JPH03255172A - Ink for ink jet recording - Google Patents

Abstract

PURPOSE:To obtain the title ink used for a specified recording system, which is excellent in foaming response to thermal energy and can realize recording free from blotting even on plain paper with excellent penetration, by using at least a coloring matter, a polyhydric alcohol (derivative), water, and a speci fied compound as the constituents. CONSTITUTION:The title ink used for a recording system wherein thermal energy corresponding to a recording signal is given to an ink in a recording head chamber and liquid droplets are splashed upon a recording medium by the energy to effect recording, which does not contain any polymer and contains at least a coloring matter (e.g. C.I. Direct Yellow 86), 2-40wt.% polyhydric alcohol (derivative) (e.g. diethylene glycol), 55-95wt.% water, and 0.01-3wt.% benzyl alcohol.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to inkjet inks, and more specifically to coated papers specially prepared for inkjet use, as well as other papers generally used in offices and homes. It has extremely good fixing properties even on non-coated paper such as copy paper, report paper, notebooks, stationery, bond paper, continuous slip paper, and so-called plain paper, and uses thermal energy that enables high-definition and high-quality recording. This invention relates to an inkjet ink suitable for the method used.

(Prior Art) Conventionally, inkjet inks with a wide variety of compositions have been reported. In particular, in recent years, detailed ink composition and physical properties have been developed to enable good recording even on plain paper such as copy paper, report paper, notebooks, and stationery, which are commonly used in offices. A lot of research and development is being carried out.

In addition, various methods have been proposed for inkjet recording, including a method in which charged droplets are continuously generated and a portion of the droplets are used for recording, and a method in which a signal is sent to a recording head having a piezoelectric element. A method 5 in which ink droplets are generated according to the signal to perform recording; or a method 5 in which thermal energy corresponding to the recording signal is applied to the ink in the chamber of the recording head, and the energy 6 generates droplets to perform recording. There are ways to do this.

In particular, a type that ejects ink through a bubbling phenomenon of ink due to thermal energy, such as that described in Japanese Patent Application Laid-Open No. 54-59936, has attracted particular attention recently because it is easy to increase the integration and density of nozzles. This is the method by which they are collected. However, since it utilizes a phenomenon called foaming that is not found in other methods, more stringent conditions are required for the ink used.

Preferred conditions for the ink used in this method are listed below: (1) The responsiveness of the i8 to thermal energy is good, droplets are always stably ejected from the fine ejection ports, and the ink is visible to the eyes. (2) If the cap is left uncapped while recording is stopped,
, Stable ejection can be obtained immediately after resuming recording, that is, the ink near the ejection port does not dry easily and does not cause clogging. (4) Fast fixing (print drying) on plain paper and no staining even if the printed matter is rubbed; (5) Good storage stability; (6) excellent safety in terms of toxicity, flammability, etc.; and (6) excellent safety in terms of toxicity and flammability.

In response to these demands, conventional ink formulations include:
The ejection method is not particularly limited to one type using thermal energy, but for example, ink generally contains a high boiling point organic solvent such as glycol for the purpose of preventing drying and clogging. When recording on plain paper with a high degree of size, it is difficult for the ink to penetrate into the inside of the paper, and the drying of the recorded area is poor, so if you touch the recorded material with your hands, the ink may stick to your hands. There were problems with fixation, such as characters being rubbed and smudged.

On the other hand, in order to improve the permeability of the ink into the inside of the paper, Japanese Patent Laid-Open No. 55-29546 proposes a method of adding a large amount of surfactant to the ink. but,
In this case, depending on the type of paper, a lot of bleeding may occur, or when ink is filled into an inkjet head, depending on the structural conditions of the head, the ink may retreat from the orifice surface and no ejection may occur. On the other hand, problems such as the entire orifice surface becoming wet and ink not being ejected were observed.

Furthermore, in Japanese Patent Application Laid-open No. 56-57862, the ink p
A method of making H strongly alkaline has been proposed, but in this case it is dangerous if the ink is touched, and it is not suitable for papers using certain sizing agents, such as neutral paper. has drawbacks such as bleeding and drying properties which may not be good.

Further, JP-A-63-139963 proposes an ink containing 2 to 15% by weight of alkyl alcohol having 5 or less carbon atoms in order to improve frequency response and ejection stability.

According to studies by the present inventors, the use of alcohol as a penetrant itself is an extremely effective means in terms of suppressing bleeding and promoting fixation. However, if the amount added exceeds 5% by weight (in the case of benzyl alcohol, it exceeds 3% by weight), irregular stagnation tends to occur.
This cannot be said to be at a level that can be used sufficiently to meet the printing quality target as intended by the present invention. This tendency can be alleviated considerably if a lower alcohol with a carbon number of 3 or less is used, but in this case, the vapor pressure of the alcohol is high, so the alcohol evaporates from the head orifice, etc., making it easier to change the ink composition. .

This phenomenon is particularly noticeable and a serious problem when the ink is used in a disposable inkjet head having an atmosphere communication hole. Furthermore, the amount of alcohol is generally 5
If it exceeds 3% by weight (in the case of benzyl alcohol, it exceeds 3% by weight), the dissolution or dispersion of the dye becomes unstable in the case of aqueous medium-based inks, and the storage stability and clogging resistance of the ink deteriorates. do.

Further, JP-A-62-119280 proposes a water-soluble ink containing benzyl alcohol in combination with a hydroxyethylated polyethyleneimine polymer. However, active addition of polymers has the problem that clogging is likely to occur during reprinting after stopping printing. Furthermore, when used in a thermal energy one-type inkjet, the heater surface tends to become scorched, which often causes significant problems in printing durability.

As mentioned above, in addition to the above, various improvements have been attempted up to now, but even if there is no limitation to use only one type of thermal energy, the above-mentioned bleeding, drying properties, and even eye resistance Up to now, there is no known ink that satisfactorily solves all problems such as clogging and storage stability, and in addition, it has the ability to respond well to the phenomenon of foaming, which is unique to thermal energy systems. Although it is important to design an ink that further has the following properties, it can be said that it is an extremely difficult task.

(Problems to be Solved by the Invention) Therefore, an object of the present invention is to provide a foaming material that has good responsiveness to thermal energy and that can be used for uncoated copy paper, report paper, notebooks, stationery, etc. commonly used in offices, etc. An object of the present invention is to provide an inkjet ink that solves the problems of ink bleeding and slow drying of recorded matter when recorded on engineered paper, so-called plain paper.

Another object of the present invention is to provide an inkjet ink that is highly safe for use in offices and homes, and is resistant to changes in composition due to evaporation or the like even when left for a long period of time.

Still another object of the present invention is to provide an inkjet ink that is less likely to cause clogging in the nozzles of an inkjet head over a long period of time and has excellent reliability such as storage stability.

(Means for solving problems) The above objects are achieved by the present invention as described below.

That is, the present invention provides an inkjet ink used in a recording method in which thermal energy corresponding to a recording signal is applied to the ink in the chamber of a recording head, and the energy is used to fly droplets onto a recording material to perform recording. For inkjet use, it contains at least a pigment, 2 to 40% by weight of polyhydric alcohol and/or its derivative, 55 to 95% by weight of water, and 0.1 to 3% by weight of benzyl alcohol. It's ink.

(Function) The present inventors have developed various ink compositions suitable for a recording method in which ink is ejected by a foaming phenomenon caused by thermal energy, and in order to improve the dregs, dryness, and permeability of ink on paper. As a result of intensive studies, we found that 2 to 40% by weight of polyhydric alcohol and/or its derivatives and 55 to 40% by weight of polyhydric alcohol and/or its derivative
The ink containing 0.01 to 3% by weight of benzyl alcohol along with 95% by weight of water has a good balance in terms of smearing and permeability, and also has no adverse effect on clogging prevention and is highly reliable. It was discovered that there is a substance with a high concentration of carbon dioxide, which led to the present invention.

In other words, according to the research conducted by the present inventors, when using surfactants used in ordinary inks, the scum and permeability of ink on paper are sometimes good and sometimes not depending on the type of paper. The cases are mixed, making it difficult to obtain stable records. On the other hand, when benzyl alcohol used in the present invention is used, extremely good results can be obtained in that stable recording with little difference in quality depending on the type of paper can be obtained.

The reason for this is that ink bleeding and permeability are largely controlled by the phenomenon of wetting at the interface between the ink and the paper, but when a surfactant is used, the ink that adheres to the paper Good results cannot be obtained because the wetting properties differ between the surface and the inside of the droplet, but with the ink of the present invention, such a problem is unlikely to occur;
Furthermore, it is thought that the ink of the present invention has an exquisitely balanced relationship between the sizing agent added to the surface or inside of paper and the ink as an inkjet ink compatible with plain paper.

On the other hand, the reason why the responsiveness to foaming is good is that water, which is an essential liquid medium of the ink of the present invention, and the above-mentioned benzyl alcohol and its content are uniquely excellent in controlling the boiling phenomenon that is optimal for recording. The mixing ratio and the wettability to each member inside the nozzle are optimal in terms of physical properties and affinity, so the cycle of bubble disappearance and generation is extremely smooth, and as a result, the frequency response is extremely high. It is presumed that this has improved.

In addition, since the ink of the present invention does not contain polymers,
The clogging resistance after stopping during printing is also good, and printing defects due to burning on the heater surface, which is a problem peculiar to thermal energy type systems, do not occur.

(Preferred Embodiments) Next, the present invention will be described in more detail by citing preferred embodiments.

The compounds used in the present invention and mainly characterizing the present invention are:
Both are benzyl alcohols and can be obtained by conventionally known methods.

The amount of benzyl alcohol added to the ink varies depending on the pigment used and other liquid medium components used together.
About 0.01 to 3% by weight in the ink, preferably 0.05%
The proportion is from 1.9% by weight, more preferably from 0.1 to 1.9% by weight.

If the amount of benzyl alcohol added is less than 0.01% by weight, there is no effect on foaming response and ink permeability, while if it exceeds 3% by weight, the surface tension of the ink will decrease. Depending on the paper, it may bleed easily and print quality may deteriorate.

In addition, the polyhydric alcohols or derivatives thereof used in the present invention are specifically oxyethylene or oxypropylene addition polymers of 3 to 3, such as diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, and tripropylene glycol. Up to about 4; ethylene glycol, propylene glycol, trimethylene glycol, butylene glycol, l.

2. Alkylene glycols in which the alkylene group has 2 to 6 carbon atoms such as 6-hexanetriol and hexylene glycol: thiodiglycol; glycerin; ethylene glycol monomethyl (or ethyl) ether, diethylene glycol monomethyl (or ethyl) ether ,
Lower alkyl ethers of polyhydric alcohols such as 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; Can be mentioned. Among them, diethylene glycol, triethylene glycol, glycerin, and 1,2.6-hexanetriol are particularly preferred.

The content of the polyhydric alcohol is generally in the range of 2 to 40% by weight, preferably 3 to 30% by weight, and more preferably 4 to 25% by weight based on the total weight of the ink. If the content of these polyhydric alcohols is less than 2% by weight, the clogging prevention effect will be insufficient, while if it exceeds 40% by weight, roughness will occur and the fixing properties will be extremely poor. decreases to

Further, the proportion of water in the ink is 55 to 95% by weight,
Preferably 60-95% by weight, more preferably 65-9%
This proportion accounts for 5% by weight. When the amount of water is less than 55% by weight, the proportion of organic solvent is high, causing the paper to curl or the quality of printing on plain paper to be significantly reduced. On the other hand, if the amount of water exceeds 95% by weight, the stability of ink ejection from the nozzle orifice and the resistance to clogging after stopping during printing will be significantly deteriorated.

The pigments constituting the ink of the present invention include direct dyes, acid dyes, food dyes, basic dyes, reactive dyes, disperse dyes,
Vat dyes, soluble architectural dyes, reactive disperse dyes, oil dyes,
Various pigments may be used, but water-soluble dyes are particularly preferred from the viewpoint of ink performance.

The content of these pigments is determined depending on the type of liquid medium components, the characteristics required of the ink, etc.

Generally, it is about 0.2 to 20% by weight in the total amount of ink,
The proportion is preferably 0.5 to 10%, more preferably 1 to 5%.

The above are the essential components constituting the ink of the present invention, but if necessary, general tt&solvents 6 used in conventionally known inks can be used in combination. However, there are some amides such as formamide, dimethylformamide, and dimethylacetamide that cannot be used due to poor compatibility with the benzyl alcohol; for example, ketones or keto alcohols such as acetone and diacetone alcohol; Ethers such as tetrahydrofuran and dioxane; sulfolane, N-methyl-2-pyrrolidone,
Examples include 1,3-dimethyl-2-imidazolidinone.

In addition, additives such as surface tension adjusters such as jetanolamine and triethanolamine; pH adjusters using buffer solutions; and fungicides can also be used.

Furthermore, the ink of the present invention better resolves the problems of ink bleeding when recorded on plain paper, dryness, and permeability of recorded materials, and improves matching with inkjet heads. Physical properties include surface tension at 25°C of 30 to 53 dyne/cm and viscosity of 1
It is desirable to adjust it to 5 cP or less, preferably 10 cP or less, more preferably 5 cP or less.

(Example) Next, the present invention will be explained in more detail by giving examples and comparative examples. In the text, parts and percentages are based on weight unless otherwise specified.

After mixing the ingredients shown in Table 1 below and stirring for 5 hours, the pH was adjusted to 7.5 with a 0.1% aqueous solution of sodium hydroxide, and a mixture with a pore size of 0.22 μm was added. Membrane filter (product name: Fluorobor filter, manufactured by Sumitomo Electric)
The mixture was filtered under pressure to obtain inks A to E of the present invention.

Next, using the obtained inks A to E, an inkjet printer BJ-130 using a heating element as an ink ejection energy source was used as an inkjet recording device.
(Product name: Canon ■) modified machine (an ink sub-tank near the head with a capacity of approximately 2 crtrJ is completely sealed except for the head and ink flow pipe, and an atmospheric communication hole with a diameter of 0.5 mm is provided at the top) ) was used to record on commercially available copy paper, and the fixability and bleeding incidence of the resulting recorded matter were evaluated.

At the same time, we also evaluated the clogging resistance during reprinting after a printing stop, clogging recovery during printing after a long printing stop, frequency response, ink storage stability, and ejection durability. .

Regarding the items of fixability and bleeding, a recovery operation was performed after a long-term suspension and evaluation was performed again. The results are shown in Table 3. In addition, evaluation is usually at 25℃ and 60%RH.
It was conducted under the following conditions.

(The following is a blank space) Inks F-L of Comparative Examples 1 to 7 were obtained in the same manner as in Examples 1 to 5 using the ingredients listed in Table 2 below, and various We conducted an evaluation. The results are shown in Table 3.

11≦Lj Table *1 Fixability Evaluation After 10 seconds and 30 seconds after printing on commercially available copy paper, rub the printed area with filter paper (product name: No., manufactured by 5C1 Toyo Roshi ■) as shown below. evaluated.

0... 1 scum in 10 seconds None ○... 1 scum in 10 seconds Small △... 1 scum in 30 seconds Small ×... 1 scum in 30 seconds Large 2 Bleeding occurrence rateAbout the smudge occurrence rate The method is to print 300 dots discontinuously on commercially available copy paper using a printer, leave it for more than an hour, then use a microscope to count the number of dots that have smudged, and display the percentage of the total number of dots as a percentage. It was evaluated as follows.

○...10% or less △...11-30% Okay, what happens when you fill the printer with the specified ink, print alphanumeric characters continuously for 10 minutes, stop printing, leave it for 10 minutes without a cap, and then print alphanumeric characters again? Evaluation was made based on the presence or absence of defective parts such as scum and missing characters.

○...- No defective parts from the first letter △...- Part of the first letter has 1 dreg or is missing ×...-
Long-term clogging recovery when characters cannot be printed at all Long-term clogging recovery refers to the clogging recovery when reprinting after a long-term printing stop. After printing alphanumeric characters, stop printing, leave it for 7 days without a cap, etc., then perform an operation to recover from clogging of the nozzle. It was determined whether normal printing without any spots was possible.

○... Normal printing is possible after 1 to 5 recovery operations △... Normal printing is possible after 6 to 10 recovery operations ×... Normal printing is possible after 11 or more recovery operations Umbrella 5 Frequency response The printed condition of the obtained printed matter, that is, the condition of scraps 1 and white spots, and the condition of poor impact points such as splash and wobbling, was observed and evaluated with the naked eye.

0: The ink follows the frequency well, and there are no dregs, white spots, or landing point defects in solid character printing.

Good: The tracking state of the ink with respect to the frequency is almost good, and there are no scum, white spots, or poor landing points in character printing, but there is a slight scum 1 in solid printing.

△: There are no spots or white spots in character printing, but there are some poor impact points. In addition, in solid printing, there are about 1/3 of the total printing with shadows and white spots.

×: There are many spots and white spots in solid printing, and there are many spots and poor landing points in character printing.

Umbrella 6 Storage stability 100ml of each ink in a heat-resistant glass bottle Pour CC one by one, seal tightly and heat to 60℃. After being stored in the tank for 3 months, it is recorded in the recording device. Installed and printed on 100 sheets of continuous slip paper and evaluated based on the following criteria.

○・・・No abnormalities ×・・・Failure to eject, irregular printing, or discoloration occurs $7 Discharge durability 5 nozzles equivalent to 10,000 pulses Perform continuous dispensing and check the dispensing condition at that point. I observed the situation.

○・・・No abnormalities ×: Non-discharge occurs even with the l nozzle.

(Effects) As explained above, the ink of the present invention has good foaming response over a long period of time to thermal energy, and is suitable for use on copy paper, report paper, notebooks, stationery, etc. commonly used in offices. Even on plain paper, it is possible to record with no bleeding, excellent quality, and good permeability.

Further, according to the present invention, it is possible to obtain an ink that is highly safe for use in offices and homes, and is resistant to compositional changes due to evaporation or the like even if left for a long period of time.

Further, according to the ink of the present invention, clogging in the nozzles of an inkjet head is less likely to occur, and recording can be performed with high reliability in terms of storage stability and the like.

Claims (1)

[Claims] (1) Contains polymers in inkjet ink used in a recording method in which thermal energy corresponding to a recording signal is applied to the ink in the chamber of the recording head, and the energy causes droplets to fly onto the recording material to perform recording. at least pigment, 2-40% by weight polyhydric alcohol and/or
or a derivative thereof, 55 to 95% by weight of water and 0.01 to
An inkjet ink characterized by containing 3% by weight of benzyl alcohol.