JPS6394429A - Base film for magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a base film having a good electromagnetic conversion characteristic and running performance by specifying the weight of the content (wt%) of the inert inorg. particle in a biaxialy oriented film essentially consisting of a compsn. composed of polyester and at least one kind of the inert inorg. particle, the average grain size D(mum) thereof, and the concn. C of the particles in the front layer of the film to prescribed relations. CONSTITUTION:The polyester consists of the structural unit selected from ethylene terephthalate, ethylene alpha,beta-bis(2-chlorophenoxy)ethane-4,4'-dicarboxylate, ethylene2,6-napthalate units. Spherical silica is used for the inert ingor. particles. The content phi, average grain size D and concn. C in the front layer are maintained at the relations expressed by equations I, II. More particularly, 0.02<phi<0.5, 0.08<D<1.2 are advantageous. The film is biaxially oriented by biaxially stretching the compsn. to about 0.94-0.97 Miller indices. The base film for magnetic recording media having the good electromagnetic conversion characteristic and running performance obtd. according to the above-mentioned constitution.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a base film for magnetic recording media.

[Prior Art] As a base film for a magnetic recording medium, a biaxially oriented film made of polyester containing fine particles of an inert free substance is known (for example, Japanese Patent Publication No. 55-40929).

[Problems to be solved by the invention] However, the above-mentioned conventional base film for magnetic recording media has the following problems:
Attempts to improve electromagnetic conversion characteristics (dropout) result in poor runnability, and attempts to improve runnability result in poor dropout.

It is an object of the present invention to solve these problems and provide a base film for magnetic recording media that is excellent in both electromagnetic conversion characteristics (dropout) and runnability.

[Means for Solving the Problems] A biaxially oriented film containing a composition consisting of polyester and at least one type of inert inorganic particles as the main components, wherein the content weight Φ (wt%) of the inert inorganic particles is ), average particle diameter D (μm), and surface layer particle concentration C of the film satisfy the following relational expressions (1) and (2).

0.01≦Φ・D≦0.15 (1) 0.
002≦C-D2≦0.07 (2) The polyester in the present invention is ethylene terephthalate,
The main component is at least one structural unit selected from ethylene α, β-bis(2-chlorophenoxy)ethane-4,4′-dicarboxylate and ethylene 2,6-naphthalate units. However, the components may be copolymerized within a range that does not impede the present invention, preferably within 5 mol%.

Also, ethylene terephthalate, ethylene alpha.

A polyester containing β-bis(2-chlorophenoxy)ethane-4,4-dicarboxylate as a main component is particularly desirable because it provides even better running properties and electromagnetic conversion characteristics.

The type of inert inorganic particles used in the present invention is not particularly limited, but silica, particularly substantially spherical silica caused by colloidal silica, is particularly desirable because the electromagnetic conversion characteristics and running properties are even better. . It is desirable that the colloidal silica referred to here be particles produced in the process of removing alkali from sodium silicate.

In the present invention, the product of the content Φ (weight %) of inert inorganic particles and its average particle diameter D (μm), Φ・D, is expressed by the following formula (1):
Preferably, it is necessary to satisfy the formula (1)*, and more preferably, the formula (1) zero*.

0.01≦Φ・D≦0.15 (1) 0.
02≦Φ・D≦0.13 ・・・・・・(1)*0.0
3≦Φ・D≦0.10 ・・・・・・(1) Ho*Φ・D
If it is smaller than the above range, the runnability will be poor, and if it is larger than the above range, the electromagnetic conversion characteristics will be poor, which is not preferable.

The content Φ of inert inorganic particles in the present invention is not particularly limited, but is 0.01 to 0.8% by weight, particularly 0.02 to 0.
．． A content of 5% by weight is particularly desirable since running properties and electromagnetic conversion characteristics become even better.

The average particle size of the inert inorganic particles in the present invention is not particularly limited, but is 0.05 to 1.5 μm, particularly 0.08 to 1 μm.
．． A thickness of 2 μm is particularly desirable because running properties and electromagnetic conversion characteristics are even better.

In the present invention, two or more types of inert inorganic particles may be used, or two or more types of the same type with different average particle sizes may be used in combination, but at least one type of particle satisfies the above formula. It is necessary that the Here, when the inorganic composition contains two or more types of particles having the same type but different average particle sizes, the average particle size of all the particles is defined as D, and the total content interval is defined as Φ.

The film of the present invention has the above-mentioned composition as a main component, but other polymers may be blended within the range that does not impede the purpose of the present invention, and antioxidants, heat stabilizers, lubricants, ultraviolet absorbers, etc. Inorganic or solid additives such as agents, nucleating agents, etc. may be added to the extent that they are normally added.

The film of the present invention is a film in which the above composition is biaxially oriented. An unstretched film or a -axis oriented film is not preferred because it results in poor running properties.

In addition, the plane orientation index representing the degree of biaxial orientation is not particularly limited, but is 0.935 to 0.975, particularly 0.94
A range of 0 to 0.970 is particularly desirable because running properties and electromagnetic conversion characteristics become even better.

In the film of the present invention, the product of the square D2 of the average particle diameter (μm) of the inert inorganic particles contained in the film and the surface particle concentration C of the particles, C-D2, is expressed by the following formula (2), preferably (2).
) * formula, more preferably <2) It is necessary to satisfy the umbrella * formula. If C-D2 is smaller than the above range, running properties will be poor, and if it is larger, electromagnetic conversion characteristics will be poor, which is not preferable.

0.002≦C-D2≦0.07 (2
)0.004≦G-02≦0.06 ・・・・・・
(2) *0, 006≦C-D2≦0.055
・・・・・・(2) Umbrellas with different inorganic compositions
When containing more than one type of inert inorganic particles, it is necessary that at least one type, preferably two or more types of particles satisfy the above relational expression. In addition, when containing inert inorganic particles of the same inorganic composition of two or more levels with different average particle diameters, the surface particle concentration C of the particles (according to the principle of surface layer particle concentration measurement, if the inorganic composition of the particles is the same, the average It is necessary that the product of C-D2, which is the product of the square of the average particle size (D2) (not distinguished even if the particle size is different) and the square of the average particle size defined above, satisfies the above range.

Further, the density index of the film of the present invention is 0.02 to 0.0
A range of 5 is particularly desirable because the running properties become even better.

The film of the present invention has an average surface roughness Ra of 0.0 in the width direction.
04-0.025μm1 Especially 0.005-0.020μm
A range of m is particularly desirable because running properties and electromagnetic conversion characteristics become even better.

The film of the present invention has a temperature of 290°C, 200 sec -IT
-The melt viscosity of
A range of 0 to 7,000 voids is particularly desirable because running properties and electromagnetic conversion characteristics are even better.

Next, a method for producing a polyester film for magnetic recording media according to the present invention will be explained.

First, as a method for incorporating inert inorganic particles into a given polyester, they can be added before, during, or after polymerization, but they can be added in the form of a slurry to ethylene glycol, which is the diol component of the polyester. , the method of dispersing and adding is effective in satisfying the relational expression of the present invention. Further, as a method for adjusting the content of inert inorganic particles, either a method of adding a predetermined amount from the beginning or a method of diluting a high concentration master pellet during film formation may be used.

After sufficiently drying the pellets containing a predetermined amount of inert inorganic particles, the pellets were fed to a known melt extruder and 27
It is extruded into a sheet through a slit-shaped die at 0 to 330°C, and cooled and solidified on a casting roll to produce an unstretched film. In this case, the draft ratio (die slit gap/unstretched film thickness) during extrusion is set in the range of 5 to 30, preferably 8 to 20 according to the relational expression (2) of the present invention.
is effective in satisfying the

Next, this unstretched film is subjected to two-wheel stretching to achieve biaxial orientation. As the stretching method, a sequential two-wheel stretching method or a simultaneous two-wheel stretching method can be used.

In the case of the sequential two-wheel stretching method, it is common to stretch in the longitudinal direction and then in the width direction, but this order may be reversed. The conditions for biaxial stretching are not necessarily constant depending on the stretching method, type of polymer, etc., but are usually in the range of 80 to 160°C, preferably 90 to 150°C in both the longitudinal and width directions, and the stretching ratio is 3.0 in each. A range of 5.0 times to 5.0 times, preferably 3.2 to 4.5 times is suitable. Further, the stretching speed is preferably in the range of 1 x 10 to 7 x 104%/min.

Here, before stretching, the unstretched film is
C. for 0.1 to 60 seconds is extremely effective in satisfying relational expression (2) of the present invention. In particular, heat treatment in steam is even more effective.

Next, this stretched film is heat treated. In this case, the heat treatment conditions are preferably 180 to 250°C, preferably 190 to 230°C for 0.5 to 60 seconds under a constant length.

[Function] In the present invention, in a film composed of polyester and inert inorganic particles, the relationship between the content of inert inorganic particles, the average particle diameter, and the surface layer particle concentration of the film satisfies a specific relational expression. It is presumed that the effects of the present invention were obtained as a result of being able to control the viscoelastic behavior of the film surface protrusions.

[Method of Measuring Physical Properties and Evaluating Effects] The methods of measuring the characteristic values and evaluating the effects of the present invention are as follows.

(1) Polyester is removed from a film with an average particle size of inorganic fine particles by plasma ashing treatment or O-chlorophenol dissolution method, and this is dispersed in ethanol, followed by stretching sedimentation method (Horiba, CAPA5).
00) is the volume average diameter measured.

(2) Content of inorganic fine particles O-chlorophenol 1°OQ in polyester 1009
and heated at 120°C for 3 hours.
Stretch separation was carried out for 40 minutes at
Vacuum dry at °C. When the fine particles are measured using a scanning differential calorimetry, if a melting peak corresponding to the polymer is observed, O-chlorophenol is soaked in the fine particles by heating and cooling, and the stretching separation operation is performed again. When the melting peak is no longer observed, the fine particles are considered to be precipitated particles. Normally, two stretching and separating operations are sufficient.

(3) Surface layer particle concentration Using a secondary ion mass spectrometer (SIMS), the concentration ratio of the metal element contained in the inert inorganic particles to the carbon element of the polyester is defined as the particle concentration, and the film surface to depth obtained by this measurement is determined as the particle concentration. The average concentration Cs of 100 people and the depth of 5000 ~
The surface particle concentration was determined as O3/CB, which is the ratio to the average concentration CB of 10,000 people. The measuring device and conditions are as follows.

■ Measuring device Secondary ion mass spectrometer (SIMS) A-DIDA3000 manufactured by ATOHIKA, West Germany ■
Measurement conditions Primary ion species: 02+ Primary ion acceleration voltage: 12KV Primary ion current: 200nA Raster area = 400μm Mouth analysis area: Gate 30% Measurement vacuum degree: 6. OX 10-9TorrE-GU
N: 0.5 to V-3,0A (3) Using an Atsube refractometer with the plane orientation index sodium D line (wavelength 5890 m) as a light source, calculate the refractive index in the thickness direction of the biaxially oriented film (referred to as A). ) and a non-oriented amorphous (amorphous) film made by melt-pressing and quenching into 10° C. water, the refractive index (referred to as B) in the thickness direction was measured, and A/B was taken as the planar orientation index. Using methylene iodide as the mounting solution,
Measurement was performed at 5° C. and 65% RH.

(5) Density Index The density of the film measured using a density gradient tube made of n-hebutane/carbon tetrachloride is dt (g/cnf), and after melt pressing, this film is rapidly cooled in water at 10°C. The difference (dl-d2) from the density d2 of the produced non-oriented amorphous film was taken as the density index.

(6) Using a melt viscosity enhancement type flow tester, it was measured at a temperature of 290°C and a speed of 200 seconds.

(7) Surface average roughness Ra Measured according to JIS-B-0601 using a stylus type surface roughness meter. However, the cutoff is 0.08+n+
n, and the measurement length was 1 mm.

(8> Electromagnetic conversion properties γ-F8203 100 parts by weight, vinyl chloride-vinyl acetate copolymer 15 parts by weight, polyurethane elastomer 15 parts by weight, carbon black 8 parts by weight, methyl ethyl ketone 120 parts by weight, ff1 in methyl imbutyl ketone 130
Part, Milistil 1! ! A magnetic paint was prepared by thoroughly mixing and dispersing 2 parts of the mixture in a sand mill, 15 parts by weight of polyisocyanate (coronate) was added to the magnetic paint, and this was applied to a sample polyester film to a thickness of 4.5 mm.
0 μm (dry thickness) coating and calender treatment (temperature 90
℃, linear pressure 200 to 9/cm), and then slit into 1/2 inch width to make a tape. This tape was inserted into a VH3 video cassette (120 minutes) to make a video cassette tape.

After recording the signal from a TV test signal generator (Shibaku fNTG-7/1 type) on this tape using a VTR, it was recorded for 100 passes (120 minutes
100 passes). Using this tape, a dropout counter was used to pick up and drop out signals with a dropout width of 5 microseconds or more and a reproduced signal attenuation of -16 dB or more. The measurement was carried out on 10 volumes of video cassettes, and when the number of dropouts per minute was less than 10, the electromagnetic conversion characteristics were considered to be good, and when it was 10 or more, the electromagnetic conversion characteristics were judged to be poor.

(9) Running properties: Set the above tape on a VTR, 25°C, 50% RH.
After running 100 passes at 40°C and 80% RH, rank each of the following items on a scale of 5 out of 5 points, and if the total score for all items is 15 to 10, the running performance is: If the rating was 9 or less, the running performance was determined to be poor.

The five-level ranking is based on the number of samples that did not satisfy each of the following items among the 50 volumes: 0 to 1.
5 points for 2 to 3 pieces, 4 points for 4 to 6 pieces, 3 points for 4 to 6 pieces, 2 points for 7 to 9 pieces, and 1 point for 10 or more pieces.

a) The edges of the tape do not break (do not buckle) b) The tape does not stretch and become seaweed-like C) Tape abrasion (fa
(Example) The present invention will be explained based on Examples.

Examples 1 to 4, Comparative Examples 1 to 4 Ethylene glycol sols of various colloidal silicas having different average particle diameters were transesterified and polycondensed with dimethyl terephthalate after adjusting the silica concentration appropriately. The polyethylene terephthalate pellets were dried under reduced pressure (3 Torr) at 180° C. for 3 hours. The pellets were fed into an extruder, melt-extruded at 300'C, the draft ratio was varied, and the surface temperature was 30°C using an electrostatic casting method.
The film was wound around a casting drum and cooled and solidified to produce an unstretched film with a thickness of about 170 μm. This unstretched film was heat treated for 1 minute at various temperatures of 100 to 200°C, and then stretched 3° and 4 times in the longitudinal direction at 90°C.

This stretching was carried out using a difference in peripheral speed between two sets of rolls, and the stretching speed was 10,000%/min. This -axis film was stretched 3.6 times in the width direction at 100°C at a stretching rate of 2000%/min using a stenter, and heat treated at 210°C for 5 seconds under constant length to obtain a film with a thickness of 14 μm. .

The silica content of this film, Φ, average particle diameter D1, surface particle temperature C1, and Φ·D, C-D2 are as shown in Table 1. As can be seen from Table 1, the above Φ・D, C
When both -D2 satisfied the relational expression of the present invention, a base film for a magnetic recording medium with good running properties and electromagnetic conversion characteristics was obtained (Examples 1 to 4). However, Φ・D,C
-D2 was outside the range of the present invention, a film having both running properties and electromagnetic conversion characteristics could not be obtained (Comparative Examples 1 to 4).

Examples 5 to 6, Comparative Example 5 Various inert inorganic particles with different average particle sizes were dispersed in ethylene glycol in the form of a slurry, the concentration of the inert inorganic particles was adjusted to an appropriate amount, and transesterification with dimethyl terephthalate was performed. reaction and polycondensation.

Using this polyethylene terephthalate pellet,
A film with a thickness of 14 μm was obtained in the same manner as in Example 1.

Inert inorganic particle content Φ of this film, average particle diameter D,
The surface layer particle concentration C1, Φ·D, and C-D2 are as shown in Table 2. As shown in Table 2, the above Φ・D
, C-D2 both satisfy the relational expression of the present invention, a base film for a magnetic recording medium having good running properties and electromagnetic conversion characteristics was obtained (Examples 5 and 6). However, Φ・D
, if either C or D2 is outside the scope of the present invention, the running performance
A film having both good electromagnetic change characteristics was not obtained (Comparative Example 5).

[Effects of the Invention] In the present invention, in a film made of polyester and inert inorganic particles, the relationship between the content of particles, the average particle diameter, and the concentration of surface particles satisfies a specific relational expression.
A base film for a magnetic recording medium was obtained which had excellent electromagnetic conversion characteristics (dropout) and runnability when used as a magnetic recording medium.

The film of the present invention can be applied to various magnetic recording media, but
It is particularly suitable as a base film for video tapes and floppy disks.

Claims (1)

[Scope of Claims] A biaxially oriented film comprising a composition comprising polyester and at least one type of inert inorganic particles as main components, the content weight Φ (weight %) of the inert inorganic particles, the average particle size A base film for a magnetic recording medium, characterized in that a diameter D (μm) and a surface layer particle concentration C of the film satisfy the following relational expressions (1) and (2). 0.01≦Φ・D≦0.15・・・・・・(1) 0.002≦C・D＾2≦0.07・・・・・・(2)