Ink, Inj-Jet Recording Process, and Instrument Using the Ink

1. Field of the Invention

The present invention relates to an ink, an ink-jet recording process, and an instrument making use of the ink. More particularly it relates to an ink, an ink-jet recording process, a recording unit, an ink-jet recording apparatus and an ink cartridge that are capable of achieving highly detailed and high-image quality recording not only on coated paper specially prepared for ink-jet recording but also on non-coated paper such as paper for copying, paper for reporting, bond paper or continuous slip paper, i.e., what is called a plain paper, commonly used in offices and homes; and also are suitable for a system that utilizes heat energy.

2. Related Background Art

Inks with greatly various manners of being composed have been hitherto reported in respect of inks for an ink-jet recording. In particular, in recent years, detailed researches and developments have been made from various approaches such as composition and physical properties so that a good record can be made even on a plain paper such as paper for copying, paper for reporting, notepaper or letter paper, commonly used in offices.

In regard to an ink-jet recording also, various methods have been proposed, including a method in which electrically charged droplets are continuously generated so that a part of the droplets is used in recording, a method in which signals are imparted to a recording head having a piezoelectric device and droplets of a recording solution are generated in accordance with the signals to carry out recording, and a method in which heat energy corresponding with a recording singal is applied to a recording solution held in a chamber of a recording head and droplets are generated by the action of this energy to carry out recording.

In particular, the ink-jet recording of the type in which the ink is ejected utilizing a phenomenon of ink bubbling caused by heat energy, as disclosed in Japanese Patent Application Laid-open No. 54-59936, facilitates higher integration and higher densification of nozzles, and is a method that has recently attracted particular notices. However, because of the utilization of the phenomenon of bubbling, which is not utilized in other methods, this method requires more strict conditions with respect to the ink used.

Preferable conditions for the ink used in this method can be enumerated as follows:

(1) The ink has a good bubbling response to the heat energy, so that droplets can be always stably ejected from minute ejection orifices to cause no clogging.

(2) Even if a printer has been left in an uncapped state when the recording is in a pause, the ink can be stably ejected immediately after the recording is restarted. In other words, the ink in the vicinity of the ejection orifices is not easily dried, so that no clogging occurs.

(3) An image with a high quality level, free from irregular feathering can be formed, in particular, on a plain paper.

(4) Print can be quickly fixed (or dried) on a plain paper, and hence may not be smeared even when rubbed.

(5) The ink has a good storage stability, and the performances of ink can be maintained over a long period of time.

(6) The ink is excellent in safety such as non-toxicity and non-inflammability.

To cope with these requirements, various manners of formulation of ink have been hitherto proposed, without any particular limitation to the heat energy type in regard to the manner of ejection. For example, inks usually contain high-boiling organic solvents such as glycols for the purposes of anti-drying, anti-clogging and so forth. When recording is carried out using such inks on a plain paper having a high degree of sizing, ink does not readily penetrate into paper and the part on which a record has been made does not well dry, so that when recorded characters or the like are touched the hand may be stained with ink or the characters are rubbed to become smeared. Thus, there have been problems.

Under such circumstances, in order to increase the penetrability of ink into paper, Japanese Patent Application Laid-open No. 55-29546 proposes a method in which a surface active agent is added in ink in a large quantity. In such an instance, the following troubles have been caused: Feathering occurs very frequently on some kind of paper; when filled in an ink-jet recording head, the ink recedes from the orifice surface depending on the structural conditions of the head, resulting in no ejection of ink, or on the other hand the whole of the orifice surface becomes wet, also resulting in no ejection of ink.

Japanese Patent Application Laid-open No. 56-57862 also proposes a method in which the pH of ink is set to the alkaline side. In this instance, however, there are the disadvantages such that the ink is harmful when touched with hands or that no good results can be obtained in view of both feathering and drying performance when the ink is used on a paper containing a certain kind of sizing agent, e.g., a neutralized paper.

Besides the foregoing, various improvements have been attempted. Up to the present, however, no ink is known which can well settle all the above problems on feathering, drying performance and safety of ink, and also the problem of clogging, even if there is no limitation that the ink is used in the heat energy type recording. In addition, it is very important, but very difficult, to design an ink that can be further capable of well responding well to the phenomenon of bubbling, which is peculiar to the heat energy type recording.

Accordingly, an object of the present invention is to provide an ink that can achieve a good bubbling response to heat energy, has settled the problems on the feathering and the drying retardation of printed characters or the like, occurring when recording is carried out on non-coated paper such as paper for copying, paper for reporting, notepaper or letter paper, i.e., what is called a plain paper, commonly used in offices; and to provide an ink-jet recording process and an instrument making use of the ink.

Another object of the present invention is to provide an ink for ink-jet recording, having a high safety even when used in offices and homes.

Still another object of the present invention is to provide an ink that is not liable to cause clogging at the nozzles of a head for ink-jet recording, and also has a good reliability; and to provide an instrument making use of the ink.

The above objects of the present invention can be achieved by the present invention described below. The present invention provides an ink comprising a recording agent and a liquid medium capable of dissolving or dispersing the recording agent, wherein said ink contains butanetriol or 2-methyl-1,2,3-propanetriol.

The present invention also provides an ink-jet recording process comprising ejecting ink droplets from an orifice in accordance with a recording signal to make a record on a recording medium, wherein the ink described above is used.

The present invention still also provides a recording unit comprising an ink container portion that has held an ink and a head from which the ink is ejected in the form of ink droplets, wherein the ink described above is used as ink.

The present invention further provides an ink cartridge comprising an ink container portion that has held an ink, wherein the ink described above is used as ink.

The present invention still further provides an ink-jet recording apparatus comprising a recording unit comprising an ink container portion that has held an ink and a head from which the ink is ejected in the form of ink droplets, wherein the ink described above is used as ink.

The present invention still further provides an ink-jet recording apparatus comprising a recording head from which ink droplets are ejected, an ink cartridge having an ink container portion that has held an ink, and an ink feeder that feeds ink from said ink cartridge to said recording head, wherein the ink described above is used as ink.

FIGS. 1A and 1B illustrate a longitudinal cross section and a transverse cross section, respectively, of a head of an ink-jet recording apparatus.

FIG. 2 is a perspective illustration of the appearance of a head comprised of a multiple set of the head as shown in FIGS. 1A and 1B.

FIG. 3 is a perspective illustration of an example of ink-jet recording apparatus.

FIG. 4 is a longitudinal cross-sectional illustration of an ink cartridge.

FIG. 5 is a perspective illustration of a recording unit.

The present inventors have made intensive studies on various manners of ink composition with a good reliability, that is suitable for a recording system in which ink is ejected utilizing a phenomenon of ink bubbling caused by heat energy, can improve anti-feathering, drying performance and penetrability of ink on paper, and also is not liable to cause clogging at nozzles of a head for ink-jet recording. As a result, they have discovered that an ink containing, as a liquid medium, butanetriol or 2-methyl-1,2,3-propanetriol together with water can be well balanced in anti-feathering and penetrability and also can achieve particularly good anti-clogging. Thus they have accomplished the present invention.

According to what is known by the present inventors, as conventional agents for preventing inks from causing clogging, glycols such as polyethylene glycol, and glycerol have been used, among which glycerol has been used as a particularly preferred anti-clogging agent because it can prevent clogging by its addition in a relatively small quantity and also is not liable to cause feathering on the surface of paper. This glycerol, however, has a poor wettability to a sizing agent present in paper and therefore has the disadvantage that it gives a greatly poor ink drying performance or penetrability on the surface of some kind of paper.

On the other hand, the butanetriol or 2-methyl-1,2,3-propanetriol used in the present invention has the same anti-clogging effect similar to glycerol and moreover has very well balanced anti-feathering and penetrability of the ink. The reasons therefor can be presumed as follows: The present compounds each have a low vapor pressure and also have three hydroxyl groups like glycerol, and hence have a superior dissolving power or dispersibility of coloring matters, so that a good anti-clogging effect can be obtained. In addition, they each have a hydrophilic part and a hydrophobic part together in the molecule because of their larger number of carbon atoms than glycerol, and hence can be contributory to a good wettability to sizing agents, so that the penetrability of ink on the surface of paper can be remarkably improved.

As for the response to bubbling, it can be particularly improved when the ink contains the above compound in an amount of from 0.1% to 30% by weight and also water in an amount of from 50% to 95% by weight. The reason therefor can be presumed to be that the properties of the ink mixed in the above proportion and the wettability thereof to the members constituting the interior of nozzles are most suited to the recording method in which ink is ejected utilizing a phenomenon of ink bubbling caused by heat energy.

The components of the ink of the present invention will be described below.

The butanetriol that is used in the present invention and chiefly characterizes the present invention may include 1,2,3-butanetriol and 1,2,4-butanetriol.

The butanetriol or the 2-methyl-1,2,3-propanetriol may be added in the ink, alone or in the form of a mixture. The amount thereof may vary depending on coloring matters used and other liquid medium components used in combination. It may be in the range of approximately from 0.1% to 30% by weight, preferably from 0.1% to 25% by weight, and more preferably from 1% to 20% by weight, based on the total weight of the ink. An amount less than 0.1% by weight can bring about no effect of anti-clogging. On the other hand, an amount more than 30% by weight causes problems on penetrability and anti-feathering.

The coloring matter that constitutes the ink of the present invention includes direct dyes, acid dyes, food dyes, basic dyes, reactive dyes, disperse dyes, vat dyes, soluble vat dyes, reactive disperse dyes, oil dyes, and all sorts of pigments. Among these, water-soluble dyes are particularly preferred in view of the performances of ink.

The amount of any of these coloring matters contained depends on the types of liquid medium components, the properties required in inks, etc. In general, the coloring matter may be contained in an amount of approximately from 0.2% to 20% by weight, preferably from 0.5% to 10% by weight, and more preferably from 1% to 5% by weight.

The liquid medium, which is an essential component of the ink of the present invention may be contained in the ink in an amount of from 50% to 95% by weight, preferably from 55% to 95% by weight, and more preferably from 60% to 95% by weight. An amount of the water less than 50% by weight results in an excessively large quantity of organic solvent to cause curling of paper or a serious deterioration of the quality level of print on plain paper or the like. An amount of the water more than 95% by weight may result in serious deterioration of the stability of ejection from orifices of nozzles.

The essential components of the ink of the present invention are as described above. It is possible to use in combination, commonly available organic solvents used in other conventionally known inks. Such organic solvents may include alcohols having 1 to 5 carbon atoms, such as methyl alcohol, ethyl alcohol, n-propyl alcohol, iso-propyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol, iso-butyl alcohol and n-pentanol; amides such as dimethylformamide and dimethylacetamide; ketones or ketoalcohols such as acetone and diacetone alcohol; ethers such as tetrahydrofuran and dioxane; oxyethylene or oxypropylene addition polymers such as diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, polyethylene glycol and polyproplene glycol; alkylene glycols whose alkylene group has 2 to 6 carbon atoms, such as ethylene glycol, propylene glycol, trimethylene glycol, butylene glycol, 1,2,6-hexanetriol and hexylene glycol; thiodiglycol; glycerol; lower alkyl ethers of polyhydric alcohols, such as ethylene glycol monomethyl or -ethyl ether, diethylene glycol monomethyl or -ethyl ether and triethylene glycol monomethyl or -ethyl ether; lower dialkyl ethers of polyhydric alcohols, such as triethylene glycol dimethyl or -ethyl ether and tetraethylene glycol dimethyl or -ethyl ether; sulfolane, N-methyl-2-pyrrolidone, and 1.3-dimethyl-2-imidazolidinone.

The above water-soluble organic solvent may be contained in an amount ranging from 1% to 49% by weight, and preferably from 2% to 30% by weight, based on the total weight of the ink.

When the mediums as described above are used, they may be used alone or in the form of a mixture. The liquid medium may most preferably be composed to contain at least one kind of water-soluble high-boiling point organic solvent as exemplified by polyhydric alcohols such as diethylene glycol, triethylene glycol and glycerol.

Other various kinds of dispersant, surface active agent, viscosity modifier, surface tension modifier, fluorescent brightening agent and so forth may optionally be added.

For example, they include viscosity modifiers such as polyvinyl alcohol, celluloses and water-soluble resins; all sorts of surface active agents of a cationic, anionic or nonionic type; surface tension modifiers such as diethanolamine and triethanolamine; pH adjusters comprising a buffer; and mildewproofing agents.

The ink of the present invention can settle the problems concerning the feathering, the drying performance of recorded characters or the like and the penetrability, arising when recording is carried out on plain paper or the like. At the same time, it can match the recording head in an improved state. From these viewpoints, the physical properties of the ink should be controlled to give a surface tension of from 30 dyne/cm to 68 dyne/cm at 25.degree. C. and a viscosity of not more than 15 cP, preferably not more than 10 cP, and more preferably not more than 5 cP.

The ink of the present invention can be particularly preferably used in the ink-jet recording in which recording is carried out by ejecting ink droplets by an action of heat energy. Needless to say, it can also be used for usual writing implements.

The method and apparatus suited to carry out recording by the use of the ink of the present invention may include a method and apparatus in which a heat energy corresponding with a recording signal is imparted to the ink held in the interior of a recording head so that ink droplets are generated by an action of the heat energy.

FIGS. 1A and 1B show an example of the construction of the head, which is a main component of the apparatus.

A head 13 is formed by bonding a glass, ceramic or plastic plate or the like having a groove 14 through which ink is passed, to a heating head 15 used in thermal recording (the drawing shows a head, to which, however, is not limited). The heating head 15 is constituted of a protection layer 16 formed of silicon oxide or the like, a heating resistor layer 18 formed of aluminum electrodes 17-1 and 17-2, nichrome and so forth, a heat accumulating layer 19, and a substrate plate 20 with a good heat dissipation property.

The ink 21 reaches an ejection orifice 22 (a minute opening) and a meniscus 23 is formed there by a pressure P.

Now, upon application of electric signals to the electrodes 17-1 and 17-2, heat is abruptly generated at the region denoted by n in the heating head 15, so that bubbles are generated in the ink 21 coming into contact with this region. The pressure thus produced thrusts out the meniscus 23 and the ink 21 is ejected from the orifice 22 in the form of recording droplets 24 to fly against a recording medium 25. FIG. 2 illustrates a multi-head comprising the head as shown in FIG. 1A arranged in a large number. The multi-head is prepared by closely adhering a glass plate 27 having a multi-grooves 26, to a heating head 28 similar to the head as illustrated in FIG. 1A.

FIG. 1A is a cross-sectional view of the head 13 along its ink flow path, and FIG. 1B is a cross-sectional view along the ling A-B in FIG. 1A.

FIG. 3 shows an example of an ink-jet recording apparatus in which such a head has been incorporated.

In FIG. 3, reference numeral 61 denotes a blade serving as a wiping member, one end of which is a stationary end retained by a blade-retaining member. The blade 61 is provided at the position adjacent to the region in which a recording head makes a record. In the present example, the blade is retained in such a form that it protrudes to the course through which the recording head is moved. Reference numeral 62 denotes a cap, which is provided at the home position adjacent to the blade 61, and is so constituted that it moves in the direction perpendicular to the direction in which the recording head is moved and comes into contact with the face of ejection openings to carry out capping. Reference numeral 63 denotes an ink absorption member provided adjoiningly to the blade 61, and, similar to the blade 61, is retained in such a form that it protrudes to the course through which the recording head is moved. The above blade 61, cap 62 and ink absorption member 63 constitute an ejection-recovery portion 64, where the blade 61 and the ink absorption member 63 remove off water, dust or the like from the ink ejection opening face.

Reference numeral 65 denotes the recording head having an ejection energy generating means and ejects ink to the recoeding medium set opposingly to the ejection opening face provided with ejection openings, to carry out recording. Reference numeral 66 denotes a carriage on which the recording head 65 is mounted so that the recording head 65 can be moved. The carriage 66 is slideably associated with a guide rod 67. A part of the carriage 66 is connected (not shown) with a belt 69 drived by a motor 68. Thus, the carriage 66 can be moved along the guide rod 67 and hence the recording head 65 can be moved from a recording region to a region adjacent thereto.

Reference numeral 51 denotes a paper feeding part from which recording mediums are inserted, and 52, a paper feed roller driven by a motor (not shown). With such construction, the recording medium is fed to the position opposing to the ejection opening face of the recording head, and, with progress of recording, outputted from a paper output section provided with a paper output roller 53.

In the above constitution, the cap 62 of the ejection-recovery portion 64 is receded from the moving course of the recording head 65 when the recording head 65 is returned to its home position, e.g., after completion of recording, and the blade 61 stands protruded to the moving course. As a result, the ejection opening face of the recording head 65 is wiped. When the cap 62 comes into contact with the ejection opening face of the recording head 65 to carry out capping, the cap 62 is moved in such a way that it protrudes to the moving course of the recording head.

When the recording head 65 is moved from its home position to the position at which recording is started, the cap 62 and the blade 61 are at the same position as the position where the ejection opening face is wiped. As a result, the ejection opening face of the recording head 65 is wiped also at the time of this movement.

The above movement of the recording head to its home position is made not only at the time of the completion of recording or restoration of ejection, but also when the recording head is moved between recording regions for the purpose of recording, during which it is moved to the home position adjacent to each recording region at given intervals, where the ejection opening face is wiped in accordance with this movement.

FIG. 4 shows an example of an ink cartridge, denoted as 45, that has held the ink being fed to the head through an ink-feeding member as exemplified by a tube (not shown). Herein reference numeral 40 denotes an ink container portion that has held the feeding ink, as exemplified by an ink bag. The top thereof is provided with a stopper 42 made of rubber. A needle (not shown) may be inserted to this stopper 42 so that the ink in the ink container portion 40 can be fed to the head. Reference numeral 44 denotes an absorption member that receives a waste ink.

It is preferred in the present invention that the ink container portion is formed of a polyolefin, in particular, polyethylene, at its surface with which the ink comes into contact.

The ink-jet recording apparatus used in the present invention may not be limited to the apparatus as described above in which the head and the ink cartridge are separately provided, and a device can also be preferably used in which these are integrally formed as shown in FIG. 5.

In FIG. 5, reference numeral 70 denotes a recording unit, in the interior of which an ink container portion that has held an ink, as exemplified by an ink absorption member, is contained. The recording unit is so constructed that the ink in such an ink absorption member is ejected in the form of ink droplets from a head 71 having a plurality of orifices. As a material for the ink absorption member, it is preferred in the present invention to use polyurethane.

Reference numeral 72 denotes an air path opening through which the interior of the recording unit is made to communicate with the atmosphere.

This recording unit 70 can be used in place of the recording head shown in FIG. 3, and is detachably mounted to the carriage 66.

The present invention will be described below in a more specific manner by giving Examples and Comparative Examples. In the following, "part(s)" and "%" are by weight unless particularly noted.

The respective components as shown below were mixed and stirred for 5 hours. Thereafter, the resulting solution was adjusted to have a pH value of 7.5 with an aqueous 0.1% sodium hydroxide solution and then subjected to pressure filtration using a membrane filter of 0.22 .mu.m in pore size. Inks A to E of the present invention were thus obtained.

Next, recording was carried out using the resulting inks A to E and also using as an ink-jet recording apparatus the ink-jet printer BJ-130 (trade name; manufactured by Canon Inc.) with a heater element as an energy source for the ejection of ink. The recording was carried out on commercially available paper for copying and bond paper to evaluate the fixing performance of recorded characters, the feathering occurrence, the anti-clogging when printing is re-started after a pause of printing, the anticlogging when printing is re-started after a long-term stop of printing, and the frequency response. Results obtained are shown in Table 1. Tests for the evaluation were usually carried out under conditions of 25.degree. C. and 60% RH.

Using the components as shown below, inks F to J of Comparative Examples 1 to 5 were obtained in the same manner as in Examples 1 to 5, and the evaluation on every item was made in the same manner as in Examples. Results obtained are shown in Table 1.

Inks K to O with the following formulation were prepared in the same way as in Example 1. Evaluation was also made in the same way. Results obtained are shown in Table 2.

As described above, it is possible according to the ink of the present invention to achieve a good bubbling response to heat energy, and to carry out recording with a superior quality level and a good penetrability, causing no feathering even on a plain paper such as paper for copying, paper for reporting, notepaper or letter paper, commonly used in offices.

It is also possible according to the present invention to obtain an ink having a high safety even when used in offices and homes.

It is still also possible according to the present invention to carry out recording that may not cause clogging at the nozzles of a head for ink-jet recording and has a good reliability.

Employment of the ink according to the present invention makes it possible to provide an instrument having a high reliability.