EP0516712A1

EP0516712A1 - Thermo- and/or photolabile microcapsules

Info

Publication number: EP0516712A1
Application number: EP19910905095
Authority: EP
Inventors: Oskar Nuyken; Jochen Dauth; Wolfgang Pekruhn
Original assignee: Mannesmann AG; Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 1990-03-02
Filing date: 1991-02-22
Publication date: 1992-12-09
Also published as: WO1991012883A1

Abstract

L'invention concerne des microcapsules dont la paroi polymère présente des groupes thermo-et/ou photolabiles en tant qu'éléments structuraux, produits par polycondensation à l'interface de monomères porteurs de groupes azoïques avec des composés plus fonctionnels sur le plan réactif avec formation de polyamides, polycarbonates, polyesters, polycarbamides ou polyuréthane.The invention relates to microcapsules whose polymer wall has thermo and / or photolabile groups as structural elements, produced by polycondensation at the interface of monomers carrying azo groups with more reactive compounds with formation. polyamides, polycarbonates, polyesters, polycarbamides or polyurethane.

Description

Thermal and / or photolabile microcapsules.

The invention relates to microcapsules, the polymeric capsule wall of which has thermo- and / or photolabile groups as structural elements, and a method for their production. Microcapsules with a polymeric capsule wall, processes for their production and various possible uses are known from "Angewandte Chemie", 1975, pages 556 to 567. These include hollow polymer particles with a size of approx. 1 μm to several millimeters, which consist for example of a core and a solid capsule wall. Depending on the intended use, the core of such a microcapsule can contain, for example, an active substance which is isolated from the environment by the capsule wall. By targeted action on the capsule wall, it can now be destroyed or made porous and permeable. The contents of the capsule come out and can have an effect there.

The capsule can be opened mechanically from the outside, for example by shearing or crushing, thermally by melting or burning the capsule wall, from the inside, for example by heating the capsule content above the boiling point and by dissolving it in a liquid medium.

Various mechanical-physical and chemical processes are known for the microencapsulation of active substances. These include interfacial polycondensation, in which the two reactants forming the polymer are contained in two different liquids which are not miscible with one another, and a dispersion of one liquid phase in the other with a desired particle diameter is produced before the polycondensation. This is done, for example, in a water dispersant solution with vigorous stirring. The reaction then begins at the interface of the dispersed droplets, forming a capsule wall that encloses the droplet itself inside. A known use of microcapsules is that of reaction writing papers, for example of the "self-contained type". These papers are coated with microcapsules that are filled with a color former. Furthermore, the coating contains a developer substance that immediately produces a visible color reaction with the color former through the printing of a writing instrument and thus represents a kind of ink contained in the paper.

Another use of microcapsules is known from GB-A-2 173 452 in connection with an image recording method. Microcapsules filled with ink are applied to a recording medium and are "exposed" with a laser beam in accordance with the image to be recorded, the capsule wall being broken open or at least made permeable to the ink. In a manner not described, the ink then reaches the recording paper and forms an image corresponding to the recording there. There is also no description of how such microcapsules could be produced or which materials would be suitable for this.

In the as yet unpublished German patent application P 39 18 146.4 it is proposed to incorporate thermo- and / or photolabile predetermined breaking points in the polymer of the capsule wall of a microcapsule in the form of azo functions (-N = N-) or peroxide groups (-0-0-). This makes it possible to set precise disintegration conditions for the microcapsule via the disintegration temperature of the azo compound or the finished azo group-containing capsule wall polymer. This is particularly advantageous when the microcapsules are used for thermal printing processes since the typeface produced is cleaner the sharper the decay conditions are defined. The size of the microcapsules also influences the print quality, which improves with a smaller capsule diameter. It is an object of the present invention to improve such microcapsules with capsule wall polymers containing azo groups and to provide new azo monomers for their preparation. This object is achieved by microcapsules according to claim 1. Further refinements of the invention can be found in subclaims 2 to 6 and a method for producing the microcapsules in claims 7 to 11. The microcapsules according to the invention are distinguished by a novel chemical structure of the capsule wall or of the polymer used for this. The polyfunctional azo group-containing monomers, or those having more than two reactive groups, represent linking points in the condensed polymer. However, since azo group-containing monomers capable of polycondensation with more than two reactive groups have not hitherto been used for the synthesis of microcapsules, the invention provides a thermo- and / or or photolabile microcapsule with increased crosslinking density of the capsule wall polymer. A higher crosslinking of the capsule wall in turn improves the thermal mechanical properties of the polymer and allows the display of a denser capsule wall with which the preferably liquid content of the microcapsule is better retained or

can be included. The degree of crosslinking also influences the glass transition temperature T _G and the hardness of the polymer. Compared to mono- and bifunctional azo group-containing monomers, the polycondensation according to the invention results in polymers with a fundamentally different chain structure. In the linking reaction (condensation) of the monomers with the corresponding at least bifunctional ones

Polymers can be formed in which the azo group is not contained in the main chain, but instead represents the link between two polymer chains. If reactants with only two correspondingly reactive groups are used to produce the polycondensate, a crosslinked polymer is formed which could have thermoplastic properties above the decomposition temperature of the azo group or of the polymer containing the azo group, provided that the radicals formed during the decomposition do not produce partial crosslinking of the polymer chain again.

With the help of the higher degree of crosslinking, the capsule wall can be made thinner with at least constant thermal-mechanical properties. A thinner capsule wall in turn allows the microcapsules to respond more quickly if the capsule contents are to be released by exceeding the decay temperature. This is particularly important for those microcapsules that are used with dye in thermal printing processes. A better "response" of the microcapsules in thermal printing requires less energy transfer and results in an improved printed image. The invention also makes new azo groups

Monomers are made available which open up a wider spectrum of possible properties, in particular possible decomposition temperatures, during the production of the microcapsules themselves. Another advantage of the microcapsules according to the invention can be seen in the decay energy which is released during the thermolysis or photolysis of the azo group. This energy, which occurs in particular as heat, supports the release of the capsule contents, so that less energy has to be used for this. On the other hand, molecular nitrogen, ie a gas, is released during the decomposition, which could mechanically support the further opening of the capsule wall or the release of the capsule contents.

Possible reactants for polycondensation with the monomers containing azo groups are known from other polycondensation reactions. For the interfacial polycondensation used here it is only necessary that the reactant for the two-phase reaction prefers a different phase than the azomonomer. Since the latter are normally readily soluble in organic solvents, a reactant which is soluble in the aqueous phase is particularly necessary. Low-molecular polyfunctional amines and alcohols are suitable for this purpose, which form themselves with carboxylic acid derivatives, isocyanates and carboxylic acids to give polyurethanes, polyureas, polyamides implement the or polyester. The properties of the microcapsules can be varied further by increasing the functionality of the reactants. The polymers of the microcapsules according to the invention can be set to decomposition temperatures of about 120 to 250 ° C. This guarantees that there is no risk of premature decomposition during transport or storage, and the microcapsules are therefore stable and stable for a long time. In addition, the capsule wall polymers are completely insoluble in relation to organic solvents, so that there is no risk of decomposition from the inside even with liquid capsule contents.

The properties of the capsule wall are of course also dependent on the type of polymer which is produced by polycondensation or polyaddition. The size of the residues bound to the azo group and the size of the reactants can be used to regulate the number of azo groups contained in the polymer per unit weight, which are decisive as breaking points for breaking open the capsule wall. A further possibility of variation of the capsule wall polymers can be set by copolymerizing the azomonomers with additional thermostable and photostable starting monomers. The process for producing the microcapsules is explained in more detail below with reference to two figures which represent two different process stages. FIG. 3 shows a coated film as an application example. In the process for producing the microcapsules, three different solutions are first prepared, each of which contains one of the three components monomer, reactant and dispersant. The solutions of the monomer and of the reactants are generated in immiscible solvents, while the third, the

Solution containing dispersant can form a single phase with one of the two preceding solutions. The type of dispersant, which is also referred to as a protective colloid, also determines which of the two phases in the Dispersion to the "solvent" is also called liquor, or which of the two phases represents the continuum or the later capsule content. The active ingredient to be encapsulated is added to the continuum before the onset or initiation of the polycondensation, while the dispersant is usually dissolved in the liquor.

Figure 1: A dispersion 1 is prepared from the dispersant and the solution of one of the two reactants with vigorous stirring. In order to obtain microcapsules or droplets with a suitable diameter (for example in the μm range), high stirring speeds of more than 1000 revolutions per minute are required. A so-called turbo stirrer is well suited for laboratory-scale approaches. The stirring speed determines the fineness of the dispersion or the size or diameter of the droplets 3 floating in the liquor 2, which represent the continuum. Once the dispersion has been generated, it remains stable due to the dispersant; the stirring speed can be reduced.

Figure 2: The solution of the second reaction partner is now added slowly and with stirring to the dispersion, the polycondensation beginning at the phase interfaces between the liquor and the continuum. Due to the high reactivity of the compounds involved, the reaction takes place completely at room temperature. After the addition is complete, stirring is continued for about 1/2 hour. The finished microcapsules 5 are usually processed further as a solution and can be used, for example, to produce a reaction writing paper.

Figure 3: The coating of a film 6 with the microcapsules 5 according to the invention is particularly simple. If, for example, polyvinyl alcohol is used as a protective colloid, the microcapsules 5 produced can be applied directly to the carrier film as an aqueous solution. The dispersant acts as a binder and produces an abrasion-resistant film 7. Not only liquids can be encapsulated with the described method, but also suspensions. For this purpose, instead of the solution forming the continuum, a suspension of the corresponding solid is generated in the solvent. When a dispersion is produced with the second solvent or the second phase, the solid remains in the original phase, thus passes into the continuum and is therefore completely encapsulated in the interfacial polycondensation. For this variant, no change in the process parameters and no other dispersant is required.

The method is explained in more detail below using exemplary embodiments. 1st example:

The following batches are prepared for the microencapsulation of the color former crystal violet lactone (KVL): Solution 1: 0.08 g of KVL in 1.1 g of 1,2-dichloroethane

dissolved with stirring at 50 °.

Solution 2: 1.0 g of 4,4'-azobis (4-cyano-pimellinoyl chloride)

(ACPDC) are dissolved with exclusion of moisture in 4.5 g of 1,2 dichloroethane with stirring.

Solution 3: 1.0 g of low molecular weight (m = 15000 g / mol) polyvinyl alcohol (PVA, which serves as a dispersing agent and protective colloid, are dissolved in 20 ml of distilled water with stirring.

Solution 4: 0.3 g diethylenetriamine and 0.4 g NaOH

dissolved in 5 ml of distilled water while cooling. Solutions 1 and 2 are combined and dispersed in solution 3 at high stirring speeds (more than 1000 rpm). Solution 4 is slowly added to the emulsion thus obtained, while cooling, by interfacial polycondensation Cross-linked microcapsules with a capsule content of 1,2-dichloroethane, KVL and ACPC and a capsule wall from the following

Form azopolyamide:

The microcapsule suspension is stirred for about 30 minutes to complete the interfacial polycondensation.

To produce a reaction writing paper, the microcapsule dispersion is mixed together with silica gel as the developer, cellulose powder as a spacer and flow agent, and polyvinyl alcohol as a binder and applied to a support (film or paper). The capsules are thermolytically broken open at 120 to 140 ° C by thermal addressing, for example by means of a thermal print head. The color former (KVL) emerges from the addressed microcapsules and creates a blue marking on the carrier. The microcapsules can also be broken open photolytically with the aid of a laser with a wavelength of approximately 350 to 400 nm. The font width that can be achieved is less than 2 mm.

Corresponding to the procedural instructions of the specified exemplary embodiment, corresponding microcapsules with an analogous structure can be produced by varying the reactive multifunctional component, for example in the form of di-, tri- or multifunctional amines or alcohols. The NaOH contained in the aqueous phase serves to neutralize the acid HCl formed.

Following the same procedure, three additional monomers with acid chloride functions (carbon or sulfonic acid chloride) were reacted as reactive groups with corresponding amines and alcohols:

According to a similar regulation, but without the addition of alkali, but with catalytic amounts of reaction accelerators (e.g. diazabicyclo-octane = DABCO) and with the same reaction partners, the conversion of monomers with isocyanate functions as reactive groups succeeds, but leads to chemically different products due to the other linking reactions, such as for example the monomer:

A slightly modified process requires azo-containing monomers with amino and alcohol functions as reactive groups. By converting the amino groups into ammonium salts, for example the corresponding hydrochlorides or converting the alcohols into corresponding alcoholates, the monomers become soluble in the aqueous phase and can be reacted with those reactive compounds which are soluble in the organic phase in the interfacial polycondensation. If the dispersant remains the same, the assignment of

Get phases, for example organic phase to the continuum and aqueous phase to the liquor in the dispersion. Only the reaction partners of the condensation reaction have reversed their phase, but react with each other in basically the same way. Reaction partners for the amines or their hydrochlorides and the alcohols or their alcoholates can be isocyanates or correspondingly reactive carboxylic acid derivatives, so that in their reaction, polymers from the class of polyamides, polyesters, polyurethanes and polyureas are formed. The following compounds are examples of azomonomers to be reacted in this way

The invention provides microcapsules, the polymeric capsule wall of which has thermo- and / or photolabile groups as structural elements. With the azo group-containing monomers presented by way of example, microcapsules can be produced by interfacial polycondensation with correspondingly reactive multifunctional compounds, the capsule wall of which can consist of a number of different types of polymer. By varying the structural elements of azomonomers or their reactants, both chemical and physical properties of the capsule wall polymers can be adjusted.

The crosslinking density of the polymers can be influenced by polyfunctional azomonomers and polyfunctional reaction partners. It is therefore possible to produce microcapsules whose relatively thin capsule wall is impervious to any capsule content, in particular an organic solvent, at normal temperatures. When the settable decomposition temperature is reached, the capsule wall polymers disintegrate in an exothermic reaction, whereby molecular nitrogen is split off from the azo groups. The capsule contents are thus released with relatively little energy expenditure.

Claims

1. microcapsules, the polymeric capsule wall of which has thermo- and / or photolabile groups as structural elements, which are obtained by interfacial polycondensation of azo groups-bearing monomers with correspondingly reactive multifunctional compounds to form polyamides, polycarbonates, polyesters, polyureas or polyurethane, the monomers being of the formula I are shown

I) R ¹ - N = N - R ² in which R ¹ and R ^{2 are the} same or different and are selected from

where Q and Q 'are the same or different and represent a linear or branched divalent alkyl radical having 1 to 6 C atoms,

R ^{3 is} CN or OAc, R ^{5 is} an alkyl radical, R ^{6 is} OH, NH ₂ or NHR ⁵ and R ^{4 is} selected from NH ₂ , NHR ⁵ , -NCO, -SO ₂ Cl, COCl or OH, with with the proviso that each monomer I has three or four identical reactive groups R or R ⁶ .

2. Microcapsules according to claim 1, that the polyfunctional compounds are water-soluble amines or alcohols.

3. Microcapsules according to claim 1 or 2, characterized in that the reactants are low molecular weight compounds with more than two reactive groups.

4. Microcapsules according to one of claims 1 to 3, d a d u r c h g e k e n n z e i c h n e t that the microcapsules are filled with active substances.

5. microcapsules according to claim 4, d a d u r c h g e k e n n z e i c h n e t that dye or color pigments are contained as the active substance.

6. microcapsules according to claim 4, d a d u r c h g e k e n n z e i c h n t that medicaments, fertilizers, pesticides, developers, hardeners or flame retardants are contained as the active substance.

7. A process for the production of microcapsules, which comprises the process steps: a) preparing a first solution of a monomer suitable for polycondensation and containing azo groups in a first organic solvent, b) preparing a second solution of a multifunctional

Compound which is capable of reacting with the monomer to form polyester, polyamide, polyurea or polyurethane in a preferably aqueous solvent which is immiscible with the organic solvent, c) preparing a third solution of a dispersant in the first organic or the second solvent and d) combining the three solutions with stirring at high stirring speed above 1000 rpm to produce a dispersion, the monomers of the formula I obeying,

I) R ¹ - N = N - R ² in which the radicals R ¹ and R ^{2 are the} same or different and are selected from the group

in which Q, like Q ', represents a linear divalent alkyl radical having 1 to 6 C atoms, R ^{3 is} CN or OAc, R ^{4 is} NH ₂ , NHR ⁵ , COOH, -NCO, -SO ₂ Cl or COX, X is Cl or Br is, R ^{5 is} an alkyl radical and R ^{6 is} OH, NH ₂ or NHR ⁵ .

8. The method according to claim 7, so that the first or the second is combined with the third solution, a dispersion is produced with vigorous stirring, and that the second or the first solution is added slowly and with stirring.

9. The method according to claim 7 or 8, d a d u r c h g e k e n n z e i c h n e t that the polycondensation is carried out at room temperature or slightly elevated temperature.

10. The method according to any one of claims 7 to 9, d a d u r c h g e k e n n z e i c h n e t that polyvinyl alcohol is used as the dispersant.

11. The method according to at least one of claims 7 to 10, d a d u r c h g e k e n n z e i c h n e t that an active ingredient is contained in the phase to be encapsulated, that is, the continuum.