Glossary
Cartonboard properties
- Brightness
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Brightness is a concept used in two different contexts:
- When referring to image reproduction, brightness describes the intensity of the colours. This is also called luminance, i.e. how light or dark an image is.
- When referring to cartonboard, brightness is expressed as the percentage of light which is reflected from a cartonboard surface at a wavelength of 457 nm (nm = nanometre).
Related Fact files - Bulk
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Describes how bulky (voluminous) the cartonboard is, measured in cubic metres per kilogram (m3/kg).
Cartonboard which is bulky (voluminous) in relation to its weight is said to have high bulk. Compact cartonboard has low bulk. Cartonboard with high bulk generally feels stiffer and thicker than cartonboard with the same grammage but with low bulk.
- Compression Strength
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When cartons are stacked on top of each other the bottom layer naturally bears the greatest load. To avoid the cartons collapsing, the most important property of cartonboard as a material is good compression strength.
Related Fact files - Density
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Describes how compact the cartonboard is, measured in kilograms per cubic metre (kg/m3).
- Dimensional Stability
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Resistance to dimensional changes in a cartonboard sheet due to changes in such properties as moisture content. Dimensional stability is important during printing and conversion to avoid such errors as misregister (see also ”REGISTER”).
- Flatness
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The cartonboard’s ability to remain flat (retain its shape) during printing and converting.
- Gloss
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The more light which is reflected by the cartonboard surface, the higher the gloss. Gloss can be achieved with various varnishing methods.
- Grammage
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The weight of the cartonboard in grams per square metre (g/m²). Paper with a grammage of more than 160 g/m² is normally called cartonboard, since it is first at that level that a fibre-based material can be sufficiently stiff and sturdy to function as packaging. Most cartonboard packaging has a grammage in the range of 200 to 500 g/m².
Related Fact files - Machine Direction
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When cartonboard is manufactured the pulp fibres are aligned parallel to the direction in which the cartonboard web is moving. This means that cartonboard is always stiffer and stronger in that direction. The machine direction is therefore at right angles to the width of the web. In terms of creasability, a crease across the machine direction is better than a crease parallel to the machine direction (See ”Creasing”).
- Opacity
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Opacity is a measurement of the capacity of cartonboard to obscure what lies behind it, and is expressed as a percentage. A high percentage corresponds to a cartonboard sheet with low transparency (high opacity). A cartonboard sheet with 100% opacity is completely opaque. The degree of opacity depends on how well the light is scattered and absorbed by the cartonboard. High opacity is important when printing is done on both sides of the cartonboard sheet.
- Stiffness
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Stiffness is one of the most important properties of cartonboard. The demand for stiffness recurs throughout the entire chain from shipping via the store shelf to the consumer. Cartonboard is the only material which has this ability to offer high stiffness per unit of weight. Without stiffness cartonboard could not fulfil its primary function, which is to protect the contents of the packaging.
Related Fact files - Surface Smoothness
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A measurement of how smooth the cartonboard surface is. A smooth cartonboard surface is important for achieving satisfactory printing and varnishing results.
Related Fact files - Surface Strength
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The cartonboard’s ability to tolerate forces on its surface, for instance from the tackiness of the ink during printing. This is important so that the cartonboard surface is not torn away by the printing ink during the printing process.
Related Fact files - Tear Strength
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The force required to tear a cartonboard sheet along an existing incision. This is important, for example so that a tear strip will work when packaging is being opened.
- Thickness
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The distance between the two surfaces of the cartonboard sheet measured in thousandths of a millimetre (µm). The material used in most cartonboard packaging has a thickness of 350 to 800 µm.
Related Fact files - Whiteness
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The cartonboard’s visual impression of whiteness. Whiteness is expressed by means of a single value.
Related Fact files