JPH06320693A - Laminated polyester film - Google Patents

Abstract

PURPOSE:To provide a film in which occurrence of a trouble upon generation of void can be suppressed and fine protrusions are formed densely and uniformly on a surface. CONSTITUTION:A laminated polyester film comprises an A layer containing polyester A as a main ingredient and laminated at least on one side surface of a B layer containing polyester B as a main ingredient, wherein surface protrusions due to fine crystal uniformly and regularly exist and a flat surface existing among the protrusions is small.

Description

Detailed Description of the Invention

[0001]

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

[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.

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). That is, the basic method of forming the surface protrusions of the conventional polyester film is to add particles to form fine protrusions on the surface.

[0004]

However, the conventional polyester film having projections formed on the surface thereof by containing particles (for example, inert particles) as described above basically has the following problems.

First, since various particles such as inert particles different from polyester are added to polyester to form surface protrusions, various side effects occur. The biggest problem is that the contained particles are foreign matter for the polyester, so that voids (cracks, voids) are easily generated around the particles by stretching. This void causes various troubles such as deterioration of transparency, reduction of electric breakdown voltage in capacitor application,
In addition, the surface projections become fragile, which causes surface abrasion.

Further, when a method by adding particles is used to form a dense surface projection, it is necessary to add particles in a considerably high concentration, and as a result, agglomeration of particles tends to occur and coarse projections are generated. Occurs, the height uniformity of the protrusions is lost, and the abrasion resistance deteriorates.

An object of the present invention is to provide a laminated polyester film which has desired fine projections formed on the surface thereof essentially without depending on the contained particles, has no voids, and has uniform and dense surface projections. To provide.

[0008]

A laminated polyester film according to the present invention for this purpose is a film in which an A layer containing polyester A as a main component is laminated on at least one side of a B layer containing polyester B as a main component. Therefore, the surface of the A layer is characterized in that surface projections caused by fine crystals are uniformly and regularly present, and there are few flat surfaces existing between the projections.

That is, in the polyester film of the present invention, the surface protrusions formed on the surface of the layer A, which are caused by the fine crystals, exist extremely uniformly and regularly, and
The projections are densely formed so that there are few flat surfaces existing between the projections. Such a uniform surface protrusion
In essence, it can be formed by utilizing the crystallization of the polyester A itself, rather than forming by containing particles. Therefore, the problem of void generation when adding particles is substantially eliminated, and the problems of various troubles associated with void generation are basically solved.

Since the polyester A layer is a layer for forming surface protrusions due to fine crystals, it is not necessary to make the A layer so thick. If the layer A is too thick, the crystal arrangement is disturbed and the height uniformity of the protrusions becomes poor, which is not preferable. Further, the influence of the highly crystallized layer A on the entire laminated film becomes too large, and the toughness of the laminated film as a whole may be insufficient. Therefore, it is preferable to consider so that the lamination ratio of the layer A to the entire thickness of the laminated film does not become too high.
It is preferably 0.5 or less.

The polyester A layer preferably contains no particles, but may contain them. However, when particles are contained, it is necessary to increase the ratio of the protrusions due to the fine crystals of polyester A in the surface protrusions of the A layer in order to prevent the occurrence of the above-mentioned problems associated with void formation. For example, 70% or more of the surface protrusions of the A layer are preferably protrusions caused by the fine crystals of the polyester A. 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). When there is substantially nothing that remains as an insoluble matter, it can be presumed that the substance that forms the protrusion is fine crystals (II). Examples of the solvent include phenol / carbon tetrachloride (weight ratio: 6
A mixed solvent of / 4) or the like is preferably used. The frequency of I and the frequency of II when the field of view is set to about 1 mm ² are obtained by this method, and it is preferable that the value of II / (I + II) is 70% or more. 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 laminated polyester film of the present invention, the crystallization parameter ΔTcg of polyester A is
Of 80 ° C. or lower and smaller than the crystallization parameter ΔTcg of polyester B, more preferably the crystallization parameter ΔTcg of polyester A is 70.
It is desirable that the temperature is not higher than ° C and is smaller than the crystallization parameter ΔTcg of polyester B. The ΔTcg of polyester A is more preferably 65 ° C. or lower, and particularly preferably 60 ° C. or lower. By setting the crystallization parameter ΔTcg of the polyester A to 80 ° C. or less, it becomes possible to easily generate fine crystals by heat treatment, and to form a target dense and uniform surface protrusion due to the fine crystals. can do. Crystallization parameter Δ
When Tcg is higher than 80 ° C., it is difficult to obtain the surface protrusion targeted by the present invention. Further, it is preferable that the crystallization parameter of the polyester B is set larger than that of the polyester A. Since the polyester B layer basically constitutes a base layer rather than a layer for forming surface protrusions, it is not necessary to particularly generate fine crystals,
In order to have the specified strength of the laminated film as a whole,
The polyester B layer may be set. By allowing the A layer and the B layer to have the above-mentioned crystallization parameter magnitude relationship, the A layer has a desired surface protrusion forming function, and the B layer has a function of exerting a desired strength and the like on the entire laminated film. It can be done even if it is clearly separated.

As the polyester A in the present invention,
It is not particularly limited as long as the above conditions are satisfied, but it is selected from ethylene terephthalate, ethylene α, β-bis (2-chlorophenoxy) ethane-4,4′-dicarboxylate and ethylene 2,6-naphthalate units. It is particularly preferable when at least one structural unit is the main constituent. Of these, polyesters whose main repeating unit is ethylene terephthalate 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.

The polyester film of the present invention is a laminated film in which an A layer containing polyester A as a main component is laminated on at least one surface of a B layer containing polyester B as a main component. As the laminated constitution, A / B two-layer constitution, A / B / A
In addition to a three-layer structure, a structure having four or more layers may be used. The type of this polyester B is not particularly limited. The polyester B preferably does not contain particles, but may contain it.

Next, an example of the method for producing the laminated polyester film of the present invention will be described, but the invention is not limited thereto. In the present invention, the layers consisting of polyester A and polyester B are laminated at the stage of polymer tube or die and discharged into a sheet to form an unstretched film. Then, at least one surface of the unstretched film is heat-treated (that is, the surface of the layer A on which surface protrusions are to be formed), and then stretched. By heat-treating the unstretched film, crystallization of the surface of the unstretched film is promoted, and a large number of fine crystals are generated.
When this unstretched film is stretched, uniform fine surface protrusions due to the fine crystals are formed so densely that flat surfaces are not formed due to the difference in hardness between the fine crystals and the other portions. At the time of stretching, the degree of orientation is 0.03 or less,
The density of the polyester A layer is 1.35 to 1.408 / cm
^The unstretched film designated as No. ³ is stretched 2.5 times or more in at least one direction, preferably in the biaxial direction. 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
It is to increase the crystallinity of the film surface before stretching to a preferable crystallinity, and as a treatment method, a method in which a film having a high temperature immediately after extrusion is gradually cooled to be crystallized, a film which has been once cooled and solidified is used. There are a method of reheating and crystallization, and a method of performing heat treatment 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 (2) is used, the 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 processing conditions, it is desirable to perform heat treatment at a temperature of 100 to 250 ° C. for 0.1 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. Also, for example, in the case of a three-layer composite film (A / B / A),
A polymer having a small ΔTcg is used for the A layer, and the heat treatment of one of the A layers is performed at a relatively high temperature (for example, 180 to 220).
It is possible to control the crystallization so that it is different between the front and back sides by applying it at a temperature of (° C.) for a short time (0.1 to 10 seconds).

Polyethylene terephthalate (PET) is preferably used as the polyester A according to the present invention. It is desirable that the polyester A contains substantially no particles. In the polymerization of polyester A, it is preferable to use antimony trioxide as a polymerization catalyst, and to use a acetate as a metal compound as a transesterification catalyst in order to reduce ΔTcg and enhance the crystal nucleating agent effect.
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. To enhance the effect of nucleating agents,
Increasing the amount of catalyst added is not preferable because it causes precipitation of internal particles and increases 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) Layer A Laminate Thickness Using a transmission electron microscope (Hitachi H-600 type), an acceleration voltage of 100 kV was used to measure the film cross section with an ultrathin section method (R
uO ₄ staining), the interface is captured, and the layer thickness is determined. The magnification is usually selected according to the laminated thickness to be judged, and is not particularly limited, but 10,000 to 100,000 times is suitable.

(2) Crystallization parameter ΔTcg DSC (differential scanning calorimeter) II manufactured by Perkin Elmer Co., Ltd.
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.

(3) Orientation degree of film The absolute value of the difference between the refractive index in the longitudinal direction of the film and the refractive index in the width direction measured by an Abbe refractometer. The refractive index was measured at 25 ° C. and 65% RH using an Abbe refractometer with sodium D line (wavelength 589 nm) as a light source. A sulfur-methylene iodide solution was used as the mount solution.

(4) Density of A layer The density is measured with a film having only the A layer manufactured under the same conditions, or with a sample obtained by removing the A layer from the laminated film.
The density was measured at 25 ° C. using a density gradient tube composed of carbon tetrachloride and n-heptane.

(5) High-definition image analysis is applied to the void measurement, and "PIAS-IV" (manufactured by Pierce Co., Ltd.) as a high-vision personal image analysis system and "Metaloplan" manufactured by Leitz as an optical microscope are used as measuring devices. used. (A) Preparation of preparation One drop of liquid paraffin is dropped on a slide glass, a film sample of about 10 mm square is placed on the slide glass, and one drop of liquid paraffin is added again. Place a cover glass on top of the film so that the film is sandwiched. Liquid paraffin is mounted on both sides of the sample, and this is used as the preparation. (B) Adjustment method and measurement conditions The objective lens of the optical microscope is set to 32 times, the transmission lens is used for microscopic observation, and the image is captured by the high-definition monitor of the image analyzer. At this time, the observation magnification on the monitor is 15
It will be 60 times. When an image is input, it is a black and white image and is processed under the condition that a green filter is applied. The input image is binarized and the brightness is converted. The brightness value representing the density level at this time is set to 160. Before the setting, the brightness of the aperture of the optical microscope is adjusted so that the average brightness value when measured under the condition that the sample is not set as a blank value is 183 in advance. (C) Measurement The sum of the pixel numbers of the individual voids obtained by binarizing the void image is measured, and the total pixel number of the measurement field of view is divided to obtain the area ratio of the void portion. As described above, the void index is used. The total number of pixels per visual field is about 2 million, and the measurement area at this time is 0.041 mm ² , and this is repeated 10 times by changing the place. The voids were defined as those having a diameter of 0.28 μm or more when formed into an equivalent circle. Void index = (sum of the number of pixels in the void portion) / (total number of pixels in the measurement visual field) × 100 (%) The void index is 1 as the criterion for determining the void generation state.
% Or less was judged to be good voids, and more than 1% was judged to be bad.

(6) Uniformity of protrusion height Two-detector type scanning electron microscope [ESM-3200,
Elionix Co., Ltd.] and cross-section measuring device [PMS-1,
Elionix Co., Ltd.] is used to measure the height of the projection when an electron beam is cross-scanned on the film surface.
AS2000, manufactured by Carl Zeiss Co., Ltd.] to reconstruct the film surface projection image on the image processing apparatus. Next, the projection portion is binarized in this surface projection image, and the highest value among the binarized individual projection portions is set as the height of the projection, and this is obtained for each projection. This measurement was repeated 500 times by changing the place, and the average height of protrusions was obtained.
In addition, the standard deviation of the height distribution was calculated based on the height data of each protrusion. The value obtained by dividing this standard deviation by the average height was taken as the relative standard deviation. The magnification of the scanning electron microscope is 100
Select a value between 0 and 8000 times. Also, height is 15n
Those with m or more were defined as protrusions. In some cases, the height information obtained using a high-precision optical interference type three-dimensional surface analyzer (TOPO-3D manufactured by WYKO, objective lens: 40 to 200 times, use of a high resolution camera is effective) is used for the SEM. You may read and use it for the value of. Based on the relative standard deviation obtained as described above, the uniformity of the height of protrusions was determined as follows. Relative standard deviation of 0.6 or less: Good protrusion (height) uniformity Good Relative standard deviation of more than 0.6: Poor protrusion (height) uniformity

(7) Scraping resistance A film is slit into a tape having a width of 1/2 inch, a single blade is pressed at an angle of 90 °, and the film is pushed 1.0 mm to run for 20 cm (speed: 6.7 cm / s, tension:
500 g). The height of adhesion of the powder scraped off by the single blade was read with a microscope and the scraped amount (μm) was taken. This scraping amount is 15
If it is less than μm, the abrasion resistance is good, and if it exceeds it, the abrasion resistance is poor. This corresponds to the abrasion resistance in the film processing process.

(8) Repeated running durability (Δμk) A tape running tester SFT-700 (manufactured by Yokohama System Research Co., Ltd.) was used by slitting a film into a tape having a width of 1/2 inch. , 20 ° C., allowed to run at 60% RH atmosphere, the friction coefficient .mu.k ₅₀ when allowed repeated running initial friction coefficient .mu.k ₁ and 50 times was calculated from the following equation (the film width was 1/2 inch). μk = 2 / πln (T ₂ / T ₁ ) Δμk = μk ₅₀ −μk ₁ where T ₁ is the inlet tension and T ₂ is the outlet tension. The guide diameter is 6 mmφ, the guide material is SUS27 (surface roughness 0.2S), the winding angle is 90 °, and the running speed is 3.
It is 3 cm / sec. When Δμk obtained by this measurement is less than 0.1, repeated running durability: good, 0.1
In the above cases, the repeated running durability was determined to be poor.

[0026]

EXAMPLES Next, the present invention will be explained based on examples. Example 1 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. )

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 (intrinsic viscosity : 0.62, melting point: 259 ° C., ΔTc
g: 84 ° C). External particles are not particularly added to both polyesters A and B.

Pellets of polyesters A and B were respectively fed to two extruders, melted at 290 ° C., and combined and laminated by a rectangular combining block (feed block) for three layers. Using an electrostatically applied casting method, wrap it around a casting drum with a surface temperature of 30 ° C., cool and solidify,
An unstretched film was made. The surface of this unstretched film which was not in contact with the drum was heat-treated for 6 seconds under the conditions that the film surface was 185 ° C. using a known radiation heater. After the heat treatment, the film was stretched 3.2 times in the longitudinal direction at a temperature of 90 ° C. and further stretched at a stretching rate of 2000% / min at 95 ° C. using a stenter.
The film was stretched 3.3 times in the width direction and further heat-treated at 210 ° C. for 5 seconds under a constant length to obtain a laminated polyester film having a total thickness of 15 μm. The supply amount from the extruder was adjusted so that the thickness of the polyester A layer was 1 μm on both sides.

FIG. 1 shows the surface shape of the laminated polyester film obtained in the above-mentioned embodiment, which was tilted by 82.5 ° in order to three-dimensionally capture the projections using an electron microscope, and the magnification was 10,000 times. It was observed at. This laminated polyester film has protrusions of uniform height on its surface so that there is substantially no flat surface between the projections (that is, in the state where there are very few flat surfaces between the projections). , Very finely and regularly formed. In addition, the presence of coarse projections was not recognized, and the height distribution was sharp, that is, uniform projections with uniform height were formed.

Examples 2 and 3 In the same manner as in Example 1, laminated polyester films having a total thickness of 15 μm were obtained. However, in Example 2, the heat treatment condition of the unstretched film was 170 ° C. for 3 seconds, and Example 3 was used.
Then, it was set to 160 ° C. for 20 seconds. FIG. 2 shows a surface photograph of the laminated polyester film obtained in Example 2 observed by the same method as described above, and FIG. 3 shows a surface photograph of the laminated polyester film obtained in Example 3. Although the protrusion density, that is, the area of the flat surface between the protrusions is slightly different from that in Example 1, it can be seen that uniform protrusions are regularly formed. In addition, in the case of Example 3, the protrusions form a mesh-like structure (that is, a form in which the protrusions are connected to each other), and such a form is particularly excellent in repeated running durability. confirmed.

Comparative Example 1 A film was obtained in the same process as in Example 1 except that pellets obtained by adding inert particles to polyester B were used instead of polyester A. The particles were added by adding a slurry in which calcium carbonate having an average particle size of 0.6 μm was dispersed in ethylene glycol so that the content of particles in the pellet was 0.
It was added at the time of polymerization so as to be 7% by weight.

FIG. 4 is an observation of the surface profile of the laminated polyester film obtained in Comparative Example 1 in the same manner as in Example 1. Compared to that of Example 1, there was a wider flat surface between the protrusions, and the heights of the protrusions were also non-uniform.

Comparative Example 2 A laminated polyester film having a total thickness of 15 μm, in which 3% by weight of spherical silica particles having an average particle diameter of 0.3 μm are contained in polyester A and the layer A has a laminated thickness of 0.4 μm, is used as an example. Obtained by the same process as 1.

FIG. 5 shows the surface profile of the laminated polyester film obtained in Comparative Example 2 as observed in the same manner as in Example 1. When the amount of added particles is increased and the projections are densely formed, coarse projections due to the agglomeration of particles are partially recognized, and the uniformity of the projection height is impaired, resulting in poor film properties. .

Table 1 shows each film characteristic in each of the above-mentioned Examples and Comparative Examples. As shown in Table 1, the laminated polyester film obtained in each of the above examples was excellent in all of voids, uniformity of protrusion height, abrasion resistance, and repeated running durability. The laminated polyester film obtained in 1. was inferior in all of these properties.

[0036]

[Table 1]

[0037]

According to the laminated polyester film of the present invention, surface projections caused by fine crystals are uniformly and regularly formed with a very small number of flat surfaces existing between the projections. Since it can be performed essentially without depending on the contained particles, it is possible to suppress the generation of voids and the occurrence of troubles due to the generation of voids, and it is possible to uniformly form extremely fine protrusions on the film surface. , The desired surface morphology is obtained.

[Brief description of drawings]

1 is an electron micrograph of the surface of the film obtained in Example 1 (a surface photograph of a thin film).

FIG. 2 is an electron micrograph of the surface of the film obtained in Example 2 (a surface photograph of a thin film).

FIG. 3 is an electron micrograph of the surface of the film obtained in Example 3 (a surface photograph of a thin film).

FIG. 4 is an electron micrograph of the surface of the film obtained in Comparative Example 1 (a surface photograph of a thin film).

5 is an electron micrograph of the surface of the film obtained in Comparative Example 2 (a surface photograph of a thin film).

Claims (5)

[Claims] 1. A film in which an A layer containing polyester A as a main component is laminated on at least one surface of a B layer containing polyester B as a main component, and the surface of the A layer is
A laminated polyester film characterized in that surface projections caused by fine crystals are uniformly and regularly present and there are few flat surfaces existing between the projections. 2. The laminated polyester film according to claim 1, wherein the crystallization parameter ΔTcg of the polyester A is 80 ° C. or lower and is smaller than the crystallization parameter ΔTcg of the polyester B. 3. The laminated polyester film according to claim 2, wherein the crystallization parameter ΔTcg of the polyester A is 70 ° C. or lower and is smaller than the crystallization parameter ΔTcg of the polyester B. 4. The laminated polyester film according to claim 1, wherein the lamination ratio of the layer A to the entire thickness of the film is 0.5 or less. 5. The laminated polyester film according to claim 1, wherein the main repeating unit of the polyester A is ethylene terephthalate.