Paper laminates
View Patent ↗The present disclosure relates to a process for making a decorative base paper for a paper laminate comprising impregnating a base paper with a pigment mixture of titanium dioxide and water wherein the titanium dioxide pigment is made by treating a mixture of titanium dioxide pigment and water with a source of phosphorus and a source of aluminum; drying the treated mixture to form a treated pigment, the treated pigment having surface hydroxyl groups; and removing a major proportion of the surface hydroxyl groups of the treated pigment. Preferably the surface hydroxyl groups are removed by thermal treatment, for example at temperatures ranging from 300° C. to 800° C. The source of phosphorus is typically phosphoric acid and the source of aluminum is typically sodium aluminate. The pigment can be characterized by an isoelectric point which is greater than pH 6 and a negative zeta potential of at least 20 mV at a pH of 7.5 or more and wherein the pigment has improved light fastness.
1. A process for making a decorative base paper for a paper laminate comprising impregnating a base paper with a pigment mixture of titanium dioxide and water wherein the titanium dioxide pigment is made by:
(a) contacting titanium dioxide pigment with water to form a mixture having a pigment concentration of from about 14 to 40 weight percent based on the weight of the mixture then adjusting the pH of this mixture to about 7 with aqueous sodium hydroxide;
(b) heating the mixture to a temperature of about 40° C.;
(c) adding to the heated mixture at a rate such that the pH of the resulting mixture is maintained at about 7 throughout this step (c) from about 0.15 to 0.65 moles of phosphoric acid per kilogram of dry pigment and at least a portion of sodium aluminate aqueous solution required to react with the phosphoric acid to form aluminum phosphate;
(d) adding any remaining aqueous sodium aluminate solution required to react with unreacted phosphoric acid to complete the formation of aluminum phosphate simultaneously with a solution of hydrochloric acid wherein the rate of addition of aluminate solution and that of the acid solution is adjusted so that that the pH of the resulting mixture from and in this step (d) is maintained in a range from 5 to 8;
(e) drying the mixture to form a dried treated pigment; and
(f) thermally treating the dried treated pigment for at least about 0.25 hour at a temperature of about 300° C. to about 800° C. to form a thermally treated pigment; whereby the thermally treated pigment exhibits an improvement in light fastness corresponding to a decrease in delta E* (color change) of at least about 40%, based on the delta E* value of the dried treated pigment of step (e).
2. The process of claim 1 further comprising between steps (e) and (f), micronizing the dried treated pigment.
3. The process of claim 1 wherein in step (c), the addition of phosphoric acid and aqueous sodium aluminate is simultaneous.
4. The process of claim 1 wherein in step (c), the addition of phosphoric acid and aqueous sodium aluminate is sequential, with phosphoric acid being added first.
5. The process of claim 1 wherein in step (c), the addition of aqueous sodium aluminate is made so that the ratio of the moles of phosphorous added to the moles of aluminum added is from about 0.2 to about 0.9.
6. The process of claim 1 wherein in step (c), the addition of the amount of phosphoric acid is from about 0.23 to 0.52 moles per kilogram of pigment.
7. The process of claim 1 wherein the titanium dioxide pigment is rutile.