MXPA97008588A - Microcapsules with employment of iminooxadiazindiona-poliisociana - Google Patents

Abstract

The present invention relates to new microcapsules characterized in that their walls are constituted by reaction products of crosslinking agents, which contain NH2 groups, with iminooxadiazoldione-isocyanates or their walls contain such reaction products. In addition, a method has been found for obtaining such microcapsules and carbon-free tracing papers, which contain such microcapsules.

Description

MICROCAPSULES WITH EMPLOYMENT OF IMINOOXADIAZINDIONA-POLITfinpt ^ -NATOS. DESCRIPTION OF THE INVENTION. The present invention relates to microcapsules with walls constituted by polyureas and by polyiminoureas, a process for obtaining them and carbon-free tracing papers, containing such microcapsules in which chromophores are found. The use of microcapsules in general in the form of dispersions of microcapsules is carried out for many applications, for example for the manufacture of carbon-free tracing paper, in the field of pharmacy, of the protection of plants, of the cosmetic, catalysis and the adhesives industry. In the case of the aforementioned application, the so-called chromophores are mixed with hydrophobic, largely inert oils and this mixture is microencapsulated, forming aqueous dispersions of capsules. The dispersed capsules usually have a diameter in the range of 3 to 25 μm. The preparation of carbon-free tracing papers is generally carried out by applying a dispersion of such capsules on paper, optionally together with binders, separators and / or additives and combining a paper of this type. type coated with capsules (CB side) with a developer paper, which contains on its upper side a developer. When this REF: 25835 paper combination is used, the microcapsules where the mechanical pressure of a writing device acts are broken. The oil, which contains the chromophore, enters there in contact with the developer. In this way, a writing image is formed on the side, which contains the developer (CF side). Combined coatings are also known, ie coatings of a paper with a mixture consisting of capsules and developer. On such papers (SC papers), uncoated paper copies can be generated. For the manufacture of the microcapsules there is a large number of known physical, chemical-physical and chemical processes. For the microencapsulation of chromophores, plant protection agents and cosmetic products, procedures based on the chemical principle of the so-called limit surface polymerization or polyaddition at the boundary surface are frequently used. These procedures are technically simple and can be carried out reproducibly. This last one is valid above all for the polyaddition in limit surface. In the case of the boundary surface polyaddition, in a first stage of the process, the products to be encapsulated in a hydrophobic oil are dissolved, combined with a polyisocyanate capable of forming the wall and then made with water to give an oil emulsion. -in-water The emulsified oil droplets in this case have a size that corresponds approximately to the size of the subsequent microcapsules. The aqueous phase of the emulsion usually contains protective colloids, for example polyvinylalcohol, carboxymethylcellulose, emulsifiers and / or stabilizers, to prevent the confluence of the oil droplets. For the formation of the capsule wall, in a second stage of the process, the oil-in-water emulsion is mixed with a so-called crosslinking agent, which is capable of reacting on the boundary surface between the oil and the water, with the isocyanate dissolved in the oil with the formation of a polymer film. The crosslinking agents can be constituted, for example, by di- or polyamines, diols, polyols, polyfunctional amino alcohols by guanidine and guanidine salts and by compounds derived therefrom. The third stage of the process covers the so-called final treatment of the capsule dispersion freshly prepared. In this case, the reaction between the polyisocyanate and the crosslinker is terminated under the control of the temperature and residence time and, if appropriate, with the use of other auxiliary agents. Such surface area polyaddition processes have been described, for example, in US-A 4 021 595, US-A 4 193 889, US-A 4 428 978, EP-A 0 392 876, DE-A 2 757 017 and EP-A 0 535 384.

In the known processes, difunctional aliphatic or aromatic isocyanates and / or with functionality greater than two are used. The polyisocyanates used hitherto for microencapsulation are, in most cases, aliphatic in type and are derived, pre-weightedly, from the following base components: Hexamethylene diisocyanate (HDD, HDI biuret, HDI isocyanurate, HDI uretdione) , oxadiazintrione of HDI, combinations of two or more of the abovementioned types and reaction products of the types mentioned above with mono- and / or polyhydroxy compounds (urethanes, allophanates) and / or di- and / or polyamines (ureas) , biurets) containing free isocyanate groups When polyisocyanates of the above-mentioned type are used in the above-described manufacture of microcapsules according to the polyaddition process at the boundary surface, some disadvantages are also presented. hexamethylene diisocyanate is problematic due to the high vapor pressure and the known unpleasant physiological properties of the diiso aliphatic cyanates monomers. The polyisocyanates of the other types mentioned are not critical respectively but in their application it has been observed that they are required for the manufacture of dispersions of microcapsules with greater possible fineness, frequently the use of relatively high shear forces for the manufacture of the described oil emulsion -in-water, which requires a high energy cost. It also happens that the proportion of capsules in the finished dispersions is frequently limited upwards by approximately 45% by weight. The possibility of manufacturing dispersions of microcapsules with a proportion in solid matter situated above 40% by weight, exceptionally even above 50% by weight, has certainly been described in its rationale. However, it requires a high cost, which is higher the higher the content of the solid material intended (see US-A 5 164 126). The polyisocyanates used for the microencapsulation must also have sufficient solubility in the hydrophobic phase. However, this occurs only in particular in the case of polyisocyanates, hexamethylene diisocyanate derivatives, uretdione, biuret, allophanate and / or isocyanurate structures. The present invention therefore had as a task to develop microcapsules that required less energy for emulsification, with maintenance or with improvement of the technical advantages of the known microcapsules, and which allowed higher proportions of capsules in the dispersions of microcapsules without a special cost. Microcapsules characterized in that their walls are constituted by reaction products of crosslinking agents containing NH2 groups with isocyanates of the formula (I) have now been found. wherein the radicals R are the same or different and represent respectively (cyclo) alkyl with 1 to 20 carbon atoms, optionally substituted, double-bonded or aralkyl with 7 to 20 carbon atoms, optionally substituted, double-bonded and X moieties are the same or different and respectively represent NCO or a moiety formed by elimination of the N-linked substituents of oligomers of diisocyanates, which have structural elements of urea, biuret, uretdione, isocyanurate, oxadiazinetrione, urethane , of allophanate and / or of iminooxadiazindione, or because their walls contain reaction products of cross-linkers containing NH2 groups with isocyanates of the formula (I). The radicals R can have saturated or unsaturated, straight-chain or branched alkyl groups (also as alkyl). Other substituents for R (in addition to X) are, for example, halogen, nitrogen, oxygen and / or sulfur atoms. In the formula (I), the radicals R are preferably identical or different and represent alkyl with from 1 to 10 carbon atoms, optionally substituted, double-bonded. The X moieties are preferably the same or different and mean NCO and / or a moiety that is formed by the removal of the N-linked substituents of oligomers of isocyanates of the formula (II) OCN-R-NCO (II), wherein R has the meaning indicated in the case of formula (I), the oligomers presenting structural elements of urea, biuret, uretdione, isocyanurate, oxadiazine-trione, urethane, allophanate and / or iminooxadiazindium -na The oligomers can have, for example, an average oligomerized degree n of 2 to 20, where n is the number of the diisocyanate units linked in the oligomer molecule. Particularly preferably all the radicals R are the same. The radicals X are, more preferably, the same or different and represent NCO and / or represent one of the preferred radicals, the radicals consisting of isocyanurate and iminooxatiazinedione structural elements constituting at least 50 mol% of all radicals X. Very particularly preferably all the radicals R mean groups R- (CH2) g.

The isocyanates of the formula (I) can be used as pure compounds, by way of arbitrary mixtures of compounds of the formula (I) with one another, as mixtures of a compound of the formula (I) with one or more isocyanates of another type or as mixtures of various compounds of the formula (I) with one or more isocyanates of another type. The isocyanates of another type can be constituted by the various aliphatic, aromatic and aromatic-aliphatic difunctional isocyanates and with a functionality greater than 2, preferably they are constituted by those known for the preparation of microcapsules. The other particularly preferred isocyanates are hexamethylene diisocyanate, isophorone diisocyanate and / or hexamethylene diisocyanate and isophorone diisocyanate derivatives, which have free isocyanate groups containing biuret, isocyanurate, uretdione and / or oxa diazintrione groups. Some of the so-called other polyisocyanates have been described, for example, in EP-A 227 562, EP-A 164 666 and EP-A 16 378. When isocyanates are used, to be used according to the invention, in a mixture with other isocyanates, these mixtures preferably contain at least 20% by weight of isocyanates to be used according to the invention. Mixtures containing at least 30% by weight of isocyanates to be used according to the invention are particularly preferred.

The mixtures of isocyanates, which can be used according to the invention, can be formed directly during the preparation of the isocyanates, but can also be prepared by mixing the individual components, the individual components being both pure compounds and also mixtures . The isocyanates of the formula (I) or those mixtures containing isocyanates can be obtained, for example, by oligomerization of the corresponding polyisocyanates (mixtures) with an NCO content of less than 75% under the effect of catalysts based on (poly) hydrogen fluorides. The catalysts may correspond, for example, in the formula (III) . { M [nF_ (HF) m]} (III), wherein m is greater than 0, preferably greater than 0.1, and more preferably greater than 0.5, and M is an n-fold charged cation or an n-valent moiety. The compounds of the formula (III) are commercially available in part or can be prepared in a simple manner and in any desired stoichiometry, by mixing the corresponding fluorides with the corresponding amounts of hydrogen fluoride. Hydrogen fluoride can be added in this case, for example, as a solution in a protic or aprotic organic solvent. Tam-well are commercially available hydrogen fluoride / amine complexes, by. example with pyridine and melamine, which are employable in this case. The hydrogen fluorides of the formula (III) are innocuous from the physiological point of view. Furthermore, the presence of free hydrogen fluoride in the prepared compounds of the formula (I) is practically excluded by the addition of hydrogen fluoride on isocyanates with the formation of carbamoyl fluorides. The proportion of hydrogen fluoride in the described catalyst systems can vary within wide limits. That is to say that the fact that they are defined compounds such as monohydrogen difluorides is not important., of dihydrogen trifluorides, etc., which are known, for example, in the form of their potassium salts or of arbitrary mixtures of such defined compounds with excess fluoride on the one hand or with excess hydrogen fluoride on the other hand. In order to obtain the isocyanates of the formula (I) and the mixtures containing them, it is not essential that the catalyst be soluble in the polyisocyanate to be oligomerized (homogeneous catalysis), or that it is not (heterogeneous catalysis). Other products or mixtures of products for catalysis can also be added, for example amines, alcohols and / or phenols, solvents for the catalyst and / or for the starting isocyanate, antioxidants and / or matrices for absorption or co-formation. valence of the catalyst. It is also possible to separately add the hydrogen fluoride, which is necessary for the formation of two compounds of the formula (III), if appropriate in dissolved form, to the isocyanate (mixture). In addition, they can be used (concomitantly) to obtain arbitrary substances, which make hydrogen fluoride available for catalysis under the conditions of the reaction. Thus, for example, carbamoyl fluorides of any type are suitable in this respect. The preparation of the isocyanates of the formula (I) and the mixtures containing them can be carried out, for example, in the temperature range of 20 to 200 ° C, preferably 30 to 90 ° C. The reaction can be carried out quantitatively or stopped at any degree of conversion. In the latter case, the reaction can be obtained, for example, by the addition of acids or acid derivatives (for example benzoyl chloride, acid esters of phosphorus-containing acids or phosphorus-containing acids, sulfonic acids, silylated acids, mineral acids, but however not hydrofluoric acid), by binding by absorption of the catalyst and subsequent separation by filtration or by thermal deactivation. The concentrations of the catalysts can be, for example, between 5 ppm and 5% by weight, based on the polyisocyanate used. Simultaneously with the formulation of the imino-oxadiazinedione-isocyanates, a trimerization with formation of isocyanurate structures, a dimerization with formation of uretho-dione structures, an incorporation of C02 with formation of oxadiazine-dione, a urethanization can take place if necessary. and / or an allophanatized. For the preparation of the polyisocyanates which are used according to the invention, it is possible to use, for example, known aliphatic, cycloaliphatic and araliphatic polyisocyanates with an NCO content of less than 70% by weight, in pure form or as arbitrary mixtures with each other. Examples which may be mentioned are: (methyl) -cyclohexane-diisocyanates, ethylcyclohexanediisocyanates, propylcyclohexanediisocyanates, methyl diethylcyclohexanediisocyanates, propanediisocyanates, butanediisocyanates, pentanediisocyanates, hexanediisocyanates (for example HDI), heptanediisocyanates, octanediisocyanates, nonanodi -triisocyanates, decanodi- and -triisocyanates, undecanodi- and -triisocyanates, dodecanedi and -triisocyanates, isophorone diisocyanate, bis (isocyanatocyclohexyl) methane and 4 (3) -isocyanatomethyl-1-methyl-cyclohexyl isocyanate. The isocyanates of the formula (I), the mixtures containing them and their preparation are covered by an earlier proprietary patent application. The high chemical and mechanical stability of the walls of the capsules prepared with isocyanates of the formula (I) and crosslinkers containing NH 2 groups is surprising, as well as the good solubility of these isocyanates in the organic solvents, inert to the isocyanates. cyanates, not miscible with water, which come into consideration for microencapsulation (for example: alkylaromatic hydrocarbons such as diisopropylnaphthalene, substituted diphenyls such as sec.-butyldiphenyl, phenyl-silyl-ethane, chlorinated paraffins, phthalates, natural oils such as soybean oil or rapeseed oil and low melting fat such as coconut oil). The aforementioned oils can be diluted, for industrial encapsulation, to reduce and / or adjust the tightness, possibly with aliphatic hydrocarbons of synthetic or natural origin. These diluents can be constituted, for example, by mixtures of para-® fines (for example Exxsol types), isohexadecane, hydrogenated naphthenic petroleum fractions (for example ® ® ® Nytex, Nyflex and Gravex) and dodecylbenzenes (for example ® Marlikan). The isocyanates of the formula (I) are suitable in an especially good manner for encapsulations, in which the oils described above or mixtures of such oils with diluents are worked. The microcapsules according to the invention are preferably used for the production of carbon-free tracing papers. These then contain dissolved chromophores as products to be encapsulated in oils. In this case, chromophores of the most diverse types are suitable, especially triphenylmethane compounds, diphenylmethane compounds, bisindo-lylphthalide compounds, bisarylcarbazolylmethane compounds, xanthan compounds, benzoxazine compounds, thiazine compounds and spiropyran compounds. , especially those that are known as chromophores for the manufacture of carbon-free tracing papers. Mixtures of various chromophores can also be used. Some employable chromo-forums have been described, for example, in EP-A 591 106, EP-A 315 901, EP-A 234 349, DE-A 3 622 262 and EP-A 187 329. In the manufacture of the microcapsules according to the invention the aqueous phase may contain, if necessary, emulsifiers, stabilizers and / or products that prevent coalescence. The emulsifiers can also be contained, if appropriate, in the oil phase. The amount of such additives can be found, for example, in the range of 0.01 to 2% by weight, based on the co-responding phase. The microcapsules according to the invention can not only contain chromophores, but also other encapsulated materials, for example perfuming essences, glues, pharmaceuticals, insecticides, herbicides or repellents. The products to be encapsulated must not, of course, react with the isocyanates under the conditions of the encapsulation. The microcapsules according to the invention are prepared from isocyanates of the formula (I) by reaction with crosslinking agents containing NH2 groups. The crosslinking agents are capable of reacting on a boundary surface between phases with the isocyanate groups. For example, the following compounds are suitable, in pure form or as mixtures with one another: hydrazine, guanidine and its salts, hydroxylamine, di- and polyamines and aminoalcohols. A preferred guanidine salt is guanidine carbonate. When guanidine salts of strong acids are used, the addition of a base is required. Examples of di- and poly-amines and aminoalcohols are: ethylenediamine, hexamethylene diamine, isophorone diamine, diethylenetriamine, ethanolamine, diethanolamine and triethanolamine. It is also possible, in principle, to act as a crosslinker of water, by generating an amino group by addition to an NCO group and subsequent dissociation of C02, which can then react with an NCO group with crosslinking. Preference is given to microcapsules with walls made from the isocyanates to be used according to the invention, guanidine carbonate, diethylenetriamine or mixtures of guanidine carbonate / diethylenetriamine. The amount of the isocyanates to be used according to the invention is moved in the usual range for the polyaddition process at the boundary surface, for example 2 and 20% by weight of wall proportion (see definition 1), referred to the whole of the oil phase provided for the encapsulation. A wall ratio in the range between 4 and 15% by weight is preferred. In the calculation of the wall proportion, the crosslinker necessary for the conversion by complete reaction for reasons of simplification will not be taken into consideration. Definition 1. % of proportion- Mass? wall socianato = x 100 Oil phase mass + isocyanate mass to be encapsulated The theoretical amount of the crosslinking agent required for wall formation is calculated from a) the isocyanate group content of the isocyanate used and b) the content of amino and / or hydroxy-reactive groups of the crosslinking component used. Usually these quantitative proportions are expressed by the so-called equivalent weight. Definition 2. 42 Equivalent weight Isocyanate = i "x 10 ° NCO content) *) = to be determined, for example, by titration (DIN 53 185) Definition 3.

Reoculating molecular weight Reticulating equivalent weight = "; _ 7 ~~~ Number of reactive groups in the molecule.

The total number of NCO groups for the reaction, which is in the oil phase, is necessarily at least »theoretically, the same as the number of NH2 and / or OH groups. It is therefore advantageous to employ the isocyanate and the crosslinker in proportions of their equivalent weights. However, it is also possible to deviate upwards or downwards from the amount of stoichiometrically calculated crosslinker since, in the case of boundary surface polyaddition processes, a secondary reaction of the isocyanate with the water present in excess can not be excluded, or an excess of component can be used. crosslinker since it is not critical. In particular, the crosslinking agent will be used in an amount which is between 50 and 150% by weight of the theoretically calculated one. Preferably, this amount is between 50 and 100% by weight, based on the theoretically calculated amount. The present invention also relates to a process for the preparation of microcapsules, in which an oil phase is emulsified, which contains an organic solvent, inert towards isocyanates, immiscible with water, the product to be encapsulated and isocyanates of the formula (I), in an aqueous phase, which optionally contains additives and a crosslinker containing NH2 groups, which can react with the isocyanate groups, is added to the emulsion. Finally, the present invention also relates to carbon-free tracing papers, which contain chromophores in microencapsulated form and characterized in that the walls of the microcapsules contain reaction products of isocyanates of the formula (I) with crosslinkers. For the preparation process according to the invention of the microcapsule dispersions and for the carbon-free tracing papers produced therefrom, the abovementioned indications relating to the microcapsules according to the invention are correspondingly valid. The present invention has the advantage that the microcapsules require considerably less energy for their manufacture and more concentrated capsule dispersions can be manufactured. In addition, the microcapsules according to the invention are characterized by high chemical stability and good aging stability. This is all the more surprising since the iminooxadiazindiones, to be used according to the invention, could also be considered as isomers of constitution of the isocyanurates, known for a long time (so-called trimerized) also formally as isocyanate trimer. On the other hand there is a structural kinship with respect to the oxadiazintriones with relation > the cyclic anhydride segments of the iminooxadiazinediones to be used according to the invention. The cited oxadiazintriones have long been established in microencapsulation technology. When the known polyisocyanates mentioned above for microencapsulation are replaced by the polyisocyanates to be used according to the invention, no improvement was really expected (in this respect also see the formulas indicated below (I), ( IV) and (V)).

Iminooxadiazinedione type according to the invention Type isocyanurate Type oxadiazintrione state of the art prior art. The advantages achievable according to the invention are especially marked when the isocyanates to be used according to the invention are used in combination with guanidine carbonate as a crosslinking agent.

Examples Examples 1 to 12 refer to dispersions of microcapsules for carbon-free tracing papers. Example 1 (comparative): A constant current was pumped (32, 0 kg / hour) of oligomer mixture constituted by bis (isocyanatohexydioadiazinetrione) with a constant current (288.0 kg / hour) of chromophore solution (3% by weight crystal violet lactone in diisopropylnaphthalene) through a static mixer, whereby a largely homogenous organic phase was formed, this was fed continuously, to a conventional emulsifying apparatus, together with a stream of an aqueous phase (420.5 kg / hour) constituted by deionized water having a content of 1% by weight of polyvinyl alcohol ® (AIRVOL 523, Air Products Ine) The last mentioned emulsifying device was built according to the rotor-stator principle, which means that two-spinning discs, which rotate rapidly, are they move with a high peripheral speed in stationary stationary chambers, also grooved, generate a high shear field.The oil and aqueous phases are transformed into such emulsifying apparatuses in the course of a few seconds in a finely divided emulsion, the size of the droplets in the emulsion being very close to the size of the subsequent microcapsules. The size of the oil droplets can be regulated by the number of revolutions of the machine. In the following example, a very high number of revolutions, of 2,400 revolutions / minute, had to be established in order to achieve an average particle size of 6.8 μm (measured with a commercially available device, Multisizer II, Coulter Electronics Inc.). The emulsion current leaving the emulsifying apparatus, approximately 40% by weight, (740.5 kg / h) was conducted to a refrigerator in a fluted cell and continuously mixed with a 9% aqueous solution therein. by weight of diethylenetriamine in deionized water (= crosslinking solution). After charging the cell, the emulsion stream and the crosslinker were stopped and the contents of the cell were heated by means of a wall heater, under slow stirring, to a temperature of approximately 60 ° C. After stirring for 2 hours at this temperature, a dispersion of capsules resulted in approximately 40% by weight (average diameter of the capsules 6.5 μm, measured as indicated above), which was used for the manufacture of a charcoal-free tracing paper. The term "emulsion stream" means x% by weight or capsule dispersion at x% by weight, the weight ratio isocyanate + chromophoric solution relative to the total weight of the emulsion or dispersion. Example 2 (according to the invention).

The technical installation described in Example 1 was used, however the isocyanate type, the amount of the chromophore solution and the amount of the aqueous phase were modified. The following were used: An isocyanate obtained according to example 15 (32.0 kg / hour). The same chromophore solution as in Example 1 (368 kg / hour). The same aqueous phase as in Example 1 (319.1 kg / hour). A 10 wt% solution of guanidine carbonate in water (80.9 kg / hour) was used as crosslinking solution. Since the crosslinker is added only after the formation of the emulsion, it has no effect on the energy necessary for the formation of the emulsion. In this example, only a number of revolutions of the emulsifier apparatus of 1,800 revolutions / minute was required to obtain droplet sizes of 6.7 μ, and this even when an emulsion of 50% by weight is present in this case. It is seen that with an isocyanate, to be used according to the invention, emulsions can be generated with the same fineness and even more concentrated than those which result when the known isocyanates are used with a clearly lower energy cost per unit mass of the oil phase ( 719.1 kg of 50% by weight emulsion according to the present example instead of 740.5 kg of 40% by weight emulsion according to example 1). Also in this example, the emulsifying apparatus was switched off after loading the fluted cell with the 50% by weight cross-linked emulsion. The contents of the vessel were heated through jacket heating at 65 ° C and stirred for another 2 hours at this temperature. A dispersion of microcapsules was obtained at approximately 50% by weight (average diameter of the capsules 6.4 μm), which was used for the production of high quality charcoal-free tracing paper. Examples 3 to 11 (according to the invention) and example 12 (not according to the invention). Overall realization. Partial stages A up to I. A Chromophore solutions. The chromophore solutions 1 to 3 were prepared by dissolving the corresponding powdery chromophore (commercial product) in various oils (commercial products) at a temperature of about 110 ° C. Chromophoric solution 1. 95.5% by weight of diisopropylnaphthalene (KMC 113, RÚTAG AG) 3.15% by weight of crystal violet lactone (Pergascript blue 12R, CIBA GEIGY AG) 0.67% by weight of Pergascript "blue SRB (CIBA GEIGY AG) and ® 0.67% by weight of Pergascript red 16B (CIBA GEIGY AG) Solution of chromophore 2. ® 95.0% by weight of coconut fat (Cocopur, Rau GmbH) ® 0.65 % by weight of Pergascript blue SRB ® 0.75% by weight of Pergascript green 12GN (CIBA GEIGY AG) ® 0.35% by weight of Pergascript red 16B 1.63% by weight of chromophore PSD 184 (Nippon Soda) and 1.62% by weight of black chromophore 15 (Yamamoto Chemicals) Chromophore solution 3. 76% by weight of SAS 296 alkylaromatic hydrocarbon (Nisseki Chemical Texas) ® 19% by weight of Nytex 800 ® 0.65% by weight of Pergascr blue pt SRB ® 0.75% by weight of Pergascript green 12GN ® 0.35% by weight of Pergascript ro or 16B 1.63% by weight of chromophore PSD 184 (Nippon Soda) and 1.62% by weight of black chromophore 15 (Yamamoto Chemicals).

B. Obtaining the polyvinyl alcohol solution (aqueous phase). In all cases, a 1.0% by weight solution of polyvinyl alcohol, prepared by ® mixing AIRVOL 523 with a corresponding amount of cold water, deionized, swelling for 15 minutes at room temperature and subsequent heating at 100 ° was used. C until complete dissolution. C. Obtaining the crosslinking solution. A 10 wt% solution of guanidine carbonate (GUCA) and a 9 wt% solution of diethylenetriamine (DETA) were used, both prepared by dissolving the corresponding crosslinker at room temperature in deionized water. D. Obtaining the active oil phase. "Active oil phase" means the mixture consisting of chromophore solution, if appropriate diluent and the polyisocyanate used. It was prepared by mixing the chromophore solution with the isocyanate component used at room temperature in the beaker until homogenized with the naked eye. E. Obtaining the preemulsion. This was obtained by mixing the active oil phase with the polyvinyl alcohol solution at room temperature with a rapid-motion lab agitator. F. Obtaining the fine emulsion. The previous emulsion was prepared by means of a high speed laboratory emulsifier device, commercially available (Megatron, KINEMATICA AG) to give a fine emulsion with the desired particle size, determining the required number of revolutions in a previous test respectively. The number of revolutions in revolutions / minute is a measure of the necessary emulsion energy. During the emulsification stage, a temperature of 30 to 33 ° C was maintained by external cooling.

G. Crosslinking of the fine emulsion. A calculated amount of crosslinking solution was added to the metered amount of the fine emulsion at room temperature under slow stirring. H. Maturation of capsule dispersion. The crosslinked dispersions were heated, under slow stirring, in the water bath, at 60 ° C (in the case of cross-linking with diethylenetriamine) or at 70 to 80 ° C (in the case of cross-linking with guanidine carbonate) and stirred for another 2 hours at this temperature. I. Test of the dispersion of the capsules. The dispersion of the resulting capsules was determined: a) the chromophore content by means of a commercially available dry scale, b) the size of the particles with a device for measuring the size of the particles commercially available, and c) the tightness of the capsules by coating a commercially available developer paper with the dispersion of the capsules by means of a doctor blade (which corresponds to 2 g of dry capsules per nr of paper), then drying in a stream of air at a temperature environment and evaluation at a glance, the blue or black coloration being a sign of non-hermetic capsules and in the case of hermetic capsules, colorations with respect to the uncoated paper can not be determined to the naked eye. The content of solid matter is the content of the dispersion of the capsules in dry capsules. The dry capsules are the proportion of the dispersion of the capsules that are not volatile at a drying temperature of 150 ° C and at normal air pressure. Examples 3 to 11 show that sealed, non-agglomerated microcapsules can be obtained according to the polyaddition process on the boundary surface from isocyanates to be used according to the invention, alone or in a mixture with the isocyanates, which are suitable in a particularly good way for the manufacture of carbon-free tracing paper. The example demonstrates that with isocyanates of another type than the one used according to the invention and with a comparable work form, otherwise, microcapsules that are not very usable are obtained. Example 13 shows the superiority of the isocyanates to be used according to the invention, in the manufacture of dispersions of highly concentrated microcapsules, free of agglomeration. The details regarding examples 3 to 12 can be seen in the following table.

) A = Obtained according to example 15, UD = uretodionapolii- ® socianato (Desmodur N 3400), BU = biuretpolyisocyanate ® (Desmodur N 3200), IC = socianuratopoliisocianato ® (Desmodur N 3300), ON = oxadiazmtrionapolyisocyanate; the numerical data are proportions by weight. 2) Determined by titration according to DIN 53 185. 3) Determined according to definition 1 in the description. 4) Referred to the stoichiometrically necessary amount. ) 45 parts by weight of GUCA and 34.3 parts by weight of DETA. 6) During the formation of the capsules there were agglomerations, the concentration of the dispersion of the capsules was not determined. z.Vgl. = Comparative Example 13. This example shows the superiority of the isocyanates to be used according to the invention, in terms of obtaining dispersions of highly concentrated microcapsules, free of agglomeration. A crude pre-emulsion was prepared from 444.4 g of the chromophore solution 1 used in Examples 3 to 12 and 33.45 g of the isocyanate obtained according to a laboratory stirrer. Example 15 and a mixture consisting of 234 g of a 1% by weight aqueous solution of polyvinyl alcohol and 84.6 g of a 10% by weight aqueous solution of guanidine carbonate (both prepared as described in the examples 3 to 12). This pre-emulsion was converted into a fine emulsion with a speed of 10,000 revolutions / minute at 25 ° C and with a high speed laboratory emulsifier device (Megatron, KINEMATICA AG). This fine emulsion heated up, under slight agitation, by means of a water bath, in the course of one hour, at 60 ° C and, at this temperature, stirred for an additional hour. It was then heated to 75 ° C and stirred for an additional 1.5 hours. A microcapsule dispersion free of agglomeration with a solids content of 60.2% by weight, a viscosity of 145 mPa-s at 25 ° C and an average capsule size of 8.8 μm resulted. The capsules were hermetic. The dye content, the size of the particles and the tightness of the capsules were determined as indicated in the case of examples 3 to 12, the determination of the viscosity was carried out with a commercially available rotary viscometer. . Example 14. The following example relates to the microcapsules of an insect repellent. 230 g of N, N-diethyltolyl amide were dissolved, under slight heating, in 230 g of coconut fat ® (COCOPUR, Walter Rau GmbH, Neuss). The clear solution was combined with 40 g of the isocyanate obtained according to Example 15 and stirred at 30 ° C until complete dissolution. This was provided by solution A. A raw pre-emulsion was prepared from solution A and 400 g of a 1.2% by weight solution of polyvinyl alcohol (AIRVOL 325) using a laboratory stirrer. , Air Products) and this pre-emulsion was prepared, with a high speed laboratory emulsifier device (MS 10 / AA 11G, Fluid Kotthoff GmbH, Essen) approximately 8,000 revolutions / minute, in 90 seconds, in a finely divided emulsion. 101 g of a 10 wt% guanidine carbonate solution in deionized water were then added under light agitation. At the same time, the mixture was heated to 70 ° C with a water bath and stirred for another 2 hours at 70 ° C. A dispersion of microcapsules with an average particle size of 13.5 μm and a concentration of 52.5% by weight was obtained, in which the repe-lens was presented in the form of microcapsules. Example 15. Obtaining an isocyanate to be used according to the invention: 2,000 g of hexamethylene diisocyanate were released in a 3-liter four-necked flask with internal thermometer, stirrer, reflux condenser, tube for the introduction of gases and a device dispenser for the catalyst solution, first at room temperature and at a pressure of approximately 0.1 mbar, over the course of 1 hour, of the gases dissolved in the diisocyanate and then heated to 50 ° C internal temperature, pass a light stream of nitrogen through it. Subsequently, at this temperature, in the course of 90 minutes, in portions, a total of 4.3 g of a 5% by weight solution of benzyltrimethylammonium fluoride (Aldrich) and 5 equivalents of HF were added (calc. on F ~) in 2-ethylhexanol in such a way that the internal temperature does not exceed 65 ° C. Once an n20D refractive index of 1.4638 was reached, the trimerization was stopped by the addition of 0.4 g of di-n-butylphosphate, stirring was continued for a further hour at 50 ° C and then it was separated from the monomeric diisocyanate, not converted, by thin layer distillation in a short-path evaporator at 0.1 mbar and at a heating medium temperature of 170 ° C. 480 g of a clear, colorless isocyanate mixture were obtained with the following data: NCO content: 23.6% by weight Residual monomer content: 0.01% by weight of hexamethylene diisocyanate Molar ratio of isocyanurates to iminooxadiazinediones the formula (I) 50:50. It is noted that, in relation to this date, the best method known by the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention. Having described the invention as above, the content of the following is claimed as property:

Claims (8)

1. CLAIMS l.- Microcapsules, characterized in that their walls are constituted by the reaction products of crosslinking agents containing NH 2 groups with isocyanates of the formula (I) wherein the radicals R are the same or different and represent respectively (cyclo) alkyl with 1 to 20 carbon atoms, optionally substituted, double-bonded or aralkyl with 7 to 20 carbon atoms, optionally substituted, double-bonded and X moieties are the same or different and respectively represent NCO or a moiety formed by elimination of the N-linked substituents of diisocyanate oligomers, which have structural elements of urea, biuret, uretdione, isocyanurate, oxadiazinetrione, of urethane, allophanate and / or iminooxadiazinedione, or because their walls contain reaction products of crosslinking agents containing NH2 groups with isocyanates of the formula (I).
2. 2. Microcapsules according to claim 1, characterized in that in the formula (I), R means alkyl with 1 to 10 carbon atoms, optionally substituted, and X means NCO and / or a residue that is formed by the elimination of the N-linked substituents of isocyanate oligomers of the formula (II) OCN-R-NCO (II), where R has the meaning indicated in the formula (I), the oligomers presenting structural elements of urea, biuret, uretdione, isocyanurate, oxadiazine-trione, urethane, allophanate and / or iminooxadiazindiumone.
3. 3. Microcapsules according to claims 1 and 2, characterized in that isocyanates of the formula (I) are used in mixture with other diisocyanates, said mixture containing at least 20% by weight of isocyanates of the formula (I).
4. 4. - Microcapsules according to claims 1 to 3, characterized in that the crosslinker is constituted by guanidine carbonate.
5. 5. Process for obtaining the microcapsules according to claims 1 to 4, characterized by emulsifying an oil phase, which contains an organic solvent, inert towards isocyanates, not miscible with water, the product to be encapsulated and isocyanates of the formula (I), in an aqueous phase, which contains additives, if appropriate, and a crosslinker containing NH2 groups, which can react with the isocyanate groups, is added to the emulsion.
6. 6. Process according to claim 5, characterized in that the organic solvents, inert towards the isocyanates, immiscible with water, are constituted by alkylaromatic hydrocarbons, substituted biphenyl, chlorinated paraffins, phthalates, natural oils or low-fat greases. fusion.
7. 7. Process according to claims 5 and 6, characterized in that the aqueous phase contains emulsifiers, stabilizers and / or products that prevent coalescence.
8. 8. Carbon-free tracing papers, which have chromophores in microencapsulated form, characterized in that the walls of the microcapsules contain reaction products of isocyanates of the formula (I) with crosslinking agents.