JPH06320618A - Polyester film and its production - Google Patents

Abstract

(57) [Summary] [Structure] A biaxially oriented film comprising polyester A as a main component, wherein the number of protrusions on at least one surface is 5 × 10 ³ / mm ² or more. A polyester film having a number of protrusions / number of particles (N _R ), which is a ratio with the number of particles contained in the surface layer forming the surface, of 2 or more and less than 5, and a method for producing the same. [Effects] Protrusions that are not easily broken can be formed, and the protrusion height and protrusion diameter can be given an appropriate distribution, which improves the wear resistance of the film surface and improves the winding stability during film production. Improvements can be achieved together.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester film and a method for producing the same, and more particularly to a polyester film having fine projections formed on its surface and a method for producing the same.

[0002]

2. Description of the Related Art Polyester films are widely used for various purposes. As the processing speed increases in the processing of polyester film, such as printing in packaging, magnetic layer coating in magnetic recording media, or thermal transfer layer coating in thermal transfer applications, or the required quality of the final product. With sophistication, the polyester film is required to have better surface properties such as running property and abrasion resistance. It is known that it is effective to uniformly form fine projections on the film surface in order to obtain good runnability. further,
In order to improve the productivity of the film, it is effective to add multiple kinds of particles with different particle sizes to the film as a means to improve the winding stability at the time of slitting, so as to have an appropriate distribution of protrusion heights. Is known to be.

A polyester film containing substantially spherical silica particles derived from colloidal silica in order to form fine projections on the surface of the film is known (for example, JP-A-59-171623). . A polyester film in which a thin layer containing particles for forming surface protrusions is laminated on a base layer is also known (for example, JP-A-2-77431).

[0004]

However, the above-mentioned conventional polyester film having projections formed on the surface only by containing particles (for example, inert particles) has the following problems.
Basically, there are the following problems.

First, since particles such as inert particles different from polyester are added to polyester to form surface protrusions, voids are easily generated around the particles. When the voids are formed, the formed projections are easily broken, the film surface is easily scraped off, or the film surface is easily scratched, which causes a problem that the abrasion resistance of the film surface is deteriorated.

Further, in order to avoid the above problems, if the amount of particles added is kept small, the number of projections that are easily scraped off can be reduced, but the number of surface projections themselves becomes too small and the target The effect of improving the running property and the effect of improving the winding stability at the time of slitting are reduced.

An object of the present invention is to provide a polyester film having desired fine projections formed on the surface thereof by utilizing crystallization of polyester essentially without depending on the contained particles, and a method for producing the same. A polyester film with good abrasion resistance and improved winding stability by setting the ratio of the number of surface protrusions due to polyester crystals that are not easily broken to the total number of protrusions on the film surface within a specific range To provide.

[0008]

The polyester film of the present invention for this purpose is a biaxially oriented film containing polyester A as a main component, and the number of projections on at least one surface is 5 × 10 ³ / mm ² or more,
The number of projections / the number of particles (N _R ) which is the ratio of the number of particles contained in the surface layer forming the surface is 2 or more and less than 5.

That is, in the polyester film of the present invention, the ratio N _R of the number of projections formed on the surface to the number of particles contained in the surface layer is 2 or more and less than 5, and most of the surface projections are essentially Specifically, it is not formed by particles, but is formed by utilizing the crystallization of polyester A itself. Therefore, the problem of void generation when adding particles is significantly reduced, and many protrusions that are not easily broken are formed. When N _R is less than 2, the proportion of protrusions formed by the contained particles increases, and the proportion of protrusions that are easily broken due to void formation increases, so that desirable wear resistance cannot be obtained.

As described above, approximately half or more of the surface protrusions are formed by utilizing the crystallization of the polyester A, and the number of surface protrusions is set to 5 × 10 ³ / mm ² or more, so that the surface protrusions are finely broken. Difficult protrusions are uniformly formed on the film surface. As a result, a polyester film having a high abrasion resistance on the surface can be obtained.

Further, since the surface protrusions formed by utilizing crystallization do not have the contained particles as the core, the surface protrusions have hardness equal to or close to that of polyester A, that is, lower than the protrusions formed by the contained particles. Has hardness. Since the projections formed are relatively soft, even when the film is run on a plastic guide, the guide surface is hardly scraped, and the problems associated with the guide surface scraping are eliminated.

The surface protrusions due to the crystals formed in the present invention are very uniform in diameter and height, and the shape of each protrusion is slightly different from that formed by adding particles. . Therefore, if the proportion of protrusions caused by crystals is increased, the height and size uniformity of the surface protrusions will be improved, and the problem of deterioration in wear resistance caused by voids will be eliminated, but the film Concerning the winding stability at the time of production, there is a possibility that it may be disadvantageous. That is, in order to improve the winding stability of the film and improve the productivity, it is necessary to provide the protrusion height or the protrusion diameter with an appropriate distribution.
It has been found that the winding stability is remarkably improved by setting the value of N _R to be less than 5. That is, when the film is wound up, the uniform protrusions caused by the crystal have an appropriate ratio of protrusions caused by the particles, which are different in height or shape from the protrusions caused by the crystal. The air release property between the film and the film is improved, and the film can be stably wound. Therefore,
By setting N _R to 2 or more and less than 5, both high wear resistance and excellent winding stability can be achieved.

Formation of the surface protrusions in the film of the present invention, including the surface protrusions utilizing the crystallization of polyester A as described above, is carried out as follows. In producing a biaxially oriented film containing polyester A as a main component and containing inert particles and the like in an appropriate ratio, at least one surface of the unstretched film is heat-treated, and then the unstretched film is biaxially stretched. As a result, desired surface protrusions utilizing crystallization are formed.

By first subjecting the unstretched film to a heat treatment, crystallization of the surface of the unstretched film is promoted, and a large number of fine crystals are produced. This unstretched film is stretched biaxially, the film is oriented biaxially and the target strength of the film itself is achieved, and due to the difference in hardness between the crystal and the other part, it is caused by the fine crystals. Uniform fine surface protrusions are formed. Here, regarding whether or not the surface protrusions are made of fine crystals of polyester A, etching is performed below the target protrusion in the film thickness direction with an appropriate solvent, and the cause of the formation of the protrusions is When it remains as an insoluble substance, it is a particle added from the outside or a particle deposited inside (I).
If there is substantially no insoluble matter remaining,
It can be presumed that the substance that forms the protrusion is a fine crystal (II). As the above-mentioned solvent, for example, a mixed solvent of phenol / carbon tetrachloride (weight ratio: 6/4) is preferably used. By this method, the frequency of I and the frequency of II when the visual field is set to about 1 mm ² is obtained, and it is preferable that the value of II / (I + II) is appropriately high. However, the method for determining whether or not the surface protrusions are made of fine crystals of polyester A is not limited to the above method, and an appropriate method can be selected.

In the present invention, the type of polyester A is not particularly limited, but the crystallization parameter ΔTcg is 8
0 ° C or lower, preferably 70 ° C or lower, more preferably 6
5 ° C. or lower, particularly preferably 60 ° C. or lower, and solution haze when dissolved in a solvent is 20% or lower, preferably 10
% Or less is desirable.

When the crystallization parameter ΔTcg is larger than 80 ° C., it is difficult to obtain the surface protrusions targeted by the present invention. Even if it is obtained, the scratch resistance of the film surface is poor.

When the solution haze is more than 20%, the amount of precipitated particles or added particles in the polymer is large, a surface which does not satisfy the target of the present invention cannot be obtained, and the abrasion resistance is poor.

The polyester A is not particularly limited as long as the above conditions are satisfied, but ethylene terephthalate, ethylene α, β-bis (2-chlorophenoxy) ethane-4,4'-dicarboxylate, ethylene 2, It is particularly preferable when at least one structural unit selected from 6-naphthalate units is the main constituent.
Of these, polyesters containing ethylene terephthalate as a main constituent are particularly preferable. Two or more kinds of polyesters may be mixed, or a copolymerized polymer may be used, as long as the object of the present invention is not impaired.

In order to form the target surface protrusions, the film containing polyester A as a main component is crystallized by heat treatment before biaxial stretching as described above, but the unstretched film before biaxial stretching. Diameter d of spherulites present in
Is preferably in the range of 0.03 to 0.45 μm. More preferably, it is in the range of 0.10 to 0.30 μm. By controlling in such a range,
The projection strength and the winding stability on the film surface after biaxial stretching are both excellent.

The polyester film of the present invention may be used as a biaxially oriented film single layer containing polyester A as a main component, or as a laminated film laminated on at least one side of a film containing polyester B as a main component. You may be asked.

The type of polyester B is not particularly limited. The polyester B preferably does not contain particles, but may contain it.

The polyester film of the present invention has a haze of 20% as a whole film regardless of whether it is a single layer or a laminated film as described above.
Less than 10%, preferably less than 10%. When the haze is 20% or more, the surface unevenness that increases the haze is often too large, the wear resistance is poor, and the electromagnetic conversion characteristics are deteriorated in the magnetic recording medium application.

Next, the method for producing the polyester film of the present invention will be described more specifically. In the present invention, at least one surface of the unstretched film is heat-treated and then biaxially stretched. Here, the unstretched film refers to a state immediately after being extruded from the die and before being cooled and solidified, to a slightly stretched (up to about 2 times) slightly in the uniaxial direction. The purpose of this heat treatment is to increase the crystallinity of the film surface before stretching to a preferable crystallinity, and as a treatment method, a method in which the film having a high temperature immediately after extrusion is gradually cooled to be crystallized,
There are a method of reheating a film once cooled and solidified to crystallize it, and a method of heat-treating it in a state of being slightly stretched in the uniaxial direction.

In order to obtain the surface morphology in accordance with the object of the present invention, the method (1) is preferable, but even if the method (1) is used, a desired surface morphology can be obtained by adopting appropriate conditions. The heat treatment method of (1) is not particularly limited, but includes a method of heat treatment in a state of being wound around a roll, a method of heat treatment using a radiator between rolls, a method of heating using a stenter, and the like. As the treatment conditions, it is desirable to perform heat treatment at a temperature of 100 to 250 ° C. for 0.5 to 150 seconds. More preferably, the heat treatment conditions of 140 to 250 ° C. for 1 to 50 seconds, and more preferably 155 to 240 ° C. for 2 to 10 seconds are required to efficiently obtain the target surface morphology in the film forming process. This is a desirable condition.

Polyethylene terephthalate (PET) is preferably used as the polyester A according to the present invention. The polyester A must contain particles in such a ratio that the ratio (N _R ) of the number of surface protrusions to the number of particles contained in the surface layer falls within the range of the present invention. The particles added to the polyester A are not particularly limited, but substantially spherical silica particles or crosslinked organic particles derived from colloidal silica, calcium carbonate, titanium dioxide, alumina, or internally precipitated particles may be used. Good.

Here, adding a large amount of particles such that the value of N _R is less than 2 causes a significant decrease in wear resistance. The average particle size of the added particles is 0.05 to
The thickness is preferably in the range of 2 μm, more preferably in the range of 0.15 to 1.2 μm, still more preferably 0.1.
When it is in the range of 3 to 0.9 μm, the distribution of the height or diameter of the protrusions caused by the crystal and the height or diameter of the protrusions caused by the particles becomes more appropriate, and wear resistance and winding It is desirable because it is possible to more easily achieve both the taking stability.

In the polymerization of polyester A, it is preferable to use antimony trioxide as a polymerization catalyst, and acetate as the metal compound as the transesterification catalyst in order to reduce ΔTcg and enhance the effect of the crystal nucleating agent. The acetate salt is not particularly limited, but it is particularly preferable to use a magnesium compound in order to achieve the object of the present invention. Further, it is preferable to use phosphonate as the phosphorus compound added during the polymerization of PET. However, the method for producing the polyester A is not limited to the above. Increasing the amount of catalyst added to enhance the nucleating agent effect is not preferable because it causes the precipitation of internal particles and increases the solution haze.

[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) Number of protrusions on the film surface A flat surface of the film surface was measured by a scanning electron microscope [ESM-3200, manufactured by Elionix Co., Ltd.] using a two-detector method and a cross-section measuring device [PMS-1, manufactured by Elionix Co., Ltd.]. The height measurement value of the protrusions when the height is 0 is sent to an image processing apparatus [IBAS2000, manufactured by Carl Zeiss Co., Ltd.] to reconstruct the film surface protrusion image on the image processing apparatus. Next, the highest value among the individual projections obtained by binarizing the projections in this surface projection image is taken as the height of the projection, and this is calculated for each projection. This measurement was repeated 500 times at different places, and those having a height of 20 nm or more were used as protrusions to determine the number of protrusions. The magnification of the scanning electron microscope is selected to be 1000 to 8000 times. In some cases, a high-precision optical interference type three-dimensional surface analyzer (WY
KO TOPO-3D, objective lens: 40-200
It is also possible to read the number information such as the peak count obtained by double use of the high resolution camera (effective) and replace it with the value of the SEM. In order to capture the projections three-dimensionally, the film was tilted by 82.5 °, and a photograph was taken with an electron microscope (SEM) at a magnification of 10,000 to 500,000 times, and the number of projections was calculated from the average value of 100 visual field measurements. It may be converted per 1 mm ² .

(2) Number of Particles Contained in Surface Layer In the present invention, the surface layer means a portion from the film surface to a depth of 3D. Here, 3D means the average particle diameter D × 3 of the particles contained in the film. The cross section of the film is observed with a transmission electron microscope (TEM), and the number of particles existing in a portion from the surface to a depth of 3D is magnified at 3,000 to 100,000.
Observation is performed twice at 500 times, and the average number of particles converted per 1 mm ² is obtained.

(3) Average particle size of particles in film The polymer is removed from the film by a plasma low temperature ashing method to expose the particles. The processing conditions are such that the polymer is incinerated but the particles are not damaged as much as possible. The particles are observed with a scanning electron microscope (SEM), and the particle image is processed with an image analyzer. The magnification of the SEM is approximately 2000 to 10,000 times, and the visual field in one measurement is appropriately selected from approximately 10 to 50 μm on each side. The volume average diameter d is obtained from the particle diameter and its volume fraction with the number of particles of 5000 or more by changing the observation location. d = Σd _i · Nv _i where d _i is the particle size and Nv _i is the volume fraction thereof. When the particles are organic particles or the like and are significantly damaged by the plasma low temperature ashing method, the following method may be used. Using a transmission electron microscope (TEM), the film cross section is 30
Observe at 00-100,000 times. The section thickness of the TEM is set to about 1000 Å, the location is changed and 500 or more visual fields are measured.

(4) Crystallization Parameter ΔTcg DSC (Differential Scanning Calorimeter) II manufactured by Perkin Elmer II
It was measured using a mold. The measurement conditions of DSC are as follows. That is, 10 mg of the sample is set in the DSC device,
After melting at a temperature of 300 ° C. for 5 minutes, it is 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. The difference between Tcc and Tg (Tcc-Tg) is defined as the crystallization parameter ΔTcg.

(5) Solution haze of polymer 2 g of polyester was dissolved in 20 ml of a mixed solvent of phenol / carbon tetrachloride (weight ratio: 6/4) to prepare ASTM-
It was measured according to D-1003-52. The optical path length is 20
The measurement was performed as mm.

(6) Average diameter of spherulites The cross section of the film is observed by an optical or electron microscope, and the measurement is repeated until a total of 100 spherulites can be observed, and the obtained values are averaged to obtain spherulites. The average diameter was used.

(7) The film haze was measured using a haze meter according to JIS-K-6714.

(8) Breaking strength of protrusions A film slit into a tape having a width of 1/2 inch is repeatedly run on a guide pin using a tape running tester. (Guide material: SUS, surface roughness:
0.3S) A load of 200 g is applied to one end of the film, the film is run for 20 passes at a wrapping angle of 90 degrees and a running speed of 3.3 cm / sec, and then the amount of white powder adhering to the guide pins is evaluated. Was observed with a differential interference microscope to evaluate the breakage of protrusions and the falling state of particles. Magnification 1
Observed in 10 fields of view at a magnification of 000, and the ratio of the locations where the particles fall out relative to the total number of protrusions is excellent (almost no particles are found), good (some particles are found but a slight amount of white powder adheres), and poor. (A large number of particles dropped out and a large amount of white powder adhered) were used for the three-level evaluation.

(9) Winding stability The film was wound up on a roll having a width of 1000 mm and a length of 18000 m (speed: 300 m / min), and the end face deviation of this winding roll and the state of vertical wrinkles were inspected in detail. It was judged. End face deviation (distance in the width direction) is 0.5
Less than 0.5 mm, no vertical wrinkles and no defects such as vertical wrinkles even after standing for 24 hours or more: excellent, end face shift was less than 0.5 mm immediately after winding the roll, and no vertical wrinkles 24 Visually slight vertical wrinkles after standing for at least the time: good, misalignment of 0.5 mm or more, or slight vertical wrinkles immediately after winding the roll: bad. Good is desirable, but good is practically usable.

[0037]

EXAMPLES Next, the present invention will be explained based on examples. Example As polyester A, polyethylene terephthalate polymerized by a conventional method (polymerization catalyst: magnesium acetate 0.1
0% by weight, antimony trioxide 0.03% by weight, dimethyl phenylphosphonate as a phosphorus compound 0.35% by weight
Was used (intrinsic viscosity: 0.60, melting point: 25)
8 ° C, ΔTcg: 51 ° C, solution haze: 0.8%).

As the polyester B, 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. : 0.62, melting point: 259 ° C., ΔTc
g: 84 ° C). If necessary, inert particles were added to these polyesters at the time of polymerization or after the completion of the polymerization, and used as raw materials.

Examples 1 and 2 A single-layer film containing polyester A as a main component was prepared. Inactive particles were added to polyester A (crosslinked polystyrene particles having an average particle size of 0.6 μm were dispersed in a water slurry and kneaded into polyester A so that the particle content was 0.08% by weight). After the pellets were dried at 180 ° C. for 3 hours, they were melt-extruded at 290 ° C. using a known extruder, and the surface temperature was 20 at 20 ° C. using the electrostatically applied casting method.
It was wound on a casting drum at ℃, cooled and solidified to prepare an unstretched film. Of this unstretched film,
The surface not in contact with the drum was subjected to heat treatment using a known radiation heater under the condition that the film surface had the following temperature. Example 1: Heat treatment at 150 ° C. for 10 seconds Example 2: Heat treatment at 190 ° C. for 3 seconds After heat treatment, the film was heated at 90 ° C. in the longitudinal direction of 3.
Stretching 4 times, and then using a stenter, stretching speed 200
The film was stretched at 0% / min at 95 ° C in the width direction by 3.5 times and further heat-treated at 210 ° C for 5 seconds under a constant length to obtain a biaxially oriented film having a total thickness of 15 µm.

Example 3 A laminated film having an A / B / A three-layer structure was prepared. Example 1,
The pellets of polyester A and polyester B to which the particles used in 2 were added are respectively fed to two extruders,
It was melted at 290 ° C., and was joined and laminated by a rectangular joining block (feed block) for three layers. A biaxially oriented laminated film having a total thickness of 15 μm was obtained by the same process as in Example 1 below. The discharge amount was adjusted so that the layer A had a laminated thickness of 1 μm on both sides.

Example 4 As polyester A, polyethylene terephthalate containing 0.06% by weight of magnesium acetate, 0.03% by weight of antimony trioxide and 0.15% by weight of dimethylphenylphosphonate as the polymerization catalyst was used (ΔTcg: 5
8 ° C., solution haze: 2.5%). This polyester A
And colloidal silica particles having an average particle size of 0.45 μm,
Using the pellets added (dispersed in ethylene glycol and added at the time of polymerization) so as to have a content of 0.2% by weight, a laminated film having an A / B / A three-layer structure was prepared in the same manner as in Example 3. The heat treatment condition for the unstretched film is 2
The temperature was 00 ° C. for 2 seconds.

Comparative Example 1 Inert particles were added to the polyester A to which the particles were not added used in Examples 1 to 3 (average particle size of 0.1.
Using a pellet (particle content: 3% by weight) in which 3 μm colloidal silica particles were dispersed and added at the time of polymerization, a biaxial shaft having a total thickness of 15 μm was prepared in the same process as in Examples 1 and 2 above. An oriented monolayer film was obtained. However, the heat treatment conditions for the unstretched film were 190 ° C. and 3 seconds.

Comparative Example 2 Using the polyester A and the polyester B to which the inert particles used in Comparative Example 1 were added, a laminated film having an A / B / A three-layer structure was prepared in the same process as in Examples 3 and 4. Obtained.
However, the heat treatment conditions for the unstretched film were 200 ° C. and 2 seconds.

Comparative Example 3 A biaxially oriented monolayer having a total thickness of 15 μm was prepared in the same process as in Example 2, using pellets obtained by adding the same inert particles as in Examples 1 and 2 to Polyester B. I got a film.

Comparative Examples 4 and 5 Biaxially oriented single-layer films were obtained by using only polyester A to which particles were not added, under the following heat treatment conditions for unstretched films. Comparative Example 4: 180 ° C., 10 seconds Comparative Example 5: 100 ° C., 600 seconds

[0046]

[Table 1]

[0047]

According to the polyester film and the method for producing the same of the present invention, a specific number or more of fine projections are formed on the film surface, and the number of projections and the number of particles contained in the surface layer forming the surface are The ratio of the protrusions utilizing the crystallization of the polyester A and the protrusions caused by the particles is controlled to be in an appropriate range by setting the ratio of B to be in an appropriate range, so that void formation is suppressed and fracture is less likely to occur. Along with being able to form protrusions, it is possible to have an appropriate distribution in protrusion height, protrusion diameter, etc., achieving both improved wear resistance on the film surface and improved winding stability during film production. can do.

Claims (10)

[Claims] 1. A biaxially oriented film containing polyester A as a main component, wherein the number of protrusions on at least one surface is 5 × 10 ³ / mm ² or more, and the number of protrusions and the surface are formed. polyester film, characterized in that the ratio a is number of projections / number of particles and the number of particles contained in the surface layer (N _R) is less than 2 or 5. 2. The polyester film according to claim 1, wherein the crystallization parameter ΔTcg of the polyester A is 80 ° C. or lower. 3. The polyester film according to claim 2, wherein the crystallization parameter ΔTcg of the polyester A is 70 ° C. or lower. 4. The polyester film according to claim 1, wherein the solution haze when the polyester A is dissolved in a solvent is 20% or less. 5. The polyester film according to claim 4, wherein the solution haze when the polyester A is dissolved in a solvent is 10% or less. 6. The diameter d of spherulites present in the unstretched film of the biaxially oriented film before biaxial stretching is 0.03 to.
The polyester film according to claim 1, which has a thickness of 0.45 μm. 7. A polyester film comprising the polyester B as a main component, and the polyester film according to claim 1 laminated on at least one side of the film. 8. The polyester film according to claim 1, wherein the haze of the entire film is less than 20%. 9. The polyester film according to claim 8, wherein the haze of the entire film is less than 10%. 10. The method for producing a polyester film according to claim 1, wherein at least one surface of the unstretched film is heat-treated, and then the unstretched film is biaxially stretched.