WO2005023920A1

WO2005023920A1 - Method for producing expanded thermoplastic polyurethanes

Info

Publication number: WO2005023920A1
Application number: PCT/EP2004/009570
Authority: WO
Inventors: Marcus Leberfinger; Carsten GÜNTHER
Original assignee: Basf Aktiengesellschaft
Priority date: 2003-09-01
Filing date: 2004-08-27
Publication date: 2005-03-17
Also published as: DE10340539A1; DE112004001516D2

Abstract

The invention relates to a method for producing expanded thermoplastic polyurethanes (TPU), comprising the following steps: a) mixing of expanding agents with a thermoplastic polyurethane and optional drying, b) thermoplastic processing of said mixture and expansion of the expanding agent. Said method is characterised in that expandable microspheres in the form of powder or master batches are used as the expanding agent and the expanding agent is mixed with the TPU in the installation, in which the thermoplastic processing is carried out.

Description

Process for the production of expanded thermoplastic polyurethanes

description

Thermoplastic polyurethanes (TPU) are semi-crystalline materials and belong to the class of thermoplastic elastomers. They are characterized by good strength, abrasion, tear resistance and chemical resistance, among other things, and can be produced in almost any hardness by suitable raw material composition.

The production takes place according to the known processes in the one-shot or prepolymer process on the belt system or on the reaction extruder. Here, the reaction components diisocyanate, long-chain diol and short-chain diol (chain extender) are combined together or in a specific order and brought to reaction. The reactants are mixed in a ratio of NCO groups to the sum of all hydrogen atoms reacting with the NCO groups of 1: 0.9-1.2, preferably 1: 0.95-1.05, in particular in a ratio of 1: 1.

It is generally known to foam thermoplastics (TPE) using blowing agents. Polystyrene and polyolefins in particular are foamed to a large extent.

Chemical blowing agents come here as blowing agents, in particular those which split off gases under thermal decomposition, such as citric acid, hydrogen carbonates or azodicarbonamides, such as Celegoene; Tracel; Hydrocerols etc., ("Hydrocerols: chemical blowing and nucleating agents for plastics; processing instructions; injection molding; rigid 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; February 4, 2003 ") or by physical blowing agents, mostly inert liquids that evaporate under the foaming conditions, or expandable microspheres (eg Expancel ^® from 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: Formulations and Processing; Paper 9, Page 1-5; Hollow microspheres made of plastics; NN; Kunststoffe 82 (1992) 4 (36366).

Methods are also known for foaming thermoplastic polyurethanes with blowing agents. In the case of TPU, chemical blowing agents lead to a comparatively very coarse foam structure and to an increased formation of voids. To remedy this defect 692 516 EP-A-discloses a method for the production of foams based on TPU, in which a mixture of chemical blowing agents and microspheres of the type Expancel ^® is used as blowing agent.

Expandable microspheres are hollow microspheres that consist of a thin plastic shell, for example polyacrylonitrile or copolymers thereof. These hollow microspheres are filled with gas, usually with hydrocarbons. The temperature acting in the thermoplastic processing softens the plastic shell and at the same time expands the enclosed gas. This leads to an expansion of the microspheres.

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

In EP-A-1174459 the process described in WO 00/44821 is improved by adding a flow agent to the TPU. This was intended to improve the surface of the moldings and reduce the molding time.

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

The blowing agents can be mixed into the base TPU as masterbatches, ie mixtures of the blowing agents with a carrier, preferably a thermoplastic, so-called concentrates, or as a powder. In the latter case it makes sense to add a binding agent (e.g. mineral oil, paraffin oil) to the TPU granulate in order to allow the powder to adhere to the granulate.

However, it can never be completely prevented that powder agglomerates and inhomogeneities in the TPU / powder mixture or segregation of TPU granules and blowing agent powder or blowing agent masterbatch occur. If TPU / blowing agent-powder mixtures are used, it can also never be avoided that powder residues adhere to the inner walls of packaging, mixers, dryers, conveyors, storage containers or other places. This leads to uncontrolled fluctuations in the concentration of the blowing agent in the TPU / blowing agent mixture, also intensified by the detachment of powder accumulations on the inner walls. All of these problems ultimately lead to fluctuations in the already sensitive foaming process in the thermoplastic processing of TPU and to density fluctuations in the finished part. The described uncontrolled powder agglomerates are also often not sufficiently homogenized or digested during plasticization and lead to bright spots in the finished part and on the finished part surface. The object of this invention was to develop a trouble-free production process in the production of expanded TPU, in which the finished parts have a constant quality and a uniform density and which is easy to operate.

The object was achieved in that the blowing agents to be metered in the form of masterbatches or as pure powder are not mixed with the TPU granules in advance, but rather the blowing agent metering is carried out only directly before or during the thermoplastic processing, directly on the plant, in which the expanded parts are produced.

The invention accordingly relates to a method for producing expanded TPU, comprising the steps

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

characterized in that expandable microspheres in the form of powder or masterbatch are used as blowing agents and the blowing agents are mixed with the TPUs directly at the plant in which the thermoplastic processing is carried out.

The systems on which expandable TPU is processed are mostly uιτ? usual and known injection molding or extrusion systems. The blowing agent and basic TPU are metered and mixed in particular in a single unit, for example a KK type premixer; Throughput 20 kg / h; Shot weight up to 200 g; Manufacturer company Koch-Technik. This unit is mounted on the intake of the palstification unit.

In one embodiment of the method according to the invention, the blowing agent is metered continuously into the system and mixed with the TPU, which is also metered continuously. The blowing agent can be fed in at the feed zone and / or in one of the subsequent screw zones, preferably at the feed of the injection molding machine or the extruder.

As described above, the expandable microspheres used for the process according to the invention are generally known and commercially available. Expancel ^® type microspheres are 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 2-10 kg / m ³ and particularly preferably 2-7 kg / m ³ . Expanded TPUs produced with such blowing agents have a particularly fine cell structure, a significantly reduced formation of voids and practically no sink marks. In addition, when using such expandable microspheres, the processing window, for example with regard to the temperature, is significantly larger than when using expandable microspheres with a different TMA density.

The expansion capacity of the microspheres can be described with the TMA density [kg / m ³ ]. The TMA density is the minimum density that can be achieved at a certain 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 microsheres 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, Essen under the brand Expancel® 093 DU 120 (powder).

The term “thermoplastic processing” means any processing which is associated with melting the TPU. The thermoplastic processing is carried out at 80-240 ° C., preferably at 120-230 ° C., particularly preferably at 170-220 ° C., on the person skilled in the art known injection molding and extrusion systems or powder sintering systems.

The content of expandable microspheres in the mixture depends on the desired density of the expanded TPU. Per 100 parts by weight of the TPU or TPU blend to be expanded, ie to be foamed, between 0.1 part by weight and 10 parts by weight, preferably between 0.2 part by weight and

6.5 parts by weight of the expandable microspheres according to the invention are used.

Expandable TPU or expanded TPU blends which contain the following components are particularly preferred: 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 TPU or blend containing TPU, 0.5% by weight to 15% by weight, preferably between 2% by weight and 8% by weight Microspheres masterbatch, 0 to 10% by weight, preferably 0.1% to 2% by weight

Dye, e.g. commonly 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 Carrier, preferably thermoplastic carrier, for example the carrier materials shown later, particularly preferably EVA (ethylene vinyl acetate).

The expandable microspheres used can be in the form of powder, on the one hand, the application to the TPU granules being carried out with and without a binder, such as 0.05-2% by weight of mineral or paraffin oil, or, on the other hand, preferably as masterbatches. Masterbatch is understood to mean 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 blends thereof, preferably a carrier with a melt index MFR; 190 ° C / 2.16 kg; ASTM D 1238) from 5 to 700 g / 10 min, preferably 50 to 600 g / 10 min, particularly preferably 150 to 500 g / 10 min and a melting point between 60 and 110 ° C., particularly preferably 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 production of these microspheres masterbatches, thermoplastics with a very low melting point and very low viscosities or high melt indices, as described above, are generally used, in order to thereby minimize the temperatures at

To be able to use masterbatch production to avoid premature expansion.

In addition to the expandable microspheres, other blowing agents can also be used. As already mentioned above, for this purpose are chemical blowing agents, especially those which split off under thermal decomposition gases, such as citric acid, hydrogen or azodicarboxamides as Celegoene ^® Trace ^®!, Hydrocerole ^®, or physical blowing agent, usually inert, called on Verschäumbedingun- evaporating liquids, for use.

The usual and known compounds can be used as the TPU, as described, for example, in the plastics handbook, volume 7 "Polyurethane", Carl Hanser Verlag, Munich, Vienna, 3rd edition 1993, pages 455 to 466.

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

For the purposes of the present invention, TPU can be understood to mean plasticizer-free and plasticizer-containing TPUs, in particular those with a content of 0-50% by weight, based on the weight of the mixture, of conventional plasticizers. Compounds known for this purpose, such as phthalates and in particular benzoates, are generally suitable as plasticizers.

Furthermore, blends of TPU with up to 70% by weight, based on the weight of the blend, of a further plastic from the group of thermoplastic materials, in particular from the group of thermoplastic elastomers or rubbers, can also be present for the process according to the invention. Mixtures containing 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 are preferred, particularly preferably between 90% by weight and 70 % By weight of TPU and between 10% by weight and 30% by weight of another thermoplastic elastomer. As other thermoplastic elastomers, z. B. rubber, e.g. Butadiene-acrylonitrile copolymers, for use.

The TPU is produced by the customary process by reacting diisocyanates with compounds having at least two hydrogen atoms reactive with isocyanate groups, preferably difunctional alcohols.

Typical aromatic, aliphatic and / or cycloaliphatic diisocyanates, for example diphenylmethane diisocyanate (MDI), tolylene 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-isocyanatomethyl-cyclohexane (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 can be used.

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, can be used as compounds which are reactive toward isocyanates , in particular 2 are used, for example polyesterols, polyetherols and / or polycarbonate diols. Polyester diols which are obtainable by reacting butanediol and hexanediol as diol with adipic acid as dicarboxylic acid are preferably used as (b), the weight ratio of butanediol to hexanediol preferably being 2 to 1. Also preferred is polytetrahydrofuran with a molecular weight of 750 to 2500 g / mol, preferably 750 to 1200 g / mol. Generally known compounds can be used as chain extenders, for example diamines and / or alkanediols having 2 to 10 carbon atoms in the alkylene radical, in particular ethylene glycol and / or 1,4-butanediol, and / or hexanediol and / or di- and / or tri- oxyalkylene glycols with 3 to 8 carbon atoms in the oxyalkylene radical, preferably corresponding oligo-polyoxypropylene glycols, it also being possible to use mixtures of the chain extenders. 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) are used. Preferred chain extenders are ethylene glycol and hexanediol, particularly preferably ethylene glycol.

Catalysts are usually used which accelerate the reaction between the NCO groups of the diisocyanates and the hydroxyl groups of the structural components, for example tertiary amines, such as triethylamine, dimethylcyclohexylamine, N-methylmorpholine, N, N'-dimethylpiperazine, 2- (dimethylaminoethoxy) - ethanol, diazabicyclc— (2,2,2) octane and similar as well as in particular organic metal compounds such as titanium esters, iron compounds such as Iron (III) acetyl acetonate, tin compounds such as tin diacetate, tin dilaurate or the tin dialkyl salts of aliphatic carboxylic acids such as dibutyl tin diacetate, dibutyl tin dilaurate or the like. The catalysts are usually used in amounts of 0.0001 to 0.1 part by weight per 100 parts by weight of polyhydroxyl compound.

In addition to catalysts, customary auxiliaries can also be added to the structural components. Examples include surface-active substances, flame retardants, nucleating agents, lubricants and mold release agents, 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 plasticizers.

To adjust the molecular weight, monofunctional compounds which are reactive toward isocyanate, preferably monoalcohols, can be used.

The TPU is usually manufactured using customary methods, such as belt 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, automotive parts, agricultural products, electrical products, damping elements; armrests; Plastic furniture elements, ski boots, bumpers, rollers, ski goggles, powder slush surfaces can be used. According to the invention, shoe soles are preferred, in particular those with a compact skin and a foamed core, in particular colored, in particular black colored shoe soles. Light-resistant aliphatic TPUs or blends made from them can also be foamed according to the invention. Examples include products for the automotive interior and exterior such as instrument panel surfaces, gear knobs, control elements and buttons, antennas and antenna feet, handles, housings, switches, cladding and cladding elements, and others.

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

Comparative experiments and experiments according to the invention were carried out. The input substances, the amounts used and the results are shown in the table.

Method 1 (comparison) addition of the blowing agent in a mixer before the production of the molded parts

In a simple concrete mixer, 0.1% paraffin oil was applied to the TPU granules as a binder, then the blowing agent or agents were added after a mixing time of 10 minutes and then mixed again for 10 minutes. This mixture was then processed thermoplastic by automatically feeding it to the injection molding machine via an automatic dryer (3 h / 75 ° C) and conveyor lines

Method 2: Continuous blowing agent metering

The base TPU and blowing agent were dosed and mixed separately using a KK pre-mixer, and fed to the injection molding machine. The pre-mixer is mounted on the intake of the injection molding system. The TPU granulate is automatically fed to the pre-mixer via the dryer (3 h / 75 ° C) and delivery lines.

Table 1: Results of experiments V1 and V2 according to the invention in comparison to the reference experiments RO-2

1) Only RO worked with emphasis, in the other cases the emphasis is switched off 2) Target weight: 151 g; Mold volume (sole tool): 203 cm ³ ; Target density: 0.74 g / cm ³ 3) No statistical error analysis because of the compact sole

Lenαende:

R comparison test

V Experiment according to the invention

093DU120 microspheres powder from Akzo

GT _MP = weight fraction of the microspheres powder used in relation to TPU

Hydrocerol BIN = Clariant; chemical blowing agent powder

GT _CT used percentage by weight of the chemical blowing agent masterbatch in relation to TPU

S70A10W commercial polyester TPU contains plasticizer from Elastogran; Application for e.g. B. shoe soles;

MW mean of 20 determinations, i.e. 20 soles

Stabwn = standard deviation from 20 determinations

Agglomerate formation: appearance of visible white agglomerates in the sole and on the sole surface 0 = no visible agglomerates ++ = highly visible agglomerates

Powder buildup: occurrence of powder deposits on the inner walls of the dryer, granulate feed lines, feed hopper 0 = no powder deposits ++ = significant powder deposits

Rejects = indicates the number of soles that are not completely filled based on 50 injections

Injection molding machine: Klöckner Ferromatic FM 160

Shoe sole tool: aluminum; Shot weight 243 g at a density of 1, 20 g / cm ³ in the case of Elastollan S70A10W compact

Tool temperature: 25 ° C; Shoe tool;

Claims

claims

1. Process for the production of expanded thermoplastic polyurethanes, comprising the steps a) mixing blowing agents to form a thermoplastic polyurethane and optionally drying,

b) thermoplastic processing of this mixture with expansion of the blowing agent, characterized in that expandable microspheres in

Form of powder or masterbatch are used and the blowing agents are mixed with the thermoplastic polyurethanes directly at the plant in which the thermoplastic processing is carried out.

2. The method according to claim 1, characterized in that the mixture of the blowing agents with the thermoplastic polyurethanes takes place immediately before the ther plastic processing at the feeder or at one of the screw zones of the system used in process step b).

3. The method according to claim 1, characterized in that the expandable microspheres have a TMA density of less than 10 kg / m ³ .

4. The method according to claim 1, characterized in that expandable further blowing agents are used in addition to the microspheres.

5. The method according to claim 1, characterized in that the thermo

plastic polyurethanes have a melt index at 190 ° C / 3.8 kg; DIN EN 1133) from 1 to 350 g / 10 min.