NO137533B - COPYING MATERIALS. - Google Patents

Description

The present invention relates to copying material equipped with acid-reactive phenol formaldehyde resin as a reactant for colorless chromogenic dye precursors, for. development of a readable color.

Oil-soluble phenol-formaldehyde novolak resins, preferably those derived by condensation of a para-substituted phenol with formaldehyde, have long been used with great economic success for the production of acid-reactive copying materials.

sheets that can develop color in base-reactive, colorless, chromo-

gene dye precursors such as crystal violet lactone (CVL). Such resins and their use are e.g. described in Norwegian patent no. 112,873.

The acid-reactive copy sheet described in

British patent no. 1212731 denotes an improvement of the copying material in relation to the first-mentioned patent. According to the latter patent, there are acidic water-soluble metal salts such as zinc chloride in the sheet coating, in a mixture with particles of oil-absorbing kaolin clay and oil-soluble resin particles of phenol-

formaldehyde. The combination of metal salt and kaolin and phenolic resin provides • improved intensity and fading resistance to the developed color in copy prints made with base-reacting colorless chromogenic dye precursors. A clear synergistic effect was found, the improvement being greater than that which could be calculated by adding together the improvements in intensity and bleaching resistance caused by each of the three agents separately (kaolin, zinc chloride and phenolic resin). Thus, certain water-soluble salts and certain oil-soluble resins in admixture with kaolin on copy receiver sheets represent an improvement in the field.

It has now been found that a further improvement in copying speed and intensity and/or fade resistance can be achieved if both the metallic part and the acidic resin form parts of the same oil-soluble molecule and both are available for the color development reaction in oil solution. This can be achieved by using certain oil-soluble metal salts of phenol-formaldehyde resins. Such salts can be produced by replacing part of the phenolic protons in the phenol-formaldehyde resin with certain metal ions to form a metal resin, also called a metal-modified resin.

The modified resinous copying material according to the present invention has a further advantage compared to previously mentioned copying materials where novolaks are used in combination with water-soluble metal salts. Finely divided novolak particles are usually glued to paper with a binder of boiled starch and latex such as styrene-butadiene latexes, but novolaks in combination with zinc chloride or other water-soluble salts cannot be suitably bonded to paper with latexes and/or a binder of boiled starch, and one therefore requires other binders such as poly(vinyl alcohol). It is difficult to achieve sufficient adhesive force with poly(vinyl alcohol) as the only binder and, moreover, such sheets have poor printing properties in offset presses and with offset inks.

According to the present invention, there is thus provided a copying material comprising a carrier sheet provided with an acid-reactive phenol-formaldehyde resin material which can give color in base-reactive, colourless, chromogenic dye precursors in solution in a common solvent for both reactants, whereby the dye precursor is either on the same carrier sheet as the acid-reactive material or on a separate carrier sheet, and this is characterized in that the acid-reactive material is an oil-soluble metal salt of a phenol formaldehyde resin which has been prepared in advance and which is dispersed in a liquid carrier prior to coating the copy sheet material.

According to the invention, it is preferred that the salt is a

zinc (II)-paraphenylphenol formaldehyde resinate. It is further preferred that the metal in the salt is chosen from among metals whose ions form complexes with acetylacetone with stability constant-logarithms (loginK .„,.,... <k>corrected to zero ionic strength) of at most 5.5 .

The common solvent for the reactants is located

in a pressure-breakable polymeric material, preferably microcapsules,

and is isolated from one or both reactants when these are on a single support layer. In a copy-pair system consisting of two carrier

sheets, the solvent is located on one of the sheets either alone or together with one of the reactants which are either dissolved in the solvent or isolated from it.

When it comes to the necessary amounts of metal ions that

is to be introduced into the phenol-formaldehyde resins in order to achieve the advantages of the invention, the weight percentage of metal ions in good metallo-resins will vary depending on the selected metal and the selected resin. In general, only small amounts of metal ions (about 1% by weight) need to be introduced to achieve considerable improvement in fade resistance and character intensity. If one chooses zinc(II) as the metal that replaces a phenolic proton in each molecule in a marketed sample of para-phenylphenol-formaldehyde resin with an average of three repeating units per molecule, one can easily introduce a maximum of approx. 6 wt% zinc. Although it is theoretically possible to replace all phenolic protons in phenol-formaldehyde novolacs with metal ions, it is clear from the literature that only approx. one phenolic proton per molecule is readily available for yield, as the other phenolic protons are less acidic due to the fact that they form part of an intra-molecular hydrogen bond. With the term "Exchangeable protons" is meant easily exchangeable protons, i.e. only approx.

one phenolic proton per molecule resin mixture. Thus, the above weight /?-range (1 to 6%) of zinc(II) in the zinc cresinate derived from the special para-phenylphenol-formaldehyde resin will constitute a metal ion yield of 15 to 100% of the exchangeable protons. To improve fade resistance and character intensity-

one for the copies, the preferred range for proton exchange or metallization in a phenol formaldehyde novolak is between 30 and

100% of exchangeable protons. For zinc(II) and the special para-phenylphenol-formaldehyde novolacs, this preferred range of proton yield will yield -a metal resin with a composition comprising 2 to 6 wt-# of zinc(II).

The color forming reagent described above for use

with basic chromogens is completely oil-soluble (unlike acid clays and the combined reagents such as para-phenylphenol-formaldehyde resins together with zinc chloride) so that they can be used in many different ways, e.g. particle coating on the base sheet, coating as a solution on the sheet, the coatings in combination with encapsulated oil solvents in or adjacent to the coatings for dissolution and transfer of colorant during use, and coatings of oil solution microdroplets of the resin isolated and contained in organic hydrophilic polymers films such as microcapsules or dried emulsion films.

The following metals as cations in para-phenylphenol-formaldehyde resins have all been shown to improve blister resistance compared to unmodified para-phenylphenol-formaldehyde resins: aluminium(III), barium(II), cadmium(II), calcium(II), cobalt(II ), copper(III), indium(III), magnesium(II), manganese(II), molybdenum(V),

nickel(II), lead(II), sodium(I), strontium(II), tin(II), fit an(IV)-, vanadium(II), zinc(II), and zirconium(IV). You will see the great variety within metal resins that have been tested and that have proven beneficial for reducing the fading tendency of printed characters, - as the metals are found in the groups IA and B, IIA, and B, HIA and B, IVA and B, VB, VIB, VIIB and VIII in the periodic table. The choice of metal for the production of the metal resins as bleach-resistant developers for chromogenic substances seems to be of little importance, as all metal resins, as far as is known, work in this way. Certain cations, namely cadmium(III), zinc(II) and zirconium(II),

provided metal-modified resins that increased the intensity of fresh-printed characters.

The effect of exchange of phenolic protons with metal ions such as zinc(II) on the intensity of the developed color can be seen in the figure. In the figure, curve 10 denotes the absorption within the visible range for a solution of CVL and resin (1 equivalent. CVL to approx. 1.4 equivalents resin), and curve 11 shows the absorption' for a solution of CVL bg zinc-modified resin according to ex. 1 (1 equivalent of CVL to about -1.3 equivalents of metal-modified resin containing 5.0% by weight zinc(II)). The optical density for the peak absorption on curve 11 is approx. 4.7 times the peak absorbance for curve 10. The solvent in both cases was benzene and the concentration of CVL was the same in both cases. Further increase of the absorption peak and therefore of the color intensity can be achieved by exchanging more resin protons with zinc(II), or by adding more zinc-modified resin to the solution, but the effect naturally becomes less apparent as the maximum effect is reached. At the point of maximum effect, the curve 11 can be increased by about 50 times the optical density for k«:itve 10...

In general, it has been found that the effectiveness of metal-modified resins in improving color production in chromogenic dye precursors such as CVL is inversely related to the complexing ability of the metal ion used in the preparation of the metallo-resin. For example, metals that form very stable complexes with acetylacetone, with logarithmic stability constants (loglnK . corrected to zero ionic strength) of over

XU S "C cL Dl J_ 3_ "C 6 "C

about. 5|5" generally do not increase CVL coloration when the metals are used in the production of metallo-modified resins. The metals of more unstable metal acetylacetone complexes, with ion constant-log rhythms of less than ca. 5" 5" will generally be found to increase CVL resin color intensity in solution. Such metal ions and resins are called color-increasing metals and color-increasing metal-modified resins in this text. This means that solutions of CVL and metal-modified resins generally show higher optical densities as the stability constants for the complexes of the selected metals and acetylacetone decrease. It should be noted, however, that there will be wide variation in oil solubility for these color-enhancing metal-modified resins, which will affect the maximum concentration of the dyes that can be achieved in a selected oil. For a selected copying material system, the most suitable metal will be color-enhancing metals whose metallo-resins are easily soluble in the solvent microdroplets used in the copying system's capsules.

In practice, the oil-blacks of colorless, chromogenic dye precursors used in the area of "carbon-free copying paper" are solutions of solid, colorless, basic chromogenic dye precursors in carrier media of oil, with a dielectric constant of approx. 5 or lower. Halogen-substituted aromatic hydrocarbons, alkylated aromatic hydrocarbons and dialkyl phthalates are typical of the oils used as ink media. The metal-modified resins used according to the invention will work well in developing the above-mentioned oily dye precursor hosts. The oil carrier medium preferred in this connection is a medium with a low degree of volatility, such as chlorinated or alkylated biphenyls, which leave a fairly moist impression on the paper surface, rather than a more volatile liquid such as xylene, which readily evaporates and leaves a dry impression . The increase in the sign or impression intensity with metal-modified resins according to the invention is considerably greater in moist or wet impressions than in dry impressions.

In the above description, it has been assumed that the metal-modified resins are coated on a receiving sheet which receives and develops color in liquid dye precursors, but the resins are not limited to this use. There are various ways of arranging the various components of a color forming system on a copying material, which includes oil soluble dye precursors, oil soluble co-reacting polymer resin and a common dissolving oil. Fig. 2 in previously mentioned Norwegian patent no. 112,873 shows a number of such arrangements. All of the metal-modified resins used in this invention can be coated on paper as particulate material or as an impression residue after printing in solution, or mixed into the fibers in the fiber substrate of the paper or the like, or dissolved in oil and encapsulated as solution microdroplets before coating on paper.

Incorporation into paper coatings of metal modified resins, of microcapsules containing a chemically inert oil solvent for the metal modified resin, provides effective transfer sheets for use with receiver sheets containing particles of colorless chromogenic dye precursors. When used, the oil-containing microcapsules will shatter under the printing pressure and release the microdrops of oil which act as a solvent for the surrounding metal-modified resin particles and effectively transfer the formed solution to nearby chromogenic particles which, by the chemical reaction, induce the color in the chromogenic particles. In the examples, the production of both types of transfer sheets containing metal-modified resins is shown: transfer sheets with a surface coating of oil-soluble metal-modified resin particles together with microcapsules containing an inert dissolution layer (Ex. 2) and transfer sheets with a surface coating of microcapsules containing metal-modified

resin dissolved in micro-oil droplets (ex. 3)»

The metal-modified resins can be applied to the substrate sheets in many different ways, among others l) application from eh print solution, 2) application as a superimposed layer under the surface of a fibrous copying material, 3) application as a particulate finely ground powder alone or in combination with an oil-absorbing clay such as kaolin and k) applying as a top layer to a coating of pigment particles such as kaolin clay particles.

Methods of making the metallothiarpix salts suitable for this invention include reacting an oil-soluble phenol-aldehyde resin, preferably a novolac resin of para-substitu-

pea phenol-formaldehyde with a desired metal hydroxide or oxide. Alternatively, a water-soluble metal resinate can be prepared as an intermediate by treating the resin with a strong aqueous base such as aqueous sodium hydroxide, for example, to form an aqueous solution of sodium resinate, followed by treatment of the sodium resinate solution with an aqueous solution of the desired metal salt, eg zinc chloride, to induce precipitation of the desired metallo-resin, in this case zinc resin.

A preferred method consists in reacting an oil-soluble phenolaldehyde novolak melt with the desired metal carboxylate or enolate. This method is described in ex. 1 where a novolak is melted and treated with zinc hydroxybenzoate powder to a zinc resinate plus benzoic acid. When zinc acetylaoetonate is used instead of zinc hydroxybenzoate, zinc resinate is formed in a similar way together with free acetylacetone during the melting reaction. As a variation of this method, a metal salt can be added to the phenol-formaldehyde reaction mixture at the same time as the resin preparation. It should be noted that in acid-catalyzed condensation of monomeric phenols and aldehydes, water and acid are usually distilled off from the reaction mixture as the reaction proceeds. Addition to the condensation reaction environment of an acidic water-soluble metal salt such as zinc chloride will add hydrochloric acid to the distillate and leave the zinc resin as a reaction product in the reaction vessel. To some extent, the latter method will probably include condensation of monomeric metal phenolates (such as zinc phenolates) with aldehydes to form the desired metal resinates.

When the metal-modified resin is to be used in solution as the core material in microcapsules, a particularly favorable method consists in dissolving the selected novolak and a carboxylate or enolate of the selected metal 1 an encapsulation oil. The novolaks used in this invention are sufficiently acidic to compete for the metal ions and act as metallo-resinates even in the presence of the added metal salt anion.

As already mentioned, the copying sheet according to the present invention represents an improvement in relation to the copying sheets described in British patent no. 1212731 in terms of the firmness of the surface. In other words, the surface is more resistant to "chilling". If the coating lacks internal cohesion or does not adhere well to the surface of the substrate, the pressure rollers will absorb fiber particles and coating material from the surface and these particles will settle on the pressure surface. Resistance to such chipping is strongly needed and desired in CF sheets so that they can be text printed for the production of copying forms. The comparable data are as follows:

The above number is called "WP unit er" which denotes the viscosity of the selected ink used in the trial printing at the selected temperature multiplied by the lowest speed of the printing roller that causes observable chipping and The apparatus used for the trial printing is en 11 I. G.T. Tests" described in the article "Surface Strength" in "Paper Tests and their Significance", Mead Corporation 2nd Edition pages 15-16 (1964). It should be emphasized

that a paper with a surface strength or "chilling strength" of approx. kO WP units or more generally will provide satisfactory printing surfaces in connection with a large number of printing inks and printing conditions. A paper with a surface strength of 25-30 WP units may be usable for special printing operations but will not be generally applicable for technical printing. A paper with a surface strength of less than 25 WP units will constitute an unsatisfactory technical quality for almost all types of printing operations.

The following table gives comparative values measured on resin-sensitized CF sheets according to Norwegian patent no. 112,873 and a metal-modified resin-sensitized CF sheet according to the invention, for use with various encapsulated transfer sheets, CB sheets, which release colorless liquid dye-precursor blacks at letterpress or machine printing.

CF sheet: Previously known sheet is a CF sheet of kaolin-phenol

produced according to the previously mentioned patent with 5.5 parts kaolin per 1 part para-phenylphenol-formaldehyde-

hyd resin to a dry coating of 6.7 g/m .

CF sheets according to the invention are manufactured according to

e.g. 1 with a slightly changed dry composition: zinc-

modified resin (12.0), kaolin clay (60.0), silica

gel (3.0), calcium carbonate.(9>0), styrene-butadiene-latex binder (7»5) in boiled starch binder (8.5). The dry composition was slurried to 30% solids and coated as before to a dry coat-

weight of 7»^ g/m • The zinc modified resin had 5.0 wt-# zinc(ll) in the resin or approx. 90-100$ of the available protons exchanged with zinc(ll).

Sheet: ARO sheet has 4.9 S/m microcapsules containing CVL

(1.5 parts) dissolved in high-boiling chlorinated biphenyl

alkane (3:l) and benzoleucomethylene blue (BLMB) (l.25

parts).

DPO sheets have k, k g/m 2 microcapsules of CVL (l.5 parts)

dissolved in diphenyl oxide-high-boiling alkane (2:1), and BLMB (1.25 parts).

DOA sheets have 5|2 g/m <2> microcapsules of CVL (1.5 parts)

in solution in dioctyl adipate-alkylated benzene (2:1) and BLMB (1.25 parts).

DOP sheets have 3»8 g/m 2 microcapsules of 2<1>anilino-6•-diethylamino-3'-methylfluorane (2 parts) dissolved in dioctyl phthalate high-boiling alkane (2:1) and BLMB (0, 5 parts).

The CB sheets used for the experiment were of such a type

type that the delivered recipient sheets had the same amount of dye by weight per surface area as possible, for comparison

purpose.

Experiment: TI stands for "Typewriter Intensity", typewriter intensity

site, and is equal to 100 times the ratio between reflection from the printed type divided by the background reflection.

A TI value of 100 thus indicates no visible darkness and

a lower TI value indicates a darker or more intense sign.

Column (l) indicates TI values read 20 minutes later

typewriting. A time of 20 minutes has been selected

: so that all prints will be fully developed and so that differences in printing speed (development speed)

will not give rise to erroneous character intensities.

Column (2) indicates TI values for fully developed de-

print aged by hanging on the wall for 3 weeks out-

set for air, natural and artificial lighting, ambient temperature and humidity. This is a measure of environmental stability

the smallness of the developed inks on the special CF sheets.

Column (3) gives TI values read 20 minutes later

printing in a typewriter, on CF sheets aged 3

weeks on the wall before printing. This is a measure of

The stability of the CF sheets with respect to developing

color in chromogenic dyes during and after they are exposed to the surrounding environment.

Column (4) gives instantaneous TI values (i.e. measured immediately after writing) on freshly produced sheets.

Column.(5) gives instantaneous TI values for sheets after the above 3 weeks of aging on the wall. A co-

equation between columns (4) and (5) gives a measure of a loss of pressure speed in aged sheets.

The above table indicates the typewriter intensities

a measure of different properties of the CF sheets for comparison,

these are:

(a) Primary typewriter intensity, the total color which

^can be developed on a freshly prepared CF sheet (versus a given CB sheet) - Column (b) Fading, the stability of the colored image after exposure to the environment - column (2) compared to column (l).

(c) Power drop, reduced ability of a CF sheet to produce

cold color in dye precursors on CB sheet after exposure of CF sheet to ambient environment - column (3) compared to column (l)o

(d) Print speed for fresh sheets - column (4) together

compared with column (l)o

(e) Print speed for aged sheets - column (5) together-

compared with column (3)"

(f) Decreased printing speed during aging - concept (d)

compared with term (e).

The invention will be better understood from the examples below where all quantity ratios are on a weight basis if nothing else is indicated.

Example 1.

A mixture of 2 kg of para-phenylphenol formaldehyde resin and 400 g of zinc hydroxybenzoate was heated and stirred for 1 hour under helium gas at an elevated temperature. The temperature was gradually increased from room temperature to approx. 200 to 220°C during approx. 45 minutes and then set aside to cool for approx. 180°C during the next 15 minutes. After the reaction was finished, the hot zinc resinate was poured out of the reaction vessel and set aside for cooling and curing. The cured resin was milled under water to a fine powder suitable for coating as particles on paper substrates. The zinc content of this metallo-resin (after discarding and not counting a small amount of inorganic sludge which was insoluble in oil and was present in the reaction product) was 5% by weight.

A paper coating slurry containing 30% solids was prepared by mixing the following ingredients:

Glued paper (49 g/m 2 ) was coated using an air knife (air pressure 0.193 kg/cm 2 ) and dried by passing it through a fan oven at high speed and medium temperature for 12 seconds. 88°C, to a dry coating of 5-9 g/m .

Marketed "NCR paper", CB sheets, with capsule coatings containing oil microdroplets of crystal violet lactone (CVL) and benzoyl leucomethylene blue (BLMB), were paired with the above CF sheets for a character producing transfer sheet pair.

Example 2.

The coating slurry from e.g. 1 was coated in an amount of 5.9 g/m 2 on a paper surface which already had a coating (3.7 g/m 2 ) of oily microcapsules glued with a binder of boiled starch.

This copy sheet was paired with a second sheet of paper that had been dipped

in a 2% solution of CVL in alcohol and dried to a CVL residue on the sheet, with the coated side of the copy sheet facing said second sheet. When the uncoated surface of the copying sheet was written on with pencil or pen, a copy of the writing appeared on the second sheet as a result of oil transfer of metal modified resin from the coated surface of the copying sheet to the CVL-containing sheet.

Example 3.

A metal-modified resin solution was prepared

by dissolving 50 parts of 1,2,4-trimethylbenzene, 10 parts of para-phenylphenol formaldehyde resin and a solution of 14.5 parts of zinc naphthenate in 25 parts of low volatile hydrocarbon solvent and dispersing the oil solution in an aqueous medium into droplets of approx. 3.5 micron mean diameter. The solution was encapsulated and the capsules coated on glued standard paper 49 g/m 2 (to a dry coating of 3.7 g/m 2 capsules) using as a binder 1 part poly(vinyl alcohol) per 10 parts capsules. The sheets coated with capsules containing metal modified resin were paired with CVL sensitized sheets to form transfer replica pairs. Writing by hand or with a typewriter on the uncoated surface of the resinous capsule-coated transfer sheet paired with the CVL-sensitized receiver sheet produced strong blue characters according to the printing pattern on the receiver sheet.

Example 4.

Self-contained pressure-sensitive copying sheets, i.e. simple

sheets containing all the color-forming elements, namely metal-modified resin, chromogenic dye precursors and isolated solvent capable of dissolving both reactants, were prepared by coating the metal-modified resin slurry according to ex. 1

on a normal "NCR paper", CB sheet, with capsule coating, or optionally by coating capsules containing metal-modified resin according to e.g. 3 directly on CVL-sensitized sheets according to the example.

Claims (3)

1. Copying material comprising a carrier sheet provided with an acid-reactive phenol-formaldehyde resin material capable of imparting color to base-reactive, colorless chromogenic dye precursors in solution in a common solvent for both reactants, whereby the dye precursor is either on the same carrier sheet as the acid-reactive material or on a separate carrier sheet, characterized in that the acid-reactive material is an oil-soluble metal salt of a phenol-formaldehyde resin which has been prepared in advance and which is dispersed in a liquid carrier prior to coating the copying sheet material. 2. Copying sheet as stated in claim 1, characterized in that the salt is a zinc (II) paraphenylphenol formal dehydresinate. 3. Copying sheet as stated in claim 1, characterized in that the metal in the salt is selected from among metals whose ions form complexes with acetylacetone with stability-constant-logarithms (l°S<->|_o^stability ^orriSed to zero ionic strength) of at most 5>5.