Ink-jet recording process

Abstract: There is disclosed ink-jet recording process for carrying out a recording by adhering ink droplets on a recording medium, wherein the recording is carried out under the condition that the ink is adhered in an amount ranging between 3.0 × 10⁵ pl/cm² and 3.0 × 10⁶ pl/cm² in solid image recording when the recording is carried out with a recording density of 10 dots/mm × 10 dots/mm or more.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to an ink-jet recording process for recording information such as images, letters and symbols on paper, light-transmissive recording medium or the like with use of an ink-jet recording apparatus. Related Background Art Ink-jet recording has been hitherto known as a superior recording method which is not particular in choice of recording mediums, and researches and development have been extensively made on recording apparatus, recording processes and recording mediums. However, in the ink-jet recording apparatus having been hitherto developed and made commercially available, it has actually been impossible to obtain; i) a recorded image having a high optical density (or OD); ii) a recorded image which is good in print quality and free from any feathering on the peripheral part of letters or images; and iii) a good dry time characteristic; unless there are used recording mediums developed for exclusive use in an ink-jet recording which are called ink-jet recording paper or ink-jet recording transparenty films. The above performances i) to iii) can not be simultaneously satisfied when recording is carried out on recording mediums such as paper including electrophotographic recording paper (PPC paper), letter paper, bond paper, post cards, writing paper, envelopes, report paper, etc. generally used in offices, homes, etc. and transparent films (OHP films) with use of conventionally known ink-jet recording apparatus. Even when an ink-jet recording paper is used, there has also been accompanied with the disadvantage such that recording can not be performed on both sides thereof since the most ink-jet recording paper is a one-side coated paper, and thus the grade of prints and the dry time characteristic may be lowered if recording is carried out on the side to which no coating is applied. Now, various developments have been made for the purpose of obtaining recorded images; i) which are not particular in choice of recording faces (or are not particular in choice of materials such as paper or films and of the reverse side or obverse side thereof); ii) which have a high optical density (OD); iii) which are good in print quality and free from feathering; and iv) which have a good dry time characteristic; and there have been developed (1) a process in which recording is carried out using a strongly alkaline ink of about pH 13 (Japanese Laid-Open Patent Application No. 102970/1982), (2) a process in which recording is carried out using an ink-jet recording apparatus of a continuous type such as a charge-controlled type, etc. However, it is known in the process of the above (1) that an ink is so strongly alkaline as to be dangerous in handling, and also that, although good printing can be performed on acidic sized paper employing rosin or the like, there are posed the disadvantages such that both dry time characteristic and grade of prints may be greatly lowered when there is used neutral paper employing an alkyl ketone dimer or the like, and also strike-through tends to occur probably because of large permeability of the ink into the inside of the paper. In the process of the above (2), although it is a process that can achieve a recording of a relatively high density, there is limitation in work precision of nozzles from which an ink is ejected, and thus fine ink droplets can be stably ejected only with difficulty. As a result, unless the recording density is controlled to substantially not more than about 9.5 dots/mm (240 dots/inch), the dry time characteristic may be lowered (i.e., the recording surface can not be readily and may be soiled when smeared with fingers) and the irregular spreading of dots called "feathering" may occur, because of an overly large amount of the ink to be fixed on the recording face, so that there is obtained a low print quality, i.e., a recorded image having unsharp peripheral parts. With the recording density of about 9.5 dots/mm, there have been accompanied with the disadvantages such that it is impossible to carry out sharp printing for close chinese characters (such as ) or sometimes difficult to carry out the recording that can be smooth and natural in oblique line part or curved line part such as "/", "⊃" or " ○", and every dot can be judged by visual observation, giving recorded images of conspicuous ruggedness and lower grade. SUMMARY OF THE INVENTION The present invention provides an ink-jet recording process for carrying out a recording by adhering ink droplets on a recording medium, wherein the recording is carried out under the condition that the ink is adhered in an amount ranging between 3.0 x 10⁵ pl/cm² and 3.0 x 10⁶ pl/cm² in solid image recording when the recording is carried out at a recording density of 10 dots/mm x 10 dots/mm or more. In another aspect of the present invention, there is provided an ink-jet recording process for carrying out a recording by adhering ink droplets on a recording medium, wherein the recording is carried out under the condition that the ink is adhered in an amount ranging between 1.0 x 10⁶ pl/cm² and 2.0 x 10⁶ pl/cm² in solid image recording when the recording is carried out with a recording density of 14 dots/mm x 14 dots/mm or more. Optionally, said ink contains 1 to 45% by weight of an organic solvent having a boiling point of 150°C or more. Further optional features are set out in claims 3 to 9. An embodiment of the present invention provides an ink-jet recording process capable of performing a recording: i) which is less particular in choice of recording faces (or is less particular in choice of materials such as paper or films and of the reverse side or obverse side thereof); ii) which achieves a high optical density (OD); iii) which is good in print quality and has reduced feathering; and iv) which achieves a good dry time characteristic. An embodiment of the present invention provides an ink-jet recording process which can reproduce a complicated chinese character and an oblique line part or curved line part of an image more smoothly and naturally. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first feature of the present embodiment is to use an ink-jet recording apparatus with a recording density of 10 dots/mm x 10 dots/mm (length x width) or more. This is based on the fact that the present inventors have researched and studied on the relationship between the recording density and the "looks" and have found that the curved line part and the oblique line part appear to be smooth and natural in feeling if the recording density is 10 dots/mm x 10 dots/mm or more. In the case that a recording density is at a level as low as about 8 dots/mm x 8 dots/mm or less, the size of every dot is so large that the abnormality such as white-spotting, color non-uniformity or density non-uniformity tended to become conspicuous when the misdirection of ink ejection was occurred for some reasons (for example, because of the sticking of dust to part of nozzles). In contrast thereto, it was also found that with a recording density of 10 dots/mm x 10 dots/mm or more, the dot is originally so small that such abnormality favorably tends to become hardly conspicuous as only a very narrow streak (white-spotting), non-uniformity in color or non-uniformity in density was produced even when the misdirection of ejection was more or less occurred. In the case that recording was carried out with a recording density of about 4 to 8 dots/mm x 4 to 8 dots/mm and using ink droplets of large size, it was further found that ink droplets impinge on the recording face before ink droplets previously adhered permeate into the recording face when the succeeding ink droplets are adhered immediately after ink droplets are adhered on the recording face, so that the ink is splashed around the dots at the part on which the dots are overlapped, to soil the recording face. In the present embodiment, recording can be satisfactorily performed when a recording density is in the range of 10 dots/mm x 10 dots/mm or more, preferably in the range of from 10 dots/mm x 10 dots/mm to 24 dots/mm x 24 dots/mm, more preferably in the range of from 14 dots/mm x 14 dots/mm to 24 dots/mm x 24 dots/mm. In the present embodiment, recording can be also satisfactorily performed when employing the on-demand system with multi-nozzles. The function of the multi-nozzles herein mentioned is that a plurality of nozzles are used for forming one image and adjacent dots are substantially simultaneously applied in printing. A second feature of the present embodiment resides in the range of the amount of the ink to be adhered on the recording face. More specifically, good results for various parameters can be obtained at the same time by setting to a given range the amount of the ink to be adhered on the recording face. If the ink is adhered in a smaller amount, a colorant on the recording face can be present only in a smaller quantity, bringing about the disadvantage that the optical density (OD) of recorded images decreases to give unsharp recorded images having the impression that they are faint as a whole. If a concentration of the dye in the ink is set to be 10 % by weight or more for the purpose of solving this problem, a sufficient value for OD can be attained, but, in the recording apparatus having multi-nozzles, a nozzle or nozzles not being in use for recording may become liable to be clogged with the ink, resulting in uselessness in practical purposes. If the ink is adhered on the recording face in a greater amount on the contrary, the dry time characteristic frequency tends to be extremely lowered under the conditions shown below, even if the colorant is contained in the ink in a decreased amount: for example; i) under the condition of a high humidity atmosphere as in the rainy season: (A dry time characteristic is lowered because the humidity is so high that a recording medium has absorbed a moisture and also medium components in an ink may be slowly evaporated from the surface of the recording medium.) ii) under the codition of a low temperature as in the winter: (It is lowered because medium components in an ink may be slowly evaporated if an atmospheric temperature is low.) iii) in the case that recording is performed on strongly sized paper: (Since sizing is applied so as to prevent the feathering, it takes a long time for an ink to permeate into the inside of the paper. Namely, dry time characteristic is lowered.) When the ink is adhered on the recording face in a greater amount and also the colorant is contained in a greater amount, there is also posed the disadvantage that the recorded images may be extremely soiled if they are smeared with sweated fingers or the like. Now, to achieve the good printing results, the present inventors have studied under the varied conditions in respect of the amount of the ink to be adhered on the recording face. As a result, they found that the recording may preferably be carried out under the condition that the amount ranges preferably between 3.0 x 10⁵ pl/cm² and 3.0 x 10⁶ pl/cm², more preferably between 5.0 x 10⁵ pl/cm² and 2.5 x 10⁶ pl/cm², and most preferably between 1.0 x 10⁶ pl/cm² and 2.0 x 10⁶ pl/cm², in solid image recording. Also in the case that color-mixed areas are formed on a recording medium with use of two or more kinds of inks of different colors as in a color printer, recording may preferably be carried out under the condition that the amount of the ink ranges as described above. For example, in the case that a yellow area is formed on the recording medium with use of yellow ink and a green area is formed by overlapping cyan ink on it, if follows that the ink is adhered on the recording medium in an amount twice the amount used in the instance of the monochrome. Thus, the amount of the ink to be adhered at the color mixed areas is required to be controlled within the range described above. To describe an ink used in the present embodiment, any of dyes and colorants can be used as coloring matters, and a kind and an amount thereof may be selected depending on what purposes they are used for. However, it is generally preferred to use such dyes, taking account of the clogging of nozzles and so forth. As for a concentration of the dye, it can be suitably used in the range of 0.5 to 10.0% by weight, preferably in the range of 1.0 to 5.0% by weight, and more preferably in the range of 1.0 to 3.0% by weight based on the total amount of the ink, taking account of the optical density (OD) of recorded images. A liquid medium for dissolving or dispersing the colorant may be any of aqueous systems in which water and water-soluble organic solvents such as glycols and glycol ethers are used in combination and non-aqueous systems containing aromatic type, aliphatic type, ester type or ether type water-insoluble organic solvents. However, taking account of the safety, smell, strike-through of paper, etc., preferred are the aqueous systems. The present inventors have further studied an organic solvent contained in the ink. As a result, they found that better results can be obtained when the ink contains 1 to 45% by weight of an organic solvent having a boiling point of 150°C or more. If the organic solvent having a boiling point of 150°C or more, among the organic solvents contained in the ink, is contained in the amount more than 45% by weight, it tends to take a long time for the solvent to be evaporated from the recording face or for the solvent to permeate into the recording face, in other words, the dry time characteristic is lowered. It was also confirmed that, particularly in respect of an organic solvent having a boiling point of 300°C or more, if contained in the ink in an amount of 10% by weight or more, the dry time characteristic tends to be lowered and also the ink tends to slowly permeate into the recording medium even when the remaining part of the ink is constituted only of the solvent having a boiling point of 150°C or less such as water, alcohol and aliphatic hydrocarbons, so that it may sometimes occur that the "whiskers" called feathering are likely to appear at the printed part when the ink permeates, making it impossible to obtain excellent images having a good print quality. The organic solvent having a boiling point of 150°C or more may be contained more preferably in the range of from 1 to 30% by weight, still more preferably in the range of from 1 to 25% by weight, and most preferably in the range of from 5 to 20% by weight. In respect of the organic solvent having a boiling point of 300°C or more, it may be contained more preferably in the range of 5% by weight or less. With regard to the organic solvent having a boiling point of 150°C or more, the dry time characteristic is considered, in a common knowledge, to be more improved as it is contained in a smaller amount. Actually, it has sometimes occurred that the dry time characteristic is lowered on the contrary if the solvent is contained in an overly small amount. Thus, it may desirably be contained in an amount of 1% by weight or more, preferably 5% by weight or more. The recording medium to be used may be any of coated paper and ordinary paper, but particularly effective for the present invention is the paper having a basis weight in the range of from 45 to 200 g/m². The amount of the ink to be adhered (pl/cm²), as used in the present embodiment, can be readily determined by any of the methods in which; 1) it is determined from the decreased amount, measured after solid image recording, of the ink in an ink tank connected to nozzles, and the area of the solid image recording; and 2) it is determined from the amount of the ink ejected from one nozzle according to one signal, and the recording density. Embodiments of the present invention will be described below in greater detail by giving Examples and Comparative Examples. Example 1 Prepared was ink having the following composition. C.I. Direct Black 62 3.0 wt.% Ethanol (b.p. 78°C) 0.5 wt.% Ethylene glycol (b.p. 197°C) 20.0 wt.% Diethylene glycol (b.p. 245°C) 5.0 wt.% Water 71.5 wt.% Using this ink and also using an ink-jet recording apparatus having a multi-nozzle on-demand type head having a nozzle number of 48, ink-jet recording was performed at a recording density of 14.2 dots/mm x 14.2 dots/mm (360 dots/inch x 360 dots/inch) on the five kinds of paper (A) to (E) shown below under the solid image recording condition such that the volume of ink ejected from one nozzle according to one signal was 58 pl, in other words, the ink was adhered on the recording face in an amount of 1.2 x 10⁶ pl/cm². As a result, the resulting recorded images had an optical density (OD) of 1.2 in an average value. The dry time (the shortest time by which the recorded images are not soiled if they are smeared with filter paper) under 80% RH at 15°C was also found to be 52 seconds in an average value; and the dry time under 55% RH at 20°C, 41 seconds in an average value. The looks of recorded images were overall evaluated by 10 panelists in respect of optical density, grade, presence of feathering, and reproducibility of an image at an oblique-line part and a curved line part thereof, to find that the five rank evaluation (5: very good .... 1: very poor) was 4.2 in an average value, showing a good result. Ink-jet recording was also performed according to the process of the present embodiment on a transparent film comprising a polyester film coated with a mixture of polyvinyl alcohol and polyvinyl pyrrolidone. As a result, there were obtained good recorded images. Paper for recorded image evaluation: (A): Canon Paper NP-DRY (available from Canon Inc,; PPC paper) (B): Xerox 4024 DP (available from Xerox Corp.; PPC paper) (C): Hammermill Bond (available from Hammermill paper Corp.; bond paper) (D): Gilbert Bond (available from Mead Corp.; bond paper) (E): New OK (available from Oji Paper Co., Ltd.; wood free paper) Examples 2 to 9 Using the inks having the composition as shown below in (2) to (9), recordings were performed in the same manner as in Example 1 but under the conditions as shown in Table 1. As a result, there were obtained good results in all as shown in Table 2. (2): C.I. Food Black 2 1.4 wt.% C.I. Direct Yellow 86 0.1 wt.% Diethylene glycol 8.0 wt.% n-Propyl alcohol (b.p. 97°C) 5.0 wt.% Water 85.5 wt.% (3): C.I. Acid Black 52 2.5 wt.% Glycerol (b.p. 290°C) 17.5 wt.% Ethylene glycol 5.0 wt.% Methanol (b.p. 64.5°C) 4.0 wt.% Water 71.0 wt.% (4): C.I. Direct Blue 199 2.0 wt.% Diethylene glycol 15.0 wt.% n-Butanol (b.p. 118°C) 1.0 wt.% Water 82.0 wt.% (5): C.I. Direct Black 154 2.0 wt.% Thiodiethanol (b.p. 282°C) 14.0 wt.% Glycerol 6.0 wt.% Ethanol 4.0 wt.% Water 74.0 wt.% (6): C.I. Acid Red 8 5.0 wt.% Polyethylene glycol 200 (b.p.> 300°C) 3.0 wt.% Ethylene glycol 30.0 wt.% Water 62.0 wt.% (7): C.I. Food Black 2 1.4 wt.% C.I. Direct Yellow 86 0.1 wt.% Glycerol 10.0 wt.% Thiodiethanol 10.0 wt.% Water 78.5 wt.% (8): C.I. Solvent Black 29 1.0 wt.% Benzyl alcohol (b.p. 205°C) 20.0 wt.% Methyl cellosolve (b.p. 125°C) 10.0 wt.% Ethanol 69.0 wt.% (9): C.I. Food Black 2 2.6 wt.% C.I. Direct Red 227 0.2 wt.% C.I. Direct Yellow 86 0.2 wt.% Diethylene glycol 11.0 wt.% Ethylene glycol 5.0 wt.% Ethanol 3.0 wt.% Water 78.0 wt.% Examples 10 and 11 Using the ink having the same composition as in Example 9, recording was performed in the same manner as in Example 1 but under the conditions as shown in Table 1. As a result, there were obtained good results in all as shown in Talbe 2. Example 12 Prepared were ink (Y) and ink (C) of the following composition. Ink (Y): C.I. Direct Yellow 86 1.5 wt.% Diethylene glycol 20.0 wt.% Ethanol 5.0 wt.% Water 73.5 wt.% Ink (C): C.I. Direct Blue 199 2.5 wt.% Diethylene glycol 20.0 wt.% Ethanol 5.0 wt.% Water 72.5 wt.% Using ink (Y) and ink (C) and also using an ink jet recording apparatus having two multi-nozzle on-demand type heads each having a nozzle number of 256, ink jet recording for green images was performed at a recording density of 15.7 dots/mm x 15.7 dots/mm (400 dots/inch x 400 dots/inch) on the five kinds of paper (A) to (E) shown in Example 1 by making a print in an overlapping fashion under the solid image recording condition such that the volume of ink ejected from one nozzle in each head according to one signal was 35 pl, in other words, the ink was adhered on the recording face in an amount of 1.7 x 10⁶ pl/cm² as a result. As a result, the resulting recorded images had an optical density (OD) of 1.3 in an average value. The dry time under 80% RH at 15°C was also found to be 47 seconds; and under 55% RH at 20°C, 32 seconds; both in average values. The overall evaluation point was 4.2, showing good results. Comparative Examples 1 and 2 Using the ink having the following composition, the recording was carried out in the same manner as in Example 1 but under the conditions as shown in Table 1. Results obtained are shown in Table 2. C.I. Food Black 2 1.9 wt.% C.I. Direct Yellow 86 0.1 wt.% Glycerol 15.0 wt.% Triethylene glycol (b.p. 288°C) 8.0 wt.% Water 75.0 wt.% Comparative examples 3 and 4 Using the ink having the following composition, the recording was carried out in the same manner as in Example 1 but under the conditions as shown in Table 1. The results obtained are shown in Table 2. C.I. Food Black 2 2.9 wt.% C.I. Direct Yellow 86 0.1 wt.% Ethylene glycol 5.0 wt.% Diethylene glycol 10.0 wt.% Ethanol 2.0 wt.% Water 70.0 wt.% As described above, the present embodiments can obtain good images superior in ink fixing performance and optical density of images, and also free from any feathering, even when ordinary paper is used in high density recording.

Claims: An ink-jet recording process for carrying out a recording by adhering ink droplets on a recording medium, wherein the recording is carried out under the condition that the ink is adhered in an amount ranging between 3.0 x 10⁵ pl/cm² and 3.0 x 10⁶ pl/cm² in solid image recording when the recording is carried out with a recording density of 10 dots/mm x 10 dots/mm or more. An ink-jet recording process for carrying out a recording by adhering ink droplets on a recording medium, wherein the recording is carried out under the condition that the ink is adhered in an amount ranging between 1.0 x 10⁶ pl/cm² and 2.0 x 10⁶ pl/cm² in solid image recording when the recording is carried out with a recording density of 14 dots/mm x 14 dots/mm or more. An ink-jet recording process according to claim 1 or 2, wherein said recording process is of a multi-nozzle on-demand system. An ink-jet recording process according to claim 1, wherein said recording density ranges between 10 dots/mm x 10 dots/mm and 24 dots/mm x 24 dots/mm. An ink-jet recording process according to any preceding claim, wherein said recording density ranges between 14 dots/mm x 14 dots/mm and 24 dots/mm x 24 dots/mm. An ink-jet recording process according to claim 1, wherein said ink is adhered in an amount ranging between 5.0 x 10⁵ pl/cm² and 2.5 x 10⁶ pl/cm². An ink-jet recording process according to claim 1, wherein said ink is adhered in an amount ranging between 1.0 x 10⁶ pl/cm² and 2.0 x 10⁶ pl/cm². An ink-jet recording process according to any preceding claim, wherein said ink contains a colorant in the range of 0.5 to 10 % by weight. An ink-jet recording process according to any preceding claim, wherein said recording medium is a sheet of paper having a basis weight ranging between 45 and 200 g/m². An ink-jet recording process according to any preceding claim, wherein said ink contains 1 to 45 % by weight of an organic solvent having a boiling point of 150 °C or more.

Inventors: IWATA KAZUO, NISHIWAKI OSAMU, TOCHIHARA SHINICHI, IWATA, KAZUO, NISHIWAKI, OSAMU, TOCHIHARA, SHINICHI
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1987
Main classification: B41J2
IPC codes: B41J2, C09D11