METHOD FOR PREPARING MELAMINE RESIN FOAMS USING GRINDED MELAMINE FOAM PARTICLES

Abstract

The present invention provides a process for producing a melamine resin foam comprising heating and foaming an aqueous mixture M using microwave radiation, said mixture M comprising melamine resin foam particles, at least one melamine-formaldehyde precondensate, at least one curative, at least one surfactant and at least one blowing agent as well as a process for recycling melamine resin foam scrap.

Claims

1.-12. (canceled)

13. A process for producing a melamine resin foam with a density in the range from 5 to 30 kg/m.sup.3 comprising heating and foaming an aqueous mixture M using microwave radiation, said mixture M comprising melamine resin foam particles, at least one melamine-formaldehyde precondensate, at least one curative, at least one surfactant and at least one blowing agent.

14. The process according to claim 13, wherein the melamine-resin foam particles have a particle size distribution with a D.sub.90 value below 150 ?m, determined by microcopy.

15. The process according to claim 13, wherein the melamine resin foam particles have a bulk density in the range from 10-500 kg/m.sup.3.

16. The process according to claim 13, wherein the weight ratio of melamine resin foam particles to melamine-formaldehyde precondensate is in the range from 0.5/100 to 10/100.

17. The process according to claim 13, wherein said 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.

18. The process according to claim 13 wherein formic acid is used as curative.

19. The process according to claim 13 wherein pentane is used as blowing agent.

20. A process for recycling melamine resin foam, wherein milled melamine resin foam scrap is used as melamine resin foam particles in the process according to claim 13.

21. A process according to claim 13, wherein the density of the melamine resin foam is in the range from 8 to 20 kg/m.sup.3.

22. A process for recycling melamine resin foam comprising the steps: a) milling melamine resin foam scrap to foam flakes with a largest dimension in the range from 2-5 cm, b) milling the foam flakes from step a) to foam particles having a particle size distribution with a D.sub.90 value below 150 ?m, determined by light microscope or sieving, c) forming an aqueous mixture M from the foam particles from step b), at least one melamine-formaldehyde precondensate, at least one curative, at least one surfactant and at least one blowing agent, d) heating and foaming the aqueous mixture M using microwave radiation to produce a melamine resin foam, and e) optionally tempering the melamine resin foam obtained in step d) at a temperature between 120-300? C.

23. A melamine resin foam obtained by the process of claim 13.

24. A method comprising utilizing the melamine resin foam according to claim 23 for acoustic and/or thermal insulation or for cleaning, grinding or polishing sponges.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0044] FIG. 1 is a microscope picture of a melamine resin foam according to the invention

[0045] Particles are fragments of the former cellular strut network and show the respective shape (struts and nods)In the foaming process the particles get wetted by the MF resin and can build up porous or compact substructures (REM pictures).

Embodiments

[0046] the present invention includes the following embodiments, wherein these include the specific combinations of embodiments [0047] 1. A process for producing a melamine resin foam comprising heating and foaming an aqueous mixture M using microwave radiation, said mixture M comprising melamine resin foam particles, at least one melamine-formaldehyde precondensate, at least one curative, at least one surfactant and at least one blowing agent. [0048] 2. The process according to embodiment 1, wherein the melamine-resin foam particles having a particle size distribution with a D.sub.90 value below 150 ?m, determined by microcopy. [0049] 3. The process according to embodiment 1 or 2, wherein the melamine resin foam particles have a bulk density in the range from 10-500 kg/m.sup.3. [0050] 4. The process according to embodiment any of embodiments 1 to 3, wherein the weight ratio of melamine resin foam particles to melamine-formaldehyde precondensate is in the range from 1/100 to 10/100. [0051] 5. The process according to any of embodiments 1 to 4, wherein said 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. [0052] 6. The process according to any of embodiments 1 to 5 wherein formic acid is used as curative. [0053] 7. The process according to any of embodiments 1 to 6 wherein pentane is used as blowing agent. [0054] 8. A process for recycling melamine resin foam, wherein milled melamine resin foam scrap is used as melamine resin foam particles in the process according to embodiment 1. [0055] 9 The process according to any of embodiments 1 to 8, wherein the density of the melamine resin foam is in the range from 5 to 30 kg/m.sup.3. [0056] 8. A process for recycling melamine resin foam comprising the steps: [0057] a) milling melamine resin foam scrap to foam flakes with a largest dimension in the range from 2-5 cm, [0058] b) milling the foam flakes from step a) to foam particles having a particle size distribution with a D.sub.90 value below 150 ?m, [0059] c) forming an aqueous mixture M from the foam particles from step b), at least one melamine-formaldehyde precondensate, at least one curative, at least one surfactant and at least one blowing agent, [0060] d) heating and foaming the aqueous mixture M using microwave radiation to produce a melamine resin foam, and [0061] e) optionally tempering the melamine resin foam obtained in step d) at a temperature between 120-300? C. [0062] 9. A melamine resin foam obtainable by the process of any of embodiments 1 to 9. [0063] 10. Use of the melamine resin foam according to embodiment 9 for acoustic and/or thermal insulation or for cleaning, grinding or polishing sponges.

EXAMPLES

[0064] Hereinafter, the present invention is described in more detail and specifically with reference to the Examples, which however are not intended to limit the present invention.

Methods of Measurement:

Ram Pressure Value [N]:

[0065] Ram pressure measurements for evaluating the mechanical quality of the melamine resin foams were all carried out as follows. A cylindrical ram having a diameter of 8 mm and a height of 10 cm was pressed into a cylindrical sample having a diameter of 11 cm and a height of 5 cm in the direction of foaming at an angle of 90% until the sample tore. The tearing force [N], hereinafter also referred to as ram pressure value, provides information as to the quality of the foam.

Cleaning Test:

[0066] The lipid emulsion consists of a mixture of 6 g Physioderm Cr?me 100, Physioderm and 0.2 g Active Char (Aktivkohle, gek?rnt, reinst 1.5 mm), Merck in 100 mL 2-Propanole is applied in ?80 mm stripes on a ceramic tile with a film thickness of ?400 ?m and dried at 160? C. for 15 minutes. The melamine-resin foam specimen (geometry: 140 mm?80 mm?30 mm) were put under water for 10 s and subsequently squeezed out by hand. Evaluation criteria: How many manual hubs (up+down=1 hub) of the wet foam specimen are necessary to remove a width of 2 cm of the dirt film coating. The less hubs are needed the better the cleaning efficacy.

Acoustic Absorbance

[0067] Acoustic absorbance was measures according to ISO 10534-2 with an impedance tube and melamine-resin foam samples with 30 mm thickness 100. mm diameter. The absorption value at 1250 Hz is given (value of 1.000=100% of absorption)

Materials Used:

[0068] MF Melamine-formaldehyde precondensate having an average molecular weight (number average) M of 350 g/mol, with a molar ratio of melamine:formaldehyde of 1:3, which apart from melamine comprised no further thermoset-formers and apart from formaldehyde comprised no further aldehydes and which was sulfite group free. [0069] T1 C.sub.12/C.sub.14-alkyl sulfate, sodium salt. [0070] T2 alkyl polyethylene glycol ether made from a linear, saturated C.sub.16/C.sub.18 fatty alcohol. [0071] MF-P Milled melamine-formaldehyde foam particles (mean particle size 60-120 ?m, bulk density 27 g/L))
Determination of Particle Size Distribution: Particle size distribution was measured by light microscope measurements using of Olympus

[0072] BX 60. For every sample 100 individual particles were measured. The resulting data was calculated as number total distribution D10, D50 and D90. 90% of particles have diameters below the D90 value. 50% of particles have diameters smaller and 50% have diameters larger than the median diameter D50.

[0073] Particle size distribution was measured by an air jet sieve ALPINE Luftstrahlsieb? 200 LS-N with the following conditions: [0074] Sample Weight: 10 g [0075] Sieves: 125, 90 and 60 ?m [0076] Vacuum (under the sieves): 40 mbar [0077] Air Flow Velocity: 50 m3/h

Preparation of Melamine-Formaldehyde Foam Particles MF-P1:

[0078] A melamine-formaldehyde foam block (Basotect?) was comminuted to foam flakes (10-100 mm) in laboratory scale with a cutting mill Pallmann PS 3.5 and sieved through square wholes of 15 mm. The flakes were further cut with a cutting mill Retsch SM 2000 and sieved by gravitation through a Condidur sieve 1 mm. The throughput was 1.4 kg per hour. The particle size was between 60-100 ?m determined by microscope. The particle size distribution determined by air jet sieve is summarized in Table 1.

Preparation of Melamine-Formaldehyde Foam Particles MF-P2:

[0079] A melamine-formaldehyde foam block (Basotect?) was comminuted to foam flakes (10-100 mm) with a cutting mill Pallmann PS 3.5 and sieved through square wholes of 15 mm. The flakes were manually dosed and further cut in production scale with a cutting mill Netzsch, SecoMy 37 (rotary speed: 1072 min-1, engine output 37 KW) and sieved through a 315 m sieve. The throughput was 300 kg per hour. The particle size was between 40-60 ?m determined by microscope. The particle size distribution determined by microscope and air jet sieve is summarized in Table 1 and 2. Bulk density was 97 kg/m.sup.3 (+/?2.5 kg/m.sup.3) at humidity 8% (+/?1%).

Preparation of Melamine-Formaldehyde Foam Particles MF-P3:

[0080] A melamine-formaldehyde foam block (Basotect?) was comminuted to foam flakes (10-100 mm) with a cutting mill Pallmann PS 3.5 and sieved through square wholes of 15 mm. The flakes were manually dosed and further cut in production scale with a cutting mill Netzsch, SecoMy 50 S (Air classifier at 3000 min-1, rotary speed: 1072 min-1, engine output 37 KW) and sieved through a 315 m sieve. The throughput was 160 kg per hour. The particle size distribution determined by microscope and air jet sieve is summarized in Table 1 and 2.

TABLE-US-00001 TABLE 1 Particle size distribution of MF-P1 to MF-P3 by light microscope Number sum Particle Particle Particle distribution size [?m] size [?m] size [?m] Sample MF-P1 MF-P2 MF-P3 D.sub.10 41.9 21.5 24.9 D.sub.50 69.3 50.8 46.0 D.sub.90 103.6 82.3 74.8

TABLE-US-00002 TABLE 2 Particle size distribution of MF-P1 to MF-P3 by air jet sieve Sample MF-P1 MF-P2 MF-P3 Particle size Residue [%] Residue [%] Residue [%] >125 ?m 3.6 1.4 0.1 >90-125 ?m 14.2 5.8 2.3 60-90 ?m 60.8 20.2 22.3 <60 ?m 21.4 72.6 75.3

Comparative Example C1

[0081] In a first step, 100 parts by weight of the melamine-formaldehyde precondensate, MF, 38 parts by weight of water, 1.2 parts by weight of anionic surfactant T1, 0.3 parts by weight of non-ionic surfactant T2, 2.5 parts of sodium formate, 3.0 parts of formic acid and 19.5 parts by weight of the pentane were mixed with one another at a temperature of 20 to 35? C. The mixture was introduced into a foaming mold of polypropylene and irradiated in a microwave oven with microwave. The foam bodies obtained after microwave irradiation were annealed in a circulating air oven at 200? C. for 20 min. The density of the foam was 10.2 g/L and Ram pressure value was 28.0 N.

Comparative Example C2

[0082] In a first step, 100 parts by weight of the melamine-formaldehyde precondensate, MF, 38 parts by weight of water, 1.2 parts by weight of anionic surfactant T1, 0.3 parts by weight of non-ionic surfactant T2, 2.5 parts of sodium formate, 3.0 parts of formic acid and 17.8 parts by weight of the pentane were mixed with one another at a temperature of 20 to 35? C. The mixture was introduced into a foaming mold of polypropylene and irradiated in a microwave oven with microwave. The foam bodies obtained after microwave irradiation were annealed in a circulating air oven at 200? C. for 20 min. The density of the foam was 8.6 g/L and Ram pressure value was 24.9 N.

Examples 1-4

[0083] In a first step, 100 parts by weight of the melamine-formaldehyde precondensate, MF, 2.5-10 parts per weight of melamine-formaldehyde foam particles MF-P1 (amount according to Table 3), 38 parts by weight of water, 1.2 parts by weight of anionic surfactant T1, 0.3 parts by weight of non-ionic surfactant T2, 2.5 parts of sodium formate, 3.0 parts of formic acid and 19.5 parts by weight of the pentane were mixed with one another at a temperature of 20 to 35? C. The mixture was introduced into a foaming mold of polypropylene and irradiated in a microwave oven with microwave. The foam bodies obtained after microwave irradiation were annealed in a circulating air oven at 200? C. for 20 min. The density of the foam was around 10 g/L and Ram pressure value was between 20 and 25 N (see Table 3).

TABLE-US-00003 TABLE 3 Amount of recycled MF-P1 form particles and properties of MF foams of Comparative Examples C1, C2 and Examples 1-4 Example C1 C2 1 2 3 4 MF-P1 [parts added 2.5 5.0 7.5 10.0 per 100 parts of MF precondensate] Density [kg/m.sup.3] 8.6 10.2 10.1 9.9 10.2 10.2 RAM pressure value 24.9 28.0 24.2 23.5 22.9 20.2 [N] Cleaning efficiency 5 5 4 3 3 3 [manual hubs] Acoustic absorbance 0.56 0.56 0.57 0.60 0.67 Not value at 1250 Hz, determined sample thickness 30 mm

Examples 5-8

[0084] Examples 1?4 were repeated using melamine-formaldehyde foam particles MF-P2. Amount of MP-P2 added per 100 parts of MF precondensate and properties of the foams obtained are summarized in Table 4.

TABLE-US-00004 TABLE 4 Amount of recycled MF-P2 form particles and properties of MF foams of Examples 5-8 Example 5 6 7 8 MF-P2 [parts added 2.5 5.0 7.5 10.0 per 100 parts of MF precondensate] Density [kg/m.sup.3] 9.3 10.2 9.9 10.5 RAM pressure value 24 21 21 19 [N] Cleaning efficiency 3 3 3 3 [manual hubs] Acoustic absorbance 0.62 0.62 0.62 Not value at 1250 Hz, determined sample thickness 30 mm

Examples 9-12

[0085] Examples 1?4 were repeated using melamine-formaldehyde foam particles MF-P3. Amount of MP-P2 added per 100 parts of MF precondensate and properties of the foams obtained are summarized in Table 5.

TABLE-US-00005 TABLE 5 Amount of recycled MF-P3 form particles and properties of MF foams of Examples 9-12 Example 9 10 11 12 MF-P3 [parts added 2.5 5.0 7.5 10.0 per 100 parts of MF precondensate] Density [kg/m.sup.3] 9.0 9.9 9.6 10.3 RAM pressure value 28 26 23 18 [N] Cleaning efficiency 4 3 3 3 [manual hubs] Acoustic absorbance 0.62 0.66 0.66 Not value at 1250 Hz, determined sample thickness 30 mm