Adhesive and application thereof

1. An adhesive comprising:

a. at least one aqueous polyurethane dispersion, wherein the aqueous polyurethane dispersion has an acid value of 0.5 mg KOH/g to 10 mg KOH/g, wherein the at least one aqueous polyurethane dispersion has a solid component in an amount of 70 wt % to 99.98 wt %, based on a total weight of solid components of the adhesive;

b. at least one surface passivated polyisocyanate, wherein the at least one surface passivated polyisocyanate has a solid component in an amount of 0.01 wt % to 30 wt %, based on the total weight of solid components of the adhesive;

c. at least one polycarbodiimide having a weight-average molecular weight of 500 to 100,000, wherein the at least one polycarbodiimide has a solid component in an amount of 0.01 wt % to 10 wt %, based on the total weight of solid components of the adhesive; and

d. optionally a carbodiimide having a carbodiimide group functionality of 1,

wherein the polycarbodiimide and the carbodiimide having a carbodiimide group functionality of 1 have an average carbodiimide group functionality of 1.1 to 50.

2. The adhesive according to claim 1 , wherein the solid component of the aqueous polyurethane dispersion has a melting enthalpy of more than 3 J/g at 20 to 100° C., based on a first heating curve measured by DSC at a heating rate of 20 K/min according to DIN 65467.

3. The adhesive according to claim 1 , wherein the polycarbodiimide has a weight-average molecular weight of 1,000 to 100,000.

4. The adhesive according to claim 1 , wherein the polycarbodiimide has a carbodiimide group functionality of 2 to 50.

5. The adhesive according to claim 1 , wherein the surface passivated polyisocyanate has a glass transition temperature of higher than 30° C.

6. The adhesive according to claim 1 , wherein the surface passivated polyisocyanate has a particle diameter d50 of 500 nm to 500 μm.

7. The adhesive according to claim 1 , wherein the surface passivated polyisocyanate has an isocyanate functionality of 2 to 100.

8. The adhesive according to claim 1 , wherein the surface passivated polyisocyanate comprises a surface passivated alicyclic polyisocyanates or a derivative of a surface passivated alicyclic polyisocyanates having a uretdione, an isocyanurate, a carbamate, an allophanate, a biuret, an imino-oxadiazinedione, an oxadiazinetrione, or a combination thereof.

9. A method for producing a bonded product comprising:

i. applying the adhesive according to claim 1 to at least one surface portion of a substrate;

ii. heating and drying the substrate surface portion to which the adhesive is applied; and

iii. contacting the substrate surface portion treated in step ii with another surface portion of the substrate itself or an additional substrate to obtain the bonded product.

10. The method according to claim 9 , further comprising:

iv. irradiating the substrate surface treated in step ii by means of actinic radiation prior to step iii.

11. The method according to claim 9 , wherein the substrate comprises: wood, plastic, metal, glass, textile, alloy, fabric, artificial leather, paper, cardboard, ethylene vinyl acetate (EVA), rubber, dermis, glass fiber, ethylene vinyl acetate copolymer, polyolefin, thermoplastic polyurethane, polyurethane foam, polymer fiber, graphite fiber, or a combination thereof.

12. A bonded product produced by the method according to claim 9 .

13. The bonded product according to claim 12 , wherein the bonded product is a shoe.

14. The adhesive according to claim 1 , wherein the at least one surface passivated polyisocyanate has an isocyanate functionality of from 3 to 100.