Cardboard Boxes

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Introduction

This article is an in-depth guide to how cardboard boxes are made.

You will learn more about topics such as:

• What is a Cardboard Box?
• How Cardboard Boxes are Made
• Types of Cardboard Boxes
• Materials Used to Make Cardboard Boxes
• And Much More &#;

Chapter One &#; What is a Cardboard Box?

A cardboard box is a shipping container made of layers of heavy-duty paper more than 0.01 inch (0.25 mm) thick. The term cardboard is used as a generic descriptor for various types of solid firm papers used to produce boxes. The general term cardboard box includes several types of paper boxes, such as corrugated boxes and chipboard boxes.

The various shapes of cardboard boxes are produced by folding, cutting, and shaping the sheets of heavy duty layered papers.

Chipboard boxes are part of the recycling industry and are made of recycled cardboard, paper, paper scraps, and sawdust that have been shredded and compressed into firm panels. It has a similar construction to that of cardboard since it consists of materials that have been compressed and glued to form solid firm sheets.

Cardboard boxes are designed and constructed to serve as protection for materials and products. They are lightweight with firm sides that can cushion impacts and contain products such as clothing and toys.

Sheets of cardboard are used as dividers for larger more durable boxes as well as padding.

A major factor in the wide use of cardboard boxes is their ability to be recycled, making them less costly than other forms of containers. The layers of paper used to produce cardboard boxes can be shredded, chemically treated, and formed into rolls to produce recycled paper or chipboard.

Ninety percent of all materials purchased are shipped using cardboard boxes, with over 88 percent being made from recycled raw materials. Making cardboard boxes from scratch requires a great deal of energy and several trees. Cardboard boxes made from recycled raw materials require drastically less energy and eliminate them from being added to a landfill where they can release harmful toxins.

Chapter Two &#; How Cardboard Boxes are Made

Cardboard boxes come in all sorts of shapes, sizes, configurations, and forms designed to fit the specific needs of a product. The standard cardboard box is made of paper from recycled boxes or the pulp of trees. The final paperboard consists of layers of pulp that have been treated, shaped, and pressed together.

The manufacture of cardboard boxes begins with heavy-duty papers created from tree pulp. The fibers from trees are put through a variety of treatments to produce the stable raw materials for making boxes.

Processes in Creating Cardboard

Pulping Process

Pulping is the process that is used to manufacture the paper for paperboard. It is a method for dispersing raw materials into single fibers referred to as paper pulp. The purpose of pulping is to dissolve the lignin of fiber materials without the loss of fibers. The method used to complete the pulping process varies between manufacturers and includes chemical, mechanical, and bio forms. The critical element in all pulping processes is 26.4 gallons (100 L) of water, which is necessary to produce one kilogram of paper.

Mechanical pulping is an aggressive physical method that separates the fibers and does not include any chemicals. Instead, wood chips, ground by stones, are bathed in water to form a pulp. The advantages of mechanical pulping include high yield and no pollution. The downside of the process is the low strength of the pulp that is produced.

Chemical pulping is a chemical and mechanical process in which wood chips are cooked and ground to produce cellulose fibers. It is a better separation process that is used to produce high-quality paper.

The presence of lignin in virgin pulp gives it a very dark brown natural color. In order for it to be used for paperboard, the pulp must be bleached to purify it and change its color. Whether pulp is being used or recycled cardboard, the bleaching process is necessary to purify the raw materials. In the case of recycled cardboard, bleaching removes any chemicals from the cardboard.

Different bleaching methods are used depending on the color of the pulp, types of chemicals used, and the types of treatment. The three categories of bleaching are delignification, oxidation, and reduction, each of which is a chemical process.

The pulp is passed through a series of blades designed to flatten the fibers and create the fibrillated ends to assist in the bonding process to make the paper stronger. Fillers are added to increase the density of the pulp and make it opaque. At this stage, the pulp is ready to be processed by the paper machine.

The paper machine consists of different machines that dry the pulp by forcing it through rotating wires and belts to remove the water. Pressure and temperature extract any remaining moisture before being placed on giant paper rolls.

Paperboard Construction

Paperboard is formed in layers of pulp that are sprayed in water onto a mesh screen to form a mat. Spraying the pulp slurry onto a mat builds up the fibers of the pulp to increase and solidify the strength of the paperboard. Each type or grade of paperboard is carefully mixed to match the requirements to meet its grade standards.

Once the mat is formed, the accumulated water has to be removed. Initially, the mat passes over a foundation screen where 20% of the water drips out by gravity. For further processing, the mat moves through sponge rollers that press and squeeze the water out of the mat. After being squeezed, the mat has sufficient strength to be stretched and heated as the final step in the drying process and water removal. The moisture content is at 5% after drying.

The fully formed paperboard is cut to various widths and rolled into huge rolls to be sent to box manufacturing. The different widths allow manufacturers to produce different size boxes in shapes, configurations, and forms to meet customer specifications.

Coating Paperboard

The dried and finished paperboard may be sent on for further processing, where it will be coated with a polymer, which consists of melted pellets that are extruded onto the surface of the paperboard in an extremely thin layer. In preparation for the coating process, a starch solution is added to bind the fibers to the surface and add strength to the board.

Before applying the coating, the paperboard is pressed between steel rolls to even its surface, increase its strength, and equalize the board&#;s thickness and density. The coating is applied on one or both sides of the board and smoothed over its surface. It is then dried and reeled onto a steel core, after which the long reel is cut into different widths. To meet customer specifications, the paperboard may be wrapped and bound as rolls or trimmed into sheets of varying sizes.

The finished paperboard has a smooth, waxy texture similar to the consistency found on a milk or juice carton.

Making Boxes

The finished paperboard is delivered to box manufacturers, which is formed into several types of boxes depending on the customer's needs. During the processing of the paperboard, handles, flaps, and slits are added, and the paperboard is scored such that it can be folded into different box shapes.

The processes for converting paperboard into lightweight cardboard boxes varies depending on the manufacturer.

Paper Rolls

Huge rolls of paper are delivered to the box-making factory. The width of the rolls comes in various to fit the boxes to be made.

Kraft Paper

Kraft, German for strength, paper is made from softwood trees with long fibers, such as pine, spruce, or fir trees. The tension of the long fibers makes Kraft paper tear and burst-resistant. Its brown or yellowish color differs depending on the types of trees from which it has been crafted. Spruce, pine, and silver birch trees produce a very dark brown kraft paper, while other trees produce yellowish Kraft paper. In addition to the different types of trees, the quality and color of Kraft paper vary depending on where in the world the trees are located.

Once the first liner is glued in place, Kraft paper is glued to the other side of the flutes. This configuration is the simplest form of corrugated board and is referred to as a single wall corrugated board, which can be seen in the image on the left below. Other forms can have two flutes and two liners with Kraft paper, pictured on the right below. Additionally, the width of the curves varies depending on the design of the box.

For many years, kraft paper has been used to produce corrugated boxes. Since it is such a durable and tear resistant paper, it has also found use in the production of rigid and sturdy cardboard boxes. One of the reasons for using kraft paper is its textured and porous surface, which makes it ideal for printing and producing display boxes.

Unlike the other papers used to produce cardboard boxes, kraft paper has a rustic and raw appearance. Its versatility offers designers a wide range of possibilities for packaging solutions and cardboard box engineering.

Processes in Creating Chipboard

Chipboard is a form of thick fiber paper made from recycled paper, wood waste, paper shreds, and sawdust that is turned into a slurry, much like paperboard, using urea formaldehyde. The slurry mixture is placed under pressure and heated to form panels. Chipboard is a very popular form of shipping material used to produce boxes, padding, and other forms of packaging.

Although the terms chipboard and cardboard are used interchangeably, they are two unique, and distinct products. Unlike cardboard or corrugated sheets made from layers of paper, chipboard is completely recycled paper that has been compressed into panels. It is an exceptionally versatile and sturdy paper stock capable of withstanding the same stresses as cardboard and corrugated sheets.

Chipboard comes in several varieties of densities or thicknesses and is a form of solid, sturdy paper. It is an ideal replacement for corrugated cardboard and is used to make cartons, boxes, and sheets of different sizes with different strengths.

The process of manufacturing chipboard involves compressing minute pieces of scrap paper, cardboard, and sawdust with glue to form firm, strong, and durable panels. The scraps used to manufacture chipboard are waste materials discarded from fabrication processes or collected from recycling bins.

Most chipboards are brown and are referred to as Kraft chipboards, with varieties made from newspapers having a grayish tinge. In some processes, it is clay coated, which gives it a thin white appearance.

Raw Materials

The raw materials used to manufacture chipboard are left over waste from other manufacturing processes or scrap cardboard, paper, and packaging material from recycling. In order to be suitable for the manufacture of chipboard, the waste materials have to be transformed into a granular form.

Shredding

In order to create the correct texture, the raw materials are put through a shredder chipper that grinds and pulverizes the material into a fine powder.

Adhesive

The fine powder is dried to remove any moisture residue that can affect the quality of the chipboard. Chipping, shredding, and drying create a uniform mixture that is mixed with an adhesive, which is normally a synthetic resin like urea formaldehyde. The resin adhesive strengthens the mixture and hardens the final chipboard sheets.

Heat and Pressure

The mixture of powder and adhesive is flattened into rectangular shapes. The application of heat and pressure ensure that the finished paper is smooth and rigid.

Chipboard is referred to a "green" paper product due to being manufactured from 100% recycled paper waste. It is flexible with exceptional durability and capable of providing protection for products, materials, and instruments. A major benefit of chipboard, aside from its protective properties, is its cost, which is less than cardboard and corrugated sheets with the same or better strength.

Chipboard Thicknesses

The thickness of chipboard is measured in points, with each point being one one thousandth of an inch. It comes in several densities, which add to its multiple uses.

• Light Chipboard has a thickness of 20 points or 0.02 inches (0.5 mm), which is the thickness of a cereal box.
• Extra Large Chipboard has a thickness of 32 points or 0.032 inches (0.8 mm), which is the thickness of a credit card.
• Extra Heavy Chipboard has a thickness between 50 and 52 points or 0.050 inch to 0.052 inches (1.27 - 1.32 mm), which is the thickness of a penny.
• Double Extra Heavy Chipboard has a thickness of 85 points or 0.09 inchse (2.23 mm), which is the thickness of two dimes.

Making and Finalizing Boxes

Flaps and Handles

Flaps and handles are cut into the paperboard sheets by a trimmer or die cutters that perforate the sheets and score them. The cutters are made from half-cylinders with different cylinders for every type of box. They have sharp blades and rubber padding, which prevents the cutters from cutting too deeply into the sheets.

The sharp blades of the die cutters or trimmers cut out the shapes of the flaps and score the sheets for folding. Although the trimmers and cylinder die cutters are the most efficient method for shaping the flaps and scoring, simple die cutters similar to those used in a die press are also used for shorter production runs. They operate much like a stamping machine and cut the flaps and scoring with force and pressure.

A press condenses overlapping panels during the cutting and scoring process to level out their thickness. The sheets feed through the mechanism at 8 kilometers an hour or 5 miles an hour, processing over 90 boxes per minute. Any trimmed material is collected and recycled.

Bending or Folding

The bending or folding machine folds the boxes along the score lines. Glue or stitching connects the sections to form the completed box. The glue that is used is hygienic, an important feature for boxes used for the food industry. Staples are used for stitching boxes destined for heavy-duty applications and forming a tighter seal.

After the glue and stitching are applied, the completed boxes are piled and banded together.

Flexographic Printing

In certain cases, boxes may need information printed on them to identify products, advertising, or other pertinent information regarding the box&#;s function and contents. Printing on boxes is a precision process that has to be carefully completed to avoid crushing the paperboard.

Feed rolls that send the boxes into the flexographic printing machine are made of soft material spaced properly for the depth of the sheets. The flexographic machine has printing plates for every color to be applied to the box. The plates are made of flexible photopolymer materials that are wound around a rotating cylinder. The process is very similar to that used by a letterpress.

Flexographic printing can apply a wide variety of colors, which are precision mixed and blended to meet the needs of the application or customer. Maintaining paperboard caliper or thickness is an essential part of ensuring the strength of the boxes.

Inspection of Boxes

The final step in the process is the inspection of the boxes before being shipped to customers. Special instrumentation is used to monitor glue placement and gap measurement. The system checks the amount and thickness of glue that has been applied and the size of the slots of the flaps. Each box is compared to the template used to produce the box.

All manufacturers pay close attention to their final products to ensure that the boxes live up to the organization&#;s standards and the high-quality materials they use. Although boxes are common types of containers that are found in manufacturing, retail, and homes, their assembly and construction require precision craftsmanship and close attention to detail.

Leading Manufacturers and Suppliers

Chapter Three &#; Grades of Paperboard

Paperboard is one of the most popular forms of materials used for retail packaging due to the fact that it can be easily shaped, designed, configured, and engineered to offer a positive and aesthetic appearance to a product. Properly made paperboard is the first impression that customers get of a product or brand and is the method for presenting and displaying a product.

The many benefits of paperboard are further divided between the different grades of paperboard, which vary depending on the manufacturer. Understanding paperboard grades is an essential part of selecting the correct paperboard to fit the needs of a product and company. The various grades fluctuate widely in quality and price.

Paperboard Grades

Solid Bleached Sulfate (SBS)

SBS is a brilliant white premium grade of paperboard that has the top ply of both sides of the board coated with clay, which allows for clear, crisp, and brilliant printing. The high quality of SBS comes from the hardwood fibers from which it is made. The internal plies of SBS are made of softwoods or blends of soft and hard-wood fibers.

In the manufacture of SBS paperboard, sulfate is used in the pulping of virgin hardwood. It is approved for use with food, has excellent foldability, is strong, and can be used in frozen applications. The many benefits of the SBS paperboard make it the most expensive of the paperboard grades.

Coated Unbleached Kraft (CUK)

CUK is made from unbleached virgin Kraft fibers that give it its brown color. It is made from softwoods, such as pine, with some hardwood fibers included in the top ply to create a smooth printable surface. The pine fibers are long and large, giving the paperboard excellent strength and tear resistance. The superior strength of CUK makes it ideal for beverage containers and heavy-duty packaging of tools and laundry detergents.

The strength and durability of CUK make it resistant to moisture. CUK is the strongest of all of the paperboard grades, is the most popular, and is less expensive than SBS.

Uncoated Unbleached Kraft (UUK)

UUK is a natural grade of brown paperboard made from a blend of softwood and hardwood. Recycled fibers are also blended with the tree fibers. It is a high-strength paperboard at a lower cost. The texture of UUK does not provide a surface for crisp printing or complex designs. It is ideal for storing hardware in moist conditions where heavy-duty use is required.

Coated Recycled Board (CRB)

CRB is made of recycled fibers with a top ply of white fibers finished with a clay coating. There are many variations of this grade, which include CCN, WLC, Duplex, GB, and CCNB. It is a very low-strength grade of paper board and is ideal for lightweight items such as chips, crackers, cereal, or snacks.

Uncoated Recycled Board (URB)

URB is made from recycled newsprint and paper. It is a thick grade of paperboard that is used as a set up box or dividers. URB is the least expensive paperboard grade and provides the highest value for the money spent.

Folding Box Board (FBB)

FBB is a multilayer paperboard made from chemical and mechanical pulp with mechanical pulp placed between layers of chemical pulp. The top ply is bleached chemical pulp, which is a low-density material with high stiffness. FBB is a virgin fiber paperboard that has purity for product safety. The combination of mechanical layers and chemical layers creates strong stiff sheets. When it is fully coated, it is printable with crispness and high resolution.

Regardless of the many positive qualities of FBB, it has the lowest strength of the grades of paperboard. By using variations in coatings and treatments, the strength of FBB can vary and be somewhat competitive with SBS. The amazing thing about FBB is its foldability. Boxes with attached lids open and close easily without any damage to the box&#;s scores.

Chapter Four &#; Other Types of Cardboard

Paperboard is the most common type of cardboard but is not the only type. Cardboard is a highly versatile material that comes in a wide variety of forms and can be structured to meet specific and specialized needs. The flexibility of cardboard allows it to be adjusted and adapted to different strengths, weights, widths, and endless functions.

Honeycomb Cardboard

Honeycomb cardboard is lightweight but durable. It has two outside panels that give it stability and strength as well as an expansive surface area. The strength of honeycomb cardboard makes it an ideal replacement for wood or plastic pallets. It can be manufactured in different strengths and sizes with an exceptional strength-to-weight ratio. In door manufacturing, honeycomb cardboard is used as filler for the door cavity.

The many thicknesses of honeycomb cardboard make it adaptable enough to be formed into resilient and durable boxes with corners secured with multi-ply cardboard. Honeycomb cardboard&#;s structure makes it possible for it to be impact resistant.

The variations in honeycomb cardboard include different sizes of the honeycombs as well as different cell sizes that range from 0.32 inches (8 mm) to 0.86 inches (22 mm). The heights of honeycombs can be from 0.23 inches (6 mm) up to 4.1 inches (104 mm).

Gray Paperboard

Gray paperboard is a thick paperboard made from recycled paper pulp and gets its name from its color. It is widely used due to its stiffness. The surface of the paperboard is gray, while its other layers can be brown or gray. Gray paperboard is used for pad backing, rigid boxes, cartons, and bookbinding.

The strength of gray paperboard is due to the process used to manufacture it, which does not involve the use of glues or adhesive. The layers or plies of gray paperboard are connected by the board&#;s long fibers that are pressed together by heavy steel rollers.

Gray Cardboard

Gray cardboard, like gray paperboard, is made using recycled paper and cardboard. It is smooth with good stiffness and slightly thicker than gray paperboard. The higher thicknesses of gray cardboard make it ideal as a replacement for laminated cardboard.

Chapter Five &#; Types of Cardboard Boxes

Cardboard boxes are the main choice for packaging, storage, and product display. Their flexibility makes them ideal for the protection and security of products while affording a pleasant appearance.

For every packing application, there is a box that easily and conveniently fits into the process. It is this characteristic of cardboard boxes that has led to innovations in packaging and shipping operations.

Slotted Container (RSC)

RSCs are typical shipping containers with flaps of equal size that meet when closed such that they can be taped and secured. The flaps at the end of the box bend inward and do not meet, while the flaps along the length of the box fold inward in such a fashion that their edges meet to be taped and secured.

Full Overlap Slotted Container (FOL)

FOL cardboard boxes follow the same pattern as RSC boxes with one slight adjustment. Unlike RSCs, the long outer flaps of a FOL cardboard box overlap when bent inward. This design provides for additional strength when the boxes are stacked and extra edge protection, which makes the box able to withstand rough handling.

Full Telescope Box (FTD)

An FTD-designed box has separate sections where one section fits inside the other section. The cover of an FTD completely covers the body of the box. The flaps on FTD boxes are stapled or taped. Their design provides compression strength when stacking heavy and large items.

Snap Bottom Box

The upper structure of a snap bottom box is similar to that of the RSC box. The flaps of the bottom of the box are cut and shaped such that they fold over each other. When the flaps are folded, they snap into slots and lock together. The design of snap bottom boxes makes them easy to assemble quickly.

One Piece Folder (OPF)

A one piece folder cardboard box is a single unit that folds along score lines to form a box. The bottom of the box is a flat cardboard piece with four sides and flaps attached. When the flaps are closed, they raise the sides of the box to make its rectangular shape. As with the RSC box, the end flaps are short and do not touch, while the side flaps can overlap or meet at their edges, depending on the design of the box.

One piece folder cardboard boxes are designed for shipping single items such as iPads, books, video games, and other flat-profiled items. The flat surface of one piece folder cardboard boxes is ideal for printing logos, images, and instructions.

Self-Locking Cardboard Box

The self-locking cardboard box, or RELF (Roll End Lock Front) die-cut cardboard box, is very similar to the one piece folder. It is a single unit of cardboard that has been scored to fold into a box. The sides of the box have flaps attached at their long ends, while the ends of the box are double-width of equally scored sections.

To form a self-locking box, the sides of the box are folded upward with their flaps placed along the scoring of the ends of the box. The double-wide ends are brought upward such that one portion of the end folds over the extended flaps and is locked in place by a slot in the bottom of the box and tabs on the extended end piece.

The lids for self-locking boxes are formed using the same method and take the form of telescoping boxes where the folded lid fits over the folded box. The unique nature of self locking boxes eliminates the need for taping or gluing the sides. Tape is only used to seal the box.

Another form of self-locking box or RELF die-cut cardboard box has a lid attached to one of the long sides with extended flaps. The box is assembled like other self-locking boxes. The lid on one of the long sides folds up with flaps that slide inside the box and flaps that slide into the self-locked edges, as can be seen below.

Types of Boxes Summary

The few boxes described here are only a sampling of the many boxes that are a vital part of the supply chain and shipping. Cardboard manufacturers constantly develop and create new designs for unique and unusual applications. Additionally, all manufacturers are ready and prepared to help their customers design boxes that perfectly fit their requirements.

Chapter Six - Uses for Chipboard Boxes

Part of the reason for the wide use of chipboard is due to its multiple sizes and thicknesses. It can be shaped, configured, and manufactured into any form to fit the needs of a wide range of applications. Its main use is as packing for commercial and industrial products.

Sensitive Technologies

The sturdiness of chipboard makes it an ideal packing material for sensitive technical equipment that requires extra protection from vibrations and impact, which can damage the circuit boards of technological instruments during transport. Chipboard is used to provide structural integrity and stability.

Bakery Boxes

Chipboard is used for bakery boxes due to its strength, durability, and flexibility, which prevent baked goods from being damaged. Additionally, the rounds placed underneath cakes are made from chipboard because it does not absorb moisture.

Tissue Boxes

Tissue boxes are made from chipboard to prevent them from being crushed during transport.

Beer Cases

Chipboard is used for beer cases due to its ability to withstand the weight of a case of beer, which can be over 20 lbs (9 kg).

Retail Displays

Retail displays present products using attractive displays that show the product in a positive and accessible way. Displays have to be lightweight yet sturdy enough to withstand constant use. Chipboard is used to meet the many factors required by retail displays and is resilient enough to last.

Notebooks and Pads of Paper

A very common use for chipboard is as backing for pads of paper, these backings have the proper consistency and strength to support paper during use. Thin chipboard that can be cut to fit the shape of any pad is durable and flexible as a backing. Additionally, chipboard is used as backing in picture frames and shipping envelopes.

Furniture Components

Chipboard is used in furniture as a structural component that can be covered with wood or veneer. It is used in the sides and backs of chairs and couches, adding stability and support.

Take Out Food Boxes

The inability of chipboard to absorb moisture is one of the main reasons it is used for the delivery of fast foods. It does not become soggy and helps retain the flavor and smells of the food.

The eight products described above are only a small sampling of the many uses for chipboard. Its ability to be configured and manufactured in a variety of shapes and sizes enables it to fit the needs of any application regardless of how demanding or rigid.

Chapter Seven &#; Benefits of Cardboard Boxes

The introduction of the cardboard box during the first industrial revolution radically changed the nature of the packaging industry. Sir Malcolm Thornhill introduced the first cardboard box in , which first appeared in the United States in , where they took off and became common packaging containers.

Small cardboard boxes of lighter paperboard became popular at the beginning of the 20th century to store and sell breakfast cereal. This use of cardboard boxes has grown rapidly to the point that most products are sold using some form of cardboard box.

Cardboard Box Benefits

Versatile Applications

Even though they are just paper and starch, cardboard boxes are strong, pliable, and moisture-resistant. They are the ideal method for shipping, protecting, promoting, and storing items of all shapes, sizes, configurations, and forms. With the proper surface finish, they can have an endless number of images and displays printed on them, including colorful graphics, creative designs, and entertaining pictures.

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Cost-Effectiveness

The main reason for the rapid rise of cardboard boxes is their cost, which is far lower than their predecessors. Cardboard boxes can be manufactured to fit the budget of any company regardless of its size. They are a perfect cost-effective way of getting a brand noticed. The low cost of cardboard boxes is related to the low cost of labor and materials in their production. Additionally, over 80% of all cardboard is recyclable and reusable, which further lowers its cost.

Sustainable Production

Sustainability has become a major push in 21st-century industry and manufacturing with the goal of preserving our environment for future generations. Cardboard boxes smoothly fit into the goals and focus of sustainability since, at the end of their life cycle, they can be reprocessed to make more boxes.

Home Grown Materials

The cardboard box industry is one of the largest industries in the United States, with a value of over $60 billion. The industry takes pride in the fact that all of its products are made from raw materials found in the United States and use American workers.

Customizable Boxes

Over the years, engineers and designers have continued to expand the use of cardboard boxes by creating innovative and practical designs. Using the many types of paperboard, and cardboard, manufacturers have been able to produce cardboard boxes to fit any shipping, packaging, and storage application.

Recyclable Materials

The main reason that cardboard has achieved increasing popularity is due to the fact that it does not end up in a landfill or garbage dump. Trash collection companies have developed special procedures to segregate cardboard materials such that they can be bundled and shipped to producers for reprocessing.

Environmentally Friendly Productino

Of the many things that are consumed and used every day, cardboard boxes are the most environmentally friendly tool. Over 80% of all cardboard produced can be reused without any restrictions. Box manufacturers can take any form of cardboard and reprocess it to make products that are comparable to virgin products. The fact that cardboard can be reused endlessly without any degradation makes it the ideal product for preserving and saving the environment.

Conclusion

• A cardboard box is a shipping container made of thick heavy-duty paper known as paperboard, which is more than 0.01 inch (0.25 mm) thick. The term cardboard is used as a generic descriptor for various types of solid firm papers used to produce boxes.
• Paperboard is one of the most popular forms of materials used for retail packaging due to the fact that it can be easily shaped, designed, configured, and engineered to offer a positive and aesthetic appearance for a product. Properly made paperboard is the first impression that customers get of a product or brand and is the method for presenting and displaying a product.
• Paperboard is the most common type of cardboard but is not the only type. Cardboard is a highly versatile material that comes in a wide variety of forms and can be structured to meet specific and specialized needs. The flexibility of cardboard allows it to be adjusted and adapted to different strengths, weights, widths, and endless functions.
• The introduction of the cardboard box during the first industrial revolution radically changed the nature of the packaging industries. The first cardboard box was introduced by Sir Malcolm Thornhill in and first appeared in the United States in , where they took off and became common packaging containers.

Leading Manufacturers and Suppliers

Introduction

Paper Packaging History

A wide range of paper and paperboard is used in packaging today for printed paper boxes, corrugated boxes and rigid paper boxes &#; from lightweight infusible tissues for tea and coffee bags to heavy duty boards used in distribution. Paper and paperboard are found wherever products are produced, distributed, marketed and used, and account for about one-third of the total packaging market. Over 40% of all paper and paperboard consumption in Europe is used for packaging and over 50% of the paper and paperboard used for packaging is used by the food industry.

One of the earliest references to the use of paper for packaging food products is a patent taken out by Charles Hildeyerd on 16 February for &#;The way and art of making blew paper used by sugar-bakers and others&#; (Hills, ).

The use of paper and paperboard for packaging purposes accelerated during the latter part of the nineteenth century to meet the needs of manufacturing industry. The manufacture of paper had progressed from a laborious manual operation, one sheet at a time, to continuous high speed production with wood pulp replacing rags as the main raw material. There were also developments in the techniques for printing and converting these materials into packaging containers.

Modern Paper Packaging

Today, examples of the use of paper and paperboard packaging for food can be found in many places, such as supermarkets, traditional markets and retail stores, mail order, fast food, dispensing machines, pharmacies, and in hospital, catering and leisure situations.

Uses can be found in packaging all the main categories of food, such as:

• Uses can be found in packaging all the main categories of food, such as:
• dry food products packaging &#; cereals, biscuits, bread and baked products, tea, coffee, sugar, &#;our, dry food mixes, etc
• frozen foods, chilled foods and ice cream packaging
• liquid foods and beverages &#; juice drinks, milk and milk derived products
• chocolate packaging and sugar confectionery
• fast foods
• fresh produce &#; fruit, vegetables, meat and &#;sh

Packaging made from paper and paperboard is found at the point of sale (primary packs), in storage and for distribution (secondary packaging).

Fibers

Paper and paperboard are sheet materials made up from an interlaced network of cellulose fibers. These materials are printable and have physical properties that enable them to be made into &#;exible and rigid packaging by cutting, creasing, folding, forming, gluing, etc.

There are many different types of paper and paperboard. They vary in appearance, strength and many other properties depending on the type(s) and amount of &#;bre used and how the &#;bres are processed in paper and paperboard manufacture.

GSM

The amount of fiber is expressed by the weight per unit area (grams per square metre, g/m2, or lbs per sq ft), thickness (microns, mm or 0.001 mm, and thou (0.001 inch), also referred to as points) and appearance (color and surface &#;nish).

Difference Between Paper and Paperboard

Paperboard is thicker than paper and has a higher weight per unit area. Paper over 200g/m2 is de&#;ned by ISO (International Organisation for Standardization) as paperboard or board. However, some products are known as paperboard even though they are manufactured in grammages less than 200g/m2.

Paper Packaging Categories

Papers and paperboard used for packaging range from thin tissues to thick boards. The main examples of paper- and paperboard-based packaging are:

• custom paper bags, wrapping, packaging papers and infusible tissues, e.g. tea and coffee bags, sachets, pouches, overwrapping paper, sugar and &#;our bags, carrier bags
• multiwall paper sacks
• folding cartons and rigid paper boxes
• corrugated boxes and solid &#;berboard boxes (shipping cases)
• paper-based tubes, tubs and composite containers
• fiber drums
• liquid packaging
• molded pulp containers
• labels
• sealing tapes
• cushioning materials
• cap liners (sealing wads) and diaphragms (membranes)

Paper and paperboard packaging is used over a wide temperature range, from frozen food storage to the high temperatures of boiling water and heating in microwave and conventional radiant heat ovens.

Whilst it is approved for direct contact with many food products, packaging made solely from paper and paperboard is permeable to water, water vapour, aqueous solutions and emulsions, organic solvents, fatty substances (except grease resistant paper grades), gases, such as oxygen, carbon dioxide and nitrogen, aggressive chemicals and to volatile &#;avours and aromas. Whilst it can be sealed with several types of adhesive, it is not itself heat sealable.

Barrier Properties

Paper and paperboard, however, can acquire barrier properties and extended functional performance, such as heat sealability for leak-proof liquid packaging, through coating and lami-nation with plastics, such as polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET or PETE) and ethylene vinyl alcohol (EVOH), and with aluminium foil, wax, and other treatments.

Packaging made solely from paperboard can provide a wide range of barrier prop-erties by being overwrapped with a heat sealable &#;lm, such as polyvinylidene chloride (PVdC) coated-oriented polypropylene (OPP or BOPP) or a similarly coated regenerated cellulose &#;lm.

PAPER AND PAPERBOARD &#; FIBRE SOURCES AND FIBRE SEPARATION (PULPING)

Paper and paperboard are sheet materials comprising an interlaced network of cellulose fibres derived from wood. Cellulose fibres are capable of developing physico-chemical bonds at their points of contact within the fibre network, thus forming a sheet. The strength of the sheet depends on the origin and type of fibre, how the fibre has been processed, the weight per unit area, and thickness.

The type of fibre also influences the colour. Most paperboards have a multilayered construction that provides specific performance advantages and gives the manufacturer flexibility of choice, depending on the packaging end use, of the type of fibre used in the individual layers. Virgin, or primary, fibre is derived directly from wood by a process known as pulping. This can be done mechanically (Fig. 8.1) or with the help of chemicals that dissolve most of the non-cellulose components of the wood, which are subsequently used to provide energy (Fig. 8.2).

The terms sulphate and sulphite refer to the chemical processes used to separate the fibres from wood, sulphate being the more dominant process today. Mechanically separated fibre retains the colour of the wood though this can be made lighter by mild chemical treatment. Chemically separated fibre is brown but it can be bleached to remove all traces of non-cellulosic material. Pure cellulose fibres are translucent individually but appear white when bulked together (Fig. 8.2).

Fibre recovered (secondary fibre) from waste paper and board, which is not de-inked and bleached, is grey or brown. Fibre recovered from brown packaging will be brown in colour. When mixed printed waste recovered paper and board is processed the colour of the pulp is grey. Pulp can be dyed during processing to meet a specific colour specification. The process whereby recovered fibre is made into paper and paperboard is an example of material recycling (Fig. 8.3).

Fibres can withstand multiple recycling but the process of recycling reduces fibre length and inter-fibre bonding, features related to sheet strength properties. Furthermore, it must also be appreciated that some papers and boards cannot be recovered by nature of their use and, hence, there is a constant need for virgin fibre to maintain the amount and strength of fibres. In practice, the proportion of fibre that is recovered and recycled in various countries is between40 and 60%. Another important factor relevant to sheet properties is the species of tree from which the fibres are derived. In general terms, the industry uses long fibres for strength and short fibres for surface smoothness and efficient sheet forming in manufacture. Long fibres are derived from coniferous softwoods, such as Spruce, Pine and Douglas Fir, and have average lengths of 3&#;4.5 mm. Short fibres, such as those derived from Birch, have  average lengths of 1&#;1.5 mm.

PAPER AND PAPERBOARD MANUFACTURE

Stock preparation

If pulp is bought in bales, it is first dispersed in water in a hydrapulper. All pulp, including pulp that comes straight from the pulpmill without drying, is then treated in various ways to prepare it for use on the paper or paperboard machine. Inter-fibre bonding can be increased  by mechanical refining, in which the surface structure of the fibre is modified by swelling the fibre in water and increasing the surface area. The degree of refining, which also influences the drainage rate at the next stage in manufacture, is adjusted to suit the properties of the intended paper or paperboard product.

Additives, such as alum or synthetic resins, are used to increase the water repellancy of the fibres. Wet strength resins can be added to increase the strength of the product when saturated with water. Fluorescent whitening agents (FWAs), also known as optical brightening agents (OBAs), can be added at this stage to increase whiteness and brightness.

Sheet forming

The fibre in water suspension, roughly 2% fibre and 98% water, is formed in an even layer. This is achieved by depositing the suspension of fibre at a constant rate onto a moving plastic mesh, known as the wire (Fig. 8.4). On some machines, forming is carried out on a wire mesh covered cylinder. Forming results in a layer of entangled fibres from which water is then removed by drainage, which may be assisted by vacuum. Tissue, paper, and thin boards can be formed in one layer. Thicker and heavier higher grammage paperboards require several layers of pulp, either the same type, or different pulps, depending on the board type, being brought together successively in the wet state.

Forming on a wire mesh in this way has two important consequences.

Firstly, there is a slight difference in appearance between the wire side of the sheet and the other side (top side). This effect is eliminated if the sheet is subsequently coated with a white mineral (china clay) coating, or if a specific type of twin wire former is used where both outer sides of the sheet are in contact with identical wire mesh surfaces.

Secondly, the method of forming influences the orientation of the fibres in the sheet. Since fibres are long and thin, they tend to line up in the direction of motion on the machine. This is called the machine direction (MD). Strength properties, such as tensile and stiffness, are higher in the MD. One of the aims of successful forming is to randomise the orientation of fibres in the sheet. Nevertheless, the orientation occurs and it is normal to measure strength properties both in the MD and in the direction at right angles to the MD, known as the cross direction (CD). The fibres form an entangled network that is assisted by creating turbulence in the headbox immediately prior to forming and, on some paper machines, by shaking the wire from side to side.

Pressing

At the end of the forming section, or wet end of the machine, the sheet is sufficiently consolidated by the removal of water to support its own weight to transfer into the press section (Fig. 8.5). Here it is held between absorbent blankets and gently pressed using steel rolls so that with vacuum assistance more water is removed, reducing the moisture content to about 60&#;65%.

Drying

The moisture is reduced to less than 10%, depending on grade, by passing the sheet over steam heated cylinders. Some machines include in their drying section a very large heated cylinder with a polished steel surface. This is an MG (machine glazing) cylinder &#; also known as a Yankee cylinder. Paper can be produced with a glazed surface on one side and on some board machines the MG cylinder is used to produce a smooth surface, whilst preserving thickness, thereby giving higher stiffness for a given grammage. A starch solution is sometimes applied towards the end of the drying section to one or both sides of the sheet. This is known as surface sizing. It improves the strength and finish of the sheet and anchors the fibres firmly in the sheet. Squeezing the sheet through a series of steel/composition rolls can enhance smoothness and thickness uniformity. This is known as calendering. Paper may be calendered at high speed in a separate process, known as supercalendering.

Coating

White pigmented coatings are applied to one or both sides of many types of paper and board on- machine. The coatings comprise mineral pigments, such as china clay and calcium carbonate, and synthetic binders (adhesives), dispersed in water. Excess coating is usually applied, it is smoothed and the excess removed. A number of techniques may be used &#; metering bar, air knife or blade coating.

One, two or three layers of coating may be applied. Coatings are dried by radiant heat and by passing the sheet over steam heated drying cylinders. They may be burnished (polished) depending on the required appearance, colour, smoothness, gloss and printing properties. Coat- ings can be applied off-line. In the cast coating process, the smooth wet coating is cast against a highly polished chromium-plated heated cylinder. When dry, the coating separates from the metal surface leaving the coating with high smoothness and gloss.

Reel-up

Finally, the paper or board is reeled up prior to finishing.

Finishing

The large diameter, full machine width reels of paper and board are then slit into narrower reels of the same or smaller diameter or cut into sheets to meet customer and market needs. Sheets may be guillotined, pile turned, counted, ream wrapped, palletised, labelled and wrapped securely, usually with moisture resistant material, such as PE coated paper or PE film.

PACKAGING PAPERS AND PAPERBOARDS

A wide range of papers and paperboards are commercially available to meet market needs resulting from the choice of fibres available, bleached and unbleached, virgin and recycled, and because fibres can be modified at the stock preparation stage.

Paper and board-based products can be made in a wide range of grammages and thicknesses. The surface finish (appearance) can be varied mechanically. Additives introduced at the stock preparation stage provide special properties.

Coatings applied, smoothed and dried, to either one or both surfaces, offer a variety of appearance and performance features that are enhanced by subsequent printing and conversion, thereby resulting in various types of packaging.

To illustrate these features of paper and paperboard, some examples are described below.

Wet strength paper

Paper sacks used in wet conditions need to retain at least 30% of their dry strength when saturated with water. To achieve wet strength, urea formaldehyde and melamine formaldehyde are added to the stock. These chemicals cross-link during drying and are deposited on the surface of the cellulose fibres making them resistant to water absorption.

Microcreping

Microcreping, e.g. as achieved by the Clupak process, builds an almost invisible crimp into paper during drying enabling paper to stretch up to 7% in the MD compared to a more normal 2%. When used in paper sacks this feature improves the ability of the paper to withstand dynamic stresses, such as occur when sacks are dropped.

Greaseproof

The hydration (refining) of fibres at the stock preparation stage, already described, is taken much further than normal. It is carried out as a batch process and is known as beating. The fibres are treated (hydrated) so that they become almost gelatinous.

Glassine

This is a supercalendered (SC) greaseproof paper. The calendering produces a very dense sheet with a high (smooth and glossy) finish. It is non-porous, greaseproof, can be laminated to board and can be silicone coated to facilitate product release. Glassine is also available in several colours.

Vegetable parchment

Bleached chemical pulp is made into paper conventionally and then passed through a bath of sulphuric acid. Some of the surface cellulose is gelatinised on passing into water and redeposited between the surface fibres forming an impervious layer. This paper has high grease resistance and wet strength.

Tissues

Neutral pH grades with low chloride and sulphate residues are laminated to aluminium foil. The grammages range from 17 to 30 g/m2. Tea and coffee bag tissue is a special light weight tissue available either as a heat sealable product (containing a proportion of polypropylene fibres), or as a non-heat sealable product, in grammages from 12 to 17 g/m2. It incorporates long fibres, such as those derived from manilla hemp, which give a strong permeable sheet at the low grammages used.

A 100% biodegradable and compostable tea and coffee bag tissue is now available with fibre based on IngeoTM (PLA, polylactic acid). This product is suitable for use on tea and coffee, packing machines that use ultrasonic sealing technology (Ahlstrom, ).

Paper labels

These may be MG (machine glazed), MF (machine finished) or calendered kraft papers (100% sulphate chemical pulp) in the grammage range 70&#;90 g/m2. The paper may be coated on- machine or cast coated for the highest gloss in an off-machine or secondary process.

The term finish in the paper industry refers to the surface appearance. This may be:

• MF &#; machine finish, smooth but not glazed
• WF &#; water finish where one or both sides are dampened and smoothed, to be smoother and glossier than MF
• MG &#; machine glazed with high gloss on one side only
• SC &#; supercalendered, i.e. dampened and polished off-machine to produce a high gloss on both sides

Bag papers

For sugar or flour, coated or uncoated bleached kraft in the range 90&#;100 g/m2 is used. Imitation kraft is a term on which there is no universally agreed definition, it can be either a blend of kraft with recycled fibre or it can be 100% recycled. It is usually dyed brown. It has many uses for wrapping and for bags where it may have an MG and a ribbed finish. Thinner grades may be used for lamination with aluminium foil and PE for use on form/fill/seal machines.

Sack kraft

Usually, this is unbleached kraft (100% sulphate chemical) pulp, though there is some use of bleached kraft. The grammage range is 70&#;100 g/m2.

Impregnated papers

Wax impregnated paper and fluorocarbon treatment for grease/fat resistance is produced on- machine.

Laminating papers

These are coated and uncoated papers (40&#;80 g/m2) based on both kraft (sulphate) and sulphite pulps. These papers can be laminated to aluminium foil and extrusion coated with PE. The heavier weights can be PE laminated to plastic films and wax or glue laminated to unlined chipboard.

Solid bleached board (SBB)

Solid bleached board is made exclusively from bleached chemical pulp (Fig. 8.6). It usually has a mineral pigment coated top surface and some grades are also coated on the back. The term SBS (solid bleached sulphate), derived from the method of pulp production, is sometimes used to describe this product.

This paperboard has excellent surface and printing characteristics. It gives wide scope for innovative structural design and can be embossed, cut, creased, folded and glued with ease.

This is a pure cellulose primary (virgin) paperboard with consistent purity for food product safety, making it the best choice for the packaging of aroma and flavour sensitive products. Examples of use include chocolate confectionery, frozen foods, cheese, tea, coffee, reheatable products and as a base for liquid packaging.

Solid unbleached board (SUB)

Solid unbleached board is made exclusively from unbleached chemical pulp (Fig. 8.7). The base board is brown in colour. This product is also known as solid unbleached sulphate. To achieve a white surface, it can be coated with a white mineral pigment coating, sometimes in combination with a layer of bleached white fibres under the coating. This board is used where there is a high strength requirement in terms of puncture and tear resistance and/or good wet strength is required, such as for bottle or can multipacks, and as a base for liquid packaging.

Folding boxboard (FBB)

Folding boxboard comprises middle layers of mechanical pulp sandwiched between layers of bleached chemical pulp (Fig. 8.8). The top layer of bleached chemical pulp is usually coated with a white mineral pigment coating. The back is cream (manilla) in colour. This is because the back layer of bleached chemical pulp is translucent allowing the colour of the middle layers to show through.

However, if the mechanical pulp in the middle layers has been given a mild chemical treatment (bleached), it is lighter in colour, and this makes the reverse side colour lighter in shade. The back layer may, however, be thicker or coated with a white mineral pigment coating, thus becoming a white back folding box board. The combination of inner layers of mechanical pulp and outer layers of bleached chemical pulp creates a board with high stiffness. Fully coated grades have a smooth surface and excellent printing characteristics. This pa- perboard is a primary (virgin fibre) product with consistent purity for food product safety and suitable for the packing of aroma and flavour sensitive products. It is widely used for food prod- ucts, such as confectionery, frozen and chilled foods, tea, coffee, bakery products and biscuits.

White lined chipboard (WLC)

White lined chipboard comprises middle plies of recycled pulp recovered from mixed papers or carton waste. The middle layers are grey in colour. The top layer, or liner of bleached chemical pulp is usually white mineral pigment coated. The second layer, or under liner, may also comprise bleached chemical pulp or mechanical pulp. This product is also known as newsboard. The term chipboard is also used, though this name is more likely to be associated with an unlined grade, i.e. without a white, or other colour, surface liner ply (Fig. 8.9).

The reverse-side outer layer usually comprises specially selected recycled pulp and is grey in colour. The external appearance may be white by the use of bleached chemical pulp and, possibly, a white mineral pigment coating. (White PE has also been used.) There are additional grades of unlined chipboard and grades with special dyed liner plies for use in the manufacture of corrugated fibreboard.

The overall content of WLC varies from about 80&#;100% recovered fibre depending on the choice of fibre used in the various layers. WLC is widely used for cereals, dried foods, frozen and chilled foods, and confectionery outers.

PROPERTIES OF PAPER AND PAPERBOARD

The features of paper and paperboard that make these materials suitable for packaging relate to appearance and performance. These features are determined by the type of paper and paper- board &#; the raw materials used and the way they have been processed.

Appearance and performance can be related to measurable properties that are controlled in the selection of  raw materials and the manufacturing process.

National and international standard test procedures have been published by British Standards (UK), DIN (Germany), ISO, and in the United States, there is TAPPI (Technical Association for the Pulp and Paper Industry) and ASTM International (formally the American Society for Testing Materials).

Appearance

Appearance relates to the visual impact of the pack and can be expressed in terms of colour, smoothness and whether the surface has a high or low gloss (matte) finish.

Colour depends on the choice of fibre for the outer surface, and also, where appropriate, the reverse side. As described above, the choice is either white, brown or grey. In addition, some liners for corrugated board comprise a mix of bleached and brown fibres.

Other colours are technically possible either by using fibres dyed to a specific colour or coated with a mineral pigment-coloured coating. Where paper and paperboard is required for quality printing, it is usually coated on the print side during manufacture with a mineral-based coating, usually white in colour, based on china clay or calcium carbonate. The reverse side may also be coated where two-side printing is required.

Performance

Performance properties are related to the level of efficiency achieved during the manufacture of the pack, in printing, cutting and creasing, gluing and the packing operation. Performance properties are also related to pack compression strength in storage, distribution, at the point of sale and in consumer use.

Specific measurable properties include stiffness, short span compression (rigidity) strength, tensile strength, wet strength, % stretch, tear strength, fold endurance, puncture resistance and ply bond strength. Other performance properties relate to moisture content, air permeability, water absorbency, surface friction, surface tension, ink absorbency, etc. Chemical properties include pH, whilst chloride and sulphate residues are relevant for aluminium foil lamination.

Flatness is easily evaluated but is a complicated issue as lack of flatness can arise from several potential causes, from the hygrosensitivity characteristics of the fibre, manufacturing variables and handling at any stage, including printing and use. Neutrality with respect to odour and taint, and product safety are performance needs that are important in the context of paper and board packaging, which is in direct or close proximity to food.

ADDITIONAL FUNCTIONAL PROPERTIES OF PAPER AND PAPERBOARD

Additional barrier and functional performance for food packaging needs can be imparted to paper and paperboard by one or more of the following processes.

Treatment during manufacture

• Hard sizing

Sizing is a term used to describe a treatment that delays the rate at which water is absorbed, both through the edges (wicking) and through the surface. It is achieved by the use of chemicals added during the stock, or pulp, preparation stage prior to forming in manufacture. This is known as internal sizing. Traditionally, alum, a natural resin, derived from wood was used. Today several synthetic sizing materials are also available. Paperboard used in packaging for frozen and chilled food and for liquid packaging needs to be hard sized.

• Sizing with wax

Sizing with wax on-machine.

• Acrylic resin dispersion

Acrylic resin dispersion (water-based) coating &#; heat sealable, moderate moisture and oxygen barrier, available as one side coating on-machine.

• Fluorocarbon dispersion

Fluorocarbon dispersion coating, high fat resistant one-side coating on-machine.

Note: The terms on-machine and off-machine are commonly used in the paper industry. The machine in question is the paper or paperboard machine. An on-machine process takes place as the paper or paperboard is being made and off-machine is a subsequent process carried out on a machine designed specially for the process concerned.

Lamination

This process applies another functional or decorative material, in sheet or reel form, to the paper or paperboard surface with the help of an adhesive. Examples are:

• aluminium foil applied to one or both sides, provides a barrier to moisture, flavour, common gases, such as oxygen, and UV light. Aluminium foil laminated to paper and paperboard  is also used for direct contact and easy release for foods that will be cooked or reheated in radiation or convection ovens. Aluminium foil is also used to provide a decorative metallic finish as, for example, on cartons for chocolate confectionery
• greaseproof paper laminated to paperboard: good grease resistance for fat containing prod- ucts, temperature resistance to 180&#;C for cooking/reheatable packs. If additionally the grease- proof paper has a release coating, this product can be used to pack sticky or tacky products
• glassine paper laminated to paperboard: grease resistance for products with moderate fat content, such as cakes or bake-in-box applications. If the glassine is coloured the pack should not be used in reheatable applications but food contact approved grades can be used for direct contact with, for example, chocolate

The adhesives used for lamination include PVA-type emulsions, starch-based, resin/solvent- based, cross-linking compounds, molten wax or PE depending on the needs of the particular laminate. The presence of wax and PE also improves the barrier to water vapour. When PE is used as an adhesive the process would be described as extrusion lamination.

Plastic extrusion coating and laminating

Polyethylene (PE) heat sealable moisture barrier. Low density polyethylene (LDPE) is widely used in the plastic extrusion coating and laminating of paper and paperboard. Easier heat sealing results when PE is modified with EVA (Ethylene vinyl acetate). Medium and high density PE has a higher temperature limit, better abrasion resistance and higher barrier properties than LDPE. One and two side coatings are available (Fig. 8.10).

Polypropylene (PP) heat sealable, moisture and fat barrier. It can withstand temperatures up to 140&#;C and is used for packing foods to be reheated in ovens up to this temperature. One and two side coatings are available.

Polyethylene terephthalate (PET) heat sealable, moisture and fat barrier. It can withstand temperatures up to 200&#;C and is dual ovenable (microwave and conventional ovens). It is coated only on the non-printing side.

Polymethylpentene (PMP) moisture and fat barrier and not heat sealable. It is, therefore, used as flat sheets, deep drawn trays and trays with mechanically locked corners. It is coated only on the non-printing side.

Ethylene vinyl alcohol (EVOH) and polyamide (PA) heat sealable, fat, oxygen and light barrier. EVOH is moisture sensitive and needs to be sandwiched between hydrophobic materials, such as PE. It can be used as a non-metallic alternative to the aluminium foil layer.

Ionomer resin (SurlynQR  ), a polyolefin with high resistance to fat, including essential oils in citrus fruit, and moisture with very good sealing properties, is used as a tie layer on aluminium foil when applying PE to foil.

Bioplastic extrusion coatings are now available as a PE alternative. This starch-based material is sustainable and meets the EN standard for compostability (Packaging News ).

The process of extrusion is often extended to include extrusion lamination so that a structure, such as paper or paperboard/PE/aluminium foil/PE, can be produced in one operation on an extruder with two extruding units.

Note: By special selection of polymers, e.g. for lids and trays, it is possible to provide easy-open peelable heat-seals.

Printing and varnishing

Usually, printing and varnishing are associated with the appearance of the pack with respect to the visual impact of the pack through colour, information, text and illustration. There are also important functional aspects of printing and varnishing that are important for food packaging.

All the main printing processes are used &#; gravure, flexographic, letterpress, silk screen and lithographic. Paper and paperboard can also be printed by the recently introduced digital process. Choice is influenced by the appearance and performance (functional) needs and commercial aspects, such as order size, lead time and price.

The inks and varnishes may be those described as traditional for the process concerned, based on pigment, resin and vehicle. The vehicle, which transports the pigment and resin from the ink or varnish reservoir to the substrate via the printing plate, varnish pick-up roll, etc., may be an organic solvent, water or a drying oil. For some processes, pigments are replaced by dyes. In recent years, inks and varnishes cured by UV radiation have also become popular, and these materials are extremely inert. They give good rub resistance in wet and dry conditions and are resistant to product absorption. The inks contain pigment, cross-linking resins and a photo-initiator; they are 100% solid and are dry immediately after printing.

The functional requirements include adherence to colour standards, light fastness, rub re- sistance, print-to-print and print-to-pack registration and stability within the conditions of use. For some food products where the print is in close proximity to the food, e.g. chocolate con- fectionery, it is important that no residual solvents from the inks and varnishes, or any other interaction between print and product affects the food product.

Post-printing roller varnishing/coating/laminating

Post-printing roller varnishing and coating is usually associated with high gloss and can involve UV cured varnishes. The process can also be used for the application of functional varnishes to meet specific end use needs. The most common example of this is the application of heat-seal coatings for blister packs.

Another example of coating is the application of wax. This can take a variety of forms:

• dry waxing where molten wax is applied to one or both sides of a printed paper or a printed/cut/creased carton blank. The appearance is a matte finish
• wet or high gloss waxing. Immediately after coating, the printed paper or carton blank is conveyed through very cold water. This causes the wax to set immediately, producing a very high gloss finish

Waxed paperboard provides water and water vapour resistance. It can be heat sealable. The first liquid packaging cartons (&#;) were waxed. Wax is also a good gas barrier and can therefore protect food products against flavour loss or ingress of contamination. The main food applications today are for bread wrap, items of sugar confectionery (paper), frozen food and ice cream (cartons) and fresh produce (corrugated board). Cellulose acetate and OPP laminated to paperboard enhance appearance after printing.

DESIGN FOR PAPER AND PAPERBOARD PACKAGING

Surface design concerns colour, text, illustrations, decoration, finish (gloss or matte) and surface texture. It is achieved by making use of the basic surface properties of the paper or paperboard and through lamination, coating, hot foil stamping, embossing, printing and varnishing. Surface design usually refers to the external surface of a pack but there are situations where the internal surface is important for the overall effect, e.g. the inside surfaces of chocolate and tea bag cartons. Structural design is concerned with the shape of packages. The functional shape is determined  by the needs of the pack, e.g. closure and opening features. Creative shape adds interest for promotional needs where that is appropriate. Paper and paperboard are materials that give a designer freedom to develop imaginative solutions in meeting customer needs. This is due to a number of factors:

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• range of surfaces, in terms of colour and finish, available
• range of strength properties, in terms of fibre type, thickness and method of manufacture, available
• choice of functional coating, lamination, decoration, printing, etc
• ease of conversion into packages in terms of cutting, creasing, folding, gluing, locking, heat sealing, etc
• innovative machinery for conversion and packing