JP2007045023A - Laminated polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a base material film constituting a release film for protecting an adhesive layer used when producing a liquid crystal constituent member such as a liquid crystal polarizing plate and a retardation plate, and to be used when producing a display member such as an LCD, PDP, or organic EL. Provided is a laminated polyester film suitable for uses such as a substrate film for various optical applications, which does not like the presence of foreign substances derived from oligomers on the film surface.
SOLUTION: At least one surface of a polyester film stretched at least in a uniaxial direction has a coating layer provided by coating a coating solution containing 70% or more of a melamine compound in a solid content and drying it. Laminated polyester film.
[Selection figure] None

Description

  The present invention relates to a laminated polyester film, and more particularly to a laminated polyester film in which the amount of oligomer precipitation is as small as possible. More specifically, for example, a liquid crystal display (hereinafter abbreviated as LCD), a plasma display panel (hereinafter abbreviated as PDP). ), Organic electroluminescence (hereinafter abbreviated as “organic EL”) and other optical uses for producing display members, etc., and laminated polyester films suitable for uses that extremely dislike the presence of oligomer-derived foreign matter on the film surface. It is to provide.

  Conventionally, a laminated polyester film provided with a coating layer having various functions such as adhesiveness and antistatic property on a polyester film is used for manufacturing display members such as liquid crystal polarizing plates, retardation plates, PDPs, and organic ELs. It is used for various optical applications. A problem in using the laminated polyester film is that oligomers deposited on the surface of the coating layer at high temperatures cause various problems in the production process. For example, in a display member manufacturing application, foreign matter existing on the film surface may cause problems such as uneven brightness of the display screen.

  In recent years, with the advancement of the IT (Information Technology) field, various problems associated with precipitation of oligomers tend to become more apparent as the quality of laminated polyester films used in the production of LCD, PDP, organic EL display members, etc. .

  Base film constituting release film for protecting adhesive layer used for LCD display production, base film for cathode ray tube (hereinafter abbreviated as CRT) or antireflection film for LCD display, base film for touch panel The substrate film for a prism lens sheet, the substrate film for a CRT glass scattering prevention film, the substrate film for electronic paper, etc., which are constituent members of a liquid crystal display device, require particularly excellent transparency.

  When laminated polyester films are used as the above-mentioned various base films, it is also an application where the so-called visibility is extremely important, especially when viewed through light. Even a foreign object that does not cause any problem is desired to be as small as possible.

When focusing on oligomers as a form of foreign matter, for example, to prevent oligomer precipitation, the oligomers contained in the raw material are reduced by solid-phase polymerization, or the hydrolysis resistance of the polyester film is improved by using a terminal blocker. Measures such as letting it go have been taken. However, in the case of solid phase polymerization, depending on the extrusion conditions, there are problems such that the number of oligomers increases at the time of extrusion or the cost increases due to solid phase polymerization. Therefore, there is a demand for a laminated polyester film that minimizes oligomer precipitation even after a manufacturing process such as a heat treatment process.
Japanese Patent Laid-Open No. 2003-191413 Japanese Patent Laid-Open No. 2004-82370 Japanese Patent Laid-Open No. 2004-256625 Japanese Patent Laid-Open No. 2005-89622

  The present invention has been made in view of the above circumstances, and the problem to be solved is to provide a laminated polyester film in which the amount of oligomer precipitation is as small as possible. For example, liquid crystal components such as liquid crystal polarizing plates and retardation plates. Due to the oligomer surface on the film surface, such as base film constituting the release film for protecting the adhesive layer used at the time of manufacture, base film for various optical applications used at the time of manufacturing display members such as LCD, PDP, organic EL, etc. It is in providing the laminated polyester film suitable for the use which dislikes a foreign material existing.

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

  That is, the gist of the present invention is that at least one surface of a polyester film stretched in a uniaxial direction has a coating layer provided by applying a coating solution containing 70% or more of a melamine compound in a solid content and drying it. It exists in the laminated polyester film characterized by this.

Hereinafter, the present invention will be described in more detail.
The polyester film that is the substrate of the laminated polyester film in the present invention may have a single layer structure or a laminated structure, and may have four layers or more unless the gist of the present invention is exceeded other than the two-layer or three-layer structure. The above multilayer may be used, and is not particularly limited.

  The polyester used for the film in the present invention may be a homopolyester or a copolyester. In the case of a homopolyester, those obtained by polycondensation of an aromatic dicarboxylic acid and an aliphatic glycol are preferred. 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. Typical polyester includes polyethylene terephthalate and the like. On the other hand, the dicarboxylic acid component of the copolyester includes isophthalic acid, phthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, oxycarboxylic acid (for example, p-oxybenzoic acid, etc.), etc. 1 type, or 2 or more types is mentioned, As a glycol component, 1 type or 2 types or more, such as ethylene glycol, diethylene glycol, propylene glycol, butanediol, 4-cyclohexane dimethanol, neopentyl glycol, is mentioned. In any case, the polyester referred to in the present invention refers to a polyester that is usually 60 mol% or more, preferably 80 mol% or more of polyethylene terephthalate or the like which is an ethylene terephthalate unit.

  In the polyester layer of the film of the present invention, it is preferable to blend particles for the main purpose of imparting slipperiness. The kind of the particle to be blended is not particularly limited as long as it is a particle capable of imparting slipperiness. Specific examples thereof include silica, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, and phosphoric acid. Examples of the particles include magnesium, kaolin, aluminum oxide, and titanium oxide. Further, the heat-resistant organic particles described in JP-B-59-5216, JP-A-59-217755 and the like may be used. Examples of other heat-resistant organic particles include thermosetting urea resins, thermosetting phenol resins, thermosetting epoxy resins, benzoguanamine resins, and the like. Furthermore, it is possible to use precipitated particles in which a part of a metal compound such as a catalyst is precipitated and finely dispersed during the manufacturing process of the film raw material.

  On the other hand, the shape of the particles to be used is not particularly limited, and any of a spherical shape, a block shape, a rod shape, a flat shape, and the like may be used. Moreover, there is no restriction | limiting in particular also about the hardness, specific gravity, a color, etc. These series of particles may be used in combination of two or more if necessary.

  Moreover, the average particle diameter of the particle | grains to be used is 0.01-3 micrometers normally, Preferably it is the range of 0.01-1 micrometer. When the average particle diameter is less than 0.01 μm, the particles are likely to aggregate and dispersibility may be insufficient. On the other hand, when the average particle diameter exceeds 3 μm, the surface roughness of the film becomes too rough and Problems may occur when various surface functional layers are applied in the process.

  Further, the content of particles in the polyester layer is usually in the range of 0.001 to 5% by weight, preferably 0.005 to 3% by weight. When the particle content is less than 0.001% by weight, the slipperiness of the film may be insufficient. On the other hand, when the content exceeds 5% by weight, the transparency of the film is insufficient. There is.

  The method for adding particles to the polyester layer is not particularly limited, and a conventionally known method can be adopted. For example, it can be added at any stage of producing the polymer constituting each layer.

  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.

  In addition to the above-mentioned particles, conventionally known antioxidants, antistatic agents, thermal stabilizers, lubricants, dyes, pigments, and the like can be added to the polyester film in the present invention as necessary.

  Although the thickness of the polyester film in this invention will not be specifically limited if it is a range which can be formed into a film as a film, Usually, 5-250 micrometers, Preferably it is the range of 10-200 micrometers.

Next, although the manufacture example of the polyester film in this invention is demonstrated concretely, it is not limited to the following manufacture examples at all.
That is, a method of using the polyester raw material described above and cooling and solidifying a molten sheet extruded from a die with a cooling roll to obtain an unstretched sheet is preferable. In this case, in order to improve the flatness of the sheet, it is necessary to improve the adhesion between the sheet and the rotary cooling drum, and an electrostatic application adhesion method and / or a liquid application adhesion method are preferably employed. Next, the obtained unstretched sheet is stretched in the biaxial direction. In that case, first, the unstretched sheet is stretched in one direction by a roll or a tenter type stretching machine. The stretching temperature is usually 70 to 120 ° C., preferably 80 to 110 ° C., and the stretching ratio is usually 2.5 to 7 times, preferably 3.0 to 6 times. Next, the film is stretched in the direction perpendicular to the first stretching direction. In that case, the stretching temperature is usually 70 to 170 ° C., and the stretching ratio is usually 3.0 to 7 times, preferably 3.5 to 6 times. is there. Subsequently, heat treatment is performed at a temperature of 180 to 270 ° C. under tension or under relaxation within 30% to obtain a biaxially oriented film. In the above-described stretching, a method in which stretching in one direction is performed in two or more stages can be employed. In that case, it is preferable to carry out so that the draw ratios in the two directions finally fall within the above ranges.

  In the present invention, the simultaneous biaxial stretching method can be adopted for the production of the polyester film constituting the laminated polyester film. The simultaneous biaxial stretching method is a method in which the unstretched sheet is usually stretched and oriented in the machine direction and the width direction at 70 to 120 ° C., preferably 80 to 110 ° C., and stretch ratio. As an area magnification, it is 4 to 50 times, preferably 7 to 35 times, and more preferably 10 to 25 times. Subsequently, heat treatment is performed at a temperature of 170 to 250 ° C. under tension or under relaxation within 30% to obtain a stretched oriented film. With respect to the simultaneous biaxial stretching apparatus that employs the above-described stretching method, a conventionally known stretching method such as a screw method, a pantograph method, or a linear driving method can be employed.

  Furthermore, what is called an in-line coating which processes the film surface during the extending | stretching process of the above-mentioned polyester film can be given. When a coating layer is provided on a polyester film by in-line coating, coating can be performed simultaneously with stretching, and the thickness of the coating layer can be changed by the stretching ratio, so that a film suitable as a polyester film can be produced. .

  Next, formation of the coating layer in the present invention will be described. The coating layer constituting the laminated polyester film in the present invention may be provided on the polyester film by the above-mentioned in-line coating, or may be adopted a so-called off-line coating that is applied outside the system on the film once manufactured. May be used in combination. In-line coating is preferably used because the production of the laminated polyester film can be inexpensively handled.

  Although in-line coating is not limited to the following, for example, in longitudinal biaxial stretching, particularly longitudinal stretching is completed, and coating treatment can be performed before lateral stretching. When a coating layer is provided on a polyester film by a coating stretching method, coating can be performed simultaneously with film formation, and the coating layer can be treated at a high temperature, and a film suitable as a polyester film can be produced.

In the present invention, it is an essential requirement to have a coating layer containing a melamine compound in a solid content of 70% or more on at least one surface of a polyester film stretched at least in a uniaxial direction. When it is less than 70% by weight, the ability to prevent oligomer precipitation decreases depending on the type of compound used other than the melamine compound contained in the coating layer.

  Examples of the melamine compound include methoxymethyl 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. Moreover, as a melamine type compound, either a monomer or the condensate which consists of a multimer more than a dimer may be sufficient. These melamine compounds may be used alone or in combination of two or more. Furthermore, when consideration is given to application to in-line coating, it is preferable to have water solubility or water dispersibility.

  In the laminated polyester film of the present invention, a binder polymer can be used in combination to improve transparency when various surface functional layers are laminated on the coated surface and to improve adhesion to various surface functional layers. It is.

  The “binder polymer” used in the present invention is a number average molecular weight (Mn) measured by gel permeation chromatography (GPC) according to a polymer compound safety evaluation flow scheme (sponsored by the Chemical Substance Council in November 1985). ) Is a polymer compound having a molecular weight of 1000 or more and having a film-forming property.

  Specific examples of the binder polymer include polyester resin, acrylic resin, urethane resin, polyvinyl (polyvinyl alcohol, polyvinyl chloride, vinyl chloride vinyl acetate copolymer, etc.), polyalkylene glycol, polyalkylene imine, methyl cellulose, hydroxy cellulose, and starch. And the like.

  Furthermore, a crosslinking agent other than the melamine compound may be used in combination in the coating layer, and specific examples include an epoxy compound, an oxazoline compound, and an isocyanate compound. These crosslinking components may be bonded in advance to the binder polymer.

  Further, for the purpose of improving the adhesion and slipperiness of the coating layer, inert particles may be contained, and specific examples include silica, alumina, kaolin, calcium carbonate, titanium oxide, organic particles, and the like.

  Furthermore, as long as it does not impair the gist of the present invention, an antifoaming agent, a coating property improver, a thickener, an organic lubricant, an antistatic agent, an antioxidant, an ultraviolet absorber, a foaming agent, a dye, etc. May be contained.

  It is preferable to produce a laminated film by applying the above-described series of compounds as a solution or a dispersion onto a film with a coating solution adjusted to a solid content concentration of about 0.1 to 50% by weight.

  Furthermore, in the case of in-line coating, the above-mentioned series of compounds is used as an aqueous solution or aqueous dispersion, and a laminated film is applied in such a manner that a coating solution adjusted with a solid content concentration of about 0.1 to 50% by weight as a guide is applied onto the film. Is preferably produced. In addition, a small amount of an organic solvent may be contained in the coating solution for the purpose of improving the dispersibility in water, improving the film forming property, and the like within the range not impairing the gist of the present invention. Only one type of organic solvent may be used, or two or more types may be used as appropriate.

A stacking films of the present invention, the coating amount of the coating layer provided on the film (after drying) is generally 0.005~1g / ^{m 2,} preferably in the range from 0.005 to 0.5 / ^{m 2.} When the coating amount is less than 0.005 g / m ² , the uniformity of coating thickness may be insufficient, and the amount of oligomer deposited from the coating layer surface after heat treatment may increase. On the other hand, when the coating is applied in excess of 1 g / m ² , problems such as a decrease in slipperiness may occur.

  In the present invention, as a method for providing the coating layer, a conventionally known coating method such as reverse gravure coating, direct gravure coating, roll coating, die coating, bar coating, curtain coating or the like can be used. Regarding the coating method, there is a description example in “Coating method” published by Yasuharu Harasaki in 1979.

  In the present invention, the drying and curing conditions for forming the coating layer on the film are not particularly limited. For example, when the coating layer is provided by off-line coating, it is usually 80 to 200 ° C. for 3 to 40 seconds. The heat treatment is preferably performed at 100 to 180 ° C. for 3 to 40 seconds as a guide.

  On the other hand, when the coating layer is provided by in-line coating, heat treatment is usually performed at 70 to 280 ° C. for 3 to 200 seconds as a guide.

  Further, irrespective 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 required. You may give surface treatment, such as a corona treatment and a plasma treatment, to the film which comprises the laminated | multilayer film in this invention previously.

After heat-treating the laminated polyester film in the present invention (180 ° C., 10 minutes), the amount of oligomer extracted from the coating layer surface with dimethylformamide is usually 1.5 mg / m ² or less, preferably 1.0 mg / m 2. ² or less, more preferably 0.5 mg / m ² or less. When the oligomer amount exceeds 1.5 mg / m ² , for example, when used for pressure-sensitive adhesive layer protection for use in the production of liquid crystal components, when the drying temperature is set higher in the drying step after pressure-sensitive adhesive application, The amount of oligomer deposited on the surface of the coating layer increases, and problems such as a decrease in the transparency of the pressure-sensitive adhesive and a decrease in the adhesive strength of the pressure-sensitive adhesive layer may occur.

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

  In addition, in the present invention, the total light transmittance of the laminated film is 80% or more, such as optical uses such as those used in the production of display members such as LCDs, PDPs, and organic ELs. Is preferable, and more preferably 85% or more. When the total light transmittance is less than 80%, the transparency becomes insufficient. For example, when used in an inspection process involving optical evaluation, there may be a problem that foreign matters are easily overlooked.

  According to the laminated polyester film of the present invention, it is possible to provide a laminated polyester film in which the amount of oligomer precipitation is as small as possible, and 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. 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 have been removed are precisely weighed, and 100 ml of a mixed solvent of phenol / tetrachloroethane = 50/50 (weight ratio) is added. It was dissolved and measured at 30 ° C.

(2) Measurement of average particle diameter (d ₅₀ : μm) Integration (weight basis) 50% in equivalent spherical distribution measured using centrifugal sedimentation type particle size distribution measuring device (SA-CP3 type manufactured by Shimadzu Corporation) Was the average particle size.

(3) Measurement of the amount of oligomer extracted from the surface of one coating layer in the laminated polyester film The unheated laminated polyester film is heated in the air at 180 ° C. for 10 minutes in advance. 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 liquid chromatography (manufactured by Shimadzu Corporation: LC-7A) to determine the amount of oligomer in DMF, and this value was divided by the film area in contact with DMF to obtain the amount of film surface oligomer (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 an oligomer (cyclic trimer) collected in advance and dissolving it in accurately measured DMF. 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

(4) Measurement and evaluation method of total light transmittance of laminated polyester film Total light transmittance (%) of laminated polyester film by Nippon Denshoku Industries Co., Ltd. integrating sphere turbidimeter NDH-300A according to JIS-K7105 Was measured. The measured value was evaluated according to the following criteria.
○: Good with a total light transmittance of 85% or more.
Δ: Total light transmittance is 80% or more and less than 85%, which is slightly good.
X: Total light transmittance is less than 80%, poor

The polyester used in the examples and comparative examples was prepared as follows.
<Manufacture of polyester>
100 parts of dimethyl terephthalate, 60 parts of ethylene glycol and 0.09 part of magnesium acetate tetrahydrate are placed in a reactor, the temperature is raised by heating, methanol is distilled off, transesterification is performed, and 4 hours are required from the start of the reaction. The temperature was raised to 230 ° C. to substantially complete the transesterification reaction. Next, 0.04 part of ethyl acid phosphate, 0.03 part of antimony trioxide and 0.01 part of silica particles having an average particle diameter of 1.5 μm were added, and then the temperature reached 280 ° C. and the pressure reached 15 mmHg in 100 minutes. After that, the pressure was gradually reduced after that to finally reach 0.3 mmHg. After 4 hours, the system was returned to normal pressure to obtain polyethylene terephthalate having an intrinsic viscosity of 0.61.

Examples of compounds constituting the coating layer are as follows.
(Compound example)
・ Melamine compound Hexamethoxymethylmelamine (A1)
Alkyrol Melamine / Urea Cocondensation (Dai Nippon Ink Chemical Co., Ltd. Becamine) (A2)
・ Binder polymer Polyvinyl alcohol resin (B1)
Polyvinyl alcohol acrylic resin (B2) having a saponification degree of 88 mol% and a polymerization degree of 350
Julimer AT-M-918 (Nippon Pure Chemicals Co., Ltd.)
Polyester resin (B3)
Water dispersion of polyester resin copolymerized with the following composition: Monomer composition: (acid component) terephthalic acid / isophthalic acid / 5-sodium sulfoisophthalic acid // (diol component) ethylene glycol / 1,4-butanediol / diethylene glycol = 56/40/4 // 70/20/10 (mol%)
・ Crosslinking agent Polyglycerol polyglycidyl ether (C1)
Oxazoline group-containing polymer (Epocross made by Nippon Shokubai) (C2)

The produced polyethylene terephthalate was dried at 180 ° C. for 4 hours in an inert gas atmosphere, melted at 290 ° C. by a melt extruder, extruded from a die, and cooled by setting the surface temperature to 40 ° C. using an electrostatic application adhesion method. It cooled and solidified on the roll and the unstretched sheet was obtained. Next, the obtained unstretched sheet was first longitudinally stretched 3.6 times at 95 ° C., and the following coating agent was applied by a bar coating method, then guided to a tenter, and successively biaxially 4.3 times transversely. Stretching was performed. Then, 3 seconds fixed heat set at 230 ° C., the coating amount (after drying) of the coating layer formed using a coating solution 1 in a concentration of 10% in the composition shown in Table 1 below of 0.05 g / m ² is provided A film having a thickness of 38 μm was obtained.

As shown in Table 2 below, the finished laminated polyester film was good with less oligomer precipitation after heating.
(Example 2 to Example 8)

  In Example 1, a laminated polyester film was obtained in the same manner as in Example 1 except that the coating composition was changed to the coating composition shown in Table 1. As shown in Table 2, the finished laminated polyester film was good with less oligomer precipitation after heating.

(Comparative Example 1)
In Example 1, it manufactured similarly to Example 1 except having not provided the application layer, and obtained the polyester film. The finished polyester film was as shown in Table 2, and the amount of oligomer precipitation after heating was large.

(Comparative Example 2 to Comparative Example 6)
In Example 1, a laminated polyester film was obtained in the same manner as in Example 1 except that the coating composition was changed to the coating composition shown in Table 1. The finished laminated polyester film was as shown in Table 2, and the amount of oligomer precipitation after heating was large.

(Comparative Example 7)
In Example 1, a laminated polyester film was obtained in the same manner as in Example 1 except that the coating layer was not provided. The finished laminated polyester film was as shown in Table 2, and the amount of oligomer precipitation after heating was large.

  The laminated polyester film of the present invention can be suitably used for, for example, LCDs, PDPs, organic ELs, and other optical uses for producing display members, as well as for applications that dislike the presence of oligomer-derived foreign matter on the film surface. it can.

Claims (1)

A laminated polyester film having a coating layer provided by applying and drying a coating solution containing 70% or more of a melamine compound in a solid content on at least one surface of a polyester film stretched at least in a uniaxial direction. .