Cleaning compositions for solid surfaces – auxiliary compositions – Cleaning compositions or processes of preparing – Solid – shaped macroscopic article or structure
Reexamination Certificate
2001-09-20
2003-02-11
Ogden, Necholus (Department: 1751)
Cleaning compositions for solid surfaces, auxiliary compositions
Cleaning compositions or processes of preparing
Solid, shaped macroscopic article or structure
C510S446000, C510S450000, C510S457000, C134S040000
Reexamination Certificate
active
06518234
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a process for the production of anionic detergent particles and detergent compositions containing them. More particularly the present invention relates to a process for the production of detergent particles having a high level of anionic surfactant which involves in situ neutralisation of an acid precursor of the anionic surfactant and drying of the surfactant thereby produced.
BACKGROUND & PRIOR ART
Granulation processes involving mixing and agglomeration to form detergent granules have been widely investigated as alternatives to spray drying processes. Such mechanical mixing processes offer a number of advantages over spray drying, e.g. production of higher bulk density products and increased formulation flexibility. These mechanical processes generally utilise technologies which are specific to the particular type of mixing apparatus being used. However, most of them involve forming the salt form of anionic surfactants by neutralising the acid form of the anionic surfactant with an alkaline neutralising agent (usually in solid form), inside the mixing apparatus. This is normally referred to as in situ neutralisation.
Although there are several types of mixing apparatus which may be employed, one common arrangement is a combination of a high speed mixer/densifer followed by a moderate speed mixer/densifier, e.g. as disclosed in EP-A-0 420 317.
Another common arrangement was a so-called fluid bed granulator, e.g. as described in WO-A-98/58046.
However, the present invention is concerned with a different class of apparatus, namely a horizontal thin-film evaporator/drier. Specifically, it is known that detergent particles having high anionic surfactant levels can be prepared by processes in which acid precursors of anionic surfactants are neutralised with a neutralising agent in horizontal thin-film evaporator/drier (WO-A-96/06916, WO-A-96/06917 & WO-A-97/32002; WO-A-98/38278 & WO-A-98/40461) and the mass is granulated and dried. As used herein, the term thin-film evaporator/drier is understood to include flash-driers and scraped-surface driers as described in WO-A-96/06916, WO-A-96/06917 & WO-A-97/32002.
Basically, a thin-film evaporator/drier comprises a cylindrical chamber in which is located a coaxial shaft on which is mounted a plurality of blade-like tools. The pitch of these tools can be set to different angles along the length of the cylindrical chamber, from input end to output end. The clearance between the tips of the blade-like tools and the internal surface of the cylindrical chamber is very small, typically 5 mm or less. The cylindrical chamber comprises at least a mixing region at or towards the input end of the cylindrical chamber, a cooling region at or towards the output end of the cylindrical chamber and a drying region between the mixing and cooling regions. The drying region typically comprises one or more heating zones and the cooling region may comprise one or more cooling zones (although usually only one cooling zone. Each of the heating and cooling zones is defined by a respective jacket around the cylindrical chamber with a respective axial gap between each and through which jackets, a heating or cooling liquid, as appropriate, is pumped during operation of the process. The layering agent is
typically an aluminosilicate or a silica.
WO 97/32002 discloses a
dry-neutralisation
process in which high anionic surfactant-content detergent particles are manufactured by contacting a pumpable acid precursor with a solid neutralising agent, such as for example sodium carbonate, in a thin-film evaporator/drier.
EP 555 622 (Procter & Gamble) describes the manufacture of detergent particles comprising anionic surfactant in which acid precursors are neutralised in a high shear mixer by a stoichiometric excess of particulate neutralising agent, preferably sodium carbonate. The neutralisation reaction is optimised by using neutralising agent of a narrowly defined particle size range, namely 50% by volume has a particle diameter of less than 5 microns.
EP 555 622 does not however relate to the production of high anionic surfactant-content detergent particles or to the use of thin-film evaporator/driers. According to the teaching of EP 555 622, the neutralising agent is preferably present in an amount of at least five times that required for stoichiometric neutralisation. In addition, the ratio of liquid ingredients (e.g. acid precursor) to powder ingredients (e.g. neutralising agent) introduced into the high shear mixer is most preferably from 1:2 to 1:3. It is not possible to make high anionic surfactant-content detergent particles using such excesses of neutralising agent and/or liquid to solid ratios. Indeed, the detergent particles of the examples contain merely 23 wt % anionic surfactant.
All such technologies produce a product with a distribution of different particle sizes. Those which are very small are sometimes called
fines
. It is common to recycle the fines to the input stage of the mixer, in order to avoid having a dusty product. This is well known for various types of mixer. However, large particles, sometimes called
oversize
, present more of a problem. Their presence in the product is undesirable, e.g. because they give rise to negative consumer perception of product quality. In other mixing processes, e.g. as described in EP-A-0 420 317 and WO-A-98/58046, it is found that oversize particles cannot be recycled without having a deleterious on the product. This means that the oversize particles have to be milled prior to recycling, which adds to production cost.
Surprisingly, it has now been found that in the case of processes utilising a horizontal thin-film evaporator/drier, oversize particles can be recycled without significantly detracting from product quality.
SUMMARY OF THE INVENTION
Accordingly, a first aspect of the present invention provides a process for the production of detergent particles, the process comprising feeding an acid precursor of an anionic surfactant and a neutralising agent into a horizontal thin-film evaporator/drier comprising a mixing region, a drying region and a cooling region, removing the detergent particles so formed from an outlet of the evaporator/drier, separating an oversize granule fraction in which at least 70 wt % of the particles have a minimum diameter of 1000 &mgr;m from the detergent particles and recycling the oversize granule fraction to be fed back into the thin film evaporator/drier.
This invention also provides detergent particles obtained by the process.
DETAILED DESCRIPTION OF THE INVENTION
The Oversize Granule Fraction
The oversize granule fraction comprises at least 70 wt % of particles having a minimum diameter of 1000 &mgr;m. However, preferably at least 95 wt % of particles in the oversize fraction have a minimum diameter of 700 &mgr;m. Particles having a minimum specified particle diameter means those particles which would be retained on a seive having a mesh size corresponding to that size.
Preferably, at least some of the recycled granule fraction is fed back into the evaporator/drier before the cooling region, i.e. into the mixing region and/or onto the drying region and/or between those two regions.
Preferably also, the recycled oversize granule fraction constitutes an average of from 1% to 50%, more preferably from 5% to 25% by weight of the total solids dosed into the evaporator/drier.
Simultaneous Neutralisation, Drying and Granulation Process in a Thin-film Evaporator/drier
The process is carried out in a horizontal thin-film evaporator/drier (hereinafter referred to as an
evaporator/drier
). A commercial scale machine typically comprises at least 300, preferably at least 500, more preferably at least 750, especially at least 1000 blade-like tools. The clearance between the blades and the internal wall of the chamber is suitably less than 20 mm, e.g. 15 mm or less, or even 10 mm or less. The blade tip speed in operation is suitably ≧15 ms
−1
, preferably ≧20 ms
−1
. The ratio of exposed blade length to shaft r
Emery William Derek
Groot Andreas Theodorus
Mitelman Rimma
Ogden Necholus
Unilever Home & Personal Care USA , division of Conopco, Inc.
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