JP2001329078A - Releasing film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a releasing film which has good processability and makes possible a hue test. SOLUTION: The release film comprises a polyester film, wherein the polyester film has equation (1) for the longitudinal heat shrinkage rate (S1) and the lateral heat shrinkage rate (S2) to satisfy and has a surface roughness Ra of 5-50 nm. S1>S2 Formula (1).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a release film, and more particularly, to a release film suitably used for a polarizing plate which is easy to inspect a product.

[0002]

2. Description of the Related Art Conventionally, a polarizing plate has been used for an antireflection filter, eyeglasses, and the like. In recent years, a small general-purpose liquid crystal display for watches and calculators, as well as for OA, liquid crystal television, and in-vehicle use. The use of high-value-added products has been expanded, and the reliability of the products has been more and more required.

[0003] A polarizing plate usually comprises a polarizing film 1, a surface protective film 2, an adhesive layer 3, and a release film 4, as shown in FIG. The polarizing film 1 is formed by coating a polarizer having a polarizing axis in which a polarizing element such as iodine or a dichroic dye or the like is adsorbed and oriented on a hydrophilic film such as a polyvinyl alcohol-based film, and a cellulose film from above and below. Or coated with an acrylic resin. As the surface protective film 2, a transparent plastic film, such as a polyester film, having low moisture permeability and little deformation such as elongation is used. The surface protective film 2 and the polarizing film 1 are usually adhered with an adhesive (not shown), and the adhesive adheres firmly to the surface protective film 2 but does not adhere to the polarizing film 1 over time. However, those which can be easily peeled are used. The pressure-sensitive adhesive layer 3 is made of a pressure-sensitive pressure-sensitive adhesive for adhering the polarizing film 1 to a liquid crystal cell (not shown), and the release film 4 is made of a plastic film such as a polyester film.

In manufacturing such a polarizing plate, although the optical characteristics such as the light transmittance, the degree of polarization, and the haze of the polarizing film 1, which is a raw material, are inspected and used in advance, during the manufacturing process for the polarizing plate. Defects may occur due to mechanical stress etc. on the polarizing film of the final product, therefore, usually use a device that has a light source inside and a polarizing film on top of it so that only polarized light can be extracted. Inspection is performed by the cross Nicol method.

Conventionally, a plastic film such as a polyester film is used as the release film 4 in the polarizing plate. However, since the plastic film has orientation and birefringence, when the polarizing plate is inspected by the crossed Nicols method, the hue change and the light transmission phenomenon are caused by the influence of the birefringence. This causes inconvenience that it is difficult to accurately inspect a hue change due to residual stress of a polarizing film or a retardation film.

In order to solve these inconveniences during inspection, a release film in which the in-plane molecular orientation of a plastic film is balanced has been proposed (Japanese Patent Laid-Open No. 6-3664).
Has been made. However, in this proposal, it is difficult to balance the orientation of the film, and in particular, it is difficult to balance the orientation uniformly in the width direction of the film, so that there is a problem that only a limited portion can be used.
Separately, a proposal of a release film in which the retardation value of a biaxially oriented polyester film is specified (Japanese Unexamined Patent Publication No.
No. 70629), however, there is a problem that wrinkles occur during lamination only when the retardation is specified.

[0007]

In view of such circumstances,
The present inventors have conducted intensive studies with the aim of finding a method capable of accurately inspecting the hue change of a product by the crossed Nicols method, and as a result, by specifying the properties of the polyester film used for the release film, The inventors have found that the above objects can be achieved, and have completed the present invention.

An object of the present invention is to provide a release film having extremely good processability and hue testability.

[0009]

The release film of the present invention comprises a polyester film, and the heat shrinkage (S1) in the longitudinal direction of the polyester film and the heat shrinkage (S2) in the direction perpendicular thereto are represented by the following formula (1). A release film that satisfies 1) and has a surface roughness Ra of 5 to 50 nm.

S1> S2 Formula (1) Further, in the release film of the present invention, the polyester film has a refractive index (n1) in the longitudinal direction of 1.500 to 1.650.
And the refractive index (n2) in the direction perpendicular to the longitudinal direction is 1.5
It is preferable that the ratio is in the range of 00 to 1.700, and the relationship between n1 and n2 satisfies the following expression (2).

0.20> n2−n1 ≧ 0.01 Equation (2)

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The release film of the present invention is basically composed of a polyester film.

The polyester constituting the polyester film used in the release film of the present invention is a polyester containing an aromatic dicarboxylic acid or an aliphatic dicarboxylic acid and a diol as main 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′-diphenyldicarboxylic acid,
4,4'-diphenyl ether dicarboxylic acid, 4,4 '
Diphenyl sulfone dicarboxylic acid and the like can be mentioned. In addition, examples of the aliphatic dicarboxylic acid include adipic acid, suberic acid, sebacic acid, dodecandionic acid, and the like. Among them, preferred dicarboxylic acids are terephthalic acid and isophthalic acid. These acid components may be used alone or in combination of two or more,
Further, an oxyacid such as hydroxybenzoic acid may be partially copolymerized.

As the diol component, for example, ethylene glycol, 1,2-propanediol, 1,3
-Propanediol, neopentyl glycol, 1,3
-Butanediol, 1,4-butanediol, 1,5-
Pentanediol, 1,6-hexanediol, 1,2
-Cyclohexane dimethanol, 1,3-cyclohexane dimethanol, 1,4-cyclohexane dimethanol, diethylene glycol, triethylene glycol,
Examples thereof include polyalkylene glycol and 2,2-bis (4-hydroxyethoxyphenyl) propane. Among them, ethylene glycol is preferably used.
These diol components may be used alone or in combination of two or more.

Preferred polyesters used in the polyester film of the present invention include polyethylene terephthalate, a copolymer of ethylene terephthalate and ethylene isophthalate, polybutylene terephthalate and its copolymer, polybutylene naphthalate and its copolymer. And polyhexamethylene terephthalate and a copolymer thereof, and polyhexamethylene naphthalate and a copolymer thereof.

The polyester constituting the polyester film 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 remove the excess diol component and polycondensate to produce a dialkyl acid. There is a method of using an ester, performing a transesterification reaction between the ester and a diol component, and then performing polycondensation in the same manner as described above. At this time, if necessary, conventionally known alkali metals, alkaline earth metals, manganese, cobalt, zinc, antimony, germanium, and titanium compounds can be used as the reaction catalyst.

The polyester in the present invention may contain, if necessary, an organic lubricant such as a flame retardant, a heat stabilizer, an antioxidant, an ultraviolet absorber, an antistatic agent, a pigment, a fatty acid ester, a wax, or a polysiloxane. A foaming agent and the like can be blended.

The intrinsic viscosity of the polyester used for the polyester film of the present invention is usually preferably 0.5 or more, more preferably 0.6 or more. Intrinsic viscosity is 0.
If it is less than 5, the film-forming stability decreases, and it becomes particularly difficult to cast a thin film.

The heat shrinkage in the longitudinal direction (S1) of the polyester film of the present invention and the heat shrinkage in the direction perpendicular thereto (S2)
Needs to satisfy the following expression (1).

S1> S2 Equation (1) If the heat shrinkage is out of this range, a problem such as wrinkling of the film occurs in the processing step of laminating the release film on the polarizing plate, and the subsequent change in hue may occur. It is not preferable because it causes inconvenience that inspection is difficult.

The heat shrinkage (S1) in the longitudinal direction of the polyester film of the present invention and the heat shrinkage (S2) in the direction perpendicular thereto.
In order to make the polyester film have the above-mentioned range, it is effective to stretch the polyester film so that the orientation in the longitudinal direction does not advance and the perpendicular direction thereof is sufficiently oriented.

The heat shrinkage in the longitudinal direction (S1) of the polyester film and the heat shrinkage in the direction perpendicular thereto (S2)
Is preferably 0 to 20%, more preferably 0 to 20%.
10%.

The surface roughness Ra of the release film of the present invention is:
It is 5 to 50 nm, preferably 10 to 30 nm. Here, the surface roughness Ra is a center line average roughness. If the surface roughness Ra is out of this range, problems such as wrinkling of the film in the processing step of laminating the release film on the polarizing plate or lamination error due to excessive slippage occur, and the subsequent hue change can be accurately performed. This is not preferable because it causes inconvenience that is difficult to inspect.

In order to keep the surface roughness Ra of the release film of the present invention within the range of the present invention, a lubricant may be provided. Although there is no particular limitation on the method for imparting lubricity, for example, clay, mica, titanium oxide, calcium carbonate, kaolin, talc, inorganic particles such as wet or dry silica, acrylic acid polymers, polystyrene and the like For example, a method using so-called internal particles formed by deactivating a catalyst or the like added during the polyester polymerization reaction, a method using a surfactant, and the like. The amount of the particles is preferably 0.005 to 10 parts by weight, more preferably 0.01 to 3 parts by weight, based on 100 parts by weight of the polyester polymer. The average diameter of the particles is preferably 0.01 to 3 μm, more preferably 0.1 to 2 μm. Of course, a plurality of particles having different types and average diameters can be used in combination.

In order to adjust the surface roughness (Ra) of the polyester film of the present invention to the above-mentioned range, a method of uniaxially stretching the unstretched polyester containing the lubricating agent, a method of stretching the unstretched polyester film in the longitudinal direction, or the like. An effective method is to stretch the film so that the alignment does not proceed, and then stretch the film so that the film is sufficiently oriented in the perpendicular direction.

The refractive index (n1) in the longitudinal direction of the polyester film of the present invention is preferably from 1.500 to 1.65.
0, the refractive index (n2) in the direction perpendicular to the longitudinal direction is 1.50
It is preferably 0 to 1.700, and it is preferable that the relationship between n1 and n2 satisfies the following expression (2) for accurate hue inspection.

0.20> n2-n1 ≧ 0.01 Equation (2) Here, the refractive index is a refractometer (ATAGO 4 manufactured by Atago Co., Ltd.).
It was determined by measuring using T). The measurement temperature was 25 ° C,
The measurement was performed using methylene iodide as the mounting solution.

If the refractive indices n1 and n2 are out of the above ranges, a hue change and a light transmission phenomenon occur when the polarizing plate is inspected by the crossed Nicols method, and the hue change due to the residual stress of the polarizing film or the retardation film. Is not preferable because it causes inconvenience in that it is difficult to accurately inspect the data.

As a method for producing a polyester film in the present invention, a polyester containing the above-mentioned lubricant in the range of the present invention is dried as required, and then supplied to a known melt extruder and passed through a desired filter. After that, the sheet is extruded into a sheet from a slit die, brought into close contact with a casting drum by a method such as electrostatic application, and cooled and solidified to obtain an unstretched film. Next, the unstretched film is immediately guided to a tenter and stretched in the lateral direction, and a uniaxial stretching method of performing a heat treatment, or stretching the unstretched film in a longitudinal direction at a magnification such that the orientation does not proceed, and then stretching the film in the transverse direction, or performing a heat treatment,
Conversely, it is a sequential biaxial stretching method in which the film is stretched in the longitudinal direction at a magnification such that the orientation does not progress after the transverse stretching, and then heat-treated.

Here, the magnification at which the orientation does not advance means that the refractive index of the film stretched in the longitudinal direction is preferably 1.
500-1.630, more preferably 1.500-1.
600. The stretching ratio is preferably from 1.5 to 5.0 times, more preferably from 2.5 to 4.5 times, when the film is stretched uniaxially in the transverse direction. In the sequential biaxial stretching method, the stretching ratio in the longitudinal direction is 1.1 to
It is preferably 4.0 times, more preferably 1.5 to 3.5.
The draw ratio in the transverse and transverse directions is preferably 1.5 to 5.0 times, and more preferably 2.5 to 4.5 times. The stretching speed is desirably 1000% / min to 200,000% / min, and the stretching temperature can be any temperature as long as it is equal to or higher than the glass transition temperature of the polyester and equal to or lower than the glass transition temperature + 100 ° C. To 120 ° C, more preferably 70 to 100 ° C.

In the case of sequential biaxial stretching, the stretching temperature in the longitudinal direction is preferably from 70 to 120 ° C., more preferably from 70 to 100 ° C. The stretching temperature in the transverse direction is preferably equal to or higher than the glass transition temperature of the polyester and equal to or lower than the stretching temperature in the longitudinal direction, and is usually preferably 70 to 120 ° C, more preferably 70 to 100 ° C.

After the stretching, the film is subjected to a heat treatment. This heat treatment is performed in an oven, on a heated roll, or the like.
It can be performed by any conventionally known method. The heat treatment temperature can be any temperature from 90 to 240 ° C, but is preferably from 90 to 220 ° C. From the viewpoint of making the physical properties uniform in the film width direction, it is preferable that after the stretching, the polymer is cooled at a temperature equal to or lower than the glass transition temperature of the polymer, and then the heat treatment is performed. Is preferred. Further, the heat treatment time can be arbitrarily set, but it is usually preferable to perform the heat treatment for 1 to 60 seconds. The heat treatment may be performed while relaxing the film in the longitudinal direction and / or the width direction.

Further, re-stretching may be performed once or more in each direction, and then heat treatment may be performed.

In the present invention, it is preferable to improve the adhesiveness by subjecting the film to a surface treatment such as a corona discharge treatment in order to further improve the characteristics. After the polyester film obtained by the heat treatment is once cooled to about room temperature, it can be further aged at a relatively low temperature of 40 to 90 ° C. for about 5 seconds to about 1 week.

It is preferable that at least one surface of the polyester film of the present invention has been subjected to a release-releasing treatment. The method for imparting releasability is not particularly limited, but silicone coating is preferred. Among them, a treatment for forming a cured silicone resin coating film is particularly preferable. The cured silicone resin coating film can be formed by applying a coating liquid containing a curable silicone resin to at least one surface of a polyester film, drying and curing. As the curable silicone resin, for example, a resin of any reaction system such as a condensation reaction system, an addition reaction system, and an ultraviolet or electron beam curing system can be used. These can be used alone or in combination of two or more.

[Method of Measuring Characteristics] (1) Thermal Shrinkage Shrinkage when a thermoplastic film cut to a width of 10 mm and a length of 200 mm is subjected to a load of 5 g and left in a gear oven heated to 150 ° C. for 30 minutes. Expressed in quantity.

(2) Surface Roughness The surface roughness Ra is the center line average roughness. The measurement was performed using a high-precision thin film step measuring device ET-10 manufactured by Kosaka Laboratory Co., Ltd. The conditions were as follows, and the average value of the 20 measurements was taken as the measured value. These measurements were made by scanning the stylus in the width direction of the film.・ Rib of tip of stylus: 0.5 μm ・ Load of stylus: 5 mg ・ Measuring length: 1 mm ・ Cutoff: 0.08 mm ・ Speed of stylus: 4 μm / sec The definition of Ra is, for example, “Surface roughness” by Jiro Nara Measurement and Evaluation Method "(Tokyo Gijutsu Center, 1983).

(3) Glass transition point (Tg), melting point (T
m) Using a differential scanning calorimeter RDC220 manufactured by Seiko Denshi Co., Ltd., 5 mg of a film sample was collected, and the melting point (Tm) was determined from the temperature of the endothermic peak when the temperature was raised from room temperature at a rate of temperature rise of 20 ° C./min. I asked. The glass transition temperature (Tg) of the film sample was raised to 280 ° C., kept at 280 ° C. for 5 minutes, quenched with liquid nitrogen, and raised again from room temperature at a rate of 2 ° C.
The temperature was measured at 0 ° C./min.

(4) Hue testability: A 200 μm thick polarizing film coated with triacetyl cellulose from above and below, with iodine adsorbed and oriented on polyvinyl alcohol, and a 10 μm adhesive applied to a thickness of 4 μm.
A surface protection film made of a 0 μm polyester protection film is stuck, and a 25 μm
It was adhered as a release film of the present invention having a thickness of 65 μm to which a pressure-sensitive adhesive was applied, and a polarizing plate having a structure shown in FIG. 1 was prepared. The obtained polarizing plate is provided with a light source inside, and a polarizing film is disposed on a device on which a polarizing film is disposed so that only polarized light can be extracted, so that light is transmitted from the release film side, and a polarizing film is formed. Was examined for hue change. The criteria are as follows.・ Precise inspection possible without hue change and light transmission → ○ ・ Color unevenness and light leakage occur, making accurate inspection difficult → × (5) Workability The above 200 μm polarizing film cut into A4 size and 10 μm The protective film of the present invention coated with the pressure-sensitive adhesive was adhered while applying tension with a silicone rubber roll heated to 70 ° C. The criteria are as follows.・ Very good bonding, no wrinkles or bubbles in protective film. → ○ ・ Insufficient lamination, or wrinkles or bubbles are generated in the protective film. → ×

[0040]

EXAMPLES Example 1 A raw material obtained by adding 0.05% by weight of calcium carbonate having an average particle diameter of 1.1 μm to a polyethylene terephthalate resin (Tg = about 75 ° C., Tm = about 260 ° C.) was used. It is supplied to an extruder, melted, extruded from a die, and cooled with a 600 mm diameter cooling drum (2
5 ° C.) to produce an unstretched film.

The obtained unstretched film was fed into a stenter type stretching machine, stretched 3.85 times in the width direction at 85 ° C. as shown in Table 1, and then passed through an intermediate cooling zone at 50 ° C. Heat treated at 140 ° C, thickness 40μm
Was obtained. Tables 2 and 3 show the evaluation results of the obtained films. Workability was good, and evaluation of hue change was also good.

(Examples 2 to 7) A raw material obtained by adding 0.05% by weight of calcium carbonate having an average particle size of 1.1 μm to a polyethylene terephthalate resin (Tg = about 75 ° C., Tm = about 260 ° C.) was used. Was extruded from a die and cast on a cooling drum (25 ° C.) having a diameter of 600 mm to form an unstretched film.

After the obtained unstretched film was stretched in the lengthwise direction by a roll heated to 95 ° C. to a magnification shown in Table 1, the stretched film was sent to a stenter type stretching machine.
The film is stretched 3.65 times in the width direction at 85 ° C. and then passed through an intermediate cooling zone at 50 ° C., and then 140, 180, 20
Heat treatment was performed at 0 ° C. to obtain a stretched film having a thickness of 40 μm. As shown in Tables 2 and 3, the evaluation results of each of the obtained films showed that the processability was good and the evaluation of the hue change was also good.

Example 8 A raw material obtained by adding 0.05% by weight of calcium carbonate having an average particle size of 1.1 μm to a polyethylene terephthalate resin (Tg = about 75 ° C., Tm = about 260 ° C.) was extruded with a screw diameter of 40 mm. The mixture was supplied to a machine, melted, extruded from a die, and cast on a cooling drum (25 ° C.) having a diameter of 600 mm to form an unstretched film.

After the obtained unstretched film was stretched 2.5 times in the length direction as shown in Table 1 by a roll heated to 95 ° C., the stretched film was fed into a stenter type stretching machine, and was heated at 85 ° C. The film is stretched 3.5 times in the width direction at, the film is once sent out from the stenter, then sent to the second stenter, and stretched 1.2 times in the transverse direction at 95 ° C.
After passing through an intermediate cooling zone at 0 ° C., heat treatment was performed at 200 ° C. to obtain a stretched film having a thickness of 40 μm. As shown in Tables 2 and 3, the evaluation results of each of the obtained films showed that the processability was good and the evaluation of the hue change was also good.

(Comparative Example 1) A thickness of 40 μm was obtained in the same manner as in Example 1 except that the longitudinal stretching ratio was 4.0 times and the transverse stretching ratio was 1.0 times as shown in Table 1. Was obtained. The evaluation results of the obtained films are as shown in Tables 2 and 3, and the workability was poor. In the evaluation of hue change, color unevenness and light leakage occurred, and it was difficult to perform an accurate inspection.

Comparative Example 2 A stretched film having a thickness of 40 μm was obtained in the same manner as in Example 1, except that no particles were added to the polyethylene terephthalate resin. The evaluation results of the obtained films are as shown in Tables 2 and 3, and the workability was poor. In the evaluation of hue change, color unevenness and light leakage occurred, and it was difficult to perform an accurate inspection.

Comparative Example 3 In Example 1, the particles added to the polyethylene terephthalate resin had an average particle size of 5.
A stretched film having a thickness of 40 μm was obtained in the same manner as in Example 1, except that silicon oxide was changed to 0 μm. The evaluation results of the obtained films are as shown in Tables 2 and 3, and the workability was poor. In the evaluation of hue change, color unevenness and light leakage occurred, and it was difficult to perform an accurate inspection.

Comparative Example 4 In Example 1, the particles added to the polyethylene terephthalate resin had an average particle size of 5.
0 μm silicon oxide, and the longitudinal stretching ratio was 4.0.
A 40-μm-thick stretched film was obtained in the same manner as in Example 1, except that the draw ratio and the transverse stretch ratio were changed to 1.0. The evaluation results of the obtained films are as shown in Tables 2 and 3, and the workability was poor. In the evaluation of hue change, color unevenness and light leakage occurred, and it was difficult to perform an accurate inspection.

[0050]

[Table 1]

[0051]

[Table 2]

[0052]

[Table 3]

[0053]

According to the present invention, the relationship between the heat shrinkage in the longitudinal direction of the polyester film and the heat shrinkage in the direction perpendicular to the polyester film and the surface roughness are defined to obtain a release film having good workability and good hue inspection. Can be

[Brief description of the drawings]

FIG. 1 is a model sectional view of a polarizing plate.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Polarizing film 2 ... Surface protection film 3 ... Adhesive layer 4 ... Release film

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) B29K 67:00 B29K 67:00 B29L 7:00 B29L 7:00 C08L 67:02 C08L 67:02 F term (reference) 2H049 BA02 BB13 BB54 BC03 BC22 2H091 FA08X FA08Z GA16 LA09 LA16 4F006 AA35 AB39 BA11 CA05 EA03 4F071 AA45 AA46 AF31Y AF61Y AH19 BA01 BB06 BB07 BB08 BC01 BC16 4F210 AA24 AE01 AG01 RA03 RC02 RG35 RG35

Claims (3)

[Claims] 1. A polyester film having a heat shrinkage (S1) in a longitudinal direction and a heat shrinkage (S2) in a direction perpendicular to the polyester film satisfying the following formula (1) and a surface roughness: A release film having a Ra of 5 to 50 nm. S1> S2 Expression (1) 2. The polyester film has a refractive index (n1) in the longitudinal direction of 1.500 to 1.650, and a refractive index (n2) in a direction perpendicular to the longitudinal direction of 1.500 to 1.700.
The release film according to claim 1, wherein the relationship between n1 and n2 satisfies the following expression (2). 0.20> n2−n1 ≧ 0.01 Expression (2) 3. A release film comprising a polyester film and satisfying the following requirements (a) to (d). (A) The heat shrinkage (S1) in the longitudinal direction of the polyester film and the heat shrinkage (S2) in the direction perpendicular thereto satisfy the following expression (1): S1> S2 (1) (b) The surface roughness Ra of the polyester film is 5 to 50
(c) the refractive index (n) in the longitudinal direction of the polyester film.
1) is 1.500 to 1.650, the refractive index (n2) in the direction perpendicular to the longitudinal direction is 1.500 to 1.700, and (d) the relationship between n1 and n2 is represented by the following formula (2). 0.20> n2−n1 ≧ 0.01 Expression (2)