"Sizing" SBS Board for metallic ink printing
This is one technique that I have suggested to other users that have limitations on the board. The issue you have is that SBS board is not the best for metallics, it's got a certain degree of absorption and if looked at under a microscope, you would see pits and toughs within the surface of that board, which causes light to scatter differently and causes the metallic to decrease in it's optical properties.
What I would propose is that you size the sheets only in the metallic areas – to do this, either print the transparent white ink as a first pass of your press using the silver printing plate – or, output TWO of the silver ink plates and use one for the white and one for the silver. Using the silver plate will only size the areas where the metallic ink prints, leaving the rest of your job as normal, which would avoid any possible color contamination – due to the opaqueness of the silver inks, the underpinning transparent white should not cause any color change for the metallic.
The biggest issue you have is trapping of the inks. Our silver ink was designed to be printed first down on press, and as such it's not been designed to trap over other inks. Whilst I don't think there will be an issue, as our inks are typically designed for other inks to trap over, so the mechanics of that ink suggest that underpinning will also work without issue. But, if you do have any trapping issues of the silver over that white, then you would need to do a double pass, as suggested above.
As with all printing, this is a "try it and see" kind of thing. With so many variations in inks, pigments, curing methods, humidity, ambient room temperature, press configuration, blankets and chemistry, it's difficult for us to say for sure what your results would be like, but this is why we have our test form file – print that out, one as normal 5 color job, then again by sizing the sheets as mentioned above, and compare the two.
If this works, you would also need to consider printing new swatch books / color charts for your customers. Maybe having two sets of color charts, one done as a normal print job, one with the sheets sized.
What I would propose is that you size the sheets only in the metallic areas – to do this, either print the transparent white ink as a first pass of your press using the silver printing plate – or, output TWO of the silver ink plates and use one for the white and one for the silver. Using the silver plate will only size the areas where the metallic ink prints, leaving the rest of your job as normal, which would avoid any possible color contamination – due to the opaqueness of the silver inks, the underpinning transparent white should not cause any color change for the metallic.
The biggest issue you have is trapping of the inks. Our silver ink was designed to be printed first down on press, and as such it's not been designed to trap over other inks. Whilst I don't think there will be an issue, as our inks are typically designed for other inks to trap over, so the mechanics of that ink suggest that underpinning will also work without issue. But, if you do have any trapping issues of the silver over that white, then you would need to do a double pass, as suggested above.
As with all printing, this is a "try it and see" kind of thing. With so many variations in inks, pigments, curing methods, humidity, ambient room temperature, press configuration, blankets and chemistry, it's difficult for us to say for sure what your results would be like, but this is why we have our test form file – print that out, one as normal 5 color job, then again by sizing the sheets as mentioned above, and compare the two.
If this works, you would also need to consider printing new swatch books / color charts for your customers. Maybe having two sets of color charts, one done as a normal print job, one with the sheets sized.