Waxes for the Corrugated Board Industry
Corrugated Waxes
The International Group, Inc is a key industry leader in the development and implementation of waxes, corrugated board and folding cartons. IGI has formulated its waxes for specific packaging requirements, ranging from simple impregnation wax treatments for added moisture barriers, to premium, multi-component curtain coating blends formulated for a customer’s particular requirement.
Corrugated board or container board is a versatile and relatively inexpensive packaging medium. It consists of a fluted sheet (called the corrugated medium) glued to one or more liners. The resulting combination of columns and arches produce a product much stronger than the paperboard from which it is made. Corrugated board is primarily used to form boxes for shipping, but it is also often used for interior product separators in boxes as bins for displaying merchandise in stores, and as corner blocks for blocking and bracing products during shipping.
According to the paper and paperboard industry, container board is the largest single grade of paper produced, and remains a growing grade. In addition, the universal use of corrugated containers for shipping manufactured goods makes this grade one of the largest forms of packaging.
Wax coatings impart moisture resistance to corrugated containers. Food packaging is the major application for wax-coated corrugated containers. Food packaging uses wax primarily as a moisture barrier to protect corrugated boxes used in the packaging of produce, seafood, meat, and poultry. Non-food items such as furniture and plant nursery stocks use waxed boxes for moisture resistance and stacking strength.
Wax coatings prevent ply separation, the loss of strength, and rigidity when the corrugated container is wet by acting as a barrier between the paperboard and the moist environment. Laboratory studies show waxed boxes are three times stronger than a nonwaxed one.
Petroleum waxes are applied to corrugated board to help protect the board's physical integrity when exposed to wet and humid conditions. The most common application methods for applying wax in the corrugated industry are saturating or cascading, and curtain coating.
A thick layer of wax is flushed or sprayed onto the finished board in saturating or cascading applications. The board will pick up 40-50% of its weight in wax. The wax is normally low melting point paraffin (approximately 130°F) slightly modified with the presence of a special additive (polyethylene).
In curtain coating applications, the corrugated board is allowed to pass horizontally through a curtain of falling wax. The weight applied is usually 6-7 pounds of wax per thousand square feet of board. Curtain coating formulations contain paraffin wax (150°F), microcrystalline wax, additives such as ethylene-vinyl acetate copolymers, tackifier resins, and antioxidants. Paraffin and microcrystalline waxes prevent the board from picking up moisture. Ethylene-vinyl acetate copolymers increase the viscosity of waxes, which produce a stable curtain. Tackifier resins increase the flexibility of coatings in order to prevent scoreline cracks from developing when bending the board. Antioxidants prevent the melt form oxidizing. Oxidation causes the formation of odor, color degradation, and drop in viscosity.
Levels of wax applied on or into the corrugated board vary according to the physical characteristics of the wax (viscosity, melt point), and the density of corrugated board waxed (high or low density linerboard). The waxing temperature and speed of travel through ovens control levels.
The most widely used wax in corrugated plants is paraffin wax. Paraffin wax is a by-product of the automotive lubricating oil refining process, which involves the distillation of crude oil in products such as naphtha, gasoline, gas oil, fuel oil and paraffin waxes.
Paraffin wax is a highly crystalline structured chemical made up of a mixture of hydrocarbon molecules. It is obtained from paraffin-base lubricating oil distillates. When fully refined, i.e., oil content reduced to less than 1%, it has a melting point range from about 120°F to 160°F. It is white, tasteless, odorless, hard and fairly brittle in consistency. When molten, paraffin wax is a clear, colorless, low viscosity liquid.
Useful wax quality control properties utilized for cascading purposes include:
- Melting Point (ASTM D-87)
- Hardness - Penetration (ASTM D-1321)
- Odor (ASTM D-1833)
- Oil Content (ASTM D-721)
- Viscosity (ASTM D-445)
- Color (ASTM D-156)
Fully impregnated wax corrugated containers are increasingly used in heavy duty, rigid when wet applications, such as packaging of iced vegetables and poultry. In this process, some of the impregnant remains as surface wax and acts as a physical barrier against water to protect the fibers from softening. Both 4722 and 4742 have been formulated for this application. At 40-60% wax pick-up based on the substrate, corrugated containers have superior stacking strength when exposed to water or water vapor and improved moisture absorption.
Corrugated board, when treated with wax has improved dry strength, improved appearance, is resistant to water, resistant to vapor transmission, and reduces abrasiveness of kraft board contacting the packaged product.
Folding Cartons
Folding cartons are made from heavy paper or paperboard and are used in many retail sales applications. The carton is printed, cut, folded into the basic carton shape, sealed or glued so that it can be folded flat, and shipped to the user. The user feeds the folding carton into an automatic filling line, where the carton will be popped open, filled with the product, sealed and loaded into a shipping container, generally a corrugated container. First creasing or scoring the board during the cutting operation makes bends or folds in folding cartons. It is important that the board fold easily through up to 180 degrees without breaking on the outside. To help this occur, forcing a male die into a female die to deform the board scores the board. The board must be able to sustain ply separation without splitting or liners failing. The board will fail a 180 degree bend if the back liner, top liner or several inner plies are damaged.
