Coating processes – Particles – flakes – or granules coated or encapsulated
Reexamination Certificate
1996-03-28
2001-04-24
Beck, Shrive (Department: 1762)
Coating processes
Particles, flakes, or granules coated or encapsulated
C427S220000, C427S421100, C510S108000, C510S441000, C510S511000
Reexamination Certificate
active
06221430
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a process for applying a full or partial coating to particles of hygroscopic material, and to detergent compositions adapted for use in machine dishwashing containing such coated particles.
BACKGROUND TO THE INVENTION
Compositions designed for use in automatic dishwasher machines are well known, and a consistent effort has been made by detergent manufacturers to improve the cleaning and/or rinsing efficiency of said compositions on chinaware, glassware and silverware, as reflected by numerous patent publications.
Particulate detergent compositions are, in general, designed to be white in colour. It has however, been seen to be desirable to include in such compositions, at low levels, particles coloured with various dyestuffs, which are commonly known as ‘speckle’ particles.
Most commonly, speckle particles are based on enzyme-containing prills to which coloured dyestuffs have been applied. This has the disadvantage to the formulator of a detergent product that the amount of speckle, and hence colour in the product is related to the in-product level of the enzyme component whose stain removal performance is highly sensitive to its level of inclusion. Varying the level of the enzyme to achieve the desirable level of speckle effect in product can thus have a major impact on the peformance of the detergent product.
In choosing an alternative speckle base/substrate the formulator faces a problem that such substrate should have no negative effect on the detergent performance of the product, and preferably should contribute to the detergency performance.
The fomulator is also faced with the problem that the speckle should have good abrasion colour stability, that is good resistance to dye abrasion (e.g. in any further packaging/processing steps). Similarly, the colour of the speckle should be resistant to being washed off in any further processing steps involving liquid application, e.g. by spraying-on, steps. The speckle furthermore should possess good in-product colour storage stability including resistance to oxidation and other processes which may cause degradation of the dyestuff.
The Applicants have now found that particles of hygroscopic material, particularly silicate material, are especially suitable speckle substrates. It has also been found that improved abrasion colour stability, stability to liquid spray contact and in-product storage stability may be achieved when the speckle is made by a process whereby an aqueous mixture of an organic binder and the dyestuff ar e sprayed onto base particles of hygroscopic material, and subsequently dried.
Surprisingly, the Applicants have also found that when such a silicate-containing speckle material is incorporated as part of a silicate-based alkalinity system, in place of a significant proportion of the usual (non-speckle) silicate, prevention of filming and clouding benefits on glassware are obtained. Such benefits are furthermore obtainable even in the absence of the dyestuff (i.e. with just the organic binder applied to the base hygroscopic particle).
SUMMARY OF THE INVENTION
There is provided a process for applying a coating to a base particle comprising a hygroscopic material comprising the steps of
(i) spraying an aqueous mixture comprising organic binder and optionally a dyestuff onto the base particle; and
(ii) drying the particle to obtain a finished particle
wherein the weight ratio of hygroscopic material to organic binder in the finished particle is from 1000:1 to 10:1, expressed on a dry weight basis.
The hygroscopic material is preferably sodium silicate having an SiO
2
:Na
2
O ratio of from 1.0 to 3.0.
According to another aspect of the present invention there is provided a detergent composition containing
(i) a water soluble builder compound; and
(ii) sodium silicate having an SiO
2
:Na
2
O ratio of from 1.0 to 3.0 present at a level of from 0.5% to 20% SiO
2
by weight of the composition
wherein sodium silicate providing at least 5% by weight of the total SiO
2
to the composition is in the form of the coated silicate particles according to the process aspect of the invention. The pH of a 1% solution of the detergent composition measured at 20° C. is preferably from 9.0 to 11.5.
DETAILED DESCRIPTION OF THE INVENTION
The process according to the present invention provides a method of applying a coating to a base particle.
The process comprises the essential steps of
(i) spraying an aqueous mixture comprising organic binder and optionally a dyestuff onto the base particle; and
(ii) drying the particle to obtain a finished particle.
Hygroscopic Material
In an essential aspect the base particle comprises a hygroscopic material, that is a material which tends to absorb moisture, particularly from the atmosphere.
It is believed that the hygroscopic nature of the material is important to the working of the process in that when the aqueous mixture of the binder, and optionally the dyestuff, are sprayed onto the base particle its hygroscopic nature tends to draw the water into the particle, thus leaving a relatively even ‘coating’ of binder and dyestuff on the surface of the particle.
It has been established that particularly suitable hygroscopic materials are those having structures with a relatively small pore size, especially those having a pore size of less than 15 &mgr;m.
The preferred hygroscopic material is sodium silicate having an SiO
2
:Na
2
O ratio of from 1.0 to 3.0, preferably from 1.6 to 2.4, most preferably 2.0. The alkali metal silicate may be in the form of either the anhydrous salt or a hydrated salt.
Other suitable hygroscopic materials include certain clays, aluminosilicates, silica and crystalline layered silicates.
Organic Binder
The aqueous mixture to be sprayed onto the base particle contains, in an essential aspect, an organic binder.
The weight ratio of hygroscopic material to organic binder in the finished particle is from 1000:1 to 10:1 preferably from 500:1 to 50:1, expressed on a dry weight basis.
Examples of suitable organic binders include the water soluble organic homo- or co-polymeric polycarboxylic acids or their salts in which the polycarboxylic acid comprises at least two carboxyl radicals separated from each other by not more than two carbon atoms. Polymers of the latter type are disclosed in GB-A-1,596,756. Preferred examples of such compounds are the polymers which contain acrylic acid, that is to say homopolymers of acrylic acid and copolymers with any suitable other monomer units, and which have a average molecular weight of from 2,000 to 100,000. Suitable other monomer units include modified acrylic, fumaric, maleic, itaconic, aconitic, mesaconic, citraconic and methylenemalonic acid or their salts, maleic anhydride, acrylamide, alkylene, vinylmethyl ether, styrene and any mixtures thereof. Preferred are the copolymers of acrylic acid and maleic anhydride having a average molecular weight of from 20,000 to 100,000.
Preferred acrylic acid containing polymers have an average molecular weight of less than 15,000, and include those sold under the tradename Sokalan PA30, PA20, PA15, PA10 and Sokalan CP10 by BASF GmbH, and those sold under the tradename Acusol 45N by Rohm and Haas.
Other preferred acrylic acid containing copolymers include those which contain as monomer units: a) from 90% to 10%, preferably from 80% to 20% by weight acrylic acid or its salts and b) from 10% to 90%, preferably from 20% to 80% by weight of a substituted acrylic monomer or its salts having the general formula —[CR
2
—CR
1
(CO—O—R
3
)]— wherein at least one of the substituents R
1
, R
2
or R
3
, preferably R
1
or R
2
is a 1 to 4 carbon alkyl or hydroxyalkyl group, R
1
or R
2
can be a hydrogen and R
3
can be a hydrogen or alkali metal salt. Most preferred is a substituted acrylic monomer wherein R
1
is methyl, R
2
is hydrogen (i.e. a methacrylic acid monomer). The most preferred copolymer of this type has a average molecular weight of from 4500 to 3000 and contains 60% to 80% by weight of acrylic acid and 40% to 20% by weight of methacrylic
Beck Shrive
Bolam Brian M.
Chen Bret B.
Miller Steven W.
The Procter & Gamble & Company
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