A tablet of compacted particulate detergent composition including surfactant and detergency builder, suitable for fabric washing, is sub-divided into a plurality of discrete regions with differing compositions. At least one region of the tablet contains a water-swellable polymer serving to promote disintegration of this region. The polymer is present in this region in a concentration greater than in at least one other region of the tablet so as to cause disintegration of the region at a greater speed than disintegration of another region of the tablet.

This invention relates to cleaning compositions in the form of tablets, eg. for use in fabric washing or machine dishwashing.
Detergent compositions in tablet form are described, for example, in U.S. Pat. No. 3,953,350 (Kao) and EP-A-711827 (Unilever), and are sold commercially in Spain. Tablets for machine dishwashing are described in W096/28530 (PandG). Tablets have advantages over powdered products in that they do not require measuring and are thus easier to handle and dispense into the washload.
Tablets of a cleaning composition are generally made by compressing or compacting a quantity of the composition in particulate form. It is desirable that tablets have adequate strength when dry, yet disperse and dissolve quickly when added to wash water. In such tablets, any surfactant functions as a binder, plasticising the tablet. However, it can also retard disintegration of the tablet by forming a viscous gel when the tablet comes into contact with water.
There have been a number of proposals for tablets which are subdivided into separate regions (eg. layers) which differ in their composition. This has been done in order to isolate components of the tablet composition during storage of the tablet.
GB-A-911204 discloses tablets in which a detergent tablet contains peroxygen bleach and a bleach activator is confined to a separate layer of the tablet or insert within it.
GB-A-1423536 discloses tablets in which bleach activator is contained in separate, polymer-coated granules while the main part of the tablets includes a soluble or swellable starch.
EP-A-481793 discloses tablets in which sodium percarbonate is isolated in a discrete region of the tablet and enhance stability.
U.S. Pat. No. 3,962,107 discloses a denture cleaning tablet in which enzyme is contained in one layer of the tablet while peroxygen bleach is contained in another, slower-dissolving layer. Both layers contain effervescence producing materials.
U.S. Pat. No. 4,099,912 teaches that fabric washing should be performed using a plurality of tablets containing a plurality of different detergent composition components.
The present invention makes use of a water-swellable polymeric material to accelerate the disintegration of at least one region of a tablet, ahead of another region or regions.
According to the present invention there is provided a tablet of compacted particulate cleaning composition containing surfactant and detergency builder, and which has a plurality of discrete regions with differing compositions, characterised in that at least one said region of the tablet contains water-swellable polymer, preferably insoluble polysaccharide, in a concentration which is from 0.1 to 8 wt. % and which is greater than in at least one other region of the tablet, to promote disintegration of the first said region(s) before the said other(s).
As mentioned above, this invention relates to a tablet which is subdivided into a plurality of discrete regions. The regions of the tablet are most likely to be separate layers within a tablet. However, a discrete region of a tablet could be a core or an insert while another discrete region could be a shell or coating around such core or insert.
The first said region(s) of the tablets which disintegrate and dissolve ahead of other regions can contain an ingredient (eg. enzyme) which is intended to function in the wash liquor before another constituent, contained in the other region(s) of the tablets, is fully released into the wash liquor.
Another possibility is that the other region(s) of the tablet which disintegrate more slowly contain an ingredient which is intended to function towards the end of the wash cycle. For example this could be an antiredeposition polymer or soil suspending polymer. If this is released later in the wash cycle, the proportion of it which is taken up in surfactant micelles and effectively wasted will be minimised.
A further possibility is that a tablet has two layers dissolving at different rates which contain materials to give different values of pH in the wash liquor at different times during a wash cycle.
A tablet of this invention may be intended for use in machine dishwashing. Such a tablet is likely to contain surfactant in a low concentration such as 0.5 to 2 wt % based on the whole tablet, although higher-conecentraions ranging up to 10 wt % may be used. Such will typically contain salts, such as over 60 wt %, often over 85 wt % of the tablet.
Water soluble salts typically used in machine dishwashing compositions are phosphates (including condensed phosphates) carbonates and silicates, generally as alkali metal salts. Water soluble alkali metal salts selected from phosphates, carbonates and silicates may provide 60 wt % or more of a dishwashing composition.
In such a machine dishwashing tablet, a discrete region which disintegrates and dissolves first may be a pre-wash composition containing enzyme(s) and some water soluble salts.
Another possibility is that a tablet of this invention will be intended for fabric washing. In this event the tablet will be likely to contain at least 2 wt %, probably at least 5 wt %, up to 40 or 50 wt % surfactant based on the whole. tablet, and from 5 to 8 wt % detergency builder, based on the whole tablet.
In such a tablet a discrete region which disintegrates and dissolves first may be a pre-wash composition containing enzyme(s). Such a pre-wash composition will generally include detergency builder as 5 to 90% by weight of the discrete region.
The remainder of the composition may then be suitable for the main fabric wash, containing from 5, preferably 10 wt % up to 40% or 50% surfactant.
It will be appreciated that within this invention it is possible that the first said region, containing water-swellable polymeric material, does not itself contain surfactant or detergency builder. It could for example contain enzyme(s) and water-soluble carrier salts which have no function as water-softeners.
However, the first said region(s) which contains water-swellable polymer will often contain detergency builder salts and may contain at least some surfactant.
For instance, for fabric washing, a pre-wash composition, used to form a discrete region of a tablet, might contain enzyme(s), 5 to 90 wt % detergency builder and from 0 to 2% surfactant, together with at least 5 wt % of particles of water-swellable polymer.
In a second aspect, this invention provides a tablet of compacted particulate detergent composition containing surfactant and detergency builder, which has a plurality of discrete regions with differing compositions, characterised in that at least one region of the tablet has a composition which causes it to disintegrate ahead of at least one other region of the tablet, wherein the first said region contains enzyme in a quantity greater than in the other said region, and the other said region contains surfactant and/or bleach in a greater quantity than in the first said region.
The disintegration of the first said region is preferably promoted by incorporation of a water-swellable polymer. However, it could be promoted by incorporation of water soluble materials, more specifically by particles containing at least 40% (by weight of these particles (ii)) of one or more materials selected from
compounds with a water-solubility exceeding 50 grams per 100 grams water
phase I sodium tripolyphosphate or
sodium tripolyphosphate which is partially hydrated so as to contain water of hydration in an amount which is at least 0.5% by weight of the sodium tripolyphosphate in the particles.
There may be a substantial difference in the times for disintegration of the first said region(s) and the other said region(s). An addition of a tablet to water at 20xc2x0 C. the said other region(s) may remain intact for at least 5 or even at least 10 minutes after disintegration of the first said region(s).
Materials which may be used in tablets of this invention will now be discussed in more detail.
The Water-swellable Polymer
Suitable water-swellable polymeric materials are usually water-insoluble. Preferably they have sufficient water-absorptivity that they can absorb at least four times their own weight of water, ie. a water uptake of at least 4 gm per gm.
A number of such materials are known, and are generally based on cellulose which may be chemically modified to enhance its water uptake capacity. Sometimes such modified celluloses have ionic substituents but for this invention it is preferred that any substituents are nonionic.
Surprisingly, we have found that such a material is more effective if it has a relatively large particle size. We therefore prefer that the polymeric material has a particle dimension of at least 400 better at least 500 micrometres. Such polymeric material with a particle dimension of at least 400 micrometres is preferably an agglomerate of smaller particles whose largest dimension is no greater than 200 micrometres, perferably no greater than 150 micrometres. This makes it possible for at least some of the polymer particles to break up during a wash cycle.
The material may exist as relatively rounded particles, or as relatively flat particles such as flakes or discs. In the latter case a dimension (diameter) of the flakes will be larger, perhaps substantially larger, than the diameter of a sphere with the same volume.
The largest dimension of particles of the polymeric material may be determined by sieve analysis, and the shape of the particles can be observed under a microscope.
It is customary to use sodium carboxymethylcellulose (SCMC) in detergent compositions, usually as not more than 3 wt % of the composition. We have found that such quantities of SCMC are generally ineffective to promote disintegration.
We have found it desirable to use swellable polymeric materials with little or no ionic character. Such materials may be polysaccharides with little or no ionic substitution.
The absence or near absence of ionic substitution can be expressed by stating that the charge density of the polymeric material is low, such as less than 10xe2x88x923, better less than 6xc3x9710xe2x88x924 or even zero. The term xe2x80x9ccharge densityxe2x80x9d denotes the number of charges on a polymer molecule divided by the molecular weight of the polymer. It is essentially the same as the average number of charges on a repeat unit of the polymer divided by the average molecular weight of a repeat unit.
The water-insoluble, water-swellable material is preferably added as particles which contain such material as at least 75% of the anhydrous weight of these particles (i.e ignoring their moisture content) and usually they will contain little or nothing except the polymer and any accompanying moisture.
These particles preferably do not provide more than 5 or 8 wt % of the tablet as a whole. However, a discrete region of a tablet may contain a higher concentration of such particles, eg. from 3 wt % up to 10 or 15 wt % of the region.
Further Disintegration-promoting Particles
The water-swellable polymer may be accompanied in the first said region(s) of the tablet by further particles which contain at least 40% of their own weight, better at least 50%, of a material which has a solubility in deionised water at 20xc2x0 C. of at least 50 grams per 100 grams of water.
The said particles may provide material of this specified solubility in an amount which is from 5 to 40 wt %, preferably 5 to 25 wt %, of the first said region(s) of the tablet.
A solubility of at least 50 grams per 100 grams of water at 20xc2x0 C. is an exceptionally high solubility: many materials which are classified as water soluble are less soluble than this.
Some highly water-soluble materials which may be used are listed below, with their solubilities expressed as grams of solid to form a saturated solution in 100 grams of water at 20xc2x0 C.
By contrast the solubilities of some other common materials at 20xc2x0 C. are:
Preferably this highly water soluble material is incorporated as particles of the material in a substantially pure form (i.e. each such particle contains over 95% by weight of the material). However, the said particles may contain material of such solubility in a mixture with other material, provided that material of the specified solubility provides at least 40% by weight of these particles.
It may be preferred that the highly water-soluble material is a salt which dissolves in water in an ionised form. As such a salt dissolves it leads to a transient local increase in ionic strength which can assist disintegration of the tablet by preventing nonionic surfactant from swelling and inhibiting dissolution of other materials.
Another possibility is that the water-swellable polymer is accompanied by further particles to promote disintegration which contain sodium tripolyphosphate with at least 40% (by weight of the further particles) of the anhydrous phase I form.
Sodium tripolyphosphate is very well known as a sequestering builder in detergent compositions. It exists in a hydrated form and two crystalline anhydrous forms. These are the normal crystalline anhydrous form, known as phase II which is the low temperature form, and phase I which is stable at high temperature. The conversion of phase II to phase I proceeds fairly rapidly on heating above the transition temperature, which is about 420xc2x0 C., but the reverse reaction is slow. Consequently phase I sodium tripolyphosphate is metastable at ambient temperature.
A process for the manufacture of particles containing a high proportion of the phase I form of sodium tripolyphosphate by spray drying below 420xc2x0 C. is given in U.S. Pat. No. 4,536,377.
Particles which contain this phase I form will often contain the phase I form of sodium tripolyphosphate as at least 50% or 55% by weight of the tripolyphosphate in the particles.
Suitable material is commercially available. Suppliers include Rhone-Poulenc, France and Albright and Wilson, UK.
Another possibility is that further particles which promote disintegration contain at least 40% (of their own weight) of sodium tripolyphosphate which is partially hydrated. The extent of hydration may lie in a range from 0.5 to 4% by weight of the sodium tripolyphosphate in the particles, or it may be higher. Indeed fully hydrated sodium tripolyphosphate may be used to provide these particles.
It is possible that the particles contain at least 40 wt % sodium tripolyphosphate which has a high phase I content but is also sufficiently hydrated so as to contain at least 0.5% water by weight of the sodium tripolyphosphate.
Particles as above may provide sodium tripolyphosphate in a quantity which is at least 8%, e.g. 8 to 30%, by weight of the composition of the first said region(s) of the tablet.
The remainder of the tablet composition used to form the first said region(s) of the tablet may include additional sodium tripolyphosphate. This may be in any form, including sodium tripolyphosphate with a high content of the anhydrous phase II form.
It is within the scope of the second aspect of this invention that the first said region includes particles containing a highly water soluble compound or particles containing phase I tripolyphosphate or hydrated tripolyphosphate, all as discussed above, without any water-swellable polymer.
Surfactant Compounds
Compositions which are compacted to form some tablet regions will contain one or more detergent surfactants. In a fabric washing composition, these preferably provide from 5 to 50% by weight of the overall tablet composition, more preferably from 8 or 9% by weight of the overall composition up to 40% or 50% by weight. Surfactant may be anionic (soap or non-soap), cationic, zwitterionic, amphoteric, nonionic or a combination of these.
Anionic surfactant may be present in an amount from 0.5 to 50% by weight, preferably from 2% or 4% up to 30% or 40% by weight of the tablet composition.
Synthetic (i.e. non-soap) anionic surfactants are well known to those skilled in the art. Examples include alkylbenzene sulphonates, particularly sodium linear alkylbenzene sulphonates having an alkyl chain length of C8-C15; olefin sulphonates; alkane sulphonates; dialkyl sulphosuccinates; and fatty acid ester sulphonates.
Primary alkyl sulphate having the formula
ROSO3xe2x88x92M+
in which R is an alkyl or alkenyl chain of 8 to 18 carbon atoms especially 10 to 14 carbon atoms and M+ is a solubilising cation, is commercially significant as an anionic surfactant. Linear alkyl benzene sulphonate of the formula
where R is linear alkyl of 8 to 15 carbon atoms and M+ is a solubilising cation, especially sodium, is also a commercially significant anionic surfactant.
Frequently, such linear alkyl benzene sulphonate or primary alkyl sulphate of the formula above, or a mixture thereof will be the desired anionic surfactant and may provide 75 to 100 wt % of any anionic non-soap surfactant in the composition.
In some forms of this invention the amount of non-soap anionic surfactant lies in a range from 5 to 20 wt % of the tablet composition.
It may also be desirable to include one or more soaps of fatty acids. These are preferably sodium soaps derived from naturally occurring fatty acids, for example, the fatty acids from coconut oil, beef tallow, sunflower or hardened rapeseed oil.
Suitable nonionic surfactant compounds which may be used include in particular the reaction products of compounds having a hydrophobic group and a reactive hydrogen atom, for example, aliphatic alcohols, acids, amides or alkyl phenols with alkylene oxides, especially ethylene oxide.
Specific nonionic surfactant compounds are alkyl (C8-22) phenol-ethylene oxide condensates, the condensation products of linear or branched aliphatic C8-20 primary or secondary alcohols with ethylene oxide, and products made by condensation of ethylene oxide with the reaction products of propylene oxide and ethylene-diamine.
Especially preferred are the primary and secondary alcohol ethoxylates, especially the C9-11 and C12-15 primary and secondary alcohols ethoxylated with an average of from 5 to moles of ethylene oxide per mole of alcohol.
In some fabric washing tablets of this invention, the amount of nonionic surfactant lies in a range from 4 to 40%, better 4 or 5 to 30% by weight of the whole tablet. Many nonionic surfactants are liquids. These may be absorbed onto particles of the composition.
In a machine dishwashing tablet the surfactant may be wholly nonionic, in an amount below 5 wt % of the whole tablet although it is known to include some anionic surfactant and to use up to 10 wt % surfactant in total.
Detergency Builder
A composition which is compacted to form some regions of tablets will contain from 5 to 80%, more usually 15 to 60% by weight of detergency builder. This may be provided wholly by water soluble materials, or may be provided in large part or even entirely by water-insoluble material with water-softening properties. Water-insoluble detergency builder may be present as 5 to 80 wt %, or from 10 to 80 wt % better 5 to 60 wt % of the composition.
Alkali metal aluminosilicates are strongly favoured as environmentally acceptable water-insoluble builders for fabric washing. Alkali metal (preferably sodium) aluminosilicates may be either crystalline or amorphous or mixtures thereof, having the general formula:
0.8-1.5Na2O.Al2O3.0.8-6SiO2.xH2O
These materials contain some bound water (indicated as xe2x80x9cxH2Oxe2x80x9d) and are required to have a calcium ion exchange capacity of at least 50 mg CaO/g. The preferred sodium aluminosilicates contain 1.5-3.5 SiO2 units (in the formula above). Both the amorphous and the crystalline materials can be prepared readily by reaction between sodium silicate and sodium aluminate, as amply described in the literature.
Suitable crystalline sodium aluminosilicate ion-exchange detergency builders are described, for example, in GB 1429143 (Procter and Gamble). The preferred sodium aluminosilicates of this type are the well known commercially available zeolites A and X, the novel zeolite P described and claimed in EP 384070 (Unilever) and mixtures thereof.
Conceivably a water-insoluble detergency builder could be a layered sodium silicate as described in U.S. Pat. No. 4,664,839. NaSKS-6 is the trademark for a crystalline layered silicate marketed by Hoechst (commonly abbreviated as xe2x80x9cSKS-6xe2x80x9d). NaSKS-6 has the delta-Na2SiO5 morphology form of layered silicate. It can be prepared by methods such as described in DE-A-3,417,649 and DE-A-3,742,043. Other such layered silicates, such as those having the general formula NaMSixO2x+1.yH2O wherein M is sodium or hydrogen, x is a number from 1.9 to 4, preferably 2, and y is a number from 0 to 20, preferably 0 can be used.
Water-soluble phosphorous-containing inorganic detergency builders, include the alkali-metal orthophosphates, metaphosphates, pyrophosphates and polyphosphates.
Specific examples of inorganic phosphate builders include sodium and potassium tripolyphosphates, orthophosphates and hexametaphosphates.
Non-phosphorous water-soluble builders may be organic or inorganic. Inorganic builders that may be present include alkali metal (generally sodium) carbonate; while organic builders include polycarboxylate polymers, such as polyacrylates, acrylic/maleic copolymers, and acrylic phosphonates, monomeric polycarboxylates such as citrates, gluconates, oxydisuccinates, glycerol mono- di- and trisuccinates, carboxymethyloxysuccinates, carboxymethyloxymalonates, dipicolinates and hydroxyethyliminodiacetates.
At least one region of a fabric washing tablet preferably include polycarboxylate polymers, more especially polyacrylates and acrylic/maleic copolymers which can function as builders and also inhibit unwanted deposition onto fabric from the wash liquor.
Bleach System
Tablets according to the invention may contain a bleach system in at least one region of a tablet. This preferably comprises one or more peroxy bleach compounds, for example, inorganic persalts or organic peroxyacids, which may be employed in conjunction with activators to improve bleaching action at low wash temperatures. If any peroxygen compound is present, the amount is likely to lie in a range from 10 to 25% by weight of the composition.
Preferred inorganic persalts are sodium perborate monohydrate and tetrahydrate, and sodium percarbonate, advantageously employed together with an activator. Bleach activators, also referred to as bleach precursors, have been widely disclosed in the art. Preferred examples include peracetic acid precursors, for example, tetraacetylethylene diamine (TAED), now in widespread commercial use in conjunction with sodium perborate; and perbenzoic acid precursors. The quaternary ammonium and phosphonium bleach activators disclosed in U.S. Pat. No. 4,751,015 and U.S. Pat. No. 4,818,426 (Lever Brothers Company) are also of interest. Another type of bleach activator which may be used, but which is not a bleach precursor, is a transition metal catalyst as disclosed in EP-A-458397, EP-A-458398 and EP-A-549272. A bleach system may also include a bleach stabiliser (heavy metal sequestrant) such as ethylenediamine tetramethylene phosphonate and diethylenetriamine pentamethylene phosphonate.
As indicated above, if a bleach is present and is a water-soluble inorganic peroxygen bleach, the amount may well be from 10% to 25% by weight of the composition.
Other Detergent Ingredients
The detergent tablets of the invention may also contain one of the detergency enzymes well known in the art for their ability to degrade and aid in the removal of various soils and stains. Suitable enzymes include the various proteases, cellulases, lipases, amylases, and mixtures thereof, which are designed to remove a variety of soils and stains from fabrics. Examples of suitable proteases are Maxatase (Trade Mark), as supplied by Gist-Brocades N.V., Delft, Holland, and Alcalase (Trade Mark), and Savinase (Trade Mark), as supplied by Novo Industri A/S, Copenhagen, Denmark. Detergency enzymes are commonly employed in the form of granules or marumes, optionally with a protective coating, in amount of from about 0.1% to about 3.0% by weight of the composition; and these granules or marumes present no problems with respect to compaction to form a tablet.
The detergent tablets of the invention may also contain a fluorescer (optical brightener), for example, Tinopal (Trade Mark) DMS or Tinopal CBS available from Ciba-Geigy AG, Basel, Switzerland. Tinopal DMS is disodium 4,4xe2x80x2bis-(2-morpholino-4-anilino-s-triazin-6-ylamino) stilbene disulphonate; and Tinopal CBS is disodium 2,2xe2x80x2-bis-(phenyl-styryl) disulphonate.
An antifoam material is advantageously included, especially if a detergent tablet is primarily intended for use in front-loading drum-type automatic washing machines. Suitable antifoam materials are usually in granular form, such as those described in EP 266863A (Unilever). Such antifoam granules typically comprise a mixture of silicone oil, petroleum jelly, hydrophobic silica and alkyl phosphate as antifoam active material, absorbed onto a porous absorbed water-soluble carbonate-based inorganic carrier material. Antifoam granules may be present in an amount up to 5% by weight of the composition.
It may also be desirable that a detergent tablet of the invention includes an amount of an alkali metal silicate, particularly sodium ortho-, meta- or disilicate. The presence of such alkali metal silicates at levels, for example, of 0.1 to 10 wt %, may be advantageous in providing protection against the corrosion of metal parts in washing machines, besides providing some measure of building and giving processing benefits in manufacture of the particulate material which is compacted into tablets.
A tablet for fabric washing will generally not contain more than 15 wt % silicate. A tablet for machine dishwashing will often contain more than 20 wt % silicate.
Further ingredients which can optionally be employed in a region of a fabric washing detergent tablet of the invention include anti-redeposition agents such as sodium carboxymethylcellulose, straight-chain polyvinyl pyrrolidone and the cellulose ethers such as methyl cellulose and ethyl hydroxyethyl cellulose, fabric-softening agents; heavy metal sequestrants such as EDTA; perfumes; and colorants or coloured speckles.
Particle Size and Distribution
Each discrete region of a detergent tablet of this invention, is a matrix of compacted particles.
Preferably the particulate composition has an average particle size in the range from 200 to 2000 xcexcm, more preferably from 250 to 1400 xcexcm. Fine particles, smaller than 180 xcexcm or 200 xcexcm may be eliminated by sieving before tableting, if desired, although we have observed that this is not always essential.
While the starting particulate composition may in principle have any bulk density, the present invention is especially relevant to tablets made by compacting powders of relatively high bulk density, because of their greater tendency to exhibit disintegration and dispersion problems. Such tablets have the advantage that, as compared with a tablet derived from a low bulk density powder, a given dose of composition can be presented as a smaller tablet.
Thus the starting particulate composition may suitably have a bulk density of at least 400 g/litre, preferably at least 500 g/litre, and perhaps at least 600 g/litre.
Granular detergent compositions of high bulk density prepared by granulation and densification in a high-speed mixer/granulator, as described and claimed in EP 340013A (Unilever), EP 352135A (Unilever), and EP 425277A (Unilever), or by the continuous granulation/densification processes described and claimed in EP 367339A (Unilever) and EP 390251A (Unilever), may be used to product at least some tablet regions.
When a tablet incorporates particles of a water-swellable polymeric material, or other particles to promote disintegration, they are preferably mixed with the remainder of the particulate composition, prior to compaction into tablets.
Manufacture of a tablet with two layers of differing composition may be carried out by placing a predetermined quantity of one composition in a mould, then adding a second composition on top, and next driving a die into the mould to cause compaction.
Alternatively, a predetermined quantity of a composition may be placed in a mould and compacted by driving a die into the mould, followed by removing the die, adding a second composition and compacting again.
Tablets with even more layers can be made by these routes, but with extra stages of loading particulate material into the die, and possibly compacting after each stage.
Tableting machinery able to carry out such operations is known, for example suitable tablet presses are available from Fette and from Korch.
Tableting may be carried out at ambient temperature or at a temperature above ambient which may allow adequate strength to be achieved with less applied pressure during compaction. In order to carry out the tableting at a temperature which is above ambient, the particulate composition is preferably supplied to the tableting machinery at an elevated temperature. This will of course supply heat to the tableting machinery, but the machinery may be heated in some other way also.
If any heat is supplied, it is envisaged that this will be supplied conventionally, such as by passing the particulate composition through an oven, rather than by any application of microwave energy.
The size of a tablet will suitably range from 10 to 160 grams, preferably from 15 to 60 g, depending on the conditions of intended use, and whether it represents a dose for an average load in a fabric washing or dishwashing machine or a fractional part of such a dose. The tablets may be of any shape. However, for ease of packaging they are preferably blocks of substantially uniform cross-section, such as cylinders or cuboids. The overall density of a tablet preferably lies in a range from 1040 or 1050 gm/litre up to 1300 gm/litre. The tablet density may well lie in a range up to no more than 1250 or even 1200 gm/litre.

Lever Brothers Company, divison of Conopco, Inc.


Provided is a burner which includes a pipe having a free end region designed to be housed in a furnace quarl. The pipe includes one or more fuel feed ducts surrounded over part of their length by a sheath which defines an oxidizer feed channel and is fastened to a flange. A jacket is disposed around at least part of the length of the end region so as itself to be housed in the quarl and to define a feed channel for a second oxidizer between the jacket and the internal wall of the quarl. The jacket is fastened to a flange for securing to the quarl and the flange for the sheath is fastened to that for the jacket. The burner has particular applicability in industrial furnaces, especially for melting non-ferrous materials, for rehearing or for annealing.

1. Field of the Invention
The present invention relates to air-fuel and/or oxygen-fuel burners intended to be fitted into industrial furnaces, especially furnaces for melting, for example, non-ferrous metals (aluminum, copper, lead, etc.), reheat furnaces, annealing furnaces, or furnaces intended for preheating ladles, and in general to burners intended for so-called xe2x80x9clow temperaturexe2x80x9d melting or heating applications. The industrial furnaces of the present invention may be used in applications at a temperature lying within a range extending from approximately 500xc2x0 C. to 1500xc2x0 C.
The invention also relates to the quarl blocks fitted with such a burner.
2. Description of the Related Art
To obtain optimum, uniform and economic heating requires the formation of a stable flame. The emission of nitrogen oxides, which are extremely harmful, also needs to be reduced.
Techniques are already known which aim to stabilize the flame in air-fuel fired operation and/or to reduce emissions of nitrogen oxides.
For example, document EP 0 644 374, which recommends rotating the injected air, describes a complex assembly of metal mechanical parts whose operation within the temperature range indicated above results in relatively rapid wear, requiring the worn parts to be periodically replaced.
Document EP 0 757 205 recommends the injection of a jet of air at an angle which takes this jet away from the first oxygen-fuel combustion zone, thus creating a recirculation zone in a refractory block. The fact that the jet of air is directed away from the jet of oxygen is not generally something which makes it easy to obtain a stable flame. Furthermore, it appears to be difficult to make a burner equipped in this way operate, as required, in oxy-fuel mode or in air-fuel mode.
Document U.S. Pat. No. 4,797,087 recommends the staging of the combustion, namely the creation of a fuel-rich first mixture followed by the injection of a second oxidizer into a second mixing zone. However, the range of working temperatures is markedly higher than that intended by the invention and the subject-matter of that document does not seem to lend itself to purely oxy-fuel operation.
The object of the invention is to remedy the drawbacks of the known techniques and to create an air-fuel/oxy-fuel burner which produces a stable flame, is of simple construction, is reliable, has small dimensions and is capable of working, as required, either in oxy-fuel mode or in virtually wholly air-fuel mode.
For this purpose, the invention relates to an air-fuel or oxy-fuel burner including a pipe having a free end region designed to be housed in a quarl of an industrial furnace, this pipe having at least one fuel feed duct; a sheath surrounding the duct or ducts over part of their length in order to define a first oxidizer feed channel between the sheath and the duct; a sheath flange extending transversely around the sheath; a jacket fitted around the sheath and disposed around at least part of the length of the free end region of the pipe, the sheath designed to be housed in the quarl and to define a second oxidizer feed channel between the jacket and the inner surface of the quarl; and a jacket flange extending transversely around the jacket for securing the jacket to the quarl and the sheath flange being fastened to the jacket flange.
By virtue of this structure, an air-fuel and/or oxy-fuel burner is obtained which is simple to manufacture, occupies little space and is easy to fit.
The burner may furthermore have one or more of the following characteristics:
each fuel feed duct comprises an injector provided at a free end of a rigid conduit, and the actual free end of the injector constitutes the free end of the duct;
the jacket is fitted around the sheath;
the jacket extends beyond the sheath, approximately so as to be in line with the free end of the fuel feed duct or ducts, in order to define, between the jacket and the ducts, an oxygen feed channel extending as far as the free end;
the jacket has a smaller cross section than that of the sheath starting from a region lying slightly beyond the free end of the sheath;
the flange for the jacket carries studs for fastening the flange for the sheath;
the pipe has a longitudinal axis with respect to which the sheath is off-centered in order to leave, between the sheath and the fuel feed duct or ducts, a wider space on one side in order to accommodate a tube for a flame control device and a pilot burner;
the sheath has a part of flared shape and one end of an oxygen feed tube emerges in this flared part;
the flange for the jacket has an opening in which one end of the a feed tube for the second oxidizer emerges;
the velocity of the fuel in the fuel feed duct or ducts lies within a range of approximately 10 m/s to 180 m/s;
oxygen flows in the first oxidizer feed channel at a velocity at most equal to approximately 20 m/s and preferably equal to approximately 8 m/s; and
natural gas flows in the fuel feed duct or ducts with a total flow rate of approximately 50 Sm3/h and at a velocity of approximately 30 m/s and oxygen flows in the first oxidizer feed channel with a flow rate of approximately 100 Sm3/h and at a velocity of approximately 8.5 m/s.
The invention also relates to a quarl block fitted with a burner as defined above, comprising a quarl passing right through the quarl block and having an inlet chamber and an outlet chamber which are joined by a transition zone flared towards the inlet chamber, and the fuel feed duct or ducts of the pipe of the burner penetrate, from the inlet chamber, right into the outlet chamber.
The quarl block may also have one or more of the following characteristics:
in the case in which the outlet chamber is approximately cylindrical, the distance L between the free end of the fuel feed ducts and the end of the quarl located on the internal side of the furnace and the diameter d of the outlet chamber satisfy the relationship 0.3dxe2x89xa6Lxe2x89xa61.8d;
the inlet chamber is off-centered with respect to a longitudinal axis of the pipe and with respect to the outlet chamber and the transition zone, in order to leave a wider space between the inner surface of the quarl and the jacket allowing the introduction of the second oxidizer;
the oxidizer feed channel is designed for an oxygen stream to flow in it, the feed channel for a second oxidizer is designed for a stream of air to flow in it and the fuel feed duct or ducts are designed for a stream of natural gas to flow in them;
oxygen flows in the oxidizer feed channel with a flow rate lying within a range going from approximately 1% to 5% of the total (oxygen, air and fuel) flow rate;
air flows in the feed channel for a second oxidizer at a velocity at most equal to approximately 50 m/s and preferably equal to approximately 30 m/s;
natural gas flows in the fuel feed duct or ducts with a total flow rate of approximately 50 Sm3/h and at a velocity of approximately 30 m/s, oxygen flows in the oxidizer feed channel with a flow rate of approximately 50 Sm3/h and at a velocity of approximately 4.25 m/s and air flows in the feed channel for a second oxidizer with a flow rate of approximately 250 Sm3/h and at a velocity of approximately 13.4 m/s; and
natural gas flows in the fuel feed duct or ducts with a total flow rate of approximately 50 Sm3/h and at a velocity of approximately 30 m/s, oxygen flows in the oxidizer feed channel with a flow rate of approximately 15 Sm3/h and at a velocity of approximately 1.3 m/s and air flows in the feed channel for a second oxidizer with a flow rate of approximately 427 Sm3/h and at a velocity of approximately 23 m/s.
By virtue of these characteristics, it is also possible to obtain a highly stable flame.

Stabilized-flame aerogas/oxygas burner and quarl block fitted with such a burner

L""Air Liquide Societe Anonyme a Directoire et Conseil de Surveillance pour l""Etude et l""Exploitation des Procedes Georges Claude


The joint compound of the present invention utilizes hollow resin microspheres with a mean particle size less than 75 microns and exhibiting no more than 1.5% increase in density under high shear stress testing.

This invention relates to a composition for a joint compound for use in filling and coating the joints between adjacent panels of gypsum wallboard. More specifically, it relates to a composition for lightweight joint compound of the drying type that reduces applicator fatigue, job completion time, and reduces shipping costs of the packaged product.
In the construction of buildings, one of the most common elements is gypsum wallboard, often known as drywall, used in the construction of walls and/or ceilings. Walls made from gypsum wallboard are traditionally constructed by affixing the panels to wood studs or metal framing, and treating the joints between adjoining panels with a specially prepared adhesive called a joint compound. The side edges of the drywall panels are tapered, thus allowing the joint compound to be applied to the seam, between adjoining panels, in such a way that a monolithic surface is created when finished. This process generally proceeds by placing a taping joint compound within the joint formed by the abutted edges of the wallboards, and embedding a liquid-permeable paper or fiberglass tape within that compound. When dry (or set), a second coating referred to as a topping joint compound is applied over the joint, which may be subsequently lightly sanded upon drying. A third or finish coat is applied, allowed to dry, and lightly sanded to create a smooth monolithic surface that conceals any indication of where the drywall seams were. Another type of joint compound is an all-purpose grade that may be used for both embedding the joint tape and for applying the finish coats. A patterned or textured effect may be given to the finished wall and joint through the use of special application tools.
There are several categories of joint compounds. Drying type compounds cure through the evaporation of water, whereas setting type joint compounds chemically react with water during the curing process. Setting type joint compounds typically use calcium sulfate hemihydrate, also known as stucco or plaster of Paris, as a base. When water is added to the setting type powder, it reacts with the calcium sulfate hemihydrate via a hydration reaction to form an interlocking matrix of calcium sulfate dihydrate crystals. The interlocking crystal matrix gives the compound increased strength. The benefit of a setting type joint compound over a drying type is the overall strength of the finished joint, resulting in less shrinking and cracking, as well as an independence from having to wait for the joint compound to be completely dry prior to further finishing. Drying type joint compounds have the advantage of ease of use, as they typically come in a ready mixed form, with water being added and mixed by the manufacturer. A third type of joint compound combines the setting action of a calcium sulfate hemihydrate based compound with the ease of use of a ready mixed compound. The properties of a ready mixed setting type joint compound are taught in U.S. Pat. No. 5,746,822, incorporated herein by reference.
Lightweight joint compounds are known in the art, such as U.S. Pat. No. 4,454,267 to Williams and U.S. Pat. No. 4,657,594 to Struss. Perlite, which is a form of glassy rock similar to obsidian, is ground, heat expanded, and immediately surface treated with a silicone-based compound to provide lightweight filler for use in a joint compound. The special treatment renders the expanded perlite water-insensitive so that it does not soak up water due to capillary action. Despite the water-insensitivity of coated perlite, it still requires a certain amount of available water to wet out and disperse. Use of large amounts of perlite negatively impacts the overall water demand, drying time, strength, bond, viscosity and surface absorption characteristics of the joint compound. The expanded perlite is also susceptible to breakdown during mixing that may further degrade the physical properties of the joint compound.
U.S. Pat. No. 4,824,879 to Montgomery, et al. teaches the addition of expanded perlite or hollow glass microspheres to reduce density and shrinkage in a joint compound. As recited above, there is a limit as to the amount of perlite that may be used in a joint compound without deterioration of certain physical properties. Glass microspheres may be used, however, they are prone to breakage. When microspheres break open, they greatly increase the density of the resultant joint compound due to the filling of the void left behind by the broken sphere with water and other additives. The glass then tends to settle, and is difficult to disperse thereby leading to an unfavorable change in rheological properties. Whenever breakage occurs, more microspheres must be added to make up for the increase in density, in turn, increasing the cost of the formulation. Glass and perlite are also disadvantageous because of the dust that can be produced. Glass microspheres are limited in size and density. These limitations require a greater amount be added to the formulation in order to lower the overall density.
The use of polyacrylate microspheres in a setting type joint compound is taught in U.S. Pat. No. 5,494,947 to Kaplan. This reference is directed to a joint compound to be used in prefabricated walls and ceilings that remain flexible after set, thereby minimizing cracking during transportation and final assembly of the prefabricated unit. The surface chemistry of these polyacrylate resins is such that it tends to stick to itself rather than disperse readily in water, making it difficult to disperse in an aqueous medium typically resulting in the formation of unacceptable clumps.
It is, therefore, an object of this invention to provide an improved lightweight joint compound with a final use density less than the density of water.
It is also an object of this invention to provide an improved lightweight joint compound that provides a smooth finished surface.
It is yet another object of this invention to provide an improved lightweight joint compound utilizing microspheres which are minimally susceptible to breakage during manufacture and end use.
It is still another object of this invention to provide an improved lightweight joint compound utilizing microspheres that readily disperse in an aqueous medium.
The above-listed objects are met or exceeded by the present invention that features hollow resin microspheres as filler in lightweight joint compound. Densities less than that of water are obtainable using the formulation of the present invention. Use of the resin microspheres at the same weight percentage as glass microspheres provides a greater change in density due to the much lower density of the resin versus the glass. Resin microspheres also avoid a reported adverse interaction when glass microspheres are used with polyvinyl alcohol, that causes the joint compound to stiffen or gel.
More specifically, the joint compound of the present invention comprises at least one binder and one or more fillers, with at least one filler including hollow resin microspheres with a mean particle size less than 75 microns and exhibiting no more than 1.5% increase in density under high shear testing. Use of hollow resin microspheres as lightweight filler provides for a formulation of an extremely light joint compound with a density less than water, and that does not exhibit a grainy surface when applied over drywall, while improving the application properties. The microspheres blend easily with other ingredients, particularly when added in a pre-wet form, also known as a cake.
Resin microspheres have a density much lower than that of glass microspheres. Because of this lower density, fewer resin microspheres are required to get the same change in resultant volume compared to glass microspheres. This allows preparation of very lightweight joint compounds without adversely affecting other properties of the joint compound.
In the following discussion, all percentages indicated are calculated as the weight of all solids on a dry basis.
The lightweight joint compound of the present invention includes a binder and one or more fillers, including hollow resin microspheres with a mean particle size less than 75 microns and exhibiting no more than 1.5% increase in density under high shear testing. A preferred embodiment uses acrylonitrile resin microspheres in a joint compound of either the setting or the drying type.
Preferably, the joint compound is made up of the binder, fillers, thickeners, preservatives and dispersing agents. Traditional joint compounds, as well as lightweight joint compounds may benefit from the formulation of the present invention. Many optional ingredients are suitable for addition to the joint compound depending on the exact use and desired properties of the joint compound.
Any binder that is suitable for use in a joint compound is appropriate for use in the present invention. The binder is used to enhance the adhesion of the joint compound to its substrate, typically drywall. Acceptable binders include, but are not limited to latex emulsions, vinyl acetates, acrylics, alcohols, and dispersible powders such as poly vinyl acetate, ethylene vinyl acetates, and starches. Latex binders are preferred in the present invention. The concentration of the latex binder in a typical joint heavyweight compound ranges from about 1% to about 2.5% of the total wet weight. The concentration of binder in a typical lightweight point compound ranges from 1% to about 3%. The concentration of binder in the present invention is usually slightly higher compared to previous lightweight joint compounds to compensate for the additional drop in density and its effect on maintaining acceptable adhesion properties. In the present invention, the concentration of the latex binder ranges from about 1% to about 3.5%.
The key ingredient in the joint compound of the present invention is hollow resin microspheres that meet certain physical properties. Preferred shell resins suitable for use in the present invention are homopolymers, copolymers, or blends of homopolymers and/or copolymers formed one or more of acrylonitrile (xe2x80x9cACNxe2x80x9d), vinylidene chloride (xe2x80x9cVDCxe2x80x9d), or methyl methacylate (xe2x80x9cMMAxe2x80x9d) monomers. Particularly preferred resins are polyacrylonitrile (xe2x80x9cPACNxe2x80x9d), polyvinylidene chroide (xe2x80x9cPVDCxe2x80x9d), copolymors formed from ACN and VDC, and copolymers found from ACN, VDC, and MMA. The microspheres demonstrate high resiliency to compression without collapse (non-friable) and are able to withstand the exerted shear stress (shear-stability) of a typical joint treatment manufacturing process and subsequent customer preparation. A standard suspension of microspheres in a thickened aqueous solution, followed by high shear mixing at 14,000 RPM in a HAMILTON BEACH(copyright) Model number 930 commercial drink mixer for eight minutes, simulates the stress placed upon the microspheres during manufacture.
The preferred density of the microspheres is about 0.009 to about 0.13 g/cc. Microspheres in this density range have an optimal effect on increasing the overall volume of the joint compound. However, they are still heavy enough to allow measurement and addition of the microspheres by weight.
A homogeneous dispersion of microspheres in water is important to achieving a smooth, uniform surface of the finished joint compound. If the microspheres do not disperse properly, an unacceptable lumpy texture results. Resins microspheres that are difficult to disperse also increase joint compound preparation time. In some manufacturing situations where undispersed microspheres are present, the joint compound manufacturing efficiency is reduced and unit cost is increased.
The particle size of the microspheres is preferably small enough that there is no noticeable difference in the surface texture of the finished joint compound compared to traditional blends. Generally, this means that the microspheres have a mean diameter less than 75 microns. If the particles are too small, the surface to volume ratio will reduce the microspheres"" ability to lower overall density. The preferred range of microsphere particle size is from about 25 to 55 microns in diameter.
The microspheres are also strong enough that very few will break under mixing conditions observed during manufacturing. When acting to reduce the weight of the joint compound, the microspheres succeed only as long as they remain intact. When they break, they collapse and allow liquids, along with other heavier materials, to occupy the void left behind. The joint compound itself then condenses, and a loss of volume is observed along with an increase in density. Breakage is detectable by comparing the calculated theoretical density, taking into account some entrained air, to the actual density of the mixture. If the microspheres collapse during the manufacturing process, the density of the resultant joint compound will increase, requiring that even more spheres be added to make up for the loss in volume and increase in density. Selective use of microspheres that are non-friable and shear stable helps prevent breakage and collapse which are usually marked by an increase in the joint compound density, a decrease in overall expected volume, and lower product yield.
A number of different stresses are present during the preparation of the joint compound that cause microsphere collapse. The greatest strain on microsphere integrity is during the manufacture of joint compound, where stresses caused by the shear force of mixing and pressures during material transfer lead to a compromise of the microsphere shell wall. Resin type, sphere size, shell thickness, and chemical environment are all factors involved in the ability of the microsphere to withstand processing and end use stresses.
In order to be suitable for use in the present invention, resin microsphere collapse, as measured by an increase in product density, is limited to no more than 1.5% increase in density under high stress testing. For the purposes of this invention, under one such test, the microspheres are suspended in a solution of water, a defoamer and a hydrous magnesium silicate, such as LAPONITE(copyright) RD (Southern Clay Products, Inc. Gonzolas, Tex.). The defoamer used for this test was HiMar D-829 (Rainbow Chemicals, Inc., Lake Bluff, Ill.). Mixing of the standard suspension with a HAMILTON BEACH(copyright) Model number 930 high-speed commercial drink mixer for up to eight minutes simulates the stress placed upon the microspheres during manufacture. High shear conditions are created by mixing the suspended hollow resin microspheres at 14,000 rpm. The mixer is equipped with a xc2xdxe2x80x3 diameter spindle 6xc2xdxe2x80x3 in length. At the bottom of the spindle is a four-fold agitator button, measuring 1xc2xdxe2x80x3 from vane tip to vane tip when fully extended. A solid, 1xe2x80x3 disk agitator is located 1xc2xcxe2x80x3up the spindle from the agitator button. The standard solution was poured into a stainless steel cup, 6xc2xexe2x80x3 deep and mixed for eight minutes.
The suspension containing a suspending agent is needed because the microspheres low density leads to immediate separation in most solvents, making density measures impractical. A synthetically made hydrous magnesium silicate creates a highly thixotropic solution when prepared in water, with excellent suspending power, preventing the lightweight microspheres from floating to the top and separating. In addition to the use of hydrous magnesium silicate as a suspension aid, a defoaming agent is used to minimize the level of entrained air during initial mixing and subsequent high shear tests.
The following standard aqueous suspension, shown in Table I, was used to evaluate the effect of high shear on a sample of microspheres:
Based upon the amount of raw materials used and their corresponding specific gravities, the theoretical densities of the aqueous suspension with and without microspheres are calculated and listed in Table II:
The Hi-Mar D-829 defoamer was stirred slightly into 550 grams of room temperature (73xc2x0 F.) water followed by the addition of 14 grams of LAPONITE(copyright) RD hydrous magnesium silicate. The solution was mixed for 20 minutes under high shear using the HAMILTON BEACH(copyright) Model 930 Mixer at which point the density of the solution was measured using a Gardco U.S. Standard Weight Per Gallon Cup and found to be 8.436 pounds per gallon (1.0106 g/cc). Twenty grams of EXPANCEL(copyright) 091WE microspheres were hand mixed into the clear thickened liquid, being careful to minimize the entrainment of air. The density of the microsphere suspension was taken using the Gardco U.S. Standard Weight Per Gallon Cup prior to high shear mixing. The suspension was then mixed under high shear using the HAMILTON BEACH(copyright) Model 930 Mixer in two-minute increments. Each two-minute segment was followed by a density measurement to determine the survival of the microspheres. Table III shows the measured density for the suspension of microspheres before and after each two-minute high shear exposure.
Table IV summarizes the preferred microsphere properties for use as filler in the manufacture of a lightweight joint compound.
The most preferred polymer resin used in the manufacture of microspheres is PACN, such as that used in EXPANCEL(copyright) 091 WE from Nobel Industries, Sweden. The resin shell of this microsphere has demonstrated acceptable resistance to stress, caused by the shear force of mixing and pressures during material transfer in the manufacture of joint compound. The average particle size of this microsphere is less than 75 microns, and when employed in a lightweight formulation, the resulting material demonstrated a smooth, non-grainy surface. The microspheres are also provided in a pre-wet cake (10% by weight) that is particularly easy to disperse in water. PVDC is optionally used in combination with PACN, or alone, in the manufacture of the microspheres. In some cases, MMA is employed, in combination with PVDC and/or PACN.
A coated microsphere, as taught in U.S. Pat. Nos. 4,722,943 and 5,342,689, herein incorporated by reference, is also available. The coating acts as a free flowing aid during the manufacturing process and subsequent use, but the coating adds greatly to the density of the material, thus requiring greater concentrations to achieve equal drops in overall joint compound formulation density. The formulation is preferably adjusted to compensate for the increased level of coating agent used on the microspheres, however, this will require additional processing time and equipment.
The joint compound of the present invention includes the resin microspheres as one of the fillers to be used. Use of additional fillers is preferred to import specific properties to the joint compound. The preferred additional filler, particularly for drying type formulations, is finely ground calcium carbonate. It is a dry powder that usually comprises at least about 50% by dry weight of the joint compound composition and generally falls within the range of about 50-98% of the dry weight. Additional fillers such as mica, talc, such as sericite, diatomaceous earth, clays, such as attapulgite, sepulite and kaolin, calcium sulfate dihydrate, calcium sulfate anhydrite, calcium sulfate hemihydrate, and pyrophylite are also suitable. The ratio of all fillers to all binders is preferably in the range of from about 15:1 to about 5:1.
Perlite or expanded perlite is another lightweight filler which may be used in addition to the microspheres where the weight of the compound is important, and is used in the lightweight formulation of the preferred embodiment. Use of expanded perlite in a lightweight joint compound is taught in U.S. Pat. No. 4,454,267, which is herein incorporated by reference. Expanded perlite is a very lightweight material that contains many cracks and fissures. It should be treated according to the teachings of U.S. Pat. No. 4,525,388, which is hereby incorporated by reference, so that the material does not increase in weight due to water absorbed by capillary action. The treated, expanded perlite, when used, is preferably present in concentrations of at least 5% based on the weight of all ingredients of the joint compound, excluding water.
Bonding between the joint compound and the substrate is improved by the addition of thickeners, plasticizers and/or polyvinyl alcohol powder. Cellulosic thickeners are preferred, with METHOCEL(copyright) 240S providing the best results. Conventional cellulosic thickeners, such as ethylhydroxy ethylcellulose, hydroxypropyl methylcellulose, methylhydoxypropyl cellulose and hydroxyethyl cellulose, are also suitable in the joint compounds of this invention. The concentration of cellulosic thickener ranges from about 0.05% to about 2% of the dry weight of the joint compound ingredients.
Polyethylene glycol (xe2x80x9cPEGxe2x80x9d) and/or methoxypolyethylene glycol may optionally be added to the present joint compound. Either of these additives can be used to control the surface absorption properties of the cured joint compound. These additives also improve the wetness and slip of the material. When used, the PEG is added in a concentration ranging from about 0.1% to 2% of the dry weight of the joint compound.
Other preferred additives of the present joint compound include surfactants, wetting agents, soaps and alkyl benzene sulfonates. A soap, or detergent, is a complex mixture of ingredients including, but not limited to acids, bases, antimicrobal agents, antiredeposition agents, colorants, fragrances, defoamers, foamers, hydrotropes, moisturizers, preservatives, solvents, thickeners or surfactants, selected from many possible functional groups. Alkyl benzene sulfonate is a specific surfactant that is particularly useful in formulations of this nature, as taught in co-pending application U.S. Ser. No. 09/724,674, now U.S. Pat. No. 6,476,099, filed concurrently herewith, for a Joint Compound Additive for Reduction of Cracking, Cratering and Shrinkage, which is herein incorporated by reference. The preferred joint compound of this invention utilizes sodium dodecyl benzene sulfonate to improve several properties of the joint compound including, crater resistance, crack resistance, and shrinkage reduction. In lightweight joint compounds, soaps and alkyl benzene sulfonates also help to decrease the density of the joint compound.
Using the formulation of the present invention significant reduction in density of joint compounds is attainable. A preferred product density is less than 8.35 pounds per gallon, less than the density of water. In the most preferred embodiment, products with densities less than 8pounds per gallon are obtained.
Use of the resin microspheres also results in a joint compound with a different scent compared to a traditional joint compound. If desired, fragrance, such as a vanilla extract, may be added to make the scent of the joint compound more agreeable.
Water is added to the ready-mix joint compound to achieve the correct viscosity. However, when making lightweight formulation, care should be take to minimize the amount of water in the compound. Water adds to the density of the product when the desired finished product density is less than that of the water itself. In addition, when the level of water is minimized, resistance to shrinkage and cracking is enhanced. When the microspheres are coated to aid in dispersion, the coating also contributes to the overall weight of the joint compound. It may be necessary to reduce the overall level of fillers in the formulation to compensate for the percentage of coating agent added to the microspheres.
Preparation of the ready-mix joint compound with pre-wet resin microspheres cake requires a different processing method compared to a joint compound with traditional fillers. Traditionally, wet and dry components are added and mixed separately prior to transfer to a main wet mixer. When the microspheres are supplied in a pre-wet cake, they tend to clog the transfer lines of the wet component system because of the their inherent lightweight nature. The wet filler cake also causes lumping when introduced into the dry component system, as the dry components tend to wet out when in contact with the filler cake, which is as high as 90% moisture. To prevent clogging, contamination of the transfer lines, and lumps of pre-wet dry additives, the resin microspheres are added directly to the main mixer, separate from the other ingredients. In the addition of the microspheres, timing is not critical. Microspheres are suitably added before, during or after the addition of other components, as long as they are not added as part of the wet component group or the dry component group.
If desired, the pre-wet resin cake may be first dispersed in water then pumped directly into the main mixer. The resin microspheres are considerably lighter than water, and will have a great tendency to float on the surface of the water. Therefore it is important to thoroughly mix the slurry to keep it dispersed during pumping to the main mixer. Water used to fluidize the wet filler cake is subtracted from the mix water usually added directly to the main mixer. The amount of water in the final ready-mix joint compound product must be adjusted accordingly.
Although the dry powder form of the resin microspheres may be mixed with other dry ingredients, care must be taken since the spheres density is so low. They readily disperse into the air, forming a cloud that settles slowly. It is preferred that the powder be handled so as to minimize release into the air.
Mixing of the joint compound is preferably carried out at a lower shear compared to traditional joint compounds. High viscosity mixing creates higher shear on the spheres. The density of the joint compound increases when microspheres break. Care should be taken to assure that there is minimal breakage by keeping the shear stress of mixing below the point at which the microspheres shell walls can be compromised.
Use of a vacuum to remove entrained air prior to transfer to the filling station negatively affects this joint compound. If the wall strength of the microspheres is exceeded when the vacuum is applied, the microsphere""s shell will be stressed, leading to collapse and resulting in densification of the joint compound. An increase in density specifically between the main mixer and the fill station results when the vacuum is used, and is due to reduction in entrained air together with breakage of the microspheres. Manufacturing trials have shown that when the formulation is mixed at a lower viscosity, there is a tendency to entrain less air making in-transfer vacuum unnecessary.
The following examples are from a preliminary manufacturing trial. The objective of the trial was to determine the feasibility of incorporating lightweight resin microspheres into a ready mix joint compound manufacturing system.