EP3535316A1

EP3535316A1 - Particle foams based on expanded thermoplastic elastomers

Info

Publication number: EP3535316A1
Application number: EP17787204.1A
Authority: EP
Inventors: Frank Prissok; Gnuni Karapetyan; Dirk Kempfert
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2016-11-04
Filing date: 2017-10-25
Publication date: 2019-09-11
Also published as: TW201821495A; WO2018082984A1

Abstract

The invention relates to foam particles based on thermoplastic elastomers, which contain at least one aryl-modified siloxane, as well as to a method for producing the foam particles, and particle foams which can be obtained by bonding the foam particles using steam or irradiation with high frequency electromagnetic radiation, or by adhesion with reactive adhesives, solvent-containing adhesives or dispersion adhesives.

Description

Particle foams based on expanded thermoplastic elastomers

The invention relates to foam particles based on thermoplastic elastomers which contain a siloxane, and to processes for producing the foam particles and particle foams, obtainable by welding foam particles by water vapor or irradiation of high-frequency radiation or by bonding with reactive adhesives, solvent-containing adhesives or dispersion adhesives.

Expanded thermoplastic polymers are used, for example, for the production of any foam solid bodies, for example for gymnastic mats, body protectors, lining elements in the automotive industry, sound and vibration absorbers, packaging or shoe soles. It is preferred to fill a mold with foam particles of an expanded polymer and to melt the individual foam particles by the action of heat on their surface and in this way to bond together to form a particle foam. Thus, in addition to simple and complex semi-finished or molded parts can be produced with undercuts. From WO-A 2007/082838 a process for the production of expanded, propellant-containing thermoplastic polyurethane is known. Therein, in a first step, a thermoplastic polyurethane is extruded into a granulate. In a second step, the granules are impregnated in aqueous suspension under pressure with a blowing agent and expanded in a third step. In a further embodiment of the method, the thermoplastic polyurethane is melted together with a blowing agent in an extruder and the melt granulated without a device that prevents foaming

WO 2015/05581 1 describes a process for the preparation of expanded thermoplastic polymer, comprising the following steps: (a) adding monomers and / or oligomers used for the preparation of the thermoplastic polymer and / or oligomers and optionally further starting materials to a first stage of a polymer processing machine, (b ) Mixing the monomers and / or oligomers as well as the optionally added further starting materials and reaction of the monomers and / or oligomers to a polymer melt in the first stage of the polymer processing machine, (c) introducing the polymer melt into a second stage of the polymer processing machine and adding a blowing agent and optionally other starting materials to obtain a blowing agent-containing polymer melt, (d) forming the blowing agent-containing polymer melt into an expanded thermoplastic polymer.

WO 2013/153190 and WO 2014/198779 likewise describe processes for producing expanded granules from thermoplastic elastomers by extrusion of a blowing agent-containing polymer melt and granulation into expanded granules. As surface-active substances, the thermoplastic molding compositions may include, inter alia, organosiloxanes, such as dimethylpolysiloxane. The object of the present invention is to provide foam particles based on thermoplastic elastomers which can be processed into particle foams having high dimensional stability and improved mechanical properties, in particular high compression hardness, rebound resilience and high tear propagation resistance at a low density, which is normal.

This object is achieved by the foam particles according to claim 1. Preferred siloxanes used are oligomeric or polymeric organosiloxanes. The siloxanes preferably have isocyanate-reactive organic groups, in particular non-reactive aromatic groups. Particularly preferred are organosilane-modified polysilioxanes having organosilane groups bonded via carbon atoms. Preferred polysiloxanes are polydiorganosiloxanes having the repeating unit - [0-SiR ² R ³ ] -, especially those of the general formula R ¹ 3Si- [0-SiR ² R ³ ] -O-SiR ¹ 3, where R ¹ , R ² and R ^{3 can} independently be hydrogen, alkyl or aryl groups. R ¹ and R ^{2 are} particularly preferably methyl and R ^{3 is} phenylethyl.

Preference is given to using siloxanes terminated with aromatic groups. Particular preference is given to using aryl-modified siloxanes, for example phenylethylmethylpolysiloxane such as Tegomer® M-Si 2650 from Evonik.

Suitable siloxanes are also siloxane block polymers having at least one organosiloxane block and a polyether block, as described, for example, in DE 10 2014 218 635. Preferred polyether blocks consist of EO, PO or PESOL. Particular preference is given to polyester siloxanes or polyether siloxanes, such as trimethylsiloxy-terminated dimethylmethyl (propyl (propylene oxide)) siloxane, for example DOW CORNING 1248 FLUID.

The siloxanes are preferably used in amounts ranging from 0.1 to 5% by weight, more preferably in the range from 0.1 to 2% by weight, based on the thermoplastic elastomer. Preference is given to using a siloxane, in particular an aryl-modified siloxane. But it can also be used more siloxanes. For several siloxanes, the amounts given refer to the total amount of all siloxanes. The siloxanes used according to the invention act as cell regulators, cell stabilizers and surface modifiers. They produce a smooth, closed-cell and shiny surface, and a gradient in the cell size distribution of larger cell diameters in the core of the foam particles to smaller cell diameters in the edge regions. The gradient in cell size distribution and the compact surface result in better weldability and associated improved mechanical properties. Due to the smooth surface, the frictional resistance is reduced and the abrasion resistance of the particle foams is improved. The foam particles in the interior preferably have an average cell diameter in the range of 200-1000 microns, preferably 200-600 microns, and in the edge region in the range of 0.1-200 microns, preferably 0.1-100 microns. By the edge region is meant the outer 20% of the radius of the particle. The core is the inner 50% around the center of the particle.

Suitable thermoplastic elastomers are, for example, thermoplastic polyurethanes (TPU), thermoplastic polyester elastomers (for example polyether esters and polyester esters), thermoplastic copolyamides (for example polyethercopolyamides) or thermoplastic styrene-butadiene block copolymers. Particular preference is given to foam particles based on thermoplastic polyurethane (TPU).

The bulk density of the foam particles is preferably in the range of 30 to 250 kg / m ³ . The foam particles may be obtained by impregnation of thermoplastic elastomer granules containing at least one siloxane with a blowing agent in suspension or by melt impregnation of molten thermoplastic elastomer with a blowing agent and subsequent granulation. Suitable processes for producing the foam particles based on thermoplastic elastomers are described, for example, in WO 2005/023920, WO 2007/082838, WO 2013/153190 and WO 2014/198779

In a variant of the method for producing foam particles, a thermoplastic elastomer containing a siloxane is melted, admixed with a blowing agent, and the blowing agent-containing melt is granulated with foaming.

Another, preferred process variant for the production of foam particles comprises the following steps:

(a) addition of monomers and / or oligomers used for the preparation of the thermoplastic elastomer, of at least one siloxane and optionally further starting materials into a first stage of a polymer processing machine,

(b) mixing the monomers and / or oligomers and the siloxanes and the optionally added further starting materials and reacting the monomers and / or oligomers to form a polymer melt in the first stage of the polymer processing machine,

(c) introducing the polymer melt into a second stage of the polymer processing machine and adding a blowing agent and optionally further starting materials in order to obtain a blowing agent-containing polymer melt,

(d) forming the blowing agent-containing polymer melt into an expanded thermoplastic elastomer. In particular, screw-type piston machines or melt pumps can be used as polymer processing machines. As screw piston machines for carrying out the method according to the invention, extruders are preferably used.

In one embodiment of the invention, steps (b) and (c) are performed in one machine. In this case, the first stage is a first section of the screw machine, in which the reaction of the monomers and / or oligomers, in the presence of a siloxane and optionally further reactants, to the polymer and the second stage, a second section of the screw machine, which is directly on connects the first section, in which the propellant is added

In the second stage of the screw machine, the propellant is then added. In order to distribute this uniformly in the polymer melt, the second stage of the screw-type piston machine has, for example, suitable mixing units on the screw. It is also possible to use a static mixer in addition.

In addition to an extruder, a melt pump can alternatively be used. In order to obtain a uniform distribution of the blowing agent in the polymer, the melt pump is preferably followed by a static mixer before it enters a granulating system.

To produce the foam particles, the polymer melt is usually extruded into strands, which are then cut into foam particles. By the addition of the blowing agent, the polymer melt expands on leaving the extruder due to the pressure drop and there is a foamed product, in the granulation in this way an expanded foam particles.

To produce the foam particles in step (d), it is preferable to press the polymer melt through a tempered perforated plate into a granulating chamber, cut it into individual expanding foam particles with a cutting device and to discharge the foam particles from the granulating chamber with a liquid stream. The temperature of the tempered perforated plate is preferably between 150 and 280 ° C.

In order to prevent an uncontrolled foaming of the polymer melt in the granulating chamber and to produce foam particles which have been foamed uniformly, it is advantageous to pressurize the granulating chamber with a pressure which is above the ambient pressure. It is furthermore particularly preferable to flood the granulation chamber with a liquid, so that the thermoplastic polymer melt containing the blowing agent is pressed directly into the liquid. Preferably, the liquid used in the granulation chamber is water. In the production of expanded foam particles from the blowing agent-containing polymer melts, the pressure in the tempering liquid flowing through the granulation chamber is preferably between 0.7 bar and 20 bar. Preferably, the pressure in the liquid is between 5 and 15 bar, more preferably a pressure between 10 and 15 bar is preferred.

The propellant in a preferred embodiment contains carbon dioxide, nitrogen or a mixture of carbon dioxide and nitrogen. Any mixture of nitrogen and carbon dioxide can be used here. Alternatively or additionally, the blowing agent may also contain an organic blowing agent, for example alkanes, halogenated hydrocarbons or a mixture of these substances. As alkanes, for example, ethane, propane, butane or pentane are suitable here. The sole use of CO2 and / or N2 and their combination as a propellant is particularly advantageous because it is inert gases that are incombustible, so that during production no explosive atmospheres can arise. As a result, cost-intensive safety precautions become unnecessary and the potential danger in the production is greatly reduced. It is also advantageous that no removal time of the products due to the evaporation of volatile combustible materials is required.

The siloxanes used are preferably oligomeric or polymeric organosiloxanes. The siloxanes preferably have isocyanate-reactive organic groups, in particular non-reactive aromatic groups. Particularly preferred are organosilane-modified polysilioxanes having organosilane groups bonded via carbon atoms. Preferred polysiloxanes are polydiorganosiloxanes having the repeating unit - [0-SiR ² R ³ ] -, especially those of the general formula R ¹ 3Si- [0-SiR ² R ³ ] -O-SiR ¹ 3, where R ¹ , R ² and R ^{3 can} independently be hydrogen, alkyl or aryl groups. R ¹ and R ^{2 are} particularly preferably methyl and R ^{3 is} phenylethyl.

The siloxanes are preferably added in amounts ranging from 0.1 to 5 wt .-%, particularly preferably in the range of 0.1 to 2 wt .-%, based on the monomers and oligomers, in step (a) and in step (b) mixed. Preference is given to using a siloxane, in particular an aryl-modified siloxane. But it can also be used more siloxanes. For several siloxanes, the amounts given refer to the total amount of all siloxanes. Further advantages result if the blowing agent-containing polymer melt additionally an o- or more nucleating agents are added as additional reactants. Particularly suitable nucleating agents are talc, calcium fluoride, sodium phenylphosphinate, aluminum oxide, carbon black, graphite, pigments and finely divided polytetrafluoroethylene, individually or else in any desired mixtures. Particularly preferred as a nucleating agent is talc. The proportion of nucleating agent based on the total mass of the thermoplastic molding composition or the polymer melt is preferably from 0 to 4 wt .-%, in particular 0.1 to 2% by weight. The nucleating agent can be added either in the first stage or in the second stage.

The addition of the propellant can be realized, for example, via an injection valve by means of a gas or liquid metering unit, depending on the state of aggregation of the propellant, in the polymer processing machine. When a thermoplastic polyurethane is used, the thermoplastic polyurethane can be any thermoplastic polyurethane known to those skilled in the art. Thermoplastic polyurethanes and processes for their preparation have already been described many times, for example in Gerhard W. Becker and Dietrich Braun, Kunststoffhandbuch, Volume 7, "Polyurethane", Carl Hanser Verlag, Munich, Vienna, 1993.

In a preferred embodiment, the thermoplastic polyurethane is prepared by reaction of a mixture of isocyanates with isocyanate-reactive compounds, preferably having a molecular weight of from 0.5 kg / mol to 10 kg / mol as monomers or oligomers and optionally chain extenders, preferably with a molecule. large weight of 0.05 kg / mol to 0.5 kg / mol. In a further preferred embodiment, at least one chain regulator, a catalyst and optionally at least one filler, auxiliary and / or additive are added to the mixture for the preparation of the thermoplastic polyurethane. In any case, a mixture of isocyanates and isocyanate-reactive compounds is required for the production of thermoplastic polyurethane. The further addition of chain extenders, chain regulators, catalysts and fillers, auxiliaries and / or additives is optional and can be done individually or in all possible variations. Further embodiments and suitable starting materials for producing the foam particles according to the invention starting from monomers and / or oligomers are described in WO

2015/05581 1 described.

The invention therefore provides a process for producing particle foams by thermal bonding of the above-described foam particles according to the invention by steam or irradiation of high-frequency electromagnetic radiation. By virtue of the siloxanes added according to the invention, foam particles and particle foams based on thermoplastic elastomers, in particular thermoplastic polyurethanes (TPU), having a smooth and glossy surface can be obtained. Because of the elastomeric properties, the particle foams of the invention are suitable for sports, footwear and packaging applications.

Examples

Comparative test

At a distance of 2 D from the beginning of a twin-screw extruder ZSK32 (Coperion) with a diameter of D = 32 mm and a length of 56 D, the following formula components are supplied with the following mass flows

72.5 g / min of 4,4'-diphenylmethane diisocyanate

143.9 g / min polytetramethylene glycol, molar mass 1000 g / mol:

12.9 g / min of 1, 4-butanediol

0.2 g / min talcum (nucleating agent)

30 ppm tin (II) dioctoate (catalyst) mixed in the extruder and reacted. The speed of the screws is 150 1 / min. The zone temperatures of zones 1 to 14 are between 170 and 230 ° C.

The reaction of the educts is driven so far by the reaction that are injected with a distance of 14 D before the end of the main extruder as blowing agent 0.49 g / min of nitrogen and 2.1 g / min of carbon dioxide by Gasdosierstationen in the melt. To separate the reaction zone from the area of the gas metering, the melt is thawed after the tenth zone by means of a recirculating screw element. Via a melt pump, the blowing agent-containing melt is forced through the perforated plate of an underwater pelletizer. The diameter of the holes is 2.5 mm. The perforated plate is heated to 190 ° C. A rotating knife in the granulation chamber generates foam particles with a particle weight of 25 mg. The particles are discharged from the granulation chamber with a granulating liquid having a pressure of 4 bar and a temperature of 30 ° C and conveyed to a centrifugal dryer, where they are separated from the water and dried. The bulk density of the expanded foam particles is 130 g / l.

Examples 1 - 4

Analogously to the comparative experiment, additional to the fourth zone (at 14 D from the beginning of the twin-screw extruder) from 0.1 to 2 wt .-%, based on the TPU melt, of the silicone (Tegomer M-Sl 2650, Evonik) metered. All other process parameters were kept the same compared to the comparative experiment. The bulk density of the expanded granules (foam particles) was also 130 g / l. Proportion of silicone and resulting cell morphology are summarized in Table 1.

The resulting foam particles were welded for 18 sec. With water vapor below 0.75 bar to 20 mm thick test specimens and cooled for 100 sec. Before removal. Conditions and mechanical properties of the specimens are summarized in Table 2. The cell structure of the comparative experiment and Examples 2 to 4 can be seen in FIGS. 1 to 4.

Measuring methods: To determine the bulk density, a 2000 ml vessel was filled with the expanded particles and the weight was determined by means of a balance. It can be assumed that an accuracy of ± 5 g / l.

The density of the test specimens (foam boards) was determined according to DIN EN ISO 1 183-1, A.

Tear resistance [N / mm] was determined on test plates with a thickness of 20 mm on the basis of ASTM D 3574 F and evaluated on the basis of DIN ISO 6133.

The compression hardness of the foam panels was measured in accordance with DIN EN ISO 3386 at 10%, 25%, 50% and 75% compression.

Table 1: Composition and cell morphology of the expanded TPU foam particles of Examples 1-4 and the comparative experiment

Example proportion Tegomer M-Sl 2650 cell morphology cell size distribution Figure.

[Wt .-%]

V 0 predominantly homogeneous Fig. 1 open-cell

1 0.1 Mainly homogeneous

closed cell

2 0.5 Mainly gradient Fig. 2 closed-cell

3 1, 0 closed-cell gradient Fig. 3

4 2,0 closed-cell strong gradient Fig. 4 Table 2: Mechanical properties of welded particle foams from the foam particles of Examples 1-4 and the comparative experiment

Example Density of the test piece Tearing resistance [N / mm] Compressive hardness 50% [kPa]

V 257 0.23 255.5

1 263 0.15 261, 5

2 270 0.65 278.2

3,282 2.68 295.8

Claims

claims

Foamed particles based on thermoplastic elastomers, characterized in that they contain at least one aryl-modified siloxane.

Foamed particles according to Claim 1, characterized in that they contain from 0.1 to 5% by weight, based on the thermoplastic elastomer, of siloxane.

Foamed particles according to claim 1 or 2, characterized in that they contain at least one polydiorganosiloxane or siloxane block copolymer.

Foamed particles according to one of claims 1 to 3, characterized in that they contain phenylethylmethylpolysiloxane.

Foamed particles according to one of claims 1 to 4, characterized in that the thermoplastic elastomer is a thermoplastic polyurethane.

Foamed particles according to one of claims 1 to 5, characterized in that they have a bulk density in the range of 30 to 350 g / l.

A process for producing foam particles according to any one of claims 1 to 6, characterized countersigned that a thermoplastic elastomer containing at least one aryl-modified siloxane, melted, mixed with a blowing agent and the blowing agent-containing melt is granulated with foaming.

Process for producing foam particles according to one of Claims 1 to 6, comprising the following steps:

Addition of monomers and / or oligomers used for the preparation of the thermoplastic elastomer, at least one aryl-modified siloxane and optionally further starting materials in a first stage of a polymer processing machine,

Mixing the monomers and / or oligomers and the siloxanes and the optionally added further starting materials and reaction of the monomers and / or oligomers to a polymer melt in the first stage of the polymer processing machine,

(9) introducing the polymer melt into a second stage of the polymer processing machine and adding a blowing agent and optionally further starting materials in order to obtain a blowing agent-containing polymer melt, (h) forming the blowing agent-containing polymer melt into an expanded thermoplastic elastomer.

9. The method according to claim 7 or 8, characterized in that the propellant contains carbon dioxide, nitrogen or a mixture of carbon dioxide and nitrogen.

10. Particle foams, obtainable by welding foam particles according to one of claims 1 to 6 by water vapor or irradiation of high-frequency electromagnetic radiation.

1 1. Particle foams obtainable by bonding foam particles according to one of claims 1 to 6 with reactive adhesives, solvent-containing adhesives or dispersion adhesives.