Method for producing a multi-layer substrate

1. A method of producing a multi-layer substrate comprising the following steps:

a) providing a first material having a first surface with at least one edge region and at least one inner region enclosed by the edge region;

b) applying a coating material to partial portions of the inner region of the first surface, the coating material comprising expandable microparticles;

c) drying the coating material; and

d) contacting the first surface of the first material with a surface of a second material to form the multi-layer substrate such that the coating material is between the first material and the second material,

wherein the inner region does not contain an adhesive

wherein the coating material consists of:

(i) 30 to 70 wt-% of VAE copolymer dispersion;

(ii) 5 to 15 wt. % of paraffin dispersion;

(iii) 15 to 30 wt. % of microparticles;

(iv) 5 to 10 wt. % of glycerol; and

(v) optionally, hydroxyethylcellulose,

wherein the total weight of the coating material and add up to 100 wt. %.

2. The method according to claim 1 , characterized in that the contacting in step d) is carried out using an adhesive, wherein the adhesive is applied continuously to the edge region of the first material.

3. The method according to claim 1 , characterized in that the coating material is dried at a temperature of 80° C. or less.

4. The method according to claim 1 , characterized in that the coating material is a polymer-based coating material which has 10 to 40 wt. %, of expandable microparticles based on the total weight of the coating material.

5. The method according to claim 4 , characterized in that the expandable microparticles are thermally expandable microparticles.

6. The method according to claim 1 , characterized in that the multi-layer substrate is converted into a packaging in a further step.

7. The method according to claim 6 , characterized in that the packaging is an envelope, a mailing bag, a bag, a carrier bag, a pouch or a carton.

8. The method according to claim 1 , characterized in that the method comprises a further step e) in which the multi-layer substrate is subjected to a treatment for expanding the expandable microparticles.

9. The method according to claim 8 , characterized in that the treatment is a heat treatment carried out at a temperature of 85° C. to 150° C.

10. The method according to claim 8 , characterized in that the treatment is carried out separately from the other method steps from time and/or location.

11. The method according to claim 8 , characterized in that the treatment is a heat treatment which is carried out using infrared radiation and/or warm air.

12. A method of producing a package using a multi-layer substrate produced by a method according to claim 1 , wherein the multi-layer substrate is formed into the package by cutting and folding.