Dec. 11, 2014  13  US 2014/0364548 Al  medium which may result in a change of the surface tension  of both the medium and the ink, thus influencing the differ› ence between the surface tension of the ink and the surface  tension of the medium.  [0190]  Generally apolar cosolvents have a low surface ten› sion, while polar cosolvents have a relative high surface ten› sion. Surfactants selected to reduce the surface tension of the  ink compositions according to the present invention, are usu› ally capable of reducing the surface tension of an aqueous  system. Upon drying of printed ink dots, the aqueous ink  system however more and more turns into an organic solvent  system. Said selected surfactants are less suitable for reduc› ing the surface tension of an organic solvent system. There› fore, upon drying the surface tension of the printed ink dots  increases, increasing the risk of puddling and dewetting. The  mixture of surfactants according to this embodiment com› prises a first surfactant that is capable of reducing the surface  tension (static and dynamic) of the total ink composition,  being a surfactant that works well with water. In the context of  the present invention the first surfactant comprises a surfac› tant of the first type and/or of the third type. The mixture of  surfactants according to this embodiment comprises a second  surfactant that is capable of reducing the surface tension of  the drying ink composition, being a surfactant that works well  with the polar cosolvent. In the context of the present inven› tion the second surfactant comprises a surfactant of the sec› ond type.  [0191]  In an embodiment, the first surfactant of the mixture  of surfactants is selected from the group consisting of dialkyl  sulfosuccinate salts (surfactant of the third type), such as  sodium dioctyl sulfosuccinate (AOT) and an ethoxylated  acetylene glycol ( surfactant of the first type), such as ethoxy› lated 2,4,7,9-tetramethyl-5-decyne-4,7-diol and ethoxylated  2,5,8,11-tetramethyl-6-dodecyne-5,8-diol (Dynol™) or a  combination thereof.  [0192]  In an embodiment, the first surfactant of the mixture  of surfactants is selected from the group consisting of dialkyl  sulfosuccinate salts (surfactant of the third type) and ethoxy› lated dodecynes (surfactant of the second type) or a combi› nation of both.  [0193]  In an embodiment, the first surfactant is selected  from sodium dioctyl sulfosuccinate (AOT; surfactant of the  third type) and ethoxylated 2,5,8,11-tetramethyl-6-dode› cyne-5,8-diol (surfactant of the second type), being Dynol  607 or a combination of both.  [0194]  In an embodiment, the second surfactant is a sili› cone surfactant (surfactant of the second type), in particular  an ethoxylated siloxane surfactant, having a general formula  as shown in Formula 4.  Formula4  wherein mis an integer ranging from 1-25, preferably from  1-20, more preferably from 2-15 and wherein n is an integer  ranging from 1-10, preferably from 1-8, more preferably  from 1-5.  [0195]  In an embodiment, the number average molar  weight  (Mn)  of the ethoxylated siloxane used as a surfactant  in an ink composition according to the present invention lies  in a range of between 300 g/mol and 1000 gr/mo!, preferably  between 350 gr/mo! and 950 gr/mo!, more preferably  between 450 gr/mo! and 850 gr/mo!.  [0196]  In an embodiment, the weight average molar weight  (Mw) of the ethoxylated siloxane used as a surfactant in an ink  composition according to the present invention lies in a range  of between 600 g/mol and 1600 gr/mo!, preferably between  700 gr/mo! and 1500 gr/mo!, more preferably between 800  gr/mo! and 1400 gr/mo!  [0197]  In an embodiment, the polydispersity factor  (D=M~Ma) of the ethoxylated siloxane used as a surfactant  in an ink composition according to the present invention lies  in a range of between 1 and 2, preferably between 1 and 1.95,  more preferably between 1.3 and 1.9.  [0198]  In an embodiment, the second surfactant is an  ethoxylated siloxane surfactant selected from the group con› sisting ofBYK 348, BYK 349, Silwet L-77 and Tegowet 240.  Structural properties of these surfactants are shown in Table 2  with reference to Formula 4. In particular, BYK 349 has  shown to be suitable for the purpose of this embodiment.  [0199]  In an embodiment, the first surfactant is selected  from the group consisting of dialkyl sulfosuccinate salts ( sur› factant of the third type) and ethoxylated dodecynes (surfac› tant of the first type) or a combination of both and the second  surfactant is an ethoxylated siloxane surfactant (surfactant of  the second type) preferably selected from the group consist› ing of BYK 348, BYK 349, Silwet L-77 and Tegowet 240.  [0200]  Inventors have found that surfactant mixtures com› prising an ethoxylated dodecyne (e.g. according to Formula  3) and an ethoxylated siloxane work extremely well in the  context of the present invention. Such mixtures are capable of  significantly reducing the static and dynamic surface tensions  of an ink composition according to the present invention and  the surface tension remains low during drying of the ink  composition.  [0201]  In an embodiment, the mixture of surfactants com› prises a third surfactant being a silicone surfactant (surfactant  of the second type) different from the second surfactant, in  particular an ethoxylated siloxane surfactant different from  the second surfactant, preferably selected from the group  consisting of BYK 348, BYK 349 (BYK), Silwet L-77  (Sabic), Tegowet 240 (Evonik).  [0202]  In particular, a mixture of BYK 348 and Tegowet  240 has shown to be suitable for the purpose of this embodi› ment.  [0203]  Inks comprising such a mixture of surfactants show  a significant improvement of print quality. In particular when  such ink compositions are used in single pass printing, such  ink compositions improve streakiness (i.e. white areas in the  print).  [0204]  In an embodiment the mixture of surfactants com› prises an acetylene glycol and a silicone surfactant, in par› ticular an ethoxylated siloxane, as is exemplified in example  1 of the present application. 