JP2013019041A - Method for forming zinc oxide film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a simple method capable of forming a zinc oxide film on both conductive base material and non-conductive base material, without requiring a large scale equipment such as a vacuum exhauster and a heating furnace.SOLUTION: The method of forming the zinc oxide film is characterized in the steps of: forming a polysilazane layer 3 on a base material 1 by coating a solution 2 containing polysilazane and drying it; dipping the base material in an aqueous solution 4 containing zinc ion; and precipitating zinc oxide on the layer of SiOand SiNwhich are generated by reaction between polysilazane and water, and the layer of SiONwhich is an intermediate solid solution of both SiOand SiN, or non-reacted polysilazane layer.

Description

  The present invention relates to a method for forming a zinc oxide film on a substrate, and more particularly to a pretreatment method for a substrate to be plated before electroless plating.

  Zinc oxide is a compound semiconductor having a forbidden band width of about 3.3 eV, and is excellent in optical transparency, piezoelectricity, conductivity, light emission, fluorescence, photocatalytic property, and the like. It is also abundant in resources, such as touch panels, transparent conductive films for solar cells, semiconductor lasers, optical waveguides, sensors for gas or humidity detection, surface acoustic wave elements, light emitting elements, various acoustic elements, thin film varistors, organic systems It is widely applied in a wide range of fields such as electronics fields such as conductive paths of solar cells and chemical industries such as photocatalysts.

  Conventionally, as a method of forming a zinc oxide film, a CVD method, a vapor deposition method, a sputtering method, a dry method such as an MBE method, a wet method such as a spray pyrrolesis method, a sol-gel method, a liquid phase growth method, etc. Attempts have been made to form a film. However, in dry methods such as sputtering, CVD, vapor deposition, and MBE, it is necessary to carry out processing such as depressurization or gas mixing in the film formation chamber and heating of the substrate during film formation. A large-scale manufacturing device including a material heating device, a high-frequency power source, and the like is required. Furthermore, these methods have the disadvantages that the film formation rate is slow and it is difficult to control the composition and film thickness.

  Also in the spray pyrolysis method and the sol-gel method, in order to obtain a zinc oxide film, it is necessary to heat at 300 to 900 ° C. after film formation on a base material. There is a problem that a low melting point material cannot be used as a base material.

  As another method for producing a zinc oxide film, for example, a technique for depositing a sponge-like zinc oxide film on a conductive substrate by electrolytic plating from an aqueous solution containing zinc ions as a semiconductor layer of a dye-sensitized solar cell is disclosed. (Patent Document 1). However, since this method is electroplating, it is necessary that the substrate on which the zinc oxide film is to be formed has good conductivity, and the zinc oxide film is formed on a non-conductive substrate such as plastic or glass. It cannot be formed.

  On the other hand, there is electroless plating as a method of creating a zinc oxide film on a non-conductive substrate. In this plating method, tin is adsorbed on a substrate by sensitizing using a solution containing tin chloride to a non-conductive substrate, and the palladium catalyst is applied to the substrate surface by activation using a solution containing palladium chloride. To give. Thereafter, it is known that a zinc oxide film can be obtained by immersing the base material in a bath obtained by adding dimethylamine borane (DMAB) to zinc nitrate (Patent Document 2). Patent Documents 3 and 4 also disclose techniques for forming a zinc oxide film by electroless plating, which also contain DMAB in the bath.

  However, this bath contains a reducing agent in addition to the DMAB metal salt. Therefore, the stability of the bath is poor, and the plating bath may be decomposed when conditions such as the composition and temperature of the bath cannot be properly managed.

  In addition, when tin chloride used in the sensitizing step is oxidized in a solution, it is deactivated as a catalyst, so that handling thereof is difficult, and man-hours increase, resulting in high costs.

  On the other hand, in the field of organic thin film solar cells, it is studied to deposit zinc oxide in an aqueous solution in the form of needles. As a method for obtaining acicular zinc oxide in this case, a solution in which equimolar amount of hexamethylenetetraamine (HMTA) is added to zinc nitrate is prepared, and a group to which zinc oxide to be a seed crystal is attached is prepared. By immersing the material, acicular zinc oxide can be grown.

  In this case, HMTA is understood to have a role of increasing pH in the vicinity of the plating interface for depositing zinc oxide or a function of complexing zinc ions (Non-patent Document 1). However, in the bath using HMTA, although zinc oxide is deposited on the substrate, zinc oxide particles are deposited when the solution is heated. That is, there is a problem that it is difficult to use as a plating bath because decomposition of the bath occurs.

JP 2004-6235 A Japanese Patent No. 3256676 JP 2005-235242 A WO2008 / 126729

L.E.Greene, et.al., Inorg.Chem., 2006,45,7536-7543.

  The present invention has been made in view of the above problems, and the main object of the present invention is to provide a non-conductive group on a conductive substrate without requiring large-scale equipment such as a vacuum exhaust apparatus or a heating furnace. It is to provide a simple method capable of forming a zinc oxide film on a material.

The invention according to claim 1 for achieving the above object is the following: an aqueous solution containing zinc ions after forming a polysilazane layer by applying and drying a solution containing polysilazane on the substrate; Zinc oxide film characterized by depositing zinc oxide on SiO ₂ , Si ₃ N ₄ and both intermediate solid solution SiO _x N _y layers of polysilazane which has been immersed in water and reacted with water, or unreacted polysilazane layer This is a forming method.

  The invention according to claim 2 is the method for forming a zinc oxide film according to claim 1, wherein the zinc ion source is zinc nitrate.

  The invention according to claim 3 is the method for forming a zinc oxide film according to claim 1 or 2, wherein the temperature of the aqueous solution containing zinc ions is in the range of 30 ° C to 90 ° C. It is what.

According to the present invention, since the plating bath has a composition that does not include a reducing agent in the bath, decomposition of the bath due to the action of the reducing agent outside the vicinity of the surface of the object to be plated can be avoided.
Moreover, it becomes possible to obtain the zinc oxide film | membrane excellent in adhesiveness with a base material by using polysilazane as an intermediate | middle layer which deposits zinc oxide on it as a plating film.
Furthermore, as the catalyst application step, there is no step of applying a catalyst such as a sensitizing-activation method, a catalyst-accelerator method, or an alkaline catalyst method, and it is only necessary to apply a solution containing polysilazane.
Accordingly, it has become possible to easily form a zinc oxide film on a non-conductive substrate and a conductive substrate at low cost.

The example of the ultraviolet-visible transmittance | permeability measurement result of the membrane | film | coat produced by the Example of this invention is shown. (A)-(e) It is process drawing explaining the manufacturing method of the zinc oxide membrane | film | coat which becomes this invention.

The present invention is based on the knowledge that when ammonia is generated from the vicinity of the object to be plated and the pH is increased from the surroundings only in the vicinity of the object to be plated, zinc oxide is precipitated in the pH increasing region.
Hereinafter, the process for realizing it, the electroless plating bath composition, and the plating conditions will be described with reference to FIG.

  The composition used in the present invention is an aqueous solution containing a polysilazane solution and zinc ions applied to an object to be plated.

  As a compound serving as a source of zinc ions, a water-soluble zinc salt may be used. Specific examples thereof include zinc nitrate, zinc sulfate, zinc chloride, zinc acetate, zinc phosphate, zinc pyrophosphate, and zinc carbonate. Can be mentioned. Each of the compounds can be used alone or in combination of two or more. In addition, when the pH increases to 6.0 or more when these zinc salts are dissolved in water, precipitates are generated in the plating bath. Therefore, use after lowering the pH with sulfuric acid, hydrochloric acid or the like. desirable. When zinc nitrate is used alone, the pH is 6 or less when dissolved in water, so there is no need to adjust the pH. Therefore, there are few unnecessary components in the bath, and a high purity zinc oxide film is formed. Is possible.

  In the present invention, the concentration of zinc ions in the aqueous solution can be adjusted in a wide range. However, when the zinc concentration is too low, zinc does not precipitate. In addition, when the zinc concentration is too high, the salt containing zinc becomes saturated and does not dissolve more than a certain amount. Therefore, the concentration of zinc ions is 0.001 mol / l to 0.5 mol / l (0.001 in terms of zinc content). 065-32.7 g / l), preferably 0.01 mol / l to 0.2 mol / l (in terms of zinc content, 0.65 to 13 g / l). More preferred.

  As the substrate 1 to be plated, a metal material such as copper, iron, and aluminum, a conductive glass such as NESA glass and ITO glass, a non-conductive glass material such as soda lime glass and alkali-free glass, a ceramic material, Examples include plastic materials.

  Examples of plastic materials include polyester resins such as polyethylene terephthalate resin (PET resin) and polyethylene naphthalate (PEN resin), polyethylene resins, polypropylene resins, methacrylic resins, polylactic acid resins, and polymethylpentene resins. , Cyclic polyolefin resin, polystyrene resin, acrylonitrile- (poly) styrene copolymer (AS resin), acrylonitrile-butadiene-styrene copolymer (ABS resin), polyvinyl chloride resin, poly (meth) acrylic resin Polycarbonate resin, polyester resin, polyamide resin, polyimide resin, polyamideimide resin, polyarylphthalate resin, silicone resin, polysulfone resin, polyphenylene sulfide resin, (Ether sulfone) resins, polyetherimide resins, epoxy resins, polyurethane resins, acetal resins, cellulose resins and the like.

  Among the above-mentioned resins, polyester resins and cyclic polyolefin resins are preferably used as those having a good balance of high heat resistance, strength, weather resistance, durability, water vapor barrier properties, and the like.

The base material 1 to be plated is required to be coated with polysilazane 3 on the surface.
Moreover, in order to improve adhesiveness with polysilazane, the easily bonding layer may be provided on the said base material 1. FIG.

  As a method for applying the polysilazane-containing solution 2 to the base material 1 to be plated, an appropriate method according to the base material may be used. Specific examples include gravure printing, microgravure printing, reverse gravure printing, comma coating, bar coating, spin coating, roll coating, flow coating, ink jet, spray coating, dip coating, flexographic printing, etc. (FIG. 2B).

  In addition, when gravure printing, flexographic printing, or inkjet printing is used, a desired pattern such as a geometric pattern can be created. In addition, as a drying method, the heat drying which hold | maintains at the temperature which a solvent dries for a fixed time may be sufficient, but you may leave in the air.

The polysilazane 3 that covers the substrate 1 to be plated is a polymer having a silicon-nitrogen bond, and is made of Si—N, Si—H, NH, or the like, SiO ₂ , Si ₃ N ₄ , and both It is an inorganic polymer which becomes a precursor of a ceramic such as an intermediate solid solution of SiO _x N _y .

  The polysilazane is a compound represented by the following chemical formula 1.

Here, each of R1, R2, and R3 in the formula is a hydrogen atom, an alkyl group, an alkenyl group, a cycloalkyl group, an aryl group, an alkylsilyl group, an alkylamino group, an alkoxy group, etc. Perhydropolysilazane in which all of R1, R2 and R3 are hydrogen atoms is particularly preferred from the viewpoint of the denseness as a gas barrier film.

  Perhydropolysilazane is presumed to have a linear structure and a ring structure centered on 6- and 8-membered rings. The molecular weight is about 600 to 2000 (polystyrene conversion) in terms of number average molecular weight (Mn), is a liquid or solid substance, and varies depending on the molecular weight. These are marketed in a solution state dissolved in an organic solvent, and the commercially available product can be used as it is as a polysilazane-containing coating solution.

  In addition, as a solvent to contain polysilazane, it is not preferable to use a solvent containing alcohol or water that easily reacts with polysilazane. Specifically, hydrocarbon solvents such as aliphatic hydrocarbons, alicyclic hydrocarbons and aromatic hydrocarbons, ethers such as halogenated hydrocarbon solvents, aliphatic ethers and alicyclic ethers can be used.

  Specific examples include hydrocarbons such as pentane, hexane, cyclohexane, toluene, xylene, solvesso and turben, halogen hydrocarbons such as methylene chloride and chloroform, ethers such as dibutyl ether, dioxane and tetrahydrofuran. These solvents may be selected according to the purpose such as the solubility of polysilazane and the evaporation rate of the solvent, and a plurality of solvents may be mixed.

  The polysilazane concentration in the polysilazane-containing solution 2 is about 0.2 to 35% by mass, although it varies depending on the target silica film thickness and the pot life of the coating solution.

When polysilazane is applied and immersed in an aqueous zinc solution, the polysilazane reacts with water to become a ceramic such as SiO ₂ , Si ₃ N ₄ , and both intermediate solid solutions SiO _x N _y . In order to promote the conversion to the silicon oxide compound, an amine or metal catalyst may be added. About these, it is possible to obtain as a commercial item, specifically, AZ Electronic Materials Co., Ltd. product Aquamica NAX120, NN110, NN120, NN310, NN320, NL110A, NL120A, NP110, NP140, NP344, SP140, etc. Is mentioned.

  Using the polysilazane composition having the above composition, the target zinc oxide film can be formed by simply applying the polysilazane-containing solution 2 to the substrate 1 and then immersing in the aqueous zinc solution 4.

  When the plating bath 6 is set to a low temperature, zinc hydroxide is precipitated, and when the plating bath is set to a high temperature, the plating bath 6 is made of polysilazane and water. The conversion reaction to the silicon compound is accelerated and the adhesion between the compound after the conversion reaction and the substrate is lowered, resulting in a weak adhesion between the zinc oxide film and the substrate. Therefore, it is preferable to set it as about 40-90 degreeC. In particular, it is more preferably about 50 to 80 ° C. in terms of having zinc oxide and having adhesiveness.

  On the other hand, the pH of the plating bath 6 is not particularly limited. However, when the pH is low, the stability of the bath is improved, but the film formation rate is reduced. On the other hand, when the pH is high, the film is formed. Although the speed is improved, the stability of the bath is lowered and precipitation is likely to be generated, making it difficult to obtain a zinc oxide film.

  When immersing the base material 1 in the plating bath 6, the plating bath may be either unstirred or stirred, and a known stirring method can be appropriately employed as a stirring method. In the present invention, ammonia and hydrogen gas are generated from the object to be plated at the time of plating. Therefore, it is more preferable to perform a defoaming treatment using a cylinder shock or ultrasonic waves (FIG. 2D).

  After the zinc oxide film is formed, post-treatment operations performed by normal electroless plating such as water washing and drying can be performed (FIG. 2 (e)).

The reason why a zinc oxide film is formed in the present invention is presumed as follows.
First, reaction mechanisms shown in Chemical Formulas 2 to 5 are known as reaction formulas of zinc oxide generated by electroless plating using DMAB.

In Chemical Formula 2 to Chemical Formula 5, DMAB reduces nitrate ions in Chemical Formula 3, and at this time, OH ⁻ is generated. As a result of this OH ⁻ increasing the pH in the vicinity of the object to be plated, zinc hydroxide is formed (Chemical Formula 4), and then stable zinc oxide (Chemical Formula 5) is obtained when returning to the vicinity of neutrality which is the atmosphere of the solution. .

On the other hand, the polysilazane according to the present invention releases ammonia when it reacts with moisture (Chemical Formula 6).
As a result, it is believed that the pH in the vicinity of the object to be plated is increased, zinc hydroxide is formed, and thereafter stable zinc oxide is obtained in the vicinity of neutrality.
From these points, the pH of the plating bath is preferably 1.0 to 6.0, and particularly preferably 4.0 to 6.0.

Examples and comparative examples are shown below.
(Examples 1-12)
First, a PET film (A4300, manufactured by Toyobo Co., Ltd.) having an easy adhesion layer was used as the substrate 1 to be plated. Next, the object to be plated was processed. For the treatment of the object to be plated, the polysilazane solution 2 (AQUAMICA NL120A-20, manufactured by AZ Electronics Co., Ltd.) was diluted 2-fold with thinner (AQUAMICA Cinner 01, manufactured by AZ Electronics Co., Ltd.) on the previously prepared PET film. After applying the solution so that the film thickness becomes 0.2 μm by dip coating (pickup speed 0.5 m / min), a treatment for drying in the air at room temperature for 10 minutes was performed (FIG. 2B). ).

  Next, Table 1. Plating was performed for 20 minutes under the plating bath conditions (FIG. 2D). In addition, the compounding quantity in a bath composition was shown by mol / l. Table 1 also shows the results in addition to the processing conditions.

(Comparative Examples 1-5)
About Comparative Examples 1-3, after performing the to-be-plated object process similarly to the Example, it plated by changing a bath composition or bath conditions.
Moreover, about the comparative examples 4 and 5, it plated about the thing to which the to-be-plated object process did not perform the process different from an Example, or the process itself. In addition, HMTA application | coating of the comparative example 4 is what apply | coated 0.1 mol / l HMTA aqueous solution on a PET film by dip coating. A list of processing conditions and results is listed in Table 2.

  As for the evaluation of the bath stability, whether or not a precipitate was generated in the bath after plating was visually observed. In addition, the presence or absence of film formation was observed using an optical microscope. The state where the film was formed uniformly was ○, the state where the film was not formed was ×, the film was formed, but zinc oxide and the substrate Those that peeled and blistered between were marked with Δ. Moreover, in order to confirm the production | generation of a zinc oxide, it measured using the ultraviolet visible spectrophotometer in the range of 200-900 nm (UV-2550, Shimadzu Corporation make).

  From Table 1, after applying polysilazane, a zinc oxide film could be formed by setting the bath composition and bath conditions to 1-12. FIG. 1 shows an example of the UV-visible transmittance measurement result of a film having a zinc oxide film.

On the other hand, when the plating temperature was 25 ° C. (Comparative Example 1), although a white film was deposited, zinc oxide was not deposited. In addition, when the plating temperature is 95 ° C. (Comparative Example 2), although a zinc oxide film is obtained in part, the adhesion between the base material and the zinc oxide film is weak, and the bulk of the zinc oxide film occurs. However, it was easy to drop off when it was rubbed with a finger.
On the other hand, in the bath containing HMTA in the plating bath composition (Comparative Example 3), decomposition of the bath occurred.
Moreover, the plating film did not arise about the comparative example 4 which performed the pretreatment immersed in the HMTA aqueous solution, and the comparison 5 which did not perform to-be-plated thing processing.

  In the present invention, a solution containing polysilazane is applied as a treatment of an object to be plated, a water-soluble salt containing zinc is used as a plating bath, and a plating temperature is appropriately selected to uniformly oxidize the substrate. Zinc can be formed (FIG. 2E).

1, base material 2, polysilazane-containing solution 3, polysilazane 4, zinc ion-containing plating solution 5, zinc oxide film 6, plating bath

Claims (3)

After applying a polysilazane-containing solution on the substrate and drying to form a polysilazane layer, the substrate is immersed in an aqueous solution containing zinc ions, and the polysilazane reacts with water, SiO ₂ , Si ₃ N ₄ , And a method of forming a zinc oxide film, characterized in that zinc oxide is deposited on both intermediate solid solution SiO _x N _y layers or unreacted polysilazane layers.   The method for forming a zinc oxide film according to claim 1, wherein the zinc ion source is zinc nitrate.   The method for forming a zinc oxide film according to claim 1 or 2, wherein the temperature of the aqueous solution containing zinc ions is in the range of 30C to 90C.