FI77605B - FOERFARANDE FOER FRAMSTAELLNING AV ETT TRYCKKAENSLIGT SJAELVKOPIERANDE PAPPER. - Google Patents

Abstract

1. Process for the production of pressure-sensitive duplicating paper containing a paper substrate, the surface of which is partly coated with a dye-producing layer of a microencapsulated solution of a dye former in an organic solvent, characterized in that the water-face microcapsules provided with a meltable coating or water-face mixtures of a finely divided meltable powder with the microcapsule powders are electrostatically applied to a paper substrate and then fixed by heat treatment.

Description

1 77605

Method for making pressure sensitive copying paper

The invention relates to a method for producing pressure-sensitive copying paper. In this method, microcapsules with a fusible coating are electrostatically separated on a paper support and then attached.

The reaction copy papers preferably consist of two or more loose superimposed papers, each with a top layer on the back side and a bottom layer on each side with a receiving layer. Thus, there is always one output layer in contact with one receiving layer. The administration layer contains microcapsules in which the core material 15 is a solution of the color-forming agent in an organic solvent, and the receiving layer contains a material which develops the color-forming agent into a colorant. When writing, the capsules break under the effect of high compression of the writing medium and the released nuclear material encounters the receiving-20 layer, so that a copy is created.

The receiving layer generally contains binders and pigments, e.g. active absorbents such as kaolin, attapulgite, montmorillonite, bentonite, acid bleach or phenolic resins. For example, acid-activated dyes can be added to the anti-25 layer and acid-reactive ingredients to the receiving layer.

A further development of these reaction copy papers are "one-component" reaction copy papers. 30 These have a pre-stage of toner, usually in the form of microcapsules, on one side of a single sheet of paper, and at the same time a color developer. When compression now takes place, e.g., with a typewriter or other writing medium, the Kap-35 backing containing the toner precursor breaks and the precursor reacts with the surrounding color developer (cf. U.S. Patent No. 2,730,456).

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According to the longest prior art, the coating of a paper substrate for the production of carbon-free reproduction systems is generally carried out entirely with an aqueous coating composition, as described, for example, in DE-A-1 934 457 and 1 955 542.

The described method has the disadvantage that after applying the coating composition, the water must be evaporated, which requires energy consumption. The need for drying 10 further requires the use of complex and expensive equipment to continuously dry a substrate coated with an aqueous coating compound. Another, but related, problem is the removal of soiled water that arises from fabrication and purification of the aqueous coating composition.

If volatile organic solvents are used in the preparation of the coatings, then the excess solvent must likewise be evaporated to dry the coating.

In this way, solvent vapors are generated, which pose a special danger.

DE-A-1 928 001 therefore proposes to separate dry microcapsules from electrostatic to a wet paper web. This procedure avoids some drying, but with this proposed method 25 only full surface coatings can be performed. In addition, an active binder in an aqueous solution is required to attach the capsules.

Full-surface coatings do not make sense because in most cases only parts of the replica system are utilized.

Therefore, numerous methods for partially applying coating compositions to a paper substrate have become known. Thus, according to the state of the art, aqueous or solvent-containing coatings can be applied in part by means of gravure printing or flexographic printing (see, for example, DE application publication 2 541 001; U.S. Pat. Nos. 3,016,308 and 3,914,511).

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These methods also have the disadvantage that the coatings have to be dried afterwards. For these reasons, for example, U.S. Patent Nos. 3,016,308, 3,079,351 and 3,684,549, as well as DE Application Nos. 2,719,914 and 5,791,935, disclose the mixing of microcapsules with waxes and the coating of paper carriers with such hot melt systems.

Although these proposed measures avoid solvent removal, the waxy coating 10 changes the nature of the paper because the waxes must be applied in relatively large amounts so that satisfactory replicas are still obtained at a microcapsule content of up to 40% by weight.

The present invention is based on the knowledge that dry, su-15 microcapsules with pallet coatings can be electrostatically separated on a paper support in an arbitrary form and attached to it by heat treatment to obtain a partially coated carbon-free copying paper.

The invention thus relates to a method for producing a partially coated carbon-free copying paper by separating microcapsules with an electrostatically fusible coating on a paper carrier and then heat-treating it.

According to the invention, the microcapsules are provided with a coating which melts after a short heat treatment and thus attaches the microcapsules to a paper carrier.

By heat treatment is meant the effect of heat, which on the one hand must not be so large that the microcapsule is damaged and on the other hand not so small that no melting takes place. A suitable temperature is e.g. 50 to 150 ° C, preferably 60 to 120 ° C.

The thermal energy 35 generated at these temperatures corresponds to the thermal energy used in conventional dry copier equipment when burning color powder.

4 77605 The duration of the effect also depends on this thermal energy, so that the higher the energy, the shorter the processing time. It can be quickly determined by a person skilled in the art by simple experiments and depends on the meltability of the coating 5, its tower capacity and the solidification time of the coating. By way of example, mention should be made of a treatment of about 5-30 seconds.

For example, standard rod resistors, IR radiators or microwave-10 devices can be used as heat sources.

Suitable materials for coating the capsules are, for example, wax compounds, thermoplastics or hot-melt adhesives, all of which have softening temperatures of 60 to 120 ° C, preferably 70 to 90 ° C.

Examples of wax pulps are paraffin waxes, ester waxes, polyethylene waxes, stearates, carnauba waxes.

Suitable thermoplastics are, for example, polymers of ethylene, vinylidene, vinyl acetates and copolymers, in particular partially saponified ethylene-vinyl acetate copolymers.

Polyamides, for example, can be used as hot melt adhesives.

Preferred coating agents are carnauba waxes and partially saponified ethylene-vinyl acetate copolymers.

Preferably, the microcapsules can be coated with said ingredients so that they are mixed with the aqueous capsule dispersion in the form of an aqueous, finely divided dispersion or emulsion, and this mixture is then converted into a roast-free powder, for example by spray-drying.

Spray drying of microcapsules is part of the prior art. Likewise, other known drying methods can be used for the preparation of capsule powder.

5 77605 For coating, the coating compositions can also be dissolved in a suitable solvent, mixed with the dry capsules and then the solvent removed.

If a sufficiently fine powder of coating material is available, mixing with microcapsule powders may be sufficient. The amount of coating material is about 5-50% by weight, preferably 10-30% by weight, based on the microcapsules.

The microcapsules coated in this way are then applied by electrostatic methods to the paper carrier in any form and subjected to heat treatment.

Ordinary wood-containing or wood-free paper grades with a basis weight of 40-200 g / m 2 can be used as paper carriers.

Thanks to the anhydrous production method, paper carriers which are not usually suitable for the production of carbon-free waste papers can also be used in accordance with the method according to the invention.

20 The method of electrostatic separation of coated microcapsules makes it possible, on a paper carrier, to partially apply the microcapsules to those parts of the paper carrier which must act as reproductions.

An electric field between the two electrodes produces an ionic current, which in turn electrically charges the coated microcapsules introduced into the electric field. The microcapsules thus charged separate on the paper support when this is located on one of the electrodes.

The electrical separation phenomenon of solids from an air-30 stream is known from many publications (e.g. Simm: Untersuchungen iiber das RUckspriihen bei der elektrischen Taubabscheidung, Chemie-Ingenieur-Technik 31, Vol. 1959 No. 1) and belongs to the prior art.

Examples of carrying out the separation method for dry capsule material are shown in Figures 1-5.

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Figure 1 explains the principle of capsule separation in a constant electric field resulting from a Corona discharge at the tip electrode 1 and the resulting ionic current between the electrode 1 and the collecting electrode 2.

An air stream in which the capsule material 4 is distributed is passed through the blow-in nozzle 3 to the spray zone between the electrodes 1 and 2. The collecting electrode is covered with a sheet of paper 5 on which the capsule material is separated. As the capsules enter the jet field 6, they are charged electrically by the charge carriers 10, in this case negative ions, and are exposed as charge carriers to the equation K = q known as the force of the electric field. In accordance with E. In the equation · K means force, q means charge and E means field force-15 in the direction of the collecting electrode. Both the field and the ion flow are generated by the voltage between the electrodes 1 and 2, which is maintained by the direct current source 7. Under the action of the force K, the capsules are pressed onto the surface of the paper 5 covering the counter electrode. At the same time, a permanent electric current 20 passes through the paper layer to the electrode 2.

A prerequisite for the functionality of the method according to the invention is sufficient permeability of the paper to electric current.

Generally, this condition is met when the resistivity 14 4 14 of the paper is less than 10 ohms. m, preferably 10-10 8 13 25 ohms. m, and particularly preferably 10-10 ohms. m. Under dried conditions, a uniformly dense layer of capsule material separates on a sheet of paper.

Figure 2 illustrates the possibility of separating the capsules in a directed manner on certain parts of the surface of the paper carrier. Namely, if the collecting electrode 30 is constructed such that it comprises insulating portions 8 and conductive portions 9 on its surface, then the ion current leaving the corona is distributed in the jet field 6 so that the charge carriers and thus the capsules are centrally separated only by conductive electrode portions.

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The condition is that the paper 5 does not fall below a certain resistivity. When the paper resistance is too low, the capsules still stand out in the intermediate areas. In the preferred resistance area, a deposition layer is formed so that the structure of the conductor parts is sharply limited. This resistance range is described in more detail above.

Figure 3 shows a more practical variant of the method, according to which the capsule material is deposited on a continuous, strip-shaped paper carrier 10. The material is fed through a funnel-shaped container 10, which is preferably vibrated to facilitate the exit of the material. A vibrating screen can also be used at this point. The strip-like paper web 11 is pulled continuously to rotate over the bearing drum 12, as indicated by the arrows in the drawing. Attached to the drum 12 is a substrate consisting of an insulating layer 13 and a conductor layer 14, which, however, is not uniform but conforms to a design designed for capsule precipitation. There is a commercial material and known method for making such 20-wire layer designs (see printed circuits, copper-coated wire plates). The conductive parts of the base are electrically connected to each other and to the support roller.

For the difference in Figures 1 and 2, the tip-25 electrode 1 is replaced here by a wire electrode 15 fixed parallel to the sheath line of the drum. In order to achieve a corona discharge, the jet receives a voltage of a few kV, e.g. 10 kV, from the voltage source 7. The polarity is in principle irrelevant, but in this case a positive voltage is still preferred because it achieves a uniformly distributed discharge zone over the entire length of the wire.

To secure the separated capsule material, the strip passes through a combustion station 17 where the material is heated and melted by heat rays.

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According to Fig. 4, instead of a metal substrate, a light guide layer can also be used on the drum jacket surface to control precipitation. The light guide layer is an insulator in the dark and a conductor in the light. Irradiation of the zone-5 with a exposure device 20 through the paper provides limited separation zones.

This embodiment has the advantage that the coating distribution can be changed very simply and quickly.

Suitable light guides are, for example, zinc oxide, cadmium sulfide and selenium.

Figure 5 shows a variant in which the light guide 21 is exposed from inside the drum. The light guide is applied to a conductive, transparent, grounded substrate 22. This substrate, which may consist of a vapor-coated film, is supported by a transparent hollow cylinder 23 which is illuminated from the inside by a lamp 24. A partially transparent pattern 25 provides a light guide which acts as a zone of exposure. with unexposed 20 zones as insulator, partial surface exposure.

The microcapsules used to carry out the method according to the invention and the methods for their preparation are largely known. Thus, microcapsules known for a long time can be used, which can be prepared by coacervation or complex co-serving from gelatin and acacia, as well as gelatin and other inorganic and organic polyanions. Various such methods are known e.g. From M. Gutcho, Capsule Technology and Microencapsulation, 30 Noyes Data Corporation 1972.

In particular, the method according to the invention uses microcapsules whose walls consist of polymers, polycondensation and polyaddition products.

The following review is quoted from G. Baxter's publication Microencapsulation, Processes and Applications, 11,977,605, published by J.E. Vandegaer, and discloses a collection of capsule wall polymers known in the art.

5 Crosslinked Capsule Reaction Components Capsule Wall Polymers for the Preparation of Wall Polymers

O O

Polyamides -N-C- -N-H + Cl-C- 10 diamine dicarbonyl-O chloride

Polyurethanes -N-C-O- -O-H + O-C-N-bisphenol diisocyanate

HO O

15 Polysulfonamides -N-S- -N-H + Cl-S- IV 11 o o diamine disulfonyl chloride

O O

20 Polyesters -O-C- -O-H + Cl-C- bisphenol dicarbonyl chloride

O O

Polycarbonates -0-C-O -O-H + Cl-C-Cl 25 bisphenol phosgene

O

• t

Polysulfonates -O-S- -O-H + disulfonyl-

II

O chloride 30

Microcapsules with walls made of special polyacrylates can also be used for the process according to the invention, as described, for example, in DE-A-2 237 545 and 2 119 933.

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Furthermore, phenolic or urea formaldehyde condensates can be used as wall material, possibly also in combination with the above-mentioned capsule wall polymers.

Preferably, the method according to the invention uses microcapsules whose shells consist of polyaddition products of polyisocyanates and polyamines.

Isocyanates used in the preparation of such microcapsules include diisocyanates such as xylene-1,4-diisocyanate, xylene-1,3-diisocyanate, trimethylene diisocyanate, hexamethylene diisocyanate, propylene 1,2-diisocyanate, butylene 1,2-diisocyanate, ethylidene diisocyanate, cyclohexyl 1,2-diisocyanate, cyclohexyl 1,4-diisocyanate, polyisocyanate prepolymers, e.g. the coupling product of hexamethylene diisocyanate and hexanetriol, the coupling product of 2,4-toluene diisocyanate with pyrocatechol, the coupling product of toluene diisocyanate with hexanetriol, the coupling product of toluene diisocyanate compounds.

Other modified aliphatic isocyanates are those based on hexamethylene-1,6-di-isocyanate, m-xylene diisocyanate, 4,4'-diisocyanate dicyclohexylmethane or isophorone diisocyanate, and those containing at least two isocyanate functional groups per molecule.

Other suitable compounds are polyisocyanates based on derivatives of hexamethylene-1,6-diisocyanates having a biuret structure, the preparation of which is disclosed in DE-A-1 101 394 and 1 543 178, and in DE-A-1 568 017 and 1,931,055.

The useful polyisocyanates can be further modified before use for microencapsulation by reaction with di- and trifunctional alcohols such as ethanediols, glycerin or trimethylolpropane or 5 carboxylic acids such as succinic acid, adipic acid, 0.5 molar equivalents of sebacic acid.

Instead of isocyanate groups, carbodiimide, uretdione, ure-10 toniimine, uretidinedione diimine, 4-iminooxazolidinone- (2) -, γ-alkylene-propiolactone can also be present as reactive groups. or cyclobutanedione (1,3) groups.

Thus, for example, polyisocyanate-polyurethonimines, such as those formed by imidating hexamethylene-containing 1,6-diisocyanate containing biuret groups with organophosphorus catalysts and further reacting the carbodiimide groups first formed with isocyanate groups, are useful. with uretone-imine groups. In addition, these iso-20 cyanates can be used in admixture with each other and with other aliphatic and aromatic isocyanates.

Depending on the particular reaction conditions, the resulting modified polyisocyanate may contain significant amounts of oxadiazine trione, triisocyananurate or 25 sym. triazinedione imine as a structural element. Such products are also suitable as shell formers. Particularly suitable are diisocyanates of the formula I.

OCN- (CH_) -N N- (CHO) -NCO

iO 2 n | | 2 n

OC CO., LTD

where n = 3-6.

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Suitable diamines for the reaction with said isocyanates are aliphatic primary or secondary di- and polyamines, such as, for example, ethylenediamine- (1,2), bis (3-aminopropyl) -amine, 5-hydrazine, hydrazine-ethanol- (2), bis (2-methylaminoethyl) methylamine, 1,4-diaminocyclohexane, 3, amino-1-methylaminopropane, N-hydroxyethylethylenediamine, N-methyl-bis- (3-aminopropyl) amine, 1, 4-diamino-n-butane, 1,6-diamino-n-hexane, ethylene- (1,2) -10 diamine-N-ethylsulfonic acid (as alkali salt), N-aminoethylethylenediamine- (1,2) ( diethylenetriamine), bis- (N, N'-aminoethyl) -ethylenediamine- (1,2) (triethylenetetramine), hydrazine and its salts are likewise considered as diamines.

Examples of color formers include triphenylmethane compounds, diphenylmethane compounds, xanthene compounds, thiazine compounds, spiropyran compounds or the like.

Examples of the above groups are as follows:

Examples of the triphenylmethane compound include 3,3-bis- (p-dimethylaminophenyl) -6-dimethylaminophthalic-di-crystal violet lactone, (hereinafter referred to as CVL) and 3,3-bis- (p-dimethylaminophenyl) -25 phthalide (malachite green). lactone).

Examples of the diphenylmethane compound are 4,4'-bis-dimethylaminobenzhydrylbenzyl ether, N-halophenylleucolamine, N-N-naphthylleucolamine, N-2,4,5-trichlorophenylleucolamine, N-2,4-dichloroamine or phenylene-phenylphenylamine.

Examples of the xanthene compound are rhodamine-β-aniline lactam, rhodamine-β- (p-nitroaniline) -actam, rhodamine-γ- (p-chloroaniline) -actam, 7-dimethylamine-2-methoxyfluorane, 7- diethylamine-3-meth-35-oxyfluorane, 7-diethylamine-3-methylfluorane, 7-tl 13 77605 diethylamine-3-chlorofluorane, 7-diethylamine-3-chloro-2-methylfluorane, 7-diethylamine-2,4- dimethylfluorane, 7-diethylamine-2,3-dimethylfluorane, 7-diethylamine- (3-acetylmethylamine) -fluorane, 5,7-diethylamine-3- (dibenzylamine) -fluorane, 7-diethylamine-3 - (methylbenzylamine) -fluorane, 7-diethylamine-3- (chloroethylmethylamino) -fluorane, 7-diethylamine-3- (dichloroethylamine) -fluorane, 7-diethylamine-3- (diethylamine) -fluorane or the like .

Examples of thiazine compounds include N-benzoyl leukomethylene blue, o-chlorobenzoyl leukomethylene blue, p-nitrolbenzoyl leukomethylene blue or the like.

Examples of the spiro compound include 3-methyl-2,2'-spirobis (benzo (f) chromium) or the like.

Solvents that dissolve these color forms include, for example, chlorinated diphenyl, chlorinated paraffin, cottonseed oil, peanut oil, silicone oil, phthalate ester, phosphate ester, sulfonate ester, monophthalenethylidene, monochlorobenzene, partially hydrochloride, further partially hydrazine. ethers, arylalkyl ethers, higher alkylated benzene, and others that can be used both alone and in combination.

Extensions, such as fuel oil, n-paraffins, isoparaffins, are often added to the solvents.

To prepare the microcapsules by the polyaddition method, the colorant and isocyanate 30 are first dissolved in said solvents and this organic phase is emulsified in a continuous aqueous phase which may contain a protective colloid and optionally emulsifiers. An aqueous solution of polyamine is added to the emulsion in a stoichiometric amount relative to the polyisocyanate in the organic phase.

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To emulsify and stabilize the resulting emulsion, protective colloids and emulsifying aids are added to the aqueous phase. Examples of such protective colloidal products are carboxime-5-style cellulose, gelatin and polyvinyl alcohol.

Examples of emulsifiers are oxyethylated 3-benzylhydroxybiphenyl, reaction products of nonylphenol with various amounts of ethylene oxide and sorbitan fatty acid ester.

10 Microcapsules can be prepared continuously or discontinuously. Dispersing devices are generally used to provide a shear gradient. Examples of these are vane, basket, instant mixers, colloid mills, homogenizers, ultrasonic dispersers, nozzles, steel nozzles, supra clay machines. The intensity of the vortex during mixing is primarily decisive for the diameter of the microcapsules obtained. Capsules ranging in size from 1 to 2000 can be prepared. Capsules with diameters between 2 and 20 μm are preferred. The capsules do not clump and have a narrow particle size distribution. The weight ratio of core material to shell material is 50-90: 5-10.

The invention is further illustrated by the following examples: Example a) (Preparation of microcapsules) The preparation of microcapsules took place according to the example of DE application publication 2 738 509.

Accordingly, a 35% aqueous microcapsule dispersion was prepared, the capsule walls of which consisted of a polyaddition product of hexamethylene diisocyanate oxadiazine trione 30 and a diamine. The capsule contents comprised a solution of 2.7% by weight of crystal violet-lactactone and 0.9% by weight of N-benzoyl leukomethylene blue in a mixture of diisopropyldiphenyl and isohexadecane (80:20 by weight). The average capsule diameter 35 was 6.5.

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Example b) (Preparation of coated microcapsule powder) To 100 parts by weight of the aqueous microcapsule dispersion obtained above were added with stirring 32 parts by weight of a 40% aqueous nonionic polyethylene dis-5 dispersion (Hordamer PE 03, Hoechst).

This mixture was then spray dried (supply air temperature 180 ° C, exhaust air temperature 80 ° C). An anti-caking powder was obtained. The average particle size was 7.0 μm in diameter. The resulting powder mixture was applied to a pape-10 concentrator.

Example c) (Preparation of coated microcapsule powder) The microcapsule dispersion a was spray-dried as in b.

The resulting powder mixture was used for precipitation on a paper support.

Example d) (Preparation of coated microcapsule powder) The microcapsule dispersion a was spray-dried as in b. Then, 40 parts by weight of carnauba wax was dissolved in 250 parts of trichloroethane with heating to 40 ° C, and 160 parts by weight of dry capsules were mixed with this solution. The trichloroethane was then evaporated in vacuo.

A free-flowing capsule powder coated with carnauba wax was obtained. The resulting powder mixture was used for precipitation on a paper support.

Embodiment 30 For paper coating, a capsule material coated with carnauba wax is used (Example d). The average capsule size is 8 .mu.m. This material is fluidized in a stream of air and blown into the discharge space of the device of Figure 2 between the tip electrode and the plate-like counter-electrode. The surface of the counter electrode is divided into insulating fields 8 and 8 conductive fields 9, whereby the conductive fields are connected to each other and to the voltage source 7. This electrode is covered with a sheet of paper which is to receive a capsule layer. The female resistance of the paper is 10 ohms. m. The distance between the tip and the plate is 10 cm. There is a voltage of 30 kV between the electrodes connected to the voltage source 7. The tip is positive. When the voltage is first applied and then the capsules are fed into the discharge state, a thin, even layer of capsules is formed in a fraction of 10 seconds at the points of the paper located on the conductive parts of the counter electrode. After this step, the coated paper is removed from the substrate and taken to a heater where it is heated to 150 ° C for 10 seconds. The wax coating of the capsules then melts on the surface of the paper and thus fixes the capsule layer. A functional reaction retardant paper is obtained.

In a similar manner, the capsule materials of Examples a-c) were used. Functionally reactive 20 paper papers were also obtained.

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Claims (6)

17 77605 A method of making a pressure-sensitive copying paper comprising a paper backing having a surface partially coated with a colorant layer consisting of a microencapsulated solution of a color former in an organic solvent, characterized in that the anhydrous melt-coated or finely coated melt-coated anhydrous mixtures of powder 10 and microcapsule powder are applied electrostatically to a paper carrier and then fixed by heat treatment. Method according to Claim 1, characterized in that waxy masses, thermoplastics or hot-melt adhesives with a softening temperature of 60 to 120 ° C are used as the fusible coating for the microcapsules. Process according to Claim 2, characterized in that carabuba waxes and / or partially saponified ethylene-vinyl acetate copolymer are used as coating. Method according to one of Claims 1 to 3, characterized in that the paper carrier 2 has a basis weight of 40 to 200 g / m 2. Method according to one of Claims 1 to 4, characterized in that the resistivity of the paper carrier 4 14 is 10 to 10 ohms. m. Process according to one of Claims 1 to 5, characterized in that the heat treatment is carried out by heating at 50 to 150 ° C.