EXPANDABLE, SHELF STABLE POLYMER BEAD

Abstract

The invention relates to an expandable bead comprising a) a polyolefin selected from polyethylene (PE), polypropylene (PP) and mixtures thereof and b) thermoplastic microspheres encapsulating a blowing agent.

Claims

1. An expandable bead comprising a) a polyolefin selected from polyethylene (PE), polypropylene (PP) and mixtures thereof and b) thermoplastic microspheres encapsulating a blowing agent, wherein an aspect ratio, defined as quotient of a largest diameter D1 of the bead to a smallest diameter D2 of the bead, is in the range from ≥1.0 to ≤1.40, wherein the smallest diameter D2 of the bead is in the range from ≥0.5 to ≤2.5 mm.

2. The expandable bead of claim 1 wherein the expandable bead comprises the polyolefin in the range from ≥70% by weight to ≤98% by weight, wherein the total amount of the polyolefin and the thermoplastic microspheres is 100% by weight.

3. The expandable bead of claim 1 comprising a polypropylene having a melt flow index (MFI) of from ≥5 to ≤60 g/10 min, as measured according to ISO 1133 at 230° C. and a load of 2.16 kg.

4. The expandable bead of claim 1 wherein the polypropylene is selected from homopolymer PP and random PP copolymer.

5. The expandable bead of claim 1 wherein the polyethylene is linear low density polyethylene (LLDPE), having a MFI in the range from ≥5 to ≤70 g/10 min as measured according to ISO 1133 at 190° C. and 2.16 kg and/or having a density in the range from ≥910 to ≤940 kg/m3 as measured according to ISO 1183; and/or high density polyethylene (HDPE), having a MFI in the range from ≥5 to ≤70 g/10 min as measured according to ISO 1133 at 190° C. and a load of 2.16 kg and/or having a density in the range from ≥940 to ≤970 kg/m3 as measured according to ISO 1183.

6. The expandable bead of claim 1 wherein the diameter D2 is in the range from ≥0.8 to ≤2.0 mm, and/or having a bulk density in the range from ≥430 to ≤600 kg/m3 and/or having a shelf-stability of at least 6 month.

7. The expandable bead of claim 1 having a bulk density after its expansion in the range from ≥20 to ≤350 kg/m3.

8. The expandable bead of claim 1, wherein the thermoplastic microspheres have a size in the range from ≥0.5 μm to ≤50 μm.

9. The expandable bead of claim 1 wherein the bead comprises a nucleating agent.

10. A process for the production of an expandable bead of claim 1 comprising the steps of: (a) feeding one or more polyolefins, into melt mixing device; wherein the polyolefin is selected from polyethylene (PE), polypropylene (PP) and mixtures thereof; (b) heating said one or more polyolefins to melt; (c) introducing microspheres into said melt mixing device to form a mixture with the one or more polyolefins within the melt mixing device; (d) supplying said mixture to a heated die comprising a plurality of holes grouped into pods on the face of said die; (e) extruding said mixture through said holes into an underwater pelletizer which may optionally utilize a pressurized fluid system; (f) cutting said mixture to form beads; (g) removing said beads from the water; and (h) drying said beads.

11. (canceled)

12. (canceled)

13. (canceled)

14. (canceled)

15. (canceled)

16. A process for making an article comprising providing a plurality of expandable beads which comprises a) a polyolefin selected from polyethylene (PE), polypropylene (PP) and mixtures thereof and b) thermoplastic microspheres encapsulating a blowing agent and molding the expandable beads.

17. (canceled)

18. The process of claim 16 wherein the expandable beads are pre-expanded before being fed into a mold where the beads are fused to each other.

19. The process of claim 18 wherein expanded beads are compressed and perfused with steam to fuse with each other.

20. The process of claim 18 wherein further expansion occurs by heating in the mold to a temperature above a softening point.

21. The process of claim 16 wherein the expandable beads comprise beads of claim 1.

22. An article made by the method of claim 16 wherein the article is an automotive part, packaging material, or furniture.

23. The article of claim 22 which is an automotive part selected from bumpers, steering column pads, sun visors, arm rests, head rests, seats, wheel house liner, side impact protectors and battery covers.

24. The article of claim 22 which is a packaging material selected from dunnage trays, transport containers, medical and food containers requiring temperature control, sterility and damage protection during transport heat and sound management.

Description

BRIEF DESCRIPTION OF FIG. 1

[0212] FIG. 1 is a scheme of the one-step extrusion setup for the process for the production of the expandable beads. The set-up includes the following elements

[0213] 1—Inlet for Polymer [0214] 2—Inlet for thermoplastic microspheres containing blowing agent [0215] 3—Extruder [0216] 4—Melt Pump [0217] 5—Polymer Diverter [0218] 6—Die Plate [0219] 7—Cutting Chamber [0220] 8—Cutter Motor [0221] 9—Water Tank [0222] 10—Water Pump [0223] 11—Pellet Dryer [0224] 12—Collection Bin

[0225] Additives

[0226] The polymers in the resin composition and also the resin composition according to the invention may contain additives, for instance nucleating agents and clarifiers, stabilizers, release agents, fillers, plasticizers, anti-oxidants, lubricants, antistatics, scratch resistance agents, thermal conductivity modifiers, high performance fillers, pigments and/or colorants, impact modifiers, blowing agents, acid scavengers, recycling additives, coupling agents, anti-microbial, anti-fogging additives, slip additives, anti-blocking additives, flame retardants, clays and polymer processing aids. These additives are well known in the art. The skilled person will choose the type and amount of additives such that they do not detrimentally influence the aimed properties of the composition.

[0227] Nucleating Agent

[0228] Nucleating agents provide a multitude of nucleating sites each of which can induce formation of a cell during foam expansion. Nucleating agents give control over the cell morphology (namely, the number of cells, the cell size, and its distribution) in thermoplastic foams.

[0229] Examples of nucleating agents are talc, magnesium silicate, carbon black, graphite, titanium dioxide, calcium carbonate, calcium hydroxide, calcium stearate, zinc stearate, aluminum stearate, azodicarbonamide and sodium bicarbonate. Polymeric materials such as Nylons and PPO may also be used as the nucleating agent. All nucleating agents have particle sizes of approximately one micrometer or smaller.

[0230] Preferably, the expandable bead comprises a nucleating agent. A preferred nucleating agent is calcium carbonate.

[0231] Expansion and Molding Process of the Expandable Bead

[0232] Expandable beads may be converted to the desired article in a two step process namely pre-expansion and molding. Each bead constitutes a foamable polymer composition comprising thermoplastic polymer matrix and thermoplastic microspheres encapsulating a blowing agent dispersed within the matrix.

[0233] Bead pre-expansion processes may be used for pre-expansion of the polymeric beads of this invention. Pre-expansion process can be summarized as transforming the beads, with the aid of a blowing agent into spheres of cellular structure possessing a larger volume and lower density.

[0234] Such pre-expansion processes comprise for example steam pre-expansion, infrared oven and hot air oven expansion.

[0235] Very common is the steam pre-expansion process, which can be a batch process or a continuous one. The steam pre-expansion processes are well known in the art. The skilled person will choose the process and the process conditions based on the downstream molding operations and intended applications of the foamed beads. It is essential to stir the expanding beads during pre-expansion to preclude beads agglomeration. Therefore, the pre-expansion vessel is normally fitted with a centrally located rotating stirrer and stationary breaker bars attached inside the vessel. Further it is required to use high pressure steam to reach a temperature to soften the beads, meaning raising the temperature close to the melting point of the polymer. The wet pre-expanded beads are discharged into a fluidized-bed where hot air dries the wet beads before they are transferred to silos for molding operations.

[0236] The steam chest molding process is commonly used for molding the pre-expanded beads into the desired articles. The steam chest molding processes for expandable polystyrene (EPS) and expanded PP beads are also well known in the art.

[0237] In short, the beads are processed to articles by fusing the beads by the use of steam. The particles are fed into a mold, compressed and then perfused with steam. Thereby, the surface areas of the beads warm up and fuse with each other. The fused article is cooled down in the mold and then removed from it.

[0238] Unlike EPS, the existing commercially available expanded PP beads do not contain any blowing agent and have to be compensated by mechanical means during the molding process. The expandable beads of this invention may overcome this issue as these beads will contain residual blowing agent to assist the sintering of the beads by further expansion in the mold. The beads are also suitable to be molded by other fusion processes which are for example steam free.

[0239] The desired shapes of the article may be made by filling the closed cavity with the pre-expanded beads under pressure and heated to temperature above to softening point. As a result of this the further expansion of beads takes place filling up the free volume, fusing beads along the binding interfaces. After a cooling period (pressure reduction) the molded article is dimensionally stable and is released from the molding.

[0240] Articles

[0241] Further the present invention relates to the use of such expandable beads for the production of expanded beads or an article, preferably molded articles, preferably for

[0242] i) automotive parts, preferably bumpers, steering column pads, sun visors, arm rests, head rests, seats, wheel house liner, side impact protectors and battery covers and/or

[0243] ii) packaging material, preferably dunnage trays, transport containers, medical and food containers requiring temperature control, sterility and damage protection during transport heat and sound management and/or

[0244] iii) furniture and safety and recreation applications.

[0245] The present invention may also relate to the use of such expandable beads for the production an article by steam chest molding. Preferably, the beads sinter by further expansion in the mold. Preferably, the beads do not need to be compensated during the molding process.

[0246] Further the invention relates to a process for making an article, preferably a molded article, preferably molded article made by fusion of the beads, more preferably a steam chest molded article, more preferably an automotive part and/or furniture and/or safety and recreation applications, by molding the expandable bead.

[0247] Further the invention relates to a process for making an article, preferably a molded article, preferably a molded article made by fusion of the beads, more preferably a steam chest molded article, more preferably an automotive part and/or furniture and/or safety and recreation applications, by molding the expandable bead, wherein the expandable bead comprises

[0248] a) a polyolefin selected from polyethylene (PE), polypropylene (PP) and mixtures thereof and

[0249] b) thermoplastic microspheres encapsulating a blowing agent

[0250] Preferably, in the process, bumpers, steering column pads, sun visors, arm rests, head rests, seats, wheel house liner, side impact protectors and battery covers and/or a packaging material, preferably dunnage trays, transport containers, medical and food containers requiring temperature control, sterility and damage protection during transport heat and sound management are produced.

[0251] Further the invention relates to a process for making an article by for examples steam chest molding, wherein the desired shapes of the article are preferably made by filling the closed cavity with the pre-expanded beads under pressure and heating to a temperature above to softening point, whereby the beads are fused along the binding interfaces.

[0252] Furthermore, the present invention relates to an article, preferably a molded article, more preferably a molded article made by fusion of the beads, more preferably a steam chest molded article comprising the expandable beads according to the invention or obtainable by a process according the invention.

[0253] The invention deals also with an article, preferably a molded article, preferably a steam chest molded article made from the expandable bead according to the invention or made from the expandable bead obtained by or obtainable by the process according to the invention.

[0254] The invention deals also with an article, preferably a molded article, preferably a molded article made by fusion of the beads, preferably a steam chest molded article made from an expandable bead, wherein the expandable bead comprises

[0255] a) a polyolefin selected from polyethylene (PE), polypropylene (PP) and mixtures thereof and

[0256] b) thermoplastic microspheres encapsulating a blowing agent

[0257] Preferably the articles are parts for automotive applications, such as bumpers, steering column pads, sun visors, arm rests, head rests, seats, wheel house liner, side impact protectors and battery covers and/or packaging material, such as dunnage trays, transport containers, medical and food containers requiring temperature control, sterility and damage protection during transport heat and sound management, made from the expandable bead according to the invention or made from the expandable bead obtained by or obtainable by the process according to the invention.

[0258] The foamed beads and foamed article made from the expandable polymer beads of the invention may have a density in the range from 10 to 400 kilograms per cubic meter (kg/m.sup.3), preferably 100 kg/m.sup.3 or less, still more preferably 50 kg/m.sup.3 or less.

[0259] Typically, the foamed beads and the foamed article made from the expandable polymer beads of the present invention have a density of 10 kg/m.sup.3 or higher, preferably 20 kg/m.sup.3 or higher, preferably 30 kg/m.sup.3 or higher in order to ensure mechanical integrity during handling. Most preferably, the density is in range from 30 to 50 kg/m.sup.3. Lower density foamed beads and foamed articles are desirable to reduce cost of manufacture and transportation as well as for ease of handling. The foam density is determined according to the method of ISO 845-95.

[0260] The open cell content of the foamed bead or the foamed article made from the expandable bead of the present invention may be 30% or less, preferably 10% or less, more preferably 5% or less, even more preferably 2% or less. The open cell content may be 1% or less or even 0%. The open cell content is determined according the method of ASTM D6226-05.

[0261] The invention will now be illustrated by the following non-limiting examples.

EXAMPLES

[0262] Materials

[0263] The materials mentioned in Table 1 were used.

TABLE-US-00001 TABLE 1 Used Materials. MFI in g/10 min Density in kg/m.sup.3 Measurement Measurement Material Grade name method method PP SABIC, 8.0 905 PP 621P ISO 1133-1:2011 ISO 1183-1:2012 2.16 kg at 230° C. PP SABIC, 45 905 QR6711K ASTM D1238 ASTM D792 2.16 kg at 230° C. LLDPE SABIC, 50 926 M500026 ASTM D1238 ASTM D1505 2.16 kg at 190° C. Microspheres Akzo Nobel Expancel 980 DU 120

[0264] Measurement Methods

[0265] The bead diameter is directly measured from the micrographs according to ISO 13322-1 (2014). The beads are attached to a standard slide and viewed by Olympus 510 digital light microscope. The images of at least 50 beads are recorded in reflected light mode. Both D1 and D2 diameters of the beads are measured using an image analysis software Image J.

[0266] The bulk density of the raw beads is measured using a one or two liter cylinder and collecting the beads into the cylinder to full capacity. Leveling the surface to the cylinder and taking the weight of the beads.

[0267] The bulk density of the expanded beads is also measured using a one or two liter cylinder and collecting the expanded beads into the cylinder to full capacity. Leveling the surface to the cylinder and taking the weight of expanded beads (these beads should be free from agglomerates or lumps).

[0268] Preparation of Beads

[0269] The expandable beads were prepared using a twin screw extruder from Berstorff and an underwater pelletizing system from Nordson BKG. The conditions of Table 2 were applied.

TABLE-US-00002 TABLE 2 Process parameters. Parameter Value Die Plate Number of holes 152 Hole Diameter (mm) 0.65 Cutter Hub Number of Blades 12-22 Inclination .sup. Angle-Straight Feed Throughput (kg/hr) 190-250 Temperature of Die Plate (° C.) 145-260 Melt Pressure Die Plate (bar) 135-225 Melt Temperature (° C.) 169-212 Process water Temperature (° C.) 31-45 Water Flow (m.sup.3/hr) 15-31 Extruder Speed (rpm) 100-120 Pelletizer Speed (rpm) 3500-3800

[0270] Expansion of the Beads

[0271] The expansion data reported in the Tables below are generated using a hot air oven. The oven was preheated to 180° C. and a known quantity of the beads was placed in the oven in an open aluminum pan. After the prescribed time the sample was withdrawn from the oven and bulk density of the beads was measured using a container of fixed volume.

TABLE-US-00003 TABLE 3a Preparation of beads with different ratios of PP QR6711K and Expancel. For expansion of the beads a temperature of 180° C. was used. Bulk Bead Bead Density of Water Diameter Bulk Expanded Bead Composition (wt %) Pressure of range Density Beads PP6711 Expancel CaCO.sub.3 UWP (bar) (mm) (kg/m.sup.3) (kg/m.sup.3) 1 100 0 0 2 1.1-1.4 560 N/A 2 100 0 0 10 1.1-1.5 560 N/A 3 97.5 2.5 0 2 1.0-1.3 531 325 4 95 5 0 3.8 0.9-1.5 490 160 5 92.5 7.5 0 3.8 1.1-1.5 475 93 6 90 10 0 3.8 1.2-1.7 440 80 7 89.55 10 0.45 3.8 1.1-1.4 450 82 8 80 20 0 10 1.2-1.7 535 57 UWP: Under Water Pelletizer

TABLE-US-00004 TABLE 3b Preparation of beads with different ratios of PP QR6711K and Expancel. StD. StD. Bead Composition (wt %) D1 D1 D2 D2 Aspect PP6711 Expancel CaCO.sub.3 (mm) (mm) (mm) (mm) ratio 1 100 0 0 1.25 0.15 1.11 0.13 1.12 2 100 0 0 1.24 0.11 1.09 0.13 1.14 3 97.5 2.5 0 1.31 0.16 1.15 0.16 1.14 4 95 5 0 1.34 0.24 1.14 0.19 1.17 5 92.5 7.5 0 1.33 0.16 1.13 0.18 1.18 6 90 10 0 1.39 0.21 1.19 0.16 1.16 7 89.55 10 0.45 1.29 0.18 1.13 0.15 1.15 8 80 20 0 1.25 0.15 1.11 0.13 1.12 D - diameter, STD - standard deviation, aspect ratio = D1/D2

TABLE-US-00005 TABLE 4 Preparation of beads with PP QR6711K and Expancel. The beads were expanded with different expansion times. For expansion of the beads a temperature of 180° C. was used. Bulk Bead Density of Bulk Bead Dia. Expansion Expanded Bead Composition (wt %) Density Range Time Beads PP Expancel CaCO.sub.3 (kg/m.sup.3) (mm) (min) (kg/m.sup.3) 8a 80 20 0 535 1.2-1.7 5 100 8 80 20 0 535 1.2-1.7 10 57 8b 80 20 0 535 1.2-1.7 15 50 Under Water Pelletizer 10 bar.

TABLE-US-00006 TABLE 5 Preparation of beads with PP QR6711K, LLDPE M500026 and Expancel. Bulk Bead Composition (wt %) Bead Density of 80/20 Bulk Bead Dia. Expanded PP/PE Density Range Beads Blend Expancel CaCO.sub.3 (kg/m.sup.3) (mm) (kg/m.sup.3) 1 100 0 0 549 1.0-1.6 N/A 2 90 10 0 545 1.1-1.6 175 3 80 20 0 509 1.1-1.6 62 Expansion Temperature 180° C., Water Pressure of Under Water Pelletizer 10 bar.

TABLE-US-00007 TABLE 6a Preparation of beads with PP 621P and Expancel. Bulk Water Bead Density of Pressure Diameter Bead Bulk Expanded Bead Composition (wt %) in UWP range Density Beads PP621 Expancel CaCO.sub.3 (bar) (mm) (kg/m.sup.3) (kg/m.sup.3) 1 100 0 0 2 1.0-1.3 550 N/A 2 97.5 2.5 0 3.8 1.1-1.5 500 350 3 95 5 0 3.8 1.2-1.4 470 187 4 90 10 0 3.8 1.2-1.6 450 120 Expansion temperature 180° C.

TABLE-US-00008 TABLE 6b Preparation of beads with PP 621P and Expancel. StD. StD. Bead Composition (wt %) D1 D1 D2 D2 Aspect PP621 Expancel CaCO.sub.3 (mm) (mm) (mm) (mm) ratio 1 100 0 0 1.33 0.16 1.13 0.15 1.17 2 97.5 2.5 0 1.35 0.16 1.14 0.13 1.18 3 95 5 0 1.37 0.14 1.18 0.12 1.16 4 90 10 0 1.27 0.08 1.08 0.11 1.18 D - diameter, STD - standard deviation, aspect ratio = D1/D2

[0272] The bead shelf life was demonstrated by pre-expanding (or molding) of the beads after storing the product at room temperature for different intervals of time. The pre-expansion (or molding) experiments were conducted at identical conditions to those used with the fresh beads. These results are shown in Table 7.

TABLE-US-00009 TABLE 7 Expansion of beads with PP QR6711K and Expancel. Bulk Density of Expanded Beads (kg/m.sup.3) Bulk Expansion after different time intervals Density of directly after Bead Composition (wt %) Bead Expansion/Molding preparation of 1 4 6 PP Expancel CaCO.sub.3 (kg/m.sup.3) Temp. the beads month month month 1 95 5 0 490 180° C. 160 160 160 160 2 89.55 10 0.45 450 180° C.  82  80  80 80 3 90.sup.(1) 10 0 545 180° C. 175 175 175 4 80 20 0 535 180° C.   75.sup.(2)   75.sup.(2)   75.sup.(2) .sup.(1)90% of a 80/20 PP/PE blend of PP QR6711K and LLDPE M500026 instead of pure PP, .sup.(2)Plaque density. (sample 1 = sample 4 of table 3, sample 2 = sample 10 of table 3, sample 3 = sample 2 of table 5, sample 4 = sample 8 of table 3.)

[0273] The results presented above clearly demonstrate the feasibility of the process of making expandable beads using a composition of PP and microspheres or a composition of blends of PP and other polyolefins and microspheres.

[0274] The results of Table 7 show that the beads are shelf stable. Shelf-stable in this context means that the beads can be stored for a certain period of time without losing their properties. In particular this means that the beads can be foamed to the extend and with the same result as they would have been foamed directly after their production provided that the same process conditions are used.

[0275] It was possible to achieve the same low bulk densities by expansion directly after their preparation and after storage of the unexpanded beads for at least 6 month. This means that the beads can be stored and transported in an unexpanded state before they are expanded. This is a huge advantage and saves transportation costs.