阅读说明：本技术 导电膜的制造方法 (Method for manufacturing conductive film ) 是由 穴井圭 福里骏 于 2018-12-19 设计创作，主要内容包括：在形成含有导电性赋予粒子的组合物的涂膜、并通过对该涂膜的光烧成来制造导电膜的方法中,在上述涂膜的光烧成之前将该涂膜沿其厚度方向压缩。在上述组合物中包含的结合剂的储能模量成为100MPa以下的温度下将上述涂膜压缩是适宜的。按照向厚度方向的压缩率成为25％以上且80％以下的方式将上述涂膜压缩也是适宜的。光烧成工序中的光的照射设定为脉冲光的照射是适宜的。(In a method for forming a coating film of a composition containing conductivity-imparting particles and producing a conductive film by photo-baking the coating film, the coating film is compressed in its thickness direction before photo-baking the coating film. It is preferable that the coating film is compressed at a temperature at which the storage modulus of the binder contained in the composition is 100MPa or less. It is also preferable that the coating film is compressed so that the compression ratio in the thickness direction is 25% to 80%. The irradiation with light in the optical firing step is preferably performed with pulsed light.)

1. A method for producing a conductive film, which comprises forming a coating film of a composition containing conductivity-imparting particles and photo-baking the coating film,

the coating film is compressed in its thickness direction before the photo-firing of the coating film.

2. The production method according to claim 1, wherein the coating film is compressed at a temperature at which a storage modulus of a binder contained in the composition becomes 100MPa or less.

3. The production method according to claim 1 or 2, wherein the coating film is compressed so that a compression ratio in a thickness direction becomes 25% or more and 80% or less.

Technical Field

The present invention relates to a method for manufacturing a conductive film.

Background

As a technique for forming a conductive pattern made of a conductive film on a substrate, for example, the following methods are known: a coating film of a predetermined pattern is formed on a substrate using a conductive ink or a conductive paste formed from a composition containing conductive particles such as metal particles and a binder, and the conductive particles in the coating film are sintered to form a conductive film. For sintering of the conductive particles, a method of heating and baking the coating film is generally used.

The firing temperature varies depending on the type of conductive particles, but it is considered that a high temperature is required to some extent in order to reliably sinter the conductive particles. However, depending on the type of substrate on which the conductive film is formed, there is a limit to increase the firing temperature.

In view of the above, a photo-sintering method has been proposed as a method for sintering conductive particles regardless of the type of substrate. In the photo-sintering method, a coating film is irradiated with light of a predetermined wavelength, whereby conductive particles in the coating film generate heat and inter-particle sintering occurs. For example, patent document 1 describes a method for producing a conductive film, in which a coating film of a coating material containing copper powder is formed on a paper base, the coating film is irradiated with light having a wavelength component in the range of 240 to 600nm to obtain a sintered conductive film, and the sintered conductive film is heated to 90 to 190 ℃ and pressurized together with the paper base to reduce the void volume in the sintered conductive film. Patent document 2 describes a method for producing a conductive film, in which a conductive paste is applied to a substrate, and the substrate is pre-baked, and then irradiated with light and baked to form a conductive film on the substrate, wherein the irradiation with light is performed at a pulse period of 500 to 2000 μ s, a pulse voltage of 1600 to 3800V, and a wavelength of 200 to 800nm, and the conductive film formed on the substrate is subjected to a compression treatment.

Disclosure of Invention

In the photo-sintering method, irradiation with strong light is effective in order to reliably cause sintering of conductive particles. However, in such a case, the binder contained in the conductive composition is decomposed by light to instantaneously generate a large amount of gas, and the conductive particles may be scattered from the coating film before sintering. Such a scattering phenomenon is an obstacle to formation of a good conductive film.

Therefore, an object of the present invention is to improve a method for manufacturing a conductive film, and more specifically, to improve a method for manufacturing a conductive film by a photo-firing method.

The present invention solves the above problems by providing a method for producing a conductive film by forming a coating film of a composition containing conductivity-imparting particles and photo-baking the coating film, wherein the coating film is compressed in the thickness direction thereof before photo-baking the coating film.

Detailed Description

The present invention will be described below based on preferred embodiments. In the present invention, a coating film of a composition containing conductivity-imparting particles is formed, and a conductive film is formed by photo-baking the coating film. The composition preferably contains a binder, a solvent, and the like in addition to the conductivity imparting particles. The composition is generally used in the form of a paste or ink containing these components.

In the present production method, first, a coating film of a composition containing conductivity-imparting particles is formed on a substrate. The method of forming the coating film is appropriately performed depending on the properties of the composition, the pattern of the coating film, and the like. Examples of the method for forming the coating film include screen printing, gravure printing, inkjet printing, transfer printing, laser printing, electrostatic printing, pad printing, spin coating, casting, dip coating, spray coating, and dispensing (dispenser).

Examples of the base material of the coating composition include various synthetic resin films, glass epoxy substrates, phenol resin substrates, liquid crystal polymers, green sheets (green sheets), ceramics, glass plates, and paper. Examples of the synthetic resin include polyimide, polyethylene terephthalate, polyethylene naphthalate, and cycloolefin polymer.

Preferably, a coating film of the composition is formed on one surface of a substrate, and then the coating film is preliminarily dried. The pre-drying may be performed in the atmosphere or in an inert gas atmosphere, for example. The drying conditions vary depending on the constituent components of the coating film and the heat resistance of the substrate, but the temperature is generally preferably 50 ℃ or higher and 250 ℃ or lower, more preferably 60 ℃ or higher and 230 ℃ or lower, and still more preferably 70 ℃ or higher and 200 ℃ or lower. By performing the preliminary drying in this temperature range, the shape retention of the coating film can be improved. Due to this, in the next step, i.e., the compression step, the coating film is compressed mainly in the thickness direction without spreading in the width direction, and therefore a conductive film of good quality can be obtained. The time for the preliminary drying is preferably 0.1 to 5.0 hours, more preferably 0.2 to 3.0 hours, with the temperature of the preliminary drying being in the above range.

After the pre-drying of the coating film is completed in this manner, the coating film is baked by light, but in the present production method, the step of compressing the coating film in the thickness direction thereof is performed before the baking by light of the coating film. By compressing the coating film, voids present in the coating film are reduced and the film density is increased. As a result, excessive movement of the conductivity-imparting particles contained in the coating film can be suppressed in the subsequent photo-baking step, and therefore scattering of the conductivity-imparting particles from the coating film can be effectively prevented. This makes it possible to obtain a conductive film of good quality.

From the viewpoint of more effectively suppressing the scattering of the electrically conductive particles from the coating film in the photo-firing step, the degree of compression of the coating film is preferably 25% or more and 80% or less, more preferably 30% or more and 70% or less, and still more preferably 30% or more and 60% or less, the compression ratio (%) is calculated from { (thickness of coating film before compression-thickness of coating film after compression)/thickness of coating film before compression } × 100.

As means for compressing the coating film, appropriate means is used depending on the kind of the base material. For example, a reciprocating press or a roller press may be used. The pressure during compression may be adjusted so that the compressibility of the coating film is within the above range, and is generally preferably 5MPa or more and 700MPa or less, more preferably 35MPa or more and 600MPa or less, and still more preferably 70MPa or more and 430MPa or less.

The compression of the coating film is preferably performed at a temperature at which the storage modulus of the binder contained in the composition constituting the coating film is 100MPa or less. When the coating film is compressed under such temperature conditions, the binder flows moderately, and therefore, the voids present in the coating film can be further filled. As a result, excessive movement of the conductivity-imparting particles contained in the coating film can be further suppressed in the photo-firing step, so that scattering of the conductivity-imparting particles from the coating film can be effectively prevented, and in addition, the sinterability of the conductivity-imparting particles is improved, and the resistance of the resulting conductive film can be further reduced. From this viewpoint, the storage modulus of the binder at the time of compression of the coating film is more preferably 80MPa or less, and still more preferably 70MPa or less. The lower limit of the storage modulus of the binder at the time of compression of the coating film is not particularly limited, but is preferably 5MPa or more, and more preferably 10MPa or more.

In the case where the storage modulus of the binder is 100MPa or less at room temperature, the compression of the coating film can be performed at room temperature. When the storage modulus of the binder exceeds 100MPa at room temperature, the compression of the coating film is preferably performed in a state where the temperature is raised until the storage modulus of the binder becomes 100MPa or less. The storage modulus of the binder can be determined by dynamic viscoelasticity measurement (DMA). When the storage modulus of the binder exceeds 100MPa at room temperature, the storage modulus of the binder can be determined by measuring the storage modulus of the binder while heating the binder at a temperature at which the storage modulus of the binder is 100MPa or less.

After the coating film is compressed, the coating film is subsequently subjected to a photo-firing step. In the photo-baking step, the coating film is irradiated with light of a predetermined wavelength. The irradiation of light is preferably performed as pulsed light because temperature control can be easily performed. The pulse light is light having a short light irradiation period (irradiation time), and when light irradiation is repeated a plurality of times, light irradiation is performed with a period during which light is not irradiated between the first light irradiation period and the second light irradiation period. The intensity of light may also change during 1 light irradiation.

The pulse width of the pulsed light is preferably 5 μ s or more and 1s or less, and more preferably 20 μ s or more and 10ms or less. The irradiation of the pulsed light may be a single pulse or may be repeated a plurality of times. When the irradiation is repeated a plurality of times, the irradiation interval is preferably 10 μ s or more and 30s or less, and more preferably 20 μ s or more and 10s or less.

As the light source used in the photo-firing step, a light source that emits light of a wavelength that can cause the conductivity-imparting particles to generate heat by irradiation of light is used. For example, a known light source such as a xenon flash lamp can be used. The xenon light has a spectrum covering a wavelength range of 200nm to 800 nm. In the case of using a xenon flash lamp, the pulse amplitude can be set to an optimum condition in a range of 5 μ s to 1s, and the pulse voltage can be set to an optimum condition in a range of 1600V to 3800V.

The conductive film produced by the photo-firing may be subjected to a post-process as necessary. As the post-step, for example, compression treatment can be mentioned. In the interior of the conductive film after photo-firing, many voids are formed due to volatilization of organic components such as a solvent contained in the coating film. When the conductive film is compressed so that the pores are crushed, the conductivity is improved. Further, the conductive film is compressed, which has an advantage of improving adhesion between the conductive film and the base material. For the compression of the conductive film, for example, a roll press may be used.

The conductive film obtained in this way can effectively prevent the conductivity-imparting particles from scattering in the photo-firing step, and therefore, the conductive film becomes a low-resistance film in which the conductivity-imparting particles are densely sintered. Therefore, the conductive film can be used as various electric circuits or electronic circuits. Or may be used as an antenna for RFID or the like.

The conductivity-imparting particles contained in the composition used in the present production method are substances that impart conductivity to a conductive film formed from the composition. The conductivity-imparting particles may have conductivity before the photo-firing, or may be a substance that exhibits conductivity by undergoing a chemical change by the photo-firing. As the conductivity-imparting particles, for example, particles made of metal can be used. Examples of the metal particles include particles of an alloy of gold, silver, copper, nickel, cobalt, zinc, tin, indium, gallium, aluminum, palladium, tantalum, niobium, and a combination of 2 or more kinds thereof. Further, particles in which a coating layer made of another metal is formed on the surface of particles made of these metals may be used. Further, particles in which a coating layer made of an oxide of the metal is formed on the surface of the particles made of the metal may be used. In addition to these particles, metal oxide particles having conductivity or metal oxide particles exhibiting conductivity by reduction can be used as the conductivity-imparting particles. Examples of the metal oxide particles include silver oxide, copper oxide, nickel oxide, cobalt oxide, zinc oxide, tin oxide, and indium tin oxide. The conductivity-imparting particles may be used alone or in combination of 2 or more. Among the above-mentioned conductivity-imparting particles, copper particles are preferably used from the viewpoint of easiness of obtaining, high or low conductivity, and the like.

The shape of the conductivity-imparting particles may be, for example, spherical, plate-like, fibrous, or the like. The conductivity-imparting particles may be 1 kind of these shapes, or may be a combination of 2 or more kinds.

From the viewpoint of obtaining a dense and low-resistance conductive film, the particle diameter of the conductivity-imparting particles is the volume cumulative particle diameter D at 50 vol% of the cumulative volume obtained by the laser diffraction scattering particle size distribution measurement method₅₀Means, preferablyIs 0.01 to 20 μm, more preferably 0.03 to 20 μm, and still more preferably 0.05 to 10 μm. From the same viewpoint, the conductivity-imparting particles may have 1 peak in the particle size distribution curve thereof, or may have 2 or more peaks.

In the composition used in the present production method, it is preferable to use an organic polymer compound as the binder, and examples of the organic polymer compound include polyamide resins, polyester resins such as polyethylene terephthalate, cellulose materials such as ethyl cellulose, methyl cellulose, cellulose acetate butyrate, cellulose acetate propionate, hydroxypropyl methyl cellulose, hydroxyethyl cellulose, propyl cellulose, nitrocellulose, and ethyl hydroxyethyl cellulose, alkyd resins, various acrylic resins such as methacrylate polymers, acrylate-methacrylate copolymers, and butyl methacrylate resins having an acrylic main chain containing acrylic acid or methacrylic acid or esters thereof as a main component, vinyl resins such as polyvinyl alcohol, polyvinyl butyral, and α -methyl styrene polymers, terpene resins, terpene phenol resins, aromatic petroleum resins, hydrogenated petroleum resins, cyclopentadiene petroleum resins, and isoprene resins, and 2 or more of these resins can be used alone or in combination with polybutadiene resins, or 2 or more of these polyether resins can be used in combination.

The binder is preferably incorporated in an amount of 0.1 part by mass or more and 20 parts by mass or less, more preferably 0.5 part by mass or more and 15 parts by mass or less, and still more preferably 1 part by mass or more and 10 parts by mass or less, per 100 parts by mass of the conductivity-imparting particles. By setting the amount of the binder to be in this range, the coating film and the conductive film can be formed smoothly.

The organic solvent may be, for example, ethyl carbitol acetate, terpineol, ethylbenzene, α terpinene, myrcene, dihydroterpinyl acetate monomer or dihydroterpinyl acetate and dihydroterpineol, butyl carbitol acetate, butyl carbitol, pentanediol, limonene, isobornyl phenol, isobornyl cyclohexanol, and the like, and these organic solvents may be used alone in 1 kind or in combination of 2 or more kinds.

The organic solvent is preferably blended in an amount of 1 part by mass or more and 50 parts by mass or less, more preferably 3 parts by mass or more and 45 parts by mass or less, and further preferably 5 parts by mass or more and 40 parts by mass or less, based on 100 parts by mass of the conductivity-imparting particles. By setting the amount of the organic solvent to be in this range, the coating film and the conductive film can be formed smoothly.

In the composition containing the conductivity imparting particles, other components may be blended as necessary in addition to the above-described binder or organic solvent. Examples of such components include photopolymerization initiators, ultraviolet absorbers, sensitizers, sensitizing aids, polymerization inhibitors, plasticizers, thickeners, organic solvents, antioxidants, dispersants, defoaming agents, and organic or inorganic precipitation inhibitors.