JPS5967018A - Preparation for polyester film - Google Patents

Abstract

PURPOSE:To contrive to raise productivity by increasing the ratio of stretching by such an arrangement wherein after a film which is prepared by melting and extruding polyester is stretched in one axial direction, it is further stretched by the second stage of operation at higher temperature, and next, it is stretched in the direction perpendicular to the previous direction and then fixed. CONSTITUTION:An amorphous non-stretched film is prepared by melting and extruding polyester containing less than 0.10wt% of infusible particles, and this film is stretched by the first stage in one axial direction until its double refractive index becomes 15X10<-3>-30X10<-3> and then it is heat-treated at such temperature higher than that of the first stage stretching so that its degree of crystallization becomes 2-15%, and after that it is further stretched by the second stage in the same direction as previous one until its double refractive index becomes higher than 80X10<-3>, and after that, it is stretched in the direction perpendicular to the previous direction and it is thermally fixed. Thermal fixation is normally carried out at 180-245 deg.C, and by this, stretching distortion of the film is removed and crystallization progresses. Thereby, it becomes possible to form a smooth film from polyeser which substantially doesn't contain infusible particles. Since projections of this film are composed of polyester itself, the film is excellent in wear resistibility.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides video magnetic tape, magnetic video disk,
The present invention relates to a polyester film suitable for magnetic recording material applications such as floppy disks.

Specifically, it has much better %H and %H characteristics than conventional products.

Alternatively, β-1 is applied to a polyester film which provides a magnetic recording medium capable of recording at higher density.

In recent years, there has been a remarkable increase in the recording density of magnetic recording media, and it is hoped that even higher recording densities will be achieved in the future.

Currently, the most promising method is to use, for example, a so-called evaporation type magnetic recording medium in which a single thin metal support layer is formed on a base film.

Such a high-density recording type magnetic recording medium has a high recording density (I see, it is necessary to reduce the thickness of the magnetic layer by 2 times, so
Along with L, it becomes necessary to modify the surface of the base film.

Similar to conventional magnetic tapes, these magnetic recording media usually undergo biaxial stretching and heat treatment because of their good heat resistance, mechanical strength, excellent weather resistance, and relatively low cost. Various problems exist when a fixed polyethylene terephthalate film is expected to be used as a substrate film or is actually applied.

One of these is that when the thickness of the magnetic layer of a magnetic tape becomes thinner, the irregularities on the surface of the base film are reflected in the irregularities on the surface of the magnetic layer more than in the past. And the unevenness on the surface of the magnetic layer is
The performance of a magnetic recording medium is determined by its electromagnetic properties (e.g. output,
envelope, 5lIJ ratio, dropout, etc.).

For this reason, the surface of the polyethylene terephthalate base film needs to be as flat as possible in order to improve the output of electromagnetic characteristics, the 5ELL ratio, etc. In order to maintain running performance, there must be a certain degree of IJ convexity. In other words, two mutually exclusive characteristics are required: on the one hand, flatness is achieved by reducing the height of the protrusions, and on the other hand, smoothness of the magnetic surface is achieved by providing the protrusions.

In addition, in order to keep the output constant, the protrusions on the film surface must be
It is necessary that their height and distribution be uniform and that they be present as densely as possible. Furthermore, since dropouts significantly reduce image quality, preventing dropouts is also an essential condition for maintaining the performance of magnetic tapes. One of the causes of dropouts is the presence of protrusions due to coarse foreign matter among the protrusions on the surface, or poor running performance between the magnetic layer and the head, resulting in stick-slip and scratches or wrinkles on the magnetic layer. This is for the sake of In addition, due to the poor wear resistance of the π-body film, the non-magnetic surface is scratched due to vibration isolation with guide rolls, etc., and the scraped powder adheres to the surface of the magnetic layer and causes damage between the surface of the magnetic layer and the magnetic head. Spacing loss can also be cited as a cause of dropouts. From the above, the base film must be flat and smooth, free of coarse foreign matter in the protrusions (and have excellent abrasion resistance against guide pins, etc.).

On the other hand, polyester film must satisfy various conditions not only at the stage where it is used as a magnetic tape, but also at each stage of the film forming process and magnetic recording body manufacturing process. It is necessary for each process to have good running properties.In other words, if the running properties of the polyester base film are poor, the film will be scratched or wrinkled and lose its value as a product.Also, in the magnetic recording material manufacturing process However, abrasion resistance is required.In this way, the requirements for the base film are wide-ranging.It is true that these requirements have existed to some extent in magnetic tapes to this day, but they are especially difficult to meet now. When producing diluted, higher-grade magnetic tapes and sieve-rich magnetic tapes, they are subject to harsher requirements than ever before.Moreover, all of these characteristics are It is necessary to be satisfied, and if even one of them is bad, there is a lot of criticism.

Various methods have been tried to date to produce polyethylene terephthalate films meeting these required properties, but no satisfactory method has yet been found. This is because if you try to satisfy one required characteristic, another! This is because the P1 nature is sacrificed.

For example, conventionally, in order to impart runnability, that is, slipperiness, to a polyester base film, a method has been adopted in which externally added particles or internally precipitated particles are included. Among these methods, the method of incorporating externally added particles is advantageous in that it is possible to thicken the protrusion density by increasing the number of particles, but it is extremely difficult to make uniform fine particles without coarse particles. Z). In other words, in order to turn the coarse powder obtained as a raw material into the desired fine particles, a process of crushing and classification is required.
Moreover, it is difficult to produce fine powder with a completely uniform particle size.

Further, as the particle size is decreased, it becomes easier to form aggregated secondary particles due to poor dispersibility, which causes coarse foreign matter.

Although these coarse foreign substances can be removed to some extent by strengthening the filter during film formation, in this case the filter life is extremely reduced and productivity is reduced. On the other hand, even if a fine powder with a uniform particle size is obtained by crushing and classifying particles, when the number of protrusions on the film surface is increased to a high density, the protrusions do not overlap and are distributed with the same taste. That is difficult. Since these protrusions on the film surface are mostly inorganic particles or similar particles, they are not compatible with the polymer (voids are formed around the particles during stretching, resulting in poor abrasion resistance). worsens,
This causes various inconveniences such as causing dropouts.

On the other hand, in the internally precipitated particle method (in other words, particles are precipitated during polymerization. The particle size, particle amount, particle composition, etc. of the precipitated particles are controlled by the amount and type of catalysts and additives added at that time. However, they cannot be controlled independently.For example, if you increase the particle size, the particle size becomes too large, or conversely, if you try to make uniform fine particles, the particle amount decreases, and all the properties change. A happy occasion that satisfies this has not yet been found.

However, unlike the method of providing protrusions on the film surface using particles as described above, a method of forming protrusions on the film surface by crystallizing the film surface is also known.

For example, as one method, a method has been proposed in which an unstretched film is crystallized using a solvent, steam, etc., and then stretched. However, since this method stretches a crystallized unstretched film, stretching unevenness is likely to occur during the stretching process.
There are drawbacks such as poor stretchability, such as increased thickness unevenness of the film and a tendency to break during stretching.

Further, when crystallized using a solvent or steam, the particle size is relatively large and the density is low, making it difficult to apply uniformly and not suitable for use in flat and smooth films. Moreover, if this treatment is to be carried out in the process, it is necessary to incorporate equipment for solvent treatment etc. into the film manufacturing process before stretching, which reduces productivity and increases costs. It has various drawbacks such as problems.

In order to improve these, a method is also known in which an amorphous unstretched film is heat-treated within a crystallization induction period so that crystals do not form in the unstretched state and are crystallized in the subsequent stretching process ( JP-A-30-7+&7f). However, in this case, although the stretching unevenness and breakage are significantly improved, it is necessary to bring the film into contact with a roll at a high temperature of, for example, /20-/30°C for several seconds or more for heat treatment. Bringing an unstretched amorphous film into contact with such a high-temperature roll tends to cause adhesion and accompanying scratches, adhesion spots, etc., and there is a risk that the film properties as a magnetic tape may be deteriorated.

The object of the present invention is to provide a method for producing a polyester film having a flat surface and good running properties by crystallizing the film surface, which improves the above-mentioned drawbacks.

According to the invention, at most 0.10 weight [%
A polyester containing only 10% polyester is melt-extruded to form an amorphous unstretched film, which has a birefringence of /! in the stretching direction.
x/Q-3 to 30X10" - 1st stage stretching in the axial direction, and then the first stage stretching so that the crystallinity is 2 to 1%.
After heat treatment at a higher temperature than the stage stretching, the second stage stretching is performed in the same direction as before until the birefringence reaches 10x10-3 or more, and then the surface properties are improved by heat setting after stretching in the 1a corner direction. An excellent biaxially oriented polyester film can be produced.

To explain the non-invention in more detail, the polyester referred to in the present invention includes aromatic dicarboxylic acids such as prephthalic acid, naphthalene, Otsu-dicarboxylic acid, etc., ethylene glycol, detramethylene glycol, It is a polymer that can be obtained by polycondensation with an aliphatic glycol such as neopentyl glycol. Typical examples of such polymers include polyethylene terephthalate and polyethylene-,2,6-Natsuta/dicarpoxylate. In addition to the homopolymer, the polymer may be copolymerized with other aromatic and aliphatic dicarboxylic acids, diols, etc., to the extent that the crystallinity is not reduced, that is, the molar ratio is below 1O. In particular, it is preferable to copolymerize a small amount of polyalkylene glycol with a high molecular weight to promote crystallization. It is also possible to mix other polymers, such as polyamides, polyolefins, polycarbonates, etc., in amounts below the IQ weight factor. However, the crystallinity decreases greatly due to mixing,
The surface roughness of the resulting film must not be too rough.

Preferred polyesters used in the method of the present invention are:
Polyethylene terephthalate, especially polyethylene terephthalate, of which 9 or more moles are composed of ethylene terephthalate units.

In the method of the present invention, the surface characteristics of the film are modified by crystallizing the surface of the film, so there is no need for the polyester raw material to contain insoluble particles that would cause irregularities on the film surface.

Rather, the effects of the present invention are more pronounced when the raw material is polyester that contains substantially no insoluble particles, or even if it does contain only a small amount of insoluble particles. Therefore, in the method of the present invention, it is preferable to use polyester as a raw material which does not substantially contain insoluble particles, and if it contains insoluble particles,
The amount should be less than 0.10 parts by weight, preferably less than 0.07 parts by weight. Furthermore, the insoluble particles must be substantially free of coarse particles. Even if the amount of coarse particles is small, they protrude from the film surface and impair the uniformity of the surface, and also cause dropouts when used as a magnetic tape. Therefore, the insoluble particles in the raw material polyester must be minute, and it is preferable that substantially no particles with a maximum diameter of 78 or more are observed when the film is formed and observed under an optical microscope. Preferred polyesters containing insoluble particles include only fine insoluble particles precipitated during the polyester manufacturing process.

In the method of the present invention, the polyester as described above is melt-extruded from an extruder in a conventional manner and solidified to form an amorphous unstretched film. At this time, it is preferable to employ a so-called electrostatic adhesion method, that is, a method in which a molten film is charged and adhered to a cooling roll. Note that if the polyester has a high specific resistance when melted, it is difficult to apply the silent whistle method or the close contact method well, so it is preferable to use a polyester whose specific resistance when melted is jX/O'' or less.

The unstretched film is first stretched in one direction, usually in the longitudinal direction (seventh stage stretching). This stretching has a birefringence index of 1 in the stretching direction.
It is necessary to perform the test so that the ratio is 6×IQ-3 to 30X/Q-3. By causing the film to be oriented so as to have a birefringence within this range in the first stage stretching, the film will not stick to the roll even if it is brought into contact with a high temperature roll in the next heat treatment step. Further, crystallization proceeds rapidly and, for reasons that are not clear, ultimately provides a biaxially stretched film with excellent surface properties. Brush/stretching is usually carried out at go-ios°C, preferably at -5°C. Since unstretched films tend to stick to rolls, it is safe to carry out the first stage stretching at a relatively low temperature, depending on the material of the rolls.

The film that has undergone the seventh stage stretching is then heat-treated at a higher temperature than the seventh stage stretching to achieve a crystallinity of λ~no! Crystallization is allowed to proceed so that the amount of carbon dioxide is reduced, preferably 5 to 10%. If the degree of crystallinity is too low, the surface properties of the final film will be poor, while if crystallization progresses too much, subsequent stretching will become difficult. During heat treatment, the birefringence becomes 5 at the same time as crystallization.
It is preferable to relax the orientation so that it decreases by at least %.

This facilitates the second-stage stretching and increases the second-stage stretching ratio. Preferably birefringence is 70%
The orientation is relaxed so as to reduce the amount by more than 100%. Heat treatment beam 0~
The film is preferably heated at 0° C., preferably at 0° C., preferably by bringing the film into contact with a heating roll or by heating it with an infrared heater.

The heat-treated film is stretched in the same direction as the seventh stage stretching (second stage stretching), then stretched in a direction perpendicular to this, and then heat set to form a biaxially stretched film. The second stage stretching is performed until the birefringence index in the stretching direction becomes OX/0-3 or more. The stretching temperature is usually 100~/2J'C1, preferably ioo~iiz℃, and the stretching ratio is usually i,3
-~3.0, preferably i3-λ,j. Generally, at high temperatures and high magnification, protrusions are likely to be formed due to surface crystallization.

The film that has undergone the second stage stretching is then stretched in a direction perpendicular to the first stage stretching. This stretching is also usually at ioo~/60°C, preferably /20-/4tO°C, and usually at λ, j-
The stretching ratio should be 3.0 to 0, preferably 3.0 to 0.

The biaxially stretched film as described above is heat-set by a conventional method to obtain a biaxially stretched polyester film. Heat fixation is usually /Il′θ~241! C., thereby removing stretching strain from the film and promoting crystallization.

According to the method of the present invention, a flat and smooth film can be easily produced from polyester containing substantially or almost no insoluble particles.

Moreover, since the protrusions of the film are formed from polyester itself, the film has extremely excellent abrasion resistance.

The biaxially stretched polyester film obtained by the method of the present invention usually has an average protrusion height of 0.0/jμ or less on its surface, and is suitable as a base film for a magnetic recording medium. For example, those with a relatively large average protrusion height are suitable for coating-type high-density recording base films using pure iron or alloy powder, and those with a small average protrusion height are particularly suitable for o,
A film having a diameter of oorμ or less is suitable for a base film for vapor-deposited high-density recording. Preferable methods for forming the magnetic layer include, for example, vacuum deposition, sputtering, and ion blasting. Further, as the ferromagnetic metal material -C, iron, cobalt, nickel, or a metal thereof is preferably used.

Products equipped with these magnetic recording layers include magnetic tape,
Examples include floppy disks and video disks.

Hereinafter, methods for measuring each physical property value used in this specification will be explained.

(1) Amount of insoluble particles in polyester 0-chlorophenol/Ql per 100 g of polyester
Add and heat at 120°C for 3 hours. Next, using an ultracentrifuge L3-50 manufactured by Peckman, 3o, ooorpi
Centrifugation was performed at n for 0 min, and the resulting particles were
Vacuum dry at o°C. When the particles are measured using a running differential calorimeter, if a melting peak corresponding to the polymer is observed, 0-chlorophenol is added to the particles, and after heating and cooling, the centrifugation operation is performed again. The number of particles at which no melting peak is observed is defined as the amount of insoluble particles in the polyester. Usually, two centrifugation operations are sufficient.

(2) The amount of wear attached to the wear-resistant A-quality ROM fixing pin was visually evaluated. The film speed is 1 OrnA higher, and the tension is approximately z
oog θ=lJO”.

(3) Coefficient of friction of the film (
(dynamic/static) was measured.

(4) Crystallinity The density (ρ) of the film was measured at -ij''C using a density gradient position 7 of a mixed solvent of IA tetrachloride and normal hebutane, and calculated using the following formula.

where /33j and /4t4Z j are the densities of the completely amorphous polyester and the fully crystallized polyester, respectively.

(5) Average protrusion sieve size Using EiT-10 type thin film step measuring device manufactured by Small Plate Research Institute ■,
Vertical magnification! 00,000 times, horizontal times ¥, 200 times, stylus force 2 / yi
Sketch the cross-sectional curve with p5. The average projection height (Ra) was determined according to Tl5-BOAO/.

(6) Birefringence (Δn) Using a polarizing microscope manufactured by Carl Zeiss, the retardation was added by 1, and the birefringence (Δn) was determined by the following formula.

Δ n = − α R = Retardation d: Film thickness Example 1 700 parts of dimethyl terephthalate (parts by weight, hereinafter also referred to as parts by weight), 60 parts of ethylene glycol, and a monohydrate of calcium acetate. 0.09 part of the salt was placed in a reactor, and a transesterification reaction was carried out. The reaction was started when the internal temperature reached iso°C, and the temperature was raised to 200°C after 2 hours, and then to 230°C after another 2 hours.

After completion of the transesterification reaction, 106 parts of ethyl acid phosphate, 1 part of antisulfate trioxide, and 4 parts of antisulfate trioxide were added, and a polycondensation reaction was carried out according to a conventional method. That is, the reaction temperature is 1
The temperature was gradually raised from 230°C at the start of the reaction, and finally 2
1! 'C, while the pressure gradually decreases to 0.
, rHHg. After 5 hours, the reaction was stopped and the pressure in the system was restored, and then the polymer was extracted and used as a chip.

When the chimp haze of this chip was measured, it was 2%. Further, the needle containing insoluble particles was 0.02% by weight.

This chip was vacuum dried at 160° C. for 10 hours, then melted at 0° C., extruded from a T-die, and rapidly cooled to obtain an unstretched film.

This unstretched film was stretched using a longitudinal stretching apparatus shown in the GA diagram, and the resulting film was then laterally stretched and further heat-set to obtain a biaxially stretched polyester film. The processing conditions are as follows.

Process temperature c℃) Stretching ratio Birefringence
Crystallinity (%) 7th stage stretching,! '4'
/, 1 no! ×10-3 heat treatment /10 /
, 03 // x 10 x 2j th stage extension / /
0. 2. / /QQ×IQ-3 horizontal stretching /
30 3. 2.20 The first stage stretching is done between rolls j, j' and O, the heat treatment is done between rolls 7 and 2, and the second stage stretching is between rolls j, j' and lO. It was done in between.

The physical properties of the obtained biaxially stretched polyester film are shown in Table 1.

Comparative Example In the method of Example 1, the film was passed through roll 7.8' at room temperature without being stretched or heat treated, and the stretching ratio of the second stage stretching was 1.2 times, and the birefringence was /0.
A biaxially stretched polynisdel film was obtained in the same manner as in Example 1, except that the film was adjusted to 0.times.0.times.0.times.0.times.0-j. The physical properties of this film are shown in Table 1. Example λ A biaxially stretched polyester film was obtained in the same manner as in Example 1 except that the processing conditions were changed as shown below.3 The physical properties of this film are shown in Table 1. .

Process Temperature ('C) Stretch double curtain Birefringence Crystallinity (97th stage stretching 9u:t3.
2s×1o-3 heat treatment / / 0 /, 0.2
．． 2.2X10-” 10th λ stage stretching) 10
/, Ta 100xl□-4 horizontal stretching /30 3
．． Heat-set 2λO Comparative Example λ In the method of Example 1, the second-stage stretching and heat treatment were omitted, and after seven stages of longitudinal stretching, transverse stretching and heat-setting were performed to obtain biaxially stretched polyester 7.ilm. Vertical stretching is 16
℃, stretching ratios J and A, and horizontal stretching was 10! ℃ and a stretching ratio of 3.3@C, and heat setting was performed at 2.20℃. The birefringence index after A1 conventional stretching was lOg×l0-3. Table 1 shows the physical properties of this film.

Comparative Example 3 A biaxially stretched polyester film was obtained in the same manner as in Example 1, except that the processing conditions were changed as described below. The physical properties of this film are shown in Table/.

Process Temperature (°C) Stretching@Rate 1st stage stretching
/ J O /, 0 / No. 2 [Jonobu II
yo 3. b Transverse stretching 100 x heat setting +2+20 [7th stage stretching is performed with rolls 3 to g, 2nd stage stretching is performed between rolls, ri' and IQ, and heat treatment is omitted] Table 7 Summary of these results Then, it is as follows.

Example 1 compared to Comparative Example 2. ．． Samples No. 2 and Comparative Example 3 are good in that the coefficient of friction is reduced even though the average protrusion height is hardly increased. Very fine irregularities were observed on these surfaces. However, Comparative Example 3 had many surface defects due to adhesion and could not be used as a magnetic tape. On the other hand, in Comparative Example No. 1, the crystallinity before the final longitudinal stretching is low, so that the smoothing effect does not appear.

Furthermore, according to the present invention, the permissible stretching ratio can be increased while maintaining the film quality at the same or higher level, so productivity can be increased even if the extrusion speed of the unstretched film remains the same. .

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the film running system used to determine the abrasion resistance of the film. FIG. 2 shows a film longitudinal stretching device. door, j′, ri1
% 72/ and / , /λ are rolls and 13 is a heater. %German person Diafoil Co., Ltd. agent Patent attorney Yo Hase and 1 other person

Claims (1)

[Scope of Claims] (1) A polyester containing at most 0.10% by weight of insoluble particles and 14% is made into an amorphous unstretched film by melt extrusion, and this is made into an amorphous unstretched film with a birefringence of /! X10-
The seventh stage is uniaxially stretched to 3~30X10-3, and then heat treated at a higher temperature than the first stage so that the crystallinity is 2~13%, and then the birefringence is adjusted in the same direction as before. A method for producing a biaxially oriented polyester film, which comprises performing a second stage of stretching until the ratio reaches 10 x 10 -3 or more, then stretching in a direction perpendicular to the previous direction, and then heat setting. (2) The method according to claim 1, characterized in that the content of the insoluble polyester particles is at most 0.07% by weight. (3) Claim 1 or The method according to claim 2, characterized in that the insoluble particles in the polyester consist only of those produced in the polyester manufacturing process. (4) Any one of claims 1 to 3. In the method described above, the heat treatment after i/stage stretching is performed so that the degree of crystallinity becomes j-19%. (5) Any one of claims 1 to 7. In the method described in , the first stage stretching is 0~/0!'C
A method characterized by: (6) In the method according to any one of claims 1 to 5, the heat treatment after the seventh stage stretching is carried out at 20-1
! A method characterized in that it is carried out at θ°C. (7) In the method according to any one of claims 1 to 2, the second stage stretching is carried out at too-1.2j°C.
A method characterized by: (8) In the method according to any one of claims 1 to 7, heat fixation is carried out. ! 'A method characterized by being carried out in C.