1.  Field
The present invention relates to an ink, an ink set and a recording device. 
2.  Description of the Related Art
JP-A-2011-219646 discloses “an ink-jet recording liquid which contains a resin for pigment dispersion that is water-soluble, wherein the mass ratio of the resin for pigment dispersion to the pigment (resin content/pigment content) is 0.3-0.6 and the mass ratio of the free resin of the resin for pigment dispersion, the free resin being not adherent to the pigment, to the pigment (free-resin amount/pigment content) is 0-0.1, the recording liquid having a dynamic surface tension, as measured at the time when the surface life is 10 ms, of 46 mN/m or higher”. 
JP-A-2006-219625 discloses “a nonaqueous ink for ink-jet recording which has the property of curing upon irradiation with light, e.g., ultraviolet light or electron beams, and has a value of dynamic surface tension as measured at 80 milliseconds of higher than 28 mN/m and in which the value obtained by subtracting the value of dynamic surface tension measured at 1,000 milliseconds from the value of dynamic surface tension measured at 80 milliseconds is less than 8 mN/m”. 
JP-A-2013-112801 discloses “an ink-jet ink which has a dynamic surface tension γ30, as measured at 30 seconds after by the plate method, in the range of 25-35 mN/m and in which the difference between γ30 and the dynamic surface tension γ600 measured at 600 seconds after satisfies γ600−γ30≦−1 mN/m”. 
JP-A-2007-261203 discloses “a method for image formation characterized in that a first liquid which contains no colorant and has a value of dynamic surface tension, as measured at a temperature of 25° C. and at a surface life of 0.1 sec, of γ1(0.1 sec) is applied to a surface of a recording medium and thereafter a second liquid which contains a colorant and has a value of dynamic surface tension, as measured at a temperature of 25° C. and at a surface life of 0.1 sec, of γ2(0.1 sec) which is larger than the γ1(0.1 sec) is applied by dropping to the area where the first liquid is present as a liquid film”. 
JP-A-2001-288390 discloses “an ink set for ink-jet recording which includes a black ink (a) having a surface tension (γa) of 40 mN/m or less and a drying time of 5 seconds or less and a black ink (b) having a surface tension (γb) of 35 mN/m or higher and a drying time of 15 seconds or longer, and in which [surface tension (γa)]<[surface tension (γb)] and the colorant in the black ink (a) and the colorant in the black ink (b) are both a pigment”. 
JP-A-2013-256108 discloses an ink for recording images on media for concealing postal cards, the ink including water, a water-soluble organic solvent, a colorant, and a surfactant and satisfying the following requirements (1) to (4). 
(1) To have a dynamic surface tension (D1) for the surface life period from 15 ms to less than 100 ms, as determined by the maximum bubble pressure method, of 30.0-60.0 mN/m
(2) To have a dynamic surface tension (D2) for the surface life period from 100 to 3,000 ms, as determined by the maximum bubble pressure method, of 27.0-35.0 mN/m
(3) D1≧D2 
(4) To have a static surface tension of 27.0 mN/m or less
JP-A-2001-262097 discloses, as a technique for reducing ink offset, “a pressure-sensitive adhesive composition that is excellent in terms of the fixability of ink-jet inks and is to be applied to the mating surfaces of a sheet and dried to form adhesive layers which in the ordinary state do not adhere and which are used in such a manner that the mating surfaces are disposed so as to face and be in contact with each other and a given pressure is applied thereto to thereby strippably bond the mating surfaces to each other, the pressure-sensitive adhesive composition being characterized by being obtained by compounding 100 parts by mass of a natural-rubber-based adhesive base with 10-50 parts by mass of a silica gel having an average particle diameter of 1-5 μm and an oil absorption of 100 mL/100 g or higher and with 10-50 parts by mass of a cationic substance”. 
JP-A-2003-213179 discloses “an ink for ink jet recording which comprises water, a colorant, and a water-soluble organic solvent as essential components, wherein the content of the colorant is 6 wt % or higher, the ink for ink-jet recording having a coefficient of absorption in plane paper of 3 mL/(m2·(msec)1/2) and a contact angle θ0 with plane paper of 10° or larger but less than 40°”.