JP5893963B2 - Laminated polyester film - Google Patents

Description

  The present invention relates to a biaxially stretched polyester film, and more specifically, suitable for various optical members used in liquid crystal displays, plasma displays, touch panels, etc., process films used in manufacturing processes in the optical field, protective films, and the like. The present invention relates to a biaxial polyester film that is excellent in optical characteristics and can be manufactured with high quality and high productivity of optical products.

  Conventionally, polyester films, especially biaxially stretched films of polyethylene terephthalate and polyethylene naphthalate, have excellent mechanical properties, heat resistance, and chemical resistance. Magnetic tape, ferromagnetic thin film tape, photographic film, packaging Widely used as materials for protective films for various films, films for electronic members, films for electronic members, electronic insulating films, films for metal laminates, films disposed on the outermost surface of displays, and the like.

  In recent years, polyester films are often used in various optical films, and prism sheets, diffusing films, brightness enhancement films, base films for reflectors, and antireflective materials for plasma displays. It is used for various applications such as base films such as films, near-infrared shielding films, electromagnetic shielding films, hard coat films as constituent members of touch panels, transparent conductive films, and base films for glass scattering prevention films. Polyester films used as substrate films in these optical products are required to have high transparency due to their usage, and must be free of foreign matter and defects that affect the displayed image when incorporated in a display. It has been.

  The polyester film used as the base film of the optical member is a relatively thick polyester film having a thickness of 100 to 250 μm. However, as the thickness increases, the film can be heated or cooled uniformly. Because it becomes difficult, during the film forming process, the polyester resin that has been melted is cooled and solidified, and in the process of making an amorphous sheet, crystallization unevenness in which polyester molecules are crystallized locally occurs in the polyester sheet, causing optical defects. The solution is desired.

  In recent years, the size of electronic displays has increased, and as a result, the size of the base material of various optical members used has increased, and as a result, polyester used as the base material of optical members has a thicker film due to its handling characteristics. Has come to be demanded.

JP 2006-181767 A JP 2006-182831 A

  This invention is made | formed in view of the said situation, Comprising: The solution subject is various optical members used for a liquid crystal display, a plasma display, a touchscreen etc., the process film used in the manufacturing process of an optical field | area, a protective film An object of the present invention is to provide a biaxial polyester film that is suitable for use in, for example, a high-quality optical product and can be manufactured with high productivity.

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

That is, the gist of the present invention is to have a thickness of 4 μm or more of both surface layers made of polyester containing 2800 ppm to 30000 ppm of a polymer having at least two epoxy groups in the molecular chain, and a laminate structure of at least 3 layers. is a laminated polyester film above 100 [mu] m, consists in laminated polyester film for optical, wherein the number of surface defects or more films diameter 30μm at 10 / m ² or less.

  The present invention has been made in view of the above circumstances, and the problem to be solved relates to a biaxially stretched polyester film having a thickness of 100 μm or more, and more specifically, various types used for liquid crystal displays, plasma displays, touch panels, and the like. It is a polyester film suitable for optical members, process films used in manufacturing processes in the optical field, protective films, etc., and has excellent optical properties and can be manufactured with improved optical product quality and high productivity. The biaxial polyester film can be provided, and its industrial value is high.

  The optical laminated polyester film of the present invention is required to be a multilayer film having at least 3 layers. The laminated polyester film for optics referred to in the present invention is a polyester film extruded by a so-called extrusion method that is melt-extruded from an extrusion die, and is oriented in the biaxial direction of the vertical direction and the horizontal direction as necessary. Film.

  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 and 2,6-naphthalenedicarboxylic acid, and examples of the aliphatic glycol include ethylene glycol, diethylene glycol, and 1,4-cyclohexanedimethanol. 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, and oxycarboxylic acids (for example, P-oxybenzoic acid). Or 2 or more types are mentioned, As a glycol component, 1 type, or 2 or more types, such as ethylene glycol, diethylene glycol, propylene glycol, butanediol, 1, 4- cyclohexane dimethanone neopentyl glycol, is mentioned.

  In the present invention, it is necessary to use a polyester containing 2800 ppm to 30000 ppm of a polymer having at least two epoxy groups in the molecular chain as the outermost layer. When the content of the epoxy group is less than 2800 ppm, the crosslinking network created by the reaction between the epoxy group and the carboxyl group remaining in the polyester resin is not sufficient, and the polyester film is formed between the polyester molecules in the process of forming the polyester film to form an amorphous sheet. It becomes difficult to suppress the crystallization of. On the other hand, when it exceeds 30000 ppm, the viscosity of the polyester increases due to cross-linking by a chemical reaction between an epoxy group and a carboxyl group, and the extrusion of the polyester by an extruder becomes difficult.

  The polymer containing at least two functional groups in the molecular chain of the epoxy group used in the present invention is not limited as long as it is a polymer having compatibility with the polyester resin. For example, polyester resin, acrylic resin, polyurethane Resin, polycarbonate resin, styrene resin, polyimide resin, polyamide resin, polyolefin resin, a mixture thereof, a copolymer, and the like. A resin that is particularly preferably used is a copolymer of an acrylic resin and a styrene resin.

  Further, the molecular weight of the polymer having at least two epoxy groups in the molecular chain used in the present invention is not limited as long as it is compatible with the polyester resin, but the molecular weight range of the polymer used suitably Has an average molecular weight of 350 g / mol to 8000 g / mol, preferably 400 g / mol to 3000 g / mol, more preferably 500 g to 3000 g / mol.

  In the film of the present invention, the thickness of the outermost layer is preferably 4 μm or more, more preferably 5 μm or more, and further preferably 6 μm or more. When the thickness of the outermost layer is less than 4 μm, the suppression effect of crystallization between the polyester molecules due to the epoxy group contained in the outermost layer is localized too much on the film surface, and contributes sufficiently to improving the quality and productivity of the entire film. It may not be possible.

  The film of the present invention relates to a thickness of 100 μm or more, and the effect of the invention is higher as the thickness increases. When the thickness of the film is 188 μm or more, it becomes more difficult to uniformly cool or heat the film in the film forming process. In particular, in the process of extruding the melted polyester resin from the die, cooling it with a cooling drum, and forming an amorphous sheet, the side opposite to the cooling drum is undercooled. A minute crystallized product may be formed, resulting in an optical defect.

  In the polyester layer of the film of the present invention, particles may be blended mainly for the purpose of imparting slipperiness and preventing scratches in each step. 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, precipitated particles obtained by precipitating and finely dispersing a part of a metal compound such as a catalyst during the polyester production process can also be used.

  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 as required.

  The average particle size of the particles to be blended in the polyester film is not particularly limited, but is usually in the range of 0.02 μm to 3 μm, preferably 0.02 μm to 2.5 μm, more preferably 0.02 μm to 2 μm. It is. When particles having an average particle size of less than 0.02 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 3 μm, the degree of roughening of the film surface becomes too large and the film may become hazy.

    Furthermore, the particle content in the polyester layer is usually in the range of 0.0005 to 0.5% by weight, preferably 0.001 to 0.3% by weight. When the particle content is less than 0.0005% by weight, the slipperiness of the film may be insufficient, resulting in poor appearance such as scratches during film processing. On the other hand, when adding over 0.5 weight%, the transparency of a film may be inadequate.

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

  The polyester film of the present invention may be formed with a coating layer on one or both sides of the film in order to impart functions such as adhesiveness, antistatic property, slipperiness and releasability to the film during and / or after the stretching process. Further, surface treatment such as corona treatment may be performed.

  In the optically laminated polyester film of the present invention, a coating layer may be provided for the purpose of improving the adhesion to the layer processed thereon, improving the slipperiness during processing, and the like. Regarding the coating layer, it may be provided by in-line coating which treats the film surface during the process of forming a polyester film, or offline coating which is applied outside the system on a once produced film may be adopted. Since the coating can be performed simultaneously with the film formation, the production can be handled at a low cost, and therefore in-line coating is preferably used.

  The in-line coating is not limited to the following, but for example, in the sequential biaxial stretching, the coating treatment can be performed particularly before the lateral stretching after the longitudinal stretching is finished. When the coating layer is provided on the polyester film by in-line coating, it is possible to apply at the same time as the film formation, and the coating layer can be processed at a high temperature in the heat treatment process of the polyester film after stretching. Performances such as adhesion to various surface functional layers that can be formed on the layer and heat-and-moisture resistance can be improved. Moreover, when coating before extending | stretching, the thickness of an application layer can also be changed with a draw ratio, and compared with off-line coating, uniform coating can be performed with a thin film. That is, a film suitable as a polyester film can be produced by in-line coating, particularly coating before stretching.

  Moreover, the coating layer of the film of the present invention comprises a surfactant, an antifoaming agent, a coating property improving agent, a thickener, an organic lubricant, organic particles, inorganic particles, an antioxidant, an ultraviolet absorber, a foaming agent, It may contain additives such as dyes and pigments. These additives may be used alone or in combination of two or more as necessary.

As long as water is the main medium, the coating agent may contain a small amount of an organic solvent for the purpose of improving dispersion in water or improving the film-forming performance. It is necessary to use the organic solvent as long as it is soluble in water. Examples of the organic solvent include aliphatic or alicyclic alcohols such as n-butyl alcohol, n-propyl alcohol, isopropyl alcohol, ethyl alcohol, and methyl alcohol, glycols such as propylene glycol, ethylene glycol, and diethylene glycol, n-butyl cellosolve, Examples include glycol derivatives such as ethyl cellosolve, methyl cellosolve, propylene glycol monomethyl ether, ethers such as dioxane and tetrahydrofuran, esters such as ethyl acetate and amyl acetate, ketones such as methyl ethyl ketone and acetone, and amides such as N-methylpyrrolidone. Can be mentioned.
These organic solvents may be used in combination of two or more as required.

  Moreover, you may use together heat treatment and active energy ray irradiation, such as ultraviolet irradiation, as needed irrespective of offline coating or in-line coating as needed. 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. Such a coat may be either single-sided or double-sided. The coating material may be either water-based and / or solvent-based for off-line coating, but is preferably water-based or water-dispersed for in-line coating.

  In addition, when the polyester film of the present invention is used for optics, a colorant, a conductive material, etc. may be added, and further, reflection of external light, electric shock due to static electricity, prevention of dust adhesion, and further electromagnetic wave shielding. An intended functional multilayer thin film may be formed.

  The coating liquid used in the present invention is preferably an aqueous solution or an aqueous dispersion in terms of handling and working environment, but contains water as the main medium and contains an organic solvent as long as it does not exceed the gist of the present invention. You may do it.

  Although there is no restriction | limiting in particular in the solid content density | concentration of a coating liquid, Usually, 0.3 to 65 weight%, Preferably it is 0.5 to 30 weight%, More preferably, it is 1 to 20 weight%. When the concentration is too high or too low than these ranges, it may be difficult to provide a coating layer having a thickness necessary for fully expressing the function.

  The thickness of a coating layer is dry thickness, and is 0.003-1.5 micrometers normally, Preferably it is 0.01-0.5 micrometer, More preferably, it is 0.01-0.3 micrometer. If the thickness of the coating layer is less than 0.003 μm, sufficient performance may not be obtained, and if it exceeds 1.5 μm, blocking between films tends to occur.

  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.

  In the present invention, it is preferable to contain inorganic particles or organic particles in the coating layer in order to further improve the slipping property, the fixing property 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 and the sharpness of the image tends to be lowered.

  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.

  The above inorganic particles and organic particles may be surface-treated. Examples of the surface treatment agent include a surfactant, a polymer as a dispersant, a silane coupling agent, a titanium coupling agent, and the like. The content of the particles in the coating layer is preferably 10% by weight or less, more preferably 5% by weight or less as an appropriate addition amount that does not impair the transparency.

  The coating layer may contain 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.

  In addition, with respect to the polyester film of the present invention, a colorant, a conductive material, etc. may be added, and further, a functional multilayer thin film for the purpose of preventing electrostatic shock, dust adhesion, and electromagnetic wave shielding may be formed thereon. Good.

  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. In addition, for the purpose of improving the slipperiness and abrasion resistance of the film, inert inorganic or organic fine particles can be blended with the polyester as necessary.

In the film of the present invention, the number of surface defects of a film having a diameter of 30 μm or more is preferably 10 / m ² or less. When deviating from the above conditions, a defect occurs in an image when used as a member of an electronic display such as a liquid crystal display or a plasma display, which causes a reduction in quality. Furthermore, scratches with a width of 10 μm or more present on the film surface are preferably 10 pieces / m ² or less, more preferably 5 pieces / m ² or less. When the number of scratches having a width of 10 μm or more is larger than 10 / m ² , the quality of an electronic display such as a liquid crystal display or a plasma display may be deteriorated as described above. In order to overcome such problems, a method of preventing foreign matters from being mixed at the time of manufacturing the polyester raw material and film and removing foreign matters by using a high-precision filter is adopted. It is necessary to take measures such as suppressing unevenness in speed at the time of contact with each roll in the process and preventing foreign matter from being mixed between the roll and the film.

  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 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) Average particle diameter (d50)
The particle size was measured by a sedimentation method based on Stokes' resistance law using a centrifugal sedimentation type particle size distribution analyzer SA-CP3 manufactured by Shimadzu Corporation.

(3) Thickness of Laminated Polyester Layer After fixing a small piece of film with an epoxy resin, it was cut with a microtome, and the cross section of the film was observed with a transmission electron micrograph. Two of the cross-sections are observed in parallel with the film surface, and the interface is observed by light and dark. The distance between the two interfaces and the film surface was measured from 10 photographs, and the average value was defined as the laminated thickness.

(4) Film surface defects Light is applied to the film surface having a width of 1500 mm and a length of 20 m (area 30 m ² ) in a dark room with a halogen lamp, and the film surface is visually observed to detect microcrystals, foreign matters, scratches, etc. The number of surface defects having a diameter of 30 μm or more was counted, and the number of surface defects per 1 m ^{2 of} film was calculated.

<Manufacture of polyester>
[Production method of polyester (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 0.63 due to a change in stirring power of the reaction tank, and the polymer was discharged under nitrogen pressure. The obtained polyester (A) had an intrinsic viscosity of 0.65 and an oligomer (cyclic trimer) content of 0.97% by weight.

[Polyester (B)]
“UVA3000PET” (polyester (B) manufactured by BASF Japan Ltd.) was used as a polyester masterbatch containing 30% by weight of an epoxy group-containing polymer. The intrinsic viscosity was 0.51.

[Production method of polyester (C)]
In the method for producing polyester (A), after adding 0.04 part of ethyl acid phosphate, 0.2 part of silica particles dispersed in ethylene glycol having an average particle diameter of 1.6 μm and 0.04 part of antimony trioxide are added. In addition, polyester (C) was obtained using the same method as the production method of polyester (A) except that the polycondensation reaction was stopped at the time corresponding to the intrinsic viscosity of 0.65. The obtained polyester (C) had an intrinsic viscosity of 0.65 and an oligomer (cyclic trimer) content of 0.82% by weight.

Example 1:
A mixed raw material obtained by mixing the polyesters (A), (B), and (C) at a ratio of 84.0% by weight, 1.0% by weight, and 15.0% by weight, respectively, is used as a raw material for the A layer, and the polyester (A) Using 100% raw material as the raw material for B layer, each is supplied to two extruders and melted at 285 ° C, then cooled to 40 ° C with A layer as the outermost layer (surface layer) and B layer as the intermediate layer On the cast drum, two types and three layers (ABA) were coextruded so as to have a thickness composition ratio of A: B: A = 6: 176: 6, and cooled and solidified to obtain a non-oriented sheet.

  Next, the film was stretched 3.4 times in the machine direction at a film temperature of 85 ° C. using the roll peripheral speed difference, and then this longitudinally stretched film was guided to a tenter and stretched 4.3 times at 120 ° C. in the transverse direction. Then, the film was wound on a roll to obtain a laminated polyester film having a thickness of 188 μm. The properties of the obtained film are shown in Table 1 below.

Example 2:
In Example 1, polyesters (A), (B), and (C) are 82.0 wt%, 3.0 wt%, and 15.0 wt%, respectively, as the raw material of the A layer, and the thickness composition ratio is A: B. : A = 6: 238: 6 A laminated polyester film was obtained in the same manner as in Example 1 except that the thickness of the obtained laminated polyester film was 250 μm. The characteristics of the obtained laminated polyester film are shown in Table 1 below.

Example 3:
In Example 1, the polyester (A), (B), and (C) are 80.0 wt%, 5.0 wt%, and 15.0 wt%, respectively, as the raw material of the A layer, and the thickness component ratio is A: B : A = 6: 338: 6 A laminated polyester film was obtained in the same manner as in Example 1 except that the thickness of the obtained laminated polyester film was 350 μm. The characteristics of the obtained laminated polyester film are shown in Table 1 below.

Example 4:
In Example 1, polyesters (A), (B), and (C) are 78.0% by weight, 7.0% by weight, and 15.0% by weight, respectively, as the raw material for the A layer, and the thickness composition ratio is A: B. : A = 6: 238: 6 A laminated polyester film was obtained in the same manner as in Example 1 except that the thickness of the obtained laminated polyester film was 250 μm. The characteristics of the obtained laminated polyester film are shown in Table 1 below.

Example 5:
In Example 1, a polyester film was obtained in the same manner as in Example 1 except that the thickness component ratio was changed to 2: 246: 2 and the thickness of the obtained laminated polyester film was 250 μm. The characteristics of the obtained laminated polyester film are shown in Table 1 below.

Comparative Example 1:
In Example 2, a polyester film was obtained in the same manner as in Example 2 except that the polyesters (A) and (C) were mixed in proportions of 85% and 15%, respectively, as the raw material for the A layer. The characteristics of the obtained laminated polyester film are shown in Table 1 below. On the anti-cooling roll surface of the obtained film, optical defects derived from microcrystallization of the polyester were generated, and characteristic deterioration was observed.

Comparative Example 2:
In Example 1, polyesters (A), (B), and (C) as raw materials for the A layer were mixed in proportions of 84.5%, 0.5%, and 15%, respectively, and the thickness composition ratio was A: B. : A = 6: 338: 6 A polyester film was obtained in the same manner as in Example 1 except that the thickness of the laminated polyester film obtained was 350 μm. The characteristics of the obtained laminated polyester film are shown in Table 1 below. On the anti-cooling roll surface of the obtained film, optical defects derived from microcrystallization of the polyester were generated, and characteristic deterioration was observed.

Comparative Example 3:
In Example 1, it is the same method as Example 1 except having mixed polyester (A), (B), (C) as a raw material of A layer in the ratio of 74%, 11%, and 15%, respectively. A polyester film was tried. When the film was formed, too much load was applied to the extruder for the A layer, and a laminated polyester film could not be obtained.

  The film of the present invention can be suitably used for, for example, various optical members used for liquid crystal displays, plasma displays, touch panels, and the like, process films and protective films used in manufacturing processes in the optical field.

Claims (1)

A laminated polyester film having a thickness of 100 μm or more, having both surface layers with a thickness of 4 μm or more and made of polyester containing 2800 ppm to 30000 ppm of a polymer having at least two epoxy groups in the molecular chain, and having a laminated structure of at least 3 layers A laminated polyester film for optics, wherein the number of surface defects of a film having a diameter of 30 μm or more is 10 / m ² or less .