Ink jet apparatus provided with a fixing mechanism

Abstract

 An ink jet recording apparatus is arranged to dry ink ejected from a recording head (4) onto a recording sheet (1) by conveying the recording sheet (1) on a heater (7) for the fixation of the ink on the recording sheet (1). Such an ink jet recording apparatus comprises an ink fixing mechanism having the area in which the recording sheet (1) is conveyed on the heater (7), the area being structured with a fixing area (8) where a heat sufficient to fix ink is transferred to the recording sheet (1), and a preliminarily heating area (7) located on the recording head (4) side from the fixing area, in which a heat lower than the fixing area is transferred to the recording sheet (1); hence making it possible to perform the fixation of the ink reliably without any occurrence of density unevenness and waving (vertical lines) of the recorded images.

Description

BACKGROUND OF THE INVENTION

Field of the Invention

[0001] The present invention relates to an ink jet apparatus for performing recording by ejecting ink from the ink discharging ports to a recording medium. More particularly, the invention relates to an ink jet apparatus provided with an improved fixing mechanism for fixing ink desirably on a recording medium.

Related Background Art

[0002] If a recording sheet with ink which is not dried immediately after recording by an ink jet apparatus is touched, there may be some cases that the recorded images are smeared or ink adheres to one's hand. In a high speed ink jet recording apparatus, it may sometimes occur that before ink on a first recording sheet has been dried, a second recording sheet is overlaid to cause the reverse side of the second recording sheet to be smeared with the ink. For ink jet recording apparatuses, particularly those capable of performing a high speed recording, therefore, it is necessary to provide them with means to enable ink on a recording medium to be fixed by drying it after the formation of images thereon.

[0003] For a fixing device of the kind, there has hitherto been proposed a structure wherein heat rays of infrared region are given directly onto ink on a recording medium as a radiant heat or a structure wherein a hot air is blown onto ink on a recording medium for the drying fixation of the ink.

[0004] In the above-mentioned conventional examples, however, since a considerable amount of water is contained in ink as its component, at the same time the region of wavelength for the cellulose which the main component of the paper serving as a recording medium being substantially equal to that of water absorption, the portion of the recording medium where no ink has been given may present a yellowish discoloration if the radiant rays are radiated in a great volume in order to dry the ink in a short period of time. Also, if a hot air is blown onto a recording medium in a great volume in order to dry ink in a short period of time, the ink droplets on the recording medium tend to be flown to spoil the recorded images. Moreover, with these methods, the ratio of the thermal energy absorbed by the recording medium and the ink droplets on the recording medium to the thermal energy generated by its heat source is low. Accordingly, the electric consumption becomes great.

[0005] Also, in a case of an ink jet recording, there is a possibility that if the recording surface is rubbed before ink has been dried, the recorded images are spoiled. As a countermeasure, there has been proposed a structure wherein a fixing unit is provided to allow a flat heater having a width which is wider than the recording sheet to be in contact with the reverse side of the recording sheet to cover it entirely to dry the ink totally.

[0006] Nevertheless, if there is an air layer between the medium and the heating plate, the transmitting calorific value to the recording medium per unite time is reduced rapidly and at the same time, if.compressing means is provided to cause the recording surface of the recording medium to be in contact with the heating plate, the recording medium is expanded because of the ink droplets involved and corrugation takes place on the medium between the foregoing compressing means and the plate to make it difficult to heat the recording medium evenly; hence generating unevenness in the density of images in some cases.

[0007] Also, for a fixing device using the flat heater, a structure is arranged to transfer the heat of the flat heater to the recording sheet efficiently by compressing the recording surface to the flat heater through portions having extremely small contacting areas such a plurality of dots or lines.

[0008] In the above-mentioned conventional example, the flat heater is in contact with the entire face of a recording sheet, but for the purpose of miniaturizing the apparatus, the flat heater is arranged a flat heater so that it will be in contact with the recording sheet immediately after recording to carry out the fixation thermally by giving a high temperature rapidly. There is a problem encountered that ink is dried before the ink droplets have been permeated into the recording sheet sufficiently and thus their diameter becomes smaller. In order to avoid this, the flat heater should be located apart from the recording portion to a certain extent; hence hindering the miniaturization of the apparatus.

[0009] Also, the recording sheet is compressed by the flat heater through extremely small portions such as a plurality of dots or lines, but the heat of the flat heater is remarkably conductive in the compressed portions to quicken drying with the result that the dot diameters becomes small to generate white stream. In contrast, the dot diameters become large in the portions which are not compressed by the heater because the ink droplets are dried after they have been permeated thereinto sufficiently; thus creating unevenness in the dot diameters in the portions compressed and not compressed. An unevenness of the kind appears as a density unevenness. In addition thereto, the difference in the fixing speeds results in the difference in the amounts of expansion of the recording sheet thereby to cause the waving (vertical lines) of the recording sheet inevitably. In other words, there is a problem that the provision of a fixing device produces adverse effects on the quality of the recorded images.

[0010] Further, depending on the amounts of ink droplets of the recorded images, the fluctuation of the thermal energy of the flat heater becomes great immediately after it is in contact with the recording sheet. This will also create the density unevenness and the waving (horizontal lines) of the recording sheet.

SUMMARY OF THE INVENTION

[0011] It is an object of the present invention to provide a fixing mechanism for ink jet recording capable of giving heat evenly to a recording medium in a short period of time with a lesser amount of image density unevenness.

[0012] Also, the present invention is designed with a view to solving the above-mentioned problems encountered in the conventional technique. It is another object of the invention,to implement a fixing mechanism for an ink jet recording apparatus suitable for its miniaturization without creating the density unevenness and waving of a recording sheet.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Fig. 1 is a view showing the structure of a first embodiment according to the present invention.

[0014] Fig. 2 is a view showing the structure of a second embodiment according to the present invention.

[0015] Fig. 3 is a view showing the structure of a third embodiment according to the present invention.

[0016] Fig. 4 is a view showing the structure of a fourth embodiment according to the present invention.

[0017] Fig. 5 is a view showing the structure of a fifth embodiment according to the present invention.

[0018] Fig. 6 is a view showing the structure of the principal part of the sixth embodiment according to the present invention.

[0019] Fig. 7 is a cross-sectional view showing the principal part of the seventh embodiment according to the present invention.

[0020] Fig. 8 is a perspective view of Fig. 7.

[0021] Fig. 9 is a side view showing the principal part of the eighth embodiment according to the present invention.

[0022] Fig. 10 is a side view showing the principal part of the ninth embodiment of an ink jet recording apparatus according to the present invention.

[0023] Fig. 11 is a side view showing the principal part of the tenth embodiment according to the present invention.

[0024] Fig. 12 is a perspective view of Fig. 11.

[0025] Fig. 13 is a view schematically showing the structure of a recording head used for each of the embodiments according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] Hereinafter, with reference to the accompanying drawings, the description will be made of the embodiments according to the present invention.

[0027] Fig. 1 is a view showing the structure of a first embodiment according to the present invention and is a cross-sectional view showing the recording and fixing portions of an ink jet recording apparatus.

[0028] The present embodiment is to perform recording and fixation for a recording sheet which is a recording medium 1.

[0029] The recording portion comprises a feed roller 2 to be driven for feeding the recording sheet 1; a feed pressure roller 3 to give a conveying force to the feed roller 2; a recording head 4 to eject ink onto the recording sheet 1 for the formation of the images to be recorded; and a platen 5.

[0030] The fixing portion comprises a plurality of fixation feed rollers 6 to convey the recording sheet 1 after recording by contacting it in the fixing portions at points or in lines on the recording surface of the recording sheet 1 so that the recorded images are not spoiled; a low temparature heater 7 to form a preliminary heated area for the provision of preliminary heating for the recording sheet 1 after recording; and a high temperature heater 8 to form a fixing area in which ink is dried and fixed. The fixation feed roller 6 is arranged to depress the recording surface side of the recording sheet 7. The low temperature heater 7 and the high temperature heater 8 are each provided with its heat generating portions to cover the total area expanding to the recording width of the recording sheet 1 and are arranged to face the fixation feed roller 6 with the recording sheet 1 therebetween. Also, the low temperature heater 7 is provided in a location closer to the recording head 4 in order to give heat to the recording sheet 1 immediately after recording. In this way, the front half portion on the recording head 4 side becomes the preliminarily heating area and the remaining half portion to follow becomes the fixing area.

[0031] Subsequent to the recording and fixation in the above-mentioned recording and fixing portions, the recording sheet 1 is exhausted outside the apparatus while being pinched by a recording sheet exhaust roller 9 and an exhaust sheet pressure roller 10 to give the conveying force to the recording sheet exhaust roller 9.

[0032] Now, the operation of the present embodiment will be described.

[0033] At first, the recording sheet 1 is conveyed into the recording portion by means of the feed roller 2 which is being driven. Then, when the recording sheet 1 is conveyed to the recording position on the platen 5, a recording is performed by the recording head 4. Ink on the recording sheet 1 immediately after recording is in a semispherically raised state and is not permeated into the recording sheet 1 due to the surface tension. The recording sheet 1 thus recorded is conveyed into the fixing portion.

[0034] The recording sheet 1 is initially heated by the low temperature heater 7. The temperature of the low temperature heater 7 is set lower than the temperature required to dry the ink recorded on the recording sheet 1 to be fixed completely. Thus, the recording 1 is in a preliminarily heated state where the ink droplets are sufficiently spread to be permeated thereinto, at the same time being warmed evenly.

[0035] Subsequently, the recording sheet 1 being in the preliminarily heated state is conveyed into the area of the high temperature heater 8. The temperature of the high temperature heater 8 is set at a temperature higher than the one to cause the ink to be fixed. Thus, the ink recorded on the recording sheet 1 is heated to a temperature at which it is dried and fixed.

[0036] Here, it is prerequisite that there is provided means for depressing the recording sheet 1 to the above-mentioned two heaters. In the present embodiment, however, the fixation feed roller 6 serves such a means dually. This fixation feed roller 6 is in contact with the recording surface directly before the ink is fixed. There is a possibility that the recorded images are affected accordingly. Therefore, a material having a high rigidity is used for the fixation feed roller 6 to allow it to be in contact with the recording surface by dots or lines with the least possible contacting area.

[0037] In the present embodiment, the recording sheet 1 immediately after recording is not heated rapidly. The structure is arranged to allow it to be in a preliminarily heated state by the use of the low temperature heater 7 so that the ink droplets are sufficiently spread and permeated thereinto, and then it is heated at a temperature to dry the ink by the use of the high temperature heater 8. As a result, it becomes possible to implement with ease a fixing portion which will not affect the recorded images without changing the fixing speed greatly. Also, it is possible to conduct the required temperature adjustments for each area precisely because the low temperature heater 7 is provided for the preliminarily heating area while the high temperature heater 8 for the fixing area separately. Thus, the recorded images are obtainable in a better condition. In addition, the locations which need modifications are limited and there is no significant cost up nor any necessity to make the size of the apparatus large.

[0038] In this respect, the surface temperature of the low temperature heater 7 used for the present embodiment is 85°C and the surface temperature of the high temperature heater 8 is 160°C. The temperature of the recording surface side of the recording sheet 1 on the low temperature heater 7 is 70°C while the temperature of the recording surface side of the recording sheet 1 on the high temperature heater 8 is 120°C. The driving amount of ink is 27 nl/mm².

[0039] Fig. 2 is a view showing the structure of a second embodiment according to the present invention.

[0040] For the present embodiment, an inclined heater 21 is arranged instead of the low temperature heater 7 and the high temperature heater 8 provided for the first embodiment shown in Fig. 1. The inclined heater is such that its front half close to the recording head 4 side is inclined so as to allow the inclined portion to be away from the recording sheet 1 immediately after recording and to be gradually positioned closer thereto as the recording sheet 1 is being conveyed. There is also provided a fixing guide 22 made of a material having a high heat conductivity and placed between the recording sheet 1 and the inclined heater 21 so as to transfer the heat emitted from the inclined heater 21 to the recording sheet 1, at the same time guiding the reverse side of the recording sheet 1 in the fixing portion. The other structures are the same as those of the first embodiment shown in Fig. 1. For the elements constituting such structures, the same reference marks as in Fig. 1 are provided and the descriptions thereof will be omitted.

[0041] The heat emitted from the inclined heater 21 according to the present embodiment is good enough to cause the ink droplets ejected upon the recording sheet 1 to be dried and fixed. However, since its front half where the inclination is provided is away from the recording sheet 1, the ink droplets can be expanded sufficiently and permeated into the recording sheet and at the same time, the sheet is warmed evenly so that it is in a preliminarily heated state.

[0042] Thus, in the present embodiment, the front half of the inclined heater 21 where the inclination is provided serves as the preliminarily heated area while the area where the inclined heater 21 is positioned closer to the recording sheet 1 can be regarded as the fixing area. In this way, it is possible to obtain the same effects as the first embodiment shown in Fig. 1.

[0043] Fig. 3 is a view showing the structure of a third embodiment according to the present invention.

[0044] The third embodiment shown in Fig. 3 is such that the inclined heater 21 represented in Fig. 2 is replaced with a staged heater 31 having a cut-off portion formed in its front half. The structures other than this are the same as the second embodiment shown in Fig. 2. Therefore, the same reference marks are given to the elements constituting such structures as in Fig. 2 and the descriptions thereof will be omitted.

[0045] With the staged heater 31 having the cut-off portion as in the third embodiment shown in Fig. 3, it is still possible to make the heat distribution of the fixing guide 22 close to that of its state in Fig. 2 even if the heater is not provided with an inclination as in the inclined heater 21 according to the second embodiment represented in Fig. 2. The fixation of ink is also performed in a desirable condition.

[0046] Fig. 4 is a view showing the structure of a fourth embodiment according to the present invention.

[0047] The present embodiment is such that the fixation feed roller 6 according to the first embodiment shown in Fig. 1 constitutes means for adjusting positions. Those plural rollers are arranged as a plurality of fixation feed rollers 46₁ and 46₂ respectively while a heater 41 is provided instead of the low temperature heater 7 and the high temperature heater 8. The fixation feed rollers 46₁ are arranged in the front half portion close to the recording head 4, which constitutes the preliminarily heating area. The fixation feed rollers 46₂ are arranged in the latter half portion which constitutes the fixing area. The heater 41 is positioned to face each of the fixation feed rollers 46₁ and 46₂ with the recording sheet 1 therebetween. Whereas the fixation feed rollers 46₂ are to depress the recording sheet 1 on the heater 41 when conveying it, the fixation feed rollers 46₁ are arranged to be placed with a distance from the heater 41.

[0048] The other structures other than this are the same as those according to the first embodiment shown in Fig. 1. Therefore, the same reference marks as in Fig. 1 are provided for such constituents and the descriptions thereof will be omitted.

[0049] Now, the description will be made of the ink drying and fixing operations in the present embodiment. In the front half portion serving as the preliminarily heating area, the fixation feed rollers 46₁ and the heater 41 are arranged with a distance between them. Thus, the recording sheet 1 is not in contact closely with the heater 41, making it possible to allow the ink droplets to be spread and permeated into the recording sheet 1 as well as to keep the recording sheet in the preliminarily heated state where it is warmed evenly. In the rear half portion serving as the fixing area, the recording sheet 1 is depressed by the fixation feed rollers 46₂ to be in contact closely with the heater 41. Thus, the heat of the heater 41 is transferred to the recording sheet 1 desirably for heating. At this juncture, the recording sheet 1 has already been heated preliminarily in the front half portion serving as the preliminarily heating area. The ink is thus dried immediately as soon as the recording sheet 1 has been conveyed to the fixing area and is fixed thereon.

[0050] As described above, in the present embodiment, the distance from the heater 41 to the rollers is arranged to differ in the front half portion and the rear half portion thereby to make the condition of heat to be transferred to the recording sheet 1 in the fixing area the same as the condition of each of the embodiments shown in Fig. 1 to Fig. 3; thus obtaining the same effects.

[0051] Also, the structure of the apparatus can be substantially the same as the conventional one because only one simple flat type heater is required, and there is no possibility that the manufacturing cost will be increased.

[0052] Fig. 5 is a view showing the structure of a fifth embodiment according to the present invention.

[0053] For the present embodiment, there are provided instead of the fixation feed rollers 46₁ and 46₂ shown in Fig. 4, three belt conveyer rollers 52₁ to 52₃ and a fixation conveyer belt 51 to constitute a conveying mechanism for the recording sheet 1.

[0054] The fixation conveyer belt 51 is arranged in such a manner that as in the fourth embodiment shown in Fig. 4, each of the belt conveyer rollers 52₁ to 52₃ is positioned to provide a distance between the recording sheet 1 and the front half portion of the belt serving as the preliminarily heating area so as not to depress the recording sheet 1 onto the heater 41 therein, and that in the vicinity of the rear half portion serving as the fixing area, the belt approaches the recording sheet 1 and in the rear half portion, the fixing area, it depresses the recording sheet 1 upon the heater 41.

[0055] The structures other than this is the same as the fourth embodiment shown in Fig. 4. Therefore, the same reference marks as in Fig. 4 are provided for the elements constituting such structures and the descriptions thereof will be omitted.

[0056] In the resent embodiment structured as described above, the distance between the conveyer belt and the heater 41 can be made different in the front and rear half portions as in the fourth embodiment shown in Fig. 4 thereby to make the state of heat transferred to the recording sheet 1 in the fixing portion the same as each of the embodiments shown in Fig. 1 to Fig. 4; thus obtaining the same effects.

[0057] Fig. 6 is a view for explaining a sixth embodiment according to the present invention.

[0058] For the present embodiment, the low temperature heater 7 and the high temperature heater 8 according to the first embodiment shown in Fig. 1 are made into one heater while the shape of the fixation feed rollers are made different so as to enable the calorific values given to the recording sheet to differ in the front half and rear half of the fixing portion.

[0059] For the fixation feed roller, there are provided a plurality of projections 61 as shown in Fig. 6, and the pitches P at which these projections 61 are provided are made wider for the fixation feed rollers arranged in the front half portion serving as the preliminarily heating area while they are made narrower for the fixation feed rollers arranged in the rear half portion serving as the fixing area. In this way, the states in which the recording sheet is being depressed upon the heater are made different in the front half, the preliminarily heating area and the rear half, the fixing area to make the state of heat transferred to the recording sheet in the fixing area the same as each of the embodiments shown in Fig. 1 to Fig. 5; hence obtaining the same effects.

[0060] Since the present invention is structures as set forth above, it is possible to obtain the effects as described below.

[0061] In other words, the temperature transferred to the recording sheet in the preliminarily heating area which is closer to the recording head is made lower than the temperature given in the fixing area thereby to heat the recording sheet gradually while allowing the ink droplets to be permeated thereinto in the preliminarily heating area and then the ink is dried in the fixing area. Hence, it is possible to effectively prevent the density unevenness and the waving (vertical lines) of the recording sheet, which tend to occur due to the rapid heating immediately after recording, without any significant cost up and necessity to make the size of the apparatus large.

[0062] Now, with reference to the accompanying drawings, the description will be made of the other embodiments according to the present invention.

[0063] Fig. 7 is a cross-sectional view showing the principal part of a seventh embodiment of the fixing mechanism for an ink jet recording apparatus according to the present invention. Fig. 8 is a perspective view thereof.

[0064] The ink jet recording head 102 of an ink jet recording apparatus is to form images on a recording sheet 101 serving as a recording medium by ejecting ink droplets from its nozzle portion 102a arranged at the leading end thereof. A platen 103 conveys the recording sheet 101, at the same time being operated in synchronism with the ejection of ink from the ink jet recording head 102.

[0065] A recording sheet inlet guide 108 guides the recording surface side of the recording sheet 101 to enable the distance between the nozzles 102a and the recording sheet 101 to be stabilized and at the same time, to determine the exhausting direction of the recording sheet 101 after it exits from the image formation portion by means of the platen 103 and the recording sheet inlet guide 108. In the present embodiment, the direction indicated by an arrowed line a in Fig. 7 is the exhausting direction of the recording sheet 101. A recording sheet reverse side guide 104 is made of aluminum, stainless steel, or other metal having a high heat conductivity.

[0066] The shape of the recording sheet reverse side guide 104 is such as shown in Fig. 7 to guide the recording sheet 101 while being in contact with the reverse side of the recording surface of the recording sheet 101 and deflect the conveying direction of the recording sheet by causing the recording sheet 101 to be against its rigidity, that is, a concave surface, and such a shape is formed with a continuous curve. With the foregoing structure, the conveying direction of the recording sheet 101 is continuously changed as it advances from the direction indicated by the arrowed line a to the direction indicated by an arrowed line b. Thus, by the rigidity of the recording sheet 101, the recording sheet 101 is biased in the direction indicated by an arrowed line c, that is, the direction toward the recording sheet reverse side guide 104.

[0067] Here, the sliding surface of the recording sheet reverse side guide 104 for the recording sheet 101 must be arranged so that the recording sheet 1 is easily conveyed by the conveying force given thereto by the platen roller 103 and the recording sheet inlet guide 108 without any buckling. In other words, the friction coefficient against the recording sheet 101 must be small, and it is not desirable that the friction coefficient of the foregoing sliding surface should change due to the ink droplets, dusts, and the like which are placed on the sliding surface by mistake. In the present embodiment, therefore, the sliding surface of the recording sheet reverse side guide 104 for the recording sheet 101 is treated with a fluoric coating having a heat resistance with a low friction coefficient and excellent capability to release dusts and others.

[0068] Also, in the present embodiment, while the foregoing sliding surface is treated with such a fluoric coating, the surface of the sliding surface can be in any states only if the above-mentioned friction coefficient, heat resistivity, and other conditions are satisfied. Also, the shape of the recording sheet reverse side guide 104 can be of a type which changes its shape suddenly, not necessarily continuous curve, only if such a shape enables the recording sheet 101 to change its direction in which it is being conveyed against the rigidity of the recording sheet 101. However, for the system in which the conveying direction has a U-turn, there is a possibility that the recording sheet is slackened while being conveyed. Therefore, such a type is not included in the scope of the present invention.

[0069] On the reverse side of the sliding surface of the recording sheet reverse side guide 104 for the recording sheet 101, a flat heater 105 is arranged to adhere tightly to the recording sheet reverse side guide 104. In the present embodiment, a silicon rubber heater, which can be easily shaped to follow the configuration of the recording sheet reverse side guide 104, is employed, and the temperature of the sliding surface of the recording sheet reverse side guide 104 for the recording sheet 101 is set at 50°C to approximately 180°C. Here, in the present embodiment, the recording sheet reverse side guide 104 and the flat heater 105 are made of different materials, but it may be possible to use the flat heater 105 directly as the recording sheet reverse side guide 104.

[0070] Now, with the foregoing structure, the recording sheet 101 is slidable on the recording sheet reverse side guide 104 flexibly in the depth direction in Fig. 7 whereas it is being biased toward the recording sheet reverse side guide 104. Therefore, it is possible for the recording sheet 101 to slide on the recording sheet reverse side guide 104 by means of the platen roller 103 while keeping the tight contact with the recording sheet reverse side guide 104 even if the recording sheet 101 absorbs ink droplets to make itself expanded and its width becomes wider by zero point several millimeters to approximately several millimeters in the direction orthogonal to the conveying direction of the recording sheet 101.

[0071] Also, an ink droplet 107a immediately after being placed on the recording sheet 101 schematically shown in Fig. 7 will gradually be fixed as represented by an ink droplet 107b to an ink droplet 107c while it is conveyed on the recording sheet reverse side guide 104, and by the ink droplet 107c, the fixation will have been completed. The exhaust rollers designated by reference numerals 106a and 106b serve to stack the fixed recording sheet 101 onto a tray 109.

[0072] Fig. 9 is a side view showing the principal part of an eighth embodiment according to the present invention.

[0073] In the present embodiment, a halogen lump heater 110 is employed instead of the silicon rubber heater 105 used for the seventh embodiment and then a reflective plate 111 capable of easily reflecting the heat rays from the halogen lump 110 is arranged behind the halogen lump heater 110. The depth arrangement of the member is the same as the arrangement perspectively shown in Fig. 8. The lengths of the halogen lump heater 110 and the reflective plate 111 in the depth direction may be those with which they can heat the recording sheet 101 sufficiently over its length in the depth direction. The structures other than this are the same as the seventh embodiment and the descriptions thereof will be omitted.

[0074] Fig. 10 is a side view showing the principal part of a ninth embodiment according to the present invention.

[0075] In the present embodiment, there is provided a recording sheet reverse side guide 114 which is formed with a curve having a smaller radial curvature than the recording sheet reverse side guide 104 provided for the seventh embodiment as well as with straight lines. Then, the recording sheet 101 is biased to the recording sheet reverse side guide 114 most intensively in the vicinity of the curved portion having the aforesaid comparatively small radial curvature. Therefore, a flat heater 115 is also arranged only in the curved portion having the aforesaid comparatively small radial curvature. The structures other than this are the same as the seventh embodiment and the descriptions thereof will be omitted.

[0076] Fig. 11 is a side view showing the principal part of an tenth embodiment according to the present invention. Fig. 12 is a perspective view thereof.

[0077] In the present embodiment, the shape of a recording sheet reverse side guide 124 is made concave in the depth direction in Fig. 11 when observing its sliding surface for the recording sheet 101 from above. A flat heater 125 also has the same configuration. In the present embodiment, not only it is possible to utilize the rigidity of the recording sheet 101 in the conveying direction of the recording sheet 101, but also utilize its rigidity in the direction orthogonal to the conveying direction of the recording sheet 101. Therefore, the biasing force exerted on the recording sheet 101 against the recording sheet reverse side guide 124 is more enhanced. The structures other than this are the same as the seventh embodiment and the descriptions thereof will be omitted.

[0078] The present embodiment is an extremely desirable fixing method because there is no conveying means which necessitates a direct contact with the recording surface for conveying the recording sheet (except the exhaust rollers which are in contact with the recording surface after the completion of the fixing processing).

[0079] As described above, according to the present invention, a guide member is provided for guiding the recording surface and reverse side of a recording medium to be deflected in the conveying direction of the recording sheet, and then by transferring a high temperature to such a guide member, it is possible to implement a fixing mechanism for an ink jet recording apparatus having a high heating efficiency and high speed fixation capability. At the same time, there is provided flexibility for the recording medium to expand itself in the direction orthogonal to the conveying direction of the recording medium. Thus, even if the recording medium is expanded due to the ink droplets permeated thereinto, it is possible to maintain the close contact between the foregoing guide member and the reverse side of the recording medium. In this way, the recording medium is heated evenly with a high heating efficiency and a high fixation speed; hence obtaining the effect that images are desirably recorded without any significant density unevenness and waving and others of the recording medium.

[0080] In the present embodiment, a flat heater is used as its heating means. However, it may be possible to constitute this heating means with the structures as shown in the first to fifth embodiments wherein the temperature for fixation immediately after recording is set low and the temperature for fixation toward the exhaust rollers is set high.

[0081] With the adoption of the structure described as above, the fixation unevenness which may take place locally by the use of the fixation feed rollers can be avoided. It is also possible to execute the fixing processing reliably by drying ink gradually at a low fixing temperature and setting it in a completely fixed state by applying a higher temperature thereto as the recording sheet is conveyed.

[0082] Furthermore, since the arrangement is made so as not to depress the recorded surface of the recording sheet when it is conveyed, there is no possibility at all that any ink smearing takes place.

[0083] According to the present embodiment, heat is transferred to the recording sheet gradually by keeping the temperature given to the recording sheet lower than the fixing temperature in the preliminarily heating area close to the recording position as described above. Therefore, the ink droplets are permeated into the recording sheet in this area. At the same time, it contributes to drying and fixing ink in the subsequent fixing area in a better condition. Thus, no density unevenness and waving (vertical lines) of the recorded images occur.

[0084] Also, according to the present invention, there are provided a guide member and heating means, and by shaping the foregoing guide member such that the conveying direction of the recording medium is deflected as the recording medium advances against its rigidity, the reverse side of the recording medium is allowed to be in contact closely with the foregoing high-temperatured guide member capable of giving heat to the recording medium in conveyance. Hence, it is made possible to transfer heat from the heat source to the recording medium quickly as well as to allow the recording medium to expand itself flexibly when absorbing ink; yet the maintenance of the close contact between the recording medium and the high-temperatured member is implemented to practice heating the recording medium evenly.

[0085] Fig. 13 is a view schematically showing the structure of the recording head 102 which is used for each of the embodiments according to the present invention as described above.

[0086] This recording head 102 comprises a substrate 201 made of silicon and others; a plurality of electro-thermal transducers 202 which are the thermal energy generating elements for generating thermal energy to cause ink to be ejected; a plurality of nozzle walls 203 for partitioning the electrothermal transducers 202; and a ceiling plate 204 arranged to face the substrate 201 each other through the nozzle walls 203, and with the utilization of the foaming energy generated when ink on the electrothermal transducers 202 is heated by energizing the electrothermal transducers 202, ink droplets are ejected from a plurality of discharging ports 208. In this respect, the aforesaid ink is supplied to a common liquid chamber 207 from an ink tank (not shown) through a supply tube 205 and connector 206, and is supplied to the nozzles (each of the spaces surrounded by the substrate 201, nozzle walls 203 and ceiling plate 204) by a capillary phenomenon.

[0087] The present invention is particularly effective for an ink jet recording head and ink jet recording apparatus having a method whereby to eject ink by the application of thermal energy among currently available ink jet recording methods.

[0088] Regarding the typical structure and operational priciple of a recording heat and recording apparatus according the present invention, it is preferable to adopt those which can be implemented using the fundamental principle disclosed in U.S. Patent Nos. 4,723,129 and 4,740,796. This method is applicable to a so-called on-demand type recording system and a continuous type recording system. Particularly, however, it is suitable for the on-demand type because the principle is such that at least one driving signal, which provides a rapid temperature rise beyond a departure from nucleation boiling point in response to recoridng information, is applied to an electrothermal transducer disposed on a liquid (ink) retaining sheet or liquid passage whereby to cause the electrothermal transducer to generate thermal energy to produce film boiling on the thermoactive portion of the recording head for the effective formation of a bubble in the recording liquid (ink) corresponding to each of the driving signals. By the production, development and contraction of the bubble, the liquid (ink) is ejected through a discharging port to produce at least one droplet. The driving signal is preferably in the form of a pulse because the development and contraction of the bubble can be effected instantaneously, and therefore, the liquid (ink) is ejected with quick response. The driving signal in the form of the pulse is preferably such as disclosed in U.S. Patent Nos. 4,463,359 and 4,345,262. In addition, the temperature increasing rate of the thermoactive surface is preferably such as disclosed in U.S. Patent No. 4,313,124 for excellent recordings in a better condition.

[0089] The structure of the recording head using U.S. Patent Nos. 4,558,333 and 4,459,600 is also included in the present invention. In these patent specifications, there disclosed a thermoactive portion disposed at a bent portion as well as the structure of the combination of the discharging ports, liquid passages, and the electro-thermal transducers (linear type liquid passage or right angle liquid passage). In addition, the present invention is applicable to the structure disclosed in Japanese Patent Laid-Open Application 59-123670 wherein a common slit is used as the discharging ports for plural electro-thermal transducers, and also to the structure disclosed in Japanese Patent Laid-Open Application 59-138461 wherein an opening for absorbing pressure wave of the thermal energy is formed corresponding to the ejecting portion.

[0090] Further, as the full line type recording head having a length corresponding to the width of a maximum recording medium on which a recording apparatus can perform its recording, it may be possible to adopt a structure such as satisfying the required length by combining plural recording heads disclosed in the above-mentioned patent specifications or a structure formed as a single recording head. The present invention demonstrates the above-mentioned effects more significantly irrespective of the structures adopted.

[0091] In addition, the present invention is effectively applicable to a replaceable chip type recording head which is connected electrically with the main apparatus and can be supplied with the ink when it is installed in the main apparatus, or to a cartridge type recording head provided with a recording head formed itself integrally with an ink tank.

[0092] Also, it is preferable to add the recording head recovery means and preliminarily auxiliary means which are provided as constituents of a recording apparatus according to the present invention. They will contribute to making the effects of the present invention more stable. To name them specifically, they are capping means for the recording head, cleaning means, compression or suction means, preliminary heating means such as electro-thermal transducers or heating elements other than such transducing type or the combination of those types of elements, and the preliminary ejection mode besides the regular ejection for recording.

[0093] Moreover, the present invention is extremely effective in its application to an apparatus having at least one of the monochromatic mode mainly with black, multi-color mode with different color ink materials and/or full-color mode using the mixture of the colors, which may be an integrally formed recording unit or a combination of plural recording heads.

[0094] Also, with alloy materials related to the present invention, it is possible to obtain an ink jet head and ink jet apparatus provided with electrothermal transducers having exothermic resistive bodies particularly superior in durability against cavitation impact, durability against errosion due to cavitation, electrochemical stability, chemical stability, anti-acidity, anti-solubility, heat-resistance, heat-resistive impactivity, mechanical durability, and others. Particularly, it is possible to obtain an ink jet head and ink jet apparatus of such a structure that the heat generating portions of the exothermic resistive bodies are in direct contact with ink in the ink passages. In the ink jet head and ink jet apparatus thus structured, the thermal energy generated in the heat generating portions of the exothermic resistive bodies can be applied to the ink directly. Therefore, the efficiency of heat conductivity to the ink is remarkable. The power consumption by the exothermic resistive bodies can be reduced. The temperature rise of the ink jet head (temperature change for the ink jet head) can be made significantly small; thus making it possible to prevent the generation of the image density changes. Also, more desirable responses can be obtained for the ejection signals applied to the exothermic resistive bodies.

[0095] Further, with the exothermic resistive bodies related to the present invention, it is possible to obtain the desired specific resistivity with a better control so as to make the unevenness of resistance values for one ink jet head extremely small.

[0096] Consequently, according to the present invention, it is possible to perform highly stable ink ejections as compared with the conventional apparatus as well as to obtain an ink jet head and ink jet apparatus having an excellent durability.

[0097] The ink jet head and ink jet apparatus having the desirable characteristics described above are particularly suitable for high-speed and high-quality recordings being developed along with the availability of multiple discharging ports.

[0098] Now, in the embodiments according to the present invention set forth above, while the ink has been described as liquid, it may be an ink material which is solidified below the room temperature but liquefied at the room temperature. Since the ink is controlled within the temperature not lower than 30°C and not higher than 70°C to stabilize its viscosity for the provision of the stabilized ejection in general, the ink may be such that it can be liquefied when the applicable recording signals are given. In addition, while preventing the temperature rise due to the thermal energy by the positive use of such energy as an energy consumed for changing states of the ink from solid to liquid, or using the ink which will be solidified when left intact for the purpose of preventing ink evaporation, it may be possible to apply to the present invention the use of an ink having a nature of being liquefied only by the application of thermal energy such as an ink capable of being ejected as ink liquid by enabling itself to be liquefied anyway when the thermal energy is given in accordance with recording signals, an ink which will have already begun solidifying itself by the time it reaches a recording medium. In such a case, it may be possible to retain the ink as a liquid or solid material in through holes or recesses formed in a porous sheet as disclosed in Japanese Patent Laid-Open Application 54-56847 or Japanese Patent Laid-Open Application 60-71260 in order to exercise a mode whereby to enable the ink to face the electrothermal transducers in such a state. For the present invention, the most effective method for each of the above-mentioned ink materials is the one which can implement the film boiling method described above.

Claims

1. An ink jet recording apparatus for drying ink ejected from a recording head onto a recording sheet by conveying the recording sheet on a heater to fix the ink on the recording sheet, comprising:
   an ink fixing mechanism having the area in which said recording sheet is conveyed on said heater, said area being structured with:
   a fixing area where a heat sufficient to fix ink is transferred to the recording sheet; and
   a preliminarily heating area located on said recording head side from said fixing area, in which a heat lower than said fixing area is transferred to the recording sheet.

2. An ink jet recording apparatus according to Claim 1, wherein said ink fixing mechanism is provided with different heaters each for the preliminarily heating area and the fixing area.

3. An ink jet recording apparatus according to Claim 1, wherein the recording sheet and the heat conductive surface of the heater are closely in contact in the fixing area and said recording sheet and the heat conductive surface of the heater a distance therebetween in the preliminarily heating area.

4. A fixing mechanism for an ink jet recording apparatus in which ink is ejected from the discharging ports of the recording head to form images on a recording medium, comprising:
   guiding means located on the downstream side in the conveying direction of the recording medium from the recording position for said ink jet recording head to guide the reverse side of the recording surface of said recording medium; and
   heating means arranged on the reverse side of the guiding surface of said guiding.means for guiding said recording medium to heat said guiding means; wherein said guiding means is formed to be in such a shape that the conveying direction of said recording medium is caused to incline against the rigidity of said recording medium.

5. A fixing mechanism for an ink jet recording apparatus according to Claim 4, wherein the shape which causes the conveying direction of the recording medium to be inclined is formed to be in a configuration having a curved surface to allow the recording surface to be curved inward with respect to the conveying direction of said recording medium.

6. A fixing mechanism for an ink jet recording apparatus according to Claim 4, wherein the shape which causes the conveying direction of the recording medium to be inclined is formed to be in a curving shape on the cross section configured by the face in the direction orthogonal to the conveying direction of said recording medium.

7. A fixing mechanism for an ink jet recording apparatus according to Claim 4, wherein a fluoric coating is provided for the sliding surface of the guiding means for the recording medium.

8. A fixing mechanism for an ink jet recording apparatus according to Claim 4, wherein the guiding means and the heating means are separate members.

9. A fixing mechanism for an ink jet recording apparatus according to Claim 4, wherein the guiding means and the heating means are a member formed together.

10. An ink jet recording apparatus for drying ink ejected from a recording head onto a recording sheet by conveying the recording sheet on a heater to fix the ink on the recording sheet, comprising:
   guiding means located on the downstream side in the conveying direction of the recording medium from the recording position for said ink jet recording head to guide the reverse side of the recording surface of said recording medium; and
   heating means arranged on the reverse side of the guiding surface of said guiding means for guiding said recording medium to heat said guiding means; wherein said guiding means is formed to be in such a shape that the conveying direction of said recording medium is caused to incline against the rigidity of said recording medium.

11. An ink jet apparatus including means for directing ink onto a recording medium; a preliminary heating means effective to heat the recording medium without completely fixing the ink; and a fixing heating means effective to heat the recording medium so as to fix the ink.

12. An ink jet apparatus according to claim 11 including conveying means for causing the recording medium to pass over the preliminary heating means, and subsequently to pass over the fixing heating means.

13. An ink jet apparatus according to claim 12 in which the preliminary and fixing heating means are formed as a single heating means, and the apparatus is arranged such that the spacing between the recording medium and the preliminary heating means is greater than the spacing between the recording medium and the fixing heating means.

14. A method of using an ink jet apparatus including the steps of directing ink onto a recording medium; applying a first amount of heat to the recording medium insufficient to completely fix the ink; and applying a second amount of heat to the recording medium sufficient to fix the ink.

Drawing