GB2353761A

GB2353761A - Pre-print humidification of a print medium to reduce cockle thereof

Info

Publication number: GB2353761A
Application number: GB0019752A
Authority: GB
Inventors: Steven P Downing
Original assignee: Hewlett Packard Co
Current assignee: HP Inc
Priority date: 1999-09-01
Filing date: 2000-08-10
Publication date: 2001-03-07
Anticipated expiration: 2020-08-10
Also published as: GB0019752D0; GB2353761B

Abstract

An inkjet printer 20 uses a humidifier 34 to reduce cockle by adding moisture uniformly across a print medium 24, for example by spray action or sponge roller, before ink is rendered onto the medium. After the ink is applied to the medium, excess moisture is removed from the medium by a dryer 38. The moisture that is removed from the medium may be recycled 40 back into the humidifier for use in humidifying subsequent print media.

Description

h.

2353761 METHOD AND APPARATUS FOR REDUCING PRINT MEDIUM COCKLE TECHNICAL FIELD

This invention generally relates to printers, and more particularly to printers utilizing techniques to reduce print medium cockle.

BACKGROUND AND SUMMARY

Many of today's printers, such as inkjet printers, operate by applying liquid ink directly onto a sheet of paper. When the ink is put onto the paper, the paper absorbs the moisture in the ink- As printing technology evolves, printers are made that put greater quantities of ink on paper in a shorter amount of time, thus increasing the moisture which is absorbed by the paper. The paper absorbs more moisture in areas where there is a higher density of ink applied, such as strips or small squares that are printed in patterns across the paper.

When one or more portions of the paper absorb more moisture than other portions of the same sheet of paper, the different portions of the paper expand at different rates and in different amounts. This causes the paper to have a wavy, uneven appearance, called G4 cockle." Cockle is a greater problem on paper that has high concentrations of ink in some portions and no ink in other portions, such as a presentation slide that has a white border which does not expand - and an ink-saturated inner portion, which attempts to expand substantially. The outer border restricts the expansion of the inner portion and results in a serious degree of cockle.

Another factor that adds to the cockle problem in some printers is chemical applications known as "fixers." Fixers are clear compounds that are applied. to a piece of paper to aid in smear fastness and smudge fastness. However, fixers not only add more moisture to a page, but when a fixer is applied to a page, more ink is required to produce acceptable optical density and this adds even more moisture to some areas of the page. This only causes a greater degree of cockle on the page.

The present invention concerns a printing system equipped with a humidifier that uniformly humidifies a print medium before the ink is applied as a way to reduce cockle.

All areas of the print medium absorb the same amount of moisture and thus, all areas expand at approximately equal rates. The print medium is saturated sufficiently so that 2 when the ink is applied to the print medium, the area to which the ink is applied does not expand any further. This reduces the expansion differential between different areas of the print medium when the ink is applied to the print medium, and cockle is thereby reduced.

After the print is rendered to the print medium, the printing system removes the excess moisture from the print medium. The moisture may then be recycled back into the humidifier for use in subsequent printing processes.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example and not limitation in the figures of the accompanying drawings. The saine numbers are used throughout the figures to reference like components and/or features.

Fig. I is a diagrammatic illustration of an inkjet printer.

Fig. 2 is a block diagram of the inkjet printer of Fig. 1.

Fig. 3 is a flow diagram showing a printing method to reduce cockle.

DETAILED DESCRIPTION

The present invention concerns printing systems that reduce cockle by humidifying the print medium prior to rendering print data onto the print medium. The invention may be implemented in a number of printing systems that operate with a printing method that adds moisture to the print medium. Printing systems that may utilize the present invention include inkjet printers, copiers that render copies with liquid ink, fax machines that utilize liquid ink, and the like. For discussion purposes, the present invention is described in the context of an inkjet printer.

Fig. I shows an inkjet printer 20 in which the present invention may be implemented. The inkjet printer 20 has a print media source 22 which holds several pieces of print media 24 for input into the inkjet printer 20.

Fig. 2 is a block diagram showing selected functional components of the inkjet printer 20. The inkjet printer 20 has a print media source 22 to store the print media 24, a print medium handler 26 to pass the print media 24 through the inkjet printer 20, and a print media output tray 28 to collect the processed print media 24.

The print medium handler 26 includes a print media input port 32, a humidifier 34, a print element 3 6, a print media dryer 3 8, a moisture recycler 40 and a print media output port 42. The print medium handler 26 also includes mechanisms to physically move the 3 print media from one component or station to the next. Such mechanisms include rollers, drives, belts, path guides, motors, tractor assembly, and other means for moving the media from the input port to the output port.

The humidifier 34 adds moisture to the print media 24 prior to printing in order to reduce cockle. The printer 20 has a fluid reservoir 50 for storing a substance used by the humidifier 34 to humidify the print media 24. The substance stored in reservoir 50 may be water or a chemical compound having desirable characteristics for implementing in the present invention. For discussion purposes, the substance will be described as water.

The humidifier 34 utilizes one of several methods to introduce moisture to the print medium 24. One method is to spray a fine mist of liquid across the print medium 24 as it is passed through the print medium handler 26. The liquid is drawn from the fluid reservoir to one or more spray nozzles (not shown) which spray a fine water mist across the print medium 24. The print medium 24 absorbs the water until it is reaches the desired level of saturation. Any water that is sprayed but not absorbed by the print medium 24 is collected and returned to the fluid reservoir 50.

Another way to add moisture to the print medium 24 is to pass the print medium 24 adjacent to and/or in contact with a moist object, such as a sponge roller (not shown). Moisture from the object is transferred from the object to the print medium 24, thereby humidifying the print medium 24 by a suitable amount.

The humidifier 34 may also be constructed as a semi-sealed, high humidity chamber through which the print medium 24 is passed. The print medium 24 absorbs moisture from the high humidity in the chamber before the print data is rendered onto the print medium 24. The high humidity in the chamber may be introduced in different ways, such as by introducing steam into the humidifier 34 so that the air inside the humidifier chamber 34 constantly remains humid.

The printer media dryer 38 removes excess moisture from the print medium after the printing is completed. This may be done by one of several methods known in the art. For example, a warm air blower (not shown) may be utilized to pass warm air across the print medium 24 to evaporate the excess moisture. Alternatively, the print medium 24 may be passed over a heated platen (not shown) to warm the print medium and evaporate the excess moisture. In this drying process, the moisture is converted from a liquid state into a gaseous state. Any excess moisture removed by the print medium dryer 38 may be recycled back to the humidifier 34 by moisture recycler 40.

4 Fig. 3 shows a method for printing on a print medium in a manner that reduces cockle. The process is described with reference to the components in Fig. 2. At step 102, the print media input port 32 accepts a print medium 24 into the print medium handler 26 from the print media source 22. The print medium handler 26 passes the print medium 24 through the humidifier 34, where moisture is added to the print medium 24 (step 104).

The humidifier 34 may act upon the print medium 24 in several ways. For example, the humidifier 34 may humidify the entire print medium 24 uniformly or it may only add moisture to those areas of the print medium 24 to which ink will not be applied, thereby providing a uniform saturation across the print medium 24. For discussion purposes, the humidifier 34 is described as uniformly adding moisture across the entire print medium 24 prior to print data being rendered onto the print medium 24.

After the print medium 24 has been humidified in the humidifier 34, the print medium handler 26 passes the print medium 24 to the print element 36 (step 106). In the described implementation, the print element 36 is an inkjet printing mechanism, although other printing types may be used. The print element 36 renders print data onto the print medium 24.

After printing, the print medium handler 26 passes the print medium 24 to the print media dryer 38, which removes excess moisture from the print medium 24 (step 108). The moisture recycler 40 collects the moisture that is removed from the print medium 24, condenses the moisture into a liquid (if the moisture is in a gaseous state), and returns the moisture to the fluid reservoir 50 (step I 10). The liquid may then be used to humidify subsequent print media processed by the inkjet printer 20.

At step 112, the print medium 24 is discharged through the print media output port 42 of the print medium handler 26 and onto the print media output tray 28. If there is more print media 24 to be printed (i.e., the "yes" branch from step 114) another piece of print medium 24 is accepted into the inkjet printer 20 (step 102). Otherwise, the printing terminates (step 116).

Although the invention has been described in language specific to structural features and/or methodological steps, it is to be understood that the invention defined in the appended claims is not necessarily limited to the specific features or steps described.

Rather, the specific features and steps are disclosed as preferred forms of implementing the claimed invention.

Claims

1. A method for printing on a print medium (24), comprising: humidifying the print medium (24) to add moisture to the print medium (24); and rendering print data onto the humidified print medium (24).

2. A method as recited in claim 1, wherein the humidifying the print medium (24) comprises applying moisture only to areas of the print medium, (24) where print data.

will not be rendered, so that all portions of the print medium (24) contain similar amounts of moisture after the print data has been rendered onto the print medium (24).

3. A method as recited in claim 0, further comprising removing moisture from the print medium (24) after rendering print onto the print medium (24).

4. A method as recited in claim 0, wherein the print medium (24) includes a first piece of print medium (24) and a subsequent piece of print medium (24), the method further comprising: removing moisture from the first piece of print medium (24) after rendering print onto the first piece of print medium (24); and using the moisture removed from the first piece of print medium (24) to humidify the subsequent piece of print medium (24).

5. A printing system (20) comprising: 25 a print medium input port (32) to receive a print medium (24); a print medium humidifier (34) to apply moisture to the print medium (24); a rendering mechanism (36) to apply print on the print medium (24); a print medium output port (42); and a print medium handler (26) to pass the print medium (24) from the print 30 medium input port (32) to the print medium output port (42) in a manner such that the humidifier (34) and the rendering mechanism (36) act upon the print medium (24).

6 6. A printing system (20) as recited in claim 5 further comprising a print medium dryer (38) to remove moisture from the print medium (24) prior to passing the print medium (24) to the print medium output port (42).

7.A printing system as recited in claim 6 further comprising a moisture recycler (40) to transfer the moisture removed from the print medium (24) to the print medium humidifier (34) for use with subsequent print media (24).

A print medium handler (26) comprising:

a print media input port (32); a print media output port (42); means for moving the print media (42) from the input port (32) to the output port (42); and a print medium humidifier (34) to add moisture uniformly across the print medium (24).

9. A print medium handler (26) as recited in claim 8 further comprising a print medium dryer (3 8) to remove excess moisture from the print medium (24).

10. A print medium handler (26) as recited in claim 9, further comprising a moisture recycler (40) to utilize the moisture removed by the print medium dryer (38) in the print medium humidifier (34) to add moisture to subsequent pieces of print media (24).