JPH043314B2 - - 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

[Detailed description of the invention]

The present invention provides a partially coated copy paper as well as a copy paper as described above in which microcapsules having a meltable coating are electrostatically deposited onto a paper substrate and then fixed. The present invention relates to a manufacturing method. Reactive copying paper preferably consists of two or more sheets loosely placed on top of each other, and in each case said sheet has a donor layer on its back.
and in each case the lower sheet contains a receiver layer on top. That is, in each case the supply layer and the receptor layer are in contact with each other. The feed layer contains microcapsules whose core substance is a dye forming agent.
The receiver layer contains a substance that develops the dye-forming agent to form a dye. During writing, the capsule ruptures under the high pressure of the recording device and the core material emerges onto the receiver layer, resulting in the production of a copy. The receiver layer usually contains binders and pigments, such as active absorbents such as kaolin, attapulgite, montmorillonite, bentonite, acid bleaching earth or phenolic resins. Something like an acid activated dye can be used in the donor layer and an acid-reactive component in the receiver layer. Another color-producing version of these reactive copy papers is the "one-component" reactive copy paper. In these papers, one side of each sheet of paper carries a dye precursor, which is also a vehicle, generally in the form of microcapsules. When pressure is applied, for example by a typewriter or other recording device, the capsule containing the dye precursor ruptures and the dye precursor reacts with the color formers around it (U.S. Pat.
2730456). The coating of the paper substrate for the production of carbonless copying paper systems is carried out on all surfaces according to the known prior art, for example in German Published Applications 1934457 and 1955542.
This is generally carried out using aqueous coating compositions such as those described in . The methods described so far have the disadvantage that after application of the coating composition the water has to be evaporated, which requires a considerable expenditure of energy. For drying needs,
It requires the use of complex and expensive equipment for continuous drying of substrates coated with aqueous coating compounds. Another problem associated therewith is that of wastewater removal resulting from the manufacture and purification of aqueous coating compositions. If volatile organic solvents are used during the preparation of the coating, the excess solvent must also be evaporated to dry the coating. In this way, solvent vapors are generated which are particularly harmful. Therefore, DE 1928001 proposes a method for electrostatically depositing dry microcapsules on a wet paper web. Although this method eliminates some of the drying, the proposed process does not allow for full surface coating. Furthermore, a binder active in aqueous solution is required to fix the capsule. In most cases, it is sufficient to use only a portion of the reproduction system, so full surface coating is uneconomical. Accordingly, various methods are known for partially applying coating compositions onto paper substrates.
Thus, according to the prior art, aqueous or solvent-containing coatings can be partially applied to paper substrates by gravure or flexography (see, for example, DE 2541001 and US Pat. No. 3,016,308 and 3,914,511). These methods also have the disadvantage that the coating has to be subsequently dried. For these reasons, for example, in US Pat. It has been proposed that it be implemented. Although these proposed methods do indeed omit solvent removal, relatively large amounts of wax must be applied to obtain satisfactory reproduction copies with a maximum microcapsule content of 40% by weight. Therefore, the wax-like coating changes the properties of the paper. The present invention provides a method of electrostatically depositing either the form of dry microcapsules with a meltable coating onto a paper substrate and fixing therein by heat treatment to obtain a partially coated carbonless copying paper. It is based on the recognition that Accordingly, the present invention provides partially coated carbonless copying papers made by electrostatically depositing microcapsules with a meltable coating onto a paper substrate and subsequently applying a heat treatment, as well as their This relates to a manufacturing method. According to the invention, the microcapsules are provided with a coating which melts upon short heat treatment, thereby fixing the microcapsules on the paper substrate. The term "heat treatment" is to be understood as an action of heat which, on the one hand, must not be so high that the microcapsules are damaged, but on the other hand, must not be so low that melting does not occur. A suitable temperature is, for example, 50-150°C, preferably 60-120°C. The thermal energy generated at these temperatures is comparable to the energy used in typical dry copying when toning powder is stoved.
The duration of action also depends on the amount of thermal energy in that the higher the energy, the shorter the treatment time. A person skilled in the art can readily determine this amount of energy by a simple test. It depends on the meltability of the coating, its cohesive strength and the setting time of the coating.
For example, processing times can range from about 5 to 30 seconds. As a heat source, for example common heating elements, infrared emitters or microwave devices can be used. Materials suitable for the exterior of the capsule include, for example, wax compositions, thermoplastics or hot melt adhesives, all of which are generally heated at temperatures between 60 and 120°C.
, preferably from 70 to 90°C. The following may be mentioned as examples of wax compositions: paraffin waxes, ester waxes, polyethylene waxes, stearates and carnauba waxes. Suitable thermoplastics are, for example, polymers and copolymers of ethylene, vinylidene, vinyl acetate, and partially saponified ethylene vinyl acetate copolymers. For example, polyamides can be used as hot-melt adhesives. Suitable sheath materials include, for example: carnauba waxes and partially saponified ethylene vinyl acetate copolymers. By stirring the above-mentioned substances in the form of an aqueous finely divided dispersion or emulsion in an aqueous capsule dispersion and then converting this mixture into a lump-free powder, e.g. by spray drying, microcapsules can be advantageously prepared with said substances. It will be packaged in The operation of spray drying capsules belongs to the known prior art. Other known drying techniques can also be used for manufacturing capsule powders. The coating composition can also be dissolved in a suitable solvent for packaging, the dry capsules are added with stirring, and the solvent is then removed. If a sufficiently finely divided powder of the envelope material is present, optionally mixing it with the microcapsule powder is sufficient. Generally, the amount of sheath material is about 5-50% by weight, preferably 10-30% by weight, based on the microcapsules. The microcapsules packaged in this way are applied by electrostatic methods to paper substrates of any form and subjected to heat treatment. Common wood-containing or wood-free types of paper having a layer weight of 40 to 200 g/m ² can be used as paper substrates. The electrostatic method for depositing the packaged microcapsules on the paper substrate allows the microcapsules to be optionally applied locally only to the part of the paper substrate where the copying function is to be fulfilled. The electric field between the two electrodes produces an ionic current that charges the sheathed microcapsules that are applied to the electric field. The microcapsules charged in this way are deposited on the paper substrate when they are placed on one of the electrodes. The process of electrolytic deposition of solid particles from air streams is described in many publications [e.g. Simm:
UntersuchungenU¨ber das Ru¨ckspru¨hen bei
der elektrischen Staubbscheidung Chemie−
Ingenieur-Technik 31, 1959 No. 1] and belongs to the prior art. Examples of deposition methods for dry capsule materials are shown below.
It is shown in Figure 5. FIG. 1 shows the principle of deposition of a capsule in an electrostatic field caused by a corona discharge at a point electrode 1 and by the ionic current generated thereby between electrode 1 and receiver electrode 2. FIG. The air stream in which the capsule material 4 is distributed is directed through the injection nozzle 3 into the discharge area between the electrodes 1 and 2. The receptor electrode is covered by a paper sheet 5, on which the capsule material is deposited. When the capsules reach the spray location 6, they are electrically charged by the charge carriers present therein and are exposed to the force effect of an electric field according to the equation K=qE, which is known as a charge carrier. In this formula, K represents force and q
denotes the charge and E denotes the field strength in the direction of the acceptor electrode. Both the field and the ionic current are supplied by a DC source 7.
This is caused by the voltage between electrodes 1 and 2 which is maintained by . The capsule is pushed by a force K onto the surface of the paper covering the countercurrent electrode. At the same time, current flows continuously through the paper layer to the electrode 2. A precondition for the operation of the method according to the invention is sufficient permeability of the paper to electric current. Generally, this condition is such that the resistivity of the paper is less than or equal to 10 ¹⁴ Ohm.m.
10 ⁴ ~ 10 ¹⁴ Ohm.m. and more preferably 10 ³ ~
It is satisfied when 10 ¹³ Ohm.m. Under the above conditions, a uniformly thick layer of encapsulant material is deposited on the paper sheet. Figure 2 illustrates a method for intentionally depositing capsules on a portion of the surface of a paper substrate. The receptor electrode is
If it is designed to be present on the surfaces of the insulating part 8 and the conducting part 9, the ionic current emanating from the corona will be distributed in the spray field 6 so that the charge carriers and the accompanying capsules Deposit only on the conductive part of the electrode in a concentrated manner. The precondition is that the paper 5 covering the countercurrent electrode does not fall below a certain resistivity. If the resistance of the paper is too low, the capsules will settle in the middle part. In the preferred resistance range, the deposited layer is produced in such a way that the structure of the conductor part is reproducible in a way that is not narrowly defined. This resistance range is explained in more detail above. Figure 3 illustrates a more practical and related variant of the method, in which the capsule material is deposited on a continuously moving strip of paper substrate. The substance is fed through a wax-shaped container 10, which is advantageously vibrated to help the substance exit. Vibrating screens can also be used for this purpose. A paper web 11 in the form of a strip is continuously stretched on a rotatably mounted drum 12, as indicated by the arrow in the drawing. The drum 12 is covered with a covering layer consisting of an insulating layer 13 and a conductive layer 14, which is however not continuous but has a pattern provided for capsule deposition. Commercial materials and known methods (eg printed circuits or copper-coated printing plates) are available for the production of such conductive layer patterns. The conductive parts of the covering layer are electrically connected together and to the carrier roller. As can be seen from the explanations in Figures 1 and 2, point electrode 1
is replaced by a line electrode 15 in Figure 3, which is stopped parallel to the convex surface line of the drum. To generate a corona discharge, the spray line is powered by a voltage of several kV from the power source 7.
It receives a voltage, for example 10kV. Although polarity is not essential in principle, a positive voltage is preferred in this case, since this results in discharge areas that are regularly distributed over the length of the line. To fix the deposited capsule material,
The strip is passed through a stoving table 17 in which the material is heated and melted by the hot wire.
According to FIG. 4, a photoconductor layer can also be used around the drum instead of a metallization layer to control the deposition. In the dark, the photoconductor layer is an insulator, and upon exposure to light, it is a conductor.
Using the exposure device 20, non-limiting deposits are obtained by partial radiation through the paper. This embodiment has the advantage that the coating distribution can be varied in a very simple and rapid manner. Suitable photoconductors include, for example, zinc oxide, cadmium sulfide, and selenium. FIG. 5 illustrates a variation in which the photoconductor 21 is exposed from inside the drum. The photoconductor is placed on a conductive, transparent, grounded carrier 22. This carrier, which can consist of an evaporated film, is applied to a transparent hollow cylinder 23, which is illuminated from inside by a lamp 24.
The partially transparent pattern 25 allows partial exposure of the photoconductor surface, where the photoconductor acts as a conductor in the exposed parts and as an insulator in the unexposed parts. A large number of microcapsules used to carry out this method are known, as are methods of making them. Therefore, previously known microcapsules can be used and they can be prepared by coacervation or by composite coacervation from gelatin and gum arabic and from gelatin and other organic and inorganic polyanions. , can be manufactured. Various methods of this type are described in particular in Capsule Technique and Microencapsulation by M. Gutcho.
and microencapsulation). Noyes Data
Corporation 1972. In particular, the method uses microcapsules whose walls consist of polymers, polycondensation products and polyaddition products. The table below is from Microencapsulation Processes and Applications by G. Baxter.
Applications), JE Vandegaer
Publication, which indicates the types of capsule wall polymers known from the prior art.

【table】 ‖
O
Microcapsules with walls made of special polyacrylates, such as those described for example in DE 2237545 and DE 2119933, can also be used for the process of the invention. Additionally, phenols or urea-formaldehyde condensates can also be used, optionally in combination with the capsule wall polymers described above. Microcapsules preferably used in this method are those whose capsule walls are made from polyaddition products of polyisocyanates and polyamines. Isocyanates used for the preparation of the microcapsules include: diisocyanates such as xylylene-1,4-
Diisocyanate, xylylene-1,3-diisocyanate, trimethylene-diisocyanates, hexamethylene-diisocyanate, propylene-1,2-diisocyanate, butylene-
1,2-diisocyanate, ethylidene diisocyanate, cyclohexyl-1,2-diisocyanate, cyclohexyl-1,4-diisocyanate, polyisocyanate prepolymers such as addition products of hexamethylene diisocyanate and hexanetriol, 2,4-toluylene −
Addition products of diisocyanate and catechol, addition products of toluylene diisocyanate and hexanetriol, addition products of toluylene diisocyanate and tri-methylolpropane or suitable polyisocyanates similar to the compounds mentioned above. Other modified aliphatic isocyanates include 1
hexamethylene-1,6-diisocyanate, m-xylylene-diisocyanate, having at least two functional isocyanate groups per molecule;
Based on 4,4-diisocyanato-dicyclohexyl-methane or isophorone diisocyanate. Other suitable compounds include polyisocyanates based on derivatives of hexamethylene-1,6-diisocyanates having a biuret structure, the preparation of which is described in the German published specification.
1101394 and 1543178 and German published specifications
1568017 and 1931055. Before their use for microencapsulation, suitable polyisocyanates are added to di- and trifunctional alcohols, such as ethanediols, glycerin, or trimethylol, in an amount of 0.01 to 0.5 mol per equivalent of isocyanate. It can also be modified by reaction with propane or carboxylic acids such as succinic acid, adipic acid and sebacines. Instead of isocyanate groups, the following groups can also be present as reactive groups: carbodiimide, uretdione, uretonimine, uretidine-dionediimine, 4-imino-oxazolidinone-(2), β-alkylene-propiolactone or cyclobutanedione. -(1,3) group. Therefore, for example, polyisocyanato-polyuretonimines are biuret group-containing hexamethylene-
They can be used because they are produced by carbodiimidation of 1,6-diisocyanate using an organophosphorus catalyst and further reaction of the initially formed carbodiimide groups with isocyanate groups to form uretonimine groups. Furthermore, these isocyanates can be used in mixtures with each other and with other aliphatic and aromatic isocyanates. Depending on the reaction conditions, the modified polyisocyanate produced may contain significant amounts of oxacyazinetrione, triisocyanurate or symmetric triazine-diionimine as structural elements. Products of this type are also suitable as capsule wall forming agents. formula Diisocyanates corresponding to are particularly suitable. Diamines suitable for reaction with the above isocyanates include: aliphatic primary or secondary di- and polyamides such as ethylenediamine-(1,2), bis (3-aminopropyl)-amine, hydrazine, hydrazine-ethanol-(2), bis-(2-methylaminoethyl)-methylamine, 1,4-diaminocyclohexane, 3-amino-1-methyl-aminopropane, N-hydroxy-ethylethylenediamine, N-methyl-bis-(3-aminopropyl)-amine, 1,4-diamino-n-butane,
1,6-diamino-n-hexane, ethylene-
(1,2)-diamine-N-ethyl-sulfonic acid (as alkali metal salt), N-amino-ethylethylenediamine-(1,2) (diethylene-triamine), bis-(N,N'-aminoethyl) -Ethylenediamino-(1,2) (triethylenetetramine), hydrazine and their salts may also be mentioned as diamines in this connection. Examples of dye formers include triphenylmethane compounds, diphenylmethane compounds, xanthene compounds, thiazine compounds and spiropyran compounds, etc. Examples of the above groups are as follows: triphenyl Examples of methane compounds include 3,3-
Bis-(p-dimethylaminophenyl)-6-dimethylaminophthalide (crystal violet lactone, hereinafter referred to as CVL) and 3,3-
Included are bis-(p-dimethylaminophenyl)-phthalide (malachite green lactone). Examples of diphenylmethane compounds include 4,4'-bis-dimethylaminobenzhydrylbenzyl ether, N-halogen-phenylleucolamine, N
-β-naphthylleucolamine, N-2,4,5-
Trichlorophenylleucolamine and N-2,4
-Dichlorophenylleucolamine and the like are included. Examples of xanthene compounds include rhodamine-β-
Anilinolactam, rhodamine-β-(p-nitroaniline)-lactam, rhodamine-β-(p-
chloroaniline)-lactam, 7-dimethylamine-2-methoxyfluorane, 7-diethylamine, -3-methoxyfluorane, 7-diethylamine-3-methyl-fluorane, 7-diethylamine-3-chloro-fluorane, 7- Diethylamine-3-chloro-2-methylfluorane, 7-
diethylamine-2,4-dimethylfluorane,
7-diethylamine-2,3-dimethylfluorane, 7-diethylamine-(3-acetyl-methylamine)-fluorane, 7-diethylamine-
3-(dibenzylamine)-fluoran, 7-diethylamine-3-(methylbenzylamine)-fluoran, 7-diethylamine-3-(chloroethylmethylamino)-fluoran, 7-diethylamine-3-(dichloroethyl-amine) )-fluoran and 7-diethylamine-3-(diethylamine)-fluoran. Examples of thiazine compounds include N-benzoylleucomethylene blue, o-chlorobenzoylleucomethylene blue, p-nitrol-benzoylleucomethylene blue, and the like. Examples of spiro compounds include 3-methyl-2,2'-
Spirobis-(benzo(f)-chromes) and the like are included. Solvents for dissolving these color formers include, for example: chlorinated diphenyl, chlorinated paraffin, cottonseed oil, peanut oil, silicone oil, phthalates, phosphates, sulfonic acids. esters, monochlorobenzenes, partially hydrogenated terphenyls,
Alkylated naphthalenes, alkylated diphenyls, aryl ethers, arylalkyl ethers, higher alkylated benzenes, etc.
These can be used alone or in combination. Dilute pesticides such as kerosene, n-paraffins and isoparaffins are often added to the solvents. In order to produce microcapsules by the polyaddition method, the dye former and the isocyanate are first dissolved in the abovementioned solvent and this organic phase is added to a continuous solution which may contain protective colloids and optionally emulsifiers. emulsify in the target aqueous phase. An aqueous polyamine solution is added to the emulsion in a stoichiometric amount relative to the polyisocyanate in the organic phase. Colloids and emulsification aids are added to the aqueous phase to emulsify and stabilize the resulting emulsion. Examples of such products that act as protective colloids include carboxymethyl cellulose,
Included are gelatin and polyvinyl alcohol. Examples of emulsifiers include oxyethylated 3-benzine-hydroxybiphenyl and reaction products of nonylphenol with different amounts of ethylene oxide and sorbitan aliphatic esters. Microcapsules can be manufactured continuously or in batches. Dispersion equipment that produces a certain shear rate is commonly used. Examples of such equipment include blade baskets and high speed stirrers, colloid mills,
Included are homogenizers, supersonic dispersers, nozzles, steel nozzles and Splaton machines. The intensity of agitation during mixing primarily determines the diameter of the microcapsules produced. Capsule is 1~2000μ
It can be manufactured in dimensions in the range of m. Capsules with a diameter of 2 to 20 μm are preferred. The capsules are non-agglomerated and have a narrow particle size distribution. The weight ratio of core material to sheath material is 50:90 to 50:10. The present invention will be explained in further detail by the following examples. Example (a) (Production of microcapsules) Microcapsules were prepared according to German publication specification 2738509.
Manufactured according to the Example. In accordance with this example, a 35% aqueous microcapsule dispersion was prepared whose capsule wall consisted of a polyaddition product of oxadiazinetrione and diamine of hexamethylene diisocyanate. The contents of the capsule were a solution of 2.7% by weight crystal violet lactone and 0.9% by weight N-benzoylleucomethylene blue in a mixture of di-isopropyldiphenyl and isohexadecane (80:20 weight ratio). The average capsule diameter was 6.5 μm. Example (b) (Preparation of packaged microcapsule powder) 32 parts by weight of a 40 aqueous nonionic polyethylene dispersion were stirred into 100 parts by weight of the aqueous microcapsule dispersion described above (Holdamer PE03, Hoechst). This mixture was then spray dried (180°C air temperature inlet, 80°C air temperature outlet). A powder without agglomerates was obtained. The average particle size was 7.0 μm in diameter. The resulting powder mixture was applied to a paper substrate. Example (c) (Preparation of packaged microcapsule powder) Microcapsule dispersion (a) was spray dried as in (b). 100 parts by weight of the produced capsule powder
20 parts by weight of partially saponified ethylene-vinyl acetate copolymer (Levasint, Bayer) in powder form
AG) and mixed well. The resulting powder dispersion was used for deposition onto a paper substrate. Example (d) (Preparation of packaged microcapsule powder) Microcapsule dispersion (a) was spray dried as in (b). Next, add 40 parts by weight of carnauba wax.
It was dissolved in 250 parts of trichloroethane with heating to 40° C. and 160 parts by weight of dry microcapsules were mixed into this solution. Trichloroethane was then removed under vacuum. A free-flowing capsule powder coated with carnauba wax was obtained. The resulting powder mixture was used for deposition onto a paper substrate. Practical Example A capsule material coated with carnauba wax (Example (d)) was used for paper coating. The average size of the capsules was 8 μm. This material was passed around in air and blown into the discharge space between the point electrode and the plate countercurrent electrode in the apparatus according to FIG. The surface of the countercurrent electrode was divided into an insulating field 8 and a conductive field 9, the conductive field being interconnected and connected to a power source 7. This electrode was covered with a sheet of paper that received the capsule layer. The paper had a resistivity of 10 ⁸ Ohm.m. The spacing between dots and plates was 10 cm. A voltage of 30 kV existed between the electrodes connected to the power source. The point was the anode. If a voltage is first applied and then applied to the discharge space, a fraction of the point on the paper placed on the conductive part of the countercurrent electrode will appear.
A regular capsule layer was generated in seconds. After this step, the paper thus coated was removed from the carrier and placed into a heating device, where it was heated to 150° C. for 10 seconds. The wax skin of the capsule melted on the paper surface and thus stuck to the capsule layer. A practical reactive copying paper was obtained. Capsule materials according to Examples a, b and c were used in the same manner. A practical sensitive copying paper was obtained.

[Brief explanation of drawings]

Figure 1 shows the principle of capsule deposition in an electrostatic field. Figure 2 shows the method of depositing capsules on a portion of a paper substrate. Figure 3 illustrates a practical related variant. Figure 4 shows an embodiment in which a photoconductor layer is used instead of a metallization layer.
Figure 5 shows a variation in which the photoconductor is exposed from inside the drum.

Claims (1)

[Scope of Claims] 1. A dye-forming layer of a solution of a dye-forming agent in an organic solvent, having a paper substrate, the surface of which is microencapsulated, in which the copying function is to be fulfilled. In the production of pressure-sensitive copying paper coated with by applying a wax composition, thermoplastic or hot melt adhesive with a softening temperature of 60 to 120°C as a meltable coating or finely divided meltable powder and then heating to 50 to 150°C. A manufacturing method characterized in that the water-free microcapsules or the water-free mixture are fixed by 2. Process according to claim 1, characterized in that carnauba wax and a partially saponified ethylene-vinyl acetate copolymer are used as coating. 3. Process according to claim 1, characterized in that carnauba wax or a partially saponified ethylene-vinyl acetate copolymer is used as coating. 4. The manufacturing method according to any one of claims 1 to 3, characterized in that the layer weight of the paper substrate is 40 to 200 g/ ^m2 . 5. The manufacturing method according to any one of claims 1 to 4, wherein the paper substrate has a specific resistance of 10 ⁴ to ^{10 12} ohm.m.