Pad printers, screen printers and UV inkjet printers all can print white over black surfaces.
The choice will depend on what current processes you're using, your budget and your overall design end goals. If you are currently using any of the methods above then yes, you can already print white over black surfaces! You will just need to make sure you have the right ink.
If you are browsing options, here is a quick guide to help you make your decision:
1. Screen Printing: Screen printing white over black surfaces gets a very opaque white, which is very attractive to companies. Overall, it is a widely used process and common for smaller apparel shops. Screen printing, unfortunately, has a long setup time and requires drying of each color before the next is placed. This is because such a large amount of ink is used in screen printing (which is what achieves the bright white).
2. Pad Printing: Pad printing and screen printing can use the same ink (solvent-based ink). However, pad printing uses less ink in the process. This may cause a slight loss in opacity but the registration with pad printing is so fine that you can do what we call a double stamp. Even double stamping will be faster than screen printing. Depending on the material you are printing on, the product may not have to be dried after each print.
3. UV Inkjet Printing: UV inkjet printing is a popular method for those who print on a variety of flat or cylindrical objects. For the most part, if you are only printing white over black surfaces, UV inkjet printing may not be for. If you are printing large parts or many of the same parts, this is a good option. UV inkjet printing uses UV inkjet ink to achieve full-color images on a variety of products. Most recently, strides in white UV curable inks has made this process in the running for having the most opaque white. Vivid White UV curable ink is the latest UV inkjet ink to hit the market.