JP2008163264A - Supporter film for producing plastic film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an excellent supporter film for a production process, enabling a high-quality film to be efficiently produced in good productivity when the polyester film is used as a supporter at the production of an optical film or the like, providing the optical film having the flat surface, hardly having defects when used for optical applications, and providing clear image in a display use. <P>SOLUTION: The polyester film for the supporter, usable as the supporter in the process for forming a plastic film has 5.0-10 nm Ra value on one surface of the film, and 1.405-1.415 g/cm<SP>3</SP>density. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a support film used for plastic film production. Specifically, the present invention can efficiently produce a high-quality film with high productivity when using a polyester film as a support, particularly when producing an optical film, and the surface of the obtained optical film is The present invention relates to an excellent support film for a production process that is flat and 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 LCD displays, polarizing films, retardation films, viewing angle enhancement films, brightness enhancement films, diffusion films, reflection films, etc. In PDP displays, functions such as electromagnetic wave cut, near infrared ray cut, ultraviolet ray cut, color tone correction, etc. 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, it has been adopted as a method having a high degree of freedom in equipment design and utilization because it is excellent in transportability and flexibility and is relatively easy to replace the support. 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 them, 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 surface of the polyester film is usually used in order to improve handling properties, slipping properties, winding properties, and the like. If there are large or high protrusions on the 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 during production of the polyester film will deteriorate, the surface will be damaged during the production process, the shape will be transferred, and the quality of the resulting optical film will deteriorate. May be invited.

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. Moreover, when the polyester is damaged by the polymer solution used in the molding step, the quality may be deteriorated due to easy removal. With respect to a polyester film used as a film-forming support, it is strongly required that the above-mentioned coarse protrusion shape transfer and transfer of foreign matters such as scraped powder do not occur.
JP-A-9-304778 Japanese Patent Laid-Open No. 10-68822

  The present invention has been made in view of the above circumstances, and the problem to be solved is to efficiently produce a high-quality film with high productivity when using a polyester film as a support when producing an optical film or the like. Provided is an excellent support film for a manufacturing process that can obtain a clear image for a display without a defect when used in an optical application, and having a flat surface of the obtained optical film. There is.

  As a result of intensive studies in view of the above circumstances, the present inventor has found that the above problem can be easily solved by using a polyester film having a specific configuration, and has 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, wherein Ra on one film surface is in the range of 5.0 to 10 nm, and the density is 1.405 to 1. The present invention resides in a polyester film for a support characterized by having a range of 415 g / cm ³ .

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 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 film referred to in the present invention is a polyester film extruded by a so-called extrusion method in which the above-mentioned polyester is usually melt-extruded from an extrusion die, and if necessary, in the biaxial direction of the vertical direction and the horizontal direction. An oriented 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.

  Since the polyester film of the present invention improves the slipperiness of the surface and does not cause problems such as blocking and makes it easy to handle, 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 μm to 5 μm, preferably 0.02 μm to 3 μm, and more preferably 0.05 μm to 3 μm. When particles having an average particle size of less than 0.01 μm are used, protrusions having an effective height cannot be formed on the film surface, and the film is flattened and the winding characteristics in the film manufacturing process are inferior. This causes problems such as scratches on the film surface. Also, if the average particle size exceeds 5 μm, the degree of roughening of the film surface becomes too large and surface shape transfer occurs when used as a support in the step of forming a film. There may be a problem that the quality of the film is deteriorated and the surface of the film is easily scraped and transferred to an optical film.

  Moreover, in this invention, the method of adding 2 or more types as an above-mentioned particle | grain as a particle type, or adding 2 or more types as an average particle diameter can also be used. In the present invention, a film is formed by forming protrusions on the surface by such a method or imparting roughness to the surface by a method such as blending particles in a coating layer to be described later. The range is from 0.0 nm to 10 nm, preferably from 5.5 to 9.5 nm, and more preferably from 6.0 nm to 9.0 nm. Rt is in the range of 30 nm to 500 nm, preferably in the range of 30 nm to 300 nm, 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.

Moreover, the density of the polyester film of this invention needs to be the range of 1.405-1.415g / 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. It is preferable to perform ~ 6 times stretching and heat treatment at 150 to 240 ° C for 1 to 600 seconds. 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. To do. 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 formed only on one side, other characteristics can be imparted by forming a coating layer different from the above-mentioned coating layer on the opposite surface as necessary. 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. Further, 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.

  As described in detail above, since the film of the present invention has a specific surface shape, particularly when used as a support when a plastic film used for optical applications is produced by a method such as a casting method, The surface flatness and transparency of the obtained molded film are very highly satisfied, and its quality and use efficiency in the process are good, so that its industrial value is high.

  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) 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.
Ra = 1 / L∫ ₀ ^L | f (x) | dx

(3) Density Film density was measured by helium specific gravity using Micrometrics Accupyc 1330 (MIcrometrics Limited, Dunstable, UK).

(4) 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.

-Film transparency rank A: obtained as a highly transparent film and high quality as an optical member Rank B: transparent and usable as an optical member 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

(5) Quality of aqueous cast film A 20 wt% 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.

-Film transparency rank A: obtained as a highly transparent film and high quality as an optical member Rank B: transparent and usable as an optical member 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

The production method of the polyester used in the following examples and comparative examples is as follows.
<Manufacture of polyester>
[Method for producing ester (A)]
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 intrinsic viscosity of the obtained polyester (A) was 0.68.

[Production method of polyester (B)]
In the production method of polyester (A), 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 previously crushed, classified and filtered were added as an ethylene glycol slurry. A polycondensation reaction was performed to obtain a polyester having an intrinsic viscosity of 0.62.

[Production method of polyester (C)]
In the method for producing polyester (A), 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 the polyester (A) except that the polycondensation reaction was stopped at the time corresponding to the intrinsic viscosity of 0.66. The obtained polyester (B) had an intrinsic viscosity of 0.62.

[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.

Example 1:
The above polyesters are blended as shown in Table 1, and each is supplied to two extruders, melted at 285 ° C., and then cooled onto 40 ° C., two types of two layers (A / B). The composition was coextruded and cooled and solidified to obtain a non-oriented sheet. 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:
In Example 1, 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 as shown in Table 1 below. 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 1. 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 A layer raw material and the heat treatment conditions were as shown in Table 1. 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.

  Table 1 summarizes the evaluation results of the films obtained in each Example and Comparative Example. The films shown in the examples were obtained as high quality films.

  The film of the present invention can be suitably used, for example, as a support film for a plastic film production process.

Claims (1)

A polyester film used as a support in the step of molding a plastic film, wherein Ra on one film surface is in the range of 5.0 to 10 nm, and the density is in the range of 1.405 to 1.415 g / cm ³ . A polyester film for a support, which is characterized by the following.