JPS615431A - Polyester film for magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain the titled polyester film for a magnetic recording medium wherein the deterioration of the electromagnetic characteristics and the generation of dropouts and color noises are prevented by incorporating a specified amt. of inactive inorganic particles so that the area mean diameter and the density of the highest protrusions may be regulated within specified limits. CONSTITUTION:Al is thinly vapor-deposited on the surface of a polyester film used as the supporting body of a magnetic recording medium, and the protruded part which looks black by the observation with a reflection metallurgical microscope is detected. The area mean diameter D1, the number mean diameter D2, and the number N of protrusions are calculated by image processing from the relation between the number Nn of protrusions having surface protrusion diameter Dn and the sum An of the areas of Dn. Meanwhile, the height P of the highest protrusion is measured by a thin-film step- difference meter. When the polyester film contg. 0.005-0.3wt% inactive inorganic particles such as colloidal silica fine particles is manufactured, the area mean diameter D1 is regulated to 0.3-0.12mu, the ratio D1/D2 of the mean diameter D1 to the number mean diameter D2 to 1-2.5, the height of the highest protrusion P to <=0.03mu, and the number density of the protrusions in the range 5X10<2>-1X10<5> unit/mm.<2>. The film is used as a supporting body for a magnetic recording medium having good traveling properties and without the generation of dropouts and color noises.

Description

[Detailed Description of the Invention] □ [Field of the Invention] (The present invention relates to a polyester film for magnetic recording media. [Prior Art] Conventionally, polyester films for magnetic recording media have been subjected to 9-winding, slitting, etc. Numerous microscopic protrusions are provided on the surface of the film to improve the tape running properties in video tape recorders. However, these microscopic protrusions deteriorate the electromagnetic conversion characteristics necessary for magnetic recording. This can cause dropouts (recording loss) and color noise.

The problem here is that the protrusions on the film surface have a wide particle size distribution even though the average protrusion diameter is relatively small. Therefore, the negative effect of coarse particles was large.

In the case of vapor-deposited video tapes in which a magnetic substance is vapor-deposited on the surface of a polyester film, the thickness of the magnetic layer is very thin, so the surface morphology of the base film used is the same as that of the vapor-deposited thin film after the magnetic substance is vapor-deposited. becomes. Therefore, if the surface roughness of the base film is rough, the electromagnetic conversion characteristics of the vapor-deposited videotape will be significantly deteriorated.゛From the viewpoint of electromagnetic conversion characteristics, it is preferable to use a paste film with a completely smooth mirror surface, but in the case of a deposited film formed on such a base film, the deposited surface maintains its mirror surface.
The adhesive properties are very poor, and unless a protective film layer is provided on the deposition surface, a large amount of scratches will occur in the tape forming process after the deposition process, making it completely impractical.

Furthermore, a serious problem in actual use of vapor-deposited videotape is the runnability of the vapor-deposited surface. In the case of conventional coated video tapes, which are made by mixing magnetic powder into an organic binder and coating it on a base film, it is possible to add a lubricant to the binder to improve the running properties of the magnetic surface. In the case of tape.

The runnability of the vapor deposition surface is generally unusable unless a protective film layer is provided, and it is difficult to uniformly provide a protective film layer to secure the vapor deposition, so in the case of vapor deposition tape.

There were drawbacks such as the inability to improve the runnability of the vapor-deposited surface, especially under the harsh conditions of actual use, that is, under high temperature and high humidity conditions.

[Purpose of the invention]

An object of the present invention is to provide a base film for a magnetic recording medium that provides smoothness, abrasion resistance, and good runnability even under high temperature and high humidity conditions without deteriorating electromagnetic characteristics.

[Structure of the invention]

The present invention has the following configuration to achieve the above object.

That is, inert inorganic particles are 0.005 to 0.3wt9
A polyester film containing J, and.

The protrusions are formed on at least one side of the film.

(a) Area average diameter [D2] is 0.6 to 1.2 μ.

(b) The ratio CD, ]/CD, between the area average diameter [D1] and the number average diameter [D2] exceeds 1 and is less than 25.

(c) The maximum protrusion height [P] is 0.06μ or less.

2) Number of protrusions [N] 5 x 103 to 1 x 105 /Nn''
It is characterized by a polyester film for magnetic recording media within the range of .

The polyester referred to in the present invention may be any polyester as long as it is mainly composed of linear polyester. For example, polyethylene terephthalate.

Polytetramethylene terephthalate, poly-1,41i
- Cyclohexylene dimethylene terephthalate.

Typical examples thereof include polyethylene-2,6-naphthalene dicarboxylate and polyethylene-P-oxybenzonite.

Further, the above polyester may be a homopolyester or a copolyester. In the case of copolyester, as a component to be copolymerized.

For example, diethylene glycol, propylene glycol, neopentyl glycol, polyethylene glycol,
Diol components such as P-xylylene glycol, j, 4=cyclohexane dimetatool.

Adipic acid, sebacic acid, phthalic acid, isophthalic acid, 2
．． Dicarboxylic acid components such as 6-naphthalene dicarboxylic acid and 5-sodium sulfoisophthalic acid.

Examples include polyfunctional dicarboxylic acid components such as trimellitic acid and pyromellitic acid, and P-oxyethoxybenzoic acid. In the case of copolymerization, the mole ratio of the components to be copolymerized is 20 or less.

Furthermore, the above-mentioned polyester is mixed with at least one of an alkali metal salt derivative of sulfonic acid that is non-reactive with the polyester, a polyalkylene glycol that is substantially insoluble in the polyester, etc., to an extent not exceeding 5% by weight. It's okay. Furthermore, when the film is stretched, it may contain internal particles consisting of polymerization residues that cause protrusions on the film surface or inert particles added from the outside, and the content thereof is determined by When the polymer is biaxially stretched, it is sufficient that the thickness is 30 μm or less and the haze per sheet is 5% or less.

Cow i The unutilized inorganic particles referred to in the present invention are not particularly limited, but may be particles having a single fine particle size, and specifically, colloidal silica is preferable.

Particle size and specific surface area of particles are not limited, but 1 particle size is 15~
250 m p, especially 55 to 200 mμ is preferred, and the specific surface area is 11 to 18 j m'/g + especially 14 to 4
9 m2/g is preferred.

Further, regarding the particle size distribution of one particle, when the average particle size is 8 microns, it is preferable that 95 wt% or more of the particles are distributed within a range of 2b microns or less, particularly 1.5a microns or less. Further, the particles are preferably dispersed to such an extent that about 10 or more particles do not aggregate in the film when the film is observed with a transmission electron microscope (magnification: 30,000 times).

The amount added per particle is 0.005 to 0.3 wt.

It is preferably 0.02 to Q and 1 wt%.

The polyester film of the present invention is a polyester film prepared by blending the above-mentioned polyester with the above-mentioned inert inorganic particles by a normal method, that is, melting the polyester and extruding it into a sheet or cylindrical shape. A film formed by stretching 4 in at least one direction, and the mechanical properties of the film are either a normal balanced type, a type strengthened in the -axial direction, or a type strengthened in the biaxial direction. It is preferable that there be.

Further, the protrusions formed on at least one surface of the film of the present invention must have a 9-order diameter.

(a) Area average diameter [D2] is 0.3 to 1.2 μ, preferably 0.4 to 0.7 μ. If it is less than 0.3μ, the running properties of the deposited magnetic surface will deteriorate, and if it exceeds 12μ, the electromagnetic conversion characteristics will deteriorate, which is not preferable.

(b) Ratio CD between the area average diameter [D2] and the number average diameter [D2], which expresses the sharpness of the distribution of surface protrusion diameters,]
/ ID, ) is greater than 1 and less than 2.5, preferably greater than 1 and less than 2.0. If it exceeds 2.5, the distribution of the protrusion diameters will be too wide, leading to deterioration of the electromagnetic conversion characteristics, especially dropout, due to coarse protrusions. It's practically unavoidable.

(c) The maximum protrusion height [P] is 0.03μ or less, preferably 0.0[)5 to 0.015μ. If it exceeds 0.03μ, electromagnetic conversion characteristics will deteriorate.

(b) Number of protrusions [N] is 5 x 10 to 1 x 10 pieces/nnn”
It is preferably 1×10 to 4×10 pieces/nlff1.

If it is less than 5 x 10 pieces/m, the running properties of the deposited magnetic surface will deteriorate;
If it exceeds 1x10/=, the electromagnetic conversion characteristics will deteriorate.

Next, a method for forming surface protrusions on such a film will be explained. However, it is not limited to this.
1 first 9
From the viewpoint of controlling the state of surface protrusions, it is most preferable to add inert inorganic particles to the polyester that forms an optically flat surface.

Desired surface protrusions can be obtained by appropriately combining the particle size, amount, and film forming conditions of the inert inorganic particles added.

In the present invention, water-based colloidal silica, which is obtained by removing dialkali content from water glass, is used as inert inorganic particles that can obtain a preferable particle size. By paying attention to agglomeration in the subsequent process and special treatment, the water-based colloidal silica is finally made into almost primary particles. It is most preferable because it exists in the form of particles. Colloidal silica may be used by mixing with glycol while containing water, or may be used by replacing water with glycol.

In the present invention, the glycol solution containing colloidal silica at the required concentration is added to the polymerization system at a temperature of 30 mmHg or less, preferably 1 to 10 mmHg, just before it is finally added into the polymerization system.
For example, ultrasonic treatment is performed for 30 minutes or more at an oscillation frequency of 20 KHz and an oscillation output of 150 W or more under reduced pressure. This special treatment removes low-boiling substances that are thought to be the cause of secondary aggregation, making use of colloidal silica's extremely sharp particle size distribution, and is effective in preventing secondary aggregation.

Further, the surface of the polyester film is preferably smooth, and specifically, the roughness of the film surface is determined by a cutoff value of 0.0811 mr on a stylus type surface roughness meter, and Ra
The value is preferably 0.015/J or less, and 0.010 μ to 0
．． 002μ is more preferred.

The Ra value is determined by using an appropriate cutoff value from the cross-sectional curve obtained from a stylus surface roughness meter.

Absolute value of the height and height of the roughness curve from the center line (calculated by making sure that the areas above and below the center line are equal) in the roughness curve excluding the ridges. (according to DIR4768).

The polyester film of the present invention can be applied to stamping foils, optical recording materials, capacitors, electrostatic recording materials, and other various uses, but it is also applicable to base films for magnetic recording media, especially base films for forming ferromagnetic metal thin films. It is preferable to do so.

Ki method, ion blating method, and vacuum evaporation method can be used. Particularly preferred is a vacuum deposition method. Note that as the first ferromagnetic metal material, iron, cobalt, nickel, an alloy thereof, a cobalt-chromium alloy, or the like can be used.

In view of the need to provide sufficient output as a high-density magnetic recording medium, the thickness of the metal deposited film is generally 0.02 to 0.5μ.
Good condition. The thickness of the metal vapor deposited film formed in this way is extremely thin, and as mentioned above, the surface condition of the base film is the same as the surface condition of the vapor deposited film, and both the electromagnetic conversion characteristics and the running properties of the vapor deposited magnetic surface are affected. In order to satisfy this requirement, the above-mentioned protrusions must be present on the surface of the base film to be deposited.

The polyester film of the present invention is preferably coated with a solution in which a lubricant is dispersed in water or a solvent in order to impart slipperiness to the surface opposite to the vapor-deposited magnetic surface. All conventionally known methods can be used to impart lubricity.9For example, a film obtained by applying an aqueous or solvent-based solution of a lubricant, a polymeric binder, and a surfactant to an unstretched, -axially stretched, or biaxially stretched film can be used. Smoothness can be imparted to a non-vapor deposited magnetic surface by coating and drying during or after film formation.

Below, methods for measuring and evaluating properties of films and tapes will be shown.

(1) Film protrusions (a) Area average diameter [D1], number average diameter [:D,
], number of protrusions [N].

Manufactured by Cambridge Instrument Co. (Made in England)
antimet” 720 was used. Aluminum was vacuum-deposited to a thickness of about 400 to 500 A on the surface of the film to be observed, and a reflection metallurgical microscope (objective 32x, eyepiece 8x) was used.
100 fields of view are observed, and the protrusions that are observed as black are detected by contrast and image processed.

Image processing measures the number of protrusions and the area of protrusions, and calculates 3.14×10
~78.5μm! Divide the range of area into 15 areas.
i.

Divide the protrusions of individual areas into steps. The protrusion diameter is calculated as a circle equivalent diameter from the area in the middle of each step,
Each step surface protrusion diameter consisting of 15 steps [Dn]
Number of protrusions [Nゎ] and surface protrusion diameter of each step [
Dn] and the sum of areas [A1] can be grasped. From the sum of the number of protrusions and the area in the surface protrusion diameter of each step, the area average diameter CD2 of the protrusion diameter and the number average diameter [D2]
are calculated using the following formulas.

Number of protrusions ['N] - ΣN (b) Maximum protrusion height [P] High-precision thin film step measuring instrument manufactured by Koita Institute ■ (Model: ET-
10) Using a stylus cone type 0.5 μR 1 needle force 5 m
g, measurement speed 4μ/sec, vertical magnification 1 million times, horizontal magnification 100 times, cut-on D,
'Draw the chart under the condition of D16m, extract a measurement length of 0.3 circles from the film surface roughness curve measured five times, and maximize the difference between the maximum peak and minimum valley among the five measurements. Let the protrusion height be [P].

(2) Tape characteristics Tape characteristics were evaluated by repeatedly recording and playing back using a commercially available VH3 type VTR.

The tape running properties were evaluated by performing playback under two conditions: normal temperature and humidity, and high temperature and high humidity, and observing screen fluctuations due to disturbances in tape running.

The evaluation criteria are as follows.

○: The vehicle runs smoothly and there is no fluctuation in the playback screen.

×: The running becomes slow in some places, and the playback screen fluctuates.

(3) Scratch resistance Evaluation of scratch resistance is performed by observing scratches on the tape thin film after running the tape 100 times under normal temperature and humidity conditions and high temperature and high humidity conditions. Ta.

The evaluation criteria are as follows.

◎: Almost no scratches are observed on the thin film surface of the tape.

○: A few extremely weak pear scratches were observed on the thin film surface of the tape.

X: Severe scratches occur on the tape thin film surface. Note that normal temperature is 25°C, 6% RH, and high temperature and high humidity is 40°C.
'c・80%RH conditions.

f4), S/N ratio The S/N ratio is 50%.A white level signal is recorded at the optimum recording current for each tape, and the ratio of the signal to noise contained in the video demodulated signal during playback is measured using a commercially available video noise meter. VH'
Comparative measurements were made using S standard tape as φdB.

(5) Dropout Dropout records a 6-step step wave signal on a magnetic recording tape at the optimum recording current, and drops the dropout for 10 minutes with a video head amplifier output attenuation of 18aB and a duration of 20μBea or more during playback. It was measured with an out counter and averaged over 1 minute.

Measurements (S/, N ratio, drop-a-H'y) were carried out under normal temperature and normal humidity conditions.

A ferromagnetic thin film, particularly a vapor-deposited magnetic thin film, provided on the polyester film for magnetic recording media of the present invention is provided on at least one side of the polyester film. The film surface area of the present invention is large, and in particular, the contact area with the magnetic head is extremely small, so that the running properties of the single ferromagnetic thin film surface are extremely good.

Next, the manufacturing method of the present invention will be explained.

A polyester polymer containing uniformly dispersed inert inorganic particles with a single ultra-fine particle size is melt-extruded using an ordinary extruder, cooled on a cooling drum, and the unoriented film is stretched in one direction using a conventional method. Thereafter, the film is stretched in the orthogonal direction, or after stretching in the orthogonal direction, it is further stretched in the one direction and then heat treated. Further, specifically, the polyester raw material described above was melt extruded using a normal film forming machine, and then cooled.

The film is uniaxially stretched 3 to 5 times, preheated to 90 to 120°C in the stenter preheating section of a biaxial stretching machine, and then transversely stretched to 2.5 to 4.5 times at a stretching temperature of 90 to 120°C. At this stage, a polyester film having substantially the surface projections of the present invention is obtained. Furthermore, this horizontally stretched film was heated at 180°C to 220°C.
The biaxially stretched polyester film of the present invention can be obtained by heat treatment at 1.1 to 1.8 times, or by longitudinal restretching and then heat treatment at iso to 220 °C.

As described above, the present invention is a polyester film having ultra-fine single surface protrusions, and the vapor-deposited thin film formed on the surface has dramatically improved surface running performance. Furthermore, the electromagnetic conversion characteristics of the vapor-deposited tape are not impaired, and since there are no coarse protrusions, dropouts do not increase.

〔Example〕

Next, an example of the production of the base film of the present invention and the production of a video chip using the Hisono base film will be described.

In the examples, the average particle size of the inert inorganic particles is a value measured by centrifugation or electron microscopy.

While adding EG little by little to Dull Silica, water was carefully distilled off to prepare EC-substituted colloidal silica with a silica concentration of 10 wt%. A small amount of silica aggregate was observed on the liquid surface and vessel wall, so this was filtered.

DMTloo, s, acetic acid 2110.02 parts, 1 system, the above EC substituted colloidal silica and additional EG,
Silica is 0.2wt% based on the weight of the polyester produced.
, D, MT under reduced pressure of 1-2 rrrmHg in EG bath solution such that the %le ratio of total EG to T is 25.

In addition to those treated with an ultrasonic disperser with an oscillation frequency of 20 KHz and an oscillation output of 300 W for about 2 hours, the temperature is 180-240℃.
The transesterification reaction was carried out. Then 0.035 part of antimony trioxide and 0.0 part of trimethylphosphoone)
4 parts were added, prepolymerization was carried out at 240-270°C under deep vacuum, and polycondensation reaction was further carried out at 270-280°C under high vacuum, and the reaction was completed in 4 hours.

The intrinsic viscosity of the prepared polyethylene terephthalate is 0.
It was 65. This polymer was made into chips, dried, extruded with a film molding machine at 290 to 300°C, and cooled with a cooling drum to create an unstretched film of 210 μm. Biaxial stretching was performed sequentially by 4.0 times.

Further, fixing was carried out at 205"C for 30 seconds to produce a polyethylene terephthalate film with a thickness of 14 microns.

Thereafter, an easy-slip coating solution containing polyurethane resin, vinyl chloride-vinyl acetate copolymer as a binder, calcium carbonate, and silicone was applied to one side of the film and dried. Next, a dicobalt-nickel alloy thin film with a thickness of 0.1 μm was formed by vacuum deposition on the opposite side to which the slippery coating liquid had been applied, and the film was cut into a predetermined width in the machine direction to give a thickness of 1 μm.
A 5μ magnetic tape was used. This characteristic is shown in Table 1.

Example 2 A magnetic tape was obtained in the same manner as in Example 1, except that the concentration of colloidal silica used in manufacturing the base film was changed to 0.1 wt%. The tape properties are shown in Table 1.

In the production of the base film in Example 1, the average particle size was 1.
A magnetic tape was obtained in the same manner as in Example 1, except that colloidal silica of 00 mμ was used at an additive concentration of 0.1 wt%. The tape properties are shown in Table 1.

Comparative Example 1 A magnetic tape was obtained in the same manner as in Example 1, except that the concentration of colloidal silica was changed to 0.4 wt % in the production of the base film. The tape properties are shown in Table 1.

Comparative Example 2 In the production of the base film of Example 1, the average particle size was 1Q.
A magnetic tape was obtained in the same manner as in Example 1 except that mμ colloidal silica was used. The tape properties are shown in Table 1.

Comparative Example 3 An EGO substitute containing colloidal silica at a concentration of 10 wt% was used when preparing the polymer of Example 1.

A magnetic tape was obtained in the same manner as in Example 1, except that EC containing 10 wt% of dry process silica with an average particle size of 60 mμ dispersed with a high-speed stirrer was used. Table 1 shows the characteristics of the magnetic tape.

〔Effect of the invention〕

As described above, the present invention is a film made of polyester with inorganic particles added thereto, and the protrusions on the surface of the film are aged to a certain extent.

When a magnetic layer was provided on this, smoothness with good electromagnetic characteristics, scratch resistance, and good runnability at high temperature and high humidity could be obtained.

Claims (1)

[Claims] (1) A polyester film containing 0.005 to 0.3 wt% of inert inorganic particles, and the protrusions formed on at least one side of the film (a) have an area average diameter [D_1] of 0. 3-1.2μ, (b) Area average diameter [
D_1] and number average diameter [D_2] ratio [D_1]/[
D_2] is more than 1 and less than 2.5, (c) maximum protrusion height [
P] is 0.03 μ or less, (d) Number of protrusions [N] is 5 x 10
A polyester film for magnetic recording media in the range of ^3 to 1 x 10^5 pieces/mm^2.