Patent Application
20060263616
The field is packaging board. More specifically it is a packaging board that may be formed into cartons and cups and has gas barrier properties.
The need for a gas barrier in paperboard packages is well known and there have been many solutions to reduce gas transfer through the paperboard. The amount and rate of gas transfer will depend on the type of barrier layer or layers that is used. The gas barrier layer is either laminated, extruded or co-extruded onto the paperboard to provide a board with gas barrier properties.
There are other factors that enter into the choice of a barrier material. Cost is a factor, both in the type and cost of the barrier material being used and also in the amount required to obtain the necessary barrier properties. Other important factors are carton durability, pinholes, and plastic char. Nylon in direct contact with an extruder die lip generates char (pyrolyzed nylon) and this char must be removed periodically to prevent contamination of the board. Char removal requires shutting down the extruder. The amount of barrier material required is also dependent on the uniformity of the barrier layer in both the machine direction and cross machine direction. Poor uniformity yields thick and thin spots which will change the gas barrier level. The type of material will also determine the amount of power required to extrude the material and therefore is a factor in the total cost of the packaging board.
Another factor is the adhesion of the material to the paperboard. Some materials adhere better than others. Some materials, such as nylon, require special board surface treatment to obtain adhesion to the paperboard. This also is reflected in the cost.
There is also the problem of pinholes. Pinholes are small holes in the plastic film that allow liquid contained in the container to contact and penetrate the paperboard. Wet paperboard is very weak and leads to poor durability and reduced shelf life. Pinholes occur when the plastic film is heated in a sealing operation. Heat generates steam in the paperboard and the steam generates bubbles in the plastic structure. Some of the bubbles burst and form pinholes. The number of pinholes can be greatly reduced if the low density polyethylene or linear low density polyethylene or other polyolefin flows into the bubble area thus sealing any pinholes.
Extrusion or co-extrusion is a faster, lower cost process than lamination. The cost of a laminate film and associated handling is also avoided.
The present invention is directed to a barrier structure which is cost effective, provides a gas barrier, and reduces the effect of pinholes.
The paperboard 12 has a first side and a second side opposite the first side. The paperboard may have a weight of 200 to 500 grams per square meter (g/m2).
A polyolefin layer 10 is applied to the outer or second surface of the paperboard 12. It provides good adhesion to the paperboard without special treatments. It also provides good printability. The layer 10 is usually low density polyethylene. If improved carton durability is required then linear low density polyethylene (LLDPE) or metallocene-catalyzed linear low density polyethylene (mLLDPE) or a blend of low density polyethylene and LLDPE or mLLDPE. These resins are tougher than low density polyethylene. The layer 10 is applied in amounts ranging from 15 to 25 grams per square meter.
A polyolefin layer 14 is applied directly to the inner or first surface of the paperboard 12. The polyolefin layer 10 has a first side and a second side and a second side opposite the first side. The first side is applied directly to the first side of the paperboard. It provides good adhesion to the paperboard without special treatments. It also eliminates exposure of the nylon to the die lip during an extrusion or co-extrusion process. Die lip contact leads to char which causes waste and downtime. The polyolefin layer 14 is usually low density polyethylene. If improved carton durability is required then linear low density polyethylene or metallocene-catalyzed linear low density polyethylene or a blend of low density polyethylene and linear low density polyethylene or metallocene-catalyzed linear low density polyethylene. These resins are tougher than low density polyethylene. It also minimizes the exposure of the nylon to oxygen during an extrusion or co-extrusion process. Linear low density polyethylene, metallocene-catalyzed linear low density polyethylene or a blend of low density polyethylene and either linear low density polyethylene or metallocene-catalyzed linear low density polyethylene provide durability. The amount of polyethylene may range from 5 to 25 grams per square meter as explained below.
A first tie layer 16 is applied directly to the polyolefin layer 14. The first tie layer has a first side and a second side opposite the first side. The first side of the tie layer is applied directly to the second side of layer 14. The first tie layer may be any appropriate adhesive resin. A typical adhesive resin is a maleic anhydride modified polyethylene resin. Other adhesive resins may be used. The usual amount of tie resin would be 3 to 9 grams per square meter.
An polyamide barrier layer 18 is applied directly to the first tie layer 16. The polyamide layer has a first side and a second side opposite the first side. The first side of the polyamide layer is applied directly to the second side of tie layer 16. The polyamide gas barrier layer 18 may be an aliphatic such as nylon 6, nylon 66, nylon 6/66, nylon 6/9, nylon 6/10, nylon 11 and nylon 12, an aromatic nylon such as MXD6, a blend of aliphatic and aromatic nylons or a copolymer of aromatic and aliphatic nylons. The amount of polyamide ranges from 5 to 15 grams per square meter. The amount will determine the gas barrier property.
A second tie layer 20 is applied directly to the polyamide layer 18. The second tie layer has a first side and a second side opposite the first side. The first side of the second tie layer is applied directly to the second side of the layer 18. The second tie layer may be any appropriate adhesive resin. A typical adhesive resin is a maleic anhydride modified polyethylene resin. Other adhesive resins may be used. The usual amount of tie resin would be 3 to 9 grams per square meter.
An inner polyolefin layer 22 is applied directly to the tie layer 20. The polyolefin layer 22 has a first side and a second side and a second side opposite the first side. The first side is applied directly to the second side of the tie layer 20. The polyolefin layer 22 is usually low density polyethylene. If improved carton durability is required then linear low density polyethylene or metallocene-catalyzed linear low density polyethylene or a blend of low density polyethylene and linear low density polyethylene or metallocene-catalyzed linear low density polyethylene. These resins are tougher than low density polyethylene. The inner polyolefin layer minimizes the exposure of the nylon to oxygen during an extrusion or co-extrusion process. The amount of polyethylene may range from 12 to 25 grams per square meter
Pinhole performance is improved significantly if the polyolefin in layer 22 is 18 g/m2 or more and the polyolefin in layer 14 is 5 g/m2 or more. Layer 22 would be in the range of 18 to 26 g/m2 and layer 14 would be in the range of 5 to 10 g/m2. Alternatively, pinhole performance is improved significantly in a cost effective manner if the polyolefin in layer 14 is 18 g/m2 or more and the polyolefin in layer 22 has 12 g/m2 or more. Layer 14 would be in the range of 18 to 26 g/m2 and layer 22 would be in the range of 12 to 16 g/m2. Layer 22 has 12 g/m2 to assure proper sealing performance during the carton forming process.
One example of a barrier coated paperboard with improved pinhole performance, using
A second example of a barrier coated paperboard with improved pinhole performance, again using
Although preferred embodiments of the invention have been described using specific terms, such description is for illustrative purposes only. The words used are words of description rather than of limitation. It is to be understood that changes and variations may be made by those of ordinary skill in the art without departing from the spirit or scope of the present invention, which is set forth in the following claims. The spirit and scope of the appended claims should not be limited to the description of the preferred versions contained herein.
