JPH09300454A - Biaxially oriented polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a biaxially oriented polyester film matching with the request of the enhancement of image quality, enhanced in handling properties and having a surface hard to damage by providing surfaces specified in the distances of respective slice levels corresponding to respective area ratios in the three-dimensional surface roughness measuring power spectrum of a polyester film. SOLUTION: In the three-dimensional surface roughness measuring power spectrum of a polyester film, surfaces being the distance A<=25nm of the respective slice levels corresponding to an area ratio of 70% and an area ratio of 20% are provided. The surface is pref. the area index B>=50 of the part surrounded by the straight line parallel to the vertical axis passing the projection height corresponding to the number of projections per 1/100 the max. number projections in a three-dimensional surface roughness measuring projection height and a projection height curve. The surface is pref. formed so that three- dimensional surface roughness is SRa<=15nm and projection height of 300-400nm number C of projections of height of 300-400nm is pref. 1/0.1m<2> or more.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester film suitable as a polyester film for a magnetic recording medium, and particularly to a video tape for broadcasting stations, a tape for 8 mm video, a tape for 1/2 inch video, a tape for audio cassette, a digital video. The present invention relates to a polyester film suitable for use in magnetic recording media such as cassette (DVC) tape, digital audio tape deck (DAT) tape, data cartridge tape, and high definition video tape.

[0002]

2. Description of the Related Art A magnetic recording medium using a polyester film is being made higher in density and higher in capacity in recent years. Therefore, the recording wavelength at the time of magnetic recording is shortened. Generally, for short wavelength recording, a smoother magnetic recording layer surface is required to minimize spacing loss with the magnetic head, but this is the same for the polyester film as the base material. In other words, it means that a smoother surface is required. That is, the smoother polyester film consequently contributes to the production of a magnetic recording medium suitable for shorter wavelength recording, and the requirement for the smoothness is basically not limited unless there are other obstructing factors. On the other hand, such a smooth film base has a drawback in that the surface of the polyester film is scratched by a roll that comes in contact with the increase in the process speed in the magnetic layer coating / calendering process in the magnetic recording medium manufacturing process. Is a problem. Further, the smoothed polyester film has a problem that the handling property is deteriorated as a problem in manufacturing the film roll, and as a result, the cost of the product is increased. It is a well-known fact that the reduction of the friction coefficient due to the formation of protrusions is generally effective for the abrasion of the film in the magnetic tape manufacturing process.
Further, in order to improve the winding property of the film, it is generally considered effective to increase the surface roughness by providing a large amount of protrusions with a filler in the film. However, on the other hand, it is important to measure the smoothness of the film surface to improve the electromagnetic conversion characteristics from the demand for high image quality. Especially for commercial video tape applications and 8 mm video tape applications with a short recording wavelength, this electromagnetic conversion characteristic The demand for the film has been prioritized, and the handleability and scraping characteristics of the film have been sacrificed in the past. Many studies have been made in the past against these dilemmas of contradictory film surface characteristics, for example, JP-A-59-171623 and JP-A-61-5.
In Japanese Patent No. 431, etc., it has been proposed to include specific particles or to specify the surface protrusion distribution.
Further, Japanese Patent Application Laid-Open No. 4-1236 proposes that the protrusion height and the number of protrusions be within a certain condition range in terms of film surface characteristic parameters and abrasion resistance.

However, in reality, it is difficult to satisfy all of the above problems even with such a known method.

[0004]

SUMMARY OF THE INVENTION The present invention solves the above problems and provides a polyester film for a magnetic recording medium which meets the demand for higher image quality, is excellent in handleability, and is not easily scratched on the surface. The purpose is to

[0005]

The problems of the present invention are as follows.
Area ratio 70 in dimensional surface roughness measurement power spectrum
% And the distance A at each slice level corresponding to an area ratio of 20%
Achieved by a polyester film having a surface that is ≤25 nm.

[0006]

The surface achieved according to the invention is
Furthermore, in the three-dimensional surface roughness measurement protrusion height distribution, the area index of the part surrounded by the straight line parallel to the vertical axis and the protrusion height curve that passes through the protrusion height corresponding to one hundredth of the maximum number of protrusions. It is preferable that B ≧ 50. The surface achieved by the present invention has a three-dimensional surface roughness SRa ≦ 15 nm and a protrusion number C of protrusion height 300 to 400 nm is 1 / 0.1.
mm ² or more.

When the present invention is applied to commercial video tapes such as Betacam SP, Digital Betacam, DI, DII, DIII, etc., in order to improve the head contact property in a VCR, the longitudinal direction and the width of the film are increased. Direction F
The sum of -5 values is 245 MPa or more, and F- in the longitudinal direction.
The 5 value is preferably 127 MPa or more. When the present invention is partially applied to beta cam applications and computer data tape applications, this is also due to the characteristics of the tape transport system in order to improve the head contactability, and conversely the F-direction in the longitudinal direction and width direction of the film. The sum of the five values is preferably smaller than 245 MPa.

Regarding the thermal characteristics of the film achieved by the present invention, it is preferable that the temperature in the width direction of the film is 100 ° C. and the thermal shrinkage ratio after 30 minutes of storage is 0.1% or less.

In order to improve the adhesion between the coated recording layer and the film, it is preferable to have a layer made of a polyester resin coating on one side or both sides of the film.

When the thickness ratio of the front and back surfaces of the composite film of three or more layers achieved by the present invention is 1.5 or more, the surface becomes smoother only in the direction of the magnetic recording layer and the handling as a whole is made. It is more preferable because the property is not impaired. The composite film achieved by the present invention is most suitable for magnetic recording medium applications.

Next, the surface parameters set in the present invention will be described. The 70% area ratio point in the power spectrum of the three-dimensional surface roughness measurement is often used as a parameter indicating the reference plane of the film surface as the initial setting of the measuring machine. On the other hand, at the area ratio 20% point, the cross section corresponding to the projection forming portion formed on the surface where the measurement surface has already left the film surface is assumed. 70% -20% here
The distance of each slice level is used as a parameter indicating how sharply the flat film surface excluding the protrusions transitions to the protrusion forming portion.The smaller this parameter is, the higher the flatness of the surface other than the protrusion portion is, It is considered to indicate that the protrusions are formed without waviness.

Further, in the three-dimensional surface roughness measuring protrusion height distribution, a portion surrounded by a straight line parallel to the vertical axis and a protrusion height curve passing through the protrusion height corresponding to one hundredth of the maximum number of protrusions. Is an index indicating how many spike protrusions are formed on the film surface with respect to the main protrusions that mainly impart surface roughness. The area index of the film surface to which single particles having a certain particle size distribution are added becomes 50 or less, and becomes 30 or less when the particle size distribution of the particles is steep. On the other hand, by adding a small amount of large particles,
This area index can be 50 or more.

Generally, the projections on the surface of the polyester film are formed by inert particles or internally precipitated particles. The above-mentioned surface in the polyester film of the present invention is achieved by adding the inert particles to the polyester. It The present invention can be achieved by appropriately setting the particle size and particle concentration at this time. Specifically, the present invention is achieved by adding a very small amount of large-diameter particles (hereinafter referred to as spike particles) to main particles added to form a required surface. At this time, by appropriately setting the main particle size, spike particle size and addition amount,
The present inventors have found that the handling property and abrasion resistance of the film can be remarkably enhanced without substantially impairing the performance (electromagnetic conversion property) of the tape after the magnetic recording layer is coated. .

The inert particles in the present invention include:
Inorganic or organic particles insoluble in polyester, inorganic particles such as calcium carbonate particles, spherical silica particles, titanium dioxide particles, titanium monoxide particles, titanium nitride particles, kaolin particles, talc particles, and organic particles such as crosslinked polystyrene particles. And so on. The weight average particle diameter of the inert particles used for the surface formation is
The thickness is preferably 0.1 to 2.0 μm, more preferably 0.15 to 1.0 μm. If the weight average particle diameter of the particles is smaller than 0.1 μm, the function of forming protrusions cannot be fulfilled and friction increases, which may deteriorate the running characteristics of a video tape. On the other hand, if it is larger than 2.0 μm, the protrusions formed on the surface are too high, and the electromagnetic conversion characteristics of the magnetic recording medium represented by a video tape may be poor. Further, it is preferable that the above-mentioned inert particles are a mixed system of plural kinds. This is composed of a main filler that forms a protrusion and spike particles that are effective in eliminating air during film winding, and the content of the main particles may be 0.01 to 8% by weight based on the polyester. Preferably, more preferably 0.05 to 2.0% by weight, and even 0.1
It is preferably about 1.0% by weight. When the content of the particles is less than 0.05% by weight, the surface protrusions are insufficiently formed, resulting in increased friction and poor handleability when used as a raw film. On the other hand, if the amount is more than 8% by weight, the electromagnetic conversion characteristics of the magnetic recording medium represented by the video tape may be poor. On the other hand, the content of spike particles is 0.005 to 1 relative to the polyester.
It is preferable to set it as a weight% and more preferably 0.01
˜0.8 wt%, and more preferably 0.015 to 0.5 wt%. When the content of the particles is less than 0.005% by weight, the formation of surface protrusions is insufficient, so that the effect of reducing the coefficient of friction is difficult to be exhibited, and the air excluding performance is poor, and as a result, handleability when used as a raw film film. May get worse. On the other hand, if the content is more than 1% by weight, the electromagnetic conversion characteristics required for the intended video tape may become poor. In the present invention, the main particles and the spike particles have a relationship in which the particle diameters of the main particles and the spike particles are smaller than the main particle diameter.

Further, in the case where the present invention requires short-wavelength recording, and the tape is provided without a back coat in order to provide the tape at a low cost, the film is used to improve the abrasion resistance of the back surface of the tape. In the three-layer composite film, it is preferable that the surface layer portion contains 0.1% by weight or more of the surface layer of inert fine particles for reinforcing the background. The inert fine particles preferably have an average primary particle size of 0.002 μm or more and less than 0.10 μm and a Mohs hardness of 7 or more. The amount of the inert fine particles added is preferably at least 0.1% by weight and 10% by weight or less, and more preferably 0.1% by weight and 0.5% by weight. Examples of the inert fine particles include those containing alumina, zirconia or the like as a component, and the specific surface area by the BET method is preferably 10 m ² / g or more, more preferably 40 m ² / g or more.

The polyester used in the present invention can be produced by a polycondensation reaction as a glycol component with a bifunctional component such as an aromatic dicarboxylic acid or its alkyl ester. Of these, those containing polyethylene terephthalate as a main component are preferable.

The polyester film of the present invention may contain a small amount of a copolymerization component that does not impair the basic properties. Examples of the copolymerization component of the copolyester include dicarboxylic acid components such as 2,6-naphthalenedicarboxylic acid and isophthalic acid, oxycarboxylic acid components such as P-oxyethoxybenzoic acid, tetramethylene glycol, propylene glycol and neopentyl glycol. , Polyoxyalkylene glycol, P-xylylene glycol,
Examples include diol components such as 1,4-cyclohexanedimethanol, polyethylene glycol, and 5-sodium sulforesorzine. Of these, a copolyester obtained by copolymerizing a diol component such as polyethylene glycol is preferable in order to improve the adhesiveness of the film to the magnetic binder and to keep the chargeability due to static electricity low.

Further, the polyester film of the present invention may contain recovered polyester mainly composed of non-product parts generated in the production stage. Furthermore, these polyesters preferably have an intrinsic viscosity of 0.5 or more, more preferably 0.55 or more.

In the present invention, the method of incorporating the projection-forming particles into polyester is not particularly limited,
Generally, it is preferred to add a slurry of inert particles during polyester production. As the addition method and the addition timing, conventionally known methods and timings can be used, but the addition method is preferably a method of adding as a slurry of ethylene glycol which is a raw material for synthesizing the polyester. The slurry concentration at this time is preferably 0.5 to 40% by weight as the weight% of the inert particles, and further 1 to
The range of 20% by weight is preferable because the particle dispersibility in polyester is improved.

Further, the water content in the glycol of the slurry at the time of addition is preferably 1% by weight or less, more preferably 0.5% by weight or less, because the particle dispersibility in the polyester is improved. The addition time may be arbitrary, and it may be added at the time of charging the monomer, at the time of transesterification reaction, or before and after it. Further, the slurry of the particles may be dispersed by adding and kneading using a uniaxial or biaxial vent type extruder or the like after polymer production.

The characteristic values in the present invention are as follows:
According to evaluation criteria.

(1) Power spectrum of film surface,
Number of protrusions and three-dimensional surface roughness (SRa) Three-dimensional roughness was measured using a contact surface roughness meter (model ET-30HK) and a three-dimensional roughness analyzer (model SPA-11) from Kosaka Laboratory. Here, as the stylus, a STULS needle having a radius of curvature (R) of 2 μm at the tip was used. The conditions are as follows, and the average value of 10 measurements was used.

Vertical magnification: 50,000 times Horizontal magnification: 200 times Cutoff: 0.25 mm Feed pitch: 2 μm Measurement length: 500 μm Measurement area: 0.08 mm ² Measurement speed: 20 μm / sec Touch Needle pressure: 49 Pa The height of the protrusion was calculated based on the cut surface at which the area ratio of the cut surface by the cut surface was 70%.

Height 200-400n measured under the above conditions
m and the number of protrusions of 400 nm or more,
It was converted to 0.1 mm ² . SRa (nm) is a three-dimensional surface roughness (center plane average roughness).

The surface parameter A in the present invention is the distance at each slice level corresponding to an area ratio of 70 and an area ratio of 20% in the power spectrum obtained by the above measuring method.

In the present invention, the surface parameter B is the vertical length passing through the protrusion height corresponding to one hundredth of the maximum number of protrusions in the three-dimensional surface roughness protrusion height distribution measured by the above measuring method. It is the area of a part surrounded by a straight line parallel to the axis y and a projection height distribution curve. At this time, the projection height distribution is plotted with the horizontal axis x at a pitch of 10 nm and the number of projections at that time as the vertical axis y.

The surface parameter C in the present invention is the number of protrusions having a protrusion height of 300 to 400 nm in the protrusion height distribution calculated by the same method as the parameter B in the above measuring method.

(2) Longitudinal (MD) direction and width (T)
D) Direction F-5 value The strength at 5% elongation was defined as F-5 value using an Instron type tensile tester. It was measured at 23 ° C. and 65% RH. A sample film having a width of 10 mm and a length of 100 mm cut out in the machine direction (MD) and the width direction (TD) of the film was subjected to tensile measurement at a speed of 200 mm / min.

(3) Thermal shrinkage in the width direction The sample film is 10 mm wide and 250 mm long in the width direction.
Cut it out and put two marked lines at intervals of about 200 mm,
The distance is accurately measured (this is Xmm). 100 ℃ with 0.4g load applied to the tip of this sample
The gap between the marked lines after leaving it in the atmosphere for 30 minutes was measured (this is Ymm), and 100 × (X−Y) / X was taken as the heat shrinkage rate.

(4) Electromagnetic conversion characteristics (C / N), RF envelope characteristics and adhesiveness A magnetic coating composition having the following composition is applied to a film by a gravure roll, magnetically oriented and dried. Further, after calendering at a temperature of 70 ° C. and a linear pressure of 200 kg / cm using a small calender (styrene / nylon roll, 5 stages),
Cure at 70 ° C. for 48 hours. 1/2 of this material
Slit to inches to make pancakes. This pancake was incorporated into a VTR cassette to form a VTR cassette tape.

(Composition of magnetic paint) -Co-containing iron oxide (BET value 50 m ² / g): 100 parts by weight-ESREC A (Sekisui chemical vinyl chloride / vinyl acetate copolymer): 10 parts by weight-Nipporan 2304 ( Nippon Urethane Polyurethane Elastomer): 10 parts by weight Coronet L (Japan Urethane Polyisocyanate)
G): 5 parts by weight Lecithin: 1 part by weight Methyl ethyl ketone: 75 parts by weight Methyl isobutyl ketone: 75 parts by weight Toluene: 75 parts by weight Carbon black: 2 parts by weight Lauric acid: 1.5 parts by weight This tape Is a TV test waveform generator (TG7 / U) manufactured by Shibasoku using a commercial VCR and a home VTR.
706), a video signal was recorded, and the Y-C / N and RF envelope characteristics were measured from the reproduced signal.

The RF envelope A is a characteristic obtained by reproducing a magnetic tape using a film having a thickness of 10 μm on a commercial VCR.

The RF envelope B is a characteristic obtained by reproducing a magnetic tape using a film having a thickness of 14 μm on a commercial VCR.

The RF envelope B is a characteristic obtained by playing back a magnetic tape using a film having a thickness of 14 μm on a home VHS video deck.

The adhesive strength was evaluated by performing a peel test on the magnetic recording layer of this tape with a cellophane tape, and visually observing the residual rate of the magnetic recording layer remaining on the base by 5 grades. 5 is the highest adhesive strength, and 1 is the lowest.

(5) Winding shape A film having a width of 1000 mm is slit into a width of 300 mm (length: 5000 m) using a slitter (share cutter) at a speed of 500 m / min. The roll after slitting was allowed to stand at 40 ° C. and 80% RH for 10 days, and then the end face was observed. The end face was flat without any unevenness, and the surface was free from vertical wrinkles. 100% is the best and 0% is the worst.

[0037]

【Example】

Example 1 As polyester A, polyethylene terephthalate polymerized by a conventional method using 0.06% by weight of magnesium acetate, 0.008% by weight of antimony trioxide, and 0.02% by weight of trimethyl phosphate was used (intrinsic viscosity:
0.62).

Polyester B has an average particle size of 0.8 μ
Using an ethylene glycol slurry containing m calcium carbonate particles, polyethylene terephthalate master pellets containing 1% by weight of calcium carbonate particles were prepared in the same manner as polyester A.

As polyester C, polyethylene terephthalate master pellets containing 1% by weight of calcium carbonate particles having an average particle diameter of 1.1 μm were prepared in the same manner as polyester B.

As the polyester D, 1% by weight of organic particles having an average particle diameter of 0.3 μm was prepared in the same manner as the polyester B.
A master pellet of polyethylene terephthalate containing was made.

As polyester E, 1% by weight of agglomerate delta type alumina oxide particles was prepared in the same manner as polyester B.
A master pellet of polyethylene terephthalate containing was made.

A three-layer structure of A / B / A is used, pellets in which 75, 20, and 5 parts by weight of polyesters A, B, and C are mixed are used for the laminated portion A, and polyester B is used for the laminated portion B. 180 ° C for each pellet separately
After drying for 3 hours, feed each to two extruders,
Melted at 290 ° C., combined and laminated in a rectangular confluent block (feed block) for 3 layers, wound on a casting drum having a surface temperature of 25 ° C., cooled and solidified by using an electrostatic applied casting method. An unstretched film was made. The unstretched film was stretched in the longitudinal direction at a temperature of 90 ° C.
The film is stretched 4 times, then coated with a water-soluble polyester solution by a known coating means, and further, using a known stenter,
Stretched 3.5 times in the width direction at 5 ° C, and further 90 in the longitudinal direction.
Stretched 1.5 times at ℃, and then at 210 ℃ under constant length 3
The width of the rail of the stenter was narrowed by 2.0% while performing heat treatment for 2 seconds to relax the stress in the width direction of the film to obtain biaxially oriented films having a thickness of 10 μm and 14 μm. At this time, the extruder rotation speed was adjusted so that the thickness of the surface layer portion of the three-layer structure was 1.0 μm. A magnetic tape was prepared from this film by a known method, and the characteristic values shown in the table were obtained. The magnetic tape using this film was excellent in high-speed winding property while maintaining high electromagnetic conversion characteristics.

Examples 2 and 5 The mixing ratios of polyesters A, B, C, D, and E are as shown in Table 1, and the same method as in Example 1 was used, except that only the stress in the width direction was 3.5%. Got The magnetic tape using this film was excellent in electromagnetic conversion characteristics and high-speed winding property, and had little dimensional change even after the coating and drying process at high temperature.

Example 3 The mixing ratios of polyesters A, B and C are shown in Table 1,
A film sample was obtained in the same manner as in Example 2 except for the above. The magnetic tape using this film was particularly excellent in electromagnetic conversion characteristics.

Examples 4 and 6 to 8 Polyesters A, B, C, D and E were mixed in the proportions shown in Table 1, and no easy adhesion coating treatment was carried out. I got a sample. The magnetic tape using this film was excellent in electromagnetic conversion characteristics and high-speed winding property. In particular, Examples 7 and 8 were excellent in winding shape.

Examples 9 and 10 The mixing ratios of polyesters A, B, C and D are set as shown in Table 1, no easy adhesion treatment was performed, and the gaps in the portions corresponding to the front and back of the merging block shown in Example 1 were set. The layer thickness ratio shown in Table 1 was adjusted by adjusting. A film sample was obtained in the same manner as in Example 2 except for the above. The magnetic tape using this film was excellent in electromagnetic conversion characteristics and high-speed winding property. In particular, Example 9 in which the lamination thickness ratio was 3 was particularly excellent in electromagnetic conversion characteristics.

Comparative Example 1 A single film structure was adopted. The mixing ratios of polyesters A, B, C, and D are set as shown in Table 1, the total thickness is set as shown in Table 1, and the other steps are the same as in Example 1 without using a confluent block. Got The magnetic tape using this film has a large surface parameter A and thus is inferior in electromagnetic conversion characteristics. Further, since the surface parameter B is small, the high speed handling property is also poor.

Comparative Example 2 The same as in Example 1 except that the mixing ratio of polyesters A, B, C and D was set as shown in Table 1 and the extruder rotation speed was adjusted so that the final laminated portion thickness was 3 μm. A film sample was obtained by the method described in 1. Although this film has a three-layer structure, since the lamination thickness is large, the position control of the particles in the depth direction is not sufficient, and as a result, the surface parameter A is large. Electromagnetic conversion characteristics are low and not preferable.

[0049]

[Table 1]

[Table 2]

[0050]

[Effects of the Invention] By setting the surface parameters in a specific area as described above, it is possible to achieve both electromagnetic conversion characteristics and handling characteristics and sharpness characteristics in a commercial / 8 mm film, which were previously incompatible. It becomes possible to design the film that becomes. Further, by designing this film to have an appropriate strength balance according to the application, the adaptability for a specific application is further enhanced. Further, in the field where electromagnetic conversion characteristics are more required, it is possible to achieve both electromagnetic conversion characteristics and handling in a higher region by designing the laminated thickness in the composite film separately for the front and back, and the applicable range of the present invention becomes wider. .

Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display location C08J 5/18 CFD C08J 5/18 CFD G11B 5/704 G11B 5/704 // B29K 67:00 B29L 7:00

Claims (10)

[Claims] 1. A polyester film having a surface with a distance A ≦ 25 nm at each slice level corresponding to an area ratio of 70% and an area ratio of 20% in a three-dimensional surface roughness measurement power spectrum. 2. A three-dimensional surface roughness measuring protrusion height distribution is surrounded by a straight line parallel to the vertical axis and a protrusion height curve passing through the protrusion height corresponding to one hundredth of the maximum number of protrusions. The polyester film according to claim 1, wherein the area index B of the part is B ≧ 50. 3. The number C of protrusions having a three-dimensional surface roughness SRa ≦ 15 nm and a protrusion height of 300 to 400 nm is 1 / 0.1.
The polyester film according to claim 1, which has a size of not less than mm ² . 4. The sum of the F-5 values in the longitudinal direction and the width direction is 2.
45 MPa or more, F-5 value in the longitudinal direction is 127 M
The polyester film according to any one of claims 1 to 3, which has Pa or more. 5. The polyester film according to claim 1, wherein a sum of F-5 values in a longitudinal direction and a width direction of the film is smaller than 245 MPa. 6. The heat shrinkage ratio after storage for 30 minutes at a temperature of 100 ° C. in the width direction of the film is 0.1% or less.
6. The polyester film according to any one of 5 to 5. 7. The polyester film according to claim 1, which has a layer made of a polyester resin coating on one side or both sides. 8. A composite film comprising three or more layers, wherein the polyester film according to any one of claims 1 to 7 is arranged in at least one layer, and the surface layer portion contains inert fine particles in an amount of 0.1% by weight or more of the surface layer. Composite polyester film to do. 9. The composite polyester film according to claim 1, wherein in a composite film having three or more layers, the thickness ratio of each layer constituting the front and back is 1.5 or more. 10. A composite polyester film for a magnetic recording medium according to claim 1.