WO2012069264A1

WO2012069264A1 - Process for making a thermoplastic polyurethane

Info

Publication number: WO2012069264A1
Application number: PCT/EP2011/068519
Authority: WO
Inventors: Thomas Welker; Dieter Kuhn; Uwe Schachtely; Uwe Kinzlinger; Henri Sautel; Ulrich Boes; Kevin Barthomeuf; Didier Lagneaux
Original assignee: Evonik Degussa Gmbh
Priority date: 2010-11-24
Filing date: 2011-10-24
Publication date: 2012-05-31
Also published as: DE102010061854A1; TW201233699A

Abstract

Process for making a thermoplastic polyurethane by reacting a mixture comprising at least one polyisocyanate, at least one polyol and fumed silica, wherein a)in a first reaction step the polyol is reacted in the presence of fumed silica with the polyisocyanate the index factor being 0,95 to 1,00 with a conversion of 95% or more, b) in a second reaction step additional polyisocyanate is added to the reaction mixture, in an amount that the overall index factor of first and second reaction step is >1,00 to 1,05, the index factor being defined as isocyanate function quantity / polyol function quantity.

Description

Process for Making a Thermoplastic Polyurethane

The invention relates to a process for making a thermoplastic polyurethane by reacting a mixture comprising at least one polyisocyanate, at least one polyol and fumed silica.

Thermoplastic polyurethanes are manufactured in large amounts and in a wide range of grades. This group of substances is in this connection, because of its good elastic properties, in combination with the possibility of thermoplastic moulding, its chemical resistance and its abrasion resistance particularly attractive. They are accordingly suitable, for example, for mechanically and thermally stressed coatings, hoses, pipes, profiles, wearing parts and other moulded articles.

Thermoplastic polyurethanes are formed from linear polyols, generally polyester or polyether polyols, organic polyisocyanates and short-chain diols (chain extenders). These compounds react in a certain ratio, usually defined as isocyanate function quantity / polyol function quantity, which is approximately 0.98 to 1 .02. It is also known that fumed silica may be used to improve the mechanical properties of the thermoplastic polyurethane. However the improvement in molecular weight and melt strength of the thermoplastic polyurethanes obtained by the processes known in the state of the art is limited.

The technical object of the present invention is therefore to provide a process that allows to improve the melt behaviour and mechanical properties of a thermoplastic polyurethane (TPU) compared to the processes known in the state of the art. In particular the process should result in a TPU having increased molecular weight and melt strength compared to TPU's prepared by known processes. The object of the invention is a process for making a thermoplastic polyurethane by reacting a mixture comprising at least one polyisocyanate, at least one polyol and fumed silica, wherein

a) in a first reaction step the polyol is reacted in the presence of fumed silica with the polyisocyanate, the index factor being 0,95 to 1 ,00, preferably 0,98 to 1 , with a conversion of 95% or more, preferably 97 to 100%,

b) in a second reaction step additional polyisocyanate is added to the reaction mixture, in an amount that the overall index factor of first and second reaction step is > 1 ,00 to 1 , 1 , preferably 1 ,02 to 1 ,05,

the index factor being defined as isocyanate function quantity / polyol function quantity.

Step a) means that most of all the polyol (polyether, ester or chain extender) is almost completely reacted, maybe fully reacted. This means that at least 95 % of the maximum M_w is reachable with the index of 0,95 to 1 ,00. Then the addition of polyisocyanate in step b) increases the M_w to a level where the process according to the state of the art cannot go.

The thermoplastic polyurethane (TPU) preferably is a high molecular weight TPU. The phrase "high molecular weight" is understood to mean that the quotient of the molecular weight M_w of the TPU obtained by the process according to the invention and the molecular weight M_w of the TPU obtained by the same process but without fumed silica is more than 1 . This relationship is shown in the following formula.

M_w [polyol + polyisocyanate + fumed silica + additional polyisocyanate]

>1 M_w [polyol + polyisocyanate + additional polyisocyanate]

Preferably the quotient is 1 .1 to 20, more preferably 2 to 10. The absolute value of the molecular weight M_w depends on the starting materials polyol and isocyanate. In a special embodiment of the invention the molecular weight M_w of a TPU prepared according to the invention is 1 ,000,000 or more, preferably 1 ,000,000 to 2,000,000. Fumed Silica

The fumed silica may be added as a powder and/or as a dispersion.

The powder itself may be a hydrophihc silica powder or a hydrophobic silica powder. The concentration of fumed silica preferably is 0,3 to 10 wt.-%, referred based on the thermoplastic polyurethane. Most preferred is range of 3 to 8 wt.-%. In general hydrophobic fumed silica gives better results.

Fumed Silica Powder

In general the hydrophihc fumed silica powder is the product of a flame oxidation or flame hydrolysis, in which a silicon compound like SiCI₄ is burned in

hydrogen/oxygen flame.

The surface of the hydrophihc fumed silica particles is bearing hydroxyl groups, the hydroxyl group density being from 1.8 to 4.7 OH/nm², usually from 1 .8 to 2.5, when determined by the method of J. Mathias and G. Wannemacher, Journal of Colloid and Interface Science 125 (1988). In general the hydrophihc fumed silica powder comprises or consists of aggregated primary particles. _The term "aggregated" is to be understood as meaning that primary particles, produced first in the genesis of the hydrophihc fumed silica particles, combine firmly together in the further course of the reaction with formation of a three-dimensional network. In contrast to agglomerates, these combinations can no longer be separated using conventional dispersing devices. Preferably the proportion of aggregates is high in comparison with isolated individual particles that are at least 80% of the hydrophihc fumed silica particles should be present in the form of aggregates. The aggregate to isolated individual particle ratio can, for example, be determined by quantitative evaluation of TEM photographs (TEM = Transmission Electron Microscopy). The primary particles are substantially free from inner pores.

The hydrophobic fumed silica powder usually is obtained by reacting the

hydrophihc fumed silica powder with a surface modifying agent. In the course of the reaction at least some of the hydroxyl groups at the surface of the hydrophihc fumed silica reacts with the surface modifying agent to create a certain degree of hydrophobicity. In general, not all of the hydroxy groups react with the surface modifying agent. The structure of the hydrophobic fumed silica particles, e.g. the degree of aggregation, is mainly the same as the hydrophihc fumed silica particles. " Hydrophobic" is understood to mean that the methanol wettability of the fumed silica particles is at least 20, preferably 20 to 50 and more preferably 25 to 45. For the determination of the methanol wettability, 0.2 g (± 0.005 g) of surface-modified silicon dioxide particles are weighed out into transparent centrifuge tubes. To each sample are added 8.0 ml of a methanol/water mixture containing respectively 10%, 20%, 30%, 40%, 50%, 60%, 70% and 80% by volume of methanol. After sealing, the tubes are shaken for 30 seconds and then centrifuged for 5 minutes at

2500 min^"1. The volumes of sediment are read off, converted to a percentage, and plotted against the methanol content (% by volume). The point of inflexion of the graph corresponds to the methanol wettability. The higher the methanol wettability, the greater the hydrophobicity of the silicon dioxide particles.

The surface modifying agent preferably is an organosilicon compound selected from the group consisting of organosilanes of the general formula

(RO)₃Si(CnH₂n₊i) and (RO)₃Si(C_mH₂m-i) with R = alkyl, such as methyl, ethyl, n- propyl, isopropyl or butyl, n = 1-20, m = 2-20; organosilanes (R¹)_x(RO)ySi(CnH_2n+i) and (R¹)_x(RO)ySi(C_mH₂m-i)

with R = alkyl, such as methyl, ethyl, n-propyl, isopropyl or butyl; R¹ = alkyl, such as methyl, ethyl, n-propyl, isopropyl, butyl or cycloalkyl; n = 1 -20; m 0 2-20; x+y = 3, x = 1 , 2; y = 1 , 2;

haloorganosilanes X₃Si(CnH_2n+i) and X3Si(C_mH_2m-i) with X = CI, Br; n = 1-20; m = 2-20;

haloorganosilanes X₂(R)Si(C_nH_2n+i) and X₂(R)Si(C_mH_2m- ) with X = CI, Br, R = alkyl, such as methyl, ethyl, n-propyl, isopropyl, butyl or cycloalkyl; n = 1-20; m = 2-20;

haloorganosilanes X(R)₂Si(C_nH_2n+i) and X(R)₂Si(C_mH_2m- ) with X = CI, Br; R = alkyl, such as methyl, ethyl, n-propyl, isopropyl, butyl or cycloalkyl; n = 1-20; m = 2-20; organosilanes (RO)3Si(CH₂)_mR¹ with R = alkyl, such as methyl, ethyl or propyl; m = 0, 1 - 20; R¹ = methyl, aryl, such as -C6H₅, substituted phenyl radicals, C₄F₉, OCF₂- CHF-CFs, C₆F₁₃, OCF₂CHF₂ or Sx-(CH₂)₃Si(OR)3; organosilanes (R2)_x(RO)_ySi(CH2)_mR¹ with R¹ = methyl, aryl, such as C6H₅, substituted phenyl radicals, C₄F₉, OCF₂-CHF-CF₃, C₆F₁₃, OCF₂CHF₂,

Sx-(CH₂)₃Si(OR)3, SH, NR³R R⁵, with R³ = alkyl or aryl; R⁴ = H, alkyl or aryl; and R⁵ = H, alkyl, aryl or benzyl, or C₂H₄NR⁶R⁷, with R⁶ = H or alkyl and R⁷ = H or alkyl; R² = alkyl; x+y=3; x=1 ,2; y=1 ,2; m=0, 1 to 20; haloorganosilanes X₃Si(CH₂)_m-R

with X = CI, Br; R = methyl, aryl, such as C6H₅, substituted phenyl radicals, C₄F₉, OCF₂-CHF-CF₃, C₆F₁₃, 0-CF₂-CHF₂, Sx-(CH₂)₃Si(OR¹)₃, in which R¹ = methyl, ethyl, propyl, butyl and x = 1 or 2, or SH; m = 0, 1 -20; haloorganosilanes R¹X₂Si(CH₂)_mR²

with X = CI, Br; R¹ = alkyl, such as methyl, ethyl or propyl; R² = methyl, aryl, such as C₆H₅, substituted phenyl radicals, C F₉, OCF₂-CHF-CF₃, C₆F₁₃, 0-CF₂-CHF₂, -OOC(CH₃)C=CH₂, -Sx-(CH₂)₃Si(OR³)₃, in which R³ = methyl, ethyl, propyl or butyl and x = 1 or 2, or SH; m = 0, 1 -20; haloorganosilanes (R¹)₂XSi(CH₂)_mR²

with X = CI, Br; R¹ = alkyl, such as methyl, ethyl or propyl; R² = methyl, aryl, such as C₆H₅, substituted phenyl radicals, C F₉, OCF₂-CHF-CF₃, C₆F₁₃, 0-CF₂-CHF₂, - Sx-(CH₂)₃Si(OR³)₃, in which R³ = methyl, ethyl, propyl or butyl and x = 1 or 2, or SH; m = 0, 1 -20; silazanes R²R¹ ₂SiNHSiR¹ ₂R² with R¹ and R² = alkyl, vinyl or aryl; cyclic polysiloxanes D3, D4, D5 and their homologues, in which D3, D4 and D5 are to be understood as meaning cyclic polysiloxanes with 3, 4 or 5 units of the -O- Si(CH₃)₂ type, e.g. octamethylcyclotetrasiloxane = D4; polysiloxanes or silicone oils of the type Y-0-[(R¹R²SiO)_m-(R³R SiO)_n]u-Y, with R¹, R², R³ and R⁴ are, independently of one another, alkyl, such as C_nH_2n+i , n = 1 -20; aryl, such as phenyl radicals and substituted phenyl radicals, (CH₂)_n-NH₂ or H; Y = CH₃, H, C₀H_2o+i , n = 2-20; Si(CH₃)₃, Si(CH₃)₂H, Si(CH₃)₂OH,

Si(CH₃)₂(OCH₃), Si(CH₃)₂(C₀H_2o+i ), o = 2-20; m = 0, 1 ,2,3, ...∞, preferably

0, 1 ,2,3, ... 100 000, n = 0, 1 ,2,3, ...∞, preferably 0,1 ,2,3, ... 100 000, u = 0, 1 , 2, 3, ... . oo, preferably 0, 1 ,2,3, ... 100 000.

Commercially available products are, for example, Rhodorsil® Oils 47 V 50, 47 V 100, 47 V 300, 47 V 350, 47 V 500 or 47 V 1000, Wacker Silicon Fluids AK 0.65, AK 10, AK 20, AK 35, AK 50, AK 100, AK 150, AK 200, AK 350, AK 500, AK 1000, AK 2000, AK 5000, AK 10000, AK 12500, AK 20000, AK 30000, AK 60000, AK 100000, AK 300000, AK 500000 or AK 1000000, or Dow Corning® 200 Fluid.

Use may preferably be made, as surface-modifying agents, of those which result in the hydrophobized metal oxide particles carrying, on their surface, the group

O O CH₃

O— Si— CH₃ O— Si— CH_{3 and/or} O— Si— CH₃

O CH₃ CH₃

The detection of these groups can be carried out spectroscopically and is known to a person skilled in the art.

Structurally modified types can also be used. The structural modification can be carried out by mechanical action and by optional remilling. The structural modification can, for example, be carried out with a bead mill or a continuously operating bead mill. The remilling can be carried out, for example, by means of an air jet mill, toothed disc mill or pin mill.

However, the best results in terms of workability were obtained using compacted types that are not structurally modified. These compacted types usually have a tapped density, determined according to DIN ISO 787/1 1 , JIS 5101 (not sieved), of 60 to 100, preferably 70 to 90 g/l.

Commercially available fumed silica "R-AEROSIL®" types (Evonik Degussa) as a powder or granules are very particularly suitable. Examples of those powders are represented in Table 1 . Fumed Silica Dispersions

In a special embodiment of the invention the fumed silica powder is added in part or completely in form of a dispersion. The liquid phase of the dispersion can comprise or consist of either a polyisocyanate or a polyol each used for the process of making TPU. The polyol can be selected from the polyesterpolyols, polyetherpolyols and polycarbonatediols discussed in the Chapter "Polyols" and polyols discussed in the Chapter "Chain Extenders". Any suitable dispersing devices may be used, like stirrers, dissolvers or rotor-stator devices.

The fumed silica concentration in the dispersion can in general vary from 1 to 40 wt.-%, preferably 5 to 20 wt.-%. The suitable concentration depends on the composition of the liquid phase. It also depends on the kind of fumed silica particles used that is the degree of hydrophilicity or hydrophobicity. It all cases have to be ensured that no gelation takes place.

It was found that a TPU produced by using a hydrophobic fumed silica dispersion gives the best results.

Polyisocyanate

The polyisocyanate may be an aromatic, aliphatic, cydoaliphatic and/or araliphatic polyisocyanate, preferably a diisocyanate. Preferably the diisocyanate is selceted from the group consisting of 2,2'-diphenylmethane diisocyanate,

2,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate (MDI),

1 .5- naphthylene diisocyanate (NDI), 2,4-toluylene diisocyanate,

2.6- Toluylene diisocyanate (TDI), 3,3'-dimethyldiphenyl diisocyanate,

1 .2- diphenylethane diisocyanate, phenylene diisocyanate, trimethylene

diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, heptamethylene diisocyanate, octamethylene diisocyanate, 2-methylpentamethylene-1 ,5-diisocyanate, 2-ethyl-butylene-1 ,4- diisocyanate, pentamethylene-1 ,5-diisocyanate, butylene-1 ,4-diisocyanate, 1 -isocyanato-3,3,5-trimethyl-5-isocyanatomethyl-cyclohexane (isophorone diisocyanate, IPDI), 1 ,4-bis(isocyanatomethyl)cyclohexane,

1 .3- bis(isocyanatomethyl)cyclohexane (HXDI), 1 ,4-cyclohexane diisocyanate, 1 -methyl-2,4-cyclohexane diisocyanate, 1 -methyl-2,6-Dicyclohexylmethane di isocyanate, 4,4'-dicyclohexylmethane diisocyanate (H12MDI),

2,4'-dicyclohexylmethane diisocyanate, 2,2'-dicyclohexylmethane-diisocyanate and mixtures thereof, the most preferred one being 4,4'-diphenylmethane diisocyanate (MDI).

Another group of polyisocyanates that can be used in the present invention are isocyanate prepolymers. These can be obtained by reacting an excess of one or more polyisocyanates (A) and compounds that are reactive towards

polyisocyanates, e.g. polyether or polyester polyols (B).

The polyisocyanates (A) can preferably be selected from the group consisting of polyisocyanates discussed above. Examples are 4,4', 2,4' und 2,2'- Diphenylmethane diisocyanate, mixtures of moomeric diphenylmethane

diisocyanates and the higher homologues of monomeric MDI (Polymer-MDI), tetramethylene diisocyanate, hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), 1 ,5-naphthalene diisocyanate (NDI), 2,4,6-toluene

trisocyanate und 2,4- und 2,6-toluene diisocyanate (TDI).

The compounds (B) that are reactive towards polyisocyanates are compounds bearing at least two hydrogen atoms that are reactive towards isocyanate groups. Preferably the reactive compouds (B) are selected from at least one of the group consisting of polyesterols, polyetherols, mixtures of polyetherols and polyols bearing a tertiary amino group.

Most preferred prepolymers are selected from the group consisting of MDI- terminated polyether prepolymers, e.g. based on polypropylene ether glycol or polytetramethylene ether glycol, MDI-terminated polyester prepolymers; HDI- terminated polyether prepolymers, HDI-terminated polyester prepolymers, HDI- terminated polycaprolactone prepolymers, HDI-terminated polycarbonate prepolymers; TDI-terminated polyether prepolymer, TDI-terminated polyester prepolymers; HMDI-terminated polyether prepolymer, e.g. based on polypropylene ether glycol or polytetramethylene ether glycol. The NCO-content of the prepolymer preferably is from 1 to 35 % and most preferably form 2 to 10 %.

Polyols

The polyols of the present invention comprises polyesterpolyols, polyetherpolyols and polycarbonatediols. Preferably polyetherpolyols are used.

The polyols usually have a molecular weight of 500 to 8000, preferably from 600 to 6000 and an average functionality from 1 .8 to 2.3, preferably from 1.9 to 2.2, in particular 2.

The Polyesters generally used are linear polyesters with an average molecular weight (M_n) of 500 to 10 000, preferably of 700 to 5000 and particularly preferably of 800 to 4000.

Polyetherpolyols may be prepared by anionic polymerisation of alkylene oxides in the presence of hydroxides or alkoxides as catalyst and at least one starter comprising 2 to 3 reactive hydrogen atoms. They may further be prepared by cationic polymerisation of alkylene oxides in the presence of a Lewis Acid, such as SbCIs or BF3 etherate. In general the alkylene oxides contain 2 to 4 carbon atoms in the alkylene part, like ethylene oxide, 1 ,2-propylene oxide, 1 ,3-propylene oxide, 1 ,2- or 2,3-butylene oxide and/or tetrahydrofurane. The straters may be selected from the group consisting of water, ethylene glycol, 1 ,2-propanediol, 1 ,3- propanediol, diethylene glycol, dipropylene glycol, glycerine, and trimethylol propane.

The polyesterpolyols may be obtained by the reaction of an dicarboxylic acid having 2 to 12 carbon atoms, preferably aliphatic dicarboxylic acids having 4 to 6 carbon atoms, and polyvalent alcohols, preferably diols having 2 to 12 carbon atoms.

The dicarboxylic acid may be selected form succhinic acid, glutaric acid, adipic acid, octanedicarboxylic acid, azelaic acid, decanedicarboxylic acid, maleic acid, fumaric acid, phthalic acid, isophthalic acid and terephthalic acid. The polyvalent alcohol may be selected from ethylene glycol, diethylene glycol, 1 ,2-propanediol, 1 ,3-propanediol, dipropylendglckol, methyl-1 ,3-propanediol,1 ,4-butanediol, 1 ,5- pentanediol 1 ,6-hexanediol, neopentylglycol, 1 , 10-decanediol, glycerine, trimethylolpropane and pentaerythrit.

Also polyesterpolyols based on lactones, e.g. epsilon-caprolactone or

hydroxycarboxylic acids, e.g. hydroxyacetic acid.

Chain Extender

The process of the present invention also includes the use of one or more chain extenders. This may be an aliphatic glycol with 2 to 10 carbon atoms, such as ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1 ,4- butanediol, 1 ,6-hexanediol, 1 ,3-butanediol, 1 ,5-pentanediol, 1 ,4- cyclohexanedimethanol, neopentyl glycol or hydroquinone (HQEE).

In addition suitable catalysts may be added which accelerate the reaction between the NCO groups of the polyisocyanate and the hydroxy groups of the polyol and chain extender. Preferably organometallic compounds of bismuth, iron tin or titan are used.

Others

Also conventional auxiliaries may be added, these are by way of example, surface-active substances, fillers, flame retardants, nucleating agents, solvents, antioxidants, lubricants, and mold-release agents, dyes, and pigments, stabilizers, e.g. with respect to hydrolysis, light, heat, or discoloration, and plasticizers.

The reaction according to the invention can be carried out using the devices known in the TPU field, such as extruders, kneaders or stirred reactors. It is preferred to use an extruder. Examples

All trials took place on a 0 26 mm twin-screw extruder with an L/D ratio of 50. The configuration of the twin screw is made for TPU processing. On this setting, we are able to feed liquid by pumping in the main hoper, fed by gravimetric system

AEROSIL^®, and we are able to add additional isocyanate at the end by micro liquid pumping.

Two formulations are used, Formulation 1 is a standard ether 90 shA TPU based on 1000 Mw polyol, MDI and BDO and Formulation 2 an ester 55 shD TPU based on 2000 Mw polyol, MDI and BDO (see Table 2).

The screw profile allows a long residence time and good dispersive elements for the fumed silica.

The temperature set-up is different for the two formulations as shown in Table 3.

The addition of the fumed silica, AEROSIL^®, has been done in two ways. Either by adding the AEROSIL directly in the polyol by high shear mixing or by adding the

AEROSIL^® directly in the extruder by weight feeding.

Table 4 displays the compositions for the preparation of TPU's based on the

formulations 1 -00, 1 -03, 2-00, 2-02, the index -00, -02 and -03 indicating an overall index factor of first and second reaction step of 1 ,00, 1 ,02 and 1 ,03 respectively.

Table 5 displays hardness, melt volume flow rate (MVR) and molecular weight, M_n and M_w, for the TPU's shown in Table 4. All, except those of Examples 15 and 16, showed good extrudability.

The molecular weight is determined by gel permeation chromatography (GPC).

Samples of the TPU prepared in the Examples 1 ,5,7,9 and 10 and dimethyl

formamide (DMF) are kept for 10 days at ambient temperature, then are filtered

and/or centrifuged (5 min, 14.000 g) in case that there is no clear solution. The

solution is subsequently analysed.

The effect of the process according to the invention can be taken from Table 4.

The TPU of Example 5 displays a very low MVR and a very high molecular weight. The molecular weight of the TPU plays a major role in the melt behaviour. If is too low, then the TPU cannot reach certain mechanical properties. Table 4 shows that the interaction between AEROSIL^® R 974V and the building of the TPU gives a TPU with a molecular weight 4 times higher than the one without AEROSIL^®. Finally, the process according to the invention in which additional isocyanate is added at the end of the machine gives the best result, achieving a molecular weight M_w of over one million.

The melt volume-flow rate (MVR) is a measure of the extrusion rate of a

polyurethane melt through a die with a specified length and diameter under set conditions of temperature and loads. The measurement is typically made according to ISO 1 133. The melt flow rate techniques are based on the principle that flow increases with decreasing viscosity for a given temperature and load test condition. A lower MVR value indicates a higher viscosity under an applied stress (load or weight in kg). It seems from Table 4 that the TPU of Example 9, overall index 1 ,03, gives a more favorable MVR than the TPU of Example 5, which is produced according to the invention, that is index 1 ,00 plus additional isocyanate. The problem with the TPU of Example 9 is that we can have gel formation in the TPU.

Table 1 : Fumed Silica powder suitable for TPU production

^* in m²/g; ca-Werte

Table 2: TPU formulations excluding fumed silica

$ Polytetramethylene Ether Glycol 1000; Molecular weight ca. 1000, Terathane, Invista; § Polyadipate 2000: polyester diol, molecular weight of 2000, Dow Chemical Company; $$ Butanediol 90 Molecular weight ca, LyondellBasell; & organobismuth catalyst, supplier Vertellus Table 3: Extruder temperature set-up [in °C]

Table 4: TPU formulations including fumed silica

$ Example 5 and 18 according to the invention; 1-4, 6-17 comparative examples; # P =powder; all powder addition to main hopper; ## D = dispersion; n.d. = not determined Table 5: Physical/chemical properties of selected TPUs

& MVR = Melt Volume-flow Rate; at 190°C;

* M_n = Number average molecular weight; M_w = Weight average molecular weight; ^**F = M_w [polyol + polyisocyanate + fumed silica + additional polyisocyanate] / M_w [polyol + polyisocyanate + additional polyisocyanate] =

M_w Example 5 / Mw Example 17 und M_w Example 18 / M_w Example 17

Claims

Patent Claims

1 . Process for making a thermoplastic polyurethane by reacting a mixture

comprising at least one polyisocyanate, at least one polyol and fumed silica, wherein

a) in a first reaction step the polyol is reacted in the presence of fumed silica with the polyisocyanate the index factor being 0,95 to 1 ,00 with a conversion of 95% or more,

b) in a second reaction step additional polyisocyanate is added to the reaction mixture, in an amount that the overall index factor of first and second reaction step is > 1 , 00 to 1 , 1 ,

2. Process according to claims 1 , characterized in that the concentration of the fumed silica, based on the thermoplastic polyurethane, is 0,3 to 10 wt.-%.

3. Process according to claims 1 or 2, characterized in that the fumed silica particles is a hydrophobic fumed silica.

4. Process according to claim 1 to 3, characterized in that the fumed silica is a part of a dispersion with the liquid phase being the polyisocyanate or the polyol.

5. Process according to claims 1 to 4, characterized in that it further comprises one or more chain extenders.

6. Process according to claims 1 to 5, characterized in that, the process is carried out in an extruder, kneader or stirred reactor.