Stabilised toothpaste composition

The present invention relates to toothpaste and in particular toothpaste comprising tri · hydrated alumina.

During the tests carried out by the Applicant on toothpastes containing alumina trihydrate as an abrasive cleaning agent, alumina sometimes caused corrosion in unvarnished aluminum tubes accompanied by swelling of the tubes due to ^ Hydrogen production¹., gaseous during storage of the toothpaste. . These cases .

JL.7 (2f)

<img file="LU59722A1_D0001.tif" />

<img file="LU59722A1_D0002.tif" />

· „· Corrosion occurs when the relatively coarse starting hydrated alumina is ground and classified by another process. The alumina trihydrate used for the tests of the Applicant is obtained by the Bayer process, according to which the alumina is precipitated from a solution of sodium aluminate, then washed and dried at low temperature. Corrosion occurs even at a pH in the neutral range and therefore cannot be due to any residual alkalinity of the alumina.

The Applicant has discovered, however, that corrosive ground hydrated alumina can be stabilized and made non-corrosive under the effect of orthophosphate ions. It has in fact been discovered with surprise that stabilization occurs when a batch of alumina causing corrosion of the tubes and the production of gas in a toothpaste conditioned in unvarnished aluminum tubes is treated beforehand by means of a 0.1 M aqueous solution of sodium dihydrogen phosphate, then washed carefully with water until there is no soluble orthophosphate.

This phenomenon results in the absence of corrosion and swelling of the tubes during the conservation of toothpastes prepared by means of the alumina treated beforehand and packaged in unvarnished aluminum tubes.

The results show that the inhibition of corrosion is due to the stabilization of the alumina and not to the effect of the phosphate ions on the aluminum tubes. The mechanism for stabilizing quality alumina if not corrosive is not elucidated # but we are led to believe that this stabilization is due, to a certain extent, to the modification of the surface properties of alumina particles: this appears differences in electrophoresis mobility of alumina particles before and after treatment.

It has also been observed that to achieve this

CH-CD JL. 14 stabilization, it is not necessary to actually undergo a prior treatment with alumina, but that the stabilizing effect of orthophosphate ions on alumina can occur by simple addition of these ions to the composition of toothpaste .

The present invention therefore relates to a toothpaste composition comprising a ground alumina · α trihydrate stabilized by orthophosphate ions, the alumina a ground trihydrate being of such a nature that, without stabilization, the toothpaste packaged in tubes of non-aluminum varnish would cause corrosion with evolution of gas. The stabilization of the alumina is preferably carried out by simple incorporation of a source of orthophosphate ions into the toothpaste composition.

The orthophosphate ions can be provided by orthophosphoric acid or one of its salts, such as the alkaline, alkaline earth and ammonium salts. Amine salts of orthophosphoric acid are also effective. As particular examples of suitable salts, mention may be made of sodium dihydrogen phosphate, disodium hydrogen phosphate, calcium hydrogen phosphate, diammonium hydrogen phosphate and bis-triethanolamine hydrogen phosphate.

The effective amount of orthophosphoric acid or its salts can be determined by testing, but is usually at least $ 0.1 of the weight of the toothpaste. Normally, an amount of $ 0.2 to $ 1 by weight is suitable depending on the amount of alumina present and the nature of the source of orthophosphate ions. Sodium dihydrogen phosphate is a preferred source of orthophosphate ions because this compound simultaneously has the effect of stabilizing the alumina and adjusting the pH. To avoid the acid or alkaline attack of aluminum, the pH of the toothpaste must be

CH-CD JL. 14.

- 3 in the range of about 6 to 8.

The invention can be applied to many toothpaste compositions, but it is particularly suitable for those with a high content of hydrated alumina, for example from 25 to 60% by weight.

The following examples illustrate the invention.

EXAMPLE 1.0n a toothpaste of the composition below is prepared using an alumina a trihydrate prepared by the Bayer process, ground and classified, the particle size of which is suitable for an abrasive agent intended for toothpaste ·

Constituent $ by weight alumina-a crushed trihydrate 55.00 sorbitol (syrup at $ 70) 27.00 sodium carboxymethylcellulose 0.80 benzoic acid 0.15 sodium lauryl sulfate 1.50 titanium dioxide 0.50 saccharin 0.20 essence mint 1.00 water, to make 100.00 pH 6.4

After storage for 3 months at 37 ° C of this toothpaste in aluminum tubes not internally varnished, a release of gas (mainly hydrogen) is observed in the tube and some corrosion of the tubes.

The incorporation of $ 0.1 sodium dihydrogen phosphate in the above toothpaste composition stabilizes the alumina.

Likewise, toothpaste is prepared in which 0.4 $ of sodium dihydrogen phosphate is incorporated, omitting benzoic acid, and it is observed that this pasta is

CH-CD JL. 14 _ 4 stable in storage for periods of up to 9 months at 65 ° C. These pastes have a pH of 6.8.

Tests carried out on toothpastes of the above composition show that part of the sodium dihydrogen phosphate is adsorbed by alumina and that this part acts as a stabilizer for alumina.

EXAMPLE 2 The ground alumina trihydrate is stabilized with a toothpaste composition as described in Example 1, by 1% in corporation. calcium hydrogen orthophosphate dihydrate. EXAMPLE 3.- '

The ground alumina trihydrate is stabilized with a toothpaste composition_}as described in Example 1, by incorporating 0.5 $ of diammonium hydrogenorthophosphate.

EXAMPLE 4 The ground alumina trihydrate of a toothpaste composition is stabilized, as described in Example 1, by incorporation of 1 $ of bis-triethanolamine hydrogen orthophosphate.