JPS63221137A - Biaxially oriented polyester film - Google Patents

Abstract

PURPOSE:To obtain the title film excellent in lubricity, chipping resistance, adaptable for high-speed processing and suitable as a base film for videotapes, by forming a composition comprising a polyester and inert inorganic particles into a film and biaxially orienting this film. CONSTITUTION:0.3-3.0wt.% slurried inert inorganic particles (e.g., TiO2) of an average particle diameter of 0.05-0.6mu are dispersed in a diol component (e.g., ethylene glycol) of a polyester and an acid component [e.g., terephthalic acid (dimethyl ester)] is added to this diol component. The mixture is transesterified and polycondensed to obtain a composition comprising a polyester and the inert inorganic particles. An unoriented film formed by extruding this composition at 270-330 deg.C with a melt extruder is biaxially oriented at a draft ratio of 3.0-5.0 and a speed of orientation of 1X10<3>-7X10<4>%/min and heat- treated at 180-250 deg.C for 0.5-60sec without elongation to obtain the title film satisfying the relationships of formulas I-III [wherein D is the average particle diameter (mu) of the inert inorganic particles; Ra is the average surface roughness (mu) along the direction of the film width; and H is the average height (mu) of surface protrusions] and having a surface orientation index of 0.935-0.970, a density index of 0.02-0.05, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to biaxially oriented polyester films.

[Prior Art] As a biaxially oriented polyester film, a polynisdel film in which the height of the surface protrusions is limited is known (for example, JP-A-54-73877@).

[Problems to be solved by the invention] However, the above conventional biaxially oriented polyester film has the following problems:
As the speed of film processing increases, such as the printing process in packaging applications and the magnetic layer coating/calendering process in magnetic recording media applications, the surface of the film is abraded by contacting rolls, causing problems in the processing process. Recently, the drawback of causing problems in product performance has become a problem.

The present invention improves these problems and improves the surface's "scratching resistance" while maintaining the "slip properties" of the film that are necessary for any application.
Our goal is to provide superior films.

[Means for solving the problem] A biaxially oriented film whose main components are a composition consisting of polyester and inert inorganic particles, the average particle diameter D (μm) of the inert inorganic particles, the width of the film A biaxially oriented polyester film characterized in that the average surface roughness Ra (μm) in the direction and the average height H (μm) of surface protrusions satisfy the following formulas (1) to (3).

0.05≦D≦0.6 (1) Ra≧0
．． 04D ・・・・・・■2Ra≦H≦8Ra
・・・・・・■ The polyester in the present invention has at least one unit selected from ethylene terephthalate, ethylene α, β-bis(2-chlorophenoxy)ethane-4,4-dicarboxylate, and ethylene 2,6-naphthalate units. The main constituent is a type of structural unit.

However, other components may be copolymerized within a range that does not interfere with the present invention, preferably within 20 mol%.

In addition, polyester containing ethylene terephthalate as a main component is particularly desirable because its slipperiness and abrasion resistance are even better.

The type of inert inorganic particles used in the present invention is not particularly limited, but includes synthetic calcium carbonate, titanium oxide, silica, α-
Alumina is preferred, and in particular, substantially spherical silica resulting from colloidal silica is particularly desirable because it provides even better slipperiness and abrasion resistance. The colloidal silica referred to herein is preferably particles produced from sodium silicate as a raw material in the process of removing alkaline content.

The average particle size of the inert inorganic particles in the present invention is 0.0
It needs to be in the range of 5 to 0.6 μm, preferably 0.1 to 0.5 μm. If the average particle diameter is smaller than the above range, the slip properties will be poor, and if it is larger, the abrasion resistance will be poor, which is not preferable. Two or more types of inert inorganic particles may be used in the present invention, or two or more types of the same type but different in average particle size may be used in combination. In such a case, when the particle size distribution has two or more peaks, the smallest of these peaks is taken as the average particle size.

The content of inert inorganic particles in the present invention is not particularly limited, but when the content is 0.3 to 3.0% by weight, especially 0.4 to 1.0% by weight, the slipperiness and abrasion resistance are improved. This is particularly desirable because it provides good results.

The film of the present invention has the above-mentioned composition as a main component, but other polymers may be blended within the range that does not impede the purpose of the present invention, and antioxidants, heat stabilizers, lubricants, ultraviolet absorbers, etc. Inorganic or organic additives such as agents, nucleating agents, etc. may be added to the extent that they are normally added.

The film of the present invention is a film in which the above composition is biaxially oriented. An unstretched film or a -axis oriented film is not preferred because it has poor slip properties and abrasion resistance.

In addition, the plane orientation index representing the degree of biaxial orientation is not particularly limited, but is 0.935 to 0.975, particularly 0.94
A range of 0 to 0.970 is particularly desirable because the slip properties and abrasion resistance become even better.

The average surface roughness Ra (μm) of the film of the present invention in the width direction and the average particle diameter D (μm) of the above-mentioned inert inorganic particles are calculated by the following formula
It is necessary to satisfy the following.

Ra≧0.04D...■ If the relationship between Ra and D does not satisfy the formula (■), it is not preferable because the abrasion resistance becomes poor. Although the upper limit of Ra is not particularly limited, the manufacturing limit is usually about 0.05 μm.

Next, the average surface protrusion height H (μm) and the above-mentioned average surface roughness in the width direction Ra (μm) of the film of the present invention must satisfy the following formula (■), preferably the following formula (■-1). be.

2Ra≦To1≦8Ra ・・・・・・■3Ra
≦ To-1 ≦ 7Ra ・・・・・・■-1 If the relationship between Tol and Ra does not satisfy the above formula (■), preferably formula (■-1), a film that has both machinability and abrasion resistance f4 cannot be obtained. I don't like it because I can't do it.

Further, the density index of the film of the present invention is 0.02 to 0.0
A range of 5 is particularly desirable because the slipperiness becomes even better.

The film of the present invention has a melt viscosity of 1,000 to 10,000 voids, particularly 200
A range of 0 to 7000 voids is particularly desirable because the abrasion resistance is even better.

Next, a method for producing the film of the present invention will be explained.

First, as a method for incorporating inert inorganic particles into a given polyester, they may be added before, during, or after polymerization, but they may be added in the form of a slurry to ethylene glycol, which is the diol component of the polyester. A method of dispersing and adding is effective in satisfying the relational expression of the present invention. In addition, as a method for adjusting the content of inert inorganic particles, a method of diluting a highly concentrated master pellet with polyester that does not substantially contain inert inorganic particles during film formation is a method that satisfies the relational expressions ① and ② of the present invention. Effective in satisfying. In this case, the content of inert inorganic particles in the master pellet is 1 to 10% by weight, or preferably 1 to 5% by weight, according to relational formula (2) of the present invention.

■It is effective to satisfy. In addition, so that the relationship between the crystallization parameter Δ-cg of this master pellet and the inert inorganic particle content Φ (weighted %) satisfies the following formula,
The relational formula of the present invention is to adjust the melt viscosity of the polyester used for the master pellet and the copolymerization ratio of other components.
It is extremely effective in satisfying (2).

70-15Φ≦△■Cg≦100-2ΦAlso, the crystallization parameter ΔTcg of the polyester which dilutes this master pellet and does not contain substantially inert inorganic particles is 10°C or more smaller than the crystallization parameter ΔTcg of the master pellet. This method is extremely effective in satisfying relational expression (2) of the present invention.

Thus, after sufficiently drying the pellet containing a predetermined amount of inert inorganic particles, it was fed to a known melt extruder and 27
It is extruded into a sheet through a slit die at 0 to 330°C, and cooled and solidified on a casting roll to make an unstretched film.

Next, this unstretched film is subjected to two-wheel stretching to achieve biaxial orientation. As the stretching method, a sequential biaxial stretching method or a simultaneous two-wheel stretching method can be used.

In the case of the sequential two-wheel stretching method, it is common to stretch in the longitudinal direction and then in the width direction, but this order may be reversed. The conditions for two-wheel stretching are not necessarily constant depending on the stretching method, the type of polymer, etc., but are usually in the range of 80 to 160°C, preferably 90 to 150°C in both the longitudinal and width directions, and the stretching ratio is 3.0 to 3.0°C, respectively. A range of 5.0 times, preferably 3.2 to 4.5 times is suitable. Further, the stretching speed is preferably in the range of 1.times.10.sup.3 to 7.times.10.sup.4%/min.

Next, this stretched film is heat treated. In this case, the heat treatment conditions are 180 to 250°C under constant length, especially 190°C.
The preferred time is 0.5 to 60 seconds within the range of ~230°C.

[Function] As a result of controlling the average particle size of the inert inorganic particles and the film surface morphology, the true contact area when the film surface contacts another object becomes smaller, and the effects of the present invention are obtained. It is estimated that

[Method of Measuring Physical Properties and Evaluating Effects] The methods of measuring the characteristic values and evaluating the effects of the present invention are as follows.

(1) Average particle size D of inorganic fine particles Polyester is removed from the film by plasma ashing treatment or O-chlorophenol dissolution method, dispersed in ethanol, and centrifugal sedimentation method (Horiba, CAPA5
00) is the volume average diameter measured.

(2) Content of inorganic fine particles: polyester 100 (J to O-chlorophenol 1°O
After adding n and heating at 120°C for 3 hours, the 17-diluted particles were
Vacuum dry at 00°C. When the fine particles are measured using a scanning calorimeter, if a melting peak corresponding to the polymer is observed, the fine particles are heated and cooled with 0-chlorophenol, and then the stretching separation operation is performed again. When the melting peak is no longer observed, the fine particles are considered to be precipitated particles. Normally, two stretching and separating operations are sufficient.

(3) Glass transition point Tg, cold crystallization temperature TCC Measured using a PerkinElmer DSC (differential scanning calorimeter) type ■. The DSC measurement conditions are as follows. That is, a sample of 10 mm is set in a DSC device, melted at a temperature of 300° C. for 5 minutes, and then rapidly cooled in liquid nitrogen. This rapidly cooled sample is heated at a rate of 10° C./min, and the glass transition point Tg is detected.

The temperature was continued to be gradually raised, and the exothermic peak temperature of crystallization from the glass state was defined as the cold crystallization temperature Tcc.

Here, the difference between TCC and Tq (Tcc - Tg>) is defined as a crystallization parameter Δcg.

(4) Surface protrusion diameter d 2-detector scanning electron microscope [ESM-3200,
manufactured by Elionix Co., Ltd.] and a cross-sectional measuring device [PMS-1,
The height measurement value obtained by scanning the smooth surface of the film with the height of O (manufactured by Elionix Co., Ltd.) is sent as a 256-level gray value to an image processing device [IBAS2000, manufactured by Carl Zeiss Co., Ltd.]. Based on this gray value I
Reconstruct the film surface projection image on BAS2000.

Next, the surface protrusion image was binarized with 10 or more gradations, and the circular phase 5 diameter was determined from the area of each protrusion obtained, and this was taken as the surface protrusion diameter. In the gray value of the 256 gradations, the O gradation is represented by black, indicating the smooth surface of the film, and the 255th gradation is represented by white. Further, the height of one gradation is the value obtained by dividing the arbitrary setting value H by 256. The arbitrary setting value 1 is a value obtained by multiplying the normally measured Ra (unit: 2 μm) of the film surface by 30. In addition, the magnification of the scanning electron microscope is selected to be between 2000 and 8000 times,
It is changed depending on the Ra of the film surface. Measurements were made at 100 to 500 points in the horizontal direction using a scanning electron microscope.
This was measured in 512 rows in the vertical direction, and the measured value was taken as a value per one field of view.

This measurement was performed for 1 mm2, and the surface protrusion diameter indicated by the highest point of the peak of the surface protrusion diameter distribution curve, and the surface protrusion diameter with the highest frequency (number of protrusions) among the surface protrusions was defined as the surface protrusion diameter d. .

(5) Surface projection height H The highest value of the gray value of the protrusion is converted into a protrusion height unit of 2 μm (gray value x arbitrarily set value (H) x 1/255). This measurement is performed for 1 mm2, and the entire surface is The surface protrusion height with the highest frequency among the protrusion heights was defined as the surface protrusion height H.

(6) Planar orientation index Using an Atsube refractometer with sodium D line (wavelength 589nll) as a light source, measure the refractive index in the thickness direction of the biaxially oriented film (referred to as A) and quench it in water at 10°C after melt pressing. The refractive index (referred to as B) in the thickness direction of the non-oriented (amorphous) film produced was measured, and A/B was taken as the plane orientation index. Methylene iodide was used as the mounting solution, and the measurement was performed at 25° C. and 65% RH.

(7) Density index The density of the film measured using a density gradient tube made of n-hebutane/carbon tetrachloride is dl (g/aT!),
This film was melt-pressed and then rapidly cooled in water at 10° C. The difference in density d2 of the non-oriented (amorphous) film was defined as the density index (dl − d2 ).

(8) Measurement was performed using a melt viscosity enhancement type flow tester at a temperature of 290° C. and a shear rate of 200 sec.

<9> Surface average roughness Ra Measured using a stylus type surface roughness meter according to J15-B-0601. However, the cutoff is OoQ 8mm,
The measurement length was 1 mm (scanned in the width direction) <10>
Slip property (friction coefficient with metal guide) Using a tape runability tester model TBT-300 (manufactured by Yokohama System Research Co., Ltd.), run in a 20'C 160% RH atmosphere to determine the initial μk (friction coefficient). was calculated from the following formula.

μ = o, 733D, ocl (T1/To) where To is the inlet tension and T1 is the outlet tension.

The guide diameter is 6mmf;5, and the guide material is 5US
27 (surface roughness 0.2S), the winding angle is 180°, and the running speed is 3.3 cm/sec.

If the above μk is 0.30 or less, the sliding property is good, 0.30
If it exceeds this value, it is determined that the slip property is poor.

A value of 0.30 for μ is the critical point in determining whether troubles due to slippage will occur during processing steps such as a printing process or a calendaring process, or during running when a magnetic tape is used.

(11) Press one blade perpendicularly against a tape-like slit of abrasion-resistant film 1/2 inch wide, push it further 0°5 mm, and run it 20 cm (running tension 500 g, running speed 6.7 cm/ seconds). At this time, the height of the scraped material on the film surface attached to the tip of the single blade is read using a microscope, and the height of the scraped material is measured in micrometers.

If this abrasion is 5 μm or less, the abrasion resistance is good.
If it exceeds μm, the abrasion resistance is judged to be poor. This value of 5 μm indicates whether or not the film surface will be scratched during processing steps such as printing and calendering, causing problems in the process or in product performance of magnetic media for short wavelength recording. This is the critical point when making strict judgments.

[Example] The present invention will be explained based on examples.

Examples 1 and 2, Comparative Examples 1 and 2 Ethylene glycol slurries of various colloidal silicas with different average particle sizes were subjected to transesterification and polycondensation with dimethyl terephthalate at a silica concentration of 1% by weight to form master pellets. Had made. The crystallization parameter ΔTcg of this master pellet was 80'C. This master pellet and pellets of polyethylene terephthalate containing no inert inorganic particles (ΔTcg was 68°C) were mixed so that the particle content was varied. This mixed pellet was dried under reduced pressure (3 Torr) at 180° C. for 3 hours.

The pellets were fed into an extruder, melt-extruded at 300°C, wound around a casting drum with a surface temperature of 30'C using an electrostatic casting method, and cooled and solidified to a thickness of about 1.
An 80 μm unstretched film was made. This unstretched film was stretched 3.4 times in the longitudinal direction at 90°C.

This stretching was carried out using a difference in peripheral speed between two sets of rolls, and the stretching speed was 10,000%/min. This -axis film was stretched 3.6 times in the width direction at 100°C at a stretching rate of 2000%/min using a stenter, and then heat-treated at 210'C for 5 seconds under constant length to form a 15 μm thick film of 1q. Ta.

The average grain size 01 of silica in these films, the average surface roughness Ra in the width direction, and the average height H of surface protrusions are as shown in Table 1. When the average particle size was outside the range of the present invention, no matter how much Ra and H were modified, a film that had both slipperiness and abrasion resistance could not be obtained.

Examples 3 to 5, Comparative Examples 3 to 5 An ethylene glycol slurry of inert inorganic particles with different average particle diameters and types was subjected to a transesterification reaction and polycondensation with dimethyl terephthalate with a silica rR degree of 1% by weight to form master pellets. made. At this time, by changing the polymerization conditions and copolymerization components, the crystallization parameter ΔTcg was changed as shown in Table 2.

This master pellet and polyethylene terephthalate pellets containing no inert inorganic particles (ΔTca65℃
) were mixed to have various particle contents, and 1q of biaxially oriented films with a thickness of 15 μm were prepared in the same manner as in Example 1. The average particle diameter D of the inert inorganic particles of these films, the average surface roughness Ra in the width direction, and the average height of surface protrusions 1
are shown in Table 3. As shown in Table 3, even if the average roughness of the film surface is almost the same, it is D.

When Ra and H satisfy the relational expression of the present invention, slipperiness,
A film having both abrasion resistance was obtained, but otherwise a film having both slipperiness and abrasion resistance could not be obtained.

Table 2 Note 1) Polyethylene terephthalate 2) Polyethylene terephthalate/isophthalate copolymer (copolymerization ratio (molar ratio): 80/20) As a result of controlling the surface morphology, a film with both slipperiness and abrasion resistance was obtained, making it suitable for faster film processing processes in the future.

The use of the film of the present invention is not particularly limited, but it is suitable for use as a magnetic recording medium, particularly a videotape base film, which requires abrasion resistance during the processing process and product performance.

Claims (1)

[Scope of Claims] A biaxially oriented film mainly composed of a composition consisting of polyester and inert inorganic particles, the average particle diameter D (μm) of the inert inorganic particles, the surface average in the width direction of the film, A biaxially oriented polyester film characterized in that the roughness Ra (μm) and the average surface protrusion height H (μm) satisfy the following formulas (1) to (3). 0.05≦D≦0.6 (1) Ra≧0.04D (2) 2Ra≦H≦8Ra (3)