JPH02129231A - Polyester film for magnetic recording medium - Google Patents

Abstract

PURPOSE:To form a polyester film for a magnetic recording medium with sufficient light-shielding characteristics and excellent surface flatness by incorporating uniformly carbon black particles and an org. compd. having infrared absorbing capability. CONSTITUTION:This polyester film for a magnetic recording medium contains carbon black particles and an org. compd. having infrared absorbing capability and exhibits characteristics satisfying the following three condition (1)-(3). (1) T900 (15mu)<=10%, (2) 0.005mu<=Ra<=0.02mu and (3) muk(50)<=0.03. In formulas 1-3, T900 (15mu) means light transmission (%) at the wavelength of 900nm in terms of film thickness of 15mum; Ra means an average surface roughness (mum) of a film and muk(50) means an abrasion coefficient of the film against a metal pin after the film is brought into contact with the metal pin and repeated runs of 50 times are preformed.

Description

[Detailed description of the invention] Child! The present invention relates to a polyester film for magnetic recording media. More specifically, the present invention relates to a polyester film useful for manufacturing magnetic recording media that has excellent light-shielding properties, flatness, and good electromagnetic conversion characteristics.

Prior art and its problems 11. Polyesters, particularly polyethylene terephthalate or polyethylene naphthalate, have excellent mechanical properties, chemical properties, etc., and are therefore widely used in film GM fibers and the like. In particular, biaxially stretched films of polyethylene terephthalate and polyethylene naphthalate are preferably used in the field of magnetic recording such as audio tapes, video tapes, and computer tapes, which have undergone remarkable development in recent years.

Magnetic tape usually senses the leader tape optically,
Since the start and end of the magnetic tape is determined, it is necessary to have excellent light shielding properties.

In recent years, there has been a strong demand for improved recording density and thinner magnetic layers for magnetic recording media, particularly video tapes. In order to meet these demands, attempts have been made to make the magnetic powder finer, increase the filling rate of the magnetic powder in the magnetic layer, etc. However, when these measures are taken, a problem arises in that the light-shielding properties of the tape are reduced. Therefore, a method of increasing the amount of carbon black in the magnetic layer in order to maintain the light-shielding property has been considered, but this approach has practical limitations because it is accompanied by deterioration in durability and a decrease in the magnetic powder filling rate.

As a method to solve these problems, a method has been proposed in which carbon black particles are contained in the base film to impart light-shielding properties to the film itself (Japanese Patent Laid-Open No. 51-5
No. 2808, JP-A-53-139511.

JP-A-59-71357, JP-A-63-43931, etc.). However, carbon black particles have strong aggregation properties and are difficult to uniformly and finely disperse in a polymer. In particular, when a film contains carbon black particles in an amount sufficient to provide light-shielding properties, a problem arises in that the surface of the film becomes extremely rough due to a large amount of aggregated particles. Therefore, if the amount of carbon black particles in the film is reduced in order to maintain the flatness of the film surface, sufficient light-shielding properties cannot be imparted. In particular, 8 of the videotapes
mm video tapes, professional tapes used by broadcasting stations, etc., require a high magnetic recording density, so the base film must be flat, and for long recording times, the base film must be thin. However, in order to achieve the same light transmittance for thin films as compared to thick films, it is necessary to increase the content of carbon black particles, and the film surface is forced to become rough. .

For this reason, films have been proposed in which a light-shielding layer such as carbon black is combined with a particle-free layer on either side or one side, but this method requires coextrusion equipment and requires the use of recycled film. It is difficult to use, for example, there are technical issues such as uniformity in producing a film of 15 μm or less, and other cost-increasing factors and technical factors make it difficult to supply in large quantities.

In view of the above-mentioned circumstances, the present inventors conducted intensive research to develop a single-layer base film that has excellent light-shielding properties and flatness, and found that it has carbon black particles and infrared absorption ability. It has been discovered that an excellent base film can be obtained by containing both the organic compound and the present invention.

Therefore, an object of the present invention is to provide a polyester film for magnetic recording media that has sufficient light-shielding properties and excellent surface flatness.

According to the present invention, an object of the present invention is to provide a film containing carbon black particles and an organic compound having infrared absorption ability, and having characteristics satisfying the following formulas 1 to 3. This is achieved by a polyester film for magnetic recording media characterized by having the following characteristics.

T (15μ)510%...10
．． 005 μ≦Ra≦0.020 μm2μk≦
0.30...3 The unique point of the present invention is that both carbon black particles and an organic compound having infrared absorption ability are uniformly contained in polyester. Another object of the present invention is to provide a polyester film having characteristics that cannot be obtained by containing only carbon black or only containing an organic compound having infrared absorption ability.

The polyester in the present invention has film-forming ability and may be a homopolymer or a copolymer. Preferred examples include polyesters in which the main acid component is terephthalic acid or 2,6-naphthalene dicarboxylic acid, and the main glycol component is ethylene glycol.

Examples of copolymerization components of this polyester include trifunctional [
Raw carboxylic acid and trimethylene glycol, 1°4-
Examples include glycols such as hexamethylene glycol and cyclohexane dimetatool. Usually 80 mol% or more of the acid component, preferably 95 mol% or more of terephthalic acid or 2,6-naphthalene dicarboxylic acid, and 80 mol% or more of the glycol component, preferably 95 mol% or more of the polyester is ethylene glycol. is used.

Particularly preferred are polyesters produced from terephthalic acid and ethylene glycol through esterification and polycondensation, or polyesters produced from dimethyl terephthalate and ethylene glycol through transesterification and polycondensation. If desired, a small amount of 5% (by weight) or less of other thermoplastic resins such as polyethylene glycol or polyphenylene sulfide may be blended with these polyesters.

If necessary, such polyester may contain inert fine particles and the like within a range that does not impair the effects of the present invention. These inert fine particles include, for example, high melting point organic compounds that are insoluble during melt film formation of polyester, crosslinked polymers,
So-called internal precipitated particles formed inside the polymer during polyester production by metal compound catalysts (e.g. alkali metal compounds, alkaline earth metal compounds, etc.) used during polyester production, and for example HgQ, ZnO, HQCC.
h.

CaC0:+, CaSO4, BaSO4, AizO:
+, 5IOz.

TfOz, SIC,L! F, clay minerals (e.g. talc, kaolin, etc.), zeolites, mica, terephthalates (
Examples include inert externally added particles such as Ca salt, Ba salt, Zn salt, Hn salt, etc.). In addition, inert organic compounds such as metal soap, starch, and carboxymethyl cellulose can also be cited as examples of inert fine particles. Of course, in addition to these particles, stabilizers, antistatic agents, antioxidants, antifoaming agents, etc. may be mixed.

Furthermore, in order to improve the slipperiness of the film, it is also preferable to contain an organic lubricant. The type of organic lubricant is not particularly limited, but examples include fatty acids, fatty acid esters, fatty acid amides, and aromatic amides. The fatty acid ester is preferably a higher fatty acid ester, and a specific example thereof is preferably montanic acid ethylene glycol ester. Further, as the aromatic amide, hexamethylene bisstearylamide and the like can be preferably exemplified.

The carbon black particles in the present invention are not particularly limited, but furnace black, channel black, thermal black 2 lamp black, etc. are preferable. Further, the size of the carbon black particles is not particularly limited, but the primary particle size is preferably 10 to 50 μm, and more preferably 15 to 40 μm. Naoriichi Bonblack is a dispersant to improve dispersibility.

It is also possible to use a material whose surface condition has been modified by surface treatment with a modifier or the like.

Further, the organic compound having infrared absorption ability in the present invention is not particularly limited, but the following compounds can be preferably exemplified.

or S where He in formulas (1-1) and (1-2) is nickel or cobalt, which provides a complex salt that is an effective IR absorber.

selected from the group consisting of copper, palladium, each X being the same or different aromatic or heterocyclic ring, or substituted derivatives of these rings, such as halonitro, alkoxy-
Indicates the atoms necessary to complete alkyl, alkyl and/or alkoxy substituted aromatic and heterocyclic rings.

Examples of useful aromatic rings, including substituted derivatives of aromatic rings, include phenyl, naphthyl, methylphenyl, methylnaphthyl, alkoxyphenyl and alkoxynaphthyl, such as dodecyloxyphenyl, halo-substituted, especially fluoro-substituted, -8- Alkyl-substituted, amino (including dialkylamino)-substituted, haloalkyl-substituted, such as trifluoromethyl-substituted phenyl and naphthyl groups, etc. are indicated.

Examples of useful heterocyclic rings include the formula: Thus, the complex salt may be monoanionic or dianionic. Y is a monovalent or divalent cation depending on the value of Z. The action of Y is the charge Z on this complex salt.
Therefore, Y is Na” K
It may be a cation such as ``Ca'' or the like. However, in a preferred embodiment of the invention, Y is a tetraphenylarsonium cation if Z is 2, and a tetrabutylammonium cation if Z is 1.

Specific examples include the following compounds.

[Wherein G is nitrogen, carbon, oxygen or sulfur. ] and substituted derivatives of these rings, including benz-substituted derivatives.

In the above formula, Z is -1 or -2, where:
He in formula (2) is selected from the group consisting of the metals nickel, palladium and platinum, R is hydrogen, an alkyl group having 1 to 6 carbon atoms, a phenyl group, an alkyl- or alkoxy-substituted phenyl group, and selected from the group consisting of thienyl group.

Specific examples include the following compounds.

[(C61-15) 4 AS] 2 In the present invention, various methods can be used to incorporate carbon black and an organic compound having infrared absorption ability into polyester.

As a typical method, the following method can be mentioned.

a) Predetermined amounts of carbon black and an organic compound having infrared absorption ability are added to the transesterification reaction product of dimethyl terephthalate and ethylene glycol or the esterification reaction product of terephthalic acid and ethylene glycol, and then polycondensation is performed to form a polyester. How to do it.

b) A method in which carbon black and an organic compound having infrared absorption ability are added in predetermined amounts to polyester and kneaded.

h) In the methods (a) and (b) above, a master polymer is produced by adding a large amount of carbon black and/or an organic compound having infrared absorbing ability, and then kneaded with a polyester that does not contain these additives. A method of producing a polyester containing a predetermined amount of carbon black and an organic compound having infrared absorbing ability.

In addition, when carbon black is added during polyester production as in (a) above, ethylene glycol is adsorbed to carbon black, kneaded with a roll mill, ball mill, etc., and then ethylene glycol is added and crushed and dispersed with a sand mill, etc. It is preferable to add it to the reaction system as a treated slurry.

In the present invention, the light transmittance of the film at a wavelength of 900 nm is 10% or less, preferably 8% or less, at a film thickness of 15 μm (converted).

It is desirable that the light transmittance of a magnetic recording medium such as a magnetic tape, in which a magnetic layer and a base film are laminated, at a wavelength of 900 nm is 1% or less. Therefore, if the T (15μ) of the base film exceeds 10%, carbon black or the like is added to give the magnetic layer a light-shielding property in order to reduce the light transmittance of the magnetic recording medium itself at a wavelength of 900 to 1% or less. This is not preferable since it must be contained in a large amount in the magnetic layer. Particularly in professional video tapes, 8 mm video tapes, etc. that require high magnetic recording density, incorporating a large amount of carbon black into the magnetic layer will substantially reduce the volume content of the magnetic powder. In order to become
The original high magnetic recording density cannot be achieved.

Furthermore, in the present invention, the average surface roughness Ra of the film is 0.
．． 0.005 to 0.020 μ, preferably 0.008 to 0.015 μ. Ra is 0.005
If it is smaller than μ, the slipperiness of the film will deteriorate, and Ra
If it exceeds 0.020μ, good electromagnetic conversion characteristics cannot be obtained, which is also not preferable.

The relationship between the added content of carbon black and an organic compound having infrared absorption ability and the light transmittance of the film at a wavelength of 900 nm follows Lambert-Beer's law. Therefore,
The larger the content m of carbon black, the lower the light transmittance, but on the other hand, the surface of the film becomes rougher. Therefore, the amount of carbon black should be determined according to the average surface roughness and coefficient of friction of the film to be obtained. For example, if the thickness of the film is 15μ, the carbon black content should be approximately 1.5% by weight or less. This is more preferable in terms of the average surface roughness of the film. In order to achieve a surface roughness and friction coefficient suitable for video tapes, etc. among magnetic recording media that are used as films, the carbon black content should be 1.5.
Amounts of less than 1.0% by weight are preferred, particularly 1.0% by weight or less. Further, in video tapes and the like, the base film usually has a thickness of 25 μm or less, and in particular, a base film of about 15 μm is often used. In a film having a thickness in this range, the light transmittance of the obtained film is insufficient with the above carbon black content. For this reason, an organic compound having infrared absorption ability is contained in accordance with the content of carbon black, and the light transmittance at a wavelength of 900 nm is adjusted to a predetermined value.

The content of the organic compound having infrared absorption ability is not an unambiguous value because it depends on the light absorption characteristics of the compound and the content of carbon black, but it is preferably 0.1 to 3% by weight.

The thickness of the film is preferably 30μ or less, particularly 15μ or less. Further, the lower limit of the thickness is preferably 2μ.

The method for forming the film of the present invention will be described by way of example, but the method is not limited to this example as long as the required characteristics of the present invention are satisfied.

After drying polyethylene terephthalate containing carbon black particles and an organic compound with infrared absorption ability, it is melted in an extruder, extruded from a die onto a cooling drum in the form of a sheet, and rapidly cooled to form a substantially non-oriented sheet. . Next, the sheet is stretched 3 times or more in each of the longitudinal and transverse directions to obtain a biaxially oriented film, and if necessary, the sheet is stretched again in the longitudinal and/or transverse directions, and then heat treated. can be mentioned.

According to the polyester film of the present invention, it is possible to produce a magnetic recording medium that is excellent in light shielding properties, flatness, and has good electromagnetic conversion characteristics.

EXAMPLES The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited to the following Examples unless the gist thereof is exceeded. Note that "parts" in the examples mean parts by weight. The method for measuring each physical property value is as follows.

(1) Light transmittance at wavelength 900 using a self-recording spectrophotometer manufactured by Hitachi, Ltd.
The light transmittance of the film in nm was measured.

(2) Film surface roughness center line average roughness: Ra (unit: μm) as JIS-BO
This is the value defined in 601. (■) Using a stylus type surface roughness meter (SURFCORDER5E-30C) from Koita Research Institute, stylus radius: 2 μm, measurement pressure: 0.03 (].

Cutoff value: A film surface roughness curve is drawn under the condition of 0.25 mm, and a part of measurement length L is taken from the film surface roughness curve in the direction of its center line, and the center line of this cut-out part is When the roughness curve is expressed as Y=f(X), where the X axis is the vertical magnification direction and the Y axis is the vertical magnification direction, the value (Ra: μm) given by the following equation is defined as the film surface roughness.

In the present invention, the reference length is 2.5 mm, and 5@1 measurements are made,
Ra was expressed as the average value of four values excluding one from the larger value.

(3) Film friction coefficient [μk] In an environment with a temperature of 20°C and a humidity of 60%, a film cut to a width of 172 inches is placed on a fixed rod (surface roughness 0.3 μm) at an angle θ = (15
2/180) yr, radians (152°) and move (friction) at a speed of 200 cm/min. Adjust the tension controller so that the entry tension T1 is 35 (], and run the film 50 times. After the film has traveled 90 m, set the exit tension at the 50th run (T2: (]). It is detected by a detector and the running friction coefficient μk is calculated using the following formula.

μk −(2,303/θ) IQ(] (T2
/ TI >= 0.86810 (1 (T2/35) > Example 1 Production of polyester After pre-kneading 50 parts of carbon black and 50 parts of ethylene glycol, they were kneaded repeatedly in a roll mill.Furthermore, 400 parts of ethylene glycol was added. After dilution and dispersion using a dispersion mill, a sand mill treatment was performed to sufficiently disperse the carbon black.

100 parts of dimethyl terephthalate and 70 parts of ethylene glycol (hereinafter abbreviated as EG) were added to a reactor, 0.035 parts of manganese acetate 4-eternal hydrate was added to the reactor, and methanol was distilled off while heating to raise the temperature. The exchange reaction was completed. Next, 0.03 part of trimethyl phosphate and 0.03 part of antimony trioxide were added. Next, 25 parts of the carbon black EG slurry (2.5% by weight as carbon black to polymer) was added without stirring, and a polycondensation reaction was carried out in a conventional manner to obtain an intrinsic viscosity of 0.6.
Polyethylene terephthalate pellets of No. 2 were obtained [hereinafter referred to as polyester A].

Production of polyester B In production of polyester A, transesterification and polycondensation reactions were carried out in the same manner as above, except that no carbon black was added, to obtain polyethylene terephthalate pellets containing no additives [hereinafter referred to as Polyester B].

Production of Polyester C (1) 895 parts of polyester and 5 parts of bis-(cis-1,2-suphenylene-ethylene-1,2-thiolate) nickel complex salt were dried and blended, and then processed using a twin-screw extruder type. Polyethylene terephthalate pellets containing an organic compound having infrared absorption ability were obtained by melt extrusion using a kneader (hereinafter referred to as polyester C).

Production of film Polyester A, Polyester 8. Polyester C was mixed to have the carbon black and organic compound contents shown in Table 1, and then dried.

Next, an unstretched film was obtained by melt extrusion at 300°C using an extruder, and the film was roughly stretched at a longitudinal stretching temperature of 100°C and a longitudinal magnification of 3.5 times.
After successive biaxial stretching at a transverse stretching temperature of 110°C and a transverse stretching ratio of 4.6 times, heat treatment was performed at 215°C to obtain a film with a thickness of 15 μm.

The properties of the obtained film are shown in Table 1.

Table 1

Claims (1)

[Claims] 1. A polyester film for magnetic recording media, characterized in that the film contains carbon black particles and an organic compound having infrared absorption ability, and has characteristics satisfying the following formulas 1 to 3. . T_9_0_0(15μ)≦10%...10.005
μ≦Ra≦0.020μ・・・2μk_(_5_0_)
≦0.30...3 [However, in the formula, T_9_0_0 (15μ) is the light transmittance (%) at a wavelength of 900 nm when the film thickness is 15μ.
), Ra indicates the average surface roughness (μ) of the film, and μk_(_5_0_) indicates the friction coefficient of the film against the metal pin after being brought into contact with a metal pin and repeatedly run 50 times. 2. The polyester film according to claim 1, wherein the thickness of the film is 15 μm or less.