THERMOPLASTIC FOAM PREPARED FROM TWO SPECIAL POLYURETHANE DISPERSIONS

1 . A foamed article produced by mixing a first polyurethane dispersion (A) with at least one second polyurethane dispersion (B), optionally with addition of further additives, foaming and subsequently drying the mixture, wherein the polyurethane dispersion (A) is obtained by preparing

A) isocyanate-functional prepolymers from

A1) organic polyisocyanates,

A2) polymeric polyols having number-average molecular weights of 400 to 8000 g/mol and OH functionalities of 1.5 to 6, and

A3) optionally hydroxyl-functional compounds having molecular weights of 62 to 399 g/mol, and

A4) optionally isocyanate-reactive, anionic or potentially anionic and optionally nonionic hydrophilizing agents,

and

B) the free NCO groups thereof are then wholly or partly reacted

B1) optionally with amino-functional compounds having molecular weights of 32 to 400 g/mol and

B2) with amino-functional, anionic or potentially anionic hydrophilizing agents

by chain extension and the prepolymers are dispersed in water before, during or after step B), and

wherein the second polyurethane dispersion (B) is obtained by reactive conversion of at least the following components:

A. an aliphatic polyisocyanate component having an average isocyanate functionality of ≥1.8 and ≤2.6,

B. a polymeric polyether polyol component,

C. an amino-functional chain extender component having at least 2 isocyanate-reactive amino groups, comprising at least one amino-functional compound C1. that does not have any ionic or ionogenic groups and/or an amino-functional compound C2. that has ionic or ionogenic groups,

D. optionally further hydrophilizing components other than C2.,

E. optionally hydroxyl-functional compounds having a molecular weight of 62 to 399 mol/g,

F. optionally further polymeric polyols other than B.,

G. a compound having exactly one isocyanate-reactive group or a compound having more than one isocyanate-reactive group where only one of the isocyanate-reactive groups reacts with the isocyanate groups present in the reaction mixture under the reaction conditions chosen, and

H. optionally an aliphatic polyisocyanate component having an average isocyanate functionality of >2.6 and ≤4,

where components B. and F. together contain ≤30% by weight of component F., based on the total mass of components B. and F.

2 . The foamed article as claimed in claim 1 , wherein the foamed article has at least one of the following properties i. to xiii.:

i. the foamed article has no cracks having a width of 2 mm;

ii. the foamed article has no surface cracks deeper than 0.4 mm;

iii. the foamed article has a crack area of 6%, based on the total area of the foamed article;

iv. the foamed article has a cell viability of 70% or a classification of 0 to 2 in a cytotoxicity test based on DIN ISO 10993-5:2009-10;

v. the foamed article has a density within a range from 80 to 500 g/l;

vi. the foamed article has a thickness (D) within a range from 0.1 to 100 mm;

vii. the foamed article has a tensile stress at break within a range from 100 to 1100 kPa measured according to DIN EN ISO 527-2:2012-06;

viii. the foamed article has an elongation at break within a range from 100% to 500%, measured according to DIN EN ISO 527-2:2012-06;

ix. the polyurethaneurea formed from the polyurethane dispersion (B) is amorphous and has a Tg ≤−25° C., determined by differential scanning calorimetry in accordance with DIN EN 61006, Method A;

x. the foamed article has a melting or softening range of 180° C., at a maximum pressure of 4 bar and has full thermoplastic processability within this range;

xi. the foamed article has an average pore size within a range from 200 to 750 μm;

xii. the foamed article has an outer layer at least on one surface of the foamed article;

xiii. the foamed article is part of a composite material.

3 . The foamed article as claimed in claim 1 , wherein the weight ratio of the polyurethane dispersion (A) to the polyurethane dispersion (B) is within a range from 1:1 to 5:1, based on the total mass of the masses of dispersions (A) and (B).

4 . The foamed article as claimed in claim 1 , wherein a film formed from the dispersion (B) has a tensile strain at break of ≤5 MPa combined with an elongation at break of 1750%.

5 . The foamed article as claimed in claim 1 , wherein the hydrophilizing agents B2) used are hydrophilizing agents containing sulfone groups.

6 . The foamed article as claimed in claim 1 , wherein the dispersion (A) has a solids content of polyurethane of 52% to 65% by weight, based on the total mass of the dispersion (A).

7 . The foamed article as claimed in claim 1 , wherein component A. or A1) is isophorone diisocyanate and/or hexamethylene diisocyanate.

8 . The foamed article as claimed in claim 1 , wherein component B. comprises or consists of poly(tetramethylene glycol) polyether polyols.

9 . The foamed article as claimed in claim 1 , wherein component B. comprises or consists of a mixture of at least two poly(tetramethylene glycol) polyether polyols, wherein the at least two poly(tetramethylene glycol) polyether polyols are of different number-average molecular weight.

10 . The foamed article as claimed in claim 1 , wherein component D. comprises nonionically hydrophilizing components.

11 . The foamed article as claimed in claim 1 , wherein component H. is used and the molar ratio of component G. to component H. is 5:1 to 1:5.

12 . The foamed article as claimed in claim 1 , wherein the polyurethane dispersion (B) is obtained by preparing isocyanate-functional polyurethane prepolymers a) from components A., B. and optionally D. and/or C2., and optionally compounds E. and/or H., and the free NCO groups thereof are then wholly or partly reacted with the amino-functional chain-extender component C., and also component G. and optionally components D. and H.

13 . A process for producing a foamed article as claimed in claim 1 , wherein the process comprises:

(V1) mixing the polyurethane dispersion (A) and the polyurethane dispersion (B) to obtain a mixture (M1),

(V2) optionally adding to (M1) at least one interface-active substance,

(V3) optionally adding to (M1) at least one surfactant,

(V4) optionally adding to (M1) a thickener,

(V5) foaming the mixture (M1) to give a foam,

(V6) optionally maturing the foam from step (V2),

(V7) optionally applying the foam formed in step (V2) or (V3) to a substrate,

(V8) drying the foam to form the foamed article.

14 . A wound dressing, a hygiene article, or a wearable patch, comprising the foamed article as claimed in claim 1 .

15 . A kit of parts at least including a polyurethane dispersion (A) and a polyurethane dispersion (B), wherein the polyurethane dispersion (A) or the polyurethane dispersion (B) includes an added material (C), wherein the dispersion (A) or (B) including the added material (C) has a cell viability of 70% in a cytotoxicity test or a classification of 0 to 2 according to DIN ISO 10993-5:2009-10.