Process for the manufacture of paper webs having CF or CB layers

Details Process for the manufacture of paper webs having CF or CB layers Process for the manufacture of paper webs having CF or CB layers

1994-07-26

1997-01-28

Bell, Janyce

Coating processes

Transfer or copy sheet making

Coating opposite sides or forming plural or nonuniform coats

427150, 427151, 427211, 427358, 427428, B41M 5124

Patent

active

055976123

DESCRIPTION:

BRIEF SUMMARY
The invention is concerned with a process for the manufacture of paper webs having a CF layer for pressure-sensitive recording papers by application of a coating composition containing color-reactive mineral pigment or organic color acceptors.
The present invention is also concerned with a process for manufacturing a paper web having a CB layer for pressure-sensitive recording papers, by application of a coating composition, which contains a color precursor solution enclosed in microcapsules.
Finally, the invention is concerned with a process for manufacturing a paper web containing microcapsules in a layer with color precursor solution and color acceptors for it, by application of a coating composition which contains the microcapsules and color acceptors.
CF (coated front) layers in pressure-sensitive recording paper are defined as color receiving or color acceptor layers, which are usually placed on the top surface of a sheet of paper and produce an image by triggering a color reaction when they are brought into contact with color precursors or color formers.
CB (coated back) layers are layers on the back side of a sheet of paper, containing compounds called color formers or color precursors, which, in contact with color acceptors, form an image upon triggering a color reaction. In the invention, CB layers are defined as those containing a color precursor enclosed in microcapsules.
Color-reactive mineral pigments have found broad application as color acceptors; these are mostly called acid clay and acidic clay, among others, and belong to the group of the bentonite clays. In the present invention, color-reactive mineral pigments are understood to mean the above clays, especially those clays in which montmorillonite is the main mineral, but also other color-reactive clays, such as attapulgite.
In the present invention, organic color acceptors are generally understood to mean acidic oil-soluble organic substances, which lead to a color reaction with suitable color precursors based on basic chromogenic compounds. They include phenolic substances, such as phenol, resorcinol, naphthols and salicylic acid, which can also be alkyl-substituted, and can be present as monomers, oligomers or polymers (resins) and are metal-modified, preferably zinc-modified. For this purpose, phenoldi- or trioxybenzenes and 1- or 2-naphthol are known from DE 14 21 395 C3 as organic color acceptors. DE 12 75 550 B1 states polymers of phenolaldehyde and phenolacetylene as organic color acceptors, while in DE 22 28 431 B2 oil-soluble metal salts of phenolformaldehyde resin, for example, zinc(II) para-phenylphenolformaldehyde resinate are described. DE 16 71 642 B2 identifies phenolcarboxylic acid alkyl esters; according to DE 21 30 456 B2, phenolaldehyde resins with the addition of a vanadium salt or other metal salts are known. Another group of organic color acceptors is concerned with salicylic acid and its derivatives, among which a polymeric reaction product of an aromatic carboxylic acid with an aldehyde or acetylene, for example, a salicylic acid-aldehyde polymer is known from DE 21 52 763 A1. DE 21 47 585 B2 is concerned with salicylic acid or its derivatives with the addition of metal compounds.
The common technical problem of clays used as color-reactive pigments lies in the fact that they exhibit a rheological behavior during the manufacture and processing of the coating composition, which deviates from the behavior of other coating pigments in the paper industry, for example, kaolin or calcium carbonate. Sometimes abnormally high viscosities occur, which limits operations at high solid content. An economically significant problem is that color-reactive pigments are expensive and therefore must be used sparingly. One is forced to use low coating weights, but, at a coating weight below 6 to 6.5 g/m.sup.2, when using the conventional coating method--equalization and metering the applied coating composition with a doctor blade and roller blade--sufficient coverage of the coating base paper is not achieved, so that the coating b

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