JP2006328329A - Base material for surface-protective film and surface-protective film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a base material for surface-protective films used for protecting the surface of a member, particularly an optical member from scratches or the like, that is not necessary to peel on inspection. <P>SOLUTION: The film is composed of an imide resin and has an in-plane retardation of at most 10 nm and a thickness-direction retardation of at most 20 nm. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a substrate for a surface protective film that is used for protecting a surface of a member, particularly an optical member from scratches, which does not need to be peeled off during inspection.

  In recent years, the number of so-called flat panel displays using a liquid crystal display (LCD), an organic EL display (OLED), a plasma display (PDP), a field emission display (FED), a surface electric field display (SED), etc. has increased dramatically. It has become. These flat panel displays are constructed with very advanced technology. In the process of transporting and inspecting each member, in the inspection process for foreign matter inspection and display function, in other handling, and further as a process that is incorporated as a display after completion of the panel, and completed as a display It is necessary to protect these optical members from scratches and prevent dust and dirt from adhering until they are provided to the user later. A surface protective film is usually used for such purposes.

  Conventionally, as the surface protective film, a film in which an adhesive is applied to polyethylene film or the like has been used.

  However, since the conventional surface protective film has a phase difference (optical anisotropy), when the inspection is performed with the surface protective film bonded to the optical member, coloring caused by the phase difference of the surface protective film Due to unevenness and interference light, inspection may be difficult or inaccurate.

  For example, in the inspection process of a liquid crystal display, performance such as contrast and color tone is inspected. However, due to the above-described coloring unevenness and interference light, the inspection may be difficult or inaccurate. It is necessary to peel off the surface protective film once, inspect it, inspect it, and then attach a new surface protective film again after the inspection is completed.

  Moreover, the surface protection film is similarly used for the polarizer, the polarizer protective film, the polarizing plate, the retardation plate, the light guide plate, the diffusion plate, etc. constituting the liquid crystal display, and has the above-described problems. .

  In this way, the new surface protective film is pasted together in the inspection process, and if the surface protective film once peeled is used again, the pasting is difficult and the appearance may be deteriorated. Moreover, when peeling, a surface protective film may extend or re-adhesiveness may deteriorate.

  Furthermore, since the process of peeling a surface protection film and the process of bonding again are required, there also exists a subject that a process becomes complicated.

  Further, when the film strength is weak, there is a possibility that the film may be stretched or torn in the middle when the surface protective film is finally peeled off upon completion.

In response to these problems, it has been proposed to use a film having optical isotropy as a base material for a surface protective film (Patent Documents 1 and 2). Specifically, a polycarbonate film produced by a solution casting method is used. However, even if the in-plane retardation (retardation) of the polycarbonate film is small, the retardation in the thickness direction is large, and if a detailed inspection is performed, uneven coloring or interference light may occur. In addition, since the orientation birefringence is large, and those conveyed in the form of a roll film, such as a polarizer and a polarizer protective film, tension is applied in the process, there is a problem that optical anisotropy occurs due to this tension (stress). is there.
JP-A-5-157914 JP-A-6-148431

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a surface protective film that does not need to be peeled off in the inspection process of the member to be protected.

  In order to solve the above problems, the present inventors have conducted intensive studies. As a result, the inventors have found that the imide resin of the present invention having excellent optical properties such as transparency and a small phase difference can solve the above-mentioned problems, leading to the present invention.

That is, the present invention
(1) A unit represented by the following general formula (1), a unit represented by the following general formula (2), and a unit represented by the following general formula (3) if necessary. Provided is a substrate for a surface protective film comprising an imide resin, having an in-plane retardation of 10 nm or less and a thickness direction retardation of 20 nm or less.

（ここで、Ｒ¹およびＲ²は、それぞれ独立に、水素または炭素数１〜８のアルキル基を示し、Ｒ³は、炭素数１〜１８のアルキル基、炭素数３〜１２のシクロアルキル基、または炭素数５〜１５の芳香環を含む置換基を示す。）

(Here, R ¹ and R ² each independently represent hydrogen or an alkyl group having 1 to 8 carbon atoms, and R ³ represents an alkyl group having 1 to 18 carbon atoms or a cycloalkyl group having 3 to 12 carbon atoms. Or a substituent containing an aromatic ring having 5 to 15 carbon atoms.)

（ここで、Ｒ⁴およびＲ⁵は、それぞれ独立に、水素または炭素数１〜８のアルキル基を示し、Ｒ⁶は、炭素数１〜１８のアルキル基、炭素数３〜１２のシクロアルキル基、または炭素数５〜１５の芳香環を含む置換基を示す。）

(Here, R ⁴ and R ⁵ each independently represent hydrogen or an alkyl group having 1 to 8 carbon atoms, and R ⁶ represents an alkyl group having 1 to 18 carbon atoms or a cycloalkyl group having 3 to 12 carbon atoms. Or a substituent containing an aromatic ring having 5 to 15 carbon atoms.)

（但し、Ｒ⁷は、水素又は炭素数１〜８のアルキル基を示し、Ｒ⁸は、炭素数６〜１０のアリール基を示す。）
（２）配向複屈折が０以上０．１×１０^-3以下である、（１）に記載の表面保護フィルム用基材、を提供する。

(However, R ⁷ represents hydrogen or an alkyl group having 1 to 8 carbon atoms, and R ⁸ represents an aryl group having 6 to 10 carbon atoms.)
(2) The surface protective film substrate according to (1), wherein the orientation birefringence is 0 or more and 0.1 × 10 ⁻³ or less.

  (3) The surface protective film substrate according to any one of (1) and (2), wherein the member to be protected is an optical member.

  (4) The surface protective film substrate according to any one of (1) to (3), wherein the optical member is a liquid crystal display panel.

  (5) The surface protection according to any one of (1) to (4), wherein the optical member is a polarizer, a polarizer protective film, a polarizing plate, a retardation plate, a light guide plate, or a diffusion plate. A film substrate is provided.

  (6) A surface protective film using the substrate for a surface protective film according to any one of (1) to (5) is provided.

  According to the present invention, the imide resin of the present invention, which has excellent optical properties such as transparency and a small phase difference, can provide a surface protective film that is not necessary to be peeled off in the inspection process of the protected member, and is useful. is there.

  The substrate for a surface protective film of the present invention is represented by a unit represented by the following general formula (1), a unit represented by the following general formula (2), and, if necessary, the following general formula (3). In-plane retardation is 10 nm or less, and thickness direction retardation is 20 nm or less.

（ここで、Ｒ¹およびＲ²は、それぞれ独立に、水素または炭素数１〜８のアルキル基を示し、Ｒ³は、炭素数１〜１８のアルキル基、炭素数３〜１２のシクロアルキル基、または炭素数５〜１５の芳香環を含む置換基を示す。）

(Here, R ¹ and R ² each independently represent hydrogen or an alkyl group having 1 to 8 carbon atoms, and R ³ represents an alkyl group having 1 to 18 carbon atoms or a cycloalkyl group having 3 to 12 carbon atoms. Or a substituent containing an aromatic ring having 5 to 15 carbon atoms.)

（ここで、Ｒ⁴およびＲ⁵は、それぞれ独立に、水素または炭素数１〜８のアルキル基を示し、Ｒ⁶は、炭素数１〜１８のアルキル基、炭素数３〜１２のシクロアルキル基、または炭素数５〜１５の芳香環を含む置換基を示す。）

(Here, R ⁴ and R ⁵ each independently represent hydrogen or an alkyl group having 1 to 8 carbon atoms, and R ⁶ represents an alkyl group having 1 to 18 carbon atoms or a cycloalkyl group having 3 to 12 carbon atoms. Or a substituent containing an aromatic ring having 5 to 15 carbon atoms.)

（但し、Ｒ⁷は、水素又は炭素数１〜８のアルキル基を示し、Ｒ⁸は、炭素数６〜１０のアリール基を示す。）
本発明のイミド樹脂を構成する、第一の構成単位は、下記一般式（１）で表されるものであり、一般的にグルタルイミド単位と呼ばれる事が多い（以下、一般式（１）をグルタルイミド単位と省略して示す事がある。）。

(However, R ⁷ represents hydrogen or an alkyl group having 1 to 8 carbon atoms, and R ⁸ represents an aryl group having 6 to 10 carbon atoms.)
The first structural unit constituting the imide resin of the present invention is represented by the following general formula (1), and is generally called a glutarimide unit (hereinafter referred to as general formula (1)). Sometimes abbreviated as glutarimide unit.)

（但し、Ｒ¹及びＲ²は、それぞれ独立に、水素または炭素数１〜８のアルキル基を示し、Ｒ³は、炭素数１〜１８のアルキル基、炭素数３〜１２のシクロアルキル基、又は炭素数６〜１０のアリール基を示す。）
好ましいグルタルイミド単位としては、Ｒ¹、Ｒ²が水素又はメチル基であり、Ｒ³が水素、メチル基、ブチル基、またはシクロヘキシル基である。Ｒ¹がメチル基であり、Ｒ²が水素であり、Ｒ³がメチル基である場合が、特に好ましい。

(However, R ¹ and R ² each independently represent hydrogen or an alkyl group having 1 to 8 carbon atoms, R ³ represents an alkyl group having 1 to 18 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, Or an aryl group having 6 to 10 carbon atoms.)
As a preferable glutarimide unit, R ¹ and R ² are hydrogen or a methyl group, and R ³ is hydrogen, a methyl group, a butyl group, or a cyclohexyl group. The case where R ¹ is a methyl group, R ² is hydrogen, and R ³ is a methyl group is particularly preferred.

The glutarimide unit may be a single type or may include a plurality of types in which R ¹ , R ² , and R ³ are different.

  The glutarimide unit can be formed by imidizing the second structural unit described below. In addition, acid anhydrides such as maleic anhydride or half esters of these and linear or branched alcohols having 1 to 20 carbon atoms; acrylic acid, methacrylic acid, maleic acid, maleic anhydride, itaconic acid, itaconic anhydride, Α, β-ethylenically unsaturated carboxylic acids such as crotonic acid, fumaric acid, and citraconic acid can also be imidized and can be used to form glutarimide units.

  The second structural unit constituting the imide resin of the present invention is represented by the following general formula (2), and is generally called a (meth) acrylic acid ester unit (hereinafter referred to as general). (Formula (2) may be abbreviated as a (meth) acrylic acid ester unit).

（但し、Ｒ⁴及びＲ⁵は、それぞれ独立に、水素又は炭素数１〜８のアルキル基を示し、Ｒ⁶は、炭素数１〜１８のアルキル基、炭素数３〜１２のシクロアルキル基、又は炭素数６〜１０のアリール基を示す。）
本発明のイミド樹脂を製造する際に、先ず（メタ）アクリル酸エステル−芳香族ビニル共重合体、または（メタ）アクリル酸エステル重合体を重合し、これを後イミド化して形成する場合、具体的に（メタ）アクリル酸エステル単位を残基として与える原料としては、特に限定するものではないが、例えば、（メタ）アクリル酸メチル、（メタ）アクリル酸エチル、（メタ）アクリル酸ブチル、（メタ）アクリル酸イソブチル、（メタ）アクリル酸ｔ−ブチル、（メタ）アクリル酸ベンジル、（メタ）アクリル酸シクロヘキシル等が挙げられる。これらの中で、メタクリル酸メチルが特に好ましい。

(However, R ⁴ and R ⁵ each independently represent hydrogen or an alkyl group having 1 to 8 carbon atoms, and R ⁶ represents an alkyl group having 1 to 18 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, Or an aryl group having 6 to 10 carbon atoms.)
When the imide resin of the present invention is produced, first, a (meth) acrylic acid ester-aromatic vinyl copolymer or a (meth) acrylic acid ester polymer is polymerized and formed by post-imidization, The raw material that gives the (meth) acrylic acid ester unit as a residue is not particularly limited. For example, methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, ( Examples include isobutyl acrylate, t-butyl (meth) acrylate, benzyl (meth) acrylate, cyclohexyl (meth) acrylate, and the like. Of these, methyl methacrylate is particularly preferred.

These second structural units may be of a single type, or may include a plurality of types in which R ⁴ , R ⁵ and R ⁶ are different. Similarly, a plurality of types of raw materials that give the (meth) acrylic acid ester unit as a residue may be used.

  The third structural unit contained in the imide resin of the present invention as needed is represented by the following general formula (3), and is generally called an aromatic vinyl unit (hereinafter, generally referred to as general vinyl). (Formula (3) may be abbreviated as an aromatic vinyl unit.)

（但し、Ｒ⁷は、水素又は炭素数１〜８のアルキル基を示し、Ｒ⁸は、炭素数６〜１０のアリール基を示す。）
好ましい芳香族ビニル構成単位としては、スチレン、α−メチルスチレン等が挙げられる。これらの中でスチレンが特に好ましい。

(However, R ⁷ represents hydrogen or an alkyl group having 1 to 8 carbon atoms, and R ⁸ represents an aryl group having 6 to 10 carbon atoms.)
Preferred aromatic vinyl structural units include styrene, α-methylstyrene, and the like. Of these, styrene is particularly preferred.

These third structural units may be of a single type, or may include a plurality of types in which R ⁷ and R ⁸ are different.

The content of the glutarimide unit represented by the general formula (1) in the imide resin of the present invention depends on, for example, the structure of R ³ , but is preferably 20% by weight or more of the imide resin. The preferable content of the glutarimide unit is 20% to 95% by weight, more preferably 40 to 90% by weight, and still more preferably 50 to 80% by weight. When the ratio of the glutarimide unit is smaller than this range, the resulting imide resin may have insufficient heat resistance or the transparency may be impaired. On the other hand, if it exceeds this range, the heat resistance and melt viscosity are unnecessarily increased, the moldability becomes worse, the mechanical strength of the resulting film becomes extremely brittle, and the transparency may be impaired.

  The content of the aromatic vinyl unit represented by the general formula (3) in the imide resin of the present invention is preferably 10% by weight or more based on the total repeating unit of the imide resin. The preferred content of the aromatic vinyl unit is 10 to 40% by weight, more preferably 15 to 30% by weight, and still more preferably 15 to 25% by weight. When the aromatic vinyl unit is larger than this range, the resulting imide resin has insufficient heat resistance. If it is smaller than this range, the mechanical strength of the resulting film may be lowered.

  By adjusting the ratios of the general formulas (1), (2), and (3), it is possible to adjust various required physical properties. For example, when the imide resin of the present invention is first formed by polymerizing a (meth) acrylic acid ester-aromatic vinyl copolymer such as a (meth) acrylic acid methyl-styrene copolymer, then, for example, The ratio of the general formula (3) is determined by adjusting the polymerization ratio of the (meth) acrylic acid ester and the aromatic vinyl (the ratio of the general formula (3) can also be set to 0). By adjusting the addition ratio of the primary amine, the ratios of the general formulas (1) and (2) can be further adjusted.

  If necessary, the imide resin of the present invention may further be copolymerized with a fourth structural unit. A constitution obtained by copolymerizing a nitrile monomer such as acrylonitrile or methacrylonitrile, or a maleimide monomer such as maleimide, N-methylmaleimide, N-phenylmaleimide or N-cyclohexylmaleimide as the fourth structural unit Units can be used. These may be directly copolymerized in the resin or may be graft copolymerized.

  When producing the imide resin of the present invention, first, a (meth) acrylic acid ester-aromatic vinyl copolymer such as a (meth) acrylic acid methyl-styrene copolymer, or a (meth) methacrylate such as a methyl methacrylate polymer. When an acrylate polymer is polymerized and converted into an imide resin, the (meth) acrylate-aromatic vinyl copolymer and (meth) acrylate polymer that can be used in the present invention are imidized. As long as reaction is possible, it may be a linear (linear) polymer, or may be a block polymer, a core-shell polymer, a branched polymer, a ladder polymer, or a crosslinked polymer. The block polymer may be an A-B type, an A-B-C type, an A-B-A type, or any other type of block polymer. The core-shell polymer may be composed of only one core and only one shell, or each may be a multilayer.

The imide resin of the present invention preferably has a weight average molecular weight of 1 × 10 ⁴ to 5 × 10 ⁵ . When the weight average molecular weight is less than 1 × 10 ⁴ , the mechanical strength in the case of a film is insufficient, and when it exceeds 5 × 10 ⁵ , the viscosity at the time of melt extrusion is high and the molding processability is lowered. , Productivity of molded products may decrease.

  The glass transition temperature of the imide resin of the present invention is preferably 110 ° C. or higher, and more preferably 120 ° C. or higher. When the glass transition temperature is lower than the above value, the application range is limited in applications where heat resistance is required.

  The imide resin of the present invention is a (meth) acrylic acid ester-aromatic vinyl copolymer such as a (meth) acrylic acid methyl-styrene copolymer, or a (meth) acrylic acid ester polymer such as a methyl methacrylate polymer. As long as it is a method for treating an imidizing agent, it can be produced by various methods, and an extruder or the like may be used, or a batch type reaction vessel (pressure vessel) or the like may be used.

  When performing the manufacturing method of the imide resin of this invention with an extruder, various extruders can be used, For example, a single screw extruder, a twin screw extruder, a multi screw extruder etc. can be used. In particular, a twin screw extruder is preferable as an extruder that can promote mixing of an imidizing agent with a raw material polymer. There are non-mesh type co-rotating type, meshing type co-rotating type, non-meshing type bi-directional rotating type, meshing type bi-directional rotating type, etc. The meshing-type co-rotating type is preferable because it can rotate at a high speed and can promote the mixing of the imidizing agent with the raw material polymer. These extruders may be used alone or connected in series.

  The extruder is preferably equipped with a vent port that can be depressurized below atmospheric pressure in order to remove unreacted imidizing agent or by-products such as methanol and monomers.

  For example, instead of an extruder, imide resin can be produced by using a high-viscosity reactor such as a horizontal biaxial reactor such as Violac manufactured by Sumitomo Heavy Industries, Ltd. or a vertical biaxial agitation tank such as Super Blend. It can be used suitably.

  The batch-type reaction vessel (pressure vessel) used for producing the imide resin of the present invention is not particularly limited as long as it has a structure capable of heating and stirring a solution in which a raw material polymer is dissolved and adding an imidizing agent. As a result, the viscosity of the polymer solution may increase, and it is preferable that the stirring efficiency is good. For example, Sumitomo Heavy Industries Co., Ltd. agitation tank Max blend etc. can be illustrated.

  When the imide resin of the present invention is produced in the presence of a solvent, an imidizing agent can be added to the acrylic resin in a solution state by using a non-reactive solvent for the imidization reaction, which can dissolve the acrylic resin. Obtained by.

  Non-reactive solvents for imidization reactions include aliphatic alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, butyl alcohol and isobutyl alcohol, and aromatic carbonization such as benzene, toluene, xylene, chlorobenzene and chlorotoluene. Examples thereof include ketones such as hydrogen, methyl ethyl ketone, tetrahydrofuran and dioxane, and ether compounds. These may be used singly or may be a mixture of at least two. Among these, toluene and a mixed solvent of toluene and methyl alcohol are preferable.

  A lower concentration of the raw material resin with respect to the non-reactive solvent is preferable from the viewpoint of production cost, and the solid content concentration is preferably 10 to 80%, particularly preferably 20 to 70%.

  The imidizing agent used in the present invention is not particularly limited as long as the glutarimide unit represented by the general formula (1) is obtained. For example, methylamine, ethylamine, n-propylamine, i-propyl Fats such as amines, aliphatic hydrocarbon group-containing amines such as amine, n-butylamine, i-butylamine, tert-butylamine, n-hexylamine, aromatic hydrocarbon group-containing amines such as aniline, toluidine, trichloroaniline, cyclohexylamine, etc. Examples include cyclic hydrocarbon group-containing amines. Ammonia can also be used. Urea compounds that generate these amines by heating, such as urea, 1,3-dimethylurea, 1,3-diethylurea, 1,3-dipropylurea, can also be used. Of these imidizing agents, methylamine is preferable from the viewpoint of cost and physical properties.

  When the raw material resin is imidized with an imidizing agent, the reaction temperature is in the range of 150 to 400 ° C. in order to advance imidization and to suppress decomposition and coloring of the resin due to excessive heat history. 180-320 degreeC is preferable, Furthermore, 200-280 degreeC is preferable.

  When imidizing with an imidizing agent, generally used catalysts, antioxidants, heat stabilizers, plasticizers, lubricants, ultraviolet absorbers, antistatic agents, coloring agents, antishrinking agents and the like are used for the purpose of the present invention. You may add in the range which is not impaired.

  The imide resin of the present invention can be modified with an esterifying agent for the purpose of reducing carboxyl groups and acid anhydride groups by-produced during production.

  Examples of esterifying agents include dimethyl carbonate, 2,2-dimethoxypropane, dimethyl sulfoxide, triethyl orthoformate, trimethyl orthoacetate, trimethyl orthoformate, diphenyl carbonate, dimethyl sulfate, methyl toluene sulfonate, methyl trifluoromethyl sulfonate. , Methyl acetate, methanol, ethanol, methyl isocyanate, p-chlorophenyl isocyanate, dimethylcarbodiimide, dimethyl-t-butylsilyl chloride, isopropenyl acetate, dimethylurea, tetramethylammonium hydroxide, dimethyldiethoxysilane, tetra-N-butoxy Silane, dimethyl (trimethylsilane) phosphite, trimethyl phosphite Trimethyl phosphate, tricresyl phosphate, diazomethane, ethylene oxide, propylene oxide, cyclohexene oxide, 2-ethylhexyl glycidyl ether, phenyl glycidyl ether, and benzyl glycidyl ether.

  The substrate for a surface protective film of the present invention uses the imide resin, and preferably has an in-plane retardation of the substrate of 10 nm or less and a thickness direction retardation of 20 nm or less. The in-plane retardation of the substrate is more preferably 5 nm or less. The thickness direction retardation is more preferably 10 nm or less. If the in-plane retardation of the substrate exceeds 10 nm or the thickness direction retardation exceeds 20 nm, coloring unevenness and interference light occur in the inspection process, which may make inspection difficult or inaccurate. .

  Here, the in-plane retardation and the thickness direction retardation are defined as follows. That is, the direction in which the in-plane refractive index is maximum is the X axis, the direction perpendicular to the X axis is the Y axis, the thickness direction of the substrate is the Z axis, and the refractive indexes in the respective axial directions are nx, ny, nz, When the thickness of the substrate is d, the in-plane retardation Re = (nx−ny) × d and the thickness direction retardation Rth = | (nx + ny) / 2−nz | × d (|| represents an absolute value) (In an ideal film that is completely optically isotropic in the three-dimensional direction, both the in-plane retardation Re and the thickness direction retardation Rth are zero).

  In the imide resin of the present invention, the type containing the general formula (3) is substantially obtained by adjusting the content of each constituent unit and glutarimide unit in the methyl (meth) acrylate-styrene copolymer. It is also possible to impart a feature having no orientation birefringence to the material (note that it is also possible to adjust and use a specific orientation birefringence if necessary). Oriented birefringence refers to birefringence that develops when stretched at a predetermined temperature and a predetermined stretch ratio. In the present specification, unless otherwise specified, it means birefringence that is manifested when stretched 100% at a temperature 5 ° C. higher than the glass transition temperature of the imide resin. Here, the orientation birefringence (Δn) is defined by Δn = nx−ny = Re / d using the above-described nx and ny, and is measured by a phase difference meter.

The orientation birefringence value of the substrate for a surface protective film of the present invention is preferably 0 or more and 0.1 × 10 ⁻³ or less, more preferably 0 or more and 0.01 × 10 ⁻³ or less. . When the orientation birefringence is outside the above range, birefringence is likely to occur with respect to environmental changes, and it becomes difficult to obtain stable optical characteristics. Or there is a possibility that orientation birefringence may occur due to the tension associated with continuous conveyance in the form of a film in the process, and there is a concern that uneven coloring and interference light may occur in the same inspection process.

  In order to obtain an imide resin having substantially no optical isotropy and orientation birefringence, a (meth) acrylate ester-aromatic vinyl copolymer such as a (meth) methyl acrylate-styrene copolymer is used. It is necessary to adjust the amount of each structural unit in the coalescence and to further adjust the degree of imidization. The repeating unit represented by the general formula (1) and the repeating unit represented by the general formula (3) are 2 in weight ratio. 0.0: 1.0 to 4.0: 1.0 is preferable, 2.5: 1.0 to 4.0: 1.0 is more preferable, and 3.0: 1.0 A range of ˜3.5: 1.0 is more preferable.

  1-500 micrometers is preferable and, as for the thickness of the base material for surface protection films of this invention, 5-200 micrometers is more preferable, However, It is not restrict | limited to this.

  The tensile strength of the substrate for a surface protective film of the present invention is preferably 20 MPa or more, and more preferably 40 MPa or more. When the tensile strength is lower than 20 MPa, it is difficult to endure in use. For example, when handling by roll conveyance, there is a possibility of breaking in the middle of the process or breaking in the middle of peeling in the final process.

  The tensile elongation of the substrate for a surface protective film of the present invention is preferably 5% or more, and more preferably 10%. When tensile elongation is lower than 5%, it is hard to endure in use.

  The base material for a surface protective film of the present invention is prepared by adding generally used antioxidants, heat stabilizers, plasticizers, lubricants, ultraviolet absorbers, antistatic agents, colorants, anti-shrinkage agents to the imide resin of the present invention. It is good also as a composition added in the range which does not impair the objective of this invention. Further, these compositions containing the imide resin of the present invention as a main component (an imide resin alone or a blend (composition) with another thermoplastic resin may be used) are injection molding, melt extrusion film molding, inflation molding, blow molding. It can be processed into various molded products by various plastic processing methods such as molding, compression molding, and spinning molding. Further, the imide resin of the present invention is dissolved in a solvent such as methylene chloride, and can be molded by a casting method or spin coating method using the resulting polymer solution. The effects of the invention are easily manifested, and are preferable from the viewpoints of production costs and the influence of solvents on the global environment and work environment.

  Alternatively, the substrate for a surface protective film of the present invention may be uniaxially or biaxially stretched.

  The substrate for a surface protective film of the present invention can be subjected to a surface treatment if necessary. Examples of the surface treatment method include corona treatment, plasma treatment, ultraviolet irradiation, and alkali treatment. In particular, when surface processing such as coating is applied to the surface of the substrate for the surface protection film, or when another film is laminated with an adhesive, surface protection is used as a means for improving mutual adhesion. It is preferable to perform the surface treatment of the film substrate. Corona treatment is a particularly preferred method. A preferable degree of surface treatment is 50 dyn / cm or more. Although the upper limit is not particularly defined, it is more preferably 80 dyn / cm or less from the viewpoint of equipment for surface treatment.

  Moreover, a coating layer such as a hard coat layer can be formed on the surface of the surface protective film substrate of the present invention as required.

  It is preferable to apply an adhesive layer to the substrate for a surface protective film of the present invention. As the adhesive layer, an appropriate material such as rubber or acrylic can be selected. Moreover, the method of forming an adhesion layer can be performed by an appropriate method, for example, the method of apply | coating an adhesive etc. can be illustrated. The pressure-sensitive adhesive is preferably an optical strain having a level that does not affect the optical isotropy of the surface protective film substrate of the present invention. The thickness of the adhesive layer is preferably 1 to 200 μm, more preferably 5 to 100 μm, but is not limited thereto.

  The substrate for a surface protective film of the present invention can be used as a surface protective film after being subjected to these treatments.

  The surface protective film of the present invention is suitable for protecting the surface of various displays. The various displays here are not particularly limited, but are suitable for protecting screens of liquid crystal display panels, organic EL displays, plasma displays, field emission displays, surface electric field displays, and the like. Of these, the liquid crystal display is particularly effective because the outer layer is formed of a resin.

  The surface protective film of the present invention is also particularly suitable for protecting the surface of an optical member constituting a liquid crystal display. The optical member constituting the liquid crystal display here is not particularly limited as long as it constitutes a liquid crystal display, and examples thereof include a polarizer, a polarizer protective film, a polarizing plate, a retardation plate, a light guide plate, and a diffusion plate. .

  In addition, the surface protective film of the present invention can be applied to surfaces other than various display surfaces. For example, the surface of a synthetic resin plate or metal can be protected.

(1) Film thickness It measured using the Digimatic indicator (made by Mitutoyo Corporation).

(2) Total light transmittance This was measured by using a spectroscopic color difference meter NDH-300A manufactured by Nippon Denshoku Industries Co., Ltd. according to the method described in 5.5 of JIS K7105-1981.

(3) Haze The haze was measured using a spectroscopic color difference meter NDH-300A manufactured by Nippon Denshoku Industries Co., Ltd. according to the method described in 6.4 of JIS K7105-1981.

(4) Oriented birefringence A sample having a width of 50 mm and a length of 150 mm was cut out from the film, and a uniaxially stretched film (100% stretched) was prepared at a stretch ratio of 2 and a temperature 5 ° C. higher than the glass transition temperature. A test piece of 35 mm × 35 mm was cut out from the center in the TD direction of this uniaxially stretched film. The phase difference of this test piece was measured using an automatic birefringence meter (KOBRA-WR manufactured by Oji Scientific Instruments Co., Ltd.) at a temperature of 23 ± 2 ° C. and a humidity of 50 ± 5% at a wavelength of 590 nm and an incident angle of 0 °. . The value obtained by dividing this phase difference by the thickness of the test piece measured using a digimatic indicator (manufactured by Mitutoyo Corporation) was defined as orientation birefringence.

(5) In-plane retardation Re and thickness direction retardation Rth
A 40 mm × 40 mm test piece was cut out from the film. Using an automatic birefringence meter (KOBRA-WR manufactured by Oji Scientific Co., Ltd.), the in-plane retardation Re was measured at a temperature of 23 ± 2 ° C. and a humidity of 50 ± 5% at a wavelength of 590 nm and an incident angle of 0 °. It was measured. The thickness d of the test piece measured using a digimatic indicator (manufactured by Mitutoyo Corporation), the refractive index n measured by an Abbe refractometer (manufactured by Atago Co., Ltd. 3T), the wavelength 590 nm measured by an automatic birefringence meter, and the surface The three-dimensional refractive index nx, ny, nz is obtained from the internal phase difference Re and the phase difference value in the 40 ° tilt direction, and the thickness direction phase difference Rth = | (nx + ny) / 2−nz | × d (|| is the absolute value) Represents).

(6) Moisture permeability Based on JIS Z 0208, it measured by the cup method at 40 degreeC, 90% RH, 80 degreeC, and 90% RH. The 40 ° C. test used paraffin for sealing, and the 80 ° C. test used polytetrafluoroethylene packing for sealing. The water vapor transmission coefficient was determined from the moisture permeability obtained (g / (m ² · 24 hr)) and from the film thickness (mm).

(7) Ratio of general formula (1) in imide resin The pellet of the product was used as it was, and IR spectrum was measured at room temperature using TravelIR manufactured by SensIR Technologies. From the obtained spectrum, the absorption intensity (Abs _Ester) attributed to the ester carbonyl group of 1720 cm ^-1, the imidization ratio from the ratio of the absorption intensity assignable to an imide carbonyl group of 1660cm ^-1 (Abs _imide) (Im % (IR)). Here, the imidation rate refers to the proportion of the imide carbonyl group in all carbonyl groups.

(8) Glass transition temperature (Tg)
Using 10 mg of the product, a differential scanning calorimeter (DSC, model DSC-50 manufactured by Shimadzu Corporation) was used and measured at a heating rate of 20 ° C./min in a nitrogen atmosphere and determined by the midpoint method.

(9) Inspection status of foreign matter The surface protective film obtained in the example was bonded to both sides of the polarizing plate, and this was further put into a crossed nicols state using two polarizing plates, placed in a light box, and light was applied from below. It was examined whether or not the presence or absence of light leakage could be confirmed visually.

(Resin production example 1)
Polymethylmethacrylate-styrene copolymer (MS) resin (composition of general formula (2) and general formula (3) is 80 mol%: 20 mol%) and monomethylamine (Mitsubishi Gas Chemical Co., Ltd.) as an imidizing agent (Made by company), and imidized MS resin was manufactured. The extruder used was a meshing type co-rotating twin screw extruder having a diameter of 15 mm. The set temperature of each temperature control zone of the extruder was 230 ° C., the screw rotation speed was 150 rpm, MS resin was supplied at 2.0 kg / hr, and the supply amount of monomethylamine was 40 parts by weight with respect to the MS resin. A methacrylic resin was introduced from a hopper, and the resin was melted and filled with a kneading block, and then monomethylamine was injected from a nozzle. A seal ring was placed at the end of the reaction zone to fill the resin. By-products after the reaction and excess methylamine were devolatilized by reducing the pressure at the vent port to -0.08 MPa. The resin that came out as a strand from a die provided at the exit of the extruder was cooled in a water tank and then pelletized with a pelletizer. This imidized MS resin is an imide obtained by copolymerizing the unit represented by the general formula (1), the unit represented by the general formula (2), and the unit represented by the general formula (3) described in the embodiment. Corresponding to the resin, the general formula (10) was 70 mol%. Tg was 156 ° C.

(Resin production example 2)
Instead of methylamine, cyclohexylamine (manufactured by Shin Nippon Rika Co., Ltd.) was used. The resin supply amount was 1.5 kg / hr, cyclohexylamine was 40 parts by weight, and the same procedure as in Resin Production Example 1 was performed. The general formula (1) was 65 mol%. Tg was 164 ° C.

(Resin production example 3)
(1) A methacrylic resin composition (core-shell polymer) was synthesized by the following method.

The following substances were charged into an 8 L polymerization apparatus equipped with a stirrer.
Deionized water 200 parts Sodium dioctylsulfosuccinate 0.25 parts Sodium formaldehyde sulfoxylate 0.15 parts Ethylenediaminetetraacetic acid-2-sodium 0.005 parts Ferrous sulfate 0.0015 parts The inside of the polymerization apparatus is nitrogen gas After sufficiently substituting and substantially free of oxygen, the internal temperature is set to 60 ° C., and 70% of butyl acrylate (BA) and 30% of methyl methacrylate (MMA) are used as raw materials for the acrylic ester-based crosslinked elastic particles. 100 parts of the monomer mixture consisting of 2 parts of allyl methacrylate (AlMA) and 0.5 parts of cumene hydride peroxide (CHP)> 20 parts continuously at a rate of 10 parts / hour After completion of the addition, the polymerization was continued for another 0.5 hours to obtain acrylic ester-based crosslinked elastic particles. The polymerization conversion was 99.5% and the average particle size was 800 mm. Thereafter, 0.3 part of sodium dioctylsulfosuccinate was charged, the internal temperature was set to 60 ° C., and a monomer mixture 100 consisting of 10% styrene (St) and 90% MMA as raw materials for the methacrylate polymer. 80 parts of a monomer mixture consisting of 0.8 part of tert-dodecyl mercaptan (tDM) and 0.5 part of CHP is continuously added at a rate of 10 parts / hour, and polymerization is continued for another hour. A methacrylic resin composition (core-shell polymer) was obtained. The polymerization conversion rate was 99.0%. The obtained latex was salted out and coagulated with calcium chloride, washed with water and dried to obtain a resin powder (1) of a methacrylic resin composition (C). Furthermore, using a single screw extruder with a 40 mmφ vent, the cylinder temperature was set to 230 ° C., and melt kneading was performed to pelletize.

  (2) The methacrylic resin composition (core-shell polymer) obtained in the above (1) was used as monomethylamine (Mitsubishi Gas Chemical Co., Ltd.) as an imidizing agent. The resin feed rate was 1.0 kg / hr, methylamine was 10 parts by weight, and the same procedure as in Resin Production Example 1 was performed to produce an imidized MS resin (core-shell polymer). The general formula (1) was 50 mol%. Tg was 135 ° C.

(Examples 1-3)
A methylene chloride solution having a solid content concentration of 20% by weight was prepared using the resins of Resin Production Examples 1 to 3, and was cast on polyethylene terephthalate (Teijin Tetron HS) laid on a glass plate using a bar coater. And left at room temperature for 60 minutes. Thereafter, the film was peeled off and sandwiched between four pieces fixing jigs, and dried at 100 ° C. for 1 hour and further at Tg + 10 ° C. of each resin for 12 hours to obtain a film. An acrylic adhesive was applied to one side of the film so as to have a thickness of 5 μm and dried. The film properties are shown in Table 1.

(Comparative Example 1)
Table 1 shows the film characteristics of a triacetyl acetate film (40 μm) manufactured by Fuji Photo Film. An acrylic adhesive was applied to one side of the film so as to have a thickness of 5 μm and dried. The film properties are shown in Table 1.

(Comparative Example 2)
A dope was prepared by adjusting a xylene solution (resin concentration = 35% by weight) of ZEONOR 1420R manufactured by Nippon Zeon. The dope was cast in the same manner as in Example 1 and allowed to stand at room temperature for 10 minutes, then further dried at 80 ° C. for 1 hour, 120 ° C. for 2 hours, and 170 ° C. for 4 hours, and then peeled off from the substrate film to obtain 50 μm A film was obtained. An acrylic pressure-sensitive adhesive was applied to one side of this film so as to have a thickness of 5 μm and dried. The film properties are shown in Table 1.

Claims (6)

From an imide resin formed including a unit represented by the following general formula (1), a unit represented by the following general formula (2), and a unit represented by the following general formula (3) as necessary The in-plane retardation is 10 nm or less, and the thickness direction retardation is 20 nm or less.

(Here, R ¹ and R ² each independently represent hydrogen or an alkyl group having 1 to 8 carbon atoms, and R ³ represents an alkyl group having 1 to 18 carbon atoms or a cycloalkyl group having 3 to 12 carbon atoms. Or a substituent containing an aromatic ring having 5 to 15 carbon atoms.)

(Here, R ⁴ and R ⁵ each independently represent hydrogen or an alkyl group having 1 to 8 carbon atoms, and R ⁶ represents an alkyl group having 1 to 18 carbon atoms or a cycloalkyl group having 3 to 12 carbon atoms. Or a substituent containing an aromatic ring having 5 to 15 carbon atoms.)

(However, R ⁷ represents hydrogen or an alkyl group having 1 to 8 carbon atoms, and R ⁸ represents an aryl group having 6 to 10 carbon atoms.) The substrate for a surface protective film according to claim 1, wherein the orientation birefringence is 0 or more and 0.1 × 10 ⁻³ or less.   3. The surface protective film substrate according to claim 1, wherein the member to be protected is an optical member.   The substrate for a surface protective film according to any one of claims 1 to 3, wherein the optical member is a liquid crystal display panel.   5. The surface protective film substrate according to claim 1, wherein the optical member is a polarizer, a polarizer protective film, a polarizing plate, a retardation plate, a light guide plate, or a diffusion plate.   The surface protection film using the base material for surface protection films in any one of Claim 1 to 5.