Water resistant corrugated paperboard

Abstract

A water resistant corrugated paperboard material is prepared wherein the paperboard components (medium and liner or liners) are each coated on both sides with a thermoplastic film which acts as a water barrier and a water resistant adhesive for bonding the components together. The corrugated medium is also pretreated with an internal size treatment to prevent edge wicking, and, for the purpose of corrugating the medium without deleteriously affecting the thermoplastic film, the corrugating rolls are preheated to a temperature slightly less than the melting point of the thermoplastic film while a lubricating material is simultaneously applied to either the corrugating rolls or the medium at the corrugating nip.

We claim: 
     
       1. In the process of manufacturing water resistant corrugated paperboard, consisting of at least one linerboard component having both sides thereof coated with a film of thermoplastic material, and at least one corrugating medium component having both sides thereof coated with a film of thermoplastic material, the steps of: a. pretreating the said corrugating medium component .Iadd., before both sides thereof are coated with the film of thermoplastic material, .Iaddend.with an internal size treatment selected from the group consisting of 0.75- 1.0% rosin with about 1.5% alum, 0.2% stearic anhydride with 0.3-0.4% alum, or 0.2% succinic anhydride with 0.3-0.4% alum to inhibit the water wicking tendencies thereof;   b. applying a direct pre-heat treatment to one side of the said coated and sized corrugating medium prior to entering the corrugating nip of a corrugating machine;   c. applying an indirect pre-heat treatment to the opposite side of the said coated and sized corrugating medium by heating at least one of the corrugating rolls of the corrugating machine;   d. applying a lubricating treatment in the form of a water spray or a water spray containing detergent to the corrugating nip of the corrugating machine;   e. applying a direct pre-heat treatment to one side of the said coated linerboard component prior to entering the bonding nip of a corrugating machine;   f. applying an indirect pre-heat treatment to the opposite side of the said coated linerboard component by heating the pressure roll of the corrugating machine;   g. applying an additional direct heating treatment at the bonding nip of the corrugating machine to render the thermoplastic film surface on one of the components tacky and bondable;   h. pressing the tacky and bondable surface of one of the components into contact with the other of said components at the bonding nip; and,   i. cooling the laminate thus formed to allow the bond to set.   
     
     
       2. The process of claim 1 wherein the thermoplastic material is a thermoplastic polyolefin. 
     
     
       3. The process of claim 2 wherein the thermoplastic polyolefin is polyethylene. 
     
     
       4. The process of claim 3 wherein the polyethylene film thickness is in the range of from 0.75 - 1.0 mil thick. 
     
     
       5. The process of claim 4 wherein the direct pre-heat treatments for both the corrugated medium components and the linerboard component are in the range of 200° F. 
     
     
       6. The process of claim 5 wherein the temperature of at least one of the corrugating rolls is in the range of from 150°-215°  F. 
     
     
       7. The process of claim 6 wherein the lubricating treatment is applied directly to both sides of the corrugated medium. 
     
     
       8. The process of claim 7 wherein the lubricating treatment is also applied to the corrugating rolls of the corrugating machine. 
     
     
       9. The process of claim .[.10.]. .Iadd.8 .Iaddend.wherein the additional direct heating treatment is of a temperature in excess of 450° F. 
     
     
       10. The process of claim 9 wherein subsequent components of the laminate are bonded to the laminate formed by pre-heating the bonding surfaces of at least two of the components to a temperature in the range of about 200° F. and applying additional direct heating treatments in excess of 450° F. at the bonding nip to render the polyethylene film surface on one of the components tacky and bondable.