KR20170096640A - Cellulose ester film having improved coating-adhesive strength and manufacturing method of the same - Google Patents

Abstract

The present invention relates to a cellulose ester film having controlled surface plasticizer content of a film and a method for producing the same. More particularly, the present invention relates to a cellulose ester film which is prepared by controlling the Tenter temperature (140 to 180 ° C) and the dryer air volume (2000 to 5000 m 3 / h) To improve the coating adhesion, and a method for producing the same.
By reducing the content of the polyester plasticizer on the surface through process control, the antireflection performance of the antireflection film is not limited, such as when a coating layer is formed using acrylic resin or urethane resin, It is possible to expect an increase in applicability as a film for coating by improving the adhesion.

Description

[0001] The present invention relates to a cellulose ester film having improved adhesion to a coating film,

The present invention relates to a cellulose ester film and a method for producing the same, and more particularly, to a cellulose ester film in which the content of a polyester plasticizer on the surface is reduced through process control such as a Tenter temperature and a dryer air volume condition, ≪ / RTI >

In recent years, the development of thin and lightweight notebook computers is under way. Accordingly, a protective film of a polarizing plate used in a display device such as a liquid crystal display device has been increasingly demanded for further thinning and higher performance. Since a liquid crystal display device displays a display by polarization control by a liquid crystal, a polarizing plate is required, and a polarizing plate in which a PVA film containing iodine is stretched is usually used. Since the polarizing plate is fragile, a polarizing plate protective film is used to protect the polarizing plate. In general, triacetylcellulose film is widely used for a polarizing plate protective film. Apart from these polarizing plate protective films, a retardation film is also used to control the retardation of the polarized light. The retardation film used in such a liquid crystal display device is used in combination with a polarizing plate to solve problems such as color compensation and view angle enlargement by using a retardation in the thickness direction (Rth), and also uses an in-plane retardation Ro And has a function of converting linearly polarized light into circularly polarized light or conversely converting circularly polarized light into linearly polarized light with respect to the wavelength of the visible light region.

The polarizing plate protective film is intended to protect the polarizing plate and it is most preferable to use a film made of cellulose acetate in order to protect the polarizing plate made of PVA containing moisture, considering the production process of the polarizing plate. On the other hand, as a retardation film, materials other than cellulose acetate have been used to exhibit optical performance. That is, conventionally, as a material of the retardation film, for example, there are polycarbonate, polysulfone, polyethersulfone, amorphous polyolefin and the like. These polymer films have such characteristics that the longer the wavelength is, the smaller the retardation, and it is difficult to impart an ideal retardation property to the entire wavelength of the visible light region.

In the case where linearly polarized light is converted into circularly polarized light with respect to the wavelength of the visible light region or conversely circularly polarized light is converted into linearly polarized light, in order to obtain the above effect with one piece of retardation film, the retardation in the wavelength? 4 < / RTI > Such a retardation film can be obtained by using, for example, a retardation film having a phase difference of? / 4 and only one polarizing plate for a reflective liquid crystal display device having a back electrode as a reflective electrode, thereby obtaining a reflective display device having excellent image quality . Further, with respect to the observer of the guest-host type liquid crystal layer, the retardation film is used on the back side, or the circularly polarized light of the reflection type polarizing plate composed of cholesteric liquid crystal or the like that reflects only one of the left and right circularly polarized light is converted into linearly polarized light It is also used as an element.

Further, the retardation film has a function of converting linearly polarized light into elliptically polarized light or circularly polarized light, or converting linearly polarized light in a certain direction into another direction, and therefore, the viewing angle, contrast, etc. of the liquid crystal display device can be improved .

Generally, a retardation film is attached to a pair of polarizing plates, respectively. At present, N-TAC of Konica Minolta Holdings, Inc. of Japan is generally used as a phase difference film for a VA mode liquid crystal display. The NTAC retardation film was a cellulose acetate propionylate (CAP) film having a retardation in the plane (reference for R0,? = 550 nm) of 50 nm and a retardation in the thickness direction (Rth,? = Lt; / RTI >

In order to improve the viewing angle characteristics (black display state (black characteristic), etc.) of the liquid crystal display device, wavelength dispersion and control techniques are required. In general, the N-TAC film exhibits an inverse wavelength dispersion characteristic in which the retardation value increases with increasing wavelength, and exhibits an excellent viewing angle characteristic improvement effect as compared with the retardation film having a regular wavelength dispersion characteristic in which the retardation value decreases with increasing wavelength. Further, in order to improve a liquid crystal display device, a retardation film having a specific retardation value and a combination thereof are used.

Conventional retardation films (PC, PSu, PA, etc.) have such characteristics that the longer the wavelength is, the smaller the retardation. It is difficult to impart an ideal retardation characteristic to the entire wavelength of the visible light region. So that necessary performance is obtained. In order to obtain such a performance in a single retardation film, it is preferable that the in-plane direction retardation Ro of the wavelength? Incident on the retardation film be? / 4, but for this purpose, The in-plane directional phase difference Ro needs to be increased. In the film made of cellulose acetate, if such a retardation property can be given, the polarizing plate protective film and the retardation film can be used together, the retardation film composed of a plurality of retardation films can be omitted, It is possible to improve the total light transmittance.

With respect to this problem, Japanese Patent Laid-Open No. 2000-137116 proposes to use an oriented film of cellulose acetate having a degree of substitution (acetylation degree) of 2.5 to 2.8 as a retardation film. According to this method, the longer the wavelength, the larger the phase difference, and the ideal phase difference characteristic is obtained with respect to the entire wavelength of the visible light region. That is, the above-mentioned patent discloses a phase difference plate in which the phase difference becomes smaller as the measurement wavelength becomes shorter with one film. A retardation film comprising a polymeric orientation film having a longer birefringence (? N) at a wavelength of 400 to 700 nm, wherein the polymeric orientation film is an orientation film of a polymeric film having an average refractive index at the above- And the like. As a means for solving this problem, a technique of orienting cellulose acetate having an acetylation degree of 2.5 to 2.8 by stretching is disclosed.

In the embodiment of the above-mentioned patent, 100 parts by weight of cellulose triacetate having an intrinsic viscosity [?] = 1.335 and an acetylation degree of 2.917 obtained from Wako Junyaku Kogyo Co., Ltd. was dissolved in 500 parts by weight of methylene chloride, Hydrolysis of cellulose triacetate with acetic acid and water at 70 DEG C for 100 minutes while removing methylene chloride by depressurization and the reaction product was precipitated with a large amount of water and washed and dried , And a cellulose acetate having an acetylation degree of 2.661 was obtained. Then, a film was prepared from a solution prepared by dissolving 100 parts by weight of this polymer and 3 parts by weight of dibutyl phthalate as a plasticizer in 700 parts by weight of a mixed solvent of methylene chloride / methanol (weight ratio 9/1) by solvent casting method, And uniaxially stretched at a temperature of 170 캜 at 1.5 times. That is, in Embodiment 1 of the patent, the retardation film having the same wavelength characteristics (wavelength dispersion characteristics) as the latter is obtained by stretching. It is also disclosed that by adjusting the retardation value, it is possible to use? / 4 or another retardation film. In Example 4 of the aforementioned patent, cellulose acetate having an acetylation degree of 2.421 was obtained. When the retardation property of the film using the film is measured, the retardation is insufficient when the film thickness is about 100 mu m (50 to 150 mu m) and when the film thickness is preferable as the self-supporting film. When the thickness of the film is as large as about 200 mu m, a preferable retardation of about 80 to 150 nm is provided. In this case, the thickness direction retardation (Rth) is excessively larger than 350 nm, It did not function as a film and was not sufficient. Furthermore, the molecular weight distribution of the obtained cellulose acetate is not described, and the control of the retardation characteristics by controlling the molecular weight distribution is not described or suggested.

In general, the cellulose ester film is excellent in dimensional stability, thickness uniformity, and optical transparency, and is widely used not only for display devices but also for various industrial materials.

However, the conventional cellulose ester film often had poor adhesion to the coating layer. When a coating layer is formed using such a resin, a refractive index of about 1.5 is usually used as a primer layer for improving the adhesion with the functional layer. Therefore, when the antireflection film is designed, . Such deterioration of the coating adhesion force is detrimental to the application as a coating film, and thus needs to be improved.

Korean Patent Publication No. 10-2015-0000105 Korean Patent Registration No. 10-0983585 Korean Registered Patent No. 10-1236098

Disclosure of Invention Technical Problem [8] The present invention has been made in order to solve the problem that conventional cellulose ester film has poor adhesion to a coating layer, and it is an object of the present invention to provide a cellulose ester film in which the content of polyester plasticizer on the surface is reduced to improve coating adhesion.

In order to improve the adhesion with the coating layer, acrylic resin or urethane resin is usually used as the primer layer. However, when the coating layer is formed using such a resin, the refractive index is about 1.5, .

The present invention relates to a cellulose ester film comprising a front layer, an inner layer and a rear layer, wherein the plasticizer content of the film surface is controlled by adjusting a temperature at a tenter of 140 to 180 ° C and a dryer air volume of 2000 to 5000 m 3 / And to a method for producing a cellulose ester film having improved coating adhesion.

When the temperature of the stretching machine is lower than 140 캜, it is difficult to secure an elongation. When the temperature is higher than 180 캜, the hardness of the film may become excessively high. Also, when the air flow rate of the dryer is less than 2000 m 3 / h, the drying speed is slow and productivity is problematic. If it is set at more than 5000 m 3 / h, economical efficiency is lowered and the physical properties of the film are uneven.

The front layer includes a polyester plasticizer and fine particles, the back layer includes a nonphosphoric ester plasticizer and fine particles, and the inner layer includes two or more plasticizers and an ultraviolet absorber.

The cellulose ester film according to the present invention reduces the content of the polyester plasticizer on the surface through process control such as Tenter temperature and dryer air volume conditions so that when the coating layer is formed by using acrylic resin or urethane resin, It is possible to expect an increase in applicability as a film for coating since the adhesion of the coating is improved without causing the problem that the anti-reflection performance of the anti-reflective film is limited.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an overall schematic view of a film production apparatus that can be used in the production of a cellulose film according to the present invention. Fig.

Hereinafter, the present invention will be described in detail.

The cellulose film according to the present invention is produced by a solution casting method. In order to produce the cellulose film according to the present invention, first, the first, second and third casting stock solutions are co-extruded onto the surface of the belt through a die and applied in the form of a sheet, The solvent present in the casting stock solution is evaporated to form a cellulose film. The die is for extruding the casting stock solution, for example, a conventional T-die may be used. The belt may be a stainless steel conveyor belt that can be used as the belt, and the thickness of the cellulose film can be controlled by controlling the movement or rotation speed of the belt.

The casting stock solution extruded from the die is also referred to as a dope, and includes a first casting stock solution forming a front layer of the film, a second casting stock solution forming an inner layer of the film, and a third casting stock solution forming a rear layer of the film . In the casting stock solution, the first casting stock solution and the third casting stock solution are mixed with a cellulose component, a solvent for dissolving the cellulose component, fine particles for reducing the coefficient of friction of the film by imparting unevenness to the surface of the film, And an ester plasticizer for imparting flexibility to the film. The second casting stock solution includes a cellulose component, a solvent for dissolving the cellulose component, a cellulose component, a solvent for dissolving the cellulose component, an ultraviolet ray An ultraviolet absorber for blocking ultraviolet light, and two or more plasticizers for imparting flexibility to the film.

As the cellulose component, cellulose acetate such as triacetyl cellulose (TAC) or cellulose acetate propionylate (CAP) may be used. Examples of the solvent include methylene chloride (MC), methyl acetic acid, An organic solvent such as an alcohol (for example, methanol) may be used. In the first, second and third casting stock solutions, the content of the cellulose component is 15 to 25 wt%, preferably 15 to 20 wt%, respectively, and the content of the solvent includes the cellulose component Except for the solid content (plasticizer, ultraviolet absorber, fine particles, etc.).

As the fine particles, fine particles for ordinary protective films having hydrophobicity may be used. For example, silicon dioxide, titanium dioxide, a mixture thereof and the like having an average particle diameter of 0.1 to 2.0 탆, preferably 0.1 to 1.0 탆 may be used have. If the average particle size of the fine particles is less than 0.1 탆, the coefficient of friction between the films may not be lowered. If the average particle size exceeds 2.0 탆, the transparency of the film may be deteriorated. The content of the fine particles is 0.005 to 0.1 part by weight, preferably 0.01 to 0.08 part by weight, more preferably 0.04 to 0.08 part by weight, more preferably 0.04 to 0.08 part by weight, based on 100 parts by weight of the cellulose component of the first casting stock solution and the third casting stock solution. If the content of the fine particles is too small, there is a fear that the coefficient of friction between the films and the moisture permeability of the film may not be lowered, and if it is too much, the transparency of the film may be lowered.

As the ultraviolet ray absorbing agent, a conventional ultraviolet ray absorbing agent used for a protective film may be used. For example, an oxybenzophenone based compound, a benzotriazole based compound, etc., and a mixture thereof may be used. The content of the ultraviolet absorber is 0.5 to 3 parts by weight, preferably 1 to 2 parts by weight, based on 100 parts by weight of the cellulose component of the second casting stock solution. If the content of the ultraviolet absorber is too small, There is a fear that it may not be possible, and if it is too much, there is a fear of bleeding out or elution.

Examples of the plasticizer include a non-phosphate ester plasticizer such as an aliphatic polyhydric alcohol ester that can prevent the bleed-out and elution of the plasticizer during a high-temperature drying process such as a cellulose film production process, A phosphate ester plasticizer such as triphenyl phosphate, tricresyl phosphate, or cresyldiphenyl phosphate can be used. Here, the first casting stock solution and the third casting stock solution contain only the nonphosphoric acid ester plasticizer, and the second casting stock solution includes two or more plasticizers, but at least one phosphate ester plasticizer is used desirable. In the first casting stock solution and the third casting stock solution, the content of the nonphosphoric ester plasticizer is 1 to 20 parts by weight, preferably 5 to 18 parts by weight, relative to 100 parts by weight of the cellulose component, In the casting stock solution, the content of the two or more plasticizers is 1 to 20 parts by weight, preferably 5 to 18 parts by weight, based on 100 parts by weight of the cellulose component. If the content of the plasticizer (non-phosphoric acid ester plasticizer, two or more plasticizers) is too small, there is a fear that the flexibility of the film is deteriorated, and if it is too much, there is a fear of bleeding out or elution.

In the present invention, the cellulose component and / or the solvent constituting the first, second, and third casting stock solutions may be the same or different from each other, and each of the cellulose solution pipe may have different components and contents of ultraviolet absorber, The plasticizer may be incorporated via side feeding to include ester plasticizers and particulates in the front and back layers and two or more plasticizers and ultraviolet absorbers in the inner layer. The thickness of the front layer and the back layer is preferably 5 to 20%, more preferably 8 to 20% of the total thickness of the film, and the total thickness of the cellulose film (final thickness after stretching and drying, hereinafter the same) To 12%, and the thickness of the inner layer is 60 to 90%, preferably 76 to 84% of the total thickness of the film. If the thicknesses of the front layer, the inner layer and the rear layer are out of the above ranges, flexibility of the film may be deteriorated or the plasticizer and ultraviolet additive may bleed out. The content of the nonphosphoric acid ester plasticizer contained in the front layer and the back layer (i.e., the first casting stock solution and the third casting stock solution) relative to 100 parts by weight of the total plasticizer contained in the cellulose film is 5 to 15 Preferably 5 to 10 parts by weight. The content can be adjusted to satisfy the above range by adjusting the thicknesses of the front layer, the inner layer and the back layer, or by adjusting the respective plasticizer contents contained in the first, second and third casting stock solutions. If the content of the ester plasticizer contained in the front layer and the rear layer is less than 5 parts by weight, the flexibility of the front layer and the back layer may be deteriorated or the bleed-out or elution of the plasticizer may not be effectively inhibited. The mechanical properties of the film may be deteriorated or the unit cost may increase. In addition, the inner layer (i.e., the second casting stock solution) contains two or more kinds of plasticizers, and at least one of them is a phosphate ester plasticizer, and the content thereof is preferably 60% or more for all two or more plasticizers contained in the inner layer By weight or more. Here, when the content of the phosphate ester plasticizer is too small, the flexibility of the film may be lowered.

Referring to FIG. 1 again, the casting stock solution applied to the belt moves together with the belt for a sufficient time and distance to be formed into a film, and then is peeled off by a peel-off roller, which is a guide roller, . The peeled film is transferred to a tenter and stretched in a transverse direction (TD) and / or a mechanical direction (MD) and dried in a dryer to form the final cellulose film Next, it is wound on a winder and shipped to the product.

The cellulose film according to the present invention has a multilayer structure including a front layer, an inner layer and a rear layer. After the preparation of the cellulose film, the degree of bleed out of the plasticizer on the surface of the cellulose film was analyzed by gas chromatography (GC) , Less than 10%, preferably 1 to 8%, more preferably 1 to 5% of the total plasticizer is bleed out on the film surface. The cellulose film of the present invention is usually attached to one side or both sides of a polarizing plate made of polyvinyl alcohol (PVA) to protect the polarizing plate, and the polarizing element to which the cellulose film is attached is attached to the upper plate and / Or the bottom plate. If necessary, the polarizing plate and the cellulose protective film according to the present invention may be positioned at a predetermined gap (Cell Gap).

Hereinafter, the present invention will be described in more detail with reference to specific examples. The following examples illustrate the present invention and are not intended to limit the scope of the present invention.

[Example]

A mixture of 18% by weight of triacetyl cellulose (TAC), 81.76% by weight of methylene chloride and 0.2% by weight of an aliphatic polyhydric alcohol ester as a nonphosphoric acid ester plasticizer and 0.002% by weight of fine particles was used to form the front layer and the rear layer of the cellulose film 15.84% by weight of triacetylcellulose (TAC), 81.76% by weight of methylene chloride and 0.1% by weight of a phosphate ester plasticizer (triphenylphosphate, tricresylphosphate, cresyldiphenylphosphate etc.) 1.4 0.2 wt% of aliphatic polyhydric alcohol ester and 0.25 wt% of benzotriazole-based compound as an ultraviolet absorber were used to prepare a second casting stock solution for forming an inner layer of a cellulose film. Each casting stock solution for forming the front layer, the inner layer and the back layer was cast on the surface of a metal belt in the form of a sheet having a thickness of 90 탆 and a width of 800 mm using a die. The solvent of the casting stock solution is evaporated, stretched and dried to obtain a film having a total thickness of 80 μm and a thickness of the front layer and the rear layer of 5 to 20% A cellulose film having a content of the non-phosphoric acid ester plasticizer in the front layer and the back layer of 7 parts by weight was prepared per 100 parts by weight of the entire plasticizer.

At this time, the temperature of the tenter was set at 140 to 180 ° C as in Examples 1 to 4 of Table 1, and the air volume of the dryer was set at 2000 or 5000 m 3 / h.

[Comparative Example]

The other process is the same as in the above embodiment except that the temperature of the tenter is set at 120 ° C and the air flow rate of the dryer is set at 2000 m 3 / h.

Comparative Example Example 1 Example 2 Example 3 Example 4 Tenter temperature (캜) 120 140 160 160 180 Dryer air volume (㎥ / h) 2000 5000 Adhesive force (n / 100) 90/100 93/100 95/100 97/100 100/100

≪ Adhesive force measuring method &

1) Coating conditions: Apply 1.5 ~ 2g of coating solution of AM composition on the produced film, and then slide the Mayor Bar down to uniformly coat (Mayer Bar # 10). The coated film is placed in an oven at 80 ° C and dried for 1 minute. When drying is completed, the coating liquid is cured by putting into a UV curing machine (light quantity: 700 mJ / cm 2).

2) Coating solution: AM composition (as shown in Table 2 below)

division content Condition Solvent MEK 13 300 rpm x 1 hr. MIBK 34 Resin ResinA 12 ResinB 5 ResinC 7 ResinD 3 Initiator Additive 1.35 300 rpm x 30 min.

3) Evaluation method: Nichiban Tape (CT-24), Cross-cut 3 times evaluation, Lupe confirmation.

Grid-shaped gold is drawn on the cured film using a cross-cut method using a cutter knife (100 squares of 11 lines horizontally and vertically). The Nichiban Tape comes in close contact with the film. Grasp the end of the tape and remove it as much as possible in the horizontal direction. Count the total number of coating layers with Lupe. 3 times.

10: Cellulose film
20: Die
30: Belt
32: Peel-off Roller
40: Tenter
50: Dryer
60: Winder

Claims (3)

The method for producing a cellulose ester film comprising a front layer, an inner layer and a back layer is characterized in that the plasticizer content of the film surface is controlled by adjusting the temperature at a tenter of from 140 to 180 DEG C and a dryer air volume of from 2000 to 5000 m & Wherein the cellulose ester film has an improved coating adhesion.
The method according to claim 1,
Wherein the coating adhesion force is 93/100 to 100/100.
A cellulose ester film produced by the method of claim 1.

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