KR970008257B1 - Preparation process for polyethylene telephthalate film - Google Patents

Abstract

In the production of biaxial drawn thermoplastic resin film, the thermoplastic resin is heated and melted at the temperature higher than the melting point. And from the extruder including a slit die, the film is extruded on the cooling drum in a film shape to produce undrawn sheet. The produced undrawn sheet is passed through between the too rollers of which rotation speed is different. The film is drawn up to 2.0-5.0 times toward the proceeding direction to obtain mono axially drawn film. Then, the mono axially drawn film is transferred to the tenter where both ends of the film are held tightly by clips to be secondly drawn toward the length direction to the proceeding direction of the film.

Description

Method for producing polyethylene terephthalate film for high density magnetic recording media

1 is an exemplary view for explaining a method for measuring an orientation angle.

2 is an exemplary view for explaining a method of measuring the tenter angle.

The present invention relates to a method for producing a polyethylene terephthalate film for a high density magnetic recording medium. More specifically, the tensile stress at 5% elongation in any direction on the film (hereinafter referred to as "F-5 value") is 10 and to 20kg / mm ^2, a and has a heat shrinkage of less than 2.0% each of the characteristic values of these variations most 0.5 relates to a process for producing a polyethylene terephthalate film.

Magnetic recording media such as magnetic recording tapes and magnetic recording disks use a binder to apply magnetic particles to the surface properties of the base film to form a magnetic layer, or cover the surface of the base film with magnetic metal by vacuum deposition, sputtering or plating. It is obtained by. There is an increasing demand for high density recording on such magnetic recording media.

As the demand for high-density recording increases, the problem of increasing heat resistance, physical properties (tensile stress at 5% elongation, Young's modulus, heat shrinkage, etc.), and isotropy for a magnetic recording medium has become an important problem. When the magnetic recording medium is made of an isotropic base film, i.e., an anisotropic base film, the magnetic recording medium is twisted and causes thermal deformation or degrades the sound quality during reproduction. In addition, when the smoothness is poor, when the magnetic side is coated or deposited on the surface to be used for magnetic tape, the magnetic layer damage and powder on the surface of the film due to contact between the recording device and the reproducing device when recording is stored on the paper tape or during recording and reproducing. Not only does it adversely affect the magnetic signal due to the generation, but also the occurrence of drop out due to the space loss increases the electronic conversion characteristics of the magnetic tape.

Meanwhile, polyesters represented by polyethylene terephthalate are used for various purposes such as magnetic tapes, electrical insulation, capacitors, photographs, graphic arts, and packaging films because of their excellent physical and chemical properties, and polyethylene terephthalate films are magnetic. It has been used as a recording film for a long time and has been trying to improve the characteristics in order to satisfy the demands of the high density magnetic recording medium. However, polyethylene terephthalate does not have sufficient heat resistance, and it is difficult to increase the mechanical strength while reducing the anisotropy of the film. The need for films with all the necessary properties has increased.

Accordingly, an object of the present invention is to achieve high-density magnetic recording, which is not anisotropic, that is, isotropic features having almost the same properties in both longitudinal and transverse directions, high mechanical strength and good dimensional stability, and very smooth surface characteristics and good productivity. It is to provide a method for producing a polyethylene terephthalate film for the medium.

In order to achieve the above object as well as another object that is easily expressed in the present invention by using a polyethylene terephthalate of a specific condition and stretched under a specific condition F-5 value of 10 to 20kg / mm ² in any direction on the film, which It was possible to obtain a high density magnetic recording medium base film having a thermal shrinkage of less than 2.0% in any direction but having a variation of 0.5 or less in each characteristic.

That is, in the present invention, the defects that are difficult to solve in the conventional method for producing a polyethylene terephthalate film, for example, anisotropy by eliminating the problems of breakage and anisotropy and silver defects that occur in the manufacturing process due to the simple expansion of the stretching direction in the width direction. Not only was this small and main orientation direction made transverse, it was possible to obtain a film having uniform physical properties and high smoothness with respect to the full width of the film.

The present invention will be described in more detail as follows.

The melt-extruded polyethylene terephthalate prepared by the method commonly used in the art to which the present invention belongs to prepare an unstretched sheet, the sheet is continuously in the longitudinal direction from 90 ℃ to 130 ℃ 3.5 to 5.0 The film of the present invention is prepared by stretching to a fold, and further stretching it in a transverse direction at 130 ° C. to 150 ° C., and then performing heat treatment for 1 second to 20 minutes at a temperature of 200 to 250 ° C. in a tenter. .

However, in order to have excellent overall properties and good processability of the film, polyethylene terephthalate must satisfy the following yarn (1).

here, (A is an item showing polymer viscoelastic properties, the unit is Dyne / cm · sq / ° C, E ″ α (T _max ) is the maximum value of the mechanical loss modulus (Dyne / cm · sq), and E ″ α (T _max ) is the temperature at which the maximum mechanical loss modulus is reached.

More preferably, the condition 2.72 × 10 ⁷ <A <3.43 × 10 ⁷ must be satisfied.

If the value of A is greater than 3.5 × 10 ⁷ , defects occur in the polymer constituting the sheet and biaxially stretched film, and the polymer main chain starts to move at low temperature, resulting in uneven stretching and adhesion in the stretching process. The yield is greatly reduced due to the occurrence of breakage in the tenter, and the produced film is not only difficult to obtain due to the uniform physical properties in both longitudinal and transverse directions, that is, isotropy, but also adversely affects the surface shape. The occurrence of large projections, the phenomenon of particle dropping, powder powder, and the like, it is very difficult to obtain a good product with a smooth surface.

When the A value is less than 2.5 × 10 ⁷ , it is difficult to set the process conditions by increasing the mechanical stretching force during the production of polyethylene terephthalate film, slip phenomenon during longitudinal stretching, uneven stretching and partial rupture in the tenter. Uneven (unbalanced) physical properties and poor surface shape appear on the produced film. In addition, in order to manufacture a film having better overall physical properties, the following formula (2) must be satisfied while satisfying the condition of the formula (1).

Here, B is the angle of orientation of the main molecule chain with respect to the transverse direction.

More preferably, the condition of -25 ° <B <25 ° should be satisfied.

In other words, in order to produce a film having low anisotropy and excellent bi-directional properties, the tenter angle is controlled when the polymer sheet satisfying the condition of the formula (1) is stretched laterally in the tenter after the longitudinal stretching is completed. By satisfying the condition of the formula (2) on the basis of the transverse direction of the orientation angle of the polymer backbone it can be produced a film showing excellent isotropic properties.

When the value of B is out of the range of the above formula (2), even though stretching in the transverse direction at the same stretching ratio, the stretching is relatively less in the transverse direction and does not develop in the main orientation angle transverse direction. By countering the increase in anisotropy, which is one of them, it is impossible to obtain a film having excellent physical properties in both the medium and the transverse directions.

In addition, the polyethylene terephthalate film that satisfies the following conditions (3) and (4) only when the above formulas (1) and (2) is satisfied can be obtained.

Here, SRa is the average roughness (mm ² ) per unit area, SRs is the number of projections of 0.01 ~ 0.05㎛ size per unit area.

In the polyethylene terephthalate film, when the surface characteristic is more than the range of the above formulas (3) and (4), coarse protrusions and powders are generated on the surface, which acts as a factor of dropout during driving, The stretching and winding of the film adversely affect the slip and shape.

The polymer of the unstretched film used by this invention can be used if the structural unit consists essentially of ethylene terephthalate, and a polyethylene terephthalate modified polymer can also be used.

Ethylene terephthalate is generally synthesized by condensing tephthalenedicarboxylic acid or a functional derivative thereof with ethylene glycol or a functional derivative thereof in the presence of a catalyst under suitable reaction conditions.

Examples of the modified polymer include copolymerization or polyester by adding a suitable one or two or more kinds of third component modifiers to the polymerized product of the polymer. As a suitable 3rd component, the compound which has a bivalent ester formation functional group, for example, dicarlo, such as a fish acid, a succinic acid, adipic acid, a phthalic acid, an isophthalic acid, a naphthalene 2,7-dicarboxylic acid, a diphenyl ether dicarboxylic acid, etc. Compounds, such as oxycarboxylic acid, such as this acid or its lower alkyl ester, and p-oxy benzoic acid, its lower alkyl ester, or dihydric alcohols, such as a propylene glycol and trimethylene glycol, are mentioned.

The polyethylene terephthalate or its modified polymer may be one in which the terminal hydroxyl group and / or carboxyl group are blocked by monofunctional compounds such as benzoic acid, benzyloxybenzoic acid, methoxypolyalkylene glycol, or the like. For example, a trifunctional ester-forming compound such as a very small amount of glycerin or pentaerythritol may be modified within a range in which a linear copolymer is substantially obtained. In addition, the polymer may contain chlorine agents such as titanium dioxide, stabilizers such as phosphoric acid, phosphorous acid and esters thereof, lubricants such as particulate silica, kaolin and the like.

The polymer used for this invention is an intrinsic viscosity measured at 35 degreeC in the orthochloro phenol solvent is 0.45 or more. In particular, an intrinsic viscosity of 0.52 to 0.82 is suitable because it is excellent in the film manufacturing process.

The biaxially oriented heat-fixed film prepared according to the present invention may be used for magnetic tape, electrical insulation material, jay of deposition film, photo, etc., and shrink film may be used as an electrical insulation material for wrapping.

The following examples and comparative examples further illustrate the present invention, but do not limit the scope of the present invention.

Examples 1-4 and Comparative Examples 1-3

A polyethylene terephthalate having the properties shown in Table 1, which was prepared by a conventional method, was extruded in a T die (DIE) to obtain an unstretched sheet having a thickness of 120 μm of “A” as shown in Table 1. The conditions were first drawn in the longitudinal direction and then in the transverse direction using a tenter. "F-5 value", "surface roughness" and "heat shrinkage" of the prepared film were measured, and the process permeability was visually judged, and the results are shown in Table 1.

TABLE 1

※ Here, ①; Cooling drum temperature (℃)

②; Speed of Production Line (mpm)

※ Property evaluation method

1) Orientation angle: Measure the refractive index using an Abbe refractometer using a sodium ray (wavelength 589nm) as a light source, and fix the diopter in the longitudinal and transverse directions and rotate it at 5 ° intervals as shown in FIG. The maximum angle is represented by the orientation angle B. At this time, the clockwise direction is represented by + and the counterclockwise direction by-.

2) Viscoelasticity measurement: Measure the mechanical loss factor of polyethylene terephthalate polymer using Leometrics

3) F-5: Using an Instron, measure a 10mm wide film sample at 25 ° C, 100mm between the chuck and 200mm / tensile speed.

4) Heat shrinkage: The test pieces were measured after being left in an oven at 150 ° C. for 1 hour in a stretched state. The heat shrinkage is calculated as

L ₀ ; Original length of the sample, L ₁ ; Specimen length after test

5) Average roughness of center line of film: SRa

Centerline average roughness is measured using a three-dimensional surface roughness meter from Kosaka, Japan.

6) Number of protrusions per unit area (mm ² ) (height 0.01 ~ 0.05㎛)

From the three-dimensional surface roughness curve obtained at the time of measuring the average surface roughness (SRa) of the film, the number of protrusions having a height of 0.01 to 0.05 μm was measured based on the center line per 1 mm ² of the film surface.

7) tenter angle: as shown in FIG. Measured by.

Claims (3)

After melt-polymerizing the glycol ester of aromatic dicarboxylic acid or its copolymer having terephthalic acid as its main component, it is molded into a polyester chip and melt-extruded to obtain an unstretched film that satisfies the condition of the following formula (1). And stretching laterally under the condition of the following formula (2), wherein the polyethylene terephthalate film for magnetic recording medium is characterized by the above-mentioned. here, (A denotes a polymer viscoelastic material, the unit is Dyne / cm · sq / ° C), (E ″ α) _max is the maximum value of the mechanical loss modulus (Dyne / cm · sq), and E ″ α (T _max ) is the temperature at which the maximum mechanical loss modulus is reached. Here, B is the angle of orientation of the main molecule chain with respect to the transverse direction. A polyethylene terephthalate film prepared by the method of claim 1, wherein the tensile stress at 5% elongation in any direction on the film is 10 to 20 kg / mm ² , has a heat shrinkage of less than 2.0%, and a variation in each characteristic value is 0.5 or less. . The polyethylene terephthalate film according to claim 2, wherein the average roughness of the film and the number of protrusions of 0.01 to 0.05 µm per unit area satisfy the following formulas (3) and (4). Here, SRa is the average roughness per unit area (nm ² ), SRs is the number of projections of 0.01 ~ 0.05㎛ size per unit area.