JP4548083B2 - Production method of polyester film - Google Patents

Description

  The present invention relates to a method for producing a polyester film. More specifically, the present invention relates to a flaw / adhesion caused in a heating process by using a specific material as a heating roll surface material of an unstretched sheet film guided to a longitudinal stretching process. The present invention relates to a method for producing a polyester film that achieves a good surface state without the above-mentioned defects.

  As a method for producing a polyester film, the resin is supplied to a melt-extrusion apparatus such as an extruder, and the molten polyester film extruded from a die having a slit is adhered and solidified by an electrostatic application method on a rotating cooling drum to be unoriented. A method is known in which a biaxially stretched film is produced by forming a film and supplying the unstretched film to a longitudinal stretching apparatus equipped with a plurality of rolls so that the film is continuously stretched in the longitudinal direction and further stretched in the transverse direction. ing.

With respect to the heated roll surface in the longitudinal stretching process that stretches in the longitudinal direction using the peripheral speed difference of the roll group, metal or metal is used on the roll surface for the purpose of reducing surface defects that occur on the film such as adhesion and scratches. There have been proposed methods of performing various surface treatments such as ceramic, Teflon (registered trademark), and rubber, and changing the surface roughness (see, for example, Patent Documents 1 and 2).
Japanese Patent Publication No. 48-44666 (page 1, column 2, line 37 to page 2, column 3, line 13) Japanese Patent Publication No. 5-41098 (Page 2, column 3, column 7-4, line 15)

  Although the stretched film obtained by the conventional technique is used for each application, the required properties for the stretched film have been advanced in recent years, and the conventional method cannot meet the demand for surface defects, or the conventional method can quickly achieve the surface. Defects occurred and productivity was reduced.

  An object of the present invention is to solve the above problems and to provide a method for producing a polyester film free from surface defects such as scratches and adhesion.

The object of the present invention is achieved by the following method. That is, the present invention (1) in a preheating step of heating an unstretched polyester film in contact with a plurality of rolls,
Among the plurality of rolls, one roll having a surface roughness Ra of 0.05 μm or more and Rmax 5 μm or less whose surface is coated with a chromium oxide ceramic (hereinafter, this roll is referred to as a chromium oxide ceramic roll A) is included.
And the surface roughness Ra of the roll on the downstream side of the chromium oxide-based ceramic roll A has a larger value than the chromium oxide-based ceramic roll A,
Furthermore, the surface temperature of the said chromium oxide type ceramic roll A is 1-20 degreeC high temperature from the glass transition temperature of polyester, The manufacturing method of the polyester film characterized by the above-mentioned.

(2) As a preferred embodiment of the present invention (1) is, (1) film temperature of chromium oxide-based ceramic roll entrance described, comprises the step of (the glass transition temperature of -10 ° C.) ~ glass transition temperature it Ru can be exemplified a method of manufacturing a polyester film characterized.

According to the method of the present invention, it becomes possible to produce a thermoplastic resin film with few surface defects such as scratches and adhesion.

  Hereinafter, the present invention will be described in detail.

  Although the kind of polyester in this invention is not specifically limited, For example, the polyester which uses aromatic dicarboxylic acid, alicyclic dicarboxylic acid or aliphatic dicarboxylic acid and diol as the main component is used preferably.

  Examples of the aromatic dicarboxylic acid component include terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, and 4,4′-diphenyldicarboxylic acid. Acid, 4,4′-diphenyl terdicarboxylic acid, 4,4′-diphenylsulfone dicarboxylic acid, and the like can be used. Among them, terephthalic acid, phthalic acid, and 2,6-naphthalenedicarboxylic acid are preferably used. be able to. Moreover, as an alicyclic dicarboxylic acid component, cyclohexane dicarboxylic acid etc. can be used, for example. As the aliphatic dicarboxylic acid component, for example, adipic acid, suberic acid, sebacic acid, dodecanedioic acid and the like can be used. These acid components may be used alone or in combination of two or more, and further, a part of oxyacids such as hydroxyethoxybenzoic acid may be copolymerized.

  Examples of the diol component include ethylene glycol, 1,2-propanediol, 1,3-propanediol, neopentyl glycol, 1,3-butanediol, 1,4-butanediol, and 1,5-pentanediol. 1,6-hexanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, diethylene glycol, triethylene glycol, polyalkylene glycol, 2,2′-bis (4 '-Β-hydroxyethoxyphenyl) propane and the like can be used. Among them, ethylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol, diethylene glycol, and the like can be used, and particularly preferably. ,ethylene It is a recall. These diol components may be used alone or in combination of two or more.

  In addition, other compounds such as monofunctional compounds such as trimellitic acid, pyromellitic acid, glycerol, pentaerythritol, 2,4-dioxybenzoic acid, lauryl alcohol, and phenyl isocyanate are used as the polyester. It may be copolymerized within the range of the shape.

  As necessary, the polyester resin used in the present invention is an organic lubricant such as a flame retardant, heat stabilizer, antioxidant, ultraviolet absorber, antistatic agent, pigment, dye, fatty acid ester, wax, or antifoaming agent. Can be blended. Organic particles containing inorganic particles such as clay, mica, titanium oxide, calcium carbonate, carion, talc, wet or dry silica, colloidal silica, calcium phosphate, barium sulfate, alumina, zirconia, acrylic acids, styrene, etc. Etc., for example, so-called internal particles that are precipitated by a catalyst added at the time of the polyester polymerization reaction, or a surfactant can be added.

  The present invention is particularly effective when used mainly with polyethylene terephthalate among the polyester resins listed above. The polyethylene terephthalate may be pure, a copolymer, or a mixture of other components in an appropriate ratio such as less than 30 mol%. If the polyester contains a polyethylene terephthalate component of 70 mol% or more, the effect of the present invention is particularly great.

  In the present invention, the polyester film may be a single layer or laminated in multiple layers.

  The polyester film in the present invention can be produced as follows. That is, a molten polyester film extruded from a base having a slit is made to adhere and solidify on a rotating cooling drum by an electrostatic application method to form an unstretched film, and this unstretched film is supplied to a longitudinal stretching apparatus having a plurality of rolls. By doing so, it can be produced by continuously stretching in the longitudinal direction and further stretching in the transverse direction.

  As one manufacturing method of the polyester film of the present invention, in the preheating step of heating an unstretched polyester film by bringing it into contact with a plurality of rolls, among the plurality of rolls, the film temperature at the roll entrance (glass transition temperature − 10 ° C) to a glass transition temperature roll, it is necessary that the temperature of the film on the roll be 6 ° C or lower. In this case, the surface material or the like of the roll is not particularly limited, but the effect is particularly large when the surface roughness is Rmax 5 μm or more. When the temperature rise on the roll is 6 ° C. or higher, Slip occurs due to thermal expansion, and scratches occur on the film. In this case, in order to regulate the temperature rise on the roll, it is necessary to add a preheating roll or adjust the temperature of the film at the longitudinal stretching entrance when the number of preheating rolls is insufficient.

  Further, as another method for producing the polyester film of the present invention, in the preheating step of heating the unstretched polyester film in contact with a plurality of rolls, the surface of the plurality of rolls is coated with a chromium oxide ceramic. The surface roughness Ra of the roll on the downstream side of the chromium oxide ceramic roll has a value larger than that of the chromium oxide roll, including one roll having a surface roughness Ra of 0.05 μm or more and Rmax 5 μm or less. In addition, it is preferable to have a step in which the film temperature at the entrance of the roll covered with the chromium oxide ceramics is (glass transition temperature-10 ° C.) to glass transition temperature.

  When the surface roughness of the chromium oxide ceramic roll is less than Ra 0.05 μm, adhesion scratches are likely to occur. When the surface roughness is greater than Rmax 5 μm, scratches are likely to occur due to thermal expansion on the roll. Since the present invention prevents scratches caused by thermal expansion on the roll, the effect is great when the unstretched polyester film is 300 μm or more, and the temperature of the film on the chromium oxide ceramic roll is increased. The effect is particularly great when the temperature is increased by 6 ° C. or more per one.

  The temperature of the chromium oxide-based ceramic roll is preferably 1 to 20 ° C. higher than the glass transition temperature. When the roll temperature is equal to or lower than the glass transition temperature, the glass transition temperature can be exceeded on the corresponding roll. If the temperature of the roll is (glass transition temperature + 20 ° C.) or higher, the roll and the film are adhered to each other, resulting in problems such as adhesive scratches and dirty defects.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows a sheet longitudinal stretching apparatus according to an embodiment of the present invention. 1 to 9 in FIG. 1 are low-speed rolls. Further, 10 to 14 are high-speed roll groups, 15 is a nip roll, and 16 is a radiation heater.

  Although an Example is described below, this invention is not limited to this. First, the physical property value evaluation method and the effect evaluation method used in the present invention will be described.

(1) Glass transition temperature Tg, melting point Tm
Using a DSC (RDSC220) manufactured by Seiko Denshi Kogyo Co., Ltd. as a differential scanning calorimeter and a disk station (SSC / 5200) manufactured by Seiko Instruments Inc. as a data analyzer, about 5 mg of a sample is heated from room temperature to 20 ° C. on an aluminum pan. The temperature was increased at a rate of / min and measured. In the obtained endothermic curve, the temperature at which the step of the curve showing the glass transition temperature appears was Tg, and the temperature of the melting peak showing the melting point was Tm.

(2) Intrinsic viscosity This is a value measured at a concentration of 0.1 mg / ml at 25 ° C. in orthochlorophenol. The unit is represented by dl / g.

(3) Film surface temperature The film surface temperature was measured from a distance of 50 cm from the film surface in the direction perpendicular to the film surface, using a radiation thermometer (IT2-100) manufactured by Keyence Co., Ltd., at the center in the film width direction.

(4) Roll temperature The roll surface temperature was measured from a distance of 50 cm from the roll surface in a direction perpendicular to the surface in contact with the roll surface with a radiation thermometer (IT2-100) manufactured by Keyence Corporation.

(5) Surface roughness In accordance with JIS B 0601, using a surface roughness meter (Surfcoder SE-400) manufactured by Kosaka Lab, the feed rate is 0.1 mm / s, the measurement length is 5.0 mm, and the cut-off value is 0. Ra and Rmax were measured at 8 mm.

(6) Scratch determination Scratch determination is carried out under a three-wavelength fluorescent lamp, a scratch having a length of 0.5 mm or more is determined to be a NG level scratch, and an NG level per 100 cm ^{2 of} film is determined. The number of scratches was defined as “number of scratches”.

( Reference Example 1 )
Polyethylene terephthalate (PET) pellets with a glass transition temperature Tg of 73 ° C, a melting point Tm of 253 ° C, and an intrinsic viscosity of 0.65 dl / g are dried, fed to an extruder, melted at 280 ° C, and passed through a filter After being discharged, it was discharged by a T-die and adhered and solidified by a static electricity application method to a cooling drum having a surface temperature of 18 ° C. to obtain a cast film having a thickness of 1175 μm and a width of 850 mm. The birefringence of the cast film was 0.001 and was substantially unoriented.

  Next, this unstretched sheet is heated and stretched by the longitudinal stretching apparatus shown in FIG. 1, and the speed setting of 1 to 9 rolls on the low speed side is 11.8 m / min, and the speed setting of 10 to 14 rolls on the high speed side is 38.9 m. As a result, the film was stretched 3.3 times in the longitudinal direction and then 3.56 times in the transverse direction. In addition, the preheating process in this invention shows 1-8 rolls in FIG. At this time, the roll material of the longitudinal stretching apparatus shown in FIG. 1 is coated with hard chrome having a surface roughness Ra of 0.1 μm on the surface of 1 to 3 rolls, and the surface of 4 to 9 rolls is Ra 1.2 μm and Rmax 11 μm. A ceramic mainly composed of white alumina was coated.

At this time, the film temperature was 41 ° C. with 1 roll and the film temperature was 87 ° C. with 9 rolls. The surface temperature of the 4 rolls at this time was 84 ° C., and this unstretched sheet was 68 ° C. at the 4 roll entrance, 73 ° C. at the 4 roll exit, and the temperature rise on the 4 rolls was 5 ° C. At this time, the obtained stretched film had good scratches and horizontal defects, and the number of scratches was 3/100 cm ² .

(Example 2)
A biaxially stretched polyester film was obtained in the same manner as in Example 1 except that the surface of the four rolls was coated with a chromium oxide ceramic having a surface roughness of Ra 0.14 μm and Rmax 3.5 μm. At this time, the obtained stretched film had very good scratches and lateral defects, and the number of scratches was 0/100 cm ² .

(Comparative Example 1)
A biaxially stretched polyester film was obtained in the same manner as in Example 1 except that the surface temperature of the 4 rolls was 90 ° C. The unstretched sheet at this time was 68 ° C. at the entrance of the 4 rolls and 77 ° C. at the exit of the 4 rolls, and the temperature rise on the 4 rolls was 9 ° C. At this time, the obtained stretched film had fine scratches, and the number of scratches was 100/100 cm ² .

( Reference Example 3 )
A biaxially stretched polyester film was obtained in the same manner as in Example 1 except that the surface of 4 rolls was coated with hard chromium having a surface roughness of 0.1 μRa in the same manner as 1-3 rolls. At this time, the obtained stretched film was inferior to Reference Example 1 due to the presence of lateral defects due to adhesion, although there was no fine scratch.

( Comparative Example 14 )
A biaxially stretched polyester film was obtained in the same manner as in Example 2 except that the surface temperature of the 4-roll surface was 94 ° C. At this time, the obtained stretched film was inferior to that of Example 2 because there was no micro scratch, but there was a horizontal step defect due to adhesion.

  The present invention is applicable not only to optical films with severe scratch requirements but also to all polyester films.

1 is a sheet longitudinal stretching apparatus showing an embodiment of the present invention.

Explanation of symbols

1-3: Rolls with a low-speed roll group and a film temperature of the glass transition temperature or less 4: Rolls with a low-speed roll group with a film temperature at the entrance of the roll (glass transition temperature -10 ° C) to a glass transition temperature 5-9: Rolls of low-speed rolls whose film temperature exceeds the glass transition temperature 10-14: High-speed rolls 15: Nip rolls 16: Radiation heaters

Claims (2)

In the preheating step of heating the unstretched polyester film in contact with a plurality of rolls,
Among the plurality of rolls, one roll having a surface roughness of Ra 0.05 μm or more and Rmax 5 μm or less (hereinafter referred to as a chromium oxide ceramic roll A) is coated. ,
And the surface roughness Ra of the downstream side of the roll of the chromium oxide-based ceramic roll A is have a value greater than the chromium oxide-based ceramic roll A,
Furthermore, the surface temperature of the said chromium oxide type ceramic roll A is 1-20 degreeC high temperature from the glass transition temperature of polyester, The manufacturing method of the polyester film characterized by the above-mentioned. The film temperature of chromium oxide-based ceramic roll A entrance, method for producing a polyester film according to claim 1, characterized by comprising the step of (the glass transition temperature of -10 ° C.) ~ glass transition temperature.

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