JP6957858B2 - Laminated polyester film for optics, laminates and touch panels - Google Patents

Description

The present invention relates to a laminated polyester film for optics, and is used as a base material for an optical member such as a touch panel.

Biaxially stretched polyester films typified by polyethylene terephthalate and polyethylene naphthalate have excellent properties such as mechanical strength, dimensional stability, flatness, heat resistance, chemical resistance, optical properties, and cost performance. Because it is also excellent, it is used for various purposes.

In recent years, it has been widely used as a base film for transparent conductive films used in touch panel display devices, base films for prism sheets used in liquid crystal displays, and optical films for so-called flat displays such as cathode ray tubes, LCDs, and PDPs. Has been done.

In particular, mobile phones (smartphones) and tablet PCs with a touch panel function, which have been in increasing demand in recent years, are more likely to be used outdoors because they can be easily carried, and the time of direct exposure to sunlight is increasing. ing. The sun's rays contain ultraviolet rays, and if they are exposed to the sun's rays for a long time, the internal components of the touch panel will deteriorate. Specifically, there may be a problem that the film base material itself turns yellow, or bubbles are generated from the adhesive material or the like, which causes problems in visibility and adhesion of the laminate.

As the touch panel display member, a film with a hard coat treatment on both sides or one side and a transparent conductive film (ITO film) on one side are provided in that the durability at the time of pen input is good and the writing quality is good due to the cushioning effect of the adhesive. A film obtained by adhering and laminating the other surface of the film with an adhesive layer is widely used. In addition, an adhesive is used to bond the image display component to other components.

Since ordinary polyester does not have the ability to absorb ultraviolet rays, exposure to ultraviolet rays outdoors for a long period of time causes deterioration of the polyester film, but in particular, bubbles are generated due to deterioration of the adhesive material, and visibility is improved. UV resistance is rigorously required, as deterioration can be a problem.

As a method for improving the light resistance of the polyester film, as in JP-A-2009-14886 (Patent Document 1), studies have been conducted in which an ultraviolet absorber is kneaded into the polyester film itself to have an ultraviolet blocking function. There is. As mobile phones and tablet PCs become smaller, lighter, and thinner, thinning of the base material of the transparent conductive layer is being studied. However, in general, when trying to obtain a polyester film containing a low molecular weight compound and having an ultraviolet absorbing ability, there is a problem that the production line is contaminated due to the bleed-out of the ultraviolet absorber and the post-process line that imparts functionality is contaminated. However, there is a problem that the bleed-out becomes more prominent as the film becomes thinner.

JP-A-2009-14886

The present invention has been made in view of the above circumstances, and the problem to be solved is that deterioration of constituent members, particularly adhesive materials, due to ultraviolet rays when incorporated into a touch panel display as a transparent electrode base material can be sufficiently reduced. Provided is a biaxially stretched polyester film in which bleed-out does not occur.

As a result of diligent studies in view of the above problems, the present inventors have found that the above problems can be easily solved by using a specific polyester film for a transparent electrode base material, and have completed the present invention.

That is, the gist of the present invention is a laminated polyester film composed of at least three layers, when the thickness of the surface layer is Aμm and the content of the ultraviolet absorber contained in the intermediate layer with respect to the entire film is B% by weight. It exists in an optical laminated polyester film characterized by a B / A ratio of 0.20 or more and 1.0 or less.

According to the present invention, as a film for a transparent electrode base material, a polyester film having high durability against ultraviolet rays can be easily and inexpensively provided, and the industrial value of the present invention is high.

Hereinafter, the present invention will be described in more detail.

The polyester referred to in the present invention refers to a polymer obtained by polycondensing one or more dicarboxylic acids and one or more diols. Examples of dicarboxylic acids include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid and 2,7-naphthalenedicarboxylic acid, adipic acid, sebacic acid, and 1,4-cyclohexanedicarboxylic acid. Examples thereof include aliphatic dicarboxylic acids such as acids. Examples of diols include ethylene glycol, trimethylene glycol, tetramethylene glycol, 1,4-cyclohexanedimethanol, neopentyl glycol and the like. In the present invention, polyethylene terephthalate, which is particularly excellent in strength and transparency, is relatively inexpensive, and is widely used in various applications, or polyester in which other ester units are copolymerized by about several mol% is recommended.

It is important that the laminated polyester film of the present invention comprises at least three layers. As long as the gist of the present invention is not exceeded, the number of layers may be four or more, and is not particularly limited.

It is preferable that the layer other than the surface layer of the laminated film of the present invention, that is, the intermediate layer, contains substantially no particles. The term "substantially free" as used herein specifically means that the content of particles is 150 ppm or less. This is because the purpose of adding the particles is to alleviate scratches in the longitudinal stretching step by the roll stretching machine, so that it is meaningless to include the particles in the intermediate layer. Although the use of particles is insignificant, it causes an increase in cost, and depending on the stretching conditions, voids may be formed around the particles to reduce transparency.

Examples of the particles to be blended in the film include silicon oxide, alumina, calcium carbonate, kaolin, titanium oxide, organic particles, and crosslinked polymer fine powder as described in Japanese Patent Publication No. 59-5216. These particles may be used alone or in combination of two or more components. The blending amount of these particles is usually in the range of 5 to 90 wt ppm or less, preferably 20 to 80 wt ppm with respect to the polyester constituting the film. When the content of the particles is small, the surface of the film cannot be made into an appropriate rough surface, and the surface tends to be scratched or the winding characteristics tend to be inferior in the film manufacturing process. Further, when the content of the particles exceeds 90 ppm by weight, the degree of roughening of the film surface becomes too large and the transparency may be impaired.

The average particle size of the particles blended in the polyester film is not particularly limited, but is usually in the range of 0.02 μm to 4.0 μm, preferably 0.6 μm to 2.5 μm. 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 manufacturing process tend to be inferior. On the other hand, when the average particle size exceeds 4.0 μm, the degree of roughening of the film surface may become too large and the film may become hazy.

On the other hand, in order to improve the transparency of the film, when a laminated film having three or more layers is formed, a method in which particles are blended only in the surface layer is also preferably adopted. In this case, the surface layer is at least one of the front and back layers, and of course, particles can be blended in both the front and back layers. The blending amount of the particles in the case of such a laminated film is preferably in the range of 0.01 to 2% by weight, more preferably 0.02 to 1% by weight, based on the polyester constituting the surface layer.

The thickness A of the surface layer of the laminated polyester film of the present invention is preferably 1.5 μm or more. If the thickness A of the surface layer is less than 1.5 μm, the stiffness of the surface layer becomes small, and the scratch mitigation effect and the slipperiness in the longitudinal stretching step are reduced, which tends to be unfavorable. On the other hand, from the viewpoint of transparency of the laminated polyester film, the upper limit is preferably 10 μm or less. Above all, from the viewpoint of productivity, the thickness A of the surface layer is more preferably 2 to 8 μm.
As mentioned above, it is more preferable that the ratio of the thickness of the intermediate layer to the total thickness is as large as possible because the particles may reduce the transparency, albeit insignificantly. Further, the thickness of the surface layer is more preferably as thin as possible as long as it exerts a sufficient function for alleviating scratches in the longitudinal stretching step.

When the thickness A of the surface layer is different on both sides of the surface layer, the one having a smaller surface layer is adopted as the thickness A.
When the laminated polyester film laminated structure has four or more layers, the layer containing the ultraviolet absorber is regarded as an intermediate layer, and the layer excluding the intermediate layer is regarded as a surface layer. When the surface layer has a plurality of layers, the total thickness is regarded as the thickness of the surface layer.

It is important that the laminated polyester film of the present invention contains an ultraviolet absorber in the intermediate layer. The ultraviolet absorber used in the present invention is not limited, and specific examples thereof include benzophenone compounds, 1,3,5-triazine compounds, benzoxazine compounds, and the like, and one or more of these. However, when the color tone is taken into consideration, a benzoxazine-based compound that is less likely to have a yellowish tint is preferably used.
Examples of the benzoxazine-based compound used as an ultraviolet absorber include 2,2- (1,4-phenylene) bis [4H-3,1-benzoxazine-4-one].

The content of the ultraviolet absorber is preferably 3.0 to 0.7% by weight, more preferably 2.5 to 0.9% by weight, and 2.0 to 1.1% by weight based on the entire film. % By weight is even more preferred. By satisfying the specified range of the content of the ultraviolet absorber, not only the yellowing of the laminated polyester film can be suppressed, but also sufficient transparency can be ensured.

The laminated polyester film of the present invention does not exclude the inclusion of an ultraviolet absorber in the surface layer, but the content ratio of the ultraviolet absorber in the surface layer is preferably 0.5% by weight or less.

Further, the laminated 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. Further, antioxidants, surfactants, fluorescent whitening agents, lubricants, light-shielding agents, matting agents, and colorants such as dyes and pigments may be blended.

In the laminated polyester film of the present invention, the ultraviolet absorber is contained in any intermediate layer other than the surface layer, and the content thereof is such that the thickness of the surface layer is Aμm and the thickness of the surface layer is Aμm with respect to the entire film of the ultraviolet absorber contained in the intermediate layer. When the content is B% by weight, the B / A ratio is 1.0 or less, preferably 0.8 or less, and more preferably 0.6 or less. When the B / A ratio exceeds 1.0, the ultraviolet absorber tends to bleed out on the surface, which may lead to deterioration of surface functionality such as deterioration of adhesiveness. On the other hand, the lower limit of the B / A ratio is 0.2 or more, preferably 0.3 or more, from the viewpoint of ultraviolet absorption and the like. If the B / A value is less than 0.2, the effect of absorbing ultraviolet rays is insufficient, and therefore, for example, when incorporated into a touch panel display as a transparent electrode base material, deterioration of constituent members due to ultraviolet rays occurs.

The laminated polyester film of the present invention has transparency, and the transparency referred to in the present invention refers to the property that the optical image obtained by separating the films is clear, and as practical property indexes, haze, 360 nm and 380 nm. It can be evaluated by the light transmittance in.

In general, polyester film is rarely used alone, and a hard coat is provided on the surface for protection, or it is attached to glass or the like with an adhesive, so that surface smoothness and scratch resistance are required. .. Therefore, in the present invention, it is preferable that the light transmittance at haze, 360 nm and 380 nm is in a specific range.

The laminated polyester film of the present invention has a light transmittance of preferably 18.0% or less, more preferably 10.0% or less, still more preferably 3.0% or less at a wavelength of 380 nm. The light transmittance at a wavelength of 360 nm is preferably 5.0% or less, more preferably 1.0% or less, and even more preferably 0.5%. When the light transmittance at a wavelength of 380 nm is greater than 18.0%, or when the light transmittance at a wavelength of 360 nm is greater than 5.0%, the adhesives that attach the functional sheets to each other by the ultraviolet rays transmitted through the polyester film. The effect of preventing the deterioration of the agent layer tends to be insufficient.

That is, the haze of the laminated polyester film of the present invention is preferably 2.0% or less, more preferably 1.5% or less, still more preferably 1.0% or less. If the haze exceeds 2.0%, the touch panel member lacks sufficient transparency in optical applications, and may be insufficient as an optical design member for which high transparency needs are required.

In the production of the laminated polyester film of the present invention, the means for forming the laminated structure is not limited, but from the viewpoint of not reducing the transparency, a coextrusion method in which there is no possibility of interfacial peeling at the laminated interface is recommended.

The laminated polyester film of the present invention may be subjected to so-called in-line coating, in which the film surface is treated during the stretching step, as long as the effects of the present invention are not impaired. It is not limited to the following, but for example, after the first-stage stretching is completed and before the second-stage stretching, improvements in antistatic properties, slipperiness, adhesiveness, etc., secondary processability improvements, and weather resistance For the purpose of improving the properties and surface hardness, a coating treatment with an aqueous solution, an aqueous emulsion, an aqueous slurry or the like can be applied. Further, various coatings may be performed by offline coating after the film is manufactured. Such a coat may be either single-sided or double-sided. The coating material may be either water-based or solvent-based in the case of offline coating, but water-based is preferable in the case of in-line coating.

Hereinafter, an example of the method for producing a laminated film of the present invention will be shown, but the present invention is not limited to the following examples.

First, polyester containing substantially no particles and polyester containing particles are melted by separate extruders, merged with a co-extrusion die, melt-extruded from a T-die, and the glass transition temperature is placed on a cast drum. Quench to less than to obtain an amorphous sheet. The amorphous sheet is stretched 3 to 4 times in the longitudinal direction at a temperature of about glass transition temperature to glass transition temperature + 30 ° C. using a roll stretching machine. Subsequently, an aqueous coating liquid containing easy-slip particles is applied, guided to a tenter stretching machine, and the coating liquid is stretched 3 to 5 times in the lateral direction while being dried. The stretching temperature at this time is appropriately selected in the range from about the same as the longitudinal stretching temperature to about 30 ° C. higher. Further, heat fixing is performed with a heat setter.

In the laminated polyester film of the present invention, if the particles are contained in a high concentration so as to have a surface protrusion size and a number sufficient to give good slipperiness, the transparency may be deteriorated in some cases. Therefore, as a means for imparting good slipperiness without reducing the transparency, it is preferable to use a method of applying and drying a coating liquid containing particles after the longitudinal stretching step. Even in this case, it is desirable that the slippery particles to be blended have an average particle size of 0.1 μm or less so that the transparency is not reduced by the slippery particles. Further, in order to impart sufficient slipperiness to the small particle size particles, the surface protrusions due to the easy-to-slip particles must be enlarged, so that the dry thickness of the coating layer must be equal to or less than the average particle size of the easy-to-slip particles. More preferred.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples as long as the gist of the present invention is not exceeded. The methods and definitions for measuring various physical properties and properties in the present invention are as follows. Further, in Examples and Comparative Examples, the term "part" means "part by weight" unless otherwise specified.

(1) Haze (%)
According to JIS-K7136, the internal haze of the film is measured with a turbidity meter NDH-300A manufactured by Nippon Denshoku Kogyo.

(2) Thickness (μm)
The sample film is embedded in epoxy resin, sectioned with an ultramicrotome, and the obtained flakes are cross-sectionally observed with a scanning electron microscope. The thickness is measured with the region where the particles are dense as the surface layer, and the thickness obtained by subtracting the thickness of each surface layer from the total thickness is defined as the thickness of the intermediate layer.

(3) Light transmittance A spectrophotometer (UV3100, manufactured by Shimadzu Corporation) is used to continuously measure the light transmittance at a low scan speed, a sampling pitch of 2 nm, and a wavelength range of 300 to 700 nm, and the wavelengths are 360 nm and 380 nm. The light transmittance of was detected.

(4) Ultraviolet resistance Using an ultraviolet long life fade meter (FAL-3 type manufactured by Suga Test Instruments Co., Ltd.), ultraviolet rays were irradiated at 63 ± 3 ° C. for 1000 hours. In the test, the pressure-sensitive adhesive solution prepared as follows was applied to one side of the laminated polyester film, dried, and then this side was bonded to a glass plate to prepare a product, which was irradiated from above the laminated polyester film. The appearance of the film after the test and the appearance of the adhesive layer were observed and evaluated according to the following criteria.
<Evaluation criteria for film appearance>
◯: No deterioration.
Δ: Slightly yellowing.
X: Yellowing deterioration is conspicuous.
<Evaluation criteria for the appearance of the adhesive layer>
◯: No deterioration.
Δ: Slightly yellowing.
X: Yellowing deterioration is conspicuous and bubbles are generated.

<Adhesive solution adjustment>
A solution of an acrylic polymer having a weight average molecular weight of 2 million consisting of a copolymer of butyl acrylate / acrylic acid / 2-hydroxyethyl acrylate in a weight ratio of 100/6 / 0.1 (solvent: toluene, concentration: about 30 weight). %), An isocyanate-based cross-linking agent (Coronate L manufactured by Nippon Polyurethane Industry Co., Ltd.), a silane coupling agent (3-glycidoxypropyltrimethoxysilane), and ethyl acetate are added, and the adhesive has a solid content concentration of 10%. An agent solution was prepared. Acrylic copolymerized polymer / coronate L / 3-glycidoxypropyltrimethoxysilane = 100/3/0.6 (weight ratio) in terms of solid content in the solution.

(5) Evaluation method of bleed-out of UV absorber The laminated polyester film produced in Examples and Comparative Examples and a polyester film (manufactured by Mitsubishi Resin Co., Ltd., T100, thickness 25 μm) containing no UV absorber as a reference sample are geared. After heating in an oven (Espec, GHPS-222) at 150 ° C. for 60 minutes, the observation was performed with a microscope (Keyence, VH-Z250R) at a magnification of 300. The polyester film obtained according to the following criteria was evaluated.
<Evaluation criteria>
◯: There is no difference between the polyester film containing no ultraviolet absorber and the precipitate.
Δ: The amount of precipitates is larger than that of the polyester film containing no ultraviolet absorber.
X: The amount of precipitates is large and the amount of precipitates is large as compared with the polyester film containing no ultraviolet absorber.

(Manufacturing of polyester)
・ 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 was used as a catalyst, the reaction start temperature was set to 150 ° C., and the reaction was gradually carried out with the distillation of methanol. The temperature was raised to 230 ° C. after 3 hours. After 4 hours, the transesterification reaction was substantially completed. 0.04 part by weight of ethyl acid phosphate and 0.04 part by weight of antimony trioxide were added to this reaction mixture, and a polycondensation reaction was carried out for 4 hours and 30 minutes. That is, the temperature was gradually raised from 230 ° C. to 280 ° C. On the other hand, the pressure was gradually reduced from the normal pressure to finally reach 0.3 mmHg. When 4 hours and 30 minutes had passed after the start of the polycondensation reaction, the reaction was stopped and the polymer was discharged under nitrogen pressurization. The intrinsic viscosity of the obtained polyester A was 0.65 dL / g, 99% by weight of the ester unit was ethylene terephthalate, and the rest was a unit obtained by condensing diethylene glycol and terephthalic acid.

・ Polyester B
After pre-crystallization of polyester A at 160 ° C, solid-phase polymerization was carried out in a nitrogen atmosphere at a temperature of 220 ° C, and the intrinsic viscosity was 0.78 dL / g, 99% by weight of the ester unit was ethylene terephthalate, and the rest was diethylene glycol. Polyester B, which is a unit obtained by polymerizing terephthalic acid, was obtained.

・ Polyester C
Similar to polyester A except that amorphous silica with an average particle size of 1.5 μm was added as an ethylene glycol slurry after the transesterification reaction, the intrinsic viscosity was 0.65 dL / g, and 99% by weight of the ester unit was ethylene terephthalate. The rest obtained diethylene glycol and polyester C, which is a terephthalic acid condensed ester unit. The silica content was 0.75 parts by weight.

・ Polyester D
Polyester A was subjected to a twin-screw extruder with a vent, and 2,2- (1,4-phenylene) bis [4H-3,1-benzoxazine-4-one] (CYASORB UV- manufactured by CYTEC) was used as an ultraviolet absorber. (3638 molecular weight 369 benzoxazine type) was supplied to a concentration of 10% by weight and melt-kneaded to form chips to prepare an ultraviolet absorber masterbatch polyester E. The intrinsic viscosity of the obtained polyester D was 0.59 dL / g.

Example 1:
The mixed raw material in which polyester A and polyester D were blended in a weight ratio of 85:15 was used as the raw material for the intermediate layer, and the mixed raw material in which polyester B and polyester C were blended in a weight ratio of 90:10 was used as the raw material for the surface layer. Each was melted by a separate twin-screw extruder and co-extruded from a T-die at a discharge rate ratio of 2:19: 2. The molten sheet was rapidly cooled to below the glass transition temperature on a cast drum to obtain an unstretched film. Subsequently, it was stretched three times in the longitudinal direction at 82 ° C. with a roll stretching machine. After that, the following coating liquid α was applied to both sides, stretched four times in the lateral direction at 100 ° C. using a tenter stretching machine, heat-fixed at 235 ° C., and then rapidly cooled to less than the glass transition temperature to reduce the thickness. A 23 μm film was obtained. Various physical properties of the obtained film were measured, and the results are shown in Table 1 below.

[Preparation of coating liquid α]
The following compounds a, b, c, and d were mixed so as to have a weight ratio of 15:55: 5: 25, respectively.
-Polyester resin (a)
Aqueous dispersion of polyester resin copolymerized with the following composition Monomer composition: (acid component) terephthalic acid / isophthalic acid / 5-sodium sulfoisophthalic acid // (diol component) ethylene glycol / 1,4-butanediol / diethylene glycol = 56/40/4 // 70/20/10 (mol%)
-Polyester resin having a condensed polycyclic aromatic (b)
Aqueous dispersion of polyester resin copolymerized with the following composition Monomer composition: (acid component) 2,6-naphthalenedicarboxylic acid / 5-sodium sulfoisophthalic acid // (diol component) ethylene glycol / diethylene glycol = 92/8 / / 80/20 (mol%)
-Epoxy compound (c)
Denacol EX-521 (manufactured by Nagase ChemteX Corporation), which is a polyglycerol polyglycidyl ether.
-Titanium oxide particles with an average particle size of 15 nm (d)

Example 2:
Conducted except that a mixed raw material in which polyester B and polyester C were blended in a weight ratio of 94: 6 was used as a raw material for the surface layer, and the discharge rate ratio between the surface layer and the intermediate layer was coextruded from a T die at a ratio of 4: 15: 4. A film having a thickness of 23 μm was obtained in the same manner as in Example 1. Various physical properties of the obtained film were measured, and the results are shown in Table 1.

Example 3:
A film having a thickness of 23 μm was obtained in the same manner as in Example 1 except that a mixed raw material obtained by blending polyester A and polyester D in a weight ratio of 80:20 was used as a raw material for the intermediate layer. Various physical properties of the obtained film were measured, and the results are shown in Table 1.

Example 4:
A film having a thickness of 23 μm was obtained in the same manner as in Example 2 except that a mixed raw material obtained by blending polyester A and polyester D in a weight ratio of 80:20 was used as a raw material for the intermediate layer. Various physical properties of the obtained film were measured, and the results are shown in Table 1.

Comparative Example 1:
A film having a thickness of 23 μm was obtained in the same manner as in Example 1 except that the raw material of the intermediate layer was 100% by weight of polyester A. Various physical properties of the obtained film were measured, and the results are shown in Table 1.

Comparative Example 2:
A film having a thickness of 23 μm was obtained in the same manner as in Example 2 except that the mixed raw material obtained by blending polyester A and polyester D at a weight ratio of 90:10 was used as an intermediate layer. Various physical properties of the obtained film were measured, and the results are shown in Table 1.

Comparative Example 3:
A film having a thickness of 23 μm was obtained in the same manner as in Example 1 except that a mixed raw material in which polyester A and polyester D were blended at a weight ratio of 70:30 was used as an intermediate layer. Various physical properties of the obtained film were measured, and the results are shown in Table 1.

The laminated polyester film of the present invention can be suitably used as a capacitive touch panel member.

Claims (5)

A laminated polyester film consisting of at least three layers and used as a base material for optical members.
Aμm the surface layer thickness, when the content ratio relative to the entire film of the ultraviolet absorber contained in the intermediate layer was set to B wt%, the ratio of B / A is Ri der 0.20 0.32 or less,
B is 0.9 or more and 3.0 or less,
The thickness of the surface layer is 1.5 μm or more and 10 μm or less.
The light transmittance at a wavelength of 380 nm is 18.0% or less, and the light transmittance at a wavelength of 360 nm is 5.0% or less.
A laminated polyester film for optics, characterized in that the total thickness is 50 μm or less. The laminated polyester film for optics according to claim 1, wherein the surface layer contains particles. The laminated polyester film for optics according to claim 1 or 2 , wherein the optical member is a transparent electrode. With a glass substrate
The optical laminated polyester film according to any one of claims 1 to 3 , which is bonded to the glass substrate via an adhesive layer.
Laminated body comprising. A touch panel using the optical laminated polyester film according to any one of claims 1 to 3 or the laminated body according to claim 4.