JP2008274176A - Substrate film for producing plastic film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyester substrate film which can very highly satisfy surface evenness and transparency of a formed film obtained when the polyester substrate film is used as a substrate film for producing a plastic film by a method such as casting and has good quality and operating efficiency in the process. <P>SOLUTION: In the polyester substrate film used as a substrate in the process for forming a plastic film, the amount of oligomer on one of the surfaces thereof is 5.0 mg/m<SP>2</SP>or less when it is measured after methyl ethyl ketone is applied to the film surface followed by drying and heat-treatment at 180°C for 10 minutes; the Ra of the film surface is in the range of 5.0 to 10 nm; and the density of the film is in the range of 1.405 to 1.415 g/cm<SP>3</SP>. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a support film used for plastic film production. Specifically, the present invention is a polyester film used as a support particularly when producing an optical film, and can produce a high-quality film efficiently with high productivity. The surface of the obtained optical film The present invention relates to an excellent support film for a production process, which is flat, has no defects when used in optical applications, and can provide a clear image for display.

  In recent years, highly transparent films have been used for optical applications, and films having various functions have been used particularly in the display field. For example, in an LCD display, a polarizing film, a retardation film, a viewing angle enhancement film, a brightness enhancement film, a diffusion film, a reflection film, etc. In a PDP display, an electromagnetic wave cut, a near infrared ray cut, an ultraviolet ray cut, a color tone correction, etc. A film having a function is used as a so-called PDP filter. Among these films, a film that is very highly transparent and has no optical anisotropy is required particularly in the LCD display field. In order to make a film satisfying such a requirement, the raw material is limited, highly transparent and free from defects due to foreign matters, etc., a so-called solution casting method in which a polymer is extruded into a sheet form as a solution and manufactured through a drying step is used. It has been adopted. Similarly, an aqueous polymer solution may be coated on a support, and a film may be formed through a drying process.

  For example, when a film for optical use is formed by a solution casting method, a method using a metal endless belt or drum as a support and a method using a plastic or metal film or sheet are generally used. In particular, when a plastic film is used as a support, since it is excellent in transportability and flexibility, and the replacement of the support is relatively simple, it is adopted as a method having a high degree of freedom in equipment design and use. In addition, since there is no problem of periodic appearance failure due to a step difference of a seam unique to an endless belt or the like, the method is suitable for obtaining a good film. Among these, a polyester film excellent in mechanical properties, heat resistance, dimensional stability, solvent resistance and the like is preferably used.

  In addition to having a high degree of transparency, the optical film can be made a film that does not deteriorate in quality due to light scattering on the surface by making the surface extremely flat. When used as a film-forming support, since the surface shape of the support is transferred, the surface of the support needs to be extremely flat. However, a method of forming fine protrusions on the film surface is usually used for the polyester film in order to improve handleability, slipperiness, winding property and the like. If there are large or high protrusions on the film surface, the quality of the resulting optical film is degraded. On the other hand, if these protrusions are eliminated or made excessively small, the handling of the polyester film will be poor, or scratches will occur on the surface during the production process, and the shape will be transferred. May cause a drop.

  In addition, when using a polyester film as a support, the film is rewound and travels in contact with several rolls and is transported to a casting process. In this process, the film is subjected to some friction. If it is scraped off, it is transferred to a cast sheet, which causes a decrease in quality when used for optics. Further, when the polyester is damaged by the polymer solution used in the molding process, the polyester may be easily scraped, and the above-described deterioration in quality may occur. Furthermore, in the process of drying the polymer solution or the polymer aqueous solution after casting, the oligomer is precipitated, and the oligomer deposited on the surface of the support may be transferred to cause deterioration in quality.

With respect to the polyester film used as a film-forming support, there is a strong demand for the transfer of the shape of the coarse protrusions and the transfer of foreign matters such as scraped powder and oligomers.
JP 2005-307038 A JP 2007-50631 A

  The present invention has been made in view of the above circumstances, and the problem to be solved is that when the plastic film is used as a support when produced by a method such as a casting method, the surface flatness and transparency of the obtained molded film are obtained. It is an object of the present invention to provide a polyester film for a support which can satisfy the properties at a very high level and has good quality, process use efficiency and the like.

  As a result of intensive studies in view of the above circumstances, the present inventors have found that the above problems can be solved by a polyester film having a specific configuration, and have completed the present invention.

That is, the gist of the present invention is a polyester film used as a support in the step of forming a plastic film, and the film surface after applying methyl ethyl ketone on one film surface, drying, and heat-treating at 180 ° C. for 10 minutes. The oligomer amount is 5.0 mg / m ² or less, the Ra of the film surface is in the range of 5.0 to 10 nm, and the film density is in the range of 1.405 to 1.415 g / cm ^3. The feature resides in a polyester film for a support.

Hereinafter, the present invention will be described in more detail.
The support polyester film of the present invention is used in the step of forming a plastic film, but the material of the film-forming film is not particularly limited as long as such a step can be adopted. For example, a polycarbonate film, a polyarylate film, a triacetyl cellulose-based film, a norbornene resin-based film, a polyimide film, polyvinyl alcohol, or the like can be used.

  In the present invention, the polyester is obtained by polycondensation of an aromatic dicarboxylic acid and an aliphatic glycol. Examples of the aromatic dicarboxylic acid include terephthalic acid, 2,6-naphthalenedicarboxylic acid, and 1,4-cyclohexanedicarboxylic acid. Examples of the aliphatic glycol include ethylene glycol, diethylene glycol, 1,4-butanediol, 1, 4-cyclohexanedimethanol etc. are mentioned. Typical polyesters include polyethylene terephthalate (PET), polyethylene-2,6-naphthalenedicarboxylate (PEN) and the like.

  The polyester used in the present invention may be a homopolyester or a copolyester. In the case of a copolyester, it is a copolymer containing usually 30 mol% or less of the third component. Examples of the dicarboxylic acid component of the copolyester include isophthalic acid, phthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, 1,4-cyclohexanedicarboxylic acid, and oxycarboxylic acid (for example, P -One kind or two or more kinds of oxybenzoic acid etc.), and the glycol component is one kind such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, neopentyl glycol, etc. Or 2 or more types are mentioned.

  The polyester of the present invention may be obtained by a melt polymerization reaction. However, if a raw material obtained by solid-phase polymerization of a polyester polyester after melt polymerization is used, it is included in the raw material. Since the amount of oligomers to be reduced can be reduced, it is preferably used. The intrinsic viscosity of the obtained polyester is preferably 0.40 dl / g or more, and more preferably 0.40 to 0.90 dl / g.

  The amount of oligomer contained in the polyester raw material is preferably 0.7% by weight or less, more preferably 0.5% by weight or less, and particularly preferably 0.3% by weight or less. When the amount of oligomer in the polyester raw material is small, the amount of oligomer contained in the polyester film of the present invention is reduced, and the effect of preventing oligomer precipitation on the film surface is particularly high.

  The polyester film of the present invention is preferably a polyester film extruded by a so-called extrusion method in which the above-described polyester is melt-extruded from an extrusion die, and is oriented in the biaxial direction of the vertical direction and the horizontal direction as necessary. Film. Further, the film may have a laminated structure using a so-called coextrusion method using two or more extruders. Such a laminated structure may be a two-layer structure of A / B, a three-layer structure of A / B / A or A / B / C, or a structure having a larger number of layers.

  In the present invention, it may be a film having a structure in which a polyester having a low oligomer content is coextruded and laminated on at least one surface of a layer made of polyester having a normal oligomer content. Thus, the effect of suppressing oligomer precipitation obtained in the present invention can be exhibited to a high degree.

In the present invention, the amount of oligomer on the film surface after applying methyl ethyl ketone on one film surface, drying, and heat-treating at 180 ° C. for 10 minutes is 5.0 mg / m ² or less, preferably 3.0 mg / m 2. ² or less, more preferably 1.0 mg / m ² or less. The amount of oligomer here refers to the amount of cyclic trimer (polyester-derived oligomer) measured by the method described later. When the amount of oligomer on the film surface exceeds 5.0 mg / m ² , when used as a film for a support, transfer / transfer to a molded film occurs, and the quality of the obtained optical film decreases. The polyester film satisfying the above requirements may be a film using a technique as disclosed in JP-A-2006-62273, for example.

  In the polyester film of the present invention, in order to improve the slipperiness of the surface to prevent problems such as blocking and to improve the handleability, the film can contain fine particles to form appropriate protrusions. Examples of such fine particles include inorganic particles such as silica, alumina, kaolin, clay, talc, calcium carbonate, titanium oxide, barium sulfate, lithium fluoride, organic particles such as calcium terephthalate and calcium oxalate, styrene-based, acrylic Examples thereof include crosslinked polymer particles such as a system, and so-called precipitated particles obtained by precipitating a catalyst and an auxiliary agent in a polyester production process.

  The average particle size of the fine particles to be blended is not particularly limited, but is usually 0.01 to 5 μm, preferably 0.02 to 3 μm, more preferably 0.05 to 3 μm. When particles having an average particle size of less than 0.01 μm are used, protrusions having an effective height may not be formed on the film surface, and the winding characteristics in the film manufacturing process may be inferior. There is a possibility that problems such as scratches occur on the film surface. Further, when the average particle diameter exceeds 5 μm, the degree of roughening of the film surface becomes too large, and surface shape transfer when used as a support in the step of forming a film occurs, resulting in an optical In some cases, the quality of the film for use may be deteriorated, or the film surface may be easily scraped and transferred to the optical film.

  In the present invention, a method of adding two or more kinds of the above-mentioned particles as a particle type or adding two or more kinds as an average particle diameter can be used.

  In the present invention, the surface is roughened by a method such as forming protrusions on the surface by such a method or blending particles in a coating layer to be described later, but the surface roughness is Ra. The range is 5.0 to 10 nm, preferably 5.5 to 9.5 nm, and more preferably 6.0 to 9.0 nm. Rt is usually in the range of 30 nm to 500 nm, preferably in the range of 30 nm to 300 nm, and more preferably in the range of 40 nm to 130 nm. When the surface roughness of the film increases, the above-mentioned problem of shape transfer occurs. On the other hand, if the surface roughness is too small, the handling of the film will be inferior, so that the winding property during production will be hindered, or the surface during film running when used as a film production process or cast support Problems such as scratches may occur.

  In order to obtain such a surface shape of the support, the particle size distribution value is 3.0 or less, further 2.5 or less, particularly 2.2 or less, in addition to setting the particles to be blended in the film to the above-mentioned particle size range. It is preferable to do. If the particle size distribution is sharp, coarse protrusions are not generated, and an extremely high effect as a support can be exhibited.

  In the present invention, the method of blending the particles with the polyester is not particularly limited, and a known method can be adopted. For example, it can be added at any stage of producing the polyester, but it is preferably added as a slurry dispersed in ethylene glycol or the like at the stage of esterification or before the start of the polycondensation reaction after completion of the transesterification reaction, The polycondensation reaction may proceed. Also, a method of blending a slurry of particles dispersed in ethylene glycol or water with a vented kneading extruder and a polyester raw material, or a blending of dried particles and a polyester raw material using a kneading extruder. It is done by methods.

The density of the polyester film of the present invention needs to be in the range of 1.405 to 1.415 g / cm ³ . When the density of the film is less than 1.405 g / cm ^{3, the} damage caused by the solution at the time of forming the polyester film is large, the abrasion is generated due to the friction during transportation, and the film is transferred to a molded plastic film, and the film is used for optical use. It may cause quality degradation when used. On the other hand, when it exceeds 1.415 g / cm ³ , troubles such as breakage are likely to occur in the production process of the polyester film, and the productivity is remarkably lowered.

  Hereinafter, the polyester film of the present invention will be specifically described, but the present invention is not particularly limited to the following examples as long as the gist of the present invention is satisfied.

  Polyester chips dried by a known method are supplied to a melt extrusion apparatus and heated to a temperature equal to or higher than the melting point of each polymer to melt. Next, the molten polymer is extruded from a die and rapidly cooled and solidified on a rotary cooling drum so that the temperature is equal to or lower than the glass transition temperature to obtain a substantially amorphous unoriented sheet. In this case, in order to improve the flatness of the sheet, it is preferable to improve the adhesion between the sheet and the rotary cooling drum. In the present invention, an electrostatic application adhesion method and / or a liquid application adhesion method is preferably employed.

  In the present invention, the sheet thus obtained is stretched biaxially to form a film. Specifically describing the stretching conditions, the unstretched sheet is preferably stretched 2 to 6 times at 70 to 145 ° C. in the longitudinal direction to form a longitudinal uniaxially stretched film, and then 2 to 90 to 160 ° C. in the lateral direction. -6 times stretching and heat treatment at 190-240 ° C for 1-600 seconds. Here, in order to obtain a film having a density in the range of the present invention, it is particularly necessary to select the temperature and time of the heat treatment. The heat treatment temperature depends on the time of the heat treatment, but is preferably 220 ° C. or higher. Preferably it is 230 degreeC or more. Further, at this time, a method of relaxing 0.1 to 20% in the longitudinal direction and / or the transverse direction in the maximum temperature zone of the heat treatment and / or the cooling zone at the heat treatment outlet is preferable. Further, it is possible to add re-longitudinal stretching and re-lateral stretching as necessary.

  In the present invention, two or three or more polyester melt extruders can be used to form a laminated film of two layers or three or more layers by a so-called coextrusion method. As a layer structure, an AB structure using an A raw material and a B raw material, or an ABA structure, and further a film having an ABC structure or other structure using a C raw material can be obtained. For example, the surface shape of the A layer can be designed by using specific particles as the A raw material, and a raw material not containing particles can be used as the B raw material to form an AB or ABA film. In this case, since the raw material of B layer can be selected freely, a cost advantage etc. are large. Further, even if the recycled material of the film is blended with the B layer, the surface roughness can be designed by the surface A layer, so that the cost advantage is further increased.

  In addition, the polyester film of the present invention has good wettability with the solution at the time of film formation and good uniformity of the sheet thickness, etc., and the peelability after removing the solvent to form a sheet is also appropriate. Therefore, a coating layer can be provided on the surface.

  In forming such a coating layer, the method of forming a film, in particular, after stretching in the longitudinal direction and before stretching in the lateral direction can form a very thin coating layer, and the coating solution drying and curing reaction Is preferable in that it can be carried out in the film forming process.

  The coating layer is preferably composed of a combination of a crosslinking agent and various binder resins, and the binder resin is used in combination with at least one polymer selected from polyester, acrylic polymer and polyurethane from the viewpoint of adhesiveness. . Each of the above polymers shall also include derivatives thereof. The derivative here refers to a polymer obtained by reacting a reactive compound with a copolymer or a functional group with another polymer. Polyvinylidene chloride, chlorinated polyolefin, etc. also form a tough film and show good adhesion to the topcoat, but since these contain chlorine, they can generate harmful dioxin compounds containing chlorine during combustion. This is not preferable in this respect. Further, when the scrap of the coated film is reused, there is a problem of coloring and generation of corrosive gas, which is not preferable in this respect.

  As the crosslinking agent resin, melamine-based, epoxy-based, and oxazoline-based resins are generally used, but melamine-based resins are particularly preferable from the viewpoints of coatability and durable adhesiveness. The melamine-based resin is not particularly limited, but melamine, a methylolated melamine derivative obtained by condensing melamine and formaldehyde, a compound partially or completely etherified by reacting methylolated melamine with a lower alcohol, And a mixture thereof can be used.

  In the present invention, it is preferable to contain inorganic particles or organic particles in the coating layer in order to further improve the slipperiness, adhesion and the like. The amount of the particles in the coating agent is usually 0.5 to 10% by weight, preferably 1 to 5% by weight. When the blending amount is less than 0.5% by weight, the blocking resistance may be insufficient. When the blending amount exceeds 10% by weight, the transparency of the film is hindered. Tend to be.

  Examples of the inorganic particles include silicon dioxide, alumina, zirconium oxide, kaolin, talc, calcium carbonate, titanium oxide, barium oxide, carbon black, molybdenum sulfide, and antimony oxide. Among these, silicon dioxide is easy to use because it is inexpensive and has various particle sizes.

  Examples of the organic particles include polystyrene or polyacrylate polymethacrylate in which a crosslinked structure is achieved by a compound (for example, divinylbenzene) containing two or more carbon-carbon double bonds in one molecule.

  Further, the coating layer may contain an antistatic agent, an antifoaming agent, a coating property improving agent, a thickener, an antioxidant, an ultraviolet absorber, a foaming agent, a dye, a pigment, and the like.

  As a coating method of the coating agent, for example, a reverse roll coater, a gravure coater, a rod coater, an air doctor coater, or a coating apparatus other than these as shown in Yuji Harasaki, Tsuji Shoten, published in 1979, “Coating Method” Can be used.

  The coating layer may be formed only on one side of the polyester film or on both sides. When it is formed only on one side, an application layer different from the above-mentioned application layer can be formed on the opposite side as necessary to give other characteristics. In addition, in order to improve the applicability | paintability and adhesiveness to the film of a coating agent, you may give a chemical process and an electrical discharge process to a film before application | coating. Moreover, in order to further improve the surface characteristics, a discharge treatment may be performed after the coating layer is formed.

  The thickness of the coating layer is usually in the range of 0.02 to 0.5 μm, preferably 0.03 to 0.3 μm, as the final dry thickness. When the thickness of the coating layer is less than 0.02 μm, the effect of the present invention may not be sufficiently exhibited. When the thickness of the coating layer exceeds 0.5 μm, the films tend to stick to each other, and particularly when the coated film is re-stretched to increase the strength of the film, it adheres to the roll in the process. There is a tendency to become easy. The above problem of sticking appears particularly when the same coating layer is formed on both sides of the film.

  The polyester film of the present invention can be mixed with other thermoplastic resins such as polyethylene naphthalate and polytrimethylene terephthalate as long as the effects of the present invention are not impaired. Moreover, you may mix | blend coloring agents, such as a ultraviolet absorber, antioxidant, surfactant, a fluorescent whitening agent, a lubricant agent, a light-shielding agent, a matting agent, and a dye, a pigment.

  When the film of the present invention is used as a support when a plastic film used for optical applications is produced by a method such as casting, the surface flatness and transparency of the resulting molded film are extremely high. Therefore, its industrial value is high because its quality and use efficiency in the process are good.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to a following example, unless the summary is exceeded. In the examples and comparative examples, “parts” means “parts by weight”. The measuring method used in the present invention is as follows.

(1) Measurement of Intrinsic Viscosity of Polyester 1 g of polyester was precisely weighed, 100 ml of a mixed solvent of phenol / tetrachloroethane = 50/50 (weight ratio) was added and dissolved, and measurement was performed at 30 ° C. For the measurement of the intrinsic viscosity of only the surface layer part, in the process of co-extrusion from the melt extruder, a method of measuring the intrinsic viscosity of the polyester extruded with the same discharge amount, or using only a suitable tool such as a knife for the surface layer It was scraped off and used for measurement.

(2) Oligomer (cyclic trimer) content in polyester A predetermined amount of polyester mixed with chloroform / 1,1,1,3,3,3-hexafluoro-2-propanol (mixing ratio: 3/2) Then, after reprecipitation with chloroform / methanol (mixing ratio: 2/1) and filtration to remove linear polyethylene terephthalate, the solvent in the obtained filtrate was evaporated using an evaporator, The obtained precipitate was dissolved in a predetermined amount of DMF. The obtained DMF was supplied to liquid chromatography (Shimadzu LC-2010C) to determine the amount of oligomer (cyclic trimer) contained in the polyester, and this value was divided by the amount of polyester used for measurement. The amount of oligomer (cyclic trimer) contained in. The amount of oligomer (cyclic trimer) determined by liquid chromatography was determined from the peak area ratio between the standard sample peak area and the measured sample peak area (absolute calibration curve method). The standard sample was prepared by weighing a preliminarily collected oligomer (cyclic trimer) and dissolving it in a weighed DMF (dimethylformamide). The conditions for the liquid chromatograph were as follows.

Mobile phase A: Acetonitrile Mobile phase B: 2% acetic acid aqueous solution Column: Shimadzu Corporation Shim-pack VP ODS
Column temperature: 40 ° C
Flow rate: 1 ml / min Detection wavelength: 254 nm

(3) Amount of oligomer on film surface after solvent treatment Methyl ethyl ketone was applied to the polyester film surface, dried in a hot air circulation oven at 120 ° C for 1 minute in a nitrogen atmosphere, and then this film was circulated in a hot air at 180 ° C in a nitrogen atmosphere. The polyester film was treated for 10 minutes in an oven. The surface of the polyester film after heat treatment was brought into contact with DMF for 3 minutes to dissolve the oligomer deposited on the surface. For this operation, for example, the method described in the elution apparatus used for the single-side elution method in the elution test can be adopted in the voluntary standard for food containers and packaging made of synthetic resin such as polyolefin.

Next, the concentration of the obtained DMF was adjusted by a method such as dilution as necessary, and the resulting DMF was supplied to liquid chromatography (Shimadzu LC-7A) to determine the amount of oligomer in DMF, and this value was contacted with DMF. Dividing by the film area yielded the amount of oligomer (mg / m ² ) on the film surface.
The amount of oligomer in DMF was determined from the peak area ratio between the standard sample peak area and the measured sample peak area (absolute calibration curve method).

  The standard sample was prepared by accurately weighing an oligomer (cyclic trimer) collected in advance and dissolving it in accurately measured DMF (dimethylformamide). The concentration of the standard sample is preferably in the range of 0.001 to 0.01 mg / ml.

The conditions of the liquid chromatograph were as follows.
Mobile phase A: Acetonitrile Mobile phase B: 2% acetic acid aqueous solution Column: MCI GEL ODS 1HU manufactured by Mitsubishi Chemical Corporation
Column temperature: 40 ° C
Flow rate: 1 ml / min Detection wavelength: 254 nm

(4) Maximum height (Rt) and centerline average roughness (Ra) (μm)
It calculated | required as follows using the Kosaka Laboratory Co., Ltd. surface roughness measuring machine (SE-3F). That is, a portion having a reference length L (2.5 mm) is extracted from the film cross-sectional curve in the direction of the center line, and the roughness curve y = where the center line of the extracted portion is the x axis and the direction of the vertical magnification is the y axis. When represented by f (x), the value given by the following formula was defined as the center line average roughness (Ra), and represented by [μm].

  The maximum height (Rt) is determined by setting the distance between the two straight lines in the direction of the vertical magnification of the cross-sectional curve when the extracted part is sandwiched by two straight lines parallel to the average line of the extracted part of the film cross-sectional curve obtained above. The measured value was taken as the maximum height (Rt) and expressed in [μm]. The maximum height and the center line average roughness were expressed as average values of the respective values of the extracted portions obtained from 10 cross-sectional curves obtained from the sample film surface. The tip radius of the stylus was 2 μm, the load was 30 mg, and the cutoff value was 0.08 mm.

(5) Density The film density was measured by helium specific gravity using a Micrometrics Accupyc 1330 (Micometrics Limited, Dunstable, UK).

(6) Quality of dichloromethane solution cast film A 20 wt% solution of polycarbonate was prepared using dichloromethane as a solvent. This solution is applied onto a support film, primarily dried at 70 ° C., and further dried at 100 ° C. until the amount of residual solvent in the cast film is 0.5% by weight or less, and wound together with the support film. It was. The obtained cast film had a thickness of 45 μm. The cast film was evaluated by peeling the support film. In addition, in order to obtain the product of a cast film, the protective film which has an adhesive layer may be bonded together, but in this invention, evaluation of the cast film was performed immediately after peeling a support body. The evaluation criteria were as follows.

・ Transparency of film Rank A: Obtained as a highly transparent film and high quality as an optical member Rank B: Transparent and usable as an optical member, but slightly inferior to A Rank C: Transparency It is inferior to that and cannot be used as an optical member.

・ Optical defects (observed visually under crossed Nicols using two polarizing plates)
Rank A: drawback 3 / ^{m 2} or less Rank B: disadvantages 20 / ^{m 2} or less Rank C: drawback exceed 20 / ^{m 2,} there is a practical problem

(7) Quality of aqueous cast film A 20% by weight aqueous solution of PVA was prepared. This solution is applied onto a support film, primarily dried at 90 ° C., and further dried at 110 ° C. until the amount of residual solvent in the cast film is 0.5% by weight or less, and wound together with the support film. It was. The obtained cast film had a thickness of 50 μm. The cast film was evaluated by peeling the support film. In addition, in order to obtain the product of a cast film, the protective film which has an adhesive layer may be bonded together, but in this invention, evaluation of the cast film was performed immediately after peeling a support body. The evaluation criteria were as follows.

・ Transparency of film Rank A: Obtained as a highly transparent film and high quality as an optical member Rank B: Transparent and usable as an optical member, but slightly inferior to A Rank C: Transparency It is inferior to the above, and cannot be used as an optical member. Optical defects (observed visually under crossed Nicols using two polarizing plates)
Rank A: drawback 3 / ^{m 2} or less Rank B: disadvantages 20 / ^{m 2} or less Rank C: drawback exceed 20 / ^{m 2,} there is a practical problem

The production method of the polyester used in the following examples and comparative examples is as follows.
<Manufacture of polyester>
[Method for producing polyester (A0)]
Using 100 parts by weight of dimethyl terephthalate and 60 parts by weight of ethylene glycol as starting materials, 0.09 parts by weight of magnesium acetate tetrahydrate as a catalyst is placed in the reactor, the reaction start temperature is set to 150 ° C., and the methanol is distilled off gradually. The reaction temperature was raised to 230 ° C. after 3 hours. After 4 hours, the transesterification reaction was substantially terminated. After adding 0.04 part of ethyl acid phosphate to this reaction mixture, 0.04 part of antimony trioxide was added, and a polycondensation reaction was carried out for 4 hours. That is, the temperature was gradually raised from 230 ° C. to 280 ° C. On the other hand, the pressure was gradually reduced from normal pressure, and finally 0.3 mmHg. After the start of the reaction, the reaction was stopped at a time corresponding to an intrinsic viscosity of 0.68 due to a change in stirring power of the reaction vessel, and the polymer was discharged under nitrogen pressure. The obtained polyester (A0) had an intrinsic viscosity of 0.63 and an oligomer content of 0.83% by weight.

[Method for producing polyester (A1)]
The polyester (A0) is pre-crystallized at 160 ° C. in advance and then solid-phase polymerized in a nitrogen atmosphere at a temperature of 220 ° C. to obtain a polyester (A1) having an intrinsic viscosity of 0.75 and an oligomer content of 0.28 wt%. It was.

[Production method of polyester (B)]
In the production method of polyester (A0), a transesterification reaction was performed in the same manner as above except that 1.5 parts of δ-alumina particles having a primary particle size of 0.02 μm which had been crushed, classified and filtered in advance were added as an ethylene glycol slurry. A polycondensation reaction was performed to obtain a polyester having an intrinsic viscosity of 0.62 and an oligomer content of 0.82% by weight.

[Production method of polyester (C)]
In the method for producing polyester (A0), 0.04 part of ethyl acid phosphate was added, 1.0 part of synthetic calcium carbonate particles having an average particle diameter of 0.4 μm dispersed in ethylene glycol, and 0.04 of antimony trioxide. A polyester (C) was obtained using the same method as the production method of polyester (A0) except that the polycondensation reaction was stopped at a time corresponding to the intrinsic viscosity of 0.66. The obtained polyester (B) had an intrinsic viscosity of 0.62 and an oligomer content of 0.83% by weight.

[Production method of polyester (D)]
In the method for producing polyester (C), polyester (D) was prepared using the same method as the method for producing polyester (C) except that the particles to be added had an average particle size of 0.7 μm and the addition amount was 2.0 parts. Obtained. The obtained polyester (D) had an intrinsic viscosity of 0.62 and an oligomer content of 0.84% by weight.

Example 1:
The above polyesters are blended as shown in Table 1 below, each supplied to two extruders, melted at 285 ° C., and then cooled onto 40 ° C., two kinds of two layers (A / B). A non-oriented sheet was obtained by coextrusion and cooling and solidification in a layer configuration. Next, the film was stretched 3.3 times in the machine direction at a film temperature of 81 ° C. using the roll peripheral speed difference, then led to a tenter, stretched 3.6 times in the transverse direction at 120 ° C., and heat treated under the conditions shown in Table 1. Then, the film was relaxed by 2% in the transverse direction to obtain a laminated polyester film having a thickness of 75 μm. As for the thickness of each layer of the obtained film, the A layer was 20 μm and the B layer was 55 μm. Moreover, it used so that it might become a contact surface of the shaping | molding film at the time of setting the surface of A layer side as a support body.

Examples 2-3:
A laminated polyester film having a total thickness of 38 μm was obtained in the same manner as in Example 1 except that the heat treatment conditions and the film thickness were changed as shown in Table 1 in Example 1. The thickness of each layer of the obtained film was 19 μm for the A layer and 19 μm for the B layer.

Comparative Example 1:
In Example 2, a polyester film having a thickness of 38 μm was obtained in the same manner as in Example 2 except that the A layer raw material and the heat treatment conditions were as shown in Table 2 below. In this case, since the surface roughness of the film was too large, the quality of the molded film obtained using this film as a support was inferior. That is, since the surface of the obtained molded film was roughened by shape transfer, the optical transparency was lowered and the quality as a member was inferior.

Comparative Example 2:
In Example 2, a polyester film having a thickness of 38 μm was obtained in the same manner as in Example 2 except that the heat treatment conditions were changed as shown in Table 2. In this case, since the film density is too low, when this film is used as a support, the film surface tends to be scraped easily during the process, and the scraped powder is transferred to a cast film and used as an optical film member. There was a problem that would be a disadvantage in doing so.

Comparative Example 3:
In Example 2, a polyester film having a thickness of 38 μm was obtained in the same manner as in Example 2 except that the layer A material and the heat treatment conditions were changed as shown in Table 2. In this case, when the film was used as a support, there was a tendency for oligomers to easily precipitate on the film surface during the process, and the quality of the resulting molded film was inferior. That is, since the surface of the obtained molded film was roughened by shape transfer, optical transparency was lowered, optical defects due to transfer were caused, and the quality as a member was inferior.

Comparative Example 4:
In Example 2, a polyester film having a thickness of 38 μm was obtained in the same manner as in Example 2 except that the heat treatment conditions were changed as shown in Table 2. In this case, since the film density was too high, breaking during film formation occurred frequently, and the productivity was remarkably reduced.

  The film of the present invention can be suitably used as a support for producing a plastic film by a method such as a casting method.

Claims (1)

A polyester film used as a support in the step of molding a plastic film, wherein the surface of one film is coated with methyl ethyl ketone, dried, and subjected to heat treatment at 180 ° C. for 10 minutes. m ² or less, Ra on the surface of the film is in the range of 5.0 to 10 nm, and the film density is in the range of 1.405 to 1.415 g / cm ^3. .