JPH09314784A - Manufacture of composite film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a composite polyester film for a magnetic recording medium which has superior properties such as travelling after being converted as a magnetic tape, electromagnetic conversion, durability and adhesion with a magnetic layer and further, is highly productive. SOLUTION: An unstretched film consists of an A layer comprising a polyester containing dibasic acid and diol an main components and 2-7mol% dibasic acid and/or diol components as a copolymer component, and a B layer comprising thermoplastic resin containing 2mol% or less the copolymer components other than the main components, coextruded in, at least, two layers as a composite film. This composite film is stretched 3-5-fold lengthwise by a single or multiple stage operation using a roll at 80-150 deg.C of stretching temperature. In addition, the refractive index of the layer A after lengthwise stretching is set to 0.080 or less, while the refractive index of the layer B after lengthwise stretching is set to at least, 0.080. Further, the film is stretched 3.5-4.5-fold crosswise at 90-150 deg.C, and if necessary, is again stretched lengthwise and/or crosswise so be thermally set.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a composite polyester film, which is particularly excellent in running property after forming a magnetic tape, electromagnetic conversion characteristics, durability, adhesiveness to a magnetic layer, and longitudinal direction before transverse stretching. The present invention relates to a method for producing a composite polyester film for a magnetic recording medium, which has a high draw ratio and is excellent in productivity.

[0002]

2. Description of the Related Art Biaxially stretched polyester films are used for various purposes in various fields due to their excellent mechanical properties, thermal properties, electrical properties, chemical resistance, etc. It is a very useful film as a film. In particular, with the rapid spread of video, an inexpensive magnetic tape for video while maintaining high quality has been demanded. In order to meet these demands, how to reduce the cost while maintaining high quality as a base film has become a major issue.

[0003]

There are various kinds of required quality items to be satisfied by the polyester film for a magnetic recording medium. Especially, the polyester film is flat for the purpose of improving running property and electromagnetic conversion property after being formed into a magnetic tape. Polyester is used to prevent slipping, good adhesion to the magnetic layer, and white powder due to process scratches in the magnetic layer coating process, and white powder due to abrasion and friction with the cassette pin when the magnetic tape is running. It is required that the film has good abrasion resistance, that the mechanical strength of the polyester film is high and that the film is inexpensive so that the film does not stretch during the recording / recording / playback process of the magnetic tape. In this case, it is necessary that the above items are balanced and good, and if one item is extremely excellent but one item is inferior,
Insufficient product. Of the above requirements,
Regarding the improvement of the smoothness of flatness of the polyester film and the adhesion to the magnetic layer, it is known from conventional studies that the lower the plane orientation ΔP of the polyester film, the better.

[0004]

[Equation 2]

[0005]

DISCLOSURE OF THE INVENTION As a result of intensive studies to meet these requirements, the present inventors have found that many of the performances required of polyester films for magnetic tapes are related to the properties of the film surface only. By paying attention, the inventors have found that the problem can be solved by forming the film into two or more layers. That is, the gist of the present invention is (1) an A layer comprising a polyester containing 2 to 7 mol% of a dibasic acid and / or diol component which is a copolymerization component in addition to the main components of a dibasic acid and a diol, and a main component. An unstretched film obtained by coextruding two or more layers B composed of a thermoplastic resin containing 2 mol% or less of a copolymer component other than 3 to 5 at a stretching temperature of 80 ° C. to 150 ° C. in the machine direction by a roll. After longitudinal stretching in a single stage or in multiple stages, the A layer after longitudinal stretching has a refractive index of 0.080 or less, and the B layer after longitudinal stretching has a refractive index of 0.080 or more, and then 90 ° C in the transverse direction. It is characterized in that it is stretched 3.5 to 4.5 times at a temperature of up to 150 ° C., and if necessary, it is re-stretched again longitudinally and / or transversely and heat-set.

[0006]

(Equation 3)

(2) The method for producing a composite polyester film as described in (1) above, wherein at least three layers are formed to form both layers of the surface where the A layer is exposed.
(3) The polyester forming the layer A is a dibasic acid and / or a copolymerization component other than the main components of the dibasic acid and diol.
Alternatively, the present invention relates to the method for producing a composite polyester film as described in (1) or (2) above, which comprises 2 to 7 mol% of a diol component.

The multi-layer film referred to in the present invention is a film which is composited in a melt state. The step of performing the liquid state composite must be performed at least prior to the final stretch orientation treatment step that the composite film as a whole undergoes. For example, (a) all layers are co-melt extruded from the die. (B) At least one layer is melt-extruded from the die and is stretched on it, or longitudinally or laterally, and then another layer is compounded, and then stretched and oriented in the direction perpendicular to the above. When compounding by the coextrusion method of (a), the compounding place does not matter as long as two or more raw materials are compounded in a molten state. That is, different caps may be compounded on the verge of ejection, or compounded in the caps. In addition, it is also preferable to use a method in which, before the die, for example, a composite is formed in a filter in a molten polymer transport tube and then extruded with the same die. Hereinafter, the laminated film will be described as having three layers, but it may have more layers or two layers.

[0009]

(Equation 4)

However, in the case of copolymerization, the proportion of the copolymerization component in the polyester containing polyethylene terephthalate as the main component must be 2 mol% or less.

On the other hand, polyester is most suitable as the thermoplastic resin of the layer A forming at least one surface of the outermost layer of the film. The polyester may be a copolyester or a blend of homopolyesters as long as the heat of crystal fusion is lowered. As the copolymerized polyester, when the main component is polyethylene terephthalate, the copolymerized component such as isophthalic acid is 2 to 7
Mol% is preferred. 2 if the copolymerization component exceeds 7 mol%
It is not suitable because it curls when laminated in layers and the strength of the entire film decreases. On the other hand, if it is less than 2 mol%, the improvement of the longitudinal stretching ratio cannot be achieved, which is not preferable. Further, the film of the layer A needs to contain inert fine particles as necessary. The content of the inert fine particles varies depending on the use of the magnetic tape and is not particularly limited, but usually 0.005 to 2 wt. % Is preferable. The average particle size of the particles is in the range of 0.005 to 5.0 μm. Examples of the inert fine particles which meet this purpose include high melting point organic compounds which are insoluble during melt film formation of polyester resin, crosslinked polymers and metal compound catalysts used in polyester synthesis, such as alkali metal compounds, alkaline earth metal compounds and P Internal particles formed inside the polymer by the compound or the like during the production of polyester and, for example, MgO, ZnO, MgCO ₃ , CaCO ₃ , or CaS.
O ₄ , BaSO ₄ , Al ₂ O ₃ , SiO ₂ , TiO ₂ , Si
Examples thereof include viscous minerals such as C, LiF, talc and kaolin, inert externally added particles such as celite and mica, and terephthalate salts such as Ca, Ba, Zn and Mn. Of course, in addition to these particles, a compound such as a dye, a pigment, an antistatic agent, a conductive substance, an antioxidant, an antifoaming agent or the like may be blended if necessary. Metal soap, starch,
Inert organic compounds such as carboxymethyl cellulose and the like can also be mentioned as additives that impart lubricity. When the particles are added, the polyester may be added before the polymerization or during the polymerization reaction, or may be kneaded in an extruder when pelletizing after the completion of the polymerization. Further, it may be added at the time of melt extrusion into a sheet shape, dispersed in an extruder and extruded.

In order to improve the runnability and electromagnetic conversion characteristics after forming a magnetic tape, which is the object of the present invention, the smoothness and flatness of the film, the adhesion to the magnetic layer and the transferability of the lubricant to the back surface of the film are required. Goodness is essential. Therefore, the effect is exerted also in the two-layer film in which the layer forming the film surface is the A layer and the B layer, but in order to sufficiently satisfy the above-mentioned necessary items, the front and back sides forming the outermost layer of the film are at least the A layer. It is preferable that the structure has three or more layers. In the case of two layers, it is naturally necessary to blend a slip agent in both A and B layers. Here, the layer A is required to be biaxially stretched and thermally fixed, and then the film should satisfy the following formula.

[0013]

(Equation 5)

[0014]

(Equation 6)

Therefore, when a copolyester is used in the layer A, an aromatic dibasic acid is used as the copolymerization component,
Preference is given to using aromatic diols. In that case, the amount of the copolymerization component is preferably 2 to 7 mol%. Amount of the number A (pieces / mm ² ) per 1 mm ² of film surface area of the unevenness unit consisting of projections and depressions having a major axis of at least 0.5 μm as a core on the surface of the A layer satisfies the formula. When present, it is much more excellent in flatness and smoothness of the film surface, and is more preferable. 0 <A ≦ 5000 ... When A exceeds 5000 pieces / mm ² , the flatness is excellent but the running property, especially the multiple-running property is poor, which is not preferable.

On the other hand, when the layer B is composed of three or more layers,
Since it forms an inner layer of the film and serves as a layer having mechanical properties, particles are not particularly required, but it is a preferable method to incorporate carbon black or the like for the purpose of improving the light-shielding property of the film, for example. However, in the case of two layers, A
It is necessary to appropriately contain the particles exemplified in the case of the layer. In the layer B, it is preferable that the amount of the protrusion A provided in the layer A is a specific amount or less, that is, an amount satisfying the formula 0 ≦ A ≦ 100 ... When A exceeds 100 pieces / mm ² , it is not suitable because it deviates from the object of the present invention of increasing the longitudinal stretching ratio of the film. See B
It is essential that each X ₁ of the layers is 0.08 or less. Thus, the film in which the A layer and the B layer are combined has an F ₅ value of 10.5 kg / mm ^{2 in} the film after heat setting.
The above is selected. F ₅ value is 10.5 kg / mm ²
If it is lower than the above range, the durability and runnability will be deteriorated, which causes edge damage in which the film end portion becomes wakame-like when running many times, which is not preferable. It is preferably 11.0 kg / mm ² or more, more preferably 11.5 kg / mm ² .

The center line average surface roughness (Ra) of the layer forming the magnetic surface of the film is appropriately selected depending on the application, but is generally 0.001 to 0.060. For example, 0.015 ≦ Ra for audio, 0.010 ≦ Ra ≦ 0.025 for general video grade, 0.006 ≦ Ra ≦ 0.015 for coating type metal video, and 0.001 ≦ Ra for vapor deposition video. ≦ 0.008, the suitability range varies depending on the application, and accordingly, the type, particle size, and particle amount of particles to be added or precipitated in the layer forming the magnetic surface,
It is preferable to change the particle shape. However, in order to prevent changes in the unevenness of the magnetic surface due to the show-through phenomenon that the unevenness of the diamagnetic layer side is transferred to the magnetic layer coated surface of the magnetic tape, the average surface roughness of the magnetic layer side and the diamagnetic layer side is Sa (Ra)
Difference of Ra (diamagnetic layer) -Ra (magnetic layer) <0.004
It is preferred that Further, the film thickness of the present invention is
Although not particularly limited, 3 μm to 500 μm is preferable. However, the proportion of the B layer in the total film thickness must be 50% or more. Below 50%,
Next, the film forming method of the film of the present invention will be specifically described. Copolymerized polyester raw material containing fine particles (A layer) and non-copolymerized raw material containing fine particles as necessary (B layer) are separately dried and separated by separate extruders. It is melt-extruded, and two or three or more layers are laminated by co-extrusion in the same die, and they are integrated and cooled and solidified on a casting drum. At that time, it is preferable to use a known method such as an electric contact method.

The composite unstretched film was rolled by a roll at a stretching temperature of 80 ° C. to 150 ° C. in a longitudinal direction of 3.0.
˜5.0 times in the longitudinal direction, the birefringence of the A layer after longitudinal stretching is 0.080 or less, and the birefringence of the B layer after longitudinal stretching is 0.0.
80 and above. This is because the A layer is copolymerized with the B layer, so that the A layer will be B even if it is longitudinally stretched at the same temperature and stretching ratio.
Since the birefringence is smaller than that of the layer, a difference in birefringence occurs between the A layer and the B layer. Thus, since the layer A suppresses the orientation after longitudinal stretching to a low level, the plane orientation after biaxial stretching and heat setting is suppressed, and nα increases accordingly. on the other hand,
Since the B layer has a difference in orientation around the particles during the longitudinal stretching, when the B layer is laterally stretched, an uneven unit having a depression is formed.
On the other hand, the layer A has a high birefringence after longitudinal stretching,
The plane orientation after the biaxial stretching also becomes high, and the concave-convex unit having depressions is not formed. Therefore, Δn of A layer is 0.080
According to the above, the unevenness unit having a dent of the layer A of 1.492 or more and having a depression is not formed, and the flat slipperiness is poor. On the other hand, when the Δn of the B layer is less than 0.080, the film strength of the B layer alone does not pose a problem, but the film strength of the A layer decreases, and the strength as a whole decreases, which is not preferable. The longitudinal stretching may be one-stage stretching, but it is preferable to perform two-stage stretching or more in multiple stages. In the multi-stage stretching, the birefringence Δn of the layer A before the final stage stretching is 0.015 to 0.055.
Then, it is appropriate to obtain the desired birefringence index in the final stage stretching. The longitudinally stretched film thus obtained is then subjected to 85 ° C.
A biaxially stretched film is obtained by transversely stretching 2.5 to 5.0 times at a temperature of 150 ° C. If necessary, the stretched film is re-stretched in the machine direction and / or the transverse direction, and then heat-fixed. Thus, according to the present invention, even if the longitudinal stretching ratio before transverse stretching is set to be high, it is possible to satisfactorily achieve various properties that the polyester film for a magnetic tape should satisfy, such as flat slipperiness. This makes it possible to prevent the deterioration of the longitudinal stretching ratio, which is the largest defect in the film having a reduced ΔP by lowering the longitudinal stretching conditions, and prevent the deterioration of productivity. Further, it is also possible to re-stretch in the machine direction and / or the transverse direction after the transverse stretching, and it is also suitable to produce a tensor film, a super tensor film, a horizontal tensor film, or the like. Films satisfying the above conditions will not reduce productivity,
It satisfies the characteristics as a polyester for magnetic tape. Needless to say, it can be used for various purposes other than the magnetic tape by utilizing the improved adhesiveness and the smoothness of flatness.

[0019]

EXAMPLES The present invention will be described below in more detail based on Examples and Comparative Examples. The measuring method of each physical property value of the film is as follows. (1) Centerline average surface roughness (Ra) The surface roughness was measured as follows by a surface roughness measuring device (SE-3FK) manufactured by Kosaka Laboratory. The tip radius of the stylus is 2 μm, and the load is 30 mg. A portion having a reference length L (2.5 mm) is extracted from the film sectional curve in the direction of the center line, and the center line of the extracted portion is taken as the X axis and the direction of longitudinal magnification is taken as the Y axis, and the roughness curve y = f ( When expressed by x), the value given by the following equation is expressed by μm. However, the cutoff value is 80 μm.
Ra was the average value of a total of 10 points, 5 points in the vertical direction and 5 points in the horizontal direction.

[0020]

(Equation 7)

(2) Coefficient of friction (μd) Fixed hard chrome plated metal roll (diameter 6 mm, 2
The film is brought into contact with S) at a winding angle of 135 ° (θ) and a load of 53 g (T ₂ ) is applied to one end at 1 m / min.
This was run at a speed of ₁ to measure the resistance force (T ₁ ) at the other end, and the friction coefficient (μ ₁ ) during the first run was determined by the following equation. As the evaluation of the repeated running property, the friction coefficient (μ ₂₀₀ ) after running 200 times was measured.

[0022]

(Equation 8)

(3) Refractive index: 25 ° C. using an Abbe refractometer (manufactured by Atago Co., Ltd.)
The value for the Na-D line measured in 1. was determined.

[0024]

[Equation 9]

[0025]

(Equation 10)

Is given by On the other hand, the plane orientation degree ΔP is calculated by using the above nα, nβ, and nγ.

[0027]

[Equation 11]

Given by (4) Chroma S / N, tape running property, and adhesion to magnetic layer Chroma S / N was measured with a Shiba Soku NTBC type video noise measuring device Q25R using a commercially available VTR for home use. A tension meter was attached to a home VTR to measure the tension when the tape was running. Chroma S / N of standard tape
Is 0 dB, and the value of the tension of the reference tape is 1.0
And On the other hand, as for the adhesiveness, the adhesive strength of the reference tape is 1. The adhesive strength of the reference tape is 1. It was set to 0.

The magnetic powder was coated by the following method. The magnetic powder coating shown below was applied onto the precleaned film with a gravure roll, and the magnetic coating layer was smoothed with a doctor knife to give about 6
A μm magnetic layer is formed. Before the magnetic paint dries, it is magnetically oriented by a conventional method, dried and calendered, then at 80 ° C.
After curing for 20 hours, it was slit into a 1/2 inch width to form a tape. Composition Part Ferromagnetic powder mainly composed of γ-Fe ₂ O ₃ 250 Polyurethane resin 50 Vinyl chloride / vinyl acetate copolymer 30 Nitrocellulose 20 Lecithin 3 Carbon 15 MEK 900 Polyisocyanate compound 15 (5) X-ray diffraction Measurement

[0030]

(Equation 12)

(6) Measurement of Surface Roughness by Multiple Interferometry After deposition of aluminum on the film surface, a surface finish microscope manufactured by Nihon Kogaku Co., Ltd. was used to measure interference fringes at a wavelength of 0.54 μ by multiple interference method. Then, the interference fringes are photographed and the number of n-th order interference fringes is counted and converted to 1 mm. In the measurement, the mirror reflectance was 65% and the microscope magnification was 200 times. H ₁ and H ₂ are primary,
The number of secondary interference fringes and the height are shown below. H ₁ : 0.27 ≤ h <0.54 H ₂ : 0.54 ≤ h <0.81 (7) F ₅ value A sample film with a 1/2 inch width and a 50 mm length between chucks was manufactured by Toyo Baldwin Tensilon. (UTN-III)
By pulling at 50 mm / min at 20 ° C. and 65% RH, dividing the load at 5% extension by the initial cross-sectional area, kg
It is expressed in units of / mm ² . (8) Shrinkage The length of the film to be measured is 50c in the longitudinal and width directions.
The film was cut into a m (l ₀ ) width of 15 mm and heat-treated in an oven at a predetermined temperature for a predetermined time, and then the length (l) of the film was measured, and the shrinkage rate was calculated from the following formula.

[0032]

(Equation 13)

(9) Birefringence The retardation was measured with a polarizing microscope manufactured by Carl Zeiss, and the birefringence (Δn) was determined by the following equation.

[0034]

[Equation 14]

Example 1 100 parts of dimethyl terephthalate and 60 parts of ethylene glycol were used as a transesterification catalyst in an amount of 0.095 part of calcium acetate monohydrate, and a polymerization catalyst in an amount of 0.04 part of Sb ₂ O ₃ .
Ethyl acid phosphate 0.06 as polymerization stabilizer
A copolymer of polyester terephthalate was polymerized by adding 9 parts by a conventional method. This polymer was taken out in a cut shape and cut into chips (raw material 1). Further, a polymer was obtained in the same manner as the raw material 1 using 90 parts of dimethyl terephthalate and 10 parts of dimethyl isophthalate (raw material 2).
Next, 100 parts of dimethyl terephthalate, 70 parts of ethylene glycol, 0.10 part of calcium acetate monohydrate and 0.17 part of lithium acetate dihydrate were charged into the reactor, and the temperature was raised by heating and methanol was distilled off. The transesterification reaction was carried out, and it took about 4 hours after the start of the reaction to reach 230 ° C., and the transesterification was substantially completed. Next, 0.35 parts of triethyl phosphate was added to this reaction product, and 0.05 part of antimony trioxide was further added as a polycondensation catalyst, followed by polymerization according to a conventional method to obtain a polyester. A large number of uniform fine particles containing calcium, lithium and phosphorus elements having a particle size of about 0.5 to 1 μm were observed in the polyester. Separately from this, a polyester raw material containing 1.4 μ of 0.4 wt% of calcium carbonate was produced and blended with the above raw material at a ratio of 9: 1 to obtain a raw material 3. These raw materials are raw material 1 / raw material 2 /
Raw materials 3 = 20/30/50 were mixed and used as a raw material for the outermost layer A (raw material I). In addition, as the raw material of the B layer which is the inner layer, the raw material 1 was used (raw material II). Each of these raw materials was adjusted so that the [η] before drying was 0.62. Each of these two types (raw material I, raw material II) is dried,
It is extruded by separate melt extruders having diameters of 60 mm and 90 mm, the raw material I is separated into two layers in the same die so that the raw material II is in the inner layer, and the raw material II is combined into three layers to be integrated. An unstretched sheet was produced by casting, cooling and solidifying on a smooth drum at 40 ° C. A, B
The discharge rate was adjusted so that the layer thickness ratio was 3: 7. A
The thickness of the layers was the same.

[0036]

(Equation 15)

In Example 2, Comparative Examples 1 and 2, the mixing ratio of the raw material I was variously changed, and the other steps were the same as those in Example 1. In Comparative Example 1, the mixing ratio of raw material I is raw material 1 / raw material 2
/ Raw material 3 = 40/10/50, raw material 1 / raw material 2 / raw material 3 = 0/50/50 in Example 2, and in Comparative Example 2 the copolymerization amount of raw material 2 was set to 20 mol% and raw material 1 / raw material 1 / Raw material 4
/ Material 3 = 10/40/50. Comparative Examples 1 and 2 are films in which the ΔP of the A layer is larger than 0.165 and smaller than 0.145, respectively.

[0038] 180 ° C. Comparative Examples 3 and 4 heat setting temperature (Comparative Example 3), except for using 250 ° C. (Comparative Example 4), was stretched in the same manner as in Example 1.

[0039]

(Equation 16)

Comparative Example 5 Raw material 1 / raw material 3 = 50/50 was extruded in a single layer to obtain Example 1
It was stretched and heat-set under the same stretching conditions. The film is
It is a single layer film having ΔP> 0.165 corresponding to the B layer alone. Comparative Example 6 Except that the heat setting temperature was 230 ° C. and the heat setting was performed in two steps
Stretching and heat setting were performed in the same manner as in Comparative Example 5.

[0041]

[Equation 17]

Example 3 and Comparative Example 7 Instead of three layers, two layers were formed, and one layer was mixed at a mixing ratio of raw material 1 / raw material 2
/ Raw material 3 = 20/30/50, and the same procedure as in Example 1 was performed except that the other layer was changed to raw material 1 / raw material 3 = 50/50. The results are shown in Tables 1-1 and 1-2. From the above, by compounding by the method of the present invention, flat easy sliding, especially excellent electromagnetic conversion characteristics after magnetic tape formation, runnability, adhesiveness, high film strength, low shrinkage rate, and excellent productivity You can get a good film.

[0043]

[Table 1-1]

[0044]

[Table 1-2]

[0045]

As described above, the present invention is a composite film in which ΔP and n of the A layer film and the B layer film are specified, respectively, and by specifying the F ₅ value of the composite film, smooth sliding is achieved. When the magnetic recording medium is made into a magnetic recording medium, the magnetic recording medium has excellent electromagnetic properties and excellent running properties and adhesiveness.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yujiro Fukuda 1000 Kamoshida-cho, Midori-ku, Yokohama-shi, Kanagawa Daifoil Co., Ltd.

Claims (3)

[Claims] 1. A dibasic acid and / or diol component, which is a copolymerization component, in addition to the dibasic acid and diol main components are 2 to 7.
An unstretched film obtained by co-extruding two or more layers of a layer A composed of polyester containing mol% and a layer B composed of a thermoplastic resin having a copolymerization component other than the main component of 2 mol% or less in a longitudinal direction by a roll. At a stretching temperature of 80 ° C. to 150 ° C. and longitudinally stretched in a single step or multiple steps at a rate of 3 to 5 times, the refractive index of the A layer after longitudinal stretching is 0.080 or less, and the refractive index of the B layer after longitudinal stretching is After setting to 0.080 or more, 9 in the lateral direction
It is characterized in that it is stretched 3.5 to 4.5 times at a temperature of 0 ° C. to 150 ° C., and further re-stretched longitudinally and / or transversely if necessary and heat set. 2. The method for producing a composite polyester film according to claim 1, wherein at least three layers are formed so as to form both layers on the surface where the A layer is exposed. 3. The polyester forming the layer A contains 2 to 7 mol% of a dibasic acid and / or diol component which is a copolymerization component in addition to the main components of the dibasic acid and diol. A method for producing the composite polyester film according to item 1 or 2.