JP2015212056A - Laminate polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminate polyester film that has good flatness and excels in productivity, cost performance and optical characteristics, to be used for various optical members used in a liquid crystal display, a touch panel, or the like or to be used for a protective film or a release film used in a process of manufacturing products in an optical field.SOLUTION: The laminate polyester film comprises at least three layers, and the film has an intrinsic viscosity (IV) of 0.55 dl/g or less, a shrinkage percentage of 0.7% or less in a film longitudinal direction (MD) after heat-treated at 150°C for 30 minutes, a shrinkage percentage of 1.0% or less in a film width direction (TD) under the same conditions as the above, and a haze value of 3.0% or less.

Description

  The present invention relates to a laminated polyester film, and more specifically, to various optical members used for liquid crystal displays, touch panels, etc., and protective films and release films used in the manufacturing process of optical products. The present invention relates to a laminated polyester film having a low heat shrinkage ratio and excellent productivity, cost performance, and optical characteristics.

  Conventionally, polyester films, especially biaxially stretched films of polyethylene terephthalate and polyethylene naphthalate, have excellent mechanical strength, dimensional stability, flatness, heat resistance, chemical resistance, optical properties, etc. Thin film tape, photographic film, packaging film, film for electronic parts, metal laminate film, film for liquid crystal display, solar cell back surface protective film, base film for transparent conductive film of touch panel display, prism used for liquid crystal display It is widely used as a material for base films for sheets, protective films for various members, and the like.

  In recent years, polyester films are often used for various optical films, such as prism sheets for LCD members, light diffusing sheets, reflectors, touch panels, and other base films, antireflection base films, and display explosion-proof base films, It is used for various applications such as PDP filter films and touch panel films.

  In these optical products, in order to obtain a bright and clear image, the base film used as an optical film has good transparency from its usage pattern and has defects such as foreign matter and scratches that affect the image. It is necessary not to.

  In addition, these members are not used alone, but undergo a processing step in which they are bonded to a film made of a composition other than polyester, such as an acrylic resin, an olefin resin, or an aluminum foil, or applied with ink. Can be obtained.

  When the heat shrinkage rate of the polyester film is high, the residual stress derived from the heat shrinkage rate of the polyester film tends to work on the processed member. As a result, the end portions of the members after pasting are curled, problems such as delamination occur, and dimensional changes of the members occur. In order to reduce the problem, it is desired to reduce the heat shrinkage rate of the polyester film.

  Patent Document 1 describes that the heat shrinkage rate is reduced by performing offline annealing after forming a polyester film. However, this is not preferable in terms of cost, and the yield is also reduced because one processing step is added. Patent Document 2 describes an invention that lowers the heat shrinkage rate of a polyester film by providing a relaxation zone during biaxial stretching of the polyester film. According to this method, it is possible to reduce the heat shrinkage rate without increasing the cost, but there is a disadvantage that the polyester film is liable to be wrinkled or slack and is not preferable in appearance.

  Therefore, we are focusing on polyester films with low intrinsic viscosity (IV) because they are easily deformable in soft, easily-molded films required for the so-called simultaneous molding transfer method. It was known that it was smaller than that of normal IV.

  However, for example, the intrinsic viscosity is low, specifically. When considering the region where the IV of the film is 0.55 or less, it has been difficult to handle in the past because of its low intrinsic viscosity, the film is inferior in continuous film-forming properties and frequently breaks. Therefore, those skilled in the art tended to use a polyester material having a high intrinsic viscosity. However, as described above, when trying to reduce the heat shrinkage rate, various characteristics such as sacrificing flatness are comprehensive. It is difficult to produce a balanced film.

  In addition, in optical applications, for example, in protective film applications intended to protect the adhesive layer, there may be a case where an inspection involving optical evaluation such as foreign matters is performed with the film still attached. In such an inspection process, if the transparency of the film is insufficient, the inspection may be hindered. Therefore, it was in the situation where a film having good film flatness and film transparency and good workability in various processing applications was required.

JP 2011-155110 A JP 2012-094699 A

  This invention is made | formed in view of the said actual condition, Comprising: The solution subject is various optical members used for a liquid crystal display, a touchscreen, etc., and the protective film and release film used in the manufacturing process of the product of an optical field | area It is to provide a laminated polyester film having good flatness and excellent productivity, cost performance, and optical characteristics.

  As a result of intensive studies in view of the above problems, the present inventors have found that the above problems can be easily solved by adopting a specific configuration, and the present invention has been completed.

  That is, the gist of the present invention is a laminated polyester film having at least three layers, the intrinsic viscosity (IV) of the film is 0.55 dl / g or less, and the film length direction after heat treatment at 150 ° C. for 30 minutes ( MD) shrinkage is 0.7% or less, shrinkage under the same conditions in the film width direction (TD) is 1.0% or less, and film haze is 3.0% or less. It exists in the laminated polyester film.

  According to the present invention, various optical members for use in liquid crystal displays, touch panels, etc., protective films and release films used in the manufacturing process of products in the optical field, etc. have a low heat shrinkage rate, productivity and A laminated polyester film excellent in cost performance and optical characteristics can be provided, and the industrial value of the present invention is high.

  The polyester film referred to in the present invention is a film obtained by stretching a sheet melt-extruded from an extrusion die according to a so-called extrusion method.

  The polyester constituting the film refers to a polymer containing an ester group obtained by polycondensation from dicarboxylic acid and diol or from hydroxycarboxylic acid. Examples of the dicarboxylic acid include terephthalic acid, isophthalic acid, adipic acid, azelaic acid, sebacic acid, 2,6-naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, and the diol includes ethylene glycol, 1,4-butane. Examples include diol, diethylene glycol, triethylene glycol, neopentyl glycol, 1,4-cyclohexanedimethanol, polyethylene glycol, and hydroxycarboxylic acids such as p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid. be able to.

  Typical examples of such polymers include polyethylene terephthalate and polyethylene-2, 6 naphthalate.

  In the present invention, particularly preferably used polyester is polyethylene terephthalate. The intrinsic viscosity (IV) of the polyester film of the present invention needs to be 0.55 dl / g or less, more preferably 0.53 dl / g or less, and particularly preferably 0.51 dl / g or less. When IV exceeds 0.55 dl / g, the heat shrinkage rate is increased, which is not preferable. Although there is no particular lower limit, if the intrinsic viscosity of the polyester resin is low, breakage tends to occur, and a film having an IV of 0.50 dl / g or less has poor productivity.

  The thickness of the polyester film of this invention is 25-250 micrometers normally, Preferably it is 25-188 micrometers, More preferably, it is 25-125 micrometers. If the film thickness is less than 25 μm, it may not be preferable in terms of the strength and stiffness of the film. If the film thickness is more than 250 μm, the heat resistance is sufficient, but weight reduction and thinning are competing. For example, it may not be preferable in product design for optical applications.

  In the present invention, two or three or more polyester melt extruders can be used to form a laminated film having at least three layers by a so-called coextrusion method. As the structure of the layer, an A / B / A structure using the A raw material and the B raw material, an A / B / C structure using the C raw material, or other three or more layers can be used.

  The polyester film in the present invention preferably contains particles for easy handling. When there are no particles, or when there are few particles, the transparency of the film will be high and the film will be good, but the slipperiness may be insufficient. Therefore, there are cases where it is necessary to devise measures such as improving slipperiness. As a layer for putting particles, particles may be put in all layers, but from the viewpoint of transparency, it is preferable that the intermediate layer has no particles or few particles.

  Examples of particles used in the present invention include inorganic particles such as calcium carbonate, calcium phosphate, silica, kaolin, talc, titanium dioxide, alumina, barium sulfate, calcium fluoride, lithium fluoride, zeolite, molybdenum sulfide, and crosslinked polymers. Examples thereof include organic particles such as particles and calcium oxalate. Examples of the method of adding particles include a method of adding particles in a polyester as a raw material, a method of adding directly to an extruder, and the like. Two methods may be used in combination.

  The average particle size of the particles used preferably satisfies the range of 0.1 to 5 μm, more preferably 0.5 to 3 μm. When the average particle size is less than 0.1 μm, the particles are likely to aggregate and dispersibility may be insufficient. On the other hand, when it exceeds 5 μm, the surface roughness of the film becomes too rough, Problems may occur in subsequent processes.

  Furthermore, the particle content in the polyester preferably satisfies 0.01 to 5% by weight, more preferably 0.01 to 3% by weight. When the particle content is less than 0.01% by weight, the slipperiness of the film may be insufficient. On the other hand, when the content exceeds 5% by weight, the smoothness of the film surface is insufficient. It may become.

  The method of adding particles to the polyester is not particularly limited, and a conventionally known method can be adopted. For example, it can be added at any stage for producing the polyester, but the polycondensation reaction may proceed preferably after the esterification stage or after the transesterification reaction. 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. It is performed by the method of blending.

  In this invention, you may add an additive other than the said particle | grain as needed. Examples of such additives include stabilizers, lubricants, cross-linking agents, anti-blocking agents, antioxidants, dyes, pigments, and ultraviolet absorbers.

  In the polyester film of the present invention, the shrinkage in the film length direction (MD) when heat-treated at 150 ° C. for 30 minutes needs to be 0.7% or less, preferably 0.5% or less, more preferably Is 0.3% or less, and the shrinkage ratio under the same condition in the width direction (TD) needs to be 1.0% or less, preferably 0.8% or less, more preferably 0.5% or less. is there. When the heat shrinkage rate of the polyester film exceeds the above upper limit value, that is, when the film is in a more shrinkable state, an acrylic resin, an olefin resin, an aluminum foil, etc., and a film made of a composition other than polyester, In the drying process of applying ink, it shrinks, and processing defects such as wrinkles, sagging, and curls are likely to occur.

  In the present invention, the haze of the film needs to be 3.0% or less, preferably 2.0% or less. When the haze is higher than 3.0%, the transparency is lowered, which is not preferable for use in optical applications.

  In the present invention, a polyester chip 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 to be melted. Next, the molten polymer is extruded from a die and rapidly cooled and solidified on a rotary cooling drum so that the temperature is equal to or lower than the glass transition point 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. 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 from 70 to 140 ° C, preferably from 80 to 120 ° C, and the stretching ratio is usually from 2.0 to 7.0 times, preferably from 3.0 to 6.0 times. Next, the film is stretched in a direction orthogonal to the first-stage stretching direction. The stretching temperature is usually 90 to 160 ° C., and the stretching ratio is usually 2.0 to 7.0 times, preferably 3.0 to 6.0 times. 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. When the intrinsic viscosity of the polyester resin is low, breakage is likely to occur in the stretching step, and it may be necessary to lower the stretch ratio in order not to cause breakage. For example, the lateral stretch ratio is preferably 4.4 times or less. .

  The polyester film of the present invention may be provided with a coating layer. That is, you may perform what is called the application | coating extending | stretching method (in-line coating) which processes the film surface during the extending | stretching process of the above-mentioned polyester film.

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

  As a coating method of the coating agent, a reverse roll coater, a gravure coater, a rod coater, an air doctor coater, or a coating apparatus other than these can be used.

  In addition, in order to improve the applicability | paintability and adhesiveness to the film of a coating agent, you may give a chemical process and an electrical discharge process to a film before application | coating. Further, in order to further improve the surface characteristics, a discharge treatment may be performed after the coating layer is formed.

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

  In addition, you may coat by the method called offline coating which coats after manufacture of a film as needed. The coating material may be either water-based and / or solvent-based in the case of off-line coating.

  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. Various physical properties and characteristics are measured or defined as follows. In the examples, “%” means “% by weight”.

(1) Intrinsic viscosity [dl / g]
1 g of a measurement sample is precisely weighed and dissolved in a solvent of phenol / tetrachloroethane = 50/50 (parts by weight) to prepare a solution having a concentration of 0.01 g / cm ³ , and a relative viscosity ηr with the solvent at 30 ° C. The intrinsic viscosity: IV [dl / g] was determined. The Huggins constant was assumed to be 0.33.

(2) Heat shrinkage [%]
It calculated by following Formula by heat-processing for 30 minutes in 150 degreeC atmosphere in a tension | tensile_strength state, and measuring the length of the sample before and behind that. Evaluation was made with respect to the longitudinal direction (MD) and the width direction (TD).
Heat shrinkage (%) = (L1-L0) / L0 × 100
(In the above formula, L1 is the sample length (mm) before heat treatment, and L0 is the sample length (mm) after heat treatment)

(3) Measurement of film haze The haze of a film was measured using the Nippon Denshoku Industries Co., Ltd. haze meter.

(4) Scratch number evaluation (i) Scratch detection Ten sample film pieces of 100 mm × 100 mm were used with a three-dimensional shape measuring device (Ryoka System Co., Ltd. Micromap MM537N-M100), wavelength 550 nm, WAVE mode, objective Under the measurement condition of 10 times the lens, observation was made from the direction perpendicular to the surface of the test piece, and defects due to scratches recognized as having a size of 50 μm or more were detected. The evaluation was made for 24 hours after the start of film formation.

(Ii) Scratch size measurement Using the three-dimensional shape measuring apparatus (Ryoka System Co., Ltd. micromap MM537N-M100), the test piece was measured under the measurement conditions of wavelength 550 nm, WAVE mode, and objective lens 10 times. Measure the size of the scratch.
When observed from the direction perpendicular to the film surface, the concavity and convexity of scratches within 50 μm are considered as the same scratch, and the length and width of the rectangle with the smallest area covering the outermost part of those scratches is the length of the scratch. And width. Then, the depth (difference in height between the highest and lowest scratches) and the length are measured. From this result, the number of all scratches having a depth of 1 μm or more and a length of 3 mm or more was determined, the unit was converted to “pieces / m 2”, and the determination was made according to the following criteria.
(Criteria)
◎: 20 pieces / m ² or less ○: 21-40 pieces / m ²
Δ: 41 to 100 / m ²
×: 101 pieces / m ² or more Δ is a practically usable level.

(5) Productivity evaluation The ease of breaking in film production was evaluated by the frequency of breaking.
<Evaluation criteria for ease of fracture>
◯: The number of breaks is 1 or less during continuous 10-hour film formation.
×: The number of breaks during the continuous 10-hour film formation is 2 times or more and 4 times or less XX: The number of breaks during the continuous 10-hour film formation is 5 times or more. It is a usable level.
(6) Ease of inspection <Manufacture of laminate (release film with polarizing plate)>
<Manufacture of release film>
In the sample film, after applying the following release layer composition on the coating layer by the reverse gravure coating method so that the coating amount (after drying) is 0.1 g / m 2, Heat treated for 2 seconds.

(Releasing layer composition)
Curing type silicone resin (KS-847H: manufactured by Shin-Etsu Chemical) 100 parts Curing agent (PL-50T: manufactured by Shin-Etsu Chemical) 1 part MEK / toluene mixed solvent (mixing ratio is 1: 1) 1500 parts

  Next, on the release layer of the obtained release film, a coating liquid composed of the following adhesive layer forming composition was applied, and then heat-treated at 100 ° C. for 5 minutes using a hot air circulation furnace. An adhesive layer having a coating amount (after drying) of 25 μm was obtained.

<Adhesive layer forming composition>
Acrylate ester copolymer (Mw = 540000 Mn = 67000 Mw / Mn = 8) obtained by random copolymerization of three components of 75 parts by mass of 2-ethylhexyl acrylate, 20 parts by mass of vinyl acetate, and 5 parts by mass of acrylic acid. An adhesive layer was formed by mixing 20 g of 4-phenylbenzophenone as a photopolymerizable initiator with respect to 1 kg of (Tg-50 ° C.). Thereafter, a polarizing plate was bonded to the exposed adhesive layer surface to obtain a laminate. When producing a laminated body, the black metal powder (foreign matter) with a magnitude | size of 50 micrometers or more was mixed so that it might become 50 piece / m <2> between the adhesion layer and the release film. Using the thus obtained release film with a polarizing plate mixed with foreign substances, white light was irradiated from the release film side, visually inspected, and judged according to the following criteria.
<Criteria>
○: Good foreign body recognition (a level that is practically acceptable)
X: Foreign object cognitive deficiency (practical problem level)
(7) Film flatness evaluation After providing the release layer on the sample film in the item (6), the flatness of the release film was determined according to the following criteria.
<Criteria>
○: No wrinkles or sagging, good flatness (practical problem level)
X: Wrinkles and sagging occur. Inferior flatness (practical problem level)

Example 1:
(Polyester chip manufacturing method)
Take 100 parts of dimethyl terephthalate, 70 parts of ethylene glycol, and 0.07 part of calcium acetate monohydrate in a reactor, heat up the temperature and distill off methanol to conduct a transesterification reaction. In short, the temperature was raised to 230 ° C., and the transesterification reaction was substantially completed.

  Next, 0.04 part of phosphoric acid and 0.035 part of antimony trioxide were added and polymerized in accordance with a conventional method. That is, the reaction temperature was gradually raised to finally 280 ° C., while the pressure was gradually reduced to finally 0.05 mmHg. After the start of the reaction, the reaction was terminated at a time corresponding to an intrinsic viscosity of 0.64 due to a change in the stirring power of the reaction vessel, and a polyester (A) was obtained by converting into chips according to a conventional method. The solution viscosity IV of the obtained polyester chip was 0.64.

(Method for producing polyester B)
When manufacturing the said polyester (A), reaction was complete | finished at the time corresponded to intrinsic viscosity 0.51 by the change of the stirring power of a reaction tank, and it chipped according to the conventional method, and obtained polyester (B). The solution viscosity IV of the obtained polyester chip was 0.51.

(Method for producing polyester C)
When manufacturing the said polyester (A), reaction was complete | finished at the time corresponded to intrinsic viscosity 0.45 by the change of the stirring power of a reaction tank, and it chipped according to the conventional method, and obtained polyester (C). The solution viscosity IV of the obtained polyester chip was 0.45.

(Method for producing polyester D)
When manufacturing the said polyester (A), 6000 ppm of amorphous silica with an average particle diameter of 3.2 micrometers was added, and polyester (D) was created.

(Manufacture of polyester film)
A mixed raw material obtained by mixing the polyesters (A) and (B) at a ratio of 45.0% and 55.0%, respectively, is used as a raw material for the B layer, and each of the polyesters (A), (B), and (D) is 40 0.0%, 50.0%, and 10.0% of the mixed raw materials are used as the raw material for the A layer, and the raw materials for the A layer and the B layer are melt-extruded by separate melt extruders (A / B). / A) A two-layer, three-layer amorphous sheet was obtained. Subsequently, the sheet was coextruded on a cooled casting drum and solidified by cooling to obtain a non-oriented sheet. Subsequently, the sheet was coextruded on a cooled casting drum and solidified by cooling to obtain a non-oriented sheet. Next, the film was stretched 3.0 times in the longitudinal direction at 90 ° C., and further subjected to a preheating step in the tenter, 4.1 times in the lateral direction at 130 ° C., and heat-treated at 230 ° C. for 10 seconds to form a film forming machine. A polyester film having a thickness of 125 μm was obtained by winding the film with a sash. The thickness constitution of this film was 7.5 μm / 110 μm / 7.5 μm.

Example 2:
In Example 1, polyester (B) was used as the raw material for layer B, and polyester (B) and (D) were mixed at a rate of 90.0% and 10.0%, respectively, as the raw material for layer A. A polyester film was obtained in the same manner as in Example 1 except that was used.

Comparative Example 1:
In Example 1, the polyester (A) is used as the raw material for the B layer, and the raw material obtained by mixing the polyester polyesters (A) and (D) at a ratio of 90% and 10%, respectively, as the raw material for the A layer. Except for this, a polyester film was obtained in the same manner as in Example 1.

Comparative Example 2:
In Example 1, a mixed raw material in which polyesters (A) and (B) were mixed at a ratio of 20.0% and 80.0%, respectively, was used as the raw material for the B layer, and the polyester (A ), (B), and (D) were obtained in the same manner as in Example 1 except that raw materials mixed at a ratio of 15.0%, 65.0%, and 20.0% were used to obtain a polyester film.

Comparative Example 3:
In Example 1, a polyester film was obtained in the same manner as in Example 1 except that the film was stretched 3.1 times in the longitudinal direction and 4.5 times in the transverse direction.

Comparative Example 4:
In Example 1, the raw material in which the polyesters (B) and (D) were mixed at a ratio of 90% and 10%, respectively, was melt-extruded by a melt extruder to obtain an amorphous sheet. A polyester film was obtained.

Comparative Example 5:
In Example 1, the raw material in which the polyesters (A) and (B) were mixed at a ratio of 45% and 55%, respectively, was melt-extruded by a melt extruder to obtain an amorphous sheet. A polyester film was obtained.

Comparative Example 6:
In Example 1, polyester (C) was used as the raw material for layer B, and polyester (C) and (D) were mixed at a rate of 90.0% and 10.0%, respectively, as the raw material for layer A. Was used to obtain a polyester film in the same manner as in Example 1, but the film could not be obtained due to frequent breakage.

Comparative Example 7:
The film obtained in Comparative Example 1 was further annealed offline at 180 ° C. for 1 minute. Although the obtained film had good heat shrinkage and flatness, the number of processing steps was increased by one because the annealing treatment step was necessary.

  The obtained results are summarized in Tables 1 and 2 below.

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

Claims (1)

It is a laminated polyester film comprising at least three layers, the intrinsic viscosity (IV) of the film is 0.55 dl / g or less, and the shrinkage in the film length direction (MD) after heat treatment at 150 ° C. for 30 minutes is 0. A laminated polyester film, characterized in that it is 7% or less, the shrinkage rate under the same conditions in the film width direction (TD) is 1.0% or less, and the haze of the film is 3.0% or less.