Paper is the major material for production of corrugated cardboard. In terms of the use and properties, paper may be split into two groups:
Liners - papers for the flat layers;;
Corrugated media - papers for corrugated layers.
Depending on their properties, liners are split into groups:
Kraftliner, referred to as sulphated paper, is obtained mainly from the cellulose pulp (virgin fibres) with a small addition of recycled waste paper pulp. Its greatest advantage consists in its resistance parameters which are the best among all liners. Kraftliners are grey and white. White kraftliners are called topliners. Testliners two later papers consisting mainly from waste paper pulp (even in 100%). They may be in natural colour or coloured. For more advanced overprints white coated testliners are manufactured. Apart from the standard papers described above there are papers with specific properties. They include the following:
- Water-proof papers (aqua liners, aqua fluting) – cellulose paper with an improved resistance to humidity, offered as a substitute for wax paper;
- Fat-proof paper – high resistance to fat or grease penetration;
- Fire-proof paper – provided with incombustibility or ignition-proof features ;
- Barrier type coated paper – paper provided with a protective layer, such as polyethylene, on one or on both sides.
There are two groups of corrugated media:
- Waste paper corrugated media – made exclusively of waste paper pulp. Corrugated media are often added with starch to improve their mechanical properties.
- Semi-chemical (SC) corrugated media – they contain about 30% of waste paper pulp and 70% of semi-chemical pulp from deciduous trees.
The starch glue is used to join particular layers of the cardboard. Its main advantages consist in its biodegradability and renewable resource origin. It is mostly obtained from maize, wheat, and sometimes from potatoes.
The corrugated cardboard is made of a number of paper layers – flat and corrugated - which are glued together. Depending on the number of paper layers we distinguish the following:
- Single-face cardboard (2 layers);
- Single-wall cardboard (3 layers);
- Double-wall cardboard (5 layers);
- Triple-wall cardboard (7 layers).
The flay layers may have natural colouring, i.e. grey and white. In terms of coating the following cardboards are distinguished:
- Grey-white – white (the white layer is external);
The corrugated layers are designated with letters and they are featured by different flute heights, fluting factor and scale. Most often they are grey, white is more rare.
The flute height (A) is the distance from the basis of the flute up to its peak.
The fluting factor is the length of paper before /after corrugating ratio.
The scale (B) is the distance between two neighbouring flute peaks adjoining the same flat surface.
The most often encountered flutes: E, B, and C, less often: D, K, A, F, G, N, O.
The flute heights and the fluting factors are presented in the table below.
|Profil (fala)||Wysokość fali w mm||Współczynnik pofalowania||Podziałka w mm|
|N||0,4 - 0,5||1,11 - 1,18||1,8|
|F||0,7 - 0,8||1,19 - 1,28||2,4 - 2,5|
|E||1,1 - 1,4||1,20 - 1,35||3,2 - 3,7|
|B||2,3 - 2,8||1,26 - 1,48||6,1 - 6,6|
|C||3,4 - 4,0||1,36 - 1,56||7,4 - 8,3|
|A||4,1 - 4,7||1,37 - 1,53||8,7 - 9,5|
This a kind of cardboard which consists of one corrugated and one flat layer. It is provided in reels (rolls) or in sheets. It is used for packing goods with irregular shapes, e.g. glass, furniture and building materials. It is also used for lamination.
It consists of two flat layers and one corrugated layer. It is manufactured and delivered to customers in sheets. It is used for making slotted-type and customised boxes..
The cardboard consists of three flat layers and two corrugated layers. It is manufactured and delivered in sheets. This type of board is used for high resistance slotted-type and customised boxes. The cardboard is made by combination of two different flutes, e.g.: B+C, B+E, C+E, E+E.
The Triple-wall cardboard consists of four flat layers and three corrugated layers. It is manufactured and delivered in sheets to make high resistance slotted-type boxes or octabins.
The following are the major parameters of cardboard:
- Edgewise Crush Test (ECT);
- Flat Crush Test (FCT);
- Bursting strength;
- Puncture Resistance Test (PET);
- Water absorption (COBB test);
- 4-point bending stiffness;
- Flexion of corrugated board (flatness).
It is the mass of a sheet of corrugated cardboard with a 1 sq.m surface area. It is expressed in g/sq.m. This parameters is one of the basic values featuring paper products. The tolerance interval of cardboard may be ± 5%. The span of corrugated cardboard grammages is very broad. It starts with 180 g/sq.m in the case of single-face cardboard, through 280-700 g/sq.m for single-wall cardboard, 480-1450 g/sq.m for double-wall cardboard and finally the triple-wall cardboard, the grammage of which is most often between 1000 and 2000 g/sq.m.
Edgewise Crush Test (ECT)
The Edgewise Crush Test is one of the most important properties of corrugated cardboard. It is expressed in kN/m. This test defines the strength of corrugated cardboard when the edge is under pressure. A rectangular sample (dimensions 100x25 mm, where the 100 mm is perpendicular to the flute and the 25 mm is parallel to the flute) is placed vertically so that the impact of the cramping force corresponds to the actual direction of pressure in the finished packaging. The sample is put to the cramping pressure test till the occurrence of deformations and subsequent loss of strength. The tolerance interval of cardboard is ± 10%.
Flat Crush Test (FCT)
The Flat Crush Test) is run on single-face and single-wall cardboard. It is not carried out on corrugated cardboard with a larger number of flute layers. The test consists in placing a round sample of corrugated cardboard flat between two cramping plates. The pressure is increased till the deformation of flutes. The results are expressed in kiloPascals (kPa). The tolerance interval of cardboard is ± 10%.
This test checks the maximum strength of a single sheet of paper or cardboard to withstand the pressure acting perpendicular to its surface. Determination of the bursting strength consists in application of a uniformly increased pressure on one side of the sample surface and recording the value at which the sample bursts. The results are expressed in kiloPascals (kPa).
During shipment and storage the surfaces of boxes are exposed to various pressures, both internal by the products contained and external. The higher the bursting strength of the cardboard used for production of the packaging, the smaller the risk of damage to the box and the products contained therein.
Puncture Resistance Test (PET)
The test consists in measuring the energy required for an effective puncture of a board sample with a head, which should be a triangular pyramid. This method is applicable to all types of corrugated board. The sample should not be smaller than 175 mm x 175 mm. Puncture strength is expressed in [J]. The tolerance interval of this parameter is ± 10%.
Water absorption COBB
The Cobb test allows the determination of water absorption by paper or cardboard. The sample is exposed to water for a predetermined period of time (between 30 and 1800 seconds). The sample is weighed precisely before and after the test. Increase in the mass is used to determine the level of absorption. The measuring unit – Cobb – defines the volume of water absorbed by 1 sq.m of the tested paper or cardboard over a specified time. Most often the maximum admissible value of this parameter is determined. It usually falls within 30-60 grams per 1 sq.m.
The level of water absorbance is a very important parameter. Water (moisture) considerably deteriorates the strength of paper, hence also of packaging produced from paper. It is assessed that corrugated cardboard loses up to 10% of its strength with each 1% of moisture content. Moisture also causes deformation of cardboard. The product itself, e.g. food or the environment where the packaging is stored may be sources of
4-point bending stiffness
The measurement defines the moment of resistance force per unit of width, exhibited by the cardboard when compressed within the limits of elastic deformation. Bending stiffness, checked in the 4 point test is expressed in newton-metres [N m]; it is one of the few methods allowing the determination of decline in strength parameters as a result of processing. The tolerance interval of this parameter is ± 10%.
Humidity in cardboard is determined as the mass loss in the tested sample after drying to the mass of sample at collection ratio, usually expressed in %.
Flexion of corrugated board (flatness)
Flexion of the sheet is defined as "H" to "L" ratio, where "H" is the height of flexion of the cardboard sheet and ":" is the length of the sheet. It is expressed in %. It should not exceed 4%.
Boxes mad from corrugated cardboard are the best and the cheapest form of packaging of a finished product to be shipped to the customer. They are ideally tailored to the product, thus facilitating the logistics and storage. They protect the product against damage. They provide a free of charge advertising space for the manufacturer, and thus they are easily identifiable and may quickly reach the shop shelves. The more colourful and well done the packaging, the deeper the customer's belief that the product inside is equally perfect. Most certainly packaging from corrugated cardboard contributes to environmental protection. They are made from resources which are 100% renewable, are fit for recycling and they are fully biodegradable.
Depending on their structure, packaging from corrugated cardboard may be split into two types:
Both these types of packaging may have no overprint, or a flexographic overprint (the most popular) and an offset overprint (laminated boxes).
The slotted-type boxes are the simplest packagings in terms of construction as they are manly meant for protection and transport of goods. They may be fitted with carry-handles to make handling the box and its contents easier, or with ventilation openings. They may be glued, stitched or both, without or with flexographic overprint. They are also called classic boxes, American box, RSC (Regular Slotted Container) or FEFCO 0201.
Customized boxes are also referred to as die-cut boxes and have a more complex structure than the slotted-type boxes. They are individually tailored to the customer's needs and to the product which is to be placed inside to be packed. Customized boxes are assembled manually or bound together is a way which ensures automatic unfolding. Contrary to the slotted-type boxes, production of customized boxes requires the use of additional equipment in form of a die. The die consists of plywood covered with rubber dampers and ejectors, with slotting, creasing and perforating knives, adjusted to the size of the specific box.
There is a number of standards which may be used for determination of the type of packaging. The FEFCO (European Federation of Corrugated Board Manufacturers) catalogue is the most often used for this purpose. The FEFCO code consists of four digits used for designation of the packaging model. The FEFCO Federation distinguishes the following types of packaging:
- Commercial rolls and sheets (0100),
- Slotted-type boxes (0200);
- Telescope-type boxes (0300);
- Folder-type boxes and trays (0400);
- Slide-type boxes (0500);
- Rigid-type boxes (0600);
- Ready-glued cases (0700);
- Interior fitments (0900).
Projekt jest współfinansowany ze środków Europejskiego Funduszu Rozwoju Regionalnego w ramach Regionalnego Programu Operacyjnego Województwa Kujawsko-Pomorskiego na lata 2007 – 2013 oraz ze środków budżetu Państwa