Record receiver having plural interactive leaves or a colorless – Having a colorless color-former – developer therefor – or... – Identified electron acceptor
Patent
1995-06-13
1997-06-10
Hess, Bruce H.
Record receiver having plural interactive leaves or a colorless
Having a colorless color-former, developer therefor, or...
Identified electron acceptor
106400, 106416, 106 3116, 106 312, 423326, 4233271, 4233282, 423331, 423332, B41M 5155
Patent
active
056375522
DESCRIPTION:
BRIEF SUMMARY
A. BACKGROUND OF INVENTION
The invention relates to a process for producing neutral to alkali color developer pigments for use in carbon-free copying paper.
Carbon-free self-copying paper or reaction transfer paper has been known since the early 1950s. They are currently used in large amounts in sets of banking and shipping forms, delivery tickets, bills and so forth. Usually they consist of two or more sheets of paper on top of one another, the upper one having a color donor layer on the back (CB=coated back), the bottom one having a color acceptor layer (CF=coated front) on the front. The main component of the color donor layer includes thick-walled microcapsules of gelatin, polyurethane, melamine-formaldehyde and similar substances which contain solutions of dyes in the so-called leuco form. These only slightly colored dye precursors, predominantly from the class of di- or triphenyl methanes, thiazines, spiropyranes or fluoranes act as electron donors (Lewis bases) and can be converted into the dye form with electron acceptors (Lewis acids) in a chemical reaction. These Lewis acids are located in the color acceptor layer in the form of acid phenolic resins, zinc salicylates or acid-activated clay minerals, for example, acid-activated smectic layer silicates. If the walls of the pertinent microcapsules are destroyed by the pressure of the writing instrument when writing on self-copying paper, the contents of the capsules, the dye solution, are released and developed on the Lewis acid acceptor layer, forming a copy.
Especially suitable color developer pigments can also be produced by acid activation of clay minerals, such as attapulgites or preferably smectic phyllosilicates such a bentonites.
Preferably calcium bentonite is used, therefore a phyllosilicate with negative layer charges which are balanced by calcium ions on intermediate layer locations. In the activation process which takes place by boiling with mineral acids, usually hydrochloric acid or sulfuric acid, the bentonite is chemically changed: first, the interlamellarly bound Ca.sup.2+ is replaced in an ion exchange step by 2 H.sup.+. Second, the layer lamella is attacked from the edges and the central octahedrally coordinated Al.sup.3+, Fe.sup.2+, Fe.sup.3+ and/or Mg.sup.2+ ions, depending on the activation conditions, are more or less dissolved and washed out. As the reaction continues these polyvalent cations are partially bound again on or between the negatively charged layers. The product can thus be described as a H.sup.+ /Al.sup.3+ /Fe.sup.3+ /Mg.sup.2+ /Ca.sup.2+ bentonite with voluminous amorphous silicic acid bound to the edges. It is characterized by very high specific surfaces of roughly 300 m.sup.2 /g (measured according to the BET method), high adsorption capacity and pore volume and by the presence of many acid centers (Bronstedt and Lewis acids) on which development of the dyes proceeds catalytically.
The high-surface, acid-activated bentonite with layer structure (x-ray diffraction spectrum) which is essentially still intact, has as a phyllosilicate a pronounced lamellar structure with very high shape factor of >30:1. In aqueous slurries and coating compositions compared to "normal" coating pigments such as calcium carbonate or kaolin, this causes unfavorable flow behavior, characterized by high structural viscosity and thixotropy at average solid contents of roughly 40%. For these reasons it is absolutely essential to disperse, treat, and coat acid-activated bentonites at pH of roughly 7-10 since at that range, the viscosity of these pigments is minimum. The pH is adjusted as usual by adding sodium hydroxide solution. In any case, problems often arise during dispersion since a strongly acid pigment must be distributed in an alkaline-medium. pH shocks occur which are expressed in formation of agglomerates and in thickening.
Thus, with these active pigments even with optimum coating composition preparation, pH control and use of dispersing agents, a solid content of the coating composition of roughly 45% cannot ordinarily be
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Hahn Reinhard
Ruf Friedrich
Cox Scott R.
Hess Bruce H.
Sud-Chemie A.G.
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