JPH0625268B2 - Polyethylene-2,6-naphthalate film - Google Patents

Description

TECHNICAL FIELD The present invention relates to a biaxially oriented polyethylene-2,6-naphthalate film having excellent mechanical properties, scratch resistance and abrasion resistance.

More specifically, the present invention relates to a biaxially oriented polyethylene-2,6-naphthalate film which is extremely resistant to scratches and abrasion powder during running of the tape and is suitable for high density magnetic recording applications.

[Problems to be Solved by Conventional Techniques and Inventions]

A polyester film is widely used as an industrial base material because of its excellent physical and chemical properties.

By the way, in recent years, there has been a strong demand for miniaturization, weight reduction, and high performance of electric and electronic devices, and accordingly, required characteristics have become more severe for films used. Under such circumstances, polyethylene-2,6-naphthalate film among polyester films has been attracting attention because of its excellent mechanical strength and heat resistance and is being put to practical use. Among these films, it is particularly excellent in mechanical strength, and also contained. A film having a small amount of oligomer is desired.

Such a film is highly valued as a base film for magnetic recording, in addition to being prized for an electric insulating material and a capacitor dielectric. For example, there is a demand for downsizing of magnetic recording media, thinning of the base film as the recording time increases, and higher strength.

By the way, the biaxially oriented film of polyethylene-2,6-naphthalate is similar to that of polyethylene terephthalate.
Longitudinal stretching is performed by using the peripheral speed difference between rolls, but in this case, the film is often scratched, and the film is often damaged by friction or abrasion between the product film and the base material such as guide pins. Scratches occur and abrasion powder is generated.

When the scratch resistance and abrasion resistance of the polyester film are insufficient as described above, the scratches of the base film are reflected on the surface of the magnetic layer in the use of the magnetic recording medium, and the electromagnetic properties are deteriorated. Further, the presence of the scraped white powdery substance often deteriorates the characteristics.

Conventionally, as a means for improving the running property and abrasion resistance of a polyethylene-2,6-naphthalate film, a method is known in which inert fine particles are present in the film to roughen the film surface appropriately, The degree of improvement was insufficient. According to the inventor of the present invention, the scratch resistance and abrasion resistance are apt to deteriorate during the production and handling of a film having particularly high mechanical strength, and its improvement has been particularly desired.

[Means for Solving the Problems]

The present invention has been made in view of the above problems, and as a result of intensive studies, it was found that a film containing a specific amount of inorganic particles having a specific Mohs hardness and a particle size can achieve such an object. It came to completion.

That is, the gist of the present invention is to contain 0.01 to 5% by weight of inorganic particles having a Mohs hardness of 8 or more and an average particle size of 5 μm or less, the sum of the F-5 values in the longitudinal direction and the transverse direction being 25 kg / mm ² or more, and the oligomer. A biaxially oriented polyethylene-2,6-naphthalate film having a content of 0.5% by weight or less.

Hereinafter, the present invention will be described in more detail.

With polyethylene-2,6-naphthalate in the present invention, naphthalene-2,6-dicarboxylic acid or its alkyl ester as a main acid component, after performing an esterification reaction or transesterification reaction with ethylene glycol as a main glycol component, This refers to a polyester obtained by carrying out a polycondensation reaction, but a part of it may be replaced with another component. For example, part of the acid component may be replaced with naphthalene-2,7-dicarboxylic acid, terephthalic acid, isophthalic acid, phthalic acid, adipic acid, sebacic acid, P-hydroxybenzoic acid or its lower alkyl ester, or glycol. A part of the components may be replaced with trimethylene glycol, tetramethylene glycol, hexamethylene glycol, neopentyl glycol, 1,4-cyclohexanedimethanol and the like. In any case, the term "polyethylene-2,6-naphthalate" as used in the present invention refers to a polyester in which 80 mol% or more, preferably 90 mol% or more is an ethylene-2,6-naphthalate unit.

Further, the polyethylene-2,6-naphthalate film of the present invention refers to a biaxially oriented film using such polyester as a starting material, and in particular to obtain a film of the present invention having high strength in the longitudinal and transverse directions. The following method is preferably adopted for:

That is, usually, polyester is extruded into a sheet form from an extruder at 280 to 320 ° C., rapidly cooled to 90 ° C. or less to form a substantially amorphous sheet, and biaxially stretched longitudinally and transversely or simultaneously biaxially. In this case, the longitudinal and transverse stretching ratios can be set to high ratios, for example, 3.5 times or more, respectively.
Stretching may be performed again in each direction at a temperature of 0 to 180 ° C.

In this case, each stretching may be performed in multiple stages, or a heat treatment or the like may be added during the stretching. In any case, the film of the present invention contains 180 ° C. or more 26 ° C. or more in order to keep the heat shrinkage rate small.
It is preferable to perform heat treatment in the temperature range of 0 ° C. or lower for 0.1 to 10 seconds.

In the present invention, the sum of the F-5 values in the machine direction and the transverse direction of the film thus obtained must be 25 kg / mm ² or more, preferably 30 kg / mm ² or more, more preferably It is 35 kg / mm ² or more. If this value is less than 25 kg / mm ² , the dimensional stability against external force is poor and it becomes unsuitable for a magnetic recording medium that requires particularly high precision. In the present invention, even if the sum of the F-5 values in the vertical direction and the horizontal direction is in the range, the F-5 value in the vertical direction is 13 kg.
/ mm ² or more, and F-5 value in the transverse direction is preferably at 12 kg / mm ² or more.

In the present invention, by blending the specific particles in the polyester film, a film having excellent scratch resistance and abrasion resistance, particularly suitable for use as a magnetic recording medium, is obtained. The Mohs hardness should be 8 or more and the average particle size should be 5 μm or less, and the compounding amount thereof should be 0.01 to 5% by weight.

Specific examples of the inorganic particles having a Mohs hardness of 8 or more that can be used in the present invention include aluminum oxide, silicon carbide, vanadium carbide, titanium carbide, boron carbide, tungsten boride, boron nitride, and the like. Among them, aluminum oxide, silicon carbide, and aluminum oxide, which are industrially easily available, are preferably used.

When a small amount of these particles having a high Mohs hardness are present in the film, the scratch resistance and abrasion resistance of the film are remarkably increased. However, when the amount is less than 0.01% by weight with respect to the polyester film, or the Mohs hardness is less than 8, especially less than 6, the effect is drastically reduced. Even if particles having a Mohs hardness of 8 or more are present in an amount of more than 5% by weight, scratch resistance and abrasion resistance are not improved any more, and coarse projections frequently occur, which is preferable. Absent. A particularly preferred range is 0.05 to 3% by weight, especially 0.1 to 0.8% by weight.

The average particle size of such particles used in the present invention is 5 μm or less, preferably 1 μm or less, and particularly preferably 0.5 μm or less.
μm or less. If this value exceeds 5 μm, the particles often peel off from the surface of the film to deteriorate wear resistance, and the surface protrusions become too large. For example, in magnetic recording applications, so-called spacing is used. The loss becomes large and the electromagnetic characteristics deteriorate.

More specifically, particles that can be particularly preferably used in the present invention include, for example, so-called thermal decomposition aluminum oxide. This particle is usually
It is produced by flame hydrolysis using anhydrous aluminum chloride as a raw material, and its particle size is about 0.01 to 0.1 μm. Further, in the present invention, aluminum oxide particles obtained by a hydrolysis method of alkoxide can also be preferably used. in this case,
Usually, Al (OC ₃ H ₇ ) ₃ or Al (OC ₄ H ₉ ) ₃ is used as a starting material, and the hydrolysis conditions are appropriately selected to obtain fine particles of 1 μm or less. Of course, in this case, an acid was added to the synthesized slurry to obtain a transparent sol, and then the sol was gelled,
It is also possible to employ a method such as heating to 500 ° C. or higher to obtain a sintered body.

Alternatively, the aluminum oxide fine powder obtained by another method, that is, by adding methyl acetate or ethyl acetate to a sodium aluminate solution and stirring to obtain AlOOH, and then heating this may be used. In any case, aluminum oxide having an average particle diameter of 1 μm or less is particularly preferably used in the present invention.

In the present invention, it is preferable to completely disperse the aluminum oxide particles up to the primary particles before use, but it may be a little aggregate and behave as the secondary particles as long as the surface condition of the film is not adversely affected. However, even in this case, the apparent average particle size is 1 μm or less, particularly 0.1 μm.
The following are preferably used. In these cases, a part of aluminum oxide, for example, less than 30% by weight is Si, Ti, Fe, N.
It does not matter even if it is substituted with an oxide such as a, K.

In order to produce a film having excellent mechanical strength of the present invention, it is necessary to highly stretch by utilizing the peripheral speed difference between the rolls in the machine direction, but in this case, it is often the case that the contact with the roll is made. The film is scratched. However, by blending specific particles having high Mohs hardness, this is remarkably reduced. Due to the presence of such particles, excellent effects are obtained in terms of scratch resistance and abrasion resistance even when the film comes into contact with another substrate.

In the present invention, such an inorganic particle may be used in combination with a particle inert to another polyester. Such inert particles are used to further improve the running property and abrasion resistance of the film as necessary, but either so-called additive particles or precipitated particles may be used, or both may be used in combination. May be. However, in any case, the average particle size is larger than the average particle size of Mohs hardness of 8 or more, and the Mohs hardness is preferably less than 8, preferably 5 or less. This is because it is desirable that the particles forming relatively large protrusions on the film surface, which have a high probability of coming into contact with the substrate, have low hardness. If these requirements are not met, the film often causes catastrophic wear to the substrate.

Specific examples of such particles that can be used in combination include chaos,
Inorganic particles such as talc, carbon, molybdenum sulfide, gypsum, rock salt, calcium carbonate, barium sulfate, lithium fluoride, calcium fluoride, zeolite, and calcium phosphate can be mentioned, but calcium carbonate is mainly used from the viewpoint of dispersibility in polyester. , Barium sulfate, zeolite, and calcium phosphate are preferably used.

In addition to these, heat-resistant polymer fine powder can be used. Examples of curved polymer fine particles include, for example, those described in Japanese Patent Publication No. 59-5216.
A copolymer of a monovinyl compound having only one lipid group unsaturated bond in the molecule and a compound having two or more lipid group unsaturated bonds in the molecule as a crosslinking agent can be exemplified. However, of course, it is not limited to these, and for example, use of fine powder of a thermosetting phenol resin, a thermosetting epoxy resin, a thermosetting urea resin, a benzoguanamine resin or a fluorine resin such as polytetrafluoroethylene. You can also In addition to the above particles, precipitated particles can also be used. The deposited particles are those in which a metal compound is deposited as fine particles in the polyester production process, and for example, an alkali metal compound or an alkaline earth metal compound is present before or after the transesterification reaction or the esterification reaction, The particles are precipitated in the presence or absence of a phosphorus compound as particles of about 0.1 to 3 μm.

When such particles are used in combination in the present invention, the blending amount with respect to the polyester film is preferably 0.05 to 2% by weight. If the amount is less than 0.05% by weight, the running property and wear resistance are not so improved, and if it exceeds 2% by weight, coarse protrusions are often formed.

As described above in detail, according to the present invention, the F-5 in the vertical direction and the horizontal direction is used.
In a polyethylene-2,6-naphthalate film having a sum of values of 25 kg / mm ² or more, the greatest feature is the presence of particles in a specific range, but at the same time, the amount of oligomer contained in the film is 0.5% by weight. When it is at most%, it can be suitably used for various applications including high density magnetic recording.

To this end, it is necessary to subject the polyethylene-2,6-naphthalate to be subjected to film formation to a thermal crystallization treatment in advance to reduce the content of oligomers and to add a device such as shortening the melting time during film formation. is there. Of course, as one form of thermal crystallization treatment, a so-called solid-phase polymerization method is adopted in which a prepolymer having an intrinsic viscosity of about 0.3 to 0.6 is heat-treated at 210 to 260 ° C. under reduced pressure or under an inert gas flow to increase the degree of polymerization. You can also do it.

The presence of oligomers on the film surface often impairs scratch resistance and abrasion resistance, but the method of allowing particles having a specific hardness to be present as in the present invention can maintain these properties to a higher degree. it can.

The amount of the oligomer is 0.5% by weight or less, preferably 0.3% by weight or less, more preferably 0.1% by weight or less.

〔Example〕

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples as long as the gist thereof is not exceeded. In the present invention and comparative examples, "part" means "part by weight".

The measuring method used in the present invention is as follows.

(1) Average particle size Measure the particle size with a microscope and calculate the equivalent volume of 50 equivalent volume.
The particle size (diameter) at the point of% is the average particle size.

(2) F-5 Stress at 5% elongation, expressed in kg / mm ² , and the measurement was performed using an Instron tensile tester.

The length of the film in the machine direction is 150m from the biaxially stretched film
Cut out 5 sample pieces with a length of 6.25 mm in the horizontal direction,
A tensile test was conducted at a pulling speed of 50 mm / mm, a gripping interval, and a gauge interval of 50 mm.

The load at 5% elongation was read from the obtained S-S curve, F-5 value was calculated according to the following equation, and the average value of 5 points was obtained.

(3) Runnability It was evaluated by the slip property of the film. The slidability was measured using the apparatus shown in FIG. That is, the film is wound around a fixed hard chrome-plated metal roll (diameter 6 mm) at an angle of 135 °, that is, 2.356 rad (θ), and a load of 53 g (T ₂ ) is applied to one end to run it at a speed of 1 m / mm. , And the resistance force (T ₁ .g) at the other end was measured, and the friction coefficient (μd) during running was determined by the following formula.

(4) Scratch resistance It was evaluated by two methods. One is the degree of scratches on the film surface by the roll during longitudinal stretching, and the film surface was observed and divided into the following three stages.

Rank 1: Scratches often occur.

Rank 2: Almost no scratches occur.

Rank 3: No scratches occur.

A magnetic layer was applied to the film, and the scratch resistance when the film surface after application was brought into contact with a metal pin was evaluated to evaluate scratch resistance.

For this purpose, a magnetic tape was first produced. That is, the following magnetic paint was applied to a polyester film, and a magnetic layer was formed so that the film thickness after drying was 2 μm. That is, 200 parts of magnetic fine powder, 30 parts of polyurethane resin, 10 parts of nitrocellulose, 10 parts of vinyl chloride-vinyl acetate copolymer, 5 parts of lecithin, 100 parts of cyclohexanone, 100 parts of methyl isobutyl ketone and 300 parts of methyl ethyl ketone were mixed with a ball mill. After mixing and dispersing for 5 hours, 5 parts of a polyisocyanate compound was added to form a magnetic paint, which was applied to a polyester film, magnetically oriented before the paint was sufficiently dried and solidified, and then dried. Further, this coated film was surface-treated with a super calendar and slit into a 1/2 inch width to obtain a video tape.

Next, the magnetic tape is attached to a hard chrome plated metal pin (diameter 6
mm, surface roughness 3S) wrap angle 135 °, tension 50g
And was rubbed at a running speed of 4 m / sec.

Next, aluminum was vapor-deposited on the rubbing surface of the magnetic tape, and the degree of scratches was visually judged and divided into the following 5 ranks.

Rank 1: There are many scratches and often deep scratches.

Rank 2: There are relatively many scratches and some deep scratches.

Rank 3: The degree of scratches is relatively small and the deep scratches are slight.

Rank 4; Slightly scratched but satisfactory level Rank 5: Almost no scratches.

(5) Abrasion resistance Using the device shown in Fig. 2, the film was run for 200 m, and the amount of white powder adhering to the fixing pin was visually judged, and the abrasion resistance rank was A (the amount of adhering was extremely small and excellent. 3) from C) to C (having a large amount of adhesion and poor practicability).

(6) Electromagnetic characteristics The electromagnetic characteristics of the above magnetic tape are NV-370 manufactured by Matsushita Electric Industrial Co., Ltd.
It measured using the 0 type video deck.

VTR head output The VTR head output at a measurement frequency of 4 MHz was measured with a synchroscope, and the blank was set to 0 decibels and the relative value was displayed in decibels.

A videotape recording a signal with a dropout number of 4.4 MHz was played back, and the dropout number was measured with a dropout counter of Okura Industry Co., Ltd. for about 20 minutes and converted into the number of dropouts per minute.

(7) Amount of Oligomer The film was made into strips of about 5 mm × 3 cm, extracted with chloroform using a Soxhlet extractor for 24 hours, and the weight of the obtained oligomer with respect to the original film was calculated.

Example 1 100 parts of dimethyl 2,6-naphthalenedicarboxylate, 60 parts of ethylene glycol and 0.09 part of magnesium acetate tetrahydrate were placed in a reactor, heated and heated, and methanol was distilled off to carry out a transesterification reaction.

Next, after adding 0.40 part of aluminum oxide having an average particle size of 0.25 μm, 0.03 part of phosphoric acid and 0.04 part of antimony trioxide were added and polycondensation reaction was carried out by a conventional method to obtain polyethylene-2,6-naphthalate having an intrinsic viscosity of 0.60. It was

Then, the obtained polymer is subjected to solid-state polymerization at 0.3 mmHg and 235 ° C. for 7 hours to obtain a polymer having an intrinsic viscosity of 0.68, which is extruded into a sheet shape at 295 ° C. from an extruder and an amorphous sheet having a thickness of 110 μm by the electrostatic cooling method Got Next, by utilizing the peripheral speed difference of the rotating roll, the film was stretched 3.8 times in the longitudinal direction and 3.5 times in the transverse direction with a tenter, and heat-treated at 220 ° C. for 5 seconds to obtain a biaxially oriented film having a thickness of 8 μm.

Then, the obtained film was coated with a magnetic layer to produce a magnetic tape.

The properties of these films and magnetic tapes are shown in Table 1 together with those of other examples and comparative examples.

Example 2 A polyethylene-2 was prepared in the same manner as in Example 1 except that the particles contained in the film in Example 1 were changed as shown in Table 1.
A 6-naphthalate film was obtained, and then a magnetic tape was obtained.

Example 3 In the same manner as in Example 1 except that the particles contained in the film in Example 1 were changed to silicon carbide as shown in Table 1, and after longitudinal and transverse stretching, 1.15 times re-stretching was performed in the longitudinal direction. To obtain a film, and then evaluated as a magnetic tape.

Comparative Examples 1, 3 and 4 Films and magnetic tapes were produced in the same manner as in Example 1 except that the particles contained in the film in Example 1 were changed as shown in Table 1.

Comparative Example 2 A polymer having an intrinsic viscosity of 0.60 was obtained by changing the particles blended with the polymer in Example 1 to calcium carbonate as shown in Table 1 and without performing solid phase polymerization.

Then, a film was formed in the same manner as in Example 3 to obtain a biaxially oriented polyethylene-2,6-naphthalate film, which was further formed into a magnetic tape.

The films of Examples 1 to 3 satisfying the requirements of the invention are excellent in scratch resistance and abrasion resistance, and have favorable characteristics in terms of mechanical characteristics and the amount of contained oligomers.

On the other hand, Comparative Example 1 is an example in which calcium carbonate having a Mohs hardness of 3 is blended, but it is inferior in scratch resistance and abrasion resistance, and the characteristics when used as a magnetic tape are also insufficient.

Comparative Example 2 is an example of a film having more excellent mechanical properties. In this case, scratches are more likely to occur than in film formation, but improvement in this point cannot be achieved by blending calcium carbonate particles.

Comparative Examples 3 and 4 are examples to show that even particles having a Mohs hardness of 8 or more have appropriate particle diameters and concentration ranges.

(Effects of the Invention) As described in detail above, the polyethylene-2,6-naphthalate film of the present invention has achieved scratch resistance and wear resistance improvement that could not be achieved in the past with simple dimensions. Therefore, in combination with its excellent mechanical properties and low content of oligomers, it can be suitably used as a base film for various applications, especially a magnetic recording medium.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a running system for evaluating the coefficient of dynamic friction between a film and a metal. In the figure, (I) is a 6 mmφ hard chrome plated fixing pin, (II) is an entrance tension meter,
(III) shows an outlet tension meter, and θ is 135 °. FIG. 2 is a schematic diagram showing a running system for evaluating the abrasion resistance of the film. In the figure, (IV) is a 6 mmφ fixed pin made of hard chrome, (V) is a tension meter, and θ is 135 °. Is.

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Claims (1)

[Claims] 1. Inorganic particles having a Mohs hardness of 8 or more and an average particle size of 5 μm or less are contained in an amount of 0.01 to 5% by weight, the sum of the F-5 values in the longitudinal direction and the transverse direction is 25 kg / mm ² or more, and the oligomer content is But
Biaxially oriented polyethylene-2,6-naphthalate film, characterized in that it is 0.5% by weight or less.