Process of making a water dispersible titanium dioxide pigment useful in paper laminates

Abstract

The present invention relates to a process for making a titanium dioxide pigment having consisting of titanium dioxide and single layer of inorganic surface treatment consisting of aluminum phosphate wherein the pigment is characterized by and isoelectric point which is greater than pH 6 and a negative zeta potential of at a pH of 7.5 or more.

Description

CROSS REFERENCE TO RELATED APPLICATIONS [0001] This application claims the benefit of U.S. Provisional Application No. 60 / 437,142 filed on Dec. 30, 2002 incorporated by reference herein in its entirety.BACKGROUND OF THE INVENTION [0002] Titanium dioxide pigments are used in many applications. One particular application demanding light fastness is the use in paper incorporated into paper laminates for decorative applications. [0003] In this application the titanium dioxide pigmented paper is saturated with a laminating resin and subjected to heat and pressure to produce a hard surface laminate in which oxygen is absent. The titanium dioxide on exposure to UV light tends to gray as the concentration of Ti2+ ions are produced without the continual conversion by air oxidation of the ions back to the Ti4+ state. [0004] Many techniques have been employed to make a light fast titanium dioxide pigment from the use of a calcination step in the pigment manufacture to the use of redox couples ...

AI Technical Summary

Benefits of technology

[0017] In step (c) of the present invention, the addition of aqueous sodium aluminate may be made so that the ratio of the moles of phosphorous added to the moles of aluminum added is from about 0.2 to 0.9; but it is more preferred to make the addition in step (c) 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 0.25 to 0.6, and most preferred that 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 about 0.5.

[0018] In the present invention, the amount of phosphoric acid added in step (c) may be from about 0.23 to 0.52 moles per kilogram of pigment; but is more preferred that the amount of phosphoric acid added in step (c) is about 0.40 moles per kilogram of pigment, and most preferred that the amount of phosphoric acid added in step (c) is about 0.44.

[0019] The present process may be varied and achieve the same result if in place of step (c), (i) first adding the phosphoric acid solution to the mixture from step (a) without the simultaneous addition of aqueous sodium aluminate, and then (ii) adding the solution of the sodium aluminate in an amount sufficient to raise the pH of the mixture from step (i) to a pH of about 7.

[0020] More particularly, the present process produces a light fast titanium dioxide pigment consisting of titanium dioxide and a single layer of inorganic surface treatment consisting of aluminum phosphate wherein the pigment is characterized by an isoelectric point wh

Problems solved by technology

But the use of such oxidation couples may lead to a yellowing of the titanium d