A homogeneously colored dark sound absorption element comprising a melamine resin foam and an azo dye

Abstract

The present invention relates to an acoustically active shaped body comprising a melamine resin foam and an azo dye, where the shaped body has a dark color with a lightness L* of below 40; and to a use of the shaped body for acoustic insulation; and to a process for producing a shaped body comprising heating and foaming an aqueous mixture M using microwave radiation, said mixture M comprising at least one melamine-formaldehyde precondensate, at least one azo dye, at least one curative, at least one surfactant and at least one blowing agent.

Description

[0001] 240388

[0002] 1

[0003] A homogeneously colored dark sound absorption element comprising a melamine resin foam and an azo dye

[0004] The present invention relates to an acoustically active shaped body comprising a melamine resin foam and an azo dye, where the shaped body has a dark color with a lightness L* of below 40; and to a use of the shaped body for acoustic insulation; and to a process for producing a shaped body comprising heating and foaming an aqueous mixture M using microwave radiation, said mixture M comprising at least one melamine-formaldehyde precondensate, at least one azo dye, at least one curative, at least one surfactant and at least one blowing agent.

[0005] For sound absorption in room acoustics or anechoic chambers the melamine resin foams should show a combination of good sound absorption, a good flame retardancy and aesthetic appearance. Therefore, it can be useful to color the foams for the use in sound absorption panels.

[0006] The coloring of sound absorption panels can be made after the cutting of the melamine formaldehyde foam blocks, e.g. by spraying the plates or other geometries or immersing them in a dye solution or pigment dispersion, or printing with a dye solution. In such cases the viscosity of the solutions and dispersion has to be low that the dye / pigment can cover the cellular structure. For both techniques a subsequent drying and curing step afterwards is mandatory. Both, the spraying of the dye solution / pigment dispersion has several drawbacks. The high handling effort and the drying step is very time consuming and expensive. Furthermore, the watering of the foam favors a hydrolysis of the polymer, and the subsequent drying step is an additional stress to the polymer and favors polymer decomposition. Both effects could lead to negative material properties like emanation and emission as well as a decreased flame retardancy behavior. These negative effects are pronounced by the use of high-concentrated and high-viscous colorants to achieve a dark colors, especially with low lightness. In addition, this could lead to a sealing of the cellular structure and results in a strong decrease in air permeability and strongly reduces the sound absorption of the foams especially in the medium to high frequency range.

[0007] EP 3816991 discloses a method of manufacturing a decorated sound absorbing panel, comprising providing a sound absorbing panel which can be made of a melamine resin foam to a digital printer.

[0008] As alternative the coloring of sound absorption panels can be made after the cutting of the melamine formaldehyde foam blocks by laminating them on the surface. Again, this could lead to a sealing of the cellular structure and results in a strong decrease in air permeability and strongly reduces the sound absorption of the foams especially in the medium to high frequency range.

[0009] US 2008 / 0230308 discloses a decorative acoustic absorber which is for example colored, forms a wall element and has an acoustic material and a visible side, wherein the acoustic material can be a melamine foam resin which is laminated on the visible side with a non-woven layer, and printing being carried out on the non-woven layer. 240388

[0010] 2

[0011] Another way is the usage of the pigment dispersion or a dye solution in the foam manufacturing process itself. However, the used pigment dispersion or a dye solution should not influence the emulsion stability as well as the cell and strut formation of the cellular network. Especially, with high concentrations of the color the foams could show irregular foam structures. This could lead to the formation of blow holes, low mechanical properties and bad processability. Furthermore, other material properties like flame retardancy and the emission behavior can be worsened as well.

[0012] The object was to find dark colored sound absorption elements of melamine resin foam, and a method to make dark colored sound absorption elements of melamine resin foam, where the cellular structure is not sealed, where the air permeability is not reduced, and where the sound absorption especially in the medium to high frequency range is still high.

[0013] Another object was to find dark colored sound absortion elements of melamine resin foam, which have a high mechanical stability as well as a low burning times in the respective fire tests.

[0014] The object was solved by an acoustically active shaped body comprising a melamine resin foam and an azo dye, where the shaped body has a dark color with a lightness L* of below 40.

[0015] The object was also solved by a use of the shaped body for acoustic insulation.

[0016] The object was also solved by a process for producing the shaped body comprising heating and foaming an aqueous mixture M using microwave radiation, said mixture M comprising at least one melamine-formaldehyde precondensate, at least one azo dye, at least one curative, at least one surfactant and at least one blowing agent.

[0017] The melamine resin foam usually an open-celled structure. The open-cell content of the melamine resin foam (e.g. measured according to DIN ISO 4590) can be more than 50 %, preferable of 95 % or higher, most preferably of 98 to 100%.

[0018] The density of the melamine resin foam can be in the range from 5 to 15 kg / m3, more preferably 6 to 12 kg / m3.

[0019] Preferably the shore hardness 000 of the melamine resin foam is in the range from 35 to 75 N, measured according to ASTM D 2240.

[0020] Preferably the ram pressure is in the range from 20 to 50 N, measured as described in US-A-4 666 948. Specimens measuring 25x25x10 cm are indented, in the direction of foaming, with a ram which has a diameter of 25 mm, a spherical cap radius of 40 mm and an edge radius of 2 mm and which meets the specimen surfaces at an angle of 90°, until tearing occurs; the tearing force is determined as a measure of the mechanical quality of the foam. 240388

[0021] 3

[0022] The melamine resin foam may comprise at least 75 wt%, preferably at least 80 wt% and in particular at least 85 wt% of cured melamine resin. The melamine resin foam may comprise 75 to 99 wt.-%, preferably of 80 to 97 wt.-% of the cured melamine resin.

[0023] The melamine-resin foam can be produced by a process comprising heating and foaming an aqueous mixture M using microwave radiation, said mixture M comprising at least one melamine-formaldehyde precondensate, at least one azo dye, at least one curative, at least one surfactant and at least one blowing agent.

[0024] The melamine resin foam can be tempered at a temperature between 120 - 300°C.

[0025] The azo dye is used in a total amount of 0.01 to 10 parts by weight, preferably from 0.1 to 6 parts by weight , and in particular from 0.2 to 4 parts by weight, based on the melamine-formaldehyde precondensate.

[0026] The azo dye can be dissolved in an aqueous solution of the melamine-formaldehyde precondensate prior to heating the mixture M.

[0027] The melamine / formaldehyde precondensates may be prepared separately or commercially available precondensates of the two components, melamine and formaldehyde may be used. Preferably a melamine- formaldehyde precondensate having a molar ratio of melamine to formaldehyde ranging from 1 : 5 to 1 : 1 .3, more preferably from 1 : 3.5 to 1 : 1 .5 is used. Preferably the number average molecular weight Mn ranges from 200 g / mol to 1000 g / mol. Preference is given to unmodified melamine / formaldehyde precondensates.

[0028] Anionic, cationic and nonionic surfactants, and also mixtures thereof can be used as dispersant / emulsifier.

[0029] Useful anionic surfactants include for example diphenylene oxide sulfonates, alkane and alkylbenzenesulfonates, alkylnaphthalenesulfonates, olefinsulfonates, alkyl ether sulfonates, fatty alcohol sulfates, ether sulfates, a-sulfo fatty acid esters, acylaminoalkanesulfonates, acyl isethionates, alkyl ether carboxylates, N-acylsarcosinates, alkyl and alkylether phosphates.

[0030] Useful nonionic surfactants include alkylphenol polyglycol ethers, fatty alcohol polyglycol ethers, fatty acid polyglycol ethers, fatty acid alkanolamides, ethylene oxide-propylene oxide block copolymers, amine oxides, glycerol fatty acid esters, sorbitan esters and alkylpolyglycosides.

[0031] Useful cationic emulsifiers include for example alkyltriammonium salts, alkylbenzyldimethylammonium salts and alkylpyridinium salts.

[0032] The dispersants / emulsifiers can be added in amounts from 0.2% to 5% by weight, based on the melamine- formaldehyde precondensate. 240388

[0033] 4

[0034] Preferably the mixture M comprises a surfactant mixture comprising a mixture of 50 to 90 wt% of at least one anionic surfactant and 10 to 50 wt% of at least one nonionic surfactant, wherein the weight percentages are each based on the total weight of the surfactant mixture.

[0035] As curatives it is possible to use acidic compounds which catalyze the further condensation of the melamine resin. The amount of these curatives is generally in the range from 0.01 % to 20% by weight and preferably in the range from 0.05% to 5% by weight, all based on the precondensate. Useful acidic compounds include organic and inorganic acids, for example selected from the group consisting of hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, formic acid, acetic acid, oxalic acid, toluene sulfonic acids, amido sulfonic acids, acid anhydrides and mixtures thereof. Preferably formic acid is used as curative.

[0036] The mixture further comprises at least one blowing agent. Useful physical blowing agents include for example hydrocarbons, such as pentane, hexane, halogenated, more particularly chlorinated and / or fluorinated, hydrocarbons, for example methylene chloride, chloroform, trichloroethane, chlorofluorocarbons, hydro fluoro olefins (HFOs)), alcohols, for example methanol, ethanol, npropanol or isopropanol, ethers, ketones and esters, for example methyl formate, ethyl formate, methyl acetate or ethyl acetate, in liquid form or air, nitrogen or carbon dioxide as gases.

[0037] The amount of blowing agent in the mixture generally depends on the desired density for the foam. Preferably the amount in relation to the melamine-formaldehyde precondensate is chosen in an amount that the density of the foam is 5 to 15 kg / m3, more preferably 6 to 12 kg / m3. The blowing agent is preferably present in the mixture in an amount of 0.5% to 60% by weight, preferably 1 % to 40% by weight and more preferably 1.5% to 30% by weight, based on the melamine-formaldehyde precondensate. It is preferable to add a physical blowing agent having a boiling point between 0 and 80°C. Most preferably pentane is used as blowing agent.

[0038] The precondensate being foamed up generally by heating the suspension of the melamine-formaldehyde precondensate to obtain a foamed material.

[0039] The introduction of energy may preferably be effectuated via electromagnetic radiation, for example via high- frequency radiation at 5 to 400 kW, preferably 5 to 200 kW and more preferably 9 to 120 kW per kilogram of the mixture used in a frequency range from 0.2 to 100 GHz, preferably 0.5 to 10 GHz. Magnetrons are a useful source of dielectric radiation, and at least one magnetron can be used at the same time.

[0040] The foamed materials produced can be finally dried, removing residual water and blowing agent from the foam. Drying is carried out preferably in a drying oven at a temperature in the range of 40 to 260°C, particularly preferably 100 to 250°C until a constant weight. The process described provides blocks or slabs of foamed material, which can be cut to size in any desired shapes. 240388

[0041] 5

[0042] The process for producing the melamine resin foam comprising preferably the steps: a) forming an aqueous mixture M from at least one melamine-formaldehyde precondensate, at least one curative, at least one surfactant, at least one azo dye and at least one blowing agent, b) heating and foaming the aqueous mixture M using microwave radiation to produce a melamine resin foam, and c) optionally tempering the melamine resin foam obtained in step b) at a temperature between 120 - 300°C.

[0043] The melamine resin foam may be post-treated by at least one of the following methods:

[0044] - Thermocompression to obtain foams with higher density, better durability and cleaning behavior.

[0045] - Hydrophobation to obtain foams with lower water uptake.

[0046] - Oleophobation to obtain foams with lower oil uptake.

[0047] - Impregnation with flame retardants to further improve the FST properties (Flame, Smoke, toxicity) in the case of fire.

[0048] The shaped body may have any geometrical form, such as cylindrical, conical, pyramidal, wedge, spherical, cuboidal, rectangluar cuboidal, or hexagonal form, where the rectangular cuboidal shaped body is preferred. The rectangular cuboid shaped body (typically a plate) can have the following dimensions: a length ranging from 0.1 m to 3.5 m, a width ranging from 0.1 m to 1.3 m and a thickness ranging from 0.03 m to 0.1 m. The melamine resin foam can be shaped into the desired shaped body by cutting devices, for example bladessaws or punching tools.

[0049] "Acoustically active" in reference to a shaped body refers to a body having an acoustic absorption of at least 90 %, preferably at least 95 %, and in particular at least 98% with the impedance tube measurement according to DIN 10534 at 2000 Hz and with a sample thickness of 50 mm.

[0050] The shaped body can be used for many applications, such as acoustical and / or thermal insulation in aircraft, ship and motor vehicle construction, in mechanical engineering or in building construction, especially the heat insulation and sound insulation of buildings and parts of buildings, especially of interwalls; further the heat insulation and sound insulation of engine and interior spaces of vehicles and aircraft and also low-temperature insulation, for example of cold rooms, oil tanks and containers of liquefied gas including LNG carriers. Owing to their high open-cell content, these foams are useful for absorbing and storing liquids of any kind. They can appreciably reduce undesired sloshing around of comparatively large quantities of liquid in moving tanks (aircraft, ships, motor vehicles). Further fields of application are the use as insulating wallcovering and also as insulating and shock-absorbing packaging material. Owing to the high hardness of the melamine resin, these foams are also useful as highly efficacious cleaning means, for example for cleaning, grinding and polishing sponges having a slightly abrasive effect. The open-cell structure of the foams additionally permits the absorption and storage of suitable cleaning, grinding and polishing agents in the interior of the foams. The foams can also be rendered hydrophobic and oleophobic for specific duties, for example by impregnation with silicone, fluorocarbon, acryl or paraffine oil emulsions. Owing to the extremely low emissions of 240388

[0051] 6 formaldehyde, the foams of the present invention can also be used in the hygiene sector, e.g., in the form of thin mats as a wound dressing or as a constituent of baby diapers, femcare and adult incontinence products.

[0052] The lightness L* can be measured using various color models, preferably by the Cl ELAB color space (e.g. on a spectrophotometer). In general, the Cl ELAB color space is a color model developed by the International Commission on Illumination (CIE) to provide a more uniform representation of colors as perceived by the human eye. It is designed to be device-independent, meaning it can be used across different devices and lighting conditions. The components of Cl ELAB colour space are typically L* (Lightness), which represents the lightness of the color and ranges from 0 (no lightness) to 100 (maximum lightness); a* (Green-Red Axis), which represents the position between green and red and where negative values indicate green, while positive values indicate red; and b* (Blue- Yellow Axis): which represents the position between blue and yellow, and negative values indicate blue, while positive values indicate yellow.

[0053] The L* value ranges in general from 0 to 100, with 0 being no lightness and 100 being maximum lightness. Instruments like spectrophotometers or colorimeters may be used to measure the lightness of a color by quantifying its luminance relative to a standard light source. The lightness may be determined (e.g. on a spectrophotometer) according to “Colorimetry — Part 4: CIE 1976 L*a*b* colour space” from the International Commission on Illumination (CIE), Vienna, Austria.

[0054] The lightness L* is below 40, preferably below 30, in particular below 25.

[0055] The shaped body is usually homogeneously colored with the dark color, which can be made by the azo dye. Typically, the azo dye is homogeneously distributed throughout the shaped body to make the dark color. The term “homogeneously colored” can be understood that the lightness L* differs in the shaped body up to plus / minus 3, preferably up to plus / minus 2, and in particular plus / minus 1.

[0056] The dark color may be black, blue, red, brown, green, or a mixture of any of these colors. Preferably the dark color is black. The dark color may be black, blue, red, brown, green, or a mixture of any of these colors, where the lightness L* is below 40, preferably below 30, in particular below 25. Preferably the dark color is black where the lightness L* is below 40, preferably below 30, in particular below 25. The dark color is usually made by the azo dye.

[0057] Suitable azo dyes include in particular monoazo or disazo dyes, for example those with a diazo component derived from an aniline or from a five-membered aromatic heterocyclic amine which has from one to three hetero atoms selected from the group consisting of nitrogen, oxygen and sulfur in the heterocyclic ring and may be fused with a benzene, thiophene, pyridine or pyrimidine ring.

[0058] Important monoazo or disazo dyes include for example those whose diazo component is derived for example from an aniline, an aminonaphthalene or from a heterocyclic amine of the pyrrole, furan, thiophene, pyrazole, imidazole, 240388

[0059] 7 oxazole, isoxazole, thiazole, isothiazole, triazole, oxadiazole, thiadiazole, benzofuran, benzothiophene, benzimidazole, benzoxazole, benzothiazole, benzisothiazole, pyridothiophene, pyrimidothiophene, thienothiophene or thienothiazole series.

[0060] Preferred azo dyes are monoazo dyes which include a diazo component derived from an aminonaphthalene.

[0061] Preferred azo dyes are free of amino groups.

[0062] The azo dye can be water soluble, such as at least 1 g / l at 25 °C, preferably at least 5 g / l at 25 °C, and in particular at least 20 g / l at 25 °C.

[0063] The azo dye is preferably an anionic azo dyes, which may contain ionic subsitutents (e.g. sulfonic acid groups). Suitable anionic azo dyes are C.l. acid black 210, C.l. acid black 1 and C.l. acid black 234. More preferred are anionic azo dyes which contain sulfonic acid groups and are free of amino groups.

[0064] The azo dye is in another preferred form a metal-complex dye, such as a 1 :1 or 1 :2 metal-complex dye. Suitable metal complex dyes are derived from o, o’-d isubstituted azo dyes. Suitable metals for the complex forming metal are chromium or cobalt. The metal ion may form a complex with the azo group and optionally other ligands, often through coordination bonds. Preferably, the metal-complex dye is free of amino groups.

[0065] A preferred metal-complex dye is an anionic metal complex dye, which may be derived from o.o’-disubstituted azo dyes. The anionic metal complex dye may exhibit anionic character based on ionic groups (e.g. sulfonic acid groups) or based on their metal-complex which is free of ionic groups. Suitable anionic metal complex dyes are C.l. acid black 194, C.l. acid black 52, C.l. acid black 82 and C.l. acid black 172, where C.l. acid black 194 is preferred.

[0066] Preferably, the azo dye is trisodium-bis(3-hydroxy-4-[2-hydroxy-1 -naphthyl)azo]-7-nitronaphthaline-1 -sulfonato- chromate, which may also be known as C.l. acid black 194.

[0067] The shaped body may comprise at least 0.01 wt%, preferably 0.1%, and in particular 0.2 % of the azo dye.

[0068] The shaped body may comprise from 0.01 to 10 wt%, preferably from 0.1 to 6 wt%, and in particular from 0.2 to 4 wt% of the azo dye. 240388

[0069] 8

[0070] Examples

[0071] Ram pressure value:

[0072] Ram pressure measurements for evaluating the mechanical quality of the melamine resin foams were all carried out as follows as described in US-A-4 666 948: Specimens measuring 25x25x10 cm were indented, in the direction of foaming, with a ram which has a diameter of 25 mm, a spherical cap radius of 40 mm and an edge radius of 2 mm and which meets the specimen surfaces at an angle of 90°, until tearing occurs; the tearing force was determined as a measure of the mechanical quality of the foam.

[0073] Burning test:

[0074] The burning test was made in a small scale burner test with the measurement of the burning time according to DIN EN ISO 11925-2:2020-07. In this test the flame is applied to the test specimen for 15 seconds. After the flame is removed, the burning time is observed to assess how long the material continues to burn. The lower the burning time the better.

[0075] Formaldehyde testing (FA-testinq):

[0076] The specimen in the size of 20 cm x 20 cm x 5 cm was conditioned at 240°C for 10 min. The formaldehyde measurement took place at 40 °C / 1 h in water and was run in accordance with DIN EN 14184-1 .

[0077] Acoustic absorption

[0078] The measurement of the acoustic absorption was done with the impedance tube measurement according to DIN 10534 at 2000 Hz and with a sample thickness of 50 mm.

[0079] Example 1

[0080] The melamine-formaldehyde precondensate HF-MF was a spray-dried melamine-formaldehyde precondensate having an average molecular weight (number average) Mn of 350 g / mol, which had a molar ratio of melamine:formaldehyde of 1 :2.8.

[0081] 100 g of the spray-dried melamine-formaldehyde precondensate HF-MF were dissolved in 35 g of water, then 1 .35 g of a sodium C12 / C14-alkyl sulfonate and 2.4 g of sodium formiate were added. The mixture was stirred for 60 s. Afterwards, 15.6 g of pentane as blowing agent and 3.3 g formic acid were added to the mixture. The mixture was stirred for 30 min and subsequently transferred to a propylene mold for foaming. The foaming was supported by microwave energy by 6 min of 4 magnetrons with 800 W respectively. After the foaming was accomplished, the foam was demolded and dried in the oven for 8 hours at 100°C. A density of about 10 + / - 1 kg / m3was obtained. 240388

[0082] 9

[0083] The commercial solution of C.l. acid black 194 (color content 23 wt%) was added after the sodium formiate adding to the mixture and the procedure was followed accordingly. The amount of recipe water was corrected by the respective water from the dye solution / particle dispersion. The amount of added dye is listed in Table 1 , where the concentration refers to the total amount of the azo dye based on 100 parts by weight of the solid HF-MF resin

[0084] The properties of the foams were determined as shown in Table 1 . The formaldehyde emission was for all samples < 40 mg / kg. All foams in Table 1 were homogeneouly colored.

[0085] T able 1 : Properties foams colored with azo dye

[0086] The examples in Table 1 demonstrated that a dark colored melamine resin foam can be obtained with a low lightness L* and excellent accoutic properties. At the same time the buring time improved to a very short time and the Ram pressure stayed on a high level.

[0087] For comparison, the above foam preparation method was repeated but instead of the azo dye a commercial aqueous pigment dispersion was added, named Colanyl® N530 from Heubach with 68 wt% solid content. The amount of added pigment is listed in Table 1 , where the concentration refers to the total amount of the solid pigment based on 100 parts of the solid HF-MF resin. 240388

[0088] 10

[0089] Table 2: Properties comparative foams colored with pigments (all data are comparative)

[0090] The examples in Table 2 demonstrated that a dark colored melamine resin foam can be obtained with a low lightness L* and excellent acoustic properties. However, the burning time got worse to a longer time and the Ram pressure decreased to a very low level.

Claims

24038811Claims1 . An acoustically active shaped body comprising a melamine resin foam and an azo dye, where the shaped body has a dark color with a lightness L* of below 40.

2. The shaped body acording to claim 1 where the shaped body comprises from 0.01 to 10 wt%, preferably from 0.1 to 6 wt%, and in particular from 0.2 to 4 wt% of the azo dye.

3. The shaped body acording to claim 1 or 2 where the lightness L* is below 30, preferably below 25.

4. The shaped body according to any of the proceeding claims where the shaped body is homogeneously colored with the dark color.

5. The shaped body according to any of the proceeding claims where the dark color is black.

6. The shaped body according to any of the proceeding claims where the azo dye is water soluble, preferably at least 1 g / l at 25 °C.

7. The shaped body according to any of the proceeding claims where the azo dye is an anionic azo dye, preferably an anionic metal complex dye.

8. The shaped body according to any of the proceeding claims where the azo dye is trisodium-bis(3-hydroxy-4-[2- hydroxy-1-naphthyl)azo]-7-nitronaphthaline-1-sulfonato-chromate.

9. The shaped body according to any of the proceeding claims where the shaped body is cylindrical, conical, pyramidal, wedge, spherical, cuboidal, rectangluar cuboidal, or hexagonal.

10. The shaped body according to any of the proceeding claims where the melamine resin foam has an open-celled structure.

11. A use of the shaped body as defined in any of the preceding claims for acoustic insulation.

12. A process for producing a shaped body as defined in any of claims 1 to 10 comprising heating and foaming an aqueous mixture M using microwave radiation, said mixture M comprising at least one melamine-formaldehyde precondensate, at least one azo dye, at least one curative, at least one surfactant and at least one blowing agent.2403881213. The process according to claim 12 where the azo dye is used in a total amount of 0.01 to 10 parts by weight, preferably from 0.1 to 6 parts by weight , and in particular from 0.2 to 4 parts by weight, based on the melamineformaldehyde precondensate.

14. The process according to claim 12 or 13 where the azo dye is dissolved in an aqueous solution of the melamine-formaldehyde precondensate prior to heating the mixture M.

15. The process according to any of claims 12 to 14 where the azo dye is water soluble, preferably at least 1 g / l at 25 °C.

16. The process according to any of claims 12 to 15 where the azo dye is trisodium-bis(3-hydroxy-4-[2-hydroxy-1- naphthyl)azo]-7-nitronaphthaline-1-sulfonato-chromate.

17. The process according to any of claims 12 to 16 comprising the steps: a) forming an aqueous mixture M from at least one melamine-formaldehyde precondensate, at least one curative, at least one surfactant, at least one azo dye and at least one blowing agent, b) heating and foaming the aqueous mixture M using microwave radiation to produce a melamine resin foam, and c) optionally tempering the melamine resin foam obtained in step b) at a temperature between 120 - 300°C.

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