JPH01292624A - Base film for magnetic tape - Google Patents

Abstract

PURPOSE:To improve surface smoothness and abrasion resistance by scratching the surface of a biaxially oriented film comprising mainly polyethylene naphthalate by use of a diamond needle the end of which has a specific radius to form streaks of specific width and by specifying the Young's modulus in longitudinal direction and 5% elongation stress of the film. CONSTITUTION:The scratches on the biaxially oriented film comprising mainly polyethylene naphthalate are formed by use of a diamond needle the end of which has a 50mum radius under 10g loading and in a constant speed of 0.2mm/ second. The maximum width of the scratches is <=23mum, and the Young's modulus in the longitudinal direction and 5% elongation stress of the film are specified as 500-1,000kg/mm<2> and 20-32kg/mm<2>, respectively. Thus, the surface smoothness and abrasion resistance can be improved.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a base film for use in magnetic tapes, which has especially high longitudinal strength, excellent surface smoothness and abrasion resistance, and heat resistance. be.

(Prior art) Polyester, typically represented by polyethylene terephthalate, has excellent physical and chemical properties, so it is used not only for textiles and molded products, but also for magnetic tapes, floppy disks, photographs, and capacitors. It is also widely used as a film for packaging, X-rays, etc.

Particularly in the field of magnetic tapes, base films containing polyethylene terephthalate as a main component are widely used, and their range of application tends to expand further. on the other hand,
As technology becomes more sophisticated, devices and magnetic tapes are required to be made smaller, which in turn requires thinner base films, that is, higher strength. Tensilizing is used to increase the strength of the tape by strongly stretching it.

(Problems to be Solved by the Invention) However, when polyethylene terephthalate is used as a raw material for tensilization, the stress at 5% elongation of the resulting base film is about 20 kg/mm at maximum,
It was insufficient to meet industry requirements.

Furthermore, even if a base film that satisfies the strength requirements is obtained by adopting special stretching conditions, strength and other properties, such as heat shrinkage properties, tend to conflict with each other. When a metal vapor deposition method is employed to process a base film into a magnetic tape, there is a problem in that the base film is heated to 100° C. or more, causing thermal contraction and deterioration of quality.

In addition, in order to use it as a base film for magnetic tape, it is necessary to form appropriate surface protrusions on the film surface in order to impart slipperiness and excellent magnetic conversion properties, and for this reason, fine inorganic particles must be added. Not only that, but also
If the surface protrusions mentioned above are missing, the slipperiness will be insufficient during the process of processing into magnetic tape and when using it as a magnetic tape, so it is necessary to remove it from the outside during processes such as the coding process when processing into base film. It must not cause wear or other deformation due to frictional force.

By using polyethylene naphthalate instead of polyethylene terephthalate, this invention eliminates the mechanical drawbacks of polyethylene terephthalate film, has excellent strength and abrasion resistance, has low heat shrinkage, and is suitable for magnetic tapes, especially high-grade magnetic The present invention provides a base film suitable for use in tapes.

(Means for Solving the Problems) In order to solve the above problems, the base film for magnetic tape of the present invention is a biaxially stretched film mainly composed of polyethylene naphthalate, and the film surface has a radius of curvature at the tip. 10'g by 50μm diamond needle
The maximum width of streak marks obtained by scratching at a constant speed of 0.2+am/sec under a load of 23 μm or less, and the Young's modulus in the longitudinal direction of the film is SOO~1000 kg/mm”
, the stress at 5% elongation is 20 to 32 kg/IW12.

The polyester used in this invention mainly contains naphthalene-2,6-dicarboxylic acid as an acid component and ethylene glycol as a glycol component, and above all, 80 mol% or more of its repeating units are ethylene naphthalate. Other copolymerized components include terephthalic acid, isophthalic acid, p-
β-oxyethoxybenzoic acid, 4,4'-dicarboxyldiphenyl, 4,4'-dicarboxylbenzophenone, bis(4-carboxylphenyl)ethane,
Dicarboxylic acid components such as adipic acid, sebacic acid, 5-sodium sulfoisophthalic acid, cycloxane-1,4-dicarboxylic acid, propylene glycol, butanediol, neopentyl glycol, diethylene glycol, cyclohexane dimetatool, Glycol components such as ethylene oxide adducts of biphenol A, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol, oxybenzoic acid components such as p-oxybenzoic acid, etc. can be arbitrarily selected and used.

A small amount of a compound containing an amide bond, a carbonate bond, etc. may be included as other copolymer components.

Any production method can be used to produce the polyester, such as a direct polymerization method in which an aromatic dicarboxylic acid and a glycol are directly reacted, or a transesterification method in which a dimethyl ester of an aromatic dicarboxylic acid and a glycol are transesterified. I can do it. Methods for manufacturing films from the polyester mentioned above include a method of simultaneously stretching in the length and width using a general roll tenter, and a method of successive stretching in the length and width, but in particular, a method of stretching in the biaxial direction and then in the uniaxial direction. It is preferable to re-stretch the film to obtain a supertensilized type biaxially stretched film. for example,
Melt extrusion of the above polyester at 280 to 320°C,
The unstretched sheet is rapidly cooled and solidified to obtain a substantially non-oriented unstretched sheet, and this unstretched sheet is stretched in the longitudinal and lateral directions at a stretching temperature of 110 to 180°C, preferably 115 to 150°C, and a stretching ratio of 3 to 7.5 times. Each is stretched and heat-set at a temperature of 1'70 to 260°C. The stretching ratio in this case is.

The vertical magnification may be made larger or smaller than the horizontal magnification, and may be further divided into two or more stages. In addition, in order to form appropriate protrusions on the film surface and improve slipperiness during film running, insoluble particles, so-called internal particles, are generated from multiple soluble inorganic compounds during the polymerization reaction, or insoluble particles are added to the polymerization system. As before, it is possible to add active inorganic particles, so-called external particles, or to use them in combination.External particles include kaolin, titanium oxide, silicon oxide, calcium carbonate, barium sulfate, etc. As an example, it is preferable to use an ethylene glycol slurry from the viewpoint of dispersibility and handleability.

(Function) Since the film of this invention has polyethylene naphthalate as its main component, the film surface hardness is improved compared to that of a film whose main component is polyethylene terephthalate, and internal particles and external particles that form protrusions on the film surface are improved. The film covering the film becomes more robust, and the width of the streaks obtained in the diamond needle scratch test becomes approximately 20% narrower, depending on the film forming conditions, such as the stretching ratio and heat setting temperature. Therefore, even if the film surface is repeatedly subjected to strong friction during slitting and coating after film formation, and during recording and playback after being made into a magnetic tape, the above-mentioned surface protrusions will not be lost, and therefore the magnetic signal will not be lost. Missing, so-called dropouts, are significantly reduced, and good slipperiness is maintained over a long period of time. In order to find out the robustness of the film surface protrusions, we conducted a model film durability test to be described later, and found that the correlation between this test result and the scratch test result using the diamond needle described above was extremely high. It was found that films with narrow streaks gave good results in the film durability test. In other words, the width of the streaks determined by the scratch test using a diamond needle is 2
It needs to be 3μ or less, preferably 21μ or less. If the above width is wider than 23μ and the surface hardness is low, the abrasion resistance when made into a tape will be insufficient, and the protrusions will be missing while the tape is running. This turns into powder and adheres to the film surface.
This causes dropouts and reduces the slipperiness during film running.

In addition, the film of the present invention limits at least the Young's modulus in the longitudinal direction and the stress at 5% elongation to the above-mentioned values among various mechanical properties, so that the properties required for magnetic tape can be achieved relatively easily. be able to. However, if the above Young's modulus is less than 500 kg/rru" or 5%
If the stress during elongation is less than 20 kg/nm2, the elastic properties will be insufficient and the thickness of the base film cannot be lowered to the desired level, and on the other hand, the Young's modulus may be 1000 kg/mm. If the stress at 5% elongation exceeds 32 kg/ll112, the heat shrinkage rate and thickness unevenness of the film will become excessive.

(Example) 100 parts of dimethyl naphthalene-2,6-dicarboxylate (
(based on weight, the same applies hereinafter), 60 parts of ethylene glycol, 0.085 parts of magnesium acetate, and 0 parts of antimony dioxide.
．． 035 parts were attached to a reactor and a transesterification reaction was carried out. The reaction temperature changes from 160℃ to 220℃ as the reaction progresses.
The temperature was adjusted to 0.degree. C., and the completion of the reaction was confirmed by the amount of methanol flowing out. After the transesterification reaction, the average particle size is 0.15.
0.25 parts of ethylene glycol slurry of μm colloidal silica as silicon oxide, and 0.25 parts of ethylene glycol solution of trimethyl phosphate as phosphorus atoms.
．． After adding 0.064 parts of each, the final temperature was 285°C and the final pressure was 0. Polycondensation was carried out at O8 mnHg to obtain polyethylene naphthalate with an intrinsic viscosity of 0.585.

After drying the above polyethylene naphthalate polymer chips, they were melt extruded at a temperature of 298°C to create an unstretched original fabric with a thickness of 150 μm, and this unstretched original fabric was used in a small model stretching machine (manufactured by TM-1ong, USA). vertically by 5
．． The film was stretched 0 times and 3.2 times in the transverse direction, and heat-set at 200° C. for 30 seconds to obtain the biaxially stretched film of Example 1 (thickness 9 μm).

On the other hand, using polyethylene terephthalate obtained by a conventional method as a raw material, a biaxially stretched film of the same thickness as that of Example 1 was obtained in the same manner as in Example 1 above.

In addition, in Example 1, as a lubricant, the average particle size was 0.9 μm.
0 m of calcium carbonate ethylene glycol slurry
．． Polymerization and film formation were carried out in the same manner as in Example 1, except that 25 parts were added, and a biaxially stretched film of Example 2 was obtained.

The biaxially stretched films of Example 1.2 and Comparative Example above were tested for average surface roughness TAR, surface hardness by scratching with a diamond needle, and model film running durability. The results are shown in the table below.

However, physical properties such as surface hardness and elastic properties were measured as follows.

(1) Young's modulus, stress at 5% elongation A tanzak-shaped sample with a length of 150 mm and a width of 10 m+ was cut out parallel to the length and width directions of the film, respectively.
A tensile test was conducted using Tensilon manufactured by Toyo Baldwin Co., Ltd. at a deformation rate of 100%/min, and the Young's modulus and stress at 5% elongation were calculated by conventional methods.

(2) A sample cut into a film surface hardness of 15 mm x 15+++n was fixed on a slide glass, and a diamond needle with a tip radius of curvature of 50 μm was pressed with a load of 10 g to obtain a 0.2 nn.
The surface of the sample was scratched at a constant speed of 1/sec, and the resulting sample was coated with aluminum vapor deposition, then observed with a microscope and photographed.Finally, the width of the streaks caused by the scratching was determined from a 400x magnified photograph. (μm).

(3) Average particle size of external particles The particle size distribution in the slurry obtained by sufficient dispersion in ethylene glycol was measured using a light transmission type centrifugal sedimentation type particle size distribution analyzer (manufactured by Shimadzu Corporation, model 5A-CF2). It was measured by use, and the cumulative value of 50% was used.

(4) Film surface average roughness TAR Three-dimensional roughness measuring instrument manufactured by Kosaka Laboratory Co., Ltd. (SE-3AK
), the film surface was cut off 0.25 + w in the length direction under the conditions of a curvature radius of the needle tip of 2 μm and a load of 30 μm.
n, measured over 1 m, divided into 500 points at a pitch of 2 μm, and measured the height of each point using a three-dimensional analysis device (SPA-1).
Incorporated into. Thereafter, the same operation was performed continuously 150 times at a pitch of 2 μm in the width direction of the film, that is, over a length of 0.3 mm in the width direction of the film, and the resultant film was loaded into the above-mentioned analyzer. Next, the average deviation of the data in the height direction was determined using an analyzer, and this was expressed in μm units to define the average roughness TAR.

(5) Film durability and running width 12. Measurement was carried out using a film slit to F+mm under the conditions of a temperature of 23° C. and a relative humidity of 65% using the apparatus shown in the figure. In the figure, 1 is a tape-like film with a width of 12.5 mm obtained by the above slit, and 2 is a tape-shaped film with a length of 25 mm.
3 is a rotatable guide roller, 4 is a guide boss of a commercially available home VTR (maximum roughness Rt = 0.1
5 μm, average roughness Ra = 0.08 μm), 5 weighs 70
The tape-like film 1 is applied to the guide roller 3 and the guide post 4 as shown in the figure, and the contact angle θ of the tape-like film 1 to the guide post 4 is set to 1.
Set the angle to 35 degrees, and place film 1 on the pin at the tip of crank 2.
Hang one end of the loop and attach the weight 5 to the other end of the film 1.
was fixed, and the crank 2 was rotated at a speed of 8 rpm -12= to bring the film 1 into sliding contact with the guide post 4. After 100 reciprocations, the film surface was observed with a microscope, and the number of scratches was evaluated in three stages. A case where a lot of streaks were observed was given as ×, a case where a small amount of streaks were seen was given as Δ, and a case where almost no streaks were seen was given as 0.

(6) Heat shrinkage rate Fish toppings Q in an oven at a temperature of 150°C. The sample was put in a non-tensioned state, taken out after 1 hour, the length Q was measured, and the formula ((
Calculated as: no-fl)/flo) x 100 (%).

(Blank below) As is clear from the table above, the biaxially stretched films of Examples 1 and 2 of the present invention have excellent abrasion resistance during running and sufficient elasticity as a base film for high-grade magnetic tapes. In addition, the heat shrinkage rate was also small. On the other hand, in the comparative film made of polyethylene terephthalate, the width of the streaks indicating surface hardness was too large, and the Young's modulus and
The stress at 5% elongation is small, and the heat shrinkage rate is excessive.
Therefore, the hardness is lower than that of Example 1.2, and the elastic properties are lower.
The heat shrinkage rate was also insufficient, making it unsuitable for use in high-grade magnetic tapes.

(Effects of the Invention) The base film for magnetic tape of the present invention is a biaxially stretched film mainly composed of polyethylene naphthalate, and has excellent surface smoothness and abrasion resistance, and high strength in the longitudinal direction. It is extremely useful as a base film for vapor-deposited high-grade magnetic tapes that require high strength, abrasion resistance, and thin film thickness.

[Brief explanation of the drawing]

=15- The drawing is a schematic diagram of a film durability running property tester. 1: tape-like film, 2: crank, 3 guide roller, 4 guide post, 5: weight. Patent applicant Toyobo Co., Ltd. Agent Patent attorney Yoshi 1) Tsukasa Ryo = 16-

Claims (1)

[Scope of Claims] [1] A biaxially stretched film containing polyethylene naphthalate as a main component, whose surface was touched under a load of 10 g by a diamond needle with a radius of curvature of 50 μm at the tip.
The maximum width of streak marks obtained by scratching at a constant speed of 0.2 mm/sec is 23 μm or less, and the Young's modulus in the longitudinal direction of the film is 500 to 1000 kg/mm^2, and the stress at 5% elongation is 20 to 32 kg. /mm^2 A base film for magnetic tape.