JPH07304167A - Inkjet printer - Google Patents

Abstract

(57) [Summary] [Object] The present invention relates to an inkjet recording apparatus, and in particular, it is an object to realize a printer capable of high-quality printing, high-speed drying, and high-speed printing independent of the quality of recording paper. In an inkjet printer that prints on a recording material by ejecting water-based ink droplets, the surface of the recording material in a region immediately before printing is pressed and dried by a belt type preheater, and the recording material that has been heated and dried is also heated. The recording material is printed on the surface of the recording material while vacuum suction and conveyance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet recording apparatus, and more particularly to an ink jet recording apparatus capable of high quality printing which does not depend on the quality of recording paper, high speed drying and high speed printing.

[0002]

2. Description of the Related Art In general, an ink used in an ink jet recording apparatus is an aqueous ink containing water as a solvent from the viewpoint of safety and the like. This water-based ink needs to have a low evaporation rate for the purpose of preventing clogging in the head, but this slows down the drying rate of the ink after printing and makes it difficult to handle the paper after printing. Not only that, in the case of color printing, the flow and color mixture of ink, the occurrence of wrinkles on the paper, the expansion and contraction of the paper, and the deterioration of the printing accuracy are brought about. Ink and recording paper have been improved for the purpose of reducing them, but in reality, it is inevitable that they are both dedicated and costly.

On the other hand, there are some proposals for high-speed drying as a measure for the recording apparatus side, and recently application to the product (Hewlett-Packard Journal, Feb.1994, P.35) has also been made. The specific method is to heat and dry the recording paper before and after printing by hot air heating, thermal radiation heating, heat transfer heating from a heating platen roller, or the like.

[0004]

However, in any of these methods, it is necessary to detect the temperature of the target recording paper and control the energization of the heating source based on it, and prevent overheating and smoke ignition due to a recording paper conveyance trouble. Measures and safety measures are essential. Moreover, the heating efficiency of these is generally low, and the power consumption is not necessarily small. Furthermore, after the power is turned on, the waiting time until printing can be started generally takes a long time determined by the temperature rising time of the heating source.

The object of the present invention is not to mention quick start and low power consumption, but there is no need to detect the temperature of the recording paper or control the energization of the heating source at all, so that overheating due to a recording paper conveyance trouble is small. It is an object of the present invention to provide an ink jet printer capable of high-speed printing by providing a method for drying recording paper that does not require smoke and fire prevention measures and can significantly reduce safety measures. Still another object of the present invention is to significantly reduce beard-like bleeding, prevent ink flow and color mixing in color printing, and further prevent deterioration of printing accuracy due to wrinkles and expansion of recording paper, and to prevent the occurrence of plain paper and recycled paper. The aim is to achieve the same print quality on paper as line paper for inkjet printers, which is expensive.

[0006]

In order to achieve the above object, in an ink jet printer which prints on a recording material by ejecting water-based ink droplets, the surface of the recording material in a region immediately before being printed is pressed and dried by a belt type preheater. In addition, the recording material which has been heated and dried is printed on the surface of the recording material while being vacuum-adsorbed and conveyed.

Further, the belt of the belt type preheater is an endless belt made of polyimide resin having a thickness of 20 to 50 μm, and the pressing roller of the belt type preheater is a soft roller made of silicone rubber, and the heating source of the belt type preheater. Is composed of a thin zirconia-added alumina ceramic heat transfer plate and a PTC heater,
The Curie point of the PTC heater is 120 ° C to 2
PT with a certain Curie point selected from the range of 30 ℃
This is achieved by constructing a C heater chip.

Further, the amount of sucked air in the vacuum suction conveyance is large up to the vicinity of the printing area and is small thereafter. By using this vacuum suction conveyance belt as an endless belt made of a porous film, the above-mentioned object is achieved. More effectively achieved.

[0009]

It is needless to say that the same effect can be obtained regardless of the type of head used in the ink jet printer of the present invention, such as the electrostatic type, the piezoelectric type and the thermal type. However, now that the present inventors have been able to obtain a large-scale, high-density integrated thermal inkjet printhead, the present invention is applied to a multi-color or full-color thermal inkjet printer capable of high-speed printing using this head. It is also clear that doing so will have the greatest impact (see Japanese Patent Application No. 05-90123). The conventional type thermal inkjet printer has a printing speed of about 0.5 pages / minute (ppm) in full-color printing, whereas the thermal inkjet printer according to the present invention has a printing speed of full-color printing. This is because, even if the drying time of the printing ink is ignored, 100 ppm is possible. That is, the limit of the printing speed of this printer is determined by the drying time of the printing ink.

In order to dry the recording paper wet with the printing ink at a high speed, only a non-contact heating and drying method or a heat transfer heating method from the back surface of the recording paper is known. It's a bad way, as I already mentioned. On the other hand, the belt type preheater of the present invention has the best heating efficiency because it is heated by pressure from the printing surface side of the recording paper before printing. Moisture content in the recording paper, which varies depending on the storage condition of the recording paper, is evaporated by this preheating, and the recording paper conveyed under the head becomes a recording material under a substantially constant condition of high temperature and low humidity. That is, it is possible to supply the recording material under the head which is always in an ideal condition without depending on the storage condition of the recording paper. Moreover, the recording material conveyed under the head is already fixed to the vacuum suction belt, and when the recording material is a breathable recording paper, landing ink droplets on the recording paper are attracted by suction from the vacuum suction belt side. It is fixed under the condition that it easily diffuses in the thickness direction. This means that the high-speed drying ability of recording paper, which has high temperature and low humidity even in the thickness direction, can be used to the fullest extent, and ink droplets of other colors that land sequentially can be printed in full color with a minimum bleeding amount and color mixture ratio. Shows. By printing on high-temperature, low-humidity recording paper, it becomes possible to greatly reduce beard-like bleeding, which was difficult to reduce by the conventional method, and is comparable to expensive special paper even on plain paper and recycled paper. It is now possible to record with print quality. The fixed conveyance of the recording paper by the vacuum suction belt minimizes the expansion and contraction deformation of the recording paper during the printing process, and minimizes the displacement of landing ink droplets during full-color printing, enabling high-quality full-color printing.

The circumstances explained above are due to the fact that the OHP is not breathable.
Even in the case of the sheet, as a result, a similar print quality is obtained. This shows that the OHP sheet has a larger heat capacity than the recording paper and exhibits a similar effect in terms of the drying speed of the ink. Is estimated. Further, as a special example, a double bag-shaped recording paper such as an envelope can be heated and dried by the belt type preheater without generating wrinkles, and high-speed printing can be performed on it.

The belt type preheater is a polyimide resin endless belt having heat resistance and rigidity, and from the viewpoint of effectively transferring the heat of the heating source to the recording material, the thermal conductivity, rigidity, lubricity, and electrical conductivity. In the examples, it is shown that the thickness is optimally 20 to 50 μm from the viewpoint of wear life due to pressure sliding with the zirconia-doped alumina ceramic heat dissipation plate having excellent insulation properties. Further, when the PTC heater is used as the heating source, the recording material can be heated to the designed temperature without performing any temperature control due to its self-temperature control performance, and this printer has at least several ppm or more. Since the color printing speed is provided, there is no inconvenience even if the printing speed is kept constant in all the printing modes, and therefore the temperature of the heating source may be kept constant. That is, the preheater may be composed of one type of PTC heater chip having a constant Curie temperature, and it is not necessary to change the set temperature. However, since the printing speed of the printer changes depending on the line head or scanning head, the PT
The Curie temperature of the C heater may be selected. However, the maximum Curie point of the PTC heater used for the purpose of avoiding overheating of the recording paper due to transport trouble or the like is preferably 230 ° C. or lower (about 180 ° C. on the heating surface of the recording paper). In addition, the amount of suction air in vacuum suction conveyance is increased up to the vicinity of the printing area, and thereafter it is reduced to secure a large suction force at the initial stage when the recording material is introduced into the conveyance section. By using an endless belt composed of a fine porous film or a mesh sheet, the vacuum suction from the conveyor belt can be made uniform over the entire area of the recording paper in the printing area, and high-quality printing can be realized over the entire area of the recording paper. is there.

[0013]

FIG. 1 shows the cross-sectional structure of a full-color thermal inkjet printer according to the present invention.

The recording material 6 is sequentially heated by the belt type preheater 2 immediately before printing, and when the recording material 6 is recording paper, the moisture content thereof is evaporated to slightly lower the temperature, and the vacuum adsorption conveyer 3 is used. It is adsorbed and fixed on the porous conveyor belt 34 and is conveyed directly below the full-color line head 1. The full color line head 1 was invented by the present inventor (Japanese Patent Application Nos. 05-90123 and 05-231913).
No. 05-318272), a large-scale, high-integration-density thermal inkjet print head is used, and ink discharge nozzles are arranged at a density of, for example, 400 dpi (dots / inch) in the full width of the recording material 6 being conveyed. Cage,
The nozzle rows are arranged in four rows in the conveying direction of the recording material 6 at intervals of about 1.5 mm, and three color ink droplets of black ink are recorded.
Full-color printing is performed by ejecting toward. Reference numeral 4 is an orifice cap, and 5 is a member related to cleaning the orifice surface, but the description thereof is omitted because it is not directly related to the present invention (see Japanese Patent Application No. 06-65005).

First, the belt type preheater 2 will be described in detail. This type of heater was conceived as a fixing device for a laser beam printer (USP 3,811,8).
28), with the objective of quick start and low power consumption. An infrared lamp or a heating resistor is used as a heating source, and accurate temperature detection and control are essential. Also,
The endless belt 24 is made of PTFE excellent in non-adhesiveness on the surface of a polyimide resin film excellent in heat resistance and high temperature rigidity.
It is a general practice to use a two-layered head that is coated with a toner to prevent toner offset. On the other hand, in the preheater 2 shown in FIG. 1, a plurality of thin PTCs (Positive Temperature Coeff) having self-temperature controllability as a heating source are used.
icient) Thermistor heater chip 22 and a zirconia-doped alumina ceramic radiator plate 21 which simultaneously satisfies the surface smoothness of this heater, the lubricity of the belt 24, and the good heat transfer property.
4 is characterized by using a polyimide resin single layer film. Since the PTC heater has its own low thermal conductivity, the so-called pinch effect is likely to occur, and there is a limit to drawing out a large amount of heat generation, but here, the thickness of the PTC heater chip is thinned to 0.9 mm, By devising the arrangement of the current-carrying electrodes, the relatively large heating capacity is brought out. However, since this thin chip is used, it is difficult to form a long single heater with good smoothness.
It was necessary to arrange the chips side by side. For this reason,
A thin heat-dissipating plate 21 that is a smooth thin plate that does not cause wrinkles on the thin endless polyimide belt 24 when it slides, has a small wear and friction coefficient, a large thermal conductivity, and is electrically insulating and inexpensive is required. Therefore, the above-mentioned zirconia-added alumina ceramic (for example, Harox-Z manufactured by Hitachi Chemical Co., Ltd.) was selected as the optimum material. The surface temperature of the discharge plate 21 when a 100 VAC power source is connected to the PTC heater 22 embedded in the heat insulating holder 23, and the surface of the recording paper when the pressure roller 26 is set and the recording paper 6 is passed through as shown in FIG. The measurement result of the outlet temperature of is shown in FIG. The polyimide belt 24 used here has a thickness of 25 μm, the heat dissipation plate 21 has a thickness of 0.3 mm, the PTC heater width and the nip width are 8 mm, the PTC heater Curie temperature is 170 ° C., and the recording paper feeding speed is 50 mm. Was / S. As can be seen from this result, it is possible to raise the temperature to almost the saturation temperature 5 to 10 seconds after the energization of the PTC heater is started. That is, the energization starts 5 under the condition of FIG. 2 (8 to 9 ppm transport speed in A4 longitudinal feed).
The recording paper introduced into this preheater after 100 seconds is 100 to 1
The recording paper is heated to 10 ° C., the water content thereof evaporates rapidly, and almost completely dried recording paper at 90 to 100 ° C. is conveyed directly below the full-color line head 1. 20-3
For a high-speed printer of 0 ppm, the Curie temperature of the PTC heater chip should be increased, and it should be 240 ° C.
PTC heater chips with Curie temperatures up to are readily available. The advantage of using a PTC heater for this preheater is that not only does temperature detection and energization control become unnecessary, but the heater width (belt width), such as when printing postcards, etc.
Even if the recording material is narrower than the above, excess current flows through the PTC heater only in the temperature reduction area due to the paper passage to recover the temperature reduction, so that the temperature across the heater width is always uniform (± 5%).
It will be maintained within a certain range). On the other hand, if an infrared lamp or a heating resistor that does not have such a function is used for heating, the heaters other than the paper passing will have the same current as the heater cooled by the paper passing, causing an abnormal temperature rise and destroying the polyimide belt. Will end up. Therefore, in order to prevent this, it seems that safety measures such as temporary interruption of printing are taken.

Next, the pressing roller 26 will be described. When performing double-sided printing on the recording paper 6, it is best that the pressure contact roller 26 that is in pressure contact with the already printed surface is made of silicone rubber having excellent non-adhesiveness. This is because it is assumed that the printing on the already printed surface is toner (a softening point of which is as low as 110 to 120 ° C. increasing) by a laser beam printer, and PTFE is not adhesive to the toner. This is because silicone rubber is far superior to silicone rubber (see Japanese Patent Application Laid-Open No. 05-341672). Of course, there is no problem on the printing surface of the liquid inkjet printer. Further, the smaller the frictional force and wear amount due to the pressure contact sliding between the heat transfer plate 21 and the endless belt 24, the better, and it is necessary to improve the efficiency of heating the recording material. In order to satisfy these at the same time, it is necessary to reduce the pressure applied to the pressure contact roller 26, increase the nip width, and lengthen the pressure contact heating time. For this purpose, it is preferable that the pressing roller is a foamed silicone rubber roller and the hardness thereof is 5 degrees or less on the JIS-A scale. By doing so, it is easy to set the nip width to about 8 mm, and FIG. 2 also shows the result under such conditions.

The time course of the dynamic friction coefficient between the zirconia-added alumina ceramic heat transfer plate 21 and the polyimide belt 24 and the amount of wear thereof were measured when they were pressed and slid under the above conditions. FIG. 3 shows the results, and it can be seen that a very small dynamic friction coefficient can be maintained without using any lubricant, including the case of a conductive polyimide belt containing fine carbon powder. In this case, the sliding speed of the belt is 50 mm / S, and 200 hours corresponds to running for 36 km. In other words, if you feed A4 paper vertically,
This is the result of passing 10,000 pages. Then, when the wear amount of the sliding surfaces of the heat transfer plate 21 and the polyimide belt 24 at this time was measured, both were within the measurement limit of 1 μm, and 25
A polyimide belt with a thickness of μm can pass 1 million pages. Depending on the printer, several million pages may be required, but from the viewpoint of heating efficiency, the thinner the polyimide belt, the better.
It is desirable to use in the range of μm or less.

Next, the vacuum suction transfer device 3 will be described. The recording material 6 heated by the belt type preheater 2 is guided by a guide (not shown) to the vacuum suction conveyance device 3 and adsorbed on the porous conveyance belt 34 which is being conveyed at a conveyance speed equal to or slightly slower than that of the preheater. And is conveyed immediately below the line head 1. As the porous conveyor belt 34, for example, a Teflon-coated or polyimide-coated glass cloth endless belt can be used. However, a "entangled weave" or a mesh sheet having many gaps is suitable for the glass cloth. And the suction hole 3 near the line head 1
2 should be opened closely, or 4 suction grooves with a width of about 1 mm should be provided at the position corresponding to each nozzle row (in the case of 4 color full color)
By opening it, the suction can be uniformly sucked from the entire surface of the recording paper in the vicinity. This suction immediately sucks the adhering ink in the thickness direction of the recording paper at the same time as the fixed conveyance of the recording paper, completely prevents bleeding, color mixing and ink flow on the entire surface of the heated recording paper, and greatly contributes to high-speed drying of the ink. What to do is as described in the section of action. The suction holes 32 at a position away from directly under the head 1 need only suck and convey the recording paper 6 softly, and in order to reduce the amount of suction air from the suction duct 33, the number of holes is significantly increased. It is reduced. In addition, these also greatly contribute to the reduction of the sliding wear amount of the porous conveyor belt and the reduction of the rotational driving force.

Now, high-speed, high-quality full-color printing up to about 30 ppm has become possible by the above-mentioned method. Here, the result is shown to show thread-like blurring in monochrome printing. FIG. 4 is an enlarged photograph of the result of printing on three types of recording papers, which are developed for ink jet printers, non-blurring special papers, plain papers for laser beam printers, and recycled papers. Here, about 6 by preheating
A print result obtained by heating to 0 ° C. and heating only is also shown in order to see the result of vacuum suction. The magnitude of the effects of heat printing and heat suction printing are clear at a glance. As described above, since the amount of attached ink is small in monochrome printing, 6
Only by preheating to about 0 ° C, this effect is recognized. However, in full-color printing, the amount of attached ink is about one digit larger, and printing while heating and drying the recording paper at 100 ° C. or higher and vacuum suction is an essential condition for high quality. However, even with such measures, even if inexpensive plain paper or recycled paper is used, the effect of obtaining the same image quality as that of expensive special-purpose special paper is great.

As can be seen from FIG. 4, satellites (sub-drops) following the main ink drops are not recognized.
This is a patent application invention of the present inventor (Japanese Patent Application No. 06-2106).
No. 0) satellite-free thermal inkjet print head is used, which reduces ghosts and reduces the drying load as much as extra ink does not adhere, contributing to further improvement in print quality. is there. It should be noted that the suction-fixed transport is effective for high-definition printing, and a particularly effective result is obtained in the case of 600 to 800 dpi, but since it is difficult to quantify the evaluation, it is omitted in the present application.

Although the above description is based on the line head, the same result can be obtained by scanning and printing a smaller scanning color head at the line head 1 in FIG. It will be needless to say what is done. It should be noted that although the OHP sheet cannot achieve high quality by suction, it is the same in that high speed drying and color mixture and ink flow due to it can be prevented.

[0022]

According to the present invention, the recording material in the area immediately before printing is heated and dried by the belt type pre-heater, and printing is performed while vacuum suction and conveyance. Since the quality can be improved and the ink can be dried at high speed, the paper can be easily handled during high-speed full-color printing. A belt type preheater using a PTC heater or the like does not require a complicated and expensive control system, and even if recording materials of various sizes are continuously printed, no inconvenience occurs and it is safe. By using a fine porous endless belt as the vacuum suction conveyance belt, it was possible to ensure high printing quality by suction and high speed drying over the entire area of the recording paper.

[Brief description of drawings]

FIG. 1 is a sectional structural view of a full-color thermal inkjet printer according to the present invention.

FIG. 2 is a time-dependent change in the surface temperature of the heat transfer plate with the heater alone of the belt type preheater and the temperature at the heater outlet when the recording paper is heated.

FIG. 3 is a change with time of a dynamic friction coefficient when a zirconia-added alumina ceramic heat transfer plate and a polyimide endless belt are in pressure contact sliding.

FIG. 4 Conventional printing on various types of recording paper, heating printing at 60 ° C., 6
It is an enlarged photograph when printing by heating at 0 ° C.

[Explanation of symbols]

1 is a full color line head, 2 is a belt type preheater, 3 is a vacuum suction transporter, 4 is an orifice cap, 5
Is a head cleaner, 6 is a recording material, 21 is a heat transfer plate, 22
Is a PTC heater chip, 23 is a heat insulation holder, 24 is an endless belt made of polyimide, 25 is a drive roller, 2
6 is a pressing roller, 31 is a carrier, 32 is a suction hole, 33 is a suction duct, 34 is a porous carrier belt, 35 is a carrier drive roller, and 36 is a tension roller.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication B65H 5/22 C

Claims (5)

[Claims] 1. In an ink jet printer which prints on a recording material by ejecting water-based ink droplets, the surface of the recording material in a region immediately before printing is pressed and dried by a belt type preheater and is also dried by heating. An inkjet printer, wherein the recording material is printed on its surface while being vacuum-adsorbed and conveyed. 2. The belt type preheater belt is an endless belt made of polyimide resin having a thickness of 20 to 50 μm, and the pressure contact roller of the belt type preheater is a soft roller made of silicone rubber, and the heating source of the belt type preheater. 2. The ink jet printer according to claim 1, wherein the ink jet printer comprises a thin zirconia-added alumina ceramic heat transfer plate and a PTC heater. 3. The inkjet printer according to claim 2, wherein the PTC heater is composed of a PTC heater chip having a Curie point selected from the range of 120 ° C. to 230 ° C. Printer. 4. The ink jet printer according to claim 1, wherein the suction air amount of the vacuum suction conveyance is large up to the vicinity of the printing area and is small thereafter. 5. The ink jet printer according to claim 1, wherein the vacuum suction conveyance belt is an endless belt made of a porous film or a mesh sheet.