JPH0148136B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing polyester film. More specifically, the present invention relates to a method for producing a polyester film in which the F-1 value in the longitudinal direction (referring to the stress at 1% elongation) and the F-1 value in the transverse direction are at extremely high levels. In conventional technology, as a method for biaxially stretching polyester film, an unstretched film is stretched at 80°C in the longitudinal direction.
A so-called vertical and horizontal sequential stretching method is known, which involves stretching 3 times or more at a temperature range of ~120°C and then stretching 3 times or more in the transverse direction at a temperature of 80°C to 120°C. Film is not available. In other words, when the longitudinal stretching ratio is increased to increase the strength in the longitudinal direction, molecular orientation and crystallization are promoted in crystalline polyester, which makes it difficult to perform smooth stretching in the next transverse stretching process. Under these conditions, the film frequently breaks during production, making it extremely difficult to obtain a film with high F-1 values in both the longitudinal and transverse directions. In addition, in the horizontal/longitudinal stretching method in which horizontal stretching is performed in the first stage and then longitudinal stretching, the operational stability of stretching is poor because the horizontal direction in the first stage is held and stretched with a tenter, and the paper is oriented only in the horizontal direction. Since a film is obtained, during the subsequent longitudinal stretching, the film contracts in the transverse direction and the molecular orientation in the transverse direction is loosened, resulting in a significant decrease in the strength in the transverse direction, making it impossible to obtain a film with high strength in the biaxial directions. do not have. A conventional biaxially stretched polyester film exhibiting a relatively high Young's modulus has an F-1 value of 4.5 to 5.0 Kg/mm ² in the longitudinal and transverse directions. Furthermore, since the development of a longitudinally reinforced biaxially stretched film (so-called tensilized film) with a longitudinal F-1 value of 6.0 to 8.0 kg/ ^mm2 , the use of film has expanded to the field of recording cassette tapes. It came. Furthermore, in recent years, with the expansion of recording video tapes and the need for long-duration recording and thinner materials, F-1
A high value is required, but the reality is that no film has yet been produced that satisfactorily meets these requirements. An object of the present invention is to provide a method for producing a vertically and horizontally biaxially high-strength polyester film that is particularly suitable for these uses and has good operational stability. As a method for producing a bidirectional high-strength polyester film that can be predicted from the conventional technology, there is a method in which a biaxially stretched film with increased strength in the machine direction is further re-stretched in the transverse direction, and a method in which a well-balanced normal polyester film is re-stretched in the transverse direction. There is a four-stage stretching method that involves horizontal stretching. However, in either method, when re-transverse stretching is performed, the film has a high tendency to break during stretching, making it difficult to produce stably. However, while researching various conditions for longitudinally re-stretching a transversely reinforced polyester film, they found manufacturing conditions that would allow a polyester film of uniform thickness to be obtained without causing any breakage during film stretching, and thus arrived at the present invention. Ivy. That is, the present invention provides a manufacturing method in which a polyester film is biaxially stretched in the longitudinal and transverse directions through at least three stretching steps. The F-1 value in the longitudinal direction (stress at 1% elongation) is 3.13 Kg/mm ² to 4 Kg/mm ² , and the F-1 value in the lateral direction is 1.7 times or more than the F-1 value in the longitudinal direction. And the F-1 value in the lateral direction is 6.3Kg/mm ² ~ 9.5
A high-strength polyester characterized by forming a transversely reinforced biaxially stretched film with a strength of Kg/ ^mm2 , and then re-stretching the biaxially stretched film by 1.4 to 1.7 times in the longitudinal direction at a temperature range of 90°C to 200°C. This is a film manufacturing method. The present invention will be explained. The polyester to which the present invention can be applied mainly includes terephthalic acid as an acid component, and contains 90 (preferably 95) mol% or more of terephthalic acid, for example, isophthalic acid, phthalic acid, adipic acid, sebacic acid, succinic acid, One or more difunctional acids such as oxalic acid, malonic acid, p-hydroxybenzoic acid, ω-hydroxycaproic acid, etc.
(preferably 5) mole% or less. In addition, as a glycol component, ethylene glycol is the main target, but ethylene glycol 90 (preferably 95) mol% or more and trimethylene glycol, hexamethylene glycol, cyclohexanedimethanol (1,4), etc.
10 mol% of one or more diol compounds such as 2,2,4,4,-tetramethylcyclobutanediol (2,4), hydroquinone, etc.
(preferably 5 mol %) or less, or a mixture of these polymers may be used.
Furthermore, other polymers of up to 10% by weight (preferably 5% by weight) may be mixed with such polyester. In the polyester, stabilizers such as phosphoric acid, phosphorous acid and their esters, matting agents such as titanium dioxide, particulate silica, and kaolin,
It may also contain a lubricant or the like. As described above, any polyester polymer composition can be used as long as it can form a biaxially stretched film that does not substantially lose the properties of polyethylene terephthalate film. The polyester of the present invention is formed into an unstretched film by a conventional method. The film forming conditions are as follows: well-dried polyester pellets are melted at a temperature above their melting point (for example, 280°C to 310°C), extruded through a narrow slit, and rapidly cooled and solidified on a casting drum for rapid cooling. For this casting, a known method of pinning using means such as an air knife or static electricity can be used.
In this way, an unstretched polyester film can be obtained. In the present invention, an unstretched film is first stretched in the longitudinal and transverse directions, and the F-1 value in the transverse direction is 6.3 kg/
mm ² or more and the F-1 value in the horizontal direction is F-1 in the vertical direction
It is necessary to obtain a biaxially stretched film (transversely reinforced type) with a value of -1 that is 1.7 times or more. Furthermore, the biaxially stretched film has a longitudinal F-1 value of 3.13 kg/
^mm2 to 4Kg/ ^mm2 , preferably 3.6Kg/ ^mm2 to 4Kg/ ^mm2
Make it so that In the present invention, the horizontal direction F-1 value/vertical direction F-1
The value is 1.7 (times) or more, and the horizontal F-1 value is
It is necessary to obtain a film with a weight of 6.3 Kg/mm ² or more in an intermediate process if the horizontal F-1 value/longitudinal F-1 value is
If the value is lower than 1.7 times or the horizontal F-1 value is
If it is lower than 6.3 Kg/mm ² , it becomes impossible or difficult to maintain the strength in the transverse direction in the next longitudinal re-stretching process, and a balanced biaxially stretched film cannot be obtained. When producing a lateral reinforced film with a lateral F-1 value of 6.3 Kg/mm ² to 9.5 Kg/mm ² , preferably 6.3 Kg/mm ² to 7.6 Kg/mm ² , the stretching ratio in the longitudinal direction is reduced;
It is desirable to increase the stretching ratio in the lateral direction.
If the stretching ratio in the longitudinal direction is too small, the thickness becomes uneven and the magnetic tape loses its value. Conversely, if the stretching ratio in the longitudinal direction is increased, the stretching ratio in the lateral direction must also be increased, which deteriorates the stability of film formation. The reason why the transverse F-1 value/longitudinal F-1 value is set to 1.7 times or more is that when performing longitudinal re-stretching, the increase in the F-1 value in the longitudinal direction is large and the decrease in the F-1 value in the transverse direction is small. be. The horizontal direction F-1 value/vertical direction F-1 value is 1.7 times or more, and the horizontal direction F-1 value is 6.3Kg/mm ² 9.5Kg/mm ² Preferably 6.3Kg/mm ² to 7.6Kg/mm ² A method for producing a transversely reinforced biaxially stretched film includes a method in which the film is first stretched in the longitudinal direction and then stretched in the transverse direction. In the method of the present invention, the transversely reinforced biaxially stretched film is longitudinally re-stretched 1.4 times to 1.7 times at 90°C to 200°C. Further, after longitudinal stretching again, heat treatment can be performed to improve dimensional stability. If the longitudinal re-stretching temperature is less than 90°C, it will be cold drawn and breakage will easily occur, and if it exceeds 200°C, the shrinkage force in the width direction will increase and the strength in the transverse direction will decrease significantly. Further, if the longitudinal re-stretching ratio is less than 1.4 times, the thickness of the film will be large, while if it exceeds 1.7 times, the film will break frequently, which is not preferable. Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Examples. Incidentally, the F-1 value in the example was determined by the following measuring method. F-1 value The film was cut into samples with a width of 10 mm and a length of 150 mm, and was stretched using an Instron type universal tensile tester at a tension speed of 10 mm/min and a chart speed of 50 mm/min with a chuck spacing of 100 mm. It was calculated from the stress at 1% elongation of the obtained load-elongation curve. Film thickness unevenness Cut the polyester film into pieces 5 cm wide and 1 m long in both the vertical and horizontal directions, and measure the thickness with a continuous thickness measuring device (manufactured by Anritsu Electric Co., Ltd.: Model K-312A).
The maximum difference R (μm) between the thick part and the thin part at a measurement length of 1 m is determined. The larger of R in the vertical direction and R in the horizontal direction is shown as a representative value. Those with R larger than 5 μm: × Those with R less than 5 μm: Shown as ○. Example 1 Polyethylene terephthalate with a viscosity of 0.65
The mixture was melted at 290°C, extruded through a die, and rapidly cooled to obtain a substantially non-oriented, amorphous, unstretched film of 170μ. This was stretched twice in the machine direction at 80°C, then stretched four times in the transverse direction at 100°C, and further heat-set at 170°C. As a result, the F-1 value in the vertical direction is 3.76Kg/ ^mm2 , and the F-1 value in the horizontal direction is 3.76Kg/mm2.
A film of 6.47 Kg/mm ² was obtained. Then re-stretch to 140
It was longitudinally re-stretched 1.2 to 1.6 times in the longitudinal direction at ℃ and heat-set at 220 ℃. The results are shown in Table 1.

[Table] Example 2 The same unstretched film obtained in Example 1 was heated at 90°C.
Stretched 1.5 times in the machine direction, then stretched at 92°C in the transverse direction
The film was stretched 4.5 times and further heat-set at 200°C.
The longitudinal direction F-1 value of this biaxially stretched film is 3.13
Kg/mm ² , and the F-1 value in the longitudinal direction was 7.61 Kg/mm ² .
Next, it was re-stretched 1.4 to 1.8 times in the longitudinal direction at 180°C, and then heat-set at 225°C. The results are shown in Table 2.

[Table] Comparative Example 1 The unstretched film obtained in Example 1 was stretched 2.5 times in the machine direction at 80°C, then stretched 4.5 times in the cross direction, and further heat-set at 181°C. Next, the film was longitudinally stretched again by 1.2 times to 1.6 times at 160°C, and then heat-set at 220°C. Table 3 shows the results.
Shown below.

【table】

Claims (1)

[Claims] 1 In a manufacturing method in which a polyester film is biaxially stretched in the longitudinal and transverse directions through at least three stretching steps, an unstretched polyester film is first stretched in the longitudinal direction and then in the transverse direction to increase the F in the longitudinal direction of the stretched film. -1 value (stress at 1% elongation)
3.13Kg/ ^mm2 to 4Kg/ ^mm2 , the F-1 value in the horizontal direction is 1.7 times or more the F-1 value in the vertical direction, and the F-1 value in the horizontal direction is 6.3Kg/ ^mm2 to 9.5Kg/mm ² in the transversely reinforced biaxially stretched film, and then the biaxially stretched film was stretched in the longitudinal direction at a temperature range of 90°C to 200°C.
A method for producing a high-strength polyester film, characterized by re-stretching it by 1.4 to 1.7 times.