PACKAGING OF DAIRY PRODUCTS

Module 2. Packaging materials

Lesson 4
CHARACTERISTICS OF PAPER, CORRUGATED PAPER, FIBER BOARD AND WOOD

4.1 Introduction

This chapter deals with characteristics of paper, corrugated paper board, fiber board and allied products.

4.2 Paper and Paper Board

4.2.1 Characteristics

• Paper and board are very popular packaging materials. Paper is thin material mainly used for writing upon, printing upon or for packaging. It is produced by pressing together moist fibers, typically cellulose pulp derived from wood, rags or grasses, and drying them into flexible sheets.

• Paper is a versatile material with many uses. Whilst the most common is for writing and printing upon, it is also widely used as a packaging material, in many cleaning products, in a number of industrial and construction processes.

• Paper pulp is produced from wood chips by acid or alkaline hydrolysis. The pulp is suspended in water and beaten with rotating impellers and knives to split the cellulose fibers longitudinally. The fibers are then refined, pressed and passed through heated rollers to reduce the moisture content and then through finishing rollers to give the final surface properties to the paper. Alkaline hydrolysis produces sulphate pulp and acid hydrolysis produces sulfite pulp.

4.2.2 Paper Types, thickness and weight

• The thickness of paper is often measured by caliper, which is typically given in thousandths of an inch. Paper may be between 0.07 millimetres (0.0028 in) and 0.18 millimetres (0.0071 in) thick.

• Paper is often characterized by weight. In using the ISO 216 paper sizing system, the weight is expressed in grammes per square metre (g/m2 or usually just gsm or grammage) of the paper. Printing paper is generally between 60 and 120 gsm. Anything heavier than 160 gsm is considered card. The weight of a ream therefore depends on the dimensions of the paper and its thickness.

4.3 Paperboard

4.3.1 Paperboard

Paperboard is material with a higher thickness than paper, usually over 0.25 mm or 10 points or grammage over 150 g/cm². It can be either single or multi-ply and is most often used in packaging and graphic printing. It is sturdier than paper but is thinner than corrugated board. Paperboard is widely used in today’s society and is used to package many popular items, most notably food products and cigarette, ice-cream packaging. It can be easily cut and formed, is lightweight, and is strong; paperboard is popular in many industries as a packaging option.

4.3.2 Production

Pulp (virgin or recycled) is used to create one or more layers of board which can be coated for a better surface and/or improved visual appearance.

4.3.2.1 General steps of paper making process

1. Pulping

2. Washing

3. Settling

4. Squeezing of slurry

5. Pressing

6. Drying, Calendaring and Sizing

4.3.2.2 Raw materials

1. Hard wood: 0.05 inches (length) e.g. Birch which has short fibres. It is generally more difficult to work with however does provide higher strength.

2. Soft wood: 0.13 inches (length) e.g. Pine and spruce which have typically long fibres.

3. Recycled: Recycled material is collected and sorted and usually mixed with virgin fibres in order to make new material. This is necessary as the recycled fibre often loses strength when reused and gets this from the added virgin fibres. Mixed waste paper is not usually de-inked for paperboard manufacture and hence the pulp may contain traces of inks, adhesives, and other residues which together give it a grey colour.

4. Others: Straw, Hemp, Cotton, Flax

4.3.2.3 Pulping

1. Mechanical Pulping: Mechanical pulping is a two stage process which results in a very high yield of the wood being converted.

2. Chemical Pulping: Chemical pulping uses chemical solutions to convert wood into pulp but yields around 30% less than mechanical pulping. It involves different processes like Soda process, Sulfate/Kraft process, Sulfite process, Semi chemical or Combination process.

4.3.2.4 Bleaching

Pulp used in the manufacture of paperboard can be bleached to increase colour and purity. Virgin pulp is naturally brown in colour because of the presence of lignin. Recycled paperboard may contain traces of inks, bonding agents and other residue which causes a grey colouration. Although bleaching is not necessary for all end uses, it is vital for many graphical and packaging purposes.

4.3.2.5 Plies

Multi ply paperboard generally has higher creasing and folding performance than single ply as a result of layering different types of pulp in a single product. In cases, where the same kind of pulp is being used in several layers, each separate layer is treated and shaped individually in order to create the highest possible quality. The benefits of multi ply paperboard are for example its higher creasing and folding performance.

4.3.2.6 Coating

In order to improve whiteness, smoothness and gloss of paperboard, one or more layers of coating are applied. Coatings are usually made up of: a pigment, which could be china clay, calcium carbonate or titanium dioxide, an adhesive or binder and water.

4.3.3 Grades of paper board

The DIN Standard 19303 "Paperboard - Terms and grades" (2005-09) defines different grades of paperboard based on the surface treatment (first letter), the main furnish (second letter) and the colour (non-D grade) or bulk (D grade only).

Table 4.1 Grades of paper boards

First letter (surface treatment)	Second letter (main furnish)	Number
A = cast-coated G = pigment coated U = uncoated	Z = bleached virgin chemical pulp C = virgin mechanical pulp N = unbleached virgin chemical pulp T = recycled/secondary fibre with white, cream or brown reverse D = recycled/secondary fibre with grey back	(all except D grades): 1 = white reverse side 2 = cream reverse side 3 = brown reverse side (D grades only): 1 = bulk >= 1.45 cm³/g 2 = bulk < 1.45 cm³/g, > 1.3 cm³/g 3 = bulk <= 1.3 cm³/g

Example: GC1 would be a "pigment coated", "virgin mechanical pulp" board with a "white reverse side". Often the used paperboard type would be FBB, which is coated on both sides.

4.3.4 Classifications of paper board

Based on the production process and the source of the pulp, different types of paperboard are produced. The common industry abbreviations are:

1. FBB (Folding Box Board)

2. SBB (Solid Bleached Board)

3. SUB (Solid Unbleached Board)

4. WLC (White Lined Chipboard)

Various types of paper and paperboard containers used as food packaging are shown in Table 4.2.

Table 4.2 Types of paper commonly used as packaging material

No.	Product	Characteristics	Example
1	Kraft paper	Brown, unbleached paper. Good strength and resistant to bursting	Heavy duty bags and sacks A layer in multilayer paper board for increased strength. Viz. Aseptic packaging material in India
2	Bleached paper	White paper, may be glossy. Less strength than unbleached paper	White bags, wrapping paper
3	Vegetable Parchment paper	Translucent paper treated with H2SO4 to gelatinize surface layers	Butter and margarine wrap
4	Greaseproof paper	High-density paper, very smooth surface	Wrapping paper requiring high resistance to grease
5	Glassine	High-density, greaseproof paper. brittle	Over wraps on candy
6	Tissue	Light weight paper produced from most pulps	Light weight and used to protect soft products from dust and bruising
7	Paperboard or cardboard	Compacted paper pulp	Cartons, boxes, trays, separators
8	Corrugated paper board	Paperboard sheets interspersed with paper corrugations	Secondary boxes of many kinds

• Kraft paper is made from at least 80% sulphate wood pulp. It is a very strong paper, which is used to make grocery bags, multiwall bags, shipping sacks, and specialty bags that require both economy and strength for bulk packaging of powders, flour, sugar, fruits, and vegetables. Bleached papers are more expensive and weaker than unbleached ones, and they have excellent printability.

• Vegetable parchment is produced from sulphate pulp, which is passed through a bath of sulphuric acid. It has a more intact surface than kraft paper and therefore has greater grease resistance and wet strength properties than kraft paper. Because of its high grease resistance and wet strength, it is used for packaging butter and shortening.

• Sulfite paper is lighter and weaker than sulphate papers. Greaseproof paper is made from sulfite pulp in which the fibers are more thoroughly beaten to produce a closer structure. It is resistant to oils and fats when dry, but these properties are lost when the paper becomes wet. Packaging applications for greaseproof papers include margarine wraps; french-fry bags, inner liners for multiwall sacks, and a liner in composite cans for packaging frozen juices. Glassine is a greaseproof sulfite paper that is given a high-gloss finish by the finishing rollers. It is used as wrapping material for candy products and certain bakery products. Tissue paper is a soft, nonresilient paper used to protect fruits against dust and bruising.

• A major disadvantage of paper as a packaging material is its poor barrier properties against moisture, gases, grease, and odors. Furthermore, it cannot be heat-sealed. To improve its barrier and heat-sealing properties, paper is often combined with wax, plastic film, metal foil, or a combination of foil and plastic film.

• Paperboard is made in a similar way to paper but is thicker in order to protect foods from mechanical damage. The main characteristics of board are thickness, stiffness, the ability to crease without cracking, the degree of whiteness, surface properties, and suitability for printing. White board is suitable for contact with food and is often coated with polyethylene, polyvinyl chloride, or wax for heat-sealability. It is commonly used to prevent freezer burn in stored frozen products. Pulp containers are made from paper pulp compressed in molds to remove moisture. Pulp containers are used for egg cartons, low-cost food trays, and cushioning of food products.

4.4 Corrugated Paper, Fiber Board, CBX etc

4.4.1 Corrugated fiberboard

• Corrugated fiberboard, also known as corrugated cardboard, is a paper-based construction material consisting of a fluted corrugated sheet and one or two flat linerboards. Corrugated board is the most common form of secondary food packaging and is used by virtually every industry in the manufacture of corrugated boxes and shipping containers.

• Corrugated board has an outer and inner lining of kraft paper with a central corrugating (or fluting) material. This is made by softening kraft paperboard with steam and passing it over corrugating rollers. The liners are then applied to each side using a suitable adhesive. The board is formed into cutouts, which are then assembled into cases at the filling line.
The corrugated medium and linerboard are made of paperboard, a paper-like material usually over ten mils (0.010 inch, or 0.25 mm) thick. Paperboard and corrugated fiberboard are sometimes called cardboard by non-specialists; although cardboard might be any heavy paper-pulp based board.

• Common corrugation / flute sizes are "A", "B", "C", "E" and "F" or microflute. The letter designation relates to the order that the flutes were invented, not the relative sizes. These vary in height and the number of flutes per unit length of board. Flute size refers to the number of flutes per linear foot, although the actual flute dimensions for different corrugator manufacturers may vary slightly. Measuring the number of flutes per linear foot is a more reliable method of identifying flute size than measuring board thickness, which can vary due to manufacturing conditions.

• They can be used alone or in combination with one another to give single-face, single-wall, double-wall, and triple-wall corrugated board constructions. Corrugated board has good impact abrasion and compression strength and is mainly used as secondary packaging containers. The most standard type of secondary packaging material is single wall C flute. High storage humidity may cause delamination of the corrugated material. This is prevented by lining with polyethylene or greaseproof paper or coating with microcrystalline wax and polyethylene.

4.4.1.1 Standard US corrugated flutes

Table 4.3 Standards of corrugated flutes

Flute Designation	Flutes per lineal foot	Flute thickness (in)	Flutes per lineal metre	Flute thickness (mm)
A flute	33 +/- 3	3/16	108 +/- 10	4.8
B flute	47 +/- 3	1/8	154 +/- 10	3.2
C flute	39 +/- 3	5/32	128 +/- 10	4.0
E flute	90 +/- 4	1/16	295 +/- 13	1.6
F flute	128 +/- 4	1/32	420 +/- 13	0.8

4.4.2 Chip board / bogus

• Old news papers, other scrap papers, various sizing material etc are beaten and converted in to paper/ board known as chipboard. Most often it comes with two to three layers of coating on the top and one layer on the reverse side. Because of its recycled content it will be grey from the inside. It is mainly used in packaging of shoes, toys etc.

• Bogus is a paper product which is made from recycled fiber, paper or an inferior pulp to imitate higher quality grades. They are usually grey or light browninsh in colour due to the raw material used. It is used as packaging material, void fill, wipes, bedding & cushioning etc.

4.5 Advantages and disadvantages of wood as a packaging material

• With a good strength-to-weight ratio, wood is an economical structural material.

• It does not require very sophisticated equipment to make a box or crate and for very rigid structures in small quantities it is the material of choice.

• For small packages or for large quantities, however, wood does not lend it self to high speed operations or automatic assembly. It therefore has a high labour factor in relation to material costs.

• It is also bulky and often presents a problem of storage space and shipping cubage.

• If rigidity, stacking, strength, protection from the hazards of shipping and light weight are essential, it is difficult to find a better material than wood.

• But if protection from moisture, rapid assembly, low cost, ready availability or attractive appearance is more important, then wooden containers may not be the best choice.