JP2507522B2 - Biaxially oriented polyester film - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a biaxially oriented polyester film.

[Prior Art] As a biaxially oriented polyester film, a film in which inert inorganic particles are contained in polyester is known (for example, JP-A-59-178224).

[Problems to be Solved by the Invention] However, the conventional biaxially oriented polyester film described above has a process speed and a process tension such as a film processing process, for example, a printing process in a packaging application, a magnetic layer coating / calendering step in a magnetic medium application, and the like. Several problems have come up with the increase of the. That is, (a) the powder generated by scraping the film surface by high speed running causes troubles in the processing process and product performance. (B) As a result of the strain imparted by the high tension, the film has a high shrinkage ratio. Problems such as skew (image distortion) when used as a video tape and print misalignment in packaging applications have become problems.

The present invention solves the above problems and provides a film that has less powder falling from the film surface during high-speed running (hereinafter referred to as good surface strength) and has a small shrinkage ratio (hereinafter referred to as good dimensional stability). It is an issue.

[Means for Solving the Problems] 90 to 99.8% by weight of polyester and 0.2 to 1 of polyolefin
A film containing a composition containing 0% by weight of a mixture of inert inorganic particles as a main component, wherein the number average molecular weight Mn of the polyolefin is 6000 to 30,000, and the ratio of the weight average molecular weight Mw to the number average molecular weight Mn. , Mw / Mn is 4.0 or less,
A biaxially oriented polyester film having a breaking elongation in the width direction of the film of 50% or more and an average protrusion height of at least one surface of 20 to 500 nm.

The polyester in the present invention has ethylene terephthalate as a main constituent. However, other components may be copolymerized within a range not to impair the present invention, preferably within 10 mol%.

The polyolefin in the present invention has a number average molecular weight Mn of
It is necessary to be in the range of 6000 to 35000, preferably 8000 to 30000, and more preferably 10000 to 27000. If the number average molecular weight Mn is smaller than the above range or larger than the above range, the surface strength becomes poor, which is not preferable.

The polyolefin in the present invention has a weight average molecular weight Mw.
And the number average molecular weight Mn ratio, Mw / Mn is 4.0 or less, preferably 3.
It should be 5 or less, and more preferably 3.0 or less. If Mw / Mn is larger than the above range, the surface strength becomes poor, which is not preferable. The lower limit of Mw / Mn is not particularly limited, but usually about 1.3 is a manufacturing limit. The type of polyolefin is not particularly limited, but polyethylene and polypropylene, particularly polypropylene are preferable because the dimensional stability is particularly good.

The content ratio of the polyester and the polyolefin of 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, and more preferably, It should be in the range of 95 to 99% by weight of polyester and 1 to 5% by weight of polyolefin. If the proportion of polyolefin is smaller than the above range, the dimensional stability becomes poor, and conversely if it is large, the surface strength becomes poor, which is not preferable.

The inert inorganic particles in the present invention are not particularly limited, but when the average particle diameter is 0.15 to 1.2 μm, they are effective for obtaining the average protrusion height within the range of the present invention. Further, the crystallization acceleration coefficient of the inert inorganic particles is 10 to 25 ° C, preferably 10 to 20 ° C.
In this case, the surface strength and the heat shrinkage rate are further improved, which is particularly desirable. As the inorganic particles of the present invention, substantially spherical silica derived from colloidal silica, synthetic calcium carbonate, α-alumina, rutile type titanium dioxide, and thermal type carbon black are preferable. In the case of colloidal silica, an ion exchange method, an alkoxide method, etc. are known as a production method. However, the alkoxide method is particularly preferable because the surface strength and the heat shrinkage rate are further improved.

The content of the inert inorganic particles of the present invention is not particularly limited, but a content of 0.3 to 1.5% by weight, particularly 0.4 to 0.8% by weight is particularly preferable because the surface strength and the heat shrinkage rate are further improved.

The film of the present invention may use internally precipitated particles in combination. However, the content of the inert inorganic particles when used in combination with the internally precipitated particles is not particularly limited, but 0.01 to 0.2, particularly 0.02 to
When it is 0.1% by weight, the surface strength and the heat shrinkage rate are further improved, which is particularly desirable. The internally deposited particles in the present invention are particles formed by binding at least one compound of calcium compound, magnesium compound and lithium compound added at the time of polyester polymerization and the polyester constituent component. The internally precipitated particles of the present invention may contain elemental phosphorus and a trace amount of other metal components, such as zinc, cobalt, antimony, germanium, and titanium, within a range that does not impair the object of the present invention. Good.

The film of the present invention comprises the above composition as a main component, but may be blended with other polymers within a range not impairing the object of the present invention, and may also be an antioxidant, a heat stabilizer, a lubricant, an ultraviolet absorber. Inorganic or organic additives such as nucleating agents may be added to the extent that they are usually added.

The film of the present invention is a film in which the above composition is biaxially oriented. In non-oriented or uniaxially oriented film,
Both surface strength and dimensional stability become poor, which is not preferable. It is necessary in terms of surface strength and dimensional stability that the Young's modulus showing the degree of orientation is 350 kg / mm ² , preferably 400 kg / mm ² or more in both the longitudinal and width directions.

The film of the present invention is required to have a breaking elongation in the width direction of 50% or more, preferably 70% or more, more preferably 80% or more. If the elongation at break is smaller than the above range, the surface strength becomes poor, which is not preferable. The upper limit of the elongation at break is not particularly limited, but when it is usually 180% or more, when the film is slit into a predetermined width depending on each application, the end face is cut poorly and becomes jagged, and the slitting property tends to be poor. It is not desirable because it exists.

The film of the present invention is required to have an average height of at least one surface protrusion of 30 to 500 nm, preferably 40 to 300 nm, more preferably 40 to 200 nm. If the average height of the protrusions on both surfaces is smaller than the above range or larger than the above range, the surface strength becomes poor, which is not preferable.

The film of the present invention has Rp of at least one surface of 60 to 300 nm,
The surface strength is more preferably in the range of 70 to 200 nm, which is particularly desirable.

The film of the present invention is particularly preferable because the surface strength is further improved when the Rp / Ra ratio (unit: nm) on at least one side is in the range of 4 to 25, preferably 6 to 20.

The film of the present invention is particularly preferable because the surface strength is further improved when the average distance between the projections on at least one side is 20 μm or less.

The film of the present invention is particularly preferable because the surface strength is further improved when the average sharpness of the projections is 0.08 or more, preferably 0.10 or more on at least one side.

The film of the present invention has a glass transition point to a melting point of 80 to 240 in the temperature rising process in the DSC (Differential Scanning Calorimeter) measurement.
When the endothermic peak is in the range of 100 ° C, preferably 100 to 230 ° C, the dimensional stability is further improved, which is particularly desirable.

The film of the present invention has a contact angle of water on at least one side of 70
Dimensional stability when it is above °, preferably above 75 °,
It is particularly desirable because the surface strength becomes even better.

The film of the present invention has at least one surface,
Atom ratio O / C of oxygen atom O and carbon atom C set by XPS (X-ray photoelectron spectrum, electron escape angle: 30 °)
When (O _1S / O _1S ) is in the range of 0.27 to 0.33, particularly 0.29 to 0.325, dimensional stability and surface strength are further improved, which is particularly desirable.

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

First, mix the specified polyolefin with polyester,
As a method of incorporating the polyester, it is effective to add it after the polymerization of polyester in order to obtain the breaking elongation within the range of the present invention.
As a method of adding after the polymerization, it may be added to the polymerization reactor at the time when the polymerization of the polyester is completed, or both pellets or powder may be melt-mixed by an extruder and pelletized. However, keeping the intrinsic viscosity of the polyester within the range of 0.55 to 0.75 is preferable because the elongation at break in the range of the present invention and the oxygen atom O captured by XPS (X-ray photoelectron spectrum, photoelectron escape angle: 30 °) in the desired range. Carbon atom C atom number ratio O / C (O _1S / C _1S ), XPS below
It is effective in obtaining abbreviated as atomic ratio. Further, the time of melt mixing is set to 3 to 40 minutes, and particularly 5 to 30 minutes,
It is effective for obtaining the breaking elongation within the range of the present invention and the XPS atomic ratio within a desirable range.

Further, as a method of containing the inert inorganic particles,
The polyester may be added before, during, or after the polymerization, but the method of mixing and dispersing in the form of slurry with ethylene glycol, which is the diol component of the polyester, and adding it is the average protrusion height within the scope of the present invention. It is effective in satisfying the desired range of Rp and Rp / Ra ratio. Also,
As a method of adjusting the content of the inert inorganic particles, high-concentration master pellets, preferably containing a predetermined polyolefin master particle concentration of 1 to 10 wt%, containing substantially inert inorganic particles. A method of diluting at the time of film formation (a method of melt-extruding mixed pellets to form a film) with a polyester or a polyester containing internally precipitated particles is the average protrusion height within the scope of the present invention, the breaking elongation, and the desirable range of Rp and Rp. It is effective to obtain the / Ra ratio and the XPS atomic number ratio. That is, 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 just before film formation.

The following method is effective as a method for generating the internally deposited particles. That is, (1) a process of polycondensation through direct esterification of a predetermined dicarboxylic acid and ethylene glycol, or (2) a polycondensation through a transesterification reaction of dimethyl ester of a predetermined dicarboxylic acid with ethylene glycol. In the process, it is produced by adding at least one of a calcium compound, a magnesium compound, a manganese compound and a lithium compound soluble in glycol, and preferably an acid and / or ester compound of phosphorus. Examples of calcium, magnesium, manganese, and lithium compounds that can be used here include inorganic acid salts such as halides, nitrates, and sulfates, organic acid salts such as acetates, oxalates, and benzoates, hydrides, and oxides. Most preferred are glycol-soluble compounds such as compounds, but two or more kinds may be used in combination. As the phosphorus compound, one or more of phosphate, phosphorous acid, phosphonic acid and their esters and partial esters are used.

Thus, pellets of polyester containing polyolefin (substantially free of inert inorganic particles,
Alternatively, the pellets containing the internally precipitated particles) and the inert inorganic particles are sufficiently dried and then supplied to a known melt extruder and extruded into a sheet form from a slit die at 270 to 330 ° C., and then on a casting roll. It is cooled and solidified with to make an unstretched film. In this case, the average protrusion height in the range of the present invention is to set the ratio of the die slit gap / the thickness of the unstretched film to 5 to 30, preferably 8 to 20 when extrusion-molding the unstretched film. It is effective for obtaining the elongation at break, Rp, Rp / Ra ratio, XPS atomic ratio, and the sharpness of protrusions in a desired range. In addition, the temperature of the feed zone of the extruder is set to 290
~ 330 ℃, the method of lowering the temperature of the melting zone 10 to 30 ℃ lower than that, the average protrusion height of the present invention, the breaking elongation, the desired range of Rp, Rp / Ra ratio, XPS atomic number ratio, protrusion point. It is effective for getting a head. Furthermore, 95% filtration accuracy (measured by Coulter counter) is 1.5-6μ during melt extrusion.
m, particularly 2 to 5 μm, and a static mixer is installed in the polymer channel before and / or after the filter, the elongation at break in the range of the present invention, Rp in the desirable range,
It is effective for obtaining Rp / Ra ratio and XPS atomic number ratio.

Next, this unstretched film is biaxially stretched and biaxially oriented. As a stretching method, a sequential biaxial stretching method or a simultaneous biaxial stretching method can be used. However, first use the sequential biaxial stretching method of stretching in the longitudinal direction, then in the width direction,
Stretching in the longitudinal direction is divided into three stages or more to obtain a total stretch ratio.
The method performed at 3.5 to 5.0 times is the average protrusion height within the range of the present invention,
It is effective in obtaining the elongation at break, Rp, Rp / Ra ratio, and XPS atomic number ratio in desired ranges. The stretching temperature is in the range of 90 to 120 ° C., the average protrusion height in the range of the present invention, the breaking elongation, and the R of the desirable range.
It is effective for obtaining p, Rp / Ra ratio and XPS atomic ratio. The stretching speed is preferably in the range of 5,000 to 50,000% / min. As a stretching method in the width direction, a method using a stenter is generally used. The draw ratio is effective in obtaining a breaking elongation in the range of the present invention in the range of 3.0 to 5.0 times, but film breakage frequently occurs in this ratio range when there is no device for extrusion as described above, Even if a film is obtained, the variation in properties tends to increase, which is not desirable. The stretching speed in the width direction is preferably in the range of 1000 to 20000% / min. Next, this stretched film is heat-treated. The heat treatment temperature in this case is 17
The range of 0 to 220 ° C and the time of 0.5 to 60 seconds are suitable. At the time of heat treatment, it may be in any state of constant length, elongation and relaxation in the width direction, but it is 1.05 to 1.3 times, especially 1.05 to 1.2 times elongation at break of the present invention range, desirable range It is effective for obtaining the protrusion interval.

[Operation] Since the present invention contains a specific polyolefin and the height of the surface projections of the film and the elongation at break are within the specific ranges, the micromolecular motion of the film is suppressed, and the viscoelastic behavior of the surface projections is suppressed. It is presumed that the effect of the present invention was obtained because of the improvement.

[Physical property measuring method and effect evaluating method] The characteristic value measuring method and effect evaluating method of the present invention are as follows.

(1) Ra, Rp, average spacing of protrusions Sm Measurement was performed using a high precision thin film step measuring instrument ET-10 manufactured by Koita Laboratory. The conditions are as follows, and the average value of 20 measurements was taken as the value.

・ Stylus tip radius: 0.5μm ・ Stylus load: 5mg ・ Measuring length: 1mm. Cut-off value: 0.08 mm The resolution of Ra, Rp, and the average spacing Sm of the protrusions is shown in, for example, Jiro Nara "Measurement and Evaluation Method of Surface Roughness" (Comprehensive Technical Center, 1983). Is.

(2) Average particle size of particles This is a volume average particle size measured by a centrifugal sedimentation method (using CAPA500 manufactured by Horiba, Ltd.) by dispersing particles in ethanol.

(3) Particle content 1.0 g of 0-chlorophenol was added to 100 g of polyester, heated at 120 ° C. for 3 hours, and then centrifuged at 30,000 rpm for 40 minutes using an ultracentrifuge 55P-72 manufactured by Hitachi Koki Co., Ltd. And the resulting particles are vacuum dried at 100 ° C. When the dissolution peak corresponding to the polymer is observed when the fine particles are measured by a scanning differential calorimeter, 0-chlorophenol is added to the fine particles, and the mixture is heated and cooled, and then centrifuged again. When the dissolution peak is no longer observed, the fine particles are designated as precipitated particles. Usually, two centrifugation operations are sufficient. The ratio (% by weight) to the total weight of the particles thus separated is β.

(4) Glass transition point Tg, cold crystallization temperature Tcc It was measured using DSC (Differential Scanning Calorimeter) Model II manufactured by Perkin Elmer. The DSC measurement conditions are as follows.
That is, 10 mg of a sample is set in a DSC apparatus, melted at a temperature of 300 ° C. for 5 minutes, and then rapidly cooled in liquid nitrogen. The temperature of this quenched sample is raised at 10 ° C./min, and the glass transition point Tg is detected.
The temperature was further raised, and the crystallization exothermic peak temperature from the glass state was set as the cold crystallization temperature Tcc. Here, the difference between Tcc and Tg (Tcc−Tg) is defined as ΔTcg.

(5) Crystallization acceleration coefficient (unit: ° C) ΔTcg (I) of polyester containing 1% by weight of inert inorganic particles by the above method, and ΔTcg (II) of polyester of the same viscosity obtained by removing inert inorganic particles therefrom. The difference between ΔTcg (II) and ΔTcg (I) [ΔTcg (II) -ΔT
cg (I) "was used as the crystallization acceleration coefficient.

(6) Height, diameter, and cusp of projections Films on a two-detector scanning electron microscope "ESM-3200, manufactured by Elionix Co., Ltd." and a cross-section measurement device [PMS-1, manufactured by Elionix Co., Ltd.] The measured value of the height of the projection when scanning with the height of the flat surface as 0 is sent to the image processing device [IBAS2000, Carl Zeiss Co., Ltd.], and based on this gray value, the image of the projection of the film surface on IBAS2000 Next, the equivalent circle diameter is calculated from the area of each protrusion obtained by binarizing the protrusion portion in this surface protrusion image, and this is used as the average diameter of the protrusion. The highest value among the individual protrusions that were created is the height of that protrusion,
The ratio of the height to the average diameter of the protrusions is taken as the surface protrusion sharpness, and is obtained for each protrusion. This measurement was repeated 500 times at different locations, and the average value of all the measured protrusions was used. The scanning electron microscope has a magnification of 1000-80
Select a value between 00 times and change it according to the Ra of the film surface.

(7) Elongation at break 25 ° C, 65% using an Instron type tensile tester according to the method specified in JIS-Z-1702
It was measured at RH.

(8) Molecular weight characteristics of polyolefin It was measured using a gel permeation chromatograph (GPC).
The measurement conditions are as follows.

・ Device: GPC-150C (WATERS) Column: Shodex / KF-80M (Showa Denko) ・ Solvent: o-dichlorobenzene (0.1% ionol added) ・ Flow rate: 1 ml / min ・ Temperature: 145 ° C ・ Sample concentration: 0.1 weight % ・ Injection amount: 0.4 ml ・ Detector: Differential refractive index detector ・ Molecular weight calibration: Monodisperse polystyrene (9) XPS atomic ratio It was measured under the following conditions using ES200 manufactured by Kokusai Electric Co., Ltd.

・ Excited X-ray: AlKα ray (1486.6eV) ・ Energy correction: The kinetic energy value of the C _1S main peak was adjusted to 1202.0V.

・ Photoelectron escape angle: 30 ° (The photoelectron escape angle is the angle between the photoelectron escape direction and the sample film) (10) Water contact angle Using the Kyowa Interface Science Co., Ltd. CA-S Micro 2 model, the droplet method (Water, 23 ° C). The measurement position was randomly changed, and 10 points were measured, and the average value was used as the value.

(11) Endothermic peak from Tg to melting point It was measured using DSC (Differential Scanning Calorimeter) II type manufactured by Perkin Elmer. The DSC measurement conditions are as follows.
That is, 10 mg of the sample was set in a DSC apparatus, and the temperature of the endothermic peak detected after Tg was detected when the temperature was raised at 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) Surface strength A film is slit into a width of 1/2 inch and a single blade is pressed vertically against it, and it is run for 20 cm while it is pushed in 0.5 mm (running tension: 500 g, running speed: 6.7 cm /
Seconds). At this time, the height of the shavings on the surface of the film attached to the tip of the single-edged blade was read with a microscope and used as the shaving amount (unit: μ
m). At least on one side, it was judged that the surface strength was good when the scraped amount was 15 μm or less, and the surface strength was poor when the scraped amount was more than 15 μm. The scraped amount: 15 μm is a critical point for determining whether or not the film surface is scraped in a processing process such as a printing process or a calendar process, which causes a problem in product performance in the process.

(14) Dimensional stability Mark lines (parallel to the width direction) at intervals of about 200 mm in the longitudinal direction of the film, and enlarge this interval with a universal projector for precise measurement (A). This sample was left at 80 ° C for 30 minutes (no strain) and then remeasured (B) to determine the heat shrinkage (100 x (A
-B) / A), unit%). When the heat shrinkage rate was less than 0.10%, the dimensional stability was good, and when it was 0.1% or more, the dimensional stability was poor.

[Examples] The present invention will be described based on examples.

Examples 1 to 4 and Comparative Examples 1 to 8 Polyethylene terephthalate powder having an intrinsic viscosity of 0.70 and polypropylene powder having various molecular weight characteristics were mixed in various ratios with a Henschel mixer, melt-mixed using a twin-screw extruder, and pelletized. did. This pellet and the average particle size
The master pellets containing 1% by weight of 0.03 to 2 μm silica were dried at 120 ° C. for 6 hours and 180 ° C. for 2 hours under reduced pressure (3 Torr), and then mixed. The mixed pellets are fed to an extruder and melt-extruded by changing the temperature of the feeding zone and the melting zone, and the ratio of the die slit gap / thickness of unstretched film is set to 3 to 20, and the surface is applied by the electrostatically applied casting method. Temperature 30
It was wound around a casting drum at ℃ and solidified by cooling to prepare an unstretched film. At this time, filters with different filtration accuracy were installed in the polymer channel between the extruder and the die. This unstretched film was stretched 3.5 times in the longitudinal direction at 90 ° C. This stretching was carried out by the difference in peripheral speed of the rolls, and the stretching speed was 20000% / min. This uniaxially stretched film was stretched 4.0 times in the width direction using a stenter. At this time, the temperature was 100 ° C. and the speed was 5000% / min. Further, it was heat-treated at 200 ° C. for 5 seconds while stretching 1.06 times in the width direction to obtain a biaxially oriented film having a thickness of 15 μm. The surface strength and dimensional stability of these films are as shown in Table 1. When the film characteristics are within the range of the present invention, the surface strength,
Good dimensional stability, but otherwise surface strength,
It can be seen that a film having both dimensional stability cannot be obtained. In the experimental examples in Table 1, the film table,
The average protrusion height was the same on the back.

[Effects of the Invention] The present invention contains a specific polyolefin, and the height of the surface protrusions of the film and the elongation at break are within specific ranges, so that a film excellent in surface strength and dimensional stability is obtained. The film processing process can be speeded up. The use of the film of the present invention is not particularly limited, but it is suitable for a magnetic recording medium in which powder generated in the processing step and an increase in heat shrinkage tend to cause troubles in product performance. When 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 medium application, non-laminating surface for packaging application, etc.).

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Claims (1)

(57) [Claims] 1. A film comprising, as a main component, a composition comprising a mixture of 90 to 99.8% by weight of polyester and 0.2 to 10% by weight of polyolefin and containing inert inorganic particles, wherein the number average molecular weight Mn of the polyolefin is 6000-3000
0, the ratio of the weight average molecular weight Mw to the number average molecular weight Mn, Mw / Mn is 4.
0 or less, the breaking elongation in the film width direction is 50% or more,
A biaxially oriented polyester film having an average protrusion height of at least one surface in the range of 20 to 500 nm.