JPS63161518A - Biaxially stretched polyester film for magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve flat slipperiness, multiple times of running performance and wear resistance by specifying the properties of a polyester film to a specific range and incorporating adequate particles therein. CONSTITUTION:The refractive index nalpha in the thickness direction of the film satisfies equation I and the number A (piece/mm<2>) per mm<2> of film surface area of the rugged units consisting of projections and recesses having at least >=0.5mum major axis with said projections as nuclei satisfies equation II. This film is formed by incorporating 0.05-1.0wt.% internal particles contg. a lithium element, calcium element and phosphorus element and 0.001-0.7wt.% inert external particles consisting of >=1 kinds selected from the oxide, org. salt and inorg. salt of calcium having 0.1-10.0mu average grain size therein. The intrinsic viscosity [eta] of the film and the crystallization temp. Tc300 in the cooling process thereof satisfy equation III. The flat slipperiness, multiple times of running performance and wear resistance are thereby improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention has excellent flatness and easy sliding properties, adhesion with the magnetic layer, and multi-running performance, and generates little white powder even when the guide portion is worn. The present invention also relates to a biaxially oriented polyester film which is particularly useful as a base film for magnetic recording media, which is resistant to scratches and has few coarse spots.

[Prior art and problems to be solved by the invention] Biaxially oriented polyester film has excellent heat resistance, mechanical properties, chemical resistance, etc., and has recently been used for magnetic recording media and for audio and video applications. Demand for magnetic sheets for magnetic tapes, floppies, etc. is rapidly increasing.

In recent years, these magnetic recording media have become increasingly high-quality and dense, and some have improved flatness and slipperiness of the base film, adhesion to the magnetic layer, and multi-run performance. It is requested. Furthermore, magnetic recording media are manufactured by applying a binder containing magnetic powder onto a base film using, for example, a combination of a coating roll and a doctor knife. Even when using a roll, friction and abrasion between the polyester film and the roll surface are severe, and the film's
The surface of the mold itself is scraped and a white powdery substance is deposited. Furthermore, white powder is generated in the calendering step in the magnetic tape production process, resulting in an increase in dropouts and a decrease in the B/N ratio. Furthermore, when a tape or sheet coated with the magnetic material is used for recording, recording, etc., friction and abrasion at the guide section may cause scratches on the film, white powder may be produced, and the stickiness may deteriorate after running many times. . In addition, there were problems such as eyebrows having many coarse spots, shortening the filter life during extrusion, and causing dropouts.

However, a base film that satisfies all of these characteristics has not yet been perfected, and there have been strong demands from film manufacturers.

[Means for solving problems]

The present inventor has developed a film that has improved wear resistance, scratch resistance (scratch resistance), and multi-time running performance while maintaining flatness and slipperiness and adhesion with the magnetic layer, and with less roughness. As a result of extensive research into the development of a polyester film, it was discovered that the above-mentioned problems could be solved by adjusting the physical properties of the polyester film to a certain range and mixing appropriate particles therein, and the present invention was achieved.

That is, the gist of the present invention is that the refractive index n, t in the thickness direction of the film satisfies the following formula 0, and the surface area of the film is a concavo-convex unit consisting of a protrusion and a depression whose major axis is at least O0S μm or more with the protrusion as the core. / ztiNumber A (pieces/mm2) satisfies the following formula 0, (a) lithium element,
The internal particles containing calcium element and phosphorus element are 0.
0! ~i, o weight cake and (b) average particle size O17μ~1
0.0μ of inert external particles consisting of one or more selected from calcium oxides, organic salts, and inorganic salts.
/~0.7 weight coefficient, and the polar E of the film
The biaxially stretched polyester film for magnetic recording media is characterized in that the limiting viscosity T7) and the crystallization temperature T3 (10) during the cooling process satisfy the following formula 0.

net≧81- ・・・・・・・・・・・・■
O≦A≦1zooo ・・・・・・・・・・・・
■T♂oo ≧-10 (7 (rH) + Colo 7...
. . . ■ The present invention will be explained in detail below. □
The polyester referred to in the present invention refers to a polyester composed of an aromatic dicarboxylic acid such as terephthalic acid, isophthalic acid, naphthalene-J, or 4-dicarboxylic acid or an ester thereof and a diol such as ethylene glycol, diethylene glycol, tetramethylene glycol, or neopentyl glycol. A crystalline aromatic polyester obtained by condensation.

The polyester can be obtained by direct polycondensation of aromatic dicarboxylic acid and glycol, or by polycondensation after transesterification of aromatic dicarboxylic acid dialkyl ester and glycol, or by polycondensation of aromatic dicarboxylic acid dialkyl ester and glycol. It can also be obtained by methods such as polycondensation of esters.

Typical examples of such polymers include polyethylene terephthalate, polyethylene-2,6-naphthalate,
Polytetramethylene terephthalate, polytetramethylene, 6-naphthalate, etc., such as polyethylene terephthalate, or polyethylene-2,6-naphthalate, etc.
Thale is terephthalic acid or 7-thalene-2,6-
Not only polyester in which dicarboxylic acid and ethylene glycol are bonded, but also ethylene terephthalate or ethylene-J, A-7 in which more than t0 molar units of the repeating unit are combined.
It is also possible for less than 10 moles of the repeating unit to be composed of another component, a repeating unit. In particular, it is preferable to copolymerize a polyalkylene glycol such as polyethylene glycol or polytetramethylene glycol as a diol component in order to improve the adhesion with the magnetic layer. When adding or mixing other polymers to polyester, it is necessary to add or mix other polymers within a range that does not essentially change the properties of the polyester. Polyester, polyolefin, polyamide, polycarbonate, other polyesters, etc. l! It can be added in a proportion less than % by weight.

In order to impart flatness and slipperiness to the film of the present invention, the refractive index n in the thickness direction of the film must satisfy the following formula 0,
Preferably, the surface area of the film should be 23 or more, and the film surface area of the unit of unevenness consisting of a protrusion and a depression with a major axis of at least 0.13 m or more with the protrusion as the core / xi number A (number of pieces / mm2) must satisfy the following formula 0.

To n≧μ tacho ・・・・・・・・・■O≦A≦
/! 000 ・・・・・・・・・・・・・・・
(2) A may be zero, but it is preferable that at least the uneven unit exists. On the other hand, if A exceeds 11,000, although the flatness is excellent, the slipperiness, especially the runnability during multiple runs, is poor, which is unsuitable.

Thus, a film that satisfies the above formulas (1) and (0) has better flatness and slipperiness than a film that does not satisfy the above conditions using the same raw material, is effective in reducing the amount of coarse particles, and is also effective in coating the magnetic layer. It has the effect of reducing the generation of white powder due to friction and abrasion with guide rolls in the process and friction and abrasion with guide bottles when used as a magnetic tape. However, it has been found that the degree of the effect varies depending on the raw materials used. Currently, there is a strong demand for higher density and higher quality magnetic recording media, and a) high-performance film is required.Among the films that satisfy the above formulas 1 and 0, the film has the highest performance characteristics. There was a pressing need to select raw materials.

In the present invention, raw materials are selected that satisfy the above-mentioned formulas (1) and (0) and also provide even higher performance characteristics.

As a raw material for polyester film, conventional methods include (1) a method of imitating a particle-containing polyester composition obtained by adding inert fine particles such as silica, titanium dioxide, kaolin, calcium carbonate, and barium sulfate during polymerization or at a high degree of polymerization; External particle addition method) ■ A method of forming a film from a particle-containing polyester composition obtained by precipitating part or all of the catalyst and color inhibitor used during polyester synthesis during the reaction process (
Many methods (internal particle generation method) have been proposed.

However, in the case of the external particle addition method, the kaolin normally used has flat particles, so the slipperiness cannot be improved even in a film that satisfies formulas (1) and 0 above. % Calendering tends to crush the particles and the slipperiness is extremely poor. In addition, titanium dioxide has little ability to form surface irregularities, and if it is contained in a sufficient amount, a large amount of white powder will be generated, making it suitable for cinema. Also, talc, calcium carbonate,
When using silica, etc., it is inevitable that coarse particles will come in, and coarsening due to agglomeration occurs during the pulverization and classification process to keep the average particle size constant. There are problems such as the problem of stupidity that causes problems and hinders production, and the problem of dropouts becoming apparent.

In this way, the external particle addition method caused the various problems mentioned above, making it extremely difficult to use it as a raw material.
As a result of intensive studies, we found that when a polyester composition containing internal particles containing lithium elements, calcium elements, and phosphorus elements was used to produce a film that satisfied the above formulas ① and 0, it was possible to improve flatness and smoothness and reduce coarse particles. It turned out to be extremely favorable. The content of lithium element in the internal particles is 0.0 j~! Weight%, calcium element is 0
．． 03-7% by weight, phosphorus element is 0. OJ to io weight % is preferred.

In this way, it was possible to obtain a film with excellent flatness and slipperiness, and a very small number of coarse particles, but the abrasion resistance was still insufficient.

As a result of further intensive studies in order to improve the abrasion resistance, even in films that satisfy formulas (1) and (2) above, a specific amount of fine internal particles made of a specific metal element and a specific amount of specific inert external particles were added. It has been found that the addition of these compounds improves the performance.

Among inorganic inert external particles, particles consisting of one or more types selected from calcium oxides, organic salts, and inorganic salts, such as C! AC! o.

CaC! 03, caso4, 0a (H, PO,)
, , 0aHPO4, Ca4(PO4)1, etc. particles with average particle diameters o, i - ro, oμ are 0.00/
-0.7% by weight in combination with the above-mentioned internally precipitated particles), it was found that a remarkable effect was produced. Although the reason is not clear, it is thought that it is distinguished from other particles by the fact that the particle diameter is close to that of a sphere and the particle hardness is appropriate. If the particle diameter of the particles exceeds 10.0 μm or the particle amount exceeds 0.7 μm, coarse particles become noticeable and are suitable for cine.

Also, the average particle size is 0. If the content is less than 0.00% by weight, the effect of reducing white powder generation, which is the objective of the present invention, will not be achieved and the O particles may be added before polyester polymerization. The mixture may be kneaded during the polymerization reaction, or may be kneaded in an extruder when pelletizing after the polymerization is completed. Furthermore, it may be added during melt extrusion into a sheet, dispersed in an extruder, and extruded.

However, as a result of further investigation, it was found that the improvement in wear resistance is proportional to the number of coarse particles in the inert outer particles. For this reason, if the number of inert external particles, especially coarse particles, is increased by one in order to improve wear resistance, the number of dropouts will increase, which will lead to a decrease in the S/N ratio. Therefore, an upper limit is set for the protrusions on the coarse side of the inert external particles, but since the particle size of the external particles generally has a distribution, it is necessary to suppress the content of the external particles themselves. As a result, it was found that although the wear resistance was improved, it was not sufficient. Therefore, a method of improving wear resistance that is completely independent of the addition of inert external particles has become desirable.

As a result of intensive studies to meet this demand, the present inventors found that the crystallization rate T, soo in the cooling process from melting of the film
It was discovered that a high value contributes to improved wear resistance. T, 106 is the intrinsic viscosity of the film (
q) Therefore, it is necessary to satisfy the following equation 0.

To3oo≧-/ 00 (7) 1247 -river-・
■Here, (7) is preferably 0. ! ! More than o
, tr or less. (q) is 0.1! In the following, the film will break frequently during film production, reducing productivity, and (2
) is 0.63 or more, it is not preferable because Tc'' is not too high and there is no improvement in abrasion resistance even if the above formula 0 is satisfied. This is thought to be because the polyester covering the protrusions crystallizes, resulting in higher film hardness and greater resistance to frictional force.

In this way, we have created a polyester film for magnetic recording media that has excellent smoothness, smoothness, adhesion, and multi-time running properties, minimizes the number of coarse protrusions that cause dropouts, and also has excellent abrasion resistance. I was able to create a film that satisfies all of the qualities I wanted.

There are various ways to increase Tc, but one known method is to change the type of phosphorus when forming internal particles6.Also, ionomers and metal salts of aliphatic α-acids are known. It is preferable to contain. It can also be achieved by copolymerizing polyalkylene glycol or by blending a copolymer. In any case, known methods for improving T;oo can be adopted, but methods that reduce the adhesion to the magnetic layer of the film or bleed out and become white powder are not recommended.
This is not preferred because it deteriorates the quality of the magnetic tape. Therefore, the most preferred method is to change the type of phosphorus and/or to include a metal salt or ionomer of a long-chain aliphatic α-acid. The most suitable type of phosphorus is trimethyl-7-osphae (TMP).

On the other hand, long-chain aliphatic α-acids have 10 carbon atoms.
~33 higher aliphatic monocarboxylic acids include acid, melisic acid, sognoceric acid, cerotic acid, montanic acid, hentriacontanic acid, heteroceric acid, oleic acid, erucic acid, linoleic acid, and acid mixtures containing these. It will be done. Among these, those having a carbon number of 1 to 33 are preferred, and more preferably 20 to 3 carbon atoms.

If the number of carbon atoms is less than 10, it is not preferable because bleed-out to the film surface is severe.

On the other hand, if it is 33 or more, the slipperiness of the film decreases, which is not preferable. The content is T. Since it is good as long as the amount is high, a very small amount is sufficient. Preferably 0. ooor~0.2 part by weight.

Generally film Tsu/EB to lower? The leather becomes too large. Therefore, it was surprisingly found that the scratch resistance was improved when the birefringence Δn of the Sifilm was brought closer to O by widening the film during heat fixation.

Up until now, it has been proposed to improve the scratch resistance by increasing the birefringence △n of the film, but this is unsatisfactory, especially in applications such as floppy disks, due to the large in-plane heterogeneity of the film. Met. On the other hand, △
It is an extremely desirable form that the scratch resistance is good even when n is set to zero.

Next, the Ha method of the polyester film of the present invention will be specifically explained, but the method of forming the film of the present invention is not limited to this example.

Internally precipitated particles and average particle size 0. /μ~/ A polymer resin containing inert external particles of one or more types selected from calcium oxides, organic salts, and inorganic salts of 0.0μ and, if necessary, a required amount of higher aliphatic monocarboxylic acids. , the mixed resin or the resin added during extrusion is dried (by a conventional method), melt-extruded through an extruder, and cooled and solidified on a rotating cooling drum to form an unstretched polyester sheet.

At this time, it is preferable to employ a known adhesion method such as electrostatic application cooling.

The thus obtained unstretched film is first stretched in the first axial direction, usually in the longitudinal direction, so that its birefringence becomes below o, or o, and then stretched in the direction perpendicular to the first axial direction at yooc~/~0°C. At a stretching temperature of 3. ! ~ri, 0 times preferably j, I-
jt, stretched 0 times to create a biaxially oriented film, and when heat-setting, loosening in the width direction by 7 to 10% while heating from 200°C to 2!
It is essential to keep lΔn below o, o r o at θ° C. in order to improve the flatness and slipperiness of the film and the adhesion with the magnetic layer.

In addition, it is also preferable to perform multi-stage stretching in the first axis direction in order to particularly improve thickness unevenness, and it is also preferable to apply super draw or near super draw stretching to increase the longitudinal stretching ratio.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the following Examples unless the gist thereof is exceeded.

The film physical properties were measured as follows.

(1) Coefficient of friction (μ) Fixed hard chrome plated metal roll (diameter 6ml+)
Then, the film is brought into contact with the wrapping angle /3r0(θ)%
! Apply a load of 39 (T2) to one end / m / mi
Let it run at the speed of x, and the resistance force at the other end ('r, C
f/')) was measured, and the coefficient of friction during running was determined using the following equation.

(2) Center line average surface roughness (Ra) It was determined as follows using a surface roughness measuring device manufactured by Koita Research Institute (sz-JFK). The tip radius of the stylus is 28 m, and the load is 30~. Cut out a part of standard length L (-2, jm) from the film cross-sectional curve in the direction of its center line,
When the roughness curve y = f (X) is expressed with the center line of this extracted portion as the X axis and the vertical magnification direction as the Y axis,
The value given and found by the following formula is expressed in μm. However, the cutoff value is 10 μm. For Ra, the average value of a total of io points, 3 points in the vertical direction and 3 points in the horizontal direction, was determined.

/L T fo I f('') l ax (3) Refractive index Jj''C using Atsube's refractometer (manufactured by Atago Co., Ltd.)
The value for the Na-D line measured in was determined.

(4) Number of concavo-convex units (propellers) with depressions around the protrusions (A) The surface of the 9 film was evaporated with aluminum using a Carl Zeiss differential interference microscope. Take a photo at 0x magnification,
Number A of unevenness units consisting of projections with a total film surface area of 1 and depressions with a major axis of at least 3 μm centered around the projections.
I counted (pieces/-).

(5) Number of coarse protrusions (L) Observe the folds of the film at a magnification of io under polarized light, mark the part that shines as a fisheye, and measure the height of the marked part using the three-beam method to determine the number of tertiary or higher projections. Sim 3!
The number of protrusions with a height of μ or more is measured per -200ctal and L! The number of coarse protrusions was set as above.

(6) Multi-rollability, abrasion resistance, scratch resistance A thin slit of film is hung on a winding chair, rubbed on a metal guide roll installed in the middle, and reciprocated at high speed for 20 times.
It was run 0 times.

The amount of white powder generated at this time was measured, and the wear resistance was ranked as follows.

Rank: Special grade: Very good grade 1 Good grade 2 Normal grade 3 Poor grade Extremely poor In addition, the scratch resistance on the film surface was observed in photographs, and the scratch resistance was ranked as follows.

Rank special grade Very good grade 1 Good grade 2 Normal grade 3 Bad Hiro grade Extremely bad (force) Intrinsic viscosity (V) Polymer l? with phenol/tetrachloroethane = zo
/lo (weight ratio) was dissolved in a mixed solvent of 100- and measured at 30°C.

(8) Tc Measured using DSCI-B-C manufactured by PernElmer. j
The sample from M7 Misaki was heated to 300℃ at 16℃/-.
At ℃! After standing for a minute, the temperature was lowered by 16° C./−, and the crystallization peak temperature at that time was defined as Tc.

Example/ (Method for producing polyester) 700 parts of dimethyl terephthalate, 70 parts of ethylene glycol, 0.10 parts of calcium acetate hydrate, and 0.17 parts of lithium acetate dihydrate were charged into a reactor, and while heating and raising the temperature, methanol was added. Distillation is carried out to carry out transesterification reaction, and after the start of the reaction, the temperature is reached to 230°C, which takes about 3 hours.
Transesterification was substantially completed.

This reaction product is then added with 0.0% trimethyl phosphate. J
After adding 0.01 part of antimony trioxide as a polycondensation catalyst, polymerization was carried out according to a conventional method to obtain a polyester. The polyester has a particle size of approximately o3~
A polyester obtained by adding uniform and fine calcium, lithium, and phosphorus elements of about 1 μm to triethyl 7-mole-7-ate was used as a material.

Separately, polyester B containing no internally precipitated particles or inert externally added particles was produced. On the other hand, as external particles in polyester B, calcium carbonate O, a weight i, with an average particle size of μ
A polyester C containing s was produced.

In addition, polyester D was produced in which polyester B contained a higher aliphatic α-acid having 30 carbon atoms and having triacontanoic acid as a main component.

(Film forming method) Polyester A% B, C! , D to A : B : C
:D=ro:3r:z:10, dried in a conventional manner, extruded at xrr''c and quenched to form an amorphous sheet.

The amorphous sheet was stretched 3.2 times at 100°C and Δn was 0.
0 F J at ♂℃/, 2 times stretched △n=
It was set to 0.042.

The longitudinally stretched film thus obtained was then stretched in a tenter for 1
Stretched in the transverse direction by J and P times at 170°C, and heat-set at 2/7°C while relaxing Ir in the width direction! ! A film of μ was obtained.

Example In Example 1, A:B:C:D=! O:ao:z:z
These examples were referred to as Examples.

Comparative Example 1 B%C in polyester: B:C=jO:1iLj
A film was formed in the same manner as in Example 1, except that the mixture was blended at a ratio of :j and without the thermal surface periodic relaxation treatment.

Comparative example λ Adding B and C to polyester: B:C=jO:ILtO
:A film was formed in the same manner as in Comparative Example 1 except that the mixture was blended at the ratio of IQ.

Comparative Example 3 Using the same raw materials as Comparative Example 1, longitudinal stretching temperature t t 'c
The film was formed at a stretching ratio of 3.7 times.

These results are shown in Table/.

The above is a comparison example with Comparative Example 3. Comparative Example/-J
It can be seen that it has excellent flatness and easy sliding properties and multi-cycle running properties.

Compared to Comparative Example 1, Comparative Example A has certainly improved abrasion resistance, but it is unsuitable as a base film for magnetic recording media because it has many coarse spots that cause dropouts.

On the other hand, Examples 1 and A are much better in abrasion resistance than Comparative Example λ, and there are very few coarse particles like those in Comparative Example A.

〔Effect of the invention〕

The film of the present invention is a film that has all the characteristics necessary for use in magnetic recording media, such as flatness and easy sliding properties, multiple running properties, abrasion resistance, and scratch resistance.

Claims (1)

[Claims] (1) The refractive index n_α in the thickness direction of the film is as follows [1]
The number A (pieces/mm^2) per 1 mm^2 of the film surface area of the unevenness unit that satisfies the formula and consists of a protrusion and a depression with a major axis of at least 0.5 μm with the protrusion as the core is as follows [2 ] formula, and (a) internal particles containing lithium element, calcium element, and phosphorus element are 0.05 to 1.0
(b) Contains 0.001 to 0.7 weight % of inert external particles consisting of one or more types selected from calcium oxides, organic salts, and inorganic salts with an average particle size of 0.1 μ to 10.0 μ. and the intrinsic viscosity [η] of the film and the crystallization temperature T^3^0^0_C during the cooling process are as follows [3]
A biaxially stretched polyester film for magnetic recording media, which satisfies the following formula: n_α≧1.492・・・・・・・・・・・・・・・［
1] 0≦A≦15000・・・・・・・・・・・・・・・
・[2]T^3^0^0_C≧-100[η]+267
......[3] (2) Film birefringence Δ
The biaxially stretched polyester film for magnetic recording media according to claim 1, wherein n is 0.015 or less.