The structural and colorimetric properties of the ink are obtained after milling. Dilution enables different additives indispensable to obtaining a high quality finished product to be incorporated. This is the step where the viscosity of the product is adjusted through the addition of thinner or solvent (depending on the type of ink manufactured). The different additions are made under slow agitation in order to correctly homogenise the ingredients and to avoid destroying the pigment / binder cohesion.
The principal manufacturing controls can be carried out on the product at this stage to ensure it meets the final specifications:
• Viscosity: This involves a physical measurement of the fluidity of the ink (which is always defined at a given temperature).
The viscometer enables the rheological characteristics of the ink, such as the flow threshold or the structure, to be determined.
Viscosity measurements:
Viscosity measurements:
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Offset inks
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Drying
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Conventional
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Dilution vehicle(s)
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Petroleum or vegetable based thinner
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Measurement apparatus
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Rotary cone-plate viscometer
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Units
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Poise (Po) (1 Po = 0.1 Pa.s)
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UV inks
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Drying
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UV
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Dilution vehicle(s)
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UV Thinner
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Measurement apparatus
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Rotary cone-plate viscometer
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Cups (Ford, DIN, AFNOR)
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Units
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Poise (Po) (1 Po = 0.1 Pa.s)
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Second(s) (flow time)
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Water based inks
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Séchage
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Conventional
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Dilution vehicle(s)
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Water / Solvents
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Measurement apparatus
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Cups (Ford, DIN, AFNOR)
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Units
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Second(s) (flow time)
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• Tack: The measurement enables the ability of the film to split into two to be quantified. The tack is measured using a temperature controlled tack-o-scope device: this measures the force required to split the ink film.
Splitting of the ink film
• Flow: The ink is deposited on a ther- mostatically controlled plate set at a fixed angle. The distance covered by the ink after a given time enables the fluidity of the ink to be characterised.
• Colorimetry: Colorimetric controls are carried out on each manufactured batch of ink to ensure it complies with the standards. The control may be carried out either visually, under controlled lighting, or by spectrocolorimetric measurement.
> See “Colour and its reproduction”
Other tests may be necessary, depending on the types of inks or the customers’ specifications.
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