DE10340539A1 - Process for the preparation of expanded thermoplastic elastomers - Google Patents

Abstract

The invention relates to a process for the preparation of expanded thermoplastic polyurethanes, comprising the steps DOLLAR A a) mixing of blowing agents to a thermoplastic polyurethane and optionally drying, DOLLAR A b) thermoplastic processing of this mixture with expansion of the blowing agent, DOLLAR A being expandable as a blowing agent Microspheres in the form of powder or masterbatch are used and the mixture of the blowing agent with the TPU directly to the plant in which the thermoplastic processing is carried out.

Description

thermoplastic Polyurethanes (TPU) are partially crystalline materials and belong to the Class of thermoplastic elastomers. They stand out due to good strength, abrasion, tear resistance and chemical resistance out, and can in almost any hardness be prepared by suitable raw material composition.

The Production takes place according to the known methods in the one-shot or Prepolymer process on the belt plant or on the reaction extruder. Here are the reaction components diisocyanate, long-chain Diol and short chain diol (chain extender) together or in specific Order combined and reacted. The reactants be in a relationship NCO groups to the sum of all hydrogen atoms reacting with the NCO groups from 1: 0.9-1.2, preferably 1: 0.95-1.05 especially in the relationship Mixed 1: 1.

It is well known, thermoplastics (TPE) under Use of blowing agents to foam. In particular polystyrene and polyolefins are in great Scope foamed.

Suitable blowing agents are chemical blowing agents, in particular those which split off gases with thermal decomposition, such as citric acid, bicarbonates or azodicarbonamides, such as celegoene; Tracel; Hydrocerols etc., ("Hydrocerols: Chemical blowing and nucleating agents for plastics; Processing instructions; Injection molding; Hard PVC foam; Foam extrusion; Product range; Clariant March 2000";"New blowing agent developments in the field of injection molding; Lübke, G .; Holzberg, T ., Seminars on plastics processing IKV; 4 February 2003 ") or by physical blowing agents, mostly inert, vaporizing in the foaming conditions, or expandable microspheres (eg Expancel ^® the Akzo or microspheres from Lehmann & Voss). Combinations of chemical blowing agents and expandable microspheres can also be used (Foaming Plastics with Expancel Microspheres; Elfving, K. Blowing Agent Systems: Formulation and Processing; Paper 9, Page 1-5; Microbubbles of Plastics; NN; Kunststoffe 82 (1992); 4 (36366).

It Processes are also known, thermoplastic polyurethanes with blowing agents to foam. In case of TPU lead chemical blowing agent to a comparatively very coarse foam structure and to an increased formation of voids.

To remedy this deficiency, EP-A-692 516 describes a process for the production of foams based on TPU, in which a mixture of chemical blowing agents and Expancel ^® microspheres is used as blowing agent.

expandable Microspheres are hollow microspheres made of a thin plastic shell, for example Polyacrylonitrile or copolymers thereof, consist. These hollow microspheres are filled with gas, usually with hydrocarbons. By the acting temperature in the thermoplastic processing it comes to a softening of the plastic shell and at the same time to a Expansion of trapped gas. This leads to a Expansion of the microspheres.

In WO 00/44821 the use of a propellant combination of microspheres of the type Expancel ^{® is} proposed in which the microspheres are filled with hydrocarbons.

In EP-A-1174459 improves the process described in WO 00/44821, by the TPU a plasticizer is added. This should improve the surface of the moldings and the molding time are lowered.

In EP-A-1174458 is said to have the same effect by the addition of plasticizers be achieved.

The Blowing agents can here as masterbatches, which are mixtures of the blowing agent with a carrier, preferably a thermoplastic, so-called concentrates or be added as a powder to the base TPU. In the latter case is it is useful to add in advance a binder (e.g., mineral oil, parafin oil) to the TPU granules to allow adhesion of the powder on the granules.

However, it is never completely possible to prevent powder agglomerates and inhomogeneities in the TPU / powder mixture or separation of TPU granules and propellant powder or propellant masterbatch. In the case of the use of TPU / propellant powder mixtures it is even if never to prevent powder residues from sticking to the inside walls of packaging, mixers, dryers, conveyors, storage containers or other places. This leads to uncontrolled concentration fluctuations of the propellant in the TPU / propellant mixture, also reinforced by redissociation of powder accumulations on inner walls. All these problems ultimately lead to fluctuations in the already sensitive foaming process in the thermoplastic processing of TPU and to density variations in the finished part. The described uncontrolled occurring powder agglomerates are often not sufficiently homogenized or digested in the plasticization and lead to bright spots in the finished part and on the finished part surface.

task This invention was to provide a trouble-free production process to develop in the manufacture of expanded TPU, in which the finished parts a consistent quality and a uniform density and easy to operate.

The Task was solved be that the propellant to be dosed in the form of masterbatches or as a pure powder is not previously mixed with the TPU granules but the propellant dosage only immediately before or while the thermoplastic processing, directly at the plant, in the the expanded parts are produced takes place.

• a) Mischen von Treibmitteln zu einem TPU und gegebenenfalls Trocknung,
• b) thermoplastische Verarbeitung dieser Mischung unter Expansion des Treibmittels,

dadurch gekennzeichnet, dass als Treibmittel expandierbare Mikrospheren in Form von Pulver oder Masterbatch eingesetzt werden und die Mischung der Treibmittel mit den TPU direkt an der Anlage, in der die thermoplastische Verarbeitung durchgeführt wird, erfolgt.The invention accordingly provides a process for producing expanded TPU comprising the steps

• a) mixing of blowing agents into a TPU and optionally drying,
• b) thermoplastic processing of this mixture with expansion of the blowing agent,

characterized in that as blowing agents expandable microspheres in the form of powder or masterbatch are used and the mixture of the blowing agent with the TPU directly to the plant in which the thermoplastic processing is carried out.

at the plants where expandable TPU is processed it is mostly around usual and known injection molding or extrusion equipment. The dosage and mixture of blowing agent and base TPU takes place in particular in a single Aggregate, for example a type KK premixer; Throughput 20 kg / h; Shot weight up to 200 g; Manufacturer Company Koch-Technik. This The unit is mounted on the feeder of the palletizing unit.

In an embodiment the method according to the invention the propellant is continuously added to the plant and with the likewise continuously metered TPU mixed. The feeder of the Propellant may in this case at the feed zone and / or in one of subsequent screw zones, preferably at the entrance of the injection molding machine or the extruder.

As described above, the expandable microspheres used in the process of the present invention are well known and commercially available. Microspheres are used of the type Expancel ^® preferred in which the microspheres are filled with hydrocarbons.

In a particularly preferred embodiment of the process according to the invention, the expandable microspheres used as blowing agents have a TMA density of less than 10 kg / m ³ , preferably from ² to 10 kg / m ³ and particularly preferably from ² to 7 kg / m ³ . Expanded TPUs made with such blowing agents have a particularly fine cell structure, significantly reduced voids formation and practically no sink marks. In addition, when using such expandable microspheres, the processing window, for example, in terms of temperature, significantly larger than when using expandable microspheres with a different TMA density.

With the TMA density [kg / m ³ ] the expansion capacity of the microspheres can be described. The TMA density is the minimum achievable density at a given temperature T _max under normal pressure before the microspheres collapse. The TMA density can be determined using a Stare Thermal Analysis System from Mettler Toledo at a heating rate of 20 ° C / min.

The expandable TPUs produced by the process according to the invention preferably have a density of <1.2 g / cm ³ , preferably 0.3-1.0 g / cm ³ , particularly preferably 0.4-0.8 g / cm ³ .

The microspheres used according to the invention preferably have a diameter between 20 μm and 40 μm. Corresponding microspheres are available from Akzo Nobel, Casco Products GmbH, Es sen under the trademark Expancel ^® 093 DU 120 (powder).

Under the term "thermoplastic Processing "is meant any processing associated with a melting of the TPU is. The thermoplastic processing takes place here at 80-240 ° C preferably at 120-230 ° C in particular preferably at 170-220 ° C, on the Professional known injection molding and extrusion equipment or powder sintering plants.

Of the Content of expandable microspheres in the mixture depends on the desired density of the expanded TPU. Preference is given to pro 100 parts by weight of the TPU or TPU blend to be foamed, that is to be foamed, between 0.1 parts by weight and 10 parts by weight, preferably between 0.2 parts by weight and 6.5 parts by weight of the expandable according to the invention Microsphreres used.

Particularly preferred are expandable TPU or expanded TPU blends which contain the following components:
From 85% by weight to 99.5% by weight, preferably between 90% by weight and 99.5% by weight, particularly preferably between 92% by weight and 98% by weight of TPU or blend comprising TPU, 0.5% by weight to 15% by weight, preferably between 2% by weight and 8% by weight of microspheres masterbatch, 0 to 10% by weight, preferably 0.1% by weight to 2% by weight % Dye, eg well-known black paste or dye additions in the form of color masterbatches.

The microspheres masterbatch preferably contains:
5% by weight to 90% by weight, preferably 25% by weight to 65% by weight, of microspheres and 10% by weight to 95% by weight, preferably 35% by weight to 75% by weight Carriers, preferably thermoplastic carriers, for example the carrier materials shown later, particularly preferably EVA (ethylene vinyl acetate).

The used expandable microspheres can on the one hand in the form of Powder, wherein the application to the TPU granules here with and without binder, such as 0.05-2 % By weight mineral or paraffin oil can, or otherwise preferably be used as masterbatches. By masterbatch is meant that the expandable microspheres in a carrier, For example, binders, waxes or a thermoplastic, such as TPU, ethylene vinyl acetate (EVA), polyvinyl chloride, polyethylene, polypropylene, Polyester, polystyrene, or thermoplastic rubber, or misery therefrom, preferably a carrier with a melt index MFR; 190 ° C / 2.16 kg; ASTM D 1238) from 5-700 g / 10 min, preferably 50-600 g / 10 min, more preferably 150-500 g / 10 min and a melting point between 60 and 110 ° C, especially preferred EVA with a melt index MFR: 80-800 g / 10 min; 125 ° C / 325 G; ASTM D 1238 are bound in granular form. In the preparation of These microspheres masterbatches are usually thermoplastics with a very low melting point and very low viscosities or high melt indices, as described above, used to thereby preferably use low temperatures in masterbatch production can, um to avoid premature expansion.

In addition to the expandable microspheres and other blowing agents can be used. As already mentioned above, for this purpose are chemical blowing agents, especially those which release gases under thermal decomposition, such as citric acid, hydrogen or azodicarboxamides as Celegoene ^® Trace ^® I, Hydrocerole ^®, or physical blowing agent, usually inert, evaporating in the foaming conditions liquids , for use.

When TPU can the usual and known compounds are used, as described for example in Kunststoffhandbuch, Volume 7 "Polyurethane", Carl Hanser Verlag Munich Vienna, 3rd edition 1993, pages 455 to 466 are described.

Prefers TPUs having a melt index or MFR 190 ° C / 3.8 kg; DIN EN 1133 from 1-350 g / 10 min, preferably from 30-150 own g / 10 min. The use of TPU for expandable or expanded However, TPU is not limited to a specific MFR.

Under TPU can for the purposes of the present invention, plasticizer-free and plasticizer-containing TPU, in particular those with a content of 0-50 wt .-%, based on the Weight of the mixture, at usual Plasticizers are understood. Plasticizers are common For this Purpose known compounds such as phthalates and in particular benzoates into consideration.

Furthermore, blends of TPU with up to 70 wt .-%, based on the weight of the blend, of another plastic from the group of thermoplastic for the inventive method Plastics, in particular from the group of thermoplastic elastomers or rubbers. Preference is given to mixtures comprising TPU and other thermoplastic elastomers between 99% by weight and 50% by weight of TPU and between 1% by weight and 50% by weight of another thermoplastic elastomer, particularly preferably between 90% by weight and 70 Wt% TPU and between 10 wt% and 30 wt% of another thermoplastic elastomer. As other thermoplastic elastomers are preferably z. As rubber, for example, butadiene-acrylonitrile copolymers, are used.

The Production of the TPU is carried out by conventional methods by reaction of diisocyanates with compounds having at least two with isocyanate groups reactive hydrogen atoms, preferably difunctional alcohols.

When Diisocyanates may contain conventional aromatic, aliphatic and / or cycloaliphatic diisocyanates, for example Diphenylmethane diisocyanate (MDI), toluene diisocyanate (TDI), tri-, Tetra-, penta-, hexa-, hepta- and / or octamethylene diisocyanate, 2-methyl-pentamethylene-diisocyanate-1,5, 2-ethyl-butylene-diisocyanate-1,4, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (isophorone diisocyanate, IPDI), 1,4- and / or 1,3-bis (isocyanatomethyl) cyclohexane (HXDI), 1,4-cyclohexane diisocyanate, 1-methyl-2,4- and / or 2,6-cyclohexane diisocyanate, 4,4'-, 2,4'- and / or 2,2'-dicyclohexylmethane diisocyanate be used.

When across from Isocyanate-reactive compounds may include well-known polyhydroxyl compounds with molecular weights of 500 to 8000, preferably 600 to 6000, in particular 800 to 4000, and preferably an average functionality of 1.8 to 2.6, preferably 1.9 to 2.2, in particular 2 are used, for example, polyesterols, polyetherols and / or polycarbonate diols. Preference is given to using (b) polyesterdiols which are obtainable by reacting butanediol and hexanediol as diol with adipic acid as dicarboxylic acid, the weight ratio from butanediol to hexanediol is preferably 2 to 1. Preference is still given Polytetrahydrofuran having a molecular weight of 750 to 2500 g / mol, preferably 750 to 1200 g / mol.

When Chain extender can well-known compounds are used, for example Diamines and / or alkanediols having 2 to 10 C atoms in the alkylene radical, in particular ethylene glycol and / or 1,4-butanediol, and / or hexanediol and / or di- and / or tri-oxyalkylenglykole having 3 to 8 carbon atoms in the oxyalkylene radical, preferably corresponding oligo-polyoxypropylene glycols, wherein mixtures of the chain extenders can be used. When chain can also 1,4-bis (hydroxymethyl) benzene (1,4-BHMB), 1,4-bis (hydroxyethyl) benzene (1,4-BHEB) or 1,4-bis (2-hydroxyethoxy) benzene (1,4-HQEE). Preferred are chain extenders Ethylene glycol and hexanediol, more preferably ethylene glycol.

Usually Catalysts are used which control the reaction between the NCO groups of the diisocyanates and the hydroxyl groups of the synthesis components accelerate, for example, tertiary amines, such as triethylamine, Dimethylcyclohexylamine, N-methylmorpholine, N, N'-dimethylpiperazine, 2- (dimethylaminoethoxy) ethanol, Diazabicyclo (2,2,2) octane and the like and in particular organic metal compounds such as titanic acid esters, Iron compounds such as e.g. Iron (III) acetyl acetonate, tin compounds such as tin diacetate, Tin dilaurate or the Zinndialkylsalze aliphatic carboxylic acids such Dibutyltin diacetate, dibutyltin dilaurate or the like. The catalysts become common in amounts of 0.0001 to 0.1 parts by weight per 100 parts by weight of polyhydroxyl compound used.

Next Catalysts can the structural components to usual Added auxiliaries become. Examples include surface-active substances, flame retardants, Nucleating agents, lubricants and demulsifiers, dyes and Pigments, inhibitors, stabilizers against hydrolysis, light, heat, Oxidation or discoloration, Protective agents against microbial degradation, inorganic and / or organic fillers, reinforcing agents and plasticizer.

to Adjustment of the molecular weight may be monohydric to isocyanate-reactive Compounds, preferably monoalcohols are used.

The Production of the TPU is usually carried out by conventional methods, such as Strip systems or reaction extruders.

The expanded TPUs produced by the process according to the invention can be used, for example, as films, hoses, profiles, fibers, cables, shoe soles, other shoe parts, ear tags, automobile parts, agricultural products, electrical products, damping elements; armrests; Plastic furniture elements, Ski boots, bumpers, wheels, ski goggles, Powderslushoberflächen be used. According to the invention, shoe soles are preferred, in particular those with a compact skin and a foamed core, in particular dyed, in particular black-colored, shoe soles. Also light-stable aliphatic TPU or blends thereof can be foamed according to the invention. Examples include automotive interior and exterior products such as instrument panel surfaces, gear knobs, controls and knobs, antennas and antenna feet, handles, housings, switches, panels and trim elements, and others.

The Invention will be described in more detail in the following examples.

It Comparative experiments and experiments according to the invention were carried out. The Input materials, the quantities used and the results shown in the table.

Method 1 (comparison)

Addition of the Propellant in a mixer before the production of the moldings

In A simple concrete mixer was added to the TPU granules 0.1% paraffin oil as a binder applied, then after a mixing time of 10 minutes or the blowing agent added and then again for 10 mixed. Thereafter, this mixture was processed thermoplastically, by putting these over an automatic dryer (3 h / 75 ° C) and delivery lines of the injection molding machine automatically fed becomes

Method 2:

continuous Propellant dosage

Based TPU and blowing agents were transferred separately a cooking technique premixer type KK dosed and mixed and the Feeder fed to the injection molding plant. The premixer is here mounted on the feeder of the injection molding plant. The TPU granules will over the premixer the dryer (3 h / 75 ° C) and delivery lines automatically fed.

Claims (5)

Process for the preparation of expanded thermoplastic polyurethanes, comprising the steps of a) mixing blowing agents into a thermoplastic polyurethane and optionally drying, b) thermoplastic processing of this mixture with expansion of the blowing agent, characterized in that as blowing agents expandable microspheres in the form of powder or masterbatch are used and the mixture of the blowing agent with the thermoplastic polyurethanes directly to the plant in which the thermoplastic processing is carried out , Method according to claim 1, characterized in that that the mixture of the blowing agent with the thermoplastic polyurethanes immediately before the thermoplastic processing on the feeder or at one of the screw zones used in step b) Plant is made. A method according to claim 1, characterized in that the expandable microspheres have a TMA density of less than 10 kg / m ³ . Method according to claim 1, characterized in that that in addition to the microspheres expandable further blowing agents used become. Method according to claim 1, characterized in that that the thermoplastic polyurethanes have a melt index at 190 ° C / 3.8 kg; DIN EN 1133) from 1 to 350 g / 10 min.