Use of co-grinding agents in a process to manufacture co-ground natural and precipitated calcium carbonates, suspensions and dry pigments obtained and their uses

A process of manufacturing co-ground GCC and PCC, comprising the stages of:

• 1. preparing
• (a) an aqueous suspension of GCC, optionally comprising at least one dispersing agent and/or at least one grinding aid agent, and
• (b) an aqueous suspension of PCC, optionally comprising at least one dispersing agent,
• 2. co-grinding the aqueous suspensions of GCC and PCC, as prepared in stage 1),
• 3. optionally concentrating the aqueous suspension of the co-ground GCC and PCC, as obtained after stage 2), and
• 4. optionally drying the aqueous suspension of the co-ground GCC and PCC, as obtained after stage 2) or 3),
• characterised in that:
• (a) a co-grinding agent is introduced:
• between stage 1) and stage 2), into the aqueous suspension of GCC prepared in stage 1(a) and/or into the aqueous suspension of PCC prepared in stage 1(b) and/or into a blend of these two suspensions,
• and/or during stage 2) of co-grinding,
• and optionally between stage 2) and stage 3),
• and optionally during stage 3, and
• (b) wherein the co-grinding agent is at least one homopolymer of acrylic acid and/or at least one copolymer of acrylic acid, which is partially neutralised, and of which 50% or less by mole of the total acid functions are neutralized, wherein the co-grinding agent has a molecular weight of 4,000-10,000 g/mole, and wherein the co-grinding agent has a polydispersity index of 1.5-2.5.