EP0272402A2 - Process for coating granules of peroxycarboxylic acids - Google Patents

Abstract

The process comprises spraying onto previously produced peroxycarboxylic acid granules, while agitating, an aqueous solution or dispersion of a polymeric carboxylic acid which is soluble in aqueous alkaline medium, and drying. The granules coated in this way have high resistance to abrasion and, mixed with other substances, low levels of chemical interactions.

Description

The present invention relates to a process for the preparation of bleaching agents in granular form which contain solid peroxycarboxylic acid as the bleaching component, and to the bleaching agents which can be prepared by this process and their use.

Bleaching agents based on peroxygen compounds are widely used in the field of textile bleaching. In particular, hydrogen peroxide and its inorganic derivatives, such as sodium perborate and sodium percarbonate, have found widespread use. On the one hand, they are very safe to handle, mild oxidizing agents and on the other hand they have a good bleaching capacity at sufficiently high temperatures. For use at lower temperatures, however, stronger oxidizing agents, such as peroxycarboxylic acids, are required in order to achieve bleaching in a sufficiently short time. Peroxycarboxylic acids, also called percarboxylic acids or simply peracids, are very aggressive oxidizing agents that tend to exothermic decomposition and explosion, and cannot be handled in their pure form without protective measures. It has therefore been proposed, inter alia, to avoid these disadvantages that these compounds only be generated in situ from the harmless inorganic per-compounds and certain acylating agents, so-called activators, which as such do not show any exothermic decomposition or oxidation reactions, but are at most sensitive to hydrolysis. This process is complex due to the use of two components to be metered separately, and the Akti also requires cation reaction between inorganic per compounds and activators, especially at very low working temperatures, an undesirably long lead time.

For these reasons, efforts have long been made to find suitable measures which make it possible to use percarboxylic acids as such for bleaching textiles, despite their instability and aggressive chemical properties. In particular for use in combination with washing processes, interest has turned to solid percarboxylic acids.

Belgian patent 560 389 describes the stabilization of solid peroxycarboxylic acids with the aid of hydratable inorganic salts, whereby granulation is also possible. The conversion into the granulated form is particularly desirable when the percarboxylic acids are to be mixed with other components, but which, for. B. may not come into direct contact with the peracids because of their oxidation sensitivity. German Offenlegungsschrift 2,422,691 mentions a special embodiment of the stabilization with salts, in which mixtures of magnesium sulfate with little sodium or potassium sulfate are used.

Another measure for preventing undesirable interactions between peroxycarboxylic acids and other components is the encapsulation of peracid particles. In French patent specification 1,262,475, hydrophilic film formers, such as gelatin, are used for this purpose. British Patent 1,387,167 proposes the use of water-impermeable materials, such as fats and waxes, for wrapping. A further variant is offered in German Offenlegungsschrift 27 37 864, in which surfactants are proposed as persuasive materials.

Furthermore, numerous proposals have been made to combine the desensitization by salt hydrates with the coating process: For example in German Offenlegungsschrift 24 22 735, which describes a mixture of two granules, one of which consists of percarboxylic acid particles containing salt hydrates and coated with fatty alcohol. Similar granules are described in US Pat. Nos. 3,770,816 and 4,170,453 and German Offenlegungsschrift 26 52 424. US Pat. No. 4,259,201 gives an example of the use of saline-containing peracid granules in detergents.

Although the measures described have solved a number of problems with the use of peroxycarboxylic acids, until recently it was still a long way from a percarboxylic acid formulation which met all requirements for safe handling, mechanical and chemical stability, solubility and economical production. For example, the granules of peracids and inorganic salts represent sufficiently desensitized forms; however, they are only slightly resistant to abrasion, so that in many cases it is not possible to prevent the release of the peroxycarboxylic acids from the granules during storage and thus the oxidation of other sensitive components of the bleaching preparations which contain these granules. The use of coating substances improves the mechanical properties of the granules and reduces the interaction with other components, but has other disadvantages, such as poor chemical stability with some hydrophilic coating substances or impairment of dissolution in water with hydrophobic coatings or those made from anhydrous surfactants.

Therefore, efforts are still being made to find new peracid formulations with overall better properties, and attempts are being made, inter alia, to determine the dependence of stability on the type of to investigate the auxiliary substances used. So many complexing agents, which are able to mask heavy metals, have proven themselves with almost all peroxycarboxylic acids as stabilizers against catalytic decomposition, while e.g. B. in certain peroxycarboxylic acids, as mentioned in US Pat. No. 3,639,285, surfactants promote decomposition. In the case of other peroxycarboxylic acids, as is evident from European laid-open specification 74 730, certain coating agents have a destabilizing effect. Based on these and other similar results, it now seems to be accepted that experience with one type of peracid can rarely be transferred to another type. According to this, optimal formulations can only be achieved by measures that are individually tailored to the respective type of percarboxylic acid.

A particularly stable formulation of solid aliphatic peroxycarboxylic acids is described in the earlier application DE 35 15 712.7. It is a granulate of peracid, hydratable inorganic salt and an organic polymer compound that is soluble in an alkaline-aqueous medium, in which all components are evenly distributed in the individual granules of the granulate and that in water alone has a pH in the weakly acidic range results.

This peroxycarboxylic acid formulation is a sufficiently desensitized, abrasion-resistant and dust-free and therefore easy to handle form of the solid aliphatic peracids. Despite the high mechanical stability, the granules quickly dissolve in water or an alkaline aqueous medium, so that the peracids contained without delay as a bleaching agent in the Fleet are available. The peracids are chemically unusually stable in this form and can therefore be stored for a long time even under unfavorable conditions. The preferred area of application is the bleaching of textiles in the washing process.

Although a particular advantage of the granules from this earlier application DE 35 15 712.7 is their compatibility with other detergent constituents, in particular alkaline substances and components sensitive to oxidation, it was found that these granules, albeit much weaker than others, showed certain advantages during storage Perfume components, which are used in detergents, can enter into disturbing reactions.

In an effort to eliminate the undesirable interactions between granulated solid peracids and easily oxidizable substances, especially perfume components, it has now been found that it is possible to encase peracid granules with very specific substances in such a way that these interactions are significantly reduced. This finding was not limited to the granules of DE 35 15 712.

The invention therefore relates to a process for coating granulated solid peroxycarboxylic acids, which consists in spraying prefabricated peracid granules while moving with the aqueous solution or dispersion of a homo- or copolymer of an unsaturated carboxylic acid containing 3 to 6 carbon atoms which is soluble in an alkaline-aqueous medium and drying simultaneously and / or subsequently. Further objects of the invention are the bleaching agents that can be produced by this method and their use.

The new process leads to a granular bleaching agent, the individual parts of which consist of a peracid-containing core with a coherent shell of polymers. Such granules tend to interact to a particularly small extent with surrounding materials and therefore, when mixed with substances sensitive to oxidation, lead to exceptional storage stability. It is particularly remarkable Resistance of substances sensitive to oxidation, especially perfumes, when they are present together with the granules in a mixture with alkaline components, for example in powder detergents.

In addition to improving the storage stability, the coating with the polymeric carboxylic acids which are soluble in an alkaline aqueous medium leads to a mechanical solidification of the granulate particles, which is noticeable in reduced abrasion and in this way makes it possible to also use granules for technical purposes previously considered to be insufficiently stable. This is achieved without significantly impairing other advantageous properties of the granules to be coated, in particular their solubility in water or in an aqueous-alkaline medium.

Suitable coating substances are polymeric carboxylic acids which are soluble in an aqueous alkaline medium and are prepared by homo- or copolymerization of unsaturated carboxylic acids having 3 to 6 carbon atoms or their anhydrides. Partial salts of these polymeric carboxylic acids are also regarded as such within the scope of the invention, provided that they do not give a pH of not more than 8, preferably not more than 6.5, in 1 percent mixture with water. The homopolymers of acrylic acid, methacrylic acid, alpha-hydroxyacrylic acid, maleic acid, fumaric acid and crotonic acid and the copolymers of these monomers with one another and the copolymers with monomers which do not carry carboxyl groups, in particular ethylene, vinyl acetate, vinyl methyl ether, styrene and the like, are particularly preferred.

Of these in turn, the copolymers of acrylic acid and / or methacrylic acid with maleic acid (molar ratio 1: 5 to 5: 1) and, in particular, polyacrylic acid are very particularly preferred as the coating material.

The average molecular weight of the polymeric carboxylic acids is usually above about 1000, preferably above about 5000, and in particular above about 10,000. The upper limit of the molecular weight is determined primarily by the viscosity of the solution and can be above 1,000,000. However, the molecular weight of the polymers used as coating substances is preferably below about 250,000, in particular below about 100,000.

Of course, it is also possible to incorporate substances other than the polymers that can be used as coating substances in the coating, provided that the properties of the coating and the granulate are not adversely affected thereby.

The coating substances can be applied using methods known per se, for example by spraying aqueous solutions or dispersions of the coating substance onto the prefabricated granules while these are being moved on a plate or in a drum. Through a suitable choice of the amount of liquid, the rate of addition and the mechanics, it can be achieved that the particles do not cake together. Drying of the granules, for example by means of an air stream, can begin while the solution is being applied, in which case it may be expedient to keep the granules moving. The degree of dryness can largely be adapted to the later requirements for the granules, but is usually chosen so that the finished granules have approximately the water content that the starting granules also had.

A particularly preferred coating method is to spray the aqueous polymer solutions or dispersions onto the granulate particles in a fluidized bed while drying with warm air at the same time. On the one hand, this method is particularly flexible with regard to the variation of almost all ver driving parameters and on the other hand provides a particularly dense coating. In the context of this invention, processes in the active bed are also considered to be processes in which the fluidized bed is not limited in the conventional sense, but the granulate particles are provided with the shell material essentially in a gas stream.

It goes without saying that the process according to the invention is carried out at temperatures which do not impair the granules used, for example as a result of melting or decomposition of the peracid. The temperature is therefore preferably controlled such that the granulate particles do not assume temperatures above 45 ° C., in particular not above 40 ° C. As long as the granules are sufficiently moist, the ambient temperature may well be above these limits. When drying with air, the supply air temperature can be up to 70 ° C and even higher, but is preferably kept between 40 and 60 ° C, in particular between 55 and 60 ° C.

The concentration of the aqueous polymer solution that is sprayed on for coating depends primarily on technical boundary conditions, such as the viscosity of the solution, the tendency of the polymers to stick and the drying rate. Usual concentrations are preferably between 10 and 40% by weight, in particular between 15 and 30% by weight.

The amount of wrapping material applied to some extent affects the effectiveness of the wrapper, with thicker layers generally providing greater protection. The objectives of the invention can usually already be fully achieved with an amount of 0.2 to 10% by weight of coating substance, calculated as a dry polymer and based on the finished granulate; Granules which have been coated with 0.5 to 5% by weight of polymers are particularly preferred.

A wide variety of peracid granules are suitable as the starting material for the process according to the invention, provided that they are wetted by aqueous polymer solutions. Accordingly, the encasable granules can contain peroxycarboxylic acids of the most varied types, such as aromatic peracids, aliphatic peracids and araliphatic peracids, which can optionally be substituted and which can contain the percarboxyl group -CO₃H one or more times in the molecule. A large number of examples of such granules can be found in the publications cited in the introduction to the description.
In addition to the peracids, the granules suitable as starting material generally contain at least one desensitizing agent, for example inorganic salt or boric acid, in addition, if appropriate, water, granulating auxiliaries, complexing agents for heavy metals and buffer substances or acids, and other additives, such as surfactants and Solubility modification substances.

In general, preferred starting granules are those which already have a high storage stability and desensitization without the coating according to the invention. The granules of solid aliphatic peroxycarboxylic acids described in the earlier application DE 35 15 712 are therefore particularly preferred as starting granules. The teaching of this application is therefore expressly made part of the subject matter of the present disclosure of the invention. Accordingly, the granules according to the invention preferably contain at their core solid aliphatic peroxycarboxylic acids having 4 to 36 carbon atoms, which have one or more carbon atoms in the molecule and contain the group -CO₃H. They may optionally contain the groups -CO₂H, -CO₂Me, -SO₃H and -SO₃Me or ether oxygen, where Me is an equivalent of a metal cation from the group Na⁺, K⁺, Mg²⁺ and Ca²⁺, but are preferably unsubstituted compounds of the formula C _(nx) H _{(2n + 2-3x)} (CO₃H) _x with n = 4 to 36 and x = 1 to 3. Particularly preferred are the monoperoxycarboxylic acids with 10 - 18 C atoms and the diperoxycarboxylic acids with 6 - 22 C atoms, of which in turn the unbranched alpha, omega-diperoxydicarboxylic acids with 9 - 13 C -Atoms are of outstanding importance because of their particularly good bleaching effect.

The peroxycarboxylic acids should be solid as pure compounds at room temperature, in particular up to 50 ° C. Those peracids which are also of technical quality, ie. i.e. are solid with a clear content of the underlying carboxylic acid up to 50 ° C. The content of peracids in the granules is 3 to 50% by weight, preferably 5 to 30% by weight, and in particular 7 to 20% by weight.

In addition to the aliphatic peracids listed, the granules of DE 35 15 712 preferred as the starting material contain inorganic salts as desensitizing agents and a polymer compound which is soluble in an alkaline aqueous medium as granulation aids, and, if appropriate, water, surfactants, complexing agents and other additives. For further details, reference is made to the text of this application.

The process according to the invention is preferably carried out in such a way that the individual particles of the prefabricated granules do not agglomerate or only agglomerate to a small extent. As a result, the grain size and the grain size distribution of the granules used are essentially retained. The bulk density is also changed insignificantly at most. The grain size and bulk density of the starting granulate are of no importance for the successful implementation of the process; it can be used, for example, on fine granules of 0.1 mm particle diameter as well as on coarse types of 5 mm particle diameter, so that the grain size and the Bulk weight can be fully adapted to the particular application of the granules. The range from 0.1 to 1.6 mm is of particular importance for incorporation into detergent, while coarser granules with grain sizes in the range from 1.6 to 4 mm can also be preferred for independently used special products. The granules according to the invention generally have bulk densities between 400 and 1200 g / l, preferably between 500 and 1100 g / l.

In addition, however, it is also possible to achieve greater agglomeration of the granules used with the method according to the invention, for example through greater moisture penetration during spraying. This can be advantageous if the starting granulate is only available in fine form, for example for manufacturing reasons, but a coarser material is required for the application.

The peracid granules according to the invention can generally be used wherever the percarboxylic acids contained can advantageously be used as oxidizing agents, bleaching agents or disinfectants. A particularly preferred area of application of the bleaching agents according to the invention is the bleaching of textiles in connection with a washing treatment. For this purpose, the granules can be used in a uniform form, ie without further admixtures, but they are preferably made up as scatterable mixtures with other solid active substances which are necessary for textile treatment. A bleaching agent based on the granules according to the invention can contain, for example, alkalizing agents, peracid activators and optionally other bleaching agents, such as perborate, as further active ingredients. For a combined detergent and bleaching agent, furthermore, in particular surfactants, builders, foam-suppressing substances, optical brighteners and perfume are to be mentioned as active ingredients. It works in these ready-made forms extremely low tendency of the granules to interact with components of the mixture which are capable of oxidation, is particularly advantageous.

Examples

• 1. A peracid granulate produced analogously to DOS 35 15 712, example 1, with a grain size of 0.2 to 1.6 mm and a bulk density of approx. 1000 g / l served as the starting granulate. It had the following composition:
  11.5% by weight of alpha, omega-diperoxydodecanedioic acid
  1.9% by weight of alpha, omega-dodecanedioic acid
  3.8 wt .-% MgSO₄
  78.8% by weight Na₂SO₄
  1.0% by weight polyacrylic acid
  3.0 wt% water
• 2. 40 kg of the granules from Example 1 were placed in a fluidized bed installation and set in motion by an air flow of approx. 35-40 m³ / min. The temperature of the supply air was increased to 60 ° C. and at the same time an aqueous solution (20% by weight) of polyacrylic acid (average molecular weight approx. 70,000) was sprayed through a central nozzle onto the moving granules at a rate of 150 g . The addition was stopped after 28 minutes; however, drying was continued for 5 minutes.
  The result was 40.5 kg of coated granules, which had 2% by weight of polyacrylic acid in its shell and showed a grain spectrum that was almost unchanged compared to the starting material. The bulk weight was approx. 950 g / l.
• 3. In the same way as in Example 2, 1 kg of the starting granules according to Example 1 were provided with a coating layer of 5% by weight of polyacrylic acid in a smaller active bed system. In this experiment the speed of the polyacrylics was acid addition (as 20 percent solution) 6 g solution per minute. It was dried for 10 minutes. In this experiment too, the product had a grain spectrum that was largely unchanged from the starting material. The bulk weight was approximately 900 g / l.
• 4. To determine the interaction between peracids and surrounding oxidizable substances, it was investigated to what extent the perfume of a commercially available, powdery, perborate heavy-duty detergent is impaired during storage if this detergent contains peracid granules.

For this purpose, the detergent was mixed with an amount of the respective granules, which corresponded to 0.05% by weight of pure peracid, based on the weight of the peracid-free detergent, and mixed thoroughly. The storage took place at 30 ° C and 80% relative humidity in non-laminated cardboard boxes. After each week, the strength and quality of the odor was assessed by trained perfumers compared to the peracid-free detergent, which was stored under the same conditions.

It was found that the two granules according to Examples 2 and 3 did not cause any odor changes in comparison with the blank sample within 4 weeks, while with the uncoated granules according to Example 1 significant changes in the odor note were found after only 1 week.

Claims (13)

1. A process for coating granulated solid peroxycarboxylic acids, characterized in that a prefabricated peracid granulate is sprayed with agitation with the aqueous solution or dispersion of a homopolymer or copolymer of an unsaturated carboxylic acid containing 3 to 6 carbon atoms which is soluble in an alkaline-aqueous medium, and simultaneously and / or is then dried. 2. The method according to claim 1, further characterized in that the polymer is a homo- or copolymer of acrylic acid, methacrylic acid, alpha-hydroxyacrylic acid, maleic acid, fumaric acid or crotonic acid. 3. The method according to claim 2, further characterized in that the polymer is a copolymer of acrylic acid and maleic acid in a molar ratio of 1: 5 to 5: 1 or, preferably, polyacrylic acid. 4. The method according to any one of claims 1 to 3, further characterized in that 0.2 to 10 wt .-%, preferably 0.5 to 5 wt .-%, of the polymer, calculated as dry matter and based on the finished coated granules , are applied. 5. The method according to any one of claims 1 to 4, further characterized in that the polymer is sprayed in the form of a 10 to 40 percent, preferably 15 to 30 percent, aqueous solution. 6. The method according to any one of claims 1 to 5, further characterized in that the spraying of the polymer and the drying of the granules are largely carried out simultaneously in the fluidized bed with the supply of heated air. 7. The method according to any one of claims 1 to 6, further characterized in that such is used as prefabricated peracid granules according to German Offenlegungsschrift 35 15 712. 8. Coated peracid granules, the individual particles of which consist of a core containing a solid peroxycarboxylic acid and a shell, the core being produced by build-up granulation, characterized in that the shell is composed of a homo- or copolymer of an unsaturated, 3 to 6 carbon atoms containing carboxylic acid is formed. 9. peracid granules according to claim 8, characterized in that the casing is formed from a homo- or copolymer of acrylic acid, methacrylic acid, alpha-hydroxyacrylic acid, maleic acid, fumaric acid or crotonic acid. 10. Peracid granules according to claim 9, characterized in that the casing is formed from a copolymer of acrylic acid and maleic acid in a molar ratio of 1: 5 to 5: 1 or, preferably, polyacrylic acid. 11. peracid granules according to any one of claims 8 to 10, further characterized in that it contains 0.2 to 10 wt .-%, preferably 0.5 to 5 wt .-%, of the enveloping polymer in the casing. 12. Peracid granules according to one of claims 8 to 11, further characterized in that the coated core is a granulate according to German Offenlegungsschrift 35 15 712. 13. Use of a peracid granulate according to any one of claims 8 to 12 for oxidation, bleaching or disinfection, preferably as a bleaching agent in combination with detergents.