Pre-treatments for ink-jet printing

A print head arrangement comprising:

• a main print head having a plurality of printing nozzles for ejecting a printing fluid;
• an auxiliary print head having a plurality of pre-treatment nozzles for ejecting a pre-treatment fluid;
• and
• a controller that is to obtain a print medium parameter and to select a subset of the plurality of pre-treatment nozzles for application of the pre-treatment fluid based on the print medium parameter, wherein the print medium parameter characterizes a thermal inertia of the print medium,
• wherein the print medium parameter further characterizes a porosity of the print medium, and
• wherein the printing nozzles are distributed over a first distance perpendicular to a scanning direction, the pre-treatment nozzles are distributed over a second distance perpendicular to the scanning direction, the second distance partially overlaps with first distance, and the subset of pre-treatment nozzles is distributed over a third distance that:
• partially overlaps with the first distance for a first type of print medium;
• completely overlaps with the first distance for a second type of print medium;
• and
• does not overlap with the first distance for a third type of print medium, the first, second and third types of print medium having different print medium parameters.

A printing device comprising a print head carriage and a controller, wherein:

• the print head carriage is movable along a scanning direction;
• the print head carriage comprises a main slot that is to receive a main print head with a plurality of printing nozzles and an auxiliary slot that is to receive an auxiliary print head with a plurality of pre-treatment nozzles;
• and
• the controller is to determine a print medium parameter and to select a subset of the plurality of pre-treatment nozzles for application of the pre-treatment fluid based on the print medium parameter, wherein the print medium parameter depends on a thermal inertia of the print medium, wherein the thermal inertia is a measure of how fast a temperature of the print medium increases when heating the print medium based on a heat capacity and a thermal conductivity of the print medium.

A printing device comprising a print head carriage and a controller, wherein:

• the print head carriage is movable along a scanning direction;
• the print head carriage comprises a main slot that is to receive a main print head with a plurality of printing nozzles and an auxiliary slot that is to receive an auxiliary print head with a plurality of pre-treatment nozzles;
• and
• the controller is to determine a print medium parameter and to select a subset of the plurality of pre-treatment nozzles for application of the pre-treatment fluid based on the print medium parameter, wherein the print medium parameter depends on a thermal conductivity of the print medium,
• wherein the subset of pre-treatment nozzles:
• partially overlaps with the printing nozzles along a media advance direction, perpendicular to the scanning direction, for a first type of print medium;
• completely overlaps with the printing nozzles along the media advance direction for a second type of print medium;
• and
• does not overlap with the printing nozzles along the media advance direction for a third type of print medium, the first, second and third types of print medium having different print medium parameters.

A method of operating a printing device, wherein

• the printing device comprises a set of print heads with a plurality of printing nozzles for ejecting a printing fluid and a plurality of pre-treatment nozzles for ejecting a pre-treatment fluid,
• the method comprising:
• determining a category that a print medium to be used with the printing device is associated with;
• selecting a pre-treatment scheme depending on the category of the print medium,
• wherein print media are grouped into the categories based on a thermal inertia of the print media, wherein the thermal inertia is a measure of how fast a temperature of the print medium increases when heating the print medium based on a heat capacity and a thermal conductivity of the print medium.

A method of operating a printing device, wherein

• the printing device comprises a set of print heads with a plurality of printing nozzles for ejecting a printing fluid and a plurality of pre-treatment nozzles for ejecting a pre-treatment fluid,
• the method comprising:
• determining a category that a print medium to be used with the printing device is associated with;
• selecting a pre-treatment scheme depending on the category of the print medium,
• wherein print media are grouped into the categories based on a heat capacity of the print media, the method further comprising:
• repeatedly passing the set of print heads across the print medium in a scanning direction;
• and
• applying the pre-treatment fluid and the printing fluid onto the print medium according to the pre-treatment scheme,
• wherein, for a first category of print media, the pre-treatment scheme comprises:
• ejecting pre-treatment fluid from a first pre-treatment nozzle during a first pass of the set of print heads without ejecting printing fluid from printing nozzles aligned with the first pre-treatment nozzle along the scanning direction during the first pass;
• and
• ejecting pre-treatment fluid from a second pre-treatment nozzle during a second pass of the set of print heads and ejecting printing fluid from a printing nozzle aligned with the second pre-treatment nozzle along the scanning direction during the second pass,
• wherein the pre-treatment scheme further comprises:
• for a second category of print media, for each pre-treatment nozzle from which pretreatment fluid is ejected during a pass of the set of print heads, ejecting printing fluid from a printing nozzle aligned with the respective pre-treatment nozzle along the scanning direction;
• and
• for a third category of print media, ejecting pre-treatment fluid from a set of pre-treatment nozzles during a pass of the set of print heads without ejecting printing fluid from any printing nozzle aligned with a nozzle of the set of pre-treatment nozzles along the scanning direction.