JP2003041020A - Polyester film and hard coating film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hard coating film free from heat curling arising in thermal processing, improved in attaching easiness of the film and reducing a production loss in applying the hard coating film. SOLUTION: This hard coating film having suppressed heat curling is achieved by a polyester film having 0.2-0.8% heat shrinkage percentage in a wide direction when heat-treated at 150 deg.C for 30 min.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a polyester film used for a laminated film having a hard coat layer on one surface.

More specifically, the present invention relates to a polyester film capable of preventing curling due to a difference in thermal behavior in the width direction between a hard coat layer and a polyester film when heat-processing a laminated film having a hard coat layer.

[0003]

2. Description of the Related Art It is generally useful in various applications to provide a hard coat layer on the surface of a polyester film to increase its hardness. By increasing the hardness of the surface, it is possible to protect the surface against contact with nails or abrasion such as wiping. In particular, when a film attached to a display or a window has a problem of deterioration in appearance due to scratches or the like, it is indispensable to process the film with a hard coat.

In such a hard coat film,
It is also performed to further enhance the function of the film by further processing the hard coat layer. For example, it can be attached to a display by adding an antireflection function, can be used as a touch key by providing a transparent electrode, or can be attached to the window of a house or car by imparting a function of absorbing ultraviolet rays or infrared rays or water repellency, or charging. It is used for various purposes, such as adding a preventive function.

In order to impart high functionality to these hard coat films, many require thermal processing. However, a phenomenon called thermal curl in which the entire laminated film is curved may occur during this heat processing. This thermal curling deteriorates the processability of the film, which is a serious problem when the film is attached to something. A specific problem is that when the hard coat film is subjected to a water repellent finish, it is heated at 150 ° C. for 1 minute to cause thermal curl, which reduces the ease of sticking the hard film.

[0006]

An object of the present invention is to prevent thermal curling of a hard coat film that occurs during thermal processing,
It is to make the hard coat film easy to attach and to suppress the production loss when the hard coat film is used.

[0007]

Means for Solving the Problems As a result of intensive studies to prevent thermal curling of the hard coat film, it was found that it is important to match the thermal behavior of the polyester film in the width direction with the hard coat layer, and the present invention was reached. did. That is, the thermal curl of the hard coat film is suppressed by 15
A polyester film having a heat shrinkage in the width direction of 0.2 to 0.8% when heat-treated at 0 ° C. for 30 minutes.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION An object of the present invention is to prevent thermal curling of a hard coat film that occurs during heat processing.

One of the causes of thermal curl is that the thermal behavior of the polyester film and the hard coat layer is different.
Focusing on the thermal behavior of the polyester film and the hard coat layer, as a result of diligent examination of the thermal physical properties of the polyester at 150 ° C., the conditions for suppressing thermal curl were found.
We have succeeded in creating a polyester film whose thermal behavior at 50 ° C optimally matches the hard coat layer.

The details will be described below.

To optimally match the thermal behavior of the polyester film at 150 ° C. with the hard coat layer, 1
When heat-treated at 50 ° C. for 30 minutes, it is necessary that the heat shrinkage ratio of the film in the width direction is 0.2 to 0.8%, more preferably 0.4 to 0.6%.

If it is less than 0.2%, the hard coat layer contracts more greatly, the hard coat layer pulls the end portion of the polyester film, and the hard coat layer is likely to bend (curl) with the hard coat layer inside. Become. 0.8
When it exceeds%, the polyester film shrinks more, the polyester film pulls the end portion of the hard coat layer, and the hard coat film is likely to be curved (curled) with the polyester film inside.

The heat shrinkage can be obtained by heating a film piece having a certain size at a constant temperature for a specified time without applying a load, then cooling to room temperature and measuring the dimensional change of the taken out film piece. The set temperature in the heat shrinkage measurement should be set according to the conditions under which the hard coat film is heated. The setting time for measuring heat shrinkage is 3
The time is not limited to 0 minutes and may be 20 to 40 minutes. If it is 20 minutes or less, there is a possibility that the measurement may be performed without sufficient time for heat shrinkage due to insufficient time.

In order to obtain a more suitable polyester film, a load of 5.0 g / mm ² is applied in the width direction at 10 ° C.
The rate of elongation when reaching 150 ° C at a heating rate of / min is-
It is preferably 0.5 to 0.5%, more preferably -0.2 to 0.2.

Outside this range, the difference in heat shrinkage between the hard coat layer and the polyester film in the curl direction becomes large, and the hard coat film is likely to curve (curl).

The above-mentioned elongation is measured by TMA. TM
A measurement is performed with a constant pressure on the film piece in the desired direction.
Apply a weight and heat at a constant rate of temperature increase to determine the elongation in that direction.
It measures continuously with respect to changes. For TMA measurement
The weighted pressure at 5.0g / mm²Not limited to, set arbitrarily
Although it can be done, if it is too heavy, the difference in heat shrinkage will be sharply opposed to the elongation.
Since it cannot be projected, 10.0 g / mm ²Less pressure preferred
Good

In practice, a hard coat film obtained by heat treatment is usually used at room temperature, and the heat treatment is often performed at a constant temperature. It is preferable to control by the heat shrinkage rate. However, since TMA measurement can see a continuous change in heat shrinkability with respect to temperature, the tendency can be grasped and it is suitable for examining the optimum heat processing temperature of the hard coat film.

Since the hard coat film is wound into a roll with the longitudinal direction of the polyester film being the running direction as it is, when the hard coat film is run and heat-processed, tension is always applied in the longitudinal direction. It means that it is heat treated in. Therefore, the degree of thermal curl in the longitudinal direction is smaller than that in the width direction, but if the thermal shrinkage is significantly different, thermal curl can occur as in the width direction.
Also, the heat shrinkability in the longitudinal direction may affect the heat shrinkability in the width direction in terms of molecular orientation. In order to obtain a more preferable hard coat film, when heat-treated at 150 ° C. for 30 minutes, the heat shrinkage ratio in the longitudinal direction of the film is 0.6.
It is preferably from 1.2 to 1.2%, more preferably from 0.
8 to 1.0.

Outside this range, the difference in heat shrinkage between the hard coat layer and the polyester film in the curling direction becomes large, and the hard coat film is likely to curve (curl).

The set temperature in the thermal shrinkage measurement should be set according to the conditions under which the hard coat film is heated. The set time in the heat shrinkage rate measurement is not limited to 30 minutes and may be 20 to 40 minutes. If it is 20 minutes or less, there is a possibility that the measurement may be performed without sufficient time for heat shrinkage due to insufficient time.

Next, the production method of the polyester film according to the present invention will be described in detail, but the present invention is not limited to this.

The polyester used in the polyester film in the present invention is a polyester containing an aromatic dicarboxylic acid or an aliphatic dicarboxylic acid and a diol as main constituent components. Here, as the aromatic dicarboxylic acid, for example, terephthalic acid, isophthalic acid, phthalic acid,
1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 4,
4'-diphenyl dicarboxylic acid, 4,4'-diphenyl ether dicarboxylic acid, 4,4'-diphenyl sulfone dicarboxylic acid and the like can be mentioned. Further, examples of the aliphatic dicarboxylic acid include adipic acid, suberic acid, sebacic acid, dodecanedioic acid and the like. Among them, terephthalic acid and isophthalic acid are preferable. These acid components may be used alone or in combination of two or more, and further, an oxy acid such as hydroxybenzoic acid may be partially copolymerized.
Examples of the diol component include ethylene glycol, 1,2-propanediol, 1,3-propanediol, neopentyl glycol, 1,3-butanediol, 1,4-butanediol and 1,5-pentanediol. 1,6-hexanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, diethylene glycol, triethylene glycol, polyalkylene glycol, 2,2-bis (4- Examples thereof include hydroxyethoxyphenyl) propane. Among them, ethylene glycol is preferably used. These diol components may be used alone or in combination of two or more.

The polyester used in the polyester film of the present invention is preferably polyethylene terephthalate, a copolymer of ethylene terephthalate and ethylene isophthalate, polybutylene terephthalate and its copolymer, polybutylene naphthalate and its copolymer, Furthermore, polyhexamethylene terephthalate and its copolymer, polyhexamethylene naphthalate and its copolymer, etc. can be mentioned, and especially polyethylene terephthalate is preferably used from the viewpoint of the balance of heat resistance, transparency and mechanical strength.

The polyester in the present invention can be produced by a conventionally known method. For example, a method in which an acid component is directly esterified with a diol component and then the product of this reaction is heated under reduced pressure to polycondense while removing the excess diol component, or a dialkyl as the acid component There is a method in which an ester is used, and a transesterification reaction is performed between this and a diol component, and then polycondensation is performed in the same manner as described above. At this time, if necessary, conventionally known alkali metal, alkaline earth metal, manganese, cobalt, zinc, antimony, germanium and titanium compounds can be used as the reaction catalyst.

The polyester in the present invention may further contain, if necessary, a flame retardant, a heat stabilizer, an antioxidant, an ultraviolet absorber, an antistatic agent, an organic lubricant such as a pigment, a fatty acid ester, a wax, or a siloxane. An antifoaming agent or the like can be added.

The polyester film of the present invention is obtained by drying the above-mentioned polyester as required, supplying it to a known melt extruder, extruding it from a slit die into a sheet of a single layer or a composite layer, and applying an electrostatic charge. According to the above method, it is obtained by adhering to a casting drum, cooling and solidifying to form an unstretched sheet, stretching in two directions, and heat treatment. The two axes in the stretching direction are preferably orthogonal to each other, and the two axes are preferably clearly distinguishable in the width direction and the longitudinal direction. As the stretching method, known techniques such as a sequential biaxial stretching method of stretching in the longitudinal direction and then in the width direction and a simultaneous biaxial stretching method of stretching in the longitudinal direction and the width direction at substantially the same time are used.

In forming the polyester film of the present invention, the stretching conditions in the width direction are important. The thermal shrinkage in the width direction is greatly related to four parameters such as a draw ratio, a stretching temperature, a heat treatment temperature after stretching, and a relaxation shrinkage rate (hereinafter referred to as a relaxation rate) during heat treatment after stretching. When forming a polyester film, generally, the draw ratio is 2.0 to 5.0 times, and the draw temperature is 80 ° C to 13
It is preferable that the temperature of the heat treatment after stretching is 0 ° C. (above the glass transition point of the polyester to below the crystallization temperature) and 140 to 240 ° C. (above the crystallization temperature of the polyester to below the melting point), but the optimum heat shrinkage ratio is obtained. The balance of the four types of parameters is important for realization. Fixing the other three of the four types to increase only the draw ratio increases the heat shrinkage, increasing the drawing temperature decreases the heat shrinkage, and increasing only the heat treatment temperature after drawing decreases the heat shrinkage. , If you increase only the relaxation rate, the heat shrinkage rate will decrease. As an example, it is preferable that the stretching temperature is 120 ° C., the heat treatment temperature is 220 ° C., and the relaxation rate is 4.0% when the width-direction magnification is 3.7, but this is not a limitation.

When the film is formed by the above-mentioned sequential biaxial stretching,
Since it is stretched in the width direction after the lengthwise direction, it is not preferable to perform heat treatment immediately after stretching in the lengthwise direction. This is because crystallization is promoted and the degree of freedom of the crystal is lost during the subsequent stretching in the width direction. Further, when the film is formed by the above-mentioned simultaneous biaxial stretching, the heat treatment in the longitudinal direction and the heat treatment in the width direction are simultaneously performed, but the heat treatment condition should be adjusted to the width direction having high priority. In either stretching method, the thermal shrinkage in the longitudinal direction is greatly related to the stretching ratio and the stretching temperature, and it is not necessary (or low) to consider the heat treatment after stretching. Similarly in the longitudinal direction, the higher the draw ratio, the higher the heat shrinkage, and conversely, the higher the draw temperature, the smaller the heat shrinkage. As an example, the longitudinal magnification is 3.
At 0 times, the stretching temperature is preferably 90 ° C., but it is not limited to this.

The polyester film of the present invention preferably has a coating film on at least one surface in order to impart adhesiveness in post-processing and machine running property (sliding property). In particular, a coating film for adhering the polyester film and the hard coat layer is essential on the side on which the hard coat layer is provided. Also on the other side,
It is preferable to have a coating film having high adhesiveness so that a necessary adhesive can be easily applied when it is attached to a display, a window, or the like.

The component constituting this coating film is not particularly limited as long as it has adhesiveness to at least the hard coat layer, but it is more preferable to have adhesiveness to the pressure-sensitive adhesive. Further, when it is used for application to a display or a window, it is preferable to use as a main component a component having a refractive index as close as possible to the refractive index of the polyester film. Considering the adhesiveness and the refractive index, it is preferable to use polyester resin, acrylic resin or urethane resin as the main component of the coating film. Also, in order to improve heat resistance and moisture resistance, a melamine-based crosslinking agent or oxazoline is used. It is preferable to use a system cross-linking agent in combination, but the constituent component of the coating film is not limited to this. Further, various additives and fine particles may be blended in the coating film, and in particular, those in which inorganic particles are added in the coating film are more preferable because slipperiness and blocking resistance are improved.

In the production of the polyester film, a preferable method for providing the coating film is a method of providing it on the film during the production process and stretching it together with the film. Above all, in view of productivity, the film forming process is preferable. Among them, the method of providing by the coating method is most preferable, but the method is not limited to this. Various coating methods such as a reverse coating method, a gravure coating method, a rod coating method, a bar coating method, a Meyer bar coating method, a die coating method and a spray coating method can be used as the coating method on the polyester film. Further, corona discharge may be applied to the surface in consideration of the coating uniformity and adhesiveness of the coating film.

The thickness of the polyester film of the present invention is
It is desirable to satisfy the requirements of heat resistance, mechanical strength, and dimensional stability that can withstand application of a hard coat layer and higher-order processing. When the thickness is 50 μm or more, the thermal and mechanical stability is good, and when the thickness is 250 μm or less, the rigidity is not too high and the handleability is good, and the roll length is easy and the productivity is good. ˜250 μm is preferable, and more preferably 100 to 200 μm.

The polyester film of the present invention is used as a hard coat film having a hard coat layer on one side. The hard coat film is used for various purposes as a highly functional laminated film by further processing. For example, an antireflection film obtained by vapor-depositing an antireflection film to make it water-repellent, a water-repellent processed window sticking film having an ultraviolet absorbing function, a touch key provided with a transparent electrode, and the like.

The hard coat layer is for suppressing the contact of the tip or nail of a pencil or a ball-point pen, and the generation of scratches due to scratching when the surface is wiped for cleaning. When the thickness is 1 μm or less, sufficient surface hardness cannot be obtained, and when the thickness is 20 μm or more, flexibility of the film as a whole may be lost and problems such as cracks and curls may occur. Preferably 5 to 15 μm
Is more preferable.

The constituent component of the hard coat layer may be any known substance such as an inorganic oxide type such as polyorganosiloxane, silica or alumina, or an organic acrylic type. As a forming method, any of known techniques such as a vacuum deposition method and a wet coating method by applying and drying a solution may be used.

The evaluation criteria in the present invention are as follows.

(1) Thermal shrinkage It was measured based on the ASTM method.

(2) TMA elongation film pieces were set in a TM-9300 type thermomechanical tester manufactured by Vacuum Riko Co., Ltd., and a temperature rising rate was kept constant from room temperature with a load of a constant pressure applied in the measuring direction. It was measured at.

(3) Evaluation of thermal curl of hard coat film The hard coat film was cut into A4 size and placed on a flat glass plate (with the inner surface of the curl facing up), 1
After standing for a period of time, the height at which each vertex rises from the glass plate is measured, and the maximum height is evaluated in three levels (○: maximum height is 5 mm.
Hereafter, Δ: maximum height exceeds 5 mm and 10 mm or less, x:
The maximum height exceeds 10 mm). (◯) and (Δ) are good without curling, and (x) is the level of abnormal curl.

[0040]

EXAMPLES The following examples are merely examples, and the present invention is not limited thereto. Example 1 Polyethylene terephthalate was sufficiently dried in vacuum, and then melt extruded at 280 ° C., and electrostatically applied 2.
An unstretched sheet was obtained by cooling on a casting drum at 0 ° C. This sheet was preheated to 80 ° C. and then stretched 3.0 times in the longitudinal direction at a temperature of 90 ° C. After that, a coating film is applied to both sides of the film by a coating method, and then 120
The film was stretched 3.7 times in the width direction at 0 ° C. and then heat-treated at 220 ° C. with a relaxation rate (relaxation / shrinkage rate) set to 4.0%.
As a result, a polyethylene terephthalate film having a thickness of 188 μm was obtained.

The heat shrinkage ratio in the width direction (heating at 150 ° C. for 30 minutes) of this film was 0.5%. In addition, TMA measurement in the width direction (load 5.0 g / mm ² ,
Elongation at 150 ° C at heating rate 10 ° C / min) is 0
%Met. Also, the heat shrinkage in the longitudinal direction (30 at 150 ° C)
Minute heating) was 1.0%.

After applying a hard coat to one side of this film, the film was subjected to a water repellent treatment by heating at 150 ° C. for 1 minute, and the curl evaluation with the hard coat side facing up was (◯).

When this water-repellent hard coat film was applied as an antireflection film to a flat display, the passing rate was 98%. [Example 2] The stretching ratio in the longitudinal direction was 3.3 times, the heat treatment temperature after stretching in the width direction was changed to 200 ° C, and the film was formed in the same manner as in Example 1 except that polyethylene having a thickness of 188 µm was used. A terephthalate film was obtained.

Thermal shrinkage of the film in the width direction (150
(Heated at 0 ° C. for 30 minutes) was 0.7%. Also, T in the width direction
MA measurement (load 5.0 g / mm ² , heating rate 10 ° C /
Min), the elongation at 150 ° C was -0.4%. The heat shrinkage in the longitudinal direction (heating at 150 ° C. for 30 minutes) is 1.
It was 5%.

After applying a hard coat on one side of this film, the film was subjected to a water repellent finish by heating at 150 ° C. for 1 minute, and the curl property evaluation with the side opposite to the hard coat facing up was (Δ). .

When this water-repellent hard coat film was attached to a flat display as an antireflection film, the attachment pass rate was 93%. [Example 3] A polyethylene terephthalate film having a thickness of 188 µm was obtained by forming the film in the same manner as in Example 1 except that the stretching temperature in the longitudinal direction was changed to 80 ° C and the stretching ratio in the width direction was changed to 3.3 times. Got

The heat shrinkage ratio of this film in the width direction (150
(Heating at 30 ° C. for 30 minutes) was 0.2%. Also, T in the width direction
MA measurement (load 5.0 g / mm ² , heating rate 10 ° C /
Min), the elongation at 150 ° C. was 0.7%.
The heat shrinkage in the longitudinal direction (heating at 150 ° C. for 30 minutes) was 1.3%.

After applying a hard coat on one surface of this film, the film was subjected to a water repellent treatment by heating at 150 ° C. for 1 minute, and the curl evaluation with the surface on the hard coat side facing up was (Δ).

When this water-repellent hard coat film was attached to a flat display as an antireflection film, the attachment pass rate was 91%. [Comparative Example 1] The relaxation ratio (relaxation / shrinkage ratio) in the width direction was changed to 6.0%, and the film was formed in the same manner as in Example 1 to obtain a polyethylene terephthalate film having a thickness of 188 µm.

The heat shrinkage ratio of this film in the width direction (150
It was -0.1%. In addition, TMA measurement in the width direction (load 5.0 g / mm ² , heating rate 10 ° C /
Min), the elongation at 150 ° C. was 0.9%.
The heat shrinkage in the longitudinal direction (heating at 150 ° C. for 30 minutes) was 1.0%.

After applying a hard coat on one surface of this film, the film was subjected to a water repellent treatment by heating at 150 ° C. for 1 minute, and the curl evaluation with the hard coat side facing up was (x).

When this water-repellent hard coat film was applied as an antireflection film to a flat display, the passing rate was 64%. [Comparative Example 2] The relaxation rate (relaxation / shrinkage rate) in the width direction was changed to 2.0%, and the film was formed in the same manner as in Example 1 to obtain a polyethylene terephthalate film having a thickness of 188 µm.

The heat shrinkage ratio of this film in the width direction (150
It was 1.0%. Also, T in the width direction
MA measurement (load 5.0 g / mm ² , heating rate 10 ° C /
Min), the elongation percentage at 150 ° C. was −0.8%. Also, heat shrinkage in the longitudinal direction (heating at 150 ° C for 30 minutes)
Was 1.0%.

After applying a hard coat on one side of this film, the film was subjected to a water repellent treatment by heating at 150 ° C. for 1 minute, and the curl evaluation with the opposite side of the hard coat facing up was (x). .

When this water-repellent hard coat film was applied as an antireflection film to a flat display, the passing rate was 69%.

The results of the characteristics of Examples 1 to 3 and Comparative Examples 1 and 2 are summarized in Table 1.

[0057]

[Table 1]

[0058]

EFFECT OF THE INVENTION By controlling the thermal behavior of the polyester film, curling during heat processing of the hard coat film can be suppressed, the sticking of the hard coat film is improved, and the productivity is improved. .

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 4F006 AA35 AB39 BA02 CA05                 4F071 AA46 AF21 AF21Y AF61                       AF61Y AH16 BA01 BB06                       BB08 BC01 BC02                 4F100 AK01A AK41B AT00B BA02                       CC00A GB41 JA03B JK12A                       JL04 YY00B

Claims (4)

[Claims] 1. A polyester film used for a laminated film having a hard coat layer on one side, wherein the film has a heat shrinkage in the width direction of 0.2 to 0.8% when heat-treated at 150 ° C. for 30 minutes. Is a polyester film. ^2. A load of 5.0 g / mm ² is applied in the width direction to 1
The elongation percentage when reaching 150 ° C. at a heating rate of 0 ° C./min is −0.5 to 0.5%.
The polyester film described in 1. 3. The polyester film according to claim 1, which has a heat shrinkage in the longitudinal direction of 0.6 to 1.2% when heat-treated at 150 ° C. for 30 minutes. 4. A hard coat film comprising the polyester film according to claim 1.