KR20130035645A - Optical film - Google Patents

Abstract

PURPOSE: An optical film is provided to provide a primer layer having an excellent adhesive property under high temperatures and high humidity by having three or more isocyanate functional groups as an end group and by including water-dispersed polyurethane resin of which the end is blocked with metal ions. CONSTITUTION: An optical film comprises a substrate film and a primer layer. The primer layer is formed by spreading a polyurethane-coating composition, which includes water-dispersed polyurethane resin made of 10-75 wt% of linear polymer having two end groups and 25-90 wt% of branch-type polymer having three or more end groups, on one or both sides of the substrate film. [Reference numerals] (AA) Evaluation;

Description

Optical film {OPTICAL FILM}

The present invention relates to an optical film used as a base film when manufacturing a prism film, and comprises a primer layer formed by applying a polyurethane coating layer on a polyester base film, and relates to a polyester film having excellent adhesion under high temperature and high humidity. .

In general, biaxially stretched polyester films have excellent dimensional stability, thickness uniformity, and optical transparency, and thus are widely used for various industrial materials as well as display devices.

When using such a biaxially stretched polyester laminated film for optical use, the primer layer generally forms a primer layer from the copolyester-type resin excellent in adhesiveness with a polyester film. However, when the copolyester-based resin is used alone, the adhesion with the polyester base film is sufficient, but when used after various post-processing treatments such as a prism lens, an antireflection layer, or a hard coating layer, the copolyester-based resin is used. Insufficient In order to compensate for this, it is excellent in easily adhesiveness, flexibility and abrasion resistance when producing polyester, and has a strong adhesiveness, so that the adhesive layer is improved by coating a primer layer using a polyurethane-based resin which is used in many fields requiring adhesiveness. How to make is studied. However, by forming a primer layer made of a polyurethane resin, the adhesive strength with the outer layer such as the hard coat layer is improved, but the adhesive force with the polyester film as the base material is not sufficient, resulting in sufficient adhesiveness with the outer layer. There was a problem not to lose.

In addition, as one of the evaluation methods of the adhesion after the post-processing treatment, when the moisture resistance evaluation of the high temperature and high humidity at 65 ℃, 90% humidity conditions, the poor adhesion due to the moisture penetration into the back surface after the post-processing treatment occurs, to compensate for Research is also in progress.

In order to overcome the above problems, Korean Patent No. 10-1050216 attempts to improve durability by forming a polymer network by applying a crosslinking agent.

Korea Patent Registration 10-1050216 (2011.07.12)

The present invention is to provide a polyester optical film having a primer layer excellent in adhesion under high temperature and high humidity.

Specifically, an object of the present invention is to provide a polyester optical film having a primer layer having excellent adhesiveness under high temperature and high humidity, including a water dispersible polyurethane resin having at least three isocyanate functional groups as end groups and blocked by metal ions. .

In order to achieve the above object, when the coating layer is formed using a water-dispersible polyurethane resin having three or more isocyanate functional groups as terminal groups in the primer layer and blocked at the end, moisture resistance under severe conditions of high temperature and high humidity This improvement was confirmed that the excellent adhesion to the optical polymer substrate film, such as prism film during the post-processing to complete the present invention.

The present invention provides a water-dispersible polyurethane resin comprising a polyester base film and 10 to 75% by weight of linear polymer having two terminal groups on one or both sides of the base film and 25 to 90% by weight of branched polymer having three or more terminal groups. It relates to an optical film comprising a primer layer formed by applying a polyurethane coating composition comprising.

In the present invention, the terminal group is preferable because it includes an isocyanate group in which some or all of the terminal groups are blocked with an inorganic acid salt group, and thus has excellent water dispersibility.

In the present invention, the water-dispersible polyurethane resin is prepared by reacting 39 to 45% by weight of polyol, 0.3 to 1.2% by weight of trimethylol propane and 50 to 57% by weight of isocyanate compound to prepare a prepolymer having an isocyanate as a terminal group, and an inorganic acid salt. It is preferable to use the one prepared by blocking 3 to 4% by weight of ionic groups at the end of isocyanate.

Preferably, the water-dispersible polyurethane resin has a weight average molecular weight of 10,000 to 20,000.

In the present invention, the polyurethane coating composition is 5 to 10% by weight of water-dispersible polyurethane binder having a solid content of 10 to 30% by weight, including the water-dispersible polyurethane resin and water, 0.1-0.5% by weight of silicone-based wetting agent, and colloid Silica particles from 0.1 to 0.5% by weight and the balance of water.

In the present invention, the colloidal silica particles use those having an average particle diameter of 50 to 1000 nm.

In the present invention, the dry coating thickness of the primer coating layer is preferably 50 ~ 100 nm.

The optical film according to the present invention has a swelling ratio of 35 to 100 as measured by Equation 1 below, a gel fraction of 75 to 85 as measured by Equation 2 below, and a glass transition temperature of 60 ° C. All of the above physical properties are satisfied. Since it is not swelled within the range of satisfying the physical properties, it has excellent adhesion between the base film and the primer coating layer, and afterwards, the adhesion with the process after laminating the functional layer shows excellent physical properties. That is, it is possible to form a primer coating layer excellent in adhesion even at high temperature and high humidity environment.

[Formula 1]

Swelling degree = (Weight after leaving-initial weight) / initial weight × 100

(In the above formula, the weight after standing means the weight measured after soaking the dry coating film of about 1g in 50g of distilled water and left at 70 ℃ for 24 hours.)

[Formula 2]

Gel fraction = (Weight after drying-initial weight) × 100

(In the above formula, the weight after drying refers to the weight measured after soaking about 1 g of the dry coating film in 50 g of distilled water, and then leaving it at 70 ° C. for 24 hours, and drying the left coating film at 120 ° C. for 3 hours.)

Hereinafter, the present invention will be described more specifically.

The base film used in the present invention is preferably a polyester film, more specifically, polyethylene terephthalate or polyethylene naphthalate film because it is excellent in light transmittance, and may include additives or particles. The polyethylene terephthalate film is preferably a stretched film, it is possible to use a uniaxial or biaxially stretched film. The base film may have a thickness of 50 μm to 250 μm, but is not limited thereto.

In the present invention, the primer layer is formed on one side or both sides of the optical polymer substrate film, and exhibits excellent adhesion and easy adhesion to facilitate adhesion with other substrates.

The primer layer is characterized by using a polyurethane coating composition comprising a water-dispersible polyurethane resin. The water-dispersible polyurethane resin is a branched polymer having at least three isocyanate functional groups as terminal groups, part or all of the isocyanate groups are blocked with an inorganic acid salt group, and more specifically, blocked with an inorganic salt such as sulfate, Two isocyanate functional groups are included, in which some or all of the isocyanate groups are blocked with inorganic acid groups, and more particularly include linear polymers blocked with inorganic salts such as sulfate.

 The water-dispersible polyurethane resin is preferably used 10 to 75% by weight of the linear polymer and 25 to 90% by weight of the branched polymer. When the content of the branched polymer is less than 25% by weight, the swelling degree and gel fraction, which are the objects of the present invention, cannot be satisfied, and it is difficult to obtain a coating film having excellent adhesion under high temperature and high humidity. In addition, when the content of the branched polymer exceeds 90% by weight, the viscosity rises rapidly due to excessive gelation, making it difficult to prepare the water dispersion composition, and defects in surface appearance such as cracking on the surface when coating on the film surface This can happen. In the present invention, the branched polymer means a resin having 3 or 3 or more isocyanate functional groups.

Polyurethane coating composition of the present invention includes the water-dispersible polyurethane resin and water 5 to 10% by weight of water-dispersible polyurethane binder having a solid content of 10 to 30% by weight, silicone-based wetting agent 0.1 to 0.5% by weight, colloidal silica 0.1 to 0.5% by weight of particles and the balance of water.

In the present invention, the water-dispersible polyurethane binder is preferably used to control the coating thickness, such that the solid content is 10 to 30% by weight, including the water-dispersible polyurethane resin and water, the content of the polyurethane coating composition Preference is given to using 5 to 10% by weight. The coating property is good at less than 5% by weight, it is difficult to implement the adhesive force, when more than 10% by weight may be excellent adhesion but difficult to implement the appearance and transparency of the coating.

For example, a method of preparing the water-dispersible polyurethane resin may include preparing a prepolymer having an isocyanate as an end group by reacting 39 to 45 wt% of a polyol, 0.3 to 1.2 wt% of a trimethylol propane, and 50 to 57 wt% of an isocyanate compound. After that, it is preferable to use an inorganic acid salt prepared by blocking 3 to 4% by weight of an ionic group of sulfate at an isocyanate end, and the inorganic acid salt is not limited thereto.

In addition, the weight average molecular weight is not gelled in the range of 10,000 to 20,000, it is preferable because it is possible to obtain a coating film that is water dispersible and excellent in physical properties at high temperature and high humidity.

The weight average molecular weight can be measured using a GPC-MALS (Multi Angle Light Scattering) system (Wyatt, Inc.), the configuration of the MALS system is as follows.

MALS system configuration

GPC; Water 1525 Binary HPLC Pump

RI detector; Optilab rex

MALS; Wyatt Dawn 8+

Column; PLgel 5㎛ Mixed-C (7.5mmΦ × 300mm) × 2 (Polymer Laboratories)

Mobile phase: DMF (50 mM LiCl)

-Flow rate: 0.5mL / min

Temperature: 50 ℃

Injection volume: 0.5%, 500µl

The polyol may be a polyester-based polyol or a polyether-based polyol, preferably a polyester-based polyol. Polyester-based polyols are polyols prepared from the reaction of carboxylic acids, sebacic acids or acid anhydrides with polyhydric alcohols. The type of the polyol is not limited, and it is preferable to use a polyester polyol having a weight average molecular weight of 600 to 3000. Polyester-based polyols include polyols prepared from the reaction of carboxylic acid, sebacic acid or an acid anhydride with a polyhydric alcohol. The type of the polyol is not limited, and it is preferable to use a polyester polyol having a weight average molecular weight of 600 to 3000. Its content is preferably 39 to 45% by weight. When used at less than 39% by weight, the molecular weight is small, the primer layer is too hard, it is difficult to stretch, the coating appearance is not excellent, and when more than 45% by weight, the ILC layer is too soft (Soft) is poor blocking properties Can be.

The trimethylol propane is used to prepare a prepolymer having a trifunctional group, and it is preferable to use 0.3 to 1.2% by weight. In case of using less than 0.3% by weight, the crosslinking density decreases, and anti-blocking property is inferior, and in the case of using more than 1.2% by weight, the crosslinking density becomes too high and elongation deteriorates. This is not excellent and the adhesion may be bad.

The isocyanate compound is not limited but preferably hexamethylene diisocyanate is used. The content can be prepared a prepolymer having a trifunctional group in the range using 50 to 57% by weight.

The inorganic acid salt is preferably used sodium hydrogen sulfate (Sodium Hydrogen Sulfate), the content is preferably used 3 to 4% by weight.

The polyurethane coating composition of the present invention may be further used as a silicon-based wetting agent, colloidal silica particles in order to facilitate the heat-resistant processing on the coating and primer layer on the optical polymer substrate film.

It is preferable to use 0.1-0.5 weight% of silicone type wetting agents, and it is preferable to contain 0.1-0.5 weight% of colloidal silica particles. In addition, the colloidal silica particles are preferably used having an average particle diameter of 50 ~ 1000 nm.

In the present invention, the dry coating thickness of the primer layer is preferably 50 ~ 100 nm. The coating method may be coated on an in-line coating applied to the surface during the stretching process of the polyester film, or may be off-line coating after film production. It is also possible to combine both. Preferably, in-line coating is applied at the same time as the film forming, and thus manufacturing cost is reduced, and the thickness of the coating layer may be changed by extension magnification.

The optical film according to the present invention is excellent in moisture resistance under high temperature and high humidity.

In addition, the optical film prepared by the manufacturing method according to the present invention is coated with a coating composition by an in-line process, the coating thickness can be adjusted by the stretching process, the process is advantageous, introducing a free polymer having a trifunctional group of the polyurethane composition By increasing the crosslinking density, moisture resistance under high temperature and high humidity is excellent. The film having excellent moisture resistance can increase the performance of the optical film by increasing anti-blocking property.

1 is a photograph showing the evaluation criteria according to the blocking evaluation method of the present invention.

Hereinafter, the present invention will be described in detail with reference to the following examples. However, the present invention is not limited to the following examples.

Physical properties were measured by the following measurement method.

1. Measurement of physical properties of coating film using polyurethane coating composition

15 g of water-dispersible polyurethane binder is placed in a round bowl of 80 mm diameter and 15 mm height, and dried at 65 ° C. for 72 hours and 120 ° C. for 3 hours. After dipping 1 g of the dry coating film in 50 g of distilled water, the film was left for 24 hours at 70 ° C., and the swelling ratio was measured. Gel Fraction is measured by drying the coated film for 3 hours at 120 ℃ and recording the weight.

1) Swelling Ratio: After dipping about 1g of dry coating film in 50g of distilled water and leaving it at 70 ℃ for 24 hours, take out the coating film and record the weight.

Swelling Ratio = (Weight after leaving-initial weight) / Initial weight * 100

2) Gel Fraction: After leaving the coating film at 120 ℃ for 3 hours, the weight is recorded.

 Gel Fraction = (Weight after drying / Initial weight) * 100

3) Tg measurement: Using a DSC (using PerkinElmer DSC 7) instrument, measure in 2nd Run mode. 10-11 mg dry coating is measured using PerkinElmer DSC7.

1st Run. = 0 ~ 200 ℃, 200 ℃ / min, Holding Time-3min // 200 ℃ ~ -40 ℃, 200 ℃ / min, Holding Time-5min

2nd Run. = -40 degreeC-200 degreeC, and it measures on 20 degree-C / min conditions.

2. Blocking evaluation method of double coated polyester film

Using Heat Gradient (TOYOSEIKI), set the temperature of each 5 stages under 0.4MPa pressure condition, press for 1 minute, remove the pressed plate after 1 minute and check the degree. Each degree of difference was evaluated based on FIG.

-Humidity evaluation: Perform at 40 ~ 50RH% of constant temperature / humidity at 20 ~ 25 ℃.

-When evaluating humidification: Perform an ultrasonic humidifier on the film under 100% RH conditions.

[Production Example 1]

Preparation of Water Dispersible Polyurethane Binder (1)

Theoretically, water-dispersed polyurethanes having a content of 25% by weight of branched polymers were prepared.

40 wt% of polyethyleneadipate diol, 0.3 wt% of trimethylol propane, and 56.7 wt% of hexamethylene diisocyanate were reacted to prepare a prepolymer having an isocyanate functional group as a prepolymer. 3% by weight of sodium hydrogen sulfate (Sodium Hydrogen Sulfate) as an ionic group was reacted with isocyanate, which is a terminal functional group of the prepolymer, to prepare a polyurethane having a ionic group and a weight average molecular weight of 10,700. 20 wt% of the polyurethane thus prepared was dispersed in 80 wt% of water to prepare a water dispersible polyurethane binder (1) having a solid content of 20 wt%.

[Production Example 2]

Preparation of Water Dispersible Polyurethane Binder (2)

Theoretically, water-dispersed polyurethanes having a content of 50% by weight of branched polymers were prepared.

40 wt% of polyethyleneadipate diol, 0.6 wt% of trimethylol propane, and 55.9 wt% of hexamethylene diisocyanate were reacted to prepare a prepolymer having an isocyanate functional group as a prepolymer. 3.5 wt% of sodium hydrogen sulfate was reacted with an isocyanate, which is a terminal functional group of the prepolymer, to prepare a polyurethane having a weight average molecular weight of 14,400. 20 wt% of the polyurethane thus prepared was dispersed in 80 wt% of water to prepare a water dispersible polyurethane having a solid content of 20 wt%.

[Production Example 3]

Preparation of Water Dispersible Polyurethane Binder (3)

Theoretically, water-dispersed polyurethanes having a content of 90% by weight of branched polymers were prepared.

40 wt% of polyethyleneadipate diol, 1.2 wt% of trimethylol propane, and 54.8 wt% of hexamethylene diisocyanate were reacted to prepare a prepolymer having an isocyanate functional group as a prepolymer. 4.0 wt% of sodium hydrogen sulfate was reacted with isocyanate, which is a terminal functional group of the prepolymer, to prepare a polyurethane having a weight average molecular weight of 19,000. 20 wt% of the polyurethane thus prepared was dispersed in 80 wt% of water to prepare a water dispersible polyurethane having a solid content of 20 wt%.

Example 1

Preparation of Polyurethane Coating Composition (1) with Excellent Crosslinking Density

5% by weight of the water-dispersible polyurethane binder prepared in Preparation Example 1, 0.3% by weight of a silicone-based wetting agent (Dow Corning, polyester siloxane copolymer), 0.3% by weight of colloidal silica particles having an average particle diameter of 140nm After stirring for 2 hours to prepare a polyurethane coating composition (1).

Preparation of Double-coated Polyester Film

After the polyethylene terephthalate chip was removed from the moisture in the extruder and melt-extruded, a polyethylene terephthalate sheet having a thickness of 2000㎛ was prepared by quenching and solidifying with a casting drum having a surface temperature of 20 ℃. The prepared polyethylene terephthalate sheet was stretched 3.5 times in the machine direction (MD) at 80 ° C. and then cooled to room temperature. Thereafter, the polyurethane coating composition 1 was coated on both sides by a bar coating method, and heated to 1 ° C. per second to 110 to 150 ° C., followed by preheating and drying, and stretched 3.5 times in the transverse direction (TD). . Thereafter, heat treatment was performed at 230 ° C. in a 5-stage tenter, and thermally fixed at 10 ° C. in the longitudinal and transverse directions at 200 ° C. to prepare a 188 μm biaxially oriented film coated on both sides. The dry coating thickness of the polyurethane coating layer was 80 nm in the first coating layer, 80 nm in the second coating layer.

[Example 2]

Preparation of polyurethane coating composition (2) excellent in crosslinking density

5 wt% of the water-dispersible polyurethane binder prepared in Preparation Example 2, 0.3 wt% of silicone-based wetting agent (Dow Corning, polyester siloxane copolymer), and 0.3 wt% of colloidal silica particles having an average particle diameter of 140 nm were added to water. After stirring for 2 hours to prepare a polyurethane coating composition (2).

Preparation of Double-coated Polyester Film

After the polyethylene terephthalate chip was removed from the moisture in the extruder and melt-extruded, a polyethylene terephthalate sheet having a thickness of 2000㎛ was prepared by quenching and solidifying with a casting drum having a surface temperature of 20 ℃. The prepared polyethylene terephthalate sheet was stretched 3.5 times in the machine direction (MD) at 80 ° C. and then cooled to room temperature. Thereafter, the polyurethane coating composition 2 was coated on both sides by a bar coating method, and heated to 1 ° C. per second to 110 to 150 ° C., followed by preheating and drying, and stretched 3.5 times in the transverse direction (TD). . Thereafter, heat treatment was performed at 230 ° C. in a 5-stage tenter, and thermally fixed at 10 ° C. in the longitudinal and transverse directions at 200 ° C. to prepare a 188 μm biaxially oriented film coated on both sides. The dry coating thickness of the polyurethane coating layer was 80 nm in the first coating layer, 80 nm in the second coating layer.

[Example 3]

Preparation of Polyurethane Coating Composition (3) with Excellent Crosslinking Density

5 wt% of the water-dispersible polyurethane binder prepared in Preparation Example 3, 0.3 wt% of silicone-based wetting agent (Dow Corning, polyester siloxane copolymer), and 0.3 wt% of colloidal silica particles having an average particle diameter of 140 nm were added to water. After stirring for 2 hours to prepare a polyurethane coating composition (3).

Preparation of Double-coated Polyester Film

After the polyethylene terephthalate chip was removed from the moisture in the extruder and melt-extruded, a polyethylene terephthalate sheet having a thickness of 2000㎛ was prepared by quenching and solidifying with a casting drum having a surface temperature of 20 ℃. The prepared polyethylene terephthalate sheet was stretched 3.5 times in the machine direction (MD) at 80 ° C. and then cooled to room temperature. Thereafter, the polyurethane coating composition 3 was coated on both sides by a bar coating method, and heated to 1 ° C. per second to 110 to 150 ° C., followed by preheating and drying, and stretched 3.5 times in the transverse direction (TD). . Thereafter, heat treatment was performed at 230 ° C. in a 5-stage tenter, and thermally fixed at 10 ° C. in the longitudinal and transverse directions at 200 ° C. to prepare a 188 μm biaxially oriented film coated on both sides. The dry coating thickness of the polyurethane coating layer was 80 nm in the first coating layer, 80 nm in the second coating layer.

Comparative Example 1

Preparation of Polyurethane Compositions

5% by weight of an aqueous polyurethane binder (UREKO H-3 from Dai-ichi kogyo seiyaku, 20% by weight solid, an aqueous polyurethane binder with two functional groups and a weight average molecular weight of 8,000), a silicone-based wetting agent (Dow Corning, polyester siloxane) Copolymer) 0.3% by weight and 0.3% by weight of colloidal silica particles having an average particle diameter of 140 nm0 were added to water, followed by stirring for 2 hours to prepare Comparative Example 1.

Using this composition, a double-coated polyester film was prepared in the same manner as in Example 1.

The physical properties of the water-dispersible polyurethane binders prepared in Preparation Examples 1 to 3 and the aqueous polyurethane binder of Comparative Example 1 were measured and shown in Table 1 below.

[Table 1]

The physical properties of the coating films according to Examples 1 to 3 and Comparative Example 1 were measured and shown in Tables 2 and 3 below.

[Table 2] Evaluation of Blocking Degree in the Normal Condition

[Table 3] Evaluation of Blocking Degree in Humidification Conditions

As shown in Table 2 and Table 3, Example 1 according to the present invention was confirmed that the blocking is lowered at 100 ℃ or more in the normal humidity conditions, Example 2 and Example 3 to the blocking properties up to 120 ℃ in the humidity conditions It was found that this was excellent.

In the case of humidification conditions, Examples 1 and 2 according to the present invention were found to have excellent blocking property up to 80 ° C., and in Example 3, it was found that the blocking property was excellent up to 110 ° C.

In summary, it can be seen that by controlling the number of end groups of the water-dispersible polyurethane binder used in the primer layer, it is possible to produce a film having excellent physical properties under high temperature and high humidity conditions.

Claims (8)

A polyester comprising a water-dispersible polyurethane resin consisting of a polyester base film and 10 to 75% by weight of the linear polymer having two terminal groups on one or both sides of the base film and 25 to 90% by weight of a branched polymer having three or more terminal groups An optical film comprising a primer layer formed by coating a urethane coating composition. The method of claim 1,
The terminal group is an isocyanate group in which part or all of the terminal groups are blocked with an inorganic acid salt group. The method of claim 2,
The water-dispersible polyurethane resin is prepared by reacting 39 to 45% by weight of polyol, 0.3 to 1.2% by weight of trimethylol propane and 50 to 57% by weight of isocyanate compound to prepare a prepolymer having an isocyanate as a terminal group, and then preparing an inorganic acid salt of 3 to 3%. An optical film prepared by blocking 4% by weight of ionic groups at the end of isocyanate. The method of claim 3, wherein
The water-dispersible polyurethane resin is an optical film having a weight average molecular weight of 10,000 ~ 20,000. The method according to any one of claims 1 to 4,
The polyurethane coating composition is 5 to 10% by weight of water-dispersible polyurethane binder having a solid content of 10 to 30% by weight, including the water-dispersible polyurethane resin and water, 0.1-0.5% by weight of silicone-based wetting agent, and colloidal silica particles 0.1 Optical film containing ~ 0.5% by weight and the balance of water. 6. The method of claim 5,
The colloidal silica particles have an average particle diameter of 50 ~ 1000nm optical film. The method of claim 1,
Dry coating thickness of the primer layer is 50 ~ 100 nm optical film. The method of claim 1,
The optical film has an swelling degree of 35 to 100 measured by Equation 1 below, a gel fraction of 75 to 85 measured by Equation 2 below, and an optical film that satisfies all physical properties of glass transition temperature of 60 ° C. or higher. film.
[Formula 1]
Swelling degree = (Weight after leaving-initial weight) / initial weight × 100
(In the above formula, the weight after standing means the weight measured after soaking the dry coating film of about 1g in 50g of distilled water and left at 70 ℃ for 24 hours.)
[Formula 2]
Gel fraction = (Weight after drying-initial weight) × 100
(In the above formula, the weight after drying refers to the weight measured after soaking about 1 g of the dry coating film in 50 g of distilled water, and then leaving it at 70 ° C. for 24 hours, and drying the left coating film at 120 ° C. for 3 hours.)

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