阅读说明：本技术 高度透明的光学膜 (Highly transparent optical film ) 是由 金昌柱 林圣植 李圭锡 洪性熙 于 2019-01-07 设计创作，主要内容包括：本发明可以提供这样制造的高度透明的光学膜：在作为常用的聚酯膜的聚对苯二甲酸乙二醇酯(PET)中使用折射率没有差异的颗粒,由此具有1.5％或更小的雾度以及对肉眼不可见的颗粒以便具有高透明性,由此适用于光学用途并且能够通过形成4nm或更大的粗糙度来改善卷绕性。(The present invention can provide a highly transparent optical film manufactured by: particles having no difference in refractive index are used in polyethylene terephthalate (PET), which is a commonly used polyester film, thereby having a haze of 1.5% or less and particles invisible to the naked eye so as to have high transparency, thereby being suitable for optical use and being capable of improving winding properties by forming a roughness of 4nm or more.)

1. A highly transparent optical film comprising particles,

wherein the difference in refractive index between the particles and the film substrate component is 0.1 or less, and

the particles have a major diameter/minor diameter ratio of 1.0 to 1.5 or less.

2. The highly transparent optical film according to claim 1, wherein the film substrate component is a polyethylene terephthalate resin.

3. The highly transparent optical film of claim 1, wherein the particles are barium sulfate (BaSO)₄) Calcium carbonate (CaCO)₃) And polystyrene.

4. The highly transparent optical film of claim 1, wherein the particles have a major diameter of 0.5 to 3 μ ι η.

5. The highly transparent optical film according to claim 1, wherein the content of the particles is from 0.0005 to 0.005% by weight based on the total weight of the resin composition.

6. The highly transparent optical film according to any one of claims 1 to 5, wherein the film has a two-dimensional surface roughness (Ra) value of 4nm or more and a haze value of 1.5% or less.

Technical Field

The present invention relates to a highly transparent optical film, and more particularly, to a highly transparent optical film exhibiting excellent transparency (which has low haze and low granular sensation visible to the naked eye), and exhibiting excellent winding characteristics and stable granular shape even after film preparation.

Background

In general, polyethylene terephthalate (PET), which is a multipurpose polymer, is generally used as a polyester film for liquid crystal displays, and has been applied to various uses such as reflectors, diffusers, prism sheets, and the like.

Although these PET films have good overall physical properties (e.g., heat resistance, weather resistance, transparency, etc.) and are easy to process, there are disadvantages in that: when the film is prepared with a single PET material, there is no roughness, causing deterioration in its workability, resulting in difficulty in winding.

Therefore, the problem of coiling is typically solved by adding particles to the PET or coating solution on the PET to form roughness thereon; however, there is a potential concern that the transparency of the product is low due to the visibility of particles in the optical film which requires high transparency (patent document 1).

Accordingly, the present inventors have completed the present invention with a design to reduce the difference in refractive index between the film and the particle component while improving the winding characteristics and transparency as a result of efforts to solve the problems of the polyester film used for the conventional liquid crystal display.

Disclosure of Invention

Technical problem

The present invention is directed to solving the problems as described above, and an object of the present invention is to provide a highly transparent optical film exhibiting excellent transparency as well as excellent winding characteristics and stable particle shape even after film production.

The above objects and advantages and other objects and advantages of the present invention will become more apparent from the following description of the preferred embodiments.

Technical scheme

The above object is achieved by a highly transparent optical film comprising particles, wherein the difference in refractive index between the particles and the film base component is 0.1 or less, and the ratio of the major diameter/minor diameter of the particles is 1.0 to 1.5 or less.

Here, the film base component is polyethylene terephthalate resin.

Preferably, the particles are barium sulfate (BaSO)₄) Calcium carbonate (CaCO)₃) And polystyrene.

Preferably, the particles have a major diameter of 0.5 μm to 3 μm.

Preferably, the content of the particles is 0.0005 wt% to 0.005 wt% based on the total weight of the resin composition.

Preferably, the film has a two-dimensional surface roughness (Ra) value of 4nm or more and a haze value of 1.5% or less.

Effects of the invention

The particles having a low haze and a low granular sensation visible to the naked eye of the present invention achieve the effect of various physical properties of a film for a liquid crystal display having excellent transparency, and the effect of having excellent winding properties by forming roughness, and the like.

Further, the present invention provides an effect that the particle shape is stabilized even after the film preparation, and the like.

However, the effects of the present invention are not limited to those described above, and additional effects not mentioned above will be clearly understood from the following description by those of ordinary skill in the art.

Drawings

Fig. 1 is a schematic cross-sectional view of a highly transparent optical film according to a preferred embodiment of the present invention.

Detailed Description

Hereinafter, the present invention will be described in detail with reference to embodiments of the present invention and the accompanying drawings. It will be apparent to those of ordinary skill in the art that these embodiments are presented by way of example only to describe the present invention in more detail, and the scope of the present invention is not limited by such embodiments.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In case of conflict, the present specification, including definitions of terms, shall control. In addition, although other methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described herein.

In describing and/or claiming the present invention, the term "copolymer" is used to refer to a polymer formed by copolymerizing two or more monomers. Such copolymers include copolymers, terpolymers or higher order copolymers.

A highly transparent optical film according to one aspect of the present invention is a highly transparent optical film comprising particles, in which a refractive index difference between the particles and a film base component may be 0.1 or less, and a ratio of a major diameter/minor diameter of the particles may be 1.0 to 1.5 or less. This is because if the ratio of the large diameter/small diameter of the particles exceeds 1.5 in this case, the roughness to be achieved in the present invention cannot be ensured.

Here, the ratio of the large diameter/small diameter (hereinafter, referred to as aspect ratio) is determined by observation using an electron microscope. The maximum diameter of the particle is considered to be the major diameter, and the maximum diameter in the direction orthogonal to the maximum diameter is considered to be the minor diameter. Specifically, the produced film was cut at the top thereof (cross section sectioning technique), photographs were taken at 5000-fold magnification using an electron scanning microscope (S-4800) from Hitachi ltd, japan, large and small diameters were measured for 10 particles, and data was obtained as an average of the large diameter/small diameter.

The present invention will be described in detail by a method for manufacturing a highly transparent optical film according to another aspect of the present invention.

The method for manufacturing a film according to the present invention may include five (5) steps as follows:

1) step 1 of producing an unstretched sheet by melt-extruding a raw material composition containing a polyester resin as a main component and then forming it into a sheet shape.

2) Step 2 of cooling the non-stretched sheet in the casting drum.

3) Step 3 of uniaxially stretching the cooled sheet.

4) Step 4 of biaxially stretching the film which has been uniaxially stretched.

5) And (5) heat-treating the biaxially stretched film.

Step 1 is a step of manufacturing an unstretched sheet by melt-extruding a raw material composition containing a polyester resin as a main component and then forming it into a sheet shape.

In one embodiment, the polyester resin used as the base resin of the polyester film may include a dicarboxylic acid component and a diol component; as the dicarboxylic acid component, it may be preferable to use terephthalic acid, triphenylamine dicarboxylic acid, isophthalic acid, 2, 6-naphthalenedicarboxylic acid, 2, 7-anthracenedicarboxylic acid, 2, 7-pyrenedicarboxylic acid, 4, 4' -diphenyldicarboxylic acid, adipic acid, or sebacic acid; and the diol component may be selected from ethylene glycol, 1, 4-butanediol, 1, 4-cyclohexanedimethanol, 1, 6-hexanediol, etc.

Further, if polyethylene terephthalate is used as the base resin for the film base component, it may be desirable to use a copolyester containing a copolymerization component preferably from 1 to 15 mol%, more preferably from 3 to 14 mol%, and most preferably from 5 to 13 mol%, based on the entire dicarboxylic acid component, or a copolyester containing a copolymerization component preferably from 1 to 15 mol%, more preferably from 3 to 14 mol%, and most preferably from 5 to 13 mol%, based on the entire diol component, from the viewpoint of film production stability. In this case, if the copolymerization component is less than 1 mol%, it is difficult to produce a film having good physical properties, and if it exceeds 15 mol%, it is also difficult to produce a film. Further, the dicarboxylic acid component as the copolymerization component may be selected from isophthalic acid, 2, 6-naphthalenedicarboxylic acid, 4' -diphenyldicarboxylic acid, adipic acid, and sebacic acid, and the diol component may be selected from ethylene glycol, 1, 4-butanediol, 1, 4-cyclohexanedimethanol, 1, 6-hexanediol, and the like. Further, isophthalic acid or 2, 6-naphthalenedicarboxylic acid in the copolymerization component is preferably used to obtain good film preparation characteristics, and 1, 4-cyclohexanedimethanol, which has the effect of stabilizing the dispersion state of the immiscible resin, is preferably used. The copolymer according to one embodiment obtained by this method preferably satisfies a glass transition temperature of 80 ℃ to 150 ℃. This is because, in this case, if the glass transition temperature is less than 80 ℃, the copolymer is not suitable for use in display applications heated to 60 ℃ or higher, whereas if the glass transition temperature exceeds 150 ℃, it is difficult to prepare a film due to a tensile load.

Further, various additives such as a fluorescent whitening agent, a crosslinking agent, a heat stabilizer, an antioxidant stabilizer, an ultraviolet absorber, an organic lubricant, inorganic fine particles, a filler, a light-resistant agent, an antistatic agent, a nucleating agent, a dye, a dispersant, a coupling agent, and the like may be added to the raw material composition within a range not to impair the effects of the present invention.

In addition, the particles (10) having compatibility with the polyester resin (20) are used in the raw material composition. In this case, at least one of barium sulfate, calcium carbonate, and polystyrene is preferably used as the particles in the present invention. In other words, these may be used alone or in a combination of two or more.

Further, the content of the particles is preferably 0.0005 to 0.005% by weight, and more preferably 0.001 to 0.002% by weight, relative to the total weight of the resin composition. This is because, in this case, if the content is less than 0.0005 wt%, there are disadvantages as follows: measurement errors become large due to too small amount and formation of roughness is insufficient, which in turn causes insignificant effect of improving the winding characteristics, while if the content exceeds 0.005 wt%, agglomeration of particles resulting from excessive addition is considered as a defect in the film, which results in higher haze and easier visibility of particles to the naked eye, thereby causing the film to be unsuitable for use as an optical film.

Further, it is preferable that the large diameter of the particles is 0.5 μm to 3 μm, and this is because if the large diameter is less than 0.5 μm, the formation of roughness is insufficient, which hardly ensures excellent winding characteristics, and if it exceeds 3 μm, there is a possibility of being regarded as a defect in the film.

Further, it is preferable that the difference in refractive index between the particles and the film base component is 0.1 or less, and the aspect ratio (ratio of major diameter/minor diameter) of the particles is 1.0 to 1.5 or less.

The unstretched sheet produced in step 1 may be a single layer or a multilayer of two or more layers.

Next, step 2 is a step of cooling the unstretched sheet formed in step 1 in a casting drum. Since this step is widely known to those of ordinary skill in the art, a detailed description thereof will not be set forth herein.

Next, step 3 is a step of producing a uniaxially stretched film by uniaxially stretching the cooled unstretched sheet, and is a step of heating the cooled unstretched sheet by heating means such as roller heating or infrared heating (heater) and first stretching it in the longitudinal direction to thereby obtain a uniaxially stretched film. The stretching is preferably performed by using a difference in peripheral speed of two or more rolls, the stretching temperature is set to a temperature equal to or higher than the glass transition temperature (Tg) of the polyester resin, and the stretching ratio is preferably 3.0 times to 5.0 times. If the stretching ratio is less than 3.0 times, the desired optical characteristics cannot be sufficiently obtained, whereas if the stretching ratio is more than 5.0 times, the film preparation stability becomes unfavorable.

Next, step 4 is a step of producing a biaxially stretched film by biaxially stretching the uniaxially stretched film, and is a step of successively biaxially stretching the film that has been uniaxially stretched in the longitudinal direction in step 3 in both the longitudinal direction and a direction perpendicular thereto (hereinafter, also referred to as "width direction"). At this time, the stretching in the width direction is started at a temperature higher than the glass transition temperature (Tg) of the polyester resin, and is performed while raising the temperature to 5 to 70 ℃ higher than the glass transition temperature (Tg). The temperature increase during the stretching process in the width direction may be continuous or stepwise (sequential), but is usually performed sequentially. For example, a stretching region in the width direction of the tenter is divided into plural along the film traveling direction, and the temperature is raised by flowing a heating medium of a predetermined temperature for each region.

Next, step 5 is a step of subjecting the biaxially stretched film to heat treatment, and is for producing a biaxially oriented film by sequentially subjecting the biaxially stretched film to heat treatment such as heat setting, heat relaxation, or the like while advancing the biaxially stretched film. Therefore, in order to complete the crystal orientation of the obtained biaxially stretched film to thereby impart planarity and dimensional stability, the heat treatment is continuously performed in a tenter at a temperature of 150 ℃ to 250 ℃ for 1 second to 30 seconds. If the heat treatment temperature is less than 150 ℃, the crystal orientation is not complete, which in turn adversely affects the strength and elongation of the film, while if it is more than 250 ℃, it is difficult to achieve the desired complete transparency due to excessive crystallization. After the heat treatment, the highly transparent optical film according to the present invention can be obtained by uniformly and slowly cooling the film to room temperature and then winding it. At this time, the relaxation treatment of 3% to 12% may be performed in the width direction or the longitudinal direction as needed during the heat treatment process.

The highly transparent optical film produced by the above-described production method preferably has a two-dimensional surface roughness (Ra) of 4nm or more and a haze value of 1.5% or less.

Hereinafter, the configuration of the present invention and its effect will be described in more detail by embodiments and comparative examples. However, these embodiments are intended to more specifically illustrate the present invention, and the scope of the present invention is not limited thereto.