Printers are designed to work within a comfortable temperature range -- a comfortable temperature range for people, and for printer ink. However, if you have field stations that are only intermittently staffed during the winter, or if your offices are unheated during cold nights, your ink could be subjected to cold temperatures. Although that could theoretically lead to problems, it's unlikely that your ink will freeze.
If your printer ink should freeze, there would be a couple undesirable consequences. The first is due to expansion. Most inks are water-based, and water expands as it freezes. In an enclosed chamber, such as a print cartridge, the expansion can put pressure on the enclosure and crack it. Even if the cartridge has room to spare, the print head and the distribution lines can split.
Inks are generally of two types: dye- or pigment-based. That is, the colorant portion of the ink is either a dye or a pigment that is combined with fluids to create a mixture with the desired properties. Dye molecules are very small, and mix in so well that every microscopic drop of the ink will have some dye in it. Pigments are composed of larger bits that are dispersed within the fluid. If you looked at a pigment-based ink with a microscope, you'd see clear liquid with some floating clumps of pigment. If pigment-based ink were to freeze, it's likely the pigment would aggregate, or clump together, and the mixture would no longer be an effective ink.
Under normal conditions, there are three states, or phases, of matter: gas, liquid and solid. When a material changes from one to another of these phases, it's called a phase transition. Phase transitions take place at the boiling point and melting point of a material. Under standard conditions, the boiling point of water is 212 degrees F, and the freezing -- or melting -- point is 32 degrees F. If inks were water with some suspended particles, those phase transition points would be just about the same as plain water. But, just as mixing salt or antifreeze with water changes the phase transition temperatures, the different components in ink fluid dramatically lower the freezing point.
The Material Safety Data Sheet, or MSDS, associated with a chemical product contains a lot of information about the composition and the properties of that product. For example, Hitachi's JP-E78 printer ink contains acetone, ethanol and propylene glycol mixed with water. That particular mixture freezes at about negative 130 degrees C, which is about negative 200 degrees F. Loveshaw's jet printer ink contains DPM Glycol Ether and Versene, and freezes at negative 143 degrees F. Most ink MSDSs state that the melting/freezing point is "not applicable," meaning that it is below 32 degrees F. Given that the composition of the inks is roughly similar, it's reasonable to conclude that printer ink will freeze, but not until temperatures fall well below the freezing point of water.
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