Patent Application
20190309457
The present invention relates to heat- and flame-resistant textile nonwovens or nonwoven fabrics comprising fibers/flocs consisting of thermoset melamine-formaldehyde. They are suitable as thermal insulator and as acoustic insulation material, and exhibit a feature that is not typical for this type of material: low emission of volatile organic compounds, in particular formaldehyde. The formaldehyde emissions of the low-emission melamine/formaldehyde nonwovens and melamine/formaldehyde nonwoven fabrics are significantly lower than the threshold values.
The production of melamine-resin nonwovens by the melt-blow process is claimed in general terms in dependent claim 29 in WO 2006/100041 A1.
The melt-blow process uses hot air emerging from a die together with the melt to lengthen the resultant filaments and to spin these to give particularly fine final fibers. These fibers are laid to give a random-laid composite, then the resultant spunbonded nonwoven is prehardened with use of gaseous HCl and then its hardening reaction is completed at high temperatures.
WO 2013/152858 A1 describes microfiber nonwovens made of fibrous flocs made of reactive low-molecular-weight resin melts which are capable of forming polymers and have solidified in the form of glasses. The diameter of the individual fibers here is less than 5 μm.
WO 2014/080003 describes a melamine/formaldehyde foam with particulate fill material and reduced formaldehyde values (determined in accordance with DIN 55666).
EP 2 616 505 B1 describes a process for the production of a melamine/formaldehyde foam with improved hydrolysis resistance.
This leads to low formaldehyde emissions at elevated temperature and moisture levels. Heat-conditioning and passage of hot air through the material are used here to achieve the following formaldehyde emission values:
<150 mg/kg in accordance with VDA 275
<40 mg/kg in accordance with DIN EN ISO 14184-1
<0.03 mg/kg in accordance with DIN 717-1.
No thermoset material based on formaldehyde has been disclosed hitherto that complies with the requirements of the automobile industry for the interior. In accordance with VDA 275, this requires formaldehyde values below 10 mg/kg.
It was an aim of the present invention to develop a textile sheet whose fibers consist essentially, i.e. to an extent of from 70 to 100% by weight, of duromers based on melamine/formaldehyde. This textile sheet is intended to comply with the requirements of the automobile industry for the interior in relation to formaldehyde emissions, and to exhibit values significantly lower than the currently applicable threshold values, so that it can continue in use in the event of possible future tightening of the threshold values in this sector.
Extensive experimentation has revealed that use of hot air flowing onto or through a material can produce a low-emission textile sheet with density less than 1.00 kg/m3, preferably with density from 5 to 20 kg/m3, and with high resilience. A progressive temperature profile is to be selected here, and the air flowing through the material must be replaced at least to some extent by fresh air. The requirements of the automobile industry in relation to formaldehyde emissions for the interior are met, and the values obtained are significantly below the currently applicable threshold values.
Raw material used comprises a melamine-formaldehyde resin in accordance with DE102006027760 with low formaldehyde content, preferably with M:F ratio 1:2, and with almost complete etherification of the methylol groups by methanol, i.e. at least 80% of methylol groups have been etherified.
The material is produced as described in WO 2013/152858 A1. The textile sheet is produced here via melting of solid, methanol-etherified melamine-formaldehyde resins followed by spinning by way of a melt-blow process. A melt stream here produced by melt dies arranged in a row alongside one another on a spinning beam is molded in a plurality of steps to give a large number of microfibers/flocs. The molten raw material here is taken up by a hot air stream with temperature above the melt temperature, fluidized, fibrized and layered in a laying system to give a nonwoven fabric.
Preferred process conditions are a mass flow rate of the melt of 0.3 to 3.0 g/min per die, preferably from 0.85 to 1.5 g/min, a melt temperature of from 80 to 200° C., particularly preferably about 160° C., and a gas stream temperature of from 130 to 330° C., particularly preferably about 310° C. The aim is to obtain structures of maximal fineness with average fiber diameters less than 10 μm, preferably less than 5 μm, and with maximized surface:volume ratio. Spinning processes used here are of the type described in WO 2013/152858 or WO 2006/100041. This gives sheets consisting of very fine individual fibers and/or flocs as depicted in
Collection of the resultant flocs or fibers can alternatively be achieved by adjusting the angle between die and laying area to be smaller than 90°, or the laying area can have a convex or concave surface. Air can be removed by suction below the perforated laying area. After collection on the laying area, the nonwoven or the nonwoven fabric has been cooled to from 40 to 20° C., i.e. to about room temperature.
It is thus possible to achieve densities of from 5 to 20 kg/m3 that are of interest for lightweight applications, as thermal insulator and as acoustic insulation material.
The nonwoven or the nonwoven fabric is then treated with hydrogen chloride gas. The gas treatment advantageously takes place in a sealed chamber, preferably at room temperature. After exposure to hydrogen chloride, the material has significantly higher reactivity. In another process step, the nonwoven or nonwoven fabric is subjected to a thermal treatment. For this, the temperature is increased continuously or gradually to from 260 to 340° C., preferably to from 260 to 320° C. The permitted temperature increase here in the range up to 160° C. for the stabilization of the structure is only at most 20° C./min. Once 160° C. has been reached, the temperature rise can be increased to 100° C./min. The nonwoven or the nonwoven fabric is then kept at the temperature reached, up to 340° C., for from 5 to 90 min, preferably for from 10 to 60 min. During the entire thermal treatment, hot air flows through or onto the material in order to improve heat transfer. From 5 to 50% of the convection air must be replaced by fresh air during the procedure.
Once the thermal treatment has concluded, rapid cooling of the hot material to from 30 to 60° C., preferably from 30 to 40° C., is imposed within a period of 5 s and at most 3 min, preferably within a period of from 20 s to 2 min, by contact with material suitable for rapid heat exchange, for example laying on a metal belt and use of cold air at a temperature of from 0° C. to 40° C. flowing through the material.
The final product is characterized by a mass per unit area in the range from 20 to 600 g/m2, the thickness of the material being up to 40 mm. The resultant low densities, and the voluminosity, provide particular acoustic and thermal properties to the final product. The heat- and flame-resistant nonwoven and, respectively, the nonwoven fabric, produced by the process described, is part of the present invention.
Resultant thermal conductivity values (in accordance with DIN EN ISO 8302) are low: from 0.028 W/(m*K) to 0.030 W/(m*K), depending on mass per unit area, fiber fineness, thickness, degree of compaction and post-treatment.
The structure of the nonwoven, and the particularly fine fibers, moreover permit construction of a nonwoven providing effective acoustic insulation. The acoustic properties are listed by way of example in the following table (in accordance with DIN ISO 10534-2; test sample diameter: 30 mm):
Achievement of the low formaldehyde emissions in the product requires the combination of the following building blocks:
The resultant nonwoven melamine-formaldehyde fabrics were subjected to the following tests to determine formaldehyde emissions:
These test methods differ in principle in the conditions to which the material is subjected and in the methods used.
In the case of DIN EN ISO 14184-1, the quantity of formaldehyde that can be liberated is determined at a temperature of 40° C. in an aqueous medium.
The test arrangement in accordance with VDA 275 suspends the test sample above water for three hours at 60° C., and the emissions are collected and then quantitatively analyzed.
Emission of formaldehyde occurs with all products based on thermoset formaldehyde compounds, because formaldehyde is a constituent, or the main constituent of the material.
However, many tests were carried out in the region of room temperatures and body temperatures, because these are the traditional usage temperatures of many materials and components.
Formaldehyde emission increases with increasing temperature and humidity. The emission values are exponentially dependent on the test temperature. This relationship can be described approximately by the empirical Arrhenius equation.
The low-emission nonwoven melamine/formaldehyde fabrics produced by the process described above achieve the following values:
The resultant sheet material is preferably used as thermal insulator and as acoustic insulation material, in particular for lightweight applications, and also in vehicle construction and the transport industry.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2016 012 034.7 | Oct 2016 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2017/075949 | 10/11/2017 | WO | 00 |
