US 7,153,817 B2  4  3  about 5% to about 60%, preferably from about 10% to about  50% of a surfactant carrier is used. Controlling the particle  size both of the limescale remover acid and of the surfactant  carrier is also important for achieving optimum stability. In  a preferred embodiment the particle size of the limescale  remover acid is in the range from about 100 µm  to about 500  µm  and more preferably from about 200 µm  to about 400 µm  while the weight average particle size of the surfactant  carrier is less than about 70 µm and more preferably less  than about 20 µm. The preferred carrier herein is selected  from alkali metal salts of strong acids, polymeric disinte› grants and mixtures thereof. Especially preferred is sodium  sulphate.  The tablet can be prepared by pre-mixing all the compo› nents and compressing the mixture in a tablet press. Accord› ing to another embodiment the tablet can be prepared by  preagglomeration of the non-ionic surfactant and the carrier,  admixing the limescale remover acid and detergency  enzyme and compressing the mixture in a tablet press.  Alternatively, the non-ionic surfactant can be preagglomer› ated with the carrier and acid.  The present invention also encompasses a cleaning  method for dishwasher and washing machine interiors, said  method comprising placing the tablet of the invention in the  machine interior, e.g., in the case of a dishwasher in the  cutlery basket, and running the unloaded machine at high or  a low temperature washing program.  Limescale remover acids preferred for use herein are  selected from water-soluble organic mono- and polycar› boxylic acids with two to six carbon atoms in the molecule  and optionally substituted by one or more hydroxy groups.  Suitable classes of limescale remover include alkanoic  acids, hydroxyalkanioc acids, alkyl polycarboxylic acids  and hydroxyalkyl polycarboxylic acids. Preferred herein are  mono- and polycarboxylic acids which have a pKa value,  related to the first dissociation stage of less than about 6.  These include for example, adipic acid, succinic acid, tar- taric acid, malic acid, glutaric acid, citric acid and mixtures  thereof. Citric acid being highly preferred.  Inorganic acids and mixtures of inorganic acids and  organic acids can also be used as the limescale remover  component. The inorganic acids are specially usefull when  mixed with organic acids. Examples of inorganic acids are  sulphonic acid derivatives, sulphamic acid (pKa=0.1 ),  hydrochloric acid (pKa<0), nitric acid (pKa<0), phosphoric  acid (pKa=2.1) and sulphuric acid (pKa=0.4). Suitable sul› phonic acid derivatives include alkyl sulphonic acids and  aryl sulphonic acids. Suitable alkyl sulphonic acids include  Cl---C6 linear or branched alkylsulphonic acids or mixtures  thereof, such as methanesulphonic acid (pKa=l.9) commer› cially available for example from Aldrich, William Blythe &  Co. Ltd. or Elf. Atochem.  Suitable aryl sulphonic acids for use herein include those  of the formula:  wherein Rl, R2, R3, R4 and R5 are each H or SO$_{3}$H, or  linear or branched C0---C4 alkyl chain; or mixtures thereof.  Preferred arylsulphonic acids to be used are those which  comprise no or only one alkyl chain. Indeed, arylsulphonic  acids are particularly effective at removing limescale, which  is not the case for their longer alkyl chain homologues. Also  arylsulphonic acids are particularly safe to the surface  treated therewith. Particularly suitable arylsulphonic acids  for use herein are benzene sulphonic acid (pKa=0.7), toluene  sulphonic acid and cumene sulphonic acid. Amongst these  three, at equal weight %, the shorter the alkyl chain, down  to no chain at all, the better the limescale removing perfor- mance.  Suitable nonionic surfactants according to the present  invention includes nonionic alkoxylated surfactants (espe› cially ethoxylates derived from C$_{6}$-C$_{18 }$ primary alcohols),  ethoxylated-propoxylated alcohols (e.g., Olin Corporation’s  Poly-Tergentfi SLF18), epoxy-capped poly(oxyalkylated)  alcohols  (e.g.,  Olin  Corporation’s  Poly-Tergentfi  SLF18B-see WO-A-94/22800), ether-capped poly(oxy› alkylated) alcohol surfactants, and block polyoxyethylene› polyoxypropylene polymeric compounds such as PLU› RONIC fi, REVERSED PLURONICfi, and TETRONICfi  by the BASF-Wyandotte Corp., Wyandotte, Mich. Surfac› tants suitable herein are disclosed, for example, in U.S. Pat.  Nos. 3,929,678, 4,259,217, EP-A-0414 549, WO-A-93/  08876 and WO-A-93/08874.  The compositions according to the present invention are  designed for cleaning machine interiors. The essential com› ponents of the composition are a limescale remover acid, a  non-ionic surfactant and a detergency enzyme. The compo› sition is presented in the form of tablet, having a pH,  measured as a 1 % solution in distilled water at 20°  C., in the  range from about 1 to about 5.  The nonionic surfactants are typically present at a level of  from about 1 % to about 20% by weight, more preferably  from about 2% to about 18% by weight, most preferably  from about 4% to about 15% by weight of composition.  Enzymes suitable herein include proteases such as Espe› raseR, AlcalaseR,  DurazymR  and SavinaseR (Novo) and Max› ataseR, MaxacalR, ProperaseR and MaxapemR (Gist-Bro› cades); and a and  ~  amylases such as Purafect Ox  AmR  (Genencor) and TermamylR,  BanR,  FungamylR, DuramylR,  Amylase  AGR  and Natalas~ (Novo); and mixtures thereof.  Enzymes are preferably added herein as prills, granulates, or  cogranulates at levels typically in the range from about 0.5%  to about 5% pure enzyme by weight of composition. In a  preferred embodiment of the present invention TermamylR is  used.  Amylases (a and/or ~) can be included for removal of  carbohydrate-based residues. WO-A-94/02597 describes  cleaning compositions which incorporate mutant amylases.  See also WO-A-95/10603. Other amylases known for use in  cleaning compositions include both a- and ~-amylases.  a-Amylases are known in the art and include those disclosed  in U.S. Pat. No. 5,003,257; EP-A-0252,666; WO-A-91/  00353; FR-A-2,676,456; EP-A-0285,123; EP-A-525,610;  EP-A-0368,341; and GB-A-1,296,839. Other suitable amy› lases are stability-enhanced amylases described in WO-A- 94/18314 and WO-A-96/05295 and amylase variants having  additional modification in the immediate parent available  from Novo NordiskA/S, disclosed in WO-A-95/10603. Also  DETAILED DESCRIPTION OF THE  INVENTION 