JP2615671B2 - Roll stretching method - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a roll stretching method, that is, a method of stretching in a longitudinal direction using a roll, and more particularly, to a method of stretching at least in a longitudinal direction without surface defects. The present invention relates to a method for stretching a rolled polyester film.

[Prior Art] A method of stretching a polyester film in the longitudinal direction using a roll, or a method of stretching a film solidified by cooling by applying an electrostatic charge, is disclosed in JP-A-46-439 and JP-B-48-29,311. It is known.

Alternatively, at the time of roll stretching, it is also possible to use a non-adhesive material roll such as a fluororesin, ceramic, or Sihacon rubber so that the film does not adhere to the roll, Japanese Patent Publication No. 47-49,827,
It is known in Japanese Patent Publication No. 48-44,666.

[Problems to be Solved by the Invention] In the above-mentioned known roll stretching method, even if a roll of a non-adhesive material is used or the stretching temperature is set to a low temperature near the glass transition temperature of the polyester film, it is longer than 3 hours. When the roll is stretched for a time, a polyester additive, a low molecular weight substance such as a monomer or oligomer of the polyester, the polyester itself, or a partially carbonized or gelled substance adheres to the roll. As a result, the surface of the stretched polyester film becomes a film having surface defects such as transfer flaws and scratches of roll surface defects, and occurrence of partial adhesion unevenness.

[Means for Solving the Problems] In the present invention, in a roll stretching method of a polyester, a low-temperature plasma treatment is performed on a cooled and solidified polyester sheet while applying an electrostatic charge to a molten polyester,
This is a roll stretching method characterized by stretching using a mirror-finished chrome plating roll.

The polyester in the present invention is a polymer compound having an ester bond in the molecular main chain obtained by condensation polymerization of dicarboxylic acid and diol. Representative polyesters include terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, Phenoxyethane dicarboxylic acid, diphenyl dicarboxylic acid, diphenyl ether dicarboxylic acid, diphenyl sulfone dicarboxylic acid, diphenyl ketone dicarboxylic acid, anthracene dicarboxylic acid, α. β-bis (2-clophenoxy) ethane-4,4′-dicarboxylic acid, aromatic dicarboxylic acid such as diphenic acid and aliphatic dicarboxylic acid such as adipic acid and sebacic acid are used as acid components, ethylene glycol, trimethylene Examples include polyester resins containing an alkylene glycol such as glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol, hexylene glycol, cyclohexane dimethanol, or polyethylene glycol as a glycol component.

Representative polyesters include polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyethylene α, β-bis (2-chlorophenoxy) ethane 4,4′-dicarboxylate, polycyclohexane dimethylene terephthalate, and the like. Modified products are typical. Of course, those known as polymeric additives, such as stabilizers, lubricants, pigments, ultraviolet absorbers, plasticizers, viscosity modifiers,
An anti-blocking agent, a nucleating agent, conductive particles and the like may be added.

A method of cooling and solidifying while applying an electrostatic charge is to apply a high voltage of direct current or / and alternating current over the entire width of the molten polymer as shown in, for example, Japanese Patent Publication No. 376142 or Japanese Patent Application Laid-Open No. 46-439. This is a method of increasing the adhesion between the cooling drum and the molten polymer and casting. The electrode to which the electrostatic charge is applied may be a die, a drum, a wire, a blade alone, or a combination thereof.

Low-temperature plasma treatment is a process in which a sheet is exposed to a sustained discharge, a so-called glow discharge, which is initiated and applied by applying a high voltage to a gas atmosphere under a low pressure, and electrons, ions, excited atoms, excited molecules, and radicals generated during the glow discharge. The sheet is treated with active particles such as ultraviolet rays, for example, a treatment method exemplified in JP-A-62-53815.

In the present invention, the gas pressure is preferably from 1 × 10 ⁻⁴ Torr to 50 Torr. When the gas pressure is less than 1 × 10 ⁻⁴ Torr, the sheet surface is colored, the surface layer is deteriorated by stretching, and the adhesive performance is improved, and the film becomes The surface defect prevention function tends to stop. When the pressure exceeds 50 Torr, the above treatment effect is hardly recognized. In particular, when the pressure is 5 × 10 ⁻³ Torr or more and 0.5 Torr, the processing effect is remarkable, which is a more preferable gas pressure range.

The frequency of the high voltage applied for discharging, starting, and sustaining is not specified, and DC, low frequency, high frequency, microwave, etc. can be used.
Films treated and processed using a frequency of KHz have a remarkable effect of improving the surface properties and are preferred frequencies.

The apparatus for low-temperature plasma processing, particularly the electrode shape, electrode arrangement and the like are not particularly limited. However, since a sheet such as a sheet, which is wide and long, and is made of a polymer resin, for example, A device having an asymmetric electrode as disclosed in JP 52-147,953 is more preferred.

In addition, the sheet is continuously introduced from the atmosphere into the low-pressure low-temperature plasma processing apparatus, where the low-temperature plasma processing is performed, and then the sheet is drawn back into the air. is there. The air-to-air method is not limited, but can be freely used depending on the application, such as a nip method and a labyrinth seal method. As a selection point of the method, whether or not a surface defect such as a scratch or a scratch is generated on the surface of the film to be processed, a necessary degree of vacuum, a thickness of the film to be processed, and the like are selected.

As the gas used in the low-temperature plasma treatment in the present invention, any of an inorganic gas, an organic compound vapor, and a mixture thereof can be used according to the required performance of the film. When an inorganic gas is used, a treatment generally called a plasma surface treatment is performed, and the surface of the sheet is chemically or physically modified. When an organic compound vapor or a mixture of the vapor and an inorganic gas is used, a treatment generally called plasma polymerization is performed to form a polymer composed of the organic compound on the sheet surface.

Inorganic gas used in the present invention is not limited to a particular gas, for example _{H 2, He, Ne, Ar} , Kr, Xe, N 2,
O _2, O _{3, air, H 2 O, N 2 O} , NO, N 2 O 4, N 2 O 3, CO, CO 2, N
Freon gas such as H ₃ , SO ₂ , Cl ₂ , CF ₄ , or a mixed gas thereof may be used, and may be appropriately selected according to the required performance of the film. Among them _{He, Ar, N 2, CO} , C
O ₂ , N ₂ O, air, or a mixed gas containing them is a more preferable gas because it can stably exhibit various surface characteristics.

The organic compound vapor used in the present invention is not particularly limited, as long as it has an appropriate vapor pressure at a specified atmospheric temperature, and can exhibit the surface performance required of the film, such as methyl alcohol. , Ethyl alcohol, xylene, general organic solvents such as toluene, unsaturated monomers such as ethylene, acetylene, vinyl chloride, styrene, allyl alcohol, acrylic acid (methacrylic acid), acrylic acid ester (methacrylic acid ester),
Silane compounds such as vinylsilane, trimethylmethoxysilane, trimethylchlorosilane, hexamethylsilazane, γ- (2-aminoethyl) aminopropyltrimethoxysilane, ethylene tetrafluoride, propylene hexafluoride,
Examples include fluorine compounds such as monochlorotrifluoroethylene, but the organic compounds used in the present invention are not limited to these compounds.

Roll stretching refers to stretching while the film is in direct contact with or immediately after contact with a heating medium such as a roll or a support, that is, when the film is stretched, it is heated to a temperature substantially suitable for the stretching temperature. The film is subjected to a stretching force while contacting the roll in some sense. Therefore, as typified by Japanese Patent Laid-Open No. 50-122,573 etc., a method in which preheating, stretching nip, cooling, etc. are all performed by rolls, or if necessary, in a heated hot air oven, after preheating the film on a transfer roll, the stretching section is limited A typical method is stretching between two pairs of stretching rolls.

Next, a method for producing the polyester film of the present invention will be described. After the polyester resin is dried, it is supplied to an extruder by a conventional method, and after being melted, is quantitatively discharged by a gear pump or the like and discharged from a molding die. While applying an electrostatic charge to the melt, the melt is brought into close contact with a cooling drum and solidified by cooling. As a method of applying an electrostatic charge, there is a method of applying a high DC voltage to a wire, a blade, or a molding die, and further, a casting drum, and the method can be arbitrarily selected depending on an application or purpose. However, in the case of the present invention, although there is no particular limitation, the method of applying to an insulating drum is excellent, but the effect of the present invention can be recognized also when applying to a wire or a molding die.

The cast sheet cooled by applying an electrostatic charge is subjected to low-temperature plasma treatment. Of course, between casting and low-temperature plasma treatment, stretching in the width direction by a tenter method or simultaneous biaxial stretching in the longitudinal and width directions, heat treatment,
Coating, embossing, corona discharge treatment and the like may be performed as necessary. The film temperature during the low-temperature plasma treatment is usually at room temperature, or, if necessary, may be heated to around the glass transition temperature of the polyester film. The processing intensity, processing time, degree of vacuum during processing, and the like can be selected within an arbitrary range in which the effects of the present invention are remarkable.

As the subsequent roll stretching, the film is stretched in the longitudinal direction using a roll. The film before stretching may be any orientation such as non-oriented, uniaxial orientation, biaxial orientation, etc.Therefore, as the roll stretching conditions, the stretching temperature is selected from the glass transition temperature Tg to the melting point Tm of the polyester film. The stretching ratio can be freely selected in the range of about 1.05 to 12 times. The roll surface material must use a chrome-plated mirror surface, but other roll surface materials include sand blast, copper plating,
Rubbers such as silicon rubber, hypalon rubber, ethylene propylene rubber, fluorine rubber, polyurethane rubber and polyester rubber, ceramics such as Al ₂ O ₃ , SiO ₂ , ZrO ₂ and TiO ₂ , “Teflon” (registered trademark of DuPont) There are a fluororesin coating film, a high-temperature baked crosslinked film such as a silicone resin, and a highly crosslinked film such as an epoxy resin or an acrylic resin. In the case of the present invention, considering that the effect is remarkable, the effect is particularly effective when a mirror-finished chrome plating roll is used. Ie
Even if the polyester film is stretched and heat-treated in the longitudinal direction while keeping the polyester film in contact with the roll surface heated to a high temperature of Tg or more for a long time, the polyester film does not show surface defects such as scratches, scratches, and uneven adhesion. In addition, no stains due to additives, gelled substances, etc. are generated on the roll surface.

[Effects of the Invention] The following excellent effects are exhibited because the sheet solidified by cooling while applying an electrostatic charge to the polyester is subjected to low-temperature plasma treatment and then roll-stretched.

(1) Even if the polyester sheet is roll-drawn for a long time, surface defects such as scratches, scratches, and uneven adhesion are not generated on the surface of the sheet.

(2) Further, at this time, the oligomer surface
No adhesion of monomers, polyester additives, carbides, polymers, etc. occurs.

Of course, neither of the effects (1) and (2) can be obtained only by the low-temperature plasma treatment, and the effect is produced only when used in combination with the electrostatic application.

(3) In addition to the above effects, the obtained polyester film has properties such as easy adhesion, easy slipping, and prevention of surface bleeding of oligomers and the like.

(4) It is effective for the production of very thin films of 2 μm or less, the stretching of films with very smooth surfaces and the surface roughness Ra of 10 μm or less, and the stretching at high temperatures, and the stretching of amorphous polyester. is there.

[Examples] Hereinafter, effects of the present invention will be described based on examples.

Example 1 A polyester was directly polymerized from terephthalic acid and ethylene glycol without transesterification, and the intrinsic viscosity was 0.61 dl.
/ g (in o-chlorophenol) of polyethylene terephthalate (containing 0.2% of 50 μm SiO ₂ particles as an additive). After vacuum drying the resin at 180 ° C., it is supplied to a 250 mm diameter extruder by a conventional method, melted at 285 ° C., measured by a gear pump, extruded from a molding die, and applied with an electrostatic charge at 40 m / min. It was brought into close contact with a mirror chromium plating roll kept at 30 ° C. and cooled and solidified to obtain a cast sheet having a thickness of 160 μm. For the electrostatic charge, a negative electrode of 20,000 V was applied as a voltage using a platinum-plated tungsten wire having a diameter of 0.1 mm. Ar is applied to the surface of the cast sheet thus obtained.
Low temperature plasma treatment with gas. The treatment was performed on both sides of the sheet by a labyrinth seal method under a vacuum of 0.04 Torr at a voltage of 110 KHz and 5 KV.

The low-temperature plasma-treated sheet thus obtained was preheated on a mirror-finished chrome plating roll heated to 90 ° C, then nipped between silicon rubber rolls heated to 98 ° C, stretched 6 times in the longitudinal direction, and immediately After stretching 4 times in the width direction in a tenter heated to 70 ° C., once cooled to 70 ° C. or less, heat-treated at 220 ° C. for 3 seconds and 160 ° C. for 6 seconds, and then cooled to room temperature to obtain a 7 μm thick. Surface roughness Ra = 5mμ
Was obtained.

The film thus obtained did not show any surface defects such as scratches, scratches, and uneven adhesion even after 7 days of film formation. It had a clean surface.

Comparative Examples 1 to 3 Comparative Examples 1 and 3 are examples in which the cast without using the electrostatic application cast used in Example 1 and Comparative Examples 2 and 3 in which the low-temperature plasma treatment is not performed. A biaxially stretched film having a thickness of 7 μm was formed in the same manner as described above.

As described above, merely performing low-temperature plasma treatment does not have the effect of preventing surface defects, but the application of an electrostatic charge eliminates the occurrence of surface defects due to the synergistic action.

The surface defect referred to here means that no streak-like or crater-like defect is seen when the film is directly or visually observed after vapor deposition, and the size of the surface unevenness is 0.5 μm or less, and even 0.2 μm or less. It is a disadvantage of less than μm.

Example 2 Polyethylene terephthalate (o-chlorophenyl intrinsic viscosity 0.65, containing 0.3% by weight of titanium oxide having an average particle size of 250 mμ as an additive) was melted at 285 ° C. in the same manner as in Example 1 and then extruded from a molding die. An insulating drum cooled to 30 ° C. (using CFC as a refrigerant) was tightly adhered to a casting drum applied with a negative voltage of 15 KV to cool and solidify. The cast sheet is stretched 3.8 times in the width direction in a tenter heated to 90 ° C., and subsequently, the first stage is stretched 3.5 times at 95 ° C. using a mirror-finished chrome plating roll, and once heated at 160 ° C., Similarly, the film was stretched at 185 ° C. in the second stage at 185 ° C. by a second step and further heat-treated with a mirror-surfaced chrome plating roll heated to 200 ° C. to obtain a 9 μm thick longitudinally strengthened film.

The film thus obtained was a uniform film with no surface defects despite the long-term film formation for 3 days. Needless to say, no attachments such as additives and oligomers were attached to the stretching roll and the heat treatment roll.

Claims (1)

(57) [Claims] In a roll stretching method of polyester, a polyester sheet cooled and solidified while applying an electrostatic charge to a molten polyester is subjected to a low-temperature plasma treatment,
A roll stretching method characterized by stretching using a mirror-finished chrome plating roll.