JP7694571B2 - METHOD FOR PRODUCING PRINTED MATTER, PRINTING INK SET AND PRINTED MATTER - Google Patents

Description

The present invention relates to a method for producing printed matter, a printing ink set, and a printed matter using the same.

Lithographic printing is a printing method that is widely used as a system for producing printed materials at high speed, in large quantities, and at low cost. In recent years, in response to environmental issues, there has been a demand to reduce the volatile components contained in ink. For this reason, the use of active energy ray-curable inks, which do not contain volatile components and cure instantly when exposed to active energy rays, is being promoted. In addition to their environmental benefits, active energy ray-curable inks can shorten the drying process, thereby improving the productivity of lithographic printing.

In recent years, the diversification of packaging has created a demand for small-lot production, particularly for film-printed materials, and there has been a shift from gravure printing, which is expensive for small-lot production, to lithographic printing and flexographic printing. Lithographic printing allows the use of inks with higher viscosity than flexographic printing, and provides stronger adhesion to the film.

In packaging applications where film prints are preferably used, it is common to laminate another plastic film, metal foil, or heat-melting film (sealant) to the print in order to protect the contents and provide heat sealing properties. Depending on the contents, further sterilization treatment using hot water may also be performed. In these processes, the ink is prone to peeling, so even higher adhesion between the substrate and the ink is required.

When printing on a transparent substrate such as film printing, it is common to increase the hiding power by printing a white ink to make characters and patterns appear clearer. As a technology for increasing the hiding power of an ink, a printing ink for letterpress or lithographic printing that is cured by electron beams and has a coloring component content in the range of 20 to 70% by mass has been proposed (see, for example, Patent Document 1). In addition, a flexographic printing method using a specific anchor coating agent has been proposed as a printing method that can obtain printed matter with excellent whiteness and hiding power (see, for example, Patent Document 2).

JP 2004-123802 A JP 2015-134914 A

However, although the printing inks described in Patent Documents 1 and 2 have excellent hiding power, they still have the problem of being insufficient in terms of the high adhesion to substrates that is required in recent years for packaging applications and the like.

Therefore, the present invention aims to provide a method for producing printed matter and a printing ink set that can produce printed matter that has excellent adhesion to the substrate and hiding power.

The present invention relates to
(1) printing at least one lithographic printing black or chromatic ink and a lithographic printing white ink (a) on a substrate; and
(2) further printing a white printing ink (b) different from the white lithographic printing ink (a);
This is a method for producing a printed matter having the above items in this order.

The present invention also relates to a printing ink set comprising at least one type of lithographic printing black or chromatic ink, a lithographic printing white ink (a) and a printing white ink (b) different from the lithographic printing white ink (a).

The present invention also relates to a printed matter using the printing ink set of the present invention, which has a cured film of the white printing ink (b) on top of a cured film of the white lithographic printing ink (a).

The method for producing printed matter and the printing ink set of the present invention make it possible to obtain printed matter that has excellent adhesion to the substrate and hiding power.

First, as a first embodiment of the present invention, a method for producing a printed matter will be described.
(1) a step of printing at least one type of lithographic printing black or chromatic ink and a lithographic printing white ink (a) on a substrate (hereinafter, sometimes referred to as "step (1)"); and
(2) a step of further printing a white printing ink (b) different from the white lithographic printing ink (a) (hereinafter, this step may be referred to as "step (2)");
in that order.

Generally, the color of a printed matter is expressed using black ink and chromatic ink. Examples of chromatic ink include indigo ink, red ink, and yellow ink. Two or more of these may be used.

As mentioned above, it is common to print white ink to make characters and patterns look clearer, and it is preferable to print a pattern on the substrate using black ink and/or chromatic ink, and then print white ink over the entire surface. At this time, the white ink forms a film on the inks and chromatic inks in the areas where these inks are printed, and on the substrate in the areas where the black ink and chromatic inks are not printed. For this reason, the white ink is required to have both hiding power and adhesion to the substrate. Therefore, in the present invention, two different types of white ink are used, and in step (1), a lithographic printing white ink (a) that has excellent adhesion to the substrate is used, and in step (2), a printing white ink (b) different from the lithographic printing white ink (a) is used to improve hiding power.

When white printing ink (b) is printed on white lithographic printing ink (a), it is preferable to select an ink with excellent hiding power, since white printing ink (b) does not affect adhesion to the substrate.

Here, the white printing ink (b) in the present invention may be one having a different composition from the white lithographic printing ink (a), and may be, for example, a white lithographic printing ink having a different composition from the white lithographic printing ink (a), a white flexographic printing ink, a white gravure printing ink, or a white ink for inkjet printing. In the present invention, it is preferable to use the ink set of the present invention described below as the black or chromatic ink for lithographic printing, the white lithographic printing ink (a), and the white printing ink.

In step (1), at least one type of lithographic printing ink or chromatic ink and a white lithographic printing ink (a) are printed on a substrate.

Examples of substrates include art paper, coated paper, cast paper, synthetic paper, newsprint, plastic film, plastic film laminated paper, metal plate, metal-deposited paper, metal-deposited plastic film, etc. Two or more of these may be used.

Examples of plastic films include films made of polyethylene terephthalate, polyethylene, polyester, polyamide, polyimide, polystyrene, polypropylene, polycarbonate, polyvinyl acetal, etc.

Examples of plastic film laminated paper include paper with the aforementioned plastic film laminated on top.

Examples of metal plates include plates made of zinc, copper, etc.

Examples of metal-vapor-deposited paper and metal-vapor-deposited plastic films include paper or plastic film onto which the metal or its oxide is vapor-deposited.

Of these, plastic films, plastic film laminated paper, metal plates, metallized paper, and metallized plastic films do not absorb ink and therefore do not adhere to the ink due to ink absorption, so their adhesion to the ink tends to decrease. Therefore, they are suitable for use in the present invention, which has excellent adhesion between the ink and the substrate.

The substrate may be subjected to an easy-adhesion treatment. This can improve the transferability of the ink to the substrate and the adhesion between the substrate and the ink. Examples of easy-adhesion treatments include surface treatments such as primer application, corona discharge treatment, and plasma treatment.

As the white ink for lithographic printing (a), it is preferable to use the white ink for lithographic printing (a) in the ink set of the present invention described below.

The printing method in step (1) is preferably lithographic printing. Either water-based or waterless lithographic printing may be used.

Next, in step (2), white printing ink (b) is printed.

As the white ink for printing (b), a white ink for lithographic printing or a white ink for flexographic printing is preferred, and a white ink for flexographic printing is more preferred. A white ink for flexographic printing can be used for flexographic printing even if it has a low viscosity, and can further improve hiding power.

As the printing method in step (2), flexographic printing is preferred because it allows the use of white ink for flexographic printing, which has excellent hiding properties.

In addition, examples of the printing method in step (2) include a wet-on-wet printing method and a dry-on-wet printing method. Among these, the wet-on-wet printing method is preferably used from the viewpoint of productivity.

When a wet-on-wet printing method is adopted, from the viewpoint of suppressing migration of the components of the printing white ink (b) to the lithographic printing white ink (a) and further improving adhesion to the substrate, it is preferable to use, as the lithographic printing white ink (a) and the printing white ink (b), inks whose surface tension, tack value, viscosity, etc. are within the preferred ranges described below.

In step (2), it is preferable to print the white ink for printing (b) so that the thickness of the cured film is larger than the thickness of the cured film of the white ink for lithographic printing (a). The white ink for printing (b) is responsible for hiding properties, while the white ink for lithographic printing (a) improves adhesion to the substrate. Therefore, by increasing the thickness of the cured film of the white ink for printing (b), the hiding properties can be further improved. The difference between the thickness of the cured film of the white ink for lithographic printing (b) and the thickness of the cured film of the white ink for printing (a) is preferably 0.1 mm or more, more preferably 0.5 mm or more, and even more preferably 1.0 mm or more.

From the viewpoint of further improving adhesion to the substrate, the thickness of the cured film of the white ink (a) for lithographic printing is preferably 0.5 mm or more and 2.0 mm or less, more preferably 0.8 mm or more and 2.0 mm or less, and even more preferably 1.1 mm or more and 2.0 mm or less.

The thickness of the cured film of the printing white ink (b) is preferably 2.0 mm or more, more preferably 2.5 mm or more, and even more preferably 3.0 mm or more, from the viewpoint of further improving the hiding power. The thickness of the cured film of the printing white ink (b) is preferably 4.0 mm or less, and more preferably 3.1 mm or less, from the viewpoint of suppressing the migration of the components of the printing white ink (b) to the lithographic printing white ink (a) and further improving the adhesion to the substrate.

Here, the film thickness of the cured film of the lithographic printing white ink (a) and the cured film of the printing white ink (b) in the present invention can be calculated by measuring the thickness of each layer in the perpendicular direction to the print at five points by observing the cross section of the print under a scanning electron microscope, and averaging the measured values.

In the present invention, when at least one of the lithographic printing ink or chromatic ink, the lithographic printing white ink (a) and the printing white ink has the property of being cured by active energy rays, it is preferable to further include a step of irradiating the printed ink with active energy rays after step (2). By irradiating the printed ink with active energy rays, it is possible to instantly cure the printed ink, thereby improving productivity. Examples of active energy rays include ultraviolet rays and electron beams. From the viewpoint of further improving adhesion, electron beams are preferred. That is, in the present invention, it is preferable to further include a step (3) of irradiating an electron beam (hereinafter, sometimes referred to as "step (3)") after step (2). In step (3), an electron beam device having an energy beam of 10 kGy to 60 kGy is preferably used.

When step (3) is provided, from the viewpoint of suppressing migration of the components of the printing white ink (b) into the lithographic printing white ink (a), the time between printing the printing white ink (b) in step (2) and irradiating the electron beam in step (3) is preferably 6.0 seconds or less, more preferably 3.0 seconds or less, and even more preferably 2.0 seconds or less.

In the method for producing a printed matter of the present invention, the difference in surface tension between the lithographic printing white ink (a) and the printing white ink (b) is preferably 5 mN/m or more and 20 mN/m or less. By making the difference in surface tension 5 mN/m or more, the migration of the components of the printing white ink (b) to the interface with the substrate via the lithographic printing white ink (a) on the printed matter can be suppressed, and the adhesion to the substrate can be further improved. The difference in surface tension is more preferably 8 mN/m or more, and even more preferably 11 mN/m or more. On the other hand, by making the difference in surface tension 20 mN/m or less, the transferability of the printing white ink (b) onto the lithographic printing white ink (a) can be improved, the film thickness of the printing white ink (b) can be increased, and the concealing property can be further improved. The difference in surface tension is more preferably 17 mN/m or less, and even more preferably 14 mN/m or less. It is noted that it does not matter which of the lithographic printing white ink (a) and the printing white ink (b) has the higher surface tension.

The surface tension of the white ink for lithographic printing (a) is preferably 45 mN/m or more and 70 mN/m or less. By setting the surface tension to 45 mN/m or more, the ink is easily peeled off from the blanket, and the ink surface transferred to the substrate becomes smooth, thereby further improving the concealing properties. The surface tension of the white ink for lithographic printing (a) is more preferably 50 mN/m or more, and even more preferably 55 mN/m or more. On the other hand, by setting the surface tension to 70 mN/m or less, the transferability onto the substrate can be improved. The surface tension of the white ink for lithographic printing (a) is more preferably 65 mN/m or less, and even more preferably 60 mN/m or less.

The surface tension of the white ink for printing (b) can be appropriately selected so that the difference with the white ink for lithographic printing (a) is preferably within the range described above.

Here, the surface tension of the lithographic printing white ink (a) and the printing white ink (b) in the present invention can be calculated from the contact angle measured by the droplet method of an automatic contact angle meter. More specifically, the ink is first applied smoothly onto a glass substrate (beveled, cleaned) with a thickness of 1 mm x length of 50 mm x width of 50 mm, and then left to stand in a dark place for 30 minutes to make the ink surface smoother. After standing, droplets of pure water and ethylene glycol, whose surface tension values are known, are deposited on the ink using a syringe. The contact angle 30 seconds after deposition is measured using an automatic contact angle meter (Drop Master DM-501, manufactured by Kyowa Interface Science Co., Ltd.) under conditions of an air temperature of 25°C and a humidity of 50%.

Next, a method for calculating the surface tension from the contact angle will be described. Generally, the surface tension γ is decomposed into a non-polar dispersion force component ^γd and a polar hydrogen bond dispersion force component ^γh as shown in the following formula (1).
γ=γ ^d + γ ^h (1)
When a drop of solution B is deposited on substance A, Young's equation shown in the following formula (2) holds for substance A and solution B. In the following formula (2), the surface tension of substance A is denoted as γ _A , the surface tension of solution B is denoted as γ _B , the surface tension between substance A and solution B is denoted as γ _A-B , and the contact angle between substance A and solution B is denoted as θ _A-B .
γ _A = γ _AB + γ _B cosθ _AB (2)
Furthermore, regarding the surface tension between a substance A and a solution B, an extended Fowkes model shown in the following formula (3) has been proposed.

When ink is used as substance A, and pure water and ethylene glycol are used as solution B, the following formulas (4) to (5) can be derived from the above formulas (1) to (3). In formulas (4) to (5), the surface tension, non-polar dispersion force component, and polar hydrogen bonding dispersion force component of ethylene glycol are E, E(d), and E(h), respectively; the polar hydrogen bonding dispersion force component of the surface tension γ _I of the ink is I(h); the surface tension, non-polar dispersion force component, and polar hydrogen bonding dispersion force component of pure water are W, W(d), and W(h), respectively; the contact angle between the ink and ethylene glycol is α; and the contact angle between the ink and pure water is β. In formulas (4) to (5), the values of the dispersion force components γ ^d and γ ^h are each equal to or greater than 0.

From the measured values of the contact angle θ _I-EG between the ink and ethylene glycol and the contact angle θ _I-W between the ink and pure water, the surface tension of the ink can be calculated using formulas (1), (4), and (5). The surface tension of pure water is γ 72.8 mN/m, the nonpolar dispersion force component γ ^d is 21.8 mN/m, and the polar hydrogen bond dispersion force component γ ^h is 51.0 mN/m, while the surface tension of ethylene glycol is γ 48.8 mN/m, the nonpolar dispersion force component γ ^d is 32.8 mN/m, and the polar hydrogen bond dispersion force component γ ^h is 16.0 mN/m.

In the method for producing a printed matter of the present invention, the difference (A)-(B) between the tack value (A) of the lithographic printing white ink (a) and the tack value (B) of the printing white ink (b) is preferably 2.0 or more and 5.0 or less. The tack value is an index of the adhesion of the ink, and the higher the tack value, the higher the adhesion of the ink. By making the tack value of the printing white ink (b) greater than the tack value (A) of the lithographic printing white ink (a) and making the difference (A)-(B) 2.0 or more, the phenomenon called reverse trapping, in which the underlayer white ink printed on the substrate is peeled off by the later-printed white ink and the film thickness of the underlayer white ink and the later-printed white ink becomes smaller, can be suppressed, and the hiding rate can be further improved. (A)-(B) is more preferably 2.5 or more, and even more preferably 3.0 or more. On the other hand, by making (A)-(B) 5.0 or less, (B) can be kept appropriately large, and the transferability can be increased by the cohesive force of the ink, the film thickness of the printing white ink (b) can be increased, and the hiding power can be further improved. (A)-(B) is more preferably 4.5 or less, and even more preferably 4.0 or less.

The tack value (A) of the lithographic printing white ink (a) is preferably 3.0 or more and 8.0 or less. By making the tack value (A) 3.0 or more, the transferability can be improved by the cohesive force of the ink, and the transferability of the printing white ink (b) onto the lithographic printing white ink (a) can be improved, thereby further improving the concealing ability. (A) is more preferably 4.5 or more, and even more preferably 6.0 or more. On the other hand, by making the tack value (A) 8.0 or less, the transferability to the substrate can be improved, and the concealing ability can be further improved. (A) is more preferably 7.5 or less, and even more preferably 7.0 or less.

The tack value (B) of the white ink for printing (b) is preferably 1.0 or more and 6.0 or less. By making (B) 1.0 or more, the cohesive force of the ink can be used to increase the transferability and further improve the hiding power. (B) is more preferably 1.5 or more, and even more preferably 2.0 or more. On the other hand, by making the tack value (B) 6.0 or less, the transferability onto the white ink for lithographic printing (a) can be increased and the hiding power can be further improved. (B) is more preferably 4.0 or less, and even more preferably 3.0 or less.

Here, the tack value of the lithographic printing white ink (a) and the printing white ink (b) of the present invention can be measured for 1.31 ml of ink weighed with an ink pipette using an ink meter (having a metal roll of 76.2 mm diameter, a top roll made of EPDM rubber with a Shore A hardness of 70° and a diameter of 79.3 mm, and a vibration roll made of EPDM rubber with a Shore A hardness of 60° and a diameter of 50.8 mm, "INKO-GRAPH" TYPE V manufactured by Tester Sangyo Co., Ltd.) at a rotation speed of 400 rpm and a temperature of 38°C. The rotation speed and temperature conditions are those that mimic the typical environment (temperature, shear rate) of the ink during printing. However, the measured value 1 minute after the start of the measurement is regarded as the tack value in the present invention.

In the method for producing a printed matter of the present invention, the difference (C)-(D) between the viscosity (C) of the lithographic printing white ink (a) and the viscosity (D) of the printing white ink (b) is preferably 5 Pa·s or more and 30 Pa·s or less. By making the viscosity difference (C)-(D) 5 Pa·s or more, migration of the components of the printing white ink (b) to the substrate interface via the lithographic printing white ink (a) on the printed matter can be suppressed, and adhesion to the substrate can be further improved. The viscosity difference is more preferably 15 Pa·s or more, and even more preferably 20 Pa·s or more. On the other hand, by making the viscosity difference (C)-(D) 30 Pa·s or less, the viscosity of the lithographic printing white ink (a) can be appropriately suppressed, the transferability of the lithographic printing white ink (a) onto the substrate can be enhanced, and the film thickness of the lithographic printing white ink (a) can be increased to suppress the migration of the components of the printing white ink (b) to the substrate interface via the lithographic printing white ink (a), thereby further improving the adhesion to the substrate. A viscosity difference of 25 Pa·s or less is more preferable.

The viscosity (C) of the white ink (a) for lithographic printing is preferably 15 Pa·s or more and 40 Pa·s or less. By making (C) 15 Pa·s or more, the cohesive force of the ink can be used to increase the transferability and further improve the concealing property. In addition, the migration of the components of the white ink (b) for printing to the substrate interface via the white ink (a) for lithographic printing can be suppressed, and the adhesion to the substrate can be further improved. (C) is more preferably 20 Pa·s or more. On the other hand, by making the viscosity (C) 40 Pa·s or less, the transferability to the substrate can be increased and the concealing property can be further improved. In addition, the migration of the components of the white ink (b) for printing to the substrate interface via the white ink (a) for lithographic printing can be suppressed, and the adhesion to the substrate can be further improved. (C) is more preferably 30 Pa·s or less, and even more preferably 25 Pa·s or less.

The viscosity (D) of the printing white ink (b) is preferably 0.1 Pa·s or more and 20 Pa·s or less. By making (D) 0.1 Pa·s or more, the transferability can be increased by the cohesive force of the ink, and the hiding power can be further improved. On the other hand, by making the viscosity (D) 20 Pa·s or less, the transferability onto the lithographic printing white ink (a) can be increased, and the hiding power can be further improved, and the migration of the components of the printing white ink (b) to the substrate interface via the lithographic printing white ink (a) can be suppressed, and the adhesion to the substrate can be further improved. (D) is more preferably 10 Pa·s or less, and even more preferably 5 Pa·s or less.

Here, the viscosity of the lithographic printing white ink (a) and printing white ink (b) in the present invention can be measured using a cone-plate type rotational viscometer equipped with a cone plate (cone angle 1°, φ=40 mm) at a temperature of 35°C and a rotation speed of 70 rpm for 0.35 ml of ink weighed with an ink pipette. These rotation speed and temperature conditions mimic the typical environment (temperature, shear rate) of the ink during printing.

As a combination of lithographic printing white ink (a) and printing white ink (b) that satisfies the above-mentioned characteristics, it is preferable to use the lithographic printing white ink (a) and printing white ink (b) in the ink set of the present invention described below.

Next, as a second embodiment of the present invention, the printing ink set of the present invention will be described. The printing ink set of the present invention contains at least one type of lithographic printing black or chromatic ink, a lithographic printing white ink (a), and a printing white ink (b) different from the lithographic printing white ink (a). As in the first embodiment, the printing white ink (b) in the present invention may have a different composition from the lithographic printing white ink (a).

It is preferable that the lithographic printing ink or chromatic ink, the lithographic printing white ink (a) and the printing white ink (b) each contain a resin, a polyfunctional (meth)acrylate, a pigment and a surfactant. Here, "(meth)acrylate" is a general term for acrylate and methacrylate. Examples of the lithographic printing ink or chromatic ink containing these include the inks described in paragraphs [0037] to [0090] of WO 2018/062108. Among these, examples of the lithographic printing white ink (a) include the inks described in International Publication No. 2018/062108, paragraphs [0037], [0039], [0041], [0043] to [0049], [0052], [0053], [0055], [0056], [0062] to [0066], and [0069 to 0090]. Examples of the printing white ink (b) include the inks described in International Publication No. 2018/062108, paragraphs [0037], [0039], [0041], [0043] to [0049], [0053], [0055], [0056], [0062] to [0066], and [0069 to 0090]. Among these, examples of combinations of lithographic printing inks or chromatic inks include the ink sets described in paragraphs [0095] to [0157] of WO 2018/062108. As the white printing ink (b), a white ink for flexographic printing is preferable.

In the ink set of the present invention, the difference in surface tension between the lithographic printing white ink (a) and the printing white ink (b), the tack value (A) of the lithographic printing white ink (a) and the tack value (B) of the printing white ink (b) and the difference (A) - (B), and the viscosity (C) of the lithographic printing white ink (a) and the viscosity (D) of the printing white ink (b) and the difference (C) - (D) are preferably within the ranges described in the first embodiment. In order to bring these properties into the above-mentioned preferred ranges, the lithographic printing white ink (a) preferably contains a resin having a hydrophilic group, a polyfunctional (meth)acrylate having a hydrophilic group, a polyfunctional (meth)acrylate not having a hydrophilic group, a pigment, and a surfactant. In addition, the printing white ink (b) preferably contains a resin having a hydrophilic group, a polyfunctional (meth)acrylate having a hydrophilic group, a (meth)acrylate having an aliphatic skeleton having 6 to 18 carbon atoms, a pigment, and a surfactant.

Here, examples of hydrophilic groups include hydroxyl groups, amino groups, mercapto groups, carboxyl groups, sulfo groups, and phosphate groups. Two or more of these may be used.

In addition, as the (meth)acrylate having an aliphatic skeleton having 6 to 18 carbon atoms, those having no hydrophilic group are preferred, for example, hexyl (meth)acrylate, octyl (meth)acrylate, nonyl (meth)acrylate, dodecyl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,7-heptanediol di(meth)acrylate, 1,8-octanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, 1,11-undecanediol di(meth)acrylate, 1,1 Examples of such di(meth)acrylates include 2-dodecanediol di(meth)acrylate, 1,13-tridecanediol di(meth)acrylate, 1,14-tetradecanediol di(meth)acrylate, 1,15-pentadecanediol di(meth)acrylate, 1,16-hexadecanediol di(meth)acrylate, 1,17-heptadecanediol di(meth)acrylate, 1,18-octadecanediol di(meth)acrylate, 4-methyl-1,10-decanediol di(meth)acrylate, 4-ethyl-1,10-decanediol di(meth)acrylate, and polyester di(meth)acrylates having an aliphatic skeleton having from 6 to 18 carbon atoms as a repeating unit.

Resins having hydrophilic groups and polyfunctional (meth)acrylates having hydrophilic groups affect the surface tension of the ink, and the more hydrophilic groups there are, the greater the surface tension tends to be. In addition, the interaction between hydrophilic groups affects the tack and viscosity of the ink, and the more hydrophilic groups there are, the greater the tack value and viscosity tends to be. Carboxyl groups are preferred as hydrophilic groups, as they have excellent pigment dispersibility and the aforementioned properties can be easily adjusted to the desired range.

On the other hand, the use of a polyfunctional (meth)acrylate that does not have a hydrophilic group maintains an appropriate content of the resin having a hydrophilic group and the polyfunctional (meth)acrylate having a hydrophilic group in the ink, making it easier to adjust the surface tension, tack value and viscosity to the desired range.

Examples of pigments include titanium dioxide, calcium carbonate, barium sulfate, and alumina white. Two or more of these may be used. Of these, titanium dioxide is preferred because it has better hiding power. Titanium dioxide is basic, but from the viewpoint of dispersing titanium dioxide well in the ink, it is preferred to include a polymeric surfactant as a surfactant in order to adjust the surface tension to the preferred range described above.

We will explain the preferred aspects of white ink (a) for lithographic printing.

In order to adjust the surface tension, tack value (A) and viscosity (C) to the above-mentioned preferred ranges, the acid value of the resin having a hydrophilic group is preferably 75 mgKOH/g or more and 150 mgKOH/g or less, the weight average molecular weight of the resin having a hydrophilic group is preferably 15,000 or more and 50,000 or less, and the content of the resin having a hydrophilic group in the lithographic printing white ink (a) is preferably 5% by mass or more and 10% by mass or less. In particular, in order to adjust the tack value (A) and viscosity (C) to the above-mentioned preferred ranges, the content of the resin having a hydrophilic group is more preferably 6.5% by mass or more and 9.5% by mass or less.

In order to adjust the surface tension, tack value (A) and viscosity (C) to the above-mentioned preferred ranges, the hydroxyl value of the polyfunctional (meth)acrylate having a hydrophilic group is preferably 80 mg KOH/g or more and 130 mg KOH/g or less, and the content of the polyfunctional (meth)acrylate having a hydrophilic group in the white ink for lithographic printing (a) is preferably 20% by mass or more and 45% by mass or less. In particular, in order to adjust the surface tension to the above-mentioned preferred ranges, the content of the polyfunctional (meth)acrylate having a hydrophilic group in the white ink for lithographic printing (a) is more preferably 27% by mass or more and 40% by mass or less.

In order to adjust the surface tension, tack value (A) and viscosity (C) to the above-mentioned preferred ranges, the content of the polyfunctional (meth)acrylate not having a hydrophilic group in the white ink for lithographic printing (a) is preferably 5% by mass or more and 25% by mass or less. In particular, in order to adjust the surface tension to the above-mentioned preferred ranges, the content of the polyfunctional (meth)acrylate not having a hydrophilic group in the white ink for lithographic printing (a) is more preferably 10% by mass or more and 20% by mass or less.

The content of polymeric surfactant in the white ink (a) for lithographic printing is preferably 0.6% by mass or more and 1.5% by mass or less, from the viewpoint of easily adjusting the surface tension to the preferred range mentioned above.

Next, preferred aspects of printing ink (b) will be described.

In order to adjust the tack value (B) and viscosity (D) to the aforementioned preferred ranges, the acid value of the resin having a hydrophilic group is preferably 50 mg KOH/g or more and 120 mg KOH/g or less, the weight average molecular weight of the resin having a hydrophilic group is preferably 5,000 or more and 40,000 or less, and the content of the resin having a hydrophilic group in the printing white ink (b) is preferably 2% by mass or more and 5% by mass or less. In particular, in order to adjust the tack value (B) to the aforementioned preferred ranges, the content of the resin having a hydrophilic group in the printing ink (b) is more preferably 2.5% by mass or more and 4.5% by mass or less.

In order to adjust the surface tension, tack value (B) and viscosity (D) to the aforementioned preferred ranges, the hydroxyl value of the polyfunctional (meth)acrylate having a hydrophilic group is preferably 5 mg KOH/g or more and 130 mg KOH/g or less, and the content of the polyfunctional (meth)acrylate having a hydrophilic group in the printing white ink (b) is preferably 20% by mass or more and 45% by mass or less.

In order to adjust the tack value (B) and viscosity (D) to the aforementioned preferred ranges, it is preferable to contain a (meth)acrylate having an aliphatic skeleton with 6 to 18 carbon atoms, and the content of the (meth)acrylate having an aliphatic skeleton with 6 to 18 carbon atoms in the printing white ink (b) is preferably 3% by mass or more and 20% by mass or less.

The content of polymeric surfactant in the printing white ink (b) is preferably 1.7% by mass or more and 3.0% by mass or less.

From the viewpoint of productivity of printed matter, it is preferable that in the printing ink set of the present invention, at least one of the lithographic printing black or chromatic ink, the lithographic printing white ink (a) and the printing white ink (b) is an electron beam curable ink that is cured by electron beam irradiation. It is more preferable that all of these inks are electron beam curable inks. If the ink set contains the aforementioned multifunctional (meth)acrylate, it can be cured by electron beam irradiation.

The printed matter of the present invention is a printed matter using the printing ink set, and has a cured film of white printing ink (b) on top of a cured film of white lithographic printing ink (a).

As in the first embodiment described above, in the printed matter of the present invention, the thickness of the cured film of the white ink for printing (b) is preferably greater than the thickness of the cured film of the white ink for lithographic printing (a). In the printed matter of the present invention, the difference between the thickness of the cured film of the white ink for lithographic printing (b) and the thickness of the cured film of the white ink for printing (a) is preferably 0.1 mm or more, more preferably 0.5 mm or more, and even more preferably 1.0 mm or more.

The thickness of the cured film of the lithographic printing white ink (a) in the printed matter of the present invention is preferably 0.5 mm or more and 2.0 mm or less, more preferably 0.8 mm or more and 2.0 mm or less, and even more preferably 1.1 mm or more and 2.0 mm or less, from the viewpoint of further improving adhesion to the substrate.

The thickness of the cured film of the printing white ink (b) in the printed matter of the present invention is preferably 2.0 mm or more, more preferably 2.5 mm or more, and even more preferably 3.0 mm or more, from the viewpoint of further improving the concealing property. The thickness of the cured film of the printing white ink (b) is preferably 4.0 mm or less, and more preferably 3.1 mm or less, from the viewpoint of suppressing the migration of the components of the printing white ink (b) to the lithographic printing white ink (a) and further improving the adhesion to the substrate.

The present invention will be described in detail below with reference to examples. However, the present invention is not limited to these examples.

<Ink raw materials>
Resin: A copolymer consisting of 25% by mass of methyl methacrylate, 25% by mass of styrene, and 50% by mass of methacrylic acid was subjected to an addition reaction with 0.55 equivalents of glycidyl methacrylate relative to the carboxyl groups of the copolymer to obtain Resin 1 having an ethylenically unsaturated group and a hydrophilic group. The obtained Resin 1 had a weight average molecular weight of 34,000, an acid value of 105 mgKOH/g, and an iodine value of 2.0 mol/kg.
(Meth)acrylate 1: a mixture of pentaerythritol triacrylate and pentaerythritol tetraacrylate (manufactured by MIWON Corporation, "Miramer" (registered trademark) M340), hydroxyl value 115 mg KOH/g
(Meth)acrylate 2: Tricyclodecane dimethanol diacrylate (manufactured by Daicel Allnex Corporation, EBECRYL 130), hydroxyl value 0 mgKOH/g
(Meth)acrylate 3: 1,10-decanediol diacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., NK Ester A-DOD-N), hydroxyl value 0 mgKOH/g
(Meth)acrylate 4: Trimethylolpropane EO modified triacrylate (manufactured by MIWON Corporation, "Miramer" (registered trademark) M3130), hydroxyl value 10 mg KOH/g
(Meth)acrylate 5: Stearyl acrylate (manufactured by MIWON Corporation, "Miramer" (registered trademark) M180), hydroxyl value 0 mg KOH/g
Pigment 1: Carbon black MA8 (manufactured by Mitsubishi Chemical Corporation)
Pigment 2: Seikacyanine Blue 4920 (manufactured by Dainichi Seika Chemicals Co., Ltd.)
Pigment 3: Carmine 6B 1483LT (manufactured by Dainichi Seika Chemicals Co., Ltd.)
Pigment 4: Fast Yellow 2300 (manufactured by Dainichi Seika Chemicals Co., Ltd.)
Pigment 5: "Tipake" (registered trademark) CR58-2 (manufactured by Ishihara Sangyo Kaisha, Ltd.)
Surfactant 1: "Disperbyk" (registered trademark) 2013 (manufactured by ALTANA)
Surfactant 2: "Solsperse" (registered trademark) 54000 (manufactured by Lubrizol), a polymeric surfactant. Surfactant 3: "Solsperse" (registered trademark) 3000 (manufactured by Lubrizol), a polymeric surfactant.

<Analysis method for ink raw materials>
(1) Weight average molecular weight A diluted solution was prepared by diluting the resin with tetrahydrofuran to a concentration of 0.25% by mass, and the diluted solution was stirred for 5 minutes at a rotation speed of 100 rpm using a mix rotor (MIX-ROTAR VMR-5, manufactured by AS ONE Corporation) to dissolve the resin, and the solution was filtered using a 0.2 μm filter (Z227536-100EA, manufactured by SIGMA Corporation). The weight average molecular weight of the resin was measured using the obtained filtrate by gel permeation chromatography (GPC) using tetrahydrofuran as the mobile phase.

Measurements were performed using an HLC-8220 (Tosoh Corporation) GPC column connected in the following order: TSKgel Super HM-H (Tosoh Corporation), TSKgel Super HM-H (Tosoh Corporation), and TSKgel Super H2000 (Tosoh Corporation), with RI detection. A calibration curve was created using polystyrene standard material. Measurement conditions were: injection volume 10 μL, analysis time 30 minutes, flow rate 0.4 mL/min, and column temperature 40°C.

(2) Acid Value The acid value of the resin was measured by the method described in the neutralization titration method in Section 3.1 of the test method of JIS K 0070:1992.

(3) Iodine Value The iodine value of the resin was measured according to the method described in JIS K 0070:1992, test method, section 6.0.

(4) Hydroxyl Value The hydroxyl value of the (meth)acrylate was measured by the neutralization titration method described in JIS K 0070:1992, test method, section 7.1.

<Evaluation method>
(1) Surface tension The inks used in the examples and comparative examples were applied to a glass substrate (beveled, cleaned, manufactured by Ishida Rika Co., Ltd.) measuring 1 mm thick × 50 mm long × 50 mm wide, and then allowed to stand in a dark place for 30 minutes to smooth the ink surface. Droplets of pure water and ethylene glycol, which have known surface tension values, were deposited on the ink after standing using a syringe, and the contact angle 30 seconds after deposition was measured using an automatic contact angle meter (Drop Master DM-501, manufactured by Kyowa Interface Science Co., Ltd.) under conditions of an air temperature of 25°C and a humidity of 50%.

Next, the surface tension γ _I of the ink was calculated from the contact angle using formulas (1), (4) and (5).
γ=γ ^d + γ ^h (1)

The surface tension γ of pure water is 72.8 mN/m, the nonpolar dispersion force component ^γd is 21.8 mN/m, and the polar hydrogen bonding dispersion force component ^γh is 51.0 mN/m. The surface tension γ of ethylene glycol is 48.8 mN/m, the nonpolar dispersion force component ^γd is 32.8 mN/m, and the polar hydrogen bonding dispersion force component ^γh is 16.0 mN/m.

(2) Tack value 1.31 ml of the ink used in each Example and Comparative Example was weighed out using an ink pipette, and the tack value was measured using an ink meter (having a metal roll of 76.2 mm in diameter, a top roll made of EPDM rubber with a Shore A hardness of 70° and a diameter of 79.3 mm, and a vibration roll made of EPDM rubber with a Shore A hardness of 60° and a diameter of 50.8 mm, "INKO-GRAPH" TYPE V manufactured by Tester Sangyo Co., Ltd.) at a rotation speed of 400 rpm and a temperature of 38° C. The measured value 1 minute after the start of the measurement was taken as the tack value in the present invention.

(3) Viscosity 0.35 ml of the ink used in each of the Examples and Comparative Examples was weighed out using an ink pipette, and the viscosity was measured at a temperature of 35° C. and a rotational speed of 70 rpm using a cone-plate type rotational viscometer rheometer (MCR301, manufactured by Anton Paar) equipped with a cone plate (cone angle 1°, φ=40 mm).

(4) Film Thickness The cross-sections of the prints obtained in each of the Examples and Comparative Examples were magnified and observed using a scanning electron microscope (S-5500, Hitachi High-Technologies Corporation), and the thickness of each layer in the perpendicular direction to the print was measured at five random locations, and the average value was taken as the film thickness.

(5) Concealment The concealment rate of the printed matter obtained in each Example and Comparative Example, which was printed with only white ink, was measured from the substrate surface in a concealment rate measurement mode using a densitometer (xEact Basic, manufactured by X-rite Corporation). It was determined that a concealment rate of less than 60% meant insufficient concealment, 60% or more but less than 65% meant slightly good concealment, 65% or more but less than 70% meant good concealment, and 70% or more meant extremely good concealment.

(6) Adhesion Among the printed matter obtained in each Example and Comparative Example, a mixture of "Takelac" (registered trademark) A-626 (manufactured by Mitsui Chemicals, Inc.) and "Takenate" (registered trademark) A-50 (manufactured by Mitsui Chemicals, Inc.) in a mass ratio of 8/1 was applied as an adhesive on the cured film of the ink in the area where only white ink was printed by a bar coat method. At this time, the coating amount was adjusted to be 4.0 g/m ² after drying at 80 ° C. for 1 minute. The printed matter coated with the adhesive and a non-oriented polypropylene film "Treyfan" (registered trademark) ZK207 (manufactured by Toray Industries, Inc., thickness 70 μm) as a sealant were laminated using a hand roller, and then aged at 40 ° C. for 72 hours to obtain a film laminate of sealant / adhesive / cured ink film / polyester film.

A piece measuring 15 mm wide and 50 mm long was cut from the film laminate, and the peel strength between the polyester film and sealant was measured using a Tensilon universal material testing machine (manufactured by A&D, model number "RTG-1210") by the 90-degree T-type peel method (JIS K 6854-3:1999), and the value at the first maximum point was taken as the laminate peel strength. The peel strength was measured under conditions of an air temperature of 25°C, humidity of 50%, and a test speed of 300 mm/min.

It was determined that a peel strength of less than 1.0 N/15 mm indicated insufficient adhesion, that a peel strength of 1.0 N/15 mm or more but less than 2.0 N/15 mm indicated somewhat good adhesion, that a peel strength of 2.0 N/15 mm or more but less than 3.0 N/15 mm indicated good adhesion, and that a peel strength of 3.0 N/15 mm or more indicated extremely good adhesion.

<Preparation of black or chromatic ink for lithographic printing>
In the "Type of Ink" section of Table 1, "Lithographic" means ink for lithographic printing, and "Flexographic" means ink for flexographic printing.

The resin and (meth)acrylate shown for each ink or chromatic color in Table 1 were weighed out, and heated at 95°C for 390 minutes while stirring at 500 rpm using a dispersing blade to obtain a varnish.

The resulting varnish was added with the ink or chromatic pigments and surfactants shown in Table 1, and passed five times at a gap of 1 using a three-roll mill "EXAKT" (registered trademark) M-80S (manufactured by EXAKT) to obtain an ink for lithographic printing.

[Example 1]
<Preparation of white ink>
In Table 1, "first layer white" refers to the white ink printed in the first layer, and "second layer white" refers to the white ink printed in the second layer.

The resin and (meth)acrylate shown in the first white layer in Table 1 were weighed out and heated at 95°C for 390 minutes while stirring at 500 rpm using a disperser blade to obtain a varnish. The pigment and surfactant shown in Table 1 were added to the obtained varnish, and the mixture was passed five times at a gap of 1 using a triple roll mill "EXAKT" (registered trademark) M-80S (manufactured by EXAKT) to obtain a white ink for lithographic printing.

The resin and (meth)acrylate shown in the second white layer in Table 1 were weighed out and heated at 95°C for 390 minutes while stirring at 500 rpm using a disperser blade to obtain a varnish. The pigment and surfactant shown in Table 1 were added to the obtained varnish and dispersed using an Eiger mill (using zirconia beads with a diameter of 0.5 mm as the media) to obtain a white ink for flexographic printing.

<Production of printed matter>
A lithographic and flexographic hybrid printing machine (CI-8, COMEXI) was used, with a waterless lithographic printing plate (TAN-E, Toray Industries, Inc.) placed on the first to fifth cylinders and a flexographic printing plate (Cyrel (registered trademark) EASY FAST EFX, DuPont) placed on the eighth cylinder, and lithographic printing inks (black, indigo, red, yellow, first layer white, and second layer white) were placed on the first to fifth and eighth cylinders, respectively. On a polyester film PTM12 (manufactured by Unitika Ltd., thickness 12 μm) as a substrate, printing was performed at a speed of 100 m/min using a blanket T414 (manufactured by Kinyosha, thickness 1.95 mm) by wet-on-wet printing method under the conditions of ink feed rate: 50%, chiller temperature setting for impression cylinder: 30° C., chiller temperature setting for oscillating roller and ink fountain: 28° C. After printing of all the inks, the inks were cured by irradiating with electron beams of 110 kV and 40 kGy using an electron beam irradiation device attached to the printing press to obtain a printed matter. At this time, the image was configured so that the printed matter had a portion where only the lithographic printing white ink (a) as the first layer and the printing white ink (b) as the second layer were printed on the substrate.

The results of evaluation of each ink and the resulting prints using the methods described above are shown in Table 1. The hiding power and adhesion were extremely good.

[Examples 2 to 4]
<Preparation of white ink>
A white ink for lithographic printing and a white ink for flexographic printing were obtained in the same manner as in Example 1, except that the composition of the white ink for the first layer was changed as shown in Table 1.

<Production of printed matter>
A printed matter was obtained in the same manner as in Example 1, except that the white ink for the first layer shown in Table 1 was used.

The results of evaluation of each ink and the resulting prints using the methods described above are shown in Table 1.

[Example 5]
<Preparation of white ink>
A white ink for lithographic printing and a white ink for flexographic printing were obtained in the same manner as in Example 1, except that the composition of the white ink for the second layer was changed as shown in Table 2.

<Production of printed matter>
A printed matter was obtained in the same manner as in Example 1, except that the second layer white ink shown in Table 2 was used.

The results of evaluation of each ink and the resulting prints using the methods described above are shown in Table 2.

[Example 6]
<Preparation of white ink>
A white ink for lithographic printing and a white ink for flexographic printing were obtained in the same manner as in Example 1, except that the composition of the white ink for the first layer was changed as shown in Table 2.

<Production of printed matter>
A printed matter was obtained in the same manner as in Example 1, except that the white ink for the first layer shown in Table 2 was used.

The results of evaluation of each ink and the resulting prints using the methods described above are shown in Table 2.

[Comparative Example 1]
<Production of printed matter>
A waterless lithographic printing plate (TAN-E, Toray Industries, Inc.) was placed on the first to sixth cylinders, and prints were obtained in the same manner as in Example 1, except that lithographic printing inks (black, indigo, red, yellow, first layer white, and second layer white) were placed on the first to sixth cylinders, respectively, in that order.

The results of evaluation of each ink and the resulting prints using the above-mentioned method are shown in Table 2. Comparative Example 1, in which a lithographic printing white ink of the same composition was used for the first and second white layers, had insufficient hiding power.

[Comparative Example 2]
A waterless lithographic printing plate (TAN-E, manufactured by Toray Industries, Inc.) was placed on the first to fourth cylinders, a flexographic printing plate ("Cyrel" (registered trademark) EASY FAST EFX, manufactured by DuPont) was placed on the eighth cylinder, and lithographic printing inks, indigo blue, red, yellow, and first layer white were placed on the first to fourth and eighth cylinders, respectively, in that order, and a print was obtained in the same manner as in Example 1, except that an image was constructed so that there were areas in the print where only the white ink for flexographic printing was printed on the substrate.

The results of evaluation of each ink and the resulting prints using the above-mentioned method are shown in Table 2. Comparative Example 2, in which only white ink for flexographic printing was used as the first white layer, showed insufficient adhesion.

Claims (15)

(1) printing at least one lithographic printing black or chromatic ink and a lithographic printing white ink (a) on a substrate; and
(2) further printing a white printing ink (b) different from the white lithographic printing ink (a);
in that order ,
the difference (C)-(D) between the viscosity (C) of the lithographic printing white ink (a) and the viscosity (D) of the printing white ink (b) is 5 Pa·s or more and 30 Pa·s or less;
A method for producing printed matter. The method for producing a printed matter according to claim 1, wherein the white printing ink (b) is a white flexographic printing ink. The method for producing a printed matter according to claim 1 or 2, wherein the difference in surface tension between the lithographic printing white ink (a) and the printing white ink (b) is 5 mN/m or more and 20 mN/m or less. 3. The method for producing a printed matter according to claim 1, wherein a difference (A) - (B) between a tack value (A) of the lithographic printing white ink (a) and a tack value (B) of the printing white ink (b) is 2.0 or more and 5.0 or less. 3. The method for producing a printed matter according to claim 1, wherein printing is performed so that the thickness of the cured film of the printing white ink (b) is greater than the thickness of the cured film of the lithographic printing white ink (a ) . 6. The method for producing a printed matter according to claim 5 , wherein printing is performed so that the thickness of the cured film of the lithographic printing white ink (a) is 0.5 μm or more and 2.0 μm or less, and the thickness of the cured film of the printing white ink (b) is 2.0 μm or more and 4.0 μm or less. The method for producing a printed matter according to claim 1 or 2 , wherein the printing in the step (2) is performed by a wet-on-wet printing method. The method for producing a printed matter according to claim 1 or 2 , further comprising the step of (3) irradiating with an electron beam after the step (2). A printing ink set comprising at least one type of lithographic printing black or chromatic ink, a lithographic printing white ink (a) and a printing white ink (b) different from the lithographic printing white ink (a), wherein the difference (C) - (D) between the viscosity (C) of the lithographic printing white ink (a) and the viscosity (D) of the printing white ink (b) is 5 Pa s or more and 30 Pa s or less . 10. The printing ink set according to claim 9 , wherein the white printing ink (b) is a white flexographic printing ink. 11. The printing ink set according to claim 9 or 10 , wherein a difference in surface tension between the lithographic printing white ink (a) and the printing white ink (b) is 5 mN/m or more and 20 mN/m or less. 11. The printing ink set according to claim 9 or 10, wherein the difference (A) - (B) between the tack value (A) of the lithographic printing white ink (a) and the tack value (B) of the printing white ink (b) is 2.0 or more and 5.0 or less. 11. A printed matter using the printing ink set according to claim 9 or 10 , comprising a cured film of the white printing ink (b) on top of a cured film of the white lithographic printing ink (a). 14. The printed matter according to claim 13 , wherein the thickness of the cured film of the white printing ink (b) is greater than the thickness of the cured film of the white lithographic printing ink (a). 15. The printed matter according to claim 14 , wherein the thickness of the cured film of the lithographic printing white ink (a) is 0.5 μm or more and 2.0 μm or less, and the thickness of the cured film of the printing white ink (b) is 2.0 μm or more and 4.0 μm or less.