Method for welding foam particles

Abstract

The present invention relates to methods for the welding of foam particles, by electromagnetic waves, wherein foam particles with a surface modification are welded in a molding tool by electromagnetic waves, wherein the surface modification is produced by contacting the foam particles with a solution containing polymers which are capable of forming intra- or inter-molecular covalent bonds, under the conditions required for this purpose.

Claims

1. Methods for welding of foam particles using electromagnetic waves, in which foam particles with a surface modification are welded in a molding tool by electromagnetic waves, wherein the surface modification is made by providing that the foam particles are contacted by a solution containing polymers that are capable of forming intra- or inter-molecular covalent bonds, and the polymers that are capable of forming intra- or inter-molecular covalent bonds have functional groups.

2. Methods according to claim 1, wherein the surface modification is hydrophilic.

3. Methods according to claim 1, wherein the foam particles with surface modification are wetted with an aqueous solution before being welded in the molding tool by electromagnetic waves.

4. Methods according to claim 1, wherein the production of the surface modification includes as an additional step the removal of the solvent used in this process.

5. Methods according to claim 1, wherein the surface modification has polar groups to improve the absorption of electromagnetic radiation, in particular in the radio-frequency range.

6. Methods according to claim 1, wherein the surface modification has polar groups to improve the absorption of electromagnetic radiation, in particular in the radio-frequency range, and the polar groups are selected from ester, acetal or urethane groups.

7. Methods according to claim 1, wherein the polymers capable of forming intra- or inter-molecular covalent bonds have functional groups selected from sulfonic acid, thiol, ammonium, carboxyl or silanol groups which are constituents of polyvinyl alcohol, polyvinyl pyrrolidone, polyvinyl formamide, polyacrylic acid (ester).

8. Methods according to claim 1, wherein the polymers capable of forming intra- or inter-molecular covalent bonds have functional groups selected from sulfonic acid, thiol, ammonium, carboxyl or silanol groups which are constituents of polyvinyl alcohol, polyvinyl pyrrolidone, polyvinyl formamide, polyacrylic acid (ester), and the foam particles are provided with a surface modification, involving contacting by a an aqueous carboxyl- or silanol-group-containing polyvinyl alcohol solution, wherein the pH value of the aqueous carboxyl- or silanol-group-containing polyvinyl alcohol solution lies between 2 and 5, and wherein the aqueous carboxyl- or silanol-group-containing polyvinyl alcohol solution where applicable comprises further substances which influence the surface tension and/or viscosity of the solution.

9. Methods according to claim 1, wherein the polymers capable of forming intra- or inter-molecular covalent bonds have functional groups selected from sulfonic acid, thiol, ammonium, carboxyl or silanol groups which are constituents of polyvinyl alcohol, polyvinyl pyrrolidone, polyvinyl formamide, polyacrylic acid (ester), the foam particles are provided with a surface modification, involving contacting by an aqueous carboxyl- or silanol-group-containing polyvinyl alcohol solution, wherein the pH value of the aqueous carboxyl- or silanol-group-containing polyvinyl alcohol solution lies between 2 and 5, and wherein the aqueous carboxyl- or silanol-group-containing polyvinyl alcohol solution where applicable comprises further substances which influence the surface tension and/or viscosity of the solution, and the concentration of the polyvinyl alcohol solution containing carboxyl or silanol groups is 0.001% (w/v) to 40% (w/v), 0.01% (w/v) to 10% (w/v), 0.5 and 2% (w/v) or 1% (w/v).

10. Methods according to claim 1, wherein the polymers capable of forming intra- or inter-molecular covalent bonds have functional groups selected from sulfonic acid, thiol, ammonium, carboxyl or silanol groups which are constituents of polyvinyl alcohol, polyvinyl pyrrolidone, polyvinyl formamide, polyacrylic acid (ester), and the resulting surface modification by adhesive bonding of water-soluble substances to the hydroxyl (—OH) groups present there is further modified by ester, acetal, urethane or ether bonding.

11. Methods according to claim 1, wherein the foam particles consist of polyurethane (ePU), or of expandable thermoplastics based on polyether block amide (ePEBA), based on polylactate (PLA), based on polyamide (ePA), based on polybutylene terephthalate (ePBT), based on polyester-ether-elastomer (eTPEE), based on polyethylene terephthalate (ePET), or of expandable polyethylene (ePE), expandable polypropylene (ePP) or expandable polystyrol (ePS).

12. Methods according to claim 1, wherein the surface modification is hydrophilic, and the foam particles with surface modification are wetted with an aqueous solution before being welded in the molding tool by electromagnetic waves.

13. Methods according to claim 1, wherein: the polymers capable of forming intra- or inter-molecular covalent bonds have functional groups selected from sulfonic acid, thiol, ammonium, carboxyl or silanol groups which are constituents of polyvinyl alcohol, polyvinyl pyrrolidone, polyvinyl formamide, polyacrylic acid (ester); the foam particles are provided with a surface modification, involving contacting by an aqueous carboxyl- or silanol-group-containing polyvinyl alcohol solution, wherein the pH value of the aqueous carboxyl- or silanol-group-containing polyvinyl alcohol solution lies between 2 and 5, and the aqueous carboxyl- or silanol-group-containing polyvinyl alcohol solution where applicable comprises further substances which influence the surface tension and/or viscosity of the solution; and the resulting surface modification by adhesive bonding of water-soluble substances to the hydroxyl (—OH) groups present there is further modified by ester, acetal, urethane or ether bonding.

14. Methods according to claim 1, wherein: the polymers capable of forming intra- or inter-molecular covalent bonds have functional groups selected from sulfonic acid, thiol, ammonium, carboxyl or silanol groups which are constituents of polyvinyl alcohol, polyvinyl pyrrolidone, polyvinyl formamide, polyacrylic acid (ester); the foam particles are provided with a surface modification, involving contacting by an aqueous carboxyl- or silanol-group-containing polyvinyl alcohol solution, wherein the pH value of the aqueous carboxyl- or silanol-group-containing polyvinyl alcohol solution lies between 2 and 5, and the aqueous carboxyl- or silanol-group-containing polyvinyl alcohol solution where applicable comprises further substances which influence the surface tension and/or viscosity of the solution; the concentration of the polyvinyl alcohol solution containing carboxyl or silanol groups is 0.001% (w/v) to 40% (w/v), 0.01% (w/v) to 10% (w/v), 0.5 to 2% (w/v) or 1% (w/v); and the resulting surface modification by adhesive bonding of water-soluble substances to the hydroxyl (—OH) groups present there is further modified by ester, acetal, urethane or ether bonding.

15. Methods according to claim 1, wherein: the polymers capable of forming intra- or inter-molecular covalent bonds have functional groups selected from sulfonic acid, thiol, ammonium, carboxyl or silanol groups which are constituents of polyvinyl alcohol, polyvinyl pyrrolidone, polyvinyl formamide, polyacrylic acid (ester); and the foam particles consist of polyurethane (ePU), or of expandable thermoplastics based on polyether block amide (ePEBA), based on polylactate (PLA), based on polyamide (ePA), based on polybutylene terephthalate (ePBT), based on polyester-ether-elastomer (eTPEE), based on polyethylene terephthalate (ePET), or of expandable polyethylene (ePE), expandable polypropylene (ePP) or expandable polystyrol (ePS).

16. Methods according to claim 1, wherein: the polymers capable of forming intra- or inter-molecular covalent bonds have functional groups selected from sulfonic acid, thiol, ammonium, carboxyl or silanol groups which are constituents of polyvinyl alcohol, polyvinyl pyrrolidone, polyvinyl formamide, polyacrylic acid (ester); the foam particles are provided with a surface modification, involving contacting by an aqueous carboxyl- or silanol-group-containing polyvinyl alcohol solution, wherein the pH value of the aqueous carboxyl- or silanol-group-containing polyvinyl alcohol solution lies between 2 and 5, and the aqueous carboxyl- or silanol-group-containing polyvinyl alcohol solution where applicable comprises further substances which influence the surface tension and/or viscosity of the solution; and the foam particles consist of polyurethane (ePU), or of expandable thermoplastics based on polyether block amide (ePEBA), based on polylactate (PLA), based on polyamide (ePA), based on polybutylene terephthalate (ePBT), based on polyester-ether-elastomer (eTPEE), based on polyethylene terephthalate (ePET), or of expandable polyethylene (ePE), expandable polypropylene (ePP) or expandable polystyrol (ePS).

17. Methods according to claim 1, wherein: the polymers capable of forming intra- or inter-molecular covalent bonds have functional groups selected from sulfonic acid, thiol, ammonium, carboxyl or silanol groups which are constituents of polyvinyl alcohol, polyvinyl pyrrolidone, polyvinyl formamide, polyacrylic acid (ester); the foam particles are provided with a surface modification, involving contacting by an aqueous carboxyl- or silanol-group-containing polyvinyl alcohol solution, wherein the pH value of the aqueous carboxyl- or silanol-group-containing polyvinyl alcohol solution lies between 2 and 5, and the aqueous carboxyl- or silanol-group-containing polyvinyl alcohol solution where applicable comprises further substances which influence the surface tension and/or viscosity of the solution; the resulting surface modification by adhesive bonding of water-soluble substances to the hydroxyl (—OH) groups present there is further modified by ester, acetal, urethane or ether bonding; and the foam particles consist of polyurethane (ePU), or of expandable thermoplastics based on polyether block amide (ePEBA), based on polylactate (PLA), based on polyamide (ePA), based on polybutylene terephthalate (ePBT), based on polyester-ether-elastomer (eTPEE), based on polyethylene terephthalate (ePET), or of expandable polyethylene (ePE), expandable polypropylene (ePP) or expandable polystyrol (ePS).

Description

EXAMPLE 1

[0090] KURARAY POVAL™ R (new product designation KURARAY POVAL™ 25-98 R) from the company Kuraray Europe GmbH, Hattersheim is used as polyvinyl alcohol containing silanol groups.

[0091] For surface modification, a 0.5% (w/v) aqueous KURARAY POVAL™ R solution is used. At room temperature, 5 g polymer are introduced into 1000 ml deionized water and then heated under constant stirring to around 90° C. until the polymer has completely dissolved. The pH is set at 3 with diluted hydrochloric acid.

[0092] Particles: Armashape. This involves particles or hollow beads of polyethylene terephthalate with a diameter of <0.5 μm from the company Armacell Benelux S.A., Thimister-Clermont, Belgium.

[0093] Contacting: Around 200 ml ArmaShape are poured into a plastic screen. The screen is placed on a suitable glass and KURARAY POVAL™ R solution is poured on to the beads until they float. They are then pressed back into the solution by a suitable plastic cover. Contacting time is around 5 min.

[0094] Drying: The polymer solution is allowed to run out of the screen. The beads are then spread out on a glass plate and dried at 70° C. in the circulating air oven.

[0095] Result: Beads contacted with KURARAY POVAL™ R solution show a clear coloring, which cannot be washed out, with Simplicol® (a dye for coloring cotton, made by the company Brauns-Heitmann, Warburg)—untreated controls did not bind the dye. Beads contacted with KURARAY POVAL™ R solution are water-wettable.

EXAMPLE 2

[0096] As example 1, only a POVAL™ K (new product designation KURARAY POVAL™ 25-88 KL) is used.

EXAMPLE 3

[0097] PET beads are surface-modified as described in Example 1, wetted with water and used to fill a glass syringe in the wet state. With the plunger rod they are compressed until no more water can be seen coming out of the syringe. The pressure of the plunger rod on the beads is maintained by suitable clamps. This construct is subjected to the electromagnetic energy of a microwave with 600 watts power for 40 min. After cooling, a stable molded body of baked-together PET beads corresponding to the syringe interior may be withdrawn.

EXAMPLE 4

[0098] Beads or foam particles of ePP from the firm Kaneka are as described in example 1 surface-modified, wetted with water and poured into a glass syringe. With the plunger rod they are compressed until no more water can be seen coming out of the syringe. The pressure of the plunger rod on the beads is maintained by suitable clamps. This construct is subjected to the electromagnetic energy of a microwave with 600 watts power for 40 min. After cooling, a stable molded body of baked-together or welded ePP beads corresponding to the syringe interior may be withdrawn.

EXAMPLE 5

[0099] Foam particles of EPP from Kaneka or EPS from the firms BASF and Knauf are welded together in a test molding tool by means of electromagnetic waves under various conditions, and specifically: [0100] wetted with distilled water (as comparative example) [0101] coated with PVA (1% (w/v) in water) in the presence of water (according to the invention) [0102] with polyethylene glycol in the presence of water (as comparative example).

[0103] As PVA, KURARAY POVAL™ R (new product designation KURARAY POVAL™ 25-98 R) in the form of a 1% (w/v) aqueous solution was used, i.e. a polyvinyl alcohol containing silanol groups.

[0104] Each experiment is repeated 5 times. The supply voltage for frequency generation applied over a period, always the same, of around 22 seconds, is around 6.5 kW. The molding space is such that, as test molding, a square foam panel measuring 100 mm×100 mm×25 mm is formed. The test molding tool or its support fixture is provided with an optical temperature sensor, which records the surface temperature of the workpiece of foam particles welded or to be welded. At the same time the wall of the mold contains a sensor which records the foam pressure, i.e. the pressure in the mold. There is also a measuring instrument in the electrical circuit, which measures the electrical power output at the capacitor in the form of radiation. This corresponds to the power absorbed by the foam particles during welding.

[0105] The maximum power absorbed in each case reflects the absorbing capacity of the material tested. The higher the measured maximum power, the greater the absorbing capacity of the tested material. The energy corresponds to the integral under the time-power curve and reflects the absorbed radiation energy.

[0106] The results are shown in the bar charts of FIGS. 1 to 3. Shown in each case is the maximum power and also the energy absorbed for the 3 different types of treatment. FIG. 1 summarizes the results for the EPS foam particles of BASF, FIG. 2 for the EPS foam particles from Knauf, and FIG. 3 for the EPP foam particles from Kaneka.

[0107] It follows from this that distilled water (in each case colorless) and polyethylene glycol (in each case grey) are both almost equally poor heat transfer media, since the maximum power absorbed and energy converted in each case, for foam particles treated with distilled water or polyethylene glycol, is distinctly lower in comparison with particles treated with PVA (in each case black).

Additional Information

[0108] In example 5 above, removal of the solution during production of the PVA coating was dispensed with. The particles provided with surface modification solution were additionally mixed with the same amount of water (14 g water and 14 group surface modification solution were used).

[0109] To avoid any possible polymerizing-out of polymer solution, e.g. PVA solution, and therefore possible adherence or sticking to mold surfaces, foam particles may be freed from solvent, i.e. dried, after production of the surface modification, and then wetted with water in the molding tool.

[0110] If removal of solvent for the purpose of drying is not provided, then surplus surface modification solution may be removed by centrifugation, for example in a tube drum screen, so that only the (minimal) amount of surface modification solution required for welding remains on the surface of the particles.

[0111] The above remarks serve to explain the invention and are not to be interpreted as restrictive.

[0112] The surface modification may also be effected by: [0113] methods for the surface modification of particles made from low-energy plastics, characterized in that the particles are contacted, under the conditions required for this purpose, by a solution containing polymers which are capable of forming covalent inter- and intra-molecular bonds, and the solvent is then removed [0114] the same methods, characterized in that aqueous solutions of polyvinyl alcohol containing carboxyl or silanol groups at pH 3±1 are used.

[0115] Particles according to the invention, made from low-energy plastics, may be characterized in that they have been surface-modified by the aforementioned methods. Such particles according to the invention may be used as substrates for the covalent bonding of (primarily) water-soluble substances through ester, urethane, acetal or ether bonds.

[0116] The particles made from low-energy plastics and surface-modified as in the two paragraphs above may be used as substrate for the production of molded bodies through heat developed close to the surface, e.g. by means of microwaves, as moisture-binding insulating material, as fillers for composite materials, as filter materials, drainage material, as substrates for the immobilization of biologically active substances, as cell culture substrates, as currentless, metallizable substrates, etc.