JP2006272730A - Inkjet recording method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet recording method whereby a high-quality image is provided without any additional equipment set in a conventional apparatus and with the use of a coated paper for printing of a low water absorbency and a superior printability. <P>SOLUTION: The inkjet recording method is applied to a recording medium whose absorption amount of water from the start of contact to 20 msec<SP>1/2</SP>is not larger than 6 mL/m<SP>2</SP>in the Bristow method. A striking amount of ink is set to be not smaller than the absorption amount from the start of contact to 20 msec<SP>1/2</SP>. Moreover, a striking time interval of adjacent dots is set to be not shorter than an ink absorbable time. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an ink jet recording method. According to the inkjet recording method of the present invention, a high-quality image can be formed on a low water-absorbing coated paper for printing.

  The ink jet recording method is a printing method in which printing is performed by ejecting ink droplets from a printer head and landing on a recording medium such as paper. The ink used in this ink jet recording method needs to have low viscosity in order to fly from the printer head, and ink with a high water content is used. Accordingly, a highly water-absorbing special paper is used as the recording medium. High-water-absorbing inkjet paper can achieve high-quality images, but the absorption amount is reduced unless a thick absorption layer for absorbing ink is provided. In addition, since fine powder silica or alumina is used as a raw material to make the absorption layer transparent, the cost is high. This high cost has become a barrier that narrows the user's applications.

  Although plain paper such as copy paper is inexpensive, its water absorption is lower than that of ink-jet dedicated paper, and thus is essentially unsuitable as a recording medium for the ink jet recording method. Various ink-jet recording inks have been developed that guarantee a high-quality image even on inexpensive plain paper, but it is essentially extremely difficult to reach the image quality of ink-jet dedicated paper.

  As paper that is cheaper than plain paper such as copy paper, there is a coated paper (coated paper) for printing. This coated paper is a composite sheet in which a coating color, which is a kind of paint, is applied to both sides or one side of a base paper for the purpose of improving printability, and is exclusively used for printing paper. This coated paper is used in recording methods that use printing inks with high viscosity and is not required to absorb water, so it has been optimized to improve its fixability and color developability. Such a thick absorption layer and high-quality fine particles with high transparency are not required. Moreover, supported by vigorous demand of several million tons per year, mass production facilities are in place and high-quality coated paper is supplied at a very low price.

Since the coated paper has a lower water absorption than the plain paper, it has been considered that the coated paper is more inappropriate than the plain paper as a recording medium for the ink jet recording method. However, since the image quality of coated paper is extremely high, a technique for using this as a recording medium for an ink jet recording method has also been proposed.
For example, an ink jet recording method is proposed in which an ink droplet is ejected onto an intermediate transfer medium having a transfer layer on a substrate to form an ink jet recorded image, and then the ink jet recorded image is re-transferred to a coated paper together with the transfer layer. (Patent Document 1). However, this technique does not directly form an ink jet recorded image on a coated paper, but uses an intermediate transfer medium, so that facilities other than the ink jet printer are required. That is, since the apparatus size increases and the apparatus cost and printing cost also increase, the advantage of the ink jet recording system that is simple and small is lost.

In addition, a technique has been proposed in which an image quality improving liquid having an action of aggregating ink on paper is sprayed simultaneously with ink discharge to suppress bleeding and to warm paper during printing to assist drying. (Patent Document 2). However, this technique causes many adverse effects due to the application of the image quality improving liquid. For example, clogging due to image quality improving liquid mist, spraying the image quality improving liquid, the amount of liquid on the recording medium increases, the effect of suppressing bleeding is reduced, and the image quality improving liquid is further handled. A dedicated cap system is required.
Japanese Patent Laid-Open No. 2002-240411 JP 2001-199151 A

As described above, combining the advantages of the inkjet recording method, which is simple and small, with the coated paper for printing that is inexpensive and has excellent printability has been awaited in the industry. However, no technology has been proposed to realize it.
Accordingly, an object of the present invention is to provide a technique that can be used as it is without providing additional equipment in an ink jet recording apparatus that has been used conventionally, and that uses a low water-absorbing printing coated paper as a recording medium. There is to do.

The above problems are solved by the present invention.
In the Bristow method, an ink jet recording method for a recording medium having a water absorption of 6 mL / m ² or less from the start of contact to 20 msec ^1/2 ,
The ink jet recording method is characterized in that the ink ejection amount is set to be greater than or equal to the absorption amount from the start of contact to 20 msec ^1/2 , and the adjacent dot ejection time interval is set to be greater than the ink absorbable time. can do.

In a preferred embodiment of the method of the present invention, the ink deposition amount is set in the range of 6.4 to 9.6 mL / m ² .
In another preferred embodiment of the method of the present invention, the ink ejection amount is set in the range of 7.5 to 8.6 mL / m ² .
In still another preferred embodiment of the method of the present invention, the time interval between adjacent dots is set to 0.4 seconds or more.
In still another preferred embodiment of the method of the present invention, an ink set consisting of cyan ink, magenta ink, and yellow ink is used.
In still another preferred embodiment of the method of the present invention, an ink set containing black ink is further used.
In still another preferred embodiment of the method of the present invention, an ink set containing red ink and blue ink is further used.
In still another preferred embodiment of the method of the present invention, an ink set using a pigment as a coloring component is used in the ink set.
The present invention also relates to a recorded image obtained by an ink jet recording method.

According to the ink jet recording method of the present invention, without providing additional equipment in the conventionally used ink jet recording apparatus, and using a coated paper for printing having low water absorption and excellent printability as a recording medium, High quality images can be obtained.
In the inkjet recording method of the present invention, a coated paper for printing (coated paper), which is a low water-absorbing recording medium, is used, and an image is formed thereon with an ink ejection amount equal to or greater than the water absorption amount per unit area. . This amount of ink shot is about half that required for forming an image on a recording medium (plain paper, ink jet dedicated paper, etc.) that has been used for conventional ink jet recording. However, a clear image can be formed. Therefore, the ink consumption can be reduced.

  In the method of the present invention, a low water-absorbing recording medium is used. In the present specification, the Bristow method is used as a method for measuring water absorption. This Bristow method is the most popular method for measuring the amount of liquid absorbed in a short time, and is also adopted by the Japan Paper Pulp Technology Association (J'TAPPI). The details of the test method are described in J'TAPPI No. 51, “Method for testing liquid absorbency of paper and paperboard”. At the time of measurement, the head box slit width of the Bristow test is adjusted according to the surface tension of the ink. Also, the point where the ink is removed from the back of the paper is excluded from the calculation.

FIG. 1 is a graph showing the results of measuring the water absorption of four types of paper by the Bristow method by the Japan Paper Pulp Technology Association. As described in the reference examples described later, the line a is a coated paper for printing (trade name = OK top coat N; manufactured by Oji Paper Co., Ltd .; hereinafter, “OKTN” is used as an abbreviation), and the line b is a high-quality PPC. Paper (product name = BM paper; manufactured by Nippon Paper Industries Co., Ltd.), line c is another PPC paper (product name = Xerox Premium Multipurpose 4024; manufactured by Xerox Corporation; hereinafter “4024” is used as an abbreviation), and line d is , Inkjet exclusive paper (trade name = super fine paper; manufactured by Seiko Epson Corporation; hereinafter, “SF paper” is used as an abbreviation) is shown.
Further, in the present specification, "water absorption amount from the start of contact to 20 msec ^1/2 is 6 mL / ^{m 2} or less" is "20" from the "0" ^{msec 1/2} of the horizontal axis of FIG. 1 ^{msec 1/2} This means that the cumulative volume of water absorbed within the time period up to (that is, 0.4 sec: 20 msec ^1/2 = 400 msec = 0.4 sec) does not exceed “6” mL / m ² on the vertical axis. That is, low water-absorbing paper is used.

  As is clear from FIG. 1, the only paper that satisfies the requirements for low water absorption defined in this specification is coated paper for printing (OKTN: line a), and other PPC paper (lines b, c) and None of the inkjet paper (SF paper: line d) satisfies the requirement of low water absorption.

  In the method of the present invention, as long as the low water-absorbing requirement is satisfied, it has been conventionally used as a printing paper for letterpress printing, flat printing (for example, offset printing), or intaglio printing (for example, gravure printing). Any coated paper can be used. This coated paper includes ordinary coated paper, cast coated paper, and matte coated paper.

  In the method of the present invention, since a low water-absorbing recording medium is used, ink is hardly absorbed into the recording medium and is fixed by drying. That is, since the coloring component in the ink is hardly absorbed in the recording medium, the amount of ink related to the color development of the image can be reduced as compared with conventionally used plain paper such as PPC paper or ink jet dedicated paper. There is. In addition, since the ink is hardly absorbed, the time until the ink is dried and fixed becomes relatively long, and the spread of the ink dots on the recording medium tends to be large. Therefore, even if the amount of ink dots or the number of ink dots per unit area is reduced as compared with the case of plain paper or ink-jet dedicated paper set by a conventional ink-jet printer, it is possible to achieve the same or better color developability.

In the method of the present invention, the ink placement amount is set to be equal to or greater than the water absorption amount of the recording medium, that is, greater than or equal to the absorption amount from the start of contact to 20 msec ^1/2 . Specifically, 6 mL / ^{m 2} or more, preferably from 6.4~9.6mL / ^{m 2,} and more preferably set in a range of 7.5~8.6mL / ^{m 2.} When the ink shot amount is 6 mL / m ² or more, a clear image having a high printing density can be obtained. In addition, if it is 9.6 mL / m ² or less, the ink is not completely absorbed by the recording medium, so that mixing between ink dots (hereinafter, this state is referred to as “mixed color”) hardly occurs. This makes it difficult for bleeding to occur in the image.

Examples of printing methods that satisfy the above conditions include the following two methods A and B.
Method A: Compared to the case of a conventional ink jet printer, the amount per ink dot (hereinafter referred to as “ink dot amount”) is set to the same amount, but the number of ink dots per unit area is reduced. How to reduce.
Method B: A method in which the amount of ink dots is reduced and the number of ink dots per unit area is made equal compared to the case of a conventional inkjet printer.

  In the ink jet recording method of the present invention, when the above method A (a method for reducing the number of ink dots per unit area) is adopted and printing is performed on a low water-absorbing recording medium, the drying property of the ink on the recording medium, the friction resistance, etc. From the viewpoint of color development and color reproducibility, the number of ink dots is preferably 30% or more and 55% or less, more preferably 35% or more and 45%, based on the number of ink dots with respect to conventional inkjet dedicated paper. It can be as follows. By printing within this range, it is possible to ensure color development and color reproducibility equivalent to or higher than when printing on conventional inkjet paper, and a clear image with less bleeding is used in the present invention. It can also be obtained on coated paper.

Further, when the method B (method for reducing the ink dot amount) is employed in the ink jet recording method of the present invention and printing is performed on a low water-absorbing recording medium, the ink dot amount with respect to conventional ink jet dedicated paper is 22 mL / m ² . On the other hand, in the method of the present invention, it is preferably 9.6 mL / m ² or less, more preferably 8.6 mL / m ² or less. By printing within this range, it is possible to ensure color development and color reproducibility equivalent to or higher than when printing on conventional inkjet paper, and a clear image with less bleeding is used in the present invention. It can also be obtained on coated paper.

In the method of the present invention, the time interval between adjacent dots is set to be longer than the ink absorbable time. Here, the ink absorbable time means a contact time necessary for obtaining a certain transfer water capacity (mL / m ² ) in the Bristow method. For example, as shown by line a in FIG. 1, the coated paper for printing (OKTN) has a contact time of 20 msec ^1/2 (ie, 0.4 sec) required to obtain a transfer water capacity of 6 mL / m ^2. Therefore, the ink absorbable time of the coated paper for printing (OKTN) is 0.4 seconds with respect to 6 mL / m ² of ink.

In the method of the present invention, as shown in the above-mentioned method B, the ink dot amount can be appropriately changed and ink can be ejected from the head, and the ink absorbable time can be changed according to the ink dot amount. it can. According to the results of experiments conducted by the present inventors on various coated papers that satisfy the above-described requirements for low water absorption, for example, when the ink ejection amount is 6 mL / m ² , the first ink dot is ejected. Later, in order to drive the next ink dot to the adjacent position, if there is an interval of 0.3 to 0.5 sec, color mixing with the adjacent dot does not occur. Further, when the ink shot amount was 7.5 mL / m ² , it was confirmed that color mixing with adjacent dots would not occur if an interval of 1.2 to 1.6 sec was provided.

  In the ink jet recording method of the present invention, an ink set used in a normal ink jet recording method, that is, an ink set composed of cyan ink, magenta ink, and yellow ink can be used as it is, but an ink set containing black ink is used. It is more preferable to use an ink set having a secondary color by mixing colors, that is, an ink set further including a red ink, a green ink, and / or a blue ink.

  In particular, in the ink jet recording method of the present invention, it is preferable to use a so-called “pigment ink” using a pigment as the coloring component of the ink. The reason for this is that when pigment ink is deposited on the low water-absorbing recording medium used in the ink jet recording method of the present invention, liquid components other than solid content such as pigments (solvent, water, etc.) present in the ink and This is because solid-liquid separation from the solid content proceeds rapidly, and coloring components (pigments) relating to the color developability of the image are effectively present on the surface of the recording medium. In this case, there is an effect that a clear image can be obtained with a smaller amount of ink dots or the number of ink dots per unit area than a “dye ink” that uses a dye as a coloring component, which has been conventionally used.

  EXAMPLES Hereinafter, the present invention will be specifically described by way of examples, but these do not limit the scope of the present invention.

<Reference example>
The water absorption of four types of paper was measured by the Bristow method by the Japan Paper Pulp Technology Association. As paper, coated paper for printing (trade name = OK top coat N; manufactured by Oji Paper Co., Ltd .; abbreviation = OKTN), high-quality PPC paper 1 (trade name = BM paper; manufactured by Nippon Paper Industries Co., Ltd.), PPC paper 2 (Trade name =: Xerox Premium Multipurpose 4024; manufactured by Xerox Corporation; abbreviation = 4024) and ink jet paper (trade name = super fine paper; manufactured by Seiko Epson Corporation; abbreviation = SF paper) were used. The absorption performance of the paper was measured using an automatic scanning absorption meter by the Bristow method.
The measurement results are shown in FIG. In FIG. 1, line a is coated paper for printing (OKTN), line b is high-quality PPC paper 1 (BM paper), line c is PPC paper 2 (4024), and line d is ink jet dedicated paper (4024). (SF paper) results are shown.

<Example 1 and Comparative Example 1>
(1) Printing conditions A six-color ink set (that is, black, cyan, magenta, yellow, red, and violet six-color ink) dedicated to the ink-jet printer in an ink-jet printer (trade name = PX-G5000; manufactured by Seiko Epson Corporation) Example 1 and Comparative Example under the conditions of large dot (7.7 ng / m ² ), middle dot (3.2 ng / m ² ), and small dot (1.6 ng / m ² ) 1 was printed.
The recording medium used in Example 1 is the coated paper for printing (OKTN) shown in the reference example, and the water absorbency (water absorption amount from the start of contact to 20 msec ^1/2 ) measured by the Bristow method is shown in FIG. As shown in 1, it was 6 mL / m ² . On the other hand, the recording medium used in Comparative Example 1 is an inkjet exclusive paper (SF paper) shown in the reference example, and the water absorbency (water absorption amount from the start of contact to 20 msec ^1/2 ) measured by the Bristow method is As shown in FIG. 1, it was 40 mL / m ² .
In Example 1 and Comparative Example 1, printing was performed with the adjacent dot implantation time interval set to 1.6 seconds.

(2) Evaluation of printability In Example 1, when the maximum duty was printed at 30%, the obtained Gamut (reproducible color space) was about 580,000.
On the other hand, in Comparative Example 1, it was necessary to print at a maximum duty of 60% or more in order to obtain the same Gamut with the inkjet dedicated paper. Therefore, it was found that the amount of ink used can be saved by 30% or more by the method of the present invention.

  The ink jet recording method of the present invention can be used as it is without providing additional equipment in a conventional ink jet recording apparatus, and has a low water absorption and excellent printability as a recording medium. Can be used to obtain a high quality image.

It is a graph which shows the result of having measured the water absorption of 4 types of paper by Bristow method.

Claims (9)

In the Bristow method, an ink jet recording method for a recording medium having a water absorption of 6 mL / m ² or less from the start of contact to 20 msec ^1/2 ,
The ink jet recording method described above, wherein the ink ejection amount is set to be equal to or greater than the absorption amount from the start of contact to 20 msec ^1/2 and the adjacent dot ejection time interval is set to be equal to or greater than the ink absorbable time. The ink jet recording method according to claim 1, wherein the ink deposition amount is set in a range of 6.4 to 9.6 mL / m ² . The ink jet recording method according to claim 2, wherein the ink ejection amount is set in a range of 7.5 to 8.6 mL / m ² .   The ink jet recording method according to any one of claims 1 to 3, wherein an adjacent dot implantation time interval is set to 0.4 seconds or more.   The ink jet recording method according to claim 1, wherein an ink set comprising a cyan ink, a magenta ink, and a yellow ink is used.   The ink jet recording method according to claim 5, further comprising using an ink set containing black ink.   Furthermore, the inkjet recording method of Claim 5 or 6 using the ink set containing a red ink and a blue ink.   The ink jet recording method according to any one of claims 5 to 7, wherein an ink set using a pigment as a coloring component is used in the ink set.   The recorded image obtained by the inkjet recording method as described in any one of Claims 1-8.

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