KR20240058526A - Coating composition - Google Patents

Abstract

The present invention relates to a coating composition with excellent heat resistance, weather resistance, and fire propagation delay performance.

Description

Paint composition {COATING COMPOSITION}

The present invention relates to a coating composition with excellent heat resistance, weather resistance, and fire propagation delay performance.

Secondary batteries are applied to a variety of fields, including portable electronic devices and automobiles, and research and development on secondary batteries with high energy density, discharge voltage, and output stability are steadily progressing. Recently, demand for electric vehicles continues to increase in terms of eco-friendliness and energy efficiency, and development of batteries used in electric vehicles (EV, Electric Vehicle) or hybrid vehicles (HEV, Hybrid Electric Vehicle) is actively underway. .

In order to produce the large amount of power required to drive a car, multiple battery modules are combined to form a car battery. When the temperature inside the battery increases rapidly due to various causes such as pressure, shock, or electrical short circuit, the battery Heat energy can be transferred sequentially between modules, resulting in a very strong fire. Therefore, batteries used in automobiles are particularly required to have high heat resistance and weather resistance.

To solve this problem, a technology for applying an insulating layer to automobile battery cells was applied. For example, Publication Patent No. 2021-0134342 discloses a method of applying an external insulating layer to the housing of a battery cell. As another example, a technology for installing a fire extinguishing pack containing fire extinguishing material between battery cell modules and a technology for adhering a urethane resin with heat resistance and insulation to the battery module have been proposed.

However, the conventional technology has the disadvantage of complicating the structure of the car battery, complicating construction, or not providing sufficient heat resistance and weather resistance to delay the speed of flame propagation.

The present invention provides a coating composition with excellent heat resistance, weather resistance, and fire propagation delay performance.

Additionally, the present invention provides a sheet manufactured from the above coating composition and having excellent heat resistance.

The coating composition of the present invention includes an epoxy resin, a diluent, and a foaming agent, and the foaming agent includes melamine and borate.

The present invention provides a coating composition with excellent heat resistance, weather resistance, and fire propagation delay performance. The coating composition of the present invention foams and forms a carbonized layer at a lower temperature than the conventional foaming temperature, and has an excellent initial fire delay effect. The paint composition of the present invention can be applied for secondary battery coating, especially for coating battery modules or battery packs of electric vehicles. In particular, it delays the spread of fire between electric vehicle battery modules to prevent battery thermal runaway caused by electric vehicle fires, thereby facilitating human evacuation. Time can be secured, and the scope of recovery when repairing a battery can be minimized by limiting the area where the fire occurs locally.

Additionally, the present invention provides a sheet manufactured from the above coating composition and having excellent heat resistance. The sheet according to the present invention can be molded according to the battery pack design and then installed inside the battery pack, and as a result, processes such as applying and drying the paint composition can be omitted and has excellent constructability.

Hereinafter, the present invention will be described in detail. However, it is not limited to the following content, and each component may be variously modified or selectively mixed as needed. Accordingly, it should be understood to include all changes, equivalents, and substitutes included in the spirit and technical scope of the present invention.

The “weight average molecular weight” used in this specification is measured by a common method known in the art, and can be measured, for example, by a GPC (gel permeation chromatograph) method. “Viscosity” is measured by conventional methods known in the art, and can be measured using, for example, a Brookfield viscometer.

<Paint composition>

The coating composition according to the present invention includes an epoxy resin, a diluent, and a foaming agent. The paint composition according to the present invention may further include additives commonly used in the relevant technical field, such as flame retardants, acid catalysts, and curing agents, if necessary.

epoxy resin

The coating composition of the present invention contains an epoxy resin. Epoxy resin plays a role in promoting adhesion to the subject and strengthening the durability of the cured coating film, and changes the coating film to a fluid state when exposed to high temperature heat in the event of a fire, allowing the coating film to expand appropriately when gas is generated, and foaming carbonization. Forms the framework of the layer.

The epoxy resin may be a bisphenol A-type epoxy resin, a bisphenol F-type epoxy resin, a flame-retardant epoxy resin, a novolak-type epoxy resin, a multifunctional amine epoxy resin, a cycloaliphatic epoxy resin, or a mixture thereof. It is not limited. For example, the epoxy resin may include one or more types selected from bisphenol A-type epoxy resin and bisphenol F-type epoxy resin.

The weight average molecular weight of the epoxy resin may be 150 to 900 g/mol, for example, 200 to 800 g/mol, and in another example, 360 to 400 g/mol. If the weight average molecular weight of the epoxy resin is less than the above-mentioned range, sagging may occur and the paint film may flow, and if it exceeds the above-mentioned range, the viscosity of the resin may increase, resulting in poor painting workability, such as a decrease in spray spraying. .

The epoxy equivalent weight of the epoxy resin may be 75 to 450 g/eq, for example, 100 to 400 g/eq, and in another example, 180 to 200 g/eq. If the epoxy equivalent weight of the epoxy resin is outside the above-mentioned range, the paint may not cure sufficiently and the paint film may not be properly formed.

The coating composition of the present invention may include 10 to 25% by weight, for example, 15 to 23% by weight, of the epoxy resin, based on the total weight of the composition. If the content of the epoxy resin is less than the above-mentioned range, the adhesion of the coating film may be reduced, and if it exceeds the above-mentioned range, the expansion rate of the coating film may be inhibited in the event of a fire, and sufficient fire resistance performance may not be achieved.

reactive diluent

The coating composition of the present invention includes a reactive diluent. The reactive diluent reacts with the hardener and participates in the formation of the paint film, lowering the viscosity of the paint and providing flexibility to the paint film. For example, the reactive diluent may include a trifunctional or higher reactive diluent and a bifunctional or lower reactive diluent.

As the trifunctional or higher reactive diluent, a reactive diluent having 3 or more reactive groups that react with the curing agent, for example, 3 to 6, or in other examples, 3 or 4, can be used. The trifunctional or higher reactive diluent may be a trifunctional or higher (meth)acrylate monomer.

Non-limiting examples of the trifunctional or higher (meth)acrylate monomer include trifunctional (meth)acrylate monomers such as trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, etc.; Tetrafunctional (meth)acrylate monomers such as pentaerythritol tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, etc.; There are dipentaerythritol poly(meth)acrylate, etc., which can be used alone or in combination of two or more types. For example, the trifunctional or higher (meth)acrylate monomer may be a trifunctional (meth)acrylate monomer, such as trimethylolpropane tri(meth)acrylate.

The trifunctional or higher reactive diluent has an epoxy equivalent weight of 70 to 130 g/eq, for example, 90 to 110 g/eq, and a viscosity of 60 to 140 cps (25°C), for example, 80 to 120 cps (25°C). It can be. If the epoxy equivalent weight of the trifunctional or higher reactive diluent is less than the above-mentioned range, the flexibility of the cured film may decrease and the physical properties of the film, such as cracks in the film, may occur at low temperatures, and if it exceeds the above-mentioned range, the hardness of the film may decrease, causing external damage. In the event of impact, the coating film can be easily damaged and the long-term durability of the coating film may be poor.

Examples of the bifunctional or lower reactive diluent include phenyl glycidyl ether, alkyl glycidyl ether, glycidyl ester of versat acid, olefin epoxide, 1,6-hexanediol diglycidyl ether, neopentyl glycol diluent, Glycidyl ether, trimethylolpropane triglycidyl ether, alkylphenyl glycidyl ether, such as methylphenyl glycidyl ether, ethylphenyl glycidyl ether, propylphenyl glycidyl ether, neodecanoic acid 2,3-epoxy Propyl ester, etc. can be used. The above-mentioned ingredients can be used individually or two or more types can be used in combination.

The bifunctional or lower reactive diluent has an epoxy equivalent weight of 100 to 350 g/eq, for example, 130 to 250 g/eq, and a viscosity of 5 to 50 cps (25°C), for example, 5 to 30 cps (25°C). ) can be. If the epoxy equivalent weight of the difunctional or lower reactive diluent is less than the above-mentioned range, the diluent may be eluted to the surface of the paint film at high temperature, causing stickiness, and if it exceeds the above-mentioned range, the carbonized layer of the paint generated in the event of a fire may easily break down. As flames are exposed through cracks, fire resistance performance can be greatly reduced.

In the present invention, the mixing ratio of the trifunctional or higher reactive diluent and the bifunctional or lower reactive diluent may be 80:20 to 20:80, for example, 70:30 to 30:70 by weight. If the ratio of the bifunctional or lower reactive diluent to the trifunctional or higher reactive diluent is less than the above-mentioned range, large pores (e.g., 1 cm or more in diameter) are likely to occur inside the carbonized layer of the paint generated in the event of a fire, and large pores The more this happens, the more easily the carbonized layer cracks during the foaming process, so flames can easily penetrate through the cracks and the fire resistance performance can drop dramatically. On the other hand, if the ratio of the bifunctional or lower reactive diluent to the trifunctional or higher reactive diluent exceeds the above-mentioned range, the hardness of the coating film may decrease and the coating film may be easily damaged upon external impact, resulting in poor long-term coating film durability.

The paint composition of the present invention may include 2 to 20% by weight, for example, 2 to 10% by weight, of the reactive diluent, based on the total weight of the composition. For example, based on the total weight of the composition, the coating composition of the present invention contains 1 to 10% by weight, such as 1 to 5% by weight, of the trifunctional or higher reactive diluent and 1 to 10% by weight, such as 1 to 10% by weight, of the bifunctional or lower reactive diluent. It may contain from 5% by weight. If the content of the reactive diluent is less than the above-mentioned range, the viscosity of the paint may increase, the flexibility of the paint film may decrease, and painting workability may be inferior, such as reduced spraying. On the other hand, if the above-mentioned range is exceeded, the hardness of the coating film may rapidly decrease, which may cause the coating film to be easily damaged by external impact, and the viscosity may be lowered, leading to a sharp decrease in sagging resistance during spray painting.

blowing agent

The coating composition of the present invention contains a foaming agent. The foaming agent is exposed to high temperature heat, softens and liquefies the cured coating film, and decomposes at the time a carbonized layer is created, generating a large amount of inert gas. As a result, it forms fine pores in the carbonized layer and plays a role in providing insulation performance. . In addition, the foaming agent decomposes in high temperature heat, causing an endothermic reaction and forming a carbonized layer, which can cool the surface and block contact with oxygen, delaying the spread of fire.

The blowing agent includes melamine and borate. The foaming temperature can be lowered by mixing the two components described above as a foaming agent. For example, the coating composition of the present invention can be foamed at a lower temperature (e.g., 150°C) compared to a conventional foaming temperature (e.g., 250°C) and form a carbonized layer, resulting in improved fire resistance performance. In particular, since the paint composition foams at a low temperature, unlike general architectural paint compositions, it is possible to prevent the battery thermal runaway phenomenon in which the battery pack is damaged in an electric vehicle fire and the internal temperature quickly rises to 800 ℃ and the fire spreads. It has the effect of preventing massive damage by improving the effect of delaying the spread of fire.

As the borate, orthoborate, diborate, metaborate, tetraborate, octaborate, boric acid, etc. can be used. For example, the borate is zinc borate, sodium metaborate, ammonium pentaborate, sporgite, ameghinite, inderite, It may include one or more species selected from the group consisting of Inyoite, Meyerhofferite, and Kurnakovite.

The foaming agent may further include common foaming agents such as urea, glycine, ammonium polyphosphate (APP), pentaerythritol, aluminum trihydrate (ATH), and expandable graphite.

The coating composition of the present invention may include 10 to 40% by weight, for example, 5 to 25% by weight, of the foaming agent, based on the total weight of the composition. If the content of the foaming agent is less than the above-mentioned range, the paint may not expand sufficiently and the heat-insulating performance may deteriorate. If it exceeds the above-mentioned range, the paint may expand excessively, causing cracks to occur in the carbonized layer and reducing strength, so that the heat-insulation performance may not be sufficient. It may not work.

For example, the coating composition of the present invention may include 2 to 20% by weight of melamine, such as 6 to 16% by weight, and 5 to 30% by weight of borate, such as 15 to 25% by weight, based on the total weight of the composition. If the melamine content is less than the above-mentioned range, foaming performance may deteriorate, and if it exceeds the above-mentioned range, a dense foam layer may not be formed and the strength of the foam layer may be reduced. In addition, if the borate content is less than the above-mentioned range, foaming performance and self-extinguishing properties may be reduced, and if it is more than the above-mentioned range, the foam layer may become too hard and the occurrence of cracks may increase, thereby reducing heat insulation performance.

For example, the mixing ratio of melamine and borate may be 1:0.25 to 20, for example, 1:0.25 to 15 weight ratio, for example, 1:10 to 20 weight ratio. When the mixing ratio of borate to melamine is within the above-described range, a carbonized layer is formed at a lower temperature (e.g., 150°C) compared to the conventional temperature (e.g., 250°C), which is effective in blocking the initial spread of fire. If the mixing ratio of borate to melamine is less than the above-mentioned range, foaming may occur excessively and the strength of the foam layer may decrease, and if it exceeds the above-mentioned range, the carbonization layer may become too hard, resulting in reduced foaming performance and increased crack generation. .

flame retardant

The coating composition of the present invention may contain a flame retardant. The flame retardant plays a role in providing flexibility to the initial foamed carbonized layer by controlling the thermal decomposition rate of the cured coating film.

The flame retardant may be a phosphorus-based flame retardant or the like. The phosphorus-based flame retardants include triphenyl phosphate (TPP), isopropylated triphenyl phosphate, tricresyl phosphate, butylated triphenyl phosphate, and cresyl diphenyl. Aryl phosphates such as cresyl diphenyl phosphate and isopropyl phenyl diphenyl phosphate; One or more bisphosphates selected from resorcinol bis(diphenyl phosphate) (RDP), bisphenol-A bis(diphenyphosphate) (BDP), etc. can be used.

The coating composition of the present invention may include 5 to 20% by weight, for example, 7 to 15% by weight, of the flame retardant, based on the total weight of the composition. If the content of the flame retardant is less than the above-mentioned range, the fire resistance performance may not be sufficiently demonstrated. If the content of the flame retardant exceeds the above-mentioned range, the melting viscosity of the coating film is lowered and the carbonized layer is easily broken due to excessive foaming, so the heat insulation performance may not be achieved.

hardener

The coating composition of the present invention may include a curing agent. The curing agent may be an amide or amido amine resin.

The method for producing the amide or amido amine resin is not particularly limited, and may be produced by methods known in the art. For example, it can be prepared by polymerizing polyethylene amine, fatty acid dimer, and fatty acid monomer with a viscosity of 200 to 800 cps (25°C), an amine value of 300 to 600 mgKOH/g, and an active hydrogen equivalent of 50 to 200 g/eq. there is.

For example, a condensation reaction is carried out by heating a mixture of polyethylene amine, fatty acid dimer, and fatty acid monomer to 200° C., and the reaction is allowed to proceed until the acid value of the reactant becomes 1 to 5. In this step, the reaction can be performed so that the molar ratio of amine/acid is 1.0 to 2.0. If the molar ratio is less than 1.0, the viscosity may be high, making it difficult to apply the paint, and if it is more than 2.0, unreacted amine may be present, making it difficult to apply the paint. It may become difficult to realize the desired physical properties.

As the polyethylene amine, ethylenediamine, diethylenetriamine, triethylenetetraamine, tetraethylenepentamine, etc. can be used, and these can be used alone or in a mixture of two or more types. The fatty acid dimers and monomers include monomers and dimers obtained from soybean oil fatty acid, tall oil fatty acid, castor oil fatty acid, rice bran oil fatty acid, flax oil fatty acid, coconut oil fatty acid, lauric acid, or linoleic acid, and these can be used singly or in combination of two types. The above can be mixed and used. For example, the fatty acid dimers and monomers may be tall oil fatty acid monomers and dimers.

When the acid value of the reactant produced by the reaction reaches 1 to 5 or less, heating is terminated to prepare an amide or amido amine resin.

The amide or amido amine resin has a viscosity of 200 to 800 cps (25°C), for example, 300 to 600 cps (25°C), and an amine value of 300 to 600 mgKOH/g, for example, 400 to 500 mgKOH/g. and the active hydrogen equivalent may be 50 to 200 g/eq, for example, 60 to 100 g/eq. When the amide or amido amine resin has physical properties within the above-mentioned range, curability can be maximized.

The paint composition of the present invention may include 10 to 15% by weight, for example, 11 to 14% by weight of the curing agent, based on the total weight of the paint composition. If the content of the hardener is less than the above-mentioned range, the adhesion of the coating film may decrease, and if it exceeds the above-mentioned range, defects in the coating film such as amine brushing may occur.

additive

In order to achieve optimal paint and film performance, the paint composition of the present invention may further include additives such as water, film former, acid catalyst, carbonizing agent, pigment, reinforcing agent, dispersing agent, anti-foaming agent, anti-freezing agent, and preservative. .

Film forming agents lower the Minimum Film Formation Temperature (MFFT) to form a film at low temperatures. The film forming agent includes 2-ethylhexyl benzoate, Acetyl Tributyl citrate (ATBC), Di-IsoButyl Adipate (DIBA), or mixtures thereof. can be used.

The acid catalyst is exposed to high temperature heat and decomposes when the cured coating film softens, promoting the creation of a carbonized layer and foaming of the carbonized layer. The acid catalyst may be ammonium phosphate, ammonium polyphosphate, melamine polyphosphate, melamine monophosphate, melamine bisphosphate, or a mixture thereof.

The carbonizing agent reacts with the foaming agent at high temperatures to form a carbonizing layer that exhibits fire resistance. Pentaerythritol, etc. may be used as the carbonizing agent.

Pigments play a role in improving fire resistance by forming a ceramic insulation layer on the foam coating film. Titanium dioxide and the like can be used as the pigment.

The thickener provides hydrophilicity so that hydrogen bonds interact within the paint to provide thixo properties, prevents the paint from flowing during painting, and improves the storability of the paint. As the thickener, water-soluble polyamide wax or the like can be used.

The reinforcing agent provides thixotropic properties to the paint to prevent flow during painting, is evenly distributed within the dry film to prevent cracks, and maintains insulation performance even at high temperatures by supplementing the strength of the foamed carbon layer in the event of a fire. Glass fiber, etc. may be used as the reinforcing agent.

The paint composition of the present invention may contain water as a solvent, which serves to adjust the viscosity of the paint and provide fluidity.

The additives may be appropriately added within the content range known in the art, and for example, each of the additives may contain 0.1 to 20% by weight based on the total weight of the composition.

<Sheet>

The present invention provides a sheet made from the above-described coating composition.

For example, the sheet of the present invention can be manufactured by filling the coating composition into a sheet mold coated with a release agent by spraying or trowel painting. As another example, the sheet of the present invention can be manufactured by curing the coating composition and then cutting it to a predetermined thickness. The thickness of the sheet is not particularly limited and may be, for example, 1 to 10 mm.

The foaming rate of the sheet may be 300 to 2,000%. The expansion rate is the rate of change in thickness before and after the fire resistance test, and is calculated by the following formula. The fire resistance test is a fire resistance test in an electric furnace (internal temperature: 950 ℃), and the thickness is measured with vernier calipers.

Expansion rate = [(Thickness after fire resistance test - Thickness before fire resistance test) / Thickness before fire resistance test]

If the expansion rate of the sheet satisfies the above-mentioned range, an excellent heat shielding effect can be obtained by forming a strong carbonized layer that protects the material from fire. If the foaming rate is less than the above-mentioned range, heat penetration into the base material may be excessive and the base material may be damaged, and if it exceeds the above-mentioned range, a solid foam layer is not formed due to over-foaming, which may cause heat penetration into the base material.

The sheet according to the present invention is applicable to secondary batteries, especially battery modules of electric vehicles. When the sheet of the present invention, which has excellent fire retardation performance, is installed in the battery module of an electric vehicle, it is possible to secure evacuation time by delaying the spread of fire between electric vehicle battery modules, and by limiting the area where the fire occurs locally, the recovery range when repairing the battery. can be minimized.

Since the sheet of the present invention can be molded according to the battery pack design and then installed inside the battery pack, processes such as applying and drying the paint composition can be omitted and has excellent constructability.

The sheet of the present invention can be inserted and installed between a plurality of battery modules constituting a battery pack. To prevent mutual clearance, flame retardant adhesive can be applied to the sheet surface, or a fixing device can be installed inside the battery pack.

Hereinafter, the present invention will be described in more detail through examples. However, the following examples are only intended to aid understanding of the present invention, and the scope of the present invention is not limited to the examples in any way.

[Example 1-4]

The paint composition of each example was prepared by adding each component according to Table 1 below.

[Comparative Example 1-6]

The paint composition of each comparative example was prepared by adding each component according to Table 2 below.

Epoxy resin: Bisphenol A epoxy (Kukdo Chemical, YD-128)

Reactive Diluent 1: Trimethylolpropane triacrylate

Reactive Diluent 2: Neopentyl glycol diglycidyl ether

Reactive diluent 3: Neodecanoic acid 2,3-epoxypropyl ester

Liquid Phosphorus-Based Flame Retardants: Triaryl Phosphates Isopropylated

Foaming agent 1: Melamine

Foaming Agent 2: Zinc Borate

Acid catalyst: Ammonium polyphosphate (JLS FLAME RETARDANTS, JLS-APP)

Dispersant: BYK, BYKW 980

Defoamer: BYK, BYK 085

Thickener 1: Organophilic phyllosilicates (BYK, GARAMITE 1958)

Thickener 2: Fumed Silica (KCC, D-200)

Colorant: Black epoxy colorant (KCC, YE2408K)

Fiber 1: Aluminosilicate fiber (UNIFRAX, HS-95C)

Fiber 2: Magnesium silicate fiber (UNIFRAX, HI-90)

Fiber 3: Mineral wool (LAPINUS, MS-615)

Fiber 4: Carbon Fiber (ACECA, 3NA)

Amine Resin: Polyamide (KCC, CRG00167)

Curing accelerator: Tris-2,4,6-dimethylaminomethyl phenol

Pigment: Titanium Dioxide

[Experimental example: Evaluation of physical properties]

After curing the coating compositions of each Example and Comparative Example, they were cut to a thickness of 1 mm to produce sheets. The physical properties of the sheet were evaluated by the following method, and the results are shown in Table 3 below.

Flame retardant

According to UL-94, the flame retardancy of each sheet was evaluated (V0 grade: Cotton Ignition not possible, extinguishment within 30 seconds).

foaming rate

As the rate of change in thickness of each sheet before and after the fire resistance test, the foaming rate was calculated using the following formula. The fire resistance test was a fire resistance test in an electric furnace (internal temperature: 950°C), and the thickness was measured with vernier calipers.

Expansion rate = [(Thickness after fire resistance test - Thickness before fire resistance test) / Thickness before fire resistance test]

fire resistance performance

A specimen was manufactured by attaching each sheet on a 140 mm x 140 mm x 3 mm aluminum specimen. A K-Type thermocouple was attached to the back of each specimen to measure the back surface temperature, and the fire resistance performance of the paint composition was evaluated according to IMO Res.MSC307(88) (electric furnace: 950°C).

Sheet processability

After curing the coating composition prepared according to each example and comparative example, sheet processability was evaluated by quantifying the degree of sheet deformation and damage when making a sheet with the required film thickness (3 (excellent) for a normal film, severe deformation) and 0 (thirteen) in case of damage.

As shown in Table 3, the coating compositions of Examples 1-4 according to the present invention showed excellent physical properties in all measurement items. On the other hand, the paint compositions of Comparative Examples 1-6, in which the content of melamine or borate was outside the scope of the present invention, showed overall inferior physical properties compared to the paint compositions of the examples.

Claims (7)

A coating composition comprising an epoxy resin, a diluent, and a foaming agent, wherein the foaming agent includes melamine and a borate,
A paint composition comprising 2 to 20% by weight of the melamine and 5 to 30% by weight of the borate, based on the total weight of the paint composition. The coating composition according to claim 1, wherein the epoxy resin has a weight average molecular weight of 150 to 900 g/mol and an epoxy equivalent weight of 75 to 450 g/eq. The method of claim 1, wherein the reactive diluent includes a trifunctional or higher reactive diluent and a bifunctional or lower reactive diluent, and the mixing ratio of the trifunctional or higher reactive diluent and the bifunctional or lower reactive diluent is 80:20 to 20:80. Paint composition in weight ratio. The method of claim 1, based on the total weight of the composition, comprising 10 to 25% by weight of the epoxy resin, 2 to 20% by weight of the reactive diluent, 2 to 20% by weight of the melamine, and 5 to 30% by weight of the borate. Paint composition. The coating composition according to claim 1, which foams at 150°C and forms a carbonized layer. A sheet manufactured from the coating composition of any one of claims 1 to 5. 7. The sheet according to claim 6, wherein the expansion rate is 300 to 2,000%:
Foaming rate = [(Thickness after fire resistance test - Thickness before fire resistance test) / Thickness before fire resistance test]
The fire resistance test is a fire resistance performance test in an electric furnace (internal temperature: 950 ℃),
Thickness is measured with vernier calipers.