Crack pattern film, transparent conductive film formation mask composed thereof, method for producing crack pattern film, method for producing transparent conductive film, method for improving adhesion of conductive film to substrate, and conductive film

Abstract

To provide a crack pattern film applicable as a metal evaporation mask for transparent conductive film formation, its production method, and a production method of a transparent conductive film employing the same.SOLUTION: The transparent conductive film according to the present invention is prepared by carrying out metal deposition with a crack pattern film as a mask, the crack pattern film composed of a film having cracks of 0.1 to 20 μm in width arranged in a network on a substrate surface, and the film being formed of a block copolymer containing a first block with a linear polyethyleneimine backbone and a second block less polar than the first block.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a crack pattern film and a mask for forming a transparent conductive film made thereof, a method for producing a crack pattern film, a method for producing a transparent conductive film, a method for improving the adhesion of a conductive film to a substrate, and a conductive film. [Background technology]

[0002] In recent years, the demand for transparent conductive films has increased with the widespread use of liquid crystal displays, solar cells, touch panels, etc. Well-known examples of such transparent conductive films include those using oxide semiconductors such as ITO (tin-doped indium oxide). Transparent conductive films are patterned and used as electrical wiring, as well as for electromagnetic wave shielding and anti-fogging of car windshields.

[0003] As an example of such a transparent conductive film, Patent Document 1 proposes dispersing a conductive material such as carbon nanotubes in a dispersion medium such as an aerosol or colloidal solution, filtering this through a membrane filter to form a thin film of the conductive material on the upstream side of the filter, and then transferring this thin film to a transparent substrate.In addition to this, several patent documents list examples of forming transparent conductive films using carbon nanotubes as the conductive material (see, for example, Patent Documents 2 and 3). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-44839 [Patent Document 2] Japanese Patent Publication No. 2022-158014 [Patent Document 3] Japanese Patent Publication No. 2023-18187 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention has been made in view of the above circumstances, and aims to provide a crack pattern film that can also be used as a metal vapor deposition mask for forming a transparent conductive film, a method for manufacturing the same, and a method for manufacturing a transparent conductive film using the same. [Means for solving the problem]

[0006] The inventors conducted extensive research to solve the above problems and found that when a composition containing a block copolymer having a first block with a linear polyethyleneimine skeleton and a second block with a lower polarity than the first block and an aqueous solvent was emulsified by applying an external force, and the resulting emulsion composition was applied to a substrate and dried to form a block copolymer film, a network of cracks on the order of μm in width was formed in the film. Furthermore, when this film was subjected to metal deposition and then washed with a solvent, the metal deposition film remained only where the cracks were present, while the metal deposition film was removed along with the block copolymer film in other areas. As a result, a thin metal film on the surface of the substrate was left in the form of an extremely fine network of μm in width, and while this area appeared transparent, resistance measurements showed a low resistance comparable to that of an ITO electrode. Furthermore, surprisingly, it was found that this fine network of metal deposition film remained extremely tightly adhered to the substrate and did not peel off even when subjected to a test equivalent to the peeling test specified in the JIS.

[0007] These cracks are a natural phenomenon that occurs widely in nature. For example, when a reservoir or dam dries up, a network of cracks forms in the soil at the bottom of the reservoir or dam. This is a phenomenon that occurs when clay, a type of colloid, dries. As the water evaporates, the clay colloids join together to form a kind of membrane. As the drying process continues, stress (tensile force) is applied to this membrane, and where it can no longer withstand this stress, it breaks, releasing the stress and forming cracks. This is a well-known phenomenon, whereby cracks form in a solid when a colloidal dispersion dries.

[0008] Next, an overview of the present invention will be described with reference to Figure 1. In the above-mentioned emulsion composition, the block copolymer incorporates the aqueous solvent inside to form a unique spherical bilayer membrane (i.e., micelle), which behaves as a hollow colloidal dispersion (Figure 1(a)). Therefore, when this hollow colloidal dispersion is applied to a substrate as shown in Figure 1(b) and dried to form a membrane, the bilayer membranes of the micelle vesicles fuse, deform, and accumulate to form a multilayer structure (Figure 1(c)). Similar to the reservoir or dam described above, a network of cracks develops in the thickness direction of this multilayer structure (Figure 1(d)). These cracks are extremely fine due to the minute colloid size, and, as shown in Figure 1(d), due to the multilayer structure, even if they extend deep, they do not reach the first molecular membrane layer in contact with the substrate. This first layer is hydrophilic on both the substrate-side surface and the crack-side surface, due to the hydrophilic nature of the outermost layer of the micelles (vesicles) formed in an aqueous solvent. As described below, this hydrophilic layer is formed from a block copolymer with a linear polyethyleneimine backbone, which has affinity for substrates and metals. In other words, an adhesive layer derived from the vesicle bilayer spontaneously forms at the bottom of the cracks, bonding the substrate to the metal. Materials (metals, semiconductors, etc.) that fit into the cracks adhere to this adhesive layer, thereby firmly adhering to the substrate. Therefore, when metal deposition is performed on the surface of the mask using a multilayer structure with such a crack pattern as a mask, as shown in Figure 1(e), countless fine metal wirings are formed on the substrate after the mask is removed, forming a microscopic network of gaps between them, as shown in Figure 1(f). Furthermore, the adhesive layer formed on the substrate surface firmly adheres the fine metal wiring to the substrate surface. As described above, the cracks contained in the mask have an extremely fine mesh structure, so that the wiring is invisible macroscopically, resulting in the formation of a conductive film that appears transparent.

[0009] According to the mechanism presumed above, the present invention forms a transparent conductive film having high adhesion on the surface of a substrate. Specifically, the present invention provides the following.

[0010] (1) The present invention is a crack pattern film comprising a film having a network of cracks of 0.1 to 20 μm width formed on the surface of a substrate, the film being formed from a block copolymer having a first block having a linear polyethyleneimine skeleton and a second block having a lower polarity than the first block.

[0011] (2) The present invention also provides the crack pattern film according to item (1), wherein the first block comprises a repeating unit represented by the following chemical formula (1): [ka]

[0012] (3) The present invention also provides a crack pattern film according to item (1) or (2), wherein the second block comprises a repeating unit represented by the following general formula (2): [ka] (In the above general formula (2), R is an alkyl group having 1 to 20 carbon atoms, an aryl group having 5 to 20 carbon atoms, an aralkyl group having 6 to 20 carbon atoms, an alkylketo group having 2 to 20 carbon atoms, or an arylketo group having 6 to 20 carbon atoms.)

[0013] (4) The present invention also provides a crack pattern film according to any one of (1) to (3), wherein the block copolymer is represented by the following general formula (3): [ka] (In the above general formula (3), b is a symbol indicating that it is a block copolymer, * each independently represents an end group of the polymer, and m and n each independently represent an integer.)

[0014] (5) The present invention also provides a mask for forming a transparent conductive film, which comprises the crack pattern film according to any one of (1) to (4).

[0015] (6) The present invention also provides a method for producing a crack pattern film, comprising: an emulsification step of applying an external force to a composition containing a block copolymer having a first block with a linear polyethyleneimine skeleton and a second block having a lower polarity than the first block, and an aqueous solvent, thereby emulsifying the composition to form an emulsion composition; a coating step of applying the emulsion composition to a substrate to form a coating film; and a drying step of drying the coating film to form a crack pattern film.

[0016] (7) The present invention also provides a method for producing a crack pattern film according to item (6), wherein the first block comprises a repeating unit represented by the following chemical formula (1): [ka]

[0017] (8) The present invention also provides a method for producing a crack pattern film according to item (6) or (7), wherein the second block comprises a repeating unit represented by the following general formula (2): [ka] (In the above general formula (2), R is an alkyl group having 1 to 20 carbon atoms, an aryl group having 5 to 20 carbon atoms, an aralkyl group having 6 to 20 carbon atoms, an alkylketo group having 2 to 20 carbon atoms, or an arylketo group having 6 to 20 carbon atoms.)

[0018] (9) The present invention also provides the method for producing a crack pattern film according to any one of (6) to (8), wherein the block copolymer is represented by the following general formula (3): [ka] (In the above general formula (3), b is a symbol indicating that it is a block copolymer, * each independently represents an end group of the polymer, and m and n each independently represent an integer.)

[0019] (10) The present invention also provides a method for producing a transparent conductive film, comprising: a pattern film forming step of forming the crack pattern film according to any one of items (1) to (4) on the surface of a substrate; a metal film forming step of forming a metal film on the entire surface of the crack pattern film; and a removal step of removing the crack pattern film with a solvent.

[0020] (11) The present invention also provides a method for producing a transparent conductive film according to the above (10), wherein the metal film is formed by metal vapor deposition in the metal film forming step.

[0021] (12) The present invention also relates to a method for improving the adhesion of a formed conductive film to a substrate, characterized in that when crack film lithography is performed, in which a crack pattern film as a mask is formed on the surface of a substrate, a metal is vapor-deposited onto the surface of the substrate through the mask, and then the mask is removed to form a conductive film on the surface of the substrate, the crack pattern film is the crack pattern film described in any one of items (1) to (4).

[0022] (13) The present invention also provides the method according to item (12), characterized in that the conductive film is a transparent conductive film having a fine mesh structure and thus having transparency.

[0023] (14) The present invention also provides a conductive film comprising a metal film formed on the surface of a substrate, characterized in that an adhesive layer is provided between the substrate and the metal film, the adhesive layer being made of a block copolymer comprising a first block having a linear polyethyleneimine skeleton and a second block having a lower polarity than the first block.

[0024] (15) The present invention also provides the conductive film according to item (14), characterized in that the conductive film is a transparent conductive film having a fine mesh structure and thus having transparency. [Effects of the Invention]

[0025] According to the present invention, there are provided a crack pattern film that can also be used as a metal vapor deposition mask for forming a transparent conductive film, a method for producing the same, and a method for producing a transparent conductive film using the same. [Brief explanation of the drawings]

[0026] [Figure 1] FIG. 1 is a schematic diagram illustrating an overview of the present invention. [Figure 2] FIG. 2 shows one embodiment of the crack pattern of the present invention, where (a) is a plan view of the crack pattern of the present invention and (b) is a side view of the crack pattern of the present invention. [Figure 3] FIG. 3 is a schematic diagram showing the block copolymer used in the present invention. [Figure 4] FIG. 4 is a schematic diagram showing the formation of a block copolymer membrane from micelles formed by the block copolymer. [Figure 5] Figure 5 is a side view showing each step of the transparent conductive film manufacturing method of the present invention, where (a) is a side view showing the state after the pattern film formation step is completed, (b) is a side view showing the state after the metal film formation step is completed, and (c) is a side view showing the state after the removal step is completed. [Figure 6] FIG. 6 is an SEM image of the crack pattern film prepared in the example. [Figure 7] FIG. 7 shows a photograph (left) taken immediately after copper deposition and a photograph (right) taken after the crack pattern film was removed in the example. [Figure 8] FIG. 8 is a microscope image of the copper pattern film obtained in the example. [Figure 9] FIG. 9 shows images showing the elemental mapping results of the copper pattern film obtained in the example by energy dispersive X-ray spectroscopy (EDX), where the upper image is an SEM image and the lower image is an image showing the copper distribution by EDX. [Figure 10]FIG. 10 shows the peeling test of the copper pattern film formed in the example, where (a) is an image showing the state of the glass substrate after the copper pattern film was formed, (b) is an image showing the state after adhesive tape was attached to the entire glass substrate, and (c) is an image showing the state after the adhesive tape was peeled off. [Figure 11] Figure 11 shows SEM and EDX images showing the state of the transparent conductive film after the adhesive tape was peeled off, where (a) is an image showing the area observed with SEM, (b) is an SEM image of the observed area, and (c) is an EDX image of the observed area. DETAILED DESCRIPTION OF THE INVENTION

[0027] Hereinafter, one embodiment of the crack pattern of the present invention, one embodiment of the method for producing a crack pattern film of the present invention, one embodiment of the mask for forming a transparent conductive film of the present invention, one embodiment of the method for producing a transparent conductive film of the present invention, one embodiment of the method for improving the adhesion of a conductive film to a substrate of the present invention, and one embodiment of the conductive film of the present invention will be described. Note that the present invention is not limited to the following embodiments and examples, and can be carried out by making appropriate changes within the scope of the present invention.

[0028] <Crack pattern film> First, one embodiment of the crack pattern film of the present invention will be described with reference to the drawings. The crack pattern film of the present invention is composed of a film having a network of cracks of 0.1 to 20 μm width formed on the surface of a substrate, and is characterized in that this film is formed from a block copolymer having a first block with a linear polyethyleneimine skeleton and a second block having a lower polarity than the first block. Figure 2 shows one embodiment of the crack pattern of the present invention, where (a) is a plan view of the crack pattern of the present invention and (b) is a side view of the crack pattern of the present invention.

[0029] The crack pattern film 1 of the present invention is made of a block copolymer film 2 and is formed on the surface of a substrate 4. Such a film is obtained by applying a solution containing micelles made of the block copolymer of the present invention to the substrate 4 and drying it. As this drying occurs, a network of cracks 3 is formed in the film, and this film becomes the crack pattern film 1. The network of cracks 3 then forms a network that connects each other throughout the entire crack pattern film 1.

[0030] As shown in Figure 2(b), the block copolymer film 2 forming the crack pattern film 1 is formed by laminating four-layer units, each consisting of a first block 21, a second block 22, a second block 22, and another first block 21, from the substrate 4 side. The first block 21 and the second block 22 correspond to the first and second blocks of the block copolymer molecule, respectively. As described below, the block copolymer film 2 is formed from micelles composed of block copolymer molecules, and each micelle is thought to form two four-layer units. The formation of two four-layer units from one micelle, i.e., an eight-layer structure, is due to the fact that the block copolymer molecules form micelles with bilayer membranes, as described below. Each four-layer unit has a structure in which the top and bottom surfaces are hydrophilic first blocks 21, sandwiched between the hydrophobic second blocks 22. As a result, each four-layer unit is composed of a hydrophilic block-hydrophobic block-hydrophilic block structure from the bottom, with a thickness of approximately 3 nm. By stacking a plurality of these units in the thickness direction, the block copolymer film 2 acquires the thickness required as a mask.

[0031] As described above, each unit (hereinafter also referred to as a unit structure) consisting of a set of four layers forms a first block 21 whose upper and lower surfaces are hydrophilic and has adhesive properties to the substrate 4 and metal. Therefore, at least one unit structure in contact with the substrate 4 becomes an adhesive layer 23 that firmly bonds the substrate 4 to the metal film 7 to be formed later. The thickness of the adhesive layer 23 depends on the depth of the crack 3 formed in the crack pattern film 1, but because the lowest unit structure is strongly adhered to the substrate 4, at least one unit structure remains as the adhesive layer 23 without forming a crack 3. Therefore, at the bottom of the crack 3, the substrate 4 is not exposed, and the adhesive layer 23 is exposed. Above the adhesive layer 23 is a structural layer 24 in which the crack 3 is formed. Although FIG. 1(b) shows the adhesive layer 23 as a single unit structure, the adhesive layer 23 does not necessarily have to be formed from a single unit structure and may be formed from multiple unit structures. In addition, in FIG. 1( b ), the structure layer 24 is shown as two unit structures, but in reality, the structure layer 24 is made up of many unit structures, which produce the thickness of the crack pattern film 1 .

[0032] As described above, the block copolymer film 2 that becomes a film has cracks 3 formed therein that penetrate from its surface to the adhesive layer 23. The width of these cracks 3 is 0.1 to 20 μm. That is, by using the crack pattern film 1 as a mask for patterning, it is possible to form mesh-like patterns with a width of 0.1 to 20 μm that corresponds to the width of the cracks 3. The width of the cracks 3 is preferably 0.1 to 15 μm, more preferably 0.1 to 10 μm, and even more preferably 0.1 to 5 μm. As already mentioned, the adhesive layer 23 is exposed at the bottom of the cracks 3.

[0033] The thickness of the block copolymer film 2 is, for example, about 0.1 μm to 7 μm, and more preferably, about 0.5 μm to 4 μm.

[0034] There is no particular limitation on the material of the substrate 4. For example, if the crack pattern film 1 is used as a mask for forming a transparent conductive film, the object on which the transparent conductive film is to be formed becomes the substrate 4. Examples of the substrate include, but are not particularly limited to, a synthetic resin film, a glass plate, an epoxy board, a Bakelite board, a glass epoxy board, and the like.

[0035] Next, the block copolymer that forms the block copolymer film 2 will be described.

[0036] The block copolymer comprises a first block having a linear polyethyleneimine skeleton and a second block having a lower polarity than the first block. Specifically, the block copolymer is formed by bonding the first block and the second block at their ends, and has a [first block]-[second block] structure.

[0037] The polyethyleneimine skeleton constituting the first block typically has a repeating unit represented by the following chemical formula (1): The repeating unit constituting the polyethyleneimine skeleton constituting the first block is not limited to that represented by the following chemical formula (1), and may, for example, have a substituent in the ethylene group portion: Even in this case, the imino group (—NH—) portion should not be substituted.

[0038] [ka]

[0039] The polyethyleneimine skeleton has a highly polar imino group and is hydrophilic. In contrast, the second block has a lower polarity than the first block having the polyethyleneimine skeleton, as described above. As a result, the block copolymer used in the present invention can be said to be amphiphilic. The degree of polymerization of the polyethyleneimine skeleton constituting the first block (i.e., the number of repeating units) can be about 10 to 500, but is not particularly limited.

[0040] The second block is selected from those having lower polarity than the first block. Although not particularly limited, preferred examples of such second blocks include those represented by the following general formula (2), in which the hydrogen atoms of the imino groups in the polyethyleneimine skeleton are substituted with organic groups having lower polarity.

[0041] [ka]

[0042] In the above general formula (2), R is an alkyl group having 1 to 20 carbon atoms, an aryl group having 5 to 20 carbon atoms, an aralkyl group having 6 to 20 carbon atoms, an alkylketo group having 2 to 20 carbon atoms, or an arylketo group having 6 to 20 carbon atoms. When the second block is represented by the above general formula (2), the degree of polymerization of the substituted polyethyleneimine skeleton constituting the second block is, for example, about 10 to 500, but is not particularly limited.

[0043] A more preferred example of the block copolymer is one represented by the following general formula (3).

[0044] [ka]

[0045] In the general formula (3), b is a symbol indicating that the copolymer is a block copolymer, * is each independently an end group of the polymer, and m and n are each independently an integer. Preferably, m and n are each about 10 to 500.

[0046] The copolymer represented by the general formula (3) can be synthesized, for example, by the following procedure. First, 2-methyl-2-oxazoline is polymerized by living polymerization. This reaction occurs by adding a compound having a substituent that acts as a leaving group in a nucleophilic substitution reaction to 2-methyl-2-oxazoline. After all of the 2-methyl-2-oxazoline has reacted, 2-phenyl-2-oxazoline is added, and the living polymerization terminal initiates living polymerization with the added 2-phenyl-2-oxazoline. Finally, the living polymerization terminal reacts with a nucleophile to obtain a block copolymer represented by the general formula on the left side of the following chemical reaction equation. This block copolymer is then hydrolyzed with acid to obtain the block copolymer represented by the general formula (3). The block copolymer used in the present invention is not limited to the one represented by general formula (3).

[0047] [ka]

[0048] <Method for manufacturing crack pattern film> Next, one embodiment of the method for producing a crack pattern film of the present invention will be described. The method for producing a crack pattern film of the present invention includes an emulsification step of applying an external force to a composition containing a block copolymer having a first block with a linear polyethyleneimine skeleton and a second block with a lower polarity than the first block, and an aqueous solvent, thereby emulsifying the composition to form an emulsion composition, a coating step of applying the emulsion composition to a substrate to form a coating film, and a drying step of drying the coating film to form a crack pattern film. Each step will be described below.

[0049] [Emulsification process] The emulsification step is a step of applying an external force to a composition containing a block copolymer having a first block with a linear polyethyleneimine skeleton and a second block having a lower polarity than the first block, and an aqueous solvent, thereby emulsifying the composition to form an emulsion composition. Note that the block copolymer used in this step has already been explained in the section on one embodiment of the crack pattern film above, and therefore, explanation of overlapping matters will be omitted.

[0050] Block copolymer 2 comprises a first block having a linear polyethyleneimine skeleton and a second block having a lower polarity than the first block. The first block is hydrophilic, while the second block is hydrophobic and has a lower polarity than the first block. That is, block copolymer 2 has a structure in which a hydrophilic block 21 and a hydrophobic block 22 are bonded intramolecularly, as shown in FIG. 3. When block copolymer 2 is dissolved in an aqueous solvent and an external force is applied, two block copolymer molecules face each other with their second blocks 22, 22 facing each other, forming a micelle 5 consisting of a bilayer membrane, as shown in FIG. 4.

[0051] Because aqueous solvent is incorporated into the interior of the micelle 5 and aqueous solvent is also present outside the micelle 5, the hydrophilic first block 21 is oriented on the outside of the bilayer membrane forming the micelle 5, and the hydrophilic first block 21 is also oriented on the inside. For the sake of explanation, if the two block copolymer molecules constituting the bilayer membrane are referred to as molecule A and molecule B, respectively, the first block 21 of molecule A is oriented on the outside surface of the micelle 5, and the first block 21 of molecule B is oriented on the inside surface. Inside the bilayer membrane of the micelle 5, the second block 22 of molecule A and the second block 22 of molecule B face each other.

[0052] Micelle 5 exists as colloidal particles emulsified in an aqueous solvent. As previously explained, colloidal particles develop cracks when they aggregate and dry to form a solid. At this time, the micelles 5 develop cracks, a characteristic of colloidal particles. As shown in Figure 4, the bilayer membrane of micelles 5 flattens as it dries, eventually integrating the two bilayer membranes to form block copolymer membrane 2. Each bilayer membrane contains four layers: hydrophilic block 21, hydrophobic block 22, hydrophobic block 22, and hydrophilic block 21. Therefore, the integration of the two bilayer membranes forms a total of eight layers, as shown in the lower part of Figure 4. As previously mentioned, this eight-layer membrane contains two unit structures. Furthermore, this membrane exhibits cracks 3, as shown in Figure 2(b).

[0053] That is, the emulsification step can be said to be a step of emulsifying the block copolymer in an aqueous solvent to form the above-mentioned micelles 5. The aqueous solvent containing the micelles 5 is called an emulsion composition.

[0054] Examples of aqueous solvents include water and alcohols having 1 to 4 carbon atoms. Among these, a mixed solvent of water and methanol is preferred as the aqueous solvent. The water used here is preferably ion-exchanged water or distilled water in order to suppress undesirable side reactions due to the presence of impurities.

[0055] In preparing the emulsion composition, the block copolymer is added to an aqueous solvent and emulsified by applying an external force. The amount of the block copolymer added is preferably about 5 to 20 mg per mL of aqueous solvent. The concentration of the block copolymer in the aqueous solvent is preferably adjusted appropriately taking into account the wettability of the substrate used, etc.

[0056] Examples of the external force include stirring, ultrasonic vibration, stirring with a homomixer or homogenizer, etc., and among these, ultrasonic irradiation is preferred. As the emulsification proceeds, the liquid becomes cloudy, and this step can be considered complete when the added block copolymer is completely dissolved and the liquid becomes cloudy.

[0057] The emulsion composition prepared in the emulsification step is subjected to the coating step. The emulsion composition obtained in this step is preferably used within two days after preparation, and more preferably used immediately after preparation.

[0058] [Coating process] The coating step is a step of applying the emulsion composition obtained in the emulsification step to a substrate to form a coating film.

[0059] The substrate is not particularly limited, but examples thereof include a synthetic resin film, a glass plate, an epoxy substrate, a Bakelite substrate, a glass epoxy substrate, etc. Methods for applying the emulsion composition to the substrate include, but are not particularly limited to, spin coating, gravure coating, spraying, dropping, brush coating, etc.

[0060] The substrate on which the emulsion composition has been applied to form a coating film is subjected to a drying step.

[0061] [Drying process] The drying step is a step of drying the coating film formed in the coating step to form a crack pattern film.

[0062] The drying method in this step is not particularly limited, and examples of such drying methods include natural drying, drying by blowing hot air, drying in an oven at 80° C. or less, but are not particularly limited.

[0063] Through this process, the crack pattern film of the present invention is formed on the surface of the substrate. As already mentioned, the adhesive layer 23 is exposed at the bottom of the crack 3. As already mentioned, the presence of this adhesive layer 23 allows the vapor-deposited metal film 7 to adhere strongly to the substrate 4.

[0064] <Mask for forming transparent conductive film> Next, one embodiment of the mask for forming a transparent conductive film of the present invention will be described. The mask for forming a transparent conductive film of the present invention comprises the crack pattern film of the present invention.

[0065] As already explained, the crack pattern film 1 of the present invention has a mesh-like structure of fine cracks 3 that penetrate from its surface to the adhesive layer 23. These mesh-like cracks 3 form a network that connects to each other throughout the entire crack pattern. The cracks 3 are minute, 0.1 to 20 μm wide, and have a mesh-like structure with many gaps. Therefore, when conductive metal wiring is formed using this as a mask, an invisible mesh-like wiring made of the metal film 7 can be formed over the entire substrate 4.

[0066] As already mentioned, an adhesive layer 23 is present at the bottom of the crack 3. This adhesive layer 23 functions as a molecular adhesion layer between the wiring made of the formed metal film 7 and the substrate 4. Due to this action, the mesh-like metal wiring formed on the surface of the substrate 4 acquires high adhesion to the substrate 4.

[0067] <Method of manufacturing transparent conductive film> Next, one embodiment of the method for producing a transparent conductive film of the present invention will be described. The method for producing a transparent conductive film of the present invention comprises a pattern film forming step of forming the crack pattern film of the present invention on the surface of a substrate, a metal film forming step of forming a metal film on the entire surface of the crack pattern film, and a removal step of removing the crack pattern film with a solvent. Each step will be described below with reference to the drawings. Figure 5 is a side view showing each step of the method for producing a transparent conductive film of the present invention, where (a) is a side view showing the state after the pattern film forming step, (b) is a side view showing the state after the metal film forming step, and (c) is a side view showing the state after the removal step.

[0068] [Pattern film formation process] The pattern film forming step is a step of forming the crack pattern film 1 of the present invention on the surface of a substrate 4. The substrate 4 is the target on which a transparent conductive film is formed. Through this step, as shown in FIG. 5(a), a block copolymer film 2 and a crack pattern film 1 including cracks 3 penetrating from the surface of the block copolymer film 2 to the adhesive layer 23 are formed on the surface of the substrate 4. The method for forming the crack pattern film 1 has already been described in the method for producing a crack pattern film of the present invention, and therefore a description thereof will be omitted here.

[0069] After the pattern film forming step, the substrate 4 having the crack pattern film 1 formed on its surface is subjected to the metal film forming step.

[0070] [Metal film formation process] The metal film forming step is a step of forming a metal film 7 over the entire surface of the crack pattern film 1. Through this step, as shown in Fig. 5(b), the metal film 7 is formed on the surface of the block copolymer film 2 in the areas of the crack pattern film 1 where the block copolymer film 2 exists, and the metal film 7 is formed on the surface of the adhesive layer 23 in the areas where the cracks 3 exist. As already mentioned, the presence of the adhesive layer 23 allows the metal film 7 to achieve high adhesion to the substrate 4.

[0071] The metal film 7 can be formed by, but not limited to, metal vapor deposition, sputtering, metal plating, etc. Among these, metal vapor deposition is preferred.

[0072] Examples of metals constituting the metal film 7 include, but are not limited to, gold, silver, copper, etc. Among these, copper is preferred. The thickness of the metal film 7 formed on the surface of the crack pattern film 1 is preferably about 100 nm.

[0073] No metal film 7 is formed on inner wall 25 of block copolymer film 2 facing crack 3, leaving structural layer 24 of block copolymer film 2 exposed. Due to the presence of this inner wall 25, in the removal step described below, a solvent comes into contact with structural layer 24 of block copolymer film 2 exposed on inner wall 25, and structural layer 24 of block copolymer film 2 is removed together with unnecessary metal film 7.

[0074] The substrate 4 that has undergone the metal film forming step is subjected to a removal step.

[0075] [Removal process] The removal process involves removing the crack pattern film 1 with a solvent. Through this process, the structural layer 24 of the block copolymer film 2 is removed together with the metal film 7 formed on its upper surface, leaving only the adhesive layer 23 and the metal film 7 formed at the bottom of the cracks 3 on the surface of the substrate 4. Therefore, a metal film 7 is formed on the surface of the substrate 4, which has the same shape in plan view as the fine mesh-like cracks formed in the crack pattern film 1. The metal film 7 thus formed forms a network interconnected across the entire surface of the substrate 4, making the entire surface of the substrate 4 conductive. Furthermore, the wiring of the metal film 7 that forms this network is extremely fine and therefore invisible to the naked eye. Therefore, the wiring of this metal film 7 is transparent from a macroscopic perspective.

[0076] A preferred solvent for removing the crack pattern film 1 is an alcohol having 1 to 5 carbon atoms, with methanol being particularly preferred. A preferred method for removing the crack pattern film 1 is to immerse the substrate 4 on which the crack pattern film 1 is formed in the solvent. When removing the crack pattern film 1 by immersion, the structural layer 24 of the block copolymer film 2 is removed together with the metal film 7 formed on its upper surface within several tens of seconds, leaving only the adhesive layer 23 and the metal film 7 formed inside the cracks 3 on the surface of the substrate 4. Since the adhesive layer 23 functions as a molecular adhesion layer, the metal film 7 has high adhesion to the substrate 4. Conventionally, transparent conductive films of this type formed on the surface of a substrate have been problematic due to peeling caused by insufficient adhesion. However, the transparent conductive film formed according to the present invention solves this peeling problem due to its high adhesion.

[0077] <Method for improving adhesion of conductive film to substrate> Next, a method for improving the adhesion of the conductive film of the present invention to a substrate will be described. The method for improving the adhesion of the conductive film of the present invention to a substrate is characterized in that the crack pattern film of the present invention is used as the crack pattern film when performing crack film lithography, which involves forming a crack pattern film as a mask on the surface of the substrate, depositing metal on the surface of the substrate through the mask, and then removing the mask to form a conductive film on the surface of the substrate.

[0078] As already mentioned, an adhesive layer 23 is formed at the bottom of the cracks 3 formed in the crack pattern film 1 of the present invention. This adhesive layer 23 functions as a molecular adhesion layer between the wiring made of the formed metal film 7 and the substrate 4. As a result, the mesh-like metal wiring formed on the surface of the substrate 4 acquires high adhesion to the substrate 4. The method of the present invention for improving the adhesion of the conductive film to the substrate was developed with this in mind. As other matters have already been explained, explanation will be omitted here.

[0079] The conductive film formed by this method may be a transparent conductive film that has a fine mesh structure and is therefore transparent, as has been described above.

[0080] <Conductive film> Next, the conductive film of the present invention will be described. The conductive film of the present invention is a conductive film consisting of a metal film formed on the surface of a substrate, characterized in that an adhesive layer composed of a block copolymer having a first block with a linear polyethyleneimine skeleton and a second block with lower polarity than the first block is provided between the substrate and the metal film. This conductive film can be formed by the above-described method for producing a transparent conductive film of the present invention. This conductive film has high adhesion to the substrate 4 because it includes an adhesive layer 23 composed of a block copolymer having a linear polyethyleneimine skeleton between the metal film 7 constituting the conductive film and the substrate 4. This conductive film may also be a transparent conductive film that is transparent due to its fine mesh structure. Even when the conductive film of the present invention has such a fine mesh structure, it maintains high adhesion to the substrate 4. Such high adhesion has not been achieved with conventionally produced conductive films of this type, demonstrating the great superiority of the conductive film of the present invention.

[0081] Other matters relating to the conductive film of the present invention have already been explained, so explanations thereof will be omitted here. [Example]

[0082] The present invention will be explained in more detail below by showing examples, but the present invention is not limited to these examples in any way.

[0083] Synthesis of polymethyloxazoline-polyphenyloxazoline block copolymer [ka]

[0084] The atmosphere in a 100 mL eggplant-shaped flask was replaced with nitrogen, and methyl p-toluenesulfonate (0.36 mL, 2.26 mmol), dry dimethylacetamide (48 mL), and distilled 2-methyl-2-oxazoline (10 mL, 118 mmol) were added to the flask. The mixture was reacted at 85°C for 24 hours in the dark. After the reaction, GPC and 1 After confirming complete consumption of 2-methyl-2-oxazoline by H-NMR, distilled 2-phenyl-2-oxazoline (15.5 mL, 118 mmol) was added to the flask. This was reacted at 100 °C for 48 hours in the dark. The reaction solution was cooled to room temperature and purified by precipitation using chloroform as a good solvent and diethyl ether as a poor solvent. The resulting precipitate was filtered off by suction filtration. Precipitation purification was repeated twice, followed by drying under reduced pressure to obtain the target product. 1 H-NMR measurements confirmed that polymethyloxazoline-polyphenyloxazoline block copolymers were synthesized, and that the degrees of polymerization were 50 for the polymethyloxazoline moiety and 42 for the polyphenyloxazoline moiety.

[0085] Synthesis of polyethyleneimine-polyphenyloxazoline block copolymer [ka]

[0086] A 100 mL reaction vessel was charged with 4 g of the polymethyloxazoline-polyphenyloxazoline block copolymer synthesized using the above procedure. 60 mL of 3 M aqueous hydrochloric acid was added and dispersed thoroughly, followed by heating to reflux at 100 °C for 2.5 hours. After the reaction, the reaction solution was cooled to room temperature and then 28% aqueous ammonia was added until the pH reached 11 or higher. The reaction solution was then placed in a dialysis membrane and dialyzed against 1 L of deionized water. Dialysis was continued for 3 days, during which the deionized water was changed 8 times. Finally, the solution in the dialysis membrane was freeze-dried to obtain the amphiphilic polymer polyethyleneimine-polyphenyloxazoline block copolymer.

[0087] [Preparation of crack pattern film] A mixture of 20 mg of the polyethyleneimine-polyphenyloxazoline block copolymer obtained by the above procedure and methanol (0.2 mL) was subjected to ultrasonic vibration to completely dissolve the copolymer. Deionized water (1.8 mL) was added to the mixture to prepare a white dispersion (polymer concentration: 10 mg / mL). The resulting dispersion was dropped onto a glass slide, and the droplet was completely dried at room temperature and atmospheric pressure to form a film.

[0088] An enlarged photograph and an SEM (scanning electron microscope) image of the obtained film are shown in Figure 6. Figure 6 shows an enlarged photograph and an SEM image of the crack pattern film obtained in the example, with the enlarged photograph on the left and the SEM image on the right.

[0089] As shown in Figure 6, cracks 3 μm wide were formed in the obtained film. Furthermore, these cracks were formed in a mesh pattern throughout the entire film. Using this film as a crack pattern film, a copper pattern film was formed using the following procedure.

[0090] [Preparation of copper pattern film using crack pattern film as a template] The crack pattern film prepared using the above procedure was placed on a substrate in a deposition system, and copper was evaporated by resistance heating. The evaporation process was stopped when the copper film reached a thickness of 1000 Å, and the evaporated crack pattern film was recovered. The crack pattern film, whose surface was covered with copper, was immersed in methanol along with the substrate. The crack pattern film peeled off along with the copper on the surface within a few tens of seconds, leaving behind a transparent copper pattern film. This transparent copper pattern film had a sheet resistance of 17.7 Ω / sq, demonstrating good conductivity comparable to ITO. The transparent copper pattern film had a transmittance of 82.9%.

[0091] Figure 7 shows a photograph taken immediately after copper deposition (left side) and a photograph taken after the crack pattern film was removed (right side). As can be seen from the photograph on the right side of Figure 7, the copper pattern formed after the crack pattern film was removed had good transparency. Figure 8 also shows a microscope image of the transparent copper pattern. As can be seen from Figure 8, a mesh-like copper pattern was formed, reflecting the mesh-like crack shape of the crack pattern film, and these copper patterns were found to form a network in which they were connected to each other. It is believed that the good conductivity described above is brought about by this interconnected network.

[0092] Next, elemental mapping was performed using energy dispersive X-ray spectroscopy (EDX) to examine the distribution of copper. The results are shown in Figure 9. In Figure 9, the upper image is an SEM image, and the lower image is an EDX image showing the distribution of copper. As shown here, the presence of copper is indicated in the mesh-like areas, and it can be understood that the transparent conductive film obtained by the present invention has a metal line structure connected in a mesh-like pattern.

[0093] [Peeling test of copper pattern film] Scotch (registered trademark) adhesive tape manufactured by 3M Company was applied to the entire glass substrate, including the copper pattern film portion obtained by the above procedure, and the adhesive tape was peeled off after leaving it for 30 minutes. The adhesive tape was peeled off so that the peeled adhesive tape remained approximately perpendicular to the glass substrate, as in the peeling test specified by JIS. The peeling test results are shown in Figure 10. Figure 10 shows the peeling test results for the copper pattern film formed in the example. (a) is an image showing the state of the glass substrate after the copper pattern film was formed, (b) is an image showing the state with the adhesive tape applied to the entire glass substrate, and (c) is an image showing the state after the adhesive tape was peeled off.

[0094] As shown in Figure 10(a), in the areas where the crack pattern film was removed with a solvent, a fine transparent conductive film formed in a mesh pattern as described above remains, making it transparent. On the other hand, in areas where the crack pattern was not present from the beginning, the evaporated copper film remains on the glass substrate as it is. When the adhesive tape is peeled off using the above procedure, the copper film that was present in areas where the crack pattern was not present from the beginning is peeled off, as shown in Figure 10(c), and the surface of the glass substrate is completely exposed. On the other hand, in the areas where the crack pattern was present, i.e., where the transparent conductive film was formed, the shape of the crack pattern can be faintly distinguished, showing a state different from when the glass substrate is completely exposed.

[0095] Next, the state of the transparent conductive film after peeling off the adhesive tape was observed using SEM and EDX. The results are shown in FIG. 11. FIG. 11 shows SEM and EDX images showing the state of the transparent conductive film after peeling off the adhesive tape. (a) is an image showing the area observed using SEM, (b) is an SEM image of the observed area, and (c) is an EDX image of the observed area. As shown in FIG. 11(a), the SEM and EDX observations were performed at the boundary between the area where the transparent conductive film was formed (i.e., the area where the crack pattern existed) and the area where the film was not formed. As a result, as shown in the SEM image in FIG. 11(b), the mesh-like pattern remained intact even after peeling off the adhesive tape. As shown in the EDX image of the same area in FIG. 11(c), it was confirmed that this mesh-like pattern was formed of copper. This demonstrates that the transparent conductive film obtained by the present invention has high adhesion to the substrate. [Explanation of symbols]

[0096] 1. Crack pattern film 2-block copolymer membrane, block copolymer 21 First block, hydrophilic block 22 Second block, hydrophobic block 23 Adhesive layer 24 structural layers 3. Crack 4 Base material 5. Micelles 7 Metal Film

Claims

1. A crack pattern film comprising a film on the surface of a substrate in which cracks of 0.1 to 20 μm in width are formed in a network pattern, the film being formed from a block copolymer having a first block with a linear polyethyleneimine skeleton and a second block having a lower polarity than the first block.

2. 2. The crack pattern film according to claim 1, wherein the first block comprises a repeating unit represented by the following chemical formula (1): 【Chemical 1】

3. 2. The crack pattern film according to claim 1, wherein the second block comprises a repeating unit represented by the following general formula (2): 【Chemistry 2】 (In the above general formula (2), R represents an alkyl group having 1 to 20 carbon atoms, an aryl group having 5 to 20 carbon atoms, an aralkyl group having 6 to 20 carbon atoms, an alkylketo group having 2 to 20 carbon atoms, or an arylketo group having 6 to 20 carbon atoms.)

4. 2. The crack pattern film according to claim 1, wherein the block copolymer is represented by the following general formula (3): 【Chemistry 3】 (In the above general formula (3), b is a symbol indicating that it is a block copolymer, * is each independently an end group of the polymer, and m and n are each independently an integer.)

5. A mask for forming a transparent conductive film, comprising the crack pattern film according to any one of claims 1 to 4.

6. an emulsification step of applying an external force to a composition containing a block copolymer including a first block having a linear polyethyleneimine skeleton and a second block having a lower polarity than the first block, and an aqueous solvent, thereby emulsifying the composition to form an emulsion composition; a coating step of applying the emulsion composition to a substrate to form a coating film; a drying step of drying the coating film to form a crack pattern film.

7. 7. The method for producing a crack pattern film according to claim 6, wherein the first block comprises a repeating unit represented by the following chemical formula (1): 【Chemistry 4】

8. 7. The method for producing a crack pattern film according to claim 6, wherein the second block comprises a repeating unit represented by the following general formula (2): 【Chemistry 5】 (In the above general formula (2), R represents an alkyl group having 1 to 20 carbon atoms, an aryl group having 5 to 20 carbon atoms, an aralkyl group having 6 to 20 carbon atoms, an alkylketo group having 2 to 20 carbon atoms, or an arylketo group having 6 to 20 carbon atoms.)

9. 7. The method for producing a crack pattern film according to claim 6, wherein the block copolymer is represented by the following general formula (3): 【Chemistry 6】 (In the above general formula (3), b is a symbol indicating that it is a block copolymer, * is each independently an end group of the polymer, and m and n are each independently an integer.)

10. a pattern film forming step of forming the crack pattern film according to any one of claims 1 to 4 on the surface of a substrate; a metal film forming step of forming a metal film on the entire surface of the crack pattern film; a removing step of removing the crack pattern film with a solvent.

11. 11. The method for producing a transparent conductive film according to claim 10, wherein the metal film is formed by metal vapor deposition in the metal film forming step.

12. In performing crack film lithography, a crack pattern film is formed as a mask on the surface of a substrate, metal is vapor-deposited on the surface of the substrate through the mask, and then the mask is removed to form a conductive film on the surface of the substrate. A method for improving the adhesion of a formed conductive film to a substrate, comprising using the crack pattern film according to any one of claims 1 to 4 as the crack pattern film.

13. 13. The method according to claim 12, wherein the conductive film is a transparent conductive film having a fine mesh structure and hence transparency.

14. A conductive film made of a metal film formed on the surface of a substrate, A conductive film characterized by having an adhesive layer between the substrate and the metal film, the adhesive layer being made of a block copolymer having a first block with a linear polyethyleneimine skeleton and a second block having a lower polarity than the first block.

15. 15. The conductive film according to claim 14, wherein the conductive film is a transparent conductive film having a fine mesh structure and thus having transparency.

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