GB2050407A - Colour developer coating colours for carbonless copying papers - Google Patents

Abstract

A colour developer coating colour for carbonless copying paper is prepared by previously blending a dispersing agent with activated clay (colour developer) and then dispersing thus pre-treated solid (powdered) activated clay in water. Thus obtained coating colour has low viscosity and good fluidity and efficiency of coating the coating colour on a support in high concentration can be improved. Furthermore, the surface quality of the coated paper is also improved.

Description

SPECIFICATION Improvements in or relating to coating colours for carbonless copying papers This invention relates to a method of making a colour developer coating colour for carbonless copying paper using a combination of microcapsules containing an electron-donating colourless organic compound colourformerwith an activated clay which is an adsorbent substance capable of developing colour upon adsorbing said colourless organic compound in which said activated clay is previously mixed with a dispersing agent and then the thus pre-treated solid (powdered) activated clay is dispersed in water.

Furthermore, this invention relates to a method for making carbonless copying papers using the above mentioned coating colour as colour developer.

Carbonless copying papers are known and as disclosed in, for example, U.S. Patent Specifications No. 2712507, 2800457,2800458, etc., they utilize microcapsules which contain a solution of an electrondonating adsorbate, colour-reactive, colourless organic compound (referred to as a "colour former" hereinafter) in an organic solvent and an electronaccepting, reactive and adsorbent substance (referred to as a "colour developer").

Hitherto, the microencapsulation is conducted by coacervation, interfacial polymerization, in situ methods, etc. Malachite Green Lactone, Crystal Violet Lactone, Benzoyl Leucomethylene Blue, Rhodamine B Lactam, 3 - dialkylamino - 7 - dial kylamylfluoran, 3 - methyl - 2,2 - spirobi(benzo - [f] chromene) and the like are used as the colourfor- mers. As the colour developers there are used solid acids such as acid clay, activated clay, attapulgite, zeolite, bentonite, etc., phenol resins such aspara tertiary butyl phenol resin,p - phenylphenol resin,p octylphenol resin, etc., organic acid compounds such as succinic acid, tannic acid, malonic acid, maleic acid, gallic acid, etc., aromatic carboxylic acids such as benzoic acid, salicyclic acid, substituted salicyclic acids, naphthoic acid, diphenic acid, etc., and metal compounds thereof.

Of these colour developers the activated clay, phenol resins and substituted salicyclic acids (salts) are used in practice in view of their characteristics.

Of these colourdevelopersthe organic colour developers such as phenol resins and substituted salicyclic acids have the disadvantages that they tend to decompose to develop a yellow discolouration when exposed to sunlight and furthermore coloured letters are low in solvent resistance and sometimes they disappear. On the other hand, the solid acids which are inorganic colour developers have no such disadvantages and papers carrying the coating thereof show excellent shelf stability.As disclosed in Japanese Published Examined Patent Publications No. 2373/66, No. 7622/66 and No. 8811/67, the activated clays used as the colour developer are those which are prepared by treating acid clays or similar clays with mineral acids to elute acid-soluble alumina, iron and other basic components to obtain a surface area of at least 200 m2/g. The activated clays are amorphous even by X-ray observation and large in surface area and have very different properties from pigments for general paper coating.

Dispersing the activated clay in water in practice requires a large amount of water because of its particle shape and surface activity. Kaolin which is a representative clay for paper coating has a fluidity at a concentration of as high as 70% or more as an aqueous dispersion while activated clays become high in viscosity with loss of fluidity and gel at a concentration of about 45%. Considering productivity and energy saving, it is desired to coat in a high concentration, butforthe reason mentioned above it is very difficult to prepare a coating colour of activated clay in high concentration. Therefore, at presend the air knife coating method for coating the coating colour in low concentration has mainly been employed.

The object of this invention is to improve the coatability of coating colours comprising activated clays in high concentration for production of colour developing sheets for carbonless copying papers by reducing the viscosity of the coating colours and thereby increase fluidity.

According to this invention, a coating colour used for production of a colour developing sheet is prepared using solid (powdery) activated clay pretreated by previously blending a dispersing agent therewith, whereby the viscosity of the coating colour satisfactory as to dispersability of activated clay and fluidity can be made low and it can be coated in high concentrations to increase the coatability, to save energy and to increase productivity. Furthermore, it has become clearthatthe qualityofthe surface of the thus coated papers is improved and simultaneously therewith smoothness is improved, smudge (colour stain caused by friction) is reduced and surface strength is increased.

Figs. 1 and 2 ofthe accompanying drawings are rheological graphs of coating colours obtained in Comparative Example 1 and Example 1 hereinafter given.

The activated clays are usually produced by treat- ing acid clays with an acid, washing the thus treated clays with water, drying and grinding them.

There are various methods for blending a dispersing agent with activated clay, e.g., (1) adding the dispersing agent as an aqueous solution to the acid clay which has been treated with acid and washed with water; (2) adding the dispersing agent in powder form to the acid-treated acid clay before being dried; (3) adding the dispersing agent in powder form to the acid clay after drying and grinding the mixture; (4) adding the dispersing agent in powdery form to the acid clay after being ground. Any of these methods can provide good results, but this is never limited to these methods.

As the dispersing agents, inorganic dispersing agents such as sodium tripolyphosphate, sodium hexametaphosphate, sodium pyrophosphate, sodium silicate, etc. and organic dispersing agents such as carboxylic acid type (polyacrylic acid salts and the like), polymaleic acid type (styrene-maleic an hydroxide copolymer and the like), sulphonic acid type (naphthalenesulphonic acid salts and the like), may be used alone or in combination.

A suitable amount of the dispersing agent to be added is 0.1 to 5%, preferably 1 to 2% by weight of the activated clay, but it may be successfully used in an amount of up to 15% by weight When it is less than 0.1%, a sufficient effect cannot be exhibited and when more than 15% a conspicuous effect cannot be obtained.

Especially effective dispersing agents are sodium pyrophosphate and sodium tripolyphosphate. The thus obtained solid (powder) activated clay which has been pre-treated by blending the dispersing agent therewith is dispersed in water to obtain a coating colour, to which known adhesives and additives are added and this is coated on a support such as paper.

When activated clay with which a dispersing agent is blended is used, the dispersability is much improved than when activated clay is dispersed in the ordinary dispersing agent and as a result the viscosity of the coating colour decreases. Furthermore, since the dispersability is good and the property of the coating colour is good, the surface quality of paper coated with the coating colour is excellent and the surface is smooth. Moreover, since the surface quality of the colour developing sheet is good, even if it is rubbed against the sheet surface coated with microcapsules, these microcapsules are mostly not ruptured so as not to cause substantially any colour stain. These effects become conspicuous with increase in concentration of the coating colour, but these effects can also be obtained even when coat ing colours of low concentration are used.

The term "high concentration" in this invention means at least 45% of coating colour and this is lower than the "high concentration" in the general coating.

Preparation of microcapsules 2 parts of Crystal Violet Lactone and 1 part of Benzoyl Leucomethylene Blue were dissolved in 100 parts of SAS Oil (Trade name for a diarylethanetype organic solvent of Nisseki Chemical Co., Ltd.). This solution was emulsified in 160 parts of 10% aqueous solution of an acid-treated gelatin (isoelectric point 7.8). This emulsion was added to a solution of 20 parts of gum arabic dissolved in 1500 parts of water and the pH was made 8.5. The temperature of the liquid was kept at 50"C and the pH was made 4.4 with acetic acid. Then, the liquid was cooled to 10 C. To this liquid was added 20 parts of 37% aqueous for malin solution. This was stirred for one day and then the pH was adjusted to 19 with sodium hydroxide.

Production of carbonless copying paper (colour forming sheet) To 100 parts (solid content) of the above mentioned microcapsules were added 50 parts of a 10% aqueous polyvinyl alcohol (PVA) solution and 30 parts of wheat starch. This liquid was coated on a high quality paper of 40 g/m2 in a coating amount of 5 g/m2 (solid content) by an air knife coater.

Production of carbonless copying paper (colour developing sheet) To 90 parts of an aqueous solution in which 1.5 part of sodium pyrophosphate was dissolved was gradually added with stirring 150 parts of activated clay and the clay was well dispersed in the solution.

Thereafter, 60 parts of 10% aqueous PVA solution and 10 parts (solid content) of SBR latex were added to the said dispersion and this was well stirred. Then, the pH was adjusted to 9.5 with 20% sodium hydroxide. The resultant coating colour of high concentration which was in gelled state was coated on a high quality paper of 40 g/m2 in a coating amount of 8 g/m2 (solid content) by a blade coater. This was taken as Comparative Example 1.

Example 1.

In accordance with the above mentioned method (4) for blending a dispersing agent with activated clay, namely, 1.5 part of powdered sodium pyrophosphate was added to 150 parts of activated clay which had been ground and they were homogeneously mixed to obtain a powdered activated clay which contained sodium pyrophosphate, namely, this was the activated clay pre-treated by blending a dispersing agent therewith. This activated clay was slowly added to 90 parts of additive water with stirring and was well dispersed therein.

Then, 60 parts of a 10% aqueous PVA solution and 10 parts (solid content) of SBR latex were added to the dispersion and this was well stirred. Thereafter, the pH was adjusted to 9.5 with 20% sodium hydroxide.

The resultant coating colour was coated on a high quality paper of 40 g/m2 in a coating amount of 8 gim2 (solid content) by a blade coater.

Example 2 Example 1 was repeated except that sodium pyrophosphate was replaced with sodium tripolyphosphate in an equal amount.

Example 3 Example 1 was repeated except that sodium pyrophosphate was replaced with sodium methacry late in an equal amount.

Example 4 Example 1 was repeated except that sodium pyrophosphate was replaced with sodium naphthalenesulphonate in an equal amount.

Example 5 150 parts of activated clay which had been ground were completely dispersed in 150 parts of an aque oussolution containing 1.5 part of sodium pyrophosphate dissolved therein. Then, this dispersion was dried at 80" to 90"C and thereafter ground to obtain powdered activated clay treated with sodium pyrophosphate. This pre-treated activated clay was slowly added to 90 parts of additive water with stirring and was well dispersed therein. Then, 60 parts of a 10% aqueous PVA solution and 10 parts (solid content) of SBR latex were added to the said dispersion and they were well stirred. Thereafter, thk pH thereof was adjusted to 9.5 with 20% sodium hydroxide. The resultant coating colour was coated on a high quality paper in the same manner as in Example 1.

Test results Thus obtained coating colours and colour developing sheets were subjected to the following tests.

1. Coating colours (1) Viscosity: Viscosity was measured by B type viscometer (manufactured by Tokyo Keiki Co., Ltd.) using rotor No.4 at 60 rpm for 1 minute. Values obtained using Hercules High Share Viscometer (manufactured by Martinson Machine Co., Ltd.) on the samples of Comparative Example 1 and Example 1 are shown in Figs. 1 and 2.

(2) Solid content: Solid content was obtained by drying the coating colour at 110"C for 16 hours and measuring the solid content.

2. Colour developing sheet (1) Smoothness: Smoothness was measured by Beck's smoothness tester manufactured by Kumagaya Riki Co., Ltd. With increase in the obtained values (second), the smoothness is better.

(2) Smudge (colour stain caused by friction): The colour developing sheetwas rubbed against the said colour forming sheet by applying a weight of 300 g/cm2. The degree of smudge which appeared on the colour developing sheet was expressed by reflectance (%) measured by a differential colorimeter manufactured by Nihon Denshoku Co. Ltd. Therefore, the high values means less smudges.

(3) Surface strength: Surface strength was measured using an lGTtesterwith IPI No.4 ink and B spring. The results are shown by "o", "A" and "x" which means "high", "medium" and "low", respec timely.

Results 1. Coating colour Table 1

Btype Solid viscosity content (cups) (O/oJ Comparative Example 1 4550 Example 1 630 51.4 2 760 51.6 3 940 50.9 4 890 51.2 5 5 750 50.9 Table 1 show that the coating colours of Examples 1-5 of this invention have viscosities lower by one order than the coating colour of Comparative Example 1 although the solid contents (%) are nearly the same.

As is clear from Figs. 1 and 2, the coating colour of Comparative Example 1 had a higher viscosity than that of Example 1 with high rotating speed and it had high viscosity and was gelled even with low rotating speed.

2. Colour developing sheet Table2

Smoothness Smudge Surface (second) (%) strength Comparative Example 1 48 89.8 A Example 1 62 92.8 o 2 61 92.7 o 3 60 92.5 o-A 4 59 92.5 o 5 58 92.1 o It is recognised from Tables 1 and 2 and Fig 1 and 2 that use of powdered activated clay pre-treated by mixing a dispersing agent therewith results in very good effects in viscosity of coating colours and smoothness, smudge and surface strength of the colour developing sheet.

Claims (10)

1. A method for making a colour developer coating colour for carbonless copying paper based on combination of microcapsules containing an electron-donating colourless organic compound with an activated clay which is an adsorbent substance capable of developing colour upon adsorbing said colourless organic compound, wherein the colour developer coating colour is prepared using activated clay pre-treated by previously blending a dispersing agent therewith.

2. A method for making a colour developer eoating colour according to Claim 1, wherein the dispersing agent is used in an amount of 0.1 to 15% by weight of the activated clay.

3. A method for making a colour developer coating colour according to Claim 2, wherein the dispersing agent is used in an amountof0.1-5% byweight of the activated clay.

4. A method for making a colour developer coating colour according to any preceding claim wherein the dispersing agent is sodium pyrophosphate and/or sodium tripolyphosphate.

5. A method according to Claim 1 substantially as herein described and exemplified.

6. A colour developer coating colour which has been made by the method claimed in any preceding claim.

7. A method of making a carbonless copying paper using the colour developer coating colour defined in Claim 6.

8. A method according to Claim 7 substantially as herein described and exemplified.

9. A carbon less copying paper which has been obtained by the method claimed in Claim 7 or Claim 8.

10. The invention substantially as herein described.