JP2007304425A - Surface protective film for polarizing plate and its application - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface protective film for polarizing plates having various functional surfaces, wherein the surface protective film for polarizing plates has such versatility that it is usable without developing or selecting a pressure-sensitive adhesive according to a function imparted to a surface of a polarizing plate. <P>SOLUTION: The surface protective film for polarizing plates consists of a base film (A), a functional layer (B) stacked on one surface of the base film, a slightly adhesive layer (C) stacked on the other surface of the base film opposite to the surface on which the functional layer has been stacked, and a detachable release film (D) stacked optionally on the slightly adhesive layer, wherein the slightly adhesive layer (C) has an adhesive power of 0.03-0.20 N/25 mm as initial value when stuck on a polarizing plate, and change in the adhesive power from the initial value is ≤±10% even after autoclave treatment at a temperature of 50-70°C and a pressure of 2-7 atm for 5-60 min. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a surface protective film for a polarizing plate and its use, and more specifically, regardless of whether or not a function is imparted to the surface of a polarizing plate as an adherend, and the adhesive and adhesive strength of the surface protective film each time. The present invention relates to a versatile surface protective film for polarizing plates that can be easily applied to those polarizing plates with one kind of pressure-sensitive adhesive or film without selection or change, and uses thereof.
The polarizing plate surface protective film as used in the present invention includes a polarizing plate surface protective adhesive film, a polarizing plate surface protective (adhesive) sheet, and a polarizing plate surface protective (adhesive) tape.

Liquid crystal displays (LCDs) are used in calculators, mobile phones, notebook computers, navigators, large liquid crystal televisions, and the like. The display principle of this LCD is that a weak electric signal is applied to a liquid crystal material sandwiched between transparent electrodes, optical distortion is created, and the distortion is visualized by passing through a polarizing plate. That is, it can be said that the polarizing plate is an important and indispensable optical member (or optical film) for the liquid crystal display.
In response to the advanced display requirements of liquid crystal displays (LCDs), the surface of the polarizing plate is from a variety (plain) of triacetylcellulose (or cellulose triacetate) (TAC) itself, and AR (anti reflection) is anti-reflective. Properties), RL (low reflection: low reflectivity), AG (anti glare: anti-glare), and the like.
A surface protective adhesive film is bonded to the polarizing plate in order to prevent scratches on the surface of the polarizing plate, adhesion of foreign substances, etc. in the manufacturing process, the processing process such as the sheet cutting process, and the transportation process. Yes.
As the surface protective adhesive film, since the surface state of the polarizing plate provided with various functions is different, depending on the surface of the polarizing plate, the surface protective film to be used, the adhesive type and the adhesive force of the tape or sheet, respectively, The protective film or sheet most suitable for the functional treatment of the polarizing plate is used.

The surface protective adhesive film generally has a structure in which an antistatic layer or an antistatic layer and an antifouling layer are provided on one side of a base film, and an adhesive layer is provided on the opposite side, that is, an antistatic layer / base. It has the structure of material film / adhesive layer or antistatic layer + antifouling layer / base film / adhesive layer. The adhesive layer is usually coated with a release film.
Here, the pressure-sensitive adhesive layer of the surface protective pressure-sensitive adhesive film is a layer for attaching to the surface of the optical film and is peeled and removed after achieving the purpose of surface protection. It is done so that the surface contamination etc. do not occur.

Thus, although it is a surface protection adhesive film which emits a useful function for the surface protection of a polarizing plate, various things are conventionally proposed as a surface protection film.
For example, rubber adhesives mainly composed of diene rubber occupy most of the adhesives for surface protection films, but because they contain unsaturated double bonds in the structure, they are inferior in weather resistance and heat resistance. Because it has problems and also has the problem that the adhesiveness to the base film is weak and there are some that peel off between the base and the adhesive layer, the acid-modified polystyrene elastomer and the tackifier And a protective film coated with an adhesive containing epoxy resin has been proposed (for example, see Patent Document 1).
In addition, from one side of the substrate in the surface protective film used for optical sheets of articles such as polarizing plates, from an adhesive composition having an acid-modified polystyrene-based thermoplastic elastomer, a polystyrene-based thermoplastic elastomer, and a crosslinking agent A surface protective film characterized by providing an adhesive layer is proposed (for example, see Patent Document 2).
Furthermore, it is an optical surface protective film in which an antifouling treatment layer is provided on one side of the polyester film and an adhesive layer is provided on the opposite side, and the polyester film is not subjected to surface treatment. An antistatic layer formed of a material containing an antistatic agent and a polyester binder is provided between the adhesive layer and the pressure sensitive adhesive layer, and the pressure sensitive adhesive layer includes an acrylic polymer containing an acid as a functional group and an epoxy type. A surface protective film for optics, particularly a polarizing plate, characterized in that it is formed of an acrylic pressure-sensitive adhesive containing a crosslinking agent and an isocyanate-based crosslinking agent has been proposed (for example, see Patent Document 3).
Furthermore, an antistatic film comprising a polyester film and an antistatic layer provided on at least one side thereof, a stain preventing layer provided on one side of the antistatic film, and an adhesive layer provided on the opposite side of the stain preventing layer. There has been proposed a surface protective film, wherein the antifouling layer comprises a modified silicone resin modified with an alkyd resin, an acrylic resin and a melamine resin (see, for example, Patent Document 4). .

However, despite the above proposal, it is said that there are the following problems.
In other words, in response to the high demands of liquid crystal displays (LCDs) in recent years, various polarizing plates with various additions and improvements have been developed and released, that is, the surface of the polarizing plate on which a surface protective film or tape is applied. Because the composition and shape of each differ, it is necessary to develop and select a surface protective film adhesive and film that match the surface of the polarizing plate each time.As a result, a uniform surface protective film is required, Ordering and inventory management are complicated, and management problems may occur.
Therefore, even if the composition and shape of the polarizing plate surface to be the adherend of the surface protective film are different, a versatile surface protective film that can be applied to various polarizing plate surfaces without changing the adhesive layer each time. There is a strong demand.
JP-A-5-186747 JP 2005-290277 A JP 2005-200607 A Japanese Patent Laying-Open No. 2005-066919

  In view of the above problems, the object of the present invention is a surface protective film for polarizing plates having various functional surfaces, and the adhesive is developed and selected each time depending on the difference in surface functionalization in the polarizing plate. And providing a versatile surface protective film for polarizing plates that can be used.

  As a result of intensive studies to solve the above problems, the present inventor has found that a base film (A) made of a plastic film and a functional layer (B) laminated on one surface of the base film (A) and the base film In the surface protective film for polarizing plates composed of the fine adhesive layer (C) laminated on the opposite side of the surface on which the functional layer (B) of (A) is laminated, the fine adhesive layer (C) is 2-ethylhexyl. Acrylate is the main constituent of the adhesive, silane coupling agent is used as an additive, and glass transition temperature (Tg) and molecular weight are designed as the base material of the adhesive to have specific adhesive properties. It has been found that the above-mentioned problems can be achieved. Based on these findings, the present invention has been further studied and completed.

That is, according to the first invention of the present invention, the base film (A), the functional layer (B) laminated on one surface of the base film (A), and the functional layer (B) are laminated. A fine-adhesive layer (C) laminated on the surface of the base film (A) opposite to the surface, and a peelable release film (D) laminated on the fine-adhesive layer (C) as desired. In the surface protective film for polarizing plate composed of), the slightly adhesive layer (C) has an adhesive strength of 0.03 to 0.20 N / 25 mm as an initial value when pasted on the polarizing plate, And after the autoclave process performed at the temperature of 50-70 degreeC, the pressure of 2-7 atm, and the time for 5-60 minutes, the change of the adhesive force from an initial value is 10% or less, It is characterized by the above-mentioned. A surface protective film for a polarizing plate is provided.
According to the second invention of the present invention, in the first invention, the pressure-sensitive adhesive forming the fine-adhesion layer (C) is composed of 2-ethylhexyl acrylate as a main raw material component, and a silane coupling agent. Is used as an additive, and a surface protective film for polarizing plates is provided.
Furthermore, according to 3rd invention of this invention, in 2nd invention, the content rate of 2-ethylhexyl acrylate in the said adhesive is 80-99.5 weight part with respect to 100 weight part of adhesives. And the content rate of a silane coupling agent is 0.05-10 weight part with respect to 100 weight part of adhesives, The surface protective film for polarizing plates characterized by the above-mentioned is provided.

According to a fourth invention of the present invention, in the first invention, the pressure-sensitive adhesive that forms the slightly adhesive layer (C) is a glass transition by a differential scanning calorimeter (DSC) of the pressure-sensitive adhesive resin substrate before crosslinking. A surface protective film for a polarizing plate, characterized in that the temperature (Tg) is in the range of −30 to −60 ° C., and the molecular weight (Mw) in terms of polystyrene by GPC is 300,000 or more.
Moreover, according to 5th invention of this invention, the said base film (A) is a polyester film in 1st invention, The surface protection film for polarizing plates characterized by the above-mentioned is provided.
Furthermore, according to a sixth aspect of the present invention, there is provided the surface protective film for a polarizing plate according to the first aspect, wherein the functional layer (B) has an antistatic property and / or an antifouling property. Provided.

According to the seventh invention of the present invention, in any one of the first to sixth inventions, without changing the type and / or adhesive force of the adhesive depending on the function imparted to the surface of the polarizing plate to be protected. There is provided a surface protective film for a polarizing plate characterized by having versatility that can be handled with one kind of pressure-sensitive adhesive.
Furthermore, according to an eighth invention of the present invention, in the seventh invention, the slightly adhesive layer (C) comprises a general-purpose (plain) polarizing plate, a polarizing plate with an antiglare (AG) function, and an antireflection (AR). There is provided a surface protective film for a polarizing plate characterized by having versatility capable of being handled with one type of pressure-sensitive adhesive with respect to a polarizing plate having a different surface state of a functional polarizing plate.

According to the ninth aspect of the present invention, the polarizing plate with a surface protective film, wherein the surface protective film for a polarizing plate according to any one of the first to eighth aspects is attached to the polarizing plate. Is provided.
Furthermore, according to the tenth invention of the present invention, the surface protective film for a polarizing plate according to any one of the first to eighth inventions is affixed to an image display device. A display device is provided.

  The surface protective film for a polarizing plate of the present invention is a surface protective film for a polarizing plate having various functional surfaces, and the adhesive of the surface protective film is applied each time depending on the function imparted to the surface of the polarizing plate. There is an excellent versatile effect that can be handled with a single type of adhesive without being developed or selected.

  The surface protective film for polarizing plates of the present invention (hereinafter also referred to as a surface protective adhesive film) is laminated on one surface of the base film (A, 1) and the base film (A) as shown in FIG. Functional layers (B, 2), a micro-adhesive layer (C, 3) laminated on the opposite side of the surface on which the functional layer (B) of the base film (A) is laminated, and fine if desired In the surface protective film for polarizing plates composed of a peelable release film (D, 4) laminated on the adhesive layer (C), the slightly adhesive layer (C) was stuck on the polarizing plate. Even after autoclave treatment having an initial value of 0.05 to 0.20 N / 25 mm adhesive force and a temperature of 50 to 70 ° C., a pressure of 2 to 7 atm, and a time of 5 to 60 minutes The change in adhesive strength from the initial value is ± 10% or less. Hereinafter, each item will be described.

1. Base film (A)
The base film (A) is not particularly limited as long as the object of the present invention can be achieved, but is in the form of a film, has strength as a surface protective adhesive film for optical use, and has optical suitability. Specifically, a polyester film (polyethylene terephthalate, polyethylene naphthalate, polyethylene isophthalate, polybutylene terephthalate, etc.) is preferably used.
The polyester film can be produced by a conventionally known method. For example, the biaxially stretched polyester film is obtained by drying the polyester and then melting it with an extruder, and then using a die (for example, T-die, I-die). Etc.) is extruded onto a rotary cooling drum and quenched to produce an unstretched film, and then the unstretched film is stretched in the machine direction and the transverse direction, and heat-fixed as necessary.

  In addition to the polyester film, other plastic films such as polycarbonate, polysulfone, polyamide, polyolefin, and liquid crystal polymer can be used. For example, a biaxially stretched film such as polypropylene or polyester is preferable. Can be used.

  Among these, a highly transparent polyethylene terephthalate film is preferably used because it has strength and optical suitability as a surface protective adhesive film for optical use films, is relatively inexpensive, and is easily available.

  Although the thickness of a base film (A) is not specifically limited, Preferably it is about 6-125 micrometers, More preferably, it is 20-50 micrometers. When the thickness is less than 6 μm, the strength as the surface protective adhesive film may not be satisfied, which is not preferable. On the other hand, when the thickness exceeds 125 μm, the handleability may be deteriorated.

Moreover, additives such as various stabilizers, ultraviolet absorbers, lubricants, pigments, antioxidants, and plasticizers may be added to the base film (A) as long as the object of the present invention is not impaired. .
Furthermore, the base film (A) may be subjected to treatment such as chemical treatment and discharge treatment, for example, corona treatment, anchor coating, adhesion improvement and coating property improvement, if necessary.

2. Functional layer (B)
The surface protective film for polarizing plates of the present invention has a functional layer (B) laminated on one surface of the base film (A).
The functional layer (B) has antistatic and / or antifouling functions.
In general, an optical member that is a constituent element of a liquid crystal display, such as a film that protects the surface of a polarizing plate, needs to have antistatic properties. This is due to the following reason. After the optical member protected by the surface protective film is bonded to the liquid crystal panel, static electricity is generated when the surface protective film is peeled off from the optical member. If a voltage is applied to the liquid crystal without removing the static electricity, the orientation of the liquid crystal molecules is lost or the panel is damaged. Therefore, in order to prevent such a problem, the surface protection film is provided with antistatic properties by providing a layer showing antistatic properties. Since the antistatic layer is formed on one surface of the surface protective film, the antistatic layer may be formed on the other surface, that is, the outermost surface after the optical member is attached to the liquid crystal panel. Many.
For the functional layer (B) having antistatic properties, for example, a surfactant (ion conductive) antistatic agent capable of imparting antistatic properties, an antistatic agent such as a conductive polymer, conductive carbon, or metal powder is used. It is done.

Examples of the antistatic agent include an anionic antistatic agent having an anionic group such as sulfate ester base, phosphate ester base, and phosphonate base, an amphoteric antistatic agent such as amino acid and aminosulfate ester, and amino alcohol. Various surfactant-type antistatic agents such as nonionic antistatic agents such as glycerin-based, glycerin-based, and polyethylene glycol-based polymers, and polymer-type antistatic agents obtained by increasing the molecular weight of the above-mentioned antistatic agents. In addition, monomers and oligomers having a tertiary amino group or a quaternary ammonium group and capable of being polymerized by ionizing radiation, such as N, N-dialkylaminoalkyl (meth) acrylate monomers, their quaternary compounds, etc. These polymerizable antistatic agents can also be used. In addition, polyoxyethylene alkylamine, polyhydric alcohol derivatives and the like can also be used.
In addition, examples of the conductive polymer include polyaniline, polypyrrole, polythiophene, and the like, and any of the commercially available conductive polymer antistatic agents can be used.

The method for laminating the functional layer (B) on one surface of the base film (A) is not particularly limited. For example, an antistatic agent such as a surfactant is blended in the plastic to form the base film. It can be formed by a method of forming, a method of applying a surfactant or a conductive resin to a base film, a method of applying, depositing or plating a conductive material such as metal or conductive metal oxide on the base film. it can.
The conductive resin is not particularly limited, and examples thereof include those in which a conductive filler such as a tin antimony filler or an indium oxide filler is dispersed in the resin.
Moreover, it does not specifically limit as a conductive substance apply | coated, vapor-deposited or plated, For example, a tin oxide, an indium oxide, a cadmium oxide, a titanium oxide, a metal indium, metal tin, gold | metal | money, silver, platinum, palladium, copper, aluminum , Nickel, chromium, titanium, iron, cobalt, copper iodide, and alloys or mixtures thereof. The type of vapor deposition or plating is not particularly limited, and examples thereof include vacuum vapor deposition, sputtering, ion plating, chemical vapor deposition, spray pyrolysis, chemical plating, and electroplating.

A preferred embodiment for forming the functional layer (B) includes, for example, a method of coating the coating liquid containing the surfactant type antistatic agent on one side of the base film (A). The antistatic performance of the functional layer (B) is preferably as low as possible, and the surface specific resistance is preferably 10 ¹² Ω / □ or less.
The surface specific resistance value is a value measured according to JIS K 6911. This is a value measured with a super insulation resistance measuring instrument after curing the film for 24 hours.

  The solid content concentration of the coating solution is preferably 30% by weight or less, more preferably 0.5 to 30% by weight, when the coating solution is 100% by weight. If the solid content concentration exceeds 30% by weight, the coating appearance may be deteriorated. On the other hand, if it is less than 0.5%, the antistatic function and the antifouling function may be insufficient, which is not preferable.

  In the coating solution, if necessary, an antifoaming agent, a coating property improver, a thickener, a surfactant, an organic lubricant, an organic polymer particle, an oxidizing agent, as long as the object of the present invention is not impaired. An inhibitor, an ultraviolet absorber, a foaming agent, a dye, a pigment and the like may be contained.

  The functional layer (B) has a function of antifouling, that is, antifouling, in addition to the antistatic property or in place of the antistatic property. As a preferred embodiment, for example, an antistatic layer can be provided as a functional layer (B) on one side of the base film, and a stain preventing layer can be provided on the layer.

The antifouling layer has an appropriate peeling force. For example, when a polarizing plate having a surface protective film bonded thereto is cut to form a chip, the adhesive that protrudes from the cut surface does not touch the surface protective film. There is an effect to make it difficult to adhere to.
The antifouling agent used in the antifouling layer is not particularly limited. For example, a polymer having a long alkyl side chain is preferred, and an alkyl acrylate having a carbon number of 12 or more, particularly an alkyl chain having 16 to 20 and acrylic acid. More preferred are copolymers of If the alkyl chain of the alkyl acrylate has less than 12 carbon atoms, sufficient peelability may not be obtained.
Among these, particularly preferred is a copolymer obtained by long-chain alkylation of polyvinyl alcohol or polyethyleneimine with chlorinated alkyloyl or alkyl isocyanate, and specifically, polyvinyl-obtained by reaction of polyvinyl alcohol and octadecyl isocyanate. Examples thereof include N-octadecyl carbamate and polyethylene imine-N-octadecyl carbamate obtained by reaction of polyethylene imine and octadecyl isocyanate.
In the present invention, a silicone-based or fluorine-based release agent can also be used as an antifouling agent.

  In addition, the coating method such as the concentration of the coating liquid, the coating method and the coating conditions in the anti-stain layer can be carried out by the same method as the coating method of the antistatic layer.

  In the present invention, the thickness of the antifouling layer is preferably from 0.01 to 1 μm, more preferably from 0.03 to 0.5 μm. If the thickness is less than 0.01 μm, a sufficient antifouling effect may not be obtained. On the other hand, a layer exceeding 1 μm is excessive in quality and uneconomical.

  Moreover, as a formation method of a functional layer (B), after adjusting a coating liquid, the method of apply | coating (coating) and drying on one surface of a base film (A), and forming a functional layer (B), for example. Can be mentioned.

As said application | coating (coating) method, the method of apply | coating a coating liquid outside a film manufacturing process, the method of apply | coating a coating liquid within a film manufacturing process, etc. are mentioned, for example.
As a method for applying the coating solution outside the film manufacturing process, for example, usual methods such as gravure, microgravure, Mayer bar, air knife, doctor knife, roll coater, wire bar, etc. are employed.
As a method of applying in the film production process, for example, a coating solution is applied to an unstretched polyester film, and a method of biaxially stretching sequentially or simultaneously, a method of applying to a uniaxially stretched polyester film, and further uniaxial stretching. Examples thereof include a method of stretching in a direction perpendicular to the direction, a method of applying to a biaxially stretched polyester film, and further stretching in the lateral and / or longitudinal direction.
In the present invention, a method of applying a coating solution outside the film production process is preferably used because of the ease of the process.

The number of coatings may be applied once on the base film (A), but may be applied a plurality of times as necessary.
The amount of coating is not particularly limited, and may be determined in consideration of the type of coating solution and required performance.
Moreover, it is preferable to dry a solvent after apply | coating a coating liquid. The drying method is not particularly limited, and a method of leaving it after application is used.

Furthermore, it is preferable that the thickness of the functional layer (B) is dried to be about 0.01 to ² g / m ² , preferably 0.03 to 1 g / m ² after drying. When the thickness is less than 0.01 g / m ² , the functional layer (B) is not preferable because it is difficult to maintain the physical strength of the layer, and when it is thicker than 2 g / m ² , the coating appearance may be deteriorated. Yes, not preferred.

3. Slight adhesion layer (C)
The present invention is a surface protection film having a configuration of “functional layer (antistatic layer, etc.) (B) / base film (A) / slightly adhesive layer (C) / release film (D)” as a preferred embodiment. However, when the surface protective film of the present invention is used to protect the polarizing plate which is an optical use film, the release film (D) is peeled off and the target optical use film is subjected to a slight adhesion layer (C). Use with affix. And after achieving the purpose of surface protection, since this surface protective film is peeled and removed, this fine adhesive layer (C) can be easily peeled off, and the adhesive remains after peeling and the surface contamination property is reduced. It is an essential requirement not to exist.

  In the present invention, the glass transition temperature (Tg) measured by a differential scanning calorimeter (DSC) in the low temperature range is used to make the general purpose wait without selecting a protective film adhesive each time due to the difference in function of the polarizing plate. ) Is −30 to −60 ° C., and the pressure-sensitive adhesive layer using a pressure-sensitive adhesive having a molecular weight (Mw) in terms of polystyrene by GPC of 300,000 or more is suitable as a surface protective adhesive film for polarizing plates. (C).

That is, the feature of the present invention resides in the slightly adhesive layer (C) composed of a specific adhesive that is versatile regardless of the surface treatment state of the polarizing plate.
The main component of the pressure-sensitive adhesive used for the slightly pressure-sensitive adhesive layer (C) is composed of 80 to 99.5 parts of 2-ethylhexyl acrylate with respect to 100 parts by weight of the pressure-sensitive adhesive, and acrylic acid, methacrylic acid, A monomer containing a hydroxyl group (—OH) and a carboxyl group (—COOH), such as hydroxyethyl (meth) acrylate, is also composed of a copolymer of acrylic copolymer.

After the polymerization, by adding 0.05 to 10 parts by weight, preferably 0.1 to 5 parts by weight of the silane coupling agent to 100 parts by weight of the pressure-sensitive adhesive, The versatility function that can be used is strongly expressed without selecting the adhesive each time.
When the addition amount of the silane coupling agent is less than 0.05 parts by weight, it is difficult to adjust the initial adhesive force and the adhesive force after the treatment for the AG (anti glare) type polarizing plate, On the other hand, if it exceeds 10 parts by weight, the polarizing plate surface may be contaminated.
As the silane coupling agent, those having a functional group that reacts with a functional group of the pressure sensitive adhesive, such as a hydroxyl group (—OH) or a carboxyl group (—COOH), or those that constitute an interpenetrating polymer network (IPN) with the pressure sensitive adhesive. Any of the silane coupling agents that are effective and commercially available can be used.

An isocyanate curing agent or the like is blended with the above-mentioned pressure-sensitive adhesive, and after application, dried and cured to cause a crosslinking reaction. As the isocyanate used for crosslinking, aliphatic, aromatic, and derivatives can be used, and can be selected depending on adhesive strength, pot life of coating liquid, and the like, and in any case, commercially available isocyanates can be used.
In addition, for example, an antioxidant, a light stabilizer, and an ultraviolet absorber (UVA) may be added to the pressure-sensitive adhesive as necessary within a range that does not impair the performance of the pressure-sensitive adhesive. it can.

The coating method of the slightly adhesive layer (C) can be performed by a usual coating method such as gravure, comma, air knife, doctor knife, die coating method, doctor blade method, etc., as in the formation of the functional layer (B).
For the installation of this layer, a method may be employed in which a pressure-sensitive adhesive is applied onto the release film (D) described below, and if necessary, is applied after heating and drying, or the functional layer (B) is applied. Adopt a method of coating the release film (D) after heating and drying, if necessary, on the side of the base film (A) where the functional layer (B) is not provided. May be.

  The adhesive strength of the slightly adhesive layer (C) is preferably 0.03 to 0.20 N / 25 mm, more preferably 0.05 to 0.15 N / 25 mm for the polarizing plate. If the adhesive strength is less than 0.03 N / 25 mm, it is not preferable because peeling or floating due to insufficient adhesive strength to the polarizing plate occurs. On the other hand, if the adhesive strength is greater than 0.20 N / 25 mm, the optical application It is not preferable because it is difficult to peel off from the polarizing plate which is a film, adhesive residue is generated after peeling, and surface contamination is increased.

  The adhesive strength of the fine adhesive layer (C) is as follows. The fine adhesive layer (C) was bonded to the polarizing plate, left at 23 ° C. × 50 RH% for 20 minutes, and then in an autoclave. X Expressed in terms of force when peeling at an angle of 180 degrees at a speed of 300 mm / min after treatment for 30 minutes and after standing for 20 minutes.

In the present invention, the adhesive thickness of the slightly adhesive layer (C) is not particularly limited, but is preferably about 1 to 100 μm, particularly preferably about 10 to 40 μm. If the thickness is less than 1 μm, the followability to shrinkage of the film is weak, and the film may be peeled off or the bonded film may be curled. Unfavorably, if it is thicker than 100 μm, it is uneconomical and bonded. Since the film is thick, problems such as handling occur, and when the obtained surface protective film is used up, when it is peeled off from the polarizing plate as the adherend, fogging or adhesive residue is generated on the surface of the polarizing plate. Is not preferable. Moreover, it is preferable that the slightly adhesion layer (C) is 5-50 g / m < ² > in dry weight.

  As described above, the adhesive force of the slightly adhesive layer (C) is selected by selecting an adhesive or adjusting the formation conditions of the slightly adhesive layer (C). A release film (D) can be bonded to the surface of the slightly adhesive layer (C) for the purpose of protecting the slightly adhesive layer (C).

4). Release film (D)
As shown in FIG. 1, in the surface protective film for polarizing plate of the present invention, a release film (D, 4) usually referred to as a separator is laminated on the slightly adhesive layer (C, 3). The slight adhesion layer (C, 3) is protected. And at the time of use of this surface protection adhesive film, this release film (D) is peeled off and the surface protection adhesive film is bonded to the polarizing plate which is an optical use film.

  As the release film (D), it is preferable that the surface of the polyester film is subjected to a release treatment using a silicon release agent or the like from the viewpoint of ease of peeling. Specifically, a polyester film and a polyethylene terephthalate film treated with silicon are preferable because they are easy to stick to and peel off from the slightly adhesive layer (C) and do not adversely affect the slightly adhesive layer (C).

  As the bonding method, there is no limitation as long as the surface protective adhesive film can be bonded to a polarizing plate which is an optical use film without problems such as the inclusion of foreign matter. Specifically, for example, manually, for optical use A method such as bonding to the polarizing plate as the optical application film while peeling the release film of the surface protective adhesive film processed into a size corresponding to the type of the polarizing plate as the film is used.

5). The polarizing plate to be protected by the surface protective film for polarizing plate of the present invention includes, for example, an elliptical polarizing plate, a reflective polarizing plate, a semi-transmissive polarizing plate, a reflective elliptical polarizing plate, and a semi-transmissive elliptical polarizing plate. And the like, which are used for forming a liquid crystal panel, etc., are not particularly limited.
In the present invention, the polarizing plate has a surface of triacetyl cellulose (or cellulose triacetate) (TAC) itself (plain) in response to the advanced display requirements of a liquid crystal display (LCD) as an image display device. In order to provide functions such as AR (anti reflection), RL (low reflection), AG (anti glare), and the like, various polarizing plates subjected to function addition are used. be able to.

  Specific examples of the polarizing plate include iodine and / or dichroism in hydrophilic polymer films such as polyvinyl alcohol films, partially formalized polyvinyl alcohol films, and ethylene / vinyl acetate copolymer partially saponified films. Examples thereof include a film obtained by adsorbing a dye and stretched, and a polyene oriented film such as a dehydrated polyvinyl alcohol product or a dehydrochlorinated polyvinyl chloride product. The polarizing plate may have a transparent protective layer on one side or both sides of the polarizing film.

  On the other hand, the reflective polarizing plate is provided with a reflective layer on the polarizing plate, and is used to form a reflective liquid crystal panel that reflects incident light from the viewing side (display side). Since there is no need to incorporate a light source such as a light, the liquid crystal panel can be easily thinned. The reflective polarizing plate can be formed, for example, by providing a reflective layer made of metal or the like on one side of the polarizing plate via a transparent protective layer or the like.

  As a specific example of this reflective polarizing plate, for example, a reflective layer made of a reflective metal such as aluminum or a foil made of a reflective metal such as aluminum is provided on one side of a matte-treated transparent protective layer. In addition, the transparent protective layer may contain fine particles so that the surface has a fine concavo-convex structure and has a reflective layer having a fine concavo-convex structure thereon. The reflective layer should be used with its reflective surface covered with a transparent protective layer, a polarizing plate, etc., to prevent a decrease in reflectivity due to oxidation, and in terms of long-lasting initial reflectivity. This is preferable in that it does not need to be provided separately.

  The above-described reflective layer having a fine concavo-convex structure has an advantage that incident light can be diffused by irregular reflection to impart omnidirectionality and antiglare property, and unevenness in brightness and darkness can be suppressed. In addition, the transparent protective layer containing fine particles can diffuse unevenness when incident light and its reflected light are transmitted therethrough, thereby further suppressing brightness and darkness unevenness. A reflective layer having a fine concavo-convex structure reflecting the surface fine concavo-convex structure of the transparent protective layer is provided by directly depositing metal on the surface of the transparent protective layer by means of vapor deposition such as vacuum deposition, ion plating, sputtering, or plating. Can be obtained.

  As a material for the transparent protective layer in the polarizing plate described above, a polymer having excellent transparency, mechanical strength, thermal stability, moisture shielding properties, and the like is preferable. Examples thereof include, but are not limited to, cellulose resins, polyester resins, acetate resins, polyether sulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, acrylic resins, or Examples thereof include thermosetting or ultraviolet curable resins such as acrylic, urethane, acrylic urethane, epoxy, and silicone.

  The transparent protective layer can be formed by an appropriate method such as applying a polymer or laminating a film. The thickness is generally preferably 500 μm or less, more preferably 1 to 300 μm, and still more preferably 5 to 200 μm. Examples of the fine particles to be contained in the transparent protective layer having a fine surface relief structure include inorganic substances such as silica, alumina, titania, zirconia, tin oxide, indium oxide, cadmium oxide, and antimony oxide having an average particle diameter of 0.5 to 50 μm. System fine particles or organic fine particles composed of a crosslinked or uncrosslinked polymer or the like is used. This surface fine concavo-convex structure can also function as an antiglare (AG) layer.

  The present invention will be specifically described by the following examples, but the present invention is not limited thereto.

[Example 1]:
(Preparation of base film with functional layer)
In advance, a PET film (T-100, 38 μm product) manufactured by Mitsubishi Polyester was used as the base film (A), and an antistatic agent (SEKISUI-A, 3% solid content, acetic acid manufactured by SKC was used on one side thereof. The base film (A) with a functional layer (B) was prepared by coating and drying the ethyl solution) so that the weight after drying was 0.6 g / m ² .

(Preparation of adhesive composition)
Next, using a conventional method, in an ethyl acetate solution, (i) 97 parts by weight of 2-ethylhexyl acrylate (2EHA), (ii) 2.7 parts by weight of 2-hydroxyethyl acrylate (2HEA), (iii) acrylic acid (AA) 0.3 parts by weight, (iv) 0.1 parts by weight of azobisisobutylnitrile (AIBN) is added, and polymerized at 70 ° C. for 8 hours, whereby the glass transition temperature as measured by DSC A pressure-sensitive adhesive solution having a solid content of 30% having a Tg of −52 ° C. and a molecular weight (Mw) in terms of polystyrene by GPC of 400,000 was obtained. To this pressure-sensitive adhesive solution, 0.5 part by weight of silane coupling agent “Z-6040” manufactured by Toray Dow Corning Co., Ltd. is added with respect to 100 parts by weight (solid content) of the pressure-sensitive adhesive. 2.6 parts by weight of an isocyanate “HXR” manufactured by the company was added to 100 parts by weight (solid content) of the pressure-sensitive adhesive to prepare a coating liquid as a pressure-sensitive adhesive composition.

(Production of surface protective adhesive film)
The obtained coating liquid was applied and dried on a separator “S31” manufactured by Teijin Limited as a release film (D) so that the weight after drying was 22 g / m ² , and a slightly adhesive layer (C) was applied. The adhesive layer of this fine adhesion layer (C) was covered with the base film (A) with a functional layer (B), and the surface protection adhesion film was produced.

(Evaluation):
The obtained surface protective adhesive film was left at 23 ° C. for 7 days to obtain a sample for evaluation.
This sample film for evaluation was bonded to a plane type and an AG type polarizing plate manufactured by Toyusha, and the initial adhesive strength (23 ° C. × 50 RH%, left for 20 minutes) and after autoclaving (processing conditions: 70) The adhesive strength was measured as: ° C x 6 atm x 30 minutes + standing 20 minutes).
The obtained results are shown in Table 1. Adhesive strength was in the range of 0.09 to 0.12 N / 25 mm, and there was no difference in adhesive strength depending on the type of polarizing plate and the presence or absence of treatment.

[Comparative Example 1]
A surface protective adhesive film and a sample for evaluation were produced in the same manner as in Example 1 except that the silane coupling agent was not added in Example 1.
The obtained sample for evaluation was evaluated in the same manner as in Example 1. The results are shown in Table 1.
Although the adhesive strength to the normal type (plain) polarizing plate showed a value of around 0.11 N / 25 mm both in the initial stage and after the autoclave treatment, in the AG type, the initial value was 0.11 N / 25 mm. The adhesive strength after autoclaving was 0.16 N / 25 mm, and the adhesion progress was large.

[Comparative Example 2]
A surface protective adhesive film and a sample for evaluation were produced in the same manner as in Example 1 except that 2EHA in Example 1 was changed to butyl acrylate.
The obtained sample for evaluation was evaluated in the same manner as in Example 1. The results are shown in Table 1.
The adhesive strength to the normal type (plain) polarizing plate was 0.08 N / 25 mm in the initial stage and 0.12 N / 25 mm after the autoclave treatment. However, in the AG type, the initial value was 0.05 N / 25 mm, but floating was confirmed by the autoclave treatment, and the function of the protective film was not achieved.

  From the evaluation results of Table 1, the surface protective film obtained in Example 1 was blended with a silane coupling agent in the main component of 2-ethylhexyl acrylate as an adhesive mainly used for the slightly adhesive layer (C). Since a specific ratio was used, there was no difference in adhesive strength depending on the type of polarizing plate and the presence or absence of autoclaving, which was good. On the other hand, as can be seen from the evaluation results in Table 1, the surface protective films of Comparative Examples 1 and 2, for example, in Comparative Example 1, the adhesive strength after autoclaving increased in the AG type polarizing plate. In Example 2, even with a plain polarizing plate, the adhesive strength after autoclaving increased as compared with the initial value. Further, with the AG type polarizing plate, floating occurred after the autoclave treatment, which was a bad evaluation.

  Since the surface protective film for polarizing plate of the present invention has versatility without selecting and changing the surface protective film due to the difference in function imparted to the surface of the polarizing plate, production management and inventory management are easy. It is suitable as a surface protective adhesive film for various polarizing plates and is highly applicable to a liquid crystal display (LCD) which is an image display device.

It is a figure which shows typically the one aspect | mode of the surface protection film of this invention.

Explanation of symbols

1 Base film (A)
2 Functional layer (B)
3 Slightly adhesive layer (C)
4 Release film (D)

Claims (10)

The base film (A), the functional layer (B) laminated on one side of the base film (A), and the base film (A) on the opposite side of the side on which the functional layer (B) is laminated In the surface protective film for polarizing plates comprised from the slightly adhesive layer (C) laminated | stacked on the surface of this, and the peelable release film (D) laminated | stacked on the slightly adhesive layer (C) as needed ,
The slightly adhesive layer (C) has an initial adhesive strength of 0.03 to 0.20 N / 25 mm when pasted on the polarizing plate, and has a temperature of 50 to 70 ° C. and a pressure of 2 to 7 atm. A surface protective film for a polarizing plate, wherein the change in adhesive strength from the initial value is ± 10% or less even after autoclaving performed for 5 to 60 minutes.   2. The polarizing plate according to claim 1, wherein the pressure-sensitive adhesive forming the slightly adhesive layer (C) comprises 2-ethylhexyl acrylate as a main raw material component and a silane coupling agent as an additive. Surface protective film.   The content ratio of 2-ethylhexyl acrylate in the pressure-sensitive adhesive is 80 to 99.5 parts by weight with respect to 100 parts by weight of the pressure-sensitive adhesive, and the content ratio of the silane coupling agent is based on 100 parts by weight of the pressure-sensitive adhesive. The surface protective film for a polarizing plate according to claim 2, which is 0.05 to 10 parts by weight.   The pressure-sensitive adhesive forming the slightly pressure-sensitive adhesive layer (C) has a glass transition temperature (Tg) measured by a differential scanning calorimeter (DSC) of the pressure-sensitive adhesive resin substrate before crosslinking in the range of −30 to −60 ° C., and GPC The surface protective film for polarizing plates according to claim 1, wherein the molecular weight (Mw) in terms of polystyrene is 300,000 or more.   The said base film (A) is a polyester film, The surface protection film for polarizing plates of Claim 1 characterized by the above-mentioned.   The surface protective film for a polarizing plate according to claim 1, wherein the functional layer (B) has antistatic properties and / or antifouling properties.   It has the versatility which can respond with one adhesive type, without changing the kind and / or adhesive force of an adhesive by the function provided to the surface of the polarizing plate to protect. The surface protection film for polarizing plates in any one of.   The slightly adhesive layer (C) is one adhesive for polarizing plates having different surface states of general-purpose (plane) polarizing plates, polarizing plates with anti-glare (AG) function, and polarizing plates with anti-reflection (AR) function. The surface protective film for polarizing plates according to claim 7, wherein the surface protective film has versatility that can be handled by seeds.   A polarizing plate with a surface protective film, wherein the surface protective film for a polarizing plate according to claim 1 is attached to the polarizing plate.   An image display device with a surface protective film, wherein the surface protective film for a polarizing plate according to claim 1 is attached to an image display device.

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