Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
1998-12-01
2001-08-21
Le, H. Thi (Department: 1773)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C106S482000, C106S491000, C427S215000, C427S221000, C427S443200, C428S407000
Reexamination Certificate
active
06277490
ABSTRACT:
The invention concerns a color developer pigment for carbonless copying papers.
BACKGROUND OF INVENTION
Self-copying papers or carbonless copying papers have been known since the early '50s. They are now used in large amounts in banking and freight forms, bills of lading, invoices, etc. They usually consist of two or more sheets of paper, one on top of the other, in which the upper sheet has a chromophore or color donor layer on the back (CB=coated back) and the lower sheet has a dye or color acceptance layer on the front (CF=coated front). The main component of the color donor layer is thick-walled microcapsules of gelatins, polyurethane, melamine-formaldehyde and similar substances that contain solutions of dyes in the so-called leucoform. These only slightly-colored dye precursors, mostly from the class of di- or triphenylmethanes, thiazines, spiropyrans, or fluorans, act as electron donors (Lewis bases) and can be converted to the dye form in a chemical reaction with electron acceptors (Lewis acids). Such Lewis acids are found in the dye acceptance layer in the form of acid phenolic resins, zinc salicylates or acid-activated clay minerals, especially in the form of acid-activated smectitic layered silicates. If the walls of the microcapsules are destroyed during writing on the carbonless copying paper by the writing pressure, the capsule contents (the dye solution) is released and develops on the Lewis acid acceptance layer, forming a copy.
The individual color developer systems have different reaction mechanisms. Thus, the organic products (phenolic resin, zinc salicylate) are partially dissolved by the capsule solvent and the color reaction occurs in a homogeneous, organic phase. The copies so developed exhibit good color stability, even at high humidity (tropical climate) and limited sensitivity to environmental effects (e.g., NO
x
, SO
2
, etc). The relatively slow development of the copies (especially at low temperatures) and severe yellowing of the paper under the influence of light are considered negative, mostly in the phenolic resins.
The acid-activated clays (smectitic layered silicates) are capable of absorbing the dyes and developing them in heterogeneous catalysis, because of their high specific surface areas of about 300 m
2
/g. The capsule solvents are absorbed, in this case, in the pores of the clay. Rapid color development, good light stability and limited yellowing tendency are advantages in the acid-activated clays. On the other hand, a problem is the sensitivity of the copy to high humidity and environmental gases.
Attempts to combine both systems (phenolic resin and acid-activated clay) have recently been observed on the market. Both compounds are combined during coating composition preparation and applied together to the base paper. The papers so produced, however, have a strong yellowing tendency and significant sensitivity to humidity.
It has now been found that the aforementioned problems can be eliminated and the quality of the color developer pigment significantly improved, if the phenolic resin is condensed on the surface of the acid-activated smectitic layered silicate.
SUMMARY OF INVENTION
The object of the invention is therefore a color developer pigment for carbonless copying papers based on acid-activated smectitic layered silicates, characterized by the fact that a phenolic resin is condensed on the acid-activated layered silicate.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The term “acid-activated smectitic layered silicate” is referred to below, in some instances, as “acid-activated clay” for simplicity.
The properties of the “phenolic resin” and “acid clay” are advantageously combined by the color developer pigment of the invention. The color developer pigment according to the invention is characterized by good rheological properties and can be processed with no significant problems with the common coating units.
The acid-activated smectitic layered silicate is preferably derived from a smectitic layered silicate from the group bentonite, beidellite, nontronite, saponite and/or hectorite.
The acid-activated smectitic layered silicate preferably has a specific surface area of about 120 to 360 m
2
/g and a pH value (in aqueous suspension) of about 1 to 5.5.
The specific surface area is determined according to the so-called BET method at liquid nitrogen temperature, described in
J Am. Chem. Soc
. 60 309 (1938) by S. Brunauer, P. H. Emmet and E. Teller (one-point method according to DIN 66 131 and 66 132). The pH value in an aqueous suspension (10 wt. %) is determined by means of a glass electrode according to DIN ISO 7879.
The acid-activated smectitic layered silicate generally has a total iron oxide content from 0.5 to 4.5 wt. %. It has also proven advantageous to dope the acid-activated smectitic layered silicate with Zn
2+
ions.
The phenolic resin, derived from a phenol substituted in the p position, and formaldehyde is preferably condensed on the acid-activated layered silicate. The substituent in the p position is preferably a lower alkyl group, more preferably a tert-butyl group or a nonyl group, a lower alkoxy or oxyalkyl group or a phenyl group. However, other phenol derivatives conventional for production of phenolic resins for carbonless copying papers can also be used.
Another object of the invention is a process for production of the color developer pigment discussed above, characterized by the fact that a solution or emulsion of at least one phenol, preferably a phenol substituted in the p position, is added to a suspension of acid-activated smectitic layered silicate, polycondensation to from the phenolic resin is carried out by adding formaldehyde and the layered silicate coated with the phenolic resin is separated from the suspension.
Condensation of the phenolic resin is preferably run in an aqueous medium by raising the temperature to about 50 to 80° C. as an acid-catalyzed reaction, in which the acid-activated layered silicate can itself serve as catalyst. However, the reaction can also be carried out by reducing the pH value to about 2 by adding an acid, like aqueous hydrochloric acid.
The layered silicate coated with the phenolic resin is preferably separated by filtration, (especially vacuum filtration) and the filter cake is washed with water to remove excess acid and any unconverted formaldehyde. The filter cake is then dried and optionally adjusted by wet grinding to the desired particle size.
A further object of the invention is an aqueous coating composition containing the aforementioned color developer pigment and optionally an extender pigment in a concentration of about 30 to 50 wt. %, preferably about 38 to 48 wt. %, as well as an ordinary binder.
A further object of the invention is a copying paper coated with the color developer pigment and the corresponding coating composition just described. The coating weight of the color developer formulation (color developer pigment according to the invention, optional extender pigment and binder) is preferably about 2 to 8 g/m
2
, especially about 4 to 6 g/m
2
. The paper is preferably in the form of a CF sheet coated with the color developer pigment.
REFERENCES:
patent: 4296948 (1981-10-01), Satoh et al.
patent: 4405371 (1983-09-01), Sugahara et al.
patent: 4867844 (1989-09-01), Dessauer
patent: 4889885 (1989-12-01), Usuki et al.
patent: 5039377 (1991-08-01), Von Raven et al.
patent: 5318939 (1994-06-01), Laver et al.
patent: 5637552 (1997-06-01), Hahn et al.
patent: 2147326 (1995-10-01), None
patent: WO94/26532 (1994-11-01), None
Cox Scott R.
Le H. Thi
Sud-Chemie AG
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