Security paper

Claim 1

A method for producing security paper which includes a security feature, which method comprises: (1) supplying paper-making fibres to a paper-machine; (2) incorporating into the paper during its manufacture at least one security feature and producing paper; (3) applying to the resulting paper a sizing agent to size the paper; (4) selecting a substantially transparent coating composition comprising an unpigmented polyurethane which may optionally comprise a functional additive provided that the presence of the functional additive does not increase the opacity of the resulting paper by more than 1% wherein said coating composition being such as to provide a film, when cast on a glass surface, having a Konig hardness of from 15 to 130 seconds, and also passing the water resistance test as defined by the following steps: (a) the total formulation to be used in the coating is cast on a glass plate so as to produce a film with a dry weight of 80 g/m 2 ; (b) the film is initially dried at 23° C. Once it is tack free it is dried for an additional hour at 80° C.; (c) the film is weighed before being wetted and tested for tensile strength, Young's Modulus and is visually checked for any change in its transparency; (d) a sample of the film is boiled in water containing 10 g/litre Na 2 CO 3 for 30 mins; (e) the film in then rinsed in cold water and the steps b) to c) are then repeated; wherein when the film is dried and re-weighed the film meets the following criteria: i) the wet tensile strength and Young's Modulus of the boiled film is not less than 90% of the initial film wet tensile strength and Young's Modulus; ii) the film shows no perceptible loss of transparency, and iii) the dried weight of the film is not less than 98% of the original weight; (5) applying the selected coating composition to one or both sides of the sized paper; (6) and thereafter drying the paper to produce the said security paper.

Claim 2

A method for producing security paper which includes a security feature, which method comprises: (1) supplying paper-making fibres to a paper-machine; (2) incorporating into the paper during its manufacture at least one security feature and producing paper; (3) applying to the resulting paper a sizing agent to size the paper; (4) selecting a substantially transparent coating composition comprising an unpigmented polyurethane which may optionally comprise a functional additive provided that the presence of the functional additive does not increase the opacity of the resulting paper by more than 1% wherein said coating composition being such as to provide a film, when cast on a glass surface, having a Konig hardness of from 15 to 130 seconds, and also passing the water resistance test as defined by the following steps: (a) the total formulation to be used in the coating is cast on a glass plate so as to produce a film with a dry weight of 80 g/m 2 ; (b) the film is initially dried at 23° C. Once it is tack free it is dried for an additional hour at 80° C.; (c) the film is weighed before being wetted and tested for tensile strength, Young's Modulus and is visually checked for any change in its transparency; (d) a sample of the film is boiled in water containing 10 g/litre Na 2 CO 3 for 30 mins; (e) the film in then rinsed in cold water and the steps b) to c) are then repeated; wherein when the film is dried and re-weighed the film meets the following criteria: i) the wet tensile strength and Young's Modulus of the boiled film is not less than 90% of the initial film wet tensile strength and Young's Modulus; ii) the film shows no perceptible loss of transparency, and iii) the dried weight of the film is not less than 98% of the original weight; (5) applying the selected coating composition to one or both sides of the sized paper; (6) and thereafter drying the paper to produce the said security paper.