Dye-containing water-soluble receptacle and method for producing a coloured aqueous alkali metal cyanide solution

A water-soluble receptacle which is suitable for accommodating an additive or an additive composition and is filled with an additive or an additive composition comprising at least one dye or at least one dye composition,

• wherein the water-soluble receptacle has a wall thickness in a range from 5 to 50 μm, and wherein the water-soluble receptacle comprises a water-soluble polymer composition, wherein the water-soluble polymer composition comprises:
• a) at least one polyvinyl alcohol copolymer P1 having a degree of hydrolysis in a range from 75 to 95 mol %,
• wherein the at least one polyvinyl alcohol copolymer P1 is a copolymer which comprises:
• vinyl alcohol repeating units,
• vinyl ester repeating units, and
• repeating units of at least one comonomer,
• wherein the at least one comonomer is selected from pentaerythritol acrylate and optionally acrylic acid;
• or
• b) at least one polyvinyl alcohol copolymer P1 having a degree of hydrolysis in a range from 75 to 95 mol %,
• wherein the at least one polyvinyl alcohol copolymer P1 is a copolymer which comprises:
• vinyl alcohol repeating units,
• vinyl ester repeating units, and
• repeating units of at least one comonomer,
• wherein the at least one comonomer is selected from pentaerythritol acrylate and optionally acrylic acid;
• and
• wherein b) further comprises at least one polyvinyl alcohol P2 having a degree of hydrolysis in a range from 87 to 95 mol %;
• wherein, in addition to the at least one polyvinyl alcohol copolymer P1 and/or the at least one polyvinyl alcohol P2, the water-soluble polymer composition can additionally optionally contain additive substances;
• wherein the water-soluble polymer composition, in the case of a) in which the water-soluble polymer composition comprises at least one polyvinyl alcohol copolymer P1 and no polyvinyl alcohol P2, has a content of repeating units of the at least one comonomer in a range from in total 10% to 20% by weight, based on the total weight of the at least one polyvinyl alcohol copolymer P1;
• wherein the water-soluble polymer composition, in the case of b) in which the water-soluble polymer composition comprises at least one polyvinyl alcohol copolymer P1 and at least one polyvinyl alcohol P2, has a content of repeating units of the at least one comonomer in a range from in total 10% to 20% by weight, based on the total weight of the at least one polyvinyl alcohol copolymer P1 and the at least one polyvinyl alcohol P2;
• wherein the degree of hydrolysis of the at least one polyvinyl alcohol copolymer P1 and of the at least one polyvinyl alcohol P2 is determined by quantitative 1H NMR spectroscopy;
• and
• wherein the water-soluble polymer composition of the at least one polyvinyl alcohol copolymer P1 and of the at least one polyvinyl alcohol P2 is determined by IR and NMR spectroscopy.