WO2012173033A1

WO2012173033A1 - Mold releasing polyester film

Info

Publication number: WO2012173033A1
Application number: PCT/JP2012/064650
Authority: WO
Inventors: 齋藤智久; 加藤優佳
Original assignee: 三菱樹脂株式会社
Priority date: 2011-06-13
Filing date: 2012-06-07
Publication date: 2012-12-20
Also published as: KR20140027103A; CN103502007A

Abstract

Provided is a polyester film that, with respect to a member such as a polarizing plate to which a mold releasing film is bonded, has an excellent sense of clarity, has excellent inspectability in a case where visual inspection is conducted for defects such as distortion or irregularities or the presence or absence of foreign matter using a crossed Nicol method, and has excellent productivity. A mold releasing film comprises a co-extruded biaxially oriented polyester film having three or more layers, wherein the surface layer on at least one side contains crosslinked styrene-divinylbenzene copolymer particles and the outermost layer on at least one surface has a silicone-based mold releasing layer.

Description

Release polyester film

The present invention relates to a release polyester film advantageous for optical inspection for optical applications.

Polyester films represented by polyethylene terephthalate and polyethylene naphthalate have excellent mechanical strength, dimensional stability, flatness, heat resistance, chemical resistance, optical properties, etc. It is used in applications. However, as the application diversifies, the processing conditions and usage conditions of the polyester film diversify. When used as a release polyester film for polarizing plates, the particle component in the release film is a bright spot when inspecting foreign matter. Thus, problems such as a decrease in inspection accuracy occur.

In recent years, with the rapid spread of mobile phones and personal computers, the demand for liquid crystal displays (LCDs) that are thinner, lighter, consume less power, and have higher image quality than the conventional display CRT is growing significantly. There is also a remarkable growth in the technology for increasing the screen size of LCDs. As an example of increasing the screen size of LCD, recently, LCD is used for large TV applications of 30 inches or more. An LCD with a large screen is often a bright LCD with a large screen by increasing the luminance of a backlight incorporated in the LCD or incorporating a film for improving the luminance into a liquid crystal unit.

In such a so-called high-brightness type LCD, a small bright spot existing in the display is often a problem, and in a component such as a polarizing plate, a retardation plate or a retardation polarizing plate incorporated in the display, As a result, there is a problem of a foreign material having a minute size that has not been a problem in conventional low-brightness LCDs. For this reason, while preventing the entry of foreign matter in the manufacturing process, it is also important to improve the inspection accuracy so that even if foreign matter is mixed, it can be recognized as a defect.

Conventionally, the particles in the polyester film are usually used to ensure the slipperiness and winding characteristics of the film, and if the appropriate particle size and blending amount are not satisfied, the desired slipperiness cannot be ensured. As a result, the winding characteristics deteriorate, and as a result, the productivity deteriorates. However, when the particle size and blending amount are within the normally used range, as described above, when used as a release film for polarizing plates, the particles become bright spots in the foreign substance inspection process, which hinders inspection. Is a problem.

For example, as a defect inspection of a polarizing plate, a visual inspection by a crossed Nicols method is generally used. Further, for example, for a polarizing plate used for a large TV application of 40 inches or more, an inspection by an automatic particle inspection device using the crossed Nicols method is used. Is also being implemented. According to this crossed Nicol method, two polarizing plates are put in a quenching state with their orientation principal axes orthogonal to each other, and if there are foreign matters or defects, they appear as bright spots, so a visual defect inspection or a line sensor camera, etc. Automatic defect inspection can be performed. Here, the pressure-sensitive adhesive layer is usually provided on the polarizing plate, and a polyester film provided with a release layer is used as the release film for that purpose. When a product having such a configuration is inspected, a crossed Nicols inspection is performed in a state where a release polyester film is sandwiched between two polarizing plates. In general, when a release polyester film is used for this, foreign matter and defects are difficult to see in the crossed Nicols inspection, and it may be easy to miss them.

Regarding these, when a polyester film is sandwiched between two polarizing plates, an inspection property is improved when the retardation value is within a certain range (see Patent Document 1). Even if these are used at a level where quality is required, accuracy may be insufficient when inspection is performed to find defects reliably.

Also, when inspecting defects such as distortion and unevenness of the polarizing plate, a visual reflection inspection under a fluorescent lamp may be performed. In this case, in order to inspect the polarizing plate provided thereunder through the release film, if the release film is extremely white, defects of the polarizing plate are difficult to see and it is easy to miss them. May occur. In this regard, in the release film to be used, the internal haze alone may leave a grainy feeling (see Patent Document 2), but the transparency of the film including the internal haze is important.

Furthermore, as one of the causes of the generation of foreign matters in the manufacturing process described above, an oligomer contained in the polyester film (hereinafter sometimes abbreviated as OL) is considered. OL, which is considered to be a low molecular weight sublimate of polyester, is deposited on the surface of the film within the production process and adheres to a roll or the like that comes into contact with the film to become a foreign matter. Moreover, in order to reduce a foreign material, although the operation | work which removes the oligomer adhering to a roll is performed, the problem that production efficiency worsens is also mentioned.

JP 2000-338327 A JP 2009-214360 A

The present invention has been made in view of the above circumstances, and a problem to be solved is to provide a release polyester film capable of realizing a high degree of accuracy in an optical inspection of a polarizing plate by a crossed Nicol method.

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

That is, the gist of the present invention consists of three or more layers of coextruded biaxially stretched polyester film, at least one surface layer contains styrene / divinylbenzene copolymer crosslinked particles, and at least one outermost layer has a silicone-based release layer. It exists in the release film characterized by having a type | mold layer.

According to the present invention, when a member such as a polarizing plate in a state in which a release film is bonded is excellent in clearness, and when inspection of defects such as distortion and unevenness and the presence of foreign matter is performed by visual inspection by the crossed Nicols method The industrial value of the present invention is excellent because it can provide a polyester film with excellent inspectability, excellent process contamination in the release film and excellent foreign matter mitigation ability to the pressure-sensitive adhesive, and excellent productivity. high.

The polyester film referred to in the present invention is a film that has been subjected to stretching, coating, and heat treatment as needed after cooling a molten polyester sheet extruded by a so-called extrusion method that is melt-extruded from an extrusion die. A film having a release layer applied thereto.

The polyester constituting the film of the present invention is obtained by polycondensation of an aromatic dicarboxylic acid and an aliphatic glycol. Examples of the aromatic dicarboxylic acid include terephthalic acid and 2,6-naphthalenedicarboxylic acid, and examples of the aliphatic glycol include ethylene glycol, diethylene glycol, and 1,4-cyclohexanedimethanol. Representative polyesters include polyethylene terephthalate (PET), polyethylene-2,6-naphthalenedicarboxylate (PEN), and the like. The polyester used may be a homopolyester or a copolyester. In the case of a copolyester, it may be a copolymer containing 30 mol% or less of the third component.
Examples of the dicarboxylic acid component of such a copolyester include isophthalic acid, phthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, and oxycarboxylic acid (eg, P-oxybenzoic acid). 1 type or 2 types or more chosen from are mentioned. One glycol component may be one or more selected from ethylene glycol, diethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, neopentyl glycol, and the like.

In the polyester obtained by the present invention, a weathering agent, a light-proofing agent, an antistatic agent, a lubricant, a light-shielding agent, an antioxidant, a fluorescent whitening agent, a matting agent, and a heat-stabilizing agent as long as the gist of the invention is not impaired You may mix | blend an agent and coloring agents, such as dye and a pigment.

Examples of the particles to be incorporated into the film include inorganic particles such as silicon dioxide, aluminum oxide, calcium carbonate, kaolin, and titanium oxide, and organic particles such as acrylic resin, melamine resin, polyethylene, and organic silicone, but transparency is required. For use, styrene-based organic particles having high affinity with polyester are preferable.

The average particle size of the particles blended in the highly transparent polyester film is 5.0 μm or less, preferably 4.0 μm or less, and more preferably 0.5 μm to 1.4 μm. When particles having an average particle size of less than 0.5 μm are used, sufficient slipperiness cannot be imparted, so that the winding characteristics in the film production process tend to be inferior. On the other hand, when the average particle diameter exceeds 5.0 μm, void formation due to stretching increases, and the graininess increases and transparency may be impaired.
In addition, the average particle diameter in the present invention means a particle diameter (d50) having an integrated volume fraction of 50% in an equivalent spherical distribution as described later.

In the present invention, styrene / divinylbenzene copolymer particles are added to at least one of the front and back layers of a laminated film of three or more layers. Of course, particles can be blended in both the front and back layers. The blending amount of the particles in the case of such a laminated film is preferably less than 20% by weight, more preferably 5 to 8% by weight with respect to the polyester constituting the surface layer. However, when the content of particles is extremely small, the transparency becomes high, but the film surface cannot be made into an appropriate rough surface, and scratches are easily generated in the film production process, and the winding property is inferior. Tend. Further, when the content of the particles is extremely large, the degree of roughening of the film surface becomes too large and the transparency is impaired.

In addition, a sharp particle size distribution is preferably used. Specifically, those having a particle size distribution value of 1.0 to 2.0, which is an index representing the sharpness of the particle size distribution, are preferable. Here, the particle size distribution value is the particle size distribution value d25 / d75 (d25 and d75 are calculated by calculating the accumulated accumulation of the particle group from the large particle side, and the particle size (μm corresponding to 25% and 75% of the total volume, respectively) Is a value defined by When the particle size distribution value exceeds 2.0, transparency may be insufficient.

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 for 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 the transesterification reaction. The condensation 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 method of blending dried particles and a polyester raw material using a kneading extruder Etc.

The polyester may be chipped after melt polymerization, and further subjected to solid phase polymerization as necessary under heating under reduced pressure or in an inert gas stream such as nitrogen. The intrinsic viscosity of the obtained polyester is preferably 0.40 dL / g or more, more preferably 0.40 to 0.90 dL / g.

The total thickness of the film of the present invention is not particularly limited as long as it can be formed as a film, but is usually 4 to 300 μm, preferably 25 to 188 μm.

Next, the method for producing the film of the present invention will be specifically described, but it is not particularly limited to the following examples as long as the gist of the present invention is satisfied.

First, a preferred example of a method for producing a polyester used in the present invention will be described. Here, an example in which polyethylene terephthalate is used as the polyester is shown, but the production conditions differ depending on the polyester used. According to a conventional method, esterification from terephthalic acid and ethylene glycol, or transesterification reaction between dimethyl terephthalate and ethylene glycol, the product is transferred to a polymerization tank, the temperature is increased while reducing pressure, and finally vacuum is applied. Under heating to 280 ° C., the polymerization reaction proceeds to obtain polyethylene terephthalate.

Next, for example, the polyester chip obtained as described above and dried by a known method is supplied to a melt-extrusion apparatus and heated to a temperature equal to or higher than the melting point of each polymer and melted. Next, the molten polymer is extruded from the die, and rapidly cooled and solidified on the rotary cooling drum so as to have a temperature 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 in the machine direction at 70 to 145 ° C. to form a uniaxially stretched film, and then 2 to 90 to 160 ° C. in the transverse direction. The film is preferably stretched up to 6 times and heat-treated at 150-240 ° C. for 1-600 seconds. Further, at this time, it is preferable to relax by 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. Further, it is possible to add re-longitudinal stretching and re-lateral stretching as necessary. Further, it is possible to simultaneously biaxially stretch the unstretched sheet so that the area magnification is 10 to 40 times.

The method for forming the coating layer on the surface of the polyester film is not particularly limited, but a method of coating the coating solution in the process of producing the polyester film is suitably employed. Specifically, a method of applying and drying a coating solution on the surface of an unstretched sheet, a method of applying and drying a coating solution on the surface of a uniaxially stretched film, and a method of applying and drying a coating solution on the surface of a biaxially stretched film Etc. Among these, it is economical to apply a coating solution on the surface of an unstretched film or a uniaxially stretched film, and then simultaneously dry and cure the coating layer in the process of heat-treating the film. Moreover, as a method for forming the coating layer, a method in which some of the above-described coating methods are used in combination can be adopted as necessary. Specifically, a method of applying a first layer on the surface of an unstretched sheet and drying, then stretching in a uniaxial direction, and then applying and drying a second layer can be used. Use the reverse roll coater, gravure coater, rod coater, air doctor coater, etc. shown in “Coating Method” by Yuji Harasaki, Tsuji Shoten, published in 1979, as a method of applying the coating solution to the surface of the polyester film. Can do.

The coating solution used in the present invention is usually preferably adjusted with water as the main medium from the viewpoint of safety and hygiene. As long as water is the main medium, a small amount of an organic solvent may be contained for the purpose of improving the dispersion in water or improving the film forming performance. The organic solvent is preferably used as long as it is dissolved in water when mixed with water, which is the main medium. However, if it is a stable emulsion (emulsion) that does not separate after standing for a long time, Alternatively, it may be used in a state where it does not dissolve in water. The organic solvent may be used alone or in combination of two or more as necessary.

In the present invention, it is usual to use a binder polymer for the coating layer, and the binder polymer is a gel permeation according to a polymer compound safety evaluation flow scheme (November 1985, sponsored by the Chemical Substances Council). It is defined as a high molecular compound having a number average molecular weight (Mn) of 1000 or more as measured by ablation chromatography (GPC) and having film-forming properties.

The component in the coating layer can be analyzed by surface analysis such as TOF-SIMS.

When providing a coating layer by in-line coating, apply the above-mentioned series of compounds as an aqueous solution or water dispersion on a polyester film with a coating solution adjusted to a solid content concentration of about 0.1 to 50% by weight. It is preferable to produce a laminated polyester film. Moreover, in the range which does not impair the main point of this invention, a small amount of organic solvents may be contained in the coating liquid for the purpose of improving dispersibility in water, improving film-forming properties, and the like. Only one type of organic solvent may be used, or two or more types may be used as appropriate.

In the present invention, the deposition of the oligomer can be prevented by providing a coating layer on the film surface by coating, and the layer usually contains 10 to 100% by weight of polyvinyl alcohol, preferably 20 to 90% by weight, more preferably 30%. Contains 90% by weight. When the content of polyvinyl alcohol is less than 10% by weight, the oligomer sealing effect tends to be insufficient.

The polyvinyl alcohol used in the present invention can be synthesized by a normal polymerization reaction and is preferably water-soluble. The degree of polymerization of polyvinyl alcohol is not particularly limited, but is usually 100 or more, preferably 300 to 40,000. When the degree of polymerization is 100 or less, the water resistance of the coating layer tends to decrease. The degree of saponification of the polyvinyl alcohol used in the present invention is not particularly limited, but a polyvinyl acetate saponified product that is usually 70 mol% or more, preferably 80 mol% or more and 99.9 mol% or less is practically used. It is done.

In the coating layer of the film of the present invention, a water-soluble or water-dispersible binder resin other than the above polyvinyl alcohol may be used in combination as necessary. Examples of the binder resin include polyester, polyurethane, acrylic resin, vinyl resin, epoxy resin, amide resin, acrylate resin, and the like. In these, each skeleton structure may have a composite structure substantially by copolymerization or the like. Examples of the binder resin having a composite structure include acrylic resin graft polyester, acrylic resin graft polyurethane, vinyl resin graft polyester, vinyl resin graft polyurethane, and acrylate resin graft polyethylene glycol. The blending amount of the binder component is preferably 50 parts by weight or less, and more preferably 30 parts by weight or less, by weight with respect to the coating layer. Furthermore, the coating layer of the film of the present invention may contain a crosslinking reactive compound as required.

Cross-linking reactive compounds include methylolated or alkylolized urea-based, melamine-based, guanamine-based, acrylamide-based, polyamide-based compounds, polyamines, epoxy compounds, oxazoline compounds, aziridine compounds, blocked isocyanate compounds, silane cups Polyfunctional low molecular compounds such as ring agents, titanium coupling agents, zirco-aluminate coupling agents, metal chelates, organic acid anhydrides, organic peroxides, thermally or photoreactive vinyl compounds and photosensitive resins, and It is selected from polymer compounds.

Crosslinkable compounds improve the cohesiveness, surface hardness, scratch resistance, solvent resistance, and water resistance of the easy-adhesive resin layer mainly by cross-linking reaction with the functional groups of the resin contained in the easy-adhesive resin layer. can do. For example, when the functional group of the easily adhesive resin is a hydroxyl group, the crosslinking reactive compound is preferably a melamine compound, a blocked isocyanate compound, an organic acid anhydride, or the like, and the functional group of the easily adhesive polyester is an organic acid or an anhydride thereof. In this case, epoxy-based compounds, melamine-based compounds, oxazoline-based compounds, metal chelates and the like are preferable as the cross-linking reactive compound. When the functional group of the easy-adhesion resin is an amine, an epoxy-based compound is preferable as the cross-linking reactive compound. It is preferable to select and use a functional group contained in the easily adhesive resin and one having a high crosslinking reaction efficiency. Examples of the melamine compound in the present invention include methoxymethylated melamine and butoxymethylated melamine which are alkylol or alkoxyalkylolated melamine compounds, and those obtained by co-condensing urea or the like with a part of melamine can also be used. .

The cross-linking reactive compound may be either a low molecular weight compound or a high molecular polymer having a reactive functional group as long as the reactive functional group is always contained in two or more functional groups in one molecule. The compounding amount of the crosslinking reactive compound is preferably 50 parts by weight or less, more preferably 30 parts by weight or less, and particularly preferably 15 parts by weight or less in terms of parts by weight with respect to the easily adhesive resin layer.
Furthermore, the easily adhesive resin layer of the present invention may contain inert particles for improving the slipperiness of the coating layer, if necessary.

Examples of the inert particles include inorganic inert particles and organic inert particles. Examples of the inorganic inert particles include silica sol, alumina sol, calcium carbonate, and titanium oxide.
Examples of the organic inert particles include fine particles containing a single or copolymer of polystyrene resin, polyacrylic resin, and polyvinyl resin, or organic particles represented by crosslinked particles in which these and a crosslinking component are combined. These inert particles preferably have a softening temperature or decomposition temperature of about 200 ° C. or higher, more preferably 250 ° C. or higher, particularly 300 ° C. or higher. The average particle diameter (d) of the inert particles is 1/3 ≦ d / L ≦ 3, and further 1/2 ≦ d / L ≦ 2, when the average film thickness of the easily adhesive resin layer is (L). It is preferable to select so as to satisfy the relationship.

The coating layer of the film of the present invention comprises a surfactant, an antifoaming agent, a coating property improving agent, a thickener, a low molecular antistatic agent, an organic lubricant, an antioxidant, an ultraviolet absorber, and foaming as necessary. A small amount of additives such as additives, dyes and pigments may be contained. These additives may be used alone or in combination of two or more as necessary. The coating layer of the film of the present invention may be formed only on one side of the polyester film or on both sides. In the case of forming only on one side, another type of coating layer can be formed on the opposite side as required, and further properties can be imparted. In addition, in order to improve the applicability | paintability and adhesiveness to the film of a coating liquid, you may give a chemical process, an electrical discharge process, etc. to the film before application | coating.

Regarding the polyester film in the present invention, the thickness of the coating layer provided on the polyester film is usually 0.002 to 1.0 g / m ² , more preferably 0.005 to 0.5 g / m ² , and still more preferably 0. The range is from 0.01 to 0.2 g / m ² . If the film thickness is less than 0.002 g / m ^2, sufficient adhesion may not be obtained, and if it exceeds 1.0 g / m ² , the appearance, transparency, and film blocking properties may be deteriorated. There is sex.

In addition, regardless of off-line coating or in-line coating, heat treatment and active energy ray irradiation such as ultraviolet irradiation may be used in combination as necessary. The polyester film constituting the laminated polyester film in the present invention may be subjected to surface treatment such as corona treatment or plasma treatment in advance.

The coated layer of the polyester film of the present invention is preferably formed by blending a binder resin and a crosslinking agent in an arbitrary ratio. In this case, since the layer forms a barrier layer densely, it can suppress OL. it can. For this reason, there is an effect that OL from the polyester film is not attached to the adhesive as much as possible and is not produced in the previous processing step. Therefore, both sides of the OL sealing layer of the polyester film of the present invention are preferable, and it is necessary to apply at least one side according to the application.

The release layer provided in the form of a coating layer in the present invention is not particularly limited as long as it contains a material having releasability. Among them, the one containing a curable silicone resin is preferable because the releasability is improved. A type having a curable silicone resin as a main component may be used, or a modified silicone type by graft polymerization with an organic resin such as a urethane resin, an epoxy resin, or an alkyd resin may be used.

As the type of the curable silicone resin, any of the curing reaction types such as an addition type, a condensation type, an ultraviolet curable type, an electron beam curable type, and a solventless type can be used.

Specific examples of the curable silicone resin include KS-774, KS-775, KS-778, KS-779H, KS-847H, KS-856, X-62-2422, X-manufactured by Shin-Etsu Chemical Co., Ltd. 62-2461, DKQ3-202, DKQ3-203, DKQ3-204, DKQ3-205, DKQ3-210, manufactured by Dow Corning Asia Co., Ltd. YSR-3022, TPR-6700, TPR-6720 manufactured by Toshiba Silicone Co., Ltd. , TPR-6721, SD7220, SD7226, SD7229 manufactured by Toray Dow Corning Co., Ltd., and the like. Further, a release control agent may be used in combination to adjust the release property of the release layer. Further, as described above, a silane compound having an amino group may be added to the release layer.

In the present invention, as a method for providing a release layer on the polyester film, a conventionally known coating method such as reverse roll coating, gravure coating, bar coating, doctor blade coating, or the like can be used. The coating amount of the release layer in the present invention is usually in the range of 0.01 to 1 g / m ² .

In the present invention, a coating layer such as an adhesive layer, an antistatic layer and an oligomer precipitation preventing layer may be provided on the surface where the release layer is not provided, and the polyester film may be subjected to corona treatment, plasma treatment, etc. A surface treatment may be applied.

Also, drying and / or curing (thermal curing, ionizing radiation curing, etc.) of the adhesive layer or release layer coating can be performed individually or simultaneously. When performing simultaneously, it is preferable to carry out at the temperature of 80 degreeC or more. The drying and curing conditions are preferably 80 ° C. or higher and 10 seconds or longer. If the drying temperature is less than 80 ° C. or the curing time is less than 10 seconds, the coating film is incompletely cured and the coating film tends to fall off.

In order to make the coated layer of the polyester film of the present invention clean and strong, it is preferable to use a transition metal catalyst. The content of the transition metal catalyst in the coating layer is usually in the range of 0.5 to 5.0% by weight, preferably 1.5 to 4.0% by weight. When the content of the transition metal catalyst in the coating layer is lower than 0.5% by weight, there may be a problem such as deterioration of the surface condition due to insufficient peeling force or insufficient curing reaction in the coating layer. On the other hand, if the content of the transition metal catalyst in the coating layer exceeds 5.0% by weight, the cost is increased, the reactivity is increased, and process defects such as generation of gel foreign matter are caused. It may end up.

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 a polyester having a normal oligomer content. In the polyester film for release film obtained by the invention, the effect of preventing bright spots due to the precipitated oligomer is obtained, which is particularly preferable.

In the present invention, the transparency of the film in the measurement method described later needs to be 83.5% or more, preferably 84% or more. When the transparency of the film is less than 83.5%, the transparency of the film is lowered. In order to set the transparency of the film within the above range, for example, the type of particles to be used, the particle size, the amount added, the strengthening of the filter in the production line, the film production conditions (film stretching temperature, draw ratio), and the film production line are used. This can be achieved by appropriately combining various conditions such as smoothing of the roll.

Further, the surface roughness (Ra) of the release layer is 9.0 nm or more, and preferably 12 nm or more. When Ra of the film is less than 9.0 nm, the film surface becomes extremely flat, and the winding characteristics in the film manufacturing process are inferior. Moreover, when Ra of the film exceeds 22 nm, the planarity of the surface may be impaired, and the film may become whitish. Therefore, the upper limit of Ra is preferably 22 nm.

The above-mentioned means for satisfying the transparency and roughness ranges of the polyester film is to optimally adjust the blending amount using appropriate organic particles having an arbitrary particle size distribution range.

In the release polyester film of the present invention, the optimization of the MOR_C value obtained by measuring the release film with a microwave molecular orientation meter is very important in order to reduce the occurrence of foreign matter and light interference colors in the optical inspection of the process. It is.

The MOR_C value of the release film of the present invention is 1.5 to 3.0, preferably 1.8 to 2.7, more preferably 2.1 to 2.4. When the MOR_C value is larger than 3.0, the release layer is not uniform, and in optical inspection, the light interference color is easily visible. When the MOR_C value is smaller than 1.5, there is a problem that the production yield of the release film itself is deteriorated.

The means for satisfying the range of the MOR_C value of the release film of the present invention is to ingenuate the stretching conditions for the desired film thickness during film formation.

In the present invention, OL (oligomer) is defined as a cyclic trimer among low molecular weight substances that crystallize and precipitate on the film surface after heat treatment.

After heat-treating the polyester film of the present invention (180 ° C., 10 minutes), the amount of OL extracted from the coating layer surface with dimethylformamide is preferably 3.0 mg / m ² or less, more preferably 1.0 mg. / M ² or less. When OL exceeds 3.0 mg / m ² , there is a process contamination, and when the pressure-sensitive adhesive is bonded, a foreign matter may be generated and a product yield may be deteriorated.

The means for satisfying the OL sealing effect of the release film of the present invention is to devise and select a material that densely forms the in-line coating thin film, and to select the thickness of the coating layer to increase the productivity. The idea is to make it thick enough not to damage it.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples unless it exceeds the gist. The measurement method and evaluation method used in the present invention are as follows.

(1) Measurement of intrinsic viscosity of polyester:
1 g of polyester from which other polymer components and pigments incompatible with polyester were removed 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.

(2) Measurement of average particle diameter (d50: μm):
The value of 50% of integration (weight basis) in the equivalent spherical distribution measured using a centrifugal sedimentation type particle size distribution measuring apparatus (SA-CP3 type manufactured by Shimadzu Corporation) was defined as the average particle diameter.

(3) Transmittance measurement of polyester film:
According to JIS K7105, the total light transmittance of the polyester film was measured with an integrating sphere turbidimeter NDH-300A manufactured by Nippon Denshoku Industries Co., Ltd. Judgment is based on the following criteria.

(4) Heat shrinkage measurement of polyester film:
The polyester film is sampled at an arbitrary length L (cm) in the longitudinal direction (hereinafter abbreviated as MD) and the lateral width direction (hereinafter abbreviated as TD). Subsequently, the sample is heated in an oven at 160 ° C. for 5 minutes, and the sample is taken out of the oven and the length l (cm) is measured. This operation is performed three times, and the average value is adopted as the value of the heat shrinkage rate. The heat shrinkage rate can be calculated by the following formula.
Heat shrinkage rate (%) = {(L−l) / L} × 100

(5) Evaluation of release force (F) of release film:
After affixing one side of a double-sided adhesive tape (“Nitto Denko“ No. 502 ”) to the surface of the release layer of the sample film, the sample film was cut to a size of 50 mm × 300 mm, and then peeled after leaving at room temperature for 1 hour. taking measurement. For the peeling force, a tensile tester (“Intesco model 2001 type” manufactured by Intesco Co., Ltd.) was used, and 180 ° peeling was performed under the condition of a tensile speed of 300 mm / min.

(6) Measurement of OL extracted from the surface of the anchor (in-line coating) layer:
In advance, an unheat-treated release film is heated in air at 180 ° C. for 10 minutes. After that, the heat-treated film is brought into close contact with the inner surface of a box having a top and width of 10 cm and a height of 3 cm, and the box shape is obtained. When the coating layer is provided, the coating layer surface is set to the inside. Next, 4 ml of DMF (dimethylformamide) is placed in the box prepared by the above method and left for 3 minutes, and then DMF is recovered. The recovered DMF was supplied to a liquid chromatography (manufactured by Shimadzu Corporation: LC-7A) to determine the amount of OL in DMF, and this value was divided by the film area in contact with DMF to obtain the amount of OL on the film surface (mg / M ² ).

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 OL (cyclic trimer) collected in advance and dissolving it in DMF accurately weighed. The concentration of the standard sample is preferably in the range of 0.001 to 0.01 mg / ml. The conditions for 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

(7) Measurement of film transparency of polyester film:
The film transparency was measured using a transparency measuring instrument (TM-1D two decimal places: light source wavelength 546 ± 5 nm) manufactured by Murakami Color Research Laboratory.

(8) Measurement of internal haze of polyester film The internal haze was measured according to JIS K7136 using a haze meter (HZ-2) manufactured by Suga Test Instruments.

(9) Measurement of two-dimensional surface roughness (Ra) of polyester film:
Ra was measured according to JIS B0601-1994 using a surface roughness measuring machine (SE3500 type) manufactured by Kosaka Laboratory. The measurement length was 2.5 mm.

(10) Observing clear feeling of polyester film under a three-wavelength fluorescent lamp:
Three-wavelength fluorescent lamp light was transmitted through the film, and the clearness of the film was visually observed. The clearness (transparency, clarity, graininess, etc.) of the film was evaluated according to the following criteria.
<Criteria for observation of particle feeling under a three-wavelength fluorescent lamp>
(Clear feeling high) A>B> C (Clear feeling low)
Of the above criteria, those above B are levels that can be used without any problem in actual use.

(11) Evaluation of scratch resistance of polyester film:
The number of scratches on the film surface was counted, and the scratch resistance was evaluated in three stages. Evaluation was performed with an A4 size film.
<Criteria for scratch resistance>
(It is hard to be scratched) A>B> C (It is easy to be scratched)
In the above criteria, only A is a level that can be used without any problem in actual use.

(12) MOR_C value measurement of polyester film by microwave molecular orientation meter:
The MOR_C value was determined from the transmission microwave intensity pattern using a microwave molecular orientation meter manufactured by Oji Scientific Instruments. Judgment is based on the following criteria.
A: 2.0 to 2.5
B: 1.5 to 1.9, or 2.6 to 3.0
C: lower than 1.5% or higher than 3.0

(13) Practical characteristics:
<Visual inspection in deflection plate inspection>
Taking the polarizing plate inspection into consideration, a widthwise direction of the release film obtained by applying a release agent on the film and obtaining a dryer temperature of 120 ° C. and a line speed of 30 m / min is parallel to the alignment axis of the polarizing film. As described above, the release film was closely adhered to the polarizing film through an adhesive to form a polarizing plate. The polarizing plate was visually observed under reflection of a fluorescent lamp, and the visual inspection property under reflected light was evaluated according to the following criteria. In the measurement, an A4 size sample was cut out.
"Criteria"
A: Good testability B: Can be inspected almost without problems C: Poor testability A and B are at a level where there is no problem in actual use.

<Foreign substance recognition inspection in deflection plate inspection>
Taking the polarizing plate inspection into consideration, a widthwise direction of the release film obtained by applying a release agent on the film and obtaining a dryer temperature of 120 ° C. and a line speed of 30 m / min is parallel to the alignment axis of the polarizing film. As described above, the release film was adhered to the polarizing film through the pressure-sensitive adhesive to obtain a polarizing plate. Here, when the polarizing plate was prepared, black metal powder (foreign matter) having a size of 50 μm or more was mixed between the pressure-sensitive adhesive and the polarizing film so as to be 50 / m ² . A polarizing plate for inspection is superimposed on the polarizing plate release film mixed with the foreign matter thus obtained so that the orientation axis is orthogonal to the width direction of the release film, and white light is irradiated from the polarizing plate side. Then, it was visually observed from a polarizing plate for inspection, and whether or not a foreign matter mixed between the adhesive and the polarizing film was found under crossed Nicols was evaluated according to the following criteria. In the measurement, A4 size samples were cut out from a total of three locations in the center and both ends in the width direction of the obtained film.
"Criteria"
A: Good recognition of foreign matter B: Foreign matter can be recognized with relatively no problem.
C: Impairment of foreign matter recognition A and B are at a level where there is no problem in actual use.

<Release properties>
The release characteristics were evaluated from the situation when the release film was peeled off from the laminated film having the adhesive layer.
A: The release film is peeled off cleanly, and the phenomenon that the adhesive adheres to the release layer is not observed.
B: The release film peels off, but the adhesive adheres to the release layer when peeled off at a high speed.
C: Adhesive adheres to the release film.

(14) Overall evaluation:
An evaluation is performed in consideration of film forming properties, productivity, inspection characteristics, etc. Judgment is based on the following criteria.
A: Even if it is produced, it can be sufficiently supplied as a product.
B: Productivity is good and the frequency of defects in optical inspection is low.
C: Productivity is poor and defects in optical inspection frequently occur.

The polyester used in the examples and comparative examples was prepared as follows.
(Production of polyester (A))
Starting from 100% by weight of dimethyl terephthalate and 60% by weight of ethylene glycol, magnesium acetate tetrahydrate is added as a catalyst to the reactor, the reaction start temperature is 150 ° C., and the reaction temperature is gradually increased as methanol is distilled off. The temperature was raised to 230 ° C. after 3 hours.
After 4 hours, the transesterification reaction was substantially terminated. Ethyl acid phosphate was added to the reaction mixture, which was then transferred to a polycondensation tank, and 0.04 part of antimony trioxide was added to carry out a polycondensation reaction 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 0.64 dL / g due to a change in the stirring power of the reaction vessel, and the polymer was discharged under nitrogen pressure to obtain a polyester chip (A). The intrinsic viscosity of this polyester was 0.64 dL / g.

(Manufacture of polyester (B))
Starting from 100 parts by weight of dimethyl terephthalate and 60 parts by weight of ethylene glycol, magnesium acetate tetrahydrate is added as a catalyst to the reactor, the reaction start temperature is 150 ° C., and the reaction temperature is gradually increased as methanol is distilled off. The temperature was raised to 230 ° C. after 3 hours.
After 4 hours, the transesterification reaction was substantially terminated. Ethyl acid phosphate was added to the reaction mixture, which was then transferred to a polycondensation tank, and 0.04 part of antimony trioxide was added to carry out a polycondensation reaction 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 0.45 due to a change in stirring power of the reaction vessel, and the polymer was discharged under nitrogen pressure to obtain a polyester chip (B). The intrinsic viscosity of this polyester was 0.45.

(Manufacture of polyester (C))
The intrinsic viscosity of this polyester chip was increased by a solid phase polycondensation method. After treatment in a preliminary crystallization tank at 170 ° C. in a nitrogen atmosphere for 0.5 hours, the moisture content becomes 0.005% at a temperature of 200 ° C. using a tower dryer that flows an inert gas. Until dried. Thereafter, it was sent to a solid phase polymerization tank and subjected to solid phase polymerization at 240 ° C. for 3 hours to obtain a polyester (C) having an intrinsic viscosity of 0.70.

(Production of polyester (D))
When producing the polyester (C), solid phase polymerization was performed in a solid phase polymerization tank for 5 hours to obtain a polyester (D) having an intrinsic viscosity of 0.80.

(Manufacture of polyester (E))
In the production method of polyester (A), after adding ethyl acid phosphate, the content of ethylene glycol slurry of styrene-divinylbenzene copolymer crosslinked particles having an average particle diameter of 1.4 μm is 0.5% by weight with respect to polyester. A polyester (E) was obtained using the same method as the production method of the polyester (A) except that it was added. The obtained polyester (E) had an intrinsic viscosity of 0.62 dL / g.

(Manufacture of polyester (F))
In the method for producing polyester (E), the same method as the method for producing polyester (E), except that the additive particles are silica particles having an average particle diameter of 2.7 μm and the content with respect to the polyester is 0.3% by weight. Was used to obtain a polyester (F). The obtained polyester (F) had an intrinsic viscosity of 0.61 dL / g.

(Manufacture of polyester (G))
In the method for producing polyester (E), the additive particles are the same as the method for producing polyester (E), except that silica particles having an average particle diameter of 3.2 μm and the content with respect to polyester are 0.6% by weight. Polyester (G) was obtained using the method. The average particle size was determined by a laser method. The obtained polyester (G) had an intrinsic viscosity of 0.62 dL / g.

Example 1:
(Manufacture of polyester film)
A mixed raw material obtained by mixing the polyester (A), (D) chip and the polyester (E), (F), (G) chip at a ratio as shown in Tables 1 and 2 below, is the outermost layer (surface layer) and The raw material for the intermediate layer is supplied to two extruders, melt-extruded at 280 ° C., and then cooled and solidified on a cooling roll set at a surface temperature of 40 ° C. using an electrostatic application adhesion method. A sheet was obtained. Next, the film was stretched 2.8 times in the longitudinal direction at 100 ° C., then led to a tenter, subjected to a preheating step in the tenter and subjected to transverse stretching of 5.1 times at 120 ° C., and then heat-treated at 220 ° C. for 10 seconds. Thereafter, 4% relaxation was added in the width direction at 180 ° C. to obtain a master roll having a width of 4000 mm. A slit was made from a position of 1400 mm from the end of the master roll, and the core roll was wound up 1000 m to obtain a polyester film. The total thickness of the obtained film was 50 μm (layer structure: surface layer 2.5 μm / intermediate layer 45 μm / surface layer 2.5 μm).

A release agent composed of release agent composition-A shown below was applied to the obtained polyester film by a reverse gravure coating method so that the coating amount (after drying) was 0.1 g / m ² , and a dryer temperature of 120 Under the conditions of ° C. and a line speed of 30 m / min, the roll peel force is 21 mN / cm, the transparency is 84.9%, the release layer surface Ra is 9.5 nm, the MOR_C value is 2.5, and the OL amount is 0.95 mg. A release polyester film of / m ² was obtained.
<Releasing agent composition-A>
Curable silicone resin (KS-847H: manufactured by Shin-Etsu Chemical) 20 parts Catalyst (PL-50T: manufactured by Shin-Etsu Chemical) 0.3 parts (1.5% by weight)
MEK / toluene mixed solvent (mixing ratio is 1: 1)

The transparency index newly introduced in the evaluation of the film this time shows a higher correlation with clearness by visual inspection than the internal haze which is a conventional transparency index.

For the obtained polyester film, a deflector plate was prepared by the following method, and optical property inspection and peeling properties were evaluated. The obtained release film had good inspection by reflection and good recognition of foreign matter, and the polarizing plate was peeled off cleanly, and the phenomenon that the adhesive adhered to the release layer was not observed. The evaluation results are summarized in Table 1.

<Manufacture of polarizing plate with release film>
The acrylic adhesive shown below is applied to the polarizing plate so that the thickness after drying is 25 μm, and after passing through a 130 ° C. drying oven in 30 seconds, the release film is bonded, and the adhesive is interposed. Thus, a polarizing plate with a release film in which the release film and the polarizing film were adhered to each other was prepared. The laminating direction of the film was performed so that the width direction of the release film was parallel to the orientation axis of the polarizing film.
・ Acrylic adhesive coating solution Acrylic adhesive (Olivein BPS429-4: Toyo Ink)
100 parts Curing agent (BPS8515: manufactured by Toyo Ink) 3 parts MEK / toluene mixed solvent (mixing ratio is 1: 1) 50 parts

Example 2 and Comparative Examples 1-8:
In Example 1, the polyester film was produced in the same manner as in Example 1 except that the draw ratio at the time of production of the polyester film, the film thickness, the particle-containing polyester type of the surface layer, and the compounding amount of the particle-containing polyester of the surface layer were changed. A film was obtained. The obtained evaluation results are summarized in Tables 2 to 4 below.

Example 3:
In Example 1, after stretching 2.8 times in the longitudinal direction of the production of the polyester film, the following coating agent is applied to one side of the longitudinally stretched film, and the coating amount (after drying) is 0.03 g / m ² . After that, after conducting a preheating step in the tenter and performing a transverse stretching of 5.1 times at 120 ° C., heat treatment is performed at 220 ° C. for 10 seconds, and then in the width direction at 180 ° C. 4% relaxation was added to obtain a master roll having a width of 4000 mm. A slit was made from a position of 1400 mm from the end of the master roll, and the core roll was wound up 1000 m to obtain a polyester film. The total thickness of the obtained film was 50 μm (layer structure: surface layer 2.5 μm / intermediate layer 45 μm / surface layer 2.5 μm).

In addition, the example of a compound which comprises an application layer is as follows.
(Compound example)
-Polyvinyl alcohol binder polymer having a saponification degree of 88 mol% and a polymerization degree of 350: A
Emulsion polymer of methyl methacrylate / ethyl acrylate / acrylonitrile / N-methylol methacrylamide = 45/45/5/5 (molar ratio) (emulsifier: anionic surfactant) Binder polymer: B
・ Crosslinking agent Hexamethoxymelamine crosslinking agent: C
・ Particulate colloidal silica (average particle diameter: 70 nm): D
Solid content ratio: A / B / C / D = 30/24/42/4

A release agent composed of release agent composition-A was applied to the coated surface of the obtained polyester film by a reverse gravure coating method so that the coating amount (after drying) was 0.1 g / m ² , and the dryer temperature was 120. The roll peel strength is 21 mN / cm, the transparency is 84.9%, the release layer surface Ra is 9.5 nm, the MOR_C value is 2.5, and the OL amount is 0.96 mg. A release polyester film of / m ² was obtained. The obtained evaluation results are summarized in Table 4 below.
<Releasing agent composition-A>
Curable silicone resin (KS-847H: manufactured by Shin-Etsu Chemical) 20 parts Catalyst (PL-50T: manufactured by Shin-Etsu Chemical) 0.3 parts (1.5 wt%)
MEK / toluene mixed solvent (mixing ratio is 1: 1)

The film of the present invention can achieve a high degree of accuracy in an optical inspection method required for polarizing plate substrate applications and the like, and can provide a release polyester that realizes the process contamination and the ability to reduce foreign matters to adhesives in the release film. It can be suitably used as a tella film.

Claims

It consists of three or more coextruded biaxially stretched polyester films, at least one surface layer contains styrene / divinylbenzene copolymer crosslinked particles, and at least one outermost layer has a silicone release layer. Release film.
2. The surface roughness (Ra) of the silicone release layer is 9.0 nm or more, the transparency of the release film is 83.5% or more, and the MOR value is 1.5 to 3.0. Release film.
The release film according to claim 1 or 2, which has a coating layer obtained by coating a coating solution containing polyvinyl alcohol on at least one side.