FAQ on Screen Printing Inks
The printing on dark substrates can be done in two different ways:
- Using water based opaque inks
- Using water based inks for Discharge printing
Dimensional stability of the paper
Condition the paper in the oven in order to eliminate the humidity in the same conditions used to dry the colours. This step is essential before printing the first colour of the transfer.
Paper storage
The paper must be stored in a dry place, protected from humidity, during the various production intervals (e.g. printed paper put in a plastic bag).
Paper “bending” – printing with water based inks
Steady the paper before to start printing. Use polyester substrates which are more suitable for printing with water-based inks.
The screen mesh is not stretched enough
Use screens which have a stretching tension between 18 and 22 N/cm.
Product pot-life
After 6-8 hours the product loses its features and is no more printable.
Too high working temperatures
Minimize to the bare essentials the power of the drying fans once the machine is set.
Wrong curing
Check the curing conditions which, for a silicone ink, must be 130°C for 3 minutes.
Surface treatment of the printing substrate
Make sure that the substrate hasn’t been treated with products which make it unsuitable for printing.
Wrong mixing ratio
Check the percentage of the catalyst.
Too low oven temperature
Check the real oven working temperature, which should be around 150°C.
Too high carpet speed
For an ideal curing, the printed product must stay in the oven for 2-3 minutes.
The ink hasn’t been properly thinned
Avoid to add too much thinner not to compromise the ink stability.
The thickness of the photoemulsion is unsuitable
Adjust the photoemulsion thickness on the screen, by changing the application process.
Light loss
The light loss of a white mesh can cause resolution loss. Use a coloured mesh, a yellow one for example.
Printing parameters
Adjust “out of contact”, speed and printing pressure. Eventually check also the screen tension.
Too high ink viscosity
Add some reactive thinner to reduce the viscosity and mix properly before use.
Check the edge of the squeegee
Make sure that this edge is completely smooth, without any scratches. Otherwise adjust the outline or eventually change the squeegee.
Presence of lumps or dry residues in the photoemulsion
Do not mix an old product with a new one. If necessary, pre-emptively filter the product.
The mesh hasn’t been properly degreased
It is recommended to accurately clean the mesh, by using Uniclear-105 (for operating indications, please refer to the technical data sheet).
Presence of oil or grease in the working tools
It is recommended to accurately clean all the tools before use.
Wrong selection of the ink
Select an opaque ink according to the effect you want to obtain.
Wrong selection of the number of screen threads
Reduce the number of th/cm according to the drawing, in order to increase the amount of deposited ink.
The adhesive is too dry
The adhesive, as for the other colours which make up the transfer, must be dried but not cured. Therefore, please check the drying conditions of the adhesive.
Unsuitable transferring conditions
Pressure, timing and temperature are fundamental parameters, therefore they need to be suitable. If it is not possible to increase the pressure, then increase the transferring time.
Wrong detachment of the transfer
Handle the garment carefully before the transfer detachment. If the transfer paper tends to rise while moving the garment from the press, the image outlines could remain detached from the garment.
The ink hasn’t been properly thinned
Avoid to add too much thinner not to compromise the ink stability.
Wrong operating parameters
Check the out of contact, the pressure and the printing speed and the squeegee tilt angle.
Wrong use of the adhesive
The adhesive used to stick the mesh to the frame has not been prepared properly. Check the percentage of the catalyst.
Drying time
Make sure the adhesive is completely dry before taking off the screen form the tension system.
Use of aggressive products
Avoid extended contacts between the screen and the washing solvents.
Bad observation of the time instructions
Avoid, if possible, to prepare the screen for the printing on the same day in which it has been stuck.
Lack in screen cleaning
Clean the frame before tensioning the screen
The photoemulsion is not perfectly dry
Let the coated screen dry completely.
The screens are not perfectly dry
Check the efficiency of the air re-circulation into the drying oven.