EP0678399A1 - Colour-developer for carbonless copy paper - Google Patents

Abstract

In a colour developer for a self-copying writing paper based on a swellable laminar silicate, (a) the amt. of swellable laminar silicate is 50-100 wt.%, and (b) the laminar silicate has a swelling vol. of 5-30 mol, w.r.t. a suspension of 2 g in 100 ml of water, and a specific surface below 140 square m/g.

Description

The invention relates to color developers for carbonless papers which adhere to the paper base (base paper) without or with very little addition of binder.

Carbonless carbonless papers or reaction carbonless papers have been known since the early 1950's. Today they are used in large quantities in bank and freight forms, delivery notes, invoices etc. Usually they consist of two or more stacked paper sheets, wherein the respective upper on the back of a color donor layer (CB = c oated b ack) having respective lower on the front of an ink receiving layer (CF = c oated f ront). The main constituent of the color donor layer are dense-walled microcapsules made of gelatin, polyurethane, melamine formaldehyde and similar substances, which contain solutions of dyes in the so-called leuco form. These are only weakly colored Dye precursors, predominantly from the class of di- or triphenylmethanes, thiazines, spiropyrans or fluorans, act as electron donors (Lewis bases) and can be converted into the dye form in a chemical reaction using electron acceptors (Lewis acids). Lewis acids of this type are in the dye receptor layer in the form of acidic phenolic resins, zinc salicylates or acid-activated clay minerals, for example acid-activated smectic layered silicates. If the walls of the microcapsules concerned are now destroyed when writing a carbonless copy due to the pen pressure, the capsule content - the dye solution - is released and developed on the Lewis acidic receiver layer, a copy being produced. Particularly suitable color developer pigments can be produced by acidic activation of clay minerals, such as attpulgites or preferably smectic layered silicates, such as bentonites.

Calcium bentonite, that is to say a layered silicate, the negative layer charges of which are compensated for by calcium ions at interlayer sites, is preferably used. In the activation process, which is carried out by boiling with mineral acids, usually hydrochloric acid or sulfuric acid, the bentontite is chemically changed: firstly, the interlamellar-bound Ca²⁺ is replaced by 2H⁺ in an ion exchange step, secondly, the layer lamella is attacked from the edges and the central, octahedrally coordinated Al³⁺, Fe²⁺, Fe³⁺ and / or Mg² + ions are more or less dissolved and washed out depending on the activation conditions.

The resulting product can be described as a combination of residual layer silicate with voluminous, amorphous silica bound at the edges. It is characterized by very high specific surface areas of about 300 m² / g (measured according to the BET method), a high adsorption capacity and pore volume, due to the presence of many acidic ones Centers (Brönstedt and Lewis acids), where the development of the dyes takes place catalytically, as well as lack of swelling capacity.

To fix these high-surface pigments on the base paper, unusually high binder use of up to 25 parts per 100 parts of pigment is required. Part of the binder is adsorbed on the surface and in the pores of the activated bentonite and is therefore not used for pigment fiber fixation. This proportion of binder even has a very negative influence on the color developer potential of bentonite, since it partially blocks and passivates the active, catalytic centers. The high binder requirement of these pigments is therefore economically and technologically disadvantageous (problematic recycling of the waste paper and of the rejects).

Furthermore, large amounts of low-concentration waste acids with considerable proportions of dissolved metal ions, such as Al³⁺, Fe³⁺, Mg²⁺, Ca²⁺ etc. arise during the activation process. These have to be complex, e.g. precipitated by neutralization and disposed of in landfills. This is considered to be ecologically disadvantageous.

EP-A-0 572 037 discloses a coating pigment for coating printing substrates, in particular paper and cardboard, which contains at least one swellable layered silicate which can be fixed on the print substrate essentially without a binder, the proportion of the swellable layered silicate being at least 30% by weight .-%, and the swelling volume of the coating pigment is 5 to 30 ml, based on a suspension of 2 g of coating pigment in 100 ml of water. Such a coating pigment can be used to produce an aqueous coating color with which a printing medium can be coated on one or both sides.

However, this document contains no evidence that the coating pigment described is used as a color developer for carbonless papers could be suitable since the known color developers based on layered silicate, as stated above, are consistently acid-activated layered silicates.

Surprisingly, it has now been found that color developers for carbonless papers can be developed on the basis of swellable layered silicates which, because of their inherent adhesion, are fixed on the paper backing without - or with only very little use of binder.

The invention thus relates to a color developer for carbonless paper based on a swellable layered silicate, which is characterized in that the proportion of swellable layered silicate is 50 to 100 wt .-%, and that the layered silicate has a swelling volume of 5 to 30 ml, based on a suspension of 2 g in 100 ml of water, and has a specific surface area of <140 m² / g.

The indicated swelling volume is very important. If the swelling volume is lower, i.e. <5 ml / 2 g, the adhesive force is no longer sufficient for the coating pigment to be fixed on the base paper without binder. Higher swelling volumes of> 30 ml / 2 g cause very poor rheological behavior with very low coating colors. The specific surface area of <140 m 2 / g turns out to be a further critical parameter for the color developers according to the invention, since color developers with higher surfaces can no longer be processed without a binder.

The CF lines obtained with the color developers according to the invention can also be recycled much better than the conventional lines known to date. Furthermore, there is no or only a very small amount of waste acid, so that the ecological balance can be significantly improved.

The proportion of the swellable layered silicate is preferably approximately 50 to 100% by weight, in particular approximately 70 to 90% by weight.

The rest consists of impurities that cannot swell, such as feldspar, mica, kaolin, dolomite, etc. in very fine-particle form. These contaminants can generally no longer be removed with the coarse-grained contaminants (grit). They do not interfere, but rather contribute to reducing the swelling volume of the layered silicate to the claimed range, since certain layered silicates in pure form have a swelling volume greater than 30 ml.

2Na⁺).The layered silicate is preferably bentonite, beidellite, nontronite, saponite, hectorite or a mixture thereof. These layered silicates can be largely dispersed in the individual lamellae in aqueous suspension under the action of shear. Because of their ability to form numerous hydrogen bonds and because of their platelet-like structure, these have a high degree of adhesion to paper fibers, so that they can be fixed in order quantities of about 0.5 to 3 g / m 2 without binder on a paper support, such as coating base paper. Due to the platelet-like structure, they continue to form a barrier on the surface that largely prevents the leuco dye from penetrating the paper. It is particularly preferred to start from calcium bentonites, the swellability of which has been improved by treatment with alkali compounds, in particular with sodium compounds (ion exchange Ca²⁺

2Na⁺).

The ion exchange can be carried out in the usual way with soda. However, the activation is preferably carried out with a mixture of soda and magnesium hydroxide, with sodium aluminate and / or with water glass. With the help of these substances, the color development capacity is surprisingly increased.

Furthermore, doping when activated with Lewis acids in amounts of about 5 to 100 mmol / 100 g has a very positive effect on the color reactivity. In general, salts of alkaline earths, zinc, cadmium, aluminum, zircon, titanium and silicon (e.g. as SiCl₄) are used as Lewis acids. The preferred Lewis acids are salts with the cations Mg²⁺, Zn²⁺, Al³⁺, Zr⁴⁺ and mixtures thereof.

Another possibility for increasing the color reactivity was the blending with certain substances. In one embodiment, the color developer according to the invention is preferably blended in proportions of 1 to 50% by weight, in particular 5 to 30% by weight, with amorphous silica and / or amorphous silicates, such as calcium silicate, calcium hydrosilicate, magnesium silicate or sodium aluminum silicate.

In this case, it may be appropriate to add small amounts of binders, such as styrene-butadiene latex, in amounts of 1 to 10% by weight, preferably about 5% by weight. It is therefore possible to work with significantly less binder than with conventional color developer pigments, which require about 22 to 25% by weight of binder.

If higher coat weights are to be achieved than the stated 0.1 to 3 g / m², e.g. 4 to 8 g / m² - the normal coating weight range for CF papers - the use of the above-mentioned amount of binder is recommended.

Furthermore, it has been found that the running properties and the dispersibility of the color developer according to the invention can be further improved if he uses hydrocolloids, e.g. of polyvinyl alcohol or guar, in amounts of 0.5 to 5% by weight, preferably 0.5 to 3% by weight.

Furthermore, the color developer according to the invention can be used in a ratio of 5 to 50% by weight, preferably 10 to 30 % By weight, blended with conventional, acid-activated layered silicates. The binder content of the color developers can be greatly reduced even in the case of relatively highly acid-activated layered silicates. Furthermore, the color developers according to the invention can also be blended with known coating pigments, such as kaolin or CaCO₃. These blends can be applied from aqueous suspensions with solids contents of 10 to 50% by weight, preferably 15 to 35% by weight, to coating units, such as the gravure coater or to film presses. It is of course also possible to order blade coaters. Spray technology can also be used. Here, the former coating units are preferred for low-gram lines of 1 to 3 g / m², while the blade coater can be used for higher orders of 4 to 8 g / m².

The color developers according to the invention can be completely or partially cationically charged by reaction with a cationizing agent. The cationizing agent is preferably a quaternary, monomeric, oligomeric or polymeric organic ammonium compound, such as a dicyandiamide formaldehyde condensate or polydate mac (poly-diallyldimethylammonium chloride).

The invention further relates to an aqueous coating color comprising the color developer defined above, the solids content being between about 5 and 50% by weight, preferably between about 15 and 35% by weight.

The pH of the aqueous coating slip is preferably about 6.5 to 9.5, in particular 7 to 8.

The invention further relates to a paper which is coated with a color developer or a coating color, as defined above. The application weight of the color developer is preferably 0.5 to 3 g / m². The color developer is preferably with an application weight of 1 to 3 g / m² applied to wood-free, wood-containing or waste paper-containing coating base paper.

The invention is illustrated in a non-limiting manner by the examples below.

Example 1 (a - d)

• a) 4 Gew.-% Natriumaluminat
• b) 6,5 Gew.-% Wasserglas 37/40
• c) 3 Gew.-% Soda / 0,4 Gew.-% Mg(OH)₂
• d) 3 Gew.- % Soda

in einem Doppelwellenkneter 5 Minuten aktiviert. Das Produkt wurde nach schonender Trocknung bei 90 °C in einem Umlufttrockenschrank auf einen Wassergehalt von etwa 10 % getrocknet und in einer Schlagrotormühle langsam vermahlen.White calcium bentonite of Turkish origin was suspended in water at 15% by weight and freed from coarser impurities (“grit”) by purification using a hydrocyclone. The grit-free fine material with a montmorillonite content of around 90% (the rest of the fine-particle impurities could no longer be cleaned using the hydrocyclone) was thickened by vacuum filtration to a water content of around 30 to 50% and with

• a) 4% by weight sodium aluminate
• b) 6.5% by weight of 37/40 water glass
• c) 3 wt .-% soda / 0.4 wt .-% Mg (OH) ₂
• d) 3% by weight of soda

activated for 5 minutes in a twin-shaft kneader. After gentle drying at 90 ° C., the product was dried in a forced-air drying cabinet to a water content of about 10% and slowly ground in a beater rotor mill.

• Quellvolumen:
  Ein kalibrierter 100 ml-Meßzylinder wird mit 100 ml destilliertem Wasser gefüllt. 2,0 g der zu messenden Substanz werden in Portionen von 0,1 bis 0, 2 g langsam auf die Wasseroberfläche gegeben. Nach dem Absinken des Materials wird das nächste Quantum aufgegeben. Nach Beendigung der Zugabe wartet man eine Stunde und liest dann das Volumen der aufgequollenen Substanz in 1 ml/2g ab.
• Spezifische Oberfläche:
  Die Messung wurde nach der BET-Methode durchgeführt. Es wurde nach der DIN 66132 gearbeitet.
• pH-Wert:
  Der PH-Wert wird mittels einer Glaselektrode nach DIN ISO 7879 ermittelt.
• Streichfarbe:
  Die aktivierten Bentontite wurden durch 5-minütige Scherung am " Ultra Turrax" zu Suspensionen mit Feststoffgehalten von 7,5 bis 35 % in Wassser verarbeitet und bei pH-Werten von 7 bis 8 auf holzfreies Streichrohpapier (45 g/m²) bei Strichgewichten von etwa 3 g/m² gerakelt. Die Bestimmungen des Strichgewichtes erfolgte durch Rückwägung.
• Strichhaftung:
  Das gestrichene und bei 50 % rel. Luftfeuchte äquilibrierte Papier wurde auf einer Länge von 15 cm mit einem 20 mm breiten Klebstreifen ("Tesa"-Streifen) beklebt, der durch Auflegen eines Gewichtes mit einem Druck von 50 kg/cm² für 30 sec. fixiert wurde. Nach zügigem Abziehen des Klebestreifens wurden die Menge und Verteilung der herausgerissenen Strichpartikel visuell beurteilt. In der Tabelle bedeutet

  +++

  völlige Fixierung des Striches; keine Strichpartikel werden abgelöst;

  ---

  keinerlei Haftung des Striches, vollständige Ablösung.

• Farbreaktivität (Kontrast) Das mit aktiviertem Bentonit gestrichene und bei 50 % rel. Luftfeuchte äquilibrierte CF-Blatt wurde zusammen mit einem auf dem Markt erhältlichen schwarzschreibenden CB (enthaltend Kristallviolettlacton als basischen kationischen Farbstoff) in einem Laborkalander entwickelt; am Ry-Filter eines Elrepho-Gerätes (Fa. Zeiss/Datacolor), wurde der Farbkontrast als Differenz des RyWertes von CF-Strich und Kopie ermittelt: $$\text{Kontrast = Ry/CF -Ry/Kopie}$$
  

The relevant data for the products are summarized in Table I. They were determined as follows:

• Swelling volume:
  A calibrated 100 ml measuring cylinder is filled with 100 ml of distilled water. 2.0 g of the substance to be measured are slowly applied to the in portions of 0.1 to 0.2 g Given water surface. After the material has dropped, the next quantum is given up. After the addition has ended, wait one hour and then read off the volume of the swollen substance in 1 ml / 2 g.
• Specific surface:
  The measurement was carried out according to the BET method. It was worked according to DIN 66132.
• PH value:
  The pH value is determined using a glass electrode according to DIN ISO 7879.
• Coating color:
  The activated bentonite was processed by shearing for 5 minutes on the "Ultra Turrax" to form suspensions with solids contents of 7.5 to 35% in water and at pH values of 7 to 8 on wood-free coating base paper (45 g / m²) with coat weights of approx 3 g / m² doctored. The determinations of the coat weight were made by weighing back.
• Line liability:
  The coated and at 50% rel. Air-equilibrated paper was stuck to a length of 15 cm with a 20 mm wide adhesive strip ("Tesa" strip), which was fixed by applying a weight with a pressure of 50 kg / cm² for 30 seconds. After the adhesive strip had been pulled off rapidly, the amount and distribution of the torn-off line particles were assessed visually. In the table means

  +++

  complete fixation of the stroke; no line particles are detached;

  ---

  no liability of the stroke, complete detachment.

• Color reactivity (contrast) Painted with activated bentonite and at 50% rel. Humidity-equilibrated CF sheet was developed in a laboratory calender together with a black writing CB (containing crystal violet lactone as a basic cationic dye) available on the market; on the Ry filter of an Elrepho device (from Zeiss / Datacolor), the color contrast was determined as the difference between the Ry value of the CF line and the copy: $$\text{Contrast = Ry / CF -Ry / copy}$$
  

Example 2 (a to c) (Comparison)

• a) 0 Teile auf 100 Teile Pigment
• b) 10 "
• c) 25 "

bei Auftragsgewichten von 3 g/m² auf ein 48 g/m² holzfreies Rohpapier gerakelt.A known color developer, fully activated with 40% hydrochloric acid, for carbonless paper based on bentonite ("Copisil Standard" ®, from Süd-Chemie AG) was made from a 35% by weight coating color with the following binder components (DL 950, from Dow Chemicals)

• a) 0 parts per 100 parts of pigment
• b) 10 "
• c) 25 "

with application weights of 3 g / m² squeegee on a 48 g / m² wood-free base paper.

The results are summarized in Table I. It can be seen that the known color developer according to Example 2 only adheres to the paper when the amount of binder used is very high. In contrast, the color developers according to the invention can be processed without binders, so that the contrast produced by the pigments is not impaired by the film-forming binder.

Example 3 (a to c)

The color developer according to the invention, which was activated only with soda, according to Example 1d, was additionally mixed with the activation of 50 mmol / 100 g of the chlorides of Zn²⁺, Al ³⁺ and Zr⁴⁺ and activated and worked up as above.

Table I shows that the doped products have an increased color reactivity.

Example 4 (a to f)

• a) 10 % Zeolex 123®
• b) 30 % Zeolex 123®
• c) 50 % Zeolex 123®
• d) 30 % Durosil®
• e) 30 % Silio CA®
• f) 30 % Copisil Standard®

Bei Zeolex 123® handelt es sich um ein amorphes Natriumaluminiumsilicat der Fa. Zeofinn OY, Durosil® ist eine gefällte Kieselsäure (Degussa), Silico CA® ist ein Calciumsilicat (van Baerle) und Copisil® Standard ist der in Beispiel 2 beschriebene Farbentwickler der Süd-Chemie AG.The color developer according to the invention according to Example 1 c, which was activated with soda and Mg (OH) ₂, was blended with the following silicates before grinding in the impact rotor mill and worked up as usual:

• a) 10% Zeolex 123®
• b) 30% Zeolex 123®
• c) 50% Zeolex 123®
• d) 30% Durosil®
• e) 30% Silio CA®
• f) 30% Copisil Standard®

Zeolex 123® is an amorphous sodium aluminum silicate from Zeofinn OY, Durosil® is a precipitated silica (Degussa), Silico CA® is a calcium silicate (van Baerle) and Copisil® Standard is the color developer described in Example 2, Süd -Chemie AG.

All blends adhered well to the base paper with only a small amount of binder added (5 parts DL 950 to 100 parts pigment) and gave good contrast values.

Example 5 (a to c)

• a) 3 Teile Mowiol 4-88® (Polyvinylalkohol der Fa. Hoechst)
• b) 3 Teile Meyprocoat 30® (Guar-Gum von Meyhall)
• c) 3 Teile Finnfix® FF10 (CMC von Metsä-Serla)

Die Hydrokolloide wurden hierbei im Anmachwasser gelöst vorgelegt. Wie die Tabelle III zeigt, genügen bereits 3 Teile der Hydrokolloide zur vollständigen Fixierung der Farbentwickler. Die Hydrokolloide wirken auch als Dispergiermittel. Auch bei längerem Stehenlassen der Farbentwicklerdispersion findet keine Agglommeratbildung und keine Sedimentation statt. Deshalb haften die Primärteilchen besser an dem Papierträger.The color developer according to Example 4 c according to the invention, ie the bentonite activated with soda and Mg (OH) ₂ in a 50/50 blend with Zeolex 123®, was incorporated into coating colors which contained the following hydrocolloids as agents for improving the running properties:

• a) 3 parts of Mowiol 4-88® (polyvinyl alcohol from Hoechst)
• b) 3 parts of Meyprocoat 30® (guar gum from Meyhall)
• c) 3 parts Finnfix® FF10 (CMC from Metsä-Serla)

The hydrocolloids were initially dissolved in the mixing water. As Table III shows, 3 parts of the hydrocolloids are sufficient to completely fix the color developer. The hydrocolloids also act as dispersants. Even if the color developer dispersion is left to stand for a long time, there is no agglomeration and no sedimentation. Therefore, the primary particles adhere better to the paper support.

Example 6

• a) 6 Gew.-% (auf Bentonit) Polymin SK® (Polyethylenimin von BASF)
• b) 4,5 Gew.-% Melflock 113® (Dicyandiamid-Formaldehydkondensat von SKW)
• c) 9% Dimethyldistearylammoniumchlorid (Hoechst)

langsam in wäßriger Lösung bzw. Suspension zugesetzt. Das Produkt wurde wie in Beispiel 1a aufgearbeitet und vermahlen.White calcium bentonite was cleaned out as described in Example 1a and activated with 4% by weight sodium aluminate. Only during activation

• a) 6% by weight (on bentonite) Polymin SK® (polyethyleneimine from BASF)
• b) 4.5% by weight of Melflock 113® (dicyandiamide formaldehyde condensate from SKW)
• c) 9% dimethyldistearylammonium chloride (Hoechst)

slowly added in aqueous solution or suspension. The product was worked up and ground as in Example 1a.

According to Table IV, the treatment gave the pigments a positive zeta potential (measured in 0.1% aqueous suspension at pH 8 on the 501 Lazer Zee Meter from Pankem). The cationized pigments 6a-c were coated with the addition of 3 parts HICAT 115® (a cationic potato starch from Roquette) at an application weight of approx. 3 g / m².

Since no suitable anionic, acidic leuco dyes are available on the market, the paper was checked with an acidic, anionic permanent dye. For this purpose, the papers were printed on a laboratory gravure printing device (well depth 1.2 μm) with a 0.2% aqueous solution of Pigmosol black X58®, an anionic dye from BASF. The contrasts were: example Contrast% 1 a 68.5 6 a 74.5 6 b 78 6 c 78

This shows the special affinity of the cationized pigments for acid dyes.

Claims (16)

Color developer for carbonless paper based on a swellable layered silicate, characterized in that the proportion of the swellable layered silicate is 50 to 100 wt .-%, and that the layered silicate has a swelling volume of 5 to 30 ml, based on a suspension of 2 g in 100 ml Water, and has a specific surface area of <140 m² / g. Color developer, characterized in that the proportion of the swellable layered silicate is 50 to 100% by weight, preferably 70 to 90% by weight. Color developer according to claim 1 or 2, characterized in that the layered silicate is bentonite, beidellite, nontronite, saponite, hectorite or a mixture thereof. Color developer according to one of Claims 1 to 3, characterized in that it is doped with a Lewis acid in amounts of 5 to 100 mmol / 100 g. Color developer according to claim 4, characterized in that the Lewis acid is a salt with the cations Zn²⁺, Al³⁺ or Zr⁴⁺. Color developer according to one of Claims 1 to 5, characterized in that it is in a ratio of 1 to 50 % By weight, preferably from 5 to 30% by weight, is blended with amorphous silica and / or amorphous silicates, such as calcium silicate, calcium hydrosilicate, magnesium silicate or sodium aluminum silicate. Color developer according to one of Claims 1 to 6, characterized in that it is blended in a ratio of 5 to 50% by weight, preferably 10 to 30% by weight, with conventional, acid-activated layered silicates. Color developer according to one of Claims 1 to 7, characterized in that it contains hydrocolloids of polyvinyl alcohol or guar in amounts of 0.5 to 5% by weight, preferably 0.5 to 3% by weight. Color developer according to one of claims 1 to 8, characterized in that it is fully or partially charged cationically by reaction with a cationizing agent. Color developer according to claim 9, characterized in that the cationizing agent is a quaternary, momomeric, oligomeric or polymeric organic ammonium compound, a dicyandiamide formaldehyde condensate or polydate mac. Aqueous coating slip containing the color developer according to one of claims 1 to 10, wherein the solids content is between about 5 and 50% by weight, preferably between about 15 and 35% by weight. Aqueous coating slip according to claim 11, characterized in that its pH is about 6.5 to 9.5, preferably about 7 to 8. Paper, characterized in that it is coated with a color developer according to one of claims 1 to 10 or with an aqueous coating color according to claim 11 or 12. Paper according to claim 13, characterized in that the application weight of the color developer is about 0.5 to 3 g / m². Paper according to claim 13 or 14, characterized in that the color developer is applied with an application weight of 1 to 3 g / m² to wood-free, wood-containing or waste paper-containing coating base paper. Paper according to one of claims 13 to 15 in the form of a CF sheet coated with the color developer according to one of claims 1 to 10.