JP7538081B2 - Paint film piece combustion suppressing stripper and paint film stripping method - Google Patents

Description

The present invention relates to a new paint stripper that can suppress combustion of peeled paint pieces, and a paint stripping method that uses the paint stripper.

For example, structures such as bridges, storage tanks, exterior staircases, and water gates (particularly metal structures) are painted to enhance their corrosion resistance (rust prevention) and weather resistance, but when they are repaired, some or all of the paint is repainted.

When repainting a metal structure, the old paint film (which should be peeled off) must be removed from the surface of the structure before a new coat of paint can be applied. There are two methods for removing this paint film: physical and chemical.

Physical methods include, for example, blasting and grinding with a disk sander. These methods are excellent in terms of removal speed, but generate large amounts of dust, which has a negative impact on workers and the surrounding environment.

One method for chemically removing the paint is to use a paint stripper. Paint strippers can be broadly divided into solvent-based paint strippers and water-based paint strippers. Solvent-based paint strippers contain an organic solvent as the main ingredient, which can lead to problems with the work environment being polluted by the evaporation of the organic solvent, as well as the risk of the evaporated organic solvent catching fire. Water-based paint strippers contain water, making them relatively safe.

For this reason, water-based paint strippers have come into widespread use in recent years, and a variety of strippers have been developed.

For example, a paint stripper containing (A) a monohydric or dihydric alcohol solvent or derivative thereof with a boiling point of 100°C or higher, (B) water, and (C) a rheology control agent, in which component (C) is a metal soap that is a non-alkali metal salt, and whose viscosity is adjusted to 25 Pa·s or less (25°C) is known (Patent Document 1).

For example, a coating stripping composition is known that has a pH in the range of 5 to 9 and contains water, benzyl alcohol, and at least one cellulose derivative (Patent Document 2).

Patent Publication 2019-131651 International Publication WO2018/179925

However, even when a water-based paint stripper is used, there is a risk of the paint pieces catching fire after removal. The reason for this is unclear, but it is thought that when a water-based paint stripper is applied to an old paint film and then the stripping process is carried out, the paint pieces are in a flammable state because, in addition to the organic components that were originally contained in the paint film, organic components in the water-based paint stripper are attached to them, making them susceptible to combustion. In this state, the paint pieces are ignited by some kind of ignition source, resulting in combustion. In this case, it is possible to increase the water content in the water-based paint stripper, but increasing the water content not only reduces the stripping ability, but may also cause a decrease in workability.

For this reason, there is a strong demand for a stripping agent that can prevent the peeled off paint pieces from catching fire, but such a stripping agent has not yet been developed.

Therefore, the main object of the present invention is to provide a paint stripper that can effectively suppress ignition of peeled paint pieces.

As a result of extensive research into the problems of the prior art, the inventors discovered that the above-mentioned objectives could be achieved by using a composition containing specific components as a paint film stripper, and thus completed the present invention.

That is, the present invention relates to the following paint piece combustion suppressing stripping agent and paint film stripping method.
1. An aqueous emulsion-based paint film stripper for stripping a paint film,
(1) The release agent is
(1a) alcohols including aromatic alcohols;
(1b) Paraffins having a melting point of 65° C. or lower;
(1c) at least one of a thixotropic agent and a low polarity solvent having a solubility parameter of 20 or less, and (1d) water;
(2) The water-containing emulsion film formed by the release agent is maintained at a temperature of 15° C. for at least 6 hours from immediately after application of the release agent.
A paint film combustion suppressing stripping agent characterized by the above.
2. The paint piece combustion retardant stripping agent according to item 1, wherein the content of the paraffins is 0.1 to 5% by weight.
3. The paint piece combustion retardant stripping agent according to claim 1 or 2, further comprising at least one of a surfactant and a thickener.
4. A method for removing a coating film, comprising the steps of:
(1) A step of forming a water-containing emulsion film by applying the paint piece combustion suppressing stripping agent described in any one of items 1 to 3 to a surface of a paint film to be stripped;
(2) a step of aging the coating for a certain period of time while maintaining the aqueous emulsion film after coating; and (3) a step of peeling off the coating film having the aqueous emulsion film.
5. The method according to item 4, wherein the coating amount (before drying) in the step of coating the coating piece combustion retardant release agent is 0.3 to 2 kg/ ^m2 .

According to the present invention, it is possible to provide a coating film stripper that can effectively suppress ignition of peeled off coating pieces. In particular, the stripper of the present invention employs a combination of paraffins having a melting point of 65°C or less, a thixotropic agent, and at least one low-polarity solvent having a solubility parameter of 20 or less, making it possible to maintain a water-containing emulsion film on the surface of the peeled off coating film for a relatively long period of time. As a result, it is possible to suppress ignition or combustion of the coating film pieces, making it possible to carry out the coating film stripping work more safely.

1. Paint piece combustion suppressing stripping agent The paint piece combustion suppressing stripping agent of the present invention (the present stripping agent) is an aqueous emulsion-based paint film stripping agent for stripping a paint film,
(1) The release agent is
(1a) alcohols including aromatic alcohols;
(1b) Paraffins having a melting point of 65° C. or lower;
(1c) at least one of a thixotropic agent and a low polarity solvent having a solubility parameter of 20 or less, and (1d) water;
(2) The water-containing emulsion film formed by the release agent is maintained at a temperature of 15° C. for at least 6 hours from immediately after application of the release agent.
It is characterized by:

The stripping agent of the present invention is basically in the form of an aqueous emulsion composed of water (aqueous phase) and an oil phase containing organic components, but a part of the organic components may be dissolved in water as long as the effect of the present invention is not hindered. By taking the form of an emulsion composed of two phases, an aqueous phase and an oil phase, when the agent is applied to the surface of the old coating film to be stripped (hereinafter also referred to as the "coating film to be stripped"), it becomes possible to more reliably form a water-containing emulsion film by the stripping agent of the present invention on the surface of the coating film to be stripped. As a result, it becomes possible to effectively suppress ignition and combustion of the stripped coating pieces. The reason for this is unclear, but it is thought to be due to the following mechanism of action. After the release agent of the present invention in the form of an emulsion is applied to the coating film to be peeled off, the coating film formed by the release agent of the present invention undergoes aging to form a layer structure of "coating film to be peeled off/water-rich layer/organic component (especially paraffin)-rich layer", and the water in the water-rich layer is prevented from evaporating due to the organic component-rich layer. This state is maintained for a long period of time, and as a result, the water-rich layer suppresses ignition of the coating film pieces, or even if a temporary fire does occur, the combustion (spread of the fire) is suppressed. In other words, the water-containing emulsion film is still maintained for a certain period of time in the coating film pieces after peeling, effectively suppressing ignition and combustion of the coating film pieces. The components that make up the release agent of the present invention are described below.

(1a) Alcohols including aromatic alcohols Aromatic alcohols mainly function as a stripping component for stripping the coating film to be stripped.

The aromatic alcohol itself is not particularly limited, and examples thereof include benzyl alcohol, phenethyl alcohol, hydroxybenzyl alcohol, hydroxyphenethyl alcohol, 4-methylbenzyl alcohol, and 2-ethylbenzyl alcohol. Among these, benzyl alcohol is preferred. These may be used alone or in combination of two or more. In addition, the same stripping components as those used in known or commercially available stripping agents may also be used.

The content of aromatic alcohol in the stripping agent of the present invention can be set appropriately depending on the type and thickness of the coating film to be stripped, but it is usually about 30 to 80% by weight, and preferably 35 to 70% by weight.

In addition, in the present invention, alcohols other than aromatic alcohols may be included. Examples include monohydric alcohols such as methanol, ethanol, propanol, isopropyl alcohol, and butanol, and polyhydric alcohols such as ethylene glycol, propylene glycol, butylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, and glycerin.

The content of alcohols other than aromatic alcohols in the release agent of the present invention can be appropriately set depending on the type and thickness of the coating film to be removed, but it is usually about 1 to 20% by weight, and preferably 3 to 10% by weight.
(1b) Paraffins having a melting point of 65°C or less (hereinafter simply referred to as "paraffins")
Paraffins mainly contribute to the formation of the organic component-rich layer in the water-containing emulsion membrane.

The melting point of paraffins is 65°C or less, and preferably 60°C or less. If the melting point exceeds 65°C, it may be difficult to form a water-containing emulsion film. The lower limit of the melting point may be, for example, about 40°C, but is not limited to this.

As such paraffins, for example, paraffin wax can be preferably used, but is not limited to these. Paraffin wax is a wax that is solid at room temperature and is separated and refined from vacuum distillate oil, and is also called "solid wax". Paraffin wax is classified into four types, 120P, 125P, 130P, and 135P, depending on the difference in melting point (Japanese Industrial Standard JIS K2235-1991). In the present invention, any type can be used, and among them, 135P can be preferably used. These paraffins can also be commercially available products. When using commercially available products, emulsion type paraffin containing a surfactant can be used. For example, commercially available products include "Paraffin Wax-115" (manufactured by Nippon Seiro Co., Ltd.) and "AQUACER 497" (manufactured by BYK Japan Co., Ltd.).

The content of paraffins in the stripping agent of the present invention can be set appropriately depending on the type and thickness of the coating film to be stripped, but is usually about 0.1 to 5% by weight, preferably 0.3 to 4% by weight, more preferably 0.5 to 3.5% by weight, and most preferably 0.5 to 2% by weight. Therefore, it can be set to, for example, 1 to 2% by weight.

(1c) At least one of a thixotropic agent and a low-polarity solvent having a solubility parameter of 20 or less The thixotropic agent and at least one of a low-polarity solvent having a solubility parameter of 20 or less are components that can mainly contribute to an excellent combustion suppression effect in combination with the paraffins.

The thixotropic agent is also known as a thixotropic agent, and various types such as amide-based, castor oil-based, polyethylene oxide-based, and vegetable oil polymerized oil-based agents can be used. Among these, amide-based thixotropic agents can be preferably used in the present invention. In terms of properties, either powder type or paste type can be used. These thixotropic agents can also be used as commercially available products. For example, commercially available products include "Disparlon F-9030", "Disparlon 6900-20X", "Disparlon A670-20M", "Disparlon A650-20X" (all manufactured by Kusumoto Chemical Co., Ltd.), "Tallen BA-600", "Tallen M-1020XFS", "Tallen M-1021B", and "Tallen VA750B" (all manufactured by Kyoeisha Chemical Co., Ltd.).

Low polarity solvents (hereinafter simply referred to as "low polarity solvents") having a solubility parameter (SP value) of 20 or less are not particularly limited, but various organic solvents such as ester solvents such as ethyl acetate (8.6) and butyl acetate (8.5); ketone solvents such as acetone (9.4) and cyclohexanone (9.8); ether solvents such as anisole (19.6), diethyl ether (7.4), tetrahydrofuran (9.1), and propylene glycol monomethyl ether acetate (9.1), aromatic solvents such as toluene (8.9) and xylene (8.8), and petroleum solvents such as naphtha (7.6) and mineral spirits (6.9) can be used. Among these, at least one of anisole and naphtha can be preferably used. The values in parentheses above are literature values of the SP value.

The solubility parameter (SP value) in the present invention may be either a literature value or an actual measurement value, but if the two are significantly different, it is preferable to adopt the actual measurement value. The actual measurement value can be performed according to a known method. For example, a solubility test is performed to determine whether a sample (usually a polymer) dissolves in 20 types of solvents (acetone, methylcyclohexane, methyl ethyl ketone, tetrahydrofuran, metaxylene hexafluoride, HFE-7100 (hydrofluoroether), dimethyl sulfoxide, diethylene glycol, N-methylpyrrolidone, acetonitrile, 2-propanol, 2-(2-ethoxyethoxy)ethanol, toluene, diiodomethane, acetophenone, benzaldehyde, acetic acid, 2-ethylhexanol, propylene carbonate, and ethanol), and an SP sphere (Hansen's dissolution sphere) is constructed from the SP values of the solvents that were able to dissolve the sample, and the Hansen SP value can be calculated based on the SP sphere (by converting units as necessary). The SP value of the monomers that make up the polymer can be calculated using commercially available calculation software.

In the release agent of the present invention, the total amount of the thixotropic agent and at least one low-polarity solvent having a solubility parameter of 20 or less can be changed as appropriate depending on, for example, the type of thixotropic agent or low-polarity solvent used, but is usually about 0.5 to 20% by weight, and preferably 0.5 to 15% by weight.

(1d) Water Water is a component that is mainly used to form a water-containing emulsion film by the stripping agent of the present invention. From this viewpoint, the content of water in the stripping agent of the present invention is preferably about 20 to 80% by weight, and more preferably 30 to 70% by weight.

In particular, in relation to aromatic alcohol, it is preferable that the weight ratio of aromatic alcohol to water is 1:1 to 1:2, and more preferably 1:1.3 to 1:1.7. By setting such a ratio, better flame retardancy can be obtained.

(1e) Other components In the stripping agent of the present invention, components other than the above-mentioned components can be appropriately blended as necessary, as long as they do not interfere with the effect of the present invention. For example, thickeners, surfactants, pH adjusters, preservatives, rust inhibitors, etc. can be mentioned. In addition, when an optional component used also functions as an essential component in the stripping agent of the present invention, the content of such optional components is included in the content of essential components. For example, in the case of a surfactant, depending on the surfactant used, it may also function as a thixotropic agent, and the content of such surfactant is included in the content of the thixotropic agent.

Either inorganic or organic thickeners can be used. Inorganic thickeners include inorganic powders such as silica, kaolin, serpentine, talc, mica, vermiculite, smectite, bentonite, and sepiolite. Organic thickeners include cellulose derivatives such as sodium alginate, propylene glycol alginate, sodium carboxymethylcellulose, calcium carboxymethylcellulose, sodium starch glycolate, sodium starch phosphate, sodium polyacrylate, and methylcellulose, synthetic products such as hydroxypropylmethylcellulose, and naturally occurring polysaccharides such as guar gum, tara gum, gum arabic, tragacanth gum, alginic acid, carrageenan, xanthan gum, dielan gum, perithin, chitin, chitosan, and chitosamine.

The surfactant may be, for example, an anionic surfactant, a cationic surfactant, an amphoteric surfactant, a nonionic surfactant, etc. Examples of the anionic surfactant include fatty acid salts, alkyl sulfate ester salts, alkylbenzene sulfonates, polyoxyethylene alkyl ether sulfates, dialkyl sulfosuccinic acids, etc. Examples of the cationic surfactant include alkylamine acetates, quaternary ammonium salts, etc. Examples of the amphoteric surfactant include alkyldimethylaminoacetate betaine, alkyldimethylamine oxide, etc. Examples of the nonionic surfactant include glycerin fatty acid esters, propylene glycol fatty acid esters, sorbitan fatty acid esters, polyoxyethylene alkyl ethers, polyoxyethylene polyoxypropylene ethers, etc.

Examples of pH adjusters include acid components such as inorganic acids, such as hydrochloric acid and phosphoric acid, and organic acids, such as acetic acid, oxalic acid, and citric acid. Examples of base components include inorganic alkalis, such as sodium hydroxide and potassium hydroxide, and organic alkalis, such as monoethanolamine, monoisopropanolamine, diethanolamine, and triethanolamine.

(2) Water-containing emulsion film formed by the stripping agent of the present invention: In the stripping agent of the present invention, the water-containing emulsion film formed by the stripping agent of the present invention is maintained at a temperature of 15° C. for at least 6 hours from immediately after application of the stripping agent.

The stripping agent of the present invention is in the form of an aqueous emulsion, and when it is applied, a water-containing emulsion film is formed. After the coating film to be stripped, which has such a water-containing emulsion film on its surface, is stripped, the water-containing emulsion film is also retained on the surface of the stripped coating film piece for a certain period of time, so that the burning of the coating film piece after stripping can be effectively suppressed. The reason for this effect is not clear, but it is thought to be due to the following mechanism. In general, the water-containing emulsion film formed with an aqueous emulsion type stripping agent begins to evaporate. With existing stripping agents, the water evaporates easily, and a dry coating film with a low water content is formed in a relatively short time. In contrast, the water-containing emulsion film formed by the stripping agent of the present invention has a layer structure of "coating film to be stripped/water-rich layer/organic component-rich layer" as described above, and the water-rich layer is in a state where the evaporation of water is hindered by the organic component-rich layer, and this state is maintained for a longer period of time, so that the water-rich layer is thought to suppress the ignition of the coating film piece, or even if it does ignite temporarily, the combustion (spread of fire) is suppressed.

The environment in which the water-containing emulsion film is maintained is one in which the stripping agent of the present invention is normally used outdoors, and therefore the environment is maintained at normal temperature and normal humidity for a specified period of time. In the present invention, the standard is a temperature of 15°C (preferably 25°C) for 6 hours or more, preferably 6 hours or more, more preferably 8 hours or more, even more preferably 12 hours or more, more preferably 18 hours or more, and most preferably 24 hours or more. The humidity may be normal humidity, for example, about 10 to 85%, but is not limited to this.

(3) Production of the release agent of the present invention The release agent of the present invention can be prepared by uniformly mixing and emulsifying each of these components. In this case, mixing can be performed using a known or commercially available mixer, kneader, etc. The order of mixing each of these components is not particularly limited as long as a homogeneous aqueous emulsion is obtained, and each component may be mixed simultaneously or sequentially. In this way, the release agent of the present invention in the form of an aqueous emulsion can be obtained.

(4) Use of the Release Agent of the Present Invention The release agent of the present invention can be preferably used in accordance with the method described below in "2. Method of removing coating film."

2. Method for removing a coating film The present invention includes a method for removing a coating film using the stripping agent of the present invention. In particular, the present invention is a method for removing a coating film, comprising the steps of:
(1) a step of forming a water-containing emulsion film by applying the release agent of the present invention to the surface of a coating film to be peeled (a coating film to be peeled) (a coating step);
(2) a step of aging the coating for a certain period of time while maintaining the aqueous emulsion film after coating (aging step); and (3) a step of peeling off the coating film having the aqueous emulsion film (peeling step).
The present invention relates to a coating peeling method comprising the steps of:

(1) Coating Step In the coating step, the release agent of the present invention is applied to the surface of the coating film to be stripped to form a water-containing emulsion film.

The coating to be peeled off (the coating to be removed) is not particularly limited as long as it is a coating formed on the surface of a structure (particularly a metal structure). The coating to be peeled off is not particularly limited as long as it is coated with a general paint, and the type of paint and the thickness of the coating to be peeled off are not particularly limited. For example, it can be applied to a coating to be peeled off that contains at least one of melamine-based resin, acrylic-based resin, phthalic acid-based resin, urethane-based resin, epoxy-based resin, etc.

The material that serves as the base for the coating film to be stripped is not limited, and may be, for example, metal, concrete, wood, etc. In particular, the stripping agent of the present invention is suitable for use with coating films that have a metal (preferably steel) base. The type of underlying structure is not particularly limited, and the agent can be applied to any structure that requires corrosion resistance and rust prevention, such as bridges, building exterior walls, storage tanks, water gates, garages, etc.

The method for applying the release agent of the present invention is not particularly limited, and can be carried out according to a known method such as spraying, roller, brush, etc. The amount of application (before drying) is not limited, but is usually about 0.3 to 2 kg/ ^m2 , and preferably 0.5 to 1 kg/ ^m2 .

(2) Aging Step In the aging step, after application of the release agent of the present invention, the aqueous emulsion film is aged for a certain period of time while being maintained.

In the aging process, the coating to be peeled is left for a time sufficient for the release agent of the present invention to penetrate into the coating to be peeled and for the coating to be peeled to swell. This time is the time during which the water-containing emulsion film is maintained on the surface of the coating to be peeled. This time depends on the working environment and season (temperature, humidity, presence or absence of sunlight), but is generally about 6 to 48 hours after application of the release agent of the present invention, and preferably about 10 to 26 hours.

The aqueous emulsion film produced by the release agent of the present invention is opaque or translucent due to the fact that the release agent of the present invention is opaque or translucent due to the emulsification, and is formed on the surface of the coating film to be peeled off in an opaque or translucent state. When most of the water in the aqueous emulsion film has evaporated, its appearance changes from opaque or translucent to transparent. Therefore, the aging time can be appropriately adjusted within a range in which such a change in appearance is not substantially noticeable to the naked eye.

In the peeling step, the coating film to be peeled off having the aqueous emulsion film is peeled off. That is, the coating film to be peeled off is peeled off and removed from the base at a stage when the aqueous emulsion film has not yet dried and its appearance has not yet changed to transparent.

The peeling method can be carried out using a known or commercially available peeling tool such as a scraper. The pieces of coating film peeled off in this way still contain the water-containing emulsion film on their surface, making them less susceptible to ignition or combustion. By collecting the pieces of coating film while they are in this state, it is possible to more reliably prevent fires caused by the pieces of coating film.

The following examples and comparative examples are presented to more specifically explain the features of the present invention. However, the scope of the present invention is not limited to the examples.

Examples 1 to 7 and Comparative Examples 1 to 4
A release agent (aqueous emulsion) was prepared by uniformly mixing each component shown in Table 1. The unit of the content of each component is "wt %."

Details of each product name in Table 1 are as follows:
・"T-SOL150" ... Ando Parachemie Co., Ltd., naphtha ・"Metolose SM4000" ... Shin-Etsu Chemical Co., Ltd., cellulose-based thickener ・"Metolose 60SH4000" ... Shin-Etsu Chemical Co., Ltd., cellulose-based thickener ・"Metolose 90SH4000" ... Shin-Etsu Chemical Co., Ltd., cellulose-based thickener ・"Disparlon F-9030" ... Kusumoto Chemical Co., Ltd., fatty acid amide-based thixotropic agent ・"Paraffin "Wax-115": Nippon Seiro Co., Ltd., paraffin with a melting point of 47°C. "AQUACER 497": BYK Japan Co., Ltd., paraffin with a melting point of 60°C, mixture of 40-50% paraffin, 1-10% stearate, 1-10% fatty acid carboxylate, and water. "No. 70-S": Sanko Chemical Industry Co., Ltd., liquid paraffin. "Docosanol": higher alcohol, melting point of 70°C.
・"Rheodor TW-O320V" ... Kao Corporation, sorbitan fatty acid ester nonionic surfactant

Test Example 1 (Confirmation of Water-containing Emulsion Film)
In Examples 1 to 7 and Comparative Examples 1 to 4, the change over time in the appearance of the water-containing emulsion film produced by each release agent was examined.
The formation of the aqueous emulsion film was carried out by applying the release agents of Examples 1 to ⁷ and Comparative Examples 1 to 4 with a brush to the surface of the coating film (film thickness 200 μm) of the steel bridge used in the following "Test Example 2 (flammability test)" so that the coating amount (before drying) was 1 kg/m2.
Each release agent was in a cloudy state, and a cloudy water-containing emulsion film was formed immediately after application. Thereafter, as drying proceeded, the appearance of the water-containing emulsion film changed to transparent. In such a series of appearance changes, it was measured whether the time from immediately after application until the water-containing emulsion film became transparent at a visual level was 6 hours or more at a temperature of 15°C. As a result, in Examples 1 to 7, the water-containing emulsion film maintained a cloudy state even after 6 hours, and maintained a cloudy state even after 24 hours. On the other hand, in Comparative Examples 1 to 4, the water-containing emulsion film became transparent within 30 minutes.

Test Example 2 (Flammability Test)
The release agents of Examples 1 to 7 and Comparative Examples 1 to 4 were applied with a brush to the surface of the coating film (film thickness approximately 200 μm) of a steel bridge so that the coating amount (before drying) was 1 kg/ ^m2 . After 24 hours had passed since the completion of application, the coating film to which the release agent had been applied was scraped with a scraper to remove the coating film. After removal, a piece of the coating film (size approximately 3 cm x 3 cm) was placed on a brick block, and a lighter flame was brought close to the coating film piece. It was held close for 15 seconds, and visually confirmed whether the coating film piece had burned. The results are shown in Table 1. Cases where there was no ignition or combustion were marked as "○", and cases where there was ignition were marked as "×".

Examples 8 to 11 and Comparative Examples 5 to 11
A release agent (aqueous emulsion) was prepared by uniformly mixing each component shown in Table 2. Each component in Table 2 is the same as that described above for Table 1. The content of each component is expressed in "wt %".

Test Example 3 (Confirmation of Water-containing Emulsion Film)
In Examples 8 to 11 and Comparative Examples 5 to 11, the change over time in the appearance of the water-containing emulsion film produced by each release agent was examined.
The formation of the water-containing emulsion film was carried out by applying with a brush the release agents of Examples 8 to 11 and Comparative Examples 5 to 11 to the coating surface of the test piece prepared in "(1) (Preparation of Coating Film Test Piece)" of "Test Example 4 (Removability Test)" below, so that the coating amount (before drying) was 1 kg/ ^m2 .
Each release agent was in a cloudy state, and a cloudy water-containing emulsion film was formed immediately after application. Thereafter, as drying proceeded, the appearance of the water-containing emulsion film changed to transparent. In such a series of appearance changes, it was measured whether the time from immediately after application until the water-containing emulsion film became transparent at a visual level was 8 hours or more at a temperature of 25°C. As a result, in Examples 8 to 11, the water-containing emulsion film maintained a cloudy state even after 8 hours, and maintained a cloudy state even after 24 hours. On the other hand, in Comparative Examples 5 to 11, the water-containing emulsion film became transparent within 8 hours.

Test Example 4 (peelability test)
(1) Preparation of coating film test piece A long-shaped etching primer (Vinylex 120 Active Primer Eco (color: dark green), manufactured by Nippon Paint Co., Ltd.) was applied to a steel plate of SS400 (Japanese Industrial Standard) that had been subjected to a blast treatment in accordance with ISO Sa 2 1/2. Two layers of lead- and chromium-free rust-preventive paint (Lasgon Safety (color: red rust, gray), manufactured by Kansai Paint Co., Ltd.) were applied thereon, and a long-oil phthalic acid resin paint intermediate coat (SD Marine Safety intermediate coat (color: white), manufactured by Kansai Paint Co., Ltd.) and a long-oil phthalic acid resin paint top coat (SD Marine Safety top coat (color: yellow), manufactured by Kansai Paint Co., Ltd.) were further applied thereon. The painted steel plate was baked at 60 ° C. for one week to prepare a coating film test piece with a coating film thickness of about 200 μm.
(2) Peeling test Each of the release agents of Examples 8 to 11 and Comparative Examples 5 to 11 was applied with a brush to the coating surface of the coating test piece prepared above so that the coating amount was 1 kg/ ^m2 . After 24 hours in an environment of a temperature of 25°C and a humidity of 50%, the coating was peeled off. When the entire coating could be peeled off, it was marked as "◯", and when a part or the entire coating could not be peeled off, it was marked as "×". The results are shown in Table 2.

Test Example 5 (Flame Retardancy Test)
The coating film peeled off in Test Example 4 (peelability test) was placed on a brick block, and a fire was brought close to it with a lighter, and it was visually confirmed whether the coating film burned or not. If the coating film did not ignite even after being brought close to the fire for 5 seconds, it was marked as "○", if the coating film ignited within 5 seconds of being brought close to the brick block but immediately went out, it was marked as "△", and if the coating film ignited within 5 seconds of being brought close to the brick block and did not go out until the coating film burned out, it was marked as "×". The results are shown in Table 2.

As is clear from the results in Table 2, Examples 8 to 10, in which 0.5% by weight or more of solid paraffin was added as an evaporation inhibitor, had good flame retardancy, whereas Comparative Examples 5 to 6, in which no evaporation inhibitor was added, had poor flame retardancy. Comparative Examples 7 to 8, in which liquid paraffin and higher alcohol were added as evaporation inhibitors, also had poor flame retardancy.

From the above, it can be said that it is desirable for the evaporation inhibitor to be a solid at room temperature and to have no hydrophilic groups such as hydroxyl groups, and that the amount of the evaporation inhibitor to be blended is desirably 0.5% by weight or more.

In addition, between Examples 8 and 9, in which the amount of benzyl alcohol is 40% by weight and the same solid paraffin is used but the blending amounts are different, Example 9 has improved flame retardancy, and when the amount of benzyl alcohol is 40% by weight, it is particularly desirable to blend in an amount of solid paraffin of 1% by weight or more.

In Examples 8 and 11 and Comparative Examples 9 and 10, 0.5% by weight of solid paraffin was added, and the ratio of the amount of benzyl alcohol to the amount of water was changed. The amounts were adjusted so that the viscosities were similar. Examples 8 to 11, which contain 0.5% by weight or more of solid paraffin and have a ratio of the weight of water to the weight of benzyl alcohol (i.e., [(water content)/(benzyl alcohol content)]] of 1 or more, have good flame retardancy, whereas Comparative Examples 9 to 11, which contain 0.5% by weight or more of solid paraffin but have a ratio of the weight of water to the weight of benzyl alcohol of less than 1, have poor flame retardancy. It is believed that by making the ratio of the weight of water to the weight of benzyl alcohol 1 or more, more water is retained in the release agent, and the cooling effect of the contained water improves flame retardancy.

The stripping agent of the present invention is effective in safely removing coatings from structures such as bridges, storage tanks, exterior staircases, and water gates.

Claims (6)

An aqueous emulsion-based paint film stripper for stripping a paint film, comprising:
(1) The release agent is
(1a) alcohols including aromatic alcohols;
(1b) Paraffins having a melting point of 65° C. or lower;
(1c) a thixotropic agent ; and (1d) water, the weight ratio of aromatic alcohol:water being 1:1.3 to 1:2;
(2) The water-containing emulsion film formed by the release agent is maintained at a temperature of 25° C. for at least 8 hours from immediately after application of the release agent.
A paint film combustion suppressing stripping agent characterized by the above. The paint piece combustion suppressing stripper according to claim 1, wherein the content of the paraffins is 0.1 to 5% by weight. 2. The paint piece burn-suppressing stripping agent according to claim 1, wherein the content of the thixotropic agent is 0.5 to 20% by weight. The paint piece burn-suppressing stripping agent according to any one of claims 1 to 3 , further comprising at least one of a surfactant and a thickener. A method for stripping a coating, comprising the steps of:
(1) A step of forming a water-containing emulsion film by applying the paint piece combustion suppressing stripping agent according to any one of claims 1 to 4 to the surface of the paint film to be stripped;
(2) a step of aging the coating for a certain period of time while maintaining the aqueous emulsion film after coating; and (3) a step of peeling off the coating film having the aqueous emulsion film. The method according to claim 5 , wherein the coating amount (before drying) in the step of coating the paint piece combustion retardant release agent is 0.3 to 2 kg/ ^m2 .