Polymer product for improving retention of hydrophobic internal sizing agents in manufacture of paper or board

A method for manufacturing paper or board, where a fibre web is formed from an aqueous suspension of fibres, the method comprising:

• providing an aqueous fibre suspension;
• optionally diluting the aqueous fibre suspension;
• delivering the aqueous fibre suspension to a headbox, draining the aqueous fibre suspension on a wire screen to form a wet web of paper or paperboard;
• pressing and drying the wet web to obtain a web of paper or board;
• wherein an internal sizing system is added at least to a fraction of the fibre suspension, the internal sizing system comprising a hydrophobic internal sizing agent as a first component selected from a group consisting of alkenyl succinic anhydride (ASA), alkyl ketene dimer (AKD), rosin sizes and any combination thereof, and
• a water-soluble polymer product comprising amphoteric polyacrylamide as a second component, which amphoteric polyacrylamide has neutral or cationic net charge at pH 7, a weight-average molecular weight of 3,500,000-18,000,000 g/mol and a total ionicity of 4-28 mol-%, and which amphoteric polyacrylamide comprises a crosslinker less than 0.002 mol-%, and wherein the first component and the second component are provided as separate components or as a combination of the first component and the second component.