TW201030766A - Conductive paste, electro-magnetic wave shielding film using the same and electro-magnetic wave shielding flexible printed wiring board - Google Patents

Abstract

The present invention provides a conductive paste which is capable of forming a shielding layer with excellent bending-resistance and both flexibility and thermo-resistance, an electro-magnetic wave shielding film using the same and an electro-magnetic wave shielding flexible printed wiring board. The conductive paste contains conductive metal powder, urethane modified polyester resin and blocked isocyanate wherein the urethane modified polyester resin is obtained from reacting an acid component, an alcohol component, and an isocyanate component containing aromatic isocyanate. A total amount of the acid component, the alcohol component and the aromatic component contained in the isocyanate component is 5 mol% or more, 50 mol% or less relative to a total amount of the acid component, the alcohol component and the isocyanate component.

Description

201030766 VI. Description of the Invention: [Technical Field] The present invention relates to a conductive paste, an electromagnetic wave shielding film using the same, and an electromagnetic wave shielding flexible printed wiring board, in particular, a flexible printed wiring board which is required to have bending resistance. related. [Prior Art] The conductive paste is obtained by mixing a conductive material such as carbon black or graphite powder, precious metal powder, copper powder or nickel powder with a resin and a solvent as a binder. When the conductive paste is applied onto a film or a substrate by a method such as e-screen printing to form a pattern, and the resin is cured, a conductive wiring is formed. With the recent tightening and weight reduction of electronic parts, their use requires a highly conductive conductive paste. Patent Document 1 describes a conductive silver paste using silver as a dip material. The shape of the silver powder used as the conductive crucible is not limited, such as granular, flake, plate, dendritic, chestnut, hazelnut, etc., and its size is 0.1 to 100 μm. Further, in the binder resin, a saturated copolymerized polyester resin and a sulphuric acid isocyanate are used. Further, Patent Document 2 discloses that the bending resistance of the conductive paste is improved, and the original particles having a particle diameter of 0.1 to 5 μm are bonded to each other on a three-dimensional element. A silver paste, a binder having a number average molecular weight of 3,000 or more, a hardener, and a solvent-based conductive paste. The binder is, for example, a polyurethane resin and a polyester resin. Moreover, the conductive paste is also used as an electromagnetic wave shielding material. In particular, recently, in order to transmit information (also information) at a high speed and use a frequency of a higher frequency band, a conductive paste having electromagnetic wave shielding characteristics of the present or higher is required. Patent Document 3 describes a combination of a conductive silver paste having a specific particle diameter and a conductive silver paste having improved conductivity and shielding properties, and an electromagnetic wave shielding -4-201030766 film obtained by using the conductive silver paste. [Patent Document 1] Japanese Laid-Open Patent Publication No. Hei No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. In the case of the shielding layer of the flexible printed wiring board, the shielding layer formed by applying and curing the conductive paste requires heat resistance, surface smoothness, and bending resistance in addition to conductivity and electric shielding properties. In particular, when it is used for a movable portion such as a hinge of a mobile phone, durability against a smaller bending radius is required due to miniaturization of the machine, so that improvement of bending resistance is a problem. The conductive paste described in Patent Document 3 discloses that the heat resistance and the flexibility after application and curing are combined, and it is preferable to use a polyester resin as the binder resin. However, it is necessary to improve the bending resistance in order to achieve the required bending resistance. In order to improve the bending resistance, flexibility is required, so that the binder resin has been conventionally used as a polyester resin of a soft resin. The polyester resin is a resin obtained by polycondensing an acid component such as a polyvalent carboxylic acid or a sour liver with an alcohol component such as a polyhydric alcohol, and the characteristics of the acid component and the alcohol component can be appropriately controlled. When a soft component such as an aliphatic dicarboxylic acid is used, the softness can be improved. However, when a lot of soft components are used, the heat resistance is lowered, and the necessary characteristics cannot be satisfied. In order to improve heat resistance, it is necessary to increase the ratio of rigid aromatic components such as citric acid (and terephthalic acid), but this reduces the softness. In view of the above problems, the present invention provides a conductive paste capable of forming an electromagnetic wave shielding layer having excellent flexibility and 201030766 heat resistance and excellent in bending resistance, and an electromagnetic wave shielding film using the conductive paste. [Means for Solving the Problem 1] The present invention relates to a conductive paste comprising a conductive metal powder, a urethane-modified polyester resin, and a blocked isocyanate, which is characterized in that the above-mentioned urethane modification The polyester resin is obtained by reacting an acid component, an alcohol component, and an isocyanate component containing an aromatic isocyanate, and the acid component, the alcohol component, and the total amount of the acid component, the alcohol component, and the isocyanate component. The total amount of the aromatic component contained in the isocyanate component is 5 mol% or more and 50 mol% or less (the invention of the first aspect of the present application). The binder resin is used as an isocyanate component containing an aromatic isocyanate: a modified urethane-modified polyester resin. In addition, the total amount of the aromatic component contained in the acid component, the alcohol component, and the isocyanate component is set to 5 mol% or more and 50 mol%, based on the total amount of the acid component, the alcohol component, and the isocyanate component. the following. With such a molecular structure, it is possible to cope with the flexibility and heat resistance required for bending resistance. The hydroxy hydrazine of the above urethane-modified polyester resin is preferably 5 mgKOH/g or more and 60 mgKOH/g or less (the invention of the second aspect of the present application). The oxindole is an index indicating the molecular weight of the number of crosslinking points of the urethane-modified polyester resin (the hydroxyl group reacted with the blocked isocyanate), and the smaller the hydroxy hydrazine, the smaller the molecular weight, and the smaller the hydroxy hydrazine, the higher the molecular weight. Big. When the oxindole is less than 5 mgKOH/g, the molecular weight is large and the flexibility is excellent, but the bridging point which reacts with the blocked isocyanate is reduced, and the heat resistance is lowered. Further, when the oxindole is more than 60 mgKOH/g, the molecular weight is rather small, and the heat resistance is improved, but the flexibility is lowered. 201030766 The above-mentioned blocked isocyanate has a number average molecular weight of 500 or more and 3,000 or less, and is a polyfunctionally-terminated polyisocyanate compound obtained by blocking an end of an isocyanate monomer and a polyhydroxy compound to be added with an isocyanate. Preferably (the invention of claim 3 of the patent application). Since such an addition type isocyanate has a large amount of a functional group (isocyanate group) in one molecule, the crosslinking density of the urethane-modified polyester resin after the reaction can be increased to improve heat resistance. The mixing ratio of the above urethane-modified polyester resin to the above-mentioned blocked isocyanate® is, for example, converted into a hydroxyl group (OH) of the above-mentioned urethane-modified polyester resin and an isocyanate group of the above-mentioned blocked isocyanate. The molar ratio (NCO/OH) of (NCO) is preferably 0.8 or more and 3.0 or less (the invention of claim 4 of the present application). If the amount of the blocked isocyanate is less than this range, the crosslinking density of the urethane-modified polyester resin is lowered and the heat resistance is also lowered. Further, when the amount of the blocked isocyanate is more than this range, the isocyanate which does not contribute to the reaction remains in the binder resin, and the heat resistance may be lowered. A more preferable range of the molar ratio is 1.0 or more and 2.0 or less. The conductive metal powder is composed of a metal powder of an average particle diameter of 55 μm to 20 μχη and a metal powder of an average particle diameter of 100 nm or less, and the ratio of the content of the metal powder A to the metal powder B is 99.5: 0.5 to 70 by weight. 30. The content ratio of the conductive metal powder is preferably 50% by weight or more and 5% by weight or less based on the solid content of the conductive paste (the fifth invention of the present application). When the content ratio of the conductive metal powder is increased, the conductivity can be improved. However, if the content is too high, the flexibility is deteriorated and the bending resistance is deteriorated. Therefore, in order to coexist the conductivity and the bending resistance, the content ratio of the conductive metal 201030766 powder is 50% by weight. More than % and not more than 85% by weight. Further, in order to obtain good conductivity, it is preferred to use metal powder A of different particle diameters and metal powder B in combination at a specific content ratio. When the gap between the metal powders A having a large particle diameter is filled with the metal powder B of the nanometer size, the surface smoothness after coating the conductive paste is improved not only by improving the conductivity. Since the surface smoothness and the electrical conductivity together affect the electromagnetic wave shielding property, the electromagnetic wave shielding characteristics can be further improved when the conductivity and the (surface) smoothness are improved. Moreover, the present invention provides an electromagnetic wave shielding film having a layer composed of the above-mentioned conductive paste on a substrate (the invention of claim 6 of the present application). Further, an electromagnetic wave shielding flexible printed wiring board having a layer composed of the above conductive paste is provided (the invention of claim 7 of the present application). Such an electromagnetic wave shielding film and an electromagnetic wave shielding flexible printed wiring board are excellent not only in bending resistance but also in heat resistance, electrical conductivity, and electromagnetic wave shielding properties. According to the present invention, a conductive paste capable of forming an electromagnetic wave shielding layer having excellent flexibility and heat resistance and excellent in bending resistance, and an electromagnetic wave shielding film using the conductive φ paste and electromagnetic wave shielding flexible printed wiring are provided. board. [Embodiment] Hereinafter, embodiments of the present invention will be described. In the drawings, the same reference numerals will be given to the same elements, and the repeated description will be omitted. Also, the size ratio of the drawings is not necessarily consistent with the description. The urethane-modified polyester resin used in the present invention is explained. The urethane-modified polyester resin is obtained by reacting an acid component, an alcohol component, and a carbamate component. In general, the polyester resin is obtained by polycondensing an acid component such as carboxylic acid 201030766 or an acid anhydride thereof with an alcohol component such as a polyhydric alcohol. The terminal hydroxyl group of the obtained polyester resin is reacted with an isocyanate component to obtain a urethane-modified polyester resin. Therefore, it is preferred to carry out the reaction by adding an isocyanate component after reacting the acid component with the alcohol component, but the acid component, the alcohol component, and the isocyanate component may be simultaneously reacted. The acid component is not particularly limited as long as it is a polyvalent carboxylic acid or an anhydride thereof. Examples thereof include aromatic dicarboxylic acids such as citric acid, isononanoic acid, p-nonanoic acid, and decanoic acid, and acid anhydrides thereof; aliphatic carboxylic acids such as succinic acid, adipic acid, glutaric acid, and sebacic acid; An acid anhydride thereof; an unsaturated dicarboxylic acid such as maleic acid, fumaric acid or itaconic acid, and an anhydride thereof. These can be used in more than two types. The acid component is not particularly limited as long as it is a polyvalent carboxylic acid or an anhydride thereof. An aliphatic binary such as ethylene glycol, diethylene glycol, triethylene glycol, neopentyl glycol, 1,3-propanediol, 1,4-butanediol, 1,4-cyclohexanediol, etc. Alcohol: an aromatic diol; an alicyclic diol; a trivalent or higher alcohol such as trimethylolpropane or neopentyl alcohol; These two or more kinds of isocyanate components have two or more isocyanate groups in one molecule, and it is necessary to have an aromatic isocyanate in the molecule. The aromatic isocyanate is, for example, dylyl diisocyanate, toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, naphthyl diisocyanate, biphenyl diisocyanate or the like. These can be used in more than two types. Further, an aliphatic diisocyanate such as trimethylhexamethylene diisocyanate, hexamethylene diisocyanate or trimethylene diisocyanate may be used together with the aromatic isocyanate in the range which does not impair the gist of the present invention. An alicyclic diisocyanate such as a cyclohexane diisocyanate may also be used. As described above, the aromatic component of the acid component, the alcohol component, and the isofluorite component is a total of 5 mol% or more and 50 mol% or less based on the total amount of the total components. These materials are reacted in the usual manner to obtain a urethane-modified polyester resin. The blocked isocyanate used in the present invention is one in which the terminal isocyanate group of the polyfunctional isocyanate is blocked with a blocking agent. Heating causes the blocking agent to thermally dissociate to form an isocyanate group. The isocyanate group is reacted with a urethane-modified polyester resin to crosslink the urethane-modified vinegar resin. As the blocking agent, a compound having an active hydroxyl group such as an alcohol, a phenol, a guanamine, an oxime, or an active methylene group. As the polyfunctional isocyanate, any isocyanate such as trimethylene diisocyanate, hexamethylene diisocyanate (HDI) or diphenylmethane diisocyanate (MDI) can be used. Among them, the addition isocyanate of the isocyanate monomer and the polyhydroxy compound represented by the following general formula (I) is preferred. Ο

II

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II HO (wherein R1 to R3 are groups in which an isocyanate group is removed by an aliphatic, alicyclic or aromatic diisocyanate, and R4 is a group in which a hydroxyl group is removed from a polyol compound.) The polyhydroxy compound has two in one molecule. A compound of the above hydroxyl group such as glycerol, trimethylolethane, trimethylolpropane, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol or the like. Further, a diisoneous acid ester such as diisocyanide-10-201030766 acid trimethylene ester, hexamethylene diisocyanate, diphenylmethane diisocyanate or the like. The conductive metal powder used in the present invention may be any metal such as copper, gold, silver, uranium or nickel, or an alloy thereof, but it is preferred to use a silver powder excellent in conductivity. Further, the shape is not particularly limited, and is, for example, a spherical shape, a sheet shape, or a granular shape. The content of the conductive metal powder can be arbitrarily selected in accordance with the characteristics required. When the content of the conductive metal powder is increased, the conductivity is improved. However, if the content of the conductive Q-shaped metal powder is too large, the agglomeration of the resin component and the conductive metal powder is weakened, and voids are formed in the conductive paste after application. Printability or reduced adhesion. Moreover, the conductivity is also reduced. Therefore, the content of the conductive metal powder is preferably 95% or less of the solid content of the conductive paste. Further, when the content of the conductive metal powder is increased, the conductive paste becomes hard and the flexibility is lowered. In order to make the conductivity and flexibility of the conductive paste coexist, it is preferable to set the content of the conductive metal powder to 50% or more and 8 or less of the solid content of the conductive paste. The conductive metal powder is made of a metal powder having an average particle diameter of 0.5 μm to 20 μm and a metal powder having an average particle diameter of 100 nm or less. The content ratio of the metal powder to the metal powder B is set to 99.5 by weight ratio: 0.5 to 70: 30 is preferred. When the content ratio of the metal powder A to the metal powder B exceeds 99.5:0.5 and the metal powder A is increased, the combination effect is reduced and the conductivity is lowered. Further, when the content ratio exceeds 70:30 and the metal powder B is increased, the increase in the amount of the metal powder B increases the cost, which is not preferable. The content ratio of the metal powder A to the metal powder b is preferably 9 9 : 1 to 9 0 : 1 0. -11- 201030766 The average particle size of the metal powder A is preferably 5.5μηι~20μιη. The conductivity is reduced below 0.5 μmη. Further, when the average particle diameter exceeds 20 μm, it is difficult to carry out fine printing processing. Similarly, it is preferred to use an ultra-large particle size, and the maximum particle size is preferably in the range of 20 μm to 50 μm. Further, the particle diameter is the largest particle diameter of each particle, and the average enthalpy is determined as the average particle diameter. A scanning electron microscope (SEM) or the like is used for measuring the particle diameter. The metal powder crucible is not limited to one type, and a plurality of powders having different average particle diameters and shapes may be used in combination. When the combination of flake silver powder and spherical silver powder © is used, the conductivity and smoothness after coating can be improved. The metal powder B is a metal powder having an average particle diameter of 100 nm or less. Although the nano-sized powders are mutually cohesive, the average particle diameter refers to the particle size of the original particles. Further, such a nano-sized powder has a large surface area and a large surface activity. Therefore, it is preferable to protect the surface to suppress secondary cohesion, and it is preferable to use the surface to cover the organic matter. Organic substances such as polycarboxylic acids, polyacrylic acids. The metal powder B having an average particle diameter of 100 nm or less can be produced by the following method. The silver nitrate was dissolved in a mixed solvent of water and a lower alcohol, and the pH was adjusted to be 1 or more with aqueous ammonia. To this, L-ascorbic acid (as a reducing agent) and polyacrylic acid (as a dispersing agent) dissolved in the above mixed solvent are added to precipitate silver particles. The precipitated silver particles are obtained by filtration, washing, and drying in a state in which secondary dispersing is suppressed by a dispersing agent. The average particle diameter of the silver particles can be changed depending on the pH, the temperature, the concentration of each material, the mixing method, and the like. The silver particles produced by the above steps are prepared in a state in which the surface is coated with a dispersant, in particular, in the case where a dispersing agent is used in the reaction step. Since the state in which the dispersant is coated on the surface of the silver particles is formed in the formation stage, it is not susceptible to the influence of the outside air, and the silver particles are in a state in which it is less likely to be secondaryly dispersed. Even if it causes cohesion, it can be easily destroyed by an organic solvent or the like due to the intervention of the dispersant. Moreover, the dispersibility to the resin is also good. The conductive metal powder, the urethane-modified polyester resin, and the blocked isocyanate are mixed to prepare a conductive paste. The urethane-modified polyester resin and the blocked isocyanate are dissolved in a solvent. As the solvent, an organic solvent such as an ester, an ether, a ketone, an ether ester, an alcohol, a hydrocarbon or an amine can be used. When the conductive paste is used in a screen printing brush, it is preferable to use a high boiling point solvent having good printability, and specifically, such as carbitol acetate or butyl carbitol acetate. Further, the conductive paste of the present invention may be added with an additive such as a thickener or a leveling agent to improve printing workability. Further, inorganic tantalum such as carbon or vermiculite may be added without impairing the performance of the present invention. These materials are mixed and dispersed in a uniform state by a ball mill, a three-roll mill, a rotary stirring defoamer or the like to prepare a conductive paste. The electromagnetic wave shielding film of the present invention has a layer composed of the above conductive paste on a substrate. After the conductive paste is applied onto a substrate, the solvent is dried and hardened to obtain an electromagnetic wave shielding film. As the substrate, a polyester film, a polyimide film, or the like can be used. Fig. 1 is a schematic cross-sectional view showing an example of an electromagnetic wave shielding film. A conductive paste layer 2 is provided on the substrate 1. In order to protect the conductive paste layer, a protective film 8 may be provided on the conductive paste layer 2. The protective film 8 is peeled off during use. When the electromagnetic wave shielding film is attached to one or both sides of the flexible printed wiring board -13-201030766, the electromagnetic wave shielding flexible printed wiring board of the present invention is obtained. Fig. 2 is a schematic cross-sectional view showing an example of an electromagnetic wave shielding flexible printed wiring board. The flexible printed wiring board 7 is formed by forming a wiring made of a copper foil 5 on a substrate 4, and is covered with a coverlay. The cover film is composed of a cover film 6a of polyimide or the like and a cover film adhesive 6b. The electromagnetic wave shielding film 3 is attached to the cover film side of the I flexible printed wiring board. Further, the conductive paste may be directly applied to the flexible printed wiring board to provide a conductive paste layer. w The thickness of the conductive paste to be applied is not particularly limited, but is preferably in the range of ΙΟμηι to 50 μmη. When the thickness is 1 Ομηη or less, the desired electromagnetic wave shielding property cannot be obtained. On the contrary, when the thickness is 50 μm or more, the flexibility of the shielding layer is poor, and the bending resistance is reduced. The coating method of the conductive paste is, for example, screen printing, gravure printing, lithographic printing, automatic dispenser method, or the like. Screen printing is most suitable for use from the viewpoint of fineness, film thickness, and productivity of the formed wiring. Further, the conductive paste of the present invention may be directly coated and cured on a flexible printed wiring board to form an electromagnetic wave shielding layer. According to each of the above methods, an electromagnetic wave shielding flexible printed wiring board having a layer composed of the conductive paste of the present invention was obtained. Similarly, when coated on an outer casing of an electronic device such as a personal computer or a mobile phone, an electromagnetic wave shielding casing having a layer composed of the conductive paste of the present invention can be obtained. EXAMPLES Next, the best mode for carrying out the invention will be described by way of examples. However, the examples do not limit the scope of the invention. -14-201030766 (Examples 1 to 3, Comparative Examples 1 to 3) (Production of Conductive Paste) The urethane-modified polycondensation obtained by reacting the acid component, the alcohol component, and the isocyanate component described in Table 1 was prepared. Ester resin. Specifically, the acid component, the alcohol component, the isocyanate component, and the mixed solution of butyl carbitol and butyl carbitol in the first table were placed in a four-necked flask, and heated to 60 ° C under a nitrogen stream. Further, an isocyanate compound was added and heated at 80 ° C for 5 hours to synthesize a urethane-modified polyester resin. ® prepared urethane-modified polyester resin, mixed with conductive metal powder (flaky silver powder with an average particle diameter of 3.0 μm and spherical silver powder with an average particle diameter of 25 nm) and blocked isocyanate to make electricity Sex paste. The compounding ratio of the urethane-modified polyester resin to the blocked isocyanate is an equivalent molar ratio, and the compounding ratio of the conductive metal powder is a ratio as follows. * Mixing ratio (weight) of flake silver powder = (weight of urethane-modified polyester resin + weight of blocked isocyanate) x2.1 * Mix ratio of spherical silver powder (weight) = (amine group A) Acid-modified polyester resin ◎ Weight + blocked isocyanate weight) x 〇. 23 3 (Production evaluation sample) An adhesive-free copper-clad laminate (2 layers) prepared by laminating copper foil on a polyimide film CCL), the copper foil portion is selectively etched by a subtractive method to form a pattern having a line width of 50 μm. Further, a cover film was attached thereto to prepare a flexible printed wiring board for evaluation. On the side of the cover film of the flexible printed wiring board, it was coated by a screen printing method to obtain a conductive paste, which was thermally cured in an oven. As for the sample for evaluation of the sliding bending property, the conductive paste was coated with -15-201030766 solder resist and thermally cured in an oven. (Evaluation of Conductive Paste: Volume Resistivity) The sample was cut at a width of 5 mm, and the resistance (the distance between the terminals was 1 〇〇 mm) was measured by a four-terminal method, and the thickness of the silver paste cured film was measured by a surface roughness meter. Volume resistivity. (Evaluation of Conductive Paste: Volume Resistivity) After the above sample was set to the reflow furnace at a maximum temperature of 260 ° C for 2 times, a slit was formed between the silver paste cured film and the cover film, and the silver paste hardened® film was oriented. The direction was bent in the direction of 180 degrees, and the adhesion strength was measured by stretching at a speed of 50 mm/min. (Evaluation of Conductive Paste: Sliding Bending Test) As described above, the sample was passed through a set maximum temperature of 260. (: After the reflow furnace was performed twice, the sliding bending was performed under the conditions of a stroke of 100 mm, a cycle of 15 seconds, a cycle, and a sliding bending radius of 1. 〇mm, and the number of times of sliding bending when the wiring resistance was increased by 20% was evaluated. Table 1. In each evaluation item, the adhesion strength is ❹ 0.8 N/cm or more, the number of sliding bending is 70,000 times or more, and the volume resistivity is 9 〇χ 10_6 Ω·cm or less. -16- 201030766 oe SI moving 】

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In the total amount of the acid component, the alcohol component, and the isocyanate component, the total amount of the aromatic component contained in the acid component, the alcohol component, and the isocyanate component is less than 5 mol%, based on the total amount of the above-mentioned acid component, alcohol component, and isocyanate component. 1. The adhesion strength after reflow treatment is low and the heat resistance is poor. Similarly, Comparative Example 2, which does not contain an aromatic component in the isocyanate component, has low adhesion strength after reflow treatment and is inferior in heat resistance. Further, in Comparative Example 3 in which the total amount of aromatic components was more than 50 mol%, the adhesive strength was good, but the sliding flexibility was poor. (Examples 4 to 8) The degree of polymerization of the urethane-modified polyester resin was changed to prepare a urethane-modified polyester resin of different oxindole. Using this resin, a conductive paste was produced in the same manner as in Examples 1 to 3, and the adhesion strength, sliding flexibility, and volume resistivity after the reflow treatment were evaluated. The results are shown in Table 2. [Table 2] Example 4 Example 5 Example 6 Example 7 Example 8 Hydroxylhydrazine (mgKOH/g) of a polyester resin 3.5 6.5 34 55 65 Evaluation results Adhesion strength (N/cm) 0.8 1.3 2.5 3.5 3.8 Sliding bending times (10,000 times) 38 36 35 12 7 Volume resistivity (χΙΟ^Ω · cm) 38 40 40 43 41 The urethane of the urethane-modified polyester resin has a positive adhesion strength after reflow treatment. Correlation, the larger the oxon, the higher the adhesion strength. In Example 4, in which the oxindole was less than 5 mgKOH/g, the adhesion strength was 〇8 N/cm, which was slightly lower. Further, in Example 8, in which oxindole exceeded 60 mgKOH/g, the number of sliding bending was slightly biased due to lack of flexibility. low. -18 - 201030766 (Examples 9 to 13) As described in Table 3, a polyfunctionally-blockable polyisocyanate compound having various number average molecular weights was prepared. The polyfunctionally-terminated polyisocyanate compound is one in which the end of the isocyanate monomer and the polyhydroxy compound to be added to the isocyanate is blocked with a blocking agent. Using the same as the urethane-modified polyester resin described in Example 1, the same conductive paste as in Examples 1 to 3 was prepared as the curing agent, and the adhesion strength, sliding flexibility, and volume after the reflow treatment were evaluated. Resistivity. The results are shown in Table 3. [Table 3] Example 9 Example 10 Example 11 Example 12 Example 13 Blocking type isocyanate molecular weight 380 650 1300 2800 3300 Evaluation result Adhesion strength (N/cm) 2.2 2.4 2.5 2.7 2.9 Sliding bending times (10,000 times) 8 12 35 38 39 Volume resistivity (χ10'6Ω · cm) 35 38 40 48 65 Ο All specimens meet the requirements of adhesion strength, sliding bendability and volume resistivity, but multi-functional end capping In Example 9, the number average molecular weight of the polyisocyanate compound was less than 500, and the number of sliding bending was 80,000 times, which was slightly lower. Further, in Example 13, in which the average molecular weight exceeded 30,000, the volume resistivity was slightly higher than 'high. (Examples 1 to 4 8) Using the urethane-modified polyester resin used in Example 1 and a polyfunctionally-terminated polyisocyanate compound, the mixing ratio of the two was changed to change the NCO/OH ratio. Conductive pastes similar to those of Examples 1 to 3, evaluation of adhesion strength, sliding flexibility, and volume resistivity after reflow treatment of -19-201030766. As a result, as shown in Table 4, in Example 14, in which the NCO/OH ratio was less than 0.8, the volume resistivity was slightly higher. It is assumed that this is because the crosslink density is reduced when the NCO/OH ratio is low. Further, in Example 18 in which the NCO/OH ratio exceeded 3.0, the adhesion strength after the reflow treatment was slightly lower. It is assumed that when the NCO/OH ratio is high, the excess hardener remains to reduce the heat resistance. [Table 4] Example 14 Example 15 Example 16 Example 17 Example 18 NCO/OH ratio 0.6 0.9 1.2 2.7 3.3 Evaluation result Adhesion strength (N/cm) 1.3 1.9 2.5 1.1 0.8 Sliding bending times (10,000 times) 9 18 35 31 26 Volume resistivity (χ10'6Ω · cm) 85 48 40 43 46 (Examples 19 to 23) Preparation of metal powder A having an average particle diameter of 4.8 μη and metal powder B having an average particle diameter of 30 nm 0 Conductive metal powder. The content ratio of the metal powder a to the metal powder B was changed to prepare a conductive paste similar to that of the examples 丨 to 3, and the adhesion strength, sliding bending property, and volume resistivity after the reflow treatment were evaluated. The total weight of the metal powder A and the metal powder B to be blended at this time was 2.333 times the weight of the urethane-modified polyester resin and the polyfunctionally-terminated polyisocyanate compound. As a result, as shown in the fifth table, in Example 19, in which the ratio of the amount of the metal powder a to the metal powder B was less than 99.5:0.5, the volume resistivity was slightly higher. Further, the content ratio of the metal powder A to the metal powder b exceeds 70: 30 -20-. 201030766 In Example 23, no improvement in characteristics was observed. Since the metal powder having an average particle diameter of a nanometer size is expensive, considering the relationship between the characteristics of the conductive paste and the cost, the ratio of the content of the metal powder A to the metal powder B is preferably in the range of 99.5:0.5 to 70:30. . [Table 5] Example 19 Example 20 Example 21 Example 22 Example 23 Gold layer m 1 powder A: Metal 艮B ratio 100 : 0 99 : 1 90 : 10 75 : 25 65 : 35 Evaluation result adhesion Strength (N/cm) 2.5 2.5 2.5 2.4 2.3 Sliding bending times (10,000 times) 30 33 35 30 30 Volume resistivity (χ10·6 Ω. cm) 78 42 40 39 40 (Example 2 4~2 8 ) Preparation by average A conductive metal powder composed of a metal powder A having a particle diameter of 4.8 μm and a metal powder B having an average particle diameter of 3 Onra. Here, the content ratio of the fixed metal powder A to the metal powder B is 90:10, but the ratio of the metal powder content of the metal powder A to the metal powder B is changed to prepare a conductive Q paste, and the adhesion strength and sliding after the reflow treatment are evaluated. Flexibility, volume resistivity. As a result, as shown in the sixth table, in Example 24, in which the metal powder content ratio was less than 50% by weight, the volume resistivity was slightly higher. Further, in Example 28, in which the metal powder content ratio exceeded 85% by weight, the sliding flexibility was slightly lower. It is assumed that this is because the softness of the metal powder content ratio is too high. The embodiments and examples presented herein are to be considered as illustrative and not restrictive. The scope of the present invention is defined by the scope of the claims, and is intended to include all modifications of the scope of the invention and the scope of the invention. [Industrial Applicability] The present invention relates to a conductive paste, an electromagnetic wave shielding film using the same, and an electromagnetic shielding flexible printed wiring board, and can be suitably applied to a flexible printed wiring board which is required to have bending resistance. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic cross-sectional view showing an electromagnetic wave shielding film of the present invention. Fig. 2 is a cross-sectional view showing the electromagnetic wave shielding flexible printed wiring board of the present invention. [Main component symbol description] 1,4 Substrate 2 Conductive paste Protective film 5 Copper foil 6a Cover film 6b Cover film adhesive

7 flexible printed wiring board -22-

Claims (1)

.201030766 VII. Patent application scope: 1. A conductive paste characterized in that it contains a conductive metal powder, a urethane-modified polyester resin, and a conductive paste of blocked isocyanate, wherein the amine The urethane-modified polyester resin is obtained by reacting an acid component, an alcohol component, and an isocyanate component containing an aromatic isocyanate, and the acid component, the total amount of the acid component, the alcohol component, and the isocyanate component The total amount of the aromatic steroid component contained in the alcohol component and the isocyanate component is 5 mol% or more and 50 mol% or less. 2. The conductive paste according to claim 1, wherein the urethane-modified polyester resin has a oxindole of 5 mgKOH/g or more and 60 mgKOH/g or less. 3. The conductive paste according to claim 1 or 2, wherein the blocked isocyanate has a number average molecular weight of 500 or more and 3,000 or less, and is an addition of an isocyanate monomer and a polyhydroxy compound by a blocking agent. A polyfunctionally-terminated polyisocyanate compound obtained by blocking an end of an isocyanate. 4. The conductive paste according to any one of claims 1 to 3, wherein a mixing ratio of the urethane-modified polyester resin to the blocked isocyanate is converted into the urethane The molar ratio (NCO/OH) of the hydroxyl group (OH) of the ester-modified polyester resin to the isocyanate group (NCO) of the blocked isocyanate is 0.8 or more and 3.0 or less. 5. As disclosed in the first to The conductive paste according to any one of the items 4, wherein the conductive metal powder is composed of a metal powder having an average particle diameter of 0·5 μm to 20 μm and a metal powder having an average particle diameter of 100 nm or less, and the metal powder-23. - .201030766 The ratio of the content of the final A to the metal powder B is 99.5:0.5 to 70:30 by weight, and the content ratio of the conductive metal powder is 50% by weight with respect to the solid content of the conductive paste. Above 85 wt%. An electromagnetic wave shielding film which is a film having a layer composed of a conductive paste according to any one of items 1 to 5 of the above-mentioned patent application. A electromagnetic wave shielding flexible printed wiring board having a layer composed of the conductive paste of any one of items 1 to 5 of the application specification. -twenty four-