BLEACH PRECURSOR PARTICLES

TECHNICAL FIELD The present invention relates to cleansing compositions in tablet form, and especially to compositions for use in cleansing dentures and the like. In particular, the invention relates to tablet-form compositions having more rapid and efficaceous denture cleansing performance and anti-bacterial activity and improved appearance, physical characteristics, dissolution and in-use performance characteristics.

BACKGROUND

Effervescent tablets for cleansing dentures and the like are well known in the art. The aim of a denture cleanser product is to clean the denture as fully and as quickly as possible and especially to remove the accumulation of plaque, mucilaginous and bacterial deposits which collect while the denture is being worn. To wear a denture which has not been completely cleaned of plaque and bacterial deposits is not only unhygenic but can also within a short space of time result in a detrimental effect on the mucous membrane. Moreover bacterial deposits can lead to so-called bacterial corrosion of the plastics material used to produce the denture with consequent color-change and malodor-formation.

Denture cleanser tablets containing peroxyacid bleach precursors as a separate tablet layer are also known; however such formulations are difficult to manufacture and suffer from poor coherency and other physical characteristics due, at least in part, to the inherent incompressibility of the bleach activator particles.

Accordingly, the present invention provides a denture cleanser which cleanses more rapidly and which is more efficacious on plaque, mucilaginous and bacterial deposits and has greater stain-removal performance than those tablet preparations which are presently known and available on the market. At the same time, the tablet compositions display excellent cohesion and other physical characteristics as well as improved dissolution and in-use performance characteristics.

According to the invention, there is provided a cleansing tablet for dentures and the like comprising visually discrete agglomerated particles of an organic peroxyacid bleach precursor dispersed in a water-soluble or water- dispersible matrix comprising an inorganic persalt bleaching agent and a solid base material which in the presence of water releases carbon dioxide or oxygen with effervescence

All percentages and ratios herein are by weight of total composition, unless otherwise indicated.

The cleansing tablets of the invention thus comprise three essential components, a bleaching agent, a peroxyacid bleach precursor and an effervescent base composition. Each of these will be discussed in turn.

The bleaching agent takes the form of an inorganic persalt and can be selected from any of the well-known bleaching agents known for use in denture cleansers such as the alkali metal and ammonium persulfates, perborates, percarbonates and perphosphates and the alkali metal and alkaline earth metal peroxides. Examples of suitable bleaching agents include potassium, ammonium, sodium and lithium persulfates and perborate mono- and tetrahydrates, sodium pyrophosphate peroxyhydrate and magnesium, calcium, strontium and zinc peroxides. Of these, however, the alkali metal persulfates, perborates and mixtures thereof are prefered for use herein, highly preferred being the alkali metal perborates. Indeed, it is a feature of the invention that the tablet compositions herein will provide excellent antimicrobial activity even in the absence of alkali metal persulfates.

The amount of bleaching agent in the total composition is generally from about 5 to about 70% preferably from about 10% to about 50%. In compositions comprising a mixture of alkali metal persulfates and perborates, the overall persulfate:perborate ratio is suitably from about 5: 1 to about 1 :5, more especially from about 2: 1 to about 1 :2.

The compositions herein also contain an organic peroxyacid precursor, which in general terms can be defined as a compound having a titre of at least 1.5ml of 0. IN sodium thiosulfate in the following peracid formation test

A test solution is prepared by dissolving the following materials in 1000 mis distilled water: sodium pyrophosphate

(Na ₄ P2θ7.10H ₂ O) 2.5g

sodium perborate

( aBO2.H2O2.3H2O) having

10.4% available oxygen 0.615g sodium dodecylbenzene sulphonate 0.5g

To this solution at 60°C an amount of activator is added such that for each atom of available oxygen present one molecular equivalent of activator is introduced.

The mixture obtained by addition of the activator is vigorously stirred and maintained at 60°C. After 5 minutes from addition, a 100 ml portion of the solution is withdrawn and immediately pipetted onto a mixture of 250 g cracked ice and 15 ml glacial acetic acid. Potassium iodide (0.4 g) is then added and the liberated iodine is immediately titrated with 0.1 N sodium thiosulphate with starch as indicator until the first disappearance of the blue colour. The amount of sodium thiosulphate solution used in ml is the titre of the bleach activator.

The organic peracid precursors are typically compounds containing one or more acyl groups, which are susceptible to perhydrolysis. The preferred activators are those of the N-acyl or O-acyl compound type containing a acyl radical R-CO wherein R is a hydrocarbon or substituted hydrocarbon group having preferably from about 1 to about 20 carbon atoms. Examples of suitable peracid precursors include: 1) Acyl organoamides of the formula RCONR1R2, where RCO is carboxylic acyl radical, R] is an acyl radical and R2 is an organic radical, as disclosed in US-A-3,117,148. Examples of compounds falling under this group include:

a) N,N - diacetylaniline and N-acetylphthalimide; b) N-acylhydantoins, such as

N,N' -diacetyl-5,5-dimethylhydantoin; c) Polyacylated alkylene diamines, such as

K N'N' -tetraacetylethylenediamine (TAED) and the corresponding hexamethylenediamine (TAHD) derivatives, as disclosed in GB-A-907,356, GB-A-907,357 and GB-A-907,358;

d) Acylated glycolurils, such as tetraacetylglycoluril, as disclosed in GB-A-1,246,338, GB-A-1,246,339 and GB-A- 1,247,429

2) Acylated sulphonamides, such as N-methyl-N-benzoyl-menthane sulphonamide and N-phenyl-N-acetyl menthane sulphonamide, as disclosed in GB-A-3, 183,266

3) Carboxylic esters as disclosed in GB-A-836,988, GB-A-963, 135 and GB- A-l, 147,871. Examples of compounds of this type include phenyl acetate, sodium acetoxy benzene sulphonate, trichloroethylacetate, sorbitol hexaacetate, fructose pentaacetate, p-nitrobenzaldehyde diacetate, isopropeneyl acetate, acetyl aceto hydroxamic acid, and acetyl salicylic acid Other examples are esters of a phenol or substituted phenol with an alpha-chlorinated lower aliphatic carboxylic acid, such as chloroacetylphenol and chloroacetylsalicylic acid, as disclosed in US-A- 3,130,165

4) Carboxylic esters having the gernal formal Ac L wherein Ac is the acyl moiety of an organic carboxylic acid comprising an optionally substituted, linear or branched C6-C20 alkyl or alkenyl moiety or a C6-C20 alkyl- substituted aryl moiety and L is a leaving group, the conjugate acid of which has a pKa in the range from 4 to 13, for example oxybenzenesulfonate or oxybenzoate Preferred compounds of this type are those wherein. a) Ac is R3-CO and R3 is a linear or branched alkyl group containing from 6 to 20, preferably 6 to 12, more preferably 7 to 9 carbon atoms and wherein the longest linear alkyl chain extending from and including the carbonyl carbon contains from 5 to 18, preferably 5 to 10 carbon atoms, R3 optionally being substituted (preferably alpha to ^* the carbonyl moiety) by Cl, Br, OCH3 or OC2H5 Examples of this class of material include sodium 3,5,5-trimethylhexanoyloxybenzene sulfonate, sodium 3,5,5-trimethylhexanoyloxybenzoate, sodium 2- ethylhexanoyl oxybenzenesulfonate, sodium nonanoyl oxybenzene sulfonate and sodium octanoyl oxybenezenesulfonate, the acyloxy group in each instance preferably being p-substituted.

b) Ac has the formula R3(AO) _m XA wherein R3 is a linear or branched alkyl or alkylaryl group containing from 6 to 20, preferably from 6 to 15 carbon atoms in the alkyl moiety, R5 being optionally substituted by Cl, Br, OCH3, or OC2H5, AO is oxyethylene or oxypropylene, m is from 0 to 100, X is O, NR4 or CO-NR4, and A is CO, CO-CO, Rg-CO, CO-Rό-CO, or CO-NR^Rό-CO wherein R4 is C _j -C alkyl and R_6 is alkylene, alkenylene, arylene or alkarylene containing from 1 to 8 carbon atoms in the alkylene or alkenylene moiety Bleach activator compounds of this type include carbonic acid derivatives of the formula R3(AO) _m OCOL, succinic acid derivatives of the formula R3OCO(CH2)2COL, glycollic acid derivatives of the formula R3OCH2COL, hydroxypropionic acid derivatives of the formula R3OCH2CH2COL, oxalic acid derivatives of the formula R3OCOCOL, maleic and fumaric acid derivatives of the formula R3OCOCH=CHCOL, acyl aminocaproic acid derivatives of the formula R3CON ι (CH2)6COL, acyl glycine derivatives of the formula R3CONR1CH2COL, and amino-6-oxocaproic acid derivatives of the formula R3N(R _j )CO(CH2)4COL. In the above, m is preferably from 0 to 10, and R3 is preferably Cg-C^, more preferably Cg-Cjo alkyl when m is zero and C9-C15 when m is non¬ zero. The leaving group L is as defined above.

5) Acyl-cyanurates, such as triacetyl- or tribenzoylcyanurates, as disclosed in US patent specification No. 3,332,882.

6) Optionally substituted anhydrides of benzoic or phthalic acid, for example, benzoic anhydride, m-chlorobenzoic anhydride and phthalic anhydride

Of all the above, preferred are organic peracid precursors of types 1 (c) and 4(a)

The level of peroxyacid bleach precursor by weight of the total composition is preferably from about 0.1% to about 10%, more preferably from about 0.5% to about 5%.

The solid base material and, in preferred embodiments, the bleach precursor agglomerates also incorporate an effervescence generator The effervescence generator utilized in the compositions herein can be selected from generators which are effective under acid, neutral or alkaline pH conditions, but preferably it consists of a combination of a generator which is effective or most effective under acid or neutral pH conditions and a generator which is effective or most effective under alkaline pH conditions. Effervescence generators which are effective under acid or neutral pH conditions include a combination of at least one alkali metal carbonate or bicarbonate, such as sodium bicarbonate, sodium carbonate, sodium sesquicarbonate, potassium carbonate, potassium bicarbonate, or mixtures thereof, in admixture with at least one non-toxic, physiologically- acceptable organic acid, such as tartaric, fumaric, citric, malic, maleic, gluconic, succinic, salicylic, adipic or sulphamic acid, sodium fumarate, sodium or potassium acid phosphates, betaine hydrochloride or mixtures thereof Of these, malic acid is preferred. Effervescence generators which are effective under alkaline pH conditions include persalts such as alkali and alkaline earth metal peroxoborates as well as perborates, persulphates, percarbonates, perphosphates and mixtures thereof as previously described, for example, a mixture of an alkali metal perborate (anhydrous, mono- or tetrahydrate) with a monopersulphate such as Caroat R marketed by E I du Point de Nemours Co. and which is a 2 1 1 mixture of monopersulphate, potassium sulphate and potassium bisulphate and which has an active oxygen content of about 4.5%.

In highly preferred compositions, the solid base material incorporates both a (bi) carbonate/acid effervescent couple and a perborate/persulphate oxygen effervescence generator while the bleach precursor agglomerates incorporates a (bi) carbonate/acid and optionally a peroxoborate oxygen effervescence generator The combination of generators is important for achieving optimum dissolution characteristics and pH conditions for generation of the peroxyacid bleach and for achieving optimum cleaning and antimicrobial activity The (bi) carbonate components generally comprise from about 5% to about 65%, preferably from about 25% to 55% of the total tablet; the acid components generally comprise from about 5% to about 50%, preferably from about 10% to about 30% of the total tablet

In one embodiment herein, the inorganic bleaching agent comprises an alkali metal perborate and the solid base material comprises at least one

component phase having an acid or neutral pH in aqueous medium, said at least one phase having incorporated therein at least a portion of the alkali metal perborate.

For optimum antiplaque and antibacterial performance, the cleansing composition of this embodiment is preferably designed in such a way that the bleach precursor agglomerates dissolve or disperse in water more slowly or later than the acid or neutral phase in order to provide, on placing the cleaning composition in water, an initial pH in the acid or neutral range, preferably from about 2 to about 7.5 and especially from about 5 to about 7 Moreover, it is preferred that the bleach precursor agglomerates have an alkaline pH in aqueous medium and be present in sufficient amount in order to shift, upon completion of effervescence, the pH of the aqueious medium into the alkaline range, preferably to a pH of from about 8 to about 10, this pH being preferred for reasons of cleaning performance and solution clarity. The initial acid or neutral pH should be maintained for a time from about 30 seconds to about 5 minutes, preferably from about 1 minute to about 3 minutes. Effervescence is preferably completed in from about 30 seconds to about 4 minutes, preferably from about 1 to about 3 minutes of the pH being shifted into the alkaline range.

The slower dissolution rate of the bleach precursor agglomerates compared with the tablet matrix base material can be achieved in various ways, for example by the use of alkaline salts or compounds which are inherently sparingly or slowly soluble such as anhydrous sodium carbonate, calcium carbonate, calcium hydroxide, magnesium oxide, or magnesium hydroxide carbonate or by mixing or compressing the bleach precursor agglomerate components with a filler which has a slow dissolution rate such as anhydrous sodium sulfate and slowly water-soluble polymers, for example, proteins, cellulose ethers, cellulose esters, polyvinyl alcohol, alginic acid esters, vegetable fatty materials of a pseudocolloidal character. Moreover, the relative rate of dissolution of the bleach precursor agglomerates and tablet matrix can be additionally controlled by appropriate formulation- and distribution of the binding/agglomerating and effervescent components of the solid base material and bleach precursor agglomerates.

In another embodiment of the invention which is preferred from the viewpoint of providing more rapid tablet dissolution, the inorganic bleaching agent comprises an alkali metal perborate and the solid base material comprising at least one component phase having an alkaline pH in aqueous medium, said at least one

phase having incorporated therein at least a portion of the alkali metal perborate For optimum antiplaque and antibacterial performance, the bleach precursor agglomerates in this embodiment preferably have an acidic or neutral pH in aqueous medium and additionally incorporate an agglomerating agent and a effervescence generator. Overall, for optimum dissolution, stability and performance, the bleach precursor agglomerates and the solid base material preferably have a pH difference in aqueous medium of from about 0.5 to about 2 pH units. The level of bleach precursor agglomerates, moreover, is preferably from about 1% to about 20%, more preferably from about 5% to about 15% by weight of the cleansing tablet

The bleach precursor agglomerates preferred for use herein generally comprise a binder or agglomerating agent in a level of from about 5% to about 40%, more especially from about 10% to about 30% by weight thereof Suitable agglomerating agents include polyvinylpyrrolidone, poly (oxyethylene) of molecular weight 20,000 to 500,000, polyethyleneglycols of molecular weight of from about 1000 to about 50,000, Carbowax having a molecular weight of from 4000 to 20,000, nonionic surfactants, fatty acids, sodium carboxymethyl cellulose, gelatin, fatty alcohols, phosphates and polyphosphates, clays, aluminosilicates and polymeric polycarboxylates. Of the above, polyethyleneglycols are highly preferred, especially those having molecular weight of from about 1,000 to about 30,000, preferably 2000 to about 10,000.

Preferred from the viewpoint of optimum dissolution and pH characteristics are bleach precursor agglomerates which comprise from about 10% to about 75%, preferably from about 20% to about 60% by weight thereof of peroxyacid bleach precursor, from about 5% to about 60% preferably from about 5% to about 50%, more preferably from about 10% to about 40% of a (bi) carbonate/acid effervescent couple, from about 0% to about 20% of a peroxoboroate, and from about 5% to about 40%, preferably from about 10% to about 30% of an agglomerating agent.

The final bleach precursor granules desirably have an average particle size of from about 500 to about 1500, preferably from about 500 to about 1,000 um, this being valuable from the viewpoint of optimum dissolution performance and aesthetics.

The compositions of the invention can be supplemented by other usual components of cleansing table formulations, especially surfactants, chelating

agents, enzymes, flavor oils such as oils of spearmint, peppermint and wintergreen. dyestuffs, sweeteners, tablet binders such as the above specified bleach precursor agglomerating agents, especially polyethyleneglycols having a molecular weight of from about 12,000 to about 30,000, foam depressants such as dimethylpolysiloxanes, foam stabilizers such as the fatty acid sugar esters, preservatives, lubricants such as talc, magnesium stearate, finely divided amorphous pyrogenic silicas, etc. The free moisture content of the final composition is desirably less than about 1% and especially less than about 0.5%.

The surface active agent used in the compositions of the invention can be selected from the many available that are compatible with the other ingredients of the denture cleanser, both in the dry state and in solution. Such materials are believed to improve the effectiveness of the other ingredients of the composition by aiding their penetration into the interdental surfaces. Also, these materials aid in the removal of food debris attached to the teeth. Between 0.1 and 5 percent by weight of the dry composition of a dry powder or granular anionic surface active agent, such as sodium lauryl sulfate, sodium N-lauroylsarcosinate, sodium lauryl sulfoacetate or dioctyl sodium sulfosuccinate or ricinoleyl sodium sulfosuccinate, may, for example, be included in the composition and preferably the surface active agent comprises between 0.5 and 4 percent of the composition.

Suitable cationic, non-ionic and ampholytic surface active agents include, for example, quaternary ammonium compounds such as cetyltrimethylammonium bromide, condensation products of alkylene oxides such as ethylene or propylene oxide with fatty alcohols, phenols, fatty amines or fatty acid alkanolamides, the fatty acid alkanolamides themselves, esters of long-chained (C -C22) fatty acids with polyalcohols or sugars, for example glycerylmonostearate or saccharosemonolaurate or sorbitolpolyoxyethylenemono-or di-stearate, betaines, sulphobetaines or long-chain alkylaminocarboxylic acids.

Chelating agents beneficially aid cleaning and bleach stability by keeping metal ions, such as calcium, magnesium, and heavy metal cations in solution. Examples of suitable chelating agents include sodium tripolyphosphate, sodium acid pyrophosphate, tetrasodium pyrophosphate, aminopolycarboxylates such as nitrilotriacetic acid and ethylenediamine tetracetic acid and salts thereof, and polyphosphonates and aminopolyphosphonates such as hydroxyethanediphosphonic acid, ethylenediamine tetramethylenephosphonic acid, diethylenetriaminepentamethylenephosphonic acid and salts thereof. The chelating

10

agent selected is not critical except that it must be compatible with the other ingredients of the denture cleanser when in the dry state and in aqueous solution. Advantageously, the chelating agent comprises between 0.1 and 60 percent by weight of the composition and preferably between 0.5 and 30 percent. Phosphonic acid chelating agents, however, preferably comprise from about 0. 1 to about 1 percent, preferably from about 0.1% to about 0.5% by weight of composition.

Enzymes suitable for use herein are exemplified by proteases, alkalases, amylases, lipases, dextranases, mutanases, glucanases etc.

The following Examples further describe and demonstrate the preferred embodiments within the scope of the present invention.

EXAMPLES I TO V

The following are representative denture cleansing tablets according to the invention. The percentages are by weight of the total tablet. The tablets are made by compressing a mixture of the granulated components in a punch and dye tabletting press at a pressure of about 10* kPa.

I π III lY V

Malic Acid 12 10 15 - 14

Citric Acid - 10 - 15 -

Sodium Carbonate 10 8 10 6 10

Sulphamic Acid 5 - - 3 3

PEG 20,000 - 3 7 8 5

PVP 40,000 6 3 - - -

Sodium Bicarbonate 23 24 25 23 24

Sodium Perborate Monohydrate 15 12 16 30 15

Potassium Monopersulphate 15 18 13 - 14

Pyrogenic Silica - 3 1 1 -

Talc 2 - - - -

EDTA - - 1 - 3

EDTMP ¹ 1 - - 1 -

Flavour/Dye 2 1 2 1 2

Bleach Precursor Agglomerate 9 8 10 12 10

Bleach Precursor Aeelomerate I π III IY V

TAED-2 2 - 4 5 2.5

TMHOS ³ 2 3 - - -

Sulphamic Acid 2 2 2 2 3.5

Sodium Bicarbonate 0.5 0.2 0.2 0.5 2

PEG 6000 - 2.5 2 2.4 2.5 1.5

Dye - 0.8 1.4 2 0.5

1. Ethylenediaminetetramethylenephosphonic acid

2. Tetraacetylethylene diamine

3. Sodium 3.5,5-trimethyl hexanoylc jxybenzene sulfonate

In Examples I to V above, the overall tablet weight is 3 g, diameter 25 mm

The denture cleansing tablets of Examples I to V display improved cleansing and anti-bacterial activity together with excellent cohesion and other physical and in-use performance characteristics