STW-compositions simultaneously clean and soften fabric during the washing stage of the laundering process, negating the need to add a separate fabric-conditioning composition to the rinse stage and/or drying stage of the laundering process. Therefore, STW-compositions provide the consumer with an efficient and easy way to clean and soften fabric during the laundering process.
Fabric-softening quaternary-ammonium di-ester compounds (di-ester-quats) are a known means of softening fabric during the rinse stage and/or drying stage of the laundering process. For example, rinse added and/or drier added compositions comprising di-ester-quats are described in EP704522, EP720645, U.S. Pat. Nos. 4,840,738 and 6,037,315. In addition, U.S. Pat. No. 6,093,336 relates to a process for making a composition comprising a di-ester-quat and a fatty acid. U.S. Pat. No. 6,093,336 discloses a process, which is said to produce compositions comprising low amounts of impurities, and that are storage stable and non-caking. Also, WO94/07978 relates to compositions comprising a di-ester-quat and a hydroxy compound. The compositions described WO94/07978 are said to have improved cold water dissolution and/or dispersability.
However, prior to the present invention, detergent manufacturers were not able to incorporate fabric-softening compounds such as di-ester-quats, in STW-compositions, especially solid STW-compositions, without adversely affecting the fabric-cleaning performance. Di-ester-quats, although capable of providing extremely good fabric-softening properties during the rinsing and/or drying stage of the laundering process, cannot be successfully incorporated into detergent compositions as they cause residues to deposit on fabric during the laundering process and also reduce the soil removal performance of the STW-composition. Thus, there is still a need to produce improved STW-compositions having both a good fabric-softening performance and a good fabric-cleaning performance.
The inventors have surprisingly found that specific di-ester-quats, when used in combination with a specific source of acid and clay, can be successfully incorporated in STW-compositions. These specific di-ester-quats, when used in combination with the specific source of acid and clay, greatly improve the fabric-softening performance of the STW-composition without adversely affecting the fabric-cleaning performance. Thus, the STW-compositions of the present invention have a surprisingly improved fabric-cleaning and fabric-softening performance.