WO2003085042A1

WO2003085042A1 - Modified thermoplastic polyurethanes

Info

Publication number: WO2003085042A1
Application number: PCT/EP2003/003588
Authority: WO
Inventors: Hugo Verbeke; Jacobus Margareta Valentijn Vanden Ecker
Original assignee: Huntsman International Llc
Priority date: 2002-04-11
Filing date: 2003-04-07
Publication date: 2003-10-16
Also published as: AU2003226790A1

Abstract

A process for preparing a modified thermoplastic polyurethane by I) reacting (a) one or more isocyanates with (b) one or more compounds reactive toward isocyanates to form thermoplastic polyurethanes II) bringing said thermoplastic polyurethane in contact with an additive, whereby the thermoplastic polyurethane is absorbed with said additive.

Description

Modified thermoplastic poiyurethanes

1. Field of the Invention

The present invention pertains to modified thermoplastic poiyurethanes. More particularly, the present invention pertains to a new process for obtaining modified thermoplastic poiyurethanes.

2. Background of the invention

Commercial applications of thermoplastic poiyurethanes (TPU) continue to grow at a rapid pace. Unlike their thermoset relatives, TPU can be processed in a manner similar to other thermoplastics in operations such as extrusion, injection molding, wire coating, etc.

It is an objective of the present invention to develop a process for preparing thermoplastic poiyurethanes by reacting a) isocyanates, b) compounds reactive towards isocyanates and additives by means of which thermoplastic poiyurethanes can be thermoplastically processed without complex processing.

It is another objective of the present invention to be able to use additives which when added to thermoplastic polyurethane , would decrease cycle time without decreasing physical properties, or the use of which may actually increase specific physical properties.

According to one embodiment, it has now been found that the afore-mentioned benefits can be obtained by a process for preparing a modified thermoplastic polyurethane by I) reacting (a) one or more isocyanates with (b) one or more compounds reactive toward isocyanates to form thermoplastic poiyurethanes II) bringing said thermoplastic polyurethane in contact with an additive, whereby the thermoplastic polyurethane is absorbed with said additive; According to another embodiment, a process is now provided for preparing a modified thermoplastic polyurethane by I) reacting (a) one or more isocyanates with (b) one or more compounds reactive toward isocyanates to form thermoplastic poiyurethanes II) bringing said thermoplastic polyurethane in contact with a compound containing an isocyanate reactive functional group , whereby the thermoplastic polyurethane is absorbed with said compound;

Preferred modified thermoplastic poiyurethanes of the present invention contain compounds having isocyanate reactive functional groups. Preferred functional groups are selected from hydroxy groups. While the conventional thermoplastic polyurethane resins have hydroxy groups only on terminals of a molecular structure, these modified thermoplastic poiyurethanes have polar functional hydroxy groups inter their molecular structure.

3. Detailed description

A. Modified thermoplastic polyurethane

According to one embodiment, the present invention is directed to a process for preparing a modified thermoplastic polyurethane by I) reacting (a) one or more isocyanates with (b) one or more compounds reactive toward isocyanates to form thermoplastic poiyurethanes II) bringing said thermoplastic polyurethane in contact with an additive, whereby the thermoplastic polyurethane is absorbed with said additive

Absorption in the context of the present invention refers to processes in which a substance penetrates into the actual interior of the thermoplastic polyurethane.

Examples of additives include catalysts, for example tertiary amines and tin compounds, surface-active agents and foam stabilisers, for example siloxane- oxyalkylene copolymers, flame retardants, antistatic agents, plasticizers, organic and inorganic fillers, pigments and internal mould release agents. Customary plasticizers which can be used are, for example, phthalates, for example di-2-ethylhexyl phthalate, dioctyl phthalate, octylbenzyl phthalate, butyl benzyl phthalate, dibutyl glycol phthalate, bis(methyl diglycol) phthalate or dibutyl phthalate, organophosphorus compounds such as tris(2-chloroethyl) phosphate, tris(chloropropyl) phosphate, dimethyl methylphosphonate, diphenyl cresyl phosphate or tricresyl phosphate, adipic, azelaic or sebacic esters, phenyl alkylsulfonates, acetyl- tributyl citrate, epoxidized fatty acid esters, generally known polyester-based, oligomeric and polymeric plasticizers, tri-2-ethylhexyl trimellitate, triisooctyl trimellitate, dibutyl adipate, dioctyl adipate and also further materials generally known as plasticizers. Preference is given to using butyl benzyl phthalate as plasticizer.

It has been found that improved characteristics of the thermoplastic poiyurethanes can be obtained by the process of the present invention. In particular, the resulting modified TPU are capable of obtaining synergistic effect of the characteristics of a thermoplastic polyurethane resin including a high slip-preventing capability .

According to another embodiment, a process is now provided for preparing a modified thermoplastic polyurethane by I) reacting (a) one or more isocyanates with (b) one or more compounds reactive toward isocyanates to form thermoplastic poiyurethanes II) bringing said thermoplastic polyurethane in contact with a compound containing an isocyanate reactive functional group , whereby the thermoplastic polyurethane is absorbed with said compound;

According to this embodiment, the modified thermoplastic polyurethane contain compounds having isocyanate reactive functional groups. Preferred functional groups are selected from hydroxy groups. While the conventional thermoplastic polyurethane resins have hydroxy groups only on terminals of a molecular structure, these modified thermoplastic poiyurethanes have polar functional hydroxy groups inter their molecular structure

Exemplary of compounds containing isocyanate reactive functional groups include the hydroxy compounds such as polyhydroxy alkanes, alkoxylated polyhydroxy alkanes, sugars, alkoxylated sugars, hydroxyl terminated polyesters, hydroxyl terminated aromatic polyethers, and methylolated or alkoxylated amines. More particularly within the category of polyhydroxy alkanes are included sugar alcohols, and glycols: for example, ethylene glycol, propylene glycol, butanediol, sorbitol, glycerine, erythritol, threitol, and 1,2,5,6-hexanetetrol. Other class of compounds containing isocyanate reactive groups suitable for the present invention does include those which have residual hydroxyl groups. An example are hydroxyl containing benzoates.

The process for absorbing the additive into the thermoplastic polyurethane is not particularly limited, but there may be adopted a process such as is mentioned below.

That is, a process in which particles, flakes or pellets or granules of the thermoplastic polyurethane are uniformly sprayed with the additive, especially a compound containing the isoreactive functional group to absorb said additive or compound into the thermoplastic polyurethane; or a process in which the thermoplastic polyurethane is dissolved in an amount of said compound. Other process that may be employed is one in which powders of the polyurethane and isoreactive functional compound are stirred and mixed together by use of a mixer; a process in which the thermoplastic polyurethane and the compound are kneaded together in a molten state by use of a hot roll, an extruder or a calendar roll; or a process in which a solution of the thermoplastic polyurethane and a solution of the isoreactive functional compound are stirred and mixed together.

The thermoplastic poiyurethanes can be mixed with the isocyanate reactive compound or mixtures comprising the compound with the thermoplastic polyurethane absorbing the compound. The temperature during the mixing procedure is preferably from 10 to 140 degree. C, but lower or higher temperatures are also suitable.

The absorption of the compound into the thermoplastic polyurethane can occur over a period of minutes after mixing the compounds, with these times depending on the temperatures and any aids employed (e.g. mixing, stirring and shaking). Procedures which accelerate this process, e.g. stirring and shaking, are preferably employed. The processing of the resulting modified thermoplastic polyurethane of the present invention is carried out by customary methods. Owing to the absorption of the hydroxy functional group into the thermoplastic polyurethane, the latter can be processed very well and the products have very good properties especially the slip - preventing capability.

In another embodiment, the present invention concerns a composition comprising (a) a TPU and (b) isocyanate reactive functional groups characterised in that said isocyanate reactive groups are present inter the molecular structure of the thermoplastic polyurethane.

According to another embodiment, the present invention is directed to a process for preparing a modified thermoplastic polyurethane by I) reacting (a) one or more polyisocyanates with (b) one or more compounds reactive toward isocyanates to form thermoplastic poiyurethanes II) bringing said thermoplastic polyurethane in contact with a compound containing an isocyanate reactive functional group , whereby the thermoplastic polyurethane is absorbed with said compound.

During the mixing of the thermoplastic polyurethane and the compound containing isocyanate functional groups, or at the time of subjecting the resulting thermoplastic polyurethane of the present invention to such molding process as compression molding, injection molding or extrusion molding, the resins or the resin composition may be incorporated, according to the application purpose , with proper amounts of such additives as pigments, dyes, inorganic fillers, stabilizers, flame retardants, blowing agent etc.

B. The thermoplastic polyurethane component

Suitable thermoplastic poiyurethanes useful to provide the TPUs of the present invention are those prepared from a diisocyanate, a polyester or polyether and a chain extender. These thermoplastic poiyurethanes are those which are substantially linear and maintain thermoplastic processing characteristics. The thermoplastic poiyurethanes are obtainable by reacting a difunctional isocyanate composition with at least one difunctional polyhydroxy compound and optionally a chain extender in such amounts that the isocyanate index is between 90 and 110, preferably between 95 and 105, and most preferably between 98 and 102.

The term 'difunctional' as used herein means that the average functionality of the isocyanate composition and the polyhydroxy compound is about 2.

The term "isocyanate index" as used herein is the ratio of isocyanate-groups over isocyanate-reactive hydrogen atoms present in a formulation, given as a percentage. In other words, the isocyanate index expresses the percentage of isocyanate actually used in a formulation with respect to the amount of isocyanate theoretically required for reacting with the amount of isocyanate-reactive hydrogen used in a formulation.

It should be observed that the isocyanate index as used herein is considered from the point of view of the actual polymer forming process involving the isocyanate ingredient and the isocyanate-reactive ingredients. Any isocyanate groups consumed in a preliminary step to produce modified polyisocyanates (including such isocyanate- derivatives referred to in the art as quasi- or semi-prepolymers) or any active hydrogens reacted with isocyanate to produce modified polyols or polyamines, are not taken into account in the calculation of the isocyanate index. Only the free isocyanate groups and the free isocyanate-reactive hydrogens present at the actual elastomer forming stage are taken into account.

The difunctional isocyanate composition may comprise any aliphatic, cycloaliphatic or aromatic isocyanates. Preferred are isocyanate compositions comprising aromatic diisocyanates and more preferably diphenylmethane diisocyanates.

The polyisocyanate composition used in the process of the present invention may consist essentially of pure 4,4'-diphenylmethane diisocyanate or mixtures of that diisocyanate with one or more other organic polyisocyanates, especially other diphenylmethane diisocyanates, for example the 2,4'-isomer optionally in conjunction with the 2,2'-isomer. The polyisocyanate component may also be an MDI variant derived from a polyisocyanate composition containing at least 95% by weight of 4,4'- diphenylmethane diisocyanate. MDI variants are well known in the art and, for use in accordance with the invention, particularly include liquid products obtained by introducing carbodiimide groups into said polyisocyanate composition and/or by reacting with one or more polyols.

Preferred polyisocyanate compositions are those containing at least 80% by weight of 4,4'-diphenylmethane diisocyanate. More preferably, the 4,4'- diphenylmethane diisocyanate content is at least 90, and most preferably at least 95% by weight.

The difunctional polyhydroxy compound used has a molecular weight of between 500 and 20000 and may be selected from polyesteramides, polythioethers, polycarbonates, polyacetals, polyolefins, polysiloxanes, polybutadienes and, especially, polyesters and polyethers, or mixtures thereof. Other dihydroxy compounds such as hydroxyl-ended styrene block copolymers like SBS, SIS, SEBS or SIBS may be used as well.

Mixtures of two or more compounds of such or other functionalities and in such ratios that the average functionality of the total composition is about 2 may also be used as the difunctional polyhydroxy compound. For polyhydroxy compounds the actual functionality may e.g. be somewhat less than the average functionality of the initiator due to some terminal unsaturation. Therefore, small amounts of trifunctional polyhydroxy compounds may be present as well in order to achieve the desired average functionality of the composition.

Polyether diols which may be used include products obtained by the polymerisation of a cyclic oxide, for example ethylene oxide, propylene oxide, butylene oxide or tetrahydrofuran in the presence, where necessary, of difunctional initiators. Suitable initiator compounds contain 2 active hydrogen atoms and include water, butanediol, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, dipropylene glycol, 1,3-propane diol, neopentyl glycol, 1,4-butanediol, 1,5-pentanediol, 1,6- pentanediol and the like. Mixtures of initiators and/or cyclic oxides may be used.

Especially useful polyether diols include polyoxypropylene diols and poly(oxyethylene-oxypropylene) diols obtained by the simultaneous or sequential addition of ethylene or propylene oxides to difunctional initiators as fully described in the prior art. Random copolymers having oxyethylene contents of 10-80%, block copolymers having oxyethylene contents of up to 25% and random/block copolymers having oxyethylene contents of up to 50%, based on the total weight of oxyalkylene units, may be mentioned, in particular those having at least part of the oxyethylene groups at the end of the polymer chain. Other useful polyether diols include polytetramethylene diols obtained by the polymerisation of tetrahydrofuran. Also suitable are polyether diols containing low unsaturation levels (i.e. less than 0.1 milliequivalents per gram diol).

Other diols which may be used comprise dispersions or solutions of addition or condensation polymers in diols of the types described above. Such modified diols, often referred to as 'polymer' diols have been fully described in the prior art and include products obtained by the in situ polymerisation of one or more vinyl monomers, for example styrene and acrylonitrile, in polymeric diols, for example polyether diols, or by the in situ reaction between a polyisocyanate and an amino- and/or hydroxyfunctional compound, such as triethanolamine, in a polymeric diol.

Polyoxyalkylene diols containing from 5 to 50% of dispersed polymer are useful as well. Particle sizes of the dispersed polymer of less than 50 microns are preferred.

Polyester diols which may be used include hydroxyl-terminated reaction products of dihydric alcohols such as ethylene glycol, propylene glycol, diethylene glycol, 1,4- butanediol, neopentyl glycol, 2-methylpropanediol, 3-methylpentane-l,5-diol, 1,6- hexanediol or cyclohexane dimethanol or mixtures of such dihydric alcohols, and dicarboxylic acids or their ester-forming derivatives, for example succinic, glutaric and adipic acids or their dimethyl esters, sebacic acid, phthalic anhydride, tetrachlorophthalic anhydride or dimethyl terephthalate or mixtures thereof.

Polyesteramides may be obtained by the inclusion of aminoalcohols such as ethanolamine in polyesterifϊcation mixtures.

Polythioether diols which may be used include products obtained by condensing thiodiglycol either alone or with other glycols, alkylene oxides, dicarboxylic acids, formaldehyde, amino-alcohols or aminocarboxylic acids. Polycarbonate diols which may be used include those prepared by reacting glycols such as diethylene glycol, triethylene glycol or hexanediol with formaldehyde. Suitable polyacetals may also be prepared by polymerising cyclic acetals.

Suitable polyolefin diols include hydroxy-terminated butadiene homo- and copolymers and suitable polysiloxane diols include polydimethylsiloxane diols.

Suitable difunctional chain extenders include aliphatic diols, such as ethylene glycl, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-propanediol, 2- methylpropanediol, 1,3-butanediol, 2,3-butanediol, 1,3-pentanediol, 1,2-hexanediol, 3-methylpentane-l,5-diol, diethylene glycol, dipropylene glycol and tripropylene glycol, and aminoalcohols such as ethanolamine, N-methyldiethanolamine and the like. 1,4-butanediol is preferred.

The TPUs suitable for processing according to the invention can be produced in the so-called one-shot, semi-prepolymer or prepolymer method, by casting, extrusion or any other process known to the person skilled in the art and are generally supplied as granules or pellets.

Optionally, small amounts, i.e. up to 30, preferably 20 and most preferably 10, wt% based on the total of the blend, of other conventional thermoplastic elastomers such as PNC, ENA or TR may be blended with the TPU.

Blowing agent may be added to the system, which may either be an exotliermic or endothermic blowing agent, or a combination of both. Most preferably however, an endothermic blowing agent is added.

Any known blowing agent used in the preparation of foamed thermoplastics may be used in the present invention as blowing agents.

Examples of suitable chemical blowing agents include gaseous compounds such as nitrogen or carbon dioxide, gas (e.g. CO2) forming compounds such as azodicarbonamides, carbonates, bicarbonates, citrates, nitrates, borohydrides, carbides such as alkaline earth and alkali metal carbonates and bicarbonates e.g. sodium bicarbonate and sodium carbonate, ammonium carbonate, diaminodiphenylsulphone, hydrazides, malonic acid, citric acid, sodium monocitrate, ureas, azodicarbonic methyl ester, diazabicylooctane and acid/carbonate mixtures.

Preferrd endothermic blowing agents comprise bicarbonates or atrates.

Examples of suitable physical blowing agents include volatile liquids such as chlorofluorocarbons, partially halogenated hydrocarbons or non-halogenated hydrocarbons like propane, n-butane, isobutane, n-pentane, isopentane and/or neopentane, CO₂, N₂ or mixtures thereof.

Preferred endothermic blowing agents are the so-called 'HYDROCEROL' blowing agents as disclosed in a.o. EP-A 158212 and EP-A 211250, which are known as such and commercially available ('HYDROCEROL' is a trademark of Boehringer Ingelheim).

Azodicarbonamide type blowing agents are preferred as exothermic blowing agents.

Thermally expandable microspheres can also be used. Microspheres containing hydrocarbons, in particular aliphatic or cycloaliphatic hydrocarbons, are preferred.

The term "hydrocarbon" as used herein is intended to include non-halogenated and partially or fully halogenated hydrocarbons.

An example of such microspheres are the EXPANCEL-DU microspheres which are marketed by AKZO Nobel Industries of Sweden ('EXPANCEL' is a trademark of AKZO Nobel Industries).

The thermoplastic poiyurethanes of the present invention can be made via a variety of processing techniques, such as extrusion, calendering, thermoforming, flow moulding or injection moulding. Injection moulding is however the preferred production method. The thermoplastic polyurethane is customarily manufactured as pellets for later processing into the desired article. The term 'pellets' is understood and used herein to encompass various geometric forms, such as squares, trapezoids, cylinders, lenticular shapes, cylinders with diagonal faces, chunks, and substantially spherical shapes including a particle of powder or a larger-size sphere. While thermoplastic poiyurethanes are often sold as pellets, the polyurethane could be in any shape or size suitable for use in the equipment used to form the final article.

The thermoplastic poiyurethanes obtainable via the process of the present invention are particularly suitable for use in any application of thermoplastic rubbers including, for example, footwear or integral skin applications like steering wheels.

Customized thermoplastic poiyurethanes may be produced more efficiently using the process according to the present invention. The customized thermoplastic poiyurethanes may be formed into any of the articles generally made with thermoplastic resins. Examples of articles are interior and exterior parts of automobiles, such as inside panels, bumpers, housing of electric devices such as television, personal computers, telephones, video cameras, watches, note-book personal computers; packaging materials; leisure goods; sporting goods and toys

The invention is illustrated, but not limited, by the following examples in which all parts, percentages and ratios are by weight.

According to the present invention, three different thermoplastic poiyurethanes were tested. A) commercially available thermoplastic polyurethane (Avalon® 65 AE)

B) thermoplastic polyurethane as in A) but absorbed with BBP (butylbenzylphtalate)

C) thermoplastic polyurethane as in A) but absorbed with a compound containing isocyanate reactive groups (Benzyl benzoaat containing residual hydroxyl groups).

The following data concerning slip resistance were produced (SATRA (Shoe and

Allied Trades Research Association) PM 144). The usefulness of the modified thermoplastic poiyurethanes via de absorption route can be easily recognized : Test Data

Slip Resistance (SATRA PM 144 9992) A)Coeff of Friction 0.135

B)Coeff. of friction 0.26 C)Coeff. of friction 0.43

The TPU is heated to 80°C in a high shear blender by friction during mixing. The additive is added and mixed until it is absorbed by the TPU. Then the TPU is taken out of the high shear blender and is ready for use.

The above data (A vs. B) shows that by altering the addition method of the additive, during TPU manufacturing process vs. absorption after TPU has been made, the slip properties improve with the latter method.

Within the same addition method for the additive the above example (B vs. C) shows that the free NCO reactive group containing benzyl benzoate significantly improves the slip performance of the TPU.

Claims

Claims:

1. A process for preparing a modified thermoplastic polyurethane by I) reacting (a) one or more isocyanates with (b) one or more compounds reactive toward isocyanates to form thermoplastic poiyurethanes II) bringing said thermoplastic polyurethane in contact with an additive, whereby the thermoplastic polyurethane is absorbed with said additive;

2. A process for preparing a modified thermoplastic polyurethane by I) reacting (a) one or more isocyanates with (b) one or more compounds reactive toward isocyanates to form thermoplastic poiyurethanes II) bringing said thermoplastic polyurethane in contact with a compound containing an isocyanate reactive functional group , whereby the thermoplastic polyurethane is absorbed with said compound;

3. A process according to claim 2 wherein said isocyanate reactive functional group is selected from hydroxy groups.

4. A modified thermoplastic polyurethane composition comprising (a) a TPU and (b) compound containing isocyanate reactive functional groups wherein said isocyanate reactive groups are present inter the molecular structure of the thermoplastic polyurethane.

5. The process according to claim 1, comprising the addition of one or more additives selected from the group consisting of plasticizers.

6. The process according to claim 5, wherein the plasticizers is butylbenzyl phthalate.