Environment-friendly indoor renovating surface treating agent, renovating color-changing paint and renovating construction method

Abstract

The invention relates to the technical field of indoor water-based coatings, and discloses an environment-friendly indoor renovating surface treating agent, renovating color-changing paint and a renovating construction method, and the renovating surface treating agent comprises 5-30 parts of turpentine, 10-25 parts of citrate, 5-10 parts of fatty alcohol-polyoxyethylene ether, 1.0-5.0 parts of short-chain sodium dodecyl sulfate, 0.5-1.0 part of a dispersing agent, 0.3-0.8 part of hydroxypropyl methyl cellulose and 32-50 parts of water. The renovating surface treating agent is a two-component water-based system, and raw materials used by the renovating surface treating agent and the renovating color-changing paint are water-based environment-friendly materials, so that the renovating surface treating agent is safe and environment- Construction is easy and convenient, operation is easy, construction procedures are few, and original base materials do not need to be dismantled.

Description

Technical Field

[0001] This invention relates to the field of water-based coatings for indoor use, and in particular to environmentally friendly indoor renovation surface treatment agents, renovation and color-changing paints, and renovation construction methods. Background Technology

[0002] Many commonly used home decoration materials, such as tiles for indoor floors, bathrooms, and kitchens, are prone to wear, stubborn stains, and scratches on some surfaces after long-term use, affecting their appearance. Removing and replacing tiles is costly, time-consuming, noisy, and polluting. Tile renovation coatings offer a more economical, faster, and environmentally friendly solution.

[0003] Current tile renovation paint technologies suffer from two main drawbacks: firstly, they use two-component solvent-based products, which are cumbersome to apply; and secondly, they have a short lifespan. The use of common silane coupling agents as adhesives results in insufficient adhesion, and the effect gradually disappears over time due to hydrolysis. For example, Chinese invention patent CN114958121A, "A Water-Based Tile Paint and Its Preparation and Application Methods," discloses a water-based tile paint comprising a main agent and a curing agent. The main agent and curing agent are mixed in a weight ratio of 100:(1-5). Through epoxy silane coupling treatment of the acrylic emulsion and the use of silane adhesion promoters, combined with pigment dispersion technology, a dense cross-linked network is formed, solving the problem of poor adhesion and water resistance of the tile paint in the short term. However, due to the insufficient cross-linking degree and cohesive force of the single-component acrylic, the product has a short lifespan. The Chinese invention patent CN118995324A, entitled "A Tile Renovation Coating System and Tile Renovation Method", discloses a coating system that includes a tile surface treatment agent and a water-based tile color-changing paint. The tile color-changing paint uses acrylic emulsion and silane coupling agent to enhance adhesion. Its drawback is that the product has a short service life due to the hydrolysis failure of the silane coupling agent over time.

[0004] Therefore, there is an urgent need for environmentally friendly interior renovation surface treatment agents, renovation and color-changing paints, and renovation construction methods to solve the above-mentioned technical problems. Summary of the Invention

[0005] The purpose of this invention is to solve the problem of adhesion and durability of interior renovation coatings, to achieve high adhesion, long-lasting wear resistance and stain resistance, and to provide environmentally friendly interior renovation surface treatment agents, renovation and color-changing paints and renovation construction methods.

[0006] To achieve the above objectives, the present invention is implemented according to the following technical solution:

[0007] An environmentally friendly interior renovation surface treatment agent, comprising the following components in parts by weight:

[0008] Turpentine oil 5-30 parts, citrate ester 10-25 parts, fatty alcohol polyoxyethylene ether 5-10 parts, short-chain sodium dodecyl sulfonate 1.0-5.0 parts, dispersant 0.5-1.0 parts, hydroxypropyl methylcellulose (HPMC) 0.3-0.8 parts, water 32-50 parts.

[0009] Preferably, the citrate is one or two of triethyl citrate, lauryl ether-7 citrate, and acetylated tributyl citrate.

[0010] Preferably, the dispersant is a sodium polycarboxylate dispersant.

[0011] The citric acid esters used in this invention are all low-odor citric acid esters.

[0012] The working principle of the surface treatment agent of this invention is as follows:

[0013] Turpentine oil has good solubility and penetrability, and can form a uniform thin film on the substrate surface. It can penetrate into the tiny pores of the substrate surface, increasing the contact area between the surface treatment agent of this invention and the substrate surface, thereby improving adhesion. At the same time, after the turpentine oil evaporates, the remaining organic components can form a certain physical adsorption with the substrate surface.

[0014] The substrates involved in this invention include ceramic tiles, flooring, wood products, etc.

[0015] Citrate esters possess good film-forming properties and flexibility, enabling them to form continuous films on substrate surfaces. They can work in conjunction with turpentine to fill uneven areas on the substrate surface, resulting in a denser film and improved adhesion. Furthermore, some groups in the citrate ester molecule can form weak chemical bonds with the chemical components on the substrate surface, further enhancing adhesion.

[0016] Turpentine and citrate esters work synergistically in an aqueous system as a substrate surface treatment agent, leveraging their respective advantages. Turpentine first penetrates into the pores of the tile, providing anchoring points for the citrate ester. The film formed by the citrate ester then fixes the turpentine to the substrate surface. Together, they give the surface treatment agent of this invention excellent adhesion to the tile surface, effectively resisting external friction, impact, and water erosion. Simultaneously, the rapid evaporation of turpentine combined with the slow-drying properties of citrate esters creates a dual cleaning mechanism of "rapid penetration and slow emulsification."

[0017] The surfactants fatty alcohol polyoxyethylene ether and short-chain sodium dodecyl sulfonate are used to uniformly disperse turpentine oil and citrate ester in water to form a stable emulsion.

[0018] Fatty alcohol polyoxyethylene ethers possess hydrophilic polyoxyethylene segments and hydrophobic fatty alcohol segments. Their working principle is that the hydrophobic fatty alcohol segments interact with non-polar substances such as turpentine and citrate esters, while the hydrophilic polyoxyethylene segments interact with water. This reduces the surface tension at the oil-water interface, allowing turpentine and citrate esters to be uniformly dispersed in water as tiny oil droplets, forming a stable emulsion and achieving the effect of water solubility.

[0019] Sodium dodecyl sulfonate is an anionic surfactant containing a hydrophilic sulfonic acid group and a hydrophobic dodecyl group in its molecule. In solution, the dodecyl group of sodium dodecyl sulfonate inserts into oil phase substances such as turpentine and citrate esters, while the sulfonic acid group faces the aqueous phase, forming a negatively charged adsorption layer on the surface of oil droplets. This causes the oil droplets to repel each other and is less likely to aggregate, thus allowing turpentine and citrate esters to be uniformly dispersed in water, achieving the purpose of mixing and dissolving in water.

[0020] The present invention also includes a renovation and color-changing paint, said renovation and color-changing paint comprising the following components in parts by weight:

[0021] 6-20 parts deionized water, 0.3-0.8 parts dispersant, 0.1-0.4 parts wetting agent, 0.5-0.8 parts defoamer, 1-4 parts inorganic nanoparticles, 18-25 parts titanium dioxide, 3-10 parts precipitated barium sulfate, 50-60 parts pure acrylic emulsion, 1.8-3 parts film-forming aid, 1.0-5 parts polytetrafluoroethylene micro powder, 0.2-0.5 parts preservative and bactericide, and 0.3-0.6 parts leveling agent.

[0022] Preferably, the dispersant is at least one of sodium polycarboxylate, ammonium polycarboxylate, maleic anhydride copolymer, and polyether-modified polysiloxane.

[0023] Preferably, the inorganic nanoparticles are at least one of nano-silicon oxide, nano-alumina, and nano-zirconia.

[0024] Preferably, the nano-zirconia has a particle size of 10–50 nm; the nano-alumina has a particle size of 20–60 nm; and the nano-silica has a particle size of 30–60 nm.

[0025] The pure acrylic emulsion of the present invention is a self-crosslinking pure acrylic emulsion, and the self-crosslinking auxiliary components are diacetone acrylamide (DAAM) and adipate dihydrazide (ADH).

[0026] The working principle of the refurbishing and color-changing paint of this invention is as follows:

[0027] The renovation and color-changing paint uses an environmentally friendly, self-crosslinking core-shell structured pure acrylic emulsion. The paint film achieves a hardness of 2H and exhibits good toughness, with excellent stain resistance and adhesion due to its dense structure. The technical principle involves using amides and bifunctional crosslinking agents. Diacetone acrylamide participates in the polymerization reaction, introducing ketone carbonyl groups into the shell layer, enriching the latex particles with ketone carbonyl groups. Adipate dihydrazide is dispersed in the aqueous phase outside the emulsion particles, and the two form a "ketone-hydrazide crosslink," improving the overall performance of the emulsion.

[0028] Inorganic nanoparticles are added to the renovation and color-changing paint. The nanoparticles have a high Mohs hardness, which can significantly improve the hardness and wear resistance of the film. The surface of the nanoparticles is rich in hydroxyl groups, which can form chemical bonds and hydrogen bonds with the resin emulsion, thereby improving the adhesion between the coating and the substrate. The nanoparticles can fill the tiny pores in the coating, reduce the air permeability and water permeability of the coating, and improve the corrosion resistance and water resistance of the coating.

[0029] The selection of dispersants in renovation and color-changing paints takes into account the synergistic effect of electrostatic repulsion and steric hindrance, thereby improving the dispersion stability of the coating and inhibiting the aggregation of nanoparticles.

[0030] The filler used is precipitated barium sulfate, which, due to its chemical inertness and regular needle-like, flake-like, or spherical particle shape, has a large specific surface area. This can improve the hardness of the coating while also enhancing the storage stability of the coating and preventing sedimentation.

[0031] The addition of polytetrafluoroethylene micro powder, due to its low surface energy and extremely low coefficient of friction between particles, further enhances the wear resistance of the coating.

[0032] The present invention also includes a renovation construction method, using the renovation surface treatment agent and the renovation color change paint described above;

[0033] The construction method includes the following steps:

[0034] S1, Preliminary cleaning of the surface of the refurbished substrate;

[0035] S2, Apply a renovation surface treatment agent to the cleaned renovation substrate surface and dry at room temperature for 2-4 hours;

[0036] S3, then continue to apply renovation and color-changing paint to the renovation surface treatment agent on the substrate surface, and dry at room temperature (20-40℃) for 24-48 hours.

[0037] Preferably, in step S2, the amount of the surface treatment agent used is 0.05–0.10 kg / m². 2 In step S3, the amount of repainting paint used is 0.15–0.20 kg / m³. 2 .

[0038] In step S1, the surface of the substrate to be refurbished is initially cleaned, mainly removing dust and other easily cleanable stains.

[0039] The renovation substrates in this invention refer to tiles, flooring, and woodwork used for indoor floors; tiles, flooring, and woodwork used for bathrooms; tiles and flooring used for kitchens, etc.

[0040] The combined application of the surface treatment agent and the color-changing paint of this invention can achieve high adhesion, long-lasting wear resistance, and stain resistance. The principle is as follows:

[0041] (1) Improve adhesion: The turpentine and citrate esters used in the renovation surface treatment agent can work together to reduce the surface tension of the renovation paint, allowing it to spread better on the substrate surface and improve the wettability of the substrate; at the same time, turpentine can dissolve the film-forming substances such as resins in the renovation paint, allowing the film-forming substances to penetrate and diffuse better on the substrate surface, forming a tighter mechanical bond; citrate esters have both hydrophilic and lipophilic groups in their molecular structure. The carboxyl groups in citrate esters can undergo esterification with the hydroxyl groups on the substrate surface to form hydrogen bonds, chemical bonds, etc. At the same time, the hydroxyl groups in citrate esters can undergo chemical reactions with the active carboxyl or hydroxyl groups in the renovation paint, increasing the adhesion between the renovation paint and the substrate.

[0042] (2) Adjusting the drying speed: The rapid evaporation of turpentine allows the refinishing paint to dry quickly on the substrate surface, forming a preliminary paint film. The presence of citrate esters can appropriately slow down the drying speed of the paint film, giving it more time to level and wet the substrate surface, thus avoiding defects such as pinholes and orange peel caused by excessively rapid drying. The synergistic effect of both can make the drying speed of the paint film more reasonable and improve the quality of the coating.

[0043] (3) Improved coating performance: Citrate esters have good plasticizing properties, which can improve the flexibility and impact resistance of the coating (the coating formed by renovation and color change paint). Terpenes in turpentine have certain antioxidant and corrosion resistance properties, which can improve the weather resistance and chemical corrosion resistance of the coating to a certain extent. The combination of the two can improve the physical and chemical properties of the coating and extend its service life.

[0044] The surface treatment agent of the present invention can also be used in combination with commercially available water-based coatings, but the surface treatment agent of the present invention works better when used in combination with the color-changing paint of the present invention.

[0045] Beneficial effects:

[0046] 1. This invention is a two-component water-based system. The raw materials used in the surface treatment agent and the color-changing paint are all water-based environmentally friendly materials, which are safe, environmentally friendly, and environmentally friendly.

[0047] 2. This invention first uses a surface treatment agent to treat the old ceramic tiles, flooring, and woodwork to ensure that the renovation and color-changing paint has a high adhesion to the substrate, which can give full play to the performance of the renovation and color-changing paint film, such as a hardness of 2H or above, an adhesion of 0 level, and a scrubbing resistance of more than 50,000 times. The film layer of the renovation and color-changing paint is scratch-resistant, stain-resistant, and easy to clean.

[0048] 3. This invention is simple to construct, easy to operate, requires few construction steps, and does not require the removal of the original substrate. Detailed Implementation

[0049] The present invention will now be described in further detail with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0050] There are no particular restrictions on the purity of any raw materials used in this invention. However, it is preferred to use industrial-grade or conventionally pure materials used in this field.

[0051] Unless otherwise specified, the apparatus used in this invention employs commonly used devices in the field.

[0052] The sources of some of the chemicals used in the following embodiments and comparative examples are shown in the table below:

[0053]

[0054] Example 1, Example 2, Example 3, Comparative Example 1, Comparative Example 2

[0055] The preparation process of the environmentally friendly indoor renovation surface treatment agent in Example 1 is as follows:

[0056] Add 20 parts of turpentine oil to a mixing container, and add 25 parts of triethyl citrate, 10 parts of fatty alcohol polyoxyethylene ether AEO-9, 4 parts of short-chain sodium dodecyl sulfonate, 0.6 parts of dispersant (sodium polycarboxylate), 40 parts of water, and 0.4 parts of hydroxypropyl methylcellulose (HPMC) in sequence while stirring at medium-low speed. Stir at 800-1500 rpm until homogeneous.

[0057] In Examples 2, 3, Comparative Example 1, and 2, the preparation process was the same as that in Example 1, and the weight parts of each component are shown in Table 1 below:

[0058] Table 1. Component ratio of refurbished surface treatment agents

[0059]

[0060] The treatment effects of the renovation surface treatment agents prepared in the above three examples (Example 1, Example 2, and Example 3) and two comparative examples were tested on the surface of old ceramic tiles. During the experiment, five old ceramic tile surfaces were treated with the renovation surface treatment agents prepared in Example 1, Example 2, Example 3, Comparative Example 1, and Comparative Example 2, respectively, and then the renovation color-changing paint of Example 4 was applied. The specific process is as follows:

[0061] S1: Perform preliminary cleaning of the old tile surface to remove dust and other easily cleanable stains;

[0062] S2: Apply a renovation surface treatment agent to the old tile surface at a dosage of 0.07 kg / m². 2 Dry at room temperature for 3 hours;

[0063] S3: Continue applying the water-based renovation and color-changing paint described in Example 4, using 0.17 kg / m³. 2 Dry at room temperature (30℃) for 36 hours.

[0064] The treated old ceramic tile surfaces were tested, and the test results are shown in Table 2:

[0065] Table 2 Adhesion test results of refurbishing surface treatment agents

[0066]

[0067] As can be seen from the results of Examples 1-3 in Table 2, firstly, the renovation surface treatment agent of this invention can effectively reduce the mirror effect of the tile glaze and improve the hydrophilicity of the tile glaze, thereby improving the adhesion of water-based renovation and color-changing paint to the tile surface. Secondly, the results of Comparative Examples 1-2 show that the adhesion of renovation surface treatment agents using turpentine or citrate alone is significantly reduced.

[0068] Examples 4, 5, and 6; Comparative Example 3, 4, and 5

[0069] The preparation process of the renovation and color-changing paint in Example 4 is as follows: 9.3 parts of deionized water were added to a stirring container. Under medium-low speed stirring, 0.5 parts of 5040 dispersant, 0.3 parts of maleic anhydride copolymer dispersant (AM-P96 dispersant), 0.2 parts of CN407 wetting agent, 0.3 parts of 3157F defoamer, and 1.8 parts of hexadecane film-forming agent were added sequentially. After stirring evenly, the speed was increased, and inorganic nanoparticles (1.5 parts of nano-alumina and 2 parts of nano-silica) and 20 parts of 699 titanium dioxide were added sequentially. Mix 5 parts of barium sulfate precipitate and 3 parts of polytetrafluoroethylene micro powder at a high speed of 2000-2500 r / min until uniformly dispersed, then reduce the speed to 600-900 r / min. Add 55 parts of pure acrylic emulsion (Baolijia emulsion 2377B), 0.2 parts of defoamer (A10 defoamer), 0.4 parts of bactericide and preservative (0.2 parts of BM5050 preservative and 0.2 parts of K15 bactericide), and 0.5 parts of leveling agent (RM2020 leveling agent). Stir evenly to obtain the renovation and color-changing coating.

[0070] In Examples 5, 6, 3, 4, and 5, the preparation process was the same as that in Example 4, and the weight parts of each component are shown in Table 2 below:

[0071] Table 2. Component ratio of refurbishment and color-changing paint

[0072]

[0073]

[0074] The performance of the renovation and color-changing paints prepared in the above three examples (Examples 4, 5, and 6) and three comparative examples (Comparative Examples 3, 4, and 5) was tested on the surface of old ceramic tiles. During the experiment on the old ceramic tile surface, the surface treatment agent prepared in Example 1 was used to treat the surface of six old ceramic tiles, and then the renovation and color-changing paints of Examples 4, 5, 6, 3, 4, and 5 were applied respectively. The specific process is as follows:

[0075] S1: Perform preliminary cleaning of the old tile surface to remove dust and other easily cleanable stains;

[0076] S2: Apply a renovation surface treatment agent to the old tile surface at a dosage of 0.07 kg / m². 2 Dry at room temperature for 3 hours;

[0077] S3: Continue by applying water-based renovation and color-changing paint, using 0.17 kg / m². 2 Dry at room temperature (30℃) for 36 hours.

[0078] The treated old ceramic tile surfaces were tested, and the results are shown in Table 4. The technical indicators of the coatings obtained in Examples 4-6 and Comparative Examples 3-5 were tested according to the technical requirements for topcoats in GB / T9755-2024 "Synthetic Resin Emulsion Interior Wall Coatings". Stain resistance was tested according to the industry standard HG / T4756-2014 "Interior Wall Stain-Resistant Latex Coatings", adhesion was tested according to GB / T 9286-2021 cross-cut adhesion test, hardness was tested according to GB / T6739-2022, and chemical resistance and water resistance were tested according to GB / T22374-2018. The test results are shown in Table 4.

[0079] Table 4 Performance Evaluation Results of Renovation and Color Change Paint

[0080]

[0081]

[0082] The data in Table 4 shows that the renovation and color-changing paints in Examples 4-6 have relatively high overall stain resistance, chemical resistance, adhesion, and hardness. They can withstand 100,000 washes, have a hardness of 3H, and their adhesion to the substrate is below level 0. Comparative Example 3 and Comparative Example 4, which do not contain nanoparticles or grinding aids, show a significant decrease in the hardness, adhesion, chemical resistance, and water resistance of their paint films, thus affecting their overall scratch resistance and durability. Comparative Example 5, which uses a conventional emulsion (styrene-acrylic emulsion), shows an even more significant decrease in the hardness and adhesion of its paint film. Its chemical resistance and water resistance are both abnormally below standard, and the overall stain resistance, scratch resistance, and durability of the paint film do not meet the requirements.

[0083] Performance tests were conducted on the combined application of the above-mentioned surface treatment agent and the color-changing paint, as well as on the application of the color-changing paint alone. The results are shown in Table 5.

[0084] The process of applying the surface treatment agent and the color-changing paint in combination (two combinations are: the surface treatment agent of Example 1 + the color-changing paint of Example 4; the surface treatment agent of Example 2 + the color-changing paint of Example 5) is as follows:

[0085] S1: Perform preliminary cleaning of the old tile surface to remove dust and other easily cleanable stains;

[0086] S2: Apply a renovation surface treatment agent to the old tile surface at a dosage of 0.07 kg / m². 2 Dry at room temperature for 3 hours;

[0087] S3: Continue by applying water-based renovation and color-changing paint, using 0.17 kg / m². 2 Dry at room temperature (30℃) for 36 hours.

[0088] The application process for renovation and color-changing paint (the renovation and color-changing paint used is: the renovation and color-changing paint of Example 4; the renovation and color-changing paint of Example 5) is as follows:

[0089] S1: Perform preliminary cleaning of the old tile surface to remove dust and other easily cleanable stains;

[0090] S2: Continue by applying water-based renovation and color-changing paint, using 0.17 kg / m². 2 Dry at room temperature (30℃) for 36 hours.

[0091] Table 5

[0092]

[0093] The data in Table 5 shows that the renovation paint and the renovation surface treatment agent have a good synergistic effect in this solution. Both are indispensable to achieve the target comprehensive performance, and the combination of these two in this solution has the best effect.

[0094] In summary, the renovation and color-changing paint of this invention exhibits good stability and excellent performance, making it particularly suitable for renovation work on tiles, floors, and woodwork. Compared to oil-based paints, this invention is environmentally friendly, odorless, and especially suitable for indoor use; compared to UV-cured paints, this invention dries naturally without special treatment, is simple to operate, and is suitable for widespread application.

[0095] The technical solutions of the present invention are not limited to the specific embodiments described above. Any technical modifications made in accordance with the technical solutions of the present invention fall within the protection scope of the present invention.

Claims

1. An environmentally friendly interior renovation surface treatment agent, characterized in that, The renovating surface treatment agent comprises the following components in parts by weight: 5-30 parts turpentine, 10-25 parts citrate, 5-10 parts fatty alcohol polyoxyethylene ether, 1.0-5.0 parts sodium dodecyl sulfonate, 0.5-1.0 parts dispersant, 0.3-0.8 parts hydroxypropyl methylcellulose, and 32-50 parts water.

2. The environmentally friendly indoor renovation surface treatment agent according to claim 1, characterized in that: The citrate is one or two of triethyl citrate, lauryl ether-7 citrate, and acetylated tributyl citrate.

3. The environmentally friendly indoor renovation surface treatment agent according to claim 1, characterized in that: The dispersant is a sodium polycarboxylate dispersant.

4. A repaint for color change, characterized in that, The refinishing and color-changing paint comprises the following components in parts by weight: 6-20 parts deionized water, 0.3-0.8 parts dispersant, 0.1-0.4 parts wetting agent, 0.5-0.8 parts defoamer, 1-4 parts inorganic nanoparticles, 18-25 parts titanium dioxide, 3-10 parts precipitated barium sulfate, 50-60 parts pure acrylic emulsion, 1.8-3 parts film-forming aid, 1.0-5 parts polytetrafluoroethylene micro powder, 0.2-0.5 parts preservative and bactericide, and 0.3-0.6 parts leveling agent.

5. The renovation and color-changing paint according to claim 4, characterized in that: The dispersant is at least one of sodium polycarboxylate, ammonium polycarboxylate, maleic anhydride copolymer, and polyether-modified polysiloxane.

6. The renovation and color-changing paint according to claim 4, characterized in that: The inorganic nanoparticles are at least one of nano-silicon oxide, nano-alumina, and nano-zirconia.

7. The renovation and color-changing paint according to claim 6, characterized in that: The nano-zirconia has a particle size of 10–50 nm; the nano-alumina has a particle size of 20–60 nm; and the nano-silica has a particle size of 30–60 nm.

8. A renovation construction method, characterized in that, Use the surface treatment agent according to any one of claims 1 to 3 and the color-changing paint according to any one of claims 4 to 7; The construction method includes the following steps: S1, Preliminary cleaning of the surface of the refurbished substrate; S2, Apply a renovation surface treatment agent to the cleaned renovation substrate surface and dry at room temperature for 2-4 hours; S3, then continue to apply renovation and color-changing paint to the renovation surface treatment agent on the substrate surface, and dry at room temperature (20-40℃) for 24-48 hours.

9. The renovation construction method according to claim 8, characterized in that: In step S2, the dosage of the surface treatment agent is 0.05–0.10 kg / m². 2 In step S3, the amount of repainting paint used is 0.15–0.20 kg / m³. 2 .

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