Cover element provided with transparent pressure-sensitive adhesive layer

A cover element provided with a transparent pressure-sensitive adhesive layer, wherein:

• the pressure-sensitive adhesive layer is made of a transparent base pressure-sensitive adhesive material and is a single-layer having two principal surfaces opposite to each other,
• the pressure-sensitive adhesive layer comprises:
• a base adhesive zone made essentially of the transparent base pressure-sensitive adhesive material and formed over a given range from a first one of the two principal surfaces of the pressure-sensitive adhesive layer in a thickness direction of the pressure-sensitive adhesive layer;
• and
• a transparent, adherent, refractive index adjustment zone formed over a given range from a second one of the two principal surfaces of the single-layered pressure-sensitive adhesive layer in the thickness direction,
• the base adhesive zone is in contact with the cover element,
• the refractive index adjustment zone includes a material having a refractive index greater than a refractive index of the base pressure-sensitive adhesive material in the single-layered pressure-sensitive adhesive layer,
• the base adhesive zone is free of the material having the refractive index greater than refractive index of the base pressure-sensitive material, and
• a boundary between the refractive index adjustment zone and the base adhesive zone in the pressure-sensitive adhesive layer is formed as an irregular undulating curve.