Computerised Ink Paste Mixing: Hubert Textiles Pty Ltd
Hubert Textiles Pty Ltd operates a textile dyeing and printing business. Significant cost savings and environmental benefits have resulted from the installation of a computerised paste mixing system. A payback of approximately 2.5 years was achieved through reduced raw material and waste costs and efficiency improvements.
Hubert Textiles Pty Ltd (Hubert Textiles), trading as Australian Textile Printing Company, is a medium sized family textile printing and dyeing business. The company commenced operating in 1961 and is located in the Melbourne suburb of Brunswick.
The company prints woven and knitted fabric with multi-colour designs (from one to 12 colours) using flat and rotary screen printing techniques. Additional dye house facilities enable Hubert Textiles to prepare and/or dye the fabric for printing and to finish the fabric after printing.
The printed fabrics are used by a range of customers for the manufacture of bedlinen and associated products, clothing and household accessories.
The screen printing process requires the colour (print paste) to pass through a stencil (the screen) onto the fabric. The print paste used for textile printing is an aqueous suspension of uncoloured stock emulsion, to which colour pigment and other chemicals (auxiliaries) are added (to provide colour fastness and other required end use properties).
The former system involved weighing the chemicals and auxiliaries by hand according to a pre-determined recipe, adding them to the paste and then mixing using a high speed mixer. This coloured paste was then strained through a mesh filter and delivered to the printing machine for use.
At the completion of the print run any left-over paste was either kept for re-use or disposed of to the sewer. The paste containers were also washed with water and the resultant waste water was also discharged to the sewer.
Cleaner Production Initiative
The cleaner production initiative implemented by Hubert Textiles has involved the introduction of a fully automatic, computer controlled paste colour mixing and dispensing system (Stork Brabant’s IPS automatic paste dispensing system). The system uses a variable speed gear pump to accurately dispense specified weights of different paste components. After adding all the required recipe components for a particular paste a label is printed and fixed to the paste bucket.
The system regularly circulates the various paste components from the storage tanks through the piping system and back to the tanks to prevent settling of solids and to maintain homogenous mixtures.
Advantages of the Process
The benefits from this system have included:
- more accurate colour matching;
- less wastage of chemicals and pigments;
- increased ability to re-use leftover paste;
- reduction in the quantity of water discharged to effluent;
- reduction in the quantity of chemicals discharged to effluent; and
- increased overall efficiency of the printing operation.
The specific benefits from the introduction of the computerised colour dispensing system are discussed in more detail below:
Sampling involves printing small pieces of test fabric for colour and design approval by customers. Small quantities of paste are mixed for use in the printing of test pieces. It had always been difficult to weigh out these small quantities of paste. In the past this was overcome by using less concentrated solutions of pigments so that reasonable quantities could be weighed out. The operators used to mix in unit amounts of 1, 2 or 3 kg for example, because this made the recipe calculations easier and a minimum amount of paste was required for a screen even if only a very small amount was actually printed onto the fabric.
The new system has significantly improved the ability to mix small quantities of paste with a very high degree of accuracy. This has enabled smaller quantities to be mixed rather than an amount which is larger than necessary.
The new paste dispensing system has completely eliminated the need for additional filtering of the paste. This has eliminated a source of paste loss and eliminated the waste water associated with washing the mesh filters.
The new system allows tracking of residual paste left over at the end of a print run. The system is capable of recording and tracking these residual amounts and recalling them next time the same or similar colour is being printed. It is also able to adjust the shade of residual pastes to allow them to be used for different colours. This is an improvement on the previous situation where excess paste was either mixed to produce low grade black pigment or disposed of to sewer.
The system has also reduced the total amount of excess paste by using process parameters to more accurately calculate the paste requirement.
The new system has eliminated many of the inherent inaccuracies in colour matching that arose with manual mixing. There was often a difference between the colour in production compared to that produced during sampling, therefore the recipes were modified slightly using a standard modification factor. In addition each printing machine produced different colour variations. The new colour mixing system has been programmed to take this into account automatically and this has resulted in a much greater degree of colour reproducibility.
In addition some colours were occasionally considered off-shade and had to be adjusted after printing commenced. This required screens and other equipment to be washed while the necessary adjustments were made. Approximately 5 per cent of the 11500 colours mixed every year required adjustment. The wastage of paste and generation of effluent associated with this has been eliminated with the new system. Errors in weighing out pigments in both sampling and production have also been eliminated.