JP7465001B2 - Coating materials for solar panels - Google Patents

Description

The present invention relates to a coating material for solar panels.

An anti-reflection film that reduces light reflection is formed on the surface of the cover glass (reinforced glass) of the solar cell panel in order to allow more sunlight to be incident on the solar cell body. For example, Patent Document 1 describes an anti-reflection film-coated substrate having an anti-reflection film containing hollow silica particles on the surface of a transparent substrate.

JP 2008-139581 A

By the way, the anti-reflection film maintains the stability of the film by increasing the adhesion to the glass surface of the solar cell panel, and as a result, the reflection of sunlight is reduced.
An object of the present invention is to provide a coating material for a solar cell panel which, when applied to the glass surface of a solar cell panel, forms an anti-reflection film that reduces the reflection of sunlight.

According to the present invention, there is provided a coating material for solar cell panels, which is an aqueous dispersion containing a hydrolyzable organosilane, an alkali metal silicate, and silica particles having an average particle size of 1 nm to 100 nm in water, wherein the aqueous dispersion contains 5 parts by weight to 30 parts by weight of the alkali metal silicate and 1,000 parts by weight to 3,000 parts by weight of the silica particles per 100 parts by weight of the hydrolyzable organosilane.
Here, the hydrolyzable organosilane is preferably a tetrafunctional hydrolyzable alkoxysilane.
The alkali metal silicate is preferably sodium silicate.
Furthermore, the silica particles are preferably a mixture of 20% by weight to 40% by weight of spherical silica particles having an average particle size of 1 nm to 100 nm and 60% by weight to 80% by weight of chain silica particles having an average length of 30 nm to 200 nm (however, the total of the spherical silica particles and the chain silica particles in the mixture is 100% by weight).

The present invention provides a coating material for solar cell panels that forms an anti-reflective film that reduces the reflection of sunlight when applied to the glass surface of a solar cell panel.

The following describes the form for carrying out the present invention (hereinafter, "embodiment"). Note that the present invention is not limited to the following embodiment, and can be carried out in various modifications within the scope of the gist of the invention.

(Hydrolyzable organosilanes)
The hydrolyzable organosilane used in the present embodiment is a silicon compound having a hydrolyzable group in the molecule that is hydrolyzed in the presence of an acidic or basic catalyst. Examples of the hydrolyzable group that the hydrolyzable organosilane has include an alkoxy group, an acetoxy group, an oxime group, an enoxy group, an amino group, an aminoxy group, and an amide group. Among these, a hydrolyzable alkoxysilane having an alkoxy group is preferred.

Examples of hydrolyzable alkoxysilanes include tetrafunctional hydrolyzable alkoxysilanes, trifunctional hydrolyzable alkoxysilanes, and difunctional hydrolyzable alkoxysilanes. Among these, tetrafunctional hydrolyzable alkoxysilanes are preferred.
Examples of the tetrafunctional hydrolyzable alkoxysilane include tetraalkoxysilanes such as tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetrabutoxysilane.

Examples of trifunctional hydrolyzable alkoxysilanes include trialkoxysilanes such as methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, propyltrimethoxysilane, propyltriethoxysilane, butyltrimethoxysilane, butyltriethoxysilane, pentyltrimethoxysilane, pentyltriethoxysilane, hexyltrimethoxysilane, hexyltriethoxysilane, heptyltrimethoxysilane, heptyltriethoxysilane, octyltrimethoxysilane, octyltriethoxysilane, stearyltrimethoxysilane, stearyltriethoxysilane, 3-chloropropyltrimethoxysilane, 3-chloropropyltriethoxysilane, 3-hydroxypropyltrimethoxysilane, 3-hydroxypropyltriethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, trifluoropropyltrimethoxysilane, and trifluoropropyltriethoxysilane.

Examples of bifunctional hydrolyzable alkoxysilanes include dialkoxysilanes such as dimethyldimethoxysilane, dimethyldiethoxysilane, etc. These compounds may be used alone or in combination of two or more kinds.
Among the above alkoxysilanes, tetraalkoxysilanes such as tetramethoxysilane and tetraethoxysilane, and trialkoxysilanes such as methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, etc. are preferred. Furthermore, tetraalkoxysilanes are preferred, with tetraethoxysilane (TEOS) being particularly preferred.

Examples of acidic catalysts used in the hydrolysis reaction of hydrolyzable alkoxysilanes include organic acids such as acetic acid, chloroacetic acid, citric acid, benzoic acid, dimethylmalonic acid, formic acid, propionic acid, glutaric acid, glycolic acid, maleic acid, malonic acid, toluenesulfonic acid, and oxalic acid; and inorganic acids such as hydrochloric acid, nitric acid, and halogenated silanes. Examples of basic catalysts include ammonia. These catalysts can be used alone or in combination. The amount of acidic catalyst used is usually in the range of 0.5 to 15 parts by weight per 100 parts by weight of hydrolyzable alkoxysilane.

Hydrolyzable alkoxysilanes are usually hydrophobic, so it is preferable to use an organic solvent that is miscible with both the hydrolyzable alkoxysilane and water as a common solvent for the hydrolysis reaction. In this case, it is preferable to dilute the hydrolyzable alkoxysilane and water separately with an organic solvent and then mix the two. The weight ratio of the organic solvent to water used is usually in the range of (organic solvent 2-15):(water 85-98) (however, the total of the organic solvent and water is 100).

Examples of organic solvents include alcohols such as methanol, ethanol, propanol, and butanol; ketones such as acetone and methyl ethyl ketone; aromatic hydrocarbons such as benzene, toluene, and xylene; glycols such as ethylene glycol, propylene glycol, and hexylene glycol; glycol ethers such as ethyl cellosolve, butyl cellosolve, ethyl carbitol, butyl carbitol, diethyl cellosolve, and diethyl carbitol; N-methylpyrrolidone, dimethylformamide, and the like. Among these, alcohols are preferred, and ethanol is particularly preferred. These organic solvents can be used alone or in combination of two or more kinds.

(alkali metal silicate)
Examples of the alkali metal silicate used in this embodiment include sodium silicate (water glass), potassium silicate, lithium silicate, and ammonium silicate.
The alkali metal silicate is thought to act as a binder for the anti-reflective film formed by applying the solar cell panel coating material to the tempered glass surface of the solar cell panel.

When an alkali metal silicate is added, it is preferable to use boric acid or a boric acid compound as a hardener. Here, boric acid is a general term for acids having a composition of (xB ₂ O ₃ .yH ₂ O), and specific examples include orthoboric acid (H ₃ BO ₃ ), metaboric acid (HBO ₂ ), and tetraboric acid (H ₂ B ₄ O ₇ ). It is believed that when an alkali metal silicate is mixed with boric acid or a boric acid compound, the alkali metal silicate gels, and the anti-reflective film formed is fixed to the surface of the reinforced glass of the solar cell panel. The amount of boric acid or a boric acid compound added is usually in the range of 10 parts by weight to 700 parts by weight per 100 parts by weight of the alkali metal silicate.

In this embodiment, when an alkali metal silicate is added, other additives can be added as necessary. Examples of additives include inorganic acid salts such as magnesium hydroxide, calcium hydroxide, magnesium carbonate, calcium carbonate, magnesium chloride, and calcium chloride; and organic acid salts such as magnesium acetate, calcium acetate, magnesium citrate, and calcium citrate. The amount of other additives added is usually in the range of 5 parts by weight to 20 parts by weight per 100 parts by weight of the alkali metal silicate.

(Silica particles)
The silica particles used in this embodiment are preferably fine silica particles having an average particle size of 1 nm to 100 nm. In this embodiment, colloidal silica in which such fine silica particles are stably dispersed in a liquid medium is used. Colloidal silica usually contains 15% to 50% by weight of silica particles as a solid content, and the amount of silica particles to be blended can be determined from this value.
As the colloidal silica, for example, a non-aqueous organic solvent-dispersed colloidal silica (organosilica sol) is preferable. Organosilica sol is a colloidal solution in which nano-level colloidal silica is stably dispersed in an organic solvent. Such fine silica particles are considered to be the main agent for forming an anti-reflection film on the glass surface of a solar panel.

Organic solvent-dispersed colloidal silica (organosilica sol) is readily available as a commercial product. The organic solvent for organic solvent-dispersed colloidal silica is not particularly limited as long as it is a hydrophilic organic solvent. Examples include lower aliphatic alcohols such as methanol, ethanol, i-propanol, n-butanol, and i-butanol; ethylene glycol derivatives such as ethylene glycol, ethylene glycol monobutyl ether, and ethylene glycol monoethyl ether acetate; diethylene glycol derivatives such as diethylene glycol and diethylene glycol monobutyl ether; and diacetone alcohol. These hydrophilic organic solvents can be used alone or in a mixture of two or more kinds. The above hydrophilic organic solvents can also be used in combination with one or more organic solvents such as toluene, xylene, hexane, heptane, ethyl acetate, butyl acetate, methyl ethyl ketone, methyl isobutyl ketone, and methyl ethyl ketoxime.

The shape of the fine silica particles may be a spherical structure (spherical silica), a chain structure (chain silica), a pearl-like structure, etc. Colloidal silica having a spherical structure, a chain structure, and a pearl-like structure may be used in combination.
Here, the spherical silica is usually silica fine particles having an average particle size selected within the range of 1 nm to 100 nm, preferably 5 nm to 80 nm. Chain silica refers to silica fine particles that are continuously chained together by chemical bonds such as siloxane bonds, and examples of such silica fine particles include those that extend linearly and those that are curved two-dimensionally or three-dimensionally. Chain silica is usually silica fine particles with an average particle size of 10 nm to 25 nm that are continuously chained together to have an average length of 30 nm to 200 nm.

In this embodiment, the silica particles are preferably a mixture of 20% to 50% by weight of spherical silica particles and 50% to 80% by weight of chain silica particles (wherein the total of the spherical silica particles and the chain silica particles in the mixture is 100% by weight). By using a mixture of spherical silica sol and chain silica sol, the strength of the coating film formed on the tempered glass surface of the solar cell panel is improved, and adhesion to the tempered glass surface tends to increase.

The coating material for solar panels to which this embodiment is applied is an aqueous dispersion containing the above-mentioned hydrolyzable organosilane, alkali metal silicate, and silica particles with an average particle size of 1 nm to 100 nm in water, and each component is contained in the aqueous dispersion in the range of 5 parts by weight to 30 parts by weight of alkali metal silicate and 1,000 parts by weight to 3,000 parts by weight of silica particles per 100 parts by weight of hydrolyzable organosilane.

Here, the water used in the aqueous dispersion containing the above-mentioned components is not particularly limited, and for example, tap water can be used. Deionized water, pure water, and ultrapure water may also be used. Desalted water is used when there is a risk of corrosion of metal materials, and pure water or ultrapure water is used when the inclusion of impurities is undesirable. In this embodiment, it is preferable to use pure water.
In the present embodiment, the concentration of the hydrolyzable alkoxysilane in the coating material for solar cell panels as an aqueous dispersion is usually in the range of 0.03% by weight to 5% by weight, and the concentration of the solid content in the coating material for solar cell panels is usually in the range of 0.5% by weight to 20% by weight, preferably 1% by weight to 10% by weight.

(Method of preparing a coating material for solar cell panels)
The method for preparing the coating material for solar cell panels to which the present embodiment is applied is not particularly limited. For example, the method includes adding the above-mentioned hydrolyzable organosilane, alkali metal silicate, and silica particles having an average particle size of 1 nm to 100 nm to, for example, pure water in a predetermined container and preparing by stirring and mixing (lump preparation method); and the method includes preparing an aqueous solution of the hydrolyzable organosilane and an aqueous solution of the alkali metal silicate separately, and preparing by stirring and mixing these together with silica particles having an average particle size of 1 nm to 100 nm and pure water (split preparation method).

In the case of the above-mentioned divisional mixing method, the aqueous solution of the hydrolyzable organosilane is preferably prepared by adding predetermined amounts of an organic solvent, an aqueous solution of an acidic or basic catalyst, and the hydrolyzable organosilane, and stirring them. The organic solvent is diluted with water beforehand before addition. The aqueous solution of the acidic or basic catalyst is preferably prepared to have a concentration of about 1 mol/L to 3 mol/L. The hydrolyzable organosilane is also preferably diluted with an organic solvent. The concentration of the hydrolyzable organosilane in such an aqueous solution is usually in the range of 0.2% by weight to 10% by weight, and preferably in the range of 0.5% by weight to 5% by weight.
The concentration of the alkali metal silicate contained in the aqueous solution of the alkali metal silicate is usually in the range of 0.05% by weight to 1% by weight, and preferably in the range of 0.1% by weight to 0.5% by weight.

Next, in another container, the aqueous solution of hydrolyzable organosilane and the aqueous solution of alkali metal silicate are mixed, and further, organosilica sol is added, and pure water is added to prepare a coating material for solar panels. Here, as described above, it is preferable to add spherical silica sol with an average particle size of 1 nm to 100 nm and chain silica sol with an average length of 30 nm to 200 nm as silica particles. The spherical silica sol and chain silica sol can be added separately, or mixed in advance, or added in portions, or any other method can be appropriately selected.

The coating material for solar cell panels prepared by the above-mentioned operation is applied to the tempered glass surface of the solar cell panel to form a coating layer. The application method is not particularly limited, and includes known general methods. Specific examples include brush application, screen printing, spray coating, spin coating, dip coating, etc.
The thickness of the coating layer is appropriately selected and is not particularly limited, but is usually in the range of 50 nm to 100 nm.

The coating layer formed on the tempered glass surface of a solar panel functions as an anti-reflective film. Normally, when the difference in refractive index between air and tempered glass is large, the reflected light becomes stronger, but by forming a coating layer on the tempered glass surface of a solar panel, the reflection of sunlight is suppressed. In this case, since the coating layer has a refractive index between air and tempered glass, light incident from the surface of the coating layer passes through air → coating layer → tempered glass, increasing the amount of transmitted light that reaches the solar cell. As a result, it is expected that the amount of electricity generated by the solar panel will increase.

The present embodiment will be described in more detail below based on examples. Note that the present embodiment is not limited to the following examples.

(Preparation of coating material for solar panel)
(1) Aqueous tetraethoxysilane solution Ethyl alcohol (manufactured by Wako Pure Chemical Industries, Ltd.), an aqueous hydrochloric acid solution (concentration: 2 mol/L), and tetraethoxysilane (manufactured by Tokyo Chemical Industry Co., Ltd.) were added to a first vessel, and pure water was added and stirred to prepare an aqueous tetraethoxysilane solution. The concentration of tetraethoxysilane in the prepared aqueous tetraethoxysilane solution was 1.09% by weight.
The ratio of each component in the tetraethoxysilane aqueous solution was 100 parts by weight of tetraethoxysilane, 816 parts by weight of ethyl alcohol, and 11 parts by weight of an aqueous hydrochloric acid solution (concentration: 2 mol/L).
(2) Sodium silicate aqueous solution Boric acid (manufactured by Wako Pure Chemical Industries, Ltd.), sodium silicate (water glass: manufactured by Kanto Chemical Co., Ltd.), and magnesium hydroxide (manufactured by Kanto Chemical Co., Ltd.) were added to a second container, and pure water was added and stirred to prepare a sodium silicate aqueous solution. The sodium silicate concentration in the prepared sodium silicate aqueous solution was 0.28% by weight.
The ratio of each component in the sodium silicate aqueous solution was 100 parts by weight of sodium silicate (water glass), 584 parts by weight of boric acid, and 13 parts by weight of magnesium hydroxide.

Next, the above-mentioned tetraethoxysilane aqueous solution and sodium silicate aqueous solution % were placed in a third container, and further a methanol silica sol containing spherical silica particles (solid content 30% by weight) (manufactured by Nissan Chemical Industries, Ltd.) and a chain methanol silica sol containing chain silica particles (solid content 20% by weight) (MA-ST-UP manufactured by Nissan Chemical Industries, Ltd.) were added, and pure water was added and stirred to prepare a coating material for solar cell panels in the form of an aqueous dispersion with a solid content concentration of 1.53% by weight.
The ratio of each component in the above-mentioned aqueous dispersion is 100 parts by weight of tetraethoxysilane, 15.6 parts by weight of sodium silicate, 577 parts by weight of spherical silica particles (contained in methanol silica sol (solid content 30% by weight)), and 1064 parts by weight of chain silica particles (contained in chain methanol silica sol (solid content 20% by weight)).

(Measurement of visible light transmittance)
The above-mentioned coating material for solar cell panels was applied to the surface of a glass plate (thickness 3.2 mm) and dried to form a coating layer having a thickness of 50 nm to 100 nm.
Next, the transmittance of the glass plate having the coating layer formed on its surface in the visible light region (wavelength 350 nm to 800 nm) was measured using a commercially available visible light transmittance meter. For comparison, the transmittance of a glass plate having no coating layer formed thereon was also measured under the same conditions. The results are shown in Table 1.

From the results in Table 1, it can be seen that the transmittance in the visible light region (wavelength 350 nm to 800 nm) of the glass plate on which a coating layer is formed by applying the above-mentioned coating material for a solar cell panel is increased compared to the glass plate without a coating layer.
As a result, a solar cell panel having a glass plate on the light-gathering side to which a coating layer is formed by applying a coating material for solar cell panels is expected to increase the amount of sunlight reaching the solar cell and thus increase the amount of electricity generated.

Claims (1)

An aqueous dispersion comprising tetraalkoxysilane, sodium silicate , boric acid or a boric acid compound, and silica particles having an average particle size of 1 nm to 100 nm in water,
The aqueous dispersion contains 5 to 30 parts by weight of the sodium silicate and 1,000 to 3,000 parts by weight of the silica particles, relative to 100 parts by weight of the tetraalkoxysilane;
The boric acid or the boric acid compound is contained in an amount of 10 to 700 parts by weight per 100 parts by weight of the sodium silicate ,
The silica particles are a mixture of 20% by weight to 40% by weight of spherical silica particles having an average particle size of 1 nm to 100 nm and 60% by weight to 80% by weight of chain silica particles having an average length of 30 nm to 200 nm (wherein the total of the spherical silica particles and the chain silica particles in the mixture is 100% by weight).