Following is the difference between hard ink and soft ink:
1.Hard ink usually printing for hard/rigid materials, like glass, plastic, metal, ceramic, wood, etc.
2.Soft ink with flexibility and ductility, usually printing for soft/flexible materials, like leather, canvas, flex banner, soft pvc, etc. The image will be no cracks no matter how you fold or bending,with better extension stretch ability.
3.If use soft ink for hard materials, you will see the image with poor adhesion. If use hard ink for soft material, you will see the split when bending.