Polyamide foam with high thermal stability

Abstract

The present invention relates to polyamide foam particles comprising (A) 5 to 99.9% by weight of at least one polyamide, (B) 0.1 to 5% by weight of at least one stabilizer selected from secondary arylamines, and (C) 0 to 49% by weight of further additives, wherein the sum of components (A) to (C) is 100% by weight, a method for producing the polyamide foam particles, and a polyamide particle foam molded article produced thereby.

Description

[Technical Field]

[0001] The present invention relates to polyamide foam particles, (A) At least one type of polyamide, 5-99.9% by weight, (B) At least one stabilizer selected from the group of secondary arylamines, 0.1 to 5% by weight. (C) Further additives 0-49% by weight The present invention relates to polyamide foam particles comprising, wherein the sum of components (A) to (C) is 100% by weight, a method for producing the polyamide foam particles, and a polyamide particle foam molded article produced thereby.

[0002] Related Prior Art Polyamide-based particle foams are well known from the literature. First, PA particle foam was published in the 1980s (Japanese Patent Publication No. 61-268737 (JP61-268737)). More recent publications describe polyamide particle foams that do not contain organic blowing agents and can be processed with established steam technology (International Publication No. 2021 / 052881 (WO2021 / 052881 A1); International Publication No. 2016 / 147582 (WO2016 / 147582A1); US Patent Application Publication No. 2021 / 0253819 (US20210253819_A1)). Most partially crystalline polyamides, such as PA6;PA66 and PA6 / 66, exhibit good mechanical properties even at temperatures above 150°C, so it would be beneficial to use parts made from polyamide particle foam at operating temperatures above 150°C.

[0003] Molded parts made from polymer particle foam are highly susceptible to thermal oxidative aging processes because they have a relatively high contact area with the surrounding air within their bubbles and in the spaces between molten beads. Established antioxidants for polyamides affect the processing properties in steam chest molding. The most effective antioxidants contain halogens, such as bromine and iodine, which are crucial for applications near metals and electronic devices due to the corrosive effects of halogens, and for the formation of toxic fumes in the event of a fire. Halogen-based thermal stabilizers, such as potassium iodide in combination with copper(I) iodide, are crucial for Global Health System (GHS) classification.

[0004] U.S. Patent Application Publication No. 2018 / 0044497 (US 2018 / 0044497) discloses a polyamide resin foam molded article comprising a polyamide resin, wherein the degree of crystallinity X is 10% to 50% and the crystallite size D is 10 nm or more, as calculated based on the peak with the narrowest peak width in the X-ray diffraction profile of the foam molded article, and a method for manufacturing this polyamide resin foam molded article.

[0005] U.S. Patent Application Publication No. 2021 / 0253819 (US 2021 / 0253819 A1) discloses polyamide resin foam particles having a crystallite size greater than 8 nm as measured by X-ray diffraction.

[0006] International Publication No. 2011 / 134996 (WO 2011 / 134996 A1) relates to foaming granules containing a polymer matrix comprising at least 55% by weight of polyamide having a crystallinity of up to 30%, wherein the granules are suitable for producing particulate foams for use in transport and / or construction in the automotive, aerospace, construction, packaging, sports and recreation industries. The granules may contain a heat stabilizer or antioxidant selected from the group consisting of copper compounds, sterically hindered phenols, sterically hindered aliphatic amines and / or aromatic amines.

[0007] Copper iodide, copper bromide, and copper chloride may be included in combination with alkaline halides; these well-known inorganic stabilizers have a negative impact on the processability during the foaming process. In addition to inorganic stabilizers, sterically hindered phenols are also well-known heat stabilizers for polyamides; however, their long-term stabilization effect is limited to temperatures up to 120°C.

[0008] International Publication No. 2021 / 052881 (WO 2021 / 052881 A1) discloses polyamide foam particles that can be obtained by a continuous one-step process and have a low bulk density, and polyamide particle foam molded articles that can be obtained by steam chest molding and have high temperature stability, which are particularly suitable for high-temperature conditions, such as electrodeposition coating processes.

[0009] U.S. Patent Application Publication No. 2022 / 0169849 (US 2022 / 0169849 A1) relates to providing polyamide resin pre-foamed particles that can be used as a raw material for polyamide resin foam molded articles having excellent mechanical strength. The polyamide resin pre-foamed particles of the disclosure contain a polyamide resin. The polyamide resin pre-foamed particles have an expansion ratio of 1.0 or more, where the expansion ratio is equal to the density ρ1 (g / cm³). 3 The density ρ2 (g / cm³) is obtained after pressurizing with 0.9 MPa air and then heating for 30 seconds using saturated steam at a temperature 5°C higher than the heat fusion temperature. 3 This is the ratio (ρ1 / ρ2) to ).

[0010] U.S. Patent No. 5,399,681 (US 5 399 681 B1) discloses a colored thermoplastic resin composition comprising a crystalline thermoplastic resin containing a black dye or a black dye and a fibrous reinforcing material, i.e., a fiber-reinforced polyamide, wherein the black dye is a black dye that can be obtained by the reaction of one or more anionic surfactants and nigrosine. The black dye has excellent dispersibility and compatibility with the crystalline thermoplastic resin, and lowers its crystallization temperature to produce molded articles with excellent appearance and high surface gloss.

[0011] International Publication No. 2021 / 191209 (WO 2021 / 191209) discloses a heat-aging polyamide molding composition comprising at least one thermoplastic polyamide; at least one polyethyleneimine homopolymer or copolymer; and a specific combination of at least one secondary arylamine and / or at least one condensation product of a secondary arylamine with an aliphatic aldehyde, aliphatic ketone, or a mixture thereof.

[0012] U.S. Patent Application Publication No. 2020 / 317878 (US 2020 / 317878) discloses a continuous method for producing polyamide foam having a smooth surface, low density, and small bubble size by an extrusion foaming method, which includes compounding a polyamide resin with a composite epoxy chain extender and maleic anhydride grafted polypropylene (MAPP) wax.

[0013] Summary of the Invention The present invention has been made in view of the above-mentioned prior art, and the object of the present invention is to provide halogen-free polyamide foam particles that can be processed into a polyamide particle foam molded article having a high closed-cell ratio and high thermal oxidation stability at high temperature and high humidity using a standard steam chest molding apparatus.

[0014] The aforementioned problem is a polyamide foam particle, (A) At least one type of polyamide, 5-99.9% by weight, (B) At least one stabilizer selected from secondary arylamines, 0.1 to 5% by weight. (C) Further additives 0-49% by weight This was resolved by the polyamide foam particles, which include, where the sum of components (A) to (C) is 100% by weight.

[0015] Preferably, the polyamide foam particles are (A) At least one type of polyamide, 84.5-99.5% by weight. (B) At least one stabilizer selected from secondary arylamines, 0.5-3% by weight. (C) Further additives 0-15% by weight It consists of the following, where the sum of components (A) to (C) is 100% by weight.

[0016] In the case of a mixture, the weight percentages shown for (A), (B), and (C) refer to the total of all polyamides, stabilizers, or additives, respectively.

[0017] The aforementioned at least one polyamide may be a homopolyamide obtained from the polymerization of lactams, such as caprolactam or lauryl lactam, a condensation product of a diamine and a dicarboxylic acid, a copolyamide thereof, or a mixture of two or more different polyamides.

[0018] Preferably, the at least one polyamide (A) has a melting point (peak melting temperature T) in the range of 150 to 350°C, determined by differential scanning calorimetry (DSC) in accordance with DIN EN ISO 11357-3:2018. pm Selected from partially crystalline polyamides having ).

[0019] Particularly preferred is polyamide (A) having a crystallinity of more than 20%, preferably in the range of 25-60%, as determined by the integration of the melting signal using differential scanning calorimetry (DSC) in accordance with DIN EN ISO 11357-3-2018 (100% crystallinity corresponds to 230 J / g) (Journal of Polymer Science Part B Polymer Physics 35 (1997) 2219-2231).

[0020] Preferably, the polyamide (A) contains at least one polyamide selected from the group consisting of polycaprolactam (PA6), polybutylene adipamide (PA4,6), polyhexamethylene adipamide (PA6,6), polyhexamethylene sebacamide (PA6,10), polyhexamethylene dodecaneamide (PA6,12), poly-11-aminoundecaneamide (PA11), polylauryl lactam (PA12), poly-m-xylylene adipamide (PAMXD6), polypentamethylene sebacamide (PA510), 6T / Z (Z = lactam), 6T / 6I, 6T / 6I / XY, 6T / XT (X = linear or branched C4-C18-diamine), XT (X = C4-C18-diamine), 6.12.PA PACM12 (PACM = p-diaminodicyclohexylmethane), PA MACM 12 (MACM = 3,3-dimethyl-p-diaminodicyclohexylmethane), PA MPMD 6 (MPMD = 2-methylpentamethylene diamine), PA MPMD T, PA MPMD 12, polyhexamethylene isophthalamide (PA6I), polyhexamethylene isophthalamide-co-hexamethylene terephthalamide (PA6I / 6T), PA6-3-T (a polyamide of terephthalic acid and a mixture of 2,2,4- and 2,4,4-trimethylhexamethylene diamine), polybutylene sebacamide (PA4,10), polydecamethylene sebacamide (PA10,10), polypentamethylene adipamide (PA5,6), PA6 / 66 and PA66 / 6, PA6Y (Y = C4-C18-diacid) and their amide exchange products.

[0021] Most preferably, the at least one polyamide (A) is selected from the group consisting of polycaprolactam (PA6), polylauryl lactam (PA12), polyhexamethylene adipamide (PA6,6), polyhexamethylene sebacamide (PA6,10), polyhexamethylene dodecaneamide (PA6,12), PA6 / 66, PA66 / 6 and copolyamide PA6 / 6,36, or a mixture thereof.

[0022] Preferably, the bulk density of the polyamide foam particles is 100-500 kg / m 3within the range of, preferably 250 to 350 kg / m 3 within this range.

[0023] The at least one stabilizer (B) described above is selected from secondary arylamines. A mixture of two or more different secondary arylamines may be used as the stabilizer (B).

[0024] Compounds having the general structure R1-NH-R2 (where R1 and R2 are aromatic moieties) may be used as the stabilizer (B).

[0025] Preferably, the at least one stabilizer (B) described above is (B1) an amine-containing heat stabilizer including bis(4-(1-methyl-1-phenylethyl)phenyl)amine, 2-ethyl-2'-ethoxy-oxalanilide, dimethylglyoxime, 2,2'-bipyridine, 1,10-phenanthroline, ortho-phenylenediamine, 1,2-diaminocyclohexane, 1,4-diaminobutane, urea, 8-hydroxyquinoline, substituted urea, and combinations thereof, (B2) a stabilizer containing nigrosine, or (B3) a stabilizer including an adduct of phenylenediamine with acetone, an adduct of phenylenediamine with linolenic acid, 4,4'-bis(α,α-dimethylbenzyl)diphenylamine, N,N'-dinaphthyl-p-phenylenediamine, N-phenyl-N'-cyclohexyl-p-phenylenediamine, or a mixture of two or more of (B1) to (B3) selected from.

[0026] Preferred compounds have structures as shown in formulas (I) to (III). [Chemical formula]

[0027] In one embodiment, the secondary arylamine may be combined with an oligomeric amine. A preferred oligomeric amine contains 0.1 to 2.0% by weight of at least one secondary arylamine and / or at least one condensation product of a secondary arylamine with an aliphatic aldehyde, aliphatic ketone, or a mixture thereof. This stabilizer is commercially available from Oka-Tec as Okaflex®.

[0028] Other secondary arylamines are commercially available as Naugard® 445 (from SI Group Sales Germany (DEAB) GmbH) or Flexamin® GR (from SI Group Sales Germany (DEAB) GmbH).

[0029] The secondary arylamines can lower the crystallization temperature of the polyamide matrix material, as observed in DSC. They are effective stabilizers against thermal and / or hydrolytic decomposition of the polyamide foam particles and the polyamide particle foam molded articles, and do not negatively affect the foam processing characteristics.

[0030] One example is nigrosine (commercially available as Solvent Black 5, Solvent Black 7, or Colorant Black 500), a condensation product of aniline and nitrobenzene. An overview of the active species in nigrosine is provided in U.S. Patent No. 6,399,681 (US6,399,681 B1). Depending on the condensation conditions, a variety of species are present in commercially available Solvent Blacks.

[0031] The present invention further provides a method for producing polyamide foam particles as described above, a) Below: At least one type of polyamide (A) 5-99.9% by weight, At least one stabilizer (B) selected from secondary amines, 0.1-5% by weight. Further additives (C) 0-49% by weight A step of melting a polymer mixture, including b) A step of impregnating the molten polymer mixture with 0.01 to 4.0% by weight of carbon dioxide, nitrogen, or a mixture thereof, based on 100% of the polymer mixture, to form an impregnated polymer melt. c) The process of extruding the impregnated polymer melt and granulating it in an underwater pelletizer to form polyamide foam particles. The method includes the foregoing.

[0032] Preferably, 0.1 to 1% by weight of talc or carbon black is used as an additional additive (C).

[0033] The present invention further provides a method for producing a polyamide particle foam molded article by steam chest molding of the above-mentioned polyamide foam particles at a temperature in the range of 100 to 170°C, and a polyamide particle foam molded article that can be obtained by this method.

[0034] The polyamide foam particles according to the present invention can be processed into halogen-free particle foam molded articles with high thermal oxidation stability using a standard steam chest molding apparatus with a steam pressure of 2 to 4 bar. The molded articles exhibit high compressive and tensile strength after storage at elevated temperatures or at elevated temperatures and humidity for more than 500 hours.

[0035] Preferably, the polyamide particle foam molded body has a density of 250 to 500 kg / m³. 3 Within the range of 300-400 kg / m 3 It has a density within the range.

[0036] Preferably, the closed-cell ratio ψr of the polyamide particle foam molded body is determined by volume expansion method (Method 2) in accordance with DIN EN ISO 4590:2016 and is in the range of 65 to 98, more preferably in the range of 85 to 95.

[0037] The polyamide particle foam molded body according to the present invention may be used for strengthening structural parts in the automotive industry, aerospace industry, and consumer industry. Further applications are for body structures, engine parts, protective parts for BEVs or as core elements for sandwich parts, especially in combination with reaction injection molding. The polyamide foam molded body can be combined with non-foamed polyamide parts to improve recyclability by one material approach.

Examples

[0038] Hereinafter, the present invention will be described in more detail and specifically with reference to examples, but the examples are not intended to limit the present invention.

[0039] Raw materials: PA1: Ultramid® Flex F 38, copolyamide 6 / 6.36, BASF SE, density 1060 - 1090 kg / m 3 , relative viscosity (RV) 3.7 - 3.9, melting point 199 °C, PA2: Ultramid® B40, polyamide 6, BASF SE, density 1120 - 1150 kg / m 3 , viscosity number (VN) 240 - 260 ml / g, melting point 220 °C Nu: Micro Talc CM: (Carbon black masterbatch): Ultrabatch 420: polyamide 6 batch containing 30 wt% Special Black 4 / beads St1: Ultrabatch 101: polyamide 6 batch containing 15.5 wt% potassium iodide and 4.5 wt% copper(I) iodide as stabilizers St2: Okaflex EM from Oka-Tec (blend of polymer amine and 4,4′-bis(α,α-dimethylbenzyl)diphenylamine (stabilizer B3, formula III) as the main component, bulk density 500 - 900 g / l, melting range > 60 °C) St3: Ultrabatch 434: Composition: 60% ULT.B27 (PA6, RV 2.7, from BASF SE), 40% COLORANT BLACK 500 (nigrosine-based; CAS 101357-15-7 (Formula II and stabilizer type B2) from Orient Chemical Industries) St4: Naugard 445 (4-(1-methyl-1-phenylethyl)-N-[4-(1-methyl-1-phenylethyl)phenyl]aniline, CAS number: 10081-67-1), (stabilizer B3, formula III) St5: Irganox (registered trademark) 1098 (N,N′-(hexane-1,6-diyl)bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propanamide]).

[0040] Test method: Closed cell ratio The volume fraction of closed cells and cell walls, the so-called closed-cell ratio ψr, was determined by the volume expansion method (Method 2) in accordance with DIN EN ISO 4590-2016. The measuring instrument used, Accupyc 1330, was manufactured by micromeritics. The closed-cell ratio ψr was calculated by the following formula, where ωr was the volume fraction of open cells. ωr had to be calculated using formula 2. Vg corresponds to the sample volume. The sample volume was measured using its geometric sample data (3). The approximate sample size was 30 × 30 × 25 mm. Vi corresponds to the sample volume of the test specimen under test conditions where air cannot enter and gas cannot escape. Vi was measured using the measuring instrument Accupyc 1330. ψr = 100 - ωr (1) ωr = [(Vg - Vi) / Vg] × 100 (2) Vg=2×[(A1+A2) / 2×(B1+B2) / 2×(C1+C2) / 2]

[0041] Compressive strength was measured at 10% before and after aging.

[0042] To evaluate the stability against thermal aging, test cubes conforming to ISO 844 were manufactured from the polyamide particle foam molded body, and their compressive strength was measured at 10% compression before storage and after 2000 hours of storage in dry air at 120°C and 150°C.

[0043] Examples 1 and 2 and Comparative Examples C1-C3: Production of foamed polyamide foam beads and polyamide particle foam molded articles Foamed polyamide beads were produced on a ZE40 extruder equipped with underwater granulation (UWG): processing rate 60 kg / h; extruder: 200 rpm; MT 270~280°C; die plate temperature: 280~310°C; melt pump pressure before UWG: 80~95 bar; UWG: water temperature 70°C, 3000 rpm; die plate 12 holes, diameter 1 mm; water pressure in the underwater pelletizer was adjusted to 1~4 bar.

[0044] The blowing agent (nitrogen, N2) was directly added to the polymer melt. All solid components were added to the feed section of the extruder.

[0045] The resulting pre-formed beads are spherical with a diameter of 2-3 mm and have an initial bulk density of 280-350 g / l.

[0046] The pre-foamed beads described above were stored for at least 24 hours before processing. The foamed particles were processed into molded parts using a standard EPP chest molding machine (Erlenbach EHV-C PP 870 x 670) in a mold with dimensions of 200 x 300 x 25 mm. The beads were melted using cross steaming and autoclave steaming at a steam pressure of 2 to 4 bar.

[0047] The molded part was dried at 80°C for 8 hours (in air), and then a test specimen with dimensions of 40 × 40 × 40 mm was produced. The test specimen was stored for 24 hours under standard conditions (23°C / 50% relative humidity) before the compression test. To evaluate the stability against thermal aging, a test cube conforming to DIN EN ISO 844:2014 was stored in dry air at 120°C and 150°C for 2000 hours, and the compressive strength at 10% compression before and after storage was measured. Since thermal aging leads to depolymerization, the weight loss of the sample after aging was also measured.

[0048] Examples 1-3 exhibit high heat resistance after aging, as demonstrated by their high compressive strength after aging at 120°C for 1000 hours, and a higher closed-cell ratio compared to comparative examples C1-C4.

[0049] [Table 1]

Claims

1. Polyamide foam particles, (A) At least one type of polyamide, 5 to 99.9% by weight, (B) At least one stabilizer selected from secondary arylamines, 0.1 to 5% by weight. (C) Further additives 0-49% by weight The polyamide foam particles comprising, wherein the sum of components (A) to (C) is 100% by weight.

2. The polyamide foam particle according to claim 1, wherein the at least one polyamide (A) is selected from partially crystalline polyamides having a melting point in the range of 150 to 350°C, as determined by differential scanning calorimetry (DSC) in accordance with DIN EN ISO 11357-3:2018.

3. The polyamide foam particle according to claim 1 or 2, wherein the at least one polyamide (A) is selected from the group consisting of polycaprolactam (PA6), polylaurolactam (PA12), polyhexamethylene adipamide (PA6,6), polyhexamethylene sebakamid (PA6,10), polyhexamethylene dodecanamide (PA6,12), PA6 / 66, PA66 / 6, and copolyamide PA6 / 6,36, or a mixture thereof.

4. The aforementioned bulk density is 100 to 500 kg / m³ ３ Polyamide foam particles according to any one of claims 1 to 3, which are within the range of [specified range].

5. The above-mentioned at least one stabilizer (B) (B1) Amine-containing heat stabilizers comprising bis(4-(1-methyl-1-phenylethyl)phenyl)amine, 2-ethyl-2'-ethoxy-oxalanilide, dimethylglyoxime, 2,2'-bipyridine, 1,10-phenanthroline, ortho-phenylenediamine, 1,2-diaminocyclohexane, 1,4-diaminobutane, urea, 8-hydroxyquinoline, substituted ureas, and combinations thereof. (B2) A stabilizer containing nigrosine, or (B3) Stabilizers containing phenylenediamine adduct with acetone, phenylenediamine adduct with linolenic acid, 4,4'-bis(α,α-dimethylbenzyl)diphenylamine, N,N'-dinaphthyl-p-phenylenediamine, and N-phenyl-N'-cyclohexyl-p-phenylenediamine. Or a mixture of two or more of (B1) to (B3). Polyamide foam particles according to any one of claims 1 to 4, selected from the above.

6. A method for producing polyamide foam particles according to any one of claims 1 to 5, a) Below: At least one type of polyamide (A) 5 to 99.9% by weight, At least one stabilizer (B) selected from secondary arylamines, 0.1 to 5% by weight. Further additives (C) 0-49% by weight A step of melting a polymer mixture, including b) A step of impregnating the molten polymer mixture with 0.01 to 4.0% by weight of carbon dioxide, nitrogen, or a mixture thereof, based on 100% of the polymer mixture, to form an impregnated polymer melt. c) The process of extruding the impregnated polymer melt and granulating it in an underwater pelletizer to form polyamide foam particles. The method, including the method described above.

7. The method according to claim 6, wherein 0.1 to 1% by weight of talc is used as a further additive (C).

8. A method for producing a polyamide particle foam molded article by steam chest molding of polyamide foam particles according to any one of claims 1 to 5 at a temperature in the range of 100 to 170°C.

9. A polyamide particle foam molded article that can be obtained by the method described in claim 8.

10. The density is 250 to 500 kg / m³. ３ A polyamide particle foam molded article according to claim 9, which is within the range.

11. The polyamide particle foam molded article according to claim 9 or 10, wherein the closed-cell ratio is in the range of 65 to 98, as determined in accordance with DIN EN ISO 4590:2016.

12. Use of polyamide particle foam molded articles according to claims 9 to 11 for reinforcing structural components in the automotive, aerospace, and consumer industries.

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