Water-based flexographic printing ink

Abstract

Provided is a water-based flexographic printing ink, in which a synthetic resin produced mainly from a fossil resource (petroleum, coal, natural gas, or the like) is not contained in a varnish and an organic solvent produced mainly from a fossil resource is not contained in a varnish, and which therefore delays the depletion of fossil resources and is environmentally friendly. In the water-based flexographic printing ink, a varnish comprises a binder component and a solvent for the binder component. The water-based flexographic printing ink is characterized in that the binder component in the varnish is hydroxypropyl methyl cellulose, the solvent is water, a synthetic resin produced by mainly using a fossil resource is not contained in the binder component, and an organic solvent is not contained as the solvent.　

Description

Water-based flexographic printing ink

[0001] The present invention relates to a water-based flexographic printing ink, and in particular to a water-based flexographic printing ink that does not contain synthetic resins (including petroleum asphalt) produced primarily from fossil resources (petroleum, coal, natural gas, etc.) in the varnish, nor does it contain organic solvents produced primarily from fossil resources, thereby reducing VOC (volatile organic compound) emissions, prolonging the depletion of fossil resources, and being environmentally friendly. (Hereinafter, "water-based flexographic printing ink" may be abbreviated as "water-based flexographic ink.")

[0002] Water-based flexographic printing is a type of letterpress printing in which ink is applied to a soft plate made of rubber or resin. It is used to print on cardboard, paper bags, cloth, and more recently on labels, film, food packaging, etc.

[0003] The components of flexographic inks can be broadly divided into colorants, varnishes (also called vehicles), and additives. Typically, pigments are used as colorants (coloring materials), and acrylic or urethane synthetic resins are used as binder components in varnishes. Water, various organic solvents, vegetable oils, and the like are used as solvents. (See, for example, paragraphs

[0066] to

[0070] and

[0072] to

[0074] of Patent Document 1 below.) Patent Document 1 below, paragraph

[0085] , in particular, suggests the use of binder resins for aqueous liquid inks. As shown in paragraphs

[0066] to

[0070] of Patent Document 1 below, these resins are primarily synthetic resins produced from fossil resources, and many of the binder components of varnishes used in flexographic printing inks currently manufactured and sold are primarily synthetic resins produced from fossil resources.

[0004] Patent No. 7333572

[0005] Incidentally, when synthetic resin components derived from fossil resources, such as those described above, are not used as the binder component of a varnish, and solvents based primarily on petroleum resources such as mineral oil are not used either, and cellulose is used as the binder component of a varnish. Cellulose is a renewable resource, and it is expected that resource depletion and environmental load will be reduced. However, it has been found that this reduces the adhesion and fixing function of the printed image to the printing medium, and causes problems such as smearing when the printed image is rubbed with a finger, a phenomenon known as chalking.

[0006] It was found that printing with ink that has had the synthetic resin component removed from the varnish component has problems such as smudges occurring when the printed area is rubbed, and print-through occurs when printed materials are stacked.

[0007] The present invention aims to provide a flexographic printing ink that does not use synthetic resin components (including asphalt) obtained primarily by synthesizing compounds derived from fossil resources as the binder component of the varnish, but instead uses hydroxypropyl methylcellulose, which is cellulose, as the main raw material component, with a low proportion of fossil resources used in the processing step that relies on fossil resources, and uses water as the solvent component of the varnish, thereby preventing the depletion of fossil resources that would otherwise be caused by a synthetic resin binder component obtained primarily by synthesizing fossil resources, thereby reducing the environmental load, and yet which exhibits satisfactory printability even without using a synthetic resin component obtained primarily by synthesizing fossil resources.

[0008] That is, the flexographic printing ink of the present invention is: (1) an aqueous flexographic printing ink in which the varnish is composed of a binder component and a solvent for the binder component, the binder component of the varnish being hydroxypropyl methylcellulose and the solvent being water, the binder component not containing a synthetic resin produced mainly using fossil resources, and the solvent not containing an organic solvent.

[0009] (2) In the aqueous flexographic printing ink described in (1) above, the ratio of hydroxypropyl methylcellulose to water is preferably 1 to 20 parts by weight of hydroxypropyl methylcellulose to 30 to 90 parts by weight of water.

[0010] (3) The water-based flexographic printing ink according to either item (1) or (2) above preferably further contains a defoaming agent.

[0011] (4) The water-based flexographic printing ink according to either item (1) or (2) above preferably further contains an anti-wear agent.

[0012] (5) In the aqueous flexographic printing ink described in (3) above, the content of the antifoaming agent is preferably 0.1 to 3 parts by mass per 1 to 20 parts by mass of hydroxypropyl methylcellulose.

[0013] (6) In the water-based flexographic printing ink described in (4) above, the content of the anti-wear agent is preferably 0.1 to 5 parts by mass per 1 to 20 parts by mass of hydroxypropyl methylcellulose.

[0014] (7) In the water-based flexographic printing ink described in the above item (3), the defoaming agent is preferably a surfactant.

[0015] (8) In the water-based flexographic printing ink described in (4) above, the abrasion-resistant agent is preferably at least one selected from polyethylene wax and polypropylene wax.

[0016] (1) The flexographic ink of the present invention does not use a synthetic resin produced primarily from compounds derived from fossil resources, which are at risk of depletion, as a binder component of the varnish. However, problems such as smearing when the printed area is rubbed and set-off when printed materials are stacked are alleviated, and an ink that can be used industrially and practically in flexographic printing can be provided.

[0017] Furthermore, as described in the above item (2) of the present invention, by adopting a preferred embodiment in which the ratio of hydroxypropyl methylcellulose to water is 1 to 20 parts by mass of hydroxypropyl methylcellulose to 30 to 90 parts by mass of water, it is possible to provide an ink that maintains ink viscosity and ensures drying properties and transferability to printing paper, which is preferable.

[0018] Furthermore, as described in the above item (3) of the present invention, by using a preferred embodiment in which the aqueous flexographic printing ink further contains an antifoaming agent, it is possible to provide an ink that can eliminate thickening and poor ink adhesion caused by the generation of bubbles during printing, which is preferable.

[0019] Furthermore, as described in the above item (4) of the present invention, by using a preferred embodiment in which the water-based flexographic printing ink further contains an anti-wear agent, it is possible to provide an ink with improved abrasion resistance to printed matter, which is preferable.

[0020] Furthermore, as described in the above item (5) of the present invention, by adopting a preferred embodiment in which the content of the antifoaming agent is 0.1 to 3 parts by mass per 1 to 20 parts by mass of hydroxypropyl methylcellulose, it is possible to provide an ink that does not suffer from thickening or poor ink adhesion due to the generation of bubbles during printing, which is preferable.

[0021] Furthermore, as described in the above item (6) of the present invention, by adopting a preferred embodiment in which the content of the abrasion-resistant agent is 0.1 to 5 parts by mass per 1 to 20 parts by mass of hydroxypropyl methylcellulose, an ink with sufficiently improved abrasion resistance can be provided to printed matter, which is preferable.

[0022] Furthermore, as described in the above item (7) of the present invention, by using a surfactant as the antifoaming agent in a preferred embodiment, it is possible to provide an ink that does not suffer from thickening or poor ink adhesion due to the generation of bubbles during printing, which is preferable.

[0023] Furthermore, as described in the above item (8) of the present invention, by using a preferred embodiment in which the abrasion-resistant agent is at least one selected from polyethylene wax and polypropylene wax, it is possible to provide an ink that can impart abrasion resistance to printed matter, which is preferable.

[0024] The flexographic ink of the present invention is broadly composed of components of a coloring material, a vehicle, and additives. As the coloring material, a pigment is usually used, and as the organic pigment, examples of yellow pigments that can be used include, but are not limited to, disazo yellow, hansa yellow, and other pigments that have conventionally been used as yellow pigments in flexographic inks.

[0025] Similarly, magenta pigments that can be used include, for example, Brilliant Carmine 6B, Lake Red C, and other magenta pigments that have been conventionally used in flexographic inks.

[0026] Similarly, as the cyan pigment, phthalocyanine blue, phthalocyanine green, alkali blue, and other pigments that have been conventionally used as cyan pigments in flexographic inks can be used.

[0027] Inorganic color pigments include carbon black for black, zinc oxide and titanium oxide for white, and other color inorganic pigments include red iron oxide and yellow lead, but are not limited to these.

[0028] Inorganic extender pigments are used as needed to act as extenders or to adjust fluidity, strength, gloss, viscosity, adhesion, etc., and examples include calcium carbonate, silicic anhydride, clay, kaolinite, talc, etc. The amount of inorganic extender pigment used is not particularly limited, and therefore does not necessarily have to be used, but if used, the amount is approximately 1 to 20 parts by mass per 100 parts by mass of the total ink composition, as a guideline.

[0029] The amount of color pigment used is not particularly limited, but as a guideline, yellow, magenta, cyan, and black are each used in a ratio of 10 to 300 parts by mass, preferably 100 to 200 parts by mass, per 100 parts by mass of hydroxypropyl methylcellulose. In the case of white pigment, it may be used in a slightly larger amount than the respective colors, and is used in a ratio of 10 to 900 parts by mass, preferably 300 to 600 parts by mass, per 100 parts by mass of hydroxypropyl methylcellulose.

[0030] Although not particularly limited, when preparing inks of each color, it is also possible to use pigments of other colors in combination as complementary colors, or to add ink compositions of other colors.

[0031] One of the features of the flexographic ink of the present invention is that it does not use synthetic resins (including petroleum asphalt) produced mainly from fossil resources (petroleum, coal, etc.) as the binder component of the varnish.

[0032] In the present invention, hydroxypropyl methylcellulose is used as the binder component of the varnish. Hydroxypropyl methylcellulose is primarily made from cellulose, and although a small amount of petroleum-derived compounds is used to process it to make it water-soluble, it is primarily made from renewable plant-derived cellulose, with approximately 76% by mass being made from biological resources. Rosin-modified phenolic resins also contain a portion of biologically derived components, but the proportion is approximately 50% by mass. Therefore, in the present invention, a synthetic resin produced primarily using fossil resources is a synthetic resin in which fossil resource-derived components account for approximately 50% by mass or more.

[0033] In the present invention, the solvent component of the varnish is water, and no organic solvents or solvents mainly derived from petroleum resources such as mineral oil are used, making it possible to provide a more environmentally friendly flexographic ink.

[0034] The ratio of hydroxypropyl methylcellulose to water for each color ink is 1 to 20 parts by weight of hydroxypropyl methylcellulose to 30 to 90 parts by weight of water, preferably 5 to 15 parts by weight of hydroxypropyl methylcellulose to 70 to 85 parts by weight of water.

[0035] The third component of ink, additives (auxiliaries), includes antifoaming agents, anti-wear agents, pigment dispersants, etc.

[0036] Furthermore, the flexographic ink of the present invention preferably contains an antifoaming agent, since the generation of bubbles during printing causes problems such as thickening of the ink and poor ink adhesion.

[0037] The antifoaming agent may be a surfactant, among which nonionic surfactants are particularly preferred because of their high antifoaming effect.

[0038] The amount of the antifoaming agent used is 0.1 to 3 parts by mass, preferably 0.5 to 2 parts by mass, per 1 to 20 parts by mass of hydroxypropylmethylcellulose for each color ink.

[0039] Furthermore, the flexographic ink of the present invention preferably contains an anti-wear agent, which is effective in preventing scratches and abrasions on the printed matter.

[0040] The amount of the anti-wear agent (also called a wear-resistant agent) used is 0.1 to 5 parts by mass, preferably 1 to 3 parts by mass, per 1 to 20 parts by mass of hydroxypropylmethylcellulose for each color ink.

[0041] In addition, small amounts of lecithin or sorbitan fatty acid ester may be added to improve pigment dispersibility, wetting properties, and prevent precipitation, and small amounts of gelling agents, butylhydroxyl toluene, and other antioxidants may be added to adjust fluidity, but these are not particularly required for the flexographic ink of the present invention.

[0042] To produce inks of various colors by mixing the coloring materials, vehicles, and additives described above, the components are mixed and then kneaded using a kneading device such as a three-roll mill or a bead mill.

[0043] The present invention will be explained in more detail below by way of examples, but the present invention is not limited to these examples in any way.

[0044] [Examples 1 and 2] 42.5 g of water was placed in a 200 ml beaker and heated to 75 to 80°C, and 15.0 g of hydroxymethyl cellulose "Metolose 60SH-03" (manufactured by Shin-Etsu Chemical Co., Ltd.) was added and stirred at a low speed (approximately 300 rpm). After the "Metolose 60SH-03" was dissolved, the mixture was cooled to room temperature (25°C). After cooling, 42.5 g of water was added and stirred to obtain a water-soluble varnish.

[0045]

[0046] A water-soluble varnish was used, and carbon black pigment, an antifoaming agent, an anti-wear agent, and water were added in the proportions shown in Table 2. After stirring, the mixture was dispersed using a paint shaker (Toyo Seiki Seisakusho, Ltd.), thereby obtaining the water-based black ink compositions of Examples 1 and 2.

[0047] The water-based black ink compositions of Examples 1 and 2 were printed on printing paper (corrugated cardboard K-liner 220 g / m) using a hand proofer (a simple test printing machine manufactured by Matsuo Sangyo Co., Ltd.). ２ ) to obtain printed matter of Examples 1 and 2. The evaluation results are shown in Table 2.

[0048]

[0049] [Evaluation Item 1: Viscosity] The viscosity of the water-based black ink composition was measured at a measurement temperature of 25°C using a B-type viscometer (manufactured by Eiko Seiki Co., Ltd.).

[0050] [Evaluation Item 2: Print Density] The density of the print was measured using a spectrophotometer (eXact manufactured by Xrite).

[0051] [Evaluation item 3: Abrasion resistance] An abrasion resistance test was conducted on the printed surface of the obtained print using an optical vibration abrasion tester (Tester Sangyo Co., Ltd.) under conditions of 200 g load and 100 reciprocations, and the degree of scratches on the ink coating surface was evaluated visually. ◎: No scratches ○: Minor scratches △: Scratches over a considerable area ×: Scratches over the entire surface

[0052] [Evaluation item 4: Antifoaming property] 30 g of the water-based black ink composition obtained above was placed in a 100 ml beaker, and an air stone (manufactured by Gex Co., Ltd.) was added for 15 seconds. The state of foaming immediately and 2 minutes later was visually compared and evaluated. ⊚: No foam remained both immediately and after 2 minutes. ◯: Almost no foam remained after 2 minutes. △: Some foam remained after 2 minutes. ×: No reduction in foam was observed from immediately to 2 minutes later.

[0053] From the above results, it can be seen that the water-based black ink compositions and printed materials obtained in Examples 1 and 2 have the same performance as general water-based inks, but can also reduce the environmental load.

[0054] Although carbon black was used as the pigment in the above examples, other pigments can also be used as described above.

[0055] The flexographic printing ink of the present invention is suitable for use in printing on cardboard, paper bags, cloth, labels, films, food packaging, and the like.

Claims

1. A water-based flexographic printing ink comprising a varnish consisting of a binder component and a solvent for the binder component, the binder component of the varnish being hydroxypropyl methylcellulose, the solvent being water, the binder component not containing a synthetic resin produced mainly using fossil resources, and the solvent not containing an organic solvent.

2. The water-based flexographic printing ink according to claim 1, wherein the ratio of the hydroxypropyl methylcellulose to water is 1 to 20 parts by weight of hydroxypropyl methylcellulose to 30 to 90 parts by weight of water.

3. The water-based flexographic printing ink according to claim 1 or 2, further comprising a defoaming agent.

4. The water-based flexographic printing ink according to claim 1 or 2, further comprising an anti-wear agent.

5. The water-based flexographic printing ink according to claim 3, wherein the content of the defoaming agent is 0.1 to 3 parts by mass per 1 to 20 parts by mass of the hydroxypropyl methylcellulose.

6. The water-based flexographic printing ink according to claim 4, wherein the content of the abrasion-resistant agent is 0.1 to 5 parts by mass per 1 to 20 parts by mass of the hydroxypropyl methylcellulose.

7. The water-based flexographic printing ink according to claim 3, wherein the defoaming agent is a surfactant.

8. The water-based flexographic printing ink according to claim 4, wherein the abrasion-resistant agent is at least one selected from the group consisting of polyethylene wax and polypropylene wax.

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