Sheet-like product and method for its manufacture

Abstract

The invention relates to a sheet-like product, such as paper. board or the like, which comprises a substrate comprising cellulosic fibres and having a first large surface, wherein at least a first coating layer and a second coating layer are applied on the first large surface of the substrate by curtain coating to form a barrier coating. The second coating layer forms the surface of the sheet-like product. The first coating layer comprises a first polymer having a first crystallization degree and a first melting point, and the second coating layer comprises a second polymer having a second crystallization degree and a second melting point. The second crystallization degree and/or the second melting point is higher than the first crystallization degree and/or the first melting point of the first polymer.

1 . A sheet-like product, such as paper, board or the like, comprising
 a substrate comprising cellulosic fibres and having a first large surface, wherein at least a first coating layer and a second coating layer are applied on the first large surface of the substrate by curtain coating to form a barrier coating, the second coating layer forming the surface of the sheet-like product, wherein
 the first coating layer comprises a first polymer having a first crystallization degree and a first melting point, and 
 the second coating layer comprises a second polymer having a second crystallization degree and a second melting point, and 
   
       wherein the first polymer is a biobased and/or biodegradable polymer, and the second crystallization degree and/or the second melting point of the second polymer is higher than the first crystallization degree and/or the first melting point of the first polymer. 
     
     
         2 . The sheet-like product according to  claim 1 , wherein the first polymer is selected from biodegradable polyesters, such as polybutylene succinate, poly(butylene succinate-co-adipate), polyhydroxyalkanoates, polycaprolactones, polylactides, any of their mixtures and copolymers. 
     
     
         3 . The sheet-like product according to  claim 2 , wherein the first polymer is a polyhydroxyalkanoate, such as polyhydroxybutyrate, polyhydroxyvalerate, polyhydroxyhexanoate or any of their copolymers. 
     
     
         4 . The sheet-like product according to  claim 1 , wherein the crystallization degree of the second polymer is higher than the crystallization degree of the first polymer. 
     
     
         5 . The sheet-like product according to  claim 1 , wherein the second polymer is selected from the group consisting of polyesters, such as polybutylene succinate, poly(butylene succinate-co-adipate), polyhydroxyalkanoates, polylactide or polycaprolactone; polyethyleneterephtalate; polyolefins, such as polyethylene or polypropylene; styrene acrylate copolymers, styrene butadiene copolymers, ethylene acrylic and methacrylic acid copolymers, poly(glycolic acid); butyl vinyl alcohol; polyvinyl alcohol; ethylene vinyl acetate; and chitosane. 
     
     
         6 . The sheet-like product according to  claim 1 , wherein the first coating layer has a coat weight in a range of 3-15 g/m 2 , preferably 5-12 g/m 2 , more preferably 5-10 g/m 2 , and/or the second coating layer has a coat weight in a range of 0.5-6 g/m 2 , preferably 1-5 g/m 2 , more preferably 1-3 g/m 2 . 
     
     
         7 . The sheet-like product according to  claim 1 , wherein the sheet-like product comprises at least one precoat layer, arranged between the surface of the substrate and the first coating layer of the barrier coating. 
     
     
         8 . The sheet-like product according to  claim 7 , wherein the precoat layer comprises a natural or synthetic polymer, such as starch; a cellulose derivative, such as carboxymethyl cellulose or hydroxyethyl cellulose; and/or polyvinyl alcohol. 
     
     
         9 . The sheet-like product according to  claim 7 , wherein the precoat layer has a coat weight of 0.3-15 g/m 2 , preferably 0.3-5 g/m 2 , more preferably 0.5-4 g/m 2 . 
     
     
         10 . The sheet-like product according to  claim 7 , wherein the precoat layer comprises inorganic mineral particles. 
     
     
         11 . The sheet-like product according to  claim 1 , wherein the first coating layer and/or the second coating layer comprises inorganic mineral particles, preferably ≤50 weight-%, preferably ≤25 weight-%, of inorganic mineral particles. 
     
     
         12 . The sheet-like product according to  claim 10 , wherein the inorganic mineral particles are selected from kaolin, talc, mica, calcium carbonate or any mixture thereof. 
     
     
         13 . The sheet-like product according to  claim 1 , wherein one or more intermediate layers are arranged between the first coating layer and the second coating layer. 
     
     
         14 . The sheet-like product according to  claim 1 , wherein the second coating layer comprises a crystallization promoter. 
     
     
         15 . A method for making a sheet-like product according to  claim 1 , the method comprising:
 forming a barrier coating comprising at least a first coating layer and a second coating layer on a first large surface of a substrate comprising cellulosic fibres, such as paper, board or the like, by applying the first coating layer and the second coating layer simultaneously by curtain coating on the first large surface of the substrate, without an intermediate drying between the first coating layer and the second coating layer, wherein the first coating layer comprises a biobased and/or biodegradable first polymer having a first crystallization degree and a first melting point, and the second coating layer comprises a second polymer having a second crystallization degree and a second melting point, which second crystallization degree and/or the second melting point is higher than the first crystallization degree and/or the first melting point of the first polymer, the second coating layer forming the surface of the sheet-like product; and   subjecting the formed barrier coating to impingement drying with hot air for increasing the temperature of the second coating layer over the second melting point.   
     
     
         16 . The method according to  claim 15 , wherein the method further comprises a step of applying at least one precoat layer on the surface of the substrate before forming the barrier coating. 
     
     
         17 . The method according to  claim 15 , wherein the temperature of the hot air in the impingement drying is at least 300° C., preferably at least 400°° C., even more preferably at least 425° C.