JP2004209976A - Inkjet recording method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet recording method which is improved in image blurring, a setting fault and a drying load, notwithstanding the use of UV-setting ink constituted of a water-based medium and a base having water-based medium absorbing properties. <P>SOLUTION: In regard to a recording method wherein recording is made on the base by inkjet by using the UV-setting ink containing at least a coloring material, a UV-polymerizable substance and a photopolymerization initiator in the water-based medium, exposure to ultraviolet rays is performed within the time of contact wherein the amount of liquid transfer of the ink to the base measured by a Bristow method becomes less than 20 mL/mm<SP>2</SP>, after the ink strikes the base. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to an image forming method in which an image is formed and fixed by an inkjet recording method using an ultraviolet curable ink that can be reacted and cured by irradiating ultraviolet light. In particular, the present invention relates to an ink jet recording method capable of obtaining a high-quality image using an ultraviolet curable ink composed of an aqueous medium.

  In recent years, a UVIJ recording method using a UV curable ink has been developed as an ink jet recording method capable of recording even on a substrate having no special ink image receiving layer, and the improvement is being actively carried out at present.

  UV-curable inks are broadly classified into solventless UV inks that hardly contain non-curable solvents, and aqueous UV inks in which a photopolymerizable composition is dissolved or dispersed in an aqueous medium or the like.

  Solventless UV inks have already been put to practical use because they have the advantages of being suitable for high-speed recording because they can cure and dry the inks only by irradiation with ultraviolet rays, and that they do not generate harmful substances such as VOCs.

  However, since the solvent-free UV ink does not undergo volume shrinkage after curing, the ink is fixed in a raised state on the recording base material, and a feeling of unevenness is generated. The leveling of the ink by improving the timing of UV irradiation and the physical properties of the ink can eliminate some unevenness, but even in that case, the texture may differ from ordinary printing due to bleeding between dots and excessive gloss. There is.

  On the other hand, since the aqueous UV ink using the aqueous medium is diluted with the aqueous solvent, a polymerizable compound having a higher viscosity can be used as compared with the solventless UV ink.By volatilizing the aqueous medium after UV curing, It is characterized in that the ink texture can be improved by reducing the ink volume and improving the texture on the substrate.

  However, if the target base material has poor absorbency of the aqueous medium, bleeding between dots and the physical properties of the ink film during UV curing are weak, and excessive load is imposed on the drying of the aqueous medium performed in a later step. Occurs. Conversely, if the absorptivity of the aqueous medium is too large, the ink and the polymerizable compound contained in the ink will penetrate deep into the substrate, and a sufficient image density cannot be obtained. It does not reach and causes poor curing. Further, poor curing means that irritating monomers remain, which is a safety problem.

  The features, problems, and the like of the UV inkjet recording method as described above are outlined in, for example, “Color Materials, 75, (8), 394 to 400 (2002)“ Prospects of UV Inkjet Technology ”.

  In any case, since the water-based UV ink can reduce the volume of the ink, there is an advantage that an image with less unevenness can be obtained than the solventless UV ink. In view of the compatibility, some contrivance is required, and practical application is difficult without it.

  Japanese Patent Application Laid-Open No. 2000-117960 discloses that a water-based UV ink is used to obtain a high-density, glossy, and good-saturation image. Thus, a printing method has been proposed in which the contact angle of the ink liquid with the base material is ≦ 60 degrees.

  However, in the above document, an example of irradiation with ultraviolet light more than a few seconds after the ink has landed is shown, and bleeding due to mixing of ink droplets becomes a problem. In addition, since only a substrate having poor ink absorbency must be used, there is a problem that the drying load for removing the solvent component is extremely large.

JP 2002-117960 A Colorants, 75, (8), 394-400 (2002) "Prospects of UV inkjet technology"

An object of the present invention is to provide a UV curable ink composed of an aqueous medium and an inkjet recording method in which image bleeding, poor curing, and drying load are improved irrespective of using an aqueous medium-absorbing substrate. I do.

  As a result of intensive studies, the present inventors have found that the object of the present invention can be achieved by adopting the following constitution.

[1] In a recording method for recording on a substrate by inkjet using an ultraviolet curable ink containing at least a coloring material, an ultraviolet polymerizable substance, and a photopolymerization initiator in an aqueous medium, the ink is applied to the substrate. An ink-jet recording method, comprising irradiating an ultraviolet ray within a contact time after landing, wherein a liquid transfer amount of the ink to the substrate by a Bristow method is less than 20 ml / mm ² .

[2] The ink jet recording method according to [1], wherein the liquid transfer amount when the contact time between the base material and the ink is 2 seconds by the Bristow method is 20 ml / mm ² or more.

  [3] The ink jet recording method according to [1] or [2], further comprising a step of removing the aqueous medium after the ultraviolet curing.

  That is, by adopting the configuration as defined in [1], it is possible to obtain a high concentration by keeping the coloring material of the ink on the surface of the base material by irradiating ultraviolet rays during the contact time when the ink absorption does not completely occur. And sufficient curability can be obtained.

To this end, if the ink absorption speed of the base material is high, ultraviolet rays are radiated at an early timing after ink landing. The timing is within the contact time when the liquid transfer amount is less than 20 ml / mm ² . More preferably, the contact time is less than 10 ml / mm ² .

Further, it is preferable to irradiate ultraviolet rays at a timing when the liquid transfer amount becomes 5 ml / mm ² or more. Irradiation with ultraviolet light at a timing when the liquid transfer amount is less than 5 ml / mm ² may cause problems such as a failure to obtain a sufficient dot diameter and poor drying properties. If the substrate has a roughness index Kr (ml / mm ² ) of 5 ml / mm ² or more as measured by the Bristow method, ultraviolet light may be applied immediately after landing.

Further, as defined in [2], if the liquid transfer amount when the contact time between the base material and the ink by the Bristow method is 2 seconds is 20 ml / mm ² or more, the aqueous medium remaining after ultraviolet irradiation and ink curing is removed. Since the substrate can be absorbed, the drying load is greatly reduced, which is preferable. More preferably, it is 25 ml / mm ² or more.

  The amount of liquid transfer by the Bristow method can be measured by a Bristow tester (Bristow Tester) according to JAPAN TAPPI UM405. The measurement is performed under the conditions of 23 ° C. ± 1 ° C. and 50% ± 2% RH. The sample to be measured is one that has been adjusted to the measurement conditions for 2 hours or more.

That is, from [1] and [2], a substrate having a high ink absorbency but a low ink absorption rate is suitable as a substrate.

Furthermore, as described in [3], the strength of the formed image can be improved by removing the aqueous medium absorbed by the substrate by drying.

  According to the present invention, it is possible to provide an ink jet recording method in which image bleeding, poor curing, and drying load are improved irrespective of using a UV curable ink composed of an aqueous medium and an aqueous medium absorbing substrate.

[Ultraviolet curable ink]
The ultraviolet curable ink containing at least the coloring material, the ultraviolet polymerizable substance, and the photopolymerization initiator in the aqueous medium used in the present invention employs the constitution of the ink material described in JP-A-2000-117960 as it is. be able to.

  A typical ink composition is such that pigments such as Pigment Yellow 74, Pigment Red 122, Pigment Blue 15: 3, and Pigment Black 7 are dispersed in water as coloring materials, and the following water-soluble ultraviolet-polymerizable substances are used as the following “ Low-viscosity, high-reactivity, water-soluble compound shown in

In addition, the composition is a combination of a compound represented by the following Chemical Formula 2 as a water-soluble photopolymerization initiator.

  Further, in the present invention, the Bristow absorption rate with respect to the base material greatly affects the appropriate timing of ultraviolet irradiation. By appropriately adding various surfactants and water-soluble solvents to the ink, it is possible to control the absorption of the ink into the substrate.

〔Base material〕
The present invention irradiates ultraviolet rays within the contact time for absorbing ink of less than 20 ml / mm ² from the ink landing, but finally, the liquid transfer when the contact time between the base material and the ink by the Bristow method is 2 seconds. Preferably, the amount is at least 20 ml / mm ² . When the liquid transfer amount is less than 20 ml / mm 2, the drying load increases, and there is a possibility that a problem such as the semi-cured ink contaminating the conveying member may occur.

The time from landing to ultraviolet irradiation is within the contact time at which the liquid transfer amount is less than 5 to ²⁰ ml / mm ² , but in consideration of bleeding between inks, it is usually 0.01 to 5 seconds, more preferably, 0.01 to 2 seconds. That is, it is preferable that the absolute amount of ink absorption is large but the ink absorption speed is low.

  Specifically, it is preferable to use papers mainly composed of cellulose having a high absorbency for an aqueous medium and reduce the water permeability by sizing the papers. Art paper for printing, coated paper, matte paper, high-quality paper, lightly coated paper, copy paper, and a substrate surface-treated with an aqueous resin or fine particles can be used as appropriate.

  The absorption rate and the absorption amount of the ink and the substrate are adjusted by controlling the surface tension of the ink and the surface wettability, water resistance, and porosity of the substrate.

(UV irradiation)
In the printing system according to the present invention, the inkjet mechanism requires an ultraviolet irradiation device.

  As a typical example of the ultraviolet irradiation apparatus, the ultraviolet irradiation is applied to the recording paper exiting the print station from above or below, or both above and below. In the case of a transparent substrate, this can be done relatively easily.

The irradiation is performed during the contact time when the liquid transfer amount is less than 20 ml / mm ² . If irradiation is performed after a longer time, the ink permeates into the base material, resulting in a decrease in density and poor curing.

  The ultraviolet irradiation lamp is preferably a so-called low-pressure mercury lamp, a high-pressure mercury lamp, a mercury lamp coated with a phosphor, or the like in which the vapor pressure of mercury is 1 to 10 Pa during operation. The emission spectrum of these mercury lamps in the ultraviolet region is in the range of 184 to 450 nm, and is suitable for efficiently reacting a polymerizable substance in black or colored ink. In addition, since a small power supply can be used even when the power supply is mounted on the printer, it is also suitable in that sense. The mercury lamp includes a metal hydride lamp, a high-pressure mercury lamp, an ultra-high-pressure mercury lamp, a xenon flash lamp, a deep UV lamp, and the like. In addition, UV lasers, UV emission type LEDs, etc. have been put into practical use, and the emission wavelength range includes the above range. Therefore, if the power supply size, input intensity, lamp shape, etc. are permitted, they are basically applicable. is there. The light source is selected according to the sensitivity of the catalyst used.

  By fixing the ink with ultraviolet rays, good fixing, abrasion resistance, water resistance and the like can be obtained. At the same time, deformation such as curling of the paper itself is suppressed, which is preferable for handling and storage.

The required ultraviolet intensity is preferably about ² to 1000 mW / cm ² from the viewpoint of the polymerization rate. If the integrated irradiation amount is insufficient, the adhesion of the fixed ink to the recording paper will not be sufficient. Further, in color recording, there is a shortage in the robustness of a printed ink image, such as insufficient water resistance.

(Drying mechanism)
Preferably, the printing method of the present invention basically has the following steps.
(1) Step of printing on a base material by an ink jet printer (2) Step of irradiating ultraviolet rays to the base material to polymerize a polymerizable substance in the ink (3) Step of removing a solvent component in the base material ) May be before or after (2).

  However, as described above, when a water-soluble organic solvent having a relatively high volatility is used or when a water-soluble organic solvent is not used, the step (3) may be omitted. For the removal of the solvent component, a heating method such as a microwave oscillator, a far-infrared lamp, or the like can be employed.

  Next, embodiments of the present invention will be described in the form of examples, and typical configurations and effects of the present invention will be described. However, of course, embodiments of the present invention are not limited to these.

(1) Preparation of ink ・ Yellow ink formulation

*) Pigment Yellow 74 dispersion; Dispersant: water-soluble polyurethane resin ・ Magenta ink formulation

*) Pigment Red 122 dispersion; dispersant: water-soluble polyurethane resin ・ Cyan ink formulation

*) Pigment Blue 15: 3 dispersion; dispersant: water-soluble polyurethane resin-Black ink formulation

*) Pigment Black 7 dispersion; dispersant: water-soluble polyurethane resin (2) Substrate The following substrate was used.

Substrate 1: coated paper The ink 20 ml / mm ² to become time measured by the Bristow method using 1.25 seconds, the liquid transfer amount at a contact time of 2 seconds was 24 ml / mm ^2. In addition, the measurement of the liquid transfer amount by the Bristow method was carried out under the conditions of 23 ° C. ± 1 ° C., 50% ± 2% RH for 2 hours, and the Bristow tester (Bristow) was used under the same conditions in accordance with JAPAN TAPPI UM405. Tester).

Substrate 2: time satisfying 20 ml / mm ² as measured by high-quality paper Bristow method is 0.8 seconds, the liquid transfer amount at a contact time of 2 seconds was 28 ml / mm ^2. (Measurement conditions are the same as those for substrate 1.)

-Substrate 3: hydrophilic treated PET film A PET film having a hydrophilic resin applied to the surface thereof was produced. The time to be 20 ml / mm ² measured by the Bristow method was 2 seconds or more, and the liquid transfer amount at a contact time of 2 seconds was 15 ml / mm ² . (Measurement conditions are the same as those for substrate 1.)

(3) Inkjet recording Example 1
Using a piezo type ink jet recording apparatus, an image pattern in which primary colors and secondary colors of yellow (Y), magenta (M), cyan (C), and black (K) are arranged is recorded on a base material, and ultraviolet irradiation is performed. went.

The recording density is 720 dpi (dpi is the number of dots per 2.54 cm), the maximum solid adhesion amount per color is 20 ml / cm ² , the time from ink landing of each color to ultraviolet irradiation is within 1 second, and ultraviolet irradiation Was carried out with an SP5 light source (365 nm) manufactured by Ushio and illuminance of the recording surface at 1000 mW / cm ² .

Evaluation Criteria Ink Density 高 い: High density of solid part ×: Infiltration of ink into base material, blurring and low density bleeding ：: No bleeding between colors and smooth gradation.

Δ: Slight bleeding, part of the gradation is rough ×: Bleeding between colors, and the gradation is conspicuous Rough ○: Slightly smelling monomer odor ×: Lots of unreacted monomer and strong smell of monomer Drying ○ : Ink solidifies quickly after UV irradiation, and surface tack decreases. ×: Surface tack remains on the ink surface after UV irradiation. The results are shown below.

Ink density Bleed Odor Drying Base 1 ○ ○ ○ ○
Substrate 2 × △ × ○
Substrate 3 ○ △ ○ ×
Example 2
Image pattern recording was performed in the same manner as in Example 1, except that an ultraviolet irradiation device was arranged so as to reduce the time until ultraviolet irradiation to a maximum of 0.5 seconds, and evaluation was performed.

The results are shown below.
Ink density Bleed Odor Drying Base 1 ○ ○ ○ ○
Substrate 2 ○ ○ ○ ○
Substrate 3 ○ △ ○ ×
Example 3
Image pattern recording was performed in the same manner as in Example 1, except that the time until ultraviolet irradiation was set to a maximum of 1.5 seconds, and an ultraviolet irradiation device was arranged and evaluated.

The results are shown below.
Ink density Bleed Odor Drying Base 1 × △ × ○
Substrate 2 × △ × ○
Substrate 3 ○ × ○ ×
Example 4
Image pattern recording was performed in the same manner as in Example 1, except that an ultraviolet irradiation device was arranged so that the time until ultraviolet irradiation was 1.6 seconds at the maximum, and evaluation was performed.

The results are shown below.
Ink density Bleed Odor Drying Base 1 × △ × ○
Substrate 2 × △ × ○
Substrate 3 ○ × ○ ×
As is clear from the above evaluation results, as in the case of the base material 1 in Example 1 and the base materials 1 and 2 in Example 2, the base material was irradiated with ultraviolet rays within a contact time of less than 20 ml / m 2 in liquid transfer amount. It can be seen that all the characteristics are good.

Example 5
The recorded matter produced in Example 2 was dried with a far infrared heater. as a result,
The samples of the substrates 1 and 2 and the substrate 3 had improved image strength, and were not scratched by finger rubbing. However, since the liquid transfer amount of the base material 3 at a contact time of 2 seconds was rather small at 15 ml / mm ² , the image strength was not improved unless dried for a longer time.

Claims (3)

At least a coloring material in an aqueous medium, an ultraviolet-polymerizable substance, using an ultraviolet-curable ink containing a photopolymerization initiator, in a recording method for recording on a substrate by inkjet, the ink lands on the substrate An inkjet recording method comprising: irradiating an ultraviolet ray within a contact time when a liquid transfer amount of the ink to the substrate by the Bristow method is less than 20 ml / mm ² . ^2. The ink jet recording method according to claim 1, wherein the liquid transfer amount when the contact time between the base material and the ink by the Bristow method is 2 seconds is 20 ml / mm ² or more. 3. The ink jet recording method according to claim 1, further comprising a step of removing the aqueous medium after the ultraviolet curing.