WO1994013776A1

WO1994013776A1 - Aqueous bleaching compositions comprising peroxy carboxylic acids

Info

Publication number: WO1994013776A1
Application number: PCT/EP1993/003380
Authority: WO
Inventors: Carole Jane Philpotts; Patricia Revell; Royston Reginald Smith
Original assignee: Unilever Plc; Unilever Nv
Priority date: 1992-12-07
Filing date: 1993-12-01
Publication date: 1994-06-23
Also published as: TR27486A; AU5650694A; GB9225519D0

Abstract

Stability of compositions comprising relatively low levels (0.5-15 % wt) of peroxycarboxylic acids can be improved by formulation such that the pH of the composition is such that it is above the pKa of the corresponding imido acid and below 6.0. Stability can be further improved by the use of a secondary alkane sulphonate surfactant and by the use of a sulphate salt other than a transition metal sulphate. Stability can be yet further improved by selection of a specific ratio of the quantity of surfactant to said sulphate such that the ratio is in the range 0.4-0.8:1, more preferably 0.6-0.8:1, as surfactant: sulphate (both being expressed as sodium salts).

Description

AQUEOUS BLEACHING COMPOSITIONS COMPRISING PEROXY CARBOXYLIC ACIDS

Technical Field

The present invention relates to improvements in bleaching and/or hygiene compositions comprising peroxy carboxylic acids. In particular the invention relates to bleaching and/or hygiene compositions for use on hard surfaces such as ceramics, plastics and metals, or in aqueous solutions contacting solid surfaces. In this specification the terms bleaching agent and hygiene agent are used interchangeably.

Background to the Invention

For many years it has been known to employ hydrogen peroxide as a water soluble bleaching and hygiene agent. To a lesser extent, other peroxides such as sodium peroxide have been employed as bleaching agents, as have soluble peracids, such as peracetic acid, either as such or as precursors such as tetra acetyl ethylene diamine, as well as performic acid and potassium mono persulphate.

Aqueous-insoluble or partially insoluble peracids have also been investigated with particular reference to their use in fabric bleaching compositions and in machine dishwashing applications, both in liquid and powder compositions. In liquid compositions a thickening agent must generally be present in order to suspend the insoluble i.e. particulate, bleaching agent. A constraint which is placed upon the choice of thickening system is that its chemical and physical properties must be such that it is stable in the presence of the reactive, peracid bleaching and/or hygiene agents. A further constraint on the overall formulation is that the peracid should be chemically stable in the presence of the thickening agent.

US patent 3996152 discloses stable low-pH gels containing peroxyacid bleach particles in a non-starch thickening agent.

Aqueous suspensions of the solid hygiene agent diperoxy- dodecanedioic acid (DPDA) are known for use as pourable bleaching compositions from EP 0176124. Another form of DPDA suspension useful as an aqueous liquid bleaching composition is disclosed in EP 0160342. DPDA is an organic peroxy acid, relatively stable to decomposition, odourless and particularly effective as an anti-bacterial agent as compared with hydrogen peroxide.

DPDA is difficult to manufacture and consequently expensive. As mentioned in US 4790949, EP 176124 and EP 412599, the substance has been known to explode when prepared in relatively pure form and subjected to heat, shock or abrasion, consequently it presents considerable handling difficulties which further increase the costs of manufacture and use.

US 4100095 discloses the stabilisation of peroxyacid bleaches by the use of certain exotherm control agents so as to prevent explosion. These agents may be selected from magnesium sulphate, sodium sulphate, boric acid and potassium sulphate. Sodium sulphate is commonly present in commercial DPDA in order to reduce the explosive tendency. EP 0412599 provides an alternative solution by using glycols as control agents. European patent application EP 0160342 (Unilever, 1984) discloses aqueous liquid bleaching compositions containing organic peroxyacid particles having a solubility of less than about 1% in water, suspended in an acidic surfactant- structured liquid containing alkyl benzene sulphonic acid and electrolyte. The Ph of the compositions disclosed in EP 160342 preferably ranges from 2-5, the preferred peroxy acid is DPDA. It is believed that the combination of alkyl benzene sulphonic acid and electrolyte forms a lamellar-dispersion thickening system which suspends the particles.

EP 0435379 (AKZO, 1989) relates to the use of i idoperoxy- carboxylic acids (as defined therein) in bleaching compositions in soaking detergents and dishwashing detergents. Preferred compositions include e-N-N- phthaloyl-amino-peroxy-caproic acid (PAP) and DPDA, as mentioned above. PAP is considerably less explosive than DPDA and has comparable stability to decomposition. PAP is less effective as a hygiene agent than DPDA on a weight for weight basis.

The formulations disclosed in EP 0435379 comprise 0.1-35%, preferably 2-10%wt sulphate and 0.5-40%wt, preferably 2- 20%wt of alkyl benzene sulphonic acid as surfactant. It is believed that the presence of the relatively inexpensive sulphate salt, as electrolyte, promotes thickening of the composition such that the level of the relatively expensive surfactant can be reduced without detriment to the suspending properties of the product.

EP 0435379 states that the total alkyl benzene sulphonic acid content may vary from 0.5-40%wt, and the total level of surfactant may vary from 0-50%wt: i.e. although the presence of this component is an essential feature of the invention, the level of surfactant does not seem to have been thought of as particularly critical, although sufficient should be used to achieve the desired physical stability.

The levels of PAP indicated in EP 0435379 are such that the active oxygen content of the compositions may range from 0.05-5%wt. PAP has a molecular weight of 277 and each molecule of PAP liberates one oxygen atom, consequently, the active oxygen content of pure PAP is 5.8%wt. An active oxygen content of 0.05%wt indicates a minimum level of l%wt PAP. Consequently, this document discloses that the PAP content can range from 1 to about 80% i.e. the document does not disclose any particular criticality in the levels of PAP.

The Ph range preferred in EP 0435379 is acid: examples are given for pH 3.5.

EP 442549 (Unilever, 1990) discloses the use of PAP as a bleaching agent in combination with secondary alkyl sulphonate and fatty acid as a suspending surfactant system. Such suspending surfactant systems are known to be bleach-stable. In keeping with the disclosure of EP 435379 the pH of the system is adjusted to pH 3.5-4.5. The compositions comprise sodium sulphate at a level such that the weight ratio of sodium sulphate to surfactant ranges from 1.67:1 to 1:3.67.

The compositions of EP 442549 suffer from the disadvantage that on storage white, needle-like crystals form in the composition and can be thrown down as a sediment. This leads to a loss of homogeneity in the composition and presents dosing problems. Moreover, the presence of crystals can abrade or scratch surfaces which are cleaned with the composition. More and worse, users can believe that the crystal-containing product has decomposed and discard the unused product, unnecessarily releasing the compound into the environment.

Other thickening systems for bleaching and hygiene agents are known. In particular it is known to thicken compositions with polymers which are stable in the presence of the bleaching or hygiene agent.

From the above it can be seen that the problems of chemical and physical stability associated with the use of imido peroxy carboxylic acids as bleaching agents are known and that solutions to these problems have proposed that products should be formulated at in particular pH ranges.

Brief Description of the Invention

We have now determined that the stability of compositions comprising relatively low levels of peroxycarboxylic acid can be improved by formulation in a specific pH range, further improved by the use of a specific surfactant and yet further improved by selection of a specific ratio of the quantity of selected sulphate salts and the preferred surfactant.

According to the present invention there is provided an aqueous bleaching composition comprising: 0.5-15%wt of an peroxy carboxylic acid wherein the pH of the composition is such that it is above the pK_a of the corresponding imido acid and below 6.0. Detailed Description of the Invention

As mentioned above, the present invention relates to aqueous bleaching composition comprising: 0.5-15%wt of an peroxy carboxylic acid wherein the pH of the composition is such that it is above the pK_a of the corresponding carboxylic acid and below 6.0.

Preferably, the pH of the composition is greater than 4.5 and less than 6.0. More preferably the pH falls into the range 4.5-6.0, and is most preferably around 5.5.

Surprisingly, we have found that increasing the pH of the compositions above 4.5, significantly reduces the rate of crystal formation. Without wishing to be bound by theory, it is believed that, at a pH below the pK_a of the corresponding acid the decomposition product of the peroxy carboxylic acid, i.e. the acid in protonated form, is insoluble and forms the white, needle like crystals.

Above a pH of 6.0, excessive hydrolysis of the acid is believed to occur.

Surfactants

Typically, the composition further comprises a surfactant component as a part of the thickening system. Preferably, the surfactant is a sulphate or sulphonate anionic surfactant.

In preferred embodiments of the invention the composition further comprises at least 3% of a sulphate salt other than a transition metal sulphate, and, preferably, 5-10% of one or more surfactant stable in the composition. It will be appreciated that commercially available sulphate and sulphonate surfactants often contain sodium sulphate as an impurity. Typical levels being around 5% Na₂SO₄/100% AD.

It is preferred that the relative levels of these further components is such that the weight ratio of said surfactant to said sulphate is in the range 0.4-0.8:1, more preferably 0.6-0.8:1, as surfactant:sulphate (both being expressed as sodium salts) .

The presence of transition metals either as sulphate salts or otherwise should be avoided as these promote the decomposition of the peracid.

Most preferably, the weight ratio of surfactant:sulphate is around 0.66:1. Without wishing to restrict the invention by reference to a theory of operation, it is believed that, whilst a lamellar thickening system can be formed with a variety of surfactant and electrolyte ratios and over a range of pH values, the most stable compositions are only formed in a particular pH range and with particular ratios of surfactant to sulphate.

Preferably, the surfactant system comprises secondary alkane sulphonate.

It is particularly preferred that compositions are free of surfactants which contain benzene rings as these have not only been found to be less stable than compositions according to the present invention which comprises secondary alkane sulphonate but these surfactants may also present environmental problems. Preferred levels of secondary alkane sulphonate range from 4.0-10%wt with levels around 5.3wt% being most preferred. Most preferably the secondary alkane sulphonate is a C12-C18 average chain length secondary alkane sulphonate.

Preferably the surfactant system further comprises a nonionic surfactant.

Preferred levels of nonionic surfactant are l-6%wt of an ethoxylated nonionic surfactant. Preferably the nonionic surfactant has an ethoxylation level of 3-12.

The most preferred levels of the ethoxylated nonionic are l-3%wt on total product. Levels toward the lower limit of the range are employed where the optional fatty acid is present.

Preferably the surfactant system further comprises fatty acids.

Suitable fatty acids comprise alkyl chains having an average of 12-18 carbon atoms.

It is particularly preferred that the surfactant system comprises a mixture of at least secondary alkane sulphonate and fatty acid.

More preferably the surfactant system comprises secondary alkane sulphonate, fatty acid and at least one nonionic surfactant. The most preferred weight ratios between these components are 4:1:1.

It is preferable that the weight ratio of the alkali metal sulphate to total surfactant falls in the range 1:0.6- 1.25, more preferably 1:0.75-1.25. The molecular weight of a typical secondary alkane sulphonate is around 300, whereas the molecular weight of a typical nonionic surfactant of the 'Synperonic' (RTM) type is around 325. Fatty acids of the types described above have molecular weights around 220. Thus, the preferred mole ratios between the surfactants are 3-5:1 for the secondary alkane sulphonate to nonionic and 2-5:1 for the secondary alkane sulphonate to fatty acid.

The molecular weight of sodium sulphate is 142.04, i.e. about half that of a typical secondary alkane sulphonate. It is preferable the molar ratio of the sulphate to the secondary alkane sulphonate is such that around 3-5 moles of sulphate are present for each mole of secondary alkane sulphonate. As the levels of sulphate present in technical grades of secondary alkane sulphonate are very much lower than this it will be appreciated that the mere use of technical grades of secondary alkane sulphonate will not achieve preferred embodiments of the invention and an addition of further sulphate will be required.

Alternative suspending systems, which do not comprise surfactant as an essential ingredient can be employed.

Bleaching Agents

Typically, the peroxy carboxylic acid is an imido peroxy- carboxylic acid, most preferably e-N-N-phthaloyl-amino- peroxycaproic acid (PAP) .

Other peroxy-carboxylic acids, are known as described above and from a publication entitled "TAED and new peroxycarboxylic acids as highly efficient bleach systems", 80th AOCS Meeting, Cincinnati OH, May 1989. It is believed that, particularly in those embodiments where the imido-peroxy-carboxylic acid is e-N-N-phthaloyl- amino-peroxycaproic acid (PAP) , the presence of even relatively low levels of the corresponding acid, e.g. the e-Ν-Ν-phthaloyl-amino-caproic acid, accelerates the formation of crystalline deposits in the formulation. It is believed the formation of these crystals is associated with the decomposition of the peracid.

Accordingly, it is preferred that the starting materials, particularly the peracid, should contain as little as possible of the corresponding acid and preferably, the ratio of the peroxy carboxylic acid to the corresponding carboxylic acid is higher than 96.5:3.5.

Preferred compositions according to the present invention have a pH in the range 4.5-5.5 and comprise:

a) 1-3%wt e-Ν-Ν-phthaloyl-amino-peroxycaproic acid,

b) not more than 0.1%wt e-Ν-Ν-phthaloyl-amino caproic acid,

c) 4.0-10%wt of a C12-C18 secondary alkane sulphonate,

d) l-6%wt of an ethoxylated nonionic surfactant, with an ethoxylation level of 3-12,

e) 0-4%wt of a C12-C18 fatty acid,

f) an alkali metal sulphate at a level such that the weight ratio of sulphate: (c) + (d) + (e) falls in the range 1:0.6-1.25. Minors

Various inessential components may also be present in the compositions according to the invention. These include colouring agents, opacifiers, perfumes, and solvents.

In order to facilitate processing, and particularly packing of the compositions according to the invention, it is convenient that formulations comprise an initial, low level of a bleach-sensitive antifoam component which is decomposed during storage of the product.

Preferably, the composition further comprises a transition metal complexing bleach stabiliser selected from phosphates, phosphonic acids or phosphonates, stannates, carboxylates.

Preferred metal ion complexing agents are selected from dipicolinic acid, ethylene diamine tetra acetic acid (EDTA) and its salts, hydroxy-ethylidene diphosphonic acid (Dequest 2010, RTM) , ethylene diamine tetra (methylene phosphonic acid) (Dequest 2040, RTM) , diethylene triamine penta(methylene phosphonic acid) (Dequest 2060, RTM), amino tri(methylene phosphonic acid) (Dequest 2000, RTM). The phosphonic acid derivatives are particularly preferred.

It is preferred that the level of metal ion complexing agent should fall into the range 0.1-5%.

In order that the present invention may be further understood it will be illustrated hereafter by way of example. EXAMPLES 1 -3

Formulations were prepared as shown in Table IA below. The materials are identified as follows:

Dequest 2010: RTM (ex. Monsanto) organic phosphonate sequestrant for metal ions .

PAP: e-N-N-phthaloyl-amino-peroxycaproic acid (ex. Ausimont) .

SAS-30: Hostapur 93, (RTM, ex Hoechst) Secondary alkane sulphonate, 93% AD diluted to 30% AD.

Synperonic A3: (RTM, ex. ICI) alcohol ethoxylate, nonionic surfactant .

Prifac 5901: (RTM, ex. Unichema) fatty acid.

Sample formulations were prepared by simple mixing of the components. The pH of the formulations was regulated by the addition of 20% w/v NaOH to the required pH as noted in the table. The formulation at pH 3.5 is below the pKa of the corresponding imido acid.

Products were stored at 37°C for three weeks in the dark and the final concentration of PAP was determined by titration under acidic conditions against thiosulphate/KI at 0°C. Products were microscopically examined for the presence of crystals using dark field polarising optical microscopy at 100 fold magnification.

Results for the levels of PAP remaining after storage and the presence of large crystals and needle-like crystals are given below in Table IA. TABLE IA

From the above it can be seen that the compositions initially differ only as regards their pH. The compositions of the present invention (example 2: pH 5.0) are more stable against both chemical and physical changes than the comparative examples 1 (pH 3.5) and 3 (pH 6.5).

As mentioned above, it is believed that, at a pH below the pK_a of the corresponding imido acid the decomposition product of the imido peracid originally present as

'normal' crystals, is insoluble and forms the white, needle like crystals. This is illustrated by comparative example 1. Above a pH of 6, (e.g. at pH 6.5 in comparative example 3), excessive hydrolysis is believed to occur.

Tables IB and 1C demonstrate that the pH effect is of particular importance in the compositions of comparative examples 1 and 3 respectively . In these tables various ratios of surfactant, sulphate and PAP were employed and the products were examined after eight weeks storage. In the tables, examples la-lg and 3a-3h are samples at pH 3.5 and 6.5 respectively with varying ratios of surfactant, sulphate and PAP present. The final levels of PAP are indicated on product as absolute values and these final levels of PAP are given as a percentage of the original level (always 2%wt on product) in the '%Final' column.

TABLE IB (PH 3.5)

All of the examples shown in Table IB exhibited the separation of white, needle like crystals as in example 1 mentioned above.

TABLE IC (PH 6.5)

From the results in Table IC it can be seen that examples having a pH of 6.5 show decomposition of the PAP irrespective of the levels of surfactant and sulphate present. All of the compositions showed the large crystal habit characteristic of a decomposed product.

EXAMPLES 4-11

Further examples are given in Table 2 below. Materials are as used in examples 1-3 above and the method of preparation was the same as used in examples 1-3. These examples illustrate the effect of variation in levels of sulphate salts in the composition at the preferred pH and surfactant level.

In all the compositions mentioned in Table 2, the level of total surfactant is fixed at 8%wt, and the surfactant system comprises that of examples 1-3, i.e. a 4:1:1 ratio of SAS to alcohol ethoxylate to fatty acid. The level of PAP was 2%, and the level of Dequest 2010 was 0.14. The pH of all the examples in Table 2 was around 5. Products were stored at 37°C for eight weeks in the dark and the final concentration of PAP was determined by titration under acidic conditions against thiosulphate/KI at 0°C.

TABLE 2

All of the compositions in examples 4-11 were milky liquids when fresh. The composition of example 4 (3% sulphate) showed some slight physical separation after storage. The results of Table 2 indicate that the most chemically stable compositions had a weight ratio of sodium sulphate:surfactant of 1:0.8.

EXAMPLES 12-17

Further examples are given in Table 3 below. Materials are as used in examples 1-3 above and the method of preparation was the same as used in examples 1-3. These examples illustrate the effect of variation in levels of surfactant levels in the composition. In all the compositions mentioned in Table 2, the level of total sulphate is fixed at 8%wt (as sodium sulphate) , and the surfactant system comprised that of examples 1-3, i.e. a 4:1:1 ratio of SAS to alcohol ethoxylate to fatty acid. The level of PAP was 2%, and the level of Dequest 2010 was 0.14. The pH of all the examples in Table 3 was around 5. Products were stored at 37°C for eight weeks in the dark and the final concentration of PAP was determined by titration under acidic conditions against thiosulphate/KI at 0°C.

TABLE 2

- li

The results of Table 3 indicate that the most stable compositions have lower levels of surfactant. However, at 6%wt surfactant the compositions were incapable of suspending the PAP and this component sedimented from the composition. It is envisaged that this lower limit on surfactant content will be in part dependent on the level of electrolyte present.

Examples 18-22

Examples 18-22, presented in table 4 below, provide further data regarding the pH stability of the compositions. Compositions were prepared as described above and buffered at pH's ranging from pH 4.5 to pH 5.5. All compositions initially comprised 10%wt surfactant (4:1:1 ratio as in examples 12-17), 10%wt sodium sulphate, 2% PAP and 0.14% Dequest 2010. The pH was determined again after 15 days storage. The percentage of PAP remaining after 15 days and after 31 days was determined by the method described above.

In the table, S indicates that phase separation had occurred, whereas L indicates that the product maintained a lamellar phase. The appearance of the crystals was again determined by dark field polarising optical microscopy at 100 fold magnification.

Table 4

10

From the results given in Table 4 it can be seen that compositions having a pH of 4.54 (comparative example 18) were not stable under the conditions of storage used, almost all of the PAP having decomposed after 31 days of storage. Compositions having a pH of 5.0-5.5 showed acceptable storage stability.

Claims

1. An aqueous bleaching composition comprising: 0.5- 15%wt of a peroxy carboxylic acid wherein the pH of the composition is such that it is above the pK_a of the corresponding peroxy carboxylic acid and below 6.0.

2. Composition according to claim 1 wherein the pH is greater than 4.5.

3. Composition according to claim 1 further comprising at least 5%wt of one or more surfactant components.

4. Composition according to claim 3 comprising at least 3% of a sulphate salt other than a transition metal sulphate.

5. Composition according to claim 3 comprising secondary alkane sulphonate.

6. Composition according to claim 3 comprising a nonionic surfactant.

7. Composition according to claim 3 comprising a fatty acid.

8. Composition according to claim 5 comprising secondary alkane sulphonate, nonionic surfactant and fatty acid wherein the mole ratios are:

a) 3 :1 to 5:1 for the secondary alkane sulphonate: nonionic surfactant, and, b) 2:1 to 5:1 for the secondary alkane sulphonate: fatty acid.

9. Composition according to claim 4 wherein the mole ratio of the sulphate salt to secondary alkane sulphonate is such that around 3-5 moles of sulphate are present for each mole of secondary alkane sulphonate.

10. Composition according to claim 1 wherein the peroxy- carboxylic acid is e-N-N-phthaloyl-amino- peroxycaproic acid.

11. Composition according to claim 1 wherein the ratio of the peroxy carboxylic acid to the corresponding carboxylic acid is higher than 96.5:3.5.

12. Composition according to claim 1, having a pH in the range 4.5-5.5 and comprising:

a) l-3%wt e-N-N-phthaloyl-amino-peroxycaproic acid,

b) not more than 0.1%wt e-N-N-phthaloyl-amino caproic acid,

c) 4.0-10%wt of a C12-C18 secondary alkane sulphonate,

e) 0-4%wt of a C12-C18 fatty acid,

f) an alkali metal sulphate at a level such that ■ the weight ratio of sulphate: (c) + (d) + (e) ratio of sulphate: (c)+(d)+(e) falls in the range 1:0.6-1.25.

13. Composition according to claim 1 comprising a transition metal complexing bleach stabiliser selected from phosphates, phosphonic acids or phosphonates, stannates, carboxylates.

14. Composition according to claim 13 wherein the transition metal complexing agent is selected from the group comprising dipicolinic acid, ethylene diamine tetra acetic acid and its salts, hydroxy- ethylidene diphosphonic acid, ethylene diamine tetra (methylene phosphonic acid) , diethylene triamine penta(methylene phosphonic acid), amino tri (methylene phosphonic acid) and mixtures thereof.