JP2014043108A - Transparent film and surface protective film using the transparent film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transparent film excellent in the scratch resistance of the back and a surface protective film having the transparent film.SOLUTION: A transparent film 10 includes a base material layer 12 made of a transparent resin material and a back layer 14 which is formed on a first surface 12A of the base material layer 12 and has a thickness of 1 μm or below. In the transparent film 10, the break starting load of the back layer 14 in a scratch test is at least 50 mN, and the friction coefficient of the back layer 14 is 0.4 or below.

Description

  The present invention relates to a transparent film that is less likely to be scratched on the back surface and a surface protective film including the film.

  A surface protective film (also referred to as a surface protective sheet) generally has a configuration in which an adhesive is provided on a film-like support. Such a protective film is attached to an adherend via the pressure-sensitive adhesive, and is used for the purpose of protecting the adherend from scratches and dirt during processing and transportation. For example, a polarizing plate to be bonded to a liquid crystal cell in the production of a liquid crystal display panel is once manufactured in a roll form, and then unwound from the roll and cut into a desired size according to the shape of the liquid crystal cell. Here, in order to prevent the polarizing plate from being rubbed and damaged by a transport roll or the like in an intermediate step (for example, a transport step in the production of a roll-shaped polarizing plate or when the polarizing plate is used) Measures are taken to attach a surface protective film to one side or both sides (typically one side). Patent documents 1 and 2 are mentioned as technical literature about a surface protection film.

Japanese Patent Laid-Open No. 2003-320631 JP 2005-314563 A

  As such a surface protective film, a transparent one is preferably used since the appearance inspection of an adherend (for example, a polarizing plate) can be performed with the film attached. In recent years, the required level for the appearance quality of the surface protection film has been increased from the viewpoint of the ease of appearance inspection. In particular, there is a demand for the property that the back surface of the surface protective film (the surface opposite to the surface attached to the adherend) is not easily scratched. This is because if the surface protective film has scratches, it cannot be determined whether the surface protective film is attached to the adherend or the surface protective film.

  Accordingly, an object of the present invention is to provide a transparent film that is less likely to be scratched on the back surface (that is, excellent in scratch resistance) and is therefore suitable for uses such as a support for a surface protective film. Another object of the present invention is to provide a surface protective film having a structure having an adhesive layer on one side of the transparent film.

  The transparent film provided by the present invention has a base material layer made of a transparent resin material, and a back layer provided on the first surface of the base material layer. The back layer has a thickness of 1 μm or less. In the transparent film, the fracture start load of the back layer in the scratch test is 50 mN or more, and the friction coefficient of the back layer is 0.4 or less.

  According to the transparent film having such a configuration, it is possible to impart good scratch resistance to the base material layer using the back layer. Thus, the transparent film excellent in scratch resistance is suitable as a support for the surface protective film because it can accurately inspect the appearance of the product through the film. Moreover, since the said back layer is small in thickness, there is little influence on the characteristics (optical characteristics, dimensional stability, etc.) of a base material layer, and it is preferable. In addition, when the thickness of the back layer is more than 1 μm, when the back layer contains components that are easily colored, the coloring of the entire transparent film becomes conspicuous, or curing shrinkage occurs with the formation of the back layer Further, the shrinkage may cause the transparent film to be easily curled. It is also preferable to reduce the thickness of the back layer within a range in which desired performance (for example, scratch resistance) is achieved, from the viewpoint that the above-described coloring and curling can be prevented or reduced. As the resin material constituting the base material layer, a material using a polyester resin such as polyethylene terephthalate resin or polyethylene naphthalate resin as a base resin can be preferably used.

  In a preferred embodiment of the technology disclosed herein, the ratio (Ps / Pb; hereinafter referred to as “plastic index ratio”) of the plastic index Ps of the back surface layer of the transparent film and the plastic index Pb of the base material layer. ) Is 1.5 or more. Here, the plastic index Ps of the back layer was measured by indenting elastic modulus and hardness at a depth of 10 nm by vertically pushing a barco pitch type diamond indenter having a radius of curvature of 0.1 μm into the back layer constituting the transparent film. The modulus of elasticity is obtained by dividing by the hardness. The plastic index ratio of the base material layer is determined by measuring the indentation elastic modulus and hardness at a depth of 10 nm by pressing the indenter vertically into the base material layer having no back layer, and dividing the elastic modulus by the hardness. Desired.

  A transparent film satisfying the above plastic index ratio has a plastic index larger than that of the base layer when the base layer is deformed when the scratch stress applied from above the back layer is applied to the base layer. The substrate layer can be deformed by following the deformation of the base material layer. This prevents the back layer from being damaged by the fretting stress (that is, the breaking start load becomes high), so that a transparent film satisfying the breaking start load and excellent in scratch resistance can be appropriately realized.

  The transparent film disclosed herein has a peeling force measured by applying an adhesive tape to the back layer, and peeling the adhesive tape from the back layer at a peeling speed of 0.3 m / min and a peeling angle of 180 degrees. It is preferable that (back surface peeling force) is 2 N / 19 mm or more. A transparent film exhibiting such peeling force is suitable as a support for the surface protective film. That is, the surface protective film that has finished its protective function is removed by peeling off from the adherend (for example, an optical member such as a polarizing plate). At this time, the surface protective film is removed by separating the end of the surface protective film from the adherend by applying the adhesive tape to the back surface (surface of the back layer) of the surface protective film and pulling the adhesive tape. The workability at the time can be improved and the burden on the adherend can be reduced. The surface protective film using the transparent film as a support is suitable for a peeling operation using the pressure-sensitive adhesive tape because the back layer has an appropriate peeling force.

  The structure of the back layer is preferably a single layer structure from the viewpoint of strength and productivity. Moreover, it is preferable that the said back surface layer is provided directly on the 1st surface of the said base material layer. In the configuration in which one or more intermediate layers are interposed between the back layer and the base material layer, the adhesion between the intermediate layer, the base material layer and the back surface layer is insufficient, and the fracture start load of the back layer is reduced. It tends to decrease (scratch resistance decreases). Therefore, in order to realize the fracture initiation load disclosed herein, it is advantageous to adopt a configuration in which the back layer is directly provided on the base material layer.

  In a preferred embodiment, the back layer is made of a resin material containing a lubricant. Here, the term “lubricant” refers to a component having an action of reducing the coefficient of friction when blended with a resin material. Thus, the back layer made of a resin material containing a lubricant is preferable because the preferable friction coefficient disclosed herein is easily realized, and thus a transparent film excellent in scratch resistance is easily realized.

  In a preferred embodiment, the back layer is made of a resin material containing an antistatic component. In the transparent film having such a configuration, scratch resistance and antistatic properties can be imparted using the back layer. Therefore, the productivity of the transparent film is better than the configuration in which the antistatic layer is provided separately from the back layer. In addition, since the adhesion between the back surface layer and the base material layer can be improved as compared with the configuration in which the antistatic layer is interposed between the back surface layer and the base material layer, the above fracture start load is satisfied and the scratch resistance is excellent. Transparent film is easy to realize. As the antistatic component, a conductive polymer can be preferably employed because it is easy to achieve both good antistatic properties and high scratch resistance.

  According to the present invention, there is also provided a surface protective film provided with any transparent film disclosed herein as a support. The surface protective film typically includes the transparent film and an adhesive layer provided on the surface of the transparent film opposite to the back layer. Such a surface protective film is particularly suitable as a surface protective film for optical parts.

It is typical sectional drawing which shows one structural example of the surface protection film which concerns on this invention. It is typical sectional drawing which shows the other structural example of the surface protection film which concerns on this invention. It is an optical microscope image which shows an example of a scratch mark. It is typical explanatory drawing which shows the measuring method of a fracture start load.

Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.
Further, the embodiment described in the drawings is schematically illustrated for clearly explaining the present invention, and accurately represents the size and scale of the transparent film or the surface protective film of the present invention actually provided as a product. It is not a thing.

  Since the transparent film disclosed here is excellent in scratch resistance, it can be preferably used for the support of the pressure-sensitive adhesive sheet and other uses. Such a pressure-sensitive adhesive sheet may generally have a form called a pressure-sensitive adhesive tape, a pressure-sensitive adhesive label, a pressure-sensitive adhesive film, or the like. Among them, it is suitable as a support for a surface protective film, and since it can accurately inspect the appearance of products through the film, it is particularly used as an optical component (for example, a liquid crystal display panel component such as a polarizing plate or a wave plate). It is suitable as a support for a surface protective film that protects the surface of the optical component during processing or transportation of the optical component. The surface protective film disclosed herein is characterized by having an adhesive layer on one side of the transparent film. The pressure-sensitive adhesive layer is typically formed continuously, but is not limited to such a form. For example, the pressure-sensitive adhesive layer is a pressure-sensitive adhesive layer formed in a regular or random pattern such as a spot or stripe. There may be. In addition, the surface protective film disclosed herein may be in the form of a roll or a single sheet.

  A typical configuration example of a surface protective film having the transparent film disclosed herein as a support is schematically shown in FIG. The surface protective film 1 includes a transparent film (support) 10 and an adhesive layer 20. The transparent film 10 includes a base material layer 12 made of a transparent resin film and a back layer 14 having a thickness of 1 μm or less provided directly on the first surface 12A. The pressure-sensitive adhesive layer 20 is provided on the opposite surface of the transparent film 10 on the opposite side to the back layer 14. The surface protective film 1 is used by sticking the pressure-sensitive adhesive layer 20 to an adherend (a surface to be protected, for example, the surface of an optical component such as a polarizing plate). As shown in FIG. 2, the protective film 1 before use (that is, before sticking to the adherend) typically has at least the pressure-sensitive adhesive on the surface of the pressure-sensitive adhesive layer 20 (sticking surface to the adherend). It may be in a form protected by a release liner 30 having a release surface on the layer 20 side. Or the form by which the adhesive layer 20 contact | abutted on the back surface (surface of the back surface layer 14) of the transparent film 10 and the surface was protected by winding the surface protection film 1 in roll shape may be sufficient.

  The base material layer of the transparent film disclosed here may be a resin film (base material film) formed by molding various resin materials into a transparent film shape. As the resin material, those capable of constituting a base film excellent in one or more properties among transparency, mechanical strength, thermal stability, moisture shielding property, isotropy, and the like are preferable. For example, polyester polymers such as polyethylene terephthalate (PET), polyethylene naphthalate, polybutylene terephthalate; cellulose polymers such as diacetyl cellulose and triacetyl cellulose; polycarbonate polymers; acrylic polymers such as polymethyl methacrylate; etc. A resin film composed of a resin material having a base resin (a main component of the resin component, that is, a component occupying 50% by mass or more) can be preferably used as the base material layer. Other examples of the resin material include styrene polymers such as polystyrene and acrylonitrile-styrene copolymers; olefin polymers such as polyethylene, polypropylene, polyolefins having a cyclic or norbornene structure, and ethylene-propylene copolymers; Examples thereof include vinyl chloride polymers; amide polymers such as nylon 6, nylon 6, 6, and aromatic polyamide; Other examples of base resins include imide polymers, sulfone polymers, polyether sulfone polymers, polyether ether ketone polymers, polyphenylene sulfide polymers, vinyl alcohol polymers, vinylidene chloride polymers, vinyl butyral polymers, arylates. Examples thereof include a polymer, a polyoxymethylene polymer, and an epoxy polymer. The base material layer may be composed of a blend of two or more of the above-described polymers. The said base material layer is so preferable that there is little anisotropy of an optical characteristic (phase difference etc.). In particular, in a transparent film used as a support for a surface protective film for optical components, it is beneficial to reduce the optical illegality of the base material layer. The base material layer may have a single layer structure or a structure in which a plurality of layers having different compositions are laminated. Typically a single layer structure.

The thickness of the base material layer can be appropriately selected according to the purpose, but it is usually appropriate to be about 10 μm to 200 μm from the viewpoint of workability such as strength and handleability and cost and appearance inspection properties. The thickness is preferably about 15 μm to 100 μm, and more preferably 20 μm to 70 μm.
The refractive index of the base material layer is usually suitably about 1.43 to 1.6, preferably about 1.45 to 1.5. From the viewpoint of the transparency of the substrate, the substrate layer preferably has a light transmittance of 70% to 99%, and the transmittance is 80% to 97% (for example, 85% to 95%). Is more preferable.

  Various additives such as antioxidants, ultraviolet absorbers, antistatic components, plasticizers, colorants (pigments, dyes, etc.) are blended in the resin material constituting the base material layer as necessary. Also good. For example, corona discharge treatment, plasma treatment, ultraviolet irradiation treatment, acid treatment, alkali treatment, and application of a primer are applied to the first surface of the base material layer (the surface on the side where the back layer is provided). Surface treatment may be performed. Such a surface treatment can be, for example, a treatment for improving the adhesion between the base material layer and the back surface layer. A surface treatment in which a polar group such as a hydroxyl group (—OH group) is introduced on the surface of the substrate layer can be preferably employed. Moreover, in the surface protective film disclosed herein, the transparent film constituting the surface protective film is the same surface treatment as described above on the second surface of the base material layer (the surface on the side where the pressure-sensitive adhesive layer is formed). May be given. Such a surface treatment may be a treatment for improving the adhesion between the transparent film (support) and the pressure-sensitive adhesive layer (the anchoring property of the pressure-sensitive adhesive layer).

The transparent film disclosed here has a back layer having a thickness of 1 μm or less (typically 0.02 μm to 1 μm) on one surface (first surface) of the base material layer. The transparent film has a fracture start load of the back layer measured by a scratch test described later of 50 mN or more. A transparent film satisfying such a fracture initiation load is excellent in scratch resistance. For example, in the scratch resistance evaluation to be described later, the back layer is not visually removed. Therefore, it is suitable as a support for a surface protective film (particularly, a surface protective film used in the production and transportation of polarizing plates and other optical components). The upper limit of the fracture start load is not particularly limited, but usually the fracture start load is set to 300 mN or less (for example, 150 mN or less) in consideration of balance with other characteristics (printability, back surface peeling force, light transmittance, etc.). Is appropriate. In a preferred embodiment of the transparent film disclosed herein, the fracture start load is 50 mN to 300 mN (for example, 50 mN to 150 mN).
For example, in the measurement environment of 23 ° C. and 50% RH, the fracture start load is increased to 0 to 300 mN using a conical diamond indenter having a tip curvature radius of 10 μm, and the back surface of the transparent film (that is, the back layer) Is obtained as a load corresponding to a location where the length of the fracture start point on the scratch mark is greater than 2 μm (more specific measurement method will be described later). See experimental example). An example of scratch marks obtained under the above conditions is shown in FIG.

The friction coefficient of the back layer constituting the transparent film is 0.4 or less. As a result, when a load (a load that causes scratching) is applied to the back surface layer, the load can be received along the surface of the back surface layer, and the frictional force due to the load can be reduced. Accordingly, it is possible to prevent an event in which the back layer is agglomerated and broken due to the frictional force, or the back layer is peeled off from the base material layer (interface breakage) to cause scratches. The lower limit of the friction coefficient is not particularly limited. However, considering the balance with other characteristics (printability, back surface peeling force, light transmittance, etc.), the friction coefficient is usually 0.1 or more (typically 0. 0). 1 to 0.4) is appropriate, and 0.15 or more (typically 0.15 to 0.4) is preferable.
As the friction coefficient, for example, a value obtained by rubbing the back surface of the transparent film (that is, the surface of the back layer) with a vertical load of 40 mN in a measurement environment of 23 ° C. and 50% RH can be adopted (more For specific measurement methods, see the experimental examples described later). As a method of reducing (adjusting) the friction coefficient so that the above friction coefficient is realized, a method of including various lubricants (leveling agents, etc.) in the back layer, addition of a cross-linking agent and adjustment of film forming conditions can be used. A method of increasing the cross-linking density can be appropriately employed.

  In a preferred embodiment of the technology disclosed herein, the structural characteristics that the thickness of the back layer constituting the transparent film is 1 μm or less, and this is particularly effective in a transparent film having such a thin back layer. Adopt a scratch improvement technique. That is, when the back layer has a certain thickness (for example, 5 μm or more), the fracture start load is improved by increasing the hardness of the back layer (in other words, a layer having a strength that can withstand the load). Forming) and improving scratch resistance. However, the present inventor has found that in the case of a transparent film having a back layer thickness of 1 μm or less, improvement in scratch resistance cannot be achieved accurately if the above technical idea is applied as it is. This is considered to be because, in a transparent film having a thin back layer structure, the load applied to the back layer easily reaches the base layer and deforms the base layer.

  As a result of examining in detail the fracture behavior of the back layer of the transparent film having a thin back layer, the present inventor found that when only the hardness of the thin back layer was increased without changing the base material layer in such a structure, It has been found that the deformation of the back surface layer cannot follow the deformation of the base material layer, and therefore, an adhesion failure occurs between the base material layer and the back surface layer, and the fracture start load is reduced. In order to prevent such an event and improve the scratch resistance, the plastic index ratio (Ps / Pb) defined as the ratio between the plastic index Ps of the back layer and the plastic index Pb of the base material layer is set to 1. It has been found that it is effective to set it to 5 or more. Here, the plastic indexes Ps and Pb are, for example, in a measurement environment of 23 ° C. and 50% RH, a barco pitch (triangular pyramid) diamond indenter having a radius of curvature of 0.1 μm is vertically pushed, and a depth of about 10 nm. It can be calculated by measuring the indentation elastic modulus and hardness and dividing the measured value of the elastic modulus by the measured value of hardness (for more specific measurement examples, see the experimental examples described later). It can be said that the higher the plasticity index, the easier it is to deform with respect to the load. That is, that Ps / Pb is 1.5 or more means that the back layer has a deformability that can sufficiently follow the deformation of the base material layer. By setting Ps / Pb to 2 or more, better scratch resistance can be realized. The upper limit of Ps / Pb is not particularly limited, but it is usually appropriate to set it to 50 or less in consideration of balance with other characteristics (friction coefficient and the like). In a preferred embodiment, Ps / Pb is 1.5 or more and 3 or less. As another preferable embodiment, Ps / Pb may be 1.5 or more and 50 or less (for example, 10 or more and 50 or less, more preferably 20 or more and 50 or less). These preferable values of Ps / Pb can be preferably applied to, for example, a transparent film in which the base material layer is made of a polyester resin material (typically, a PET resin material). In addition, the plastic index of a general PET film is about 10-20.

  According to the transparent film configured to satisfy both the preferable plastic index ratio (Ps / Pb) and the friction coefficient disclosed herein, the above-described preferable fracture initiation load can be easily achieved. Such a transparent film can efficiently reduce the frictional force by having the friction coefficient with respect to the frictional force received on the back surface thereof, and the base material by the frictional force by having the plastic index ratio. Combined with the fact that the back layer can sufficiently follow the deformation of the layer, it can exhibit particularly high scratch resistance. Therefore, such a transparent film is suitable as a support for the surface protective film.

  The back layer has a peel force (back peel force) of 2 N / 19 mm or more measured by peeling off under the conditions of a peel speed of 0.3 m / min and a peel angle of 180 degrees by sticking an adhesive tape to the back layer. It is preferably 3N / 19 mm or more. When the technique disclosed herein is applied to a surface protective film, it is particularly meaningful to have the above-described peeling force. If the peeling force is too low, the workability at the time of removing the surface protective film from the adherend by attaching an adhesive tape to the release layer may tend to be reduced. The upper limit of the peeling force is not particularly limited, but in consideration of the balance with other characteristics (coefficient of friction, etc.), and when the roll is rewound after being rolled up, the adhesive adheres to the back surface (glue residue) In order to prevent this, it is usually preferably 10 N / 19 mm or less, for example, 6 N / 19 mm or less. In a preferable aspect of the technology disclosed herein, the back surface peeling force is 2 to 10 N / 19 mm (more preferably 3 to 6 N / 19 mm). In addition, the said peeling force is obtained by measuring in the environment of 23 degreeC and 50% RH using the single-sided adhesive tape by the Nitto Denko Corporation, brand name "No. 31B", for example (more specific measurement). For the method, refer to the experimental examples described later).

  The printability in the technology disclosed herein refers to a property that can be easily printed with oil-based ink (for example, using an oil-based marking pen). In the process of processing and transporting an adherend (for example, an optical component) using a surface protective film, there is a demand for displaying the identification number of the adherend to be protected on the surface protective film. Therefore, a transparent film excellent in printability in addition to scratch resistance and a surface protective film provided with the transparent film are preferable. For example, it is preferable that the solvent is alcohol-based and has high printability for oil-based inks containing pigments. Moreover, it is preferable that the printed ink is difficult to be removed by rubbing or transfer (that is, excellent in print adhesion). The degree of the printability can be grasped by, for example, printability evaluation described later.

  The material of the resin constituting the back layer can be appropriately selected so as to realize the preferable fracture initiation load and friction coefficient (more preferably, the plastic index ratio) disclosed herein. It is preferable to select a resin that is excellent in scratch resistance, can form a layer having sufficient strength, and has excellent light transmittance. Such resin may be various types of resins such as thermosetting resin, ultraviolet curable resin, electron beam curable resin, and two-component mixed resin.

  Specific examples of thermosetting resins include polysiloxanes, polysilazanes, polyurethanes, acrylic-urethanes, acrylic-styrenes, fluororesins, acrylic silicones, acrylics, polyesters, polyolefins, etc. Are listed. Of these, polyurethane-based, acrylic-urethane-based, acrylic-styrene-based thermosetting resins are preferable in that they have high elasticity and can easily form a layer having a preferable plastic index ratio disclosed herein. . In addition, a thermosetting resin such as polysiloxane or polysilazane is preferable in that a high-hardness layer can be easily formed. Further, the fluororesin-based thermosetting resin is preferable in that it contains a slip component in the molecular structure and can easily form a layer having a preferable coefficient of friction disclosed herein. A resin having a soft segment and a hard segment is preferred. Here, the soft segment refers to a resin component having a flexible main chain structure or characteristics, and the hard segment refers to a resin component having a rigid main chain structure or characteristics (at least stiffer than the soft segment). Any of the thermosetting resins used for forming the back layer in Samples A-4 to A-10 described later corresponds to a resin having a soft segment and a hard segment. Moreover, the resin of the emulsion form which the resin component disperse | distributed to the aqueous solvent can be used preferably. According to the above-mentioned emulsion form, even if it is a resin component having a large molecular weight and a long main chain, the viscosity and concentration can be easily adjusted by dispersing it in an aqueous medium as emulsion particles. Such a resin component is suitable for forming a coating film excellent in plastic deformability. Therefore, according to the resin in emulsion form (for example, thermosetting resin), the above-described back layer exhibiting the preferable plastic index ratio (high plastic index ratio) can be suitably realized.

  Specific examples of the ultraviolet curable resin include monomers, oligomers, polymers, and mixtures of various resins such as polyester, acrylic, urethane, amide, silicone, and epoxy. A polyfunctional monomer having two or more (more preferably three or more, for example, about 3 to 6) UV-polymerizable functional groups in one molecule, since it is easy to form a high-hardness layer having a high UV-curing property and An ultraviolet curable resin containing / or an oligomer thereof can be preferably used. As the polyfunctional monomer, acrylic monomers such as polyfunctional acrylates and polyfunctional methacrylates can be preferably used. From the viewpoint of adhesion to the base material layer, it is advantageous to use a thermosetting resin rather than an ultraviolet curable resin.

  The thickness of the back layer can be, for example, about 0.02 μm to 1 μm, and preferably about 0.05 to 0.5 μm (for example, 0.05 to 0.2 μm). When the thickness of the back layer is too large, appearance quality such as coloring and curling may be easily deteriorated due to the back layer. If the thickness of the back layer is too small, it becomes difficult to achieve desired scratch resistance. The thickness of the layer constituting the transparent film or the surface film (for example, the back layer) disclosed herein is determined by subjecting the back layer to heavy metal dyeing in advance and then cutting the transparent film in the cross-sectional direction. The obtained sample can be grasped by a high-resolution observation technique using a transmission electron microscope (TEM) or the like. This technique can be preferably applied to a layer having a thickness of about 0.01 μm or more. For thinner layers, various thickness detectors (for example, surface roughness meters, interference thickness meters, infrared spectrometers, various X-ray diffractometers, etc.) and thicknesses obtained by electron microscope observation By creating a calibration curve for the correlation, the approximate thickness can be calculated. In some cases, the TEM can be used to observe the layer configuration in the cross-sectional direction (the number of layers in the stacked structure and the thickness of each layer). Further, when each layer has a thickness of about 0.1 μm or more, the layer configuration can be examined by an interference thickness meter.

The back layer in the technology disclosed herein includes, if necessary, a lubricant (leveling agent, etc.), an antistatic component, a crosslinking agent, an antioxidant, a colorant (pigment, dye, etc.), a fluidity modifier (thixotropy). Agents, thickeners, etc.), film-forming aids, catalysts (for example, an ultraviolet polymerization initiator in a composition containing an ultraviolet curable resin), and the like can be added. As the crosslinking agent, an isocyanate-based, epoxy-based, or melamine-based crosslinking agent used for crosslinking of general resins can be appropriately selected and used. For example, an isocyanate-based cross-linking agent can be preferably employed because it can be bonded to a hydroxyl group that may be present on the surface of the base material layer to improve adhesion. In particular, when a back surface layer is formed on a base material layer that has been subjected to a surface treatment (for example, corona treatment) in which a hydroxyl group is introduced, the use of an isocyanate-based crosslinking agent is effective.
The back layer can be suitably formed by a technique including applying to the base layer a liquid composition in which the resin component and additives used as necessary are dispersed or dissolved in a suitable solvent. For example, a method of applying the liquid composition (the composition for forming the back layer) to the base material layer and drying it, and performing a curing treatment (heat treatment, ultraviolet treatment, etc.) as necessary can be preferably employed. The solid content of the composition can be, for example, about 0.1 to 10% by mass, and is usually about 0.5 to 5%. If the solid content is too high, it may be difficult to form a thin and uniform back layer.

  The solvent constituting the back layer forming composition may be an organic solvent, water, or a mixed solvent thereof. Examples of the organic solvent include one or two selected from methyl ethyl ketone, acetone, ethyl acetate, tetrahydrofuran (THF), dioxane, cyclohexanone, n-hexane, toluene, xylene, methanol, ethanol, n-propanol, isopropanol, and the like. The above can be used. In the technique disclosed herein, the solvent constituting the back layer forming composition is preferably an aqueous solvent from the viewpoint of reducing environmental burden. Here, the “aqueous solvent” refers to water or a mixed solvent containing water as a main component (a component occupying 50% by volume or more). As components other than water constituting such an aqueous mixed solvent, a hydrophilic solvent is preferably used. For example, methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, tert-butanol, n-amyl alcohol, isoamyl alcohol, sec-amyl alcohol, tert-amyl alcohol, 1-ethyl 1- One or more selected from alcohols such as propanol, 2-methyl 1-butanol, n-hexanol, and cyclohexanol can be preferably used.

  When the back layer contains a lubricant, a general fluorine-based or silicone-based lubricant can be preferably used as the lubricant. The use of silicone-based lubricants is particularly preferred. Specific examples of the silicone lubricant include polydimethylsiloxane, polyether-modified polydimethylsiloxane, and polymethylalkylsiloxane. A lubricant containing a fluorine compound or a silicone compound having an aryl group or an aralkyl group (sometimes called a printable lubricant because it can give a resin film with good printability) may be used. Moreover, you may use the lubricant (reactive lubricant) containing the fluorine compound or silicone compound which has a crosslinkable reactive group.

  The addition amount of the lubricant can be about 25 parts by mass or less (typically 0.01 to 25 parts by mass) per 100 parts by mass of the resin component constituting the back layer, and usually about 15 parts by mass or less (typically In particular, it is preferably 0.02 to 15 parts by mass, for example, about 0.5 to 15 parts by mass, and more preferably about 1 to 10 parts by mass. If the amount of the lubricant added is too large, the printability tends to be insufficient, or the light transmittance of the back layer tends to be lowered.

  It is inferred that such a lubricant bleeds on the surface of the back layer and imparts slipperiness to the surface, thereby reducing the coefficient of friction. Therefore, the scratch resistance can be improved through the reduction of the friction coefficient by appropriate use of the lubricant. The lubricant can make the surface tension of the back layer uniform and contribute to the reduction of thickness unevenness and interference fringes. This is particularly significant in the surface protective film for optical members. Further, when the resin component constituting the back layer is an ultraviolet curable resin, when a fluorine-based or silicone-based lubricant is added thereto, the lubricant is applied when the back layer forming composition is applied to a substrate and dried. Bleeds to the surface of the coating film (interface with the air), whereby the inhibition of curing by oxygen during ultraviolet irradiation is suppressed, and the ultraviolet curable resin can be sufficiently cured even on the outermost surface of the back layer.

  The antistatic component is a component having an action of preventing charging of a transparent film or a surface protective film using the film. When an antistatic component is contained in the back layer, as the antistatic component, for example, an organic or inorganic conductive substance, various antistatic agents, and the like can be used. Of these, the use of an organic conductive material is preferable. A transparent film having a back layer provided with an antistatic property by containing such an antistatic component is a surface protective film used in the processing or transporting process of articles that dislike static electricity such as liquid crystal cells and semiconductor devices. It is suitable as.

  As the organic conductive material, various conductive polymers can be preferably used. Examples of such conductive polymers include polyaniline, polypyrrole, polythiophene, polyethyleneimine, and allylamine polymers. Such a conductive polymer may be used individually by 1 type, and may be used in combination of 2 or more type. Moreover, you may use in combination with another antistatic component (an inorganic electroconductive substance, an antistatic agent, etc.). The amount of the organic conductive substance (typically conductive polymer) used can be, for example, about 0.2 to 20 parts by mass with respect to 100 parts by mass of the resin component constituting the back layer. It is appropriate that the amount is about 10 parts by mass.

As such a conductive polymer, those in the form of an aqueous solution or an aqueous dispersion can be preferably used. For example, by dissolving or dispersing a conductive polymer having a hydrophilic functional group (which can be synthesized by a technique such as copolymerizing a monomer having a hydrophilic functional group in the molecule) in water, Aqueous solutions or dispersions can be prepared. Examples of the hydrophilic functional group include sulfo group, amino group, amide group, imino group, hydroxyl group, mercapto group, hydrazino group, carboxyl group, quaternary ammonium group, sulfate ester group (—O—SO ₃ H), phosphorus An acid ester group (for example, —O—PO (OH) ₂ ) and the like are exemplified. Such hydrophilic functional groups may form a salt. An example of a commercially available product of polyaniline sulfonic acid in the form of an aqueous solution or water dispersion is “Aqua-PASS” manufactured by Mitsubishi Rayon Co., Ltd. Examples of commercially available products of polythiophene in the form of an aqueous solution or an aqueous dispersion include “Denatron” series manufactured by Nagase Chemtech.

Examples of the conductive polymer that can be preferably used in the technology disclosed herein include polyaniline and polythiophene. The polyaniline preferably has a polystyrene-equivalent weight average molecular weight (hereinafter referred to as “Mw”) of 50 × 10 ⁴ or less, more preferably 30 × 10 ⁴ or less. As polythiophene, what Mw is 40x10 < ⁴ > or less is preferable, and 30x10 < ⁴ > or less is more preferable. Further, the Mw of these conductive polymers is usually preferably 0.1 × 10 ⁴ or more, more preferably 0.5 × 10 ⁴ or more. Such a conductive polymer having Mw is also preferable because it can be easily prepared in the form of an aqueous solution or an aqueous dispersion.

  Examples of the inorganic conductive material include tin oxide, antimony oxide, indium oxide, cadmium oxide, titanium oxide, zinc oxide, indium, tin, antimony, gold, silver, copper, aluminum, nickel, chromium, titanium, iron, Fine particles composed of cobalt, copper iodide, and alloys or mixtures thereof can be used. Fine particles such as ITO (indium oxide / tin oxide) and ATO (antimony oxide / tin oxide) may be used. The average particle diameter of the fine particles is usually preferably about 0.1 μm or less (typically 0.01 μm to 0.1 μm). Such inorganic conductive materials (inorganic conductive materials) may be used alone or in combination of two or more. Moreover, you may use in combination with another antistatic component. The usage-amount of an inorganic electroconductive substance can be about 5-500 mass parts with respect to 100 mass parts of resin components which comprise a back layer, and is normally 10-500 mass parts (for example, 100-500 mass parts). It is appropriate to set the degree.

  Examples of the antistatic agent include a cationic antistatic agent, an anionic antistatic agent, an amphoteric ion antistatic agent, a nonionic antistatic agent, and the above cationic, anionic and zwitterionic ion conductive groups. Examples thereof include an ion conductive polymer obtained by polymerizing or copolymerizing a monomer having the same. Such an antistatic agent may be used individually by 1 type, and may be used in combination of 2 or more type. Moreover, you may use in combination with another antistatic component. The amount of the antistatic agent used can be, for example, about 0.5 to 50 parts by mass, and usually 1 to 30 parts by mass with respect to 100 parts by mass of the resin component constituting the back layer. .

  Examples of the cationic antistatic agent include those having a cationic functional group such as a quaternary ammonium salt, a pyridinium salt, a primary, secondary, or tertiary amino group. More specifically: an acrylic copolymer having a quaternary ammonium group such as alkyltrimethylammonium salt, acyloylamidopropyltrimethylammonium methosulfate, alkylbenzylmethylammonium salt, acylcholine chloride, polydimethylaminoethyl methacrylate; polyvinyl Examples thereof include styrene copolymers having a quaternary ammonium group such as benzyltrimethylammonium chloride; diallylamine copolymers having a quaternary ammonium group such as polydiallyldimethylammonium chloride;

  Examples of the anionic antistatic agent include those having an anionic functional group such as sulfonate, sulfate ester salt, phosphonate salt, and phosphate ester salt. More specifically, alkyl sulfonate, alkyl benzene sulfonate, alkyl sulfate ester salt, alkyl ethoxy sulfate ester salt, alkyl phosphate ester salt, sulfonic acid group-containing styrene copolymer and the like are exemplified.

  Examples of zwitterionic antistatic agents include alkylbetaines and their derivatives, imidazolines and their derivatives, alanine and their derivatives. More specifically, alkyl betaines, alkyl imidazolium betaines, carbobetaine graft copolymers, and the like are exemplified.

  Examples of nonionic antistatic agents include amino alcohol and derivatives thereof, glycerin and derivatives thereof, polyethylene glycol and derivatives thereof. More specifically, fatty acid alkylolamide, di (2-hydroxyethyl) alkylamine, polyoxyethylene alkylamine, fatty acid glycerin ester, polyoxyethylene glycol fatty acid ester, sorbitan fatty acid ester, polyoxysorbitan fatty acid ester, polyoxy Examples thereof include ethylene alkyl phenyl ether, polyoxyethylene alkyl ether, polyethylene glycol, polyoxyethylene diamine, a copolymer comprising polyether, polyester and polyamide, and methoxy polyethylene glycol (meth) acrylate.

  In addition, as a method for imparting antistatic properties to the transparent film, instead of or in addition to the method of adding an antistatic component to the back layer as described above, the base layer contains an antistatic component. A method, a method of providing an antistatic layer on the first surface and / or the second surface of the base material layer, and the like can be employed.

  The method of incorporating the antistatic component into the base material layer can be preferably performed by, for example, forming the base material layer by forming a resin material containing the antistatic component (kneaded) into a film shape. As the antistatic component used in such a method, the same materials as those exemplified above as the antistatic component contained in the back layer can be employed. The blending amount of the antistatic component can be, for example, about 20% by mass or less (typically 0.05 to 20% by mass) with respect to the total mass of the base material layer. It is suitable to set it as the range of -10 mass%. The method of kneading the antistatic component is not particularly limited as long as the antistatic agent can be uniformly mixed with the resin material for forming the base layer. For example, a heating roll, a Banbury mixer, a pressure kneader, two A method of kneading using a shaft kneader or the like can be mentioned.

  The method of providing an antistatic layer on the first side (back side, that is, between the base layer and the back layer) and / or the second side (adhesive layer side) of the base layer is the antistatic component and, if necessary, It can be preferably carried out by applying an antistatic coating agent containing a resin component used in the step to a base material layer (preferably a pre-molded resin film). As the antistatic component, the same materials as those exemplified above as the antistatic component contained in the back layer can be employed. The use of conductive polymers or antistatic agents is preferred. As the resin component used for the antistatic coating agent, for example, a general-purpose resin such as a polyester resin, an acrylic resin, a polyvinyl resin, a urethane resin, a melamine resin, and an epoxy resin can be used. In addition, the antistatic coating agent contains a methylol- or alkylol-containing melamine-based, urea-based, glyoxal-based, acrylamide-based compound, epoxy compound, isocyanate-based compound, etc. as a crosslinking agent for the resin component. May be. In the case of a polymer type antistatic component (typically a conductive polymer), the use of a resin component may be omitted.

  As a method of applying the antistatic coating agent, a known coating method can be appropriately used. Specific examples include a roll coating method, a gravure coating method, a reverse coating method, a roll brush method, a spray coating method, an air knife coating method, an impregnation method, and a curtain coating method. The thickness of the antistatic layer is usually suitably about 0.01 μm to 1 μm, preferably about 0.015 μm to 0.1 μm.

  In a preferred embodiment of the technology disclosed herein, the back layer is provided directly on the first surface of the base material layer. The transparent film having such a configuration is preferable because it has excellent adhesion between the base material layer and the back layer, and thus easily satisfies the above-described preferable fracture start load. Therefore, when the antistatic layer is provided on the surface of the base material layer, the antistatic layer is preferably provided only on the second surface of the base material layer.

  As the pressure-sensitive adhesive layer constituting the surface protective film disclosed herein, a pressure-sensitive adhesive composition capable of forming a pressure-sensitive adhesive layer having properties suitable for the surface protective film (peeling power to the adherend surface, non-contamination, etc.) It can form suitably using a thing. For example, a method of forming the pressure-sensitive adhesive layer by directly applying the pressure-sensitive adhesive composition to the base material layer and drying or curing (direct method); and applying the pressure-sensitive adhesive composition to the surface (release surface) of the release liner Adhesive layer is formed on the surface by drying and curing, and this adhesive layer is bonded to the base material layer and transferred to the base material layer (transfer method); etc. can do. From the viewpoint of anchoring property of the pressure-sensitive adhesive layer, usually, the above direct method can be preferably employed. For the application (typically coating) of the pressure-sensitive adhesive composition, a pressure-sensitive adhesive such as a roll coating method, a gravure coating method, a reverse coating method, a roll brush method, a spray coating method, an air knife coating method, a coating method using a die coater, etc. Various conventionally known methods can be appropriately employed in the field of sheets. Although not particularly limited, the thickness of the pressure-sensitive adhesive layer can be, for example, about 3 μm to 100 μm, and usually about 5 μm to 50 μm is preferable. In addition, as a method of obtaining the surface protection film disclosed here, the method of forming the said adhesive layer in the base material layer (namely, transparent film) in which the back layer was provided previously, and an adhesive layer on a base material layer Any of the methods of forming the back layer after providing the film can be employed. Usually, a method of providing an adhesive layer on a transparent film is preferred.

  The surface protective film disclosed herein has a release liner bonded to the pressure-sensitive adhesive surface for the purpose of protecting the pressure-sensitive adhesive surface (the surface of the pressure-sensitive adhesive layer that is attached to the adherend), if necessary. It can be provided in the form (in the form of a surface protective film with a release liner). As the base material constituting the release liner, paper, a synthetic resin film or the like can be used, and a synthetic resin film is suitably used from the viewpoint of excellent surface smoothness. For example, a resin film made of the same resin material as the base material layer can be preferably used as the base material of the release liner. The thickness of the release liner can be, for example, about 5 μm to 200 μm, and usually about 10 μm to 100 μm is preferable. The surface of the release liner to be bonded to the pressure-sensitive adhesive layer is released using a conventionally known release agent (eg, silicone, fluorine, long chain alkyl, fatty acid amide, etc.) or silica powder. Or antifouling processing may be given.

  Hereinafter, some experimental examples related to the present invention will be described, but the present invention is not intended to be limited to those shown in the specific examples. In the following description, “part” and “%” are based on mass unless otherwise specified. Each characteristic in the following description was measured or evaluated as follows.

1. Fracture starting load A nano scratch tester manufactured by CSM Instruments SA was used as a measuring device for the fracture starting load. The adhesive surface of each surface protective film sample was affixed to a slide glass, and the back layer was faced up and fixed to the stage of the measuring apparatus. Then, using a cantilever ST-150 equipped with a conical diamond indenter (tip radius of curvature 10 μm) in a measurement environment of 23 ° C. and 50% RH, a load of 0 to 300 mN was applied in the continuous load mode of the above apparatus. A scratch test was carried out by rubbing in one direction while increasing (scratch load).
Using the optical microscope (manufactured by Nikon Corporation) attached to the apparatus, the scratch marks were observed on the surface of the sample subjected to the scratch test with an objective lens 20 times. Then, as shown in FIG. 4, the first location where the back layer is peeled longer than 2 μm in the scratch direction on the scratch mark is taken as the fracture start point, and the length of the fracture start point with respect to the scratch direction (destruction length) The scratch load corresponding to the center was taken as the fracture start load.

2. Friction coefficient 23 ° C, 50% RH in the measurement environment of the nano scratch tester (vertical load 40mN ± 3mN), the surface of each sample attached to the slide glass in the same manner as above (back layer side) Was abraded at a length of 5 mm, and the average value of the friction coefficient at this time was defined as the friction coefficient of the back layer. The friction coefficient is calculated as a ratio of the friction force and the load in the direction perpendicular to the sample surface (that is, friction coefficient = friction force / load).

3. Plasticity Index The plasticity index was evaluated using a nano-intender, model “DCM SA2” manufactured by MTS Systems. That is, each sample was affixed to slite glass in the same manner as described above, and fixed on the stage so that the back layer faced upward. The measurement was performed by using a barco pitch (triangular pyramid) diamond indenter (tip radius of curvature 0.1 μm) in a measurement environment of 23 ° C. and 50% RH, and vertically pushing to a maximum depth of 500 nm, and a depth of 10 nm. The indentation modulus (Indentation Modulus) and hardness (Hardness) in the vicinity were measured. Then, the plasticity index was calculated by dividing the measured value of the elastic modulus by the measured value of hardness (that is, plastic index = elastic modulus / hardness).

4). Plasticity index ratio 3. The plasticity index Ps of each sample (a back layer is provided on the base material) obtained by the above is divided by the plastic index Pb of the base material (base material not having the back layer) constituting the sample. The index ratio was calculated (ie, plastic index ratio = Ps / Pb).

5. Peeling force measurement Each surface protection film sample was cut into a size of 70 mm width and 100 mm length to make an adherend. A single-sided adhesive tape (No. 31B manufactured by Nitto Denko Corporation) was cut into a size of 19 mm in width and 100 mm in length, and the adhesive surface of the adhesive tape was placed on the back layer of the adherend at a pressure of 0.25 MPa, 0. Crimping was performed at a speed of 3 m / min. This was left in an environment of 23 ° C. and 50% RH for 30 minutes, and then the adhesive tape was peeled from the adherend using the universal tensile tester in the same environment at a peeling speed of 0.3 m / min and a peeling angle of 180 degrees. The peeling force at this time was measured.

6). Scratch resistance evaluation Each sample was affixed to a slide glass in the same manner as described above, and each sample was placed on a precision balance using a coin (a new 10-yen coin was used) in a measurement environment of 23 ° C. and 50% RH. Was abraded with a load of 300 g. The scratch marks were observed with an optical microscope, and the case where the presence of falling debris in the back layer was confirmed was evaluated as x, and the case where the presence of the falling debris was not confirmed was evaluated as o.

7). Substrate adhesion Each sample was prepared by mixing a small amount of blue pigment into the composition for forming the back layer. Under a measurement environment of 23 ° C. and 50% RH, the back layer forming side surface of each sample was cut into 10 squares × 10 squares (total of 100 squares) at intervals of 1 mm in length and breadth, and single-sided adhesive was applied from above. A tape (No. 31B manufactured by Nitto Denko Corporation, width 19 mm) was pressure-bonded under the same conditions as in the above-mentioned peeling force measurement, and then a cross-cut peel test was performed to peel the single-sided adhesive tape by hand. In the cross cut test, 1 point was given when the dropout was 50 squares or more, 2 points were given when the dropout was 11 squares or more and 49 squares or less, and 3 points were given when the dropout was 10 squares or less.

8). Evaluation of printability (print adhesion) After printing on the back layer using an X stamper manufactured by Shachihata Co., Ltd. under a measurement environment of 23 ° C. and 50% RH, cellophane adhesive tape manufactured by Nichiban Co., Ltd. (Product No. 405, width 19 mm) was attached, and then peeled off under the conditions of a peeling speed of 30 m / min and a peeling angle of 180 degrees. By visual evaluation, x indicates that 50% or more of the printed area is peeled, Δ indicates that 25% of the printed area is peeled off and less than 50% is peeled, and 75% or more of the printed area remains without being peeled. The case was rated as ○.

9. Whitening and unevenness evaluation Whitening evaluation: The haze value of each sample was measured with a haze meter (manufactured by Murakami Color Research Laboratory, model “HM-150”), and a haze value of 5 or less was accepted.
Evaluation of unevenness: The appearance of the sample was visually evaluated in a bright room, and a case where no appearance abnormality such as a streak was observed was regarded as acceptable.
Samples that passed both the whitening and unevenness evaluations were rated as whitening / unevenness as ◯, Δ when either evaluation was unacceptable, and X evaluation when both were unacceptable.

10. Curl evaluation Each sample was cut into a 100 mm square and stored for one day in an environment of 40 ° C. and 90% RH. This was left on a horizontal plane with the back layer facing up, and the height at which the end of the sample curled and floated from the plane was measured. The case where the height of the largest floating portion (maximum floating height) was 3 mm or less was rated as “◯”, and the case where the maximum floating height exceeded 3 mm was evaluated as “x”.

<Experimental example 1>
(Sample A-1)
Urethane acrylate ultraviolet curable resin (manufactured by Nippon Synthetic Chemical Co., Ltd., trade name “purple light UV-1700B”; hereinafter also referred to as “resin R1”) and radical polymerization initiator (trade name, manufactured by Ciba Geigy Co., Ltd.) "Darocur 1173") was mixed so that the mass ratio of the solid content was 100: 4, and dissolved in a solvent containing toluene as a main component to prepare a coating liquid B-1 having a solid content concentration of 30%. .

As the base material, a transparent polyethylene terephthalate (PET) film (hereinafter also referred to as “base material F1”) having a thickness of 38 μm and subjected to corona treatment on one side was used. The coating liquid B-1 is applied to one surface (corona-treated surface) of the substrate F1 so that the thickness after drying is 8 μm (according to TEM observation; the same applies hereinafter), and a curing treatment is performed by irradiating with ultraviolet rays. A back layer was formed. The irradiation of the ultraviolet rays was performed under the condition of 450 mJ / cm ² using a metal halide lamp. Thus, the transparent film C-1 with which the back layer was provided in the single side | surface (corona treatment surface) of the base material F1 was obtained.

  A release sheet having a release treatment with a silicone release treatment agent is prepared on one side of a PET film, and an acrylic pressure-sensitive adhesive having a thickness of 25 μm is provided on the release surface (the release treatment surface) of the release sheet. A layer was formed. The pressure-sensitive adhesive layer was transferred to the other surface of the transparent film C-1 (the surface on which the back layer was not provided) to prepare a surface protective film sample A-1. The plastic index of Sample A-1 was determined by the above method and found to be 22.6 (elastic modulus 6.6 GPa, hardness 0.29 GPa). In addition, the plastic index Pb of the PET film used here was 13.6 (elastic modulus 4.8 GPa, hardness 0.35 GPa). The PET film had a refractive index of 1.63 and a light transmittance of 89%.

(Sample A-2)
The coating liquid B-1 was further diluted with the above solvent to prepare a coating liquid B-2 having a solid content concentration of 1%. A transparent film C-2 was obtained in the same manner as in the preparation of Sample A-1, except that this coating liquid B-2 was applied so that the thickness after drying was 0.1 μm, and the adhesive layer was transferred in the same manner. A surface protective film sample A-2 was prepared. The plastic index of this sample A-2 was 14.4 (elastic modulus 4.8 GPa, hardness 0.33 GPa).

(Sample A-3)
A coating liquid B-3 was prepared in the same manner as the coating liquid B-2 except that 5 parts (solid content conversion) of a lubricant was blended per 100 parts of the solid content of the resin R1. Here, a polyether-modified polydimethylsiloxane leveling agent (manufactured by BYK Chemie, trade name “BYK-333”; hereinafter sometimes referred to as “lubricant L1”) was used as the lubricant. A transparent film C-3 was obtained in the same manner as in the preparation of Sample A-1, except that the coating liquid B-3 was applied so that the thickness after drying was 0.1 μm, and the adhesive layer was transferred in the same manner. A surface protective film sample A-3 was prepared. The plastic index of Sample A-3 was 13.2 (elastic modulus 4.4 GPa, hardness 0.34 GPa).

  Table 1 shows the schematic configuration of the back layer and Table 2 shows the results of the various measurements and evaluations described above.

  As shown in these tables, Sample A-1 having a back layer thickness of 8 μm showed good scratch resistance, but Sample A- having the same composition and a back layer thickness of 0.1 μm was used. In No. 2, scratch resistance was insufficient. This is because, in a configuration in which the thickness of the back surface layer is small, the hardness of the back surface layer is too high compared to the base material layer (therefore, the plastic index ratio is too small), and when the external force (friction force) is applied, It is thought that it becomes easy to break because it cannot follow the deformation. Moreover, it is surmised that the friction coefficient of A-2 is higher than that of sample A-1 because the load related to the breakage of the back layer was detected in the measurement of the friction coefficient. In sample A-3 containing 5 parts of the lubricant, although the friction coefficient was reduced and the fracture initiation load was improved as compared with A-2, the desired scratch resistance was not achieved. Further, when the amount of the lubricant is increased, whitening / unevenness becomes remarkable, so that it is determined that 5 parts or more is inappropriate.

<Experimental example 2>
(Sample A-4)
A water-dispersible polyurethane thermosetting resin (manufactured by Nippon Polyurethane Co., Ltd., trade name “Takelac WS-4100”; hereinafter sometimes referred to as “resin R2”) is diluted with distilled water to obtain a solid content concentration. A 20% coating solution B-4 was prepared. The coating liquid B-4 is applied to one surface (corona-treated surface) of the substrate F1 so that the thickness after drying is 8 μm, and is subjected to thermosetting treatment, thereby providing a back layer on one surface of the substrate F1. Thus obtained transparent film C-4 was obtained. The pressure-sensitive adhesive layer was transferred to the other surface of the transparent film C-4 in the same manner as described above to prepare a surface protective film sample A-4. The plastic index of this sample A-4 was 21.8 (elastic modulus 3.4 GPa, hardness 0.16 GPa).

(Sample A-5)
The coating liquid B-4 was further diluted with distilled water to prepare a coating liquid B-5 having a solid content concentration of 1%. A transparent film C-5 was obtained in the same manner as in the preparation of Sample A-4, except that this coating liquid B-5 was applied so that the thickness after drying was 0.1 μm, and the adhesive layer was transferred in the same manner. Thus, a surface protective film sample A-5 was produced. The plasticity index was 17.6 (elastic modulus 4.9 GPa, hardness 0.28 GPa).

(Sample A-6)
A coating liquid B-6 was prepared in the same manner as the coating liquid B-5 except that 5 parts (in terms of solid content) of the lubricant L1 was blended per 100 parts of the solid content of the resin R2. A transparent film C-6 was obtained in the same manner as in the preparation of Sample A-4 except that the coating liquid B-6 was applied so that the thickness after drying was 0.1 μm, and the adhesive layer was transferred in the same manner. Thus, a surface protective film sample A-6 was produced. The plasticity index was 29.5 (elastic modulus 2.5 GPa, hardness 0.09 GPa).

(Sample A-7)
A transparent film C-7 was obtained in the same manner as in the preparation of Sample A-6, except that the blending amount of the lubricant L1 was 10 parts per 100 parts of the solid content of the resin R2 (in terms of solid content). The surface protective film sample A-7 was produced by transfer. The plasticity index was 37.7 (elastic modulus 2.1 GPa, hardness 0.05 GPa).

(Sample A-8)
A water-dispersible acrylic-styrene thermosetting resin (manufactured by DIC, trade name “VONCOAT CG-8490”; hereinafter sometimes referred to as “resin R3”) is diluted with distilled water. A coating liquid B-8 having a solid content concentration of 3% was prepared. The coating liquid B-8 is applied to one surface (corona-treated surface) of the base material F1 so that the thickness after drying is 0.1 μm, and is subjected to thermosetting treatment, whereby a back layer is formed on one surface of the base material F1. A transparent film C-8 provided with was obtained. The pressure-sensitive adhesive layer was transferred to the other surface of the transparent film C-8 in the same manner as described above to prepare a surface protective film sample A-8. The plastic index of Sample A-8 was 361.7 (elastic modulus 3.61 GPa, hardness 0.01 GPa).

(Sample A-9)
Resin R3, lubricant L1, and conductive polymer as an antistatic component (manufactured by Mitsubishi Rayon Co., Ltd., an aqueous dispersion of polyaniline sulfonic acid having a weight average molecular weight of about 15 × 10 ⁴ , trade name “aqua-PASS”; AS1 ”) is mixed so that the mass ratio of the solid content is 100: 2: 6, diluted with distilled water, and the coating liquid B-9 having a solid content concentration of 3% is obtained. Prepared. A transparent film C-9 was obtained in the same manner as in the preparation of Sample A-8, except that the coating liquid B-9 was applied so that the thickness after drying was 0.1 μm, and the adhesive layer was transferred in the same manner. Thus, a surface protective film sample A-9 was produced. The plastic index of this sample A-9 was 298 (elastic modulus 2.7 GPa, hardness 0.009 GPa).

(Sample A-10)
Resin R3, lubricant L1, and conductive filler as an antistatic component (tin oxide sol manufactured by Taki Chemical Co., Ltd., trade name “Cerames S-8”; hereinafter sometimes referred to as “AS2”). The mixture was mixed so that the mass ratio of the solid content was 100: 2: 300, and diluted with distilled water to prepare a coating liquid B-10 having a solid content concentration of 3%. A transparent film C-10 was obtained in the same manner as in the preparation of Sample A-8, except that this coating liquid B-10 was applied so that the thickness after drying was 0.1 μm, and the adhesive layer was transferred in the same manner. Thus, a surface protective film sample A-10 was produced. The plasticity index was 15.4 (elastic modulus 6.1 GPa, hardness 0.40 GPa).

  Table 3 shows the schematic configuration of the back layer and Table 4 shows the results of the various measurements and evaluations described above.

  As shown in these tables, samples A-6 and A-7 in which the friction coefficient is adjusted to 0.4 or less by adding a lubricant to the back layer composition of A-5 and the plastic index ratio is 2 or more. According to the results, a high fracture start load of 50 mN or more was achieved despite the thin back layer of 0.1 μm, and excellent scratch resistance was realized. Similarly, Sample A-9, which has a different back layer resin composition from A-6 and A-7, also exhibits a high fracture initiation load by exhibiting a friction coefficient of 0.4 or less and a plastic index ratio of 2 or more. And excellent scratch resistance was realized. These samples A-6, 7, and 9 all had an appropriate peeling force of 3 to 6 N / 19 mm, and exhibited good substrate adhesion and printability. Further, no whitening or unevenness was observed, and the degree of curling was small. Sample A-9 having a plastic index ratio in the range of 10 to 50 (more specifically 20 to 50) exhibited particularly good substrate adhesion.

  On the other hand, Sample A-5, in which the lubricant was omitted from Sample A-6, had a high friction coefficient, a low fracture initiation load, and lacked scratch resistance, probably due to the plastic index ratio being too small. In the back layer composition according to Sample A-5, scratch resistance was insufficient even in Sample A-4 having a large thickness. Sample A-10, which has a different antistatic component from sample A-9, has a high friction coefficient, a low fracture initiation load, and lacks scratch resistance, possibly because the plastic index ratio is too small. Met.

  The transparent film disclosed herein can be preferably used for applications such as a support for various surface protective films. Further, the surface protective film disclosed herein is an optical member used in the production or transportation of an optical member used as a component of a liquid crystal display panel, a plasma display panel (PDP), an organic electroluminescence (EL) display, or the like. It is suitable for the use which protects. In particular, it is useful as a surface protective film applied to optical members such as polarizing plates (polarizing films) for liquid crystal display panels, wave plates, retardation plates, optical compensation films, brightness enhancement films, light diffusion sheets, and reflective sheets. .

1: Surface protective film 10: Transparent film 12: Base material layer 14: Back layer 20: Adhesive layer 30: Release liner

Claims (9)

A transparent film having a base material layer made of a transparent resin material and a back layer provided on the first surface of the base material layer,
The thickness of the back layer is 1 μm or less,
The fracture start load of the back layer in the scratch test is 50 mN or more, and the friction coefficient of the back layer is 0.4 or less,
Transparent film.   A barcopitch diamond indenter having a tip radius of curvature of 0.1 μm was pressed vertically into the back layer to measure the indentation elastic modulus and hardness at a depth of 10 nm, and the plasticity index Ps obtained by dividing the elastic modulus by the hardness; The transparent film of Claim 1 whose ratio (Ps / Pb) with the plastic index Pb calculated | required similarly about the said base material layer is 1.5 or more.   A peeling force measured by attaching an adhesive tape to the back layer and peeling the adhesive tape from the back layer at a peeling speed of 0.3 m / min and a peeling angle of 180 degrees is 2 N / 19 mm or more. Item 3. The transparent film according to Item 1 or 2.   The transparent film according to any one of claims 1 to 3, wherein the back layer has a single-layer structure and is provided directly on the base material layer.   The said back layer is a transparent film as described in any one of Claim 1 to 4 which consists of a resin material containing a lubricant.   The said back layer is a transparent film as described in any one of Claim 1 to 5 which consists of a resin material containing an antistatic component.   The transparent film according to claim 6, wherein the antistatic component is a conductive polymer.   The base film which comprises the said base material layer is a transparent film as described in any one of Claim 1 to 7 which is a polyethylene terephthalate resin or a polyethylene naphthalate resin. The transparent film according to any one of claims 1 to 8,
An adhesive layer provided on the surface of the transparent film opposite to the back layer;
A surface protective film.