Methods and apparatus for ink drying

Ink drying methods and apparatus are disclosed. One example ink drying apparatus includes a resistive heating element having a first power dissipation density adjacent to a center region of a print media travel path and a second power dissipation density adjacent to an edge region of the print media travel path, wherein the first and second power densities are not equal.

BACKGROUND

While some printing inks air dry or dry without the use of heat, some other types of printing inks may bleed or diffuse over the print substrate if they do not dry quickly and may reduce print quality. Thus, some of these inks are subjected to heat to speed the drying process to maintain print quality.

DETAILED DESCRIPTION

Certain examples are shown in the above-identified figures and described in detail below. Several examples are described throughout this specification. The figures are not necessarily to scale and certain features and certain views of the figures may be shown exaggerated in scale or in schematic for clarity and/or conciseness. Although the following discloses example methods and apparatus, it should be noted that such methods and apparatus are merely illustrative and should not be considered as limiting the scope of this disclosure.

The example methods and apparatus described herein may be used to apply heat to dry inks deposited on a print substrate in a large format printer. Some described example ink drying apparatus include a resistive wire having multiple resistive portions. The resistive portions are positioned adjacent to respective ones of edge regions and a center region of an ink drying area of the printer. In some examples, the resistive portions adjacent the edge regions have a higher power dissipation density (e.g., resistivity) than the resistive portion adjacent the center region. The resistive wire may be configured to have different power dissipation densities along its length by using different materials having different resistivities in the different regions or portions of the wire and/or by having different lengths of the resistive wire in the different regions. Accordingly, as used herein, power dissipation density may refer to the power dissipation per unit length of the resistive wire and/or may refer to the power dissipation per unit length of the ink drying area.

Some example methods described herein include applying ink to a print substrate traveling through a print area in a first direction and moving the print media to an ink drying location or area located after the print area in the first direction. The print drying area includes a center region and first and second edge regions. The example methods further include heating a first portion of a resistive element adjacent the center region at a first power density, heating a second portion of the resistive element adjacent the first edge region at a second power density greater than the first power density, and heating a third portion of the resistive element adjacent the second edge region at the second power density or a third power density.

In contrast to known ink drying apparatus, the example methods and apparatus described herein use a smaller printer footprint (floor area) and apply a substantially constant temperature over the ink drying area. Decreasing the size of the printer footprint may result in reduced manufacturing and/or other costs associated with making, using, and/or maintaining the printer, and/or may increase sales of printers by increasing the number of customers that may purchase the printer to fit within a limited operating space.

FIG. 1is a block diagram of an example large format printer100including an ink heating system102. The printer100further includes one or more print substrate source(s)106(e.g., sheet feeders, roll feeders) to feed print substrate(s)108and110(e.g., printer paper and/or other print media) to printhead(s)104for application of ink.

The print substrate(s)108and110are directed from the print substrate source(s) to the printhead(s)104, which apply one or more layer(s) of ink to the print substrate(s)108and110. After having ink applied, the print substrate110moves to an ink drying area112adjacent the ink drying apparatus102. The example ink drying apparatus102applies heat to the ink on the print substrate110at a substantially constant temperature to dry the ink. After the ink dries, the print substrate110is directed out of the ink drying area112and the print substrate108may be directed into the ink drying area112.

FIG. 2is a schematic diagram of the example ink heating system102ofFIG. 1. The example ink heating system102includes an energy or power source (e.g., a voltage source, a current source)202, switching devices204aand204b,a controller206, and a resistive heating element208. The resistive heating element208is located adjacent the ink drying area112ofFIG. 1to apply heat to the print substrate110. In general, the ink drying area112may be divided into three portions: first and second edge regions210and212and a center region214. The edge regions210and212are the lateral end portions of the ink drying area112and/or the print substrate110in a direction of print travel. These edge regions210and212may be subject to changes in temperature due to their relative proximities to non-heated portions of the printer100. The center region214is generally defined as the portion of the ink drying area112located between the edge regions210and212. The width of the center region214may change based on the upper width limit of the printer100and/or the print substrates108and110used by the printer100. However, the widths of the edge regions210and212may be substantially constant, given a similar structure of the printer100, because the edge regions210and212are proximate to similar external non-heated structures and/or spaces of the printer100. However, in some examples the edge regions210and212may be larger or smaller, proportionally or in absolute measurements.

The example resistive heating element208includes two resistive wires216and218. The resistive wires216and218are each shown as several resistors in series to illustrate different regions or portions of the respective resistive wires216and218. In particular, the resistive wire216includes three resistive portions220,222, and224and the resistive wire218includes three resistive portions226,228, and230. The resistive portions220and226are generally adjacent the first edge region210, the resistive portions224and230are generally adjacent the second edge region212, and the resistive portions222and228are generally adjacent the center region214. While the example resistive heating element208is shown having two resistive wires216and218, the resistive heating element208may have one resistive wire or more than two resistive wires.

As illustrated inFIG. 2, the resistive portions222and228each have a first resistivity (i.e., resistance per unit length) ρ. The resistive portions220,224,226, and230each have a second resistivity of about 1.25ρ, or 25% higher than the first resistivity. In some examples, the resistive portions220,224,226, and230may each have a second resistivity between about 20% and about 25% higher than the first resistivity. As a result, the power dissipated per unit length adjacent the edge regions210and212is about 25% higher than the power dissipated per unit length adjacent the center region214. However, the ratio of the resistivities of any of the resistive portions220,224,226, and230to the either of the resistive portions222and228may be increased or decreased based on the length of the resistive wires216and218relative to the width of the ink drying area112. The resistance values of the resistive portions220-230and, more generally, the resistive wires216and218depend on the desired temperature to which the print substrate110will be subjected to dry the ink.

The resistivities of the resistive portions222and228may be selected based on the desired temperature at which ink on the print substrate110is to be dried. The resistivity of the resistive portions220,224,226, and230may be selected based on the desired temperature and temperature losses (e.g., observed, expected) associated with the edge regions210and212and/or based on the desired width of the resistive heating element208. The resistivity ratio(s) may increase, for example, as the width of the resistive heating element208is decreased because the cooling effects of the surrounding structure of the printer100have a larger impact on the temperature in the edge regions210and212. Conversely, the resistivity ratio(s) may decrease when, for example, the width of the resistive heating element208is increased, because the cooling effects of the surrounding structure of the printer100have a decreased effect and the edge regions210and212appear more like the center region214.

The power source202provides electrical energy to the resistive heating element208(e.g., the resistive wires216and218), which radiates heat (e.g., via infrared radiation) to the ink drying area112. The controller206controls the switching elements204aand204bto control the flow of current to the resistive wires216and218, thereby controlling the amount of infrared radiation generated by the resistive wires216and218and, thus, the temperature of the ink drying area112. For example, the controller206may open one or both of the switching elements204aand204bto cut off the flow of energy, thereby cooling the ink drying area112, or may close one or both of the switching elements204aand204bto enable the flow of energy, thereby increasing the temperature of the ink drying area112. The controller206may increase or decrease the temperature in the ink drying area112to accommodate different inks, different print substrates108and110, and/or changing ambient conditions around the printer100. A temperature sensor232determines one or more temperature(s) in the ink drying area112(e.g., at a single point in the ink drying area112, over the width of the ink drying area112, etc.) and provides the temperature(s) to the controller206.

FIG. 3is a side view of an example of the resistive heating element208shown in the schematic diagram ofFIG. 2. The resistive heating element208includes an outer sheath302, the resistive wires216and218(only the resistive wire216is shown), first and second connecting assemblies304and306, a mounting bracket308, and an insulation material310. The example resistive heating element208is illustrated adjacent the print substrate110in the ink drying area112.

The example outer sheath302is constructed using an American Iron and Steel Institute (AISI) Type 309 Stainless Steel and has a circular cross-section with an 8.5 millimeter (mm) diameter. However, in some other examples, the outer sheath302may be constructed using AISI Types 304-321 and/or other protective materials and/or may have a different cross section. The example insulation310is a magnesium oxide (MgO) powder, although other types of insulation materials may additionally or alternatively be used. The insulation310is used to fill the space between the resistive wires316and318and the outer sheath302to prevent short-circuiting the resistive wires316and318to the metallic outer sheath302.

As described above, the example resistive wire216includes three resistive portions220-224. The example resistive portions220-224may be constructed by forming the resistive wire216into a helix or coil shape having a first helical pitch (distance from center to center of the resistive wire216between adjacent turns). The example resistive portion222may then be stretched to increase the helical pitch (i.e., increase the distance per turn) of the resistive portion222, thereby decreasing the resistivity and power dissipated per unit distance. After the resistive portion222is stretched, the example resistive portions220and224have a first helical pitch and the resistive portion222has a second, larger helical pitch. Accordingly, the resistive portions220and224have larger power dissipation densities than the resistive portion222.

The example first and second connecting assemblies304and306, which are described in more detail below, include electrically conductive connectors to couple the resistive wires316and318to the power source202and/or the switching elements204aand204b.

The example mounting bracket308may be attached to the printer100to attach the resistive heating element208to the printer100in a substantially fixed position adjacent the ink drying area112. The mounting bracket308may be attached to the outer sheath302and/or the printer100using any attachment method(s), device(s), and/or combination of methods(s) and/or device(s), including but not limited to welding, soldering, brazing, and/or fastening. The example resistive heating element208includes approximately 90-degree bends312and314, having bend radii of about 15 mm, to position the resistive portions220-230adjacent the ink drying area112. The bends312and314may be formed to have any desired angle and/or radius, but may result in the printer100having a larger lateral footprint to accommodate a wider footprint of the resistive heating element208.

The example resistive heating element208has a width W of about 1100 mm. The example portions of the resistive heating element208that are adjacent the edge regions210and212of the ink drying area112each have widths X of about 68 mm. In the example, a straight portion of the resistive heating element208(the portion of the resistive element between the bends312and314) has a width Y about equal to the upper width of the print substrate110. Thus, the width W of the example resistive heating element208is about 18 mm longer on each side than the width of the print substrate110(e.g., 36 mm longer total). Accordingly, to obtain the desired temperature at the surface of the print substrate110, each of the resistive portions220,224,226, and230has a resistance between about 81.16 ohms (Ω) and about 89.7 Ω, and each of the resistive portions222and228has a resistance between about 61.26 Ω and about 67.7 Ω. The example power source202ofFIG. 2provides a potential of about 254 Volts. However, any or all of the above example specifications may be modified based on the ink, the width of the resistive heating element208, the type of the print substrate110, the print speed, and/or other requirements of a particular application. For example, the width W of the example resistive heating element208may be less than 36 mm or longer than 36 mm.

FIG. 4is another view of the example resistive heating element208ofFIG. 3. As described above, the resistive heating element208includes the resistive wires216and218, the outer sheath302, the connecting assemblies304and306, and the mounting bracket308. While the resistive wires216and218are shown side-by-side inFIG. 4, the resistive wires216and218may be arranged within the outer sheath302in any desired manner (e.g., intertwined, side-by-side, top-bottom, etc.). However, the resistive wires216and218are separated by space and/or by the insulation310to ensure that the desired control is exercised over the heating of the resistive wires216and218via the switching elements204aand204b.

The example connecting assembly304includes connecting pins402and404to electrically couple respective ones of the resistive wires316and318to a power source (e.g., the power source202ofFIG. 2) and/or a controller (e.g., the switching elements204aand204band/or the controller206ofFIG. 2). Similarly, the connecting assembly306includes connecting pins406and408to electrically couple respective ones of the resistive wires316and318to the power source and/or the controller206(FIG. 2). Thus, the connecting pins402and406may complete a circuit between the power source202, the switching element204a,and the resistive wire216and the connecting pins404and408may complete a circuit between the power source202, the switching element204b,and the resistive wire218.

FIG. 5is a cutaway view of the example connecting assembly304ofFIG. 3. As mentioned above, the connecting assembly304connects the resistive wire216to a power source and/or a controller. The example connecting assembly304includes the connecting pins402and404(the connecting pin404is obscured inFIG. 5), a connecting wire502, a sealant504, an inner sheath506, and an outer cover508. While the example view ofFIG. 5shows one connecting wire502and one inner sheath506, an additional connecting wire and an additional inner sheath are also included in the connecting assembly304but are obscured by the illustrated connecting wire502and the inner sheath506.

The connecting wire502is electrically coupled to the resistive wire216. The example connecting wire502is constructed using American Wire Gauge (AWG) 16 gauge, Underwriters' Laboratories (UL) Style 5288 wire. The sealant504seals the outer sheath302to, for example, reduce or prevent the escape of the insulation310from the outer sheath302. The example sealant504is RTV116 silicone sealant.

The inner sheath506is a non-conductive sheath that is wrapped around the connecting wire502to, for example, prevent short-circuiting the connecting wire502to other electrically conductive components (e.g., the connecting wire connected to the connecting pin404ofFIG. 4). The example inner sheath506is a fiberglass sheath including silicone rubber. The outer cover508protects the connecting wire502, the sealant504, the inner sheath506, and respective portions of the connecting pins402and404from damage. The example outer cover508is a SRFR round silicone rubber heat shrink.

While some example materials and geometries are provided for the example outer sheath302, the insulation310, the connecting wire502, the sealant504, the inner sheath506, and the outer cover508, the examples are not limited to the example materials. To the contrary, the examples may be modified to use alternative materials and/or geometries.

FIG. 6illustrates the example resistive wire216ofFIG. 3having multiple helical pitches602and604. The resistive portions220and224have a first pitch602and the resistive portion222has a second pitch604. The differences between the example pitches602and604are not to scale and are exaggerated for clarity. However, in accordance with the example resistivities described above, the helical pitch604is larger than the helical pitch602by a factor of about 1.25. Thus, the example resistive wire216may have a substantially uniform resistivity per unit length of material and still have different resistivities between the different resistive portions220,222, and224.

As noted at the beginning of this Description, the examples shown in the figures and described above illustrate but do not limit the disclosure. Other forms, details, and embodiments may be made and implemented. Therefore, the foregoing description should not be construed to limit the scope of the disclosure, which is defined in the following claims.