JP2016199627A - Polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester film that is, since the diffuse transmittance is suppressed and the transparency is also excellent, suitable also for use as a protective film for an adhesive layer, as well as that is also excellent in continuous productivity.SOLUTION: Provided are: a polyester film characterized in containing organic particles having a thermal decomposition temperature of 335°C or more and having a diffuse transmittance of less than 50%; said polyester film characterized in having a total light transmittance of 75% or more; and said polyester film including two or more layers, and at least one layer contains organic particles.SELECTED DRAWING: None

Description

  The present invention relates to a polyester film suitable for a pressure-sensitive adhesive layer protective film with reduced diffuse transmittance.

Films with adhesive layers, such as various adhesive sheets that make up touch panels and process materials for electronic devices, are widely used. To protect the adhesive layers of these sheets and films (hereinafter simply referred to as "adhesive sheets") For the purpose, a polyester film is used as a protective film. In many cases, these pressure-sensitive adhesive sheets are inspected in a state where a protective film is bonded to the pressure-sensitive adhesive layer in order to prevent process contamination and process omission. Therefore, the protective film needs to have a certain degree of transparency while suppressing the diffuse transmittance.

  On the other hand, an unevenness | corrugation can also be formed in the surface of a protective film so that it may not block between adhesive sheets, when an adhesive sheet is wound up with a roll at a protective film. As a method for forming a concavo-convex shape on the surface, a method of incorporating particles into a film is widely known. For example, as in Patent Document 1, there is a method in which inorganic particles typified by silica particles are contained in a film. However, the polyester film containing inorganic particles has a problem that in the stretching process, the inorganic particles are peeled off from the polyester resin to form voids called voids, and light scattering tends to occur, making it unsuitable for a protective film. Further, since inorganic particles are difficult to deform, there is a problem that filter filtration is easily clogged in the melt extrusion process.

  Therefore, there is a method using organic particles instead of inorganic particles. Organic particles are easier to deform than inorganic particles, so that voids are less likely to occur during stretching, and the refractive index is relatively easy to adjust. There is an effect of improving. Furthermore, as in Patent Document 2, for example, even if the particle size is large, there is an advantage that it is difficult to pressurize the organic particles.

Patent No. 4927246 JP 2013-47356 A

  However, when organic particles are used, there is a problem in that the dies of the T dice for forming the sheet are likely to be damaged, and this causes a film streak, which is a fatal defect of the film. In order to avoid this, it is necessary to stop the production operation of the film and clean the base, resulting in a problem that the yield is deteriorated.

The present invention is intended to solve the above problems, and is suitable for the protective film application of the pressure-sensitive adhesive layer because of its low diffusion transmittance and excellent transparency, and also for continuous productivity. It is to provide an excellent polyester film.

  As a result of intensive studies, the present inventor has found that the above problem can be solved by a polyester film containing specific organic particles, and has reached the present invention.

  That is, the present invention is, firstly, a polyester film characterized by containing organic particles having a thermal decomposition temperature of 335 ° C. or higher and having a diffuse transmittance of less than 50%, and secondly, a total light transmission. The polyester film is characterized in that the rate is 75% or more. Third, the polyester film is composed of two or more layers, and at least one layer contains organic particles, and fourth, contains organic particles. The polyester film is characterized in that the thickness of the layer is one quarter or more of the average particle diameter of the organic particles, and fifth, the average particle diameter of the organic particles in the layer containing the organic particles is 0.2 to It is the said polyester film characterized by being 20 micrometers and content being 0.1-8 mass%, Sixth, the sum total of the thickness of the layer containing an organic particle is 1 of the thickness of the whole polyester film. It is the polyester film is 50%.

  ADVANTAGE OF THE INVENTION According to this invention, the polyester film excellent in continuous productivity suitable as a protective film of an adhesive sheet can be provided.

  There is no restriction | limiting in particular as a polyester resin which comprises the polyester film of this invention, For example, a polyethylene terephthalate, a polybutylene terephthalate, a polytrimethylene terephthalate etc. are mentioned. Among these, polyethylene terephthalate can be suitably used because it is excellent in the balance between heat resistance and mechanical properties and excellent in stretchability. Polyethylene terephthalate is usually a method of transesterification from dimethyl terephthalate and ethylene glycol, or a method of melt polymerization or further solid phase polymerization after obtaining an oligomer by direct esterification from terephthalic acid and ethylene glycol. Is obtained.

  The polyester resin can be copolymerized with other components. Other copolymer components include dicarboxylic acid components such as isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, 5-sodium sulfoisophthalic acid, oxalic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, dodecane Examples include acid, dimer acid, maleic anhydride, maleic acid, fumaric acid, itaconic acid, citraconic acid, and mesaconic acid. In addition, as other copolymer components, glycol components include diethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol, cyclohexanedimethanol, and triethylene. Examples include glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, ethylene oxide adducts of bisphenol A and bisphenol S, and the like.

The polyester film of the present invention needs to have a diffuse transmittance of less than 50%, preferably 35% or less, in order to improve the discrimination performance when bonded to an adhesive sheet as a protective film. More preferably, it is 10% or less. If it is 50% or more, it is not preferable because the state of the bonded film cannot be identified. In addition, although there is no special restriction on the low diffuse transmittance, there is almost no difference in performance at 10% or less.
In addition, the polyester film of the present invention preferably has a total light transmittance of 75% or more, more preferably 85% or more. If it is 75% or less, there is a problem in the identification performance, which is not preferable. There is no special limit on the upper limit, but at 85% or more, there is almost no performance difference in identification.

  The polyester film of the present invention needs to contain organic particles in at least one surface layer of the polyester film in order to form surface irregularities for preventing blocking. The organic particles can be contained in the entire film or in at least one layer of two or more coextruded laminated films. This layer containing organic particles is referred to as A layer. Further, from the viewpoint of reducing the diffuse transmittance and the total light transmittance, it is preferable that the layers other than the A layer do not contain particles. However, when the polyester film is formed on the surface layer, the particles are used from the viewpoint of film running. It is preferable to include. If the diffuse transmittance is within the above range, it may be contained regardless of organic particles and inorganic particles. The layers other than the A layer are referred to as a B layer.

The thickness of the layer containing the organic particles of the polyester film of the present invention preferably has a thickness of 1/4 or more of the average particle diameter of the organic particles, and more preferably 1/2 or more. A thickness of less than a quarter is not preferable because the particles cannot be held in the film and easily fall off. An upper limit is not particularly provided, but the diffusion transmittance increases as the thickness increases. Therefore, the upper limit is preferably not more than twice the average particle diameter.
In the polyester film of the present invention, the total thickness of the layers containing organic particles is preferably 1 to 50% of the total thickness of the polyester film, more preferably 5 to 30%, because the diffusion transmittance is lowered. .

    In the present invention, it was found that the cause of the T die die is the decomposition component of the organic particles, and the heat resistance of the organic particles needs to be as follows. That is, the thermal decomposition temperature of the organic particles needs to be 335 ° C. or higher, and more preferably 340 ° C. or higher. Here, the thermal decomposition temperature is a temperature when the weight is reduced by 5% in the thermal analysis (TG / DTA) under a nitrogen atmosphere. When the decomposition temperature is less than 335 ° C., even if the melt extrusion temperature is 280 ° C., the shape of the decomposition gas and particles due to decomposition during melt extrusion deteriorates the operation due to film streaks and bubble discharge due to Mayani. It is not preferable.

  In addition, the component of the organic particle used by this invention may be a single component, and may use 2 or more components simultaneously. Examples include organic particles such as crosslinked acrylic, crosslinked polystyrene, and crosslinked melamine.

  The average particle size of the organic particles used in the present invention is not particularly limited because it varies depending on the intended use of the polyester film, but is preferably in the range of 0.2 μm to 20 μm, and more preferably in the range of 0.5 to 12 μm. When the thickness is 0.2 μm or less, the unevenness of the film surface becomes too low, so that the films are likely to be blocked, and meandering and winding deviation tend to occur. On the other hand, when the thickness is 20 μm or more, film dropping or film cutting is likely to occur.

  The organic particle content in the film of the present invention is not limited as long as the diffuse transmittance is in the range, but specifically, the range of 0.0.01% by mass to 8% by mass is preferable, and 0.1-5 A range of mass% is more preferred. If it is less than 0.01% by mass, there are too few protrusions on the film surface, so that the anti-blocking function cannot be exhibited, and if it exceeds 10% by mass, it becomes difficult to hold the particles in the film. Falls off and the film is easily broken.

The layer containing organic particles may contain a small amount of different kinds of particles within a range not impairing the effects of the present invention. Blocking, meandering and winding deviation can be suppressed. The different types of particles may be organic particles or inorganic particles, but the average particle size of the particles is preferably smaller than the previous organic particles.

Examples of inorganic particles added for the above purpose include silicon oxide, titanium oxide, calcium carbonate, barium sulfate, aluminum oxide, zeolite, kaolin, clay, talc, and mica. Moreover, as an organic particle, organic particles, such as a melamine resin, a polystyrene, an organic silicone resin, an acryl-styrene copolymer, are mentioned, for example. In particular, silicon oxide (silica) is preferable because it has an excellent particle size distribution and is inexpensive.

Next, an example of the manufacturing method of the polyester film of this invention is demonstrated.
In the case where the polyester film of the present invention is a laminated film, a film obtained by stretching and heat-setting in biaxial directions is preferred, in which all layers are extruded by co-extrusion from a die. As a coextrusion method, any of a feed block type or a multi-manifold type may be used.

The polyester A layer containing a predetermined amount of specific organic particles and the B layer other than the A layer are supplied to different melt extrusion apparatuses, and melted at a temperature of the melting point of each polyester resin to (melting point + 40 ° C.), Extruded into a sheet shape by T-die through each filter. Then, the extruded laminated sheet-like body is brought into close contact with a cooling drum whose temperature is adjusted to 30 ° C. or lower by a known method such as an electrostatic application casting method or an air knife method so that the temperature becomes a glass transition temperature or lower. Rapid solidification is performed to obtain an unstretched sheet having a desired thickness. Next, a polyester film excellent in mechanical properties and dimensional stability can be obtained by biaxially stretching the obtained unstretched sheet in the longitudinal direction and the transverse direction. As a biaxial stretching method, a simultaneous biaxial stretching method in which stretching is performed simultaneously in the machine direction and the transverse direction with a tenter type simultaneous biaxial machine, or in a transverse direction with a tenter type transverse stretching machine after stretching in the longitudinal direction with a roll type stretching machine. A sequential biaxial stretching method for stretching can be used.
The draw ratio of the polyester film is preferably 3 times or more, more preferably 4 to 20 times, and still more preferably 6 to 15 times. When the draw ratio exceeds 20 times, the void becomes too large, and the predetermined diffuse transmittance cannot be achieved. In addition to this, the frequency of breakage of the film increases, which is not preferable.

  The stretching temperature is preferably in the range of (glass transition temperature + 5 ° C.) to (glass transition temperature + 60 ° C.), more preferably in the range of (glass transition temperature + 15 ° C.) to (glass transition temperature + 55 ° C.). This is because if the film is stretched in the vicinity of the glass transition temperature, voids are likely to be large, and diffusion transmittance cannot be achieved. The film after stretching of the glass transition temperature is heat treated for several seconds at a temperature of 150 ° C. to (polyester melting point−5 ° C.) in a tenter with a relaxation rate of 0 to 10% in the machine direction and transverse direction, and then cooled to room temperature. Winding is performed at a speed of 20 to 200 m / min. Thereby, a film having a desired thickness can be obtained.

  The heat treatment after stretching described above is a process necessary for reducing the thermal shrinkage of the polyester film. As a heat treatment method, a method of blowing hot air, a method of irradiating infrared rays, a method of irradiating microwaves, or the like can be used. Among them, a method of blowing hot air is preferable because it can be heated uniformly and accurately. Although the thickness of a film is not specifically limited, The range of 5-500 micrometers is preferable.

  The present invention will be specifically described below with reference to examples.

1. Measurement method (1) Average particle diameter of particles The particle diameter was measured with a laser diffraction / scattering particle diameter measuring machine (SALD-7100 manufactured by Shimadzu Corporation), and the volume average particle diameter was defined as the average particle diameter of the particles. The measurement solution was prepared by dissolving the master batch chip in a mixed solvent of phenol / tetrachloroethane = 50/50 (mass ratio) so that the diffracted / scattered light intensity was 40 to 60%, and this was used as the measurement solution. .

(2) Diffuse transmittance and total light transmittance The diffuse transmittance and the total light transmittance of the film were measured with a ball turbidimeter NDH-300A manufactured by Nippon Denshoku Industries Co., Ltd.

(3) Thermal decomposition temperature of organic particles After drying the organic particles under reduced pressure at 60 ° C. for 4 hours, using a differential thermothermal gravimetric simultaneous measurement device (STG Nanotechnology, “TG / DTA 7200”), 200 mL / min. The temperature was raised from 30 ° C. to 400 ° C. at 20 ° C./min in a nitrogen atmosphere. The temperature at which the mass decreased by 5 mass% with respect to the mass before the temperature elevation was defined as the thermal decomposition temperature.

(4) Surface roughness Sa, Sz
Using a non-contact type surface roughness measuring device (Taylor Hobson Tarisurf CCI6000 type), the sample fixed on the slide glass was actually measured with an objective lens 20 times, and a robust Gaussian filter 0.25 mm was used. Analyzing the surface roughness of the sample, the arithmetic average value of the deviation from the average value is defined as the centerline average roughness Sa (μm), and the average value obtained by adding the top five heights and the top five depths is 10 The point average height Sz was used.
(5) Operational polyester film productivity was evaluated according to the following criteria.
○: No problem including film appearance in operation for 15 hours or more.
X: In an operation for less than 15 hours, the film could not be produced due to film breakage, film streaks, and roll contamination.

Each masterbatch containing particles was prepared as follows and used to form the A layer.
(M-1) Polyester terephthalate pellets having an intrinsic viscosity of 0.68 dl / g and cross-linked acrylic particles having an average particle size of 10.1 μm and a 5% thermal decomposition temperature of 341 ° C. are melt blended in a biaxial kneader, and a conventional method is used. A master batch containing the crosslinked acrylic particles was obtained by discharging and pelletizing.
(M-2) A master batch was obtained in the same manner as M-1, except that crosslinked acrylic particles having an average particle size of 5.1 μm and a 5% thermal decomposition temperature of 341 ° C. were used.
(M-3) A blended acrylic particle having an average particle size of 5.1 μm and a 5% pyrolysis temperature of 341 ° C. and silica particles having an average particle size of 2.6 μm were melt blended in a biaxial kneader in the same manner as M-1. Thus, a master batch containing crosslinked acrylic particles and silica particles was obtained.
(M-4) A master batch was obtained in the same manner as M-1, except that crosslinked acrylic particles having an average particle size of 0.6 μm and a 5% thermal decomposition temperature of 337 ° C. were used.
(M-5) A master batch was obtained in the same manner as M-1, except that crosslinked polystyrene particles having an average particle size of 9.9 μm and a 5% thermal decomposition temperature of 352 ° C. were used.
(M-6) A master batch was obtained in the same manner as M-1, except that crosslinked styrene-acrylic particles having an average particle size of 10.0 μm and a 5% thermal decomposition temperature of 331 ° C. were used.
(M-7) A master batch was obtained in the same manner as M-1 except that silica particles having an average particle diameter of 10.0 μm were used.
(M-8) A master batch was obtained in the same manner as M-1, except that crosslinked acrylic particles having an average particle diameter of 21.9 μm and a thermal decomposition temperature of 341 ° C. were used.
(M-9) A master batch was obtained in the same manner as M-1, except that silica particles having an average particle diameter of 2.6 μm were used.

Example 1
As a layer A, after blending the master batch M-1 and polyethylene terephthalate pellets having an intrinsic viscosity of 0.69 dl / g not containing particles so that the content of particles is 2.5 mass%, Dry, melt in an extruder, and as layer B, masterbatch M-9 so that the content of particles is 0.05% by mass, and polyethylene terephthalate pellets with an intrinsic viscosity of 0.69 dl / g that do not contain particles After being blended together, the mixture is dried by a conventional method, melted in a sub-extruder, and the molten resin for forming the A layer and the molten resin for forming the B layer are merged in the feed block. Then, the film was extruded from a T die and brought into close contact with an electrostatic application method on a cooling drum whose surface temperature was adjusted to 20 ° C., and rapidly cooled to obtain an unstretched film having a thickness of 650 μm.
Subsequently, after preheating with a preheating roll group whose temperature is adjusted to 90 ° C., the film is longitudinally stretched 3.5 times by changing the peripheral speed between the stretching rolls adjusted to 90 ° C. to obtain a longitudinally stretched film having a thickness of 180 μm. It was.
Subsequently, the longitudinally stretched film is guided to a tenter type stretching machine, and is stretched 5 times at a preheating temperature of 90 ° C. and a stretching temperature of 120 ° C., followed by heat treatment at 245 ° C., and a relaxation treatment of 3% in the transverse direction at 200 ° C. Went.
The film coming out of the tenter was wound up at a film speed of 90 m / min. Thus, a biaxially stretched polyester film having a thickness of 38 μm (A layer / B layer = 10/28) was obtained. The evaluation results of the obtained film are shown in Table 1.

Examples 2-7, Comparative Examples 1-5
As shown in Table 1, a film roll was obtained in the same manner as in Example 1 except that the kind and content of the inert particles were changed. In Examples 3 and 5, a two-layer / three-layer film structure of A / B / A was used, and in Example 6, a single-layer film structure having only an A layer was used.

Since Examples 1-7 were polyester films formed with predetermined organic particles, they were excellent in diffuse transmittance and total light transmittance, and could be stably operated for a long time.
(Comparative Examples 1 and 4)
The diffuse transmittance exceeded 50%, and the polyester film was inferior in discrimination performance.
(Comparative Example 2)
Since the thickness of the A layer was too thin, particles dropped off. There was also a problem in operability due to contamination of the production line due to particle dropping.
(Comparative Example 3)
About 9 hours of production, film streaks occurred and production was interrupted.
(Comparative Example 5)
Since the average particle diameter of the organic particles was too large, the film was frequently broken, and the intended film could not be obtained.

Claims (6)

A polyester film characterized by containing organic particles having a thermal decomposition temperature of 335 ° C. or higher and a diffuse transmittance of less than 50%. The polyester film according to claim 1, wherein the total light transmittance is 75% or more. The polyester film according to claim 1 or 2, comprising at least two layers, wherein at least one layer contains organic particles. The polyester film according to any one of claims 1 to 3, wherein the thickness of the layer containing organic particles is at least one-fourth of the average particle diameter of the organic particles. The average particle diameter of the organic particles in the layer containing the organic particles is 0.2 to 20 µm, and the content thereof is 0.1 to 8% by mass. Polyester film. The polyester film according to claim 3, wherein the total thickness of the layers containing organic particles is 1% to 50% of the thickness of the entire polyester film.