JPH01230641A - Biaxially oriented polyester film - Google Patents

Abstract

PURPOSE:To make it possible to improve the surface strength and dimensional stability of a biaxially oriented polyester film comprising a polyester, a polyolefin and inert inorganic particles by specifying the molecular weight, crosswise strength at break and average height of protrusions on either surface. CONSTITUTION:This biaxially oriented polyester film is based on a composition comprising 90-99.8wt.%, particularly, 95-99% polyester (A) mainly consisting of ethylene terephthalate units, 0.2-10wt.%, particularly, 1-5wt.% polyolefin (B), desirably, polypropylene and 0.3-1.5wt.%, particularly, 0.4-0.8wt.% inert inorganic particles (C), desirably, colloidal silica of a mean particle diameter of 0.15-1.2mum prepared by the alkoxide process, wherein an Mn of component B is 6000-30000, desirably, 10000-27000, an Mw/Mn ratio <=4.0, desirably, 3.0-1.3, a crosswise elongation at break >=50%, desirably, >=80% and an average protrusion height on at least either surface is 20-500nm, desirably, 40-200nm. This film is desirable as a magnetic recording medium.

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 film made of polyester containing inert inorganic particles is known (for example, JP-A-59-178224).

[Problem to be solved by the invention] However, the above conventional biaxially oriented polyester film has the following problems:
Several problems have arisen as process speeds and process tensions increase in film processing processes, such as printing processes in packaging applications, magnetic layer coating and calendering processes in magnetic media applications, and the like.

In other words, (a) the powder generated when the film surface is scraped due to high-speed running causes problems in the processing process and product performance; and (b) the film has a high shrinkage rate as a result of being strained by high tension. However, problems such as skew (image distortion) when used as a videotape and printing misalignment when used for packaging have become a problem.

The present invention improves these problems, and provides less peeling from the film surface during high-speed running (hereinafter referred to as "good surface strength") and a small shrinkage rate (hereinafter referred to as "good dimensional stability").
The challenge is to provide film.

[Means for solving the problem] 90 to 99.8% by weight of polyester and 0% of polyolefin
．． A film whose main component is a composition containing inert inorganic particles in a mixture of 2 to 10% by weight,
The number average molecular weight Mn of the polyolefin is 6000 to 30
000, weight average molecule ff1Mw and number average molecule ffiM
The film is characterized in that the ratio of n, Mw/Mn is 4.0 or less, the elongation at break in the film width direction is 50% or more, and the average protrusion height on at least one side is in the range of 20 to 500 nm. It is an axially oriented polyester film.

The polyester in the present invention contains ethylene terephthalate as a main component. However, other components may be copolymerized within a range that does not interfere with the present invention, preferably within 10E-le%.

The polyolefin in the present invention has a number average molecular weight Mn of 6,000 to 35,000, preferably 8,000 to 3,000.
0. It is generally necessary that it be within the range of 10,000 to 27,000. It is not preferable if the number average molecule fflMn is smaller than the above range or conversely larger than the above range because the surface strength becomes poor.

The polyolefin in the present invention has a weight average molecular ffi
The ratio of MW to number average molecule ffiMn, MW/Mn is 4.0
Below, preferably 3.5 or less, more preferably 3.
It needs to be 0 or less. If MW/Mn is larger than the above range, the surface strength will be poor, which is not preferable. The lower limit of Mw/Mn is not particularly limited, but usually about 1.3 is the manufacturing limit. The type of polyolefin is not particularly limited, but polyethylene, polypropylene, and especially polypropylene are preferred because they have particularly good dimensional stability.

The content ratio of the polyester and polyolefin in the film of the present invention is 90 to 99.8% by weight of polyester and 0.2 to 10% by weight of polyolefin, preferably 93 to 99% by weight of polyester and 1 to 7% by weight of polyolefin. More preferably, the content should be in the range of 95 to 99% by weight of polyester and 1 to 5% by weight of polyolefin. If the ratio of polyolefin is smaller than the above range, the dimensional stability will be poor, and if it is larger, the surface strength will be poor, which is not preferable.

Although the inert inorganic particles in the present invention are not particularly limited,
When the average particle diameter is 0.15 to 1.2 μm, it is effective to obtain the average protrusion height within the range of the present invention. Further, the crystallization promotion coefficient of the inert inorganic particles is 10 to 25°C, preferably 1
A temperature of 0 to 20° C. is particularly desirable since the surface strength and heat shrinkage rate become even better. The inorganic particles of the present invention include:
Preferred are substantially spherical silica derived from colloidal silica, synthetic calcium carbonate, α-alumina, rutile type titanium dioxide, and thermal type carbon black.

In the case of colloidal silica, the ion exchange method, the alkoxide method, and the like are known as manufacturing methods, but the alkoxide method is particularly preferable because the surface strength and heat shrinkage rate are even better.

The content of the inert inorganic particles of the present invention is not particularly limited, but when the content is 0.3 to 1.5% by weight, especially 0.4 to 0.8% by weight, the surface strength and heat shrinkage rate are even better. This is particularly desirable.

The film of the present invention may also contain internally precipitated particles. However, the content of inert inorganic particles when used together with internal precipitated particles is not particularly limited, but may be 0°01 to 0.2, special G,
:o, 02 to 0.1ffiffi% (7) 373% is particularly desirable since the surface strength and heat shrinkage rate become even better. The internally precipitated particles in J5 of the present invention are particles produced by the combination of polyester constituents and at least one of calcium compounds, magnesium compounds, and lithium compounds added during polyester polymerization. The internally precipitated particles of the present invention may contain elemental phosphorus and trace amounts of other metal components, such as zinc, cobalt, antimony, germanium,
It may also contain titanium or the like.

The film of the present invention has the above composition as its 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, and ultraviolet absorbers may be added. , nucleating agents, and other inorganic or organic additives 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. Non-oriented or -axially oriented films are not preferred because both surface strength and dimensional stability are poor. Young's modulus, which indicates the degree of orientation, is 350 kCJ/mm2 in both the longitudinal and width directions, preferably 400 kQ/mm2
This is necessary from the viewpoint of surface strength and dimensional stability.

The film of the present invention needs to have an elongation at break in the width direction of 50% or more, preferably 70% or more, and more preferably 80% or more. If the elongation at break is smaller than the above range, the surface strength will be poor, which is not preferable. The upper limit of the elongation at break is not particularly limited, but if it is usually 180% or more, the edges tend to be jagged and have poor slitting properties when the film is slit to a predetermined width depending on the application. Therefore, it is not desirable.

The average height of the surface protrusions on at least one side of the film of the present invention is required to be in the range of 30 to 500 nm, preferably 40 to 300 nm, and more preferably 40 to 200 nm. If it is smaller than the range, or conversely if it is larger than the range, the surface strength will be poor, so it is not preferable.

The film of the present invention has an Rp of at least one side of 60 to 300.
nm, preferably in the range of 70 to 200 nm, is particularly desirable because the surface strength becomes even better.

It is particularly desirable for the film of the present invention that the Rp/Ra ratio (both in nm) on at least one side is in the range of 4 to 25, preferably 6 to 20, since the surface strength will be even better.

The film of the present invention is particularly desirable when the average distance between the protrusions on at least one side is 20 μm or less because the surface strength becomes even better.

In the film of the present invention, it is particularly desirable that the average cusps of the protrusions on at least one side be 0.08 or more, preferably 0.10 or more, since the surface strength will be even better.

The film of the present invention has a temperature of 80 to 2
40'C1, preferably exhibiting an endothermic peak in the range of 100 to 230'C, is particularly desirable because the dimensional stability is even better.

The film of the present invention has a water contact angle of 70 on at least one side.
It is particularly desirable that the angle is at least 75°, preferably at least 75°, since the dimensional stability and surface strength will be even better.

The film of the present invention has an X
PS (X-ray photoelectron spectrum, electron escape angle: 30'
) Dimensionally stable when the atomic ratio O/C (01,/C1,) of oxygen atoms O and carbon atoms C is in the range of 0°27 to 0.33, especially 0.29 to 0.325. This is particularly desirable because the properties and surface strength are even better.

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

First, as a method for mixing and incorporating a predetermined polyolefin into polyester, it is effective to add the polyolefin after polymerization of the polyester in order to obtain the elongation at break within the range of the present invention. As for the method of adding after polymerization, it may be added into the polymerization reactor when the polymerization of polyester is completed, or the pellets or powder of both may be melt-mixed in an extruder and used as pellets. . However, keeping the intrinsic viscosity of the polyester in the range of 0.55 to 0.75 is important for achieving the elongation at break within the range of the present invention and oxygen captured by XPS (X-ray photoelectron spectrum, photoelectron escape angle: 300) within the desired range. Atomic ratio O/C (01s/
C15), hereinafter abbreviated as xps atomic ratio. Furthermore, setting the melt mixing time to 3 to 40 minutes, particularly 5 to 30 minutes, is effective in achieving the elongation at break within the range of the present invention and the XPS atomic ratio within the desired range by 1.

In addition, inert inorganic particles may be added before, during, or after polymerization of polyester, but they may be added in the form of a slurry to ethylene glycol, which is the diol component of polyester. The method of adding in a dispersed manner is effective in satisfying the average protrusion height within the range of the present invention, Rp and RD/Ra ratio within the desired range. In addition, as a method for adjusting the content of inert inorganic particles,
High temperature master pellets, preferably 1-10%
A method in which a master pellet with a particle temperature of This method is effective in obtaining the average protrusion height, elongation at break, R1), Rp/Ra ratio, and XPS atomic ratio within the range of the present invention. In other words, it is an effective method for obtaining the film of the present invention that the polyolefin and the inert inorganic particles are not mixed until immediately before film formation.

The following method is effective for generating internally precipitated particles. That is, (1) a process of polycondensation through direct esterification of a predetermined dicarboxylic acid and ethylene glycol, or
(2) In the process of polycondensation through the transesterification reaction between the dimethyl ester of a predetermined dicarboxylic acid and ethylene glycol, at least one of glycol-soluble calcium compounds, magnesium compounds, manganese compounds, and lithium compounds and preferably phosphorus are added. is produced by adding an acid and/or ester compound. Compounds of calcium, magnesium, manganese, and lithium that can be used here include halides, nitrates, inorganic acid salts such as sulfur salts, acetates, oxalates,
Organic acid salts such as benzoates, glycol-soluble compounds such as hydrides and oxides are most preferably used, but two or more thereof may be used in combination. Further, as the phosphorus compound, one or more of phosphates, phosphorous acid, bosphonic acid, and their esters and partial esters are used.

After sufficiently drying the pellets made of polyester containing polyolenoin (substantially not containing inert inorganic particles or containing internally precipitated particles) and the pellets containing inert inorganic particles, the pellets were dried using a known melt extruder. The film is supplied to a temperature of 270 to 330'C, extruded into a sheet through a slit-like goo, and cooled and solidified on a casting roll to form an unstretched film. In this case, when extruding into an unstretched film, the ratio of the die slit gap/unstretched film thickness is set in the range of 5 to 30, preferably 8 to 20, so that the average protrusion height within the range of the present invention, It is effective in obtaining elongation at break, Rp in the desired range, Rp/Ra ratio, XPS atomic ratio, and protrusion cuspsiness. In addition, the method of setting the temperature of the extrusion supply zone to 290 to 330°C and lowering the temperature of the melting zone by 10 to 30°C lowers the average protrusion height, breaking elongation, and desired range of RD and RD in the range of the present invention.
/Ra ratio, XPS atomic number ratio, and protrusion cuspsiness by 1q. Furthermore, during melt extrusion, the 95% filtration accuracy (one round of measurement with a Coulter counter) is 1.5 to 6 μm,
In particular, it is recommended to use a 2 to 5 μm filter and install a static mixer 4-no in front of it and/or in the polymer flow path to achieve a breaking elongation within the range of the present invention and a P within the desired range.
It is effective and necessary for obtaining CI, Rp/Ra ratio, and XPS atomic ratio.

Next, this unstretched film is biaxially stretched and biaxially oriented. As the stretching method, a sequential biaxial stretching method or a simultaneous biaxial stretching method can be used. However, by using a sequential biaxial stretching method in which stretching is performed first in the longitudinal direction and then in the width direction, the longitudinal stretching is divided into three or more stages, and the total stretching ratio is 3.
．． The method carried out at 5 to 5.0 times the average protrusion height, breaking elongation within the range of the present invention, Rp within the desired range, R1)/Ra ratio,
This is effective for obtaining the XPS atomic ratio. The stretching temperature is 90
The range of 120'C to 120'C is effective for obtaining the average protrusion height, fracture elongation, R1), Rp/Ra ratio, and XPS atomic ratio within the range of the present invention. Stretching speed is 5000~5
A range of 0000%/min is preferred. A common method for stretching in the width direction is to use a stenter. As for the stretching ratio, a range of 3.0 to 5.0 times is effective for increasing the elongation at break of 1q within the range of the present invention, but if there is no devising at the time of extrusion as described above, this 18 ratio range is effective. This is undesirable because the film tends to break frequently, and even if the film is processed, there is a tendency for variations in properties to become large. The stretching speed in the width direction is preferably in the range of 1000%/min to 20000%/min. Next, this stretched film is heat treated. In this case, the heat treatment temperature is suitably in the range of 170 to 220 DEG C. and 0.5 to 60 seconds for one hour.

During heat treatment, it may be in any state of constant length, elongation, or relaxation in the width direction, but it may be 1.05 to 1.3 times, especially 1.05
Elongation of ~1.2 times is effective in obtaining the elongation at break within the range of the present invention and the distance between protrusions within the desired range of 17.

[Function] The present invention contains a specific polyolefin, and the height and breaking elongation of the surface protrusions of the film are set within a specific range, so the microscopic molecular movement of the film is suppressed, and the viscoelastic behavior of the surface protrusions is suppressed. It is presumed that the effect of the present invention was obtained because of the improvement.

[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) Ra, Rp, average distance between protrusions 3 mm Measured using a high-precision thin film step measuring instrument ET-10 manufactured by Shoshaku Kyusho. The conditions were as follows, and the average value of 20 measurements was taken as the value.

・Stylus tip radius: 065μm ・Stylus load: 5mg ・Measurement length: 1mm ・Cutoff (direction: 0.03mm) Note that Ra, Rp, and the average spacing of protrusions of 3m are determined by, for example, the surface Roughness Measurement and Evaluation Method” (Sogo Technological Center, 1983).

(2> Average particle size of the particles The particles are dispersed in ethanol, and the volume average diameter is measured by a centrifugal sedimentation method (Horiba, Ltd., using CAPA500).

(3) Add 1.0 liter of O-chlorophenol to the 1-side polyester 100Q particles, heat at 120'C for 3 hours, and then heat at 30°C using a Hitachi Koki (Tama) ultracentrifuge G155P-72.
Centrifugation is performed at 0 rpm for 40 minutes and the resulting particles are vacuum dried at 100'C. When the fine particles are measured using a scanning differential calorimeter, if a dissolution peak corresponding to the polymer is observed, O-chlorophenol is added to the fine particles.
After heating and cooling, perform centrifugation again. D. The fine particles in which the dissolution peak is no longer observed are defined as precipitated particles. Normally, two centrifugation operations are sufficient. The ratio (% by weight) of the thus separated particles to the total ffiffl is defined as β.

(4) Glass transition temperature, cold crystallization temperature TCC Measured using a DSC (differential scanning calorimeter) type ■ manufactured by PerkinElmer. The measurement conditions for DSC must be as follows. Transfer 10 mg of sample to DSCSC Ra 1,
After melting at a temperature of 'C for 5 minutes, it is quenched into liquid nitrogen. This rapidly cooled sample is heated at a rate of 10'C/min, and the glass transition point TO is detected.

The temperature was continued to be gradually raised, and the exothermic peak temperature of 1 m for crystallization from the glass state was determined to be the cold crystallization temperature Tcc.

Here, the difference between Tcc and Tg (TCC-TC+> is ΔTcg
It is defined as

(5) Crystallization promotion coefficient (unit: °C) ΔTCg (1) of polyester containing 1% by weight of inert inorganic particles by the above method, and ΔTCQ of polyester of the same viscosity from which inert inorganic particles are removed ( II)
Measure the difference between △TCg (II) and Heding CQ (1) [
[Delta]TCCI (II) - [Delta]TCΩ (■)] was taken as the crystallization promotion coefficient.

(6) Height, diameter, and kurtosis of protrusions Two-detector scanning electron microscope [ESM-3200,
manufactured by Elionix Co., Ltd.] and a cross-sectional measuring device [PMS-1,
Manufactured by Elionix Co., Ltd.], the height of the protrusion is measured when scanning with the height of the flat surface of the film set as O.
Processing device [I BAS2000, Carl Zeiss Co., Ltd.
The film surface protrusion image is reconstructed on IBAS2000 based on this gray one-shot image. Next, a circular equivalent diameter is determined from the area of each protrusion obtained by binarizing the protrusion portion using this surface protrusion image, and this is taken as the average diameter of the protrusion. Further, the highest value among the binarized individual protrusion portions is defined as the height of the protrusion, and the ratio of the height to the average diameter of the protrusion is determined as the surface protrusion cuspsiness for each protrusion. This measurement was repeated 500 times at different locations, and the average value for all the measured protrusions was used. Moreover, the magnification of the scanning electron microscope is selected from a value between 1000 and 500 times, and is changed depending on the Ra of the film surface.

(7) Elongation at break: 25% using an Instron type tensile tester according to the method specified in Jl5-Z-1702.
Measurement was performed at °C and 165% RH.

(8) Molecular weight characteristics of polyolefin It was measured using gel permeation chromatography (GPC).

The measurement conditions are as follows.

・ Equipment: GPC-150C (TER3 to W)・
Column: 5hodex/F-80M (Showa Denko)
Solvent: O-dichlorobenzene (0.1% ionol added) ・Flow rate: 1 mD,/min ・Temperature = 145°C ・Sample concentration: 0.1% by weight ・Injection amount: 0.4 mQ ・Detector: Differential refractive index Detector/molecular weight calibration: Monodisperse polystyrene (9) XPS atomic ratio Measurement was carried out under the following conditions using ES200 manufactured by Kokusai Electric Co., Ltd.

・Excitation X-ray: AIKα ray (1486, 6eV) ・Energy correction: The kinetic energy value of C13 main peak is set to 1
202. Adjusted to OV.

・Photoelectron escape angle: 30° (Photoelectron escape angle is the angle between the photoelectron escape direction and the sample film) (10) Water contact angle Using the CA-3 Micro 2 model from Kyowa Interface Science Co., Ltd., droplet method (Water, 23°C). Measurement positions were changed randomly, measurements were taken at 10 points, and the average was taken as one shift.

(11) Endothermic peak from Tq to melting point Measured using a PerkinElmer DSC (differential scanning calorimeter) type II. The DSC measurement conditions are as follows. That is, the sample 'Jon(l) was set in a DSC device, and the temperature of the endothermic peak detected after Tg was detected when the temperature was raised to 40°C was measured.

(12) 95% filtration accuracy The cut rate measured using a Coulter counter is 95%.
95% filtration accuracy (unit μ
m).

(13) Press one blade vertically into a tape-like slit of surface strength film with a width of 172 inches, push it further 0.5 mm and run it for 20 cm (Traveling tension crab 500C1,
Running speed: 6.7 cm/sec). At this time, the height of the scraped material on the film surface attached to the tip of the single blade was read using a microscope and was defined as the amount of scraped material (unit: μm).

For at least one side, if the amount of abrasion was 15 μm or less, the surface strength was determined to be good, and if it exceeded 15 μm, the surface strength was determined to be poor. This value of 15 μm of the amount of abrasion is a critical point for determining whether or not problems in process and product performance will occur due to abrasion of the film surface during processing steps such as printing and calendering.

(14) Add gauge lines (parallel to the width direction) at approximately 200 mm intervals in the longitudinal direction of the dimensionally stable film, and enlarge these intervals using a universal projection to measure accurately (A>. This sample was heated to 80'C Leave it for 30 minutes (no tension) and then re-measure.B), heat shrinkage rate (1
00x (A-B)/A>, unit %). If this heat shrinkage rate is less than 0.10%, the dimensional stability is good, 0.1
% or more, it was determined that the dimensional stability was poor.

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

Examples 1 to 4, Comparative Examples 1 to 8 Polyethylene terephthalate powder with an intrinsic viscosity of 0.70 and polypropylene powder with various molecular weight characteristics were mixed in various ratios using a Henschel mixer and melted using a 2@It extruder. Mixed and pelletized. This pellet and the master pellet containing 1% by weight of silica with an average particle size of 0.03 to 2 μm were heated at 120°C for 6 hours and then heated to 180°C.
The mixture was dried under reduced pressure at C for 2 hours (3 TOrr) and then mixed. The mixed pellets are supplied before extrusion, and the temperatures of the supply zone and melting zone are changed to melt and extrude the pellets.
An unstretched film was prepared by setting the unstretched film thickness ratio to 3 to 20, winding it around a casting drum with a surface temperature of 30° C. using an electrostatic casting method, and cooling and solidifying the unstretched film.

At this time, filters with different filtration accuracy were installed in the polymer flow path between the extruder and the die. This unstretched film
It was stretched 3.5 times in the longitudinal direction at 'C. Note that this stretching was carried out using a difference in the circumferential speed of the rolls, and the stretching speed was 20,000%/min. This -axis stretched film was stretched 4.0 times in the width direction using a stenter. The temperature at this time is 100'C
1 speed was 5000%/min. Furthermore, 1 in the width direction
．． Heat treated at 200'C for 5 seconds while stretching 06 times,
A biaxially oriented film with a thickness of 15 μm was obtained. The surface strength and dimensional stability of these films are shown in Table 1, and when the film properties are within the range of the present invention, both surface strength and dimensional stability are good. It can be seen that a film with both stability cannot be obtained. In addition, in the experimental examples shown in Table 1, the average protrusion height was the same on the front and back sides of the film.

[Effects of the Invention] The present invention contains a specific polyolefin, and the height of the surface protrusions and elongation at break of the film are set within specific ranges, so a film with excellent surface strength and dimensional stability can be obtained. , which can respond to faster film processing processes.

Although the use of the film of the present invention is not particularly limited, it is suitable for use in magnetic recording media where an increase in heat shrinkage due to powder generated during processing steps tends to cause problems in product performance. If only one side of the film is within the scope of the present invention, it is necessary to use that side as a running surface (non-magnetic surface for magnetic recording media applications, non-laminated surface for packaging applications, etc.).

Claims (1)

[Claims] 90-99.8% by weight of polyester and 0 polyolefin
．． A film whose main component is a composition containing inert inorganic particles in a mixture of 2 to 10% by weight,
The number average molecular weight Mn of the polyolefin is 6000 to 30
000) ratio of weight average molecular weight Mw to number average molecular weight Mn,
A biaxially oriented polyester film, characterized in that Mw/Mn is 4.0 or less, the elongation at break in the film width direction is 50% or more, and the average protrusion height on at least one side is in the range of 20 to 500 nm. .