DE69115637T2 - Encapsulated active substrates that can be released again - Google Patents

Abstract

This invention relates to a process for releasably encapsulating an active substrate which comprises inter alia a bleach activator in a metal salt of an inorganic acid, said salt being soluble in an aqueous medium such that when the encapsulated active substrate is brought into contact with the aqueous medium, the active substrate is released into said medium. This invention is useful for the controlled release of bleach activators into a wash cycle and to stabilise some bleach activators which may otherwise lack stability.

Description

The present invention relates to active substrates, such as bleach activators, releasably encapsulated in a coating thereon, and methods of using the same.

It is well known to use bleaches and bleach activators in detergent formulations. One of the important aspects of such formulations is that they should be able to be stored for a significantly long period of time both by the manufacturers of such formulations, the distributors of the product, and by the end user, e.g. the housewife who usually buys in bulk and wishes to use it in small quantities for washing when and as needed. However, it is also well known that the components of such formulations, in particular the bleaches and bleach activators, have an unacceptably short shelf life due to their tendency to undergo undesirable physical or chemical changes, leading to deterioration of the formulation, which manifests itself, for example, as loss of activity, discoloration, loss of abrasion resistance, hygroscopicity and thus caking by absorption of moisture, staining of the washed garments or malodor. It has been found that the bleaches and in particular the bleach activators are prone to such undesirable changes.

It has been known to apply protective barrier coatings to relatively unstable compounds to improve their storage stability. Catalysts used in chemical reactions are a well-known example where barrier coatings have been used.

Peroxygen compounds for use in bleaching formulations are protected with barrier coatings comprising metal salts in e.g. US-A-4105827 and FR-A-2229768. Various types of bleach activators are encapsulated in metal salt protective coatings in EP-A-174132 and CA-A-0676777.

In the case of active substrates, such as bleach activators, there is an additional problem that any coating applied should be such that:

(a) the active species is readily released upon contact with the aqueous wash system,

(b) it mitigates any problems of dye deterioration or staining through the use of a bleach activator,

(c) the barrier coating itself should not interfere with the other components in the formulation,

(d) the barrier coating does not adversely affect the laundry or the washed garments with regard to causing dye deterioration or staining; and

(e) should be user-friendly and environmentally friendly when discharged with the washing water.

It has now been found that the relative instability of active substrates, such as bleach activators, or the risk of dye damage or staining caused by them, can be mitigated by encapsulating the substrate in powder or granular form in a barrier coating capable of releasing the active substrate in the aqueous wash system without having an adverse effect on the washed garments, the consumer or the environment.

Accordingly, the present invention relates to a method for encapsulating a bleach activator, which comprises the following steps:

i) forming a particulate composite substrate having a particle size in the range 200-2000 µm consisting of the bleach activator and a binder and optionally containing a disintegrant, a surfactant and/or a filler,

(ii) coating the particulate composite substrate with a solution of a metal salt of an inorganic acid which is soluble in water to a level of at least 3 g per 100 g at 15ºC, and

iii) drying the coated particles.

The process is particularly useful for encapsulating cyclic anhydride activators of formula 1 and lactones of formula II and in the process the activator preferably comprises at least one compound consisting of a cyclic anhydride of Structural formula (I) or a lactone of structural formula (II) below:

wherein Q is a divalent organic group such that Q and N together with the carbonyl and oxygen functions form one or more cyclic structures, and R in (I) is H, an alkyl, aryl, halogen, a carboxyl or a carbonyl-containing function and R in (II) is a C2 or higher alkyl, alkaryl, aryl, aralkyl, alkoxyl, haloalkyl, amino, aminoalkyl, dialkylamino, carboxyl or a carbonyl-containing function.

By the term "active substrate" as used herein and throughout the specification is meant a bleach activator as such or a composite comprising such a bleach activator and one or more other components including conventional binders such as a bentonite clay; surfactants such as polyoxyalkylene sorbitan oleate esters, e.g. Tween (registered trademark) and alkali metal salt of a polycarboxylic acid, e.g. Dispex-G40 (registered trademark, ex Allied Colloids, UK); disintegrants such as cross-linked carboxymethylcellulose derivatives, e.g. Ac-di-sol (registered trademark) or a polyacrylate; and fillers such as cellulose type, e.g. Avicel (registered trademark).

Bleach activators of formula (I) are claimed and described in our published EP-A-331300 and those of formula (II) are claimed and described in our published EP-A-332294 and are incorporated herein by reference.

In particular, such compounds include bleach activators such as 2-hydrocarbyl-(4H)-3,1-benzoxazin-4-ones (particularly the 2-methyl and 2-aryl derivatives), the 2-N,N-dialkylamino-(4H)-3,1- benzoxazin-4-one (particularly the 2-N,N-dimethyl derivative) and isatoic anhydride and its homologues and derivatives). Bleach activators described in published EP-A-170386 (N-alkoyl-6-aminoperoxycarboxylic acids and their salts) and in GB-A-2832021 (tetraacetylethylenediamine) may also be encapsulated in a coating to improve their stability and are incorporated herein by reference.

The term "aqueous medium" as used herein and throughout the specification is intended to encompass the aqueous alkaline medium present in a wash cycle or during a wash operation.

The metal salts of inorganic acids which may be used to form the encapsulating coating must be soluble in the aqueous medium, although it would be advantageous if they were soluble in water. The solubility should preferably be at least 3 g/100 g of the aqueous medium at ambient temperatures, e.g. 15°C, but the higher the solubility the better. Examples of such compounds include the water-soluble carbonates, sulphates and phosphates of the metals in Groups I-III of the Periodic Table, particularly the alkali metals, some alkaline earth metals such as magnesium, zinc and Group III metals such as aluminium. Particularly preferred are the sulphates and phosphates of sodium, potassium, zinc and aluminium. Whatever metal salt is chosen, the salt should be such that it is capable of forming an encapsulating barrier coating on the active substrate.

In the case of some compounds of structure type (II), especially when the compound is a 2-aryl-substituted benzoxazin-4-one, such activators cause dye damage. The performance of such activators can be improved by using an encapsulating coating of a zinc salt such as zinc sulfate. In contrast, for activators of type (I), i.e. those having an isatoic anhydride type structure, the problems of staining and dye damage can be mitigated by using an encapsulating coating of an aluminium salt such as aluminium sulfate.

The encapsulating coating should suitably form a minor proportion of the encapsulated product. That is, the active substrate should be at least 50% w/w of the encapsulated product; preferably more than 65% w/w of the encapsulated product and most preferably 65-80% w/w.

Ideally, the thickness of the coating encapsulating the active substrate is suitably such that it does not flake off or cannot be easily removed by rubbing, and preferably is at least 0.03 µm.

However, the encapsulation should be such that it completely covers the coated active substrate. The active substrate is preferably in the form of powder or granules prior to encapsulation. The initial particle size of the substrate should preferably be 50-200 µm for the powder and 200-2000 µm for the granules. Substrates having particle sizes in this range can be prepared from commercially available material by milling and/or attrition, granulation or, preferably, by the process of extrusion and spheronization. The powder or granules of the active substrate may be in the form of a composite when prepared comprising the bleach activator, binder, dispersing aid, surfactants and fillers as described above. The encapsulating coating may be applied to the substrate in a conventional manner. It is preferable to create a fluidized bed of the substrate particles and spray them with a solution of the metal salt. When using this method, conditions should be carefully controlled to achieve satisfactory encapsulation. For example, the fluidization of the substrate particles should be such that they are suspended in the fluidizing medium as separate and individual particles in the coating environment for a sufficiently long period of time to allow the spray of the metal salt to substantially completely encapsulate and hermetically seal each particle individually. At the same time, the residence time in the coating environment and the temperature in the coating environment should be such that the encapsulated particles are substantially dry and resistant to (a) frictional coating loss and (b) agglomeration before leaving the environment. In In this context, the choice of a fluidizing medium is also important in that it should be substantially inert to the encapsulation process and should not adversely affect the nature of the substrate being encapsulated or the encapsulating coating. An example of a suitable fluidizing medium is air.

The present invention is further explained with reference to the following Examples.

example 1

In the example below, the following components were used in a formulation to prepare the active substrate:

Isatoic Anhydride (Bleach Activator) 80% w/w

Bentonite clay (binder) 9% w/w

Ac-di-sol* (disintegrant) 2% w/w

Avicel* (a cellulosic filler) 9% w/w

* Registered trademark

The above components were doughed in water and subjected to extrusion followed by spheronization to obtain granules with a particle size of 500-1000 µm.

The grains were then fluidized in a Strea-1 fluidized bed reactor at a spray rate of about 6 g/min through a two-fluid nozzle with an atomizing air pressure of about 0.8 bar.

Air was used as the fluidizing medium at an air flow rate of 10 units on Strea 1. The air inlet temperature was 48ºC and the air outlet temperature was 36ºC.

A solution of 150 g of anhydrous sodium sulfate in 700 g of water was used as the encapsulating solution.

This sodium sulfate solution was prepared using a Wurster column in a direction consistent with the fluidizing air. Spraying the solution to encapsulate the grains took approximately 1.5 hours. The encapsulated grains were then dried for an additional 20 minutes, during which the temperature was increased to 52ºC at the inlet port and 46ºC at the outlet port to bake the encapsulating coating into a solid, dry barrier layer.

The encapsulated granules thus prepared were mixed at a concentration of 5% w/w with a detergent powder containing 80% w/w ECE base (from Westlairds Limited, North Green, Datchet, Slough SL3 9JH, Berkshire, UK) and 15% w/w of a perborate bleach and stored in open packs at 37ºC and 70% relative humidity. The resulting detergent formulation did not suffer any discolouration or significant loss of activity after 2 months of storage.

The fact that the solubility of the coating in the aqueous medium is not affected is illustrated by a comparison of coated and uncoated beads from the above formulation, from which it can be seen that there is no significant difference between whole and broken beads:

Test conditions: 40ºC, 2.5% active isatoic anhydride (hereinafter "IA") was used in a detergent base containing sodium perborate tetrahydrate. Washing was carried out in a Terg-o-tometer for 20 minutes. 5.85 g detergent base plus 0.15 g bleach activator with 100% activity was used, i.e. 0.3 g of the formulated isatoic anhydride beads.

Substrate fabric measurements: EMPA 114 red wine stains and WPK BC-1 tea stains Reflectance measurements were made using an ICS-Texicon Micromatch spectrometer. The results are expressed as percentage stain removal (% FE) calculated using the following equation:

%FE = L (End) - L (Start)/ L (Default) - L (End) x 100

L (End) = Final reflection value

L (initial) = initial reflection value

L (Standard) = Standard reflection value

The L-value is the reflection value as defined by the Committee Internationale D'Eclarage LAB System (CIELAB). FORM Isatoic anhydride (from BASF), whole beads as per formulation broken beads as per formulation Tetraacetylethylenediamine Blank Isatoic anhydride (least difference) coated with Na₂SO₄ Activity in IA 50% (neat, from Warwick Int.) Detergent base only 53-106 microns

Example 2

Granules containing 80% isatoic anhydride bleach activator were encapsulated with the inorganic salts detailed below. These coated granules (20 parts) were mixed with a phosphate-free detergent base containing 25% sodium perborate monohydrate (80 parts). Samples of the detergent formulations thus prepared were then sprinkled in narrow strips approximately 2 cm wide on a white cotton test fabric (EMPA 221). This fabric had previously been placed on a tray and moistened with sufficient water to be absorbed by and moisten the strips of detergent formulation. After 30 minutes, the cotton test fabric was thoroughly rinsed under Rinsed with running tap water and air dried.

The above test was repeated three more times. A panel of five observers was then used to compare the degree of brown stain formation on the cotton fabric under artificial daylight (D65) lighting in an ICS Texicon light box. Each observer was asked to rate the stain formation beneath the detergent strips on a scale of 1 to 5, where the fabric(s) with the fewest stains = 1 and the fabric(s) with the most stains = 5.

The grades received are given below. Formulation containing a bleach activator encapsulated with Average result Zinc sulphate heptahydrate (approx. 38% w/w) Zinc sulphate heptahydrate (approx. 31% w/w) Zinc sulphate heptahydrate (approx. 25% w/w) Aluminium sulphate hexadecahydrate (approx. 38% w/w) Aluminium sulphate hexadecahydrate (approx. 31% w/w) Aluminium sulphate hexadecahydrate (approx. 25% w/w) Sodium acetate (approx. 38% w/w)

The results show that the bleach activator grains encapsulated with the zinc and aluminum salts show a significantly lower tendency to stain the test fabric than those encapsulated with a salt of an organic acid.

Example 3

Granules containing 82% 2-phenylbenzoxazin-4-one (2PB4) bleach activator were encapsulated with the inorganic salts detailed below. These coated granules (20 parts) were mixed with a phosphate-free detergent base containing 25% sodium perborate monohydrate (80 parts). Samples of the detergent formulations thus prepared were then spread in narrow strips approximately 2 cm wide on a test fabric made of cotton dyed with Immedial Black (EMPA 115). This fabric had previously been placed on a tray and diluted with sufficient water moistened to absorb into and moisten the strips of detergent formulation. After 30 minutes, the cotton test fabric was thoroughly rinsed under running tap water and air dried. The above test was repeated.

Reflectance measurements were taken using an ICS-Texicon Micromatch spectrometer. The average results from 10 readings below each test strip on each test fabric are expressed as percent stain removal (%FE).

Composition of 2PB4 grains:

2PB4 82% w/w

Bentonite Clay 13% w/w

Dispex G40 2% w/w

Avicel 3% w/w

Formulation containing 2P84 bleach activator encapsulated with: %FE

Aluminium sulphate (approx. 38% w/w coating) 14.4

Zinc sulfate (approx. 38% w/w coating) 13.7

Uncoated grains 27.6

Visual inspection confirmed the significant reduction in dye damage caused by "pore formation" for the grains coated with zinc and aluminum sulfate compared to uncoated grains.

The results show that the bleach activator grains encapsulated with zinc and aluminum salts have a significantly lower tendency to damage dyes.

Claims (11)

1. A method for encapsulating a bleach activator, comprising the following steps: i) forming a particulate composite substrate having a particle size in the range 200-2000 µm, consisting of the bleach activator and a binder and optionally containing a disintegrant, a surfactant and/or a filler, (ii) coating the particulate composite substrate with a solution of a metal salt of an inorganic acid which is soluble in water to a level of at least 3 g per 100 g at 15ºC, and iii) drying the coated particles. 2. The method of claim 1, wherein the particulate composite substrate is suspended in air in a fluidized bed during the coating step. 3. A method according to any preceding claim, in which the metal salt is used in an amount which inhibits damage to dye and/or soiling of the fabric. 4. A process according to claim 3, wherein the thickness of the salt layer of the product is at least 0.03 µm. 5. A process according to any preceding claim, in which the metal of the metal salt is selected from alkali metals, alkaline earth metals, zinc and Group II metals. 6. The method of claim 5, wherein the metal salt is a zinc or aluminum salt. 7. The method of claim 6, wherein the metal salt is selected from zinc sulfate and aluminum sulfate. 8. A process according to any preceding claim, in which the encapsulated activator is incorporated into a detergent powder containing a peroxygen bleach source. 9. A process according to any preceding claim, wherein the activator is at least one compound selected from a cyclic anhydride of structural formula I or a lactone of structural formula II below wherein Q is a divalent organic group such that Q and N together with the carbonyl and oxygen functions form one or more cyclic structures, and R in (I) is H, an alkyl, aryl, halogen, a carboxyl or a carbonyl-containing function and R in (II) is a C2 or higher alkyl, alkaryl, aryl, aralkyl, alkoxyl, haloalkyl, amino, aminoalkyl, dialkylamino, carboxyl or a carbonyl-containing function. 10. The method of claim 9, wherein the bleach activator is selected from 2-hydrocarbyl-(4H)-3,1-benzoxazin-4-one, 2-aryl-(4H)-3,1-benzoxazin-4-one, 2-N,N-dialkylamino-(4H)-3,1-benzoxazin-4-one and isatoic anhydride. 11. A process according to any preceding claim, in which the binder is a bentonite clay, the surfactant is a polyoxyalkylene sorbitan oleate ester or an alkali metal salt of a polycarboxylic acid, the disintegrant is a cross-linked hydroxymethylcellulose derivative and the filler is a cellulose type filler.