EP0643763B1

EP0643763B1 - Releasably encapsulated active substrates

Info

Publication number: EP0643763B1
Application number: EP93910229A
Authority: EP
Inventors: Barry Neil Love; Colin Young
Original assignee: Warwick International Group Ltd
Current assignee: Warwick International Group Ltd
Priority date: 1992-05-29
Filing date: 1993-05-19
Publication date: 1996-07-31
Anticipated expiration: 2013-05-19
Also published as: DE69303900T2; ATE140955T1; DE69303900D1; ES2090997T3; AU4081693A; WO1993024604A1; EP0643763A1; JPH10500433A; CA2136833A1

Abstract

This invention relates to an encapsulated active substrate comprising a bleach and/or a bleach activator releasably encapsulated in a coating of at least one metal salt of an inorganic acid, said salt being soluble in an aqueous medium such that upon contacting the encapsulated substrate with the aqueous medium, the active substrate is released into said aqueous medium, characterized in that the substrate has a preliminary coating of an alkali metal carbonate or a bicarbonate and a final encapsulating coating of a metal salt of an inorganic acid. The coating technique controls the activity of the bleach or bleach activator and minimises dye damage or pinholing of the fabrics washed.

Description

The present invention relates to active substrates such as bleach activators releasably encapsulated in a coating thereon and methods of applying the same.
It is well known to use bleach activators in detergent formulations. One of the important aspects of such formulations is that they should be capable of being stored over a significantly long period both by the producers of such formulations, the retailers of the product and by the end user, eg the housewife, who usually buys in bulk and likes to use it in small aliquots for washing as and when necessary. However, it is also well recognised that the components of such formulations, especially the bleaches and bleach activators, may have an unacceptably short storage life due to their tendency to undergo undesirable physical or chemical changes, thereby resulting in deterioration of the formulation which may manifest itself as, eg loss of activity, discolouration, loss of attrition resistance. hygroscopicity and hence caking by absorption of moisture, staining the clothes washed or as malodour. It has been found that bleaches and bleach activators in particular are prone to such undesirable changes.
It is known to apply protective barrier coatings on relatively unstable compounds to improve their storage stability. Catalysts used in chemical reactions are a well known example where barrier coatings have been applied. In the case of active substrates such as bleaches and bleach activators there is the added problem that any coating applied should be such that:

a. the active species is readily released when in contact with the aqueous wash system, especially at low temperatures;
b. it mitigates any problems of dye damage or staining by the use of a bleach or 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 wash or the clothes being washed in terms of causing dye damage or staining, and
e. should be user friendly and friendly towards the environment when discarded with the wash water.

Of these, (a.) above is fairly critical in determining whether or not a particular barrier coating is suitable. Our published EP-A-0482807 describes barrier coatings for bleach activators of this type with a metal salt of an inorganic acid which is soluble in the aqueous wash system. The reason for using a barrier coating with bleach activators is to minimise the pinholing or dye damage caused by such very active activators. This technique works very well at wash temperatures of around 40°C. However, it has been found that in some cases, especially when the wash temperature is of the order of about 20°C, the coating prevents the activator from being rapidly released into the wash system but by and large meets all the other criteria listed above.
Again, US-A-4105827 describes a process for stabilizing bleaches which are particulate peroxygen compounds by providing a hermetic coating on said compounds with a mixed salt obtained by crystallization of sodium carbonate with another inorganic salt selected from sodium bicarbonate and sodium sulphate. These products are said to be capable of dissolving the peroxygen compounds in a cold wash eg at 20°C but no actual data is given. There is also no evidence in this reference whether such a method of coating minimises dye damage or pinholing caused by the bleach and there is no data on bleach activators.
It has now been found that these problems can be mitigated by encapsulating the substrate with a series of coatings applied sequentially.
Accordingly, the present invention is an encapsulated active substrate comprising a bleach and/or a bleach activator releasably encapsulated in a coating of at least one metal salt of an inorganic acid, said salt being soluble in an aqueous medium such that upon contacting the encapsulated substrate with the aqueous medium, the active substrate is released into said medium, characterised in that the substrate has a preliminary coating of an alkali metal carbonate or alkali metal bicarbonate and a final encapsulating coating of a metal salt of an inorganic acid.
By the term "active substrate" is meant here and throughout the specification a bleach, a bleach activator, a mixture of the two or either of them as such or admixed with the other when formed into a composite with one or more other components including conventional binders such as eg a bentonite clay; surfactants such as polyoxyalkylene sorbitan oleate esters, eg Tween^TM, and an alkali metal salt of a polycarboxylic acid, eg Dispex-G40^TM; disintegrating aids such as cross-linked carboxymethyl cellulose derivatives, eg Ac-di-sol^TM or a polyacrylate; and fillers such as the cellulosic type, eg Avicel^TM.
Examples of bleaches which may be encapsulated in this manner include the peroxygenated compounds such as the percarbonates, the perpyrophosphates. the pertripolyphosphates, the perborates, the percarboxylates such as peracetates, peroxymonosulphates and peroxyphthalates.
Examples of bleach activators which can be encapsulated in this manner include cyclic anhydrides of the structural formula (I) or a lactone of the structural formula (II) shown below:
where Q is at least a divalent organic grouping such that Q and N together with the carbonyl and oxygen functions form one or more cyclic structures and in (I) R is H, an alkyl, aryl, halogen, a carboxylic- or a carbonyl-containing function, and in (II) R is a C₂ or higher alkyl, alkaryl, aryl, aralkyl, alkoxy, haloalkyl, amino, alkylamino, dialkylamino, carboxylic- or a carbonyl-containing function.
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.
In particular, such compounds include bleach activators such as 2-hydrocarbyl-(4H)-3,1-benzoxazin-4-ones (especially the 2-methyl and the 2-phenyl derivatives), the 2-N,N-dialkylamino-(4H)-3,1-benzoxazin-4-ones (especially the 2-N,N-dimethyl derivative), and isatoic anhydride and its homologues and derivatives.
Other bleach activators described in published EP-A-170386 (eg N-alkoyl-6-aminoperoxycarboxylic acids and their salts) and in GB-A-2832021 (eg tetra-acetyl ethylenediamine) can also be encapsulated in a coating according to the present invention to improve their performance and stability.
The term "aqueous medium" as used herein and throughout the specification is meant to include the aqueous alkaline medium encountered in a wash cycle or during a washing procedure.
The active substrate is suitably in the form of a powder or granules prior to the preliminary coating with an alkali metal carbonate or bicarbonate. The initial particle size of the substrate should be preferably from 0.1-200µm for powder and from 200-2000µm for the granules. The choice of particle size of the powder to be granulated will depend upon the nature of the bleach or the bleach activator used. For instance, in the case of 2-phenyl-(4H)-3,1-benzoxazin-4-one (hereafter referred to as "2PB4"), it may be necessary to grind this bleach activator a very fine particle size, eg below 10µm before being granulated. Thus, substrates having the desired particle size within this range can be produced from commercially available material by milling and/or grinding followed by granulation, preferably by the technique of extrusion and spheronisation. Methods of extrusion and spheronisation are described extensively in our published EP-A-0482806. When producing the powder or granules of the active substrate they may be in the form of a composite comprising the bleach and/or bleach activator, binders, dispersing aids, surfactants and fillers as described above. The initial coating of the carbonate or bicarbonate can be applied on the substrate by conventional means. It is preferable to create a fluidised bed of the active substrate particles and to spray the particles with a solution of the alkali metal carbonate or bicarbonate. In this initial step it is not necessary for the active substrate particles to be completely encapsulated by the alkali metal carbonate or bicarbonate coating. This is due to the fact that the function of the alkali metal carbonate or bicarbonate coating is to facilitate the final encapsulating coating of the inorganic acid metal salt to be broken up upon contact with water thereby releasing the active substrate into the wash system..
The preliminary coating is suitably of sodium carbonate or sodium bicarbonate, but is preferably that of sodium carbonate.
The thickness of the preliminary coating is such that it suitably forms less than 5%w/w of the final coated product, preferably less than 2%w/w, eg 1%w/w of the final coated product.
The final encapsulating coating with the metal salt of an inorganic acid can be applied in a manner similar to that described for the preliminary coating of an alkali metal carbonate or bicarbonate. However, in this case the conditions used for coating should be controlled to ensure that the active substrate already having a preliminary coating of an alkali metal carbonate or bicarbonate thereon is substantially completely encapsulated by the final coating. For instance, the fluidisation of the particles in this case should be such that they float in the fluidising medium as separate distinct particles for a sufficiently long time in the coating environment so as to enable the spray of the metal salt solution to completely encapsulate and hermetically seal all of the particles individually. At the same time, the residence time within the coating environment and the temperature within the coating environment are preferably such that before the encapsulated particles emerge from the environment, they are substantially dry and resistant to (a) loss of coating by attrition and (b) agglomeration. In this context, the choice of a fluidising medium is also important in that it should be substantially inert to the encapsulating process and should not adversely affect the nature of the substrate being encapsulated or the encapsulating coating. Examples of suitable fluidising media include air and nitrogen.
The metal salt of the inorganic acid used to form the final encapsulating coating must be soluble in the aqueous medium although it would be advantageous if they are soluble in water. The solubility should be preferably at least 3g/100g of the aqueous medium at ambient temperatures, eg 15°C, although the greater the solubility the better. Examples of such metal salts suitably include the water-soluble sulphates, phosphates and carbonates of the metals in Groups II and III of the Periodic Table, preferably the salts of magnesium, zinc and aluminium. Thus, the final encapsulating coating is most preferably that of aluminium sulphate or zinc sulphate. The thickness of the final encapsulating coating should be such that it does not peel off or is not readily removed or dislodged from the active substrate surface by eg attrition and preferably has a thickness of at least 0.03µm. The final encapsulating coating only forms a minor proportion of the encapsulated product. That is, the active substrate should be at least 50% w/w of the encapsulated product, preferably greater than 65% w/w and most preferably from 65-85Zw/w of the encapsulated product. This means that the encapsulating coating itself suitably forms only 15-35%w/w, eg 18% of the final product, It has been found that ideally, the mole ratio of the preliminary coating material to the final encapsulating coating material is no greater than 1:1.
As stated above, the function of the preliminary coating of an alkali metal carbonate or bicarbonate is to facilitate the release of the active substrate from its encapsulating final coating into the wash system. However, due to the nature of the two coating steps and compounds used for the coatings involved, it is likely that in some cases, the final encapsulating coating step, eg with the aluminium or zinc salt, will in itself result in a premature reaction between the encapsulating metal salt and the preliminary coating of carbonate and bicarbonate, thereby damaging the encapsulating coating and hence detracting from the desired storage stability or release rate of the final product. In order to minimise this effect, it has now been found that it is advantageous to have an intermediate coating between the preliminary carbonate/bicarbonate coating and the final encapsulating metal salt coating. This intermediate coating should be of a compound readily soluble in water or at least in the aqueous medium used for the wash and is suitably, though not necessarily, an alkali metal salt of the same inorganic acid as that used for producing the aluminium or zinc salt of the final coating. Thus, if the final coating is of an aluminium or zinc sulphate, the intermediate coating is preferably that of sodium sulphate.
The intermediate coating can be applied using the same technique as described above and should cover all the carbonate/bicarbonate sites on the active substrate surface formed in the preliminary coating step in order to prevent premature reaction thereof with the final encapsulating coating.
The thickness of the intermediate coating should be such that it suitably forms less than 10%w/w, preferably from 2-5%w/w of the final encapsulated product.
The present invention is further illustrated with reference to the following Examples:

EXAMPLES:

2PB4 was sieved to <1mm prior to fine grinding in a Hosokawa Micron Ltd AF G100 fluid air jet mill and classifier. The resulting product had a particle size of <10µm as determined by a Sympatec laser diffraction spectrometer.
Granules were then prepared from the components tabulated below by mixing with water to form a dough, followed by extrusion, spheronisation and drying to obtain granules having a particle size of up to 2 mm. Granules A and B were produced on a Caleva Ltd model 10 extruder and model 120 spheroniser. Granules C, D and E were produced on a NICA System AB model E140 extruder and model S320 spheroniser. Drying was carried out in an Aeromatic Strea-l fluid bed drier. The dry granules were sieved and the fraction between 600 and 1180µm retained.

Granule Ref. A B C D E

2PB4 85 85 76 76 76

ASB 60 clay (tradename) 12 12 17 17 17

Avicel® PH101 2 2 6 6 6

Dispex® G40 1 1 1 1 1

The granules B, D and E were then coated in a Strea-l fluid bed apparatus using a Wurster column and co-current spraying through a 0.8mm nozzle with air as the atomising medium. Coating solutions were heated to approximately 50°C.

Coating Data:
Granule Ref:	B	D	E
Wt of Granules (g)	250	200	200

1st coating:
Metal Salt	Al₂(SO₄)₃.18H₂O	Na₂CO₃	Na₂CO₃
Wt of salt (g)	53.5	2.5	2.7
Wt of water (g)	150	50	50
Inlet temp (°C)	62	56	56
Coating time(min)	44	14	15
Drying time (min)	11	6	6

2nd coating:	n/a
Metal salt		Na₂SO₄	Na₂SO₄
Wt of salt (g)		5.0	5.5
Wt of water (g)		50	50
Inlet temp (°C)		56	56
Coating time (min)		15	15
Drying time (min)		10	10

3rd coating:	n/a
Metal salt			Al₂(SO₄)₃.18H₂O
Wt of salt (g)		45.6	65.7
Wt of water (g)		150	150
Inlet temp (°C)		56	56
Coating time (min)		39	65
Drying time (min)		8	10

The final theoretical activities of the granules (%) can be summarised as follows:

Granule Ref:	A	B	C	D	E
2PB4	85	70	76	60	55.5
Coatings:
Na₂CO₃	-	0	-	1	1
Na₂SO₄	-	0	-	2	2
Al₂(SO₄)₃·18H₂O	-	17.6	-	18	24

Granules A, B and C are comparative granules and granules D and E illustrate the invention.

Detergent Formulations:

The granules produced as above were mixed with the following materials to give a detergent formulation containing 4% 2PB4 (expressed as 100% active bleach activator).

ECE Base (tradename): 56.7% (Westlairds Ltd)
Sokolan® CP5: 2.0% (BASF)
Dequest® 4046: 1.0% (Monsanto)
Tinopal® CBS-X: 0.2% (Ciba-Geigy)
Antifoam DB100: 0,1% (Dow Corning)
Sodium perborate.H₂O: 12.0% (Interox)
2PB4 granules: q.s. to give 4% active 2PB4
Na₂SO₄: q.s. to 100%

Wash tests were carried out using the above formulation in Miele W784 automatic washing machines,
20°C setting, programme 4 short spin option, using 90g of test powder in the main wash. Each machine contained a 2Kg ballast load of mixed fibre materials and two 7.5 cm² tea stained test cloths (CFT BC-1, Centre for Test materials, Vlaardingen, Holland). Reflectance measurements were taken with an ICS-Texicon Micromatch spectrometer. The results obtained are expressed as a percentage stain removal (%SR) calculated from the following expression: $%SR = \frac{L _{(final)} - L _{(initial)}}{L _{(standard)} - L _{(initial)}} x 100$
wherein
L value is reflectance value as defined in the Committee International D'Eclarage LAB system (CIELAB)
L_(final) = final reflectance value
L_(initial) = initial reflectance value
and L_(standard) = standard reflectance value of clean cloth.
The following results compare the effect of a single coating of aluminium sulphate (granule B) on the performance of the activator compared with the same granule crushed in a pestle and mortar (to destroy the effectiveness of the coating) and also compared with the uncoated granule (A).
DETERGENT POWDER CONTAINING 4% 2PB4 AS:

Granule B (crushed) Granule B Granule A

%SR tea stain at 20°C 34 40 40

(least significant difference = 1.3)
The following results demonstrate that sequentially coated granules according to the invention (Granules D and E) show no loss of performance at 20°C when compared with the uncoated Granules C.
DETERGENT POWDER CONTAINING 4% 2PB4 AS:

Granule D Granule E Granule C

%SR tea stain at 20°C 38 39 38

(least significant difference = 1.0)

Pinholing Dye Damage:

The effectiveness of the sequential coated granules in reducing "pinholing" dye damage was assessed as follows:
Samples of the detergent powders containing the granules D, E and C were spread in narrow strips of ca.
1 cm width onto a test cloth of cotton dyed with immedial black (EMPA 115). This cloth had been placed in a tray and dampened with sufficient water to absorb into and dampen the strips of detergent formulation. After 30 minutes the test cloth was thoroughly rinsed in running tap water and air dried.
Visual observations showed a marked reduction of "pinholing" dye damage for the coated granules D and E when compared with the uncoated granules C.

Claims

An encapsulated active substrate comprising a bleach, a bleach activator or mixtures thereof releasably encapsulated in a coating of at least one metal salt of an inorganic acid, said salt being soluble in an aqueous medium such that upon contacting the encapsulated substrate with the aqueous medium, the active substrate is released into said medium, characterised in that the substrate has a preliminary coating of an alkali metal carbonate or alkali metal bicarbonate and a final encapsulating coating of a metal salt of an inorganic acid.
An encapsulated active substrate according to Claim 1 wherein the bleach so encapsulated is a peroxygenated compound selected from the group consisting of percarbonates, perpyrophosphates, pertripolyphosphates, perborates, percarboxylates, permonosulphates and peroxyphthalates.
An encapsulated active substrate according to Claim 1 wherein the bleach activator so encapsulated is either a cyclic anhydride of formula (I) or a lactone of formula (II):
where Q is at least a divalent organic grouping such that Q and N together with the carbonyl and oxygen functions forms one or more cyclic structures and in (I) R is H, an alkyl, aryl, halogen, a carboxylic- or a carbonyl-containing function, and in (II) R is a C₂ or higher alkyl, alkaryl, aryl, aralkyl, alkoxy, haloalkyl, amino, alkylamino, dialkylamino, carboxylic- or a carbonyl-containing function.
An encapsulated active substrate according to any one of the preceding Claims wherein the final encapsulating coating is that of a metal salt of an inorganic acid, selected from the group consisting of a sulphate, a phosphate or a carbonate of a metal from Groups II and III of the Periodic Table.
An encapsulated active substrate according to any one of the preceding Claims wherein the final encapsulating coating is that of a metal salt of an inorganic acid which is a salt of magnesium, zinc or aluminum.
An encapsulated active substrate according to any one of the preceding Claims wherein the final encapsulating coating has a thickness of at least 0.03µm.
An encapsulated active substrate according to any one of the preceding Claims wherein the mole ratio of the preliminary coating of an alkali metal carbonate or bicarbonate to the final encapsulating coating of the metal salt of an inorganic acid is no greater than 1:1.
An encapsulated active substrate according to any one of the preceding Claims wherein an intermediate coating of an inorganic compound soluble in water or in the aqueous medium is applied on the substrate having a preliminary coating of an alkali metal carbonate or bicarbonate thereon prior to applying the final encapsulating coating.
A method of encapsulating an active substrate comprising a bleach and/or a bleach activator in a coating, said method comprising:
a. fluidising a particulate bed of the active substrate in powder or granular form and spraying said particles with a spray of a solution of an alkali metal carbonate or an alkali metal bicarbonate so as to form a preliminary coating thereon,

b. further fluidising the particles having the preliminary coating of an alkali metal carbonate or bicarbonate thereon in a fluidising medium such that the particles with the preliminary coating thereon float as separate particles in the fluidising medium for a sufficiently long time to enable application of an encapsulating coating of an inorganic metal salt thereon,

c. applying on the particles having the preliminary coating so floated a spray of a solution of the inorganic metal salt until each particle having the preliminary coating thereon is completely encapsulated and hermetically sealed by a final coating of the inorganic metal salt.
A method according to Claim 9 wherein the fluidisation of the particles having preliminary coating thereon and the duration of the final coating with the inorganic metal salt is so controlled that the encapsulated particles emerging from the final coating stage are substantially dry and resistant to loss of coating by attrition and agglomeration.