse protrusions on the surface of the film, and causing deterioration of properties after forming into a magnetic tape. There is.

[Means for solving problems]

In view of the above-mentioned circumstances, the present inventors conducted intensive studies to obtain a biaxially stretched film that has uniform surface irregularities, excellent film handling properties, and abrasion resistance, and is particularly suitable as a base film for magnetic recording media. As a result, it was discovered that a biaxially stretched film containing silica particles having specific properties and having a refractive index within a specific range has excellent properties, leading to the present invention.

That is, the gist of the present invention is that the particle size distribution B1 volume shape coefficient φ
7 and the specific surface area ratio R satisfy the following formulas (1) to (3) % formula % (1 (In the above formulas (1) and (3), B and R are defined as.) It contains 0.0/~3.0% by weight of silica particles with a particle size of 0003~2 μm, and the average refractive index i and the refractive index nα in the thickness direction of the film are expressed by the following formula (4) and (
5) A polyester film for magnetic recording media is provided, which satisfies the following formula.

/, 60θ≦n≦Halo01. - (4Jnα≧hada9- (5) The present invention will be described in detail below.

Polyester in the present invention refers to terephthalic acid, λ, 6
It refers to a polyester obtained using an aromatic dicarboxylic acid such as 7tale dicarboxylic acid or its ester and ethylene glycol as the main starting materials, but it may contain other third components. In this case, the dicarboxylic acid component includes one or two of, for example, isophthalic acid, 7-thalic acid, -96-naphthalene dicarboxylic acid, terephthalic acid, adipic acid, sebacic acid, and oxycarboxylic acid component, such as p-ogyethoxybenzoic acid. The above can be used. As the glycol component, one or more of diethylene glycol, 7'C11:'L/glycol, butanediol, Hehiro-cyclohexane dimetatool, neopentyl glycol, etc. can be used. In any case, the polyester of the present invention is preferably a polyester in which go% or more of the repeating structural units have ethylene terephthalate units or ethylene co- or 6-naphthalene units.

The present invention is characterized by the refractive index of the particles and film blended into the polyester. That is, in order to improve the handling properties, abrasion resistance, and other properties of a polyester film, it is necessary to include fine particles with a specific shape that are inert to polyester. That is, such particles have an average particle diameter of 0.1 to 2 μm, a particle size distribution of 3 or less, which is extremely sharp as defined by the above formulas (1) to (3), and a volume shape coefficient of O, Using silica particles that are almost perfectly spherical (U~π/6) and have a specific surface area ratio of S or more, the average refractive index of the film is L400~/6 to further improve the characteristics.
The inventors have discovered that these characteristics can be achieved by keeping the refractive index in the thickness direction within the range of 0 A and making the refractive index in the thickness direction greater than 1, leading to the present invention.

It has been found that even better properties can be obtained by adding ethylene glycol residues to the particle surface.

The silica particles used in the present invention can be obtained, for example, by using an alkoxysilane as a starting material and performing a hydrolysis and condensation reaction using an amine catalyst. The particle size is controlled and the specific surface area ratio is changed by changing the reaction temperature and time, additional addition of Alfukidisilane, etc. Ethylene glycol residues are added to the particle surface at around 100℃ when replacing the particle dispersion medium with ethylene glycol. This can be achieved by heating.

The average particle size of the silica particles used in the present invention is 0.05 to 2μ
m1 is preferably 0.70 to 0 μm. If the average particle size is less than O, OS μm, the film handling properties and abrasion resistance effects are insufficient, and coarse protrusions may occur on the film surface due to particle aggregation, which is undesirable, leading to a decrease in film quality. If it exceeds 0 or -μm, the roughness of the film becomes too large and the electromagnetic conversion characteristics deteriorate, which is not preferable.

The content of the silica particles in the film is 0.0/~J,
0% by weight, preferably 0.05 to 0.0% by weight. If the content is less than 0.012% by weight, the handling properties and abrasion resistance effects of the film will be insufficient; 0% by weight
Exceeding this is not preferable because the surface roughness of the film becomes unnecessarily high or coarse protrusions are formed due to agglomeration. Since the silica particles of the present invention have a particle size distribution B of 7.3 or less, which is extremely sharp, no special pulverization treatment or classification treatment is required, and furthermore, the filterability of the slurry is extremely excellent. Furthermore, the specific surface area ratio of the 7-Li force particles of the present invention is 5 or more, preferably 10-100. If the specific surface area ratio is less than 5, the affinity with polyester is poor and the abrasion resistance effect is insufficient, which is not preferable. If it exceeds 100, interaction between particles will increase and agglomeration will occur, resulting in poor filterability of the slurry filter and formation of coarse protrusions on the film, which is not preferable. Incidentally, when ethylene glycol residues are added to the surface of the particles, an effect of further improving the properties can be observed.

The present invention uses the particles and further provides a film with an average refractive index of /, 6θO or more /, 1. It is essential to make the OA or less and the refractive index in the thickness direction to be tI92 or more. Here, the average refractive index is an index of the crystallinity of the film, and the refractive index in the thickness direction is an index of the degree of planar orientation. The average refractive index is 1. bol.

If it is larger, the film becomes brittle due to high crystallization and wear resistance deteriorates, which is not preferable. Also, the average refractive index is /, 6θ
If it is less than θ, the dimensional stability of the film at high temperatures will be poor, and when formed into a magnetic tape, the skinny characteristics etc. will deteriorate, which is not preferable.

On the other hand, the refractive index in the thickness direction is /, Tei? Below λ, slipperiness,
This is not preferred because the effect of imparting wear resistance is insufficient.

In the present invention, the method of applying force to the particles into polyester is N
It may be carried out before the start of condensation, during N-condensation, or after condensation, but particularly preferably before polycondensation and at the beginning of polycondensation. still,
The polycondensation reaction catalyst is usually an antimony compound, Go
, Ti, Sn.

and S1 compounds are used.

〔Effect of the invention〕

As detailed above, the present invention can be used as a base film for magnetic recording media that requires high-density recording.It has excellent handling workability and abrasion resistance, has good electromagnetic properties when made into a magnetic tape, and has low dropout. The purpose of obtaining a film was achieved by a simple method of containing specific silica particles and making the film have a specific refractive index, and the present invention has great significance. The invention will be explained in more detail with reference to examples, but the invention is not limited to the following examples unless the gist of the invention is exceeded. The various physical properties of the present invention were measured by the following methods.

In the examples, "part" and "1-%" mean "part by weight" and "% by weight," respectively.

(】) The average refractive index of the film and the refractive index in the thickness direction. When the refractive index in the orientation direction is nr and the refractive index in the direction perpendicular to the main orientation direction is nβ, it is given by Fr = '/(na+n/+ny).

(2) The average particle size and particle size distribution of silica particles are photographed using an electron microscope and measured using a photographic method. particles, about 1o
Measure oo particle sizes, convert each particle size into volume, and integrate. The area where the volume fraction is go% is defined as the average particle size, and the particle size distribution is expressed as the ratio of the particle size at the volume fraction C] and tS%.

(3) Volume shape factor The volumetric shape factor is given by the following equation.

φy = v/d' Here, V is the volume calculated from the average particle diameter determined by the sedimentation method, and d is the arithmetic average value of the particle diameters measured by electron microscopy.

(4) Specific surface area ratio The specific surface area ratio B is defined by the following formula.

Here, the specific surface area value determined by the BIT method is a value determined from the amount of nitrogen gas adsorbed at the temperature of liquid nitrogen.

(5) Evaluation of abrasion resistance Using the tape abrasion evaluation machine shown in Fig. 1, a polyester film with a width of io% was run over a length of 2 (777FFl), and the fixing pins (diameter 6~, Material 5
The amount of abrasion powder adhering to US41co0-:J2, finish θ, -8) was visually evaluated and divided into Darank. The running speed of the film was 1 m 1 min, and the tension was detected by the tensilan pickup shown in (1), and the initial tension was 3 o
o gr % When wrapping the film, the angle θ is / J
5”.

Rank A: No adhesion observed at all.

Rank B: Very slight adhesion is observed, but there is no problem in practical use.

Rank C: The amount of adhesion is slightly large and may cause problems if used for a long time.

Rank D: Many items are attached, making it difficult to use in practice.

(6) Handling workability After the polyester film is formed, it is slit to a predetermined product width and PJ [judged comprehensively from the viewpoint of wrinkles in the film when rolled up on a foot length roll, irregularities in the roll end surface, etc. and ranked.

No wrinkles were observed in the middle and top windings of the 08 take-up roll, and the roll end faces were even.

Δ: The roll is slightly wrinkled, but the end faces are even.

×; Misalignment of the roll end face and wrinkles in the roll were observed.
As a product, it is extremely inferior.

(7) Number of coarse protrusions Aluminum was deposited on the film surface and measured using a Nikon Optiphoto interference microscope using a two-beam method. Measurement wavelength! r Q Protrusion showing third-order or higher interference fringes at Onm (
Protrusion height 0. g 7 μm or more) was measured across an area of /00 parts m'' to determine the number of coarse protrusions.

(8) Number of traces of particles falling off Gold vapor deposition was applied to the film surface, and a photograph was taken with a scanning electron microscope at a magnification of λ, 000 times. The number of shaped pieces was measured and converted into per unit area. The smaller this value is, the better.

(9) Magnetic tape characteristics First, the following magnetic paint was applied to a polyester film to form a magnetic coating so that the film thickness after drying was 1 μm. That is, 200 parts of magnetic fine powder, 30 parts of polyurethane resin,
parts, 10 parts of nitrocellulose, 10 parts of salt-vinyl acetate copolymer,
3 parts lecithin, 100s cyclohexanone.

After dispersing ioo part of methyl isobutyl ketone and 3θθ part of methyl ethyl ketone in a ball mill for 44 g for an hour, 3 parts of a polyisocyanate compound was added to make a magnetic paint, and after applying this to a polyester film, it was magnetically oriented before the paint was sufficiently dried and solidified. , then dried.

Further, this coated film was subjected to surface treatment using a super calender and slit into ZL and η inch widths to make a videotape. Is this videotape manufactured by Matsushita Electric ■ NV-? ?
The following magnetic tape characteristics were evaluated using a θθ video deck.

VTR head output: The VTR head output at a measurement frequency of 100 MHz was measured using a synchroscope, and the sample of Example 3 in Table 7 was set to 0.0 decibel (dB), and its relative value was expressed in decibel (aB).

Number of dropouts: A videotape recording a 1I megahertz signal was played back, and the number of dropouts at 75μθθC-20dB was measured for about 20 minutes using a dropout counter manufactured by Taishoku Industry ■, resulting in a dropout of 7.1 minutes. It was converted into number (ke/min).

Example/~Ioo parts of dimethyl terephthalate, 60 parts of ethylene glycol, magnesium acetate, and 0.09 parts of tetrahydrate were placed in a reactor, heated to an elevated temperature, methanol was distilled off, and a transesterification reaction was carried out. The temperature was raised to 30°C over a period of time, and after the ester conversion reaction had substantially completed, 7.5 parts of an ethylene glycol slurry of silica particles (g/g/list) was added, and further ethyl acid phosphoryl was added. 0.04 parts, antimony trioxide O, OU
After drying the polyester in vacuum, it was extruded into a sheet form from an extruder at a temperature of θ°C, and by an electrostatic cooling method, a polyethylene terephthalate resin of 200 μm was obtained. An amorphous sheet was created.

Next, this amorphous sheet was longitudinally stretched 3.7 times using a multi-stage longitudinal stretching machine, then laterally stretched 9.0 times using a stenter, and further stretched 20 times laterally using a stenter.
Heat setting was carried out in a temperature range of 0° C. or higher to obtain a biaxially stretched film with a thickness of 1 μm. Table 1 shows the properties of the obtained film and the properties after it was made into a magnetic tape.

Comparative Example/~IO Average refractive index (fl) by changing longitudinal stretching and heat setting temperatures,
Biaxially stretched films were obtained by changing the refractive index in the thickness direction 9 and various types of particles. The properties of the film are shown in Table 1.

In all of the films of Example/-j that meet the requirements of the present invention, when rolled into a roll after slitting, an extremely good roll was obtained, with no irregularities on the end surface or wrinkles of the film.
The abrasion resistance during the magnetic tape forming process was also good, and the magnetic properties were also extremely good.

On the other hand, Comparative Example 1 is an example in which the refractive index in the thickness direction is lowered, but the wear resistance is slightly inferior.

Comparative Example - is an example in which the average refractive index exceeds the upper limit of the present invention, but the film has a high degree of crystallinity and becomes brittle.
In this case as well, the wear resistance was poor.

Comparative Examples 3 and DA are examples in which the content of silica particles exceeds the lower and upper limits of the range of the present invention; however, when the content exceeds the lower limit, the handling workability of the film deteriorates and the abrasion resistance is poor. there were.

Moreover, if the upper limit is exceeded, the surface roughness becomes large, leading to a decrease in electrical properties, and if the particle diameter is less than 0.1 Am, coarse protrusions are formed due to aggregation, the Dφ number increases, and it is difficult to draw.

Comparative Examples 3 and 6 are examples in which the particle diameter of the silica particles is outside the range of the present invention. If the particle size exceeds the lower limit of the range and is small, coarse protrusions are formed due to aggregation, which increases the Dφ number, which is not good.

On the other hand, if it exceeds the upper limit of the range, the surface roughness increases, which is not good as it leads to a decrease in electrical property.

Comparative Examples 7 to 9 are examples in which particles other than those of the present invention were contained, but they had poor affinity with polyester and poor abrasion resistance. Also, depending on the particle type, the workability may be poor.

Comparative Example IO is an example using silica particles that do not meet the requirements of the present invention, but coarse projections are formed due to aggregation, and the number of Dφ is large, which is not good.

[Brief explanation of drawings]

Figure 7 is a diagram showing the running system for evaluating wear resistance. This is a run pickup. Also, when wrapping the film around the fixing pin, the corner 0 is 13
It is 5°.

Claims (1)

[Claims] (1) Particle size distribution B, volume shape coefficient φ_v, and specific surface area ratio R are the following formulas (1) to (3) B≦1.3-(1) 0.4≦φ_v≦π/6-(2) R ≧5.0-(3) (In the above formulas (1) and (3), B and R are B = (particle diameter when the cumulative volume of particles is 25%)/(particle diameter when the cumulative volume of particles is 75%) Silica particles with an average particle diameter of 0.05 to 2 μm that satisfy R = (specific surface area value determined by the BET method) / (specific surface area value converted to an equivalent sphere) 0.01 to 3.0% by weight, and the average refractive index n and the refractive index n_α in the thickness direction of the film satisfy the following formulas (4) and (5). Polyester film. 1.600≦@n@≦1.606-(4) n_α≧1.492-(5)