JPH0789026A - Laminated polyester film - Google Patents

Abstract

PURPOSE:To provide a laminated polyester film having antistatic capacity under economically advantageous conditions without damaging the mechanical characteristics of the film. CONSTITUTION:In a co-extruded laminated polyester film consisting of at least three layers, the surface resistivity values of both outer layers and inner layer thereof satisfy formula rhoo=10<5>-10<12>OMEGA/square, rhoi=10<7>-10<14>OMEGA/square and rhoi/rhoo=1-10<4> (wherein p is the surface resistivity of each of both outer layers and rhoi is the surface resistivity of the inner layer).

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 biaxially oriented laminated polyester film having an antistatic property.

[0002]

2. Description of the Related Art Biaxially oriented polyester film has excellent properties such as mechanical strength, dimensional stability, flatness, heat resistance, chemical resistance, and transparency, so that it can be used for base film and plate making of magnetic recording media. It is used for various purposes including films. However, the biaxially stretched polyester film has a drawback that static electricity is easily generated and the film is easily charged, like other plastic films.

Generally, as a method of preventing static charge of a polyester film, a method of kneading an anionic surfactant type low molecular weight compound such as an organic sulfonate, a method of depositing a metal compound, an anionic compound, a cationic compound or A method of applying a conductive compound to the surface is known.

Each of the above-mentioned antistatic methods is appropriately selected and employed according to the required antistatic performance, etc. In particular, the method of kneading the antistatic agent can be carried out relatively easily, and further, Since the antistatic effect is often practically sufficient, it is preferably used.

[0005]

On the other hand, in recent years, a laminated polyester film produced by a co-extrusion method has attracted attention and has been partially put to practical use in applications such as magnetic recording and transparent slippage. Such a laminated film, for example, to improve the transparency of the entire film by blending particles only in the surface layer,
It can exhibit excellent functions such as changing the roughness of the front and back. In particular, a laminated polyester film having a layer structure of three or more layers has a high degree of freedom in giving various functions to each layer, and thus can be preferably used.

By the way, even in the above-mentioned laminated film, antistatic performance is often required, but when a large amount of an antistatic agent is added to each layer, the mechanical properties of the film are often deteriorated and the film is economical. It will also be a disadvantage.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a laminated film provided with an antistatic property under economically advantageous conditions without impairing the mechanical properties of the film. To provide.

[0008]

Means for Solving the Problems As a result of intensive studies to achieve the above object, the present inventors have made the surface specific resistances of both outer layers and inner layers of a laminated film of three or more layers within a certain range. It has been found that, if designed, excellent antistatic performance is exhibited by using a relatively small amount of antistatic agent.

The present invention has been completed based on the above findings, and the gist thereof is a coextrusion laminated polyester film having at least three layers, and the surface specific resistance values of both outer layers and inner layers are represented by the following formula. And a biaxially oriented polyester film.

[0010]

## EQU2 ## ρ _o = 10 ⁵ to 10 ¹² Ω / □ ρ _i = 10 ⁷ to 10 ¹⁴ Ω / □ ρ _i / ρ _o = 10 to 10 ⁴ (where ρ _o is each surface resistivity of both outer layers, ρ _i represents the surface resistivity when the inner layer is made into a film by itself.)

The present invention will be described in detail below. As the polyester in the present invention, typically, for example, polyethylene terephthalate in which 80 mol% or more of the constituent unit is ethylene terephthalate, and 80 mol% of the constituent unit
The above is polyethylene-2,6-naphthalate, which is ethylene-2,6-naphthalate, and poly-1,4-cyclohexanedimethylene terephthalate, in which 80 mol% or more of the structural units is 1,4-cyclohexanedimethylene terephthalate. To be Other examples include polyethylene isophthalate and polybutylene terephthalate.

Examples of copolymerization components other than the above-mentioned superior constituent components include diol components such as diethylene glycol, propylene glycol, neopentyl glycol, polyethylene glycol, polytetramethylene glycol, isophthalic acid, 2,7-naphthalenedicarboxylic acid,
Dicarboxylic acid components such as 5-sodium sulfoisophthalic acid, adipic acid, azelaic acid and sebacic acid, and ester-forming derivatives such as oxymonocarboxylic acid can be used. Further, as the polyester, in addition to a homopolymer or a copolymer, a blend with a small proportion of another resin can be used.

The laminated polyester film of the present invention (hereinafter abbreviated as "laminated film") has a three-layer structure as a basis and is laminated by a coextrusion method. Specifically, co-extrusion is performed using a co-extrusion laminating apparatus such as a feed block or a multi-manifold die in a molten state of the polyester forming the inner layer and the polyester forming both outer layers. Then, the obtained molten sheet is rapidly cooled to form an amorphous unstretched sheet, and then biaxially oriented and heat-treated according to a conventional method. The thickness of each layer of the laminated film can be usually controlled by adjusting the polymer discharge rate by a gear pump. In the present invention, if necessary, a layer structure having two or more inner layers, that is, a total of four or more layers can be adopted.

The greatest feature of the laminated film of the present invention is that the surface resistivity of both the outer layer and the inner layer is designed within a certain range. And the design of such surface resistivity is
Mainly, it is carried out by blending an antistatic agent with the polyester of the substrate. Specifically, a method of adding an antistatic agent to a raw material in a polyester production process, and a method of compounding an antistatic agent or a masterbatch containing the antistatic agent in a raw material resin during film formation are preferably used.

As the above-mentioned antistatic agent, a sulfonate or phosphate derivative can be given as a typical example of the ion conductive compound. The most typical example is a metal salt of alkylsulfonic acid or a metal salt of alkylbenzenesulfonic acid. When these are used, the antistatic effect is often increased by using polyalkylene glycol together. Carbon black can be given as a representative example of the electronically conductive compound.

In the present invention, each surface specific resistance ρ _o (Ω / □) of both outer layers of the laminated film is 10 ⁵
It should be in the range of -10 ¹² Ω / □, preferably 10 ⁶ -10 ¹¹ Ω / □, and more preferably 10 ⁷ -10 ¹⁰ Ω / □. When the value of surface resistivity of both outer layers is less than 10 ⁵ Ω / □, a large amount of antistatic agent is added,
The mechanical and thermal properties of the film deteriorate. When the surface resistivity of both outer layers exceeds 10 ¹² Ω / □,
The antistatic effect is weakened, dust is adsorbed, and when the contact with the base material (plastic pin or the like) is strong, the running property becomes unstable.

In the present invention, the surface resistivity ρ _i (Ω / □) of the inner layer of the laminated film is 10 ⁷ to 10 ¹⁴
Ω / □, preferably in the range of 10 ⁸ to 10 ¹³ Ω / □. By the way, the surface resistivity of the inner layer of the laminated film cannot be directly measured. Therefore, the above value represents the surface resistivity when the inner layer is formed into a film by itself, specifically, the inner layer is formed into a film under the same conditions as in the case of a laminated film, and the surface resistivity of the obtained film is obtained. Represents When there are many inner layers, the surface resistivity when blending them into a single-layer film is ρ
_i .

According to the knowledge of the present inventors, even if the antistatic performance is imparted only to both outer layers of the laminated film, the durability thereof is often insufficient, while the inner layer is weaker than the outer layer but constant. In the case of imparting the antistatic performance of (1), a preferable antistatic effect is imparted to the laminated film.

That is, the surface resistivity ρ _{i of the} inner layer is 10
^When it is less than ⁷ Ω / □ or when ρ _i / ρ _o is less than 10, the mechanical and thermal properties of the film are often impaired. When ρ _i exceeds 10 ¹⁴ Ω / □ or ρ _i
When / ρ _o exceeds 10 ⁴ , the antistatic effect is often lost. Therefore, in the present invention,
The ratio ρ _i / ρ _o between the surface resistivity of the inner layer and each surface resistivity pair of both outer layers is 10 to 10 ⁴ , preferably 10 to 10 ^3.
Must be in the range.

In the present invention, the total thickness of the laminated film is usually 2 to 500 μm, preferably 4 to 250 μm, and the total thickness of both outer layers is about 1 to 30% with respect to the entire laminated film. The effect of the present invention is more effectively exerted when the relationship between the outer layer thickness t (μm) of any one of the front and back surfaces and ρ _i / ρ _o satisfies the following equation.

[0021]

(3) 10 ≦ ρ _i / ρ _o ≦ 10 ^{t / 3 + 2}

The laminated film of the present invention may contain added particles, precipitated particles, other catalyst residues and the like as a protrusion forming agent in order to impart a function other than antistatic, for example, slipperiness. The type, size,
The blending amount is appropriately selected according to the desired slipperiness, transparency and the like.

Further, as an additive other than the protrusion-forming agent, a stabilizer, a lubricant, a cross-linking agent, an anti-blocking agent, an antioxidant, an ultraviolet absorber, a light-blocking agent, a coloring agent, etc. are contained as required. May be. These additives may be contained in either the outer layer or the inner layer as long as they do not interfere with the gist of the present invention.

Further, in the present invention, it is preferable to form a coating layer on at least one surface of the outer layer. The laminated film having a coating layer formed on the outer layer can be widely used by taking advantage of the characteristics of the coating layer.

That is, the surface of the polyester film may be modified by a so-called coating method in order to impart functions such as slipperiness, adhesiveness, releasability and abrasion resistance. Further, in the case of the laminated film of the present invention, due to its excellent antistatic performance, there is no problem such as dust adhesion, and therefore the coating can be performed smoothly.

Among the coating methods, in the case of a so-called in-line coating method in which a water-based coating agent is coated in the production process of a polyester film and then stretched in at least one direction and heat-treated, the coating film obtained is usually 0. It is extremely thin at 0.01 to 0.3 μm. Therefore,
In the case of the laminated film of the present invention, sufficient antistatic performance can be maintained even if the antistatic treatment is not performed again on the coating film.

In the present invention, of course, if necessary, at least one side of the outer layer of the laminated film may be coated with the main purpose of preventing static electricity, thereby ensuring the antistatic effect. Can be done.

The laminated film of the present invention is produced by obtaining a non-stretched sheet by the above-mentioned coextrusion method, and specifically using a roll or tenter type stretching machine and employing the following conditions. You can do it.

That is, first, the unstretched sheet is stretched in one direction. The stretching temperature of the first stage is usually 60 to
The temperature is 120 ° C., preferably 70 to 100 ° C., and the draw ratio is usually 3.0 to 7 times, preferably 3.5 to 7 times. Next, the film is stretched in a direction orthogonal to the above-mentioned one direction to obtain a biaxially oriented film. The stretching temperature of the second stage is usually 80 to 130 ° C., preferably 85 to 120 ° C., and the stretching ratio is usually 3.0 to 7 times, preferably 3.
The range is 5 to 7 times.

In the present invention, it is possible to employ a method in which the above-mentioned stretching in each direction is performed in two or more steps. In that case, however, the final stretching ratio is preferably within the above range. It is also possible to adopt the simultaneous biaxial stretching method and simultaneously stretch the unstretched sheet in two directions so that the area ratio becomes 7 to 20 times.

The laminated film of the present invention, utilizing its excellent characteristics and economy, is used in the magnetic recording field such as video tapes, audio tapes, floppy disks, magnetic cards, etc., for photography, microfilm, plate making, tracing film, etc. In the graphic arts field of
It can be suitably used in fields such as displays and building materials.

[0032]

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded. In Examples and Comparative Examples, "part" and "%" mean "part by weight" and "% by weight", respectively. The physical property (characteristic) measuring method and the raw material polyester are as follows.

<Surface resistivity> Concentric electrode "16008A (trade name)" by Yokogawa / Hewlett-Packard
The sample was placed on (inner electrode 50 mm diameter, outer electrode 70 mm diameter) and a voltage of 100 V was applied.
The surface resistivity of the sample was measured with "329A (trade name)". The conditions of the measurement atmosphere are 23 ° C. and 50% RH.

<Evaluation of Practical Properties of Antistatic Performance> (1) Running Stability: Tensile force 1 on a film having a width of 12.5 mm
After winding 100 g and reciprocating 100 times between the pins made of plastic, the winding appearance was observed, and evaluation was performed by classifying into the following three ranks.

[0035]

[Table 1] O: No winding disorder. Δ: The edges are slightly uneven. X: The edges are slightly uneven.

(2) Durability: The film is wiped with a gauze soaked in ethanol and then air-dried.
Repeat the times, and then measure the surface resistivity of the film. Then, it was compared with the surface specific resistance value before the treatment and evaluated by dividing into the following three ranks based on the increase of the surface specific resistance (Ω / □).

[0037]

[Table 2] ○: The surface resistivity (Ω / □) increases by less than one digit. Δ: The surface specific resistance (Ω / □) increased by one digit or more and less than two digits. X: Surface specific resistance (Ω / □) increased by two digits or more.

<Intrinsic Viscosity> 1 g of polyester chips or film is phenol / tetrachloroethane = 50/5
It was dissolved in 100 ml of a mixed solvent of 0 (weight ratio) and measured at 30 ° C.

<Surface Roughness (Ra)> Center Line Average Roughness Ra
The surface roughness was defined as (μm). And Ra was calculated | required as follows using the surface roughness measuring device (SE-3F) by Kosaka Laboratory Ltd. company. That is, a portion having a reference length L (2.5 mm) is extracted from the film sectional curve in the direction of its center line, and the center line of this extracted portion is taken as the x-axis, and the direction of longitudinal magnification is taken as the y-axis. When represented by (x), the value given by the following equation is represented by [μm].

[0040]

[Equation 4]

The center line average roughness Ra is represented by the average value of the center line average roughness of the extracted portions obtained from the ten section curves obtained from the surface of the sample film. The tip radius of the stylus was 2 μm, the load was 30 mg, and the cutoff value was 0.08 mm.

<Material Polyester> (1) Polyester A: 0.2% by weight of spherical silica having an average particle size of 0.5 μm, 1.2% by weight of sodium dodecylbenzenesulfonate, and 1% of polyethylene glycol having a molecular weight of 8,000. Polyethylene terephthalate having an intrinsic viscosity of 0.650 containing 0.0% by weight.

(2) Polyester B: average particle size 0.5 μ
Polyethylene terephthalate having an intrinsic viscosity of 0.650 containing 0.2% by weight of spherical silica of m, 0.3% by weight of sodium dodecylbenzenesulfonate and 0.8% by weight of polyethylene glycol having a molecular weight of 8,000.

(3) Polyester C: average particle size 0.6 μ
m Kaolin 0.05% by weight, sodium dodecyl sulfonate 1.0% by weight, polyethylene glycol having a molecular weight of 8,000 1.0% by weight, intrinsic viscosity 0.650
Polyethylene terephthalate.

(4) Polyester D: 0.5 μm average particle size
Intrinsic viscosity 0.6 containing 0.1% by weight of cross-linked polymer particles of m
50 polyethylene terephthalates.

Example 1 Polyesters A and B were used, laminated in a die so as to have an A / B / A layer structure, extruded at 290 ° C. from a die into a sheet, and rapidly cooled on a cooling rotary drum, A non-oriented sheet having a three-layer structure was obtained. The obtained non-oriented sheet was stretched 3.3 times at 85 ° C. in the length direction and 3.8 times at 95 ° C. in the width direction, and then heat-treated at 225 ° C. for 2 seconds to obtain a biaxially oriented laminated polyester film. .

The obtained laminated film has a thickness of 1 μm / 13 μm.
It had a thickness constitution of m / 1 μm. The measurement results of the physical properties and characteristics of the laminated film are shown in Table 3. The laminated film shows good antistatic property in spite of the small absolute amount of the antistatic agent contained, and the film forming step. It was a preferable laminated film in which the decrease in the molecular weight of the polyester was small. A single-layer biaxially oriented polyester film was obtained in the same manner as in the production of the above-mentioned laminated film by using only the polyester B, and its surface resistivity was measured and found to be 7 × 10 ¹² Ω / □.

Example 2 A was produced in the same manner as in Example 1 except that polyesters A, B and C were used and laminated in a die so as to have an A / B / C layer structure. / B / C (1 μm /
A biaxially oriented laminated polyester film having a three-layer structure (13 μm / 1 μm) was obtained. The results of measuring the physical properties and characteristics of the obtained laminated film are shown in Table 3. The laminated film was a useful laminated film having excellent antistatic properties and different front and back roughness.

Example 3 Example 3 was repeated except that the thickness of the A / B / C film was changed to 0.3 μm / 14.4 μm / 0.3 μm.
A biaxially oriented laminated polyester film was obtained in the same manner as in Example 2. The results of measurement of the physical properties and characteristics of the obtained laminated film are shown in Table 3. The laminated film was a preferable laminated film which showed good antistatic properties and showed little decrease in the molecular weight of polyester. .

Comparative Example 1 A monolayer biaxially oriented polyester film having a thickness of 15 μm was obtained in the same manner as in Example 1 except that only polyester A was used. The measurement results of the physical properties and characteristics of the obtained film are shown in Table 4. Although the film is excellent in antistatic property, the total amount of the antistatic agent used is considerably large and the intrinsic viscosity also decreases. It was remarkable and unsatisfactory.

Comparative Example 2 In Example 1, polyesters A and D were used, and D
D / A / D (1 μm / 13) in the same manner as in Example 1 except that the layers were laminated in a die so as to have a layer structure of / A / D.
A biaxially oriented laminated polyester film having a three-layer structure (μm / 1 μm) was obtained. The measurement results of the physical properties and characteristics of the obtained laminated film are shown in Table 4. The laminated film had a large charging property and was difficult to use.

Comparative Example 3 In Example 1, polyesters A and D were used, and A
A / D / A (0.3 .mu.m / m) in the same manner as in Example 1 except that the layers were laminated in a die so as to have a layer structure of / D / A.
A biaxially oriented laminated polyester film having a three-layer structure of 14.4 μm / 0.3 μm) was obtained. The results of measuring the physical properties and characteristics of the obtained laminated film are shown in Table 4. The laminated film was unstable in running, especially when repeatedly run.

Example 4 In the same manner as in Example 1 except that after stretching in the length direction, an in-line coating coat was applied on one side to improve the adhesiveness with printing ink or the like. A biaxially oriented laminated polyester film having a three-layer structure having an easily adhesive coating film on one surface was obtained. The in-line coating coat is a 10% by weight water dispersion of "Finetex ES-650" (trade name) manufactured by Dainippon Ink and Chemicals, Inc. and "Inplanil DL11" (trade name) manufactured by Bayer Co., Ltd. at a weight ratio of 20:80. The solution was used and the dry thickness was 0.03 μm. The laminated film was an excellent laminated film with a small increase in the charging property even when the in-line coating coated surface was run as the contact surface.

[0054]

[Table 3] ──────────────────────────────────── Example 1 2 3 <Film layer structure > Front A / B / Back A Front A / B / Back C Front A / B / Back C <Surface resistivity (Ω / □)> Front layer (ρ _o ) 8 × 10 ¹⁰ 8 × 10 ¹⁰ 8 × 10 ¹⁰ Back Layer (ρ _o ) 8 × 10 ¹⁰ 7 × 10 ⁹ 7 × 10 ⁹ Inner layer (ρ _i ) 7 × 10 ¹² 7 × 10 ¹² 7 × 10 ¹² ρ _i / Surface layer ρ _o 1.1 × 10 ² 1.1 × 10 ² 1.1 × 10 ² ρ _i / Back layer ρ _o 1.1 × 10 ² 1.0 × 10 ³ 1.0 × 10 ³ <Intrinsic viscosity> 0.636 0.637 0.638 <Ra (μm)> Surface layer 0.015 0.015 0.011 Back layer 0.015 0.010 0.007 <Running stability> ○ ○ ○ <Durability> ○ ○ ○ ──────────────────────────────────── (Note) The intrinsic viscosity is Represents the value for the entire film.

[0055]

[Table 4] ──────────────────────────────────── Comparative Example 1 2 3 <Film layer structure > A Front D / A / Back D Front A / D / Back A <Surface resistivity (Ω / □)> Surface layer (ρ _o ) 8 × 10 ¹⁰ 1 × 10 ¹⁶ 8 × 10 ¹⁰ Back layer (ρ _o ) − 1 × 10 ¹⁶ 8 × 10 ¹⁰ inner layer (ρ _i ) − 8 × 10 ¹⁰ 1 × 10 ¹⁶ ρ _i / surface layer ρ _o ⁻⁸ × 10 ⁻⁶ 1.2 × 10 ⁵ ρ _i / back layer ρ _o −8 × 10 ^{− 6} 1.2 × 10 ⁵ <Intrinsic viscosity> 0.619 0.637 0.638 <Ra (μm)> Surface layer 0.015 0.014 0.015 Back layer (0.015) 0.014 0.015 <Running stability> ○ × △ <Durability> ○ − △ ────── ────────────────────────────── (Note) Intrinsic viscosity indicates the value for the entire film.

[0056]

According to the present invention described above, a laminated film provided with an antistatic property without impairing the mechanical properties of the film and under economically advantageous conditions is provided. The film can be suitably used particularly in the fields of magnetic recording applications and graphic arts.

Claims (2)

[Claims] 1. A biaxially oriented laminated polyester film comprising a coextruded laminated polyester film comprising at least three layers, wherein the surface specific resistance values of both outer layers and inner layers satisfy the following formula. ## EQU1 ## ρ _o = 10 ⁵ to 10 ¹² Ω / □ ρ _i = 10 ⁷ to 10 ¹⁴ Ω / □ ρ _i / ρ _o = 10 to 10 ⁴ (where ρ _o is each surface resistivity of both outer layers, ρ _i represents the surface resistivity when the inner layer is made into a film by itself.) 2. The biaxially oriented laminated polyester film according to claim 1, wherein a coating layer is formed on at least one surface of the outer layer.