JPH0670149B2 - Polyester film for magnetic recording media - Google Patents

Description

TECHNICAL FIELD The present invention relates to a polyester film for a magnetic recording medium. More specifically, the present invention relates to a polyester film which is useful for producing a magnetic recording medium having excellent light-shielding properties and flatness and good electromagnetic conversion characteristics.

Prior art and its problems Polyester, especially polyethylene terephthalate or polyethylene naphthalate, is widely used for films, fibers and the like because of its excellent mechanical properties and chemical properties. In particular, in the magnetic recording field of audio tapes, video tapes, computer tapes, etc., which have made remarkable progress in recent years, biaxially stretched films of polyethylene terephthalate and polyethylene naphthalate are preferably used.

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

In recent years, there has been a strong demand for improvement in recording density and thinning of magnetic layers for magnetic recording media, especially video tapes. In order to satisfy these requirements, attempts have been made to miniaturize the magnetic powder and increase the filling rate of the magnetic powder in the magnetic layer. However, if these measures are taken, there arises a problem accompanied by a decrease in the light shielding property of the tape. Therefore, a method of increasing the amount of carbon black in the magnetic layer in order to maintain the light-shielding property is conceivable, but this has a practical limit because it deteriorates the durability and reduces the filling rate of the magnetic powder.

As a method for solving these problems, a method has been proposed in which carbon black particles are contained in a base film to impart a light-shielding property to the film itself (JP-A-51-52808).
JP-A-53-139511, JP-A-59-71357, JP-A-63-
No. 43931). However, carbon black particles have a strong cohesive property, and it is difficult to uniformly and finely disperse them in a polymer. In particular, when carbon black particles are contained in the film in an amount sufficient to provide a light-shielding property, a large amount of aggregated particles causes a problem that the surface of the film is significantly roughened. Therefore, if the amount of carbon black particles in the film is reduced in order to maintain the flatness of the film surface, the light-shielding property cannot be sufficiently imparted. Of the video tapes, 8mm video tapes and professional tapes used in broadcasting stations require a high magnetic recording density, so a flat base film is required, and it is a base film for long-term recording. Thin film is required, but the thin film needs to contain a large amount of carbon black particles in order to have the same light transmittance as the thick film, and the film surface must be rough. I am in a situation where I do not get.

Therefore, a film in which a layer containing no particles is combined on both sides or one side of a layer having a light-shielding property such as carbon black has been proposed, but this method requires the equipment of a coextrusion device. It is difficult to use, for example, there are technical factors such as uniformity in producing a film having a size of 15 μm or less.

OBJECTS OF THE INVENTION In view of the above-mentioned circumstances, the present inventors have earnestly studied to develop a single-layer base film excellent in both light-shielding property and flatness, and as a result, carbon black particles and an organic compound having infrared absorbing ability are developed. It was found that an excellent base film can be obtained by containing both of the above and the present invention, and the present invention has been accomplished.

Therefore, an object of the present invention is to provide a polyester film for a magnetic recording medium having a sufficient light-shielding property and an excellent surface flatness.

According to the present invention, an object of the present invention is to contain carbon black particles and an organic compound having an infrared absorbing ability in a film, and to have a characteristic satisfying the following formulas 1 to 3. It is achieved by a polyester film for a magnetic recording medium which is characteristic.

The peculiar point of the present invention resides in that both the carbon black particles and the organic compound having an infrared absorbing ability are uniformly contained in the polyester. Another object of the present invention is to provide a polyester film having properties that cannot be obtained by containing only carbon black or only an organic compound having an infrared absorbing ability.

The polyester in the present invention has a film forming ability and may be a homopolymer or a copolymer. Preferred is a polyester whose main acid component is terephthalic acid or 2,6-naphthalenedicarboxylic acid and whose main glycol component is ethylene glycol. Examples of the copolymerization component of this polyester include difunctional carboxylic acids such as isophthalic acid, adipic acid, sebacic acid, 5-sodium sulfoisophthalic acid, p-hydroxybenzoic acid and trimethylene glycol, 1,4-hexamethylene glycol. And glycols such as cyclohexanedimethanol. Polyester in which 80 mol% or more, preferably 95 mol% or more of the acid component is usually terephthalic acid or 2,6-naphthalenedicarboxylic acid, and 80 mol% or more, preferably 95 mol% or more of the glycol component is ethylene glycol Is used. Particularly preferred is a polyester produced from terephthalic acid and ethylene glycol through esterification and polycondensation, or a polyester produced from dimethyl terephthalate and ethylene glycol through transesterification and polycondensation. Further, if desired, it is possible to use a mixture of these polyesters with other thermoplastic resins such as polyethylene glycol and polyphenylene sulfide in a small amount of 5 (wt)% or less.

If necessary, the polyester may contain inert fine particles and the like within a range that does not impair the effects of the present invention. The inert fine particles include, for example, a high melting point organic compound, a cross-linking polymer, which is insoluble during the melt film formation of polyester.
So-called internally precipitated particles formed inside the polymer at the time of the production by a metal compound catalyst (for example, an alkali metal compound, an alkaline earth metal compound, etc.) used during the production of polyester, and for example MgO, ZnO, MgCO ₃ , CaCO ₃ , CaSO ₄ ,
BaSO ₄ , Al ₂ O ₃ , SiO ₂ , TiO ₂ , SiC, LiF, clay minerals (eg talc, kaolin, etc.), zeolite, mica, terephthalate (eg Ca salt, Ba salt, Zn salt, Mn salt, etc.) And the like, such as inert externally added particles. In addition, inert organic compounds such as metallic soap, starch, carboxymethyl cellulose and the like can be cited as examples of the inert fine particles. Of course, in addition to these particles, stabilizers, antistatic agents, antioxidants, defoaming agents, etc. may be mixed.

Furthermore, in order to improve the slipperiness of the film, it is preferable to add an organic lubricant. The type of organic lubricant is not particularly limited, but fatty acids, fatty acid esters, fatty acid amides, aromatic amides and the like can be exemplified.
The fatty acid ester is preferably a higher fatty acid ester, and a specific example thereof is preferably ethylene glycol montanate ester. As the aromatic amide, hexamethylenebisstearylamide 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, lamp black and the like are preferable. The size of the carbon black particles is also not particularly limited, but the primary particle size is preferably 10 to 50 μm, more preferably 15 to 40 μm. The carbon black may be surface-modified with a dispersant, a modifier or the like in order to improve the dispersibility, and the surface state thereof may be modified.

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

(1) Or Here, Me in the formulas (1-1) and (1-2) is selected from the group consisting of nickel, cobalt, copper, and palladium, which provides a complex salt that is an effective IR absorber, and whether each X is the same or not. Or different aromatic or heterocyclic rings, or substituted derivatives of these rings, eg halonitro, alkoxy-alkyl,
The atoms necessary to complete the alkyl and / or alkoxy substituted aromatic and heterocyclic rings are indicated.

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

Examples of useful heterocyclic rings include formulas [In the formula, 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, therefore 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 to neutralize the charged Z on this complex, and thus Y may be a cation such as Na ⁺ , K ⁺ , 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.

(2) Here, Me in the formula (2) is selected from the group consisting of metals of nickel, palladium and platinum, R is hydrogen,
An alkyl group having 1 to 6 carbon atoms, a phenyl group,
It is selected from the group consisting of alkyl- or alkoxy-substituted phenyl, and thienyl groups.

Specific examples include the following compounds.

In the present invention, various methods can be used for incorporating carbon black and an organic compound having an infrared absorbing ability into the polyester. The following methods can be mentioned as typical methods.

A) Carbon black and an organic compound having an infrared absorbing ability are added in a predetermined amount to a transesterification reaction product of dimethyl terephthalate and ethylene glycol or an esterification reaction product of terephthalic acid and ethylene glycol, and then polycondensed to produce a polyester. And how to.

(A) A method in which a predetermined amount of carbon black and an organic compound having an infrared absorbing ability are added to polyester and kneading is performed.

C) In the above methods (a) and (a), a large amount of carbon black and / or an organic compound having an infrared absorbing ability is added to produce a master polymer, which is kneaded with a polyester containing no such additives. And a polyester containing a predetermined amount of carbon black and an organic compound having an infrared absorbing ability.

When carbon black is added during polyester production as in (a) above, ethylene glycol is adsorbed on the carbon black and kneaded with a roll mill, ball mill, etc., and then ethylene glycol is added and crushed and dispersed with a sand mill or the like. It is preferably added 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 when the film thickness is 15 μ (converted).

The light transmittance at a wavelength of 900 nm of a magnetic recording medium such as a magnetic tape in which a magnetic layer and a base film are laminated is 1%.
The following is desirable. For this reason, when the T ₉₀₀ (15μ) of the base film exceeds 10%, it is necessary to reduce the light transmittance of the magnetic recording medium itself at a wavelength of 900 nm to 1% or less by using carbon black or the like for imparting the light shielding property of the magnetic layer. Is required to be contained in a large amount in the magnetic layer, which is not preferable. 8mm for professional video tapes that require particularly high magnetic recording density
In a video tape or the like, if a large amount of carbon black is contained in the magnetic layer, the volume content of the magnetic powder is substantially reduced, so that the original high magnetic recording density cannot be achieved.

In the present invention, the average surface roughness Ra of the film is 0.00
Must be 5 to 0.020μ, preferably 0.008 to 0.015
is μ. When Ra is less than 0.005μ, the slipperiness of the film is deteriorated, and when Ra exceeds 0.020μ, good electromagnetic conversion characteristics cannot be obtained, which is also not preferable.

The relationship between the added contents of carbon black and an organic compound having an infrared absorption ability and the light transmittance of the film at a wavelength of 900 nm follows Lambert-Beer's law. Therefore, the higher the carbon black content, the lower the light transmittance, but the surface of the film becomes rough. Therefore, the amount of carbon black corresponds to the average surface roughness and friction coefficient of the film to be obtained.For example, when the film thickness is 15 μ, the carbon black content is approximately 1.
The amount of 5% by weight or less is preferable from the viewpoint of the average surface roughness of the film. The content of carbon black is preferably less than 1.5% by weight, particularly 1.0% by weight or less, in order to obtain a surface roughness and a coefficient of friction suitable for video tapes in the magnetic recording medium used for the film. preferable.
In video tapes and the like, the thickness of the base film is usually 25 μm or less, and particularly about 15 μm is often used. With a film having a thickness in this region, the above-mentioned carbon black content results in insufficient light transmittance of the obtained film. Therefore, an organic compound having an infrared absorbing ability is added according to 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 an infrared absorbing ability is The value is not unique because it depends on the light absorption characteristics of the compound and the carbon black content, but 0.1-3% by weight
Is preferred.

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

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

After drying polyethylene terephthalate containing carbon black particles and an organic compound having an infrared absorbing ability, it is melted in an extruder, extruded from a die on a cooling drum in a sheet shape, and rapidly cooled to be a substantially non-oriented sheet. . Then, the sheet is stretched in the machine direction and the transverse direction three times or more to obtain a biaxially oriented film, and if necessary, the film is stretched again in the machine direction and / or the transverse direction, and then heat-treated. Is mentioned.

According to the polyester film of the present invention, it is possible to manufacture a magnetic recording medium having excellent light-shielding properties and flatness and good electromagnetic conversion characteristics.

EXAMPLES The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded. In addition, "part" in an Example means a weight part. Moreover, the measuring method of each physical property value is as follows.

(1) Light transmittance Using Hitachi's own recording spectrophotometer, wavelength 900nm
The light transmittance of the film was measured.

(2) Film surface roughness The center line average roughness is a value defined by JIS-BO601 as Ra (unit: μm). Using a stylus type surface roughness meter (SURFCORDER SE-30C) from Kosaka Laboratory, Ltd., stylus radius: 2 μm,
A film surface roughness curve is placed under the conditions of measuring pressure: 0.03 g, cutoff value: 0.25 mm, and a part of the measuring length L is extracted from the film surface roughness curve in the direction of its center line. When the roughness curve is represented by Y = f (x) with the center line of X as the X axis and the vertical magnification direction as the Y axis, the value (Ra: μm) given by the following formula is used as the film surface roughness. Define.

In the present invention, 5 pieces were measured with a reference length of 2.5 mm, and Ra was expressed as an average value of 4 pieces excluding one piece having a larger value.

(3) Friction coefficient of film [μk ₍₅₀₎ ] A film cut into 1/2 inch width at a temperature of 20 ° C and a humidity of 60% is attached to a fixed rod (surface roughness 0.3μm) at an angle θ = (1
52/180) π radian (152 °) contact and move (rub) at a speed of 200 cm per minute. Entrance tension T ₁ is 35g
Adjust the tension controller so that, and run the film repeatedly 50 times. The exit tension (T ₂ : g) during the 50th run is detected by the exit tension detector after the film has run 90 m, and the running friction coefficient μk is calculated by the following formula.

_{μk (50) = (2.303 /} θ) log (T 2 / T 1) = 0.868log (T 2/35) after the production of carbon black 50 parts ethylene glycol 50 parts of Example 1 Polyester A were pre-kneaded, roll mill And kneaded repeatedly. Further, 400 parts of ethylene glycol was added, diluted and dispersed with a Dispers mill, and then sand milled to sufficiently disperse the carbon black.

100 parts of dimethyl terephthalate and 70 parts of ethylene glycol (hereinafter abbreviated as EG) were added to the reactor, 0.035 parts of manganese acetate tetrahydrate was further added, and the temperature was raised by heating and methanol was distilled off to conduct a transesterification reaction. Finished. Next, 0.03 part of trimethyl phosphate and 0.03 part of antimony trioxide were added. Then, 25 parts of the carbon black EG slurry (2.5% by weight as carbon black relative to the polymer) was added under stirring and then a polycondensation reaction was carried out in the usual manner to obtain polyethylene terephthalate pellets having an intrinsic viscosity of 0.62 [hereinafter, Polyester A].

Production of Polyester B In the production of Polyester A, a transesterification reaction and a polycondensation reaction were performed in the same manner as above except that carbon black was not added to obtain polyethylene terephthalate pellets with no additive added [hereinafter, Polyester B].

Production of Polyester C 95 parts of polyester B and 5 parts of bis- (cis-1,2-bis-phenyl-ethylene-1,2-thiolate) / nickel complex salt are each dried and then blended, followed by twin-screw extruder type kneading It was melt-extruded by a machine to obtain polyethylene terephthalate pellets containing an organic compound having an infrared absorbing ability [hereinafter referred to as polyester C].

Production of Film Polyester A, Polyester B, and Polyester C were mixed so as to have the contents of carbon black and organic compounds shown in Table 1, and then dried. Then 300 ℃ in the extruder
Melt-extruded to obtain an unstretched film, and the longitudinal stretching temperature
After sequentially biaxially stretching at 100 ° C., a longitudinal stretching ratio of 3.5 times, 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 having a thickness of 15 μ.

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

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Claims (2)

[Claims] 1. A film containing carbon black particles and an organic compound capable of absorbing infrared rays and having the following formula 1
A polyester film for a magnetic recording medium, which has characteristics satisfying 3 to 3. 2. The thickness of the film is 15 μm or less.
The described polyester film.