JPH0360858B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a polyester film, and more specifically, to a polyester film that has excellent surface characteristics, including no surface defects or minute surface irregularities, and particularly no continuous thickness unevenness in the longitudinal direction. be. [Prior Art] In order to eliminate surface defects of polyester films, the following methods have been conventionally carried out. (1) Eliminate dead paste to prevent abnormal retention of polymer in the extrusion system. (2) Use a material for the polymer system that prevents the molten polymer from adhering to or corroding the walls of the extrusion system. (3) Improve the surface finish accuracy of polymer systems, make the flow behavior of the polymer uniform, and prevent the adhesion of minute foreign matter. (4) In the stretching system or film transport system, ensure that there is no difference in surface peripheral speed between the film and the roll. [Problems to be solved by the invention] However, despite these various measures,
At present, it is impossible to eliminate minute scratches on the surface of polyester film, fixation lines in the longitudinal direction, and even minute irregularities on the surface. In particular, in recent years, it has become desirable to have completely defect-free surfaces for substrates for vapor deposition recording and for photographic recording, and it has become nearly impossible to manufacture such materials using conventional methods. . [Means for Solving the Problems] The present invention provides a polyester film containing 1 to 100 ppm of a polyorganosiloxane compound based on 100 parts by weight of polyester, in which the silicon atoms relative to the carbon atoms in the surface layer of the polyester film are The present invention relates to a polyester film characterized in that the ratio R=rs/ _rc of the mass ratio r _s of R to the same mass ratio r _c at 100 _Å from the surface layer of the film is in the range of 1.2 to 10. The polyester in the present invention is a polymer with ester bonds obtained by condensation polymerization from dicarboxylic acid and diol, and dicarboxylic acid components include terephthalic acid, phthalic acid, isophthalic acid, adipic acid, sebacic acid, naphthalene dicarboxylic acid, Diol components include ethylene glycol, diethylene glycol, propylene glycol, butylene glycol, cyclohexanedimethanol, dihydroxycyclohexane, resorcinol, hydroquinone, dihydroxynaphthalene, polyethylene glycol, etc. Polyesters can also be obtained from oxyacids such as hydroxyethoxy)benzoic acid, p-oxybenzoic acid, and the like. The intrinsic viscosity of polyester is 0.4 or more,
It is preferably in the range of 0.6 to 1.0. Polyesters suitable for the present invention include polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, and the like. Of course, optional additives such as slip agents,
A heat stabilizer, an antiblocking agent, an antioxidant, a coloring agent, an antistatic agent, an ultraviolet absorber, a viscosity increasing (reducing) agent, etc. may be contained. When casting using the electrostatic casting method, Zn, Mg, Mn,
It is preferable to contain a metal compound such as Co in an amount of about 20 to 1000 ppm in terms of atomic weight based on the polyester. Polyorganosiloxane is a general term for organic polymer compounds having a siloxane bond consisting of a bond between silicon and oxygen, and includes alkyl, allyl, etc. , aralkyl,
There are polysiloxanes containing phenyl, as well as other polyorganosiloxanes, their copolymers, blend pairs, etc. In the case of the present invention, dimethylpolysiloxane, methylphenylpolysiloxane, and further methylphenylpolysiloxane are used. is particularly preferred. It is preferable to add the polyorganosiloxane before the polymerization of the polyester, especially before the esterification reaction, but the timing is not necessarily limited to this.
It may be added after polymerization and before melt extrusion, although the effect will be a little weaker. In the case of the present invention, the viscosity of polyorganosiloxane is 10~
5000 centistokes (cs) is preferred. When it is less than 10 cs, not only is the effect of improving surface defects such as streaks on the melt sheet weak, but also the transparency and adhesion of the obtained film tend to deteriorate.
On the other hand, if it exceeds 5000 cs, the compatibility and dispersibility with polyethylene terephthalate will deteriorate, and the effect of improving the above-mentioned streak-like surface defects will almost disappear. The content of the polyorganosiloxane compound is 1 to 100 ppm, preferably 2 to 100 ppm, based on the polyester.
Must be in the 20ppm range. The content is
If it is less than 1 ppm, the surface defects of the polyester film, which is the objective of the present invention, cannot be completely eliminated. For example, longitudinal streak-like defects appear on the polyester melt sheet, and in severe cases, the melt near the streaks and Air/bubbles are trapped on the surface of the cooling body,
Not only is it not possible to obtain a sheet with a uniform thickness and no surface defects, but when this sheet is stretched, especially in the width direction, stretching unevenness and surface defects become noticeable. On the other hand, if it exceeds 100 ppm, the molten material tends to peel off from the surface of the cooling material, making it impossible to obtain strong adhesion, and the resulting film may have crater-like defects, poor adhesion, poor transparency, and surface roughness. As a result, surface undulations become apparent. In this way, simply containing a specific amount of a polyorganosiloxane compound does not make the polyester film surface completely defect-free, and the surface concentration of silicon atoms caused by the polyorganosiloxane compound has a specific distribution. Otherwise, the surface of the present invention cannot be made completely defect-free. A specific Si surface concentration distribution is the ratio of the mass ratio r of silicon atoms Si to carbon atoms C in the surface layer r _s to the ratio r _c at a depth of 100 Å from the surface R = r _s / r _p
must be in the range of 1.2 to 10, preferably 1.2 to 5.0. In other words, it is essential that Si atoms exist at a fairly high concentration in the outermost layer of the film. The concentration distribution of the Si atoms and C atoms in the film is determined by the SIMS method described below. If the value of R is less than 1.2, not only the surface defect-free which is the objective of the present invention cannot be achieved, but also the thickness unevenness due to minute irregularities cannot be eliminated. Conversely, if the value of R exceeds 10, This is due to the occurrence of crater-like defects on the film surface, poor adhesion, deterioration of transparency, surface waviness, and even uneven flow during melting. Next, the method for manufacturing the polyester film of the present invention will be explained. A polyester represented by polyethylene terephthalate, polyethylene naphthalate, etc. is obtained by a condensation reaction from a dicarboxylic acid component and a diol component by a conventional transesterification method (DMT method) or a direct polymerization method. In the case of the present invention, it is particularly effective for direct polymerization polyesters. In the case of the DMT method, the timing of addition of the polyorganosiloxane compound contained in the polyester is preferably before the transesterification reaction, but is not particularly limited to this, and may be added before the polymerization reaction or after completion. Further, it may be added at the time of charging the extruder, but considering the amount added in the present invention, it is preferable to add it before polyester polymerization in order to uniformly contain a small amount added. Of course, it is clear that master pellets containing a high concentration of polyorganosiloxane may be diluted with virgin pellets that do not contain a high concentration of polyorganosiloxane. Additionally, known additives to polyester may be added, such as lubricants, antioxidants, pigments, dyes, nucleating agents, antiblocking agents, heat stabilizers, fillers, plasticizers, antistatic agents, ultraviolet absorbers, color inhibitors, etc. may be included. In the case of the present invention, it is particularly preferable to subject the polyester to a biaxial stretching film different from the conventional method as described below so that silicon atoms are selectively arranged on the surface layer of the polyester film. That is, the polyester is sufficiently dried, the discharge pressure p during melt extrusion is increased to 110 to 250 kg/ ^cm2 , and the residence time of the polymer is increased to 20 to 60 minutes, so that the hydrolysis and thermal decomposition reactions substantially proceed. Then, the molten polymer is discharged from the die, dropped onto an electrically insulated cast drum charged with static electricity, and cooled and solidified in the charged state to obtain a cast sheet. . The sheet is stretched 3 to 8 times in one or multiple stages at 85 to 130°C in the longitudinal direction, and then stretched at 80 to 200°C in the width direction.
The film is stretched 3 to 6 times and heat treated at 100 to 240°C. If necessary, heat treatment may be performed again after stretching in the longitudinal direction and/or width direction. The silicon atoms contained in the polyether film thus obtained are selectively arranged on the surface layer.
Also, the thickness of the polyester film is 0.5 to 125 μm.
Preferably, those having a diameter of about 3 to 80 μm are effective and often used. [Applications] The thus obtained polyester film of the present invention can be used as a base film for magnetic recording or optical recording, where surface defects are a particular problem, or as a recording film for capacitors, where minute unevenness in surface thickness is a problem, or The film can have particularly excellent properties as a base film for vapor deposition. [Effects of the Invention] In this way, the concentration of polyorganosiloxane added to polyester is limited, and the concentration distribution in the cross-sectional direction of the film is specified, so that the surface of the obtained film has no craters, bubble marks, streaks, etc.
Not only can a high-quality cast film with small thickness unevenness and no surface defects such as waviness or scratches be obtained, but also stable casting can be achieved even at high speeds, and a uniform ultra-thin polyester film without surface defects can be obtained. Furthermore, the polyester film of the present invention not only has excellent stretchability, but also has excellent slitting suitability and winding properties. [Method for Measuring Characteristics, Method for Evaluating Effects] Methods for measuring and evaluating characteristic values of the present invention are as follows. (1) The mass concentration distribution of carbon (silicon) atoms is determined by secondary ion mass spectrometry.
Obtained by Spectrometry (hereinafter referred to as SIMS). SIMS is a method in which an ion beam with an energy of about 5 to 15 Kev is applied to the sample surface, and secondary ions generated from the sample are subjected to mass spectrometry by sputtering. West Germany as a device,
Using A-DIDA3000 manufactured by ATOMIKA, O ₂ ⁺ as the primary ion species, primary ion acceleration voltage 12KV,
Primary ion current 200nA, raster area 400μ ² ,
Measurement vacuum level 1×10 ^-8 Torr, E-gun0, 5KV-
Measured under 3A conditions. Silicon atom Si and polyester constituent atoms
(C) Measure in the depth direction. The measurement depth is
After the SIMS measurement, the depth of the crater in the sputter area is determined using a surface roughness meter (DEKTAK, manufactured by Sloan) and that value is used. From the thus obtained concentration distribution of each atom in the thickness direction, the Si/c ratio is replotted in the depth direction of the film to determine the Si/c concentration distribution r with respect to the film thickness. (2) Surface roughness: Ra (μm) Shown as a value measured using a stylus type surface roughness meter (cutoff value c/o 0.25 mm, measurement length 4 mm, however,
In accordance with JIS-B-0601. ) Surface roughness (μm) (c/o0.25mm): 0.10 or more × 0.05 or more to less than 0.10 △ 0.01 or more to less than 0.05 ○ Less than 0.01 ◎ (3) Slip property ASTM-D-1894-63 Slip tester according to this method The static friction coefficient (μs) and the dynamic friction coefficient (μd) were measured using the following. Generally, the range in which a film is considered to have excellent slipperiness is 1.0 or less in μs and 0.8 or less in μd. Slip property (μs): 1.6 or more × 1.0 or more to less than 1.6 △ 0.7 or more to less than 1.0 ○ Less than 0.7 ◎ (4) Surface defects Deposit AI equivalent to 200 Å on the sample and observe the surface in 20 fields of view with a stereomicroscope at 60x magnification Judgment is made based on the degree of surface scratches. Classification ◎ No scratches at all ○ 1 to 2 scratches in the field △ 〃 3 to 5 fields × Scratches in the entire field (5) Fixing streaks When the film is placed under an orthogonal Nirol film, it is thicker than the surrounding area. When continuous streak-like coloring unevenness appears in the longitudinal direction due to fluctuation, it is classified as follows depending on its degree. Classification Thickness variation value (mμ) Coloring unevenness ◎ None less than 100 ○ Slightly visible △ Less than 500 × More than 500 (6) Adhesion The film to be measured was placed in a hot air oven kept at 70°C. The surface wetting tension γ _cA of the film and the surface wetting tension γ _c of the film before treatment are measured according to JIS K6768-1971, and the adhesion is determined according to the following criteria. Judgment γ _cA | γ _c - γ _cA | ◎ 38 or more, less than 1 ○ Same as above 1 to 3 △ 30 or more, less than 38 3 or more, less than 10 × Less than 30 10 or more [Example] The effects of the present invention will be clearly explained below. In order to achieve this, comparative examples will be given and explained below. Example 1 Colloidal silica SiO ₂ with an average particle size of 300 μm was uniformly dispersed, and ethylene glycol from which coarse particles of 6 μm or more were removed was mixed with dimethyl terephthalate using lithium acetate as a transesterification catalyst.
500 centistokes of methylphenylpolysiloxane was mixed as a surface defect improver, heated to an elevated temperature, and a transesterification reaction was performed by removing methanol. Next, antimony trioxide was added to this reaction product together with phosphoric acid and triethyl phosphate, and the polymerization was completed according to a conventional method, and the intrinsic viscosity [η] =
0.65 polyethylene terephthalate was obtained. After vacuum drying the polyethylene terephthalate at 180°C for 2 hours, it was fed to an extruder and heated at 285°C.
and discharged from the T-die nozzle under the conditions of discharge pressure p = 150 Kg/cm ² and polymer residence time of 40 minutes, and a casting drum that was electrically insulated and applied a high voltage (using front gas as the refrigerant). It was cooled in close contact with the That is, the molten sheet was cooled to the glass transition temperature of polyethylene terephthalate of 70° C. or lower while still being charged. The cast sheet thus obtained is longitudinally
Stretched 1.8 times at 125℃, further stretched 3.1 times in the same direction at 90℃, then stretched 4 times in the width direction at 95℃, then stretched at 150℃
Heat set for 3 seconds at
After axial stretching, it was heat set at 185° C. for 2 seconds while being relaxed by 2% in both the longitudinal and width directions. The quality of the polyethylene terephthalate film thus obtained with a thickness of 9 μm is shown in Table 1.

[Table] It is thus seen that by adding a specific polyorganosiloxane and forming a film under specific conditions, a film with a smooth and easily slippery surface without surface defects can be obtained. Comparative Example 1 The casting method used in Example 1 was changed, and an electrostatic charge was applied to the molten sheet discharged from the T-die die from a tungsten wire placed between the die and the casting drum to charge the molten sheet. After that, it was tightly fixed on a grounded casting drum (using water as a refrigerant). Furthermore, the discharge pressure P and residence time were changed to the values shown in Table 2, but the other steps were carried out in exactly the same manner as in Example 1 to produce biaxially oriented polyethylene terephthalate having the properties shown in Table 2. I got the film.

[Table] As shown above, it can be seen that even if the composition is the same, the surface characteristics can vary widely depending on the film forming conditions. Comparative Example 2 A polyethylene terephthalate film with a thickness of 9 μm was obtained in the same manner as in Example 1, except that the content of methylphenylpolysiloxane in Example 1 was increased from 8 ppm to 300 ppm.

[Table] It is thus seen that even if a large amount of polysiloxane is contained, not only the surface defects are not eliminated, but also the adhesiveness is significantly reduced.

Claims (1)

[Claims] 1. In a polyester film containing 1 to 100 ppm of a polyorganosiloxane compound based on 100 parts by weight of polyester, the mass ratio r _s of silicon atoms to carbon atoms in the surface layer of the polyester film and the Same mass ratio r _c
A polyester film characterized in that the ratio R= _rs / _rc is in the range of 1.2 to 10.