JP2002060707A - Surface protective film and its laminate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a surface protective film having body excellent close adhesion and peelability without varying with time and without deteriorating the inspectability of a laminated surface to be protected. SOLUTION: This surface protective film is a laminated film having an adhesive mass layer formed on one surface of a biaxially stretched polyester film and a protective layer formed on the other surface. The adhesive mass layer simultaneously has >=-60 and <=-20 deg.C glass transition temperature, >=0.1 and <=0.2 MPa tensile modulus of elasticity, >=15 and <=25 μN/cm surface tension, >=30 and <=500 mN/25 mm adhesive strength (A) after being laminated onto a stainless steel plate and allowed to stand at 23 deg.C for 1 day and >=0.5 and <=2 value obtained by dividing the adhesive strength (B) after being laminated onto a stainless steel plate and allowed to stand at 60 deg.C for 1 week by the adhesive strength (A) and >=3 and <=50 μm thickness.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface protective film, and more particularly, to a protective surface having a rough surface, even if it is bonded to a surface to be protected. The present invention relates to a highly transparent surface protective film provided with an improved pressure-sensitive adhesive layer that peels off lightly regardless of time, and which does not impair the inspection property of a bonded protected surface.

[0002]

2. Description of the Related Art A surface protective film generally comprises a plastic film substrate and an adhesive layer provided on one surface of the substrate, and is used for protecting the surface of optical components. Here, the optical component includes, for example, a display such as a television, a computer, a word processor, or a car navigation system.The surface protection is a process in which a component to be protected is manufactured by attaching a surface protection film to a surface thereof and assembling the component. It means use such as peeling off the surface protective film after completion or during actual use. In addition, since liquid crystal displays are rapidly growing, surface protective films are used to protect the surface of liquid crystal displays, and also to protect the surface of optical components used in the manufacturing process, such as polarizing plates, retarders, and viewing angle widening films. It has been heavily used.

By the way, these surface protective films are:
Generally, a transparent olefin-based film such as polyethylene or polypropylene has been used as a substrate. However, due to the recent trend toward higher definition and higher responsiveness of a liquid crystal display typified by a TFT system (thin film transistor system), the demand for a surface protective film used during the production thereof has become severer. Insufficient ones have been obtained with surface protective films. For example, in the case of using an olefin-based film such as a conventional polyethylene film as a base material, the transparency is poor, or there are many gels such as fish eyes or the like, and the surface of the film is not easily produced when manufacturing a polarizing plate or a liquid crystal display. If the product is inspected for defects while the protective film is adhered, there is a problem that the foreign matter on the surface protective film becomes a foreign matter defect and reduces the inspection accuracy of the product. This problem is important because simplification of the inspection process is required.

In addition, once a surface protective film is attached to a polarizing plate, a liquid crystal display, or the like, the surface protective film may remain attached for a long time until the next manufacturing step, such as when the surface protective film is used in an inspection process. Many. Then, when the surface protection film is peeled off after the inspection or the like is completed, if the peeling becomes heavy, the workability deteriorates, and a part of the adhesive remains on a protected surface such as a display. The latter problem is an important problem because it causes defects such as foreign matter and distortion in display inspection and the like.

Further, some liquid crystal display components such as a polarizing plate have a small unevenness on the surface to suppress the reflection of light in order to suppress the glare of the display portion. A surface protective film is also used for these, but the pressure-sensitive adhesive layer of the surface protective film generally has a reduced adhesive strength in order to have removability. As a means for weakening the adhesive strength, generally, a method of increasing the cohesive strength of the adhesive or hardening the adhesive layer by including a component having a high glass transition temperature (Tg) or a large number of hard segments is often adopted. However, when a surface protective film having such a pressure-sensitive adhesive layer with reduced adhesive strength is bonded to a protected surface such as a polarizing plate provided with irregularities on the surface, the adhesive of the surface protective film is insufficient due to the irregularities. However, there is a problem that the portion that does not contact and spread does not increase, and air or the like does not escape completely in that portion. This problem is an important problem because the air becomes bubbles and hinders the appearance of foreign substances and the like during an inspection.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art, not to impair the inspectability of the bonded protected surface, and to obtain excellent adhesion and peelability which does not change with time. An object of the present invention is to provide a surface protective film having both functions.

[0007]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the present inventor has found that a biaxially oriented polyester film is used as a base material, and that a pressure-sensitive adhesive layer having appropriate softness and wettability is used. It has been found that an improved surface protective film can be obtained by using the pressure-sensitive adhesive of the present invention, and the present invention has been achieved.

Thus, according to the present invention, there is provided a laminated film comprising a biaxially oriented polyester film provided with an adhesive layer on one side and a protective layer on the other side, wherein the adhesive layer comprises (1) a glass transition (2) Tensile modulus is 0.1 MPa or more and 0.2 MPa or less; (3) Surface tension is 15 μN / cm or more and 25 μN / cm or less. (4) Adhesive strength (A) after being attached to a stainless steel plate and allowed to stand at 23 ° C. for 1 day is 30 mN / 25 mm or more and 500 m
N / 25 mm or less; (5) The value obtained by dividing the adhesive strength (B) after being stuck to a stainless steel plate and allowed to stand at 60 ° C. for 1 week by the adhesive strength (A) is 0.5.
2 or less; and (6) a thickness of 3 μm or more and 50 μm or less.

According to the present invention, a biaxially oriented polyester film has a length of 210 mm on one side and a length of 148 m on a side orthogonal to the biaxially oriented polyester film.
25μ per 25m area (310.8cm ² area)
m or more, and a size of 5 μm or more and 25
The number of foreign substances having a particle size of less than 10 μm or less, the protective layer contains a release agent and an antistatic agent, and the peeling force of the protective layer from the pressure-sensitive adhesive layer is 10 mN / 25 mm or more and 5000 mN.
/ 25 mm or less, or a visible light transmittance of the surface protective film of 70% or more and a haze of 10% or less.

Further, according to the present invention, the above-mentioned surface protective film and a release paper laminated on the pressure-sensitive adhesive layer of the film, particularly, the surface of the release paper to be bonded to the pressure-sensitive adhesive layer is made of silicone. There is also provided a laminate comprising a release paper in which at least one selected from a resin, a fluororesin, and an aliphatic wax is formed as a release layer.

According to the present invention, the surface protective film and the laminate of the present invention are used for protecting the surface of at least one laminate selected from a polarizing plate, a retardation plate and a viewing angle widening film.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The surface protective film of the present invention comprises a biaxially oriented polyester film as a substrate, a pressure-sensitive adhesive layer laminated on one surface of the substrate and a protective layer laminated on the other surface. Become. First, the biaxially oriented polyester film, the pressure-sensitive adhesive layer, and the protective layer will be described below.

[Biaxially Oriented Polyester Film] As the substrate of the surface protective film in the present invention, a biaxially oriented polyester film excellent in transparency, productivity and workability is used. The biaxially oriented polyester film is not particularly limited, but is preferably a biaxially oriented polyethylene terephthalate film or a biaxially oriented polyethylene-2,6-naphthalenedicarboxylate film. Also, the biaxially oriented polyester film is a single-layer film,
It may be a multi-layer film in which a plurality of layers are laminated by co-extrusion.

The polyester constituting the biaxially oriented polyester film in the present invention is preferably a crystalline linear saturated polyester comprising an aromatic dibasic acid component and a diol component. Examples of the polyester include polyethylene terephthalate, polypropylene terephthalate, and polystyrene. Butylene terephthalate, polyethylene-2,6-naphthalenedicarboxylate and the like can be mentioned. Further, a copolymer in which a part of these is substituted by another component, or a mixture with polyalkylene glycol or another resin may be used.

The method for producing a biaxially oriented polyester film in the present invention may be a conventionally known method such as a sequential biaxial stretching method or a simultaneous biaxial stretching method. For example, in the sequential biaxial stretching method, after sufficiently drying the above-mentioned polyester polymer, the polyester polymer is extruded from a die (for example, a T-die, an I-die, etc.) onto a cooling drum by a melt extrusion method, quenched, and then cooled. A stretched film or a co-extruded unstretched film is produced, and the unstretched film is stretched in the longitudinal direction at a temperature of 60 to 140 ° C. in the range of 2 to 5 times, and
It can be manufactured by stretching in the lateral direction at a temperature of 150 ° C. in a range of 2 to 5 times, and heat-setting at a temperature of 160 to 260 ° C. for 1 to 100 seconds. The heat setting may be performed in a state where shrinkage is restricted, and it is preferable to use an electrostatic contact method during melt extrusion.

The biaxially oriented polyester film in the present invention should be as isotropic as possible in order not to cause breakage in a specific direction. For example, the stretching ratio in the longitudinal direction and the transverse direction is set to be the same. Is preferred. The thickness of the film is preferably from 5 to 500 μm. The thickness of the film is more preferably 10 to 200 μm in order to improve the processability such as lamination and the productivity.

Further, the biaxially oriented polyester film of the present invention is intended to improve the slipperiness at the time of winding the film or the handling at the time of processing such as application of an adhesive.
It is preferable to include a lubricant. Preferred lubricants include inorganic fine particles such as calcium carbonate, alumina, kaolin, silica, titanium oxide, barium sulfate or zeolite, and organic fine particles such as silicone resin, cross-linked polystyrene or acrylic resin.
Of course, in addition to these lubricants, the biaxially oriented polyester film of the present invention may contain other additives such as a stabilizer, an ultraviolet absorber, a flame retardant, and an antistatic agent. The addition time of the fine particles and additives is not particularly limited as long as it is a stage until the biaxially oriented polyester film is formed.For example, it may be added at the polymerization stage, or may be added at the time of film formation. Good.

The surface roughness of the biaxially oriented polyester film in the present invention is preferably such that the center line average roughness (Ra) is 2 nm or more and 500 nm or less. If the center line average roughness is less than 2 nm, there is a possibility that the transferability such as slippage during processing may be impaired. On the other hand, the center line average roughness is 5
When the thickness is larger than 00 nm, the transparency is deteriorated to deteriorate the testability, and when the pressure-sensitive adhesive layer is provided, particularly when the pressure-sensitive adhesive is applied to the protective surface and the pressure-sensitive adhesive layer is provided on the biaxially oriented polyester film by the transfer method, In some cases, the pressure-sensitive adhesive and the biaxially oriented polyester film do not adhere uniformly due to the unevenness of the axially oriented polyester film.

Finally, the biaxially oriented polyester film of the present invention has a size of 25 μm or more in a film (area: 310.8 cm ² ) having a side length of 210 mm and a side length of 148 mm perpendicular thereto. It is preferable that there is no foreign matter and no more than 10 foreign matters have a size of 5 μm or more and less than 25 μm. When a foreign substance having a size of 25 μm or more is present, voids or the like are generated at the time of applying or transferring the adhesive, and the adhesive is removed only in that portion beyond its size,
Or, it may cause a local appearance defect that can be visually confirmed because of swelling. Also, 5μ
If there are more than 10 foreign particles having a size of m or more and less than 25 μm, the size of the particles is hard to be confirmed by visual inspection, but the defects may be noticeable due to the large number. Below, the length of one side 2
The number of foreign substances having a size of 25 μm or more existing in the film per 10 mm and the width (the area of 310.8 cm ² ) of the side having a length of 148 mm orthogonal to the number of foreign substances is visually recognized. Sometimes referred to as the number of foreign substances.

[Adhesive layer] The adhesive layer in the present invention comprises:
It is necessary to have a property that can be easily adhered to a protected surface (such as a polarizing plate or a stainless steel plate) and that it can be easily peeled off. (1) The glass transition temperature is −60 ° C. or more and −20 ° C. or less; (2) The tensile elastic modulus is 0.1 MPa or more and 0.2 MPa or less; (3) The surface tension is 15 μN / cm or more and 25 μN / (4) Adhesive strength (A) after being attached to a stainless steel plate and left at 23 ° C. for 1 day is 30 mN / 25 mm or more and 500 m
N / 25 mm or less; (5) The value obtained by dividing the adhesive strength (B) after being stuck to a stainless steel plate and allowed to stand at 60 ° C. for 1 week by the adhesive strength (A) is 0.5.
Not less than 2; and (6) the thickness is not less than 3 μm and not more than 50 μm.

The glass transition temperature (Tg) of the pressure-sensitive adhesive layer is -6.
When the temperature is less than 0 ° C. or the tensile elasticity of the pressure-sensitive adhesive layer is less than 0.1 MPa, it is extremely soft even in a normal use environment such as room temperature, and spreads unnecessarily onto the bonded protected surface, resulting in excessive The adhesiveness is increased and the releasability is poor. On the other hand, the glass transition temperature of the adhesive layer is -20 ° C.
Or the tensile modulus of the adhesive layer is 0.2MP
If it exceeds a, it will lack in softness in an environment such as room temperature, and will not sufficiently spread to the bonded protected surface. If the surface tension of the adhesive layer is less than 15 μN / cm, the desired adhesive strength with the protected surface to be bonded cannot be obtained, while 25 μN / cm.
If it exceeds cm, an unnecessarily high adhesive force is generated between the surface and the surface to be protected, resulting in a lack of releasability.

The adhesive strength (A) after being bonded to a stainless steel plate and left at 23 ° C. for 1 day is 30 mN / 25 mm.
If it is less than the above, end-turning occurs or the film is easily peeled off by any contact. The term “end-turning” means that, for example, when a polarizing plate is cut into a specific rectangle, the displacement of the polarizing plate under temperature and humidity is large, so that the displacement cannot be sufficiently absorbed. Means a phenomenon that the protective film (protective film) is easily peeled off.
On the other hand, if the adhesive strength (A) exceeds 500 mN / 25 mm, the adhesive may not be easily peeled off in the step of peeling from the protected surface, and may damage the unprotected surface. In addition, the said adhesive force A may only be hereafter called adhesive force A.

Furthermore, it is necessary that the adhesion to the stainless steel plate does not change with time, and the adhesion (B) after being attached to the stainless steel plate and left at 60 ° C. for one week is determined by the above-mentioned adhesion (A). If the divided value is less than 0.5 times or more than 2 times, the adhesive force changes excessively, so that setting and management when automatically peeling off the surface protective film by a machine becomes complicated, and in the case of more severe In addition, the surface to be protected may be damaged at the time of peeling, or may be peeled off before peeling, so that the surface to be protected cannot be protected. In addition, the said adhesive force B may only be hereafter called adhesive force B simply.

Lastly, when the thickness of the pressure-sensitive adhesive layer is less than 3 μm, when the pressure-sensitive adhesive layer is laminated on a polarizing plate or the like having irregularities, it is governed by the hardness of the biaxially oriented polyester film which is the base material of the surface protective film, The pressure-sensitive adhesive does not sufficiently spread on the surface of the polarizing plate, or a partial lifting occurs when the pressure-sensitive adhesive is laminated without obtaining the required adhesive strength. On the other hand, if the thickness is greater than 50 μm, the adhesive force becomes excessively high, or uneven thickness occurs when applying the adhesive, or the applied adhesive layer is not uniformly cured, Furthermore, the production cost rises.

Preferred embodiments of the pressure-sensitive adhesive layer in the present invention are described below. The center line average roughness (Ra) of the pressure-sensitive adhesive layer in the present invention is preferably from 2 nm to 500 nm. There is no particular problem in the case where the center line average roughness is small, but when the center line average roughness is larger than 500 nm, the thickness, the adhesive strength, and the peeling strength of the pressure-sensitive adhesive layer satisfy the above-mentioned ranges when they are bonded to a polarizing plate or the like. However, even if they are not in close contact, they may be distorted or bubbles may be formed in the dents.

The pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer in the present invention does not deteriorate not only indoors but also outdoors.
It is necessary to be able to withstand various light rays, particularly ultraviolet rays, at the time of inspection and not to transfer components of the pressure-sensitive adhesive layer to the bonded protected surface, and an acrylic pressure-sensitive adhesive is preferable. The acrylic pressure-sensitive adhesive includes a solvent-based pressure-sensitive adhesive, an emulsion-based pressure-sensitive adhesive, and the like, and a solvent-based pressure-sensitive adhesive that easily provides the physical properties of the pressure-sensitive adhesive is particularly preferable. The acrylic solvent-based pressure-sensitive adhesive can be produced by solution polymerization so as to satisfy various properties, and as a raw material, a known material for solution polymerization of an acrylic pressure-sensitive adhesive can be used.

A preferred acrylic solvent-based pressure-sensitive adhesive is one whose main monomer is an acrylate ester such as ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate or octyl acrylate, and whose comonomer for improving cohesion is vinyl acetate or acrylonitrile. And styrene or methyl methacrylate, and those in which the functional group-containing monomer that further promotes high cross-linking and imparts stable and low adhesion is methacrylic acid, acrylic acid, itaconic acid, hydroxyethyl methacrylate or glycidyl methacrylate. Among these, those containing a large number of hydroxyl groups that can be highly crosslinked with an isocyanate-based curing agent, an aziridine-based curing agent, or the like are preferable because they can have low tackiness and tackiness and high cohesion. Further, in order to prevent the generation of air bubbles when bonded to a protected surface having irregularities, it is necessary to make the pressure-sensitive adhesive layer softer than usual, and among the above components, a skeleton having a low glass transition temperature (Tg) It is preferable to use a large amount of a main monomer component as a component and to reduce a comonomer component for improving a high Tg cohesive force.

The method for synthesizing the pressure-sensitive adhesive in the present invention can be carried out by a method known per se. For example, in the presence of an organic solvent such as ethyl acetate or toluene, the necessary raw materials are charged into a reaction tank, and heated using a peroxide system such as benzoyl peroxide or an azobis system such as azobisisobutyronitrile as a catalyst. It may be polymerized below. In order to increase the molecular weight, for example, it is preferable to use a method in which monomers are charged all at once in the initial stage, or to use ethyl acetate because toluene has a large chain transfer coefficient and suppresses polymer growth because of the organic solvent used. At this time, the weight average molecular weight (Mw) is preferably 300,000 or more, more preferably 400,000 or more. If the molecular weight is less than 300,000, even if cross-linked with an isocyanate curing agent, sufficient cohesion cannot be obtained,
Even if it is dropped immediately in the holding force evaluation under load, or if it is aged after pasting on a stainless steel plate or polarizing adhesive layer etc., when peeled, the adhesive will be protected surface such as stainless steel plate or polarizing plate May remain. In order to increase the molecular weight, control at the polymerization stage is important, but in general, the solvent system does not increase the molecular weight even if sufficient adhesive strength is obtained. It is necessary to improve the rate.

The curing agent for the pressure-sensitive adhesive is not particularly specified, but, in particular, an acrylic solvent-based general isocyanate-based, epoxy-based, or aziridine-based curing agent can be used. The adhesive may contain additives such as a stabilizer, an ultraviolet absorber, a flame retardant, and an antistatic agent. Further, the additive is necessary to suppress the increase in the adhesive force by using an adhesive having a low glass transition temperature, and also to suppress the increase in the adhesive force over time. Organic resin such as wax, silicone oil,
Although a fluorine-based resin or the like can be used, it is preferable that those components do not migrate to the bonded protected surface and do not impair the testability. For this reason, it is good that the adhesive component is partially reacted with, for example, in an organic resin such as a wax, a higher fatty acid ester having a reactive functional group such as a hydroxyl group, a carboxyl group, an epoxy group, an amine group, and an isocyanate group is used. It is preferably used.

The application of the pressure-sensitive adhesive solution to the biaxially oriented polyester film can be performed at any stage. Also,
When applying the coating solution to the biaxially oriented polyester film, if necessary, as a preliminary treatment to improve the adhesion, coating properties, flame treatment, corona discharge treatment, the biaxially oriented polyester film surface, By applying a physical surface treatment such as a plasma discharge treatment, or by applying a chemical surface treatment to apply an organic resin-based or inorganic resin-based paint during or after film formation, the adhesive and the biaxial The adhesion of the oriented polyester film can be strengthened.

As a method for applying the pressure-sensitive adhesive, any known method can be used, and for example, a die coater method, a gravure roll coater method, a blade coater method, a spray coater method, an air knife coat method, a dip coat method, and the like are preferable. And can be used alone or in combination.
The drying temperature when applying the pressure-sensitive adhesive is preferably such that the residual solvent is as small as possible.
It is preferable to dry at ~ 150 ° C for a drying time of 10 seconds to 5 minutes. Since the pressure-sensitive adhesive has fluidity, or when an isocyanate-based curing agent or the like is used as a crosslinking agent, the reaction is not completed immediately after heating and drying, and the reaction is completed to obtain a stable pressure-sensitive adhesive force. Therefore, it is preferable to perform curing. In general, curing is preferably performed for about one week or more at room temperature, and three days or more for heating at, for example, about 50 ° C. In the case of heating, if the temperature is too high, the planarity of the biaxially oriented polyester film as the base material may be deteriorated.

[Protective Layer] The protective layer according to the present invention is a component that protects an engineering component, for example, a transistor of a TFT type display panel, which is protected by peeling charge generated when the pressure-sensitive adhesive layer is peeled from a counterpart structure. It is preferable to prevent the occurrence of dust, or to prevent dust from adhering to the surface of the surface protective film or to easily remove the attached dust, and it is preferable to include a release agent or an antistatic agent. The release agent and the antistatic agent may be mixed and provided as a single layer, or an antistatic layer containing an antistatic agent may be provided first, and a release layer containing a release agent may be provided thereon. . The antistatic agent may be mixed with the pressure-sensitive adhesive layer or provided between the pressure-sensitive adhesive layer and the biaxially oriented polyester film. In this case, the protective layer may not contain the antistatic agent.

The release agent and the antistatic agent are added to the binder in order to improve the strength, water resistance, solvent resistance or blocking property of the protective layer or to improve the adhesion to the biaxially oriented polyester film. Is preferably formed. Examples of the binder include a thermoplastic resin such as a thermoplastic polyester resin and an acrylic resin or a thermosetting acrylic resin, or a polymer compound such as a thermosetting resin such as a urethane resin, a melamine resin, or an epoxy resin. As the crosslinking agent used together with the above resin, it is particularly preferable to include at least one selected from methylolated or alkylolated melamine-based, urea-based or acrylamide-based compounds, epoxy compounds and polyisocyanates. In addition,
When the antistatic layer and the release layer are separately provided, it is preferable that the binder components used for both have similar main components because of excellent adhesion.

The antistatic agent in the present invention is not particularly limited, but may be a quaternary ammonium salt, a pyridinium salt,
Various cationic antistatic agents having a cationic property such as a primary to primary amino group, a sulfonate group, a nitrate ester group,
Various types of anionic antistatic agents such as phosphate bases, etc., amphoteric antistatic agents such as amino acids and aminosulfates, and nonionic antistatic agents such as amino alcohols, glycerin and polyethylene glycol Surfactant-type antistatic agents, and those obtained by polymerizing these, can be preferably used. Further, those in which conductive polymers such as polyaniline, polypyrrole, and polythiophene and oxide-based fillers such as tin and antimony are dispersed can also be preferably used. Further, as the antistatic layer, a layer provided with a metal layer of silver, tin, or the like by a vapor phase growth method, a vacuum evaporation method, a sputtering method, a plasma CVD method, or the like is also preferable.

When the surface of the protective layer is a release layer, the release force of the release layer from the pressure-sensitive adhesive layer is 10 mN / 2 from the viewpoint of preventing contamination of the surface protective film surface and improving the wiping property of the dirt.
It is preferable that it is 5 mm or more and 5000 mN / 25 mm or less. When the peeling force is less than 10 mN / 25 mm, it is not preferable because it becomes slippery in handling. Also 50
If it exceeds 00 mN / 25 mm, deposits such as dirt cannot be easily removed, which is not preferable. Examples of the release agent include a silicone-based, fluorine-based, or alkyl polymer-based release agent, and an alkyl polymer-based material having a particularly low migration property is preferable in order to prevent contamination in the process. Preferred alkyl polymer systems are polymers having long alkyl side chains, having 12 or more carbon atoms, especially 16 carbon atoms.
Copolymers of alkyl acrylates having -20 alkyl groups and acrylic acid are preferred. When the number of carbon atoms in the alkyl chain of the alkyl acrylate is less than 12, sufficient releasability may not be obtained. Among them, copolymers obtained by long-chain alkylation of polyvinyl alcohol or polyethyleneamine with chlorinated alkylol or alkyl isocyanate are particularly preferable.

The method for forming a protective layer according to the present invention may be carried out by applying a coating liquid for forming a protective layer at the time of forming the film before the crystal orientation of the biaxially oriented polyester film is completed or after forming the film after the crystal orientation is completed. Good. As a method for coating the biaxially oriented polyester film, any known method can be applied. For example, a roll coating method, a gravure coating method, a reverse coating method, a spray coating method, or the like can be used alone or in combination. The coating of the protective layer is performed by applying a coating liquid containing the components for forming each of the protective layers to a substrate, and drying by heating to form a coating film. The heating conditions are 80-160 ° C and 1
It is preferably from 0 to 120 seconds, particularly from 120 to 150C for 20 to 60 seconds. Also, when applying the coating liquid to the biaxially oriented polyester film, if necessary, as a preliminary treatment for improving the adhesion and coating properties, the same biaxial as in the case of applying the pressure-sensitive adhesive layer described above. Physical surface treatment such as flame treatment, corona discharge treatment, plasma discharge treatment, etc. on the oriented polyester film surface, or chemical surface treatment applying organic or inorganic resin paint during or after film formation Is preferably applied.

The surface protective film of the present invention comprising the above-mentioned biaxially oriented polyester film, the pressure-sensitive adhesive layer and the protective layer preferably has high transparency in order to ensure easier testability. Visible light transmittance 70%
As described above, the haze is preferably 10% or less. When the light transmittance is less than 70% or the haze is more than 10%, transparency is poor, and for example, there is a concern that foreign matter cannot be detected in a defect inspection such as a foreign matter when a surface protective film is bonded to a polarizing plate. . Further, when the surface protective film of the present invention is provided with a protective layer containing the above-described release agent, it can be used in a state of a film roll in which the protective layer and the pressure-sensitive adhesive layer are superimposed. It may be a laminate in which another film, that is, a release paper, is superposed on the surface. The release paper in the present invention will be described below.

[Release Paper] In the present invention, for the purpose of protecting the pressure-sensitive adhesive layer of the surface protection film, a laminate in which release paper and the surface protection film are stacked may be used. Of course, it is not necessary to use a release paper by replacing the protective layer with a release layer of the release paper. As the base material of the release paper, it is preferable to use the above-described biaxially oriented polyester film. The release paper is
It is preferable that a release layer is formed on at least one side, and the release layer component is preferably a silicone resin, a fluororesin, an aliphatic wax, or an olefin resin. Depending on the type of the pressure-sensitive adhesive, there may be cases where it is not necessary to provide a release layer, and the components forming the release layer may be blended with various known additives as long as the object of the present invention is not hindered. good. Examples of the additive include an ultraviolet absorber, a pigment, an antifoaming agent, and an antistatic agent. The release layer can be applied by applying a coating liquid containing a component forming the release layer to a base film and drying by heating to form a coating film. The heating conditions are 80 to 160 ° C. for 10 to 120 seconds, especially 120 to 150 ° C. for 20 to 60 seconds.
Seconds are preferred. As the coating method, any known method can be used, and examples thereof include a roll coater method and a blade coater method.

In the present invention, it is preferable to provide an adhesive layer between the base film and the release layer in order to enhance the adhesion between the biaxially oriented polyester film as the base film for release paper and the release layer. . As a component forming the adhesive layer, for example, when the release layer is a silicone resin layer, a silane coupling agent is preferable. Those represented by the general formula Y-Si-X ₃ is more preferred as the silane coupling agent. Here, Y is, for example, an amino group, an epoxy group,
X represents a functional group represented by a vinyl group, a methacryl group, a mercapto group and the like, and X represents a hydrolyzable functional group represented by an alkoxy group. The thickness of the adhesive layer is 0.01 to 5 μm
Is preferable, and the range of 0.02 to 2 μm is particularly preferable. When the thickness of the adhesive layer is within the above range, the adhesion between the base film and the release layer becomes good, and the base film provided with the adhesive layer is difficult to block, so that problems in handling the release film are unlikely to occur. There are advantages.

[0040]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the present invention is limited to these Examples. In addition, each physical property value in an Example was measured and evaluated by the following methods.

(1) Peeling force Nitto 31B tape (manufactured by Nitto Denko Corporation) is adhered to the protective layer surface of the surface protective film with a rubber roller, and reciprocated once from above with a 2 kg rubber roller to make close contact. 30 ° C under the condition of 23 ° C and 55 ± 5% RH
Leave for a minute and cut into strips 25 mm wide. This was measured with a tensile tester (Strograph manufactured by Toyo Seiki Co., Ltd.) using 31B
The tape is pulled at 180 ° at 300 mm / min, and the strength is defined as the peeling force.

(2) Adhesive force with stainless steel plate (A) The adhesive layer surface of the surface protection film is directly adhered to the washed stainless steel plate with a rubber roller.
Reciprocate one time with a kg rubber roller to make close contact. It is left as it is under the condition of a temperature of 23 ° C. and a humidity of 55 ± 5% RH for one day, and then cut into strips having a width of 25 mm. This was attached to a tensile tester (Strograph manufactured by Toyo Seiki Co., Ltd.), and a stainless steel plate was fixed.
Per minute at 180 °, and the strength is defined as the adhesive force (A) with the stainless steel plate.

(3) Adhesion to stainless steel plate (B) A sample prepared in the same manner as the adhesion (A) was subjected to
For 1 week, return to room temperature, measure the adhesive strength after standing for 30 minutes with a tensile tester, and determine the strength as the adhesive strength (B) with the stainless steel plate.

(4) Glass transition temperature (Tg) Only the pressure-sensitive adhesive layer was formed into a sheet having a uniform thickness, and a dynamic viscoelasticity measuring device (Vibron manufactured by A & D Corp.) was used. Measure under the condition of ° C / min. The storage modulus (E ') is greatly reduced and ta
The temperature at which the maximum value of nδ becomes the glass transition temperature (Tg).

(5) Tensile modulus of pressure-sensitive adhesive Only the pressure-sensitive adhesive layer was formed into a sheet having a uniform thickness,
Make it a narrow strip. At this time, the thickness of the sheet is measured. Next, this is attached to a tensile tester (Strograph manufactured by Toyo Seiki Co., Ltd.), and is pulled at a speed of 5 mm / min to create a stress / strain curve. The slope of the tangent at the time of rising is determined, divided by the cross-sectional area, and defined as the tensile modulus.

(6) Surface Tension of Adhesive Water (surface tension within 72.8 μN / cm, non-polar component 21.8 μN / cm, polar component 51.0 μN /
cm), ethylene glycol (surface tension 48.0 μN /
cm, non-polar component 29.0 μN / cm, polar component 1
9.0 μN / cm), diiodomethane (surface tension 50.
Three liquids of 8 μN / cm, a non-polar component of 50.8 μN / cm, and a polar component of 0 μN / cm) are dropped, and the contact angle of each liquid is measured. Expand Fork from each of these components
Use the es equation to produce the surface tension of the adhesive.

(7) Light transmittance Transmittance was measured at a wavelength of 550 nm (Poic haze meter SEP-HS-D, manufactured by Nippon Seimitsu Kogaku Co., Ltd.).
Type 1).

(8) Number of Foreign Substances in Plastic Film A plastic film sample was 210 mm in length × 14 in width.
8 mm (area 310.8 cm ² ) was cut out, and the whole area of the film was inspected for foreign substances by visual inspection by the cross Nicol method. Next, the detected foreign matter in the sample film was observed with transmitted light using an optical microscope, and the maximum diameter of a portion observed as an optically abnormal range was defined as the size of the foreign matter. In addition, when a cavity (void) existing around the foreign particle is observed as an optically abnormal range, it is included in the size of the foreign particle. Then, the size of the foreign particles was divided into those having a size of 5 μm or more and less than 25 μm and those having a size of 25 μm or more.

(9) Number of surface defects The obtained surface protective film was bonded to a polarizing plate,
The sample was cut out to a size of 0 mm × width 148 mm (area 310.8 cm ² ), and the number was counted under a fluorescent lamp so that the unevenness of the surface could be visually confirmed by the reflected light.

Example 1 An intrinsic viscosity of 0.62 containing 0.1% by weight of true spherical silica particles having an average particle size of 0.15 μm.
The polyethylene terephthalate polymer of (35 ° C.-orthochlorophenol solution) is melted by an extruder, and is adhered to a rotating cooling drum maintained at 40 ° C. from a die by using an electrostatic adhesion method, rapidly cooled, and not stretched. A film was obtained. This unstretched film was stretched 3.5 times in the machine direction and 3.6 times in the transverse direction, and heat-set at 220 ° C. to obtain a biaxially oriented polyethylene terephthalate film having a thickness of 50 μm. Corona treatment was performed on both surfaces of the obtained biaxially oriented polyethylene terephthalate film, and on one surface, an antistatic layer was provided as a first protective layer, and a release layer was provided as a second protective layer in this order. The antistatic layer was composed of 25 parts of a thiophene derivative polymer and 75 parts of a copolymerized polyester (60 mol% of terephthalic acid as a dicarboxylic acid component,
An aqueous coating liquid containing 35% by weight of isophthalic acid, 5% by mole of adipic acid, 95% by mole of glycol as a glycol component, 5% by mole of diethylene glycol), and 3% by weight of a solid component composed of 5 parts of a nonionic surfactant is dried. The release layer was formed by coating so as to have a thickness of 0.1 μm. The release layer was formed of polyethyleneimine octadecyl carbamate (RP-20, manufactured by Nippon Shokubai Co., Ltd.).
Parts, 100 parts of a polyester-based polyester resin (Espel 1510, manufactured by Hitachi Chemical Co., Ltd.) and melamine resin (Nikarac NS-11, manufactured by Sanwa Chemical Co., Ltd.) 3 as in the case of the antistatic layer.
0 parts, the coating liquid obtained by drying has a thickness of 0.2
It was formed by coating to a thickness of μm, drying and curing at 140 ° C. for 1 minute.

Next, as an acrylic pressure-sensitive adhesive, 2-ethylhexyl acrylate (main monomer), n-butyl acrylate (main monomer), vinyl acetate (comonomer), and hydroxyethyl methacrylate (functional group-containing monomer) were 5: 2: A composition mixed at a weight ratio of 2: 1 and an additive composed of epoxy-modified stearyl acrylate were added so that 0.5 part by weight of the latter additive was added to 10 parts by weight of the former composition. Solution polymerization was carried out using azobisisobutyronitrile as a reaction catalyst in a solvent of ethyl. The weight average molecular weight of the obtained pressure-sensitive adhesive polymer was about 350,000. This adhesive polymer is TDI
After the system isocyanate crosslinking agent was added, it was applied to one side of the release paper so that the thickness after drying was 15 μm, to obtain a laminate of the release paper and the pressure-sensitive adhesive.

Then, the surface of the laminate on the side of the pressure-sensitive adhesive is changed to the other surface of the biaxially oriented polyethylene terephthalate subjected to the above-described corona treatment, that is, a surface different from the side on which the release layer is formed. After laminating, drying at 100 ° C. for 2 minutes, winding and aging at 45 ° C. for 1 week, a laminate of a surface protective film and a release paper was obtained. The release paper was peeled off from the obtained laminate, and the characteristics of the surface protective film were measured.
Table 1 shows the properties of the obtained surface protective film.

Example 2 In Example 1, the composition used for solution polymerization of the acrylic pressure-sensitive adhesive was changed to 2-ethylhexyl acrylate, n-butyl acrylate, vinyl acetate and hydroxyethyl methacrylate in the form of 2:
Changed to a mixture in a weight ratio of 4: 2.5: 1.5,
The same operation was repeated except that the amount of the epoxy-modified stearyl acrylate was changed to 0.7 part with respect to 10 parts of the composition. The weight average molecular weight of the pressure-sensitive adhesive polymer obtained at this time was about 400,000. The thickness of the pressure-sensitive adhesive layer applied to the release paper was 5 μm. Table 1 shows the properties of the obtained surface protective film.

Example 3 In Example 1, the composition used for solution polymerization of the acrylic pressure-sensitive adhesive was changed to 2-ethylhexyl acrylate, vinyl acetate and hydroxyethyl methacrylate in a ratio of 7.5: 1.5: 1. The same operation was repeated except that the mixture was changed to a mixture by weight ratio, and the addition amount of the epoxy-modified stearyl acrylate was changed to 0.8 part with respect to 10 parts of the composition. The weight average molecular weight of the pressure-sensitive adhesive polymer obtained at this time was about 440,000.
The pressure-sensitive adhesive layer applied to the release paper had a thickness of 23 μm. Table 1 shows the properties of the obtained surface protective film.

Comparative Example 1 In Example 1, the composition used for solution polymerization of the acrylic pressure-sensitive adhesive was prepared by mixing 2-ethylhexyl acrylate, n-butyl acrylate and hydroxyethyl methacrylate in a weight ratio of 7: 2: 1. And the same operation was repeated except that the amount of the epoxy-modified stearyl acrylate was changed to 0.1 part with respect to 10 parts of the composition. Table 1 shows the properties of the obtained surface protective film.

[Comparative Example 2] In Example 1, the base material of the surface protective film was a polyethylene resin having a density of 0.925 and a melt index of 2.5 formed by inflation. The same operation was repeated, except that the procedure was changed to. Table 1 shows the properties of the obtained surface protective film.

[Comparative Example 3] In Example 1, the composition used for solution polymerization of the acrylic pressure-sensitive adhesive was changed to 2-ethylhexyl acrylate, n-butyl acrylate, vinyl acetate and hydroxyethyl methacrylate in the form of 2:
The same operation was repeated except that the mixture was changed to a mixture having a weight ratio of 3: 3: 2, and the addition amount of the epoxy-modified stearyl acrylate was changed to 2 parts per 10 parts of the composition.
The weight-average molecular weight of the pressure-sensitive adhesive polymer obtained at this time was about 250,000. The thickness of the pressure-sensitive adhesive layer applied to the release paper was 10 μm. Table 1 shows the properties of the obtained surface protective film.

[0058]

[Table 1]

Consider Table 1 below. Embodiment 1 of the present invention
The surface protective films of Nos. 1 to 3 were both excellent in sticking and releasability that did not fluctuate with time, and were excellent without impairing the inspectability of the bonded protected surface. On the other hand, the surface protective film of Comparative Example 1, which has an adhesive force that is too strong to be peeled off, and that is more difficult to peel off over time, has a handleability that damages the surface of the protected surface when peeled off in severe cases. Was lacking. Further, the surface protective film of Comparative Example 2 using a polyethylene film as the base material,
This impaired the inspectability of the bonded protected surface. Furthermore, the surface protection film of Comparative Example 3 in which the adhesive force is excessively light and the adhesive force is further reduced with time is lacking in the reliability of spontaneous peeling while being bonded to the protected surface. .

[0060]

The surface protective film of the present invention can be used at the time of manufacturing parts related to a liquid crystal display such as a polarizing plate.
No bubbles are mixed into the protected surface with irregularities on the surface, its adhesive strength is low and its change with time is small. Since the film is used as the base material, the testability can be improved. In addition, by providing an antistatic treatment or a release treatment on the opposite surface of the adhesive layer, it is possible to easily suppress charge at the time of peeling and easily remove dust and the like on the surface.

Continued on the front page F-term (reference) 4F100 AJ11D AK17D AK25 AK36 AK41B AK51 AK52D AR00A AR00C BA03 BA06 BA10A BA10C BA10E CA22A CA30A DE01A DG10E EJ38B JEJLJJJJLJJJLJJLJJLJJLJJL AB01 CA06 CC02 CC05 CD05 CD06 DB02 FA04

Claims (6)

[Claims] 1. A laminated film comprising a biaxially oriented polyester film having an adhesive layer on one surface and a protective layer on the other surface, wherein the adhesive layer has (1) a glass transition temperature of -60 ° C. or higher. (2) Tensile modulus is 0.1 MPa or more and 0.2 MPa or less; (3) Surface tension is 15 μN / cm or more and 25 μN / cm or less; (4) Stainless steel plate Adhesive strength (A) after being left at 23 ° C. for 1 day after being bonded to the substrate is 30 mN / 25 mm or more and 500 m
N / 25 mm or less; (5) The value obtained by dividing the adhesive strength (B) after being stuck to a stainless steel plate and allowed to stand at 60 ° C. for 1 week by the adhesive strength (A) is 0.5.
(2) a surface protective film, which simultaneously has a thickness of 3 μm or more and 50 μm or less. 2. A biaxially oriented polyester film has a length of 210 mm on one side and a length of 148 mm on a side perpendicular to the length (area of 310.8 cm ² ), and there is no foreign matter having a size of 25 μm or more, and Size 5μm or more and 25μm
2. The surface protective film according to claim 1, wherein the number of foreign matters less than 10 is 10 or less. 3. The protective layer contains a release agent and an antistatic agent, and the protective layer has a peel strength of 10 m from the pressure-sensitive adhesive layer.
The surface protective film according to claim 1, which has a thickness of N / 25 mm or more and 5000 mN / 25 mm or less. 4. The visible light transmittance of the surface protective film is 7
The surface protective film according to claim 1, wherein the haze is 0% or more and the haze is 10% or less. 5. The method according to claim 1, which is used for protecting the surface of a polarizing plate, a retardation plate, a viewing angle widening film or a laminate thereof.
5. The surface protective film according to any one of items 1 to 4. 6. A laminate obtained by laminating a release paper on the pressure-sensitive adhesive layer (B) of the surface protective film according to any one of claims 1 to 4, wherein the laminate is bonded to the pressure-sensitive adhesive layer of the release paper. The surface protection laminate is characterized in that at least one selected from the group consisting of a silicone resin, a fluororesin and an aliphatic wax is formed as a release layer.